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Commander.js

The complete solution for node.js command-line interfaces, inspired by Ruby’s commander.

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Commander.js

Installation

npm install commander

Declaring program variable

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

const program = require('commander');
program.version('0.0.1');

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

 const commander = require('commander');
 const program = new commander.Command();
 program.version('0.0.1');

Options

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.

The options can be accessed as properties on the Command object. Multi-word options such as “--template-engine” are camel-cased, becoming program.templateEngine etc. Multiple short flags may be combined as a single arg, for example -abc is equivalent to -a -b -c.

See also optional new behaviour to avoid name clashes.

Common option types, boolean and value

The two most used option types are a boolean flag, and an option which takes a value (declared using angle brackets). Both are undefined unless specified on command line.

const program = require('commander');

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);

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

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

program.parse(arguments) processes the arguments, leaving any args not consumed by the options as the program.args array.

Default option value

You can specify a default value for an option which takes a value.

const program = require('commander');

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

program.parse(process.argv);

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

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

Other option types, negatable boolean and flag|value

You can specify 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. You can specify a default boolean value for a boolean flag and it can be overridden on command line.

const program = require('commander');

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

const sauceStr = program.sauce ? 'sauce' : 'no sauce';
const cheeseStr = (program.cheese === false) ? 'no cheese' : `${program.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 functions as a flag but may also take a value (declared using square brackets).

const program = require('commander');

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

program.parse(process.argv);

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

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

Custom option processing

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

This allows you to coerce the option value 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.

const program = require('commander');

function myParseInt(value, dummyPrevious) {
  // parseInt takes a string and an optional radix
  return parseInt(value);
}

function increaseVerbosity(dummyValue, previous) {
  return previous + 1;
}

function collect(value, previous) {
  return previous.concat([value]);
}

function commaSeparatedList(value, dummyPrevious) {
  return value.split(',');
}

program
  .option('-f, --float <number>', 'float argument', parseFloat)
  .option('-i, --integer <number>', 'integer argument', myParseInt)
  .option('-v, --verbose', 'verbosity that can be increased', increaseVerbosity, 0)
  .option('-c, --collect <value>', 'repeatable value', collect, [])
  .option('-l, --list <items>', 'comma separated list', commaSeparatedList)
;

program.parse(process.argv);

if (program.float !== undefined) console.log(`float: ${program.float}`);
if (program.integer !== undefined) console.log(`integer: ${program.integer}`);
if (program.verbose > 0) console.log(`verbosity: ${program.verbose}`);
if (program.collect.length > 0) console.log(program.collect);
if (program.list !== undefined) console.log(program.list);

$ custom -f 1e2
float: 100
$ custom --integer 2
integer: 2
$ custom -v -v -v
verbose: 3
$ custom -c a -c b -c c
[ 'a', 'b', 'c' ]
$ custom --list x,y,z
[ 'x', 'y', 'z' ]

Required option

You may specify a required (mandatory) option using .requiredOption. The option must be specified on the command line, or by having a default value. The method is otherwise the same as .option in format, taking flags and description, and optional default value or custom processing.

const program = require('commander');

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

program.parse(process.argv);

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

Version option

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. The version flags can be named anything, but a long name is required.

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

Commands

You can specify (sub)commands for your top-level command using .command. There are two ways these can be implemented: using an action handler attached to the command, or as a separate executable file (described in more detail later). In the first parameter to .command you specify the command name and any command arguments. The arguments may be <required> or [optional], and the last argument may also be variadic....

For example:

// Command implemented using action handler (description is supplied separately to `.command`)
// Returns new command for configuring.
program
  .command('clone <source> [destination]')
  .description('clone a repository into a newly created directory')
  .action((source, destination) => {
    console.log('clone command called');
  });

// Command implemented using separate executable file (description is second parameter to `.command`)
// Returns top-level command for adding more commands.
program
  .command('start <service>', 'start named service')
  .command('stop [service]', 'stop named service, or all if no name supplied');

Specify the argument syntax

You use .arguments to specify the arguments for the top-level command, and for subcommands they are included in the .command call. Angled brackets (e.g. <required>) indicate required input. Square brackets (e.g. [optional]) indicate optional input.

const program = require('commander');

program
  .version('0.1.0')
  .arguments('<cmd> [env]')
  .action(function (cmd, env) {
    cmdValue = cmd;
    envValue = env;
  });

program.parse(process.argv);

if (typeof cmdValue === 'undefined') {
  console.error('no command given!');
  process.exit(1);
}
console.log('command:', cmdValue);
console.log('environment:', envValue || "no environment given");

The last argument of a command can be variadic, and only the last argument. To make an argument variadic you append ... to the argument name. For example:

const program = require('commander');

program
  .version('0.1.0')
  .command('rmdir <dir> [otherDirs...]')
  .action(function (dir, otherDirs) {
    console.log('rmdir %s', dir);
    if (otherDirs) {
      otherDirs.forEach(function (oDir) {
        console.log('rmdir %s', oDir);
      });
    }
  });

program.parse(process.argv);

The variadic argument is passed to the action handler as an array. (And this also applies to program.args.)

