3 @setfilename coreutils.info
4 @settitle @sc{gnu} Coreutils
9 @include constants.texi
11 @c Define new indices.
15 @c Put everything in one index (arbitrarily chosen to be the concept index).
25 * Coreutils: (coreutils). Core GNU (file, text, shell) utilities.
26 * Common options: (coreutils)Common options. Common options.
27 * File permissions: (coreutils)File permissions. Access modes.
28 * Date input formats: (coreutils)Date input formats.
31 @c FIXME: the following need documentation
32 @c * [: (coreutils)[ invocation. File/string tests.
33 @c * pinky: (coreutils)pinky invocation. FIXME.
35 @dircategory Individual utilities
37 * arch: (coreutils)arch invocation. Print machine hardware name.
38 * base64: (coreutils)base64 invocation. Base64 encode/decode data.
39 * basename: (coreutils)basename invocation. Strip directory and suffix.
40 * cat: (coreutils)cat invocation. Concatenate and write files.
41 * chcon: (coreutils)chcon invocation. Change SELinux CTX of files.
42 * chgrp: (coreutils)chgrp invocation. Change file groups.
43 * chmod: (coreutils)chmod invocation. Change file permissions.
44 * chown: (coreutils)chown invocation. Change file owners/groups.
45 * chroot: (coreutils)chroot invocation. Specify the root directory.
46 * cksum: (coreutils)cksum invocation. Print POSIX CRC checksum.
47 * comm: (coreutils)comm invocation. Compare sorted files by line.
48 * cp: (coreutils)cp invocation. Copy files.
49 * csplit: (coreutils)csplit invocation. Split by context.
50 * cut: (coreutils)cut invocation. Print selected parts of lines.
51 * date: (coreutils)date invocation. Print/set system date and time.
52 * dd: (coreutils)dd invocation. Copy and convert a file.
53 * df: (coreutils)df invocation. Report file system disk usage.
54 * dir: (coreutils)dir invocation. List directories briefly.
55 * dircolors: (coreutils)dircolors invocation. Color setup for ls.
56 * dirname: (coreutils)dirname invocation. Strip last file name component.
57 * du: (coreutils)du invocation. Report on disk usage.
58 * echo: (coreutils)echo invocation. Print a line of text.
59 * env: (coreutils)env invocation. Modify the environment.
60 * expand: (coreutils)expand invocation. Convert tabs to spaces.
61 * expr: (coreutils)expr invocation. Evaluate expressions.
62 * factor: (coreutils)factor invocation. Print prime factors
63 * false: (coreutils)false invocation. Do nothing, unsuccessfully.
64 * fmt: (coreutils)fmt invocation. Reformat paragraph text.
65 * fold: (coreutils)fold invocation. Wrap long input lines.
66 * groups: (coreutils)groups invocation. Print group names a user is in.
67 * head: (coreutils)head invocation. Output the first part of files.
68 * hostid: (coreutils)hostid invocation. Print numeric host identifier.
69 * hostname: (coreutils)hostname invocation. Print or set system name.
70 * id: (coreutils)id invocation. Print user identity.
71 * install: (coreutils)install invocation. Copy and change attributes.
72 * join: (coreutils)join invocation. Join lines on a common field.
73 * kill: (coreutils)kill invocation. Send a signal to processes.
74 * link: (coreutils)link invocation. Make hard links between files.
75 * ln: (coreutils)ln invocation. Make links between files.
76 * logname: (coreutils)logname invocation. Print current login name.
77 * ls: (coreutils)ls invocation. List directory contents.
78 * md5sum: (coreutils)md5sum invocation. Print or check MD5 digests.
79 * mkdir: (coreutils)mkdir invocation. Create directories.
80 * mkfifo: (coreutils)mkfifo invocation. Create FIFOs (named pipes).
81 * mknod: (coreutils)mknod invocation. Create special files.
82 * mktemp: (coreutils)mktemp invocation. Create temporary files.
83 * mv: (coreutils)mv invocation. Rename files.
84 * nice: (coreutils)nice invocation. Modify niceness.
85 * nl: (coreutils)nl invocation. Number lines and write files.
86 * nohup: (coreutils)nohup invocation. Immunize to hangups.
87 * nproc: (coreutils)nproc invocation. Print the number of processors.
88 * od: (coreutils)od invocation. Dump files in octal, etc.
89 * paste: (coreutils)paste invocation. Merge lines of files.
90 * pathchk: (coreutils)pathchk invocation. Check file name portability.
91 * pr: (coreutils)pr invocation. Paginate or columnate files.
92 * printenv: (coreutils)printenv invocation. Print environment variables.
93 * printf: (coreutils)printf invocation. Format and print data.
94 * ptx: (coreutils)ptx invocation. Produce permuted indexes.
95 * pwd: (coreutils)pwd invocation. Print working directory.
96 * readlink: (coreutils)readlink invocation. Print referent of a symlink.
97 * rm: (coreutils)rm invocation. Remove files.
98 * rmdir: (coreutils)rmdir invocation. Remove empty directories.
99 * runcon: (coreutils)runcon invocation. Run in specified SELinux CTX.
100 * seq: (coreutils)seq invocation. Print numeric sequences
101 * sha1sum: (coreutils)sha1sum invocation. Print or check SHA-1 digests.
102 * sha2: (coreutils)sha2 utilities. Print or check SHA-2 digests.
103 * shred: (coreutils)shred invocation. Remove files more securely.
104 * shuf: (coreutils)shuf invocation. Shuffling text files.
105 * sleep: (coreutils)sleep invocation. Delay for a specified time.
106 * sort: (coreutils)sort invocation. Sort text files.
107 * split: (coreutils)split invocation. Split into fixed-size pieces.
108 * stat: (coreutils)stat invocation. Report file(system) status.
109 * stdbuf: (coreutils)stdbuf invocation. Modify stdio buffering.
110 * stty: (coreutils)stty invocation. Print/change terminal settings.
111 * su: (coreutils)su invocation. Modify user and group ID.
112 * sum: (coreutils)sum invocation. Print traditional checksum.
113 * sync: (coreutils)sync invocation. Synchronize memory and disk.
114 * tac: (coreutils)tac invocation. Reverse files.
115 * tail: (coreutils)tail invocation. Output the last part of files.
116 * tee: (coreutils)tee invocation. Redirect to multiple files.
117 * test: (coreutils)test invocation. File/string tests.
118 * timeout: (coreutils)timeout invocation. Run with time limit.
119 * touch: (coreutils)touch invocation. Change file timestamps.
120 * tr: (coreutils)tr invocation. Translate characters.
121 * true: (coreutils)true invocation. Do nothing, successfully.
122 * truncate: (coreutils)truncate invocation. Shrink/extend size of a file.
123 * tsort: (coreutils)tsort invocation. Topological sort.
124 * tty: (coreutils)tty invocation. Print terminal name.
125 * uname: (coreutils)uname invocation. Print system information.
126 * unexpand: (coreutils)unexpand invocation. Convert spaces to tabs.
127 * uniq: (coreutils)uniq invocation. Uniquify files.
128 * unlink: (coreutils)unlink invocation. Removal via unlink(2).
129 * uptime: (coreutils)uptime invocation. Print uptime and load.
130 * users: (coreutils)users invocation. Print current user names.
131 * vdir: (coreutils)vdir invocation. List directories verbosely.
132 * wc: (coreutils)wc invocation. Line, word, and byte counts.
133 * who: (coreutils)who invocation. Print who is logged in.
134 * whoami: (coreutils)whoami invocation. Print effective user ID.
135 * yes: (coreutils)yes invocation. Print a string indefinitely.
139 This manual documents version @value{VERSION} of the @sc{gnu} core
140 utilities, including the standard programs for text and file manipulation.
142 Copyright @copyright{} 1994-1996, 2000-2010 Free Software Foundation, Inc.
145 Permission is granted to copy, distribute and/or modify this document
146 under the terms of the GNU Free Documentation License, Version 1.3 or
147 any later version published by the Free Software Foundation; with no
148 Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
149 Texts. A copy of the license is included in the section entitled ``GNU
150 Free Documentation License''.
155 @title @sc{gnu} @code{Coreutils}
156 @subtitle Core GNU utilities
157 @subtitle for version @value{VERSION}, @value{UPDATED}
158 @author David MacKenzie et al.
161 @vskip 0pt plus 1filll
174 @cindex core utilities
175 @cindex text utilities
176 @cindex shell utilities
177 @cindex file utilities
180 * Introduction:: Caveats, overview, and authors
181 * Common options:: Common options
182 * Output of entire files:: cat tac nl od base64
183 * Formatting file contents:: fmt pr fold
184 * Output of parts of files:: head tail split csplit
185 * Summarizing files:: wc sum cksum md5sum sha1sum sha2
186 * Operating on sorted files:: sort shuf uniq comm ptx tsort
187 * Operating on fields:: cut paste join
188 * Operating on characters:: tr expand unexpand
189 * Directory listing:: ls dir vdir dircolors
190 * Basic operations:: cp dd install mv rm shred
191 * Special file types:: mkdir rmdir unlink mkfifo mknod ln link readlink
192 * Changing file attributes:: chgrp chmod chown touch
193 * Disk usage:: df du stat sync truncate
194 * Printing text:: echo printf yes
195 * Conditions:: false true test expr
197 * File name manipulation:: dirname basename pathchk mktemp
198 * Working context:: pwd stty printenv tty
199 * User information:: id logname whoami groups users who
200 * System context:: date arch nproc uname hostname hostid uptime
201 * SELinux context:: chcon runcon
202 * Modified command invocation:: chroot env nice nohup stdbuf su timeout
203 * Process control:: kill
205 * Numeric operations:: factor seq
206 * File permissions:: Access modes
207 * Date input formats:: Specifying date strings
208 * Opening the software toolbox:: The software tools philosophy
209 * GNU Free Documentation License:: Copying and sharing this manual
210 * Concept index:: General index
213 --- The Detailed Node Listing ---
217 * Exit status:: Indicating program success or failure
218 * Backup options:: Backup options
219 * Block size:: Block size
220 * Signal specifications:: Specifying signals
221 * Disambiguating names and IDs:: chgrp and chown owner and group syntax
222 * Random sources:: Sources of random data
223 * Target directory:: Target directory
224 * Trailing slashes:: Trailing slashes
225 * Traversing symlinks:: Traversing symlinks to directories
226 * Treating / specially:: Treating / specially
227 * Standards conformance:: Standards conformance
229 Output of entire files
231 * cat invocation:: Concatenate and write files
232 * tac invocation:: Concatenate and write files in reverse
233 * nl invocation:: Number lines and write files
234 * od invocation:: Write files in octal or other formats
235 * base64 invocation:: Transform data into printable data
237 Formatting file contents
239 * fmt invocation:: Reformat paragraph text
240 * pr invocation:: Paginate or columnate files for printing
241 * fold invocation:: Wrap input lines to fit in specified width
243 Output of parts of files
245 * head invocation:: Output the first part of files
246 * tail invocation:: Output the last part of files
247 * split invocation:: Split a file into fixed-size pieces
248 * csplit invocation:: Split a file into context-determined pieces
252 * wc invocation:: Print newline, word, and byte counts
253 * sum invocation:: Print checksum and block counts
254 * cksum invocation:: Print CRC checksum and byte counts
255 * md5sum invocation:: Print or check MD5 digests
256 * sha1sum invocation:: Print or check SHA-1 digests
257 * sha2 utilities:: Print or check SHA-2 digests
259 Operating on sorted files
261 * sort invocation:: Sort text files
262 * shuf invocation:: Shuffle text files
263 * uniq invocation:: Uniquify files
264 * comm invocation:: Compare two sorted files line by line
265 * ptx invocation:: Produce a permuted index of file contents
266 * tsort invocation:: Topological sort
268 @command{ptx}: Produce permuted indexes
270 * General options in ptx:: Options which affect general program behavior
271 * Charset selection in ptx:: Underlying character set considerations
272 * Input processing in ptx:: Input fields, contexts, and keyword selection
273 * Output formatting in ptx:: Types of output format, and sizing the fields
274 * Compatibility in ptx:: The @acronym{GNU} extensions to @command{ptx}
278 * cut invocation:: Print selected parts of lines
279 * paste invocation:: Merge lines of files
280 * join invocation:: Join lines on a common field
282 Operating on characters
284 * tr invocation:: Translate, squeeze, and/or delete characters
285 * expand invocation:: Convert tabs to spaces
286 * unexpand invocation:: Convert spaces to tabs
288 @command{tr}: Translate, squeeze, and/or delete characters
290 * Character sets:: Specifying sets of characters
291 * Translating:: Changing one set of characters to another
292 * Squeezing:: Squeezing repeats and deleting
296 * ls invocation:: List directory contents
297 * dir invocation:: Briefly list directory contents
298 * vdir invocation:: Verbosely list directory contents
299 * dircolors invocation:: Color setup for @command{ls}
301 @command{ls}: List directory contents
303 * Which files are listed:: Which files are listed
304 * What information is listed:: What information is listed
305 * Sorting the output:: Sorting the output
306 * Details about version sort:: More details about version sort
307 * General output formatting:: General output formatting
308 * Formatting the file names:: Formatting the file names
312 * cp invocation:: Copy files and directories
313 * dd invocation:: Convert and copy a file
314 * install invocation:: Copy files and set attributes
315 * mv invocation:: Move (rename) files
316 * rm invocation:: Remove files or directories
317 * shred invocation:: Remove files more securely
321 * link invocation:: Make a hard link via the link syscall
322 * ln invocation:: Make links between files
323 * mkdir invocation:: Make directories
324 * mkfifo invocation:: Make FIFOs (named pipes)
325 * mknod invocation:: Make block or character special files
326 * readlink invocation:: Print value of a symlink or canonical file name
327 * rmdir invocation:: Remove empty directories
328 * unlink invocation:: Remove files via unlink syscall
330 Changing file attributes
332 * chown invocation:: Change file owner and group
333 * chgrp invocation:: Change group ownership
334 * chmod invocation:: Change access permissions
335 * touch invocation:: Change file timestamps
339 * df invocation:: Report file system disk space usage
340 * du invocation:: Estimate file space usage
341 * stat invocation:: Report file or file system status
342 * sync invocation:: Synchronize data on disk with memory
343 * truncate invocation:: Shrink or extend the size of a file
347 * echo invocation:: Print a line of text
348 * printf invocation:: Format and print data
349 * yes invocation:: Print a string until interrupted
353 * false invocation:: Do nothing, unsuccessfully
354 * true invocation:: Do nothing, successfully
355 * test invocation:: Check file types and compare values
356 * expr invocation:: Evaluate expressions
358 @command{test}: Check file types and compare values
360 * File type tests:: File type tests
361 * Access permission tests:: Access permission tests
362 * File characteristic tests:: File characteristic tests
363 * String tests:: String tests
364 * Numeric tests:: Numeric tests
366 @command{expr}: Evaluate expression
368 * String expressions:: + : match substr index length
369 * Numeric expressions:: + - * / %
370 * Relations for expr:: | & < <= = == != >= >
371 * Examples of expr:: Examples of using @command{expr}
375 * tee invocation:: Redirect output to multiple files or processes
377 File name manipulation
379 * basename invocation:: Strip directory and suffix from a file name
380 * dirname invocation:: Strip last file name component
381 * pathchk invocation:: Check file name validity and portability
382 * mktemp invocation:: Create temporary file or directory
386 * pwd invocation:: Print working directory
387 * stty invocation:: Print or change terminal characteristics
388 * printenv invocation:: Print all or some environment variables
389 * tty invocation:: Print file name of terminal on standard input
391 @command{stty}: Print or change terminal characteristics
393 * Control:: Control settings
394 * Input:: Input settings
395 * Output:: Output settings
396 * Local:: Local settings
397 * Combination:: Combination settings
398 * Characters:: Special characters
399 * Special:: Special settings
403 * id invocation:: Print user identity
404 * logname invocation:: Print current login name
405 * whoami invocation:: Print effective user ID
406 * groups invocation:: Print group names a user is in
407 * users invocation:: Print login names of users currently logged in
408 * who invocation:: Print who is currently logged in
412 * arch invocation:: Print machine hardware name
413 * date invocation:: Print or set system date and time
414 * nproc invocation:: Print the number of processors
415 * uname invocation:: Print system information
416 * hostname invocation:: Print or set system name
417 * hostid invocation:: Print numeric host identifier
418 * uptime invocation:: Print system uptime and load
420 @command{date}: Print or set system date and time
422 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
423 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
424 * Literal conversion specifiers:: %[%nt]
425 * Padding and other flags:: Pad with zeros, spaces, etc.
426 * Setting the time:: Changing the system clock
427 * Options for date:: Instead of the current time
428 * Date input formats:: Specifying date strings
429 * Examples of date:: Examples
433 * chcon invocation:: Change SELinux context of file
434 * runcon invocation:: Run a command in specified SELinux context
436 Modified command invocation
438 * chroot invocation:: Run a command with a different root directory
439 * env invocation:: Run a command in a modified environment
440 * nice invocation:: Run a command with modified niceness
441 * nohup invocation:: Run a command immune to hangups
442 * stdbuf invocation:: Run a command with modified I/O buffering
443 * su invocation:: Run a command with substitute user and group ID
444 * timeout invocation:: Run a command with a time limit
448 * kill invocation:: Sending a signal to processes.
452 * sleep invocation:: Delay for a specified time
456 * factor invocation:: Print prime factors
457 * seq invocation:: Print numeric sequences
461 * Mode Structure:: Structure of file mode bits
462 * Symbolic Modes:: Mnemonic representation of file mode bits
463 * Numeric Modes:: File mode bits as octal numbers
464 * Directory Setuid and Setgid:: Set-user-ID and set-group-ID on directories
468 * General date syntax:: Common rules
469 * Calendar date items:: 19 Dec 1994
470 * Time of day items:: 9:20pm
471 * Time zone items:: @sc{est}, @sc{pdt}, @sc{gmt}
472 * Day of week items:: Monday and others
473 * Relative items in date strings:: next tuesday, 2 years ago
474 * Pure numbers in date strings:: 19931219, 1440
475 * Seconds since the Epoch:: @@1078100502
476 * Specifying time zone rules:: TZ="America/New_York", TZ="UTC0"
477 * Authors of get_date:: Bellovin, Eggert, Salz, Berets, et al
479 Opening the software toolbox
481 * Toolbox introduction:: Toolbox introduction
482 * I/O redirection:: I/O redirection
483 * The who command:: The @command{who} command
484 * The cut command:: The @command{cut} command
485 * The sort command:: The @command{sort} command
486 * The uniq command:: The @command{uniq} command
487 * Putting the tools together:: Putting the tools together
491 * GNU Free Documentation License:: Copying and sharing this manual
498 @chapter Introduction
500 This manual is a work in progress: many sections make no attempt to explain
501 basic concepts in a way suitable for novices. Thus, if you are interested,
502 please get involved in improving this manual. The entire @sc{gnu} community
505 @cindex @acronym{POSIX}
506 The @sc{gnu} utilities documented here are mostly compatible with the
507 @acronym{POSIX} standard.
508 @cindex bugs, reporting
509 Please report bugs to @email{bug-coreutils@@gnu.org}. Remember
510 to include the version number, machine architecture, input files, and
511 any other information needed to reproduce the bug: your input, what you
512 expected, what you got, and why it is wrong. Diffs are welcome, but
513 please include a description of the problem as well, since this is
514 sometimes difficult to infer. @xref{Bugs, , , gcc, Using and Porting GNU CC}.
520 @cindex MacKenzie, D.
523 This manual was originally derived from the Unix man pages in the
524 distributions, which were written by David MacKenzie and updated by Jim
525 Meyering. What you are reading now is the authoritative documentation
526 for these utilities; the man pages are no longer being maintained. The
527 original @command{fmt} man page was written by Ross Paterson. Fran@,{c}ois
528 Pinard did the initial conversion to Texinfo format. Karl Berry did the
529 indexing, some reorganization, and editing of the results. Brian
530 Youmans of the Free Software Foundation office staff combined the
531 manuals for textutils, fileutils, and sh-utils to produce the present
532 omnibus manual. Richard Stallman contributed his usual invaluable
533 insights to the overall process.
536 @chapter Common options
540 @itemx @w{@kbd{--backup}[=@var{method}]}
543 @vindex VERSION_CONTROL
544 @cindex backups, making
545 @xref{Backup options}.
546 Make a backup of each file that would otherwise be overwritten or removed.
549 @macro optBackupSuffix
550 @item -S @var{suffix}
551 @itemx --suffix=@var{suffix}
554 Append @var{suffix} to each backup file made with @option{-b}.
555 @xref{Backup options}.
558 @macro optTargetDirectory
559 @item -t @var{directory}
560 @itemx @w{@kbd{--target-directory}=@var{directory}}
562 @opindex --target-directory
563 @cindex target directory
564 @cindex destination directory
565 Specify the destination @var{directory}.
566 @xref{Target directory}.
569 @macro optNoTargetDirectory
571 @itemx --no-target-directory
573 @opindex --no-target-directory
574 @cindex target directory
575 @cindex destination directory
576 Do not treat the last operand specially when it is a directory or a
577 symbolic link to a directory. @xref{Target directory}.
585 @cindex output @sc{nul}-byte-terminated lines
586 Output a zero byte (@acronym{ASCII} @sc{nul}) at the end of each line,
587 rather than a newline. This option enables other programs to parse the
588 output of @command{\cmd\} even when that output would contain data
589 with embedded newlines.
596 Append an SI-style abbreviation to each size, such as @samp{M} for
597 megabytes. Powers of 1000 are used, not 1024; @samp{M} stands for
598 1,000,000 bytes. This option is equivalent to
599 @option{--block-size=si}. Use the @option{-h} or
600 @option{--human-readable} option if
601 you prefer powers of 1024.
604 @macro optHumanReadable
606 @itemx --human-readable
608 @opindex --human-readable
609 @cindex human-readable output
610 Append a size letter to each size, such as @samp{M} for mebibytes.
611 Powers of 1024 are used, not 1000; @samp{M} stands for 1,048,576 bytes.
612 This option is equivalent to @option{--block-size=human-readable}.
613 Use the @option{--si} option if you prefer powers of 1000.
616 @macro optStripTrailingSlashes
617 @itemx @w{@kbd{--strip-trailing-slashes}}
618 @opindex --strip-trailing-slashes
619 @cindex stripping trailing slashes
620 Remove any trailing slashes from each @var{source} argument.
621 @xref{Trailing slashes}.
624 @macro mayConflictWithShellBuiltIn{cmd}
625 @cindex conflicts with shell built-ins
626 @cindex built-in shell commands, conflicts with
627 Due to shell aliases and built-in @command{\cmd\} command, using an
628 unadorned @command{\cmd\} interactively or in a script may get you
629 different functionality than that described here. Invoke it via
630 @command{env} (i.e., @code{env \cmd\ @dots{}}) to avoid interference
635 @macro multiplierSuffixes{varName}
636 @var{\varName\} may be, or may be an integer optionally followed by,
637 one of the following multiplicative suffixes:
639 @samp{b} => 512 ("blocks")
640 @samp{KB} => 1000 (KiloBytes)
641 @samp{K} => 1024 (KibiBytes)
642 @samp{MB} => 1000*1000 (MegaBytes)
643 @samp{M} => 1024*1024 (MebiBytes)
644 @samp{GB} => 1000*1000*1000 (GigaBytes)
645 @samp{G} => 1024*1024*1024 (GibiBytes)
647 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
650 @c FIXME: same as above, but no ``blocks'' line.
651 @macro multiplierSuffixesNoBlocks{varName}
652 @var{\varName\} may be, or may be an integer optionally followed by,
653 one of the following multiplicative suffixes:
655 @samp{KB} => 1000 (KiloBytes)
656 @samp{K} => 1024 (KibiBytes)
657 @samp{MB} => 1000*1000 (MegaBytes)
658 @samp{M} => 1024*1024 (MebiBytes)
659 @samp{GB} => 1000*1000*1000 (GigaBytes)
660 @samp{G} => 1024*1024*1024 (GibiBytes)
662 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
665 @cindex common options
667 Certain options are available in all of these programs. Rather than
668 writing identical descriptions for each of the programs, they are
669 described here. (In fact, every @sc{gnu} program accepts (or should accept)
672 @vindex POSIXLY_CORRECT
673 Normally options and operands can appear in any order, and programs act
674 as if all the options appear before any operands. For example,
675 @samp{sort -r passwd -t :} acts like @samp{sort -r -t : passwd}, since
676 @samp{:} is an option-argument of @option{-t}. However, if the
677 @env{POSIXLY_CORRECT} environment variable is set, options must appear
678 before operands, unless otherwise specified for a particular command.
680 A few programs can usefully have trailing operands with leading
681 @samp{-}. With such a program, options must precede operands even if
682 @env{POSIXLY_CORRECT} is not set, and this fact is noted in the
683 program description. For example, the @command{env} command's options
684 must appear before its operands, since in some cases the operands
685 specify a command that itself contains options.
687 Most programs that accept long options recognize unambiguous
688 abbreviations of those options. For example, @samp{rmdir
689 --ignore-fail-on-non-empty} can be invoked as @samp{rmdir
690 --ignore-fail} or even @samp{rmdir --i}. Ambiguous options, such as
691 @samp{ls --h}, are identified as such.
693 Some of these programs recognize the @option{--help} and @option{--version}
694 options only when one of them is the sole command line argument. For
695 these programs, abbreviations of the long options are not always recognized.
702 Print a usage message listing all available options, then exit successfully.
706 @cindex version number, finding
707 Print the version number, then exit successfully.
711 @cindex option delimiter
712 Delimit the option list. Later arguments, if any, are treated as
713 operands even if they begin with @samp{-}. For example, @samp{sort --
714 -r} reads from the file named @file{-r}.
718 @cindex standard input
719 @cindex standard output
720 A single @samp{-} operand is not really an option, though it looks like one. It
721 stands for standard input, or for standard output if that is clear from
722 the context. For example, @samp{sort -} reads from standard input,
723 and is equivalent to plain @samp{sort}, and @samp{tee -} writes an
724 extra copy of its input to standard output. Unless otherwise
725 specified, @samp{-} can appear as any operand that requires a file
729 * Exit status:: Indicating program success or failure.
730 * Backup options:: -b -S, in some programs.
731 * Block size:: BLOCK_SIZE and --block-size, in some programs.
732 * Signal specifications:: Specifying signals using the --signal option.
733 * Disambiguating names and IDs:: chgrp and chown owner and group syntax
734 * Random sources:: --random-source, in some programs.
735 * Target directory:: Specifying a target directory, in some programs.
736 * Trailing slashes:: --strip-trailing-slashes, in some programs.
737 * Traversing symlinks:: -H, -L, or -P, in some programs.
738 * Treating / specially:: --preserve-root and --no-preserve-root.
739 * Special built-in utilities:: @command{break}, @command{:}, @command{eval}, @dots{}
740 * Standards conformance:: Conformance to the @acronym{POSIX} standard.
748 An exit status of zero indicates success,
749 and a nonzero value indicates failure.
752 Nearly every command invocation yields an integral @dfn{exit status}
753 that can be used to change how other commands work.
754 For the vast majority of commands, an exit status of zero indicates
755 success. Failure is indicated by a nonzero value---typically
756 @samp{1}, though it may differ on unusual platforms as @acronym{POSIX}
757 requires only that it be nonzero.
759 However, some of the programs documented here do produce
760 other exit status values and a few associate different
761 meanings with the values @samp{0} and @samp{1}.
762 Here are some of the exceptions:
763 @command{chroot}, @command{env}, @command{expr}, @command{nice},
764 @command{nohup}, @command{printenv}, @command{sort}, @command{stdbuf},
765 @command{su}, @command{test}, @command{timeout}, @command{tty}.
769 @section Backup options
771 @cindex backup options
773 Some @sc{gnu} programs (at least @command{cp}, @command{install},
774 @command{ln}, and @command{mv}) optionally make backups of files
775 before writing new versions.
776 These options control the details of these backups. The options are also
777 briefly mentioned in the descriptions of the particular programs.
782 @itemx @w{@kbd{--backup}[=@var{method}]}
785 @vindex VERSION_CONTROL
786 @cindex backups, making
787 Make a backup of each file that would otherwise be overwritten or removed.
788 Without this option, the original versions are destroyed.
789 Use @var{method} to determine the type of backups to make.
790 When this option is used but @var{method} is not specified,
791 then the value of the @env{VERSION_CONTROL}
792 environment variable is used. And if @env{VERSION_CONTROL} is not set,
793 the default backup type is @samp{existing}.
795 Note that the short form of this option, @option{-b} does not accept any
796 argument. Using @option{-b} is equivalent to using @option{--backup=existing}.
798 @vindex version-control @r{Emacs variable}
799 This option corresponds to the Emacs variable @samp{version-control};
800 the values for @var{method} are the same as those used in Emacs.
801 This option also accepts more descriptive names.
802 The valid @var{method}s are (unique abbreviations are accepted):
807 @opindex none @r{backup method}
812 @opindex numbered @r{backup method}
813 Always make numbered backups.
817 @opindex existing @r{backup method}
818 Make numbered backups of files that already have them, simple backups
823 @opindex simple @r{backup method}
824 Always make simple backups. Please note @samp{never} is not to be
825 confused with @samp{none}.
829 @item -S @var{suffix}
830 @itemx --suffix=@var{suffix}
833 @cindex backup suffix
834 @vindex SIMPLE_BACKUP_SUFFIX
835 Append @var{suffix} to each backup file made with @option{-b}. If this
836 option is not specified, the value of the @env{SIMPLE_BACKUP_SUFFIX}
837 environment variable is used. And if @env{SIMPLE_BACKUP_SUFFIX} is not
838 set, the default is @samp{~}, just as in Emacs.
847 Some @sc{gnu} programs (at least @command{df}, @command{du}, and
848 @command{ls}) display sizes in ``blocks''. You can adjust the block size
849 and method of display to make sizes easier to read. The block size
850 used for display is independent of any file system block size.
851 Fractional block counts are rounded up to the nearest integer.
853 @opindex --block-size=@var{size}
856 @vindex DF_BLOCK_SIZE
857 @vindex DU_BLOCK_SIZE
858 @vindex LS_BLOCK_SIZE
859 @vindex POSIXLY_CORRECT@r{, and block size}
861 The default block size is chosen by examining the following environment
862 variables in turn; the first one that is set determines the block size.
867 This specifies the default block size for the @command{df} command.
868 Similarly, @env{DU_BLOCK_SIZE} specifies the default for @command{du} and
869 @env{LS_BLOCK_SIZE} for @command{ls}.
872 This specifies the default block size for all three commands, if the
873 above command-specific environment variables are not set.
876 This specifies the default block size for all values that are normally
877 printed as blocks, if neither @env{BLOCK_SIZE} nor the above
878 command-specific environment variables are set. Unlike the other
879 environment variables, @env{BLOCKSIZE} does not affect values that are
880 normally printed as byte counts, e.g., the file sizes contained in
883 @item POSIXLY_CORRECT
884 If neither @env{@var{command}_BLOCK_SIZE}, nor @env{BLOCK_SIZE}, nor
885 @env{BLOCKSIZE} is set, but this variable is set, the block size
890 If none of the above environment variables are set, the block size
891 currently defaults to 1024 bytes in most contexts, but this number may
892 change in the future. For @command{ls} file sizes, the block size
895 @cindex human-readable output
898 A block size specification can be a positive integer specifying the number
899 of bytes per block, or it can be @code{human-readable} or @code{si} to
900 select a human-readable format. Integers may be followed by suffixes
901 that are upward compatible with the
902 @uref{http://www.bipm.fr/enus/3_SI/si-prefixes.html, SI prefixes}
903 for decimal multiples and with the
904 @uref{http://physics.nist.gov/cuu/Units/binary.html, IEC 60027-2
905 prefixes for binary multiples}.
907 With human-readable formats, output sizes are followed by a size letter
908 such as @samp{M} for megabytes. @code{BLOCK_SIZE=human-readable} uses
909 powers of 1024; @samp{M} stands for 1,048,576 bytes.
910 @code{BLOCK_SIZE=si} is similar, but uses powers of 1000 and appends
911 @samp{B}; @samp{MB} stands for 1,000,000 bytes.
914 A block size specification preceded by @samp{'} causes output sizes to
915 be displayed with thousands separators. The @env{LC_NUMERIC} locale
916 specifies the thousands separator and grouping. For example, in an
917 American English locale, @samp{--block-size="'1kB"} would cause a size
918 of 1234000 bytes to be displayed as @samp{1,234}. In the default C
919 locale, there is no thousands separator so a leading @samp{'} has no
922 An integer block size can be followed by a suffix to specify a
923 multiple of that size. A bare size letter,
924 or one followed by @samp{iB}, specifies
925 a multiple using powers of 1024. A size letter followed by @samp{B}
926 specifies powers of 1000 instead. For example, @samp{1M} and
927 @samp{1MiB} are equivalent to @samp{1048576}, whereas @samp{1MB} is
928 equivalent to @samp{1000000}.
930 A plain suffix without a preceding integer acts as if @samp{1} were
931 prepended, except that it causes a size indication to be appended to
932 the output. For example, @samp{--block-size="kB"} displays 3000 as
935 The following suffixes are defined. Large sizes like @code{1Y}
936 may be rejected by your computer due to limitations of its arithmetic.
940 @cindex kilobyte, definition of
941 kilobyte: @math{10^3 = 1000}.
945 @cindex kibibyte, definition of
946 kibibyte: @math{2^{10} = 1024}. @samp{K} is special: the SI prefix is
947 @samp{k} and the IEC 60027-2 prefix is @samp{Ki}, but tradition and
948 @acronym{POSIX} use @samp{k} to mean @samp{KiB}.
950 @cindex megabyte, definition of
951 megabyte: @math{10^6 = 1,000,000}.
954 @cindex mebibyte, definition of
955 mebibyte: @math{2^{20} = 1,048,576}.
957 @cindex gigabyte, definition of
958 gigabyte: @math{10^9 = 1,000,000,000}.
961 @cindex gibibyte, definition of
962 gibibyte: @math{2^{30} = 1,073,741,824}.
964 @cindex terabyte, definition of
965 terabyte: @math{10^{12} = 1,000,000,000,000}.
968 @cindex tebibyte, definition of
969 tebibyte: @math{2^{40} = 1,099,511,627,776}.
971 @cindex petabyte, definition of
972 petabyte: @math{10^{15} = 1,000,000,000,000,000}.
975 @cindex pebibyte, definition of
976 pebibyte: @math{2^{50} = 1,125,899,906,842,624}.
978 @cindex exabyte, definition of
979 exabyte: @math{10^{18} = 1,000,000,000,000,000,000}.
982 @cindex exbibyte, definition of
983 exbibyte: @math{2^{60} = 1,152,921,504,606,846,976}.
985 @cindex zettabyte, definition of
986 zettabyte: @math{10^{21} = 1,000,000,000,000,000,000,000}
989 @math{2^{70} = 1,180,591,620,717,411,303,424}.
990 (@samp{Zi} is a @acronym{GNU} extension to IEC 60027-2.)
992 @cindex yottabyte, definition of
993 yottabyte: @math{10^{24} = 1,000,000,000,000,000,000,000,000}.
996 @math{2^{80} = 1,208,925,819,614,629,174,706,176}.
997 (@samp{Yi} is a @acronym{GNU} extension to IEC 60027-2.)
1002 @opindex --block-size
1003 @opindex --human-readable
1006 Block size defaults can be overridden by an explicit
1007 @option{--block-size=@var{size}} option. The @option{-k}
1008 option is equivalent to @option{--block-size=1K}, which
1009 is the default unless the @env{POSIXLY_CORRECT} environment variable is
1010 set. The @option{-h} or @option{--human-readable} option is equivalent to
1011 @option{--block-size=human-readable}. The @option{--si} option is
1012 equivalent to @option{--block-size=si}.
1014 @node Signal specifications
1015 @section Signal specifications
1016 @cindex signals, specifying
1018 A @var{signal} may be a signal name like @samp{HUP}, or a signal
1019 number like @samp{1}, or an exit status of a process terminated by the
1020 signal. A signal name can be given in canonical form or prefixed by
1021 @samp{SIG}. The case of the letters is ignored. The following signal names
1022 and numbers are supported on all @acronym{POSIX} compliant systems:
1028 2. Terminal interrupt.
1034 9. Kill (cannot be caught or ignored).
1042 Other supported signal names have system-dependent corresponding
1043 numbers. All systems conforming to @acronym{POSIX} 1003.1-2001 also
1044 support the following signals:
1048 Access to an undefined portion of a memory object.
1050 Child process terminated, stopped, or continued.
1052 Continue executing, if stopped.
1054 Erroneous arithmetic operation.
1056 Illegal Instruction.
1058 Write on a pipe with no one to read it.
1060 Invalid memory reference.
1062 Stop executing (cannot be caught or ignored).
1066 Background process attempting read.
1068 Background process attempting write.
1070 High bandwidth data is available at a socket.
1072 User-defined signal 1.
1074 User-defined signal 2.
1078 @acronym{POSIX} 1003.1-2001 systems that support the @acronym{XSI} extension
1079 also support the following signals:
1085 Profiling timer expired.
1089 Trace/breakpoint trap.
1091 Virtual timer expired.
1093 CPU time limit exceeded.
1095 File size limit exceeded.
1099 @acronym{POSIX} 1003.1-2001 systems that support the @acronym{XRT} extension
1100 also support at least eight real-time signals called @samp{RTMIN},
1101 @samp{RTMIN+1}, @dots{}, @samp{RTMAX-1}, @samp{RTMAX}.
1103 @node Disambiguating names and IDs
1104 @section chown and chgrp: Disambiguating user names and IDs
1105 @cindex user names, disambiguating
1106 @cindex user IDs, disambiguating
1107 @cindex group names, disambiguating
1108 @cindex group IDs, disambiguating
1109 @cindex disambiguating group names and IDs
1111 Since the @var{owner} and @var{group} arguments to @command{chown} and
1112 @command{chgrp} may be specified as names or numeric IDs, there is an
1114 What if a user or group @emph{name} is a string of digits?
1115 @footnote{Using a number as a user name is common in some environments.}
1116 Should the command interpret it as a user name or as an ID?
1117 @acronym{POSIX} requires that @command{chown} and @command{chgrp}
1118 first attempt to resolve the specified string as a name, and
1119 only once that fails, then try to interpret it as an ID.
1120 This is troublesome when you want to specify a numeric ID, say 42,
1121 and it must work even in a pathological situation where
1122 @samp{42} is a user name that maps to some other user ID, say 1000.
1123 Simply invoking @code{chown 42 F}, will set @file{F}s owner ID to
1124 1000---not what you intended.
1126 GNU @command{chown} and @command{chgrp} provide a way to work around this,
1127 that at the same time may result in a significant performance improvement
1128 by eliminating a database look-up.
1129 Simply precede each numeric user ID and/or group ID with a @samp{+},
1130 in order to force its interpretation as an integer:
1134 chgrp +$numeric_group_id another-file
1138 GNU @command{chown} and @command{chgrp}
1139 skip the name look-up process for each @samp{+}-prefixed string,
1140 because a string containing @samp{+} is never a valid user or group name.
1141 This syntax is accepted on most common Unix systems, but not on Solaris 10.
1143 @node Random sources
1144 @section Sources of random data
1146 @cindex random sources
1148 The @command{shuf}, @command{shred}, and @command{sort} commands
1149 sometimes need random data to do their work. For example, @samp{sort
1150 -R} must choose a hash function at random, and it needs random data to
1151 make this selection.
1153 By default these commands use an internal pseudorandom generator
1154 initialized by a small amount of entropy, but can be directed to use
1155 an external source with the @option{--random-source=@var{file}} option.
1156 An error is reported if @var{file} does not contain enough bytes.
1158 For example, the device file @file{/dev/urandom} could be used as the
1159 source of random data. Typically, this device gathers environmental
1160 noise from device drivers and other sources into an entropy pool, and
1161 uses the pool to generate random bits. If the pool is short of data,
1162 the device reuses the internal pool to produce more bits, using a
1163 cryptographically secure pseudorandom number generator. But be aware
1164 that this device is not designed for bulk random data generation
1165 and is relatively slow.
1167 @file{/dev/urandom} suffices for most practical uses, but applications
1168 requiring high-value or long-term protection of private data may
1169 require an alternate data source like @file{/dev/random} or
1170 @file{/dev/arandom}. The set of available sources depends on your
1173 To reproduce the results of an earlier invocation of a command, you
1174 can save some random data into a file and then use that file as the
1175 random source in earlier and later invocations of the command.
1177 @node Target directory
1178 @section Target directory
1180 @cindex target directory
1182 The @command{cp}, @command{install}, @command{ln}, and @command{mv}
1183 commands normally treat the last operand specially when it is a
1184 directory or a symbolic link to a directory. For example, @samp{cp
1185 source dest} is equivalent to @samp{cp source dest/source} if
1186 @file{dest} is a directory. Sometimes this behavior is not exactly
1187 what is wanted, so these commands support the following options to
1188 allow more fine-grained control:
1193 @itemx --no-target-directory
1194 @opindex --no-target-directory
1195 @cindex target directory
1196 @cindex destination directory
1197 Do not treat the last operand specially when it is a directory or a
1198 symbolic link to a directory. This can help avoid race conditions in
1199 programs that operate in a shared area. For example, when the command
1200 @samp{mv /tmp/source /tmp/dest} succeeds, there is no guarantee that
1201 @file{/tmp/source} was renamed to @file{/tmp/dest}: it could have been
1202 renamed to @file{/tmp/dest/source} instead, if some other process
1203 created @file{/tmp/dest} as a directory. However, if @file{mv
1204 -T /tmp/source /tmp/dest} succeeds, there is no
1205 question that @file{/tmp/source} was renamed to @file{/tmp/dest}.
1207 In the opposite situation, where you want the last operand to be
1208 treated as a directory and want a diagnostic otherwise, you can use
1209 the @option{--target-directory} (@option{-t}) option.
1211 @item -t @var{directory}
1212 @itemx @w{@kbd{--target-directory}=@var{directory}}
1213 @opindex --target-directory
1214 @cindex target directory
1215 @cindex destination directory
1216 Use @var{directory} as the directory component of each destination
1219 The interface for most programs is that after processing options and a
1220 finite (possibly zero) number of fixed-position arguments, the remaining
1221 argument list is either expected to be empty, or is a list of items
1222 (usually files) that will all be handled identically. The @command{xargs}
1223 program is designed to work well with this convention.
1225 The commands in the @command{mv}-family are unusual in that they take
1226 a variable number of arguments with a special case at the @emph{end}
1227 (namely, the target directory). This makes it nontrivial to perform some
1228 operations, e.g., ``move all files from here to ../d/'', because
1229 @code{mv * ../d/} might exhaust the argument space, and @code{ls | xargs ...}
1230 doesn't have a clean way to specify an extra final argument for each
1231 invocation of the subject command. (It can be done by going through a
1232 shell command, but that requires more human labor and brain power than
1235 The @w{@kbd{--target-directory}} (@option{-t}) option allows the @command{cp},
1236 @command{install}, @command{ln}, and @command{mv} programs to be used
1237 conveniently with @command{xargs}. For example, you can move the files
1238 from the current directory to a sibling directory, @code{d} like this:
1241 ls | xargs mv -t ../d --
1244 However, this doesn't move files whose names begin with @samp{.}.
1245 If you use the @sc{gnu} @command{find} program, you can move those
1246 files too, with this command:
1249 find . -mindepth 1 -maxdepth 1 \
1253 But both of the above approaches fail if there are no files in the
1254 current directory, or if any file has a name containing a blank or
1255 some other special characters.
1256 The following example removes those limitations and requires both
1257 @sc{gnu} @command{find} and @sc{gnu} @command{xargs}:
1260 find . -mindepth 1 -maxdepth 1 -print0 \
1261 | xargs --null --no-run-if-empty \
1268 The @option{--target-directory} (@option{-t}) and
1269 @option{--no-target-directory} (@option{-T})
1270 options cannot be combined.
1272 @node Trailing slashes
1273 @section Trailing slashes
1275 @cindex trailing slashes
1277 Some @sc{gnu} programs (at least @command{cp} and @command{mv}) allow you to
1278 remove any trailing slashes from each @var{source} argument before
1279 operating on it. The @w{@kbd{--strip-trailing-slashes}} option enables
1282 This is useful when a @var{source} argument may have a trailing slash and
1283 @c FIXME: mv's behavior in this case is system-dependent
1284 specify a symbolic link to a directory. This scenario is in fact rather
1285 common because some shells can automatically append a trailing slash when
1286 performing file name completion on such symbolic links. Without this
1287 option, @command{mv}, for example, (via the system's rename function) must
1288 interpret a trailing slash as a request to dereference the symbolic link
1289 and so must rename the indirectly referenced @emph{directory} and not
1290 the symbolic link. Although it may seem surprising that such behavior
1291 be the default, it is required by @acronym{POSIX} and is consistent with
1292 other parts of that standard.
1294 @node Traversing symlinks
1295 @section Traversing symlinks
1297 @cindex symbolic link to directory, controlling traversal of
1299 The following options modify how @command{chown} and @command{chgrp}
1300 @c FIXME: note that `du' has these options, too, but they have slightly
1301 @c different meaning.
1302 traverse a hierarchy when the @option{--recursive} (@option{-R})
1303 option is also specified.
1304 If more than one of the following options is specified, only the final
1306 These options specify whether processing a symbolic link to a directory
1307 entails operating on just the symbolic link or on all files in the
1308 hierarchy rooted at that directory.
1310 These options are independent of @option{--dereference} and
1311 @option{--no-dereference} (@option{-h}), which control whether to modify
1312 a symlink or its referent.
1319 @cindex symbolic link to directory, traverse each that is specified on the command line
1320 If @option{--recursive} (@option{-R}) is specified and
1321 a command line argument is a symbolic link to a directory, traverse it.
1328 @cindex symbolic link to directory, traverse each that is encountered
1329 In a recursive traversal, traverse every symbolic link to a directory
1330 that is encountered.
1337 @cindex symbolic link to directory, never traverse
1338 Do not traverse any symbolic links.
1339 This is the default if none of @option{-H}, @option{-L},
1340 or @option{-P} is specified.
1347 @node Treating / specially
1348 @section Treating @file{/} specially
1350 Certain commands can operate destructively on entire hierarchies.
1351 For example, if a user with appropriate privileges mistakenly runs
1352 @samp{rm -rf / tmp/junk}, that may remove
1353 all files on the entire system. Since there are so few
1354 legitimate uses for such a command,
1355 @sc{gnu} @command{rm} normally declines to operate on any directory
1356 that resolves to @file{/}. If you really want to try to remove all
1357 the files on your system, you can use the @option{--no-preserve-root}
1358 option, but the default behavior, specified by the
1359 @option{--preserve-option}, is safer for most purposes.
1361 The commands @command{chgrp}, @command{chmod} and @command{chown}
1362 can also operate destructively on entire hierarchies, so they too
1363 support these options. Although, unlike @command{rm}, they don't
1364 actually unlink files, these commands are arguably more dangerous
1365 when operating recursively on @file{/}, since they often work much
1366 more quickly, and hence damage more files before an alert user can
1367 interrupt them. Tradition and @acronym{POSIX} require these commands
1368 to operate recursively on @file{/}, so they default to
1369 @option{--no-preserve-root}, but using the @option{--preserve-root}
1370 option makes them safer for most purposes. For convenience you can
1371 specify @option{--preserve-root} in an alias or in a shell function.
1373 Note that the @option{--preserve-root} option also ensures
1374 that @command{chgrp} and @command{chown} do not modify @file{/}
1375 even when dereferencing a symlink pointing to @file{/}.
1377 @node Special built-in utilities
1378 @section Special built-in utilities
1380 Some programs like @command{nice} can invoke other programs; for
1381 example, the command @samp{nice cat file} invokes the program
1382 @command{cat} by executing the command @samp{cat file}. However,
1383 @dfn{special built-in utilities} like @command{exit} cannot be invoked
1384 this way. For example, the command @samp{nice exit} does not have a
1385 well-defined behavior: it may generate an error message instead of
1388 Here is a list of the special built-in utilities that are standardized
1389 by @acronym{POSIX} 1003.1-2004.
1392 @t{.@: : break continue eval exec exit export readonly
1393 return set shift times trap unset}
1396 For example, because @samp{.}, @samp{:}, and @samp{exec} are special,
1397 the commands @samp{nice . foo.sh}, @samp{nice :}, and @samp{nice exec
1398 pwd} do not work as you might expect.
1400 Many shells extend this list. For example, Bash has several extra
1401 special built-in utilities like @command{history}, and
1402 @command{suspend}, and with Bash the command @samp{nice suspend}
1403 generates an error message instead of suspending.
1405 @node Standards conformance
1406 @section Standards conformance
1408 @vindex POSIXLY_CORRECT
1409 In a few cases, the @sc{gnu} utilities' default behavior is
1410 incompatible with the @acronym{POSIX} standard. To suppress these
1411 incompatibilities, define the @env{POSIXLY_CORRECT} environment
1412 variable. Unless you are checking for @acronym{POSIX} conformance, you
1413 probably do not need to define @env{POSIXLY_CORRECT}.
1415 Newer versions of @acronym{POSIX} are occasionally incompatible with older
1416 versions. For example, older versions of @acronym{POSIX} required the
1417 command @samp{sort +1} to sort based on the second and succeeding
1418 fields in each input line, but starting with @acronym{POSIX} 1003.1-2001
1419 the same command is required to sort the file named @file{+1}, and you
1420 must instead use the command @samp{sort -k 2} to get the field-based
1423 @vindex _POSIX2_VERSION
1424 The @sc{gnu} utilities normally conform to the version of @acronym{POSIX}
1425 that is standard for your system. To cause them to conform to a
1426 different version of @acronym{POSIX}, define the @env{_POSIX2_VERSION}
1427 environment variable to a value of the form @var{yyyymm} specifying
1428 the year and month the standard was adopted. Two values are currently
1429 supported for @env{_POSIX2_VERSION}: @samp{199209} stands for
1430 @acronym{POSIX} 1003.2-1992, and @samp{200112} stands for @acronym{POSIX}
1431 1003.1-2001. For example, if you have a newer system but are running software
1432 that assumes an older version of @acronym{POSIX} and uses @samp{sort +1}
1433 or @samp{tail +10}, you can work around any compatibility problems by setting
1434 @samp{_POSIX2_VERSION=199209} in your environment.
1436 @node Output of entire files
1437 @chapter Output of entire files
1439 @cindex output of entire files
1440 @cindex entire files, output of
1442 These commands read and write entire files, possibly transforming them
1446 * cat invocation:: Concatenate and write files.
1447 * tac invocation:: Concatenate and write files in reverse.
1448 * nl invocation:: Number lines and write files.
1449 * od invocation:: Write files in octal or other formats.
1450 * base64 invocation:: Transform data into printable data.
1453 @node cat invocation
1454 @section @command{cat}: Concatenate and write files
1457 @cindex concatenate and write files
1458 @cindex copying files
1460 @command{cat} copies each @var{file} (@samp{-} means standard input), or
1461 standard input if none are given, to standard output. Synopsis:
1464 cat [@var{option}] [@var{file}]@dots{}
1467 The program accepts the following options. Also see @ref{Common options}.
1475 Equivalent to @option{-vET}.
1478 @itemx --number-nonblank
1480 @opindex --number-nonblank
1481 Number all nonempty output lines, starting with 1.
1485 Equivalent to @option{-vE}.
1490 @opindex --show-ends
1491 Display a @samp{$} after the end of each line.
1497 Number all output lines, starting with 1.
1500 @itemx --squeeze-blank
1502 @opindex --squeeze-blank
1503 @cindex squeezing empty lines
1504 Suppress repeated adjacent empty lines; output just one empty line
1509 Equivalent to @option{-vT}.
1514 @opindex --show-tabs
1515 Display TAB characters as @samp{^I}.
1519 Ignored; for @acronym{POSIX} compatibility.
1522 @itemx --show-nonprinting
1524 @opindex --show-nonprinting
1525 Display control characters except for LFD and TAB using
1526 @samp{^} notation and precede characters that have the high bit set with
1531 On systems like MS-DOS that distinguish between text and binary files,
1532 @command{cat} normally reads and writes in binary mode. However,
1533 @command{cat} reads in text mode if one of the options
1534 @option{-bensAE} is used or if @command{cat} is reading from standard
1535 input and standard input is a terminal. Similarly, @command{cat}
1536 writes in text mode if one of the options @option{-bensAE} is used or
1537 if standard output is a terminal.
1544 # Output f's contents, then standard input, then g's contents.
1547 # Copy standard input to standard output.
1552 @node tac invocation
1553 @section @command{tac}: Concatenate and write files in reverse
1556 @cindex reversing files
1558 @command{tac} copies each @var{file} (@samp{-} means standard input), or
1559 standard input if none are given, to standard output, reversing the
1560 records (lines by default) in each separately. Synopsis:
1563 tac [@var{option}]@dots{} [@var{file}]@dots{}
1566 @dfn{Records} are separated by instances of a string (newline by
1567 default). By default, this separator string is attached to the end of
1568 the record that it follows in the file.
1570 The program accepts the following options. Also see @ref{Common options}.
1578 The separator is attached to the beginning of the record that it
1579 precedes in the file.
1585 Treat the separator string as a regular expression. Users of @command{tac}
1586 on MS-DOS/MS-Windows should note that, since @command{tac} reads files in
1587 binary mode, each line of a text file might end with a CR/LF pair
1588 instead of the Unix-style LF.
1590 @item -s @var{separator}
1591 @itemx --separator=@var{separator}
1593 @opindex --separator
1594 Use @var{separator} as the record separator, instead of newline.
1602 @section @command{nl}: Number lines and write files
1605 @cindex numbering lines
1606 @cindex line numbering
1608 @command{nl} writes each @var{file} (@samp{-} means standard input), or
1609 standard input if none are given, to standard output, with line numbers
1610 added to some or all of the lines. Synopsis:
1613 nl [@var{option}]@dots{} [@var{file}]@dots{}
1616 @cindex logical pages, numbering on
1617 @command{nl} decomposes its input into (logical) pages; by default, the
1618 line number is reset to 1 at the top of each logical page. @command{nl}
1619 treats all of the input files as a single document; it does not reset
1620 line numbers or logical pages between files.
1622 @cindex headers, numbering
1623 @cindex body, numbering
1624 @cindex footers, numbering
1625 A logical page consists of three sections: header, body, and footer.
1626 Any of the sections can be empty. Each can be numbered in a different
1627 style from the others.
1629 The beginnings of the sections of logical pages are indicated in the
1630 input file by a line containing exactly one of these delimiter strings:
1641 The two characters from which these strings are made can be changed from
1642 @samp{\} and @samp{:} via options (see below), but the pattern and
1643 length of each string cannot be changed.
1645 A section delimiter is replaced by an empty line on output. Any text
1646 that comes before the first section delimiter string in the input file
1647 is considered to be part of a body section, so @command{nl} treats a
1648 file that contains no section delimiters as a single body section.
1650 The program accepts the following options. Also see @ref{Common options}.
1654 @item -b @var{style}
1655 @itemx --body-numbering=@var{style}
1657 @opindex --body-numbering
1658 Select the numbering style for lines in the body section of each
1659 logical page. When a line is not numbered, the current line number
1660 is not incremented, but the line number separator character is still
1661 prepended to the line. The styles are:
1667 number only nonempty lines (default for body),
1669 do not number lines (default for header and footer),
1671 number only lines that contain a match for the basic regular
1672 expression @var{bre}.
1673 @xref{Regular Expressions, , Regular Expressions, grep, The GNU Grep Manual}.
1677 @itemx --section-delimiter=@var{cd}
1679 @opindex --section-delimiter
1680 @cindex section delimiters of pages
1681 Set the section delimiter characters to @var{cd}; default is
1682 @samp{\:}. If only @var{c} is given, the second remains @samp{:}.
1683 (Remember to protect @samp{\} or other metacharacters from shell
1684 expansion with quotes or extra backslashes.)
1686 @item -f @var{style}
1687 @itemx --footer-numbering=@var{style}
1689 @opindex --footer-numbering
1690 Analogous to @option{--body-numbering}.
1692 @item -h @var{style}
1693 @itemx --header-numbering=@var{style}
1695 @opindex --header-numbering
1696 Analogous to @option{--body-numbering}.
1698 @item -i @var{number}
1699 @itemx --line-increment=@var{number}
1701 @opindex --line-increment
1702 Increment line numbers by @var{number} (default 1).
1704 @item -l @var{number}
1705 @itemx --join-blank-lines=@var{number}
1707 @opindex --join-blank-lines
1708 @cindex empty lines, numbering
1709 @cindex blank lines, numbering
1710 Consider @var{number} (default 1) consecutive empty lines to be one
1711 logical line for numbering, and only number the last one. Where fewer
1712 than @var{number} consecutive empty lines occur, do not number them.
1713 An empty line is one that contains no characters, not even spaces
1716 @item -n @var{format}
1717 @itemx --number-format=@var{format}
1719 @opindex --number-format
1720 Select the line numbering format (default is @code{rn}):
1724 @opindex ln @r{format for @command{nl}}
1725 left justified, no leading zeros;
1727 @opindex rn @r{format for @command{nl}}
1728 right justified, no leading zeros;
1730 @opindex rz @r{format for @command{nl}}
1731 right justified, leading zeros.
1735 @itemx --no-renumber
1737 @opindex --no-renumber
1738 Do not reset the line number at the start of a logical page.
1740 @item -s @var{string}
1741 @itemx --number-separator=@var{string}
1743 @opindex --number-separator
1744 Separate the line number from the text line in the output with
1745 @var{string} (default is the TAB character).
1747 @item -v @var{number}
1748 @itemx --starting-line-number=@var{number}
1750 @opindex --starting-line-number
1751 Set the initial line number on each logical page to @var{number} (default 1).
1753 @item -w @var{number}
1754 @itemx --number-width=@var{number}
1756 @opindex --number-width
1757 Use @var{number} characters for line numbers (default 6).
1765 @section @command{od}: Write files in octal or other formats
1768 @cindex octal dump of files
1769 @cindex hex dump of files
1770 @cindex ASCII dump of files
1771 @cindex file contents, dumping unambiguously
1773 @command{od} writes an unambiguous representation of each @var{file}
1774 (@samp{-} means standard input), or standard input if none are given.
1778 od [@var{option}]@dots{} [@var{file}]@dots{}
1779 od [-abcdfilosx]@dots{} [@var{file}] [[+]@var{offset}[.][b]]
1780 od [@var{option}]@dots{} --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
1783 Each line of output consists of the offset in the input, followed by
1784 groups of data from the file. By default, @command{od} prints the offset in
1785 octal, and each group of file data is a C @code{short int}'s worth of input
1786 printed as a single octal number.
1788 If @var{offset} is given, it specifies how many input bytes to skip
1789 before formatting and writing. By default, it is interpreted as an
1790 octal number, but the optional trailing decimal point causes it to be
1791 interpreted as decimal. If no decimal is specified and the offset
1792 begins with @samp{0x} or @samp{0X} it is interpreted as a hexadecimal
1793 number. If there is a trailing @samp{b}, the number of bytes skipped
1794 will be @var{offset} multiplied by 512.
