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

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

With yargs, ye be havin' a map that leads straight to yer treasure! Treasure of course, being a simple option hash.

Yargs is the official successor to optimist. Please feel free to submit issues and pull requests. If you'd like to contribute and don't know where to start, have a look at the issue list :)

examples

With yargs, the options be just a hash!

plunder.js:

#!/usr/bin/env node
var 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!

But don't walk the plank just yet! There be more! You can do short options:

short.js:

#!/usr/bin/env node
var argv = require('yargs').argv;
console.log('(%d,%d)', argv.x, argv.y);

---

$ ./short.js -x 10 -y 21
(10,21)

And booleans, both long, short, and even grouped:

bool.js:

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

if (argv.s) {
    process.stdout.write(argv.fr ? 'Le perroquet dit: ' : 'The parrot says: ');
}
console.log(
    (argv.fr ? 'couac' : 'squawk') + (argv.p ? '!' : '')
);

---

$ ./bool.js -s
The parrot says: squawk

$ ./bool.js -sp
The parrot says: squawk!

$ ./bool.js -sp --fr
Le perroquet dit: couac!

And non-hyphenated options too! Just use argv._!

nonopt.js:

#!/usr/bin/env node
var argv = require('yargs').argv;
console.log('(%d,%d)', argv.x, argv.y);
console.log(argv._);

---

$ ./nonopt.js -x 6.82 -y 3.35 rum
(6.82,3.35)
[ 'rum' ]

$ ./nonopt.js "me hearties" -x 0.54 yo -y 1.12 ho
(0.54,1.12)
[ 'me hearties', 'yo', 'ho' ]

Yargs even counts your booleans!

count.js:

#!/usr/bin/env node
var argv = require('yargs')
    .count('verbose')
    .alias('v', 'verbose')
    .argv;

VERBOSE_LEVEL = argv.verbose;

function WARN()  { VERBOSE_LEVEL >= 0 && console.log.apply(console, arguments); }
function INFO()  { VERBOSE_LEVEL >= 1 && console.log.apply(console, arguments); }
function DEBUG() { VERBOSE_LEVEL >= 2 && console.log.apply(console, arguments); }

WARN("Showing only important stuff");
INFO("Showing semi-important stuff too");
DEBUG("Extra chatty mode");

---

$ node count.js
Showing only important stuff

$ node count.js -v
Showing only important stuff
Showing semi-important stuff too

$ node count.js -vv
Showing only important stuff
Showing semi-important stuff too
Extra chatty mode

$ node count.js -v --verbose
Showing only important stuff
Showing semi-important stuff too
Extra chatty mode

Tell users how to use yer options and make demands.

area.js:

#!/usr/bin/env node
var argv = require('yargs')
    .usage('Usage: $0 -w [num] -h [num]')
    .demandOption(['w','h'])
    .argv;

console.log("The area is:", argv.w * argv.h);

---

$ ./area.js -w 55 -h 11
The area is: 605

$ node ./area.js -w 4.91 -w 2.51
Usage: area.js -w [num] -h [num]

Options:
  -w  [required]
  -h  [required]

Missing required arguments: h

After yer demands have been met, demand more! Ask for non-hyphenated arguments!

demand_count.js:

#!/usr/bin/env node
var argv = require('yargs')
    .demandCommand(2)
    .argv;
console.dir(argv);

---

$ ./demand_count.js a

Not enough non-option arguments: got 1, need at least 2

$ ./demand_count.js a b
{ _: [ 'a', 'b' ], '$0': 'demand_count.js' }

$ ./demand_count.js a b c
{ _: [ 'a', 'b', 'c' ], '$0': 'demand_count.js' }

EVEN MORE SHIVER ME TIMBERS!

default_singles.js:

#!/usr/bin/env node
var argv = require('yargs')
    .default('x', 10)
    .default('y', 10)
    .argv
;
console.log(argv.x + argv.y);

---

$ ./default_singles.js -x 5
15

default_hash.js:

#!/usr/bin/env node
var argv = require('yargs')
    .default({ x : 10, y : 10 })
    .argv
;
console.log(argv.x + argv.y);

---

$ ./default_hash.js -y 7
17

And if you really want to get all descriptive about it...

boolean_single.js:

#!/usr/bin/env node
var argv = require('yargs')
    .boolean('v')
    .argv
;
console.dir(argv.v);
console.dir(argv._);

---

$ ./boolean_single.js -v "me hearties" yo ho
true
[ 'me hearties', 'yo', 'ho' ]

boolean_double.js:

#!/usr/bin/env node
var argv = require('yargs')
    .boolean(['x','y','z'])
    .argv
;
console.dir([ argv.x, argv.y, argv.z ]);
console.dir(argv._);

---

$ ./boolean_double.js -x -z one two three
[ true, false, true ]
[ 'one', 'two', 'three' ]

Yargs is here to help you...

