bash
User Commands BASH(1)NAME
bash - GNU Bourne-Again SHellSYNOPSIS
bash [options] [file] COPYRIGHT Bash is Copyright (C) 1989-1999 by the Free Software Founda- tion, 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 inter- prets 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 interac- tive. -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. -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 exe- cuted. -- 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. GNU Last change: 1999 Jan 20 1 User Commands BASH(1) --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. --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 if 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. --rcfile file Execute commands from file instead of the standard per- sonal initialization file ~/.bashrc if the shell is interactive (see INVOCATION below). --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 com- mands. If bash is invoked in this fashion, $0 is set to the name of the file, and the positional parameters are set to the remaining arguments. Bash reads and executes 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. GNU Last change: 1999 Jan 20 2 User Commands BASH(1) 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 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 $- includes i if bash is interactive, allowing a shell script or a startup file to test this state. The following paragraphs describe how bash executes its startup files. If any of the files exist but cannot be read, bash reports an error. Tildes are expanded in file names as described below under Tilde Expansion in the EXPAN- SION section. When bash is invoked as an interactive login shell, or as a non-interactive shell with the --login option, it first reads and executes commands from the file /etc/profile, if that file exists. After reading that file, it looks for ~/.bash_profile, ~/.bash_login, and ~/.profile, in that order, and reads and executes commands from the first one that exists and is readable. The --noprofile option may be used when the shell is started to inhibit this behavior. When a login shell exits, bash reads and executes commands from the file ~/.bash_logout, if it exists. When an interactive shell that is not a login shell is started, bash reads and executes commands from ~/.bashrc, if that file exists. This may be inhibited by using the --norc option. The --rcfile file option will force bash to read and execute commands from file instead of ~/.bashrc. When bash is started non-interactively, to run a shell script, for example, it looks for the variable BASH_ENV in the environment, expands its value if it appears there, and uses the expanded value as the name of a file to read and execute. Bash behaves as if the following command were exe- cuted: if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi 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 ~/.pro- file, in that order. The --noprofile option may be used to inhibit this behavior. When invoked as an interactive shell GNU Last change: 1999 Jan 20 3 User Commands BASH(1) 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 com- mand 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 gen- erally 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 effec- tive 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: | & ; ( ) < > space tab control operator A token that performs a control function. It is one of GNU Last change: 1999 Jan 20 4 User Commands BASH(1) the following symbols: || & && ; ;; ( ) | <newline> 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 com- mand: ! 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 assign- ments followed by blank-separated words and redirections, and terminated by a control operator. The first word speci- fies the command to be executed. 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 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. GNU Last change: 1999 Jan 20 5 User Commands BASH(1) 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 ter- minated by one of ;, &, or <newline>. 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 command && command2 command2 is executed if, and only if, command returns an exit status of zero. An OR list has the form command || command2 command2 is executed if and only if command 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 environ- ment do not remain in effect after the command com- pletes. The return status is the exit status of list. { list; } list is simply executed in the current shell environ- ment. list must be terminated with a newline or semi- colon. This is known as a group command. The return status is the exit status of list. ((expression)) The expression is evaluated according to the rules GNU Last change: 1999 Jan 20 6 User Commands BASH(1) 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 expan- sion, arithmetic expansion, command substitution, pro- cess 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 opera- tors, 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 ele- ment of this list in turn, and list is executed each time. If the in word is omitted, the for command exe- cutes 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. GNU Last change: 1999 Jan 20 7 User Commands BASH(1) 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 com- pletes. 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 or return 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 match- ing 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. fi if list; then list; [ elif list; then list; ] ... [ else list; ] 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 GNU Last change: 1999 Jan 20 8 User Commands BASH(1) 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 interac- tive 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 they are to represent themselves. 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 fol- lows, with the exception of <newline>. If a \<newline> pair appears, and the backslash is not itself quoted, the \<new- line> is treated as a line continuation (that is, it is removed from the input stream and effectively ignored). Enclosing characters in single quotes preserves the 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 excep- tion 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 follow- ing characters: $, `, ", \, or <newline>. 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). GNU Last change: 1999 Jan 20 9 User Commands BASH(1) Words of the form $'string' are treated specially. The word expands to string, with backslash-escaped characters replaced as specifed by the ANSI C standard. Backslash escape sequences, if present, are decoded as follows: \a alert (bell) \b backspace \e an escape character \f form feed \n new line \r carriage return \t horizontal tab \v vertical tab \\ backslash \nnn the character whose ASCII code is the octal value nnn (one to three digits) \xnnn the character whose ASCII code is the hexadecimal value nnn (one to three digits) The translated result is single-quoted, as if the dollar sign had not been present. A double-quoted string preceded by a dollar sign ($) will cause the string to be translated according to the current locale. If the current locale is 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 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, string expansion, command substitution, arithmetic expansion, and quote removal (see EXPANSION below). If the variable has its integer attribute set (see declare below in SHELL BUILTIN COMMANDS) then value is sub- ject to arithmetic expansion even if the $((...)) expansion is not used (see Arithmetic Expansion below). Word split- ting is not performed, with the exception of "$@" as GNU Last change: 1999 Jan 20 10 User Commands BASH(1) explained below under Special Parameters. Pathname expan- sion is not performed. Positional