Building a Simple CLI

Step-by-step guide to create a CLI tool using commander.js and plain Node.js to count words or lines in a file, plus comparison.

What is Commander.js?

Commander.js is a powerful Node.js library for building CLI applications.

It provides:

Command parsing
Option handling
Help generation

All with a clean and declarative API.

Using commander.js makes building CLIs in Node.js easy and clean.

Handles argument parsing.
Automatically generates help.
Supports options and arguments out of the box.

Goal

We will build a CLI tool that:

Accepts a file path as an argument.
Has options to count:
- Number of words (--words)
- Number of lines (--lines)

Approach 1: Using Commander.js

1. Initialize Project

mkdir file-counter-cli
cd file-counter-cli
npm init -y
npm install commander

2. Create CLI with Commander.js

#!/usr/bin/env node

const fs = require('fs');
const { Command } = require('commander');
const program = new Command();

program
  .name('file-counter')
  .description('CLI to count words or lines in a file')
  .version('1.0.0')
  .argument('<file>', 'Path to the file')
  .option('-w, --words', 'Count words')
  .option('-l, --lines', 'Count lines')
  .action((file, options) => {
    fs.readFile(file, 'utf8', (err, data) => {
      if (err) {
        console.error('Error reading file:', err.message);
        process.exit(1);
      }

      if (options.words) {
        const wordCount = data.split(/\s+/).filter(Boolean).length;
        console.log(`Word count: ${wordCount}`);
      }

      if (options.lines) {
        const lineCount = data.split(/\r?\n/).length;
        console.log(`Line count: ${lineCount}`);
      }

      if (!options.words && !options.lines) {
        console.log('Please provide --words and/or --lines');
      }
    });
  });

program.parse();

Approach 2: Plain Node.js without Commander.js

Create Simple CLI

#!/usr/bin/env node

const fs = require('fs');

// Get arguments manually
const args = process.argv.slice(2);
const file = args.find(arg => !arg.startsWith('--'));
const options = args.filter(arg => arg.startsWith('--'));

if (!file) {
  console.error('Error: No file specified.');
  process.exit(1);
}

fs.readFile(file, 'utf8', (err, data) => {
  if (err) {
    console.error('Error reading file:', err.message);
    process.exit(1);
  }

  if (options.includes('--words')) {
    const wordCount = data.split(/\s+/).filter(Boolean).length;
    console.log(`Word count: ${wordCount}`);
  }

  if (options.includes('--lines')) {
    const lineCount = data.split(/\r?\n/).length;
    console.log(`Line count: ${lineCount}`);
  }

  if (!options.includes('--words') && !options.includes('--lines')) {
    console.log('Please provide --words and/or --lines');
  }
});

Comparison

Feature	Commander.js	Plain Node.js
Argument Parsing	Built-in, declarative	Manual, error-prone
Help Generation	Auto-generated	Not available by default
Option Handling	Supports aliases, defaults	Manual string checks
Code Cleanliness	Clear, readable API	Messy with manual logic
Recommended Use Case	Complex CLI tools	Simple or one-off scripts

Example Usage

With Commander.js

file-counter sample.txt --words --lines

Without Commander.js

node index.js sample.txt --words --lines

Building a Simple CLI

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