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1BASH(1) General Commands Manual BASH(1)
2
3NAME
4 bash - GNU Bourne-Again SHell
5
6SYNOPSIS
7 bash [options] [command_string | file]
8
9COPYRIGHT
10 Bash is Copyright (C) 1989-2016 by the Free Software Foundation, Inc.
11
12DESCRIPTION
13 Bash is an sh-compatible command language interpreter that executes commands read from the standard input or from a file. Bash also incorporates useful features from the Korn
14 and C shells (ksh and csh).
15
16 Bash is intended to be a conformant implementation of the Shell and Utilities portion of the IEEE POSIX specification (IEEE Standard 1003.1). Bash can be configured to be
17 POSIX-conformant by default.
18
19OPTIONS
20 All of the single-character shell options documented in the description of the set builtin command can be used as options when the shell is invoked. In addition, bash inter‐
21 prets the following options when it is invoked:
22
23 -c If the -c option is present, then commands are read from the first non-option argument command_string. If there are arguments after the command_string, the first
24 argument is assigned to $0 and any remaining arguments are assigned to the positional parameters. The assignment to $0 sets the name of the shell, which is used in
25 warning and error messages.
26 -i If the -i option is present, the shell is interactive.
27 -l Make bash act as if it had been invoked as a login shell (see INVOCATION below).
28 -r If the -r option is present, the shell becomes restricted (see RESTRICTED SHELL below).
29 -s If the -s option is present, or if no arguments remain after option processing, then commands are read from the standard input. This option allows the positional
30 parameters to be set when invoking an interactive shell.
31 -v Print shell input lines as they are read.
32 -x Print commands and their arguments as they are executed.
33 -D A list of all double-quoted strings preceded by $ is printed on the standard output. These are the strings that are subject to language translation when the current
34 locale is not C or POSIX. This implies the -n option; no commands will be executed.
35 [-+]O [shopt_option]
36 shopt_option is one of the shell options accepted by the shopt builtin (see SHELL BUILTIN COMMANDS below). If shopt_option is present, -O sets the value of that
37 option; +O unsets it. If shopt_option is not supplied, the names and values of the shell options accepted by shopt are printed on the standard output. If the invoca‐
38 tion option is +O, the output is displayed in a format that may be reused as input.
39 -- A -- signals the end of options and disables further option processing. Any arguments after the -- are treated as filenames and arguments. An argument of - is equiv‐
40 alent to --.
41
42 Bash also interprets a number of multi-character options. These options must appear on the command line before the single-character options to be recognized.
43
44 --debugger
45 Arrange for the debugger profile to be executed before the shell starts. Turns on extended debugging mode (see the description of the extdebug option to the shopt
46 builtin below).
47 --dump-po-strings
48 Equivalent to -D, but the output is in the GNU gettext po (portable object) file format.
49 --dump-strings
50 Equivalent to -D.
51 --help Display a usage message on standard output and exit successfully.
52 --init-file file
53 --rcfile file
54 Execute commands from file instead of the system wide initialization file /etc/bash.bashrc and the standard personal initialization file ~/.bashrc if the shell is inter‐
55 active (see INVOCATION below).
56
57 --login
58 Equivalent to -l.
59
60 --noediting
61 Do not use the GNU readline library to read command lines when the shell is interactive.
62
63 --noprofile
64 Do not read either the system-wide startup file /etc/profile or any of the personal initialization files ~/.bash_profile, ~/.bash_login, or ~/.profile. By default, bash
65 reads these files when it is invoked as a login shell (see INVOCATION below).
66
67 --norc Do not read and execute the system wide initialization file /etc/bash.bashrc and the personal initialization file ~/.bashrc if the shell is interactive. This option is
68 on by default if the shell is invoked as sh.
69
70 --posix
71 Change the behavior of bash where the default operation differs from the POSIX standard to match the standard (posix mode). See SEE ALSO below for a reference to a docu‐
72 ment that details how posix mode affects bash's behavior.
73
74 --restricted
75 The shell becomes restricted (see RESTRICTED SHELL below).
76
77 --verbose
78 Equivalent to -v.
79
80 --version
81 Show version information for this instance of bash on the standard output and exit successfully.
82
83ARGUMENTS
84 If arguments remain after option processing, and neither the -c nor the -s option has been supplied, the first argument is assumed to be the name of a file containing shell com‐
85 mands. If bash is invoked in this fashion, $0 is set to the name of the file, and the positional parameters are set to the remaining arguments. Bash reads and executes com‐
86 mands from this file, then exits. Bash's exit status is the exit status of the last command executed in the script. If no commands are executed, the exit status is 0. An
87 attempt is first made to open the file in the current directory, and, if no file is found, then the shell searches the directories in PATH for the script.
88
89INVOCATION
90 A login shell is one whose first character of argument zero is a -, or one started with the --login option.
91
92 An interactive shell is one started without non-option arguments (unless -s is specified) and without the -c option whose standard input and error are both connected to termi‐
93 nals (as determined by isatty(3)), or one started with the -i option. PS1 is set and $- includes i if bash is interactive, allowing a shell script or a startup file to test
94 this state.
95
96 The following paragraphs describe how bash executes its startup files. If any of the files exist but cannot be read, bash reports an error. Tildes are expanded in filenames as
97 described below under Tilde Expansion in the EXPANSION section.
98
99 When bash is invoked as an interactive login shell, or as a non-interactive shell with the --login option, it first reads and executes commands from the file /etc/profile, if
100 that file exists. After reading that file, it looks for ~/.bash_profile, ~/.bash_login, and ~/.profile, in that order, and reads and executes commands from the first one that
101 exists and is readable. The --noprofile option may be used when the shell is started to inhibit this behavior.
102
103 When an interactive login shell exits, or a non-interactive login shell executes the exit builtin command, bash reads and executes commands from the file ~/.bash_logout, if it
104 exists.
105
106 When an interactive shell that is not a login shell is started, bash reads and executes commands from /etc/bash.bashrc and ~/.bashrc, if these files exist. This may be inhib‐
107 ited by using the --norc option. The --rcfile file option will force bash to read and execute commands from file instead of /etc/bash.bashrc and ~/.bashrc.
108
109 When bash is started non-interactively, to run a shell script, for example, it looks for the variable BASH_ENV in the environment, expands its value if it appears there, and
110 uses the expanded value as the name of a file to read and execute. Bash behaves as if the following command were executed:
111 if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
112 but the value of the PATH variable is not used to search for the filename.
113
114 If bash is invoked with the name sh, it tries to mimic the startup behavior of historical versions of sh as closely as possible, while conforming to the POSIX standard as well.
115 When invoked as an interactive login shell, or a non-interactive shell with the --login option, it first attempts to read and execute commands from /etc/profile and ~/.profile,
116 in that order. The --noprofile option may be used to inhibit this behavior. When invoked as an interactive shell with the name sh, bash looks for the variable ENV, expands its
117 value if it is defined, and uses the expanded value as the name of a file to read and execute. Since a shell invoked as sh does not attempt to read and execute commands from
118 any other startup files, the --rcfile option has no effect. A non-interactive shell invoked with the name sh does not attempt to read any other startup files. When invoked as
119 sh, bash enters posix mode after the startup files are read.
120
121 When bash is started in posix mode, as with the --posix command line option, it follows the POSIX standard for startup files. In this mode, interactive shells expand the ENV
122 variable and commands are read and executed from the file whose name is the expanded value. No other startup files are read.
123
124 Bash attempts to determine when it is being run with its standard input connected to a network connection, as when executed by the remote shell daemon, usually rshd, or the
125 secure shell daemon sshd. If bash determines it is being run in this fashion, it reads and executes commands from ~/.bashrc and ~/.bashrc, if these files exist and are read‐
126 able. It will not do this if invoked as sh. The --norc option may be used to inhibit this behavior, and the --rcfile option may be used to force another file to be read, but
127 neither rshd nor sshd generally invoke the shell with those options or allow them to be specified.
128
129 If the shell is started with the effective user (group) id not equal to the real user (group) id, and the -p option is not supplied, no startup files are read, shell functions
130 are not inherited from the environment, the SHELLOPTS, BASHOPTS, CDPATH, and GLOBIGNORE variables, if they appear in the environment, are ignored, and the effective user id is
131 set to the real user id. If the -p option is supplied at invocation, the startup behavior is the same, but the effective user id is not reset.
132
133DEFINITIONS
134 The following definitions are used throughout the rest of this document.
135 blank A space or tab.
136 word A sequence of characters considered as a single unit by the shell. Also known as a token.
137 name A word consisting only of alphanumeric characters and underscores, and beginning with an alphabetic character or an underscore. Also referred to as an identifier.
138 metacharacter
139 A character that, when unquoted, separates words. One of the following:
140 | & ; ( ) < > space tab newline
141 control operator
142 A token that performs a control function. It is one of the following symbols:
143 || & && ; ;; ;& ;;& ( ) | |& <newline>
144
145RESERVED WORDS
146 Reserved words are words that have a special meaning to the shell. The following words are recognized as reserved when unquoted and either the first word of a simple command
147 (see SHELL GRAMMAR below) or the third word of a case or for command:
148
149 ! case coproc do done elif else esac fi for function if in select then until while { } time [[ ]]
150
151SHELL GRAMMAR
152 Simple Commands
153 A simple command is a sequence of optional variable assignments followed by blank-separated words and redirections, and terminated by a control operator. The first word speci‐
154 fies the command to be executed, and is passed as argument zero. The remaining words are passed as arguments to the invoked command.
155
156 The return value of a simple command is its exit status, or 128+n if the command is terminated by signal n.
157
158 Pipelines
159 A pipeline is a sequence of one or more commands separated by one of the control operators | or |&. The format for a pipeline is:
160
161 [time [-p]] [ ! ] command [ [|⎪|&] command2 ... ]
162
163 The standard output of command is connected via a pipe to the standard input of command2. This connection is performed before any redirections specified by the command (see RE‐
164 DIRECTION below). If |& is used, command's standard error, in addition to its standard output, is connected to command2's standard input through the pipe; it is shorthand for
165 2>&1 |. This implicit redirection of the standard error to the standard output is performed after any redirections specified by the command.
166
167 The return status of a pipeline is the exit status of the last command, unless the pipefail option is enabled. If pipefail is enabled, the pipeline's return status is the value
168 of the last (rightmost) command to exit with a non-zero status, or zero if all commands exit successfully. If the reserved word ! precedes a pipeline, the exit status of that
169 pipeline is the logical negation of the exit status as described above. The shell waits for all commands in the pipeline to terminate before returning a value.
170
171 If the time reserved word precedes a pipeline, the elapsed as well as user and system time consumed by its execution are reported when the pipeline terminates. The -p option
172 changes the output format to that specified by POSIX. When the shell is in posix mode, it does not recognize time as a reserved word if the next token begins with a `-'. The
173 TIMEFORMAT variable may be set to a format string that specifies how the timing information should be displayed; see the description of TIMEFORMAT under Shell Variables below.
174
175 When the shell is in posix mode, time may be followed by a newline. In this case, the shell displays the total user and system time consumed by the shell and its children. The
176 TIMEFORMAT variable may be used to specify the format of the time information.
177
178 Each command in a pipeline is executed as a separate process (i.e., in a subshell).
179
180 Lists
181 A list is a sequence of one or more pipelines separated by one of the operators ;, &, &&, or ||, and optionally terminated by one of ;, &, or <newline>.
182
183 Of these list operators, && and || have equal precedence, followed by ; and &, which have equal precedence.
184
185 A sequence of one or more newlines may appear in a list instead of a semicolon to delimit commands.
186
187 If a command is terminated by the control operator &, the shell executes the command in the background in a subshell. The shell does not wait for the command to finish, and the
188 return status is 0. Commands separated by a ; are executed sequentially; the shell waits for each command to terminate in turn. The return status is the exit status of the
189 last command executed.
190
191 AND and OR lists are sequences of one or more pipelines separated by the && and || control operators, respectively. AND and OR lists are executed with left associativity. An
192 AND list has the form
193
194 command1 && command2
195
196 command2 is executed if, and only if, command1 returns an exit status of zero.
197
198 An OR list has the form
199
200 command1 || command2
201
202 command2 is executed if and only if command1 returns a non-zero exit status. The return status of AND and OR lists is the exit status of the last command executed in the list.
203
204 Compound Commands
205 A compound command is one of the following. In most cases a list in a command's description may be separated from the rest of the command by one or more newlines, and may be
206 followed by a newline in place of a semicolon.
207
208 (list) list is executed in a subshell environment (see COMMAND EXECUTION ENVIRONMENT below). Variable assignments and builtin commands that affect the shell's environment do
209 not remain in effect after the command completes. The return status is the exit status of list.
210
211 { list; }
212 list is simply executed in the current shell environment. list must be terminated with a newline or semicolon. This is known as a group command. The return status is
213 the exit status of list. Note that unlike the metacharacters ( and ), { and } are reserved words and must occur where a reserved word is permitted to be recognized.
214 Since they do not cause a word break, they must be separated from list by whitespace or another shell metacharacter.
215
216 ((expression))
217 The expression is evaluated according to the rules described below under ARITHMETIC EVALUATION. If the value of the expression is non-zero, the return status is 0; oth‐
218 erwise the return status is 1. This is exactly equivalent to let "expression".
219
220 [[ expression ]]
221 Return a status of 0 or 1 depending on the evaluation of the conditional expression expression. Expressions are composed of the primaries described below under CONDI‐
222 TIONAL EXPRESSIONS. Word splitting and pathname expansion are not performed on the words between the [[ and ]]; tilde expansion, parameter and variable expansion, arith‐
223 metic expansion, command substitution, process substitution, and quote removal are performed. Conditional operators such as -f must be unquoted to be recognized as pri‐
224 maries.
225
226 When used with [[, the < and > operators sort lexicographically using the current locale.
227
228 See the description of the test builtin command (section SHELL BUILTIN COMMANDS below) for the handling of parameters (i.e. missing parameters).
229
230 When the == and != operators are used, the string to the right of the operator is considered a pattern and matched according to the rules described below under Pattern Matching,
231 as if the extglob shell option were enabled. The = operator is equivalent to ==. If the nocasematch shell option is enabled, the match is performed without regard to the case
232 of alphabetic characters. The return value is 0 if the string matches (==) or does not match (!=) the pattern, and 1 otherwise. Any part of the pattern may be quoted to force
233 the quoted portion to be matched as a string.
234
235 An additional binary operator, =~, is available, with the same precedence as == and !=. When it is used, the string to the right of the operator is considered an extended regu‐
236 lar expression and matched accordingly (as in regex(3)). The return value is 0 if the string matches the pattern, and 1 otherwise. If the regular expression is syntactically
237 incorrect, the conditional expression's return value is 2. If the nocasematch shell option is enabled, the match is performed without regard to the case of alphabetic charac‐
238 ters. Any part of the pattern may be quoted to force the quoted portion to be matched as a string. Bracket expressions in regular expressions must be treated carefully, since
239 normal quoting characters lose their meanings between brackets. If the pattern is stored in a shell variable, quoting the variable expansion forces the entire pattern to be
240 matched as a string. Substrings matched by parenthesized subexpressions within the regular expression are saved in the array variable BASH_REMATCH. The element of BASH_REMATCH
241 with index 0 is the portion of the string matching the entire regular expression. The element of BASH_REMATCH with index n is the portion of the string matching the nth paren‐
242 thesized subexpression.
243
244 Expressions may be combined using the following operators, listed in decreasing order of precedence:
245
246 ( expression )
247 Returns the value of expression. This may be used to override the normal precedence of operators.
248 ! expression
249 True if expression is false.
250 expression1 && expression2
251 True if both expression1 and expression2 are true.
252 expression1 || expression2
253 True if either expression1 or expression2 is true.
254
255 The && and || operators do not evaluate expression2 if the value of expression1 is sufficient to determine the return value of the entire conditional expression.
256
257 for name [ [ in [ word ... ] ] ; ] do list ; done
258 The list of words following in is expanded, generating a list of items. The variable name is set to each element of this list in turn, and list is executed each time.
259 If the in word is omitted, the for command executes list once for each positional parameter that is set (see PARAMETERS below). The return status is the exit status of
260 the last command that executes. If the expansion of the items following in results in an empty list, no commands are executed, and the return status is 0.
261
262 for (( expr1 ; expr2 ; expr3 )) ; do list ; done
263 First, the arithmetic expression expr1 is evaluated according to the rules described below under ARITHMETIC EVALUATION. The arithmetic expression expr2 is then evaluated
264 repeatedly until it evaluates to zero. Each time expr2 evaluates to a non-zero value, list is executed and the arithmetic expression expr3 is evaluated. If any expres‐
265 sion is omitted, it behaves as if it evaluates to 1. The return value is the exit status of the last command in list that is executed, or false if any of the expressions
266 is invalid.
267
268 select name [ in word ] ; do list ; done
269 The list of words following in is expanded, generating a list of items. The set of expanded words is printed on the standard error, each preceded by a number. If the in
270 word is omitted, the positional parameters are printed (see PARAMETERS below). The PS3 prompt is then displayed and a line read from the standard input. If the line
271 consists of a number corresponding to one of the displayed words, then the value of name is set to that word. If the line is empty, the words and prompt are displayed
272 again. If EOF is read, the command completes. Any other value read causes name to be set to null. The line read is saved in the variable REPLY. The list is executed
273 after each selection until a break command is executed. The exit status of select is the exit status of the last command executed in list, or zero if no commands were
274 executed.
275
276 case word in [ [(] pattern [ | pattern ] ... ) list ;; ] ... esac
277 A case command first expands word, and tries to match it against each pattern in turn, using the same matching rules as for pathname expansion (see Pathname Expansion
278 below). The word is expanded using tilde expansion, parameter and variable expansion, arithmetic expansion, command substitution, process substitution and quote removal.
279 Each pattern examined is expanded using tilde expansion, parameter and variable expansion, arithmetic expansion, command substitution, and process substitution. If the
280 nocasematch shell option is enabled, the match is performed without regard to the case of alphabetic characters. When a match is found, the corresponding list is exe‐
281 cuted. If the ;; operator is used, no subsequent matches are attempted after the first pattern match. Using ;& in place of ;; causes execution to continue with the list
282 associated with the next set of patterns. Using ;;& in place of ;; causes the shell to test the next pattern list in the statement, if any, and execute any associated
283 list on a successful match. The exit status is zero if no pattern matches. Otherwise, it is the exit status of the last command executed in list.
284
285 if list; then list; [ elif list; then list; ] ... [ else list; ] fi
286 The if list is executed. If its exit status is zero, the then list is executed. Otherwise, each elif list is executed in turn, and if its exit status is zero, the cor‐
287 responding then list is executed and the command completes. Otherwise, the else list is executed, if present. The exit status is the exit status of the last command
288 executed, or zero if no condition tested true.
289
290 while list-1; do list-2; done
291 until list-1; do list-2; done
292 The while command continuously executes the list list-2 as long as the last command in the list list-1 returns an exit status of zero. The until command is identical to
293 the while command, except that the test is negated: list-2 is executed as long as the last command in list-1 returns a non-zero exit status. The exit status of the while
294 and until commands is the exit status of the last command executed in list-2, or zero if none was executed.
295
296 Coprocesses
297 A coprocess is a shell command preceded by the coproc reserved word. A coprocess is executed asynchronously in a subshell, as if the command had been terminated with the & con‐
298 trol operator, with a two-way pipe established between the executing shell and the coprocess.
299
300 The format for a coprocess is:
301
302 coproc [NAME] command [redirections]
303
304 This creates a coprocess named NAME. If NAME is not supplied, the default name is COPROC. NAME must not be supplied if command is a simple command (see above); otherwise, it
305 is interpreted as the first word of the simple command. When the coprocess is executed, the shell creates an array variable (see Arrays below) named NAME in the context of the
306 executing shell. The standard output of command is connected via a pipe to a file descriptor in the executing shell, and that file descriptor is assigned to NAME[0]. The stan‐
307 dard input of command is connected via a pipe to a file descriptor in the executing shell, and that file descriptor is assigned to NAME[1]. This pipe is established before any
308 redirections specified by the command (see REDIRECTION below). The file descriptors can be utilized as arguments to shell commands and redirections using standard word expan‐
309 sions. The file descriptors are not available in subshells. The process ID of the shell spawned to execute the coprocess is available as the value of the variable NAME_PID.
310 The wait builtin command may be used to wait for the coprocess to terminate.
311
312 Since the coprocess is created as an asynchronous command, the coproc command always returns success. The return status of a coprocess is the exit status of command.
313
314 Shell Function Definitions
315 A shell function is an object that is called like a simple command and executes a compound command with a new set of positional parameters. Shell functions are declared as fol‐
316 lows:
317
318 name () compound-command [redirection]
319 function name [()] compound-command [redirection]
320 This defines a function named name. The reserved word function is optional. If the function reserved word is supplied, the parentheses are optional. The body of the
321 function is the compound command compound-command (see Compound Commands above). That command is usually a list of commands between { and }, but may be any command
322 listed under Compound Commands above, with one exception: If the function reserved word is used, but the parentheses are not supplied, the braces are required. com‐
323 pound-command is executed whenever name is specified as the name of a simple command. When in posix mode, name may not be the name of one of the POSIX special builtins.
324 Any redirections (see REDIRECTION below) specified when a function is defined are performed when the function is executed. The exit status of a function definition is
325 zero unless a syntax error occurs or a readonly function with the same name already exists. When executed, the exit status of a function is the exit status of the last
326 command executed in the body. (See FUNCTIONS below.)
327
328COMMENTS
329 In a non-interactive shell, or an interactive shell in which the interactive_comments option to the shopt builtin is enabled (see SHELL BUILTIN COMMANDS below), a word beginning
330 with # causes that word and all remaining characters on that line to be ignored. An interactive shell without the interactive_comments option enabled does not allow comments.
331 The interactive_comments option is on by default in interactive shells.
332
333QUOTING
334 Quoting is used to remove the special meaning of certain characters or words to the shell. Quoting can be used to disable special treatment for special characters, to prevent
335 reserved words from being recognized as such, and to prevent parameter expansion.
336
337 Each of the metacharacters listed above under DEFINITIONS has special meaning to the shell and must be quoted if it is to represent itself.
338
339 When the command history expansion facilities are being used (see HISTORY EXPANSION below), the history expansion character, usually !, must be quoted to prevent history expan‐
340 sion.
341
342 There are three quoting mechanisms: the escape character, single quotes, and double quotes.
343
344 A non-quoted backslash (\) is the escape character. It preserves the literal value of the next character that follows, with the exception of <newline>. If a \<newline> pair
345 appears, and the backslash is not itself quoted, the \<newline> is treated as a line continuation (that is, it is removed from the input stream and effectively ignored).
346
347 Enclosing characters in single quotes preserves the literal value of each character within the quotes. A single quote may not occur between single quotes, even when preceded by
348 a backslash.
349
350 Enclosing characters in double quotes preserves the literal value of all characters within the quotes, with the exception of $, `, \, and, when history expansion is enabled, !.
351 When the shell is in posix mode, the ! has no special meaning within double quotes, even when history expansion is enabled. The characters $ and ` retain their special meaning
352 within double quotes. The backslash retains its special meaning only when followed by one of the following characters: $, `, ", \, or <newline>. A double quote may be quoted
353 within double quotes by preceding it with a backslash. If enabled, history expansion will be performed unless an ! appearing in double quotes is escaped using a backslash.
354 The backslash preceding the ! is not removed.
355
356 The special parameters * and @ have special meaning when in double quotes (see PARAMETERS below).
357
358 Words of the form $'string' are treated specially. The word expands to string, with backslash-escaped characters replaced as specified by the ANSI C standard. Backslash escape
359 sequences, if present, are decoded as follows:
360 \a alert (bell)
361 \b backspace
362 \e
363 \E an escape character
364 \f form feed
365 \n new line
366 \r carriage return
367 \t horizontal tab
368 \v vertical tab
369 \\ backslash
370 \' single quote
371 \" double quote
372 \? question mark
373 \nnn the eight-bit character whose value is the octal value nnn (one to three digits)
374 \xHH the eight-bit character whose value is the hexadecimal value HH (one or two hex digits)
375 \uHHHH the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHH (one to four hex digits)
376 \UHHHHHHHH
377 the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHHHHHH (one to eight hex digits)
378 \cx a control-x character
379
380 The expanded result is single-quoted, as if the dollar sign had not been present.
381
382 A double-quoted string preceded by a dollar sign ($"string") will cause the string to be translated according to the current locale. If the current locale is C or POSIX, the
383 dollar sign is ignored. If the string is translated and replaced, the replacement is double-quoted.
384
385PARAMETERS
386 A parameter is an entity that stores values. It can be a name, a number, or one of the special characters listed below under Special Parameters. A variable is a parameter
387 denoted by a name. A variable has a value and zero or more attributes. Attributes are assigned using the declare builtin command (see declare below in SHELL BUILTIN COMMANDS).
388
389 A parameter is set if it has been assigned a value. The null string is a valid value. Once a variable is set, it may be unset only by using the unset builtin command (see
390 SHELL BUILTIN COMMANDS below).
391
392 A variable may be assigned to by a statement of the form
393
394 name=[value]
395
396 If value is not given, the variable is assigned the null string. All values undergo tilde expansion, parameter and variable expansion, command substitution, arithmetic expan‐
397 sion, and quote removal (see EXPANSION below). If the variable has its integer attribute set, then value is evaluated as an arithmetic expression even if the $((...)) expansion
398 is not used (see Arithmetic Expansion below). Word splitting is not performed, with the exception of "$@" as explained below under Special Parameters. Pathname expansion is
399 not performed. Assignment statements may also appear as arguments to the alias, declare, typeset, export, readonly, and local builtin commands (declaration commands). When in
400 posix mode, these builtins may appear in a command after one or more instances of the command builtin and retain these assignment statement properties.
401
402 In the context where an assignment statement is assigning a value to a shell variable or array index, the += operator can be used to append to or add to the variable's previous
403 value. This includes arguments to builtin commands such as declare that accept assignment statements (declaration commands). When += is applied to a variable for which the
404 integer attribute has been set, value is evaluated as an arithmetic expression and added to the variable's current value, which is also evaluated. When += is applied to an
405 array variable using compound assignment (see Arrays below), the variable's value is not unset (as it is when using =), and new values are appended to the array beginning at one
406 greater than the array's maximum index (for indexed arrays) or added as additional key-value pairs in an associative array. When applied to a string-valued variable, value is
407 expanded and appended to the variable's value.
408
409 A variable can be assigned the nameref attribute using the -n option to the declare or local builtin commands (see the descriptions of declare and local below) to create a
410 nameref, or a reference to another variable. This allows variables to be manipulated indirectly. Whenever the nameref variable is referenced, assigned to, unset, or has its
411 attributes modified (other than using or changing the nameref attribute itself), the operation is actually performed on the variable specified by the nameref variable's value.
412 A nameref is commonly used within shell functions to refer to a variable whose name is passed as an argument to the function. For instance, if a variable name is passed to a
413 shell function as its first argument, running
414 declare -n ref=$1
415 inside the function creates a nameref variable ref whose value is the variable name passed as the first argument. References and assignments to ref, and changes to its
416 attributes, are treated as references, assignments, and attribute modifications to the variable whose name was passed as $1. If the control variable in a for loop has the
417 nameref attribute, the list of words can be a list of shell variables, and a name reference will be established for each word in the list, in turn, when the loop is executed.
418 Array variables cannot be given the nameref attribute. However, nameref variables can reference array variables and subscripted array variables. Namerefs can be unset using
419 the -n option to the unset builtin. Otherwise, if unset is executed with the name of a nameref variable as an argument, the variable referenced by the nameref variable will be
420 unset.
421
422 Positional Parameters
423 A positional parameter is a parameter denoted by one or more digits, other than the single digit 0. Positional parameters are assigned from the shell's arguments when it is
424 invoked, and may be reassigned using the set builtin command. Positional parameters may not be assigned to with assignment statements. The positional parameters are temporar‐
425 ily replaced when a shell function is executed (see FUNCTIONS below).
426
427 When a positional parameter consisting of more than a single digit is expanded, it must be enclosed in braces (see EXPANSION below).
428
429 Special Parameters
430 The shell treats several parameters specially. These parameters may only be referenced; assignment to them is not allowed.
431 * Expands to the positional parameters, starting from one. When the expansion is not within double quotes, each positional parameter expands to a separate word. In con‐
432 texts where it is performed, those words are subject to further word splitting and pathname expansion. When the expansion occurs within double quotes, it expands to a
433 single word with the value of each parameter separated by the first character of the IFS special variable. That is, "$*" is equivalent to "$1c$2c...", where c is the
434 first character of the value of the IFS variable. If IFS is unset, the parameters are separated by spaces. If IFS is null, the parameters are joined without intervening
435 separators.
436 @ Expands to the positional parameters, starting from one. When the expansion occurs within double quotes, each parameter expands to a separate word. That is, "$@" is
437 equivalent to "$1" "$2" ... If the double-quoted expansion occurs within a word, the expansion of the first parameter is joined with the beginning part of the original
438 word, and the expansion of the last parameter is joined with the last part of the original word. When there are no positional parameters, "$@" and $@ expand to nothing
439 (i.e., they are removed).