Parameters A positional parameter is a parameter denoted by one or more digits, other than the single digit 0. Positional parame- ters are assigned from the shell's arguments when it is invoked, and may be reassigned using the set builtin com- mand. Positional parameters may not be assigned to with assignment statements. The positional parameters are tem- porarily 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 EXPAN- SION below). Special Parameters The shell treats several parameters specially. These param- eters 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, "$*" is equivalent to "$1c$2c...", where c is the first character of the value of the IFS variable. If IFS is unset, the param- eters are separated by spaces. If IFS is null, the parameters are joined without intervening separators. @ Expands to the positional parameters, starting from one. When the expansion occurs within double quotes, each parameter expands to a separate word. That is, "$@" is equivalent to "$1" "$2" ... When there are no positional parameters, "$@" and $@ expand to nothing (i.e., they are removed). # Expands to the number of positional parameters in decimal. ? Expands to the status of the most recently executed foreground pipeline. - Expands to the current option flags as specified upon invocation, by the 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 () sub- shell, 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 GNU Last change: 1999 Jan 20 11 User Commands BASH(1) 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 argu- ment 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: PPID The process ID of the shell's parent. This variable is readonly. PWD The current working directory as set by the cd command. OLDPWD The previous working directory as set by the cd com- mand. REPLY Set to the line of input read by the read builtin com- mand when no arguments are supplied. UID Expands to the user ID of the current user, initialized at shell startup. This variable is readonly. EUID Expands to the effective user ID of the current user, initialized at shell startup. This variable is readonly. GROUPS An array variable containing the list of groups of which the current user is a member. This variable is readonly. BASH Expands to the full file name used to invoke this instance of bash. BASH_VERSION Expands to a string describing the version of 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. GNU Last change: 1999 Jan 20 12 User Commands BASH(1) SHLVL Incremented by one each time an instance of bash is started. 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 spe- cial properties, even if it is subsequently reset. 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 subse- quent 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. LINENO Each time this parameter is referenced, the shell sub- stitutes 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 meaning- ful. If LINENO is unset, it loses its special proper- ties, 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. 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. 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 con- tain only a single command). GNU Last change: 1999 Jan 20 13 User Commands BASH(1) 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). 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. OSTYPE Automatically set to a string that describes the operating system on which bash is executing. The default is system-dependent. 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. 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. The following variables are used by the shell. In some cases, bash assigns a default value to a variable; these cases are noted below. 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 ``<space><tab><newline>''. PATH The search path for commands. It is a colon-separated list of directories in which the shell looks for com- mands (see COMMAND EXECUTION below). The default path is system-dependent, and is set by the administrator who installs bash. A common value is GNU Last change: 1999 Jan 20 14 User Commands BASH(1) ``/usr/gnu/bin:/usr/local/bin:/usr/ucb:/bin:/usr/bin:.''. 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. 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 com- mand. A sample value is ``.:~:/usr''. BASH_ENV If this parameter is set when bash is executing a shell script, its value is interpreted as a filename contain- ing commands to initialize the shell, as in ~/.bashrc. The value of BASH_ENV is subjected to parameter expan- sion, command substitution, and arithmetic expansion before being interpreted as a file name. PATH is not used to search for the resultant file name. MAIL If this parameter is set to a file name and the MAIL- PATH 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 pri- mary prompt. If this variable is unset, the shell dis- ables 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, $_ expands to the name of the current mailfile. Example: MAILPATH='/usr/spool/mail/bfox?"You have mail":~/shell-mail?"$_ has mail!"' Bash supplies a default value for this variable, but the location of the user mail files that it uses is system dependent (e.g., /usr/spool/mail/$USER). 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 GNU Last change: 1999 Jan 20 15 User Commands BASH(1) 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 MMmSS.FFs. The value of p deter- mines whether or not the fraction is included. If this variable is not set, bash acts as if it had the value $'\nreal\t%3lR\nuser\t%3lU\nsys%3lS'. If the value is null, no timing information is displayed. A trailing newline is added when the format string is displayed. HISTSIZE The number of commands to remember in the command his- tory (see HISTORY below). The default value is 500. 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 his- tory 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. OPTERR GNU Last change: 1999 Jan 20 16 User Commands BASH(1) 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. 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 deter- mines the behavior of range expressions, equivalence classes, and collating sequences within pathname expan- sion and pattern matching. LC_CTYPE This variable determines the interpretation of charac- ters and the behavior of character classes within path- name expansion and pattern matching. LC_MESSAGES This variable determines the locale used to translate double-quoted strings preceded by a $. PROMPT_COMMAND If set, the value is executed as a command prior to issuing each primary prompt. 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. 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. FCEDIT GNU Last change: 1999 Jan 20 17 User Commands BASH(1) The default editor for the fc builtin command. FIGNORE A colon-separated list of suffixes to ignore when per- forming 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:~''. 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. INPUTRC The filename for the readline startup file, overriding the default of ~/.inputrc (see READLINE below). 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. 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 fully specify the 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 char- acters, `&' 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. histchars The two or three characters which control history expansion and tokenization (see HISTORY EXPANSION GNU Last change: 1999 Jan 20 18 User Commands BASH(1) 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. 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 file may be changed interac- tively; the next time hostname completion is attempted bash adds the contents of the new file to the already existing database. 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 sub- string 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 analo- gous to the % job identifier. 