Introduction to Caporal

Caporal is a versatile and comprehensive command line framework for Node.js that is designed to make building CLI applications easier and more efficient. It provides a simple interface to define commands, arguments, options, and automated help generation.

Getting Started with Caporal

To start using Caporal, you need to install it via npm:

  npm install caporal --save

Basic Usage

Here is a simple example of a Caporal-based application:

  const caporal = require('caporal');

  caporal
    .version('1.0.0')
    .description('Simple CLI example')
    .command('greet', 'Greet someone')
    .argument('', 'Name to greet')
    .action((args) => {
      console.log(`Hello, ${args.name}!`);
    });

  caporal.parse(process.argv);

Defining Commands

Commands in Caporal can be defined using the .command() method. Each command can have its own description, arguments, and options. Here’s an example:

  caporal
    .command('calculate', 'Perform calculations')
    .argument('', 'First number')
    .argument('', 'Second number')
    .option('--operation <operation>', 'Operation to perform', caporal.STRING, 'add')
    .action((args, options) => {
      const { number1, number2 } = args;
      const { operation } = options;
      let result;
      switch (operation) {
        case 'add':
          result = number1 + number2;
          break;
        case 'subtract':
          result = number1 - number2;
          break;
        case 'multiply':
          result = number1 * number2;
          break;
        case 'divide':
          result = number1 / number2;
          break;
        default:
          result = 'Unknown operation';
      }
      console.log(`Result: ${result}`);
    });

Using Options

Options are similar to arguments but they are prefixed with dashes and have a name-value pair structure. An example of using options:

  caporal
    .command('serve', 'Start the server')
    .option('--port <port>', 'Port to bind on', caporal.INT, 3000)
    .action((args, options) => {
      const { port } = options;
      console.log(`Server is running on port ${port}`);
    });

Arguments and Variadic Arguments

Arguments can be positional or variadic. Variadic arguments help capture multiple values from the command line:

  caporal
    .command('concat', 'Concatenate words')
    .argument('[words...]', 'Words to concatenate', caporal.ARRAY)
    .action((args) => {
      console.log(args.words.join(' '));
    });

Generating Help

Caporal automatically generates help documentation based on the defined commands, arguments, and options. You can access the help by running:

  node yourapp.js --help

Application Example

Here is a more comprehensive example that combines multiple features of Caporal:

  const caporal = require('caporal');

  caporal
    .version('2.0.0')
    .description('Comprehensive CLI application')
    .command('math', 'Perform a mathematical operation')
    .argument('', 'Operation to perform (add, subtract, multiply, divide)')
    .argument('', 'First number')
    .argument('', 'Second number')
    .action((args) => {
      const { operation, number1, number2 } = args;
      let result;
      switch (operation) {
        case 'add':
          result = parseFloat(number1) + parseFloat(number2);
          break;
        case 'subtract':
          result = parseFloat(number1) - parseFloat(number2);
          break;
        case 'multiply':
          result = parseFloat(number1) * parseFloat(number2);
          break;
        case 'divide':
          if (number2 == 0) {
            console.error('Cannot divide by zero');
            process.exit(1);
          }
          result = parseFloat(number1) / parseFloat(number2);
          break;
        default:
          console.error('Unknown operation');
          process.exit(1);
      }
      console.log(`Result: ${result}`);
    });

  caporal
    .command('serve', 'Start the server')
    .option('--port <port>', 'Port to bind on', caporal.INT, 3000)
    .action((args, options) => {
      const { port } = options;
      console.log(`Server running on port ${port}`);
    });

  caporal.parse(process.argv);

With Caporal, you can easily build robust and user-friendly CLI applications with minimal effort. Its flexibility and powerful features make it a perfect choice for modern Node.js development.

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