Ye can describe parameters fer help messages and set aliases. Yargs figures out how ter format a handy help string automatically.

line_count.js:

#!/usr/bin/env node
var argv = require('yargs')
    .usage('Usage: $0 <command> [options]')
    .command('count', 'Count the lines in a file')
    .example('$0 count -f foo.js', 'count the lines in the given file')
    .alias('f', 'file')
    .nargs('f', 1)
    .describe('f', 'Load a file')
    .demandOption(['f'])
    .help('h')
    .alias('h', 'help')
    .epilog('copyright 2015')
    .argv;

var fs = require('fs');
var s = fs.createReadStream(argv.file);

var lines = 0;
s.on('data', function (buf) {
    lines += buf.toString().match(/\n/g).length;
});

s.on('end', function () {
    console.log(lines);
});

---

$ node line_count.js count
Usage: line_count.js <command> [options]

Commands:
  count    Count the lines in a file

Options:
  -f, --file  Load a file        [required]
  -h, --help  Show help           [boolean]

Examples:
  line_count.js count -f foo.js  count the lines in the given file

copyright 2015

Missing required arguments: f

$ node line_count.js count --file line_count.js
26

$ node line_count.js count -f line_count.js
26

methods

By itself,

require('yargs').argv

will use the process.argv array to construct the argv object.

You can pass in the process.argv yourself:

require('yargs')([ '-x', '1', '-y', '2' ]).argv

or use .parse() to do the same thing:

require('yargs').parse([ '-x', '1', '-y', '2' ])

The rest of these methods below come in just before the terminating .argv.

.alias(key, alias)

Set key names as equivalent such that updates to a key will propagate to aliases and vice-versa.

Optionally .alias() can take an object that maps keys to aliases. Each key of this object should be the canonical version of the option, and each value should be a string or an array of strings.

.argv

Get the arguments as a plain old object.

Arguments without a corresponding flag show up in the argv._ array.

The script name or node command is available at argv.$0 similarly to how $0 works in bash or perl.

If yargs is executed in an environment that embeds node and there's no script name (e.g. Electron or nw.js), it will ignore the first parameter since it expects it to be the script name. In order to override this behavior, use .parse(process.argv.slice(1)) instead of .argv and the first parameter won't be ignored.

.array(key)

Tell the parser to interpret key as an array. If .array('foo') is set, --foo foo bar will be parsed as ['foo', 'bar'] rather than as 'foo'.

.boolean(key)

Interpret key as a boolean. If a non-flag option follows key in process.argv, that string won't get set as the value of key.

key will default to false, unless a default(key, undefined) is explicitly set.

If key is an array, interpret all the elements as booleans.

.check(fn, [global=true])

Check that certain conditions are met in the provided arguments.

fn is called with two arguments, the parsed argv hash and an array of options and their aliases.

If fn throws or returns a non-truthy value, show the thrown error, usage information, and exit.

global indicates whether check() should be enabled both at the top-level and for each sub-command.

.choices(key, choices)

Limit valid values for key to a predefined set of choices, given as an array or as an individual value.

var argv = require('yargs')
  .alias('i', 'ingredient')
  .describe('i', 'choose your sandwich ingredients')
  .choices('i', ['peanut-butter', 'jelly', 'banana', 'pickles'])
  .help('help')
  .argv

If this method is called multiple times, all enumerated values will be merged together. Choices are generally strings or numbers, and value matching is case-sensitive.

Optionally .choices() can take an object that maps multiple keys to their choices.

Choices can also be specified as choices in the object given to option().

var argv = require('yargs')
  .option('size', {
    alias: 's',
    describe: 'choose a size',
    choices: ['xs', 's', 'm', 'l', 'xl']
  })
  .argv

.coerce(key, fn)

Provide a synchronous function to coerce or transform the value(s) given on the command line for key.

The coercion function should accept one argument, representing the parsed value from the command line, and should return a new value or throw an error. The returned value will be used as the value for key (or one of its aliases) in argv.

If the function throws, the error will be treated as a validation failure, delegating to either a custom .fail() handler or printing the error message in the console.

Coercion will be applied to a value after all other modifications, such as .normalize().

Examples:

var argv = require('yargs')
  .coerce('file', function (arg) {
    return require('fs').readFileSync(arg, 'utf8')
  })
  .argv

Optionally .coerce() can take an object that maps several keys to their respective coercion function.

var argv = require('yargs')
  .coerce({
    date: Date.parse,
    json: JSON.parse
  })
  .argv

You can also map the same function to several keys at one time. Just pass an array of keys as the first argument to .coerce():

var path = require('path')
var argv = require('yargs')
  .coerce(['src', 'dest'], path.resolve)
  .argv

If you are using dot-notion or arrays, .e.g., user.email and user.password, coercion will be applied to the final object that has been parsed:

// --user.name Batman --user.password 123
// gives us: {name: 'batman', password: '[SECRET]'}
var argv = require('yargs')
  .option('user')
  .coerce('user', opt => {
    opt.name = opt.name.toLowerCase()
    opt.password = '[SECRET]'
    return opt
  })
  .argv

.command(cmd, desc, [builder], [handler])

.command(cmd, desc, [module])

.command(module)

Define the commands exposed by your application.

cmd should be a string representing the command or an array of strings representing the command and its aliases. Read more about command aliases in the subsection below.

Use desc to provide a description for each command your application accepts (the values stored in argv._). Set desc to false to create a hidden command. Hidden commands don't show up in the help output and aren't available for completion.

