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BASH(1) BASH(1) NNAAMMEE bash - GNU Bourne-Again SHell SSYYNNOOPPSSIISS bbaasshh [options] [file] CCOOPPYYRRIIGGHHTT Bash is Copyright (C) 1989, 1991, 1993, 1995, 1996 by the Free Software Foundation, Inc. DDEESSCCRRIIPPTTIIOONN BBaasshh is an sshh-compatible command language interpreter that executes commands read from the standard input or from a file. BBaasshh also incorporates useful features from the _K_o_r_n and _C shells (kksshh and ccsshh). BBaasshh is intended to be a conformant implementation of the IEEE POSIX Shell and Tools specification (IEEE Working Group 1003.2). OOPPTTIIOONNSS In addition to the single-character shell options docu- mented in the description of the sseett builtin command, bbaasshh interprets the following options when it is invoked: --cc _s_t_r_i_n_g If the --cc option is present, then commands are read from _s_t_r_i_n_g. If there are arguments after the _s_t_r_i_n_g, they are assigned to the positional parameters, starting with $$00. --rr If the --rr option is present, the shell becomes _r_e_s_t_r_i_c_t_e_d (see RREESSTTRRIICCTTEEDD SSHHEELLLL below). --ii If the --ii option is present, the shell is _i_n_t_e_r_- _a_c_t_i_v_e. --ss If the --ss option is present, or if no arguments remain after option processing, then commands are read from the standard input. This option allows the positional parameters to be set when invoking an interactive shell. --DD A list of all double-quoted strings preceded by $$ is printed on the standard ouput. These are the strings that are subject to language trans- lation when the current locale is not C or POSIX. This implies the --nn option; no commands will be executed. ---- A ---- signals the end of options and disables further option processing. Any arguments after the ---- are treated as filenames and arguments. An argument of -- is equivalent to ----. BBaasshh also interprets a number of multi-character options. These options must appear on the command line before the single-character options in order for them to be recog- nized. GNU 1998 Apr 1 1 BASH(1) BASH(1) ----dduummpp--ppoo--ssttrriinnggss Equivalent to --DD, but the output is in the GNU _g_e_t_- _t_e_x_t ppoo (portable object) file format. ----dduummpp--ssttrriinnggss Equivalent to --DD. ----hheellpp Display a usage message on standard output and exit successfully. ----llooggiinn Make bbaasshh act as if it had been invoked as a login shell (see IINNVVOOCCAATTIIOONN below). ----nnooeeddiittiinngg Do not use the GNU rreeaaddlliinnee library to read command lines if interactive. ----nnoopprrooffiillee Do not read either the system-wide startup file _/_e_t_c_/_p_r_o_f_i_l_e or any of the personal initialization files _~_/_._b_a_s_h___p_r_o_f_i_l_e, _~_/_._b_a_s_h___l_o_g_i_n, or _~_/_._p_r_o_- _f_i_l_e. By default, bbaasshh reads these files when it is invoked as a login shell (see IINNVVOOCCAATTIIOONN below). ----nnoorrcc Do not read and execute the personal initialization file _~_/_._b_a_s_h_r_c if the shell is interactive. This option is on by default if the shell is invoked as sshh. ----ppoossiixx Change the behavior of bbaasshh where the default oper- ation differs from the POSIX 1003.2 standard to match the standard. ----rrccffiillee _f_i_l_e Execute commands from _f_i_l_e instead of the standard personal initialization file _~_/_._b_a_s_h_r_c if the shell is interactive (see IINNVVOOCCAATTIIOONN below). ----rreessttrriicctteedd The shell becomes restricted (see RREESSTTRRIICCTTEEDD SSHHEELLLL below). ----vveerrbboossee Equivalent to --vv. ----vveerrssiioonn Show version information for this instance of bbaasshh on the standard output and exit successfully. AARRGGUUMMEENNTTSS If arguments remain after option processing, and neither the --cc nor the --ss option has been supplied, the first argument is assumed to be the name of a file containing shell commands. If bbaasshh is invoked in this fashion, $$00 is set to the name of the file, and the positional parameters are set to the remaining arguments. BBaasshh reads and exe- cutes commands from this file, then exits. BBaasshh's exit status is the exit status of the last command executed in the script. If no commands are executed, the exit status is 0. IINNVVOOCCAATTIIOONN A _l_o_g_i_n _s_h_e_l_l is one whose first character of argument GNU 1998 Apr 1 2 BASH(1) BASH(1) zero is a --, or one started with the ----llooggiinn option. An _i_n_t_e_r_a_c_t_i_v_e shell is one whose standard input and out- put are both connected to terminals (as determined by _i_s_a_t_t_y(3)), or one started with the --ii option. PPSS11 is set and $$-- includes ii if bbaasshh is interactive, allowing a shell script or a startup file to test this state. The following paragraphs describe how bbaasshh executes its startup files. If any of the files exist but cannot be read, bbaasshh reports an error. Tildes are expanded in file names as described below under TTiillddee EExxppaannssiioonn in the EEXXPPAANNSSIIOONN section. When bbaasshh is invoked as an interactive login shell, it first reads and executes commands from the file _/_e_t_c_/_p_r_o_- _f_i_l_e, if that file exists. After reading that file, it looks for _~_/_._b_a_s_h___p_r_o_f_i_l_e, _~_/_._b_a_s_h___l_o_g_i_n, and _~_/_._p_r_o_f_i_l_e, in that order, and reads and executes commands from the first one that exists and is readable. The ----nnoopprrooffiillee option may be used when the shell is started to inhibit this behavior. When a login shell exits, bbaasshh reads and executes commands from the file _~_/_._b_a_s_h___l_o_g_o_u_t, if it exists. When an interactive shell that is not a login shell is started, bbaasshh reads and executes commands from _~_/_._b_a_s_h_r_c, if that file exists. This may be inhibited by using the ----nnoorrcc option. The ----rrccffiillee _f_i_l_e option will force bbaasshh to read and execute commands from _f_i_l_e instead of _~_/_._b_a_s_h_r_c. When bbaasshh is started non-interactively, to run a shell script, for example, it looks for the variable BBAASSHH__EENNVV in the environment, expands its value if it appears there, and uses the expanded value as the name of a file to read and execute. BBaasshh behaves as if the following command were executed: if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi bbuutt tthhee vvaalluuee ooff tthhee PPAATTHH variable is not used to search for the file name. If bbaasshh is invoked with the name sshh, it tries to mimic the startup behavior of historical versions of sshh as closely as possible, while conforming to the POSIX standard as well. When invoked as an interactive login shell, it first attempts to read and execute commands from _/_e_t_c_/_p_r_o_- _f_i_l_e and _~_/_._p_r_o_f_i_l_e, in that order. The ----nnoopprrooffiillee option may be used to inhibit this behavior. When invoked as an interactive shell with the name sshh, bbaasshh looks for the variable EENNVV, expands its value if it is defined, and uses the expanded value as the name of a file to read and execute. Since a shell invoked as sshh does not attempt to GNU 1998 Apr 1 3 BASH(1) BASH(1) read and execute commands from any other startup files, the ----rrccffiillee option has no effect. A non-interactive shell invoked with the name sshh does not attempt to read any startup files. When invoked as sshh, bbaasshh enters _p_o_s_i_x mode after the startup files are read. When bbaasshh is started in _p_o_s_i_x mode, as with the ----ppoossiixx command line option, it follows the POSIX standard for startup files. In this mode, interactive shells expand the EENNVV variable and commands are read and executed from the file whose name is the expanded value. No other startup files are read. BBaasshh attempts to determine when it is being run by the remote shell daemon, usually _r_s_h_d. If bbaasshh determines it is being run by _r_s_h_d, it reads and executes commands from _~_/_._b_a_s_h_r_c, if that file exists and is readable. It will not do this if invoked as sshh. The ----nnoorrcc option may be used to inhibit this behavior, and the ----rrccffiillee option may be used to force another file to be read, but _r_s_h_d does not generally invoke the shell with those options or allow them to be specified. DDEEFFIINNIITTIIOONNSS The following definitions are used throughout the rest of this document. bbllaannkk A space or tab. wwoorrdd A sequence of characters considered as a single unit by the shell. Also known as a ttookkeenn. nnaammee A _w_o_r_d consisting only of alphanumeric characters and underscores, and beginning with an alphabetic character or an underscore. Also referred to as an iiddeennttiiffiieerr. mmeettaacchhaarraacctteerr A character that, when unquoted, separates words. One of the following: || && ;; (( )) << >> ssppaaccee ttaabb ccoonnttrrooll ooppeerraattoorr A _t_o_k_e_n that performs a control function. It is one of the following symbols: |||| && &&&& ;; ;;;; (( )) || <<nneewwlliinnee>> RREESSEERRVVEEDD WWOORRDDSS _R_e_s_e_r_v_e_d _w_o_r_d_s are words that have a special meaning to the shell. The following words are recognized as reserved when unquoted and either the first word of a simple com- mand (see SSHHEELLLL GGRRAAMMMMAARR below) or the third word of a ccaassee or ffoorr command: !! ccaassee ddoo ddoonnee eelliiff eellssee eessaacc ffii ffoorr ffuunnccttiioonn iiff iinn sseelleecctt tthheenn uunnttiill wwhhiillee {{ }} ttiimmee [[[[ ]]]] SSHHEELLLL GGRRAAMMMMAARR GNU 1998 Apr 1 4 BASH(1) BASH(1) SSiimmppllee CCoommmmaannddss A _s_i_m_p_l_e _c_o_m_m_a_n_d is a sequence of optional variable assignments followed by bbllaannkk-separated words and redirec- tions, and terminated by a _c_o_n_t_r_o_l _o_p_e_r_a_t_o_r. The first word specifies the command to be executed. The remaining words are passed as arguments to the invoked command. The return value of a _s_i_m_p_l_e _c_o_m_m_a_n_d is its exit status, or 128+_n if the command is terminated by signal _n. PPiippeelliinneess A _p_i_p_e_l_i_n_e is a sequence of one or more commands separated by the character ||. The format for a pipeline is: [ttiimmee [--pp]] [ ! ] _c_o_m_m_a_n_d [ || _c_o_m_m_a_n_d_2 ... ] The standard output of _c_o_m_m_a_n_d is connected to the stan- dard input of _c_o_m_m_a_n_d_2. This connection is performed before any redirections specified by the command (see RREEDDIIRREECCTTIIOONN below). If the reserved word !! precedes a pipeline, the exit sta- tus of that pipeline is the logical NOT of the exit status of the last command. Otherwise, the status of the pipeline is the exit status of the last command. The shell waits for all commands in the pipeline to terminate before returning a value. If the ttiimmee reserved word precedes a pipeline, the elapsed as well as user and system time consumed by its execution are reported when the pipeline terminates. The --pp option changes the output format to that specified by POSIX. The TTIIMMEEFFOORRMMAATT variable may be set to a format string that specifies how the timing information should be displayed; see the description of TTIIMMEEFFOORRMMAATT under SShheellll VVaarriiaabblleess below. Each command in a pipeline is executed as a separate pro- cess (i.e., in a subshell). LLiissttss A _l_i_s_t is a sequence of one or more pipelines separated by one of the operators ;;, &&, &&&&, or ||||, and optionally ter- minated by one of ;;, &&, or <<nneewwlliinnee>>. Of these list operators, &&&& and |||| have equal precedence, followed by ;; and &&,, which have equal precedence. If a command is terminated by the control operator &&, the shell executes the command in the _b_a_c_k_g_r_o_u_n_d in a sub- shell. The shell does not wait for the command to finish, and the return status is 0. Commands separated by a ;; are executed sequentially; the shell waits for each command to terminate in turn. The return status is the exit status GNU 1998 Apr 1 5 BASH(1) BASH(1) of the last command executed. The control operators &&&& and |||| denote AND lists and OR lists, respectively. An AND list has the form _c_o_m_m_a_n_d &&&& _c_o_m_m_a_n_d_2 _c_o_m_m_a_n_d_2 is executed if, and only if, _c_o_m_m_a_n_d returns an exit status of zero. An OR list has the form _c_o_m_m_a_n_d |||| _c_o_m_m_a_n_d_2 _c_o_m_m_a_n_d_2 is executed if and only if _c_o_m_m_a_n_d returns a non- zero exit status. The return status of AND and OR lists is the exit status of the last command executed in the list. CCoommppoouunndd CCoommmmaannddss A _c_o_m_p_o_u_n_d _c_o_m_m_a_n_d is one of the following: (_l_i_s_t) _l_i_s_t is executed in a subshell. Variable assign- ments and builtin commands that affect the shell's environment do not remain in effect after the com- mand completes. The return status is the exit sta- tus of _l_i_s_t. { _l_i_s_t; } _l_i_s_t is simply executed in the current shell envi- ronment. _l_i_s_t must be terminated with a newline or semicolon. This is known as a _g_r_o_u_p _c_o_m_m_a_n_d. The return status is the exit status of _l_i_s_t. ((_e_x_p_r_e_s_s_i_o_n)) The _e_x_p_r_e_s_s_i_o_n is evaluated according to the rules described below under AARRIITTHHMMEETTIICC EEVVAALLUUAATTIIOONN. If the value of the expression is non-zero, the return status is 0; otherwise the return status is 1. This is exactly equivalent to lleett ""_e_x_p_r_e_s_s_i_o_n"". [[[[ _e_x_p_r_e_s_s_i_o_n ]]]] Return a status of 0 or 1 depending on the evalua- tion of the conditional expression _e_x_p_r_e_s_s_i_o_n. Expressions are composed of the primaries described below under CCOONNDDIITTIIOONNAALL EEXXPPRREESSSSIIOONNSS. Word split- ting and pathname expansion are not performed on the words between the [[[[ and ]]]]; tilde expansion, parameter and variable expansion, arithmetic expan- sion, command substitution, process substitution, and quote removal are performed. When the ==== and !!== operators are used, the string GNU 1998 Apr 1 6 BASH(1) BASH(1) to the right of the operator is considered a pat- tern and matched according to the rules described below under PPaatttteerrnn MMaattcchhiinngg. The return value is 0 if the string matches or does not match the pat- tern, respectively, and 1 otherwise. Any part of the pattern may be quoted to force it to be matched as a string. Expressions may be combined using the following operators, listed in decreasing order of prece- dence: (( _e_x_p_r_e_s_s_i_o_n )) Returns the value of _e_x_p_r_e_s_s_i_o_n. This may be used to override the normal precedence of operators. !! _e_x_p_r_e_s_s_i_o_n True if _e_x_p_r_e_s_s_i_o_n is false. _e_x_p_r_e_s_s_i_o_n_1 &&&& _e_x_p_r_e_s_s_i_o_n_2 True if both _e_x_p_r_e_s_s_i_o_n_1 and _e_x_p_r_e_s_s_i_o_n_2 are true. _e_x_p_r_e_s_s_i_o_n_1 |||| _e_x_p_r_e_s_s_i_o_n_2 True if either _e_x_p_r_e_s_s_i_o_n_1 or _e_x_p_r_e_s_s_i_o_n_2 is true. The &&&& and |||| operators do not execute _e_x_p_r_e_s_s_i_o_n_2 if the value of _e_x_p_r_e_s_s_i_o_n_1 is sufficient to determine the return value of the entire conditional expression. ffoorr _n_a_m_e [ iinn _w_o_r_d; ] ddoo _l_i_s_t ; ddoonnee The list of words following iinn is expanded, gener- ating a list of items. The variable _n_a_m_e is set to each element of this list in turn, and _l_i_s_t is exe- cuted each time. If the iinn _w_o_r_d is omitted, the ffoorr command executes _l_i_s_t once for each positional parameter that is set (see PPAARRAAMMEETTEERRSS below). The return status is the exit status of the last com- mand that executes. If the expansion of the items following iinn results in an empty list, no commands are executed, and the return status is 0. sseelleecctt _n_a_m_e [ iinn _w_o_r_d; ] ddoo _l_i_s_t ; ddoonnee The list of words following iinn is expanded, gener- ating a list of items. The set of expanded words is printed on the standard error, each preceded by a number. If the iinn _w_o_r_d is omitted, the posi- tional parameters are printed (see PPAARRAAMMEETTEERRSS below). The PPSS33 prompt is then displayed and a line read from the standard input. If the line consists of a number corresponding to one of the displayed words, then the value of _n_a_m_e is set to that word. If the line is empty, the words and prompt are displayed again. If EOF is read, the command completes. Any other value read causes GNU 1998 Apr 1 7 BASH(1) BASH(1) _n_a_m_e to be set to null. The line read is saved in the variable RREEPPLLYY. The _l_i_s_t is executed after each selection until a bbrreeaakk or rreettuurrnn command is executed. The exit status of sseelleecctt is the exit status of the last command executed in _l_i_s_t, or zero if no commands were executed. ccaassee _w_o_r_d iinn [ ( _p_a_t_t_e_r_n [ || _p_a_t_t_e_r_n ] ... ) _l_i_s_t ;; ] ... eessaacc A ccaassee command first expands _w_o_r_d, and tries to match it against each _p_a_t_t_e_r_n in turn, using the same matching rules as for pathname expansion (see PPaatthhnnaammee EExxppaannssiioonn below). When a match is found, the corresponding _l_i_s_t is executed. After the first match, no subsequent matches are attempted. The exit status is zero if no pattern matches. Otherwise, it is the exit status of the last com- mand executed in _l_i_s_t. iiff _l_i_s_t; tthheenn _l_i_s_t_; [ eelliiff _l_i_s_t; tthheenn _l_i_s_t; ] ... [ eellssee _l_i_s_t; ] ffii The iiff _l_i_s_t is executed. If its exit status is zero, the tthheenn _l_i_s_t is executed. Otherwise, each eelliiff _l_i_s_t is executed in turn, and if its exit sta- tus is zero, the corresponding tthheenn _l_i_s_t is exe- cuted and the command completes. Otherwise, the eellssee _l_i_s_t is executed, if present. The exit status is the exit status of the last command executed, or zero if no condition tested true. wwhhiillee _l_i_s_t; ddoo _l_i_s_t; ddoonnee uunnttiill _l_i_s_t; ddoo _l_i_s_t; ddoonnee The wwhhiillee command continuously executes the ddoo _l_i_s_t as long as the last command in _l_i_s_t returns an exit status of zero. The uunnttiill command is identical to the wwhhiillee command, except that the test is negated; the ddoo _l_i_s_t is executed as long as the last command in _l_i_s_t returns a non-zero exit status. The exit status of the wwhhiillee and uunnttiill commands is the exit status of the last ddoo _l_i_s_t command executed, or zero if none was executed. [ ffuunnccttiioonn ] _n_a_m_e () { _l_i_s_t; } This defines a function named _n_a_m_e. The _b_o_d_y of the function is the _l_i_s_t of commands between { and }. This list is executed whenever _n_a_m_e is speci- fied as the name of a simple command. The exit status of a function is the exit status of the last command executed in the body. (See FFUUNNCCTTIIOONNSS below.) CCOOMMMMEENNTTSS In a non-interactive shell, or an interactive shell in which the iinntteerraaccttiivvee__ccoommmmeennttss option to the sshhoopptt builtin GNU 1998 Apr 1 8 BASH(1) BASH(1) is enabled (see SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS below), a word beginning with ## causes that word and all remaining char- acters on that line to be ignored. An interactive shell without the iinntteerraaccttiivvee__ccoommmmeennttss option enabled does not allow comments. The iinntteerraaccttiivvee__ccoommmmeennttss option is on by default in interactive shells. QQUUOOTTIINNGG _Q_u_o_t_i_n_g is used to remove the special meaning of certain characters or words to the shell. Quoting can be used to disable special treatment for special characters, to pre- vent reserved words from being recognized as such, and to prevent parameter expansion. Each of the _m_e_t_a_c_h_a_r_a_c_t_e_r_s listed above under DDEEFFIINNIITTIIOONNSS has special meaning to the shell and must be quoted if they are to represent themselves. There are three quoting mechanisms: the _e_s_c_a_p_e _c_h_a_r_a_c_t_e_r, single quotes, and dou- ble quotes. A non-quoted backslash (\\) is the _e_s_c_a_p_e _c_h_a_r_a_c_t_e_r. It preserves the literal value of the next character that follows, with the exception of <newline>. If a \\<newline> pair appears, and the backslash is not itself quoted, the \\<newline> is treated as a line continuation (that is, it is removed from the input stream and effectively ignored). Enclosing characters in single quotes preserves the lit- eral value of each character within the quotes. A single quote may not occur between single quotes, even when pre- ceded by a backslash. Enclosing characters in double quotes preserves the lit- eral value of all characters within the quotes, with the exception of $$, ``, and \\. The characters $$ and `` retain their special meaning within double quotes. The backslash retains its special meaning only when followed by one of the following characters: $$, ``, "", \\, or <<nneewwlliinnee>>. A double quote may be quoted within double quotes by preced- ing it with a backslash. The special parameters ** and @@ have special meaning when in double quotes (see PPAARRAAMMEETTEERRSS below). Words of the form $$'_s_t_r_i_n_g' are treated specially. The word expands to _s_t_r_i_n_g, with backslash-escaped characters replaced as specifed by the ANSI C standard. Backslash escape sequences, if present, are decoded as follows: \\aa alert (bell) \\bb backspace \\ee an escape character \\ff form feed \\nn new line \\rr carriage return GNU 1998 Apr 1 9 BASH(1) BASH(1) \\tt horizontal tab \\vv vertical tab \\\\ backslash \\_n_n_n the character whose ASCII code is the octal value _n_n_n (one to three digits) \\xx_n_n_n the character whose ASCII code is the hex- adecimal value _n_n_n (one to three digits) The translated result is single-quoted, as if the dollar sign had not been present. A double-quoted string preceded by a dollar sign ($$) will cause the string to be translated according to the current locale. If the current locale is CC or PPOOSSIIXX, the dollar sign is ignored. If the string is translated and replaced, the replacement is double-quoted. PPAARRAAMMEETTEERRSS A _p_a_r_a_m_e_t_e_r is an entity that stores values. It can be a _n_a_m_e, a number, or one of the special characters listed below under SSppeecciiaall PPaarraammeetteerrss. For the shell's purposes, a _v_a_r_i_a_b_l_e is a parameter denoted by a _n_a_m_e. A parameter is set if it has been assigned a value. The null string is a valid value. Once a variable is set, it may be unset only by using the uunnsseett builtin command (see SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS below). A _v_a_r_i_a_b_l_e may be assigned to by a statement of the form _n_a_m_e=[_v_a_l_u_e] If _v_a_l_u_e is not given, the variable is assigned the null string. All _v_a_l_u_e_s undergo tilde expansion, parameter and variable expansion, string expansion, command substitu- tion, arithmetic expansion, and quote removal (see EEXXPPAANN-- SSIIOONN below). If the variable has its iinntteeggeerr attribute set (see ddeeccllaarree below in SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS) then _v_a_l_u_e is subject to arithmetic expansion even if the $((...)) expansion is not used (see AArriitthhmmeettiicc EExxppaannssiioonn below). Word splitting is not performed, with the excep- tion of ""$$@@"" as explained below under SSppeecciiaall PPaarraammeetteerrss. Pathname expansion is not performed. PPoossiittiioonnaall PPaarraammeetteerrss A _p_o_s_i_t_i_o_n_a_l _p_a_r_a_m_e_t_e_r is a parameter denoted by one or more digits, other than the single digit 0. Positional parameters are assigned from the shell's arguments when it is invoked, and may be reassigned using the sseett builtin command. Positional parameters may not be assigned to with assignment statements. The positional parameters are temporarily replaced when a shell function is executed (see FFUUNNCCTTIIOONNSS below). GNU 1998 Apr 1 10 BASH(1) BASH(1) When a positional parameter consisting of more than a sin- gle digit is expanded, it must be enclosed in braces (see EEXXPPAANNSSIIOONN below). SSppeecciiaall PPaarraammeetteerrss The shell treats several parameters specially. These parameters may only be referenced; assignment to them is not allowed. ** Expands to the positional parameters, starting from one. When the expansion occurs within double quotes, it expands to a single word with the value of each parameter separated by the first character of the IIFFSS special variable. That is, "$$**" is equivalent to "$$11_c$$22_c......", where _c is the first character of the value of the IIFFSS variable. If IIFFSS is unset, the parameters are separated by spaces. If IIFFSS is null, the parameters are joined without intervening separators. @@ Expands to the positional parameters, starting from one. When the expansion occurs within double quotes, each parameter expands to a separate word. That is, "$$@@" is equivalent to "$$11" "$$22" ... When there are no positional parameters, "$$@@" and $$@@ expand to nothing (i.e., they are removed). ## Expands to the number of positional parameters in decimal. ?? Expands to the status of the most recently executed foreground pipeline. -- Expands to the current option flags as specified upon invocation, by the sseett builtin command, or those set by the shell itself (such as the --ii option). $$ Expands to the process ID of the shell. In a () subshell, it expands to the process ID of the cur- rent shell, not the subshell. !! Expands to the process ID of the most recently exe- cuted background (asynchronous) command. 