440 # Expands to the number of positional parameters in decimal.
441 ? Expands to the exit status of the most recently executed foreground pipeline.
442 - Expands to the current option flags as specified upon invocation, by the set builtin command, or those set by the shell itself (such as the -i option).
443 $ Expands to the process ID of the shell. In a () subshell, it expands to the process ID of the current shell, not the subshell.
444 ! Expands to the process ID of the job most recently placed into the background, whether executed as an asynchronous command or using the bg builtin (see JOB CONTROL
445 below).
446 0 Expands to the name of the shell or shell script. This is set at shell initialization. If bash is invoked with a file of commands, $0 is set to the name of that file.
447 If bash is started with the -c option, then $0 is set to the first argument after the string to be executed, if one is present. Otherwise, it is set to the filename used
448 to invoke bash, as given by argument zero.
449 _ At shell startup, set to the absolute pathname used to invoke the shell or shell script being executed as passed in the environment or argument list. Subsequently,
450 expands to the last argument to the previous command, after expansion. Also set to the full pathname used to invoke each command executed and placed in the environment
451 exported to that command. When checking mail, this parameter holds the name of the mail file currently being checked.
452
453 Shell Variables
454 The following variables are set by the shell:
455
456 BASH Expands to the full filename used to invoke this instance of bash.
457 BASHOPTS
458 A colon-separated list of enabled shell options. Each word in the list is a valid argument for the -s option to the shopt builtin command (see SHELL BUILTIN COMMANDS
459 below). The options appearing in BASHOPTS are those reported as on by shopt. If this variable is in the environment when bash starts up, each shell option in the list
460 will be enabled before reading any startup files. This variable is read-only.
461 BASHPID
462 Expands to the process ID of the current bash process. This differs from $$ under certain circumstances, such as subshells that do not require bash to be re-initialized.
463 BASH_ALIASES
464 An associative array variable whose members correspond to the internal list of aliases as maintained by the alias builtin. Elements added to this array appear in the
465 alias list; however, unsetting array elements currently does not cause aliases to be removed from the alias list. If BASH_ALIASES is unset, it loses its special proper‐
466 ties, even if it is subsequently reset.
467 BASH_ARGC
468 An array variable whose values are the number of parameters in each frame of the current bash execution call stack. The number of parameters to the current subroutine
469 (shell function or script executed with . or source) is at the top of the stack. When a subroutine is executed, the number of parameters passed is pushed onto BASH_ARGC.
470 The shell sets BASH_ARGC only when in extended debugging mode (see the description of the extdebug option to the shopt builtin below)
471 BASH_ARGV
472 An array variable containing all of the parameters in the current bash execution call stack. The final parameter of the last subroutine call is at the top of the stack;
473 the first parameter of the initial call is at the bottom. When a subroutine is executed, the parameters supplied are pushed onto BASH_ARGV. The shell sets BASH_ARGV
474 only when in extended debugging mode (see the description of the extdebug option to the shopt builtin below)
475 BASH_CMDS
476 An associative array variable whose members correspond to the internal hash table of commands as maintained by the hash builtin. Elements added to this array appear in
477 the hash table; however, unsetting array elements currently does not cause command names to be removed from the hash table. If BASH_CMDS is unset, it loses its special
478 properties, even if it is subsequently reset.
479 BASH_COMMAND
480 The command currently being executed or about to be executed, unless the shell is executing a command as the result of a trap, in which case it is the command executing
481 at the time of the trap.
482 BASH_EXECUTION_STRING
483 The command argument to the -c invocation option.
484 BASH_LINENO
485 An array variable whose members are the line numbers in source files where each corresponding member of FUNCNAME was invoked. ${BASH_LINENO[$i]} is the line number in
486 the source file (${BASH_SOURCE[$i+1]}) where ${FUNCNAME[$i]} was called (or ${BASH_LINENO[$i-1]} if referenced within another shell function). Use LINENO to obtain the
487 current line number.
488 BASH_LOADABLES_PATH
489 A colon-separated list of directories in which the shell looks for dynamically loadable builtins specified by the enable command.
490 BASH_REMATCH
491 An array variable whose members are assigned by the =~ binary operator to the [[ conditional command. The element with index 0 is the portion of the string matching the
492 entire regular expression. The element with index n is the portion of the string matching the nth parenthesized subexpression. This variable is read-only.
493 BASH_SOURCE
494 An array variable whose members are the source filenames where the corresponding shell function names in the FUNCNAME array variable are defined. The shell function
495 ${FUNCNAME[$i]} is defined in the file ${BASH_SOURCE[$i]} and called from ${BASH_SOURCE[$i+1]}.
496 BASH_SUBSHELL
497 Incremented by one within each subshell or subshell environment when the shell begins executing in that environment. The initial value is 0.
498 BASH_VERSINFO
499 A readonly array variable whose members hold version information for this instance of bash. The values assigned to the array members are as follows:
500 BASH_VERSINFO[0] The major version number (the release).
501 BASH_VERSINFO[1] The minor version number (the version).
502 BASH_VERSINFO[2] The patch level.
503 BASH_VERSINFO[3] The build version.
504 BASH_VERSINFO[4] The release status (e.g., beta1).
505 BASH_VERSINFO[5] The value of MACHTYPE.
506 BASH_VERSION
507 Expands to a string describing the version of this instance of bash.
508 COMP_CWORD
509 An index into ${COMP_WORDS} of the word containing the current cursor position. This variable is available only in shell functions invoked by the programmable completion
510 facilities (see Programmable Completion below).
511 COMP_KEY
512 The key (or final key of a key sequence) used to invoke the current completion function.
513 COMP_LINE
514 The current command line. This variable is available only in shell functions and external commands invoked by the programmable completion facilities (see Programmable
515 Completion below).
516 COMP_POINT
517 The index of the current cursor position relative to the beginning of the current command. If the current cursor position is at the end of the current command, the value
518 of this variable is equal to ${#COMP_LINE}. This variable is available only in shell functions and external commands invoked by the programmable completion facilities
519 (see Programmable Completion below).
520 COMP_TYPE
521 Set to an integer value corresponding to the type of completion attempted that caused a completion function to be called: TAB, for normal completion, ?, for listing com‐
522 pletions after successive tabs, !, for listing alternatives on partial word completion, @, to list completions if the word is not unmodified, or %, for menu completion.
523 This variable is available only in shell functions and external commands invoked by the programmable completion facilities (see Programmable Completion below).
524 COMP_WORDBREAKS
525 The set of characters that the readline library treats as word separators when performing word completion. If COMP_WORDBREAKS is unset, it loses its special properties,
526 even if it is subsequently reset.
527 COMP_WORDS
528 An array variable (see Arrays below) consisting of the individual words in the current command line. The line is split into words as readline would split it, using
529 COMP_WORDBREAKS as described above. This variable is available only in shell functions invoked by the programmable completion facilities (see Programmable Completion
530 below).
531 COPROC An array variable (see Arrays below) created to hold the file descriptors for output from and input to an unnamed coprocess (see Coprocesses above).
532 DIRSTACK
533 An array variable (see Arrays below) containing the current contents of the directory stack. Directories appear in the stack in the order they are displayed by the dirs
534 builtin. Assigning to members of this array variable may be used to modify directories already in the stack, but the pushd and popd builtins must be used to add and
535 remove directories. Assignment to this variable will not change the current directory. If DIRSTACK is unset, it loses its special properties, even if it is subsequently
536 reset.
537 EUID Expands to the effective user ID of the current user, initialized at shell startup. This variable is readonly.
538 FUNCNAME
539 An array variable containing the names of all shell functions currently in the execution call stack. The element with index 0 is the name of any currently-executing
540 shell function. The bottom-most element (the one with the highest index) is "main". This variable exists only when a shell function is executing. Assignments to FUNC‐
541 NAME have no effect. If FUNCNAME is unset, it loses its special properties, even if it is subsequently reset.
542
543 This variable can be used with BASH_LINENO and BASH_SOURCE. Each element of FUNCNAME has corresponding elements in BASH_LINENO and BASH_SOURCE to describe the call
544 stack. For instance, ${FUNCNAME[$i]} was called from the file ${BASH_SOURCE[$i+1]} at line number ${BASH_LINENO[$i]}. The caller builtin displays the current call stack
545 using this information.
546 GROUPS An array variable containing the list of groups of which the current user is a member. Assignments to GROUPS have no effect. If GROUPS is unset, it loses its special
547 properties, even if it is subsequently reset.
548 HISTCMD
549 The history number, or index in the history list, of the current command. If HISTCMD is unset, it loses its special properties, even if it is subsequently reset.
550 HOSTNAME
551 Automatically set to the name of the current host.
552 HOSTTYPE
553 Automatically set to a string that uniquely describes the type of machine on which bash is executing. The default is system-dependent.
554 LINENO Each time this parameter is referenced, the shell substitutes a decimal number representing the current sequential line number (starting with 1) within a script or func‐
555 tion. When not in a script or function, the value substituted is not guaranteed to be meaningful. If LINENO is unset, it loses its special properties, even if it is
556 subsequently reset.
557 MACHTYPE
558 Automatically set to a string that fully describes the system type on which bash is executing, in the standard GNU cpu-company-system format. The default is system-
559 dependent.
560 MAPFILE
561 An array variable (see Arrays below) created to hold the text read by the mapfile builtin when no variable name is supplied.
562 OLDPWD The previous working directory as set by the cd command.
563 OPTARG The value of the last option argument processed by the getopts builtin command (see SHELL BUILTIN COMMANDS below).
564 OPTIND The index of the next argument to be processed by the getopts builtin command (see SHELL BUILTIN COMMANDS below).
565 OSTYPE Automatically set to a string that describes the operating system on which bash is executing. The default is system-dependent.
566 PIPESTATUS
567 An array variable (see Arrays below) containing a list of exit status values from the processes in the most-recently-executed foreground pipeline (which may contain only
568 a single command).
569 PPID The process ID of the shell's parent. This variable is readonly.
570 PWD The current working directory as set by the cd command.
571 RANDOM Each time this parameter is referenced, a random integer between 0 and 32767 is generated. The sequence of random numbers may be initialized by assigning a value to RAN‐
572 DOM. If RANDOM is unset, it loses its special properties, even if it is subsequently reset.
573 READLINE_LINE
574 The contents of the readline line buffer, for use with "bind -x" (see SHELL BUILTIN COMMANDS below).
575 READLINE_POINT
576 The position of the insertion point in the readline line buffer, for use with "bind -x" (see SHELL BUILTIN COMMANDS below).
577 REPLY Set to the line of input read by the read builtin command when no arguments are supplied.
578 SECONDS
579 Each time this parameter is referenced, the number of seconds since shell invocation is returned. If a value is assigned to SECONDS, the value returned upon subsequent
580 references is the number of seconds since the assignment plus the value assigned. If SECONDS is unset, it loses its special properties, even if it is subsequently reset.
581 SHELLOPTS
582 A colon-separated list of enabled shell options. Each word in the list is a valid argument for the -o option to the set builtin command (see SHELL BUILTIN COMMANDS
583 below). The options appearing in SHELLOPTS are those reported as on by set -o. If this variable is in the environment when bash starts up, each shell option in the list
584 will be enabled before reading any startup files. This variable is read-only.
585 SHLVL Incremented by one each time an instance of bash is started.
586 UID Expands to the user ID of the current user, initialized at shell startup. This variable is readonly.
587
588 The following variables are used by the shell. In some cases, bash assigns a default value to a variable; these cases are noted below.
589
590 BASH_COMPAT
591 The value is used to set the shell's compatibility level. See the description of the shopt builtin below under SHELL BUILTIN COMMANDS for a description of the various
592 compatibility levels and their effects. The value may be a decimal number (e.g., 4.2) or an integer (e.g., 42) corresponding to the desired compatibility level. If
593 BASH_COMPAT is unset or set to the empty string, the compatibility level is set to the default for the current version. If BASH_COMPAT is set to a value that is not one
594 of the valid compatibility levels, the shell prints an error message and sets the compatibility level to the default for the current version. The valid compatibility
595 levels correspond to the compatibility options accepted by the shopt builtin described below (for example, compat42 means that 4.2 and 42 are valid values). The current
596 version is also a valid value.
597 BASH_ENV
598 If this parameter is set when bash is executing a shell script, its value is interpreted as a filename containing commands to initialize the shell, as in ~/.bashrc. The
599 value of BASH_ENV is subjected to parameter expansion, command substitution, and arithmetic expansion before being interpreted as a filename. PATH is not used to search
600 for the resultant filename.
601 BASH_XTRACEFD
602 If set to an integer corresponding to a valid file descriptor, bash will write the trace output generated when set -x is enabled to that file descriptor. The file
603 descriptor is closed when BASH_XTRACEFD is unset or assigned a new value. Unsetting BASH_XTRACEFD or assigning it the empty string causes the trace output to be sent to
604 the standard error. Note that setting BASH_XTRACEFD to 2 (the standard error file descriptor) and then unsetting it will result in the standard error being closed.
605 CDPATH The search path for the cd command. This is a colon-separated list of directories in which the shell looks for destination directories specified by the cd command. A
606 sample value is ".:~:/usr".
607 CHILD_MAX
608 Set the number of exited child status values for the shell to remember. Bash will not allow this value to be decreased below a POSIX-mandated minimum, and there is a
609 maximum value (currently 8192) that this may not exceed. The minimum value is system-dependent.
610 COLUMNS
611 Used by the select compound command to determine the terminal width when printing selection lists. Automatically set if the checkwinsize option is enabled or in an
612 interactive shell upon receipt of a SIGWINCH.
613 COMPREPLY
614 An array variable from which bash reads the possible completions generated by a shell function invoked by the programmable completion facility (see Programmable Comple‐
615 tion below). Each array element contains one possible completion.
616 EMACS If bash finds this variable in the environment when the shell starts with value "t", it assumes that the shell is running in an Emacs shell buffer and disables line edit‐
617 ing.
618 ENV Similar to BASH_ENV; used when the shell is invoked in POSIX mode.
619 EXECIGNORE
620 A colon-separated list of shell patterns (see Pattern Matching) defining the list of filenames to be ignored by command search using PATH. Files whose full pathnames
621 match one of these patterns are not considered executable files for the purposes of completion and command execution via PATH lookup. This does not affect the behavior
622 of the [, test, and [[ commands. Full pathnames in the command hash table are not subject to EXECIGNORE. Use this variable to ignore shared library files that have the
623 executable bit set, but are not executable files. The pattern matching honors the setting of the extglob shell option.
624 FCEDIT The default editor for the fc builtin command.
625 FIGNORE
626 A colon-separated list of suffixes to ignore when performing filename completion (see READLINE below). A filename whose suffix matches one of the entries in FIGNORE is
627 excluded from the list of matched filenames. A sample value is ".o:~" (Quoting is needed when assigning a value to this variable, which contains tildes).
628 FUNCNEST
629 If set to a numeric value greater than 0, defines a maximum function nesting level. Function invocations that exceed this nesting level will cause the current command to
630 abort.
631 GLOBIGNORE
632 A colon-separated list of patterns defining the set of filenames to be ignored by pathname expansion. If a filename matched by a pathname expansion pattern also matches
633 one of the patterns in GLOBIGNORE, it is removed from the list of matches.
634 HISTCONTROL
635 A colon-separated list of values controlling how commands are saved on the history list. If the list of values includes ignorespace, lines which begin with a space char‐
636 acter are not saved in the history list. A value of ignoredups causes lines matching the previous history entry to not be saved. A value of ignoreboth is shorthand for
637 ignorespace and ignoredups. A value of erasedups causes all previous lines matching the current line to be removed from the history list before that line is saved. Any
638 value not in the above list is ignored. If HISTCONTROL is unset, or does not include a valid value, all lines read by the shell parser are saved on the history list,
639 subject to the value of HISTIGNORE. The second and subsequent lines of a multi-line compound command are not tested, and are added to the history regardless of the value
640 of HISTCONTROL.
641 HISTFILE
642 The name of the file in which command history is saved (see HISTORY below). The default value is ~/.bash_history. If unset, the command history is not saved when a
643 shell exits.
644 HISTFILESIZE
645 The maximum number of lines contained in the history file. When this variable is assigned a value, the history file is truncated, if necessary, to contain no more than
646 that number of lines by removing the oldest entries. The history file is also truncated to this size after writing it when a shell exits. If the value is 0, the history
647 file is truncated to zero size. Non-numeric values and numeric values less than zero inhibit truncation. The shell sets the default value to the value of HISTSIZE after
648 reading any startup files.
649 HISTIGNORE
650 A colon-separated list of patterns used to decide which command lines should be saved on the history list. Each pattern is anchored at the beginning of the line and must
651 match the complete line (no implicit `*' is appended). Each pattern is tested against the line after the checks specified by HISTCONTROL are applied. In addition to the
652 normal shell pattern matching characters, `&' matches the previous history line. `&' may be escaped using a backslash; the backslash is removed before attempting a
653 match. The second and subsequent lines of a multi-line compound command are not tested, and are added to the history regardless of the value of HISTIGNORE. The pattern
654 matching honors the setting of the extglob shell option.
655 HISTSIZE
656 The number of commands to remember in the command history (see HISTORY below). If the value is 0, commands are not saved in the history list. Numeric values less than
657 zero result in every command being saved on the history list (there is no limit). The shell sets the default value to 500 after reading any startup files.
658 HISTTIMEFORMAT
659 If this variable is set and not null, its value is used as a format string for strftime(3) to print the time stamp associated with each history entry displayed by the
660 history builtin. If this variable is set, time stamps are written to the history file so they may be preserved across shell sessions. This uses the history comment
661 character to distinguish timestamps from other history lines.
662 HOME The home directory of the current user; the default argument for the cd builtin command. The value of this variable is also used when performing tilde expansion.
663 HOSTFILE
664 Contains the name of a file in the same format as /etc/hosts that should be read when the shell needs to complete a hostname. The list of possible hostname completions
665 may be changed while the shell is running; the next time hostname completion is attempted after the value is changed, bash adds the contents of the new file to the exist‐
666 ing list. If HOSTFILE is set, but has no value, or does not name a readable file, bash attempts to read /etc/hosts to obtain the list of possible hostname completions.
667 When HOSTFILE is unset, the hostname list is cleared.
668 IFS The Internal Field Separator that is used for word splitting after expansion and to split lines into words with the read builtin command. The default value is
669 ``<space><tab><newline>''.
670 IGNOREEOF
671 Controls the action of an interactive shell on receipt of an EOF character as the sole input. If set, the value is the number of consecutive EOF characters which must be
672 typed as the first characters on an input line before bash exits. If the variable exists but does not have a numeric value, or has no value, the default value is 10. If
673 it does not exist, EOF signifies the end of input to the shell.
674 INPUTRC
675 The filename for the readline startup file, overriding the default of ~/.inputrc (see READLINE below).
676 LANG Used to determine the locale category for any category not specifically selected with a variable starting with LC_.
677 LC_ALL This variable overrides the value of LANG and any other LC_ variable specifying a locale category.
678 LC_COLLATE
679 This variable determines the collation order used when sorting the results of pathname expansion, and determines the behavior of range expressions, equivalence classes,
680 and collating sequences within pathname expansion and pattern matching.
681 LC_CTYPE
682 This variable determines the interpretation of characters and the behavior of character classes within pathname expansion and pattern matching.
683 LC_MESSAGES
684 This variable determines the locale used to translate double-quoted strings preceded by a $.
685 LC_NUMERIC
686 This variable determines the locale category used for number formatting.
687 LC_TIME
688 This variable determines the locale category used for data and time formatting.
689 LINES Used by the select compound command to determine the column length for printing selection lists. Automatically set if the checkwinsize option is enabled or in an inter‐
690 active shell upon receipt of a SIGWINCH.
691 MAIL If this parameter is set to a file or directory name and the MAILPATH variable is not set, bash informs the user of the arrival of mail in the specified file or Maildir-
692 format directory.
693 MAILCHECK
694 Specifies how often (in seconds) bash checks for mail. The default is 60 seconds. When it is time to check for mail, the shell does so before displaying the primary
695 prompt. If this variable is unset, or set to a value that is not a number greater than or equal to zero, the shell disables mail checking.
696 MAILPATH
697 A colon-separated list of filenames to be checked for mail. The message to be printed when mail arrives in a particular file may be specified by separating the filename
698 from the message with a `?'. When used in the text of the message, $_ expands to the name of the current mailfile. Example:
699 MAILPATH='/var/mail/bfox?"You have mail":~/shell-mail?"$_ has mail!"'
700 Bash can be configured to supply a default value for this variable (there is no value by default), but the location of the user mail files that it uses is system depen‐
701 dent (e.g., /var/mail/$USER).
702 OPTERR If set to the value 1, bash displays error messages generated by the getopts builtin command (see SHELL BUILTIN COMMANDS below). OPTERR is initialized to 1 each time the
703 shell is invoked or a shell script is executed.
704 PATH The search path for commands. It is a colon-separated list of directories in which the shell looks for commands (see COMMAND EXECUTION below). A zero-length (null)
705 directory name in the value of PATH indicates the current directory. A null directory name may appear as two adjacent colons, or as an initial or trailing colon. The
706 default path is system-dependent, and is set by the administrator who installs bash. A common value is ``/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin:/bin:/sbin''.
707 POSIXLY_CORRECT
708 If this variable is in the environment when bash starts, the shell enters posix mode before reading the startup files, as if the --posix invocation option had been sup‐
709 plied. If it is set while the shell is running, bash enables posix mode, as if the command set -o posix had been executed.
710 PROMPT_COMMAND
711 If set, the value is executed as a command prior to issuing each primary prompt.
712 PROMPT_DIRTRIM
713 If set to a number greater than zero, the value is used as the number of trailing directory components to retain when expanding the \w and \W prompt string escapes (see
714 PROMPTING below). Characters removed are replaced with an ellipsis.
715 PS0 The value of this parameter is expanded (see PROMPTING below) and displayed by interactive shells after reading a command and before the command is executed.
716 PS1 The value of this parameter is expanded (see PROMPTING below) and used as the primary prompt string. The default value is ``\s-\v\$ ''.
717 PS2 The value of this parameter is expanded as with PS1 and used as the secondary prompt string. The default is ``> ''.
718 PS3 The value of this parameter is used as the prompt for the select command (see SHELL GRAMMAR above).
719 PS4 The value of this parameter is expanded as with PS1 and the value is printed before each command bash displays during an execution trace. The first character of PS4 is
720 replicated multiple times, as necessary, to indicate multiple levels of indirection. The default is ``+ ''.
721 SHELL The full pathname to the shell is kept in this environment variable. If it is not set when the shell starts, bash assigns to it the full pathname of the current user's
722 login shell.
723 TIMEFORMAT
724 The value of this parameter is used as a format string specifying how the timing information for pipelines prefixed with the time reserved word should be displayed. The
725 % character introduces an escape sequence that is expanded to a time value or other information. The escape sequences and their meanings are as follows; the braces
726 denote optional portions.
727 %% A literal %.
728 %[p][l]R The elapsed time in seconds.
729 %[p][l]U The number of CPU seconds spent in user mode.
730 %[p][l]S The number of CPU seconds spent in system mode.
731 %P The CPU percentage, computed as (%U + %S) / %R.
732
733 The optional p is a digit specifying the precision, the number of fractional digits after a decimal point. A value of 0 causes no decimal point or fraction to be output.
734 At most three places after the decimal point may be specified; values of p greater than 3 are changed to 3. If p is not specified, the value 3 is used.
735
736 The optional l specifies a longer format, including minutes, of the form MMmSS.FFs. The value of p determines whether or not the fraction is included.
737
738 If this variable is not set, bash acts as if it had the value $'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS'. If the value is null, no timing information is displayed. A trail‐
739 ing newline is added when the format string is displayed.
740 TMOUT If set to a value greater than zero, TMOUT is treated as the default timeout for the read builtin. The select command terminates if input does not arrive after TMOUT
741 seconds when input is coming from a terminal. In an interactive shell, the value is interpreted as the number of seconds to wait for a line of input after issuing the
742 primary prompt. Bash terminates after waiting for that number of seconds if a complete line of input does not arrive.
743 TMPDIR If set, bash uses its value as the name of a directory in which bash creates temporary files for the shell's use.
744 auto_resume
745 This variable controls how the shell interacts with the user and job control. If this variable is set, single word simple commands without redirections are treated as
746 candidates for resumption of an existing stopped job. There is no ambiguity allowed; if there is more than one job beginning with the string typed, the job most recently
747 accessed is selected. The name of a stopped job, in this context, is the command line used to start it. If set to the value exact, the string supplied must match the
748 name of a stopped job exactly; if set to substring, the string supplied needs to match a substring of the name of a stopped job. The substring value provides functional‐
749 ity analogous to the %? job identifier (see JOB CONTROL below). If set to any other value, the supplied string must be a prefix of a stopped job's name; this provides
750 functionality analogous to the %string job identifier.
751 histchars
752 The two or three characters which control history expansion and tokenization (see HISTORY EXPANSION below). The first character is the history expansion character, the
753 character which signals the start of a history expansion, normally `!'. The second character is the quick substitution character, which is used as shorthand for re-run‐
754 ning the previous command entered, substituting one string for another in the command. The default is `^'. The optional third character is the character which indicates
755 that the remainder of the line is a comment when found as the first character of a word, normally `#'. The history comment character causes history substitution to be
756 skipped for the remaining words on the line. It does not necessarily cause the shell parser to treat the rest of the line as a comment.
757
758 Arrays
759 Bash provides one-dimensional indexed and associative array variables. Any variable may be used as an indexed array; the declare builtin will explicitly declare an array.
760 There is no maximum limit on the size of an array, nor any requirement that members be indexed or assigned contiguously. Indexed arrays are referenced using integers (including
761 arithmetic expressions) and are zero-based; associative arrays are referenced using arbitrary strings. Unless otherwise noted, indexed array indices must be non-negative inte‐
762 gers.
763
764 An indexed array is created automatically if any variable is assigned to using the syntax name[subscript]=value. The subscript is treated as an arithmetic expression that must
765 evaluate to a number. To explicitly declare an indexed array, use declare -a name (see SHELL BUILTIN COMMANDS below). declare -a name[subscript] is also accepted; the sub‐
766 script is ignored.
767
768 Associative arrays are created using declare -A name.
769
770 Attributes may be specified for an array variable using the declare and readonly builtins. Each attribute applies to all members of an array.
771
772 Arrays are assigned to using compound assignments of the form name=(value1 ... valuen), where each value is of the form [subscript]=string. Indexed array assignments do not
773 require anything but string. When assigning to indexed arrays, if the optional brackets and subscript are supplied, that index is assigned to; otherwise the index of the ele‐
774 ment assigned is the last index assigned to by the statement plus one. Indexing starts at zero.
775
776 When assigning to an associative array, the subscript is required.
777
778 This syntax is also accepted by the declare builtin. Individual array elements may be assigned to using the name[subscript]=value syntax introduced above. When assigning to an
779 indexed array, if name is subscripted by a negative number, that number is interpreted as relative to one greater than the maximum index of name, so negative indices count back
780 from the end of the array, and an index of -1 references the last element.
781
782 Any element of an array may be referenced using ${name[subscript]}. The braces are required to avoid conflicts with pathname expansion. If subscript is @ or *, the word
783 expands to all members of name. These subscripts differ only when the word appears within double quotes. If the word is double-quoted, ${name[*]} expands to a single word with
784 the value of each array member separated by the first character of the IFS special variable, and ${name[@]} expands each element of name to a separate word. When there are no
785 array members, ${name[@]} expands to nothing. If the double-quoted expansion occurs within a word, the expansion of the first parameter is joined with the beginning part of the
786 original word, and the expansion of the last parameter is joined with the last part of the original word. This is analogous to the expansion of the special parameters * and @
787 (see Special Parameters above). ${#name[subscript]} expands to the length of ${name[subscript]}. If subscript is * or @, the expansion is the number of elements in the array.
788 If the subscript used to reference an element of an indexed array evaluates to a number less than zero, it is interpreted as relative to one greater than the maximum index of
789 the array, so negative indices count back from the end of the array, and an index of -1 references the last element.
790
791 Referencing an array variable without a subscript is equivalent to referencing the array with a subscript of 0. Any reference to a variable using a valid subscript is legal,
792 and bash will create an array if necessary.
793
794 An array variable is considered set if a subscript has been assigned a value. The null string is a valid value.
795
796 It is possible to obtain the keys (indices) of an array as well as the values. ${!name[@]} and ${!name[*]} expand to the indices assigned in array variable name. The treatment
797 when in double quotes is similar to the expansion of the special parameters @ and * within double quotes.
798
799 The unset builtin is used to destroy arrays. unset name[subscript] destroys the array element at index subscript. Negative subscripts to indexed arrays are interpreted as
800 described above. Care must be taken to avoid unwanted side effects caused by pathname expansion. unset name, where name is an array, or unset name[subscript], where subscript
801 is * or @, removes the entire array.
802
803 The declare, local, and readonly builtins each accept a -a option to specify an indexed array and a -A option to specify an associative array. If both options are supplied, -A
804 takes precedence. The read builtin accepts a -a option to assign a list of words read from the standard input to an array. The set and declare builtins display array values in
805 a way that allows them to be reused as assignments.