Optionally, you can provide a builder object to give hints about the options that your command accepts:

yargs
  .command('get', 'make a get HTTP request', {
    url: {
      alias: 'u',
      default: 'http://yargs.js.org/'
    }
  })
  .help()
  .argv

builder can also be a function. This function is executed with a yargs instance, and can be used to provide advanced command specific help:

yargs
  .command('get', 'make a get HTTP request', function (yargs) {
    return yargs.option('url', {
      alias: 'u',
      default: 'http://yargs.js.org/'
    })
  })
  .help()
  .argv

You can also provide a handler function, which will be executed with the parsed argv object:

yargs
  .command(
    'get',
    'make a get HTTP request',
    function (yargs) {
      return yargs.option('u', {
        alias: 'url',
        describe: 'the URL to make an HTTP request to'
      })
    },
    function (argv) {
      console.log(argv.url)
    }
  )
  .help()
  .argv

Default Commands

To specify a default command use the character *. A default command will be run if the positional arguments provided match no known commands:

const argv = require('yargs')
  .command('*', 'the default command', () => {}, (argv) => {
    console.log('this command will be run by default')
  })

The command defined above will be executed if the program is run with ./my-cli.js --x=22.

Default commands can also be used as a command alias, like so:

const argv = require('yargs')
  .command(['serve', '*'], 'the serve command', () => {}, (argv) => {
    console.log('this command will be run by default')
  })

The command defined above will be executed if the program is run with ./my-cli.js --x=22, or with ./my-cli.js serve --x=22.

Positional Arguments

Commands can accept optional and required positional arguments. Required positional arguments take the form <foo>, and optional arguments take the form [bar]. The parsed positional arguments will be populated in argv:

yargs.command('get <source> [proxy]', 'make a get HTTP request')
  .help()
  .argv

Positional Argument Aliases

Aliases can be provided for positional arguments using the | character. As an example, suppose our application allows either a username or an email as the first argument:

yargs.command('get <username|email> [password]', 'fetch a user by username or email.')
  .help()
  .argv

In this way, both argv.username and argv.email would be populated with the same value when the command is executed.

Variadic Positional Arguments

The last positional argument can optionally accept an array of values, by using the .. operator:

yargs.command('download <url> [files..]', 'download several files')
  .help()
  .argv

Command Execution

When a command is given on the command line, yargs will execute the following:

1. push the command into the current context
2. reset non-global configuration
3. apply command configuration via the builder, if given
4. parse and validate args from the command line, including positional args
5. if validation succeeds, run the handler function, if given
6. pop the command from the current context

Command Aliases

You can define aliases for a command by putting the command and all of its aliases into an array.

Alternatively, a command module may specify an aliases property, which may be a string or an array of strings. All aliases defined via the command property and the aliases property will be concatenated together.

The first element in the array is considered the canonical command, which may define positional arguments, and the remaining elements in the array are considered aliases. Aliases inherit positional args from the canonical command, and thus any positional args defined in the aliases themselves are ignored.

If either the canonical command or any of its aliases are given on the command line, the command will be executed.

#!/usr/bin/env node
require('yargs')
  .command(['start [app]', 'run', 'up'], 'Start up an app', {}, (argv) => {
    console.log('starting up the', argv.app || 'default', 'app')
  })
  .command({
    command: 'configure <key> [value]',
    aliases: ['config', 'cfg'],
    desc: 'Set a config variable',
    builder: (yargs) => yargs.default('value', 'true'),
    handler: (argv) => {
      console.log(`setting ${argv.key} to ${argv.value}`)
    }
  })
  .demandCommand()
  .help()
  .wrap(72)
  .argv

$ ./svc.js help
Commands:
  start [app]              Start up an app            [aliases: run, up]
  configure <key> [value]  Set a config variable  [aliases: config, cfg]

Options:
  --help  Show help                                            [boolean]

$ ./svc.js cfg concurrency 4
setting concurrency to 4

$ ./svc.js run web
starting up the web app

Providing a Command Module

For complicated commands you can pull the logic into a module. A module simply needs to export:

• exports.command: string (or array of strings) that executes this command when given on the command line, first string may contain positional args
• exports.aliases: array of strings (or a single string) representing aliases of exports.command, positional args defined in an alias are ignored
• exports.describe: string used as the description for the command in help text, use false for a hidden command
• exports.builder: object declaring the options the command accepts, or a function accepting and returning a yargs instance
• exports.handler: a function which will be passed the parsed argv.

// my-module.js
exports.command = 'get <source> [proxy]'

exports.describe = 'make a get HTTP request'

exports.builder = {
  banana: {
    default: 'cool'
  },
  batman: {
    default: 'sad'
  }
}

exports.handler = function (argv) {
  // do something with argv.
}

You then register the module like so:

yargs.command(require('my-module'))
  .help()
  .argv

Or if the module does not export command and describe (or if you just want to override them):

yargs.command('get <source> [proxy]', 'make a get HTTP request', require('my-module'))
  .help()
  .argv

.commandDir(directory, [opts])

Apply command modules from a directory relative to the module calling this method.

This allows you to organize multiple commands into their own modules under a single directory and apply all of them at once instead of calling .command(require('./dir/module')) multiple times.

By default, it ignores subdirectories. This is so you can use a directory structure to represent your command hierarchy, where each command applies its subcommands using this method in its builder function. See the example below.

Note that yargs assumes all modules in the given directory are command modules and will error if non-command modules are encountered. In this scenario, you can either move your module to a different directory or use the exclude or visit option to manually filter it out. More on that below.

directory is a relative directory path as a string (required).

opts is an options object (optional). The following options are valid:

• recurse: boolean, default false

  Look for command modules in all subdirectories and apply them as a flattened (non-hierarchical) list.