00 Expands to the name of the shell or shell script. This is set at shell initialization. If bbaasshh is invoked with a file of commands, $$00 is set to the name of that file. If bbaasshh is started with the --cc option, then $$00 is set to the first argument after the string to be executed, if one is present. Oth- erwise, it is set to the file name used to invoke bbaasshh, as given by argument zero. __ At shell startup, set to the absolute file name of the shell or shell script being executed as passed in the argument list. Subsequently, expands to the last argument to the previous command, after expan- sion. Also set to the full file name of each com- mand executed and placed in the environment exported to that command. When checking mail, this parameter holds the name of the mail file currently being checked. GNU 1998 Apr 1 11 BASH(1) BASH(1) SShheellll VVaarriiaabblleess The following variables are set by the shell: PPPPIIDD The process ID of the shell's parent. This vari- able is readonly. PPWWDD The current working directory as set by the ccdd com- mand. OOLLDDPPWWDD The previous working directory as set by the ccdd command. RREEPPLLYY Set to the line of input read by the rreeaadd builtin command when no arguments are supplied. UUIIDD Expands to the user ID of the current user, ini- tialized at shell startup. This variable is read- only. EEUUIIDD Expands to the effective user ID of the current user, initialized at shell startup. This variable is readonly. GGRROOUUPPSS An array variable containing the list of groups of which the current user is a member. This variable is readonly. BBAASSHH Expands to the full file name used to invoke this instance of bbaasshh. BBAASSHH__VVEERRSSIIOONN Expands to a string describing the version of this instance of bbaasshh. BBAASSHH__VVEERRSSIINNFFOO A readonly array variable whose members hold ver- sion information for this instance of bbaasshh. The values assigned to the array members are as fol- lows: BBAASSHH__VVEERRSSIINNFFOO[[0]] The major version number (the _r_e_l_e_a_s_e). BBAASSHH__VVEERRSSIINNFFOO[[1]] The minor version number (the _v_e_r_s_i_o_n). BBAASSHH__VVEERRSSIINNFFOO[[2]] The patch level. BBAASSHH__VVEERRSSIINNFFOO[[3]] The build version. BBAASSHH__VVEERRSSIINNFFOO[[4]] The release status (e.g., _b_e_t_a_1). BBAASSHH__VVEERRSSIINNFFOO[[5]] The value of MMAACCHHTTYYPPEE. SSHHLLVVLL Incremented by one each time an instance of bbaasshh is started. RRAANNDDOOMM Each time this parameter is referenced, a random integer between 0 and 32767 is generated. The sequence of random numbers may be initialized by assigning a value to RRAANNDDOOMM. If RRAANNDDOOMM is unset, it loses its special properties, even if it is sub- sequently reset. SSEECCOONNDDSS Each time this parameter is referenced, the number of seconds since shell invocation is returned. If a value is assigned to SSEECCOONNDDSS, the value returned GNU 1998 Apr 1 12 BASH(1) BASH(1) upon subsequent references is the number of seconds since the assignment plus the value assigned. If SSEECCOONNDDSS is unset, it loses its special properties, even if it is subsequently reset. LLIINNEENNOO Each time this parameter is referenced, the shell substitutes a decimal number representing the cur- rent sequential line number (starting with 1) within a script or function. When not in a script or function, the value substituted is not guaran- teed to be meaningful. If LLIINNEENNOO is unset, it loses its special properties, even if it is subse- quently reset. HHIISSTTCCMMDD The history number, or index in the history list, of the current command. If HHIISSTTCCMMDD is unset, it loses its special properties, even if it is subse- quently reset. DDIIRRSSTTAACCKK An array variable (see AArrrraayyss below) containing the current contents of the directory stack. Directo- ries appear in the stack in the order they are dis- played by the ddiirrss builtin. Assigning to members of this array variable may be used to modify direc- tories already in the stack, but the ppuusshhdd and ppooppdd builtins must be used to add and remove directo- ries. Assignment to this variable will not change the current directory. If DDIIRRSSTTAACCKK is unset, it loses its special properties, even if it is subse- quently reset. PPIIPPEESSTTAATTUUSS An array variable (see AArrrraayyss below) containing a list of exit status values from the processes in the most-recently-executed foreground pipeline (which may contain only a single command). OOPPTTAARRGG The value of the last option argument processed by the ggeettooppttss builtin command (see SSHHEELLLL BBUUIILLTTIINN CCOOMM-- MMAANNDDSS below). OOPPTTIINNDD The index of the next argument to be processed by the ggeettooppttss builtin command (see SSHHEELLLL BBUUIILLTTIINN CCOOMM-- MMAANNDDSS below). HHOOSSTTNNAAMMEE Automatically set to the name of the current host. HHOOSSTTTTYYPPEE Automatically set to a string that uniquely describes the type of machine on which bbaasshh is exe- cuting. The default is system-dependent. GNU 1998 Apr 1 13 BASH(1) BASH(1) OOSSTTYYPPEE Automatically set to a string that describes the operating system on which bbaasshh is executing. The default is system-dependent. MMAACCHHTTYYPPEE Automatically set to a string that fully describes the system type on which bbaasshh is executing, in the standard GNU _c_p_u_-_c_o_m_p_a_n_y_-_s_y_s_t_e_m format. The default is system-dependent. SSHHEELLLLOOPPTTSS A colon-separated list of enabled shell options. Each word in the list is a valid argument for the --oo option to the sseett builtin command (see SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS below). The options appearing in SSHHEELLLLOOPPTTSS are those reported as _o_n by sseett --oo. If this variable is in the environment when bbaasshh starts up, each shell option in the list will be enabled before reading any startup files. This variable is read-only. The following variables are used by the shell. In some cases, bbaasshh assigns a default value to a variable; these cases are noted below. IIFFSS The _I_n_t_e_r_n_a_l _F_i_e_l_d _S_e_p_a_r_a_t_o_r that is used for word splitting after expansion and to split lines into words with the rreeaadd builtin command. The default value is ``<space><tab><newline>''. PPAATTHH The search path for commands. It is a colon-sepa- rated list of directories in which the shell looks for commands (see CCOOMMMMAANNDD EEXXEECCUUTTIIOONN below). The default path is system-dependent, and is set by the administrator who installs bbaasshh. A common value is ``/usr/gnu/bin:/usr/local/bin:/usr/ucb:/bin:/usr/bin:.''. HHOOMMEE The home directory of the current user; the default argument for the ccdd builtin command. The value of this variable is also used when performing tilde expansion. CCDDPPAATTHH The search path for the ccdd command. This is a colon-separated list of directories in which the shell looks for destination directories specified by the ccdd command. A sample value is ``.:~:/usr''. BBAASSHH__EENNVV If this parameter is set when bbaasshh is executing a shell script, its value is interpreted as a file- name containing commands to initialize the shell, as in _~_/_._b_a_s_h_r_c. The value of BBAASSHH__EENNVV is sub- jected to parameter expansion, command substitu- tion, and arithmetic expansion before being inter- preted as a file name. PPAATTHH is not used to search for the resultant file name. MMAAIILL If this parameter is set to a file name and the MMAAIILLPPAATTHH variable is not set, bbaasshh informs the user GNU 1998 Apr 1 14 BASH(1) BASH(1) of the arrival of mail in the specified file. MMAAIILLCCHHEECCKK Specifies how often (in seconds) bbaasshh checks for mail. The default is 60 seconds. When it is time to check for mail, the shell does so before dis- playing the primary prompt. If this variable is unset, the shell disables mail checking. MMAAIILLPPAATTHH A colon-separated list of file names to be checked for mail. The message to be printed when mail arrives in a particular file may be specified by separating the file name from the message with a `?'. When used in the text of the message, $$__ expands to the name of the current mailfile. Exam- ple: MMAAIILLPPAATTHH='/usr/spool/mail/bfox?"You have mail":~/shell-mail?"$_ has mail!"' BBaasshh supplies a default value for this variable, but the location of the user mail files that it uses is system dependent (e.g., /usr/spool/mail/$$UUSSEERR). PPSS11 The value of this parameter is expanded (see PPRROOMMPPTTIINNGG below) and used as the primary prompt string. The default value is ``\\ss--\\vv\\$$ ''. PPSS22 The value of this parameter is expanded as with PPSS11 and used as the secondary prompt string. The default is ``>> ''. PPSS33 The value of this parameter is used as the prompt for the sseelleecctt command (see SSHHEELLLL GGRRAAMMMMAARR above). PPSS44 The value of this parameter is expanded as with PPSS11 and the value is printed before each command bbaasshh displays during an execution trace. The first character of PPSS44 is replicated multiple times, as necessary, to indicate multiple levels of indirec- tion. The default is ``++ ''. TTIIMMEEFFOORRMMAATT The value of this parameter is used as a format string specifying how the timing information for pipelines prefixed with the ttiimmee reserved word should be displayed. The %% character introduces an escape sequence that is expanded to a time value or other information. The escape sequences and their meanings are as follows; the braces denote optional portions. %%%% A literal %%. %%[[_p]][[ll]]RR The elapsed time in seconds. %%[[_p]][[ll]]UU The number of CPU seconds spent in user mode. %%[[_p]][[ll]]SS The number of CPU seconds spent in system mode. %%PP The CPU percentage, computed as (%U + %S) / %R. The optional _p is a digit specifying the _p_r_e_c_i_s_i_o_n, GNU 1998 Apr 1 15 BASH(1) BASH(1) the number of fractional digits after a decimal point. A value of 0 causes no decimal point or fraction to be output. At most three places after the decimal point may be specified; values of _p greater than 3 are changed to 3. If _p is not spec- ified, the value 3 is used. The optional ll specifies a longer format, including minutes, of the form _M_Mm_S_S._F_Fs. The value of _p determines whether or not the fraction is included. If this variable is not set, bbaasshh acts as if it had the value $$''\\nnrreeaall\\tt%%33llRR\\nnuusseerr\\tt%%33llUU\\nnssyyss%%33llSS''. If the value is null, no timing information is dis- played. A trailing newline is added when the for- mat string is displayed. HHIISSTTSSIIZZEE The number of commands to remember in the command history (see HHIISSTTOORRYY below). The default value is 500. HHIISSTTFFIILLEE The name of the file in which command history is saved (see HHIISSTTOORRYY below). The default value is _~_/_._b_a_s_h___h_i_s_t_o_r_y. If unset, the command history is not saved when an interactive shell exits. HHIISSTTFFIILLEESSIIZZEE The maximum number of lines contained in the his- tory file. When this variable is assigned a value, the history file is truncated, if necessary, to contain no more than that number of lines. The default value is 500. The history file is also truncated to this size after writing it when an interactive shell exits. OOPPTTEERRRR If set to the value 1, bbaasshh displays error messages generated by the ggeettooppttss builtin command (see SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS below). OOPPTTEERRRR is initialized to 1 each time the shell is invoked or a shell script is executed. LLAANNGG Used to determine the locale category for any cate- gory not specifically selected with a variable starting with LLCC__. LLCC__AALLLL This variable overrides the value of LLAANNGG and any other LLCC__ variable specifying a locale category. LLCC__CCOOLLLLAATTEE This variable determines the collation order used when sorting the results of pathname expansion, and determines the behavior of range expressions, GNU 1998 Apr 1 16 BASH(1) BASH(1) equivalence classes, and collating sequences within pathname expansion and pattern matching. LLCC__CCTTYYPPEE This variable determines the interpretation of characters and the behavior of character classes within pathname expansion and pattern matching. LLCC__MMEESSSSAAGGEESS This variable determines the locale used to trans- late double-quoted strings preceded by a $$. PPRROOMMPPTT__CCOOMMMMAANNDD If set, the value is executed as a command prior to issuing each primary prompt. IIGGNNOORREEEEOOFF Controls the action of an interactive shell on receipt of an EEOOFF character as the sole input. If set, the value is the number of consecutive EEOOFF characters which must be typed as the first charac- ters on an input line before bbaasshh exits. If the variable exists but does not have a numeric value, or has no value, the default value is 10. If it does not exist, EEOOFF signifies the end of input to the shell. TTMMOOUUTT If set to a value greater than zero, the value is interpreted as the number of seconds to wait for input after issuing the primary prompt. BBaasshh ter- minates after waiting for that number of seconds if input does not arrive. FFCCEEDDIITT The default editor for the ffcc builtin command. FFIIGGNNOORREE A colon-separated list of suffixes to ignore when performing filename completion (see RREEAADDLLIINNEE below). A filename whose suffix matches one of the entries in FFIIGGNNOORREE is excluded from the list of matched filenames. A sample value is ``.o:~''. GGLLOOBBIIGGNNOORREE A colon-separated list of patterns defining the set of filenames to be ignored by pathname expansion. If a filename matched by a pathname expansion pat- tern also matches one of the patterns in GGLLOOBBIIGG-- NNOORREE, it is removed from the list of matches. IINNPPUUTTRRCC The filename for the rreeaaddlliinnee startup file, over- riding the default of _~_/_._i_n_p_u_t_r_c (see RREEAADDLLIINNEE below). GNU 1998 Apr 1 17 BASH(1) BASH(1) HHIISSTTCCOONNTTRROOLL If set to a value of _i_g_n_o_r_e_s_p_a_c_e, lines which begin with a ssppaaccee character are not entered on the his- tory list. If set to a value of _i_g_n_o_r_e_d_u_p_s, lines matching the last history line are not entered. A value of _i_g_n_o_r_e_b_o_t_h combines the two options. If unset, or if set to any other value than those above, all lines read by the parser are saved on the history list, subject to the value of HHIISSTTIIGG-- NNOORREE. This variable's function is superseded by HHIISSTTIIGGNNOORREE. The second and subsequent lines of a multi-line compound command are not tested, and are added to the history regardless of the value of HHIISSTTCCOONNTTRROOLL. HHIISSTTIIGGNNOORREE A colon-separated list of patterns used to decide which command lines should be saved on the history list. Each pattern is anchored at the beginning of the line and must fully specify the line (no implicit `**' is appended). Each pattern is tested against the line after the checks specified by HHIISSTTCCOONNTTRROOLL are applied. In addition to the normal shell pattern matching characters, `&&' matches the previous history line. `&&' may be escaped using a backslash. The backslash is removed before attempting a match. The second and subsequent lines of a multi-line compound command are not tested, and are added to the history regardless of the value of HHIISSTTIIGGNNOORREE. hhiissttcchhaarrss The two or three characters which control history expansion and tokenization (see HHIISSTTOORRYY EEXXPPAANNSSIIOONN below). The first character is the _h_i_s_t_o_r_y _e_x_p_a_n_- _s_i_o_n _c_h_a_r_a_c_t_e_r, the character which signals the start of a history expansion, normally `!!'. The second character is the _q_u_i_c_k _s_u_b_s_t_i_t_u_t_i_o_n charac- ter, which is used as shorthand for re-running the previous command entered, substituting one string for another in the command. The default is `^^'. The optional third character is the character which indicates that the remainder of the line is a com- ment when found as the first character of a word, normally `##'. The history comment character causes history substitution to be skipped for the remain- ing words on the line. It does not necessarily cause the shell parser to treat the rest of the line as a comment. HHOOSSTTFFIILLEE Contains the name of a file in the same format as _/_e_t_c_/_h_o_s_t_s that should be read when the shell needs to complete a hostname. The file may be changed GNU 1998 Apr 1 18 BASH(1) BASH(1) interactively; the next time hostname completion is attempted bbaasshh adds the contents of the new file to the already existing database. aauuttoo__rreessuummee This variable controls how the shell interacts with the user and job control. If this variable is set, single word simple commands without redirections are treated as candidates for resumption of an existing stopped job. There is no ambiguity allowed; if there is more than one job beginning with the string typed, the job most recently accessed is selected. The _n_a_m_e of a stopped job, in this context, is the command line used to start it. If set to the value _e_x_a_c_t, the string supplied must match the name of a stopped job exactly; if set to _s_u_b_s_t_r_i_n_g, the string supplied needs to match a substring of the name of a stopped job. The _s_u_b_s_t_r_i_n_g value provides functionality analo- gous to the %%?? job identifier (see JJOOBB CCOONNTTRROOLL below). If set to any other value, the supplied string must be a prefix of a stopped job's name; this provides functionality analogous to the %% job identifier. AArrrraayyss BBaasshh provides one-dimensional array variables. Any vari- able may be used as an array; the ddeeccllaarree builtin will explicitly declare an array. There is no maximum limit on the size of an array, nor any requirement that members be indexed or assigned contiguously. Arrays are indexed using integers and are zero-based. An array is created automatically if any variable is assigned to using the syntax _n_a_m_e[_s_u_b_s_c_r_i_p_t]=_v_a_l_u_e. The _s_u_b_s_c_r_i_p_t is treated as an arithmetic expression that must evaluate to a number greater than or equal to zero. To explicitly declare an array, use ddeeccllaarree --aa _n_a_m_e (see SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS below). ddeeccllaarree --aa _n_a_m_e[[_s_u_b_s_c_r_i_p_t]] is also accepted; the _s_u_b_s_c_r_i_p_t is ignored. Attributes may be specified for an array variable using the ddeeccllaarree and rreeaaddoonnllyy builtins. Each attribute applies to all mem- bers of an array. Arrays are assigned to using compound assignments of the form _n_a_m_e=((value_1 ... value_n)), where each _v_a_l_u_e is of the form [_s_u_b_s_c_r_i_p_t]=_s_t_r_i_n_g. Only _s_t_r_i_n_g is required. If the optional brackets and subscript are supplied, that index is assigned to; otherwise the index of the element assigned is the last index assigned to by the statement plus one. Indexing starts at zero. This syntax is also accepted by the ddeeccllaarree builtin. Individual array ele- ments may be assigned to using the _n_a_m_e[_s_u_b_s_c_r_i_p_t]=_v_a_l_u_e syntax introduced above. GNU 1998 Apr 1 19 BASH(1) BASH(1) Any element of an array may be referenced using ${_n_a_m_e[_s_u_b_s_c_r_i_p_t]}. The braces are required to avoid con- flicts with pathname expansion. If _s_u_b_s_c_r_i_p_t is @@ or **, the word expands to all members of _n_a_m_e. These subscripts differ only when the word appears within double quotes. If the word is double-quoted, ${_n_a_m_e[*]} expands to a sin- gle word with the value of each array member separated by the first character of the IIFFSS special variable, and ${_n_a_m_e[@]} expands each element of _n_a_m_e to a separate word. When there are no array members, ${_n_a_m_e[@]} expands to nothing. This is analogous to the expansion of the special parameters ** and @@ (see SSppeecciiaall PPaarraammeetteerrss above). ${#_n_a_m_e[_s_u_b_s_c_r_i_p_t]} expands to the length of ${_n_a_m_e[_s_u_b_- _s_c_r_i_p_t]}. If _s_u_b_s_c_r_i_p_t is ** or @@, the expansion is the number of elements in the array. Referencing an array variable without a subscript is equivalent to referencing element zero. The uunnsseett builtin is used to destroy arrays. uunnsseett nnaammee[_s_u_b_s_c_r_i_p_t] destroys the array element at index _s_u_b_- _s_c_r_i_p_t. uunnsseett _n_a_m_e, where _n_a_m_e is an array, or uunnsseett _n_a_m_e[_s_u_b_s_c_r_i_p_t], where _s_u_b_s_c_r_i_p_t is ** or @@, removes the entire array. The ddeeccllaarree, llooccaall, and rreeaaddoonnllyy builtins each accept a --aa option to specify an array. The rreeaadd builtin accepts a --aa option to assign a list of words read from the standard input to an array. The sseett and ddeeccllaarree builtins display array values in a way that allows them to be reused as assignments. EEXXPPAANNSSIIOONN Expansion is performed on the command line after it has been split into words. There are seven kinds of expansion performed: _b_r_a_c_e _e_x_p_a_n_s_i_o_n, _t_i_l_d_e _e_x_p_a_n_s_i_o_n, _p_a_r_a_m_e_t_e_r _a_n_d _v_a_r_i_a_b_l_e _e_x_p_a_n_s_i_o_n, _c_o_m_m_a_n_d _s_u_b_s_t_i_t_u_t_i_o_n, _a_r_i_t_h_m_e_t_i_c _e_x_p_a_n_s_i_o_n, _w_o_r_d _s_p_l_i_t_t_i_n_g, and _p_a_t_h_n_a_m_e _e_x_p_a_n_s_i_o_n. The order of expansions is: brace expansion, tilde expan- sion, parameter, variable and arithmetic expansion and command substitution (done in a left-to-right fashion), word splitting, and pathname expansion. On systems that can support it, there is an additional expansion available: _p_r_o_c_e_s_s _s_u_b_s_t_i_t_u_t_i_o_n. Only brace expansion, word splitting, and