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) 1989-2016 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 can be used as options when the shell is
26 invoked. In addition, bash interprets the following options when it is
27 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
32 assigned to $0 and any remaining arguments are assigned to
33 the positional parameters. The assignment to $0 sets the
34 name of the shell, which is used in warning and error mes‐
35 sages.
36 -i If the -i option is present, the shell is interactive.
37 -l Make bash act as if it had been invoked as a login shell (see
38 INVOCATION below).
39 -r If the -r option is present, the shell becomes restricted
40 (see RESTRICTED SHELL below).
41 -s If the -s option is present, or if no arguments remain after
42 option processing, then commands are read from the standard
43 input. This option allows the positional parameters to be
44 set when invoking an interactive shell.
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
63 options must appear on the command line before the single-character
64 options 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
81 INVOCATION 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
95 below).
96 --norc Do not read and execute the personal initialization file
98 ~/.bashrc if the shell is interactive. This option is on by
99 default 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
132 executed, 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
141 (unless -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 $- includes i if
144 bash is interactive, allowing a shell script or a startup file to test
145 this state.
146 The following paragraphs describe how bash executes its startup files.
148 If any of the files exist but cannot be read, bash reports an error.
149 Tildes are expanded in filenames as described below under Tilde Expan‐
150 sion in the EXPANSION section.
151 When bash is invoked as an interactive login shell, or as a non-inter‐
153 active shell with the --login option, it first reads and executes com‐
154 mands from the file /etc/profile, if that file exists. After reading
155 that file, it looks for ~/.bash_profile, ~/.bash_login, and ~/.profile,
156 in that order, and reads and executes commands from the first one that
157 exists and is readable. The --noprofile option may be used when the
158 shell is started to inhibit this behavior.
159 When an interactive login shell exits, or a non-interactive login shell
161 executes the exit builtin command, bash reads and executes commands
162 from the files ~/.bash_logout and /etc/bash.bash_logout, if the files
163 exists.
164 When an interactive shell that is not a login shell is started, bash
166 reads and executes commands from ~/.bashrc, if that file exists. This
167 may be inhibited by using the --norc option. The --rcfile file option
168 will force bash to read and execute commands from file instead of
169 ~/.bashrc.
170 When bash is started non-interactively, to run a shell script, for
172 example, it looks for the variable BASH_ENV in the environment, expands
173 its value if it appears there, and uses the expanded value as the name
174 of a file to read and execute. Bash behaves as if the following com‐
175 mand were executed:
176 if [ -n "$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
181 behavior of historical versions of sh as closely as possible, while
182 conforming to the POSIX standard as well. When invoked as an interac‐
183 tive login shell, or a non-interactive shell with the --login option,
184 it first attempts to read and execute commands from /etc/profile and
185 ~/.profile, in that order. The --noprofile option may be used to
186 inhibit 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
192 attempt to read any other startup files. When invoked as sh, bash
193 enters 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
215 appear in the environment, are ignored, and the effective user id is
216 set to the real user id. If the -p option is supplied at invocation,
217 the startup behavior is the same, but the effective user id is not
218 reset.
219
221 The following definitions are used throughout the rest of this docu‐
222 ment.
223 blank A space or tab.
224 word A sequence of characters considered as a single unit by the
225 shell. Also known as a token.
226 name A word consisting only of alphanumeric characters and under‐
227 scores, and beginning with an alphabetic character or an under‐
228 score. Also referred to as an identifier.
229 metacharacter
230 A character that, when unquoted, separates words. One of the
231 following:
232 | & ; ( ) < > space tab newline
233 control operator
234 A token that performs a control function. It is one of the fol‐
235 lowing symbols:
236 || & && ; ;; ;& ;;& ( ) | |& <newline>
237
239 Reserved words are words that have a special meaning to the shell. The
240 following words are recognized as reserved when unquoted and either the
241 first word of a simple command (see SHELL GRAMMAR below) or the third
242 word of a case or for command:
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
253 arguments 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).
298 Lists
300 A list is a sequence of one or more pipelines separated by one of the
301 operators ;, &, &&, or ||, and optionally terminated by one of ;, &, or
302 <newline>.
303 Of these list operators, && and || have equal precedence, followed by ;
305 and &, which have equal precedence.
306 A sequence of one or more newlines may appear in a list instead of a
308 semicolon to delimit commands.
309 If a command is terminated by the control operator &, the shell exe‐
311 cutes the command in the background in a subshell. The shell does not
312 wait for the command to finish, and the return status is 0. Commands
313 separated by a ; are executed sequentially; the shell waits for each
314 command to terminate in turn. The return status is the exit status of
315 the last command executed.
316 AND and OR lists are sequences of one or more pipelines separated by
318 the && and || control operators, respectively. AND and OR lists are
319 executed with left associativity. An AND list has the form
320 command1 && command2
322 command2 is executed if, and only if, command1 returns an exit status
324 of zero.
325 An OR list has the form
327 command1 || command2
329 command2 is executed if and only if command1 returns a non-zero exit
331 status. The return status of AND and OR lists is the exit status of
332 the last command executed in the list.
333 Compound Commands
335 A compound command is one of the following. In most cases a list in a
336 command's description may be separated from the rest of the command by
337 one or more newlines, and may be followed by a newline in place of a
338 semicolon.
339 (list) list is executed in a subshell environment (see COMMAND EXECU‐
341 TION ENVIRONMENT below). Variable assignments and builtin com‐
342 mands that affect the shell's environment do not remain in
343 effect after the command completes. The return status is the
344 exit status of list.
345 { list; }
347 list is simply executed in the current shell environment. list
348 must be terminated with a newline or semicolon. This is known
349 as a group command. The return status is the exit status of
350 list. Note that unlike the metacharacters ( and ), { and } are
351 reserved words and must occur where a reserved word is permitted
352 to be recognized. Since they do not cause a word break, they
353 must be separated from list by whitespace or another shell
354 metacharacter.
355 ((expression))
357 The expression is evaluated according to the rules described
358 below under ARITHMETIC EVALUATION. If the value of the expres‐
359 sion is non-zero, the return status is 0; otherwise the return
360 status is 1. This is exactly equivalent to let "expression".
361 [[ expression ]]
363 Return a status of 0 or 1 depending on the evaluation of the
364 conditional expression expression. Expressions are composed of
365 the primaries described below under CONDITIONAL EXPRESSIONS.
366 Word splitting and pathname expansion are not performed on the
367 words between the [[ and ]]; tilde expansion, parameter and
368 variable expansion, arithmetic expansion, command substitution,
369 process substitution, and quote removal are performed. Condi‐
370 tional operators such as -f must be unquoted to be recognized as
371 primaries.
372 When used with [[, the < and > operators sort lexicographically
374 using the current locale.
375 When the == and != operators are used, the string to the right
377 of the operator is considered a pattern and matched according to
378 the rules described below under Pattern Matching, as if the ext‐
379 glob shell option were enabled. The = operator is equivalent to
380 ==. If the nocasematch shell option is enabled, the match is
381 performed without regard to the case of alphabetic characters.
382 The return value is 0 if the string matches (==) or does not
383 match (!=) the pattern, and 1 otherwise. Any part of the pat‐
384 tern may be quoted to force the quoted portion to be matched as
385 a string.
386 An additional binary operator, =~, is available, with the same
388 precedence as == and !=. When it is used, the string to the
389 right of the operator is considered an extended regular expres‐
390 sion and matched accordingly (as in regex(3)). The return value
391 is 0 if the string matches the pattern, and 1 otherwise. If the
392 regular expression is syntactically incorrect, the conditional
393 expression's return value is 2. If the nocasematch shell option
394 is enabled, the match is performed without regard to the case of
395 alphabetic characters. Any part of the pattern may be quoted to
396 force the quoted portion to be matched as a string. Bracket
397 expressions in regular expressions must be treated carefully,
398 since normal quoting characters lose their meanings between
399 brackets. If the pattern is stored in a shell variable, quoting
400 the variable expansion forces the entire pattern to be matched
401 as a string. Substrings matched by parenthesized subexpressions
402 within the regular expression are saved in the array variable
403 BASH_REMATCH. The element of BASH_REMATCH with index 0 is the
404 portion of the string matching the entire regular expression.
405 The element of BASH_REMATCH with index n is the portion of the
406 string matching the nth parenthesized subexpression.
407 Expressions may be combined using the following operators,
409 listed in decreasing order of precedence:
410 ( expression )
412 Returns the value of expression. This may be used to
413 override the normal precedence of operators.
414 ! expression
415 True if expression is false.
416 expression1 && expression2
417 True if both expression1 and expression2 are true.
418 expression1 || expression2
419 True if either expression1 or expression2 is true.
420 The && and || operators do not evaluate expression2 if the value
422 of expression1 is sufficient to determine the return value of
423 the entire conditional expression.
424 for name [ [ in [ word ... ] ] ; ] do list ; done
426 The list of words following in is expanded, generating a list of
427 items. The variable name is set to each element of this list in
428 turn, and list is executed each time. If the in word is omit‐
429 ted, the for command executes list once for each positional
430 parameter that is set (see PARAMETERS below). The return status
431 is the exit status of the last command that executes. If the
432 expansion of the items following in results in an empty list, no
433 commands are executed, and the return status is 0.
434 for (( expr1 ; expr2 ; expr3 )) ; do list ; done
436 First, the arithmetic expression expr1 is evaluated according to
437 the rules described below under ARITHMETIC EVALUATION. The
438 arithmetic expression expr2 is then evaluated repeatedly until
439 it evaluates to zero. Each time expr2 evaluates to a non-zero
440 value, list is executed and the arithmetic expression expr3 is
441 evaluated. If any expression is omitted, it behaves as if it
442 evaluates to 1. The return value is the exit status of the last
443 command in list that is executed, or false if any of the expres‐
444 sions is invalid.
445 select name [ in word ] ; do list ; done
447 The list of words following in is expanded, generating a list of
448 items. The set of expanded words is printed on the standard
449 error, each preceded by a number. If the in word is omitted,
450 the positional parameters are printed (see PARAMETERS below).
451 The PS3 prompt is then displayed and a line read from the stan‐
452 dard input. If the line consists of a number corresponding to
453 one of the displayed words, then the value of name is set to
454 that word. If the line is empty, the words and prompt are dis‐
455 played again. If EOF is read, the command completes. Any other
456 value read causes name to be set to null. The line read is
457 saved in the variable REPLY. The list is executed after each
458 selection until a break command is executed. The exit status of
459 select is the exit status of the last command executed in list,
460 or zero if no commands were executed.
461 case word in [ [(] pattern [ | pattern ] ... ) list ;; ] ... esac
463 A case command first expands word, and tries to match it against
464 each pattern in turn, using the same matching rules as for path‐
465 name expansion (see Pathname Expansion below). The word is
466 expanded using tilde expansion, parameter and variable expan‐
467 sion, arithmetic expansion, command substitution, process sub‐
468 stitution and quote removal. Each pattern examined is expanded
469 using tilde expansion, parameter and variable expansion, arith‐
470 metic expansion, command substitution, and process substitution.
471 If the nocasematch shell option is enabled, the match is per‐
472 formed without regard to the case of alphabetic characters.
473 When a match is found, the corresponding list is executed. If
474 the ;; operator is used, no subsequent matches are attempted
475 after the first pattern match. Using ;& in place of ;; causes
476 execution to continue with the list associated with the next set
477 of patterns. Using ;;& in place of ;; causes the shell to test
478 the next pattern list in the statement, if any, and execute any
479 associated list on a successful match. The exit status is zero
480 if no pattern matches. Otherwise, it is the exit status of the
481 last command executed in list.
482 if list; then list; [ elif list; then list; ] ... [ else list; ] fi
484 The if list is executed. If its exit status is zero, the then
485 list is executed. Otherwise, each elif list is executed in
486 turn, and if its exit status is zero, the corresponding then
487 list is executed and the command completes. Otherwise, the else
488 list is executed, if present. The exit status is the exit sta‐
489 tus of the last command executed, or zero if no condition tested
490 true.
491 while list-1; do list-2; done
493 until list-1; do list-2; done
494 The while command continuously executes the list list-2 as long
495 as the last command in the list list-1 returns an exit status of
496 zero. The until command is identical to the while command,
497 except that the test is negated: list-2 is executed as long as
498 the last command in list-1 returns a non-zero exit status. The
499 exit status of the while and until commands is the exit status
500 of the last command executed in list-2, or zero if none was exe‐
501 cuted.
502 Coprocesses
504 A coprocess is a shell command preceded by the coproc reserved word. A
505 coprocess is executed asynchronously in a subshell, as if the command
506 had been terminated with the & control operator, with a two-way pipe
507 established between the executing shell and the coprocess.
508 The format for a coprocess is:
510 coproc [NAME] command [redirections]
512 This creates a coprocess named NAME. If NAME is not supplied, the
514 default name is COPROC. NAME must not be supplied if command is a sim‐
515 ple command (see above); otherwise, it is interpreted as the first word
516 of the simple command. When the coprocess is executed, the shell cre‐
517 ates an array variable (see Arrays below) named NAME in the context of
518 the executing shell. The standard output of command is connected via a
519 pipe to a file descriptor in the executing shell, and that file
520 descriptor is assigned to NAME[0]. The standard input of command is
521 connected via a pipe to a file descriptor in the executing shell, and
522 that file descriptor is assigned to NAME[1]. This pipe is established
523 before any redirections specified by the command (see REDIRECTION
524 below). The file descriptors can be utilized as arguments to shell
525 commands and redirections using standard word expansions. The file
526 descriptors are not available in subshells. The process ID of the
527 shell spawned to execute the coprocess is available as the value of the
528 variable NAME_PID. The wait builtin command may be used to wait for
529 the coprocess to terminate.
530 Since the coprocess is created as an asynchronous command, the coproc
532 command always returns success. The return status of a coprocess is
533 the exit status of command.
534 Shell Function Definitions
536 A shell function is an object that is called like a simple command and
537 executes a compound command with a new set of positional parameters.
538 Shell functions are declared as follows:
539 name () compound-command [redirection]
541 function name [()] compound-command [redirection]
542 This defines a function named name. The reserved word function
543 is optional. If the function reserved word is supplied, the
544 parentheses are optional. The body of the function is the com‐
545 pound command compound-command (see Compound Commands above).
546 That command is usually a list of commands between { and }, but
547 may be any command listed under Compound Commands above, with
548 one exception: If the function reserved word is used, but the
549 parentheses are not supplied, the braces are required. com‐
550 pound-command is executed whenever name is specified as the name
551 of a simple command. When in posix mode, name may not be the
552 name of one of the POSIX special builtins. Any redirections
553 (see REDIRECTION below) specified when a function is defined are
554 performed when the function is executed. The exit status of a
555 function definition is zero unless a syntax error occurs or a
556 readonly function with the same name already exists. When exe‐
557 cuted, the exit status of a function is the exit status of the
558 last command executed in the body. (See FUNCTIONS below.)
559
561 In a non-interactive shell, or an interactive shell in which the inter‐
562 active_comments option to the shopt builtin is enabled (see SHELL
563 BUILTIN COMMANDS below), a word beginning with # causes that word and
564 all remaining characters on that line to be ignored. An interactive
565 shell without the interactive_comments option enabled does not allow
566 comments. The interactive_comments option is on by default in interac‐
567 tive shells.
568
570 Quoting is used to remove the special meaning of certain characters or
571 words to the shell. Quoting can be used to disable special treatment
572 for special characters, to prevent reserved words from being recognized
573 as such, and to prevent parameter expansion.
574 Each of the metacharacters listed above under DEFINITIONS has special
576 meaning to the shell and must be quoted if it is to represent itself.
577 When the command history expansion facilities are being used (see HIS‐
579 TORY EXPANSION below), the history expansion character, usually !, must
580 be quoted to prevent history expansion.
581 There are three quoting mechanisms: the escape character, single
583 quotes, and double quotes.
584 A non-quoted backslash (\) is the escape character. It preserves the
586 literal value of the next character that follows, with the exception of
587 <newline>. If a \<newline> pair appears, and the backslash is not
588 itself quoted, the \<newline> is treated as a line continuation (that
589 is, it is removed from the input stream and effectively ignored).
590 Enclosing characters in single quotes preserves the literal value of
592 each character within the quotes. A single quote may not occur between
593 single quotes, even when preceded by a backslash.
594 Enclosing characters in double quotes preserves the literal value of
596 all characters within the quotes, with the exception of $, `, \, and,
597 when history expansion is enabled, !. When the shell is in posix mode,
598 the ! has no special meaning within double quotes, even when history
599 expansion is enabled. The characters $ and ` retain their special
600 meaning within double quotes. The backslash retains its special mean‐
601 ing only when followed by one of the following characters: $, `, ", \,
602 or <newline>. A double quote may be quoted within double quotes by
603 preceding it with a backslash. If enabled, history expansion will be
604 performed unless an ! appearing in double quotes is escaped using a
605 backslash. The backslash preceding the ! is not removed.
606 The special parameters * and @ have special meaning when in double
608 quotes (see PARAMETERS below).
609 Words of the form $'string' are treated specially. The word expands to
611 string, with backslash-escaped characters replaced as specified by the
612 ANSI C standard. Backslash escape sequences, if present, are decoded
613 as follows:
614 \a alert (bell)
615 \b backspace
616 \e
617 \E an escape character
618 \f form feed
619 \n new line
620 \r carriage return
621 \t horizontal tab
622 \v vertical tab
623 \\ backslash
624 \' single quote
625 \" double quote
626 \? question mark
627 \nnn the eight-bit character whose value is the octal value
628 nnn (one to three digits)
629 \xHH the eight-bit character whose value is the hexadecimal
630 value HH (one or two hex digits)
631 \uHHHH the Unicode (ISO/IEC 10646) character whose value is the
632 hexadecimal value HHHH (one to four hex digits)
633 \UHHHHHHHH
634 the Unicode (ISO/IEC 10646) character whose value is the
635 hexadecimal value HHHHHHHH (one to eight hex digits)
636 \cx a control-x character
637 The expanded result is single-quoted, as if the dollar sign had not
639 been present.
640 A double-quoted string preceded by a dollar sign ($"string") will cause
642 the string to be translated according to the current locale. If the
643 current locale is C or POSIX, the dollar sign is ignored. If the
644 string is translated and replaced, the replacement is double-quoted.
645
647 A parameter is an entity that stores values. It can be a name, a num‐
648 ber, or one of the special characters listed below under Special Param‐
649 eters. A variable is a parameter denoted by a name. A variable has a
650 value and zero or more attributes. Attributes are assigned using the
651 declare builtin command (see declare below in SHELL BUILTIN COMMANDS).
652 A parameter is set if it has been assigned a value. The null string is
654 a valid value. Once a variable is set, it may be unset only by using
655 the unset builtin command (see SHELL BUILTIN COMMANDS below).
656 A variable may be assigned to by a statement of the form
658 name=[value]
660 If value is not given, the variable is assigned the null string. All
662 values undergo tilde expansion, parameter and variable expansion, com‐
663 mand substitution, arithmetic expansion, and quote removal (see EXPAN‐
664 SION below). If the variable has its integer attribute set, then value
665 is evaluated as an arithmetic expression even if the $((...)) expansion
666 is not used (see Arithmetic Expansion below). Word splitting is not
667 performed, with the exception of "$@" as explained below under Special
668 Parameters. Pathname expansion is not performed. Assignment state‐
669 ments may also appear as arguments to the alias, declare, typeset,
670 export, readonly, and local builtin commands (declaration commands).
671 When in posix mode, these builtins may appear in a command after one or
672 more instances of the command builtin and retain these assignment
673 statement properties.
674 In the context where an assignment statement is assigning a value to a
676 shell variable or array index, the += operator can be used to append to
677 or add to the variable's previous value. This includes arguments to
678 builtin commands such as declare that accept assignment statements
679 (declaration commands). When += is applied to a variable for which the
680 integer attribute has been set, value is evaluated as an arithmetic
681 expression and added to the variable's current value, which is also
682 evaluated. When += is applied to an array variable using compound
683 assignment (see Arrays below), the variable's value is not unset (as it
684 is when using =), and new values are appended to the array beginning at
685 one greater than the array's maximum index (for indexed arrays) or
686 added as additional key-value pairs in an associative array. When
687 applied to a string-valued variable, value is expanded and appended to
688 the variable's value.
689 A variable can be assigned the nameref attribute using the -n option to
691 the declare or local builtin commands (see the descriptions of declare
692 and local below) to create a nameref, or a reference to another vari‐
693 able. This allows variables to be manipulated indirectly. Whenever
694 the nameref variable is referenced, assigned to, unset, or has its
695 attributes modified (other than using or changing the nameref attribute
696 itself), the operation is actually performed on the variable specified
697 by the nameref variable's value. A nameref is commonly used within
698 shell functions to refer to a variable whose name is passed as an argu‐
699 ment to the function. For instance, if a variable name is passed to a
700 shell function as its first argument, running
701 declare -n ref=$1
702 inside the function creates a nameref variable ref whose value is the
703 variable name passed as the first argument. References and assignments
704 to ref, and changes to its attributes, are treated as references,
705 assignments, and attribute modifications to the variable whose name was
706 passed as $1. If the control variable in a for loop has the nameref
707 attribute, the list of words can be a list of shell variables, and a
708 name reference will be established for each word in the list, in turn,
709 when the loop is executed. Array variables cannot be given the nameref
710 attribute. However, nameref variables can reference array variables
711 and subscripted array variables. Namerefs can be unset using the -n
712 option to the unset builtin. Otherwise, if unset is executed with the
713 name of a nameref variable as an argument, the variable referenced by
714 the nameref variable will be unset.
715 Positional Parameters
717 A positional parameter is a parameter denoted by one or more digits,
718 other than the single digit 0. Positional parameters are assigned from
719 the shell's arguments when it is invoked, and may be reassigned using
720 the set builtin command. Positional parameters may not be assigned to
721 with assignment statements. The positional parameters are temporarily
722 replaced when a shell function is executed (see FUNCTIONS below).
723 When a positional parameter consisting of more than a single digit is
725 expanded, it must be enclosed in braces (see EXPANSION below).
726 Special Parameters
728 The shell treats several parameters specially. These parameters may
729 only be referenced; assignment to them is not allowed.
730 * Expands to the positional parameters, starting from one. When
731 the expansion is not within double quotes, each positional
732 parameter expands to a separate word. In contexts where it is
733 performed, those words are subject to further word splitting and
734 pathname expansion. When the expansion occurs within double
735 quotes, it expands to a single word with the value of each
736 parameter separated by the first character of the IFS special
737 variable. That is, "$*" is equivalent to "$1c$2c...", where c
738 is the first character of the value of the IFS variable. If IFS
739 is unset, the parameters are separated by spaces. If IFS is
740 null, the parameters are joined without intervening separators.
741 @ Expands to the positional parameters, starting from one. When
742 the expansion occurs within double quotes, each parameter
743 expands to a separate word. That is, "$@" is equivalent to "$1"
744 "$2" ... If the double-quoted expansion occurs within a word,
745 the expansion of the first parameter is joined with the begin‐
746 ning part of the original word, and the expansion of the last
747 parameter is joined with the last part of the original word.
748 When there are no positional parameters, "$@" and $@ expand to
749 nothing (i.e., they are removed).
750 # Expands to the number of positional parameters in decimal.
751 ? Expands to the exit status of the most recently executed fore‐
752 ground pipeline.
753 - Expands to the current option flags as specified upon invoca‐
754 tion, by the set builtin command, or those set by the shell
755 itself (such as the -i option).
756 $ Expands to the process ID of the shell. In a () subshell, it
757 expands to the process ID of the current shell, not the sub‐
758 shell.
759 ! Expands to the process ID of the job most recently placed into
760 the background, whether executed as an asynchronous command or
761 using the bg builtin (see JOB CONTROL below).
762 0 Expands to the name of the shell or shell script. This is set
763 at shell initialization. If bash is invoked with a file of com‐
764 mands, $0 is set to the name of that file. If bash is started
765 with the -c option, then $0 is set to the first argument after
766 the string to be executed, if one is present. Otherwise, it is
767 set to the filename used to invoke bash, as given by argument
768 zero.
769 _ At shell startup, set to the absolute pathname used to invoke
770 the shell or shell script being executed as passed in the envi‐
771 ronment or argument list. Subsequently, expands to the last
772 argument to the previous command, after expansion. Also set to
773 the full pathname used to invoke each command executed and
774 placed in the environment exported to that command. When check‐
775 ing mail, this parameter holds the name of the mail file cur‐
776 rently being checked.
777 Shell Variables
779 The following variables are set by the shell:
780 BASH Expands to the full filename used to invoke this instance of
782 bash.
783 BASHOPTS
784 A colon-separated list of enabled shell options. Each word in
785 the list is a valid argument for the -s option to the shopt
786 builtin command (see SHELL BUILTIN COMMANDS below). The options
787 appearing in BASHOPTS are those reported as on by shopt. If
788 this variable is in the environment when bash starts up, each
789 shell option in the list will be enabled before reading any
790 startup files. This variable is read-only.
791 BASHPID
792 Expands to the process ID of the current bash process. This
793 differs from $$ under certain circumstances, such as subshells
794 that do not require bash to be re-initialized.
795 BASH_ALIASES
796 An associative array variable whose members correspond to the
797 internal list of aliases as maintained by the alias builtin.
798 Elements added to this array appear in the alias list; however,
799 unsetting array elements currently does not cause aliases to be
800 removed from the alias list. If BASH_ALIASES is unset, it loses
801 its special properties, even if it is subsequently reset.
802 BASH_ARGC
803 An array variable whose values are the number of parameters in
804 each frame of the current bash execution call stack. The number
805 of parameters to the current subroutine (shell function or
806 script executed with . or source) is at the top of the stack.
807 When a subroutine is executed, the number of parameters passed
808 is pushed onto BASH_ARGC. The shell sets BASH_ARGC only when in
809 extended debugging mode (see the description of the extdebug
810 option to the shopt builtin below)
811 BASH_ARGV
812 An array variable containing all of the parameters in the cur‐
813 rent bash execution call stack. The final parameter of the last
814 subroutine call is at the top of the stack; the first parameter
815 of the initial call is at the bottom. When a subroutine is exe‐
816 cuted, the parameters supplied are pushed onto BASH_ARGV. The
817 shell sets BASH_ARGV only when in extended debugging mode (see
818 the description of the extdebug option to the shopt builtin
819 below)
820 BASH_CMDS
821 An associative array variable whose members correspond to the
822 internal hash table of commands as maintained by the hash
823 builtin. Elements added to this array appear in the hash table;
824 however, unsetting array elements currently does not cause com‐
825 mand names to be removed from the hash table. If BASH_CMDS is
826 unset, it loses its special properties, even if it is subse‐
827 quently reset.
828 BASH_COMMAND
829 The command currently being executed or about to be executed,
830 unless the shell is executing a command as the result of a trap,
831 in which case it is the command executing at the time of the
832 trap.
833 BASH_EXECUTION_STRING
834 The command argument to the -c invocation option.
835 BASH_LINENO
836 An array variable whose members are the line numbers in source
837 files where each corresponding member of FUNCNAME was invoked.
838 ${BASH_LINENO[$i]} is the line number in the source file
839 (${BASH_SOURCE[$i+1]}) where ${FUNCNAME[$i]} was called (or
840 ${BASH_LINENO[$i-1]} if referenced within another shell func‐
841 tion). Use LINENO to obtain the current line number.
842 BASH_LOADABLES_PATH
843 A colon-separated list of directories in which the shell looks
844 for dynamically loadable builtins specified by the enable com‐
845 mand.
846 BASH_REMATCH
847 An array variable whose members are assigned by the =~ binary
848 operator to the [[ conditional command. The element with index
849 0 is the portion of the string matching the entire regular
850 expression. The element with index n is the portion of the
851 string matching the nth parenthesized subexpression. This vari‐
852 able is read-only.
853 BASH_SOURCE
854 An array variable whose members are the source filenames where
855 the corresponding shell function names in the FUNCNAME array
856 variable are defined. The shell function ${FUNCNAME[$i]} is
857 defined in the file ${BASH_SOURCE[$i]} and called from
858 ${BASH_SOURCE[$i+1]}.
859 BASH_SUBSHELL
860 Incremented by one within each subshell or subshell environment
861 when the shell begins executing in that environment. The ini‐
862 tial value is 0.
863 BASH_VERSINFO
864 A readonly array variable whose members hold version information
865 for this instance of bash. The values assigned to the array
866 members are as follows:
867 BASH_VERSINFO[0] The major version number (the release).
868 BASH_VERSINFO[1] The minor version number (the version).
869 BASH_VERSINFO[2] The patch level.
870 BASH_VERSINFO[3] The build version.
871 BASH_VERSINFO[4] The release status (e.g., beta1).
872 BASH_VERSINFO[5] The value of MACHTYPE.
873 BASH_VERSION
874 Expands to a string describing the version of this instance of
875 bash.
876 COMP_CWORD
877 An index into ${COMP_WORDS} of the word containing the current
878 cursor position. This variable is available only in shell func‐
879 tions invoked by the programmable completion facilities (see
880 Programmable Completion below).
881 COMP_KEY
882 The key (or final key of a key sequence) used to invoke the cur‐
883 rent completion function.
884 COMP_LINE
885 The current command line. This variable is available only in
886 shell functions and external commands invoked by the program‐
887 mable completion facilities (see Programmable Completion below).
888 COMP_POINT
889 The index of the current cursor position relative to the begin‐
890 ning of the current command. If the current cursor position is
891 at the end of the current command, the value of this variable is
892 equal to ${#COMP_LINE}. This variable is available only in
893 shell functions and external commands invoked by the program‐
894 mable completion facilities (see Programmable Completion below).
895 COMP_TYPE
896 Set to an integer value corresponding to the type of completion
897 attempted that caused a completion function to be called: TAB,
898 for normal completion, ?, for listing completions after succes‐
899 sive tabs, !, for listing alternatives on partial word comple‐
900 tion, @, to list completions if the word is not unmodified, or
901 %, for menu completion. This variable is available only in
902 shell functions and external commands invoked by the program‐
903 mable completion facilities (see Programmable Completion below).
904 COMP_WORDBREAKS
905 The set of characters that the readline library treats as word
906 separators when performing word completion. If COMP_WORDBREAKS
907 is unset, it loses its special properties, even if it is subse‐
908 quently reset.
909 COMP_WORDS
910 An array variable (see Arrays below) consisting of the individ‐
911 ual words in the current command line. The line is split into
912 words as readline would split it, using COMP_WORDBREAKS as
913 described above. This variable is available only in shell func‐
914 tions invoked by the programmable completion facilities (see
915 Programmable Completion below).
916 COPROC An array variable (see Arrays below) created to hold the file
917 descriptors for output from and input to an unnamed coprocess
918 (see Coprocesses above).