1796 If a command is of both the first and second forms, the second form is
1797 assumed if the last operand begins with @samp{+} or (if there are two
1798 operands) a digit. For example, in @samp{od foo 10} and @samp{od +10}
1799 the @samp{10} is an offset, whereas in @samp{od 10} the @samp{10} is a
1802 The program accepts the following options. Also see @ref{Common options}.
1806 @item -A @var{radix}
1807 @itemx --address-radix=@var{radix}
1809 @opindex --address-radix
1810 @cindex radix for file offsets
1811 @cindex file offset radix
1812 Select the base in which file offsets are printed. @var{radix} can
1813 be one of the following:
1823 none (do not print offsets).
1826 The default is octal.
1828 @item -j @var{bytes}
1829 @itemx --skip-bytes=@var{bytes}
1831 @opindex --skip-bytes
1832 Skip @var{bytes} input bytes before formatting and writing. If
1833 @var{bytes} begins with @samp{0x} or @samp{0X}, it is interpreted in
1834 hexadecimal; otherwise, if it begins with @samp{0}, in octal; otherwise,
1836 @multiplierSuffixes{bytes}
1838 @item -N @var{bytes}
1839 @itemx --read-bytes=@var{bytes}
1841 @opindex --read-bytes
1842 Output at most @var{bytes} bytes of the input. Prefixes and suffixes on
1843 @code{bytes} are interpreted as for the @option{-j} option.
1845 @item -S @var{bytes}
1846 @itemx --strings[=@var{bytes}]
1849 @cindex string constants, outputting
1850 Instead of the normal output, output only @dfn{string constants}: at
1851 least @var{bytes} consecutive @acronym{ASCII} graphic characters,
1852 followed by a zero byte (@acronym{ASCII} @sc{nul}).
1853 Prefixes and suffixes on @code{bytes} are interpreted as for the
1856 If @var{n} is omitted with @option{--strings}, the default is 3.
1859 @itemx --format=@var{type}
1862 Select the format in which to output the file data. @var{type} is a
1863 string of one or more of the below type indicator characters. If you
1864 include more than one type indicator character in a single @var{type}
1865 string, or use this option more than once, @command{od} writes one copy
1866 of each output line using each of the data types that you specified,
1867 in the order that you specified.
1869 Adding a trailing ``z'' to any type specification appends a display
1870 of the @acronym{ASCII} character representation of the printable characters
1871 to the output line generated by the type specification.
1875 named character, ignoring high-order bit
1877 @acronym{ASCII} character or backslash escape,
1890 The type @code{a} outputs things like @samp{sp} for space, @samp{nl} for
1891 newline, and @samp{nul} for a zero byte. Only the least significant
1892 seven bits of each byte is used; the high-order bit is ignored.
1893 Type @code{c} outputs
1894 @samp{ }, @samp{\n}, and @code{\0}, respectively.
1897 Except for types @samp{a} and @samp{c}, you can specify the number
1898 of bytes to use in interpreting each number in the given data type
1899 by following the type indicator character with a decimal integer.
1900 Alternately, you can specify the size of one of the C compiler's
1901 built-in data types by following the type indicator character with
1902 one of the following characters. For integers (@samp{d}, @samp{o},
1903 @samp{u}, @samp{x}):
1916 For floating point (@code{f}):
1928 @itemx --output-duplicates
1930 @opindex --output-duplicates
1931 Output consecutive lines that are identical. By default, when two or
1932 more consecutive output lines would be identical, @command{od} outputs only
1933 the first line, and puts just an asterisk on the following line to
1934 indicate the elision.
1937 @itemx --width[=@var{n}]
1940 Dump @code{n} input bytes per output line. This must be a multiple of
1941 the least common multiple of the sizes associated with the specified
1944 If this option is not given at all, the default is 16. If @var{n} is
1945 omitted, the default is 32.
1949 The next several options are shorthands for format specifications.
1950 @sc{gnu} @command{od} accepts any combination of shorthands and format
1951 specification options. These options accumulate.
1957 Output as named characters. Equivalent to @samp{-t a}.
1961 Output as octal bytes. Equivalent to @samp{-t o1}.
1965 Output as @acronym{ASCII} characters or backslash escapes. Equivalent to
1970 Output as unsigned decimal two-byte units. Equivalent to @samp{-t u2}.
1974 Output as floats. Equivalent to @samp{-t fF}.
1978 Output as decimal ints. Equivalent to @samp{-t dI}.
1982 Output as decimal long ints. Equivalent to @samp{-t dL}.
1986 Output as octal two-byte units. Equivalent to @option{-t o2}.
1990 Output as decimal two-byte units. Equivalent to @option{-t d2}.
1994 Output as hexadecimal two-byte units. Equivalent to @samp{-t x2}.
1997 @opindex --traditional
1998 Recognize the non-option label argument that traditional @command{od}
1999 accepted. The following syntax:
2002 od --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
2006 can be used to specify at most one file and optional arguments
2007 specifying an offset and a pseudo-start address, @var{label}.
2008 The @var{label} argument is interpreted
2009 just like @var{offset}, but it specifies an initial pseudo-address. The
2010 pseudo-addresses are displayed in parentheses following any normal
2017 @node base64 invocation
2018 @section @command{base64}: Transform data into printable data
2021 @cindex base64 encoding
2023 @command{base64} transforms data read from a file, or standard input,
2024 into (or from) base64 encoded form. The base64 encoded form uses
2025 printable @acronym{ASCII} characters to represent binary data.
2029 base64 [@var{option}]@dots{} [@var{file}]
2030 base64 --decode [@var{option}]@dots{} [@var{file}]
2033 The base64 encoding expands data to roughly 133% of the original.
2034 The format conforms to
2035 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc4648.txt, RFC 4648}.
2037 The program accepts the following options. Also see @ref{Common options}.
2042 @itemx --wrap=@var{cols}
2046 @cindex column to wrap data after
2047 During encoding, wrap lines after @var{cols} characters. This must be
2050 The default is to wrap after 76 characters. Use the value 0 to
2051 disable line wrapping altogether.
2057 @cindex Decode base64 data
2058 @cindex Base64 decoding
2059 Change the mode of operation, from the default of encoding data, to
2060 decoding data. Input is expected to be base64 encoded data, and the
2061 output will be the original data.
2064 @itemx --ignore-garbage
2066 @opindex --ignore-garbage
2067 @cindex Ignore garbage in base64 stream
2068 When decoding, newlines are always accepted.
2069 During decoding, ignore unrecognized bytes,
2070 to permit distorted data to be decoded.
2077 @node Formatting file contents
2078 @chapter Formatting file contents
2080 @cindex formatting file contents
2082 These commands reformat the contents of files.
2085 * fmt invocation:: Reformat paragraph text.
2086 * pr invocation:: Paginate or columnate files for printing.
2087 * fold invocation:: Wrap input lines to fit in specified width.
2091 @node fmt invocation
2092 @section @command{fmt}: Reformat paragraph text
2095 @cindex reformatting paragraph text
2096 @cindex paragraphs, reformatting
2097 @cindex text, reformatting
2099 @command{fmt} fills and joins lines to produce output lines of (at most)
2100 a given number of characters (75 by default). Synopsis:
2103 fmt [@var{option}]@dots{} [@var{file}]@dots{}
2106 @command{fmt} reads from the specified @var{file} arguments (or standard
2107 input if none are given), and writes to standard output.
2109 By default, blank lines, spaces between words, and indentation are
2110 preserved in the output; successive input lines with different
2111 indentation are not joined; tabs are expanded on input and introduced on
2114 @cindex line-breaking
2115 @cindex sentences and line-breaking
2116 @cindex Knuth, Donald E.
2117 @cindex Plass, Michael F.
2118 @command{fmt} prefers breaking lines at the end of a sentence, and tries to
2119 avoid line breaks after the first word of a sentence or before the last
2120 word of a sentence. A @dfn{sentence break} is defined as either the end
2121 of a paragraph or a word ending in any of @samp{.?!}, followed by two
2122 spaces or end of line, ignoring any intervening parentheses or quotes.
2123 Like @TeX{}, @command{fmt} reads entire ``paragraphs'' before choosing line
2124 breaks; the algorithm is a variant of that given by Donald E. Knuth
2125 and Michael F. Plass in ``Breaking Paragraphs Into Lines'',
2126 @cite{Software---Practice & Experience} @b{11}, 11 (November 1981),
2129 The program accepts the following options. Also see @ref{Common options}.
2134 @itemx --crown-margin
2136 @opindex --crown-margin
2137 @cindex crown margin
2138 @dfn{Crown margin} mode: preserve the indentation of the first two
2139 lines within a paragraph, and align the left margin of each subsequent
2140 line with that of the second line.
2143 @itemx --tagged-paragraph
2145 @opindex --tagged-paragraph
2146 @cindex tagged paragraphs
2147 @dfn{Tagged paragraph} mode: like crown margin mode, except that if
2148 indentation of the first line of a paragraph is the same as the
2149 indentation of the second, the first line is treated as a one-line
2155 @opindex --split-only
2156 Split lines only. Do not join short lines to form longer ones. This
2157 prevents sample lines of code, and other such ``formatted'' text from
2158 being unduly combined.
2161 @itemx --uniform-spacing
2163 @opindex --uniform-spacing
2164 Uniform spacing. Reduce spacing between words to one space, and spacing
2165 between sentences to two spaces.
2168 @itemx -w @var{width}
2169 @itemx --width=@var{width}
2170 @opindex -@var{width}
2173 Fill output lines up to @var{width} characters (default 75). @command{fmt}
2174 initially tries to make lines about 7% shorter than this, to give it
2175 room to balance line lengths.
2177 @item -p @var{prefix}
2178 @itemx --prefix=@var{prefix}
2179 Only lines beginning with @var{prefix} (possibly preceded by whitespace)
2180 are subject to formatting. The prefix and any preceding whitespace are
2181 stripped for the formatting and then re-attached to each formatted output
2182 line. One use is to format certain kinds of program comments, while
2183 leaving the code unchanged.
2191 @section @command{pr}: Paginate or columnate files for printing
2194 @cindex printing, preparing files for
2195 @cindex multicolumn output, generating
2196 @cindex merging files in parallel
2198 @command{pr} writes each @var{file} (@samp{-} means standard input), or
2199 standard input if none are given, to standard output, paginating and
2200 optionally outputting in multicolumn format; optionally merges all
2201 @var{file}s, printing all in parallel, one per column. Synopsis:
2204 pr [@var{option}]@dots{} [@var{file}]@dots{}
2208 By default, a 5-line header is printed at each page: two blank lines;
2209 a line with the date, the file name, and the page count; and two more
2210 blank lines. A footer of five blank lines is also printed.
2211 The default @var{page_length} is 66
2212 lines. The default number of text lines is therefore 56.
2213 The text line of the header takes the form
2214 @samp{@var{date} @var{string} @var{page}}, with spaces inserted around
2215 @var{string} so that the line takes up the full @var{page_width}. Here,
2216 @var{date} is the date (see the @option{-D} or @option{--date-format}
2217 option for details), @var{string} is the centered header string, and
2218 @var{page} identifies the page number. The @env{LC_MESSAGES} locale
2219 category affects the spelling of @var{page}; in the default C locale, it
2220 is @samp{Page @var{number}} where @var{number} is the decimal page
2223 Form feeds in the input cause page breaks in the output. Multiple form
2224 feeds produce empty pages.
2226 Columns are of equal width, separated by an optional string (default
2227 is @samp{space}). For multicolumn output, lines will always be truncated to
2228 @var{page_width} (default 72), unless you use the @option{-J} option.
2230 column output no line truncation occurs by default. Use @option{-W} option to
2231 truncate lines in that case.
2233 The following changes were made in version 1.22i and apply to later
2234 versions of @command{pr}:
2235 @c FIXME: this whole section here sounds very awkward to me. I
2236 @c made a few small changes, but really it all needs to be redone. - Brian
2237 @c OK, I fixed another sentence or two, but some of it I just don't understand.
2242 Some small @var{letter options} (@option{-s}, @option{-w}) have been
2243 redefined for better @acronym{POSIX} compliance. The output of some further
2244 cases has been adapted to other Unix systems. These changes are not
2245 compatible with earlier versions of the program.
2248 Some @var{new capital letter} options (@option{-J}, @option{-S}, @option{-W})
2249 have been introduced to turn off unexpected interferences of small letter
2250 options. The @option{-N} option and the second argument @var{last_page}
2251 of @samp{+FIRST_PAGE} offer more flexibility. The detailed handling of
2252 form feeds set in the input files requires the @option{-T} option.
2255 Capital letter options override small letter ones.
2258 Some of the option-arguments (compare @option{-s}, @option{-e},
2259 @option{-i}, @option{-n}) cannot be specified as separate arguments from the
2260 preceding option letter (already stated in the @acronym{POSIX} specification).
2263 The program accepts the following options. Also see @ref{Common options}.
2267 @item +@var{first_page}[:@var{last_page}]
2268 @itemx --pages=@var{first_page}[:@var{last_page}]
2269 @c The two following @opindex lines evoke warnings because they contain `:'
2270 @c The `info' spec does not permit that. If we use those lines, we end
2271 @c up with truncated index entries that don't work.
2272 @c @opindex +@var{first_page}[:@var{last_page}]
2273 @c @opindex --pages=@var{first_page}[:@var{last_page}]
2274 @opindex +@var{page_range}
2275 @opindex --pages=@var{page_range}
2276 Begin printing with page @var{first_page} and stop with @var{last_page}.
2277 Missing @samp{:@var{last_page}} implies end of file. While estimating
2278 the number of skipped pages each form feed in the input file results
2279 in a new page. Page counting with and without @samp{+@var{first_page}}
2280 is identical. By default, counting starts with the first page of input
2281 file (not first page printed). Line numbering may be altered by @option{-N}
2285 @itemx --columns=@var{column}
2286 @opindex -@var{column}
2288 @cindex down columns
2289 With each single @var{file}, produce @var{column} columns of output
2290 (default is 1) and print columns down, unless @option{-a} is used. The
2291 column width is automatically decreased as @var{column} increases; unless
2292 you use the @option{-W/-w} option to increase @var{page_width} as well.
2293 This option might well cause some lines to be truncated. The number of
2294 lines in the columns on each page are balanced. The options @option{-e}
2295 and @option{-i} are on for multiple text-column output. Together with
2296 @option{-J} option column alignment and line truncation is turned off.
2297 Lines of full length are joined in a free field format and @option{-S}
2298 option may set field separators. @option{-@var{column}} may not be used
2299 with @option{-m} option.
2305 @cindex across columns
2306 With each single @var{file}, print columns across rather than down. The
2307 @option{-@var{column}} option must be given with @var{column} greater than one.
2308 If a line is too long to fit in a column, it is truncated.
2311 @itemx --show-control-chars
2313 @opindex --show-control-chars
2314 Print control characters using hat notation (e.g., @samp{^G}); print
2315 other nonprinting characters in octal backslash notation. By default,
2316 nonprinting characters are not changed.
2319 @itemx --double-space
2321 @opindex --double-space
2322 @cindex double spacing
2323 Double space the output.
2325 @item -D @var{format}
2326 @itemx --date-format=@var{format}
2327 @cindex time formats
2328 @cindex formatting times
2329 Format header dates using @var{format}, using the same conventions as
2330 for the command @samp{date +@var{format}}; @xref{date invocation}.
2331 Except for directives, which start with
2332 @samp{%}, characters in @var{format} are printed unchanged. You can use
2333 this option to specify an arbitrary string in place of the header date,
2334 e.g., @option{--date-format="Monday morning"}.
2336 @vindex POSIXLY_CORRECT
2338 The default date format is @samp{%Y-%m-%d %H:%M} (for example,
2339 @samp{2001-12-04 23:59});
2340 but if the @env{POSIXLY_CORRECT} environment variable is set
2341 and the @env{LC_TIME} locale category specifies the @acronym{POSIX}
2342 locale, the default is @samp{%b %e %H:%M %Y} (for example,
2343 @samp{Dec@ @ 4 23:59 2001}.
2346 Time stamps are listed according to the time zone rules specified by
2347 the @env{TZ} environment variable, or by the system default rules if
2348 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
2349 with @env{TZ}, libc, The GNU C Library Reference Manual}.
2351 @item -e[@var{in-tabchar}[@var{in-tabwidth}]]
2352 @itemx --expand-tabs[=@var{in-tabchar}[@var{in-tabwidth}]]
2354 @opindex --expand-tabs
2356 Expand @var{tab}s to spaces on input. Optional argument @var{in-tabchar} is
2357 the input tab character (default is the TAB character). Second optional
2358 argument @var{in-tabwidth} is the input tab character's width (default
2366 @opindex --form-feed
2367 Use a form feed instead of newlines to separate output pages. This does
2368 not alter the default page length of 66 lines.
2370 @item -h @var{header}
2371 @itemx --header=@var{header}
2374 Replace the file name in the header with the centered string @var{header}.
2375 When using the shell, @var{header} should be quoted and should be
2376 separated from @option{-h} by a space.
2378 @item -i[@var{out-tabchar}[@var{out-tabwidth}]]
2379 @itemx --output-tabs[=@var{out-tabchar}[@var{out-tabwidth}]]
2381 @opindex --output-tabs
2383 Replace spaces with @var{tab}s on output. Optional argument @var{out-tabchar}
2384 is the output tab character (default is the TAB character). Second optional
2385 argument @var{out-tabwidth} is the output tab character's width (default
2391 @opindex --join-lines
2392 Merge lines of full length. Used together with the column options
2393 @option{-@var{column}}, @option{-a -@var{column}} or @option{-m}. Turns off
2394 @option{-W/-w} line truncation;
2395 no column alignment used; may be used with
2396 @option{--sep-string[=@var{string}]}. @option{-J} has been introduced
2397 (together with @option{-W} and @option{--sep-string})
2398 to disentangle the old (@acronym{POSIX}-compliant) options @option{-w} and
2399 @option{-s} along with the three column options.
2402 @item -l @var{page_length}
2403 @itemx --length=@var{page_length}
2406 Set the page length to @var{page_length} (default 66) lines, including
2407 the lines of the header [and the footer]. If @var{page_length} is less
2408 than or equal to 10, the header and footer are omitted, as if the
2409 @option{-t} option had been given.
2415 Merge and print all @var{file}s in parallel, one in each column. If a
2416 line is too long to fit in a column, it is truncated, unless the @option{-J}
2417 option is used. @option{--sep-string[=@var{string}]} may be used.
2419 some @var{file}s (form feeds set) produce empty columns, still marked
2420 by @var{string}. The result is a continuous line numbering and column
2421 marking throughout the whole merged file. Completely empty merged pages
2422 show no separators or line numbers. The default header becomes
2423 @samp{@var{date} @var{page}} with spaces inserted in the middle; this
2424 may be used with the @option{-h} or @option{--header} option to fill up
2425 the middle blank part.
2427 @item -n[@var{number-separator}[@var{digits}]]
2428 @itemx --number-lines[=@var{number-separator}[@var{digits}]]
2430 @opindex --number-lines
2431 Provide @var{digits} digit line numbering (default for @var{digits} is
2432 5). With multicolumn output the number occupies the first @var{digits}
2433 column positions of each text column or only each line of @option{-m}
2434 output. With single column output the number precedes each line just as
2435 @option{-m} does. Default counting of the line numbers starts with the
2436 first line of the input file (not the first line printed, compare the
2437 @option{--page} option and @option{-N} option).
2438 Optional argument @var{number-separator} is the character appended to
2439 the line number to separate it from the text followed. The default
2440 separator is the TAB character. In a strict sense a TAB is always
2441 printed with single column output only. The TAB width varies
2442 with the TAB position, e.g., with the left @var{margin} specified
2443 by @option{-o} option. With multicolumn output priority is given to
2444 @samp{equal width of output columns} (a @acronym{POSIX} specification).
2445 The TAB width is fixed to the value of the first column and does
2446 not change with different values of left @var{margin}. That means a
2447 fixed number of spaces is always printed in the place of the
2448 @var{number-separator} TAB. The tabification depends upon the output
2451 @item -N @var{line_number}
2452 @itemx --first-line-number=@var{line_number}
2454 @opindex --first-line-number
2455 Start line counting with the number @var{line_number} at first line of
2456 first page printed (in most cases not the first line of the input file).
2458 @item -o @var{margin}
2459 @itemx --indent=@var{margin}
2462 @cindex indenting lines
2464 Indent each line with a margin @var{margin} spaces wide (default is zero).
2465 The total page width is the size of the margin plus the @var{page_width}
2466 set with the @option{-W/-w} option. A limited overflow may occur with
2467 numbered single column output (compare @option{-n} option).
2470 @itemx --no-file-warnings
2472 @opindex --no-file-warnings
2473 Do not print a warning message when an argument @var{file} cannot be
2474 opened. (The exit status will still be nonzero, however.)
2476 @item -s[@var{char}]
2477 @itemx --separator[=@var{char}]
2479 @opindex --separator
2480 Separate columns by a single character @var{char}. The default for
2481 @var{char} is the TAB character without @option{-w} and @samp{no
2482 character} with @option{-w}. Without @option{-s} the default separator
2483 @samp{space} is set. @option{-s[char]} turns off line truncation of all
2484 three column options (@option{-COLUMN}|@option{-a -COLUMN}|@option{-m}) unless
2485 @option{-w} is set. This is a @acronym{POSIX}-compliant formulation.
2488 @item -S@var{string}
2489 @itemx --sep-string[=@var{string}]
2491 @opindex --sep-string
2492 Use @var{string} to separate output columns. The @option{-S} option doesn't
2493 affect the @option{-W/-w} option, unlike the @option{-s} option which does. It
2494 does not affect line truncation or column alignment.
2495 Without @option{-S}, and with @option{-J}, @command{pr} uses the default output
2497 Without @option{-S} or @option{-J}, @command{pr} uses a @samp{space}
2498 (same as @option{-S"@w{ }"}). @option{--sep-string} with no
2499 @samp{=@var{string}} is equivalent to @option{--sep-string=""}.
2502 @itemx --omit-header
2504 @opindex --omit-header
2505 Do not print the usual header [and footer] on each page, and do not fill
2506 out the bottom of pages (with blank lines or a form feed). No page
2507 structure is produced, but form feeds set in the input files are retained.
2508 The predefined pagination is not changed. @option{-t} or @option{-T} may be
2509 useful together with other options; e.g.: @option{-t -e4}, expand TAB characters
2510 in the input file to 4 spaces but don't make any other changes. Use of
2511 @option{-t} overrides @option{-h}.
2514 @itemx --omit-pagination
2516 @opindex --omit-pagination
2517 Do not print header [and footer]. In addition eliminate all form feeds
2518 set in the input files.
2521 @itemx --show-nonprinting
2523 @opindex --show-nonprinting
2524 Print nonprinting characters in octal backslash notation.
2526 @item -w @var{page_width}
2527 @itemx --width=@var{page_width}
2530 Set page width to @var{page_width} characters for multiple text-column
2531 output only (default for @var{page_width} is 72). @option{-s[CHAR]} turns
2532 off the default page width and any line truncation and column alignment.
2533 Lines of full length are merged, regardless of the column options
2534 set. No @var{page_width} setting is possible with single column output.
2535 A @acronym{POSIX}-compliant formulation.
2537 @item -W @var{page_width}
2538 @itemx --page_width=@var{page_width}
2540 @opindex --page_width
2541 Set the page width to @var{page_width} characters. That's valid with and
2542 without a column option. Text lines are truncated, unless @option{-J}
2543 is used. Together with one of the three column options
2544 (@option{-@var{column}}, @option{-a -@var{column}} or @option{-m}) column
2545 alignment is always used. The separator options @option{-S} or @option{-s}
2546 don't affect the @option{-W} option. Default is 72 characters. Without
2547 @option{-W @var{page_width}} and without any of the column options NO line
2548 truncation is used (defined to keep downward compatibility and to meet
2549 most frequent tasks). That's equivalent to @option{-W 72 -J}. The header
2550 line is never truncated.
2557 @node fold invocation
2558 @section @command{fold}: Wrap input lines to fit in specified width
2561 @cindex wrapping long input lines
2562 @cindex folding long input lines
2564 @command{fold} writes each @var{file} (@option{-} means standard input), or
2565 standard input if none are given, to standard output, breaking long
2569 fold [@var{option}]@dots{} [@var{file}]@dots{}
2572 By default, @command{fold} breaks lines wider than 80 columns. The output
2573 is split into as many lines as necessary.
2575 @cindex screen columns
2576 @command{fold} counts screen columns by default; thus, a tab may count more
2577 than one column, backspace decreases the column count, and carriage
2578 return sets the column to zero.
2580 The program accepts the following options. Also see @ref{Common options}.
2588 Count bytes rather than columns, so that tabs, backspaces, and carriage
2589 returns are each counted as taking up one column, just like other
2596 Break at word boundaries: the line is broken after the last blank before
2597 the maximum line length. If the line contains no such blanks, the line
2598 is broken at the maximum line length as usual.
2600 @item -w @var{width}
2601 @itemx --width=@var{width}
2604 Use a maximum line length of @var{width} columns instead of 80.
2606 For compatibility @command{fold} supports an obsolete option syntax
2607 @option{-@var{width}}. New scripts should use @option{-w @var{width}}
2615 @node Output of parts of files
2616 @chapter Output of parts of files
2618 @cindex output of parts of files
2619 @cindex parts of files, output of
2621 These commands output pieces of the input.
2624 * head invocation:: Output the first part of files.
2625 * tail invocation:: Output the last part of files.
2626 * split invocation:: Split a file into fixed-size pieces.
2627 * csplit invocation:: Split a file into context-determined pieces.
2630 @node head invocation
2631 @section @command{head}: Output the first part of files
2634 @cindex initial part of files, outputting
2635 @cindex first part of files, outputting
2637 @command{head} prints the first part (10 lines by default) of each
2638 @var{file}; it reads from standard input if no files are given or
2639 when given a @var{file} of @option{-}. Synopsis:
2642 head [@var{option}]@dots{} [@var{file}]@dots{}
2645 If more than one @var{file} is specified, @command{head} prints a
2646 one-line header consisting of:
2649 ==> @var{file name} <==
2653 before the output for each @var{file}.
2655 The program accepts the following options. Also see @ref{Common options}.
2660 @itemx --bytes=@var{k}
2663 Print the first @var{k} bytes, instead of initial lines.
2664 However, if @var{k} starts with a @samp{-},
2665 print all but the last @var{k} bytes of each file.
2666 @multiplierSuffixes{k}
2669 @itemx --lines=@var{k}
2672 Output the first @var{k} lines.
2673 However, if @var{k} starts with a @samp{-},
2674 print all but the last @var{k} lines of each file.
2675 Size multiplier suffixes are the same as with the @option{-c} option.
2683 Never print file name headers.
2689 Always print file name headers.
2693 For compatibility @command{head} also supports an obsolete option syntax
2694 @option{-@var{count}@var{options}}, which is recognized only if it is
2695 specified first. @var{count} is a decimal number optionally followed
2696 by a size letter (@samp{b}, @samp{k}, @samp{m}) as in @option{-c}, or
2697 @samp{l} to mean count by lines, or other option letters (@samp{cqv}).
2698 Scripts intended for standard hosts should use @option{-c @var{count}}
2699 or @option{-n @var{count}} instead. If your script must also run on
2700 hosts that support only the obsolete syntax, it is usually simpler to
2701 avoid @command{head}, e.g., by using @samp{sed 5q} instead of
2707 @node tail invocation
2708 @section @command{tail}: Output the last part of files
2711 @cindex last part of files, outputting
2713 @command{tail} prints the last part (10 lines by default) of each
2714 @var{file}; it reads from standard input if no files are given or
2715 when given a @var{file} of @samp{-}. Synopsis:
2718 tail [@var{option}]@dots{} [@var{file}]@dots{}
2721 If more than one @var{file} is specified, @command{tail} prints a
2722 one-line header consisting of:
2725 ==> @var{file name} <==
2729 before the output for each @var{file}.
2731 @cindex BSD @command{tail}
2732 @sc{gnu} @command{tail} can output any amount of data (some other versions of
2733 @command{tail} cannot). It also has no @option{-r} option (print in
2734 reverse), since reversing a file is really a different job from printing
2735 the end of a file; BSD @command{tail} (which is the one with @option{-r}) can
2736 only reverse files that are at most as large as its buffer, which is
2737 typically 32 KiB@. A more reliable and versatile way to reverse files is
2738 the @sc{gnu} @command{tac} command.
2740 The program accepts the following options. Also see @ref{Common options}.
2745 @itemx --bytes=@var{k}
2748 Output the last @var{k} bytes, instead of final lines.
2749 However, if @var{k} starts with a @samp{+}, start printing with the
2750 @var{k}th byte from the start of each file, instead of from the end.
2751 @multiplierSuffixes{k}
2754 @itemx --follow[=@var{how}]
2757 @cindex growing files
2758 @vindex name @r{follow option}
2759 @vindex descriptor @r{follow option}
2760 Loop forever trying to read more characters at the end of the file,
2761 presumably because the file is growing.
2762 If more than one file is given, @command{tail} prints a header whenever it
2763 gets output from a different file, to indicate which file that output is
2766 There are two ways to specify how you'd like to track files with this option,
2767 but that difference is noticeable only when a followed file is removed or
2769 If you'd like to continue to track the end of a growing file even after
2770 it has been unlinked, use @option{--follow=descriptor}. This is the default
2771 behavior, but it is not useful if you're tracking a log file that may be
2772 rotated (removed or renamed, then reopened). In that case, use
2773 @option{--follow=name} to track the named file, perhaps by reopening it
2774 periodically to see if it has been removed and recreated by some other program.
2775 Note that the inotify-based implementation handles this case without
2776 the need for any periodic reopening.
2778 No matter which method you use, if the tracked file is determined to have
2779 shrunk, @command{tail} prints a message saying the file has been truncated
2780 and resumes tracking the end of the file from the newly-determined endpoint.
2782 When a file is removed, @command{tail}'s behavior depends on whether it is
2783 following the name or the descriptor. When following by name, tail can
2784 detect that a file has been removed and gives a message to that effect,
2785 and if @option{--retry} has been specified it will continue checking
2786 periodically to see if the file reappears.
2787 When following a descriptor, tail does not detect that the file has
2788 been unlinked or renamed and issues no message; even though the file
2789 may no longer be accessible via its original name, it may still be
2792 The option values @samp{descriptor} and @samp{name} may be specified only
2793 with the long form of the option, not with @option{-f}.
2795 The @option{-f} option is ignored if
2796 no @var{file} operand is specified and standard input is a FIFO or a pipe.
2797 Likewise, the @option{-f} option has no effect for any
2798 operand specified as @samp{-}, when standard input is a FIFO or a pipe.
2802 This option is the same as @option{--follow=name --retry}. That is, tail
2803 will attempt to reopen a file when it is removed. Should this fail, tail
2804 will keep trying until it becomes accessible again.
2808 This option is useful mainly when following by name (i.e., with
2809 @option{--follow=name}).
2810 Without this option, when tail encounters a file that doesn't
2811 exist or is otherwise inaccessible, it reports that fact and
2812 never checks it again.
2814 @itemx --sleep-interval=@var{number}
2815 @opindex --sleep-interval
2816 Change the number of seconds to wait between iterations (the default is 1.0).
2817 During one iteration, every specified file is checked to see if it has
2819 Historical implementations of @command{tail} have required that
2820 @var{number} be an integer. However, GNU @command{tail} accepts
2821 an arbitrary floating point number (using a period before any
2824 @itemx --pid=@var{pid}
2826 When following by name or by descriptor, you may specify the process ID,
2827 @var{pid}, of the sole writer of all @var{file} arguments. Then, shortly
2828 after that process terminates, tail will also terminate. This will
2829 work properly only if the writer and the tailing process are running on
2830 the same machine. For example, to save the output of a build in a file
2831 and to watch the file grow, if you invoke @command{make} and @command{tail}
2832 like this then the tail process will stop when your build completes.
2833 Without this option, you would have had to kill the @code{tail -f}
2837 $ make >& makerr & tail --pid=$! -f makerr
2840 If you specify a @var{pid} that is not in use or that does not correspond
2841 to the process that is writing to the tailed files, then @command{tail}
2842 may terminate long before any @var{file}s stop growing or it may not
2843 terminate until long after the real writer has terminated.
2844 Note that @option{--pid} cannot be supported on some systems; @command{tail}
2845 will print a warning if this is the case.
2847 @itemx --max-unchanged-stats=@var{n}
2848 @opindex --max-unchanged-stats
2849 When tailing a file by name, if there have been @var{n} (default
2850 n=@value{DEFAULT_MAX_N_UNCHANGED_STATS_BETWEEN_OPENS}) consecutive
2851 iterations for which the file has not changed, then
2852 @code{open}/@code{fstat} the file to determine if that file name is
2853 still associated with the same device/inode-number pair as before.
2854 When following a log file that is rotated, this is approximately the
2855 number of seconds between when tail prints the last pre-rotation lines
2856 and when it prints the lines that have accumulated in the new log file.
2857 This option is meaningful only when following by name.
2860 @itemx --lines=@var{k}
2863 Output the last @var{k} lines.
2864 However, if @var{k} starts with a @samp{+}, start printing with the
2865 @var{k}th line from the start of each file, instead of from the end.
2866 Size multiplier suffixes are the same as with the @option{-c} option.
2874 Never print file name headers.
2880 Always print file name headers.
2884 For compatibility @command{tail} also supports an obsolete usage
2885 @samp{tail -[@var{count}][bcl][f] [@var{file}]}, which is recognized
2886 only if it does not conflict with the usage described
2887 above. This obsolete form uses exactly one option and at most one
2888 file. In the option, @var{count} is an optional decimal number optionally
2889 followed by a size letter (@samp{b}, @samp{c}, @samp{l}) to mean count
2890 by 512-byte blocks, bytes, or lines, optionally followed by @samp{f}
2891 which has the same meaning as @option{-f}.
2893 @vindex _POSIX2_VERSION
2894 On older systems, the leading @samp{-} can be replaced by @samp{+} in
2895 the obsolete option syntax with the same meaning as in counts, and
2896 obsolete usage overrides normal usage when the two conflict.
2897 This obsolete behavior can be enabled or disabled with the
2898 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
2901 Scripts intended for use on standard hosts should avoid obsolete
2902 syntax and should use @option{-c @var{count}[b]}, @option{-n
2903 @var{count}}, and/or @option{-f} instead. If your script must also
2904 run on hosts that support only the obsolete syntax, you can often
2905 rewrite it to avoid problematic usages, e.g., by using @samp{sed -n
2906 '$p'} rather than @samp{tail -1}. If that's not possible, the script
2907 can use a test like @samp{if tail -c +1 </dev/null >/dev/null 2>&1;
2908 then @dots{}} to decide which syntax to use.
2910 Even if your script assumes the standard behavior, you should still
2911 beware usages whose behaviors differ depending on the @acronym{POSIX}
2912 version. For example, avoid @samp{tail - main.c}, since it might be
2913 interpreted as either @samp{tail main.c} or as @samp{tail -- -
2914 main.c}; avoid @samp{tail -c 4}, since it might mean either @samp{tail
2915 -c4} or @samp{tail -c 10 4}; and avoid @samp{tail +4}, since it might
2916 mean either @samp{tail ./+4} or @samp{tail -n +4}.
2921 @node split invocation
2922 @section @command{split}: Split a file into fixed-size pieces
2925 @cindex splitting a file into pieces
2926 @cindex pieces, splitting a file into
2928 @command{split} creates output files containing consecutive sections of
2929 @var{input} (standard input if none is given or @var{input} is
2930 @samp{-}). Synopsis:
2933 split [@var{option}] [@var{input} [@var{prefix}]]
2936 By default, @command{split} puts 1000 lines of @var{input} (or whatever is
2937 left over for the last section), into each output file.
2939 @cindex output file name prefix
2940 The output files' names consist of @var{prefix} (@samp{x} by default)
2941 followed by a group of characters (@samp{aa}, @samp{ab}, @dots{} by
2942 default), such that concatenating the output files in traditional
2943 sorted order by file name produces
2944 the original input file. If the output file names are exhausted,
2945 @command{split} reports an error without deleting the output files
2948 The program accepts the following options. Also see @ref{Common options}.
2952 @item -l @var{lines}
2953 @itemx --lines=@var{lines}
2956 Put @var{lines} lines of @var{input} into each output file.
2958 For compatibility @command{split} also supports an obsolete
2959 option syntax @option{-@var{lines}}. New scripts should use @option{-l
2960 @var{lines}} instead.
2963 @itemx --bytes=@var{size}
2966 Put @var{size} bytes of @var{input} into each output file.
2967 @multiplierSuffixes{size}
2970 @itemx --line-bytes=@var{size}
2972 @opindex --line-bytes
2973 Put into each output file as many complete lines of @var{input} as
2974 possible without exceeding @var{size} bytes. Individual lines longer than
2975 @var{size} bytes are broken into multiple files.
2976 @var{size} has the same format as for the @option{--bytes} option.
2978 @item -a @var{length}
2979 @itemx --suffix-length=@var{length}
2981 @opindex --suffix-length
2982 Use suffixes of length @var{length}. The default @var{length} is 2.
2985 @itemx --numeric-suffixes
2987 @opindex --numeric-suffixes
2988 Use digits in suffixes rather than lower-case letters.
2992 Write a diagnostic just before each output file is opened.
2999 @node csplit invocation
3000 @section @command{csplit}: Split a file into context-determined pieces
3003 @cindex context splitting
3004 @cindex splitting a file into pieces by context
3006 @command{csplit} creates zero or more output files containing sections of
3007 @var{input} (standard input if @var{input} is @samp{-}). Synopsis:
3010 csplit [@var{option}]@dots{} @var{input} @var{pattern}@dots{}
3013 The contents of the output files are determined by the @var{pattern}
3014 arguments, as detailed below. An error occurs if a @var{pattern}
3015 argument refers to a nonexistent line of the input file (e.g., if no
3016 remaining line matches a given regular expression). After every
3017 @var{pattern} has been matched, any remaining input is copied into one
3020 By default, @command{csplit} prints the number of bytes written to each
3021 output file after it has been created.
3023 The types of pattern arguments are:
3028 Create an output file containing the input up to but not including line
3029 @var{n} (a positive integer). If followed by a repeat count, also
3030 create an output file containing the next @var{n} lines of the input
3031 file once for each repeat.
3033 @item /@var{regexp}/[@var{offset}]
3034 Create an output file containing the current line up to (but not
3035 including) the next line of the input file that contains a match for
3036 @var{regexp}. The optional @var{offset} is an integer.
3037 If it is given, the input up to (but not including) the
3038 matching line plus or minus @var{offset} is put into the output file,
3039 and the line after that begins the next section of input.
3041 @item %@var{regexp}%[@var{offset}]
3042 Like the previous type, except that it does not create an output
3043 file, so that section of the input file is effectively ignored.
3045 @item @{@var{repeat-count}@}
3046 Repeat the previous pattern @var{repeat-count} additional
3047 times. The @var{repeat-count} can either be a positive integer or an
3048 asterisk, meaning repeat as many times as necessary until the input is
3053 The output files' names consist of a prefix (@samp{xx} by default)
3054 followed by a suffix. By default, the suffix is an ascending sequence
3055 of two-digit decimal numbers from @samp{00} to @samp{99}. In any case,
3056 concatenating the output files in sorted order by file name produces the
3057 original input file.
3059 By default, if @command{csplit} encounters an error or receives a hangup,
3060 interrupt, quit, or terminate signal, it removes any output files
3061 that it has created so far before it exits.
3063 The program accepts the following options. Also see @ref{Common options}.
3067 @item -f @var{prefix}
3068 @itemx --prefix=@var{prefix}
3071 @cindex output file name prefix
3072 Use @var{prefix} as the output file name prefix.
3074 @item -b @var{suffix}
3075 @itemx --suffix=@var{suffix}
3078 @cindex output file name suffix
3079 Use @var{suffix} as the output file name suffix. When this option is
3080 specified, the suffix string must include exactly one
3081 @code{printf(3)}-style conversion specification, possibly including
3082 format specification flags, a field width, a precision specifications,
3083 or all of these kinds of modifiers. The format letter must convert a
3084 binary integer argument to readable form; thus, only @samp{d}, @samp{i},
3085 @samp{u}, @samp{o}, @samp{x}, and @samp{X} conversions are allowed. The
3086 entire @var{suffix} is given (with the current output file number) to
3087 @code{sprintf(3)} to form the file name suffixes for each of the
3088 individual output files in turn. If this option is used, the
3089 @option{--digits} option is ignored.
3091 @item -n @var{digits}
3092 @itemx --digits=@var{digits}
3095 Use output file names containing numbers that are @var{digits} digits
3096 long instead of the default 2.
3101 @opindex --keep-files
3102 Do not remove output files when errors are encountered.
3105 @itemx --elide-empty-files
3107 @opindex --elide-empty-files
3108 Suppress the generation of zero-length output files. (In cases where
3109 the section delimiters of the input file are supposed to mark the first
3110 lines of each of the sections, the first output file will generally be a
3111 zero-length file unless you use this option.) The output file sequence
3112 numbers always run consecutively starting from 0, even when this option
3123 Do not print counts of output file sizes.
3129 Here is an example of its usage.
3130 First, create an empty directory for the exercise,
3137 Now, split the sequence of 1..14 on lines that end with 0 or 5:
3140 $ seq 14 | csplit - '/[05]$/' '@{*@}'
3146 Each number printed above is the size of an output
3147 file that csplit has just created.
3148 List the names of those output files:
3155 Use @command{head} to show their contents:
3180 @node Summarizing files
3181 @chapter Summarizing files
3183 @cindex summarizing files
3185 These commands generate just a few numbers representing entire
3189 * wc invocation:: Print newline, word, and byte counts.
3190 * sum invocation:: Print checksum and block counts.
3191 * cksum invocation:: Print CRC checksum and byte counts.
3192 * md5sum invocation:: Print or check MD5 digests.
3193 * sha1sum invocation:: Print or check SHA-1 digests.
3194 * sha2 utilities:: Print or check SHA-2 digests.
3199 @section @command{wc}: Print newline, word, and byte counts
3203 @cindex character count
3207 @command{wc} counts the number of bytes, characters, whitespace-separated
3208 words, and newlines in each given @var{file}, or standard input if none
3209 are given or for a @var{file} of @samp{-}. Synopsis:
3212 wc [@var{option}]@dots{} [@var{file}]@dots{}
3215 @cindex total counts
3216 @command{wc} prints one line of counts for each file, and if the file was
3217 given as an argument, it prints the file name following the counts. If
3218 more than one @var{file} is given, @command{wc} prints a final line
3219 containing the cumulative counts, with the file name @file{total}. The
3220 counts are printed in this order: newlines, words, characters, bytes,
3221 maximum line length.
3222 Each count is printed right-justified in a field with at least one
3223 space between fields so that the numbers and file names normally line
3224 up nicely in columns. The width of the count fields varies depending
3225 on the inputs, so you should not depend on a particular field width.
3226 However, as a @acronym{GNU} extension, if only one count is printed,
3227 it is guaranteed to be printed without leading spaces.
3229 By default, @command{wc} prints three counts: the newline, words, and byte
3230 counts. Options can specify that only certain counts be printed.
3231 Options do not undo others previously given, so
3238 prints both the byte counts and the word counts.
3240 With the @option{--max-line-length} option, @command{wc} prints the length
3241 of the longest line per file, and if there is more than one file it
3242 prints the maximum (not the sum) of those lengths. The line lengths here
3243 are measured in screen columns, according to the current locale and
3244 assuming tab positions in every 8th column.
3246 The program accepts the following options. Also see @ref{Common options}.
3254 Print only the byte counts.
3260 Print only the character counts.
3266 Print only the word counts.
3272 Print only the newline counts.
3275 @itemx --max-line-length
3277 @opindex --max-line-length
3278 Print only the maximum line lengths.
3280 @macro filesZeroFromOption{cmd,withTotalOption,subListOutput}
3281 @itemx --files0-from=@var{file}
3282 @opindex --files0-from=@var{file}
3283 @c This is commented out to avoid a texi2dvi failure.
3284 @c texi2dvi (GNU Texinfo 4.11) 1.104
3285 @c @cindex including files from @command{\cmd\}
3286 Disallow processing files named on the command line, and instead process
3287 those named in file @var{file}; each name being terminated by a zero byte
3288 (@acronym{ASCII} @sc{nul}).
3289 This is useful \withTotalOption\
3290 when the list of file names is so long that it may exceed a command line
3292 In such cases, running @command{\cmd\} via @command{xargs} is undesirable
3293 because it splits the list into pieces and makes @command{\cmd\} print
3294 \subListOutput\ for each sublist rather than for the entire list.
3295 One way to produce a list of @acronym{ASCII} @sc{nul} terminated file names is with @sc{gnu}
3296 @command{find}, using its @option{-print0} predicate.
3297 If @var{file} is @samp{-} then the @acronym{ASCII} @sc{nul} terminated file names
3298 are read from standard input.
3300 @filesZeroFromOption{wc,,a total}
3302 For example, to find the length of the longest line in any @file{.c} or
3303 @file{.h} file in the current hierarchy, do this:
3306 find . -name '*.[ch]' -print0 |
3307 wc -L --files0-from=- | tail -n1
3315 @node sum invocation
3316 @section @command{sum}: Print checksum and block counts
3319 @cindex 16-bit checksum
3320 @cindex checksum, 16-bit
3322 @command{sum} computes a 16-bit checksum for each given @var{file}, or
3323 standard input if none are given or for a @var{file} of @samp{-}. Synopsis:
3326 sum [@var{option}]@dots{} [@var{file}]@dots{}
3329 @command{sum} prints the checksum for each @var{file} followed by the
3330 number of blocks in the file (rounded up). If more than one @var{file}
3331 is given, file names are also printed (by default). (With the
3332 @option{--sysv} option, corresponding file names are printed when there is
3333 at least one file argument.)
3335 By default, @sc{gnu} @command{sum} computes checksums using an algorithm
3336 compatible with BSD @command{sum} and prints file sizes in units of
3339 The program accepts the following options. Also see @ref{Common options}.
3345 @cindex BSD @command{sum}
3346 Use the default (BSD compatible) algorithm. This option is included for
3347 compatibility with the System V @command{sum}. Unless @option{-s} was also
3348 given, it has no effect.
3354 @cindex System V @command{sum}
3355 Compute checksums using an algorithm compatible with System V
3356 @command{sum}'s default, and print file sizes in units of 512-byte blocks.
3360 @command{sum} is provided for compatibility; the @command{cksum} program (see
3361 next section) is preferable in new applications.
3366 @node cksum invocation
3367 @section @command{cksum}: Print CRC checksum and byte counts
3370 @cindex cyclic redundancy check
3371 @cindex CRC checksum
3373 @command{cksum} computes a cyclic redundancy check (CRC) checksum for each
3374 given @var{file}, or standard input if none are given or for a
3375 @var{file} of @samp{-}. Synopsis:
3378 cksum [@var{option}]@dots{} [@var{file}]@dots{}
3381 @command{cksum} prints the CRC checksum for each file along with the number
3382 of bytes in the file, and the file name unless no arguments were given.
3384 @command{cksum} is typically used to ensure that files
3385 transferred by unreliable means (e.g., netnews) have not been corrupted,
3386 by comparing the @command{cksum} output for the received files with the
3387 @command{cksum} output for the original files (typically given in the
3390 The CRC algorithm is specified by the @acronym{POSIX} standard. It is not
3391 compatible with the BSD or System V @command{sum} algorithms (see the
3392 previous section); it is more robust.
3394 The only options are @option{--help} and @option{--version}. @xref{Common
3400 @node md5sum invocation
3401 @section @command{md5sum}: Print or check MD5 digests
3405 @cindex 128-bit checksum
3406 @cindex checksum, 128-bit
3407 @cindex fingerprint, 128-bit
3408 @cindex message-digest, 128-bit
3410 @command{md5sum} computes a 128-bit checksum (or @dfn{fingerprint} or
3411 @dfn{message-digest}) for each specified @var{file}.
3413 Note: The MD5 digest is more reliable than a simple CRC (provided by
3414 the @command{cksum} command) for detecting accidental file corruption,
3415 as the chances of accidentally having two files with identical MD5
3416 are vanishingly small. However, it should not be considered truly
3417 secure against malicious tampering: although finding a file with a
3418 given MD5 fingerprint, or modifying a file so as to retain its MD5 are
3419 considered infeasible at the moment, it is known how to produce
3420 different files with identical MD5 (a ``collision''), something which
3421 can be a security issue in certain contexts. For more secure hashes,
3422 consider using SHA-1 or SHA-2. @xref{sha1sum invocation}, and
3423 @ref{sha2 utilities}.
3425 If a @var{file} is specified as @samp{-} or if no files are given
3426 @command{md5sum} computes the checksum for the standard input.
3427 @command{md5sum} can also determine whether a file and checksum are
3428 consistent. Synopsis:
3431 md5sum [@var{option}]@dots{} [@var{file}]@dots{}
3434 For each @var{file}, @samp{md5sum} outputs the MD5 checksum, a flag
3435 indicating a binary or text input file, and the file name.
3436 If @var{file} contains a backslash or newline, the
3437 line is started with a backslash, and each problematic character in
3438 the file name is escaped with a backslash, making the output
3439 unambiguous even in the presence of arbitrary file names.
3440 If @var{file} is omitted or specified as @samp{-}, standard input is read.
3442 The program accepts the following options. Also see @ref{Common options}.
3450 @cindex binary input files
3451 Treat each input file as binary, by reading it in binary mode and
3452 outputting a @samp{*} flag. This is the inverse of @option{--text}.
3453 On systems like @acronym{GNU} that do not distinguish between binary
3454 and text files, this option merely flags each input file as binary:
3455 the MD5 checksum is unaffected. This option is the default on systems
3456 like MS-DOS that distinguish between binary and text files, except
3457 for reading standard input when standard input is a terminal.
3461 Read file names and checksum information (not data) from each
3462 @var{file} (or from stdin if no @var{file} was specified) and report
3463 whether the checksums match the contents of the named files.
3464 The input to this mode of @command{md5sum} is usually the output of
3465 a prior, checksum-generating run of @samp{md5sum}.
3466 Each valid line of input consists of an MD5 checksum, a binary/text
3467 flag, and then a file name.
3468 Binary files are marked with @samp{*}, text with @samp{ }.
3469 For each such line, @command{md5sum} reads the named file and computes its
3470 MD5 checksum. Then, if the computed message digest does not match the
3471 one on the line with the file name, the file is noted as having
3472 failed the test. Otherwise, the file passes the test.
3473 By default, for each valid line, one line is written to standard
3474 output indicating whether the named file passed the test.
3475 After all checks have been performed, if there were any failures,
3476 a warning is issued to standard error.
3477 Use the @option{--status} option to inhibit that output.
3478 If any listed file cannot be opened or read, if any valid line has
3479 an MD5 checksum inconsistent with the associated file, or if no valid
3480 line is found, @command{md5sum} exits with nonzero status. Otherwise,
3481 it exits successfully.
3485 @cindex verifying MD5 checksums
3486 This option is useful only when verifying checksums.
3487 When verifying checksums, don't generate an 'OK' message per successfully
3488 checked file. Files that fail the verification are reported in the
3489 default one-line-per-file format. If there is any checksum mismatch,
3490 print a warning summarizing the failures to standard error.
3494 @cindex verifying MD5 checksums
3495 This option is useful only when verifying checksums.
3496 When verifying checksums, don't generate the default one-line-per-file
3497 diagnostic and don't output the warning summarizing any failures.
3498 Failures to open or read a file still evoke individual diagnostics to
3500 If all listed files are readable and are consistent with the associated
3501 MD5 checksums, exit successfully. Otherwise exit with a status code
3502 indicating there was a failure.
3508 @cindex text input files
3509 Treat each input file as text, by reading it in text mode and
3510 outputting a @samp{ } flag. This is the inverse of @option{--binary}.
3511 This option is the default on systems like @acronym{GNU} that do not
3512 distinguish between binary and text files. On other systems, it is
3513 the default for reading standard input when standard input is a
3520 @cindex verifying MD5 checksums
3521 When verifying checksums, warn about improperly formatted MD5 checksum lines.
3522 This option is useful only if all but a few lines in the checked input
3530 @node sha1sum invocation
3531 @section @command{sha1sum}: Print or check SHA-1 digests
3535 @cindex 160-bit checksum
3536 @cindex checksum, 160-bit
3537 @cindex fingerprint, 160-bit
3538 @cindex message-digest, 160-bit
3540 @command{sha1sum} computes a 160-bit checksum for each specified
3541 @var{file}. The usage and options of this command are precisely the
3542 same as for @command{md5sum}. @xref{md5sum invocation}.
3544 Note: The SHA-1 digest is more secure than MD5, and no collisions of
3545 it are known (different files having the same fingerprint). However,
3546 it is known that they can be produced with considerable, but not
3547 unreasonable, resources. For this reason, it is generally considered
3548 that SHA-1 should be gradually phased out in favor of the more secure
3549 SHA-2 hash algorithms. @xref{sha2 utilities}.
3552 @node sha2 utilities
3553 @section sha2 utilities: Print or check SHA-2 digests
3560 @cindex 224-bit checksum
3561 @cindex 256-bit checksum
3562 @cindex 384-bit checksum
3563 @cindex 512-bit checksum
3564 @cindex checksum, 224-bit
3565 @cindex checksum, 256-bit
3566 @cindex checksum, 384-bit
3567 @cindex checksum, 512-bit
3568 @cindex fingerprint, 224-bit
3569 @cindex fingerprint, 256-bit
3570 @cindex fingerprint, 384-bit
3571 @cindex fingerprint, 512-bit
3572 @cindex message-digest, 224-bit
3573 @cindex message-digest, 256-bit
3574 @cindex message-digest, 384-bit
3575 @cindex message-digest, 512-bit
3577 The commands @command{sha224sum}, @command{sha256sum},
3578 @command{sha384sum} and @command{sha512sum} compute checksums of
3579 various lengths (respectively 224, 256, 384 and 512 bits),
3580 collectively known as the SHA-2 hashes. The usage and options of
3581 these commands are precisely the same as for @command{md5sum}.
3582 @xref{md5sum invocation}.
3584 Note: The SHA384 and SHA512 digests are considerably slower to
3585 compute, especially on 32-bit computers, than SHA224 or SHA256.
3588 @node Operating on sorted files
3589 @chapter Operating on sorted files
3591 @cindex operating on sorted files
3592 @cindex sorted files, operations on
3594 These commands work with (or produce) sorted files.
3597 * sort invocation:: Sort text files.
3598 * shuf invocation:: Shuffle text files.
3599 * uniq invocation:: Uniquify files.
3600 * comm invocation:: Compare two sorted files line by line.
3601 * ptx invocation:: Produce a permuted index of file contents.
3602 * tsort invocation:: Topological sort.
3606 @node sort invocation
3607 @section @command{sort}: Sort text files
3610 @cindex sorting files
3612 @command{sort} sorts, merges, or compares all the lines from the given
3613 files, or standard input if none are given or for a @var{file} of
3614 @samp{-}. By default, @command{sort} writes the results to standard
3618 sort [@var{option}]@dots{} [@var{file}]@dots{}
3621 @command{sort} has three modes of operation: sort (the default), merge,
3622 and check for sortedness. The following options change the operation
3629 @itemx --check=diagnose-first
3632 @cindex checking for sortedness
3633 Check whether the given file is already sorted: if it is not all
3634 sorted, print a diagnostic containing the first out-of-order line and
3635 exit with a status of 1.
3636 Otherwise, exit successfully.
3637 At most one input file can be given.
3640 @itemx --check=quiet
3641 @itemx --check=silent
3644 @cindex checking for sortedness
3645 Exit successfully if the given file is already sorted, and
3646 exit with status 1 otherwise.
3647 At most one input file can be given.
3648 This is like @option{-c}, except it does not print a diagnostic.
3654 @cindex merging sorted files
3655 Merge the given files by sorting them as a group. Each input file must
3656 always be individually sorted. It always works to sort instead of
3657 merge; merging is provided because it is faster, in the case where it
3662 @cindex sort stability
3663 @cindex sort's last-resort comparison
3664 A pair of lines is compared as follows:
3665 @command{sort} compares each pair of fields, in the
3666 order specified on the command line, according to the associated
3667 ordering options, until a difference is found or no fields are left.
3668 If no key fields are specified, @command{sort} uses a default key of
3669 the entire line. Finally, as a last resort when all keys compare
3670 equal, @command{sort} compares entire lines as if no ordering options
3671 other than @option{--reverse} (@option{-r}) were specified. The
3672 @option{--stable} (@option{-s}) option disables this @dfn{last-resort
3673 comparison} so that lines in which all fields compare equal are left
3674 in their original relative order. The @option{--unique}
3675 (@option{-u}) option also disables the last-resort comparison.
3679 Unless otherwise specified, all comparisons use the character collating
3680 sequence specified by the @env{LC_COLLATE} locale.@footnote{If you
3681 use a non-@acronym{POSIX} locale (e.g., by setting @env{LC_ALL}
3682 to @samp{en_US}), then @command{sort} may produce output that is sorted
3683 differently than you're accustomed to. In that case, set the @env{LC_ALL}
3684 environment variable to @samp{C}. Note that setting only @env{LC_COLLATE}
3685 has two problems. First, it is ineffective if @env{LC_ALL} is also set.
3686 Second, it has undefined behavior if @env{LC_CTYPE} (or @env{LANG}, if
3687 @env{LC_CTYPE} is unset) is set to an incompatible value. For example,
3688 you get undefined behavior if @env{LC_CTYPE} is @code{ja_JP.PCK} but
3689 @env{LC_COLLATE} is @code{en_US.UTF-8}.}
3691 @sc{gnu} @command{sort} (as specified for all @sc{gnu} utilities) has no
3692 limit on input line length or restrictions on bytes allowed within lines.
3693 In addition, if the final byte of an input file is not a newline, @sc{gnu}
3694 @command{sort} silently supplies one. A line's trailing newline is not
3695 part of the line for comparison purposes.
3697 @cindex exit status of @command{sort}
3701 0 if no error occurred
3702 1 if invoked with @option{-c} or @option{-C} and the input is not sorted
3703 2 if an error occurred
3707 If the environment variable @env{TMPDIR} is set, @command{sort} uses its
3708 value as the directory for temporary files instead of @file{/tmp}. The
3709 @option{--temporary-directory} (@option{-T}) option in turn overrides
3710 the environment variable.
3712 The following options affect the ordering of output lines. They may be
3713 specified globally or as part of a specific key field. If no key
3714 fields are specified, global options apply to comparison of entire
3715 lines; otherwise the global options are inherited by key fields that do
3716 not specify any special options of their own. In pre-@acronym{POSIX}
3717 versions of @command{sort}, global options affect only later key fields,
3718 so portable shell scripts should specify global options first.
