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BASH !!!BASH NAME SYNOPSIS COPYRIGHT DESCRIPTION OPTIONS ARGUMENTS INVOCATION DEFINITIONS RESERVED WORDS SHELL GRAMMAR COMMENTS QUOTING PARAMETERS EXPANSION REDIRECTION ALIASES FUNCTIONS ARITHMETIC EVALUATION CONDITIONAL EXPRESSIONS SIMPLE COMMAND EXPANSION COMMAND EXECUTION COMMAND EXECUTION ENVIRONMENT ENVIRONMENT EXIT STATUS SIGNALS JOB CONTROL PROMPTING READLINE HISTORY HISTORY EXPANSION SHELL BUILTIN COMMANDS RESTRICTED SHELL SEE ALSO FILES AUTHORS BUG REPORTS BUGS ---- !!NAME bash - GNU Bourne-Again SHell !!SYNOPSIS __bash__ [[options] [[file] !!COPYRIGHT Bash is Copyright 1989-2001 by the Free Software Foundation, Inc. !!DESCRIPTION __Bash__ is an __sh__-compatible command language interpreter that executes commands read from the standard input or from a file. __Bash__ also incorporates useful features from the ''Korn'' and ''C'' shells (__ksh__ and __csh__). __Bash__ is intended to be a conformant implementation of the IEEE POSIX Shell and Tools specification (IEEE Working Group 1003.2). !!OPTIONS In addition to the single-character shell options documented in the description of the __set__ builtin command, __bash__ interprets the following options when it is invoked: __-c__ ''string'' If the __-c__ option is present, then commands are read from ''string''. If there are arguments after the ''string'', they are assigned to the positional parameters, starting with __$0__. __-r__ If the __-r__ option is present, the shell becomes ''restricted'' (see __RESTRICTED SHELL__ below). __-i__ If the __-i__ option is present, the shell is ''interactive''. __-s__ If the __-s__ option is present, or if no arguments remain after option processing, then commands are read from the standard input. This option allows the positional parameters to be set when invoking an interactive shell. __-v__ Print shell input lines as they are read. __-x__ Print commands and their arguments as they are executed. __-D__ A list of all double-quoted strings preceded by __$__ is printed on the standard ouput. These are the strings that are subject to language translation when the current locale is not __C__ or __POSIX__. This implies the __-n__ option; no commands will be executed. __[[-+]O [[__''shopt_option''__]__ ''shopt_option'' is one of the shell options accepted by the __shopt__ builtin (see __SHELL BUILTIN COMMANDS__ below). If ''shopt_option'' is present, __-O__ sets the value of that option; __+O__ unsets it. If ''shopt_option'' is not supplied, the names and values of the shell options accepted by __shopt__ are printed on the standard output. If the invocation option is __+O__, the output is displayed in a format that may be reused as input. __--__ 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 __--__. __Bash__ 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 recognized. __--dump-po-strings__ Equivalent to __-D__, but the output is in the GNU ''gettext'' __po__ (portable object) file format. __--dump-strings__ Equivalent to __-D__. __--help__ Display a usage message on standard output and exit successfully. __--init-file__ ''file'' __--rcfile__ ''file'' Execute commands from ''file'' instead of the standard personal initialization file ''~/.bashrc'' if the shell is interactive (see __INVOCATION__ below). __--login__ Make __bash__ act as if it had been invoked as a login shell (see __INVOCATION__ below). __--noediting__ Do not use the GNU __readline__ library to read command lines when the shell is interactive. __--noprofile__ Do not read either the system-wide startup file ''/etc/profile'' or any of the personal initialization files ''~/.bash_profile'', ''~/.bash_login'', or ''~/.profile''. By default, __bash__ reads these files when it is invoked as a login shell (see __INVOCATION__ below). __--norc__ Do not read and execute the personal initialization file ''~/.bashrc'' if the shell is interactive. This option is on by default if the shell is invoked as __sh__. __--posix__ Change the behavior of __bash__ where the default operation differs from the POSIX 1003.2 standard to match the standard (''posix mode''). __--restricted__ The shell becomes restricted (see __RESTRICTED SHELL__ below). __--verbose__ Equivalent to __-v__. __--version__ Show version information for this instance of __bash__ on the standard output and exit successfully. !!ARGUMENTS If arguments remain after option processing, and neither the __-c__ nor the __-s__ option has been supplied, the first argument is assumed to be the name of a file containing shell commands. If __bash__ is invoked in this fashion, __$0__ is set to the name of the file, and the positional parameters are set to the remaining arguments. __Bash__ reads and executes commands from this file, then exits. __Bash__'s exit status is the exit status of the last command executed in the script. If no commands are executed, the exit status is 0. An attempt is first made to open the file in the current directory, and, if no file is found, then the shell searches the directories in __PATH__ for the script. !!INVOCATION A ''login shell'' is one whose first character of argument zero is a __-__, or one started with the __--login__ option. An ''interactive'' shell is one started without non-option arguments and without the __-c__ option whose standard input and output are both connected to terminals (as determined by isatty(3)), or one started with the __-i__ option. __PS1__ is set and __$-__ includes __i__ if __bash__ is interactive, allowing a shell script or a startup file to test this state. The following paragraphs describe how __bash__ executes its startup files. If any of the files exist but cannot be read, __bash__ reports an error. Tildes are expanded in file names as described below under __Tilde Expansion__ in the __EXPANSION__ section. When __bash__ is invoked as an interactive login shell, or as a non-interactive shell with the __--login__ option, it first reads and executes commands from the file ''/etc/profile'', if that file exists. After reading that file, it looks for ''~/.bash_profile'', ''~/.bash_login'', and ''~/.profile'', in that order, and reads and executes commands from the first one that exists and is readable. The __--noprofile__ option may be used when the shell is started to inhibit this behavior. When a login shell exits, __bash__ reads and executes commands from the file ''~/.bash_logout'', if it exists. When an interactive shell that is not a login shell is started, __bash__ reads and executes commands from ''~/.bashrc'', if that file exists. This may be inhibited by using the __--norc__ option. The __--rcfile__ ''file'' option will force __bash__ to read and execute commands from ''file'' instead of ''~/.bashrc''. When __bash__ is started non-interactively, to run a shell script, for example, it looks for the variable __BASH_ENV__ in the environment, expands its value if it appears there, and uses the expanded value as the name of a file to read and execute. __Bash__ behaves as if the following command were executed: if [[ -n but the value of the __PATH__ variable is not used to search for the file name. If __bash__ is invoked with the name __sh__, it tries to mimic the startup behavior of historical versions of __sh__ as closely as possible, while conforming to the POSIX standard as well. When invoked as an interactive login shell, or a non-interactive shell with the __--login__ option, it first attempts to read and execute commands from ''/etc/profile'' and ''~/.profile'', in that order. The __--noprofile__ option may be used to inhibit this behavior. When invoked as an interactive shell with the name __sh__, __bash__ looks for the variable __ENV__, expands its value if it is defined, and uses the expanded value as the name of a file to read and execute. Since a shell invoked as __sh__ does not attempt to read and execute commands from any other startup files, the __--rcfile__ option has no effect. A non-interactive shell invoked with the name __sh__ does not attempt to read any other startup files. When invoked as __sh__, __bash__ enters ''posix'' mode after the startup files are read. When __bash__ is started in ''posix'' mode, as with the __--posix__ command line option, it follows the POSIX standard for startup files. In this mode, interactive shells expand the __ENV__ variable and commands are read and executed from the file whose name is the expanded value. No other startup files are read. __Bash__ attempts to determine when it is being run by the remote shell daemon, usually ''rshd''. If __bash__ determines it is being run by ''rshd'', it reads and executes commands from ''~/.bashrc'', if that file exists and is readable. It will not do this if invoked as __sh__. The __--norc__ option may be used to inhibit this behavior, and the __--rcfile__ option may be used to force another file to be read, but ''rshd'' does not generally invoke the shell with those options or allow them to be specified. If the shell is started with the effective user (group) id not equal to the real user (group) id, and the __-p__ option is not supplied, no startup files are read, shell functions are not inherited from the environment, the __SHELLOPTS__ variable, if it appears in the environment, is ignored, and the effective user id is set to the real user id. If the __-p__ option is supplied at invocation, the startup behavior is the same, but the effective user id is not reset. !!DEFINITIONS The following definitions are used throughout the rest of this document. __blank__ A space or tab. __word__ A sequence of characters considered as a single unit by the shell. Also known as a __token__. __name__ A ''word'' consisting only of alphanumeric characters and underscores, and beginning with an alphabetic character or an underscore. Also referred to as an __identifier__. __metacharacter__ A character that, when unquoted, separates words. One of the following: __| __ __control operator__ A ''token'' that performs a control function. It is one of the following symbols: __ __ !!RESERVED WORDS ''Reserved words'' are words that have a special meaning to the shell. The following words are recognized as reserved when unquoted and either the first word of a simple command (see __SHELL GRAMMAR__ below) or the third word of a __case__ or __for__ command: __! case do done elif else esac fi for function if in select then until while { } time [[[[ ]]__ !!SHELL GRAMMAR __Simple Commands__ A ''simple command'' is a sequence of optional variable assignments followed by __blank__-separated words and redirections, and terminated by a ''control operator''. The first word specifies the command to be executed, and is passed as argument zero. The remaining words are passed as arguments to the invoked command. The return value of a ''simple command'' is its exit status, or 128+''n'' if the command is terminated by signal ''n''. __Pipelines__ A ''pipeline'' is a sequence of one or more commands separated by the character __|__. The format for a pipeline is: [[__time__ [[__-p__]] [[ ! ] ''command'' [[ __|__ ''command2'' ... ] The standard output of ''command'' is connected via a pipe to the standard input of ''command2''. This connection is performed before any redirections specified by the command (see __REDIRECTION__ below). If the reserved word __!__ precedes a pipeline, the exit status 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 __time__ reserved word precedes a pipeline, the elapsed as well as user and system time consumed by its execution are reported when the pipeline terminates. The __-p__ option changes the output format to that specified by POSIX. The __TIMEFORMAT__ variable may be set to a format string that specifies how the timing information should be displayed; see the description of __TIMEFORMAT__ under __Shell Variables__ below. Each command in a pipeline is executed as a separate process (i.e., in a subshell). __Lists__ A ''list'' is a sequence of one or more pipelines separated by one of the operators __;__, ____, ____, or , and optionally terminated by one of __;__, ____, or ____. 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 ''background'' in a subshell. 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 of the last command executed. The control operators ____ and denote AND lists and OR lists, respectively. An AND list has the form ''command1'' ____ ''command2'' ''command2'' is executed if, and only if, ''command1'' returns an exit status of zero. An OR list has the form ''command1 command2'' ''command2'' is executed if and only if ''command1'' returns a non-zero exit status. The return status of AND and OR lists is the exit status of the last command executed in the list. __Compound Commands__ A ''compound command'' is one of the following: (''list'') ''list'' is executed in a subshell. Variable assignments and builtin commands that affect the shell's environment do not remain in effect after the command completes. The return status is the exit status of ''list''. { ''list''; } ''list'' is simply executed in the current shell environment. ''list'' must be terminated with a newline or semicolon. This is known as a ''group command''. The return status is the exit status of ''list''. Note that unlike the metacharacters __(__ and , __{__ and __}__ are ''reserved words'' and must occur where a reserved word is permitted to be recognized. Since they do not cause a word break, they must be separated from ''list'' by whitespace. ((''expression'')) The ''expression'' is evaluated according to the rules described below under __ARITHMETIC EVALUATION__. If the value of the expression is non-zero, the return status is 0; otherwise the return status is 1. This is exactly equivalent to __let __''expression''____. __[[[[__ ''expression'' __]]__ Return a status of 0 or 1 depending on the evaluation of the conditional expression ''expression''. Expressions are composed of the primaries described below under __CONDITIONAL EXPRESSIONS__. Word splitting and pathname expansion are not performed on the words between the __[[[[__ and __]]__; tilde expansion, parameter and variable expansion, arithmetic expansion, command substitution, process substitution, and quote removal are performed. When the __==__ and __!=__ operators are used, the string to the right of the operator is considered a pattern and matched according to the rules described below under __Pattern Matching__. The return value is 0 if the string matches or does not match the pattern, 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 precedence: __(__ ''expression'' __)__ Returns the value of ''expression''. This may be used to override the normal precedence of operators. __!__ ''expression'' True if ''expression'' is false. ''expression1'' ____ ''expression2'' True if both ''expression1'' and ''expression2'' are true. ''expression1 expression2'' True if either ''expression1'' or ''expression2'' is true. The ____ and operators do not execute ''expression2'' if the value of ''expression1'' is sufficient to determine the return value of the entire conditional expression. __for__ ''name'' [[ __in__ ''word'' ] ; __do__ ''list'' ; __done__ The list of words following __in__ is expanded, generating a list of items. The variable ''name'' is set to each element of this list in turn, and ''list'' is executed each time. If the __in__ ''word'' is omitted, the __for__ command executes ''list'' once for each positional parameter that is set (see __PARAMETERS__ below). The return status is the exit status of the last command that executes. If the expansion of the items following __in__ results in an empty list, no commands are executed, and the return status is 0. __for__ (( ''expr1'' ; ''expr2'' ; ''expr3'' )) ; __do__ ''list'' ; __done__ First, the arithmetic expression ''expr1'' is evaluated according to the rules described below under __ARITHMETIC EVALUATION__. The arithmetic expression ''expr2'' is then evaluated repeatedly until it evaluates to zero. Each time ''expr2'' evaluates to a non-zero value, ''list'' is executed and the arithmetic expression ''expr3'' is evaluated. If any expression is omitted, it behaves as if it evaluates to 1. The return value is the exit status of the last command in ''list'' that is executed, or false if any of the expressions is invalid. __select__ ''name'' [[ __in__ ''word'' ] ; __do__ ''list'' ; __done__ The list of words following __in__ is expanded, generating a list of items. The set of expanded words is printed on the standard error, each preceded by a number. If the __in__ ''word'' is omitted, the positional parameters are printed (see __PARAMETERS__ below). The __PS3__ prompt is then displayed and a line read from the standard input. If the line consists of a number corresponding to one of the displayed words, then the value of ''name'' is set to that word. If the line is empty, the words and prompt are displayed again. If EOF is read, the command completes. Any other value read causes ''name'' to be set to null. The line read is saved in the variable __REPLY__. The ''list'' is executed after each selection until a __break__ command is executed. The exit status of __select__ is the exit status of the last command executed in ''list'', or zero if no commands were executed. __case__ ''word'' __in__ [[ [[(] ''pattern'' [[ __|__ ''pattern'' ] ... ) ''list'' ;; ] ... __esac__ A __case__ command first expands ''word'', and tries to match it against each ''pattern'' in turn, using the same matching rules as for pathname expansion (see __Pathname Expansion__ below). When a match is found, the corresponding ''list'' 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 command executed in ''list''. __if__ ''list''; __then__ ''list;'' [[ __elif__ ''list''; __then__ ''list''; ] ... [[ __else__ ''list''; ] __fi__ The __if__ ''list'' is executed. If its exit status is zero, the __then__ ''list'' is executed. Otherwise, each __elif__ ''list'' is executed in turn, and if its exit status is zero, the corresponding __then__ ''list'' is executed and the command completes. Otherwise, the __else__ ''list'' is executed, if present. The exit status is the exit status of the last command executed, or zero if no condition tested true. __while__ ''list''; __do__ ''list''; __done__ __until__ ''list''; __do__ ''list''; __done__ The __while__ command continuously executes the __do__ ''list'' as long as the last command in ''list'' returns an exit status of zero. The __until__ command is identical to the __while__ command, except that the test is negated; the __do__ ''list'' is executed as long as the last command in ''list'' returns a non-zero exit status. The exit status of the __while__ and __until__ commands is the exit status of the last __do__ ''list'' command executed, or zero if none was executed. [[ __function__ ] ''name'' () { ''list''; } This defines a function named ''name''. The ''body'' of the function is the ''list'' of commands between { and }. This list is executed whenever ''name'' is specified 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 __FUNCTIONS__ below.) !!COMMENTS In a non-interactive shell, or an interactive shell in which the __interactive_comments__ option to the __shopt__ builtin is enabled (see __SHELL BUILTIN COMMANDS__ below), a word beginning with __#__ causes that word and all remaining characters on that line to be ignored. An interactive shell without the __interactive_comments__ option enabled does not allow comments. The __interactive_comments__ option is on by default in interactive shells. !!QUOTING ''Quoting'' is used to remove the special meaning of certain characters or words to the shell. Quoting can be used to disable special treatment for special characters, to prevent reserved words from being recognized as such, and to prevent parameter expansion. Each of the ''metacharacters'' listed above under __DEFINITIONS__ has special meaning to the shell and must be quoted if it is to represent itself. When the command history expansion facilities are being used, the ''history expansion'' character, usually __!__, must be quoted to prevent history expansion. There are three quoting mechanisms: the ''escape character'', single quotes, and double quotes. A non-quoted backslash (__\__) is the ''escape character''. It preserves the literal value of the next character that follows, with the exception of ''\__ __\__ __ Enclosing characters in single quotes preserves the literal value of each character within the quotes. A single quote may not occur between single quotes, even when preceded by a backslash. Enclosing characters in double quotes preserves the literal 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: __$__, __`__, ____, __\__, or ____. A double quote may be quoted within double quotes by preceding it with a backslash. The special parameters __*__ and __@__ have special meaning when in double quotes (see __PARAMETERS__ below). Words of the form __$__'''string''' are treated specially. The word expands to ''string'', with backslash-escaped characters replaced as specifed by the ANSI C standard. Backslash escape sequences, if present, are decoded as follows: __a__ alert (bell) __b__ backspace __e__ an escape character __f__ form feed __n__ new line __r__ carriage return __t__ horizontal tab __v__ vertical tab __\__ backslash __'__ single quote __\__''nnn'' the eight-bit character whose value is the octal value ''nnn'' (one to three digits) __x__''HH'' the eight-bit character whose value is the hexadecimal value ''HH'' (one or two hex digits) The expanded 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 __C__ or __POSIX__, the dollar sign is ignored. If the string is translated and replaced, the replacement is double-quoted. !!PARAMETERS A ''parameter'' is an entity that stores values. It can be a ''name'', a number, or one of the special characters listed below under __Special Parameters__. For the shell's purposes, a ''variable'' is a parameter denoted by a ''name''. A variable has a ''value'' and zero or more ''attributes''. Attributes are assigned using the __declare__ builtin command (see __declare__ below in __SHELL BUILTIN COMMANDS__). A parameter is set if it has been assigned a value. The null string is a valid value. Once a variable is set, it may be unset only by using the __unset__ builtin command (see __SHELL BUILTIN COMMANDS__ below). A ''variable'' may be assigned to by a statement of the form ''name''=[[''value''] If ''value'' is not given, the variable is assigned the null string. All ''values'' undergo tilde expansion, parameter and variable expansion, command substitution, arithmetic expansion, and quote removal (see __EXPANSION__ below). If the variable has its __integer__ attribute set, then ''value'' is subject to arithmetic expansion even if the $((...)) expansion is not used (see __Arithmetic Expansion__ below). Word splitting is not performed, with the exception of ____ as explained below under __Special Parameters__. Pathname expansion is not performed. Assignment statements may also appear as arguments to the __declare__, __typeset__, __export__, __readonly__, and __local__ builtin commands. __Positional Parameters__ A ''positional parameter'' is a parameter denoted by one or more digits, other than the single digit 0. Positional parameters are assigned from the shell's arguments when it is invoked, and may be reassigned using the __set__ builtin command. Positional parameters may not be assigned to with assignment statements. The positional parameters are temporarily replaced when a shell function is executed (see __FUNCTIONS__ below). When a positional parameter consisting of more than a single digit is expanded, it must be enclosed in braces (see __EXPANSION__ below). __Special Parameters__ The shell treats several parameters specially. These parameters may only be referenced; assignment to them is not allowed. __*__ Expands to the positional parameters, starting from one. When the expansion occurs within double quotes, it expands to a single word with the value of each parameter separated by the first character of the __IFS__ special variable. That is, __$*__ __$1__''c''__$2__''c''__...