Action handler (sub)commands

You can add options to a command that uses an action handler. The action handler gets passed a parameter for each argument you declared, and one additional argument which is the command object itself. This command argument has the values for the command-specific options added as properties.

const program = require('commander');

program
  .command('rm <dir>')
  .option('-r, --recursive', 'Remove recursively')
  .action(function (dir, cmdObj) {
    console.log('remove ' + dir + (cmdObj.recursive ? ' recursively' : ''))
  })

program.parse(process.argv)

You may supply an async action handler, in which case you call .parseAsync rather than .parse.

async function run() { /* code goes here */ }

async function main() {
  program
    .command('run')
    .action(run);
  await program.parseAsync(process.argv);
}

A command’s options on the command line are validated when the command is used. Any unknown options will be reported as an error. However, if an action-based command does not define an action, then the options are not validated.

Configuration options can be passed with the call to .command(). Specifying true for opts.noHelp will remove the command from the generated help output.

Git-style executable (sub)commands

When .command() is invoked with a description argument, this tells commander that you’re going to use separate executables for sub-commands, much like git(1) and other popular tools. Commander will search the executables in the directory of the entry script (like ./examples/pm) with the name program-subcommand, like pm-install, pm-search. You can specify a custom name with the executableFile configuration option.

You handle the options for an executable (sub)command in the executable, and don’t declare them at the top-level.

// file: ./examples/pm
const program = require('commander');

program
  .version('0.1.0')
  .command('install [name]', 'install one or more packages')
  .command('search [query]', 'search with optional query')
  .command('update', 'update installed packages', {executableFile: 'myUpdateSubCommand'})
  .command('list', 'list packages installed', {isDefault: true})
  .parse(process.argv);

Configuration options can be passed with the call to .command(). Specifying true for opts.noHelp will remove the command from the generated help output. Specifying true for opts.isDefault will run the subcommand if no other subcommand is specified. Specifying a name with executableFile will override the default constructed name.

If the program is designed to be installed globally, make sure the executables have proper modes, like 755.

Automated --help

The help information is auto-generated based on the information commander already knows about your program, so the following --help info is for free:

$ ./examples/pizza --help
Usage: pizza [options]

An application for pizzas ordering

Options:
  -V, --version        output the version number
  -p, --peppers        Add peppers
  -P, --pineapple      Add pineapple
  -b, --bbq            Add bbq sauce
  -c, --cheese <type>  Add the specified type of cheese (default: "marble")
  -C, --no-cheese      You do not want any cheese
  -h, --help           output usage information

Custom help

You can display arbitrary -h, --help information by listening for “--help”. Commander will automatically exit once you are done so that the remainder of your program does not execute causing undesired behaviors, for example in the following executable “stuff” will not output when --help is used.

#!/usr/bin/env node

const program = require('commander');

program
  .version('0.1.0')
  .option('-f, --foo', 'enable some foo')
  .option('-b, --bar', 'enable some bar')
  .option('-B, --baz', 'enable some baz');

// must be before .parse() since
// node's emit() is immediate

program.on('--help', function(){
  console.log('')
  console.log('Examples:');
  console.log('  $ custom-help --help');
  console.log('  $ custom-help -h');
});

program.parse(process.argv);

console.log('stuff');

Yields the following help output when node script-name.js -h or node script-name.js --help are run:

Usage: custom-help [options]

Options:
  -h, --help     output usage information
  -V, --version  output the version number
  -f, --foo      enable some foo
  -b, --bar      enable some bar
  -B, --baz      enable some baz

Examples:
  $ custom-help --help
  $ custom-help -h

.usage and .name

These allow you to customise the usage description in the first line of the help. The name is otherwise deduced from the (full) program arguments. Given:

program
  .name("my-command")
  .usage("[global options] command")

The help will start with:

Usage: my-command [global options] command

.outputHelp(cb)

Output help information without exiting. Optional callback cb allows post-processing of help text before it is displayed.