806
807EXPANSION
808 Expansion is performed on the command line after it has been split into words. There are seven kinds of expansion performed: brace expansion, tilde expansion, parameter and
809 variable expansion, command substitution, arithmetic expansion, word splitting, and pathname expansion.
810
811 The order of expansions is: brace expansion; tilde expansion, parameter and variable expansion, arithmetic expansion, and command substitution (done in a left-to-right fashion);
812 word splitting; and pathname expansion.
813
814 On systems that can support it, there is an additional expansion available: process substitution. This is performed at the same time as tilde, parameter, variable, and arith‐
815 metic expansion and command substitution.
816
817 After these expansions are performed, quote characters present in the original word are removed unless they have been quoted themselves (quote removal).
818
819 Only brace expansion, word splitting, and pathname expansion can change the number of words of the expansion; other expansions expand a single word to a single word. The only
820 exceptions to this are the expansions of "$@" and "${name[@]}" as explained above (see PARAMETERS).
821
822 Brace Expansion
823 Brace expansion is a mechanism by which arbitrary strings may be generated. This mechanism is similar to pathname expansion, but the filenames generated need not exist. Pat‐
824 terns to be brace expanded take the form of an optional preamble, followed by either a series of comma-separated strings or a sequence expression between a pair of braces, fol‐
825 lowed by an optional postscript. The preamble is prefixed to each string contained within the braces, and the postscript is then appended to each resulting string, expanding
826 left to right.
827
828 Brace expansions may be nested. The results of each expanded string are not sorted; left to right order is preserved. For example, a{d,c,b}e expands into `ade ace abe'.
829
830 A sequence expression takes the form {x..y[..incr]}, where x and y are either integers or single characters, and incr, an optional increment, is an integer. When integers are
831 supplied, the expression expands to each number between x and y, inclusive. Supplied integers may be prefixed with 0 to force each term to have the same width. When either x
832 or y begins with a zero, the shell attempts to force all generated terms to contain the same number of digits, zero-padding where necessary. When characters are supplied, the
833 expression expands to each character lexicographically between x and y, inclusive, using the default C locale. Note that both x and y must be of the same type. When the incre‐
834 ment is supplied, it is used as the difference between each term. The default increment is 1 or -1 as appropriate.
835
836 Brace expansion is performed before any other expansions, and any characters special to other expansions are preserved in the result. It is strictly textual. Bash does not
837 apply any syntactic interpretation to the context of the expansion or the text between the braces.
838
839 A correctly-formed brace expansion must contain unquoted opening and closing braces, and at least one unquoted comma or a valid sequence expression. Any incorrectly formed
840 brace expansion is left unchanged. A { or , may be quoted with a backslash to prevent its being considered part of a brace expression. To avoid conflicts with parameter expan‐
841 sion, the string ${ is not considered eligible for brace expansion.
842
843 This construct is typically used as shorthand when the common prefix of the strings to be generated is longer than in the above example:
844
845 mkdir /usr/local/src/bash/{old,new,dist,bugs}
846 or
847 chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}
848
849 Brace expansion introduces a slight incompatibility with historical versions of sh. sh does not treat opening or closing braces specially when they appear as part of a word,
850 and preserves them in the output. Bash removes braces from words as a consequence of brace expansion. For example, a word entered to sh as file{1,2} appears identically in the
851 output. The same word is output as file1 file2 after expansion by bash. If strict compatibility with sh is desired, start bash with the +B option or disable brace expansion
852 with the +B option to the set command (see SHELL BUILTIN COMMANDS below).
853
854 Tilde Expansion
855 If a word begins with an unquoted tilde character (`~'), all of the characters preceding the first unquoted slash (or all characters, if there is no unquoted slash) are consid‐
856 ered a tilde-prefix. If none of the characters in the tilde-prefix are quoted, the characters in the tilde-prefix following the tilde are treated as a possible login name. If
857 this login name is the null string, the tilde is replaced with the value of the shell parameter HOME. If HOME is unset, the home directory of the user executing the shell is
858 substituted instead. Otherwise, the tilde-prefix is replaced with the home directory associated with the specified login name.
859
860 If the tilde-prefix is a `~+', the value of the shell variable PWD replaces the tilde-prefix. If the tilde-prefix is a `~-', the value of the shell variable OLDPWD, if it is
861 set, is substituted. If the characters following the tilde in the tilde-prefix consist of a number N, optionally prefixed by a `+' or a `-', the tilde-prefix is replaced with
862 the corresponding element from the directory stack, as it would be displayed by the dirs builtin invoked with the tilde-prefix as an argument. If the characters following the
863 tilde in the tilde-prefix consist of a number without a leading `+' or `-', `+' is assumed.
864
865 If the login name is invalid, or the tilde expansion fails, the word is unchanged.
866
867 Each variable assignment is checked for unquoted tilde-prefixes immediately following a : or the first =. In these cases, tilde expansion is also performed. Consequently, one
868 may use filenames with tildes in assignments to PATH, MAILPATH, and CDPATH, and the shell assigns the expanded value.
869
870 Parameter Expansion
871 The `$' character introduces parameter expansion, command substitution, or arithmetic expansion. The parameter name or symbol to be expanded may be enclosed in braces, which
872 are optional but serve to protect the variable to be expanded from characters immediately following it which could be interpreted as part of the name.
873
874 When braces are used, the matching ending brace is the first `}' not escaped by a backslash or within a quoted string, and not within an embedded arithmetic expansion, command
875 substitution, or parameter expansion.
876
877 ${parameter}
878 The value of parameter is substituted. The braces are required when parameter is a positional parameter with more than one digit, or when parameter is followed by a
879 character which is not to be interpreted as part of its name. The parameter is a shell parameter as described above PARAMETERS) or an array reference (Arrays).
880
881 If the first character of parameter is an exclamation point (!), and parameter is not a nameref, it introduces a level of variable indirection. Bash uses the value of the vari‐
882 able formed from the rest of parameter as the name of the variable; this variable is then expanded and that value is used in the rest of the substitution, rather than the value
883 of parameter itself. This is known as indirect expansion. If parameter is a nameref, this expands to the name of the variable referenced by parameter instead of performing the
884 complete indirect expansion. The exceptions to this are the expansions of ${!prefix*} and ${!name[@]} described below. The exclamation point must immediately follow the left
885 brace in order to introduce indirection.
886
887 In each of the cases below, word is subject to tilde expansion, parameter expansion, command substitution, and arithmetic expansion.
888
889 When not performing substring expansion, using the forms documented below (e.g., :-), bash tests for a parameter that is unset or null. Omitting the colon results in a test
890 only for a parameter that is unset.
891
892 ${parameter:-word}
893 Use Default Values. If parameter is unset or null, the expansion of word is substituted. Otherwise, the value of parameter is substituted.
894 ${parameter:=word}
895 Assign Default Values. If parameter is unset or null, the expansion of word is assigned to parameter. The value of parameter is then substituted. Positional parameters
896 and special parameters may not be assigned to in this way.
897 ${parameter:?word}
898 Display Error if Null or Unset. If parameter is null or unset, the expansion of word (or a message to that effect if word is not present) is written to the standard
899 error and the shell, if it is not interactive, exits. Otherwise, the value of parameter is substituted.
900 ${parameter:+word}
901 Use Alternate Value. If parameter is null or unset, nothing is substituted, otherwise the expansion of word is substituted.
902 ${parameter:offset}
903 ${parameter:offset:length}
904 Substring Expansion. Expands to up to length characters of the value of parameter starting at the character specified by offset. If parameter is @, an indexed array
905 subscripted by @ or *, or an associative array name, the results differ as described below. If length is omitted, expands to the substring of the value of parameter
906 starting at the character specified by offset and extending to the end of the value. length and offset are arithmetic expressions (see ARITHMETIC EVALUATION below).
907
908 If offset evaluates to a number less than zero, the value is used as an offset in characters from the end of the value of parameter. If length evaluates to a number less
909 than zero, it is interpreted as an offset in characters from the end of the value of parameter rather than a number of characters, and the expansion is the characters
910 between offset and that result. Note that a negative offset must be separated from the colon by at least one space to avoid being confused with the :- expansion.
911
912 If parameter is @, the result is length positional parameters beginning at offset. A negative offset is taken relative to one greater than the greatest positional param‐
913 eter, so an offset of -1 evaluates to the last positional parameter. It is an expansion error if length evaluates to a number less than zero.
914
915 If parameter is an indexed array name subscripted by @ or *, the result is the length members of the array beginning with ${parameter[offset]}. A negative offset is
916 taken relative to one greater than the maximum index of the specified array. It is an expansion error if length evaluates to a number less than zero.
917
918 Substring expansion applied to an associative array produces undefined results.
919
920 Substring indexing is zero-based unless the positional parameters are used, in which case the indexing starts at 1 by default. If offset is 0, and the positional parame‐
921 ters are used, $0 is prefixed to the list.
922
923 ${!prefix*}
924 ${!prefix@}
925 Names matching prefix. Expands to the names of variables whose names begin with prefix, separated by the first character of the IFS special variable. When @ is used and
926 the expansion appears within double quotes, each variable name expands to a separate word.
927
928 ${!name[@]}
929 ${!name[*]}
930 List of array keys. If name is an array variable, expands to the list of array indices (keys) assigned in name. If name is not an array, expands to 0 if name is set and
931 null otherwise. When @ is used and the expansion appears within double quotes, each key expands to a separate word.
932
933 ${#parameter}
934 Parameter length. The length in characters of the value of parameter is substituted. If parameter is * or @, the value substituted is the number of positional parame‐
935 ters. If parameter is an array name subscripted by * or @, the value substituted is the number of elements in the array. If parameter is an indexed array name sub‐
936 scripted by a negative number, that number is interpreted as relative to one greater than the maximum index of parameter, so negative indices count back from the end of
937 the array, and an index of -1 references the last element.
938
939 ${parameter#word}
940 ${parameter##word}
941 Remove matching prefix pattern. The word is expanded to produce a pattern just as in pathname expansion. If the pattern matches the beginning of the value of parameter,
942 then the result of the expansion is the expanded value of parameter with the shortest matching pattern (the ``#'' case) or the longest matching pattern (the ``##'' case)
943 deleted. If parameter is @ or *, the pattern removal operation is applied to each positional parameter in turn, and the expansion is the resultant list. If parameter is
944 an array variable subscripted with @ or *, the pattern removal operation is applied to each member of the array in turn, and the expansion is the resultant list.
945
946 ${parameter%word}
947 ${parameter%%word}
948 Remove matching suffix pattern. The word is expanded to produce a pattern just as in pathname expansion. If the pattern matches a trailing portion of the expanded value
949 of parameter, then the result of the expansion is the expanded value of parameter with the shortest matching pattern (the ``%'' case) or the longest matching pattern (the
950 ``%%'' case) deleted. If parameter is @ or *, the pattern removal operation is applied to each positional parameter in turn, and the expansion is the resultant list. If
951 parameter is an array variable subscripted with @ or *, the pattern removal operation is applied to each member of the array in turn, and the expansion is the resultant
952 list.
953
954 ${parameter/pattern/string}
955 Pattern substitution. The pattern is expanded to produce a pattern just as in pathname expansion. Parameter is expanded and the longest match of pattern against its
956 value is replaced with string. If pattern begins with /, all matches of pattern are replaced with string. Normally only the first match is replaced. If pattern begins
957 with #, it must match at the beginning of the expanded value of parameter. If pattern begins with %, it must match at the end of the expanded value of parameter. If
958 string is null, matches of pattern are deleted and the / following pattern may be omitted. If the nocasematch shell option is enabled, the match is performed without
959 regard to the case of alphabetic characters. If parameter is @ or *, the substitution operation is applied to each positional parameter in turn, and the expansion is the
960 resultant list. If parameter is an array variable subscripted with @ or *, the substitution operation is applied to each member of the array in turn, and the expansion
961 is the resultant list.
962
963 ${parameter^pattern}
964 ${parameter^^pattern}
965 ${parameter,pattern}
966 ${parameter,,pattern}
967 Case modification. This expansion modifies the case of alphabetic characters in parameter. The pattern is expanded to produce a pattern just as in pathname expansion.
968 Each character in the expanded value of parameter is tested against pattern, and, if it matches the pattern, its case is converted. The pattern should not attempt to
969 match more than one character. The ^ operator converts lowercase letters matching pattern to uppercase; the , operator converts matching uppercase letters to lowercase.
970 The ^^ and ,, expansions convert each matched character in the expanded value; the ^ and , expansions match and convert only the first character in the expanded value.
971 If pattern is omitted, it is treated like a ?, which matches every character. If parameter is @ or *, the case modification operation is applied to each positional
972 parameter in turn, and the expansion is the resultant list. If parameter is an array variable subscripted with @ or *, the case modification operation is applied to each
973 member of the array in turn, and the expansion is the resultant list.
974
975 ${parameter@operator}
976 Parameter transformation. The expansion is either a transformation of the value of parameter or information about parameter itself, depending on the value of operator.
977 Each operator is a single letter:
978
979 Q The expansion is a string that is the value of parameter quoted in a format that can be reused as input.
980 E The expansion is a string that is the value of parameter with backslash escape sequences expanded as with the $'...' quoting mechansim.
981 P The expansion is a string that is the result of expanding the value of parameter as if it were a prompt string (see PROMPTING below).
982 A The expansion is a string in the form of an assignment statement or declare command that, if evaluated, will recreate parameter with its attributes and value.
983 a The expansion is a string consisting of flag values representing parameter's attributes.
984
985 If parameter is @ or *, the operation is applied to each positional parameter in turn, and the expansion is the resultant list. If parameter is an array variable sub‐
986 scripted with @ or *, the case modification operation is applied to each member of the array in turn, and the expansion is the resultant list.
987
988 The result of the expansion is subject to word splitting and pathname expansion as described below.
989
990 Command Substitution
991 Command substitution allows the output of a command to replace the command name. There are two forms:
992
993 $(command)
994 or
995 `command`
996
997 Bash performs the expansion by executing command in a subshell environment and replacing the command substitution with the standard output of the command, with any trailing new‐
998 lines deleted. Embedded newlines are not deleted, but they may be removed during word splitting. The command substitution $(cat file) can be replaced by the equivalent but
999 faster $(< file).
1000
1001 When the old-style backquote form of substitution is used, backslash retains its literal meaning except when followed by $, `, or \. The first backquote not preceded by a back‐
1002 slash terminates the command substitution. When using the $(command) form, all characters between the parentheses make up the command; none are treated specially.
1003
1004 Command substitutions may be nested. To nest when using the backquoted form, escape the inner backquotes with backslashes.
1005
1006 If the substitution appears within double quotes, word splitting and pathname expansion are not performed on the results.
1007
1008 Arithmetic Expansion
1009 Arithmetic expansion allows the evaluation of an arithmetic expression and the substitution of the result. The format for arithmetic expansion is:
1010
1011 $((expression))
1012
1013 The old format $[expression] is deprecated and will be removed in upcoming versions of bash.
1014
1015 The expression is treated as if it were within double quotes, but a double quote inside the parentheses is not treated specially. All tokens in the expression undergo parameter
1016 and variable expansion, command substitution, and quote removal. The result is treated as the arithmetic expression to be evaluated. Arithmetic expansions may be nested.
1017
1018 The evaluation is performed according to the rules listed below under ARITHMETIC EVALUATION. If expression is invalid, bash prints a message indicating failure and no substitu‐
1019 tion occurs.
1020
1021 Process Substitution
1022 Process substitution allows a process's input or output to be referred to using a filename. It takes the form of <(list) or >(list). The process list is run asynchronously,
1023 and its input or output appears as a filename. This filename is passed as an argument to the current command as the result of the expansion. If the >(list) form is used, writ‐
1024 ing to the file will provide input for list. If the <(list) form is used, the file passed as an argument should be read to obtain the output of list. Process substitution is
1025 supported on systems that support named pipes (FIFOs) or the /dev/fd method of naming open files.
1026
1027 When available, process substitution is performed simultaneously with parameter and variable expansion, command substitution, and arithmetic expansion.
1028
1029 Word Splitting
1030 The shell scans the results of parameter expansion, command substitution, and arithmetic expansion that did not occur within double quotes for word splitting.
1031
1032 The shell treats each character of IFS as a delimiter, and splits the results of the other expansions into words using these characters as field terminators. If IFS is unset,
1033 or its value is exactly <space><tab><newline>, the default, then sequences of <space>, <tab>, and <newline> at the beginning and end of the results of the previous expansions
1034 are ignored, and any sequence of IFS characters not at the beginning or end serves to delimit words. If IFS has a value other than the default, then sequences of the whitespace
1035 characters space, tab, and newline are ignored at the beginning and end of the word, as long as the whitespace character is in the value of IFS (an IFS whitespace character).
1036 Any character in IFS that is not IFS whitespace, along with any adjacent IFS whitespace characters, delimits a field. A sequence of IFS whitespace characters is also treated as
1037 a delimiter. If the value of IFS is null, no word splitting occurs.
1038
1039 Explicit null arguments ("" or '') are retained and passed to commands as empty strings. Unquoted implicit null arguments, resulting from the expansion of parameters that have
1040 no values, are removed. If a parameter with no value is expanded within double quotes, a null argument results and is retained and passed to a command as an empty string. When
1041 a quoted null argument appears as part of a word whose expansion is non-null, the null argument is removed. That is, the word -d'' becomes -d after word splitting and null
1042 argument removal.
1043
1044 Note that if no expansion occurs, no splitting is performed.
1045
1046 Pathname Expansion
1047 After word splitting, unless the -f option has been set, bash scans each word for the characters *, ?, and [. If one of these characters appears, then the word is regarded as a
1048 pattern, and replaced with an alphabetically sorted list of filenames matching the pattern (see Pattern Matching below). If no matching filenames are found, and the shell
1049 option nullglob is not enabled, the word is left unchanged. If the nullglob option is set, and no matches are found, the word is removed. If the failglob shell option is set,
1050 and no matches are found, an error message is printed and the command is not executed. If the shell option nocaseglob is enabled, the match is performed without regard to the
1051 case of alphabetic characters. Note that when using range expressions like [a-z] (see below), letters of the other case may be included, depending on the setting of LC_COLLATE.
1052 When a pattern is used for pathname expansion, the character ``.'' at the start of a name or immediately following a slash must be matched explicitly, unless the shell option
1053 dotglob is set. When matching a pathname, the slash character must always be matched explicitly. In other cases, the ``.'' character is not treated specially. See the
1054 description of shopt below under SHELL BUILTIN COMMANDS for a description of the nocaseglob, nullglob, failglob, and dotglob shell options.
1055
1056 The GLOBIGNORE shell variable may be used to restrict the set of filenames matching a pattern. If GLOBIGNORE is set, each matching filename that also matches one of the pat‐
1057 terns in GLOBIGNORE is removed from the list of matches. If the nocaseglob option is set, the matching against the patterns in GLOBIGNORE is performed without regard to case.
1058 The filenames ``.'' and ``..'' are always ignored when GLOBIGNORE is set and not null. However, setting GLOBIGNORE to a non-null value has the effect of enabling the dotglob
1059 shell option, so all other filenames beginning with a ``.'' will match. To get the old behavior of ignoring filenames beginning with a ``.'', make ``.*'' one of the patterns
1060 in GLOBIGNORE. The dotglob option is disabled when GLOBIGNORE is unset. The pattern matching honors the setting of the extglob shell option.
1061
1062 Pattern Matching
1063
1064 Any character that appears in a pattern, other than the special pattern characters described below, matches itself. The NUL character may not occur in a pattern. A backslash
1065 escapes the following character; the escaping backslash is discarded when matching. The special pattern characters must be quoted if they are to be matched literally.
1066
1067 The special pattern characters have the following meanings:
1068
1069 * Matches any string, including the null string. When the globstar shell option is enabled, and * is used in a pathname expansion context, two adjacent *s used as a
1070 single pattern will match all files and zero or more directories and subdirectories. If followed by a /, two adjacent *s will match only directories and subdirec‐
1071 tories.
1072 ? Matches any single character.
1073 [...] Matches any one of the enclosed characters. A pair of characters separated by a hyphen denotes a range expression; any character that falls between those two
1074 characters, inclusive, using the current locale's collating sequence and character set, is matched. If the first character following the [ is a ! or a ^ then any
1075 character not enclosed is matched. The sorting order of characters in range expressions is determined by the current locale and the values of the LC_COLLATE or
1076 LC_ALL shell variables, if set. To obtain the traditional interpretation of range expressions, where [a-d] is equivalent to [abcd], set value of the LC_ALL shell
1077 variable to C, or enable the globasciiranges shell option. A - may be matched by including it as the first or last character in the set. A ] may be matched by
1078 including it as the first character in the set.
1079
1080 Within [ and ], character classes can be specified using the syntax [:class:], where class is one of the following classes defined in the POSIX standard:
1081 alnum alpha ascii blank cntrl digit graph lower print punct space upper word xdigit
1082 A character class matches any character belonging to that class. The word character class matches letters, digits, and the character _.
1083
1084 Within [ and ], an equivalence class can be specified using the syntax [=c=], which matches all characters with the same collation weight (as defined by the cur‐
1085 rent locale) as the character c.
1086
1087 Within [ and ], the syntax [.symbol.] matches the collating symbol symbol.
1088
1089 If the extglob shell option is enabled using the shopt builtin, several extended pattern matching operators are recognized. In the following description, a pattern-list is a
1090 list of one or more patterns separated by a |. Composite patterns may be formed using one or more of the following sub-patterns:
1091
1092 ?(pattern-list)
1093 Matches zero or one occurrence of the given patterns
1094 *(pattern-list)
1095 Matches zero or more occurrences of the given patterns
1096 +(pattern-list)
1097 Matches one or more occurrences of the given patterns
1098 @(pattern-list)
1099 Matches one of the given patterns
1100 !(pattern-list)
1101 Matches anything except one of the given patterns
1102
1103 Quote Removal
1104 After the preceding expansions, all unquoted occurrences of the characters \, ', and " that did not result from one of the above expansions are removed.
1105
1106REDIRECTION
1107 Before a command is executed, its input and output may be redirected using a special notation interpreted by the shell. Redirection allows commands' file handles to be dupli‐
1108 cated, opened, closed, made to refer to different files, and can change the files the command reads from and writes to. Redirection may also be used to modify file handles in
1109 the current shell execution environment. The following redirection operators may precede or appear anywhere within a simple command or may follow a command. Redirections are
1110 processed in the order they appear, from left to right.
1111
1112 Each redirection that may be preceded by a file descriptor number may instead be preceded by a word of the form {varname}. In this case, for each redirection operator except
1113 >&- and <&-, the shell will allocate a file descriptor greater than or equal to 10 and assign it to varname. If >&- or <&- is preceded by {varname}, the value of varname
1114 defines the file descriptor to close.
1115
1116 In the following descriptions, if the file descriptor number is omitted, and the first character of the redirection operator is <, the redirection refers to the standard input
1117 (file descriptor 0). If the first character of the redirection operator is >, the redirection refers to the standard output (file descriptor 1).
1118
1119 The word following the redirection operator in the following descriptions, unless otherwise noted, is subjected to brace expansion, tilde expansion, parameter and variable
1120 expansion, command substitution, arithmetic expansion, quote removal, pathname expansion, and word splitting. If it expands to more than one word, bash reports an error.
1121
1122 Note that the order of redirections is significant. For example, the command
1123
1124 ls > dirlist 2>&1
1125
1126 directs both standard output and standard error to the file dirlist, while the command
1127
1128 ls 2>&1 > dirlist
1129
1130 directs only the standard output to file dirlist, because the standard error was duplicated from the standard output before the standard output was redirected to dirlist.
1131
1132 Bash handles several filenames specially when they are used in redirections, as described in the following table. If the operating system on which bash is running provides
1133 these special files, bash will use them; otherwise it will emulate them internally with the behavior described below.
1134
1135 /dev/fd/fd
1136 If fd is a valid integer, file descriptor fd is duplicated.
1137 /dev/stdin
1138 File descriptor 0 is duplicated.
1139 /dev/stdout
1140 File descriptor 1 is duplicated.
1141 /dev/stderr
1142 File descriptor 2 is duplicated.
1143 /dev/tcp/host/port
1144 If host is a valid hostname or Internet address, and port is an integer port number or service name, bash attempts to open the corresponding TCP socket.
1145 /dev/udp/host/port
1146 If host is a valid hostname or Internet address, and port is an integer port number or service name, bash attempts to open the corresponding UDP socket.
1147
1148 A failure to open or create a file causes the redirection to fail.
1149
1150 Redirections using file descriptors greater than 9 should be used with care, as they may conflict with file descriptors the shell uses internally.
1151
1152 Note that the exec builtin command can make redirections take effect in the current shell.
1153
1154 Redirecting Input
1155 Redirection of input causes the file whose name results from the expansion of word to be opened for reading on file descriptor n, or the standard input (file descriptor 0) if n
1156 is not specified.
1157
1158 The general format for redirecting input is:
1159
1160 [n]<word
1161
1162 Redirecting Output
1163 Redirection of output causes the file whose name results from the expansion of word to be opened for writing on file descriptor n, or the standard output (file descriptor 1) if
1164 n is not specified. If the file does not exist it is created; if it does exist it is truncated to zero size.
1165
1166 The general format for redirecting output is:
1167
1168 [n]>word
1169
1170 If the redirection operator is >, and the noclobber option to the set builtin has been enabled, the redirection will fail if the file whose name results from the expansion of
1171 word exists and is a regular file. If the redirection operator is >|, or the redirection operator is > and the noclobber option to the set builtin command is not enabled, the
1172 redirection is attempted even if the file named by word exists.
1173
1174 Appending Redirected Output
1175 Redirection of output in this fashion causes the file whose name results from the expansion of word to be opened for appending on file descriptor n, or the standard output (file
1176 descriptor 1) if n is not specified. If the file does not exist it is created.
1177
1178 The general format for appending output is:
1179
1180 [n]>>word
1181
1182 Redirecting Standard Output and Standard Error
1183 This construct allows both the standard output (file descriptor 1) and the standard error output (file descriptor 2) to be redirected to the file whose name is the expansion of
1184 word.
1185
1186 There are two formats for redirecting standard output and standard error:
1187
1188 &>word
1189 and
1190 >&word
1191
1192 Of the two forms, the first is preferred. This is semantically equivalent to
1193
1194 >word 2>&1
1195
1196 When using the second form, word may not expand to a number or -. If it does, other redirection operators apply (see Duplicating File Descriptors below) for compatibility rea‐
1197 sons.
1198
1199 Appending Standard Output and Standard Error
1200 This construct allows both the standard output (file descriptor 1) and the standard error output (file descriptor 2) to be appended to the file whose name is the expansion of
1201 word.
1202
1203 The format for appending standard output and standard error is:
1204
1205 &>>word
1206
1207 This is semantically equivalent to
1208
1209 >>word 2>&1
1210
1211 (see Duplicating File Descriptors below).
1212
1213 Here Documents
1214 This type of redirection instructs the shell to read input from the current source until a line containing only delimiter (with no trailing blanks) is seen. All of the lines
1215 read up to that point are then used as the standard input (or file descriptor n if n is specified) for a command.
1216
1217 The format of here-documents is:
1218
1219 [n]<<[-]word
1220 here-document
1221 delimiter
1222
1223 No parameter and variable expansion, command substitution, arithmetic expansion, or pathname expansion is performed on word. If any part of word is quoted, the delimiter is the
1224 result of quote removal on word, and the lines in the here-document are not expanded. If word is unquoted, all lines of the here-document are subjected to parameter expansion,
1225 command substitution, and arithmetic expansion, the character sequence \<newline> is ignored, and \ must be used to quote the characters \, $, and `.
1226
1227 If the redirection operator is <<-, then all leading tab characters are stripped from input lines and the line containing delimiter. This allows here-documents within shell
1228 scripts to be indented in a natural fashion.
1229
1230 Here Strings
1231 A variant of here documents, the format is:
1232
1233 [n]<<<word
1234
1235 The word undergoes brace expansion, tilde expansion, parameter and variable expansion, command substitution, arithmetic expansion, and quote removal. Pathname expansion and
1236 word splitting are not performed. The result is supplied as a single string, with a newline appended, to the command on its standard input (or file descriptor n if n is speci‐
1237 fied).
1238
1239 Duplicating File Descriptors
1240 The redirection operator
1241
1242 [n]<&word
1243
1244 is used to duplicate input file descriptors. If word expands to one or more digits, the file descriptor denoted by n is made to be a copy of that file descriptor. If the dig‐
1245 its in word do not specify a file descriptor open for input, a redirection error occurs. If word evaluates to -, file descriptor n is closed. If n is not specified, the stan‐
1246 dard input (file descriptor 0) is used.
1247
1248 The operator
1249
1250 [n]>&word
1251
1252 is used similarly to duplicate output file descriptors. If n is not specified, the standard output (file descriptor 1) is used. If the digits in word do not specify a file
1253 descriptor open for output, a redirection error occurs. If word evaluates to -, file descriptor n is closed. As a special case, if n is omitted, and word does not expand to
1254 one or more digits or -, the standard output and standard error are redirected as described previously.
