Understanding Linux Environment Variables

By Admin · Feb 25, 2026 · Updated Apr 23, 2026 · 65 views · 1 min read

What Are Environment Variables?

Environment variables are key-value pairs that configure the behavior of processes and applications. They store settings like paths, credentials, and runtime configurations.

Viewing Variables

# Show all environment variables
env
printenv

# Show a specific variable
echo $PATH
echo $HOME
printenv USER

Setting Variables

# Set for current session only
export MY_VAR="hello"
export DATABASE_URL="mysql://user:pass@localhost/mydb"

# Set for a single command
DATABASE_URL="..." php artisan migrate

Persistent Variables

# For current user — add to ~/.bashrc or ~/.profile
echo 'export MY_VAR="hello"' >> ~/.bashrc
source ~/.bashrc

# System-wide — add to /etc/environment
MY_VAR="hello"

# For systemd services
# In the .service file:
Environment=MY_VAR=hello
EnvironmentFile=/etc/myapp/env

Common System Variables

Variable	Purpose
`PATH`	Directories to search for executables
`HOME`	Current user home directory
`USER`	Current username
`SHELL`	Current shell
`LANG`	System locale
`EDITOR`	Default text editor
`TZ`	Timezone

Application Configuration

Modern applications use environment variables for configuration instead of config files:

# .env file (loaded by frameworks)
DB_HOST=localhost
DB_USER=myapp
DB_PASS=secretpassword
REDIS_URL=redis://localhost:6379
API_KEY=sk_live_xxx

Security

Never commit .env files to version control
Use chmod 600 .env to restrict access
Environment variables in docker run -e are visible in docker inspect