🚀 Making a CLI with Node.js

I recently started learning Node.js and JavaScript basics. To strengthen my understanding of backend and JavaScript fundamentals, we're going to build a simple CLI tool from scratch.

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📘 Theory

1. What is CLI?

A CLI (Command-Line Interface) is a text-based interface that allows users to interact with a computer's operating system or software by typing commands. (Think of cmd in Windows)

Source: Google

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2. Required Node.js Knowledge

• Path Module (Read article)

  • Only path.join() is enough for this project.

• File System Module (fs) (Read article)

  • Only fs.readFile and fs.writeFile are needed.
  • Use asynchronous methods for both.

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3. Required JavaScript Knowledge

• Basic Syntax

  • Writing console.log("Hello, World!")

• Control Flow

  • if, else
  • switch

• Loops

  • for, while

• Functions

  • Function declarations & calls
  • Arrow functions (=>)
  • Callback functions
  • Higher-order functions

• Async JS and DOM (Optional)

  • Promises
  • Async/Await
  • Basic DOM manipulation (optional)

📚 Resources

1. JavaScript Basics
2. Higher-order functions
3. Callback functions

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🛠️ Let's Start Coding

✅ Step 1: Read a File Using Pure Node.js

Create two files:

• a.txt → Add some sample text.
• index.js → Paste the following code:

// CLI to count words using plain Node.js
const fs = require('fs');

function ReadFile(filename) {
  fs.readFile(filename, 'utf-8', (err, data) => {
    if (err) {
      console.log("Error reading file:", err);
      return;
    }

    let total = 0;
    for (let i = 0; i < data.length; i++) {
      if (data[i] === " ") total++;
    }
    console.log("Total words (approx.):", total + 1); // +1 to include the last word
  });
}

// Static call
ReadFile('a.txt');

// Dynamic usage
ReadFile(process.argv[2]);  // e.g., `node index.js a.txt`

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❌ Problem

This approach gives you the basic logic but it isn't a real CLI tool — there’s:

• No help or description.
• No argument validation.
• No commands like count_word, etc.

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✅ Solution: Use the commander Library

We’ll now use commander, a popular package to build real CLIs in Node.js.

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🧑‍💻 Final CLI Tool (with Commander)

// CLI with commander to count words
const { Command } = require('commander');
const fs = require('fs');

const program = new Command();

program
  .name('Count')
  .description("CLI to count how many words are there in a file")
  .version('0.0.1');

// Define the CLI command
program
  .command('count_word')
  .description('Count how many words are in the given file')
  .argument('<file>', 'File to count words from')
  .action((file) => {
    fs.readFile(file, 'utf-8', (err, data) => {
      if (err) {
        console.log("Error:", err.message);
        return;
      }

      // Use regex to split and count actual words
      const words = data.trim().split(/\s+/);
      console.log(`There are ${words.length} words in the file.`);
    });
  });

program.parse();

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🧪 How to Use

Run this in the terminal:

node server.js count_word "C:\\Users\\HP\\Desktop\\my-corhot\\node-js\\b.txt"

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✅ Output

👇 Input File (b.txt)

Hey there!
This is a test file.

🖥 Terminal Output

There are 8 words in the file.

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📸 Screenshots