919 DIRSTACK
920 An array variable (see Arrays below) containing the current con‐
921 tents of the directory stack. Directories appear in the stack
922 in the order they are displayed by the dirs builtin. Assigning
923 to members of this array variable may be used to modify directo‐
924 ries already in the stack, but the pushd and popd builtins must
925 be used to add and remove directories. Assignment to this vari‐
926 able will not change the current directory. If DIRSTACK is
927 unset, it loses its special properties, even if it is subse‐
928 quently reset.
929 EUID Expands to the effective user ID of the current user, initial‐
930 ized at shell startup. This variable is readonly.
931 FUNCNAME
932 An array variable containing the names of all shell functions
933 currently in the execution call stack. The element with index 0
934 is the name of any currently-executing shell function. The bot‐
935 tom-most element (the one with the highest index) is "main".
936 This variable exists only when a shell function is executing.
937 Assignments to FUNCNAME have no effect. If FUNCNAME is unset,
938 it loses its special properties, even if it is subsequently
939 reset.
940 This variable can be used with BASH_LINENO and BASH_SOURCE.
942 Each element of FUNCNAME has corresponding elements in
943 BASH_LINENO and BASH_SOURCE to describe the call stack. For
944 instance, ${FUNCNAME[$i]} was called from the file
945 ${BASH_SOURCE[$i+1]} at line number ${BASH_LINENO[$i]}. The
946 caller builtin displays the current call stack using this infor‐
947 mation.
948 GROUPS An array variable containing the list of groups of which the
949 current user is a member. Assignments to GROUPS have no effect.
950 If GROUPS is unset, it loses its special properties, even if it
951 is subsequently reset.
952 HISTCMD
953 The history number, or index in the history list, of the current
954 command. If HISTCMD is unset, it loses its special properties,
955 even if it is subsequently reset.
956 HOSTNAME
957 Automatically set to the name of the current host.
958 HOSTTYPE
959 Automatically set to a string that uniquely describes the type
960 of machine on which bash is executing. The default is system-
961 dependent.
962 LINENO Each time this parameter is referenced, the shell substitutes a
963 decimal number representing the current sequential line number
964 (starting with 1) within a script or function. When not in a
965 script or function, the value substituted is not guaranteed to
966 be meaningful. If LINENO is unset, it loses its special proper‐
967 ties, even if it is subsequently reset.
968 MACHTYPE
969 Automatically set to a string that fully describes the system
970 type on which bash is executing, in the standard GNU cpu-com‐
971 pany-system format. The default is system-dependent.
972 MAPFILE
973 An array variable (see Arrays below) created to hold the text
974 read by the mapfile builtin when no variable name is supplied.
975 OLDPWD The previous working directory as set by the cd command.
976 OPTARG The value of the last option argument processed by the getopts
977 builtin command (see SHELL BUILTIN COMMANDS below).
978 OPTIND The index of the next argument to be processed by the getopts
979 builtin command (see SHELL BUILTIN COMMANDS below).
980 OSTYPE Automatically set to a string that describes the operating sys‐
981 tem on which bash is executing. The default is system-depen‐
982 dent.
983 PIPESTATUS
984 An array variable (see Arrays below) containing a list of exit
985 status values from the processes in the most-recently-executed
986 foreground pipeline (which may contain only a single command).
987 PPID The process ID of the shell's parent. This variable is read‐
988 only.
989 PWD The current working directory as set by the cd command.
990 RANDOM Each time this parameter is referenced, a random integer between
991 0 and 32767 is generated. The sequence of random numbers may be
992 initialized by assigning a value to RANDOM. If RANDOM is unset,
993 it loses its special properties, even if it is subsequently
994 reset.
995 READLINE_LINE
996 The contents of the readline line buffer, for use with "bind -x"
997 (see SHELL BUILTIN COMMANDS below).
998 READLINE_POINT
999 The position of the insertion point in the readline line buffer,
1000 for use with "bind -x" (see SHELL BUILTIN COMMANDS below).
1001 REPLY Set to the line of input read by the read builtin command when
1002 no arguments are supplied.
1003 SECONDS
1004 Each time this parameter is referenced, the number of seconds
1005 since shell invocation is returned. If a value is assigned to
1006 SECONDS, the value returned upon subsequent references is the
1007 number of seconds since the assignment plus the value assigned.
1008 If SECONDS is unset, it loses its special properties, even if it
1009 is subsequently reset.
1010 SHELLOPTS
1011 A colon-separated list of enabled shell options. Each word in
1012 the list is a valid argument for the -o option to the set
1013 builtin command (see SHELL BUILTIN COMMANDS below). The options
1014 appearing in SHELLOPTS are those reported as on by set -o. If
1015 this variable is in the environment when bash starts up, each
1016 shell option in the list will be enabled before reading any
1017 startup files. This variable is read-only.
1018 SHLVL Incremented by one each time an instance of bash is started.
1019 UID Expands to the user ID of the current user, initialized at shell
1020 startup. This variable is readonly.
1021 The following variables are used by the shell. In some cases, bash
1023 assigns a default value to a variable; these cases are noted below.
1024 BASH_COMPAT
1026 The value is used to set the shell's compatibility level. See
1027 the description of the shopt builtin below under SHELL BUILTIN
1028 COMMANDS for a description of the various compatibility levels
1029 and their effects. The value may be a decimal number (e.g.,
1030 4.2) or an integer (e.g., 42) corresponding to the desired com‐
1031 patibility level. If BASH_COMPAT is unset or set to the empty
1032 string, the compatibility level is set to the default for the
1033 current version. If BASH_COMPAT is set to a value that is not
1034 one of the valid compatibility levels, the shell prints an error
1035 message and sets the compatibility level to the default for the
1036 current version. The valid compatibility levels correspond to
1037 the compatibility options accepted by the shopt builtin
1038 described below (for example, compat42 means that 4.2 and 42 are
1039 valid values). The current version is also a valid value.
1040 BASH_ENV
1041 If this parameter is set when bash is executing a shell script,
1042 its value is interpreted as a filename containing commands to
1043 initialize the shell, as in ~/.bashrc. The value of BASH_ENV is
1044 subjected to parameter expansion, command substitution, and
1045 arithmetic expansion before being interpreted as a filename.
1046 PATH is not used to search for the resultant filename.
1047 BASH_XTRACEFD
1048 If set to an integer corresponding to a valid file descriptor,
1049 bash will write the trace output generated when set -x is
1050 enabled to that file descriptor. The file descriptor is closed
1051 when BASH_XTRACEFD is unset or assigned a new value. Unsetting
1052 BASH_XTRACEFD or assigning it the empty string causes the trace
1053 output to be sent to the standard error. Note that setting
1054 BASH_XTRACEFD to 2 (the standard error file descriptor) and then
1055 unsetting it will result in the standard error being closed.
1056 CDPATH The search path for the cd command. This is a colon-separated
1057 list of directories in which the shell looks for destination
1058 directories specified by the cd command. A sample value is
1059 ".:~:/usr".
1060 CHILD_MAX
1061 Set the number of exited child status values for the shell to
1062 remember. Bash will not allow this value to be decreased below
1063 a POSIX-mandated minimum, and there is a maximum value (cur‐
1064 rently 8192) that this may not exceed. The minimum value is
1065 system-dependent.
1066 COLUMNS
1067 Used by the select compound command to determine the terminal
1068 width when printing selection lists. Automatically set if the
1069 checkwinsize option is enabled or in an interactive shell upon
1070 receipt of a SIGWINCH.
1071 COMPREPLY
1072 An array variable from which bash reads the possible completions
1073 generated by a shell function invoked by the programmable com‐
1074 pletion facility (see Programmable Completion below). Each
1075 array element contains one possible completion.
1076 EMACS If bash finds this variable in the environment when the shell
1077 starts with value "t", it assumes that the shell is running in
1078 an Emacs shell buffer and disables line editing.
1079 ENV Similar to BASH_ENV; used when the shell is invoked in POSIX
1080 mode.
1081 EXECIGNORE
1082 A colon-separated list of shell patterns (see Pattern Matching)
1083 defining the list of filenames to be ignored by command search
1084 using PATH. Files whose full pathnames match one of these pat‐
1085 terns are not considered executable files for the purposes of
1086 completion and command execution via PATH lookup. This does not
1087 affect the behavior of the [, test, and [[ commands. Full path‐
1088 names in the command hash table are not subject to EXECIGNORE.
1089 Use this variable to ignore shared library files that have the
1090 executable bit set, but are not executable files. The pattern
1091 matching honors the setting of the extglob shell option.
1092 FCEDIT The default editor for the fc builtin command.
1093 FIGNORE
1094 A colon-separated list of suffixes to ignore when performing
1095 filename completion (see READLINE below). A filename whose suf‐
1096 fix matches one of the entries in FIGNORE is excluded from the
1097 list of matched filenames. A sample value is ".o:~".
1098 FUNCNEST
1099 If set to a numeric value greater than 0, defines a maximum
1100 function nesting level. Function invocations that exceed this
1101 nesting level will cause the current command to abort.
1102 GLOBIGNORE
1103 A colon-separated list of patterns defining the set of filenames
1104 to be ignored by pathname expansion. If a filename matched by a
1105 pathname expansion pattern also matches one of the patterns in
1106 GLOBIGNORE, it is removed from the list of matches.
1107 HISTCONTROL
1108 A colon-separated list of values controlling how commands are
1109 saved on the history list. If the list of values includes
1110 ignorespace, lines which begin with a space character are not
1111 saved in the history list. A value of ignoredups causes lines
1112 matching the previous history entry to not be saved. A value of
1113 ignoreboth is shorthand for ignorespace and ignoredups. A value
1114 of erasedups causes all previous lines matching the current line
1115 to be removed from the history list before that line is saved.
1116 Any value not in the above list is ignored. If HISTCONTROL is
1117 unset, or does not include a valid value, all lines read by the
1118 shell parser are saved on the history list, subject to the value
1119 of HISTIGNORE. The second and subsequent lines of a multi-line
1120 compound command are not tested, and are added to the history
1121 regardless of the value of HISTCONTROL.
1122 HISTFILE
1123 The name of the file in which command history is saved (see HIS‐
1124 TORY below). The default value is ~/.bash_history. If unset,
1125 the command history is not saved when a shell exits.
1126 HISTFILESIZE
1127 The maximum number of lines contained in the history file. When
1128 this variable is assigned a value, the history file is trun‐
1129 cated, if necessary, to contain no more than that number of
1130 lines by removing the oldest entries. The history file is also
1131 truncated to this size after writing it when a shell exits. If
1132 the value is 0, the history file is truncated to zero size.
1133 Non-numeric values and numeric values less than zero inhibit
1134 truncation. The shell sets the default value to the value of
1135 HISTSIZE after reading any startup files.
1136 HISTIGNORE
1137 A colon-separated list of patterns used to decide which command
1138 lines should be saved on the history list. Each pattern is
1139 anchored at the beginning of the line and must match the com‐
1140 plete line (no implicit `*' is appended). Each pattern is
1141 tested against the line after the checks specified by HISTCON‐
1142 TROL are applied. In addition to the normal shell pattern
1143 matching characters, `&' matches the previous history line. `&'
1144 may be escaped using a backslash; the backslash is removed
1145 before attempting a match. The second and subsequent lines of a
1146 multi-line compound command are not tested, and are added to the
1147 history regardless of the value of HISTIGNORE. The pattern
1148 matching honors the setting of the extglob shell option.
1149 HISTSIZE
1150 The number of commands to remember in the command history (see
1151 HISTORY below). If the value is 0, commands are not saved in
1152 the history list. Numeric values less than zero result in every
1153 command being saved on the history list (there is no limit).
1154 The shell sets the default value to 500 after reading any
1155 startup files.
1156 HISTTIMEFORMAT
1157 If this variable is set and not null, its value is used as a
1158 format string for strftime(3) to print the time stamp associated
1159 with each history entry displayed by the history builtin. If
1160 this variable is set, time stamps are written to the history
1161 file so they may be preserved across shell sessions. This uses
1162 the history comment character to distinguish timestamps from
1163 other history lines.
1164 HOME The home directory of the current user; the default argument for
1165 the cd builtin command. The value of this variable is also used
1166 when performing tilde expansion.
1167 HOSTFILE
1168 Contains the name of a file in the same format as /etc/hosts
1169 that should be read when the shell needs to complete a hostname.
1170 The list of possible hostname completions may be changed while
1171 the shell is running; the next time hostname completion is
1172 attempted after the value is changed, bash adds the contents of
1173 the new file to the existing list. If HOSTFILE is set, but has
1174 no value, or does not name a readable file, bash attempts to
1175 read /etc/hosts to obtain the list of possible hostname comple‐
1176 tions. When HOSTFILE is unset, the hostname list is cleared.
1177 IFS The Internal Field Separator that is used for word splitting
1178 after expansion and to split lines into words with the read
1179 builtin command. The default value is ``<space><tab><new‐
1180 line>''.
1181 IGNOREEOF
1182 Controls the action of an interactive shell on receipt of an EOF
1183 character as the sole input. If set, the value is the number of
1184 consecutive EOF characters which must be typed as the first
1185 characters on an input line before bash exits. If the variable
1186 exists but does not have a numeric value, or has no value, the
1187 default value is 10. If it does not exist, EOF signifies the
1188 end of input to the shell.
1189 INPUTRC
1190 The filename for the readline startup file, overriding the
1191 default of ~/.inputrc (see READLINE below).
1192 LANG Used to determine the locale category for any category not
1193 specifically selected with a variable starting with LC_.
1194 LC_ALL This variable overrides the value of LANG and any other LC_
1195 variable specifying a locale category.
1196 LC_COLLATE
1197 This variable determines the collation order used when sorting
1198 the results of pathname expansion, and determines the behavior
1199 of range expressions, equivalence classes, and collating
1200 sequences within pathname expansion and pattern matching.
1201 LC_CTYPE
1202 This variable determines the interpretation of characters and
1203 the behavior of character classes within pathname expansion and
1204 pattern matching.
1205 LC_MESSAGES
1206 This variable determines the locale used to translate double-
1207 quoted strings preceded by a $.
1208 LC_NUMERIC
1209 This variable determines the locale category used for number
1210 formatting.
1211 LC_TIME
1212 This variable determines the locale category used for data and
1213 time formatting.
1214 LINES Used by the select compound command to determine the column
1215 length for printing selection lists. Automatically set if the
1216 checkwinsize option is enabled or in an interactive shell upon
1217 receipt of a SIGWINCH.
1218 MAIL If this parameter is set to a file or directory name and the
1219 MAILPATH variable is not set, bash informs the user of the
1220 arrival of mail in the specified file or Maildir-format direc‐
1221 tory.
1222 MAILCHECK
1223 Specifies how often (in seconds) bash checks for mail. The
1224 default is 60 seconds. When it is time to check for mail, the
1225 shell does so before displaying the primary prompt. If this
1226 variable is unset, or set to a value that is not a number
1227 greater than or equal to zero, the shell disables mail checking.
1228 MAILPATH
1229 A colon-separated list of filenames to be checked for mail. The
1230 message to be printed when mail arrives in a particular file may
1231 be specified by separating the filename from the message with a
1232 `?'. When used in the text of the message, $_ expands to the
1233 name of the current mailfile. Example:
1234 MAILPATH='/var/mail/bfox?"You have mail":~/shell-mail?"$_ has
1235 mail!"'
1236 Bash can be configured to supply a default value for this vari‐
1237 able (there is no value by default), but the location of the
1238 user mail files that it uses is system dependent (e.g.,
1239 /var/mail/$USER).
1240 OPTERR If set to the value 1, bash displays error messages generated by
1241 the getopts builtin command (see SHELL BUILTIN COMMANDS below).
1242 OPTERR is initialized to 1 each time the shell is invoked or a
1243 shell script is executed.
1244 PATH The search path for commands. It is a colon-separated list of
1245 directories in which the shell looks for commands (see COMMAND
1246 EXECUTION below). A zero-length (null) directory name in the
1247 value of PATH indicates the current directory. A null directory
1248 name may appear as two adjacent colons, or as an initial or
1249 trailing colon. The default path is system-dependent, and is
1250 set by the administrator who installs bash. A common value is
1251 ``/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin:/bin:/sbin''.
1252 POSIXLY_CORRECT
1253 If this variable is in the environment when bash starts, the
1254 shell enters posix mode before reading the startup files, as if
1255 the --posix invocation option had been supplied. If it is set
1256 while the shell is running, bash enables posix mode, as if the
1257 command set -o posix had been executed.
1258 PROMPT_COMMAND
1259 If set, the value is executed as a command prior to issuing each
1260 primary prompt.
1261 PROMPT_DIRTRIM
1262 If set to a number greater than zero, the value is used as the
1263 number of trailing directory components to retain when expanding
1264 the \w and \W prompt string escapes (see PROMPTING below).
1265 Characters removed are replaced with an ellipsis.
1266 PS0 The value of this parameter is expanded (see PROMPTING below)
1267 and displayed by interactive shells after reading a command and
1268 before the command is executed.
1269 PS1 The value of this parameter is expanded (see PROMPTING below)
1270 and used as the primary prompt string. The default value is
1271 ``\s-\v\$ ''.
1272 PS2 The value of this parameter is expanded as with PS1 and used as
1273 the secondary prompt string. The default is ``> ''.
1274 PS3 The value of this parameter is used as the prompt for the select
1275 command (see SHELL GRAMMAR above).
1276 PS4 The value of this parameter is expanded as with PS1 and the
1277 value is printed before each command bash displays during an
1278 execution trace. The first character of PS4 is replicated mul‐
1279 tiple times, as necessary, to indicate multiple levels of indi‐
1280 rection. The default is ``+ ''.
1281 SHELL The full pathname to the shell is kept in this environment vari‐
1282 able. If it is not set when the shell starts, bash assigns to
1283 it the full pathname of the current user's login shell.
1284 TIMEFORMAT
1285 The value of this parameter is used as a format string specify‐
1286 ing how the timing information for pipelines prefixed with the
1287 time reserved word should be displayed. The % character intro‐
1288 duces an escape sequence that is expanded to a time value or
1289 other information. The escape sequences and their meanings are
1290 as follows; the braces denote optional portions.
1291 %% A literal %.
1292 %[p][l]R The elapsed time in seconds.
1293 %[p][l]U The number of CPU seconds spent in user mode.
1294 %[p][l]S The number of CPU seconds spent in system mode.
1295 %P The CPU percentage, computed as (%U + %S) / %R.
1296 The optional p is a digit specifying the precision, the number
1298 of fractional digits after a decimal point. A value of 0 causes
1299 no decimal point or fraction to be output. At most three places
1300 after the decimal point may be specified; values of p greater
1301 than 3 are changed to 3. If p is not specified, the value 3 is
1302 used.
1303 The optional l specifies a longer format, including minutes, of
1305 the form MMmSS.FFs. The value of p determines whether or not
1306 the fraction is included.
1307 If this variable is not set, bash acts as if it had the value
1309 $'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS'. If the value is null,
1310 no timing information is displayed. A trailing newline is added
1311 when the format string is displayed.
1312 TMOUT If set to a value greater than zero, TMOUT is treated as the
1313 default timeout for the read builtin. The select command termi‐
1314 nates if input does not arrive after TMOUT seconds when input is
1315 coming from a terminal. In an interactive shell, the value is
1316 interpreted as the number of seconds to wait for a line of input
1317 after issuing the primary prompt. Bash terminates after waiting
1318 for that number of seconds if a complete line of input does not
1319 arrive.
1320 TMPDIR If set, bash uses its value as the name of a directory in which
1321 bash creates temporary files for the shell's use.
1322 auto_resume
1323 This variable controls how the shell interacts with the user and
1324 job control. If this variable is set, single word simple com‐
1325 mands without redirections are treated as candidates for resump‐
1326 tion of an existing stopped job. There is no ambiguity allowed;
1327 if there is more than one job beginning with the string typed,
1328 the job most recently accessed is selected. The name of a
1329 stopped job, in this context, is the command line used to start
1330 it. If set to the value exact, the string supplied must match
1331 the name of a stopped job exactly; if set to substring, the
1332 string supplied needs to match a substring of the name of a
1333 stopped job. The substring value provides functionality analo‐
1334 gous to the %? job identifier (see JOB CONTROL below). If set
1335 to any other value, the supplied string must be a prefix of a
1336 stopped job's name; this provides functionality analogous to the
1337 %string job identifier.
1338 histchars
1339 The two or three characters which control history expansion and
1340 tokenization (see HISTORY EXPANSION below). The first character
1341 is the history expansion character, the character which signals
1342 the start of a history expansion, normally `!'. The second
1343 character is the quick substitution character, which is used as
1344 shorthand for re-running the previous command entered, substi‐
1345 tuting one string for another in the command. The default is
1346 `^'. The optional third character is the character which indi‐
1347 cates that the remainder of the line is a comment when found as
1348 the first character of a word, normally `#'. The history com‐
1349 ment character causes history substitution to be skipped for the
1350 remaining words on the line. It does not necessarily cause the
1351 shell parser to treat the rest of the line as a comment.
1352 Arrays
1354 Bash provides one-dimensional indexed and associative array variables.
1355 Any variable may be used as an indexed array; the declare builtin will
1356 explicitly declare an array. There is no maximum limit on the size of
1357 an array, nor any requirement that members be indexed or assigned con‐
1358 tiguously. Indexed arrays are referenced using integers (including
1359 arithmetic expressions) and are zero-based; associative arrays are ref‐
1360 erenced using arbitrary strings. Unless otherwise noted, indexed array
1361 indices must be non-negative integers.
1362 An indexed array is created automatically if any variable is assigned
1364 to using the syntax name[subscript]=value. The subscript is treated as
1365 an arithmetic expression that must evaluate to a number. To explicitly
1366 declare an indexed array, use declare -a name (see SHELL BUILTIN COM‐
1367 MANDS below). declare -a name[subscript] is also accepted; the sub‐
1368 script is ignored.
1369 Associative arrays are created using declare -A name.
1371 Attributes may be specified for an array variable using the declare and
1373 readonly builtins. Each attribute applies to all members of an array.
1374 Arrays are assigned to using compound assignments of the form
1376 name=(value1 ... valuen), where each value is of the form [sub‐
1377 script]=string. Indexed array assignments do not require anything but
1378 string. When assigning to indexed arrays, if the optional brackets and
1379 subscript are supplied, that index is assigned to; otherwise the index
1380 of the element assigned is the last index assigned to by the statement
1381 plus one. Indexing starts at zero.
1382 When assigning to an associative array, the subscript is required.
1384 This syntax is also accepted by the declare builtin. Individual array
1386 elements may be assigned to using the name[subscript]=value syntax
1387 introduced above. When assigning to an indexed array, if name is sub‐
1388 scripted by a negative number, that number is interpreted as relative
1389 to one greater than the maximum index of name, so negative indices
1390 count back from the end of the array, and an index of -1 references the
1391 last element.
1392 Any element of an array may be referenced using ${name[subscript]}.
1394 The braces are required to avoid conflicts with pathname expansion. If
1395 subscript is @ or *, the word expands to all members of name. These
1396 subscripts differ only when the word appears within double quotes. If
1397 the word is double-quoted, ${name[*]} expands to a single word with the
1398 value of each array member separated by the first character of the IFS
1399 special variable, and ${name[@]} expands each element of name to a sep‐
1400 arate word. When there are no array members, ${name[@]} expands to
1401 nothing. If the double-quoted expansion occurs within a word, the
1402 expansion of the first parameter is joined with the beginning part of
1403 the original word, and the expansion of the last parameter is joined
1404 with the last part of the original word. This is analogous to the
1405 expansion of the special parameters * and @ (see Special Parameters
1406 above). ${#name[subscript]} expands to the length of ${name[sub‐
1407 script]}. If subscript is * or @, the expansion is the number of ele‐
1408 ments in the array. If the subscript used to reference an element of
1409 an indexed array evaluates to a number less than zero, it is inter‐
1410 preted as relative to one greater than the maximum index of the array,
1411 so negative indices count back from the end of the array, and an index
1412 of -1 references the last element.
1413 Referencing an array variable without a subscript is equivalent to ref‐
1415 erencing the array with a subscript of 0. Any reference to a variable
1416 using a valid subscript is legal, and bash will create an array if nec‐
1417 essary.
1418 An array variable is considered set if a subscript has been assigned a
1420 value. The null string is a valid value.
1421 It is possible to obtain the keys (indices) of an array as well as the
1423 values. ${!name[@]} and ${!name[*]} expand to the indices assigned in
1424 array variable name. The treatment when in double quotes is similar to
1425 the expansion of the special parameters @ and * within double quotes.
1426 The unset builtin is used to destroy arrays. unset name[subscript]
1428 destroys the array element at index subscript. Negative subscripts to
1429 indexed arrays are interpreted as described above. Care must be taken
1430 to avoid unwanted side effects caused by pathname expansion. unset
1431 name, where name is an array, or unset name[subscript], where subscript
1432 is * or @, removes the entire array.
1433 The declare, local, and readonly builtins each accept a -a option to
1435 specify an indexed array and a -A option to specify an associative
1436 array. If both options are supplied, -A takes precedence. The read
1437 builtin accepts a -a option to assign a list of words read from the
1438 standard input to an array. The set and declare builtins display array
1439 values in a way that allows them to be reused as assignments.
1440
1442 Expansion is performed on the command line after it has been split into
1443 words. There are seven kinds of expansion performed: brace expansion,
1444 tilde expansion, parameter and variable expansion, command substitu‐
1445 tion, arithmetic expansion, word splitting, and pathname expansion.
1446 The order of expansions is: brace expansion; tilde expansion, parameter
1448 and variable expansion, arithmetic expansion, and command substitution
1449 (done in a left-to-right fashion); word splitting; and pathname expan‐
1450 sion.
1451 On systems that can support it, there is an additional expansion avail‐
1453 able: process substitution. This is performed at the same time as
1454 tilde, parameter, variable, and arithmetic expansion and command sub‐
1455 stitution.
1456 After these expansions are performed, quote characters present in the
1458 original word are removed unless they have been quoted themselves
1459 (quote removal).
1460 Only brace expansion, word splitting, and pathname expansion can change
1462 the number of words of the expansion; other expansions expand a single
1463 word to a single word. The only exceptions to this are the expansions
1464 of "$@" and "${name[@]}" as explained above (see PARAMETERS).
1465 Brace Expansion
1467 Brace expansion is a mechanism by which arbitrary strings may be gener‐
1468 ated. This mechanism is similar to pathname expansion, but the file‐
1469 names generated need not exist. Patterns to be brace expanded take the
1470 form of an optional preamble, followed by either a series of comma-sep‐
1471 arated strings or a sequence expression between a pair of braces, fol‐
1472 lowed by an optional postscript. The preamble is prefixed to each
1473 string contained within the braces, and the postscript is then appended
1474 to each resulting string, expanding left to right.
1475 Brace expansions may be nested. The results of each expanded string
1477 are not sorted; left to right order is preserved. For example,
1478 a{d,c,b}e expands into `ade ace abe'.
1479 A sequence expression takes the form {x..y[..incr]}, where x and y are
1481 either integers or single characters, and incr, an optional increment,
1482 is an integer. When integers are supplied, the expression expands to
1483 each number between x and y, inclusive. Supplied integers may be pre‐
1484 fixed with 0 to force each term to have the same width. When either x
1485 or y begins with a zero, the shell attempts to force all generated
1486 terms to contain the same number of digits, zero-padding where neces‐
1487 sary. When characters are supplied, the expression expands to each
1488 character lexicographically between x and y, inclusive, using the
1489 default C locale. Note that both x and y must be of the same type.
1490 When the increment is supplied, it is used as the difference between
1491 each term. The default increment is 1 or -1 as appropriate.
1492 Brace expansion is performed before any other expansions, and any char‐
1494 acters special to other expansions are preserved in the result. It is
1495 strictly textual. Bash does not apply any syntactic interpretation to
1496 the context of the expansion or the text between the braces.
1497 A correctly-formed brace expansion must contain unquoted opening and
1499 closing braces, and at least one unquoted comma or a valid sequence
1500 expression. Any incorrectly formed brace expansion is left unchanged.
1501 A { or , may be quoted with a backslash to prevent its being considered
1502 part of a brace expression. To avoid conflicts with parameter expan‐
1503 sion, the string ${ is not considered eligible for brace expansion.
1504 This construct is typically used as shorthand when the common prefix of
1506 the strings to be generated is longer than in the above example:
1507 mkdir /usr/local/src/bash/{old,new,dist,bugs}
1509 or
1510 chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}
1511 Brace expansion introduces a slight incompatibility with historical
1513 versions of sh. sh does not treat opening or closing braces specially
1514 when they appear as part of a word, and preserves them in the output.
1515 Bash removes braces from words as a consequence of brace expansion.
1516 For example, a word entered to sh as file{1,2} appears identically in
1517 the output. The same word is output as file1 file2 after expansion by
1518 bash. If strict compatibility with sh is desired, start bash with the
1519 +B option or disable brace expansion with the +B option to the set com‐
1520 mand (see SHELL BUILTIN COMMANDS below).
1521 Tilde Expansion
1523 If a word begins with an unquoted tilde character (`~'), all of the
1524 characters preceding the first unquoted slash (or all characters, if
1525 there is no unquoted slash) are considered a tilde-prefix. If none of
1526 the characters in the tilde-prefix are quoted, the characters in the
1527 tilde-prefix following the tilde are treated as a possible login name.
1528 If this login name is the null string, the tilde is replaced with the
1529 value of the shell parameter HOME. If HOME is unset, the home direc‐
1530 tory of the user executing the shell is substituted instead. Other‐
1531 wise, the tilde-prefix is replaced with the home directory associated
1532 with the specified login name.
1533 If the tilde-prefix is a `~+', the value of the shell variable PWD
1535 replaces the tilde-prefix. If the tilde-prefix is a `~-', the value of
1536 the shell variable OLDPWD, if it is set, is substituted. If the char‐
1537 acters following the tilde in the tilde-prefix consist of a number N,
1538 optionally prefixed by a `+' or a `-', the tilde-prefix is replaced
1539 with the corresponding element from the directory stack, as it would be
1540 displayed by the dirs builtin invoked with the tilde-prefix as an argu‐
1541 ment. If the characters following the tilde in the tilde-prefix con‐
1542 sist of a number without a leading `+' or `-', `+' is assumed.
1543 If the login name is invalid, or the tilde expansion fails, the word is
1545 unchanged.
1546 Each variable assignment is checked for unquoted tilde-prefixes immedi‐
1548 ately following a : or the first =. In these cases, tilde expansion is
1549 also performed. Consequently, one may use filenames with tildes in
1550 assignments to PATH, MAILPATH, and CDPATH, and the shell assigns the
1551 expanded value.
1552 Parameter Expansion
1554 The `$' character introduces parameter expansion, command substitution,
1555 or arithmetic expansion. The parameter name or symbol to be expanded
1556 may be enclosed in braces, which are optional but serve to protect the
1557 variable to be expanded from characters immediately following it which
1558 could be interpreted as part of the name.
1559 When braces are used, the matching ending brace is the first `}' not
1561 escaped by a backslash or within a quoted string, and not within an
1562 embedded arithmetic expansion, command substitution, or parameter
1563 expansion.
