Master Linux Environment and Shell Variables: Definitions, Commands, and Persistence

What Are Environment and Shell Variables?

In Linux, environment variables are key‑value pairs available to a program and all of its child processes, often used to store defaults like the editor, browser, or executable paths. Shell variables exist only in the current shell session and can hold temporary data such as the current user ID.

Syntax of Environment Variables

Single‑value variables are written as: KEY=value1 Multiple values are separated by a colon: KEY=value1:value2:value3 If a value contains spaces, wrap it in quotes:

KEY="value with spaces"

Common Environment and Shell Variables

Some frequently used variables include: TERM: terminal type USER: logged‑in user PWD: current working directory PATH: directories searched for executables LANG: locale and encoding

Typical shell‑specific variables are: BASHOPTS: enabled Bash options BASH_VERSION: human‑readable Bash version COLUMNS: width of output HISTSIZE: number of commands kept in history PS1: primary prompt string

Viewing Variables

Use the following commands: env or printenv: list all environment variables set: list both environment and shell variables plus functions

Example to query a single variable: $ printenv SHELL Output:

/bin/bash

Setting and Exporting Variables

Define a shell variable in the current session: $ MYVAR=lxlinux Export it to become an environment variable: $ export MYVAR Verify: $ printenv MYVAR To set a variable with a value containing spaces in one line: $ export MYNEWVAR="My New Variable" To remove a variable entirely, use unset:

$ unset MYVAR

Persisting Environment Variables

To avoid re‑defining variables each session, add them to startup files that Bash reads: /etc/environment: system‑wide variables /etc/profile: variables for login shells ~/.bashrc: user‑specific variables

After editing, load the changes with:

$ source ~/.bashrc

Conclusion

The article covered the essential concepts, common examples, and practical commands for managing Linux environment and shell variables, as well as how to make them persistent across sessions, providing a solid foundation for everyday command‑line work.