pathname expan- sion can change the number of words of the expansion; other expansions expand a single word to a single word. The only exceptions to this are the expansions of "$$@@" and "$${{_n_a_m_e[[@@]]}}" as explained above (see PPAARRAAMMEETTEERRSS). BBrraaccee EExxppaannssiioonn _B_r_a_c_e _e_x_p_a_n_s_i_o_n is a mechanism by which arbitrary strings GNU 1998 Apr 1 20 BASH(1) BASH(1) may be generated. This mechanism is similar to _p_a_t_h_n_a_m_e _e_x_p_a_n_s_i_o_n, but the filenames generated need not exist. Patterns to be brace expanded take the form of an optional _p_r_e_a_m_b_l_e, followed by a series of comma-separated strings between a pair of braces, followed by an optional _p_o_s_t_s_c_r_i_p_t. The preamble is prefixed to each string con- tained within the braces, and the postscript is then appended to each resulting string, expanding left to right. Brace expansions may be nested. The results of each expanded string are not sorted; left to right order is preserved. For example, a{{d,c,b}}e expands into `ade ace abe'. Brace expansion is performed before any other expansions, and any characters special to other expansions are pre- served in the result. It is strictly textual. BBaasshh does not apply any syntactic interpretation to the context of the expansion or the text between the braces. A correctly-formed brace expansion must contain unquoted opening and closing braces, and at least one unquoted comma. Any incorrectly formed brace expansion is left unchanged. A {{ or ,, may be quoted with a backslash to prevent its being considered part of a brace expression. This construct is typically used as shorthand when the common prefix of the strings to be generated is longer than in the above example: mkdir /usr/local/src/bash/{old,new,dist,bugs} or chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}} Brace expansion introduces a slight incompatibility with historical versions of sshh. sshh does not treat opening or closing braces specially when they appear as part of a word, and preserves them in the output. BBaasshh removes braces from words as a consequence of brace expansion. For example, a word entered to sshh as _f_i_l_e_{_1_,_2_} appears identically in the output. The same word is output as _f_i_l_e_1 _f_i_l_e_2 after expansion by bbaasshh. If strict compati- bility with sshh is desired, start bbaasshh with the ++BB option or disable brace expansion with the ++BB option to the sseett command (see SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS below). TTiillddee EExxppaannssiioonn If a word begins with an unquoted tilde character (`~~'), all of the characters preceding the first unquoted slash (or all characters, if there is no unquoted slash) are considered a _t_i_l_d_e_-_p_r_e_f_i_x. If none of the characters in the tilde-prefix are quoted, the characters in the tilde- prefix following the tilde are treated as a possible _l_o_g_i_n GNU 1998 Apr 1 21 BASH(1) BASH(1) _n_a_m_e. If this login name is the null string, the tilde is replaced with the value of the shell parameter HHOOMMEE. If HHOOMMEE is unset, the home directory of the user executing the shell is substituted instead. Otherwise, the tilde- prefix is replaced with the home directory associated with the specified login name. If the tilde-prefix is a `~+', the value of the shell variable PPWWDD replaces the tilde-prefix. If the tilde-pre- fix is a `~-', the value of the shell variable OOLLDDPPWWDD, if it is set, is substituted. If the characters following the tilde in the tilde-prefix consist of a number _N, optionally prefixed by a `+' or a `-', the tilde-prefix is replaced with the corresponding element from the directory stack, as it would be displayed by the ddiirrss builtin invoked with the tilde-prefix as an argument. If the characters following the tilde in the tilde-prefix consist of a number without a leading `+' or `-', `+' is assumed. If the login name is invalid, or the tilde expansion fails, the word is unchanged. Each variable assignment is checked for unquoted tilde- prefixes immediately following a :: or ==. In these cases, tilde expansion is also performed. Consequently, one may use file names with tildes in assignments to PPAATTHH, MMAAIILL-- PPAATTHH, and CCDDPPAATTHH, and the shell assigns the expanded value. PPaarraammeetteerr EExxppaannssiioonn The `$$' character introduces parameter expansion, command substitution, or arithmetic expansion. The parameter name or symbol to be expanded may be enclosed in braces, which are optional but serve to protect the variable to be expanded from characters immediately following it which could be interpreted as part of the name. When braces are used, the matching ending brace is the first `}}' not escaped by a backslash or within a quoted string, and not within an embedded arithmetic expansion, command substitution, or paramter expansion. ${_p_a_r_a_m_e_t_e_r} The value of _p_a_r_a_m_e_t_e_r is substituted. The braces are required when _p_a_r_a_m_e_t_e_r is a positional parame- ter with more than one digit, or when _p_a_r_a_m_e_t_e_r is followed by a character which is not to be inter- preted as part of its name. If the first character of _p_a_r_a_m_e_t_e_r is an exclamation point, a level of variable indirection is introduced. BBaasshh uses the value of the variable formed from the rest of _p_a_r_a_m_e_t_e_r as the name of the variable; this variable is then expanded and that value used in the rest of the GNU 1998 Apr 1 22 BASH(1) BASH(1) substitution, rather than the value of _p_a_r_a_m_e_t_e_r itself. This is known as _i_n_d_i_r_e_c_t _e_x_p_a_n_s_i_o_n. In each of the cases below, _w_o_r_d is subject to tilde expansion, parameter expansion, command substitution, and arithmetic expansion. When not performing substring expansion, bbaasshh tests for a parameter that is unset or null; omitting the colon results in a test only for a parameter that is unset. ${_p_a_r_a_m_e_t_e_r::--_w_o_r_d} UUssee DDeeffaauulltt VVaalluueess. If _p_a_r_a_m_e_t_e_r is unset or null, the expansion of _w_o_r_d is substituted. Otherwise, the value of _p_a_r_a_m_e_t_e_r is substituted. ${_p_a_r_a_m_e_t_e_r::==_w_o_r_d} AAssssiiggnn DDeeffaauulltt VVaalluueess. If _p_a_r_a_m_e_t_e_r is unset or null, the expansion of _w_o_r_d is assigned to _p_a_r_a_m_e_- _t_e_r. The value of _p_a_r_a_m_e_t_e_r is then substituted. Positional parameters and special parameters may not be assigned to in this way. ${_p_a_r_a_m_e_t_e_r::??_w_o_r_d} DDiissppllaayy EErrrroorr iiff NNuullll oorr UUnnsseett. If _p_a_r_a_m_e_t_e_r is null or unset, the expansion of _w_o_r_d (or a message to that effect if _w_o_r_d is not present) is written to the standard error and the shell, if it is not interactive, exits. Otherwise, the value of _p_a_r_a_m_- _e_t_e_r is substituted. ${_p_a_r_a_m_e_t_e_r::++_w_o_r_d} UUssee AAlltteerrnnaattee VVaalluuee. If _p_a_r_a_m_e_t_e_r is null or unset, nothing is substituted, otherwise the expan- sion of _w_o_r_d is substituted. ${_p_a_r_a_m_e_t_e_r::_o_f_f_s_e_t} ${_p_a_r_a_m_e_t_e_r::_o_f_f_s_e_t::_l_e_n_g_t_h} SSuubbssttrriinngg EExxppaannssiioonn.. Expands to up to _l_e_n_g_t_h char- acters of _p_a_r_a_m_e_t_e_r, starting at the characters specified by _o_f_f_s_e_t. If _l_e_n_g_t_h is omitted, expands to the substring of _p_a_r_a_m_e_t_e_r, starting at the character specified by _o_f_f_s_e_t. _l_e_n_g_t_h and _o_f_f_s_e_t are arithmetic expressions (see AARRIITTHHMMEETTIICC EEVVAALLUUAA-- TTIIOONN below). _l_e_n_g_t_h must evaluate to a number greater than or equal to zero. If _o_f_f_s_e_t evaluates to a number less than zero, the value is used as an offset from the end of the value of _p_a_r_a_m_e_t_e_r. If _p_a_r_a_m_e_t_e_r is @@, the result is _l_e_n_g_t_h positional parameters beginning at _o_f_f_s_e_t. If _p_a_r_a_m_e_t_e_r is an array name indexed by @ or *, the result is the _l_e_n_g_t_h members of the array beginning with ${_p_a_r_a_m_- _e_t_e_r[_o_f_f_s_e_t]}. Substring indexing is zero-based unless the positional parameters are used, in which case the indexing starts at 1. ${##_p_a_r_a_m_e_t_e_r} The length in characters of the value of _p_a_r_a_m_e_t_e_r is substituted. If _p_a_r_a_m_e_t_e_r is ** or @@, the value GNU 1998 Apr 1 23 BASH(1) BASH(1) substituted is the number of positional parameters. If _p_a_r_a_m_e_t_e_r is an array name subscripted by ** or @@, the value substituted is the number of elements in the array. ${_p_a_r_a_m_e_t_e_r##_w_o_r_d} ${_p_a_r_a_m_e_t_e_r####_w_o_r_d} The _w_o_r_d is expanded to produce a pattern just as in pathname expansion. If the pattern matches the beginning of the value of _p_a_r_a_m_e_t_e_r, then the result of the expansion is the expanded value of _p_a_r_a_m_e_t_e_r with the shortest matching pattern (the ``##'' case) or the longest matching pattern (the ``####'' case) deleted. If _p_a_r_a_m_e_t_e_r is @@ or **, the pattern removal operation is applied to each posi- tional parameter in turn, and the expansion is the resultant list. If _p_a_r_a_m_e_t_e_r is an array variable subscripted with @@ or **, the pattern removal opera- tion is applied to each member of the array in turn, and the expansion is the resultant list. ${_p_a_r_a_m_e_t_e_r%%_w_o_r_d} ${_p_a_r_a_m_e_t_e_r%%%%_w_o_r_d} The _w_o_r_d is expanded to produce a pattern just as in pathname expansion. If the pattern matches a trailing portion of the expanded value of _p_a_r_a_m_e_- _t_e_r, then the result of the expansion is the expanded value of _p_a_r_a_m_e_t_e_r with the shortest matching pattern (the ``%%'' case) or the longest matching pattern (the ``%%%%'' case) deleted. If _p_a_r_a_m_e_t_e_r is @@ or **, the pattern removal operation is applied to each positional parameter in turn, and the expansion is the resultant list. If _p_a_r_a_m_- _e_t_e_r is an array variable subscripted with @@ or **, the pattern removal operation is applied to each member of the array in turn, and the expansion is the resultant list. ${_p_a_r_a_m_e_t_e_r//_p_a_t_t_e_r_n//_s_t_r_i_n_g} ${_p_a_r_a_m_e_t_e_r////_p_a_t_t_e_r_n//_s_t_r_i_n_g} The _p_a_t_t_e_r_n is expanded to produce a pattern just as in pathname expansion. _P_a_r_a_m_e_t_e_r is expanded and the longest match of _p_a_t_t_e_r_n against its value is replaced with _s_t_r_i_n_g. In the first form, only the first match is replaced. The second form causes all matches of _p_a_t_t_e_r_n to be replaced with _s_t_r_i_n_g. If _p_a_t_t_e_r_n begins with ##, it must match at the beginning of _s_t_r_i_n_g. If _p_a_t_t_e_r_n begins with %%, it must match at the end of _s_t_r_i_n_g. If _s_t_r_i_n_g is null, matches of _p_a_t_t_e_r_n are deleted and the // fol- lowing _p_a_t_t_e_r_n may be omitted. If _p_a_r_a_m_e_t_e_r is @@ or **, the substitution operation is applied to each positional parameter in turn, and the expansion is the resultant list. If _p_a_r_a_m_e_t_e_r is an array GNU 1998 Apr 1 24 BASH(1) BASH(1) variable subscripted with @@ or **, the substitution operation is applied to each member of the array in turn, and the expansion is the resultant list. CCoommmmaanndd SSuubbssttiittuuttiioonn _C_o_m_m_a_n_d _s_u_b_s_t_i_t_u_t_i_o_n allows the output of a command to replace the command name. There are two forms: $$((_c_o_m_m_a_n_d)) or ``_c_o_m_m_a_n_d`` BBaasshh performs the expansion by executing _c_o_m_m_a_n_d and replacing the command substitution with the standard out- put of the command, with any trailing newlines deleted. Embedded newlines are not deleted, but they may be removed during word splitting. The command substitution $$((ccaatt _f_i_l_e)) can be replaced by the equivalent but faster $$((<< _f_i_l_e)). When the old-style backquote form of substitution is used, backslash retains its literal meaning except when followed by $$, ``, or \\. The first backquote not preceded by a backslash terminates the command substitution. When using the $(_c_o_m_m_a_n_d) form, all characters between the parenthe- ses make up the command; none are treated specially. Command substitutions may be nested. To nest when using the backquoted form, escape the inner backquotes with backslashes. If the substitution appears within double quotes, word splitting and pathname expansion are not performed on the results. AArriitthhmmeettiicc EExxppaannssiioonn Arithmetic expansion allows the evaluation of an arith- metic expression and the substitution of the result. The format for arithmetic expansion is: $$((((_e_x_p_r_e_s_s_i_o_n)))) The _e_x_p_r_e_s_s_i_o_n is treated as if it were within double quotes, but a double quote inside the parentheses is not treated specially. All tokens in the expression undergo parameter expansion, string expansion, command substitu- tion, and quote removal. Arithmetic substitutions may be nested. The evaluation is performed according to the rules listed below under AARRIITTHHMMEETTIICC EEVVAALLUUAATTIIOONN. If _e_x_p_r_e_s_s_i_o_n is invalid, bbaasshh prints a message indicating failure and no substitution occurs. GNU 1998 Apr 1 25 BASH(1) BASH(1) PPrroocceessss SSuubbssttiittuuttiioonn _P_r_o_c_e_s_s _s_u_b_s_t_i_t_u_t_i_o_n is supported on systems that support named pipes (_F_I_F_O_s) or the //ddeevv//ffdd method of naming open files. It takes the form of <<((_l_i_s_t)) or >>((_l_i_s_t)). The pro- cess _l_i_s_t is run with its input or output connected to a _F_I_F_O or some file in //ddeevv//ffdd. The name of this file is passed as an argument to the current command as the result of the expansion. If the >>((_l_i_s_t)) form is used, writing to the file will provide input for _l_i_s_t. If the <<((_l_i_s_t)) form is used, the file passed as an argument should be read to obtain the output of _l_i_s_t. When available, _p_r_o_c_e_s_s _s_u_b_s_t_i_t_u_t_i_o_n is performed simulta- neously with parameter and variable expansion, command substitution, and arithmetic expansion. WWoorrdd SSpplliittttiinngg The shell scans the results of parameter expansion, com- mand substitution, and arithmetic expansion that did not occur within double quotes for _w_o_r_d _s_p_l_i_t_t_i_n_g. The shell treats each character of IIFFSS as a delimiter, and splits the results of the other expansions into words on these characters. If IIFFSS is unset, or its value is exactly <<ssppaaccee>><<ttaabb>><<nneewwlliinnee>>, the default, then any sequence of IIFFSS characters serves to delimit words. If IIFFSS has a value other than the default, then sequences of the whitespace characters ssppaaccee and ttaabb are ignored at the beginning and end of the word, as long as the whitespace character is in the value of IIFFSS (an IIFFSS whitespace char- acter). Any character in IIFFSS that is not IIFFSS whitespace, along with any adjacent IIFFSS whitespace characters, delim- its a field. A sequence of IIFFSS whitespace characters is also treated as a delimiter. If the value of IIFFSS is null, no word splitting occurs. Explicit null arguments ("""" or '''') are retained. Unquoted implicit null arguments, resulting from the expansion of _p_a_r_a_m_e_t_e_r_s that have no values, are removed. If a parame- ter with no value is expanded within double quotes, a null argument results and is retained. Note that if no expansion occurs, no splitting is per- formed. PPaatthhnnaammee EExxppaannssiioonn After word splitting, unless the --ff option has been set, bbaasshh scans each word for the characters **, ??, ((, and [[. If one of these characters appears, then the word is regarded as a _p_a_t_t_e_r_n, and replaced with an alphabetically sorted list of file names matching the pattern. If no matching file names are found, and the shell option nnuullll-- gglloobb is disabled, the word is left unchanged. If the nnuullllgglloobb option is set, and no matches are found, the word GNU 1998 Apr 1 26 BASH(1) BASH(1) is removed. If the shell option nnooccaasseegglloobb is enabled, the match is performed without regard to the case of alphabetic characters. When a pattern is used for path- name expansion, the character ````..'''' at the start of a name or immediately following a slash must be matched explicitly, unless the shell option ddoottgglloobb is set. When matching a pathname, the slash character must always be matched explicitly. In other cases, the ````..'''' character is not treated specially. See the description of sshhoopptt below under SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS for a description of the nnooccaasseegglloobb, nnuullllgglloobb, and ddoottgglloobb shell options. The GGLLOOBBIIGGNNOORREE shell variable may be used to restrict the set of file names matching a _p_a_t_t_e_r_n. If GGLLOOBBIIGGNNOORREE is set, each matching file name that also matches one of the patterns in GGLLOOBBIIGGNNOORREE is removed from the list of matches. The file names ````..'''' and ````....'''' are always ignored, even when GGLLOOBBIIGGNNOORREE is set. However, setting GGLLOOBBIIGGNNOORREE has the effect of enabling the ddoottgglloobb shell option, so all other file names beginning with a ````..'''' will match. To get the old behavior of ignoring file names beginning with a ````..'''', make ````..**'''' one of the pat- terns in GGLLOOBBIIGGNNOORREE. The ddoottgglloobb option is disabled when GGLLOOBBIIGGNNOORREE is unset. PPaatttteerrnn MMaattcchhiinngg Any character that appears in a pattern, other than the special pattern characters described below, matches itself. The NUL character may not occur in a pattern. The special pattern characters must be quoted if they are to be matched literally. The special pattern characters have the following mean- ings: ** Matches any string, including the null string. ?? Matches any single character. [[......]] Matches any one of the enclosed characters. A pair of characters separated by a minus sign denotes a _r_a_n_g_e; any character lexically between those two characters, inclusive, is matched. If the first character following the [[ is a !! or a ^^ then any character not enclosed is matched. A -- may be matched by including it as the first or last char- acter in the set. A ]] may be matched by including it as the first character in the set. Within [[ and ]], _c_h_a_r_a_c_t_e_r _c_l_a_s_s_e_s can be specified using the syntax [[::_c_l_a_s_s::]], where _c_l_a_s_s is one of the following classes defined in the POSIX.2 stan- dard: aallnnuumm aallpphhaa aasscciiii bbllaannkk ccnnttrrll ddiiggiitt ggrraapphh lloowweerr pprriinntt ppuunncctt ssppaaccee uuppppeerr xxddiiggiitt GNU 1998 Apr 1 27 BASH(1) BASH(1) A character class matches any character belonging to that class. Within [[ and ]], an _e_q_u_i_v_a_l_e_n_c_e _c_l_a_s_s can be speci- fied using the syntax [[==_c==]], which matches all characters with the same collation weight (as defined by the current locale) as the character _c. Within [[ and ]], the syntax [[.._s_y_m_b_o_l..]] matches the collating symbol _s_y_m_b_o_l. If the eexxttgglloobb shell option is enabled using the sshhoopptt builtin, several extended pattern matching operators are recognized. In the following description, a _p_a_t_t_e_r_n_-_l_i_s_t is a list of one or more patterns separated by a ||. Com- posite patterns may be formed using one or more of the following sub-patterns: ??((_p_a_t_t_e_r_n_-_l_i_s_t)) Matches zero or one occurrence of the given patterns **((_p_a_t_t_e_r_n_-_l_i_s_t)) Matches zero or more occurrences of the given patterns ++((_p_a_t_t_e_r_n_-_l_i_s_t)) Matches one or more occurrences of the given patterns @@((_p_a_t_t_e_r_n_-_l_i_s_t)) Matches exactly one of the given patterns !!((_p_a_t_t_e_r_n_-_l_i_s_t)) Matches anything except one of the given patterns QQuuoottee RReemmoovvaall After the preceding expansions, all unquoted occurrences of the characters \\, '', and "" that did not result from one of the above expansions are removed. RREEDDIIRREECCTTIIOONN Before a command is executed, its input and output may be _r_e_d_i_r_e_c_t_e_d using a special notation interpreted by the shell. Redirection may also be used to open and close files for the current shell execution environment. The following redirection operators may precede or appear any- where within a _s_i_m_p_l_e _c_o_m_m_a_n_d or may follow a _c_o_m_m_a_n_d. Redirections are processed in the order they appear, from left to right. In the following descriptions, if the file descriptor num- ber is omitted, and the first character of the redirection operator is <<, the redirection refers to the standard input (file descriptor 0). If the first character of the redirection operator is >>, the redirection refers to the standard output (file descriptor 1). GNU 1998 Apr 1 28 BASH(1) BASH(1) The word following the redirection operator in the follow- ing descriptions, unless otherwise noted, is subjected to brace expansion, tilde expansion, parameter expansion, command substitution, arithmetic expansion, quote removal, and pathname expansion. If it expands to more than one word, bbaasshh reports an error. Note that the order of redirections is significant. For example, the command ls >> dirlist 2>>&&1 directs both standard output and standard error to the file _d_i_r_l_i_s_t, while the command ls 2>>&&1 >> dirlist directs only the standard output to file _d_i_r_l_i_s_t, because the standard error was duplicated as standard output before the standard output was redirected to _d_i_r_l_i_s_t. A failure to open or create a file causes the redirection to fail. RReeddiirreeccttiinngg IInnppuutt Redirection of input causes the file whose name results from the expansion of _w_o_r_d to be opened for reading on file descriptor _n, or the standard input (file descriptor 0) if _n is not specified. The general format for redirecting input is: [_n]<<_w_o_r_d RReeddiirreeccttiinngg OOuuttppuutt Redirection of output causes the file whose name results from the expansion of _w_o_r_d to be opened for writing on file descriptor _n, or the standard output (file descriptor 1) if _n is not specified. If the file does not exist it is created; if it does exist it is truncated to zero size. The general format for redirecting output is: [_n]>>_w_o_r_d If the redirection operator is >>, and the nnoocclloobbbbeerr option to the sseett builtin has been enabled, the redirection will fail if the filename whose name results from the expansion of _w_o_r_d exists and is a regular file. If the redirection operator is >>||, or the redirection operator is >> and the nnoocclloobbbbeerr option to the sseett builtin command is not enabled, the redirection is attempted even if the file named by _w_o_r_d exists. GNU 1998 Apr 1 29 BASH(1) BASH(1) AAppppeennddiinngg RReeddiirreecctteedd OOuuttppuutt Redirection of output in this fashion causes the file whose name results from the expansion of _w_o_r_d to be opened for appending on file descriptor _n, or the standard output (file descriptor 1) if _n is not specified. If the file does not exist it is created. The general format for appending output is: [_n]>>>>_w_o_r_d RReeddiirreeccttiinngg SSttaannddaarrdd OOuuttppuutt aanndd SSttaannddaarrdd EErrrroorr BBaasshh allows both the standard output (file descriptor 1) and the standard error output (file descriptor 2) to be redirected to the file whose name is the expansion of _w_o_r_d with this construct. There are two formats for redirecting standard output and standard error: &&>>_w_o_r_d and >>&&_w_o_r_d Of the two forms, the first is preferred. This is seman- tically equivalent to >>_w_o_r_d 2>>&&1 HHeerree DDooccuummeennttss This type of