Additional documentation

For more details refer to the official API reference document on the yargs.js.org website.

This document is the Yargs API reference. There are more documentation files in docs in the Yargs source tree:

• Examples
• Advanced Topics
• TypeScript usage examples
• Browser usage example
• Bundling
• Parsing Tricks

API reference

You can pass Yargs the process.argv without any additional configuration and it will do its best to parse it into an object:

require('yargs/yargs')(process.argv.slice(2)).argv

You can also pass in an arbitrary array of arguments:

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

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

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

Calling .parse() with no arguments is equivalent to calling .argv:

require('yargs/yargs')(process.argv.slice(2)).parse()

When passing in the arguments yourself, note that Yargs expects the passed array to contain only the arguments after the program name, while process.argv usually starts with extra elements. For example, Node’s process.argv array starts with two extra elements:process.execPath and the path to the JavaScript file being executed. So if you’re getting your arguments from process.argv in Node, pass process.argv.slice(2) to Yargs.

Note: Yargs exposes the helper hideBin, which handles the process.argv.slice logic for you.

const { hideBin } = require('yargs/helpers')
const argv = yargs(hideBin(process.argv)).argv

The rest of these methods below come in just before the terminating .argv or terminating .parse().

.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. Note that elements of argv._ may be converted to numbers by default.

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.

Note: .argv should only be used at the top level, not inside a command's builder function.

.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'. Also, if you use the option multiple times all the values will be flattened in one array so --foo foo --foo bar will be parsed as ['foo', 'bar']

When the option is used with a positional, use -- to tell yargs to stop adding values to the array.

For example: --foo foo bar -- val will be parsed as

{
  _: ['val'],
  foo: ['foo', 'bar']
}

.boolean(key)

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

key can be set false explicitly using the --no- prefix, more.

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 the parsed argv hash.

If fn throws anything, returns an instance of error, returns a string, or returns any non-truthy value, Yargs will show the thrown error and usage information. Yargs will then exit, unless .exitProcess() was used to prevent Yargs from exiting after a failed check.

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

const argv = require('yargs/yargs')(process.argv.slice(2))
  .check((argv, options) => {
    const filePaths = argv._
    if (filePaths.length > 1) {
      throw new Error("Only 0 or 1 files may be passed.")
    } else {
      return true // tell Yargs that the arguments passed the check
    }
  })
  .argv

.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/yargs')(process.argv.slice(2))
  .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/yargs')(process.argv.slice(2))
  .option('size', {
    alias: 's',
    describe: 'choose a size',
    choices: ['xs', 's', 'm', 'l', 'xl']
  })
  .argv

.coerce(key, fn)

Provide a 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 (an array if multiple values are parsed for the key), 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/yargs')(process.argv.slice(2))
  .coerce('file', function (arg) {
    return await require('fs').promises.readFile(arg, 'utf8')
  })
  .argv

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

var argv = require('yargs/yargs')(process.argv.slice(2))
  .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/yargs')(process.argv.slice(2))
  .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/yargs')(process.argv.slice(2))
  .option('user')
  .coerce('user', opt => {
    opt.name = opt.name.toLowerCase()
    opt.password = '[SECRET]'
    return opt
  })
  .argv

.commandDir(directory, [opts])

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

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

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

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

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

visit: 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: Allow list certain modules. See require-directory for details.

exclude: Block list certain modules. See require-directory for details.

.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, which can be used to provide command-specific configuration, and the boolean helpOrVersionSet, which indicates whether or not the --help or --version flag was set prior to calling the builder.

yargs
  .command('get', 'make a get HTTP request', function (yargs, helpOrVersionSet) {
    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

Note: .parse() and .argv should only be used at the top level, not inside a command's builder function.

Please see Advanced Topics: Commands for a thorough discussion of the advanced features exposed in the Command API.

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

Enable bash/zsh-completion shortcuts for commands and options.