• extensions: array of strings, default ['js']

  The types of files to look for when requiring command modules.

• visit: function

  A synchronous function called for each command module encountered. Accepts commandObject, pathToFile, and filename as arguments. Returns commandObject to include the command; any falsy value to exclude/skip it.

• include: RegExp or function

  Whitelist certain modules. See require-directory whitelisting for details.

• exclude: RegExp or function

  Blacklist certain modules. See require-directory blacklisting for details.

Example command hierarchy using .commandDir()

Desired CLI:

$ myapp --help
$ myapp init
$ myapp remote --help
$ myapp remote add base http://yargs.js.org
$ myapp remote prune base
$ myapp remote prune base fork whatever

Directory structure:

myapp/
├─ cli.js
└─ cmds/
   ├─ init.js
   ├─ remote.js
   └─ remote_cmds/
      ├─ add.js
      └─ prune.js

cli.js:

#!/usr/bin/env node
require('yargs')
  .commandDir('cmds')
  .demandCommand()
  .help()
  .argv

cmds/init.js:

exports.command = 'init [dir]'
exports.desc = 'Create an empty repo'
exports.builder = {
  dir: {
    default: '.'
  }
}
exports.handler = function (argv) {
  console.log('init called for dir', argv.dir)
}

cmds/remote.js:

exports.command = 'remote <command>'
exports.desc = 'Manage set of tracked repos'
exports.builder = function (yargs) {
  return yargs.commandDir('remote_cmds')
}
exports.handler = function (argv) {}

cmds/remote_cmds/add.js:

exports.command = 'add <name> <url>'
exports.desc = 'Add remote named <name> for repo at url <url>'
exports.builder = {}
exports.handler = function (argv) {
  console.log('adding remote %s at url %s', argv.name, argv.url)
}

cmds/remote_cmds/prune.js:

exports.command = 'prune <name> [names..]'
exports.desc = 'Delete tracked branches gone stale for remotes'
exports.builder = {}
exports.handler = function (argv) {
  console.log('pruning remotes %s', [].concat(argv.name).concat(argv.names).join(', '))
}

.completion([cmd], [description], [fn])

Enable bash-completion shortcuts for commands and options.

cmd: When present in argv._, will result in the .bashrc completion script being outputted. To enable bash completions, concat the generated script to your .bashrc or .bash_profile.

description: Provide a description in your usage instructions for the command that generates bash completion scripts.

fn: Rather than relying on yargs' default completion functionality, which shiver me timbers is pretty awesome, you can provide your own completion method.

If invoked without parameters, .completion() will make completion the command to output the completion script.

var argv = require('yargs')
  .completion('completion', function(current, argv) {
    // 'current' is the current command being completed.
    // 'argv' is the parsed arguments so far.
    // simply return an array of completions.
    return [
      'foo',
      'bar'
    ];
  })
  .argv;

You can also provide asynchronous completions.

var argv = require('yargs')
  .completion('completion', function(current, argv, done) {
    setTimeout(function() {
      done([
        'apple',
        'banana'
      ]);
    }, 500);
  })
  .argv;

But wait, there's more! You can return an asynchronous promise.

var argv = require('yargs')
  .completion('completion', function(current, argv, done) {
    return new Promise(function (resolve, reject) {
      setTimeout(function () {
        resolve(['apple', 'banana'])
      }, 10)
    })
  })
  .argv;

.config([key], [description], [parseFn])

.config(object)

Tells the parser that if the option specified by key is passed in, it should be interpreted as a path to a JSON config file. The file is loaded and parsed, and its properties are set as arguments. Because the file is loaded using Node's require(), the filename MUST end in .json to be interpreted correctly.

If invoked without parameters, .config() will make --config the option to pass the JSON config file.

An optional description can be provided to customize the config (key) option in the usage string.

An optional parseFn can be used to provide a custom parser. The parsing function must be synchronous, and should return an object containing key value pairs or an error.

var argv = require('yargs')
  .config('settings', function (configPath) {
    return JSON.parse(fs.readFileSync(configPath, 'utf-8'))
  })
  .argv

You can also pass an explicit configuration object, it will be parsed and its properties will be set as arguments.

var argv = require('yargs')
  .config({foo: 1, bar: 2})
  .argv
console.log(argv)

$ node test.js
{ _: [],
  foo: 1,
  bar: 2,
  '$0': 'test.js' }

Note that a configuration object may extend from a JSON file using the "extends" property. When doing so, the "extends" value should be a path (relative or absolute) to the extended JSON file.

.conflicts(x, y)

Given the key x is set, the key y must not be set.

Optionally .conflicts() can accept an object specifying multiple conflicting keys.

.count(key)

Interpret key as a boolean flag, but set its parsed value to the number of flag occurrences rather than true or false. Default value is thus 0.

.default(key, value, [description])

.defaults(key, value, [description])

Note: The .defaults() alias is deprecated. It will be removed in the next major version.

Set argv[key] to value if no option was specified in process.argv.

Optionally .default() can take an object that maps keys to default values.