redirection instructs the shell to read input from the current source until a line containing only _w_o_r_d (with no trailing blanks) is seen. All of the lines read up to that point are then used as the standard input for a command. The format of here-documents is as follows: <<<<[--]_w_o_r_d _h_e_r_e_-_d_o_c_u_m_e_n_t _d_e_l_i_m_i_t_e_r No parameter expansion, command substitution, pathname expansion, or arithmetic expansion is performed on _w_o_r_d. If any characters in _w_o_r_d are quoted, the _d_e_l_i_m_i_t_e_r is the result of quote removal on _w_o_r_d, and the lines in the here-document are not expanded. If _w_o_r_d is unquoted, all lines of the here-document are subjected to parameter expansion, command substitution, and arithmetic expansion. In the latter case, the pair \\<<nneewwlliinnee>> is ignored, and \\ must be used to quote the characters \\, $$, and ``. If the redirection operator is <<<<--, then all leading tab GNU 1998 Apr 1 30 BASH(1) BASH(1) characters are stripped from input lines and the line con- taining _d_e_l_i_m_i_t_e_r. This allows here-documents within shell scripts to be indented in a natural fashion. DDuupplliiccaattiinngg FFiillee DDeessccrriippttoorrss The redirection operator [_n]<<&&_w_o_r_d is used to duplicate input file descriptors. If _w_o_r_d expands to one or more digits, the file descriptor denoted by _n is made to be a copy of that file descriptor. If the digits in _w_o_r_d do not specify a file descriptor open for input, a redirection error occurs. If _w_o_r_d evaluates to --, file descriptor _n is closed. If _n is not specified, the standard input (file descriptor 0) is used. The operator [_n]>>&&_w_o_r_d is used similarly to duplicate output file descriptors. If _n is not specified, the standard output (file descrip- tor 1) is used. If the digits in _w_o_r_d do not specify a file descriptor open for output, a redirection error occurs. As a special case, if _n is omitted, and _w_o_r_d does not expand to one or more digits, the standard output and standard error are redirected as described previously. OOppeenniinngg FFiillee DDeessccrriippttoorrss ffoorr RReeaaddiinngg aanndd WWrriittiinngg The redirection operator [_n]<<>>_w_o_r_d causes the file whose name is the expansion of _w_o_r_d to be opened for both reading and writing on file descriptor _n, or on file descriptor 0 if _n is not specified. If the file does not exist, it is created. AALLIIAASSEESS Aliases allow a string to be substituted for a word when it is used as the first word of a simple command. The shell maintains a list of _a_l_i_a_s_e_s that may be set and unset with the aalliiaass and uunnaalliiaass builtin commands (see SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS below). The first word of each command, if unquoted, is checked to see if it has an alias. If so, that word is replaced by the text of the alias. The alias name and the replacement text may con- tain any valid shell input, including the _m_e_t_a_c_h_a_r_a_c_t_e_r_s listed above, with the exception that the alias name may not contain _=. The first word of the replacement text is tested for aliases, but a word that is identical to an alias being expanded is not expanded a second time. This means that one may alias llss to llss --FF, for instance, and GNU 1998 Apr 1 31 BASH(1) BASH(1) bbaasshh does not try to recursively expand the replacement text. If the last character of the alias value is a _b_l_a_n_k, then the next command word following the alias is also checked for alias expansion. Aliases are created and listed with the aalliiaass command, and removed with the uunnaalliiaass command. There is no mechanism for using arguments in the replace- ment text. If arguments are needed, a shell function should be used. Aliases are not expanded when the shell is not interac- tive, unless the eexxppaanndd__aalliiaasseess shell option is set using sshhoopptt (see the description of sshhoopptt under SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS below). The rules concerning the definition and use of aliases are somewhat confusing. BBaasshh always reads at least one com- plete line of input before executing any of the commands on that line. Aliases are expanded when a command is read, not when it is executed. Therefore, an alias defi- nition appearing on the same line as another command does not take effect until the next line of input is read. The commands following the alias definition on that line are not affected by the new alias. This behavior is also an issue when functions are executed. Aliases are expanded when a function definition is read, not when the function is executed, because a function definition is itself a compound command. As a consequence, aliases defined in a function are not available until after that function is executed. To be safe, always put alias definitions on a separate line, and do not use aalliiaass in compound commands. For almost every purpose, aliases are superseded by shell functions. FFUUNNCCTTIIOONNSS A shell function, defined as described above under SSHHEELLLL GGRRAAMMMMAARR, stores a series of commands for later execution. Functions are executed in the context of the current shell; no new process is created to interpret them (con- trast this with the execution of a shell script). When a function is executed, the arguments to the function become the positional parameters during its execution. The spe- cial parameter ## is updated to reflect the change. Posi- tional parameter 0 is unchanged. All other aspects of the shell execution environment are identical between a func- tion and its caller with the exception that the DDEEBBUUGG trap (see the description of the ttrraapp builtin under SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS below) is not inherited. Variables local to the function may be declared with the llooccaall builtin command. Ordinarily, variables and their GNU 1998 Apr 1 32 BASH(1) BASH(1) values are shared between the function and its caller. If the builtin command rreettuurrnn is executed in a function, the function completes and execution resumes with the next command after the function call. When a function com- pletes, the values of the positional parameters and the special parameter ## are restored to the values they had prior to the function's execution. Function names and definitions may be listed with the --ff option to the ddeeccllaarree or ttyyppeesseett builtin commands. The --FF option to ddeeccllaarree or ttyyppeesseett will list the function names only. Functions may be exported so that subshells auto- matically have them defined with the --ff option to the eexxppoorrtt builtin. Functions may be recursive. No limit is imposed on the number of recursive calls. AARRIITTHHMMEETTIICC EEVVAALLUUAATTIIOONN The shell allows arithmetic expressions to be evaluated, under certain circumstances (see the lleett builtin command and AArriitthhmmeettiicc EExxppaannssiioonn). Evaluation is done in long integers with no check for overflow, though division by 0 is trapped and flagged as an error. The following list of operators is grouped into levels of equal-precedence oper- ators. The levels are listed in order of decreasing precedence. -- ++ unary minus and plus !! ~~ logical and bitwise negation **** exponentiation ** // %% multiplication, division, remainder ++ -- addition, subtraction <<<< >>>> left and right bitwise shifts <<== >>== << >> comparison ==== !!== equality and inequality && bitwise AND ^^ bitwise exclusive OR || bitwise OR &&&& logical AND |||| logical OR _e_x_p_r??_e_x_p_r::_e_x_p_r conditional evaluation == **== //== %%== ++== --== <<<<== >>>>== &&== ^^== ||== assignment Shell variables are allowed as operands; parameter expan- sion is performed before the expression is evaluated. The value of a parameter is coerced to a long integer within an expression. A shell variable need not have its integer attribute turned on to be used in an expression. GNU 1998 Apr 1 33 BASH(1) BASH(1) Constants with a leading 0 are interpreted as octal num- bers. A leading 0x or 0X denotes hexadecimal. Otherwise, numbers take the form [_b_a_s_e_#]n, where _b_a_s_e is a decimal number between 2 and 64 representing the arithmetic base, and _n is a number in that base. If _b_a_s_e is omitted, then base 10 is used. The digits greater than 9 are repre- sented by the lowercase letters, the uppercase letters, _, and @, in that order. If _b_a_s_e is less than or equal to 36, lowercase and uppercase letters may be used inter- changably to represent numbers between 10 and 35. Operators are evaluated in order of precedence. Sub- expressions in parentheses are evaluated first and may override the precedence rules above. CCOONNDDIITTIIOONNAALL EEXXPPRREESSSSIIOONNSS Conditional expressions are used by the [[[[ compound com- mand and the tteesstt and [[ builtin commands to test file attributes and perform string and arithmetic comparisons. Expressions are formed from the following unary or binary primaries. If any _f_i_l_e argument to one of the primaries is of the form /dev/fd/_n, then file descriptor _n is checked. --aa _f_i_l_e True if _f_i_l_e exists. --bb _f_i_l_e True if _f_i_l_e exists and is a block special file. --cc _f_i_l_e True if _f_i_l_e exists and is a character special file. --dd _f_i_l_e True if _f_i_l_e exists and is a directory. --ee _f_i_l_e True if _f_i_l_e exists. --ff _f_i_l_e True if _f_i_l_e exists and is a regular file. --gg _f_i_l_e True if _f_i_l_e exists and is set-group-id. --kk _f_i_l_e True if _f_i_l_e exists and its ``sticky'' bit is set. --pp _f_i_l_e True if _f_i_l_e exists and is a named pipe (FIFO). --rr _f_i_l_e True if _f_i_l_e exists and is readable. --ss _f_i_l_e True if _f_i_l_e exists and has a size greater than zero. --tt _f_d True if file descriptor _f_d is open and refers to a terminal. --uu _f_i_l_e True if _f_i_l_e exists and its set-user-id bit is set. --ww _f_i_l_e True if _f_i_l_e exists and is writable. GNU 1998 Apr 1 34 BASH(1) BASH(1) --xx _f_i_l_e True if _f_i_l_e exists and is executable. --OO _f_i_l_e True if _f_i_l_e exists and is owned by the effective user id. --GG _f_i_l_e True if _f_i_l_e exists and is owned by the effective group id. --LL _f_i_l_e True if _f_i_l_e exists and is a symbolic link. --SS _f_i_l_e True if _f_i_l_e exists and is a socket. --NN _f_i_l_e True if _f_i_l_e exists and has been modified since it was last read. _f_i_l_e_1 -nntt _f_i_l_e_2 True if _f_i_l_e_1 is newer (according to modification date) than _f_i_l_e_2. _f_i_l_e_1 -oott _f_i_l_e_2 True if _f_i_l_e_1 is older than _f_i_l_e_2. _f_i_l_e_1 --eeff _f_i_l_e_2 True if _f_i_l_e_1 and _f_i_l_e_2 have the same device and inode numbers. --oo _o_p_t_n_a_m_e True if shell option _o_p_t_n_a_m_e is enabled. See the list of options under the description of the --oo option to the sseett builtin below. --zz _s_t_r_i_n_g True if the length of _s_t_r_i_n_g is zero. --nn _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. == may be used in place of ====. _s_t_r_i_n_g_1 !!== _s_t_r_i_n_g_2 True if the strings are not equal. _s_t_r_i_n_g_1 << _s_t_r_i_n_g_2 True if _s_t_r_i_n_g_1 sorts before _s_t_r_i_n_g_2 lexicographi- cally in the current locale. _s_t_r_i_n_g_1 >> _s_t_r_i_n_g_2 True if _s_t_r_i_n_g_1 sorts after _s_t_r_i_n_g_2 lexicographi- cally in the current locale. _a_r_g_1 OOPP _a_r_g_2 OOPP is one of --eeqq, --nnee, --lltt, --llee, --ggtt, or --ggee. These arithmetic binary operators return true if _a_r_g_1 is equal to, not equal to, less than, less than or equal to, greater than, or greater than or equal to _a_r_g_2, respectively. _A_r_g_1 and _a_r_g_2 may be positive or negative integers. SSIIMMPPLLEE CCOOMMMMAANNDD EEXXPPAANNSSIIOONN When a simple command is executed, the shell performs the following expansions, assignments, and redirections, from left to right. GNU 1998 Apr 1 35 BASH(1) BASH(1) 1. The words that the parser has marked as variable assignments (those preceding the command name) and redirections are saved for later processing. 2. The words that are not variable assignments or redirections are expanded. If any words remain after expansion, the first word is taken to be the name of the command and the remaining words are the arguments. 3. Redirections are performed as described above under RREEDDIIRREECCTTIIOONN. 4. The text after the == in each variable assignment undergoes tilde expansion, parameter expansion, command substitution, arithmetic expansion, and quote removal before being assigned to the vari- able. If no command name results, the variable assignments affect the current shell environment. Otherwise, the variables are added to the environment of the executed command and do not affect the current shell environment. If any of the assignments attempts to assign a value to a readonly variable, an error occurs, and the command exits with a non-zero status. If no command name results, redirections are performed, but do not affect the current shell environment. A redi- rection error causes the command to exit with a non-zero status. If there is a command name left after expansion, execution proceeds as described below. Otherwise, the command exits. If one of the expansions contained a command sub- stitution, the exit status of the command is the exit sta- tus of the last command substitution performed. If there were no command substitutions, the command exits with a status of zero. CCOOMMMMAANNDD EEXXEECCUUTTIIOONN After a command has been split into words, if it results in a simple command and an optional list of arguments, the following actions are taken. If the command name contains no slashes, the shell attempts to locate it. If there exists a shell function by that name, that function is invoked as described above in FFUUNNCCTTIIOONNSS. If the name does not match a function, the shell searches for it in the list of shell builtins. If a match is found, that builtin is invoked. If the name is neither a shell function nor a builtin, and contains no slashes, bbaasshh searches each element of the GNU 1998 Apr 1 36 BASH(1) BASH(1) PPAATTHH for a directory containing an executable file by that name. BBaasshh uses a hash table to remember the full file names of executable files (see hhaasshh under SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS below). A full search of the directories in PPAATTHH is performed only if the command is not found in the hash table. If the search is unsuccessful, the shell prints an error message and returns an exit status of 127. If the search is successful, or if the command name con- tains one or more slashes, the shell executes the named program in a separate execution environment. Argument 0 is set to the name given, and the remaining arguments to the command are set to the arguments given, if any. If this execution fails because the file is not in exe- cutable format, and the file is not a directory, it is assumed to be a _s_h_e_l_l _s_c_r_i_p_t, a file containing shell com- mands. A subshell is spawned to execute it. This sub- shell reinitializes itself, so that the effect is as if a new shell had been invoked to handle the script, with the exception that the locations of commands remembered by the parent (see hhaasshh below under SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS) are retained by the child. If the program is a file beginning with ##!!, the remainder of the first line specifies an interpreter for the pro- gram. The shell executes the specified interpreter on operating systems that do not handle this executable for- mat themselves. The arguments to the interpreter consist of a single optional argument following the interpreter name on the first line of the program, followed by the name of the program, followed by the command arguments, if any. CCOOMMMMAANNDD EEXXEECCUUTTIIOONN EENNVVIIRROONNMMEENNTT The shell has an _e_x_e_c_u_t_i_o_n _e_n_v_i_r_o_n_m_e_n_t, which consists of the following: +o open files inherited by the shell at invocation, as modified by redirections supplied to the eexxeecc builtin +o the current working directory as set by ccdd, ppuusshhdd, or ppooppdd, or inherited by the shell at invocation +o the file creation mode mask as set by uummaasskk or inherited from the shell's parent +o current traps set by ttrraapp +o shell parameters that are set by variable assign- ment or with sseett or inherited from the shell's par- ent in the environment GNU 1998 Apr 1 37 BASH(1) BASH(1) +o shell functions defined during execution or inher- ited from the shell's parent in the environment +o options enabled at invocation (either by default or with command-line arguments) or by sseett +o options enabled by sshhoopptt +o shell aliases defined with aalliiaass +o various process IDs, including those of background jobs, the value of $$$$, and the value of $$PPPPIIDD When a simple command other than a builtin or shell func- tion is to be executed, it is invoked in a separate execu- tion environment that consists of the following. Unless otherwise noted, the values are inherited from the shell. +o the shell's open files, plus any modifications and additions specified by redirections to the command +o the current working directory +o the file creation mode mask +o shell variables marked for export, along with vari- ables exported for the command, passed in the envi- ronment +o traps caught by the shell are reset to the values the inherited from the shell's parent, and traps ignored by the shell are ignored A command invoked in this separate environment cannot affect the shell's execution environment. Command substitution and asynchronous commands are invoked in a subshell environment that is a duplicate of the shell environment, except that traps caught by the shell are reset to the values that the shell inherited from its par- ent at invocation. Builtin commands that are invoked as part of a pipeline are also executed in a subshell envi- ronment. Changes made to the subshell environment cannot affect the shell's execution environment. EENNVVIIRROONNMMEENNTT When a program is invoked it is given an array of strings called the _e_n_v_i_r_o_n_m_e_n_t. This is a list of _n_a_m_e-_v_a_l_u_e pairs, of the form _n_a_m_e=_v_a_l_u_e. The shell allows you to manipulate the environment in sev- eral ways. On invocation, the shell scans its own envi- ronment and creates a parameter for each name found, GNU 1998 Apr 1 38 BASH(1) BASH(1) automatically marking it for _e_x_p_o_r_t to child processes. Executed commands inherit the environment. The eexxppoorrtt and ddeeccllaarree --xx commands allow parameters and functions to be added to and deleted from the environment. If the value of a parameter in the environment is modified, the new value becomes part of the environment, replacing the old. The environment inherited by any executed command consists of the shell's initial environment, whose values may be modified in the shell, less any pairs removed by the uunnsseett command, plus any additions via the eexxppoorrtt and ddeeccllaarree --xx commands. The environment for any _s_i_m_p_l_e _c_o_m_m_a_n_d or function may be augmented temporarily by prefixing it with parameter assignments, as described above in PPAARRAAMMEETTEERRSS. These assignment statements affect only the environment seen by that command. If the --kk option is set (see the sseett builtin command below), then _a_l_l parameter assignments are placed in the environment for a command, not just those that precede the command name. When bbaasshh invokes an external command, the variable __ is set to the full file name of the command and passed to that command in its environment. EEXXIITT SSTTAATTUUSS For the shell's purposes, a command which exits with a zero exit status has succeeded. An exit status of zero indicates success. A non-zero exit status indicates fail- ure. When a command terminates on a fatal signal, bbaasshh uses the value of 128+ssiiggnnaall as the exit status. If a command is not found, the child process created to execute it returns a status of 127. If a command is found but is not executable, the return status is 126. If a command fails because of an error during expansion or redirection, the exit status is greater than zero. Shell builtin commands return a status of 0 (_t_r_u_e) if suc- cessful, and non-zero (_f_a_l_s_e) if an error occurs while they execute. All builtins return an exit status of 2 to indicate incorrect usage. BBaasshh itself returns the exit status of the last command executed, unless a syntax error occurs, in which case it exits with a non-zero value. See also the eexxiitt builtin command below. SSIIGGNNAALLSS When bbaasshh is interactive, in the absence of any traps, it ignores SSIIGGTTEERRMM (so that kkiillll 00 does not kill an GNU 1998 Apr 1 39 BASH(1) BASH(1) interactive shell), and SSIIGGIINNTT is caught and handled (so that the wwaaiitt builtin is interruptible). In all cases, bbaasshh ignores SSIIGGQQUUIITT. If job control is in effect, bbaasshh ignores SSIIGGTTTTIINN, SSIIGGTTTTOOUU, and SSIIGGTTSSTTPP. Synchronous jobs started by bbaasshh have signal handlers set to the values inherited by the shell from its parent. When job control is not in effect, asynchronous commands ignore SSIIGGIINNTT and SSIIGGQQUUIITT as well. Commands run as a result of command substitution ignore the keyboard-gener- ated job control signals SSIIGGTTTTIINN, SSIIGGTTTTOOUU, and SSIIGGTTSSTTPP. The shell exits by default upon receipt of a SSIIGGHHUUPP. Before exiting, it resends the SSIIGGHHUUPP to all jobs, running or stopped. Stopped jobs are sent SSIIGGCCOONNTT to ensure that they receive the SSIIGGHHUUPP. To prevent the shell from send- ing the signal to a particular job, it should be removed from the jobs table with the ddiissoowwnn builtin (see SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS below) or marked to not receive SSIIGGHHUUPP using ddiissoowwnn --hh. If the hhuuppoonneexxiitt shell option has been set with sshhoopptt, bbaasshh sends a SSIIGGHHUUPP to all jobs when an interactive login shell exits. When bbaasshh receives a signal for which a trap has been set while waiting for a command to complete, the trap will not be executed until the command completes. When bbaasshh is waiting for an asynchronous command via the wwaaiitt builtin, the reception of a signal for which a trap has been set will cause the wwaaiitt builtin to return immediately with an exit status greater than 128, immediately after which the trap is executed. JJOOBB CCOONNTTRROOLL _J_o_b _c_o_n_t_r_o_l refers to the ability to selectively stop (_s_u_s_p_e_n_d) the execution of processes and continue (_r_e_s_u_m_e) their execution at a later point. A user typically employs this facility via an interactive interface sup- plied jointly by the system's terminal driver and bbaasshh. The shell associates a _j_o_b with each pipeline. It keeps a table of currently executing jobs, which may be listed with the jjoobbss command. When bbaasshh starts a job asyn- chronously (in the _b_a_c_k_g_r_o_u_n_d), it prints a line that looks like: [1] 25647 indicating that this job is job number 1 and that the pro- cess ID of the last process in the pipeline associated with this job is 25647. All of the processes in a single pipeline are members of the same job. BBaasshh uses the _j_o_b abstraction as the basis for job control. GNU 1998 Apr 1 40 BASH(1) BASH(1) To facilitate the implementation