1BASH(1) General Commands Manual BASH(1)
2
6 bash - GNU Bourne-Again SHell
7
9 bash [options] [command_string | file]
10
12 Bash is Copyright (C) 1989-2020 by the Free Software Foundation, Inc.
13
15 Bash is an sh-compatible command language interpreter that executes
16 commands read from the standard input or from a file. Bash also incor‐
17 porates useful features from the Korn and C shells (ksh and csh).
18 Bash is intended to be a conformant implementation of the Shell and
20 Utilities portion of the IEEE POSIX specification (IEEE Standard
21 1003.1). Bash can be configured to be POSIX-conformant by default.
22
24 All of the single-character shell options documented in the description
25 of the set builtin command, including -o, can be used as options when
26 the shell is invoked. In addition, bash interprets the following op‐
27 tions when it is invoked:
28 -c If the -c option is present, then commands are read from the
30 first non-option argument command_string. If there are argu‐
31 ments after the command_string, the first argument is as‐
32 signed to $0 and any remaining arguments are assigned to the
33 positional parameters. The assignment to $0 sets the name of
34 the shell, which is used in warning and error messages.
35 -i If the -i option is present, the shell is interactive.
36 -l Make bash act as if it had been invoked as a login shell (see
37 INVOCATION below).
38 -r If the -r option is present, the shell becomes restricted
39 (see RESTRICTED SHELL below).
40 -s If the -s option is present, or if no arguments remain after
41 option processing, then commands are read from the standard
42 input. This option allows the positional parameters to be
43 set when invoking an interactive shell or when reading input
44 through a pipe.
45 -D A list of all double-quoted strings preceded by $ is printed
46 on the standard output. These are the strings that are sub‐
47 ject to language translation when the current locale is not C
48 or POSIX. This implies the -n option; no commands will be
49 executed.
50 [-+]O [shopt_option]
51 shopt_option is one of the shell options accepted by the
52 shopt builtin (see SHELL BUILTIN COMMANDS below). If
53 shopt_option is present, -O sets the value of that option; +O
54 unsets it. If shopt_option is not supplied, the names and
55 values of the shell options accepted by shopt are printed on
56 the standard output. If the invocation option is +O, the
57 output is displayed in a format that may be reused as input.
58 -- A -- signals the end of options and disables further option
59 processing. Any arguments after the -- are treated as file‐
60 names and arguments. An argument of - is equivalent to --.
61 Bash also interprets a number of multi-character options. These op‐
63 tions must appear on the command line before the single-character op‐
64 tions to be recognized.
65 --debugger
67 Arrange for the debugger profile to be executed before the shell
68 starts. Turns on extended debugging mode (see the description
69 of the extdebug option to the shopt builtin below).
70 --dump-po-strings
71 Equivalent to -D, but the output is in the GNU gettext po (por‐
72 table object) file format.
73 --dump-strings
74 Equivalent to -D.
75 --help Display a usage message on standard output and exit success‐
76 fully.
77 --init-file file
78 --rcfile file
79 Execute commands from file instead of the standard personal ini‐
80 tialization file ~/.bashrc if the shell is interactive (see IN‐
81 VOCATION below).
82 --login
84 Equivalent to -l.
85 --noediting
87 Do not use the GNU readline library to read command lines when
88 the shell is interactive.
89 --noprofile
91 Do not read either the system-wide startup file /etc/profile or
92 any of the personal initialization files ~/.bash_profile,
93 ~/.bash_login, or ~/.profile. By default, bash reads these
94 files when it is invoked as a login shell (see INVOCATION be‐
95 low).
96 --norc Do not read and execute the personal initialization file
98 ~/.bashrc if the shell is interactive. This option is on by de‐
99 fault if the shell is invoked as sh.
100 --posix
102 Change the behavior of bash where the default operation differs
103 from the POSIX standard to match the standard (posix mode). See
104 SEE ALSO below for a reference to a document that details how
105 posix mode affects bash's behavior.
106 --restricted
108 The shell becomes restricted (see RESTRICTED SHELL below).
109 --rpm-requires
111 Produce the list of files that are required for the shell script
112 to run. This implies '-n' and is subject to the same limita‐
113 tions as compile time error checking checking; Command substitu‐
114 tions, Conditional expressions and eval builtin are not parsed
115 so some dependencies may be missed.
116 --verbose
118 Equivalent to -v.
119 --version
121 Show version information for this instance of bash on the stan‐
122 dard output and exit successfully.
123
125 If arguments remain after option processing, and neither the -c nor the
126 -s option has been supplied, the first argument is assumed to be the
127 name of a file containing shell commands. If bash is invoked in this
128 fashion, $0 is set to the name of the file, and the positional parame‐
129 ters are set to the remaining arguments. Bash reads and executes com‐
130 mands from this file, then exits. Bash's exit status is the exit sta‐
131 tus of the last command executed in the script. If no commands are ex‐
132 ecuted, the exit status is 0. An attempt is first made to open the
133 file in the current directory, and, if no file is found, then the shell
134 searches the directories in PATH for the script.
135
137 A login shell is one whose first character of argument zero is a -, or
138 one started with the --login option.
139 An interactive shell is one started without non-option arguments (un‐
141 less -s is specified) and without the -c option whose standard input
142 and error are both connected to terminals (as determined by isatty(3)),
143 or one started with the -i option. PS1 is set and $- includes i if
144 bash is interactive, allowing a shell script or a startup file to test
145 this state.
146 The following paragraphs describe how bash executes its startup files.
148 If any of the files exist but cannot be read, bash reports an error.
149 Tildes are expanded in filenames as described below under Tilde Expan‐
150 sion in the EXPANSION section.
151 When bash is invoked as an interactive login shell, or as a non-inter‐
153 active shell with the --login option, it first reads and executes com‐
154 mands from the file /etc/profile, if that file exists. After reading
155 that file, it looks for ~/.bash_profile, ~/.bash_login, and ~/.profile,
156 in that order, and reads and executes commands from the first one that
157 exists and is readable. The --noprofile option may be used when the
158 shell is started to inhibit this behavior.
159 When an interactive login shell exits, or a non-interactive login shell
161 executes the exit builtin command, bash reads and executes commands
162 from the files ~/.bash_logout and /etc/bash.bash_logout, if the files
163 exists.
164 When an interactive shell that is not a login shell is started, bash
166 reads and executes commands from ~/.bashrc, if that file exists. This
167 may be inhibited by using the --norc option. The --rcfile file option
168 will force bash to read and execute commands from file instead of
169 ~/.bashrc.
170 When bash is started non-interactively, to run a shell script, for ex‐
172 ample, it looks for the variable BASH_ENV in the environment, expands
173 its value if it appears there, and uses the expanded value as the name
174 of a file to read and execute. Bash behaves as if the following com‐
175 mand were executed:
176 if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
177 but the value of the PATH variable is not used to search for the file‐
178 name.
179 If bash is invoked with the name sh, it tries to mimic the startup be‐
181 havior of historical versions of sh as closely as possible, while con‐
182 forming to the POSIX standard as well. When invoked as an interactive
183 login shell, or a non-interactive shell with the --login option, it
184 first attempts to read and execute commands from /etc/profile and
185 ~/.profile, in that order. The --noprofile option may be used to in‐
186 hibit this behavior. When invoked as an interactive shell with the
187 name sh, bash looks for the variable ENV, expands its value if it is
188 defined, and uses the expanded value as the name of a file to read and
189 execute. Since a shell invoked as sh does not attempt to read and exe‐
190 cute commands from any other startup files, the --rcfile option has no
191 effect. A non-interactive shell invoked with the name sh does not at‐
192 tempt to read any other startup files. When invoked as sh, bash enters
193 posix mode after the startup files are read.
194 When bash is started in posix mode, as with the --posix command line
196 option, it follows the POSIX standard for startup files. In this mode,
197 interactive shells expand the ENV variable and commands are read and
198 executed from the file whose name is the expanded value. No other
199 startup files are read.
200 Bash attempts to determine when it is being run with its standard input
202 connected to a network connection, as when executed by the remote shell
203 daemon, usually rshd, or the secure shell daemon sshd. If bash deter‐
204 mines it is being run in this fashion, it reads and executes commands
205 from ~/.bashrc, if that file exists and is readable. It will not do
206 this if invoked as sh. The --norc option may be used to inhibit this
207 behavior, and the --rcfile option may be used to force another file to
208 be read, but neither rshd nor sshd generally invoke the shell with
209 those options or allow them to be specified.
210 If the shell is started with the effective user (group) id not equal to
212 the real user (group) id, and the -p option is not supplied, no startup
213 files are read, shell functions are not inherited from the environment,
214 the SHELLOPTS, BASHOPTS, CDPATH, and GLOBIGNORE variables, if they ap‐
215 pear in the environment, are ignored, and the effective user id is set
216 to the real user id. If the -p option is supplied at invocation, the
217 startup behavior is the same, but the effective user id is not reset.
218
220 The following definitions are used throughout the rest of this docu‐
221 ment.
222 blank A space or tab.
223 word A sequence of characters considered as a single unit by the
224 shell. Also known as a token.
225 name A word consisting only of alphanumeric characters and under‐
226 scores, and beginning with an alphabetic character or an under‐
227 score. Also referred to as an identifier.
228 metacharacter
229 A character that, when unquoted, separates words. One of the
230 following:
231 | & ; ( ) < > space tab newline
232 control operator
233 A token that performs a control function. It is one of the fol‐
234 lowing symbols:
235 || & && ; ;; ;& ;;& ( ) | |& <newline>
236
238 Reserved words are words that have a special meaning to the shell. The
239 following words are recognized as reserved when unquoted and either the
240 first word of a command (see SHELL GRAMMAR below), the third word of a
241 case or select command (only in is valid), or the third word of a for
242 command (only in and do are valid):
243 ! case coproc do done elif else esac fi for function if in select
245 then until while { } time [[ ]]
246
248 Simple Commands
249 A simple command is a sequence of optional variable assignments fol‐
250 lowed by blank-separated words and redirections, and terminated by a
251 control operator. The first word specifies the command to be executed,
252 and is passed as argument zero. The remaining words are passed as ar‐
253 guments to the invoked command.
254 The return value of a simple command is its exit status, or 128+n if
256 the command is terminated by signal n.
257 Pipelines
259 A pipeline is a sequence of one or more commands separated by one of
260 the control operators | or |&. The format for a pipeline is:
261 [time [-p]] [ ! ] command [ [|⎪|&] command2 ... ]
263 The standard output of command is connected via a pipe to the standard
265 input of command2. This connection is performed before any redirec‐
266 tions specified by the command (see REDIRECTION below). If |& is used,
267 command's standard error, in addition to its standard output, is con‐
268 nected to command2's standard input through the pipe; it is shorthand
269 for 2>&1 |. This implicit redirection of the standard error to the
270 standard output is performed after any redirections specified by the
271 command.
272 The return status of a pipeline is the exit status of the last command,
274 unless the pipefail option is enabled. If pipefail is enabled, the
275 pipeline's return status is the value of the last (rightmost) command
276 to exit with a non-zero status, or zero if all commands exit success‐
277 fully. If the reserved word ! precedes a pipeline, the exit status of
278 that pipeline is the logical negation of the exit status as described
279 above. The shell waits for all commands in the pipeline to terminate
280 before returning a value.
281 If the time reserved word precedes a pipeline, the elapsed as well as
283 user and system time consumed by its execution are reported when the
284 pipeline terminates. The -p option changes the output format to that
285 specified by POSIX. When the shell is in posix mode, it does not rec‐
286 ognize time as a reserved word if the next token begins with a `-'.
287 The TIMEFORMAT variable may be set to a format string that specifies
288 how the timing information should be displayed; see the description of
289 TIMEFORMAT under Shell Variables below.
290 When the shell is in posix mode, time may be followed by a newline. In
292 this case, the shell displays the total user and system time consumed
293 by the shell and its children. The TIMEFORMAT variable may be used to
294 specify the format of the time information.
295 Each command in a pipeline is executed as a separate process (i.e., in
297 a subshell). See COMMAND EXECUTION ENVIRONMENT for a description of a
298 subshell environment. If the lastpipe option is enabled using the
299 shopt builtin (see the description of shopt below), the last element of
300 a pipeline may be run by the shell process.
301 Lists
303 A list is a sequence of one or more pipelines separated by one of the
304 operators ;, &, &&, or ||, and optionally terminated by one of ;, &, or
305 <newline>.
306 Of these list operators, && and || have equal precedence, followed by ;
308 and &, which have equal precedence.
309 A sequence of one or more newlines may appear in a list instead of a
311 semicolon to delimit commands.
312 If a command is terminated by the control operator &, the shell exe‐
314 cutes the command in the background in a subshell. The shell does not
315 wait for the command to finish, and the return status is 0. These are
316 referred to as asynchronous commands. Commands separated by a ; are
317 executed sequentially; the shell waits for each command to terminate in
318 turn. The return status is the exit status of the last command exe‐
319 cuted.
320 AND and OR lists are sequences of one or more pipelines separated by
322 the && and || control operators, respectively. AND and OR lists are
323 executed with left associativity. An AND list has the form
324 command1 && command2
326 command2 is executed if, and only if, command1 returns an exit status
328 of zero (success).
329 An OR list has the form
331 command1 || command2
333 command2 is executed if, and only if, command1 returns a non-zero exit
335 status. The return status of AND and OR lists is the exit status of
336 the last command executed in the list.
337 Compound Commands
339 A compound command is one of the following. In most cases a list in a
340 command's description may be separated from the rest of the command by
341 one or more newlines, and may be followed by a newline in place of a
342 semicolon.
343 (list) list is executed in a subshell environment (see COMMAND EXECU‐
345 TION ENVIRONMENT below). Variable assignments and builtin com‐
346 mands that affect the shell's environment do not remain in ef‐
347 fect after the command completes. The return status is the exit
348 status of list.
349 { list; }
351 list is simply executed in the current shell environment. list
352 must be terminated with a newline or semicolon. This is known
353 as a group command. The return status is the exit status of
354 list. Note that unlike the metacharacters ( and ), { and } are
355 reserved words and must occur where a reserved word is permitted
356 to be recognized. Since they do not cause a word break, they
357 must be separated from list by whitespace or another shell
358 metacharacter.
359 ((expression))
361 The expression is evaluated according to the rules described be‐
362 low under ARITHMETIC EVALUATION. If the value of the expression
363 is non-zero, the return status is 0; otherwise the return status
364 is 1. This is exactly equivalent to let "expression".
365 [[ expression ]]
367 Return a status of 0 or 1 depending on the evaluation of the
368 conditional expression expression. Expressions are composed of
369 the primaries described below under CONDITIONAL EXPRESSIONS.
370 Word splitting and pathname expansion are not performed on the
371 words between the [[ and ]]; tilde expansion, parameter and
372 variable expansion, arithmetic expansion, command substitution,
373 process substitution, and quote removal are performed. Condi‐
374 tional operators such as -f must be unquoted to be recognized as
375 primaries.
376 When used with [[, the < and > operators sort lexicographically
378 using the current locale.
379 When the == and != operators are used, the string to the right
381 of the operator is considered a pattern and matched according to
382 the rules described below under Pattern Matching, as if the ext‐
383 glob shell option were enabled. The = operator is equivalent to
384 ==. If the nocasematch shell option is enabled, the match is
385 performed without regard to the case of alphabetic characters.
386 The return value is 0 if the string matches (==) or does not
387 match (!=) the pattern, and 1 otherwise. Any part of the pat‐
388 tern may be quoted to force the quoted portion to be matched as
389 a string.
390 An additional binary operator, =~, is available, with the same
392 precedence as == and !=. When it is used, the string to the
393 right of the operator is considered a POSIX extended regular ex‐
394 pression and matched accordingly (using the POSIX regcomp and
395 regexec interfaces usually described in regex(3)). The return
396 value is 0 if the string matches the pattern, and 1 otherwise.
397 If the regular expression is syntactically incorrect, the condi‐
398 tional expression's return value is 2. If the nocasematch shell
399 option is enabled, the match is performed without regard to the
400 case of alphabetic characters. Any part of the pattern may be
401 quoted to force the quoted portion to be matched as a string.
402 Bracket expressions in regular expressions must be treated care‐
403 fully, since normal quoting characters lose their meanings be‐
404 tween brackets. If the pattern is stored in a shell variable,
405 quoting the variable expansion forces the entire pattern to be
406 matched as a string.
407 The pattern will match if it matches any part of the string.
409 Anchor the pattern using the ^ and $ regular expression opera‐
410 tors to force it to match the entire string. The array variable
411 BASH_REMATCH records which parts of the string matched the pat‐
412 tern. The element of BASH_REMATCH with index 0 contains the
413 portion of the string matching the entire regular expression.
414 Substrings matched by parenthesized subexpressions within the
415 regular expression are saved in the remaining BASH_REMATCH in‐
416 dices. The element of BASH_REMATCH with index n is the portion
417 of the string matching the nth parenthesized subexpression.
418 Expressions may be combined using the following operators,
420 listed in decreasing order of precedence:
421 ( expression )
423 Returns the value of expression. This may be used to
424 override the normal precedence of operators.
425 ! expression
426 True if expression is false.
427 expression1 && expression2
428 True if both expression1 and expression2 are true.
429 expression1 || expression2
430 True if either expression1 or expression2 is true.
431 The && and || operators do not evaluate expression2 if the value
433 of expression1 is sufficient to determine the return value of
434 the entire conditional expression.
435 for name [ [ in [ word ... ] ] ; ] do list ; done
437 The list of words following in is expanded, generating a list of
438 items. The variable name is set to each element of this list in
439 turn, and list is executed each time. If the in word is omit‐
440 ted, the for command executes list once for each positional pa‐
441 rameter that is set (see PARAMETERS below). The return status
442 is the exit status of the last command that executes. If the
443 expansion of the items following in results in an empty list, no
444 commands are executed, and the return status is 0.
445 for (( expr1 ; expr2 ; expr3 )) ; do list ; done
447 First, the arithmetic expression expr1 is evaluated according to
448 the rules described below under ARITHMETIC EVALUATION. The
449 arithmetic expression expr2 is then evaluated repeatedly until
450 it evaluates to zero. Each time expr2 evaluates to a non-zero
451 value, list is executed and the arithmetic expression expr3 is
452 evaluated. If any expression is omitted, it behaves as if it
453 evaluates to 1. The return value is the exit status of the last
454 command in list that is executed, or false if any of the expres‐
455 sions is invalid.
456 select name [ in word ] ; do list ; done
458 The list of words following in is expanded, generating a list of
459 items. The set of expanded words is printed on the standard er‐
460 ror, each preceded by a number. If the in word is omitted, the
461 positional parameters are printed (see PARAMETERS below). The
462 PS3 prompt is then displayed and a line read from the standard
463 input. If the line consists of a number corresponding to one of
464 the displayed words, then the value of name is set to that word.
465 If the line is empty, the words and prompt are displayed again.
466 If EOF is read, the command completes. Any other value read
467 causes name to be set to null. The line read is saved in the
468 variable REPLY. The list is executed after each selection until
469 a break command is executed. The exit status of select is the
470 exit status of the last command executed in list, or zero if no
471 commands were executed.
472 case word in [ [(] pattern [ | pattern ] ... ) list ;; ] ... esac
474 A case command first expands word, and tries to match it against
475 each pattern in turn, using the matching rules described under
476 Pattern Matching below. The word is expanded using tilde expan‐
477 sion, parameter and variable expansion, arithmetic expansion,
478 command substitution, process substitution and quote removal.
479 Each pattern examined is expanded using tilde expansion, parame‐
480 ter and variable expansion, arithmetic expansion, command sub‐
481 stitution, and process substitution. If the nocasematch shell
482 option is enabled, the match is performed without regard to the
483 case of alphabetic characters. When a match is found, the cor‐
484 responding list is executed. If the ;; operator is used, no
485 subsequent matches are attempted after the first pattern match.
486 Using ;& in place of ;; causes execution to continue with the
487 list associated with the next set of patterns. Using ;;& in
488 place of ;; causes the shell to test the next pattern list in
489 the statement, if any, and execute any associated list on a suc‐
490 cessful match, continuing the case statement execution as if the
491 pattern list had not matched. The exit status is zero if no
492 pattern matches. Otherwise, it is the exit status of the last
493 command executed in list.
494 if list; then list; [ elif list; then list; ] ... [ else list; ] fi
496 The if list is executed. If its exit status is zero, the then
497 list is executed. Otherwise, each elif list is executed in
498 turn, and if its exit status is zero, the corresponding then
499 list is executed and the command completes. Otherwise, the else
500 list is executed, if present. The exit status is the exit sta‐
501 tus of the last command executed, or zero if no condition tested
502 true.
503 while list-1; do list-2; done
505 until list-1; do list-2; done
506 The while command continuously executes the list list-2 as long
507 as the last command in the list list-1 returns an exit status of
508 zero. The until command is identical to the while command, ex‐
509 cept that the test is negated: list-2 is executed as long as the
510 last command in list-1 returns a non-zero exit status. The exit
511 status of the while and until commands is the exit status of the
512 last command executed in list-2, or zero if none was executed.
513 Coprocesses
515 A coprocess is a shell command preceded by the coproc reserved word. A
516 coprocess is executed asynchronously in a subshell, as if the command
517 had been terminated with the & control operator, with a two-way pipe
518 established between the executing shell and the coprocess.
519 The format for a coprocess is:
521 coproc [NAME] command [redirections]
523 This creates a coprocess named NAME. If NAME is not supplied, the de‐
525 fault name is COPROC. NAME must not be supplied if command is a simple
526 command (see above); otherwise, it is interpreted as the first word of
527 the simple command. When the coprocess is executed, the shell creates
528 an array variable (see Arrays below) named NAME in the context of the
529 executing shell. The standard output of command is connected via a
530 pipe to a file descriptor in the executing shell, and that file de‐
531 scriptor is assigned to NAME[0]. The standard input of command is con‐
532 nected via a pipe to a file descriptor in the executing shell, and that
533 file descriptor is assigned to NAME[1]. This pipe is established be‐
534 fore any redirections specified by the command (see REDIRECTION below).
535 The file descriptors can be utilized as arguments to shell commands and
536 redirections using standard word expansions. Other than those created
537 to execute command and process substitutions, the file descriptors are
538 not available in subshells. The process ID of the shell spawned to ex‐
539 ecute the coprocess is available as the value of the variable NAME_PID.
540 The wait builtin command may be used to wait for the coprocess to ter‐
541 minate.
542 Since the coprocess is created as an asynchronous command, the coproc
544 command always returns success. The return status of a coprocess is
545 the exit status of command.
546 Shell Function Definitions
548 A shell function is an object that is called like a simple command and
549 executes a compound command with a new set of positional parameters.
550 Shell functions are declared as follows:
551 fname () compound-command [redirection]
553 function fname [()] compound-command [redirection]
554 This defines a function named fname. The reserved word function
555 is optional. If the function reserved word is supplied, the
556 parentheses are optional. The body of the function is the com‐
557 pound command compound-command (see Compound Commands above).
558 That command is usually a list of commands between { and }, but
559 may be any command listed under Compound Commands above, with
560 one exception: If the function reserved word is used, but the
561 parentheses are not supplied, the braces are required. com‐
562 pound-command is executed whenever fname is specified as the
563 name of a simple command. When in posix mode, fname must be a
564 valid shell name and may not be the name of one of the POSIX
565 special builtins. In default mode, a function name can be any
566 unquoted shell word that does not contain $. Any redirections
567 (see REDIRECTION below) specified when a function is defined are
568 performed when the function is executed. The exit status of a
569 function definition is zero unless a syntax error occurs or a
570 readonly function with the same name already exists. When exe‐
571 cuted, the exit status of a function is the exit status of the
572 last command executed in the body. (See FUNCTIONS below.)
573
575 In a non-interactive shell, or an interactive shell in which the inter‐
576 active_comments option to the shopt builtin is enabled (see SHELL
577 BUILTIN COMMANDS below), a word beginning with # causes that word and
578 all remaining characters on that line to be ignored. An interactive
579 shell without the interactive_comments option enabled does not allow
580 comments. The interactive_comments option is on by default in interac‐
581 tive shells.
582
584 Quoting is used to remove the special meaning of certain characters or
585 words to the shell. Quoting can be used to disable special treatment
586 for special characters, to prevent reserved words from being recognized
587 as such, and to prevent parameter expansion.
588 Each of the metacharacters listed above under DEFINITIONS has special
590 meaning to the shell and must be quoted if it is to represent itself.
591 When the command history expansion facilities are being used (see HIS‐
593 TORY EXPANSION below), the history expansion character, usually !, must
594 be quoted to prevent history expansion.
595 There are three quoting mechanisms: the escape character, single
597 quotes, and double quotes.
598 A non-quoted backslash (\) is the escape character. It preserves the
600 literal value of the next character that follows, with the exception of
601 <newline>. If a \<newline> pair appears, and the backslash is not it‐
602 self quoted, the \<newline> is treated as a line continuation (that is,
603 it is removed from the input stream and effectively ignored).
604 Enclosing characters in single quotes preserves the literal value of
606 each character within the quotes. A single quote may not occur between
607 single quotes, even when preceded by a backslash.
608 Enclosing characters in double quotes preserves the literal value of
610 all characters within the quotes, with the exception of $, `, \, and,
611 when history expansion is enabled, !. When the shell is in posix mode,
612 the ! has no special meaning within double quotes, even when history
613 expansion is enabled. The characters $ and ` retain their special
614 meaning within double quotes. The backslash retains its special mean‐
615 ing only when followed by one of the following characters: $, `, ", \,
616 or <newline>. A double quote may be quoted within double quotes by
617 preceding it with a backslash. If enabled, history expansion will be
618 performed unless an ! appearing in double quotes is escaped using a
619 backslash. The backslash preceding the ! is not removed.
620 The special parameters * and @ have special meaning when in double
622 quotes (see PARAMETERS below).
623 Words of the form $'string' are treated specially. The word expands to
625 string, with backslash-escaped characters replaced as specified by the
626 ANSI C standard. Backslash escape sequences, if present, are decoded
627 as follows:
628 \a alert (bell)
629 \b backspace
630 \e
631 \E an escape character
632 \f form feed
633 \n new line
634 \r carriage return
635 \t horizontal tab
636 \v vertical tab
637 \\ backslash
638 \' single quote
639 \" double quote
640 \? question mark
641 \nnn the eight-bit character whose value is the octal value
642 nnn (one to three octal digits)
643 \xHH the eight-bit character whose value is the hexadecimal
644 value HH (one or two hex digits)
645 \uHHHH the Unicode (ISO/IEC 10646) character whose value is the
646 hexadecimal value HHHH (one to four hex digits)
647 \UHHHHHHHH
648 the Unicode (ISO/IEC 10646) character whose value is the
649 hexadecimal value HHHHHHHH (one to eight hex digits)
650 \cx a control-x character
651 The expanded result is single-quoted, as if the dollar sign had not
653 been present.
654 A double-quoted string preceded by a dollar sign ($"string") will cause
656 the string to be translated according to the current locale. The get‐
657 text infrastructure performs the message catalog lookup and transla‐
658 tion, using the LC_MESSAGES and TEXTDOMAIN shell variables. If the
659 current locale is C or POSIX, or if there are no translations avail‐
660 able, the dollar sign is ignored. If the string is translated and re‐
661 placed, the replacement is double-quoted.
662
664 A parameter is an entity that stores values. It can be a name, a num‐
665 ber, or one of the special characters listed below under Special Param‐
666 eters. A variable is a parameter denoted by a name. A variable has a
667 value and zero or more attributes. Attributes are assigned using the
668 declare builtin command (see declare below in SHELL BUILTIN COMMANDS).
669 A parameter is set if it has been assigned a value. The null string is
671 a valid value. Once a variable is set, it may be unset only by using
672 the unset builtin command (see SHELL BUILTIN COMMANDS below).
673 A variable may be assigned to by a statement of the form
675 name=[value]
677 If value is not given, the variable is assigned the null string. All
679 values undergo tilde expansion, parameter and variable expansion, com‐
680 mand substitution, arithmetic expansion, and quote removal (see EXPAN‐
681 SION below). If the variable has its integer attribute set, then value
682 is evaluated as an arithmetic expression even if the $((...)) expansion
683 is not used (see Arithmetic Expansion below). Word splitting is not
684 performed, with the exception of "$@" as explained below under Special
685 Parameters. Pathname expansion is not performed. Assignment state‐
686 ments may also appear as arguments to the alias, declare, typeset, ex‐
687 port, readonly, and local builtin commands (declaration commands).
688 When in posix mode, these builtins may appear in a command after one or
689 more instances of the command builtin and retain these assignment
690 statement properties.
691 In the context where an assignment statement is assigning a value to a
693 shell variable or array index, the += operator can be used to append to
694 or add to the variable's previous value. This includes arguments to
695 builtin commands such as declare that accept assignment statements
696 (declaration commands). When += is applied to a variable for which the
697 integer attribute has been set, value is evaluated as an arithmetic ex‐
698 pression and added to the variable's current value, which is also eval‐
699 uated. When += is applied to an array variable using compound assign‐
700 ment (see Arrays below), the variable's value is not unset (as it is
701 when using =), and new values are appended to the array beginning at
702 one greater than the array's maximum index (for indexed arrays) or
703 added as additional key-value pairs in an associative array. When ap‐
704 plied to a string-valued variable, value is expanded and appended to
705 the variable's value.
706 A variable can be assigned the nameref attribute using the -n option to
708 the declare or local builtin commands (see the descriptions of declare
709 and local below) to create a nameref, or a reference to another vari‐
710 able. This allows variables to be manipulated indirectly. Whenever
711 the nameref variable is referenced, assigned to, unset, or has its at‐
712 tributes modified (other than using or changing the nameref attribute
713 itself), the operation is actually performed on the variable specified
714 by the nameref variable's value. A nameref is commonly used within
715 shell functions to refer to a variable whose name is passed as an argu‐
716 ment to the function. For instance, if a variable name is passed to a
717 shell function as its first argument, running
718 declare -n ref=$1
719 inside the function creates a nameref variable ref whose value is the
720 variable name passed as the first argument. References and assignments
721 to ref, and changes to its attributes, are treated as references, as‐
722 signments, and attribute modifications to the variable whose name was
723 passed as $1. If the control variable in a for loop has the nameref
724 attribute, the list of words can be a list of shell variables, and a
725 name reference will be established for each word in the list, in turn,
726 when the loop is executed. Array variables cannot be given the nameref
727 attribute. However, nameref variables can reference array variables
728 and subscripted array variables. Namerefs can be unset using the -n
729 option to the unset builtin. Otherwise, if unset is executed with the
730 name of a nameref variable as an argument, the variable referenced by
731 the nameref variable will be unset.
732 Positional Parameters
734 A positional parameter is a parameter denoted by one or more digits,
735 other than the single digit 0. Positional parameters are assigned from
736 the shell's arguments when it is invoked, and may be reassigned using
737 the set builtin command. Positional parameters may not be assigned to
738 with assignment statements. The positional parameters are temporarily
739 replaced when a shell function is executed (see FUNCTIONS below).
740 When a positional parameter consisting of more than a single digit is
742 expanded, it must be enclosed in braces (see EXPANSION below).
743 Special Parameters
745 The shell treats several parameters specially. These parameters may
746 only be referenced; assignment to them is not allowed.
747 * Expands to the positional parameters, starting from one. When
748 the expansion is not within double quotes, each positional pa‐
749 rameter expands to a separate word. In contexts where it is
750 performed, those words are subject to further word splitting and
751 pathname expansion. When the expansion occurs within double
752 quotes, it expands to a single word with the value of each pa‐
753 rameter separated by the first character of the IFS special
754 variable. That is, "$*" is equivalent to "$1c$2c...", where c
755 is the first character of the value of the IFS variable. If IFS
756 is unset, the parameters are separated by spaces. If IFS is
757 null, the parameters are joined without intervening separators.
758 @ Expands to the positional parameters, starting from one. In
759 contexts where word splitting is performed, this expands each
760 positional parameter to a separate word; if not within double
761 quotes, these words are subject to word splitting. In contexts
762 where word splitting is not performed, this expands to a single
763 word with each positional parameter separated by a space. When
764 the expansion occurs within double quotes, each parameter ex‐
765 pands to a separate word. That is, "$@" is equivalent to "$1"
766 "$2" ... If the double-quoted expansion occurs within a word,
767 the expansion of the first parameter is joined with the begin‐
768 ning part of the original word, and the expansion of the last
769 parameter is joined with the last part of the original word.
770 When there are no positional parameters, "$@" and $@ expand to
771 nothing (i.e., they are removed).
772 # Expands to the number of positional parameters in decimal.
773 ? Expands to the exit status of the most recently executed fore‐
774 ground pipeline.
775 - Expands to the current option flags as specified upon invoca‐
776 tion, by the set builtin command, or those set by the shell it‐
777 self (such as the -i option).
778 $ Expands to the process ID of the shell. In a () subshell, it
779 expands to the process ID of the current shell, not the sub‐
780 shell.
781 ! Expands to the process ID of the job most recently placed into
782 the background, whether executed as an asynchronous command or
783 using the bg builtin (see JOB CONTROL below).
784 0 Expands to the name of the shell or shell script. This is set
785 at shell initialization. If bash is invoked with a file of com‐
786 mands, $0 is set to the name of that file. If bash is started
787 with the -c option, then $0 is set to the first argument after
788 the string to be executed, if one is present. Otherwise, it is
789 set to the filename used to invoke bash, as given by argument
790 zero.
791 Shell Variables
793 The following variables are set by the shell:
794 _ At shell startup, set to the pathname used to invoke the shell
796 or shell script being executed as passed in the environment or
797 argument list. Subsequently, expands to the last argument to
798 the previous simple command executed in the foreground, after
799 expansion. Also set to the full pathname used to invoke each
800 command executed and placed in the environment exported to that
801 command. When checking mail, this parameter holds the name of
802 the mail file currently being checked.
803 BASH Expands to the full filename used to invoke this instance of
804 bash.
805 BASHOPTS
806 A colon-separated list of enabled shell options. Each word in
807 the list is a valid argument for the -s option to the shopt
808 builtin command (see SHELL BUILTIN COMMANDS below). The options
809 appearing in BASHOPTS are those reported as on by shopt. If
810 this variable is in the environment when bash starts up, each
811 shell option in the list will be enabled before reading any
812 startup files. This variable is read-only.
813 BASHPID
814 Expands to the process ID of the current bash process. This
815 differs from $$ under certain circumstances, such as subshells
816 that do not require bash to be re-initialized. Assignments to
817 BASHPID have no effect. If BASHPID is unset, it loses its spe‐
818 cial properties, even if it is subsequently reset.
819 BASH_ALIASES
820 An associative array variable whose members correspond to the
821 internal list of aliases as maintained by the alias builtin.
