Commander.js

The complete solution for node.js command-line interfaces.

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• Commander.js
  • Installation
  • Quick Start
  • Declaring program variable
  • Options
    • Common option types, boolean and value
    • Default option value
    • Other option types, negatable boolean and boolean|value
    • Required option
    • Variadic option
    • Version option
    • More configuration
    • Custom option processing
  • Commands
    • Command-arguments
      • More configuration
      • Custom argument processing
    • Action handler
    • Stand-alone executable (sub)commands
    • Life cycle hooks
  • Automated help
    • Custom help
    • Display help after errors
    • Display help from code
    • .name
    • .usage
    • .description and .summary
    • .helpOption(flags, description)
    • .helpCommand()
    • Help Groups
    • More configuration
  • Custom event listeners
  • Bits and pieces
    • .parse() and .parseAsync()
    • Parsing Configuration
    • Legacy options as properties
    • TypeScript
    • createCommand()
    • Node options such as --harmony
    • Debugging stand-alone executable subcommands
    • npm run-script
    • Display error
    • Override exit and output handling
    • Additional documentation
  • Support
    • Commander for enterprise

For information about terms used in this document see: terminology

npm install commander

You write code to describe your command line interface. Commander looks after parsing the arguments into options and command-arguments, displays usage errors for problems, and implements a help system.

Commander is strict and displays an error for unrecognised options. The two most used option types are a boolean option, and an option which takes its value from the following argument.

Example file: split.js

const { program } = require('commander');

program
  .option('--first')
  .option('-s, --separator <char>')
  .argument('<string>');

program.parse();

const options = program.opts();
const limit = options.first ? 1 : undefined;
console.log(program.args[0].split(options.separator, limit));

$ node split.js -s / --fits a/b/c
error: unknown option '--fits'
(Did you mean --first?)
$ node split.js -s / --first a/b/c
[ 'a' ]

Here is a more complete program using a subcommand and with descriptions for the help. In a multi-command program, you have an action handler for each command (or stand-alone executables for the commands).

Example file: string-util.js

const { Command } = require('commander');
const program = new Command();

program
  .name('string-util')
  .description('CLI to some JavaScript string utilities')
  .version('0.8.0');

program.command('split')
  .description('Split a string into substrings and display as an array')
  .argument('<string>', 'string to split')
  .option('--first', 'display just the first substring')
  .option('-s, --separator <char>', 'separator character', ',')
  .action((str, options) => {
    const limit = options.first ? 1 : undefined;
    console.log(str.split(options.separator, limit));
  });

program.parse();

$ node string-util.js help split
Usage: string-util split [options] <string>

Split a string into substrings and display as an array.

Arguments:
  string                  string to split

Options:
  --first                 display just the first substring
  -s, --separator <char>  separator character (default: ",")
  -h, --help              display help for command

$ node string-util.js split --separator=/ a/b/c
[ 'a', 'b', 'c' ]

More samples can be found in the examples directory.

Commander exports a global object which is convenient for quick programs. This is used in the examples in this README for brevity.

// CommonJS (.cjs)
const { program } = require('commander');

For larger programs which may use commander in multiple ways, including unit testing, it is better to create a local Command object to use.

// CommonJS (.cjs)
const { Command } = require('commander');
const program = new Command();

// ECMAScript (.mjs)
import { Command } from 'commander';
const program = new Command();

// TypeScript (.ts)
import { Command } from 'commander';
const program = new Command();

Options are defined with the .option() method, also serving as documentation for the options. Each option can have a short flag (single character) and a long name, separated by a comma or space or vertical bar ('|'). To allow a wider range of short-ish flags than just single characters, you may also have two long options. Examples:

program
  .option('-p, --port <number>', 'server port number')
  .option('--trace', 'add extra debugging output')
  .option('--ws, --workspace <name>', 'use a custom workspace')

The parsed options can be accessed by calling .opts() on a Command object, and are passed to the action handler.

Multi-word options such as "--template-engine" are camel-cased, becoming program.opts().templateEngine etc.

