05 - Process & Environment

The process Object

process is a global. No import needed. It gives you info about the running Node.js process.

console.log(process.version);   // v20.11.0
console.log(process.platform);  // "darwin", "linux", or "win32"
console.log(process.pid);       // 12345
console.log(process.cwd());     // /Users/you/project

Environment Variables

Access them through process.env. They're all strings.

console.log(process.env.HOME);  // /Users/you
console.log(process.env.PATH);  // /usr/local/bin:/usr/bin:...

Set them when running a command:

PORT=3000 node server.js

const port = process.env.PORT || 3000;
console.log(port); // "3000" (it's a string!)

Remember: process.env values are always strings. process.env.PORT is "3000", not 3000.

.env Files

Node.js 20.6+ has built-in .env support:

# .env
DATABASE_URL=postgresql://localhost:5432/mydb
API_KEY=abc123

node --env-file=.env app.js

console.log(process.env.DATABASE_URL);
// "postgresql://localhost:5432/mydb"

No extra packages needed. For older Node versions, people use the dotenv package.

Command Line Arguments

process.argv is an array of everything passed to the command.

node app.js hello world

console.log(process.argv);
// [
//   '/usr/local/bin/node',   // [0] path to node
//   '/Users/you/app.js',     // [1] path to your script
//   'hello',                 // [2] first argument
//   'world'                  // [3] second argument
// ]

const args = process.argv.slice(2);
console.log(args); // ['hello', 'world']

The first two elements are always node path and script path. Your actual arguments start at index 2.

Exit Codes

// Success (default)
process.exit(0);

// Error
process.exit(1);

Exit code 0 means success. Anything else means failure. Other tools (CI, scripts) check this to know if your program worked.

if (!process.env.DATABASE_URL) {
  console.error('DATABASE_URL is required');
  process.exit(1);
}

Standard I/O

Node.js has three standard streams:

// Write to stdout (normal output)
process.stdout.write('Hello\n');

// Write to stderr (errors, not captured by pipes)
process.stderr.write('Something went wrong\n');

// console.log uses stdout, console.error uses stderr
console.log('info');    // goes to stdout
console.error('error'); // goes to stderr

This matters when piping output:

node app.js > output.txt  # stdout goes to file, stderr still shows
node app.js 2> errors.txt # stderr goes to file

Handling Signals

In a real app, you'd add these to a server or long-running process. Here's a quick example you can test:

process.on('SIGINT', () => {
  console.log('Caught Ctrl+C, cleaning up...');
  process.exit(0);
});

process.on('SIGTERM', () => {
  console.log('Received kill signal, shutting down...');
  process.exit(0);
});

// Keep the process alive so you can test Ctrl+C
console.log('Running... press Ctrl+C to stop');
let seconds = 0;
setInterval(() => {
  seconds++;
  console.log(`Running for ${seconds}s...`);
}, 1000);

SIGINT is Ctrl+C. SIGTERM is what Docker and Kubernetes send to stop your process. Handle them for graceful shutdown.

Key Takeaways

process is global, gives you version, platform, pid, and cwd
process.env values are always strings, convert numbers yourself
Node 20.6+ supports --env-file=.env natively, no dotenv needed
process.argv.slice(2) gives you the actual command line arguments
Exit code 0 = success, anything else = failure
stdout is for output, stderr is for errors, they can be piped separately
Handle SIGINT and SIGTERM for graceful shutdown in servers