The full pathname used to execute the current instance of Bash.

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. See Bash Startup Files.

The version number of the current instance of Bash.

A readonly array variable whose members hold version information for this instance of Bash. The values assigned to the array members are as follows:

An array variable (see Arrays) 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.

The numeric effective user id of the current user. This variable is readonly.

The editor used as a default by the `-e' option to the fc builtin command.

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:~'

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.

An array variable containing the list of groups of which the current user is a member. This variable is readonly.

Up to three characters which control history expansion, quick substitution, and tokenization (see History Interaction). The first character is the history-expansion-char, 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.

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.

Set to a value of `ignorespace', it means don't enter lines which begin with a space or tab into the history list. Set to a value of `ignoredups', it means don't 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.

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 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.

The name of the file to which the command history is saved. The default is `~/.bash_history'.

The maximum number of commands to remember on the history list. The default value is 500.

The maximum number of lines contained in the history file. When this variable is assigned a value, the history file is truncated, if necessary, to contain no more than that number of lines. The default value is 500. The history file is also truncated to this size after writing it when an interactive shell exits.

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. You can change the file interactively; the next time you attempt to complete a hostname, Bash will add the contents of the new file to the already existing database.

The name of the current host.

A string describing the machine Bash is running on.

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.

The name of the Readline startup file, overriding the default of `~/.inputrc'.

Used to determine the locale category for any category not specifically selected with a variable starting with LC_.

This variable overrides the value of LANG and any other LC_ variable specifying a locale category.

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 (see Filename Expansion).

This variable determines the interpretation of characters and the behavior of character classes within filename expansion and pattern matching (see Filename Expansion).

This variable determines the locale used to translate double-quoted strings preceded by a `$' (see Locale Translation).

The line number in the script or shell function currently executing.

A string that fully describes the system type on which Bash is executing, in the standard GNU cpu-company-system format.

How often (in seconds) that the shell should check for mail in the files specified in the MAILPATH or MAIL variables.

The previous working directory as set by the cd builtin.

If set to the value 1, Bash displays error messages generated by the getopts builtin command.

A string describing the operating system Bash is running on.

An array variable (see 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).

The process id of the shell's parent process. This variable is readonly.

If present, this contains a string which is a command to execute before the printing of each primary prompt ($PS1).

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 `#? '

This is the prompt printed before the command line is echoed when the `-x' option is set (see The Set Builtin). The first character of PS4 is replicated multiple times, as necessary, to indicate multiple levels of indirection. The default is `+ '.

The current working directory as set by the cd builtin.

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.

The default variable for the read builtin.

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.

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 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.

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.

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.

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.

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 that number of seconds if input does not arrive.

The numeric real user id of the current user. This variable is readonly.