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BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1) NAME bash, :, ., alias, bg, bind, break, builtin, bye, case, cd, command, continue, declare, dirs, echo, enable, eval, exec, exit, export, fc, fg, for, getopts, hash, help, history, if, jobs, kill, let, local, logout, popd, pushd, pwd, read, readonly, return, set, shift, source, suspend, test, times, trap, type, typeset, ulimit, umask, unalias, unset, until, wait, while - bash built-in commands, see bash(1) BASH BUILTIN COMMANDS : [_a_r_g_u_m_e_n_t_s] No effect; the command does nothing beyond expanding _a_r_g_u_m_e_n_t_s and performing any specified redirections. A zero exit code is returned. . _f_i_l_e_n_a_m_e [_a_r_g_u_m_e_n_t_s] source _f_i_l_e_n_a_m_e [_a_r_g_u_m_e_n_t_s] Read and execute commands from _f_i_l_e_n_a_m_e in the current shell environment and return the exit status of the last command executed from _f_i_l_e_n_a_m_e. If _f_i_l_e_n_a_m_e does not contain a slash, pathnames in PATH are used to find the directory containing _f_i_l_e_n_a_m_e. The file searched for in PATH need not be executable. The current direc- tory is searched if no file is found in PATH. If any _a_r_g_u_m_e_n_t_s are supplied, they become the positional parameters when _f_i_l_e is executed. Otherwise the posi- tional parameters are unchanged. The return status is the status of the last command exited within the script (0 if no commands are executed), and false if _f_i_l_e_n_a_m_e is not found. alias [_n_a_m_e[=_v_a_l_u_e] ...] Alias with no arguments prints the list of aliases in the form _n_a_m_e=_v_a_l_u_e on standard output. When arguments are supplied, an alias is defined for each _n_a_m_e whose _v_a_l_u_e is given. A trailing space in _v_a_l_u_e causes the next word to be checked for alias substitution when the alias is expanded. For each _n_a_m_e in the argument list for which no _v_a_l_u_e is supplied, the name and value of the alias is printed. Alias returns true unless a _n_a_m_e is given for which no alias has been defined. bg [_j_o_b_s_p_e_c] Place _j_o_b_s_p_e_c in the background, as if it had been started with &. If _j_o_b_s_p_e_c is not present, the shell's notion of the _c_u_r_r_e_n_t _j_o_b is used. bg _j_o_b_s_p_e_c returns 0 unless run when job control is disabled or, when run with job control enabled, if _j_o_b_s_p_e_c was not found or started without job control. bind [-m _k_e_y_m_a_p] [-lvd] [-q _n_a_m_e] bind [-m _k_e_y_m_a_p] -f _f_i_l_e_n_a_m_e GNU Last change: 1993 September 16 1 BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1) bind [-m _k_e_y_m_a_p] _k_e_y_s_e_q:_f_u_n_c_t_i_o_n-_n_a_m_e Display current readline key and function bindings, or bind a key sequence to a readline function or macro. The binding syntax accepted is identical to that of ._i_n_p_u_t_r_c, but each binding 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 _k_e_y_m_a_p Use _k_e_y_m_a_p as the keymap to be affected by the subsequent bindings. Acceptable _k_e_y_m_a_p names are _e_m_a_c_s, _e_m_a_c_s-_s_t_a_n_d_a_r_d, _e_m_a_c_s-_m_e_t_a, _e_m_a_c_s-_c_t_l_x, _v_i, _v_i-_m_o_v_e, _v_i-_c_o_m_m_a_n_d, and _v_i-_i_n_s_e_r_t. _v_i is equivalent to _v_i-_c_o_m_m_a_n_d; _e_m_a_c_s is equivalent to _e_m_a_c_s-_s_t_a_n_d_a_r_d. -l List the names of all readline functions -v List current function names and bindings -d Dump function names and bindings in such a way that they can be re-read -f _f_i_l_e_n_a_m_e Read key bindings from _f_i_l_e_n_a_m_e -q _f_u_n_c_t_i_o_n Query about which keys invoke the named _f_u_n_c_t_i_o_n The return value is 0 unless an unrecognized option is given or an error occurred. break [_n] Exit from within a for, while, or until loop. If _n is specified, break _n levels. _n must be >_ 1. If _n is greater than the number of enclosing loops, all enclos- ing loops are exited. The return value is 0 unless the shell is not executing a loop when break is executed. builtin _s_h_e_l_l-_b_u_i_l_t_i_n [_a_r_g_u_m_e_n_t_s] Execute the specified shell builtin, passing it _a_r_g_u_- _m_e_n_t_s, and return its exit status. This is useful when you wish to define a function whose name is the same as a shell builtin, but need the functionality of the builtin within the function itself. The cd builtin is commonly redefined this way. The return status is false if _s_h_e_l_l-_b_u_i_l_t_i_n is not a shell builtin command. cd [_d_i_r] Change the current directory to _d_i_r. The variable HOME is the default _d_i_r. The variable CDPATH defines the search path for the directory containing _d_i_r. Alterna- tive directory names are separated by a colon (:). A null directory name in CDPATH is the same as the current directory, i.e., ``.''