1255
1256 Moving File Descriptors
1257 The redirection operator
1258
1259 [n]<&digit-
1260
1261 moves the file descriptor digit to file descriptor n, or the standard input (file descriptor 0) if n is not specified. digit is closed after being duplicated to n.
1262
1263 Similarly, the redirection operator
1264
1265 [n]>&digit-
1266
1267 moves the file descriptor digit to file descriptor n, or the standard output (file descriptor 1) if n is not specified.
1268
1269 Opening File Descriptors for Reading and Writing
1270 The redirection operator
1271
1272 [n]<>word
1273
1274 causes the file whose name is the expansion of word to be opened for both reading and writing on file descriptor n, or on file descriptor 0 if n is not specified. If the file
1275 does not exist, it is created.
1276
1277ALIASES
1278 Aliases allow a string to be substituted for a word when it is used as the first word of a simple command. The shell maintains a list of aliases that may be set and unset with
1279 the alias and unalias builtin commands (see SHELL BUILTIN COMMANDS below). The first word of each simple command, if unquoted, is checked to see if it has an alias. If so,
1280 that word is replaced by the text of the alias. The characters /, $, `, and = and any of the shell metacharacters or quoting characters listed above may not appear in an alias
1281 name. The replacement text may contain any valid shell input, including shell metacharacters. The first word of the replacement text is tested for aliases, but a word that is
1282 identical to an alias being expanded is not expanded a second time. This means that one may alias ls to ls -F, for instance, and bash does not try to recursively expand the
1283 replacement text. If the last character of the alias value is a blank, then the next command word following the alias is also checked for alias expansion.
1284
1285 Aliases are created and listed with the alias command, and removed with the unalias command.
1286
1287 There is no mechanism for using arguments in the replacement text. If arguments are needed, a shell function should be used (see FUNCTIONS below).
1288
1289 Aliases are not expanded when the shell is not interactive, unless the expand_aliases shell option is set using shopt (see the description of shopt under SHELL BUILTIN COMMANDS
1290 below).
1291
1292 The rules concerning the definition and use of aliases are somewhat confusing. Bash always reads at least one complete line of input before executing any of the commands on
1293 that line. Aliases are expanded when a command is read, not when it is executed. Therefore, an alias definition appearing on the same line as another command does not take
1294 effect until the next line of input is read. The commands following the alias definition on that line are not affected by the new alias. This behavior is also an issue when
1295 functions are executed. Aliases are expanded when a function definition is read, not when the function is executed, because a function definition is itself a command. As a
1296 consequence, aliases defined in a function are not available until after that function is executed. To be safe, always put alias definitions on a separate line, and do not use
1297 alias in compound commands.
1298
1299 For almost every purpose, aliases are superseded by shell functions.
1300
1301FUNCTIONS
1302 A shell function, defined as described above under SHELL GRAMMAR, stores a series of commands for later execution. When the name of a shell function is used as a simple command
1303 name, the list of commands associated with that function name is executed. Functions are executed in the context of the current shell; no new process is created to interpret
1304 them (contrast this with the execution of a shell script). When a function is executed, the arguments to the function become the positional parameters during its execution.
1305 The special parameter # is updated to reflect the change. Special parameter 0 is unchanged. The first element of the FUNCNAME variable is set to the name of the function while
1306 the function is executing.
1307
1308 All other aspects of the shell execution environment are identical between a function and its caller with these exceptions: the DEBUG and RETURN traps (see the description of
1309 the trap builtin under SHELL BUILTIN COMMANDS below) are not inherited unless the function has been given the trace attribute (see the description of the declare builtin below)
1310 or the -o functrace shell option has been enabled with the set builtin (in which case all functions inherit the DEBUG and RETURN traps), and the ERR trap is not inherited unless
1311 the -o errtrace shell option has been enabled.
1312
1313 Variables local to the function may be declared with the local builtin command. Ordinarily, variables and their values are shared between the function and its caller.
1314
1315 The FUNCNEST variable, if set to a numeric value greater than 0, defines a maximum function nesting level. Function invocations that exceed the limit cause the entire command
1316 to abort.
1317
1318 If the builtin command return is executed in a function, the function completes and execution resumes with the next command after the function call. Any command associated with
1319 the RETURN trap is executed before execution resumes. When a function completes, the values of the positional parameters and the special parameter # are restored to the values
1320 they had prior to the function's execution.
1321
1322 Function names and definitions may be listed with the -f option to the declare or typeset builtin commands. The -F option to declare or typeset will list the function names
1323 only (and optionally the source file and line number, if the extdebug shell option is enabled). Functions may be exported so that subshells automatically have them defined with
1324 the -f option to the export builtin. A function definition may be deleted using the -f option to the unset builtin. Note that shell functions and variables with the same name
1325 may result in multiple identically-named entries in the environment passed to the shell's children. Care should be taken in cases where this may cause a problem.
1326
1327 Functions may be recursive. The FUNCNEST variable may be used to limit the depth of the function call stack and restrict the number of function invocations. By default, no
1328 limit is imposed on the number of recursive calls.
1329
1330ARITHMETIC EVALUATION
1331 The shell allows arithmetic expressions to be evaluated, under certain circumstances (see the let and declare builtin commands, the (( compound command, and Arithmetic Expan‐
1332 sion). Evaluation is done in fixed-width integers with no check for overflow, though division by 0 is trapped and flagged as an error. The operators and their precedence,
1333 associativity, and values are the same as in the C language. The following list of operators is grouped into levels of equal-precedence operators. The levels are listed in
1334 order of decreasing precedence.
1335
1336 id++ id--
1337 variable post-increment and post-decrement
1338 ++id --id
1339 variable pre-increment and pre-decrement
1340 - + unary minus and plus
1341 ! ~ logical and bitwise negation
1342 ** exponentiation
1343 * / % multiplication, division, remainder
1344 + - addition, subtraction
1345 << >> left and right bitwise shifts
1346 <= >= < >
1347 comparison
1348 == != equality and inequality
1349 & bitwise AND
1350 ^ bitwise exclusive OR
1351 | bitwise OR
1352 && logical AND
1353 || logical OR
1354 expr?expr:expr
1355 conditional operator
1356 = *= /= %= += -= <<= >>= &= ^= |=
1357 assignment
1358 expr1 , expr2
1359 comma
1360
1361 Shell variables are allowed as operands; parameter expansion is performed before the expression is evaluated. Within an expression, shell variables may also be referenced by
1362 name without using the parameter expansion syntax. A shell variable that is null or unset evaluates to 0 when referenced by name without using the parameter expansion syntax.
1363 The value of a variable is evaluated as an arithmetic expression when it is referenced, or when a variable which has been given the integer attribute using declare -i is
1364 assigned a value. A null value evaluates to 0. A shell variable need not have its integer attribute turned on to be used in an expression.
1365
1366 Constants with a leading 0 are interpreted as octal numbers. A leading 0x or 0X denotes hexadecimal. Otherwise, numbers take the form [base#]n, where the optional base is a
1367 decimal number between 2 and 64 representing the arithmetic base, and n is a number in that base. If base# is omitted, then base 10 is used. When specifying n, the digits
1368 greater than 9 are represented by the lowercase letters, the uppercase letters, @, and _, in that order. If base is less than or equal to 36, lowercase and uppercase letters
1369 may be used interchangeably to represent numbers between 10 and 35.
1370
1371 Operators are evaluated in order of precedence. Sub-expressions in parentheses are evaluated first and may override the precedence rules above.
1372
1373CONDITIONAL EXPRESSIONS
1374 Conditional expressions are used by the [[ compound command and the test and [ builtin commands to test file attributes and perform string and arithmetic comparisons. Expres‐
1375 sions are formed from the following unary or binary primaries. Bash handles several filenames specially when they are used in expressions. If the operating system on which
1376 bash is running provides these special files, bash will use them; otherwise it will emulate them internally with this behavior: If any file argument to one of the primaries is
1377 of the form /dev/fd/n, then file descriptor n is checked. If the file argument to one of the primaries is one of /dev/stdin, /dev/stdout, or /dev/stderr, file descriptor 0, 1,
1378 or 2, respectively, is checked.
1379
1380 Unless otherwise specified, primaries that operate on files follow symbolic links and operate on the target of the link, rather than the link itself.
1381
1382 When used with [[, the < and > operators sort lexicographically using the current locale. The test command sorts using ASCII ordering.
1383
1384 -a file
1385 True if file exists.
1386 -b file
1387 True if file exists and is a block special file.
1388 -c file
1389 True if file exists and is a character special file.
1390 -d file
1391 True if file exists and is a directory.
1392 -e file
1393 True if file exists.
1394 -f file
1395 True if file exists and is a regular file.
1396 -g file
1397 True if file exists and is set-group-id.
1398 -h file
1399 True if file exists and is a symbolic link.
1400 -k file
1401 True if file exists and its ``sticky'' bit is set.
1402 -p file
1403 True if file exists and is a named pipe (FIFO).
1404 -r file
1405 True if file exists and is readable.
1406 -s file
1407 True if file exists and has a size greater than zero.
1408 -t fd True if file descriptor fd is open and refers to a terminal.
1409 -u file
1410 True if file exists and its set-user-id bit is set.
1411 -w file
1412 True if file exists and is writable.
1413 -x file
1414 True if file exists and is executable.
1415 -G file
1416 True if file exists and is owned by the effective group id.
1417 -L file
1418 True if file exists and is a symbolic link.
1419 -N file
1420 True if file exists and has been modified since it was last read.
1421 -O file
1422 True if file exists and is owned by the effective user id.
1423 -S file
1424 True if file exists and is a socket.
1425 file1 -ef file2
1426 True if file1 and file2 refer to the same device and inode numbers.
1427 file1 -nt file2
1428 True if file1 is newer (according to modification date) than file2, or if file1 exists and file2 does not.
1429 file1 -ot file2
1430 True if file1 is older than file2, or if file2 exists and file1 does not.
1431 -o optname
1432 True if the shell option optname is enabled. See the list of options under the description of the -o option to the set builtin below.
1433 -v varname
1434 True if the shell variable varname is set (has been assigned a value).
1435 -R varname
1436 True if the shell variable varname is set and is a name reference.
1437 -z string
1438 True if the length of string is zero.
1439 string
1440 -n string
1441 True if the length of string is non-zero.
1442
1443 string1 == string2
1444 string1 = string2
1445 True if the strings are equal. = should be used with the test command for POSIX conformance. When used with the [[ command, this performs pattern matching as described
1446 above (Compound Commands).
1447
1448 string1 != string2
1449 True if the strings are not equal.
1450
1451 string1 < string2
1452 True if string1 sorts before string2 lexicographically.
1453
1454 string1 > string2
1455 True if string1 sorts after string2 lexicographically.
1456
1457 arg1 OP arg2
1458 OP is one of -eq, -ne, -lt, -le, -gt, or -ge. These arithmetic binary operators return true if arg1 is equal to, not equal to, less than, less than or equal to, greater
1459 than, or greater than or equal to arg2, respectively. Arg1 and arg2 may be positive or negative integers.
1460
1461SIMPLE COMMAND EXPANSION
1462 When a simple command is executed, the shell performs the following expansions, assignments, and redirections, from left to right.
1463
1464 1. The words that the parser has marked as variable assignments (those preceding the command name) and redirections are saved for later processing.
1465
1466 2. The words that are not variable assignments or redirections are expanded. If any words remain after expansion, the first word is taken to be the name of the command and
1467 the remaining words are the arguments.
1468
1469 3. Redirections are performed as described above under REDIRECTION.
1470
1471 4. The text after the = in each variable assignment undergoes tilde expansion, parameter expansion, command substitution, arithmetic expansion, and quote removal before
1472 being assigned to the variable.
1473
1474 If no command name results, the variable assignments affect the current shell environment. Otherwise, the variables are added to the environment of the executed command and do
1475 not affect the current shell environment. If any of the assignments attempts to assign a value to a readonly variable, an error occurs, and the command exits with a non-zero
1476 status.
1477
1478 If no command name results, redirections are performed, but do not affect the current shell environment. A redirection error causes the command to exit with a non-zero status.
1479
1480 If there is a command name left after expansion, execution proceeds as described below. Otherwise, the command exits. If one of the expansions contained a command substitu‐
1481 tion, the exit status of the command is the exit status of the last command substitution performed. If there were no command substitutions, the command exits with a status of
1482 zero.
1483
1484COMMAND EXECUTION
1485 After a command has been split into words, if it results in a simple command and an optional list of arguments, the following actions are taken.
1486
1487 If the command name contains no slashes, the shell attempts to locate it. If there exists a shell function by that name, that function is invoked as described above in FUNC‐
1488 TIONS. If the name does not match a function, the shell searches for it in the list of shell builtins. If a match is found, that builtin is invoked.
1489
1490 If the name is neither a shell function nor a builtin, and contains no slashes, bash searches each element of the PATH for a directory containing an executable file by that
1491 name. Bash uses a hash table to remember the full pathnames of executable files (see hash under SHELL BUILTIN COMMANDS below). A full search of the directories in PATH is per‐
1492 formed only if the command is not found in the hash table. If the search is unsuccessful, the shell searches for a defined shell function named command_not_found_handle. If
1493 that function exists, it is invoked with the original command and the original command's arguments as its arguments, and the function's exit status becomes the exit status of
1494 the shell. If that function is not defined, the shell prints an error message and returns an exit status of 127.
1495
1496 If the search is successful, or if the command name contains one or more slashes, the shell executes the named program in a separate execution environment. Argument 0 is set to
1497 the name given, and the remaining arguments to the command are set to the arguments given, if any.
1498
1499 If this execution fails because the file is not in executable format, and the file is not a directory, it is assumed to be a shell script, a file containing shell commands. A
1500 subshell is spawned to execute it. This subshell reinitializes itself, so that the effect is as if a new shell had been invoked to handle the script, with the exception that
1501 the locations of commands remembered by the parent (see hash below under SHELL BUILTIN COMMANDS) are retained by the child.
1502
1503 If the program is a file beginning with #!, the remainder of the first line specifies an interpreter for the program. The shell executes the specified interpreter on operating
1504 systems that do not handle this executable format themselves. The arguments to the interpreter consist of a single optional argument following the interpreter name on the first
1505 line of the program, followed by the name of the program, followed by the command arguments, if any.
1506
1507COMMAND EXECUTION ENVIRONMENT
1508 The shell has an execution environment, which consists of the following:
1509
1510 · open files inherited by the shell at invocation, as modified by redirections supplied to the exec builtin
1511
1512 · the current working directory as set by cd, pushd, or popd, or inherited by the shell at invocation
1513
1514 · the file creation mode mask as set by umask or inherited from the shell's parent
1515
1516 · current traps set by trap
1517
1518 · shell parameters that are set by variable assignment or with set or inherited from the shell's parent in the environment
1519
1520 · shell functions defined during execution or inherited from the shell's parent in the environment
1521
1522 · options enabled at invocation (either by default or with command-line arguments) or by set
1523
1524 · options enabled by shopt
1525
1526 · shell aliases defined with alias
1527
1528 · various process IDs, including those of background jobs, the value of $$, and the value of PPID
1529
1530 When a simple command other than a builtin or shell function is to be executed, it is invoked in a separate execution environment that consists of the following. Unless other‐
1531 wise noted, the values are inherited from the shell.
1532
1533 · the shell's open files, plus any modifications and additions specified by redirections to the command
1534
1535 · the current working directory
1536
1537 · the file creation mode mask
1538
1539 · shell variables and functions marked for export, along with variables exported for the command, passed in the environment
1540
1541 · traps caught by the shell are reset to the values inherited from the shell's parent, and traps ignored by the shell are ignored
1542
1543 A command invoked in this separate environment cannot affect the shell's execution environment.
1544
1545 Command substitution, commands grouped with parentheses, and asynchronous commands are invoked in a subshell environment that is a duplicate of the shell environment, except
1546 that traps caught by the shell are reset to the values that the shell inherited from its parent at invocation. Builtin commands that are invoked as part of a pipeline are also
1547 executed in a subshell environment. Changes made to the subshell environment cannot affect the shell's execution environment.
1548
1549 Subshells spawned to execute command substitutions inherit the value of the -e option from the parent shell. When not in posix mode, bash clears the -e option in such sub‐
1550 shells.
1551
1552 If a command is followed by a & and job control is not active, the default standard input for the command is the empty file /dev/null. Otherwise, the invoked command inherits
1553 the file descriptors of the calling shell as modified by redirections.
1554
1555ENVIRONMENT
1556 When a program is invoked it is given an array of strings called the environment. This is a list of name-value pairs, of the form name=value.
1557
1558 The shell provides several ways to manipulate the environment. On invocation, the shell scans its own environment and creates a parameter for each name found, automatically
1559 marking it for export to child processes. Executed commands inherit the environment. The export and declare -x commands allow parameters and functions to be added to and
1560 deleted from the environment. If the value of a parameter in the environment is modified, the new value becomes part of the environment, replacing the old. The environment
1561 inherited by any executed command consists of the shell's initial environment, whose values may be modified in the shell, less any pairs removed by the unset command, plus any
1562 additions via the export and declare -x commands.
1563
1564 The environment for any simple command or function may be augmented temporarily by prefixing it with parameter assignments, as described above in PARAMETERS. These assignment
1565 statements affect only the environment seen by that command.
1566
1567 If the -k option is set (see the set builtin command below), then all parameter assignments are placed in the environment for a command, not just those that precede the command
1568 name.
1569
1570 When bash invokes an external command, the variable _ is set to the full filename of the command and passed to that command in its environment.
1571
1572EXIT STATUS
1573 The exit status of an executed command is the value returned by the waitpid system call or equivalent function. Exit statuses fall between 0 and 255, though, as explained
1574 below, the shell may use values above 125 specially. Exit statuses from shell builtins and compound commands are also limited to this range. Under certain circumstances, the
1575 shell will use special values to indicate specific failure modes.
1576
1577 For the shell's purposes, a command which exits with a zero exit status has succeeded. An exit status of zero indicates success. A non-zero exit status indicates failure.
1578 When a command terminates on a fatal signal N, bash uses the value of 128+N as the exit status.
1579
1580 If a command is not found, the child process created to execute it returns a status of 127. If a command is found but is not executable, the return status is 126.
1581
1582 If a command fails because of an error during expansion or redirection, the exit status is greater than zero.
1583
1584 Shell builtin commands return a status of 0 (true) if successful, and non-zero (false) if an error occurs while they execute. All builtins return an exit status of 2 to indi‐
1585 cate incorrect usage, generally invalid options or missing arguments.
1586
1587 Bash itself returns the exit status of the last command executed, unless a syntax error occurs, in which case it exits with a non-zero value. See also the exit builtin command
1588 below.
1589
1590SIGNALS
1591 When bash is interactive, in the absence of any traps, it ignores SIGTERM (so that kill 0 does not kill an interactive shell), and SIGINT is caught and handled (so that the wait
1592 builtin is interruptible). In all cases, bash ignores SIGQUIT. If job control is in effect, bash ignores SIGTTIN, SIGTTOU, and SIGTSTP.
1593
1594 Non-builtin commands run by bash have signal handlers set to the values inherited by the shell from its parent. When job control is not in effect, asynchronous commands ignore
1595 SIGINT and SIGQUIT in addition to these inherited handlers. Commands run as a result of command substitution ignore the keyboard-generated job control signals SIGTTIN, SIGTTOU,
1596 and SIGTSTP.
1597
1598 The shell exits by default upon receipt of a SIGHUP. Before exiting, an interactive shell resends the SIGHUP to all jobs, running or stopped. Stopped jobs are sent SIGCONT to
1599 ensure that they receive the SIGHUP. To prevent the shell from sending the signal to a particular job, it should be removed from the jobs table with the disown builtin (see
1600 SHELL BUILTIN COMMANDS below) or marked to not receive SIGHUP using disown -h.
1601
1602 If the huponexit shell option has been set with shopt, bash sends a SIGHUP to all jobs when an interactive login shell exits.
1603
1604 If bash is waiting for a command to complete and receives a signal for which a trap has been set, the trap will not be executed until the command completes. When bash is wait‐
1605 ing for an asynchronous command via the wait builtin, the reception of a signal for which a trap has been set will cause the wait builtin to return immediately with an exit sta‐
1606 tus greater than 128, immediately after which the trap is executed.
1607
1608JOB CONTROL
1609 Job control refers to the ability to selectively stop (suspend) the execution of processes and continue (resume) their execution at a later point. A user typically employs this
1610 facility via an interactive interface supplied jointly by the operating system kernel's terminal driver and bash.
1611
1612 The shell associates a job with each pipeline. It keeps a table of currently executing jobs, which may be listed with the jobs command. When bash starts a job asynchronously
1613 (in the background), it prints a line that looks like:
1614
1615 [1] 25647
1616
1617 indicating that this job is job number 1 and that the process ID of the last process in the pipeline associated with this job is 25647. All of the processes in a single pipe‐
1618 line are members of the same job. Bash uses the job abstraction as the basis for job control.
1619
1620 To facilitate the implementation of the user interface to job control, the operating system maintains the notion of a current terminal process group ID. Members of this process
1621 group (processes whose process group ID is equal to the current terminal process group ID) receive keyboard-generated signals such as SIGINT. These processes are said to be in
1622 the foreground. Background processes are those whose process group ID differs from the terminal's; such processes are immune to keyboard-generated signals. Only foreground
1623 processes are allowed to read from or, if the user so specifies with stty tostop, write to the terminal. Background processes which attempt to read from (write to when stty
1624 tostop is in effect) the terminal are sent a SIGTTIN (SIGTTOU) signal by the kernel's terminal driver, which, unless caught, suspends the process.
1625
1626 If the operating system on which bash is running supports job control, bash contains facilities to use it. Typing the suspend character (typically ^Z, Control-Z) while a
1627 process is running causes that process to be stopped and returns control to bash. Typing the delayed suspend character (typically ^Y, Control-Y) causes the process to be
1628 stopped when it attempts to read input from the terminal, and control to be returned to bash. The user may then manipulate the state of this job, using the bg command to con‐
1629 tinue it in the background, the fg command to continue it in the foreground, or the kill command to kill it. A ^Z takes effect immediately, and has the additional side effect
1630 of causing pending output and typeahead to be discarded.
1631
1632 There are a number of ways to refer to a job in the shell. The character % introduces a job specification (jobspec). Job number n may be referred to as %n. A job may also be
1633 referred to using a prefix of the name used to start it, or using a substring that appears in its command line. For example, %ce refers to a stopped ce job. If a prefix
1634 matches more than one job, bash reports an error. Using %?ce, on the other hand, refers to any job containing the string ce in its command line. If the substring matches more
1635 than one job, bash reports an error. The symbols %% and %+ refer to the shell's notion of the current job, which is the last job stopped while it was in the foreground or
1636 started in the background. The previous job may be referenced using %-. If there is only a single job, %+ and %- can both be used to refer to that job. In output pertaining
1637 to jobs (e.g., the output of the jobs command), the current job is always flagged with a +, and the previous job with a -. A single % (with no accompanying job specification)
1638 also refers to the current job.
1639
1640 Simply naming a job can be used to bring it into the foreground: %1 is a synonym for ``fg %1'', bringing job 1 from the background into the foreground. Similarly, ``%1 &''
1641 resumes job 1 in the background, equivalent to ``bg %1''.
1642
1643 The shell learns immediately whenever a job changes state. Normally, bash waits until it is about to print a prompt before reporting changes in a job's status so as to not
1644 interrupt any other output. If the -b option to the set builtin command is enabled, bash reports such changes immediately. Any trap on SIGCHLD is executed for each child that
1645 exits.
1646
1647 If an attempt to exit bash is made while jobs are stopped (or, if the checkjobs shell option has been enabled using the shopt builtin, running), the shell prints a warning mes‐
1648 sage, and, if the checkjobs option is enabled, lists the jobs and their statuses. The jobs command may then be used to inspect their status. If a second attempt to exit is
1649 made without an intervening command, the shell does not print another warning, and any stopped jobs are terminated.
1650
1651PROMPTING
1652 When executing interactively, bash displays the primary prompt PS1 when it is ready to read a command, and the secondary prompt PS2 when it needs more input to complete a com‐
1653 mand. Bash displays PS0 after it reads a command but before executing it. Bash allows these prompt strings to be customized by inserting a number of backslash-escaped special
1654 characters that are decoded as follows:
1655 \a an ASCII bell character (07)
1656 \d the date in "Weekday Month Date" format (e.g., "Tue May 26")
1657 \D{format}
1658 the format is passed to strftime(3) and the result is inserted into the prompt string; an empty format results in a locale-specific time representation. The
1659 braces are required
1660 \e an ASCII escape character (033)
1661 \h the hostname up to the first `.'
1662 \H the hostname
1663 \j the number of jobs currently managed by the shell
1664 \l the basename of the shell's terminal device name
1665 \n newline
1666 \r carriage return
1667 \s the name of the shell, the basename of $0 (the portion following the final slash)
1668 \t the current time in 24-hour HH:MM:SS format
1669 \T the current time in 12-hour HH:MM:SS format
1670 \@ the current time in 12-hour am/pm format
1671 \A the current time in 24-hour HH:MM format
1672 \u the username of the current user
1673 \v the version of bash (e.g., 2.00)
1674 \V the release of bash, version + patch level (e.g., 2.00.0)
1675 \w the current working directory, with $HOME abbreviated with a tilde (uses the value of the PROMPT_DIRTRIM variable)
1676 \W the basename of the current working directory, with $HOME abbreviated with a tilde
1677 \! the history number of this command
1678 \# the command number of this command
1679 \$ if the effective UID is 0, a #, otherwise a $
1680 \nnn the character corresponding to the octal number nnn
1681 \\ a backslash
1682 \[ begin a sequence of non-printing characters, which could be used to embed a terminal control sequence into the prompt
1683 \] end a sequence of non-printing characters
1684
1685 The command number and the history number are usually different: the history number of a command is its position in the history list, which may include commands restored from
1686 the history file (see HISTORY below), while the command number is the position in the sequence of commands executed during the current shell session. After the string is
1687 decoded, it is expanded via parameter expansion, command substitution, arithmetic expansion, and quote removal, subject to the value of the promptvars shell option (see the
1688 description of the shopt command under SHELL BUILTIN COMMANDS below).
1689
1690READLINE
1691 This is the library that handles reading input when using an interactive shell, unless the --noediting option is given at shell invocation. Line editing is also used when using
1692 the -e option to the read builtin. By default, the line editing commands are similar to those of Emacs. A vi-style line editing interface is also available. Line editing can
1693 be enabled at any time using the -o emacs or -o vi options to the set builtin (see SHELL BUILTIN COMMANDS below). To turn off line editing after the shell is running, use the
1694 +o emacs or +o vi options to the set builtin.
1695
1696 Readline Notation
1697 In this section, the Emacs-style notation is used to denote keystrokes. Control keys are denoted by C-key, e.g., C-n means Control-N. Similarly, meta keys are denoted by
1698 M-key, so M-x means Meta-X. (On keyboards without a meta key, M-x means ESC x, i.e., press the Escape key then the x key. This makes ESC the meta prefix. The combination
1699 M-C-x means ESC-Control-x, or press the Escape key then hold the Control key while pressing the x key.)
1700
1701 Readline commands may be given numeric arguments, which normally act as a repeat count. Sometimes, however, it is the sign of the argument that is significant. Passing a nega‐
1702 tive argument to a command that acts in the forward direction (e.g., kill-line) causes that command to act in a backward direction. Commands whose behavior with arguments devi‐
1703 ates from this are noted below.
1704
1705 When a command is described as killing text, the text deleted is saved for possible future retrieval (yanking). The killed text is saved in a kill ring. Consecutive kills
1706 cause the text to be accumulated into one unit, which can be yanked all at once. Commands which do not kill text separate the chunks of text on the kill ring.
1707
1708 Readline Initialization
1709 Readline is customized by putting commands in an initialization file (the inputrc file). The name of this file is taken from the value of the INPUTRC variable. If that vari‐
1710 able is unset, the default is ~/.inputrc. When a program which uses the readline library starts up, the initialization file is read, and the key bindings and variables are set.
1711 There are only a few basic constructs allowed in the readline initialization file. Blank lines are ignored. Lines beginning with a # are comments. Lines beginning with a $
1712 indicate conditional constructs. Other lines denote key bindings and variable settings.
1713
1714 The default key-bindings may be changed with an inputrc file. Other programs that use this library may add their own commands and bindings.
1715
1716 For example, placing
1717
1718 M-Control-u: universal-argument
1719 or
1720 C-Meta-u: universal-argument
1721 into the inputrc would make M-C-u execute the readline command universal-argument.
1722
1723 The following symbolic character names are recognized: RUBOUT, DEL, ESC, LFD, NEWLINE, RET, RETURN, SPC, SPACE, and TAB.
1724
1725 In addition to command names, readline allows keys to be bound to a string that is inserted when the key is pressed (a macro).
1726
1727 Readline Key Bindings
1728 The syntax for controlling key bindings in the inputrc file is simple. All that is required is the name of the command or the text of a macro and a key sequence to which it
1729 should be bound. The name may be specified in one of two ways: as a symbolic key name, possibly with Meta- or Control- prefixes, or as a key sequence.