But wait, there's more! The default value can be a function which returns a value. The name of the function will be used in the usage string:

var argv = require('yargs')
  .default('random', function randomValue() {
    return Math.random() * 256;
  }).argv;

Optionally, description can also be provided and will take precedence over displaying the value in the usage instructions:

.default('timeout', 60000, '(one-minute)')

.demand(count, [max], [msg]) [DEPRECATED]

demand() has been deprecated, please instead see demandOption() and demandCommand().

.demandOption(key, [msg | boolean])

.demandOption(key, msg)

If key is a string, show the usage information and exit if key wasn't specified in process.argv.

If key is an array, demand each element.

If a msg string is given, it will be printed when the argument is missing, instead of the standard error message.

// demand an array of keys to be provided
require('yargs')
  .option('run', {
    alias: 'r',
    describe: 'run your program'
  })
  .option('path', {
    alias: 'p',
    describe: 'provide a path to file'
  })
  .option('spec', {
    alias: 's',
    describe: 'program specifications'
  })
  .demandOption(['run', 'path'], 'Please provide both run and path arguments to work with this tool')
  .help()
  .argv

which will provide the following output:

Options:
  --run, -r   run your program                [required]
  --path, -p  provide a path to file          [required]
  --spec, -s  program specifications
  --help      Show help                        [boolean]

  Missing required arguments: run, path
  Please provide both run and path arguments to work with this tool

If a boolean value is given, it controls whether the option is demanded; this is useful when using .options() to specify command line parameters.

// demand individual options within the option constructor
require('yargs')
  .options({
    'run': {
      alias: 'r',
      describe: 'run your program',
      demandOption: true
    },
    'path': {
      alias: 'p',
      describe: 'provide a path to file',
      demandOption: true
    },
    'spec': {
      alias: 's',
      describe: 'program specifications'
    }
  })
  .help()
  .argv

which will provide the following output:

Options:
  --run, -r   run your program                                       [required]
  --path, -p  provide a path to file                                 [required]
  --spec, -s  program specifications
  --help      Show help                                               [boolean]

Missing required arguments: run, path

.demandCommand([min=1], [minMsg])

.demandCommand([min=1], [max], [minMsg], [maxMsg])

Demand in context of commands. You can demand a minimum and a maximum number a user can have within your program, as well as provide corresponding error messages if either of the demands is not met.

require('yargs')
  .command({
    command: 'configure <key> [value]',
    aliases: ['config', 'cfg'],
    desc: 'Set a config variable',
    builder: (yargs) => yargs.default('value', 'true'),
    handler: (argv) => {
      console.log(`setting ${argv.key} to ${argv.value}`)
    }
  })
  // provide a minimum demand and a minimum demand message
  .demandCommand(1, 'You need at least one command before moving on')
  .help()
  .argv

which will provide the following output:

Commands:
  configure <key> [value]  Set a config variable         [aliases: config, cfg]

Options:
  --help  Show help                                                   [boolean]

You need at least one command before moving on

Note: in minMsg and maxMsg, every occurrence of $0 will be replaced with the observed value, and every instance of $1 will be replaced with the expected value.

.describe(key, desc)

Describe a key for the generated usage information.

Optionally .describe() can take an object that maps keys to descriptions.

.detectLocale(boolean)

Should yargs attempt to detect the os' locale? Defaults to true.

.env([prefix])

Tell yargs to parse environment variables matching the given prefix and apply them to argv as though they were command line arguments.

Use the "__" separator in the environment variable to indicate nested options. (e.g. prefix_nested__foo => nested.foo)

If this method is called with no argument or with an empty string or with true, then all env vars will be applied to argv.

Program arguments are defined in this order of precedence:

1. Command line args
2. Env vars
3. Config file/objects
4. Configured defaults

var argv = require('yargs')
  .env('MY_PROGRAM')
  .option('f', {
    alias: 'fruit-thing',
    default: 'apple'
  })
  .argv
console.log(argv)

$ node fruity.js
{ _: [],
  f: 'apple',
  'fruit-thing': 'apple',
  fruitThing: 'apple',
  '$0': 'fruity.js' }

$ MY_PROGRAM_FRUIT_THING=banana node fruity.js
{ _: [],
  fruitThing: 'banana',
  f: 'banana',
  'fruit-thing': 'banana',
  '$0': 'fruity.js' }

$ MY_PROGRAM_FRUIT_THING=banana node fruity.js -f cat
{ _: [],
  f: 'cat',
  'fruit-thing': 'cat',
  fruitThing: 'cat',
  '$0': 'fruity.js' }

Env var parsing is disabled by default, but you can also explicitly disable it by calling .env(false), e.g. if you need to undo previous configuration.

.epilog(str)

.epilogue(str)

A message to print at the end of the usage instructions, e.g.

var argv = require('yargs')
  .epilogue('for more information, find our manual at http://example.com');

.example(cmd, desc)

Give some example invocations of your program. Inside cmd, the string $0 will get interpolated to the current script name or node command for the present script similar to how $0 works in bash or perl. Examples will be printed out as part of the help message.

.exitProcess(enable)

By default, yargs exits the process when the user passes a help flag, uses the .version functionality, or when validation fails. Calling .exitProcess(false) disables this behavior, enabling further actions after yargs have been validated.