__ __c'' is the first character of the value of the __IFS__ variable. If __IFS__ is unset, the parameters are separated by spaces. If __IFS__ is null, the parameters are joined without intervening 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, $@____$1__ __$2__ __$@____$@__ expand to nothing (i.e., they are removed). __#__ Expands to the number of positional parameters in decimal. __?__ Expands to the status of the most recently executed foreground pipeline. __-__ Expands to the current option flags as specified upon invocation, by the __set__ builtin command, or those set by the shell itself (such as the __-i__ option). __$__ Expands to the process ID of the shell. In a () subshell, it expands to the process ID of the current shell, not the subshell. __!__ Expands to the process ID of the most recently executed background (asynchronous) command. __0__ Expands to the name of the shell or shell script. This is set at shell initialization. If __bash__ is invoked with a file of commands, __$0__ is set to the name of that file. If __bash__ is started with the __-c__ option, then __$0__ is set to the first argument after the string to be executed, if one is present. Otherwise, it is set to the file name used to invoke __bash__, as given by argument zero. _____ At shell startup, set to the absolute file name of the shell or shell script being executed as passed in the argument list. Subsequently, expands to the last argument to the previous command, after expansion. Also set to the full file name of each command executed and placed in the environment exported to that command. When checking mail, this parameter holds the name of the mail file currently being checked. __Shell Variables__ The following variables are set by the shell: __BASH__ Expands to the full file name used to invoke this instance of __bash__. __BASH_VERSINFO__ A readonly array variable whose members hold version information for this instance of __bash__. The values assigned to the array members are as follows: __BASH_VERSINFO[[__0__]__ The major version number (the ''release''). __BASH_VERSINFO[[__1__]__ The minor version number (the ''version''). __BASH_VERSINFO[[__2__]__ The patch level. __BASH_VERSINFO[[__3__]__ The build version. __BASH_VERSINFO[[__4__]__ The release status (e.g., ''beta1''). __BASH_VERSINFO[[__5__]__ The value of __MACHTYPE__. __BASH_VERSION__ Expands to a string describing the version of this instance of __bash__. __COMP_CWORD__ An index into __${COMP_WORDS}__ of the word containing the current cursor position. This variable is available only in shell functions invoked by the programmable completion facilities (see __Programmable Completion__ below). __COMP_LINE__ The current command line. This variable is available only in shell functions and external commands invoked by the programmable completion facilities (see __Programmable Completion__ below). __COMP_POINT__ The index of the current cursor position relative to the beginning of the current command. If the current cursor position is at the end of the current command, the value of this variable is equal to __${#COMP_LINE}__. This variable is available only in shell functions and external commands invoked by the programmable completion facilities (see __Programmable Completion__ below). __COMP_WORDS__ An array variable (see __Arrays__ below) consisting of the individual words in the current command line. This variable is available only in shell functions invoked by the programmable completion facilities (see __Programmable Completion__ below). __DIRSTACK__ An array variable (see __Arrays__ below) containing the current contents of the directory stack. Directories appear in the stack in the order they are displayed by the __dirs__ builtin. Assigning to members of this array variable may be used to modify directories already in the stack, but the __pushd__ and __popd__ builtins must be used to add and remove directories. Assignment to this variable will not change the current directory. If __DIRSTACK__ is unset, it loses its special properties, even if it is subsequently reset. __EUID__ Expands to the effective user ID of the current user, initialized at shell startup. This variable is readonly. __FUNCNAME__ The name of any currently-executing shell function. This variable exists only when a shell function is executing. Assignments to __FUNCNAME__ have no effect and return an error status. If __FUNCNAME__ is unset, it loses its special properties, even if it is subsequently reset. __GROUPS__ An array variable containing the list of groups of which the current user is a member. Assignments to __GROUPS__ have no effect and return an error status. If __GROUPS__ is unset, it loses its special properties, even if it is subsequently reset. __HISTCMD__ The history number, or index in the history list, of the current command. If __HISTCMD__ is unset, it loses its special properties, even if it is subsequently reset. __HOSTNAME__ Automatically set to the name of the current host. __HOSTTYPE__ Automatically set to a string that uniquely describes the type of machine on which __bash__ is executing. The default is system-dependent. __LINENO__ Each time this parameter is referenced, the shell substitutes a decimal number representing the current sequential line number (starting with 1) within a script or function. When not in a script or function, the value substituted is not guaranteed to be meaningful. If __LINENO__ is unset, it loses its special properties, even if it is subsequently reset. __MACHTYPE__ Automatically set to a string that fully describes the system type on which __bash__ is executing, in the standard GNU ''cpu-company-system'' format. The default is system-dependent. __OLDPWD__ The previous working directory as set by the __cd__ command. __OPTARG__ The value of the last option argument processed by the __getopts__ builtin command (see __SHELL BUILTIN COMMANDS__ below). __OPTIND__ The index of the next argument to be processed by the __getopts__ builtin command (see __SHELL BUILTIN COMMANDS__ below). __OSTYPE__ Automatically set to a string that describes the operating system on which __bash__ is executing. The default is system-dependent. __PIPESTATUS__ An array variable (see __Arrays__ below) containing a list of exit status values from the processes in the most-recently-executed foreground pipeline (which may contain only a single command). __PPID__ The process ID of the shell's parent. This variable is readonly. __PWD__ The current working directory as set by the __cd__ command. __RANDOM__ Each time this parameter is referenced, a random integer between 0 and 32767 is generated. The sequence of random numbers may be initialized by assigning a value to __RANDOM__. If __RANDOM__ is unset, it loses its special properties, even if it is subsequently reset. __REPLY__ Set to the line of input read by the __read__ builtin command when no arguments are supplied. __SECONDS__ Each time this parameter is referenced, the number of seconds since shell invocation is returned. If a value is assigned to __SECONDS__, the value returned upon subsequent references is the number of seconds since the assignment plus the value assigned. If __SECONDS__ is unset, it loses its special properties, even if it is subsequently reset. __SHELLOPTS__ A colon-separated list of enabled shell options. Each word in the list is a valid argument for the __-o__ option to the __set__ builtin command (see __SHELL BUILTIN COMMANDS__ below). The options appearing in __SHELLOPTS__ are those reported as ''on'' by __set -o__. If this variable is in the environment when __bash__ starts up, each shell option in the list will be enabled before reading any startup files. This variable is read-only. __SHLVL__ Incremented by one each time an instance of __bash__ is started. __UID__ Expands to the user ID of the current user, initialized at shell startup. This variable is readonly. The following variables are used by the shell. In some cases, __bash__ assigns a default value to a variable; these cases are noted below. __BASH_ENV__ If this parameter is set when __bash__ is executing a shell script, its value is interpreted as a filename containing commands to initialize the shell, as in ''~/.bashrc''. The value of __BASH_ENV__ is subjected to parameter expansion, command substitution, and arithmetic expansion before being interpreted as a file name. __PATH__ is not used to search for the resultant file name. __CDPATH__ The search path for the __cd__ command. This is a colon-separated list of directories in which the shell looks for destination directories specified by the __cd__ command. A sample value is ``.:~:/usr''. __COLUMNS__ Used by the __select__ builtin command to determine the terminal width when printing selection lists. Automatically set upon receipt of a SIGWINCH. __COMPREPLY__ An array variable from which __bash__ reads the possible completions generated by a shell function invoked by the programmable completion facility (see __Programmable Completion__ below). __FCEDIT__ The default editor for the __fc__ builtin command. __FIGNORE__ A colon-separated list of suffixes to ignore when performing filename completion (see __READLINE__ below). A filename whose suffix matches one of the entries in __FIGNORE__ is excluded from the list of matched filenames. A sample value is ``.o:~'' (Quoting is needed when assigning a value to this variable, which contains tildes). __GLOBIGNORE__ A colon-separated list of patterns defining the set of filenames to be ignored by pathname expansion. If a filename matched by a pathname expansion pattern also matches one of the patterns in __GLOBIGNORE__, it is removed from the list of matches. __HISTCONTROL__ If set to a value of ''ignorespace'', lines which begin with a __space__ character are not entered on the history list. If set to a value of ''ignoredups'', lines matching the last history line are not entered. A value of ''ignoreboth'' 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 __HISTIGNORE__. This variable's function is superseded by __HISTIGNORE__. The second and subsequent lines of a multi-line compound command are not tested, and are added to the history regardless of the value of __HISTCONTROL__. __HISTFILE__ The name of the file in which command history is saved (see __HISTORY__ below). The default value is ''~/.bash_history''. If unset, the command history is not saved when an interactive shell exits. __HISTFILESIZE__ The maximum number of lines contained in the history file. When this variable is assigned a value, the history file is truncated, if necessary, to contain no more than 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. __HISTIGNORE__ 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 match the complete line (no implicit `__*__' is appended). Each pattern is tested against the line after the checks specified by __HISTCONTROL__ are applied. In addition to the 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 __HISTIGNORE__. __HISTSIZE__ The number of commands to remember in the command history (see __HISTORY__ below). The default value is 500. __HOME__ The home directory of the current user; the default argument for the __cd__ builtin command. The value of this variable is also used when performing tilde expansion. __HOSTFILE__ Contains the name of a file in the same format as ''/etc/hosts'' that should be read when the shell needs to complete a hostname. The list of possible hostname completions may be changed while the shell is running; the next time hostname completion is attempted after the value is changed, __bash__ adds the contents of the new file to the existing list. If __HOSTFILE__ is set, but has no value, __bash__ attempts to read ''/etc/hosts'' to obtain the list of possible hostname completions. When __HOSTFILE__ is unset, the hostname list is cleared. __IFS__ The ''Internal Field Separator'' that is used for word splitting after expansion and to split lines into words with the __read__ builtin command. The default value is ``__ __IGNOREEOF__ Controls the action of an interactive shell on receipt of an __EOF__ character as the sole input. If set, the value is the number of consecutive __EOF__ characters which must be typed as the first characters on an input line before __bash__ exits. If the variable exists but does not have a numeric value, or has no value, the default value is 10. If it does not exist, __EOF__ signifies the end of input to the shell. __INPUTRC__ The filename for the __readline__ startup file, overriding the default of ''~/.inputrc'' (see __READLINE__ below). __LANG__ Used to determine the locale category for any category not specifically selected with a variable starting with __LC___. __LC_ALL__ This variable overrides the value of __LANG__ and any other __LC___ variable specifying a locale category. __LC_COLLATE__ This variable determines the collation order used when sorting the results of pathname expansion, and determines the behavior of range expressions, equivalence classes, and collating sequences within pathname expansion and pattern matching. __LC_CTYPE__ This variable determines the interpretation of characters and the behavior of character classes within pathname expansion and pattern matching. __LC_MESSAGES__ This variable determines the locale used to translate double-quoted strings preceded by a __$__. __LC_NUMERIC__ This variable determines the locale category used for number formatting. __LINES__ Used by the __select__ builtin command to determine the column length for printing selection lists. Automatically set upon receipt of a SIGWINCH. __MAIL__ If this parameter is set to a file name and the __MAILPATH__ variable is not set, __bash__ informs the user of the arrival of mail in the specified file. __MAILCHECK__ Specifies how often (in seconds) __bash__ checks for mail. The default is 60 seconds. When it is time to check for mail, the shell does so before displaying the primary prompt. If this variable is unset, or set to a value that is not a number greater than or equal to zero, the shell disables mail checking. __MAILPATH__ 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, __$___ expands to the name of the current mailfile. Example: __MAILPATH__='/var/mail/bfox? __ __Bash__ supplies a default value for this variable, but the location of the user mail files that it uses is system dependent (e.g., /var/mail/__$USER__). __OPTERR__ If set to the value 1, __bash__ displays error messages generated by the __getopts__ builtin command (see __SHELL BUILTIN COMMANDS__ below). __OPTERR__ is initialized to 1 each time the shell is invoked or a shell script is executed. __PATH__ The search path for commands. It is a colon-separated list of directories in which the shell looks for commands (see __COMMAND EXECUTION__ below). The default path is system-dependent, and is set by the administrator who installs __bash__. A common value is /usr/gnu/bin:/usr/local/bin:/usr/ucb:/bin:/usr/bin:.. __POSIXLY_CORRECT__ If this variable is in the environment when __bash__ starts, the shell enters ''posix mode'' before reading the startup files, as if the __--posix__ invocation option had been supplied. If it is set while the shell is running, __bash__ enables ''posix mode'', as if the command set -o posix had been executed. __PROMPT_COMMAND__ If set, the value is executed as a command prior to issuing each primary prompt. __PS1__ The value of this parameter is expanded (see __PROMPTING__ below) and used as the primary prompt string. The default value is ``__s-v$__ ''. __PS2__ The value of this parameter is expanded as with __PS1__ and used as the secondary prompt string. The default is ``____ ''. __PS3__ The value of this parameter is used as the prompt for the __select__ command (see __SHELL GRAMMAR__ above). __PS4__ The value of this parameter is expanded as with __PS1__ and the value is printed before each command __bash__ displays during an execution trace. The first character of __PS4__ is replicated multiple times, as necessary, to indicate multiple levels of indirection. The default is ``__+__ ''. __TIMEFORMAT__ The value of this parameter is used as a format string specifying how the timing information for pipelines prefixed with the __time__ reserved word should be displayed. The __%__ character introduces an escape sequence that is expanded to a time value or other information. The escape sequences and their meanings are as follows; the braces denote optional portions. __%%__ A literal __%__. __%[[__''p''__][[l]R__ The elapsed time in seconds. __%[[__''p''__][[l]U__ The number of CPU seconds spent in user mode. __%[[__''p''__][[l]S__ The number of CPU seconds spent in system mode. __%P__ The CPU percentage, computed as (%U + %S) / %R. The optional ''p'' is a digit specifying the ''precision'', the number of fractional digits after a decimal point. A value of 0 causes no decimal point or fraction to be output. At most three places after the decimal point may be specified; values of ''p'' greater than 3 are changed to 3. If ''p'' is not specified, the value 3 is used. The optional __l__ specifies a longer format, including minutes, of the form ''MM''m''SS''.''FF''s. The value of ''p'' determines whether or not the fraction is included. If this variable is not set, __bash__ acts as if it had the value __$'nrealt%3lRnusert%3lUnsys%3lS'__. If the value is null, no timing information is displayed. A trailing newline is added when the format string is displayed. __TMOUT__ 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. __Bash__ terminates after waiting for that number of seconds if input does not arrive. __auto_resume__ 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 ''name'' of a stopped job, in this context, is the command line used to start it. If set to the value ''exact'', the string supplied must match the name of a stopped job exactly; if set to ''substring'', the string supplied needs to match a substring of the name of a stopped job. The ''substring'' value provides functionality analogous to the __%?__ job identifier (see __JOB CONTROL__ below). If set to any other value, the supplied string must be a prefix of a stopped job's name; this provides functionality analogous to the __%__ job identifier. __histchars__ The two or three characters which control history expansion and tokenization (see __HISTORY EXPANSION__ below). The first character is the ''history expansion'' character, the character which signals the start of a history expansion, normally `__!__'. The second character is the ''quick substitution'' character, which is used as shorthand for re-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 comment when found as the first character of a word, normally `__#__'. The history comment character causes history substitution to be skipped for the remaining words on the line. It does not necessarily cause the shell parser to treat the rest of the line as a comment. __Arrays__ __Bash__ provides one-dimensional array variables. Any variable may be used as an array; the __declare__ 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 ''name''[[''subscript'']=''value''. The ''subscript'' is treated as an arithmetic expression that must evaluate to a number greater than or equal to zero. To explicitly declare an array, use __declare -a__ ''name'' (see __SHELL BUILTIN COMMANDS__ below). __declare -a__ ''name''__[[__''subscript''__]__ is also accepted; the ''subscript'' is ignored. Attributes may be specified for an array variable using the __declare__ and __readonly__ builtins. Each attribute applies to all members of an array. Arrays are assigned to using compound assignments of the form ''name''=__(__value''1'' ... value''n''__)__, where each ''value'' is of the form [[''subscript'']=''string''. Only ''string'' 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 __declare__ builtin. Individual array elements may be assigned to using the ''name''[[''subscript'']=''value'' syntax introduced above. Any element of an array may be referenced using ${''name''[[''subscript'']}. The braces are required to avoid conflicts with pathname expansion. If ''subscript'' is __@__ or __*__, the word expands to all members of ''name''. These subscripts differ only when the word appears within double quotes. If the word is double-quoted, ${''name''[[*]} expands to a single word with the value of each array member separated by the first character of the __IFS__ special variable, and ${''name''[[@]} expands each element of ''name'' to a separate word. When there are no array members, ${''name''[[@]} expands to nothing. This is analogous to the expansion of the special parameters __*__ and __@__ (see __Special Parameters__ above). ${#''name''[[''subscript'']} expands to the length of ${''name''[[''subscript'']}. If ''subscript'' is __*__ or __@__, the expansion is the number of elements in the array. Referencing an array variable without a subscript is equivalent to referencing element zero. The __unset__ builtin is used to destroy arrays. __unset__ ''name''[[''subscript''] destroys the array element at index ''subscript''. __unset__ ''name'', where ''name'' is an array, or __unset__ ''name''[[''subscript''], where ''subscript'' is __*__ or __@__, removes the entire array. The __declare__, __local__, and __readonly__ builtins each accept a __-a__ option to specify an array. The __read__ builtin accepts a __-a__ option to assign a list of words read from the standard input to an array. The __set__ and __declare__ builtins display array values in a way that allows them to be reused as assignments. !!EXPANSION Expansion is performed on the command line after it has been split into words. There are seven kinds of expansion performed: ''brace expansion'', ''tilde expansion'', ''parameter and variable expansion'', ''command substitution'', ''arithmetic expansion'', ''word splitting'', and ''pathname expansion''. The order of expansions is: brace expansion, tilde expansion, 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: ''process substitution''. Only brace expansion, word splitting, and pathname expansion can change the number of words of the expansion; other expansions expand a single word to a single word. The only exceptions to this are the expansions of $@__ __${__''name''__[[@]}__ __PARAMETERS__). __Brace Expansion__ ''Brace expansion'' is a mechanism by which arbitrary strings may be generated. This mechanism is similar to ''pathname expansion'', but the filenames generated need not exist. Patterns to be brace expanded take the form of an optional ''preamble'', followed by a series of comma-separated strings between a pair of braces, followed by an optional ''postscript''. The preamble is prefixed to each string contained within the braces, and the postscript is then appended to each resulting string, expanding 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 preserved in the result. It is strictly textual. __Bash__ 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. To avoid conflicts with parameter expansion, the string __${__ is not considered eligible for brace expansion. 