of the user interface to job control, the system maintains the notion of a _c_u_r_r_e_n_t _t_e_r_m_i_n_a_l _p_r_o_c_e_s_s _g_r_o_u_p _I_D. Members of this process group (processes whose process group ID is equal to the current terminal process group ID) receive keyboard-generated sig- nals such as SSIIGGIINNTT. These processes are said to be in the _f_o_r_e_g_r_o_u_n_d. _B_a_c_k_g_r_o_u_n_d processes are those whose pro- cess group ID differs from the terminal's; such processes are immune to keyboard-generated signals. Only foreground processes are allowed to read from or write to the termi- nal. Background processes which attempt to read from (write to) the terminal are sent a SSIIGGTTTTIINN ((SSIIGGTTTTOOUU)) sig- nal by the terminal driver, which, unless caught, suspends the process. If the operating system on which bbaasshh is running supports job control, bbaasshh allows you to use it. Typing the _s_u_s_- _p_e_n_d character (typically ^^ZZ, Control-Z) while a process is running causes that process to be stopped and returns you to bbaasshh. Typing the _d_e_l_a_y_e_d _s_u_s_p_e_n_d character (typi- cally ^^YY, Control-Y) causes the process to be stopped when it attempts to read input from the terminal, and control to be returned to bbaasshh. The user may then manipulate the state of this job, using the bbgg command to continue it in the background, the ffgg command to continue it in the fore- ground, or the kkiillll command to kill it. A ^^ZZ takes effect immediately, and has the additional side effect of causing pending output and typeahead to be discarded. There are a number of ways to refer to a job in the shell. The character %% introduces a job name. Job number _n may be referred to as %%nn. A job may also be referred to using a prefix of the name used to start it, or using a sub- string that appears in its command line. For example, %%ccee refers to a stopped ccee job. If a prefix matches more than one job, bbaasshh reports an error. Using %%??ccee, on the other hand, refers to any job containing the string ccee in its command line. If the substring matches more than one job, bbaasshh reports an error. The symbols %%%% and %%++ refer to the shell's notion of the _c_u_r_r_e_n_t _j_o_b, which is the last job stopped while it was in the foreground or started in the background. The _p_r_e_v_i_o_u_s _j_o_b may be referenced using %%--. In output pertaining to jobs (e.g., the output of the jjoobbss command), the current job is always flagged with a ++, and the previous job with a --. Simply naming a job can be used to bring it into the fore- ground: %%11 is a synonym for ````ffgg %%11'''', bringing job 1 from the background into the foreground. Similarly, ````%%11 &&'''' resumes job 1 in the background, equivalent to ````bbgg %%11''''. The shell learns immediately whenever a job changes state. Normally, bbaasshh waits until it is about to print a prompt before reporting changes in a job's status so as to not GNU 1998 Apr 1 41 BASH(1) BASH(1) interrupt any other output. If the --bb option to the sseett builtin command is enabled, bbaasshh reports such changes immediately. If an attempt to exit bbaasshh is made while jobs are stopped, the shell prints a warning message. The jjoobbss command may then be used to inspect their status. If a second attempt to exit is made without an intervening command, the shell does not print another warning, and the stopped jobs are terminated. PPRROOMMPPTTIINNGG When executing interactively, bbaasshh displays the primary prompt PPSS11 when it is ready to read a command, and the secondary prompt PPSS22 when it needs more input to complete a command. BBaasshh allows these prompt strings to be cus- tomized by inserting a number of backslash-escaped special characters that are decoded as follows: \\aa an ASCII bell character (07) \\dd the date in "Weekday Month Date" format (e.g., "Tue May 26") \\ee an ASCII escape character (033) \\hh the hostname up to the first `.' \\HH the hostname \\nn newline \\rr carriage return \\ss the name of the shell, the basename of $$00 (the portion following the final slash) \\tt the current time in 24-hour HH:MM:SS format \\TT the current time in 12-hour HH:MM:SS format \\@@ the current time in 12-hour am/pm format \\uu the username of the current user \\vv the version of bbaasshh (e.g., 2.00) \\VV the release of bbaasshh, version + patchlevel (e.g., 2.00.0) \\ww the current working directory \\WW the basename of the current working direc- tory \\!! the history number of this command \\## the command number of this command \\$$ if the effective UID is 0, a ##, otherwise a $$ \\_n_n_n the character corresponding to the octal number _n_n_n \\\\ a backslash \\[[ begin a sequence of non-printing characters, which could be used to embed a terminal con- trol sequence into the prompt \\]] end a sequence of non-printing characters The command number and the history number are usually dif- ferent: the history number of a command is its position in the history list, which may include commands restored from the history file (see HHIISSTTOORRYY below), while the command GNU 1998 Apr 1 42 BASH(1) BASH(1) number is the position in the sequence of commands exe- cuted during the current shell session. After the string is decoded, it is expanded via parameter expansion, com- mand substitution, arithmetic expansion, string expansion, and quote removal, subject to the value of the pprroommppttvvaarrss shell option (see the description of the sshhoopptt command under SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS below). RREEAADDLLIINNEE This is the library that handles reading input when using an interactive shell, unless the ----nnooeeddiittiinngg option is given at shell invocation. By default, the line editing commands are similar to those of emacs. A vi-style line editing interface is also available. To turn off line editing after the shell is running, use the ++oo eemmaaccss or ++oo vvii options to the sseett builtin (see SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS below). RReeaaddlliinnee NNoottaattiioonn In this section, the emacs-style notation is used to denote keystrokes. Control keys are denoted by C-_k_e_y, e.g., C-n means Control-N. Similarly, _m_e_t_a keys are denoted by M-_k_e_y, so M-x means Meta-X. (On keyboards without a _m_e_t_a key, M-_x means ESC _x, i.e., press the Escape key then the _x key. This makes ESC the _m_e_t_a _p_r_e_- _f_i_x. The combination M-C-_x means ESC-Control-_x, or press the Escape key then hold the Control key while pressing the _x key.) Readline commands may be given numeric _a_r_g_u_m_e_n_t_s, which normally act as a repeat count. Sometimes, however, it is the sign of the argument that is significant. Passing a negative argument to a command that acts in the forward direction (e.g., kkiillll--lliinnee) causes that command to act in a backward direction. Commands whose behavior with argu- ments deviates from this are noted below. When a command is described as _k_i_l_l_i_n_g text, the text deleted is saved for possible future retrieval (_y_a_n_k_i_n_g). The killed text is saved in a _k_i_l_l _r_i_n_g. Consecutive kills cause the text to be accumulated into one unit, which can be yanked all at once. Commands which do not kill text separate the chunks of text on the kill ring. RReeaaddlliinnee IInniittiiaalliizzaattiioonn Readline is customized by putting commands in an initial- ization file (the _i_n_p_u_t_r_c file). The name of this file is taken from the value of the IINNPPUUTTRRCC variable. If that variable is unset, the default is _~_/_._i_n_p_u_t_r_c. When a pro- gram which uses the readline library starts up, the ini- tialization file is read, and the key bindings and vari- ables are set. There are only a few basic constructs allowed in the readline initialization file. Blank lines are ignored. Lines beginning with a ## are comments. GNU 1998 Apr 1 43 BASH(1) BASH(1) Lines beginning with a $$ indicate conditional constructs. Other lines denote key bindings and variable settings. The default key-bindings may be changed with an _i_n_p_u_t_r_c file. Other programs that use this library may add their own commands and bindings. For example, placing M-Control-u: universal-argument or C-Meta-u: universal-argument into the _i_n_p_u_t_r_c would make M-C-u execute the readline command _u_n_i_v_e_r_s_a_l_-_a_r_g_u_m_e_n_t. The following symbolic character names are recognized: _R_U_B_O_U_T, _D_E_L, _E_S_C, _L_F_D, _N_E_W_L_I_N_E, _R_E_T, _R_E_T_U_R_N, _S_P_C, _S_P_A_C_E, and _T_A_B. In addition to command names, readline allows keys to be bound to a string that is inserted when the key is pressed (a _m_a_c_r_o). RReeaaddlliinnee KKeeyy BBiinnddiinnggss The syntax for controlling key bindings in the _i_n_p_u_t_r_c file is simple. All that is required is the name of the command or the text of a macro and a key sequence to which it should be bound. The name may be specified in one of two ways: as a symbolic key name, possibly with _M_e_t_a_- or _C_o_n_t_r_o_l_- prefixes, or as a key sequence. When using the form kkeeyynnaammee:_f_u_n_c_t_i_o_n_-_n_a_m_e or _m_a_c_r_o, _k_e_y_n_a_m_e is the name of a key spelled out in English. For example: Control-u: universal-argument Meta-Rubout: backward-kill-word Control-o: "> output" In the above example, _C_-_u is bound to the function uunniivveerr-- ssaall--aarrgguummeenntt, _M_-_D_E_L is bound to the function bbaacckk-- wwaarrdd--kkiillll--wwoorrdd, and _C_-_o is bound to run the macro expressed on the right hand side (that is, to insert the text _> _o_u_t_p_u_t into the line). In the second form, ""kkeeyysseeqq"":_f_u_n_c_t_i_o_n_-_n_a_m_e or _m_a_c_r_o, kkeeyy-- sseeqq differs from kkeeyynnaammee above in that strings denoting an entire key sequence may be specified by placing the sequence within double quotes. Some GNU Emacs style key escapes can be used, as in the following example. "\C-u": universal-argument "\C-x\C-r": re-read-init-file "\e[11~": "Function Key 1" In this example, _C_-_u is again bound to the function uunnii-- vveerrssaall--aarrgguummeenntt. _C_-_x _C_-_r is bound to the function rree--rreeaadd--iinniitt--ffiillee, and _E_S_C _[ _1 _1 _~ is bound to insert the GNU 1998 Apr 1 44 BASH(1) BASH(1) text FFuunnccttiioonn KKeeyy 11. The full set of GNU Emacs style escape sequences is \\CC-- control prefix \\MM-- meta prefix \\ee an escape character \\\\ backslash \\"" literal " \\'' literal ' In addition to the GNU Emacs style escape sequences, a second set of backslash escapes is available: \\aa alert (bell) \\bb backspace \\dd delete \\ff form feed \\nn newline \\rr carriage return \\tt horizontal tab \\vv vertical tab \\_n_n_n the character whose ASCII code is the octal value _n_n_n (one to three digits) \\xx_n_n_n the character whose ASCII code is the hex- adecimal value _n_n_n (one to three digits) When entering the text of a macro, single or double quotes must be used to indicate a macro definition. Unquoted text is assumed to be a function name. In the macro body, the backslash escapes described above are expanded. Back- slash will quote any other character in the macro text, including " and '. BBaasshh allows the current readline key bindings to be dis- played or modified with the bbiinndd builtin command. The editing mode may be switched during interactive use by using the --oo option to the sseett builtin command (see SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS below). RReeaaddlliinnee VVaarriiaabblleess Readline has variables that can be used to further cus- tomize its behavior. A variable may be set in the _i_n_p_u_t_r_c file with a statement of the form sseett _v_a_r_i_a_b_l_e_-_n_a_m_e _v_a_l_u_e Except where noted, readline variables can take the values OOnn or OOffff. The variables and their default values are: bbeellll--ssttyyllee ((aauuddiibbllee)) Controls what happens when readline wants to ring the terminal bell. If set to nnoonnee, readline never rings the bell. If set to vviissiibbllee, readline uses a visible bell if one is available. If set to aauuddii-- bbllee, readline attempts to ring the terminal's bell. GNU 1998 Apr 1 45 BASH(1) BASH(1) ccoommmmeenntt--bbeeggiinn ((````##'''')) The string that is inserted when the rreeaaddlliinnee iinnsseerrtt--ccoommmmeenntt command is executed. This command is bound to MM--## in emacs mode and to ## in vi com- mand mode. ccoommpplleettiioonn--iiggnnoorree--ccaassee ((OOffff)) If set to OOnn, readline performs filename matching and completion in a case-insensitive fashion. ccoommpplleettiioonn--qquueerryy--iitteemmss ((110000)) This determines when the user is queried about viewing the number of possible completions gener- ated by the ppoossssiibbllee--ccoommpplleettiioonnss command. It may be set to any integer value greater than or equal to zero. If the number of possible completions is greater than or equal to the value of this vari- able, the user is asked whether or not he wishes to view them; otherwise they are simply listed on the terminal. ccoonnvveerrtt--mmeettaa ((OOnn)) If set to OOnn, readline will convert characters with the eighth bit set to an ASCII key sequence by stripping the eighth bit and prepending an escape character (in effect, using escape as the _m_e_t_a _p_r_e_- _f_i_x). ddiissaabbllee--ccoommpplleettiioonn ((OOffff)) If set to OOnn, readline will inhibit word comple- tion. Completion characters will be inserted into the line as if they had been mapped to sseellff--iinnsseerrtt. eeddiittiinngg--mmooddee ((eemmaaccss)) Controls whether readline begins with a set of key bindings similar to _e_m_a_c_s or _v_i. eeddiittiinngg--mmooddee can be set to either eemmaaccss or vvii. eennaabbllee--kkeeyyppaadd ((OOffff)) When set to OOnn, readline will try to enable the application keypad when it is called. Some systems need this to enable the arrow keys. eexxppaanndd--ttiillddee ((OOffff)) If set to oonn, tilde expansion is performed when readline attempts word completion. hhoorriizzoonnttaall--ssccrroollll--mmooddee ((OOffff)) When set to OOnn, makes readline use a single line for display, scrolling the input horizontally on a single screen line when it becomes longer than the screen width rather than wrapping to a new line. iinnppuutt--mmeettaa ((OOffff)) If set to OOnn, readline will enable eight-bit input (that is, it will not strip the high bit from the characters it reads), regardless of what the termi- nal claims it can support. The name mmeettaa--ffllaagg is a synonym for this variable. kkeeyymmaapp ((eemmaaccss)) Set the current readline keymap. The set of valid keymap names is _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_-_c_o_m_m_a_n_d, and _v_i_-_i_n_s_e_r_t. _v_i is GNU 1998 Apr 1 46 BASH(1) BASH(1) 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. The default value is _e_m_a_c_s; the value of eeddiittiinngg--mmooddee also affects the default keymap. mmaarrkk--ddiirreeccttoorriieess ((OOnn)) If set to OOnn, completed directory names have a slash appended. mmaarrkk--mmooddiiffiieedd--lliinneess ((OOffff)) If set to OOnn, history lines that have been modified are displayed with a preceding asterisk (**). oouuttppuutt--mmeettaa ((OOffff)) If set to OOnn, readline will display characters with the eighth bit set directly rather than as a meta- prefixed escape sequence. pprriinntt--ccoommpplleettiioonnss--hhoorriizzoonnttaallllyy ((OOffff)) If set to OOnn, readline will display completions with matches sorted horizontally in alphabetical order, rather than down the screen. sshhooww--aallll--iiff--aammbbiigguuoouuss ((OOffff)) This alters the default behavior of the completion functions. If set to oonn, words which have more than one possible completion cause the matches to be listed immediately instead of ringing the bell. vviissiibbllee--ssttaattss ((OOffff)) If set to OOnn, a character denoting a file's type as reported by _s_t_a_t(2) is appended to the filename when listing possible completions. RReeaaddlliinnee CCoonnddiittiioonnaall CCoonnssttrruuccttss Readline implements a facility similar in spirit to the conditional compilation features of the C preprocessor which allows key bindings and variable settings to be per- formed as the result of tests. There are four parser directives used. $$iiff The $$iiff construct allows bindings to be made based on the editing mode, the terminal being used, or the application using readline. The text of the test extends to the end of the line; no characters are required to isolate it. mmooddee The mmooddee== form of the $$iiff directive is used to test whether readline is in emacs or vi mode. This may be used in conjunction with the sseett kkeeyymmaapp command, for instance, to set bindings in the _e_m_a_c_s_-_s_t_a_n_d_a_r_d and _e_m_a_c_s_-_c_t_l_x keymaps only if readline is starting out in emacs mode. tteerrmm The tteerrmm== form may be used to include termi- nal-specific key bindings, perhaps to bind the key sequences output by the terminal's function keys. The word on the right side of the == is tested against the both full GNU 1998 Apr 1 47 BASH(1) BASH(1) name of the terminal and the portion of the terminal name before the first --. This allows _s_u_n to match both _s_u_n and _s_u_n_-_c_m_d, for instance. aapppplliiccaattiioonn The aapppplliiccaattiioonn construct is used to include application-specific settings. Each program using the readline library sets the _a_p_p_l_i_c_a_- _t_i_o_n _n_a_m_e, and an initialization file can test for a particular value. This could be used to bind key sequences to functions use- ful for a specific program. For instance, the following command adds a key sequence that quotes the current or previous word in Bash: $$iiff Bash # Quote the current or previous word "\C-xq": "\eb\"\ef\"" $$eennddiiff $$eennddiiff This command, as seen in the previous example, ter- minates an $$iiff command. $$eellssee Commands in this branch of the $$iiff directive are executed if the test fails. $$iinncclluuddee This directive takes a single filename as an argu- ment and reads commands and bindings from that file. For example, the following directive would read _/_e_t_c_/_i_n_p_u_t_r_c: $$iinncclluuddee _/_e_t_c_/_i_n_p_u_t_r_c SSeeaarrcchhiinngg Readline provides commands for searching through the com- mand history (see HHIISSTTOORRYY below) for lines containing a specified string. There are two search modes: _i_n_c_r_e_m_e_n_t_a_l and _n_o_n_-_i_n_c_r_e_m_e_n_t_a_l. Incremental searches begin before the user has finished typing the search string. As each character of the search string is typed, readline displays the next entry from the history matching the string typed so far. An incremental search requires only as many characters as needed to find the desired history entry. The Escape character is used to terminate an incremental search. Control-J will also terminate the search. Control-G will abort an incremental search and restore the original line. When the search is terminated, the history entry containing the search string becomes the current line. To find other matching entries in the history list, type Control-S or Control-R as GNU 1998 Apr 1 48 BASH(1) BASH(1) appropriate. This will search backward or forward in the history for the next entry matching the search string typed so far. Any other key sequence bound to a readline command will terminate the search and execute that com- mand. For instance, a _n_e_w_l_i_n_e will terminate the search and accept the line, thereby executing the command from the history list. Non-incremental searches read the entire search string before starting to search for matching history lines. The search string may be typed by the user or be part of the contents of the current line. RReeaaddlliinnee CCoommmmaanndd NNaammeess The following is a list of the names of the commands and the default key sequences to which they are bound. Com- mand names without an accompanying key sequence are unbound by default. CCoommmmaannddss ffoorr MMoovviinngg bbeeggiinnnniinngg--ooff--lliinnee ((CC--aa)) Move to the start of the current line. eenndd--ooff--lliinnee ((CC--ee)) Move to the end of the line. ffoorrwwaarrdd--cchhaarr ((CC--ff)) Move forward a character. bbaacckkwwaarrdd--cchhaarr ((CC--bb)) Move back a character. ffoorrwwaarrdd--wwoorrdd ((MM--ff)) Move forward to the end of the next word. Words are composed of alphanumeric characters (letters and digits). bbaacckkwwaarrdd--wwoorrdd ((MM--bb)) Move back to the start of this, or the previous, word. Words are composed of alphanumeric charac- ters (letters and digits). cclleeaarr--ssccrreeeenn ((CC--ll)) Clear the screen leaving the current line at the top of the screen. With an argument, refresh the current line without clearing the screen. rreeddrraaww--ccuurrrreenntt--lliinnee Refresh the current line. CCoommmmaannddss ffoorr MMaanniippuullaattiinngg tthhee HHiissttoorryy aacccceepptt--lliinnee ((NNeewwlliinnee,, RReettuurrnn)) Accept the line regardless of where the cursor is. If this line is non-empty, add it to the history list according to the state of the HHIISSTTCCOONNTTRROOLL variable. If the line is a modified history line, then restore the history line to its original state. pprreevviioouuss--hhiissttoorryy ((CC--pp)) Fetch the previous command from the history list, moving back in the list. GNU 1998 Apr 1 49 BASH(1) BASH(1) nneexxtt--hhiissttoorryy ((CC--nn)) Fetch the next command from the history list, mov- ing forward in the list. bbeeggiinnnniinngg--ooff--hhiissttoorryy ((MM--<<)) Move to the first line in the history. eenndd--ooff--hhiissttoorryy ((MM-->>)) Move to the end of the input history, i.e., the line currently being entered. rreevveerrssee--sseeaarrcchh--hhiissttoorryy ((CC--rr)) Search backward starting at the current line and moving `up' through the history as necessary. This is an incremental search. ffoorrwwaarrdd--sseeaarrcchh--hhiissttoorryy ((CC--ss)) Search forward starting at the current line and moving `down' through the history as necessary. This is an incremental search. nnoonn--iinnccrreemmeennttaall--rreevveerrssee--sseeaarrcchh--hhiissttoorryy ((MM--pp)) Search backward through the history starting at the current line using a non-incremental search for a string supplied by the user. nnoonn--iinnccrreemmeennttaall--ffoorrwwaarrdd--sseeaarrcchh--hhiissttoorryy ((MM--nn)) Search forward through the history using a non- incremental search for a string supplied by the user. hhiissttoorryy--sseeaarrcchh--ffoorrwwaarrdd Search forward through the history for the string of characters between the start of the current line and the current cursor position (the _p_o_i_n_t). This is a non-incremental search. hhiissttoorryy--sseeaarrcchh--bbaacckkwwaarrdd Search backward through the history for the string of characters between the start of the current line and the point. This is a non-incremental search. yyaannkk--nntthh--aarrgg ((MM--CC--yy)) Insert the first argument to the previous command (usually the second word on the previous line) at point (the current cursor position). With an argu- ment _n, insert the _nth word from the previous com- mand (the words in the previous command begin with word 0). A negative argument inserts the _nth word from the end of the previous command. yyaannkk--llaasstt--aarrgg ((MM--..,, MM--__)) Insert the last argument to the previous command (the last word of the previous history entry). With an