.fail(fn)

Method to execute when a failure occurs, rather than printing the failure message.

fn is called with the failure message that would have been printed, the Error instance originally thrown and yargs state when the failure occured.

var argv = require('yargs')
  .fail(function (msg, err, yargs) {
    if (err) throw err // preserve stack
    console.error('You broke it!')
    console.error(msg)
    console.error('You should be doing', yargs.help())
    process.exit(1)
  })
  .argv

.getCompletion(args, done);

Allows to programmatically get completion choices for any line.

args: An array of the words in the command line to complete.

done: The callback to be called with the resulting completions.

For example:

require('yargs')
  .option('foobar')
  .option('foobaz')
  .completion()
  .getCompletion(['./test.js', '--foo'], function (completions) {
    console.log(completions)
  })

Outputs the same completion choices as ./test.js --fooTAB: --foobar and --foobaz

.global(globals, [global=true])

Indicate that an option (or group of options) should not be reset when a command is executed, as an example:

var argv = require('yargs')
  .option('a', {
    alias: 'all',
    default: true,
    global: false
  })
  .option('n', {
    alias: 'none',
    default: true,
    global: false
  })
  .command('foo', 'foo command', function (yargs) {
    return yargs.option('b', {
      alias: 'bar'
    })
  })
  .help('help')
  .global('a')
  .argv

If the foo command is executed the all option will remain, but the none option will have been eliminated.

Options default to being global.

.group(key(s), groupName)

Given a key, or an array of keys, places options under an alternative heading when displaying usage instructions, e.g.,

var yargs = require('yargs')(['--help'])
  .help()
  .group('batman', 'Heroes:')
  .describe('batman', "world's greatest detective")
  .wrap(null)
  .argv

---

Heroes:
  --batman  world's greatest detective

Options:
  --help  Show help  [boolean]

.help()

.help([option | boolean])

.help([option, [description | boolean]])

.help([option, [description, [boolean]]])

Add an option (e.g. --help) and implicit command that displays the usage string and exits the process.

If present, the description parameter customizes the description of the help option in the usage string.

If a boolean argument is provided, it will enable or disable the use of an implicit command. The implicit command is enabled by default, but it can be disabled by passing false.

Note that any multi-char aliases (e.g. help) used for the help option will also be used for the implicit command. If there are no multi-char aliases (e.g. h), then all single-char aliases will be used for the command.

If invoked without parameters, .help() will use --help as the option and help as the implicit command to trigger help output.

Example:

var yargs = require("yargs")(['--help'])
  .usage("$0 -operand1 number -operand2 number -operation [add|subtract]")
  .help()
  .argv

Later on, argv can be retrieved with yargs.argv.

.implies(x, y)

Given the key x is set, it is required that the key y is set.

Optionally .implies() can accept an object specifying multiple implications.

.locale()

Return the locale that yargs is currently using.

By default, yargs will auto-detect the operating system's locale so that yargs-generated help content will display in the user's language.

To override this behavior with a static locale, pass the desired locale as a string to this method (see below).

.locale(locale)

Override the auto-detected locale from the user's operating system with a static locale. Note that the OS locale can be modified by setting/exporting the LC_ALL environment variable.

var argv = require('yargs')
  .usage('./$0 - follow ye instructions true')
  .option('option', {
    alias: 'o',
    describe: "'tis a mighty fine option",
    demandOption: true
  })
  .command('run', "Arrr, ya best be knowin' what yer doin'")
  .example('$0 run foo', "shiver me timbers, here's an example for ye")
  .help('help')
  .wrap(70)
  .locale('pirate')
  .argv

---

./test.js - follow ye instructions true

Choose yer command:
  run  Arrr, ya best be knowin' what yer doin'

Options for me hearties!
  --option, -o  'tis a mighty fine option               [requi-yar-ed]
  --help        Parlay this here code of conduct             [boolean]

Ex. marks the spot:
  test.js run foo  shiver me timbers, here's an example for ye

Ye be havin' to set the followin' argument land lubber: option

Locales currently supported:

• de: German.
• en: American English.
• es: Spanish.
• fr: French.
• hi: Hindi.
• hu: Hungarian.
• id: Indonesian.
• it: Italian.
• ja: Japanese.
• ko: Korean.
• nb: Norwegian Bokmål.
• pirate: American Pirate.
• pl: Polish.
• pt: Portuguese.
• pt_BR: Brazilian Portuguese.
• ru: Russian.
• th: Thai.
• tr: Turkish.
• zh_CN: Chinese.

To submit a new translation for yargs:

1. use ./locales/en.json as a starting point.
2. submit a pull request with the new locale file.

The Microsoft Terminology Search can be useful for finding the correct terminology in your locale.

.nargs(key, count)

The number of arguments that should be consumed after a key. This can be a useful hint to prevent parsing ambiguity. For example:

var argv = require('yargs')
  .nargs('token', 1)
  .parse(['--token', '-my-token']);

parses as:

{ _: [], token: '-my-token', '$0': 'node test' }

Optionally .nargs() can take an object of key/narg pairs.

.normalize(key)

The key provided represents a path and should have path.normalize() applied.

.number(key)

Tell the parser to always interpret key as a number.

If key is an array, all elements will be parsed as numbers.

If the option is given on the command line without a value, argv will be populated with undefined.

If the value given on the command line cannot be parsed as a number, argv will be populated with NaN.

Note that decimals, hexadecimals, and scientific notation are all accepted.

var argv = require('yargs')
  .number('n')
  .number(['width', 'height'])
  .argv

.option(key, [opt])

.options(key, [opt])

This method can be used to make yargs aware of options that could exist. You can also pass an opt object which can hold further customization, like .alias(), .demandOption() etc. for that option.

