Passing Node.js Program Command Line Arguments

Accessing Command Line Arguments in Node.js

JavaScript with Node.js

// server.js
const http = require('http');
const url = require('url');
const fs = require('fs');
const path = require('path');

// Get the folder from the command line arguments
const folder = process.argv[2];

// Check if the folder argument is provided
if (!folder) {
  console.error('Please provide a folder path');
  process.exit(1);
}

const server = http.createServer((req, res) => {
  const parsedUrl = url.parse(req.url);
  let pathname = path.join(folder, parsedUrl.pathname);

  fs.readFile(pathname, (err, data) => {
    if (err) {
      res.statusCode = 404;
      res.end(`File not found: ${pathname}`);
    } else {
      res.statusCode = 200;
      res.end(data);
    }
  });
});

server.listen(3000, () => {
  console.log('Server listening on port 3000');
  console.log(`Serving files from ${folder}`);
});

Launching the Server with a Specific Folder

Command Line

# Launch the server with the specified folder
$ node server.js path/to/your/folder

Explanation of the Command Line Arguments in Node.js

JavaScript with Node.js

// process.argv is an array containing command line arguments
// process.argv[0] is 'node'
// process.argv[1] is the path to the script being executed
// process.argv[2] and beyond are the additional command line arguments
console.log(process.argv);

/* Output when running 'node server.js folder':
  [
    '/usr/local/bin/node',
    '/path/to/server.js',
    'folder'
  ]
*/

Common Questions About Node.js Command Line Arguments

1. How do I access command line arguments in Node.js?
2. You can access command line arguments using the process.argv array.
3. What is the use of minimist in handling command line arguments?
4. minimist is a library that helps in parsing command line arguments into a more manageable object format.
5. Can I set default values for command line arguments?
6. Yes, libraries like yargs and minimist allow setting default values for arguments.
7. How can I enforce required arguments?
8. Using libraries like yargs, you can define which arguments are required and provide error messages if they are missing.
9. How do I handle different data types for command line arguments?
10. With libraries like minimist, you can specify argument types, such as number, boolean, or string.
11. What are argument aliases and how are they useful?
12. Argument aliases are alternative names for command line options, making the CLI more user-friendly. You can set aliases using libraries like yargs.
13. Is it possible to combine multiple arguments into one?
14. Yes, by using argument parsing libraries, you can combine multiple arguments and handle them as a single configuration object.
15. How do I handle errors in command line argument parsing?
16. Libraries like yargs provide built-in error handling mechanisms to display user-friendly error messages.
17. Can I use environment variables along with command line arguments?
18. Yes, it's common to use both environment variables and command line arguments for configuring Node.js applications.

Final Thoughts on Node.js Command Line Arguments

Understanding how to pass and access command line arguments in Node.js is crucial for building flexible and dynamic applications. By leveraging built-in modules and third-party libraries, developers can handle arguments efficiently, set defaults, and enforce requirements. This knowledge not only improves code robustness but also enhances user experience by providing clear and manageable command line options. Mastering these techniques is a valuable skill for any Node.js developer aiming to create configurable and scalable applications.