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BASH_BUILTINS(1) BASH_BUILTINS(1)
NAME
bash, :, ., [, alias, bg, bind, break, builtin, cd, command, compgen, complete,
continue, declare, dirs, disown, echo, enable, eval, exec, exit, export, fc, fg,
getopts, hash, help, history, jobs, kill, let, local, logout, popd, printf, pushd,
pwd, read, readonly, return, set, shift, shopt, source, suspend, test, times, trap,
type, typeset, ulimit, umask, unalias, unset, wait - bash built-in commands, see
bash(1)
BASH BUILTIN COMMANDS
Unless otherwise noted, each builtin command documented in this section as accept-
ing options preceded by - accepts -- to signify the end of the options.
: [arguments]
No effect; the command does nothing beyond expanding arguments and perform-
ing any specified redirections. A zero exit code is returned.
. filename [arguments]
source filename [arguments]
Read and execute commands from filename in the current shell environment and
return the exit status of the last command executed from filename. If file-
name does not contain a slash, file names 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 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 any arguments
are supplied, they become the positional parameters when filename is exe-
cuted. Otherwise the positional parameters are unchanged. The return sta-
tus is the status of the last command exited within the script (0 if no com-
mands are executed), and false if filename is not found or cannot be read.
alias [-p] [name[=value] ...]
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 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 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 been defined.
bg [jobspec]
Resume the suspended job jobspec in the background, as if it had been
started with &. If jobspec is not present, the shell’s notion of the cur-
rent job is used. bg jobspec returns 0 unless run when job control is dis-
abled or, when run with job control enabled, if jobspec was not found or
started without job control.
bind [-m keymap] [-lpsvPSV]
bind [-m keymap] [-q function] [-u function] [-r keyseq]
bind [-m keymap] -f filename
bind [-m keymap] -x keyseq:shell-command
bind [-m keymap] keyseq:function-name
bind readline-command
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 command 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 the following meanings:
-m keymap
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, vi-command, and vi-insert. vi is equivalent
to vi-command; emacs is equivalent to emacs-standard.
-l List the names of all readline functions.
-p Display readline function names and bindings in such a way that they
can be re-read.
-P List current readline function names and bindings.
-v Display readline variable names and values in such a way that they
can be re-read.
-V List current readline variable names and values.
-s Display readline key sequences bound to macros and the strings they
output in such a way that they can be re-read.
-S Display readline key sequences bound to macros and the strings they
output.
-f filename
Read key bindings from filename.
-q function
Query about which keys invoke the named function.
-u function
Unbind all keys bound to the named function.
-r keyseq
Remove any current binding for keyseq.
-x keyseq:shell-command
Cause shell-command to be executed whenever keyseq is entered.
The return value is 0 unless an unrecognized option is given or an error
occurred.
break [n]
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 enclos-
ing loops, all enclosing loops are exited. The return value is 0 unless the
shell is not executing a loop when break is executed.
builtin shell-builtin [arguments]
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, 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 shell builtin command.
cd [-L|-P] [dir]
Change the current directory to dir. The variable HOME is the default dir.
The variable CDPATH defines the search path for the directory containing
dir. Alternative directory names in CDPATH 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 used. The -P
option says to use the physical directory structure instead of following
symbolic links (see also the -P option to the set builtin command); the -L
option forces symbolic links to be followed. An argument of - is equivalent
to $OLDPWD. 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 working directory is written to the standard output.
The return value is true if the directory was successfully changed; false
otherwise.
caller [expr]
Returns the context of any active subroutine call (a shell function or a
script executed with the . or source builtins. Without expr, caller dis-
plays the line number and source filename of the current subroutine call.
If a non-negative integer is supplied as expr, caller displays the line num-
ber, subroutine name, and source file corresponding to that position in the
current execution call stack. This extra information may be used, for exam-
ple, to print a stack trace. The current frame is frame 0. 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.
command [-pVv] command [arg ...]
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 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 description of command is printed.
The -v option causes a single word indicating the command or file name used
to invoke command to be displayed; the -V option produces a 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
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.
compgen [option] [word]
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 write the matches to the standard output. When using the
-F or -C options, the various shell variables set by the programmable com-
pletion facilities, while available, will not have useful values.