3723 @itemx --ignore-leading-blanks
3725 @opindex --ignore-leading-blanks
3726 @cindex blanks, ignoring leading
3728 Ignore leading blanks when finding sort keys in each line.
3729 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3730 can change this. Note blanks may be ignored by your locale's collating
3731 rules, but without this option they will be significant for character
3732 positions specified in keys with the @option{-k} option.
3735 @itemx --dictionary-order
3737 @opindex --dictionary-order
3738 @cindex dictionary order
3739 @cindex phone directory order
3740 @cindex telephone directory order
3742 Sort in @dfn{phone directory} order: ignore all characters except
3743 letters, digits and blanks when sorting.
3744 By default letters and digits are those of @acronym{ASCII} and a blank
3745 is a space or a tab, but the @env{LC_CTYPE} locale can change this.
3748 @itemx --ignore-case
3750 @opindex --ignore-case
3751 @cindex ignoring case
3752 @cindex case folding
3754 Fold lowercase characters into the equivalent uppercase characters when
3755 comparing so that, for example, @samp{b} and @samp{B} sort as equal.
3756 The @env{LC_CTYPE} locale determines character types.
3757 When used with @option{--unique} those lower case equivalent lines are
3758 thrown away. (There is currently no way to throw away the upper case
3759 equivalent instead. (Any @option{--reverse} given would only affect
3760 the final result, after the throwing away.))
3763 @itemx --general-numeric-sort
3764 @itemx --sort=general-numeric
3766 @opindex --general-numeric-sort
3768 @cindex general numeric sort
3770 Sort numerically, using the standard C function @code{strtold} to convert
3771 a prefix of each line to a long double-precision floating point number.
3772 This allows floating point numbers to be specified in scientific notation,
3773 like @code{1.0e-34} and @code{10e100}.
3774 The @env{LC_NUMERIC} locale determines the decimal-point character.
3775 Do not report overflow, underflow, or conversion errors.
3776 Use the following collating sequence:
3780 Lines that do not start with numbers (all considered to be equal).
3782 NaNs (``Not a Number'' values, in IEEE floating point arithmetic)
3783 in a consistent but machine-dependent order.
3787 Finite numbers in ascending numeric order (with @math{-0} and @math{+0} equal).
3792 Use this option only if there is no alternative; it is much slower than
3793 @option{--numeric-sort} (@option{-n}) and it can lose information when
3794 converting to floating point.
3797 @itemx --human-numeric-sort
3798 @itemx --sort=human-numeric
3800 @opindex --human-numeric-sort
3802 @cindex human numeric sort
3804 Sort numerically, as per the @option{--numeric-sort} option below, and in
3805 addition handle IEC or SI suffixes like MiB, MB etc (@ref{Block size}).
3806 Note a mixture of IEC and SI suffixes is not supported and will
3807 be flagged as an error. Also the numbers must be abbreviated uniformly.
3808 I.E. values with different precisions like 6000K and 5M will be sorted
3812 @itemx --ignore-nonprinting
3814 @opindex --ignore-nonprinting
3815 @cindex nonprinting characters, ignoring
3816 @cindex unprintable characters, ignoring
3818 Ignore nonprinting characters.
3819 The @env{LC_CTYPE} locale determines character types.
3820 This option has no effect if the stronger @option{--dictionary-order}
3821 (@option{-d}) option is also given.
3827 @opindex --month-sort
3829 @cindex months, sorting by
3831 An initial string, consisting of any amount of blanks, followed
3832 by a month name abbreviation, is folded to UPPER case and
3833 compared in the order @samp{JAN} < @samp{FEB} < @dots{} < @samp{DEC}.
3834 Invalid names compare low to valid names. The @env{LC_TIME} locale
3835 category determines the month spellings.
3836 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3840 @itemx --numeric-sort
3841 @itemx --sort=numeric
3843 @opindex --numeric-sort
3845 @cindex numeric sort
3847 Sort numerically. The number begins each line and consists
3848 of optional blanks, an optional @samp{-} sign, and zero or more
3849 digits possibly separated by thousands separators, optionally followed
3850 by a decimal-point character and zero or more digits. An empty
3851 number is treated as @samp{0}. The @env{LC_NUMERIC}
3852 locale specifies the decimal-point character and thousands separator.
3853 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3856 Comparison is exact; there is no rounding error.
3858 Neither a leading @samp{+} nor exponential notation is recognized.
3859 To compare such strings numerically, use the
3860 @option{--general-numeric-sort} (@option{-g}) option.
3863 @itemx --version-sort
3865 @opindex --version-sort
3866 @cindex version number sort
3867 Sort by version name and number. It behaves like a standard sort,
3868 except that each sequence of decimal digits is treated numerically
3869 as an index/version number. (@xref{Details about version sort}.)
3875 @cindex reverse sorting
3876 Reverse the result of comparison, so that lines with greater key values
3877 appear earlier in the output instead of later.
3880 @itemx --random-sort
3881 @itemx --sort=random
3883 @opindex --random-sort
3886 Sort by hashing the input keys and then sorting the hash values.
3887 Choose the hash function at random, ensuring that it is free of
3888 collisions so that differing keys have differing hash values. This is
3889 like a random permutation of the inputs (@pxref{shuf invocation}),
3890 except that keys with the same value sort together.
3892 If multiple random sort fields are specified, the same random hash
3893 function is used for all fields. To use different random hash
3894 functions for different fields, you can invoke @command{sort} more
3897 The choice of hash function is affected by the
3898 @option{--random-source} option.
3906 @item --compress-program=@var{prog}
3907 Compress any temporary files with the program @var{prog}.
3909 With no arguments, @var{prog} must compress standard input to standard
3910 output, and when given the @option{-d} option it must decompress
3911 standard input to standard output.
3913 Terminate with an error if @var{prog} exits with nonzero status.
3915 White space and the backslash character should not appear in
3916 @var{prog}; they are reserved for future use.
3918 @filesZeroFromOption{sort,,sorted output}
3920 @item -k @var{pos1}[,@var{pos2}]
3921 @itemx --key=@var{pos1}[,@var{pos2}]
3925 Specify a sort field that consists of the part of the line between
3926 @var{pos1} and @var{pos2} (or the end of the line, if @var{pos2} is
3927 omitted), @emph{inclusive}.
3929 Each @var{pos} has the form @samp{@var{f}[.@var{c}][@var{opts}]},
3930 where @var{f} is the number of the field to use, and @var{c} is the number
3931 of the first character from the beginning of the field. Fields and character
3932 positions are numbered starting with 1; a character position of zero in
3933 @var{pos2} indicates the field's last character. If @samp{.@var{c}} is
3934 omitted from @var{pos1}, it defaults to 1 (the beginning of the field);
3935 if omitted from @var{pos2}, it defaults to 0 (the end of the field).
3936 @var{opts} are ordering options, allowing individual keys to be sorted
3937 according to different rules; see below for details. Keys can span
3940 Example: To sort on the second field, use @option{--key=2,2}
3941 (@option{-k 2,2}). See below for more notes on keys and more examples.
3942 See also the @option{--debug} option to help determine the part
3943 of the line being used in the sort.
3946 Highlight the portion of each line used for sorting.
3947 Also issue warnings about questionable usage to stderr.
3949 @item --batch-size=@var{nmerge}
3950 @opindex --batch-size
3951 @cindex number of inputs to merge, nmerge
3952 Merge at most @var{nmerge} inputs at once.
3954 When @command{sort} has to merge more than @var{nmerge} inputs,
3955 it merges them in groups of @var{nmerge}, saving the result in
3956 a temporary file, which is then used as an input in a subsequent merge.
3958 A large value of @var{nmerge} may improve merge performance and decrease
3959 temporary storage utilization at the expense of increased memory usage
3960 and I/0. Conversely a small value of @var{nmerge} may reduce memory
3961 requirements and I/0 at the expense of temporary storage consumption and
3964 The value of @var{nmerge} must be at least 2. The default value is
3965 currently 16, but this is implementation-dependent and may change in
3968 The value of @var{nmerge} may be bounded by a resource limit for open
3969 file descriptors. The commands @samp{ulimit -n} or @samp{getconf
3970 OPEN_MAX} may display limits for your systems; these limits may be
3971 modified further if your program already has some files open, or if
3972 the operating system has other limits on the number of open files. If
3973 the value of @var{nmerge} exceeds the resource limit, @command{sort}
3974 silently uses a smaller value.
3976 @item -o @var{output-file}
3977 @itemx --output=@var{output-file}
3980 @cindex overwriting of input, allowed
3981 Write output to @var{output-file} instead of standard output.
3982 Normally, @command{sort} reads all input before opening
3983 @var{output-file}, so you can safely sort a file in place by using
3984 commands like @code{sort -o F F} and @code{cat F | sort -o F}.
3985 However, @command{sort} with @option{--merge} (@option{-m}) can open
3986 the output file before reading all input, so a command like @code{cat
3987 F | sort -m -o F - G} is not safe as @command{sort} might start
3988 writing @file{F} before @command{cat} is done reading it.
3990 @vindex POSIXLY_CORRECT
3991 On newer systems, @option{-o} cannot appear after an input file if
3992 @env{POSIXLY_CORRECT} is set, e.g., @samp{sort F -o F}. Portable
3993 scripts should specify @option{-o @var{output-file}} before any input
3996 @item --random-source=@var{file}
3997 @opindex --random-source
3998 @cindex random source for sorting
3999 Use @var{file} as a source of random data used to determine which
4000 random hash function to use with the @option{-R} option. @xref{Random
4007 @cindex sort stability
4008 @cindex sort's last-resort comparison
4010 Make @command{sort} stable by disabling its last-resort comparison.
4011 This option has no effect if no fields or global ordering options
4012 other than @option{--reverse} (@option{-r}) are specified.
4015 @itemx --buffer-size=@var{size}
4017 @opindex --buffer-size
4018 @cindex size for main memory sorting
4019 Use a main-memory sort buffer of the given @var{size}. By default,
4020 @var{size} is in units of 1024 bytes. Appending @samp{%} causes
4021 @var{size} to be interpreted as a percentage of physical memory.
4022 Appending @samp{K} multiplies @var{size} by 1024 (the default),
4023 @samp{M} by 1,048,576, @samp{G} by 1,073,741,824, and so on for
4024 @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}. Appending
4025 @samp{b} causes @var{size} to be interpreted as a byte count, with no
4028 This option can improve the performance of @command{sort} by causing it
4029 to start with a larger or smaller sort buffer than the default.
4030 However, this option affects only the initial buffer size. The buffer
4031 grows beyond @var{size} if @command{sort} encounters input lines larger
4034 @item -t @var{separator}
4035 @itemx --field-separator=@var{separator}
4037 @opindex --field-separator
4038 @cindex field separator character
4039 Use character @var{separator} as the field separator when finding the
4040 sort keys in each line. By default, fields are separated by the empty
4041 string between a non-blank character and a blank character.
4042 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
4045 That is, given the input line @w{@samp{ foo bar}}, @command{sort} breaks it
4046 into fields @w{@samp{ foo}} and @w{@samp{ bar}}. The field separator is
4047 not considered to be part of either the field preceding or the field
4048 following, so with @samp{sort @w{-t " "}} the same input line has
4049 three fields: an empty field, @samp{foo}, and @samp{bar}.
4050 However, fields that extend to the end of the line,
4051 as @option{-k 2}, or fields consisting of a range, as @option{-k 2,3},
4052 retain the field separators present between the endpoints of the range.
4054 To specify @acronym{ASCII} @sc{nul} as the field separator,
4055 use the two-character string @samp{\0}, e.g., @samp{sort -t '\0'}.
4057 @item -T @var{tempdir}
4058 @itemx --temporary-directory=@var{tempdir}
4060 @opindex --temporary-directory
4061 @cindex temporary directory
4063 Use directory @var{tempdir} to store temporary files, overriding the
4064 @env{TMPDIR} environment variable. If this option is given more than
4065 once, temporary files are stored in all the directories given. If you
4066 have a large sort or merge that is I/O-bound, you can often improve
4067 performance by using this option to specify directories on different
4068 disks and controllers.
4074 @cindex uniquifying output
4076 Normally, output only the first of a sequence of lines that compare
4077 equal. For the @option{--check} (@option{-c} or @option{-C}) option,
4078 check that no pair of consecutive lines compares equal.
4080 This option also disables the default last-resort comparison.
4082 The commands @code{sort -u} and @code{sort | uniq} are equivalent, but
4083 this equivalence does not extend to arbitrary @command{sort} options.
4084 For example, @code{sort -n -u} inspects only the value of the initial
4085 numeric string when checking for uniqueness, whereas @code{sort -n |
4086 uniq} inspects the entire line. @xref{uniq invocation}.
4088 @macro zeroTerminatedOption
4090 @itemx --zero-terminated
4092 @opindex --zero-terminated
4093 @cindex process zero-terminated items
4094 Delimit items with a zero byte rather than a newline (@acronym{ASCII} @sc{lf}).
4095 I.E. treat input as items separated by @acronym{ASCII} @sc{nul}
4096 and terminate output items with @acronym{ASCII} @sc{nul}.
4097 This option can be useful in conjunction with @samp{perl -0} or
4098 @samp{find -print0} and @samp{xargs -0} which do the same in order to
4099 reliably handle arbitrary file names (even those containing blanks
4100 or other special characters).
4102 @zeroTerminatedOption
4106 Historical (BSD and System V) implementations of @command{sort} have
4107 differed in their interpretation of some options, particularly
4108 @option{-b}, @option{-f}, and @option{-n}. @sc{gnu} sort follows the @acronym{POSIX}
4109 behavior, which is usually (but not always!) like the System V behavior.
4110 According to @acronym{POSIX}, @option{-n} no longer implies @option{-b}. For
4111 consistency, @option{-M} has been changed in the same way. This may
4112 affect the meaning of character positions in field specifications in
4113 obscure cases. The only fix is to add an explicit @option{-b}.
4115 A position in a sort field specified with @option{-k} may have any
4116 of the option letters @samp{MbdfghinRrV} appended to it, in which case no
4117 global ordering options are inherited by that particular field. The
4118 @option{-b} option may be independently attached to either or both of
4119 the start and end positions of a field specification, and if it is
4120 inherited from the global options it will be attached to both.
4121 If input lines can contain leading or adjacent blanks and @option{-t}
4122 is not used, then @option{-k} is typically combined with @option{-b} or
4123 an option that implicitly ignores leading blanks (@samp{Mghn}) as otherwise
4124 the varying numbers of leading blanks in fields can cause confusing results.
4126 If the start position in a sort field specifier falls after the end of
4127 the line or after the end field, the field is empty. If the @option{-b}
4128 option was specified, the @samp{.@var{c}} part of a field specification
4129 is counted from the first nonblank character of the field.
4131 @vindex _POSIX2_VERSION
4132 @vindex POSIXLY_CORRECT
4133 On older systems, @command{sort} supports an obsolete origin-zero
4134 syntax @samp{+@var{pos1} [-@var{pos2}]} for specifying sort keys.
4135 The obsolete sequence @samp{sort +@var{a}.@var{x} -@var{b}.@var{y}}
4136 is equivalent to @samp{sort -k @var{a+1}.@var{x+1},@var{b}} if @var{y}
4137 is @samp{0} or absent, otherwise it is equivalent to @samp{sort -k
4138 @var{a+1}.@var{x+1},@var{b+1}.@var{y}}.
4140 This obsolete behavior can be enabled or disabled with the
4141 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4142 conformance}); it can also be enabled when @env{POSIXLY_CORRECT} is
4143 not set by using the obsolete syntax with @samp{-@var{pos2}} present.
4145 Scripts intended for use on standard hosts should avoid obsolete
4146 syntax and should use @option{-k} instead. For example, avoid
4147 @samp{sort +2}, since it might be interpreted as either @samp{sort
4148 ./+2} or @samp{sort -k 3}. If your script must also run on hosts that
4149 support only the obsolete syntax, it can use a test like @samp{if sort
4150 -k 1 </dev/null >/dev/null 2>&1; then @dots{}} to decide which syntax
4153 Here are some examples to illustrate various combinations of options.
4158 Sort in descending (reverse) numeric order.
4165 Sort alphabetically, omitting the first and second fields
4166 and the blanks at the start of the third field.
4167 This uses a single key composed of the characters beginning
4168 at the start of the first nonblank character in field three
4169 and extending to the end of each line.
4176 Sort numerically on the second field and resolve ties by sorting
4177 alphabetically on the third and fourth characters of field five.
4178 Use @samp{:} as the field delimiter.
4181 sort -t : -k 2,2n -k 5.3,5.4
4184 Note that if you had written @option{-k 2n} instead of @option{-k 2,2n}
4185 @command{sort} would have used all characters beginning in the second field
4186 and extending to the end of the line as the primary @emph{numeric}
4187 key. For the large majority of applications, treating keys spanning
4188 more than one field as numeric will not do what you expect.
4190 Also note that the @samp{n} modifier was applied to the field-end
4191 specifier for the first key. It would have been equivalent to
4192 specify @option{-k 2n,2} or @option{-k 2n,2n}. All modifiers except
4193 @samp{b} apply to the associated @emph{field}, regardless of whether
4194 the modifier character is attached to the field-start and/or the
4195 field-end part of the key specifier.
4198 Sort the password file on the fifth field and ignore any
4199 leading blanks. Sort lines with equal values in field five
4200 on the numeric user ID in field three. Fields are separated
4204 sort -t : -k 5b,5 -k 3,3n /etc/passwd
4205 sort -t : -n -k 5b,5 -k 3,3 /etc/passwd
4206 sort -t : -b -k 5,5 -k 3,3n /etc/passwd
4209 These three commands have equivalent effect. The first specifies that
4210 the first key's start position ignores leading blanks and the second
4211 key is sorted numerically. The other two commands rely on global
4212 options being inherited by sort keys that lack modifiers. The inheritance
4213 works in this case because @option{-k 5b,5b} and @option{-k 5b,5} are
4214 equivalent, as the location of a field-end lacking a @samp{.@var{c}}
4215 character position is not affected by whether initial blanks are
4219 Sort a set of log files, primarily by IPv4 address and secondarily by
4220 time stamp. If two lines' primary and secondary keys are identical,
4221 output the lines in the same order that they were input. The log
4222 files contain lines that look like this:
4225 4.150.156.3 - - [01/Apr/2004:06:31:51 +0000] message 1
4226 211.24.3.231 - - [24/Apr/2004:20:17:39 +0000] message 2
4229 Fields are separated by exactly one space. Sort IPv4 addresses
4230 lexicographically, e.g., 212.61.52.2 sorts before 212.129.233.201
4231 because 61 is less than 129.
4234 sort -s -t ' ' -k 4.9n -k 4.5M -k 4.2n -k 4.14,4.21 file*.log |
4235 sort -s -t '.' -k 1,1n -k 2,2n -k 3,3n -k 4,4n
4238 This example cannot be done with a single @command{sort} invocation,
4239 since IPv4 address components are separated by @samp{.} while dates
4240 come just after a space. So it is broken down into two invocations of
4241 @command{sort}: the first sorts by time stamp and the second by IPv4
4242 address. The time stamp is sorted by year, then month, then day, and
4243 finally by hour-minute-second field, using @option{-k} to isolate each
4244 field. Except for hour-minute-second there's no need to specify the
4245 end of each key field, since the @samp{n} and @samp{M} modifiers sort
4246 based on leading prefixes that cannot cross field boundaries. The
4247 IPv4 addresses are sorted lexicographically. The second sort uses
4248 @samp{-s} so that ties in the primary key are broken by the secondary
4249 key; the first sort uses @samp{-s} so that the combination of the two
4253 Generate a tags file in case-insensitive sorted order.
4256 find src -type f -print0 | sort -z -f | xargs -0 etags --append
4259 The use of @option{-print0}, @option{-z}, and @option{-0} in this case means
4260 that file names that contain blanks or other special characters are
4262 by the sort operation.
4264 @c This example is a bit contrived and needs more explanation.
4266 @c Sort records separated by an arbitrary string by using a pipe to convert
4267 @c each record delimiter string to @samp{\0}, then using sort's -z option,
4268 @c and converting each @samp{\0} back to the original record delimiter.
4271 @c printf 'c\n\nb\n\na\n'|perl -0pe 's/\n\n/\n\0/g'|sort -z|perl -0pe 's/\0/\n/g'
4275 Use the common @acronym{DSU, Decorate Sort Undecorate} idiom to
4276 sort lines according to their length.
4279 awk '@{print length, $0@}' /etc/passwd | sort -n | cut -f2- -d' '
4282 In general this technique can be used to sort data that the @command{sort}
4283 command does not support, or is inefficient at, sorting directly.
4286 Shuffle a list of directories, but preserve the order of files within
4287 each directory. For instance, one could use this to generate a music
4288 playlist in which albums are shuffled but the songs of each album are
4292 ls */* | sort -t / -k 1,1R -k 2,2
4298 @node shuf invocation
4299 @section @command{shuf}: Shuffling text
4302 @cindex shuffling files
4304 @command{shuf} shuffles its input by outputting a random permutation
4305 of its input lines. Each output permutation is equally likely.
4309 shuf [@var{option}]@dots{} [@var{file}]
4310 shuf -e [@var{option}]@dots{} [@var{arg}]@dots{}
4311 shuf -i @var{lo}-@var{hi} [@var{option}]@dots{}
4314 @command{shuf} has three modes of operation that affect where it
4315 obtains its input lines. By default, it reads lines from standard
4316 input. The following options change the operation mode:
4324 @cindex command-line operands to shuffle
4325 Treat each command-line operand as an input line.
4327 @item -i @var{lo}-@var{hi}
4328 @itemx --input-range=@var{lo}-@var{hi}
4330 @opindex --input-range
4331 @cindex input range to shuffle
4332 Act as if input came from a file containing the range of unsigned
4333 decimal integers @var{lo}@dots{}@var{hi}, one per line.
4337 @command{shuf}'s other options can affect its behavior in all
4342 @item -n @var{lines}
4343 @itemx --head-count=@var{count}
4345 @opindex --head-count
4346 @cindex head of output
4347 Output at most @var{count} lines. By default, all input lines are
4350 @item -o @var{output-file}
4351 @itemx --output=@var{output-file}
4354 @cindex overwriting of input, allowed
4355 Write output to @var{output-file} instead of standard output.
4356 @command{shuf} reads all input before opening
4357 @var{output-file}, so you can safely shuffle a file in place by using
4358 commands like @code{shuf -o F <F} and @code{cat F | shuf -o F}.
4360 @item --random-source=@var{file}
4361 @opindex --random-source
4362 @cindex random source for shuffling
4363 Use @var{file} as a source of random data used to determine which
4364 permutation to generate. @xref{Random sources}.
4366 @zeroTerminatedOption
4382 might produce the output
4392 Similarly, the command:
4395 shuf -e clubs hearts diamonds spades
4409 and the command @samp{shuf -i 1-4} might output:
4419 These examples all have four input lines, so @command{shuf} might
4420 produce any of the twenty-four possible permutations of the input. In
4421 general, if there are @var{n} input lines, there are @var{n}! (i.e.,
4422 @var{n} factorial, or @var{n} * (@var{n} - 1) * @dots{} * 1) possible
4423 output permutations.
4428 @node uniq invocation
4429 @section @command{uniq}: Uniquify files
4432 @cindex uniquify files
4434 @command{uniq} writes the unique lines in the given @file{input}, or
4435 standard input if nothing is given or for an @var{input} name of
4439 uniq [@var{option}]@dots{} [@var{input} [@var{output}]]
4442 By default, @command{uniq} prints its input lines, except that
4443 it discards all but the first of adjacent repeated lines, so that
4444 no output lines are repeated. Optionally, it can instead discard
4445 lines that are not repeated, or all repeated lines.
4447 The input need not be sorted, but repeated input lines are detected
4448 only if they are adjacent. If you want to discard non-adjacent
4449 duplicate lines, perhaps you want to use @code{sort -u}.
4450 @xref{sort invocation}.
4453 Comparisons honor the rules specified by the @env{LC_COLLATE}
4456 If no @var{output} file is specified, @command{uniq} writes to standard
4459 The program accepts the following options. Also see @ref{Common options}.
4464 @itemx --skip-fields=@var{n}
4466 @opindex --skip-fields
4467 Skip @var{n} fields on each line before checking for uniqueness. Use
4468 a null string for comparison if a line has fewer than @var{n} fields. Fields
4469 are sequences of non-space non-tab characters that are separated from
4470 each other by at least one space or tab.
4472 For compatibility @command{uniq} supports an obsolete option syntax
4473 @option{-@var{n}}. New scripts should use @option{-f @var{n}} instead.
4476 @itemx --skip-chars=@var{n}
4478 @opindex --skip-chars
4479 Skip @var{n} characters before checking for uniqueness. Use a null string
4480 for comparison if a line has fewer than @var{n} characters. If you use both
4481 the field and character skipping options, fields are skipped over first.
4483 @vindex _POSIX2_VERSION
4484 On older systems, @command{uniq} supports an obsolete option syntax
4486 This obsolete behavior can be enabled or disabled with the
4487 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4488 conformance}), but portable scripts should avoid commands whose
4489 behavior depends on this variable.
4490 For example, use @samp{uniq ./+10} or @samp{uniq -s 10} rather than
4491 the ambiguous @samp{uniq +10}.
4497 Print the number of times each line occurred along with the line.
4500 @itemx --ignore-case
4502 @opindex --ignore-case
4503 Ignore differences in case when comparing lines.
4509 @cindex repeated lines, outputting
4510 Discard lines that are not repeated. When used by itself, this option
4511 causes @command{uniq} to print the first copy of each repeated line,
4515 @itemx --all-repeated[=@var{delimit-method}]
4517 @opindex --all-repeated
4518 @cindex all repeated lines, outputting
4519 Do not discard the second and subsequent repeated input lines,
4520 but discard lines that are not repeated.
4521 This option is useful mainly in conjunction with other options e.g.,
4522 to ignore case or to compare only selected fields.
4523 The optional @var{delimit-method} tells how to delimit
4524 groups of repeated lines, and must be one of the following:
4529 Do not delimit groups of repeated lines.
4530 This is equivalent to @option{--all-repeated} (@option{-D}).
4533 Output a newline before each group of repeated lines.
4534 With @option{--zero-terminated} (@option{-z}), use a zero
4535 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4538 Separate groups of repeated lines with a single newline.
4539 With @option{--zero-terminated} (@option{-z}), use a zero
4540 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4541 This is the same as using @samp{prepend}, except that
4542 no delimiter is inserted before the first group, and hence
4543 may be better suited for output direct to users.
4546 Note that when groups are delimited and the input stream contains
4547 two or more consecutive blank lines, then the output is ambiguous.
4548 To avoid that, filter the input through @samp{tr -s '\n'} to replace
4549 each sequence of consecutive newlines with a single newline.
4551 This is a @sc{gnu} extension.
4552 @c FIXME: give an example showing *how* it's useful
4558 @cindex unique lines, outputting
4559 Discard the first repeated line. When used by itself, this option
4560 causes @command{uniq} to print unique lines, and nothing else.
4563 @itemx --check-chars=@var{n}
4565 @opindex --check-chars
4566 Compare at most @var{n} characters on each line (after skipping any specified
4567 fields and characters). By default the entire rest of the lines are
4570 @zeroTerminatedOption
4577 @node comm invocation
4578 @section @command{comm}: Compare two sorted files line by line
4581 @cindex line-by-line comparison
4582 @cindex comparing sorted files
4584 @command{comm} writes to standard output lines that are common, and lines
4585 that are unique, to two input files; a file name of @samp{-} means
4586 standard input. Synopsis:
4589 comm [@var{option}]@dots{} @var{file1} @var{file2}
4593 Before @command{comm} can be used, the input files must be sorted using the
4594 collating sequence specified by the @env{LC_COLLATE} locale.
4595 If an input file ends in a non-newline
4596 character, a newline is silently appended. The @command{sort} command with
4597 no options always outputs a file that is suitable input to @command{comm}.
4599 @cindex differing lines
4600 @cindex common lines
4601 With no options, @command{comm} produces three-column output. Column one
4602 contains lines unique to @var{file1}, column two contains lines unique
4603 to @var{file2}, and column three contains lines common to both files.
4604 Columns are separated by a single TAB character.
4605 @c FIXME: when there's an option to supply an alternative separator
4606 @c string, append `by default' to the above sentence.
4611 The options @option{-1}, @option{-2}, and @option{-3} suppress printing of
4612 the corresponding columns (and separators). Also see @ref{Common options}.
4614 Unlike some other comparison utilities, @command{comm} has an exit
4615 status that does not depend on the result of the comparison.
4616 Upon normal completion @command{comm} produces an exit code of zero.
4617 If there is an error it exits with nonzero status.
4619 @macro checkOrderOption{cmd}
4620 If the @option{--check-order} option is given, unsorted inputs will
4621 cause a fatal error message. If the option @option{--nocheck-order}
4622 is given, unsorted inputs will never cause an error message. If
4623 neither of these options is given, wrongly sorted inputs are diagnosed
4624 only if an input file is found to contain unpairable lines. If an
4625 input file is diagnosed as being unsorted, the @command{\cmd\} command
4626 will exit with a nonzero status (and the output should not be used).
4628 Forcing @command{\cmd\} to process wrongly sorted input files
4629 containing unpairable lines by specifying @option{--nocheck-order} is
4630 not guaranteed to produce any particular output. The output will
4631 probably not correspond with whatever you hoped it would be.
4633 @checkOrderOption{comm}
4638 Fail with an error message if either input file is wrongly ordered.
4640 @item --nocheck-order
4641 Do not check that both input files are in sorted order.
4645 @item --output-delimiter=@var{str}
4646 Print @var{str} between adjacent output columns,
4647 rather than the default of a single TAB character.
4649 The delimiter @var{str} may not be empty.
4653 @node ptx invocation
4654 @section @command{ptx}: Produce permuted indexes
4658 @command{ptx} reads a text file and essentially produces a permuted index, with
4659 each keyword in its context. The calling sketch is either one of:
4662 ptx [@var{option} @dots{}] [@var{file} @dots{}]
4663 ptx -G [@var{option} @dots{}] [@var{input} [@var{output}]]
4666 The @option{-G} (or its equivalent: @option{--traditional}) option disables
4667 all @sc{gnu} extensions and reverts to traditional mode, thus introducing some
4668 limitations and changing several of the program's default option values.
4669 When @option{-G} is not specified, @sc{gnu} extensions are always enabled.
4670 @sc{gnu} extensions to @command{ptx} are documented wherever appropriate in this
4671 document. For the full list, see @xref{Compatibility in ptx}.
4673 Individual options are explained in the following sections.
4675 When @sc{gnu} extensions are enabled, there may be zero, one or several
4676 @var{file}s after the options. If there is no @var{file}, the program
4677 reads the standard input. If there is one or several @var{file}s, they
4678 give the name of input files which are all read in turn, as if all the
4679 input files were concatenated. However, there is a full contextual
4680 break between each file and, when automatic referencing is requested,
4681 file names and line numbers refer to individual text input files. In
4682 all cases, the program outputs the permuted index to the standard
4685 When @sc{gnu} extensions are @emph{not} enabled, that is, when the program
4686 operates in traditional mode, there may be zero, one or two parameters
4687 besides the options. If there are no parameters, the program reads the
4688 standard input and outputs the permuted index to the standard output.
4689 If there is only one parameter, it names the text @var{input} to be read
4690 instead of the standard input. If two parameters are given, they give
4691 respectively the name of the @var{input} file to read and the name of
4692 the @var{output} file to produce. @emph{Be very careful} to note that,
4693 in this case, the contents of file given by the second parameter is
4694 destroyed. This behavior is dictated by System V @command{ptx}
4695 compatibility; @sc{gnu} Standards normally discourage output parameters not
4696 introduced by an option.
4698 Note that for @emph{any} file named as the value of an option or as an
4699 input text file, a single dash @kbd{-} may be used, in which case
4700 standard input is assumed. However, it would not make sense to use this
4701 convention more than once per program invocation.
4704 * General options in ptx:: Options which affect general program behavior.
4705 * Charset selection in ptx:: Underlying character set considerations.
4706 * Input processing in ptx:: Input fields, contexts, and keyword selection.
4707 * Output formatting in ptx:: Types of output format, and sizing the fields.
4708 * Compatibility in ptx::
4712 @node General options in ptx
4713 @subsection General options
4718 @itemx --traditional
4719 As already explained, this option disables all @sc{gnu} extensions to
4720 @command{ptx} and switches to traditional mode.
4723 Print a short help on standard output, then exit without further
4727 Print the program version on standard output, then exit without further
4735 @node Charset selection in ptx
4736 @subsection Charset selection
4738 @c FIXME: People don't necessarily know what an IBM-PC was these days.
4739 As it is set up now, the program assumes that the input file is coded
4740 using 8-bit @acronym{ISO} 8859-1 code, also known as Latin-1 character set,
4741 @emph{unless} it is compiled for MS-DOS, in which case it uses the
4742 character set of the IBM-PC@. (@sc{gnu} @command{ptx} is not known to work on
4743 smaller MS-DOS machines anymore.) Compared to 7-bit @acronym{ASCII}, the set
4744 of characters which are letters is different; this alters the behavior
4745 of regular expression matching. Thus, the default regular expression
4746 for a keyword allows foreign or diacriticized letters. Keyword sorting,
4747 however, is still crude; it obeys the underlying character set ordering
4753 @itemx --ignore-case
4754 Fold lower case letters to upper case for sorting.
4759 @node Input processing in ptx
4760 @subsection Word selection and input processing
4765 @itemx --break-file=@var{file}
4767 This option provides an alternative (to @option{-W}) method of describing
4768 which characters make up words. It introduces the name of a
4769 file which contains a list of characters which can@emph{not} be part of
4770 one word; this file is called the @dfn{Break file}. Any character which
4771 is not part of the Break file is a word constituent. If both options
4772 @option{-b} and @option{-W} are specified, then @option{-W} has precedence and
4773 @option{-b} is ignored.
4775 When @sc{gnu} extensions are enabled, the only way to avoid newline as a
4776 break character is to write all the break characters in the file with no
4777 newline at all, not even at the end of the file. When @sc{gnu} extensions
4778 are disabled, spaces, tabs and newlines are always considered as break
4779 characters even if not included in the Break file.
4782 @itemx --ignore-file=@var{file}
4784 The file associated with this option contains a list of words which will
4785 never be taken as keywords in concordance output. It is called the
4786 @dfn{Ignore file}. The file contains exactly one word in each line; the
4787 end of line separation of words is not subject to the value of the
4791 @itemx --only-file=@var{file}
4793 The file associated with this option contains a list of words which will
4794 be retained in concordance output; any word not mentioned in this file
4795 is ignored. The file is called the @dfn{Only file}. The file contains
4796 exactly one word in each line; the end of line separation of words is
4797 not subject to the value of the @option{-S} option.
4799 There is no default for the Only file. When both an Only file and an
4800 Ignore file are specified, a word is considered a keyword only
4801 if it is listed in the Only file and not in the Ignore file.
4806 On each input line, the leading sequence of non-white space characters will be
4807 taken to be a reference that has the purpose of identifying this input
4808 line in the resulting permuted index. For more information about reference
4809 production, see @xref{Output formatting in ptx}.
4810 Using this option changes the default value for option @option{-S}.
4812 Using this option, the program does not try very hard to remove
4813 references from contexts in output, but it succeeds in doing so
4814 @emph{when} the context ends exactly at the newline. If option
4815 @option{-r} is used with @option{-S} default value, or when @sc{gnu} extensions
4816 are disabled, this condition is always met and references are completely
4817 excluded from the output contexts.
4819 @item -S @var{regexp}
4820 @itemx --sentence-regexp=@var{regexp}
4822 This option selects which regular expression will describe the end of a
4823 line or the end of a sentence. In fact, this regular expression is not
4824 the only distinction between end of lines or end of sentences, and input
4825 line boundaries have no special significance outside this option. By
4826 default, when @sc{gnu} extensions are enabled and if @option{-r} option is not
4827 used, end of sentences are used. In this case, this @var{regex} is
4828 imported from @sc{gnu} Emacs:
4831 [.?!][]\"')@}]*\\($\\|\t\\| \\)[ \t\n]*
4834 Whenever @sc{gnu} extensions are disabled or if @option{-r} option is used, end
4835 of lines are used; in this case, the default @var{regexp} is just:
4841 Using an empty @var{regexp} is equivalent to completely disabling end of
4842 line or end of sentence recognition. In this case, the whole file is
4843 considered to be a single big line or sentence. The user might want to
4844 disallow all truncation flag generation as well, through option @option{-F
4845 ""}. @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
4848 When the keywords happen to be near the beginning of the input line or
4849 sentence, this often creates an unused area at the beginning of the
4850 output context line; when the keywords happen to be near the end of the
4851 input line or sentence, this often creates an unused area at the end of
4852 the output context line. The program tries to fill those unused areas
4853 by wrapping around context in them; the tail of the input line or
4854 sentence is used to fill the unused area on the left of the output line;
4855 the head of the input line or sentence is used to fill the unused area
4856 on the right of the output line.
4858 As a matter of convenience to the user, many usual backslashed escape
4859 sequences from the C language are recognized and converted to the
4860 corresponding characters by @command{ptx} itself.
4862 @item -W @var{regexp}
4863 @itemx --word-regexp=@var{regexp}
4865 This option selects which regular expression will describe each keyword.
4866 By default, if @sc{gnu} extensions are enabled, a word is a sequence of
4867 letters; the @var{regexp} used is @samp{\w+}. When @sc{gnu} extensions are
4868 disabled, a word is by default anything which ends with a space, a tab
4869 or a newline; the @var{regexp} used is @samp{[^ \t\n]+}.
4871 An empty @var{regexp} is equivalent to not using this option.
4872 @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
4875 As a matter of convenience to the user, many usual backslashed escape
4876 sequences, as found in the C language, are recognized and converted to
4877 the corresponding characters by @command{ptx} itself.
4882 @node Output formatting in ptx
4883 @subsection Output formatting
4885 Output format is mainly controlled by the @option{-O} and @option{-T} options
4886 described in the table below. When neither @option{-O} nor @option{-T} are
4887 selected, and if @sc{gnu} extensions are enabled, the program chooses an
4888 output format suitable for a dumb terminal. Each keyword occurrence is
4889 output to the center of one line, surrounded by its left and right
4890 contexts. Each field is properly justified, so the concordance output
4891 can be readily observed. As a special feature, if automatic
4892 references are selected by option @option{-A} and are output before the
4893 left context, that is, if option @option{-R} is @emph{not} selected, then
4894 a colon is added after the reference; this nicely interfaces with @sc{gnu}
4895 Emacs @code{next-error} processing. In this default output format, each
4896 white space character, like newline and tab, is merely changed to
4897 exactly one space, with no special attempt to compress consecutive
4898 spaces. This might change in the future. Except for those white space
4899 characters, every other character of the underlying set of 256
4900 characters is transmitted verbatim.
4902 Output format is further controlled by the following options.
4906 @item -g @var{number}
4907 @itemx --gap-size=@var{number}
4909 Select the size of the minimum white space gap between the fields on the
4912 @item -w @var{number}
4913 @itemx --width=@var{number}
4915 Select the maximum output width of each final line. If references are
4916 used, they are included or excluded from the maximum output width
4917 depending on the value of option @option{-R}. If this option is not
4918 selected, that is, when references are output before the left context,
4919 the maximum output width takes into account the maximum length of all
4920 references. If this option is selected, that is, when references are
4921 output after the right context, the maximum output width does not take
4922 into account the space taken by references, nor the gap that precedes
4926 @itemx --auto-reference
4928 Select automatic references. Each input line will have an automatic
4929 reference made up of the file name and the line ordinal, with a single
4930 colon between them. However, the file name will be empty when standard
4931 input is being read. If both @option{-A} and @option{-r} are selected, then
4932 the input reference is still read and skipped, but the automatic
4933 reference is used at output time, overriding the input reference.
4936 @itemx --right-side-refs
4938 In the default output format, when option @option{-R} is not used, any
4939 references produced by the effect of options @option{-r} or @option{-A} are
4940 placed to the far right of output lines, after the right context. With
4941 default output format, when the @option{-R} option is specified, references
4942 are rather placed at the beginning of each output line, before the left
4943 context. For any other output format, option @option{-R} is
4944 ignored, with one exception: with @option{-R} the width of references
4945 is @emph{not} taken into account in total output width given by @option{-w}.
4947 This option is automatically selected whenever @sc{gnu} extensions are
4950 @item -F @var{string}
4951 @itemx --flac-truncation=@var{string}
4953 This option will request that any truncation in the output be reported
4954 using the string @var{string}. Most output fields theoretically extend
4955 towards the beginning or the end of the current line, or current
4956 sentence, as selected with option @option{-S}. But there is a maximum
4957 allowed output line width, changeable through option @option{-w}, which is
4958 further divided into space for various output fields. When a field has
4959 to be truncated because it cannot extend beyond the beginning or the end of
4960 the current line to fit in, then a truncation occurs. By default,
4961 the string used is a single slash, as in @option{-F /}.
4963 @var{string} may have more than one character, as in @option{-F ...}.
4964 Also, in the particular case when @var{string} is empty (@option{-F ""}),
4965 truncation flagging is disabled, and no truncation marks are appended in
4968 As a matter of convenience to the user, many usual backslashed escape
4969 sequences, as found in the C language, are recognized and converted to
4970 the corresponding characters by @command{ptx} itself.
4972 @item -M @var{string}
4973 @itemx --macro-name=@var{string}
4975 Select another @var{string} to be used instead of @samp{xx}, while
4976 generating output suitable for @command{nroff}, @command{troff} or @TeX{}.
4979 @itemx --format=roff
4981 Choose an output format suitable for @command{nroff} or @command{troff}
4982 processing. Each output line will look like:
4985 .xx "@var{tail}" "@var{before}" "@var{keyword_and_after}" "@var{head}" "@var{ref}"
4988 so it will be possible to write a @samp{.xx} roff macro to take care of
4989 the output typesetting. This is the default output format when @sc{gnu}
4990 extensions are disabled. Option @option{-M} can be used to change
4991 @samp{xx} to another macro name.
4993 In this output format, each non-graphical character, like newline and
4994 tab, is merely changed to exactly one space, with no special attempt to
4995 compress consecutive spaces. Each quote character: @kbd{"} is doubled
4996 so it will be correctly processed by @command{nroff} or @command{troff}.
5001 Choose an output format suitable for @TeX{} processing. Each output
5002 line will look like:
5005 \xx @{@var{tail}@}@{@var{before}@}@{@var{keyword}@}@{@var{after}@}@{@var{head}@}@{@var{ref}@}
5009 so it will be possible to write a @code{\xx} definition to take care of
5010 the output typesetting. Note that when references are not being
5011 produced, that is, neither option @option{-A} nor option @option{-r} is
5012 selected, the last parameter of each @code{\xx} call is inhibited.
5013 Option @option{-M} can be used to change @samp{xx} to another macro
5016 In this output format, some special characters, like @kbd{$}, @kbd{%},
5017 @kbd{&}, @kbd{#} and @kbd{_} are automatically protected with a
5018 backslash. Curly brackets @kbd{@{}, @kbd{@}} are protected with a
5019 backslash and a pair of dollar signs (to force mathematical mode). The
5020 backslash itself produces the sequence @code{\backslash@{@}}.
5021 Circumflex and tilde diacritical marks produce the sequence @code{^\@{ @}} and
5022 @code{~\@{ @}} respectively. Other diacriticized characters of the
5023 underlying character set produce an appropriate @TeX{} sequence as far
5024 as possible. The other non-graphical characters, like newline and tab,
5025 and all other characters which are not part of @acronym{ASCII}, are merely
5026 changed to exactly one space, with no special attempt to compress
5027 consecutive spaces. Let me know how to improve this special character
5028 processing for @TeX{}.
5033 @node Compatibility in ptx
5034 @subsection The @sc{gnu} extensions to @command{ptx}
5036 This version of @command{ptx} contains a few features which do not exist in
5037 System V @command{ptx}. These extra features are suppressed by using the
5038 @option{-G} command line option, unless overridden by other command line
5039 options. Some @sc{gnu} extensions cannot be recovered by overriding, so the
5040 simple rule is to avoid @option{-G} if you care about @sc{gnu} extensions.
5041 Here are the differences between this program and System V @command{ptx}.
5046 This program can read many input files at once, it always writes the
5047 resulting concordance on standard output. On the other hand, System V
5048 @command{ptx} reads only one file and sends the result to standard output
5049 or, if a second @var{file} parameter is given on the command, to that
5052 Having output parameters not introduced by options is a dangerous
5053 practice which @sc{gnu} avoids as far as possible. So, for using @command{ptx}
5054 portably between @sc{gnu} and System V, you should always use it with a
5055 single input file, and always expect the result on standard output. You
5056 might also want to automatically configure in a @option{-G} option to
5057 @command{ptx} calls in products using @command{ptx}, if the configurator finds
5058 that the installed @command{ptx} accepts @option{-G}.
5061 The only options available in System V @command{ptx} are options @option{-b},
5062 @option{-f}, @option{-g}, @option{-i}, @option{-o}, @option{-r}, @option{-t} and
5063 @option{-w}. All other options are @sc{gnu} extensions and are not repeated in
5064 this enumeration. Moreover, some options have a slightly different
5065 meaning when @sc{gnu} extensions are enabled, as explained below.
5068 By default, concordance output is not formatted for @command{troff} or
5069 @command{nroff}. It is rather formatted for a dumb terminal. @command{troff}
5070 or @command{nroff} output may still be selected through option @option{-O}.
5073 Unless @option{-R} option is used, the maximum reference width is
5074 subtracted from the total output line width. With @sc{gnu} extensions
5075 disabled, width of references is not taken into account in the output
5076 line width computations.
5079 All 256 bytes, even @acronym{ASCII} @sc{nul} bytes, are always read and
5080 processed from input file with no adverse effect, even if @sc{gnu} extensions
5081 are disabled. However, System V @command{ptx} does not accept 8-bit characters,
5082 a few control characters are rejected, and the tilde @kbd{~} is also rejected.
5085 Input line length is only limited by available memory, even if @sc{gnu}
5086 extensions are disabled. However, System V @command{ptx} processes only
5087 the first 200 characters in each line.
5090 The break (non-word) characters default to be every character except all
5091 letters of the underlying character set, diacriticized or not. When @sc{gnu}
5092 extensions are disabled, the break characters default to space, tab and
5096 The program makes better use of output line width. If @sc{gnu} extensions
5097 are disabled, the program rather tries to imitate System V @command{ptx},
5098 but still, there are some slight disposition glitches this program does
5099 not completely reproduce.
5102 The user can specify both an Ignore file and an Only file. This is not
5103 allowed with System V @command{ptx}.
5108 @node tsort invocation
5109 @section @command{tsort}: Topological sort
5112 @cindex topological sort
5114 @command{tsort} performs a topological sort on the given @var{file}, or
5115 standard input if no input file is given or for a @var{file} of
5116 @samp{-}. For more details and some history, see @ref{tsort background}.
5120 tsort [@var{option}] [@var{file}]
5123 @command{tsort} reads its input as pairs of strings, separated by blanks,
5124 indicating a partial ordering. The output is a total ordering that
5125 corresponds to the given partial ordering.
5139 will produce the output
5150 Consider a more realistic example.
5151 You have a large set of functions all in one file, and they may all be
5152 declared static except one. Currently that one (say @code{main}) is the
5153 first function defined in the file, and the ones it calls directly follow
5154 it, followed by those they call, etc. Let's say that you are determined
5155 to take advantage of prototypes, so you have to choose between declaring
5156 all of those functions (which means duplicating a lot of information from
5157 the definitions) and rearranging the functions so that as many as possible
5158 are defined before they are used. One way to automate the latter process
5159 is to get a list for each function of the functions it calls directly.
5160 Many programs can generate such lists. They describe a call graph.
5161 Consider the following list, in which a given line indicates that the
5162 function on the left calls the one on the right directly.
5168 tail_file pretty_name
5169 tail_file write_header
5171 tail_forever recheck
5172 tail_forever pretty_name
5173 tail_forever write_header
5174 tail_forever dump_remainder
5177 tail_lines start_lines
5178 tail_lines dump_remainder
5179 tail_lines file_lines
5180 tail_lines pipe_lines
5182 tail_bytes start_bytes
5183 tail_bytes dump_remainder
5184 tail_bytes pipe_bytes
5185 file_lines dump_remainder
5189 then you can use @command{tsort} to produce an ordering of those
5190 functions that satisfies your requirement.
5193 example$ tsort call-graph | tac
5213 @command{tsort} detects any cycles in the input and writes the first cycle
5214 encountered to standard error.
5216 Note that for a given partial ordering, generally there is no unique
5217 total ordering. In the context of the call graph above, the function
5218 @code{parse_options} may be placed anywhere in the list as long as it
5219 precedes @code{main}.
5221 The only options are @option{--help} and @option{--version}. @xref{Common
5227 * tsort background:: Where tsort came from.
5230 @node tsort background
5231 @subsection @command{tsort}: Background
5233 @command{tsort} exists because very early versions of the Unix linker processed
5234 an archive file exactly once, and in order. As @command{ld} read each object
5235 in the archive, it decided whether it was needed in the program based on
5236 whether it defined any symbols which were undefined at that point in
5239 This meant that dependencies within the archive had to be handled
5240 specially. For example, @code{scanf} probably calls @code{read}. That means
5241 that in a single pass through an archive, it was important for @code{scanf.o}
5242 to appear before read.o, because otherwise a program which calls
5243 @code{scanf} but not @code{read} might end up with an unexpected unresolved
5244 reference to @code{read}.
5246 The way to address this problem was to first generate a set of
5247 dependencies of one object file on another. This was done by a shell
5248 script called @command{lorder}. The GNU tools don't provide a version of
5249 lorder, as far as I know, but you can still find it in BSD
5252 Then you ran @command{tsort} over the @command{lorder} output, and you used the
5253 resulting sort to define the order in which you added objects to the archive.
5255 This whole procedure has been obsolete since about 1980, because
5256 Unix archives now contain a symbol table (traditionally built by
5257 @command{ranlib}, now generally built by @command{ar} itself), and the Unix
5258 linker uses the symbol table to effectively make multiple passes over
5261 Anyhow, that's where tsort came from. To solve an old problem with
5262 the way the linker handled archive files, which has since been solved
5266 @node Operating on fields
5267 @chapter Operating on fields
5270 * cut invocation:: Print selected parts of lines.
5271 * paste invocation:: Merge lines of files.
5272 * join invocation:: Join lines on a common field.
5276 @node cut invocation
5277 @section @command{cut}: Print selected parts of lines
5280 @command{cut} writes to standard output selected parts of each line of each
5281 input file, or standard input if no files are given or for a file name of
5285 cut @var{option}@dots{} [@var{file}]@dots{}
5288 In the table which follows, the @var{byte-list}, @var{character-list},
5289 and @var{field-list} are one or more numbers or ranges (two numbers
5290 separated by a dash) separated by commas. Bytes, characters, and
5291 fields are numbered starting at 1. Incomplete ranges may be
5292 given: @option{-@var{m}} means @samp{1-@var{m}}; @samp{@var{n}-} means
5293 @samp{@var{n}} through end of line or last field. The list elements
5294 can be repeated, can overlap, and can be specified in any order; but
5295 the selected input is written in the same order that it is read, and
5296 is written exactly once.
5298 The program accepts the following options. Also see @ref{Common
5303 @item -b @var{byte-list}
5304 @itemx --bytes=@var{byte-list}
5307 Select for printing only the bytes in positions listed in
5308 @var{byte-list}. Tabs and backspaces are treated like any other
5309 character; they take up 1 byte. If an output delimiter is specified,
5310 (see the description of @option{--output-delimiter}), then output that
5311 string between ranges of selected bytes.
5313 @item -c @var{character-list}
5314 @itemx --characters=@var{character-list}
5316 @opindex --characters
5317 Select for printing only the characters in positions listed in
5318 @var{character-list}. The same as @option{-b} for now, but
5319 internationalization will change that. Tabs and backspaces are
5320 treated like any other character; they take up 1 character. If an
5321 output delimiter is specified, (see the description of
5322 @option{--output-delimiter}), then output that string between ranges
5325 @item -f @var{field-list}
5326 @itemx --fields=@var{field-list}
5329 Select for printing only the fields listed in @var{field-list}.
5330 Fields are separated by a TAB character by default. Also print any
5331 line that contains no delimiter character, unless the
5332 @option{--only-delimited} (@option{-s}) option is specified.
5333 Note @command{cut} does not support specifying runs of whitespace as a
5334 delimiter, so to achieve that common functionality one can pre-process
5335 with @command{tr} like:
5337 tr -s '[:blank:]' '\t' | cut -f@dots{}
5340 @item -d @var{input_delim_byte}
5341 @itemx --delimiter=@var{input_delim_byte}
5343 @opindex --delimiter
5344 With @option{-f}, use the first byte of @var{input_delim_byte} as
5345 the input fields separator (default is TAB).
5349 Do not split multi-byte characters (no-op for now).
5352 @itemx --only-delimited
5354 @opindex --only-delimited
5355 For @option{-f}, do not print lines that do not contain the field separator
5356 character. Normally, any line without a field separator is printed verbatim.
5358 @item --output-delimiter=@var{output_delim_string}
5359 @opindex --output-delimiter
5360 With @option{-f}, output fields are separated by @var{output_delim_string}.
5361 The default with @option{-f} is to use the input delimiter.
5362 When using @option{-b} or @option{-c} to select ranges of byte or
5363 character offsets (as opposed to ranges of fields),
5364 output @var{output_delim_string} between non-overlapping
5365 ranges of selected bytes.
5368 @opindex --complement
5369 This option is a @acronym{GNU} extension.
5370 Select for printing the complement of the bytes, characters or fields
5371 selected with the @option{-b}, @option{-c} or @option{-f} options.
5372 In other words, do @emph{not} print the bytes, characters or fields
5373 specified via those options. This option is useful when you have
5374 many fields and want to print all but a few of them.
5381 @node paste invocation
5382 @section @command{paste}: Merge lines of files
5385 @cindex merging files
5387 @command{paste} writes to standard output lines consisting of sequentially
5388 corresponding lines of each given file, separated by a TAB character.
5389 Standard input is used for a file name of @samp{-} or if no input files
5411 paste [@var{option}]@dots{} [@var{file}]@dots{}
5414 The program accepts the following options. Also see @ref{Common options}.
5422 Paste the lines of one file at a time rather than one line from each
5423 file. Using the above example data:
5426 $ paste -s num2 let3
5431 @item -d @var{delim-list}
5432 @itemx --delimiters=@var{delim-list}
5434 @opindex --delimiters
5435 Consecutively use the characters in @var{delim-list} instead of
5436 TAB to separate merged lines. When @var{delim-list} is
5437 exhausted, start again at its beginning. Using the above example data:
5440 $ paste -d '%_' num2 let3 num2
5451 @node join invocation
5452 @section @command{join}: Join lines on a common field
5455 @cindex common field, joining on
5457 @command{join} writes to standard output a line for each pair of input
5458 lines that have identical join fields. Synopsis:
5461 join [@var{option}]@dots{} @var{file1} @var{file2}
5464 Either @var{file1} or @var{file2} (but not both) can be @samp{-},
5465 meaning standard input. @var{file1} and @var{file2} should be
5466 sorted on the join fields.
5469 Normally, the sort order is that of the
5470 collating sequence specified by the @env{LC_COLLATE} locale. Unless
5471 the @option{-t} option is given, the sort comparison ignores blanks at
5472 the start of the join field, as in @code{sort -b}. If the
5473 @option{--ignore-case} option is given, the sort comparison ignores
5474 the case of characters in the join field, as in @code{sort -f}.
5476 The @command{sort} and @command{join} commands should use consistent
5477 locales and options if the output of @command{sort} is fed to
5478 @command{join}. You can use a command like @samp{sort -k 1b,1} to
5479 sort a file on its default join field, but if you select a non-default
5480 locale, join field, separator, or comparison options, then you should
5481 do so consistently between @command{join} and @command{sort}.
5482 If @samp{join -t ''} is specified then the whole line is considered which
5483 matches the default operation of sort.
5485 If the input has no unpairable lines, a @acronym{GNU} extension is
5486 available; the sort order can be any order that considers two fields
5487 to be equal if and only if the sort comparison described above
5488 considers them to be equal. For example:
5505 @checkOrderOption{join}
5509 @item the join field is the first field in each line;
5510 @item fields in the input are separated by one or more blanks, with leading
5511 blanks on the line ignored;
5512 @item fields in the output are separated by a space;
5513 @item each output line consists of the join field, the remaining
5514 fields from @var{file1}, then the remaining fields from @var{file2}.
5517 The program accepts the following options. Also see @ref{Common options}.
5521 @item -a @var{file-number}
5523 Print a line for each unpairable line in file @var{file-number} (either
5524 @samp{1} or @samp{2}), in addition to the normal output.
5527 Fail with an error message if either input file is wrongly ordered.
5529 @item --nocheck-order
5530 Do not check that both input files are in sorted order. This is the default.
5532 @item -e @var{string}
5534 Replace those output fields that are missing in the input with
5539 Treat the first line of each input file as a header line. The header lines will
5540 be joined and printed as the first output line. If @option{-o} is used to
5541 specify output format, the header line will be printed according to the
5542 specified format. The header lines will not be checked for ordering even if
5543 @option{--check-order} is specified. Also if the header lines from each file
5544 do not match, the heading fields from the first file will be used.
5547 @itemx --ignore-case
5549 @opindex --ignore-case
5550 Ignore differences in case when comparing keys.
5551 With this option, the lines of the input files must be ordered in the same way.
5552 Use @samp{sort -f} to produce this ordering.
5554 @item -1 @var{field}
5556 Join on field @var{field} (a positive integer) of file 1.
5558 @item -2 @var{field}
5560 Join on field @var{field} (a positive integer) of file 2.
5562 @item -j @var{field}
5563 Equivalent to @option{-1 @var{field} -2 @var{field}}.
5565 @item -o @var{field-list}
5566 Construct each output line according to the format in @var{field-list}.
5567 Each element in @var{field-list} is either the single character @samp{0} or
5568 has the form @var{m.n} where the file number, @var{m}, is @samp{1} or
5569 @samp{2} and @var{n} is a positive field number.
5571 A field specification of @samp{0} denotes the join field.
5572 In most cases, the functionality of the @samp{0} field spec
5573 may be reproduced using the explicit @var{m.n} that corresponds
5574 to the join field. However, when printing unpairable lines
5575 (using either of the @option{-a} or @option{-v} options), there is no way
5576 to specify the join field using @var{m.n} in @var{field-list}
5577 if there are unpairable lines in both files.
5578 To give @command{join} that functionality, @acronym{POSIX} invented the @samp{0}
5579 field specification notation.
5581 The elements in @var{field-list}
5582 are separated by commas or blanks.
5583 Blank separators typically need to be quoted for the shell. For
5584 example, the commands @samp{join -o 1.2,2.2} and @samp{join -o '1.2
5585 2.2'} are equivalent.
5587 All output lines---including those printed because of any -a or -v
5588 option---are subject to the specified @var{field-list}.