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 GNU Last change: 1999 Jan 20 19 User Commands BASH(1) 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=(value1 ... valuen), 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 intro- duced above. Any element of an array may be referenced using ${name[subscript]}. The braces are required to avoid con- flicts 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 ${name[subscript]}. If subscript is * or @, the expansion is the number of elements in the array. Referencing an array variable without a subscript is equivalent to referencing element zero. The unset builtin is used to destroy arrays. unset name[subscript] destroys the array element at index sub- script. unset name, where name is an array, or unset name[subscript], where subscript is * or @, removes the entire array. The declare, local, and readonly builtins each accept a -a option to specify an array. The read builtin accepts a -a option to assign a list of words read from the standard input to an array. The set and declare builtins display array values in a way that allows them to be reused as assignments. EXPANSION Expansion is performed on the command line after it has been GNU Last change: 1999 Jan 20 20 User Commands BASH(1) split into words. There are seven kinds of expansion per- formed: brace expansion, tilde expansion, parameter and variable expansion, command substitution, arithmetic expan- sion, word splitting, and pathname expansion. The order of expansions is: brace expansion, tilde expan- sion, parameter, variable and arithmetic expansion and com- mand substitution (done in a left-to-right fashion), word splitting, and pathname expansion. On systems that can support it, there is an additional expansion available: process substitution. Only brace expansion, word splitting, and pathname expansion can change the number of words of the expansion; other expansions expand a single word to a single word. The only exceptions to this are the expansions of "$@" and "${name[@]}" as explained above (see 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. Pat- terns 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 con- tained within the braces, and the postscript is then appended to each resulting string, expanding left to right. Brace expansions may be nested. The results of each expanded string are not sorted; left to right order is preserved. For example, a{d,c,b}e expands into `ade ace abe'. Brace expansion is performed before any other expansions, and any characters special to other expansions are 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. This construct is typically used as shorthand when the com- mon prefix of the strings to be generated is longer than in the above example: GNU Last change: 1999 Jan 20 21 User Commands BASH(1) 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 expan- sion 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 substi- tuted 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 vari- able 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 pre- fixed 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 GNU Last change: 1999 Jan 20 22 User Commands BASH(1) 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 used in the rest of the substitution, rather than the value of parameter itself. This is known as indirect expansion. In each of the cases below, word is subject to tilde expan- sion, parameter expansion, command substitution, and arith- metic 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 stan- dard error and the shell, if it is not interactive, exits. Otherwise, the value of parameter is substi- tuted. ${parameter:+word} GNU Last change: 1999 Jan 20 23 User Commands BASH(1) 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 charac- ters of parameter, starting at the characters specified by offset. If length is omitted, expands to the sub- string of parameter, starting at the character speci- fied 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. ${#parameter} The length in characters of the value of parameter is substituted. If parameter is * or @, the value substi- tuted 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 begin- ning 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 long- est 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 param- eter with the shortest matching pattern (the ``%'' GNU Last change: 1999 Jan 20 24 User Commands BASH(1) 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 resul- tant 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 replac- ing the command substitution with the standard output of the command, with any trailing newlines deleted. Embedded new- lines 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. GNU Last change: 1999 Jan 20 25 User Commands BASH(1) 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 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 pro- cess 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 simultane- ously with parameter and variable expansion, command substi- tution, 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 <space><tab><newline>, the default, then any sequence of IFS characters serves to delimit words. If IFS has a value GNU Last change: 1999 Jan 20 26 User Commands BASH(1) 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 charac- ter in IFS that is not IFS whitespace, along with any adja- cent 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 argu- ment 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 dis- abled, 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 per- formed 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 charac- ter must always be matched explicitly. In other cases, the ``.'' character is not treated specially. See the descrip- tion 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 pat- terns 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. GNU Last change: 1999 Jan 20 27 User Commands BASH(1) Pattern Matching Any character that appears in a pattern, other than the spe- cial 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 minus sign denotes a range; any character lexically between those two characters, inclusive, is matched. If the first character follow- ing the [ is a ! or a ^ then any character not enclosed is matched. 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 col- lating symbol symbol. If the extglob shell option is enabled using the shopt buil- tin, several extended pattern matching operators are recog- nized. 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 pat- terns *(pattern-list) Matches zero or more occurrences of the given pat- terns +(pattern-list) GNU Last change: 1999 Jan 20 28 User Commands BASH(1) Matches one or more occurrences of the given pat- terns @(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 redirec- tion 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, and path- name expansion. 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. A failure to open or create a file causes the redirection to fail. GNU Last change: 1999 Jan 20 29 User Commands BASH(1) 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 filename 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 GNU Last change: 1999 Jan 20 30 User Commands BASH(1) >&word Of the two forms, the first is preferred. This is semanti- cally 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 com- mand. The format of here-documents is as follows: <<[-]word here-document delimiter No parameter expansion, command substitution, pathname expansion, or arithmetic 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 pair \<newline> 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 con- taining 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 GNU Last change: 1999 Jan 20 31 User Commands BASH(1) 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 excep- tion 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. 