For example:

var argv = require('yargs')
    .option('f', {
        alias: 'file',
        demandOption: true,
        default: '/etc/passwd',
        describe: 'x marks the spot',
        type: 'string'
    })
    .argv
;

is the same as

var argv = require('yargs')
    .alias('f', 'file')
    .demandOption('f')
    .default('f', '/etc/passwd')
    .describe('f', 'x marks the spot')
    .string('f')
    .argv
;

Optionally .options() can take an object that maps keys to opt parameters.

var argv = require('yargs')
    .options({
      'f': {
        alias: 'file',
        demandOption: true,
        default: '/etc/passwd',
        describe: 'x marks the spot',
        type: 'string'
      }
    })
    .argv
;

Valid opt keys include:

• alias: string or array of strings, alias(es) for the canonical option key, see alias()
• array: boolean, interpret option as an array, see array()
• boolean: boolean, interpret option as a boolean flag, see boolean()
• choices: value or array of values, limit valid option arguments to a predefined set, see choices()
• coerce: function, coerce or transform parsed command line values into another value, see coerce()
• config: boolean, interpret option as a path to a JSON config file, see config()
• configParser: function, provide a custom config parsing function, see config()
• conflicts: string or object, require certain keys not to be set, see conflicts()
• count: boolean, interpret option as a count of boolean flags, see count()
• default: value, set a default value for the option, see default()
• defaultDescription: string, use this description for the default value in help content, see default()
• demandOption: boolean or string, demand the option be given, with optional error message, see demandOption()
• desc/describe/description: string, the option description for help content, see describe()
• global: boolean, indicate that this key should not be reset when a command is invoked, see global()
• group: string, when displaying usage instructions place the option under an alternative group heading, see group()
• implies: string or object, require certain keys to be set, see implies()
• nargs: number, specify how many arguments should be consumed for the option, see nargs()
• normalize: boolean, apply path.normalize() to the option, see normalize()
• number: boolean, interpret option as a number, number()
• requiresArg: boolean, require the option be specified with a value, see requiresArg()
• skipValidation: boolean, skips validation if the option is present, see skipValidation()
• string: boolean, interpret option as a string, see string()
• type: one of the following strings
  • 'array': synonymous for array: true, see array()
  • 'boolean': synonymous for boolean: true, see boolean()
  • 'count': synonymous for count: true, see count()
  • 'number': synonymous for number: true, see number()
  • 'string': synonymous for string: true, see string()

.parse(args, [context], [parseCallback])

Parse args instead of process.argv. Returns the argv object. args may either be a pre-processed argv array, or a raw argument string.

A context object can optionally be given as the second argument to parse(), providing a useful mechanism for passing state information to commands:

const parser = yargs
  .command('lunch-train <restaurant>', 'start lunch train', function () {}, function (argv) {
    console.log(argv.restaurant, argv.time)
  })
  .parse("lunch-train rudy's", {time: '12:15'})

A parseCallback can also be provided to .parse(). If a callback is given, it will be invoked with three arguments:

1. err: populated if any validation errors raised while parsing.
2. argv: the parsed argv object.
3. output: any text that would have been output to the terminal, had a callback not been provided.

// providing the `fn` argument to `parse()` runs yargs in headless mode, this
// makes it easy to use yargs in contexts other than the CLI, e.g., writing
// a chat-bot.
const parser = yargs
  .command('lunch-train <restaurant> <time>', 'start lunch train', function () {}, function (argv) {
    api.scheduleLunch(argv.restaurant, moment(argv.time))
  })
  .help()

parser.parse(bot.userText, function (err, argv, output) {
  if (output) bot.respond(output)
})

Note: Providing a callback to parse() disables the exitProcess setting until after the callback is invoked.

.pkgConf(key, [cwd])

Similar to config(), indicates that yargs should interpret the object from the specified key in package.json as a configuration object.

cwd can optionally be provided, the package.json will be read from this location.

Note that a configuration stanza in package.json may extend from an identically keyed stanza in another package.json file using the "extends" property. When doing so, the "extends" value should be a path (relative or absolute) to the extended package.json file.

.recommendCommands()

Should yargs provide suggestions regarding similar commands if no matching command is found?

.require(key, [msg | boolean])

.required(key, [msg | boolean])

An alias for demand(). See docs there.

.requiresArg(key)

Specifies either a single option key (string), or an array of options that must be followed by option values. If any option value is missing, show the usage information and exit.

The default behavior is to set the value of any key not followed by an option value to true.

.reset()

Reset the argument object built up so far. This is useful for creating nested command line interfaces. Use global to specify keys that should not be reset.

var yargs = require('yargs')
  .usage('$0 command')
  .command('hello', 'hello command')
  .command('world', 'world command')
  .demandCommand(1, 'must provide a valid command'),
  argv = yargs.argv,
  command = argv._[0];

if (command === 'hello') {
  yargs.reset()
    .usage('$0 hello')
    .help('h')
    .example('$0 hello', 'print the hello message!')
    .argv

  console.log('hello!');
} else if (command === 'world'){
  yargs.reset()
    .usage('$0 world')
    .help('h')
    .example('$0 world', 'print the world message!')
    .argv

  console.log('world!');
} else {
  yargs.showHelp();
}

.showCompletionScript()

Generate a bash completion script. Users of your application can install this script in their .bashrc, and yargs will provide completion shortcuts for commands and options.