5591 Use character @var{char} as the input and output field separator.
5592 Treat as significant each occurrence of @var{char} in the input file.
5593 Use @samp{sort -t @var{char}}, without the @option{-b} option of
5594 @samp{sort}, to produce this ordering. If @samp{join -t ''} is specified,
5595 the whole line is considered, matching the default operation of sort.
5596 If @samp{-t '\0'} is specified then the @acronym{ASCII} @sc{nul}
5597 character is used to delimit the fields.
5599 @item -v @var{file-number}
5600 Print a line for each unpairable line in file @var{file-number}
5601 (either @samp{1} or @samp{2}), instead of the normal output.
5608 @node Operating on characters
5609 @chapter Operating on characters
5611 @cindex operating on characters
5613 This commands operate on individual characters.
5616 * tr invocation:: Translate, squeeze, and/or delete characters.
5617 * expand invocation:: Convert tabs to spaces.
5618 * unexpand invocation:: Convert spaces to tabs.
5623 @section @command{tr}: Translate, squeeze, and/or delete characters
5630 tr [@var{option}]@dots{} @var{set1} [@var{set2}]
5633 @command{tr} copies standard input to standard output, performing
5634 one of the following operations:
5638 translate, and optionally squeeze repeated characters in the result,
5640 squeeze repeated characters,
5644 delete characters, then squeeze repeated characters from the result.
5647 The @var{set1} and (if given) @var{set2} arguments define ordered
5648 sets of characters, referred to below as @var{set1} and @var{set2}. These
5649 sets are the characters of the input that @command{tr} operates on.
5650 The @option{--complement} (@option{-c}, @option{-C}) option replaces
5652 complement (all of the characters that are not in @var{set1}).
5654 Currently @command{tr} fully supports only single-byte characters.
5655 Eventually it will support multibyte characters; when it does, the
5656 @option{-C} option will cause it to complement the set of characters,
5657 whereas @option{-c} will cause it to complement the set of values.
5658 This distinction will matter only when some values are not characters,
5659 and this is possible only in locales using multibyte encodings when
5660 the input contains encoding errors.
5662 The program accepts the @option{--help} and @option{--version}
5663 options. @xref{Common options}. Options must precede operands.
5668 * Character sets:: Specifying sets of characters.
5669 * Translating:: Changing one set of characters to another.
5670 * Squeezing:: Squeezing repeats and deleting.
5674 @node Character sets
5675 @subsection Specifying sets of characters
5677 @cindex specifying sets of characters
5679 The format of the @var{set1} and @var{set2} arguments resembles
5680 the format of regular expressions; however, they are not regular
5681 expressions, only lists of characters. Most characters simply
5682 represent themselves in these strings, but the strings can contain
5683 the shorthands listed below, for convenience. Some of them can be
5684 used only in @var{set1} or @var{set2}, as noted below.
5688 @item Backslash escapes
5689 @cindex backslash escapes
5691 The following backslash escape sequences are recognized:
5709 The character with the value given by @var{ooo}, which is 1 to 3
5715 While a backslash followed by a character not listed above is
5716 interpreted as that character, the backslash also effectively
5717 removes any special significance, so it is useful to escape
5718 @samp{[}, @samp{]}, @samp{*}, and @samp{-}.
5723 The notation @samp{@var{m}-@var{n}} expands to all of the characters
5724 from @var{m} through @var{n}, in ascending order. @var{m} should
5725 collate before @var{n}; if it doesn't, an error results. As an example,
5726 @samp{0-9} is the same as @samp{0123456789}.
5728 @sc{gnu} @command{tr} does not support the System V syntax that uses square
5729 brackets to enclose ranges. Translations specified in that format
5730 sometimes work as expected, since the brackets are often transliterated
5731 to themselves. However, they should be avoided because they sometimes
5732 behave unexpectedly. For example, @samp{tr -d '[0-9]'} deletes brackets
5735 Many historically common and even accepted uses of ranges are not
5736 portable. For example, on @acronym{EBCDIC} hosts using the @samp{A-Z}
5737 range will not do what most would expect because @samp{A} through @samp{Z}
5738 are not contiguous as they are in @acronym{ASCII}.
5739 If you can rely on a @acronym{POSIX} compliant version of @command{tr}, then
5740 the best way to work around this is to use character classes (see below).
5741 Otherwise, it is most portable (and most ugly) to enumerate the members
5744 @item Repeated characters
5745 @cindex repeated characters
5747 The notation @samp{[@var{c}*@var{n}]} in @var{set2} expands to @var{n}
5748 copies of character @var{c}. Thus, @samp{[y*6]} is the same as
5749 @samp{yyyyyy}. The notation @samp{[@var{c}*]} in @var{string2} expands
5750 to as many copies of @var{c} as are needed to make @var{set2} as long as
5751 @var{set1}. If @var{n} begins with @samp{0}, it is interpreted in
5752 octal, otherwise in decimal.
5754 @item Character classes
5755 @cindex character classes
5757 The notation @samp{[:@var{class}:]} expands to all of the characters in
5758 the (predefined) class @var{class}. The characters expand in no
5759 particular order, except for the @code{upper} and @code{lower} classes,
5760 which expand in ascending order. When the @option{--delete} (@option{-d})
5761 and @option{--squeeze-repeats} (@option{-s}) options are both given, any
5762 character class can be used in @var{set2}. Otherwise, only the
5763 character classes @code{lower} and @code{upper} are accepted in
5764 @var{set2}, and then only if the corresponding character class
5765 (@code{upper} and @code{lower}, respectively) is specified in the same
5766 relative position in @var{set1}. Doing this specifies case conversion.
5767 The class names are given below; an error results when an invalid class
5779 Horizontal whitespace.
5788 Printable characters, not including space.
5794 Printable characters, including space.
5797 Punctuation characters.
5800 Horizontal or vertical whitespace.
5809 @item Equivalence classes
5810 @cindex equivalence classes
5812 The syntax @samp{[=@var{c}=]} expands to all of the characters that are
5813 equivalent to @var{c}, in no particular order. Equivalence classes are
5814 a relatively recent invention intended to support non-English alphabets.
5815 But there seems to be no standard way to define them or determine their
5816 contents. Therefore, they are not fully implemented in @sc{gnu} @command{tr};
5817 each character's equivalence class consists only of that character,
5818 which is of no particular use.
5824 @subsection Translating
5826 @cindex translating characters
5828 @command{tr} performs translation when @var{set1} and @var{set2} are
5829 both given and the @option{--delete} (@option{-d}) option is not given.
5830 @command{tr} translates each character of its input that is in @var{set1}
5831 to the corresponding character in @var{set2}. Characters not in
5832 @var{set1} are passed through unchanged. When a character appears more
5833 than once in @var{set1} and the corresponding characters in @var{set2}
5834 are not all the same, only the final one is used. For example, these
5835 two commands are equivalent:
5842 A common use of @command{tr} is to convert lowercase characters to
5843 uppercase. This can be done in many ways. Here are three of them:
5846 tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
5848 tr '[:lower:]' '[:upper:]'
5852 But note that using ranges like @code{a-z} above is not portable.
5854 When @command{tr} is performing translation, @var{set1} and @var{set2}
5855 typically have the same length. If @var{set1} is shorter than
5856 @var{set2}, the extra characters at the end of @var{set2} are ignored.
5858 On the other hand, making @var{set1} longer than @var{set2} is not
5859 portable; @acronym{POSIX} says that the result is undefined. In this situation,
5860 BSD @command{tr} pads @var{set2} to the length of @var{set1} by repeating
5861 the last character of @var{set2} as many times as necessary. System V
5862 @command{tr} truncates @var{set1} to the length of @var{set2}.
5864 By default, @sc{gnu} @command{tr} handles this case like BSD @command{tr}.
5865 When the @option{--truncate-set1} (@option{-t}) option is given,
5866 @sc{gnu} @command{tr} handles this case like the System V @command{tr}
5867 instead. This option is ignored for operations other than translation.
5869 Acting like System V @command{tr} in this case breaks the relatively common
5873 tr -cs A-Za-z0-9 '\012'
5877 because it converts only zero bytes (the first element in the
5878 complement of @var{set1}), rather than all non-alphanumerics, to
5882 By the way, the above idiom is not portable because it uses ranges, and
5883 it assumes that the octal code for newline is 012.
5884 Assuming a @acronym{POSIX} compliant @command{tr}, here is a better way to write it:
5887 tr -cs '[:alnum:]' '[\n*]'
5892 @subsection Squeezing repeats and deleting
5894 @cindex squeezing repeat characters
5895 @cindex deleting characters
5897 When given just the @option{--delete} (@option{-d}) option, @command{tr}
5898 removes any input characters that are in @var{set1}.
5900 When given just the @option{--squeeze-repeats} (@option{-s}) option,
5901 @command{tr} replaces each input sequence of a repeated character that
5902 is in @var{set1} with a single occurrence of that character.
5904 When given both @option{--delete} and @option{--squeeze-repeats}, @command{tr}
5905 first performs any deletions using @var{set1}, then squeezes repeats
5906 from any remaining characters using @var{set2}.
5908 The @option{--squeeze-repeats} option may also be used when translating,
5909 in which case @command{tr} first performs translation, then squeezes
5910 repeats from any remaining characters using @var{set2}.
5912 Here are some examples to illustrate various combinations of options:
5917 Remove all zero bytes:
5924 Put all words on lines by themselves. This converts all
5925 non-alphanumeric characters to newlines, then squeezes each string
5926 of repeated newlines into a single newline:
5929 tr -cs '[:alnum:]' '[\n*]'
5933 Convert each sequence of repeated newlines to a single newline:
5940 Find doubled occurrences of words in a document.
5941 @c Separate the following two "the"s, so typo checkers don't complain.
5942 For example, people often write ``the @w{}the'' with the repeated words
5943 separated by a newline. The Bourne shell script below works first
5944 by converting each sequence of punctuation and blank characters to a
5945 single newline. That puts each ``word'' on a line by itself.
5946 Next it maps all uppercase characters to lower case, and finally it
5947 runs @command{uniq} with the @option{-d} option to print out only the words
5953 | tr -s '[:punct:][:blank:]' '[\n*]' \
5954 | tr '[:upper:]' '[:lower:]' \
5959 Deleting a small set of characters is usually straightforward. For example,
5960 to remove all @samp{a}s, @samp{x}s, and @samp{M}s you would do this:
5966 However, when @samp{-} is one of those characters, it can be tricky because
5967 @samp{-} has special meanings. Performing the same task as above but also
5968 removing all @samp{-} characters, we might try @code{tr -d -axM}, but
5969 that would fail because @command{tr} would try to interpret @option{-a} as
5970 a command-line option. Alternatively, we could try putting the hyphen
5971 inside the string, @code{tr -d a-xM}, but that wouldn't work either because
5972 it would make @command{tr} interpret @code{a-x} as the range of characters
5973 @samp{a}@dots{}@samp{x} rather than the three.
5974 One way to solve the problem is to put the hyphen at the end of the list
5981 Or you can use @samp{--} to terminate option processing:
5987 More generally, use the character class notation @code{[=c=]}
5988 with @samp{-} (or any other character) in place of the @samp{c}:
5994 Note how single quotes are used in the above example to protect the
5995 square brackets from interpretation by a shell.
6000 @node expand invocation
6001 @section @command{expand}: Convert tabs to spaces
6004 @cindex tabs to spaces, converting
6005 @cindex converting tabs to spaces
6007 @command{expand} writes the contents of each given @var{file}, or standard
6008 input if none are given or for a @var{file} of @samp{-}, to standard
6009 output, with tab characters converted to the appropriate number of
6013 expand [@var{option}]@dots{} [@var{file}]@dots{}
6016 By default, @command{expand} converts all tabs to spaces. It preserves
6017 backspace characters in the output; they decrement the column count for
6018 tab calculations. The default action is equivalent to @option{-t 8} (set
6019 tabs every 8 columns).
6021 The program accepts the following options. Also see @ref{Common options}.
6025 @item -t @var{tab1}[,@var{tab2}]@dots{}
6026 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
6029 @cindex tab stops, setting
6030 If only one tab stop is given, set the tabs @var{tab1} spaces apart
6031 (default is 8). Otherwise, set the tabs at columns @var{tab1},
6032 @var{tab2}, @dots{} (numbered from 0), and replace any tabs beyond the
6033 last tab stop given with single spaces. Tab stops can be separated by
6034 blanks as well as by commas.
6036 For compatibility, GNU @command{expand} also accepts the obsolete
6037 option syntax, @option{-@var{t1}[,@var{t2}]@dots{}}. New scripts
6038 should use @option{-t @var{t1}[,@var{t2}]@dots{}} instead.
6044 @cindex initial tabs, converting
6045 Only convert initial tabs (those that precede all non-space or non-tab
6046 characters) on each line to spaces.
6053 @node unexpand invocation
6054 @section @command{unexpand}: Convert spaces to tabs
6058 @command{unexpand} writes the contents of each given @var{file}, or
6059 standard input if none are given or for a @var{file} of @samp{-}, to
6060 standard output, converting blanks at the beginning of each line into
6061 as many tab characters as needed. In the default @acronym{POSIX}
6062 locale, a @dfn{blank} is a space or a tab; other locales may specify
6063 additional blank characters. Synopsis:
6066 unexpand [@var{option}]@dots{} [@var{file}]@dots{}
6069 By default, @command{unexpand} converts only initial blanks (those
6070 that precede all non-blank characters) on each line. It
6071 preserves backspace characters in the output; they decrement the column
6072 count for tab calculations. By default, tabs are set at every 8th
6075 The program accepts the following options. Also see @ref{Common options}.
6079 @item -t @var{tab1}[,@var{tab2}]@dots{}
6080 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
6083 If only one tab stop is given, set the tabs @var{tab1} columns apart
6084 instead of the default 8. Otherwise, set the tabs at columns
6085 @var{tab1}, @var{tab2}, @dots{} (numbered from 0), and leave blanks
6086 beyond the tab stops given unchanged. Tab stops can be separated by
6087 blanks as well as by commas. This option implies the @option{-a} option.
6089 For compatibility, GNU @command{unexpand} supports the obsolete option syntax,
6090 @option{-@var{tab1}[,@var{tab2}]@dots{}}, where tab stops must be
6091 separated by commas. (Unlike @option{-t}, this obsolete option does
6092 not imply @option{-a}.) New scripts should use @option{--first-only -t
6093 @var{tab1}[,@var{tab2}]@dots{}} instead.
6099 Also convert all sequences of two or more blanks just before a tab stop,
6100 even if they occur after non-blank characters in a line.
6107 @node Directory listing
6108 @chapter Directory listing
6110 This chapter describes the @command{ls} command and its variants @command{dir}
6111 and @command{vdir}, which list information about files.
6114 * ls invocation:: List directory contents.
6115 * dir invocation:: Briefly ls.
6116 * vdir invocation:: Verbosely ls.
6117 * dircolors invocation:: Color setup for ls, etc.
6122 @section @command{ls}: List directory contents
6125 @cindex directory listing
6127 The @command{ls} program lists information about files (of any type,
6128 including directories). Options and file arguments can be intermixed
6129 arbitrarily, as usual.
6131 For non-option command-line arguments that are directories, by default
6132 @command{ls} lists the contents of directories, not recursively, and
6133 omitting files with names beginning with @samp{.}. For other non-option
6134 arguments, by default @command{ls} lists just the file name. If no
6135 non-option argument is specified, @command{ls} operates on the current
6136 directory, acting as if it had been invoked with a single argument of @samp{.}.
6139 By default, the output is sorted alphabetically, according to the locale
6140 settings in effect.@footnote{If you use a non-@acronym{POSIX}
6141 locale (e.g., by setting @env{LC_ALL} to @samp{en_US}), then @command{ls} may
6142 produce output that is sorted differently than you're accustomed to.
6143 In that case, set the @env{LC_ALL} environment variable to @samp{C}.}
6144 If standard output is
6145 a terminal, the output is in columns (sorted vertically) and control
6146 characters are output as question marks; otherwise, the output is listed
6147 one per line and control characters are output as-is.
6149 Because @command{ls} is such a fundamental program, it has accumulated many
6150 options over the years. They are described in the subsections below;
6151 within each section, options are listed alphabetically (ignoring case).
6152 The division of options into the subsections is not absolute, since some
6153 options affect more than one aspect of @command{ls}'s operation.
6155 @cindex exit status of @command{ls}
6160 1 minor problems (e.g., failure to access a file or directory not
6161 specified as a command line argument. This happens when listing a
6162 directory in which entries are actively being removed or renamed.)
6163 2 serious trouble (e.g., memory exhausted, invalid option, failure
6164 to access a file or directory specified as a command line argument
6165 or a directory loop)
6168 Also see @ref{Common options}.
6171 * Which files are listed::
6172 * What information is listed::
6173 * Sorting the output::
6174 * Details about version sort::
6175 * General output formatting::
6176 * Formatting file timestamps::
6177 * Formatting the file names::
6181 @node Which files are listed
6182 @subsection Which files are listed
6184 These options determine which files @command{ls} lists information for.
6185 By default, @command{ls} lists files and the contents of any
6186 directories on the command line, except that in directories it ignores
6187 files whose names start with @samp{.}.
6195 In directories, do not ignore file names that start with @samp{.}.
6200 @opindex --almost-all
6201 In directories, do not ignore all file names that start with @samp{.};
6202 ignore only @file{.} and @file{..}. The @option{--all} (@option{-a})
6203 option overrides this option.
6206 @itemx --ignore-backups
6208 @opindex --ignore-backups
6209 @cindex backup files, ignoring
6210 In directories, ignore files that end with @samp{~}. This option is
6211 equivalent to @samp{--ignore='*~' --ignore='.*~'}.
6216 @opindex --directory
6217 List just the names of directories, as with other types of files, rather
6218 than listing their contents.
6219 @c The following sentence is the same as the one for -F.
6220 Do not follow symbolic links listed on the
6221 command line unless the @option{--dereference-command-line} (@option{-H}),
6222 @option{--dereference} (@option{-L}), or
6223 @option{--dereference-command-line-symlink-to-dir} options are specified.
6226 @itemx --dereference-command-line
6228 @opindex --dereference-command-line
6229 @cindex symbolic links, dereferencing
6230 If a command line argument specifies a symbolic link, show information
6231 for the file the link references rather than for the link itself.
6233 @itemx --dereference-command-line-symlink-to-dir
6234 @opindex --dereference-command-line-symlink-to-dir
6235 @cindex symbolic links, dereferencing
6236 Do not dereference symbolic links, with one exception:
6237 if a command line argument specifies a symbolic link that refers to
6238 a directory, show information for that directory rather than for the
6240 This is the default behavior when no other dereferencing-related
6241 option has been specified (@option{--classify} (@option{-F}),
6242 @option{--directory} (@option{-d}),
6244 @option{--dereference} (@option{-L}), or
6245 @option{--dereference-command-line} (@option{-H})).
6247 @item --group-directories-first
6248 @opindex --group-directories-first
6249 Group all the directories before the files and then sort the
6250 directories and the files separately using the selected sort key
6251 (see --sort option).
6252 That is, this option specifies a primary sort key,
6253 and the --sort option specifies a secondary key.
6254 However, any use of @option{--sort=none}
6255 (@option{-U}) disables this option altogether.
6257 @item --hide=PATTERN
6258 @opindex --hide=@var{pattern}
6259 In directories, ignore files whose names match the shell pattern
6260 @var{pattern}, unless the @option{--all} (@option{-a}) or
6261 @option{--almost-all} (@option{-A}) is also given. This
6262 option acts like @option{--ignore=@var{pattern}} except that it has no
6263 effect if @option{--all} (@option{-a}) or @option{--almost-all}
6264 (@option{-A}) is also given.
6266 This option can be useful in shell aliases. For example, if
6267 @command{lx} is an alias for @samp{ls --hide='*~'} and @command{ly} is
6268 an alias for @samp{ls --ignore='*~'}, then the command @samp{lx -A}
6269 lists the file @file{README~} even though @samp{ly -A} would not.
6271 @item -I @var{pattern}
6272 @itemx --ignore=@var{pattern}
6274 @opindex --ignore=@var{pattern}
6275 In directories, ignore files whose names match the shell pattern
6276 (not regular expression) @var{pattern}. As
6277 in the shell, an initial @samp{.} in a file name does not match a
6278 wildcard at the start of @var{pattern}. Sometimes it is useful
6279 to give this option several times. For example,
6282 $ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*'
6285 The first option ignores names of length 3 or more that start with @samp{.},
6286 the second ignores all two-character names that start with @samp{.}
6287 except @samp{..}, and the third ignores names that start with @samp{#}.
6290 @itemx --dereference
6292 @opindex --dereference
6293 @cindex symbolic links, dereferencing
6294 When showing file information for a symbolic link, show information
6295 for the file the link references rather than the link itself.
6296 However, even with this option, @command{ls} still prints the name
6297 of the link itself, not the name of the file that the link points to.
6302 @opindex --recursive
6303 @cindex recursive directory listing
6304 @cindex directory listing, recursive
6305 List the contents of all directories recursively.
6310 @node What information is listed
6311 @subsection What information is listed
6313 These options affect the information that @command{ls} displays. By
6314 default, only file names are shown.
6320 @cindex hurd, author, printing
6321 List each file's author when producing long format directory listings.
6322 In GNU/Hurd, file authors can differ from their owners, but in other
6323 operating systems the two are the same.
6329 @cindex dired Emacs mode support
6330 With the long listing (@option{-l}) format, print an additional line after
6334 //DIRED// @var{beg1} @var{end1} @var{beg2} @var{end2} @dots{}
6338 The @var{begn} and @var{endn} are unsigned integers that record the
6339 byte position of the beginning and end of each file name in the output.
6340 This makes it easy for Emacs to find the names, even when they contain
6341 unusual characters such as space or newline, without fancy searching.
6343 If directories are being listed recursively (@option{-R}), output a similar
6344 line with offsets for each subdirectory name:
6347 //SUBDIRED// @var{beg1} @var{end1} @dots{}
6350 Finally, output a line of the form:
6353 //DIRED-OPTIONS// --quoting-style=@var{word}
6357 where @var{word} is the quoting style (@pxref{Formatting the file names}).
6359 Here is an actual example:
6362 $ mkdir -p a/sub/deeper a/sub2
6364 $ touch a/sub/deeper/file
6365 $ ls -gloRF --dired a
6368 -rw-r--r-- 1 0 Jun 10 12:27 f1
6369 -rw-r--r-- 1 0 Jun 10 12:27 f2
6370 drwxr-xr-x 3 4096 Jun 10 12:27 sub/
6371 drwxr-xr-x 2 4096 Jun 10 12:27 sub2/
6375 drwxr-xr-x 2 4096 Jun 10 12:27 deeper/
6379 -rw-r--r-- 1 0 Jun 10 12:27 file
6383 //DIRED// 48 50 84 86 120 123 158 162 217 223 282 286
6384 //SUBDIRED// 2 3 167 172 228 240 290 296
6385 //DIRED-OPTIONS// --quoting-style=literal
6388 Note that the pairs of offsets on the @samp{//DIRED//} line above delimit
6389 these names: @file{f1}, @file{f2}, @file{sub}, @file{sub2}, @file{deeper},
6391 The offsets on the @samp{//SUBDIRED//} line delimit the following
6392 directory names: @file{a}, @file{a/sub}, @file{a/sub/deeper}, @file{a/sub2}.
6394 Here is an example of how to extract the fifth entry name, @samp{deeper},
6395 corresponding to the pair of offsets, 222 and 228:
6398 $ ls -gloRF --dired a > out
6399 $ dd bs=1 skip=222 count=6 < out 2>/dev/null; echo
6403 Note that although the listing above includes a trailing slash
6404 for the @samp{deeper} entry, the offsets select the name without
6405 the trailing slash. However, if you invoke @command{ls} with @option{--dired}
6406 along with an option like @option{--escape} (aka @option{-b}) and operate
6407 on a file whose name contains special characters, notice that the backslash
6412 $ ls -blog --dired 'a b'
6413 -rw-r--r-- 1 0 Jun 10 12:28 a\ b
6415 //DIRED-OPTIONS// --quoting-style=escape
6418 If you use a quoting style that adds quote marks
6419 (e.g., @option{--quoting-style=c}), then the offsets include the quote marks.
6420 So beware that the user may select the quoting style via the environment
6421 variable @env{QUOTING_STYLE}. Hence, applications using @option{--dired}
6422 should either specify an explicit @option{--quoting-style=literal} option
6423 (aka @option{-N} or @option{--literal}) on the command line, or else be
6424 prepared to parse the escaped names.
6427 @opindex --full-time
6428 Produce long format directory listings, and list times in full. It is
6429 equivalent to using @option{--format=long} with
6430 @option{--time-style=full-iso} (@pxref{Formatting file timestamps}).
6434 Produce long format directory listings, but don't display owner information.
6440 Inhibit display of group information in a long format directory listing.
6441 (This is the default in some non-@sc{gnu} versions of @command{ls}, so we
6442 provide this option for compatibility.)
6450 @cindex inode number, printing
6451 Print the inode number (also called the file serial number and index
6452 number) of each file to the left of the file name. (This number
6453 uniquely identifies each file within a particular file system.)
6456 @itemx --format=long
6457 @itemx --format=verbose
6460 @opindex long ls @r{format}
6461 @opindex verbose ls @r{format}
6462 In addition to the name of each file, print the file type, file mode bits,
6463 number of hard links, owner name, group name, size, and
6464 timestamp (@pxref{Formatting file timestamps}), normally
6465 the modification time. Print question marks for information that
6466 cannot be determined.
6468 Normally the size is printed as a byte count without punctuation, but
6469 this can be overridden (@pxref{Block size}). For example, @option{-h}
6470 prints an abbreviated, human-readable count, and
6471 @samp{--block-size="'1"} prints a byte count with the thousands
6472 separator of the current locale.
6474 For each directory that is listed, preface the files with a line
6475 @samp{total @var{blocks}}, where @var{blocks} is the total disk allocation
6476 for all files in that directory. The block size currently defaults to 1024
6477 bytes, but this can be overridden (@pxref{Block size}).
6478 The @var{blocks} computed counts each hard link separately;
6479 this is arguably a deficiency.
6481 The file type is one of the following characters:
6483 @c The commented-out entries are ones we're not sure about.
6491 character special file
6493 high performance (``contiguous data'') file
6497 door (Solaris 2.5 and up)
6499 @c semaphore, if this is a distinct file type
6503 @c multiplexed file (7th edition Unix; obsolete)
6505 off-line (``migrated'') file (Cray DMF)
6507 network special file (HP-UX)
6511 port (Solaris 10 and up)
6513 @c message queue, if this is a distinct file type
6517 @c shared memory object, if this is a distinct file type
6519 @c typed memory object, if this is a distinct file type
6521 @c whiteout (4.4BSD; not implemented)
6523 some other file type
6526 @cindex permissions, output by @command{ls}
6527 The file mode bits listed are similar to symbolic mode specifications
6528 (@pxref{Symbolic Modes}). But @command{ls} combines multiple bits into the
6529 third character of each set of permissions as follows:
6533 If the set-user-ID or set-group-ID bit and the corresponding executable bit
6537 If the set-user-ID or set-group-ID bit is set but the corresponding
6538 executable bit is not set.
6541 If the restricted deletion flag or sticky bit, and the
6542 other-executable bit, are both set. The restricted deletion flag is
6543 another name for the sticky bit. @xref{Mode Structure}.
6546 If the restricted deletion flag or sticky bit is set but the
6547 other-executable bit is not set.
6550 If the executable bit is set and none of the above apply.
6556 Following the file mode bits is a single character that specifies
6557 whether an alternate access method such as an access control list
6558 applies to the file. When the character following the file mode bits is a
6559 space, there is no alternate access method. When it is a printing
6560 character, then there is such a method.
6562 GNU @command{ls} uses a @samp{.} character to indicate a file
6563 with an SELinux security context, but no other alternate access method.
6565 A file with any other combination of alternate access methods
6566 is marked with a @samp{+} character.
6569 @itemx --numeric-uid-gid
6571 @opindex --numeric-uid-gid
6572 @cindex numeric uid and gid
6573 @cindex numeric user and group IDs
6574 Produce long format directory listings, but
6575 display numeric user and group IDs instead of the owner and group names.
6579 Produce long format directory listings, but don't display group information.
6580 It is equivalent to using @option{--format=long} with @option{--no-group} .
6586 @cindex disk allocation
6587 @cindex size of files, reporting
6588 Print the disk allocation of each file to the left of the file name.
6589 This is the amount of disk space used by the file, which is usually a
6590 bit more than the file's size, but it can be less if the file has holes.
6592 Normally the disk allocation is printed in units of
6593 1024 bytes, but this can be overridden (@pxref{Block size}).
6595 @cindex NFS mounts from BSD to HP-UX
6596 For files that are NFS-mounted from an HP-UX system to a BSD system,
6597 this option reports sizes that are half the correct values. On HP-UX
6598 systems, it reports sizes that are twice the correct values for files
6599 that are NFS-mounted from BSD systems. This is due to a flaw in HP-UX;
6600 it also affects the HP-UX @command{ls} program.
6609 @cindex security context
6610 Display the SELinux security context or @samp{?} if none is found.
6611 When used with the @option{-l} option, print the security context
6612 to the left of the size column.
6617 @node Sorting the output
6618 @subsection Sorting the output
6620 @cindex sorting @command{ls} output
6621 These options change the order in which @command{ls} sorts the information
6622 it outputs. By default, sorting is done by character code
6623 (e.g., @acronym{ASCII} order).
6629 @itemx --time=status
6632 @opindex ctime@r{, printing or sorting by}
6633 @opindex status time@r{, printing or sorting by}
6634 @opindex use time@r{, printing or sorting files by}
6635 If the long listing format (e.g., @option{-l}, @option{-o}) is being used,
6636 print the status change time (the @samp{ctime} in the inode) instead of
6637 the modification time.
6638 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6639 or when not using a long listing format,
6640 sort according to the status change time.
6644 @cindex unsorted directory listing
6645 @cindex directory order, listing by
6646 Primarily, like @option{-U}---do not sort; list the files in whatever
6647 order they are stored in the directory. But also enable @option{-a} (list
6648 all files) and disable @option{-l}, @option{--color}, and @option{-s} (if they
6649 were specified before the @option{-f}).
6655 @cindex reverse sorting
6656 Reverse whatever the sorting method is---e.g., list files in reverse
6657 alphabetical order, youngest first, smallest first, or whatever.
6663 @opindex size of files@r{, sorting files by}
6664 Sort by file size, largest first.
6670 @opindex modification time@r{, sorting files by}
6671 Sort by modification time (the @samp{mtime} in the inode), newest first.
6675 @itemx --time=access
6679 @opindex use time@r{, printing or sorting files by}
6680 @opindex atime@r{, printing or sorting files by}
6681 @opindex access time@r{, printing or sorting files by}
6682 If the long listing format (e.g., @option{--format=long}) is being used,
6683 print the last access time (the @samp{atime} in the inode).
6684 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6685 or when not using a long listing format, sort according to the access time.
6691 @opindex none@r{, sorting option for @command{ls}}
6692 Do not sort; list the files in whatever order they are
6693 stored in the directory. (Do not do any of the other unrelated things
6694 that @option{-f} does.) This is especially useful when listing very large
6695 directories, since not doing any sorting can be noticeably faster.
6698 @itemx --sort=version
6701 @opindex version@r{, sorting option for @command{ls}}
6702 Sort by version name and number, lowest first. It behaves like a default
6703 sort, except that each sequence of decimal digits is treated numerically
6704 as an index/version number. (@xref{Details about version sort}.)
6707 @itemx --sort=extension
6710 @opindex extension@r{, sorting files by}
6711 Sort directory contents alphabetically by file extension (characters
6712 after the last @samp{.}); files with no extension are sorted first.
6717 @node Details about version sort
6718 @subsection Details about version sort
6720 Version sorting handles the fact that file names frequently include indices or
6721 version numbers. Standard sorting usually does not produce the order that one
6722 expects because comparisons are made on a character-by-character basis.
6723 Version sorting is especially useful when browsing directories that contain
6724 many files with indices/version numbers in their names:
6728 abc.zml-1.gz abc.zml-1.gz
6729 abc.zml-12.gz abc.zml-2.gz
6730 abc.zml-2.gz abc.zml-12.gz
6733 Version-sorted strings are compared such that if @var{ver1} and @var{ver2}
6734 are version numbers and @var{prefix} and @var{suffix} (@var{suffix} matching
6735 the regular expression @samp{(\.[A-Za-z~][A-Za-z0-9~]*)*}) are strings then
6736 @var{ver1} < @var{ver2} implies that the name composed of
6737 ``@var{prefix} @var{ver1} @var{suffix}'' sorts before
6738 ``@var{prefix} @var{ver2} @var{suffix}''.
6740 Note also that leading zeros of numeric parts are ignored:
6744 abc-1.007.tgz abc-1.01a.tgz
6745 abc-1.012b.tgz abc-1.007.tgz
6746 abc-1.01a.tgz abc-1.012b.tgz
6749 This functionality is implemented using gnulib's @code{filevercmp} function,
6750 which has some caveats worth noting.
6753 @item @env{LC_COLLATE} is ignored, which means @samp{ls -v} and @samp{sort -V}
6754 will sort non-numeric prefixes as if the @env{LC_COLLATE} locale category
6755 was set to @samp{C}.
6756 @item Some suffixes will not be matched by the regular
6757 expression mentioned above. Consequently these examples may
6758 not sort as you expect:
6766 abc-1.2.3.4.x86_64.rpm
6767 abc-1.2.3.x86_64.rpm
6771 @node General output formatting
6772 @subsection General output formatting
6774 These options affect the appearance of the overall output.
6779 @itemx --format=single-column
6782 @opindex single-column @r{output of files}
6783 List one file per line. This is the default for @command{ls} when standard
6784 output is not a terminal.
6787 @itemx --format=vertical
6790 @opindex vertical @r{sorted files in columns}
6791 List files in columns, sorted vertically. This is the default for
6792 @command{ls} if standard output is a terminal. It is always the default
6793 for the @command{dir} program.
6794 @sc{gnu} @command{ls} uses variable width columns to display as many files as
6795 possible in the fewest lines.
6797 @item --color [=@var{when}]
6799 @cindex color, distinguishing file types with
6800 Specify whether to use color for distinguishing file types. @var{when}
6801 may be omitted, or one of:
6804 @vindex none @r{color option}
6805 - Do not use color at all. This is the default.
6807 @vindex auto @r{color option}
6808 @cindex terminal, using color iff
6809 - Only use color if standard output is a terminal.
6811 @vindex always @r{color option}
6814 Specifying @option{--color} and no @var{when} is equivalent to
6815 @option{--color=always}.
6816 Piping a colorized listing through a pager like @command{more} or
6817 @command{less} usually produces unreadable results. However, using
6818 @code{more -f} does seem to work.
6822 @itemx --indicator-style=classify
6825 @opindex --indicator-style
6826 @cindex file type and executables, marking
6827 @cindex executables and file type, marking
6828 Append a character to each file name indicating the file type. Also,
6829 for regular files that are executable, append @samp{*}. The file type
6830 indicators are @samp{/} for directories, @samp{@@} for symbolic links,
6831 @samp{|} for FIFOs, @samp{=} for sockets, @samp{>} for doors,
6832 and nothing for regular files.
6833 @c The following sentence is the same as the one for -d.
6834 Do not follow symbolic links listed on the
6835 command line unless the @option{--dereference-command-line} (@option{-H}),
6836 @option{--dereference} (@option{-L}), or
6837 @option{--dereference-command-line-symlink-to-dir} options are specified.
6840 @itemx --indicator-style=file-type
6841 @opindex --file-type
6842 @opindex --indicator-style
6843 @cindex file type, marking
6844 Append a character to each file name indicating the file type. This is
6845 like @option{-F}, except that executables are not marked.
6847 @item --indicator-style=@var{word}
6848 @opindex --indicator-style
6849 Append a character indicator with style @var{word} to entry names,
6854 Do not append any character indicator; this is the default.
6856 Append @samp{/} for directories. This is the same as the @option{-p}
6859 Append @samp{/} for directories, @samp{@@} for symbolic links, @samp{|}
6860 for FIFOs, @samp{=} for sockets, and nothing for regular files. This is
6861 the same as the @option{--file-type} option.
6863 Append @samp{*} for executable regular files, otherwise behave as for
6864 @samp{file-type}. This is the same as the @option{-F} or
6865 @option{--classify} option.
6870 Print file sizes in 1024-byte blocks, overriding the default block
6871 size (@pxref{Block size}).
6872 This option is equivalent to @option{--block-size=1K}.
6875 @itemx --format=commas
6878 @opindex commas@r{, outputting between files}
6879 List files horizontally, with as many as will fit on each line,
6880 separated by @samp{, } (a comma and a space).
6883 @itemx --indicator-style=slash
6885 @opindex --indicator-style
6886 @cindex file type, marking
6887 Append a @samp{/} to directory names.
6890 @itemx --format=across
6891 @itemx --format=horizontal
6894 @opindex across@r{, listing files}
6895 @opindex horizontal@r{, listing files}
6896 List the files in columns, sorted horizontally.
6899 @itemx --tabsize=@var{cols}
6902 Assume that each tab stop is @var{cols} columns wide. The default is 8.
6903 @command{ls} uses tabs where possible in the output, for efficiency. If
6904 @var{cols} is zero, do not use tabs at all.
6906 @c FIXME: remove in 2009, if Apple Terminal has been fixed for long enough.
6907 Some terminal emulators (at least Apple Terminal 1.5 (133) from Mac OS X 10.4.8)
6908 do not properly align columns to the right of a TAB following a
6909 non-@acronym{ASCII} byte. If you use such a terminal emulator, use the
6910 @option{-T0} option or put @code{TABSIZE=0} in your environment to tell
6911 @command{ls} to align using spaces, not tabs.
6914 @itemx --width=@var{cols}
6918 Assume the screen is @var{cols} columns wide. The default is taken
6919 from the terminal settings if possible; otherwise the environment
6920 variable @env{COLUMNS} is used if it is set; otherwise the default
6926 @node Formatting file timestamps
6927 @subsection Formatting file timestamps
6929 By default, file timestamps are listed in abbreviated form. Most
6930 locales use a timestamp like @samp{2002-03-30 23:45}. However, the
6931 default @acronym{POSIX} locale uses a date like @samp{Mar 30@ @ 2002}
6932 for non-recent timestamps, and a date-without-year and time like
6933 @samp{Mar 30 23:45} for recent timestamps.
6935 A timestamp is considered to be @dfn{recent} if it is less than six
6936 months old, and is not dated in the future. If a timestamp dated
6937 today is not listed in recent form, the timestamp is in the future,
6938 which means you probably have clock skew problems which may break
6939 programs like @command{make} that rely on file timestamps.
6942 Time stamps are listed according to the time zone rules specified by
6943 the @env{TZ} environment variable, or by the system default rules if
6944 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
6945 with @env{TZ}, libc, The GNU C Library Reference Manual}.
6947 The following option changes how file timestamps are printed.
6950 @item --time-style=@var{style}
6951 @opindex --time-style
6953 List timestamps in style @var{style}. The @var{style} should
6954 be one of the following:
6959 List timestamps using @var{format}, where @var{format} is interpreted
6960 like the format argument of @command{date} (@pxref{date invocation}).
6961 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
6962 @command{ls} to list timestamps like @samp{2002-03-30 23:45:56}. As
6963 with @command{date}, @var{format}'s interpretation is affected by the
6964 @env{LC_TIME} locale category.
6966 If @var{format} contains two format strings separated by a newline,
6967 the former is used for non-recent files and the latter for recent
6968 files; if you want output columns to line up, you may need to insert
6969 spaces in one of the two formats.
6972 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
6973 format with nanosecond precision, e.g., @samp{2002-03-30
6974 23:45:56.477817180 -0700}. This style is equivalent to
6975 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
6977 This is useful because the time output includes all the information that
6978 is available from the operating system. For example, this can help
6979 explain @command{make}'s behavior, since @acronym{GNU} @command{make}
6980 uses the full timestamp to determine whether a file is out of date.
6983 List @acronym{ISO} 8601 date and time in minutes, e.g.,
6984 @samp{2002-03-30 23:45}. These timestamps are shorter than
6985 @samp{full-iso} timestamps, and are usually good enough for everyday
6986 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
6989 List @acronym{ISO} 8601 dates for non-recent timestamps (e.g.,
6990 @samp{2002-03-30@ }), and @acronym{ISO} 8601 month, day, hour, and
6991 minute for recent timestamps (e.g., @samp{03-30 23:45}). These
6992 timestamps are uglier than @samp{long-iso} timestamps, but they carry
6993 nearly the same information in a smaller space and their brevity helps
6994 @command{ls} output fit within traditional 80-column output lines.
6995 The following two @command{ls} invocations are equivalent:
7000 ls -l --time-style="+%Y-%m-%d $newline%m-%d %H:%M"
7001 ls -l --time-style="iso"
7006 List timestamps in a locale-dependent form. For example, a Finnish
7007 locale might list non-recent timestamps like @samp{maalis 30@ @ 2002}
7008 and recent timestamps like @samp{maalis 30 23:45}. Locale-dependent
7009 timestamps typically consume more space than @samp{iso} timestamps and
7010 are harder for programs to parse because locale conventions vary so
7011 widely, but they are easier for many people to read.
7013 The @env{LC_TIME} locale category specifies the timestamp format. The
7014 default @acronym{POSIX} locale uses timestamps like @samp{Mar 30@
7015 @ 2002} and @samp{Mar 30 23:45}; in this locale, the following two
7016 @command{ls} invocations are equivalent:
7021 ls -l --time-style="+%b %e %Y$newline%b %e %H:%M"
7022 ls -l --time-style="locale"
7025 Other locales behave differently. For example, in a German locale,
7026 @option{--time-style="locale"} might be equivalent to
7027 @option{--time-style="+%e. %b %Y $newline%e. %b %H:%M"}
7028 and might generate timestamps like @samp{30. M@"ar 2002@ } and
7029 @samp{30. M@"ar 23:45}.
7031 @item posix-@var{style}
7033 List @acronym{POSIX}-locale timestamps if the @env{LC_TIME} locale
7034 category is @acronym{POSIX}, @var{style} timestamps otherwise. For
7035 example, the @samp{posix-long-iso} style lists
7036 timestamps like @samp{Mar 30@ @ 2002} and @samp{Mar 30 23:45} when in
7037 the @acronym{POSIX} locale, and like @samp{2002-03-30 23:45} otherwise.
7042 You can specify the default value of the @option{--time-style} option
7043 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
7044 the default style is @samp{locale}. @acronym{GNU} Emacs 21.3 and
7045 later use the @option{--dired} option and therefore can parse any date
7046 format, but if you are using Emacs 21.1 or 21.2 and specify a
7047 non-@acronym{POSIX} locale you may need to set
7048 @samp{TIME_STYLE="posix-long-iso"}.
7050 To avoid certain denial-of-service attacks, timestamps that would be
7051 longer than 1000 bytes may be treated as errors.
7054 @node Formatting the file names
7055 @subsection Formatting the file names
7057 These options change how file names themselves are printed.
7063 @itemx --quoting-style=escape
7066 @opindex --quoting-style
7067 @cindex backslash sequences for file names
7068 Quote nongraphic characters in file names using alphabetic and octal
7069 backslash sequences like those used in C.
7073 @itemx --quoting-style=literal
7076 @opindex --quoting-style
7077 Do not quote file names. However, with @command{ls} nongraphic
7078 characters are still printed as question marks if the output is a
7079 terminal and you do not specify the @option{--show-control-chars}
7083 @itemx --hide-control-chars
7085 @opindex --hide-control-chars
7086 Print question marks instead of nongraphic characters in file names.
7087 This is the default if the output is a terminal and the program is
7092 @itemx --quoting-style=c
7094 @opindex --quote-name
7095 @opindex --quoting-style
7096 Enclose file names in double quotes and quote nongraphic characters as
7099 @item --quoting-style=@var{word}
7100 @opindex --quoting-style
7101 @cindex quoting style
7102 Use style @var{word} to quote file names and other strings that may
7103 contain arbitrary characters. The @var{word} should
7104 be one of the following:
7108 Output strings as-is; this is the same as the @option{-N} or
7109 @option{--literal} option.
7111 Quote strings for the shell if they contain shell metacharacters or would
7112 cause ambiguous output.
7113 The quoting is suitable for @acronym{POSIX}-compatible shells like
7114 @command{bash}, but it does not always work for incompatible shells
7117 Quote strings for the shell, even if they would normally not require quoting.
7119 Quote strings as for C character string literals, including the
7120 surrounding double-quote characters; this is the same as the
7121 @option{-Q} or @option{--quote-name} option.
7123 Quote strings as for C character string literals, except omit the
7124 surrounding double-quote
7125 characters; this is the same as the @option{-b} or @option{--escape} option.
7127 Quote strings as for C character string literals, except use
7128 surrounding quotation marks appropriate for the
7131 @c Use @t instead of @samp to avoid duplicate quoting in some output styles.
7132 Quote strings as for C character string literals, except use
7133 surrounding quotation marks appropriate for the locale, and quote
7134 @t{`like this'} instead of @t{"like
7135 this"} in the default C locale. This looks nicer on many displays.
7138 You can specify the default value of the @option{--quoting-style} option
7139 with the environment variable @env{QUOTING_STYLE}. If that environment
7140 variable is not set, the default value is @samp{literal}, but this
7141 default may change to @samp{shell} in a future version of this package.
7143 @item --show-control-chars
7144 @opindex --show-control-chars
7145 Print nongraphic characters as-is in file names.
7146 This is the default unless the output is a terminal and the program is
7152 @node dir invocation
7153 @section @command{dir}: Briefly list directory contents
7156 @cindex directory listing, brief
7158 @command{dir} is equivalent to @code{ls -C
7159 -b}; that is, by default files are listed in columns, sorted vertically,
7160 and special characters are represented by backslash escape sequences.
7162 @xref{ls invocation, @command{ls}}.
7165 @node vdir invocation
7166 @section @command{vdir}: Verbosely list directory contents
7169 @cindex directory listing, verbose
7171 @command{vdir} is equivalent to @code{ls -l
7172 -b}; that is, by default files are listed in long format and special
7173 characters are represented by backslash escape sequences.
7175 @node dircolors invocation
7176 @section @command{dircolors}: Color setup for @command{ls}
7180 @cindex setup for color
7182 @command{dircolors} outputs a sequence of shell commands to set up the
7183 terminal for color output from @command{ls} (and @command{dir}, etc.).
7187 eval "`dircolors [@var{option}]@dots{} [@var{file}]`"
7190 If @var{file} is specified, @command{dircolors} reads it to determine which
7191 colors to use for which file types and extensions. Otherwise, a
7192 precompiled database is used. For details on the format of these files,
7193 run @samp{dircolors --print-database}.
7195 To make @command{dircolors} read a @file{~/.dircolors} file if it
7196 exists, you can put the following lines in your @file{~/.bashrc} (or
7197 adapt them to your favorite shell):
7201 test -r $d && eval "$(dircolors $d)"
7205 @vindex SHELL @r{environment variable, and color}
7206 The output is a shell command to set the @env{LS_COLORS} environment
7207 variable. You can specify the shell syntax to use on the command line,
7208 or @command{dircolors} will guess it from the value of the @env{SHELL}
7209 environment variable.
7211 The program accepts the following options. Also see @ref{Common options}.
7216 @itemx --bourne-shell
7219 @opindex --bourne-shell
7220 @cindex Bourne shell syntax for color setup
7221 @cindex @command{sh} syntax for color setup
7222 Output Bourne shell commands. This is the default if the @env{SHELL}
7223 environment variable is set and does not end with @samp{csh} or
7232 @cindex C shell syntax for color setup
7233 @cindex @command{csh} syntax for color setup
7234 Output C shell commands. This is the default if @code{SHELL} ends with
7235 @command{csh} or @command{tcsh}.
7238 @itemx --print-database
7240 @opindex --print-database
7241 @cindex color database, printing
7242 @cindex database for color setup, printing
7243 @cindex printing color database
7244 Print the (compiled-in) default color configuration database. This
7245 output is itself a valid configuration file, and is fairly descriptive
7246 of the possibilities.
7253 @node Basic operations
7254 @chapter Basic operations
7256 @cindex manipulating files
7258 This chapter describes the commands for basic file manipulation:
7259 copying, moving (renaming), and deleting (removing).
7262 * cp invocation:: Copy files.
7263 * dd invocation:: Convert and copy a file.
7264 * install invocation:: Copy files and set attributes.
7265 * mv invocation:: Move (rename) files.
7266 * rm invocation:: Remove files or directories.
7267 * shred invocation:: Remove files more securely.
7272 @section @command{cp}: Copy files and directories
7275 @cindex copying files and directories
7276 @cindex files, copying
7277 @cindex directories, copying
7279 @command{cp} copies files (or, optionally, directories). The copy is
7280 completely independent of the original. You can either copy one file to
7281 another, or copy arbitrarily many files to a destination directory.
7285 cp [@var{option}]@dots{} [-T] @var{source} @var{dest}
7286 cp [@var{option}]@dots{} @var{source}@dots{} @var{directory}
7287 cp [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
7292 If two file names are given, @command{cp} copies the first file to the
7296 If the @option{--target-directory} (@option{-t}) option is given, or
7297 failing that if the last file is a directory and the
7298 @option{--no-target-directory} (@option{-T}) option is not given,
7299 @command{cp} copies each @var{source} file to the specified directory,
7300 using the @var{source}s' names.
7303 Generally, files are written just as they are read. For exceptions,
7304 see the @option{--sparse} option below.
7306 By default, @command{cp} does not copy directories. However, the
7307 @option{-R}, @option{-a}, and @option{-r} options cause @command{cp} to
7308 copy recursively by descending into source directories and copying files
7309 to corresponding destination directories.
7311 When copying from a symbolic link, @command{cp} normally follows the
7312 link only when not copying
7313 recursively. This default can be overridden with the
7314 @option{--archive} (@option{-a}), @option{-d}, @option{--dereference}
7315 (@option{-L}), @option{--no-dereference} (@option{-P}), and
7316 @option{-H} options. If more than one of these options is specified,
7317 the last one silently overrides the others.
7319 When copying to a symbolic link, @command{cp} follows the
7320 link only when it refers to an existing regular file.
7321 However, when copying to a dangling symbolic link, @command{cp}
7322 refuses by default, and fails with a diagnostic, since the operation
7323 is inherently dangerous. This behavior is contrary to historical
7324 practice and to @acronym{POSIX}.
7325 Set @env{POSIXLY_CORRECT} to make @command{cp} attempt to create
7326 the target of a dangling destination symlink, in spite of the possible risk.
7327 Also, when an option like
7328 @option{--backup} or @option{--link} acts to rename or remove the
7329 destination before copying, @command{cp} renames or removes the
7330 symbolic link rather than the file it points to.
7332 By default, @command{cp} copies the contents of special files only
7333 when not copying recursively. This default can be overridden with the
7334 @option{--copy-contents} option.
7336 @cindex self-backups
7337 @cindex backups, making only
7338 @command{cp} generally refuses to copy a file onto itself, with the
7339 following exception: if @option{--force --backup} is specified with
7340 @var{source} and @var{dest} identical, and referring to a regular file,
7341 @command{cp} will make a backup file, either regular or numbered, as
7342 specified in the usual ways (@pxref{Backup options}). This is useful when
7343 you simply want to make a backup of an existing file before changing it.
7345 The program accepts the following options. Also see @ref{Common options}.
7352 Preserve as much as possible of the structure and attributes of the
7353 original files in the copy (but do not attempt to preserve internal
7354 directory structure; i.e., @samp{ls -U} may list the entries in a copied
7355 directory in a different order).
7356 Try to preserve SELinux security context and extended attributes (xattr),
7357 but ignore any failure to do that and print no corresponding diagnostic.
7358 Equivalent to @option{-dR --preserve=all} with the reduced diagnostics.
7361 @itemx @w{@kbd{--backup}[=@var{method}]}
7364 @vindex VERSION_CONTROL
7365 @cindex backups, making
7366 @xref{Backup options}.
7367 Make a backup of each file that would otherwise be overwritten or removed.
7368 As a special case, @command{cp} makes a backup of @var{source} when the force
7369 and backup options are given and @var{source} and @var{dest} are the same
7370 name for an existing, regular file. One useful application of this
7371 combination of options is this tiny Bourne shell script:
7375 # Usage: backup FILE...
7376 # Create a @sc{gnu}-style backup of each listed FILE.
7378 cp --backup --force -- "$i" "$i"
7382 @item --copy-contents
7383 @cindex directories, copying recursively
7384 @cindex copying directories recursively
7385 @cindex recursively copying directories
7386 @cindex non-directories, copying as special files
7387 If copying recursively, copy the contents of any special files (e.g.,
7388 FIFOs and device files) as if they were regular files. This means
7389 trying to read the data in each source file and writing it to the
7390 destination. It is usually a mistake to use this option, as it
7391 normally has undesirable effects on special files like FIFOs and the
7392 ones typically found in the @file{/dev} directory. In most cases,
7393 @code{cp -R --copy-contents} will hang indefinitely trying to read
7394 from FIFOs and special files like @file{/dev/console}, and it will
7395 fill up your destination disk if you use it to copy @file{/dev/zero}.
7396 This option has no effect unless copying recursively, and it does not
7397 affect the copying of symbolic links.
7401 @cindex symbolic links, copying
7402 @cindex hard links, preserving
7403 Copy symbolic links as symbolic links rather than copying the files that
7404 they point to, and preserve hard links between source files in the copies.
7405 Equivalent to @option{--no-dereference --preserve=links}.
7411 When copying without this option and an existing destination file cannot
7412 be opened for writing, the copy fails. However, with @option{--force}),
7413 when a destination file cannot be opened, @command{cp} then removes it and
7414 tries to open it again. Contrast this behavior with that enabled by
7415 @option{--link} and @option{--symbolic-link}, whereby the destination file
7416 is never opened but rather is removed unconditionally. Also see the
7417 description of @option{--remove-destination}.
7419 This option is independent of the @option{--interactive} or
7420 @option{-i} option: neither cancels the effect of the other.
7422 This option is redundant if the @option{--no-clobber} or @option{-n} option is
7427 If a command line argument specifies a symbolic link, then copy the
7428 file it points to rather than the symbolic link itself. However,
7429 copy (preserving its nature) any symbolic link that is encountered
7430 via recursive traversal.
7433 @itemx --interactive
7435 @opindex --interactive
7436 When copying a file other than a directory, prompt whether to
7437 overwrite an existing destination file. The @option{-i} option overrides
7438 a previous @option{-n} option.
7444 Make hard links instead of copies of non-directories.
7447 @itemx --dereference
7449 @opindex --dereference
7450 Follow symbolic links when copying from them.
7451 With this option, @command{cp} cannot create a symbolic link.
7452 For example, a symlink (to regular file) in the source tree will be copied to
7453 a regular file in the destination tree.
7458 @opindex --no-clobber
7459 Do not overwrite an existing file. The @option{-n} option overrides a previous
7460 @option{-i} option. This option is mutually exclusive with @option{-b} or
7461 @option{--backup} option.
7464 @itemx --no-dereference
7466 @opindex --no-dereference
7467 @cindex symbolic links, copying
7468 Copy symbolic links as symbolic links rather than copying the files that
7469 they point to. This option affects only symbolic links in the source;
7470 symbolic links in the destination are always followed if possible.
7473 @itemx @w{@kbd{--preserve}[=@var{attribute_list}]}
7476 @cindex file information, preserving, extended attributes, xattr
7477 Preserve the specified attributes of the original files.
7478 If specified, the @var{attribute_list} must be a comma-separated list
7479 of one or more of the following strings:
7483 Preserve the file mode bits and access control lists.
7485 Preserve the owner and group. On most modern systems,
7486 only users with appropriate privileges may change the owner of a file,
7488 may preserve the group ownership of a file only if they happen to be
7489 a member of the desired group.
7491 Preserve the times of last access and last modification, when possible.
7492 On older systems, it is not possible to preserve these attributes
7493 when the affected file is a symbolic link.
7494 However, many systems now provide the @code{utimensat} function,
7495 which makes it possible even for symbolic links.
7497 Preserve in the destination files
7498 any links between corresponding source files.
7499 Note that with @option{-L} or @option{-H}, this option can convert
7500 symbolic links to hard links. For example,
7502 $ mkdir c; : > a; ln -s a b; cp -aH a b c; ls -i1 c
7507 Note the inputs: @file{b} is a symlink to regular file @file{a},
7508 yet the files in destination directory, @file{c/}, are hard-linked.
7509 Since @option{-a} implies @option{--preserve=links}, and since @option{-H}
7510 tells @command{cp} to dereference command line arguments, it sees two files
7511 with the same inode number, and preserves the perceived hard link.
7513 Here is a similar example that exercises @command{cp}'s @option{-L} option:
7515 $ mkdir b c; (cd b; : > a; ln -s a b); cp -aL b c; ls -i1 c/b
7521 Preserve SELinux security context of the file, or fail with full diagnostics.
7523 Preserve extended attributes of the file, or fail with full diagnostics.
7524 If @command{cp} is built without xattr support, ignore this option.
7525 If SELinux context, ACLs or Capabilities are implemented using xattrs,
7526 they are preserved by this option as well.
7528 Preserve all file attributes.
7529 Equivalent to specifying all of the above, but with the difference
7530 that failure to preserve SELinux security context or extended attributes
7531 does not change @command{cp}'s exit status. In contrast to @option{-a},
7532 all but @samp{Operation not supported} warnings are output.
7535 Using @option{--preserve} with no @var{attribute_list} is equivalent
7536 to @option{--preserve=mode,ownership,timestamps}.
7538 In the absence of this option, each destination file is created with the
7539 mode bits of the corresponding source file, minus the bits set in the
7540 umask and minus the set-user-ID and set-group-ID bits.
7541 @xref{File permissions}.
7543 @itemx @w{@kbd{--no-preserve}=@var{attribute_list}}
7544 @cindex file information, preserving
7545 Do not preserve the specified attributes. The @var{attribute_list}
7546 has the same form as for @option{--preserve}.
7550 @cindex parent directories and @command{cp}
7551 Form the name of each destination file by appending to the target
7552 directory a slash and the specified name of the source file. The last
7553 argument given to @command{cp} must be the name of an existing directory.
7554 For example, the command:
7557 cp --parents a/b/c existing_dir
7561 copies the file @file{a/b/c} to @file{existing_dir/a/b/c}, creating
7562 any missing intermediate directories.
7569 @opindex --recursive
7570 @cindex directories, copying recursively
7571 @cindex copying directories recursively
7572 @cindex recursively copying directories
7573 @cindex non-directories, copying as special files
7574 Copy directories recursively. By default, do not follow symbolic
7575 links in the source; see the @option{--archive} (@option{-a}), @option{-d},
7576 @option{--dereference} (@option{-L}), @option{--no-dereference}
7577 (@option{-P}), and @option{-H} options. Special files are copied by
7578 creating a destination file of the same type as the source; see the
7579 @option{--copy-contents} option. It is not portable to use
7580 @option{-r} to copy symbolic links or special files. On some
7581 non-@sc{gnu} systems, @option{-r} implies the equivalent of
7582 @option{-L} and @option{--copy-contents} for historical reasons.
