yargs

What is yargs?

The yargs npm package is a command-line argument parser that helps in building interactive command line tools, by parsing arguments and generating an elegant user interface. It provides a simple and efficient way to handle command line arguments for Node.js applications.

What are yargs's main functionalities?

Command Parsing

Yargs allows you to define commands and associated options. This feature is useful for CLI applications that perform different actions based on the command provided.

const yargs = require('yargs/yargs')(process.argv.slice(2));
yargs.command('get', 'make a get HTTP request', () => {}, (argv) => {
  console.log(`Request made to URL: ${argv.url}`);
}).argv;

Option Parsing

Yargs can parse options (also known as flags or switches) with additional configuration such as aliases, types, and descriptions.

const yargs = require('yargs/yargs')(process.argv.slice(2));
yargs.option('verbose', {
  alias: 'v',
  type: 'boolean',
  description: 'Run with verbose logging'
}).argv;

Default Values

Yargs allows setting default values for options, which will be used if no value is provided by the user.

const yargs = require('yargs/yargs')(process.argv.slice(2));
yargs.default('port', 8080).argv;

Automatic Help and Version Information

Yargs can automatically generate help and version information for the CLI tool, making it easier for users to understand how to use the application.

const yargs = require('yargs/yargs')(process.argv.slice(2));
yargs.help().version().argv;

Custom Validation

Yargs provides a way to define custom validation rules for the provided arguments, ensuring that the input meets certain criteria before the application proceeds.

const yargs = require('yargs/yargs')(process.argv.slice(2));
yargs.option('port', {
  describe: 'The port to bind on',
  demandOption: true,
  number: true
}).check((argv, options) => {
  if (argv.port < 1024) {
    throw new Error('Port must be at least 1024');
  }
  return true;
}).argv;

Other packages similar to yargs

commander

Commander is another popular npm package for parsing command-line options. It provides a high-level API for defining commands and options, similar to yargs. Commander is known for its simplicity and declarative approach to command-line arguments.

minimist

Minimist is a minimalistic command-line argument parser. It is more lightweight than yargs and focuses on parsing a list of arguments into an object, without the additional features like command handling, help text generation, or validation.

meow

Meow is a CLI helper for creating Node.js command-line apps. It provides a simpler and more opinionated API compared to yargs, with built-in help text, version output, and flag aliasing. Meow is suitable for smaller projects that require less customization.

caporal

Caporal is a full-featured framework for building command-line applications. It offers a rich set of features including argument parsing, validation, autocomplete, and more. Caporal is more framework-like compared to yargs, which might be more suitable for complex CLI tools.

README

Yargs

Having problems? want to contribute? join our community slack.

Yargs be a node.js library fer hearties tryin' ter parse optstrings.

Yargs helps you build interactive command line tools, by parsing arguments and generating an elegant user interface. It gives you:

• commands and (grouped) options (my-program.js serve --port=5000).
• a dynamically generated help menu based on your arguments.

• bash-completion shortcuts for commands and options.
• and tons more.

Installation

npm i yargs --save

Simple Example

#!/usr/bin/env node
const argv = require('yargs').argv

if (argv.ships > 3 && argv.distance < 53.5) {
  console.log('Plunder more riffiwobbles!')
} else {
  console.log('Retreat from the xupptumblers!')
}

$ ./plunder.js --ships=4 --distance=22
Plunder more riffiwobbles!

$ ./plunder.js --ships 12 --distance 98.7
Retreat from the xupptumblers!

Complex Example

#!/usr/bin/env node
require('yargs') // eslint-disable-line
  .command('serve [port]', 'start the server', (yargs) => {
    yargs
      .positional('port', {
        describe: 'port to bind on',
        default: 5000
      })
  }, (argv) => {
    if (argv.verbose) console.info(`start server on :${argv.port}`)
    serve(argv.port)
  })
  .option('verbose', {
    alias: 'v',
    default: false
  })
  .argv

Run the example above with --help to see the help for the application.

Table of Contents

• Yargs' API
• Examples
• Parsing Tricks
  • Stop the Parser
  • Negating Boolean Arguments
  • Numbers
  • Arrays
  • Objects
• Advanced Topics
  • Composing Your App Using Commands
  • Building Configurable CLI Apps
  • Customizing Yargs' Parser
• Contributing