1564 ${parameter}
1566 The value of parameter is substituted. The braces are required
1567 when parameter is a positional parameter with more than one
1568 digit, or when parameter is followed by a character which is not
1569 to be interpreted as part of its name. The parameter is a shell
1570 parameter as described above PARAMETERS) or an array reference
1571 (Arrays).
1572 If the first character of parameter is an exclamation point (!), and
1574 parameter is not a nameref, it introduces a level of variable indirec‐
1575 tion. Bash uses the value of the variable formed from the rest of
1576 parameter as the name of the variable; this variable is then expanded
1577 and that value is used in the rest of the substitution, rather than the
1578 value of parameter itself. This is known as indirect expansion. If
1579 parameter is a nameref, this expands to the name of the variable refer‐
1580 enced by parameter instead of performing the complete indirect expan‐
1581 sion. The exceptions to this are the expansions of ${!prefix*} and
1582 ${!name[@]} described below. The exclamation point must immediately
1583 follow the left brace in order to introduce indirection.
1584 In each of the cases below, word is subject to tilde expansion, parame‐
1586 ter expansion, command substitution, and arithmetic expansion.
1587 When not performing substring expansion, using the forms documented
1589 below (e.g., :-), bash tests for a parameter that is unset or null.
1590 Omitting the colon results in a test only for a parameter that is
1591 unset.
1592 ${parameter:-word}
1594 Use Default Values. If parameter is unset or null, the expan‐
1595 sion of word is substituted. Otherwise, the value of parameter
1596 is substituted.
1597 ${parameter:=word}
1598 Assign Default Values. If parameter is unset or null, the
1599 expansion of word is assigned to parameter. The value of param‐
1600 eter is then substituted. Positional parameters and special
1601 parameters may not be assigned to in this way.
1602 ${parameter:?word}
1603 Display Error if Null or Unset. If parameter is null or unset,
1604 the expansion of word (or a message to that effect if word is
1605 not present) is written to the standard error and the shell, if
1606 it is not interactive, exits. Otherwise, the value of parameter
1607 is substituted.
1608 ${parameter:+word}
1609 Use Alternate Value. If parameter is null or unset, nothing is
1610 substituted, otherwise the expansion of word is substituted.
1611 ${parameter:offset}
1612 ${parameter:offset:length}
1613 Substring Expansion. Expands to up to length characters of the
1614 value of parameter starting at the character specified by off‐
1615 set. If parameter is @, an indexed array subscripted by @ or *,
1616 or an associative array name, the results differ as described
1617 below. If length is omitted, expands to the substring of the
1618 value of parameter starting at the character specified by offset
1619 and extending to the end of the value. length and offset are
1620 arithmetic expressions (see ARITHMETIC EVALUATION below).
1621 If offset evaluates to a number less than zero, the value is
1623 used as an offset in characters from the end of the value of
1624 parameter. If length evaluates to a number less than zero, it
1625 is interpreted as an offset in characters from the end of the
1626 value of parameter rather than a number of characters, and the
1627 expansion is the characters between offset and that result.
1628 Note that a negative offset must be separated from the colon by
1629 at least one space to avoid being confused with the :- expan‐
1630 sion.
1631 If parameter is @, the result is length positional parameters
1633 beginning at offset. A negative offset is taken relative to one
1634 greater than the greatest positional parameter, so an offset of
1635 -1 evaluates to the last positional parameter. It is an expan‐
1636 sion error if length evaluates to a number less than zero.
1637 If parameter is an indexed array name subscripted by @ or *, the
1639 result is the length members of the array beginning with
1640 ${parameter[offset]}. A negative offset is taken relative to
1641 one greater than the maximum index of the specified array. It
1642 is an expansion error if length evaluates to a number less than
1643 zero.
1644 Substring expansion applied to an associative array produces
1646 undefined results.
1647 Substring indexing is zero-based unless the positional parame‐
1649 ters are used, in which case the indexing starts at 1 by
1650 default. If offset is 0, and the positional parameters are
1651 used, $0 is prefixed to the list.
1652 ${!prefix*}
1654 ${!prefix@}
1655 Names matching prefix. Expands to the names of variables whose
1656 names begin with prefix, separated by the first character of the
1657 IFS special variable. When @ is used and the expansion appears
1658 within double quotes, each variable name expands to a separate
1659 word.
1660 ${!name[@]}
1662 ${!name[*]}
1663 List of array keys. If name is an array variable, expands to
1664 the list of array indices (keys) assigned in name. If name is
1665 not an array, expands to 0 if name is set and null otherwise.
1666 When @ is used and the expansion appears within double quotes,
1667 each key expands to a separate word.
1668 ${#parameter}
1670 Parameter length. The length in characters of the value of
1671 parameter is substituted. If parameter is * or @, the value
1672 substituted is the number of positional parameters. If parame‐
1673 ter is an array name subscripted by * or @, the value substi‐
1674 tuted is the number of elements in the array. If parameter is
1675 an indexed array name subscripted by a negative number, that
1676 number is interpreted as relative to one greater than the maxi‐
1677 mum index of parameter, so negative indices count back from the
1678 end of the array, and an index of -1 references the last ele‐
1679 ment.
1680 ${parameter#word}
1682 ${parameter##word}
1683 Remove matching prefix pattern. The word is expanded to produce
1684 a pattern just as in pathname expansion. If the pattern matches
1685 the beginning of the value of parameter, then the result of the
1686 expansion is the expanded value of parameter with the shortest
1687 matching pattern (the ``#'' case) or the longest matching pat‐
1688 tern (the ``##'' case) deleted. If parameter is @ or *, the
1689 pattern removal operation is applied to each positional parame‐
1690 ter in turn, and the expansion is the resultant list. If param‐
1691 eter is an array variable subscripted with @ or *, the pattern
1692 removal operation is applied to each member of the array in
1693 turn, and the expansion is the resultant list.
1694 ${parameter%word}
1696 ${parameter%%word}
1697 Remove matching suffix pattern. The word is expanded to produce
1698 a pattern just as in pathname expansion. If the pattern matches
1699 a trailing portion of the expanded value of parameter, then the
1700 result of the expansion is the expanded value of parameter with
1701 the shortest matching pattern (the ``%'' case) or the longest
1702 matching pattern (the ``%%'' case) deleted. If parameter is @
1703 or *, the pattern removal operation is applied to each posi‐
1704 tional parameter in turn, and the expansion is the resultant
1705 list. If parameter is an array variable subscripted with @ or
1706 *, the pattern removal operation is applied to each member of
1707 the array in turn, and the expansion is the resultant list.
1708 ${parameter/pattern/string}
1710 Pattern substitution. The pattern is expanded to produce a pat‐
1711 tern just as in pathname expansion. Parameter is expanded and
1712 the longest match of pattern against its value is replaced with
1713 string. If pattern begins with /, all matches of pattern are
1714 replaced with string. Normally only the first match is
1715 replaced. If pattern begins with #, it must match at the begin‐
1716 ning of the expanded value of parameter. If pattern begins with
1717 %, it must match at the end of the expanded value of parameter.
1718 If string is null, matches of pattern are deleted and the / fol‐
1719 lowing pattern may be omitted. If the nocasematch shell option
1720 is enabled, the match is performed without regard to the case of
1721 alphabetic characters. If parameter is @ or *, the substitution
1722 operation is applied to each positional parameter in turn, and
1723 the expansion is the resultant list. If parameter is an array
1724 variable subscripted with @ or *, the substitution operation is
1725 applied to each member of the array in turn, and the expansion
1726 is the resultant list.
1727 ${parameter^pattern}
1729 ${parameter^^pattern}
1730 ${parameter,pattern}
1731 ${parameter,,pattern}
1732 Case modification. This expansion modifies the case of alpha‐
1733 betic characters in parameter. The pattern is expanded to pro‐
1734 duce a pattern just as in pathname expansion. Each character in
1735 the expanded value of parameter is tested against pattern, and,
1736 if it matches the pattern, its case is converted. The pattern
1737 should not attempt to match more than one character. The ^
1738 operator converts lowercase letters matching pattern to upper‐
1739 case; the , operator converts matching uppercase letters to low‐
1740 ercase. The ^^ and ,, expansions convert each matched character
1741 in the expanded value; the ^ and , expansions match and convert
1742 only the first character in the expanded value. If pattern is
1743 omitted, it is treated like a ?, which matches every character.
1744 If parameter is @ or *, the case modification operation is
1745 applied to each positional parameter in turn, and the expansion
1746 is the resultant list. If parameter is an array variable sub‐
1747 scripted with @ or *, the case modification operation is applied
1748 to each member of the array in turn, and the expansion is the
1749 resultant list.
1750 ${parameter@operator}
1752 Parameter transformation. The expansion is either a transforma‐
1753 tion of the value of parameter or information about parameter
1754 itself, depending on the value of operator. Each operator is a
1755 single letter:
1756 Q The expansion is a string that is the value of parameter
1758 quoted in a format that can be reused as input.
1759 E The expansion is a string that is the value of parameter
1760 with backslash escape sequences expanded as with the
1761 $'...' quoting mechansim.
1762 P The expansion is a string that is the result of expanding
1763 the value of parameter as if it were a prompt string (see
1764 PROMPTING below).
1765 A The expansion is a string in the form of an assignment
1766 statement or declare command that, if evaluated, will
1767 recreate parameter with its attributes and value.
1768 a The expansion is a string consisting of flag values rep‐
1769 resenting parameter's attributes.
1770 If parameter is @ or *, the operation is applied to each posi‐
1772 tional parameter in turn, and the expansion is the resultant
1773 list. If parameter is an array variable subscripted with @ or
1774 *, the case modification operation is applied to each member of
1775 the array in turn, and the expansion is the resultant list.
1776 The result of the expansion is subject to word splitting and
1778 pathname expansion as described below.
1779 Command Substitution
1781 Command substitution allows the output of a command to replace the com‐
1782 mand name. There are two forms:
1783 $(command)
1785 or
1786 `command`
1787 Bash performs the expansion by executing command in a subshell environ‐
1789 ment and replacing the command substitution with the standard output of
1790 the command, with any trailing newlines deleted. Embedded newlines are
1791 not deleted, but they may be removed during word splitting. The com‐
1792 mand substitution $(cat file) can be replaced by the equivalent but
1793 faster $(< file).
1794 When the old-style backquote form of substitution is used, backslash
1796 retains its literal meaning except when followed by $, `, or \. The
1797 first backquote not preceded by a backslash terminates the command sub‐
1798 stitution. When using the $(command) form, all characters between the
1799 parentheses make up the command; none are treated specially.
1800 Command substitutions may be nested. To nest when using the backquoted
1802 form, escape the inner backquotes with backslashes.
1803 If the substitution appears within double quotes, word splitting and
1805 pathname expansion are not performed on the results.
1806 Arithmetic Expansion
1808 Arithmetic expansion allows the evaluation of an arithmetic expression
1809 and the substitution of the result. The format for arithmetic expan‐
1810 sion is:
1811 $((expression))
1813 The expression is treated as if it were within double quotes, but a
1815 double quote inside the parentheses is not treated specially. All
1816 tokens in the expression undergo parameter and variable expansion, com‐
1817 mand substitution, and quote removal. The result is treated as the
1818 arithmetic expression to be evaluated. Arithmetic expansions may be
1819 nested.
1820 The evaluation is performed according to the rules listed below under
1822 ARITHMETIC EVALUATION. If expression is invalid, bash prints a message
1823 indicating failure and no substitution occurs.
1824 Process Substitution
1826 Process substitution allows a process's input or output to be referred
1827 to using a filename. It takes the form of <(list) or >(list). The
1828 process list is run asynchronously, and its input or output appears as
1829 a filename. This filename is passed as an argument to the current com‐
1830 mand as the result of the expansion. If the >(list) form is used,
1831 writing to the file will provide input for list. If the <(list) form
1832 is used, the file passed as an argument should be read to obtain the
1833 output of list. Process substitution is supported on systems that sup‐
1834 port named pipes (FIFOs) or the /dev/fd method of naming open files.
1835 When available, process substitution is performed simultaneously with
1837 parameter and variable expansion, command substitution, and arithmetic
1838 expansion.
1839 Word Splitting
1841 The shell scans the results of parameter expansion, command substitu‐
1842 tion, and arithmetic expansion that did not occur within double quotes
1843 for word splitting.
1844 The shell treats each character of IFS as a delimiter, and splits the
1846 results of the other expansions into words using these characters as
1847 field terminators. If IFS is unset, or its value is exactly
1848 <space><tab><newline>, the default, then sequences of <space>, <tab>,
1849 and <newline> at the beginning and end of the results of the previous
1850 expansions are ignored, and any sequence of IFS characters not at the
1851 beginning or end serves to delimit words. If IFS has a value other
1852 than the default, then sequences of the whitespace characters space,
1853 tab, and newline are ignored at the beginning and end of the word, as
1854 long as the whitespace character is in the value of IFS (an IFS white‐
1855 space character). Any character in IFS that is not IFS whitespace,
1856 along with any adjacent IFS whitespace characters, delimits a field. A
1857 sequence of IFS whitespace characters is also treated as a delimiter.
1858 If the value of IFS is null, no word splitting occurs.
1859 Explicit null arguments ("" or '') are retained and passed to commands
1861 as empty strings. Unquoted implicit null arguments, resulting from the
1862 expansion of parameters that have no values, are removed. If a parame‐
1863 ter with no value is expanded within double quotes, a null argument
1864 results and is retained and passed to a command as an empty string.
1865 When a quoted null argument appears as part of a word whose expansion
1866 is non-null, the null argument is removed. That is, the word -d''
1867 becomes -d after word splitting and null argument removal.
1868 Note that if no expansion occurs, no splitting is performed.
1870 Pathname Expansion
1872 After word splitting, unless the -f option has been set, bash scans
1873 each word for the characters *, ?, and [. If one of these characters
1874 appears, then the word is regarded as a pattern, and replaced with an
1875 alphabetically sorted list of filenames matching the pattern (see Pat‐
1876 tern Matching below). If no matching filenames are found, and the
1877 shell option nullglob is not enabled, the word is left unchanged. If
1878 the nullglob option is set, and no matches are found, the word is
1879 removed. If the failglob shell option is set, and no matches are
1880 found, an error message is printed and the command is not executed. If
1881 the shell option nocaseglob is enabled, the match is performed without
1882 regard to the case of alphabetic characters. When a pattern is used
1883 for pathname expansion, the character ``.'' at the start of a name or
1884 immediately following a slash must be matched explicitly, unless the
1885 shell option dotglob is set. When matching a pathname, the slash char‐
1886 acter must always be matched explicitly. In other cases, the ``.''
1887 character is not treated specially. See the description of shopt below
1888 under SHELL BUILTIN COMMANDS for a description of the nocaseglob, null‐
1889 glob, failglob, and dotglob shell options.
1890 The GLOBIGNORE shell variable may be used to restrict the set of file‐
1892 names matching a pattern. If GLOBIGNORE is set, each matching filename
1893 that also matches one of the patterns in GLOBIGNORE is removed from the
1894 list of matches. If the nocaseglob option is set, the matching against
1895 the patterns in GLOBIGNORE is performed without regard to case. The
1896 filenames ``.'' and ``..'' are always ignored when GLOBIGNORE is set
1897 and not null. However, setting GLOBIGNORE to a non-null value has the
1898 effect of enabling the dotglob shell option, so all other filenames
1899 beginning with a ``.'' will match. To get the old behavior of ignor‐
1900 ing filenames beginning with a ``.'', make ``.*'' one of the patterns
1901 in GLOBIGNORE. The dotglob option is disabled when GLOBIGNORE is
1902 unset. The pattern matching honors the setting of the extglob shell
1903 option.
1904 Pattern Matching
1906 Any character that appears in a pattern, other than the special pattern
1908 characters described below, matches itself. The NUL character may not
1909 occur in a pattern. A backslash escapes the following character; the
1910 escaping backslash is discarded when matching. The special pattern
1911 characters must be quoted if they are to be matched literally.
1912 The special pattern characters have the following meanings:
1914 * Matches any string, including the null string. When the
1916 globstar shell option is enabled, and * is used in a
1917 pathname expansion context, two adjacent *s used as a
1918 single pattern will match all files and zero or more
1919 directories and subdirectories. If followed by a /, two
1920 adjacent *s will match only directories and subdirecto‐
1921 ries.
1922 ? Matches any single character.
1923 [...] Matches any one of the enclosed characters. A pair of
1924 characters separated by a hyphen denotes a range expres‐
1925 sion; any character that falls between those two charac‐
1926 ters, inclusive, using the current locale's collating
1927 sequence and character set, is matched. If the first
1928 character following the [ is a ! or a ^ then any charac‐
1929 ter not enclosed is matched. The sorting order of char‐
1930 acters in range expressions is determined by the current
1931 locale and the values of the LC_COLLATE or LC_ALL shell
1932 variables, if set. To obtain the traditional interpreta‐
1933 tion of range expressions, where [a-d] is equivalent to
1934 [abcd], set value of the LC_ALL shell variable to C, or
1935 enable the globasciiranges shell option. A - may be
1936 matched by including it as the first or last character in
1937 the set. A ] may be matched by including it as the first
1938 character in the set.
1939 Within [ and ], character classes can be specified using
1941 the syntax [:class:], where class is one of the following
1942 classes defined in the POSIX standard:
1943 alnum alpha ascii blank cntrl digit graph lower print
1944 punct space upper word xdigit
1945 A character class matches any character belonging to that
1946 class. The word character class matches letters, digits,
1947 and the character _.
1948 Within [ and ], an equivalence class can be specified
1950 using the syntax [=c=], which matches all characters with
1951 the same collation weight (as defined by the current
1952 locale) as the character c.
1953 Within [ and ], the syntax [.symbol.] matches the collat‐
1955 ing symbol symbol.
1956 If the extglob shell option is enabled using the shopt builtin, several
1958 extended pattern matching operators are recognized. In the following
1959 description, a pattern-list is a list of one or more patterns separated
1960 by a |. Composite patterns may be formed using one or more of the fol‐
1961 lowing sub-patterns:
1962 ?(pattern-list)
1964 Matches zero or one occurrence of the given patterns
1965 *(pattern-list)
1966 Matches zero or more occurrences of the given patterns
1967 +(pattern-list)
1968 Matches one or more occurrences of the given patterns
1969 @(pattern-list)
1970 Matches one of the given patterns
1971 !(pattern-list)
1972 Matches anything except one of the given patterns
1973 Quote Removal
1975 After the preceding expansions, all unquoted occurrences of the charac‐
1976 ters \, ', and " that did not result from one of the above expansions
1977 are removed.
1978
1980 Before a command is executed, its input and output may be redirected
1981 using a special notation interpreted by the shell. Redirection allows
1982 commands' file handles to be duplicated, opened, closed, made to refer
1983 to different files, and can change the files the command reads from and
1984 writes to. Redirection may also be used to modify file handles in the
1985 current shell execution environment. The following redirection opera‐
1986 tors may precede or appear anywhere within a simple command or may fol‐
1987 low a command. Redirections are processed in the order they appear,
1988 from left to right.
1989 Each redirection that may be preceded by a file descriptor number may
1991 instead be preceded by a word of the form {varname}. In this case, for
1992 each redirection operator except >&- and <&-, the shell will allocate a
1993 file descriptor greater than or equal to 10 and assign it to varname.
1994 If >&- or <&- is preceded by {varname}, the value of varname defines
1995 the file descriptor to close.
1996 In the following descriptions, if the file descriptor number is omit‐
1998 ted, and the first character of the redirection operator is <, the re‐
1999 direction refers to the standard input (file descriptor 0). If the
2000 first character of the redirection operator is >, the redirection
2001 refers to the standard output (file descriptor 1).
2002 The word following the redirection operator in the following descrip‐
2004 tions, unless otherwise noted, is subjected to brace expansion, tilde
2005 expansion, parameter and variable expansion, command substitution,
2006 arithmetic expansion, quote removal, pathname expansion, and word
2007 splitting. If it expands to more than one word, bash reports an error.
2008 Note that the order of redirections is significant. For example, the
2010 command
2011 ls > dirlist 2>&1
2013 directs both standard output and standard error to the file dirlist,
2015 while the command
2016 ls 2>&1 > dirlist
2018 directs only the standard output to file dirlist, because the standard
2020 error was duplicated from the standard output before the standard out‐
2021 put was redirected to dirlist.
2022 Bash handles several filenames specially when they are used in redirec‐
2024 tions, as described in the following table. If the operating system on
2025 which bash is running provides these special files, bash will use them;
2026 otherwise it will emulate them internally with the behavior described
2027 below.
2028 /dev/fd/fd
2030 If fd is a valid integer, file descriptor fd is dupli‐
2031 cated.
2032 /dev/stdin
2033 File descriptor 0 is duplicated.
2034 /dev/stdout
2035 File descriptor 1 is duplicated.
2036 /dev/stderr
2037 File descriptor 2 is duplicated.
2038 /dev/tcp/host/port
2039 If host is a valid hostname or Internet address, and port
2040 is an integer port number or service name, bash attempts
2041 to open the corresponding TCP socket.
2042 /dev/udp/host/port
2043 If host is a valid hostname or Internet address, and port
2044 is an integer port number or service name, bash attempts
2045 to open the corresponding UDP socket.
2046 A failure to open or create a file causes the redirection to fail.
2048 Redirections using file descriptors greater than 9 should be used with
2050 care, as they may conflict with file descriptors the shell uses inter‐
2051 nally.
2052 Redirecting Input
2054 Redirection of input causes the file whose name results from the expan‐
2055 sion of word to be opened for reading on file descriptor n, or the
2056 standard input (file descriptor 0) if n is not specified.
2057 The general format for redirecting input is:
2059 [n]<word
2061 Redirecting Output
2063 Redirection of output causes the file whose name results from the
2064 expansion of word to be opened for writing on file descriptor n, or the
2065 standard output (file descriptor 1) if n is not specified. If the file
2066 does not exist it is created; if it does exist it is truncated to zero
2067 size.
2068 The general format for redirecting output is:
2070 [n]>word
2072 If the redirection operator is >, and the noclobber option to the set
2074 builtin has been enabled, the redirection will fail if the file whose
2075 name results from the expansion of word exists and is a regular file.
2076 If the redirection operator is >|, or the redirection operator is > and
2077 the noclobber option to the set builtin command is not enabled, the re‐
2078 direction is attempted even if the file named by word exists.
2079 Appending Redirected Output
2081 Redirection of output in this fashion causes the file whose name
2082 results from the expansion of word to be opened for appending on file
2083 descriptor n, or the standard output (file descriptor 1) if n is not
2084 specified. If the file does not exist it is created.
2085 The general format for appending output is:
2087 [n]>>word
2089 Redirecting Standard Output and Standard Error
2091 This construct allows both the standard output (file descriptor 1) and
2092 the standard error output (file descriptor 2) to be redirected to the
2093 file whose name is the expansion of word.
2094 There are two formats for redirecting standard output and standard
2096 error:
2097 &>word
2099 and
2100 >&word
2101 Of the two forms, the first is preferred. This is semantically equiva‐
2103 lent to
2104 >word 2>&1
2106 When using the second form, word may not expand to a number or -. If
2108 it does, other redirection operators apply (see Duplicating File
2109 Descriptors below) for compatibility reasons.
2110 Appending Standard Output and Standard Error
2112 This construct allows both the standard output (file descriptor 1) and
2113 the standard error output (file descriptor 2) to be appended to the
2114 file whose name is the expansion of word.
2115 The format for appending standard output and standard error is:
2117 &>>word
2119 This is semantically equivalent to
2121 >>word 2>&1
2123 (see Duplicating File Descriptors below).
2125 Here Documents
2127 This type of redirection instructs the shell to read input from the
2128 current source until a line containing only delimiter (with no trailing
2129 blanks) is seen. All of the lines read up to that point are then used
2130 as the standard input (or file descriptor n if n is specified) for a
2131 command.
2132 The format of here-documents is:
2134 [n]<<[-]word
2136 here-document
2137 delimiter
2138 No parameter and variable expansion, command substitution, arithmetic
2140 expansion, or pathname expansion is performed on word. If any part of
2141 word is quoted, the delimiter is the result of quote removal on word,
2142 and the lines in the here-document are not expanded. If word is
2143 unquoted, all lines of the here-document are subjected to parameter
2144 expansion, command substitution, and arithmetic expansion, the charac‐
2145 ter sequence \<newline> is ignored, and \ must be used to quote the
2146 characters \, $, and `.
2147 If the redirection operator is <<-, then all leading tab characters are
2149 stripped from input lines and the line containing delimiter. This
2150 allows here-documents within shell scripts to be indented in a natural
2151 fashion.
2152 Here Strings
2154 A variant of here documents, the format is:
2155 [n]<<<word
2157 The word undergoes brace expansion, tilde expansion, parameter and
2159 variable expansion, command substitution, arithmetic expansion, and
2160 quote removal. Pathname expansion and word splitting are not per‐
2161 formed. The result is supplied as a single string, with a newline
2162 appended, to the command on its standard input (or file descriptor n if
2163 n is specified).
2164 Duplicating File Descriptors
2166 The redirection operator
2167 [n]<&word
2169 is used to duplicate input file descriptors. If word expands to one or
2171 more digits, the file descriptor denoted by n is made to be a copy of
2172 that file descriptor. If the digits in word do not specify a file
2173 descriptor open for input, a redirection error occurs. If word evalu‐
2174 ates to -, file descriptor n is closed. If n is not specified, the
2175 standard input (file descriptor 0) is used.
2176 The operator
2178 [n]>&word
2180 is used similarly to duplicate output file descriptors. If n is not
2182 specified, the standard output (file descriptor 1) is used. If the
2183 digits in word do not specify a file descriptor open for output, a re‐
2184 direction error occurs. If word evaluates to -, file descriptor n is
2185 closed. As a special case, if n is omitted, and word does not expand
2186 to one or more digits or -, the standard output and standard error are
2187 redirected as described previously.
2188 Moving File Descriptors
2190 The redirection operator
2191 [n]<&digit-
2193 moves the file descriptor digit to file descriptor n, or the standard
2195 input (file descriptor 0) if n is not specified. digit is closed after
2196 being duplicated to n.
2197 Similarly, the redirection operator
2199 [n]>&digit-
2201 moves the file descriptor digit to file descriptor n, or the standard
2203 output (file descriptor 1) if n is not specified.
2204 Opening File Descriptors for Reading and Writing
2206 The redirection operator
2207 [n]<>word
2209 causes the file whose name is the expansion of word to be opened for
2211 both reading and writing on file descriptor n, or on file descriptor 0
2212 if n is not specified. If the file does not exist, it is created.
2213
2215 Aliases allow a string to be substituted for a word when it is used as
2216 the first word of a simple command. The shell maintains a list of
2217 aliases that may be set and unset with the alias and unalias builtin
2218 commands (see SHELL BUILTIN COMMANDS below). The first word of each
2219 simple command, if unquoted, is checked to see if it has an alias. If
2220 so, that word is replaced by the text of the alias. The characters /,
2221 $, `, and = and any of the shell metacharacters or quoting characters
2222 listed above may not appear in an alias name. The replacement text may
2223 contain any valid shell input, including shell metacharacters. The
2224 first word of the replacement text is tested for aliases, but a word
2225 that is identical to an alias being expanded is not expanded a second
2226 time. This means that one may alias ls to ls -F, for instance, and
2227 bash does not try to recursively expand the replacement text. If the
2228 last character of the alias value is a blank, then the next command
2229 word following the alias is also checked for alias expansion.
2230 Aliases are created and listed with the alias command, and removed with
2232 the unalias command.
2233 There is no mechanism for using arguments in the replacement text. If
2235 arguments are needed, a shell function should be used (see FUNCTIONS
2236 below).
2237 Aliases are not expanded when the shell is not interactive, unless the
2239 expand_aliases shell option is set using shopt (see the description of
2240 shopt under SHELL BUILTIN COMMANDS below).
2241 The rules concerning the definition and use of aliases are somewhat
2243 confusing. Bash always reads at least one complete line of input
2244 before executing any of the commands on that line. Aliases are
2245 expanded when a command is read, not when it is executed. Therefore,
2246 an alias definition appearing on the same line as another command does
2247 not take effect until the next line of input is read. The commands
2248 following the alias definition on that line are not affected by the new
2249 alias. This behavior is also an issue when functions are executed.
2250 Aliases are expanded when a function definition is read, not when the
2251 function is executed, because a function definition is itself a com‐
2252 mand. As a consequence, aliases defined in a function are not avail‐
2253 able until after that function is executed. To be safe, always put
2254 alias definitions on a separate line, and do not use alias in compound
2255 commands.
2256 For almost every purpose, aliases are superseded by shell functions.
2258
2260 A shell function, defined as described above under SHELL GRAMMAR,
2261 stores a series of commands for later execution. When the name of a
2262 shell function is used as a simple command name, the list of commands
2263 associated with that function name is executed. Functions are executed
2264 in the context of the current shell; no new process is created to
2265 interpret them (contrast this with the execution of a shell script).
2266 When a function is executed, the arguments to the function become the
2267 positional parameters during its execution. The special parameter # is
2268 updated to reflect the change. Special parameter 0 is unchanged. The
2269 first element of the FUNCNAME variable is set to the name of the func‐
2270 tion while the function is executing.
2271 All other aspects of the shell execution environment are identical
2273 between a function and its caller with these exceptions: the DEBUG and
2274 RETURN traps (see the description of the trap builtin under SHELL
2275 BUILTIN COMMANDS below) are not inherited unless the function has been
2276 given the trace attribute (see the description of the declare builtin
2277 below) or the -o functrace shell option has been enabled with the set
2278 builtin (in which case all functions inherit the DEBUG and RETURN
2279 traps), and the ERR trap is not inherited unless the -o errtrace shell
2280 option has been enabled.
2281 Variables local to the function may be declared with the local builtin
2283 command. Ordinarily, variables and their values are shared between the
2284 function and its caller.
2285 The FUNCNEST variable, if set to a numeric value greater than 0,
2287 defines a maximum function nesting level. Function invocations that
2288 exceed the limit cause the entire command to abort.
2289 If the builtin command return is executed in a function, the function
2291 completes and execution resumes with the next command after the func‐
2292 tion call. Any command associated with the RETURN trap is executed
2293 before execution resumes. When a function completes, the values of the
2294 positional parameters and the special parameter # are restored to the
2295 values they had prior to the function's execution.
2296 Function names and definitions may be listed with the -f option to the
2298 declare or typeset builtin commands. The -F option to declare or type‐
2299 set will list the function names only (and optionally the source file
2300 and line number, if the extdebug shell option is enabled). Functions
2301 may be exported so that subshells automatically have them defined with
2302 the -f option to the export builtin. A function definition may be
2303 deleted using the -f option to the unset builtin. Note that shell
2304 functions and variables with the same name may result in multiple iden‐
2305 tically-named entries in the environment passed to the shell's chil‐
2306 dren. Care should be taken in cases where this may cause a problem.
2307 Functions may be recursive. The FUNCNEST variable may be used to limit
2309 the depth of the function call stack and restrict the number of func‐
2310 tion invocations. By default, no limit is imposed on the number of
2311 recursive calls.