. If _d_i_r begins with a slash (/), then CDPATH is not used. An argument of - is equivalent to $OLDPWD. The return value is true if the directory was successfully changed; false GNU Last change: 1993 September 16 2 BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1) otherwise. command [-pVv] _c_o_m_m_a_n_d [_a_r_g ...] Run _c_o_m_m_a_n_d with _a_r_g_s 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 _c_o_m_m_a_n_d 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 _c_o_m_m_a_n_d is printed. The -v option causes a single word indicating the command or pathname used to invoke _c_o_m_m_a_n_d to be printed; the -V option produces a more verbose descrip- tion. An argument of -- disables option checking for the rest of the arguments. If the -V or -v option is supplied, the exit status is 0 if _c_o_m_m_a_n_d was found, and 1 if not. If neither option is supplied and an error occurred or _c_o_m_m_a_n_d cannot be found, the exit status is 127. Otherwise, the exit status of the com- mand builtin is the exit status of _c_o_m_m_a_n_d. continue [_n] Resume the next iteration of the enclosing for, while, or until 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 con- tinue is executed. declare [-frxi] [_n_a_m_e[=_v_a_l_u_e]] typeset [-frxi] [_n_a_m_e[=_v_a_l_u_e]] Declare variables and/or give them attributes. If no _n_a_m_es are given, then display the values of variables instead. The options can be used to restrict output to variables with the specified attribute. -f Use function names only -r Make _n_a_m_es readonly. These names cannot then be assigned values by subsequent assignment state- ments. -x Mark _n_a_m_es for export to subsequent commands via the environment. -i The variable is treated as an integer; arithmetic evaluation (see ARITHMETIC EVALUATION ) is per- formed when the variable is assigned a value. Using `+' instead of `-' turns off the attribute instead. When used in a function, makes _n_a_m_es local, as with the local command. The return value is 0 unless an illegal option is encountered, an attempt is made to define a function using "-f foo=bar", one of the _n_a_m_e_s is not a legal shell variable name, an GNU Last change: 1993 September 16 3 BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1) attempt is made to turn off readonly status for a readonly variable, or an attempt is made to display a non-existant function with -f. dirs [-l] [+/-n] Display the list of currently remembered directories. Directories are added to the list with the pushd com- mand; the popd command moves back up through 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. -l produces a longer listing; the default listing format uses a tilde to denote the home directory. The return value is 0 unless an illegal option is sup- plied or _n indexes beyond the end of the directory stack. echo [-neE] [_a_r_g ...] Output the _a_r_gs, separated by spaces. 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 char- acters is enabled. The -E option disables the interpretation of these escape characters, even on sys- tems where they are interpreted by default. \a alert (bell) \b backspace \c suppress trailing newline \f form feed \n new line \r carriage return \t horizontal tab \v vertical tab \\ backslash \nnn the character whose ASCII code is _n_n_n (octal) enable [-n] [-all] [_n_a_m_e ...] Enable and disable builtin shell commands. This allows the execution of a disk command which has the same name as a shell builtin without specifying a full pathname. If -n is used, each _n_a_m_e is disabled; otherwise, _n_a_m_e_s are enabled. For example, to use the test binary found via the PATH instead of the shell builtin version, type ``enable -n test''. If no arguments