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 GNU Last change: 1999 Jan 20 32 User Commands BASH(1) 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 func- tion definition is itself a compound command. As a conse- quence, 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. 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 posi- tional parameters during its execution. The special parame- ter # is updated to reflect the change. Positional parame- ter 0 is unchanged. All other aspects of the shell execu- tion 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 com- mand 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 automati- cally 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. GNU Last change: 1999 Jan 20 33 User Commands BASH(1) 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 following list of operators is grouped into levels of equal-precedence operators. The lev- els are listed in order of decreasing precedence. - + unary minus and plus ! ~ logical and bitwise negation ** exponentiation * / % multiplication, division, remainder + - addition, subtraction << >> left and right bitwise shifts <= >= < > comparison == != equality and inequality & bitwise AND ^ bitwise exclusive OR | bitwise OR && logical AND || logical OR expr?expr:expr conditional evaluation = *= /= %= += -= assignment Shell variables are allowed as operands; parameter expansion is performed before the expression is evaluated. The value of a parameter is coerced to a long integer within an expression. A shell variable need not have its integer attribute turned on to be used in an expression. 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 over- ride the precedence rules above. GNU Last change: 1999 Jan 20 34 User Commands BASH(1) 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. -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 ter- minal. -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 GNU Last change: 1999 Jan 20 35 User Commands BASH(1) 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 nega- tive 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 redirec- tions are expanded. If any words remain after expan- sion, the first word is taken to be the name of the command and the remaining words are the arguments. GNU Last change: 1999 Jan 20 36 User Commands BASH(1) 3. Redirections are performed as described above under REDIRECTION. 4. The text after the = in each variable assignment under- goes tilde expansion, parameter expansion, command sub- stitution, 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 assign- ments 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 com- mand 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 fol- lowing 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 FUNC- TIONS. If the name does not match a function, the shell searches for it in the list of shell builtins. If a match is found, that builtin is invoked. 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 file names of executable files (see hash under SHELL BUILTIN COMMANDS below). A full search of the directories in PATH is per- formed 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 GNU Last change: 1999 Jan 20 37 User Commands BASH(1) set to the arguments given, if any. If this execution fails because the file is not in execut- able 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 reinitial- izes 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 them- selves. The arguments to the interpreter consist of a sin- gle optional argument following the interpreter name on the first line of the program, followed by the name of the pro- gram, 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 inher- ited 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 GNU Last change: 1999 Jan 20 38 User Commands BASH(1) 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 other- wise 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. 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 allows you to manipulate the environment in several ways. 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 modi- fied in the shell, less any pairs removed by the unset com- mand, plus any additions via the export and declare -x GNU Last change: 1999 Jan 20 39 User Commands BASH(1) commands. The environment for any simple command or function may be augmented temporarily by prefixing it with parameter assign- ments, 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 com- mand 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, bash uses the value of 128+signal as the exit status. If a command is not found, the child process created to exe- cute 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 suc- cessful, 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 exe- cuted, 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 SIG- INT and SIGQUIT as well. Commands run as a result of com- mand substitution ignore the keyboard-generated job control GNU Last change: 1999 Jan 20 40 User Commands BASH(1) signals SIGTTIN, SIGTTOU, and SIGTSTP. The shell exits by default upon receipt of a SIGHUP. Before exiting, it 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 COM- MANDS 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 wait- ing for an asynchronous command via the wait builtin, the reception of a signal for which a trap has been set will cause the wait builtin to return immediately with an exit 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 pro- cess ID of the last process in the pipeline associated with this job is 25647. All of the processes in a single pipe- line 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 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 sig- nals 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 GNU Last change: 1999 Jan 20 41 User Commands BASH(1) 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 ter- minal driver, which, unless caught, suspends the process. If the operating system on which bash is running supports job control, bash allows you to use it. Typing the suspend character (typically ^Z, Control-Z) while a process is run- ning causes that process to be stopped and returns you 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 fore- ground: %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. 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 GNU Last change: 1999 Jan 20 42 User Commands BASH(1) 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 charac- ters that are decoded as follows: \a an ASCII bell character (07) \d the date in "Weekday Month Date" format (e.g., "Tue May 26") \e an ASCII escape character (033) \h the hostname up to the first `.' \H the hostname \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 \u the username of the current user \v the version of bash (e.g., 2.00) \V the release of bash, version + patchlevel (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 dif- ferent: the history number of a command is its position in the history list, which may include commands restored from the history file (see 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, string 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). GNU Last change: 1999 Jan 20 43 User Commands BASH(1) 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 inter- face 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 nor- mally act as a repeat count. Sometimes, however, it is the sign of the argument that is significant. Passing a nega- tive argument to a command that acts in the forward direc- tion (e.g., kill-line) causes that command to act in a back- ward direction. Commands whose behavior with arguments devi- ates 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 initializa- tion file (the inputrc