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 __sh__. __sh__ does not treat opening or closing braces specially when they appear as part of a word, and preserves them in the output. __Bash__ removes braces from words as a consequence of brace expansion. For example, a word entered to __sh__ as ''file{1,2}'' appears identically in the output. The same word is output as ''file1 file2'' after expansion by __bash__. If strict compatibility with __sh__ is desired, start __bash__ with the __+B__ option or disable brace expansion with the __+B__ option to the __set__ command (see __SHELL BUILTIN COMMANDS__ below). __Tilde Expansion__ 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 ''tilde-prefix''. If none of the characters in the tilde-prefix are quoted, the characters in the tilde-prefix following the tilde are treated as a possible ''login name''. If this login name is the null string, the tilde is replaced with the value of the shell parameter __HOME__. If __HOME__ is unset, the home directory of the user executing the shell is 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 __PWD__ replaces the tilde-prefix. If the tilde-prefix is a `~-', the value of the shell variable __OLDPWD__, 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 __dirs__ 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 __PATH__, __MAILPATH__, and __CDPATH__, and the shell assigns the expanded value. __Parameter Expansion__ 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. ${''parameter''} The value of ''parameter'' is substituted. The braces are required when ''parameter'' is a positional parameter with more than one digit, or when ''parameter'' is followed by a character which is not to be interpreted as part of its name. If the first character of ''parameter'' is an exclamation point, a level of variable indirection is introduced. __Bash__ uses the value of the variable formed from the rest of ''parameter'' as the name of the variable; this variable is then expanded and that value is used in the rest of the substitution, rather than the value of ''parameter'' itself. This is known as ''indirect expansion''. The exception to this is the expansion of ${!''prefix''*} described below. In each of the cases below, ''word'' is subject to tilde expansion, parameter expansion, command substitution, and arithmetic expansion. When not performing substring expansion, __bash__ tests for a parameter that is unset or null; omitting the colon results in a test only for a parameter that is unset. ${''parameter''__:-__''word''} __Use Default Values__. If ''parameter'' is unset or null, the expansion of ''word'' is substituted. Otherwise, the value of ''parameter'' is substituted. ${''parameter''__:=__''word''} __Assign Default Values__. If ''parameter'' is unset or null, the expansion of ''word'' is assigned to ''parameter''. The value of ''parameter'' is then substituted. Positional parameters and special parameters may not be assigned to in this way. ${''parameter''__:?__''word''} __Display Error if Null or Unset__. If ''parameter'' is null or unset, the expansion of ''word'' (or a message to that effect if ''word'' is not present) is written to the standard error and the shell, if it is not interactive, exits. Otherwise, the value of ''parameter'' is substituted. ${''parameter''__:+__''word''} __Use Alternate Value__. If ''parameter'' is null or unset, nothing is substituted, otherwise the expansion of ''word'' is substituted. ${''parameter''__:__''offset''} ${''parameter''__:__''offset''__:__''length''} __Substring Expansion.__ Expands to up to ''length'' characters of ''parameter'' starting at the character specified by ''offset''. If ''length'' is omitted, expands to the substring of ''parameter'' starting at the character specified by ''offset''. ''length'' and ''offset'' are arithmetic expressions (see __ARITHMETIC EVALUATION__ below). ''length'' must evaluate to a number greater than or equal to zero. If ''offset'' evaluates to a number less than zero, the value is used as an offset from the end of the value of ''parameter''. If ''parameter'' is __@__, the result is ''length'' positional parameters beginning at ''offset''. If ''parameter'' is an array name indexed by @ or *, the result is the ''length'' members of the array beginning with ${''parameter''[[''offset'']}. Substring indexing is zero-based unless the positional parameters are used, in which case the indexing starts at 1. ${__!__''prefix''__*__} Expands to the names of variables whose names begin with ''prefix'', separated by the first character of the __IFS__ special variable. ${__#__''parameter''} The length in characters of the value of ''parameter'' is substituted. If ''parameter'' is __*__ or __@__, the value substituted is the number of positional parameters. If ''parameter'' is an array name subscripted by __*__ or __@__, the value substituted is the number of elements in the array. ${''parameter''__#__''word''} ${''parameter''__##__''word''} The ''word'' is expanded to produce a pattern just as in pathname expansion. If the pattern matches the beginning of the value of ''parameter'', then the result of the expansion is the expanded value of ''parameter'' with the shortest matching pattern (the ``__#__'' case) or the longest matching pattern (the ``__##__'' case) deleted. If ''parameter'' is __@__ or __*__, the pattern removal operation is applied to each positional parameter in turn, and the expansion is the resultant list. If ''parameter'' is an array variable subscripted with __@__ or __*__, the pattern removal operation is applied to each member of the array in turn, and the expansion is the resultant list. ${''parameter''__%__''word''} ${''parameter''__%%__''word''} The ''word'' is expanded to produce a pattern just as in pathname expansion. If the pattern matches a trailing portion of the expanded value of ''parameter'', then the result of the expansion is the expanded value of ''parameter'' with the shortest matching pattern (the ``__%__'' case) or the longest matching pattern (the ``__%%__'' case) deleted. If ''parameter'' is __@__ or __*__, the pattern removal operation is applied to each positional parameter in turn, and the expansion is the resultant list. If ''parameter'' is an array variable subscripted with __@__ or __*__, the pattern removal operation is applied to each member of the array in turn, and the expansion is the resultant list. ${''parameter''__/__''pattern''__/__''string''} ${''parameter''__//__''pattern''__/__''string''} The ''pattern'' is expanded to produce a pattern just as in pathname expansion. ''Parameter'' is expanded and the longest match of ''pattern'' against its value is replaced with ''string''. In the first form, only the first match is replaced. The second form causes all matches of ''pattern'' to be replaced with ''string''. If ''pattern'' begins with __#__, it must match at the beginning of the expanded value of ''parameter''. If ''pattern'' begins with __%__, it must match at the end of the expanded value of ''parameter''. If ''string'' is null, matches of ''pattern'' are deleted and the __/__ following ''pattern'' may be omitted. If ''parameter'' is __@__ or __*__, the substitution operation is applied to each positional parameter in turn, and the expansion is the resultant list. If ''parameter'' is an array variable subscripted with __@__ or __*__, the substitution operation is applied to each member of the array in turn, and the expansion is the resultant list. __Command Substitution__ ''Command substitution'' allows the output of a command to replace the command name. There are two forms: __$(__''command''__)__ or __`__''command''__`__ __Bash__ performs the expansion by executing ''command'' and replacing the command substitution with the standard output of the command, with any trailing newlines deleted. Embedded newlines are not deleted, but they may be removed during word splitting. The command substitution __$(cat__ ''file''__)__ can be replaced by the equivalent but faster __$(__ ''file''__)__. 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 $(''command'') form, all characters between the parentheses make up the command; none are treated specially. Command substitutions may be nested. To nest when using the backquoted form, escape the inner backquotes with backslashes. If the substitution appears within double quotes, word splitting and pathname expansion are not performed on the results. __Arithmetic Expansion__ Arithmetic expansion allows the evaluation of an arithmetic expression and the substitution of the result. The format for arithmetic expansion is: __$((__''expression''__))__ The old format __$[[[[__''expression''__]]__ is deprecated and will be removed in upcoming versions of bash. The ''expression'' is treated as if it were within double quotes, but a double quote inside the parentheses is not treated specially. All tokens in the expression undergo parameter expansion, string expansion, command substitution, and quote removal. Arithmetic substitutions may be nested. The evaluation is performed according to the rules listed below under __ARITHMETIC EVALUATION__. If ''expression'' is invalid, __bash__ prints a message indicating failure and no substitution occurs. __Process Substitution__ ''Process substitution'' is supported on systems that support named pipes (''FIFOs'') or the __/dev/fd__ method of naming open files. It takes the form of ____''list''__)__ or ____''list''__)__. The process ''list'' is run with its input or output connected to a ''FIFO'' or some file in __/dev/fd__. The name of this file is passed as an argument to the current command as the result of the expansion. If the ____''list''__)__ form is used, writing to the file will provide input for ''list''. If the ____''list''__)__ form is used, the file passed as an argument should be read to obtain the output of ''list''. When available, process substitution is performed simultaneously with parameter and variable expansion, command substitution, and arithmetic expansion. __Word Splitting__ The shell scans the results of parameter expansion, command substitution, and arithmetic expansion that did not occur within double quotes for ''word splitting''. The shell treats each character of __IFS__ as a delimiter, and splits the results of the other expansions into words on these characters. If __IFS__ is unset, or its value is exactly ____, the default, then any sequence of __IFS__ characters serves to delimit words. If __IFS__ has a value other than the default, then sequences of the whitespace characters __space__ and __tab__ are ignored at the beginning and end of the word, as long as the whitespace character is in the value of __IFS__ (an __IFS__ whitespace character). Any character in __IFS__ that is not __IFS__ whitespace, along with any adjacent __IFS__ whitespace characters, delimits a field. A sequence of __IFS__ whitespace characters is also treated as a delimiter. If the value of __IFS__ is null, no word splitting occurs. Explicit null arguments (____ or __''__) are retained. Unquoted implicit null arguments, resulting from the expansion of parameters that have no values, are removed. If a parameter with no value is expanded within double quotes, a null argument results and is retained. Note that if no expansion occurs, no splitting is performed. __Pathname Expansion__ After word splitting, unless the __-f__ option has been set, __bash__ scans each word for the characters __*__, __?__, and __[[__. If one of these characters appears, then the word is regarded as a ''pattern'', and replaced with an alphabetically sorted list of file names matching the pattern. If no matching file names are found, and the shell option __nullglob__ is disabled, the word is left unchanged. If the __nullglob__ option is set, and no matches are found, the word is removed. If the shell option __nocaseglob__ is enabled, the match is performed without regard to the case of alphabetic characters. When a pattern is used for pathname expansion, the character __``.''__ at the start of a name or immediately following a slash must be matched explicitly, unless the shell option __dotglob__ is set. When matching a pathname, the slash character must always be matched explicitly. In other cases, the __``.''__ character is not treated specially. See the description of __shopt__ below under __SHELL BUILTIN COMMANDS__ for a description of the __nocaseglob__, __nullglob__, and __dotglob__ shell options. The __GLOBIGNORE__ shell variable may be used to restrict the set of file names matching a ''pattern''. If __GLOBIGNORE__ is set, each matching file name that also matches one of the patterns in __GLOBIGNORE__ is removed from the list of matches. The file names __``.''__ and __``..''__ are always ignored, even when __GLOBIGNORE__ is set. However, setting __GLOBIGNORE__ has the effect of enabling the __dotglob__ 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 patterns in __GLOBIGNORE__. The __dotglob__ option is disabled when __GLOBIGNORE__ is unset. __Pattern Matching__ 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 meanings: __*__ 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 hyphen denotes a ''range expression''; any character that sorts between those two characters, inclusive, using the current locale's collating sequence and character set, is matched. If the first character following the __[[__ is a __!__ or a __^__ then any character not enclosed is matched. The sorting order of characters in range expressions is determined by the current locale and the value of the __LC_COLLATE__ shell variable, if set. A __-__ may be matched by including it as the first or last character in the set. A __]__ may be matched by including it as the first character in the set. Within __[[__ and __]__, ''character classes'' can be specified using the syntax __[[:__''class''__:]__, where ''class'' is one of the following classes defined in the POSIX.2 standard: __alnum alpha ascii blank cntrl digit graph lower print punct space upper xdigit__ A character class matches any character belonging to that class. Within __[[__ and __]__, an ''equivalence class'' can be specified using the syntax __[[=__''c''__=]__, which matches all characters with the same collation weight (as defined by the current locale) as the character ''c''. Within __[[__ and __]__, the syntax __[[.__''symbol''__.]__ matches the collating symbol ''symbol''. If the __extglob__ shell option is enabled using the __shopt__ builtin, several extended pattern matching operators are recognized. In the following description, a ''pattern-list'' is a list of one or more patterns separated by a __|__. Composite patterns may be formed using one or more of the following sub-patterns: __?(__''pattern-list''__)__ Matches zero or one occurrence of the given patterns __*(__''pattern-list''__)__ Matches zero or more occurrences of the given patterns __+(__''pattern-list''__)__ Matches one or more occurrences of the given patterns __@(__''pattern-list''__)__ Matches exactly one of the given patterns __!(__''pattern-list''__)__ Matches anything except one of the given patterns __Quote Removal__ After the preceding expansions, all unquoted occurrences of the characters __\__, __'__, and ____ that did not result from one of the above expansions are removed. !!REDIRECTION Before a command is executed, its input and output may be ''redirected'' 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 anywhere within a ''simple command'' or may follow a ''command''. Redirections are processed in the order they appear, from left to right. In the following descriptions, if the file descriptor number is omitted, and the first character of the redirection operator is ____, the redirection refers to the standard input (file descriptor 0). If the first character of the redirection operator is ____, the redirection refers to the standard output (file descriptor 1). The word following the redirection operator in the following descriptions, unless otherwise noted, is subjected to brace expansion, tilde expansion, parameter expansion, command substitution, arithmetic expansion, quote removal, pathname expansion, and word splitting. If it expands to more than one word, __bash__ 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 ''dirlist'', while the command ls 2____1 ____ dirlist directs only the standard output to file ''dirlist'', because the standard error was duplicated as standard output before the standard output was redirected to ''dirlist''. __Bash__ handles several filenames specially when they are used in redirections, as described in the following table: __/dev/fd/__''fd'' If ''fd'' is a valid integer, file descriptor ''fd'' is duplicated. __/dev/stdin__ File descriptor 0 is duplicated. __/dev/stdout__ File descriptor 1 is duplicated. __/dev/stderr__ File descriptor 2 is duplicated. __/dev/tcp/__''host''__/__''port'' If ''host'' is a valid hostname or Internet address, and ''port'' is an integer port number or service name, __bash__ attempts to open a TCP connection to the corresponding socket. __/dev/udp/__''host''__/__''port'' If ''host'' is a valid hostname or Internet address, and ''port'' is an integer port number or service name, __bash__ attempts to open a UDP connection to the corresponding socket. A failure to open or create a file causes the redirection to fail. __Redirecting Input__ Redirection of input causes the file whose name results from the expansion of ''word'' to be opened for reading on file descriptor ''n'', or the standard input (file descriptor 0) if ''n'' is not specified. The general format for redirecting input is: [[''n'']____''word'' __Redirecting Output__ Redirection of output causes the file whose name results from the expansion of ''word'' to be opened for writing on file descriptor ''n'', or the standard output (file descriptor 1) if ''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'']____''word'' If the redirection operator is ____, and the __noclobber__ option to the __set__ builtin has been enabled, the redirection will fail if the file whose name results from the expansion of ''word'' exists and is a regular file. If the redirection operator is ____, or the redirection operator is ____ and the __noclobber__ option to the __set__ builtin command is not enabled, the redirection is attempted even if the file named by ''word'' exists. __Appending Redirected Output__ Redirection of output in this fashion causes the file whose name results from the expansion of ''word'' to be opened for appending on file descriptor ''n'', or the standard output (file descriptor 1) if ''n'' is not specified. If the file does not exist it is created. The general format for appending output is: [[''n'']____''word'' __Redirecting Standard Output and Standard Error__ __Bash__ 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 ''word'' with this construct. There are two formats for redirecting standard output and standard error: ____''word'' and ____''word'' Of the two forms, the first is preferred. This is semantically equivalent to ____''word'' 2____1 __Here Documents__ This type of redirection instructs the shell to read input from the current source until a line containing only ''word'' (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: ____[[__-__]''word here-document delimiter '' No parameter expansion, command substitution, arithmetic expansion, or pathname expansion is performed on ''word''. If any characters in ''word'' are quoted, the ''delimiter'' is the result of quote removal on ''word'', and the lines in the here-document are not expanded. If ''word'' is unquoted, all lines of the here-document are subjected to parameter expansion, command substitution, and arithmetic expansion. In the latter case, the character sequence ____ is ignored, and __\__ must be used to quote the characters __\__, __$__, and __`__. If the redirection operator is ____, then all leading tab characters are stripped from input lines and the line containing ''delimiter''. This allows here-documents within shell scripts to be indented in a natural fashion. __Duplicating File Descriptors__ The redirection operator [[''n'']____''word'' is used to duplicate input file descriptors. If ''word'' expands to one or more digits, the file descriptor denoted by ''n'' is made to be a copy of that file descriptor. If the digits in ''word'' do not specify a file descriptor open for input, a redirection error occurs. If ''word'' evaluates to __-__, file descriptor ''n'' is closed. If ''n'' is not specified, the standard input (file descriptor 0) is used. The operator [[''n'']____''word'' is used similarly to duplicate output file descriptors. If ''n'' is not specified, the standard output (file descriptor 1) is used. If the digits in ''word'' do not specify a file descriptor open for output, a redirection error occurs. As a special case, if ''n'' is omitted, and ''word'' does not expand to one or more digits, the standard output and standard error are redirected as described previously. __Opening File Descriptors for Reading and Writing__ The redirection operator [[''n'']____''word'' causes the file whose name is the expansion of ''word'' to be opened for both reading and writing on file descriptor ''n'', or on file descriptor 0 if ''n'' is not specified. If the file does not exist, it is created. !!ALIASES ''Aliases'' allow a string to be substituted for a word when it is used as the first word of a simple command. The shell maintains a list of aliases that may be set and unset with the __alias__ and __unalias__ builtin commands (see __SHELL BUILTIN COMMANDS__ 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 contain any valid shell input, including the ''metacharacters'' 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 __ls__ to __ls -F__, for instance, and __bash__ does not try to recursively expand the replacement text. If the last character of the alias value is a ''blank'', then the next command word following the alias is also checked for alias expansion. Aliases are created and listed with the __alias__ command, and removed with the __unalias__ command. There is no mechanism for using arguments in the replacement text. If arguments are needed, a shell function should be used (see __FUNCTIONS__ below). Aliases are not expanded when the shell is not interactive, unless the __expand_aliases__ shell option is set using __shopt__ (see the description of __shopt__ under __SHELL BUILTIN COMMANDS__ below). The rules concerning the definition and use of aliases are somewhat confusing. __Bash__ always reads at least one complete line of input before executing any of the commands on that line. Aliases are expanded when a command is read, not when it is executed. Therefore, an alias definition appearing on the same line as another command does not take 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 __alias__ in compound commands. For almost every purpose, aliases are superseded by shell functions. !!FUNCTIONS A shell function, defined as described above under __SHELL GRAMMAR__, stores a series of commands for later execution. When the name of a shell function is used as a simple command name, the list of commands associated with that function name is executed. Functions are executed in the context of the current shell; no new process is created to interpret them (contrast this with the execution of a shell script). When a function is executed, the arguments to the function become the positional parameters during its execution. The special parameter __#__ is updated to reflect the change. Positional parameter 0 is unchanged. The __FUNCNAME__ variable is set to the name of the function while the function is executing. All other aspects of the shell execution environment are identical between a function and its caller with the exception that the __DEBUG__ trap (see the description of the __trap__ builtin under __SHELL BUILTIN COMMANDS__ below) is not inherited. Variables local to the function may be declared with the __local__ builtin command. Ordinarily, variables and their values are shared between the function and its caller. If the builtin command __return__ is executed in a function, the function completes and execution resumes with the next command after the function call. When a function completes, 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 __-f__ option to the __declare__ or __typeset__ builtin commands. The __-F__ option to __declare__ or __typeset__ will list the function names only. Functions may be exported so that subshells automatically have them defined with the __-f__ option to the __export__ builtin. Functions may be recursive. No limit is imposed on the number of recursive calls. !!ARITHMETIC EVALUATION The shell allows arithmetic expressions to be evaluated, under certain circumstances (see the __let__ builtin command and __Arithmetic Expansion__). Evaluation is done in long integers with no check for overflow, though division by 0 is trapped and flagged as an error. The operators and their precedence and associativity are the same as in the C language. The following list of operators is grouped into levels of equal-precedence operators. The levels are listed in order of decreasing precedence. ''id''__++__ ''id''__--__ variable post-increment and post-decrement __++__''id'' __--__''id'' variable pre-increment and pre-decrement __- +__ 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 ''expr''__?