are given, a list of all enabled shell builtins is printed. If only -n is supplied, a list of all disabled builtins is printed. If only -all is supplied, the list printed includes all builtins, with an indication of whether or GNU Last change: 1993 September 16 4 BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1) not each is enabled. enable accepts -a as a synonym for -all. The return value is 0 unless a _n_a_m_e is not a shell builtin. eval [_a_r_g ...] The _a_r_gs are read and concatenated together into a sin- gle command. This command is then read and executed by the shell, and its exit status is returned as the value of the eval command. If there are no _a_r_g_s, or only null arguments, eval returns true. exec [[-] _c_o_m_m_a_n_d [_a_r_g_u_m_e_n_t_s]] If _c_o_m_m_a_n_d is specified, it replaces the shell. No new process is created. The _a_r_g_u_m_e_n_t_s become the arguments to _c_o_m_m_a_n_d. If the first argument is -, the shell places a dash in the zeroth arg passed to _c_o_m_m_a_n_d. This is what login does. If the file cannot be exe- cuted for some reason, a non-interactive shell exits, unless the shell variable no_exit_on_failed_exec exists, in which case it returns failure. An interac- tive shell returns failure if the file cannot be exe- cuted. If _c_o_m_m_a_n_d is not specified, any redirections take effect in the current shell, and the return status is 0. exit [_n] 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 terminates. export [-nf] [_n_a_m_e[=_w_o_r_d]] ... export -p The supplied _n_a_m_e_s are marked for automatic export to the environment of subsequently executed commands. If the -f option is given, the _n_a_m_e_s refer to functions. If no _n_a_m_e_s 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 the named variables. An argument of -- disables option checking for the rest of the arguments. export returns an exit status of 0 unless an illegal option is encountered, one of the _n_a_m_e_s is not a legal shell variable name, or -f is supplied with a _n_a_m_e that is not a function. fc [-e _e_n_a_m_e] [-nlr] [_f_i_r_s_t] [_l_a_s_t] fc -s [_p_a_t=_r_e_p] [_c_m_d] Fix Command. In the first form, a range of commands from _f_i_r_s_t to _l_a_s_t is selected from the history list. _F_i_r_s_t and _l_a_s_t may be specified as a string (to locate the last command beginning with that string) or as a GNU Last change: 1993 September 16 5 BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1) number (an index into the history list, where a nega- tive number is used as an offset from the current com- mand number). If _l_a_s_t is not specified it is set to the current command for listing (so that fc -l -10 prints the last 10 commands) and to _f_i_r_s_t otherwise. If _f_i_r_s_t is not specified it is set to the previous command for editing and -16 for listing. The -n flag suppresses the command numbers when list- ing. The -r flag reverses the order of the commands. If the -l flag is given, the commands are listed on standard output. Otherwise, the editor given by _e_n_a_m_e is invoked on a file containing those commands. If _e_n_a_m_e 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 com- plete, the edited commands are echoed and executed. In the second form, _c_o_m_m_a_n_d is re-executed after each instance of _p_a_t is replaced by _r_e_p. 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 illegal option is encountered or _f_i_r_s_t or _l_a_s_t specify history lines out of range. If the -e option is supplied, 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 return status is that of the command re- executed, unless _c_m_d does not specify a valid history line, in which case fc returns failure. fg [_j_o_b_s_p_e_c] Place _j_o_b_s_p_e_c in the foreground, and make it the current job. If _j_o_b_s_p_e_c is not present, the shell's notion of the _c_u_r_r_e_n_t _j_o_b 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 _j_o_b_s_p_e_c does not specify a valid job or _j_o_b_s_p_e_c specifies a job that was started without job control. getopts _o_p_t_s_t_r_i_n_g _n_a_m_e [_a_r_g_s] getopts is used by shell procedures to parse positional parameters. _o_p_t_s_t_r_i_n_g contains the option letters to be recognized; if