822 Elements added to this array appear in the alias list; however,
823 unsetting array elements currently does not cause aliases to be
824 removed from the alias list. If BASH_ALIASES is unset, it loses
825 its special properties, even if it is subsequently reset.
826 BASH_ARGC
827 An array variable whose values are the number of parameters in
828 each frame of the current bash execution call stack. The number
829 of parameters to the current subroutine (shell function or
830 script executed with . or source) is at the top of the stack.
831 When a subroutine is executed, the number of parameters passed
832 is pushed onto BASH_ARGC. The shell sets BASH_ARGC only when in
833 extended debugging mode (see the description of the extdebug op‐
834 tion to the shopt builtin below). Setting extdebug after the
835 shell has started to execute a script, or referencing this vari‐
836 able when extdebug is not set, may result in inconsistent val‐
837 ues.
838 BASH_ARGV
839 An array variable containing all of the parameters in the cur‐
840 rent bash execution call stack. The final parameter of the last
841 subroutine call is at the top of the stack; the first parameter
842 of the initial call is at the bottom. When a subroutine is exe‐
843 cuted, the parameters supplied are pushed onto BASH_ARGV. The
844 shell sets BASH_ARGV only when in extended debugging mode (see
845 the description of the extdebug option to the shopt builtin be‐
846 low). Setting extdebug after the shell has started to execute a
847 script, or referencing this variable when extdebug is not set,
848 may result in inconsistent values.
849 BASH_ARGV0
850 When referenced, this variable expands to the name of the shell
851 or shell script (identical to $0; see the description of special
852 parameter 0 above). Assignment to BASH_ARGV0 causes the value
853 assigned to also be assigned to $0. If BASH_ARGV0 is unset, it
854 loses its special properties, even if it is subsequently reset.
855 BASH_CMDS
856 An associative array variable whose members correspond to the
857 internal hash table of commands as maintained by the hash
858 builtin. Elements added to this array appear in the hash table;
859 however, unsetting array elements currently does not cause com‐
860 mand names to be removed from the hash table. If BASH_CMDS is
861 unset, it loses its special properties, even if it is subse‐
862 quently reset.
863 BASH_COMMAND
864 The command currently being executed or about to be executed,
865 unless the shell is executing a command as the result of a trap,
866 in which case it is the command executing at the time of the
867 trap. If BASH_COMMAND is unset, it loses its special proper‐
868 ties, even if it is subsequently reset.
869 BASH_EXECUTION_STRING
870 The command argument to the -c invocation option.
871 BASH_LINENO
872 An array variable whose members are the line numbers in source
873 files where each corresponding member of FUNCNAME was invoked.
874 ${BASH_LINENO[$i]} is the line number in the source file
875 (${BASH_SOURCE[$i+1]}) where ${FUNCNAME[$i]} was called (or
876 ${BASH_LINENO[$i-1]} if referenced within another shell func‐
877 tion). Use LINENO to obtain the current line number.
878 BASH_LOADABLES_PATH
879 A colon-separated list of directories in which the shell looks
880 for dynamically loadable builtins specified by the enable com‐
881 mand.
882 BASH_REMATCH
883 An array variable whose members are assigned by the =~ binary
884 operator to the [[ conditional command. The element with index
885 0 is the portion of the string matching the entire regular ex‐
886 pression. The element with index n is the portion of the string
887 matching the nth parenthesized subexpression.
888 BASH_SOURCE
889 An array variable whose members are the source filenames where
890 the corresponding shell function names in the FUNCNAME array
891 variable are defined. The shell function ${FUNCNAME[$i]} is de‐
892 fined in the file ${BASH_SOURCE[$i]} and called from
893 ${BASH_SOURCE[$i+1]}.
894 BASH_SUBSHELL
895 Incremented by one within each subshell or subshell environment
896 when the shell begins executing in that environment. The ini‐
897 tial value is 0. If BASH_SUBSHELL is unset, it loses its spe‐
898 cial properties, even if it is subsequently reset.
899 BASH_VERSINFO
900 A readonly array variable whose members hold version information
901 for this instance of bash. The values assigned to the array
902 members are as follows:
903 BASH_VERSINFO[0] The major version number (the release).
904 BASH_VERSINFO[1] The minor version number (the version).
905 BASH_VERSINFO[2] The patch level.
906 BASH_VERSINFO[3] The build version.
907 BASH_VERSINFO[4] The release status (e.g., beta1).
908 BASH_VERSINFO[5] The value of MACHTYPE.
909 BASH_VERSION
910 Expands to a string describing the version of this instance of
911 bash.
912 COMP_CWORD
913 An index into ${COMP_WORDS} of the word containing the current
914 cursor position. This variable is available only in shell func‐
915 tions invoked by the programmable completion facilities (see
916 Programmable Completion below).
917 COMP_KEY
918 The key (or final key of a key sequence) used to invoke the cur‐
919 rent completion function.
920 COMP_LINE
921 The current command line. This variable is available only in
922 shell functions and external commands invoked by the program‐
923 mable completion facilities (see Programmable Completion below).
924 COMP_POINT
925 The index of the current cursor position relative to the begin‐
926 ning of the current command. If the current cursor position is
927 at the end of the current command, the value of this variable is
928 equal to ${#COMP_LINE}. This variable is available only in
929 shell functions and external commands invoked by the program‐
930 mable completion facilities (see Programmable Completion below).
931 COMP_TYPE
932 Set to an integer value corresponding to the type of completion
933 attempted that caused a completion function to be called: TAB,
934 for normal completion, ?, for listing completions after succes‐
935 sive tabs, !, for listing alternatives on partial word comple‐
936 tion, @, to list completions if the word is not unmodified, or
937 %, for menu completion. This variable is available only in
938 shell functions and external commands invoked by the program‐
939 mable completion facilities (see Programmable Completion below).
940 COMP_WORDBREAKS
941 The set of characters that the readline library treats as word
942 separators when performing word completion. If COMP_WORDBREAKS
943 is unset, it loses its special properties, even if it is subse‐
944 quently reset.
945 COMP_WORDS
946 An array variable (see Arrays below) consisting of the individ‐
947 ual words in the current command line. The line is split into
948 words as readline would split it, using COMP_WORDBREAKS as de‐
949 scribed above. This variable is available only in shell func‐
950 tions invoked by the programmable completion facilities (see
951 Programmable Completion below).
952 COPROC An array variable (see Arrays below) created to hold the file
953 descriptors for output from and input to an unnamed coprocess
954 (see Coprocesses above).
955 DIRSTACK
956 An array variable (see Arrays below) containing the current con‐
957 tents of the directory stack. Directories appear in the stack
958 in the order they are displayed by the dirs builtin. Assigning
959 to members of this array variable may be used to modify directo‐
960 ries already in the stack, but the pushd and popd builtins must
961 be used to add and remove directories. Assignment to this vari‐
962 able will not change the current directory. If DIRSTACK is un‐
963 set, it loses its special properties, even if it is subsequently
964 reset.
965 EPOCHREALTIME
966 Each time this parameter is referenced, it expands to the number
967 of seconds since the Unix Epoch (see time(3)) as a floating
968 point value with micro-second granularity. Assignments to
969 EPOCHREALTIME are ignored. If EPOCHREALTIME is unset, it loses
970 its special properties, even if it is subsequently reset.
971 EPOCHSECONDS
972 Each time this parameter is referenced, it expands to the number
973 of seconds since the Unix Epoch (see time(3)). Assignments to
974 EPOCHSECONDS are ignored. If EPOCHSECONDS is unset, it loses
975 its special properties, even if it is subsequently reset.
976 EUID Expands to the effective user ID of the current user, initial‐
977 ized at shell startup. This variable is readonly.
978 FUNCNAME
979 An array variable containing the names of all shell functions
980 currently in the execution call stack. The element with index 0
981 is the name of any currently-executing shell function. The bot‐
982 tom-most element (the one with the highest index) is "main".
983 This variable exists only when a shell function is executing.
984 Assignments to FUNCNAME have no effect. If FUNCNAME is unset,
985 it loses its special properties, even if it is subsequently re‐
986 set.
987 This variable can be used with BASH_LINENO and BASH_SOURCE.
989 Each element of FUNCNAME has corresponding elements in
990 BASH_LINENO and BASH_SOURCE to describe the call stack. For in‐
991 stance, ${FUNCNAME[$i]} was called from the file
992 ${BASH_SOURCE[$i+1]} at line number ${BASH_LINENO[$i]}. The
993 caller builtin displays the current call stack using this infor‐
994 mation.
995 GROUPS An array variable containing the list of groups of which the
996 current user is a member. Assignments to GROUPS have no effect.
997 If GROUPS is unset, it loses its special properties, even if it
998 is subsequently reset.
999 HISTCMD
1000 The history number, or index in the history list, of the current
1001 command. Assignments to HISTCMD are ignored. If HISTCMD is un‐
1002 set, it loses its special properties, even if it is subsequently
1003 reset.
1004 HOSTNAME
1005 Automatically set to the name of the current host.
1006 HOSTTYPE
1007 Automatically set to a string that uniquely describes the type
1008 of machine on which bash is executing. The default is system-
1009 dependent.
1010 LINENO Each time this parameter is referenced, the shell substitutes a
1011 decimal number representing the current sequential line number
1012 (starting with 1) within a script or function. When not in a
1013 script or function, the value substituted is not guaranteed to
1014 be meaningful. If LINENO is unset, it loses its special proper‐
1015 ties, even if it is subsequently reset.
1016 MACHTYPE
1017 Automatically set to a string that fully describes the system
1018 type on which bash is executing, in the standard GNU cpu-com‐
1019 pany-system format. The default is system-dependent.
1020 MAPFILE
1021 An array variable (see Arrays below) created to hold the text
1022 read by the mapfile builtin when no variable name is supplied.
1023 OLDPWD The previous working directory as set by the cd command.
1024 OPTARG The value of the last option argument processed by the getopts
1025 builtin command (see SHELL BUILTIN COMMANDS below).
1026 OPTIND The index of the next argument to be processed by the getopts
1027 builtin command (see SHELL BUILTIN COMMANDS below).
1028 OSTYPE Automatically set to a string that describes the operating sys‐
1029 tem on which bash is executing. The default is system-depen‐
1030 dent.
1031 PIPESTATUS
1032 An array variable (see Arrays below) containing a list of exit
1033 status values from the processes in the most-recently-executed
1034 foreground pipeline (which may contain only a single command).
1035 PPID The process ID of the shell's parent. This variable is read‐
1036 only.
1037 PWD The current working directory as set by the cd command.
1038 RANDOM Each time this parameter is referenced, it expands to a random
1039 integer between 0 and 32767. Assigning a value to RANDOM ini‐
1040 tializes (seeds) the sequence of random numbers. If RANDOM is
1041 unset, it loses its special properties, even if it is subse‐
1042 quently reset.
1043 READLINE_LINE
1044 The contents of the readline line buffer, for use with "bind -x"
1045 (see SHELL BUILTIN COMMANDS below).
1046 READLINE_MARK
1047 The position of the mark (saved insertion point) in the readline
1048 line buffer, for use with "bind -x" (see SHELL BUILTIN COMMANDS
1049 below). The characters between the insertion point and the mark
1050 are often called the region.
1051 READLINE_POINT
1052 The position of the insertion point in the readline line buffer,
1053 for use with "bind -x" (see SHELL BUILTIN COMMANDS below).
1054 REPLY Set to the line of input read by the read builtin command when
1055 no arguments are supplied.
1056 SECONDS
1057 Each time this parameter is referenced, the number of seconds
1058 since shell invocation is returned. If a value is assigned to
1059 SECONDS, the value returned upon subsequent references is the
1060 number of seconds since the assignment plus the value assigned.
1061 The number of seconds at shell invocation and the current time
1062 is always determined by querying the system clock. If SECONDS
1063 is unset, it loses its special properties, even if it is subse‐
1064 quently reset.
1065 SHELLOPTS
1066 A colon-separated list of enabled shell options. Each word in
1067 the list is a valid argument for the -o option to the set
1068 builtin command (see SHELL BUILTIN COMMANDS below). The options
1069 appearing in SHELLOPTS are those reported as on by set -o. If
1070 this variable is in the environment when bash starts up, each
1071 shell option in the list will be enabled before reading any
1072 startup files. This variable is read-only.
1073 SHLVL Incremented by one each time an instance of bash is started.
1074 SRANDOM
1075 This variable expands to a 32-bit pseudo-random number each time
1076 it is referenced. The random number generator is not linear on
1077 systems that support /dev/urandom or arc4random, so each re‐
1078 turned number has no relationship to the numbers preceding it.
1079 The random number generator cannot be seeded, so assignments to
1080 this variable have no effect. If SRANDOM is unset, it loses its
1081 special properties, even if it is subsequently reset.
1082 UID Expands to the user ID of the current user, initialized at shell
1083 startup. This variable is readonly.
1084 The following variables are used by the shell. In some cases, bash as‐
1086 signs a default value to a variable; these cases are noted below.
1087 BASH_COMPAT
1089 The value is used to set the shell's compatibility level. See
1090 SHELL COMPATIBILITY MODE below for a description of the various
1091 compatibility levels and their effects. The value may be a dec‐
1092 imal number (e.g., 4.2) or an integer (e.g., 42) corresponding
1093 to the desired compatibility level. If BASH_COMPAT is unset or
1094 set to the empty string, the compatibility level is set to the
1095 default for the current version. If BASH_COMPAT is set to a
1096 value that is not one of the valid compatibility levels, the
1097 shell prints an error message and sets the compatibility level
1098 to the default for the current version. The valid values corre‐
1099 spond to the compatibility levels described below under BSHELL‐
1100 COMPATIBILITYMODE. For example, 4.2 and 42 are valid values
1101 that correspond to the compat42 shopt option and set the compat‐
1102 ibility level to 42. The current version is also a valid value.
1103 BASH_ENV
1104 If this parameter is set when bash is executing a shell script,
1105 its value is interpreted as a filename containing commands to
1106 initialize the shell, as in ~/.bashrc. The value of BASH_ENV is
1107 subjected to parameter expansion, command substitution, and
1108 arithmetic expansion before being interpreted as a filename.
1109 PATH is not used to search for the resultant filename.
1110 BASH_XTRACEFD
1111 If set to an integer corresponding to a valid file descriptor,
1112 bash will write the trace output generated when set -x is en‐
1113 abled to that file descriptor. The file descriptor is closed
1114 when BASH_XTRACEFD is unset or assigned a new value. Unsetting
1115 BASH_XTRACEFD or assigning it the empty string causes the trace
1116 output to be sent to the standard error. Note that setting
1117 BASH_XTRACEFD to 2 (the standard error file descriptor) and then
1118 unsetting it will result in the standard error being closed.
1119 CDPATH The search path for the cd command. This is a colon-separated
1120 list of directories in which the shell looks for destination di‐
1121 rectories specified by the cd command. A sample value is
1122 ".:~:/usr".
1123 CHILD_MAX
1124 Set the number of exited child status values for the shell to
1125 remember. Bash will not allow this value to be decreased below
1126 a POSIX-mandated minimum, and there is a maximum value (cur‐
1127 rently 8192) that this may not exceed. The minimum value is
1128 system-dependent.
1129 COLUMNS
1130 Used by the select compound command to determine the terminal
1131 width when printing selection lists. Automatically set if the
1132 checkwinsize option is enabled or in an interactive shell upon
1133 receipt of a SIGWINCH.
1134 COMPREPLY
1135 An array variable from which bash reads the possible completions
1136 generated by a shell function invoked by the programmable com‐
1137 pletion facility (see Programmable Completion below). Each ar‐
1138 ray element contains one possible completion.
1139 EMACS If bash finds this variable in the environment when the shell
1140 starts with value "t", it assumes that the shell is running in
1141 an Emacs shell buffer and disables line editing.
1142 ENV Expanded and executed similarly to BASH_ENV (see INVOCATION
1143 above) when an interactive shell is invoked in posix mode.
1144 EXECIGNORE
1145 A colon-separated list of shell patterns (see Pattern Matching)
1146 defining the list of filenames to be ignored by command search
1147 using PATH. Files whose full pathnames match one of these pat‐
1148 terns are not considered executable files for the purposes of
1149 completion and command execution via PATH lookup. This does not
1150 affect the behavior of the [, test, and [[ commands. Full path‐
1151 names in the command hash table are not subject to EXECIGNORE.
1152 Use this variable to ignore shared library files that have the
1153 executable bit set, but are not executable files. The pattern
1154 matching honors the setting of the extglob shell option.
1155 FCEDIT The default editor for the fc builtin command.
1156 FIGNORE
1157 A colon-separated list of suffixes to ignore when performing
1158 filename completion (see READLINE below). A filename whose suf‐
1159 fix matches one of the entries in FIGNORE is excluded from the
1160 list of matched filenames. A sample value is ".o:~".
1161 FUNCNEST
1162 If set to a numeric value greater than 0, defines a maximum
1163 function nesting level. Function invocations that exceed this
1164 nesting level will cause the current command to abort.
1165 GLOBIGNORE
1166 A colon-separated list of patterns defining the set of file
1167 names to be ignored by pathname expansion. If a file name
1168 matched by a pathname expansion pattern also matches one of the
1169 patterns in GLOBIGNORE, it is removed from the list of matches.
1170 HISTCONTROL
1171 A colon-separated list of values controlling how commands are
1172 saved on the history list. If the list of values includes ig‐
1173 norespace, lines which begin with a space character are not
1174 saved in the history list. A value of ignoredups causes lines
1175 matching the previous history entry to not be saved. A value of
1176 ignoreboth is shorthand for ignorespace and ignoredups. A value
1177 of erasedups causes all previous lines matching the current line
1178 to be removed from the history list before that line is saved.
1179 Any value not in the above list is ignored. If HISTCONTROL is
1180 unset, or does not include a valid value, all lines read by the
1181 shell parser are saved on the history list, subject to the value
1182 of HISTIGNORE. The second and subsequent lines of a multi-line
1183 compound command are not tested, and are added to the history
1184 regardless of the value of HISTCONTROL.
1185 HISTFILE
1186 The name of the file in which command history is saved (see HIS‐
1187 TORY below). The default value is ~/.bash_history. If unset,
1188 the command history is not saved when a shell exits.
1189 HISTFILESIZE
1190 The maximum number of lines contained in the history file. When
1191 this variable is assigned a value, the history file is trun‐
1192 cated, if necessary, to contain no more than that number of
1193 lines by removing the oldest entries. The history file is also
1194 truncated to this size after writing it when a shell exits. If
1195 the value is 0, the history file is truncated to zero size.
1196 Non-numeric values and numeric values less than zero inhibit
1197 truncation. The shell sets the default value to the value of
1198 HISTSIZE after reading any startup files.
1199 HISTIGNORE
1200 A colon-separated list of patterns used to decide which command
1201 lines should be saved on the history list. Each pattern is an‐
1202 chored at the beginning of the line and must match the complete
1203 line (no implicit `*' is appended). Each pattern is tested
1204 against the line after the checks specified by HISTCONTROL are
1205 applied. In addition to the normal shell pattern matching char‐
1206 acters, `&' matches the previous history line. `&' may be es‐
1207 caped using a backslash; the backslash is removed before at‐
1208 tempting a match. The second and subsequent lines of a multi-
1209 line compound command are not tested, and are added to the his‐
1210 tory regardless of the value of HISTIGNORE. The pattern match‐
1211 ing honors the setting of the extglob shell option.
1212 HISTSIZE
1213 The number of commands to remember in the command history (see
1214 HISTORY below). If the value is 0, commands are not saved in
1215 the history list. Numeric values less than zero result in every
1216 command being saved on the history list (there is no limit).
1217 The shell sets the default value to 500 after reading any
1218 startup files.
1219 HISTTIMEFORMAT
1220 If this variable is set and not null, its value is used as a
1221 format string for strftime(3) to print the time stamp associated
1222 with each history entry displayed by the history builtin. If
1223 this variable is set, time stamps are written to the history
1224 file so they may be preserved across shell sessions. This uses
1225 the history comment character to distinguish timestamps from
1226 other history lines.
1227 HOME The home directory of the current user; the default argument for
1228 the cd builtin command. The value of this variable is also used
1229 when performing tilde expansion.
1230 HOSTFILE
1231 Contains the name of a file in the same format as /etc/hosts
1232 that should be read when the shell needs to complete a hostname.
1233 The list of possible hostname completions may be changed while
1234 the shell is running; the next time hostname completion is at‐
1235 tempted after the value is changed, bash adds the contents of
1236 the new file to the existing list. If HOSTFILE is set, but has
1237 no value, or does not name a readable file, bash attempts to
1238 read /etc/hosts to obtain the list of possible hostname comple‐
1239 tions. When HOSTFILE is unset, the hostname list is cleared.
1240 IFS The Internal Field Separator that is used for word splitting af‐
1241 ter expansion and to split lines into words with the read
1242 builtin command. The default value is ``<space><tab><new‐
1243 line>''.
1244 IGNOREEOF
1245 Controls the action of an interactive shell on receipt of an EOF
1246 character as the sole input. If set, the value is the number of
1247 consecutive EOF characters which must be typed as the first
1248 characters on an input line before bash exits. If the variable
1249 exists but does not have a numeric value, or has no value, the
1250 default value is 10. If it does not exist, EOF signifies the
1251 end of input to the shell.
1252 INPUTRC
1253 The filename for the readline startup file, overriding the de‐
1254 fault of ~/.inputrc (see READLINE below).
1255 INSIDE_EMACS
1256 If this variable appears in the environment when the shell
1257 starts, bash assumes that it is running inside an Emacs shell
1258 buffer and may disable line editing, depending on the value of
1259 TERM.
1260 LANG Used to determine the locale category for any category not
1261 specifically selected with a variable starting with LC_.
1262 LC_ALL This variable overrides the value of LANG and any other LC_
1263 variable specifying a locale category.
1264 LC_COLLATE
1265 This variable determines the collation order used when sorting
1266 the results of pathname expansion, and determines the behavior
1267 of range expressions, equivalence classes, and collating se‐
1268 quences within pathname expansion and pattern matching.
1269 LC_CTYPE
1270 This variable determines the interpretation of characters and
1271 the behavior of character classes within pathname expansion and
1272 pattern matching.
1273 LC_MESSAGES
1274 This variable determines the locale used to translate double-
1275 quoted strings preceded by a $.
1276 LC_NUMERIC
1277 This variable determines the locale category used for number
1278 formatting.
1279 LC_TIME
1280 This variable determines the locale category used for data and
1281 time formatting.
1282 LINES Used by the select compound command to determine the column
1283 length for printing selection lists. Automatically set if the
1284 checkwinsize option is enabled or in an interactive shell upon
1285 receipt of a SIGWINCH.
1286 MAIL If this parameter is set to a file or directory name and the
1287 MAILPATH variable is not set, bash informs the user of the ar‐
1288 rival of mail in the specified file or Maildir-format directory.
1289 MAILCHECK
1290 Specifies how often (in seconds) bash checks for mail. The de‐
1291 fault is 60 seconds. When it is time to check for mail, the
1292 shell does so before displaying the primary prompt. If this
1293 variable is unset, or set to a value that is not a number
1294 greater than or equal to zero, the shell disables mail checking.
1295 MAILPATH
1296 A colon-separated list of filenames to be checked for mail. The
1297 message to be printed when mail arrives in a particular file may
1298 be specified by separating the filename from the message with a
1299 `?'. When used in the text of the message, $_ expands to the
1300 name of the current mailfile. Example:
1301 MAILPATH='/var/mail/bfox?"You have mail":~/shell-mail?"$_ has
1302 mail!"'
1303 Bash can be configured to supply a default value for this vari‐
1304 able (there is no value by default), but the location of the
1305 user mail files that it uses is system dependent (e.g.,
1306 /var/mail/$USER).
1307 OPTERR If set to the value 1, bash displays error messages generated by
1308 the getopts builtin command (see SHELL BUILTIN COMMANDS below).
1309 OPTERR is initialized to 1 each time the shell is invoked or a
1310 shell script is executed.
1311 PATH The search path for commands. It is a colon-separated list of
1312 directories in which the shell looks for commands (see COMMAND
1313 EXECUTION below). A zero-length (null) directory name in the
1314 value of PATH indicates the current directory. A null directory
1315 name may appear as two adjacent colons, or as an initial or
1316 trailing colon. The default path is system-dependent, and is
1317 set by the administrator who installs bash. A common value is
1318 ``/usr/local/bin:/usr/lo‐
1319 cal/sbin:/usr/bin:/usr/sbin:/bin:/sbin''.
1320 POSIXLY_CORRECT
1321 If this variable is in the environment when bash starts, the
1322 shell enters posix mode before reading the startup files, as if
1323 the --posix invocation option had been supplied. If it is set
1324 while the shell is running, bash enables posix mode, as if the
1325 command set -o posix had been executed. When the shell enters
1326 posix mode, it sets this variable if it was not already set.
1327 PROMPT_COMMAND
1328 If this variable is set, and is an array, the value of each set
1329 element is executed as a command prior to issuing each primary
1330 prompt. If this is set but not an array variable, its value is
1331 used as a command to execute instead.
1332 PROMPT_DIRTRIM
1333 If set to a number greater than zero, the value is used as the
1334 number of trailing directory components to retain when expanding
1335 the \w and \W prompt string escapes (see PROMPTING below).
1336 Characters removed are replaced with an ellipsis.
1337 PS0 The value of this parameter is expanded (see PROMPTING below)
1338 and displayed by interactive shells after reading a command and
1339 before the command is executed.
1340 PS1 The value of this parameter is expanded (see PROMPTING below)
1341 and used as the primary prompt string. The default value is
1342 ``\s-\v\$ ''.
1343 PS2 The value of this parameter is expanded as with PS1 and used as
1344 the secondary prompt string. The default is ``> ''.
1345 PS3 The value of this parameter is used as the prompt for the select
1346 command (see SHELL GRAMMAR above).
1347 PS4 The value of this parameter is expanded as with PS1 and the
1348 value is printed before each command bash displays during an ex‐
1349 ecution trace. The first character of the expanded value of PS4
1350 is replicated multiple times, as necessary, to indicate multiple
1351 levels of indirection. The default is ``+ ''.
1352 SHELL This variable expands to the full pathname to the shell. If it
1353 is not set when the shell starts, bash assigns to it the full
1354 pathname of the current user's login shell.
1355 TIMEFORMAT
1356 The value of this parameter is used as a format string specify‐
1357 ing how the timing information for pipelines prefixed with the
1358 time reserved word should be displayed. The % character intro‐
1359 duces an escape sequence that is expanded to a time value or
1360 other information. The escape sequences and their meanings are
1361 as follows; the braces denote optional portions.
1362 %% A literal %.
1363 %[p][l]R The elapsed time in seconds.
1364 %[p][l]U The number of CPU seconds spent in user mode.
1365 %[p][l]S The number of CPU seconds spent in system mode.
1366 %P The CPU percentage, computed as (%U + %S) / %R.
1367 The optional p is a digit specifying the precision, the number
1369 of fractional digits after a decimal point. A value of 0 causes
1370 no decimal point or fraction to be output. At most three places
1371 after the decimal point may be specified; values of p greater
1372 than 3 are changed to 3. If p is not specified, the value 3 is
1373 used.
1374 The optional l specifies a longer format, including minutes, of
1376 the form MMmSS.FFs. The value of p determines whether or not
1377 the fraction is included.
1378 If this variable is not set, bash acts as if it had the value
1380 $'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS'. If the value is null,
1381 no timing information is displayed. A trailing newline is added
1382 when the format string is displayed.
1383 TMOUT If set to a value greater than zero, TMOUT is treated as the de‐
1384 fault timeout for the read builtin. The select command termi‐
1385 nates if input does not arrive after TMOUT seconds when input is
1386 coming from a terminal. In an interactive shell, the value is
1387 interpreted as the number of seconds to wait for a line of input
1388 after issuing the primary prompt. Bash terminates after waiting
1389 for that number of seconds if a complete line of input does not
1390 arrive.
1391 TMPDIR If set, bash uses its value as the name of a directory in which
1392 bash creates temporary files for the shell's use.
1393 auto_resume
1394 This variable controls how the shell interacts with the user and
1395 job control. If this variable is set, single word simple com‐
1396 mands without redirections are treated as candidates for resump‐
1397 tion of an existing stopped job. There is no ambiguity allowed;
1398 if there is more than one job beginning with the string typed,
1399 the job most recently accessed is selected. The name of a
1400 stopped job, in this context, is the command line used to start
1401 it. If set to the value exact, the string supplied must match
1402 the name of a stopped job exactly; if set to substring, the
1403 string supplied needs to match a substring of the name of a
1404 stopped job. The substring value provides functionality analo‐
1405 gous to the %? job identifier (see JOB CONTROL below). If set
1406 to any other value, the supplied string must be a prefix of a
1407 stopped job's name; this provides functionality analogous to the
1408 %string job identifier.
1409 histchars
1410 The two or three characters which control history expansion and
1411 tokenization (see HISTORY EXPANSION below). The first character
1412 is the history expansion character, the character which signals
1413 the start of a history expansion, normally `!'. The second
1414 character is the quick substitution character, which is used as
1415 shorthand for re-running the previous command entered, substi‐
1416 tuting one string for another in the command. The default is
1417 `^'. The optional third character is the character which indi‐
1418 cates that the remainder of the line is a comment when found as
1419 the first character of a word, normally `#'. The history com‐
1420 ment character causes history substitution to be skipped for the
1421 remaining words on the line. It does not necessarily cause the
1422 shell parser to treat the rest of the line as a comment.
1423 Arrays
1425 Bash provides one-dimensional indexed and associative array variables.
1426 Any variable may be used as an indexed array; the declare builtin will
1427 explicitly declare an array. There is no maximum limit on the size of
1428 an array, nor any requirement that members be indexed or assigned con‐
1429 tiguously. Indexed arrays are referenced using integers (including
1430 arithmetic expressions) and are zero-based; associative arrays are ref‐
1431 erenced using arbitrary strings. Unless otherwise noted, indexed array
1432 indices must be non-negative integers.
1433 An indexed array is created automatically if any variable is assigned
1435 to using the syntax name[subscript]=value. The subscript is treated as
1436 an arithmetic expression that must evaluate to a number. To explicitly
1437 declare an indexed array, use declare -a name (see SHELL BUILTIN COM‐
1438 MANDS below). declare -a name[subscript] is also accepted; the sub‐
1439 script is ignored.
1440 Associative arrays are created using declare -A name.
1442 Attributes may be specified for an array variable using the declare and
1444 readonly builtins. Each attribute applies to all members of an array.
1445 Arrays are assigned to using compound assignments of the form
1447 name=(value1 ... valuen), where each value may be of the form [sub‐
1448 script]=string. Indexed array assignments do not require anything but
1449 string. Each value in the list is expanded using all the shell expan‐
1450 sions described below under EXPANSION. When assigning to indexed ar‐
1451 rays, if the optional brackets and subscript are supplied, that index
1452 is assigned to; otherwise the index of the element assigned is the last
1453 index assigned to by the statement plus one. Indexing starts at zero.
1454 When assigning to an associative array, the words in a compound assign‐
1456 ment may be either assignment statements, for which the subscript is
1457 required, or a list of words that is interpreted as a sequence of al‐
1458 ternating keys and values: name=( key1 value1 key2 value2 ...). These
1459 are treated identically to name=( [key1]=value1 [key2]=value2 ...).
1460 The first word in the list determines how the remaining words are in‐
1461 terpreted; all assignments in a list must be of the same type. When
1462 using key/value pairs, the keys may not be missing or empty; a final
1463 missing value is treated like the empty string.
1464 This syntax is also accepted by the declare builtin. Individual array
1466 elements may be assigned to using the name[subscript]=value syntax in‐
1467 troduced above. When assigning to an indexed array, if name is sub‐
1468 scripted by a negative number, that number is interpreted as relative
1469 to one greater than the maximum index of name, so negative indices
1470 count back from the end of the array, and an index of -1 references the
1471 last element.
1472 Any element of an array may be referenced using ${name[subscript]}.
1474 The braces are required to avoid conflicts with pathname expansion. If
1475 subscript is @ or *, the word expands to all members of name. These
1476 subscripts differ only when the word appears within double quotes. If
1477 the word is double-quoted, ${name[*]} expands to a single word with the
1478 value of each array member separated by the first character of the IFS
1479 special variable, and ${name[@]} expands each element of name to a sep‐
1480 arate word. When there are no array members, ${name[@]} expands to
1481 nothing. If the double-quoted expansion occurs within a word, the ex‐
1482 pansion of the first parameter is joined with the beginning part of the
1483 original word, and the expansion of the last parameter is joined with
1484 the last part of the original word. This is analogous to the expansion
1485 of the special parameters * and @ (see Special Parameters above).
1486 ${#name[subscript]} expands to the length of ${name[subscript]}. If
1487 subscript is * or @, the expansion is the number of elements in the ar‐
1488 ray. If the subscript used to reference an element of an indexed array
1489 evaluates to a number less than zero, it is interpreted as relative to
1490 one greater than the maximum index of the array, so negative indices
1491 count back from the end of the array, and an index of -1 references the
1492 last element.
1493 Referencing an array variable without a subscript is equivalent to ref‐
1495 erencing the array with a subscript of 0. Any reference to a variable
1496 using a valid subscript is legal, and bash will create an array if nec‐
1497 essary.
1498 An array variable is considered set if a subscript has been assigned a
1500 value. The null string is a valid value.
1501 It is possible to obtain the keys (indices) of an array as well as the
1503 values. ${!name[@]} and ${!name[*]} expand to the indices assigned in
1504 array variable name. The treatment when in double quotes is similar to
1505 the expansion of the special parameters @ and * within double quotes.
1506 The unset builtin is used to destroy arrays. unset name[subscript] de‐
1508 stroys the array element at index subscript, for both indexed and asso‐
1509 ciative arrays. Negative subscripts to indexed arrays are interpreted
1510 as described above. Unsetting the last element of an array variable
1511 does not unset the variable. unset name, where name is an array, or
1512 unset name[subscript], where subscript is * or @, removes the entire
1513 array.
1514 When using a variable name with a subscript as an argument to a com‐
1516 mand, such as with unset, without using the word expansion syntax de‐
1517 scribed above, the argument is subject to pathname expansion. If path‐
1518 name expansion is not desired, the argument should be quoted.
1519 The declare, local, and readonly builtins each accept a -a option to
1521 specify an indexed array and a -A option to specify an associative ar‐
1522 ray. If both options are supplied, -A takes precedence. The read
1523 builtin accepts a -a option to assign a list of words read from the
1524 standard input to an array. The set and declare builtins display array
1525 values in a way that allows them to be reused as assignments.
1526
1528 Expansion is performed on the command line after it has been split into
1529 words. There are seven kinds of expansion performed: brace expansion,
1530 tilde expansion, parameter and variable expansion, command substitu‐
1531 tion, arithmetic expansion, word splitting, and pathname expansion.