An option and its option-argument can be separated by a space, or combined into the same argument. The option-argument can follow the short option directly or follow an = for a long option.

serve -p 80
serve -p80
serve --port 80
serve --port=80

You can use -- to indicate the end of the options, and any remaining arguments will be used without being interpreted.

By default, options on the command line are not positional, and can be specified before or after other arguments.

There are additional related routines for when .opts() is not enough:

• .optsWithGlobals() returns merged local and global option values
• .getOptionValue() and .setOptionValue() work with a single option value
• .getOptionValueSource() and .setOptionValueWithSource() include where the option value came from

The two most used option types are a boolean option, and an option which takes its value from the following argument (declared with angle brackets like --expect <value>). Both are undefined unless specified on command line.

Example file: options-common.js

program
  .option('-d, --debug', 'output extra debugging')
  .option('-s, --small', 'small pizza size')
  .option('-p, --pizza-type <type>', 'flavour of pizza');

program.parse(process.argv);

const options = program.opts();
if (options.debug) console.log(options);
console.log('pizza details:');
if (options.small) console.log('- small pizza size');
if (options.pizzaType) console.log(`- ${options.pizzaType}`);

$ pizza-options -p
error: option '-p, --pizza-type <type>' argument missing
$ pizza-options -d -s -p vegetarian
{ debug: true, small: true, pizzaType: 'vegetarian' }
pizza details:
- small pizza size
- vegetarian
$ pizza-options --pizza-type=cheese
pizza details:
- cheese

Multiple boolean short options may be combined following the dash, and may be followed by a single short option taking a value. For example -d -s -p cheese may be written as -ds -p cheese or even -dsp cheese.

Options with an expected option-argument are greedy and will consume the following argument whatever the value. So --id -xyz reads -xyz as the option-argument.

program.parse(arguments) processes the arguments, leaving any args not consumed by the program options in the program.args array. The parameter is optional and defaults to process.argv.

You can specify a default value for an option.

Example file: options-defaults.js

program
  .option('-c, --cheese <type>', 'add the specified type of cheese', 'blue');

program.parse();

console.log(`cheese: ${program.opts().cheese}`);

$ pizza-options
cheese: blue
$ pizza-options --cheese stilton
cheese: stilton

You can define a boolean option long name with a leading no- to set the option value to false when used. Defined alone this also makes the option true by default.

If you define --foo first, adding --no-foo does not change the default value from what it would otherwise be.

Example file: options-negatable.js

program
  .option('--no-sauce', 'Remove sauce')
  .option('--cheese <flavour>', 'cheese flavour', 'mozzarella')
  .option('--no-cheese', 'plain with no cheese')
  .parse();

const options = program.opts();
const sauceStr = options.sauce ? 'sauce' : 'no sauce';
const cheeseStr = (options.cheese === false) ? 'no cheese' : `${options.cheese} cheese`;
console.log(`You ordered a pizza with ${sauceStr} and ${cheeseStr}`);

$ pizza-options
You ordered a pizza with sauce and mozzarella cheese
$ pizza-options --sauce
error: unknown option '--sauce'
$ pizza-options --cheese=blue
You ordered a pizza with sauce and blue cheese
$ pizza-options --no-sauce --no-cheese
You ordered a pizza with no sauce and no cheese

You can specify an option which may be used as a boolean option but may optionally take an option-argument (declared with square brackets like --optional [value]).

Example file: options-boolean-or-value.js

program
  .option('-c, --cheese [type]', 'Add cheese with optional type');

program.parse(process.argv);

const options = program.opts();
if (options.cheese === undefined) console.log('no cheese');
else if (options.cheese === true) console.log('add cheese');
else console.log(`add cheese type ${options.cheese}`);

$ pizza-options
no cheese
$ pizza-options --cheese
add cheese
$ pizza-options --cheese mozzarella
add cheese type mozzarella

Options with an optional option-argument are not greedy and will ignore arguments starting with a dash. So id behaves as a boolean option for --id -ABCD, but you can use a combined form if needed like --id=-ABCD. Negative numbers are special and are accepted as an option-argument.

For information about possible ambiguous cases, see options taking varying arguments.