a letter is followed by a colon, the option is expected to have an argument, which should be separated from it by white space. Each time it is invoked, getopts places the next option in the shell variable _n_a_m_e, initializing _n_a_m_e if it does not exist, GNU Last change: 1993 September 16 6 BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1) 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 argu- ment 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. getopts can report errors in two ways. If the first character of _o_p_t_s_t_r_i_n_g is a colon, _s_i_l_e_n_t error report- ing is used. In normal operation diagnostic messages are printed when illegal options or missing option arguments are encountered. If the variable OPTERR is set to 0, no error message will be displayed, even if the first character of _o_p_t_s_t_r_i_n_g is not a colon. If an illegal option is seen, getopts places ? into _n_a_m_e and, if not silent, prints an error message and unsets OPTARG. If getopts is silent, the option char- acter found is placed in OPTARG and no diagnostic mes- sage is printed. If a required argument is not found, and getopts is not silent, a question mark (?) is placed in _n_a_m_e, OPTARG is unset, and a diagnostic message is printed. If getopts is silent, then a colon (:) is placed in _n_a_m_e and OPTARG is set to the option character found. getopts normally parses the positional parameters, but if more arguments are given in _a_r_g_s, getopts parses those instead. 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 [-r] [_n_a_m_e] For each _n_a_m_e, the full pathname of the command is determined and remembered. The -r option causes the shell to forget all remembered locations. If no argu- ments are given, information about remembered commands is printed. An argument of -- disables option checking for the rest of the arguments. The return status is true unless a _n_a_m_e is not found or an illegal option is supplied. help [_p_a_t_t_e_r_n] Display helpful information about builtin commands. If _p_a_t_t_e_r_n is specified, help gives detailed help on all commands matching _p_a_t_t_e_r_n; otherwise a list of the builtins is printed. The return status is 0 unless no command matches _p_a_t_t_e_r_n. GNU Last change: 1993 September 16 7 BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1) history [_n] history -rwan [_f_i_l_e_n_a_m_e] With no options, display the command history list with line numbers. Lines listed with a * have been modi- fied. An argument of _n lists only the last _n lines. If a non-option argument 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: -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 history file's contents. The return value is 0 unless an illegal option is encountered or an error occurs while reading or writing the history file. jobs [-lnp] [ _j_o_b_s_p_e_c ... ] jobs -x _c_o_m_m_a_n_d [ _a_r_g_s ... ] The first form lists the active jobs. The -l option lists process IDs in addition to the normal informa- tion; the -p option lists only the process ID of the job's process group leader. The -n option displays only jobs that have changed status since last notified. If _j_o_b_s_p_e_c is given, output is restricted to informa- tion about that job. The return status is 0 unless an illegal option is encountered or an illegal _j_o_b_s_p_e_c is supplied. If the -x option is supplied, jobs replaces any _j_o_b_s_p_e_c found in _c_o_m_m_a_n_d or _a_r_g_s with the corresponding process group ID, and executes _c_o_m_m_a_n_d passing it _a_r_g_s, return- ing its exit status. kill [-s sigspec | -sigspec] [_p_i_d | _j_o_b_s_p_e_c] ... kill -l [_s_i_g_n_u_m] Send the signal named by _s_i_g_s_p_e_c to the processes named by _p_i_d or _j_o_b_s_p_e_c. _s_i_g_s_p_e_c is either a signal name such as SIGKILL or a signal number. If _s_i_g_s_p_e_c is a signal name, the name is case insensitive and may be given with or without the SIG prefix. If _s_i_g_s_p_e_c is not present, then SIGTERM is assumed. An argument of -l lists the signal names. If any arguments are sup- plied when -l is given, the names of the specified GNU Last change: 1993 September 16 8 BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1) signals