Toolbox Aid

August 12th, 2024 10:14 AM Mr. Q Categories: Command

Variable	Description
HOME	Path to the current user’s home directory.
PATH	List of directories that the shell searches for executable files.
USER	Username of the currently logged-in user.
SHELL	Path to the current user’s default shell.
PWD	Current working directory.
OLDPWD	Previous working directory, before the last directory change.
LANG	Default system language and locale settings.
EDITOR	Default text editor used by commands like crontab -e.
HISTSIZE	Number of commands to remember in the command history.
HISTFILE	Path to the file where the command history is stored (e.g., ~/.bash_history).
LOGNAME	Username of the current user (same as USER).
MAIL	Path to the file where user mail is stored.
TERM	Terminal type used for communication between the terminal and the system.
TMPDIR	Directory for temporary files used by programs.
PS1	Primary prompt string for the shell. Defines the appearance of the command prompt.
PS2	Secondary prompt string for the shell, used for multi-line commands.
LANGUAGE	Language preferences for localization, often used alongside LANG.
LC_ALL	Overrides all other locale settings, used for setting language and regional preferences.
SSH_AUTH_SOCK	Path to the Unix domain socket used by the SSH agent for communication.
SSH_CLIENT	Contains the IP address, incoming port, and outgoing port of the SSH client session.
SSH_CONNECTION	Information about the SSH connection, including client IP, client port, server IP, and server port.
HOSTNAME	The system’s hostname.
DISPLAY	Used to specify the display server for graphical applications on a networked system.
XAUTHORITY	Location of the X server authority file, used for X session authentication.
TZ	Time zone setting for the system.
LD_LIBRARY_PATH	List of directories where the system looks for dynamic libraries.
MANPATH	Directories that contain manual pages, searched by the man command.
SHLVL	Shell level, indicating the number of nested shell sessions.
BASH_VERSION	Version of the Bash shell.
PROMPT_COMMAND	Command to be executed before the prompt is displayed, often used to update the terminal prompt.
HOSTTYPE	Describes the type of hardware running the system (e.g., x86_64).
OSTYPE	Describes the operating system (e.g., linux-gnu).
MACHTYPE	Describes the machine hardware and operating system (e.g., x86_64-pc-linux-gnu).
UID	User ID of the current user.
GID	Group ID of the current user.
PWD	Current working directory.
CDPATH	Directories to search when using the cd command.
IFS	Internal Field Separator, which determines how the shell splits input text into words (default is space, tab, newline).
HISTCONTROL	Controls how the command history is saved, with options like ignorespace and ignoredups.
HISTIGNORE	List of patterns to exclude from the command history.
HISTTIMEFORMAT	Format for timestamps in the history file, useful for tracking when commands were executed.

Examples

Check Environment Variables:

printenv

Print a Specific Variable:

echo $HOME

Set an Environment Variable Temporarily:

export VAR_NAME=value

Set an Environment Variable Permanently:
Add the export command to your shell’s startup file, e.g., ~/.bashrc or ~/.bash_profile:

echo 'export VAR_NAME=value' >> ~/.bashrc
source ~/.bashrc

Understanding and managing these environment variables allows for greater control over the behavior of the system and applications, enabling customization of the environment to suit specific needs.