1730
1731 When using the form keyname:function-name or macro, keyname is the name of a key spelled out in English. For example:
1732
1733 Control-u: universal-argument
1734 Meta-Rubout: backward-kill-word
1735 Control-o: "> output"
1736
1737 In the above example, C-u is bound to the function universal-argument, M-DEL is bound to the function backward-kill-word, and C-o is bound to run the macro expressed on the
1738 right hand side (that is, to insert the text ``> output'' into the line).
1739
1740 In the second form, "keyseq":function-name or macro, keyseq differs from keyname above in that strings denoting an entire key sequence may be specified by placing the sequence
1741 within double quotes. Some GNU Emacs style key escapes can be used, as in the following example, but the symbolic character names are not recognized.
1742
1743 "\C-u": universal-argument
1744 "\C-x\C-r": re-read-init-file
1745 "\e[11~": "Function Key 1"
1746
1747 In this example, C-u is again bound to the function universal-argument. C-x C-r is bound to the function re-read-init-file, and ESC [ 1 1 ~ is bound to insert the text ``Func‐
1748 tion Key 1''.
1749
1750 The full set of GNU Emacs style escape sequences is
1751 \C- control prefix
1752 \M- meta prefix
1753 \e an escape character
1754 \\ backslash
1755 \" literal "
1756 \' literal '
1757
1758 In addition to the GNU Emacs style escape sequences, a second set of backslash escapes is available:
1759 \a alert (bell)
1760 \b backspace
1761 \d delete
1762 \f form feed
1763 \n newline
1764 \r carriage return
1765 \t horizontal tab
1766 \v vertical tab
1767 \nnn the eight-bit character whose value is the octal value nnn (one to three digits)
1768 \xHH the eight-bit character whose value is the hexadecimal value HH (one or two hex digits)
1769
1770 When entering the text of a macro, single or double quotes must be used to indicate a macro definition. Unquoted text is assumed to be a function name. In the macro body, the
1771 backslash escapes described above are expanded. Backslash will quote any other character in the macro text, including " and '.
1772
1773 Bash allows the current readline key bindings to be displayed or modified with the bind builtin command. The editing mode may be switched during interactive use by using the -o
1774 option to the set builtin command (see SHELL BUILTIN COMMANDS below).
1775
1776 Readline Variables
1777 Readline has variables that can be used to further customize its behavior. A variable may be set in the inputrc file with a statement of the form
1778
1779 set variable-name value
1780
1781 Except where noted, readline variables can take the values On or Off (without regard to case). Unrecognized variable names are ignored. When a variable value is read, empty or
1782 null values, "on" (case-insensitive), and "1" are equivalent to On. All other values are equivalent to Off. The variables and their default values are:
1783
1784 bell-style (audible)
1785 Controls what happens when readline wants to ring the terminal bell. If set to none, readline never rings the bell. If set to visible, readline uses a visible bell if
1786 one is available. If set to audible, readline attempts to ring the terminal's bell.
1787 bind-tty-special-chars (On)
1788 If set to On, readline attempts to bind the control characters treated specially by the kernel's terminal driver to their readline equivalents.
1789 blink-matching-paren (Off)
1790 If set to On, readline attempts to briefly move the cursor to an opening parenthesis when a closing parenthesis is inserted.
1791 colored-completion-prefix (Off)
1792 If set to On, when listing completions, readline displays the common prefix of the set of possible completions using a different color. The color definitions are taken
1793 from the value of the LS_COLORS environment variable.
1794 colored-stats (Off)
1795 If set to On, readline displays possible completions using different colors to indicate their file type. The color definitions are taken from the value of the LS_COLORS
1796 environment variable.
1797 comment-begin (``#'')
1798 The string that is inserted when the readline insert-comment command is executed. This command is bound to M-# in emacs mode and to # in vi command mode.
1799 completion-display-width (-1)
1800 The number of screen columns used to display possible matches when performing completion. The value is ignored if it is less than 0 or greater than the terminal screen
1801 width. A value of 0 will cause matches to be displayed one per line. The default value is -1.
1802 completion-ignore-case (Off)
1803 If set to On, readline performs filename matching and completion in a case-insensitive fashion.
1804 completion-map-case (Off)
1805 If set to On, and completion-ignore-case is enabled, readline treats hyphens (-) and underscores (_) as equivalent when performing case-insensitive filename matching and
1806 completion.
1807 completion-prefix-display-length (0)
1808 The length in characters of the common prefix of a list of possible completions that is displayed without modification. When set to a value greater than zero, common
1809 prefixes longer than this value are replaced with an ellipsis when displaying possible completions.
1810 completion-query-items (100)
1811 This determines when the user is queried about viewing the number of possible completions generated by the possible-completions command. It may be set to any integer
1812 value greater than or equal to zero. If the number of possible completions is greater than or equal to the value of this variable, the user is asked whether or not he
1813 wishes to view them; otherwise they are simply listed on the terminal.
1814 convert-meta (On)
1815 If set to On, readline will convert characters with the eighth bit set to an ASCII key sequence by stripping the eighth bit and prefixing an escape character (in effect,
1816 using escape as the meta prefix). The default is On, but readline will set it to Off if the locale contains eight-bit characters.
1817 disable-completion (Off)
1818 If set to On, readline will inhibit word completion. Completion characters will be inserted into the line as if they had been mapped to self-insert.
1819 echo-control-characters (On)
1820 When set to On, on operating systems that indicate they support it, readline echoes a character corresponding to a signal generated from the keyboard.
1821 editing-mode (emacs)
1822 Controls whether readline begins with a set of key bindings similar to Emacs or vi. editing-mode can be set to either emacs or vi.
1823 enable-bracketed-paste (Off)
1824 When set to On, readline will configure the terminal in a way that will enable it to insert each paste into the editing buffer as a single string of characters, instead
1825 of treating each character as if it had been read from the keyboard. This can prevent pasted characters from being interpreted as editing commands.
1826 enable-keypad (Off)
1827 When set to On, readline will try to enable the application keypad when it is called. Some systems need this to enable the arrow keys.
1828 enable-meta-key (On)
1829 When set to On, readline will try to enable any meta modifier key the terminal claims to support when it is called. On many terminals, the meta key is used to send
1830 eight-bit characters.
1831 expand-tilde (Off)
1832 If set to On, tilde expansion is performed when readline attempts word completion.
1833 history-preserve-point (Off)
1834 If set to On, the history code attempts to place point at the same location on each history line retrieved with previous-history or next-history.
1835 history-size (unset)
1836 Set the maximum number of history entries saved in the history list. If set to zero, any existing history entries are deleted and no new entries are saved. If set to a
1837 value less than zero, the number of history entries is not limited. By default, the number of history entries is set to the value of the HISTSIZE shell variable. If an
1838 attempt is made to set history-size to a non-numeric value, the maximum number of history entries will be set to 500.
1839 horizontal-scroll-mode (Off)
1840 When set to On, makes readline use a single line for display, scrolling the input horizontally on a single screen line when it becomes longer than the screen width rather
1841 than wrapping to a new line.
1842 input-meta (Off)
1843 If set to On, readline will enable eight-bit input (that is, it will not strip the eighth bit from the characters it reads), regardless of what the terminal claims it can
1844 support. The name meta-flag is a synonym for this variable. The default is Off, but readline will set it to On if the locale contains eight-bit characters.
1845 isearch-terminators (``C-[C-J'')
1846 The string of characters that should terminate an incremental search without subsequently executing the character as a command. If this variable has not been given a
1847 value, the characters ESC and C-J will terminate an incremental search.
1848 keymap (emacs)
1849 Set the current readline keymap. The set of valid keymap names is emacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-command, and vi-insert. vi is equivalent to
1850 vi-command; emacs is equivalent to emacs-standard. The default value is emacs; the value of editing-mode also affects the default keymap.
1851 emacs-mode-string (@)
1852 This string is displayed immediately before the last line of the primary prompt when emacs editing mode is active. The value is expanded like a key binding, so the stan‐
1853 dard set of meta- and control prefixes and backslash escape sequences is available. Use the \1 and \2 escapes to begin and end sequences of non-printing characters,
1854 which can be used to embed a terminal control sequence into the mode string.
1855 keyseq-timeout (500)
1856 Specifies the duration readline will wait for a character when reading an ambiguous key sequence (one that can form a complete key sequence using the input read so far,
1857 or can take additional input to complete a longer key sequence). If no input is received within the timeout, readline will use the shorter but complete key sequence.
1858 The value is specified in milliseconds, so a value of 1000 means that readline will wait one second for additional input. If this variable is set to a value less than or
1859 equal to zero, or to a non-numeric value, readline will wait until another key is pressed to decide which key sequence to complete.
1860 mark-directories (On)
1861 If set to On, completed directory names have a slash appended.
1862 mark-modified-lines (Off)
1863 If set to On, history lines that have been modified are displayed with a preceding asterisk (*).
1864 mark-symlinked-directories (Off)
1865 If set to On, completed names which are symbolic links to directories have a slash appended (subject to the value of mark-directories).
1866 match-hidden-files (On)
1867 This variable, when set to On, causes readline to match files whose names begin with a `.' (hidden files) when performing filename completion. If set to Off, the leading
1868 `.' must be supplied by the user in the filename to be completed.
1869 menu-complete-display-prefix (Off)
1870 If set to On, menu completion displays the common prefix of the list of possible completions (which may be empty) before cycling through the list.
1871 output-meta (Off)
1872 If set to On, readline will display characters with the eighth bit set directly rather than as a meta-prefixed escape sequence. The default is Off, but readline will set
1873 it to On if the locale contains eight-bit characters.
1874 page-completions (On)
1875 If set to On, readline uses an internal more-like pager to display a screenful of possible completions at a time.
1876 print-completions-horizontally (Off)
1877 If set to On, readline will display completions with matches sorted horizontally in alphabetical order, rather than down the screen.
1878 revert-all-at-newline (Off)
1879 If set to On, readline will undo all changes to history lines before returning when accept-line is executed. By default, history lines may be modified and retain indi‐
1880 vidual undo lists across calls to readline.
1881 show-all-if-ambiguous (Off)
1882 This alters the default behavior of the completion functions. If set to On, words which have more than one possible completion cause the matches to be listed immediately
1883 instead of ringing the bell.
1884 show-all-if-unmodified (Off)
1885 This alters the default behavior of the completion functions in a fashion similar to show-all-if-ambiguous. If set to On, words which have more than one possible comple‐
1886 tion without any possible partial completion (the possible completions don't share a common prefix) cause the matches to be listed immediately instead of ringing the
1887 bell.
1888 show-mode-in-prompt (Off)
1889 If set to On, add a character to the beginning of the prompt indicating the editing mode: emacs (@), vi command (:) or vi insertion (+).
1890 skip-completed-text (Off)
1891 If set to On, this alters the default completion behavior when inserting a single match into the line. It's only active when performing completion in the middle of a
1892 word. If enabled, readline does not insert characters from the completion that match characters after point in the word being completed, so portions of the word follow‐
1893 ing the cursor are not duplicated.
1894 vi-cmd-mode-string ((cmd))
1895 This string is displayed immediately before the last line of the primary prompt when vi editing mode is active and in command mode. The value is expanded like a key
1896 binding, so the standard set of meta- and control prefixes and backslash escape sequences is available. Use the \1 and \2 escapes to begin and end sequences of non-
1897 printing characters, which can be used to embed a terminal control sequence into the mode string.
1898 vi-ins-mode-string ((ins))
1899 This string is displayed immediately before the last line of the primary prompt when vi editing mode is active and in insertion mode. The value is expanded like a key
1900 binding, so the standard set of meta- and control prefixes and backslash escape sequences is available. Use the \1 and \2 escapes to begin and end sequences of non-
1901 printing characters, which can be used to embed a terminal control sequence into the mode string.
1902 visible-stats (Off)
1903 If set to On, a character denoting a file's type as reported by stat(2) is appended to the filename when listing possible completions.
1904
1905 Readline Conditional Constructs
1906 Readline implements a facility similar in spirit to the conditional compilation features of the C preprocessor which allows key bindings and variable settings to be performed as
1907 the result of tests. There are four parser directives used.
1908
1909 $if The $if construct allows bindings to be made based on the editing mode, the terminal being used, or the application using readline. The text of the test extends to the
1910 end of the line; no characters are required to isolate it.
1911
1912 mode The mode= form of the $if directive is used to test whether readline is in emacs or vi mode. This may be used in conjunction with the set keymap command, for
1913 instance, to set bindings in the emacs-standard and emacs-ctlx keymaps only if readline is starting out in emacs mode.
1914
1915 term The term= form may be used to include terminal-specific key bindings, perhaps to bind the key sequences output by the terminal's function keys. The word on the
1916 right side of the = is tested against both the full name of the terminal and the portion of the terminal name before the first -. This allows sun to match both
1917 sun and sun-cmd, for instance.
1918
1919 application
1920 The application construct is used to include application-specific settings. Each program using the readline library sets the application name, and an initializa‐
1921 tion file can test for a particular value. This could be used to bind key sequences to functions useful for a specific program. For instance, the following com‐
1922 mand adds a key sequence that quotes the current or previous word in bash:
1923
1924 $if Bash
1925 # Quote the current or previous word
1926 "\C-xq": "\eb\"\ef\""
1927 $endif
1928
1929 $endif This command, as seen in the previous example, terminates an $if command.
1930
1931 $else Commands in this branch of the $if directive are executed if the test fails.
1932
1933 $include
1934 This directive takes a single filename as an argument and reads commands and bindings from that file. For example, the following directive would read /etc/inputrc:
1935
1936 $include /etc/inputrc
1937
1938 Searching
1939 Readline provides commands for searching through the command history (see HISTORY below) for lines containing a specified string. There are two search modes: incremental and
1940 non-incremental.
1941
1942 Incremental searches begin before the user has finished typing the search string. As each character of the search string is typed, readline displays the next entry from the
1943 history matching the string typed so far. An incremental search requires only as many characters as needed to find the desired history entry. The characters present in the
1944 value of the isearch-terminators variable are used to terminate an incremental search. If that variable has not been assigned a value the Escape and Control-J characters will
1945 terminate an incremental search. Control-G will abort an incremental search and restore the original line. When the search is terminated, the history entry containing the
1946 search string becomes the current line.
1947
1948 To find other matching entries in the history list, type Control-S or Control-R as appropriate. This will search backward or forward in the history for the next entry matching
1949 the search string typed so far. Any other key sequence bound to a readline command will terminate the search and execute that command. For instance, a newline will terminate
1950 the search and accept the line, thereby executing the command from the history list.
1951
1952 Readline remembers the last incremental search string. If two Control-Rs are typed without any intervening characters defining a new search string, any remembered search string
1953 is used.
1954
1955 Non-incremental searches read the entire search string before starting to search for matching history lines. The search string may be typed by the user or be part of the con‐
1956 tents of the current line.
1957
1958 Readline Command Names
1959 The following is a list of the names of the commands and the default key sequences to which they are bound. Command names without an accompanying key sequence are unbound by
1960 default. In the following descriptions, point refers to the current cursor position, and mark refers to a cursor position saved by the set-mark command. The text between the
1961 point and mark is referred to as the region.
1962
1963 Commands for Moving
1964 beginning-of-line (C-a)
1965 Move to the start of the current line.
1966 end-of-line (C-e)
1967 Move to the end of the line.
1968 forward-char (C-f)
1969 Move forward a character.
1970 backward-char (C-b)
1971 Move back a character.
1972 forward-word (M-f)
1973 Move forward to the end of the next word. Words are composed of alphanumeric characters (letters and digits).
1974 backward-word (M-b)
1975 Move back to the start of the current or previous word. Words are composed of alphanumeric characters (letters and digits).
1976 shell-forward-word
1977 Move forward to the end of the next word. Words are delimited by non-quoted shell metacharacters.
1978 shell-backward-word
1979 Move back to the start of the current or previous word. Words are delimited by non-quoted shell metacharacters.
1980 clear-screen (C-l)
1981 Clear the screen leaving the current line at the top of the screen. With an argument, refresh the current line without clearing the screen.
1982 redraw-current-line
1983 Refresh the current line.
1984
1985 Commands for Manipulating the History
1986 accept-line (Newline, Return)
1987 Accept the line regardless of where the cursor is. If this line is non-empty, add it to the history list according to the state of the HISTCONTROL variable. If the line
1988 is a modified history line, then restore the history line to its original state.
1989 previous-history (C-p)
1990 Fetch the previous command from the history list, moving back in the list.
1991 next-history (C-n)
1992 Fetch the next command from the history list, moving forward in the list.
1993 beginning-of-history (M-<)
1994 Move to the first line in the history.
1995 end-of-history (M->)
1996 Move to the end of the input history, i.e., the line currently being entered.
1997 reverse-search-history (C-r)
1998 Search backward starting at the current line and moving `up' through the history as necessary. This is an incremental search.
1999 forward-search-history (C-s)
2000 Search forward starting at the current line and moving `down' through the history as necessary. This is an incremental search.
2001 non-incremental-reverse-search-history (M-p)
2002 Search backward through the history starting at the current line using a non-incremental search for a string supplied by the user.
2003 non-incremental-forward-search-history (M-n)
2004 Search forward through the history using a non-incremental search for a string supplied by the user.
2005 history-search-forward
2006 Search forward through the history for the string of characters between the start of the current line and the point. This is a non-incremental search.
2007 history-search-backward
2008 Search backward through the history for the string of characters between the start of the current line and the point. This is a non-incremental search.
2009 yank-nth-arg (M-C-y)
2010 Insert the first argument to the previous command (usually the second word on the previous line) at point. With an argument n, insert the nth word from the previous com‐
2011 mand (the words in the previous command begin with word 0). A negative argument inserts the nth word from the end of the previous command. Once the argument n is com‐
2012 puted, the argument is extracted as if the "!n" history expansion had been specified.
2013 yank-last-arg (M-., M-_)
2014 Insert the last argument to the previous command (the last word of the previous history entry). With a numeric argument, behave exactly like yank-nth-arg. Successive
2015 calls to yank-last-arg move back through the history list, inserting the last word (or the word specified by the argument to the first call) of each line in turn. Any
2016 numeric argument supplied to these successive calls determines the direction to move through the history. A negative argument switches the direction through the history
2017 (back or forward). The history expansion facilities are used to extract the last word, as if the "!$" history expansion had been specified.
2018 shell-expand-line (M-C-e)
2019 Expand the line as the shell does. This performs alias and history expansion as well as all of the shell word expansions. See HISTORY EXPANSION below for a description
2020 of history expansion.
2021 history-expand-line (M-^)
2022 Perform history expansion on the current line. See HISTORY EXPANSION below for a description of history expansion.
2023 magic-space
2024 Perform history expansion on the current line and insert a space. See HISTORY EXPANSION below for a description of history expansion.
2025 alias-expand-line
2026 Perform alias expansion on the current line. See ALIASES above for a description of alias expansion.
2027 history-and-alias-expand-line
2028 Perform history and alias expansion on the current line.
2029 insert-last-argument (M-., M-_)
2030 A synonym for yank-last-arg.
2031 operate-and-get-next (C-o)
2032 Accept the current line for execution and fetch the next line relative to the current line from the history for editing. Any argument is ignored.
2033 edit-and-execute-command (C-xC-e)
2034 Invoke an editor on the current command line, and execute the result as shell commands. Bash attempts to invoke $VISUAL, $EDITOR, and emacs as the editor, in that order.
2035
2036 Commands for Changing Text
2037 end-of-file (usually C-d)
2038 The character indicating end-of-file as set, for example, by ``stty''. If this character is read when there are no characters on the line, and point is at the beginning
2039 of the line, Readline interprets it as the end of input and returns EOF.
2040 delete-char (C-d)
2041 Delete the character at point. If this function is bound to the same character as the tty EOF character, as C-d commonly is, see above for the effects.
2042 backward-delete-char (Rubout)
2043 Delete the character behind the cursor. When given a numeric argument, save the deleted text on the kill ring.
2044 forward-backward-delete-char
2045 Delete the character under the cursor, unless the cursor is at the end of the line, in which case the character behind the cursor is deleted.
2046 quoted-insert (C-q, C-v)
2047 Add the next character typed to the line verbatim. This is how to insert characters like C-q, for example.
2048 tab-insert (C-v TAB)
2049 Insert a tab character.
2050 self-insert (a, b, A, 1, !, ...)
2051 Insert the character typed.
2052 transpose-chars (C-t)
2053 Drag the character before point forward over the character at point, moving point forward as well. If point is at the end of the line, then this transposes the two char‐
2054 acters before point. Negative arguments have no effect.
2055 transpose-words (M-t)
2056 Drag the word before point past the word after point, moving point over that word as well. If point is at the end of the line, this transposes the last two words on the
2057 line.
2058 upcase-word (M-u)
2059 Uppercase the current (or following) word. With a negative argument, uppercase the previous word, but do not move point.
2060 downcase-word (M-l)
2061 Lowercase the current (or following) word. With a negative argument, lowercase the previous word, but do not move point.
2062 capitalize-word (M-c)
2063 Capitalize the current (or following) word. With a negative argument, capitalize the previous word, but do not move point.
2064 overwrite-mode
2065 Toggle overwrite mode. With an explicit positive numeric argument, switches to overwrite mode. With an explicit non-positive numeric argument, switches to insert mode.
2066 This command affects only emacs mode; vi mode does overwrite differently. Each call to readline() starts in insert mode. In overwrite mode, characters bound to
2067 self-insert replace the text at point rather than pushing the text to the right. Characters bound to backward-delete-char replace the character before point with a
2068 space. By default, this command is unbound.
2069
2070 Killing and Yanking
2071 kill-line (C-k)
2072 Kill the text from point to the end of the line.
2073 backward-kill-line (C-x Rubout)
2074 Kill backward to the beginning of the line.
2075 unix-line-discard (C-u)
2076 Kill backward from point to the beginning of the line. The killed text is saved on the kill-ring.
2077 kill-whole-line
2078 Kill all characters on the current line, no matter where point is.
2079 kill-word (M-d)
2080 Kill from point to the end of the current word, or if between words, to the end of the next word. Word boundaries are the same as those used by forward-word.
2081 backward-kill-word (M-Rubout)
2082 Kill the word behind point. Word boundaries are the same as those used by backward-word.
2083 shell-kill-word
2084 Kill from point to the end of the current word, or if between words, to the end of the next word. Word boundaries are the same as those used by shell-forward-word.
2085 shell-backward-kill-word
2086 Kill the word behind point. Word boundaries are the same as those used by shell-backward-word.
2087 unix-word-rubout (C-w)
2088 Kill the word behind point, using white space as a word boundary. The killed text is saved on the kill-ring.
2089 unix-filename-rubout
2090 Kill the word behind point, using white space and the slash character as the word boundaries. The killed text is saved on the kill-ring.
2091 delete-horizontal-space (M-\)
2092 Delete all spaces and tabs around point.
2093 kill-region
2094 Kill the text in the current region.
2095 copy-region-as-kill
2096 Copy the text in the region to the kill buffer.
2097 copy-backward-word
2098 Copy the word before point to the kill buffer. The word boundaries are the same as backward-word.
2099 copy-forward-word
2100 Copy the word following point to the kill buffer. The word boundaries are the same as forward-word.
2101 yank (C-y)
2102 Yank the top of the kill ring into the buffer at point.
2103 yank-pop (M-y)
2104 Rotate the kill ring, and yank the new top. Only works following yank or yank-pop.
2105
2106 Numeric Arguments
2107 digit-argument (M-0, M-1, ..., M--)
2108 Add this digit to the argument already accumulating, or start a new argument. M-- starts a negative argument.
2109 universal-argument
2110 This is another way to specify an argument. If this command is followed by one or more digits, optionally with a leading minus sign, those digits define the argument.
2111 If the command is followed by digits, executing universal-argument again ends the numeric argument, but is otherwise ignored. As a special case, if this command is imme‐
2112 diately followed by a character that is neither a digit nor minus sign, the argument count for the next command is multiplied by four. The argument count is initially
2113 one, so executing this function the first time makes the argument count four, a second time makes the argument count sixteen, and so on.
2114
2115 Completing
2116 complete (TAB)
2117 Attempt to perform completion on the text before point. Bash attempts completion treating the text as a variable (if the text begins with $), username (if the text
2118 begins with ~), hostname (if the text begins with @), or command (including aliases and functions) in turn. If none of these produces a match, filename completion is
2119 attempted.
2120 possible-completions (M-?)
2121 List the possible completions of the text before point.
2122 insert-completions (M-*)
2123 Insert all completions of the text before point that would have been generated by possible-completions.
2124 menu-complete
2125 Similar to complete, but replaces the word to be completed with a single match from the list of possible completions. Repeated execution of menu-complete steps through
2126 the list of possible completions, inserting each match in turn. At the end of the list of completions, the bell is rung (subject to the setting of bell-style) and the
2127 original text is restored. An argument of n moves n positions forward in the list of matches; a negative argument may be used to move backward through the list. This
2128 command is intended to be bound to TAB, but is unbound by default.
2129 menu-complete-backward
2130 Identical to menu-complete, but moves backward through the list of possible completions, as if menu-complete had been given a negative argument. This command is unbound
2131 by default.
2132 delete-char-or-list
2133 Deletes the character under the cursor if not at the beginning or end of the line (like delete-char). If at the end of the line, behaves identically to possible-comple‐
2134 tions. This command is unbound by default.
2135 complete-filename (M-/)
2136 Attempt filename completion on the text before point.
2137 possible-filename-completions (C-x /)
2138 List the possible completions of the text before point, treating it as a filename.
2139 complete-username (M-~)
2140 Attempt completion on the text before point, treating it as a username.
2141 possible-username-completions (C-x ~)
2142 List the possible completions of the text before point, treating it as a username.
2143 complete-variable (M-$)
2144 Attempt completion on the text before point, treating it as a shell variable.
2145 possible-variable-completions (C-x $)
2146 List the possible completions of the text before point, treating it as a shell variable.
2147 complete-hostname (M-@)
2148 Attempt completion on the text before point, treating it as a hostname.
2149 possible-hostname-completions (C-x @)
2150 List the possible completions of the text before point, treating it as a hostname.
2151 complete-command (M-!)
2152 Attempt completion on the text before point, treating it as a command name. Command completion attempts to match the text against aliases, reserved words, shell func‐
2153 tions, shell builtins, and finally executable filenames, in that order.
2154 possible-command-completions (C-x !)
2155 List the possible completions of the text before point, treating it as a command name.
2156 dynamic-complete-history (M-TAB)
2157 Attempt completion on the text before point, comparing the text against lines from the history list for possible completion matches.
2158 dabbrev-expand
2159 Attempt menu completion on the text before point, comparing the text against lines from the history list for possible completion matches.
2160 complete-into-braces (M-{)
2161 Perform filename completion and insert the list of possible completions enclosed within braces so the list is available to the shell (see Brace Expansion above).
2162
2163 Keyboard Macros
2164 start-kbd-macro (C-x ()
2165 Begin saving the characters typed into the current keyboard macro.
2166 end-kbd-macro (C-x ))
2167 Stop saving the characters typed into the current keyboard macro and store the definition.
2168 call-last-kbd-macro (C-x e)
2169 Re-execute the last keyboard macro defined, by making the characters in the macro appear as if typed at the keyboard.
2170 print-last-kbd-macro ()
2171 Print the last keyboard macro defined in a format suitable for the inputrc file.
2172
2173 Miscellaneous
2174 re-read-init-file (C-x C-r)
2175 Read in the contents of the inputrc file, and incorporate any bindings or variable assignments found there.
2176 abort (C-g)
2177 Abort the current editing command and ring the terminal's bell (subject to the setting of bell-style).
2178 do-uppercase-version (M-a, M-b, M-x, ...)
2179 If the metafied character x is lowercase, run the command that is bound to the corresponding uppercase character.
2180 prefix-meta (ESC)
2181 Metafy the next character typed. ESC f is equivalent to Meta-f.
2182 undo (C-_, C-x C-u)
2183 Incremental undo, separately remembered for each line.
2184 revert-line (M-r)
2185 Undo all changes made to this line. This is like executing the undo command enough times to return the line to its initial state.
2186 tilde-expand (M-&)
2187 Perform tilde expansion on the current word.
2188 set-mark (C-@, M-<space>)
2189 Set the mark to the point. If a numeric argument is supplied, the mark is set to that position.
2190 exchange-point-and-mark (C-x C-x)
2191 Swap the point with the mark. The current cursor position is set to the saved position, and the old cursor position is saved as the mark.
2192 character-search (C-])
2193 A character is read and point is moved to the next occurrence of that character. A negative count searches for previous occurrences.
2194 character-search-backward (M-C-])
2195 A character is read and point is moved to the previous occurrence of that character. A negative count searches for subsequent occurrences.
2196 skip-csi-sequence
2197 Read enough characters to consume a multi-key sequence such as those defined for keys like Home and End. Such sequences begin with a Control Sequence Indicator (CSI),
2198 usually ESC-[. If this sequence is bound to "\[", keys producing such sequences will have no effect unless explicitly bound to a readline command, instead of inserting
2199 stray characters into the editing buffer. This is unbound by default, but usually bound to ESC-[.