file). The name of this file is taken from the value of the INPUTRC variable. If that vari- able is unset, the default is ~/.inputrc. When a program which uses the readline library starts up, the initializa- tion 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. GNU Last change: 1999 Jan 20 44 User Commands BASH(1) 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 com- mand 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- pre- fixes, 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: "> output" 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 > output into the line). In the second form, "keyseq":function-name or macro, keyseq differs from keyname above in that strings denoting an entire key sequence may be specified by placing the sequence within double quotes. Some GNU Emacs style key escapes can be used, as in the following example. "\C-u": universal-argument "\C-x\C-r": re-read-init-file "\e[11~": "Function Key 1" In this example, C-u is again bound to the function 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 GNU Last change: 1999 Jan 20 45 User Commands BASH(1) \\ 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 character whose ASCII code is the octal value nnn (one to three digits) \xnnn the character whose ASCII code is the hexadecimal value nnn (one to three digits) When entering the text of a macro, single or double quotes must be used to indicate a macro definition. Unquoted text is assumed to be a function name. In the macro body, the backslash escapes described above are expanded. Backslash will quote any other character in the macro text, including " and '. 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 GNU Last change: 1999 Jan 20 46 User Commands BASH(1) 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 prepending 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 appli- cation 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 read- line attempts word completion. 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 char- acters 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 ter- minate an incremental search. keymap (emacs) Set the current readline keymap. The set of valid GNU Last change: 1999 Jan 20 47 User Commands BASH(1) 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 (*). 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 con- ditional 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 key- map 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 GNU Last change: 1999 Jan 20 48 User Commands BASH(1) 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 particu- lar value. This could be used to bind key sequences to functions useful for a specific pro- gram. 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 "\C-xq": "\eb\"\ef\"" $endif $endif This command, as seen in the previous example, ter- minates an $if command. $else Commands in this branch of the $if directive are exe- cuted 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 typ- ing 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 ter- minate an incremental search. If that variable has not been assigned a value the Escape and Control-J characters will GNU Last change: 1999 Jan 20 49 User Commands BASH(1) 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 for- ward 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. 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. 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 this, or the 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 GNU Last change: 1999 Jan 20 50 User Commands BASH(1) 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, mov- ing 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 current cursor position (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 (usu- ally the second word on the previous line) at point (the current cursor position). With an argument n, insert the nth word from the previous command (the words in the previous command begin with word 0). A negative argument inserts the nth 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. GNU Last change: 1999 Jan 20 51 User Commands BASH(1) 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 descrip- tion 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 under the cursor. 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 cur- sor is at the end of the line, in which case the char- acter behind the cursor is deleted. By default, this is not bound to a key. 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 char- acter at point. Point moves forward as well. If point is at the end of the line, then transpose the two GNU Last change: 1999 Jan 20 52 User Commands BASH(1) characters before point. Negative arguments don't work. transpose-words (M-t) Drag the word behind the cursor past the word in front of the cursor moving the cursor over that word as well. 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 the current cursor position 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 the cursor is. kill-word (M-d) Kill from the cursor to the end of the current word, or if between words, to the end of the next word. Word boundaries are the same as those used by forward-word. backward-kill-word (M-Rubout) Kill the word behind the cursor. Word boundaries are the same as those used by backward-word. unix-word-rubout (C-w) Kill the word behind the cursor, using white space as a word boundary. The word boundaries are different from backward-kill-word. delete-horizontal-space (M-\) Delete all spaces and tabs around point. kill-region Kill the text between the point and mark (saved cursor position). This text is referred to as the 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. GNU Last change: 1999 Jan 20 53 User Commands BASH(1) 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 the cursor. 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, exe- cuting universal-argument again ends the numeric argu- ment, 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 vari- able (if the text begins with $), username (if the text begins with ~), hostname (if the text begins with @), or command (including aliases and functions) in turn. If none of these produces a match, filename completion is attempted. possible-completions (M-?) List the possible completions of the text before point. insert-completions (M-*) Insert all completions of the text before point that would have been generated by possible-completions. menu-complete Similar to complete, but replaces the word to be com- pleted with a single match from the list of possible completions. Repeated execution of menu-complete steps through the list of possible completions, inserting each match in turn. At the end of the list of comple- tions, the bell is rung and the original text is restored. An argument of n moves n positions forward in the list of matches; a negative argument may be used GNU Last change: 1999 Jan 20 54 User Commands BASH(1) to move backward through the list. This command is intended to be bound to TAB, but is unbound by default. delete-char-or-list Deletes the character under the cursor if not at the beginning or end of the line (like delete-char). If at the end of the line, behaves identically to possible- completions. This command is unbound by default. complete-filename (M-/) Attempt filename completion on the text before point. possible-filename-completions (C-x /) List the possible completions of the text before point, treating it as a filename. complete-username (M-~) Attempt completion on the text before point, treating it as a username. possible-username-completions (C-x ~) List the possible completions of the text before point, treating it as a username. complete-variable (M-$) 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 possi- ble completion matches. complete-into-braces (M-{) Perform filename completion and return the list of pos- sible 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 key- board macro. GNU Last change: 1999 Jan 20 55 User Commands BASH(1) end-kbd-macro (C-x )) Stop saving the characters typed into the current key- board 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 incor- porate 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 com- mand that is bound to the corresponding uppercase char- acter. 