1532 The order of expansions is: brace expansion; tilde expansion, parameter
1534 and variable expansion, arithmetic expansion, and command substitution
1535 (done in a left-to-right fashion); word splitting; and pathname expan‐
1536 sion.
1537 On systems that can support it, there is an additional expansion avail‐
1539 able: process substitution. This is performed at the same time as
1540 tilde, parameter, variable, and arithmetic expansion and command sub‐
1541 stitution.
1542 After these expansions are performed, quote characters present in the
1544 original word are removed unless they have been quoted themselves
1545 (quote removal).
1546 Only brace expansion, word splitting, and pathname expansion can in‐
1548 crease the number of words of the expansion; other expansions expand a
1549 single word to a single word. The only exceptions to this are the ex‐
1550 pansions of "$@" and "${name[@]}", and, in most cases, $* and
1551 ${name[*]} as explained above (see PARAMETERS).
1552 Brace Expansion
1554 Brace expansion is a mechanism by which arbitrary strings may be gener‐
1555 ated. This mechanism is similar to pathname expansion, but the file‐
1556 names generated need not exist. Patterns to be brace expanded take the
1557 form of an optional preamble, followed by either a series of comma-sep‐
1558 arated strings or a sequence expression between a pair of braces, fol‐
1559 lowed by an optional postscript. The preamble is prefixed to each
1560 string contained within the braces, and the postscript is then appended
1561 to each resulting string, expanding left to right.
1562 Brace expansions may be nested. The results of each expanded string
1564 are not sorted; left to right order is preserved. For example,
1565 a{d,c,b}e expands into `ade ace abe'.
1566 A sequence expression takes the form {x..y[..incr]}, where x and y are
1568 either integers or single characters, and incr, an optional increment,
1569 is an integer. When integers are supplied, the expression expands to
1570 each number between x and y, inclusive. Supplied integers may be pre‐
1571 fixed with 0 to force each term to have the same width. When either x
1572 or y begins with a zero, the shell attempts to force all generated
1573 terms to contain the same number of digits, zero-padding where neces‐
1574 sary. When characters are supplied, the expression expands to each
1575 character lexicographically between x and y, inclusive, using the de‐
1576 fault C locale. Note that both x and y must be of the same type. When
1577 the increment is supplied, it is used as the difference between each
1578 term. The default increment is 1 or -1 as appropriate.
1579 Brace expansion is performed before any other expansions, and any char‐
1581 acters special to other expansions are preserved in the result. It is
1582 strictly textual. Bash does not apply any syntactic interpretation to
1583 the context of the expansion or the text between the braces.
1584 A correctly-formed brace expansion must contain unquoted opening and
1586 closing braces, and at least one unquoted comma or a valid sequence ex‐
1587 pression. Any incorrectly formed brace expansion is left unchanged. A
1588 { or , may be quoted with a backslash to prevent its being considered
1589 part of a brace expression. To avoid conflicts with parameter expan‐
1590 sion, the string ${ is not considered eligible for brace expansion, and
1591 inhibits brace expansion until the closing }.
1592 This construct is typically used as shorthand when the common prefix of
1594 the strings to be generated is longer than in the above example:
1595 mkdir /usr/local/src/bash/{old,new,dist,bugs}
1597 or
1598 chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}
1599 Brace expansion introduces a slight incompatibility with historical
1601 versions of sh. sh does not treat opening or closing braces specially
1602 when they appear as part of a word, and preserves them in the output.
1603 Bash removes braces from words as a consequence of brace expansion.
1604 For example, a word entered to sh as file{1,2} appears identically in
1605 the output. The same word is output as file1 file2 after expansion by
1606 bash. If strict compatibility with sh is desired, start bash with the
1607 +B option or disable brace expansion with the +B option to the set com‐
1608 mand (see SHELL BUILTIN COMMANDS below).
1609 Tilde Expansion
1611 If a word begins with an unquoted tilde character (`~'), all of the
1612 characters preceding the first unquoted slash (or all characters, if
1613 there is no unquoted slash) are considered a tilde-prefix. If none of
1614 the characters in the tilde-prefix are quoted, the characters in the
1615 tilde-prefix following the tilde are treated as a possible login name.
1616 If this login name is the null string, the tilde is replaced with the
1617 value of the shell parameter HOME. If HOME is unset, the home direc‐
1618 tory of the user executing the shell is substituted instead. Other‐
1619 wise, the tilde-prefix is replaced with the home directory associated
1620 with the specified login name.
1621 If the tilde-prefix is a `~+', the value of the shell variable PWD re‐
1623 places the tilde-prefix. If the tilde-prefix is a `~-', the value of
1624 the shell variable OLDPWD, if it is set, is substituted. If the char‐
1625 acters following the tilde in the tilde-prefix consist of a number N,
1626 optionally prefixed by a `+' or a `-', the tilde-prefix is replaced
1627 with the corresponding element from the directory stack, as it would be
1628 displayed by the dirs builtin invoked with the tilde-prefix as an argu‐
1629 ment. If the characters following the tilde in the tilde-prefix con‐
1630 sist of a number without a leading `+' or `-', `+' is assumed.
1631 If the login name is invalid, or the tilde expansion fails, the word is
1633 unchanged.
1634 Each variable assignment is checked for unquoted tilde-prefixes immedi‐
1636 ately following a : or the first =. In these cases, tilde expansion is
1637 also performed. Consequently, one may use filenames with tildes in as‐
1638 signments to PATH, MAILPATH, and CDPATH, and the shell assigns the ex‐
1639 panded value.
1640 Bash also performs tilde expansion on words satisfying the conditions
1642 of variable assignments (as described above under PARAMETERS) when they
1643 appear as arguments to simple commands. Bash does not do this, except
1644 for the declaration commands listed above, when in posix mode.
1645 Parameter Expansion
1647 The `$' character introduces parameter expansion, command substitution,
1648 or arithmetic expansion. The parameter name or symbol to be expanded
1649 may be enclosed in braces, which are optional but serve to protect the
1650 variable to be expanded from characters immediately following it which
1651 could be interpreted as part of the name.
1652 When braces are used, the matching ending brace is the first `}' not
1654 escaped by a backslash or within a quoted string, and not within an em‐
1655 bedded arithmetic expansion, command substitution, or parameter expan‐
1656 sion.
1657 ${parameter}
1659 The value of parameter is substituted. The braces are required
1660 when parameter is a positional parameter with more than one
1661 digit, or when parameter is followed by a character which is not
1662 to be interpreted as part of its name. The parameter is a shell
1663 parameter as described above PARAMETERS) or an array reference
1664 (Arrays).
1665 If the first character of parameter is an exclamation point (!), and
1667 parameter is not a nameref, it introduces a level of indirection. Bash
1668 uses the value formed by expanding the rest of parameter as the new pa‐
1669 rameter; this is then expanded and that value is used in the rest of
1670 the expansion, rather than the expansion of the original parameter.
1671 This is known as indirect expansion. The value is subject to tilde ex‐
1672 pansion, parameter expansion, command substitution, and arithmetic ex‐
1673 pansion. If parameter is a nameref, this expands to the name of the
1674 parameter referenced by parameter instead of performing the complete
1675 indirect expansion. The exceptions to this are the expansions of
1676 ${!prefix*} and ${!name[@]} described below. The exclamation point
1677 must immediately follow the left brace in order to introduce indirec‐
1678 tion.
1679 In each of the cases below, word is subject to tilde expansion, parame‐
1681 ter expansion, command substitution, and arithmetic expansion.
1682 When not performing substring expansion, using the forms documented be‐
1684 low (e.g., :-), bash tests for a parameter that is unset or null.
1685 Omitting the colon results in a test only for a parameter that is un‐
1686 set.
1687 ${parameter:-word}
1689 Use Default Values. If parameter is unset or null, the expan‐
1690 sion of word is substituted. Otherwise, the value of parameter
1691 is substituted.
1692 ${parameter:=word}
1693 Assign Default Values. If parameter is unset or null, the ex‐
1694 pansion of word is assigned to parameter. The value of parame‐
1695 ter is then substituted. Positional parameters and special pa‐
1696 rameters may not be assigned to in this way.
1697 ${parameter:?word}
1698 Display Error if Null or Unset. If parameter is null or unset,
1699 the expansion of word (or a message to that effect if word is
1700 not present) is written to the standard error and the shell, if
1701 it is not interactive, exits. Otherwise, the value of parameter
1702 is substituted.
1703 ${parameter:+word}
1704 Use Alternate Value. If parameter is null or unset, nothing is
1705 substituted, otherwise the expansion of word is substituted.
1706 ${parameter:offset}
1707 ${parameter:offset:length}
1708 Substring Expansion. Expands to up to length characters of the
1709 value of parameter starting at the character specified by off‐
1710 set. If parameter is @, an indexed array subscripted by @ or *,
1711 or an associative array name, the results differ as described
1712 below. If length is omitted, expands to the substring of the
1713 value of parameter starting at the character specified by offset
1714 and extending to the end of the value. length and offset are
1715 arithmetic expressions (see ARITHMETIC EVALUATION below).
1716 If offset evaluates to a number less than zero, the value is
1718 used as an offset in characters from the end of the value of pa‐
1719 rameter. If length evaluates to a number less than zero, it is
1720 interpreted as an offset in characters from the end of the value
1721 of parameter rather than a number of characters, and the expan‐
1722 sion is the characters between offset and that result. Note
1723 that a negative offset must be separated from the colon by at
1724 least one space to avoid being confused with the :- expansion.
1725 If parameter is @, the result is length positional parameters
1727 beginning at offset. A negative offset is taken relative to one
1728 greater than the greatest positional parameter, so an offset of
1729 -1 evaluates to the last positional parameter. It is an expan‐
1730 sion error if length evaluates to a number less than zero.
1731 If parameter is an indexed array name subscripted by @ or *, the
1733 result is the length members of the array beginning with ${pa‐
1734 rameter[offset]}. A negative offset is taken relative to one
1735 greater than the maximum index of the specified array. It is an
1736 expansion error if length evaluates to a number less than zero.
1737 Substring expansion applied to an associative array produces un‐
1739 defined results.
1740 Substring indexing is zero-based unless the positional parame‐
1742 ters are used, in which case the indexing starts at 1 by de‐
1743 fault. If offset is 0, and the positional parameters are used,
1744 $0 is prefixed to the list.
1745 ${!prefix*}
1747 ${!prefix@}
1748 Names matching prefix. Expands to the names of variables whose
1749 names begin with prefix, separated by the first character of the
1750 IFS special variable. When @ is used and the expansion appears
1751 within double quotes, each variable name expands to a separate
1752 word.
1753 ${!name[@]}
1755 ${!name[*]}
1756 List of array keys. If name is an array variable, expands to
1757 the list of array indices (keys) assigned in name. If name is
1758 not an array, expands to 0 if name is set and null otherwise.
1759 When @ is used and the expansion appears within double quotes,
1760 each key expands to a separate word.
1761 ${#parameter}
1763 Parameter length. The length in characters of the value of pa‐
1764 rameter is substituted. If parameter is * or @, the value sub‐
1765 stituted is the number of positional parameters. If parameter
1766 is an array name subscripted by * or @, the value substituted is
1767 the number of elements in the array. If parameter is an indexed
1768 array name subscripted by a negative number, that number is in‐
1769 terpreted as relative to one greater than the maximum index of
1770 parameter, so negative indices count back from the end of the
1771 array, and an index of -1 references the last element.
1772 ${parameter#word}
1774 ${parameter##word}
1775 Remove matching prefix pattern. The word is expanded to produce
1776 a pattern just as in pathname expansion, and matched against the
1777 expanded value of parameter using the rules described under Pat‐
1778 tern Matching below. If the pattern matches the beginning of
1779 the value of parameter, then the result of the expansion is the
1780 expanded value of parameter with the shortest matching pattern
1781 (the ``#'' case) or the longest matching pattern (the ``##''
1782 case) deleted. If parameter is @ or *, the pattern removal op‐
1783 eration is applied to each positional parameter in turn, and the
1784 expansion is the resultant list. If parameter is an array vari‐
1785 able subscripted with @ or *, the pattern removal operation is
1786 applied to each member of the array in turn, and the expansion
1787 is the resultant list.
1788 ${parameter%word}
1790 ${parameter%%word}
1791 Remove matching suffix pattern. The word is expanded to produce
1792 a pattern just as in pathname expansion, and matched against the
1793 expanded value of parameter using the rules described under Pat‐
1794 tern Matching below. If the pattern matches a trailing portion
1795 of the expanded value of parameter, then the result of the ex‐
1796 pansion is the expanded value of parameter with the shortest
1797 matching pattern (the ``%'' case) or the longest matching pat‐
1798 tern (the ``%%'' case) deleted. If parameter is @ or *, the
1799 pattern removal operation is applied to each positional parame‐
1800 ter in turn, and the expansion is the resultant list. If param‐
1801 eter is an array variable subscripted with @ or *, the pattern
1802 removal operation is applied to each member of the array in
1803 turn, and the expansion is the resultant list.
1804 ${parameter/pattern/string}
1806 Pattern substitution. The pattern is expanded to produce a pat‐
1807 tern just as in pathname expansion, Parameter is expanded and
1808 the longest match of pattern against its value is replaced with
1809 string. The match is performed using the rules described under
1810 Pattern Matching below. If pattern begins with /, all matches
1811 of pattern are replaced with string. Normally only the first
1812 match is replaced. If pattern begins with #, it must match at
1813 the beginning of the expanded value of parameter. If pattern
1814 begins with %, it must match at the end of the expanded value of
1815 parameter. If string is null, matches of pattern are deleted
1816 and the / following pattern may be omitted. If the nocasematch
1817 shell option is enabled, the match is performed without regard
1818 to the case of alphabetic characters. If parameter is @ or *,
1819 the substitution operation is applied to each positional parame‐
1820 ter in turn, and the expansion is the resultant list. If param‐
1821 eter is an array variable subscripted with @ or *, the substitu‐
1822 tion operation is applied to each member of the array in turn,
1823 and the expansion is the resultant list.
1824 ${parameter^pattern}
1826 ${parameter^^pattern}
1827 ${parameter,pattern}
1828 ${parameter,,pattern}
1829 Case modification. This expansion modifies the case of alpha‐
1830 betic characters in parameter. The pattern is expanded to pro‐
1831 duce a pattern just as in pathname expansion. Each character in
1832 the expanded value of parameter is tested against pattern, and,
1833 if it matches the pattern, its case is converted. The pattern
1834 should not attempt to match more than one character. The ^ op‐
1835 erator converts lowercase letters matching pattern to uppercase;
1836 the , operator converts matching uppercase letters to lowercase.
1837 The ^^ and ,, expansions convert each matched character in the
1838 expanded value; the ^ and , expansions match and convert only
1839 the first character in the expanded value. If pattern is omit‐
1840 ted, it is treated like a ?, which matches every character. If
1841 parameter is @ or *, the case modification operation is applied
1842 to each positional parameter in turn, and the expansion is the
1843 resultant list. If parameter is an array variable subscripted
1844 with @ or *, the case modification operation is applied to each
1845 member of the array in turn, and the expansion is the resultant
1846 list.
1847 ${parameter@operator}
1849 Parameter transformation. The expansion is either a transforma‐
1850 tion of the value of parameter or information about parameter
1851 itself, depending on the value of operator. Each operator is a
1852 single letter:
1853 U The expansion is a string that is the value of parameter
1855 with lowercase alphabetic characters converted to upper‐
1856 case.
1857 u The expansion is a string that is the value of parameter
1858 with the first character converted to uppercase, if it is
1859 alphabetic.
1860 L The expansion is a string that is the value of parameter
1861 with uppercase alphabetic characters converted to lower‐
1862 case.
1863 Q The expansion is a string that is the value of parameter
1864 quoted in a format that can be reused as input.
1865 E The expansion is a string that is the value of parameter
1866 with backslash escape sequences expanded as with the
1867 $'...' quoting mechanism.
1868 P The expansion is a string that is the result of expanding
1869 the value of parameter as if it were a prompt string (see
1870 PROMPTING below).
1871 A The expansion is a string in the form of an assignment
1872 statement or declare command that, if evaluated, will
1873 recreate parameter with its attributes and value.
1874 K Produces a possibly-quoted version of the value of param‐
1875 eter, except that it prints the values of indexed and as‐
1876 sociative arrays as a sequence of quoted key-value pairs
1877 (see Arrays above).
1878 a The expansion is a string consisting of flag values rep‐
1879 resenting parameter's attributes.
1880 If parameter is @ or *, the operation is applied to each posi‐
1882 tional parameter in turn, and the expansion is the resultant
1883 list. If parameter is an array variable subscripted with @ or
1884 *, the operation is applied to each member of the array in turn,
1885 and the expansion is the resultant list.
1886 The result of the expansion is subject to word splitting and
1888 pathname expansion as described below.
1889 Command Substitution
1891 Command substitution allows the output of a command to replace the com‐
1892 mand name. There are two forms:
1893 $(command)
1895 or
1896 `command`
1897 Bash performs the expansion by executing command in a subshell environ‐
1899 ment and replacing the command substitution with the standard output of
1900 the command, with any trailing newlines deleted. Embedded newlines are
1901 not deleted, but they may be removed during word splitting. The com‐
1902 mand substitution $(cat file) can be replaced by the equivalent but
1903 faster $(< file).
1904 When the old-style backquote form of substitution is used, backslash
1906 retains its literal meaning except when followed by $, `, or \. The
1907 first backquote not preceded by a backslash terminates the command sub‐
1908 stitution. When using the $(command) form, all characters between the
1909 parentheses make up the command; none are treated specially.
1910 Command substitutions may be nested. To nest when using the backquoted
1912 form, escape the inner backquotes with backslashes.
1913 If the substitution appears within double quotes, word splitting and
1915 pathname expansion are not performed on the results.
1916 Arithmetic Expansion
1918 Arithmetic expansion allows the evaluation of an arithmetic expression
1919 and the substitution of the result. The format for arithmetic expan‐
1920 sion is:
1921 $((expression))
1923 The expression is treated as if it were within double quotes, but a
1925 double quote inside the parentheses is not treated specially. All to‐
1926 kens in the expression undergo parameter and variable expansion, com‐
1927 mand substitution, and quote removal. The result is treated as the
1928 arithmetic expression to be evaluated. Arithmetic expansions may be
1929 nested.
1930 The evaluation is performed according to the rules listed below under
1932 ARITHMETIC EVALUATION. If expression is invalid, bash prints a message
1933 indicating failure and no substitution occurs.
1934 Process Substitution
1936 Process substitution allows a process's input or output to be referred
1937 to using a filename. It takes the form of <(list) or >(list). The
1938 process list is run asynchronously, and its input or output appears as
1939 a filename. This filename is passed as an argument to the current com‐
1940 mand as the result of the expansion. If the >(list) form is used,
1941 writing to the file will provide input for list. If the <(list) form
1942 is used, the file passed as an argument should be read to obtain the
1943 output of list. Process substitution is supported on systems that sup‐
1944 port named pipes (FIFOs) or the /dev/fd method of naming open files.
1945 When available, process substitution is performed simultaneously with
1947 parameter and variable expansion, command substitution, and arithmetic
1948 expansion.
1949 Word Splitting
1951 The shell scans the results of parameter expansion, command substitu‐
1952 tion, and arithmetic expansion that did not occur within double quotes
1953 for word splitting.
1954 The shell treats each character of IFS as a delimiter, and splits the
1956 results of the other expansions into words using these characters as
1957 field terminators. If IFS is unset, or its value is exactly
1958 <space><tab><newline>, the default, then sequences of <space>, <tab>,
1959 and <newline> at the beginning and end of the results of the previous
1960 expansions are ignored, and any sequence of IFS characters not at the
1961 beginning or end serves to delimit words. If IFS has a value other
1962 than the default, then sequences of the whitespace characters space,
1963 tab, and newline are ignored at the beginning and end of the word, as
1964 long as the whitespace character is in the value of IFS (an IFS white‐
1965 space character). Any character in IFS that is not IFS whitespace,
1966 along with any adjacent IFS whitespace characters, delimits a field. A
1967 sequence of IFS whitespace characters is also treated as a delimiter.
1968 If the value of IFS is null, no word splitting occurs.
1969 Explicit null arguments ("" or '') are retained and passed to commands
1971 as empty strings. Unquoted implicit null arguments, resulting from the
1972 expansion of parameters that have no values, are removed. If a parame‐
1973 ter with no value is expanded within double quotes, a null argument re‐
1974 sults and is retained and passed to a command as an empty string. When
1975 a quoted null argument appears as part of a word whose expansion is
1976 non-null, the null argument is removed. That is, the word -d'' becomes
1977 -d after word splitting and null argument removal.
1978 Note that if no expansion occurs, no splitting is performed.
1980 Pathname Expansion
1982 After word splitting, unless the -f option has been set, bash scans
1983 each word for the characters *, ?, and [. If one of these characters
1984 appears, and is not quoted, then the word is regarded as a pattern, and
1985 replaced with an alphabetically sorted list of filenames matching the
1986 pattern (see Pattern Matching below). If no matching filenames are
1987 found, and the shell option nullglob is not enabled, the word is left
1988 unchanged. If the nullglob option is set, and no matches are found,
1989 the word is removed. If the failglob shell option is set, and no
1990 matches are found, an error message is printed and the command is not
1991 executed. If the shell option nocaseglob is enabled, the match is per‐
1992 formed without regard to the case of alphabetic characters. When a
1993 pattern is used for pathname expansion, the character ``.'' at the
1994 start of a name or immediately following a slash must be matched ex‐
1995 plicitly, unless the shell option dotglob is set. The filenames ``.''
1996 and ``..'' must always be matched explicitly, even if dotglob is set.
1997 In other cases, the ``.'' character is not treated specially. When
1998 matching a pathname, the slash character must always be matched explic‐
1999 itly by a slash in the pattern, but in other matching contexts it can
2000 be matched by a special pattern character as described below under Pat‐
2001 tern Matching. See the description of shopt below under SHELL BUILTIN
2002 COMMANDS for a description of the nocaseglob, nullglob, failglob, and
2003 dotglob shell options.
2004 The GLOBIGNORE shell variable may be used to restrict the set of file
2006 names matching a pattern. If GLOBIGNORE is set, each matching file
2007 name that also matches one of the patterns in GLOBIGNORE is removed
2008 from the list of matches. If the nocaseglob option is set, the match‐
2009 ing against the patterns in GLOBIGNORE is performed without regard to
2010 case. The filenames ``.'' and ``..'' are always ignored when GLOBIG‐
2011 NORE is set and not null. However, setting GLOBIGNORE to a non-null
2012 value has the effect of enabling the dotglob shell option, so all other
2013 filenames beginning with a ``.'' will match. To get the old behavior
2014 of ignoring filenames beginning with a ``.'', make ``.*'' one of the
2015 patterns in GLOBIGNORE. The dotglob option is disabled when GLOBIGNORE
2016 is unset. The pattern matching honors the setting of the extglob shell
2017 option.
2018 Pattern Matching
2020 Any character that appears in a pattern, other than the special pattern
2022 characters described below, matches itself. The NUL character may not
2023 occur in a pattern. A backslash escapes the following character; the
2024 escaping backslash is discarded when matching. The special pattern
2025 characters must be quoted if they are to be matched literally.
2026 The special pattern characters have the following meanings:
2028 * Matches any string, including the null string. When the
2030 globstar shell option is enabled, and * is used in a
2031 pathname expansion context, two adjacent *s used as a
2032 single pattern will match all files and zero or more di‐
2033 rectories and subdirectories. If followed by a /, two
2034 adjacent *s will match only directories and subdirecto‐
2035 ries.
2036 ? Matches any single character.
2037 [...] Matches any one of the enclosed characters. A pair of
2038 characters separated by a hyphen denotes a range expres‐
2039 sion; any character that falls between those two charac‐
2040 ters, inclusive, using the current locale's collating se‐
2041 quence and character set, is matched. If the first char‐
2042 acter following the [ is a ! or a ^ then any character
2043 not enclosed is matched. The sorting order of characters
2044 in range expressions is determined by the current locale
2045 and the values of the LC_COLLATE or LC_ALL shell vari‐
2046 ables, if set. To obtain the traditional interpretation
2047 of range expressions, where [a-d] is equivalent to
2048 [abcd], set value of the LC_ALL shell variable to C, or
2049 enable the globasciiranges shell option. A - may be
2050 matched by including it as the first or last character in
2051 the set. A ] may be matched by including it as the first
2052 character in the set.
2053 Within [ and ], character classes can be specified using
2055 the syntax [:class:], where class is one of the following
2056 classes defined in the POSIX standard:
2057 alnum alpha ascii blank cntrl digit graph lower print
2058 punct space upper word xdigit
2059 A character class matches any character belonging to that
2060 class. The word character class matches letters, digits,
2061 and the character _.
2062 Within [ and ], an equivalence class can be specified us‐
2064 ing the syntax [=c=], which matches all characters with
2065 the same collation weight (as defined by the current lo‐
2066 cale) as the character c.
2067 Within [ and ], the syntax [.symbol.] matches the collat‐
2069 ing symbol symbol.
2070 If the extglob shell option is enabled using the shopt builtin, several
2072 extended pattern matching operators are recognized. In the following
2073 description, a pattern-list is a list of one or more patterns separated
2074 by a |. Composite patterns may be formed using one or more of the fol‐
2075 lowing sub-patterns:
2076 ?(pattern-list)
2078 Matches zero or one occurrence of the given patterns
2079 *(pattern-list)
2080 Matches zero or more occurrences of the given patterns
2081 +(pattern-list)
2082 Matches one or more occurrences of the given patterns
2083 @(pattern-list)
2084 Matches one of the given patterns
2085 !(pattern-list)
2086 Matches anything except one of the given patterns
2087 Complicated extended pattern matching against long strings is slow, es‐
2089 pecially when the patterns contain alternations and the strings contain
2090 multiple matches. Using separate matches against shorter strings, or
2091 using arrays of strings instead of a single long string, may be faster.
2092 Quote Removal
2094 After the preceding expansions, all unquoted occurrences of the charac‐
2095 ters \, ', and " that did not result from one of the above expansions
2096 are removed.
2097
2099 Before a command is executed, its input and output may be redirected
2100 using a special notation interpreted by the shell. Redirection allows
2101 commands' file handles to be duplicated, opened, closed, made to refer
2102 to different files, and can change the files the command reads from and
2103 writes to. Redirection may also be used to modify file handles in the
2104 current shell execution environment. The following redirection opera‐
2105 tors may precede or appear anywhere within a simple command or may fol‐
2106 low a command. Redirections are processed in the order they appear,
2107 from left to right.
2108 Each redirection that may be preceded by a file descriptor number may
2110 instead be preceded by a word of the form {varname}. In this case, for
2111 each redirection operator except >&- and <&-, the shell will allocate a
2112 file descriptor greater than or equal to 10 and assign it to varname.
2113 If >&- or <&- is preceded by {varname}, the value of varname defines
2114 the file descriptor to close. If {varname} is supplied, the redirect‐
2115 ion persists beyond the scope of the command, allowing the shell pro‐
2116 grammer to manage the file descriptor himself.
2117 In the following descriptions, if the file descriptor number is omit‐
2119 ted, and the first character of the redirection operator is <, the re‐
2120 direction refers to the standard input (file descriptor 0). If the
2121 first character of the redirection operator is >, the redirection
2122 refers to the standard output (file descriptor 1).
2123 The word following the redirection operator in the following descrip‐
2125 tions, unless otherwise noted, is subjected to brace expansion, tilde
2126 expansion, parameter and variable expansion, command substitution,
2127 arithmetic expansion, quote removal, pathname expansion, and word
2128 splitting. If it expands to more than one word, bash reports an error.
2129 Note that the order of redirections is significant. For example, the
2131 command
2132 ls > dirlist 2>&1
2134 directs both standard output and standard error to the file dirlist,
2136 while the command
2137 ls 2>&1 > dirlist
2139 directs only the standard output to file dirlist, because the standard
2141 error was duplicated from the standard output before the standard out‐
2142 put was redirected to dirlist.
2143 Bash handles several filenames specially when they are used in redirec‐
2145 tions, as described in the following table. If the operating system on
2146 which bash is running provides these special files, bash will use them;
2147 otherwise it will emulate them internally with the behavior described
2148 below.
2149 /dev/fd/fd
2151 If fd is a valid integer, file descriptor fd is dupli‐
2152 cated.
2153 /dev/stdin
2154 File descriptor 0 is duplicated.
2155 /dev/stdout
2156 File descriptor 1 is duplicated.
2157 /dev/stderr
2158 File descriptor 2 is duplicated.
2159 /dev/tcp/host/port
2160 If host is a valid hostname or Internet address, and port
2161 is an integer port number or service name, bash attempts
2162 to open the corresponding TCP socket.
2163 /dev/udp/host/port
2164 If host is a valid hostname or Internet address, and port
2165 is an integer port number or service name, bash attempts
2166 to open the corresponding UDP socket.
2167 A failure to open or create a file causes the redirection to fail.
2169 Redirections using file descriptors greater than 9 should be used with
2171 care, as they may conflict with file descriptors the shell uses inter‐
2172 nally.
2173 Redirecting Input
2175 Redirection of input causes the file whose name results from the expan‐
2176 sion of word to be opened for reading on file descriptor n, or the
2177 standard input (file descriptor 0) if n is not specified.
2178 The general format for redirecting input is:
2180 [n]<word
2182 Redirecting Output
2184 Redirection of output causes the file whose name results from the ex‐
2185 pansion of word to be opened for writing on file descriptor n, or the
2186 standard output (file descriptor 1) if n is not specified. If the file
2187 does not exist it is created; if it does exist it is truncated to zero
2188 size.
2189 The general format for redirecting output is:
2191 [n]>word
2193 If the redirection operator is >, and the noclobber option to the set
2195 builtin has been enabled, the redirection will fail if the file whose
2196 name results from the expansion of word exists and is a regular file.
2197 If the redirection operator is >|, or the redirection operator is > and
2198 the noclobber option to the set builtin command is not enabled, the re‐
2199 direction is attempted even if the file named by word exists.
2200 Appending Redirected Output
2202 Redirection of output in this fashion causes the file whose name re‐
2203 sults from the expansion of word to be opened for appending on file de‐
2204 scriptor n, or the standard output (file descriptor 1) if n is not
2205 specified. If the file does not exist it is created.
2206 The general format for appending output is:
2208 [n]>>word
2210 Redirecting Standard Output and Standard Error
2212 This construct allows both the standard output (file descriptor 1) and
2213 the standard error output (file descriptor 2) to be redirected to the
2214 file whose name is the expansion of word.
2215 There are two formats for redirecting standard output and standard er‐
2217 ror:
2218 &>word
2220 and
2221 >&word
2222 Of the two forms, the first is preferred. This is semantically equiva‐
2224 lent to
2225 >word 2>&1
2227 When using the second form, word may not expand to a number or -. If
2229 it does, other redirection operators apply (see Duplicating File De‐
2230 scriptors below) for compatibility reasons.
2231 Appending Standard Output and Standard Error
2233 This construct allows both the standard output (file descriptor 1) and
2234 the standard error output (file descriptor 2) to be appended to the
2235 file whose name is the expansion of word.
2236 The format for appending standard output and standard error is:
2238 &>>word
2240 This is semantically equivalent to
2242 >>word 2>&1
2244 (see Duplicating File Descriptors below).
2246 Here Documents
2248 This type of redirection instructs the shell to read input from the
2249 current source until a line containing only delimiter (with no trailing
2250 blanks) is seen. All of the lines read up to that point are then used
2251 as the standard input (or file descriptor n if n is specified) for a
2252 command.
2253 The format of here-documents is:
2255 [n]<<[-]word
2257 here-document
2258 delimiter
2259 No parameter and variable expansion, command substitution, arithmetic
2261 expansion, or pathname expansion is performed on word. If any part of
2262 word is quoted, the delimiter is the result of quote removal on word,
2263 and the lines in the here-document are not expanded. If word is un‐
2264 quoted, all lines of the here-document are subjected to parameter ex‐
2265 pansion, command substitution, and arithmetic expansion, the character
2266 sequence \<newline> is ignored, and \ must be used to quote the charac‐
2267 ters \, $, and `.
2268 If the redirection operator is <<-, then all leading tab characters are
2270 stripped from input lines and the line containing delimiter. This al‐
2271 lows here-documents within shell scripts to be indented in a natural
2272 fashion.
2273 Here Strings
2275 A variant of here documents, the format is:
2276 [n]<<<word
2278 The word undergoes tilde expansion, parameter and variable expansion,
2280 command substitution, arithmetic expansion, and quote removal. Path‐
2281 name expansion and word splitting are not performed. The result is
2282 supplied as a single string, with a newline appended, to the command on
2283 its standard input (or file descriptor n if n is specified).
2284 Duplicating File Descriptors
2286 The redirection operator
2287 [n]<&word
2289 is used to duplicate input file descriptors. If word expands to one or
2291 more digits, the file descriptor denoted by n is made to be a copy of
2292 that file descriptor. If the digits in word do not specify a file de‐
2293 scriptor open for input, a redirection error occurs. If word evaluates
2294 to -, file descriptor n is closed. If n is not specified, the standard
2295 input (file descriptor 0) is used.
2296 The operator
2298 [n]>&word
2300 is used similarly to duplicate output file descriptors. If n is not
2302 specified, the standard output (file descriptor 1) is used. If the
2303 digits in word do not specify a file descriptor open for output, a re‐
2304 direction error occurs. If word evaluates to -, file descriptor n is
2305 closed. As a special case, if n is omitted, and word does not expand
2306 to one or more digits or -, the standard output and standard error are
2307 redirected as described previously.
2308 Moving File Descriptors
2310 The redirection operator
2311 [n]<&digit-
2313 moves the file descriptor digit to file descriptor n, or the standard
2315 input (file descriptor 0) if n is not specified. digit is closed after
2316 being duplicated to n.
2317 Similarly, the redirection operator
2319 [n]>&digit-
2321 moves the file descriptor digit to file descriptor n, or the standard
2323 output (file descriptor 1) if n is not specified.
2324 Opening File Descriptors for Reading and Writing
2326 The redirection operator
2327 [n]<>word
2329 causes the file whose name is the expansion of word to be opened for
2331 both reading and writing on file descriptor n, or on file descriptor 0
2332 if n is not specified. If the file does not exist, it is created.
2333
2335 Aliases allow a string to be substituted for a word when it is used as
2336 the first word of a simple command. The shell maintains a list of
2337 aliases that may be set and unset with the alias and unalias builtin
2338 commands (see SHELL BUILTIN COMMANDS below). The first word of each
2339 simple command, if unquoted, is checked to see if it has an alias. If
2340 so, that word is replaced by the text of the alias. The characters /,
2341 $, `, and = and any of the shell metacharacters or quoting characters
2342 listed above may not appear in an alias name. The replacement text may
2343 contain any valid shell input, including shell metacharacters. The
2344 first word of the replacement text is tested for aliases, but a word
2345 that is identical to an alias being expanded is not expanded a second
2346 time. This means that one may alias ls to ls -F, for instance, and
2347 bash does not try to recursively expand the replacement text. If the
2348 last character of the alias value is a blank, then the next command
2349 word following the alias is also checked for alias expansion.
