yargs-parser

yargs-parser

The mighty option parser used by yargs.

visit the yargs website for more examples, and thorough usage instructions.

Example

npm i yargs-parser --save

const argv = require('yargs-parser')(process.argv.slice(2))
console.log(argv)

$ node example.js --foo=33 --bar hello
{ _: [], foo: 33, bar: 'hello' }

or parse a string!

const argv = require('yargs-parser')('--foo=99 --bar=33')
console.log(argv)

{ _: [], foo: 99, bar: 33 }

Convert an array of mixed types before passing to yargs-parser:

const parse = require('yargs-parser')
parse(['-f', 11, '--zoom', 55].join(' '))   // <-- array to string
parse(['-f', 11, '--zoom', 55].map(String)) // <-- array of strings

Deno Example

As of v19 yargs-parser supports Deno:

import parser from "https://deno.land/x/yargs_parser/deno.ts";

const argv = parser('--foo=99 --bar=9987930', {
  string: ['bar']
})
console.log(argv)

ESM Example

As of v19 yargs-parser supports ESM (both in Node.js and in the browser):

Node.js:

import parser from 'yargs-parser'

const argv = parser('--foo=99 --bar=9987930', {
  string: ['bar']
})
console.log(argv)

Browsers:

<!doctype html>
<body>
  <script type="module">
    import parser from "https://unpkg.com/yargs-parser@19.0.0/browser.js";

    const argv = parser('--foo=99 --bar=9987930', {
      string: ['bar']
    })
    console.log(argv)
  </script>
</body>

API

parser(args, opts={})

Parses command line arguments returning a simple mapping of keys and values.

expects:

• args: a string or array of strings representing the options to parse.
• opts: provide a set of hints indicating how args should be parsed:
  • opts.alias: an object representing the set of aliases for a key: {alias: {foo: ['f']}}.
  • opts.array: indicate that keys should be parsed as an array: {array: ['foo', 'bar']}.
    Indicate that keys should be parsed as an array and coerced to booleans / numbers:
    {array: [{ key: 'foo', boolean: true }, {key: 'bar', number: true}]}.
  • opts.boolean: arguments should be parsed as booleans: {boolean: ['x', 'y']}.
  • opts.coerce: provide a custom synchronous function that returns a coerced value from the argument provided (or throws an error). For arrays the function is called only once for the entire array:
    {coerce: {foo: function (arg) {return modifiedArg}}}.
  • opts.config: indicate a key that represents a path to a configuration file (this file will be loaded and parsed).
  • opts.configObjects: configuration objects to parse, their properties will be set as arguments:
    {configObjects: [{'x': 5, 'y': 33}, {'z': 44}]}.
  • opts.configuration: provide configuration options to the yargs-parser (see: configuration).
  • opts.count: indicate a key that should be used as a counter, e.g., -vvv = {v: 3}.
  • opts.default: provide default values for keys: {default: {x: 33, y: 'hello world!'}}.
  • opts.envPrefix: environment variables (process.env) with the prefix provided should be parsed.
  • opts.narg: specify that a key requires n arguments: {narg: {x: 2}}.
  • opts.normalize: path.normalize() will be applied to values set to this key.
  • opts.number: keys should be treated as numbers.
  • opts.string: keys should be treated as strings (even if they resemble a number -x 33).

returns:

• obj: an object representing the parsed value of args
  • key/value: key value pairs for each argument and their aliases.
  • _: an array representing the positional arguments.
  • [optional] --: an array with arguments after the end-of-options flag --.

require('yargs-parser').detailed(args, opts={})

Parses a command line string, returning detailed information required by the yargs engine.

expects:

• args: a string or array of strings representing options to parse.
• opts: provide a set of hints indicating how args, inputs are identical to require('yargs-parser')(args, opts={}).

returns:

• argv: an object representing the parsed value of args
  • key/value: key value pairs for each argument and their aliases.
  • _: an array representing the positional arguments.
  • [optional] --: an array with arguments after the end-of-options flag --.
• error: populated with an error object if an exception occurred during parsing.
• aliases: the inferred list of aliases built by combining lists in opts.alias.
• newAliases: any new aliases added via camel-case expansion:
  • boolean: { fooBar: true }
• defaulted: any new argument created by opts.default, no aliases included.
  • boolean: { foo: true }
• configuration: given by default settings and opts.configuration.

