As in one of my last articles I posted about shell commands I decided to publish a proper list of the bash environment variables.
Environment variables are used by programs, scripts or users to store or access data needed for the running of a specific program or just to give the user information needed.As stated in my previous articles, remember that the Linux Shell is case-sensitive. You will find that the environment variables may and will certainly change slightly from distribution to distribution.You can see your environment variables by typing the command ”set” or “printenv” in your console.
Hope this helps anyone studying scripting, computer science or any related subject.
Default Bash Shell Environment Variables:
$* - Contains all of the command line parameters as a single text value.
$@ - Contains all of the command line parameters as separate text values.
$# - The number of command line parameters.
$? - The exit status of the most recently used foreground process.
$- - The current command line option flags.
$$ - The process ID (PID) of the current shell.
$! - The PID of the most recently executed background process.
$0 - The name of the command from the command line.
$ - The absolute pathname of the shell.
BASH - The full filename used to invoke the shell.
BASH_ARGC - The number of parameters in the current subroutine.
BASH_ARGV - An array containing all of the command line parameters specified.
BASH_COMMAND - The name of the command currently being executed.
BASH_ENV - When set, each bash script attempts to execute a startup file defined by this variable before running.
BASH_EXECUTION_STRING - The command used in the -c command line option.
BASH_LINENO - An array containing the line numbers of each command in the script.
BASH_REMATCH - An array containing text elements that match a specified regular expression.
BASH_SOURCE - An array containing source filenames for the declared functions in the shell.
BASH_SUBSHELL - The number of subshells spawned by the current shell.
BASH_VERSION - The version number of the current instance of the bash shell.
BASH_VERSINFO - A variable array that contains the individual major and minor version numbers of the current instance of the bash shell.
COLUMNS - Contains the terminal width of the terminal used for the current instance of the bash shell.
COMP_CWORD - An index into the variable COMP_WORDS, which contains the current cursor position.
COMP_LINE - The current command line.
COMP_POINT - The index of the current cursor position relative to the beginning of the current command.
COM_WORDBREAKS - A set of characters used as word separators when performing word completion.
COMP_WORDS - A variable array that contains the individual words on the current command line.
COMPREPLY - A variable array that contains the possible completion codes generated by a shell function.
DIRSTACK A - Variable array that contains the current contents of the directory stack.
EUID - The numeric effective user ID of the current user.
FCEDIT - The default editor used by the fc command.
FIGNORE - A colon-separated list of suffixes to ignore when performing filename completion.
FUNCNAME - The name of the currently executing shell function.
GLOBIGNORE - A colon-separated list of patterns defining the set of filenames to be ignored by filename expansion.
GROUPS - A variable array containing the list of groups of which the current user is a member.
histchars - Up to three characters that control history expansion.
HISTCMD – The history number of the current command.
HISTCONTROL - Controls what commands are entered in the shell history list.
HISTFILE - The name of the file to save the shell history list (.bash_history by default).
HISTFILESIZE - The maximum number of lines to save in the history file.
HISTIGNORE - A colon-separated list of patterns used to decide which commands are ignored for the history file.
HISTSIZE - The maximum number of commands stored in the history file.
HOSTFILE - Contains the name of the file that should be read when the shell needs to complete a hostname.
HOSTNAME - The name of the current host.
HOSTTYPE - A string describing the machine the bash shell is running on.
IGNOREEOF - The number of consecutive EOF characters the shell must receive before exiting. If this value doesn’t exist, the default is one.
INPUTRC - The name of the Readline initialization file (the default is .inputrc).
LANG - The local category for the shell.
LC_ALL – Overrides the LANG variable, defining a local category.
LC_COLLATE - Sets the collation order used when sorting string values.
LC_CTYPE - Determines the interpretation of characters used in filename expansion and pattern matching.
LC_MESSAGES - Determines the local setting used when interpreting double-quoted strings preceded by a dollar sign.
LC_NUMERIC - Determines the local setting used when formatting numbers.
LINENO - The line number in a script currently executing.
LINES - Defines the number of lines available on the terminal.
MACHTYPE - A string defining the system type in cpu-company-system format.
MAILCHECK - How often (in seconds) the shell should check for new mail (default is 60).
OLDPWD - The previous working directory used in the shell.
OPTERR - If set to 1, the bash shell displays errors generated by the getopts command.
OSTYPE - A string defining the operating system the shell is running on.
PIPESTATUS - A variable array containing a list of exit status values from the processes in the foreground process.
POSIXLY_CORRECT - If set, bash starts in POSIX mode.
PPID - The process ID (PID) of the bash shell’s parent process.
PROMPT_COMMAND - If set, the command to execute before displaying the primary prompt.
PS1 - The primary command line prompt string.
PS2 - The secondary command line prompt string.
PS3 - The prompt to use for the select command.
PS4 - The prompt displayed before the command line is echoed if the bash -x parameter is used.
PWD - The current working directory.
RANDOM - Returns a random number between 0 and 32767. Assigning a value to this variable seeds the random number generator.
REPLY - The default variable for the read command.
SECONDS - The number of seconds since the shell was started. Assigning a value resets the timer to the value.
SHELLOPTS - A colon-separated list of enabled bash shell options.
SHLVL - Indicates the shell level, incremented by one each time a new bash shell is started.
TIMEFORMAT - A format specifying how the shell displays time values.
TMOUT - The value of how long (in seconds) the select and read commands should wait for input. The default of zero indicates to wait indefinitely.
UID - The numeric real user ID of the current user.
Filed under: Linux, Linux Command Line Made Easy Tagged: Bash, Command-line interface, Environment variable, Operating system, Process identifier, Shell, Unix, Working directory
