Advanced Bash & AutomationLesson 6.4

Environment variables and .env files in Linux

export, env, printenv, .env file pattern, source command, dotenv in scripts, /etc/environment, profile vs bashrc vs bash_profile, secrets management basics

Environment Variables Configure Programs at Runtime

Environment variables are key-value pairs accessible to any process. They are the standard way to pass config, secrets, and runtime settings to programs without hardcoding values. Never commit secrets to source control — use env vars.

Inspecting the Environment

# Print all environment variables
env
printenv

# Print a specific variable
printenv PATH
echo $HOME

# Check if a variable is set
if [[ -z "${DATABASE_URL:-}" ]]; then
  echo "DATABASE_URL is not set"
  exit 1
fi

Exporting and .env Files

# Set and export (makes it available to child processes)
export NODE_ENV=production
export PORT=3000

# .env file pattern
# .env contents:
# DATABASE_URL=postgres://user:pass@localhost/mydb
# SECRET_KEY=supersecret
# PORT=8080

# Source it in your script
source .env
# or
. .env

# Pass env vars to a single command without exporting globally
NODE_ENV=test npm test

Shell Init Files

~/.bashrc runs for every interactive non-login shell. ~/.bash_profile runs for login shells. Put PATH modifications and exports in ~/.bashrc (for interactive use) or /etc/environment (system-wide, all processes).

# Add to ~/.bashrc for permanent PATH addition
export PATH="$HOME/.local/bin:$PATH"