The matches will be generated in the same way as if the programmable comple-
tion code had generated them directly from a completion specification with
the same flags. If word is specified, only those completions matching word
will be displayed.
The return value is true unless an invalid option is supplied, or no matches
were generated.
complete [-abcdefgjksuv] [-o comp-option] [-A action] [-G globpat] [-W wordlist]
[-P prefix] [-S suffix]
[-X filterpat] [-F function] [-C command] name [name ...]
complete -pr [name ...]
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 way that allows them to be reused as input. The -r option
removes a completion specification for each name, or, if no names are sup-
plied, all completion specifications.
The process of applying these completion specifications when word completion
is attempted is described above under Programmable Completion.
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 protect them from expansion before the complete builtin is
invoked.
-o comp-option
The comp-option controls several aspects of the compspec’s behavior
beyond the simple generation of completions. comp-option may be one
of:
bashdefault
Perform the rest of the default bash completions if the
compspec generates no matches.
default Use readline’s default filename completion if the compspec
generates no matches.
dirnames
Perform directory name completion if the compspec generates
no matches.
filenames
Tell readline that the compspec generates filenames, so it
can perform any filename-specific processing (like adding a
slash to directory names or suppressing trailing spaces).
Intended to be used with shell functions.
nospace Tell readline not to append a space (the default) to words
completed at the end of the line.
-A action
The action may be one of the following to generate a list of possi-
ble completions:
alias Alias names. May also be specified as -a.
arrayvar
Array variable names.
binding Readline key binding names.
builtin Names of shell builtin commands. May also be specified as
-b.
command Command names. May also be specified as -c.
directory
Directory names. May also be specified as -d.
disabled
Names of disabled shell builtins.
enabled Names of enabled shell builtins.
export Names of exported shell variables. May also be specified as
-e.
file File names. May also be specified as -f.
function
Names of shell functions.
group Group names. May also be specified as -g.
helptopic
Help topics as accepted by the help builtin.
hostname
Hostnames, as taken from the file specified by the HOSTFILE
shell variable.
job Job names, if job control is active. May also be specified
as -j.
keyword Shell reserved words. May also be specified as -k.
running Names of running jobs, if job control is active.
service Service names. May also be specified as -s.
setopt Valid arguments for the -o option to the set builtin.
shopt Shell option names as accepted by the shopt builtin.
signal Signal names.
stopped Names of stopped jobs, if job control is active.
user User names. May also be specified as -u.
variable
Names of all shell variables. May also be specified as -v.
-G globpat
The filename expansion pattern globpat is expanded to generate the
possible completions.
-W wordlist
The wordlist is split using the characters in the IFS special vari-
able as delimiters, and each resultant word is expanded. The possi-
ble completions are the members of the resultant list which match
the word being completed.
-C command
command is executed in a subshell environment, and its output is
used as the possible completions.
-F function
The shell function function is executed in the current shell envi-
ronment. When it finishes, the possible completions are retrieved
from the value of the COMPREPLY array variable.
-X filterpat
filterpat is a pattern as used for filename expansion. It is
applied to the list of possible completions generated by the preced-
ing options and arguments, and each completion matching filterpat is
removed from the list. A leading ! in filterpat negates the pat-
tern; in this case, any completion not matching filterpat is
removed.
-P prefix
prefix is added at the beginning of each possible completion after
all other options have been applied.
-S suffix
suffix is appended to each possible completion after all other
options have been applied.
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 completion specification for a name for which no specification
exists, or an error occurs adding a completion specification.
continue [n]
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 the number of enclosing loops, the last enclosing loop
(the ‘‘top-level’’ loop) is resumed. The return value is 0 unless the shell
is not executing a loop when continue is executed.
declare [-afFirtx] [-p] [name[=value] ...]
typeset [-afFirtx] [-p] [name[=value] ...]
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 name. When -p is used, additional options are ignored.
The -F option inhibits the display of function definitions; only the func-
tion name and attributes are printed. If the extdebug shell option is
enabled using shopt, the source file name and line number where the function
is defined are displayed as well. The -F option implies -f. The following
options can be used to restrict output to variables with the specified
attribute or to give variables attributes:
-a Each name is an array variable (see Arrays above).