2312
2314 The shell allows arithmetic expressions to be evaluated, under certain
2315 circumstances (see the let and declare builtin commands, the (( com‐
2316 pound command, and Arithmetic Expansion). Evaluation is done in fixed-
2317 width integers with no check for overflow, though division by 0 is
2318 trapped and flagged as an error. The operators and their precedence,
2319 associativity, and values are the same as in the C language. The fol‐
2320 lowing list of operators is grouped into levels of equal-precedence
2321 operators. The levels are listed in order of decreasing precedence.
2322 id++ id--
2324 variable post-increment and post-decrement
2325 ++id --id
2326 variable pre-increment and pre-decrement
2327 - + unary minus and plus
2328 ! ~ logical and bitwise negation
2329 ** exponentiation
2330 * / % multiplication, division, remainder
2331 + - addition, subtraction
2332 << >> left and right bitwise shifts
2333 <= >= < >
2334 comparison
2335 == != equality and inequality
2336 & bitwise AND
2337 ^ bitwise exclusive OR
2338 | bitwise OR
2339 && logical AND
2340 || logical OR
2341 expr?expr:expr
2342 conditional operator
2343 = *= /= %= += -= <<= >>= &= ^= |=
2344 assignment
2345 expr1 , expr2
2346 comma
2347 Shell variables are allowed as operands; parameter expansion is per‐
2349 formed before the expression is evaluated. Within an expression, shell
2350 variables may also be referenced by name without using the parameter
2351 expansion syntax. A shell variable that is null or unset evaluates to
2352 0 when referenced by name without using the parameter expansion syntax.
2353 The value of a variable is evaluated as an arithmetic expression when
2354 it is referenced, or when a variable which has been given the integer
2355 attribute using declare -i is assigned a value. A null value evaluates
2356 to 0. A shell variable need not have its integer attribute turned on
2357 to be used in an expression.
2358 Constants with a leading 0 are interpreted as octal numbers. A leading
2360 0x or 0X denotes hexadecimal. Otherwise, numbers take the form
2361 [base#]n, where the optional base is a decimal number between 2 and 64
2362 representing the arithmetic base, and n is a number in that base. If
2363 base# is omitted, then base 10 is used. When specifying n, the digits
2364 greater than 9 are represented by the lowercase letters, the uppercase
2365 letters, @, and _, in that order. If base is less than or equal to 36,
2366 lowercase and uppercase letters may be used interchangeably to repre‐
2367 sent numbers between 10 and 35.
2368 Operators are evaluated in order of precedence. Sub-expressions in
2370 parentheses are evaluated first and may override the precedence rules
2371 above.
2372
2374 Conditional expressions are used by the [[ compound command and the
2375 test and [ builtin commands to test file attributes and perform string
2376 and arithmetic comparisons. Expressions are formed from the following
2377 unary or binary primaries. Bash handles several filenames specially
2378 when they are used in expressions. If the operating system on which
2379 bash is running provides these special files, bash will use them; oth‐
2380 erwise it will emulate them internally with this behavior: If any file
2381 argument to one of the primaries is of the form /dev/fd/n, then file
2382 descriptor n is checked. If the file argument to one of the primaries
2383 is one of /dev/stdin, /dev/stdout, or /dev/stderr, file descriptor 0,
2384 1, or 2, respectively, is checked.
2385 Unless otherwise specified, primaries that operate on files follow sym‐
2387 bolic links and operate on the target of the link, rather than the link
2388 itself.
2389 When used with [[, the < and > operators sort lexicographically using
2391 the current locale. The test command sorts using ASCII ordering.
2392 -a file
2394 True if file exists.
2395 -b file
2396 True if file exists and is a block special file.
2397 -c file
2398 True if file exists and is a character special file.
2399 -d file
2400 True if file exists and is a directory.
2401 -e file
2402 True if file exists.
2403 -f file
2404 True if file exists and is a regular file.
2405 -g file
2406 True if file exists and is set-group-id.
2407 -h file
2408 True if file exists and is a symbolic link.
2409 -k file
2410 True if file exists and its ``sticky'' bit is set.
2411 -p file
2412 True if file exists and is a named pipe (FIFO).
2413 -r file
2414 True if file exists and is readable.
2415 -s file
2416 True if file exists and has a size greater than zero.
2417 -t fd True if file descriptor fd is open and refers to a terminal.
2418 -u file
2419 True if file exists and its set-user-id bit is set.
2420 -w file
2421 True if file exists and is writable.
2422 -x file
2423 True if file exists and is executable.
2424 -G file
2425 True if file exists and is owned by the effective group id.
2426 -L file
2427 True if file exists and is a symbolic link.
2428 -N file
2429 True if file exists and has been modified since it was last
2430 read.
2431 -O file
2432 True if file exists and is owned by the effective user id.
2433 -S file
2434 True if file exists and is a socket.
2435 file1 -ef file2
2436 True if file1 and file2 refer to the same device and inode num‐
2437 bers.
2438 file1 -nt file2
2439 True if file1 is newer (according to modification date) than
2440 file2, or if file1 exists and file2 does not.
2441 file1 -ot file2
2442 True if file1 is older than file2, or if file2 exists and file1
2443 does not.
2444 -o optname
2445 True if the shell option optname is enabled. See the list of
2446 options under the description of the -o option to the set
2447 builtin below.
2448 -v varname
2449 True if the shell variable varname is set (has been assigned a
2450 value).
2451 -R varname
2452 True if the shell variable varname is set and is a name refer‐
2453 ence.
2454 -z string
2455 True if the length of string is zero.
2456 string
2457 -n string
2458 True if the length of string is non-zero.
2459 string1 == string2
2461 string1 = string2
2462 True if the strings are equal. = should be used with the test
2463 command for POSIX conformance. When used with the [[ command,
2464 this performs pattern matching as described above (Compound Com‐
2465 mands).
2466 string1 != string2
2468 True if the strings are not equal.
2469 string1 < string2
2471 True if string1 sorts before string2 lexicographically.
2472 string1 > string2
2474 True if string1 sorts after string2 lexicographically.
2475 arg1 OP arg2
2477 OP is one of -eq, -ne, -lt, -le, -gt, or -ge. These arithmetic
2478 binary operators return true if arg1 is equal to, not equal to,
2479 less than, less than or equal to, greater than, or greater than
2480 or equal to arg2, respectively. Arg1 and arg2 may be positive
2481 or negative integers.
2482
2484 When a simple command is executed, the shell performs the following
2485 expansions, assignments, and redirections, from left to right.
2486 1. The words that the parser has marked as variable assignments
2488 (those preceding the command name) and redirections are saved
2489 for later processing.
2490 2. The words that are not variable assignments or redirections are
2492 expanded. If any words remain after expansion, the first word
2493 is taken to be the name of the command and the remaining words
2494 are the arguments.
2495 3. Redirections are performed as described above under REDIRECTION.
2497 4. The text after the = in each variable assignment undergoes tilde
2499 expansion, parameter expansion, command substitution, arithmetic
2500 expansion, and quote removal before being assigned to the vari‐
2501 able.
2502 If no command name results, the variable assignments affect the current
2504 shell environment. Otherwise, the variables are added to the environ‐
2505 ment of the executed command and do not affect the current shell envi‐
2506 ronment. If any of the assignments attempts to assign a value to a
2507 readonly variable, an error occurs, and the command exits with a non-
2508 zero status.
2509 If no command name results, redirections are performed, but do not
2511 affect the current shell environment. A redirection error causes the
2512 command to exit with a non-zero status.
2513 If there is a command name left after expansion, execution proceeds as
2515 described below. Otherwise, the command exits. If one of the expan‐
2516 sions contained a command substitution, the exit status of the command
2517 is the exit status of the last command substitution performed. If
2518 there were no command substitutions, the command exits with a status of
2519 zero.
2520
2522 After a command has been split into words, if it results in a simple
2523 command and an optional list of arguments, the following actions are
2524 taken.
2525 If the command name contains no slashes, the shell attempts to locate
2527 it. If there exists a shell function by that name, that function is
2528 invoked as described above in FUNCTIONS. If the name does not match a
2529 function, the shell searches for it in the list of shell builtins. If
2530 a match is found, that builtin is invoked.
2531 If the name is neither a shell function nor a builtin, and contains no
2533 slashes, bash searches each element of the PATH for a directory con‐
2534 taining an executable file by that name. Bash uses a hash table to
2535 remember the full pathnames of executable files (see hash under SHELL
2536 BUILTIN COMMANDS below). A full search of the directories in PATH is
2537 performed only if the command is not found in the hash table. If the
2538 search is unsuccessful, the shell searches for a defined shell function
2539 named command_not_found_handle. If that function exists, it is invoked
2540 with the original command and the original command's arguments as its
2541 arguments, and the function's exit status becomes the exit status of
2542 the shell. If that function is not defined, the shell prints an error
2543 message and returns an exit status of 127.
2544 If the search is successful, or if the command name contains one or
2546 more slashes, the shell executes the named program in a separate execu‐
2547 tion environment. Argument 0 is set to the name given, and the remain‐
2548 ing arguments to the command are set to the arguments given, if any.
2549 If this execution fails because the file is not in executable format,
2551 and the file is not a directory, it is assumed to be a shell script, a
2552 file containing shell commands. A subshell is spawned to execute it.
2553 This subshell reinitializes itself, so that the effect is as if a new
2554 shell had been invoked to handle the script, with the exception that
2555 the locations of commands remembered by the parent (see hash below
2556 under SHELL BUILTIN COMMANDS) are retained by the child.
2557 If the program is a file beginning with #!, the remainder of the first
2559 line specifies an interpreter for the program. The shell executes the
2560 specified interpreter on operating systems that do not handle this exe‐
2561 cutable format themselves. The arguments to the interpreter consist of
2562 a single optional argument following the interpreter name on the first
2563 line of the program, followed by the name of the program, followed by
2564 the command arguments, if any.
2565
2567 The shell has an execution environment, which consists of the follow‐
2568 ing:
2569 · open files inherited by the shell at invocation, as modified by
2571 redirections supplied to the exec builtin
2572 · the current working directory as set by cd, pushd, or popd, or
2574 inherited by the shell at invocation
2575 · the file creation mode mask as set by umask or inherited from
2577 the shell's parent
2578 · current traps set by trap
2580 · shell parameters that are set by variable assignment or with set
2582 or inherited from the shell's parent in the environment
2583 · shell functions defined during execution or inherited from the
2585 shell's parent in the environment
2586 · options enabled at invocation (either by default or with com‐
2588 mand-line arguments) or by set
2589 · options enabled by shopt
2591 · shell aliases defined with alias
2593 · various process IDs, including those of background jobs, the
2595 value of $$, and the value of PPID
2596 When a simple command other than a builtin or shell function is to be
2598 executed, it is invoked in a separate execution environment that con‐
2599 sists of the following. Unless otherwise noted, the values are inher‐
2600 ited from the shell.
2601 · the shell's open files, plus any modifications and additions
2604 specified by redirections to the command
2605 · the current working directory
2607 · the file creation mode mask
2609 · shell variables and functions marked for export, along with
2611 variables exported for the command, passed in the environment
2612 · traps caught by the shell are reset to the values inherited from
2614 the shell's parent, and traps ignored by the shell are ignored
2615 A command invoked in this separate environment cannot affect the
2617 shell's execution environment.
2618 Command substitution, commands grouped with parentheses, and asynchro‐
2620 nous commands are invoked in a subshell environment that is a duplicate
2621 of the shell environment, except that traps caught by the shell are
2622 reset to the values that the shell inherited from its parent at invoca‐
2623 tion. Builtin commands that are invoked as part of a pipeline are also
2624 executed in a subshell environment. Changes made to the subshell envi‐
2625 ronment cannot affect the shell's execution environment.
2626 Subshells spawned to execute command substitutions inherit the value of
2628 the -e option from the parent shell. When not in posix mode, bash
2629 clears the -e option in such subshells.
2630 If a command is followed by a & and job control is not active, the
2632 default standard input for the command is the empty file /dev/null.
2633 Otherwise, the invoked command inherits the file descriptors of the
2634 calling shell as modified by redirections.
2635
2637 When a program is invoked it is given an array of strings called the
2638 environment. This is a list of name-value pairs, of the form
2639 name=value.
2640 The shell provides several ways to manipulate the environment. On
2642 invocation, the shell scans its own environment and creates a parameter
2643 for each name found, automatically marking it for export to child pro‐
2644 cesses. Executed commands inherit the environment. The export and
2645 declare -x commands allow parameters and functions to be added to and
2646 deleted from the environment. If the value of a parameter in the envi‐
2647 ronment is modified, the new value becomes part of the environment,
2648 replacing the old. The environment inherited by any executed command
2649 consists of the shell's initial environment, whose values may be modi‐
2650 fied in the shell, less any pairs removed by the unset command, plus
2651 any additions via the export and declare -x commands.
2652 The environment for any simple command or function may be augmented
2654 temporarily by prefixing it with parameter assignments, as described
2655 above in PARAMETERS. These assignment statements affect only the envi‐
2656 ronment seen by that command.
2657 If the -k option is set (see the set builtin command below), then all
2659 parameter assignments are placed in the environment for a command, not
2660 just those that precede the command name.
2661 When bash invokes an external command, the variable _ is set to the
2663 full filename of the command and passed to that command in its environ‐
2664 ment.
2665
2667 The exit status of an executed command is the value returned by the
2668 waitpid system call or equivalent function. Exit statuses fall between
2669 0 and 255, though, as explained below, the shell may use values above
2670 125 specially. Exit statuses from shell builtins and compound commands
2671 are also limited to this range. Under certain circumstances, the shell
2672 will use special values to indicate specific failure modes.
2673 For the shell's purposes, a command which exits with a zero exit status
2675 has succeeded. An exit status of zero indicates success. A non-zero
2676 exit status indicates failure. When a command terminates on a fatal
2677 signal N, bash uses the value of 128+N as the exit status.
2678 If a command is not found, the child process created to execute it
2680 returns a status of 127. If a command is found but is not executable,
2681 the return status is 126.
2682 If a command fails because of an error during expansion or redirection,
2684 the exit status is greater than zero.
2685 Shell builtin commands return a status of 0 (true) if successful, and
2687 non-zero (false) if an error occurs while they execute. All builtins
2688 return an exit status of 2 to indicate incorrect usage, generally
2689 invalid options or missing arguments.
2690 Bash itself returns the exit status of the last command executed,
2692 unless a syntax error occurs, in which case it exits with a non-zero
2693 value. See also the exit builtin command below.
2694
2696 When bash is interactive, in the absence of any traps, it ignores
2697 SIGTERM (so that kill 0 does not kill an interactive shell), and SIGINT
2698 is caught and handled (so that the wait builtin is interruptible). In
2699 all cases, bash ignores SIGQUIT. If job control is in effect, bash
2700 ignores SIGTTIN, SIGTTOU, and SIGTSTP.
2701 Non-builtin commands run by bash have signal handlers set to the values
2703 inherited by the shell from its parent. When job control is not in
2704 effect, asynchronous commands ignore SIGINT and SIGQUIT in addition to
2705 these inherited handlers. Commands run as a result of command substi‐
2706 tution ignore the keyboard-generated job control signals SIGTTIN, SIGT‐
2707 TOU, and SIGTSTP.
2708 The shell exits by default upon receipt of a SIGHUP. Before exiting,
2710 an interactive shell resends the SIGHUP to all jobs, running or
2711 stopped. Stopped jobs are sent SIGCONT to ensure that they receive the
2712 SIGHUP. To prevent the shell from sending the signal to a particular
2713 job, it should be removed from the jobs table with the disown builtin
2714 (see SHELL BUILTIN COMMANDS below) or marked to not receive SIGHUP
2715 using disown -h.
2716 If the huponexit shell option has been set with shopt, bash sends a
2718 SIGHUP to all jobs when an interactive login shell exits.
2719 If bash is waiting for a command to complete and receives a signal for
2721 which a trap has been set, the trap will not be executed until the com‐
2722 mand completes. When bash is waiting for an asynchronous command via
2723 the wait builtin, the reception of a signal for which a trap has been
2724 set will cause the wait builtin to return immediately with an exit sta‐
2725 tus greater than 128, immediately after which the trap is executed.
2726
2728 Job control refers to the ability to selectively stop (suspend) the
2729 execution of processes and continue (resume) their execution at a later
2730 point. A user typically employs this facility via an interactive
2731 interface supplied jointly by the operating system kernel's terminal
2732 driver and bash.
2733 The shell associates a job with each pipeline. It keeps a table of
2735 currently executing jobs, which may be listed with the jobs command.
2736 When bash starts a job asynchronously (in the background), it prints a
2737 line that looks like:
2738 [1] 25647
2740 indicating that this job is job number 1 and that the process ID of the
2742 last process in the pipeline associated with this job is 25647. All of
2743 the processes in a single pipeline are members of the same job. Bash
2744 uses the job abstraction as the basis for job control.
2745 To facilitate the implementation of the user interface to job control,
2747 the operating system maintains the notion of a current terminal process
2748 group ID. Members of this process group (processes whose process group
2749 ID is equal to the current terminal process group ID) receive keyboard-
2750 generated signals such as SIGINT. These processes are said to be in
2751 the foreground. Background processes are those whose process group ID
2752 differs from the terminal's; such processes are immune to keyboard-gen‐
2753 erated signals. Only foreground processes are allowed to read from or,
2754 if the user so specifies with stty tostop, write to the terminal.
2755 Background processes which attempt to read from (write to when stty
2756 tostop is in effect) the terminal are sent a SIGTTIN (SIGTTOU) signal
2757 by the kernel's terminal driver, which, unless caught, suspends the
2758 process.
2759 If the operating system on which bash is running supports job control,
2761 bash contains facilities to use it. Typing the suspend character (typ‐
2762 ically ^Z, Control-Z) while a process is running causes that process to
2763 be stopped and returns control to bash. Typing the delayed suspend
2764 character (typically ^Y, Control-Y) causes the process to be stopped
2765 when it attempts to read input from the terminal, and control to be
2766 returned to bash. The user may then manipulate the state of this job,
2767 using the bg command to continue it in the background, the fg command
2768 to continue it in the foreground, or the kill command to kill it. A ^Z
2769 takes effect immediately, and has the additional side effect of causing
2770 pending output and typeahead to be discarded.
2771 There are a number of ways to refer to a job in the shell. The charac‐
2773 ter % introduces a job specification (jobspec). Job number n may be
2774 referred to as %n. A job may also be referred to using a prefix of the
2775 name used to start it, or using a substring that appears in its command
2776 line. For example, %ce refers to a stopped ce job. If a prefix
2777 matches more than one job, bash reports an error. Using %?ce, on the
2778 other hand, refers to any job containing the string ce in its command
2779 line. If the substring matches more than one job, bash reports an
2780 error. The symbols %% and %+ refer to the shell's notion of the cur‐
2781 rent job, which is the last job stopped while it was in the foreground
2782 or started in the background. The previous job may be referenced using
2783 %-. If there is only a single job, %+ and %- can both be used to refer
2784 to that job. In output pertaining to jobs (e.g., the output of the
2785 jobs command), the current job is always flagged with a +, and the pre‐
2786 vious job with a -. A single % (with no accompanying job specifica‐
2787 tion) also refers to the current job.
2788 Simply naming a job can be used to bring it into the foreground: %1 is
2790 a synonym for ``fg %1'', bringing job 1 from the background into the
2791 foreground. Similarly, ``%1 &'' resumes job 1 in the background,
2792 equivalent to ``bg %1''.
2793 The shell learns immediately whenever a job changes state. Normally,
2795 bash waits until it is about to print a prompt before reporting changes
2796 in a job's status so as to not interrupt any other output. If the -b
2797 option to the set builtin command is enabled, bash reports such changes
2798 immediately. Any trap on SIGCHLD is executed for each child that
2799 exits.
2800 If an attempt to exit bash is made while jobs are stopped (or, if the
2802 checkjobs shell option has been enabled using the shopt builtin, run‐
2803 ning), the shell prints a warning message, and, if the checkjobs option
2804 is enabled, lists the jobs and their statuses. The jobs command may
2805 then be used to inspect their status. If a second attempt to exit is
2806 made without an intervening command, the shell does not print another
2807 warning, and any stopped jobs are terminated.
2808
2810 When executing interactively, bash displays the primary prompt PS1 when
2811 it is ready to read a command, and the secondary prompt PS2 when it
2812 needs more input to complete a command. Bash displays PS0 after it
2813 reads a command but before executing it. Bash allows these prompt
2814 strings to be customized by inserting a number of backslash-escaped
2815 special characters that are decoded as follows:
2816 \a an ASCII bell character (07)
2817 \d the date in "Weekday Month Date" format (e.g., "Tue May
2818 26")
2819 \D{format}
2820 the format is passed to strftime(3) and the result is
2821 inserted into the prompt string; an empty format results
2822 in a locale-specific time representation. The braces are
2823 required
2824 \e an ASCII escape character (033)
2825 \h the hostname up to the first `.'
2826 \H the hostname
2827 \j the number of jobs currently managed by the shell
2828 \l the basename of the shell's terminal device name
2829 \n newline
2830 \r carriage return
2831 \s the name of the shell, the basename of $0 (the portion
2832 following the final slash)
2833 \t the current time in 24-hour HH:MM:SS format
2834 \T the current time in 12-hour HH:MM:SS format
2835 \@ the current time in 12-hour am/pm format
2836 \A the current time in 24-hour HH:MM format
2837 \u the username of the current user
2838 \v the version of bash (e.g., 2.00)
2839 \V the release of bash, version + patch level (e.g., 2.00.0)
2840 \w the current working directory, with $HOME abbreviated
2841 with a tilde (uses the value of the PROMPT_DIRTRIM vari‐
2842 able)
2843 \W the basename of the current working directory, with $HOME
2844 abbreviated with a tilde
2845 \! the history number of this command
2846 \# the command number of this command
2847 \$ if the effective UID is 0, a #, otherwise a $
2848 \nnn the character corresponding to the octal number nnn
2849 \\ a backslash
2850 \[ begin a sequence of non-printing characters, which could
2851 be used to embed a terminal control sequence into the
2852 prompt
2853 \] end a sequence of non-printing characters
2854 The command number and the history number are usually different: the
2856 history number of a command is its position in the history list, which
2857 may include commands restored from the history file (see HISTORY
2858 below), while the command number is the position in the sequence of
2859 commands executed during the current shell session. After the string
2860 is decoded, it is expanded via parameter expansion, command substitu‐
2861 tion, arithmetic expansion, and quote removal, subject to the value of
2862 the promptvars shell option (see the description of the shopt command
2863 under SHELL BUILTIN COMMANDS below).
2864
2866 This is the library that handles reading input when using an interac‐
2867 tive shell, unless the --noediting option is given at shell invocation.
2868 Line editing is also used when using the -e option to the read builtin.
2869 By default, the line editing commands are similar to those of Emacs. A
2870 vi-style line editing interface is also available. Line editing can be
2871 enabled at any time using the -o emacs or -o vi options to the set
2872 builtin (see SHELL BUILTIN COMMANDS below). To turn off line editing
2873 after the shell is running, use the +o emacs or +o vi options to the
2874 set builtin.
2875 Readline Notation
2877 In this section, the Emacs-style notation is used to denote keystrokes.
2878 Control keys are denoted by C-key, e.g., C-n means Control-N. Simi‐
2879 larly, meta keys are denoted by M-key, so M-x means Meta-X. (On key‐
2880 boards without a meta key, M-x means ESC x, i.e., press the Escape key
2881 then the x key. This makes ESC the meta prefix. The combination M-C-x
2882 means ESC-Control-x, or press the Escape key then hold the Control key
2883 while pressing the x key.)
2884 Readline commands may be given numeric arguments, which normally act as
2886 a repeat count. Sometimes, however, it is the sign of the argument
2887 that is significant. Passing a negative argument to a command that
2888 acts in the forward direction (e.g., kill-line) causes that command to
2889 act in a backward direction. Commands whose behavior with arguments
2890 deviates from this are noted below.
2891 When a command is described as killing text, the text deleted is saved
2893 for possible future retrieval (yanking). The killed text is saved in a
2894 kill ring. Consecutive kills cause the text to be accumulated into one
2895 unit, which can be yanked all at once. Commands which do not kill text
2896 separate the chunks of text on the kill ring.
2897 Readline Initialization
2899 Readline is customized by putting commands in an initialization file
2900 (the inputrc file). The name of this file is taken from the value of
2901 the INPUTRC variable. If that variable is unset, the default is
2902 ~/.inputrc. When a program which uses the readline library starts up,
2903 the initialization file is read, and the key bindings and variables are
2904 set. There are only a few basic constructs allowed in the readline
2905 initialization file. Blank lines are ignored. Lines beginning with a
2906 # are comments. Lines beginning with a $ indicate conditional con‐
2907 structs. Other lines denote key bindings and variable settings.
2908 The default key-bindings may be changed with an inputrc file. Other
2910 programs that use this library may add their own commands and bindings.
2911 For example, placing
2913 M-Control-u: universal-argument
2915 or
2916 C-Meta-u: universal-argument
2917 into the inputrc would make M-C-u execute the readline command univer‐
2918 sal-argument.
2919 The following symbolic character names are recognized: RUBOUT, DEL,
2921 ESC, LFD, NEWLINE, RET, RETURN, SPC, SPACE, and TAB.
2922 In addition to command names, readline allows keys to be bound to a
2924 string that is inserted when the key is pressed (a macro).
2925 Readline Key Bindings
2927 The syntax for controlling key bindings in the inputrc file is simple.
2928 All that is required is the name of the command or the text of a macro
2929 and a key sequence to which it should be bound. The name may be speci‐
2930 fied in one of two ways: as a symbolic key name, possibly with Meta- or
2931 Control- prefixes, or as a key sequence.
2932 When using the form keyname:function-name or macro, keyname is the name
2934 of a key spelled out in English. For example:
2935 Control-u: universal-argument
2937 Meta-Rubout: backward-kill-word
2938 Control-o: "> output"
2939 In the above example, C-u is bound to the function universal-argument,
2941 M-DEL is bound to the function backward-kill-word, and C-o is bound to
2942 run the macro expressed on the right hand side (that is, to insert the
2943 text ``> output'' into the line).
2944 In the second form, "keyseq":function-name or macro, keyseq differs
2946 from keyname above in that strings denoting an entire key sequence may
2947 be specified by placing the sequence within double quotes. Some GNU
2948 Emacs style key escapes can be used, as in the following example, but
2949 the symbolic character names are not recognized.
2950 "\C-u": universal-argument
2952 "\C-x\C-r": re-read-init-file
2953 "\e[11~": "Function Key 1"
2954 In this example, C-u is again bound to the function universal-argument.
2956 C-x C-r is bound to the function re-read-init-file, and ESC [ 1 1 ~ is
2957 bound to insert the text ``Function Key 1''.
2958 The full set of GNU Emacs style escape sequences is
2960 \C- control prefix
2961 \M- meta prefix
2962 \e an escape character
2963 \\ backslash
2964 \" literal "
2965 \' literal '
2966 In addition to the GNU Emacs style escape sequences, a second set of
2968 backslash escapes is available:
2969 \a alert (bell)
2970 \b backspace
2971 \d delete
2972 \f form feed
2973 \n newline
2974 \r carriage return
2975 \t horizontal tab
2976 \v vertical tab
2977 \nnn the eight-bit character whose value is the octal value
2978 nnn (one to three digits)
2979 \xHH the eight-bit character whose value is the hexadecimal
2980 value HH (one or two hex digits)
2981 When entering the text of a macro, single or double quotes must be used
2983 to indicate a macro definition. Unquoted text is assumed to be a func‐
2984 tion name. In the macro body, the backslash escapes described above
2985 are expanded. Backslash will quote any other character in the macro
2986 text, including " and '.
2987 Bash allows the current readline key bindings to be displayed or modi‐
2989 fied with the bind builtin command. The editing mode may be switched
2990 during interactive use by using the -o option to the set builtin com‐
2991 mand (see SHELL BUILTIN COMMANDS below).
2992 Readline Variables
2994 Readline has variables that can be used to further customize its behav‐
2995 ior. A variable may be set in the inputrc file with a statement of the
2996 form
2997 set variable-name value
2999 Except where noted, readline variables can take the values On or Off
3001 (without regard to case). Unrecognized variable names are ignored.
3002 When a variable value is read, empty or null values, "on" (case-insen‐
3003 sitive), and "1" are equivalent to On. All other values are equivalent
3004 to Off. The variables and their default values are:
3005 bell-style (audible)
3007 Controls what happens when readline wants to ring the terminal
3008 bell. If set to none, readline never rings the bell. If set to
3009 visible, readline uses a visible bell if one is available. If
3010 set to audible, readline attempts to ring the terminal's bell.
3011 bind-tty-special-chars (On)
3012 If set to On, readline attempts to bind the control characters
3013 treated specially by the kernel's terminal driver to their read‐
3014 line equivalents.
3015 blink-matching-paren (Off)
3016 If set to On, readline attempts to briefly move the cursor to an
3017 opening parenthesis when a closing parenthesis is inserted.
3018 colored-completion-prefix (Off)
3019 If set to On, when listing completions, readline displays the
3020 common prefix of the set of possible completions using a differ‐
3021 ent color. The color definitions are taken from the value of
3022 the LS_COLORS environment variable.
3023 colored-stats (Off)
3024 If set to On, readline displays possible completions using dif‐
3025 ferent colors to indicate their file type. The color defini‐
3026 tions are taken from the value of the LS_COLORS environment
3027 variable.
3028 comment-begin (``#'')
3029 The string that is inserted when the readline insert-comment
3030 command is executed. This command is bound to M-# in emacs mode
3031 and to # in vi command mode.
3032 completion-display-width (-1)
3033 The number of screen columns used to display possible matches
3034 when performing completion. The value is ignored if it is less
3035 than 0 or greater than the terminal screen width. A value of 0
3036 will cause matches to be displayed one per line. The default
3037 value is -1.
3038 completion-ignore-case (Off)
3039 If set to On, readline performs filename matching and completion
3040 in a case-insensitive fashion.
3041 completion-map-case (Off)
3042 If set to On, and completion-ignore-case is enabled, readline
3043 treats hyphens (-) and underscores (_) as equivalent when per‐
3044 forming case-insensitive filename matching and completion.
3045 completion-prefix-display-length (0)
3046 The length in characters of the common prefix of a list of pos‐
3047 sible completions that is displayed without modification. When
3048 set to a value greater than zero, common prefixes longer than
3049 this value are replaced with an ellipsis when displaying possi‐
3050 ble completions.
3051 completion-query-items (100)
3052 This determines when the user is queried about viewing the num‐
3053 ber of possible completions generated by the possible-comple‐
3054 tions command. It may be set to any integer value greater than
3055 or equal to zero. If the number of possible completions is
3056 greater than or equal to the value of this variable, the user is
3057 asked whether or not he wishes to view them; otherwise they are
3058 simply listed on the terminal.
