Introduction to nopt

nopt is a powerful and flexible command-line argument parser for Node.js applications. It allows you to easily define expected options, handle input arguments, and provide informative help messages. With its robust features, nopt is essential for building user-friendly CLI applications.

Setting Up nopt

  npm install nopt

Basic Usage

To start using nopt, import the module and define the options you want to handle.

  const nopt = require('nopt');
  const knownOpts = {
    "help": Boolean,
    "version": Boolean,
    "config": String,
    "verbose": Boolean,
  };
  const shortHands = {
    "h": ["--help"],
    "v": ["--version"],
    "c": ["--config"],
    "vv": ["--verbose"]
  };
  const parsed = nopt(knownOpts, shortHands, process.argv, 2);

Advanced Features of nopt

Default Values

  const defaults = {
    verbose: false,
    config: 'default-config.json'
  };
  const options = nopt(knownOpts, shortHands, process.argv, 2, defaults);

Custom Type Handlers

  const url = require('url');
  function urlHandler(input) {
    return url.parse(input);
  }
  const knownOpts = {
    "endpoint": urlHandler,
    "requestTimeout": Number
  };
  const options = nopt(knownOpts, {}, process.argv, 2);

Mixing Argument Types

  const options = nopt({
    "log-level": ["info", "warn", "error"],
    "port": [null, Number]
  }, {
    "l": "--log-level",
    "p": "--port"
  });

Building a CLI Application with nopt

Below is an example of a CLI application that uses nopt to handle various command-line options.

  // cli-app.js
  const nopt = require('nopt');
  const knownOpts = {
    "help": Boolean,
    "version": Boolean,
    "config": String,
    "verbose": Boolean,
    "port": Number
  };
  const shortHands = {
    "h": ["--help"],
    "v": ["--version"],
    "c": ["--config"],
    "vv": ["--verbose"],
    "p": ["--port"]
  };

  const parsed = nopt(knownOpts, shortHands, process.argv, 2);

  if (parsed.help) {
    console.log("Help: Use this CLI app with the following options...");
    process.exit(0);
  }

  if (parsed.version) {
    console.log("Version: 1.0.0");
    process.exit(0);
  }

  if (parsed.config) {
    console.log(`Loading config file: ${parsed.config}`);
    // Load configuration logic
  }

  if (parsed.verbose) {
    console.log("Verbose mode is ON");
  }

  console.log(`Server running on port: ${parsed.port || 8080}`);

Conclusion

nopt is a versatile and powerful tool for Node.js developers. Its ability to handle various argument types, provide default values, and integrate custom logic makes it an excellent choice for building robust CLI applications. Start leveraging the capabilities of nopt in your next Node.js project and enhance your command-line interfaces effortlessly.

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