__''expr''__:__''expr'' conditional evaluation __= *= /= %= += -= __ assignment ''expr1'' __,__ ''expr2'' comma Shell variables are allowed as operands; parameter expansion is performed before the expression is evaluated. Within an expression, shell variables may also be referenced by name without using the parameter expansion syntax. The value of a variable is evaluated as an arithmetic expression when it is referenced. A shell variable need not have its integer attribute turned on to be used in an expression. Constants with a leading 0 are interpreted as octal numbers. A leading 0x or 0X denotes hexadecimal. Otherwise, numbers take the form [[''base#'']n, where ''base'' is a decimal number between 2 and 64 representing the arithmetic base, and ''n'' is a number in that base. If ''base#'' is omitted, then base 10 is used. The digits greater than 9 are represented by the lowercase letters, the uppercase letters, @, and _, in that order. If ''base'' is less than or equal to 36, lowercase and uppercase letters may be used interchangably 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. !!CONDITIONAL EXPRESSIONS Conditional expressions are used by the __[[[[__ compound command and the __test__ 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 ''file'' argument to one of the primaries is of the form ''/dev/fd/n'', then file descriptor ''n'' is checked. If the ''file'' argument to one of the primaries is one of ''/dev/stdin'', ''/dev/stdout'', or ''/dev/stderr'', file descriptor 0, 1, or 2, respectively, is checked. __-a__ ''file'' True if ''file'' exists. __-b__ ''file'' True if ''file'' exists and is a block special file. __-c__ ''file'' True if ''file'' exists and is a character special file. __-d__ ''file'' True if ''file'' exists and is a directory. __-e__ ''file'' True if ''file'' exists. __-f__ ''file'' True if ''file'' exists and is a regular file. __-g__ ''file'' True if ''file'' exists and is set-group-id. __-h__ ''file'' True if ''file'' exists and is a symbolic link. __-k__ ''file'' True if ''file'' exists and its ``sticky'' bit is set. __-p__ ''file'' True if ''file'' exists and is a named pipe (FIFO). __-r__ ''file'' True if ''file'' exists and is readable. __-s__ ''file'' True if ''file'' exists and has a size greater than zero. __-t__ ''fd'' True if file descriptor ''fd'' is open and refers to a terminal. __-u__ ''file'' True if ''file'' exists and its set-user-id bit is set. __-w__ ''file'' True if ''file'' exists and is writable. __-x__ ''file'' True if ''file'' exists and is executable. __-O__ ''file'' True if ''file'' exists and is owned by the effective user id. __-G__ ''file'' True if ''file'' exists and is owned by the effective group id. __-L__ ''file'' True if ''file'' exists and is a symbolic link. __-S__ ''file'' True if ''file'' exists and is a socket. __-N__ ''file'' True if ''file'' exists and has been modified since it was last read. ''file1'' -__nt__ ''file2'' True if ''file1'' is newer (according to modification date) than ''file2''. ''file1'' -__ot__ ''file2'' True if ''file1'' is older than ''file2''. ''file1'' __-ef__ ''file2'' True if ''file1'' and ''file2'' have the same device and inode numbers. __-o__ ''optname'' True if shell option ''optname'' is enabled. See the list of options under the description of the __-o__ option to the __set__ builtin below. __-z__ ''string'' True if the length of ''string'' is zero. __-n__ ''string'' ''string'' True if the length of ''string'' is non-zero. ''string1'' __==__ ''string2'' True if the strings are equal. __=__ may be used in place of __==__. ''string1'' __!=__ ''string2'' True if the strings are not equal. ''string1'' ____ ''string2'' True if ''string1'' sorts before ''string2'' lexicographically in the current locale. ''string1'' ____ ''string2'' True if ''string1'' sorts after ''string2'' lexicographically in the current locale. ''arg1'' __OP__ ''arg2'' __OP__ is one of __-eq__, __-ne__, __-lt__, __-le__, __-gt__, or __-ge__. These arithmetic binary operators return true if ''arg1'' is equal to, not equal to, less than, less than or equal to, greater than, or greater than or equal to ''arg2'', respectively. ''Arg1'' and ''arg2'' may be positive or negative integers. !!SIMPLE COMMAND EXPANSION When a simple command is executed, the shell performs the following expansions, assignments, and redirections, from left to right. 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 __REDIRECTION__. 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 variable. 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 redirection 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 substitution, the exit status of the command is the exit status of the last command substitution performed. If there were no command substitutions, the command exits with a status of zero. !!COMMAND EXECUTION 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 __FUNCTIONS__. 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, __bash__ searches each element of the __PATH__ for a directory containing an executable file by that name. __Bash__ uses a hash table to remember the full pathnames of executable files (see __hash__ under __SHELL BUILTIN COMMANDS__ below). A full search of the directories in __PATH__ is 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 contains 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 executable format, and the file is not a directory, it is assumed to be a ''shell script'', a file containing shell commands. A subshell is spawned to execute it. This subshell reinitializes itself, so that the effect is as if a new shell had been invoked to handle the script, with the exception that the locations of commands remembered by the parent (see __hash__ below under __SHELL BUILTIN COMMANDS__) are retained by the child. If the program is a file beginning with __#!__, the remainder of the first line specifies an interpreter for the program. The shell executes the specified interpreter on operating systems that do not handle this executable format themselves. The arguments to the interpreter consist of a single optional argument following the interpreter name on the first line of the program, followed by the name of the program, followed by the command arguments, if any. !!COMMAND EXECUTION ENVIRONMENT The shell has an ''execution environment'', which consists of the following: open files inherited by the shell at invocation, as modified by redirections supplied to the __exec__ builtin the current working directory as set by __cd__, __pushd__, or __popd__, or inherited by the shell at invocation the file creation mode mask as set by __umask__ or inherited from the shell's parent current traps set by __trap__ shell parameters that are set by variable assignment or with __set__ or inherited from the shell's parent in the environment shell functions defined during execution or inherited from the shell's parent in the environment options enabled at invocation (either by default or with command-line arguments) or by __set__ options enabled by __shopt__ shell aliases defined with __alias__ various process IDs, including those of background jobs, the value of __$$__, and the value of __$PPID__ When a simple command other than a builtin or shell function is to be executed, it is invoked in a separate execution environment that consists of the following. Unless otherwise noted, the values are inherited from the shell. the shell's open files, plus any modifications and additions specified by redirections to the command the current working directory the file creation mode mask shell variables marked for export, along with variables exported for the command, passed in the environment 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 parent at invocation. Builtin commands that are invoked as part of a pipeline are also executed in a subshell environment. Changes made to the subshell environment cannot affect the shell's execution environment. If a command is followed by a ____ and job control is not active, the default standard input for the command is the empty file ''/dev/null''. Otherwise, the invoked command inherits the file descriptors of the calling shell as modified by redirections. !!ENVIRONMENT When a program is invoked it is given an array of strings called the ''environment''. This is a list of ''name''-''value'' pairs, of the form ''name''=''value''. The shell provides several ways to manipulate the environment. On invocation, the shell scans its own environment and creates a parameter for each name found, automatically marking it for ''export'' to child processes. Executed commands inherit the environment. The __export__ and __declare -x__ commands allow parameters and functions to be added to and 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 __unset__ command, plus any additions via the __export__ and __declare -x__ commands. The environment for any ''simple command'' or function may be augmented temporarily by prefixing it with parameter assignments, as described above in __PARAMETERS__. These assignment statements affect only the environment seen by that command. If the __-k__ option is set (see the __set__ builtin command below), then ''all'' parameter assignments are placed in the environment for a command, not just those that precede the command name. When __bash__ invokes an external command, the variable _____ is set to the full file name of the command and passed to that command in its environment. !!EXIT STATUS For the shell's purposes, a command which exits with a zero exit status has succeeded. An exit status of zero indicates success. A non-zero exit status indicates failure. When a command terminates on a fatal signal ''N'', __bash__ uses the value of 128+''N'' 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 (''true'') if successful, and non-zero (''false'') if an error occurs while they execute. All builtins return an exit status of 2 to indicate incorrect usage. __Bash__ itself returns the exit status of the last command executed, unless a syntax error occurs, in which case it exits with a non-zero value. See also the __exit__ builtin command below. !!SIGNALS When __bash__ is interactive, in the absence of any traps, it ignores __SIGTERM__ (so that __kill 0__ does not kill an interactive shell), and __SIGINT__ is caught and handled (so that the __wait__ builtin is interruptible). In all cases, __bash__ ignores __SIGQUIT__. If job control is in effect, __bash__ ignores __SIGTTIN__, __SIGTTOU__, and __SIGTSTP__. Synchronous jobs started by __bash__ have signal handlers set to the values inherited by the shell from its parent. When job control is not in effect, asynchronous commands ignore __SIGINT__ and __SIGQUIT__ as well. Commands run as a result of command substitution ignore the keyboard-generated job control signals __SIGTTIN__, __SIGTTOU__, and __SIGTSTP__. The shell exits by default upon receipt of a __SIGHUP__. Before exiting, an interactive shell resends the __SIGHUP__ to all jobs, running or stopped. Stopped jobs are sent __SIGCONT__ to ensure that they receive the __SIGHUP__. To prevent the shell from sending the signal to a particular job, it should be removed from the jobs table with the __disown__ builtin (see __SHELL BUILTIN COMMANDS__ below) or marked to not receive __SIGHUP__ using __disown -h__. If the __huponexit__ shell option has been set with __shopt__, __bash__ sends a __SIGHUP__ to all jobs when an interactive login shell exits. When __bash__ 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 __bash__ is waiting for an asynchronous command via the __wait__ builtin, the reception of a signal for which a trap has been set will cause the __wait__ builtin to return immediately with an exit status greater than 128, immediately after which the trap is executed. !!JOB CONTROL ''Job control'' refers to the ability to selectively stop (''suspend'') the execution of processes and continue (''resume'') their execution at a later point. A user typically employs this facility via an interactive interface supplied jointly by the system's terminal driver and __bash__. The shell associates a ''job'' with each pipeline. It keeps a table of currently executing jobs, which may be listed with the __jobs__ command. When __bash__ starts a job asynchronously (in the ''background''), it prints a line that looks like: [[1] 25647 indicating that this job is job number 1 and that the process ID of the last process in the pipeline associated with this job is 25647. All of the processes in a single pipeline are members of the same job. __Bash__ uses the ''job'' abstraction as the basis for job control. To facilitate the implementation of the user interface to job control, the operating system maintains the notion of a ''current terminal process group ID''. Members of this process group (processes whose process group ID is equal to the current terminal process group ID) receive keyboard-generated signals such as __SIGINT__. These processes are said to be in the ''foreground''. ''Background'' processes are those whose process group ID differs from the terminal's; such processes are immune to keyboard-generated signals. Only foreground processes are allowed to read from or write to the terminal. Background processes which attempt to read from (write to) the terminal are sent a __SIGTTIN (SIGTTOU)__ signal by the terminal driver, which, unless caught, suspends the process. If the operating system on which __bash__ is running supports job control, __bash__ contains facilities to use it. Typing the ''suspend'' character (typically __^Z__, Control-Z) while a process is running causes that process to be stopped and returns control to __bash__. Typing the ''delayed suspend'' character (typically __^Y__, Control-Y) causes the process to be stopped when it attempts to read input from the terminal, and control to be returned to __bash__. The user may then manipulate the state of this job, using the __bg__ command to continue it in the background, the __fg__ command to continue it in the foreground, or the __kill__ command to kill it. A __^Z__ takes effect immediately, and has the additional side effect 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 __%n__. A job may also be referred to using a prefix of the name used to start it, or using a substring that appears in its command line. For example, __%ce__ refers to a stopped __ce__ job. If a prefix matches more than one job, __bash__ reports an error. Using __%?ce__, on the other hand, refers to any job containing the string __ce__ in its command line. If the substring matches more than one job, __bash__ reports an error. The symbols __%%__ and __%+__ refer to the shell's notion of the ''current job'', which is the last job stopped while it was in the foreground or started in the background. The ''previous job'' may be referenced using __%-__. In output pertaining to jobs (e.g., the output of the __jobs__ 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 foreground: __%1__ is a synonym for __``fg %1''__, bringing job 1 from the background into the foreground. Similarly, __``%1 __ resumes job 1 in the background, equivalent to __``bg %1''__. The shell learns immediately whenever a job changes state. Normally, __bash__ waits until it is about to print a prompt before reporting changes in a job's status so as to not interrupt any other output. If the __-b__ option to the __set__ builtin command is enabled, __bash__ reports such changes immediately. Any trap on __SIGCHLD__ is executed for each child that exits. If an attempt to exit __bash__ is made while jobs are stopped, the shell prints a warning message. The __jobs__ 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. !!PROMPTING When executing interactively, __bash__ displays the primary prompt __PS1__ when it is ready to read a command, and the secondary prompt __PS2__ when it needs more input to complete a command. __Bash__ allows these prompt strings to be customized by inserting a number of backslash-escaped special characters that are decoded as follows: __a__ an ASCII bell character (07) __d__ the date in __e__ an ASCII escape character (033) __h__ the hostname up to the first `.' __H__ the hostname __j__ the number of jobs currently managed by the shell __l__ the basename of the shell's terminal device name __n__ newline __r__ carriage return __s__ the name of the shell, the basename of __$0__ (the portion following the final slash) __t__ the current time in 24-hour HH:MM:SS format __T__ the current time in 12-hour HH:MM:SS format __@__ the current time in 12-hour am/pm format __A__ the current time in 24-hour HH:MM format __u__ the username of the current user __v__ the version of __bash__ (e.g., 2.00) __V__ the release of __bash__, version + patchelvel (e.g., 2.00.0) __w__ the current working directory __W__ the basename of the current working directory __!__ the history number of this command __#__ the command number of this command __$__ if the effective UID is 0, a __#__, otherwise a __$__ __\__''nnn'' the character corresponding to the octal number ''nnn'' __\__ a backslash __[[__ begin a sequence of non-printing characters, which could be used to embed a terminal control sequence into the prompt __]__ end a sequence of non-printing characters The command number and the history number are usually different: the history number of a command is its position in the history list, which may include commands restored from the history file (see __HISTORY__ below), while the command number is the position in the sequence of commands executed during the current shell session. After the string is decoded, it is expanded via parameter expansion, command substitution, arithmetic expansion, and quote removal, subject to the value of the __promptvars__ shell option (see the description of the __shopt__ command under __SHELL BUILTIN COMMANDS__ below). !!READLINE This is the library that handles reading input when using an interactive shell, unless the __--noediting__ 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 __+o emacs__ or __+o vi__ options to the __set__ builtin (see __SHELL BUILTIN COMMANDS__ below). __Readline Notation__ In this section, the emacs-style notation is used to denote keystrokes. Control keys are denoted by C-''key'', e.g., C-n means Control-N. Similarly, ''meta'' keys are denoted by M-''key'', so M-x means Meta-X. (On keyboards without a ''meta'' key, M-''x'' means ESC ''x'', i.e., press the Escape key then the ''x'' key. This makes ESC the ''meta prefix''. The combination 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 ''arguments'', 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., __kill-line__) causes that command to act in a backward direction. Commands whose behavior with arguments deviates from this are noted below. When a command is described as ''killing'' text, the text deleted is saved for possible future retrieval (''yanking''). The killed text is saved in a ''kill ring''. Consecutive kills 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. __Readline Initialization__ Readline is customized by putting commands in an initialization file (the ''inputrc'' file). The name of this file is taken from the value of the __INPUTRC__ variable. If that variable is unset, the default is ''~/.inputrc''. When a program which uses the readline library starts up, the initialization file is read, and the key bindings and variables are set. There are only a few basic constructs allowed in the readline initialization file. Blank lines are ignored. Lines beginning with a __#__ are comments. Lines beginning with a __$__ indicate conditional constructs. Other lines denote key bindings and variable settings. The default key-bindings may be changed with an ''inputrc'' 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 ''inputrc'' would make M-C-u execute the readline command ''universal-argument''. The following symbolic character names are recognized: ''RUBOUT'', ''DEL'', ''ESC'', ''LFD'', ''NEWLINE'', ''RET'', ''RETURN'', ''SPC'', ''SPACE'', and ''TAB''. In addition to command names, readline allows keys to be bound to a string that is inserted when the key is pressed (a ''macro''). __Readline Key Bindings__ The syntax for controlling key bindings in the ''inputrc'' file is simple. All that is required is the name of the command or the text of a macro and a key sequence to which it should be bound. The name may be specified in one of two ways: as a symbolic key name, possibly with ''Meta-'' or ''Control-'' prefixes, or as a key sequence. When using the form __keyname__:''function-name'' or ''macro'', ''keyname'' is the name of a key spelled out in English. For example: Control-u: universal-argument Meta-Rubout: backward-kill-word Control-o: In the above example, ''C-u'' is bound to the function __universal-argument__, ''M-DEL'' is bound to the function __backward-kill-word__, and ''C-o'' is bound to run the macro expressed on the right hand side (that is, to insert the text into the line). In the second form, ____:''function-name'' or ''macro'', __keyseq__ differs from __keyname__ 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, but the symbolic character names are not recognized. In this example, ''C-u'' is again bound to the function __universal-argument__. ''C-x C-r'' is bound to the function __re-read-init-file__, and ''ESC [[ 1 1 ~'' is bound to insert the text Function Key 1. The full set of GNU Emacs style escape sequences is __C-__ control prefix __M-__ meta prefix __e__ an escape character __\__ backslash ____ literal __'__ literal ' In addition to the GNU Emacs style escape sequences, a second set of backslash escapes is available: __a__ alert (bell) __b__ backspace __d__ delete __f__ form feed __n__ newline __r__ carriage return __t__ horizontal tab __v__ vertical tab __\__''nnn'' the eight-bit character whose value is the octal value ''nnn'' (one to three digits) __x__''HH'' the eight-bit character whose value is the hexadecimal value ''HH'' (one or two hex 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. Backslash will quote any other character in the macro text, including __Bash__ allows the current readline key bindings to be displayed or modified with the __bind__ builtin command. The editing mode may be switched during interactive use by using the __-o__ option to the __set__ builtin command (see __SHELL BUILTIN COMMANDS__ below). __Readline Variables__ Readline has variables that can be used to further customize its behavior. A variable may be set in the ''inputrc'' file with a statement of the form __set__ ''variable-name value'' Except where noted, readline variables can take the values __On__ or __Off__. The variables and their default values are: __bell-style (audible)__ Controls what happens when readline wants to ring the terminal bell. If set to __none__, readline never rings the bell. If set to __visible__, readline uses a visible bell if one is available. If set to __audible__, readline attempts to ring the terminal's bell. __comment-begin (``#'')__ The string that is inserted when the readline __insert-comment__ command is executed. This command is bound to __M-#__ in emacs mode and to __#__ in vi command mode. __completion-ignore-case (Off)__ If set to __On__, readline performs filename matching and completion in a case-insensitive fashion. __completion-query-items (100)__ This determines when the user is queried about viewing the number of possible completions generated by the __possible-completions__ command. It may be set to any integer value greater than or equal to zero. If the number of possible completions is greater than or equal to the value of this variable, the user is asked whether or not he wishes to view them; otherwise they are simply listed on the terminal. __convert-meta (On)__ If set to __On__, readline will convert