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

description: Provide a description in your usage instructions for the command that generates the 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/yargs')(process.argv.slice(2))
  .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/yargs')(process.argv.slice(2))
  .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/yargs')(process.argv.slice(2))
  .completion('completion', function(current, argv) {
    return new Promise(function (resolve, reject) {
      setTimeout(function () {
        resolve(['apple', 'banana'])
      }, 10)
    })
  })
  .argv;

Using default completions in a custom implementation. When invoked with no arguments, completionFilter will fallback to the default completion function. There is no need to call done in this case. When provided with a callback function, you can get access to defaultCompletions and call done with your processed version of them.

var argv = require('yargs/yargs')(process.argv.slice(2))
  .completion('completion', function(current, argv, completionFilter, done) {
    // if 'apple' present return default completions
    if (argv._.includes('apple')) {
      completionFilter();
    } else {
      completionFilter((err, defaultCompletions) => {
        const filteredCompletions = defaultCompletions.filter(
          completion => !completion.includes('banana'),
        );
        // else return default completions w/o 'banana'
        done(filteredCompletions);
      });
    }
  })
  .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/yargs')(process.argv.slice(2))
  .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/yargs')(process.argv.slice(2))
  .config({foo: 1, bar: 2})
  .argv
console.log(argv)

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

extends Keyword

config and pkgConf can provide the extends keyword to indicate that configuration should inherit from another location.

The value of extends can be either a relative or absolute path to a JSON configuration file, e.g.,

yargs.config({
  extends: './configs/a.json',
  logLevel: 'verbose'
})

Or, a module can be provided (this is useful for creating functionality like babel-presets).

my-library.js

yargs.pkgConf('nyc')

consuming package.json

{
  "nyc": {
    "extends": "nyc-babel-config"
  }
}

Where nyc-babel-config is a package that exports configuration in its index.

.conflicts(x, y)

Given the key x is set, the key y must not be set. y can either be a single string or an array of argument names that x conflicts with.

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]) [DEPRECATED]

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

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/yargs')(process.argv.slice(2))
  .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/yargs')(process.argv.slice(2))
  .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/yargs')(process.argv.slice(2))
  .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/yargs')(process.argv.slice(2))
  .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.

.deprecateOption(key, [msg | boolean])

Shows a [deprecated] notice in front of the option.

require('yargs/yargs')(process.argv.slice(2))
  .option('old')
  .deprecateOption('old')
  .option('new')

Options:
  --old                                     [deprecated]
  --new

You can also specify a message

require('yargs/yargs')(process.argv.slice(2))
  .option('old')
  .deprecateOption('old', 'use --new')
  .option('new')

Options:
  --old                          [deprecated: use --new]
  --new

You can also use it within the option constructor

require('yargs/yargs')(process.argv.slice(2))
  .option('old', { deprecated: true })

.describe(key, desc)

Describe a key for the generated usage information.

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

.hide(key)

Hides a key from the generated usage information. Unless a --show-hidden option is also passed with --help (see showHidden()).

.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/yargs')(process.argv.slice(2))
  .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/yargs')(process.argv.slice(2))
  .epilogue('for more information, find our manual at http://example.com');

.example(cmd, desc)

.example([[cmd1, desc1], [cmd2, desc2], ...])

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.

If you want to add multiple examples at once, just pass an array of examples, e.g

require('yargs/yargs')(process.argv.slice(2))
  .example([
    ['$0 --config "~/config.json"', 'Use custom config'],
    ['$0 --safe', 'Start in safe mode']
  ]);

.exitProcess(enable)

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

Note: .exitProcess(false) should not be used when .command() is called with a handler returning a promise, as it would lead to a duplicated error message when this promise rejects

.exit(code, err)

Manually indicate that the program should exit, and provide context about why we wanted to exit. Follows the behavior set by .exitProcess().

.fail(fn | boolean)

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

Providing false as a value for fn can be used to prevent yargs from exiting and printing a failure message. This is useful if you wish to handle failures yourself using try/catch and .getHelp().

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

var argv = require('yargs/yargs')(process.argv.slice(2))
  .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: Optional callback which will be invoked with err, or the resulting completions.

If no done callback is provided, getCompletion returns a promise that resolves with the completions.

For example:

require('yargs/yargs')(process.argv.slice(2))
  .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

.getHelp()

Returns a promise that resolves with a string equivalent to what would be output by .showHelp(), or by running yargs with --help.

.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/yargs')(process.argv.slice(2))
  .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.,

require('yargs/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]])

Configure an (e.g. --help) and implicit command that displays the usage string and exits the process. By default yargs enables help on the --help option.

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

If the boolean argument false is provided, it will disable --help.

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

.implies(x, y)

Given the key x is set, it is required that the key y is set. y can either be the name of an argument to imply, a number indicating the position of an argument or an array of multiple implications to associate with x.