2350 Aliases are created and listed with the alias command, and removed with
2352 the unalias command.
2353 There is no mechanism for using arguments in the replacement text. If
2355 arguments are needed, a shell function should be used (see FUNCTIONS
2356 below).
2357 Aliases are not expanded when the shell is not interactive, unless the
2359 expand_aliases shell option is set using shopt (see the description of
2360 shopt under SHELL BUILTIN COMMANDS below).
2361 The rules concerning the definition and use of aliases are somewhat
2363 confusing. Bash always reads at least one complete line of input, and
2364 all lines that make up a compound command, before executing any of the
2365 commands on that line or the compound command. Aliases are expanded
2366 when a command is read, not when it is executed. Therefore, an alias
2367 definition appearing on the same line as another command does not take
2368 effect until the next line of input is read. The commands following
2369 the alias definition on that line are not affected by the new alias.
2370 This behavior is also an issue when functions are executed. Aliases
2371 are expanded when a function definition is read, not when the function
2372 is executed, because a function definition is itself a command. As a
2373 consequence, aliases defined in a function are not available until af‐
2374 ter that function is executed. To be safe, always put alias defini‐
2375 tions on a separate line, and do not use alias in compound commands.
2376 For almost every purpose, aliases are superseded by shell functions.
2378
2380 A shell function, defined as described above under SHELL GRAMMAR,
2381 stores a series of commands for later execution. When the name of a
2382 shell function is used as a simple command name, the list of commands
2383 associated with that function name is executed. Functions are executed
2384 in the context of the current shell; no new process is created to in‐
2385 terpret them (contrast this with the execution of a shell script).
2386 When a function is executed, the arguments to the function become the
2387 positional parameters during its execution. The special parameter # is
2388 updated to reflect the change. Special parameter 0 is unchanged. The
2389 first element of the FUNCNAME variable is set to the name of the func‐
2390 tion while the function is executing.
2391 All other aspects of the shell execution environment are identical be‐
2393 tween a function and its caller with these exceptions: the DEBUG and
2394 RETURN traps (see the description of the trap builtin under SHELL
2395 BUILTIN COMMANDS below) are not inherited unless the function has been
2396 given the trace attribute (see the description of the declare builtin
2397 below) or the -o functrace shell option has been enabled with the set
2398 builtin (in which case all functions inherit the DEBUG and RETURN
2399 traps), and the ERR trap is not inherited unless the -o errtrace shell
2400 option has been enabled.
2401 Variables local to the function may be declared with the local builtin
2403 command. Ordinarily, variables and their values are shared between the
2404 function and its caller. If a variable is declared local, the vari‐
2405 able's visible scope is restricted to that function and its children
2406 (including the functions it calls). Local variables "shadow" variables
2407 with the same name declared at previous scopes. For instance, a local
2408 variable declared in a function hides a global variable of the same
2409 name: references and assignments refer to the local variable, leaving
2410 the global variable unmodified. When the function returns, the global
2411 variable is once again visible.
2412 The shell uses dynamic scoping to control a variable's visibility
2414 within functions. With dynamic scoping, visible variables and their
2415 values are a result of the sequence of function calls that caused exe‐
2416 cution to reach the current function. The value of a variable that a
2417 function sees depends on its value within its caller, if any, whether
2418 that caller is the "global" scope or another shell function. This is
2419 also the value that a local variable declaration "shadows", and the
2420 value that is restored when the function returns.
2421 For example, if a variable var is declared as local in function func1,
2423 and func1 calls another function func2, references to var made from
2424 within func2 will resolve to the local variable var from func1, shadow‐
2425 ing any global variable named var.
2426 The unset builtin also acts using the same dynamic scope: if a variable
2428 is local to the current scope, unset will unset it; otherwise the unset
2429 will refer to the variable found in any calling scope as described
2430 above. If a variable at the current local scope is unset, it will re‐
2431 main so until it is reset in that scope or until the function returns.
2432 Once the function returns, any instance of the variable at a previous
2433 scope will become visible. If the unset acts on a variable at a previ‐
2434 ous scope, any instance of a variable with that name that had been
2435 shadowed will become visible.
2436 The FUNCNEST variable, if set to a numeric value greater than 0, de‐
2438 fines a maximum function nesting level. Function invocations that ex‐
2439 ceed the limit cause the entire command to abort.
2440 If the builtin command return is executed in a function, the function
2442 completes and execution resumes with the next command after the func‐
2443 tion call. Any command associated with the RETURN trap is executed be‐
2444 fore execution resumes. When a function completes, the values of the
2445 positional parameters and the special parameter # are restored to the
2446 values they had prior to the function's execution.
2447 Function names and definitions may be listed with the -f option to the
2449 declare or typeset builtin commands. The -F option to declare or type‐
2450 set will list the function names only (and optionally the source file
2451 and line number, if the extdebug shell option is enabled). Functions
2452 may be exported so that subshells automatically have them defined with
2453 the -f option to the export builtin. A function definition may be
2454 deleted using the -f option to the unset builtin.
2455 Functions may be recursive. The FUNCNEST variable may be used to limit
2457 the depth of the function call stack and restrict the number of func‐
2458 tion invocations. By default, no limit is imposed on the number of re‐
2459 cursive calls.
2460
2462 The shell allows arithmetic expressions to be evaluated, under certain
2463 circumstances (see the let and declare builtin commands, the (( com‐
2464 pound command, and Arithmetic Expansion). Evaluation is done in fixed-
2465 width integers with no check for overflow, though division by 0 is
2466 trapped and flagged as an error. The operators and their precedence,
2467 associativity, and values are the same as in the C language. The fol‐
2468 lowing list of operators is grouped into levels of equal-precedence op‐
2469 erators. The levels are listed in order of decreasing precedence.
2470 id++ id--
2472 variable post-increment and post-decrement
2473 - + unary minus and plus
2474 ++id --id
2475 variable pre-increment and pre-decrement
2476 ! ~ logical and bitwise negation
2477 ** exponentiation
2478 * / % multiplication, division, remainder
2479 + - addition, subtraction
2480 << >> left and right bitwise shifts
2481 <= >= < >
2482 comparison
2483 == != equality and inequality
2484 & bitwise AND
2485 ^ bitwise exclusive OR
2486 | bitwise OR
2487 && logical AND
2488 || logical OR
2489 expr?expr:expr
2490 conditional operator
2491 = *= /= %= += -= <<= >>= &= ^= |=
2492 assignment
2493 expr1 , expr2
2494 comma
2495 Shell variables are allowed as operands; parameter expansion is per‐
2497 formed before the expression is evaluated. Within an expression, shell
2498 variables may also be referenced by name without using the parameter
2499 expansion syntax. A shell variable that is null or unset evaluates to
2500 0 when referenced by name without using the parameter expansion syntax.
2501 The value of a variable is evaluated as an arithmetic expression when
2502 it is referenced, or when a variable which has been given the integer
2503 attribute using declare -i is assigned a value. A null value evaluates
2504 to 0. A shell variable need not have its integer attribute turned on
2505 to be used in an expression.
2506 Integer constants follow the C language definition, without suffixes or
2508 character constants. Constants with a leading 0 are interpreted as oc‐
2509 tal numbers. A leading 0x or 0X denotes hexadecimal. Otherwise, num‐
2510 bers take the form [base#]n, where the optional base is a decimal num‐
2511 ber between 2 and 64 representing the arithmetic base, and n is a num‐
2512 ber in that base. If base# is omitted, then base 10 is used. When
2513 specifying n, if a non-digit is required, the digits greater than 9 are
2514 represented by the lowercase letters, the uppercase letters, @, and _,
2515 in that order. If base is less than or equal to 36, lowercase and up‐
2516 percase letters may be used interchangeably to represent numbers be‐
2517 tween 10 and 35.
2518 Operators are evaluated in order of precedence. Sub-expressions in
2520 parentheses are evaluated first and may override the precedence rules
2521 above.
2522
2524 Conditional expressions are used by the [[ compound command and the
2525 test and [ builtin commands to test file attributes and perform string
2526 and arithmetic comparisons. The test and [ commands determine their
2527 behavior based on the number of arguments; see the descriptions of
2528 those commands for any other command-specific actions.
2529 Expressions are formed from the following unary or binary primaries.
2531 Bash handles several filenames specially when they are used in expres‐
2532 sions. If the operating system on which bash is running provides these
2533 special files, bash will use them; otherwise it will emulate them in‐
2534 ternally with this behavior: If any file argument to one of the pri‐
2535 maries is of the form /dev/fd/n, then file descriptor n is checked. If
2536 the file argument to one of the primaries is one of /dev/stdin,
2537 /dev/stdout, or /dev/stderr, file descriptor 0, 1, or 2, respectively,
2538 is checked.
2539 Unless otherwise specified, primaries that operate on files follow sym‐
2541 bolic links and operate on the target of the link, rather than the link
2542 itself.
2543 When used with [[, the < and > operators sort lexicographically using
2545 the current locale. The test command sorts using ASCII ordering.
2546 -a file
2548 True if file exists.
2549 -b file
2550 True if file exists and is a block special file.
2551 -c file
2552 True if file exists and is a character special file.
2553 -d file
2554 True if file exists and is a directory.
2555 -e file
2556 True if file exists.
2557 -f file
2558 True if file exists and is a regular file.
2559 -g file
2560 True if file exists and is set-group-id.
2561 -h file
2562 True if file exists and is a symbolic link.
2563 -k file
2564 True if file exists and its ``sticky'' bit is set.
2565 -p file
2566 True if file exists and is a named pipe (FIFO).
2567 -r file
2568 True if file exists and is readable.
2569 -s file
2570 True if file exists and has a size greater than zero.
2571 -t fd True if file descriptor fd is open and refers to a terminal.
2572 -u file
2573 True if file exists and its set-user-id bit is set.
2574 -w file
2575 True if file exists and is writable.
2576 -x file
2577 True if file exists and is executable.
2578 -G file
2579 True if file exists and is owned by the effective group id.
2580 -L file
2581 True if file exists and is a symbolic link.
2582 -N file
2583 True if file exists and has been modified since it was last
2584 read.
2585 -O file
2586 True if file exists and is owned by the effective user id.
2587 -S file
2588 True if file exists and is a socket.
2589 file1 -ef file2
2590 True if file1 and file2 refer to the same device and inode num‐
2591 bers.
2592 file1 -nt file2
2593 True if file1 is newer (according to modification date) than
2594 file2, or if file1 exists and file2 does not.
2595 file1 -ot file2
2596 True if file1 is older than file2, or if file2 exists and file1
2597 does not.
2598 -o optname
2599 True if the shell option optname is enabled. See the list of
2600 options under the description of the -o option to the set
2601 builtin below.
2602 -v varname
2603 True if the shell variable varname is set (has been assigned a
2604 value).
2605 -R varname
2606 True if the shell variable varname is set and is a name refer‐
2607 ence.
2608 -z string
2609 True if the length of string is zero.
2610 string
2611 -n string
2612 True if the length of string is non-zero.
2613 string1 == string2
2615 string1 = string2
2616 True if the strings are equal. = should be used with the test
2617 command for POSIX conformance. When used with the [[ command,
2618 this performs pattern matching as described above (Compound Com‐
2619 mands).
2620 string1 != string2
2622 True if the strings are not equal.
2623 string1 < string2
2625 True if string1 sorts before string2 lexicographically.
2626 string1 > string2
2628 True if string1 sorts after string2 lexicographically.
2629 arg1 OP arg2
2631 OP is one of -eq, -ne, -lt, -le, -gt, or -ge. These arithmetic
2632 binary operators return true if arg1 is equal to, not equal to,
2633 less than, less than or equal to, greater than, or greater than
2634 or equal to arg2, respectively. Arg1 and arg2 may be positive
2635 or negative integers. When used with the [[ command, Arg1 and
2636 Arg2 are evaluated as arithmetic expressions (see ARITHMETIC
2637 EVALUATION above).
2638
2640 When a simple command is executed, the shell performs the following ex‐
2641 pansions, assignments, and redirections, from left to right, in the
2642 following order.
2643 1. The words that the parser has marked as variable assignments
2645 (those preceding the command name) and redirections are saved
2646 for later processing.
2647 2. The words that are not variable assignments or redirections are
2649 expanded. If any words remain after expansion, the first word
2650 is taken to be the name of the command and the remaining words
2651 are the arguments.
2652 3. Redirections are performed as described above under REDIRECTION.
2654 4. The text after the = in each variable assignment undergoes tilde
2656 expansion, parameter expansion, command substitution, arithmetic
2657 expansion, and quote removal before being assigned to the vari‐
2658 able.
2659 If no command name results, the variable assignments affect the current
2661 shell environment. Otherwise, the variables are added to the environ‐
2662 ment of the executed command and do not affect the current shell envi‐
2663 ronment. If any of the assignments attempts to assign a value to a
2664 readonly variable, an error occurs, and the command exits with a non-
2665 zero status.
2666 If no command name results, redirections are performed, but do not af‐
2668 fect the current shell environment. A redirection error causes the
2669 command to exit with a non-zero status.
2670 If there is a command name left after expansion, execution proceeds as
2672 described below. Otherwise, the command exits. If one of the expan‐
2673 sions contained a command substitution, the exit status of the command
2674 is the exit status of the last command substitution performed. If
2675 there were no command substitutions, the command exits with a status of
2676 zero.
2677
2679 After a command has been split into words, if it results in a simple
2680 command and an optional list of arguments, the following actions are
2681 taken.
2682 If the command name contains no slashes, the shell attempts to locate
2684 it. If there exists a shell function by that name, that function is
2685 invoked as described above in FUNCTIONS. If the name does not match a
2686 function, the shell searches for it in the list of shell builtins. If
2687 a match is found, that builtin is invoked.
2688 If the name is neither a shell function nor a builtin, and contains no
2690 slashes, bash searches each element of the PATH for a directory con‐
2691 taining an executable file by that name. Bash uses a hash table to re‐
2692 member the full pathnames of executable files (see hash under SHELL
2693 BUILTIN COMMANDS below). A full search of the directories in PATH is
2694 performed only if the command is not found in the hash table. If the
2695 search is unsuccessful, the shell searches for a defined shell function
2696 named command_not_found_handle. If that function exists, it is invoked
2697 in a separate execution environment with the original command and the
2698 original command's arguments as its arguments, and the function's exit
2699 status becomes the exit status of that subshell. If that function is
2700 not defined, the shell prints an error message and returns an exit sta‐
2701 tus of 127.
2702 If the search is successful, or if the command name contains one or
2704 more slashes, the shell executes the named program in a separate execu‐
2705 tion environment. Argument 0 is set to the name given, and the remain‐
2706 ing arguments to the command are set to the arguments given, if any.
2707 If this execution fails because the file is not in executable format,
2709 and the file is not a directory, it is assumed to be a shell script, a
2710 file containing shell commands. A subshell is spawned to execute it.
2711 This subshell reinitializes itself, so that the effect is as if a new
2712 shell had been invoked to handle the script, with the exception that
2713 the locations of commands remembered by the parent (see hash below un‐
2714 der SHELL BUILTIN COMMANDS) are retained by the child.
2715 If the program is a file beginning with #!, the remainder of the first
2717 line specifies an interpreter for the program. The shell executes the
2718 specified interpreter on operating systems that do not handle this exe‐
2719 cutable format themselves. The arguments to the interpreter consist of
2720 a single optional argument following the interpreter name on the first
2721 line of the program, followed by the name of the program, followed by
2722 the command arguments, if any.
2723
2725 The shell has an execution environment, which consists of the follow‐
2726 ing:
2727 • open files inherited by the shell at invocation, as modified by
2729 redirections supplied to the exec builtin
2730 • the current working directory as set by cd, pushd, or popd, or
2732 inherited by the shell at invocation
2733 • the file creation mode mask as set by umask or inherited from
2735 the shell's parent
2736 • current traps set by trap
2738 • shell parameters that are set by variable assignment or with set
2740 or inherited from the shell's parent in the environment
2741 • shell functions defined during execution or inherited from the
2743 shell's parent in the environment
2744 • options enabled at invocation (either by default or with com‐
2746 mand-line arguments) or by set
2747 • options enabled by shopt
2749 • shell aliases defined with alias
2751 • various process IDs, including those of background jobs, the
2753 value of $$, and the value of PPID
2754 When a simple command other than a builtin or shell function is to be
2756 executed, it is invoked in a separate execution environment that con‐
2757 sists of the following. Unless otherwise noted, the values are inher‐
2758 ited from the shell.
2759 • the shell's open files, plus any modifications and additions
2762 specified by redirections to the command
2763 • the current working directory
2765 • the file creation mode mask
2767 • shell variables and functions marked for export, along with
2769 variables exported for the command, passed in the environment
2770 • traps caught by the shell are reset to the values inherited from
2772 the shell's parent, and traps ignored by the shell are ignored
2773 A command invoked in this separate environment cannot affect the
2775 shell's execution environment.
2776 Command substitution, commands grouped with parentheses, and asynchro‐
2778 nous commands are invoked in a subshell environment that is a duplicate
2779 of the shell environment, except that traps caught by the shell are re‐
2780 set to the values that the shell inherited from its parent at invoca‐
2781 tion. Builtin commands that are invoked as part of a pipeline are also
2782 executed in a subshell environment. Changes made to the subshell envi‐
2783 ronment cannot affect the shell's execution environment.
2784 Subshells spawned to execute command substitutions inherit the value of
2786 the -e option from the parent shell. When not in posix mode, bash
2787 clears the -e option in such subshells.
2788 If a command is followed by a & and job control is not active, the de‐
2790 fault standard input for the command is the empty file /dev/null. Oth‐
2791 erwise, the invoked command inherits the file descriptors of the call‐
2792 ing shell as modified by redirections.
2793
2795 When a program is invoked it is given an array of strings called the
2796 environment. This is a list of name-value pairs, of the form
2797 name=value.
2798 The shell provides several ways to manipulate the environment. On in‐
2800 vocation, the shell scans its own environment and creates a parameter
2801 for each name found, automatically marking it for export to child pro‐
2802 cesses. Executed commands inherit the environment. The export and de‐
2803 clare -x commands allow parameters and functions to be added to and
2804 deleted from the environment. If the value of a parameter in the envi‐
2805 ronment is modified, the new value becomes part of the environment, re‐
2806 placing the old. The environment inherited by any executed command
2807 consists of the shell's initial environment, whose values may be modi‐
2808 fied in the shell, less any pairs removed by the unset command, plus
2809 any additions via the export and declare -x commands.
2810 The environment for any simple command or function may be augmented
2812 temporarily by prefixing it with parameter assignments, as described
2813 above in PARAMETERS. These assignment statements affect only the envi‐
2814 ronment seen by that command.
2815 If the -k option is set (see the set builtin command below), then all
2817 parameter assignments are placed in the environment for a command, not
2818 just those that precede the command name.
2819 When bash invokes an external command, the variable _ is set to the
2821 full filename of the command and passed to that command in its environ‐
2822 ment.
2823
2825 The exit status of an executed command is the value returned by the
2826 waitpid system call or equivalent function. Exit statuses fall between
2827 0 and 255, though, as explained below, the shell may use values above
2828 125 specially. Exit statuses from shell builtins and compound commands
2829 are also limited to this range. Under certain circumstances, the shell
2830 will use special values to indicate specific failure modes.
2831 For the shell's purposes, a command which exits with a zero exit status
2833 has succeeded. An exit status of zero indicates success. A non-zero
2834 exit status indicates failure. When a command terminates on a fatal
2835 signal N, bash uses the value of 128+N as the exit status.
2836 If a command is not found, the child process created to execute it re‐
2838 turns a status of 127. If a command is found but is not executable,
2839 the return status is 126.
2840 If a command fails because of an error during expansion or redirection,
2842 the exit status is greater than zero.
2843 Shell builtin commands return a status of 0 (true) if successful, and
2845 non-zero (false) if an error occurs while they execute. All builtins
2846 return an exit status of 2 to indicate incorrect usage, generally in‐
2847 valid options or missing arguments.
2848 Bash itself returns the exit status of the last command executed, un‐
2850 less a syntax error occurs, in which case it exits with a non-zero
2851 value. See also the exit builtin command below.
2852
2854 When bash is interactive, in the absence of any traps, it ignores
2855 SIGTERM (so that kill 0 does not kill an interactive shell), and SIGINT
2856 is caught and handled (so that the wait builtin is interruptible). In
2857 all cases, bash ignores SIGQUIT. If job control is in effect, bash ig‐
2858 nores SIGTTIN, SIGTTOU, and SIGTSTP.
2859 Non-builtin commands run by bash have signal handlers set to the values
2861 inherited by the shell from its parent. When job control is not in ef‐
2862 fect, asynchronous commands ignore SIGINT and SIGQUIT in addition to
2863 these inherited handlers. Commands run as a result of command substi‐
2864 tution ignore the keyboard-generated job control signals SIGTTIN, SIGT‐
2865 TOU, and SIGTSTP.
2866 The shell exits by default upon receipt of a SIGHUP. Before exiting,
2868 an interactive shell resends the SIGHUP to all jobs, running or
2869 stopped. Stopped jobs are sent SIGCONT to ensure that they receive the
2870 SIGHUP. To prevent the shell from sending the signal to a particular
2871 job, it should be removed from the jobs table with the disown builtin
2872 (see SHELL BUILTIN COMMANDS below) or marked to not receive SIGHUP us‐
2873 ing disown -h.
2874 If the huponexit shell option has been set with shopt, bash sends a
2876 SIGHUP to all jobs when an interactive login shell exits.
2877 If bash is waiting for a command to complete and receives a signal for
2879 which a trap has been set, the trap will not be executed until the com‐
2880 mand completes. When bash is waiting for an asynchronous command via
2881 the wait builtin, the reception of a signal for which a trap has been
2882 set will cause the wait builtin to return immediately with an exit sta‐
2883 tus greater than 128, immediately after which the trap is executed.
2884
2886 Job control refers to the ability to selectively stop (suspend) the ex‐
2887 ecution of processes and continue (resume) their execution at a later
2888 point. A user typically employs this facility via an interactive in‐
2889 terface supplied jointly by the operating system kernel's terminal
2890 driver and bash.
2891 The shell associates a job with each pipeline. It keeps a table of
2893 currently executing jobs, which may be listed with the jobs command.
2894 When bash starts a job asynchronously (in the background), it prints a
2895 line that looks like:
2896 [1] 25647
2898 indicating that this job is job number 1 and that the process ID of the
2900 last process in the pipeline associated with this job is 25647. All of
2901 the processes in a single pipeline are members of the same job. Bash
2902 uses the job abstraction as the basis for job control.
2903 To facilitate the implementation of the user interface to job control,
2905 the operating system maintains the notion of a current terminal process
2906 group ID. Members of this process group (processes whose process group
2907 ID is equal to the current terminal process group ID) receive keyboard-
2908 generated signals such as SIGINT. These processes are said to be in
2909 the foreground. Background processes are those whose process group ID
2910 differs from the terminal's; such processes are immune to keyboard-gen‐
2911 erated signals. Only foreground processes are allowed to read from or,
2912 if the user so specifies with stty tostop, write to the terminal.
2913 Background processes which attempt to read from (write to when stty
2914 tostop is in effect) the terminal are sent a SIGTTIN (SIGTTOU) signal
2915 by the kernel's terminal driver, which, unless caught, suspends the
2916 process.
2917 If the operating system on which bash is running supports job control,
2919 bash contains facilities to use it. Typing the suspend character (typ‐
2920 ically ^Z, Control-Z) while a process is running causes that process to
2921 be stopped and returns control to bash. Typing the delayed suspend
2922 character (typically ^Y, Control-Y) causes the process to be stopped
2923 when it attempts to read input from the terminal, and control to be re‐
2924 turned to bash. The user may then manipulate the state of this job,
2925 using the bg command to continue it in the background, the fg command
2926 to continue it in the foreground, or the kill command to kill it. A ^Z
2927 takes effect immediately, and has the additional side effect of causing
2928 pending output and typeahead to be discarded.
2929 There are a number of ways to refer to a job in the shell. The charac‐
2931 ter % introduces a job specification (jobspec). Job number n may be
2932 referred to as %n. A job may also be referred to using a prefix of the
2933 name used to start it, or using a substring that appears in its command
2934 line. For example, %ce refers to a stopped job whose command name be‐
2935 gins with ce. If a prefix matches more than one job, bash reports an
2936 error. Using %?ce, on the other hand, refers to any job containing the
2937 string ce in its command line. If the substring matches more than one
2938 job, bash reports an error. The symbols %% and %+ refer to the shell's
2939 notion of the current job, which is the last job stopped while it was
2940 in the foreground or started in the background. The previous job may
2941 be referenced using %-. If there is only a single job, %+ and %- can
2942 both be used to refer to that job. In output pertaining to jobs (e.g.,
2943 the output of the jobs command), the current job is always flagged with
2944 a +, and the previous job with a -. A single % (with no accompanying
2945 job specification) also refers to the current job.
2946 Simply naming a job can be used to bring it into the foreground: %1 is
2948 a synonym for ``fg %1'', bringing job 1 from the background into the
2949 foreground. Similarly, ``%1 &'' resumes job 1 in the background,
2950 equivalent to ``bg %1''.
2951 The shell learns immediately whenever a job changes state. Normally,
2953 bash waits until it is about to print a prompt before reporting changes
2954 in a job's status so as to not interrupt any other output. If the -b
2955 option to the set builtin command is enabled, bash reports such changes
2956 immediately. Any trap on SIGCHLD is executed for each child that ex‐
2957 its.
2958 If an attempt to exit bash is made while jobs are stopped (or, if the
2960 checkjobs shell option has been enabled using the shopt builtin, run‐
2961 ning), the shell prints a warning message, and, if the checkjobs option
2962 is enabled, lists the jobs and their statuses. The jobs command may
2963 then be used to inspect their status. If a second attempt to exit is
2964 made without an intervening command, the shell does not print another
2965 warning, and any stopped jobs are terminated.
2966 When the shell is waiting for a job or process using the wait builtin,
2968 and job control is enabled, wait will return when the job changes
2969 state. The -f option causes wait to wait until the job or process ter‐
2970 minates before returning.
2971
2973 When executing interactively, bash displays the primary prompt PS1 when
2974 it is ready to read a command, and the secondary prompt PS2 when it
2975 needs more input to complete a command. Bash displays PS0 after it
2976 reads a command but before executing it. Bash displays PS4 as de‐
2977 scribed above before tracing each command when the -x option is en‐
2978 abled. Bash allows these prompt strings to be customized by inserting
2979 a number of backslash-escaped special characters that are decoded as
2980 follows:
2981 \a an ASCII bell character (07)
2982 \d the date in "Weekday Month Date" format (e.g., "Tue May
2983 26")
2984 \D{format}
2985 the format is passed to strftime(3) and the result is in‐
2986 serted into the prompt string; an empty format results in
2987 a locale-specific time representation. The braces are
2988 required
2989 \e an ASCII escape character (033)
2990 \h the hostname up to the first `.'
2991 \H the hostname
2992 \j the number of jobs currently managed by the shell
2993 \l the basename of the shell's terminal device name
2994 \n newline
2995 \r carriage return
2996 \s the name of the shell, the basename of $0 (the portion
2997 following the final slash)
2998 \t the current time in 24-hour HH:MM:SS format
2999 \T the current time in 12-hour HH:MM:SS format
3000 \@ the current time in 12-hour am/pm format
3001 \A the current time in 24-hour HH:MM format
3002 \u the username of the current user
3003 \v the version of bash (e.g., 2.00)
3004 \V the release of bash, version + patch level (e.g., 2.00.0)
3005 \w the current working directory, with $HOME abbreviated
3006 with a tilde (uses the value of the PROMPT_DIRTRIM vari‐
3007 able)
3008 \W the basename of the current working directory, with $HOME
3009 abbreviated with a tilde
3010 \! the history number of this command
3011 \# the command number of this command
3012 \$ if the effective UID is 0, a #, otherwise a $
3013 \nnn the character corresponding to the octal number nnn
3014 \\ a backslash
3015 \[ begin a sequence of non-printing characters, which could
3016 be used to embed a terminal control sequence into the
3017 prompt
3018 \] end a sequence of non-printing characters
3019 The command number and the history number are usually different: the
3021 history number of a command is its position in the history list, which
3022 may include commands restored from the history file (see HISTORY be‐
3023 low), while the command number is the position in the sequence of com‐
3024 mands executed during the current shell session. After the string is
3025 decoded, it is expanded via parameter expansion, command substitution,
3026 arithmetic expansion, and quote removal, subject to the value of the
3027 promptvars shell option (see the description of the shopt command under
3028 SHELL BUILTIN COMMANDS below). This can have unwanted side effects if
3029 escaped portions of the string appear within command substitution or
3030 contain characters special to word expansion.
3031
3033 This is the library that handles reading input when using an interac‐
3034 tive shell, unless the --noediting option is given at shell invocation.
3035 Line editing is also used when using the -e option to the read builtin.
3036 By default, the line editing commands are similar to those of Emacs. A
3037 vi-style line editing interface is also available. Line editing can be
3038 enabled at any time using the -o emacs or -o vi options to the set
3039 builtin (see SHELL BUILTIN COMMANDS below). To turn off line editing
3040 after the shell is running, use the +o emacs or +o vi options to the
3041 set builtin.
3042 Readline Notation
3044 In this section, the Emacs-style notation is used to denote keystrokes.
3045 Control keys are denoted by C-key, e.g., C-n means Control-N. Simi‐
3046 larly, meta keys are denoted by M-key, so M-x means Meta-X. (On key‐
3047 boards without a meta key, M-x means ESC x, i.e., press the Escape key
3048 then the x key. This makes ESC the meta prefix. The combination M-C-x
3049 means ESC-Control-x, or press the Escape key then hold the Control key
3050 while pressing the x key.)
3051 Readline commands may be given numeric arguments, which normally act as
3053 a repeat count. Sometimes, however, it is the sign of the argument
3054 that is significant. Passing a negative argument to a command that
3055 acts in the forward direction (e.g., kill-line) causes that command to
3056 act in a backward direction. Commands whose behavior with arguments
3057 deviates from this are noted below.
3058 When a command is described as killing text, the text deleted is saved
3060 for possible future retrieval (yanking). The killed text is saved in a
3061 kill ring. Consecutive kills cause the text to be accumulated into one
3062 unit, which can be yanked all at once. Commands which do not kill text
3063 separate the chunks of text on the kill ring.
3064 Readline Initialization
3066 Readline is customized by putting commands in an initialization file
3067 (the inputrc file). The name of this file is taken from the value of
3068 the INPUTRC variable. If that variable is unset, the default is ~/.in‐
3069 putrc. If that file does not exist or cannot be read, the ultimate
3070 default is /etc/inputrc. When a program which uses the readline li‐
3071 brary starts up, the initialization file is read, and the key bindings
3072 and variables are set. There are only a few basic constructs allowed
3073 in the readline initialization file. Blank lines are ignored. Lines
3074 beginning with a # are comments. Lines beginning with a $ indicate
3075 conditional constructs. Other lines denote key bindings and variable
3076 settings.
3077 The default key-bindings may be changed with an inputrc file. Other
3079 programs that use this library may add their own commands and bindings.
3080 For example, placing
3082 M-Control-u: universal-argument
3084 or
3085 C-Meta-u: universal-argument
3086 into the inputrc would make M-C-u execute the readline command univer‐
3087 sal-argument.
3088 The following symbolic character names are recognized: RUBOUT, DEL,
3090 ESC, LFD, NEWLINE, RET, RETURN, SPC, SPACE, and TAB.
3091 In addition to command names, readline allows keys to be bound to a
3093 string that is inserted when the key is pressed (a macro).
3094 Readline Key Bindings
3096 The syntax for controlling key bindings in the inputrc file is simple.
3097 All that is required is the name of the command or the text of a macro
3098 and a key sequence to which it should be bound. The name may be speci‐
3099 fied in one of two ways: as a symbolic key name, possibly with Meta- or
3100 Control- prefixes, or as a key sequence.
3101 When using the form keyname:function-name or macro, keyname is the name
3103 of a key spelled out in English. For example:
3104 Control-u: universal-argument
3106 Meta-Rubout: backward-kill-word
3107 Control-o: "> output"
3108 In the above example, C-u is bound to the function universal-argument,
3110 M-DEL is bound to the function backward-kill-word, and C-o is bound to
3111 run the macro expressed on the right hand side (that is, to insert the
3112 text ``> output'' into the line).
3113 In the second form, "keyseq":function-name or macro, keyseq differs
3115 from keyname above in that strings denoting an entire key sequence may
3116 be specified by placing the sequence within double quotes. Some GNU
3117 Emacs style key escapes can be used, as in the following example, but
3118 the symbolic character names are not recognized.
3119 "\C-u": universal-argument
3121 "\C-x\C-r": re-read-init-file
3122 "\e[11~": "Function Key 1"
3123 In this example, C-u is again bound to the function universal-argument.
3125 C-x C-r is bound to the function re-read-init-file, and ESC [ 1 1 ~ is
3126 bound to insert the text ``Function Key 1''.
3127 The full set of GNU Emacs style escape sequences is
3129 \C- control prefix
3130 \M- meta prefix
3131 \e an escape character
3132 \\ backslash
3133 \" literal "
3134 \' literal '
3135 In addition to the GNU Emacs style escape sequences, a second set of
3137 backslash escapes is available:
3138 \a alert (bell)
3139 \b backspace
3140 \d delete
3141 \f form feed
3142 \n newline
3143 \r carriage return
3144 \t horizontal tab
3145 \v vertical tab
3146 \nnn the eight-bit character whose value is the octal value
3147 nnn (one to three digits)
3148 \xHH the eight-bit character whose value is the hexadecimal
3149 value HH (one or two hex digits)
3150 When entering the text of a macro, single or double quotes must be used
3152 to indicate a macro definition. Unquoted text is assumed to be a func‐
3153 tion name. In the macro body, the backslash escapes described above
3154 are expanded. Backslash will quote any other character in the macro
3155 text, including " and '.
3156 Bash allows the current readline key bindings to be displayed or modi‐
3158 fied with the bind builtin command. The editing mode may be switched
3159 during interactive use by using the -o option to the set builtin com‐
3160 mand (see SHELL BUILTIN COMMANDS below).
3161 Readline Variables
3163 Readline has variables that can be used to further customize its behav‐
3164 ior. A variable may be set in the inputrc file with a statement of the
3165 form
3166 set variable-name value
3168 or using the bind builtin command (see SHELL BUILTIN COMMANDS below).