-f Use function names only.
-i The variable is treated as an integer; arithmetic evaluation (see
ARITHMETIC EVALUATION ) is performed when the variable is assigned a
value.
-r Make names readonly. These names cannot then be assigned values by
subsequent assignment statements or unset.
-t Give each name the trace attribute. Traced functions inherit the
DEBUG trap from the calling shell. The trace attribute has no spe-
cial meaning for variables.
-x Mark names for export to subsequent commands via the environment.
Using ‘+’ instead of ‘-’ turns off the attribute instead, with the exception
that +a may not be used to destroy an array variable. When used in a func-
tion, makes each name local, as with the local command. If a variable name
is followed by =value, the value of the variable is set to value. The
return value is 0 unless an invalid option is encountered, an attempt is
made to define a function using ‘‘-f 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 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
to turn off array status for an array variable, or an attempt is made to
display a non-existent function with -f.
dirs [-clpv] [+n] [-n]
Without options, displays the list of currently remembered directories. The
default display is on a single line with directory names separated by
spaces. Directories are added to the list with the pushd command; the popd
command removes entries from the list.
+n Displays the nth entry counting from the left of the list shown by
dirs when invoked without options, starting with zero.
-n Displays the nth entry counting from the right of the list shown by
dirs when invoked without options, starting with zero.
-c Clears the directory stack by deleting all of the entries.
-l Produces a longer listing; the default listing format uses a tilde to
denote the home directory.
-p Print the directory stack with one entry per line.
-v Print the directory stack with one entry per line, prefixing each
entry with its index in the stack.
The return value is 0 unless an invalid option is supplied or n indexes
beyond the end of the directory stack.
disown [-ar] [-h] [jobspec ...]
Without options, each jobspec is removed from the table of active jobs. 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 is present, and neither the -a nor the -r option is supplied,
the current job is used. If no jobspec 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 jobspec does not
specify a valid job.
echo [-neE] [arg ...]
Output the args, separated by spaces, followed by a newline. The return
status is always 0. If -n is specified, the trailing newline is suppressed.
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, 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 by default. echo does not inter-
pret -- to mean the end of options. echo interprets the following escape
sequences:
\a alert (bell)
\b backspace
\c suppress trailing newline
\e an escape character
\f form feed
\n new line
\r carriage return
\t horizontal tab
\v vertical tab
\\ backslash
\0nnn the eight-bit character whose value is the octal value nnn (zero to
three octal digits)
\nnn the eight-bit character whose value is the octal value nnn (one to
three octal digits)
\xHH the eight-bit character whose value is the hexadecimal value HH (one
or two hex digits)
enable [-adnps] [-f filename] [name ...]
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 with-
out specifying a full pathname, even though the shell normally searches for
builtins before disk commands. If -n is used, each name is disabled; other-
wise, names are enabled. For example, to 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 object file-
name, 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 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 disabled 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 output 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 object.
eval [arg ...]
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 eval. If there are no args, or only null argu-
ments, eval returns 0.
exec [-cl] [-a name] [command [arguments]]
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 sup-
plied, the shell places a dash at the beginning of the zeroth arg passed to
command. This is what login(1) does. The -c option causes command to be
executed with an empty environment. 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 exits, unless the shell
option execfail is enabled, in which case it returns failure. An interac-
tive shell returns failure if the file cannot be executed. If command 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.
exit [n]
Cause the shell to exit with a status of n. If n is omitted, the exit sta-
tus is that of the last command executed. A trap on EXIT is executed before
the shell terminates.
export [-fn] [name[=word]] ...
export -p
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 names are given, or if the -p option is supplied, a
list of all names that are exported in this shell is printed. The -n option
causes the export property to be removed from each 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 of
the names is not a valid shell variable name, or -f is supplied with a name
that is not a function.
fc [-e ename] [-nlr] [first] [last]
fc -s [pat=rep] [cmd]
Fix Command. In the first form, a range of commands from first to last is
selected from the history list. First and last may be specified as a 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 current 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 com-
mands) and to first otherwise. If first is not specified it is set to the
previous command for editing and -16 for listing.