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/yargs')(process.argv.slice(2))
  .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:

• be: Belarusian.
• de: German.
• en: American English.
• es: Spanish.
• fr: French.
• hi: Hindi.
• hu: Hungarian.
• id: Indonesian.
• it: Italian.
• ja: Japanese.
• ko: Korean.
• nb: Norwegian Bokmål.
• nl: Dutch.
• nn: Norwegian Nynorsk.
• pirate: American Pirate.
• pl: Polish.
• pt: Portuguese.
• pt_BR: Brazilian Portuguese.
• ru: Russian.
• uz: Uzbek.
• th: Thai.
• tr: Turkish.
• zh_CN: Chinese (Mainland China).
• zh_TW: Chinese (Taiwan).

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.

.middleware(callbacks, [applyBeforeValidation])

Define global middleware functions to be called first, in list order, for all cli command.

The callbacks parameter can be a function or a list of functions. Each callback gets passed a reference to argv.

const mwFunc1 = argv => console.log('I\'m a middleware function');
const mwFunc2 = argv => console.log('I\'m another middleware function');

yargs
  .command('myCommand', 'some command', {}, function(argv){
    console.log('Running myCommand!');
  })
  .middleware([mwFunc1, mwFunc2]).argv;

When calling myCommand from the command line, mwFunc1 gets called first, then mwFunc2, and finally the command's handler. The console output is:

I'm a middleware function
I'm another middleware function
Running myCommand!

Middleware can be applied before validation by setting the second parameter to true. This will execute the middleware prior to validation checks, but after parsing.

Middleware is passed two parameters argv, the current parsed options object, and yargs the yargs instance itself, which provides contextual information about the current state of parsing.

A modified argv object will ultimately be what is passed to a command's handler function.

// populating home directory from an environment variable.
require('yargs/yargs')(process.argv.slice(2))
  .middleware(function (argv) {
    if (process.env.HOME) argv.home = process.env.HOME
  }, true)
  .command('configure-home', "do something with a user's home directory",
    {
      'home': {
        'demand': true,
        'string': true
      }
    },
    function(argv) {
      console.info(`we know the user's home directory is ${argv.home}`)
    }
  )
  .parse()

Example, Using middleware to apply a transformation on argv after choices have been enforced (see #756):

require('yargs')
  .command('$0', 'accept username', () => {}, (argv) => {
    // The middleware will have been applied before the default
    // command is called:
    console.info(argv);
  })
  .choices('user', ['Goofy', 'Miky'])
  .middleware(argv => {
    console.info('gots here');
    const user = argv.user;
    switch (user) {
      case 'Goofy':
        argv.user = {
          firstName: 'Mark',
          lastName: 'Pipe',
        };
        break;
      case 'Miky':
        argv.user = {
          firstName: 'Elon',
          lastName: 'Stone',
        };
        break;
    }
    return argv;
  })
  .parse('--user Miky');

.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/yargs')(process.argv.slice(2))
  .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/yargs')(process.argv.slice(2))
  .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/yargs')(process.argv.slice(2))
    .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/yargs')(process.argv.slice(2))
    .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/yargs')(process.argv.slice(2))
    .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 array of strings, 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()
• deprecate/deprecated: boolean or string, mark option as deprecated, see deprecateOption()
• 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()
• hidden: don't display option in help output.
• implies: string or array of strings, 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 by yargs 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() prevents Yargs from exiting automatically while there is still work in the event loop, as if the exitProcess setting were set to false.

Note: the output parameter of a parse() callback only contains text output by yargs using its internal logger. It does not include any text output by user-supplied callback, such as console.log() outputs in a command handler, for example.

Note: when using command() with a handler returning a promise, if this promise is rejected, the resulting error and output will not be passed to the parse() callback (the error message will be displayed directly)

Note: parse() should be called only once when command() is called with a handler returning a promise. If your use case requires parse() to be called several times, any asynchronous operation performed in a command handler should not result in the handler returning a promise.

Note: .parse() should only be used at the top level, not inside a command's builder function.

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

Identical to .parse() except always returns a promise for a parsed argv object, regardless of whether an async builder, handler, or middleware is used.

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

Identical to .parse() except an exception is thrown if an asynchronous builder, handler, or middleware is used.

.parsed [DEPRECATED]

If the arguments have not been parsed, this property is false.

