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(bashref.info)Bash Variables
Bash Variables ============== These variables are set or used by Bash, but other shells do not normally treat them specially. A few variables used by Bash are described in different chapters: variables for controlling the job control facilities (Note: Job Control Variables). `BASH' The full pathname used to execute the current instance of Bash. `BASH_ENV' If this variable is set when Bash is invoked to execute a shell script, its value is expanded and used as the name of a startup file to read before executing the script. Note: Bash Startup Files. `BASH_VERSION' The version number of the current instance of Bash. `BASH_VERSINFO' A readonly array variable (Note: Arrays) 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'. `COLUMNS' Used by the `select' builtin command to determine the terminal width when printing selection lists. Automatically set upon receipt of a `SIGWINCH'. `COMP_CWORD' An index into `${COMP_WORDS}' of the word containing the current cursor position. This variable is available only in shell functions invoked by the programmable completion facilities (Note: Programmable Completion). `COMP_LINE' The current command line. This variable is available only in shell functions and external commands invoked by the programmable completion facilities (Note: Programmable Completion). `COMP_POINT' The index of the current cursor position relative to the beginning of the current command. If the current cursor position is at the end of the current command, the value of this variable is equal to `${#COMP_LINE}'. This variable is available only in shell functions and external commands invoked by the programmable completion facilities (Note: Programmable Completion). `COMP_WORDS' An array variable consisting of the individual words in the current command line. This variable is available only in shell functions invoked by the programmable completion facilities (Note: Programmable Completion). `COMPREPLY' An array variable from which Bash reads the possible completions generated by a shell function invoked by the programmable completion facility (Note: Programmable Completion). `DIRSTACK' An array variable containing the current contents of the directory stack. Directories appear in the stack in the order they are displayed by the `dirs' builtin. Assigning to members of this array variable may be used to modify directories already in the stack, but the `pushd' and `popd' builtins must be used to add and remove directories. Assignment to this variable will not change the current directory. If `DIRSTACK' is unset, it loses its special properties, even if it is subsequently reset. `EUID' The numeric effective user id of the current user. This variable is readonly. `FCEDIT' The editor used as a default by the `-e' option to the `fc' builtin command. `FIGNORE' A colon-separated list of suffixes to ignore when performing filename completion. A file name whose suffix matches one of the entries in `FIGNORE' is excluded from the list of matched file names. A sample value is `.o:~' `FUNCNAME' The name of any currently-executing shell function. This variable exists only when a shell function is executing. Assignments to `FUNCNAME' have no effect and return an error status. If `FUNCNAME' is unset, it loses its special properties, even if it is subsequently reset. `GLOBIGNORE' A colon-separated list of patterns defining the set of filenames to be ignored by filename expansion. If a filename matched by a filename expansion pattern also matches one of the patterns in `GLOBIGNORE', it is removed from the list of matches. `GROUPS' An array variable containing the list of groups of which the current user is a member. Assignments to `GROUPS' have no effect and return an error status. If `GROUPS' is unset, it loses its special properties, even if it is subsequently reset. `histchars' Up to three characters which control history expansion, quick substitution, and tokenization (Note: History Interaction). The first character is the HISTORY EXPANSION character, that is, the character which signifies the start of a history expansion, normally `!'. The second character is the character which signifies `quick substitution' when seen as the first character on a line, normally `^'. 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, usually `#'. 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. `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. `HISTCONTROL' A value of `ignorespace' means to not enter lines which begin with a space or tab into the history list. A value of `ignoredups' means to not enter lines which match the last entered line. A value of `ignoreboth' combines the two options. Unset, or set to any other value than those above, means to save all lines on the history list. The second and subsequent lines of a multi-line compound command are not tested, and are added to the history regardless of the value of `HISTCONTROL'. `HISTFILE' The name of the file to which the command history is saved. The default value is `~/.bash_history'. `HISTFILESIZE' The maximum number of lines contained in the history file. When this variable is assigned a value, the history file is truncated, if necessary, to contain no more than that number of lines. The history file is also truncated to this size after writing it when an interactive shell exits. The default value is 500. `HISTIGNORE' A colon-separated list of patterns used to decide which command lines should be saved on the history list. Each pattern is anchored at the beginning of the line and must match the complete line (no implicit `*' is appended). Each pattern is tested against the line after the checks specified by `HISTCONTROL' are applied. In addition to the normal shell pattern matching characters, `&' matches the previous history line. `&' may be escaped using a backslash; the backslash is removed before attempting a match. The second and subsequent lines of a multi-line compound command are not tested, and are added to the history regardless of the value of `HISTIGNORE'. `HISTIGNORE' subsumes the function of `HISTCONTROL'. A pattern of `&' is identical to `ignoredups', and a pattern of `[ ]*' is identical to `ignorespace'. Combining these two patterns, separating them with a colon, provides the functionality of `ignoreboth'. `HISTSIZE' The maximum number of commands to remember on the history list. The default value is 500. `HOSTFILE' Contains the name of a file in