.showHelp(consoleLevel='error')

Print the usage data using the console function consoleLevel for printing.

Example:

var yargs = require("yargs")
  .usage("$0 -operand1 number -operand2 number -operation [add|subtract]");
yargs.showHelp(); //prints to stderr using console.error()

Or, to print the usage data to stdout instead, you can specify the use of console.log:

yargs.showHelp("log"); //prints to stdout using console.log()

Later on, argv can be retrieved with yargs.argv.

.showHelpOnFail(enable, [message])

By default, yargs outputs a usage string if any error is detected. Use the .showHelpOnFail() method to customize this behavior. If enable is false, the usage string is not output. If the message parameter is present, this message is output after the error message.

line_count.js:

#!/usr/bin/env node
var argv = require('yargs')
    .usage('Count the lines in a file.\nUsage: $0 -f <file>')
    .demandOption('f')
    .alias('f', 'file')
    .describe('f', 'Load a file')
    .string('f')
    .showHelpOnFail(false, 'Specify --help for available options')
    .help('help')
    .argv;

// etc.

---

$ node line_count.js
Missing argument value: f

Specify --help for available options

.skipValidation(key)

Specifies either a single option key (string), or an array of options. If any of the options is present, yargs validation is skipped.

.strict([global=true])

Any command-line argument given that is not demanded, or does not have a corresponding description, will be reported as an error.

global indicates whether strict() should be enabled both at the top-level and for each sub-command.

.string(key)

Tell the parser logic not to interpret key as a number or boolean. This can be useful if you need to preserve leading zeros in an input.

If key is an array, interpret all the elements as strings.

.string('_') will result in non-hyphenated arguments being interpreted as strings, regardless of whether they resemble numbers.

.updateLocale(obj)

.updateStrings(obj)

Override the default strings used by yargs with the key/value pairs provided in obj:

var argv = require('yargs')
  .command('run', 'the run command')
  .help('help')
  .updateStrings({
    'Commands:': 'My Commands -->\n'
  })
  .wrap(null)
  .argv

---

My Commands -->

  run  the run command

Options:
  --help  Show help  [boolean]

If you explicitly specify a locale(), you should do so before calling updateStrings().

.usage(message, [opts])

Set a usage message to show which commands to use. Inside message, the string $0 will get interpolated to the current script name or node command for the present script similar to how $0 works in bash or perl.

opts is optional and acts like calling .options(opts).

.version([option], [description], [version])

Add an option (e.g. --version) that displays the version number (given by the version parameter) and exits the process.

If no arguments are passed to version (.version()), yargs will parse the package.json of your module and use its version value. The default value of option is --version.

You can provide a function for version, rather than a string. This is useful if you want to use a version stored in a location other than package.json:

var argv = require('yargs')
  .version(function() {
    return require('../lib/version').version;
  })
  .argv;

.wrap(columns)

Format usage output to wrap at columns many columns.

By default wrap will be set to Math.min(80, windowWidth). Use .wrap(null) to specify no column limit (no right-align). Use .wrap(yargs.terminalWidth()) to maximize the width of yargs' usage instructions.

parsing tricks

stop parsing

Use -- to stop parsing flags and stuff the remainder into argv._.

$ node examples/reflect.js -a 1 -b 2 -- -c 3 -d 4
{ _: [ '-c', '3', '-d', '4' ],
  a: 1,
  b: 2,
  '$0': 'examples/reflect.js' }

negate fields

If you want to explicitly set a field to false instead of just leaving it undefined or to override a default you can do --no-key.

$ node examples/reflect.js -a --no-b
{ _: [], a: true, b: false, '$0': 'examples/reflect.js' }

numbers

Every argument that looks like a number (!isNaN(Number(arg))) is converted to one. This way you can just net.createConnection(argv.port) and you can add numbers out of argv with + without having that mean concatenation, which is super frustrating.

duplicates

If you specify a flag multiple times it will get turned into an array containing all the values in order.

$ node examples/reflect.js -x 5 -x 8 -x 0
{ _: [], x: [ 5, 8, 0 ], '$0': 'examples/reflect.js' }

dot notation

When you use dots (.s) in argument names, an implicit object path is assumed. This lets you organize arguments into nested objects.

$ node examples/reflect.js --foo.bar.baz=33 --foo.quux=5
{ _: [],
  foo: { bar: { baz: 33 }, quux: 5 },
  '$0': 'examples/reflect.js' }

short numbers

Short numeric -n5 style arguments work too:

$ node examples/reflect.js -n123 -m456
{ _: [], n: 123, m: 456, '$0': 'examples/reflect.js' }

installation

With npm, just do:

npm install yargs

or clone this project on github:

git clone http://github.com/yargs/yargs.git

To run the tests with npm, just do:

npm test

configuration

Using the yargs stanza in your package.json you can turn on and off some of yargs' parsing features:

{
  "yargs": {
    "short-option-groups": true,
    "camel-case-expansion": true,
    "dot-notation": true,
    "parse-numbers": true,
    "boolean-negation": true
  }
}

See the yargs-parser module for detailed documentation of this feature.

inspired by

This module is loosely inspired by Perl's Getopt::Casual.