are listed, and the return status is 0. An argument of -- disables option checking for the rest of the arguments. kill returns true if at least one sig- nal was successfully sent, or false if an error occurs or an illegal option is encountered. let _a_r_g [_a_r_g ...] Each _a_r_g is an arithmetic expression to be evaluated (see ARITHMETIC EVALUATION). If the last _a_r_g evaluates to 0, let returns 1; 0 is returned otherwise. local [_n_a_m_e[=_v_a_l_u_e] ...] For each argument, create a local variable named _n_a_m_e, and assign it _v_a_l_u_e. When local is used within a func- tion, it causes the variable _n_a_m_e to have a visible scope restricted to that function and its children. With no operands, local writes a list of local vari- ables 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, or an ille- gal _n_a_m_e is supplied. logout Exit a login shell. popd [+/-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. +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. If the popd command is successful, a dirs is performed as well, and the return status is 0. popd returns false if an illegal option is encountered, the direc- tory stack is empty, a non-existent directory stack entry is specified, or the directory change fails. pushd [_d_i_r] pushd +/-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. +n Rotates the stack so that the _nth directory GNU Last change: 1993 September 16 9 BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1) (counting from the left of the list shown by dirs) is at the top. -n Rotates the stack so that the _nth directory (counting from the right) is at the top. dir adds _d_i_r 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 _d_i_r fails. With the second form, pushd returns 0 unless the directory stack is empty, a non-existant directory stack element is specified, or the directory change to the specified new current directory fails. pwd Print the absolute pathname of the current working directory. The path printed contains no symbolic links if the -P option to the set builtin command is set. See also the description of nolinks under Shell Vari- ables above). The return status is 0 unless an error occurs while reading the pathname of the current direc- tory. read [-r] [_n_a_m_e ...] One line is read from the standard input, and the first word is assigned to the first _n_a_m_e, the second word to the second _n_a_m_e, and so on, with leftover words assigned to the last _n_a_m_e. Only the characters in IFS are recognized as word delimiters. If no _n_a_m_e_s are supplied, the line read is assigned to the variable REPLY. The return code is zero, unless end-of-file is encountered. If the -r option is given, a backslash- newline pair is not ignored, and the backslash is con- sidered to be part of the line. readonly [-f] [_n_a_m_e ...] readonly -p The given _n_a_m_e_s are marked readonly and the values of these _n_a_m_e_s may not be changed by subsequent assign- ment. If the -f option is supplied, the functions corresponding to the _n_a_m_e_s are so marked. If no argu- ments are given, or if the -p option is supplied, a list of all readonly names is printed. An argument of -- disables option checking for the rest of the argu- ments. The return status is 0 unless an illegal option is encountered, one of the _n_a_m_e_s is not a legal shell variable name, or -f is supplied with a _n_a_m_e that is not a function. return [_n] Causes a function to exit with the return value speci- fied by _n. If _n is omitted, the return status is that GNU Last change: 1993 September 16 10 BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1) of the last command executed in the function 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 out- side a function and not during execution of a script by ., the return status is false. set [--abefhkmnptuvxldCHP] [-o _o_p_t_i_o_n] [_a_r_g ...] -a Automatically mark variables which are modified or created for export to the environment of subsequent commands. -b Cause the status of terminated background jobs to be reported immediately, rather than before the next primary prompt. (Also see notify under Shell Variables above). -e Exit immediately if a _s_i_m_p_l_e-_c_o_m_m_a_n_d (see SHELL GRAMMAR above) exits with a non-zero status. The shell does not exit if the command that fails is part of an _u_n_t_i_l or _w_h_i_l_e loop, part of an _i_f statement, part of a && or || list, or if the command's return value is being inverted via !. -f Disable pathname expansion. -h Locate and remember function commands as func- tions are defined. Function commands are nor- mally looked up when the function is executed. -k All keyword arguments are placed in the environment for a command, not just those that precede the command name. -m Monitor mode. Job control is enabled. This flag 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 for interactive shells. -o _o_p_t_i_o_n-_n_a_m_e The _o_p_t_i_o_n-_n_a_m_e can be one of the following: allexport Same as -a. braceexpand The shell performs brace expansion (see Brace Expansion above). This is on by default. emacs Use an emacs-style command line editing interface. This is enabled by default when the shell is interactive, unless GNU Last change: 1993 September 16 11 BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1) the shell is started with the -nol- ineediting option. errexit Same as -e. histexpand Same as -H. ignoreeof The effect is as if the shell command `IGNOREEOF=10' had been executed (see Shell Variables above). interactive-comments 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). monitor Same as -m. noclobber Same as -C. noexec Same as -n. noglob Same as -f. nohash Same as -d. notify Same as -b. nounset Same as -u. physical Same as -P. posix Change the behavior of bash where the default operation differs from the Posix 1003.2 standard to match the standard. privileged Same as -p. verbose Same as -v. vi Use a vi-style command line editing interface. xtrace Same as -x. If no _o_p_t_i_o_n-_n_a_m_e is supplied, the values of the current options are printed. -p Turn on _p_r_i_v_i_l_e_g_e_d mode. In this mode, the $ENV file is not processed, and shell functions are not inherited from the environment. This is enabled automatically on startup if the effective user (group) id is not equal to the real user (group) id. 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 perform- ing parameter expansion. If expansion is attempted on an unset variable, the shell prints an error message, and, if not interac- tive, exits with a non-zero status. -v Print shell input lines as they are read. -x After expanding each _s_i_m_p_l_e-_c_o_m_m_a_n_d, bash GNU Last change: 1993 September 16 12 BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1) displays the expanded value of PS4, followed by the command and its expanded arguments. -l Save and restore the binding of _n_a_m_e in a for _n_a_m_e [in word] command (see SHELL GRAMMAR above). -d Disable the hashing of commands that are looked up for execution. Normally, commands are remembered in a hash table, and once found, do not have to be looked up again. -C The effect is as if the shell command `noclobber=' had been executed (see Shell Vari- ables above). -H Enable ! style history substitution. This flag is on by default when the shell is interactive. -P If set, do not follow symbolic links when per- forming commands such as cd which change the current directory. The physical directory is used instead. -- If no arguments follow this flag, then the positional parameters are unset. Otherwise, the positional parameters are set to the _a_r_gs, even if some of them begin with a -. - Signal the end of options, cause all remaining _a_r_gs to be assigned to the positional parame- ters. The -x and -v options are turned off. If there are no _a_r_gs, the positional parameters remain unchanged. The flags are off by default unless otherwise noted. Using + rather than - causes these flags to be turned off. The flags can also be specified as options to an invocation of the shell. The current set of flags may be found in $-. After the option arguments are pro- cessed, the remaining _n _a_r_gs are treated as values for the positional parameters and are assigned, in order, to $1, $2, ... $_n. If no options or _a_r_gs are supplied, all shell variables are printed. The return status is always true unless an illegal option is encountered. shift [_n] The positional parameters from _n+1 ... are renamed to $1 .... If _n is not given, it is assumed to be 1. The exit status is 1 if _n is greater than $#; otherwise 0. 