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 exe- cuting 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-<space>) Set the mark to the current point. If a numeric argu- ment 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 posi- tion 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. This makes the current line a shell comment. glob-expand-word (C-x *) GNU Last change: 1999 Jan 20 56 User Commands BASH(1) The word before point is treated as a pattern for path- name 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. 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 text of the last HISTSIZE commands (default 500) is saved in a history list. The shell stores each command in the history list prior to parameter and variable expansion (see 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). HISTFILE is truncated, if necessary, to contain no more than HIST- FILESIZE lines. 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 descrip- tion 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 can be used to display or GNU Last change: 1999 Jan 20 57 User Commands BASH(1) modify the history list and manipulate the history file. When using the 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 simi- lar 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 his- tory 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 con- sidered 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 GNU Last change: 1999 Jan 20 58 User Commands BASH(1) substitutions are not immediately passed to the shell parser. Instead, the expanded line is reloaded into the readline editing buffer for further modification. If read- line 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 begin- ning 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 nth word. ^ The first argument. That is, word 1. GNU Last change: 1999 Jan 20 59 User Commands BASH(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 specifica- tion, 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 substitu- tions. 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 char- acter of the event line. The delimiter may be quoted in old and new with a single backslash. If & appears in new, it is replaced by old. A single backslash will quote the &. If old is null, it is set to the last old substituted, or, if no previous history substitutions took place, the last string in a !?string[?] search. & 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 delim- iter 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. GNU Last change: 1999 Jan 20 60 User Commands BASH(1) : [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. 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 job- spec 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] 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., '"\C-x\C-r": re-read-init-file'. GNU Last change: 1999 Jan 20 61 User Commands BASH(1) Options, if supplied, have the following meanings: -m keymap Use keymap as the keymap to be affected by the subsequent bindings. Acceptable keymap names are emacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-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. 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 argu- ments, 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 rede- fined 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. GNU Last change: 1999 Jan 20 62 User Commands BASH(1) 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 other- wise. 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. Oth- erwise, the exit status of the command builtin is the exit status of command. continue [n] Resume the next iteration of the enclosing for, while, until, or select loop. If n is specified, resume at the nth enclosing loop. n must be > 1. If n is greater than the number of enclosing loops, the last enclosing loop (the ``top-level'' loop) is resumed. The return value is 0 unless the shell is not executing a loop when continue is executed. declare [-afFirx] [-p] [name[=value]] typeset [-afFirx] [-p] [name[=value]] Declare variables and/or give them attributes. If no names are given then display the values of variables. The -p option will display the attributes and values of each name. When -p is used, additional options are ignored. The -F option inhibits the display of func- tion 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). GNU Last change: 1999 Jan 20 63 User Commands BASH(1) -f Use function names only. -i The variable is treated as an integer; arithmetic evaluation (see ARITHMETIC EVALUATION ) is per- formed when the variable is assigned a value. -r Make names readonly. These names cannot then be assigned values by subsequent assignment state- ments or unset. -x Mark names for export to subsequent commands via the environment. Using `+' instead of `-' turns off the attribute instead, with the exception that +a may not be used to destroy an array variable. When used in a function, makes each name local, as with the local command. The return value is 0 unless an invalid option is encoun- tered, 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 assign- ment 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 func- tion with -f. dirs [-clpv] [+n] [-n] Without options, displays the list of currently remem- bered directories. The default display is on a single line with directory names separated by spaces. Direc- tories are added to the list with the pushd command; the popd command removes entries from the list. +n Displays the nth entry counting from the left of the list shown by dirs when invoked without options, starting with zero. -n Displays the nth entry counting from the right of the list shown by dirs when invoked without options, starting with zero. -c Clears the directory stack by deleting all of the entries. -l Produces a longer listing; the default listing format uses a tilde to denote the home directory. -p Print the directory stack with one entry per line. -v Print the directory stack with one entry per line, prefixing each entry with its index in the stack. The return value is 0 unless an invalid option is sup- plied or n indexes beyond the end of the directory stack. disown [-ar] [-h] [jobspec ...] Without options, each jobspec is removed from the table GNU Last change: 1999 Jan 20 64 User Commands BASH(1) of active jobs. If the -h option is given, each job- spec 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 nei- ther the -a nor the -r option is supplied, the current job is used. If no jobspec is supplied, the -a option means to remove or mark all jobs; the -r option without a jobspec argument restricts operation to running jobs. The return value is 0 unless a jobspec does not specify a valid job. echo [-neE] [arg ...] Output the args, separated by spaces, followed by a newline. The return status is always 0. If -n is specified, the trailing newline is suppressed. If the -e option is given, interpretation of the following backslash-escaped characters is enabled. The -E option disables the interpretation of these escape characters, even on systems where they are interpreted by default. 