Commander.js Patterns Skill

Provides comprehensive Commander.js patterns, templates, and examples for building robust Node.js CLI applications with TypeScript support.

Overview

Commander.js is the complete solution for Node.js command-line interfaces. This skill provides battle-tested patterns for:

• Command class instantiation and configuration
• Options with flags, choices, and defaults
• Arguments (required, optional, variadic)
• Nested subcommands and command hierarchies
• Option class with advanced validation
• Action handlers and middleware
• Error handling and validation

Instructions

Basic Command Setup

1. Create program instance:

   import { Command } from 'commander';
   const program = new Command();
   
   program
     .name('mycli')
     .description('CLI description')
     .version('1.0.0');
   

2. Add simple command:

   program
     .command('init')
     .description('Initialize project')
     .action(() => {
       // Command logic
     });
   

3. Parse arguments:

   program.parse();
   

Command with Options

Use options for named flags with values:

program
  .command('deploy')
  .description('Deploy application')
  .option('-e, --env <environment>', 'target environment', 'dev')
  .option('-f, --force', 'force deployment', false)
  .option('-v, --verbose', 'verbose output')
  .action((options) => {
    console.log('Environment:', options.env);
    console.log('Force:', options.force);
    console.log('Verbose:', options.verbose);
  });

Command with Arguments

Use arguments for positional parameters:

program
  .command('deploy <environment>')
  .description('Deploy to environment')
  .argument('<environment>', 'target environment')
  .argument('[region]', 'optional region', 'us-east-1')
  .action((environment, region, options) => {
    console.log(`Deploying to ${environment} in ${region}`);
  });

Option Class Usage

For advanced option configuration:

import { Command, Option } from 'commander';

program
  .command('deploy')
  .addOption(
    new Option('-m, --mode <mode>', 'deployment mode')
      .choices(['fast', 'safe', 'rollback'])
      .default('safe')
      .makeOptionMandatory()
  )
  .addOption(
    new Option('-r, --replicas <count>', 'replica count')
      .argParser(parseInt)
      .default(3)
  )
  .action((options) => {
    console.log(`Mode: ${options.mode}, Replicas: ${options.replicas}`);
  });

Nested Subcommands

Create command hierarchies:

const config = program
  .command('config')
  .description('Manage configuration');

config
  .command('get <key>')
  .description('Get config value')
  .action((key) => {
    console.log(`Config ${key}:`, getConfig(key));
  });

config
  .command('set <key> <value>')
  .description('Set config value')
  .action((key, value) => {
    setConfig(key, value);
    console.log(`✓ Set ${key} = ${value}`);
  });

config
  .command('list')
  .description('List all config')
  .action(() => {
    console.log(getAllConfig());
  });

Variadic Arguments

Accept multiple values:

program
  .command('add <items...>')
  .description('Add multiple items')
  .action((items) => {
    console.log('Adding items:', items);
  });

// Usage: mycli add item1 item2 item3

Custom Argument Parsing

Transform argument values:

program
  .command('wait <delay>')
  .description('Wait for specified time')
  .argument('<delay>', 'delay in seconds', parseFloat)
  .action((delay) => {
    console.log(`Waiting ${delay} seconds...`);
  });

Global Options

Options available to all commands:

program
  .option('-c, --config <path>', 'config file path')
  .option('-v, --verbose', 'verbose output')
  .option('--no-color', 'disable colors');

program
  .command('deploy')
  .action((options, command) => {
    const globalOpts = command.parent?.opts();
    console.log('Config:', globalOpts?.config);
    console.log('Verbose:', globalOpts?.verbose);
  });

Error Handling

program
  .command('deploy <environment>')
  .action((environment) => {
    if (!['dev', 'staging', 'prod'].includes(environment)) {
      throw new Error(`Invalid environment: ${environment}`);
    }
    // Deploy logic
  });

program.exitOverride();
try {
  program.parse();
} catch (err) {
  console.error('Error:', err.message);
  process.exit(1);
}

Available Scripts

• validate-commander-structure.sh: Validates Commander.js CLI structure and patterns
• generate-command.sh: Scaffolds new command with options and arguments
• generate-subcommand.sh: Creates nested subcommand structure
• test-commander-cli.sh: Tests CLI commands with various inputs
• extract-command-help.sh: Extracts help text from CLI for documentation

Templates

TypeScript Templates

• basic-commander.ts: Minimal Commander.js setup
• command-with-options.ts: Command with various option types
• command-with-arguments.ts: Command with required/optional arguments
• nested-subcommands.ts: Multi-level command hierarchy
• option-class-advanced.ts: Advanced Option class usage
• full-cli-example.ts: Complete CLI with all patterns
• commander-with-inquirer.ts: Interactive prompts integration
• commander-with-validation.ts: Input validation patterns

JavaScript Templates

• basic-commander.js: ES modules Commander.js setup
• commonjs-commander.js: CommonJS Commander.js setup

Configuration Templates

• tsconfig.commander.json: TypeScript config for Commander.js projects
• package.json.template: Package.json with Commander.js dependencies

