Lesson 6.2: Environment variables

Shell variables and environment variables: setting, reading, exporting and unsetting them; the important ones ($HOME, $USER, $PATH, $PWD, $LANG); what PATH really does; and why secrets in variables can leak.

16 min

You will learn to

Set and read a shell variable
Explain the difference between a shell variable and an exported environment variable
List the environment with env and printenv
Explain and extend PATH
Set a variable for one command only

Key terms

Shell variable: A name with a value, stored in the current shell only. Created with NAME=value (no spaces), read with $NAME.
Environment variable: A variable marked for export: a copy is passed to every program started from the shell.
export / unset: export NAME (or export NAME=value) puts a variable into the environment; unset NAME deletes it.
env / printenv: Print the current environment; printenv NAME prints one value. env NAME=value command runs one command with an extra variable.
Important variables: HOME your home directory, USER your name, SHELL your login shell, PWD current directory, LANG language and character set, PATH command search path, EDITOR your preferred editor.
PATH: Colon-separated directories searched in order for a command name. The current directory is deliberately not included, which is why you type ./script.

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