3169 Except where noted, readline variables can take the values On or Off
3171 (without regard to case). Unrecognized variable names are ignored.
3172 When a variable value is read, empty or null values, "on" (case-insen‐
3173 sitive), and "1" are equivalent to On. All other values are equivalent
3174 to Off. The variables and their default values are:
3175 bell-style (audible)
3177 Controls what happens when readline wants to ring the terminal
3178 bell. If set to none, readline never rings the bell. If set to
3179 visible, readline uses a visible bell if one is available. If
3180 set to audible, readline attempts to ring the terminal's bell.
3181 bind-tty-special-chars (On)
3182 If set to On, readline attempts to bind the control characters
3183 treated specially by the kernel's terminal driver to their read‐
3184 line equivalents.
3185 blink-matching-paren (Off)
3186 If set to On, readline attempts to briefly move the cursor to an
3187 opening parenthesis when a closing parenthesis is inserted.
3188 colored-completion-prefix (Off)
3189 If set to On, when listing completions, readline displays the
3190 common prefix of the set of possible completions using a differ‐
3191 ent color. The color definitions are taken from the value of
3192 the LS_COLORS environment variable.
3193 colored-stats (Off)
3194 If set to On, readline displays possible completions using dif‐
3195 ferent colors to indicate their file type. The color defini‐
3196 tions are taken from the value of the LS_COLORS environment
3197 variable.
3198 comment-begin (``#'')
3199 The string that is inserted when the readline insert-comment
3200 command is executed. This command is bound to M-# in emacs mode
3201 and to # in vi command mode.
3202 completion-display-width (-1)
3203 The number of screen columns used to display possible matches
3204 when performing completion. The value is ignored if it is less
3205 than 0 or greater than the terminal screen width. A value of 0
3206 will cause matches to be displayed one per line. The default
3207 value is -1.
3208 completion-ignore-case (Off)
3209 If set to On, readline performs filename matching and completion
3210 in a case-insensitive fashion.
3211 completion-map-case (Off)
3212 If set to On, and completion-ignore-case is enabled, readline
3213 treats hyphens (-) and underscores (_) as equivalent when per‐
3214 forming case-insensitive filename matching and completion.
3215 completion-prefix-display-length (0)
3216 The length in characters of the common prefix of a list of pos‐
3217 sible completions that is displayed without modification. When
3218 set to a value greater than zero, common prefixes longer than
3219 this value are replaced with an ellipsis when displaying possi‐
3220 ble completions.
3221 completion-query-items (100)
3222 This determines when the user is queried about viewing the num‐
3223 ber of possible completions generated by the possible-comple‐
3224 tions command. It may be set to any integer value greater than
3225 or equal to zero. If the number of possible completions is
3226 greater than or equal to the value of this variable, readline
3227 will ask whether or not the user wishes to view them; otherwise
3228 they are simply listed on the terminal.
3229 convert-meta (On)
3230 If set to On, readline will convert characters with the eighth
3231 bit set to an ASCII key sequence by stripping the eighth bit and
3232 prefixing an escape character (in effect, using escape as the
3233 meta prefix). The default is On, but readline will set it to
3234 Off if the locale contains eight-bit characters.
3235 disable-completion (Off)
3236 If set to On, readline will inhibit word completion. Completion
3237 characters will be inserted into the line as if they had been
3238 mapped to self-insert.
3239 echo-control-characters (On)
3240 When set to On, on operating systems that indicate they support
3241 it, readline echoes a character corresponding to a signal gener‐
3242 ated from the keyboard.
3243 editing-mode (emacs)
3244 Controls whether readline begins with a set of key bindings sim‐
3245 ilar to Emacs or vi. editing-mode can be set to either emacs or
3246 vi.
3247 emacs-mode-string (@)
3248 If the show-mode-in-prompt variable is enabled, this string is
3249 displayed immediately before the last line of the primary prompt
3250 when emacs editing mode is active. The value is expanded like a
3251 key binding, so the standard set of meta- and control prefixes
3252 and backslash escape sequences is available. Use the \1 and \2
3253 escapes to begin and end sequences of non-printing characters,
3254 which can be used to embed a terminal control sequence into the
3255 mode string.
3256 enable-bracketed-paste (On)
3257 When set to On, readline will configure the terminal in a way
3258 that will enable it to insert each paste into the editing buffer
3259 as a single string of characters, instead of treating each char‐
3260 acter as if it had been read from the keyboard. This can pre‐
3261 vent pasted characters from being interpreted as editing com‐
3262 mands.
3263 enable-keypad (Off)
3264 When set to On, readline will try to enable the application key‐
3265 pad when it is called. Some systems need this to enable the ar‐
3266 row keys.
3267 enable-meta-key (On)
3268 When set to On, readline will try to enable any meta modifier
3269 key the terminal claims to support when it is called. On many
3270 terminals, the meta key is used to send eight-bit characters.
3271 expand-tilde (Off)
3272 If set to On, tilde expansion is performed when readline at‐
3273 tempts word completion.
3274 history-preserve-point (Off)
3275 If set to On, the history code attempts to place point at the
3276 same location on each history line retrieved with previous-his‐
3277 tory or next-history.
3278 history-size (unset)
3279 Set the maximum number of history entries saved in the history
3280 list. If set to zero, any existing history entries are deleted
3281 and no new entries are saved. If set to a value less than zero,
3282 the number of history entries is not limited. By default, the
3283 number of history entries is set to the value of the HISTSIZE
3284 shell variable. If an attempt is made to set history-size to a
3285 non-numeric value, the maximum number of history entries will be
3286 set to 500.
3287 horizontal-scroll-mode (Off)
3288 When set to On, makes readline use a single line for display,
3289 scrolling the input horizontally on a single screen line when it
3290 becomes longer than the screen width rather than wrapping to a
3291 new line. This setting is automatically enabled for terminals
3292 of height 1.
3293 input-meta (Off)
3294 If set to On, readline will enable eight-bit input (that is, it
3295 will not strip the eighth bit from the characters it reads), re‐
3296 gardless of what the terminal claims it can support. The name
3297 meta-flag is a synonym for this variable. The default is Off,
3298 but readline will set it to On if the locale contains eight-bit
3299 characters.
3300 isearch-terminators (``C-[C-J'')
3301 The string of characters that should terminate an incremental
3302 search without subsequently executing the character as a com‐
3303 mand. If this variable has not been given a value, the charac‐
3304 ters ESC and C-J will terminate an incremental search.
3305 keymap (emacs)
3306 Set the current readline keymap. The set of valid keymap names
3307 is emacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-com‐
3308 mand, and vi-insert. vi is equivalent to vi-command; emacs is
3309 equivalent to emacs-standard. The default value is emacs; the
3310 value of editing-mode also affects the default keymap.
3311 keyseq-timeout (500)
3312 Specifies the duration readline will wait for a character when
3313 reading an ambiguous key sequence (one that can form a complete
3314 key sequence using the input read so far, or can take additional
3315 input to complete a longer key sequence). If no input is re‐
3316 ceived within the timeout, readline will use the shorter but
3317 complete key sequence. The value is specified in milliseconds,
3318 so a value of 1000 means that readline will wait one second for
3319 additional input. If this variable is set to a value less than
3320 or equal to zero, or to a non-numeric value, readline will wait
3321 until another key is pressed to decide which key sequence to
3322 complete.
3323 mark-directories (On)
3324 If set to On, completed directory names have a slash appended.
3325 mark-modified-lines (Off)
3326 If set to On, history lines that have been modified are dis‐
3327 played with a preceding asterisk (*).
3328 mark-symlinked-directories (Off)
3329 If set to On, completed names which are symbolic links to direc‐
3330 tories have a slash appended (subject to the value of mark-di‐
3331 rectories).
3332 match-hidden-files (On)
3333 This variable, when set to On, causes readline to match files
3334 whose names begin with a `.' (hidden files) when performing
3335 filename completion. If set to Off, the leading `.' must be
3336 supplied by the user in the filename to be completed.
3337 menu-complete-display-prefix (Off)
3338 If set to On, menu completion displays the common prefix of the
3339 list of possible completions (which may be empty) before cycling
3340 through the list.
3341 output-meta (Off)
3342 If set to On, readline will display characters with the eighth
3343 bit set directly rather than as a meta-prefixed escape sequence.
3344 The default is Off, but readline will set it to On if the locale
3345 contains eight-bit characters.
3346 page-completions (On)
3347 If set to On, readline uses an internal more-like pager to dis‐
3348 play a screenful of possible completions at a time.
3349 print-completions-horizontally (Off)
3350 If set to On, readline will display completions with matches
3351 sorted horizontally in alphabetical order, rather than down the
3352 screen.
3353 revert-all-at-newline (Off)
3354 If set to On, readline will undo all changes to history lines
3355 before returning when accept-line is executed. By default, his‐
3356 tory lines may be modified and retain individual undo lists
3357 across calls to readline.
3358 show-all-if-ambiguous (Off)
3359 This alters the default behavior of the completion functions.
3360 If set to On, words which have more than one possible completion
3361 cause the matches to be listed immediately instead of ringing
3362 the bell.
3363 show-all-if-unmodified (Off)
3364 This alters the default behavior of the completion functions in
3365 a fashion similar to show-all-if-ambiguous. If set to On, words
3366 which have more than one possible completion without any possi‐
3367 ble partial completion (the possible completions don't share a
3368 common prefix) cause the matches to be listed immediately in‐
3369 stead of ringing the bell.
3370 show-mode-in-prompt (Off)
3371 If set to On, add a string to the beginning of the prompt indi‐
3372 cating the editing mode: emacs, vi command, or vi insertion.
3373 The mode strings are user-settable (e.g., emacs-mode-string).
3374 skip-completed-text (Off)
3375 If set to On, this alters the default completion behavior when
3376 inserting a single match into the line. It's only active when
3377 performing completion in the middle of a word. If enabled,
3378 readline does not insert characters from the completion that
3379 match characters after point in the word being completed, so
3380 portions of the word following the cursor are not duplicated.
3381 vi-cmd-mode-string ((cmd))
3382 If the show-mode-in-prompt variable is enabled, this string is
3383 displayed immediately before the last line of the primary prompt
3384 when vi editing mode is active and in command mode. The value
3385 is expanded like a key binding, so the standard set of meta- and
3386 control prefixes and backslash escape sequences is available.
3387 Use the \1 and \2 escapes to begin and end sequences of non-
3388 printing characters, which can be used to embed a terminal con‐
3389 trol sequence into the mode string.
3390 vi-ins-mode-string ((ins))
3391 If the show-mode-in-prompt variable is enabled, this string is
3392 displayed immediately before the last line of the primary prompt
3393 when vi editing mode is active and in insertion mode. The value
3394 is expanded like a key binding, so the standard set of meta- and
3395 control prefixes and backslash escape sequences is available.
3396 Use the \1 and \2 escapes to begin and end sequences of non-
3397 printing characters, which can be used to embed a terminal con‐
3398 trol sequence into the mode string.
3399 visible-stats (Off)
3400 If set to On, a character denoting a file's type as reported by
3401 stat(2) is appended to the filename when listing possible com‐
3402 pletions.
3403 Readline Conditional Constructs
3405 Readline implements a facility similar in spirit to the conditional
3406 compilation features of the C preprocessor which allows key bindings
3407 and variable settings to be performed as the result of tests. There
3408 are four parser directives used.
3409 $if The $if construct allows bindings to be made based on the edit‐
3411 ing mode, the terminal being used, or the application using
3412 readline. The text of the test, after any comparison operator,
3413 extends to the end of the line; unless otherwise noted, no
3414 characters are required to isolate it.
3415 mode The mode= form of the $if directive is used to test
3417 whether readline is in emacs or vi mode. This may be
3418 used in conjunction with the set keymap command, for in‐
3419 stance, to set bindings in the emacs-standard and
3420 emacs-ctlx keymaps only if readline is starting out in
3421 emacs mode.
3422 term The term= form may be used to include terminal-specific
3424 key bindings, perhaps to bind the key sequences output by
3425 the terminal's function keys. The word on the right side
3426 of the = is tested against both the full name of the ter‐
3427 minal and the portion of the terminal name before the
3428 first -. This allows sun to match both sun and sun-cmd,
3429 for instance.
3430 version
3432 The version test may be used to perform comparisons
3433 against specific readline versions. The version expands
3434 to the current readline version. The set of comparison
3435 operators includes =, (and ==), !=, <=, >=, <, and >.
3436 The version number supplied on the right side of the op‐
3437 erator consists of a major version number, an optional
3438 decimal point, and an optional minor version (e.g., 7.1).
3439 If the minor version is omitted, it is assumed to be 0.
3440 The operator may be separated from the string version and
3441 from the version number argument by whitespace.
3442 application
3444 The application construct is used to include application-
3445 specific settings. Each program using the readline li‐
3446 brary sets the application name, and an initialization
3447 file can test for a particular value. This could be used
3448 to bind key sequences to functions useful for a specific
3449 program. For instance, the following command adds a key
3450 sequence that quotes the current or previous word in
3451 bash:
3452 $if Bash
3454 # Quote the current or previous word
3455 "\C-xq": "\eb\"\ef\""
3456 $endif
3457 variable
3459 The variable construct provides simple equality tests for
3460 readline variables and values. The permitted comparison
3461 operators are =, ==, and !=. The variable name must be
3462 separated from the comparison operator by whitespace; the
3463 operator may be separated from the value on the right
3464 hand side by whitespace. Both string and boolean vari‐
3465 ables may be tested. Boolean variables must be tested
3466 against the values on and off.
3467 $endif This command, as seen in the previous example, terminates an $if
3469 command.
3470 $else Commands in this branch of the $if directive are executed if the
3472 test fails.
3473 $include
3475 This directive takes a single filename as an argument and reads
3476 commands and bindings from that file. For example, the follow‐
3477 ing directive would read /etc/inputrc:
3478 $include /etc/inputrc
3480 Searching
3482 Readline provides commands for searching through the command history
3483 (see HISTORY below) for lines containing a specified string. There are
3484 two search modes: incremental and non-incremental.
3485 Incremental searches begin before the user has finished typing the
3487 search string. As each character of the search string is typed, read‐
3488 line displays the next entry from the history matching the string typed
3489 so far. An incremental search requires only as many characters as
3490 needed to find the desired history entry. The characters present in
3491 the value of the isearch-terminators variable are used to terminate an
3492 incremental search. If that variable has not been assigned a value the
3493 Escape and Control-J characters will terminate an incremental search.
3494 Control-G will abort an incremental search and restore the original
3495 line. When the search is terminated, the history entry containing the
3496 search string becomes the current line.
3497 To find other matching entries in the history list, type Control-S or
3499 Control-R as appropriate. This will search backward or forward in the
3500 history for the next entry matching the search string typed so far.
3501 Any other key sequence bound to a readline command will terminate the
3502 search and execute that command. For instance, a newline will termi‐
3503 nate the search and accept the line, thereby executing the command from
3504 the history list.
3505 Readline remembers the last incremental search string. If two Control-
3507 Rs are typed without any intervening characters defining a new search
3508 string, any remembered search string is used.
3509 Non-incremental searches read the entire search string before starting
3511 to search for matching history lines. The search string may be typed
3512 by the user or be part of the contents of the current line.
3513 Readline Command Names
3515 The following is a list of the names of the commands and the default
3516 key sequences to which they are bound. Command names without an accom‐
3517 panying key sequence are unbound by default. In the following descrip‐
3518 tions, point refers to the current cursor position, and mark refers to
3519 a cursor position saved by the set-mark command. The text between the
3520 point and mark is referred to as the region.
3521 Commands for Moving
3523 beginning-of-line (C-a)
3524 Move to the start of the current line.
3525 end-of-line (C-e)
3526 Move to the end of the line.
3527 forward-char (C-f)
3528 Move forward a character.
3529 backward-char (C-b)
3530 Move back a character.
3531 forward-word (M-f)
3532 Move forward to the end of the next word. Words are composed of
3533 alphanumeric characters (letters and digits).
3534 backward-word (M-b)
3535 Move back to the start of the current or previous word. Words
3536 are composed of alphanumeric characters (letters and digits).
3537 shell-forward-word
3538 Move forward to the end of the next word. Words are delimited
3539 by non-quoted shell metacharacters.
3540 shell-backward-word
3541 Move back to the start of the current or previous word. Words
3542 are delimited by non-quoted shell metacharacters.
3543 previous-screen-line
3544 Attempt to move point to the same physical screen column on the
3545 previous physical screen line. This will not have the desired
3546 effect if the current Readline line does not take up more than
3547 one physical line or if point is not greater than the length of
3548 the prompt plus the screen width.
3549 next-screen-line
3550 Attempt to move point to the same physical screen column on the
3551 next physical screen line. This will not have the desired effect
3552 if the current Readline line does not take up more than one
3553 physical line or if the length of the current Readline line is
3554 not greater than the length of the prompt plus the screen width.
3555 clear-display (M-C-l)
3556 Clear the screen and, if possible, the terminal's scrollback
3557 buffer, then redraw the current line, leaving the current line
3558 at the top of the screen.
3559 clear-screen (C-l)
3560 Clear the screen, then redraw the current line, leaving the cur‐
3561 rent line at the top of the screen. With an argument, refresh
3562 the current line without clearing the screen.
3563 redraw-current-line
3564 Refresh the current line.
3565 Commands for Manipulating the History
3567 accept-line (Newline, Return)
3568 Accept the line regardless of where the cursor is. If this line
3569 is non-empty, add it to the history list according to the state
3570 of the HISTCONTROL variable. If the line is a modified history
3571 line, then restore the history line to its original state.
3572 previous-history (C-p)
3573 Fetch the previous command from the history list, moving back in
3574 the list.
3575 next-history (C-n)
3576 Fetch the next command from the history list, moving forward in
3577 the list.
3578 beginning-of-history (M-<)
3579 Move to the first line in the history.
3580 end-of-history (M->)
3581 Move to the end of the input history, i.e., the line currently
3582 being entered.
3583 reverse-search-history (C-r)
3584 Search backward starting at the current line and moving `up'
3585 through the history as necessary. This is an incremental
3586 search.
3587 forward-search-history (C-s)
3588 Search forward starting at the current line and moving `down'
3589 through the history as necessary. This is an incremental
3590 search.
3591 non-incremental-reverse-search-history (M-p)
3592 Search backward through the history starting at the current line
3593 using a non-incremental search for a string supplied by the
3594 user.
3595 non-incremental-forward-search-history (M-n)
3596 Search forward through the history using a non-incremental
3597 search for a string supplied by the user.
3598 history-search-forward
3599 Search forward through the history for the string of characters
3600 between the start of the current line and the point. This is a
3601 non-incremental search.
3602 history-search-backward
3603 Search backward through the history for the string of characters
3604 between the start of the current line and the point. This is a
3605 non-incremental search.
3606 history-substring-search-backward
3607 Search backward through the history for the string of characters
3608 between the start of the current line and the current cursor po‐
3609 sition (the point). The search string may match anywhere in a
3610 history line. This is a non-incremental search.
3611 history-substring-search-forward
3612 Search forward through the history for the string of characters
3613 between the start of the current line and the point. The search
3614 string may match anywhere in a history line. This is a non-in‐
3615 cremental search.
3616 yank-nth-arg (M-C-y)
3617 Insert the first argument to the previous command (usually the
3618 second word on the previous line) at point. With an argument n,
3619 insert the nth word from the previous command (the words in the
3620 previous command begin with word 0). A negative argument in‐
3621 serts the nth word from the end of the previous command. Once
3622 the argument n is computed, the argument is extracted as if the
3623 "!n" history expansion had been specified.
3624 yank-last-arg (M-., M-_)
3625 Insert the last argument to the previous command (the last word
3626 of the previous history entry). With a numeric argument, behave
3627 exactly like yank-nth-arg. Successive calls to yank-last-arg
3628 move back through the history list, inserting the last word (or
3629 the word specified by the argument to the first call) of each
3630 line in turn. Any numeric argument supplied to these successive
3631 calls determines the direction to move through the history. A
3632 negative argument switches the direction through the history
3633 (back or forward). The history expansion facilities are used to
3634 extract the last word, as if the "!$" history expansion had been
3635 specified.
3636 shell-expand-line (M-C-e)
3637 Expand the line as the shell does. This performs alias and his‐
3638 tory expansion as well as all of the shell word expansions. See
3639 HISTORY EXPANSION below for a description of history expansion.
3640 history-expand-line (M-^)
3641 Perform history expansion on the current line. See HISTORY EX‐
3642 PANSION below for a description of history expansion.
3643 magic-space
3644 Perform history expansion on the current line and insert a
3645 space. See HISTORY EXPANSION below for a description of history
3646 expansion.
3647 alias-expand-line
3648 Perform alias expansion on the current line. See ALIASES above
3649 for a description of alias expansion.
3650 history-and-alias-expand-line
3651 Perform history and alias expansion on the current line.
3652 insert-last-argument (M-., M-_)
3653 A synonym for yank-last-arg.
3654 operate-and-get-next (C-o)
3655 Accept the current line for execution and fetch the next line
3656 relative to the current line from the history for editing. A
3657 numeric argument, if supplied, specifies the history entry to
3658 use instead of the current line.
3659 edit-and-execute-command (C-x C-e)
3660 Invoke an editor on the current command line, and execute the
3661 result as shell commands. Bash attempts to invoke $VISUAL, $ED‐
3662 ITOR, and emacs as the editor, in that order.
3663 Commands for Changing Text
3665 end-of-file (usually C-d)
3666 The character indicating end-of-file as set, for example, by
3667 ``stty''. If this character is read when there are no charac‐
3668 ters on the line, and point is at the beginning of the line,
3669 Readline interprets it as the end of input and returns EOF.
3670 delete-char (C-d)
3671 Delete the character at point. If this function is bound to the
3672 same character as the tty EOF character, as C-d commonly is, see
3673 above for the effects.
3674 backward-delete-char (Rubout)
3675 Delete the character behind the cursor. When given a numeric
3676 argument, save the deleted text on the kill ring.
3677 forward-backward-delete-char
3678 Delete the character under the cursor, unless the cursor is at
3679 the end of the line, in which case the character behind the cur‐
3680 sor is deleted.
3681 quoted-insert (C-q, C-v)
3682 Add the next character typed to the line verbatim. This is how
3683 to insert characters like C-q, for example.
3684 tab-insert (C-v TAB)
3685 Insert a tab character.
3686 self-insert (a, b, A, 1, !, ...)
3687 Insert the character typed.
3688 transpose-chars (C-t)
3689 Drag the character before point forward over the character at
3690 point, moving point forward as well. If point is at the end of
3691 the line, then this transposes the two characters before point.
3692 Negative arguments have no effect.
3693 transpose-words (M-t)
3694 Drag the word before point past the word after point, moving
3695 point over that word as well. If point is at the end of the
3696 line, this transposes the last two words on the line.
3697 upcase-word (M-u)
3698 Uppercase the current (or following) word. With a negative ar‐
3699 gument, uppercase the previous word, but do not move point.
3700 downcase-word (M-l)
3701 Lowercase the current (or following) word. With a negative ar‐
3702 gument, lowercase the previous word, but do not move point.
3703 capitalize-word (M-c)
3704 Capitalize the current (or following) word. With a negative ar‐
3705 gument, capitalize the previous word, but do not move point.
3706 overwrite-mode
3707 Toggle overwrite mode. With an explicit positive numeric argu‐
3708 ment, switches to overwrite mode. With an explicit non-positive
3709 numeric argument, switches to insert mode. This command affects
3710 only emacs mode; vi mode does overwrite differently. Each call
3711 to readline() starts in insert mode. In overwrite mode, charac‐
3712 ters bound to self-insert replace the text at point rather than
3713 pushing the text to the right. Characters bound to back‐
3714 ward-delete-char replace the character before point with a
3715 space. By default, this command is unbound.
3716 Killing and Yanking
3718 kill-line (C-k)
3719 Kill the text from point to the end of the line.
3720 backward-kill-line (C-x Rubout)
3721 Kill backward to the beginning of the line.
3722 unix-line-discard (C-u)
3723 Kill backward from point to the beginning of the line. The
3724 killed text is saved on the kill-ring.
3725 kill-whole-line
3726 Kill all characters on the current line, no matter where point
3727 is.
3728 kill-word (M-d)
3729 Kill from point to the end of the current word, or if between
3730 words, to the end of the next word. Word boundaries are the
3731 same as those used by forward-word.
3732 backward-kill-word (M-Rubout)
3733 Kill the word behind point. Word boundaries are the same as
3734 those used by backward-word.
3735 shell-kill-word
3736 Kill from point to the end of the current word, or if between
3737 words, to the end of the next word. Word boundaries are the
3738 same as those used by shell-forward-word.
3739 shell-backward-kill-word
3740 Kill the word behind point. Word boundaries are the same as
3741 those used by shell-backward-word.
3742 unix-word-rubout (C-w)
3743 Kill the word behind point, using white space as a word bound‐
3744 ary. The killed text is saved on the kill-ring.
3745 unix-filename-rubout
3746 Kill the word behind point, using white space and the slash
3747 character as the word boundaries. The killed text is saved on
3748 the kill-ring.
3749 delete-horizontal-space (M-\)
3750 Delete all spaces and tabs around point.
3751 kill-region
3752 Kill the text in the current region.
3753 copy-region-as-kill
3754 Copy the text in the region to the kill buffer.
3755 copy-backward-word
3756 Copy the word before point to the kill buffer. The word bound‐
3757 aries are the same as backward-word.
3758 copy-forward-word
3759 Copy the word following point to the kill buffer. The word
3760 boundaries are the same as forward-word.
3761 yank (C-y)
3762 Yank the top of the kill ring into the buffer at point.
3763 yank-pop (M-y)
3764 Rotate the kill ring, and yank the new top. Only works follow‐
3765 ing yank or yank-pop.
3766 Numeric Arguments
3768 digit-argument (M-0, M-1, ..., M--)
3769 Add this digit to the argument already accumulating, or start a
3770 new argument. M-- starts a negative argument.
3771 universal-argument
3772 This is another way to specify an argument. If this command is
3773 followed by one or more digits, optionally with a leading minus
3774 sign, those digits define the argument. If the command is fol‐
3775 lowed by digits, executing universal-argument again ends the nu‐
3776 meric argument, but is otherwise ignored. As a special case, if
3777 this command is immediately followed by a character that is nei‐
3778 ther a digit nor minus sign, the argument count for the next
3779 command is multiplied by four. The argument count is initially
3780 one, so executing this function the first time makes the argu‐
3781 ment count four, a second time makes the argument count sixteen,
3782 and so on.
3783 Completing
3785 complete (TAB)
3786 Attempt to perform completion on the text before point. Bash
3787 attempts completion treating the text as a variable (if the text
3788 begins with $), username (if the text begins with ~), hostname
3789 (if the text begins with @), or command (including aliases and
3790 functions) in turn. If none of these produces a match, filename
3791 completion is attempted.
3792 possible-completions (M-?)
3793 List the possible completions of the text before point.
3794 insert-completions (M-*)
3795 Insert all completions of the text before point that would have
3796 been generated by possible-completions.
3797 menu-complete
3798 Similar to complete, but replaces the word to be completed with
3799 a single match from the list of possible completions. Repeated
3800 execution of menu-complete steps through the list of possible
3801 completions, inserting each match in turn. At the end of the
3802 list of completions, the bell is rung (subject to the setting of
3803 bell-style) and the original text is restored. An argument of n
3804 moves n positions forward in the list of matches; a negative ar‐
3805 gument may be used to move backward through the list. This com‐
3806 mand is intended to be bound to TAB, but is unbound by default.
3807 menu-complete-backward
3808 Identical to menu-complete, but moves backward through the list
3809 of possible completions, as if menu-complete had been given a
3810 negative argument. This command is unbound by default.
3811 delete-char-or-list
3812 Deletes the character under the cursor if not at the beginning
3813 or end of the line (like delete-char). If at the end of the
3814 line, behaves identically to possible-completions. This command
3815 is unbound by default.
3816 complete-filename (M-/)
3817 Attempt filename completion on the text before point.
3818 possible-filename-completions (C-x /)
3819 List the possible completions of the text before point, treating
3820 it as a filename.
3821 complete-username (M-~)
3822 Attempt completion on the text before point, treating it as a
3823 username.
3824 possible-username-completions (C-x ~)
3825 List the possible completions of the text before point, treating
3826 it as a username.
3827 complete-variable (M-$)
3828 Attempt completion on the text before point, treating it as a
3829 shell variable.
3830 possible-variable-completions (C-x $)
3831 List the possible completions of the text before point, treating
3832 it as a shell variable.
3833 complete-hostname (M-@)
3834 Attempt completion on the text before point, treating it as a
3835 hostname.
3836 possible-hostname-completions (C-x @)
3837 List the possible completions of the text before point, treating
3838 it as a hostname.
3839 complete-command (M-!)
3840 Attempt completion on the text before point, treating it as a
3841 command name. Command completion attempts to match the text
3842 against aliases, reserved words, shell functions, shell
3843 builtins, and finally executable filenames, in that order.
3844 possible-command-completions (C-x !)
3845 List the possible completions of the text before point, treating
3846 it as a command name.
3847 dynamic-complete-history (M-TAB)
3848 Attempt completion on the text before point, comparing the text
3849 against lines from the history list for possible completion
3850 matches.
3851 dabbrev-expand
3852 Attempt menu completion on the text before point, comparing the
3853 text against lines from the history list for possible completion
3854 matches.
3855 complete-into-braces (M-{)
3856 Perform filename completion and insert the list of possible com‐
3857 pletions enclosed within braces so the list is available to the
3858 shell (see Brace Expansion above).
3859 Keyboard Macros
3861 start-kbd-macro (C-x ()
3862 Begin saving the characters typed into the current keyboard
3863 macro.
3864 end-kbd-macro (C-x ))
3865 Stop saving the characters typed into the current keyboard macro
3866 and store the definition.
3867 call-last-kbd-macro (C-x e)
3868 Re-execute the last keyboard macro defined, by making the char‐
3869 acters in the macro appear as if typed at the keyboard.
3870 print-last-kbd-macro ()
3871 Print the last keyboard macro defined in a format suitable for
3872 the inputrc file.
3873 Miscellaneous
3875 re-read-init-file (C-x C-r)
3876 Read in the contents of the inputrc file, and incorporate any
3877 bindings or variable assignments found there.
3878 abort (C-g)
3879 Abort the current editing command and ring the terminal's bell
3880 (subject to the setting of bell-style).
3881 do-lowercase-version (M-A, M-B, M-x, ...)
3882 If the metafied character x is uppercase, run the command that
3883 is bound to the corresponding metafied lowercase character. The
3884 behavior is undefined if x is already lowercase.
3885 prefix-meta (ESC)
3886 Metafy the next character typed. ESC f is equivalent to Meta-f.
3887 undo (C-_, C-x C-u)
3888 Incremental undo, separately remembered for each line.
3889 revert-line (M-r)
3890 Undo all changes made to this line. This is like executing the
3891 undo command enough times to return the line to its initial
3892 state.
3893 tilde-expand (M-&)
3894 Perform tilde expansion on the current word.
3895 set-mark (C-@, M-<space>)
3896 Set the mark to the point. If a numeric argument is supplied,
3897 the mark is set to that position.
3898 exchange-point-and-mark (C-x C-x)
3899 Swap the point with the mark. The current cursor position is
3900 set to the saved position, and the old cursor position is saved
3901 as the mark.
3902 character-search (C-])
3903 A character is read and point is moved to the next occurrence of
3904 that character. A negative count searches for previous occur‐
3905 rences.
3906 character-search-backward (M-C-])
3907 A character is read and point is moved to the previous occur‐
3908 rence of that character. A negative count searches for subse‐
3909 quent occurrences.
3910 skip-csi-sequence
3911 Read enough characters to consume a multi-key sequence such as
3912 those defined for keys like Home and End. Such sequences begin
3913 with a Control Sequence Indicator (CSI), usually ESC-[. If this
3914 sequence is bound to "\[", keys producing such sequences will
3915 have no effect unless explicitly bound to a readline command,
3916 instead of inserting stray characters into the editing buffer.
3917 This is unbound by default, but usually bound to ESC-[.
3918 insert-comment (M-#)
3919 Without a numeric argument, the value of the readline com‐
3920 ment-begin variable is inserted at the beginning of the current
3921 line. If a numeric argument is supplied, this command acts as a
3922 toggle: if the characters at the beginning of the line do not
3923 match the value of comment-begin, the value is inserted, other‐
3924 wise the characters in comment-begin are deleted from the begin‐
3925 ning of the line. In either case, the line is accepted as if a
3926 newline had been typed. The default value of comment-begin
3927 causes this command to make the current line a shell comment.
3928 If a numeric argument causes the comment character to be re‐
3929 moved, the line will be executed by the shell.
3930 glob-complete-word (M-g)
3931 The word before point is treated as a pattern for pathname ex‐
3932 pansion, with an asterisk implicitly appended. This pattern is
3933 used to generate a list of matching filenames for possible com‐
3934 pletions.
3935 glob-expand-word (C-x *)
3936 The word before point is treated as a pattern for pathname ex‐
3937 pansion, and the list of matching filenames is inserted, replac‐
3938 ing the word. If a numeric argument is supplied, an asterisk is
3939 appended before pathname expansion.
3940 glob-list-expansions (C-x g)
3941 The list of expansions that would have been generated by
3942 glob-expand-word is displayed, and the line is redrawn. If a
3943 numeric argument is supplied, an asterisk is appended before
3944 pathname expansion.
3945 dump-functions
3946 Print all of the functions and their key bindings to the read‐
3947 line output stream. If a numeric argument is supplied, the out‐
3948 put is formatted in such a way that it can be made part of an
3949 inputrc file.
3950 dump-variables
3951 Print all of the settable readline variables and their values to
3952 the readline output stream. If a numeric argument is supplied,
3953 the output is formatted in such a way that it can be made part
3954 of an inputrc file.
3955 dump-macros
3956 Print all of the readline key sequences bound to macros and the
3957 strings they output. If a numeric argument is supplied, the
3958 output is formatted in such a way that it can be made part of an
3959 inputrc file.
3960 display-shell-version (C-x C-v)
3961 Display version information about the current instance of bash.
3962 Programmable Completion
3964 When word completion is attempted for an argument to a command for
3965 which a completion specification (a compspec) has been defined using
3966 the complete builtin (see SHELL BUILTIN COMMANDS below), the program‐
3967 mable completion facilities are invoked.
3968 First, the command name is identified. If the command word is the
3970 empty string (completion attempted at the beginning of an empty line),
3971 any compspec defined with the -E option to complete is used. If a
3972 compspec has been defined for that command, the compspec is used to
3973 generate the list of possible completions for the word. If the command
3974 word is a full pathname, a compspec for the full pathname is searched
3975 for first. If no compspec is found for the full pathname, an attempt
3976 is made to find a compspec for the portion following the final slash.