argument, behave exactly like yyaannkk--nntthh--aarrgg. Successive calls to yyaannkk--llaasstt--aarrgg move back through the history list, inserting the last argument of each line in turn. sshheellll--eexxppaanndd--lliinnee ((MM--CC--ee)) Expand the line as the shell does. This performs alias and history expansion as well as all of the shell word expansions. See HHIISSTTOORRYY EEXXPPAANNSSIIOONN below for a description of history expansion. GNU 1998 Apr 1 50 BASH(1) BASH(1) hhiissttoorryy--eexxppaanndd--lliinnee ((MM--^^)) Perform history expansion on the current line. See HHIISSTTOORRYY EEXXPPAANNSSIIOONN below for a description of his- tory expansion. mmaaggiicc--ssppaaccee Perform history expansion on the current line and insert a space. See HHIISSTTOORRYY EEXXPPAANNSSIIOONN below for a description of history expansion. aalliiaass--eexxppaanndd--lliinnee Perform alias expansion on the current line. See AALLIIAASSEESS above for a description of alias expansion. hhiissttoorryy--aanndd--aalliiaass--eexxppaanndd--lliinnee Perform history and alias expansion on the current line. iinnsseerrtt--llaasstt--aarrgguummeenntt ((MM--..,, MM--__)) A synonym for yyaannkk--llaasstt--aarrgg. ooppeerraattee--aanndd--ggeett--nneexxtt ((CC--oo)) Accept the current line for execution and fetch the next line relative to the current line from the history for editing. Any argument is ignored. CCoommmmaannddss ffoorr CChhaannggiinngg TTeexxtt ddeelleettee--cchhaarr ((CC--dd)) Delete the character under the cursor. If point is at the beginning of the line, there are no charac- ters in the line, and the last character typed was not bound to ddeelleettee--cchhaarr, then return EEOOFF. bbaacckkwwaarrdd--ddeelleettee--cchhaarr ((RRuubboouutt)) Delete the character behind the cursor. When given a numeric argument, save the deleted text on the kill ring. qquuootteedd--iinnsseerrtt ((CC--qq,, CC--vv)) Add the next character typed to the line verbatim. This is how to insert characters like CC--qq, for example. ttaabb--iinnsseerrtt ((CC--vv TTAABB)) Insert a tab character. sseellff--iinnsseerrtt ((aa,, bb,, AA,, 11,, !!,, ......)) Insert the character typed. ttrraannssppoossee--cchhaarrss ((CC--tt)) Drag the character before point forward over the character at point. Point moves forward as well. If point is at the end of the line, then transpose the two characters before point. Negative argu- ments don't work. ttrraannssppoossee--wwoorrddss ((MM--tt)) Drag the word behind the cursor past the word in front of the cursor moving the cursor over that word as well. uuppccaassee--wwoorrdd ((MM--uu)) Uppercase the current (or following) word. With a negative argument, uppercase the previous word, but do not move point. GNU 1998 Apr 1 51 BASH(1) BASH(1) ddoowwnnccaassee--wwoorrdd ((MM--ll)) Lowercase the current (or following) word. With a negative argument, lowercase the previous word, but do not move point. ccaappiittaalliizzee--wwoorrdd ((MM--cc)) Capitalize the current (or following) word. With a negative argument, capitalize the previous word, but do not move point. KKiilllliinngg aanndd YYaannkkiinngg kkiillll--lliinnee ((CC--kk)) Kill the text from the current cursor position to the end of the line. bbaacckkwwaarrdd--kkiillll--lliinnee ((CC--xx RRuubboouutt)) Kill backward to the beginning of the line. uunniixx--lliinnee--ddiissccaarrdd ((CC--uu)) Kill backward from point to the beginning of the line. The killed text is saved on the kill-ring. kkiillll--wwhhoollee--lliinnee Kill all characters on the current line, no matter where the cursor is. kkiillll--wwoorrdd ((MM--dd)) Kill from the cursor to the end of the current word, or if between words, to the end of the next word. Word boundaries are the same as those used by ffoorrwwaarrdd--wwoorrdd. bbaacckkwwaarrdd--kkiillll--wwoorrdd ((MM--RRuubboouutt)) Kill the word behind the cursor. Word boundaries are the same as those used by bbaacckkwwaarrdd--wwoorrdd. uunniixx--wwoorrdd--rruubboouutt ((CC--ww)) Kill the word behind the cursor, using white space as a word boundary. The word boundaries are dif- ferent from bbaacckkwwaarrdd--kkiillll--wwoorrdd. ddeelleettee--hhoorriizzoonnttaall--ssppaaccee ((MM--\\)) Delete all spaces and tabs around point. kkiillll--rreeggiioonn Kill the text between the point and _m_a_r_k (saved cursor position). This text is referred to as the _r_e_g_i_o_n. ccooppyy--rreeggiioonn--aass--kkiillll Copy the text in the region to the kill buffer. ccooppyy--bbaacckkwwaarrdd--wwoorrdd Copy the word before point to the kill buffer. The word boundaries are the same as bbaacckkwwaarrdd--wwoorrdd. ccooppyy--ffoorrwwaarrdd--wwoorrdd Copy the word following point to the kill buffer. The word boundaries are the same as ffoorrwwaarrdd--wwoorrdd. yyaannkk ((CC--yy)) Yank the top of the kill ring into the buffer at the cursor. yyaannkk--ppoopp ((MM--yy)) Rotate the kill ring, and yank the new top. Only works following yyaannkk or yyaannkk--ppoopp. GNU 1998 Apr 1 52 BASH(1) BASH(1) NNuummeerriicc AArrgguummeennttss ddiiggiitt--aarrgguummeenntt ((MM--00,, MM--11,, ......,, MM----)) Add this digit to the argument already accumulat- ing, or start a new argument. M-- starts a nega- tive argument. uunniivveerrssaall--aarrgguummeenntt This is another way to specify an argument. If this command is followed by one or more digits, optionally with a leading minus sign, those digits define the argument. If the command is followed by digits, executing uunniivveerrssaall--aarrgguummeenntt again ends the numeric argument, but is otherwise ignored. As a special case, if this command is immediately fol- lowed by a character that is neither a digit or minus sign, the argument count for the next command is multiplied by four. The argument count is ini- tially one, so executing this function the first time makes the argument count four, a second time makes the argument count sixteen, and so on. CCoommpplleettiinngg ccoommpplleettee ((TTAABB)) Attempt to perform completion on the text before point. BBaasshh attempts completion treating the text as a variable (if the text begins with $$), username (if the text begins with ~~), hostname (if the text begins with @@), or command (including aliases and functions) in turn. If none of these produces a match, filename completion is attempted. ppoossssiibbllee--ccoommpplleettiioonnss ((MM--??)) List the possible completions of the text before point. iinnsseerrtt--ccoommpplleettiioonnss ((MM--**)) Insert all completions of the text before point that would have been generated by ppoossssiibbllee--ccoommppllee-- ttiioonnss. mmeennuu--ccoommpplleettee Similar to ccoommpplleettee, but replaces the word to be completed with a single match from the list of pos- sible completions. Repeated execution of mmeennuu--ccoomm-- pplleettee steps through the list of possible comple- tions, inserting each match in turn. At the end of the list of completions, the bell is rung and the original text is restored. An argument of _n moves _n positions forward in the list of matches; a nega- tive argument may be used to move backward through the list. This command is intended to be bound to TTAABB, but is unbound by default. ccoommpplleettee--ffiilleennaammee ((MM--//)) Attempt filename completion on the text before point. ppoossssiibbllee--ffiilleennaammee--ccoommpplleettiioonnss ((CC--xx //)) List the possible completions of the text before point, treating it as a filename. GNU 1998 Apr 1 53 BASH(1) BASH(1) ccoommpplleettee--uusseerrnnaammee ((MM--~~)) Attempt completion on the text before point, treat- ing it as a username. ppoossssiibbllee--uusseerrnnaammee--ccoommpplleettiioonnss ((CC--xx ~~)) List the possible completions of the text before point, treating it as a username. ccoommpplleettee--vvaarriiaabbllee ((MM--$$)) Attempt completion on the text before point, treat- ing it as a shell variable. ppoossssiibbllee--vvaarriiaabbllee--ccoommpplleettiioonnss ((CC--xx $$)) List the possible completions of the text before point, treating it as a shell variable. ccoommpplleettee--hhoossttnnaammee ((MM--@@)) Attempt completion on the text before point, treat- ing it as a hostname. ppoossssiibbllee--hhoossttnnaammee--ccoommpplleettiioonnss ((CC--xx @@)) List the possible completions of the text before point, treating it as a hostname. ccoommpplleettee--ccoommmmaanndd ((MM--!!)) Attempt completion on the text before point, treat- ing it as a command name. Command completion attempts to match the text against aliases, reserved words, shell functions, shell builtins, and finally executable filenames, in that order. ppoossssiibbllee--ccoommmmaanndd--ccoommpplleettiioonnss ((CC--xx !!)) List the possible completions of the text before point, treating it as a command name. ddyynnaammiicc--ccoommpplleettee--hhiissttoorryy ((MM--TTAABB)) Attempt completion on the text before point, com- paring the text against lines from the history list for possible completion matches. ccoommpplleettee--iinnttoo--bbrraacceess ((MM--{{)) Perform filename completion and return the list of possible completions enclosed within braces so the list is available to the shell (see BBrraaccee EExxppaannssiioonn above). KKeeyybbooaarrdd MMaaccrrooss ssttaarrtt--kkbbdd--mmaaccrroo ((CC--xx (()) Begin saving the characters typed into the current keyboard macro. eenndd--kkbbdd--mmaaccrroo ((CC--xx )))) Stop saving the characters typed into the current keyboard macro and store the definition. ccaallll--llaasstt--kkbbdd--mmaaccrroo ((CC--xx ee)) Re-execute the last keyboard macro defined, by mak- ing the characters in the macro appear as if typed at the keyboard. MMiisscceellllaanneeoouuss rree--rreeaadd--iinniitt--ffiillee ((CC--xx CC--rr)) Read in the contents of the _i_n_p_u_t_r_c file, and incorporate any bindings or variable assignments found there. GNU 1998 Apr 1 54 BASH(1) BASH(1) aabboorrtt ((CC--gg)) Abort the current editing command and ring the ter- minal's bell (subject to the setting of bbeellll--ssttyyllee). ddoo--uuppppeerrccaassee--vveerrssiioonn ((MM--aa,, MM--bb,, MM--_x,, ......)) If the metafied character _x is lowercase, run the command that is bound to the corresponding upper- case character. pprreeffiixx--mmeettaa ((EESSCC)) Metafy the next character typed. EESSCC ff is equiva- lent to MMeettaa--ff. uunnddoo ((CC--__,, CC--xx CC--uu)) Incremental undo, separately remembered for each line. rreevveerrtt--lliinnee ((MM--rr)) Undo all changes made to this line. This is like executing the uunnddoo command enough times to return the line to its initial state. ttiillddee--eexxppaanndd ((MM--~~)) Perform tilde expansion on the current word. sseett--mmaarrkk ((CC--@@,, MM--<<ssppaaccee>>)) Set the mark to the current point. If a numeric argument is supplied, the mark is set to that posi- tion. eexxcchhaannggee--ppooiinntt--aanndd--mmaarrkk ((CC--xx CC--xx)) Swap the point with the mark. The current cursor position is set to the saved position, and the old cursor position is saved as the mark. cchhaarraacctteerr--sseeaarrcchh ((CC--]])) A character is read and point is moved to the next occurrence of that character. A negative count searches for previous occurrences. cchhaarraacctteerr--sseeaarrcchh--bbaacckkwwaarrdd ((MM--CC--]])) A character is read and point is moved to the pre- vious occurrence of that character. A negative count searches for subsequent occurrences. iinnsseerrtt--ccoommmmeenntt ((MM--##)) The value of the rreeaaddlliinnee ccoommmmeenntt--bbeeggiinn variable is inserted at the beginning of the current line, and the line is accepted as if a newline had been typed. This makes the current line a shell com- ment. gglloobb--eexxppaanndd--wwoorrdd ((CC--xx **)) The word before point is treated as a pattern for pathname expansion, and the list of matching file names is inserted, replacing the word. gglloobb--lliisstt--eexxppaannssiioonnss ((CC--xx gg)) The list of expansions that would have been gener- ated by gglloobb--eexxppaanndd--wwoorrdd is displayed, and the line is redrawn. dduummpp--ffuunnccttiioonnss Print all of the functions and their key bindings to the readline output stream. If a numeric argu- ment is supplied, the output is formatted in such a GNU 1998 Apr 1 55 BASH(1) BASH(1) way that it can be made part of an _i_n_p_u_t_r_c file. dduummpp--vvaarriiaabblleess Print all of the settable readline variables and their values to the readline output stream. If a numeric argument is supplied, the output is format- ted in such a way that it can be made part of an _i_n_p_u_t_r_c file. dduummpp--mmaaccrrooss Print all of the readline key sequences bound to macros and the strings they ouput. If a numeric argument is supplied, the output is formatted in such a way that it can be made part of an _i_n_p_u_t_r_c file. ddiissppllaayy--sshheellll--vveerrssiioonn ((CC--xx CC--vv)) Display version information about the current instance of bbaasshh. HHIISSTTOORRYY When the --oo hhiissttoorryy option to the sseett builtin is enabled, the shell provides access to the _c_o_m_m_a_n_d _h_i_s_t_o_r_y, the list of commands previously typed. The text of the last HHIISSTT-- SSIIZZEE commands (default 500) is saved in a history list. The shell stores each command in the history list prior to parameter and variable expansion (see EEXXPPAANNSSIIOONN above) but after history expansion is performed, subject to the val- ues of the shell variables HHIISSTTIIGGNNOORREE and HHIISSTTCCOONNTTRROOLL. On startup, the history is initialized from the file named by the variable HHIISSTTFFIILLEE (default _~_/_._b_a_s_h___h_i_s_t_o_r_y). HHIISSTTFFIILLEE is truncated, if necessary, to contain no more than HHIISSTT-- FFIILLEESSIIZZEE lines. When an interactive shell exits, the last HHIISSTTSSIIZZEE lines are copied from the history list to HHIISSTT-- FFIILLEE. If the hhiissttaappppeenndd shell option is enabled (see the description of sshhoopptt under SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS below), the lines are appended to the history file, otherwise the history file is overwritten. If HHIISSTTFFIILLEE is unset, or if the history file is unwritable, the history is not saved. After saving the history, the history file is truncated to contain no more than HHIISSTTFFIILLEESSIIZZEE lines. If HHIISSTTFFIILLEESSIIZZEE is not set, no truncation is performed. The builtin command ffcc (see SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS below) may be used to list or edit and re-execute a portion of the history list. The hhiissttoorryy builtin can be used to dis- play or modify the history list and manipulate the history file. When using the command-line editing, search com- mands are available in each editing mode that provide access to the history list. The shell allows control over which commands are saved on the history list. The HHIISSTTCCOONNTTRROOLL and HHIISSTTIIGGNNOORREE vari- ables may be set to cause the shell to save only a subset of the commands entered. The ccmmddhhiisstt shell option, if enabled, causes the shell to attempt to save each line of a multi-line command in the same history entry, adding GNU 1998 Apr 1 56 BASH(1) BASH(1) semicolons where necessary to preserve syntactic correct- ness. The lliitthhiisstt shell option causes the shell to save the command with embedded newlines instead of semicolons. See the description of the sshhoopptt builtin below under SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS for information on setting and unsetting shell options. HHIISSTTOORRYY EEXXPPAANNSSIIOONN The shell supports a history expansion feature that is similar to the history expansion in ccsshh.. This section describes what syntax features are available. This fea- ture is enabled by default for interactive shells, and can be disabled using the ++HH option to the sseett builtin command (see SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS below). Non-interactive shells do not perform history expansion by default. History expansions introduce words from the history list into the input stream, making it easy to repeat commands, insert the arguments to a previous command into the cur- rent input line, or fix errors in previous commands quickly. History expansion is performed immediately after a com- plete line is read, before the shell breaks it into words. It takes place in two parts. The first is to determine which line from the history list to use during substitu- tion. The second is to select portions of that line for inclusion into the current one. The line selected from the history is the _e_v_e_n_t, and the portions of that line that are acted upon are _w_o_r_d_s. Various _m_o_d_i_f_i_e_r_s are available to manipulate the selected words. The line is broken into words in the same fashion as when reading input, so that several _m_e_t_a_c_h_a_r_a_c_t_e_r-separated words sur- rounded by quotes are considered one word. History expan- sions are introduced by the appearance of the history expansion character, which is !! by default. Only back- slash (\\) and single quotes can quote the history expan- sion character. Several shell options settable with the sshhoopptt builtin may be used to tailor the behavior of history expansion. If the hhiissttvveerriiffyy shell option is enabled (see the descrip- tion of the sshhoopptt builtin), and rreeaaddlliinnee is being used, history substitutions are not immediately passed to the shell parser. Instead, the expanded line is reloaded into the rreeaaddlliinnee editing buffer for further modification. If rreeaaddlliinnee is being used, and the hhiissttrreeeeddiitt shell option is enabled, a failed history substitution will be reloaded into the rreeaaddlliinnee editing buffer for correction. The --pp option to the hhiissttoorryy builtin command may be used to see what a history expansion will do before using it. The --ss option to the hhiissttoorryy builtin may be used to add commands to the end of the history list without actually executing them, so that they are available for subsequent recall. GNU 1998 Apr 1 57 BASH(1) BASH(1) The shell allows control of the various characters used by the history expansion mechanism (see the description of hhiissttcchhaarrss above under SShheellll VVaarriiaabblleess). EEvveenntt DDeessiiggnnaattoorrss An event designator is a reference to a command line entry in the history list. !! Start a history substitution, except when followed by a bbllaannkk, newline, = or (. !!_n Refer to command line _n. !!--_n Refer to the current command line minus _n. !!!! Refer to the previous command. This is a synonym for `!-1'. !!_s_t_r_i_n_g Refer to the most recent command starting with _s_t_r_i_n_g. !!??_s_t_r_i_n_g[[??]] Refer to the most recent command containing _s_t_r_i_n_g. The trailing ?? may be omitted if _s_t_r_i_n_g is followed immediately by a newline. ^^_s_t_r_i_n_g_1^^_s_t_r_i_n_g_2^^ Quick substitution. Repeat the last command, replacing _s_t_r_i_n_g_1 with _s_t_r_i_n_g_2. Equivalent to ``!!:s/_s_t_r_i_n_g_1/_s_t_r_i_n_g_2/'' (see MMooddiiffiieerrss below). !!## The entire command line typed so far. WWoorrdd DDeessiiggnnaattoorrss Word designators are used to select desired words from the event. A :: separates the event specification from the word designator. It may be omitted if the word designator begins with a ^^, $$, **, --, or %%. Words are numbered from the beginning of the line, with the first word being denoted by 0 (zero). Words are inserted into the current line separated by single spaces. 00 ((zzeerroo)) The zeroth word. For the shell, this is the com- mand word. _n The _nth word. ^^ The first argument. That is, word 1. $$ The last argument. %% The word matched by the most recent `?_s_t_r_i_n_g?' search. _x--_y A range of words; `-_y' abbreviates `0-_y'. ** All of the words but the zeroth. This is a synonym for `_1_-_$'. It is not an error to use ** if there is just one word in the event; the empty string is returned in that case. xx** Abbreviates _x_-_$. xx-- Abbreviates _x_-_$ like xx**, but omits the last word. If a word designator is supplied without an event specifi- cation, the previous command is used as the event. GNU 1998 Apr 1 58 BASH(1) BASH(1) MMooddiiffiieerrss After the optional word designator, there may appear a sequence of one or more of the following modifiers, each preceded by a `:'. hh Remove a trailing file name component, leaving only the head. tt Remove all leading file name components, leaving the tail. rr Remove a trailing suffix of the form _._x_x_x, leaving the basename. ee Remove all but the trailing suffix. pp Print the new command but do not execute it. qq Quote the substituted words, escaping further sub- stitutions. xx Quote the substituted words as with qq, but break into words at bbllaannkkss and newlines. ss//_o_l_d//_n_e_w// Substitute _n_e_w for the first occurrence of _o_l_d in the event line. Any delimiter can be used in place of /. The final delimiter is optional if it is the last character of the event line. The delimiter may be quoted in _o_l_d and _n_e_w with a single back- slash. If & appears in _n_e_w, it is replaced by _o_l_d. A single backslash will quote the &. If _o_l_d is null, it is set to the last _o_l_d substituted, or, if no previous history substitutions took place, the last _s_t_r_i_n_g in a !!??