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 anyway. 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 _e_x_p_r GNU Last change: 1993 September 16 13 BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1) [ _e_x_p_r ] Return a status of 0 (true) or 1 (false) depending on the evaluation of the conditional expression _e_x_p_r. Expressions may be unary or binary. Unary expressions are often used to examine the status of a file. There are string operators and numeric comparison operators as well. Each operator and operand must be a separate argument. If _f_i_l_e is of the form /dev/fd/_n, then file descriptor _n is checked. -b _f_i_l_e True if _f_i_l_e exists and is block special. -c _f_i_l_e True if _f_i_l_e exists and is character special. -d _f_i_l_e True if _f_i_l_e exists and is a directory. -e _f_i_l_e True if _f_i_l_e exists. -f _f_i_l_e True if _f_i_l_e exists and is a regular file. -g _f_i_l_e True if _f_i_l_e exists and is set-group-id. -k _f_i_l_e True if _f_i_l_e has its ``sticky'' bit set. -L _f_i_l_e True if _f_i_l_e exists and is a symbolic link. -p _f_i_l_e True if _f_i_l_e exists and is a named pipe. -r _f_i_l_e True if _f_i_l_e exists and is readable. -s _f_i_l_e True if _f_i_l_e exists and has a size greater than zero. -S _f_i_l_e True if _f_i_l_e exists and is a socket. -t _f_d True if _f_d is opened on a terminal. -u _f_i_l_e True if _f_i_l_e exists and its set-user-id bit is set. -w _f_i_l_e True if _f_i_l_e exists and is writable. -x _f_i_l_e True if _f_i_l_e exists and is executable. -O _f_i_l_e True if _f_i_l_e exists and is owned by the effective user id. -G _f_i_l_e True if _f_i_l_e exists and is owned by the effective group id. _f_i_l_e_1 -nt _f_i_l_e_2 True if _f_i_l_e_1 is newer (according to modification date) than _f_i_l_e_2. GNU Last change: 1993 September 16 14 BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1) _f_i_l_e_1 -ot _f_i_l_e_2 True if _f_i_l_e_1 is older than file2. _f_i_l_e_1 -ef _f_i_l_e True if _f_i_l_e_1 and _f_i_l_e_2 have the same device and inode numbers. -z _s_t_r_i_n_g True if the length of _s_t_r_i_n_g is zero. -n _s_t_r_i_n_g _s_t_r_i_n_g True if the length of _s_t_r_i_n_g is non-zero. _s_t_r_i_n_g_1 = _s_t_r_i_n_g_2 True if the strings are equal. _s_t_r_i_n_g_1 != _s_t_r_i_n_g_2 True if the strings are not equal. ! _e_x_p_r True if _e_x_p_r is false. _e_x_p_r_1 -a _e_x_p_r_2 True if both _e_x_p_r_1 AND _e_x_p_r_2 are true. _e_x_p_r_1 -o _e_x_p_r_2 True if either _e_x_p_r_1 OR _e_x_p_r_2 is true. _a_r_g_1 OP _a_r_g_2 OP is one of -eq, -ne, -lt, -le, -gt, or -ge. These arithmetic binary operators return true if _a_r_g_1 is equal, not-equal, less-than, less-than- or-equal, greater-than, or greater-than-or-equal than _a_r_g_2, respectively. _A_r_g_1 and _a_r_g_2 may be positive integers, negative integers, or the spe- cial expression -l _s_t_r_i_n_g, which evaluates to the length of _s_t_r_i_n_g. times Print the accumulated user and system times for the shell and for processes run from the shell. The return status is 0. trap [-l] [_a_r_g] [_s_i_g_s_p_e_c] The command _a_r_g is to be read and executed when the shell receives signal(s) _s_i_g_s_p_e_c. If _a_r_g is absent or -, all specified signals are reset to their original values (the values they had upon entrance to the shell). If _a_r_g is the null string this signal is ignored by the shell and by the commands it invokes. _s_i_g_s_p_e_c is either a signal name defined in <_s_i_g_n_a_l._h>, or a signal number. If _s_i_g_s_p_e_c is EXIT (0) the command _a_r_g is executed on exit from the shell. With no argu- ments, trap prints the list of commands associated with each signal number. The -l option causes the shell to print a list of signal names and their corresponding numbers. An argument of -- disables option checking for the rest of the arguments. Signals ignored upon entry to the shell cannot be trapped or reset. Trapped signals are reset to their original values in a child GNU Last change: 1993 September 16 15 BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1) process