Environment Variables

Overview

Environment variables are named values that the shell and the programs it launches can read. They configure behavior — like where to find executables (PATH) or which editor to use (EDITOR) — without hardcoding values into programs. Understanding them is key to configuring tools and writing portable scripts.

Syntax / Usage

Set variables, export them to child processes, and read them with $.

NAME="Stackademic"        # a shell variable (this session only)
echo "$NAME"              # read the value

export API_URL="https://api.example.com"  # export to child processes
env                       # list all environment variables
echo "$PATH"              # show the executable search path
printenv HOME             # print a single variable

unset API_URL             # remove a variable

Examples

Set a variable for a single command without exporting it globally:

NODE_ENV=production node server.js

Add a directory to your PATH so its programs are runnable:

export PATH="$HOME/bin:$PATH"

Read a configuration value inside a script:

echo "Deploying to $API_URL"

Common Mistakes

• Forgetting export, so child processes can't see the variable
• Putting spaces around =, e.g. NAME = value, which the shell rejects
• Not quoting "$VAR", causing word-splitting when the value has spaces
• Overwriting PATH instead of appending, which breaks common commands
• Expecting variables set in one terminal session to persist to another

See Also

command-line-navigation command-line-shell-scripting