_s_t_r_i_n_g[[??]] search. && Repeat the previous substitution. gg Cause changes to be applied over the entire event line. This is used in conjunction with `::ss' (e.g., `::ggss//_o_l_d//_n_e_w//') or `::&&'. If used with `::ss', any delimiter can be used in place of /, and the final delimiter is optional if it is the last character of the event line. SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS Unless otherwise noted, each builtin command documented in this section as accepting options preceded by -- accepts ---- to signify the end of the options. :: [_a_r_g_u_m_e_n_t_s] No effect; the command does nothing beyond expand- ing _a_r_g_u_m_e_n_t_s and performing any specified redirec- tions. A zero exit code is returned. .. _f_i_l_e_n_a_m_e [_a_r_g_u_m_e_n_t_s] ssoouurrccee _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 cur- rent 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, file names in PPAATTHH are used to find the directory containing _f_i_l_e_n_a_m_e. The file searched for in PPAATTHH need not be executable. The current directory is searched GNU 1998 Apr 1 59 BASH(1) BASH(1) if no file is found in PPAATTHH. If the ssoouurrcceeppaatthh option to the sshhoopptt builtin command is turned off, the PPAATTHH is not searched. If any _a_r_g_u_m_e_n_t_s are supplied, they become the positional parameters when _f_i_l_e_n_a_m_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 or cannot be read. aalliiaass [--pp] [_n_a_m_e[=_v_a_l_u_e] ...] AAlliiaass with no arguments or with the --pp option prints the list of aliases in the form aalliiaass _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. AAlliiaass returns true unless a _n_a_m_e is given for which no alias has been defined. bbgg [_j_o_b_s_p_e_c] Resume the suspended job _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. bbgg _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 with- out job control. bbiinndd [--mm _k_e_y_m_a_p] [--llppssvvPPSSVV] bbiinndd [--mm _k_e_y_m_a_p] [--qq _f_u_n_c_t_i_o_n] [--uu _f_u_n_c_t_i_o_n] [--rr _k_e_y_s_e_q] bbiinndd [--mm _k_e_y_m_a_p] --ff _f_i_l_e_n_a_m_e bbiinndd [--mm _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 rreeaaddlliinnee key and function bindings, or bind a key sequence to a rreeaaddlliinnee 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: --mm _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_-_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. --ll List the names of all rreeaaddlliinnee functions. --pp Display rreeaaddlliinnee function names and bindings in such a way that they can be re-read. --PP List current rreeaaddlliinnee function names and GNU 1998 Apr 1 60 BASH(1) BASH(1) bindings. --vv Display rreeaaddlliinnee variable names and values in such a way that they can be re-read. --VV List current rreeaaddlliinnee variable names and values. --ss Display rreeaaddlliinnee key sequences bound to macros and the strings they output in such a way that they can be re-read. --SS Display rreeaaddlliinnee key sequences bound to macros and the strings they output. --ff _f_i_l_e_n_a_m_e Read key bindings from _f_i_l_e_n_a_m_e. --qq _f_u_n_c_t_i_o_n Query about which keys invoke the named _f_u_n_c_t_i_o_n. --uu _f_u_n_c_t_i_o_n Unbind all keys bound to the named _f_u_n_c_t_i_o_n. --rr _k_e_y_s_e_q Remove any current binding for _k_e_y_s_e_q. The return value is 0 unless an unrecognized option is given or an error occurred. bbrreeaakk [_n] Exit from within a ffoorr, wwhhiillee, uunnttiill, or sseelleecctt loop. If _n is specified, break _n levels. _n must be >= 1. If _n is greater than the number of enclosing loops, all enclosing loops are exited. The return value is 0 unless the shell is not exe- cuting a loop when bbrreeaakk is executed. bbuuiillttiinn _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 defining a function whose name is the same as a shell builtin, retaining the functional- ity of the builtin within the function. The ccdd 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. ccdd [--LLPP] [_d_i_r] Change the current directory to _d_i_r. The variable HHOOMMEE is the default _d_i_r. The variable CCDDPPAATTHH defines the search path for the directory contain- ing _d_i_r. Alternative directory names in CCDDPPAATTHH are separated by a colon (:). A null directory name in CCDDPPAATTHH is the same as the current directory, i.e., ``..''. If _d_i_r begins with a slash (/), then CCDDPPAATTHH is not used. The --PP option says to use the physical directory structure instead of following symbolic links (see also the --PP option to the sseett builtin command); the --LL option forces symbolic links to be followed. An argument of -- is equivalent to GNU 1998 Apr 1 61 BASH(1) BASH(1) $$OOLLDDPPWWDD. The return value is true if the directory was successfully changed; false otherwise. ccoommmmaanndd [--ppVVvv] _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 PPAATTHH are executed. If the --pp option is given, the search for _c_o_m_m_a_n_d is performed using a default value for PPAATTHH that is guaranteed to find all of the standard utilities. If either the --VV or --vv option is supplied, a description of _c_o_m_m_a_n_d is printed. The --vv option causes a single word indi- cating the command or file name used to invoke _c_o_m_- _m_a_n_d to be displayed; the --VV option produces a more verbose description. If the --VV or --vv 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 ccoommmmaanndd builtin is the exit status of _c_o_m_- _m_a_n_d. ccoonnttiinnuuee [_n] Resume the next iteration of the enclosing ffoorr, wwhhiillee, uunnttiill, or sseelleecctt 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 ccoonnttiinnuuee is executed. ddeeccllaarree [--aaffFFiirrxx] [--pp] [_n_a_m_e[=_v_a_l_u_e]] ttyyppeesseett [--aaffFFiirrxx] [--pp] [_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 vari- ables. The --pp option will display the attributes and values of each _n_a_m_e. When --pp is used, addi- tional options are ignored. The --FF option inhibits the display of function definitions; only the func- tion name and attributes are printed. The --FF option implies --ff. The following options can be used to restrict output to variables with the spec- ified attribute or to give variables attributes: --aa Each _n_a_m_e is an array variable (see AArrrraayyss above). --ff Use function names only. --ii The variable is treated as an integer; arithmetic evaluation (see AARRIITTHHMMEETTIICC EEVVAALLUU-- AATTIIOONN )) is performed when the variable is assigned a value. --rr Make _n_a_m_es readonly. These names cannot then be assigned values by subsequent assignment statements or unset. --xx Mark _n_a_m_es for export to subsequent commands GNU 1998 Apr 1 62 BASH(1) BASH(1) via the environment. Using `+' instead of `-' turns off the attribute instead, with the exception that ++aa may not be used to destroy an array variable. When used in a func- tion, makes each _n_a_m_e local, as with the llooccaall com- mand. 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 vari- able without using the compound assignment syntax (see AArrrraayyss above), one of the _n_a_m_e_s 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 vari- able, or an attempt is made to display a non-exis- tent function with -f. ddiirrss [[--ccllppvv]] [[++_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 ppuusshhdd command; the ppooppdd command removes entries from the list. ++_n Displays the _nth entry counting from the left of the list shown by ddiirrss when invoked without options, starting with zero. --_n Displays the _nth entry counting from the right of the list shown by ddiirrss when invoked without options, starting with zero. --cc Clears the directory stack by deleting all of the entries. --ll Produces a longer listing; the default list- ing format uses a tilde to denote the home directory. --pp Print the directory stack with one entry per line. --vv 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 direc- tory stack. ddiissoowwnn [--aarr] [--hh] [_j_o_b_s_p_e_c ...] Without options, each _j_o_b_s_p_e_c is removed from the table of active jobs. If the --hh option is given, each _j_o_b_s_p_e_c is not removed from the table, but is marked so that SSIIGGHHUUPP is not sent to the job if the shell receives a SSIIGGHHUUPP. If no _j_o_b_s_p_e_c is present, and neither the --aa nor the --rr option is supplied, GNU 1998 Apr 1 63 BASH(1) BASH(1) the _c_u_r_r_e_n_t _j_o_b is used. If no _j_o_b_s_p_e_c is sup- plied, the --aa option means to remove or mark all jobs; the --rr option without a _j_o_b_s_p_e_c argument restricts operation to running jobs. The return value is 0 unless a _j_o_b_s_p_e_c does not specify a valid job. eecchhoo [--nneeEE] [_a_r_g ...] Output the _a_r_gs, separated by spaces, followed by a newline. The return status is always 0. If --nn is specified, the trailing newline is suppressed. If the --ee option is given, interpretation of the fol- lowing backslash-escaped characters is enabled. The --EE option disables the interpretation of these escape characters, even on systems where they are interpreted by default. eecchhoo does not interpret ---- to mean the end of options. eecchhoo interprets the following escape sequences: \\aa alert (bell) \\bb backspace \\cc suppress trailing newline \\ee an escape character \\ff form feed \\nn new line \\rr carriage return \\tt horizontal tab \\vv vertical tab \\\\ backslash \\_n_n_n the character whose ASCII code is the octal value _n_n_n (one to three digits) \\xx_n_n_n the character whose ASCII code is the hex- adecimal value _n_n_n (one to three digits) eennaabbllee [--aaddnnppss] [--ff _f_i_l_e_n_a_m_e] [_n_a_m_e ...] Enable and disable builtin shell commands. Dis- abling a builtin allows a disk command which has the same name as a shell builtin to be executed with specifying a full pathname, even though the shell normally searches for builtins before disk commands. If --nn is used, each _n_a_m_e is disabled; otherwise, _n_a_m_e_s are enabled. For example, to use the tteesstt binary found via the PPAATTHH instead of the shell builtin version, run enable -n test.. TThhee --ff option means to load the new builtin command _n_a_m_e from shared object _f_i_l_e_n_a_m_e, on systems that sup- port dynamic loading. The --dd option will delete a builtin previously loaded with --ff. If no _n_a_m_e arguments are given, or if the --pp option is sup- plied, a list of shell builtins is printed. With no other option arguments, the list consists of all enabled shell builtins. If --nn is supplied, only disabled builtins are printed. If --aa is supplied, the list printed includes all builtins, with an indication of whether or not each is enabled. If GNU 1998 Apr 1 64 BASH(1) BASH(1) --ss is supplied, the output is restricted to the POSIX _s_p_e_c_i_a_l builtins. The return value is 0 unless a _n_a_m_e is not a shell builtin or there is a problem loading a new builtin from a shared object. eevvaall [_a_r_g ...] The _a_r_gs are read and concatenated together into a single command. This command is then read and exe- cuted by the shell, and its exit status is returned as the value of eevvaall. If there are no _a_r_g_s, or only null arguments, eevvaall returns 0. eexxeecc [--ccll] [--aa _n_a_m_e] [_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 --ll option is sup- plied, the shell places a dash in the zeroth arg passed to _c_o_m_m_a_n_d. This is what _l_o_g_i_n(1) does. The --cc option causes _c_o_m_m_a_n_d to be executed with an empty environment. If --aa is supplied, the shell passes _n_a_m_e as the zeroth argument to the executed command. If _c_o_m_m_a_n_d cannot be executed for some reason, a non-interactive shell exits, unless the shell option eexxeeccffaaiill is enabled, in which case it returns failure. An interactive shell returns failure if the file cannot be executed. 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. If there is a redirection error, the return status is 1. eexxiitt [_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 EEXXIITT is executed before the shell terminates. eexxppoorrtt [--ffnn] [_n_a_m_e[=_w_o_r_d]] ... eexxppoorrtt --pp The supplied _n_a_m_e_s are marked for automatic export to the environment of subsequently executed com- mands. If the --ff option is given, the _n_a_m_e_s refer to functions. If no _n_a_m_e_s are given, or if the --pp option is supplied, a list of all names that are exported in this shell is printed. The --nn option causes the export property to be removed from the named variables. eexxppoorrtt returns an exit status of 0 unless an invalid option is encountered, one of the _n_a_m_e_s is not a valid shell variable name, or --ff is supplied with a _n_a_m_e that is not a function. ffcc [--ee _e_n_a_m_e] [--nnllrr] [_f_i_r_s_t] [_l_a_s_t] ffcc --ss [_p_a_t=_r_e_p] [_c_m_d] Fix Command. In the first form, a range of GNU 1998 Apr 1 65 BASH(1) BASH(1) 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 number (an index into the his- tory list, where a negative number is used as an offset from the current command number). If _l_a_s_t is not specified it is set to the current command for listing (so that ffcc --ll --1100 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 --nn option suppresses the command numbers when listing. The --rr option reverses the order of the commands. If the --ll option is given, the commands are listed on standard output. Otherwise, the edi- tor 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 FFCCEEDDIITT variable is used, and the value of EEDDIITTOORR if FFCCEEDDIITT is not set. If neither variable is set, _v_i is used. When editing is complete, 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 typ- ing ``r cc'' runs the last command beginning with ``cc'' and typing ``r'' re-executes the last com- mand. If the first form is used, the return value is 0 unless an invalid option is encountered or _f_i_r_s_t or _l_a_s_t specify history lines out of range. If the --ee 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 spec- ify a valid history line, in which case ffcc returns failure. ffgg [_j_o_b_s_p_e_c] Resume _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 con- trol. ggeettooppttss _o_p_t_s_t_r_i_n_g _n_a_m_e [_a_r_g_s] ggeettooppttss is used by shell procedures to parse GNU 1998 Apr 1 66 BASH(1) BASH(1) 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, ggeettooppttss places the next option in the shell variable _n_a_m_e, initializing _n_a_m_e if it does not exist, and the index of the next argument to be processed into the variable OOPPTTIINNDD. OOPPTTIINNDD is initialized to 1 each time the shell or a shell script is invoked. When an option requires an argument, ggeettooppttss places that argument into the variable OOPPTTAARRGG. The shell does not reset OOPPTTIINNDD automatically; it must be manually reset between multiple calls to ggeettooppttss within the same shell invocation if a new set of parameters is to be used. When the end of options is encountered, ggeettooppttss exits with a return value greater than zero. OOPPTTIINNDD is set to the index of the first non-option argument, and nnaammee is set to ?. ggeettooppttss normally parses the positional parameters, but if more arguments are given in _a_r_g_s, ggeettooppttss parses those instead. ggeettooppttss 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 reporting is used. In normal operation diag- nostic messages are printed when invalid options or missing option arguments are encountered. If the variable OOPPTTEERRRR is set to 0, no error messages will be displayed, even if the first character of _o_p_t_- _s_t_r_i_n_g is not a colon. If an invalid option is seen, ggeettooppttss places ? into _n_a_m_e and, if not silent, prints an error message and unsets OOPPTTAARRGG. If ggeettooppttss is silent, the option character found is placed in OOPPTTAARRGG and no diagnostic message is printed. If a required argument is not found, and ggeettooppttss is not silent, a question mark (??) is placed in _n_a_m_e, OOPPTTAARRGG is unset, and a diagnostic message is printed. If ggeettooppttss is silent, then a colon (::) is placed in _n_a_m_e and OOPPTTAARRGG is set to the option character found. ggeettooppttss returns true if an option, specified or unspecified, is found. It returns false if the end of options is encountered or an error occurs. hhaasshh [--rr] [--pp _f_i_l_e_n_a_m_e] [_n_a_m_e] For each _n_a_m_e, the full file name of the command is GNU 1998 Apr 1 67 BASH(1) BASH(1) determined by searching the directories in $$PPAATTHH and remembered. If the --pp option is supplied, no path search is performed, and _f_i_l_e_n_a_m_e is used as the full file name of the command. The --rr option causes the shell to forget all remembered loca- tions. If no arguments are given, information about remembered commands is printed. The return status is true unless a _n_a_m_e is not found or an invalid option is supplied. hheellpp [_p_a_t_t_e_r_n] Display helpful information about builtin commands. If _p_a_t_t_e_r_n is specified, hheellpp gives detailed help on all commands matching _p_a_t_t_e_r_n; otherwise help for all the builtins and shell control structures is printed. The return status is 0 unless no com- mand matches _p_a_t_t_e_r_n. hhiissttoorryy [--cc] [_n] hhiissttoorryy --aannrrww [_f_i_l_e_n_a_m_e] hhiissttoorryy --pp _a_r_g [_a_r_g _._._.] hhiissttoorryy --ss _a_r_g [_a_r_g _._._.] 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 _f_i_l_e_n_a_m_e is supplied, it is used as the name of the history file; if not, the value of HHIISSTTFFIILLEE is used. Options, if supplied, have the following meanings: --aa Append the ``new'' history lines (history lines entered since the beginning of the current bbaasshh session) to the history file. --nn Read the history lines not already read from the history file into the current history list. These are lines appended to the his- tory file since the beginning of the current bbaasshh session. --rr Read the contents of the history file and use them as the current history. --ww Write the current history to the history file, overwriting the history file's con- tents. --cc Clear the history list by deleting all the entries. --pp Perform history substitution on the follow- ing _a_r_g_s and display the result on the stan- dard output. Does not store the results in the history list. Each _a_r_g must be quoted to disable normal history expansion. --ss Store the _a_r_g_s in the history list as a sin- gle entry. The last command in the history list is removed before the _a_r_g_s are added. The return value is 0 unless an invalid option is GNU 1998 Apr 1 68 BASH(1) BASH(1) encountered or an error occurs while reading or writing the history file. jjoobbss [--llnnpprrss] [ _j_o_b_s_p_e_c ... ] jjoobbss --xx _c_o_m_m_a_n_d [ _a_r_g_s ... ] The first form lists the active jobs. The options have the following meanings: --ll List process IDs in addition to the normal information. --pp List only the process ID of the job's pro- cess group leader. --nn Display information only about jobs that have changed status since the user was last notified of their status. --rr Restrict output to running jobs. --ss Restrict output to stopped jobs. If _j_o_b_s_p_e_c is given, output is restricted to infor- mation about that job. The return status is 0 unless an invalid option is encountered or an invalid _j_o_b_s_p_e_c is supplied. If the --xx option is supplied, jjoobbss 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 corre- sponding process group ID, and executes _c_o_m_m_a_n_d passing it _a_r_g_s, returning its exit status. kkiillll [--ss _s_i_g_s_p_e_c | --nn _s_i_g_n_u_m | --_s_i_g_s_p_e_c] [_p_i_d | _j_o_b_s_p_e_c] ... kkiillll --ll [_s_i_g_s_p_e_c | _e_x_i_t___s_t_a_t_u_s] Send the signal named by _s_i_g_s_p_e_c or _s_i_g_n_u_m 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 SSIIGGKKIILLLL or a signal number; _s_i_g_n_u_m is a signal number. If _s_i_g_s_p_e_c is a signal name, the name may be given with or without the SSIIGG prefix. If _s_i_g_s_p_e_c is not present, then SSIIGGTTEERRMM is assumed. An argument of --ll lists the signal names. If any arguments are supplied when --ll is given, the names of the signals corresponding to the arguments are listed, and the return status is 0. The _e_x_i_t___s_t_a_t_u_s argument to --ll is a number specifying either a signal number or the exit sta- tus of a process terminated by a signal. kkiillll returns true if at least one signal was success- fully sent, or false if an error occurs or an invalid option is encountered. lleett _a_r_g [_a_r_g ...] Each _a_r_g is an arithmetic expression to be evalu- ated (see AARRIITTHHMMEETTIICC EEVVAALLUUAATTIIOONN). If the last _a_r_g evaluates to 0, lleett returns 1; 0 is returned other- wise. GNU 1998 Apr 1 69 BASH(1) BASH(1) llooccaall [_n_a_m_e[=_v_a_l_u_e] ...] For each argument, a local variable named _n_a_m_e is created, and assigned _v_a_l_u_e. When llooccaall is used within a function, it causes the variable _n_a_m_e to have a visible scope restricted to that function and its children. With no operands, llooccaall writes a list of local variables to the standard output. It is an error to use llooccaall when not within a func- tion. The return status is 0 unless llooccaall is used outside a function, or an invalid _n_a_m_e is supplied. llooggoouutt Exit a login shell. ppooppdd [-nn] [+_n] [-_n] Removes entries from the directory stack. With no arguments, removes the top directory from the stack, and performs a ccdd to the new top directory. Arguments, if supplied, have the following mean- ings: ++_n Removes the _nth entry counting from the left of the list shown by ddiirrss, 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 ddiirrss, starting with zero. For example: ``popd -0'' removes the last directory, ``popd -1'' the next to last. --nn Suppresses the normal change of directory when removing directories from the stack, so that only the stack is manipulated. If the ppooppdd command is successful, a ddiirrss is per- formed as well, and the return status is 0. ppooppdd returns false if an invalid option is encountered, the directory stack is empty, a non-existent direc- tory stack entry is specified, or the directory change fails. pprriinnttff _f_o_r_m_a_t [_a_r_g_u_m_e_n_t_s] Write the formatted _a_r_g_u_m_e_n_t_s to the standard out- put under the control of the _f_o_r_m_a_t. The _f_o_r_m_a_t is a character string which contains three types of objects: plain characters, which are simply copied to standard output, character escape sequences, which are converted and copied to the standard out- put, and format specifications, each of which causes printing of the next successive _a_r_g_u_m_e_n_t. In addition to the standard _p_r_i_n_t_f(1) formats, %b causes pprriinnttff to expand backslash escape sequences in the corresponding _a_r_g_u_m_e_n_t, and %q causes pprriinnttff to output the corresponding _a_r_g_u_m_e_n_t in a format that can be reused as shell input. GNU 1998 Apr 1 70 BASH(1) BASH(1) The _f_o_r_m_a_t is reused as necessary to consume all of the _a_r_g_u_m_e_n_t_s. If the _f_o_r_m_a_t requires more _a_r_g_u_- _m_e_n_t_s than are supplied, the extra format specifi- cations behave as if a zero value or null string, as appropriate, had been supplied. ppuusshhdd [--nn] [_d_i_r] ppuusshhdd [--nn] [+_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 argu- ments, 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 ddiirrss, 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 ddiirrss, starting with zero) is at the top. --nn Suppresses the normal change of directory when adding directories to the stack, so that only the stack is manipulated. ddiirr Adds _d_i_r to the directory stack at the top, making it the new current working directory. If the ppuusshhdd command is successful, a ddiirrss is per- formed as well. If the first form is used, ppuusshhdd returns 0 unless the cd to _d_i_r fails. With the second form, ppuusshhdd returns 0 unless the directory stack is empty, a non-existent directory stack ele- ment is specified, or the directory change to the specified new current directory fails. ppwwdd [--LLPP] Print the absolute file name of the current working directory. The file name printed contains no sym- bolic links if the --PP option is supplied or the --oo pphhyyssiiccaall option to the sseett builtin command is enabled. If the --LL option is used, symbolic links are followed. The return status is 0 unless an error occurs while reading the name of the current directory or an invalid option is supplied. rreeaadd [--eerr] [--aa _a_n_a_m_e] [--pp _p_r_o_m_p_t] [_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 sec- ond word to the second _n_a_m_e, and so on, with left- over words and their intervening separators assigned to the last _n_a_m_e. If there are fewer words read from the standard input than names, the remaining names are assigned empty values. The characters in IIFFSS are used to split the line into GNU 1998 Apr 1 71 BASH(1) BASH(1) words. Options, if supplied, have the following meanings: --rr A backslash-newline pair is not ignored, and the backslash is considered to be part of the line. --pp Display _p_r_o_m_p_t, without a trailing newline, before attempting to read any input. The prompt is displayed only if input is coming from a terminal. --aa The words are assigned to sequential indices of the array variable _a_n_a_m_e, starting at 0. _a_n_a_m_e is unset before any new values are assigned. Other _n_a_m_e arguments are ignored. --ee If the standard input is coming from a ter- minal, rreeaaddlliinnee (see RREEAADDLLIINNEE above) is used to obtain the line. If no _n_a_m_e_s are supplied, the line read is assigned to the variable RREEPPLLYY. The return code is zero, unless end-of-file is encountered. rreeaaddoonnllyy [--aappff] [_n_a_m_e ...] The given _n_a_m_e_s are marked readonly; the values of these _n_a_m_e_s may not be changed by subsequent assignment. If the --ff option is supplied, the functions corresponding to the _n_a_m_e_s are so marked. The --aa option restricts the variables to arrays. If no _n_a_m_e arguments are given, or if the --pp option is supplied, a list of all readonly names is printed. The --pp option causes output to be dis- played in a format thatmay be reused as input. The return status is 0 unless an invalid option is encountered, one of the _n_a_m_e_s is not a valid shell variable name, or --ff is supplied with a _n_a_m_e that is not a function. rreettuurrnn [_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 .. (ssoouurrccee) 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 sta- tus of the script. If used outside a function and not during execution of a script by .., the return status is false. sseett [----aabbeeffhhkkmmnnppttuuvvxxBBCCHHPP] [--oo _o_p_t_i_o_n] [_a_r_g ...] 