characters with the eighth bit set to an ASCII key sequence by stripping the eighth bit and prefixing an escape character (in effect, using escape as the ''meta prefix''). __disable-completion (Off)__ If set to __On__, readline will inhibit word completion. Completion characters will be inserted into the line as if they had been mapped to __self-insert__. __editing-mode (emacs)__ Controls whether readline begins with a set of key bindings similar to ''emacs'' or ''vi''. __editing-mode__ can be set to either __emacs__ or __vi__. __enable-keypad (Off)__ When set to __On__, readline will try to enable the application keypad when it is called. Some systems need this to enable the arrow keys. __expand-tilde (Off)__ If set to __on__, tilde expansion is performed when readline attempts word completion. __history-preserve-point__ If set to __on__, the history code attempts to place point at the same location on each history line retrived with __previous-history__ or __next-history__. __horizontal-scroll-mode (Off)__ When set to __On__, makes readline use a single line for display, scrolling the input horizontally on a single screen line when it becomes longer than the screen width rather than wrapping to a new line. __input-meta (Off)__ If set to __On__, readline will enable eight-bit input (that is, it will not strip the high bit from the characters it reads), regardless of what the terminal claims it can support. The name __meta-flag__ is a synonym for this variable. __isearch-terminators (``C-[[C-J'')__ The string of characters that should terminate an incremental search without subsequently executing the character as a command. If this variable has not been given a value, the characters ''ESC'' and ''C-J'' will terminate an incremental search. __keymap (emacs)__ Set the current readline keymap. The set of valid keymap names is ''emacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-command'', and ''vi-insert''. ''vi'' is equivalent to ''vi-command''; ''emacs'' is equivalent to ''emacs-standard''. The default value is ''emacs''; the value of __editing-mode__ also affects the default keymap. __mark-directories (On)__ If set to __On__, completed directory names have a slash appended. __mark-modified-lines (Off)__ If set to __On__, history lines that have been modified are displayed with a preceding asterisk (__*__). __match-hidden-files (On)__ This variable, when set to __On__, causes readline to match files whose names begin with a `.' (hidden files) when performing filename completion, unless the leading `.' is supplied by the user in the filename to be completed. __output-meta (Off)__ If set to __On__, readline will display characters with the eighth bit set directly rather than as a meta-prefixed escape sequence. __print-completions-horizontally (Off)__ If set to __On__, readline will display completions with matches sorted horizontally in alphabetical order, rather than down the screen. __show-all-if-ambiguous (Off)__ This alters the default behavior of the completion functions. If set to __on__, words which have more than one possible completion cause the matches to be listed immediately instead of ringing the bell. __visible-stats (Off)__ If set to __On__, a character denoting a file's type as reported by stat(2) is appended to the filename when listing possible completions. __Readline Conditional Constructs__ Readline implements a facility similar in spirit to the conditional compilation features of the C preprocessor which allows key bindings and variable settings to be performed as the result of tests. There are four parser directives used. __$if__ The __$if__ construct allows bindings to be made based on the editing mode, the terminal being used, or the application using readline. The text of the test extends to the end of the line; no characters are required to isolate it. __mode__ The __mode=__ form of the __$if__ directive is used to test whether readline is in emacs or vi mode. This may be used in conjunction with the __set keymap__ command, for instance, to set bindings in the ''emacs-standard'' and ''emacs-ctlx'' keymaps only if readline is starting out in emacs mode. __term__ The __term=__ form may be used to include terminal-specific key bindings, perhaps to bind the key sequences output by the terminal's function keys. The word on the right side of the __=__ is tested against the both full name of the terminal and the portion of the terminal name before the first __-__. This allows ''sun'' to match both ''sun'' and ''sun-cmd'', for instance. __application__ The __application__ construct is used to include application-specific settings. Each program using the readline library sets the ''application name'', and an initialization file can test for a particular value. This could be used to bind key sequences to functions useful for a specific program. For instance, the following command adds a key sequence that quotes the current or previous word in Bash: __$if__ Bash # Quote the current or previous word __$endif __ __$endif__ This command, as seen in the previous example, terminates an __$if__ command. __$else__ Commands in this branch of the __$if__ directive are executed if the test fails. __$include__ This directive takes a single filename as an argument and reads commands and bindings from that file. For example, the following directive would read ''/etc/inputrc'': __$include__ '' /etc/inputrc '' __Searching__ Readline provides commands for searching through the command history (see __HISTORY__ below) for lines containing a specified string. There are two search modes: ''incremental'' and ''non-incremental''. 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 characters present in the value of the __isearch-terminators__ variable are used to terminate an incremental search. If that variable has not been assigned a value the Escape and Control-J characters will terminate an incremental search. Control-G will abort an incremental search and restore the original line. When the search is terminated, the history entry containing the search string becomes the current line. To find other matching entries in the history list, type Control-S or Control-R as appropriate. This will search backward or forward in the history for the next entry matching the search string typed so far. Any other key sequence bound to a readline command will terminate the search and execute that command. For instance, a ''newline'' will terminate the search and accept the line, thereby executing the command from the history list. Readline remembers the last incremental search string. If two Control-Rs are typed without any intervening characters defining a new search string, any remembered search string is used. 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. __Readline Command Names__ The following is a list of the names of the commands and the default key sequences to which they are bound. Command names without an accompanying key sequence are unbound by default. In the following descriptions, ''point'' refers to the current cursor position, and ''mark'' refers to a cursor position saved by the __set-mark__ command. The text between the point and mark is referred to as the ''region''. __Commands for Moving__ __beginning-of-line (C-a)__ Move to the start of the current line. __end-of-line (C-e)__ Move to the end of the line. __forward-char (C-f)__ Move forward a character. __backward-char (C-b)__ Move back a character. __forward-word (M-f)__ Move forward to the end of the next word. Words are composed of alphanumeric characters (letters and digits). __backward-word (M-b)__ Move back to the start of the current or previous word. Words are composed of alphanumeric characters (letters and digits). __clear-screen (C-l)__ Clear the screen leaving the current line at the top of the screen. With an argument, refresh the current line without clearing the screen. __redraw-current-line__ Refresh the current line. __Commands for Manipulating the History__ __accept-line (Newline, Return)__ Accept the line regardless of where the cursor is. If this line is non-empty, add it to the history list according to the state of the __HISTCONTROL__ variable. If the line is a modified history line, then restore the history line to its original state. __previous-history (C-p)__ Fetch the previous command from the history list, moving back in the list. __next-history (C-n)__ Fetch the next command from the history list, moving forward in the list. __beginning-of-history (M-__ Move to the first line in the history. __end-of-history (M-__ Move to the end of the input history, i.e., the line currently being entered. __reverse-search-history (C-r)__ Search backward starting at the current line and moving `up' through the history as necessary. This is an incremental search. __forward-search-history (C-s)__ Search forward starting at the current line and moving `down' through the history as necessary. This is an incremental search. __non-incremental-reverse-search-history (M-p)__ Search backward through the history starting at the current line using a non-incremental search for a string supplied by the user. __non-incremental-forward-search-history (M-n)__ Search forward through the history using a non-incremental search for a string supplied by the user. __history-search-forward__ Search forward through the history for the string of characters between the start of the current line and the point. This is a non-incremental search. __history-search-backward__ 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. __yank-nth-arg (M-C-y)__ Insert the first argument to the previous command (usually the second word on the previous line) at point. With an argument ''n'', insert the ''n''th word from the previous command (the words in the previous command begin with word 0). A negative argument inserts the ''n''th word from the end of the previous command. __yank-last-arg (M-., M-_)__ Insert the last argument to the previous command (the last word of the previous history entry). With an argument, behave exactly like __yank-nth-arg__. Successive calls to __yank-last-arg__ move back through the history list, inserting the last argument of each line in turn. __shell-expand-line (M-C-e)__ Expand the line as the shell does. This performs alias and history expansion as well as all of the shell word expansions. See __HISTORY EXPANSION__ below for a description of history expansion. __history-expand-line (M-^)__ Perform history expansion on the current line. See __HISTORY EXPANSION__ below for a description of history expansion. __magic-space__ Perform history expansion on the current line and insert a space. See __HISTORY EXPANSION__ below for a description of history expansion. __alias-expand-line__ Perform alias expansion on the current line. See __ALIASES__ above for a description of alias expansion. __history-and-alias-expand-line__ Perform history and alias expansion on the current line. __insert-last-argument (M-., M-_)__ A synonym for __yank-last-arg__. __operate-and-get-next (C-o)__ 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. __Commands for Changing Text__ __delete-char (C-d)__ Delete the character at point. If point is at the beginning of the line, there are no characters in the line, and the last character typed was not bound to __delete-char__, then return __EOF__. __backward-delete-char (Rubout)__ Delete the character behind the cursor. When given a numeric argument, save the deleted text on the kill ring. __forward-backward-delete-char__ Delete the character under the cursor, unless the cursor is at the end of the line, in which case the character behind the cursor is deleted. __quoted-insert (C-q, C-v)__ Add the next character typed to the line verbatim. This is how to insert characters like __C-q__, for example. __tab-insert (C-v TAB)__ Insert a tab character. __self-insert (a, b, A, 1, !, ...)__ Insert the character typed. __transpose-chars (C-t)__ Drag the character before point forward over the character at point, moving point forward as well. If point is at the end of the line, then this transposes the two characters before point. Negative arguments have no effect. __transpose-words (M-t)__ Drag the word before point past the word after point, moving point over that word as well. If point is at the end of the line, this transposes the last two words on the line. __upcase-word (M-u)__ Uppercase the current (or following) word. With a negative argument, uppercase the previous word, but do not move point. __downcase-word (M-l)__ Lowercase the current (or following) word. With a negative argument, lowercase the previous word, but do not move point. __capitalize-word (M-c)__ Capitalize the current (or following) word. With a negative argument, capitalize the previous word, but do not move point. __Killing and Yanking__ __kill-line (C-k)__ Kill the text from point to the end of the line. __backward-kill-line (C-x Rubout)__ Kill backward to the beginning of the line. __unix-line-discard (C-u)__ Kill backward from point to the beginning of the line. The killed text is saved on the kill-ring. __kill-whole-line__ Kill all characters on the current line, no matter where point is. __kill-word (M-d)__ Kill from point to the end of the current word, or if between words, to the end of the next word. Word boundaries are the same as those used by __forward-word__. __backward-kill-word (M-Rubout)__ Kill the word behind point. Word boundaries are the same as those used by __backward-word__. __unix-word-rubout (C-w)__ Kill the word behind point, using white space as a word boundary. The killed text is saved on the kill-ring. __delete-horizontal-space (M-)__ Delete all spaces and tabs around point. __kill-region__ Kill the text in the current region. __copy-region-as-kill__ Copy the text in the region to the kill buffer. __copy-backward-word__ Copy the word before point to the kill buffer. The word boundaries are the same as __backward-word__. __copy-forward-word__ Copy the word following point to the kill buffer. The word boundaries are the same as __forward-word__. __yank (C-y)__ Yank the top of the kill ring into the buffer at point. __yank-pop (M-y)__ Rotate the kill ring, and yank the new top. Only works following __yank__ or __yank-pop__. __Numeric Arguments__ __digit-argument (M-0, M-1, ..., M--)__ Add this digit to the argument already accumulating, or start a new argument. M-- starts a negative argument. __universal-argument__ 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 __universal-argument__ again ends the numeric argument, but is otherwise ignored. As a special case, if this command is immediately followed 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 initially one, so executing this function the first time makes the argument count four, a second time makes the argument count sixteen, and so on. __Completing__ __complete (TAB)__ Attempt to perform completion on the text before point. __Bash__ attempts completion treating the text as a variable (if the text begins with __$__), username (if the text 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. __possible-completions (M-?)__ List the possible completions of the text before point. __insert-completions (M-*)__ Insert all completions of the text before point that would have been generated by __possible-completions__. __menu-complete__ Similar to __complete__, but replaces the word to be completed with a single match from the list of possible completions. Repeated execution of __menu-complete__ steps through the list of possible completions, inserting each match in turn. At the end of the list of completions, the bell is rung (subject to the setting of __bell-style__) and the original text is restored. An argument of ''n'' moves ''n'' positions forward in the list of matches; a negative argument may be used to move backward through the list. This command is intended to be bound to __TAB__, but is unbound by default. __delete-char-or-list__ Deletes the character under the cursor if not at the beginning or end of the line (like __delete-char__). If at the end of the line, behaves identically to __possible-completions__. This command is unbound by default. __complete-filename (M-/)__ Attempt filename completion on the text before point. __possible-filename-completions (C-x /)__ List the possible completions of the text before point, treating it as a filename. __complete-username (M-~)__ Attempt completion on the text before point, treating it as a username. __possible-username-completions (C-x ~)__ List the possible completions of the text before point, treating it as a username. __complete-variable (M-$)__ Attempt completion on the text before point, treating it as a shell variable. __possible-variable-completions (C-x $)__ List the possible completions of the text before point, treating it as a shell variable. __complete-hostname (M-@)__ Attempt completion on the text before point, treating it as a hostname. __possible-hostname-completions (C-x @)__ List the possible completions of the text before point, treating it as a hostname. __complete-command (M-!)__ Attempt completion on the text before point, treating it as a command name. Command completion attempts to match the text against aliases, reserved words, shell functions, shell builtins, and finally executable filenames, in that order. __possible-command-completions (C-x !)__ List the possible completions of the text before point, treating it as a command name. __dynamic-complete-history (M-TAB)__ Attempt completion on the text before point, comparing the text against lines from the history list for possible completion matches. __complete-into-braces (M-{)__ Perform filename completion and insert the list of possible completions enclosed within braces so the list is available to the shell (see __Brace Expansion__ above). __Keyboard Macros__ __start-kbd-macro (C-x ()__ Begin saving the characters typed into the current keyboard macro. __end-kbd-macro (C-x ))__ Stop saving the characters typed into the current keyboard macro and store the definition. __call-last-kbd-macro (C-x e)__ Re-execute the last keyboard macro defined, by making the characters in the macro appear as if typed at the keyboard. __Miscellaneous__ __re-read-init-file (C-x C-r)__ Read in the contents of the ''inputrc'' file, and incorporate any bindings or variable assignments found there. __abort (C-g)__ Abort the current editing command and ring the terminal's bell (subject to the setting of __bell-style__). __do-uppercase-version (M-a, M-b, M-__''x''__, ...)__ If the metafied character ''x'' is lowercase, run the command that is bound to the corresponding uppercase character. __prefix-meta (ESC)__ Metafy the next character typed. __ESC f__ is equivalent to __Meta-f__. __undo (C-_, C-x C-u)__ Incremental undo, separately remembered for each line. __revert-line (M-r)__ Undo all changes made to this line. This is like executing the __undo__ command enough times to return the line to its initial state. __tilde-expand (M-__ Perform tilde expansion on the current word. __set-mark (C-@, M-__ Set the mark to the point. If a numeric argument is supplied, the mark is set to that position. __exchange-point-and-mark (C-x C-x)__ 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. __character-search (C-])__ A character is read and point is moved to the next occurrence of that character. A negative count searches for previous occurrences. __character-search-backward (M-C-])__ A character is read and point is moved to the previous occurrence of that character. A negative count searches for subsequent occurrences. __insert-comment (M-#)__ The value of the readline __comment-begin__ variable is inserted at the beginning of the current line, and the line is accepted as if a newline had been typed. The default value of __comment-begin__ causes this command to make the current line a shell comment. __glob-expand-word (C-x *)__ The word before point is treated as a pattern for pathname expansion, and the list of matching file names is inserted, replacing the word. __glob-list-expansions (C-x g)__ The list of expansions that would have been generated by __glob-expand-word__ is displayed, and the line is redrawn. __dump-functions__ Print all of the functions and their key bindings to the readline output stream. If a numeric argument is supplied, the output is formatted in such a way that it can be made part of an ''inputrc'' file. __dump-variables__ Print all of the settable readline variables and their values to the readline output stream. If a numeric argument is supplied, the output is formatted in such a way that it can be made part of an ''inputrc'' file. __dump-macros__ 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 ''inputrc'' file. __display-shell-version (C-x C-v)__ Display version information about the current instance of __bash__. __Programmable Completion__ When word completion is attempted for an argument to a command for which a completion specification (a ''compspec'') has been defined using the __complete__ builtin (see __SHELL BUILTIN COMMANDS__ below), the programmable completion facilities are invoked. First, the command name is identified. If a compspec has been defined for that command, the compspec is used to generate the list of possible completions for the word. If the command word is a full pathname, a compspec for the full pathname is searched for first. If no compspec is found for the full pathname, an attempt is made to find a compspec for the portion following the final slash. Once a compspec has been found, it is used to generate the list of matching words. If a compspec is not found, the default __bash__ completion as described above under __Completing__ is performed. First, the actions specified by the compspec are used. Only matches which are prefixed by the word being completed are returned. When the __-f__ or __-d__ option is used for filename or directory name completion, the shell variable __FIGNORE__ is used to filter the matches. Any completions specified by a filename expansion pattern to the __-G__ option are generated next. The words generated by the pattern need not match the word being completed. The __GLOBIGNORE__ shell variable is not used to filter the matches, but the __FIGNORE__ variable is used. Next, the string specified as the argument to the __-W__ option is considered. The string is first split using the characters in the __IFS__ special variable as delimiters. Shell quoting is honored. Each word is then expanded using brace expansion, tilde expansion, parameter and variable expansion, command substitution, arithmetic expansion, and pathname expansion, as described above under __EXPANSION__. The results are split using the rules described above under __Word Splitting__. The results of the expansion are prefix-matched against the word being completed, and the matching words become the possible completions. After these matches have been generated, any shell function or command specified with the __-F__ and __-C__ options is invoked. When the command or function is invoked, the __COMP_LINE__ and __COMP_POINT__ variables are assigned values as described above under __Shell Variables__. If a shell function is being invoked, the __COMP_WORDS__ and __COMP_CWORD__ variables are also set. When the function or command is invoked, the first argument is the name of the command whose arguments are being completed, the second argument is the word being completed, and the third argument is the word preceding the word being completed on the current command line. No filtering of the generated completions against the word being completed is performed; the function or command has complete freedom in generating the matches. Any function specified with __-F__ is invoked first. The function may use any of the shell facilities, including the __compgen__ builtin described below, to generate the matches. It must put the possible completions in the __COMPREPLY__ array variable. Next, any command specified with the __-C__ option is invoked in an environment equivalent to command substitution. It should print a list of completions, one per line, to the standard output. Backslash may be used to escape a newline, if necessary. After all of the possible completions are generated, any filter specified with the __-X__ option is applied to the list. The filter is a pattern as used for pathname expansion; a ____ in the pattern is replaced with the text of the word being completed. A literal ____ may be escaped with a backslash; the backslash is removed before attempting a match. Any completion that matches the pattern will be removed from the list. A leading __!