7583 Also, it is not portable to use @option{-R} to copy symbolic links
7584 unless you also specify @option{-P}, as @acronym{POSIX} allows
7585 implementations that dereference symbolic links by default.
7587 @item --reflink[=@var{when}]
7588 @opindex --reflink[=@var{when}]
7591 @cindex copy on write
7592 Perform a lightweight, copy-on-write (COW) copy.
7593 Copying with this option can succeed only on some file systems.
7594 Once it has succeeded, beware that the source and destination files
7595 share the same disk data blocks as long as they remain unmodified.
7596 Thus, if a disk I/O error affects data blocks of one of the files,
7597 the other suffers the exact same fate.
7599 The @var{when} value can be one of the following:
7603 The default behavior: if the copy-on-write operation is not supported
7604 then report the failure for each file and exit with a failure status.
7607 If the copy-on-write operation is not supported then fall back
7608 to the standard copy behaviour.
7612 @item --remove-destination
7613 @opindex --remove-destination
7614 Remove each existing destination file before attempting to open it
7615 (contrast with @option{-f} above).
7617 @item --sparse=@var{when}
7618 @opindex --sparse=@var{when}
7619 @cindex sparse files, copying
7620 @cindex holes, copying files with
7621 @findex read @r{system call, and holes}
7622 A @dfn{sparse file} contains @dfn{holes}---a sequence of zero bytes that
7623 does not occupy any physical disk blocks; the @samp{read} system call
7624 reads these as zeros. This can both save considerable disk space and
7625 increase speed, since many binary files contain lots of consecutive zero
7626 bytes. By default, @command{cp} detects holes in input source files via a crude
7627 heuristic and makes the corresponding output file sparse as well.
7628 Only regular files may be sparse.
7630 The @var{when} value can be one of the following:
7634 The default behavior: if the input file is sparse, attempt to make
7635 the output file sparse, too. However, if an output file exists but
7636 refers to a non-regular file, then do not attempt to make it sparse.
7639 For each sufficiently long sequence of zero bytes in the input file,
7640 attempt to create a corresponding hole in the output file, even if the
7641 input file does not appear to be sparse.
7642 This is useful when the input file resides on a file system
7643 that does not support sparse files
7644 (for example, @samp{efs} file systems in SGI IRIX 5.3 and earlier),
7645 but the output file is on a type of file system that does support them.
7646 Holes may be created only in regular files, so if the destination file
7647 is of some other type, @command{cp} does not even try to make it sparse.
7650 Never make the output file sparse.
7651 This is useful in creating a file for use with the @command{mkswap} command,
7652 since such a file must not have any holes.
7655 @optStripTrailingSlashes
7658 @itemx --symbolic-link
7660 @opindex --symbolic-link
7661 @cindex symbolic links, copying with
7662 Make symbolic links instead of copies of non-directories. All source
7663 file names must be absolute (starting with @samp{/}) unless the
7664 destination files are in the current directory. This option merely
7665 results in an error message on systems that do not support symbolic links.
7671 @optNoTargetDirectory
7677 @cindex newer files, copying only
7678 Do not copy a non-directory that has an existing destination with the
7679 same or newer modification time. If time stamps are being preserved,
7680 the comparison is to the source time stamp truncated to the
7681 resolutions of the destination file system and of the system calls
7682 used to update time stamps; this avoids duplicate work if several
7683 @samp{cp -pu} commands are executed with the same source and
7690 Print the name of each file before copying it.
7693 @itemx --one-file-system
7695 @opindex --one-file-system
7696 @cindex file systems, omitting copying to different
7697 Skip subdirectories that are on different file systems from the one that
7698 the copy started on.
7699 However, mount point directories @emph{are} copied.
7707 @section @command{dd}: Convert and copy a file
7710 @cindex converting while copying a file
7712 @command{dd} copies a file (from standard input to standard output, by
7713 default) with a changeable I/O block size, while optionally performing
7714 conversions on it. Synopses:
7717 dd [@var{operand}]@dots{}
7721 The only options are @option{--help} and @option{--version}.
7722 @xref{Common options}. @command{dd} accepts the following operands.
7728 Read from @var{file} instead of standard input.
7732 Write to @var{file} instead of standard output. Unless
7733 @samp{conv=notrunc} is given, @command{dd} truncates @var{file} to zero
7734 bytes (or the size specified with @samp{seek=}).
7736 @item ibs=@var{bytes}
7738 @cindex block size of input
7739 @cindex input block size
7740 Set the input block size to @var{bytes}.
7741 This makes @command{dd} read @var{bytes} per block.
7742 The default is 512 bytes.
7744 @item obs=@var{bytes}
7746 @cindex block size of output
7747 @cindex output block size
7748 Set the output block size to @var{bytes}.
7749 This makes @command{dd} write @var{bytes} per block.
7750 The default is 512 bytes.
7752 @item bs=@var{bytes}
7755 Set both input and output block sizes to @var{bytes}.
7756 This makes @command{dd} read and write @var{bytes} per block,
7757 overriding any @samp{ibs} and @samp{obs} settings.
7758 In addition, if no data-transforming @option{conv} option is specified,
7759 each input block is copied to the output as a single block,
7760 without aggregating short reads.
7762 @item cbs=@var{bytes}
7764 @cindex block size of conversion
7765 @cindex conversion block size
7766 @cindex fixed-length records, converting to variable-length
7767 @cindex variable-length records, converting to fixed-length
7768 Set the conversion block size to @var{bytes}.
7769 When converting variable-length records to fixed-length ones
7770 (@option{conv=block}) or the reverse (@option{conv=unblock}),
7771 use @var{bytes} as the fixed record length.
7773 @item skip=@var{blocks}
7775 Skip @var{blocks} @samp{ibs}-byte blocks in the input file before copying.
7777 @item seek=@var{blocks}
7779 Skip @var{blocks} @samp{obs}-byte blocks in the output file before copying.
7781 @item count=@var{blocks}
7783 Copy @var{blocks} @samp{ibs}-byte blocks from the input file, instead
7784 of everything until the end of the file.
7788 Do not print the overall transfer rate and volume statistics
7789 that normally make up the third status line when @command{dd} exits.
7791 @item conv=@var{conversion}[,@var{conversion}]@dots{}
7793 Convert the file as specified by the @var{conversion} argument(s).
7794 (No spaces around any comma(s).)
7801 @opindex ascii@r{, converting to}
7802 Convert @acronym{EBCDIC} to @acronym{ASCII},
7803 using the conversion table specified by @acronym{POSIX}.
7804 This provides a 1:1 translation for all 256 bytes.
7807 @opindex ebcdic@r{, converting to}
7808 Convert @acronym{ASCII} to @acronym{EBCDIC}.
7809 This is the inverse of the @samp{ascii} conversion.
7812 @opindex alternate ebcdic@r{, converting to}
7813 Convert @acronym{ASCII} to alternate @acronym{EBCDIC},
7814 using the alternate conversion table specified by @acronym{POSIX}.
7815 This is not a 1:1 translation, but reflects common historical practice
7816 for @samp{~}, @samp{[}, and @samp{]}.
7818 The @samp{ascii}, @samp{ebcdic}, and @samp{ibm} conversions are
7822 @opindex block @r{(space-padding)}
7823 For each line in the input, output @samp{cbs} bytes, replacing the
7824 input newline with a space and padding with spaces as necessary.
7828 Remove any trailing spaces in each @samp{cbs}-sized input block,
7829 and append a newline.
7831 The @samp{block} and @samp{unblock} conversions are mutually exclusive.
7834 @opindex lcase@r{, converting to}
7835 Change uppercase letters to lowercase.
7838 @opindex ucase@r{, converting to}
7839 Change lowercase letters to uppercase.
7841 The @samp{lcase} and @samp{ucase} conversions are mutually exclusive.
7844 @opindex swab @r{(byte-swapping)}
7845 @cindex byte-swapping
7846 Swap every pair of input bytes. @sc{gnu} @command{dd}, unlike others, works
7847 when an odd number of bytes are read---the last byte is simply copied
7848 (since there is nothing to swap it with).
7852 @cindex read errors, ignoring
7853 Continue after read errors.
7857 @cindex creating output file, avoiding
7858 Do not create the output file; the output file must already exist.
7862 @cindex creating output file, requiring
7863 Fail if the output file already exists; @command{dd} must create the
7866 The @samp{excl} and @samp{nocreat} conversions are mutually exclusive.
7870 @cindex truncating output file, avoiding
7871 Do not truncate the output file.
7874 @opindex sync @r{(padding with @acronym{ASCII} @sc{nul}s)}
7875 Pad every input block to size of @samp{ibs} with trailing zero bytes.
7876 When used with @samp{block} or @samp{unblock}, pad with spaces instead of
7881 @cindex synchronized data writes, before finishing
7882 Synchronize output data just before finishing. This forces a physical
7883 write of output data.
7887 @cindex synchronized data and metadata writes, before finishing
7888 Synchronize output data and metadata just before finishing. This
7889 forces a physical write of output data and metadata.
7893 @item iflag=@var{flag}[,@var{flag}]@dots{}
7895 Access the input file using the flags specified by the @var{flag}
7896 argument(s). (No spaces around any comma(s).)
7898 @item oflag=@var{flag}[,@var{flag}]@dots{}
7900 Access the output file using the flags specified by the @var{flag}
7901 argument(s). (No spaces around any comma(s).)
7903 Here are the flags. Not every flag is supported on every operating
7910 @cindex appending to the output file
7911 Write in append mode, so that even if some other process is writing to
7912 this file, every @command{dd} write will append to the current
7913 contents of the file. This flag makes sense only for output.
7914 If you combine this flag with the @samp{of=@var{file}} operand,
7915 you should also specify @samp{conv=notrunc} unless you want the
7916 output file to be truncated before being appended to.
7920 @cindex concurrent I/O
7921 Use concurrent I/O mode for data. This mode performs direct I/O
7922 and drops the @acronym{POSIX} requirement to serialize all I/O to the same file.
7923 A file cannot be opened in CIO mode and with a standard open at the
7929 Use direct I/O for data, avoiding the buffer cache.
7930 Note that the kernel may impose restrictions on read or write buffer sizes.
7931 For example, with an ext4 destination file system and a linux-based kernel,
7932 using @samp{oflag=direct} will cause writes to fail with @code{EINVAL} if the
7933 output buffer size is not a multiple of 512.
7937 @cindex directory I/O
7939 Fail unless the file is a directory. Most operating systems do not
7940 allow I/O to a directory, so this flag has limited utility.
7944 @cindex synchronized data reads
7945 Use synchronized I/O for data. For the output file, this forces a
7946 physical write of output data on each write. For the input file,
7947 this flag can matter when reading from a remote file that has been
7948 written to synchronously by some other process. Metadata (e.g.,
7949 last-access and last-modified time) is not necessarily synchronized.
7953 @cindex synchronized data and metadata I/O
7954 Use synchronized I/O for both data and metadata.
7958 @cindex nonblocking I/O
7959 Use non-blocking I/O.
7964 Do not update the file's access time.
7965 Some older file systems silently ignore this flag, so it is a good
7966 idea to test it on your files before relying on it.
7970 @cindex controlling terminal
7971 Do not assign the file to be a controlling terminal for @command{dd}.
7972 This has no effect when the file is not a terminal.
7973 On many hosts (e.g., @acronym{GNU}/Linux hosts), this option has no effect
7978 @cindex symbolic links, following
7979 Do not follow symbolic links.
7984 Fail if the file has multiple hard links.
7989 Use binary I/O. This option has an effect only on nonstandard
7990 platforms that distinguish binary from text I/O.
7995 Use text I/O. Like @samp{binary}, this option has no effect on
8000 Accumulate full blocks from input. The @code{read} system call
8001 may return early if a full block is not available.
8002 When that happens, continue calling @code{read} to fill the remainder
8004 This flag can be used only with @code{iflag}.
8008 These flags are not supported on all systems, and @samp{dd} rejects
8009 attempts to use them when they are not supported. When reading from
8010 standard input or writing to standard output, the @samp{nofollow} and
8011 @samp{noctty} flags should not be specified, and the other flags
8012 (e.g., @samp{nonblock}) can affect how other processes behave with the
8013 affected file descriptors, even after @command{dd} exits.
8017 @cindex multipliers after numbers
8018 The numeric-valued strings above (@var{bytes} and @var{blocks}) can be
8019 followed by a multiplier: @samp{b}=512, @samp{c}=1,
8020 @samp{w}=2, @samp{x@var{m}}=@var{m}, or any of the
8021 standard block size suffixes like @samp{k}=1024 (@pxref{Block size}).
8023 Any block size you specify via @samp{bs=}, @samp{ibs=}, @samp{obs=}, @samp{cbs=}
8024 should not be too large---values larger than a few megabytes
8025 are generally wasteful or (as in the gigabyte..exabyte case) downright
8026 counterproductive or error-inducing.
8028 Use different @command{dd} invocations to use different block sizes for
8029 skipping and I/O@. For example, the following shell commands copy data
8030 in 512 KiB blocks between a disk and a tape, but do not save or restore a
8031 4 KiB label at the start of the disk:
8034 disk=/dev/rdsk/c0t1d0s2
8037 # Copy all but the label from disk to tape.
8038 (dd bs=4k skip=1 count=0 && dd bs=512k) <$disk >$tape
8040 # Copy from tape back to disk, but leave the disk label alone.
8041 (dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk
8044 Sending an @samp{INFO} signal to a running @command{dd}
8045 process makes it print I/O statistics to standard error
8046 and then resume copying. In the example below,
8047 @command{dd} is run in the background to copy 10 million blocks.
8048 The @command{kill} command makes it output intermediate I/O statistics,
8049 and when @command{dd} completes normally or is killed by the
8050 @code{SIGINT} signal, it outputs the final statistics.
8053 $ dd if=/dev/zero of=/dev/null count=10MB & pid=$!
8054 $ kill -s INFO $pid; wait $pid
8055 3385223+0 records in
8056 3385223+0 records out
8057 1733234176 bytes (1.7 GB) copied, 6.42173 seconds, 270 MB/s
8058 10000000+0 records in
8059 10000000+0 records out
8060 5120000000 bytes (5.1 GB) copied, 18.913 seconds, 271 MB/s
8063 @vindex POSIXLY_CORRECT
8064 On systems lacking the @samp{INFO} signal @command{dd} responds to the
8065 @samp{USR1} signal instead, unless the @env{POSIXLY_CORRECT}
8066 environment variable is set.
8071 @node install invocation
8072 @section @command{install}: Copy files and set attributes
8075 @cindex copying files and setting attributes
8077 @command{install} copies files while setting their file mode bits and, if
8078 possible, their owner and group. Synopses:
8081 install [@var{option}]@dots{} [-T] @var{source} @var{dest}
8082 install [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8083 install [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8084 install [@var{option}]@dots{} -d @var{directory}@dots{}
8089 If two file names are given, @command{install} copies the first file to the
8093 If the @option{--target-directory} (@option{-t}) option is given, or
8094 failing that if the last file is a directory and the
8095 @option{--no-target-directory} (@option{-T}) option is not given,
8096 @command{install} copies each @var{source} file to the specified
8097 directory, using the @var{source}s' names.
8100 If the @option{--directory} (@option{-d}) option is given,
8101 @command{install} creates each @var{directory} and any missing parent
8102 directories. Parent directories are created with mode
8103 @samp{u=rwx,go=rx} (755), regardless of the @option{-m} option or the
8104 current umask. @xref{Directory Setuid and Setgid}, for how the
8105 set-user-ID and set-group-ID bits of parent directories are inherited.
8108 @cindex Makefiles, installing programs in
8109 @command{install} is similar to @command{cp}, but allows you to control the
8110 attributes of destination files. It is typically used in Makefiles to
8111 copy programs into their destination directories. It refuses to copy
8112 files onto themselves.
8114 @cindex extended attributes, xattr
8115 @command{install} never preserves extended attributes (xattr).
8117 The program accepts the following options. Also see @ref{Common options}.
8127 Compare each pair of source and destination files, and if the destination has
8128 identical content and any specified owner, group, permissions, and possibly
8129 SELinux context, then do not modify the destination at all.
8133 Ignored; for compatibility with old Unix versions of @command{install}.
8137 Create any missing parent directories of @var{dest},
8138 then copy @var{source} to @var{dest}.
8139 This option is ignored if a destination directory is specified
8140 via @option{--target-directory=DIR}.
8145 @opindex --directory
8146 @cindex directories, creating with given attributes
8147 @cindex parent directories, creating missing
8148 @cindex leading directories, creating missing
8149 Create any missing parent directories, giving them the default
8150 attributes. Then create each given directory, setting their owner,
8151 group and mode as given on the command line or to the defaults.
8153 @item -g @var{group}
8154 @itemx --group=@var{group}
8157 @cindex group ownership of installed files, setting
8158 Set the group ownership of installed files or directories to
8159 @var{group}. The default is the process's current group. @var{group}
8160 may be either a group name or a numeric group ID.
8163 @itemx --mode=@var{mode}
8166 @cindex permissions of installed files, setting
8167 Set the file mode bits for the installed file or directory to @var{mode},
8168 which can be either an octal number, or a symbolic mode as in
8169 @command{chmod}, with @samp{a=} (no access allowed to anyone) as the
8170 point of departure (@pxref{File permissions}).
8171 The default mode is @samp{u=rwx,go=rx,a-s}---read, write, and
8172 execute for the owner, read and execute for group and other, and with
8173 set-user-ID and set-group-ID disabled.
8174 This default is not quite the same as @samp{755}, since it disables
8175 instead of preserving set-user-ID and set-group-ID on directories.
8176 @xref{Directory Setuid and Setgid}.
8178 @item -o @var{owner}
8179 @itemx --owner=@var{owner}
8182 @cindex ownership of installed files, setting
8183 @cindex appropriate privileges
8184 @vindex root @r{as default owner}
8185 If @command{install} has appropriate privileges (is run as root), set the
8186 ownership of installed files or directories to @var{owner}. The default
8187 is @code{root}. @var{owner} may be either a user name or a numeric user
8190 @item --preserve-context
8191 @opindex --preserve-context
8193 @cindex security context
8194 Preserve the SELinux security context of files and directories.
8195 Failure to preserve the context in all of the files or directories
8196 will result in an exit status of 1. If SELinux is disabled then
8197 print a warning and ignore the option.
8200 @itemx --preserve-timestamps
8202 @opindex --preserve-timestamps
8203 @cindex timestamps of installed files, preserving
8204 Set the time of last access and the time of last modification of each
8205 installed file to match those of each corresponding original file.
8206 When a file is installed without this option, its last access and
8207 last modification times are both set to the time of installation.
8208 This option is useful if you want to use the last modification times
8209 of installed files to keep track of when they were last built as opposed
8210 to when they were last installed.
8216 @cindex symbol table information, stripping
8217 @cindex stripping symbol table information
8218 Strip the symbol tables from installed binary executables.
8220 @itemx --strip-program=@var{program}
8221 @opindex --strip-program
8222 @cindex symbol table information, stripping, program
8223 Program used to strip binaries.
8229 @optNoTargetDirectory
8235 Print the name of each file before copying it.
8237 @item -Z @var{context}
8238 @itemx --context=@var{context}
8242 @cindex security context
8243 Set the default SELinux security context to be used for any
8244 created files and directories. If SELinux is disabled then
8245 print a warning and ignore the option.
8253 @section @command{mv}: Move (rename) files
8257 @command{mv} moves or renames files (or directories). Synopses:
8260 mv [@var{option}]@dots{} [-T] @var{source} @var{dest}
8261 mv [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8262 mv [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8267 If two file names are given, @command{mv} moves the first file to the
8271 If the @option{--target-directory} (@option{-t}) option is given, or
8272 failing that if the last file is a directory and the
8273 @option{--no-target-directory} (@option{-T}) option is not given,
8274 @command{mv} moves each @var{source} file to the specified
8275 directory, using the @var{source}s' names.
8278 @command{mv} can move any type of file from one file system to another.
8279 Prior to version @code{4.0} of the fileutils,
8280 @command{mv} could move only regular files between file systems.
8281 For example, now @command{mv} can move an entire directory hierarchy
8282 including special device files from one partition to another. It first
8283 uses some of the same code that's used by @code{cp -a} to copy the
8284 requested directories and files, then (assuming the copy succeeded)
8285 it removes the originals. If the copy fails, then the part that was
8286 copied to the destination partition is removed. If you were to copy
8287 three directories from one partition to another and the copy of the first
8288 directory succeeded, but the second didn't, the first would be left on
8289 the destination partition and the second and third would be left on the
8292 @cindex extended attributes, xattr
8293 @command{mv} always tries to copy extended attributes (xattr), which may
8294 include SELinux context, ACLs or Capabilities.
8295 Upon failure all but @samp{Operation not supported} warnings are output.
8297 @cindex prompting, and @command{mv}
8298 If a destination file exists but is normally unwritable, standard input
8299 is a terminal, and the @option{-f} or @option{--force} option is not given,
8300 @command{mv} prompts the user for whether to replace the file. (You might
8301 own the file, or have write permission on its directory.) If the
8302 response is not affirmative, the file is skipped.
8304 @emph{Warning}: Avoid specifying a source name with a trailing slash,
8305 when it might be a symlink to a directory.
8306 Otherwise, @command{mv} may do something very surprising, since
8307 its behavior depends on the underlying rename system call.
8308 On a system with a modern Linux-based kernel, it fails with @code{errno=ENOTDIR}.
8309 However, on other systems (at least FreeBSD 6.1 and Solaris 10) it silently
8310 renames not the symlink but rather the directory referenced by the symlink.
8311 @xref{Trailing slashes}.
8313 The program accepts the following options. Also see @ref{Common options}.
8323 @cindex prompts, omitting
8324 Do not prompt the user before removing a destination file.
8326 If you specify more than one of the @option{-i}, @option{-f}, @option{-n}
8327 options, only the final one takes effect.
8332 @itemx --interactive
8334 @opindex --interactive
8335 @cindex prompts, forcing
8336 Prompt whether to overwrite each existing destination file, regardless
8338 If the response is not affirmative, the file is skipped.
8344 @opindex --no-clobber
8345 @cindex prompts, omitting
8346 Do not overwrite an existing file.
8348 This option is mutually exclusive with @option{-b} or @option{--backup} option.
8354 @cindex newer files, moving only
8355 Do not move a non-directory that has an existing destination with the
8356 same or newer modification time.
8357 If the move is across file system boundaries, the comparison is to the
8358 source time stamp truncated to the resolutions of the destination file
8359 system and of the system calls used to update time stamps; this avoids
8360 duplicate work if several @samp{mv -u} commands are executed with the
8361 same source and destination.
8367 Print the name of each file before moving it.
8369 @optStripTrailingSlashes
8375 @optNoTargetDirectory
8383 @section @command{rm}: Remove files or directories
8386 @cindex removing files or directories
8388 @command{rm} removes each given @var{file}. By default, it does not remove
8389 directories. Synopsis:
8392 rm [@var{option}]@dots{} [@var{file}]@dots{}
8395 @cindex prompting, and @command{rm}
8396 If the @option{-I} or @option{--interactive=once} option is given,
8397 and there are more than three files or the @option{-r}, @option{-R},
8398 or @option{--recursive} are given, then @command{rm} prompts the user
8399 for whether to proceed with the entire operation. If the response is
8400 not affirmative, the entire command is aborted.
8402 Otherwise, if a file is unwritable, standard input is a terminal, and
8403 the @option{-f} or @option{--force} option is not given, or the
8404 @option{-i} or @option{--interactive=always} option @emph{is} given,
8405 @command{rm} prompts the user for whether to remove the file.
8406 If the response is not affirmative, the file is skipped.
8408 Any attempt to remove a file whose last file name component is
8409 @file{.} or @file{..} is rejected without any prompting.
8411 @emph{Warning}: If you use @command{rm} to remove a file, it is usually
8412 possible to recover the contents of that file. If you want more assurance
8413 that the contents are truly unrecoverable, consider using @command{shred}.
8415 The program accepts the following options. Also see @ref{Common options}.
8423 Ignore nonexistent files and never prompt the user.
8424 Ignore any previous @option{--interactive} (@option{-i}) option.
8428 Prompt whether to remove each file.
8429 If the response is not affirmative, the file is skipped.
8430 Ignore any previous @option{--force} (@option{-f}) option.
8431 Equivalent to @option{--interactive=always}.
8435 Prompt once whether to proceed with the command, if more than three
8436 files are named or if a recursive removal is requested. Ignore any
8437 previous @option{--force} (@option{-f}) option. Equivalent to
8438 @option{--interactive=once}.
8440 @itemx --interactive [=@var{when}]
8441 @opindex --interactive
8442 Specify when to issue an interactive prompt. @var{when} may be
8446 @vindex never @r{interactive option}
8447 - Do not prompt at all.
8449 @vindex once @r{interactive option}
8450 - Prompt once if more than three files are named or if a recursive
8451 removal is requested. Equivalent to @option{-I}.
8453 @vindex always @r{interactive option}
8454 - Prompt for every file being removed. Equivalent to @option{-i}.
8456 @option{--interactive} with no @var{when} is equivalent to
8457 @option{--interactive=always}.
8459 @itemx --one-file-system
8460 @opindex --one-file-system
8461 @cindex one file system, restricting @command{rm} to
8462 When removing a hierarchy recursively, skip any directory that is on a
8463 file system different from that of the corresponding command line argument.
8465 This option is useful when removing a build ``chroot'' hierarchy,
8466 which normally contains no valuable data. However, it is not uncommon
8467 to bind-mount @file{/home} into such a hierarchy, to make it easier to
8468 use one's start-up file. The catch is that it's easy to forget to
8469 unmount @file{/home}. Then, when you use @command{rm -rf} to remove
8470 your normally throw-away chroot, that command will remove everything
8471 under @file{/home}, too.
8472 Use the @option{--one-file-system} option, and it will
8473 warn about and skip directories on other file systems.
8474 Of course, this will not save your @file{/home} if it and your
8475 chroot happen to be on the same file system.
8477 @itemx --preserve-root
8478 @opindex --preserve-root
8479 @cindex root directory, disallow recursive destruction
8480 Fail upon any attempt to remove the root directory, @file{/},
8481 when used with the @option{--recursive} option.
8482 This is the default behavior.
8483 @xref{Treating / specially}.
8485 @itemx --no-preserve-root
8486 @opindex --no-preserve-root
8487 @cindex root directory, allow recursive destruction
8488 Do not treat @file{/} specially when removing recursively.
8489 This option is not recommended unless you really want to
8490 remove all the files on your computer.
8491 @xref{Treating / specially}.
8498 @opindex --recursive
8499 @cindex directories, removing (recursively)
8500 Remove the listed directories and their contents recursively.
8506 Print the name of each file before removing it.
8510 @cindex files beginning with @samp{-}, removing
8511 @cindex @samp{-}, removing files beginning with
8512 One common question is how to remove files whose names begin with a
8513 @samp{-}. @sc{gnu} @command{rm}, like every program that uses the @code{getopt}
8514 function to parse its arguments, lets you use the @samp{--} option to
8515 indicate that all following arguments are non-options. To remove a file
8516 called @file{-f} in the current directory, you could type either:
8529 @opindex - @r{and Unix @command{rm}}
8530 The Unix @command{rm} program's use of a single @samp{-} for this purpose
8531 predates the development of the getopt standard syntax.
8536 @node shred invocation
8537 @section @command{shred}: Remove files more securely
8540 @cindex data, erasing
8541 @cindex erasing data
8543 @command{shred} overwrites devices or files, to help prevent even
8544 very expensive hardware from recovering the data.
8546 Ordinarily when you remove a file (@pxref{rm invocation}), the data is
8547 not actually destroyed. Only the index listing where the file is
8548 stored is destroyed, and the storage is made available for reuse.
8549 There are undelete utilities that will attempt to reconstruct the index
8550 and can bring the file back if the parts were not reused.
8552 On a busy system with a nearly-full drive, space can get reused in a few
8553 seconds. But there is no way to know for sure. If you have sensitive
8554 data, you may want to be sure that recovery is not possible by actually
8555 overwriting the file with non-sensitive data.
8557 However, even after doing that, it is possible to take the disk back
8558 to a laboratory and use a lot of sensitive (and expensive) equipment
8559 to look for the faint ``echoes'' of the original data underneath the
8560 overwritten data. If the data has only been overwritten once, it's not
8563 The best way to remove something irretrievably is to destroy the media
8564 it's on with acid, melt it down, or the like. For cheap removable media
8565 like floppy disks, this is the preferred method. However, hard drives
8566 are expensive and hard to melt, so the @command{shred} utility tries
8567 to achieve a similar effect non-destructively.
8569 This uses many overwrite passes, with the data patterns chosen to
8570 maximize the damage they do to the old data. While this will work on
8571 floppies, the patterns are designed for best effect on hard drives.
8572 For more details, see the source code and Peter Gutmann's paper
8573 @uref{http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html,
8574 @cite{Secure Deletion of Data from Magnetic and Solid-State Memory}},
8575 from the proceedings of the Sixth @acronym{USENIX} Security Symposium (San Jose,
8576 California, July 22--25, 1996).
8578 @strong{Please note} that @command{shred} relies on a very important assumption:
8579 that the file system overwrites data in place. This is the traditional
8580 way to do things, but many modern file system designs do not satisfy this
8581 assumption. Exceptions include:
8586 Log-structured or journaled file systems, such as those supplied with
8587 AIX and Solaris, and JFS, ReiserFS, XFS, Ext3 (in @code{data=journal} mode),
8588 BFS, NTFS, etc.@: when they are configured to journal @emph{data}.
8591 File systems that write redundant data and carry on even if some writes
8592 fail, such as RAID-based file systems.
8595 File systems that make snapshots, such as Network Appliance's NFS server.
8598 File systems that cache in temporary locations, such as NFS version 3
8602 Compressed file systems.
8605 In the particular case of ext3 file systems, the above disclaimer applies (and
8606 @command{shred} is thus of limited effectiveness) only in @code{data=journal}
8607 mode, which journals file data in addition to just metadata. In both
8608 the @code{data=ordered} (default) and @code{data=writeback} modes,
8609 @command{shred} works as usual. Ext3 journaling modes can be changed
8610 by adding the @code{data=something} option to the mount options for a
8611 particular file system in the @file{/etc/fstab} file, as documented in
8612 the mount man page (man mount).
8614 If you are not sure how your file system operates, then you should assume
8615 that it does not overwrite data in place, which means that shred cannot
8616 reliably operate on regular files in your file system.
8618 Generally speaking, it is more reliable to shred a device than a file,
8619 since this bypasses the problem of file system design mentioned above.
8620 However, even shredding devices is not always completely reliable. For
8621 example, most disks map out bad sectors invisibly to the application; if
8622 the bad sectors contain sensitive data, @command{shred} won't be able to
8625 @command{shred} makes no attempt to detect or report this problem, just as
8626 it makes no attempt to do anything about backups. However, since it is
8627 more reliable to shred devices than files, @command{shred} by default does
8628 not truncate or remove the output file. This default is more suitable
8629 for devices, which typically cannot be truncated and should not be
8632 Finally, consider the risk of backups and mirrors.
8633 File system backups and remote mirrors may contain copies of the
8634 file that cannot be removed, and that will allow a shredded file
8635 to be recovered later. So if you keep any data you may later want
8636 to destroy using @command{shred}, be sure that it is not backed up or mirrored.
8639 shred [@var{option}]@dots{} @var{file}[@dots{}]
8642 The program accepts the following options. Also see @ref{Common options}.
8650 @cindex force deletion
8651 Override file permissions if necessary to allow overwriting.
8654 @itemx -n @var{number}
8655 @itemx --iterations=@var{number}
8656 @opindex -n @var{number}
8657 @opindex --iterations=@var{number}
8658 @cindex iterations, selecting the number of
8659 By default, @command{shred} uses @value{SHRED_DEFAULT_PASSES} passes of
8660 overwrite. You can reduce this to save time, or increase it if you think it's
8661 appropriate. After 25 passes all of the internal overwrite patterns will have
8662 been used at least once.
8664 @item --random-source=@var{file}
8665 @opindex --random-source
8666 @cindex random source for shredding
8667 Use @var{file} as a source of random data used to overwrite and to
8668 choose pass ordering. @xref{Random sources}.
8670 @item -s @var{bytes}
8671 @itemx --size=@var{bytes}
8672 @opindex -s @var{bytes}
8673 @opindex --size=@var{bytes}
8674 @cindex size of file to shred
8675 Shred the first @var{bytes} bytes of the file. The default is to shred
8676 the whole file. @var{bytes} can be followed by a size specification like
8677 @samp{K}, @samp{M}, or @samp{G} to specify a multiple. @xref{Block size}.
8683 @cindex removing files after shredding
8684 After shredding a file, truncate it (if possible) and then remove it.
8685 If a file has multiple links, only the named links will be removed.
8691 Display to standard error all status updates as sterilization proceeds.
8697 By default, @command{shred} rounds the size of a regular file up to the next
8698 multiple of the file system block size to fully erase the last block of the file.
8699 Use @option{--exact} to suppress that behavior.
8700 Thus, by default if you shred a 10-byte regular file on a system with 512-byte
8701 blocks, the resulting file will be 512 bytes long. With this option,
8702 shred does not increase the apparent size of the file.
8708 Normally, the last pass that @command{shred} writes is made up of
8709 random data. If this would be conspicuous on your hard drive (for
8710 example, because it looks like encrypted data), or you just think
8711 it's tidier, the @option{--zero} option adds an additional overwrite pass with
8712 all zero bits. This is in addition to the number of passes specified
8713 by the @option{--iterations} option.
8717 You might use the following command to erase all trace of the
8718 file system you'd created on the floppy disk in your first drive.
8719 That command takes about 20 minutes to erase a ``1.44MB'' (actually
8723 shred --verbose /dev/fd0
8726 Similarly, to erase all data on a selected partition of
8727 your hard disk, you could give a command like this:
8730 shred --verbose /dev/sda5
8733 A @var{file} of @samp{-} denotes standard output.
8734 The intended use of this is to shred a removed temporary file.
8741 echo "Hello, world" >&3
8746 However, the command @samp{shred - >file} does not shred the contents
8747 of @var{file}, since the shell truncates @var{file} before invoking
8748 @command{shred}. Use the command @samp{shred file} or (if using a
8749 Bourne-compatible shell) the command @samp{shred - 1<>file} instead.
8754 @node Special file types
8755 @chapter Special file types
8757 @cindex special file types
8758 @cindex file types, special
8760 This chapter describes commands which create special types of files (and
8761 @command{rmdir}, which removes directories, one special file type).
8763 @cindex special file types
8765 Although Unix-like operating systems have markedly fewer special file
8766 types than others, not @emph{everything} can be treated only as the
8767 undifferentiated byte stream of @dfn{normal files}. For example, when a
8768 file is created or removed, the system must record this information,
8769 which it does in a @dfn{directory}---a special type of file. Although
8770 you can read directories as normal files, if you're curious, in order
8771 for the system to do its job it must impose a structure, a certain
8772 order, on the bytes of the file. Thus it is a ``special'' type of file.
8774 Besides directories, other special file types include named pipes
8775 (FIFOs), symbolic links, sockets, and so-called @dfn{special files}.
8778 * link invocation:: Make a hard link via the link syscall
8779 * ln invocation:: Make links between files.
8780 * mkdir invocation:: Make directories.
8781 * mkfifo invocation:: Make FIFOs (named pipes).
8782 * mknod invocation:: Make block or character special files.
8783 * readlink invocation:: Print value of a symlink or canonical file name.
8784 * rmdir invocation:: Remove empty directories.
8785 * unlink invocation:: Remove files via the unlink syscall
8789 @node link invocation
8790 @section @command{link}: Make a hard link via the link syscall
8793 @cindex links, creating
8794 @cindex hard links, creating
8795 @cindex creating links (hard only)
8797 @command{link} creates a single hard link at a time.
8798 It is a minimalist interface to the system-provided
8799 @code{link} function. @xref{Hard Links, , , libc,
8800 The GNU C Library Reference Manual}.
8801 It avoids the bells and whistles of the more commonly-used
8802 @command{ln} command (@pxref{ln invocation}).
8806 link @var{filename} @var{linkname}
8809 @var{filename} must specify an existing file, and @var{linkname}
8810 must specify a nonexistent entry in an existing directory.
8811 @command{link} simply calls @code{link (@var{filename}, @var{linkname})}
8814 On a @acronym{GNU} system, this command acts like @samp{ln --directory
8815 --no-target-directory @var{filename} @var{linkname}}. However, the
8816 @option{--directory} and @option{--no-target-directory} options are
8817 not specified by @acronym{POSIX}, and the @command{link} command is
8818 more portable in practice.
8820 If @var{filename} is a symbolic link, it is unspecified whether
8821 @var{linkname} will be a hard link to the symbolic link or to the
8822 target of the symbolic link. Use @command{ln -P} or @command{ln -L}
8823 to specify which behavior is desired.
8829 @section @command{ln}: Make links between files
8832 @cindex links, creating
8833 @cindex hard links, creating
8834 @cindex symbolic (soft) links, creating
8835 @cindex creating links (hard or soft)
8837 @cindex file systems and hard links
8838 @command{ln} makes links between files. By default, it makes hard links;
8839 with the @option{-s} option, it makes symbolic (or @dfn{soft}) links.
8843 ln [@var{option}]@dots{} [-T] @var{target} @var{linkname}
8844 ln [@var{option}]@dots{} @var{target}
8845 ln [@var{option}]@dots{} @var{target}@dots{} @var{directory}
8846 ln [@var{option}]@dots{} -t @var{directory} @var{target}@dots{}
8852 If two file names are given, @command{ln} creates a link to the first
8853 file from the second.
8856 If one @var{target} is given, @command{ln} creates a link to that file
8857 in the current directory.
8860 If the @option{--target-directory} (@option{-t}) option is given, or
8861 failing that if the last file is a directory and the
8862 @option{--no-target-directory} (@option{-T}) option is not given,
8863 @command{ln} creates a link to each @var{target} file in the specified
8864 directory, using the @var{target}s' names.
8868 Normally @command{ln} does not remove existing files. Use the
8869 @option{--force} (@option{-f}) option to remove them unconditionally,
8870 the @option{--interactive} (@option{-i}) option to remove them
8871 conditionally, and the @option{--backup} (@option{-b}) option to
8874 @cindex hard link, defined
8875 @cindex inode, and hard links
8876 A @dfn{hard link} is another name for an existing file; the link and the
8877 original are indistinguishable. Technically speaking, they share the
8878 same inode, and the inode contains all the information about a
8879 file---indeed, it is not incorrect to say that the inode @emph{is} the
8880 file. Most systems prohibit making a hard link to
8881 a directory; on those where it is allowed, only the super-user can do
8882 so (and with caution, since creating a cycle will cause problems to many
8883 other utilities). Hard links cannot cross file system boundaries. (These
8884 restrictions are not mandated by @acronym{POSIX}, however.)
8886 @cindex dereferencing symbolic links
8887 @cindex symbolic link, defined
8888 @dfn{Symbolic links} (@dfn{symlinks} for short), on the other hand, are
8889 a special file type (which not all kernels support: System V release 3
8890 (and older) systems lack symlinks) in which the link file actually
8891 refers to a different file, by name. When most operations (opening,
8892 reading, writing, and so on) are passed the symbolic link file, the
8893 kernel automatically @dfn{dereferences} the link and operates on the
8894 target of the link. But some operations (e.g., removing) work on the
8895 link file itself, rather than on its target. The owner and group of a
8896 symlink are not significant to file access performed through
8897 the link, but do have implications on deleting a symbolic link from a
8898 directory with the restricted deletion bit set. On the GNU system,
8899 the mode of a symlink has no significance and cannot be changed, but
8900 on some BSD systems, the mode can be changed and will affect whether
8901 the symlink will be traversed in file name resolution. @xref{Symbolic Links,,,
8902 libc, The GNU C Library Reference Manual}.
8904 Symbolic links can contain arbitrary strings; a @dfn{dangling symlink}
8905 occurs when the string in the symlink does not resolve to a file.
8906 There are no restrictions against creating dangling symbolic links.
8907 There are trade-offs to using absolute or relative symlinks. An
8908 absolute symlink always points to the same file, even if the directory
8909 containing the link is moved. However, if the symlink is visible from
8910 more than one machine (such as on a networked file system), the file
8911 pointed to might not always be the same. A relative symbolic link is
8912 resolved in relation to the directory that contains the link, and is
8913 often useful in referring to files on the same device without regards
8914 to what name that device is mounted on when accessed via networked
8917 When creating a relative symlink in a different location than the
8918 current directory, the resolution of the symlink will be different
8919 than the resolution of the same string from the current directory.
8920 Therefore, many users prefer to first change directories to the
8921 location where the relative symlink will be created, so that
8922 tab-completion or other file resolution will find the same target as
8923 what will be placed in the symlink.
8925 The program accepts the following options. Also see @ref{Common options}.
8936 @opindex --directory
8937 @cindex hard links to directories
8938 Allow users with appropriate privileges to attempt to make hard links
8940 However, note that this will probably fail due to
8941 system restrictions, even for the super-user.
8947 Remove existing destination files.
8950 @itemx --interactive
8952 @opindex --interactive
8953 @cindex prompting, and @command{ln}
8954 Prompt whether to remove existing destination files.
8960 If @option{-s} is not in effect, and the source file is a symbolic
8961 link, create the hard link to the file referred to by the symbolic
8962 link, rather than the symbolic link itself.
8965 @itemx --no-dereference
8967 @opindex --no-dereference
8968 Do not treat the last operand specially when it is a symbolic link to
8969 a directory. Instead, treat it as if it were a normal file.
8971 When the destination is an actual directory (not a symlink to one),
8972 there is no ambiguity. The link is created in that directory.
8973 But when the specified destination is a symlink to a directory,
8974 there are two ways to treat the user's request. @command{ln} can
8975 treat the destination just as it would a normal directory and create
8976 the link in it. On the other hand, the destination can be viewed as a
8977 non-directory---as the symlink itself. In that case, @command{ln}
8978 must delete or backup that symlink before creating the new link.
8979 The default is to treat a destination that is a symlink to a directory
8980 just like a directory.
8982 This option is weaker than the @option{--no-target-directory}
8983 (@option{-T}) option, so it has no effect if both options are given.
8989 If @option{-s} is not in effect, and the source file is a symbolic
8990 link, create the hard link to the symbolic link itself. On platforms
8991 where this is not supported by the kernel, this option creates a
8992 symbolic link with identical contents; since symbolic link contents
8993 cannot be edited, any file name resolution performed through either
8994 link will be the same as if a hard link had been created.
9000 Make symbolic links instead of hard links. This option merely produces
9001 an error message on systems that do not support symbolic links.
9007 @optNoTargetDirectory
9013 Print the name of each file after linking it successfully.
9017 @cindex hard links to symbolic links
9018 @cindex symbolic links and @command{ln}
9019 If @option{-L} and @option{-P} are both given, the last one takes
9020 precedence. If @option{-s} is also given, @option{-L} and @option{-P}
9021 are silently ignored. If neither option is given, then this
9022 implementation defaults to @option{-P} if the system @code{link} supports
9023 hard links to symbolic links (such as the GNU system), and @option{-L}
9024 if @code{link} follows symbolic links (such as on BSD).
9033 # Create link ../a pointing to a in that directory.
9034 # Not really useful because it points to itself.
9039 # Change to the target before creating symlinks to avoid being confused.
9045 # Hard coded file names don't move well.
9046 ln -s $(pwd)/a /some/dir/
9050 # Relative file names survive directory moves and also
9051 # work across networked file systems.
9052 ln -s afile anotherfile
9053 ln -s ../adir/afile yetanotherfile
9057 @node mkdir invocation
9058 @section @command{mkdir}: Make directories
9061 @cindex directories, creating
9062 @cindex creating directories
9064 @command{mkdir} creates directories with the specified names. Synopsis:
9067 mkdir [@var{option}]@dots{} @var{name}@dots{}
9070 @command{mkdir} creates each directory @var{name} in the order given.
9071 It reports an error if @var{name} already exists, unless the
9072 @option{-p} option is given and @var{name} is a directory.
9074 The program accepts the following options. Also see @ref{Common options}.
9079 @itemx --mode=@var{mode}
9082 @cindex modes of created directories, setting
9083 Set the file permission bits of created directories to @var{mode},
9084 which uses the same syntax as
9085 in @command{chmod} and uses @samp{a=rwx} (read, write and execute allowed for
9086 everyone) for the point of the departure. @xref{File permissions}.
9088 Normally the directory has the desired file mode bits at the moment it
9089 is created. As a @acronym{GNU} extension, @var{mode} may also mention
9090 special mode bits, but in this case there may be a temporary window
9091 during which the directory exists but its special mode bits are
9092 incorrect. @xref{Directory Setuid and Setgid}, for how the
9093 set-user-ID and set-group-ID bits of directories are inherited unless
9094 overridden in this way.
9100 @cindex parent directories, creating
9101 Make any missing parent directories for each argument, setting their
9102 file permission bits to the umask modified by @samp{u+wx}. Ignore
9103 existing parent directories, and do not change their file permission
9106 To set the file permission bits of any newly-created parent
9107 directories to a value that includes @samp{u+wx}, you can set the
9108 umask before invoking @command{mkdir}. For example, if the shell
9109 command @samp{(umask u=rwx,go=rx; mkdir -p P/Q)} creates the parent
9110 @file{P} it sets the parent's permission bits to @samp{u=rwx,go=rx}.
9111 To set a parent's special mode bits as well, you can invoke
9112 @command{chmod} after @command{mkdir}. @xref{Directory Setuid and
9113 Setgid}, for how the set-user-ID and set-group-ID bits of
9114 newly-created parent directories are inherited.
9120 Print a message for each created directory. This is most useful with
9123 @item -Z @var{context}
9124 @itemx --context=@var{context}
9128 @cindex security context
9129 Set the default SELinux security context to be used for created directories.
9136 @node mkfifo invocation
9137 @section @command{mkfifo}: Make FIFOs (named pipes)
9140 @cindex FIFOs, creating
9141 @cindex named pipes, creating
9142 @cindex creating FIFOs (named pipes)
9144 @command{mkfifo} creates FIFOs (also called @dfn{named pipes}) with the
9145 specified names. Synopsis:
9148 mkfifo [@var{option}] @var{name}@dots{}
9151 A @dfn{FIFO} is a special file type that permits independent processes
9152 to communicate. One process opens the FIFO file for writing, and
9153 another for reading, after which data can flow as with the usual
9154 anonymous pipe in shells or elsewhere.
9156 The program accepts the following option. Also see @ref{Common options}.
9161 @itemx --mode=@var{mode}
9164 @cindex modes of created FIFOs, setting
9165 Set the mode of created FIFOs to @var{mode}, which is symbolic as in
9166 @command{chmod} and uses @samp{a=rw} (read and write allowed for everyone)
9167 for the point of departure. @var{mode} should specify only file
9168 permission bits. @xref{File permissions}.
9170 @item -Z @var{context}
9171 @itemx --context=@var{context}
9175 @cindex security context
9176 Set the default SELinux security context to be used for created FIFOs.
9183 @node mknod invocation
9184 @section @command{mknod}: Make block or character special files
9187 @cindex block special files, creating
9188 @cindex character special files, creating
9190 @command{mknod} creates a FIFO, character special file, or block special
9191 file with the specified name. Synopsis:
9194 mknod [@var{option}]@dots{} @var{name} @var{type} [@var{major} @var{minor}]
9197 @cindex special files
9198 @cindex block special files
9199 @cindex character special files
9200 Unlike the phrase ``special file type'' above, the term @dfn{special
9201 file} has a technical meaning on Unix: something that can generate or
9202 receive data. Usually this corresponds to a physical piece of hardware,
9203 e.g., a printer or a disk. (These files are typically created at
9204 system-configuration time.) The @command{mknod} command is what creates
9205 files of this type. Such devices can be read either a character at a
9206 time or a ``block'' (many characters) at a time, hence we say there are
9207 @dfn{block special} files and @dfn{character special} files.
9209 @c mknod is a shell built-in at least with OpenBSD's /bin/sh
9210 @mayConflictWithShellBuiltIn{mknod}
9212 The arguments after @var{name} specify the type of file to make:
9217 @opindex p @r{for FIFO file}
9221 @opindex b @r{for block special file}
9222 for a block special file
9225 @c Don't document the `u' option -- it's just a synonym for `c'.
9226 @c Do *any* versions of mknod still use it?
9228 @opindex c @r{for character special file}
9229 @c @opindex u @r{for character special file}
9230 for a character special file
9234 When making a block or character special file, the major and minor
9235 device numbers must be given after the file type.
9236 If a major or minor device number begins with @samp{0x} or @samp{0X},
9237 it is interpreted as hexadecimal; otherwise, if it begins with @samp{0},
9238 as octal; otherwise, as decimal.
9240 The program accepts the following option. Also see @ref{Common options}.
9245 @itemx --mode=@var{mode}
9248 Set the mode of created files to @var{mode}, which is symbolic as in
9249 @command{chmod} and uses @samp{a=rw} as the point of departure.
9250 @var{mode} should specify only file permission bits.
9251 @xref{File permissions}.
9253 @item -Z @var{context}
9254 @itemx --context=@var{context}
9258 @cindex security context
9259 Set the default SELinux security context to be used for created files.
9266 @node readlink invocation
9267 @section @command{readlink}: Print value of a symlink or canonical file name
9270 @cindex displaying value of a symbolic link
9271 @cindex canonical file name
9272 @cindex canonicalize a file name
9276 @command{readlink} may work in one of two supported modes:
9282 @command{readlink} outputs the value of the given symbolic link.
9283 If @command{readlink} is invoked with an argument other than the name
9284 of a symbolic link, it produces no output and exits with a nonzero exit code.
9286 @item Canonicalize mode
9288 @command{readlink} outputs the absolute name of the given file which contains
9289 no @file{.}, @file{..} components nor any repeated separators
9290 (@file{/}) or symbolic links.
9295 readlink [@var{option}] @var{file}
9298 By default, @command{readlink} operates in readlink mode.
9300 The program accepts the following options. Also see @ref{Common options}.
9305 @itemx --canonicalize
9307 @opindex --canonicalize
9308 Activate canonicalize mode.
9309 If any component of the file name except the last one is missing or unavailable,
9310 @command{readlink} produces no output and exits with a nonzero exit
9311 code. A trailing slash is ignored.
9314 @itemx --canonicalize-existing
9316 @opindex --canonicalize-existing
9317 Activate canonicalize mode.
9318 If any component is missing or unavailable, @command{readlink} produces
9319 no output and exits with a nonzero exit code. A trailing slash
9320 requires that the name resolve to a directory.
9323 @itemx --canonicalize-missing
9325 @opindex --canonicalize-missing
9326 Activate canonicalize mode.
9327 If any component is missing or unavailable, @command{readlink} treats it
9333 @opindex --no-newline
9334 Do not output the trailing newline.
9344 Suppress most error messages.
9350 Report error messages.
9354 The @command{readlink} utility first appeared in OpenBSD 2.1.
9356 There is a @command{realpath} command on some systems
9357 which operates like @command{readlink} in canonicalize mode.
9362 @node rmdir invocation
9363 @section @command{rmdir}: Remove empty directories
9366 @cindex removing empty directories
9367 @cindex directories, removing empty
9369 @command{rmdir} removes empty directories. Synopsis:
9372 rmdir [@var{option}]@dots{} @var{directory}@dots{}
9375 If any @var{directory} argument does not refer to an existing empty
9376 directory, it is an error.
9378 The program accepts the following options. Also see @ref{Common options}.
9382 @item --ignore-fail-on-non-empty
9383 @opindex --ignore-fail-on-non-empty
9384 @cindex directory deletion, ignoring failures
9385 Ignore each failure to remove a directory that is solely because
9386 the directory is non-empty.
9392 @cindex parent directories, removing
9393 Remove @var{directory}, then try to remove each component of @var{directory}.
9394 So, for example, @samp{rmdir -p a/b/c} is similar to @samp{rmdir a/b/c a/b a}.
9395 As such, it fails if any of those directories turns out not to be empty.
9396 Use the @option{--ignore-fail-on-non-empty} option to make it so such
9397 a failure does not evoke a diagnostic and does not cause @command{rmdir} to
9398 exit unsuccessfully.
9404 @cindex directory deletion, reporting
9405 Give a diagnostic for each successful removal.
9406 @var{directory} is removed.
9410 @xref{rm invocation}, for how to remove non-empty directories (recursively).
9415 @node unlink invocation
9416 @section @command{unlink}: Remove files via the unlink syscall
9419 @cindex removing files or directories (via the unlink syscall)
9421 @command{unlink} deletes a single specified file name.
9422 It is a minimalist interface to the system-provided
9423 @code{unlink} function. @xref{Deleting Files, , , libc,
9424 The GNU C Library Reference Manual}. Synopsis:
9425 It avoids the bells and whistles of the more commonly-used
9426 @command{rm} command (@pxref{rm invocation}).
9429 unlink @var{filename}
9432 On some systems @code{unlink} can be used to delete the name of a
9433 directory. On others, it can be used that way only by a privileged user.
9434 In the GNU system @code{unlink} can never delete the name of a directory.
9436 The @command{unlink} command honors the @option{--help} and
9437 @option{--version} options. To remove a file whose name begins with
9438 @samp{-}, prefix the name with @samp{./}, e.g., @samp{unlink ./--help}.
9443 @node Changing file attributes
9444 @chapter Changing file attributes
9446 @cindex changing file attributes
9447 @cindex file attributes, changing
9448 @cindex attributes, file
9450 A file is not merely its contents, a name, and a file type
9451 (@pxref{Special file types}). A file also has an owner (a user ID), a
9452 group (a group ID), permissions (what the owner can do with the file,
9453 what people in the group can do, and what everyone else can do), various
9454 timestamps, and other information. Collectively, we call these a file's
9457 These commands change file attributes.
9460 * chgrp invocation:: Change file groups.
9461 * chmod invocation:: Change access permissions.
9462 * chown invocation:: Change file owners and groups.
9463 * touch invocation:: Change file timestamps.
9467 @node chown invocation
9468 @section @command{chown}: Change file owner and group
9471 @cindex file ownership, changing
9472 @cindex group ownership, changing
9473 @cindex changing file ownership
9474 @cindex changing group ownership
9476 @command{chown} changes the user and/or group ownership of each given @var{file}
9477 to @var{new-owner} or to the user and group of an existing reference file.
9481 chown [@var{option}]@dots{} @{@var{new-owner} | --reference=@var{ref_file}@} @var{file}@dots{}
9484 If used, @var{new-owner} specifies the new owner and/or group as follows
9485 (with no embedded white space):
9488 [@var{owner}] [ : [@var{group}] ]
9495 If only an @var{owner} (a user name or numeric user ID) is given, that
9496 user is made the owner of each given file, and the files' group is not
9499 @item owner@samp{:}group
9500 If the @var{owner} is followed by a colon and a @var{group} (a
9501 group name or numeric group ID), with no spaces between them, the group
9502 ownership of the files is changed as well (to @var{group}).
9505 If a colon but no group name follows @var{owner}, that user is
9506 made the owner of the files and the group of the files is changed to
9507 @var{owner}'s login group.
9510 If the colon and following @var{group} are given, but the owner
9511 is omitted, only the group of the files is changed; in this case,
9512 @command{chown} performs the same function as @command{chgrp}.
9515 If only a colon is given, or if @var{new-owner} is empty, neither the
9516 owner nor the group is changed.
9520 If @var{owner} or @var{group} is intended to represent a numeric user
9521 or group ID, then you may specify it with a leading @samp{+}.
9522 @xref{Disambiguating names and IDs}.
9524 Some older scripts may still use @samp{.} in place of the @samp{:} separator.
9525 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) does not
9526 require support for that, but for backward compatibility @acronym{GNU}
9527 @command{chown} supports @samp{.} so long as no ambiguity results.
9528 New scripts should avoid the use of @samp{.} because it is not
9529 portable, and because it has undesirable results if the entire
9530 @var{owner@samp{.}group} happens to identify a user whose name
9533 The @command{chown} command sometimes clears the set-user-ID or
9534 set-group-ID permission bits. This behavior depends on the policy and
9535 functionality of the underlying @code{chown} system call, which may
9536 make system-dependent file mode modifications outside the control of
9537 the @command{chown} command. For example, the @command{chown} command
9538 might not affect those bits when invoked by a user with appropriate
9539 privileges, or when the
9540 bits signify some function other than executable permission (e.g.,
9542 When in doubt, check the underlying system behavior.
9544 The program accepts the following options. Also see @ref{Common options}.
9552 @cindex changed owners, verbosely describing
9553 Verbosely describe the action for each @var{file} whose ownership
9562 @cindex error messages, omitting
9563 Do not print error messages about files whose ownership cannot be
9566 @itemx @w{@kbd{--from}=@var{old-owner}}
9568 @cindex symbolic links, changing owner
9569 Change a @var{file}'s ownership only if it has current attributes specified
9570 by @var{old-owner}. @var{old-owner} has the same form as @var{new-owner}
9572 This option is useful primarily from a security standpoint in that
9573 it narrows considerably the window of potential abuse.
9574 For example, to reflect a user ID numbering change for one user's files
9575 without an option like this, @code{root} might run
9578 find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER
9581 But that is dangerous because the interval between when the @command{find}
9582 tests the existing file's owner and when the @command{chown} is actually run
9584 One way to narrow the gap would be to invoke chown for each file
9588 find / -owner OLDUSER -exec chown -h NEWUSER @{@} \;
9591 But that is very slow if there are many affected files.
9592 With this option, it is safer (the gap is narrower still)
9593 though still not perfect:
9596 chown -h -R --from=OLDUSER NEWUSER /
9600 @opindex --dereference
9601 @cindex symbolic links, changing owner
9603 Do not act on symbolic links themselves but rather on what they point to.
9604 This is the default.
9607 @itemx --no-dereference
9609 @opindex --no-dereference
9610 @cindex symbolic links, changing owner
9612 Act on symbolic links themselves instead of what they point to.
9613 This mode relies on the @code{lchown} system call.
9614 On systems that do not provide the @code{lchown} system call,
9615 @command{chown} fails when a file specified on the command line
9617 By default, no diagnostic is issued for symbolic links encountered
9618 during a recursive traversal, but see @option{--verbose}.
9620 @itemx --preserve-root
9621 @opindex --preserve-root
9622 @cindex root directory, disallow recursive modification
9623 Fail upon any attempt to recursively change the root directory, @file{/}.
9624 Without @option{--recursive}, this option has no effect.
9625 @xref{Treating / specially}.
9627 @itemx --no-preserve-root
9628 @opindex --no-preserve-root
9629 @cindex root directory, allow recursive modification
9630 Cancel the effect of any preceding @option{--preserve-root} option.
9631 @xref{Treating / specially}.
9633 @item --reference=@var{ref_file}
9634 @opindex --reference
9635 Change the user and group of each @var{file} to be the same as those of
9636 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
9637 user and group of the symbolic link, but rather those of the file it
9644 Output a diagnostic for every file processed.
9645 If a symbolic link is encountered during a recursive traversal
9646 on a system without the @code{lchown} system call, and @option{--no-dereference}
9647 is in effect, then issue a diagnostic saying neither the symbolic link nor
9648 its referent is being changed.
