codex-lv4-may-2025

╔═══════════════════════════════════════════════════════════════╗
║                                                               ║
║    🌍  Environment Variables  🌍                             ║
║                                                               ║
║    ┌─────────────────────────────────┐                       ║
║    │ $ export PORT=3000              │                       ║
║    │ $ export API_KEY=secret123      │                       ║
║    │ $ echo $PORT                    │                       ║
║    │ 3000                            │                       ║
║    └─────────────────────────────────┘                       ║
║                                                               ║
║         Your app's secret configuration storage! 🎯          ║
║                                                               ║
╚═══════════════════════════════════════════════════════════════╝

All About Environment Variables

Environment variables are configuration values stored outside of your code that can be accessed by your application at runtime. They’re useful for keeping sensitive information (like API keys) out of your codebase and for configuring your app differently across environments (development, staging, production).

Basic Usage

Setting a Variable

Set an environment variable in your terminal:

PORT=3000

Exporting a Variable

The export command makes the variable available to child processes:

export PORT=3000

This sets the variable for the current session and any processes started from that session.

Viewing a Variable

Use echo to display the value of an environment variable:

echo $PORT

Persistent Configuration

Shell Configuration Files

To make environment variables persistent across terminal sessions, add them to your shell configuration file:

• Bash: ~/.bashrc
• Zsh: ~/.zshrc

Add a line like:

export PORT=3000

Then restart your terminal or run source ~/.bashrc (or source ~/.zshrc) to reload the configuration.

Project-Specific Files

For project-specific environment variables, use .env.local (or .env):

In .env.local or .env for your project.

PORT=3000
DATABASE_URL=postgresql://localhost:5432/mydb
API_KEY=your-secret-key

Then use a package like dotenv in Node.js to load these variables automatically.

Video Resource

For a more in-depth explanation, check out this video: Environment Variables Explained

Example: Express App with PORT

Here’s a simple Express application that uses the PORT environment variable:

const express = require('express');
const app = express();

const port = process.env.PORT || 3000;

app.get('/', (req, res) => {
  res.send('Hello World!');
});

app.listen(port, () => {
  console.log(`Server running on port ${port}`);
});

Running the App

To run this app with a custom port, set the PORT variable before starting the server:

PORT=8080 node app.js

Note: This will set the PORT environment variable only for this specific command because we did not use export. After the command finishes, the variable won’t persist in your terminal session. If you wanted it to persist, you would need to use export PORT=8080 first.

The server will start on port 8080. If no PORT is set, it defaults to 3000.