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 character whose ASCII code is the octal value nnn (one to three digits) \xnnn the character whose ASCII code is the hexadecimal value nnn (one to three digits) enable [-adnps] [-f filename] [name ...] Enable and disable builtin shell commands. Disabling a builtin allows a disk command which has the same name as a shell builtin to be executed with 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 com- mand 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 argu- ments are given, or if the -p option is supplied, a list of shell builtins is printed. With no other GNU Last change: 1999 Jan 20 65 User Commands BASH(1) option arguments, the list consists of all enabled shell builtins. If -n is supplied, only disabled buil- tins 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 a problem loading a new builtin from a shared object. eval [arg ...] The args are read and concatenated together into a sin- gle command. This command is then read and executed by the shell, and its exit status is returned as the value of 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 in the zeroth arg passed to command. This is what login(1) does. The -c option causes com- mand to be executed with an empty environment. If -a is supplied, the shell passes name as the zeroth argu- ment 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 encoun- tered, one of the names is not a valid shell variable name, or -f is supplied with a name that is not a GNU Last change: 1999 Jan 20 66 User Commands BASH(1) 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 nega- tive number is used as an offset from the current com- mand 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 list- ing. 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. GNU Last change: 1999 Jan 20 67 User Commands BASH(1) getopts optstring name [args] getopts is used by shell procedures to parse positional parameters. optstring contains the option letters to be recognized; if a letter is followed by a colon, the option is expected to have an argument, which should be separated from it by white space. Each time it is invoked, getopts places the next option in the shell variable 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 argu- ment into the variable OPTARG. The shell does not reset OPTIND automatically; it must be manually reset between multiple calls to getopts within the same shell invocation if a new set of parameters is to be used. 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 report- ing 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 char- acter found is placed in OPTARG and no diagnostic mes- sage is printed. If a required argument is not found, and getopts is not silent, a question mark (?) is placed in 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] [name] For each name, the full file name of the command is GNU Last change: 1999 Jan 20 68 User Commands BASH(1) 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 no argu- ments 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 [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 return status is 0 unless no command matches pattern. history [-c] [n] 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 modi- fied. 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: -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. -c Clear the history list by deleting all the entries. -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 or an error occurs while reading or writing the history file. GNU Last change: 1999 Jan 20 69 User Commands BASH(1) 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 infor- mation. -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 informa- tion 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, return- ing 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 argu- ments 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 [name[=value] ...] For each argument, a local variable named name is created, and assigned value. When local is used within a function, it causes the variable name to have a visi- ble scope restricted to that function and its children. GNU Last change: 1999 Jan 20 70 User Commands BASH(1) With no operands, local writes a list of local vari- ables to the standard output. It is an error to use local when not within a function. The return status is 0 unless local is used outside a function, or an invalid name is supplied. logout Exit a login shell. popd [-n] [+n] [-n] Removes entries from the directory stack. With no arguments, removes the top directory from the stack, and performs a cd to the new top directory. Arguments, if supplied, have the following meanings: +n Removes the nth entry counting from the left of the list shown by dirs, starting with zero. For example: ``popd +0'' removes the first directory, ``popd +1'' the second. -n Removes the nth entry counting from the right of the list shown by dirs, starting with zero. For example: ``popd -0'' removes the last directory, ``popd -1'' the next to last. -n Suppresses the normal change of directory when removing directories from the stack, so that only the stack is manipulated. If the popd command is successful, a dirs is performed as well, and the return status is 0. popd returns false if an invalid option is encountered, the direc- tory 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 char- acter 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 specifi- cations, each of which causes printing of the next suc- cessive 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. GNU Last change: 1999 Jan 20 71 User Commands BASH(1) 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 nth directory (counting from the left of the list shown by dirs, starting with zero) is at the top. -n Rotates the stack so that the nth directory (counting from the right of the list shown by dirs, starting with zero) is at the top. -n Suppresses the normal change of directory when adding directories to the stack, so that only the stack is manipulated. dir Adds dir to the directory stack at the top, making it the new current working directory. If the pushd command is successful, a dirs is performed as well. If the first form is used, pushd returns 0 unless the cd to dir fails. With the second form, pushd returns 0 unless the directory stack is empty, a non-existent directory stack element is specified, or the directory change to the specified new current directory fails. pwd [-LP] Print the absolute file name of the current working directory. The file name 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, symbolic links are followed. The return status is 0 unless an error occurs while reading the name of the current directory or an invalid option is supplied. read [-er] [-a aname] [-p prompt] [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 charac- ter read and for line continuation. Options, if sup- plied, have the following meanings: -r Backslash does not act as an escape character. The backslash is considered to be part of the GNU Last change: 1999 Jan 20 72 User Commands BASH(1) line. In particular, a backslash-newline pair may not be used as a line continuation. -p Display prompt, without a trailing newline, before attempting to read any input. The prompt is displayed only if input is coming from a terminal. -a 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. -e If the standard input is coming from a terminal, readline (see READLINE above) is used to obtain the line. 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. readonly [-apf] [name ...] The given names are marked readonly; the values of these names may not be changed by subsequent assign- ment. 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 thatmay 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 speci- fied 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 out- side 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 vari- able 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 GNU Last change: 1999 Jan 20 73 User Commands BASH(1) following meanings: -a Automatically mark variables 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 pri- mary 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 !. -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 state- ments are placed in the environment for a com- mand, 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 --noedit- ing 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 GNU Last change: 1999 Jan 20 74 User Commands BASH(1) 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. 