Shell Variables

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 command.
REPLY: Set to the line of input read by the read builtin command 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. Assignments to .SM GROUPS have no effect and are silently discarded. If .SM GROUPS is unset, it loses its special properties, even if it is subsequently reset.
BASH: Expands to the full file name used to invoke this instance of .BR bash .
BASH_VERSION: Expands to a string describing the version of this instance of .BR bash .
BASH_VERSINFO: A readonly array variable whose members hold version information for this instance of .BR bash . The values assigned to the array members are as follows: .sp .5

BASH_VERSINFO[0\fP]
The major version number (the release\fP).

BASH_VERSINFO[1\fP]
The minor version number (the version\fP).

BASH_VERSINFO[2\fP]
The patch level.

BASH_VERSINFO[3\fP]
The build version.

BASH_VERSINFO[4\fP]
The release status (e.g., beta1\fP).

BASH_VERSINFO[5\fP]
The value of MACHTYPE\fP.
BASH_VERSINFO[0\fP]: The major version number (the release\fP).
BASH_VERSINFO[1\fP]: The minor version number (the version\fP).
BASH_VERSINFO[2\fP]: The patch level.
BASH_VERSINFO[3\fP]: The build version.
BASH_VERSINFO[4\fP]: The release status (e.g., beta1\fP).
BASH_VERSINFO[5\fP]: The value of MACHTYPE\fP.
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 .SM .BR RANDOM . If .SM RANDOM is unset, it loses its special 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 .SM .BR SECONDS , the value returned upon subsequent references is the number of seconds since the assignment plus the value assigned. If .SM SECONDS is unset, it loses its special properties, even if it is subsequently reset.
LINENO: Each time this parameter is referenced, the shell substitutes a decimal number representing the current sequential line number (starting with 1) within a script or function. When not in a script or function, the value substituted is not guaranteed to be meaningful. If .SM LINENO is unset, it loses its special properties, even if it is subsequently reset.
HISTCMD: The history number, or index in the history list, of the current command. If .SM HISTCMD is unset, it loses its special properties, even if it is subsequently reset.
FUNCNAME: The name of any currently-executing shell function. This variable exists only when a shell function is executing. Assignments to .SM FUNCNAME have no effect and are silently discarded. If .SM FUNCNAME 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 .SM 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 contain only a single command).
OPTARG: The value of the last option argument processed by the getopts builtin command (see .SM SHELL BUILTIN COMMANDS below).
OPTIND: The index of the next argument to be processed by the getopts builtin command (see .SM 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\fP 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 .SM "SHELL BUILTIN COMMANDS" below). The options appearing in .SM SHELLOPTS are those reported as on by set -o\fP. 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.
COMP_WORDS: An array variable (see Arrays\fP below) consisting of the individual words in the current command line. This variable is available only in shell functions invoked by the programmable completion facilities (see Programmable Completion\fP below).
COMP_CWORD: An index into ${COMP_WORDS}\fP of the word containing the current cursor position. This variable is available only in shell functions invoked by the programmable completion facilities (see Programmable Completion\fP below).
COMP_LINE: The current command line. This variable is available only in shell functions and external commands invoked by the programmable completion facilities (see Programmable Completion\fP below).
COMP_POINT: The index of the current cursor position relative to the beginning of the current command. If the current cursor position is at the end of the current command, the value of this variable is equal to ${#COMP_LINE}\fP. This variable is available only in shell functions and external commands invoked by the programmable completion facilities (see Programmable Completion\fP below).

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 commands (see .SM COMMAND EXECUTION below). The default path is system-dependent, and is set by the administrator who installs .BR bash . A common value is ``/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\fP 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 command. A sample value is ``.:~:/usr''.
BASH_ENV: If this parameter is set when bash\fP is executing a shell script, its value is interpreted as a filename containing commands to initialize the shell, as in .IR ~/.bashrc . The value of .SM BASH_ENV is subjected to parameter expansion, command substitution, and arithmetic expansion before being interpreted as a file name. .SM PATH is not used to search for the resultant file name.
MAIL: If this parameter is set to a file name and the .SM MAILPATH variable is not set, bash informs the user of the arrival of mail in the specified file.
MAILCHECK: Specifies how often (in seconds) bash checks for mail. The default is 60 seconds. When it is time to check for mail, the shell does so before displaying the primary prompt. If this variable is unset, the shell disables mail checking.
MAILPATH: A colon-separated list of file names to be checked for mail. The message to be printed when mail arrives in a particular file may be specified by separating the file name from the message with a `?'. When used in the text of the message, $_\fP expands to the name of the current mailfile. Example:

MAILPATH\fP='/var/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., /var/mail/$USER\fP).