__ negates the pattern; in this case any completion not matching the pattern will be removed. Finally, any prefix and suffix specified with the __-P__ and __-S__ options are added to each member of the completion list, and the result is returned to the readline completion code as the list of possible completions. If the previously-applied actions do not generate any matches, and the __-o dirnames__ option was supplied to __complete__ when the compspec was defined, directory name completion is attempted. By default, if a compspec is found, whatever it generates is returned to the completion code as the full set of possible completions. The default __bash__ completions are not attempted, and the readline default of filename completion is disabled. If the __-o default__ option was supplied to __complete__ when the compspec was defined, readline's default completion will be performed if the compspec generates no matches. !!HISTORY When the __-o history__ option to the __set__ builtin is enabled, the shell provides access to the ''command history'', the list of commands previously typed. The value of the __HISTSIZE__ variable is used as the number of commands to save in a history list. The text of the last __HISTSIZE__ commands (default 500) is saved. The shell stores each command in the history list prior to parameter and variable expansion (see __EXPANSION__ above) but after history expansion is performed, subject to the values of the shell variables __HISTIGNORE__ and __HISTCONTROL__. On startup, the history is initialized from the file named by the variable __HISTFILE__ (default ''~/.bash_history''). The file named by the value of __HISTFILE__ is truncated, if necessary, to contain no more than the number of lines specified by the value of __HISTFILESIZE__. When an interactive shell exits, the last __$HISTSIZE__ lines are copied from the history list to __$HISTFILE__. If the __histappend__ shell option is enabled (see the description of __shopt__ under __SHELL BUILTIN COMMANDS__ below), the lines are appended to the history file, otherwise the history file is overwritten. If __HISTFILE__ is unset, or if the history file is unwritable, the history is not saved. After saving the history, the history file is truncated to contain no more than __HISTFILESIZE__ lines. If __HISTFILESIZE__ is not set, no truncation is performed. The builtin command __fc__ (see __SHELL BUILTIN COMMANDS__ below) may be used to list or edit and re-execute a portion of the history list. The __history__ builtin may be used to display or modify the history list and manipulate the history file. When using command-line editing, search commands are available in each editing mode that provide access to the history list. The shell allows control over which commands are saved on the history list. The __HISTCONTROL__ and __HISTIGNORE__ variables may be set to cause the shell to save only a subset of the commands entered. The __cmdhist__ shell option, if enabled, causes the shell to attempt to save each line of a multi-line command in the same history entry, adding semicolons where necessary to preserve syntactic correctness. The __lithist__ shell option causes the shell to save the command with embedded newlines instead of semicolons. See the description of the __shopt__ builtin below under __SHELL BUILTIN COMMANDS__ for information on setting and unsetting shell options. !!HISTORY EXPANSION The shell supports a history expansion feature that is similar to the history expansion in __csh.__ This section describes what syntax features are available. This feature is enabled by default for interactive shells, and can be disabled using the __+H__ option to the __set__ builtin command (see __SHELL BUILTIN COMMANDS__ below). Non-interactive shells do not 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 current input line, or fix errors in previous commands quickly. History expansion is performed immediately after a complete line is read, before the shell breaks it into words. It takes place in two parts. The first is to determine which line from the history list to use during substitution. The second is to select portions of that line for inclusion into the current one. The line selected from the history is the ''event'', and the portions of that line that are acted upon are ''words''. Various ''modifiers'' are available to manipulate the selected words. The line is broken into words in the same fashion as when reading input, so that several ''metacharacter''-separated words surrounded by quotes are considered one word. History expansions are introduced by the appearance of the history expansion character, which is __!__ by default. Only backslash (__\__) and single quotes can quote the history expansion character. Several shell options settable with the __shopt__ builtin may be used to tailor the behavior of history expansion. If the __histverify__ shell option is enabled (see the description of the __shopt__ builtin), and __readline__ is being used, history substitutions are not immediately passed to the shell parser. Instead, the expanded line is reloaded into the __readline__ editing buffer for further modification. If __readline__ is being used, and the __histreedit__ shell option is enabled, a failed history substitution will be reloaded into the __readline__ editing buffer for correction. The __-p__ option to the __history__ builtin command may be used to see what a history expansion will do before using it. The __-s__ option to the __history__ builtin may be used to add commands to the end of the history list without actually executing them, so that they are available for subsequent recall. The shell allows control of the various characters used by the history expansion mechanism (see the description of __histchars__ above under __Shell Variables__). __Event Designators__ An event designator is a reference to a command line entry in the history list. __!__ Start a history substitution, except when followed by a __blank__, 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'. __!__''string'' Refer to the most recent command starting with ''string''. __!?__''string''__[[?]__ Refer to the most recent command containing ''string''. The trailing __?__ may be omitted if ''string'' is followed immediately by a newline. __^__ ''string1'' __^__ ''string2'' __^__ Quick substitution. Repeat the last command, replacing ''string1'' with ''string2''. Equivalent to ``!!:s/''string1''/''string2''/'' (see __Modifiers__ below). __!#__ The entire command line typed so far. __Word Designators__ 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. __0 (zero)__ The zeroth word. For the shell, this is the command word. ''n'' The ''n''th word. __^__ The first argument. That is, word 1. __$__ The last argument. __%__ The word matched by the most recent `?''string''?' search. ''x''__-__''y'' A range of words; `-''y''' abbreviates `0-''y'''. __*__ All of the words but the zeroth. This is a synonym for `''1-$'''. It is not an error to use __*__ if there is just one word in the event; the empty string is returned in that case. __x*__ Abbreviates ''x-$''. __x-__ Abbreviates ''x-$'' like __x*__, but omits the last word. If a word designator is supplied without an event specification, the previous command is used as the event. __Modifiers__ After the optional word designator, there may appear a sequence of one or more of the following modifiers, each preceded by a `:'. __h__ Remove a trailing file name component, leaving only the head. __t__ Remove all leading file name components, leaving the tail. __r__ Remove a trailing suffix of the form ''.xxx'', leaving the basename. __e__ Remove all but the trailing suffix. __p__ Print the new command but do not execute it. __q__ Quote the substituted words, escaping further substitutions. __x__ Quote the substituted words as with __q__, but break into words at __blanks__ and newlines. __s/__''old''__/__''new''__/__ Substitute ''new'' for the first occurrence of ''old'' in the event line. Any delimiter can be used in place of /. The final delimiter is optional if it is the last character of the event line. The delimiter may be quoted in ''old'' and ''new'' with a single backslash. If ''new'', it is replaced by ''old''. A single backslash will quote the ''old'' is null, it is set to the last ''old'' substituted, or, if no previous history substitutions took place, the last ''string'' in a __!?__''string''__[[?]__ search. ____ Repeat the previous substitution. __g__ Cause changes to be applied over the entire event line. This is used in conjunction with `__:s__' (e.g., `__:gs/__''old''__/__''new''__/__') or `__:__'. If used with `__:s__', any delimiter can be used in place of /, and the final delimiter is optional if it is the last character of the event line. !!SHELL BUILTIN COMMANDS Unless otherwise noted, each builtin command documented in this section as accepting options preceded by __-__ accepts __--__ to signify the end of the options. __:__ [[''arguments''] No effect; the command does nothing beyond expanding ''arguments'' and performing any specified redirections. A zero exit code is returned. __.__ ''filename'' [[''arguments''] __source__ ''filename'' [[''arguments''] Read and execute commands from ''filename'' in the current shell environment and return the exit status of the last command executed from ''filename''. If ''filename'' does not contain a slash, file names in __PATH__ are used to find the directory containing ''filename''. The file searched for in __PATH__ need not be executable. When __bash__ is not in ''posix mode'', the current directory is searched if no file is found in __PATH__. If the __sourcepath__ option to the __shopt__ builtin command is turned off, the __PATH__ is not searched. If any ''arguments'' are supplied, they become the positional parameters when ''filename'' is executed. Otherwise the positional 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 ''filename'' is not found or cannot be read. __alias__ [[__-p__] [[''name''[[=''value''] ...] __Alias__ with no arguments or with the __-p__ option prints the list of aliases in the form __alias__ ''name''=''value'' on standard output. When arguments are supplied, an alias is defined for each ''name'' whose ''value'' is given. A trailing space in ''value'' causes the next word to be checked for alias substitution when the alias is expanded. For each ''name'' in the argument list for which no ''value'' is supplied, the name and value of the alias is printed. __Alias__ returns true unless a ''name'' is given for which no alias has been defined. __bg__ [[''jobspec''] Resume the suspended job ''jobspec'' in the background, as if it had been started with ____. If ''jobspec'' is not present, the shell's notion of the ''current job'' is used. __bg__ ''jobspec'' returns 0 unless run when job control is disabled or, when run with job control enabled, if ''jobspec'' was not found or started without job control. __bind__ [[__-m__ ''keymap''] [[__-lpsvPSV__] __bind__ [[__-m__ ''keymap''] [[__-q__ ''function''] [[__-u__ ''function''] [[__-r__ ''keyseq''] __bind__ [[__-m__ ''keymap''] __-f__ ''filename'' __bind__ [[__-m__ ''keymap''] __-x__ ''keyseq'':''shell-command'' __bind__ [[__-m__ ''keymap''] ''keyseq'':''function-name'' Display current __readline__ key and function bindings, or bind a key sequence to a __readline__ function or macro. The binding syntax accepted is identical to that of ''.inputrc'', but each binding must be passed as a separate argument; e.g., ' '' __-m__ ''keymap'' Use ''keymap'' as the keymap to be affected by the subsequent bindings. Acceptable ''keymap'' names are ''emacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-move, vi-command'', and ''vi-insert''. ''vi'' is equivalent to ''vi-command''; ''emacs'' is equivalent to ''emacs-standard''. __-l__ List the names of all __readline__ functions. __-p__ Display __readline__ function names and bindings in such a way that they can be re-read. __-P__ List current __readline__ function names and bindings. __-v__ Display __readline__ variable names and values in such a way that they can be re-read. __-V__ List current __readline__ variable names and values. __-s__ Display __readline__ key sequences bound to macros and the strings they output in such a way that they can be re-read. __-S__ Display __readline__ key sequences bound to macros and the strings they output. __-f__ ''filename'' Read key bindings from ''filename''. __-q__ ''function'' Query about which keys invoke the named ''function''. __-u__ ''function'' Unbind all keys bound to the named ''function''. __-r__ ''keyseq'' Remove any current binding for ''keyseq''. __-x__ ''keyseq''__:__''shell-command'' Cause ''shell-command'' to be executed whenever ''keyseq'' is entered. The return value is 0 unless an unrecognized option is given or an error occurred. __break__ [[''n''] Exit from within a __for__, __while__, __until__, or __select__ loop. If ''n'' is specified, break ''n'' levels. ''n'' must be 1. If ''n'' is greater than the number of enclosing loops, all enclosing loops are exited. The return value is 0 unless the shell is not executing a loop when __break__ is executed. __builtin__ ''shell-builtin'' [[''arguments''] Execute the specified shell builtin, passing it ''arguments'', and return its exit status. This is useful when defining a function whose name is the same as a shell builtin, retaining the functionality of the builtin within the function. The __cd__ builtin is commonly redefined this way. The return status is false if ''shell-builtin'' is not a shell builtin command. __cd__ [[__-LP__] [[''dir''] Change the current directory to ''dir''. The variable __HOME__ is the default ''dir''. The variable __CDPATH__ defines the search path for the directory containing ''dir''. Alternative directory names in __CDPATH__ are separated by a colon (:). A null directory name in __CDPATH__ is the same as the current directory, i.e., ``__.__''. If ''dir'' begins with a slash (/), then __CDPATH__ is not used. The __-P__ option says to use the physical directory structure instead of following symbolic links (see also the __-P__ option to the __set__ builtin command); the __-L__ option forces symbolic links to be followed. An argument of __-__ is equivalent to __$OLDPWD__. The return value is true if the directory was successfully changed; false otherwise. __command__ [[__-pVv__] ''command'' [[''arg'' ...] Run ''command'' with ''args'' suppressing the normal shell function lookup. Only builtin commands or commands found in the __PATH__ are executed. If the __-p__ option is given, the search for ''command'' is performed using a default value for __PATH__ that is guaranteed to find all of the standard utilities. If either the __-V__ or __-v__ option is supplied, a description of ''command'' is printed. The __-v__ option causes a single word indicating the command or file name used to invoke ''command'' to be displayed; the __-V__ option produces a more verbose description. If the __-V__ or __-v__ option is supplied, the exit status is 0 if ''command'' was found, and 1 if not. If neither option is supplied and an error occurred or ''command'' cannot be found, the exit status is 127. Otherwise, the exit status of the __command__ builtin is the exit status of ''command''. __compgen__ [[''option''] [[''word''] Generate possible completion matches for ''word'' according to the ''option''s, which may be any option accepted by the __complete__ builtin with the exception of __-p__ and __-r__, and write the matches to the standard output. When using the __-F__ or __-C__ options, the various shell variables set by the programmable completion facilities, while available, will not have useful values. The matches will be generated in the same way as if the programmable completion code had generated them directly from a completion specification with the same flags. If ''word'' is specified, only those completions matching ''word'' will be displayed. The return value is true unless an invalid option is supplied, or no matches were generated. __complete__ [[__-abcdefgjksvu__] [[__-o__ ''comp-option''] [[__-A__ ''action''] [[__-G__ ''globpat''] [[__-W__ ''wordlist''] [[__-P__ ''prefix''] [[__-S__ ''suffix''] [[__-X__ ''filterpat''] [[__-F__ ''function''] [[__-C__ ''command''] ''name'' [[''name ...''] __complete -pr__ [[''name'' ...] Specify how arguments to each ''name'' should be completed. If the __-p__ option is supplied, or if no options are supplied, existing completion specifications are printed in a way that allows them to be reused as input. The __-r__ option removes a completion specification for each ''name'', or, if no ''name''s are supplied, all completion specifications. The process of applying these completion specifications when word completion is attempted is described above under __Programmable Completion__. Other options, if specified, have the following meanings. The arguments to the __-G__, __-W__, and __-X__ options (and, if necessary, the __-P__ and __-S__ options) should be quoted to protect them from expansion before the __complete__ builtin is invoked. __-o__ ''comp-option'' The ''comp-option'' controls several aspects of the compspec's behavior beyond the simple generation of completions. ''comp-option'' may be one of: __default__ Use readline's default completion if the compspec generates no matches. __dirnames__ Perform directory name completion if the compspec generates no matches. __filenames__ Tell readline that the compspec generates filenames, so it can perform any filename-specific processing (like adding a slash to directory names or suppressing trailing spaces). Intended to be used with shell functions. __-A__ ''action'' The ''action'' may be one of the following to generate a list of possible completions: __alias__ Alias names. May also be specified as __-a__. __arrayvar__ Array variable names. __binding__ __Readline__ key binding names. __builtin__ Names of shell builtin commands. May also be specified as __-b__. __command__ Command names. May also be specified as __-c__. __directory__ Directory names. May also be specified as __-d__. __disabled__ Names of disabled shell builtins. __enabled__ Names of enabled shell builtins. __export__ Names of exported shell variables. May also be specified as __-e__. __file__ File names. May also be specified as __-f__. __function__ Names of shell functions. __group__ Group names. May also be specified as __-g__. __helptopic__ Help topics as accepted by the __help__ builtin. __hostname__ Hostnames, as taken from the file specified by the __HOSTFILE__ shell variable. __job__ Job names, if job control is active. May also be specified as __-j__. __keyword__ Shell reserved words. May also be specified as __-k__. __running__ Names of running jobs, if job control is active. __service__ Service names. May also be specified as __-s__. __setopt__ Valid arguments for the __-o__ option to the __set__ builtin. __shopt__ Shell option names as accepted by the __shopt__ builtin. __signal__ Signal names. __stopped__ Names of stopped jobs, if job control is active. __user__ User names. May also be specified as __-u__. __variable__ Names of all shell variables. May also be specified as __-v__. __-G__ ''globpat'' The filename expansion pattern ''globpat'' is expanded to generate the possible completions. __-W__ ''wordlist'' The ''wordlist'' is split using the characters in the __IFS__ special variable as delimiters, and each resultant word is expanded. The possible completions are the members of the resultant list which match the word being completed. __-C__ ''command'' ''command'' is executed in a subshell environment, and its output is used as the possible completions. __-F__ ''function'' The shell function ''function'' is executed in the current shell environment. When it finishes, the possible completions are retrieved from the value of the __COMPREPLY__ array variable. __-X__ ''filterpat'' ''filterpat'' is a pattern as used for filename expansion. It is applied to the list of possible completions generated by the preceding options and arguments, and each completion matching ''filterpat'' is removed from the list. A leading __!