3977 If those searches do not result in a compspec, any compspec defined
3978 with the -D option to complete is used as the default. If there is no
3979 default compspec, bash attempts alias expansion on the command word as
3980 a final resort, and attempts to find a compspec for the command word
3981 from any successful expansion.
3982 Once a compspec has been found, it is used to generate the list of
3984 matching words. If a compspec is not found, the default bash comple‐
3985 tion as described above under Completing is performed.
3986 First, the actions specified by the compspec are used. Only matches
3988 which are prefixed by the word being completed are returned. When the
3989 -f or -d option is used for filename or directory name completion, the
3990 shell variable FIGNORE is used to filter the matches.
3991 Any completions specified by a pathname expansion pattern to the -G op‐
3993 tion are generated next. The words generated by the pattern need not
3994 match the word being completed. The GLOBIGNORE shell variable is not
3995 used to filter the matches, but the FIGNORE variable is used.
3996 Next, the string specified as the argument to the -W option is consid‐
3998 ered. The string is first split using the characters in the IFS spe‐
3999 cial variable as delimiters. Shell quoting is honored. Each word is
4000 then expanded using brace expansion, tilde expansion, parameter and
4001 variable expansion, command substitution, and arithmetic expansion, as
4002 described above under EXPANSION. The results are split using the rules
4003 described above under Word Splitting. The results of the expansion are
4004 prefix-matched against the word being completed, and the matching words
4005 become the possible completions.
4006 After these matches have been generated, any shell function or command
4008 specified with the -F and -C options is invoked. When the command or
4009 function is invoked, the COMP_LINE, COMP_POINT, COMP_KEY, and COMP_TYPE
4010 variables are assigned values as described above under Shell Variables.
4011 If a shell function is being invoked, the COMP_WORDS and COMP_CWORD
4012 variables are also set. When the function or command is invoked, the
4013 first argument ($1) is the name of the command whose arguments are be‐
4014 ing completed, the second argument ($2) is the word being completed,
4015 and the third argument ($3) is the word preceding the word being com‐
4016 pleted on the current command line. No filtering of the generated com‐
4017 pletions against the word being completed is performed; the function or
4018 command has complete freedom in generating the matches.
4019 Any function specified with -F is invoked first. The function may use
4021 any of the shell facilities, including the compgen builtin described
4022 below, to generate the matches. It must put the possible completions
4023 in the COMPREPLY array variable, one per array element.
4024 Next, any command specified with the -C option is invoked in an envi‐
4026 ronment equivalent to command substitution. It should print a list of
4027 completions, one per line, to the standard output. Backslash may be
4028 used to escape a newline, if necessary.
4029 After all of the possible completions are generated, any filter speci‐
4031 fied with the -X option is applied to the list. The filter is a pat‐
4032 tern as used for pathname expansion; a & in the pattern is replaced
4033 with the text of the word being completed. A literal & may be escaped
4034 with a backslash; the backslash is removed before attempting a match.
4035 Any completion that matches the pattern will be removed from the list.
4036 A leading ! negates the pattern; in this case any completion not match‐
4037 ing the pattern will be removed. If the nocasematch shell option is
4038 enabled, the match is performed without regard to the case of alpha‐
4039 betic characters.
4040 Finally, any prefix and suffix specified with the -P and -S options are
4042 added to each member of the completion list, and the result is returned
4043 to the readline completion code as the list of possible completions.
4044 If the previously-applied actions do not generate any matches, and the
4046 -o dirnames option was supplied to complete when the compspec was de‐
4047 fined, directory name completion is attempted.
4048 If the -o plusdirs option was supplied to complete when the compspec
4050 was defined, directory name completion is attempted and any matches are
4051 added to the results of the other actions.
4052 By default, if a compspec is found, whatever it generates is returned
4054 to the completion code as the full set of possible completions. The
4055 default bash completions are not attempted, and the readline default of
4056 filename completion is disabled. If the -o bashdefault option was sup‐
4057 plied to complete when the compspec was defined, the bash default com‐
4058 pletions are attempted if the compspec generates no matches. If the -o
4059 default option was supplied to complete when the compspec was defined,
4060 readline's default completion will be performed if the compspec (and,
4061 if attempted, the default bash completions) generate no matches.
4062 When a compspec indicates that directory name completion is desired,
4064 the programmable completion functions force readline to append a slash
4065 to completed names which are symbolic links to directories, subject to
4066 the value of the mark-directories readline variable, regardless of the
4067 setting of the mark-symlinked-directories readline variable.
4068 There is some support for dynamically modifying completions. This is
4070 most useful when used in combination with a default completion speci‐
4071 fied with complete -D. It's possible for shell functions executed as
4072 completion handlers to indicate that completion should be retried by
4073 returning an exit status of 124. If a shell function returns 124, and
4074 changes the compspec associated with the command on which completion is
4075 being attempted (supplied as the first argument when the function is
4076 executed), programmable completion restarts from the beginning, with an
4077 attempt to find a new compspec for that command. This allows a set of
4078 completions to be built dynamically as completion is attempted, rather
4079 than being loaded all at once.
4080 For instance, assuming that there is a library of compspecs, each kept
4082 in a file corresponding to the name of the command, the following de‐
4083 fault completion function would load completions dynamically:
4084 _completion_loader()
4086 {
4087 . "/etc/bash_completion.d/$1.sh" >/dev/null 2>&1 && return 124
4088 }
4089 complete -D -F _completion_loader -o bashdefault -o default
4090
4093 When the -o history option to the set builtin is enabled, the shell
4094 provides access to the command history, the list of commands previously
4095 typed. The value of the HISTSIZE variable is used as the number of
4096 commands to save in a history list. The text of the last HISTSIZE com‐
4097 mands (default 500) is saved. The shell stores each command in the
4098 history list prior to parameter and variable expansion (see EXPANSION
4099 above) but after history expansion is performed, subject to the values
4100 of the shell variables HISTIGNORE and HISTCONTROL.
4101 On startup, the history is initialized from the file named by the vari‐
4103 able HISTFILE (default ~/.bash_history). The file named by the value
4104 of HISTFILE is truncated, if necessary, to contain no more than the
4105 number of lines specified by the value of HISTFILESIZE. If HISTFILE‐
4106 SIZE is unset, or set to null, a non-numeric value, or a numeric value
4107 less than zero, the history file is not truncated. When the history
4108 file is read, lines beginning with the history comment character fol‐
4109 lowed immediately by a digit are interpreted as timestamps for the fol‐
4110 lowing history line. These timestamps are optionally displayed depend‐
4111 ing on the value of the HISTTIMEFORMAT variable. When a shell with
4112 history enabled exits, the last $HISTSIZE lines are copied from the
4113 history list to $HISTFILE. If the histappend shell option is enabled
4114 (see the description of shopt under SHELL BUILTIN COMMANDS below), the
4115 lines are appended to the history file, otherwise the history file is
4116 overwritten. If HISTFILE is unset, or if the history file is un‐
4117 writable, the history is not saved. If the HISTTIMEFORMAT variable is
4118 set, time stamps are written to the history file, marked with the his‐
4119 tory comment character, so they may be preserved across shell sessions.
4120 This uses the history comment character to distinguish timestamps from
4121 other history lines. After saving the history, the history file is
4122 truncated to contain no more than HISTFILESIZE lines. If HISTFILESIZE
4123 is unset, or set to null, a non-numeric value, or a numeric value less
4124 than zero, the history file is not truncated.
4125 The builtin command fc (see SHELL BUILTIN COMMANDS below) may be used
4127 to list or edit and re-execute a portion of the history list. The his‐
4128 tory builtin may be used to display or modify the history list and ma‐
4129 nipulate the history file. When using command-line editing, search
4130 commands are available in each editing mode that provide access to the
4131 history list.
4132 The shell allows control over which commands are saved on the history
4134 list. The HISTCONTROL and HISTIGNORE variables may be set to cause the
4135 shell to save only a subset of the commands entered. The cmdhist shell
4136 option, if enabled, causes the shell to attempt to save each line of a
4137 multi-line command in the same history entry, adding semicolons where
4138 necessary to preserve syntactic correctness. The lithist shell option
4139 causes the shell to save the command with embedded newlines instead of
4140 semicolons. See the description of the shopt builtin below under SHELL
4141 BUILTIN COMMANDS for information on setting and unsetting shell op‐
4142 tions.
4143
4145 The shell supports a history expansion feature that is similar to the
4146 history expansion in csh. This section describes what syntax features
4147 are available. This feature is enabled by default for interactive
4148 shells, and can be disabled using the +H option to the set builtin com‐
4149 mand (see SHELL BUILTIN COMMANDS below). Non-interactive shells do not
4150 perform history expansion by default.
4151 History expansions introduce words from the history list into the input
4153 stream, making it easy to repeat commands, insert the arguments to a
4154 previous command into the current input line, or fix errors in previous
4155 commands quickly.
4156 History expansion is performed immediately after a complete line is
4158 read, before the shell breaks it into words, and is performed on each
4159 line individually without taking quoting on previous lines into ac‐
4160 count. It takes place in two parts. The first is to determine which
4161 line from the history list to use during substitution. The second is
4162 to select portions of that line for inclusion into the current one.
4163 The line selected from the history is the event, and the portions of
4164 that line that are acted upon are words. Various modifiers are avail‐
4165 able to manipulate the selected words. The line is broken into words
4166 in the same fashion as when reading input, so that several metacharac‐
4167 ter-separated words surrounded by quotes are considered one word. His‐
4168 tory expansions are introduced by the appearance of the history expan‐
4169 sion character, which is ! by default. Only backslash (\) and single
4170 quotes can quote the history expansion character, but the history ex‐
4171 pansion character is also treated as quoted if it immediately precedes
4172 the closing double quote in a double-quoted string.
4173 Several characters inhibit history expansion if found immediately fol‐
4175 lowing the history expansion character, even if it is unquoted: space,
4176 tab, newline, carriage return, and =. If the extglob shell option is
4177 enabled, ( will also inhibit expansion.
4178 Several shell options settable with the shopt builtin may be used to
4180 tailor the behavior of history expansion. If the histverify shell op‐
4181 tion is enabled (see the description of the shopt builtin below), and
4182 readline is being used, history substitutions are not immediately
4183 passed to the shell parser. Instead, the expanded line is reloaded
4184 into the readline editing buffer for further modification. If readline
4185 is being used, and the histreedit shell option is enabled, a failed
4186 history substitution will be reloaded into the readline editing buffer
4187 for correction. The -p option to the history builtin command may be
4188 used to see what a history expansion will do before using it. The -s
4189 option to the history builtin may be used to add commands to the end of
4190 the history list without actually executing them, so that they are
4191 available for subsequent recall.
4192 The shell allows control of the various characters used by the history
4194 expansion mechanism (see the description of histchars above under Shell
4195 Variables). The shell uses the history comment character to mark his‐
4196 tory timestamps when writing the history file.
4197 Event Designators
4199 An event designator is a reference to a command line entry in the his‐
4200 tory list. Unless the reference is absolute, events are relative to
4201 the current position in the history list.
4202 ! Start a history substitution, except when followed by a blank,
4204 newline, carriage return, = or ( (when the extglob shell option
4205 is enabled using the shopt builtin).
4206 !n Refer to command line n.
4207 !-n Refer to the current command minus n.
4208 !! Refer to the previous command. This is a synonym for `!-1'.
4209 !string
4210 Refer to the most recent command preceding the current position
4211 in the history list starting with string.
4212 !?string[?]
4213 Refer to the most recent command preceding the current position
4214 in the history list containing string. The trailing ? may be
4215 omitted if string is followed immediately by a newline. If
4216 string is missing, the string from the most recent search is
4217 used; it is an error if there is no previous search string.
4218 ^string1^string2^
4219 Quick substitution. Repeat the previous command, replacing
4220 string1 with string2. Equivalent to ``!!:s^string1^string2^''
4221 (see Modifiers below).
4222 !# The entire command line typed so far.
4223 Word Designators
4225 Word designators are used to select desired words from the event. A :
4226 separates the event specification from the word designator. It may be
4227 omitted if the word designator begins with a ^, $, *, -, or %. Words
4228 are numbered from the beginning of the line, with the first word being
4229 denoted by 0 (zero). Words are inserted into the current line sepa‐
4230 rated by single spaces.
4231 0 (zero)
4233 The zeroth word. For the shell, this is the command word.
4234 n The nth word.
4235 ^ The first argument. That is, word 1.
4236 $ The last word. This is usually the last argument, but will ex‐
4237 pand to the zeroth word if there is only one word in the line.
4238 % The first word matched by the most recent `?string?' search, if
4239 the search string begins with a character that is part of a
4240 word.
4241 x-y A range of words; `-y' abbreviates `0-y'.
4242 * All of the words but the zeroth. This is a synonym for `1-$'.
4243 It is not an error to use * if there is just one word in the
4244 event; the empty string is returned in that case.
4245 x* Abbreviates x-$.
4246 x- Abbreviates x-$ like x*, but omits the last word. If x is miss‐
4247 ing, it defaults to 0.
4248 If a word designator is supplied without an event specification, the
4250 previous command is used as the event.
4251 Modifiers
4253 After the optional word designator, there may appear a sequence of one
4254 or more of the following modifiers, each preceded by a `:'. These mod‐
4255 ify, or edit, the word or words selected from the history event.
4256 h Remove a trailing filename component, leaving only the head.
4258 t Remove all leading filename components, leaving the tail.
4259 r Remove a trailing suffix of the form .xxx, leaving the basename.
4260 e Remove all but the trailing suffix.
4261 p Print the new command but do not execute it.
4262 q Quote the substituted words, escaping further substitutions.
4263 x Quote the substituted words as with q, but break into words at
4264 blanks and newlines. The q and x modifiers are mutually exclu‐
4265 sive; the last one supplied is used.
4266 s/old/new/
4267 Substitute new for the first occurrence of old in the event
4268 line. Any character may be used as the delimiter in place of /.
4269 The final delimiter is optional if it is the last character of
4270 the event line. The delimiter may be quoted in old and new with
4271 a single backslash. If & appears in new, it is replaced by old.
4272 A single backslash will quote the &. If old is null, it is set
4273 to the last old substituted, or, if no previous history substi‐
4274 tutions took place, the last string in a !?string[?] search.
4275 If new is null, each matching old is deleted.
4276 & Repeat the previous substitution.
4277 g Cause changes to be applied over the entire event line. This is
4278 used in conjunction with `:s' (e.g., `:gs/old/new/') or `:&'.
4279 If used with `:s', any delimiter can be used in place of /, and
4280 the final delimiter is optional if it is the last character of
4281 the event line. An a may be used as a synonym for g.
4282 G Apply the following `s' or `&' modifier once to each word in the
4283 event line.
4284
4286 Unless otherwise noted, each builtin command documented in this section
4287 as accepting options preceded by - accepts -- to signify the end of the
4288 options. The :, true, false, and test/[ builtins do not accept options
4289 and do not treat -- specially. The exit, logout, return, break, con‐
4290 tinue, let, and shift builtins accept and process arguments beginning
4291 with - without requiring --. Other builtins that accept arguments but
4292 are not specified as accepting options interpret arguments beginning
4293 with - as invalid options and require -- to prevent this interpreta‐
4294 tion.
4295 : [arguments]
4296 No effect; the command does nothing beyond expanding arguments
4297 and performing any specified redirections. The return status is
4298 zero.
4299 . filename [arguments]
4301 source filename [arguments]
4302 Read and execute commands from filename in the current shell en‐
4303 vironment and return the exit status of the last command exe‐
4304 cuted from filename. If filename does not contain a slash,
4305 filenames in PATH are used to find the directory containing
4306 filename. The file searched for in PATH need not be executable.
4307 When bash is not in posix mode, the current directory is
4308 searched if no file is found in PATH. If the sourcepath option
4309 to the shopt builtin command is turned off, the PATH is not
4310 searched. If any arguments are supplied, they become the posi‐
4311 tional parameters when filename is executed. Otherwise the po‐
4312 sitional parameters are unchanged. If the -T option is enabled,
4313 source inherits any trap on DEBUG; if it is not, any DEBUG trap
4314 string is saved and restored around the call to source, and
4315 source unsets the DEBUG trap while it executes. If -T is not
4316 set, and the sourced file changes the DEBUG trap, the new value
4317 is retained when source completes. The return status is the
4318 status of the last command exited within the script (0 if no
4319 commands are executed), and false if filename is not found or
4320 cannot be read.
4321 alias [-p] [name[=value] ...]
4323 Alias with no arguments or with the -p option prints the list of
4324 aliases in the form alias name=value on standard output. When
4325 arguments are supplied, an alias is defined for each name whose
4326 value is given. A trailing space in value causes the next word
4327 to be checked for alias substitution when the alias is expanded.
4328 For each name in the argument list for which no value is sup‐
4329 plied, the name and value of the alias is printed. Alias re‐
4330 turns true unless a name is given for which no alias has been
4331 defined.
4332 bg [jobspec ...]
4334 Resume each suspended job jobspec in the background, as if it
4335 had been started with &. If jobspec is not present, the shell's
4336 notion of the current job is used. bg jobspec returns 0 unless
4337 run when job control is disabled or, when run with job control
4338 enabled, any specified jobspec was not found or was started
4339 without job control.
4340 bind [-m keymap] [-lpsvPSVX]
4342 bind [-m keymap] [-q function] [-u function] [-r keyseq]
4343 bind [-m keymap] -f filename
4344 bind [-m keymap] -x keyseq:shell-command
4345 bind [-m keymap] keyseq:function-name
4346 bind [-m keymap] keyseq:readline-command
4347 Display current readline key and function bindings, bind a key
4348 sequence to a readline function or macro, or set a readline
4349 variable. Each non-option argument is a command as it would ap‐
4350 pear in .inputrc, but each binding or command must be passed as
4351 a separate argument; e.g., '"\C-x\C-r": re-read-init-file'. Op‐
4352 tions, if supplied, have the following meanings:
4353 -m keymap
4354 Use keymap as the keymap to be affected by the subsequent
4355 bindings. Acceptable keymap names are emacs, emacs-stan‐
4356 dard, emacs-meta, emacs-ctlx, vi, vi-move, vi-command,
4357 and vi-insert. vi is equivalent to vi-command (vi-move
4358 is also a synonym); emacs is equivalent to emacs-stan‐
4359 dard.
4360 -l List the names of all readline functions.
4361 -p Display readline function names and bindings in such a
4362 way that they can be re-read.
4363 -P List current readline function names and bindings.
4364 -s Display readline key sequences bound to macros and the
4365 strings they output in such a way that they can be re-
4366 read.
4367 -S Display readline key sequences bound to macros and the
4368 strings they output.
4369 -v Display readline variable names and values in such a way
4370 that they can be re-read.
4371 -V List current readline variable names and values.
4372 -f filename
4373 Read key bindings from filename.
4374 -q function
4375 Query about which keys invoke the named function.
4376 -u function
4377 Unbind all keys bound to the named function.
4378 -r keyseq
4379 Remove any current binding for keyseq.
4380 -x keyseq:shell-command
4381 Cause shell-command to be executed whenever keyseq is en‐
4382 tered. When shell-command is executed, the shell sets
4383 the READLINE_LINE variable to the contents of the read‐
4384 line line buffer and the READLINE_POINT and READLINE_MARK
4385 variables to the current location of the insertion point
4386 and the saved insertion point (the mark), respectively.
4387 If the executed command changes the value of any of READ‐
4388 LINE_LINE, READLINE_POINT, or READLINE_MARK, those new
4389 values will be reflected in the editing state.
4390 -X List all key sequences bound to shell commands and the
4391 associated commands in a format that can be reused as in‐
4392 put.
4393 The return value is 0 unless an unrecognized option is given or
4395 an error occurred.
4396 break [n]
4398 Exit from within a for, while, until, or select loop. If n is
4399 specified, break n levels. n must be ≥ 1. If n is greater than
4400 the number of enclosing loops, all enclosing loops are exited.
4401 The return value is 0 unless n is not greater than or equal to
4402 1.
4403 builtin shell-builtin [arguments]
4405 Execute the specified shell builtin, passing it arguments, and
4406 return its exit status. This is useful when defining a function
4407 whose name is the same as a shell builtin, retaining the func‐
4408 tionality of the builtin within the function. The cd builtin is
4409 commonly redefined this way. The return status is false if
4410 shell-builtin is not a shell builtin command.
4411 caller [expr]
4413 Returns the context of any active subroutine call (a shell func‐
4414 tion or a script executed with the . or source builtins). With‐
4415 out expr, caller displays the line number and source filename of
4416 the current subroutine call. If a non-negative integer is sup‐
4417 plied as expr, caller displays the line number, subroutine name,
4418 and source file corresponding to that position in the current
4419 execution call stack. This extra information may be used, for
4420 example, to print a stack trace. The current frame is frame 0.
4421 The return value is 0 unless the shell is not executing a sub‐
4422 routine call or expr does not correspond to a valid position in
4423 the call stack.
4424 cd [-L|[-P [-e]] [-@]] [dir]
4426 Change the current directory to dir. if dir is not supplied,
4427 the value of the HOME shell variable is the default. Any addi‐
4428 tional arguments following dir are ignored. The variable CDPATH
4429 defines the search path for the directory containing dir: each
4430 directory name in CDPATH is searched for dir. Alternative di‐
4431 rectory names in CDPATH are separated by a colon (:). A null
4432 directory name in CDPATH is the same as the current directory,
4433 i.e., ``.''. If dir begins with a slash (/), then CDPATH is not
4434 used. The -P option causes cd to use the physical directory
4435 structure by resolving symbolic links while traversing dir and
4436 before processing instances of .. in dir (see also the -P option
4437 to the set builtin command); the -L option forces symbolic links
4438 to be followed by resolving the link after processing instances
4439 of .. in dir. If .. appears in dir, it is processed by removing
4440 the immediately previous pathname component from dir, back to a
4441 slash or the beginning of dir. If the -e option is supplied
4442 with -P, and the current working directory cannot be success‐
4443 fully determined after a successful directory change, cd will
4444 return an unsuccessful status. On systems that support it, the
4445 -@ option presents the extended attributes associated with a
4446 file as a directory. An argument of - is converted to $OLDPWD
4447 before the directory change is attempted. If a non-empty direc‐
4448 tory name from CDPATH is used, or if - is the first argument,
4449 and the directory change is successful, the absolute pathname of
4450 the new working directory is written to the standard output.
4451 The return value is true if the directory was successfully
4452 changed; false otherwise.
4453 command [-pVv] command [arg ...]
4455 Run command with args suppressing the normal shell function
4456 lookup. Only builtin commands or commands found in the PATH are
4457 executed. If the -p option is given, the search for command is
4458 performed using a default value for PATH that is guaranteed to
4459 find all of the standard utilities. If either the -V or -v op‐
4460 tion is supplied, a description of command is printed. The -v
4461 option causes a single word indicating the command or filename
4462 used to invoke command to be displayed; the -V option produces a
4463 more verbose description. If the -V or -v option is supplied,
4464 the exit status is 0 if command was found, and 1 if not. If
4465 neither option is supplied and an error occurred or command can‐
4466 not be found, the exit status is 127. Otherwise, the exit sta‐
4467 tus of the command builtin is the exit status of command.
4468 compgen [option] [word]
4470 Generate possible completion matches for word according to the
4471 options, which may be any option accepted by the complete
4472 builtin with the exception of -p and -r, and write the matches
4473 to the standard output. When using the -F or -C options, the
4474 various shell variables set by the programmable completion fa‐
4475 cilities, while available, will not have useful values.
4476 The matches will be generated in the same way as if the program‐
4478 mable completion code had generated them directly from a comple‐
4479 tion specification with the same flags. If word is specified,
4480 only those completions matching word will be displayed.
4481 The return value is true unless an invalid option is supplied,
4483 or no matches were generated.
4484 complete [-abcdefgjksuv] [-o comp-option] [-DEI] [-A action] [-G glob‐
4486 pat] [-W wordlist]
4487 [-F function] [-C command] [-X filterpat] [-P prefix] [-S suf‐
4488 fix] name [name ...]
4489 complete -pr [-DEI] [name ...]
4490 Specify how arguments to each name should be completed. If the
4491 -p option is supplied, or if no options are supplied, existing
4492 completion specifications are printed in a way that allows them
4493 to be reused as input. The -r option removes a completion spec‐
4494 ification for each name, or, if no names are supplied, all com‐
4495 pletion specifications. The -D option indicates that other sup‐
4496 plied options and actions should apply to the ``default'' com‐
4497 mand completion; that is, completion attempted on a command for
4498 which no completion has previously been defined. The -E option
4499 indicates that other supplied options and actions should apply
4500 to ``empty'' command completion; that is, completion attempted
4501 on a blank line. The -I option indicates that other supplied
4502 options and actions should apply to completion on the initial
4503 non-assignment word on the line, or after a command delimiter
4504 such as ; or |, which is usually command name completion. If
4505 multiple options are supplied, the -D option takes precedence
4506 over -E, and both take precedence over -I. If any of -D, -E, or
4507 -I are supplied, any other name arguments are ignored; these
4508 completions only apply to the case specified by the option.
4509 The process of applying these completion specifications when
4511 word completion is attempted is described above under Program‐
4512 mable Completion.
4513 Other options, if specified, have the following meanings. The
4515 arguments to the -G, -W, and -X options (and, if necessary, the
4516 -P and -S options) should be quoted to protect them from expan‐
4517 sion before the complete builtin is invoked.
4518 -o comp-option
4519 The comp-option controls several aspects of the comp‐
4520 spec's behavior beyond the simple generation of comple‐
4521 tions. comp-option may be one of:
4522 bashdefault
4523 Perform the rest of the default bash completions
4524 if the compspec generates no matches.
4525 default Use readline's default filename completion if
4526 the compspec generates no matches.
4527 dirnames
4528 Perform directory name completion if the comp‐
4529 spec generates no matches.
4530 filenames
4531 Tell readline that the compspec generates file‐
4532 names, so it can perform any filename-specific
4533 processing (like adding a slash to directory
4534 names, quoting special characters, or suppress‐
4535 ing trailing spaces). Intended to be used with
4536 shell functions.
4537 noquote Tell readline not to quote the completed words
4538 if they are filenames (quoting filenames is the
4539 default).
4540 nosort Tell readline not to sort the list of possible
4541 completions alphabetically.
4542 nospace Tell readline not to append a space (the de‐
4543 fault) to words completed at the end of the
4544 line.
4545 plusdirs
4546 After any matches defined by the compspec are
4547 generated, directory name completion is at‐
4548 tempted and any matches are added to the results
4549 of the other actions.
4550 -A action
4551 The action may be one of the following to generate a
4552 list of possible completions:
4553 alias Alias names. May also be specified as -a.
4554 arrayvar
4555 Array variable names.
4556 binding Readline key binding names.
4557 builtin Names of shell builtin commands. May also be
4558 specified as -b.
4559 command Command names. May also be specified as -c.
4560 directory
4561 Directory names. May also be specified as -d.
4562 disabled
4563 Names of disabled shell builtins.
4564 enabled Names of enabled shell builtins.
4565 export Names of exported shell variables. May also be
4566 specified as -e.
4567 file File names. May also be specified as -f.
4568 function
4569 Names of shell functions.
4570 group Group names. May also be specified as -g.
4571 helptopic
4572 Help topics as accepted by the help builtin.
4573 hostname
4574 Hostnames, as taken from the file specified by
4575 the HOSTFILE shell variable.
4576 job Job names, if job control is active. May also
4577 be specified as -j.
4578 keyword Shell reserved words. May also be specified as
4579 -k.
4580 running Names of running jobs, if job control is active.
4581 service Service names. May also be specified as -s.
4582 setopt Valid arguments for the -o option to the set
4583 builtin.
4584 shopt Shell option names as accepted by the shopt
4585 builtin.
4586 signal Signal names.
4587 stopped Names of stopped jobs, if job control is active.
4588 user User names. May also be specified as -u.
4589 variable
4590 Names of all shell variables. May also be spec‐
4591 ified as -v.
4592 -C command
4593 command is executed in a subshell environment, and its
4594 output is used as the possible completions.
4595 -F function
4596 The shell function function is executed in the current
4597 shell environment. When the function is executed, the
4598 first argument ($1) is the name of the command whose ar‐
4599 guments are being completed, the second argument ($2) is
4600 the word being completed, and the third argument ($3) is
4601 the word preceding the word being completed on the cur‐
4602 rent command line. When it finishes, the possible com‐
4603 pletions are retrieved from the value of the COMPREPLY
4604 array variable.
4605 -G globpat
4606 The pathname expansion pattern globpat is expanded to
4607 generate the possible completions.
4608 -P prefix
4609 prefix is added at the beginning of each possible com‐
4610 pletion after all other options have been applied.
4611 -S suffix
4612 suffix is appended to each possible completion after all
4613 other options have been applied.
4614 -W wordlist
4615 The wordlist is split using the characters in the IFS
4616 special variable as delimiters, and each resultant word
4617 is expanded. Shell quoting is honored within wordlist,
4618 in order to provide a mechanism for the words to contain
4619 shell metacharacters or characters in the value of IFS.
4620 The possible completions are the members of the resul‐
4621 tant list which match the word being completed.
4622 -X filterpat
4623 filterpat is a pattern as used for pathname expansion.
4624 It is applied to the list of possible completions gener‐
4625 ated by the preceding options and arguments, and each
4626 completion matching filterpat is removed from the list.
4627 A leading ! in filterpat negates the pattern; in this
4628 case, any completion not matching filterpat is removed.
4629 The return value is true unless an invalid option is supplied,
4631 an option other than -p or -r is supplied without a name argu‐
4632 ment, an attempt is made to remove a completion specification
4633 for a name for which no specification exists, or an error occurs
4634 adding a completion specification.
4635 compopt [-o option] [-DEI] [+o option] [name]
4637 Modify completion options for each name according to the op‐
4638 tions, or for the currently-executing completion if no names are
4639 supplied. If no options are given, display the completion op‐
4640 tions for each name or the current completion. The possible
4641 values of option are those valid for the complete builtin de‐
4642 scribed above. The -D option indicates that other supplied op‐
4643 tions should apply to the ``default'' command completion; that
4644 is, completion attempted on a command for which no completion
4645 has previously been defined. The -E option indicates that other
4646 supplied options should apply to ``empty'' command completion;
4647 that is, completion attempted on a blank line. The -I option
4648 indicates that other supplied options should apply to completion
4649 on the initial non-assignment word on the line, or after a com‐
4650 mand delimiter such as ; or |, which is usually command name
4651 completion.
4652 The return value is true unless an invalid option is supplied,
4654 an attempt is made to modify the options for a name for which no
4655 completion specification exists, or an output error occurs.
4656 continue [n]
4658 Resume the next iteration of the enclosing for, while, until, or
4659 select loop. If n is specified, resume at the nth enclosing
4660 loop. n must be ≥ 1. If n is greater than the number of en‐
4661 closing loops, the last enclosing loop (the ``top-level'' loop)
4662 is resumed. The return value is 0 unless n is not greater than
4663 or equal to 1.
4664 declare [-aAfFgiIlnrtux] [-p] [name[=value] ...]
4666 typeset [-aAfFgiIlnrtux] [-p] [name[=value] ...]
4667 Declare variables and/or give them attributes. If no names are
4668 given then display the values of variables. The -p option will
4669 display the attributes and values of each name. When -p is used
4670 with name arguments, additional options, other than -f and -F,
4671 are ignored. When -p is supplied without name arguments, it
4672 will display the attributes and values of all variables having
4673 the attributes specified by the additional options. If no other
4674 options are supplied with -p, declare will display the at‐
4675 tributes and values of all shell variables. The -f option will
4676 restrict the display to shell functions. The -F option inhibits
4677 the display of function definitions; only the function name and
4678 attributes are printed. If the extdebug shell option is enabled
4679 using shopt, the source file name and line number where each
4680 name is defined are displayed as well. The -F option implies
4681 -f. The -g option forces variables to be created or modified at
4682 the global scope, even when declare is executed in a shell func‐
4683 tion. It is ignored in all other cases. The -I option causes
4684 local variables to inherit the attributes (except the nameref
4685 attribute) and value of any existing variable with the same name
4686 at a surrounding scope. If there is no existing variable, the
4687 local variable is initially unset. The following options can be
4688 used to restrict output to variables with the specified attri‐
4689 bute or to give variables attributes:
4690 -a Each name is an indexed array variable (see Arrays
4691 above).
4692 -A Each name is an associative array variable (see Arrays
4693 above).
4694 -f Use function names only.
4695 -i The variable is treated as an integer; arithmetic evalua‐
4696 tion (see ARITHMETIC EVALUATION above) is performed when
4697 the variable is assigned a value.
4698 -l When the variable is assigned a value, all upper-case
4699 characters are converted to lower-case. The upper-case
4700 attribute is disabled.
4701 -n Give each name the nameref attribute, making it a name
4702 reference to another variable. That other variable is
4703 defined by the value of name. All references, assign‐
4704 ments, and attribute modifications to name, except those
4705 using or changing the -n attribute itself, are performed
4706 on the variable referenced by name's value. The nameref
4707 attribute cannot be applied to array variables.
4708 -r Make names readonly. These names cannot then be assigned
4709 values by subsequent assignment statements or unset.
4710 -t Give each name the trace attribute. Traced functions in‐
4711 herit the DEBUG and RETURN traps from the calling shell.
4712 The trace attribute has no special meaning for variables.
4713 -u When the variable is assigned a value, all lower-case
4714 characters are converted to upper-case. The lower-case
4715 attribute is disabled.
4716 -x Mark names for export to subsequent commands via the en‐
4717 vironment.
4718 Using `+' instead of `-' turns off the attribute instead, with
4720 the exceptions that +a and +A may not be used to destroy array
4721 variables and +r will not remove the readonly attribute. When
4722 used in a function, declare and typeset make each name local, as
4723 with the local command, unless the -g option is supplied. If a
4724 variable name is followed by =value, the value of the variable
4725 is set to value. When using -a or -A and the compound assign‐
4726 ment syntax to create array variables, additional attributes do
4727 not take effect until subsequent assignments. The return value
4728 is 0 unless an invalid option is encountered, an attempt is made
4729 to define a function using ``-f foo=bar'', an attempt is made to
4730 assign a value to a readonly variable, an attempt is made to as‐
4731 sign a value to an array variable without using the compound as‐
4732 signment syntax (see Arrays above), one of the names is not a
4733 valid shell variable name, an attempt is made to turn off read‐
4734 only status for a readonly variable, an attempt is made to turn
4735 off array status for an array variable, or an attempt is made to
4736 display a non-existent function with -f.
4737 dirs [-clpv] [+n] [-n]
4739 Without options, displays the list of currently remembered di‐
4740 rectories. The default display is on a single line with direc‐
4741 tory names separated by spaces. Directories are added to the
4742 list with the pushd command; the popd command removes entries
4743 from the list. The current directory is always the first direc‐
4744 tory in the stack.