PS1: The value of this parameter is expanded (see .SM PROMPTING below) and used as the primary prompt string. The default value is ``\s-\v\$ \fP''.
PS2: The value of this parameter is expanded as with PS1 and used as the secondary prompt string. The default is ``> \fP''.
PS3: The value of this parameter is used as the prompt for the select command (see .SM 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 .SM PS4 is replicated multiple times, as necessary, to indicate multiple levels of indirection. The default is ``+ \fP''.
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 %\fP 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. .sp .5

%%
A literal %\fP.

%[p\fP][l]R
The elapsed time in seconds.

%[p\fP][l]U
The number of CPU seconds spent in user mode.

%[p\fP][l]S
The number of CPU seconds spent in system mode.

%P
The CPU percentage, computed as (%U + %S) / %R.
%%: A literal %\fP.
%[p\fP][l]R: The elapsed time in seconds.
%[p\fP][l]U: The number of CPU seconds spent in user mode.
%[p\fP][l]S: The number of CPU seconds spent in system mode.
%P: The CPU percentage, computed as (%U + %S) / %R.

The optional p\fP is a digit specifying the precision\fP, 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\fP greater than 3 are changed to 3. If p\fP is not specified, the value 3 is used.

The optional l\fP specifies a longer format, including minutes, of the form MM\fPmSS\fP.FF\fPs. The value of p\fP determines whether or not the fraction is included.

If this variable is not set, bash\fP acts as if it had the value $'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS'\fP. 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 history (see .SM HISTORY below). The default value is 500.
HISTFILE: The name of the file in which command history is saved (see .SM HISTORY below). The default value is ~/.bash_history\fP. If unset, the command history is not saved when an interactive shell exits.
HISTFILESIZE: The maximum number of lines contained in the history file. When this variable is assigned a value, the history file is truncated, if necessary, to contain no more than that number of lines. The default value is 500. The history file is also truncated to this size after writing it when an interactive shell exits.
OPTERR: If set to the value 1, bash displays error messages generated by the getopts builtin command (see .SM SHELL BUILTIN COMMANDS below). .SM 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_\fP.
LC_ALL: This variable overrides the value of LANG\fP and any other LC_\fP variable specifying a locale category.
LC_COLLATE: This variable determines the collation order used when sorting the results of pathname expansion, and determines the behavior of range expressions, equivalence classes, and collating sequences within pathname expansion and pattern matching.
LC_CTYPE: This variable determines the interpretation of characters and the behavior of character classes within pathname expansion and pattern matching.
LC_MESSAGES: This variable determines the locale used to translate double-quoted strings preceded by a $\fP.
LC_NUMERIC: This variable determines the locale category used for number formatting.
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 .SM EOF character as the sole input. If set, the value is the number of consecutive .SM 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, .SM 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: The default editor for the fc builtin command.
FIGNORE: A colon-separated list of suffixes to ignore when performing filename completion (see .SM READLINE below). A filename whose suffix matches one of the entries in .SM 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 .SM .BR GLOBIGNORE , it is removed from the list of matches.
INPUTRC: The filename for the readline startup file, overriding the default of .FN ~/.inputrc (see .SM READLINE below).
HISTCONTROL: If set to a value of .IR ignorespace , lines which begin with a space character are not entered on the history list. If set to a value of .IR 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 .BR HISTIGNORE . This variable's function is superseded by .BR 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 .BR 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 match the complete line (no implicit `*\fP' 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, `&\fP' matches the previous history line. `&\fP' 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 .BR HISTIGNORE .
histchars: The two or three characters which control history expansion and tokenization (see .SM HISTORY EXPANSION below). The first character is the history expansion\fP character, the character which signals the start of a history expansion, normally `!\fP'. The second character is the quick substitution\fP character, which is used as shorthand for re-running the previous command entered, substituting one string for another in the command. The default is `^\fP'. 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 `#\fP'. 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 .FN /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 .SM HOSTFILE is set, but has no value, bash\fP attempts to read .FN /etc/hosts to obtain the list of possible hostname completions. When .SM HOSTFILE is unset, the hostname list is cleared.
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 .IR exact , the string supplied must match the name of a stopped job exactly; if set to .IR substring , the string supplied needs to match a substring of the name of a stopped job. The substring value provides functionality analogous to the %? job identifier (see .SM JOB CONTROL below). If set to any other value, the supplied string must be a prefix of a stopped job's name; this provides functionality analogous to the % job identifier.
COMPREPLY: An array variable from which bash\fP reads the possible completions generated by a shell function invoked by the programmable completion facility (see Programmable Completion\fP below).

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