Building CLI Tools

You've used CLI (Command Line Interface) tools like git, npm, and node. Now, let's build our own!

A CLI tool is just a Node.js script that you run from the terminal to perform tasks (like creating files, calculating math, or fetching data).

1. The Shebang Line (#!) 💥

To make a script executable like a real program (instead of typing node script.js), we add a special line at the top.

This tells the operating system: "Use Node.js to run this file."

2. Reading Arguments (process.argv) 📥

When you run node app.js hello world, how does your code know you typed "hello" and "world"?

It uses process.argv (Argument Vector). It's an array containing:

1. Path to Node.js executable.
2. Path to your script file.
3. Your arguments (starting from index 2).

3. Interactive Input (readline) 💬

Sometimes you want to ask the user a question.

4. Practical Example: File Creator 🛠️

Let's build a tool that creates a file with some text. Usage: node create.js <filename> <text>

5. Making it Global 🌍

To run your tool from any folder (just by typing mytool), you need to:

1. Add "bin" to your package.json.
2. Run npm link.

// package.json
{
  "name": "my-cool-cli",
  "bin": {
    "mytool": "./index.js"
  }
}

Now, typing mytool in the terminal runs your script!

Quiz

Key Takeaways

✅ process.argv reads command-line inputs.
✅ process.exit(1) quits with an error.
✅ readline takes interactive user input.
✅ bin in package.json creates global commands.

What's Next?

We've mastered the terminal. Now let's conquer the web! Next up: HTTP Server Basics.

Keep coding! 🚀