2200 insert-comment (M-#)
2201 Without a numeric argument, the value of the readline comment-begin variable is inserted at the beginning of the current line. If a numeric argument is supplied, this
2202 command acts as a toggle: if the characters at the beginning of the line do not match the value of comment-begin, the value is inserted, otherwise the characters in com‐
2203 ment-begin are deleted from the beginning of the line. In either case, the line is accepted as if a newline had been typed. The default value of comment-begin causes
2204 this command to make the current line a shell comment. If a numeric argument causes the comment character to be removed, the line will be executed by the shell.
2205 glob-complete-word (M-g)
2206 The word before point is treated as a pattern for pathname expansion, with an asterisk implicitly appended. This pattern is used to generate a list of matching filenames
2207 for possible completions.
2208 glob-expand-word (C-x *)
2209 The word before point is treated as a pattern for pathname expansion, and the list of matching filenames is inserted, replacing the word. If a numeric argument is sup‐
2210 plied, an asterisk is appended before pathname expansion.
2211 glob-list-expansions (C-x g)
2212 The list of expansions that would have been generated by glob-expand-word is displayed, and the line is redrawn. If a numeric argument is supplied, an asterisk is
2213 appended before pathname expansion.
2214 dump-functions
2215 Print all of the functions and their key bindings to the readline output stream. If a numeric argument is supplied, the output is formatted in such a way that it can be
2216 made part of an inputrc file.
2217 dump-variables
2218 Print all of the settable readline variables and their values to the readline output stream. If a numeric argument is supplied, the output is formatted in such a way
2219 that it can be made part of an inputrc file.
2220 dump-macros
2221 Print all of the readline key sequences bound to macros and the strings they output. If a numeric argument is supplied, the output is formatted in such a way that it can
2222 be made part of an inputrc file.
2223 display-shell-version (C-x C-v)
2224 Display version information about the current instance of bash.
2225
2226 Programmable Completion
2227 When word completion is attempted for an argument to a command for which a completion specification (a compspec) has been defined using the complete builtin (see SHELL BUILTIN
2228 COMMANDS below), the programmable completion facilities are invoked.
2229
2230 First, the command name is identified. If the command word is the empty string (completion attempted at the beginning of an empty line), any compspec defined with the -E option
2231 to complete is used. If a compspec has been defined for that command, the compspec is used to generate the list of possible completions for the word. If the command word is a
2232 full pathname, a compspec for the full pathname is searched for first. If no compspec is found for the full pathname, an attempt is made to find a compspec for the portion fol‐
2233 lowing the final slash. If those searches do not result in a compspec, any compspec defined with the -D option to complete is used as the default.
2234
2235 Once a compspec has been found, it is used to generate the list of matching words. If a compspec is not found, the default bash completion as described above under Completing
2236 is performed.
2237
2238 First, the actions specified by the compspec are used. Only matches which are prefixed by the word being completed are returned. When the -f or -d option is used for filename
2239 or directory name completion, the shell variable FIGNORE is used to filter the matches.
2240
2241 Any completions specified by a pathname expansion pattern to the -G option are generated next. The words generated by the pattern need not match the word being completed. The
2242 GLOBIGNORE shell variable is not used to filter the matches, but the FIGNORE variable is used.
2243
2244 Next, the string specified as the argument to the -W option is considered. The string is first split using the characters in the IFS special variable as delimiters. Shell
2245 quoting is honored. Each word is then expanded using brace expansion, tilde expansion, parameter and variable expansion, command substitution, and arithmetic expansion, as
2246 described above under EXPANSION. The results are split using the rules described above under Word Splitting. The results of the expansion are prefix-matched against the word
2247 being completed, and the matching words become the possible completions.
2248
2249 After these matches have been generated, any shell function or command specified with the -F and -C options is invoked. When the command or function is invoked, the COMP_LINE,
2250 COMP_POINT, COMP_KEY, and COMP_TYPE variables are assigned values as described above under Shell Variables. If a shell function is being invoked, the COMP_WORDS and COMP_CWORD
2251 variables are also set. When the function or command is invoked, the first argument ($1) is the name of the command whose arguments are being completed, the second argument
2252 ($2) is the word being completed, and the third argument ($3) is the word preceding the word being completed on the current command line. No filtering of the generated comple‐
2253 tions against the word being completed is performed; the function or command has complete freedom in generating the matches.
2254
2255 Any function specified with -F is invoked first. The function may use any of the shell facilities, including the compgen builtin described below, to generate the matches. It
2256 must put the possible completions in the COMPREPLY array variable, one per array element.
2257
2258 Next, any command specified with the -C option is invoked in an environment equivalent to command substitution. It should print a list of completions, one per line, to the
2259 standard output. Backslash may be used to escape a newline, if necessary.
2260
2261 After all of the possible completions are generated, any filter specified with the -X option is applied to the list. The filter is a pattern as used for pathname expansion; a &
2262 in the pattern is replaced with the text of the word being completed. A literal & may be escaped with a backslash; the backslash is removed before attempting a match. Any com‐
2263 pletion that matches the pattern will be removed from the list. A leading ! negates the pattern; in this case any completion not matching the pattern will be removed. If the
2264 nocasematch shell option is enabled, the match is performed without regard to the case of alphabetic characters.
2265
2266 Finally, any prefix and suffix specified with the -P and -S options are added to each member of the completion list, and the result is returned to the readline completion code
2267 as the list of possible completions.
2268
2269 If the previously-applied actions do not generate any matches, and the -o dirnames option was supplied to complete when the compspec was defined, directory name completion is
2270 attempted.
2271
2272 If the -o plusdirs option was supplied to complete when the compspec was defined, directory name completion is attempted and any matches are added to the results of the other
2273 actions.
2274
2275 By default, if a compspec is found, whatever it generates is returned to the completion code as the full set of possible completions. The default bash completions are not
2276 attempted, and the readline default of filename completion is disabled. If the -o bashdefault option was supplied to complete when the compspec was defined, the bash default
2277 completions are attempted if the compspec generates no matches. If the -o default option was supplied to complete when the compspec was defined, readline's default completion
2278 will be performed if the compspec (and, if attempted, the default bash completions) generate no matches.
2279
2280 When a compspec indicates that directory name completion is desired, the programmable completion functions force readline to append a slash to completed names which are symbolic
2281 links to directories, subject to the value of the mark-directories readline variable, regardless of the setting of the mark-symlinked-directories readline variable.
2282
2283 There is some support for dynamically modifying completions. This is most useful when used in combination with a default completion specified with complete -D. It's possible
2284 for shell functions executed as completion handlers to indicate that completion should be retried by returning an exit status of 124. If a shell function returns 124, and
2285 changes the compspec associated with the command on which completion is being attempted (supplied as the first argument when the function is executed), programmable completion
2286 restarts from the beginning, with an attempt to find a new compspec for that command. This allows a set of completions to be built dynamically as completion is attempted,
2287 rather than being loaded all at once.
2288
2289 For instance, assuming that there is a library of compspecs, each kept in a file corresponding to the name of the command, the following default completion function would load
2290 completions dynamically:
2291
2292 _completion_loader()
2293 {
2294 . "/etc/bash_completion.d/$1.sh" >/dev/null 2>&1 && return 124
2295 }
2296 complete -D -F _completion_loader -o bashdefault -o default
2297
2298HISTORY
2299 When the -o history option to the set builtin is enabled, the shell provides access to the command history, the list of commands previously typed. The value of the HISTSIZE
2300 variable is used as the number of commands to save in a history list. The text of the last HISTSIZE commands (default 500) is saved. The shell stores each command in the his‐
2301 tory list prior to parameter and variable expansion (see EXPANSION above) but after history expansion is performed, subject to the values of the shell variables HISTIGNORE and
2302 HISTCONTROL.
2303
2304 On startup, the history is initialized from the file named by the variable HISTFILE (default ~/.bash_history). The file named by the value of HISTFILE is truncated, if neces‐
2305 sary, to contain no more than the number of lines specified by the value of HISTFILESIZE. If HISTFILESIZE is unset, or set to null, a non-numeric value, or a numeric value less
2306 than zero, the history file is not truncated. When the history file is read, lines beginning with the history comment character followed immediately by a digit are interpreted
2307 as timestamps for the preceding history line. These timestamps are optionally displayed depending on the value of the HISTTIMEFORMAT variable. When a shell with history
2308 enabled exits, the last $HISTSIZE lines are copied from the history list to $HISTFILE. If the histappend shell option is enabled (see the description of shopt under SHELL
2309 BUILTIN COMMANDS below), the lines are appended to the history file, otherwise the history file is overwritten. If HISTFILE is unset, or if the history file is unwritable, the
2310 history is not saved. If the HISTTIMEFORMAT variable is set, time stamps are written to the history file, marked with the history comment character, so they may be preserved
2311 across shell sessions. This uses the history comment character to distinguish timestamps from other history lines. After saving the history, the history file is truncated to
2312 contain no more than HISTFILESIZE lines. If HISTFILESIZE is unset, or set to null, a non-numeric value, or a numeric value less than zero, the history file is not truncated.
2313
2314 The builtin command fc (see SHELL BUILTIN COMMANDS below) may be used to list or edit and re-execute a portion of the history list. The history builtin may be used to display
2315 or modify the history list and manipulate the history file. When using command-line editing, search commands are available in each editing mode that provide access to the his‐
2316 tory list.
2317
2318 The shell allows control over which commands are saved on the history list. The HISTCONTROL and HISTIGNORE variables may be set to cause the shell to save only a subset of the
2319 commands entered. The cmdhist shell option, if enabled, causes the shell to attempt to save each line of a multi-line command in the same history entry, adding semicolons where
2320 necessary to preserve syntactic correctness. The lithist shell option causes the shell to save the command with embedded newlines instead of semicolons. See the description of
2321 the shopt builtin below under SHELL BUILTIN COMMANDS for information on setting and unsetting shell options.
2322
2323HISTORY EXPANSION
2324 The shell supports a history expansion feature that is similar to the history expansion in csh. This section describes what syntax features are available. This feature is
2325 enabled by default for interactive shells, and can be disabled using the +H option to the set builtin command (see SHELL BUILTIN COMMANDS below). Non-interactive shells do not
2326 perform history expansion by default.
2327
2328 History expansions introduce words from the history list into the input stream, making it easy to repeat commands, insert the arguments to a previous command into the current
2329 input line, or fix errors in previous commands quickly.
2330
2331 History expansion is performed immediately after a complete line is read, before the shell breaks it into words. It takes place in two parts. The first is to determine which
2332 line from the history list to use during substitution. The second is to select portions of that line for inclusion into the current one. The line selected from the history is
2333 the event, and the portions of that line that are acted upon are words. Various modifiers are available to manipulate the selected words. The line is broken into words in the
2334 same fashion as when reading input, so that several metacharacter-separated words surrounded by quotes are considered one word. History expansions are introduced by the appear‐
2335 ance of the history expansion character, which is ! by default. Only backslash (\) and single quotes can quote the history expansion character, but the history expansion char‐
2336 acter is also treated as quoted if it immediately precedes the closing double quote in a double-quoted string.
2337
2338 Several characters inhibit history expansion if found immediately following the history expansion character, even if it is unquoted: space, tab, newline, carriage return, and =.
2339 If the extglob shell option is enabled, ( will also inhibit expansion.
2340
2341 Several shell options settable with the shopt builtin may be used to tailor the behavior of history expansion. If the histverify shell option is enabled (see the description of
2342 the shopt builtin below), and readline is being used, history substitutions are not immediately passed to the shell parser. Instead, the expanded line is reloaded into the
2343 readline editing buffer for further modification. If readline is being used, and the histreedit shell option is enabled, a failed history substitution will be reloaded into the
2344 readline editing buffer for correction. The -p option to the history builtin command may be used to see what a history expansion will do before using it. The -s option to the
2345 history builtin may be used to add commands to the end of the history list without actually executing them, so that they are available for subsequent recall.
2346
2347 The shell allows control of the various characters used by the history expansion mechanism (see the description of histchars above under Shell Variables). The shell uses the
2348 history comment character to mark history timestamps when writing the history file.
2349
2350 Event Designators
2351 An event designator is a reference to a command line entry in the history list. Unless the reference is absolute, events are relative to the current position in the history
2352 list.
2353
2354 ! Start a history substitution, except when followed by a blank, newline, carriage return, = or ( (when the extglob shell option is enabled using the shopt builtin).
2355 !n Refer to command line n.
2356 !-n Refer to the current command minus n.
2357 !! Refer to the previous command. This is a synonym for `!-1'.
2358 !string
2359 Refer to the most recent command preceding the current position in the history list starting with string.
2360 !?string[?]
2361 Refer to the most recent command preceding the current position in the history list containing string. The trailing ? may be omitted if string is followed immediately by
2362 a newline.
2363 ^string1^string2^
2364 Quick substitution. Repeat the previous command, replacing string1 with string2. Equivalent to ``!!:s/string1/string2/'' (see Modifiers below).
2365 !# The entire command line typed so far.
2366
2367 Word Designators
2368 Word designators are used to select desired words from the event. A : separates the event specification from the word designator. It may be omitted if the word designator
2369 begins with a ^, $, *, -, or %. Words are numbered from the beginning of the line, with the first word being denoted by 0 (zero). Words are inserted into the current line sep‐
2370 arated by single spaces.
2371
2372 0 (zero)
2373 The zeroth word. For the shell, this is the command word.
2374 n The nth word.
2375 ^ The first argument. That is, word 1.
2376 $ The last word. This is usually the last argument, but will expand to the zeroth word if there is only one word in the line.
2377 % The word matched by the most recent `?string?' search.
2378 x-y A range of words; `-y' abbreviates `0-y'.
2379 * All of the words but the zeroth. This is a synonym for `1-$'. It is not an error to use * if there is just one word in the event; the empty string is returned in that
2380 case.
2381 x* Abbreviates x-$.
2382 x- Abbreviates x-$ like x*, but omits the last word.
2383
2384 If a word designator is supplied without an event specification, the previous command is used as the event.
2385
2386 Modifiers
2387 After the optional word designator, there may appear a sequence of one or more of the following modifiers, each preceded by a `:'.
2388
2389 h Remove a trailing filename component, leaving only the head.
2390 t Remove all leading filename components, leaving the tail.
2391 r Remove a trailing suffix of the form .xxx, leaving the basename.
2392 e Remove all but the trailing suffix.
2393 p Print the new command but do not execute it.
2394 q Quote the substituted words, escaping further substitutions.
2395 x Quote the substituted words as with q, but break into words at blanks and newlines.
2396 s/old/new/
2397 Substitute new for the first occurrence of old in the event line. Any delimiter can be used in place of /. The final delimiter is optional if it is the last character
2398 of the event line. The delimiter may be quoted in old and new with a single backslash. If & appears in new, it is replaced by old. A single backslash will quote the &.
2399 If old is null, it is set to the last old substituted, or, if no previous history substitutions took place, the last string in a !?string[?] search.
2400 & Repeat the previous substitution.
2401 g Cause changes to be applied over the entire event line. This is used in conjunction with `:s' (e.g., `:gs/old/new/') or `:&'. If used with `:s', any delimiter can be
2402 used in place of /, and the final delimiter is optional if it is the last character of the event line. An a may be used as a synonym for g.
2403 G Apply the following `s' modifier once to each word in the event line.
2404
2405SHELL BUILTIN COMMANDS
2406 Unless otherwise noted, each builtin command documented in this section as accepting options preceded by - accepts -- to signify the end of the options. The :, true, false, and
2407 test builtins do not accept options and do not treat -- specially. The exit, logout, return, break, continue, let, and shift builtins accept and process arguments beginning
2408 with - without requiring --. Other builtins that accept arguments but are not specified as accepting options interpret arguments beginning with - as invalid options and require
2409 -- to prevent this interpretation.
2410 : [arguments]
2411 No effect; the command does nothing beyond expanding arguments and performing any specified redirections. The return status is zero.
2412
2413 . filename [arguments]
2414 source filename [arguments]
2415 Read and execute commands from filename in the current shell environment and return the exit status of the last command executed from filename. If filename does not con‐
2416 tain a slash, filenames in PATH are used to find the directory containing filename. The file searched for in PATH need not be executable. When bash is not in posix
2417 mode, the current directory is searched if no file is found in PATH. If the sourcepath option to the shopt builtin command is turned off, the PATH is not searched. If
2418 any arguments are supplied, they become the positional parameters when filename is executed. Otherwise the positional parameters are unchanged. If the -T option is
2419 enabled, source inherits any trap on DEBUG; if it is not, any DEBUG trap string is saved and restored around the call to source, and source unsets the DEBUG trap while it
2420 executes. If -T is not set, and the sourced file changes the DEBUG trap, the new value is retained when source completes. The return status is the status of the last
2421 command exited within the script (0 if no commands are executed), and false if filename is not found or cannot be read.
2422
2423 alias [-p] [name[=value] ...]
2424 Alias with no arguments or with the -p option prints the list of aliases in the form alias name=value on standard output. When arguments are supplied, an alias is
2425 defined for each name whose value is given. A trailing space in value causes the next word to be checked for alias substitution when the alias is expanded. For each
2426 name in the argument list for which no value is supplied, the name and value of the alias is printed. Alias returns true unless a name is given for which no alias has
2427 been defined.
2428
2429 bg [jobspec ...]
2430 Resume each suspended job jobspec in the background, as if it had been started with &. If jobspec is not present, the shell's notion of the current job is used. bg job‐
2431 spec returns 0 unless run when job control is disabled or, when run with job control enabled, any specified jobspec was not found or was started without job control.
2432
2433 bind [-m keymap] [-lpsvPSVX]
2434 bind [-m keymap] [-q function] [-u function] [-r keyseq]
2435 bind [-m keymap] -f filename
2436 bind [-m keymap] -x keyseq:shell-command
2437 bind [-m keymap] keyseq:function-name
2438 bind [-m keymap] keyseq:readline-command
2439 Display current readline key and function bindings, bind a key sequence to a readline function or macro, or set a readline variable. Each non-option argument is a com‐
2440 mand as it would appear in .inputrc, but each binding or command must be passed as a separate argument; e.g., '"\C-x\C-r": re-read-init-file'. Options, if supplied, have
2441 the following meanings:
2442 -m keymap
2443 Use keymap as the keymap to be affected by the subsequent bindings. Acceptable keymap names are emacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-move,
2444 vi-command, and vi-insert. vi is equivalent to vi-command (vi-move is also a synonym); emacs is equivalent to emacs-standard.
2445 -l List the names of all readline functions.
2446 -p Display readline function names and bindings in such a way that they can be re-read.
2447 -P List current readline function names and bindings.
2448 -s Display readline key sequences bound to macros and the strings they output in such a way that they can be re-read.
2449 -S Display readline key sequences bound to macros and the strings they output.
2450 -v Display readline variable names and values in such a way that they can be re-read.
2451 -V List current readline variable names and values.
2452 -f filename
2453 Read key bindings from filename.
2454 -q function
2455 Query about which keys invoke the named function.
2456 -u function
2457 Unbind all keys bound to the named function.
2458 -r keyseq
2459 Remove any current binding for keyseq.
2460 -x keyseq:shell-command
2461 Cause shell-command to be executed whenever keyseq is entered. When shell-command is executed, the shell sets the READLINE_LINE variable to the contents of the
2462 readline line buffer and the READLINE_POINT variable to the current location of the insertion point. If the executed command changes the value of READLINE_LINE or
2463 READLINE_POINT, those new values will be reflected in the editing state.
2464 -X List all key sequences bound to shell commands and the associated commands in a format that can be reused as input.
2465
2466 The return value is 0 unless an unrecognized option is given or an error occurred.
2467
2468 break [n]
2469 Exit from within a for, while, until, or select loop. If n is specified, break n levels. n must be ≥ 1. If n is greater than the number of enclosing loops, all enclos‐
2470 ing loops are exited. The return value is 0 unless n is not greater than or equal to 1.
2471
2472 builtin shell-builtin [arguments]
2473 Execute the specified shell builtin, passing it arguments, and return its exit status. This is useful when defining a function whose name is the same as a shell builtin,
2474 retaining the functionality of the builtin within the function. The cd builtin is commonly redefined this way. The return status is false if shell-builtin is not a
2475 shell builtin command.
2476
2477 caller [expr]
2478 Returns the context of any active subroutine call (a shell function or a script executed with the . or source builtins). Without expr, caller displays the line number
2479 and source filename of the current subroutine call. If a non-negative integer is supplied as expr, caller displays the line number, subroutine name, and source file cor‐
2480 responding to that position in the current execution call stack. This extra information may be used, for example, to print a stack trace. The current frame is frame 0.
2481 The return value is 0 unless the shell is not executing a subroutine call or expr does not correspond to a valid position in the call stack.
2482
2483 cd [-L|[-P [-e]] [-@]] [dir]
2484 Change the current directory to dir. if dir is not supplied, the value of the HOME shell variable is the default. Any additional arguments following dir are ignored.
2485 The variable CDPATH defines the search path for the directory containing dir: each directory name in CDPATH is searched for dir. Alternative directory names in CDPATH
2486 are separated by a colon (:). A null directory name in CDPATH is the same as the current directory, i.e., ``.''. If dir begins with a slash (/), then CDPATH is not
2487 used. The -P option causes cd to use the physical directory structure by resolving symbolic links while traversing dir and before processing instances of .. in dir (see
2488 also the -P option to the set builtin command); the -L option forces symbolic links to be followed by resolving the link after processing instances of .. in dir. If ..
2489 appears in dir, it is processed by removing the immediately previous pathname component from dir, back to a slash or the beginning of dir. If the -e option is supplied
2490 with -P, and the current working directory cannot be successfully determined after a successful directory change, cd will return an unsuccessful status. On systems that
2491 support it, the -@ option presents the extended attributes associated with a file as a directory. An argument of - is converted to $OLDPWD before the directory change is
2492 attempted. If a non-empty directory name from CDPATH is used, or if - is the first argument, and the directory change is successful, the absolute pathname of the new
2493 working directory is written to the standard output. The return value is true if the directory was successfully changed; false otherwise.
2494
2495 command [-pVv] command [arg ...]
2496 Run command with args suppressing the normal shell function lookup. Only builtin commands or commands found in the PATH are executed. If the -p option is given, the
2497 search for command is performed using a default value for PATH that is guaranteed to find all of the standard utilities. If either the -V or -v option is supplied, a
2498 description of command is printed. The -v option causes a single word indicating the command or filename used to invoke command to be displayed; the -V option produces a
2499 more verbose description. If the -V or -v option is supplied, the exit status is 0 if command was found, and 1 if not. If neither option is supplied and an error
2500 occurred or command cannot be found, the exit status is 127. Otherwise, the exit status of the command builtin is the exit status of command.
2501
2502 compgen [option] [word]
2503 Generate possible completion matches for word according to the options, which may be any option accepted by the complete builtin with the exception of -p and -r, and
2504 write the matches to the standard output. When using the -F or -C options, the various shell variables set by the programmable completion facilities, while available,
2505 will not have useful values.
2506
2507 The matches will be generated in the same way as if the programmable completion code had generated them directly from a completion specification with the same flags. If
2508 word is specified, only those completions matching word will be displayed.
2509
2510 The return value is true unless an invalid option is supplied, or no matches were generated.
2511
2512 complete [-abcdefgjksuv] [-o comp-option] [-DE] [-A action] [-G globpat] [-W wordlist] [-F function] [-C command]
2513 [-X filterpat] [-P prefix] [-S suffix] name [name ...]
2514 complete -pr [-DE] [name ...]
2515 Specify how arguments to each name should be completed. If the -p option is supplied, or if no options are supplied, existing completion specifications are printed in a
2516 way that allows them to be reused as input. The -r option removes a completion specification for each name, or, if no names are supplied, all completion specifications.
2517 The -D option indicates that the remaining options and actions should apply to the ``default'' command completion; that is, completion attempted on a command for which no
2518 completion has previously been defined. The -E option indicates that the remaining options and actions should apply to ``empty'' command completion; that is, completion
2519 attempted on a blank line.
2520
2521 The process of applying these completion specifications when word completion is attempted is described above under Programmable Completion.
2522
2523 Other options, if specified, have the following meanings. The arguments to the -G, -W, and -X options (and, if necessary, the -P and -S options) should be quoted to pro‐
2524 tect them from expansion before the complete builtin is invoked.
2525 -o comp-option
2526 The comp-option controls several aspects of the compspec's behavior beyond the simple generation of completions. comp-option may be one of:
2527 bashdefault
2528 Perform the rest of the default bash completions if the compspec generates no matches.
2529 default Use readline's default filename completion if the compspec generates no matches.
2530 dirnames
2531 Perform directory name completion if the compspec generates no matches.
2532 filenames
2533 Tell readline that the compspec generates filenames, so it can perform any filename-specific processing (like adding a slash to directory names, quoting
2534 special characters, or suppressing trailing spaces). Intended to be used with shell functions.
2535 noquote Tell readline not to quote the completed words if they are filenames (quoting filenames is the default).
2536 nosort Tell readline not to sort the list of possible completions alphabetically.
2537 nospace Tell readline not to append a space (the default) to words completed at the end of the line.
2538 plusdirs
2539 After any matches defined by the compspec are generated, directory name completion is attempted and any matches are added to the results of the other
2540 actions.
2541 -A action
2542 The action may be one of the following to generate a list of possible completions:
2543 alias Alias names. May also be specified as -a.
2544 arrayvar
2545 Array variable names.
2546 binding Readline key binding names.
2547 builtin Names of shell builtin commands. May also be specified as -b.
2548 command Command names. May also be specified as -c.
2549 directory
2550 Directory names. May also be specified as -d.
2551 disabled
2552 Names of disabled shell builtins.
2553 enabled Names of enabled shell builtins.
2554 export Names of exported shell variables. May also be specified as -e.
2555 file File names. May also be specified as -f.
2556 function
2557 Names of shell functions.
2558 group Group names. May also be specified as -g.
2559 helptopic
2560 Help topics as accepted by the help builtin.
2561 hostname
2562 Hostnames, as taken from the file specified by the HOSTFILE shell variable.
2563 job Job names, if job control is active. May also be specified as -j.
2564 keyword Shell reserved words. May also be specified as -k.
2565 running Names of running jobs, if job control is active.
2566 service Service names. May also be specified as -s.
2567 setopt Valid arguments for the -o option to the set builtin.
2568 shopt Shell option names as accepted by the shopt builtin.
2569 signal Signal names.
2570 stopped Names of stopped jobs, if job control is active.
2571 user User names. May also be specified as -u.
2572 variable
2573 Names of all shell variables. May also be specified as -v.
2574 -C command
2575 command is executed in a subshell environment, and its output is used as the possible completions.
2576 -F function
2577 The shell function function is executed in the current shell environment. When the function is executed, the first argument ($1) is the name of the command whose
2578 arguments are being completed, the second argument ($2) is the word being completed, and the third argument ($3) is the word preceding the word being completed on
2579 the current command line. When it finishes, the possible completions are retrieved from the value of the COMPREPLY array variable.
2580 -G globpat
2581 The pathname expansion pattern globpat is expanded to generate the possible completions.
2582 -P prefix
2583 prefix is added at the beginning of each possible completion after all other options have been applied.
2584 -S suffix
2585 suffix is appended to each possible completion after all other options have been applied.
2586 -W wordlist
2587 The wordlist is split using the characters in the IFS special variable as delimiters, and each resultant word is expanded. The possible completions are the mem‐
2588 bers of the resultant list which match the word being completed.
2589 -X filterpat
2590 filterpat is a pattern as used for pathname expansion. It is applied to the list of possible completions generated by the preceding options and arguments, and
2591 each completion matching filterpat is removed from the list. A leading ! in filterpat negates the pattern; in this case, any completion not matching filterpat is
2592 removed.
2593
2594 The return value is true unless an invalid option is supplied, an option other than -p or -r is supplied without a name argument, an attempt is made to remove a comple‐
2595 tion specification for a name for which no specification exists, or an error occurs adding a completion specification.
2596
2597 compopt [-o option] [-DE] [+o option] [name]
2598 Modify completion options for each name according to the options, or for the currently-executing completion if no names are supplied. If no options are given, display
2599 the completion options for each name or the current completion. The possible values of option are those valid for the complete builtin described above. The -D option
2600 indicates that the remaining options should apply to the ``default'' command completion; that is, completion attempted on a command for which no completion has previously
2601 been defined. The -E option indicates that the remaining options should apply to ``empty'' command completion; that is, completion attempted on a blank line.
2602
2603 The return value is true unless an invalid option is supplied, an attempt is made to modify the options for a name for which no completion specification exists, or an
2604 output error occurs.
2605
2606 continue [n]
2607 Resume the next iteration of the enclosing for, while, until, or select loop. If n is specified, resume at the nth enclosing loop. n must be ≥ 1. If n is greater than
2608 the number of enclosing loops, the last enclosing loop (the ``top-level'' loop) is resumed. The return value is 0 unless n is not greater than or equal to 1.
2609
2610 declare [-aAfFgilnrtux] [-p] [name[=value] ...]
2611 typeset [-aAfFgilnrtux] [-p] [name[=value] ...]