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 standard 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 the value of EDITOR if FCEDIT is
not set. If neither variable is set, is used. When editing is complete,
the edited commands are echoed and executed.
In the second form, command is re-executed after each instance of pat is
replaced by rep. A useful alias to use with this is ‘‘r="fc -s"’’, so that
typing ‘‘r cc’’ runs the last command beginning with ‘‘cc’’ and typing ‘‘r’’
re-executes the last command.
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 supplied, the return value is the value of the last command exe-
cuted or failure if an error occurs with the temporary file of commands. If
the second form is used, the return status is that of the command re-exe-
cuted, unless cmd does not specify a valid history line, in which case fc
returns failure.
fg [jobspec]
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 command placed into the foreground, or failure if run
when job control is disabled or, when run with job control enabled, if job-
spec does not specify a valid job or jobspec specifies a job that was
started without job control.
getopts optstring name [args]
getopts is used by shell procedures to parse positional parameters. opt-
string contains the option characters to be recognized; if a character is
followed by a colon, the 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. 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 processed
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 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 invocation if a new set of parameters is to be
used.
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 argu-
ment, and name is set to ?.
getopts normally parses the positional parameters, but if more arguments are
given in args, getopts parses those instead.
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 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 character of optstring is not a colon.
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 is placed in OPTARG and no diagnostic message is printed.
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 is silent, then a colon (:) is placed in name and
OPTARG is set to the option character found.
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.
hash [-lr] [-p filename] [-dt] [name]
For each name, the full file name of the command is determined by searching
the directories in $PATH and remembered. If the -p option is supplied, no
path search is performed, and filename is used as the full file name of the
command. The -r option causes the shell to 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 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 be displayed in a format that may be reused as input. If no argu-
ments are given, or if only -l is supplied, information about remembered
commands is printed. The return status is true unless a name is not found
or an invalid option is supplied.
help [-s] [pattern]
Display helpful information about builtin commands. If pattern is speci-
fied, help gives detailed help on all commands matching pattern; otherwise
help for all the builtins and shell control structures is printed. The -s
option restricts the information displayed to a short usage synopsis. The
return status is 0 unless no command matches pattern.
history [n]
history -c
history -d offset
history -anrw [filename]
history -p arg [arg ...]
history -s arg [arg ...]
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 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. 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 value of HISTFILE is used.
Options, if supplied, have the following meanings:
-c Clear the history list by deleting all the entries.
-d offset
Delete the history entry at position offset.
-a Append the ‘‘new’’ history lines (history lines entered since the
beginning of the current bash session) to the history file.
-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 the current bash session.
-r Read the contents of the history file and use them as the current
history.
-w Write the current history to the history file, overwriting the his-
tory file’s contents.
-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 be quoted to disable normal history
expansion.
-s Store the args in the history list as a single entry. The last com-
mand in the history list is removed before the args are added.
If the HISTTIMEFORMAT is set, the time stamp information associated with
each history entry is written to the history file. 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 an argument to
-d, or the history expansion supplied as an argument to -p fails.
jobs [-lnprs] [ jobspec ... ]
jobs -x command [ args ... ]
The first form lists the active jobs. The options have the following mean-
ings:
-l List process IDs in addition to the normal information.
-p List only the process ID of the job’s process group leader.
-n Display information only about jobs that have changed status since
the user was last notified of their status.
-r Restrict output to running jobs.
-s Restrict output to stopped jobs.
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 supplied.
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 its exit status.
kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...
kill -l [sigspec | exit_status]
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 the SIG prefix) or a signal number; signum is a signal num-
ber. If sigspec is not present, then SIGTERM is assumed. An argument of -l
lists the signal names. If any 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 is a number specifying
either a signal number or the exit status of a process terminated by a sig-
nal. kill returns true if at least one signal was successfully sent, or
false if an error occurs or an invalid option is encountered.
let arg [arg ...]
Each arg is an arithmetic expression to be evaluated (see ARITHMETIC EVALUA-
TION). If the last arg evaluates to 0, let returns 1; 0 is returned other-
wise.
local [option] [name[=value] ...]