9653 @opindex --recursive
9654 @cindex recursively changing file ownership
9655 Recursively change ownership of directories and their contents.
9658 @xref{Traversing symlinks}.
9661 @xref{Traversing symlinks}.
9664 @xref{Traversing symlinks}.
9673 # Change the owner of /u to "root".
9676 # Likewise, but also change its group to "staff".
9679 # Change the owner of /u and subfiles to "root".
9684 @node chgrp invocation
9685 @section @command{chgrp}: Change group ownership
9688 @cindex group ownership, changing
9689 @cindex changing group ownership
9691 @command{chgrp} changes the group ownership of each given @var{file}
9692 to @var{group} (which can be either a group name or a numeric group ID)
9693 or to the group of an existing reference file. Synopsis:
9696 chgrp [@var{option}]@dots{} @{@var{group} | --reference=@var{ref_file}@} @var{file}@dots{}
9699 If @var{group} is intended to represent a
9700 numeric group ID, then you may specify it with a leading @samp{+}.
9701 @xref{Disambiguating names and IDs}.
9703 The program accepts the following options. Also see @ref{Common options}.
9711 @cindex changed files, verbosely describing
9712 Verbosely describe the action for each @var{file} whose group actually
9721 @cindex error messages, omitting
9722 Do not print error messages about files whose group cannot be
9726 @opindex --dereference
9727 @cindex symbolic links, changing owner
9729 Do not act on symbolic links themselves but rather on what they point to.
9730 This is the default.
9733 @itemx --no-dereference
9735 @opindex --no-dereference
9736 @cindex symbolic links, changing group
9738 Act on symbolic links themselves instead of what they point to.
9739 This mode relies on the @code{lchown} system call.
9740 On systems that do not provide the @code{lchown} system call,
9741 @command{chgrp} fails when a file specified on the command line
9743 By default, no diagnostic is issued for symbolic links encountered
9744 during a recursive traversal, but see @option{--verbose}.
9746 @itemx --preserve-root
9747 @opindex --preserve-root
9748 @cindex root directory, disallow recursive modification
9749 Fail upon any attempt to recursively change the root directory, @file{/}.
9750 Without @option{--recursive}, this option has no effect.
9751 @xref{Treating / specially}.
9753 @itemx --no-preserve-root
9754 @opindex --no-preserve-root
9755 @cindex root directory, allow recursive modification
9756 Cancel the effect of any preceding @option{--preserve-root} option.
9757 @xref{Treating / specially}.
9759 @item --reference=@var{ref_file}
9760 @opindex --reference
9761 Change the group of each @var{file} to be the same as that of
9762 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
9763 group of the symbolic link, but rather that of the file it refers to.
9769 Output a diagnostic for every file processed.
9770 If a symbolic link is encountered during a recursive traversal
9771 on a system without the @code{lchown} system call, and @option{--no-dereference}
9772 is in effect, then issue a diagnostic saying neither the symbolic link nor
9773 its referent is being changed.
9778 @opindex --recursive
9779 @cindex recursively changing group ownership
9780 Recursively change the group ownership of directories and their contents.
9783 @xref{Traversing symlinks}.
9786 @xref{Traversing symlinks}.
9789 @xref{Traversing symlinks}.
9798 # Change the group of /u to "staff".
9801 # Change the group of /u and subfiles to "staff".
9806 @node chmod invocation
9807 @section @command{chmod}: Change access permissions
9810 @cindex changing access permissions
9811 @cindex access permissions, changing
9812 @cindex permissions, changing access
9814 @command{chmod} changes the access permissions of the named files. Synopsis:
9817 chmod [@var{option}]@dots{} @{@var{mode} | --reference=@var{ref_file}@} @var{file}@dots{}
9820 @cindex symbolic links, permissions of
9821 @command{chmod} never changes the permissions of symbolic links, since
9822 the @command{chmod} system call cannot change their permissions.
9823 This is not a problem since the permissions of symbolic links are
9824 never used. However, for each symbolic link listed on the command
9825 line, @command{chmod} changes the permissions of the pointed-to file.
9826 In contrast, @command{chmod} ignores symbolic links encountered during
9827 recursive directory traversals.
9829 A successful use of @command{chmod} clears the set-group-ID bit of a
9830 regular file if the file's group ID does not match the user's
9831 effective group ID or one of the user's supplementary group IDs,
9832 unless the user has appropriate privileges. Additional restrictions
9833 may cause the set-user-ID and set-group-ID bits of @var{mode} or
9834 @var{ref_file} to be ignored. This behavior depends on the policy and
9835 functionality of the underlying @code{chmod} system call. When in
9836 doubt, check the underlying system behavior.
9838 If used, @var{mode} specifies the new file mode bits.
9839 For details, see the section on @ref{File permissions}.
9840 If you really want @var{mode} to have a leading @samp{-}, you should
9841 use @option{--} first, e.g., @samp{chmod -- -w file}. Typically,
9842 though, @samp{chmod a-w file} is preferable, and @command{chmod -w
9843 file} (without the @option{--}) complains if it behaves differently
9844 from what @samp{chmod a-w file} would do.
9846 The program accepts the following options. Also see @ref{Common options}.
9854 Verbosely describe the action for each @var{file} whose permissions
9863 @cindex error messages, omitting
9864 Do not print error messages about files whose permissions cannot be
9867 @itemx --preserve-root
9868 @opindex --preserve-root
9869 @cindex root directory, disallow recursive modification
9870 Fail upon any attempt to recursively change the root directory, @file{/}.
9871 Without @option{--recursive}, this option has no effect.
9872 @xref{Treating / specially}.
9874 @itemx --no-preserve-root
9875 @opindex --no-preserve-root
9876 @cindex root directory, allow recursive modification
9877 Cancel the effect of any preceding @option{--preserve-root} option.
9878 @xref{Treating / specially}.
9884 Verbosely describe the action or non-action taken for every @var{file}.
9886 @item --reference=@var{ref_file}
9887 @opindex --reference
9888 Change the mode of each @var{file} to be the same as that of @var{ref_file}.
9889 @xref{File permissions}.
9890 If @var{ref_file} is a symbolic link, do not use the mode
9891 of the symbolic link, but rather that of the file it refers to.
9896 @opindex --recursive
9897 @cindex recursively changing access permissions
9898 Recursively change permissions of directories and their contents.
9905 @node touch invocation
9906 @section @command{touch}: Change file timestamps
9909 @cindex changing file timestamps
9910 @cindex file timestamps, changing
9911 @cindex timestamps, changing file
9913 @command{touch} changes the access and/or modification times of the
9914 specified files. Synopsis:
9917 touch [@var{option}]@dots{} @var{file}@dots{}
9920 @cindex empty files, creating
9921 Any @var{file} argument that does not exist is created empty, unless
9922 option @option{--no-create} (@option{-c}) or @option{--no-dereference}
9923 (@option{-h}) was in effect.
9925 A @var{file} argument string of @samp{-} is handled specially and
9926 causes @command{touch} to change the times of the file associated with
9929 @cindex permissions, for changing file timestamps
9930 If changing both the access and modification times to the current
9931 time, @command{touch} can change the timestamps for files that the user
9932 running it does not own but has write permission for. Otherwise, the
9933 user must own the files.
9935 Although @command{touch} provides options for changing two of the times---the
9936 times of last access and modification---of a file, there is actually
9937 a standard third one as well: the inode change time. This is often
9938 referred to as a file's @code{ctime}.
9939 The inode change time represents the time when the file's meta-information
9940 last changed. One common example of this is when the permissions of a
9941 file change. Changing the permissions doesn't access the file, so
9942 the atime doesn't change, nor does it modify the file, so the mtime
9943 doesn't change. Yet, something about the file itself has changed,
9944 and this must be noted somewhere. This is the job of the ctime field.
9945 This is necessary, so that, for example, a backup program can make a
9946 fresh copy of the file, including the new permissions value.
9947 Another operation that modifies a file's ctime without affecting
9948 the others is renaming. In any case, it is not possible, in normal
9949 operations, for a user to change the ctime field to a user-specified value.
9950 Some operating systems and file systems support a fourth time: the
9951 birth time, when the file was first created; by definition, this
9952 timestamp never changes.
9955 Time stamps assume the time zone rules specified by the @env{TZ}
9956 environment variable, or by the system default rules if @env{TZ} is
9957 not set. @xref{TZ Variable,, Specifying the Time Zone with @env{TZ},
9958 libc, The GNU C Library Reference Manual}.
9959 You can avoid ambiguities during
9960 daylight saving transitions by using @sc{utc} time stamps.
9962 The program accepts the following options. Also see @ref{Common options}.
9968 @itemx --time=access
9972 @opindex atime@r{, changing}
9973 @opindex access @r{time, changing}
9974 @opindex use @r{time, changing}
9975 Change the access time only.
9980 @opindex --no-create
9981 Do not warn about or create files that do not exist.
9984 @itemx --date=@var{time}
9988 Use @var{time} instead of the current time. It can contain month names,
9989 time zones, @samp{am} and @samp{pm}, @samp{yesterday}, etc. For
9990 example, @option{--date="2004-02-27 14:19:13.489392193 +0530"}
9991 specifies the instant of time that is 489,392,193 nanoseconds after
9992 February 27, 2004 at 2:19:13 PM in a time zone that is 5 hours and 30
9993 minutes east of @acronym{UTC}. @xref{Date input formats}.
9994 File systems that do not support high-resolution time stamps
9995 silently ignore any excess precision here.
9999 @cindex BSD @command{touch} compatibility
10000 Ignored; for compatibility with BSD versions of @command{touch}.
10003 @itemx --no-dereference
10005 @opindex --no-dereference
10006 @cindex symbolic links, changing time
10008 Attempt to change the timestamps of a symbolic link, rather than what
10009 the link refers to. When using this option, empty files are not
10010 created, but option @option{-c} must also be used to avoid warning
10011 about files that do not exist. Not all systems support changing the
10012 timestamps of symlinks, since underlying system support for this
10013 action was not required until @acronym{POSIX} 2008. Also, on some
10014 systems, the mere act of examining a symbolic link changes the access
10015 time, such that only changes to the modification time will persist
10016 long enough to be observable. When coupled with option @option{-r}, a
10017 reference timestamp is taken from a symbolic link rather than the file
10021 @itemx --time=mtime
10022 @itemx --time=modify
10025 @opindex mtime@r{, changing}
10026 @opindex modify @r{time, changing}
10027 Change the modification time only.
10029 @item -r @var{file}
10030 @itemx --reference=@var{file}
10032 @opindex --reference
10033 Use the times of the reference @var{file} instead of the current time.
10034 If this option is combined with the @option{--date=@var{time}}
10035 (@option{-d @var{time}}) option, the reference @var{file}'s time is
10036 the origin for any relative @var{time}s given, but is otherwise ignored.
10037 For example, @samp{-r foo -d '-5 seconds'} specifies a time stamp
10038 equal to five seconds before the corresponding time stamp for @file{foo}.
10039 If @var{file} is a symbolic link, the reference timestamp is taken
10040 from the target of the symlink, unless @option{-h} was also in effect.
10042 @item -t [[@var{cc}]@var{yy}]@var{mmddhhmm}[.@var{ss}]
10043 Use the argument (optional four-digit or two-digit years, months,
10044 days, hours, minutes, optional seconds) instead of the current time.
10045 If the year is specified with only two digits, then @var{cc}
10046 is 20 for years in the range 0 @dots{} 68, and 19 for years in
10047 69 @dots{} 99. If no digits of the year are specified,
10048 the argument is interpreted as a date in the current year.
10049 Note that @var{ss} may be @samp{60}, to accommodate leap seconds.
10053 @vindex _POSIX2_VERSION
10054 On older systems, @command{touch} supports an obsolete syntax, as follows.
10055 If no timestamp is given with any of the @option{-d}, @option{-r}, or
10056 @option{-t} options, and if there are two or more @var{file}s and the
10057 first @var{file} is of the form @samp{@var{mmddhhmm}[@var{yy}]} and this
10058 would be a valid argument to the @option{-t} option (if the @var{yy}, if
10059 any, were moved to the front), and if the represented year
10060 is in the range 1969--1999, that argument is interpreted as the time
10061 for the other files instead of as a file name.
10062 This obsolete behavior can be enabled or disabled with the
10063 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
10064 conformance}), but portable scripts should avoid commands whose
10065 behavior depends on this variable.
10066 For example, use @samp{touch ./12312359 main.c} or @samp{touch -t
10067 12312359 main.c} rather than the ambiguous @samp{touch 12312359 main.c}.
10073 @chapter Disk usage
10077 No disk can hold an infinite amount of data. These commands report
10078 how much disk storage is in use or available, report other file and
10079 file status information, and write buffers to disk.
10082 * df invocation:: Report file system disk space usage.
10083 * du invocation:: Estimate file space usage.
10084 * stat invocation:: Report file or file system status.
10085 * sync invocation:: Synchronize memory and disk.
10086 * truncate invocation:: Shrink or extend the size of a file.
10090 @node df invocation
10091 @section @command{df}: Report file system disk space usage
10094 @cindex file system disk usage
10095 @cindex disk usage by file system
10097 @command{df} reports the amount of disk space used and available on
10098 file systems. Synopsis:
10101 df [@var{option}]@dots{} [@var{file}]@dots{}
10104 With no arguments, @command{df} reports the space used and available on all
10105 currently mounted file systems (of all types). Otherwise, @command{df}
10106 reports on the file system containing each argument @var{file}.
10108 Normally the disk space is printed in units of
10109 1024 bytes, but this can be overridden (@pxref{Block size}).
10110 Non-integer quantities are rounded up to the next higher unit.
10112 @cindex disk device file
10113 @cindex device file, disk
10114 If an argument @var{file} is a disk device file containing a mounted
10115 file system, @command{df} shows the space available on that file system
10116 rather than on the file system containing the device node (i.e., the root
10117 file system). @sc{gnu} @command{df} does not attempt to determine the disk usage
10118 on unmounted file systems, because on most kinds of systems doing so
10119 requires extremely nonportable intimate knowledge of file system
10122 The program accepts the following options. Also see @ref{Common options}.
10130 @cindex automounter file systems
10131 @cindex ignore file systems
10132 Include in the listing dummy file systems, which
10133 are omitted by default. Such file systems are typically special-purpose
10134 pseudo-file-systems, such as automounter entries.
10136 @item -B @var{size}
10137 @itemx --block-size=@var{size}
10139 @opindex --block-size
10140 @cindex file system sizes
10141 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10142 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10146 @cindex grand total of disk size, usage and available space
10147 Print a grand total of all arguments after all arguments have
10148 been processed. This can be used to find out the total disk size, usage
10149 and available space of all listed devices.
10155 Equivalent to @option{--si}.
10161 @cindex inode usage
10162 List inode usage information instead of block usage. An inode (short
10163 for index node) contains information about a file such as its owner,
10164 permissions, timestamps, and location on the disk.
10168 @cindex kibibytes for file system sizes
10169 Print sizes in 1024-byte blocks, overriding the default block size
10170 (@pxref{Block size}).
10171 This option is equivalent to @option{--block-size=1K}.
10177 @cindex file system types, limiting output to certain
10178 Limit the listing to local file systems. By default, remote file systems
10183 @cindex file system space, retrieving old data more quickly
10184 Do not invoke the @code{sync} system call before getting any usage data.
10185 This may make @command{df} run significantly faster on systems with many
10186 disks, but on some systems (notably SunOS) the results may be slightly
10187 out of date. This is the default.
10190 @itemx --portability
10192 @opindex --portability
10193 @cindex one-line output format
10194 @cindex @acronym{POSIX} output format
10195 @cindex portable output format
10196 @cindex output format, portable
10197 Use the @acronym{POSIX} output format. This is like the default format except
10202 The information about each file system is always printed on exactly
10203 one line; a mount device is never put on a line by itself. This means
10204 that if the mount device name is more than 20 characters long (e.g., for
10205 some network mounts), the columns are misaligned.
10208 The labels in the header output line are changed to conform to @acronym{POSIX}.
10211 The default block size and output format are unaffected by the
10212 @env{DF_BLOCK_SIZE}, @env{BLOCK_SIZE} and @env{BLOCKSIZE} environment
10213 variables. However, the default block size is still affected by
10214 @env{POSIXLY_CORRECT}: it is 512 if @env{POSIXLY_CORRECT} is set, 1024
10215 otherwise. @xref{Block size}.
10222 @cindex file system space, retrieving current data more slowly
10223 Invoke the @code{sync} system call before getting any usage data. On
10224 some systems (notably SunOS), doing this yields more up to date results,
10225 but in general this option makes @command{df} much slower, especially when
10226 there are many or very busy file systems.
10228 @item -t @var{fstype}
10229 @itemx --type=@var{fstype}
10232 @cindex file system types, limiting output to certain
10233 Limit the listing to file systems of type @var{fstype}. Multiple
10234 file system types can be specified by giving multiple @option{-t} options.
10235 By default, nothing is omitted.
10238 @itemx --print-type
10240 @opindex --print-type
10241 @cindex file system types, printing
10242 Print each file system's type. The types printed here are the same ones
10243 you can include or exclude with @option{-t} and @option{-x}. The particular
10244 types printed are whatever is supported by the system. Here are some of
10245 the common names (this list is certainly not exhaustive):
10250 @cindex @acronym{NFS} file system type
10251 An @acronym{NFS} file system, i.e., one mounted over a network from another
10252 machine. This is the one type name which seems to be used uniformly by
10255 @item 4.2@r{, }ufs@r{, }efs@dots{}
10256 @cindex Linux file system types
10257 @cindex local file system types
10258 @opindex 4.2 @r{file system type}
10259 @opindex ufs @r{file system type}
10260 @opindex efs @r{file system type}
10261 A file system on a locally-mounted hard disk. (The system might even
10262 support more than one type here; Linux does.)
10264 @item hsfs@r{, }cdfs
10265 @cindex CD-ROM file system type
10266 @cindex High Sierra file system
10267 @opindex hsfs @r{file system type}
10268 @opindex cdfs @r{file system type}
10269 A file system on a CD-ROM drive. HP-UX uses @samp{cdfs}, most other
10270 systems use @samp{hsfs} (@samp{hs} for ``High Sierra'').
10273 @cindex PC file system
10274 @cindex DOS file system
10275 @cindex MS-DOS file system
10276 @cindex diskette file system
10278 An MS-DOS file system, usually on a diskette.
10282 @item -x @var{fstype}
10283 @itemx --exclude-type=@var{fstype}
10285 @opindex --exclude-type
10286 Limit the listing to file systems not of type @var{fstype}.
10287 Multiple file system types can be eliminated by giving multiple
10288 @option{-x} options. By default, no file system types are omitted.
10291 Ignored; for compatibility with System V versions of @command{df}.
10296 Failure includes the case where no output is generated, so you can
10297 inspect the exit status of a command like @samp{df -t ext3 -t reiserfs
10298 @var{dir}} to test whether @var{dir} is on a file system of type
10299 @samp{ext3} or @samp{reiserfs}.
10302 @node du invocation
10303 @section @command{du}: Estimate file space usage
10306 @cindex file space usage
10307 @cindex disk usage for files
10309 @command{du} reports the amount of disk space used by the specified files
10310 and for each subdirectory (of directory arguments). Synopsis:
10313 du [@var{option}]@dots{} [@var{file}]@dots{}
10316 With no arguments, @command{du} reports the disk space for the current
10317 directory. Normally the disk space is printed in units of
10318 1024 bytes, but this can be overridden (@pxref{Block size}).
10319 Non-integer quantities are rounded up to the next higher unit.
10321 If two or more hard links point to the same file, only one of the hard
10322 links is counted. The @var{file} argument order affects which links
10323 are counted, and changing the argument order may change the numbers
10324 that @command{du} outputs.
10326 The program accepts the following options. Also see @ref{Common options}.
10334 Show counts for all files, not just directories.
10336 @itemx --apparent-size
10337 @opindex --apparent-size
10338 Print apparent sizes, rather than disk usage. The apparent size of a
10339 file is the number of bytes reported by @code{wc -c} on regular files,
10340 or more generally, @code{ls -l --block-size=1} or @code{stat --format=%s}.
10341 For example, a file containing the word @samp{zoo} with no newline would,
10342 of course, have an apparent size of 3. Such a small file may require
10343 anywhere from 0 to 16 KiB or more of disk space, depending on
10344 the type and configuration of the file system on which the file resides.
10345 However, a sparse file created with this command:
10348 dd bs=1 seek=2GiB if=/dev/null of=big
10352 has an apparent size of 2 GiB, yet on most modern
10353 systems, it actually uses almost no disk space.
10359 Equivalent to @code{--apparent-size --block-size=1}.
10361 @item -B @var{size}
10362 @itemx --block-size=@var{size}
10364 @opindex --block-size
10366 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10367 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10373 @cindex grand total of disk space
10374 Print a grand total of all arguments after all arguments have
10375 been processed. This can be used to find out the total disk usage of
10376 a given set of files or directories.
10379 @itemx --dereference-args
10381 @opindex --dereference-args
10382 Dereference symbolic links that are command line arguments.
10383 Does not affect other symbolic links. This is helpful for finding
10384 out the disk usage of directories, such as @file{/usr/tmp}, which
10385 are often symbolic links.
10387 @c --files0-from=FILE
10388 @filesZeroFromOption{du,, with the @option{--total} (@option{-c}) option}
10394 Equivalent to @option{--dereference-args} (@option{-D}).
10398 @cindex kibibytes for file sizes
10399 Print sizes in 1024-byte blocks, overriding the default block size
10400 (@pxref{Block size}).
10401 This option is equivalent to @option{--block-size=1K}.
10404 @itemx --count-links
10406 @opindex --count-links
10407 @cindex hard links, counting in @command{du}
10408 Count the size of all files, even if they have appeared already (as a
10412 @itemx --dereference
10414 @opindex --dereference
10415 @cindex symbolic links, dereferencing in @command{du}
10416 Dereference symbolic links (show the disk space used by the file
10417 or directory that the link points to instead of the space used by
10422 @cindex mebibytes for file sizes
10423 Print sizes in 1,048,576-byte blocks, overriding the default block size
10424 (@pxref{Block size}).
10425 This option is equivalent to @option{--block-size=1M}.
10428 @itemx --no-dereference
10430 @opindex --no-dereference
10431 @cindex symbolic links, dereferencing in @command{du}
10432 For each symbolic links encountered by @command{du},
10433 consider the disk space used by the symbolic link.
10435 @item -d @var{depth}
10436 @item --max-depth=@var{depth}
10437 @opindex -d @var{depth}
10438 @opindex --max-depth=@var{depth}
10439 @cindex limiting output of @command{du}
10440 Show the total for each directory (and file if --all) that is at
10441 most MAX_DEPTH levels down from the root of the hierarchy. The root
10442 is at level 0, so @code{du --max-depth=0} is equivalent to @code{du -s}.
10451 @opindex --summarize
10452 Display only a total for each argument.
10455 @itemx --separate-dirs
10457 @opindex --separate-dirs
10458 Normally, in the output of @command{du} (when not using @option{--summarize}),
10459 the size listed next to a directory name, @var{d}, represents the sum
10460 of sizes of all entries beneath @var{d} as well as the size of @var{d} itself.
10461 With @option{--separate-dirs}, the size reported for a directory name,
10462 @var{d}, is merely the @code{stat.st_size}-derived size of the directory
10467 @cindex last modified dates, displaying in @command{du}
10468 Show time of the most recent modification of any file in the directory,
10469 or any of its subdirectories.
10471 @itemx --time=ctime
10472 @itemx --time=status
10475 @opindex ctime@r{, show the most recent}
10476 @opindex status time@r{, show the most recent}
10477 @opindex use time@r{, show the most recent}
10478 Show the most recent status change time (the @samp{ctime} in the inode) of
10479 any file in the directory, instead of the modification time.
10481 @itemx --time=atime
10482 @itemx --time=access
10484 @opindex atime@r{, show the most recent}
10485 @opindex access time@r{, show the most recent}
10486 Show the most recent access time (the @samp{atime} in the inode) of
10487 any file in the directory, instead of the modification time.
10489 @item --time-style=@var{style}
10490 @opindex --time-style
10492 List timestamps in style @var{style}. This option has an effect only if
10493 the @option{--time} option is also specified. The @var{style} should
10494 be one of the following:
10497 @item +@var{format}
10499 List timestamps using @var{format}, where @var{format} is interpreted
10500 like the format argument of @command{date} (@pxref{date invocation}).
10501 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
10502 @command{du} to list timestamps like @samp{2002-03-30 23:45:56}. As
10503 with @command{date}, @var{format}'s interpretation is affected by the
10504 @env{LC_TIME} locale category.
10507 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
10508 format with nanosecond precision, e.g., @samp{2002-03-30
10509 23:45:56.477817180 -0700}. This style is equivalent to
10510 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
10513 List @acronym{ISO} 8601 date and time in minutes, e.g.,
10514 @samp{2002-03-30 23:45}. These timestamps are shorter than
10515 @samp{full-iso} timestamps, and are usually good enough for everyday
10516 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
10519 List @acronym{ISO} 8601 dates for timestamps, e.g., @samp{2002-03-30}.
10520 This style is equivalent to @samp{+%Y-%m-%d}.
10524 You can specify the default value of the @option{--time-style} option
10525 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
10526 the default style is @samp{long-iso}. For compatibility with @command{ls},
10527 if @env{TIME_STYLE} begins with @samp{+} and contains a newline,
10528 the newline and any later characters are ignored; if @env{TIME_STYLE}
10529 begins with @samp{posix-} the @samp{posix-} is ignored; and if
10530 @env{TIME_STYLE} is @samp{locale} it is ignored.
10533 @itemx --one-file-system
10535 @opindex --one-file-system
10536 @cindex one file system, restricting @command{du} to
10537 Skip directories that are on different file systems from the one that
10538 the argument being processed is on.
10540 @item --exclude=@var{pattern}
10541 @opindex --exclude=@var{pattern}
10542 @cindex excluding files from @command{du}
10543 When recursing, skip subdirectories or files matching @var{pattern}.
10544 For example, @code{du --exclude='*.o'} excludes files whose names
10547 @item -X @var{file}
10548 @itemx --exclude-from=@var{file}
10549 @opindex -X @var{file}
10550 @opindex --exclude-from=@var{file}
10551 @cindex excluding files from @command{du}
10552 Like @option{--exclude}, except take the patterns to exclude from @var{file},
10553 one per line. If @var{file} is @samp{-}, take the patterns from standard
10558 @cindex NFS mounts from BSD to HP-UX
10559 On BSD systems, @command{du} reports sizes that are half the correct
10560 values for files that are NFS-mounted from HP-UX systems. On HP-UX
10561 systems, it reports sizes that are twice the correct values for
10562 files that are NFS-mounted from BSD systems. This is due to a flaw
10563 in HP-UX; it also affects the HP-UX @command{du} program.
10568 @node stat invocation
10569 @section @command{stat}: Report file or file system status
10572 @cindex file status
10573 @cindex file system status
10575 @command{stat} displays information about the specified file(s). Synopsis:
10578 stat [@var{option}]@dots{} [@var{file}]@dots{}
10581 With no option, @command{stat} reports all information about the given files.
10582 But it also can be used to report the information of the file systems the
10583 given files are located on. If the files are links, @command{stat} can
10584 also give information about the files the links point to.
10586 @mayConflictWithShellBuiltIn{stat}
10591 @itemx --dereference
10593 @opindex --dereference
10594 @cindex symbolic links, dereferencing in @command{stat}
10595 Change how @command{stat} treats symbolic links.
10596 With this option, @command{stat} acts on the file referenced
10597 by each symbolic link argument.
10598 Without it, @command{stat} acts on any symbolic link argument directly.
10601 @itemx --file-system
10603 @opindex --file-system
10604 @cindex file systems
10605 Report information about the file systems where the given files are located
10606 instead of information about the files themselves.
10609 @itemx --format=@var{format}
10611 @opindex --format=@var{format}
10612 @cindex output format
10613 Use @var{format} rather than the default format.
10614 @var{format} is automatically newline-terminated, so
10615 running a command like the following with two or more @var{file}
10616 operands produces a line of output for each operand:
10618 $ stat --format=%d:%i / /usr
10623 @itemx --printf=@var{format}
10624 @opindex --printf=@var{format}
10625 @cindex output format
10626 Use @var{format} rather than the default format.
10627 Like @option{--format}, but interpret backslash escapes,
10628 and do not output a mandatory trailing newline.
10629 If you want a newline, include @samp{\n} in the @var{format}.
10630 Here's how you would use @option{--printf} to print the device
10631 and inode numbers of @file{/} and @file{/usr}:
10633 $ stat --printf='%d:%i\n' / /usr
10642 @cindex terse output
10643 Print the information in terse form, suitable for parsing by other programs.
10647 The valid @var{format} directives for files with @option{--format} and
10648 @option{--printf} are:
10651 @item %a - Access rights in octal
10652 @item %A - Access rights in human readable form
10653 @item %b - Number of blocks allocated (see @samp{%B})
10654 @item %B - The size in bytes of each block reported by @samp{%b}
10655 @item %d - Device number in decimal
10656 @item %D - Device number in hex
10657 @item %f - Raw mode in hex
10658 @item %F - File type
10659 @item %g - Group ID of owner
10660 @item %G - Group name of owner
10661 @item %h - Number of hard links
10662 @item %i - Inode number
10663 @item %n - File name
10664 @item %N - Quoted file name with dereference if symbolic link
10665 @item %o - I/O block size
10666 @item %s - Total size, in bytes
10667 @item %t - Major device type in hex
10668 @item %T - Minor device type in hex
10669 @item %u - User ID of owner
10670 @item %U - User name of owner
10671 @item %x - Time of last access
10672 @item %X - Time of last access as seconds since Epoch
10673 @item %y - Time of last modification
10674 @item %Y - Time of last modification as seconds since Epoch
10675 @item %z - Time of last change
10676 @item %Z - Time of last change as seconds since Epoch
10679 When listing file system information (@option{--file-system} (@option{-f})),
10680 you must use a different set of @var{format} directives:
10683 @item %a - Free blocks available to non-super-user
10684 @item %b - Total data blocks in file system
10685 @item %c - Total file nodes in file system
10686 @item %d - Free file nodes in file system
10687 @item %f - Free blocks in file system
10688 @item %i - File System ID in hex
10689 @item %l - Maximum length of file names
10690 @item %n - File name
10691 @item %s - Block size (for faster transfers)
10692 @item %S - Fundamental block size (for block counts)
10693 @item %t - Type in hex
10694 @item %T - Type in human readable form
10698 Time stamps are listed according to the time zone rules specified by
10699 the @env{TZ} environment variable, or by the system default rules if
10700 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
10701 with @env{TZ}, libc, The GNU C Library Reference Manual}.
10706 @node sync invocation
10707 @section @command{sync}: Synchronize data on disk with memory
10710 @cindex synchronize disk and memory
10712 @cindex superblock, writing
10713 @cindex inodes, written buffered
10714 @command{sync} writes any data buffered in memory out to disk. This can
10715 include (but is not limited to) modified superblocks, modified inodes,
10716 and delayed reads and writes. This must be implemented by the kernel;
10717 The @command{sync} program does nothing but exercise the @code{sync} system
10720 @cindex crashes and corruption
10721 The kernel keeps data in memory to avoid doing (relatively slow) disk
10722 reads and writes. This improves performance, but if the computer
10723 crashes, data may be lost or the file system corrupted as a
10724 result. The @command{sync} command ensures everything in memory
10725 is written to disk.
10727 Any arguments are ignored, except for a lone @option{--help} or
10728 @option{--version} (@pxref{Common options}).
10733 @node truncate invocation
10734 @section @command{truncate}: Shrink or extend the size of a file
10737 @cindex truncating, file sizes
10739 @command{truncate} shrinks or extends the size of each @var{file} to the
10740 specified size. Synopsis:
10743 truncate @var{option}@dots{} @var{file}@dots{}
10746 @cindex files, creating
10747 Any @var{file} that does not exist is created.
10749 @cindex sparse files, creating
10750 @cindex holes, creating files with
10751 If a @var{file} is larger than the specified size, the extra data is lost.
10752 If a @var{file} is shorter, it is extended and the extended part (or hole)
10753 reads as zero bytes.
10755 The program accepts the following options. Also see @ref{Common options}.
10762 @opindex --no-create
10763 Do not create files that do not exist.
10768 @opindex --io-blocks
10769 Treat @var{size} as number of I/O blocks of the @var{file} rather than bytes.
10771 @item -r @var{rfile}
10772 @itemx --reference=@var{rfile}
10774 @opindex --reference
10775 Base the size of each @var{file} on the size of @var{rfile}.
10777 @item -s @var{size}
10778 @itemx --size=@var{size}
10781 Set or adjust the size of each @var{file} according to @var{size}.
10782 @multiplierSuffixesNoBlocks{size}
10784 @var{size} may also be prefixed by one of the following to adjust
10785 the size of each @var{file} based on their current size:
10787 @samp{+} => extend by
10788 @samp{-} => reduce by
10789 @samp{<} => at most
10790 @samp{>} => at least
10791 @samp{/} => round down to multiple of
10792 @samp{%} => round up to multiple of
10800 @node Printing text
10801 @chapter Printing text
10803 @cindex printing text, commands for
10804 @cindex commands for printing text
10806 This section describes commands that display text strings.
10809 * echo invocation:: Print a line of text.
10810 * printf invocation:: Format and print data.
10811 * yes invocation:: Print a string until interrupted.
10815 @node echo invocation
10816 @section @command{echo}: Print a line of text
10819 @cindex displaying text
10820 @cindex printing text
10821 @cindex text, displaying
10822 @cindex arbitrary text, displaying
10824 @command{echo} writes each given @var{string} to standard output, with a
10825 space between each and a newline after the last one. Synopsis:
10828 echo [@var{option}]@dots{} [@var{string}]@dots{}
10831 @mayConflictWithShellBuiltIn{echo}
10833 The program accepts the following options. Also see @ref{Common options}.
10834 Options must precede operands, and the normally-special argument
10835 @samp{--} has no special meaning and is treated like any other
10841 Do not output the trailing newline.
10845 @cindex backslash escapes
10846 Enable interpretation of the following backslash-escaped characters in
10855 produce no further output
10871 the eight-bit value that is the octal number @var{nnn}
10872 (zero to three octal digits)
10874 the eight-bit value that is the octal number @var{nnn}
10875 (one to three octal digits)
10877 the eight-bit value that is the hexadecimal number @var{hh}
10878 (one or two hexadecimal digits)
10883 @cindex backslash escapes
10884 Disable interpretation of backslash escapes in each @var{string}.
10885 This is the default. If @option{-e} and @option{-E} are both
10886 specified, the last one given takes effect.
10890 @vindex POSIXLY_CORRECT
10891 If the @env{POSIXLY_CORRECT} environment variable is set, then when
10892 @command{echo}'s first argument is not @option{-n} it outputs
10893 option-like arguments instead of treating them as options. For
10894 example, @code{echo -ne hello} outputs @samp{-ne hello} instead of
10895 plain @samp{hello}.
10897 @acronym{POSIX} does not require support for any options, and says
10898 that the behavior of @command{echo} is implementation-defined if any
10899 @var{string} contains a backslash or if the first argument is
10900 @option{-n}. Portable programs can use the @command{printf} command
10901 if they need to omit trailing newlines or output control characters or
10902 backslashes. @xref{printf invocation}.
10907 @node printf invocation
10908 @section @command{printf}: Format and print data
10911 @command{printf} does formatted printing of text. Synopsis:
10914 printf @var{format} [@var{argument}]@dots{}
10917 @command{printf} prints the @var{format} string, interpreting @samp{%}
10918 directives and @samp{\} escapes to format numeric and string arguments
10919 in a way that is mostly similar to the C @samp{printf} function.
10920 @xref{Output Conversion Syntax,, @command{printf} format directives,
10921 libc, The GNU C Library Reference Manual}, for details.
10922 The differences are listed below.
10924 @mayConflictWithShellBuiltIn{printf}
10929 The @var{format} argument is reused as necessary to convert all the
10930 given @var{argument}s. For example, the command @samp{printf %s a b}
10934 Missing @var{argument}s are treated as null strings or as zeros,
10935 depending on whether the context expects a string or a number. For
10936 example, the command @samp{printf %sx%d} prints @samp{x0}.
10940 An additional escape, @samp{\c}, causes @command{printf} to produce no
10941 further output. For example, the command @samp{printf 'A%sC\cD%sF' B
10942 E} prints @samp{ABC}.
10945 The hexadecimal escape sequence @samp{\x@var{hh}} has at most two
10946 digits, as opposed to C where it can have an unlimited number of
10947 digits. For example, the command @samp{printf '\x07e'} prints two
10948 bytes, whereas the C statement @samp{printf ("\x07e")} prints just
10953 @command{printf} has an additional directive, @samp{%b}, which prints its
10954 argument string with @samp{\} escapes interpreted in the same way as in
10955 the @var{format} string, except that octal escapes are of the form
10956 @samp{\0@var{ooo}} where @var{ooo} is 0 to 3 octal digits.
10957 If a precision is also given, it limits the number of bytes printed
10958 from the converted string.
10961 Numeric arguments must be single C constants, possibly with leading
10962 @samp{+} or @samp{-}. For example, @samp{printf %.4d -3} outputs
10966 @vindex POSIXLY_CORRECT
10967 If the leading character of a numeric argument is @samp{"} or @samp{'}
10968 then its value is the numeric value of the immediately following
10969 character. Any remaining characters are silently ignored if the
10970 @env{POSIXLY_CORRECT} environment variable is set; otherwise, a
10971 warning is printed. For example, @samp{printf "%d" "'a"} outputs
10972 @samp{97} on hosts that use the @acronym{ASCII} character set, since
10973 @samp{a} has the numeric value 97 in @acronym{ASCII}.
10978 A floating-point argument must use a period before any fractional
10979 digits, but is printed according to the @env{LC_NUMERIC} category of the
10980 current locale. For example, in a locale whose radix character is a
10981 comma, the command @samp{printf %g 3.14} outputs @samp{3,14} whereas
10982 the command @samp{printf %g 3,14} is an error.
10986 @command{printf} interprets @samp{\@var{ooo}} in @var{format} as an octal number
10987 (if @var{ooo} is 1 to 3 octal digits) specifying a character to print,
10988 and @samp{\x@var{hh}} as a hexadecimal number (if @var{hh} is 1 to 2 hex
10989 digits) specifying a character to print.
10994 @cindex ISO/IEC 10646
10996 @command{printf} interprets two character syntaxes introduced in
10997 @acronym{ISO} C 99:
10998 @samp{\u} for 16-bit Unicode (@acronym{ISO}/@acronym{IEC} 10646)
10999 characters, specified as
11000 four hexadecimal digits @var{hhhh}, and @samp{\U} for 32-bit Unicode
11001 characters, specified as eight hexadecimal digits @var{hhhhhhhh}.
11002 @command{printf} outputs the Unicode characters
11003 according to the @env{LC_CTYPE} locale. Unicode characters in the ranges
11004 U+0000...U+009F, U+D800...U+DFFF cannot be specified by this syntax, except
11005 for U+0024 ($), U+0040 (@@), and U+0060 (@`).
11007 The processing of @samp{\u} and @samp{\U} requires a full-featured
11008 @code{iconv} facility. It is activated on systems with glibc 2.2 (or newer),
11009 or when @code{libiconv} is installed prior to this package. Otherwise
11010 @samp{\u} and @samp{\U} will print as-is.
11012 The only options are a lone @option{--help} or
11013 @option{--version}. @xref{Common options}.
11014 Options must precede operands.
11016 The Unicode character syntaxes are useful for writing strings in a locale
11017 independent way. For example, a string containing the Euro currency symbol
11020 $ env printf '\u20AC 14.95'
11024 will be output correctly in all locales supporting the Euro symbol
11025 (@acronym{ISO}-8859-15, UTF-8, and others). Similarly, a Chinese string
11028 $ env printf '\u4e2d\u6587'
11032 will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8, etc).
11034 Note that in these examples, the @command{printf} command has been
11035 invoked via @command{env} to ensure that we run the program found via
11036 your shell's search path, and not a shell alias or a built-in function.
11038 For larger strings, you don't need to look up the hexadecimal code
11039 values of each character one by one. @acronym{ASCII} characters mixed with \u
11040 escape sequences is also known as the JAVA source file encoding. You can
11041 use GNU recode 3.5c (or newer) to convert strings to this encoding. Here
11042 is how to convert a piece of text into a shell script which will output
11043 this text in a locale-independent way:
11046 $ LC_CTYPE=zh_CN.big5 /usr/local/bin/printf \
11047 '\u4e2d\u6587\n' > sample.txt
11048 $ recode BIG5..JAVA < sample.txt \
11049 | sed -e "s|^|/usr/local/bin/printf '|" -e "s|$|\\\\n'|" \
11056 @node yes invocation
11057 @section @command{yes}: Print a string until interrupted
11060 @cindex repeated output of a string
11062 @command{yes} prints the command line arguments, separated by spaces and
11063 followed by a newline, forever until it is killed. If no arguments are
11064 given, it prints @samp{y} followed by a newline forever until killed.
11066 Upon a write error, @command{yes} exits with status @samp{1}.
11068 The only options are a lone @option{--help} or @option{--version}.
11069 To output an argument that begins with
11070 @samp{-}, precede it with @option{--}, e.g., @samp{yes -- --help}.
11071 @xref{Common options}.
11075 @chapter Conditions
11078 @cindex commands for exit status
11079 @cindex exit status commands
11081 This section describes commands that are primarily useful for their exit
11082 status, rather than their output. Thus, they are often used as the
11083 condition of shell @code{if} statements, or as the last command in a
11087 * false invocation:: Do nothing, unsuccessfully.
11088 * true invocation:: Do nothing, successfully.
11089 * test invocation:: Check file types and compare values.
11090 * expr invocation:: Evaluate expressions.
11094 @node false invocation
11095 @section @command{false}: Do nothing, unsuccessfully
11098 @cindex do nothing, unsuccessfully
11099 @cindex failure exit status
11100 @cindex exit status of @command{false}
11102 @command{false} does nothing except return an exit status of 1, meaning
11103 @dfn{failure}. It can be used as a place holder in shell scripts
11104 where an unsuccessful command is needed.
11105 In most modern shells, @command{false} is a built-in command, so when
11106 you use @samp{false} in a script, you're probably using the built-in
11107 command, not the one documented here.
11109 @command{false} honors the @option{--help} and @option{--version} options.
11111 This version of @command{false} is implemented as a C program, and is thus
11112 more secure and faster than a shell script implementation, and may safely
11113 be used as a dummy shell for the purpose of disabling accounts.
11115 Note that @command{false} (unlike all other programs documented herein)
11116 exits unsuccessfully, even when invoked with
11117 @option{--help} or @option{--version}.
11119 Portable programs should not assume that the exit status of
11120 @command{false} is 1, as it is greater than 1 on some
11121 non-@acronym{GNU} hosts.
11124 @node true invocation
11125 @section @command{true}: Do nothing, successfully
11128 @cindex do nothing, successfully
11130 @cindex successful exit
11131 @cindex exit status of @command{true}
11133 @command{true} does nothing except return an exit status of 0, meaning
11134 @dfn{success}. It can be used as a place holder in shell scripts
11135 where a successful command is needed, although the shell built-in
11136 command @code{:} (colon) may do the same thing faster.
11137 In most modern shells, @command{true} is a built-in command, so when
11138 you use @samp{true} in a script, you're probably using the built-in
11139 command, not the one documented here.
11141 @command{true} honors the @option{--help} and @option{--version} options.
11143 Note, however, that it is possible to cause @command{true}
11144 to exit with nonzero status: with the @option{--help} or @option{--version}
11145 option, and with standard
11146 output already closed or redirected to a file that evokes an I/O error.
11147 For example, using a Bourne-compatible shell:
11150 $ ./true --version >&-
11151 ./true: write error: Bad file number
11152 $ ./true --version > /dev/full
11153 ./true: write error: No space left on device
11156 This version of @command{true} is implemented as a C program, and is thus
11157 more secure and faster than a shell script implementation, and may safely
11158 be used as a dummy shell for the purpose of disabling accounts.
11160 @node test invocation
11161 @section @command{test}: Check file types and compare values
11164 @cindex check file types
11165 @cindex compare values
11166 @cindex expression evaluation
11168 @command{test} returns a status of 0 (true) or 1 (false) depending on the
11169 evaluation of the conditional expression @var{expr}. Each part of the
11170 expression must be a separate argument.
11172 @command{test} has file status checks, string operators, and numeric
11173 comparison operators.
11175 @command{test} has an alternate form that uses opening and closing
11176 square brackets instead a leading @samp{test}. For example, instead
11177 of @samp{test -d /}, you can write @samp{[ -d / ]}. The square
11178 brackets must be separate arguments; for example, @samp{[-d /]} does
11179 not have the desired effect. Since @samp{test @var{expr}} and @samp{[
11180 @var{expr} ]} have the same meaning, only the former form is discussed
11186 test @var{expression}
11188 [ @var{expression} ]
11193 @mayConflictWithShellBuiltIn{test}
11195 If @var{expression} is omitted, @command{test} returns false.
11196 If @var{expression} is a single argument,
11197 @command{test} returns false if the argument is null and true otherwise. The argument
11198 can be any string, including strings like @samp{-d}, @samp{-1},
11199 @samp{--}, @samp{--help}, and @samp{--version} that most other
11200 programs would treat as options. To get help and version information,
11201 invoke the commands @samp{[ --help} and @samp{[ --version}, without
11202 the usual closing brackets. @xref{Common options}.
11204 @cindex exit status of @command{test}
11208 0 if the expression is true,
11209 1 if the expression is false,
11210 2 if an error occurred.
11214 * File type tests:: -[bcdfhLpSt]
11215 * Access permission tests:: -[gkruwxOG]
11216 * File characteristic tests:: -e -s -nt -ot -ef
11217 * String tests:: -z -n = !=
11218 * Numeric tests:: -eq -ne -lt -le -gt -ge
11219 * Connectives for test:: ! -a -o
11223 @node File type tests
11224 @subsection File type tests
11226 @cindex file type tests
11228 These options test for particular types of files. (Everything's a file,
11229 but not all files are the same!)
11233 @item -b @var{file}
11235 @cindex block special check
11236 True if @var{file} exists and is a block special device.
11238 @item -c @var{file}
11240 @cindex character special check
11241 True if @var{file} exists and is a character special device.
11243 @item -d @var{file}
11245 @cindex directory check
11246 True if @var{file} exists and is a directory.
11248 @item -f @var{file}
11250 @cindex regular file check
11251 True if @var{file} exists and is a regular file.
11253 @item -h @var{file}
11254 @itemx -L @var{file}
11257 @cindex symbolic link check
11258 True if @var{file} exists and is a symbolic link.
11259 Unlike all other file-related tests, this test does not dereference
11260 @var{file} if it is a symbolic link.
11262 @item -p @var{file}
11264 @cindex named pipe check
11265 True if @var{file} exists and is a named pipe.
11267 @item -S @var{file}
11269 @cindex socket check
11270 True if @var{file} exists and is a socket.
11274 @cindex terminal check
11275 True if @var{fd} is a file descriptor that is associated with a
11281 @node Access permission tests
11282 @subsection Access permission tests
11284 @cindex access permission tests
11285 @cindex permission tests
11287 These options test for particular access permissions.
11291 @item -g @var{file}
11293 @cindex set-group-ID check
11294 True if @var{file} exists and has its set-group-ID bit set.
11296 @item -k @var{file}
11298 @cindex sticky bit check
11299 True if @var{file} exists and has its @dfn{sticky} bit set.
11301 @item -r @var{file}
11303 @cindex readable file check
11304 True if @var{file} exists and read permission is granted.
11306 @item -u @var{file}
11308 @cindex set-user-ID check
11309 True if @var{file} exists and has its set-user-ID bit set.
11311 @item -w @var{file}
11313 @cindex writable file check
11314 True if @var{file} exists and write permission is granted.
11316 @item -x @var{file}
11318 @cindex executable file check
11319 True if @var{file} exists and execute permission is granted
11320 (or search permission, if it is a directory).
11322 @item -O @var{file}
11324 @cindex owned by effective user ID check
11325 True if @var{file} exists and is owned by the current effective user ID.
11327 @item -G @var{file}
11329 @cindex owned by effective group ID check
11330 True if @var{file} exists and is owned by the current effective group ID.
11334 @node File characteristic tests
11335 @subsection File characteristic tests
11337 @cindex file characteristic tests
11339 These options test other file characteristics.
11343 @item -e @var{file}
11345 @cindex existence-of-file check
11346 True if @var{file} exists.
11348 @item -s @var{file}
11350 @cindex nonempty file check
11351 True if @var{file} exists and has a size greater than zero.
11353 @item @var{file1} -nt @var{file2}
11355 @cindex newer-than file check
11356 True if @var{file1} is newer (according to modification date) than
11357 @var{file2}, or if @var{file1} exists and @var{file2} does not.
11359 @item @var{file1} -ot @var{file2}
11361 @cindex older-than file check
11362 True if @var{file1} is older (according to modification date) than
11363 @var{file2}, or if @var{file2} exists and @var{file1} does not.
11365 @item @var{file1} -ef @var{file2}
11367 @cindex same file check
11368 @cindex hard link check
11369 True if @var{file1} and @var{file2} have the same device and inode
11370 numbers, i.e., if they are hard links to each other.
11376 @subsection String tests
11378 @cindex string tests
11380 These options test string characteristics. You may need to quote
11381 @var{string} arguments for the shell. For example:
11387 The quotes here prevent the wrong arguments from being passed to
11388 @command{test} if @samp{$V} is empty or contains special characters.
11392 @item -z @var{string}
11394 @cindex zero-length string check
11395 True if the length of @var{string} is zero.
11397 @item -n @var{string}
11398 @itemx @var{string}
11400 @cindex nonzero-length string check
11401 True if the length of @var{string} is nonzero.
11403 @item @var{string1} = @var{string2}
11405 @cindex equal string check
11406 True if the strings are equal.
11408 @item @var{string1} != @var{string2}
11410 @cindex not-equal string check
11411 True if the strings are not equal.
11416 @node Numeric tests
11417 @subsection Numeric tests
11419 @cindex numeric tests
11420 @cindex arithmetic tests
11422 Numeric relational operators. The arguments must be entirely numeric
11423 (possibly negative), or the special expression @w{@code{-l @var{string}}},
11424 which evaluates to the length of @var{string}.
11428 @item @var{arg1} -eq @var{arg2}
11429 @itemx @var{arg1} -ne @var{arg2}
11430 @itemx @var{arg1} -lt @var{arg2}
11431 @itemx @var{arg1} -le @var{arg2}
11432 @itemx @var{arg1} -gt @var{arg2}
11433 @itemx @var{arg1} -ge @var{arg2}
11440 These arithmetic binary operators return true if @var{arg1} is equal,
11441 not-equal, less-than, less-than-or-equal, greater-than, or
11442 greater-than-or-equal than @var{arg2}, respectively.
11449 test -1 -gt -2 && echo yes
11451 test -l abc -gt 1 && echo yes
11454 @error{} test: integer expression expected before -eq
11458 @node Connectives for test
11459 @subsection Connectives for @command{test}
11461 @cindex logical connectives
11462 @cindex connectives, logical
11464 The usual logical connectives.
11470 True if @var{expr} is false.
11472 @item @var{expr1} -a @var{expr2}
11474 @cindex logical and operator
11475 @cindex and operator
11476 True if both @var{expr1} and @var{expr2} are true.
11478 @item @var{expr1} -o @var{expr2}
11480 @cindex logical or operator
11481 @cindex or operator
11482 True if either @var{expr1} or @var{expr2} is true.
11487 @node expr invocation
11488 @section @command{expr}: Evaluate expressions
11491 @cindex expression evaluation
11492 @cindex evaluation of expressions
11494 @command{expr} evaluates an expression and writes the result on standard
11495 output. Each token of the expression must be a separate argument.
11497 Operands are either integers or strings. Integers consist of one or
11498 more decimal digits, with an optional leading @samp{-}.
11499 @command{expr} converts
11500 anything appearing in an operand position to an integer or a string
11501 depending on the operation being applied to it.
11503 Strings are not quoted for @command{expr} itself, though you may need to
11504 quote them to protect characters with special meaning to the shell,
11505 e.g., spaces. However, regardless of whether it is quoted, a string
11506 operand should not be a parenthesis or any of @command{expr}'s
11507 operators like @code{+}, so you cannot safely pass an arbitrary string
11508 @code{$str} to expr merely by quoting it to the shell. One way to
11509 work around this is to use the @sc{gnu} extension @code{+},
11510 (e.g., @code{+ "$str" = foo}); a more portable way is to use
11511 @code{@w{" $str"}} and to adjust the rest of the expression to take
11512 the leading space into account (e.g., @code{@w{" $str" = " foo"}}).
11514 You should not pass a negative integer or a string with leading
11515 @samp{-} as @command{expr}'s first argument, as it might be
11516 misinterpreted as an option; this can be avoided by parenthesization.
11517 Also, portable scripts should not use a string operand that happens to
11518 take the form of an integer; this can be worked around by inserting
11519 leading spaces as mentioned above.
11521 @cindex parentheses for grouping
11522 Operators may be given as infix symbols or prefix keywords. Parentheses
11523 may be used for grouping in the usual manner. You must quote
11524 parentheses and many operators to avoid the shell evaluating them,
11527 When built with support for the GNU MP library, @command{expr} uses
11528 arbitrary-precision arithmetic; otherwise, it uses native arithmetic
11529 types and may fail due to arithmetic overflow.
11531 The only options are @option{--help} and @option{--version}. @xref{Common
11532 options}. Options must precede operands.
11534 @cindex exit status of @command{expr}
11538 0 if the expression is neither null nor 0,
11539 1 if the expression is null or 0,
11540 2 if the expression is invalid,
11541 3 if an internal error occurred (e.g., arithmetic overflow).
11545 * String expressions:: + : match substr index length
11546 * Numeric expressions:: + - * / %
11547 * Relations for expr:: | & < <= = == != >= >
11548 * Examples of expr:: Examples.
11552 @node String expressions
11553 @subsection String expressions
11555 @cindex string expressions
11556 @cindex expressions, string
11558 @command{expr} supports pattern matching and other string operators. These
11559 have higher precedence than both the numeric and relational operators (in
11560 the next sections).
11564 @item @var{string} : @var{regex}
11565 @cindex pattern matching
11566 @cindex regular expression matching
11567 @cindex matching patterns
11568 Perform pattern matching. The arguments are converted to strings and the
11569 second is considered to be a (basic, a la GNU @code{grep}) regular
11570 expression, with a @code{^} implicitly prepended. The first argument is
11571 then matched against this regular expression.
11573 If the match succeeds and @var{regex} uses @samp{\(} and @samp{\)}, the
11574 @code{:} expression returns the part of @var{string} that matched the
11575 subexpression; otherwise, it returns the number of characters matched.
11577 If the match fails, the @code{:} operator returns the null string if
11578 @samp{\(} and @samp{\)} are used in @var{regex}, otherwise 0.
11580 @kindex \( @r{regexp operator}
11581 Only the first @samp{\( @dots{} \)} pair is relevant to the return
11582 value; additional pairs are meaningful only for grouping the regular
11583 expression operators.
11585 @kindex \+ @r{regexp operator}
11586 @kindex \? @r{regexp operator}
11587 @kindex \| @r{regexp operator}
11588 In the regular expression, @code{\+}, @code{\?}, and @code{\|} are
11589 operators which respectively match one or more, zero or one, or separate
11590 alternatives. SunOS and other @command{expr}'s treat these as regular
11591 characters. (@acronym{POSIX} allows either behavior.)
11592 @xref{Top, , Regular Expression Library, regex, Regex}, for details of
11593 regular expression syntax. Some examples are in @ref{Examples of expr}.
11595 @item match @var{string} @var{regex}
11597 An alternative way to do pattern matching. This is the same as
11598 @w{@samp{@var{string} : @var{regex}}}.
11600 @item substr @var{string} @var{position} @var{length}
11602 Returns the substring of @var{string} beginning at @var{position}
11603 with length at most @var{length}. If either @var{position} or
11604 @var{length} is negative, zero, or non-numeric, returns the null string.
11606 @item index @var{string} @var{charset}
11608 Returns the first position in @var{string} where the first character in
11609 @var{charset} was found. If no character in @var{charset} is found in
11610 @var{string}, return 0.
11612 @item length @var{string}
11614 Returns the length of @var{string}.
11616 @item + @var{token}
11618 Interpret @var{token} as a string, even if it is a keyword like @var{match}
11619 or an operator like @code{/}.
11620 This makes it possible to test @code{expr length + "$x"} or
11621 @code{expr + "$x" : '.*/\(.\)'} and have it do the right thing even if
11622 the value of @var{$x} happens to be (for example) @code{/} or @code{index}.
11623 This operator is a @acronym{GNU} extension. Portable shell scripts should use
11624 @code{@w{" $token"} : @w{' \(.*\)'}} instead of @code{+ "$token"}.
11628 To make @command{expr} interpret keywords as strings, you must use the
11629 @code{quote} operator.
11632 @node Numeric expressions
11633 @subsection Numeric expressions
11635 @cindex numeric expressions
11636 @cindex expressions, numeric
11638 @command{expr} supports the usual numeric operators, in order of increasing
11639 precedence. These numeric operators have lower precedence than the
11640 string operators described in the previous section, and higher precedence
11641 than the connectives (next section).
11649 @cindex subtraction
11650 Addition and subtraction. Both arguments are converted to integers;
11651 an error occurs if this cannot be done.
11657 @cindex multiplication
11660 Multiplication, division, remainder. Both arguments are converted to
11661 integers; an error occurs if this cannot be done.
11666 @node Relations for expr
11667 @subsection Relations for @command{expr}
11669 @cindex connectives, logical
11670 @cindex logical connectives
11671 @cindex relations, numeric or string
11673 @command{expr} supports the usual logical connectives and relations. These
11674 have lower precedence than the string and numeric operators
11675 (previous sections). Here is the list, lowest-precedence operator first.
11681 @cindex logical or operator
11682 @cindex or operator
11683 Returns its first argument if that is neither null nor zero, otherwise
11684 its second argument if it is neither null nor zero, otherwise 0. It
11685 does not evaluate its second argument if its first argument is neither
11690 @cindex logical and operator
11691 @cindex and operator
11692 Return its first argument if neither argument is null or zero, otherwise
11693 0. It does not evaluate its second argument if its first argument is
11696 @item < <= = == != >= >
11703 @cindex comparison operators
11705 Compare the arguments and return 1 if the relation is true, 0 otherwise.
11706 @code{==} is a synonym for @code{=}. @command{expr} first tries to convert
11707 both arguments to integers and do a numeric comparison; if either
11708 conversion fails, it does a lexicographic comparison using the character
11709 collating sequence specified by the @env{LC_COLLATE} locale.