4745 -c Clears the directory stack by deleting all of the en‐
4746 tries.
4747 -l Produces a listing using full pathnames; the default
4748 listing format uses a tilde to denote the home directory.
4749 -p Print the directory stack with one entry per line.
4750 -v Print the directory stack with one entry per line, pre‐
4751 fixing each entry with its index in the stack.
4752 +n Displays the nth entry counting from the left of the list
4753 shown by dirs when invoked without options, starting with
4754 zero.
4755 -n Displays the nth entry counting from the right of the
4756 list shown by dirs when invoked without options, starting
4757 with zero.
4758 The return value is 0 unless an invalid option is supplied or n
4760 indexes beyond the end of the directory stack.
4761 disown [-ar] [-h] [jobspec ... | pid ... ]
4763 Without options, remove each jobspec from the table of active
4764 jobs. If jobspec is not present, and neither the -a nor the -r
4765 option is supplied, the current job is used. If the -h option
4766 is given, each jobspec is not removed from the table, but is
4767 marked so that SIGHUP is not sent to the job if the shell re‐
4768 ceives a SIGHUP. If no jobspec is supplied, the -a option means
4769 to remove or mark all jobs; the -r option without a jobspec ar‐
4770 gument restricts operation to running jobs. The return value is
4771 0 unless a jobspec does not specify a valid job.
4772 echo [-neE] [arg ...]
4774 Output the args, separated by spaces, followed by a newline.
4775 The return status is 0 unless a write error occurs. If -n is
4776 specified, the trailing newline is suppressed. If the -e option
4777 is given, interpretation of the following backslash-escaped
4778 characters is enabled. The -E option disables the interpreta‐
4779 tion of these escape characters, even on systems where they are
4780 interpreted by default. The xpg_echo shell option may be used
4781 to dynamically determine whether or not echo expands these es‐
4782 cape characters by default. echo does not interpret -- to mean
4783 the end of options. echo interprets the following escape se‐
4784 quences:
4785 \a alert (bell)
4786 \b backspace
4787 \c suppress further output
4788 \e
4789 \E an escape character
4790 \f form feed
4791 \n new line
4792 \r carriage return
4793 \t horizontal tab
4794 \v vertical tab
4795 \\ backslash
4796 \0nnn the eight-bit character whose value is the octal value
4797 nnn (zero to three octal digits)
4798 \xHH the eight-bit character whose value is the hexadecimal
4799 value HH (one or two hex digits)
4800 \uHHHH the Unicode (ISO/IEC 10646) character whose value is the
4801 hexadecimal value HHHH (one to four hex digits)
4802 \UHHHHHHHH
4803 the Unicode (ISO/IEC 10646) character whose value is the
4804 hexadecimal value HHHHHHHH (one to eight hex digits)
4805 enable [-a] [-dnps] [-f filename] [name ...]
4807 Enable and disable builtin shell commands. Disabling a builtin
4808 allows a disk command which has the same name as a shell builtin
4809 to be executed without specifying a full pathname, even though
4810 the shell normally searches for builtins before disk commands.
4811 If -n is used, each name is disabled; otherwise, names are en‐
4812 abled. For example, to use the test binary found via the PATH
4813 instead of the shell builtin version, run ``enable -n test''.
4814 The -f option means to load the new builtin command name from
4815 shared object filename, on systems that support dynamic loading.
4816 The -d option will delete a builtin previously loaded with -f.
4817 If no name arguments are given, or if the -p option is supplied,
4818 a list of shell builtins is printed. With no other option argu‐
4819 ments, the list consists of all enabled shell builtins. If -n
4820 is supplied, only disabled builtins are printed. If -a is sup‐
4821 plied, the list printed includes all builtins, with an indica‐
4822 tion of whether or not each is enabled. If -s is supplied, the
4823 output is restricted to the POSIX special builtins. The return
4824 value is 0 unless a name is not a shell builtin or there is an
4825 error loading a new builtin from a shared object.
4826 eval [arg ...]
4828 The args are read and concatenated together into a single com‐
4829 mand. This command is then read and executed by the shell, and
4830 its exit status is returned as the value of eval. If there are
4831 no args, or only null arguments, eval returns 0.
4832 exec [-cl] [-a name] [command [arguments]]
4834 If command is specified, it replaces the shell. No new process
4835 is created. The arguments become the arguments to command. If
4836 the -l option is supplied, the shell places a dash at the begin‐
4837 ning of the zeroth argument passed to command. This is what lo‐
4838 gin(1) does. The -c option causes command to be executed with
4839 an empty environment. If -a is supplied, the shell passes name
4840 as the zeroth argument to the executed command. If command can‐
4841 not be executed for some reason, a non-interactive shell exits,
4842 unless the execfail shell option is enabled. In that case, it
4843 returns failure. An interactive shell returns failure if the
4844 file cannot be executed. A subshell exits unconditionally if
4845 exec fails. If command is not specified, any redirections take
4846 effect in the current shell, and the return status is 0. If
4847 there is a redirection error, the return status is 1.
4848 exit [n]
4850 Cause the shell to exit with a status of n. If n is omitted,
4851 the exit status is that of the last command executed. A trap on
4852 EXIT is executed before the shell terminates.
4853 export [-fn] [name[=word]] ...
4855 export -p
4856 The supplied names are marked for automatic export to the envi‐
4857 ronment of subsequently executed commands. If the -f option is
4858 given, the names refer to functions. If no names are given, or
4859 if the -p option is supplied, a list of names of all exported
4860 variables is printed. The -n option causes the export property
4861 to be removed from each name. If a variable name is followed by
4862 =word, the value of the variable is set to word. export returns
4863 an exit status of 0 unless an invalid option is encountered, one
4864 of the names is not a valid shell variable name, or -f is sup‐
4865 plied with a name that is not a function.
4866 fc [-e ename] [-lnr] [first] [last]
4868 fc -s [pat=rep] [cmd]
4869 The first form selects a range of commands from first to last
4870 from the history list and displays or edits and re-executes
4871 them. First and last may be specified as a string (to locate
4872 the last command beginning with that string) or as a number (an
4873 index into the history list, where a negative number is used as
4874 an offset from the current command number). When listing, a
4875 first or last of 0 is equivalent to -1 and -0 is equivalent to
4876 the current command (usually the fc command); otherwise 0 is
4877 equivalent to -1 and -0 is invalid. If last is not specified,
4878 it is set to the current command for listing (so that ``fc -l
4879 -10'' prints the last 10 commands) and to first otherwise. If
4880 first is not specified, it is set to the previous command for
4881 editing and -16 for listing.
4882 The -n option suppresses the command numbers when listing. The
4884 -r option reverses the order of the commands. If the -l option
4885 is given, the commands are listed on standard output. Other‐
4886 wise, the editor given by ename is invoked on a file containing
4887 those commands. If ename is not given, the value of the FCEDIT
4888 variable is used, and the value of EDITOR if FCEDIT is not set.
4889 If neither variable is set, vi is used. When editing is com‐
4890 plete, the edited commands are echoed and executed.
4891 In the second form, command is re-executed after each instance
4893 of pat is replaced by rep. Command is interpreted the same as
4894 first above. A useful alias to use with this is ``r="fc -s"'',
4895 so that typing ``r cc'' runs the last command beginning with
4896 ``cc'' and typing ``r'' re-executes the last command.
4897 If the first form is used, the return value is 0 unless an in‐
4899 valid option is encountered or first or last specify history
4900 lines out of range. If the -e option is supplied, the return
4901 value is the value of the last command executed or failure if an
4902 error occurs with the temporary file of commands. If the second
4903 form is used, the return status is that of the command re-exe‐
4904 cuted, unless cmd does not specify a valid history line, in
4905 which case fc returns failure.
4906 fg [jobspec]
4908 Resume jobspec in the foreground, and make it the current job.
4909 If jobspec is not present, the shell's notion of the current job
4910 is used. The return value is that of the command placed into
4911 the foreground, or failure if run when job control is disabled
4912 or, when run with job control enabled, if jobspec does not spec‐
4913 ify a valid job or jobspec specifies a job that was started
4914 without job control.
4915 getopts optstring name [arg ...]
4917 getopts is used by shell procedures to parse positional parame‐
4918 ters. optstring contains the option characters to be recog‐
4919 nized; if a character is followed by a colon, the option is ex‐
4920 pected to have an argument, which should be separated from it by
4921 white space. The colon and question mark characters may not be
4922 used as option characters. Each time it is invoked, getopts
4923 places the next option in the shell variable name, initializing
4924 name if it does not exist, and the index of the next argument to
4925 be processed into the variable OPTIND. OPTIND is initialized to
4926 1 each time the shell or a shell script is invoked. When an op‐
4927 tion requires an argument, getopts places that argument into the
4928 variable OPTARG. The shell does not reset OPTIND automatically;
4929 it must be manually reset between multiple calls to getopts
4930 within the same shell invocation if a new set of parameters is
4931 to be used.
4932 When the end of options is encountered, getopts exits with a re‐
4934 turn value greater than zero. OPTIND is set to the index of the
4935 first non-option argument, and name is set to ?.
4936 getopts normally parses the positional parameters, but if more
4938 arguments are supplied as arg values, getopts parses those in‐
4939 stead.
4940 getopts can report errors in two ways. If the first character
4942 of optstring is a colon, silent error reporting is used. In
4943 normal operation, diagnostic messages are printed when invalid
4944 options or missing option arguments are encountered. If the
4945 variable OPTERR is set to 0, no error messages will be dis‐
4946 played, even if the first character of optstring is not a colon.
4947 If an invalid option is seen, getopts places ? into name and, if
4949 not silent, prints an error message and unsets OPTARG. If
4950 getopts is silent, the option character found is placed in OP‐
4951 TARG and no diagnostic message is printed.
4952 If a required argument is not found, and getopts is not silent,
4954 a question mark (?) is placed in name, OPTARG is unset, and a
4955 diagnostic message is printed. If getopts is silent, then a
4956 colon (:) is placed in name and OPTARG is set to the option
4957 character found.
4958 getopts returns true if an option, specified or unspecified, is
4960 found. It returns false if the end of options is encountered or
4961 an error occurs.
4962 hash [-lr] [-p filename] [-dt] [name]
4964 Each time hash is invoked, the full pathname of the command name
4965 is determined by searching the directories in $PATH and remem‐
4966 bered. Any previously-remembered pathname is discarded. If the
4967 -p option is supplied, no path search is performed, and filename
4968 is used as the full filename of the command. The -r option
4969 causes the shell to forget all remembered locations. The -d op‐
4970 tion causes the shell to forget the remembered location of each
4971 name. If the -t option is supplied, the full pathname to which
4972 each name corresponds is printed. If multiple name arguments
4973 are supplied with -t, the name is printed before the hashed full
4974 pathname. The -l option causes output to be displayed in a for‐
4975 mat that may be reused as input. If no arguments are given, or
4976 if only -l is supplied, information about remembered commands is
4977 printed. The return status is true unless a name is not found
4978 or an invalid option is supplied.
4979 help [-dms] [pattern]
4981 Display helpful information about builtin commands. If pattern
4982 is specified, help gives detailed help on all commands matching
4983 pattern; otherwise help for all the builtins and shell control
4984 structures is printed.
4985 -d Display a short description of each pattern
4986 -m Display the description of each pattern in a manpage-like
4987 format
4988 -s Display only a short usage synopsis for each pattern
4989 The return status is 0 unless no command matches pattern.
4991 history [n]
4993 history -c
4994 history -d offset
4995 history -d start-end
4996 history -anrw [filename]
4997 history -p arg [arg ...]
4998 history -s arg [arg ...]
4999 With no options, display the command history list with line num‐
5000 bers. Lines listed with a * have been modified. An argument of
5001 n lists only the last n lines. If the shell variable HISTTIME‐
5002 FORMAT is set and not null, it is used as a format string for
5003 strftime(3) to display the time stamp associated with each dis‐
5004 played history entry. No intervening blank is printed between
5005 the formatted time stamp and the history line. If filename is
5006 supplied, it is used as the name of the history file; if not,
5007 the value of HISTFILE is used. Options, if supplied, have the
5008 following meanings:
5009 -c Clear the history list by deleting all the entries.
5010 -d offset
5011 Delete the history entry at position offset. If offset
5012 is negative, it is interpreted as relative to one greater
5013 than the last history position, so negative indices count
5014 back from the end of the history, and an index of -1
5015 refers to the current history -d command.
5016 -d start-end
5017 Delete the history entries between positions start and
5018 end, inclusive. Positive and negative values for start
5019 and end are interpreted as described above.
5020 -a Append the ``new'' history lines to the history file.
5021 These are history lines entered since the beginning of
5022 the current bash session, but not already appended to the
5023 history file.
5024 -n Read the history lines not already read from the history
5025 file into the current history list. These are lines ap‐
5026 pended to the history file since the beginning of the
5027 current bash session.
5028 -r Read the contents of the history file and append them to
5029 the current history list.
5030 -w Write the current history list to the history file, over‐
5031 writing the history file's contents.
5032 -p Perform history substitution on the following args and
5033 display the result on the standard output. Does not
5034 store the results in the history list. Each arg must be
5035 quoted to disable normal history expansion.
5036 -s Store the args in the history list as a single entry.
5037 The last command in the history list is removed before
5038 the args are added.
5039 If the HISTTIMEFORMAT variable is set, the time stamp informa‐
5041 tion associated with each history entry is written to the his‐
5042 tory file, marked with the history comment character. When the
5043 history file is read, lines beginning with the history comment
5044 character followed immediately by a digit are interpreted as
5045 timestamps for the following history entry. The return value is
5046 0 unless an invalid option is encountered, an error occurs while
5047 reading or writing the history file, an invalid offset is sup‐
5048 plied as an argument to -d, or the history expansion supplied as
5049 an argument to -p fails.
5050 jobs [-lnprs] [ jobspec ... ]
5052 jobs -x command [ args ... ]
5053 The first form lists the active jobs. The options have the fol‐
5054 lowing meanings:
5055 -l List process IDs in addition to the normal information.
5056 -n Display information only about jobs that have changed
5057 status since the user was last notified of their status.
5058 -p List only the process ID of the job's process group
5059 leader.
5060 -r Display only running jobs.
5061 -s Display only stopped jobs.
5062 If jobspec is given, output is restricted to information about
5064 that job. The return status is 0 unless an invalid option is
5065 encountered or an invalid jobspec is supplied.
5066 If the -x option is supplied, jobs replaces any jobspec found in
5068 command or args with the corresponding process group ID, and ex‐
5069 ecutes command passing it args, returning its exit status.
5070 kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...
5072 kill -l|-L [sigspec | exit_status]
5073 Send the signal named by sigspec or signum to the processes
5074 named by pid or jobspec. sigspec is either a case-insensitive
5075 signal name such as SIGKILL (with or without the SIG prefix) or
5076 a signal number; signum is a signal number. If sigspec is not
5077 present, then SIGTERM is assumed. An argument of -l lists the
5078 signal names. If any arguments are supplied when -l is given,
5079 the names of the signals corresponding to the arguments are
5080 listed, and the return status is 0. The exit_status argument to
5081 -l is a number specifying either a signal number or the exit
5082 status of a process terminated by a signal. The -L option is
5083 equivalent to -l. kill returns true if at least one signal was
5084 successfully sent, or false if an error occurs or an invalid op‐
5085 tion is encountered.
5086 let arg [arg ...]
5088 Each arg is an arithmetic expression to be evaluated (see ARITH‐
5089 METIC EVALUATION above). If the last arg evaluates to 0, let
5090 returns 1; 0 is returned otherwise.
5091 local [option] [name[=value] ... | - ]
5093 For each argument, a local variable named name is created, and
5094 assigned value. The option can be any of the options accepted
5095 by declare. When local is used within a function, it causes the
5096 variable name to have a visible scope restricted to that func‐
5097 tion and its children. If name is -, the set of shell options
5098 is made local to the function in which local is invoked: shell
5099 options changed using the set builtin inside the function are
5100 restored to their original values when the function returns.
5101 The restore is effected as if a series of set commands were exe‐
5102 cuted to restore the values that were in place before the func‐
5103 tion. With no operands, local writes a list of local variables
5104 to the standard output. It is an error to use local when not
5105 within a function. The return status is 0 unless local is used
5106 outside a function, an invalid name is supplied, or name is a
5107 readonly variable.
5108 logout Exit a login shell.
5110 mapfile [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C
5112 callback] [-c quantum] [array]
5113 readarray [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C
5114 callback] [-c quantum] [array]
5115 Read lines from the standard input into the indexed array vari‐
5116 able array, or from file descriptor fd if the -u option is sup‐
5117 plied. The variable MAPFILE is the default array. Options, if
5118 supplied, have the following meanings:
5119 -d The first character of delim is used to terminate each
5120 input line, rather than newline. If delim is the empty
5121 string, mapfile will terminate a line when it reads a NUL
5122 character.
5123 -n Copy at most count lines. If count is 0, all lines are
5124 copied.
5125 -O Begin assigning to array at index origin. The default
5126 index is 0.
5127 -s Discard the first count lines read.
5128 -t Remove a trailing delim (default newline) from each line
5129 read.
5130 -u Read lines from file descriptor fd instead of the stan‐
5131 dard input.
5132 -C Evaluate callback each time quantum lines are read. The
5133 -c option specifies quantum.
5134 -c Specify the number of lines read between each call to
5135 callback.
5136 If -C is specified without -c, the default quantum is 5000.
5138 When callback is evaluated, it is supplied the index of the next
5139 array element to be assigned and the line to be assigned to that
5140 element as additional arguments. callback is evaluated after
5141 the line is read but before the array element is assigned.
5142 If not supplied with an explicit origin, mapfile will clear ar‐
5144 ray before assigning to it.
5145 mapfile returns successfully unless an invalid option or option
5147 argument is supplied, array is invalid or unassignable, or if
5148 array is not an indexed array.
5149 popd [-n] [+n] [-n]
5151 Removes entries from the directory stack. With no arguments,
5152 removes the top directory from the stack, and performs a cd to
5153 the new top directory. Arguments, if supplied, have the follow‐
5154 ing meanings:
5155 -n Suppresses the normal change of directory when removing
5156 directories from the stack, so that only the stack is ma‐
5157 nipulated.
5158 +n Removes the nth entry counting from the left of the list
5159 shown by dirs, starting with zero. For example: ``popd
5160 +0'' removes the first directory, ``popd +1'' the second.
5161 -n Removes the nth entry counting from the right of the list
5162 shown by dirs, starting with zero. For example: ``popd
5163 -0'' removes the last directory, ``popd -1'' the next to
5164 last.
5165 If the popd command is successful, a dirs is performed as well,
5167 and the return status is 0. popd returns false if an invalid
5168 option is encountered, the directory stack is empty, a non-exis‐
5169 tent directory stack entry is specified, or the directory change
5170 fails.
5171 printf [-v var] format [arguments]
5173 Write the formatted arguments to the standard output under the
5174 control of the format. The -v option causes the output to be
5175 assigned to the variable var rather than being printed to the
5176 standard output.
5177 The format is a character string which contains three types of
5179 objects: plain characters, which are simply copied to standard
5180 output, character escape sequences, which are converted and
5181 copied to the standard output, and format specifications, each
5182 of which causes printing of the next successive argument. In
5183 addition to the standard printf(1) format specifications, printf
5184 interprets the following extensions:
5185 %b causes printf to expand backslash escape sequences in the
5186 corresponding argument in the same way as echo -e.
5187 %q causes printf to output the corresponding argument in a
5188 format that can be reused as shell input.
5189 %(datefmt)T
5190 causes printf to output the date-time string resulting
5191 from using datefmt as a format string for strftime(3).
5192 The corresponding argument is an integer representing the
5193 number of seconds since the epoch. Two special argument
5194 values may be used: -1 represents the current time, and
5195 -2 represents the time the shell was invoked. If no ar‐
5196 gument is specified, conversion behaves as if -1 had been
5197 given. This is an exception to the usual printf behav‐
5198 ior.
5199 The %b, %q, and %T directives all use the field width and preci‐
5201 sion arguments from the format specification and write that many
5202 bytes from (or use that wide a field for) the expanded argument,
5203 which usually contains more characters than the original.
5204 Arguments to non-string format specifiers are treated as C con‐
5206 stants, except that a leading plus or minus sign is allowed, and
5207 if the leading character is a single or double quote, the value
5208 is the ASCII value of the following character.
5209 The format is reused as necessary to consume all of the argu‐
5211 ments. If the format requires more arguments than are supplied,
5212 the extra format specifications behave as if a zero value or
5213 null string, as appropriate, had been supplied. The return
5214 value is zero on success, non-zero on failure.
5215 pushd [-n] [+n] [-n]
5217 pushd [-n] [dir]
5218 Adds a directory to the top of the directory stack, or rotates
5219 the stack, making the new top of the stack the current working
5220 directory. With no arguments, pushd exchanges the top two di‐
5221 rectories and returns 0, unless the directory stack is empty.
5222 Arguments, if supplied, have the following meanings:
5223 -n Suppresses the normal change of directory when rotating
5224 or adding directories to the stack, so that only the
5225 stack is manipulated.
5226 +n Rotates the stack so that the nth directory (counting
5227 from the left of the list shown by dirs, starting with
5228 zero) is at the top.
5229 -n Rotates the stack so that the nth directory (counting
5230 from the right of the list shown by dirs, starting with
5231 zero) is at the top.
5232 dir Adds dir to the directory stack at the top, making it the
5233 new current working directory as if it had been supplied
5234 as the argument to the cd builtin.
5235 If the pushd command is successful, a dirs is performed as well.
5237 If the first form is used, pushd returns 0 unless the cd to dir
5238 fails. With the second form, pushd returns 0 unless the direc‐
5239 tory stack is empty, a non-existent directory stack element is
5240 specified, or the directory change to the specified new current
5241 directory fails.
5242 pwd [-LP]
5244 Print the absolute pathname of the current working directory.
5245 The pathname printed contains no symbolic links if the -P option
5246 is supplied or the -o physical option to the set builtin command
5247 is enabled. If the -L option is used, the pathname printed may
5248 contain symbolic links. The return status is 0 unless an error
5249 occurs while reading the name of the current directory or an in‐
5250 valid option is supplied.
5251 read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p
5253 prompt] [-t timeout] [-u fd] [name ...]
5254 One line is read from the standard input, or from the file de‐
5255 scriptor fd supplied as an argument to the -u option, split into
5256 words as described above under Word Splitting, and the first
5257 word is assigned to the first name, the second word to the sec‐
5258 ond name, and so on. If there are more words than names, the
5259 remaining words and their intervening delimiters are assigned to
5260 the last name. If there are fewer words read from the input
5261 stream than names, the remaining names are assigned empty val‐
5262 ues. The characters in IFS are used to split the line into
5263 words using the same rules the shell uses for expansion (de‐
5264 scribed above under Word Splitting). The backslash character
5265 (\) may be used to remove any special meaning for the next char‐
5266 acter read and for line continuation. Options, if supplied,
5267 have the following meanings:
5268 -a aname
5269 The words are assigned to sequential indices of the array
5270 variable aname, starting at 0. aname is unset before any
5271 new values are assigned. Other name arguments are ig‐
5272 nored.
5273 -d delim
5274 The first character of delim is used to terminate the in‐
5275 put line, rather than newline. If delim is the empty
5276 string, read will terminate a line when it reads a NUL
5277 character.
5278 -e If the standard input is coming from a terminal, readline
5279 (see READLINE above) is used to obtain the line. Read‐
5280 line uses the current (or default, if line editing was
5281 not previously active) editing settings, but uses Read‐
5282 line's default filename completion.
5283 -i text
5284 If readline is being used to read the line, text is
5285 placed into the editing buffer before editing begins.
5286 -n nchars
5287 read returns after reading nchars characters rather than
5288 waiting for a complete line of input, but honors a delim‐
5289 iter if fewer than nchars characters are read before the
5290 delimiter.
5291 -N nchars
5292 read returns after reading exactly nchars characters
5293 rather than waiting for a complete line of input, unless
5294 EOF is encountered or read times out. Delimiter charac‐
5295 ters encountered in the input are not treated specially
5296 and do not cause read to return until nchars characters
5297 are read. The result is not split on the characters in
5298 IFS; the intent is that the variable is assigned exactly
5299 the characters read (with the exception of backslash; see
5300 the -r option below).
5301 -p prompt
5302 Display prompt on standard error, without a trailing new‐
5303 line, before attempting to read any input. The prompt is
5304 displayed only if input is coming from a terminal.
5305 -r Backslash does not act as an escape character. The back‐
5306 slash is considered to be part of the line. In particu‐
5307 lar, a backslash-newline pair may not then be used as a
5308 line continuation.
5309 -s Silent mode. If input is coming from a terminal, charac‐
5310 ters are not echoed.
5311 -t timeout
5312 Cause read to time out and return failure if a complete
5313 line of input (or a specified number of characters) is
5314 not read within timeout seconds. timeout may be a deci‐
5315 mal number with a fractional portion following the deci‐
5316 mal point. This option is only effective if read is
5317 reading input from a terminal, pipe, or other special
5318 file; it has no effect when reading from regular files.
5319 If read times out, read saves any partial input read into
5320 the specified variable name. If timeout is 0, read re‐
5321 turns immediately, without trying to read any data. The
5322 exit status is 0 if input is available on the specified
5323 file descriptor, non-zero otherwise. The exit status is
5324 greater than 128 if the timeout is exceeded.
5325 -u fd Read input from file descriptor fd.
5326 If no names are supplied, the line read, without the ending de‐
5328 limiter but otherwise unmodified, is assigned to the variable
5329 REPLY. The exit status is zero, unless end-of-file is encoun‐
5330 tered, read times out (in which case the status is greater than
5331 128), a variable assignment error (such as assigning to a read‐
5332 only variable) occurs, or an invalid file descriptor is supplied
5333 as the argument to -u.
5334 readonly [-aAf] [-p] [name[=word] ...]
5336 The given names are marked readonly; the values of these names
5337 may not be changed by subsequent assignment. If the -f option
5338 is supplied, the functions corresponding to the names are so
5339 marked. The -a option restricts the variables to indexed ar‐
5340 rays; the -A option restricts the variables to associative ar‐
5341 rays. If both options are supplied, -A takes precedence. If no
5342 name arguments are given, or if the -p option is supplied, a
5343 list of all readonly names is printed. The other options may be
5344 used to restrict the output to a subset of the set of readonly
5345 names. The -p option causes output to be displayed in a format
5346 that may be reused as input. If a variable name is followed by
5347 =word, the value of the variable is set to word. The return
5348 status is 0 unless an invalid option is encountered, one of the
5349 names is not a valid shell variable name, or -f is supplied with
5350 a name that is not a function.
5351 return [n]
5353 Causes a function to stop executing and return the value speci‐
5354 fied by n to its caller. If n is omitted, the return status is
5355 that of the last command executed in the function body. If re‐
5356 turn is executed by a trap handler, the last command used to de‐
5357 termine the status is the last command executed before the trap
5358 handler. If return is executed during a DEBUG trap, the last
5359 command used to determine the status is the last command exe‐
5360 cuted by the trap handler before return was invoked. If return
5361 is used outside a function, but during execution of a script by
5362 the . (source) command, it causes the shell to stop executing
5363 that script and return either n or the exit status of the last
5364 command executed within the script as the exit status of the
5365 script. If n is supplied, the return value is its least signif‐
5366 icant 8 bits. The return status is non-zero if return is sup‐
5367 plied a non-numeric argument, or is used outside a function and
5368 not during execution of a script by . or source. Any command
5369 associated with the RETURN trap is executed before execution re‐
5370 sumes after the function or script.
5371 set [--abefhkmnptuvxBCEHPT] [-o option-name] [arg ...]
5373 set [+abefhkmnptuvxBCEHPT] [+o option-name] [arg ...]
5374 Without options, the name and value of each shell variable are
5375 displayed in a format that can be reused as input for setting or
5376 resetting the currently-set variables. Read-only variables can‐
5377 not be reset. In posix mode, only shell variables are listed.
5378 The output is sorted according to the current locale. When op‐
5379 tions are specified, they set or unset shell attributes. Any
5380 arguments remaining after option processing are treated as val‐
5381 ues for the positional parameters and are assigned, in order, to
5382 $1, $2, ... $n. Options, if specified, have the following
5383 meanings:
5384 -a Each variable or function that is created or modified is
5385 given the export attribute and marked for export to the
5386 environment of subsequent commands.
5387 -b Report the status of terminated background jobs immedi‐
5388 ately, rather than before the next primary prompt. This
5389 is effective only when job control is enabled.
5390 -e Exit immediately if a pipeline (which may consist of a
5391 single simple command), a list, or a compound command
5392 (see SHELL GRAMMAR above), exits with a non-zero status.
5393 The shell does not exit if the command that fails is
5394 part of the command list immediately following a while
5395 or until keyword, part of the test following the if or
5396 elif reserved words, part of any command executed in a
5397 && or || list except the command following the final &&
5398 or ||, any command in a pipeline but the last, or if the
5399 command's return value is being inverted with !. If a
5400 compound command other than a subshell returns a non-
5401 zero status because a command failed while -e was being
5402 ignored, the shell does not exit. A trap on ERR, if
5403 set, is executed before the shell exits. This option
5404 applies to the shell environment and each subshell envi‐
5405 ronment separately (see COMMAND EXECUTION ENVIRONMENT
5406 above), and may cause subshells to exit before executing
5407 all the commands in the subshell.
5408 If a compound command or shell function executes in a
5410 context where -e is being ignored, none of the commands
5411 executed within the compound command or function body
5412 will be affected by the -e setting, even if -e is set
5413 and a command returns a failure status. If a compound
5414 command or shell function sets -e while executing in a
5415 context where -e is ignored, that setting will not have
5416 any effect until the compound command or the command
5417 containing the function call completes.
5418 -f Disable pathname expansion.
5419 -h Remember the location of commands as they are looked up
5420 for execution. This is enabled by default.
5421 -k All arguments in the form of assignment statements are
5422 placed in the environment for a command, not just those
5423 that precede the command name.
5424 -m Monitor mode. Job control is enabled. This option is
5425 on by default for interactive shells on systems that
5426 support it (see JOB CONTROL above). All processes run
5427 in a separate process group. When a background job com‐
5428 pletes, the shell prints a line containing its exit sta‐
5429 tus.
5430 -n Read commands but do not execute them. This may be used
5431 to check a shell script for syntax errors. This is ig‐
5432 nored by interactive shells.
5433 -o option-name
5434 The option-name can be one of the following:
5435 allexport
5436 Same as -a.
5437 braceexpand
5438 Same as -B.
5439 emacs Use an emacs-style command line editing inter‐
5440 face. This is enabled by default when the shell
5441 is interactive, unless the shell is started with
5442 the --noediting option. This also affects the
5443 editing interface used for read -e.
5444 errexit Same as -e.
5445 errtrace
5446 Same as -E.
5447 functrace
5448 Same as -T.
5449 hashall Same as -h.
5450 histexpand
5451 Same as -H.
5452 history Enable command history, as described above under
5453 HISTORY. This option is on by default in inter‐
5454 active shells.
5455 ignoreeof
5456 The effect is as if the shell command ``IG‐
5457 NOREEOF=10'' had been executed (see Shell Vari‐
5458 ables above).
5459 keyword Same as -k.
5460 monitor Same as -m.
5461 noclobber
5462 Same as -C.
5463 noexec Same as -n.
5464 noglob Same as -f.
5465 nolog Currently ignored.
5466 notify Same as -b.
5467 nounset Same as -u.
5468 onecmd Same as -t.
5469 physical
5470 Same as -P.
5471 pipefail
5472 If set, the return value of a pipeline is the
5473 value of the last (rightmost) command to exit
5474 with a non-zero status, or zero if all commands
5475 in the pipeline exit successfully. This option
5476 is disabled by default.
5477 posix Change the behavior of bash where the default
5478 operation differs from the POSIX standard to
5479 match the standard (posix mode). See SEE ALSO
5480 below for a reference to a document that details
5481 how posix mode affects bash's behavior.
5482 privileged
5483 Same as -p.
5484 verbose Same as -v.
5485 vi Use a vi-style command line editing interface.
5486 This also affects the editing interface used for
5487 read -e.
5488 xtrace Same as -x.
5489 If -o is supplied with no option-name, the values of the
5490 current options are printed. If +o is supplied with no
5491 option-name, a series of set commands to recreate the
5492 current option settings is displayed on the standard
5493 output.
5494 -p Turn on privileged mode. In this mode, the $ENV and
5495 $BASH_ENV files are not processed, shell functions are
5496 not inherited from the environment, and the SHELLOPTS,
5497 BASHOPTS, CDPATH, and GLOBIGNORE variables, if they ap‐
5498 pear in the environment, are ignored. If the shell is
5499 started with the effective user (group) id not equal to
5500 the real user (group) id, and the -p option is not sup‐
5501 plied, these actions are taken and the effective user id
5502 is set to the real user id. If the -p option is sup‐
5503 plied at startup, the effective user id is not reset.
5504 Turning this option off causes the effective user and
5505 group ids to be set to the real user and group ids.
5506 -t Exit after reading and executing one command.
5507 -u Treat unset variables and parameters other than the spe‐
5508 cial parameters "@" and "*" as an error when performing
5509 parameter expansion. If expansion is attempted on an
5510 unset variable or parameter, the shell prints an error
5511 message, and, if not interactive, exits with a non-zero
5512 status.
5513 -v Print shell input lines as they are read.
5514 -x After expanding each simple command, for command, case
5515 command, select command, or arithmetic for command, dis‐
5516 play the expanded value of PS4, followed by the command
5517 and its expanded arguments or associated word list.
5518 -B The shell performs brace expansion (see Brace Expansion
5519 above). This is on by default.
5520 -C If set, bash does not overwrite an existing file with
5521 the >, >&, and <> redirection operators. This may be
5522 overridden when creating output files by using the redi‐
5523 rection operator >| instead of >.
5524 -E If set, any trap on ERR is inherited by shell functions,
5525 command substitutions, and commands executed in a sub‐
5526 shell environment. The ERR trap is normally not inher‐
5527 ited in such cases.
5528 -H Enable ! style history substitution. This option is on
5529 by default when the shell is interactive.
5530 -P If set, the shell does not resolve symbolic links when
5531 executing commands such as cd that change the current
5532 working directory. It uses the physical directory
5533 structure instead. By default, bash follows the logical
5534 chain of directories when performing commands which
5535 change the current directory.
5536 -T If set, any traps on DEBUG and RETURN are inherited by
5537 shell functions, command substitutions, and commands ex‐
5538 ecuted in a subshell environment. The DEBUG and RETURN
5539 traps are normally not inherited in such cases.
5540 -- If no arguments follow this option, then the positional
5541 parameters are unset. Otherwise, the positional parame‐
5542 ters are set to the args, even if some of them begin
5543 with a -.