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 function, it causes the variable name to have a visi-
ble scope restricted to that function and its children. With 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 is used outside a function, an invalid name is supplied, or
name is a readonly variable.
logout Exit a login shell.
popd [-n] [+n] [-n]
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 supplied, have the following meanings:
+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 second.
-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 next to last.
-n Suppresses the normal change of directory when removing directories
from the stack, so that only the stack is manipulated.
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 is empty, a non-existent directory stack entry is speci-
fied, or the directory change fails.
printf format [arguments]
Write the formatted arguments to the standard output under the control of
the format. The format is a character string which contains three types of
objects: plain characters, which are simply copied to standard output, char-
acter escape sequences, which are converted and copied to the standard out-
put, and format specifications, each of which causes printing of the next
successive argument. In addition to the standard printf(1) formats, %b
causes printf to expand backslash escape sequences in the corresponding
argument (except that \c terminates output, backslashes in \â€â€™, \", and \?
are not removed, and octal escapes beginning with \0 may contain up to four
digits), and %q causes printf to output the corresponding argument in a for-
mat that can be reused as shell input.
The format is reused as necessary to consume all of the arguments. If the
format requires more arguments than are supplied, the extra format specifi-
cations behave as if a zero value or null string, as appropriate, had been
supplied. The return value is zero on success, non-zero on failure.
pushd [-n] [dir]
pushd [-n] [+n] [-n]
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, exchanges the top two directories and returns 0, unless the
directory stack is empty. Arguments, if supplied, have the following mean-
ings:
+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.
-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.
-n Suppresses the normal change of directory when adding directories to
the stack, so that only the stack is manipulated.
dir Adds dir to the directory stack at the top, making it the new current
working directory.
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 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.
pwd [-LP]
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 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 reading the name of the current directory or
an invalid option is supplied.
read [-ers] [-u fd] [-t timeout] [-a aname] [-p prompt] [-n nchars] [-d delim]
[name ...]
One line is read from the standard input, or from the file descriptor fd
supplied as an argument to the -u option, and the first word is assigned to
the first name, the second word to the second name, and so on, with leftover
words and their intervening separators 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 characters in IFS are used to split the line
into words. The backslash character (\) may be used to remove any special
meaning for the next character read and for line continuation. Options, if
supplied, have the following meanings:
-a aname
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 are ignored.
-d delim
The first character of delim is used to terminate the input line,
rather than newline.
-e If the standard input is coming from a terminal, readline (see READ-
LINE above) is used to obtain the line.
-n nchars
read returns after reading nchars characters rather than waiting for
a complete line of input.
-p prompt
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 terminal.
-r Backslash does not act as an escape character. The backslash is con-
sidered to be part of the line. In particular, a backslash-newline
pair may not be used as a line continuation.
-s Silent mode. If input is coming from a terminal, characters are not
echoed.
-t timeout
Cause read to time out and return failure if a complete line of input
is not read within timeout seconds. This option has no effect if
read is not reading input from the terminal or a pipe.
-u fd Read input from file descriptor fd.
If no names are supplied, the line read is assigned to the variable REPLY.
The return code is zero, unless end-of-file is encountered, read times out,
or an invalid file descriptor is supplied as the argument to -u.
readonly [-apf] [name[=word] ...]
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 func-
tions corresponding to the names are so marked. The -a option restricts the
variables to arrays. If no name arguments are given, or if the -p option is
supplied, a list of all readonly names is printed. The -p option causes
output to be displayed in a format that may be reused as input. If a vari-
able name is 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 variable name, or -f is supplied with a name that
is not a function.
return [n]
Causes a function to exit with the return value specified by n. If n is
omitted, the return status is that of the last command executed in the func-
tion body. If used 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 of the last command executed within
the script as the exit status of the script. If used outside a function and
not during execution of a script by ., the return status is false. Any com-
mand associated with the RETURN trap is executed before execution resumes
after the function or script.
set [--abefhkmnptuvxBCHP] [-o option] [arg ...]
Without options, the name and value of each shell variable are displayed in
a format that can be reused as input. The output is sorted according to the
current locale. When options are specified, they set or unset shell
attributes. Any arguments remaining after the options are processed are
treated as values for the positional parameters and are assigned, in order,
to $1, $2, ... $n. Options, if specified, have the following meanings:
-a Automatically mark variables and functions which are modified or
created for export to the environment of subsequent commands.