Examples

• basic-usage.md: Simple CLI with 2-3 commands
• options-arguments-demo.md: Comprehensive options and arguments examples
• nested-commands-demo.md: Building command hierarchies
• advanced-option-class.md: Option class validation and parsing
• interactive-cli.md: Combining Commander.js with Inquirer.js
• error-handling-patterns.md: Robust error handling strategies
• testing-commander-cli.md: Unit and integration testing patterns

Commander.js Key Concepts

Command Class

new Command()
  .name('cli-name')
  .description('CLI description')
  .version('1.0.0')
  .command('subcommand')

Option Types

• Flag option: -v, --verbose (boolean)
• Value option: -p, --port <port> (required value)
• Optional value: -p, --port [port] (optional value)
• Negatable: --no-color (inverse boolean)
• Variadic: --files <files...> (multiple values)

Argument Types

• Required: <name>
• Optional: [name]
• Variadic: <items...> or [items...]

Option Class Methods

• .choices(['a', 'b', 'c']): Restrict to specific values
• .default(value): Set default value
• .argParser(fn): Custom parsing function
• .makeOptionMandatory(): Require option
• .conflicts(option): Mutually exclusive options
• .implies(option): Implies another option
• .env(name): Read from environment variable

Action Handler Signatures

// No arguments
.action(() => {})

// With options only
.action((options) => {})

// With arguments
.action((arg1, arg2, options) => {})

// With command reference
.action((options, command) => {})

Pattern Recipes

Pattern 1: Simple CLI with Subcommands

Use template: templates/basic-commander.ts

Pattern 2: CLI with Rich Options

Use template: templates/option-class-advanced.ts

Pattern 3: Interactive CLI

Use template: templates/commander-with-inquirer.ts

Pattern 4: CLI with Validation

Use template: templates/commander-with-validation.ts

Pattern 5: Multi-level Commands

Use template: templates/nested-subcommands.ts

Integration with Other Tools

With Inquirer.js (Interactive Prompts)

import inquirer from 'inquirer';

program
  .command('setup')
  .action(async () => {
    const answers = await inquirer.prompt([
      { type: 'input', name: 'name', message: 'Project name:' },
      { type: 'list', name: 'template', message: 'Template:', choices: ['basic', 'advanced'] }
    ]);
    // Use answers
  });

With Chalk (Colored Output)

import chalk from 'chalk';

program
  .command('deploy')
  .action(() => {
    console.log(chalk.green('✓ Deployment successful'));
    console.log(chalk.red('✗ Deployment failed'));
  });

With Ora (Spinners)

import ora from 'ora';

program
  .command('build')
  .action(async () => {
    const spinner = ora('Building...').start();
    await build();
    spinner.succeed('Build complete');
  });

Best Practices

1. Use Option class for complex options: Provides better validation and type safety
2. Keep action handlers thin: Delegate to separate functions
3. Provide clear descriptions: Help users understand commands
4. Set sensible defaults: Reduce required options
5. Validate early: Check inputs before processing
6. Handle errors gracefully: Provide helpful error messages
7. Use TypeScript: Better type safety and IDE support
8. Test thoroughly: Unit test commands and options
9. Document examples: Show common usage patterns
10. Version your CLI: Use semantic versioning

Common Patterns

Pattern: Config Command Group

const config = program.command('config');
config.command('get <key>').action(getConfig);
config.command('set <key> <value>').action(setConfig);
config.command('list').action(listConfig);
config.command('delete <key>').action(deleteConfig);

Pattern: CRUD Commands

program.command('create <name>').action(create);
program.command('read <id>').action(read);
program.command('update <id>').action(update);
program.command('delete <id>').action(deleteItem);
program.command('list').action(list);

Pattern: Deploy with Environments

program
  .command('deploy')
  .addOption(new Option('-e, --env <env>').choices(['dev', 'staging', 'prod']))
  .option('-f, --force', 'force deployment')
  .action(deploy);

Troubleshooting

Issue: Options not parsed

Solution: Ensure program.parse() is called

Issue: Arguments not received

Solution: Check action handler signature matches argument count

Issue: Subcommands not working

Solution: Verify subcommand is attached before parse()

Issue: TypeScript errors

Solution: Install @types/node and configure tsconfig

Issue: Help not showing

Solution: Commander.js auto-generates help from descriptions

Success Criteria

✅ Command structure follows Commander.js conventions ✅ Options and arguments properly typed ✅ Help text is clear and descriptive ✅ Error handling covers edge cases ✅ CLI tested with various inputs ✅ TypeScript compiles without errors ✅ Commands execute as expected

Related Skills

• click-patterns - Python Click framework patterns
• typer-patterns - Python Typer framework patterns
• clap-patterns - Rust Clap framework patterns

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Skill Type: Framework Patterns + Code Templates Language: TypeScript/JavaScript (Node.js) Framework: Commander.js v12+ Auto-invocation: Yes (via description matching)