3059 convert-meta (On)
3060 If set to On, readline will convert characters with the eighth
3061 bit set to an ASCII key sequence by stripping the eighth bit and
3062 prefixing an escape character (in effect, using escape as the
3063 meta prefix). The default is On, but readline will set it to
3064 Off if the locale contains eight-bit characters.
3065 disable-completion (Off)
3066 If set to On, readline will inhibit word completion. Completion
3067 characters will be inserted into the line as if they had been
3068 mapped to self-insert.
3069 echo-control-characters (On)
3070 When set to On, on operating systems that indicate they support
3071 it, readline echoes a character corresponding to a signal gener‐
3072 ated from the keyboard.
3073 editing-mode (emacs)
3074 Controls whether readline begins with a set of key bindings sim‐
3075 ilar to Emacs or vi. editing-mode can be set to either emacs or
3076 vi.
3077 enable-bracketed-paste (Off)
3078 When set to On, readline will configure the terminal in a way
3079 that will enable it to insert each paste into the editing buffer
3080 as a single string of characters, instead of treating each char‐
3081 acter as if it had been read from the keyboard. This can pre‐
3082 vent pasted characters from being interpreted as editing com‐
3083 mands.
3084 enable-keypad (Off)
3085 When set to On, readline will try to enable the application key‐
3086 pad when it is called. Some systems need this to enable the
3087 arrow keys.
3088 enable-meta-key (On)
3089 When set to On, readline will try to enable any meta modifier
3090 key the terminal claims to support when it is called. On many
3091 terminals, the meta key is used to send eight-bit characters.
3092 expand-tilde (Off)
3093 If set to On, tilde expansion is performed when readline
3094 attempts word completion.
3095 history-preserve-point (Off)
3096 If set to On, the history code attempts to place point at the
3097 same location on each history line retrieved with previous-his‐
3098 tory or next-history.
3099 history-size (unset)
3100 Set the maximum number of history entries saved in the history
3101 list. If set to zero, any existing history entries are deleted
3102 and no new entries are saved. If set to a value less than zero,
3103 the number of history entries is not limited. By default, the
3104 number of history entries is set to the value of the HISTSIZE
3105 shell variable. If an attempt is made to set history-size to a
3106 non-numeric value, the maximum number of history entries will be
3107 set to 500.
3108 horizontal-scroll-mode (Off)
3109 When set to On, makes readline use a single line for display,
3110 scrolling the input horizontally on a single screen line when it
3111 becomes longer than the screen width rather than wrapping to a
3112 new line.
3113 input-meta (Off)
3114 If set to On, readline will enable eight-bit input (that is, it
3115 will not strip the eighth bit from the characters it reads),
3116 regardless of what the terminal claims it can support. The name
3117 meta-flag is a synonym for this variable. The default is Off,
3118 but readline will set it to On if the locale contains eight-bit
3119 characters.
3120 isearch-terminators (``C-[C-J'')
3121 The string of characters that should terminate an incremental
3122 search without subsequently executing the character as a com‐
3123 mand. If this variable has not been given a value, the charac‐
3124 ters ESC and C-J will terminate an incremental search.
3125 keymap (emacs)
3126 Set the current readline keymap. The set of valid keymap names
3127 is emacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-com‐
3128 mand, and vi-insert. vi is equivalent to vi-command; emacs is
3129 equivalent to emacs-standard. The default value is emacs; the
3130 value of editing-mode also affects the default keymap.
3131 emacs-mode-string (@)
3132 This string is displayed immediately before the last line of the
3133 primary prompt when emacs editing mode is active. The value is
3134 expanded like a key binding, so the standard set of meta- and
3135 control prefixes and backslash escape sequences is available.
3136 Use the \1 and \2 escapes to begin and end sequences of non-
3137 printing characters, which can be used to embed a terminal con‐
3138 trol sequence into the mode string.
3139 keyseq-timeout (500)
3140 Specifies the duration readline will wait for a character when
3141 reading an ambiguous key sequence (one that can form a complete
3142 key sequence using the input read so far, or can take additional
3143 input to complete a longer key sequence). If no input is
3144 received within the timeout, readline will use the shorter but
3145 complete key sequence. The value is specified in milliseconds,
3146 so a value of 1000 means that readline will wait one second for
3147 additional input. If this variable is set to a value less than
3148 or equal to zero, or to a non-numeric value, readline will wait
3149 until another key is pressed to decide which key sequence to
3150 complete.
3151 mark-directories (On)
3152 If set to On, completed directory names have a slash appended.
3153 mark-modified-lines (Off)
3154 If set to On, history lines that have been modified are dis‐
3155 played with a preceding asterisk (*).
3156 mark-symlinked-directories (Off)
3157 If set to On, completed names which are symbolic links to direc‐
3158 tories have a slash appended (subject to the value of
3159 mark-directories).
3160 match-hidden-files (On)
3161 This variable, when set to On, causes readline to match files
3162 whose names begin with a `.' (hidden files) when performing
3163 filename completion. If set to Off, the leading `.' must be
3164 supplied by the user in the filename to be completed.
3165 menu-complete-display-prefix (Off)
3166 If set to On, menu completion displays the common prefix of the
3167 list of possible completions (which may be empty) before cycling
3168 through the list.
3169 output-meta (Off)
3170 If set to On, readline will display characters with the eighth
3171 bit set directly rather than as a meta-prefixed escape sequence.
3172 The default is Off, but readline will set it to On if the locale
3173 contains eight-bit characters.
3174 page-completions (On)
3175 If set to On, readline uses an internal more-like pager to dis‐
3176 play a screenful of possible completions at a time.
3177 print-completions-horizontally (Off)
3178 If set to On, readline will display completions with matches
3179 sorted horizontally in alphabetical order, rather than down the
3180 screen.
3181 revert-all-at-newline (Off)
3182 If set to On, readline will undo all changes to history lines
3183 before returning when accept-line is executed. By default, his‐
3184 tory lines may be modified and retain individual undo lists
3185 across calls to readline.
3186 show-all-if-ambiguous (Off)
3187 This alters the default behavior of the completion functions.
3188 If set to On, words which have more than one possible completion
3189 cause the matches to be listed immediately instead of ringing
3190 the bell.
3191 show-all-if-unmodified (Off)
3192 This alters the default behavior of the completion functions in
3193 a fashion similar to show-all-if-ambiguous. If set to On, words
3194 which have more than one possible completion without any possi‐
3195 ble partial completion (the possible completions don't share a
3196 common prefix) cause the matches to be listed immediately
3197 instead of ringing the bell.
3198 show-mode-in-prompt (Off)
3199 If set to On, add a character to the beginning of the prompt
3200 indicating the editing mode: emacs (@), vi command (:) or vi
3201 insertion (+).
3202 skip-completed-text (Off)
3203 If set to On, this alters the default completion behavior when
3204 inserting a single match into the line. It's only active when
3205 performing completion in the middle of a word. If enabled,
3206 readline does not insert characters from the completion that
3207 match characters after point in the word being completed, so
3208 portions of the word following the cursor are not duplicated.
3209 vi-cmd-mode-string ((cmd))
3210 This string is displayed immediately before the last line of the
3211 primary prompt when vi editing mode is active and in command
3212 mode. The value is expanded like a key binding, so the standard
3213 set of meta- and control prefixes and backslash escape sequences
3214 is available. Use the \1 and \2 escapes to begin and end
3215 sequences of non-printing characters, which can be used to embed
3216 a terminal control sequence into the mode string.
3217 vi-ins-mode-string ((ins))
3218 This string is displayed immediately before the last line of the
3219 primary prompt when vi editing mode is active and in insertion
3220 mode. The value is expanded like a key binding, so the standard
3221 set of meta- and control prefixes and backslash escape sequences
3222 is available. Use the \1 and \2 escapes to begin and end
3223 sequences of non-printing characters, which can be used to embed
3224 a terminal control sequence into the mode string.
3225 visible-stats (Off)
3226 If set to On, a character denoting a file's type as reported by
3227 stat(2) is appended to the filename when listing possible com‐
3228 pletions.
3229 Readline Conditional Constructs
3231 Readline implements a facility similar in spirit to the conditional
3232 compilation features of the C preprocessor which allows key bindings
3233 and variable settings to be performed as the result of tests. There
3234 are four parser directives used.
3235 $if The $if construct allows bindings to be made based on the edit‐
3237 ing mode, the terminal being used, or the application using
3238 readline. The text of the test extends to the end of the line;
3239 no characters are required to isolate it.
3240 mode The mode= form of the $if directive is used to test
3242 whether readline is in emacs or vi mode. This may be
3243 used in conjunction with the set keymap command, for
3244 instance, to set bindings in the emacs-standard and
3245 emacs-ctlx keymaps only if readline is starting out in
3246 emacs mode.
3247 term The term= form may be used to include terminal-specific
3249 key bindings, perhaps to bind the key sequences output by
3250 the terminal's function keys. The word on the right side
3251 of the = is tested against both the full name of the ter‐
3252 minal and the portion of the terminal name before the
3253 first -. This allows sun to match both sun and sun-cmd,
3254 for instance.
3255 application
3257 The application construct is used to include application-
3258 specific settings. Each program using the readline
3259 library sets the application name, and an initialization
3260 file can test for a particular value. This could be used
3261 to bind key sequences to functions useful for a specific
3262 program. For instance, the following command adds a key
3263 sequence that quotes the current or previous word in
3264 bash:
3265 $if Bash
3267 # Quote the current or previous word
3268 "\C-xq": "\eb\"\ef\""
3269 $endif
3270 $endif This command, as seen in the previous example, terminates an $if
3272 command.
3273 $else Commands in this branch of the $if directive are executed if the
3275 test fails.
3276 $include
3278 This directive takes a single filename as an argument and reads
3279 commands and bindings from that file. For example, the follow‐
3280 ing directive would read /etc/inputrc:
3281 $include /etc/inputrc
3283 Searching
3285 Readline provides commands for searching through the command history
3286 (see HISTORY below) for lines containing a specified string. There are
3287 two search modes: incremental and non-incremental.
3288 Incremental searches begin before the user has finished typing the
3290 search string. As each character of the search string is typed, read‐
3291 line displays the next entry from the history matching the string typed
3292 so far. An incremental search requires only as many characters as
3293 needed to find the desired history entry. The characters present in
3294 the value of the isearch-terminators variable are used to terminate an
3295 incremental search. If that variable has not been assigned a value the
3296 Escape and Control-J characters will terminate an incremental search.
3297 Control-G will abort an incremental search and restore the original
3298 line. When the search is terminated, the history entry containing the
3299 search string becomes the current line.
3300 To find other matching entries in the history list, type Control-S or
3302 Control-R as appropriate. This will search backward or forward in the
3303 history for the next entry matching the search string typed so far.
3304 Any other key sequence bound to a readline command will terminate the
3305 search and execute that command. For instance, a newline will termi‐
3306 nate the search and accept the line, thereby executing the command from
3307 the history list.
3308 Readline remembers the last incremental search string. If two Control-
3310 Rs are typed without any intervening characters defining a new search
3311 string, any remembered search string is used.
3312 Non-incremental searches read the entire search string before starting
3314 to search for matching history lines. The search string may be typed
3315 by the user or be part of the contents of the current line.
3316 Readline Command Names
3318 The following is a list of the names of the commands and the default
3319 key sequences to which they are bound. Command names without an accom‐
3320 panying key sequence are unbound by default. In the following descrip‐
3321 tions, point refers to the current cursor position, and mark refers to
3322 a cursor position saved by the set-mark command. The text between the
3323 point and mark is referred to as the region.
3324 Commands for Moving
3326 beginning-of-line (C-a)
3327 Move to the start of the current line.
3328 end-of-line (C-e)
3329 Move to the end of the line.
3330 forward-char (C-f)
3331 Move forward a character.
3332 backward-char (C-b)
3333 Move back a character.
3334 forward-word (M-f)
3335 Move forward to the end of the next word. Words are composed of
3336 alphanumeric characters (letters and digits).
3337 backward-word (M-b)
3338 Move back to the start of the current or previous word. Words
3339 are composed of alphanumeric characters (letters and digits).
3340 shell-forward-word
3341 Move forward to the end of the next word. Words are delimited
3342 by non-quoted shell metacharacters.
3343 shell-backward-word
3344 Move back to the start of the current or previous word. Words
3345 are delimited by non-quoted shell metacharacters.
3346 clear-screen (C-l)
3347 Clear the screen leaving the current line at the top of the
3348 screen. With an argument, refresh the current line without
3349 clearing the screen.
3350 redraw-current-line
3351 Refresh the current line.
3352 Commands for Manipulating the History
3354 accept-line (Newline, Return)
3355 Accept the line regardless of where the cursor is. If this line
3356 is non-empty, add it to the history list according to the state
3357 of the HISTCONTROL variable. If the line is a modified history
3358 line, then restore the history line to its original state.
3359 previous-history (C-p)
3360 Fetch the previous command from the history list, moving back in
3361 the list.
3362 next-history (C-n)
3363 Fetch the next command from the history list, moving forward in
3364 the list.
3365 beginning-of-history (M-<)
3366 Move to the first line in the history.
3367 end-of-history (M->)
3368 Move to the end of the input history, i.e., the line currently
3369 being entered.
3370 reverse-search-history (C-r)
3371 Search backward starting at the current line and moving `up'
3372 through the history as necessary. This is an incremental
3373 search.
3374 forward-search-history (C-s)
3375 Search forward starting at the current line and moving `down'
3376 through the history as necessary. This is an incremental
3377 search.
3378 non-incremental-reverse-search-history (M-p)
3379 Search backward through the history starting at the current line
3380 using a non-incremental search for a string supplied by the
3381 user.
3382 non-incremental-forward-search-history (M-n)
3383 Search forward through the history using a non-incremental
3384 search for a string supplied by the user.
3385 history-search-forward
3386 Search forward through the history for the string of characters
3387 between the start of the current line and the point. This is a
3388 non-incremental search.
3389 history-search-backward
3390 Search backward through the history for the string of characters
3391 between the start of the current line and the point. This is a
3392 non-incremental search.
3393 yank-nth-arg (M-C-y)
3394 Insert the first argument to the previous command (usually the
3395 second word on the previous line) at point. With an argument n,
3396 insert the nth word from the previous command (the words in the
3397 previous command begin with word 0). A negative argument
3398 inserts the nth word from the end of the previous command. Once
3399 the argument n is computed, the argument is extracted as if the
3400 "!n" history expansion had been specified.
3401 yank-last-arg (M-., M-_)
3402 Insert the last argument to the previous command (the last word
3403 of the previous history entry). With a numeric argument, behave
3404 exactly like yank-nth-arg. Successive calls to yank-last-arg
3405 move back through the history list, inserting the last word (or
3406 the word specified by the argument to the first call) of each
3407 line in turn. Any numeric argument supplied to these successive
3408 calls determines the direction to move through the history. A
3409 negative argument switches the direction through the history
3410 (back or forward). The history expansion facilities are used to
3411 extract the last word, as if the "!$" history expansion had been
3412 specified.
3413 shell-expand-line (M-C-e)
3414 Expand the line as the shell does. This performs alias and his‐
3415 tory expansion as well as all of the shell word expansions. See
3416 HISTORY EXPANSION below for a description of history expansion.
3417 history-expand-line (M-^)
3418 Perform history expansion on the current line. See HISTORY
3419 EXPANSION below for a description of history expansion.
3420 magic-space
3421 Perform history expansion on the current line and insert a
3422 space. See HISTORY EXPANSION below for a description of history
3423 expansion.
3424 alias-expand-line
3425 Perform alias expansion on the current line. See ALIASES above
3426 for a description of alias expansion.
3427 history-and-alias-expand-line
3428 Perform history and alias expansion on the current line.
3429 insert-last-argument (M-., M-_)
3430 A synonym for yank-last-arg.
3431 operate-and-get-next (C-o)
3432 Accept the current line for execution and fetch the next line
3433 relative to the current line from the history for editing. Any
3434 argument is ignored.
3435 edit-and-execute-command (C-xC-e)
3436 Invoke an editor on the current command line, and execute the
3437 result as shell commands. Bash attempts to invoke $VISUAL,
3438 $EDITOR, and emacs as the editor, in that order.
3439 Commands for Changing Text
3441 end-of-file (usually C-d)
3442 The character indicating end-of-file as set, for example, by
3443 ``stty''. If this character is read when there are no charac‐
3444 ters on the line, and point is at the beginning of the line,
3445 Readline interprets it as the end of input and returns EOF.
3446 delete-char (C-d)
3447 Delete the character at point. If this function is bound to the
3448 same character as the tty EOF character, as C-d commonly is, see
3449 above for the effects.
3450 backward-delete-char (Rubout)
3451 Delete the character behind the cursor. When given a numeric
3452 argument, save the deleted text on the kill ring.
3453 forward-backward-delete-char
3454 Delete the character under the cursor, unless the cursor is at
3455 the end of the line, in which case the character behind the cur‐
3456 sor is deleted.
3457 quoted-insert (C-q, C-v)
3458 Add the next character typed to the line verbatim. This is how
3459 to insert characters like C-q, for example.
3460 tab-insert (C-v TAB)
3461 Insert a tab character.
3462 self-insert (a, b, A, 1, !, ...)
3463 Insert the character typed.
3464 transpose-chars (C-t)
3465 Drag the character before point forward over the character at
3466 point, moving point forward as well. If point is at the end of
3467 the line, then this transposes the two characters before point.
3468 Negative arguments have no effect.
3469 transpose-words (M-t)
3470 Drag the word before point past the word after point, moving
3471 point over that word as well. If point is at the end of the
3472 line, this transposes the last two words on the line.
3473 upcase-word (M-u)
3474 Uppercase the current (or following) word. With a negative
3475 argument, uppercase the previous word, but do not move point.
3476 downcase-word (M-l)
3477 Lowercase the current (or following) word. With a negative
3478 argument, lowercase the previous word, but do not move point.
3479 capitalize-word (M-c)
3480 Capitalize the current (or following) word. With a negative
3481 argument, capitalize the previous word, but do not move point.
3482 overwrite-mode
3483 Toggle overwrite mode. With an explicit positive numeric argu‐
3484 ment, switches to overwrite mode. With an explicit non-positive
3485 numeric argument, switches to insert mode. This command affects
3486 only emacs mode; vi mode does overwrite differently. Each call
3487 to readline() starts in insert mode. In overwrite mode, charac‐
3488 ters bound to self-insert replace the text at point rather than
3489 pushing the text to the right. Characters bound to back‐
3490 ward-delete-char replace the character before point with a
3491 space. By default, this command is unbound.
3492 Killing and Yanking
3494 kill-line (C-k)
3495 Kill the text from point to the end of the line.
3496 backward-kill-line (C-x Rubout)
3497 Kill backward to the beginning of the line.
3498 unix-line-discard (C-u)
3499 Kill backward from point to the beginning of the line. The
3500 killed text is saved on the kill-ring.
3501 kill-whole-line
3502 Kill all characters on the current line, no matter where point
3503 is.
3504 kill-word (M-d)
3505 Kill from point to the end of the current word, or if between
3506 words, to the end of the next word. Word boundaries are the
3507 same as those used by forward-word.
3508 backward-kill-word (M-Rubout)
3509 Kill the word behind point. Word boundaries are the same as
3510 those used by backward-word.
3511 shell-kill-word
3512 Kill from point to the end of the current word, or if between
3513 words, to the end of the next word. Word boundaries are the
3514 same as those used by shell-forward-word.
3515 shell-backward-kill-word
3516 Kill the word behind point. Word boundaries are the same as
3517 those used by shell-backward-word.
3518 unix-word-rubout (C-w)
3519 Kill the word behind point, using white space as a word bound‐
3520 ary. The killed text is saved on the kill-ring.
3521 unix-filename-rubout
3522 Kill the word behind point, using white space and the slash
3523 character as the word boundaries. The killed text is saved on
3524 the kill-ring.
3525 delete-horizontal-space (M-\)
3526 Delete all spaces and tabs around point.
3527 kill-region
3528 Kill the text in the current region.
3529 copy-region-as-kill
3530 Copy the text in the region to the kill buffer.
3531 copy-backward-word
3532 Copy the word before point to the kill buffer. The word bound‐
3533 aries are the same as backward-word.
3534 copy-forward-word
3535 Copy the word following point to the kill buffer. The word
3536 boundaries are the same as forward-word.
3537 yank (C-y)
3538 Yank the top of the kill ring into the buffer at point.
3539 yank-pop (M-y)
3540 Rotate the kill ring, and yank the new top. Only works follow‐
3541 ing yank or yank-pop.
3542 Numeric Arguments
3544 digit-argument (M-0, M-1, ..., M--)
3545 Add this digit to the argument already accumulating, or start a
3546 new argument. M-- starts a negative argument.
3547 universal-argument
3548 This is another way to specify an argument. If this command is
3549 followed by one or more digits, optionally with a leading minus
3550 sign, those digits define the argument. If the command is fol‐
3551 lowed by digits, executing universal-argument again ends the
3552 numeric argument, but is otherwise ignored. As a special case,
3553 if this command is immediately followed by a character that is
3554 neither a digit nor minus sign, the argument count for the next
3555 command is multiplied by four. The argument count is initially
3556 one, so executing this function the first time makes the argu‐
3557 ment count four, a second time makes the argument count sixteen,
3558 and so on.
3559 Completing
3561 complete (TAB)
3562 Attempt to perform completion on the text before point. Bash
3563 attempts completion treating the text as a variable (if the text
3564 begins with $), username (if the text begins with ~), hostname
3565 (if the text begins with @), or command (including aliases and
3566 functions) in turn. If none of these produces a match, filename
3567 completion is attempted.
3568 possible-completions (M-?)
3569 List the possible completions of the text before point.
3570 insert-completions (M-*)
3571 Insert all completions of the text before point that would have
3572 been generated by possible-completions.
3573 menu-complete
3574 Similar to complete, but replaces the word to be completed with
3575 a single match from the list of possible completions. Repeated
3576 execution of menu-complete steps through the list of possible
3577 completions, inserting each match in turn. At the end of the
3578 list of completions, the bell is rung (subject to the setting of
3579 bell-style) and the original text is restored. An argument of n
3580 moves n positions forward in the list of matches; a negative
3581 argument may be used to move backward through the list. This
3582 command is intended to be bound to TAB, but is unbound by
3583 default.
3584 menu-complete-backward
3585 Identical to menu-complete, but moves backward through the list
3586 of possible completions, as if menu-complete had been given a
3587 negative argument. This command is unbound by default.
3588 delete-char-or-list
3589 Deletes the character under the cursor if not at the beginning
3590 or end of the line (like delete-char). If at the end of the
3591 line, behaves identically to possible-completions. This command
3592 is unbound by default.
3593 complete-filename (M-/)
3594 Attempt filename completion on the text before point.
3595 possible-filename-completions (C-x /)
3596 List the possible completions of the text before point, treating
3597 it as a filename.
3598 complete-username (M-~)
3599 Attempt completion on the text before point, treating it as a
3600 username.
3601 possible-username-completions (C-x ~)
3602 List the possible completions of the text before point, treating
3603 it as a username.
3604 complete-variable (M-$)
3605 Attempt completion on the text before point, treating it as a
3606 shell variable.
3607 possible-variable-completions (C-x $)
3608 List the possible completions of the text before point, treating
3609 it as a shell variable.
3610 complete-hostname (M-@)
3611 Attempt completion on the text before point, treating it as a
3612 hostname.
3613 possible-hostname-completions (C-x @)
3614 List the possible completions of the text before point, treating
3615 it as a hostname.
3616 complete-command (M-!)
3617 Attempt completion on the text before point, treating it as a
3618 command name. Command completion attempts to match the text
3619 against aliases, reserved words, shell functions, shell
3620 builtins, and finally executable filenames, in that order.
3621 possible-command-completions (C-x !)
3622 List the possible completions of the text before point, treating
3623 it as a command name.
3624 dynamic-complete-history (M-TAB)
3625 Attempt completion on the text before point, comparing the text
3626 against lines from the history list for possible completion
3627 matches.
3628 dabbrev-expand
3629 Attempt menu completion on the text before point, comparing the
3630 text against lines from the history list for possible completion
3631 matches.
3632 complete-into-braces (M-{)
3633 Perform filename completion and insert the list of possible com‐
3634 pletions enclosed within braces so the list is available to the
3635 shell (see Brace Expansion above).
3636 Keyboard Macros
3638 start-kbd-macro (C-x ()
3639 Begin saving the characters typed into the current keyboard
3640 macro.
3641 end-kbd-macro (C-x ))
3642 Stop saving the characters typed into the current keyboard macro
3643 and store the definition.
3644 call-last-kbd-macro (C-x e)
3645 Re-execute the last keyboard macro defined, by making the char‐
3646 acters in the macro appear as if typed at the keyboard.
3647 print-last-kbd-macro ()
3648 Print the last keyboard macro defined in a format suitable for
3649 the inputrc file.
3650 Miscellaneous
3652 re-read-init-file (C-x C-r)
3653 Read in the contents of the inputrc file, and incorporate any
3654 bindings or variable assignments found there.
3655 abort (C-g)
3656 Abort the current editing command and ring the terminal's bell
3657 (subject to the setting of bell-style).
3658 do-uppercase-version (M-a, M-b, M-x, ...)
3659 If the metafied character x is lowercase, run the command that
3660 is bound to the corresponding uppercase character.
3661 prefix-meta (ESC)
3662 Metafy the next character typed. ESC f is equivalent to Meta-f.
3663 undo (C-_, C-x C-u)
3664 Incremental undo, separately remembered for each line.
3665 revert-line (M-r)
3666 Undo all changes made to this line. This is like executing the
3667 undo command enough times to return the line to its initial
3668 state.
3669 tilde-expand (M-&)
3670 Perform tilde expansion on the current word.
3671 set-mark (C-@, M-<space>)
3672 Set the mark to the point. If a numeric argument is supplied,
3673 the mark is set to that position.
3674 exchange-point-and-mark (C-x C-x)
3675 Swap the point with the mark. The current cursor position is
3676 set to the saved position, and the old cursor position is saved
3677 as the mark.
3678 character-search (C-])
3679 A character is read and point is moved to the next occurrence of
3680 that character. A negative count searches for previous occur‐
3681 rences.
3682 character-search-backward (M-C-])
3683 A character is read and point is moved to the previous occur‐
3684 rence of that character. A negative count searches for subse‐
3685 quent occurrences.
3686 skip-csi-sequence
3687 Read enough characters to consume a multi-key sequence such as
3688 those defined for keys like Home and End. Such sequences begin
3689 with a Control Sequence Indicator (CSI), usually ESC-[. If this
3690 sequence is bound to "\[", keys producing such sequences will
3691 have no effect unless explicitly bound to a readline command,
3692 instead of inserting stray characters into the editing buffer.
3693 This is unbound by default, but usually bound to ESC-[.
3694 insert-comment (M-#)
3695 Without a numeric argument, the value of the readline com‐
3696 ment-begin variable is inserted at the beginning of the current
3697 line. If a numeric argument is supplied, this command acts as a
3698 toggle: if the characters at the beginning of the line do not
3699 match the value of comment-begin, the value is inserted, other‐
3700 wise the characters in comment-begin are deleted from the begin‐
3701 ning of the line. In either case, the line is accepted as if a
3702 newline had been typed. The default value of comment-begin
3703 causes this command to make the current line a shell comment.
3704 If a numeric argument causes the comment character to be
3705 removed, the line will be executed by the shell.
3706 glob-complete-word (M-g)
3707 The word before point is treated as a pattern for pathname
3708 expansion, with an asterisk implicitly appended. This pattern
3709 is used to generate a list of matching filenames for possible
3710 completions.
3711 glob-expand-word (C-x *)
3712 The word before point is treated as a pattern for pathname
3713 expansion, and the list of matching filenames is inserted,
3714 replacing the word. If a numeric argument is supplied, an
3715 asterisk is appended before pathname expansion.
3716 glob-list-expansions (C-x g)
3717 The list of expansions that would have been generated by
3718 glob-expand-word is displayed, and the line is redrawn. If a
3719 numeric argument is supplied, an asterisk is appended before
3720 pathname expansion.
3721 dump-functions
3722 Print all of the functions and their key bindings to the read‐
3723 line output stream. If a numeric argument is supplied, the out‐
3724 put is formatted in such a way that it can be made part of an
3725 inputrc file.
3726 dump-variables
3727 Print all of the settable readline variables and their values to
3728 the readline output stream. If a numeric argument is supplied,
3729 the output is formatted in such a way that it can be made part
3730 of an inputrc file.
3731 dump-macros
3732 Print all of the readline key sequences bound to macros and the
3733 strings they output. If a numeric argument is supplied, the
3734 output is formatted in such a way that it can be made part of an
3735 inputrc file.
3736 display-shell-version (C-x C-v)
3737 Display version information about the current instance of bash.
3738 Programmable Completion
3740 When word completion is attempted for an argument to a command for
3741 which a completion specification (a compspec) has been defined using
3742 the complete builtin (see SHELL BUILTIN COMMANDS below), the program‐
3743 mable completion facilities are invoked.
3744 First, the command name is identified. If the command word is the
3746 empty string (completion attempted at the beginning of an empty line),
3747 any compspec defined with the -E option to complete is used. If a
3748 compspec has been defined for that command, the compspec is used to
3749 generate the list of possible completions for the word. If the command
3750 word is a full pathname, a compspec for the full pathname is searched
3751 for first. If no compspec is found for the full pathname, an attempt
3752 is made to find a compspec for the portion following the final slash.
3753 If those searches do not result in a compspec, any compspec defined
3754 with the -D option to complete is used as the default.
3755 Once a compspec has been found, it is used to generate the list of
3757 matching words. If a compspec is not found, the default bash comple‐
3758 tion as described above under Completing is performed.
3759 First, the actions specified by the compspec are used. Only matches
3761 which are prefixed by the word being completed are returned. When the
3762 -f or -d option is used for filename or directory name completion, the
3763 shell variable FIGNORE is used to filter the matches.
3764 Any completions specified by a pathname expansion pattern to the -G
3766 option are generated next. The words generated by the pattern need not
3767 match the word being completed. The GLOBIGNORE shell variable is not
3768 used to filter the matches, but the FIGNORE variable is used.
3769 Next, the string specified as the argument to the -W option is consid‐
3771 ered. The string is first split using the characters in the IFS spe‐
3772 cial variable as delimiters. Shell quoting is honored. Each word is
3773 then expanded using brace expansion, tilde expansion, parameter and
3774 variable expansion, command substitution, and arithmetic expansion, as
3775 described above under EXPANSION. The results are split using the rules
3776 described above under Word Splitting. The results of the expansion are
3777 prefix-matched against the word being completed, and the matching words
3778 become the possible completions.
3779 After these matches have been generated, any shell function or command
3781 specified with the -F and -C options is invoked. When the command or
3782 function is invoked, the COMP_LINE, COMP_POINT, COMP_KEY, and COMP_TYPE
3783 variables are assigned values as described above under Shell Variables.