-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.
-e Exit immediately if a simple command (see SHELL GRAMMAR above) exits
with a non-zero status. 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 in an if statement, part of a && or
â”│â”│ list, or if the command’s return value is being inverted via !.
A trap on ERR, if set, is executed before the shell exits.
-f Disable pathname expansion.
-h Remember the location of commands as they are looked up for execu-
tion. This is enabled by default.
-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.
-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). Background processes run in a separate process group and a
line containing their exit status is printed upon their completion.
-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.
-o option-name
The option-name can be one of the following:
allexport
Same as -a.
braceexpand
Same as -B.
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 --noediting option.
errtrace
Same as -E.
functrace
Same as -T.
errexit Same as -e.
hashall Same as -h.
histexpand
Same as -H.
history Enable command history, as described above under HISTORY.
This option is on by default in interactive shells.
ignoreeof
The effect is as if the shell command ‘‘IGNOREEOF=10’’ had
been executed (see Shell Variables above).
keyword Same as -k.
monitor Same as -m.
noclobber
Same as -C.
noexec Same as -n.
noglob Same as -f. nolog Currently ignored.
notify Same as -b.
nounset Same as -u.
onecmd Same as -t.
physical
Same as -P.
pipefail
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 pipeline exit successfully.
This option is disabled by default.
posix Change the behavior of bash where the default operation dif-
fers from the POSIX 1003.2 standard to match the standard
(‘posix mode).
privileged
Same as -p.
verbose Same as -v.
vi Use a vi-style command line editing interface.
xtrace Same as -x.
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 the current option settings is
displayed on the standard output.
-p Turn on privileged mode. In this mode, the $ENV and $BASH_ENV files
are not processed, shell functions are not inherited from the envi-
ronment, and the SHELLOPTS variable, if it appears in the environ-
ment, is ignored. 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, these actions are taken and the effective user id
is set to the real user id. If the -p option is 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 ids.
-t Exit after reading and executing one command.
-u Treat unset variables as an error when performing parameter expan-
sion. If expansion is attempted on an unset variable, the shell
prints an error message, and, if not interactive, exits with a non-
zero status.
-v Print shell input lines as they are read.
-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 command and its expanded arguments or
associated word list.
-B The shell performs brace expansion (see Brace Expansion above).
This is on by default.
-C If set, bash does not overwrite an existing file with the >, >&, and
<> redirection operators. This may be overridden when creating out-
put files by using the redirection operator >| instead of >.
-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 inherited in such cases.
-H Enable ! style history substitution. This option is on by default
when the shell is interactive.
-P If set, the shell does not follow symbolic links when executing com-
mands such as cd that change the current working directory. It uses
the physical directory structure instead. By default, bash follows
the logical chain of directories when performing commands which
change the current directory.
-T If set, any trap on DEBUG is inherited by shell functions, command
substitutions, and commands executed in a subshell environment. The
DEBUG trap is normally not inherited in such cases.
-- 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 begin with a -.
- 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 positional parameters remain unchanged.
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 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.
shift [n]
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 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 changed. The return status is greater
than zero if n is greater than $# or less than zero; otherwise 0.
shopt [-pqsu] [-o] [optname ...]
Toggle the values of variables controlling optional shell behavior. 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 set. The -p option causes out-
put to be displayed in a form that may be reused as input. Other options
have the following meanings:
-s Enable (set) each optname.
-u Disable (unset) each optname.
-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 return status is zero if all optnames are
enabled; non-zero otherwise.
-o Restricts the values of optname to be those defined for the -o option
to the set builtin.
If either -s or -u is used with no optname arguments, the display is limited
to those options which are set or unset, respectively. Unless otherwise
noted, the shopt options are disabled (unset) by default.
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 optname is not a valid shell option.
The list of shopt options is:
cdable_vars
If set, an argument to the cd builtin command that is not a direc-
tory is assumed to be the name of a variable whose value is the
directory to change to.
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 character, and one character too many. If a
correction is found, the corrected file name is printed, and the
command proceeds. This option is only used by interactive shells.
checkhash
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 performed.
checkwinsize
If set, bash checks the window size after each command and, if nec-
essary, updates the values of LINES and COLUMNS.