the same format as `/etc/hosts' that should be read when the shell needs to complete a hostname. The list of possible hostname completions may be changed while the shell is running; the next time hostname completion is attempted after the value is changed, Bash adds the contents of the new file to the existing list. If `HOSTFILE' is set, but has no value, Bash attempts to read `/etc/hosts' to obtain the list of possible hostname completions. When `HOSTFILE' is unset, the hostname list is cleared. `HOSTNAME' The name of the current host. `HOSTTYPE' A string describing the machine Bash is running on. `IGNOREEOF' Controls the action of the shell on receipt of an `EOF' character as the sole input. If set, the value denotes the number of consecutive `EOF' characters that can be read as the first character on an input line before the shell will exit. If the variable exists but does not have a numeric value (or has no value) then the default is 10. If the variable does not exist, then `EOF' signifies the end of input to the shell. This is only in effect for interactive shells. `INPUTRC' The name of the Readline initialization file, overriding the default of `~/.inputrc'. `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 filename expansion, and determines the behavior of range expressions, equivalence classes, and collating sequences within filename expansion and pattern matching (Note: Filename Expansion). `LC_CTYPE' This variable determines the interpretation of characters and the behavior of character classes within filename expansion and pattern matching (Note: Filename Expansion). `LC_MESSAGES' This variable determines the locale used to translate double-quoted strings preceded by a `$' (Note: Locale Translation). `LC_NUMERIC' This variable determines the locale category used for number formatting. `LINENO' The line number in the script or shell function currently executing. `LINES' Used by the `select' builtin command to determine the column length for printing selection lists. Automatically set upon receipt of a `SIGWINCH'. `MACHTYPE' A string that fully describes the system type on which Bash is executing, in the standard GNU CPU-COMPANY-SYSTEM format. `MAILCHECK' How often (in seconds) that the shell should check for mail in the files specified in the `MAILPATH' or `MAIL' variables. The default is 60 seconds. When it is time to check for mail, the shell does so before displaying the primary prompt. If this variable is unset, or set to a value that is not a number greater than or equal to zero, the shell disables mail checking. `OLDPWD' The previous working directory as set by the `cd' builtin. `OPTERR' If set to the value 1, Bash displays error messages generated by the `getopts' builtin command. `OSTYPE' A string describing the operating system Bash is running on. `PIPESTATUS' An array variable (Note: Arrays) containing a list of exit status values from the processes in the most-recently-executed foreground pipeline (which may contain only a single command). `POSIXLY_CORRECT' If this variable is in the environment when `bash' starts, the shell enters POSIX mode (Note: Bash POSIX Mode) before reading the startup files, as if the `--posix' invocation option had been supplied. If it is set while the shell is running, `bash' enables POSIX mode, as if the command `set -o posix' had been executed. `PPID' The process ID of the shell's parent process. This variable is readonly. `PROMPT_COMMAND' If set, the value is interpreted as a command to execute before the printing of each primary prompt (`$PS1'). `PS3' The value of this variable is used as the prompt for the `select' command. If this variable is not set, the `select' command prompts with `#? ' `PS4' The value is the prompt printed before the command line is echoed when the `-x' option is set (Note: The Set Builtin). The first character of `PS4' is replicated multiple times, as necessary, to indicate multiple levels of indirection. The default is `+ '. `PWD' The current working directory as set by the `cd' builtin. `RANDOM' Each time this parameter is referenced, a random integer between 0 and 32767 is generated. Assigning a value to this variable seeds the random number generator. `REPLY' The default variable for the `read' builtin. `SECONDS' This variable expands to the number of seconds since the shell was started. Assignment to this variable resets the count to the value assigned, and the expanded value becomes the value assigned plus the number of seconds since the assignment. `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 (Note: The Set Builtin). 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 readonly. `SHLVL' Incremented by one each time a new instance of Bash is started. This is intended to be a count of how deeply your Bash shells are nested. `TIMEFORMAT' The value of this parameter is used as a format string specifying how the timing information for pipelines prefixed with the `time' reserved word should be displayed. The `%' character introduces an escape sequence that is expanded to a time value or other information. The escape sequences and their meanings are as follows; the braces denote optional portions. `%%' A literal `%'. `%[P][l]R' The elapsed time in seconds. `%[P][l]U' The number of CPU seconds spent in user mode. `%[P][l]S' The number of CPU seconds spent in system mode. `%P' The CPU percentage, computed as (%U + %S) / %R. The optional P is a digit specifying the precision, the number of fractional digits after a decimal point. A value of 0 causes no decimal point or fraction to be output. At most three places after the decimal point may be specified; values of P greater than 3 are changed to 3. If P is not specified, the value 3 is used. The optional `l' specifies a longer format, including minutes, of the form MMmSS.FFs. The value of P determines whether or not the fraction is included. If this variable is not set, Bash acts as if it had the value `$'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS'' If the value is null, no timing information is displayed. A trailing newline is added when the format string is displayed. `TMOUT' If set to a value greater than zero, the value is interpreted as the number of seconds to wait for input after issuing the primary prompt when the shell is interactive. Bash terminates after that number of seconds if input does not arrive. `UID' The numeric real user id of the current user. This variable is readonly.
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