Summary  
This chapter covers retrieving environment variables in code using process.env, which returns strings or undefined if a variable is unset, and emphasizes secure handling of sensitive values.

General domain of usage  
Application configuration

Ly8gQWNjZXNzaW5nIGFuIGVudmlyb25tZW50IHZhcmlhYmxlIGluIE5vZGUuanMKY29uc3Qgbm9kZUVudiA9IHByb2Nlc3MuZW52Lk5PREVfRU5WOwpjb25zb2xlLmxvZygiVGhlIGN1cnJlbnQgZW52aXJvbm1lbnQgaXM6Iiwgbm9kZUVudik7

When you use `process.env`, you retrieve environment variables as strings. If a variable is not set, accessing it returns `undefined`. Common use cases include:
- Storing secret keys and passwords;
- Configuring database connection details;
- Setting application mode (such as "development" or "production");
- Defining API endpoints or feature flags.

**Always be cautious when working with environment variables.** Avoid printing sensitive values to logs or exposing them in client-side code. Use environment variable management tools or `.env` files with care, ensuring these files are not committed to public repositories. This helps maintain the security and flexibility of your applications.

Explore how Node.js connects event-driven programming with powerful process management tools. Create custom event emitters, manage processes and signals, and control child processes for advanced application workflows. Combine these concepts to design efficient, scalable systems built on Node’s asynchronous architecture.

Explore the foundation of Node's asynchronous design and how the event-driven model powers its performance. Understand the events module, create custom event emitters, and handle data flow efficiently through listeners and event triggers.

Deepen your understanding of Node's event system by applying advanced patterns and connecting them to process control. Work with the global process object to manage environment variables, handle signals, and monitor application behavior.

Run external commands, manage background processes, and build complex workflows by combining event-driven and process-based approaches. Use the child_process module for inter-process communication and orchestrate multiple processes in real-world applications.

Accessing Environment Variables