5544 - Signal the end of options, cause all remaining args to
5545 be assigned to the positional parameters. The -x and -v
5546 options are turned off. If there are no args, the posi‐
5547 tional parameters remain unchanged.
5548 The options are off by default unless otherwise noted. Using +
5550 rather than - causes these options to be turned off. The op‐
5551 tions can also be specified as arguments to an invocation of the
5552 shell. The current set of options may be found in $-. The re‐
5553 turn status is always true unless an invalid option is encoun‐
5554 tered.
5555 shift [n]
5557 The positional parameters from n+1 ... are renamed to $1 ....
5558 Parameters represented by the numbers $# down to $#-n+1 are un‐
5559 set. n must be a non-negative number less than or equal to $#.
5560 If n is 0, no parameters are changed. If n is not given, it is
5561 assumed to be 1. If n is greater than $#, the positional param‐
5562 eters are not changed. The return status is greater than zero
5563 if n is greater than $# or less than zero; otherwise 0.
5564 shopt [-pqsu] [-o] [optname ...]
5566 Toggle the values of settings controlling optional shell behav‐
5567 ior. The settings can be either those listed below, or, if the
5568 -o option is used, those available with the -o option to the set
5569 builtin command. With no options, or with the -p option, a list
5570 of all settable options is displayed, with an indication of
5571 whether or not each is set; if optnames are supplied, the output
5572 is restricted to those options. The -p option causes output to
5573 be displayed in a form that may be reused as input. Other op‐
5574 tions have the following meanings:
5575 -s Enable (set) each optname.
5576 -u Disable (unset) each optname.
5577 -q Suppresses normal output (quiet mode); the return status
5578 indicates whether the optname is set or unset. If multi‐
5579 ple optname arguments are given with -q, the return sta‐
5580 tus is zero if all optnames are enabled; non-zero other‐
5581 wise.
5582 -o Restricts the values of optname to be those defined for
5583 the -o option to the set builtin.
5584 If either -s or -u is used with no optname arguments, shopt
5586 shows only those options which are set or unset, respectively.
5587 Unless otherwise noted, the shopt options are disabled (unset)
5588 by default.
5589 The return status when listing options is zero if all optnames
5591 are enabled, non-zero otherwise. When setting or unsetting op‐
5592 tions, the return status is zero unless an optname is not a
5593 valid shell option.
5594 The list of shopt options is:
5596 assoc_expand_once
5598 If set, the shell suppresses multiple evaluation of as‐
5599 sociative array subscripts during arithmetic expression
5600 evaluation, while executing builtins that can perform
5601 variable assignments, and while executing builtins that
5602 perform array dereferencing.
5603 autocd If set, a command name that is the name of a directory
5604 is executed as if it were the argument to the cd com‐
5605 mand. This option is only used by interactive shells.
5606 cdable_vars
5607 If set, an argument to the cd builtin command that is
5608 not a directory is assumed to be the name of a variable
5609 whose value is the directory to change to.
5610 cdspell If set, minor errors in the spelling of a directory com‐
5611 ponent in a cd command will be corrected. The errors
5612 checked for are transposed characters, a missing charac‐
5613 ter, and one character too many. If a correction is
5614 found, the corrected filename is printed, and the com‐
5615 mand proceeds. This option is only used by interactive
5616 shells.
5617 checkhash
5618 If set, bash checks that a command found in the hash ta‐
5619 ble exists before trying to execute it. If a hashed
5620 command no longer exists, a normal path search is per‐
5621 formed.
5622 checkjobs
5623 If set, bash lists the status of any stopped and running
5624 jobs before exiting an interactive shell. If any jobs
5625 are running, this causes the exit to be deferred until a
5626 second exit is attempted without an intervening command
5627 (see JOB CONTROL above). The shell always postpones ex‐
5628 iting if any jobs are stopped.
5629 checkwinsize
5630 If set, bash checks the window size after each external
5631 (non-builtin) command and, if necessary, updates the
5632 values of LINES and COLUMNS. This option is enabled by
5633 default.
5634 cmdhist If set, bash attempts to save all lines of a multiple-
5635 line command in the same history entry. This allows
5636 easy re-editing of multi-line commands. This option is
5637 enabled by default, but only has an effect if command
5638 history is enabled, as described above under HISTORY.
5639 compat31
5640 compat32
5641 compat40
5642 compat41
5643 compat42
5644 compat43
5645 compat44
5646 These control aspects of the shell's compatibility mode
5647 (see SHELL COMPATIBILITY MODE below).
5648 complete_fullquote
5650 If set, bash quotes all shell metacharacters in file‐
5651 names and directory names when performing completion.
5652 If not set, bash removes metacharacters such as the dol‐
5653 lar sign from the set of characters that will be quoted
5654 in completed filenames when these metacharacters appear
5655 in shell variable references in words to be completed.
5656 This means that dollar signs in variable names that ex‐
5657 pand to directories will not be quoted; however, any
5658 dollar signs appearing in filenames will not be quoted,
5659 either. This is active only when bash is using back‐
5660 slashes to quote completed filenames. This variable is
5661 set by default, which is the default bash behavior in
5662 versions through 4.2.
5663 direxpand
5665 If set, bash replaces directory names with the results
5666 of word expansion when performing filename completion.
5667 This changes the contents of the readline editing buf‐
5668 fer. If not set, bash attempts to preserve what the
5669 user typed.
5670 dirspell
5672 If set, bash attempts spelling correction on directory
5673 names during word completion if the directory name ini‐
5674 tially supplied does not exist.
5675 dotglob If set, bash includes filenames beginning with a `.' in
5677 the results of pathname expansion. The filenames ``.''
5678 and ``..'' must always be matched explicitly, even if
5679 dotglob is set.
5680 execfail
5682 If set, a non-interactive shell will not exit if it can‐
5683 not execute the file specified as an argument to the
5684 exec builtin command. An interactive shell does not
5685 exit if exec fails.
5686 expand_aliases
5688 If set, aliases are expanded as described above under
5689 ALIASES. This option is enabled by default for interac‐
5690 tive shells.
5691 extdebug
5693 If set at shell invocation, or in a shell startup file,
5694 arrange to execute the debugger profile before the shell
5695 starts, identical to the --debugger option. If set af‐
5696 ter invocation, behavior intended for use by debuggers
5697 is enabled:
5698 1. The -F option to the declare builtin displays the
5700 source file name and line number corresponding to
5701 each function name supplied as an argument.
5702 2. If the command run by the DEBUG trap returns a
5704 non-zero value, the next command is skipped and
5705 not executed.
5706 3. If the command run by the DEBUG trap returns a
5708 value of 2, and the shell is executing in a sub‐
5709 routine (a shell function or a shell script exe‐
5710 cuted by the . or source builtins), the shell
5711 simulates a call to return.
5712 4. BASH_ARGC and BASH_ARGV are updated as described
5714 in their descriptions above.
5715 5. Function tracing is enabled: command substitu‐
5717 tion, shell functions, and subshells invoked with
5718 ( command ) inherit the DEBUG and RETURN traps.
5719 6. Error tracing is enabled: command substitution,
5721 shell functions, and subshells invoked with (
5722 command ) inherit the ERR trap.
5723 extglob If set, the extended pattern matching features described
5725 above under Pathname Expansion are enabled.
5726 extquote
5728 If set, $'string' and $"string" quoting is performed
5729 within ${parameter} expansions enclosed in double
5730 quotes. This option is enabled by default.
5731 failglob
5733 If set, patterns which fail to match filenames during
5734 pathname expansion result in an expansion error.
5735 force_fignore
5737 If set, the suffixes specified by the FIGNORE shell
5738 variable cause words to be ignored when performing word
5739 completion even if the ignored words are the only possi‐
5740 ble completions. See SHELL VARIABLES above for a de‐
5741 scription of FIGNORE. This option is enabled by de‐
5742 fault.
5743 globasciiranges
5745 If set, range expressions used in pattern matching
5746 bracket expressions (see Pattern Matching above) behave
5747 as if in the traditional C locale when performing com‐
5748 parisons. That is, the current locale's collating se‐
5749 quence is not taken into account, so b will not collate
5750 between A and B, and upper-case and lower-case ASCII
5751 characters will collate together.
5752 globstar
5754 If set, the pattern ** used in a pathname expansion con‐
5755 text will match all files and zero or more directories
5756 and subdirectories. If the pattern is followed by a /,
5757 only directories and subdirectories match.
5758 gnu_errfmt
5760 If set, shell error messages are written in the standard
5761 GNU error message format.
5762 histappend
5764 If set, the history list is appended to the file named
5765 by the value of the HISTFILE variable when the shell ex‐
5766 its, rather than overwriting the file.
5767 histreedit
5769 If set, and readline is being used, a user is given the
5770 opportunity to re-edit a failed history substitution.
5771 histverify
5773 If set, and readline is being used, the results of his‐
5774 tory substitution are not immediately passed to the
5775 shell parser. Instead, the resulting line is loaded
5776 into the readline editing buffer, allowing further modi‐
5777 fication.
5778 hostcomplete
5780 If set, and readline is being used, bash will attempt to
5781 perform hostname completion when a word containing a @
5782 is being completed (see Completing under READLINE
5783 above). This is enabled by default.
5784 huponexit
5786 If set, bash will send SIGHUP to all jobs when an inter‐
5787 active login shell exits.
5788 inherit_errexit
5790 If set, command substitution inherits the value of the
5791 errexit option, instead of unsetting it in the subshell
5792 environment. This option is enabled when posix mode is
5793 enabled.
5794 interactive_comments
5796 If set, allow a word beginning with # to cause that word
5797 and all remaining characters on that line to be ignored
5798 in an interactive shell (see COMMENTS above). This op‐
5799 tion is enabled by default.
5800 lastpipe
5802 If set, and job control is not active, the shell runs
5803 the last command of a pipeline not executed in the back‐
5804 ground in the current shell environment.
5805 lithist If set, and the cmdhist option is enabled, multi-line
5807 commands are saved to the history with embedded newlines
5808 rather than using semicolon separators where possible.
5809 localvar_inherit
5811 If set, local variables inherit the value and attributes
5812 of a variable of the same name that exists at a previous
5813 scope before any new value is assigned. The nameref at‐
5814 tribute is not inherited.
5815 localvar_unset
5817 If set, calling unset on local variables in previous
5818 function scopes marks them so subsequent lookups find
5819 them unset until that function returns. This is identi‐
5820 cal to the behavior of unsetting local variables at the
5821 current function scope.
5822 login_shell
5824 The shell sets this option if it is started as a login
5825 shell (see INVOCATION above). The value may not be
5826 changed.
5827 mailwarn
5829 If set, and a file that bash is checking for mail has
5830 been accessed since the last time it was checked, the
5831 message ``The mail in mailfile has been read'' is dis‐
5832 played.
5833 no_empty_cmd_completion
5835 If set, and readline is being used, bash will not at‐
5836 tempt to search the PATH for possible completions when
5837 completion is attempted on an empty line.
5838 nocaseglob
5840 If set, bash matches filenames in a case-insensitive
5841 fashion when performing pathname expansion (see Pathname
5842 Expansion above).
5843 nocasematch
5845 If set, bash matches patterns in a case-insensitive
5846 fashion when performing matching while executing case or
5847 [[ conditional commands, when performing pattern substi‐
5848 tution word expansions, or when filtering possible com‐
5849 pletions as part of programmable completion.
5850 nullglob
5852 If set, bash allows patterns which match no files (see
5853 Pathname Expansion above) to expand to a null string,
5854 rather than themselves.
5855 progcomp
5857 If set, the programmable completion facilities (see Pro‐
5858 grammable Completion above) are enabled. This option is
5859 enabled by default.
5860 progcomp_alias
5862 If set, and programmable completion is enabled, bash
5863 treats a command name that doesn't have any completions
5864 as a possible alias and attempts alias expansion. If it
5865 has an alias, bash attempts programmable completion us‐
5866 ing the command word resulting from the expanded alias.
5867 promptvars
5869 If set, prompt strings undergo parameter expansion, com‐
5870 mand substitution, arithmetic expansion, and quote re‐
5871 moval after being expanded as described in PROMPTING
5872 above. This option is enabled by default.
5873 restricted_shell
5875 The shell sets this option if it is started in re‐
5876 stricted mode (see RESTRICTED SHELL below). The value
5877 may not be changed. This is not reset when the startup
5878 files are executed, allowing the startup files to dis‐
5879 cover whether or not a shell is restricted.
5880 shift_verbose
5882 If set, the shift builtin prints an error message when
5883 the shift count exceeds the number of positional parame‐
5884 ters.
5885 sourcepath
5887 If set, the source (.) builtin uses the value of PATH to
5888 find the directory containing the file supplied as an
5889 argument. This option is enabled by default.
5890 syslog_history
5892 If set, command history is logged to syslog.
5893 xpg_echo
5895 If set, the echo builtin expands backslash-escape se‐
5896 quences by default.
5897 suspend [-f]
5899 Suspend the execution of this shell until it receives a SIGCONT
5900 signal. A login shell cannot be suspended; the -f option can be
5901 used to override this and force the suspension. The return sta‐
5902 tus is 0 unless the shell is a login shell and -f is not sup‐
5903 plied, or if job control is not enabled.
5904 test expr
5906 [ expr ]
5907 Return a status of 0 (true) or 1 (false) depending on the evalu‐
5908 ation of the conditional expression expr. Each operator and op‐
5909 erand must be a separate argument. Expressions are composed of
5910 the primaries described above under CONDITIONAL EXPRESSIONS.
5911 test does not accept any options, nor does it accept and ignore
5912 an argument of -- as signifying the end of options.
5913 Expressions may be combined using the following operators,
5915 listed in decreasing order of precedence. The evaluation de‐
5916 pends on the number of arguments; see below. Operator prece‐
5917 dence is used when there are five or more arguments.
5918 ! expr True if expr is false.
5919 ( expr )
5920 Returns the value of expr. This may be used to override
5921 the normal precedence of operators.
5922 expr1 -a expr2
5923 True if both expr1 and expr2 are true.
5924 expr1 -o expr2
5925 True if either expr1 or expr2 is true.
5926 test and [ evaluate conditional expressions using a set of rules
5928 based on the number of arguments.
5929 0 arguments
5931 The expression is false.
5932 1 argument
5933 The expression is true if and only if the argument is not
5934 null.
5935 2 arguments
5936 If the first argument is !, the expression is true if and
5937 only if the second argument is null. If the first argu‐
5938 ment is one of the unary conditional operators listed
5939 above under CONDITIONAL EXPRESSIONS, the expression is
5940 true if the unary test is true. If the first argument is
5941 not a valid unary conditional operator, the expression is
5942 false.
5943 3 arguments
5944 The following conditions are applied in the order listed.
5945 If the second argument is one of the binary conditional
5946 operators listed above under CONDITIONAL EXPRESSIONS, the
5947 result of the expression is the result of the binary test
5948 using the first and third arguments as operands. The -a
5949 and -o operators are considered binary operators when
5950 there are three arguments. If the first argument is !,
5951 the value is the negation of the two-argument test using
5952 the second and third arguments. If the first argument is
5953 exactly ( and the third argument is exactly ), the result
5954 is the one-argument test of the second argument. Other‐
5955 wise, the expression is false.
5956 4 arguments
5957 If the first argument is !, the result is the negation of
5958 the three-argument expression composed of the remaining
5959 arguments. Otherwise, the expression is parsed and eval‐
5960 uated according to precedence using the rules listed
5961 above.
5962 5 or more arguments
5963 The expression is parsed and evaluated according to
5964 precedence using the rules listed above.
5965 When used with test or [, the < and > operators sort lexico‐
5967 graphically using ASCII ordering.
5968 times Print the accumulated user and system times for the shell and
5970 for processes run from the shell. The return status is 0.
5971 trap [-lp] [[arg] sigspec ...]
5973 The command arg is to be read and executed when the shell re‐
5974 ceives signal(s) sigspec. If arg is absent (and there is a sin‐
5975 gle sigspec) or -, each specified signal is reset to its origi‐
5976 nal disposition (the value it had upon entrance to the shell).
5977 If arg is the null string the signal specified by each sigspec
5978 is ignored by the shell and by the commands it invokes. If arg
5979 is not present and -p has been supplied, then the trap commands
5980 associated with each sigspec are displayed. If no arguments are
5981 supplied or if only -p is given, trap prints the list of com‐
5982 mands associated with each signal. The -l option causes the
5983 shell to print a list of signal names and their corresponding
5984 numbers. Each sigspec is either a signal name defined in <sig‐
5985 nal.h>, or a signal number. Signal names are case insensitive
5986 and the SIG prefix is optional.
5987 If a sigspec is EXIT (0) the command arg is executed on exit
5989 from the shell. If a sigspec is DEBUG, the command arg is exe‐
5990 cuted before every simple command, for command, case command,
5991 select command, every arithmetic for command, and before the
5992 first command executes in a shell function (see SHELL GRAMMAR
5993 above). Refer to the description of the extdebug option to the
5994 shopt builtin for details of its effect on the DEBUG trap. If a
5995 sigspec is RETURN, the command arg is executed each time a shell
5996 function or a script executed with the . or source builtins fin‐
5997 ishes executing.
5998 If a sigspec is ERR, the command arg is executed whenever a
6000 pipeline (which may consist of a single simple command), a list,
6001 or a compound command returns a non-zero exit status, subject to
6002 the following conditions. The ERR trap is not executed if the
6003 failed command is part of the command list immediately following
6004 a while or until keyword, part of the test in an if statement,
6005 part of a command executed in a && or || list except the command
6006 following the final && or ||, any command in a pipeline but the
6007 last, or if the command's return value is being inverted using
6008 !. These are the same conditions obeyed by the errexit (-e) op‐
6009 tion.
6010 Signals ignored upon entry to the shell cannot be trapped, reset
6012 or listed. Trapped signals that are not being ignored are reset
6013 to their original values in a subshell or subshell environment
6014 when one is created. The return status is false if any sigspec
6015 is invalid; otherwise trap returns true.
6016 type [-aftpP] name [name ...]
6018 With no options, indicate how each name would be interpreted if
6019 used as a command name. If the -t option is used, type prints a
6020 string which is one of alias, keyword, function, builtin, or
6021 file if name is an alias, shell reserved word, function,
6022 builtin, or disk file, respectively. If the name is not found,
6023 then nothing is printed, and an exit status of false is re‐
6024 turned. If the -p option is used, type either returns the name
6025 of the disk file that would be executed if name were specified
6026 as a command name, or nothing if ``type -t name'' would not re‐
6027 turn file. The -P option forces a PATH search for each name,
6028 even if ``type -t name'' would not return file. If a command is
6029 hashed, -p and -P print the hashed value, which is not necessar‐
6030 ily the file that appears first in PATH. If the -a option is
6031 used, type prints all of the places that contain an executable
6032 named name. This includes aliases and functions, if and only if
6033 the -p option is not also used. The table of hashed commands is
6034 not consulted when using -a. The -f option suppresses shell
6035 function lookup, as with the command builtin. type returns true
6036 if all of the arguments are found, false if any are not found.
6037 ulimit [-HS] -a
6039 ulimit [-HS] [-bcdefiklmnpqrstuvxPRT [limit]]
6040 Provides control over the resources available to the shell and
6041 to processes started by it, on systems that allow such control.
6042 The -H and -S options specify that the hard or soft limit is set
6043 for the given resource. A hard limit cannot be increased by a
6044 non-root user once it is set; a soft limit may be increased up
6045 to the value of the hard limit. If neither -H nor -S is speci‐
6046 fied, both the soft and hard limits are set. The value of limit
6047 can be a number in the unit specified for the resource or one of
6048 the special values hard, soft, or unlimited, which stand for the
6049 current hard limit, the current soft limit, and no limit, re‐
6050 spectively. If limit is omitted, the current value of the soft
6051 limit of the resource is printed, unless the -H option is given.
6052 When more than one resource is specified, the limit name and
6053 unit, if appropriate, are printed before the value. Other op‐
6054 tions are interpreted as follows:
6055 -a All current limits are reported; no limits are set
6056 -b The maximum socket buffer size
6057 -c The maximum size of core files created
6058 -d The maximum size of a process's data segment
6059 -e The maximum scheduling priority ("nice")
6060 -f The maximum size of files written by the shell and its
6061 children
6062 -i The maximum number of pending signals
6063 -k The maximum number of kqueues that may be allocated
6064 -l The maximum size that may be locked into memory
6065 -m The maximum resident set size (many systems do not honor
6066 this limit)
6067 -n The maximum number of open file descriptors (most systems
6068 do not allow this value to be set)
6069 -p The pipe size in 512-byte blocks (this may not be set)
6070 -q The maximum number of bytes in POSIX message queues
6071 -r The maximum real-time scheduling priority
6072 -s The maximum stack size
6073 -t The maximum amount of cpu time in seconds
6074 -u The maximum number of processes available to a single
6075 user
6076 -v The maximum amount of virtual memory available to the
6077 shell and, on some systems, to its children
6078 -x The maximum number of file locks
6079 -P The maximum number of pseudoterminals
6080 -R The maximum time a real-time process can run before
6081 blocking, in microseconds
6082 -T The maximum number of threads
6083 If limit is given, and the -a option is not used, limit is the
6085 new value of the specified resource. If no option is given,
6086 then -f is assumed. Values are in 1024-byte increments, except
6087 for -t, which is in seconds; -R, which is in microseconds; -p,
6088 which is in units of 512-byte blocks; -P, -T, -b, -k, -n, and
6089 -u, which are unscaled values; and, when in posix mode, -c and
6090 -f, which are in 512-byte increments. The return status is 0
6091 unless an invalid option or argument is supplied, or an error
6092 occurs while setting a new limit. In POSIX Mode 512-byte blocks
6093 are used for the `-c' and `-f' options.
6094 umask [-p] [-S] [mode]
6096 The user file-creation mask is set to mode. If mode begins with
6097 a digit, it is interpreted as an octal number; otherwise it is
6098 interpreted as a symbolic mode mask similar to that accepted by
6099 chmod(1). If mode is omitted, the current value of the mask is
6100 printed. The -S option causes the mask to be printed in sym‐
6101 bolic form; the default output is an octal number. If the -p
6102 option is supplied, and mode is omitted, the output is in a form
6103 that may be reused as input. The return status is 0 if the mode
6104 was successfully changed or if no mode argument was supplied,
6105 and false otherwise.
6106 unalias [-a] [name ...]
6108 Remove each name from the list of defined aliases. If -a is
6109 supplied, all alias definitions are removed. The return value
6110 is true unless a supplied name is not a defined alias.
6111 unset [-fv] [-n] [name ...]
6113 For each name, remove the corresponding variable or function.
6114 If the -v option is given, each name refers to a shell variable,
6115 and that variable is removed. Read-only variables may not be
6116 unset. If -f is specified, each name refers to a shell func‐
6117 tion, and the function definition is removed. If the -n option
6118 is supplied, and name is a variable with the nameref attribute,
6119 name will be unset rather than the variable it references. -n
6120 has no effect if the -f option is supplied. If no options are
6121 supplied, each name refers to a variable; if there is no vari‐
6122 able by that name, a function with that name, if any, is unset.
6123 Each unset variable or function is removed from the environment
6124 passed to subsequent commands. If any of BASH_ALIASES,
6125 BASH_ARGV0, BASH_CMDS, BASH_COMMAND, BASH_SUBSHELL, BASHPID,
6126 COMP_WORDBREAKS, DIRSTACK, EPOCHREALTIME, EPOCHSECONDS, FUNC‐
6127 NAME, GROUPS, HISTCMD, LINENO, RANDOM, SECONDS, or SRANDOM are
6128 unset, they lose their special properties, even if they are sub‐
6129 sequently reset. The exit status is true unless a name is read‐
6130 only.
6131 wait [-fn] [-p varname] [id ...]
6133 Wait for each specified child process and return its termination
6134 status. Each id may be a process ID or a job specification; if
6135 a job spec is given, all processes in that job's pipeline are
6136 waited for. If id is not given, wait waits for all running
6137 background jobs and the last-executed process substitution, if
6138 its process id is the same as $!, and the return status is zero.
6139 If the -n option is supplied, wait waits for a single job from
6140 the list of ids or, if no ids are supplied, any job, to complete
6141 and returns its exit status. If none of the supplied arguments
6142 is a child of the shell, or if no arguments are supplied and the
6143 shell has no unwaited-for children, the exit status is 127. If
6144 the -p option is supplied, the process or job identifier of the
6145 job for which the exit status is returned is assigned to the
6146 variable varname named by the option argument. The variable
6147 will be unset initially, before any assignment. This is useful
6148 only when the -n option is supplied. Supplying the -f option,
6149 when job control is enabled, forces wait to wait for id to ter‐
6150 minate before returning its status, instead of returning when it
6151 changes status. If id specifies a non-existent process or job,
6152 the return status is 127. Otherwise, the return status is the
6153 exit status of the last process or job waited for.
6154
6156 Bash-4.0 introduced the concept of a `shell compatibility level', spec‐
6157 ified as a set of options to the shopt builtin compat31, compat32, com‐
6158 pat40, compat41, and so on). There is only one current compatibility
6159 level -- each option is mutually exclusive. The compatibility level is
6160 intended to allow users to select behavior from previous versions that
6161 is incompatible with newer versions while they migrate scripts to use
6162 current features and behavior. It's intended to be a temporary solu‐
6163 tion.
6164 This section does not mention behavior that is standard for a particu‐
6166 lar version (e.g., setting compat32 means that quoting the rhs of the
6167 regexp matching operator quotes special regexp characters in the word,
6168 which is default behavior in bash-3.2 and above).
6169 If a user enables, say, compat32, it may affect the behavior of other
6171 compatibility levels up to and including the current compatibility
6172 level. The idea is that each compatibility level controls behavior
6173 that changed in that version of bash, but that behavior may have been
6174 present in earlier versions. For instance, the change to use locale-
6175 based comparisons with the [[ command came in bash-4.1, and earlier
6176 versions used ASCII-based comparisons, so enabling compat32 will enable
6177 ASCII-based comparisons as well. That granularity may not be suffi‐
6178 cient for all uses, and as a result users should employ compatibility
6179 levels carefully. Read the documentation for a particular feature to
6180 find out the current behavior.
6181 Bash-4.3 introduced a new shell variable: BASH_COMPAT. The value as‐
6183 signed to this variable (a decimal version number like 4.2, or an inte‐
6184 ger corresponding to the compatNN option, like 42) determines the com‐
6185 patibility level.
6186 Starting with bash-4.4, Bash has begun deprecating older compatibility
6188 levels. Eventually, the options will be removed in favor of BASH_COM‐
6189 PAT.
6190 Bash-5.0 is the final version for which there will be an individual
6192 shopt option for the previous version. Users should use BASH_COMPAT on
6193 bash-5.0 and later versions.
6194 The following table describes the behavior changes controlled by each
6196 compatibility level setting. The compatNN tag is used as shorthand for
6197 setting the compatibility level to NN using one of the following mecha‐
6198 nisms. For versions prior to bash-5.0, the compatibility level may be
6199 set using the corresponding compatNN shopt option. For bash-4.3 and
6200 later versions, the BASH_COMPAT variable is preferred, and it is re‐
6201 quired for bash-5.1 and later versions.
6202 compat31
6204 • quoting the rhs of the [[ command's regexp matching oper‐
6205 ator (=~) has no special effect
6206 compat32
6208 • interrupting a command list such as "a ; b ; c" causes
6209 the execution of the next command in the list (in
6210 bash-4.0 and later versions, the shell acts as if it re‐
6211 ceived the interrupt, so interrupting one command in a
6212 list aborts the execution of the entire list)
6213 compat40
6215 • the < and > operators to the [[ command do not consider
6216 the current locale when comparing strings; they use ASCII
6217 ordering. Bash versions prior to bash-4.1 use ASCII col‐
6218 lation and strcmp(3); bash-4.1 and later use the current
6219 locale's collation sequence and strcoll(3).
6220 compat41
6222 • in posix mode, time may be followed by options and still
6223 be recognized as a reserved word (this is POSIX interpre‐
6224 tation 267)
6225 • in posix mode, the parser requires that an even number of
6226 single quotes occur in the word portion of a double-
6227 quoted parameter expansion and treats them specially, so
6228 that characters within the single quotes are considered
6229 quoted (this is POSIX interpretation 221)
6230 compat42
6232 • the replacement string in double-quoted pattern substitu‐
6233 tion does not undergo quote removal, as it does in ver‐
6234 sions after bash-4.2
6235 • in posix mode, single quotes are considered special when
6236 expanding the word portion of a double-quoted parameter
6237 expansion and can be used to quote a closing brace or
6238 other special character (this is part of POSIX interpre‐
6239 tation 221); in later versions, single quotes are not
6240 special within double-quoted word expansions
6241 compat43
6243 • the shell does not print a warning message if an attempt
6244 is made to use a quoted compound assignment as an argu‐
6245 ment to declare (declare -a foo='(1 2)'). Later versions
6246 warn that this usage is deprecated
6247 • word expansion errors are considered non-fatal errors
6248 that cause the current command to fail, even in posix
6249 mode (the default behavior is to make them fatal errors
6250 that cause the shell to exit)
6251 • when executing a shell function, the loop state
6252 (while/until/etc.) is not reset, so break or continue in
6253 that function will break or continue loops in the calling
6254 context. Bash-4.4 and later reset the loop state to pre‐
6255 vent this
6256 compat44
6258 • the shell sets up the values used by BASH_ARGV and
6259 BASH_ARGC so they can expand to the shell's positional
6260 parameters even if extended debugging mode is not enabled
6261 • a subshell inherits loops from its parent context, so
6262 break or continue will cause the subshell to exit.
6263 Bash-5.0 and later reset the loop state to prevent the
6264 exit
6265 • variable assignments preceding builtins like export and
6266 readonly that set attributes continue to affect variables
6267 with the same name in the calling environment even if the
6268 shell is not in posix mode
6269 compat50
6271 • Bash-5.1 changed the way $RANDOM is generated to intro‐
6272 duce slightly more randomness. If the shell compatibility
6273 level is set to 50 or lower, it reverts to the method
6274 from bash-5.0 and previous versions, so seeding the ran‐
6275 dom number generator by assigning a value to RANDOM will
6276 produce the same sequence as in bash-5.0
6277 • If the command hash table is empty, bash versions prior
6278 to bash-5.1 printed an informational message to that ef‐
6279 fect, even when producing output that can be reused as
6280 input. Bash-5.1 suppresses that message when the -l op‐
6281 tion is supplied.
6282
6284 If bash is started with the name rbash, or the -r option is supplied at
6285 invocation, the shell becomes restricted. A restricted shell is used
6286 to set up an environment more controlled than the standard shell. It
6287 behaves identically to bash with the exception that the following are
6288 disallowed or not performed:
6289 • changing directories with cd
6291 • setting or unsetting the values of SHELL, PATH, HISTFILE, ENV,
6293 or BASH_ENV
6294 • specifying command names containing /
6296 • specifying a filename containing a / as an argument to the .
6298 builtin command
6299 • specifying a filename containing a slash as an argument to the
6301 history builtin command
6302 • specifying a filename containing a slash as an argument to the
6304 -p option to the hash builtin command
6305 • importing function definitions from the shell environment at
6307 startup
6308 • parsing the value of SHELLOPTS from the shell environment at
6310 startup
6311 • redirecting output using the >, >|, <>, >&, &>, and >> redirect‐
6313 ion operators
6314 • using the exec builtin command to replace the shell with another
6316 command
6317 • adding or deleting builtin commands with the -f and -d options
6319 to the enable builtin command
6320 • using the enable builtin command to enable disabled shell
6322 builtins
6323 • specifying the -p option to the command builtin command
6325 • turning off restricted mode with set +r or set +o restricted.
6327 These restrictions are enforced after any startup files are read.
6329 When a command that is found to be a shell script is executed (see COM‐
6331 MAND EXECUTION above), rbash turns off any restrictions in the shell
6332 spawned to execute the script.
6333
6335 Bash Reference Manual, Brian Fox and Chet Ramey
6336 The Gnu Readline Library, Brian Fox and Chet Ramey
6337 The Gnu History Library, Brian Fox and Chet Ramey
6338 Portable Operating System Interface (POSIX) Part 2: Shell and Utili‐
6339 ties, IEEE --
6340 http://pubs.opengroup.org/onlinepubs/9699919799/
6341 http://tiswww.case.edu/~chet/bash/POSIX -- a description of posix mode
6342 sh(1), ksh(1), csh(1)
6343 emacs(1), vi(1)
6344 readline(3)
6345
6347 /bin/bash
6348 The bash executable
6349 /etc/profile
6350 The systemwide initialization file, executed for login shells
6351 /etc/bash.bash_logout
6352 The systemwide login shell cleanup file, executed when a login
6353 shell exits
6354 ~/.bash_profile
6355 The personal initialization file, executed for login shells
6356 ~/.bashrc
6357 The individual per-interactive-shell startup file
6358 ~/.bash_logout
6359 The individual login shell cleanup file, executed when a login
6360 shell exits
6361 ~/.inputrc
6362 Individual readline initialization file
6363
6365 Brian Fox, Free Software Foundation
6366 bfox@gnu.org
6367 Chet Ramey, Case Western Reserve University
6369 chet.ramey@case.edu
6370
6372 If you find a bug in bash, you should report it. But first, you should
6373 make sure that it really is a bug, and that it appears in the latest
6374 version of bash. The latest version is always available from
6375 ftp://ftp.gnu.org/pub/gnu/bash/.
6376 Once you have determined that a bug actually exists, use the bashbug
6378 command to submit a bug report. If you have a fix, you are encouraged
6379 to mail that as well! Suggestions and `philosophical' bug reports may
6380 be mailed to bug-bash@gnu.org or posted to the Usenet newsgroup
6381 gnu.bash.bug.
6382 ALL bug reports should include:
6384 The version number of bash
6386 The hardware and operating system
6387 The compiler used to compile
6388 A description of the bug behaviour
6389 A short script or `recipe' which exercises the bug
6390 bashbug inserts the first three items automatically into the template
6392 it provides for filing a bug report.
6393 Comments and bug reports concerning this manual page should be directed
6395 to chet.ramey@case.edu.
6396
6398 It's too big and too slow.
6399 There are some subtle differences between bash and traditional versions
6401 of sh, mostly because of the POSIX specification.
6402 Aliases are confusing in some uses.
6404 Shell builtin commands and functions are not stoppable/restartable.
6406 Compound commands and command sequences of the form `a ; b ; c' are not
6408 handled gracefully when process suspension is attempted. When a
6409 process is stopped, the shell immediately executes the next command in
6410 the sequence. It suffices to place the sequence of commands between
6411 parentheses to force it into a subshell, which may be stopped as a
6412 unit.
6413 Array variables may not (yet) be exported.
6415 There may be only one active coprocess at a time.
6417GNU Bash 5.1 2020 October 29 BASH(1)