Environment Variables

What are environment variables and how do you use them in Linux? How do you make them persistent?

Linuxbeginner

// interview question

What are environment variables and how do you use them in Linux? How do you make them persistent?

Sample answer

Environment variables are dynamic values that affect processes and programs. Set temporarily with export VAR=value, view with echo $VAR or printenv. For persistence: add to ~/.bashrc (user-specific) or /etc/environment (system-wide). Common vars include PATH, HOME, USER, and custom app configs.

Why this matters

Environment variables are crucial for configuring applications without hardcoding values. They're the standard way to pass configuration to containers, manage secrets (though not ideal for sensitive data), and customize behavior across environments like dev, staging, and production.

Code examples

Setting and viewing variables

bash

# Set variable for current session
export DATABASE_URL='postgres://localhost:5432/mydb'

# View specific variable
echo $DATABASE_URL

# View all environment variables
printenv

# Set variable for single command
DEBUG=true ./my-script.sh

Making variables persistent

bash

# Add to ~/.bashrc for user persistence
echo 'export API_KEY=abc123' >> ~/.bashrc
source ~/.bashrc

# Or add to /etc/environment for system-wide
sudo echo 'API_KEY=abc123' >> /etc/environment

# Check if variable is set
if [ -z "$API_KEY" ]; then
  echo 'API_KEY not set'
fi

Common mistakes to avoid

Forgetting to export variables (they won't be available to child processes)
Putting spaces around the = sign (VAR = value won't work)
Storing secrets in plain text environment variables in production

Likely follow-ups

What's the difference between setting a variable with and without export?
How do environment variables work with Docker containers?
Why shouldn't you store sensitive secrets in environment variables?

Answer out loud first, then check yourself against the model answer.

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#linux#environment#configuration#bash#fundamentals

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