If the arguments have been parsed, this contain detailed parsed arguments. See the documentation in yargs-parser .detailed() for details of this object

.parserConfiguration(obj)

parserConfiguration() allows you to configure advanced yargs features.

See yargs-parser's configuration for valid configuration options. Yargs also supports the following options:

• sort-commands when set to true (boolean) will sort the commands added, the default is false.

yargs.parserConfiguration({
  "short-option-groups": true,
  "camel-case-expansion": true,
  "dot-notation": true,
  "parse-numbers": true,
  "parse-positional-numbers": true,
  "boolean-negation": true,
  "deep-merge-config": false
})

.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.

.positional(key, opt)

.positional() allows you to configure a command's positional arguments with an API similar to .option(). .positional() should be called in a command's builder function, and is not available on the top-level yargs instance.

you can describe top-level positional arguments using default commands.

const argv = require('yargs/yargs')('run --help')
  .command('run <port> <guid>', 'run the server', (yargs) => {
    yargs.positional('guid', {
      describe: 'a unique identifier for the server',
      type: 'string'
    })
  }).argv
console.log(argv)

Valid opt keys include:

• alias: string or array of strings, see alias()
• 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()
• conflicts: string or object, require certain keys not to be set, see conflicts()
• 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()
• desc/describe/description: string, the option description for help content, see describe()
• implies: string or object, require certain keys to be set, see implies()
• normalize: boolean, apply path.normalize() to the option, see normalize()
• type: one of the following strings
  • 'boolean': synonymous for boolean: true, see boolean()
  • 'number': synonymous for number: true, see number()
  • 'string': synonymous for string: true, see string()

.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.

.scriptName($0)

Set the name of your script ($0). Default is the base filename executed by node (process.argv[1] or process.argv[0] for built electron apps)

Example:

var yargs = require("yargs")
  .scriptName("my-script")
  .help()
  .argv

.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 | printCallback])

Print the usage data.

If no argument is provided, usage data is printed using console.error.

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

If a string is specified, usage data is printed using the console function consoleLevel.

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

If a function is specified, it is called with a single argument - the usage data as a string.

yargs.showHelp(s => myStream.write(s)); //prints to myStream

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

.showVersion([consoleLevel | printCallback])

Print the version data.

If no argument is provided, version data is printed using console.error.

var yargs = require('yargs/yargs')(process.argv.slice(2));
yargs.version('1.0.0');
yargs.showVersion(); //prints to stderr using console.error()

If a string is specified, version data is printed using the console function consoleLevel.

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

If a function is specified, it is called with a single argument - the version data as a string.

yargs.showVersion(s => myStream.write(s)); //prints to myStream

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/yargs')(process.argv.slice(2))
    .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

.showHidden()

.showHidden([option | boolean])

.showHidden([option, [description]])

Configure the --show-hidden option that displays the hidden keys (see hide()).

If the first argument is a boolean, it enables/disables this option altogether. i.e. hidden keys will be permanently hidden if first argument is false.

If the first argument is a string it changes the key name ("--show-hidden").

Second argument changes the default description ("Show hidden options")

Example:

var yargs = require("yargs")(['--help'])
  .showHidden('show-hidden', 'Show hidden options')
  .argv

.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([enabled=true])

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

Unrecognized commands will also be reported as errors.

.strictCommands([enabled=true])

Similar to .strict(), except that it only applies to unrecognized commands. A user can still provide arbitrary options, but unknown positional commands will raise an error.

.strictOptions([enabled=true])

Similar to .strict(), except that it only applies to unrecognized options. A user can still provide arbitrary positional commands, but unknown options will raise an error.

.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/yargs')(process.argv.slice(2))
  .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|command>, [desc], [builder], [handler])

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.

If the optional desc/builder/handler are provided, .usage() acts an an alias for .command(). This allows you to use .usage() to configure the default command that will be run as an entry-point to your application and allows you to provide configuration for the positional arguments accepted by your program:

const argv = require('yargs/yargs')(process.argv.slice(2))
  .usage('$0 <port>', 'start the application server', (yargs) => {
    yargs.positional('port', {
      describe: 'the port that your application should bind to',
      type: 'number'
    })
  }).argv

.version()

.version([version|boolean])

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

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

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

If the boolean argument false is provided, it will disable --version.

.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.