You may specify a required (mandatory) option using .requiredOption(). The option must have a value after parsing, usually specified on the command line, or perhaps from a default value (say from environment). The method is otherwise the same as .option() in format, taking flags and description, and optional default value or custom processing.

Example file: options-required.js

program
  .requiredOption('-c, --cheese <type>', 'pizza must have cheese');

program.parse();

$ pizza
error: required option '-c, --cheese <type>' not specified

You may make an option variadic by appending ... to the value placeholder when declaring the option. On the command line you can then specify multiple option-arguments, and the parsed option value will be an array. The extra arguments are read until the first argument starting with a dash. The special argument -- stops option processing entirely. If a value is specified in the same argument as the option then no further values are read.

Example file: options-variadic.js

program
  .option('-n, --number <numbers...>', 'specify numbers')
  .option('-l, --letter [letters...]', 'specify letters');

program.parse();

console.log('Options: ', program.opts());
console.log('Remaining arguments: ', program.args);

$ collect -n 1 2 3 --letter a b c
Options:  { number: [ '1', '2', '3' ], letter: [ 'a', 'b', 'c' ] }
Remaining arguments:  []
$ collect --letter=A -n80 operand
Options:  { number: [ '80' ], letter: [ 'A' ] }
Remaining arguments:  [ 'operand' ]
$ collect --letter -n 1 -n 2 3 -- operand
Options:  { number: [ '1', '2', '3' ], letter: true }
Remaining arguments:  [ 'operand' ]

For information about possible ambiguous cases, see options taking varying arguments.

The optional version method adds handling for displaying the command version. The default option flags are -V and --version, and when present the command prints the version number and exits.

program.version('0.0.1');

$ ./examples/pizza -V
0.0.1

You may change the flags and description by passing additional parameters to the version method, using the same syntax for flags as the option method.

program.version('0.0.1', '-v, --vers', 'output the current version');

You can add most options using the .option() method, but there are some additional features available by constructing an Option explicitly for less common cases.

Example files: options-extra.js, options-env.js, options-conflicts.js, options-implies.js

program
  .addOption(new Option('-s, --secret').hideHelp())
  .addOption(new Option('-t, --timeout <delay>', 'timeout in seconds').default(60, 'one minute'))
  .addOption(new Option('-d, --drink <size>', 'drink size').choices(['small', 'medium', 'large']))
  .addOption(new Option('-p, --port <number>', 'port number').env('PORT'))
  .addOption(new Option('--donate [amount]', 'optional donation in dollars').preset('20').argParser(parseFloat))
  .addOption(new Option('--disable-server', 'disables the server').conflicts('port'))
  .addOption(new Option('--free-drink', 'small drink included free ').implies({ drink: 'small' }));

$ extra --help
Usage: help [options]

Options:
  -t, --timeout <delay>  timeout in seconds (default: one minute)
  -d, --drink <size>     drink cup size (choices: "small", "medium", "large")
  -p, --port <number>    port number (env: PORT)
  --donate [amount]      optional donation in dollars (preset: "20")
  --disable-server       disables the server
  --free-drink           small drink included free
  -h, --help             display help for command

$ extra --drink huge
error: option '-d, --drink <size>' argument 'huge' is invalid. Allowed choices are small, medium, large.

$ PORT=80 extra --donate --free-drink
Options:  { timeout: 60, donate: 20, port: '80', freeDrink: true, drink: 'small' }

$ extra --disable-server --port 8000
error: option '--disable-server' cannot be used with option '-p, --port <number>'

Specify a required (mandatory) option using the Option method .makeOptionMandatory(). This matches the Command method .requiredOption().

You may specify a function to do custom processing of option-arguments. The callback function receives two parameters, the user specified option-argument and the previous value for the option. It returns the new value for the option.

This allows you to coerce the option-argument to the desired type, or accumulate values, or do entirely custom processing.

You can optionally specify the default/starting value for the option after the function parameter.

Example file: options-custom-processing.js

function myParseInt(value, dummyPrevious) {
  // parseInt takes a string and a radix
  const parsedValue = parseInt(value, 10);
  if