11714 @node Examples of expr
11715 @subsection Examples of using @command{expr}
11717 @cindex examples of @command{expr}
11718 Here are a few examples, including quoting for shell metacharacters.
11720 To add 1 to the shell variable @code{foo}, in Bourne-compatible shells:
11723 foo=`expr $foo + 1`
11726 To print the non-directory part of the file name stored in
11727 @code{$fname}, which need not contain a @code{/}:
11730 expr $fname : '.*/\(.*\)' '|' $fname
11733 An example showing that @code{\+} is an operator:
11741 expr abc : 'a\(.\)c'
11743 expr index abcdef cz
11746 @error{} expr: syntax error
11747 expr index + index a
11753 @chapter Redirection
11755 @cindex redirection
11756 @cindex commands for redirection
11758 Unix shells commonly provide several forms of @dfn{redirection}---ways
11759 to change the input source or output destination of a command. But one
11760 useful redirection is performed by a separate command, not by the shell;
11761 it's described here.
11764 * tee invocation:: Redirect output to multiple files or processes.
11768 @node tee invocation
11769 @section @command{tee}: Redirect output to multiple files or processes
11772 @cindex pipe fitting
11773 @cindex destinations, multiple output
11774 @cindex read from stdin and write to stdout and files
11776 The @command{tee} command copies standard input to standard output and also
11777 to any files given as arguments. This is useful when you want not only
11778 to send some data down a pipe, but also to save a copy. Synopsis:
11781 tee [@var{option}]@dots{} [@var{file}]@dots{}
11784 If a file being written to does not already exist, it is created. If a
11785 file being written to already exists, the data it previously contained
11786 is overwritten unless the @option{-a} option is used.
11788 A @var{file} of @samp{-} causes @command{tee} to send another copy of
11789 input to standard output, but this is typically not that useful as the
11790 copies are interleaved.
11792 The program accepts the following options. Also see @ref{Common options}.
11799 Append standard input to the given files rather than overwriting
11803 @itemx --ignore-interrupts
11805 @opindex --ignore-interrupts
11806 Ignore interrupt signals.
11810 The @command{tee} command is useful when you happen to be transferring a large
11811 amount of data and also want to summarize that data without reading
11812 it a second time. For example, when you are downloading a DVD image,
11813 you often want to verify its signature or checksum right away.
11814 The inefficient way to do it is simply:
11817 wget http://example.com/some.iso && sha1sum some.iso
11820 One problem with the above is that it makes you wait for the
11821 download to complete before starting the time-consuming SHA1 computation.
11822 Perhaps even more importantly, the above requires reading
11823 the DVD image a second time (the first was from the network).
11825 The efficient way to do it is to interleave the download
11826 and SHA1 computation. Then, you'll get the checksum for
11827 free, because the entire process parallelizes so well:
11830 # slightly contrived, to demonstrate process substitution
11831 wget -O - http://example.com/dvd.iso \
11832 | tee >(sha1sum > dvd.sha1) > dvd.iso
11835 That makes @command{tee} write not just to the expected output file,
11836 but also to a pipe running @command{sha1sum} and saving the final
11837 checksum in a file named @file{dvd.sha1}.
11839 Note, however, that this example relies on a feature of modern shells
11840 called @dfn{process substitution}
11841 (the @samp{>(command)} syntax, above;
11842 @xref{Process Substitution,,Process Substitution, bashref,
11843 The Bash Reference Manual}.),
11844 so it works with @command{zsh}, @command{bash}, and @command{ksh},
11845 but not with @command{/bin/sh}. So if you write code like this
11846 in a shell script, be sure to start the script with @samp{#!/bin/bash}.
11848 Since the above example writes to one file and one process,
11849 a more conventional and portable use of @command{tee} is even better:
11852 wget -O - http://example.com/dvd.iso \
11853 | tee dvd.iso | sha1sum > dvd.sha1
11856 You can extend this example to make @command{tee} write to two processes,
11857 computing MD5 and SHA1 checksums in parallel. In this case,
11858 process substitution is required:
11861 wget -O - http://example.com/dvd.iso \
11862 | tee >(sha1sum > dvd.sha1) \
11863 >(md5sum > dvd.md5) \
11867 This technique is also useful when you want to make a @emph{compressed}
11868 copy of the contents of a pipe.
11869 Consider a tool to graphically summarize disk usage data from @samp{du -ak}.
11870 For a large hierarchy, @samp{du -ak} can run for a long time,
11871 and can easily produce terabytes of data, so you won't want to
11872 rerun the command unnecessarily. Nor will you want to save
11873 the uncompressed output.
11875 Doing it the inefficient way, you can't even start the GUI
11876 until after you've compressed all of the @command{du} output:
11879 du -ak | gzip -9 > /tmp/du.gz
11880 gzip -d /tmp/du.gz | xdiskusage -a
11883 With @command{tee} and process substitution, you start the GUI
11884 right away and eliminate the decompression completely:
11887 du -ak | tee >(gzip -9 > /tmp/du.gz) | xdiskusage -a
11890 Finally, if you regularly create more than one type of
11891 compressed tarball at once, for example when @code{make dist} creates
11892 both @command{gzip}-compressed and @command{bzip2}-compressed tarballs,
11893 there may be a better way.
11894 Typical @command{automake}-generated @file{Makefile} rules create
11895 the two compressed tar archives with commands in sequence, like this
11896 (slightly simplified):
11899 tardir=your-pkg-M.N
11900 tar chof - "$tardir" | gzip -9 -c > your-pkg-M.N.tar.gz
11901 tar chof - "$tardir" | bzip2 -9 -c > your-pkg-M.N.tar.bz2
11904 However, if the hierarchy you are archiving and compressing is larger
11905 than a couple megabytes, and especially if you are using a multi-processor
11906 system with plenty of memory, then you can do much better by reading the
11907 directory contents only once and running the compression programs in parallel:
11910 tardir=your-pkg-M.N
11911 tar chof - "$tardir" \
11912 | tee >(gzip -9 -c > your-pkg-M.N.tar.gz) \
11913 | bzip2 -9 -c > your-pkg-M.N.tar.bz2
11919 @node File name manipulation
11920 @chapter File name manipulation
11922 @cindex file name manipulation
11923 @cindex manipulation of file names
11924 @cindex commands for file name manipulation
11926 This section describes commands that manipulate file names.
11929 * basename invocation:: Strip directory and suffix from a file name.
11930 * dirname invocation:: Strip last file name component.
11931 * pathchk invocation:: Check file name validity and portability.
11932 * mktemp invocation:: Create temporary file or directory.
11936 @node basename invocation
11937 @section @command{basename}: Strip directory and suffix from a file name
11940 @cindex strip directory and suffix from file names
11941 @cindex directory, stripping from file names
11942 @cindex suffix, stripping from file names
11943 @cindex file names, stripping directory and suffix
11944 @cindex leading directory components, stripping
11946 @command{basename} removes any leading directory components from
11947 @var{name}. Synopsis:
11950 basename @var{name} [@var{suffix}]
11953 If @var{suffix} is specified and is identical to the end of @var{name},
11954 it is removed from @var{name} as well. Note that since trailing slashes
11955 are removed prior to suffix matching, @var{suffix} will do nothing if it
11956 contains slashes. @command{basename} prints the result on standard
11959 @c This test is used both here and in the section on dirname.
11960 @macro basenameAndDirname
11961 Together, @command{basename} and @command{dirname} are designed such
11962 that if @samp{ls "$name"} succeeds, then the command sequence @samp{cd
11963 "$(dirname "$name")"; ls "$(basename "$name")"} will, too. This works
11964 for everything except file names containing a trailing newline.
11966 @basenameAndDirname
11968 @acronym{POSIX} allows the implementation to define the results if
11969 @var{name} is empty or @samp{//}. In the former case, @acronym{GNU}
11970 @command{basename} returns the empty string. In the latter case, the
11971 result is @samp{//} on platforms where @var{//} is distinct from
11972 @var{/}, and @samp{/} on platforms where there is no difference.
11974 The only options are @option{--help} and @option{--version}. @xref{Common
11975 options}. Options must precede operands.
11983 basename /usr/bin/sort
11986 basename include/stdio.h .h
11990 @node dirname invocation
11991 @section @command{dirname}: Strip last file name component
11994 @cindex directory components, printing
11995 @cindex stripping non-directory suffix
11996 @cindex non-directory suffix, stripping
11998 @command{dirname} prints all but the final slash-delimited component of
11999 @var{name}. Slashes on either side of the final component are also
12000 removed. If the string contains no slash, @command{dirname} prints
12001 @samp{.} (meaning the current directory). Synopsis:
12007 @var{name} need not be a file name, but if it is, this operation
12008 effectively lists the directory that contains the final component,
12009 including the case when the final component is itself a directory.
12011 @basenameAndDirname
12013 @acronym{POSIX} allows the implementation to define the results if
12014 @var{name} is @samp{//}. With @acronym{GNU} @command{dirname}, the
12015 result is @samp{//} on platforms where @var{//} is distinct from
12016 @var{/}, and @samp{/} on platforms where there is no difference.
12018 The only options are @option{--help} and @option{--version}. @xref{Common
12026 # Output "/usr/bin".
12027 dirname /usr/bin/sort
12028 dirname /usr/bin//.//
12035 @node pathchk invocation
12036 @section @command{pathchk}: Check file name validity and portability
12039 @cindex file names, checking validity and portability
12040 @cindex valid file names, checking for
12041 @cindex portable file names, checking for
12043 @command{pathchk} checks validity and portability of file names. Synopsis:
12046 pathchk [@var{option}]@dots{} @var{name}@dots{}
12049 For each @var{name}, @command{pathchk} prints an error message if any of
12050 these conditions is true:
12054 One of the existing directories in @var{name} does not have search
12055 (execute) permission,
12057 The length of @var{name} is larger than the maximum supported by the
12060 The length of one component of @var{name} is longer than
12061 its file system's maximum.
12064 A nonexistent @var{name} is not an error, so long a file with that
12065 name could be created under the above conditions.
12067 The program accepts the following options. Also see @ref{Common options}.
12068 Options must precede operands.
12074 Instead of performing checks based on the underlying file system,
12075 print an error message if any of these conditions is true:
12079 A file name is empty.
12082 A file name contains a character outside the @acronym{POSIX} portable file
12083 name character set, namely, the ASCII letters and digits, @samp{.},
12084 @samp{_}, @samp{-}, and @samp{/}.
12087 The length of a file name or one of its components exceeds the
12088 @acronym{POSIX} minimum limits for portability.
12093 Print an error message if a file name is empty, or if it contains a component
12094 that begins with @samp{-}.
12096 @item --portability
12097 @opindex --portability
12098 Print an error message if a file name is not portable to all @acronym{POSIX}
12099 hosts. This option is equivalent to @samp{-p -P}.
12103 @cindex exit status of @command{pathchk}
12107 0 if all specified file names passed all checks,
12111 @node mktemp invocation
12112 @section @command{mktemp}: Create temporary file or directory
12115 @cindex file names, creating temporary
12116 @cindex directory, creating temporary
12117 @cindex temporary files and directories
12119 @command{mktemp} manages the creation of temporary files and
12120 directories. Synopsis:
12123 mktemp [@var{option}]@dots{} [@var{template}]
12126 Safely create a temporary file or directory based on @var{template},
12127 and print its name. If given, @var{template} must include at least
12128 three consecutive @samp{X}s in the last component. If omitted, the template
12129 @samp{tmp.XXXXXXXXXX} is used, and option @option{--tmpdir} is
12130 implied. The final run of @samp{X}s in the @var{template} will be replaced
12131 by alpha-numeric characters; thus, on a case-sensitive file system,
12132 and with a @var{template} including a run of @var{n} instances of @samp{X},
12133 there are @samp{62**@var{n}} potential file names.
12135 Older scripts used to create temporary files by simply joining the
12136 name of the program with the process id (@samp{$$}) as a suffix.
12137 However, that naming scheme is easily predictable, and suffers from a
12138 race condition where the attacker can create an appropriately named
12139 symbolic link, such that when the script then opens a handle to what
12140 it thought was an unused file, it is instead modifying an existing
12141 file. Using the same scheme to create a directory is slightly safer,
12142 since the @command{mkdir} will fail if the target already exists, but
12143 it is still inferior because it allows for denial of service attacks.
12144 Therefore, modern scripts should use the @command{mktemp} command to
12145 guarantee that the generated name will be unpredictable, and that
12146 knowledge of the temporary file name implies that the file was created
12147 by the current script and cannot be modified by other users.
12149 When creating a file, the resulting file has read and write
12150 permissions for the current user, but no permissions for the group or
12151 others; these permissions are reduced if the current umask is more
12154 Here are some examples (although note that if you repeat them, you
12155 will most likely get different file names):
12160 Create a temporary file in the current directory.
12167 Create a temporary file with a known suffix.
12169 $ mktemp --suffix=.txt file-XXXX
12171 $ mktemp file-XXXX-XXXX.txt
12176 Create a secure fifo relative to the user's choice of @env{TMPDIR},
12177 but falling back to the current directory rather than @file{/tmp}.
12178 Note that @command{mktemp} does not create fifos, but can create a
12179 secure directory in which the fifo can live. Exit the shell if the
12180 directory or fifo could not be created.
12182 $ dir=$(mktemp -p "$@{TMPDIR:-.@}" -d dir-XXXX) || exit 1
12184 $ mkfifo "$fifo" || @{ rmdir "$dir"; exit 1; @}
12188 Create and use a temporary file if possible, but ignore failure. The
12189 file will reside in the directory named by @env{TMPDIR}, if specified,
12190 or else in @file{/tmp}.
12192 $ file=$(mktemp -q) && @{
12193 > # Safe to use $file only within this block. Use quotes,
12194 > # since $TMPDIR, and thus $file, may contain whitespace.
12195 > echo ... > "$file"
12201 Act as a semi-random character generator (it is not fully random,
12202 since it is impacted by the contents of the current directory). To
12203 avoid security holes, do not use the resulting names to create a file.
12213 The program accepts the following options. Also see @ref{Common options}.
12220 @opindex --directory
12221 Create a directory rather than a file. The directory will have read,
12222 write, and search permissions for the current user, but no permissions
12223 for the group or others; these permissions are reduced if the current
12224 umask is more restrictive.
12230 Suppress diagnostics about failure to create a file or directory. The
12231 exit status will still reflect whether a file was created.
12237 Generate a temporary name that does not name an existing file, without
12238 changing the file system contents. Using the output of this command
12239 to create a new file is inherently unsafe, as there is a window of
12240 time between generating the name and using it where another process
12241 can create an object by the same name.
12244 @itemx --tmpdir[=@var{dir}]
12247 Treat @var{template} relative to the directory @var{dir}. If
12248 @var{dir} is not specified (only possible with the long option
12249 @option{--tmpdir}) or is the empty string, use the value of
12250 @env{TMPDIR} if available, otherwise use @samp{/tmp}. If this is
12251 specified, @var{template} must not be absolute. However,
12252 @var{template} can still contain slashes, although intermediate
12253 directories must already exist.
12255 @item --suffix=@var{suffix}
12257 Append @var{suffix} to the @var{template}. @var{suffix} must not
12258 contain slash. If @option{--suffix} is specified, @var{template} must
12259 end in @samp{X}; if it is not specified, then an appropriate
12260 @option{--suffix} is inferred by finding the last @samp{X} in
12261 @var{template}. This option exists for use with the default
12262 @var{template} and for the creation of a @var{suffix} that starts with
12267 Treat @var{template} as a single file relative to the value of
12268 @env{TMPDIR} if available, or to the directory specified by
12269 @option{-p}, otherwise to @samp{/tmp}. @var{template} must not
12270 contain slashes. This option is deprecated; the use of @option{-p}
12271 without @option{-t} offers better defaults (by favoring the command
12272 line over @env{TMPDIR}) and more flexibility (by allowing intermediate
12277 @cindex exit status of @command{mktemp}
12281 0 if the file was created,
12286 @node Working context
12287 @chapter Working context
12289 @cindex working context
12290 @cindex commands for printing the working context
12292 This section describes commands that display or alter the context in
12293 which you are working: the current directory, the terminal settings, and
12294 so forth. See also the user-related commands in the next section.
12297 * pwd invocation:: Print working directory.
12298 * stty invocation:: Print or change terminal characteristics.
12299 * printenv invocation:: Print environment variables.
12300 * tty invocation:: Print file name of terminal on standard input.
12304 @node pwd invocation
12305 @section @command{pwd}: Print working directory
12308 @cindex print name of current directory
12309 @cindex current working directory, printing
12310 @cindex working directory, printing
12313 @command{pwd} prints the name of the current directory. Synopsis:
12316 pwd [@var{option}]@dots{}
12319 The program accepts the following options. Also see @ref{Common options}.
12326 If the contents of the environment variable @env{PWD} provide an
12327 absolute name of the current directory with no @samp{.} or @samp{..}
12328 components, but possibly with symbolic links, then output those
12329 contents. Otherwise, fall back to default @option{-P} handling.
12334 @opindex --physical
12335 Print a fully resolved name for the current directory. That is, all
12336 components of the printed name will be actual directory names---none
12337 will be symbolic links.
12340 @cindex symbolic links and @command{pwd}
12341 If @option{-L} and @option{-P} are both given, the last one takes
12342 precedence. If neither option is given, then this implementation uses
12343 @option{-P} as the default unless the @env{POSIXLY_CORRECT}
12344 environment variable is set.
12346 @mayConflictWithShellBuiltIn{pwd}
12351 @node stty invocation
12352 @section @command{stty}: Print or change terminal characteristics
12355 @cindex change or print terminal settings
12356 @cindex terminal settings
12357 @cindex line settings of terminal
12359 @command{stty} prints or changes terminal characteristics, such as baud rate.
12363 stty [@var{option}] [@var{setting}]@dots{}
12364 stty [@var{option}]
12367 If given no line settings, @command{stty} prints the baud rate, line
12368 discipline number (on systems that support it), and line settings
12369 that have been changed from the values set by @samp{stty sane}.
12370 By default, mode reading and setting are performed on the tty line
12371 connected to standard input, although this can be modified by the
12372 @option{--file} option.
12374 @command{stty} accepts many non-option arguments that change aspects of
12375 the terminal line operation, as described below.
12377 The program accepts the following options. Also see @ref{Common options}.
12384 Print all current settings in human-readable form. This option may not
12385 be used in combination with any line settings.
12387 @item -F @var{device}
12388 @itemx --file=@var{device}
12391 Set the line opened by the file name specified in @var{device} instead of
12392 the tty line connected to standard input. This option is necessary
12393 because opening a @acronym{POSIX} tty requires use of the @code{O_NONDELAY} flag to
12394 prevent a @acronym{POSIX} tty from blocking until the carrier detect line is high if
12395 the @code{clocal} flag is not set. Hence, it is not always possible
12396 to allow the shell to open the device in the traditional manner.
12402 @cindex machine-readable @command{stty} output
12403 Print all current settings in a form that can be used as an argument to
12404 another @command{stty} command to restore the current settings. This option
12405 may not be used in combination with any line settings.
12409 Many settings can be turned off by preceding them with a @samp{-}.
12410 Such arguments are marked below with ``May be negated'' in their
12411 description. The descriptions themselves refer to the positive
12412 case, that is, when @emph{not} negated (unless stated otherwise,
12415 Some settings are not available on all @acronym{POSIX} systems, since they use
12416 extensions. Such arguments are marked below with ``Non-@acronym{POSIX}'' in their
12417 description. On non-@acronym{POSIX} systems, those or other settings also may not
12418 be available, but it's not feasible to document all the variations: just
12424 * Control:: Control settings
12425 * Input:: Input settings
12426 * Output:: Output settings
12427 * Local:: Local settings
12428 * Combination:: Combination settings
12429 * Characters:: Special characters
12430 * Special:: Special settings
12435 @subsection Control settings
12437 @cindex control settings
12443 @cindex two-way parity
12444 Generate parity bit in output and expect parity bit in input.
12450 @cindex even parity
12451 Set odd parity (even if negated). May be negated.
12458 @cindex character size
12459 @cindex eight-bit characters
12460 Set character size to 5, 6, 7, or 8 bits.
12465 Send a hangup signal when the last process closes the tty. May be
12471 Use two stop bits per character (one if negated). May be negated.
12475 Allow input to be received. May be negated.
12479 @cindex modem control
12480 Disable modem control signals. May be negated.
12484 @cindex hardware flow control
12485 @cindex flow control, hardware
12486 @cindex RTS/CTS flow control
12487 Enable RTS/CTS flow control. Non-@acronym{POSIX}. May be negated.
12492 @subsection Input settings
12494 @cindex input settings
12495 These settings control operations on data received from the terminal.
12500 @cindex breaks, ignoring
12501 Ignore break characters. May be negated.
12505 @cindex breaks, cause interrupts
12506 Make breaks cause an interrupt signal. May be negated.
12510 @cindex parity, ignoring
12511 Ignore characters with parity errors. May be negated.
12515 @cindex parity errors, marking
12516 Mark parity errors (with a 255-0-character sequence). May be negated.
12520 Enable input parity checking. May be negated.
12524 @cindex eight-bit input
12525 Clear high (8th) bit of input characters. May be negated.
12529 @cindex newline, translating to return
12530 Translate newline to carriage return. May be negated.
12534 @cindex return, ignoring
12535 Ignore carriage return. May be negated.
12539 @cindex return, translating to newline
12540 Translate carriage return to newline. May be negated.
12544 @cindex input encoding, UTF-8
12545 Assume input characters are UTF-8 encoded. May be negated.
12549 @kindex C-s/C-q flow control
12550 @cindex XON/XOFF flow control
12551 Enable XON/XOFF flow control (that is, @kbd{CTRL-S}/@kbd{CTRL-Q}). May
12558 @cindex software flow control
12559 @cindex flow control, software
12560 Enable sending of @code{stop} character when the system input buffer
12561 is almost full, and @code{start} character when it becomes almost
12562 empty again. May be negated.
12566 @cindex uppercase, translating to lowercase
12567 Translate uppercase characters to lowercase. Non-@acronym{POSIX}. May be
12568 negated. Note ilcuc is not implemented, as one would not be able to issue
12569 almost any (lowercase) Unix command, after invoking it.
12573 Allow any character to restart output (only the start character
12574 if negated). Non-@acronym{POSIX}. May be negated.
12578 @cindex beeping at input buffer full
12579 Enable beeping and not flushing input buffer if a character arrives
12580 when the input buffer is full. Non-@acronym{POSIX}. May be negated.
12585 @subsection Output settings
12587 @cindex output settings
12588 These settings control operations on data sent to the terminal.
12593 Postprocess output. May be negated.
12597 @cindex lowercase, translating to output
12598 Translate lowercase characters to uppercase. Non-@acronym{POSIX}. May be
12599 negated. (Note ouclc is not currently implemented.)
12603 @cindex return, translating to newline
12604 Translate carriage return to newline. Non-@acronym{POSIX}. May be negated.
12608 @cindex newline, translating to crlf
12609 Translate newline to carriage return-newline. Non-@acronym{POSIX}. May be
12614 Do not print carriage returns in the first column. Non-@acronym{POSIX}.
12619 Newline performs a carriage return. Non-@acronym{POSIX}. May be negated.
12623 @cindex pad instead of timing for delaying
12624 Use fill (padding) characters instead of timing for delays. Non-@acronym{POSIX}.
12629 @cindex pad character
12630 Use @acronym{ASCII} @sc{del} characters for fill instead of
12631 @acronym{ASCII} @sc{nul} characters. Non-@acronym{POSIX}.
12637 Newline delay style. Non-@acronym{POSIX}.
12644 Carriage return delay style. Non-@acronym{POSIX}.
12650 @opindex tab@var{n}
12651 Horizontal tab delay style. Non-@acronym{POSIX}.
12656 Backspace delay style. Non-@acronym{POSIX}.
12661 Vertical tab delay style. Non-@acronym{POSIX}.
12666 Form feed delay style. Non-@acronym{POSIX}.
12671 @subsection Local settings
12673 @cindex local settings
12678 Enable @code{interrupt}, @code{quit}, and @code{suspend} special
12679 characters. May be negated.
12683 Enable @code{erase}, @code{kill}, @code{werase}, and @code{rprnt}
12684 special characters. May be negated.
12688 Enable non-@acronym{POSIX} special characters. May be negated.
12692 Echo input characters. May be negated.
12698 Echo @code{erase} characters as backspace-space-backspace. May be
12703 @cindex newline echoing after @code{kill}
12704 Echo a newline after a @code{kill} character. May be negated.
12708 @cindex newline, echoing
12709 Echo newline even if not echoing other characters. May be negated.
12713 @cindex flushing, disabling
12714 Disable flushing after @code{interrupt} and @code{quit} special
12715 characters. May be negated.
12719 @cindex case translation
12720 Enable input and output of uppercase characters by preceding their
12721 lowercase equivalents with @samp{\}, when @code{icanon} is set.
12722 Non-@acronym{POSIX}. May be negated.
12726 @cindex background jobs, stopping at terminal write
12727 Stop background jobs that try to write to the terminal. Non-@acronym{POSIX}.
12734 Echo erased characters backward, between @samp{\} and @samp{/}.
12735 Non-@acronym{POSIX}. May be negated.
12741 @cindex control characters, using @samp{^@var{c}}
12742 @cindex hat notation for control characters
12743 Echo control characters in hat notation (@samp{^@var{c}}) instead
12744 of literally. Non-@acronym{POSIX}. May be negated.
12750 Echo the @code{kill} special character by erasing each character on
12751 the line as indicated by the @code{echoprt} and @code{echoe} settings,
12752 instead of by the @code{echoctl} and @code{echok} settings. Non-@acronym{POSIX}.
12758 @subsection Combination settings
12760 @cindex combination settings
12761 Combination settings:
12768 Same as @code{parenb -parodd cs7}. May be negated. If negated, same
12769 as @code{-parenb cs8}.
12773 Same as @code{parenb parodd cs7}. May be negated. If negated, same
12774 as @code{-parenb cs8}.
12778 Same as @code{-icrnl -onlcr}. May be negated. If negated, same as
12779 @code{icrnl -inlcr -igncr onlcr -ocrnl -onlret}.
12783 Reset the @code{erase} and @code{kill} special characters to their default
12790 @c This is too long to write inline.
12792 cread -ignbrk brkint -inlcr -igncr icrnl -ixoff
12793 -iuclc -ixany imaxbel opost -olcuc -ocrnl onlcr
12794 -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0
12795 ff0 isig icanon iexten echo echoe echok -echonl
12796 -noflsh -xcase -tostop -echoprt echoctl echoke
12800 and also sets all special characters to their default values.
12804 Same as @code{brkint ignpar istrip icrnl ixon opost isig icanon}, plus
12805 sets the @code{eof} and @code{eol} characters to their default values
12806 if they are the same as the @code{min} and @code{time} characters.
12807 May be negated. If negated, same as @code{raw}.
12814 -ignbrk -brkint -ignpar -parmrk -inpck -istrip
12815 -inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany
12816 -imaxbel -opost -isig -icanon -xcase min 1 time 0
12820 May be negated. If negated, same as @code{cooked}.
12824 Same as @option{-icanon}. May be negated. If negated, same as
12829 @cindex eight-bit characters
12830 Same as @code{-parenb -istrip cs8}. May be negated. If negated,
12831 same as @code{parenb istrip cs7}.
12835 Same as @option{-parenb -istrip -opost cs8}. May be negated.
12836 If negated, same as @code{parenb istrip opost cs7}.
12840 Same as @option{-ixany}. Non-@acronym{POSIX}. May be negated.
12844 Same as @code{tab0}. Non-@acronym{POSIX}. May be negated. If negated, same
12851 Same as @code{xcase iuclc olcuc}. Non-@acronym{POSIX}. May be negated.
12852 (Used for terminals with uppercase characters only.)
12856 Same as @code{echoe echoctl echoke}.
12860 Same as @code{echoe echoctl echoke -ixany intr ^C erase ^? kill C-u}.
12865 @subsection Special characters
12867 @cindex special characters
12868 @cindex characters, special
12870 The special characters' default values vary from system to system.
12871 They are set with the syntax @samp{name value}, where the names are
12872 listed below and the value can be given either literally, in hat
12873 notation (@samp{^@var{c}}), or as an integer which may start with
12874 @samp{0x} to indicate hexadecimal, @samp{0} to indicate octal, or
12875 any other digit to indicate decimal.
12877 @cindex disabling special characters
12878 @kindex u@r{, and disabling special characters}
12879 For GNU stty, giving a value of @code{^-} or @code{undef} disables that
12880 special character. (This is incompatible with Ultrix @command{stty},
12881 which uses a value of @samp{u} to disable a special character. GNU
12882 @command{stty} treats a value @samp{u} like any other, namely to set that
12883 special character to @key{U}.)
12889 Send an interrupt signal.
12893 Send a quit signal.
12897 Erase the last character typed.
12901 Erase the current line.
12905 Send an end of file (terminate the input).
12913 Alternate character to end the line. Non-@acronym{POSIX}.
12917 Switch to a different shell layer. Non-@acronym{POSIX}.
12921 Restart the output after stopping it.
12929 Send a terminal stop signal.
12933 Send a terminal stop signal after flushing the input. Non-@acronym{POSIX}.
12937 Redraw the current line. Non-@acronym{POSIX}.
12941 Erase the last word typed. Non-@acronym{POSIX}.
12945 Enter the next character typed literally, even if it is a special
12946 character. Non-@acronym{POSIX}.
12951 @subsection Special settings
12953 @cindex special settings
12958 Set the minimum number of characters that will satisfy a read until
12959 the time value has expired, when @option{-icanon} is set.
12963 Set the number of tenths of a second before reads time out if the minimum
12964 number of characters have not been read, when @option{-icanon} is set.
12966 @item ispeed @var{n}
12968 Set the input speed to @var{n}.
12970 @item ospeed @var{n}
12972 Set the output speed to @var{n}.
12976 Tell the tty kernel driver that the terminal has @var{n} rows. Non-@acronym{POSIX}.
12979 @itemx columns @var{n}
12982 Tell the kernel that the terminal has @var{n} columns. Non-@acronym{POSIX}.
12988 Print the number of rows and columns that the kernel thinks the
12989 terminal has. (Systems that don't support rows and columns in the kernel
12990 typically use the environment variables @env{LINES} and @env{COLUMNS}
12991 instead; however, GNU @command{stty} does not know anything about them.)
12992 Non-@acronym{POSIX}.
12996 Use line discipline @var{n}. Non-@acronym{POSIX}.
13000 Print the terminal speed.
13003 @cindex baud rate, setting
13004 Set the input and output speeds to @var{n}. @var{n} can be one of: 0
13005 50 75 110 134 134.5 150 200 300 600 1200 1800 2400 4800 9600 19200
13006 38400 @code{exta} @code{extb}. @code{exta} is the same as 19200;
13007 @code{extb} is the same as 38400. Many systems, including GNU/Linux,
13008 support higher speeds. The @command{stty} command includes support
13025 4000000 where the system supports these.
13026 0 hangs up the line if @option{-clocal} is set.
13030 @node printenv invocation
13031 @section @command{printenv}: Print all or some environment variables
13034 @cindex printing all or some environment variables
13035 @cindex environment variables, printing
13037 @command{printenv} prints environment variable values. Synopsis:
13040 printenv [@var{option}] [@var{variable}]@dots{}
13043 If no @var{variable}s are specified, @command{printenv} prints the value of
13044 every environment variable. Otherwise, it prints the value of each
13045 @var{variable} that is set, and nothing for those that are not set.
13047 The program accepts the following option. Also see @ref{Common options}.
13055 @cindex exit status of @command{printenv}
13059 0 if all variables specified were found
13060 1 if at least one specified variable was not found
13061 2 if a write error occurred
13065 @node tty invocation
13066 @section @command{tty}: Print file name of terminal on standard input
13069 @cindex print terminal file name
13070 @cindex terminal file name, printing
13072 @command{tty} prints the file name of the terminal connected to its standard
13073 input. It prints @samp{not a tty} if standard input is not a terminal.
13077 tty [@var{option}]@dots{}
13080 The program accepts the following option. Also see @ref{Common options}.
13090 Print nothing; only return an exit status.
13094 @cindex exit status of @command{tty}
13098 0 if standard input is a terminal
13099 1 if standard input is not a terminal
13100 2 if given incorrect arguments
13101 3 if a write error occurs
13105 @node User information
13106 @chapter User information
13108 @cindex user information, commands for
13109 @cindex commands for printing user information
13111 This section describes commands that print user-related information:
13112 logins, groups, and so forth.
13115 * id invocation:: Print user identity.
13116 * logname invocation:: Print current login name.
13117 * whoami invocation:: Print effective user ID.
13118 * groups invocation:: Print group names a user is in.
13119 * users invocation:: Print login names of users currently logged in.
13120 * who invocation:: Print who is currently logged in.
13124 @node id invocation
13125 @section @command{id}: Print user identity
13128 @cindex real user and group IDs, printing
13129 @cindex effective user and group IDs, printing
13130 @cindex printing real and effective user and group IDs
13132 @command{id} prints information about the given user, or the process
13133 running it if no user is specified. Synopsis:
13136 id [@var{option}]@dots{} [@var{username}]
13139 @vindex POSIXLY_CORRECT
13140 By default, it prints the real user ID, real group ID, effective user ID
13141 if different from the real user ID, effective group ID if different from
13142 the real group ID, and supplemental group IDs.
13143 In addition, if SELinux
13144 is enabled and the @env{POSIXLY_CORRECT} environment variable is not set,
13145 then print @samp{context=@var{c}}, where @var{c} is the security context.
13147 Each of these numeric values is preceded by an identifying string and
13148 followed by the corresponding user or group name in parentheses.
13150 The options cause @command{id} to print only part of the above information.
13151 Also see @ref{Common options}.
13158 Print only the group ID.
13164 Print only the group ID and the supplementary groups.
13170 Print the user or group name instead of the ID number. Requires
13171 @option{-u}, @option{-g}, or @option{-G}.
13177 Print the real, instead of effective, user or group ID. Requires
13178 @option{-u}, @option{-g}, or @option{-G}.
13184 Print only the user ID.
13191 @cindex security context
13192 Print only the security context of the current user.
13193 If SELinux is disabled then print a warning and
13194 set the exit status to 1.
13200 @macro primaryAndSupplementaryGroups{cmd,arg}
13201 Primary and supplementary groups for a process are normally inherited
13202 from its parent and are usually unchanged since login. This means
13203 that if you change the group database after logging in, @command{\cmd\}
13204 will not reflect your changes within your existing login session.
13205 Running @command{\cmd\} with a \arg\ causes the user and group
13206 database to be consulted afresh, and so will give a different result.
13208 @primaryAndSupplementaryGroups{id,user argument}
13210 @node logname invocation
13211 @section @command{logname}: Print current login name
13214 @cindex printing user's login name
13215 @cindex login name, printing
13216 @cindex user name, printing
13219 @command{logname} prints the calling user's name, as found in a
13220 system-maintained file (often @file{/var/run/utmp} or
13221 @file{/etc/utmp}), and exits with a status of 0. If there is no entry
13222 for the calling process, @command{logname} prints
13223 an error message and exits with a status of 1.
13225 The only options are @option{--help} and @option{--version}. @xref{Common
13231 @node whoami invocation
13232 @section @command{whoami}: Print effective user ID
13235 @cindex effective user ID, printing
13236 @cindex printing the effective user ID
13238 @command{whoami} prints the user name associated with the current
13239 effective user ID. It is equivalent to the command @samp{id -un}.
13241 The only options are @option{--help} and @option{--version}. @xref{Common
13247 @node groups invocation
13248 @section @command{groups}: Print group names a user is in
13251 @cindex printing groups a user is in
13252 @cindex supplementary groups, printing
13254 @command{groups} prints the names of the primary and any supplementary
13255 groups for each given @var{username}, or the current process if no names
13256 are given. If more than one name is given, the name of each user is
13258 the list of that user's groups and the user name is separated from the
13259 group list by a colon. Synopsis:
13262 groups [@var{username}]@dots{}
13265 The group lists are equivalent to the output of the command @samp{id -Gn}.
13267 @primaryAndSupplementaryGroups{groups,list of users}
13269 The only options are @option{--help} and @option{--version}. @xref{Common
13275 @node users invocation
13276 @section @command{users}: Print login names of users currently logged in
13279 @cindex printing current usernames
13280 @cindex usernames, printing current
13282 @cindex login sessions, printing users with
13283 @command{users} prints on a single line a blank-separated list of user
13284 names of users currently logged in to the current host. Each user name
13285 corresponds to a login session, so if a user has more than one login
13286 session, that user's name will appear the same number of times in the
13295 With no @var{file} argument, @command{users} extracts its information from
13296 a system-maintained file (often @file{/var/run/utmp} or
13297 @file{/etc/utmp}). If a file argument is given, @command{users} uses
13298 that file instead. A common choice is @file{/var/log/wtmp}.
13300 The only options are @option{--help} and @option{--version}. @xref{Common
13306 @node who invocation
13307 @section @command{who}: Print who is currently logged in
13310 @cindex printing current user information
13311 @cindex information, about current users
13313 @command{who} prints information about users who are currently logged on.
13317 @command{who} [@var{option}] [@var{file}] [am i]
13320 @cindex terminal lines, currently used
13322 @cindex remote hostname
13323 If given no non-option arguments, @command{who} prints the following
13324 information for each user currently logged on: login name, terminal
13325 line, login time, and remote hostname or X display.
13329 If given one non-option argument, @command{who} uses that instead of
13330 a default system-maintained file (often @file{/var/run/utmp} or
13331 @file{/etc/utmp}) as the name of the file containing the record of
13332 users logged on. @file{/var/log/wtmp} is commonly given as an argument
13333 to @command{who} to look at who has previously logged on.
13337 If given two non-option arguments, @command{who} prints only the entry
13338 for the user running it (determined from its standard input), preceded
13339 by the hostname. Traditionally, the two arguments given are @samp{am
13340 i}, as in @samp{who am i}.
13343 Time stamps are listed according to the time zone rules specified by
13344 the @env{TZ} environment variable, or by the system default rules if
13345 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
13346 with @env{TZ}, libc, The GNU C Library Reference Manual}.
13348 The program accepts the following options. Also see @ref{Common options}.
13356 Same as @samp{-b -d --login -p -r -t -T -u}.
13362 Print the date and time of last system boot.
13368 Print information corresponding to dead processes.
13374 Print a line of column headings.
13380 List only the entries that correspond to processes via which the
13381 system is waiting for a user to login. The user name is always @samp{LOGIN}.
13385 Attempt to canonicalize hostnames found in utmp through a DNS lookup. This
13386 is not the default because it can cause significant delays on systems with
13387 automatic dial-up internet access.
13391 Same as @samp{who am i}.
13397 List active processes spawned by init.
13403 Print only the login names and the number of users logged on.
13404 Overrides all other options.
13409 @opindex --runlevel
13410 Print the current (and maybe previous) run-level of the init process.
13414 Ignored; for compatibility with other versions of @command{who}.
13420 Print last system clock change.
13425 After the login time, print the number of hours and minutes that the
13426 user has been idle. @samp{.} means the user was active in the last minute.
13427 @samp{old} means the user has been idle for more than 24 hours.
13438 @opindex --writable
13439 @cindex message status
13440 @pindex write@r{, allowed}
13441 After each login name print a character indicating the user's message status:
13444 @samp{+} allowing @code{write} messages
13445 @samp{-} disallowing @code{write} messages
13446 @samp{?} cannot find terminal device
13454 @node System context
13455 @chapter System context
13457 @cindex system context
13458 @cindex context, system
13459 @cindex commands for system context
13461 This section describes commands that print or change system-wide
13465 * date invocation:: Print or set system date and time.
13466 * arch invocation:: Print machine hardware name.
13467 * nproc invocation:: Print the number of processors.
13468 * uname invocation:: Print system information.
13469 * hostname invocation:: Print or set system name.
13470 * hostid invocation:: Print numeric host identifier.
13471 * uptime invocation:: Print system uptime and load.
13474 @node date invocation
13475 @section @command{date}: Print or set system date and time
13478 @cindex time, printing or setting
13479 @cindex printing the current time
13484 date [@var{option}]@dots{} [+@var{format}]
13485 date [-u|--utc|--universal] @c this avoids a newline in the output
13486 [ MMDDhhmm[[CC]YY][.ss] ]
13490 Invoking @command{date} with no @var{format} argument is equivalent to invoking
13491 it with a default format that depends on the @env{LC_TIME} locale category.
13492 In the default C locale, this format is @samp{'+%a %b %e %H:%M:%S %Z %Y'},
13493 so the output looks like @samp{Thu Mar @ 3 13:47:51 PST 2005}.
13496 Normally, @command{date} uses the time zone rules indicated by the
13497 @env{TZ} environment variable, or the system default rules if @env{TZ}
13498 is not set. @xref{TZ Variable,, Specifying the Time Zone with
13499 @env{TZ}, libc, The GNU C Library Reference Manual}.
13501 @findex strftime @r{and @command{date}}
13502 @cindex time formats
13503 @cindex formatting times
13504 If given an argument that starts with a @samp{+}, @command{date} prints the
13505 current date and time (or the date and time specified by the
13506 @option{--date} option, see below) in the format defined by that argument,
13507 which is similar to that of the @code{strftime} function. Except for
13508 conversion specifiers, which start with @samp{%}, characters in the
13509 format string are printed unchanged. The conversion specifiers are
13515 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
13516 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
13517 * Literal conversion specifiers:: %[%nt]
13518 * Padding and other flags:: Pad with zeros, spaces, etc.
13519 * Setting the time:: Changing the system clock.
13520 * Options for date:: Instead of the current time.
13522 * Date input formats:: Specifying date strings.
13524 * Examples of date:: Examples.
13527 @node Time conversion specifiers
13528 @subsection Time conversion specifiers
13530 @cindex time conversion specifiers
13531 @cindex conversion specifiers, time
13533 @command{date} conversion specifiers related to times.
13537 hour (@samp{00}@dots{}@samp{23})
13539 hour (@samp{01}@dots{}@samp{12})
13541 hour (@samp{ 0}@dots{}@samp{23}).
13542 This is a @acronym{GNU} extension.
13544 hour (@samp{ 1}@dots{}@samp{12}).
13545 This is a @acronym{GNU} extension.
13547 minute (@samp{00}@dots{}@samp{59})
13549 nanoseconds (@samp{000000000}@dots{}@samp{999999999}).
13550 This is a @acronym{GNU} extension.
13552 locale's equivalent of either @samp{AM} or @samp{PM};
13553 blank in many locales.
13554 Noon is treated as @samp{PM} and midnight as @samp{AM}.
13556 like @samp{%p}, except lower case.
13557 This is a @acronym{GNU} extension.
13559 locale's 12-hour clock time (e.g., @samp{11:11:04 PM})
13561 24-hour hour and minute. Same as @samp{%H:%M}.
13562 This is a @acronym{GNU} extension.
13564 @cindex epoch, seconds since
13565 @cindex seconds since the epoch
13566 @cindex beginning of time
13567 seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC.
13568 Leap seconds are not counted unless leap second support is available.
13569 @xref{%s-examples}, for examples.
13570 This is a @acronym{GNU} extension.
13572 second (@samp{00}@dots{}@samp{60}).
13573 This may be @samp{60} if leap seconds are supported.
13575 24-hour hour, minute, and second. Same as @samp{%H:%M:%S}.
13577 locale's time representation (e.g., @samp{23:13:48})
13579 @w{@acronym{RFC} 2822/@acronym{ISO} 8601} style numeric time zone
13580 (e.g., @samp{-0600} or @samp{+0530}), or nothing if no
13581 time zone is determinable. This value reflects the numeric time zone
13582 appropriate for the current time, using the time zone rules specified
13583 by the @env{TZ} environment variable.
13584 The time (and optionally, the time zone rules) can be overridden
13585 by the @option{--date} option.
13586 This is a @acronym{GNU} extension.
13588 @w{@acronym{RFC} 3339/@acronym{ISO} 8601} style numeric time zone with
13589 @samp{:} (e.g., @samp{-06:00} or @samp{+05:30}), or nothing if no time
13590 zone is determinable.
13591 This is a @acronym{GNU} extension.
13593 Numeric time zone to the nearest second with @samp{:} (e.g.,
13594 @samp{-06:00:00} or @samp{+05:30:00}), or nothing if no time zone is
13596 This is a @acronym{GNU} extension.
13598 Numeric time zone with @samp{:} using the minimum necessary precision
13599 (e.g., @samp{-06}, @samp{+05:30}, or @samp{-04:56:02}), or nothing if
13600 no time zone is determinable.
13601 This is a @acronym{GNU} extension.
13603 alphabetic time zone abbreviation (e.g., @samp{EDT}), or nothing if no
13604 time zone is determinable. See @samp{%z} for how it is determined.
13608 @node Date conversion specifiers
13609 @subsection Date conversion specifiers
13611 @cindex date conversion specifiers
13612 @cindex conversion specifiers, date
13614 @command{date} conversion specifiers related to dates.
13618 locale's abbreviated weekday name (e.g., @samp{Sun})
13620 locale's full weekday name, variable length (e.g., @samp{Sunday})
13622 locale's abbreviated month name (e.g., @samp{Jan})
13624 locale's full month name, variable length (e.g., @samp{January})
13626 locale's date and time (e.g., @samp{Thu Mar @ 3 23:05:25 2005})
13628 century. This is like @samp{%Y}, except the last two digits are omitted.
13629 For example, it is @samp{20} if @samp{%Y} is @samp{2000},
13630 and is @samp{-0} if @samp{%Y} is @samp{-001}.
13631 It is normally at least two characters, but it may be more.
13633 day of month (e.g., @samp{01})
13635 date; same as @samp{%m/%d/%y}
13637 day of month, space padded; same as @samp{%_d}
13639 full date in @acronym{ISO} 8601 format; same as @samp{%Y-%m-%d}.
13640 This is a good choice for a date format, as it is standard and
13641 is easy to sort in the usual case where years are in the range
13643 This is a @acronym{GNU} extension.
13645 year corresponding to the @acronym{ISO} week number, but without the century
13646 (range @samp{00} through @samp{99}). This has the same format and value
13647 as @samp{%y}, except that if the @acronym{ISO} week number (see
13649 to the previous or next year, that year is used instead.
13650 This is a @acronym{GNU} extension.
13652 year corresponding to the @acronym{ISO} week number. This has the
13653 same format and value as @samp{%Y}, except that if the @acronym{ISO}
13655 @samp{%V}) belongs to the previous or next year, that year is used
13657 It is normally useful only if @samp{%V} is also used;
13658 for example, the format @samp{%G-%m-%d} is probably a mistake,
13659 since it combines the ISO week number year with the conventional month and day.
13660 This is a @acronym{GNU} extension.
13664 day of year (@samp{001}@dots{}@samp{366})
13666 month (@samp{01}@dots{}@samp{12})
13668 day of week (@samp{1}@dots{}@samp{7}) with @samp{1} corresponding to Monday
13670 week number of year, with Sunday as the first day of the week
13671 (@samp{00}@dots{}@samp{53}).
13672 Days in a new year preceding the first Sunday are in week zero.
13674 @acronym{ISO} week number, that is, the
13675 week number of year, with Monday as the first day of the week
13676 (@samp{01}@dots{}@samp{53}).
13677 If the week containing January 1 has four or more days in
13678 the new year, then it is considered week 1; otherwise, it is week 53 of
13679 the previous year, and the next week is week 1. (See the @acronym{ISO} 8601
13682 day of week (@samp{0}@dots{}@samp{6}) with 0 corresponding to Sunday
13684 week number of year, with Monday as first day of week
13685 (@samp{00}@dots{}@samp{53}).
13686 Days in a new year preceding the first Monday are in week zero.
13688 locale's date representation (e.g., @samp{12/31/99})
13690 last two digits of year (@samp{00}@dots{}@samp{99})
13692 year. This is normally at least four characters, but it may be more.
13693 Year @samp{0000} precedes year @samp{0001}, and year @samp{-001}
13694 precedes year @samp{0000}.
13698 @node Literal conversion specifiers
13699 @subsection Literal conversion specifiers
13701 @cindex literal conversion specifiers
13702 @cindex conversion specifiers, literal
13704 @command{date} conversion specifiers that produce literal strings.
13716 @node Padding and other flags
13717 @subsection Padding and other flags
13719 @cindex numeric field padding
13720 @cindex padding of numeric fields
13721 @cindex fields, padding numeric
13723 Unless otherwise specified, @command{date} normally pads numeric fields
13724 with zeros, so that, for
13725 example, numeric months are always output as two digits.
13726 Seconds since the epoch are not padded, though,
13727 since there is no natural width for them.
13729 As a @acronym{GNU} extension, @command{date} recognizes any of the
13730 following optional flags after the @samp{%}:
13734 (hyphen) Do not pad the field; useful if the output is intended for
13737 (underscore) Pad with spaces; useful if you need a fixed
13738 number of characters in the output, but zeros are too distracting.
13740 (zero) Pad with zeros even if the conversion specifier
13741 would normally pad with spaces.
13743 Use upper case characters if possible.
13745 Use opposite case characters if possible.
13746 A field that is normally upper case becomes lower case, and vice versa.
13750 Here are some examples of padding:
13753 date +%d/%m -d "Feb 1"
13755 date +%-d/%-m -d "Feb 1"
13757 date +%_d/%_m -d "Feb 1"
13761 As a @acronym{GNU} extension, you can specify the field width
13762 (after any flag, if present) as a decimal number. If the natural size of the
13763 output of the field has less than the specified number of characters,
13764 the result is written right adjusted and padded to the given
13765 size. For example, @samp{%9B} prints the right adjusted month name in
13766 a field of width 9.
13768 An optional modifier can follow the optional flag and width
13769 specification. The modifiers are:
13773 Use the locale's alternate representation for date and time. This
13774 modifier applies to the @samp{%c}, @samp{%C}, @samp{%x}, @samp{%X},
13775 @samp{%y} and @samp{%Y} conversion specifiers. In a Japanese locale, for
13776 example, @samp{%Ex} might yield a date format based on the Japanese
13780 Use the locale's alternate numeric symbols for numbers. This modifier
13781 applies only to numeric conversion specifiers.
13784 If the format supports the modifier but no alternate representation
13785 is available, it is ignored.
13788 @node Setting the time
13789 @subsection Setting the time
13791 @cindex setting the time
13792 @cindex time setting
13793 @cindex appropriate privileges
13795 If given an argument that does not start with @samp{+}, @command{date} sets
13796 the system clock to the date and time specified by that argument (as
13797 described below). You must have appropriate privileges to set the
13798 system clock. The @option{--date} and @option{--set} options may not be
13799 used with such an argument. The @option{--universal} option may be used
13800 with such an argument to indicate that the specified date and time are
13801 relative to Coordinated Universal Time rather than to the local time
13804 The argument must consist entirely of digits, which have the following
13817 first two digits of year (optional)
13819 last two digits of year (optional)
13824 The @option{--set} option also sets the system clock; see the next section.
13827 @node Options for date
13828 @subsection Options for @command{date}
13830 @cindex @command{date} options
13831 @cindex options for @command{date}
13833 The program accepts the following options. Also see @ref{Common options}.
13837 @item -d @var{datestr}
13838 @itemx --date=@var{datestr}
13841 @cindex parsing date strings
13842 @cindex date strings, parsing
13843 @cindex arbitrary date strings, parsing
13846 @opindex next @var{day}
13847 @opindex last @var{day}
13848 Display the date and time specified in @var{datestr} instead of the
13849 current date and time. @var{datestr} can be in almost any common
13850 format. It can contain month names, time zones, @samp{am} and @samp{pm},
13851 @samp{yesterday}, etc. For example, @option{--date="2004-02-27
13852 14:19:13.489392193 +0530"} specifies the instant of time that is
13853 489,392,193 nanoseconds after February 27, 2004 at 2:19:13 PM in a
13854 time zone that is 5 hours and 30 minutes east of @acronym{UTC}.@*
13855 Note: input currently must be in locale independent format. E.g., the
13856 LC_TIME=C below is needed to print back the correct date in many locales:
13858 date -d "$(LC_TIME=C date)"
13860 @xref{Date input formats}.
13862 @item -f @var{datefile}
13863 @itemx --file=@var{datefile}
13866 Parse each line in @var{datefile} as with @option{-d} and display the
13867 resulting date and time. If @var{datefile} is @samp{-}, use standard
13868 input. This is useful when you have many dates to process, because the
13869 system overhead of starting up the @command{date} executable many times can
13872 @item -r @var{file}
13873 @itemx --reference=@var{file}
13875 @opindex --reference
13876 Display the date and time of the last modification of @var{file},
13877 instead of the current date and time.
13884 @opindex --rfc-2822
13885 Display the date and time using the format @samp{%a, %d %b %Y %H:%M:%S
13886 %z}, evaluated in the C locale so abbreviations are always in English.
13890 Fri, 09 Sep 2005 13:51:39 -0700
13893 This format conforms to
13894 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc2822.txt, Internet
13895 @acronym{RFCs} 2822} and
13896 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc822.txt, 822}, the
13897 current and previous standards for Internet email.
13899 @item --rfc-3339=@var{timespec}
13900 @opindex --rfc-3339=@var{timespec}
13901 Display the date using a format specified by
13902 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc3339.txt, Internet
13903 @acronym{RFC} 3339}. This is a subset of the @acronym{ISO} 8601
13904 format, except that it also permits applications to use a space rather
13905 than a @samp{T} to separate dates from times. Unlike the other
13906 standard formats, @acronym{RFC} 3339 format is always suitable as
13907 input for the @option{--date} (@option{-d}) and @option{--file}
13908 (@option{-f}) options, regardless of the current locale.
13910 The argument @var{timespec} specifies how much of the time to include.
13911 It can be one of the following:
13915 Print just the full-date, e.g., @samp{2005-09-14}.
13916 This is equivalent to the format @samp{%Y-%m-%d}.
13919 Print the full-date and full-time separated by a space, e.g.,
13920 @samp{2005-09-14 00:56:06+05:30}. The output ends with a numeric
13921 time-offset; here the @samp{+05:30} means that local time is five
13922 hours and thirty minutes east of @acronym{UTC}. This is equivalent to
13923 the format @samp{%Y-%m-%d %H:%M:%S%:z}.
13926 Like @samp{seconds}, but also print nanoseconds, e.g.,
13927 @samp{2005-09-14 00:56:06.998458565+05:30}.
13928 This is equivalent to the format @samp{%Y-%m-%d %H:%M:%S.%N%:z}.
13932 @item -s @var{datestr}
13933 @itemx --set=@var{datestr}
13936 Set the date and time to @var{datestr}. See @option{-d} above.
13943 @opindex --universal
13944 @cindex Coordinated Universal Time
13946 @cindex Greenwich Mean Time
13949 Use Coordinated Universal Time (@acronym{UTC}) by operating as if the
13950 @env{TZ} environment variable were set to the string @samp{UTC0}.
13952 Universal Time is often called ``Greenwich Mean Time'' (@sc{gmt}) for
13953 historical reasons.
13957 @node Examples of date
13958 @subsection Examples of @command{date}
13960 @cindex examples of @command{date}
13962 Here are a few examples. Also see the documentation for the @option{-d}
13963 option in the previous section.
13968 To print the date of the day before yesterday:
13971 date --date='2 days ago'
13975 To print the date of the day three months and one day hence:
13978 date --date='3 months 1 day'
13982 To print the day of year of Christmas in the current year:
13985 date --date='25 Dec' +%j
13989 To print the current full month name and the day of the month:
13995 But this may not be what you want because for the first nine days of
13996 the month, the @samp{%d} expands to a zero-padded two-digit field,
13997 for example @samp{date -d 1may '+%B %d'} will print @samp{May 01}.
14000 To print a date without the leading zero for one-digit days
14001 of the month, you can use the (@acronym{GNU} extension)
14002 @samp{-} flag to suppress
14003 the padding altogether:
14006 date -d 1may '+%B %-d
14010 To print the current date and time in the format required by many
14011 non-@acronym{GNU} versions of @command{date} when setting the system clock:
14014 date +%m%d%H%M%Y.%S
14018 To set the system clock forward by two minutes:
14021 date --set='+2 minutes'
14025 To print the date in @acronym{RFC} 2822 format,
14026 use @samp{date --rfc-2822}. Here is some example output:
14029 Fri, 09 Sep 2005 13:51:39 -0700
14032 @anchor{%s-examples}
14034 To convert a date string to the number of seconds since the epoch
14035 (which is 1970-01-01 00:00:00 UTC), use the @option{--date} option with
14036 the @samp{%s} format. That can be useful in sorting and/or graphing
14037 and/or comparing data by date. The following command outputs the
14038 number of the seconds since the epoch for the time two minutes after the
14042 date --date='1970-01-01 00:02:00 +0000' +%s
14046 If you do not specify time zone information in the date string,
14047 @command{date} uses your computer's idea of the time zone when
14048 interpreting the string. For example, if your computer's time zone is
14049 that of Cambridge, Massachusetts, which was then 5 hours (i.e., 18,000
14050 seconds) behind UTC:
14053 # local time zone used
14054 date --date='1970-01-01 00:02:00' +%s
14059 If you're sorting or graphing dated data, your raw date values may be
14060 represented as seconds since the epoch. But few people can look at
14061 the date @samp{946684800} and casually note ``Oh, that's the first second
14062 of the year 2000 in Greenwich, England.''
14065 date --date='2000-01-01 UTC' +%s
14069 An alternative is to use the @option{--utc} (@option{-u}) option.
14070 Then you may omit @samp{UTC} from the date string. Although this
14071 produces the same result for @samp{%s} and many other format sequences,
14072 with a time zone offset different from zero, it would give a different
14073 result for zone-dependent formats like @samp{%z}.
14076 date -u --date=2000-01-01 +%s
14080 To convert such an unwieldy number of seconds back to
14081 a more readable form, use a command like this:
14084 # local time zone used
14085 date -d '1970-01-01 UTC 946684800 seconds' +"%Y-%m-%d %T %z"
14086 1999-12-31 19:00:00 -0500
14089 Or if you do not mind depending on the @samp{@@} feature present since
14090 coreutils 5.3.0, you could shorten this to:
14093 date -d @@946684800 +"%F %T %z"
14094 1999-12-31 19:00:00 -0500
14097 Often it is better to output UTC-relative date and time:
14100 date -u -d '1970-01-01 946684800 seconds' +"%Y-%m-%d %T %z"
14101 2000-01-01 00:00:00 +0000
14107 @node arch invocation
14108 @section @command{arch}: Print machine hardware name
14111 @cindex print machine hardware name
14112 @cindex system information, printing
14114 @command{arch} prints the machine hardware name,
14115 and is equivalent to @samp{uname -m}.
14119 arch [@var{option}]
14122 The program accepts the @ref{Common options} only.
14127 @node nproc invocation
14128 @section @command{nproc}: Print the number of available processors
14131 @cindex Print the number of processors
14132 @cindex system information, printing
14134 Print the number of processing units available to the current process,
14135 which may be less than the number of online processors.