__ in ''filterpat'' negates the pattern; in this case, any completion not matching ''filterpat'' is removed. __-P__ ''prefix'' ''prefix'' is added at the beginning of each possible completion after all other options have been applied. __-S__ ''suffix'' ''suffix'' is appended to each possible completion after all other options have been applied. The return value is true unless an invalid option is supplied, an option other than __-p__ or __-r__ is supplied without a ''name'' argument, an attempt is made to remove a completion specification for a ''name'' for which no specification exists, or an error occurs adding a completion specification. __continue__ [[''n''] Resume the next iteration of the enclosing __for__, __while__, __until__, or __select__ loop. If ''n'' is specified, resume at the ''n''th enclosing loop. ''n'' must be 1. If ''n'' is greater than the number of enclosing loops, the last enclosing loop (the ``top-level'' loop) is resumed. The return value is 0 unless the shell is not executing a loop when __continue__ is executed. __declare__ [[__-afFirx__] [[__-p__] [[''name''[[=''value'']] __typeset__ [[__-afFirx__] [[__-p__] [[''name''[[=''value'']] Declare variables and/or give them attributes. If no ''name''s are given then display the values of variables. The __-p__ option will display the attributes and values of each ''name''. When __-p__ is used, additional options are ignored. The __-F__ option inhibits the display of function definitions; only the function name and attributes are printed. The __-F__ option implies __-f__. The following options can be used to restrict output to variables with the specified attribute or to give variables attributes: __-a__ Each ''name'' is an array variable (see __Arrays__ above). __-f__ Use function names only. __-i__ The variable is treated as an integer; arithmetic evaluation (see __ARITHMETIC EVALUATION )__ is performed when the variable is assigned a value. __-r__ Make ''name''s readonly. These names cannot then be assigned values by subsequent assignment statements or unset. __-x__ Mark ''name''s for export to subsequent commands via the environment. Using `+' instead of `-' turns off the attribute instead, with the exception that __+a__ may not be used to destroy an array variable. When used in a function, makes each ''name'' local, as with the __local__ command. The return value is 0 unless an invalid option is encountered, an attempt is made to define a function using -f foo=bar, an attempt is made to assign a value to a readonly variable, an attempt is made to assign a value to an array variable without using the compound assignment syntax (see __Arrays__ above), one of the ''names'' is not a valid shell variable name, an attempt is made to turn off readonly status for a readonly variable, an attempt is made to turn off array status for an array variable, or an attempt is made to display a non-existent function with __-f__. __dirs [[-clpv] [[+__''n''__] [[-__''n''__]__ Without options, displays the list of currently remembered directories. The default display is on a single line with directory names separated by spaces. Directories are added to the list with the __pushd__ command; the __popd__ command removes entries from the list. __+__''n'' Displays the ''n''th entry counting from the left of the list shown by __dirs__ when invoked without options, starting with zero. __-__''n'' Displays the ''n''th entry counting from the right of the list shown by __dirs__ when invoked without options, starting with zero. __-c__ Clears the directory stack by deleting all of the entries. __-l__ Produces a longer listing; the default listing format uses a tilde to denote the home directory. __-p__ Print the directory stack with one entry per line. __-v__ Print the directory stack with one entry per line, prefixing each entry with its index in the stack. The return value is 0 unless an invalid option is supplied or ''n'' indexes beyond the end of the directory stack. __disown__ [[__-ar__] [[__-h__] [[''jobspec'' ...] Without options, each ''jobspec'' is removed from the table of active jobs. If the __-h__ option is given, each ''jobspec'' is not removed from the table, but is marked so that __SIGHUP__ is not sent to the job if the shell receives a __SIGHUP__. If no ''jobspec'' is present, and neither the __-a__ nor the __-r__ option is supplied, the ''current job'' is used. If no ''jobspec'' is supplied, the __-a__ option means to remove or mark all jobs; the __-r__ option without a ''jobspec'' argument restricts operation to running jobs. The return value is 0 unless a ''jobspec'' does not specify a valid job. __echo__ [[__-neE__] [[''arg'' ...] Output the ''arg''s, separated by spaces, followed by a newline. The return status is always 0. If __-n__ is specified, the trailing newline is suppressed. If the __-e__ option is given, interpretation of the following backslash-escaped characters is enabled. The __-E__ option disables the interpretation of these escape characters, even on systems where they are interpreted by default. The __xpg_echo__ shell option may be used to dynamically determine whether or not __echo__ expands these escape characters by default. __echo__ does not interpret __--__ to mean the end of options. __echo__ interprets the following escape sequences: __a__ alert (bell) __b__ backspace __c__ suppress trailing newline __e__ an escape character __f__ form feed __n__ new line __r__ carriage return __t__ horizontal tab __v__ vertical tab __\__ backslash __\__''nnn'' the eight-bit character whose value is the octal value ''nnn'' (one to three digits) __x__''HH'' the eight-bit character whose value is the hexadecimal value ''HH'' (one or two hex digits) __enable__ [[__-adnps__] [[__-f__ ''filename''] [[''name'' ...] Enable and disable builtin shell commands. Disabling a builtin allows a disk command which has the same name as a shell builtin to be executed without specifying a full pathname, even though the shell normally searches for builtins before disk commands. If __-n__ is used, each ''name'' is disabled; otherwise, ''names'' are enabled. For example, to use the __test__ binary found via the __PATH__ instead of the shell builtin version, run enable -n test. The __-f__ option means to load the new builtin command ''name'' from shared object ''filename'', on systems that support dynamic loading. The __-d__ option will delete a builtin previously loaded with __-f__. If no ''name'' arguments are given, or if the __-p__ option is supplied, a list of shell builtins is printed. With no other option arguments, the list consists of all enabled shell builtins. If __-n__ is supplied, only disabled builtins are printed. If __-a__ is supplied, the list printed includes all builtins, with an indication of whether or not each is enabled. If __-s__ is supplied, the output is restricted to the POSIX ''special'' builtins. The return value is 0 unless a ''name'' is not a shell builtin or there is an error loading a new builtin from a shared object. __eval__ [[''arg'' ...] The ''arg''s are read and concatenated together into a single command. This command is then read and executed by the shell, and its exit status is returned as the value of __eval__. If there are no ''args'', or only null arguments, __eval__ returns 0. __exec__ [[__-cl__] [[__-a__ ''name''] [[''command'' [[''arguments'']] If ''command'' is specified, it replaces the shell. No new process is created. The ''arguments'' become the arguments to ''command''. If the __-l__ option is supplied, the shell places a dash at the beginning of the zeroth arg passed to ''command''. This is what login(1) does. The __-c__ option causes ''command'' to be executed with an empty environment. If __-a__ is supplied, the shell passes ''name'' as the zeroth argument to the executed command. If ''command'' cannot be executed for some reason, a non-interactive shell exits, unless the shell option __execfail__ is enabled, in which case it returns failure. An interactive shell returns failure if the file cannot be executed. If ''command'' is not specified, any redirections take effect in the current shell, and the return status is 0. If there is a redirection error, the return status is 1. __exit__ [[''n''] Cause the shell to exit with a status of ''n''. If ''n'' is omitted, the exit status is that of the last command executed. A trap on __EXIT__ is executed before the shell terminates. __export__ [[__-fn__] [[''name''[[=''word'']] ... __export -p__ The supplied ''names'' are marked for automatic export to the environment of subsequently executed commands. If the __-f__ option is given, the ''names'' refer to functions. If no ''names'' are given, or if the __-p__ option is supplied, a list of all names that are exported in this shell is printed. The __-n__ option causes the export property to be removed from the named variables. __export__ returns an exit status of 0 unless an invalid option is encountered, one of the ''names'' is not a valid shell variable name, or __-f__ is supplied with a ''name'' that is not a function. __fc__ [[__-e__ ''ename''] [[__-nlr__] [[''first''] [[''last''] __fc -s__ [[''pat''=''rep''] [[''cmd''] Fix Command. In the first form, a range of commands from ''first'' to ''last'' is selected from the history list. ''First'' and ''last'' may be specified as a string (to locate the last command beginning with that string) or as a number (an index into the history list, where a negative number is used as an offset from the current command number). If ''last'' is not specified it is set to the current command for listing (so that fc -l -10 prints the last 10 commands) and to ''first'' otherwise. If ''first'' is not specified it is set to the previous command for editing and -16 for listing. The __-n__ option suppresses the command numbers when listing. The __-r__ option reverses the order of the commands. If the __-l__ option is given, the commands are listed on standard output. Otherwise, the editor given by ''ename'' is invoked on a file containing those commands. If ''ename'' is not given, the value of the __FCEDIT__ variable is used, and the value of __EDITOR__ if __FCEDIT__ is not set. If neither variable is set, ''vi'' is used. When editing is complete, the edited commands are echoed and executed. In the second form, ''command'' is re-executed after each instance of ''pat'' is replaced by ''rep''. A useful alias to use with this is r='fc -s', so that typing r cc runs the last command beginning with cc and typing r re-executes the last command. If the first form is used, the return value is 0 unless an invalid option is encountered or ''first'' or ''last'' specify history lines out of range. If the __-e__ option is supplied, the return value is the value of the last command 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 ''cmd'' does not specify a valid history line, in which case __fc__ returns failure. __fg__ [[''jobspec''] Resume ''jobspec'' in the foreground, and make it the current job. If ''jobspec'' is not present, the shell's notion of the ''current job'' is used. The return value is that of the command placed into the foreground, or failure if run when job control is disabled or, when run with job control enabled, if ''jobspec'' does not specify a valid job or ''jobspec'' specifies a job that was started without job control. __getopts__ ''optstring name'' [[''args''] __getopts__ is used by shell procedures to parse positional parameters. ''optstring'' contains the option characters to be recognized; if a character is followed by a colon, the option is expected to have an argument, which should be separated from it by white space. The colon and question mark characters may not be used as option characters. Each time it is invoked, __getopts__ places the next option in the shell variable ''name'', initializing ''name'' if it does not exist, and the index of the next argument to be processed into the variable __OPTIND__. __OPTIND__ is initialized to 1 each time the shell or a shell script is invoked. When an option requires an argument, __getopts__ places that argument into the variable __OPTARG__. The shell does not reset __OPTIND__ automatically; it must be manually reset between multiple calls to __getopts__ within the same shell invocation if a new set of parameters is to be used. When the end of options is encountered, __getopts__ exits with a return value greater than zero. __OPTIND__ is set to the index of the first non-option argument, and __name__ is set to ?. __getopts__ normally parses the positional parameters, but if more arguments are given in ''args'', __getopts__ parses those instead. __getopts__ can report errors in two ways. If the first character of ''optstring'' is a colon, ''silent'' error reporting is used. In normal operation diagnostic messages are printed when invalid options or missing option arguments are encountered. If the variable __OPTERR__ is set to 0, no error messages will be displayed, even if the first character of ''optstring'' is not a colon. If an invalid option is seen, __getopts__ places ? into ''name'' and, if not silent, prints an error message and unsets __OPTARG__. If __getopts__ is silent, the option character found is placed in __OPTARG__ and no diagnostic message is printed. If a required argument is not found, and __getopts__ is not silent, a question mark (__?__) is placed in ''name'', __OPTARG__ is unset, and a diagnostic message is printed. If __getopts__ is silent, then a colon (__:__) is placed in ''name'' and __OPTARG__ is set to the option character found. __getopts__ returns true if an option, specified or unspecified, is found. It returns false if the end of options is encountered or an error occurs. __hash__ [[__-r__] [[__-p__ ''filename''] [[__-t__] [[''name''] For each ''name'', the full file name of the command is determined by searching the directories in __$PATH__ and remembered. If the __-p__ option is supplied, no path search is performed, and ''filename'' is used as the full file name of the command. The __-r__ option causes the shell to forget all remembered locations. If the __-t__ option is supplied, the full pathname to which each ''name'' corresponds is printed. If multiple ''name'' arguments are supplied with __-t__, the ''name'' is printed before the hashed full pathname. If no arguments are given, information about remembered commands is printed. The return status is true unless a ''name'' is not found or an invalid option is supplied. __help__ [[__-s__] [[''pattern''] Display helpful information about builtin commands. If ''pattern'' is specified, __help__ gives detailed help on all commands matching ''pattern''; otherwise help for all the builtins and shell control structures is printed. The __-s__ option restricts the information displayed to a short usage synopsis. The return status is 0 unless no command matches ''pattern''. __history [[__''n''__]__ __history -c__ __history -d__ ''offset'' __history -anrw__ [[''filename''] __history -p__ ''arg'' [[''arg ...''] __history -s__ ''arg'' [[''arg ...''] With no options, display the command history list with line numbers. Lines listed with a __*__ have been modified. An argument of ''n'' lists only the last ''n'' lines. If ''filename'' is supplied, it is used as the name of the history file; if not, the value of __HISTFILE__ is used. Options, if supplied, have the following meanings: __-c__ Clear the history list by deleting all the entries. __-d__ ''offset'' Delete the history entry at position ''offset''. __-a__ Append the ``new'' history lines (history lines entered since the beginning of the current __bash__ session) to the history file. __-n__ Read the history lines not already read from the history file into the current history list. These are lines appended to the history file since the beginning of the current __bash__ session. __-r__ Read the contents of the history file and use them as the current history. __-w__ Write the current history to the history file, overwriting the history file's contents. __-p__ Perform history substitution on the following ''args'' and display the result on the standard output. Does not store the results in the history list. Each ''arg'' must be quoted to disable normal history expansion. __-s__ Store the ''args'' in the history list as a single entry. The last command in the history list is removed before the ''args'' are added. The return value is 0 unless an invalid option is encountered, an error occurs while reading or writing the history file, an invalid ''offset'' is supplied as an argument to __-d__, or the history expansion supplied as an argument to __-p__ fails. __jobs__ [[__-lnprs__] [[ ''jobspec'' ... ] __jobs -x__ ''command'' [[ ''args'' ... ] The first form lists the active jobs. The options have the following meanings: __-l__ List process IDs in addition to the normal information. __-p__ List only the process ID of the job's process group leader. __-n__ Display information only about jobs that have changed status since the user was last notified of their status. __-r__ Restrict output to running jobs. __-s__ Restrict output to stopped jobs. If ''jobspec'' is given, output is restricted to information about that job. The return status is 0 unless an invalid option is encountered or an invalid ''jobspec'' is supplied. If the __-x__ option is supplied, __jobs__ replaces any ''jobspec'' found in ''command'' or ''args'' with the corresponding process group ID, and executes ''command'' passing it ''args'', returning its exit status. __kill__ [[__-s__ ''sigspec'' | __-n__ ''signum'' | __-__''sigspec''] [[''pid'' | ''jobspec''] ... __kill -l__ [[''sigspec'' | ''exit_status''] Send the signal named by ''sigspec'' or ''signum'' to the processes named by ''pid'' or ''jobspec''. ''sigspec'' is either a signal name such as __SIGKILL__ or a signal number; ''signum'' is a signal number. If ''sigspec'' is a signal name, the name may be given with or without the __SIG__ prefix. If ''sigspec'' is not present, then __SIGTERM__ is assumed. An argument of __-l__ lists the signal names. If any arguments are supplied when __-l__ is given, the names of the signals corresponding to the arguments are listed, and the return status is 0. The ''exit_status'' argument to __-l__ is a number specifying either a signal number or the exit status of a process terminated by a signal. __kill__ returns true if at least one signal was successfully sent, or false if an error occurs or an invalid option is encountered. __let__ ''arg'' [[''arg'' ...] Each ''arg'' is an arithmetic expression to be evaluated (see __ARITHMETIC EVALUATION__). If the last ''arg'' evaluates to 0, __let__ returns 1; 0 is returned otherwise. __local__ [[''option''] [[''name''[[=''value''] ...] For each argument, a local variable named ''name'' is created, and assigned ''value''. The ''option'' can be any of the options accepted by __declare__. When __local__ is used within a function, it causes the variable ''name'' to have a visible scope restricted to that function and its children. With no operands, __local__ writes a list of local variables to the standard output. It is an error to use __local__ when not within a function. The return status is 0 unless __local__ is used outside a function, an invalid ''name'' is supplied, or ''name'' is a readonly variable. __logout__ Exit a login shell. __popd__ [[-__n__] [[+''n''] [[-''n''] Removes entries from the directory stack. With no arguments, removes the top directory from the stack, and performs a __cd__ to the new top directory. Arguments, if supplied, have the following meanings: __+__''n'' Removes the ''n''th entry counting from the left of the list shown by __dirs__, starting with zero. For example: popd +0 removes the first directory, popd +1 the second. __-__''n'' Removes the ''n''th entry counting from the right of the list shown by __dirs__, starting with zero. For example: popd -0 removes the last directory, popd -1 the next to last. __-n__ Suppresses the normal change of directory when removing directories from the stack, so that only the stack is manipulated. If the __popd__ command is successful, a __dirs__ is performed as well, and the return status is 0. __popd__ returns false if an invalid option is encountered, the directory stack is empty, a non-existent directory stack entry is specified, or the directory change fails. __printf__ ''format'' [[''arguments''] Write the formatted ''arguments'' to the standard output under the control of the ''format''. The ''format'' is a character string which contains three types of objects: plain characters, which are simply copied to standard output, character escape sequences, which are converted and copied to the standard output, and format specifications, each of which causes printing of the next successive ''argument''. In addition to the standard printf(1) formats, __%b__ causes __printf__ to expand backslash escape sequences in the corresponding ''argument'', and __%q__ causes __printf__ to output the corresponding ''argument'' in a format that can be reused as shell input. The ''format'' is reused as necessary to consume all of the ''arguments''. If the ''format'' requires more ''arguments'' than are supplied, the extra format specifications behave as if a zero value or null string, as appropriate, had been supplied. The return value is zero on success, non-zero on failure. __pushd__ [[__-n__] [[''dir''] __pushd__ [[__-n__] [[+''n''] [[-''n''] Adds a directory to the top of the directory stack, or rotates the stack, making the new top of the stack the current working directory. With no arguments, exchanges the top two directories and returns 0, unless the directory stack is empty. Arguments, if supplied, have the following meanings: __+__''n'' Rotates the stack so that the ''n''th directory (counting from the left of the list shown by __dirs__, starting with zero) is at the top. __-__''n'' Rotates the stack so that the ''n''th directory (counting from the right of the list shown by __dirs__, starting with zero) is at the top. __-n__ Suppresses the normal change of directory when adding directories to the stack, so that only the stack is manipulated. ''dir'' Adds ''dir'' to the directory stack at the top, making it the new current working directory. If the __pushd__ command is successful, a __dirs__ is performed as well. If the first form is used, __pushd__ returns 0 unless the cd to ''dir'' fails. With the second form, __pushd__ returns 0 unless the directory stack is empty, a non-existent directory stack element is specified, or the directory change to the specified new current directory fails. __pwd__ [[__-LP__] Print the absolute pathname of the current working directory. The pathname printed contains no symbolic links if the __-P__ option is supplied or the __-o physical__ option to the __set__ builtin command is enabled. If the __-L__ option is used, the pathname printed may contain symbolic links. The return status is 0 unless an error occurs while reading the name of the current directory or an invalid option is supplied. __read__ [[__-ers__] [[__-t__ ''timeout''] [[__-a__ ''aname''] [[__-p__ ''prompt''] [[__-n__ ''nchars''] [[__-d__ ''delim''] [[''name'' ...] One line is read from the standard input, and the first word is assigned to the first ''name'', the second word to the second ''name'', and so on, with leftover words and their intervening separators assigned to the last ''name''. If there are fewer words read from the standard input than names, the remaining names are assigned empty values. The characters in __IFS__ are used to split the line into words. The backslash character (__\__) may be used to remove any special meaning for the next character read and for line continuation. Options, if supplied, have the following meanings: __-a__ ''aname'' The words are assigned to sequential indices of the array variable ''aname'', starting at 0. ''aname'' is unset before any new values are assigned. Other ''name'' arguments are ignored. __-d__ ''delim'' The first character of ''delim'' is used to terminate the input line, rather than newline. __-e__ If the standard input is coming from a terminal, __readline__ (see __READLINE__ above) is used to obtain the line. __-n__ ''nchars'' __read__ returns after reading ''nchars'' characters rather than waiting for a complete line of input. __-p__ ''prompt'' Display ''prompt'' on standard error, without a trailing newline, before attempting to read any input. The prompt is displayed only if input is coming from a terminal. __-r__ Backslash does not act as an escape character. The backslash is considered to be part of the line. In particular, a backslash-newline pair may not be used as a line continuation. __-s__ Silent mode. If input is coming from a terminal, characters are not echoed. __-t__ ''timeout'' Cause __read__ to time out and return failure if a complete line of input is not read within ''timeout'' seconds. This option has no effect if __read__ is not reading input from the terminal or a pipe. If no ''names'' are supplied, the line read is assigned to the variable __REPLY__. The return code is zero, unless end-of-file is encountered or __read__ times out. __readonly__ [[__-apf__] [[''name'' ...] The given ''names'' are marked readonly; the values of these ''names'' may not be changed by subsequent assignment. If the __-f__ option is supplied, the functions corresponding to the ''names'' are so marked. The __-a__ option restricts the variables to arrays. If no ''name'' arguments are given, or if the __-p__ option is supplied, a list of all readonly names is printed. The __-p__ option causes output to be displayed in a format that may be reused as input. The return status is 0 unless an invalid option is encountered, one of the ''names'' is not a valid shell variable name, or __-f__ is supplied with a ''name'' that is not a function. __return__ [[''n''] Causes a function to exit with the return value specified by ''n''. If ''n'' is omitted, the return status is that of the last command executed in the function body. If used outside a function, but during execution of a script by the __.__ (__source__) command, it causes the shell to stop executing that script and return either ''n'' or the exit status of the last command executed within the script as the exit status of the script. If used outside a function and not during execution of a script by __.__, the return status is false. __set__ [[__--abefhkmnptuvxBCHP__] [[__-o__ ''option''] [[''arg'' ...] Without options, the name and value of each shell variable are displayed in a format that can be reused as input. The output is sorted according to the current locale. When options are specified, they set or unset shell attributes. Any arguments remaining after the options are processed are treated as values for the positional parameters and are assigned, in order, to __$1__, __$2__, __... $__''n''. Options, if specified, have the following meanings: __-a__ Automatically mark variables and functions which are modified or created for export to the environment of subsequent commands. __-b__ Report the status of terminated background jobs immediately, rather than before the next primary prompt. This is effective only when job control is enabled. __-e__ Exit immediately if a ''simple command'' (see __SHELL GRAMMAR__ above) exits with a non-zero status. The shell does not exit if the command that fails is part of an ''until'' or ''while'' loop, part of an ''if'' statement, part of a ____ or list, or if the command's return value is being inverted via __!