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.
dotglob If set, bash includes filenames beginning with a ‘.’ in the results
of pathname expansion.
execfail
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 exit if exec fails.
expand_aliases
If set, aliases are expanded as described above under ALIASES. This
option is enabled by default for interactive shells.
extdebug
If set, behavior intended for use by debuggers is enabled:
1. The -F option to the declare builtin displays the source file
name and line number corresponding to each function name sup-
plied as an argument.
2. If the command run by the DEBUG trap returns a non-zero
value, the next command is skipped and not executed.
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 . or source builtins), a
call to return is simulated.
extglob If set, the extended pattern matching features described above under
Pathname Expansion are enabled.
extquote
If set, $’string’ and $"string" quoting is performed within ${param-
eter} expansions enclosed in double quotes. This option is enabled
by default.
failglob
If set, patterns which fail to match filenames during pathname
expansion result in an expansion error.
force_fignore
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 possible completions. See SHELL VARI-
ABLES above for a description of FIGNORE. This option is enabled by
default.
gnu_errfmt
If set, shell error messages are written in the standard GNU error
message format.
histappend
If set, the history list is appended to the file named by the value
of the HISTFILE variable when the shell exits, rather than overwrit-
ing the file.
histreedit
If set, and readline is being used, a user is given the opportunity
to re-edit a failed history substitution.
histverify
If set, and readline is being used, the results of history substitu-
tion are not immediately passed to the shell parser. Instead, the
resulting line is loaded into the readline editing buffer, allowing
further modification.
hostcomplete
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 above). This is enabled by default.
huponexit
If set, bash will send SIGHUP to all jobs when an interactive login
shell exits.
interactive_comments
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). This option is enabled by default.
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 possible.
login_shell
The shell sets this option if it is started as a login shell (see
INVOCATION above). The value may not be changed.
mailwarn
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 mail-
file has been read’’ is displayed.
no_empty_cmd_completion
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.
nocaseglob
If set, bash matches filenames in a case-insensitive fashion when
performing pathname expansion (see Pathname Expansion above).
nullglob
If set, bash allows patterns which match no files (see Pathname
Expansion above) to expand to a null string, rather than themselves.
progcomp
If set, the programmable completion facilities (see Programmable
Completion above) are enabled. This option is enabled by default.
promptvars
If set, prompt strings undergo parameter expansion, command substi-
tution, arithmetic expansion, and quote removal after being expanded
as described in PROMPTING above. This option is enabled by default.
restricted_shell
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 files are executed, allowing the startup
files to discover whether or not a shell is restricted.
shift_verbose
If set, the shift builtin prints an error message when the shift
count exceeds the number of positional parameters.
sourcepath
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.
xpg_echo
If set, the echo builtin expands backslash-escape sequences by
default.
suspend [-f]
Suspend the execution of this shell until it receives a SIGCONT signal. The
-f option says not to complain if this is a login shell; just suspend any-
way. The return status is 0 unless the shell is a login shell and -f is not
supplied, or if job control is not enabled.
test expr
[ expr ]
Return a status of 0 or 1 depending on the evaluation of the conditional
expression expr. Each operator and operand must be a separate argument.
Expressions are composed of the primaries described above under CONDITIONAL
EXPRESSIONS.
Expressions may be combined using the following operators, listed in
decreasing order of precedence.
! expr True if expr is false.
( expr )
Returns the value of expr. This may be used to override the normal
precedence of operators.
expr1 -a expr2
True if both expr1 and expr2 are true.
expr1 -o expr2
True if either expr1 or expr2 is true.
test and [ evaluate conditional expressions using a set of rules based on
the number of arguments.
0 arguments
The expression is false.
1 argument
The expression is true if and only if the argument is not null.
2 arguments
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 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 expression is false.
3 arguments
If the second argument is one of the binary conditional operators
listed above under CONDITIONAL EXPRESSIONS, the result of the
expression is the result of the binary test using the first and third
arguments as operands. If the first argument is !, the value is the
negation of the two-argument test using the second and third argu-
ments. If the first argument is exactly ( and the third argument is
exactly ), the result is the one-argument test of the second argu-
ment. Otherwise, the expression is false. The -a and -o operators
are considered binary operators in this case.