14136 If this information is not accessible, then print the number of
14137 processors installed. If the @env{OMP_NUM_THREADS} environment variable is
14138 set, then it will determine the returned value. The result is guaranteed to be
14139 greater than zero. Synopsis:
14142 nproc [@var{option}]
14145 The program accepts the following options. Also see @ref{Common options}.
14151 Print the number of installed processors on the system, which may
14152 be greater than the number online or available to the current process.
14153 The @env{OMP_NUM_THREADS} environment variable is not honored in this case.
14155 @item --ignore=@var{number}
14157 If possible, exclude this @var{number} of processing units.
14164 @node uname invocation
14165 @section @command{uname}: Print system information
14168 @cindex print system information
14169 @cindex system information, printing
14171 @command{uname} prints information about the machine and operating system
14172 it is run on. If no options are given, @command{uname} acts as if the
14173 @option{-s} option were given. Synopsis:
14176 uname [@var{option}]@dots{}
14179 If multiple options or @option{-a} are given, the selected information is
14180 printed in this order:
14183 @var{kernel-name} @var{nodename} @var{kernel-release} @var{kernel-version}
14184 @var{machine} @var{processor} @var{hardware-platform} @var{operating-system}
14187 The information may contain internal spaces, so such output cannot be
14188 parsed reliably. In the following example, @var{release} is
14189 @samp{2.2.18ss.e820-bda652a #4 SMP Tue Jun 5 11:24:08 PDT 2001}:
14193 @result{} Linux dum 2.2.18 #4 SMP Tue Jun 5 11:24:08 PDT 2001 i686 unknown unknown GNU/Linux
14197 The program accepts the following options. Also see @ref{Common options}.
14205 Print all of the below information, except omit the processor type
14206 and the hardware platform name if they are unknown.
14209 @itemx --hardware-platform
14211 @opindex --hardware-platform
14212 @cindex implementation, hardware
14213 @cindex hardware platform
14214 @cindex platform, hardware
14215 Print the hardware platform name
14216 (sometimes called the hardware implementation).
14217 Print @samp{unknown} if the kernel does not make this information
14218 easily available, as is the case with Linux kernels.
14224 @cindex machine type
14225 @cindex hardware class
14226 @cindex hardware type
14227 Print the machine hardware name (sometimes called the hardware class
14233 @opindex --nodename
14236 @cindex network node name
14237 Print the network node hostname.
14242 @opindex --processor
14243 @cindex host processor type
14244 Print the processor type (sometimes called the instruction set
14245 architecture or ISA).
14246 Print @samp{unknown} if the kernel does not make this information
14247 easily available, as is the case with Linux kernels.
14250 @itemx --operating-system
14252 @opindex --operating-system
14253 @cindex operating system name
14254 Print the name of the operating system.
14257 @itemx --kernel-release
14259 @opindex --kernel-release
14260 @cindex kernel release
14261 @cindex release of kernel
14262 Print the kernel release.
14265 @itemx --kernel-name
14267 @opindex --kernel-name
14268 @cindex kernel name
14269 @cindex name of kernel
14270 Print the kernel name.
14271 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) calls this
14272 ``the implementation of the operating system'', because the
14273 @acronym{POSIX} specification itself has no notion of ``kernel''.
14274 The kernel name might be the same as the operating system name printed
14275 by the @option{-o} or @option{--operating-system} option, but it might
14276 differ. Some operating systems (e.g., FreeBSD, HP-UX) have the same
14277 name as their underlying kernels; others (e.g., GNU/Linux, Solaris)
14281 @itemx --kernel-version
14283 @opindex --kernel-version
14284 @cindex kernel version
14285 @cindex version of kernel
14286 Print the kernel version.
14293 @node hostname invocation
14294 @section @command{hostname}: Print or set system name
14297 @cindex setting the hostname
14298 @cindex printing the hostname
14299 @cindex system name, printing
14300 @cindex appropriate privileges
14302 With no arguments, @command{hostname} prints the name of the current host
14303 system. With one argument, it sets the current host name to the
14304 specified string. You must have appropriate privileges to set the host
14308 hostname [@var{name}]
14311 The only options are @option{--help} and @option{--version}. @xref{Common
14317 @node hostid invocation
14318 @section @command{hostid}: Print numeric host identifier
14321 @cindex printing the host identifier
14323 @command{hostid} prints the numeric identifier of the current host
14324 in hexadecimal. This command accepts no arguments.
14325 The only options are @option{--help} and @option{--version}.
14326 @xref{Common options}.
14328 For example, here's what it prints on one system I use:
14335 On that system, the 32-bit quantity happens to be closely
14336 related to the system's Internet address, but that isn't always
14341 @node uptime invocation
14342 @section @command{uptime}: Print system uptime and load
14345 @cindex printing the system uptime and load
14347 @command{uptime} prints the current time, the system's uptime, the
14348 number of logged-in users and the current load average.
14350 If an argument is specified, it is used as the file to be read
14351 to discover how many users are logged in. If no argument is
14352 specified, a system default is used (@command{uptime --help} indicates
14353 the default setting).
14355 The only options are @option{--help} and @option{--version}.
14356 @xref{Common options}.
14358 For example, here's what it prints right now on one system I use:
14362 14:07 up 3:35, 3 users, load average: 1.39, 1.15, 1.04
14365 The precise method of calculation of load average varies somewhat
14366 between systems. Some systems calculate it as the average number of
14367 runnable processes over the last 1, 5 and 15 minutes, but some systems
14368 also include processes in the uninterruptible sleep state (that is,
14369 those processes which are waiting for disk I/O). The Linux kernel
14370 includes uninterruptible processes.
14372 @node SELinux context
14373 @chapter SELinux context
14375 @cindex SELinux context
14376 @cindex SELinux, context
14377 @cindex commands for SELinux context
14379 This section describes commands for operations with SELinux
14383 * chcon invocation:: Change SELinux context of file
14384 * runcon invocation:: Run a command in specified SELinux context
14387 @node chcon invocation
14388 @section @command{chcon}: Change SELinux context of file
14391 @cindex changing security context
14392 @cindex change SELinux context
14394 @command{chcon} changes the SELinux security context of the selected files.
14398 chcon [@var{option}]@dots{} @var{context} @var{file}@dots{}
14399 chcon [@var{option}]@dots{} [-u @var{user}] [-r @var{role}] [-l @var{range}] [-t @var{type}] @var{file}@dots{}
14400 chcon [@var{option}]@dots{} --reference=@var{rfile} @var{file}@dots{}
14403 Change the SELinux security context of each @var{file} to @var{context}.
14404 With @option{--reference}, change the security context of each @var{file}
14405 to that of @var{rfile}.
14407 The program accepts the following options. Also see @ref{Common options}.
14412 @itemx --no-dereference
14414 @opindex --no-dereference
14415 @cindex no dereference
14416 Affect symbolic links instead of any referenced file.
14418 @item --reference=@var{rfile}
14419 @opindex --reference
14420 @cindex reference file
14421 Use @var{rfile}'s security context rather than specifying a @var{context} value.
14426 @opindex --recursive
14427 Operate on files and directories recursively.
14430 @xref{Traversing symlinks}.
14433 @xref{Traversing symlinks}.
14436 @xref{Traversing symlinks}.
14443 Output a diagnostic for every file processed.
14445 @item -u @var{user}
14446 @itemx --user=@var{user}
14449 Set user @var{user} in the target security context.
14451 @item -r @var{role}
14452 @itemx --role=@var{role}
14455 Set role @var{role} in the target security context.
14457 @item -t @var{type}
14458 @itemx --type=@var{type}
14461 Set type @var{type} in the target security context.
14463 @item -l @var{range}
14464 @itemx --range=@var{range}
14467 Set range @var{range} in the target security context.
14473 @node runcon invocation
14474 @section @command{runcon}: Run a command in specified SELinux context
14477 @cindex run with security context
14480 @command{runcon} runs file in specified SELinux security context.
14484 runcon @var{context} @var{command} [@var{args}]
14485 runcon [ -c ] [-u @var{user}] [-r @var{role}] [-t @var{type}] [-l @var{range}] @var{command} [@var{args}]
14488 Run @var{command} with completely-specified @var{context}, or with
14489 current or transitioned security context modified by one or more of @var{level},
14490 @var{role}, @var{type} and @var{user}.
14492 If none of @option{-c}, @option{-t}, @option{-u}, @option{-r}, or @option{-l}
14493 is specified, the first argument is used as the complete context.
14494 Any additional arguments after @var{command}
14495 are interpreted as arguments to the command.
14497 With neither @var{context} nor @var{command}, print the current security context.
14499 The program accepts the following options. Also see @ref{Common options}.
14507 Compute process transition context before modifying.
14509 @item -u @var{user}
14510 @itemx --user=@var{user}
14513 Set user @var{user} in the target security context.
14515 @item -r @var{role}
14516 @itemx --role=@var{role}
14519 Set role @var{role} in the target security context.
14521 @item -t @var{type}
14522 @itemx --type=@var{type}
14525 Set type @var{type} in the target security context.
14527 @item -l @var{range}
14528 @itemx --range=@var{range}
14531 Set range @var{range} in the target security context.
14535 @cindex exit status of @command{runcon}
14539 126 if @var{command} is found but cannot be invoked
14540 127 if @command{runcon} itself fails or if @var{command} cannot be found
14541 the exit status of @var{command} otherwise
14544 @node Modified command invocation
14545 @chapter Modified command invocation
14547 @cindex modified command invocation
14548 @cindex invocation of commands, modified
14549 @cindex commands for invoking other commands
14551 This section describes commands that run other commands in some context
14552 different than the current one: a modified environment, as a different
14556 * chroot invocation:: Modify the root directory.
14557 * env invocation:: Modify environment variables.
14558 * nice invocation:: Modify niceness.
14559 * nohup invocation:: Immunize to hangups.
14560 * stdbuf invocation:: Modify buffering of standard streams.
14561 * su invocation:: Modify user and group ID.
14562 * timeout invocation:: Run with time limit.
14566 @node chroot invocation
14567 @section @command{chroot}: Run a command with a different root directory
14570 @cindex running a program in a specified root directory
14571 @cindex root directory, running a program in a specified
14573 @command{chroot} runs a command with a specified root directory.
14574 On many systems, only the super-user can do this.@footnote{However,
14575 some systems (e.g., FreeBSD) can be configured to allow certain regular
14576 users to use the @code{chroot} system call, and hence to run this program.
14577 Also, on Cygwin, anyone can run the @command{chroot} command, because the
14578 underlying function is non-privileged due to lack of support in MS-Windows.}
14582 chroot @var{option} @var{newroot} [@var{command} [@var{args}]@dots{}]
14583 chroot @var{option}
14586 Ordinarily, file names are looked up starting at the root of the
14587 directory structure, i.e., @file{/}. @command{chroot} changes the root to
14588 the directory @var{newroot} (which must exist) and then runs
14589 @var{command} with optional @var{args}. If @var{command} is not
14590 specified, the default is the value of the @env{SHELL} environment
14591 variable or @command{/bin/sh} if not set, invoked with the @option{-i} option.
14592 @var{command} must not be a special built-in utility
14593 (@pxref{Special built-in utilities}).
14595 The program accepts the following options. Also see @ref{Common options}.
14596 Options must precede operands.
14600 @itemx --userspec=@var{user}[:@var{group}]
14601 @opindex --userspec
14602 By default, @var{command} is run with the same credentials
14603 as the invoking process.
14604 Use this option to run it as a different @var{user} and/or with a
14605 different primary @var{group}.
14607 @itemx --groups=@var{groups}
14609 Use this option to specify the supplementary @var{groups} to be
14610 used by the new process.
14611 The items in the list (names or numeric IDs) must be separated by commas.
14615 Here are a few tips to help avoid common problems in using chroot.
14616 To start with a simple example, make @var{command} refer to a statically
14617 linked binary. If you were to use a dynamically linked executable, then
14618 you'd have to arrange to have the shared libraries in the right place under
14619 your new root directory.
14621 For example, if you create a statically linked @command{ls} executable,
14622 and put it in @file{/tmp/empty}, you can run this command as root:
14625 $ chroot /tmp/empty /ls -Rl /
14628 Then you'll see output like this:
14633 -rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls
14636 If you want to use a dynamically linked executable, say @command{bash},
14637 then first run @samp{ldd bash} to see what shared objects it needs.
14638 Then, in addition to copying the actual binary, also copy the listed
14639 files to the required positions under your intended new root directory.
14640 Finally, if the executable requires any other files (e.g., data, state,
14641 device files), copy them into place, too.
14643 @cindex exit status of @command{chroot}
14647 125 if @command{chroot} itself fails
14648 126 if @var{command} is found but cannot be invoked
14649 127 if @var{command} cannot be found
14650 the exit status of @var{command} otherwise
14654 @node env invocation
14655 @section @command{env}: Run a command in a modified environment
14658 @cindex environment, running a program in a modified
14659 @cindex modified environment, running a program in a
14660 @cindex running a program in a modified environment
14662 @command{env} runs a command with a modified environment. Synopses:
14665 env [@var{option}]@dots{} [@var{name}=@var{value}]@dots{} @c
14666 [@var{command} [@var{args}]@dots{}]
14670 Operands of the form @samp{@var{variable}=@var{value}} set
14671 the environment variable @var{variable} to value @var{value}.
14672 @var{value} may be empty (@samp{@var{variable}=}). Setting a variable
14673 to an empty value is different from unsetting it.
14674 These operands are evaluated left-to-right, so if two operands
14675 mention the same variable the earlier is ignored.
14677 Environment variable names can be empty, and can contain any
14678 characters other than @samp{=} and @acronym{ASCII} @sc{nul}.
14679 However, it is wise to limit yourself to names that
14680 consist solely of underscores, digits, and @acronym{ASCII} letters,
14681 and that begin with a non-digit, as applications like the shell do not
14682 work well with other names.
14685 The first operand that does not contain the character @samp{=}
14686 specifies the program to invoke; it is
14687 searched for according to the @env{PATH} environment variable. Any
14688 remaining arguments are passed as arguments to that program.
14689 The program should not be a special built-in utility
14690 (@pxref{Special built-in utilities}).
14692 Modifications to @env{PATH} take effect prior to searching for
14693 @var{command}. Use caution when reducing @env{PATH}; behavior is
14694 not portable when @env{PATH} is undefined or omits key directories
14695 such as @file{/bin}.
14697 In the rare case that a utility contains a @samp{=} in the name, the
14698 only way to disambiguate it from a variable assignment is to use an
14699 intermediate command for @var{command}, and pass the problematic
14700 program name via @var{args}. For example, if @file{./prog=} is an
14701 executable in the current @env{PATH}:
14704 env prog= true # runs 'true', with prog= in environment
14705 env ./prog= true # runs 'true', with ./prog= in environment
14706 env -- prog= true # runs 'true', with prog= in environment
14707 env sh -c '\prog= true' # runs 'prog=' with argument 'true'
14708 env sh -c 'exec "$@@"' sh prog= true # also runs 'prog='
14711 @cindex environment, printing
14713 If no command name is specified following the environment
14714 specifications, the resulting environment is printed. This is like
14715 specifying the @command{printenv} program.
14717 For some examples, suppose the environment passed to @command{env}
14718 contains @samp{LOGNAME=rms}, @samp{EDITOR=emacs}, and
14719 @samp{PATH=.:/gnubin:/hacks}:
14724 Output the current environment.
14726 $ env | LC_ALL=C sort
14729 PATH=.:/gnubin:/hacks
14733 Run @command{foo} with a reduced environment, preserving only the
14734 original @env{PATH} to avoid problems in locating @command{foo}.
14736 env - PATH="$PATH" foo
14740 Run @command{foo} with the environment containing @samp{LOGNAME=rms},
14741 @samp{EDITOR=emacs}, and @samp{PATH=.:/gnubin:/hacks}, and guarantees
14742 that @command{foo} was found in the file system rather than as a shell
14749 Run @command{nemacs} with the environment containing @samp{LOGNAME=foo},
14750 @samp{EDITOR=emacs}, @samp{PATH=.:/gnubin:/hacks}, and
14751 @samp{DISPLAY=gnu:0}.
14753 env DISPLAY=gnu:0 LOGNAME=foo nemacs
14757 Attempt to run the program @command{/energy/--} (as that is the only
14758 possible path search result); if the command exists, the environment
14759 will contain @samp{LOGNAME=rms} and @samp{PATH=/energy}, and the
14760 arguments will be @samp{e=mc2}, @samp{bar}, and @samp{baz}.
14762 env -u EDITOR PATH=/energy -- e=mc2 bar baz
14768 The program accepts the following options. Also see @ref{Common options}.
14769 Options must precede operands.
14775 @item -u @var{name}
14776 @itemx --unset=@var{name}
14779 Remove variable @var{name} from the environment, if it was in the
14784 @itemx --ignore-environment
14787 @opindex --ignore-environment
14788 Start with an empty environment, ignoring the inherited environment.
14792 @cindex exit status of @command{env}
14796 0 if no @var{command} is specified and the environment is output
14797 125 if @command{env} itself fails
14798 126 if @var{command} is found but cannot be invoked
14799 127 if @var{command} cannot be found
14800 the exit status of @var{command} otherwise
14804 @node nice invocation
14805 @section @command{nice}: Run a command with modified niceness
14809 @cindex scheduling, affecting
14810 @cindex appropriate privileges
14812 @command{nice} prints or modifies a process's @dfn{niceness},
14813 a parameter that affects whether the process is scheduled favorably.
14817 nice [@var{option}]@dots{} [@var{command} [@var{arg}]@dots{}]
14820 If no arguments are given, @command{nice} prints the current niceness.
14821 Otherwise, @command{nice} runs the given @var{command} with its
14822 niceness adjusted. By default, its niceness is incremented by 10.
14824 Niceness values range at least from @minus{}20 (process has high priority
14825 and gets more resources, thus slowing down other processes) through 19
14826 (process has lower priority and runs slowly itself, but has less impact
14827 on the speed of other running processes). Some systems
14828 may have a wider range of nicenesses; conversely, other systems may
14829 enforce more restrictive limits. An attempt to set the niceness
14830 outside the supported range is treated as an attempt to use the
14831 minimum or maximum supported value.
14833 A niceness should not be confused with a scheduling priority, which
14834 lets applications determine the order in which threads are scheduled
14835 to run. Unlike a priority, a niceness is merely advice to the
14836 scheduler, which the scheduler is free to ignore. Also, as a point of
14837 terminology, @acronym{POSIX} defines the behavior of @command{nice} in
14838 terms of a @dfn{nice value}, which is the nonnegative difference
14839 between a niceness and the minimum niceness. Though @command{nice}
14840 conforms to @acronym{POSIX}, its documentation and diagnostics use the
14841 term ``niceness'' for compatibility with historical practice.
14843 @var{command} must not be a special built-in utility (@pxref{Special
14844 built-in utilities}).
14846 @mayConflictWithShellBuiltIn{nice}
14848 The program accepts the following option. Also see @ref{Common options}.
14849 Options must precede operands.
14852 @item -n @var{adjustment}
14853 @itemx --adjustment=@var{adjustment}
14855 @opindex --adjustment
14856 Add @var{adjustment} instead of 10 to the command's niceness. If
14857 @var{adjustment} is negative and you lack appropriate privileges,
14858 @command{nice} issues a warning but otherwise acts as if you specified
14861 For compatibility @command{nice} also supports an obsolete
14862 option syntax @option{-@var{adjustment}}. New scripts should use
14863 @option{-n @var{adjustment}} instead.
14867 @cindex exit status of @command{nice}
14871 0 if no @var{command} is specified and the niceness is output
14872 125 if @command{nice} itself fails
14873 126 if @var{command} is found but cannot be invoked
14874 127 if @var{command} cannot be found
14875 the exit status of @var{command} otherwise
14878 It is sometimes useful to run a non-interactive program with reduced niceness.
14881 $ nice factor 4611686018427387903
14884 Since @command{nice} prints the current niceness,
14885 you can invoke it through itself to demonstrate how it works.
14887 The default behavior is to increase the niceness by @samp{10}:
14898 The @var{adjustment} is relative to the current niceness. In the
14899 next example, the first @command{nice} invocation runs the second one
14900 with niceness 10, and it in turn runs the final one with a niceness
14904 $ nice nice -n 3 nice
14908 Specifying a niceness larger than the supported range
14909 is the same as specifying the maximum supported value:
14912 $ nice -n 10000000000 nice
14916 Only a privileged user may run a process with lower niceness:
14920 nice: cannot set niceness: Permission denied
14922 $ sudo nice -n -1 nice
14927 @node nohup invocation
14928 @section @command{nohup}: Run a command immune to hangups
14931 @cindex hangups, immunity to
14932 @cindex immunity to hangups
14933 @cindex logging out and continuing to run
14936 @command{nohup} runs the given @var{command} with hangup signals ignored,
14937 so that the command can continue running in the background after you log
14941 nohup @var{command} [@var{arg}]@dots{}
14944 If standard input is a terminal, it is redirected from
14945 @file{/dev/null} so that terminal sessions do not mistakenly consider
14946 the terminal to be used by the command. This is a @acronym{GNU}
14947 extension; programs intended to be portable to non-@acronym{GNU} hosts
14948 should use @samp{nohup @var{command} [@var{arg}]@dots{} </dev/null}
14952 If standard output is a terminal, the command's standard output is appended
14953 to the file @file{nohup.out}; if that cannot be written to, it is appended
14954 to the file @file{$HOME/nohup.out}; and if that cannot be written to, the
14955 command is not run.
14956 Any @file{nohup.out} or @file{$HOME/nohup.out} file created by
14957 @command{nohup} is made readable and writable only to the user,
14958 regardless of the current umask settings.
14960 If standard error is a terminal, it is normally redirected to the same file
14961 descriptor as the (possibly-redirected) standard output.
14962 However, if standard output is closed, standard error terminal output
14963 is instead appended to the file @file{nohup.out} or
14964 @file{$HOME/nohup.out} as above.
14966 To capture the command's output to a file other than @file{nohup.out}
14967 you can redirect it. For example, to capture the output of
14971 nohup make > make.log
14974 @command{nohup} does not automatically put the command it runs in the
14975 background; you must do that explicitly, by ending the command line
14976 with an @samp{&}. Also, @command{nohup} does not alter the
14977 niceness of @var{command}; use @command{nice} for that,
14978 e.g., @samp{nohup nice @var{command}}.
14980 @var{command} must not be a special built-in utility (@pxref{Special
14981 built-in utilities}).
14983 The only options are @option{--help} and @option{--version}. @xref{Common
14984 options}. Options must precede operands.
14986 @cindex exit status of @command{nohup}
14990 125 if @command{nohup} itself fails, and @env{POSIXLY_CORRECT} is not set
14991 126 if @var{command} is found but cannot be invoked
14992 127 if @var{command} cannot be found
14993 the exit status of @var{command} otherwise
14996 If @env{POSIXLY_CORRECT} is set, internal failures give status 127
15000 @node stdbuf invocation
15001 @section @command{stdbuf}: Run a command with modified I/O stream buffering
15004 @cindex standard streams, buffering
15005 @cindex line buffered
15007 @command{stdbuf} allows one to modify the buffering operations of the
15008 three standard I/O streams associated with a program. Synopsis:
15011 stdbuf @var{option}@dots{} @var{command}
15014 Any additional @var{arg}s are passed as additional arguments to the
15017 The program accepts the following options. Also see @ref{Common options}.
15021 @item -i @var{mode}
15022 @itemx --input=@var{mode}
15025 Adjust the standard input stream buffering.
15027 @item -o @var{mode}
15028 @itemx --output=@var{mode}
15031 Adjust the standard output stream buffering.
15033 @item -e @var{mode}
15034 @itemx --error=@var{mode}
15037 Adjust the standard error stream buffering.
15041 The @var{mode} can be specified as follows:
15046 Set the stream to line buffered mode.
15047 In this mode data is coalesced until a newline is output or
15048 input is read from any stream attached to a terminal device.
15049 This option is invalid with standard input.
15052 Disable buffering of the selected stream.
15053 In this mode data is output immediately and only the
15054 amount of data requested is read from input.
15057 Specify the size of the buffer to use in fully buffered mode.
15058 @multiplierSuffixesNoBlocks{size}
15062 NOTE: If @var{command} adjusts the buffering of its standard streams
15063 (@command{tee} does for e.g.) then that will override corresponding settings
15064 changed by @command{stdbuf}. Also some filters (like @command{dd} and
15065 @command{cat} etc.) don't use streams for I/O, and are thus unaffected
15066 by @command{stdbuf} settings.
15068 @cindex exit status of @command{stdbuf}
15072 125 if @command{stdbuf} itself fails
15073 126 if @var{command} is found but cannot be invoked
15074 127 if @var{command} cannot be found
15075 the exit status of @var{command} otherwise
15079 @node su invocation
15080 @section @command{su}: Run a command with substitute user and group ID
15083 @cindex substitute user and group IDs
15084 @cindex user ID, switching
15085 @cindex super-user, becoming
15086 @cindex root, becoming
15088 @command{su} allows one user to temporarily become another user. It runs a
15089 command (often an interactive shell) with the real and effective user
15090 ID, group ID, and supplemental groups of a given @var{user}. Synopsis:
15093 su [@var{option}]@dots{} [@var{user} [@var{arg}]@dots{}]
15096 @cindex passwd entry, and @command{su} shell
15098 @flindex /etc/passwd
15099 If no @var{user} is given, the default is @code{root}, the super-user.
15100 The shell to use is taken from @var{user}'s @code{passwd} entry, or
15101 @file{/bin/sh} if none is specified there. If @var{user} has a
15102 password, @command{su} prompts for the password unless run by a user with
15103 effective user ID of zero (the super-user).
15109 @cindex login shell
15110 By default, @command{su} does not change the current directory.
15111 It sets the environment variables @env{HOME} and @env{SHELL}
15112 from the password entry for @var{user}, and if @var{user} is not
15113 the super-user, sets @env{USER} and @env{LOGNAME} to @var{user}.
15114 By default, the shell is not a login shell.
15116 Any additional @var{arg}s are passed as additional arguments to the
15119 @cindex @option{-su}
15120 GNU @command{su} does not treat @file{/bin/sh} or any other shells specially
15121 (e.g., by setting @code{argv[0]} to @option{-su}, passing @option{-c} only
15122 to certain shells, etc.).
15125 @command{su} can optionally be compiled to use @code{syslog} to report
15126 failed, and optionally successful, @command{su} attempts. (If the system
15127 supports @code{syslog}.) However, GNU @command{su} does not check if the
15128 user is a member of the @code{wheel} group; see below.
15130 The program accepts the following options. Also see @ref{Common options}.
15133 @item -c @var{command}
15134 @itemx --command=@var{command}
15137 Pass @var{command}, a single command line to run, to the shell with
15138 a @option{-c} option instead of starting an interactive shell.
15145 @cindex file name pattern expansion, disabled
15146 @cindex globbing, disabled
15147 Pass the @option{-f} option to the shell. This probably only makes sense
15148 if the shell run is @command{csh} or @command{tcsh}, for which the @option{-f}
15149 option prevents reading the startup file (@file{.cshrc}). With
15150 Bourne-like shells, the @option{-f} option disables file name pattern
15151 expansion (globbing), which is not likely to be useful.
15159 @c other variables already indexed above
15162 @cindex login shell, creating
15163 Make the shell a login shell. This means the following. Unset all
15164 environment variables except @env{TERM}, @env{HOME}, and @env{SHELL}
15165 (which are set as described above), and @env{USER} and @env{LOGNAME}
15166 (which are set, even for the super-user, as described above), and set
15167 @env{PATH} to a compiled-in default value. Change to @var{user}'s home
15168 directory. Prepend @samp{-} to the shell's name, intended to make it
15169 read its login startup file(s).
15173 @itemx --preserve-environment
15176 @opindex --preserve-environment
15177 @cindex environment, preserving
15178 @flindex /etc/shells
15179 @cindex restricted shell
15180 Do not change the environment variables @env{HOME}, @env{USER},
15181 @env{LOGNAME}, or @env{SHELL}. Run the shell given in the environment
15182 variable @env{SHELL} instead of the shell from @var{user}'s passwd
15183 entry, unless the user running @command{su} is not the super-user and
15184 @var{user}'s shell is restricted. A @dfn{restricted shell} is one that
15185 is not listed in the file @file{/etc/shells}, or in a compiled-in list
15186 if that file does not exist. Parts of what this option does can be
15187 overridden by @option{--login} and @option{--shell}.
15189 @item -s @var{shell}
15190 @itemx --shell=@var{shell}
15193 Run @var{shell} instead of the shell from @var{user}'s passwd entry,
15194 unless the user running @command{su} is not the super-user and @var{user}'s
15195 shell is restricted (see @option{-m} just above).
15199 @cindex exit status of @command{su}
15203 125 if @command{su} itself fails
15204 126 if subshell is found but cannot be invoked
15205 127 if subshell cannot be found
15206 the exit status of the subshell otherwise
15209 @cindex wheel group, not supported
15210 @cindex group wheel, not supported
15212 @subsection Why GNU @command{su} does not support the @samp{wheel} group
15214 (This section is by Richard Stallman.)
15218 Sometimes a few of the users try to hold total power over all the
15219 rest. For example, in 1984, a few users at the MIT AI lab decided to
15220 seize power by changing the operator password on the Twenex system and
15221 keeping it secret from everyone else. (I was able to thwart this coup
15222 and give power back to the users by patching the kernel, but I
15223 wouldn't know how to do that in Unix.)
15225 However, occasionally the rulers do tell someone. Under the usual
15226 @command{su} mechanism, once someone learns the root password who
15227 sympathizes with the ordinary users, he or she can tell the rest. The
15228 ``wheel group'' feature would make this impossible, and thus cement the
15229 power of the rulers.
15231 I'm on the side of the masses, not that of the rulers. If you are
15232 used to supporting the bosses and sysadmins in whatever they do, you
15233 might find this idea strange at first.
15236 @node timeout invocation
15237 @section @command{timeout}: Run a command with a time limit
15241 @cindex run commands with bounded time
15243 @command{timeout} runs the given @var{command} and kills it if it is
15244 still running after the specified time interval. Synopsis:
15247 timeout [@var{option}] @var{duration} @var{command} [@var{arg}]@dots{}
15250 @var{command} must not be a special built-in utility (@pxref{Special
15251 built-in utilities}).
15253 The program accepts the following options. Also see @ref{Common options}.
15254 Options must precede operands.
15257 @item -k @var{duration}
15258 @itemx --kill-after=@var{duration}
15260 @opindex --kill-after
15261 Ensure the monitored @var{command} is killed by also sending a @samp{KILL}
15262 signal, after the specified @var{duration}. Without this option, if the
15263 selected signal proves not to be fatal, @command{timeout} does not kill
15266 @item -s @var{signal}
15267 @itemx --signal=@var{signal}
15270 Send this @var{signal} to @var{command} on timeout, rather than the
15271 default @samp{TERM} signal. @var{signal} may be a name like @samp{HUP}
15272 or a number. Also see @xref{Signal specifications}.
15276 @var{duration} is an integer followed by an optional unit:
15278 @samp{s} for seconds (the default)
15279 @samp{m} for minutes
15283 A duration of 0 disables the associated timeout.
15285 @cindex exit status of @command{timeout}
15289 124 if @var{command} times out
15290 125 if @command{timeout} itself fails
15291 126 if @var{command} is found but cannot be invoked
15292 127 if @var{command} cannot be found
15293 the exit status of @var{command} otherwise
15297 @node Process control
15298 @chapter Process control
15300 @cindex processes, commands for controlling
15301 @cindex commands for controlling processes
15304 * kill invocation:: Sending a signal to processes.
15308 @node kill invocation
15309 @section @command{kill}: Send a signal to processes
15312 @cindex send a signal to processes
15314 The @command{kill} command sends a signal to processes, causing them
15315 to terminate or otherwise act upon receiving the signal in some way.
15316 Alternatively, it lists information about signals. Synopses:
15319 kill [-s @var{signal} | --signal @var{signal} | -@var{signal}] @var{pid}@dots{}
15320 kill [-l | --list | -t | --table] [@var{signal}]@dots{}
15323 @mayConflictWithShellBuiltIn{kill}
15325 The first form of the @command{kill} command sends a signal to all
15326 @var{pid} arguments. The default signal to send if none is specified
15327 is @samp{TERM}. The special signal number @samp{0} does not denote a
15328 valid signal, but can be used to test whether the @var{pid} arguments
15329 specify processes to which a signal could be sent.
15331 If @var{pid} is positive, the signal is sent to the process with the
15332 process ID @var{pid}. If @var{pid} is zero, the signal is sent to all
15333 processes in the process group of the current process. If @var{pid}
15334 is @minus{}1, the signal is sent to all processes for which the user has
15335 permission to send a signal. If @var{pid} is less than @minus{}1, the signal
15336 is sent to all processes in the process group that equals the absolute
15337 value of @var{pid}.
15339 If @var{pid} is not positive, a system-dependent set of system
15340 processes is excluded from the list of processes to which the signal
15343 If a negative @var{pid} argument is desired as the first one, it
15344 should be preceded by @option{--}. However, as a common extension to
15345 @acronym{POSIX}, @option{--} is not required with @samp{kill
15346 -@var{signal} -@var{pid}}. The following commands are equivalent:
15355 The first form of the @command{kill} command succeeds if every @var{pid}
15356 argument specifies at least one process that the signal was sent to.
15358 The second form of the @command{kill} command lists signal information.
15359 Either the @option{-l} or @option{--list} option, or the @option{-t}
15360 or @option{--table} option must be specified. Without any
15361 @var{signal} argument, all supported signals are listed. The output
15362 of @option{-l} or @option{--list} is a list of the signal names, one
15363 per line; if @var{signal} is already a name, the signal number is
15364 printed instead. The output of @option{-t} or @option{--table} is a
15365 table of signal numbers, names, and descriptions. This form of the
15366 @command{kill} command succeeds if all @var{signal} arguments are valid
15367 and if there is no output error.
15369 The @command{kill} command also supports the @option{--help} and
15370 @option{--version} options. @xref{Common options}.
15372 A @var{signal} may be a signal name like @samp{HUP}, or a signal
15373 number like @samp{1}, or an exit status of a process terminated by the
15374 signal. A signal name can be given in canonical form or prefixed by
15375 @samp{SIG}. The case of the letters is ignored, except for the
15376 @option{-@var{signal}} option which must use upper case to avoid
15377 ambiguity with lower case option letters. For a list of supported
15378 signal names and numbers see @xref{Signal specifications}.
15383 @cindex delaying commands
15384 @cindex commands for delaying
15386 @c Perhaps @command{wait} or other commands should be described here also?
15389 * sleep invocation:: Delay for a specified time.
15393 @node sleep invocation
15394 @section @command{sleep}: Delay for a specified time
15397 @cindex delay for a specified time
15399 @command{sleep} pauses for an amount of time specified by the sum of
15400 the values of the command line arguments.
15404 sleep @var{number}[smhd]@dots{}
15408 Each argument is a number followed by an optional unit; the default
15409 is seconds. The units are:
15422 Historical implementations of @command{sleep} have required that
15423 @var{number} be an integer, and only accepted a single argument
15424 without a suffix. However, GNU @command{sleep} accepts
15425 arbitrary floating point numbers (using a period before any fractional
15428 The only options are @option{--help} and @option{--version}. @xref{Common
15431 @c sleep is a shell built-in at least with Solaris 11's /bin/sh
15432 @mayConflictWithShellBuiltIn{sleep}
15437 @node Numeric operations
15438 @chapter Numeric operations
15440 @cindex numeric operations
15441 These programs do numerically-related operations.
15444 * factor invocation:: Show factors of numbers.
15445 * seq invocation:: Print sequences of numbers.
15449 @node factor invocation
15450 @section @command{factor}: Print prime factors
15453 @cindex prime factors
15455 @command{factor} prints prime factors. Synopses:
15458 factor [@var{number}]@dots{}
15459 factor @var{option}
15462 If no @var{number} is specified on the command line, @command{factor} reads
15463 numbers from standard input, delimited by newlines, tabs, or spaces.
15465 The @command{factor} command supports only a small number of options:
15469 Print a short help on standard output, then exit without further
15473 Print the program version on standard output, then exit without further
15477 Factoring the product of the eighth and ninth Mersenne primes
15478 takes about 30 milliseconds of CPU time on a 2.2 GHz Athlon.
15481 M8=`echo 2^31-1|bc` ; M9=`echo 2^61-1|bc`
15482 /usr/bin/time -f '%U' factor $(echo "$M8 * $M9" | bc)
15483 4951760154835678088235319297: 2147483647 2305843009213693951
15487 Similarly, factoring the eighth Fermat number @math{2^{256}+1} takes
15488 about 20 seconds on the same machine.
15490 Factoring large numbers is, in general, hard. The Pollard Rho
15491 algorithm used by @command{factor} is particularly effective for
15492 numbers with relatively small factors. If you wish to factor large
15493 numbers which do not have small factors (for example, numbers which
15494 are the product of two large primes), other methods are far better.
15496 If @command{factor} is built without using GNU MP, only
15497 single-precision arithmetic is available, and so large numbers
15498 (typically @math{2^{64}} and above) will not be supported. The single-precision
15499 code uses an algorithm which is designed for factoring smaller
15505 @node seq invocation
15506 @section @command{seq}: Print numeric sequences
15509 @cindex numeric sequences
15510 @cindex sequence of numbers
15512 @command{seq} prints a sequence of numbers to standard output. Synopses:
15515 seq [@var{option}]@dots{} @var{last}
15516 seq [@var{option}]@dots{} @var{first} @var{last}
15517 seq [@var{option}]@dots{} @var{first} @var{increment} @var{last}
15520 @command{seq} prints the numbers from @var{first} to @var{last} by
15521 @var{increment}. By default, each number is printed on a separate line.
15522 When @var{increment} is not specified, it defaults to @samp{1},
15523 even when @var{first} is larger than @var{last}.
15524 @var{first} also defaults to @samp{1}. So @code{seq 1} prints
15525 @samp{1}, but @code{seq 0} and @code{seq 10 5} produce no output.
15526 Floating-point numbers
15527 may be specified (using a period before any fractional digits).
15529 The program accepts the following options. Also see @ref{Common options}.
15530 Options must precede operands.
15533 @item -f @var{format}
15534 @itemx --format=@var{format}
15535 @opindex -f @var{format}
15536 @opindex --format=@var{format}
15537 @cindex formatting of numbers in @command{seq}
15538 Print all numbers using @var{format}.
15539 @var{format} must contain exactly one of the @samp{printf}-style
15540 floating point conversion specifications @samp{%a}, @samp{%e},
15541 @samp{%f}, @samp{%g}, @samp{%A}, @samp{%E}, @samp{%F}, @samp{%G}.
15542 The @samp{%} may be followed by zero or more flags taken from the set
15543 @samp{-+#0 '}, then an optional width containing one or more digits,
15544 then an optional precision consisting of a @samp{.} followed by zero
15545 or more digits. @var{format} may also contain any number of @samp{%%}
15546 conversion specifications. All conversion specifications have the
15547 same meaning as with @samp{printf}.
15549 The default format is derived from @var{first}, @var{step}, and
15550 @var{last}. If these all use a fixed point decimal representation,
15551 the default format is @samp{%.@var{p}f}, where @var{p} is the minimum
15552 precision that can represent the output numbers exactly. Otherwise,
15553 the default format is @samp{%g}.
15555 @item -s @var{string}
15556 @itemx --separator=@var{string}
15557 @cindex separator for numbers in @command{seq}
15558 Separate numbers with @var{string}; default is a newline.
15559 The output always terminates with a newline.
15562 @itemx --equal-width
15563 Print all numbers with the same width, by padding with leading zeros.
15564 @var{first}, @var{step}, and @var{last} should all use a fixed point
15565 decimal representation.
15566 (To have other kinds of padding, use @option{--format}).
15570 You can get finer-grained control over output with @option{-f}:
15573 $ seq -f '(%9.2E)' -9e5 1.1e6 1.3e6
15579 If you want hexadecimal integer output, you can use @command{printf}
15580 to perform the conversion:
15583 $ printf '%x\n' `seq 1048575 1024 1050623`
15589 For very long lists of numbers, use xargs to avoid
15590 system limitations on the length of an argument list:
15593 $ seq 1000000 | xargs printf '%x\n' | tail -n 3
15599 To generate octal output, use the printf @code{%o} format instead
15602 On most systems, seq can produce whole-number output for values up to
15603 at least @math{2^{53}}. Larger integers are approximated. The details
15604 differ depending on your floating-point implementation, but a common
15605 case is that @command{seq} works with integers through @math{2^{64}},
15606 and larger integers may not be numerically correct:
15609 $ seq 18446744073709551616 1 18446744073709551618
15610 18446744073709551616
15611 18446744073709551616
15612 18446744073709551618
15615 Be careful when using @command{seq} with outlandish values: otherwise
15616 you may see surprising results, as @command{seq} uses floating point
15617 internally. For example, on the x86 platform, where the internal
15618 representation uses a 64-bit fraction, the command:
15621 seq 1 0.0000000000000000001 1.0000000000000000009
15624 outputs 1.0000000000000000007 twice and skips 1.0000000000000000008.
15629 @node File permissions
15630 @chapter File permissions
15633 @include getdate.texi
15637 @node Opening the software toolbox
15638 @chapter Opening the Software Toolbox
15640 An earlier version of this chapter appeared in
15641 @uref{http://www.linuxjournal.com/article.php?sid=2762, the
15642 @cite{What's GNU?} column of @cite{Linux Journal}, 2 (June, 1994)}.
15643 It was written by Arnold Robbins.
15646 * Toolbox introduction:: Toolbox introduction
15647 * I/O redirection:: I/O redirection
15648 * The who command:: The @command{who} command
15649 * The cut command:: The @command{cut} command
15650 * The sort command:: The @command{sort} command
15651 * The uniq command:: The @command{uniq} command
15652 * Putting the tools together:: Putting the tools together
15656 @node Toolbox introduction
15657 @unnumberedsec Toolbox Introduction
15659 This month's column is only peripherally related to the GNU Project, in
15660 that it describes a number of the GNU tools on your GNU/Linux system and how they
15661 might be used. What it's really about is the ``Software Tools'' philosophy
15662 of program development and usage.
15664 The software tools philosophy was an important and integral concept
15665 in the initial design and development of Unix (of which Linux and GNU are
15666 essentially clones). Unfortunately, in the modern day press of
15667 Internetworking and flashy GUIs, it seems to have fallen by the
15668 wayside. This is a shame, since it provides a powerful mental model
15669 for solving many kinds of problems.
15671 Many people carry a Swiss Army knife around in their pants pockets (or
15672 purse). A Swiss Army knife is a handy tool to have: it has several knife
15673 blades, a screwdriver, tweezers, toothpick, nail file, corkscrew, and perhaps
15674 a number of other things on it. For the everyday, small miscellaneous jobs
15675 where you need a simple, general purpose tool, it's just the thing.
15677 On the other hand, an experienced carpenter doesn't build a house using
15678 a Swiss Army knife. Instead, he has a toolbox chock full of specialized
15679 tools---a saw, a hammer, a screwdriver, a plane, and so on. And he knows
15680 exactly when and where to use each tool; you won't catch him hammering nails
15681 with the handle of his screwdriver.
15683 The Unix developers at Bell Labs were all professional programmers and trained
15684 computer scientists. They had found that while a one-size-fits-all program
15685 might appeal to a user because there's only one program to use, in practice
15690 difficult to write,
15693 difficult to maintain and
15697 difficult to extend to meet new situations.
15700 Instead, they felt that programs should be specialized tools. In short, each
15701 program ``should do one thing well.'' No more and no less. Such programs are
15702 simpler to design, write, and get right---they only do one thing.
15704 Furthermore, they found that with the right machinery for hooking programs
15705 together, that the whole was greater than the sum of the parts. By combining
15706 several special purpose programs, you could accomplish a specific task
15707 that none of the programs was designed for, and accomplish it much more
15708 quickly and easily than if you had to write a special purpose program.
15709 We will see some (classic) examples of this further on in the column.
15710 (An important additional point was that, if necessary, take a detour
15711 and build any software tools you may need first, if you don't already
15712 have something appropriate in the toolbox.)
15714 @node I/O redirection
15715 @unnumberedsec I/O Redirection
15717 Hopefully, you are familiar with the basics of I/O redirection in the
15718 shell, in particular the concepts of ``standard input,'' ``standard output,''
15719 and ``standard error''. Briefly, ``standard input'' is a data source, where
15720 data comes from. A program should not need to either know or care if the
15721 data source is a disk file, a keyboard, a magnetic tape, or even a punched
15722 card reader. Similarly, ``standard output'' is a data sink, where data goes
15723 to. The program should neither know nor care where this might be.
15724 Programs that only read their standard input, do something to the data,
15725 and then send it on, are called @dfn{filters}, by analogy to filters in a
15728 With the Unix shell, it's very easy to set up data pipelines:
15731 program_to_create_data | filter1 | ... | filterN > final.pretty.data
15734 We start out by creating the raw data; each filter applies some successive
15735 transformation to the data, until by the time it comes out of the pipeline,
15736 it is in the desired form.
15738 This is fine and good for standard input and standard output. Where does the
15739 standard error come in to play? Well, think about @command{filter1} in
15740 the pipeline above. What happens if it encounters an error in the data it
15741 sees? If it writes an error message to standard output, it will just
15742 disappear down the pipeline into @command{filter2}'s input, and the
15743 user will probably never see it. So programs need a place where they can send
15744 error messages so that the user will notice them. This is standard error,
15745 and it is usually connected to your console or window, even if you have
15746 redirected standard output of your program away from your screen.
15748 For filter programs to work together, the format of the data has to be
15749 agreed upon. The most straightforward and easiest format to use is simply
15750 lines of text. Unix data files are generally just streams of bytes, with
15751 lines delimited by the @acronym{ASCII} @sc{lf} (Line Feed) character,
15752 conventionally called a ``newline'' in the Unix literature. (This is
15753 @code{'\n'} if you're a C programmer.) This is the format used by all
15754 the traditional filtering programs. (Many earlier operating systems
15755 had elaborate facilities and special purpose programs for managing
15756 binary data. Unix has always shied away from such things, under the
15757 philosophy that it's easiest to simply be able to view and edit your
15758 data with a text editor.)
15760 OK, enough introduction. Let's take a look at some of the tools, and then
15761 we'll see how to hook them together in interesting ways. In the following
15762 discussion, we will only present those command line options that interest
15763 us. As you should always do, double check your system documentation
15764 for the full story.
15766 @node The who command
15767 @unnumberedsec The @command{who} Command
15769 The first program is the @command{who} command. By itself, it generates a
15770 list of the users who are currently logged in. Although I'm writing
15771 this on a single-user system, we'll pretend that several people are
15776 @print{} arnold console Jan 22 19:57
15777 @print{} miriam ttyp0 Jan 23 14:19(:0.0)
15778 @print{} bill ttyp1 Jan 21 09:32(:0.0)
15779 @print{} arnold ttyp2 Jan 23 20:48(:0.0)
15782 Here, the @samp{$} is the usual shell prompt, at which I typed @samp{who}.
15783 There are three people logged in, and I am logged in twice. On traditional
15784 Unix systems, user names are never more than eight characters long. This
15785 little bit of trivia will be useful later. The output of @command{who} is nice,
15786 but the data is not all that exciting.
15788 @node The cut command
15789 @unnumberedsec The @command{cut} Command
15791 The next program we'll look at is the @command{cut} command. This program
15792 cuts out columns or fields of input data. For example, we can tell it
15793 to print just the login name and full name from the @file{/etc/passwd}
15794 file. The @file{/etc/passwd} file has seven fields, separated by
15798 arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/bash
15801 To get the first and fifth fields, we would use @command{cut} like this:
15804 $ cut -d: -f1,5 /etc/passwd
15805 @print{} root:Operator
15807 @print{} arnold:Arnold D. Robbins
15808 @print{} miriam:Miriam A. Robbins
15812 With the @option{-c} option, @command{cut} will cut out specific characters
15813 (i.e., columns) in the input lines. This is useful for input data
15814 that has fixed width fields, and does not have a field separator. For
15815 example, list the Monday dates for the current month:
15817 @c Is using cal ok? Looked at gcal, but I don't like it.
15828 @node The sort command
15829 @unnumberedsec The @command{sort} Command
15831 Next we'll look at the @command{sort} command. This is one of the most
15832 powerful commands on a Unix-style system; one that you will often find
15833 yourself using when setting up fancy data plumbing.
15836 command reads and sorts each file named on the command line. It then
15837 merges the sorted data and writes it to standard output. It will read
15838 standard input if no files are given on the command line (thus
15839 making it into a filter). The sort is based on the character collating
15840 sequence or based on user-supplied ordering criteria.
15843 @node The uniq command
15844 @unnumberedsec The @command{uniq} Command
15846 Finally (at least for now), we'll look at the @command{uniq} program. When
15847 sorting data, you will often end up with duplicate lines, lines that
15848 are identical. Usually, all you need is one instance of each line.
15849 This is where @command{uniq} comes in. The @command{uniq} program reads its
15850 standard input. It prints only one
15851 copy of each repeated line. It does have several options. Later on,
15852 we'll use the @option{-c} option, which prints each unique line, preceded
15853 by a count of the number of times that line occurred in the input.
15856 @node Putting the tools together
15857 @unnumberedsec Putting the Tools Together
15859 Now, let's suppose this is a large ISP server system with dozens of users
15860 logged in. The management wants the system administrator to write a program that will
15861 generate a sorted list of logged in users. Furthermore, even if a user
15862 is logged in multiple times, his or her name should only show up in the
15865 The administrator could sit down with the system documentation and write a C
15866 program that did this. It would take perhaps a couple of hundred lines
15867 of code and about two hours to write it, test it, and debug it.
15868 However, knowing the software toolbox, the administrator can instead start out
15869 by generating just a list of logged on users:
15879 Next, sort the list:
15882 $ who | cut -c1-8 | sort
15889 Finally, run the sorted list through @command{uniq}, to weed out duplicates:
15892 $ who | cut -c1-8 | sort | uniq
15898 The @command{sort} command actually has a @option{-u} option that does what
15899 @command{uniq} does. However, @command{uniq} has other uses for which one
15900 cannot substitute @samp{sort -u}.
15902 The administrator puts this pipeline into a shell script, and makes it available for
15903 all the users on the system (@samp{#} is the system administrator,
15904 or @code{root}, prompt):
15907 # cat > /usr/local/bin/listusers
15908 who | cut -c1-8 | sort | uniq
15910 # chmod +x /usr/local/bin/listusers
15913 There are four major points to note here. First, with just four
15914 programs, on one command line, the administrator was able to save about two
15915 hours worth of work. Furthermore, the shell pipeline is just about as
15916 efficient as the C program would be, and it is much more efficient in
15917 terms of programmer time. People time is much more expensive than
15918 computer time, and in our modern ``there's never enough time to do
15919 everything'' society, saving two hours of programmer time is no mean
15922 Second, it is also important to emphasize that with the
15923 @emph{combination} of the tools, it is possible to do a special
15924 purpose job never imagined by the authors of the individual programs.
15926 Third, it is also valuable to build up your pipeline in stages, as we did here.
15927 This allows you to view the data at each stage in the pipeline, which helps
15928 you acquire the confidence that you are indeed using these tools correctly.
15930 Finally, by bundling the pipeline in a shell script, other users can use
15931 your command, without having to remember the fancy plumbing you set up for
15932 them. In terms of how you run them, shell scripts and compiled programs are
15935 After the previous warm-up exercise, we'll look at two additional, more
15936 complicated pipelines. For them, we need to introduce two more tools.
15938 The first is the @command{tr} command, which stands for ``transliterate.''
15939 The @command{tr} command works on a character-by-character basis, changing
15940 characters. Normally it is used for things like mapping upper case to
15944 $ echo ThIs ExAmPlE HaS MIXED case! | tr '[:upper:]' '[:lower:]'
15945 @print{} this example has mixed case!
15948 There are several options of interest:
15952 work on the complement of the listed characters, i.e.,
15953 operations apply to characters not in the given set
15956 delete characters in the first set from the output
15959 squeeze repeated characters in the output into just one character.
15962 We will be using all three options in a moment.
15964 The other command we'll look at is @command{comm}. The @command{comm}
15965 command takes two sorted input files as input data, and prints out the
15966 files' lines in three columns. The output columns are the data lines
15967 unique to the first file, the data lines unique to the second file, and
15968 the data lines that are common to both. The @option{-1}, @option{-2}, and
15969 @option{-3} command line options @emph{omit} the respective columns. (This is
15970 non-intuitive and takes a little getting used to.) For example:
15992 The file name @file{-} tells @command{comm} to read standard input
15993 instead of a regular file.
15995 Now we're ready to build a fancy pipeline. The first application is a word
15996 frequency counter. This helps an author determine if he or she is over-using
15999 The first step is to change the case of all the letters in our input file
16000 to one case. ``The'' and ``the'' are the same word when doing counting.
16003 $ tr '[:upper:]' '[:lower:]' < whats.gnu | ...
16006 The next step is to get rid of punctuation. Quoted words and unquoted words
16007 should be treated identically; it's easiest to just get the punctuation out of
16011 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | ...
16014 The second @command{tr} command operates on the complement of the listed
16015 characters, which are all the letters, the digits, the underscore, and
16016 the blank. The @samp{\n} represents the newline character; it has to
16017 be left alone. (The @acronym{ASCII} tab character should also be included for
16018 good measure in a production script.)
16020 At this point, we have data consisting of words separated by blank space.
16021 The words only contain alphanumeric characters (and the underscore). The
16022 next step is break the data apart so that we have one word per line. This
16023 makes the counting operation much easier, as we will see shortly.
16026 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16027 > tr -s ' ' '\n' | ...
16030 This command turns blanks into newlines. The @option{-s} option squeezes
16031 multiple newline characters in the output into just one. This helps us
16032 avoid blank lines. (The @samp{>} is the shell's ``secondary prompt.''
16033 This is what the shell prints when it notices you haven't finished
16034 typing in all of a command.)
16036 We now have data consisting of one word per line, no punctuation, all one
16037 case. We're ready to count each word:
16040 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16041 > tr -s ' ' '\n' | sort | uniq -c | ...
16044 At this point, the data might look something like this:
16057 The output is sorted by word, not by count! What we want is the most
16058 frequently used words first. Fortunately, this is easy to accomplish,
16059 with the help of two more @command{sort} options:
16063 do a numeric sort, not a textual one
16066 reverse the order of the sort
16069 The final pipeline looks like this:
16072 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16073 > tr -s ' ' '\n' | sort | uniq -c | sort -n -r
16082 Whew! That's a lot to digest. Yet, the same principles apply. With six
16083 commands, on two lines (really one long one split for convenience), we've
16084 created a program that does something interesting and useful, in much
16085 less time than we could have written a C program to do the same thing.
16087 A minor modification to the above pipeline can give us a simple spelling
16088 checker! To determine if you've spelled a word correctly, all you have to
16089 do is look it up in a dictionary. If it is not there, then chances are
16090 that your spelling is incorrect. So, we need a dictionary.
16091 The conventional location for a dictionary is @file{/usr/dict/words}.
16092 On my GNU/Linux system,@footnote{Redhat Linux 6.1, for the November 2000
16093 revision of this article.}
16094 this is a sorted, 45,402 word dictionary.
16096 Now, how to compare our file with the dictionary? As before, we generate
16097 a sorted list of words, one per line:
16100 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16101 > tr -s ' ' '\n' | sort -u | ...
16104 Now, all we need is a list of words that are @emph{not} in the
16105 dictionary. Here is where the @command{comm} command comes in.
16108 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16109 > tr -s ' ' '\n' | sort -u |
16110 > comm -23 - /usr/dict/words
16113 The @option{-2} and @option{-3} options eliminate lines that are only in the
16114 dictionary (the second file), and lines that are in both files. Lines
16115 only in the first file (standard input, our stream of words), are
16116 words that are not in the dictionary. These are likely candidates for
16117 spelling errors. This pipeline was the first cut at a production
16118 spelling checker on Unix.
16120 There are some other tools that deserve brief mention.
16124 search files for text that matches a regular expression
16127 count lines, words, characters
16130 a T-fitting for data pipes, copies data to files and to standard output
16133 the stream editor, an advanced tool
16136 a data manipulation language, another advanced tool
16139 The software tools philosophy also espoused the following bit of
16140 advice: ``Let someone else do the hard part.'' This means, take
16141 something that gives you most of what you need, and then massage it the
16142 rest of the way until it's in the form that you want.
16148 Each program should do one thing well. No more, no less.
16151 Combining programs with appropriate plumbing leads to results where
16152 the whole is greater than the sum of the parts. It also leads to novel
16153 uses of programs that the authors might never have imagined.
16156 Programs should never print extraneous header or trailer data, since these
16157 could get sent on down a pipeline. (A point we didn't mention earlier.)
16160 Let someone else do the hard part.
16163 Know your toolbox! Use each program appropriately. If you don't have an
16164 appropriate tool, build one.
16167 As of this writing, all the programs we've discussed are available via
16168 anonymous @command{ftp} from: @*
16169 @uref{ftp://gnudist.gnu.org/textutils/textutils-1.22.tar.gz}. (There may
16170 be more recent versions available now.)
16172 None of what I have presented in this column is new. The Software Tools
16173 philosophy was first introduced in the book @cite{Software Tools}, by
16174 Brian Kernighan and P.J. Plauger (Addison-Wesley, ISBN 0-201-03669-X).
16175 This book showed how to write and use software tools. It was written in
16176 1976, using a preprocessor for FORTRAN named @command{ratfor} (RATional
16177 FORtran). At the time, C was not as ubiquitous as it is now; FORTRAN
16178 was. The last chapter presented a @command{ratfor} to FORTRAN
16179 processor, written in @command{ratfor}. @command{ratfor} looks an awful
16180 lot like C; if you know C, you won't have any problem following the
16183 In 1981, the book was updated and made available as @cite{Software Tools
16184 in Pascal} (Addison-Wesley, ISBN 0-201-10342-7). Both books are
16185 still in print and are well worth
16186 reading if you're a programmer. They certainly made a major change in
16187 how I view programming.
16189 The programs in both books are available from
16190 @uref{http://cm.bell-labs.com/who/bwk, Brian Kernighan's home page}.
16191 For a number of years, there was an active
16192 Software Tools Users Group, whose members had ported the original
16193 @command{ratfor} programs to essentially every computer system with a
16194 FORTRAN compiler. The popularity of the group waned in the middle 1980s
16195 as Unix began to spread beyond universities.
16197 With the current proliferation of GNU code and other clones of Unix programs,
16198 these programs now receive little attention; modern C versions are
16199 much more efficient and do more than these programs do. Nevertheless, as
16200 exposition of good programming style, and evangelism for a still-valuable
16201 philosophy, these books are unparalleled, and I recommend them highly.
16203 Acknowledgment: I would like to express my gratitude to Brian Kernighan
16204 of Bell Labs, the original Software Toolsmith, for reviewing this column.
16206 @node GNU Free Documentation License
16207 @appendix GNU Free Documentation License
16211 @node Concept index
16218 @c Local variables:
16219 @c texinfo-column-for-description: 32