__. A trap on __ERR__, if set, is executed before the shell exits. __-f__ Disable pathname expansion. __-h__ Remember the location of commands as they are looked up for execution. This is enabled by default. __-k__ All arguments in the form of assignment statements are placed in the environment for a command, not just those that precede the command name. __-m__ Monitor mode. Job control is enabled. This option is on by default for interactive shells on systems that support it (see __JOB CONTROL__ above). Background processes run in a separate process group and a line containing their exit status is printed upon their completion. __-n__ Read commands but do not execute them. This may be used to check a shell script for syntax errors. This is ignored by interactive shells. __-o__ ''option-name'' The ''option-name'' can be one of the following: __allexport__ Same as __-a__. __braceexpand__ Same as __-B__. __emacs__ Use an emacs-style command line editing interface. This is enabled by default when the shell is interactive, unless the shell is started with the __--noediting__ option. __errexit__ Same as __-e__. __hashall__ Same as __-h__. __histexpand__ Same as __-H__. __history__ Enable command history, as described above under __HISTORY__. This option is on by default in interactive shells. __ignoreeof__ The effect is as if the shell command IGNOREEOF=10 had been executed (see __Shell Variables__ above). __keyword__ Same as __-k__. __monitor__ Same as __-m__. __noclobber__ Same as __-C__. __noexec__ Same as __-n__. __noglob__ Same as __-f__. __nolog__ Currently ignored. __notify__ Same as __-b__. __nounset__ Same as __-u__. __onecmd__ Same as __-t__. __physical__ Same as __-P__. __posix__ Change the behavior of __bash__ where the default operation differs from the POSIX 1003.2 standard to match the standard (''posix mode''). __privileged__ Same as __-p__. __verbose__ Same as __-v__. __vi__ Use a vi-style command line editing interface. __xtrace__ Same as __-x__. If __-o__ is supplied with no ''option-name'', the values of the current options are printed. If __+o__ is supplied with no ''option-name'', a series of __set__ commands to recreate the current option settings is displayed on the standard output. __-p__ Turn on ''privileged'' mode. In this mode, the __$ENV__ and __$BASH_ENV__ files are not processed, shell functions are not inherited from the environment, and the __SHELLOPTS__ variable, if it appears in the environment, is ignored. If the shell is started with the effective user (group) id not equal to the real user (group) id, and the __-p__ option is not supplied, these actions are taken and the effective user id is set to the real user id. If the __-p__ option is supplied at startup, the effective user id is not reset. Turning this option off causes the effective user and group ids to be set to the real user and group ids. __-t__ Exit after reading and executing one command. __-u__ Treat unset variables as an error when performing parameter 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. __-v__ Print shell input lines as they are read. __-x__ After expanding each ''simple command'', display the expanded value of __PS4__, followed by the command and its expanded arguments. __-B__ The shell performs brace expansion (see __Brace Expansion__ above). This is on by default. __-C__ If set, __bash__ does not overwrite an existing file with the ____, ____, and ____ redirection operators. This may be overridden when creating output files by using the redirection operator ____ instead of ____. __-H__ Enable __!__ style history substitution. This option is on by default when the shell is interactive. __-P__ If set, the shell does not follow symbolic links when executing commands such as __cd__ that change the current working directory. It uses the physical directory structure instead. By default, __bash__ follows the logical chain of directories when performing commands which change the current directory. __--__ If no arguments follow this option, then the positional parameters are unset. Otherwise, the positional parameters are set to the ''arg''s, even if some of them begin with a __-__. __-__ Signal the end of options, cause all remaining ''arg''s to be assigned to the positional parameters. The __-x__ and __-v__ options are turned off. If there are no ''arg''s, the positional parameters remain unchanged. The options are off by default unless otherwise noted. Using + rather than - causes these options to be turned off. The options can also be specified as arguments to an invocation of the shell. The current set of options may be found in __$-__. The return status is always true unless an invalid option is encountered. __shift__ [[''n''] The positional parameters from ''n''+1 ... are renamed to __$1 ....__ Parameters represented by the numbers __$#__ down to __$#__-''n''+1 are unset. ''n'' must be a non-negative number less than or equal to __$#__. If ''n'' is 0, no parameters are changed. If ''n'' is not given, it is assumed to be 1. If ''n'' is greater than __$#__, the positional parameters are not changed. The return status is greater than zero if ''n'' is greater than __$#__ or less than zero; otherwise 0. __shopt__ [[__-pqsu__] [[__-o__] [[''optname'' ...] Toggle the values of variables controlling optional shell behavior. With no options, or with the __-p__ option, a list of all settable options is displayed, with an indication of whether or not each is set. The __-p__ option causes output to be displayed in a form that may be reused as input. Other options have the following meanings: __-s__ Enable (set) each ''optname''. __-u__ Disable (unset) each ''optname''. __-q__ Suppresses normal output (quiet mode); the return status indicates whether the ''optname'' is set or unset. If multiple ''optname'' arguments are given with __-q__, the return status is zero if all ''optnames'' are enabled; non-zero otherwise. __-o__ Restricts the values of ''optname'' to be those defined for the __-o__ option to the __set__ builtin. If either __-s__ or __-u__ is used with no ''optname'' arguments, the display is limited to those options which are set or unset, respectively. Unless otherwise noted, the __shopt__ options are disabled (unset) by default. The return status when listing options is zero if all ''optnames'' are enabled, non-zero otherwise. When setting or unsetting options, the return status is zero unless an ''optname'' is not a valid shell option. The list of __shopt__ options is: __cdable_vars__ If set, an argument to the __cd__ builtin command that is not a directory is assumed to be the name of a variable whose value is the directory to change to. __cdspell__ If set, minor errors in the spelling of a directory component in a __cd__ command will be corrected. The errors checked for are transposed characters, a missing character, and one character too many. If a correction is found, the corrected file name is printed, and the command proceeds. This option is only used by interactive shells. __checkhash__ If set, __bash__ checks that a command found in the hash table exists before trying to execute it. If a hashed command no longer exists, a normal path search is performed. __checkwinsize__ If set, __bash__ checks the window size after each command and, if necessary, updates the values of __LINES__ and __COLUMNS__. __cmdhist__ If set, __bash__ attempts to save all lines of a multiple-line command in the same history entry. This allows easy re-editing of multi-line commands. __dotglob__ If set, __bash__ includes filenames beginning with a `.' in the results of pathname expansion. __execfail__ If set, a non-interactive shell will not exit if it cannot execute the file specified as an argument to the __exec__ builtin command. An interactive shell does not exit if __exec__ fails. __expand_aliases__ If set, aliases are expanded as described above under __ALIASES__. This option is enabled by default for interactive shells. __extglob__ If set, the extended pattern matching features described above under __Pathname Expansion__ are enabled. __histappend__ If set, the history list is appended to the file named by the value of the __HISTFILE__ variable when the shell exits, rather than overwriting the file. __histreedit__ If set, and __readline__ is being used, a user is given the opportunity to re-edit a failed history substitution. __histverify__ If set, and __readline__ is being used, the results of history substitution are not immediately passed to the shell parser. Instead, the resulting line is loaded into the __readline__ editing buffer, allowing further modification. __hostcomplete__ If set, and __readline__ is being used, __bash__ will attempt to perform hostname completion when a word containing a __@__ is being completed (see __Completing__ under __READLINE__ above). This is enabled by default. __huponexit__ If set, __bash__ will send __SIGHUP__ to all jobs when an interactive login shell exits. __interactive_comments__ If set, allow a word beginning with __#__ to cause that word and all remaining characters on that line to be ignored in an interactive shell (see __COMMENTS__ above). This option is enabled by default. __lithist__ If set, and the __cmdhist__ option is enabled, multi-line commands are saved to the history with embedded newlines rather than using semicolon separators where possible. __login_shell__ The shell sets this option if it is started as a login shell (see __INVOCATION__ above). The value may not be changed. __mailwarn__ If set, and a file that __bash__ is checking for mail has been accessed since the last time it was checked, the message ``The mail in ''mailfile'' has been read'' is displayed. __no_empty_cmd_completion__ If set, and __readline__ is being used, __bash__ will not attempt to search the __PATH__ for possible completions when completion is attempted on an empty line. __nocaseglob__ If set, __bash__ matches filenames in a case-insensitive fashion when performing pathname expansion (see __Pathname Expansion__ above). __nullglob__ If set, __bash__ allows patterns which match no files (see __Pathname Expansion__ above) to expand to a null string, rather than themselves. __progcomp__ If set, the programmable completion facilities (see __Programmable Completion__ above) are enabled. This option is enabled by default. __promptvars__ If set, prompt strings undergo variable and parameter expansion after being expanded as described in __PROMPTING__ above. This option is enabled by default. __restricted_shell__ The shell sets this option if it is started in restricted mode (see __RESTRICTED SHELL__ below). The value may not be changed. This is not reset when the startup files are executed, allowing the startup files to discover whether or not a shell is restricted. __shift_verbose__ If set, the __shift__ builtin prints an error message when the shift count exceeds the number of positional parameters. __sourcepath__ If set, the __source__ (__.__) builtin uses the value of __PATH__ to find the directory containing the file supplied as an argument. This option is enabled by default. __xpg_echo__ If set, the __echo__ builtin expands backslash-escape sequences by default. __suspend__ [[__-f__] Suspend the execution of this shell until it receives a __SIGCONT__ signal. The __-f__ option says not to complain if this is a login shell; just suspend anyway. The return status is 0 unless the shell is a login shell and __-f__ is not supplied, or if job control is not enabled. __test__ ''expr'' __[[__ ''expr'' __]__ Return a status of 0 or 1 depending on the evaluation of the conditional expression ''expr''. Each operator and operand must be a separate argument. Expressions are composed of the primaries described above under __CONDITIONAL EXPRESSIONS__. Expressions may be combined using the following operators, listed in decreasing order of precedence. __!__ ''expr'' True if ''expr'' is false. __(__ ''expr'' __)__ Returns the value of ''expr''. This may be used to override the normal precedence of operators. ''expr1'' -__a__ ''expr2'' True if both ''expr1'' and ''expr2'' are true. ''expr1'' -__o__ ''expr2'' True if either ''expr1'' or ''expr2'' is true. __test__ and __[[__ evaluate conditional expressions using a set of rules based on the number of arguments. 0 arguments The expression is false. 1 argument The expression is true if and only if the argument is not null. 2 arguments If the first argument is __!__, the expression is true if and only if the second argument is null. If the first argument is one of the unary conditional operators listed above under __CONDITIONAL EXPRESSIONS__, the expression is true if the unary test is true. If the first argument is not a valid unary conditional operator, the expression is false. 3 arguments If the second argument is one of the binary conditional operators listed above under __CONDITIONAL EXPRESSIONS__, the result of the expression is the result of the binary test using the first and third arguments as operands. If the first argument is __!__, the value is the negation of the two-argument test using the second and third arguments. If the first argument is exactly __(__ and the third argument is exactly __)__, the result is the one-argument test of the second argument. Otherwise, the expression is false. The __-a__ and __-o__ operators are considered binary operators in this case. 4 arguments If the first argument is __!__, the result is the negation of the three-argument expression composed of the remaining arguments. Otherwise, the expression is parsed and evaluated according to precedence using the rules listed above. 5 or more arguments The expression is parsed and evaluated according to precedence using the rules listed above. __times__ Print the accumulated user and system times for the shell and for processes run from the shell. The return status is 0. __trap__ [[__-lp__] [[''arg''] [[''sigspec'' ...] The command ''arg'' is to be read and executed when the shell receives signal(s) ''sigspec''. If ''arg'' is absent or __-__, all specified signals are reset to their original values (the values they had upon entrance to the shell). If ''arg'' is the null string the signal specified by each ''sigspec'' is ignored by the shell and by the commands it invokes. If ''arg'' is not present and __-p__ has been supplied, then the trap commands associated with each ''sigspec'' are displayed. If no arguments are supplied or if only __-p__ is given, __trap__ prints the list of commands associated with each signal number. Each ''sigspec'' is either a signal name defined in ''signal.h'' ''sigspec'' is __EXIT__ (0) the command ''arg'' is executed on exit from the shell. If a ''sigspec'' is __DEBUG__, the command ''arg'' is executed after every ''simple command'' (see __SHELL GRAMMAR__ above). If a ''sigspec'' is __ERR__, the command ''arg'' is executed whenever a simple command has a non-zero exit status. The __ERR__ trap is not executed if the failed command is part of an ''until'' or ''while'' loop, part of an ''if'' statement, part of a ____ or list, or if the command's return value is being inverted via __!__. The __-l__ option causes the shell to print a list of signal names and their corresponding numbers. Signals 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 ''sigspec'' is invalid; otherwise __trap__ returns true. __type__ [[__-atp__] ''name'' [[''name'' ...] With no options, indicate how each ''name'' would be interpreted if used as a command name. If the __-t__ option is used, __type__ prints a string which is one of ''alias'', ''keyword'', ''function'', ''builtin'', or ''file'' if ''name'' is an alias, shell reserved word, function, builtin, or disk file, respectively. If the ''name'' is not found, then nothing is printed, and an exit status of false is returned. If the __-p__ option is used, __type__ either returns the name of the disk file that would be executed if ''name'' were specified as a command name, or nothing if type -t name would not return ''file''. If a command is hashed, __-p__ prints the hashed value, not necessarily the file that appears first in __PATH__. If the __-a__ option is used, __type__ prints all of the places that contain an executable named ''name''. This includes aliases and functions, if and only if the __-p__ option is not also used. The table of hashed commands is not consulted when using __-a__. __type__ returns true if any of the arguments are found, false if none are found. __ulimit__ [[__-SHacdflmnpstuv__ [[''limit'']] Provides control over the resources available to the shell and to processes started by it, on systems that allow such control. The __-H__ and __-S__ options specify that the hard or soft limit is set for the given resource. A hard limit cannot be increased once it is set; a soft limit may be increased up to the value of the hard limit. If neither __-H__ nor __-S__ is specified, both the soft and hard limits are set. The value of ''limit'' can be a number in the unit specified for the resource or one of the special values __hard__, __soft__, or __unlimited__, which stand for the current hard limit, the current soft limit, and no limit, respectively. If ''limit'' is omitted, the current value of the soft limit of the resource is printed, unless the __-H__ option is given. When more than one resource is specified, the limit name and unit are printed before the value. Other options are interpreted as follows: __-a__ All current limits are reported __-c__ The maximum size of core files created __-d__ The maximum size of a process's data segment __-f__ The maximum size of files created by the shell __-l__ The maximum size that may be locked into memory __-m__ The maximum resident set size __-n__ The maximum number of open file descriptors (most systems do not allow this value to be set) __-p__ The pipe size in 512-byte blocks (this may not be set) __-s__ The maximum stack size __-t__ The maximum amount of cpu time in seconds __-u__ The maximum number of processes available to a single user __-v__ The maximum amount of virtual memory available to the shell If ''limit'' is given, it is the new value of the specified resource (the __-a__ option is display only). If no option is given, then __-f__ is assumed. Values are in 1024-byte increments, except for __-t__, which is in seconds, __-p__, which is in units of 512-byte blocks, and __-n__ and __-u__, which are unscaled values. The return status is 0 unless an invalid option or argument is supplied, or an error occurs while setting a new limit. __umask__ [[__-p__] [[__-S__] [[''mode''] The user file-creation mask is set to ''mode''. If ''mode'' begins with a digit, it is interpreted as an octal number; otherwise it is interpreted as a symbolic mode mask similar to that accepted by chmod(1). If ''mode'' is omitted, the current value of the mask is printed. The __-S__ option causes the mask to be printed in symbolic form; the default output is an octal number. If the __-p__ option is supplied, and ''mode'' is omitted, the output is in a form that may be reused as input. The return status is 0 if the mode was successfully changed or if no ''mode'' argument was supplied, and false otherwise. __unalias__ [[-__a__] [[''name'' ...] Remove each ''name'' from the list of defined aliases. If __-a__ is supplied, all alias definitions are removed. The return value is true unless a supplied ''name'' is not a defined alias. __unset__ [[-__fv__] [[''name'' ...] For each ''name'', remove the corresponding variable or function. If no options are supplied, or the __-v__ option is given, each ''name'' refers to a shell variable. Read-only variables may not be unset. If __-f__ is specifed, each ''name'' refers to a shell function, and the function definition is removed. Each unset variable or function is removed from the environment passed to subsequent commands. If any of __RANDOM__, __SECONDS__, __LINENO__, __HISTCMD__, __FUNCNAME__, __GROUPS__, or __DIRSTACK__ are unset, they lose their special properties, even if they are subsequently reset. The exit status is true unless a ''name'' does not exist or is readonly. __wait__ [[''n''] Wait for the specified process and return its termination status. ''n'' may be a process ID or a job specification; if a job spec is given, all processes in that job's pipeline are waited for. If ''n'' is not given, all currently active child processes are waited for, and the return status is zero. If ''n'' specifies a non-existent process or job, the return status is 127. Otherwise, the return status is the exit status of the last process or job waited for. !!RESTRICTED SHELL If __bash__ is started with the name __rbash__, or the __-r__ option is supplied at invocation, the shell becomes restricted. A restricted shell is used to set up an environment more controlled than the standard shell. It behaves identically to __bash__ with the exception that the following are disallowed or not performed: changing directories with __cd__ setting or unsetting the values of __SHELL__, __PATH__, __ENV__, or __BASH_ENV__ specifying command names containing __/__ specifying a file name containing a __/__ as an argument to the __.__ builtin command Specifying a filename containing a slash as an argument to the __-p__ option to the __hash__ builtin command importing function definitions from the shell environment at startup parsing the value of __SHELLOPTS__ from the shell environment at startup redirecting output using the using the __exec__ builtin command to replace the shell with another command adding or deleting builtin commands with the __-f__ and __-d__ options to the __enable__ builtin command specifying the __-p__ option to the __command__ builtin command turning off restricted mode with __set +r__ or __set +o restricted__. These restrictions are enforced after any startup files are read. When a command that is found to be a shell script is executed (see __COMMAND EXECUTION__ above), __rbash__ turns off any restrictions in the shell spawned to execute the script. !!SEE ALSO ''Bash Reference Manual'', Brian Fox and Chet Ramey ''The Gnu Readline Library'', Brian Fox and Chet Ramey ''The Gnu History Library'', Brian Fox and Chet Ramey ''Portable Operating System Interface (POSIX) Part 2: Shell and Utilities'', IEEE sh(1), ksh(1), csh(1) emacs(1), vi(1) readline(3) !!FILES ''/bin/bash'' The __bash__ executable ''/etc/profile'' The systemwide initialization file, executed for login shells ''~/.bash_profile'' The personal initialization file, executed for login shells ''~/.bashrc'' The individual per-interactive-shell startup file ''~/.bash_logout'' The individual login shell cleanup file, executed when a login shell exits ''~/.inputrc'' Individual ''readline'' initialization file !!AUTHORS Brian Fox, Free Software Foundation bfox@gnu.org Chet Ramey, Case Western Reserve University chet@ins.CWRU.Edu !!BUG REPORTS If you find a bug in __bash,__ you should report it. But first, you should make sure that it really is a bug, and that it appears in the latest version of __bash__ that you have. Once you have determined that a bug actually exists, use the ''bashbug'' command to submit a bug report. If you have a fix, you are encouraged to mail that as well! Suggestions and `philosophical' bug reports may be mailed to ''bug-bash@gnu.org'' or posted to the Usenet newsgroup __gnu.bash.bug__. ALL bug reports should include: The version number of __bash__ 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 ''bashbug'' 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 ''chet@ins.CWRU.Edu''. !!BUGS It's too big and too slow. There are some subtle differences between __bash__ and traditional versions of __sh__, mostly because of the __POSIX__ specification. Aliases are confusing in some uses. Shell builtin commands and functions are not stoppable/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 immediately executes the next command in the sequence. It suffices to place the sequence of commands between parentheses to force it into a subshell, which may be stopped as a unit. 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. ----
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