Light-weight option parsing with an argv hash. No optstrings attached.

npm install yargs
20 079 downloads in the last day
80 062 downloads in the last week
103 378 downloads in the last month


Yargs be a node.js library fer hearties tryin' ter parse optstrings against their will where even the boo box be not enough to coerce them. This here module is fer scallywags lookin' ter plunder all the sunken -shipz of their --treasures thru program usage but be tired of optstrings disincling to acquiesce to yer requests.

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

Build Status Dependency Status NPM version

NOTE: Yargs is a fork of optimist by substack (James Halliday). It is obvious that substack is stretched pretty thin maintaining over 300 modules on npm at the time of this writing. So rather than complain in the project issue tracker I thought I'd just pick up the torch and maintain a proper fork. Currently the project is totally backward compatible with optimist but this may change in the future (if it does I will update this notice to inform you of this). For now though, enjoy optimist with about 5 months worth of fixes and updates rolled in, most of them pulled from optimist's own stale pull requests.


With yargs, the options be just a hash! No optstrings be attached.


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

if (argv.rif - 5 * argv.xup > 7.138) {
    console.log('Plunder more riffiwobbles!');
else {
    console.log('Drop the xupptumblers!');

$ ./xup.js --rif=55 --xup=9.52
Plunder more riffiwobbles!

$ ./xup.js --rif 12 --xup 8.1
Drop the xupptumblers!

Joe was one optimistic pirate.

But don' walk the plank jus' yet! Ther' be more! Ye can do short options:


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

$ ./short.js -x 10 -y 21

And gold doubooleans, both long an' short (an' grouped!):


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

if (argv.s) {
    util.print(argv.fr ? 'Le perroquet dit: ' : 'The parrot says: ');
    (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._!


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

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

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

Yargs even counts yer gold doubooleans!


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

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-mportant 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 yer friends how ter use yer options and make demands from yer enemies.


#!/usr/bin/env node
var argv = require('yargs')
    .usage('Usage: $0 -x [num] -y [num]')

console.log(argv.x / argv.y);

$ ./divide.js -x 55 -y 11

$ node ./divide.js -x 4.91 -z 2.51
Usage: node ./divide.js -x [num] -y [num]

  -x  [required]
  -y  [required]

Missing required arguments: y

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


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

$ ./demand_count.js a
Not enough arguments, expected 2, but only found 1
$ ./demand_count.js a b
{ _: [ 'a', 'b' ], '$0': 'node ./demand_count.js' }
$ ./demand_count.js a b c
{ _: [ 'a', 'b', 'c' ], '$0': 'node ./demand_count.js' }



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

$ ./default_singles.js -x 5


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

$ ./default_hash.js -y 7

And if ye really want ter get all descriptive about it...


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

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


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

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

Yargs is here ter help ye...

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


#!/usr/bin/env node
var argv = require('yargs')
    .usage('Count the lines in a file.\nUsage: $0')
    .example('$0 -f', 'count the lines in the given file')
    .alias('f', 'file')
    .describe('f', 'Load a file')

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 () {

$ node line_count.js
Count the lines in a file.
Usage: node ./line_count.js

  node ./line_count.js -f   count the lines in the given file

  -f, --file  Load a file  [required]

Missing required arguments: f

$ node line_count.js --file line_count.js 

$ node line_count.js -f line_count.js 


By itself,


will use 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.

.default(key, value)

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

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

.demand(key, [msg])

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

If key is a number, demand at least as many non-option arguments, which show up in argv._.

If key is an Array, demand each element.

If msg is supplied, it will be printed when the argument is missing, instead of the standard error message. This is especially helpful for the non-option arguments in argv._.

.describe(key, desc)

Describe a key for the generated usage information.

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

.options(key, opt)

Instead of chaining together .alias().demand().default(), you can specify keys in opt for each of the chainable methods.

For example:

var argv = require('yargs')
    .options('f', {
        alias : 'file',
        default : '/etc/passwd',

is the same as

var argv = require('yargs')
    .alias('f', 'file')
    .default('f', '/etc/passwd')

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


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.

.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.


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 false, show the thrown error, usage information, and exit.


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.

If key never shows up as a flag in process.arguments, argv[key] will be false.

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


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.


Tells the parser to interpret key as a path to a JSON config file. The file is loaded and parsed, and its properties are set as arguments.


Format usage output to wrap at columns many columns.


Return the generated usage string.


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

Later on, argv can be retrived with yargs.argv


Print the usage data using fn for printing.


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

Later on, argv can be retrived with yargs.argv


Parse args instead of process.argv. Returns the argv object.


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.

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' ],
  '$0': 'node ./examples/reflect.js',
  a: 1,
  b: 2 }

negate fields

If you want to explicity 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
{ _: [],
  '$0': 'node ./examples/reflect.js',
  a: true,
  b: false }


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.


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

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

short numbers

Short numeric head -n5 style argument work too:

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


With npm, just do:

npm install yargs

or clone this project on github:

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

To run the tests with expresso, just do:


inspired By

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

npm loves you