2612 Declare variables and/or give them attributes. If no names are given then display the values of variables. The -p option will display the attributes and values of each
2613 name. When -p is used with name arguments, additional options, other than -f and -F, are ignored. When -p is supplied without name arguments, it will display the
2614 attributes and values of all variables having the attributes specified by the additional options. If no other options are supplied with -p, declare will display the
2615 attributes and values of all shell variables. The -f option will restrict the display to shell functions. The -F option inhibits the display of function definitions;
2616 only the function name and attributes are printed. If the extdebug shell option is enabled using shopt, the source file name and line number where each name is defined
2617 are displayed as well. The -F option implies -f. The -g option forces variables to be created or modified at the global scope, even when declare is executed in a shell
2618 function. It is ignored in all other cases. The following options can be used to restrict output to variables with the specified attribute or to give variables
2619 attributes:
2620 -a Each name is an indexed array variable (see Arrays above).
2621 -A Each name is an associative array variable (see Arrays above).
2622 -f Use function names only.
2623 -i The variable is treated as an integer; arithmetic evaluation (see ARITHMETIC EVALUATION above) is performed when the variable is assigned a value.
2624 -l When the variable is assigned a value, all upper-case characters are converted to lower-case. The upper-case attribute is disabled.
2625 -n Give each name the nameref attribute, making it a name reference to another variable. That other variable is defined by the value of name. All references,
2626 assignments, and attribute modifications to name, except those using or changing the -n attribute itself, are performed on the variable referenced by name's value.
2627 The nameref attribute cannot be applied to array variables.
2628 -r Make names readonly. These names cannot then be assigned values by subsequent assignment statements or unset.
2629 -t Give each name the trace attribute. Traced functions inherit the DEBUG and RETURN traps from the calling shell. The trace attribute has no special meaning for
2630 variables.
2631 -u When the variable is assigned a value, all lower-case characters are converted to upper-case. The lower-case attribute is disabled.
2632 -x Mark names for export to subsequent commands via the environment.
2633
2634 Using `+' instead of `-' turns off the attribute instead, with the exceptions that +a may not be used to destroy an array variable and +r will not remove the readonly
2635 attribute. When used in a function, declare and typeset make each name local, as with the local command, unless the -g option is supplied. If a variable name is fol‐
2636 lowed by =value, the value of the variable is set to value. When using -a or -A and the compound assignment syntax to create array variables, additional attributes do
2637 not take effect until subsequent assignments. The return value is 0 unless an invalid option is encountered, an attempt is made to define a function using ``-f
2638 foo=bar'', an attempt is made to assign a value to a readonly variable, an attempt is made to assign a value to an array variable without using the compound assignment
2639 syntax (see Arrays above), one of the names is not a valid shell variable name, an attempt is made to turn off readonly status for a readonly variable, an attempt is made
2640 to turn off array status for an array variable, or an attempt is made to display a non-existent function with -f.
2641
2642 dirs [-clpv] [+n] [-n]
2643 Without options, displays the list of currently remembered directories. The default display is on a single line with directory names separated by spaces. Directories
2644 are added to the list with the pushd command; the popd command removes entries from the list. The current directory is always the first directory in the stack.
2645 -c Clears the directory stack by deleting all of the entries.
2646 -l Produces a listing using full pathnames; the default listing format uses a tilde to denote the home directory.
2647 -p Print the directory stack with one entry per line.
2648 -v Print the directory stack with one entry per line, prefixing each entry with its index in the stack.
2649 +n Displays the nth entry counting from the left of the list shown by dirs when invoked without options, starting with zero.
2650 -n Displays the nth entry counting from the right of the list shown by dirs when invoked without options, starting with zero.
2651
2652 The return value is 0 unless an invalid option is supplied or n indexes beyond the end of the directory stack.
2653
2654 disown [-ar] [-h] [jobspec ... | pid ... ]
2655 Without options, remove each jobspec from the table of active jobs. If jobspec is not present, and neither the -a nor the -r option is supplied, the current job is used.
2656 If the -h option is given, each jobspec is not removed from the table, but is marked so that SIGHUP is not sent to the job if the shell receives a SIGHUP. If no jobspec
2657 is supplied, the -a option means to remove or mark all jobs; the -r option without a jobspec argument restricts operation to running jobs. The return value is 0 unless a
2658 jobspec does not specify a valid job.
2659
2660 echo [-neE] [arg ...]
2661 Output the args, separated by spaces, followed by a newline. The return status is 0 unless a write error occurs. If -n is specified, the trailing newline is suppressed.
2662 If the -e option is given, interpretation of the following backslash-escaped characters is enabled. The -E option disables the interpretation of these escape characters,
2663 even on systems where they are interpreted by default. The xpg_echo shell option may be used to dynamically determine whether or not echo expands these escape characters
2664 by default. echo does not interpret -- to mean the end of options. echo interprets the following escape sequences:
2665 \a alert (bell)
2666 \b backspace
2667 \c suppress further output
2668 \e
2669 \E an escape character
2670 \f form feed
2671 \n new line
2672 \r carriage return
2673 \t horizontal tab
2674 \v vertical tab
2675 \\ backslash
2676 \0nnn the eight-bit character whose value is the octal value nnn (zero to three octal digits)
2677 \xHH the eight-bit character whose value is the hexadecimal value HH (one or two hex digits)
2678 \uHHHH the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHH (one to four hex digits)
2679 \UHHHHHHHH
2680 the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHHHHHH (one to eight hex digits)
2681
2682 enable [-a] [-dnps] [-f filename] [name ...]
2683 Enable and disable builtin shell commands. Disabling a builtin allows a disk command which has the same name as a shell builtin to be executed without specifying a full
2684 pathname, even though the shell normally searches for builtins before disk commands. If -n is used, each name is disabled; otherwise, names are enabled. For example, to
2685 use the test binary found via the PATH instead of the shell builtin version, run ``enable -n test''. The -f option means to load the new builtin command name from shared
2686 object filename, on systems that support dynamic loading. The -d option will delete a builtin previously loaded with -f. If no name arguments are given, or if the -p
2687 option is supplied, a list of shell builtins is printed. With no other option arguments, the list consists of all enabled shell builtins. If -n is supplied, only dis‐
2688 abled builtins are printed. If -a is supplied, the list printed includes all builtins, with an indication of whether or not each is enabled. If -s is supplied, the out‐
2689 put is restricted to the POSIX special builtins. The return value is 0 unless a name is not a shell builtin or there is an error loading a new builtin from a shared
2690 object.
2691
2692 eval [arg ...]
2693 The args are read and concatenated together into a single command. This command is then read and executed by the shell, and its exit status is returned as the value of
2694 eval. If there are no args, or only null arguments, eval returns 0.
2695
2696 exec [-cl] [-a name] [command [arguments]]
2697 If command is specified, it replaces the shell. No new process is created. The arguments become the arguments to command. If the -l option is supplied, the shell
2698 places a dash at the beginning of the zeroth argument passed to command. This is what login(1) does. The -c option causes command to be executed with an empty environ‐
2699 ment. If -a is supplied, the shell passes name as the zeroth argument to the executed command. If command cannot be executed for some reason, a non-interactive shell
2700 exits, unless the execfail shell option is enabled. In that case, it returns failure. An interactive shell returns failure if the file cannot be executed. If command
2701 is not specified, any redirections take effect in the current shell, and the return status is 0. If there is a redirection error, the return status is 1.
2702
2703 exit [n]
2704 Cause the shell to exit with a status of n. If n is omitted, the exit status is that of the last command executed. A trap on EXIT is executed before the shell termi‐
2705 nates.
2706
2707 export [-fn] [name[=word]] ...
2708 export -p
2709 The supplied names are marked for automatic export to the environment of subsequently executed commands. If the -f option is given, the names refer to functions. If no
2710 names are given, or if the -p option is supplied, a list of names of all exported variables is printed. The -n option causes the export property to be removed from each
2711 name. If a variable name is followed by =word, the value of the variable is set to word. export returns an exit status of 0 unless an invalid option is encountered, one
2712 of the names is not a valid shell variable name, or -f is supplied with a name that is not a function.
2713
2714 fc [-e ename] [-lnr] [first] [last]
2715 fc -s [pat=rep] [cmd]
2716 The first form selects a range of commands from first to last from the history list and displays or edits and re-executes them. First and last may be specified as a
2717 string (to locate the last command beginning with that string) or as a number (an index into the history list, where a negative number is used as an offset from the cur‐
2718 rent command number). If last is not specified it is set to the current command for listing (so that ``fc -l -10'' prints the last 10 commands) and to first otherwise.
2719 If first is not specified it is set to the previous command for editing and -16 for listing.
2720
2721 The -n option suppresses the command numbers when listing. The -r option reverses the order of the commands. If the -l option is given, the commands are listed on stan‐
2722 dard output. Otherwise, the editor given by ename is invoked on a file containing those commands. If ename is not given, the value of the FCEDIT variable is used, and
2723 the value of EDITOR if FCEDIT is not set. If neither variable is set, vi is used. When editing is complete, the edited commands are echoed and executed.
2724
2725 In the second form, command is re-executed after each instance of pat is replaced by rep. Command is intepreted the same as first above. A useful alias to use with this
2726 is ``r="fc -s"'', so that typing ``r cc'' runs the last command beginning with ``cc'' and typing ``r'' re-executes the last command.
2727
2728 If the first form is used, the return value is 0 unless an invalid option is encountered or first or last specify history lines out of range. If the -e option is sup‐
2729 plied, the return value is the value of the last command executed or failure if an error occurs with the temporary file of commands. If the second form is used, the
2730 return status is that of the command re-executed, unless cmd does not specify a valid history line, in which case fc returns failure.
2731
2732 fg [jobspec]
2733 Resume jobspec in the foreground, and make it the current job. If jobspec is not present, the shell's notion of the current job is used. The return value is that of the
2734 command placed into the foreground, or failure if run when job control is disabled or, when run with job control enabled, if jobspec does not specify a valid job or job‐
2735 spec specifies a job that was started without job control.
2736
2737 getopts optstring name [args]
2738 getopts is used by shell procedures to parse positional parameters. optstring contains the option characters to be recognized; if a character is followed by a colon, the
2739 option is expected to have an argument, which should be separated from it by white space. The colon and question mark characters may not be used as option characters.
2740 Each time it is invoked, getopts places the next option in the shell variable name, initializing name if it does not exist, and the index of the next argument to be pro‐
2741 cessed into the variable OPTIND. OPTIND is initialized to 1 each time the shell or a shell script is invoked. When an option requires an argument, getopts places that
2742 argument into the variable OPTARG. The shell does not reset OPTIND automatically; it must be manually reset between multiple calls to getopts within the same shell invo‐
2743 cation if a new set of parameters is to be used.
2744
2745 When the end of options is encountered, getopts exits with a return value greater than zero. OPTIND is set to the index of the first non-option argument, and name is set
2746 to ?.
2747
2748 getopts normally parses the positional parameters, but if more arguments are given in args, getopts parses those instead.
2749
2750 getopts can report errors in two ways. If the first character of optstring is a colon, silent error reporting is used. In normal operation, diagnostic messages are
2751 printed when invalid options or missing option arguments are encountered. If the variable OPTERR is set to 0, no error messages will be displayed, even if the first
2752 character of optstring is not a colon.
2753
2754 If an invalid option is seen, getopts places ? into name and, if not silent, prints an error message and unsets OPTARG. If getopts is silent, the option character found
2755 is placed in OPTARG and no diagnostic message is printed.
2756
2757 If a required argument is not found, and getopts is not silent, a question mark (?) is placed in name, OPTARG is unset, and a diagnostic message is printed. If getopts
2758 is silent, then a colon (:) is placed in name and OPTARG is set to the option character found.
2759
2760 getopts returns true if an option, specified or unspecified, is found. It returns false if the end of options is encountered or an error occurs.
2761
2762 hash [-lr] [-p filename] [-dt] [name]
2763 Each time hash is invoked, the full pathname of the command name is determined by searching the directories in $PATH and remembered. Any previously-remembered pathname
2764 is discarded. If the -p option is supplied, no path search is performed, and filename is used as the full filename of the command. The -r option causes the shell to
2765 forget all remembered locations. The -d option causes the shell to forget the remembered location of each name. If the -t option is supplied, the full pathname to which
2766 each name corresponds is printed. If multiple name arguments are supplied with -t, the name is printed before the hashed full pathname. The -l option causes output to
2767 be displayed in a format that may be reused as input. If no arguments are given, or if only -l is supplied, information about remembered commands is printed. The return
2768 status is true unless a name is not found or an invalid option is supplied.
2769
2770 help [-dms] [pattern]
2771 Display helpful information about builtin commands. If pattern is specified, help gives detailed help on all commands matching pattern; otherwise help for all the
2772 builtins and shell control structures is printed.
2773 -d Display a short description of each pattern
2774 -m Display the description of each pattern in a manpage-like format
2775 -s Display only a short usage synopsis for each pattern
2776
2777 The return status is 0 unless no command matches pattern.
2778
2779 history [n]
2780 history -c
2781 history -d offset
2782 history -anrw [filename]
2783 history -p arg [arg ...]
2784 history -s arg [arg ...]
2785 With no options, display the command history list with line numbers. Lines listed with a * have been modified. An argument of n lists only the last n lines. If the
2786 shell variable HISTTIMEFORMAT is set and not null, it is used as a format string for strftime(3) to display the time stamp associated with each displayed history entry.
2787 No intervening blank is printed between the formatted time stamp and the history line. If filename is supplied, it is used as the name of the history file; if not, the
2788 value of HISTFILE is used. Options, if supplied, have the following meanings:
2789 -c Clear the history list by deleting all the entries.
2790 -d offset
2791 Delete the history entry at position offset.
2792 -a Append the ``new'' history lines to the history file. These are history lines entered since the beginning of the current bash session, but not already appended to
2793 the history file.
2794 -n Read the history lines not already read from the history file into the current history list. These are lines appended to the history file since the beginning of
2795 the current bash session.
2796 -r Read the contents of the history file and append them to the current history list.
2797 -w Write the current history list to the history file, overwriting the history file's contents.
2798 -p Perform history substitution on the following args and display the result on the standard output. Does not store the results in the history list. Each arg must
2799 be quoted to disable normal history expansion.
2800 -s Store the args in the history list as a single entry. The last command in the history list is removed before the args are added.
2801
2802 If the HISTTIMEFORMAT variable is set, the time stamp information associated with each history entry is written to the history file, marked with the history comment char‐
2803 acter. When the history file is read, lines beginning with the history comment character followed immediately by a digit are interpreted as timestamps for the following
2804 history entry. The return value is 0 unless an invalid option is encountered, an error occurs while reading or writing the history file, an invalid offset is supplied as
2805 an argument to -d, or the history expansion supplied as an argument to -p fails.
2806
2807 jobs [-lnprs] [ jobspec ... ]
2808 jobs -x command [ args ... ]
2809 The first form lists the active jobs. The options have the following meanings:
2810 -l List process IDs in addition to the normal information.
2811 -n Display information only about jobs that have changed status since the user was last notified of their status.
2812 -p List only the process ID of the job's process group leader.
2813 -r Display only running jobs.
2814 -s Display only stopped jobs.
2815
2816 If jobspec is given, output is restricted to information about that job. The return status is 0 unless an invalid option is encountered or an invalid jobspec is sup‐
2817 plied.
2818
2819 If the -x option is supplied, jobs replaces any jobspec found in command or args with the corresponding process group ID, and executes command passing it args, returning
2820 its exit status.
2821
2822 kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...
2823 kill -l|-L [sigspec | exit_status]
2824 Send the signal named by sigspec or signum to the processes named by pid or jobspec. sigspec is either a case-insensitive signal name such as SIGKILL (with or without
2825 the SIG prefix) or a signal number; signum is a signal number. If sigspec is not present, then SIGTERM is assumed. An argument of -l lists the signal names. If any
2826 arguments are supplied when -l is given, the names of the signals corresponding to the arguments are listed, and the return status is 0. The exit_status argument to -l
2827 is a number specifying either a signal number or the exit status of a process terminated by a signal. The -L option is equivalent to -l. kill returns true if at least
2828 one signal was successfully sent, or false if an error occurs or an invalid option is encountered.
2829
2830 let arg [arg ...]
2831 Each arg is an arithmetic expression to be evaluated (see ARITHMETIC EVALUATION above). If the last arg evaluates to 0, let returns 1; 0 is returned otherwise.
2832
2833 local [option] [name[=value] ... | - ]
2834 For each argument, a local variable named name is created, and assigned value. The option can be any of the options accepted by declare. When local is used within a
2835 function, it causes the variable name to have a visible scope restricted to that function and its children. If name is -, the set of shell options is made local to the
2836 function in which local is invoked: shell options changed using the set builtin inside the function are restored to their original values when the function returns. With
2837 no operands, local writes a list of local variables to the standard output. It is an error to use local when not within a function. The return status is 0 unless local
2838 is used outside a function, an invalid name is supplied, or name is a readonly variable.
2839
2840 logout Exit a login shell.
2841
2842 mapfile [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quantum] [array]
2843 readarray [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quantum] [array]
2844 Read lines from the standard input into the indexed array variable array, or from file descriptor fd if the -u option is supplied. The variable MAPFILE is the default
2845 array. Options, if supplied, have the following meanings:
2846 -d The first character of delim is used to terminate each input line, rather than newline.
2847 -n Copy at most count lines. If count is 0, all lines are copied.
2848 -O Begin assigning to array at index origin. The default index is 0.
2849 -s Discard the first count lines read.
2850 -t Remove a trailing delim (default newline) from each line read.
2851 -u Read lines from file descriptor fd instead of the standard input.
2852 -C Evaluate callback each time quantum lines are read. The -c option specifies quantum.
2853 -c Specify the number of lines read between each call to callback.
2854
2855 If -C is specified without -c, the default quantum is 5000. When callback is evaluated, it is supplied the index of the next array element to be assigned and the line to
2856 be assigned to that element as additional arguments. callback is evaluated after the line is read but before the array element is assigned.
2857
2858 If not supplied with an explicit origin, mapfile will clear array before assigning to it.
2859
2860 mapfile returns successfully unless an invalid option or option argument is supplied, array is invalid or unassignable, or if array is not an indexed array.
2861
2862 popd [-n] [+n] [-n]
2863 Removes entries from the directory stack. With no arguments, removes the top directory from the stack, and performs a cd to the new top directory. Arguments, if sup‐
2864 plied, have the following meanings:
2865 -n Suppresses the normal change of directory when removing directories from the stack, so that only the stack is manipulated.
2866 +n Removes the nth entry counting from the left of the list shown by dirs, starting with zero. For example: ``popd +0'' removes the first directory, ``popd +1'' the
2867 second.
2868 -n Removes the nth entry counting from the right of the list shown by dirs, starting with zero. For example: ``popd -0'' removes the last directory, ``popd -1'' the
2869 next to last.
2870
2871 If the popd command is successful, a dirs is performed as well, and the return status is 0. popd returns false if an invalid option is encountered, the directory stack
2872 is empty, a non-existent directory stack entry is specified, or the directory change fails.
2873
2874 printf [-v var] format [arguments]
2875 Write the formatted arguments to the standard output under the control of the format. The -v option causes the output to be assigned to the variable var rather than
2876 being printed to the standard output.
2877
2878 The format is a character string which contains three types of objects: plain characters, which are simply copied to standard output, character escape sequences, which
2879 are converted and copied to the standard output, and format specifications, each of which causes printing of the next successive argument. In addition to the standard
2880 printf(1) format specifications, printf interprets the following extensions:
2881 %b causes printf to expand backslash escape sequences in the corresponding argument in the same way as echo -e.
2882 %q causes printf to output the corresponding argument in a format that can be reused as shell input.
2883 %(datefmt)T
2884 causes printf to output the date-time string resulting from using datefmt as a format string for strftime(3). The corresponding argument is an integer represent‐
2885 ing the number of seconds since the epoch. Two special argument values may be used: -1 represents the current time, and -2 represents the time the shell was
2886 invoked. If no argument is specified, conversion behaves as if -1 had been given. This is an exception to the usual printf behavior.
2887
2888 Arguments to non-string format specifiers are treated as C constants, except that a leading plus or minus sign is allowed, and if the leading character is a single or
2889 double quote, the value is the ASCII value of the following character.
2890
2891 The format is reused as necessary to consume all of the arguments. If the format requires more arguments than are supplied, the extra format specifications behave as if
2892 a zero value or null string, as appropriate, had been supplied. The return value is zero on success, non-zero on failure.
2893
2894 pushd [-n] [+n] [-n]
2895 pushd [-n] [dir]
2896 Adds a directory to the top of the directory stack, or rotates the stack, making the new top of the stack the current working directory. With no arguments, pushd
2897 exchanges the top two directories and returns 0, unless the directory stack is empty. Arguments, if supplied, have the following meanings:
2898 -n Suppresses the normal change of directory when rotating or adding directories to the stack, so that only the stack is manipulated.
2899 +n Rotates the stack so that the nth directory (counting from the left of the list shown by dirs, starting with zero) is at the top.
2900 -n Rotates the stack so that the nth directory (counting from the right of the list shown by dirs, starting with zero) is at the top.
2901 dir Adds dir to the directory stack at the top, making it the new current working directory as if it had been supplied as the argument to the cd builtin.
2902
2903 If the pushd command is successful, a dirs is performed as well. If the first form is used, pushd returns 0 unless the cd to dir fails. With the second form, pushd
2904 returns 0 unless the directory stack is empty, a non-existent directory stack element is specified, or the directory change to the specified new current directory fails.
2905
2906 pwd [-LP]
2907 Print the absolute pathname of the current working directory. The pathname printed contains no symbolic links if the -P option is supplied or the -o physical option to
2908 the set builtin command is enabled. If the -L option is used, the pathname printed may contain symbolic links. The return status is 0 unless an error occurs while read‐
2909 ing the name of the current directory or an invalid option is supplied.
2910
2911 read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p prompt] [-t timeout] [-u fd] [name ...]
2912 One line is read from the standard input, or from the file descriptor fd supplied as an argument to the -u option, split into words as described above under Word Split‐
2913 ting, and the first word is assigned to the first name, the second word to the second name, and so on. If there are more words than names, the remaining words and their
2914 intervening delimiters are assigned to the last name. If there are fewer words read from the input stream than names, the remaining names are assigned empty values. The
2915 characters in IFS are used to split the line into words using the same rules the shell uses for expansion (described above under Word Splitting). The backslash character
2916 (\) may be used to remove any special meaning for the next character read and for line continuation. Options, if supplied, have the following meanings:
2917 -a aname
2918 The words are assigned to sequential indices of the array variable aname, starting at 0. aname is unset before any new values are assigned. Other name arguments
2919 are ignored.
2920 -d delim
2921 The first character of delim is used to terminate the input line, rather than newline.
2922 -e If the standard input is coming from a terminal, readline (see READLINE above) is used to obtain the line. Readline uses the current (or default, if line editing
2923 was not previously active) editing settings.
2924 -i text
2925 If readline is being used to read the line, text is placed into the editing buffer before editing begins.
2926 -n nchars
2927 read returns after reading nchars characters rather than waiting for a complete line of input, but honors a delimiter if fewer than nchars characters are read
2928 before the delimiter.
2929 -N nchars
2930 read returns after reading exactly nchars characters rather than waiting for a complete line of input, unless EOF is encountered or read times out. Delimiter
2931 characters encountered in the input are not treated specially and do not cause read to return until nchars characters are read. The result is not split on the
2932 characters in IFS; the intent is that the variable is assigned exactly the characters read (with the exception of backslash; see the -r option below).
2933 -p prompt
2934 Display prompt on standard error, without a trailing newline, before attempting to read any input. The prompt is displayed only if input is coming from a termi‐
2935 nal.
2936 -r Backslash does not act as an escape character. The backslash is considered to be part of the line. In particular, a backslash-newline pair may not be used as a
2937 line continuation.
2938 -s Silent mode. If input is coming from a terminal, characters are not echoed.
2939 -t timeout
2940 Cause read to time out and return failure if a complete line of input (or a specified number of characters) is not read within timeout seconds. timeout may be a
2941 decimal number with a fractional portion following the decimal point. This option is only effective if read is reading input from a terminal, pipe, or other spe‐
2942 cial file; it has no effect when reading from regular files. If read times out, read saves any partial input read into the specified variable name. If timeout is
2943 0, read returns immediately, without trying to read any data. The exit status is 0 if input is available on the specified file descriptor, non-zero otherwise.
2944 The exit status is greater than 128 if the timeout is exceeded.
2945 -u fd Read input from file descriptor fd.
2946
2947 If no names are supplied, the line read is assigned to the variable REPLY. The exit status is zero, unless end-of-file is encountered, read times out (in which case the
2948 status is greater than 128), a variable assignment error (such as assigning to a readonly variable) occurs, or an invalid file descriptor is supplied as the argument to
2949 -u.
2950
2951 readonly [-aAf] [-p] [name[=word] ...]
2952 The given names are marked readonly; the values of these names may not be changed by subsequent assignment. If the -f option is supplied, the functions corresponding to
2953 the names are so marked. The -a option restricts the variables to indexed arrays; the -A option restricts the variables to associative arrays. If both options are sup‐
2954 plied, -A takes precedence. If no name arguments are given, or if the -p option is supplied, a list of all readonly names is printed. The other options may be used to
2955 restrict the output to a subset of the set of readonly names. The -p option causes output to be displayed in a format that may be reused as input. If a variable name is
2956 followed by =word, the value of the variable is set to word. The return status is 0 unless an invalid option is encountered, one of the names is not a valid shell vari‐
2957 able name, or -f is supplied with a name that is not a function.
2958
2959 return [n]
2960 Causes a function to stop executing and return the value specified by n to its caller. If n is omitted, the return status is that of the last command executed in the
2961 function body. If return is executed by a trap handler, the last command used to determine the status is the last command executed before the trap handler. if return is
2962 executed during a DEBUG trap, the last command used to determine the status is the last command executed by the trap handler before return was invoked. If return is used
2963 outside a function, but during execution of a script by the . (source) command, it causes the shell to stop executing that script and return either n or the exit status
2964 of the last command executed within the script as the exit status of the script. If n is supplied, the return value is its least significant 8 bits. The return status
2965 is non-zero if return is supplied a non-numeric argument, or is used outside a function and not during execution of a script by . or source. Any command associated with
2966 the RETURN trap is executed before execution resumes after the function or script.
2967
2968 set [--abefhkmnptuvxBCEHPT] [-o option-name] [arg ...]
2969 set [+abefhkmnptuvxBCEHPT] [+o option-name] [arg ...]
2970 Without options, the name and value of each shell variable are displayed in a format that can be reused as input for setting or resetting the currently-set variables.
2971 Read-only variables cannot be reset. In posix mode, only shell variables are listed. The output is sorted according to the current locale. When options are specified,
2972 they set or unset shell attributes. Any arguments remaining after option processing are treated as values for the positional parameters and are assigned, in order, to
2973 $1, $2, ... $n. Options, if specified, have the following meanings:
2974 -a Each variable or function that is created or modified is given the export attribute and marked for export to the environment of subsequent commands.
2975 -b Report the status of terminated background jobs immediately, rather than before the next primary prompt. This is effective only when job control is enabled.
2976 -e Exit immediately if a pipeline (which may consist of a single simple command), a list, or a compound command (see SHELL GRAMMAR above), exits with a non-zero sta‐
2977 tus. The shell does not exit if the command that fails is part of the command list immediately following a while or until keyword, part of the test following the
2978 if or elif reserved words, part of any command executed in a && or || list except the command following the final && or ||, any command in a pipeline but the
2979 last, or if the command's return value is being inverted with !. If a compound command other than a subshell returns a non-zero status because a command failed
2980 while -e was being ignored, the shell does not exit. A trap on ERR, if set, is executed before the shell exits. This option applies to the shell environment and
2981 each subshell environment separately (see COMMAND EXECUTION ENVIRONMENT above), and may cause subshells to exit before executing all the commands in the subshell.
2982
2983 If a compound command or shell function executes in a context where -e is being ignored, none of the commands executed within the compound command or function
2984 body will be affected by the -e setting, even if -e is set and a command returns a failure status. If a compound command or shell function sets -e while execut‐
2985 ing in a context where -e is ignored, that setting will not have any effect until the compound command or the command containing the function call completes.
2986 -f Disable pathname expansion.
2987 -h Remember the location of commands as they are looked up for execution. This is enabled by default.
2988 -k All arguments in the form of assignment statements are placed in the environment for a command, not just those that precede the command name.
2989 -m Monitor mode. Job control is enabled. This option is on by default for interactive shells on systems that support it (see JOB CONTROL above). All processes run
2990 in a separate process group. When a background job completes, the shell prints a line containing its exit status.
2991 -n Read commands but do not execute them. This may be used to check a shell script for syntax errors. This is ignored by interactive shells.
2992 -o option-name
2993 The option-name can be one of the following:
2994 allexport
2995 Same as -a.
2996 braceexpand
2997 Same as -B.
2998 emacs Use an emacs-style command line editing interface. This is enabled by default when the shell is interactive, unless the shell is started with the
2999 --noediting option. This also affects the editing interface used for read -e.
3000 errexit Same as -e.