3784 If a shell function is being invoked, the COMP_WORDS and COMP_CWORD
3785 variables are also set. When the function or command is invoked, the
3786 first argument ($1) is the name of the command whose arguments are
3787 being completed, the second argument ($2) is the word being completed,
3788 and the third argument ($3) is the word preceding the word being com‐
3789 pleted on the current command line. No filtering of the generated com‐
3790 pletions against the word being completed is performed; the function or
3791 command has complete freedom in generating the matches.
3792 Any function specified with -F is invoked first. The function may use
3794 any of the shell facilities, including the compgen builtin described
3795 below, to generate the matches. It must put the possible completions
3796 in the COMPREPLY array variable, one per array element.
3797 Next, any command specified with the -C option is invoked in an envi‐
3799 ronment equivalent to command substitution. It should print a list of
3800 completions, one per line, to the standard output. Backslash may be
3801 used to escape a newline, if necessary.
3802 After all of the possible completions are generated, any filter speci‐
3804 fied with the -X option is applied to the list. The filter is a pat‐
3805 tern as used for pathname expansion; a & in the pattern is replaced
3806 with the text of the word being completed. A literal & may be escaped
3807 with a backslash; the backslash is removed before attempting a match.
3808 Any completion that matches the pattern will be removed from the list.
3809 A leading ! negates the pattern; in this case any completion not match‐
3810 ing the pattern will be removed. If the nocasematch shell option is
3811 enabled, the match is performed without regard to the case of alpha‐
3812 betic characters.
3813 Finally, any prefix and suffix specified with the -P and -S options are
3815 added to each member of the completion list, and the result is returned
3816 to the readline completion code as the list of possible completions.
3817 If the previously-applied actions do not generate any matches, and the
3819 -o dirnames option was supplied to complete when the compspec was
3820 defined, directory name completion is attempted.
3821 If the -o plusdirs option was supplied to complete when the compspec
3823 was defined, directory name completion is attempted and any matches are
3824 added to the results of the other actions.
3825 By default, if a compspec is found, whatever it generates is returned
3827 to the completion code as the full set of possible completions. The
3828 default bash completions are not attempted, and the readline default of
3829 filename completion is disabled. If the -o bashdefault option was sup‐
3830 plied to complete when the compspec was defined, the bash default com‐
3831 pletions are attempted if the compspec generates no matches. If the -o
3832 default option was supplied to complete when the compspec was defined,
3833 readline's default completion will be performed if the compspec (and,
3834 if attempted, the default bash completions) generate no matches.
3835 When a compspec indicates that directory name completion is desired,
3837 the programmable completion functions force readline to append a slash
3838 to completed names which are symbolic links to directories, subject to
3839 the value of the mark-directories readline variable, regardless of the
3840 setting of the mark-symlinked-directories readline variable.
3841 There is some support for dynamically modifying completions. This is
3843 most useful when used in combination with a default completion speci‐
3844 fied with complete -D. It's possible for shell functions executed as
3845 completion handlers to indicate that completion should be retried by
3846 returning an exit status of 124. If a shell function returns 124, and
3847 changes the compspec associated with the command on which completion is
3848 being attempted (supplied as the first argument when the function is
3849 executed), programmable completion restarts from the beginning, with an
3850 attempt to find a new compspec for that command. This allows a set of
3851 completions to be built dynamically as completion is attempted, rather
3852 than being loaded all at once.
3853 For instance, assuming that there is a library of compspecs, each kept
3855 in a file corresponding to the name of the command, the following
3856 default completion function would load completions dynamically:
3857 _completion_loader()
3859 {
3860 . "/etc/bash_completion.d/$1.sh" >/dev/null 2>&1 && return 124
3861 }
3862 complete -D -F _completion_loader -o bashdefault -o default
3863
3866 When the -o history option to the set builtin is enabled, the shell
3867 provides access to the command history, the list of commands previously
3868 typed. The value of the HISTSIZE variable is used as the number of
3869 commands to save in a history list. The text of the last HISTSIZE com‐
3870 mands (default 500) is saved. The shell stores each command in the
3871 history list prior to parameter and variable expansion (see EXPANSION
3872 above) but after history expansion is performed, subject to the values
3873 of the shell variables HISTIGNORE and HISTCONTROL.
3874 On startup, the history is initialized from the file named by the vari‐
3876 able HISTFILE (default ~/.bash_history). The file named by the value
3877 of HISTFILE is truncated, if necessary, to contain no more than the
3878 number of lines specified by the value of HISTFILESIZE. If HISTFILE‐
3879 SIZE is unset, or set to null, a non-numeric value, or a numeric value
3880 less than zero, the history file is not truncated. When the history
3881 file is read, lines beginning with the history comment character fol‐
3882 lowed immediately by a digit are interpreted as timestamps for the pre‐
3883 ceding history line. These timestamps are optionally displayed depend‐
3884 ing on the value of the HISTTIMEFORMAT variable. When a shell with
3885 history enabled exits, the last $HISTSIZE lines are copied from the
3886 history list to $HISTFILE. If the histappend shell option is enabled
3887 (see the description of shopt under SHELL BUILTIN COMMANDS below), the
3888 lines are appended to the history file, otherwise the history file is
3889 overwritten. If HISTFILE is unset, or if the history file is
3890 unwritable, the history is not saved. If the HISTTIMEFORMAT variable
3891 is set, time stamps are written to the history file, marked with the
3892 history comment character, so they may be preserved across shell ses‐
3893 sions. This uses the history comment character to distinguish time‐
3894 stamps from other history lines. After saving the history, the history
3895 file is truncated to contain no more than HISTFILESIZE lines. If HIST‐
3896 FILESIZE is unset, or set to null, a non-numeric value, or a numeric
3897 value less than zero, the history file is not truncated.
3898 The builtin command fc (see SHELL BUILTIN COMMANDS below) may be used
3900 to list or edit and re-execute a portion of the history list. The his‐
3901 tory builtin may be used to display or modify the history list and
3902 manipulate the history file. When using command-line editing, search
3903 commands are available in each editing mode that provide access to the
3904 history list.
3905 The shell allows control over which commands are saved on the history
3907 list. The HISTCONTROL and HISTIGNORE variables may be set to cause the
3908 shell to save only a subset of the commands entered. The cmdhist shell
3909 option, if enabled, causes the shell to attempt to save each line of a
3910 multi-line command in the same history entry, adding semicolons where
3911 necessary to preserve syntactic correctness. The lithist shell option
3912 causes the shell to save the command with embedded newlines instead of
3913 semicolons. See the description of the shopt builtin below under SHELL
3914 BUILTIN COMMANDS for information on setting and unsetting shell
3915 options.
3916
3918 The shell supports a history expansion feature that is similar to the
3919 history expansion in csh. This section describes what syntax features
3920 are available. This feature is enabled by default for interactive
3921 shells, and can be disabled using the +H option to the set builtin com‐
3922 mand (see SHELL BUILTIN COMMANDS below). Non-interactive shells do not
3923 perform history expansion by default.
3924 History expansions introduce words from the history list into the input
3926 stream, making it easy to repeat commands, insert the arguments to a
3927 previous command into the current input line, or fix errors in previous
3928 commands quickly.
3929 History expansion is performed immediately after a complete line is
3931 read, before the shell breaks it into words. It takes place in two
3932 parts. The first is to determine which line from the history list to
3933 use during substitution. The second is to select portions of that line
3934 for inclusion into the current one. The line selected from the history
3935 is the event, and the portions of that line that are acted upon are
3936 words. Various modifiers are available to manipulate the selected
3937 words. The line is broken into words in the same fashion as when read‐
3938 ing input, so that several metacharacter-separated words surrounded by
3939 quotes are considered one word. History expansions are introduced by
3940 the appearance of the history expansion character, which is ! by
3941 default. Only backslash (\) and single quotes can quote the history
3942 expansion character, but the history expansion character is also
3943 treated as quoted if it immediately precedes the closing double quote
3944 in a double-quoted string.
3945 Several characters inhibit history expansion if found immediately fol‐
3947 lowing the history expansion character, even if it is unquoted: space,
3948 tab, newline, carriage return, and =. If the extglob shell option is
3949 enabled, ( will also inhibit expansion.
3950 Several shell options settable with the shopt builtin may be used to
3952 tailor the behavior of history expansion. If the histverify shell
3953 option is enabled (see the description of the shopt builtin below), and
3954 readline is being used, history substitutions are not immediately
3955 passed to the shell parser. Instead, the expanded line is reloaded
3956 into the readline editing buffer for further modification. If readline
3957 is being used, and the histreedit shell option is enabled, a failed
3958 history substitution will be reloaded into the readline editing buffer
3959 for correction. The -p option to the history builtin command may be
3960 used to see what a history expansion will do before using it. The -s
3961 option to the history builtin may be used to add commands to the end of
3962 the history list without actually executing them, so that they are
3963 available for subsequent recall.
3964 The shell allows control of the various characters used by the history
3966 expansion mechanism (see the description of histchars above under Shell
3967 Variables). The shell uses the history comment character to mark his‐
3968 tory timestamps when writing the history file.
3969 Event Designators
3971 An event designator is a reference to a command line entry in the his‐
3972 tory list. Unless the reference is absolute, events are relative to
3973 the current position in the history list.
3974 ! Start a history substitution, except when followed by a blank,
3976 newline, carriage return, = or ( (when the extglob shell option
3977 is enabled using the shopt builtin).
3978 !n Refer to command line n.
3979 !-n Refer to the current command minus n.
3980 !! Refer to the previous command. This is a synonym for `!-1'.
3981 !string
3982 Refer to the most recent command preceding the current position
3983 in the history list starting with string.
3984 !?string[?]
3985 Refer to the most recent command preceding the current position
3986 in the history list containing string. The trailing ? may be
3987 omitted if string is followed immediately by a newline.
3988 ^string1^string2^
3989 Quick substitution. Repeat the previous command, replacing
3990 string1 with string2. Equivalent to ``!!:s/string1/string2/''
3991 (see Modifiers below).
3992 !# The entire command line typed so far.
3993 Word Designators
3995 Word designators are used to select desired words from the event. A :
3996 separates the event specification from the word designator. It may be
3997 omitted if the word designator begins with a ^, $, *, -, or %. Words
3998 are numbered from the beginning of the line, with the first word being
3999 denoted by 0 (zero). Words are inserted into the current line sepa‐
4000 rated by single spaces.
4001 0 (zero)
4003 The zeroth word. For the shell, this is the command word.
4004 n The nth word.
4005 ^ The first argument. That is, word 1.
4006 $ The last word. This is usually the last argument, but will
4007 expand to the zeroth word if there is only one word in the line.
4008 % The word matched by the most recent `?string?' search.
4009 x-y A range of words; `-y' abbreviates `0-y'.
4010 * All of the words but the zeroth. This is a synonym for `1-$'.
4011 It is not an error to use * if there is just one word in the
4012 event; the empty string is returned in that case.
4013 x* Abbreviates x-$.
4014 x- Abbreviates x-$ like x*, but omits the last word.
4015 If a word designator is supplied without an event specification, the
4017 previous command is used as the event.
4018 Modifiers
4020 After the optional word designator, there may appear a sequence of one
4021 or more of the following modifiers, each preceded by a `:'.
4022 h Remove a trailing filename component, leaving only the head.
4024 t Remove all leading filename components, leaving the tail.
4025 r Remove a trailing suffix of the form .xxx, leaving the basename.
4026 e Remove all but the trailing suffix.
4027 p Print the new command but do not execute it.
4028 q Quote the substituted words, escaping further substitutions.
4029 x Quote the substituted words as with q, but break into words at
4030 blanks and newlines.
4031 s/old/new/
4032 Substitute new for the first occurrence of old in the event
4033 line. Any delimiter can be used in place of /. The final
4034 delimiter is optional if it is the last character of the event
4035 line. The delimiter may be quoted in old and new with a single
4036 backslash. If & appears in new, it is replaced by old. A sin‐
4037 gle backslash will quote the &. If old is null, it is set to
4038 the last old substituted, or, if no previous history substitu‐
4039 tions took place, the last string in a !?string[?] search.
4040 & Repeat the previous substitution.
4041 g Cause changes to be applied over the entire event line. This is
4042 used in conjunction with `:s' (e.g., `:gs/old/new/') or `:&'.
4043 If used with `:s', any delimiter can be used in place of /, and
4044 the final delimiter is optional if it is the last character of
4045 the event line. An a may be used as a synonym for g.
4046 G Apply the following `s' modifier once to each word in the event
4047 line.
4048
4050 Unless otherwise noted, each builtin command documented in this section
4051 as accepting options preceded by - accepts -- to signify the end of the
4052 options. The :, true, false, and test builtins do not accept options
4053 and do not treat -- specially. The exit, logout, return, break, con‐
4054 tinue, let, and shift builtins accept and process arguments beginning
4055 with - without requiring --. Other builtins that accept arguments but
4056 are not specified as accepting options interpret arguments beginning
4057 with - as invalid options and require -- to prevent this interpreta‐
4058 tion.
4059 : [arguments]
4060 No effect; the command does nothing beyond expanding arguments
4061 and performing any specified redirections. The return status is
4062 zero.
4063 . filename [arguments]
4065 source filename [arguments]
4066 Read and execute commands from filename in the current shell
4067 environment and return the exit status of the last command exe‐
4068 cuted from filename. If filename does not contain a slash,
4069 filenames in PATH are used to find the directory containing
4070 filename. The file searched for in PATH need not be executable.
4071 When bash is not in posix mode, the current directory is
4072 searched if no file is found in PATH. If the sourcepath option
4073 to the shopt builtin command is turned off, the PATH is not
4074 searched. If any arguments are supplied, they become the posi‐
4075 tional parameters when filename is executed. Otherwise the
4076 positional parameters are unchanged. If the -T option is
4077 enabled, source inherits any trap on DEBUG; if it is not, any
4078 DEBUG trap string is saved and restored around the call to
4079 source, and source unsets the DEBUG trap while it executes. If
4080 -T is not set, and the sourced file changes the DEBUG trap, the
4081 new value is retained when source completes. The return status
4082 is the status of the last command exited within the script (0 if
4083 no commands are executed), and false if filename is not found or
4084 cannot be read.
4085 alias [-p] [name[=value] ...]
4087 Alias with no arguments or with the -p option prints the list of
4088 aliases in the form alias name=value on standard output. When
4089 arguments are supplied, an alias is defined for each name whose
4090 value is given. A trailing space in value causes the next word
4091 to be checked for alias substitution when the alias is expanded.
4092 For each name in the argument list for which no value is sup‐
4093 plied, the name and value of the alias is printed. Alias
4094 returns true unless a name is given for which no alias has been
4095 defined.
4096 bg [jobspec ...]
4098 Resume each suspended job jobspec in the background, as if it
4099 had been started with &. If jobspec is not present, the shell's
4100 notion of the current job is used. bg jobspec returns 0 unless
4101 run when job control is disabled or, when run with job control
4102 enabled, any specified jobspec was not found or was started
4103 without job control.
4104 bind [-m keymap] [-lpsvPSVX]
4106 bind [-m keymap] [-q function] [-u function] [-r keyseq]
4107 bind [-m keymap] -f filename
4108 bind [-m keymap] -x keyseq:shell-command
4109 bind [-m keymap] keyseq:function-name
4110 bind [-m keymap] keyseq:readline-command
4111 Display current readline key and function bindings, bind a key
4112 sequence to a readline function or macro, or set a readline
4113 variable. Each non-option argument is a command as it would
4114 appear in .inputrc, but each binding or command must be passed
4115 as a separate argument; e.g., '"\C-x\C-r": re-read-init-file'.
4116 Options, if supplied, have the following meanings:
4117 -m keymap
4118 Use keymap as the keymap to be affected by the subsequent
4119 bindings. Acceptable keymap names are emacs, emacs-stan‐
4120 dard, emacs-meta, emacs-ctlx, vi, vi-move, vi-command,
4121 and vi-insert. vi is equivalent to vi-command (vi-move
4122 is also a synonym); emacs is equivalent to emacs-stan‐
4123 dard.
4124 -l List the names of all readline functions.
4125 -p Display readline function names and bindings in such a
4126 way that they can be re-read.
4127 -P List current readline function names and bindings.
4128 -s Display readline key sequences bound to macros and the
4129 strings they output in such a way that they can be re-
4130 read.
4131 -S Display readline key sequences bound to macros and the
4132 strings they output.
4133 -v Display readline variable names and values in such a way
4134 that they can be re-read.
4135 -V List current readline variable names and values.
4136 -f filename
4137 Read key bindings from filename.
4138 -q function
4139 Query about which keys invoke the named function.
4140 -u function
4141 Unbind all keys bound to the named function.
4142 -r keyseq
4143 Remove any current binding for keyseq.
4144 -x keyseq:shell-command
4145 Cause shell-command to be executed whenever keyseq is
4146 entered. When shell-command is executed, the shell sets
4147 the READLINE_LINE variable to the contents of the read‐
4148 line line buffer and the READLINE_POINT variable to the
4149 current location of the insertion point. If the executed
4150 command changes the value of READLINE_LINE or READ‐
4151 LINE_POINT, those new values will be reflected in the
4152 editing state.
4153 -X List all key sequences bound to shell commands and the
4154 associated commands in a format that can be reused as
4155 input.
4156 The return value is 0 unless an unrecognized option is given or
4158 an error occurred.
4159 break [n]
4161 Exit from within a for, while, until, or select loop. If n is
4162 specified, break n levels. n must be ≥ 1. If n is greater than
4163 the number of enclosing loops, all enclosing loops are exited.
4164 The return value is 0 unless n is not greater than or equal to
4165 1.
4166 builtin shell-builtin [arguments]
4168 Execute the specified shell builtin, passing it arguments, and
4169 return its exit status. This is useful when defining a function
4170 whose name is the same as a shell builtin, retaining the func‐
4171 tionality of the builtin within the function. The cd builtin is
4172 commonly redefined this way. The return status is false if
4173 shell-builtin is not a shell builtin command.
4174 caller [expr]
4176 Returns the context of any active subroutine call (a shell func‐
4177 tion or a script executed with the . or source builtins). With‐
4178 out expr, caller displays the line number and source filename of
4179 the current subroutine call. If a non-negative integer is sup‐
4180 plied as expr, caller displays the line number, subroutine name,
4181 and source file corresponding to that position in the current
4182 execution call stack. This extra information may be used, for
4183 example, to print a stack trace. The current frame is frame 0.
4184 The return value is 0 unless the shell is not executing a sub‐
4185 routine call or expr does not correspond to a valid position in
4186 the call stack.
4187 cd [-L|[-P [-e]] [-@]] [dir]
4189 Change the current directory to dir. if dir is not supplied,
4190 the value of the HOME shell variable is the default. Any addi‐
4191 tional arguments following dir are ignored. The variable CDPATH
4192 defines the search path for the directory containing dir: each
4193 directory name in CDPATH is searched for dir. Alternative
4194 directory names in CDPATH are separated by a colon (:). A null
4195 directory name in CDPATH is the same as the current directory,
4196 i.e., ``.''. If dir begins with a slash (/), then CDPATH is not
4197 used. The -P option causes cd to use the physical directory
4198 structure by resolving symbolic links while traversing dir and
4199 before processing instances of .. in dir (see also the -P option
4200 to the set builtin command); the -L option forces symbolic links
4201 to be followed by resolving the link after processing instances
4202 of .. in dir. If .. appears in dir, it is processed by removing
4203 the immediately previous pathname component from dir, back to a
4204 slash or the beginning of dir. If the -e option is supplied
4205 with -P, and the current working directory cannot be success‐
4206 fully determined after a successful directory change, cd will
4207 return an unsuccessful status. On systems that support it, the
4208 -@ option presents the extended attributes associated with a
4209 file as a directory. An argument of - is converted to $OLDPWD
4210 before the directory change is attempted. If a non-empty direc‐
4211 tory name from CDPATH is used, or if - is the first argument,
4212 and the directory change is successful, the absolute pathname of
4213 the new working directory is written to the standard output.
4214 The return value is true if the directory was successfully
4215 changed; false otherwise.
4216 command [-pVv] command [arg ...]
4218 Run command with args suppressing the normal shell function
4219 lookup. Only builtin commands or commands found in the PATH are
4220 executed. If the -p option is given, the search for command is
4221 performed using a default value for PATH that is guaranteed to
4222 find all of the standard utilities. If either the -V or -v
4223 option is supplied, a description of command is printed. The -v
4224 option causes a single word indicating the command or filename
4225 used to invoke command to be displayed; the -V option produces a
4226 more verbose description. If the -V or -v option is supplied,
4227 the exit status is 0 if command was found, and 1 if not. If
4228 neither option is supplied and an error occurred or command can‐
4229 not be found, the exit status is 127. Otherwise, the exit sta‐
4230 tus of the command builtin is the exit status of command.
4231 compgen [option] [word]
4233 Generate possible completion matches for word according to the
4234 options, which may be any option accepted by the complete
4235 builtin with the exception of -p and -r, and write the matches
4236 to the standard output. When using the -F or -C options, the
4237 various shell variables set by the programmable completion
4238 facilities, while available, will not have useful values.
4239 The matches will be generated in the same way as if the program‐
4241 mable completion code had generated them directly from a comple‐
4242 tion specification with the same flags. If word is specified,
4243 only those completions matching word will be displayed.
4244 The return value is true unless an invalid option is supplied,
4246 or no matches were generated.
4247 complete [-abcdefgjksuv] [-o comp-option] [-DE] [-A action] [-G glob‐
4249 pat] [-W wordlist] [-F function] [-C command]
4250 [-X filterpat] [-P prefix] [-S suffix] name [name ...]
4251 complete -pr [-DE] [name ...]
4252 Specify how arguments to each name should be completed. If the
4253 -p option is supplied, or if no options are supplied, existing
4254 completion specifications are printed in a way that allows them
4255 to be reused as input. The -r option removes a completion spec‐
4256 ification for each name, or, if no names are supplied, all com‐
4257 pletion specifications. The -D option indicates that the
4258 remaining options and actions should apply to the ``default''
4259 command completion; that is, completion attempted on a command
4260 for which no completion has previously been defined. The -E
4261 option indicates that the remaining options and actions should
4262 apply to ``empty'' command completion; that is, completion
4263 attempted on a blank line.
4264 The process of applying these completion specifications when
4266 word completion is attempted is described above under Program‐
4267 mable Completion.
4268 Other options, if specified, have the following meanings. The
4270 arguments to the -G, -W, and -X options (and, if necessary, the
4271 -P and -S options) should be quoted to protect them from expan‐
4272 sion before the complete builtin is invoked.
4273 -o comp-option
4274 The comp-option controls several aspects of the comp‐
4275 spec's behavior beyond the simple generation of comple‐
4276 tions. comp-option may be one of:
4277 bashdefault
4278 Perform the rest of the default bash completions
4279 if the compspec generates no matches.
4280 default Use readline's default filename completion if
4281 the compspec generates no matches.
4282 dirnames
4283 Perform directory name completion if the comp‐
4284 spec generates no matches.
4285 filenames
4286 Tell readline that the compspec generates file‐
4287 names, so it can perform any filename-specific
4288 processing (like adding a slash to directory
4289 names, quoting special characters, or suppress‐
4290 ing trailing spaces). Intended to be used with
4291 shell functions.
4292 noquote Tell readline not to quote the completed words
4293 if they are filenames (quoting filenames is the
4294 default).
4295 nosort Tell readline not to sort the list of possible
4296 completions alphabetically.
4297 nospace Tell readline not to append a space (the
4298 default) to words completed at the end of the
4299 line.
4300 plusdirs
4301 After any matches defined by the compspec are
4302 generated, directory name completion is
4303 attempted and any matches are added to the
4304 results of the other actions.
4305 -A action
4306 The action may be one of the following to generate a
4307 list of possible completions:
4308 alias Alias names. May also be specified as -a.
4309 arrayvar
4310 Array variable names.
4311 binding Readline key binding names.
4312 builtin Names of shell builtin commands. May also be
4313 specified as -b.
4314 command Command names. May also be specified as -c.
4315 directory
4316 Directory names. May also be specified as -d.
4317 disabled
4318 Names of disabled shell builtins.
4319 enabled Names of enabled shell builtins.
4320 export Names of exported shell variables. May also be
4321 specified as -e.
4322 file File names. May also be specified as -f.
4323 function
4324 Names of shell functions.
4325 group Group names. May also be specified as -g.
4326 helptopic
4327 Help topics as accepted by the help builtin.
4328 hostname
4329 Hostnames, as taken from the file specified by
4330 the HOSTFILE shell variable.
4331 job Job names, if job control is active. May also
4332 be specified as -j.
4333 keyword Shell reserved words. May also be specified as
4334 -k.
4335 running Names of running jobs, if job control is active.
4336 service Service names. May also be specified as -s.
4337 setopt Valid arguments for the -o option to the set
4338 builtin.
4339 shopt Shell option names as accepted by the shopt
4340 builtin.
4341 signal Signal names.
4342 stopped Names of stopped jobs, if job control is active.
4343 user User names. May also be specified as -u.
4344 variable
4345 Names of all shell variables. May also be spec‐
4346 ified as -v.
4347 -C command
4348 command is executed in a subshell environment, and its
4349 output is used as the possible completions.
4350 -F function
4351 The shell function function is executed in the current
4352 shell environment. When the function is executed, the
4353 first argument ($1) is the name of the command whose
4354 arguments are being completed, the second argument ($2)
4355 is the word being completed, and the third argument ($3)
4356 is the word preceding the word being completed on the
4357 current command line. When it finishes, the possible
4358 completions are retrieved from the value of the COMPRE‐
4359 PLY array variable.
4360 -G globpat
4361 The pathname expansion pattern globpat is expanded to
4362 generate the possible completions.
4363 -P prefix
4364 prefix is added at the beginning of each possible com‐
4365 pletion after all other options have been applied.
4366 -S suffix
4367 suffix is appended to each possible completion after all
4368 other options have been applied.
4369 -W wordlist
4370 The wordlist is split using the characters in the IFS
4371 special variable as delimiters, and each resultant word
4372 is expanded. The possible completions are the members
4373 of the resultant list which match the word being com‐
4374 pleted.
4375 -X filterpat
4376 filterpat is a pattern as used for pathname expansion.
4377 It is applied to the list of possible completions gener‐
4378 ated by the preceding options and arguments, and each
4379 completion matching filterpat is removed from the list.
4380 A leading ! in filterpat negates the pattern; in this
4381 case, any completion not matching filterpat is removed.
4382 The return value is true unless an invalid option is supplied,
4384 an option other than -p or -r is supplied without a name argu‐
4385 ment, an attempt is made to remove a completion specification
4386 for a name for which no specification exists, or an error occurs
4387 adding a completion specification.
4388 compopt [-o option] [-DE] [+o option] [name]
4390 Modify completion options for each name according to the
4391 options, or for the currently-executing completion if no names
4392 are supplied. If no options are given, display the completion
4393 options for each name or the current completion. The possible
4394 values of option are those valid for the complete builtin
4395 described above. The -D option indicates that the remaining
4396 options should apply to the ``default'' command completion; that
4397 is, completion attempted on a command for which no completion
4398 has previously been defined. The -E option indicates that the
4399 remaining options should apply to ``empty'' command completion;
4400 that is, completion attempted on a blank line.
4401 The return value is true unless an invalid option is supplied,
4403 an attempt is made to modify the options for a name for which no
4404 completion specification exists, or an output error occurs.
4405 continue [n]
4407 Resume the next iteration of the enclosing for, while, until, or
4408 select loop. If n is specified, resume at the nth enclosing
4409 loop. n must be ≥ 1. If n is greater than the number of
4410 enclosing loops, the last enclosing loop (the ``top-level''
4411 loop) is resumed. The return value is 0 unless n is not greater
4412 than or equal to 1.
4413 declare [-aAfFgilnrtux] [-p] [name[=value] ...]
4415 typeset [-aAfFgilnrtux] [-p] [name[=value] ...]
4416 Declare variables and/or give them attributes. If no names are
4417 given then display the values of variables. The -p option will
4418 display the attributes and values of each name. When -p is used
4419 with name arguments, additional options, other than -f and -F,
4420 are ignored. When -p is supplied without name arguments, it
4421 will display the attributes and values of all variables having
4422 the attributes specified by the additional options. If no other
4423 options are supplied with -p, declare will display the
4424 attributes and values of all shell variables. The -f option
4425 will restrict the display to shell functions. The -F option
4426 inhibits the display of function definitions; only the function
4427 name and attributes are printed. If the extdebug shell option
4428 is enabled using shopt, the source file name and line number
4429 where each name is defined are displayed as well. The -F option
4430 implies -f. The -g option forces variables to be created or
4431 modified at the global scope, even when declare is executed in a
4432 shell function. It is ignored in all other cases. The follow‐
4433 ing options can be used to restrict output to variables with the
4434 specified attribute or to give variables attributes:
4435 -a Each name is an indexed array variable (see Arrays
4436 above).
4437 -A Each name is an associative array variable (see Arrays
4438 above).
4439 -f Use function names only.
4440 -i The variable is treated as an integer; arithmetic evalua‐
4441 tion (see ARITHMETIC EVALUATION above) is performed when
4442 the variable is assigned a value.
4443 -l When the variable is assigned a value, all upper-case
4444 characters are converted to lower-case. The upper-case
4445 attribute is disabled.
4446 -n Give each name the nameref attribute, making it a name
4447 reference to another variable. That other variable is
4448 defined by the value of name. All references, assign‐
4449 ments, and attribute modifications to name, except those
4450 using or changing the -n attribute itself, are performed
4451 on the variable referenced by name's value. The nameref
4452 attribute cannot be applied to array variables.
4453 -r Make names readonly. These names cannot then be assigned
4454 values by subsequent assignment statements or unset.
4455 -t Give each name the trace attribute. Traced functions
4456 inherit the DEBUG and RETURN traps from the calling
4457 shell. The trace attribute has no special meaning for
4458 variables.
4459 -u When the variable is assigned a value, all lower-case
4460 characters are converted to upper-case. The lower-case
4461 attribute is disabled.
4462 -x Mark names for export to subsequent commands via the
4463 environment.
4464 Using `+' instead of `-' turns off the attribute instead, with
4466 the exceptions that +a may not be used to destroy an array vari‐
4467 able and +r will not remove the readonly attribute. When used
4468 in a function, declare and typeset make each name local, as with
4469 the local command, unless the -g option is supplied. If a vari‐
4470 able name is followed by =value, the value of the variable is
4471 set to value. When using -a or -A and the compound assignment
4472 syntax to create array variables, additional attributes do not
4473 take effect until subsequent assignments. The return value is 0
4474 unless an invalid option is encountered, an attempt is made to
4475 define a function using ``-f foo=bar'', an attempt is made to
4476 assign a value to a readonly variable, an attempt is made to
4477 assign a value to an array variable without using the compound
4478 assignment syntax (see Arrays above), one of the names is not a
4479 valid shell variable name, an attempt is made to turn off read‐
4480 only status for a readonly variable, an attempt is made to turn
4481 off array status for an array variable, or an attempt is made to
4482 display a non-existent function with -f.