4 arguments
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 and evaluated according to precedence using
the rules listed above.
5 or more arguments
The expression is parsed and evaluated according to precedence using
the rules listed above.
times Print the accumulated user and system times for the shell and for processes
run from the shell. The return status is 0.
trap [-lp] [[arg] sigspec ...]
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 speci-
fied signal is 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 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 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 corre-
sponding numbers. Each sigspec is either a signal name defined in <sig-
nal.h>, or a signal number. Signal names are case insensitive and the SIG
prefix is optional. 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, 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 of the
extglob option to the shopt builtin for details of its effect on the DEBUG
trap. If a sigspec is ERR, the command arg is executed whenever a simple
command has a non-zero exit 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 keyword, part of the test in an
if statement, part of a && or â”│â”│ list, or if the command’s return value is
being inverted via !. These are the same conditions obeyed by the errexit
option. If a sigspec is RETURN, the command arg is executed each time a
shell function or a script executed with the . or source builtins finishes
executing. Signals ignored upon entry to the shell cannot be trapped or
reset. Trapped signals are reset to their original values in a child pro-
cess when it is created. The return status is false if any sigspec is
invalid; otherwise trap returns true.
type [-aftpP] name [name ...]
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, 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, 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 command 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 command is hashed, -p and -P print the hashed value, not necessarily
the file that appears first in PATH. If the -a option is used, type prints
all of the 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 consulted when using -a. The -f option sup-
presses shell function lookup, as with the command builtin. type returns
true if any of the arguments are found, false if none are found.
ulimit [-SHacdflmnpstuv [limit]]
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 hard or soft limit is set for the given resource. A hard
limit cannot be increased once it is set; a soft limit may be increased up
to the value of 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 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 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
before the value. Other options are interpreted as follows:
-a All current limits are reported
-c The maximum size of core files created
-d The maximum size of a process’s data segment
-f The maximum size of files created by the shell
-l The maximum size that may be locked into memory
-m The maximum resident set size
-n The maximum number of open file descriptors (most systems do not
allow this value to be set)
-p The pipe size in 512-byte blocks (this may not be set)
-s The maximum stack size
-t The maximum amount of cpu time in seconds
-u The maximum number of processes available to a single user
-v The maximum amount of virtual memory available to the shell
If limit is given, it is the new value of the specified resource (the -a
option is display only). If no option is given, then -f is assumed. Values
are in 1024-byte increments, except for -t, which is in seconds, -p, which
is in units of 512-byte blocks, and -n and -u, which are unscaled values.
The return status is 0 unless an invalid option or argument is supplied, or
an error occurs while setting a new limit.
umask [-p] [-S] [mode]
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 similar 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 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 mode was successfully
changed or if no mode argument was supplied, and false otherwise.
unalias [-a] [name ...]
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 defined alias.
unset [-fv] [name ...]
For each name, remove the corresponding variable or function. If no options
are supplied, or the -v option is given, each name refers to a shell vari-
able. Read-only variables may not be unset. If -f is specifed, each name
refers to a shell function, and the function definition is removed. Each
unset variable or function is removed from the environment passed to subse-
quent commands. If any of RANDOM, SECONDS, LINENO, HISTCMD, FUNCNAME,
GROUPS, or DIRSTACK are unset, they lose their special properties, even if
they are subsequently reset. The exit status is true unless a name is read-
only.
wait [n]
Wait for the specified process and return its termination status. n may be
a process ID or a job specification; if a job spec is given, all processes
in that 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 n
specifies a non-existent process or job, the return status is 127. Other-
wise, the return status is the exit status of the last process or job waited
for.
SEE ALSO
bash(1), sh(1)
GNU Bash-3.0 2004 Apr 20 BASH_BUILTINS(1)
Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
On Apache/1.3.41 (Unix) PHP/5.2.5 mod_perl/1.30 mod_gzip/1.3.26.1a
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2008-09-06 07:47 @38.103.63.61 CrawledBy CCBot/1.0 (+http://www.commoncrawl.org/bot.html)