Variables

Enumerate

env	Displays environment variables.
printenv	Similar to env, also lists environment variables.
set	Lists shell variables and functions (bash-specific).
declare -p	Lists shell variables with their attributes (bash-specific).
export	Displays exported variables (visible to child processes).

Modify

export VAR_NAME=VALUE	Sets an environment variable for the current shell and child processes.
VAR_NAME=VALUE	Sets a variable for the current shell only (not inherited by child processes).

Sourcing files

Use source filename or . filename to import variables from a file into the current shell environment.

Environment Variables

PATH	Contains a colon-separated list of directories where executable files are located.
HOME	Stores the absolute path to the user's home directory.
USER (or LOGNAME)	Contains the username of the currently logged-in user.
SHELL	Specifies the default shell for the user.
PS1	Defines the primary shell prompt.
PS2	Defines the secondary prompt used when entering multi-line commands.
PS3	Specifies the prompt for the select loop in shell scripts.
PS4	Specifies the prompt for debugging shell scripts with the -x option.
PWD	Holds the current working directory.
OLDPWD	Contains the previous working directory.
TZ	Specifies the system's timezone.
IFS	Defines the Internal Field Separator, which is used to separate words in shell commands.
TERM	Specifies the type of terminal or terminal emulator being used.
EDITOR	Sets the default text editor used by some command-line utilities.
VISUAL	Specifies the default visual (graphical) editor used by some utilities.
LANG	Specifies the default system language and localization settings.
LC_*	A family of variables used for localization and character encoding settings.
MAIL	Points to the location of the user's mailbox or mail spool file.
MAILCHECK	Specifies how often to check for new mail.
MAILPATH	Contains a list of files to check for new mail.
LD_LIBRARY_PATH	Lists directories where the dynamic linker/loader searches for shared libraries.
LD_PRELOAD	Specifies shared libraries to be loaded before all others when a program is run.
MANPATH	Defines the path to the directory containing manual pages (man pages).

File Locations

Environment Variables	Often set in startup scripts like .bashrc, .bash_profile, or system-wide configuration files.
User Environment Variables	Typically set in the user's shell initialization files (e.g., .bashrc, .bash_profile, .profile) or by using the export command in the shell.
System Environment Variables	System-wide environment variables can be set in system-wide initialization scripts, such as /etc/environment on some Linux distributions.
Global System Variables	Some system-level variables are stored in system configuration files or directories. These can include variables related to network configuration, system parameters, and system behavior. These variables are often stored in files located in /etc or other system directories.
User-Specific Configuration Files	User-specific configuration files may store variables related to a specific user's environment and preferences. For example, the ~/.bashrc or ~/.bash_profile files can contain user-specific variables and configurations.