4483 dirs [-clpv] [+n] [-n]
4485 Without options, displays the list of currently remembered
4486 directories. The default display is on a single line with
4487 directory names separated by spaces. Directories are added to
4488 the list with the pushd command; the popd command removes
4489 entries from the list. The current directory is always the
4490 first directory in the stack.
4491 -c Clears the directory stack by deleting all of the
4492 entries.
4493 -l Produces a listing using full pathnames; the default
4494 listing format uses a tilde to denote the home directory.
4495 -p Print the directory stack with one entry per line.
4496 -v Print the directory stack with one entry per line, pre‐
4497 fixing each entry with its index in the stack.
4498 +n Displays the nth entry counting from the left of the list
4499 shown by dirs when invoked without options, starting with
4500 zero.
4501 -n Displays the nth entry counting from the right of the
4502 list shown by dirs when invoked without options, starting
4503 with zero.
4504 The return value is 0 unless an invalid option is supplied or n
4506 indexes beyond the end of the directory stack.
4507 disown [-ar] [-h] [jobspec ... | pid ... ]
4509 Without options, remove each jobspec from the table of active
4510 jobs. If jobspec is not present, and neither the -a nor the -r
4511 option is supplied, the current job is used. If the -h option
4512 is given, each jobspec is not removed from the table, but is
4513 marked so that SIGHUP is not sent to the job if the shell
4514 receives a SIGHUP. If no jobspec is supplied, the -a option
4515 means to remove or mark all jobs; the -r option without a job‐
4516 spec argument restricts operation to running jobs. The return
4517 value is 0 unless a jobspec does not specify a valid job.
4518 echo [-neE] [arg ...]
4520 Output the args, separated by spaces, followed by a newline.
4521 The return status is 0 unless a write error occurs. If -n is
4522 specified, the trailing newline is suppressed. If the -e option
4523 is given, interpretation of the following backslash-escaped
4524 characters is enabled. The -E option disables the interpreta‐
4525 tion of these escape characters, even on systems where they are
4526 interpreted by default. The xpg_echo shell option may be used
4527 to dynamically determine whether or not echo expands these
4528 escape characters by default. echo does not interpret -- to
4529 mean the end of options. echo interprets the following escape
4530 sequences:
4531 \a alert (bell)
4532 \b backspace
4533 \c suppress further output
4534 \e
4535 \E an escape character
4536 \f form feed
4537 \n new line
4538 \r carriage return
4539 \t horizontal tab
4540 \v vertical tab
4541 \\ backslash
4542 \0nnn the eight-bit character whose value is the octal value
4543 nnn (zero to three octal digits)
4544 \xHH the eight-bit character whose value is the hexadecimal
4545 value HH (one or two hex digits)
4546 \uHHHH the Unicode (ISO/IEC 10646) character whose value is the
4547 hexadecimal value HHHH (one to four hex digits)
4548 \UHHHHHHHH
4549 the Unicode (ISO/IEC 10646) character whose value is the
4550 hexadecimal value HHHHHHHH (one to eight hex digits)
4551 enable [-a] [-dnps] [-f filename] [name ...]
4553 Enable and disable builtin shell commands. Disabling a builtin
4554 allows a disk command which has the same name as a shell builtin
4555 to be executed without specifying a full pathname, even though
4556 the shell normally searches for builtins before disk commands.
4557 If -n is used, each name is disabled; otherwise, names are
4558 enabled. For example, to use the test binary found via the PATH
4559 instead of the shell builtin version, run ``enable -n test''.
4560 The -f option means to load the new builtin command name from
4561 shared object filename, on systems that support dynamic loading.
4562 The -d option will delete a builtin previously loaded with -f.
4563 If no name arguments are given, or if the -p option is supplied,
4564 a list of shell builtins is printed. With no other option argu‐
4565 ments, the list consists of all enabled shell builtins. If -n
4566 is supplied, only disabled builtins are printed. If -a is sup‐
4567 plied, the list printed includes all builtins, with an indica‐
4568 tion of whether or not each is enabled. If -s is supplied, the
4569 output is restricted to the POSIX special builtins. The return
4570 value is 0 unless a name is not a shell builtin or there is an
4571 error loading a new builtin from a shared object.
4572 eval [arg ...]
4574 The args are read and concatenated together into a single com‐
4575 mand. This command is then read and executed by the shell, and
4576 its exit status is returned as the value of eval. If there are
4577 no args, or only null arguments, eval returns 0.
4578 exec [-cl] [-a name] [command [arguments]]
4580 If command is specified, it replaces the shell. No new process
4581 is created. The arguments become the arguments to command. If
4582 the -l option is supplied, the shell places a dash at the begin‐
4583 ning of the zeroth argument passed to command. This is what
4584 login(1) does. The -c option causes command to be executed with
4585 an empty environment. If -a is supplied, the shell passes name
4586 as the zeroth argument to the executed command. If command can‐
4587 not be executed for some reason, a non-interactive shell exits,
4588 unless the execfail shell option is enabled. In that case, it
4589 returns failure. An interactive shell returns failure if the
4590 file cannot be executed. If command is not specified, any redi‐
4591 rections take effect in the current shell, and the return status
4592 is 0. If there is a redirection error, the return status is 1.
4593 exit [n]
4595 Cause the shell to exit with a status of n. If n is omitted,
4596 the exit status is that of the last command executed. A trap on
4597 EXIT is executed before the shell terminates.
4598 export [-fn] [name[=word]] ...
4600 export -p
4601 The supplied names are marked for automatic export to the envi‐
4602 ronment of subsequently executed commands. If the -f option is
4603 given, the names refer to functions. If no names are given, or
4604 if the -p option is supplied, a list of names of all exported
4605 variables is printed. The -n option causes the export property
4606 to be removed from each name. If a variable name is followed by
4607 =word, the value of the variable is set to word. export returns
4608 an exit status of 0 unless an invalid option is encountered, one
4609 of the names is not a valid shell variable name, or -f is sup‐
4610 plied with a name that is not a function.
4611 fc [-e ename] [-lnr] [first] [last]
4613 fc -s [pat=rep] [cmd]
4614 The first form selects a range of commands from first to last
4615 from the history list and displays or edits and re-executes
4616 them. First and last may be specified as a string (to locate
4617 the last command beginning with that string) or as a number (an
4618 index into the history list, where a negative number is used as
4619 an offset from the current command number). If last is not
4620 specified it is set to the current command for listing (so that
4621 ``fc -l -10'' prints the last 10 commands) and to first other‐
4622 wise. If first is not specified it is set to the previous com‐
4623 mand for editing and -16 for listing.
4624 The -n option suppresses the command numbers when listing. The
4626 -r option reverses the order of the commands. If the -l option
4627 is given, the commands are listed on standard output. Other‐
4628 wise, the editor given by ename is invoked on a file containing
4629 those commands. If ename is not given, the value of the FCEDIT
4630 variable is used, and the value of EDITOR if FCEDIT is not set.
4631 If neither variable is set, vi is used. When editing is com‐
4632 plete, the edited commands are echoed and executed.
4633 In the second form, command is re-executed after each instance
4635 of pat is replaced by rep. Command is intepreted the same as
4636 first above. A useful alias to use with this is ``r="fc -s"'',
4637 so that typing ``r cc'' runs the last command beginning with
4638 ``cc'' and typing ``r'' re-executes the last command.
4639 If the first form is used, the return value is 0 unless an
4641 invalid option is encountered or first or last specify history
4642 lines out of range. If the -e option is supplied, the return
4643 value is the value of the last command executed or failure if an
4644 error occurs with the temporary file of commands. If the second
4645 form is used, the return status is that of the command re-exe‐
4646 cuted, unless cmd does not specify a valid history line, in
4647 which case fc returns failure.
4648 fg [jobspec]
4650 Resume jobspec in the foreground, and make it the current job.
4651 If jobspec is not present, the shell's notion of the current job
4652 is used. The return value is that of the command placed into
4653 the foreground, or failure if run when job control is disabled
4654 or, when run with job control enabled, if jobspec does not spec‐
4655 ify a valid job or jobspec specifies a job that was started
4656 without job control.
4657 getopts optstring name [args]
4659 getopts is used by shell procedures to parse positional parame‐
4660 ters. optstring contains the option characters to be recog‐
4661 nized; if a character is followed by a colon, the option is
4662 expected to have an argument, which should be separated from it
4663 by white space. The colon and question mark characters may not
4664 be used as option characters. Each time it is invoked, getopts
4665 places the next option in the shell variable name, initializing
4666 name if it does not exist, and the index of the next argument to
4667 be processed into the variable OPTIND. OPTIND is initialized to
4668 1 each time the shell or a shell script is invoked. When an
4669 option requires an argument, getopts places that argument into
4670 the variable OPTARG. The shell does not reset OPTIND automati‐
4671 cally; it must be manually reset between multiple calls to
4672 getopts within the same shell invocation if a new set of parame‐
4673 ters is to be used.
4674 When the end of options is encountered, getopts exits with a
4676 return value greater than zero. OPTIND is set to the index of
4677 the first non-option argument, and name is set to ?.
4678 getopts normally parses the positional parameters, but if more
4680 arguments are given in args, getopts parses those instead.
4681 getopts can report errors in two ways. If the first character
4683 of optstring is a colon, silent error reporting is used. In
4684 normal operation, diagnostic messages are printed when invalid
4685 options or missing option arguments are encountered. If the
4686 variable OPTERR is set to 0, no error messages will be dis‐
4687 played, even if the first character of optstring is not a colon.
4688 If an invalid option is seen, getopts places ? into name and, if
4690 not silent, prints an error message and unsets OPTARG. If
4691 getopts is silent, the option character found is placed in
4692 OPTARG and no diagnostic message is printed.
4693 If a required argument is not found, and getopts is not silent,
4695 a question mark (?) is placed in name, OPTARG is unset, and a
4696 diagnostic message is printed. If getopts is silent, then a
4697 colon (:) is placed in name and OPTARG is set to the option
4698 character found.
4699 getopts returns true if an option, specified or unspecified, is
4701 found. It returns false if the end of options is encountered or
4702 an error occurs.
4703 hash [-lr] [-p filename] [-dt] [name]
4705 Each time hash is invoked, the full pathname of the command name
4706 is determined by searching the directories in $PATH and remem‐
4707 bered. Any previously-remembered pathname is discarded. If the
4708 -p option is supplied, no path search is performed, and filename
4709 is used as the full filename of the command. The -r option
4710 causes the shell to forget all remembered locations. The -d
4711 option causes the shell to forget the remembered location of
4712 each name. If the -t option is supplied, the full pathname to
4713 which each name corresponds is printed. If multiple name argu‐
4714 ments are supplied with -t, the name is printed before the
4715 hashed full pathname. The -l option causes output to be dis‐
4716 played in a format that may be reused as input. If no arguments
4717 are given, or if only -l is supplied, information about remem‐
4718 bered commands is printed. The return status is true unless a
4719 name is not found or an invalid option is supplied.
4720 help [-dms] [pattern]
4722 Display helpful information about builtin commands. If pattern
4723 is specified, help gives detailed help on all commands matching
4724 pattern; otherwise help for all the builtins and shell control
4725 structures is printed.
4726 -d Display a short description of each pattern
4727 -m Display the description of each pattern in a manpage-like
4728 format
4729 -s Display only a short usage synopsis for each pattern
4730 The return status is 0 unless no command matches pattern.
4732 history [n]
4734 history -c
4735 history -d offset
4736 history -anrw [filename]
4737 history -p arg [arg ...]
4738 history -s arg [arg ...]
4739 With no options, display the command history list with line num‐
4740 bers. Lines listed with a * have been modified. An argument of
4741 n lists only the last n lines. If the shell variable HISTTIME‐
4742 FORMAT is set and not null, it is used as a format string for
4743 strftime(3) to display the time stamp associated with each dis‐
4744 played history entry. No intervening blank is printed between
4745 the formatted time stamp and the history line. If filename is
4746 supplied, it is used as the name of the history file; if not,
4747 the value of HISTFILE is used. Options, if supplied, have the
4748 following meanings:
4749 -c Clear the history list by deleting all the entries.
4750 -d offset
4751 Delete the history entry at position offset.
4752 -a Append the ``new'' history lines to the history file.
4753 These are history lines entered since the beginning of
4754 the current bash session, but not already appended to the
4755 history file.
4756 -n Read the history lines not already read from the history
4757 file into the current history list. These are lines
4758 appended to the history file since the beginning of the
4759 current bash session.
4760 -r Read the contents of the history file and append them to
4761 the current history list.
4762 -w Write the current history list to the history file, over‐
4763 writing the history file's contents.
4764 -p Perform history substitution on the following args and
4765 display the result on the standard output. Does not
4766 store the results in the history list. Each arg must be
4767 quoted to disable normal history expansion.
4768 -s Store the args in the history list as a single entry.
4769 The last command in the history list is removed before
4770 the args are added.
4771 If the HISTTIMEFORMAT variable is set, the time stamp informa‐
4773 tion associated with each history entry is written to the his‐
4774 tory file, marked with the history comment character. When the
4775 history file is read, lines beginning with the history comment
4776 character followed immediately by a digit are interpreted as
4777 timestamps for the following history entry. The return value is
4778 0 unless an invalid option is encountered, an error occurs while
4779 reading or writing the history file, an invalid offset is sup‐
4780 plied as an argument to -d, or the history expansion supplied as
4781 an argument to -p fails.
4782 jobs [-lnprs] [ jobspec ... ]
4784 jobs -x command [ args ... ]
4785 The first form lists the active jobs. The options have the fol‐
4786 lowing meanings:
4787 -l List process IDs in addition to the normal information.
4788 -n Display information only about jobs that have changed
4789 status since the user was last notified of their status.
4790 -p List only the process ID of the job's process group
4791 leader.
4792 -r Display only running jobs.
4793 -s Display only stopped jobs.
4794 If jobspec is given, output is restricted to information about
4796 that job. The return status is 0 unless an invalid option is
4797 encountered or an invalid jobspec is supplied.
4798 If the -x option is supplied, jobs replaces any jobspec found in
4800 command or args with the corresponding process group ID, and
4801 executes command passing it args, returning its exit status.
4802 kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...
4804 kill -l|-L [sigspec | exit_status]
4805 Send the signal named by sigspec or signum to the processes
4806 named by pid or jobspec. sigspec is either a case-insensitive
4807 signal name such as SIGKILL (with or without the SIG prefix) or
4808 a signal number; signum is a signal number. If sigspec is not
4809 present, then SIGTERM is assumed. An argument of -l lists the
4810 signal names. If any arguments are supplied when -l is given,
4811 the names of the signals corresponding to the arguments are
4812 listed, and the return status is 0. The exit_status argument to
4813 -l is a number specifying either a signal number or the exit
4814 status of a process terminated by a signal. The -L option is
4815 equivalent to -l. kill returns true if at least one signal was
4816 successfully sent, or false if an error occurs or an invalid
4817 option is encountered.
4818 let arg [arg ...]
4820 Each arg is an arithmetic expression to be evaluated (see ARITH‐
4821 METIC EVALUATION above). If the last arg evaluates to 0, let
4822 returns 1; 0 is returned otherwise.
4823 local [option] [name[=value] ... | - ]
4825 For each argument, a local variable named name is created, and
4826 assigned value. The option can be any of the options accepted
4827 by declare. When local is used within a function, it causes the
4828 variable name to have a visible scope restricted to that func‐
4829 tion and its children. If name is -, the set of shell options
4830 is made local to the function in which local is invoked: shell
4831 options changed using the set builtin inside the function are
4832 restored to their original values when the function returns.
4833 With no operands, local writes a list of local variables to the
4834 standard output. It is an error to use local when not within a
4835 function. The return status is 0 unless local is used outside a
4836 function, an invalid name is supplied, or name is a readonly
4837 variable.
4838 logout Exit a login shell.
4840 mapfile [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C
4842 callback] [-c quantum] [array]
4843 readarray [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C
4844 callback] [-c quantum] [array]
4845 Read lines from the standard input into the indexed array vari‐
4846 able array, or from file descriptor fd if the -u option is sup‐
4847 plied. The variable MAPFILE is the default array. Options, if
4848 supplied, have the following meanings:
4849 -d The first character of delim is used to terminate each
4850 input line, rather than newline.
4851 -n Copy at most count lines. If count is 0, all lines are
4852 copied.
4853 -O Begin assigning to array at index origin. The default
4854 index is 0.
4855 -s Discard the first count lines read.
4856 -t Remove a trailing delim (default newline) from each line
4857 read.
4858 -u Read lines from file descriptor fd instead of the stan‐
4859 dard input.
4860 -C Evaluate callback each time quantum lines are read. The
4861 -c option specifies quantum.
4862 -c Specify the number of lines read between each call to
4863 callback.
4864 If -C is specified without -c, the default quantum is 5000.
4866 When callback is evaluated, it is supplied the index of the next
4867 array element to be assigned and the line to be assigned to that
4868 element as additional arguments. callback is evaluated after
4869 the line is read but before the array element is assigned.
4870 If not supplied with an explicit origin, mapfile will clear
4872 array before assigning to it.
4873 mapfile returns successfully unless an invalid option or option
4875 argument is supplied, array is invalid or unassignable, or if
4876 array is not an indexed array.
4877 popd [-n] [+n] [-n]
4879 Removes entries from the directory stack. With no arguments,
4880 removes the top directory from the stack, and performs a cd to
4881 the new top directory. Arguments, if supplied, have the follow‐
4882 ing meanings:
4883 -n Suppresses the normal change of directory when removing
4884 directories from the stack, so that only the stack is
4885 manipulated.
4886 +n Removes the nth entry counting from the left of the list
4887 shown by dirs, starting with zero. For example: ``popd
4888 +0'' removes the first directory, ``popd +1'' the second.
4889 -n Removes the nth entry counting from the right of the list
4890 shown by dirs, starting with zero. For example: ``popd
4891 -0'' removes the last directory, ``popd -1'' the next to
4892 last.
4893 If the popd command is successful, a dirs is performed as well,
4895 and the return status is 0. popd returns false if an invalid
4896 option is encountered, the directory stack is empty, a non-exis‐
4897 tent directory stack entry is specified, or the directory change
4898 fails.
4899 printf [-v var] format [arguments]
4901 Write the formatted arguments to the standard output under the
4902 control of the format. The -v option causes the output to be
4903 assigned to the variable var rather than being printed to the
4904 standard output.
4905 The format is a character string which contains three types of
4907 objects: plain characters, which are simply copied to standard
4908 output, character escape sequences, which are converted and
4909 copied to the standard output, and format specifications, each
4910 of which causes printing of the next successive argument. In
4911 addition to the standard printf(1) format specifications, printf
4912 interprets the following extensions:
4913 %b causes printf to expand backslash escape sequences in the
4914 corresponding argument in the same way as echo -e.
4915 %q causes printf to output the corresponding argument in a
4916 format that can be reused as shell input.
4917 %(datefmt)T
4918 causes printf to output the date-time string resulting
4919 from using datefmt as a format string for strftime(3).
4920 The corresponding argument is an integer representing the
4921 number of seconds since the epoch. Two special argument
4922 values may be used: -1 represents the current time, and
4923 -2 represents the time the shell was invoked. If no
4924 argument is specified, conversion behaves as if -1 had
4925 been given. This is an exception to the usual printf
4926 behavior.
4927 Arguments to non-string format specifiers are treated as C con‐
4929 stants, except that a leading plus or minus sign is allowed, and
4930 if the leading character is a single or double quote, the value
4931 is the ASCII value of the following character.
4932 The format is reused as necessary to consume all of the argu‐
4934 ments. If the format requires more arguments than are supplied,
4935 the extra format specifications behave as if a zero value or
4936 null string, as appropriate, had been supplied. The return
4937 value is zero on success, non-zero on failure.
4938 pushd [-n] [+n] [-n]
4940 pushd [-n] [dir]
4941 Adds a directory to the top of the directory stack, or rotates
4942 the stack, making the new top of the stack the current working
4943 directory. With no arguments, pushd exchanges the top two
4944 directories and returns 0, unless the directory stack is empty.
4945 Arguments, if supplied, have the following meanings:
4946 -n Suppresses the normal change of directory when rotating
4947 or adding directories to the stack, so that only the
4948 stack is manipulated.
4949 +n Rotates the stack so that the nth directory (counting
4950 from the left of the list shown by dirs, starting with
4951 zero) is at the top.
4952 -n Rotates the stack so that the nth directory (counting
4953 from the right of the list shown by dirs, starting with
4954 zero) is at the top.
4955 dir Adds dir to the directory stack at the top, making it the
4956 new current working directory as if it had been supplied
4957 as the argument to the cd builtin.
4958 If the pushd command is successful, a dirs is performed as well.
4960 If the first form is used, pushd returns 0 unless the cd to dir
4961 fails. With the second form, pushd returns 0 unless the direc‐
4962 tory stack is empty, a non-existent directory stack element is
4963 specified, or the directory change to the specified new current
4964 directory fails.
4965 pwd [-LP]
4967 Print the absolute pathname of the current working directory.
4968 The pathname printed contains no symbolic links if the -P option
4969 is supplied or the -o physical option to the set builtin command
4970 is enabled. If the -L option is used, the pathname printed may
4971 contain symbolic links. The return status is 0 unless an error
4972 occurs while reading the name of the current directory or an
4973 invalid option is supplied.
4974 read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p
4976 prompt] [-t timeout] [-u fd] [name ...]
4977 One line is read from the standard input, or from the file
4978 descriptor fd supplied as an argument to the -u option, split
4979 into words as described above under Word Splitting, and the
4980 first word is assigned to the first name, the second word to the
4981 second name, and so on. If there are more words than names, the
4982 remaining words and their intervening delimiters are assigned to
4983 the last name. If there are fewer words read from the input
4984 stream than names, the remaining names are assigned empty val‐
4985 ues. The characters in IFS are used to split the line into
4986 words using the same rules the shell uses for expansion
4987 (described above under Word Splitting). The backslash character
4988 (\) may be used to remove any special meaning for the next char‐
4989 acter read and for line continuation. Options, if supplied,
4990 have the following meanings:
4991 -a aname
4992 The words are assigned to sequential indices of the array
4993 variable aname, starting at 0. aname is unset before any
4994 new values are assigned. Other name arguments are
4995 ignored.
4996 -d delim
4997 The first character of delim is used to terminate the
4998 input line, rather than newline.
4999 -e If the standard input is coming from a terminal, readline
5000 (see READLINE above) is used to obtain the line. Read‐
5001 line uses the current (or default, if line editing was
5002 not previously active) editing settings.
5003 -i text
5004 If readline is being used to read the line, text is
5005 placed into the editing buffer before editing begins.
5006 -n nchars
5007 read returns after reading nchars characters rather than
5008 waiting for a complete line of input, but honors a delim‐
5009 iter if fewer than nchars characters are read before the
5010 delimiter.
5011 -N nchars
5012 read returns after reading exactly nchars characters
5013 rather than waiting for a complete line of input, unless
5014 EOF is encountered or read times out. Delimiter charac‐
5015 ters encountered in the input are not treated specially
5016 and do not cause read to return until nchars characters
5017 are read. The result is not split on the characters in
5018 IFS; the intent is that the variable is assigned exactly
5019 the characters read (with the exception of backslash; see
5020 the -r option below).
5021 -p prompt
5022 Display prompt on standard error, without a trailing new‐
5023 line, before attempting to read any input. The prompt is
5024 displayed only if input is coming from a terminal.
5025 -r Backslash does not act as an escape character. The back‐
5026 slash is considered to be part of the line. In particu‐
5027 lar, a backslash-newline pair may not be used as a line
5028 continuation.
5029 -s Silent mode. If input is coming from a terminal, charac‐
5030 ters are not echoed.
5031 -t timeout
5032 Cause read to time out and return failure if a complete
5033 line of input (or a specified number of characters) is
5034 not read within timeout seconds. timeout may be a deci‐
5035 mal number with a fractional portion following the deci‐
5036 mal point. This option is only effective if read is
5037 reading input from a terminal, pipe, or other special
5038 file; it has no effect when reading from regular files.
5039 If read times out, read saves any partial input read into
5040 the specified variable name. If timeout is 0, read
5041 returns immediately, without trying to read any data.
5042 The exit status is 0 if input is available on the speci‐
5043 fied file descriptor, non-zero otherwise. The exit sta‐
5044 tus is greater than 128 if the timeout is exceeded.
5045 -u fd Read input from file descriptor fd.
5046 If no names are supplied, the line read is assigned to the vari‐
5048 able REPLY. The exit status is zero, unless end-of-file is
5049 encountered, read times out (in which case the status is greater
5050 than 128), a variable assignment error (such as assigning to a
5051 readonly variable) occurs, or an invalid file descriptor is sup‐
5052 plied as the argument to -u.
5053 readonly [-aAf] [-p] [name[=word] ...]
5055 The given names are marked readonly; the values of these names
5056 may not be changed by subsequent assignment. If the -f option
5057 is supplied, the functions corresponding to the names are so
5058 marked. The -a option restricts the variables to indexed
5059 arrays; the -A option restricts the variables to associative
5060 arrays. If both options are supplied, -A takes precedence. If
5061 no name arguments are given, or if the -p option is supplied, a
5062 list of all readonly names is printed. The other options may be
5063 used to restrict the output to a subset of the set of readonly
5064 names. The -p option causes output to be displayed in a format
5065 that may be reused as input. If a variable name is followed by
5066 =word, the value of the variable is set to word. The return
5067 status is 0 unless an invalid option is encountered, one of the
5068 names is not a valid shell variable name, or -f is supplied with
5069 a name that is not a function.
5070 return [n]
5072 Causes a function to stop executing and return the value speci‐
5073 fied by n to its caller. If n is omitted, the return status is
5074 that of the last command executed in the function body. If
5075 return is executed by a trap handler, the last command used to
5076 determine the status is the last command executed before the
5077 trap handler. if return is executed during a DEBUG trap, the
5078 last command used to determine the status is the last command
5079 executed by the trap handler before return was invoked. If
5080 return is used outside a function, but during execution of a
5081 script by the . (source) command, it causes the shell to stop
5082 executing that script and return either n or the exit status of
5083 the last command executed within the script as the exit status
5084 of the script. If n is supplied, the return value is its least
5085 significant 8 bits. The return status is non-zero if return is
5086 supplied a non-numeric argument, or is used outside a function
5087 and not during execution of a script by . or source. Any com‐
5088 mand associated with the RETURN trap is executed before execu‐
5089 tion resumes after the function or script.
5090 set [--abefhkmnptuvxBCEHPT] [-o option-name] [arg ...]
5092 set [+abefhkmnptuvxBCEHPT] [+o option-name] [arg ...]
5093 Without options, the name and value of each shell variable are
5094 displayed in a format that can be reused as input for setting or
5095 resetting the currently-set variables. Read-only variables can‐
5096 not be reset. In posix mode, only shell variables are listed.
5097 The output is sorted according to the current locale. When
5098 options are specified, they set or unset shell attributes. Any
5099 arguments remaining after option processing are treated as val‐
5100 ues for the positional parameters and are assigned, in order, to
5101 $1, $2, ... $n. Options, if specified, have the following
5102 meanings:
5103 -a Each variable or function that is created or modified is
5104 given the export attribute and marked for export to the
5105 environment of subsequent commands.
5106 -b Report the status of terminated background jobs immedi‐
5107 ately, rather than before the next primary prompt. This
5108 is effective only when job control is enabled.
5109 -e Exit immediately if a pipeline (which may consist of a
5110 single simple command), a list, or a compound command
5111 (see SHELL GRAMMAR above), exits with a non-zero status.
5112 The shell does not exit if the command that fails is
5113 part of the command list immediately following a while
5114 or until keyword, part of the test following the if or
5115 elif reserved words, part of any command executed in a
5116 && or || list except the command following the final &&
5117 or ||, any command in a pipeline but the last, or if the
5118 command's return value is being inverted with !. If a
5119 compound command other than a subshell returns a non-
5120 zero status because a command failed while -e was being
5121 ignored, the shell does not exit. A trap on ERR, if
5122 set, is executed before the shell exits. This option
5123 applies to the shell environment and each subshell envi‐
5124 ronment separately (see COMMAND EXECUTION ENVIRONMENT
5125 above), and may cause subshells to exit before executing
5126 all the commands in the subshell.
5127 If a compound command or shell function executes in a
5129 context where -e is being ignored, none of the commands
5130 executed within the compound command or function body
5131 will be affected by the -e setting, even if -e is set
5132 and a command returns a failure status. If a compound
5133 command or shell function sets -e while executing in a
5134 context where -e is ignored, that setting will not have
5135 any effect until the compound command or the command
5136 containing the function call completes.
5137 -f Disable pathname expansion.
5138 -h Remember the location of commands as they are looked up
5139 for execution. This is enabled by default.
5140 -k All arguments in the form of assignment statements are
5141 placed in the environment for a command, not just those
5142 that precede the command name.
5143 -m Monitor mode. Job control is enabled. This option is
5144 on by default for interactive shells on systems that
5145 support it (see JOB CONTROL above). All processes run
5146 in a separate process group. When a background job com‐
5147 pletes, the shell prints a line containing its exit sta‐
5148 tus.
5149 -n Read commands but do not execute them. This may be used
5150 to check a shell script for syntax errors. This is
5151 ignored by interactive shells.
5152 -o option-name
5153 The option-name can be one of the following:
5154 allexport
5155 Same as -a.
5156 braceexpand
5157 Same as -B.
5158 emacs Use an emacs-style command line editing inter‐
5159 face. This is enabled by default when the shell
5160 is interactive, unless the shell is started with
5161 the --noediting option. This also affects the
5162 editing interface used for read -e.
5163 errexit Same as -e.
5164 errtrace
5165 Same as -E.
5166 functrace
5167 Same as -T.
5168 hashall Same as -h.
5169 histexpand
5170 Same as -H.
5171 history Enable command history, as described above under
5172 HISTORY. This option is on by default in inter‐
5173 active shells.
5174 ignoreeof
5175 The effect is as if the shell command
5176 ``IGNOREEOF=10'' had been executed (see Shell
5177 Variables above).
5178 keyword Same as -k.
5179 monitor Same as -m.
5180 noclobber
5181 Same as -C.
5182 noexec Same as -n.
5183 noglob Same as -f.
5184 nolog Currently ignored.
5185 notify Same as -b.
5186 nounset Same as -u.
5187 onecmd Same as -t.
5188 physical
5189 Same as -P.
5190 pipefail
5191 If set, the return value of a pipeline is the
5192 value of the last (rightmost) command to exit
5193 with a non-zero status, or zero if all commands
5194 in the pipeline exit successfully. This option
5195 is disabled by default.
5196 posix Change the behavior of bash where the default
5197 operation differs from the POSIX standard to
5198 match the standard (posix mode). See SEE ALSO
5199 below for a reference to a document that details
5200 how posix mode affects bash's behavior.
5201 privileged
5202 Same as -p.
5203 verbose Same as -v.
5204 vi Use a vi-style command line editing interface.
