Yargs Patterns

yargs Patterns Skill

Comprehensive patterns and templates for building CLI applications with yargs, the modern Node.js argument parsing library.

Overview

yargs is a powerful argument parsing library for Node.js that provides:

• Automatic help generation
• Rich command syntax (positional args, options, flags)
• Type coercion and validation
• Subcommands with isolated option namespaces
• Middleware for preprocessing
• Completion scripts for bash/zsh

Quick Reference

Basic Setup

#!/usr/bin/env node
const yargs = require('yargs/yargs');
const { hideBin } = require('yargs/helpers');

yargs(hideBin(process.argv))
  .command('* <name>', 'greet someone', (yargs) => {
    yargs.positional('name', {
      describe: 'Name to greet',
      type: 'string'
    });
  }, (argv) => {
    console.log(`Hello, ${argv.name}!`);
  })
  .parse();

Subcommands

yargs(hideBin(process.argv))
  .command('init <project>', 'initialize a new project', (yargs) => {
    yargs
      .positional('project', {
        describe: 'Project name',
        type: 'string'
      })
      .option('template', {
        alias: 't',
        describe: 'Project template',
        choices: ['basic', 'advanced', 'minimal'],
        default: 'basic'
      });
  }, (argv) => {
    console.log(`Initializing ${argv.project} with ${argv.template} template`);
  })
  .command('build [entry]', 'build the project', (yargs) => {
    yargs
      .positional('entry', {
        describe: 'Entry point file',
        type: 'string',
        default: 'index.js'
      })
      .option('output', {
        alias: 'o',
        describe: 'Output directory',
        type: 'string',
        default: 'dist'
      })
      .option('minify', {
        describe: 'Minify output',
        type: 'boolean',
        default: false
      });
  }, (argv) => {
    console.log(`Building from ${argv.entry} to ${argv.output}`);
  })
  .parse();

Options and Flags

yargs(hideBin(process.argv))
  .option('verbose', {
    alias: 'v',
    type: 'boolean',
    description: 'Run with verbose logging',
    default: false
  })
  .option('config', {
    alias: 'c',
    type: 'string',
    description: 'Path to config file',
    demandOption: true  // Required option
  })
  .option('port', {
    alias: 'p',
    type: 'number',
    description: 'Port number',
    default: 3000
  })
  .option('env', {
    alias: 'e',
    type: 'string',
    choices: ['development', 'staging', 'production'],
    description: 'Environment'
  })
  .parse();

Validation

yargs(hideBin(process.argv))
  .command('deploy <service>', 'deploy a service', (yargs) => {
    yargs
      .positional('service', {
        describe: 'Service name',
        type: 'string'
      })
      .option('version', {
        describe: 'Version to deploy',
        type: 'string',
        coerce: (arg) => {
          // Custom validation
          if (!/^\d+\.\d+\.\d+$/.test(arg)) {
            throw new Error('Version must be in format X.Y.Z');
          }
          return arg;
        }
      })
      .option('replicas', {
        describe: 'Number of replicas',
        type: 'number',
        default: 1
      })
      .check((argv) => {
        // Cross-field validation
        if (argv.replicas > 10 && argv.env === 'development') {
          throw new Error('Cannot deploy more than 10 replicas in development');
        }
        return true;
      });
  }, (argv) => {
    console.log(`Deploying ${argv.service} v${argv.version} with ${argv.replicas} replicas`);
  })
  .parse();

Middleware

yargs(hideBin(process.argv))
  .middleware((argv) => {
    // Preprocessing middleware
    if (argv.verbose) {
      console.log('Running in verbose mode');
      console.log('Arguments:', argv);
    }
  })
  .middleware((argv) => {
    // Load config file
    if (argv.config) {
      const config = require(path.resolve(argv.config));
      return { ...argv, ...config };
    }
  })
  .command('run', 'run the application', {}, (argv) => {
    console.log('Application running with config:', argv);
  })
  .parse();

Advanced Features

Conflicts and Implies

yargs(hideBin(process.argv))
  .option('json', {
    describe: 'Output as JSON',
    type: 'boolean'
  })
  .option('yaml', {
    describe: 'Output as YAML',
    type: 'boolean'
  })
  .conflicts('json', 'yaml')  // Can't use both
  .option('output', {
    describe: 'Output file',
    type: 'string'
  })
  .option('format', {
    describe: 'Output format',
    choices: ['json', 'yaml'],
    implies: 'output'  // format requires output
  })
  .parse();

Array Options

yargs(hideBin(process.argv))
  .option('include', {
    describe: 'Files to include',
    type: 'array',
    default: []
  })
  .option('exclude', {
    describe: 'Files to exclude',
    type: 'array',
    default: []
  })
  .parse();

// Usage: cli --include file1.js file2.js --exclude test.js

Count Options

yargs(hideBin(process.argv))
  .option('verbose', {
    alias: 'v',
    describe: 'Verbosity level',
    type: 'count'  // -v, -vv, -vvv
  })
  .parse();

Templates

See templates/ directory for:

• basic-cli.js - Simple CLI with commands
• advanced-cli.js - Full-featured CLI with validation
• config-cli.js - CLI with configuration file support
• interactive-cli.js - CLI with prompts
• plugin-cli.js - Plugin-based CLI architecture

Scripts

See scripts/ directory for:

• generate-completion.sh - Generate bash/zsh completion
• validate-args.js - Argument validation helper
• test-cli.sh - CLI testing script

Examples

See examples/ directory for complete working examples.

Resources

• yargs Documentation
• yargs GitHub
• yargs Best Practices