3001 errtrace
3002 Same as -E.
3003 functrace
3004 Same as -T.
3005 hashall Same as -h.
3006 histexpand
3007 Same as -H.
3008 history Enable command history, as described above under HISTORY. This option is on by default in interactive shells.
3009 ignoreeof
3010 The effect is as if the shell command ``IGNOREEOF=10'' had been executed (see Shell Variables above).
3011 keyword Same as -k.
3012 monitor Same as -m.
3013 noclobber
3014 Same as -C.
3015 noexec Same as -n.
3016 noglob Same as -f.
3017 nolog Currently ignored.
3018 notify Same as -b.
3019 nounset Same as -u.
3020 onecmd Same as -t.
3021 physical
3022 Same as -P.
3023 pipefail
3024 If set, the return value of a pipeline is the value of the last (rightmost) command to exit with a non-zero status, or zero if all commands in the pipe‐
3025 line exit successfully. This option is disabled by default.
3026 posix Change the behavior of bash where the default operation differs from the POSIX standard to match the standard (posix mode). See SEE ALSO below for a ref‐
3027 erence to a document that details how posix mode affects bash's behavior.
3028 privileged
3029 Same as -p.
3030 verbose Same as -v.
3031 vi Use a vi-style command line editing interface. This also affects the editing interface used for read -e.
3032 xtrace Same as -x.
3033 If -o is supplied with no option-name, the values of the current options are printed. If +o is supplied with no option-name, a series of set commands to recreate
3034 the current option settings is displayed on the standard output.
3035 -p Turn on privileged mode. In this mode, the $ENV and $BASH_ENV files are not processed, shell functions are not inherited from the environment, and the SHELLOPTS,
3036 BASHOPTS, CDPATH, and GLOBIGNORE variables, if they appear in the environment, are ignored. If the shell is started with the effective user (group) id not equal
3037 to the real user (group) id, and the -p option is not supplied, these actions are taken and the effective user id is set to the real user id. If the -p option is
3038 supplied at startup, the effective user id is not reset. Turning this option off causes the effective user and group ids to be set to the real user and group
3039 ids.
3040 -t Exit after reading and executing one command.
3041 -u Treat unset variables and parameters other than the special parameters "@" and "*" as an error when performing parameter expansion. If expansion is attempted on
3042 an unset variable or parameter, the shell prints an error message, and, if not interactive, exits with a non-zero status.
3043 -v Print shell input lines as they are read.
3044 -x After expanding each simple command, for command, case command, select command, or arithmetic for command, display the expanded value of PS4, followed by the com‐
3045 mand and its expanded arguments or associated word list.
3046 -B The shell performs brace expansion (see Brace Expansion above). This is on by default.
3047 -C If set, bash does not overwrite an existing file with the >, >&, and <> redirection operators. This may be overridden when creating output files by using the re‐
3048 direction operator >| instead of >.
3049 -E If set, any trap on ERR is inherited by shell functions, command substitutions, and commands executed in a subshell environment. The ERR trap is normally not
3050 inherited in such cases.
3051 -H Enable ! style history substitution. This option is on by default when the shell is interactive.
3052 -P If set, the shell does not resolve symbolic links when executing commands such as cd that change the current working directory. It uses the physical directory
3053 structure instead. By default, bash follows the logical chain of directories when performing commands which change the current directory.
3054 -T If set, any traps on DEBUG and RETURN are inherited by shell functions, command substitutions, and commands executed in a subshell environment. The DEBUG and
3055 RETURN traps are normally not inherited in such cases.
3056 -- If no arguments follow this option, then the positional parameters are unset. Otherwise, the positional parameters are set to the args, even if some of them
3057 begin with a -.
3058 - Signal the end of options, cause all remaining args to be assigned to the positional parameters. The -x and -v options are turned off. If there are no args, the
3059 positional parameters remain unchanged.
3060
3061 The options are off by default unless otherwise noted. Using + rather than - causes these options to be turned off. The options can also be specified as arguments to an
3062 invocation of the shell. The current set of options may be found in $-. The return status is always true unless an invalid option is encountered.
3063
3064 shift [n]
3065 The positional parameters from n+1 ... are renamed to $1 .... Parameters represented by the numbers $# down to $#-n+1 are unset. n must be a non-negative number less
3066 than or equal to $#. If n is 0, no parameters are changed. If n is not given, it is assumed to be 1. If n is greater than $#, the positional parameters are not
3067 changed. The return status is greater than zero if n is greater than $# or less than zero; otherwise 0.
3068
3069 shopt [-pqsu] [-o] [optname ...]
3070 Toggle the values of settings controlling optional shell behavior. The settings can be either those listed below, or, if the -o option is used, those available with the
3071 -o option to the set builtin command. With no options, or with the -p option, a list of all settable options is displayed, with an indication of whether or not each is
3072 set. The -p option causes output to be displayed in a form that may be reused as input. Other options have the following meanings:
3073 -s Enable (set) each optname.
3074 -u Disable (unset) each optname.
3075 -q Suppresses normal output (quiet mode); the return status indicates whether the optname is set or unset. If multiple optname arguments are given with -q, the
3076 return status is zero if all optnames are enabled; non-zero otherwise.
3077 -o Restricts the values of optname to be those defined for the -o option to the set builtin.
3078
3079 If either -s or -u is used with no optname arguments, shopt shows only those options which are set or unset, respectively. Unless otherwise noted, the shopt options are
3080 disabled (unset) by default.
3081
3082 The return status when listing options is zero if all optnames are enabled, non-zero otherwise. When setting or unsetting options, the return status is zero unless an
3083 optname is not a valid shell option.
3084
3085 The list of shopt options is:
3086
3087 autocd If set, a command name that is the name of a directory is executed as if it were the argument to the cd command. This option is only used by interactive shells.
3088 cdable_vars
3089 If set, an argument to the cd builtin command that is not a directory is assumed to be the name of a variable whose value is the directory to change to.
3090 cdspell If set, minor errors in the spelling of a directory component in a cd command will be corrected. The errors checked for are transposed characters, a missing
3091 character, and one character too many. If a correction is found, the corrected filename is printed, and the command proceeds. This option is only used by inter‐
3092 active shells.
3093 checkhash
3094 If set, bash checks that a command found in the hash table exists before trying to execute it. If a hashed command no longer exists, a normal path search is per‐
3095 formed.
3096 checkjobs
3097 If set, bash lists the status of any stopped and running jobs before exiting an interactive shell. If any jobs are running, this causes the exit to be deferred
3098 until a second exit is attempted without an intervening command (see JOB CONTROL above). The shell always postpones exiting if any jobs are stopped.
3099 checkwinsize
3100 If set, bash checks the window size after each command and, if necessary, updates the values of LINES and COLUMNS.
3101 cmdhist If set, bash attempts to save all lines of a multiple-line command in the same history entry. This allows easy re-editing of multi-line commands.
3102 compat31
3103 If set, bash changes its behavior to that of version 3.1 with respect to quoted arguments to the [[ conditional command's =~ operator and locale-specific string
3104 comparison when using the [[ conditional command's < and > operators. Bash versions prior to bash-4.1 use ASCII collation and strcmp(3); bash-4.1 and later use
3105 the current locale's collation sequence and strcoll(3).
3106 compat32
3107 If set, bash changes its behavior to that of version 3.2 with respect to locale-specific string comparison when using the [[ conditional command's < and > opera‐
3108 tors (see previous item) and the effect of interrupting a command list. Bash versions 3.2 and earlier continue with the next command in the list after one termi‐
3109 nates due to an interrupt.
3110 compat40
3111 If set, bash changes its behavior to that of version 4.0 with respect to locale-specific string comparison when using the [[ conditional command's < and > opera‐
3112 tors (see description of compat31) and the effect of interrupting a command list. Bash versions 4.0 and later interrupt the list as if the shell received the
3113 interrupt; previous versions continue with the next command in the list.
3114 compat41
3115 If set, bash, when in posix mode, treats a single quote in a double-quoted parameter expansion as a special character. The single quotes must match (an even num‐
3116 ber) and the characters between the single quotes are considered quoted. This is the behavior of posix mode through version 4.1. The default bash behavior
3117 remains as in previous versions.
3118 compat42
3119 If set, bash does not process the replacement string in the pattern substitution word expansion using quote removal.
3120 compat43
3121 If set, bash does not print a warning message if an attempt is made to use a quoted compound array assignment as an argument to declare, makes word expansion
3122 errors non-fatal errors that cause the current command to fail (the default behavior is to make them fatal errors that cause the shell to exit), and does not
3123 reset the loop state when a shell function is executed (this allows break or continue in a shell function to affect loops in the caller's context).
3124 complete_fullquote
3125 If set, bash quotes all shell metacharacters in filenames and directory names when performing completion. If not set, bash removes metacharacters such as the
3126 dollar sign from the set of characters that will be quoted in completed filenames when these metacharacters appear in shell variable references in words to be
3127 completed. This means that dollar signs in variable names that expand to directories will not be quoted; however, any dollar signs appearing in filenames will
3128 not be quoted, either. This is active only when bash is using backslashes to quote completed filenames. This variable is set by default, which is the default
3129 bash behavior in versions through 4.2.
3130 direxpand
3131 If set, bash replaces directory names with the results of word expansion when performing filename completion. This changes the contents of the readline editing
3132 buffer. If not set, bash attempts to preserve what the user typed.
3133 dirspell
3134 If set, bash attempts spelling correction on directory names during word completion if the directory name initially supplied does not exist.
3135 dotglob If set, bash includes filenames beginning with a `.' in the results of pathname expansion.
3136 execfail
3137 If set, a non-interactive shell will not exit if it cannot execute the file specified as an argument to the exec builtin command. An interactive shell does not
3138 exit if exec fails.
3139 expand_aliases
3140 If set, aliases are expanded as described above under ALIASES. This option is enabled by default for interactive shells.
3141 extdebug
3142 If set at shell invocation, arrange to execute the debugger profile before the shell starts, identical to the --debugger option. If set after invocation, behav‐
3143 ior intended for use by debuggers is enabled:
3144 1. The -F option to the declare builtin displays the source file name and line number corresponding to each function name supplied as an argument.
3145 2. If the command run by the DEBUG trap returns a non-zero value, the next command is skipped and not executed.
3146 3. If the command run by the DEBUG trap returns a value of 2, and the shell is executing in a subroutine (a shell function or a shell script executed by the .
3147 or source builtins), the shell simulates a call to return.
3148 4. BASH_ARGC and BASH_ARGV are updated as described in their descriptions above.
3149 5. Function tracing is enabled: command substitution, shell functions, and subshells invoked with ( command ) inherit the DEBUG and RETURN traps.
3150 6. Error tracing is enabled: command substitution, shell functions, and subshells invoked with ( command ) inherit the ERR trap.
3151 extglob If set, the extended pattern matching features described above under Pathname Expansion are enabled.
3152 extquote
3153 If set, $'string' and $"string" quoting is performed within ${parameter} expansions enclosed in double quotes. This option is enabled by default.
3154 failglob
3155 If set, patterns which fail to match filenames during pathname expansion result in an expansion error.
3156 force_fignore
3157 If set, the suffixes specified by the FIGNORE shell variable cause words to be ignored when performing word completion even if the ignored words are the only pos‐
3158 sible completions. See SHELL VARIABLES above for a description of FIGNORE. This option is enabled by default.
3159 globasciiranges
3160 If set, range expressions used in pattern matching bracket expressions (see Pattern Matching above) behave as if in the traditional C locale when performing com‐
3161 parisons. That is, the current locale's collating sequence is not taken into account, so b will not collate between A and B, and upper-case and lower-case ASCII
3162 characters will collate together.
3163 globstar
3164 If set, the pattern ** used in a pathname expansion context will match all files and zero or more directories and subdirectories. If the pattern is followed by a
3165 /, only directories and subdirectories match.
3166 gnu_errfmt
3167 If set, shell error messages are written in the standard GNU error message format.
3168 histappend
3169 If set, the history list is appended to the file named by the value of the HISTFILE variable when the shell exits, rather than overwriting the file.
3170 histreedit
3171 If set, and readline is being used, a user is given the opportunity to re-edit a failed history substitution.
3172 histverify
3173 If set, and readline is being used, the results of history substitution are not immediately passed to the shell parser. Instead, the resulting line is loaded
3174 into the readline editing buffer, allowing further modification.
3175 hostcomplete
3176 If set, and readline is being used, bash will attempt to perform hostname completion when a word containing a @ is being completed (see Completing under READLINE
3177 above). This is enabled by default.
3178 huponexit
3179 If set, bash will send SIGHUP to all jobs when an interactive login shell exits.
3180 inherit_errexit
3181 If set, command substitution inherits the value of the errexit option, instead of unsetting it in the subshell environment. This option is enabled when posix
3182 mode is enabled.
3183 interactive_comments
3184 If set, allow a word beginning with # to cause that word and all remaining characters on that line to be ignored in an interactive shell (see COMMENTS above).
3185 This option is enabled by default.
3186 lastpipe
3187 If set, and job control is not active, the shell runs the last command of a pipeline not executed in the background in the current shell environment.
3188 lithist If set, and the cmdhist option is enabled, multi-line commands are saved to the history with embedded newlines rather than using semicolon separators where possi‐
3189 ble.
3190 login_shell
3191 The shell sets this option if it is started as a login shell (see INVOCATION above). The value may not be changed.
3192 mailwarn
3193 If set, and a file that bash is checking for mail has been accessed since the last time it was checked, the message ``The mail in mailfile has been read'' is dis‐
3194 played.
3195 no_empty_cmd_completion
3196 If set, and readline is being used, bash will not attempt to search the PATH for possible completions when completion is attempted on an empty line.
3197 nocaseglob
3198 If set, bash matches filenames in a case-insensitive fashion when performing pathname expansion (see Pathname Expansion above).
3199 nocasematch
3200 If set, bash matches patterns in a case-insensitive fashion when performing matching while executing case or [[ conditional commands, when performing pattern sub‐
3201 stitution word expansions, or when filtering possible completions as part of programmable completion.
3202 nullglob
3203 If set, bash allows patterns which match no files (see Pathname Expansion above) to expand to a null string, rather than themselves.
3204 progcomp
3205 If set, the programmable completion facilities (see Programmable Completion above) are enabled. This option is enabled by default.
3206 promptvars
3207 If set, prompt strings undergo parameter expansion, command substitution, arithmetic expansion, and quote removal after being expanded as described in PROMPTING
3208 above. This option is enabled by default.
3209 restricted_shell
3210 The shell sets this option if it is started in restricted mode (see RESTRICTED SHELL below). The value may not be changed. This is not reset when the startup
3211 files are executed, allowing the startup files to discover whether or not a shell is restricted.
3212 shift_verbose
3213 If set, the shift builtin prints an error message when the shift count exceeds the number of positional parameters.
3214 sourcepath
3215 If set, the source (.) builtin uses the value of PATH to find the directory containing the file supplied as an argument. This option is enabled by default.
3216 xpg_echo
3217 If set, the echo builtin expands backslash-escape sequences by default.
3218
3219 suspend [-f]
3220 Suspend the execution of this shell until it receives a SIGCONT signal. A login shell cannot be suspended; the -f option can be used to override this and force the sus‐
3221 pension. The return status is 0 unless the shell is a login shell and -f is not supplied, or if job control is not enabled.
3222
3223 test expr
3224 [ expr ]
3225 Return a status of 0 (true) or 1 (false) depending on the evaluation of the conditional expression expr. Each operator and operand must be a separate argument. Expres‐
3226 sions are composed of the primaries described above under CONDITIONAL EXPRESSIONS. test does not accept any options, nor does it accept and ignore an argument of -- as
3227 signifying the end of options.
3228
3229 Expressions may be combined using the following operators, listed in decreasing order of precedence. The evaluation depends on the number of arguments; see below. Oper‐
3230 ator precedence is used when there are five or more arguments.
3231 ! expr True if expr is false.
3232 ( expr )
3233 Returns the value of expr. This may be used to override the normal precedence of operators.
3234 expr1 -a expr2
3235 True if both expr1 and expr2 are true.
3236 expr1 -o expr2
3237 True if either expr1 or expr2 is true.
3238
3239 test and [ evaluate conditional expressions using a set of rules based on the number of arguments.
3240
3241 0 arguments
3242 The expression is false.
3243 1 argument
3244 The expression is true if and only if the argument is not null.
3245 2 arguments
3246 If the first argument is !, the expression is true if and only if the second argument is null. If the first argument is one of the unary conditional operators
3247 listed above under CONDITIONAL EXPRESSIONS, the expression is true if the unary test is true. If the first argument is not a valid unary conditional operator, the
3248 expression is false.
3249 3 arguments
3250 The following conditions are applied in the order listed. If the second argument is one of the binary conditional operators listed above under CONDITIONAL EXPRES‐
3251 SIONS, the result of the expression is the result of the binary test using the first and third arguments as operands. The -a and -o operators are considered
3252 binary operators when there are three arguments. If the first argument is !, the value is the negation of the two-argument test using the second and third argu‐
3253 ments. If the first argument is exactly ( and the third argument is exactly ), the result is the one-argument test of the second argument. Otherwise, the expres‐
3254 sion is false.
3255 4 arguments
3256 If the first argument is !, the result is the negation of the three-argument expression composed of the remaining arguments. Otherwise, the expression is parsed
3257 and evaluated according to precedence using the rules listed above.
3258 5 or more arguments
3259 The expression is parsed and evaluated according to precedence using the rules listed above.
3260
3261 When used with test or [, the < and > operators sort lexicographically using ASCII ordering.
3262
3263 times Print the accumulated user and system times for the shell and for processes run from the shell. The return status is 0.
3264
3265 trap [-lp] [[arg] sigspec ...]
3266 The command arg is to be read and executed when the shell receives signal(s) sigspec. If arg is absent (and there is a single sigspec) or -, each specified signal is
3267 reset to its original disposition (the value it had upon entrance to the shell). If arg is the null string the signal specified by each sigspec is ignored by the shell
3268 and by the commands it invokes. If arg is not present and -p has been supplied, then the trap commands associated with each sigspec are displayed. If no arguments are
3269 supplied or if only -p is given, trap prints the list of commands associated with each signal. The -l option causes the shell to print a list of signal names and their
3270 corresponding numbers. Each sigspec is either a signal name defined in <signal.h>, or a signal number. Signal names are case insensitive and the SIG prefix is optional.
3271
3272 If a sigspec is EXIT (0) the command arg is executed on exit from the shell. If a sigspec is DEBUG, the command arg is executed before every simple command, for command,
3273 case command, select command, every arithmetic for command, and before the first command executes in a shell function (see SHELL GRAMMAR above). Refer to the description
3274 of the extdebug option to the shopt builtin for details of its effect on the DEBUG trap. If a sigspec is RETURN, the command arg is executed each time a shell function
3275 or a script executed with the . or source builtins finishes executing.
3276
3277 If a sigspec is ERR, the command arg is executed whenever a pipeline (which may consist of a single simple command), a list, or a compound command returns a non-zero exit
3278 status, subject to the following conditions. The ERR trap is not executed if the failed command is part of the command list immediately following a while or until key‐
3279 word, part of the test in an if statement, part of a command executed in a && or || list except the command following the final && or ||, any command in a pipeline but
3280 the last, or if the command's return value is being inverted using !. These are the same conditions obeyed by the errexit (-e) option.
3281
3282 Signals ignored upon entry to the shell cannot be trapped or reset. Trapped signals that are not being ignored are reset to their original values in a subshell or sub‐
3283 shell environment when one is created. The return status is false if any sigspec is invalid; otherwise trap returns true.
3284
3285 type [-aftpP] name [name ...]
3286 With no options, indicate how each name would be interpreted if used as a command name. If the -t option is used, type prints a string which is one of alias, keyword,
3287 function, builtin, or file if name is an alias, shell reserved word, function, builtin, or disk file, respectively. If the name is not found, then nothing is printed,
3288 and an exit status of false is returned. If the -p option is used, type either returns the name of the disk file that would be executed if name were specified as a com‐
3289 mand name, or nothing if ``type -t name'' would not return file. The -P option forces a PATH search for each name, even if ``type -t name'' would not return file. If a
3290 command is hashed, -p and -P print the hashed value, which is not necessarily the file that appears first in PATH. If the -a option is used, type prints all of the
3291 places that contain an executable named name. This includes aliases and functions, if and only if the -p option is not also used. The table of hashed commands is not
3292 consulted when using -a. The -f option suppresses shell function lookup, as with the command builtin. type returns true if all of the arguments are found, false if any
3293 are not found.
3294
3295 ulimit [-HSabcdefiklmnpqrstuvxPT [limit]]
3296 Provides control over the resources available to the shell and to processes started by it, on systems that allow such control. The -H and -S options specify that the
3297 hard or soft limit is set for the given resource. A hard limit cannot be increased by a non-root user once it is set; a soft limit may be increased up to the value of
3298 the hard limit. If neither -H nor -S is specified, both the soft and hard limits are set. The value of limit can be a number in the unit specified for the resource or
3299 one of the special values hard, soft, or unlimited, which stand for the current hard limit, the current soft limit, and no limit, respectively. If limit is omitted, the
3300 current value of the soft limit of the resource is printed, unless the -H option is given. When more than one resource is specified, the limit name and unit are printed
3301 before the value. Other options are interpreted as follows:
3302 -a All current limits are reported
3303 -b The maximum socket buffer size
3304 -c The maximum size of core files created
3305 -d The maximum size of a process's data segment
3306 -e The maximum scheduling priority ("nice")
3307 -f The maximum size of files written by the shell and its children
3308 -i The maximum number of pending signals
3309 -k The maximum number of kqueues that may be allocated
3310 -l The maximum size that may be locked into memory
3311 -m The maximum resident set size (many systems do not honor this limit)
3312 -n The maximum number of open file descriptors (most systems do not allow this value to be set)
3313 -p The pipe size in 512-byte blocks (this may not be set)
3314 -q The maximum number of bytes in POSIX message queues
3315 -r The maximum real-time scheduling priority
3316 -s The maximum stack size
3317 -t The maximum amount of cpu time in seconds
3318 -u The maximum number of processes available to a single user
3319 -v The maximum amount of virtual memory available to the shell and, on some systems, to its children
3320 -x The maximum number of file locks
3321 -P The maximum number of pseudoterminals
3322 -T The maximum number of threads
3323
3324 If limit is given, and the -a option is not used, limit is the new value of the specified resource. If no option is given, then -f is assumed. Values are in 1024-byte
3325 increments, except for -t, which is in seconds; -p, which is in units of 512-byte blocks; -P, -T, -b, -k, -n, and -u, which are unscaled values; and, when in Posix mode,
3326 -c and -f, which are in 512-byte increments. The return status is 0 unless an invalid option or argument is supplied, or an error occurs while setting a new limit.
3327
3328 umask [-p] [-S] [mode]
3329 The user file-creation mask is set to mode. If mode begins with a digit, it is interpreted as an octal number; otherwise it is interpreted as a symbolic mode mask simi‐
3330 lar to that accepted by chmod(1). If mode is omitted, the current value of the mask is printed. The -S option causes the mask to be printed in symbolic form; the
3331 default output is an octal number. If the -p option is supplied, and mode is omitted, the output is in a form that may be reused as input. The return status is 0 if the
3332 mode was successfully changed or if no mode argument was supplied, and false otherwise.
3333
3334 unalias [-a] [name ...]
3335 Remove each name from the list of defined aliases. If -a is supplied, all alias definitions are removed. The return value is true unless a supplied name is not a
3336 defined alias.
3337
3338 unset [-fv] [-n] [name ...]
3339 For each name, remove the corresponding variable or function. If the -v option is given, each name refers to a shell variable, and that variable is removed. Read-only
3340 variables may not be unset. If -f is specified, each name refers to a shell function, and the function definition is removed. If the -n option is supplied, and name is
3341 a variable with the nameref attribute, name will be unset rather than the variable it references. -n has no effect if the -f option is supplied. If no options are sup‐
3342 plied, each name refers to a variable; if there is no variable by that name, any function with that name is unset. Each unset variable or function is removed from the
3343 environment passed to subsequent commands. If any of COMP_WORDBREAKS, RANDOM, SECONDS, LINENO, HISTCMD, FUNCNAME, GROUPS, or DIRSTACK are unset, they lose their special
3344 properties, even if they are subsequently reset. The exit status is true unless a name is readonly.
3345
3346 wait [-n] [n ...]
3347 Wait for each specified child process and return its termination status. Each n may be a process ID or a job specification; if a job spec is given, all processes in that
3348 job's pipeline are waited for. If n is not given, all currently active child processes are waited for, and the return status is zero. If the -n option is supplied, wait
3349 waits for any job to terminate and returns its exit status. If n specifies a non-existent process or job, the return status is 127. Otherwise, the return status is the
3350 exit status of the last process or job waited for.
3351
3352RESTRICTED SHELL
3353 If bash is started with the name rbash, or the -r option is supplied at invocation, the shell becomes restricted. A restricted shell is used to set up an environment more con‐
3354 trolled than the standard shell. It behaves identically to bash with the exception that the following are disallowed or not performed:
3355
3356 · changing directories with cd
3357
3358 · setting or unsetting the values of SHELL, PATH, ENV, or BASH_ENV
3359
3360 · specifying command names containing /
3361
3362 · specifying a filename containing a / as an argument to the . builtin command
3363
3364 · specifying a filename containing a slash as an argument to the -p option to the hash builtin command
3365
3366 · importing function definitions from the shell environment at startup
3367
3368 · parsing the value of SHELLOPTS from the shell environment at startup
3369
3370 · redirecting output using the >, >|, <>, >&, &>, and >> redirection operators
3371
3372 · using the exec builtin command to replace the shell with another command
3373
3374 · adding or deleting builtin commands with the -f and -d options to the enable builtin command
3375
3376 · using the enable builtin command to enable disabled shell builtins
3377
3378 · specifying the -p option to the command builtin command
3379
3380 · turning off restricted mode with set +r or set +o restricted.
3381
3382 These restrictions are enforced after any startup files are read.
3383
3384 When a command that is found to be a shell script is executed (see COMMAND EXECUTION above), rbash turns off any restrictions in the shell spawned to execute the script.
3385
3386SEE ALSO
3387 Bash Reference Manual, Brian Fox and Chet Ramey
3388 The Gnu Readline Library, Brian Fox and Chet Ramey
3389 The Gnu History Library, Brian Fox and Chet Ramey
3390 Portable Operating System Interface (POSIX) Part 2: Shell and Utilities, IEEE --
3391 http://pubs.opengroup.org/onlinepubs/9699919799/
3392 http://tiswww.case.edu/~chet/bash/POSIX -- a description of posix mode
3393 sh(1), ksh(1), csh(1)
3394 emacs(1), vi(1)
3395 readline(3)
3396
3397FILES
3398 /bin/bash
3399 The bash executable
3400 /etc/profile
3401 The systemwide initialization file, executed for login shells
3402 /etc/bash.bashrc
3403 The systemwide per-interactive-shell startup file
3404 /etc/bash.bash.logout
3405 The systemwide login shell cleanup file, executed when a login shell exits
3406 ~/.bash_profile
3407 The personal initialization file, executed for login shells
3408 ~/.bashrc
3409 The individual per-interactive-shell startup file
3410 ~/.bash_logout
3411 The individual login shell cleanup file, executed when a login shell exits
3412 ~/.inputrc
3413 Individual readline initialization file
3414
3415AUTHORS
3416 Brian Fox, Free Software Foundation
3417 bfox@gnu.org
3418
3419 Chet Ramey, Case Western Reserve University
3420 chet.ramey@case.edu
3421
3422BUG REPORTS
3423 If you find a bug in bash, you should report it. But first, you should make sure that it really is a bug, and that it appears in the latest version of bash. The latest version
3424 is always available from ftp://ftp.gnu.org/pub/gnu/bash/.
3425
3426 Once you have determined that a bug actually exists, use the bashbug command to submit a bug report. If you have a fix, you are encouraged to mail that as well! Suggestions
3427 and `philosophical' bug reports may be mailed to bug-bash@gnu.org or posted to the Usenet newsgroup gnu.bash.bug.
3428
3429 ALL bug reports should include:
3430
3431 The version number of bash
3432 The hardware and operating system
3433 The compiler used to compile
3434 A description of the bug behaviour
3435 A short script or `recipe' which exercises the bug
3436
3437 bashbug inserts the first three items automatically into the template it provides for filing a bug report.
3438
3439 Comments and bug reports concerning this manual page should be directed to chet.ramey@case.edu.
3440
3441BUGS
3442 It's too big and too slow.
3443
3444 There are some subtle differences between bash and traditional versions of sh, mostly because of the POSIX specification.
3445
3446 Aliases are confusing in some uses.
3447
3448 Shell builtin commands and functions are not stoppable/restartable.
3449
3450 Compound commands and command sequences of the form `a ; b ; c' are not handled gracefully when process suspension is attempted. When a process is stopped, the shell immedi‐
3451 ately executes the next command in the sequence. It suffices to place the sequence of commands between parentheses to force it into a subshell, which may be stopped as a unit.
3452
3453 Array variables may not (yet) be exported.
3454
3455 There may be only one active coprocess at a time.
3456
3457GNU Bash 4.4 2016 August 26 BASH(1)