5205 This also affects the editing interface used for
5206 read -e.
5207 xtrace Same as -x.
5208 If -o is supplied with no option-name, the values of the
5209 current options are printed. If +o is supplied with no
5210 option-name, a series of set commands to recreate the
5211 current option settings is displayed on the standard
5212 output.
5213 -p Turn on privileged mode. In this mode, the $ENV and
5214 $BASH_ENV files are not processed, shell functions are
5215 not inherited from the environment, and the SHELLOPTS,
5216 BASHOPTS, CDPATH, and GLOBIGNORE variables, if they
5217 appear in the environment, are ignored. If the shell is
5218 started with the effective user (group) id not equal to
5219 the real user (group) id, and the -p option is not sup‐
5220 plied, these actions are taken and the effective user id
5221 is set to the real user id. If the -p option is sup‐
5222 plied at startup, the effective user id is not reset.
5223 Turning this option off causes the effective user and
5224 group ids to be set to the real user and group ids.
5225 -t Exit after reading and executing one command.
5226 -u Treat unset variables and parameters other than the spe‐
5227 cial parameters "@" and "*" as an error when performing
5228 parameter expansion. If expansion is attempted on an
5229 unset variable or parameter, the shell prints an error
5230 message, and, if not interactive, exits with a non-zero
5231 status.
5232 -v Print shell input lines as they are read.
5233 -x After expanding each simple command, for command, case
5234 command, select command, or arithmetic for command, dis‐
5235 play the expanded value of PS4, followed by the command
5236 and its expanded arguments or associated word list.
5237 -B The shell performs brace expansion (see Brace Expansion
5238 above). This is on by default.
5239 -C If set, bash does not overwrite an existing file with
5240 the >, >&, and <> redirection operators. This may be
5241 overridden when creating output files by using the redi‐
5242 rection operator >| instead of >.
5243 -E If set, any trap on ERR is inherited by shell functions,
5244 command substitutions, and commands executed in a sub‐
5245 shell environment. The ERR trap is normally not inher‐
5246 ited in such cases.
5247 -H Enable ! style history substitution. This option is on
5248 by default when the shell is interactive.
5249 -P If set, the shell does not resolve symbolic links when
5250 executing commands such as cd that change the current
5251 working directory. It uses the physical directory
5252 structure instead. By default, bash follows the logical
5253 chain of directories when performing commands which
5254 change the current directory.
5255 -T If set, any traps on DEBUG and RETURN are inherited by
5256 shell functions, command substitutions, and commands
5257 executed in a subshell environment. The DEBUG and
5258 RETURN traps are normally not inherited in such cases.
5259 -- If no arguments follow this option, then the positional
5260 parameters are unset. Otherwise, the positional parame‐
5261 ters are set to the args, even if some of them begin
5262 with a -.
5263 - Signal the end of options, cause all remaining args to
5264 be assigned to the positional parameters. The -x and -v
5265 options are turned off. If there are no args, the posi‐
5266 tional parameters remain unchanged.
5267 The options are off by default unless otherwise noted. Using +
5269 rather than - causes these options to be turned off. The
5270 options can also be specified as arguments to an invocation of
5271 the shell. The current set of options may be found in $-. The
5272 return status is always true unless an invalid option is encoun‐
5273 tered.
5274 shift [n]
5276 The positional parameters from n+1 ... are renamed to $1 ....
5277 Parameters represented by the numbers $# down to $#-n+1 are
5278 unset. n must be a non-negative number less than or equal to
5279 $#. If n is 0, no parameters are changed. If n is not given,
5280 it is assumed to be 1. If n is greater than $#, the positional
5281 parameters are not changed. The return status is greater than
5282 zero if n is greater than $# or less than zero; otherwise 0.
5283 shopt [-pqsu] [-o] [optname ...]
5285 Toggle the values of settings controlling optional shell behav‐
5286 ior. The settings can be either those listed below, or, if the
5287 -o option is used, those available with the -o option to the set
5288 builtin command. With no options, or with the -p option, a list
5289 of all settable options is displayed, with an indication of
5290 whether or not each is set. The -p option causes output to be
5291 displayed in a form that may be reused as input. Other options
5292 have the following meanings:
5293 -s Enable (set) each optname.
5294 -u Disable (unset) each optname.
5295 -q Suppresses normal output (quiet mode); the return status
5296 indicates whether the optname is set or unset. If multi‐
5297 ple optname arguments are given with -q, the return sta‐
5298 tus is zero if all optnames are enabled; non-zero other‐
5299 wise.
5300 -o Restricts the values of optname to be those defined for
5301 the -o option to the set builtin.
5302 If either -s or -u is used with no optname arguments, shopt
5304 shows only those options which are set or unset, respectively.
5305 Unless otherwise noted, the shopt options are disabled (unset)
5306 by default.
5307 The return status when listing options is zero if all optnames
5309 are enabled, non-zero otherwise. When setting or unsetting
5310 options, the return status is zero unless an optname is not a
5311 valid shell option.
5312 The list of shopt options is:
5314 autocd If set, a command name that is the name of a directory
5316 is executed as if it were the argument to the cd com‐
5317 mand. This option is only used by interactive shells.
5318 cdable_vars
5319 If set, an argument to the cd builtin command that is
5320 not a directory is assumed to be the name of a variable
5321 whose value is the directory to change to.
5322 cdspell If set, minor errors in the spelling of a directory com‐
5323 ponent in a cd command will be corrected. The errors
5324 checked for are transposed characters, a missing charac‐
5325 ter, and one character too many. If a correction is
5326 found, the corrected filename is printed, and the com‐
5327 mand proceeds. This option is only used by interactive
5328 shells.
5329 checkhash
5330 If set, bash checks that a command found in the hash ta‐
5331 ble exists before trying to execute it. If a hashed
5332 command no longer exists, a normal path search is per‐
5333 formed.
5334 checkjobs
5335 If set, bash lists the status of any stopped and running
5336 jobs before exiting an interactive shell. If any jobs
5337 are running, this causes the exit to be deferred until a
5338 second exit is attempted without an intervening command
5339 (see JOB CONTROL above). The shell always postpones
5340 exiting if any jobs are stopped.
5341 checkwinsize
5342 If set, bash checks the window size after each command
5343 and, if necessary, updates the values of LINES and COL‐
5344 UMNS.
5345 cmdhist If set, bash attempts to save all lines of a multiple-
5346 line command in the same history entry. This allows
5347 easy re-editing of multi-line commands.
5348 compat31
5349 If set, bash changes its behavior to that of version 3.1
5350 with respect to quoted arguments to the [[ conditional
5351 command's =~ operator and locale-specific string compar‐
5352 ison when using the [[ conditional command's < and >
5353 operators. Bash versions prior to bash-4.1 use ASCII
5354 collation and strcmp(3); bash-4.1 and later use the cur‐
5355 rent locale's collation sequence and strcoll(3).
5356 compat32
5357 If set, bash changes its behavior to that of version 3.2
5358 with respect to locale-specific string comparison when
5359 using the [[ conditional command's < and > operators
5360 (see previous item) and the effect of interrupting a
5361 command list. Bash versions 3.2 and earlier continue
5362 with the next command in the list after one terminates
5363 due to an interrupt.
5364 compat40
5365 If set, bash changes its behavior to that of version 4.0
5366 with respect to locale-specific string comparison when
5367 using the [[ conditional command's < and > operators
5368 (see description of compat31) and the effect of inter‐
5369 rupting a command list. Bash versions 4.0 and later
5370 interrupt the list as if the shell received the inter‐
5371 rupt; previous versions continue with the next command
5372 in the list.
5373 compat41
5374 If set, bash, when in posix mode, treats a single quote
5375 in a double-quoted parameter expansion as a special
5376 character. The single quotes must match (an even num‐
5377 ber) and the characters between the single quotes are
5378 considered quoted. This is the behavior of posix mode
5379 through version 4.1. The default bash behavior remains
5380 as in previous versions.
5381 compat42
5382 If set, bash does not process the replacement string in
5383 the pattern substitution word expansion using quote
5384 removal.
5385 compat43
5386 If set, bash does not print a warning message if an
5387 attempt is made to use a quoted compound array assign‐
5388 ment as an argument to declare, makes word expansion
5389 errors non-fatal errors that cause the current command
5390 to fail (the default behavior is to make them fatal
5391 errors that cause the shell to exit), and does not reset
5392 the loop state when a shell function is executed (this
5393 allows break or continue in a shell function to affect
5394 loops in the caller's context).
5395 complete_fullquote
5396 If set, bash quotes all shell metacharacters in file‐
5397 names and directory names when performing completion.
5398 If not set, bash removes metacharacters such as the dol‐
5399 lar sign from the set of characters that will be quoted
5400 in completed filenames when these metacharacters appear
5401 in shell variable references in words to be completed.
5402 This means that dollar signs in variable names that
5403 expand to directories will not be quoted; however, any
5404 dollar signs appearing in filenames will not be quoted,
5405 either. This is active only when bash is using back‐
5406 slashes to quote completed filenames. This variable is
5407 set by default, which is the default bash behavior in
5408 versions through 4.2.
5409 direxpand
5410 If set, bash replaces directory names with the results
5411 of word expansion when performing filename completion.
5412 This changes the contents of the readline editing buf‐
5413 fer. If not set, bash attempts to preserve what the
5414 user typed.
5415 dirspell
5416 If set, bash attempts spelling correction on directory
5417 names during word completion if the directory name ini‐
5418 tially supplied does not exist.
5419 dotglob If set, bash includes filenames beginning with a `.' in
5420 the results of pathname expansion.
5421 execfail
5422 If set, a non-interactive shell will not exit if it can‐
5423 not execute the file specified as an argument to the
5424 exec builtin command. An interactive shell does not
5425 exit if exec fails.
5426 expand_aliases
5427 If set, aliases are expanded as described above under
5428 ALIASES. This option is enabled by default for interac‐
5429 tive shells.
5430 extdebug
5431 If set at shell invocation, arrange to execute the
5432 debugger profile before the shell starts, identical to
5433 the --debugger option. If set after invocation, behav‐
5434 ior intended for use by debuggers is enabled:
5435 1. The -F option to the declare builtin displays the
5436 source file name and line number corresponding to
5437 each function name supplied as an argument.
5438 2. If the command run by the DEBUG trap returns a
5439 non-zero value, the next command is skipped and
5440 not executed.
5441 3. If the command run by the DEBUG trap returns a
5442 value of 2, and the shell is executing in a sub‐
5443 routine (a shell function or a shell script exe‐
5444 cuted by the . or source builtins), the shell
5445 simulates a call to return.
5446 4. BASH_ARGC and BASH_ARGV are updated as described
5447 in their descriptions above.
5448 5. Function tracing is enabled: command substitu‐
5449 tion, shell functions, and subshells invoked with
5450 ( command ) inherit the DEBUG and RETURN traps.
5451 6. Error tracing is enabled: command substitution,
5452 shell functions, and subshells invoked with (
5453 command ) inherit the ERR trap.
5454 extglob If set, the extended pattern matching features described
5455 above under Pathname Expansion are enabled.
5456 extquote
5457 If set, $'string' and $"string" quoting is performed
5458 within ${parameter} expansions enclosed in double
5459 quotes. This option is enabled by default.
5460 failglob
5461 If set, patterns which fail to match filenames during
5462 pathname expansion result in an expansion error.
5463 force_fignore
5464 If set, the suffixes specified by the FIGNORE shell
5465 variable cause words to be ignored when performing word
5466 completion even if the ignored words are the only possi‐
5467 ble completions. See SHELL VARIABLES above for a
5468 description of FIGNORE. This option is enabled by
5469 default.
5470 globasciiranges
5471 If set, range expressions used in pattern matching
5472 bracket expressions (see Pattern Matching above) behave
5473 as if in the traditional C locale when performing com‐
5474 parisons. That is, the current locale's collating
5475 sequence is not taken into account, so b will not col‐
5476 late between A and B, and upper-case and lower-case
5477 ASCII characters will collate together.
5478 globstar
5479 If set, the pattern ** used in a pathname expansion con‐
5480 text will match all files and zero or more directories
5481 and subdirectories. If the pattern is followed by a /,
5482 only directories and subdirectories match.
5483 gnu_errfmt
5484 If set, shell error messages are written in the standard
5485 GNU error message format.
5486 histappend
5487 If set, the history list is appended to the file named
5488 by the value of the HISTFILE variable when the shell
5489 exits, rather than overwriting the file.
5490 histreedit
5491 If set, and readline is being used, a user is given the
5492 opportunity to re-edit a failed history substitution.
5493 histverify
5494 If set, and readline is being used, the results of his‐
5495 tory substitution are not immediately passed to the
5496 shell parser. Instead, the resulting line is loaded
5497 into the readline editing buffer, allowing further modi‐
5498 fication.
5499 hostcomplete
5500 If set, and readline is being used, bash will attempt to
5501 perform hostname completion when a word containing a @
5502 is being completed (see Completing under READLINE
5503 above). This is enabled by default.
5504 huponexit
5505 If set, bash will send SIGHUP to all jobs when an inter‐
5506 active login shell exits.
5507 inherit_errexit
5508 If set, command substitution inherits the value of the
5509 errexit option, instead of unsetting it in the subshell
5510 environment. This option is enabled when posix mode is
5511 enabled.
5512 interactive_comments
5513 If set, allow a word beginning with # to cause that word
5514 and all remaining characters on that line to be ignored
5515 in an interactive shell (see COMMENTS above). This
5516 option is enabled by default.
5517 lastpipe
5518 If set, and job control is not active, the shell runs
5519 the last command of a pipeline not executed in the back‐
5520 ground in the current shell environment.
5521 lithist If set, and the cmdhist option is enabled, multi-line
5522 commands are saved to the history with embedded newlines
5523 rather than using semicolon separators where possible.
5524 login_shell
5525 The shell sets this option if it is started as a login
5526 shell (see INVOCATION above). The value may not be
5527 changed.
5528 mailwarn
5529 If set, and a file that bash is checking for mail has
5530 been accessed since the last time it was checked, the
5531 message ``The mail in mailfile has been read'' is dis‐
5532 played.
5533 no_empty_cmd_completion
5534 If set, and readline is being used, bash will not
5535 attempt to search the PATH for possible completions when
5536 completion is attempted on an empty line.
5537 nocaseglob
5538 If set, bash matches filenames in a case-insensitive
5539 fashion when performing pathname expansion (see Pathname
5540 Expansion above).
5541 nocasematch
5542 If set, bash matches patterns in a case-insensitive
5543 fashion when performing matching while executing case or
5544 [[ conditional commands, when performing pattern substi‐
5545 tution word expansions, or when filtering possible com‐
5546 pletions as part of programmable completion.
5547 nullglob
5548 If set, bash allows patterns which match no files (see
5549 Pathname Expansion above) to expand to a null string,
5550 rather than themselves.
5551 progcomp
5552 If set, the programmable completion facilities (see Pro‐
5553 grammable Completion above) are enabled. This option is
5554 enabled by default.
5555 promptvars
5556 If set, prompt strings undergo parameter expansion, com‐
5557 mand substitution, arithmetic expansion, and quote
5558 removal after being expanded as described in PROMPTING
5559 above. This option is enabled by default.
5560 restricted_shell
5561 The shell sets this option if it is started in
5562 restricted mode (see RESTRICTED SHELL below). The value
5563 may not be changed. This is not reset when the startup
5564 files are executed, allowing the startup files to dis‐
5565 cover whether or not a shell is restricted.
5566 shift_verbose
5567 If set, the shift builtin prints an error message when
5568 the shift count exceeds the number of positional parame‐
5569 ters.
5570 sourcepath
5571 If set, the source (.) builtin uses the value of PATH to
5572 find the directory containing the file supplied as an
5573 argument. This option is enabled by default.
5574 xpg_echo
5575 If set, the echo builtin expands backslash-escape
5576 sequences by default.
5577 suspend [-f]
5579 Suspend the execution of this shell until it receives a SIGCONT
5580 signal. A login shell cannot be suspended; the -f option can be
5581 used to override this and force the suspension. The return sta‐
5582 tus is 0 unless the shell is a login shell and -f is not sup‐
5583 plied, or if job control is not enabled.
5584 test expr
5586 [ expr ]
5587 Return a status of 0 (true) or 1 (false) depending on the evalu‐
5588 ation of the conditional expression expr. Each operator and op‐
5589 erand must be a separate argument. Expressions are composed of
5590 the primaries described above under CONDITIONAL EXPRESSIONS.
5591 test does not accept any options, nor does it accept and ignore
5592 an argument of -- as signifying the end of options.
5593 Expressions may be combined using the following operators,
5595 listed in decreasing order of precedence. The evaluation
5596 depends on the number of arguments; see below. Operator prece‐
5597 dence is used when there are five or more arguments.
5598 ! expr True if expr is false.
5599 ( expr )
5600 Returns the value of expr. This may be used to override
5601 the normal precedence of operators.
5602 expr1 -a expr2
5603 True if both expr1 and expr2 are true.
5604 expr1 -o expr2
5605 True if either expr1 or expr2 is true.
5606 test and [ evaluate conditional expressions using a set of rules
5608 based on the number of arguments.
5609 0 arguments
5611 The expression is false.
5612 1 argument
5613 The expression is true if and only if the argument is not
5614 null.
5615 2 arguments
5616 If the first argument is !, the expression is true if and
5617 only if the second argument is null. If the first argu‐
5618 ment is one of the unary conditional operators listed
5619 above under CONDITIONAL EXPRESSIONS, the expression is
5620 true if the unary test is true. If the first argument is
5621 not a valid unary conditional operator, the expression is
5622 false.
5623 3 arguments
5624 The following conditions are applied in the order listed.
5625 If the second argument is one of the binary conditional
5626 operators listed above under CONDITIONAL EXPRESSIONS, the
5627 result of the expression is the result of the binary test
5628 using the first and third arguments as operands. The -a
5629 and -o operators are considered binary operators when
5630 there are three arguments. If the first argument is !,
5631 the value is the negation of the two-argument test using
5632 the second and third arguments. If the first argument is
5633 exactly ( and the third argument is exactly ), the result
5634 is the one-argument test of the second argument. Other‐
5635 wise, the expression is false.
5636 4 arguments
5637 If the first argument is !, the result is the negation of
5638 the three-argument expression composed of the remaining
5639 arguments. Otherwise, the expression is parsed and eval‐
5640 uated according to precedence using the rules listed
5641 above.
5642 5 or more arguments
5643 The expression is parsed and evaluated according to
5644 precedence using the rules listed above.
5645 When used with test or [, the < and > operators sort lexico‐
5647 graphically using ASCII ordering.
5648 times Print the accumulated user and system times for the shell and
5650 for processes run from the shell. The return status is 0.
5651 trap [-lp] [[arg] sigspec ...]
5653 The command arg is to be read and executed when the shell
5654 receives signal(s) sigspec. If arg is absent (and there is a
5655 single sigspec) or -, each specified signal is reset to its
5656 original disposition (the value it had upon entrance to the
5657 shell). If arg is the null string the signal specified by each
5658 sigspec is ignored by the shell and by the commands it invokes.
5659 If arg is not present and -p has been supplied, then the trap
5660 commands associated with each sigspec are displayed. If no
5661 arguments are supplied or if only -p is given, trap prints the
5662 list of commands associated with each signal. The -l option
5663 causes the shell to print a list of signal names and their cor‐
5664 responding numbers. Each sigspec is either a signal name
5665 defined in <signal.h>, or a signal number. Signal names are
5666 case insensitive and the SIG prefix is optional.
5667 If a sigspec is EXIT (0) the command arg is executed on exit
5669 from the shell. If a sigspec is DEBUG, the command arg is exe‐
5670 cuted before every simple command, for command, case command,
5671 select command, every arithmetic for command, and before the
5672 first command executes in a shell function (see SHELL GRAMMAR
5673 above). Refer to the description of the extdebug option to the
5674 shopt builtin for details of its effect on the DEBUG trap. If a
5675 sigspec is RETURN, the command arg is executed each time a shell
5676 function or a script executed with the . or source builtins fin‐
5677 ishes executing.
5678 If a sigspec is ERR, the command arg is executed whenever a
5680 pipeline (which may consist of a single simple command), a list,
5681 or a compound command returns a non-zero exit status, subject to
5682 the following conditions. The ERR trap is not executed if the
5683 failed command is part of the command list immediately following
5684 a while or until keyword, part of the test in an if statement,
5685 part of a command executed in a && or || list except the command
5686 following the final && or ||, any command in a pipeline but the
5687 last, or if the command's return value is being inverted using
5688 !. These are the same conditions obeyed by the errexit (-e)
5689 option.
5690 Signals ignored upon entry to the shell cannot be trapped, reset
5692 or listed. Trapped signals that are not being ignored are reset
5693 to their original values in a subshell or subshell environment
5694 when one is created. The return status is false if any sigspec
5695 is invalid; otherwise trap returns true.
5696 type [-aftpP] name [name ...]
5698 With no options, indicate how each name would be interpreted if
5699 used as a command name. If the -t option is used, type prints a
5700 string which is one of alias, keyword, function, builtin, or
5701 file if name is an alias, shell reserved word, function,
5702 builtin, or disk file, respectively. If the name is not found,
5703 then nothing is printed, and an exit status of false is
5704 returned. If the -p option is used, type either returns the
5705 name of the disk file that would be executed if name were speci‐
5706 fied as a command name, or nothing if ``type -t name'' would not
5707 return file. The -P option forces a PATH search for each name,
5708 even if ``type -t name'' would not return file. If a command is
5709 hashed, -p and -P print the hashed value, which is not necessar‐
5710 ily the file that appears first in PATH. If the -a option is
5711 used, type prints all of the places that contain an executable
5712 named name. This includes aliases and functions, if and only if
5713 the -p option is not also used. The table of hashed commands is
5714 not consulted when using -a. The -f option suppresses shell
5715 function lookup, as with the command builtin. type returns true
5716 if all of the arguments are found, false if any are not found.
5717 ulimit [-HSabcdefiklmnpqrstuvxPT [limit]]
5719 Provides control over the resources available to the shell and
5720 to processes started by it, on systems that allow such control.
5721 The -H and -S options specify that the hard or soft limit is set
5722 for the given resource. A hard limit cannot be increased by a
5723 non-root user once it is set; a soft limit may be increased up
5724 to the value of the hard limit. If neither -H nor -S is speci‐
5725 fied, both the soft and hard limits are set. The value of limit
5726 can be a number in the unit specified for the resource or one of
5727 the special values hard, soft, or unlimited, which stand for the
5728 current hard limit, the current soft limit, and no limit,
5729 respectively. If limit is omitted, the current value of the
5730 soft limit of the resource is printed, unless the -H option is
5731 given. When more than one resource is specified, the limit name
5732 and unit are printed before the value. Other options are inter‐
5733 preted as follows:
5734 -a All current limits are reported
5735 -b The maximum socket buffer size
5736 -c The maximum size of core files created
5737 -d The maximum size of a process's data segment
5738 -e The maximum scheduling priority ("nice")
5739 -f The maximum size of files written by the shell and its
5740 children
5741 -i The maximum number of pending signals
5742 -k The maximum number of kqueues that may be allocated
5743 -l The maximum size that may be locked into memory
5744 -m The maximum resident set size (many systems do not honor
5745 this limit)
5746 -n The maximum number of open file descriptors (most systems
5747 do not allow this value to be set)
5748 -p The pipe size in 512-byte blocks (this may not be set)
5749 -q The maximum number of bytes in POSIX message queues
5750 -r The maximum real-time scheduling priority
5751 -s The maximum stack size
5752 -t The maximum amount of cpu time in seconds
5753 -u The maximum number of processes available to a single
5754 user
5755 -v The maximum amount of virtual memory available to the
5756 shell and, on some systems, to its children
5757 -x The maximum number of file locks
5758 -P The maximum number of pseudoterminals
5759 -T The maximum number of threads
5760 If limit is given, and the -a option is not used, limit is the
5762 new value of the specified resource. If no option is given,
5763 then -f is assumed. Values are in 1024-byte increments, except
5764 for -t, which is in seconds; -p, which is in units of 512-byte
5765 blocks; -P, -T, -b, -k, -n, and -u, which are unscaled values;
5766 and, when in Posix mode, -c and -f, which are in 512-byte incre‐
5767 ments. The return status is 0 unless an invalid option or argu‐
5768 ment is supplied, or an error occurs while setting a new limit.
5769 In POSIX Mode 512-byte blocks are used for the `-c' and `-f'
5770 options.
5771 umask [-p] [-S] [mode]
5773 The user file-creation mask is set to mode. If mode begins with
5774 a digit, it is interpreted as an octal number; otherwise it is
5775 interpreted as a symbolic mode mask similar to that accepted by
5776 chmod(1). If mode is omitted, the current value of the mask is
5777 printed. The -S option causes the mask to be printed in sym‐
5778 bolic form; the default output is an octal number. If the -p
5779 option is supplied, and mode is omitted, the output is in a form
5780 that may be reused as input. The return status is 0 if the mode
5781 was successfully changed or if no mode argument was supplied,
5782 and false otherwise.
5783 unalias [-a] [name ...]
5785 Remove each name from the list of defined aliases. If -a is
5786 supplied, all alias definitions are removed. The return value
5787 is true unless a supplied name is not a defined alias.
5788 unset [-fv] [-n] [name ...]
5790 For each name, remove the corresponding variable or function.
5791 If the -v option is given, each name refers to a shell variable,
5792 and that variable is removed. Read-only variables may not be
5793 unset. If -f is specified, each name refers to a shell func‐
5794 tion, and the function definition is removed. If the -n option
5795 is supplied, and name is a variable with the nameref attribute,
5796 name will be unset rather than the variable it references. -n
5797 has no effect if the -f option is supplied. If no options are
5798 supplied, each name refers to a variable; if there is no vari‐
5799 able by that name, any function with that name is unset. Each
5800 unset variable or function is removed from the environment
5801 passed to subsequent commands. If any of COMP_WORDBREAKS, RAN‐
5802 DOM, SECONDS, LINENO, HISTCMD, FUNCNAME, GROUPS, or DIRSTACK are
5803 unset, they lose their special properties, even if they are sub‐
5804 sequently reset. The exit status is true unless a name is read‐
5805 only.
5806 wait [-n] [n ...]
5808 Wait for each specified child process and return its termination
5809 status. Each n may be a process ID or a job specification; if a
5810 job spec is given, all processes in that job's pipeline are
5811 waited for. If n is not given, all currently active child pro‐
5812 cesses are waited for, and the return status is zero. If the -n
5813 option is supplied, wait waits for any job to terminate and
5814 returns its exit status. If n specifies a non-existent process
5815 or job, the return status is 127. Otherwise, the return status
5816 is the exit status of the last process or job waited for.
5817
5819 If bash is started with the name rbash, or the -r option is supplied at
5820 invocation, the shell becomes restricted. A restricted shell is used
5821 to set up an environment more controlled than the standard shell. It
5822 behaves identically to bash with the exception that the following are
5823 disallowed or not performed:
5824 · changing directories with cd
5826 · setting or unsetting the values of SHELL, PATH, ENV, or BASH_ENV
5828 · specifying command names containing /
5830 · specifying a filename containing a / as an argument to the .
5832 builtin command
5833 · specifying a filename containing a slash as an argument to the
5835 -p option to the hash builtin command
5836 · importing function definitions from the shell environment at
5838 startup
5839 · parsing the value of SHELLOPTS from the shell environment at
5841 startup
5842 · redirecting output using the >, >|, <>, >&, &>, and >> redirect‐
5844 ion operators
5845 · using the exec builtin command to replace the shell with another
5847 command
5848 · adding or deleting builtin commands with the -f and -d options
5850 to the enable builtin command
5851 · using the enable builtin command to enable disabled shell
5853 builtins
5854 · specifying the -p option to the command builtin command
5856 · turning off restricted mode with set +r or set +o restricted.
5858 These restrictions are enforced after any startup files are read.
5860 When a command that is found to be a shell script is executed (see COM‐
5862 MAND EXECUTION above), rbash turns off any restrictions in the shell
5863 spawned to execute the script.
5864
5866 Bash Reference Manual, Brian Fox and Chet Ramey
5867 The Gnu Readline Library, Brian Fox and Chet Ramey
5868 The Gnu History Library, Brian Fox and Chet Ramey
5869 Portable Operating System Interface (POSIX) Part 2: Shell and Utili‐
5870 ties, IEEE --
5871 http://pubs.opengroup.org/onlinepubs/9699919799/
5872 http://tiswww.case.edu/~chet/bash/POSIX -- a description of posix mode
5873 sh(1), ksh(1), csh(1)
5874 emacs(1), vi(1)
5875 readline(3)
5876
5878 /bin/bash
5879 The bash executable
5880 /etc/profile
5881 The systemwide initialization file, executed for login shells
5882 /etc/bash.bash_logout
5883 The systemwide login shell cleanup file, executed when a login
5884 shell exits
5885 ~/.bash_profile
5886 The personal initialization file, executed for login shells
5887 ~/.bashrc
5888 The individual per-interactive-shell startup file
5889 ~/.bash_logout
5890 The individual login shell cleanup file, executed when a login
5891 shell exits
5892 ~/.inputrc
5893 Individual readline initialization file
5894
5896 Brian Fox, Free Software Foundation
5897 bfox@gnu.org
5898 Chet Ramey, Case Western Reserve University
5900 chet.ramey@case.edu
5901
5903 If you find a bug in bash, you should report it. But first, you should
5904 make sure that it really is a bug, and that it appears in the latest
5905 version of bash. The latest version is always available from
5906 ftp://ftp.gnu.org/pub/gnu/bash/.
5907 Once you have determined that a bug actually exists, use the bashbug
5909 command to submit a bug report. If you have a fix, you are encouraged
5910 to mail that as well! Suggestions and `philosophical' bug reports may
5911 be mailed to bug-bash@gnu.org or posted to the Usenet newsgroup
5912 gnu.bash.bug.
5913 ALL bug reports should include:
5915 The version number of bash
5917 The hardware and operating system
5918 The compiler used to compile
5919 A description of the bug behaviour
5920 A short script or `recipe' which exercises the bug
5921 bashbug inserts the first three items automatically into the template
5923 it provides for filing a bug report.
5924 Comments and bug reports concerning this manual page should be directed
5926 to chet.ramey@case.edu.
5927
5929 It's too big and too slow.
5930 There are some subtle differences between bash and traditional versions
5932 of sh, mostly because of the POSIX specification.
5933 Aliases are confusing in some uses.
5935 Shell builtin commands and functions are not stoppable/restartable.
5937 Compound commands and command sequences of the form `a ; b ; c' are not
5939 handled gracefully when process suspension is attempted. When a
5940 process is stopped, the shell immediately executes the next command in
5941 the sequence. It suffices to place the sequence of commands between
5942 parentheses to force it into a subshell, which may be stopped as a
5943 unit.
5944 Array variables may not (yet) be exported.
5946 There may be only one active coprocess at a time.
5948GNU Bash 4.4 2016 August 26 BASH(1)