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Linux Environment Variables and PATH Explained

Set shell and environment variables with export, understand PATH, make settings permanent in .bashrc, create aliases, and keep secrets out of your commands.

Intermediate5 min readUpdated
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An environment variable is a named value that programs can read. Programs use them for settings such as the language, your home folder, or a database address.

See variables#

Terminal
echo $HOME
echo $USER
printenv SHELL
env | grep -c .
Output
/home/asha
asha
/bin/bash
10

env or printenv lists everything. By convention, names are in capitals.

Shell variables and environment variables#

A plain assignment creates a shell variable, which child programs cannot see. export makes it an environment variable:

Terminal
CITY=Hyderabad
bash -c 'echo "Child sees: [$CITY]"'
export CITY
bash -c 'echo "Child sees: [$CITY]"'
Output
Child sees: []
Child sees: [Hyderabad]

There must be no spaces around =. For a single command, put the value in front of it:

Terminal
GREETING=Namaste bash -c 'echo $GREETING'
echo "After: [$GREETING]"
Output
Namaste
After: []

This is how you pass settings to a program, as in PORT=3000 node app.js.

PATH#

When you type ls, the shell looks through the folders listed in PATH, in order, and runs the first match:

Terminal
echo $PATH | tr ':' '\n' | head -n 3
which python3
Output
/usr/local/bin
/usr/bin
/bin
/usr/bin/python3

"Command not found" often means that the program's folder is not in PATH. Add your own folder to the front:

Terminal
mkdir -p ~/bin
echo 'echo "Hello from my tool"' > ~/bin/mytool
chmod +x ~/bin/mytool
export PATH="$HOME/bin:$PATH"
mytool
which mytool
Output
Hello from my tool
/home/asha/bin/mytool

Make it permanent#

Variables disappear when the shell closes. Add them to ~/.bashrc, which runs for each new interactive shell:

Terminal
echo 'export EDITOR=nano' >> ~/.bashrc
echo 'export PATH="$HOME/bin:$PATH"' >> ~/.bashrc
tail -n 2 ~/.bashrc
Output
export EDITOR=nano
export PATH="$HOME/bin:$PATH"

Then load it into the current shell:

Terminal
source ~/.bashrc
FileUsed for
~/.bashrcYour interactive shell settings
~/.profileSettings at login
/etc/environmentSystem-wide variables

Aliases#

An alias is a short name for a command. Add these to ~/.bashrc too:

Terminal
alias ll='ls -lah'
alias gs='git status'
alias ..='cd ..'

Run alias to list them, and unalias name to remove one.

Secrets#

Do not type passwords directly on the command line, because they are saved in your history and may be visible in process lists. For development, keep them in a .env file, which you add to .gitignore:

Terminal
echo 'API_KEY=example-not-real' > .env
chmod 600 .env
set -a
source .env
set +a
bash -c 'echo "Key length: ${#API_KEY}"'
Output
Key length: 16

set -a exports everything assigned until set +a.

Common mistakes#

Practice#

Practice exercise

Run printenv APP_MODE so that it prints production, without exporting the variable, then show that APP_MODE is empty afterwards.

Show solution
Terminal
APP_MODE=production printenv APP_MODE
echo "[$APP_MODE]"
Output
production
[]

Key takeaway#

Next: Processes.

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