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, GNU 1998 Apr 1 72 BASH(1) BASH(1) 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 $$11, $$22, ...... $$_n. Options, if specified, have the following meanings: --aa Automatically mark variables which are mod- ified or created for export to the environ- ment of subsequent commands. --bb Report the status of terminated background jobs immediately, rather than before the next primary prompt. This is effective only when job control is enabled. --ee Exit immediately if a _s_i_m_p_l_e _c_o_m_m_a_n_d (see SSHHEELLLL GGRRAAMMMMAARR 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 !!. --ff Disable pathname expansion. --hh Remember the location of commands as they are looked up for execution. This is enabled by default. --kk All arguments in the form of assignment statements are placed in the environment for a command, not just those that precede the command name. --mm Monitor mode. Job control is enabled. This option is on by default for interac- tive shells on systems that support it (see JJOOBB CCOONNTTRROOLL above). Background processes run in a separate process group and a line containing their exit status is printed upon their completion. --nn 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. --oo _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 follow- ing: aalllleexxppoorrtt Same as --aa. bbrraacceeeexxppaanndd Same as --BB. eemmaaccss Use an emacs-style command line editing interface. This is enabled by default when the shell is inter- active, unless the shell is started with the ----nnooeeddiittiinngg option. eerrrreexxiitt Same as --ee. hhaasshhaallll Same as --hh. hhiisstteexxppaanndd Same as --HH. GNU 1998 Apr 1 73 BASH(1) BASH(1) hhiissttoorryy Enable command history, as described above under HHIISSTTOORRYY. This option is on by default in interactive shells. iiggnnoorreeeeooff The effect is as if the shell com- mand IGNOREEOF=10 hhaadd bbeeeenn eexxeeccuutteedd ((sseeee SShheellll VVaarriiaabblleess above). kkeeyywwoorrdd Same as --kk. mmoonniittoorr Same as --mm. nnoocclloobbbbeerr Same as --CC. nnooeexxeecc Same as --nn. nnoogglloobb Same as --ff. nnoottiiffyy Same as --bb. nnoouunnsseett Same as --uu. oonneeccmmdd Same as --tt. pphhyyssiiccaall Same as --PP. ppoossiixx Change the behavior of bbaasshh where the default operation differs from the POSIX 1003.2 standard to match the standard. pprriivviilleeggeedd Same as --pp. vveerrbboossee Same as --vv. vvii Use a vi-style command line editing interface. xxttrraaccee Same as --xx. If --oo is supplied with no _o_p_t_i_o_n_-_n_a_m_e, the values of the current options are printed. If ++oo is supplied with no _o_p_t_i_o_n_-_n_a_m_e, a series of sseett commands to recreate the cur- rent option settings is displayed on the standard output. --pp Turn on _p_r_i_v_i_l_e_g_e_d mode. In this mode, the $$EENNVV file is not processed, shell functions are not inherited from the environment, and the variable The SSHHEELLLLOOPPTTSS variable, if it appears in the environment, is ignored. 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. --tt Exit after reading and executing one com- mand. --uu Treat unset variables as an error when per- forming parameter expansion. If expansion is attempted on an unset variable, the shell prints an error message, and, if not interactive, exits with a non-zero status. --vv Print shell input lines as they are read. GNU 1998 Apr 1 74 BASH(1) BASH(1) --xx After expanding each _s_i_m_p_l_e _c_o_m_m_a_n_d, dis- play the expanded value of PPSS44, followed by the command and its expanded arguments. --BB The shell performs brace expansion (see BBrraaccee EExxppaannssiioonn above). This is on by default. --CC If set, bbaasshh does not overwrite an existing file with the >>, >>&&, and <<>> redirection operators. This may be overridden when creating output files by using the redirec- tion operator >>|| instead of >>. --HH Enable !! style history substitution. This option is on by default when the shell is interactive. --PP If set, the shell does not follow symbolic links when executing commands such as ccdd that change the current working directory. It uses the physical directory structure instead. By default, bbaasshh follows the log- ical chain of directories when performing commands which change the current direc- tory. ---- If no arguments follow this option, then the positional parameters are unset. Oth- erwise, 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 posi- tional parameters. The --xx and --vv options are turned off. If there are no _a_r_gs, 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 speci- fied as arguments to an invocation of the shell. The current set of options may be found in $$--. The return status is always true unless an invalid option is encountered. sshhiifftt [_n] The positional parameters from _n+1 ... are renamed to $$11 ........ Parameters represented by the numbers $$## down to $$##-_n+1 are unset. _n must be a non-nega- tive 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. sshhoopptt [--ppqqssuu] [--oo] [_o_p_t_n_a_m_e ...] Toggle the values of variables controlling optional GNU 1998 Apr 1 75 BASH(1) BASH(1) shell behavior. With no options, or with the --pp option, a list of all settable options is dis- played, with an indication of whether or not each is set. The --pp option causes output to be dis- played in a form that may be reused as input. Other options have the following meanings: --ss Enable (set) each _o_p_t_n_a_m_e. --uu Disable (unset) each _o_p_t_n_a_m_e. --qq Suppresses normal output (quiet mode); the return status indicates whether the _o_p_t_n_a_m_e is set or unset. If multiple _o_p_t_n_a_m_e argu- ments are given with --qq, the return status is zero if all _o_p_t_n_a_m_e_s are enabled; non- zero otherwise. --oo Restricts the values of _o_p_t_n_a_m_e to be those defined for the --oo option to the sseett builtin. If either --ss or --uu is used with no _o_p_t_n_a_m_e argu- ments, the display is limited to those options which are set or unset, respectively. Unless oth- erwise noted, the sshhoopptt options are disabled (unset) by default. The return status when listing options is zero if all _o_p_t_n_a_m_e_s are enabled, non-zero otherwise. When setting or unsetting options, the return status is zero unless an _o_p_t_n_a_m_e is not a valid shell option. The list of sshhoopptt options is: ccddaabbllee__vvaarrss If set, an argument to the ccdd builtin com- mand that is not a directory is assumed to be the name of a variable whose value is the directory to change to. ccddssppeellll If set, minor errors in the spelling of a directory component in a ccdd command will be corrected. The errors checked for are transposed characters, a missing character, and one character too many. If a correc- tion is found, the corrected file name is printed, and the command proceeds. This option is only used by interactive shells. cchheecckkhhaasshh If set, bbaasshh checks that a command found in the hash table exists before trying to exe- cute it. If a hashed command no longer exists, a normal path search is performed. cchheecckkwwiinnssiizzee If set, bbaasshh checks the window size after each command and, if necessary, updates the values of LLIINNEESS and CCOOLLUUMMNNSS. ccmmddhhiisstt If set, bbaasshh attempts to save all lines of GNU 1998 Apr 1 76 BASH(1) BASH(1) a multiple-line command in the same history entry. This allows easy re-editing of multi-line commands. ddoottgglloobb If set, bbaasshh includes filenames beginning with a `.' in the results of pathname expansion. eexxeeccffaaiill If set, a non-interactive shell will not exit if it cannot execute the file speci- fied as an argument to the eexxeecc builtin command. An interactive shell does not exit if eexxeecc fails. eexxppaanndd__aalliiaasseess If set, aliases are expanded as described above under AALLIIAASSEESS. This option is enabled by default for interactive shells. eexxttgglloobb If set, the extended pattern matching fea- tures described above under PPaatthhnnaammee EExxppaann-- ssiioonn are enabled. hhiissttaappppeenndd If set, the history list is appended to the file named by the value of the HHIISSTTFFIILLEE variable when the shell exits, rather than overwriting the file. hhiissttrreeeeddiitt If set, and rreeaaddlliinnee is being used, a user is given the opportunity to re-edit a failed history substitution. hhiissttvveerriiffyy If set, and rreeaaddlliinnee is being used, the results of history substitution are not immediately passed to the shell parser. Instead, the resulting line is loaded into the rreeaaddlliinnee editing buffer, allowing fur- ther modification. hhoossttccoommpplleettee If set, and rreeaaddlliinnee is being used, bbaasshh will attempt to perform hostname completion when a word containing a @@ is being com- pleted (see CCoommpplleettiinngg under RREEAADDLLIINNEE above). This is enabled by default. hhuuppoonneexxiitt If set, bbaasshh will send SSIIGGHHUUPP to all jobs when an interactive login shell exits. iinntteerraaccttiivvee__ccoommmmeennttss If set, allow a word beginning with ## to cause that word and all remaining charac- ters on that line to be ignored in an interactive shell (see CCOOMMMMEENNTTSS above). This option is enabled by default. lliitthhiisstt If set, and the ccmmddhhiisstt option is enabled, multi-line commands are saved to the his- tory with embedded newlines rather than using semicolon separators where possible. GNU 1998 Apr 1 77 BASH(1) BASH(1) mmaaiillwwaarrnn If set, and a file that bbaasshh is checking for mail has been accessed since the last time it was checked, the message ``The mail in _m_a_i_l_f_i_l_e has been read'' is displayed. nnooccaasseegglloobb If set, bbaasshh matches filenames in a case-insensitive fashion when performing pathname expansion (see PPaatthhnnaammee EExxppaannssiioonn above). nnuullllgglloobb If set, bbaasshh allows patterns which match no files (see PPaatthhnnaammee EExxppaannssiioonn above) to expand to a null string, rather than them- selves. pprroommppttvvaarrss If set, prompt strings undergo variable and parameter expansion after being expanded as described in PPRROOMMPPTTIINNGG above. This option is enabled by default. sshhiifftt__vveerrbboossee If set, the sshhiifftt builtin prints an error message when the shift count exceeds the number of positional parameters. ssoouurrcceeppaatthh If set, the ssoouurrccee (..) builtin uses the value of PPAATTHH to find the directory con- taining the file supplied as an argument. This option is enabled by default. ssuussppeenndd [--ff] Suspend the execution of this shell until it receives a SSIIGGCCOONNTT signal. The --ff 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 --ff is not supplied, or if job control is not enabled. tteesstt _e_x_p_r [[ _e_x_p_r ]] Return a status of 0 or 1 depending on the evalua- tion of the conditional expression _e_x_p_r. Each operator and operand must be a separate argument. Expressions are composed of the primaries described above under CCOONNDDIITTIIOONNAALL EEXXPPRREESSSSIIOONNSS. Expressions may be combined using the following operators, listed in decreasing order of prece- dence. !! _e_x_p_r True if _e_x_p_r is false. (( _e_x_p_r )) Returns the value of _e_x_p_r. This may be used to override the normal precedence of opera- tors. _e_x_p_r_1 -aa _e_x_p_r_2 True if both _e_x_p_r_1 and _e_x_p_r_2 are true. GNU 1998 Apr 1 78 BASH(1) BASH(1) _e_x_p_r_1 -oo _e_x_p_r_2 True if either _e_x_p_r_1 or _e_x_p_r_2 is true. tteesstt 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 CCOONNDDIITTIIOONNAALL EEXXPPRREESSSSIIOONNSS, the expres- sion is true if the unary test is true. If the first argument is not a valid unary con- ditional operator, the expression is false. 3 arguments If the second argument is one of the binary conditional operators listed above under CCOONNDDIITTIIOONNAALL EEXXPPRREESSSSIIOONNSS, 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 arguments. 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 --aa and --oo operators are considered binary operators in this case. 4 arguments If the first argument is !!, the result is the negation of the three-argument expres- sion 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. ttiimmeess Print the accumulated user and system times for the shell and for processes run from the shell. The return status is 0. ttrraapp [--llpp] [_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 GNU 1998 Apr 1 79 BASH(1) BASH(1) 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 the sig- nal specified by each _s_i_g_s_p_e_c is ignored by the shell and by the commands it invokes. If _a_r_g is --pp then the trap commands associated with each _s_i_g_s_p_e_c are displayed. If no arguments are supplied or if only --pp is given, ttrraapp prints the list of commands associated with each signal number. Each _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 a _s_i_g_s_p_e_c is EEXXIITT (0) the com- mand _a_r_g is executed on exit from the shell. If a _s_i_g_s_p_e_c is DDEEBBUUGG, the command _a_r_g is executed after every _s_i_m_p_l_e _c_o_m_m_a_n_d (see SSHHEELLLL GGRRAAMMMMAARR above). The --ll option causes the shell to print a list of signal names and their corresponding numbers. Sig- nals ignored upon entry to the shell cannot be trapped or reset. Trapped signals are reset to their original values in a child process when it is created. The return status is false if any _s_i_g_s_p_e_c is invalid; otherwise ttrraapp returns true. ttyyppee [--aattpp] _n_a_m_e [_n_a_m_e ...] With no options, indicate how each _n_a_m_e would be interpreted if used as a command name. If the --tt option is used, ttyyppee prints a string 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 _n_a_m_e is not found, then nothing is printed, and an exit status of false is returned. If the --pp option is used, ttyyppee 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 -t name _w_o_u_l_d _n_o_t _r_e_t_u_r_n _f_i_l_e. If a command is hashed, --pp prints the hashed value, not necessarily the file that appears first in PPAATTHH. If the --aa option is used, ttyyppee prints all of the places that contain an executable named _n_a_m_e. This includes aliases and functions, if and only if the --pp option is not also used. The table of hashed commands is not consulted when using --aa. ttyyppee returns true if any of the argu- ments are found, false if none are found. uulliimmiitt [--SSHHaaccddffllmmnnppssttuuvv [_l_i_m_i_t]] Provides control over the resources available to the shell and to processes started by it, on sys- tems 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 uunnlliimmiitteedd. The --HH and --SS 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 GNU 1998 Apr 1 80 BASH(1) BASH(1) neither --HH nor --SS is specified, both the soft and hard limits are set. If _l_i_m_i_t is omitted, the cur- rent value of the soft limit of the resource is printed, unless the --HH 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: --aa All current limits are reported --cc The maximum size of core files created --dd The maximum size of a process's data segment --ff The maximum size of files created by the shell --ll The maximum size that may be locked into memory --mm The maximum resident set size --nn The maximum number of open file descriptors (most systems do not allow this value to be set) --pp The pipe size in 512-byte blocks (this may not be set) --ss The maximum stack size --tt The maximum amount of cpu time in seconds --uu The maximum number of processes available to a single user --vv The maximum amount of virtual memory avail- able to the shell If _l_i_m_i_t is given, it is the new value of the spec- ified resource (the --aa option is display only). If no option is given, then --ff is assumed. Values are in 1024-byte increments, except for --tt, which is in seconds, --pp, which is in units of 512-byte blocks, and --nn and --uu, which are unscaled values. The return status is 0 unless an invalid option is encountered, a non-numeric argument other than uunnlliimmiitteedd is supplied as _l_i_m_i_t, or an error occurs while setting a new limit. uummaasskk [--pp] [--SS] [_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 sym- bolic mode mask similar to that accepted by _c_h_m_o_d(1). If _m_o_d_e is omitted, or if the --SS option is supplied, the current value of the mask is printed. The --SS option causes the mask to be printed in symbolic form; the default output is an octal number. If the --pp option is supplied, and _m_o_d_e 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 _m_o_d_e argu- ment was supplied, and false otherwise. GNU 1998 Apr 1 81 BASH(1) BASH(1) uunnaalliiaass [-aa] [_n_a_m_e ...] Remove _n_a_m_es from the list of defined aliases. If --aa is supplied, all alias definitions are removed. The return value is true unless a supplied _n_a_m_e is not a defined alias. uunnsseett [-ffvv] [_n_a_m_e ...] For each _n_a_m_e, remove the corresponding variable or function. If no options are supplied, or the --vv option is given, each _n_a_m_e refers to a shell vari- able. Read-only variables may not be unset. If --ff is specifed, each _n_a_m_e refers to a shell function, and the function definition is removed. Each unset variable or function is removed from the environ- ment passed to subsequent commands. If any of RRAANN-- DDOOMM, SSEECCOONNDDSS, LLIINNEENNOO, HHIISSTTCCMMDD, or DDIIRRSSTTAACCKK 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 readonly. wwaaiitt [_n] Wait for the specified process and return its ter- mination status. _n may be a process ID or a job specification; if a job spec is given, all pro- cesses 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. Otherwise, the return status is the exit status of the last process or job waited for. RREESSTTRRIICCTTEEDD SSHHEELLLL If bbaasshh is started with the name rrbbaasshh, or the --rr option is supplied at invocation, the shell becomes restricted. A restricted shell is used to set up an environment more controlled than the standard shell. It behaves identi- cally to bbaasshh with the exception that the following are disallowed or not performed: +o changing directories with ccdd +o setting or unsetting the values of SSHHEELLLL or PPAATTHH +o specifying command names containing // +o specifying a file name containing a // as an argu- ment to the .. builtin command +o importing function definitions from the shell envi- ronment at startup +o parsing the value of SSHHEELLLLOOPPTTSS from the shell envi- ronment at startup GNU 1998 Apr 1 82 BASH(1) BASH(1) +o redirecting output using the >, >|, <>, >&, &>, and >> redirection operators +o using the eexxeecc builtin command to replace the shell with another command +o adding or deleting builtin commands with the --ff and --dd options to the eennaabbllee builtin command +o specifying the --pp option to the ccoommmmaanndd builtin command +o turning off restricted mode with sseett ++rr or sseett ++oo rreessttrriicctteedd. These restrictions are enforced after any startup files are read. When a command that is found to be a shell script is exe- cuted (see CCOOMMMMAANNDD EEXXEECCUUTTIIOONN above), rrbbaasshh turns off any restrictions in the shell spawned to execute the script. SSEEEE AALLSSOO _B_a_s_h _F_e_a_t_u_r_e_s, Brian Fox and Chet Ramey _T_h_e _G_n_u _R_e_a_d_l_i_n_e _L_i_b_r_a_r_y, Brian Fox and Chet Ramey _T_h_e _G_n_u _H_i_s_t_o_r_y _L_i_b_r_a_r_y, Brian Fox and Chet Ramey _P_o_r_t_a_b_l_e _O_p_e_r_a_t_i_n_g _S_y_s_t_e_m _I_n_t_e_r_f_a_c_e _(_P_O_S_I_X_) _P_a_r_t _2_: _S_h_e_l_l _a_n_d _U_t_i_l_i_t_i_e_s, IEEE _s_h(1), _k_s_h(1), _c_s_h(1) _e_m_a_c_s(1), _v_i(1) _r_e_a_d_l_i_n_e(3) FFIILLEESS _/_b_i_n_/_b_a_s_h The bbaasshh executable _/_e_t_c_/_p_r_o_f_i_l_e The systemwide initialization file, executed for login shells _~_/_._b_a_s_h___p_r_o_f_i_l_e The personal initialization file, executed for login shells _~_/_._b_a_s_h_r_c The individual per-interactive-shell startup file _~_/_._i_n_p_u_t_r_c Individual _r_e_a_d_l_i_n_e initialization file AAUUTTHHOORRSS Brian Fox, Free Software Foundation bfox@gnu.ai.MIT.Edu Chet Ramey, Case Western Reserve University chet@ins.CWRU.Edu GNU 1998 Apr 1 83 BASH(1) BASH(1) BBUUGG RREEPPOORRTTSS If you find a bug in bbaasshh,, you should report it. But first, you should make sure that it really is a bug, and that it appears in the latest version of bbaasshh that you have. Once you have determined that a bug actually exists, use the _b_a_s_h_b_u_g command to submit a bug report. If you have a fix, you are encouraged to mail that as well! Suggestions and `philosophical' bug reports may be mailed to _b_u_g_- _b_a_s_h_@_g_n_u_._o_r_g or posted to the Usenet newsgroup ggnnuu..bbaasshh..bbuugg. ALL bug reports should include: The version number of bbaasshh The hardware and operating system The compiler used to compile A description of the bug behaviour A short script or `recipe' which exercises the bug _b_a_s_h_b_u_g inserts the first three items automatically into the template it provides for filing a bug report. Comments and bug reports concerning this manual page should be directed to _c_h_e_t_@_i_n_s_._C_W_R_U_._E_d_u. BBUUGGSS It's too big and too slow. There are some subtle differences between bbaasshh and tradi- tional versions of sshh, mostly because of the PPOOSSIIXX speci- fication. Aliases are confusing in some uses. Shell builtin commands and functions are not stop- pable/restartable. Compound commands and command sequences of the form `a ; b ; c' are not handled gracefully when process suspension is attempted. When a process is stopped, the shell immedi- ately executes the next command in the sequence. It suf- fices to place the sequence of commands between parenthe- ses to force it into a subshell, which may be stopped as a unit. Commands inside of $$((...)) command substitution are not parsed until substitution is attempted. This will delay error reporting until some time after the command is entered. Array variables may not (yet) be exported. GNU 1998 Apr 1 84