If you want to display help by default (e.g. if no command was provided), you can use something like:

const program = require('commander');
const colors = require('colors');

program
  .version('0.1.0')
  .command('getstream [url]', 'get stream URL')
  .parse(process.argv);

if (!process.argv.slice(2).length) {
  program.outputHelp(make_red);
}

function make_red(txt) {
  return colors.red(txt); //display the help text in red on the console
}

.helpOption(flags, description)

Override the default help flags and description.

program
  .helpOption('-e, --HELP', 'read more information');

.help(cb)

Output help information and exit immediately. Optional callback cb allows post-processing of help text before it is displayed.

Custom event listeners

You can execute custom actions by listening to command and option events.

program.on('option:verbose', function () {
  process.env.VERBOSE = this.verbose;
});

// error on unknown commands
program.on('command:*', function () {
  console.error('Invalid command: %s\nSee --help for a list of available commands.', program.args.join(' '));
  process.exit(1);
});

Bits and pieces

Avoiding option name clashes

The original and default behaviour is that the option values are stored as properties on the program, and the action handler is passed a command object with the options values stored as properties. This is very convenient to code, but the downside is possible clashes with existing properties of Command.

There are two new routines to change the behaviour, and the default behaviour may change in the future:

storeOptionsAsProperties: whether to store option values as properties on command object, or store separately (specify false) and access using .opts()
passCommandToAction: whether to pass command to action handler, or just the options (specify false)

// file: ./examples/storeOptionsAsProperties.action.js
program
  .storeOptionsAsProperties(false)
  .passCommandToAction(false);

program
  .name('my-program-name')
  .option('-n,--name <name>');

program
  .command('show')
  .option('-a,--action <action>')
  .action((options) => {
    console.log(options.action);
  });

program.parse(process.argv);

const programOptions = program.opts();
console.log(programOptions.name);

TypeScript

The Commander package includes its TypeScript Definition file, but also requires the node types which you need to install yourself. e.g.

npm install commander
npm install --save-dev @types/node

If you use ts-node and git-style sub-commands written as .ts files, you need to call your program through node to get the sub-commands called correctly. e.g.

node -r ts-node/register pm.ts

Node options such as `--harmony`

You can enable --harmony option in two ways:

Use #! /usr/bin/env node --harmony in the sub-commands scripts. (Note Windows does not support this pattern.)
Use the --harmony option when call the command, like node --harmony examples/pm publish. The --harmony option will be preserved when spawning sub-command process.

Node debugging

If you are using the node inspector for debugging git-style executable (sub)commands using node --inspect et al, the inspector port is incremented by 1 for the spawned subcommand.

Override exit handling

By default Commander calls process.exit when it detects errors, or after displaying the help or version. You can override this behaviour and optionally supply a callback. The default override throws a CommanderError.

The override callback is passed a CommanderError with properties exitCode number, code string, and message. The default override behaviour is to throw the error, except for async handling of executable subcommand completion which carries on. The normal display of error messages or version or help is not affected by the override which is called after the display.

program.exitOverride();

try {
  program.parse(process.argv);
} catch (err) {
  // custom processing...
}

Examples

const program = require('commander');

program
  .version('0.1.0')
  .option('-C, --chdir <path>', 'change the working directory')
  .option('-c, --config <path>', 'set config path. defaults to ./deploy.conf')
  .option('-T, --no-tests', 'ignore test hook');

program
  .command('setup [env]')
  .description('run setup commands for all envs')
  .option("-s, --setup_mode [mode]", "Which setup mode to use")
  .action(function(env, options){
    const mode = options.setup_mode || "normal";
    env = env || 'all';
    console.log('setup for %s env(s) with %s mode', env, mode);
  });

program
  .command('exec <cmd>')
  .alias('ex')
  .description('execute the given remote cmd')
  .option("-e, --exec_mode <mode>", "Which exec mode to use")
  .action(function(cmd, options){
    console.log('exec "%s" using %s mode', cmd, options.exec_mode);
  }).on('--help', function() {
    console.log('');
    console.log('Examples:');
    console.log('');
    console.log('  $ deploy exec sequential');
    console.log('  $ deploy exec async');
  });

program
  .command('*')
  .action(function(env){
    console.log('deploying "%s"', env);
  });

program.parse(process.argv);

More Demos can be found in the examples directory.

License

MIT

Support

Commander 4.x is supported on Node 8 and above, and is likely to work with Node 6 but not tested. (For versions of Node below Node 6, use Commander 3.x or 2.x.)

The main forum for free and community support is the project Issues on GitHub.

Commander for enterprise

Available as part of the Tidelift Subscription

The maintainers of Commander and thousands of other packages are working with Tidelift to deliver commercial support and maintenance for the open source dependencies you use to build your applications. Save time, reduce risk, and improve code health, while paying the maintainers of the exact dependencies you use. Learn more.

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