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. 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 perform- ing parameter expansion. If expansion is attempted on an unset variable, the shell prints an error message, and, if not interac- tive, exits with a non-zero status. -v Print shell input lines as they are read. -x After expanding each simple command, display the expanded value of PS4, followed by the com- mand and its expanded arguments. GNU Last change: 1999 Jan 20 75 User Commands BASH(1) -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 opera- tors. 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 args, even if some of them begin with a -. - Signal the end of options, cause all remaining args to be assigned to the positional parame- ters. The -x and -v options are turned off. If there are no args, the positional parameters remain unchanged. The options are off by default unless otherwise noted. Using + rather than - causes these options to be turned off. The options can also be specified as arguments to an invocation of the shell. The current set of options may be found in $-. The return status is always true unless an invalid option is encountered. shift [n] The positional parameters from n+1 ... are renamed to $1 .... Parameters represented by the numbers $# down to $#-n+1 are unset. n must be a non-negative number less than or equal to $#. If n is 0, no parameters are changed. If n is not given, it is assumed to be 1. If n is greater than $#, the positional parameters are not changed. The return status is greater than zero if n is greater than $# or less than zero; otherwise 0. shopt [-pqsu] [-o] [optname ...] Toggle the values of variables controlling optional shell behavior. With no options, or with the -p option, a list of all settable options is displayed, with an indication of whether or not each is set. The -p option causes output to be displayed in a form that may be reused as input. Other options have the follow- ing meanings: GNU Last change: 1999 Jan 20 76 User Commands BASH(1) -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 tran- sposed 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 GNU Last change: 1999 Jan 20 77 User Commands BASH(1) 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 vari- able 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 his- tory 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 semi- colon separators where possible. 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. nocaseglob If set, bash matches filenames in a case-insensitive fashion when performing GNU Last change: 1999 Jan 20 78 User Commands BASH(1) 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. 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 mes- sage 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. 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 CONDI- TIONAL EXPRESSIONS. Expressions may be combined using the following opera- tors, 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. GNU Last change: 1999 Jan 20 79 User Commands BASH(1) 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 EXPRES- SIONS, 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 condi- tional 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 argu- ment is !, the value is the negation of the two- argument test using the second and third argu- ments. If the first argument is exactly ( and the third argument is exactly ), the result is the one-argument test of the second argument. Other- wise, 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 GNU Last change: 1999 Jan 20 80 User Commands BASH(1) commands it invokes. If arg is -p then the trap com- mands 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>, or a signal number. If a sigspec is EXIT (0) the command arg is executed on exit from the shell. If a sigspec is DEBUG, the command arg is exe- cuted after every simple command (see SHELL GRAMMAR above). The -l option causes the shell to print a list of signal names and their corresponding numbers. Sig- nals ignored upon entry to the shell cannot be trapped or reset. Trapped signals are reset to their original values in a child process when it is created. The return status is false if any sigspec is invalid; oth- erwise trap returns true. type [-atp] name [name ...] With no options, indicate how each name would be inter- preted if used as a command name. If the -t option is used, type prints a string which is one of alias, key- word, 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 value of limit can be a number in the unit specified for the resource, or the value unlimited. The -H and -S options specify that the hard or soft limit is set for the given resource. A hard limit cannot be increased once it is set; a soft limit may be increased up to the value of the hard limit. If neither -H nor -S is specified, both the soft and hard limits are set. 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 GNU Last change: 1999 Jan 20 81 User Commands BASH(1) 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 is encountered, a non-numeric argument other than unlimited is supplied as limit, 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, or if the -S option is supplied, the current value of the mask is printed. The -S option causes the mask to be printed in symbolic form; the default output is an octal number. 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 names 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- GNU Last change: 1999 Jan 20 82 User Commands BASH(1) 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, or DIRSTACK are unset, they lose their special proper- ties, 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 termina- tion status. n may be a process ID or a job specifica- tion; if a job spec is given, all processes in that job's pipeline are waited for. If n is not given, all currently active child processes are waited for, and the return status is zero. If n specifies a non- 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 con- trolled 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 + importing function definitions from the shell environ- ment at startup + parsing the value of SHELLOPTS from the shell environ- ment at startup + redirecting output using the >, >|, <>, >&, &>, and >> redirection operators + using the exec builtin command to replace the shell with another command + adding or deleting builtin commands with the -f and -d GNU Last change: 1999 Jan 20 83 User Commands BASH(1) 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 res- tricted. These restrictions are enforced after any startup files are read. When a command that is found to be a shell script is exe- cuted (see COMMAND EXECUTION above), rbash turns off any restrictions in the shell spawned to execute the script.SEE ALSO
Bash Features, Brian Fox and Chet Ramey The Gnu Readline Library, Brian Fox and Chet Ramey The Gnu History Library, Brian Fox and Chet Ramey Utilities, IEEE Portable Operating System Interface (POSIX) Part 2: Shell and sh(1), ksh(1), csh(1) vi(1)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.ai.MIT.Edu 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. GNU Last change: 1999 Jan 20 84 User Commands BASH(1) 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 tradi- tional versions of sh, mostly because of the POSIX specifi- cation. 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.NOTES
Source for bash is available in the SUNWbashS package. GNU Last change: 1999 Jan 20 85