when it is created. The return status is false if either the trap name or number is invalid; otherwise trap returns true. type [-all] [-type | -path] _n_a_m_e [_n_a_m_e ...] With no options, indicate how each _n_a_m_e would be inter- preted if used as a command name. If the -type flag is used, type prints a phrase which is one of _a_l_i_a_s, _k_e_y_- _w_o_r_d, _f_u_n_c_t_i_o_n, _b_u_i_l_t_i_n, or _f_i_l_e if _n_a_m_e 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 -path flag is used, type either returns the name of the disk file that would be executed if _n_a_m_e were specified as a command name, or nothing if -type would not return _f_i_l_e. If a command is hashed, -path prints the hashed value, not necessarily the file that appears first in PATH. If the -all flag is used, type prints all of the places that contain an executable named _n_a_m_e. This includes aliases and functions, if and only if the -path flag is not also used. The table of hashed commands is not consulted when using -all. type accepts -a, -t, and -p in place of -all, -type, and -path, respectively. An argument of -- disables option checking for the rest of the arguments. type returns true if any of the arguments are found, false if none are found. ulimit [-SHacdfmstpnuv [_l_i_m_i_t]] Ulimit provides control over the resources available to the shell and to processes started by it, on systems that allow such control. The value of _l_i_m_i_t can be a number in the unit specified for the resource, or the value unlimited. 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, the command applies to the soft limit. If _l_i_m_i_t 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 is printed before the value. Other options are inter- preted 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 -m the maximum resident set size -s the maximum stack size -t the maximum amount of cpu time in seconds -p the pipe size in 512-byte blocks (this may not be GNU Last change: 1993 September 16 16 BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1) set) -n the maximum number of open file descriptors (most systems do not allow this value to be set, only displayed) -u the maximum number of processes available to a single user -v The maximum amount of virtual memory available to the shell An argument of -- disables option checking for the rest of the arguments. If _l_i_m_i_t 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 illegal option is encountered, a non-numeric argument other than unlimited is supplied as _l_i_m_i_t, or an error occurs while setting a new limit. umask [-S] [_m_o_d_e] The user file-creation mask is set to _m_o_d_e. If _m_o_d_e 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 _c_h_m_o_d(1). If _m_o_d_e is omitted, or if the -S option is supplied, 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. An argument of -- disables option checking for the rest of the arguments. The return status is 0 if the mode was successfully changed or if no _m_o_d_e argument was supplied, and false otherwise. unalias [-a] [_n_a_m_e ...] Remove _n_a_m_es from the list of defined aliases. If -a is supplied, all alias definitions are removed. The return value is true unless a supplied _n_a_m_e is not a defined alias. unset [-fv] [_n_a_m_e ...] For each _n_a_m_e, remove the corresponding variable or, given the -f option, function. An argument of -- dis- ables option checking for the rest of the arguments. Note that PATH, IFS, PPID, PS1, PS2, UID, and EUID can- not be unset. If any of RANDOM, SECONDS, LINENO, or HISTCMD are unset, they lose their special properties, even if they are subsequently reset. The exit status is true unless a _n_a_m_e does not exist or is non- unsettable. wait [_n] GNU Last change: 1993 September 16 17 BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1) Wait for the specified process and return its termina- tion status. _n may be a process ID or a job specifica- tion; 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- existant process or job, the return status is 127. Otherwise, the return status is the exit status of the last process or job waited for. SEE ALSO bash(1), sh(1) GNU Last change: 1993 September 16 18