Configuration

The yargs-parser applies several automated transformations on the keys provided in args. These features can be turned on and off using the configuration field of opts.

var parsed = parser(['--no-dice'], {
  configuration: {
    'boolean-negation': false
  }
})

short option groups

• default: true.
• key: short-option-groups.

Should a group of short-options be treated as boolean flags?

$ node example.js -abc
{ _: [], a: true, b: true, c: true }

if disabled:

$ node example.js -abc
{ _: [], abc: true }

camel-case expansion

• default: true.
• key: camel-case-expansion.

Should hyphenated arguments be expanded into camel-case aliases?

$ node example.js --foo-bar
{ _: [], 'foo-bar': true, fooBar: true }

if disabled:

$ node example.js --foo-bar
{ _: [], 'foo-bar': true }

dot-notation

• default: true
• key: dot-notation

Should keys that contain . be treated as objects?

$ node example.js --foo.bar
{ _: [], foo: { bar: true } }

if disabled:

$ node example.js --foo.bar
{ _: [], "foo.bar": true }

parse numbers

• default: true
• key: parse-numbers

Should keys that look like numbers be treated as such?

$ node example.js --foo=99.3
{ _: [], foo: 99.3 }

if disabled:

$ node example.js --foo=99.3
{ _: [], foo: "99.3" }

parse positional numbers

• default: true
• key: parse-positional-numbers

Should positional keys that look like numbers be treated as such.

$ node example.js 99.3
{ _: [99.3] }

if disabled:

$ node example.js 99.3
{ _: ['99.3'] }

boolean negation

• default: true
• key: boolean-negation

Should variables prefixed with --no be treated as negations?

$ node example.js --no-foo
{ _: [], foo: false }

if disabled:

$ node example.js --no-foo
{ _: [], "no-foo": true }

combine arrays

• default: false
• key: combine-arrays

Should arrays be combined when provided by both command line arguments and a configuration file.

duplicate arguments array

• default: true
• key: duplicate-arguments-array

Should arguments be coerced into an array when duplicated:

$ node example.js -x 1 -x 2
{ _: [], x: [1, 2] }

if disabled:

$ node example.js -x 1 -x 2
{ _: [], x: 2 }

flatten duplicate arrays

• default: true
• key: flatten-duplicate-arrays

Should array arguments be coerced into a single array when duplicated:

$ node example.js -x 1 2 -x 3 4
{ _: [], x: [1, 2, 3, 4] }

if disabled:

$ node example.js -x 1 2 -x 3 4
{ _: [], x: [[1, 2], [3, 4]] }

greedy arrays

• default: true
• key: greedy-arrays

Should arrays consume more than one positional argument following their flag.

$ node example --arr 1 2
{ _: [], arr: [1, 2] }

if disabled:

$ node example --arr 1 2
{ _: [2], arr: [1] }

Note: in v18.0.0 we are considering defaulting greedy arrays to false.

nargs eats options

• default: false
• key: nargs-eats-options

Should nargs consume dash options as well as positional arguments.

negation prefix

• default: no-
• key: negation-prefix

The prefix to use for negated boolean variables.

$ node example.js --no-foo
{ _: [], foo: false }

if set to quux:

$ node example.js --quuxfoo
{ _: [], foo: false }

populate --

• default: false.
• key: populate--

Should unparsed flags be stored in -- or _.

If disabled:

$ node example.js a -b -- x y
{ _: [ 'a', 'x', 'y' ], b: true }

If enabled:

$ node example.js a -b -- x y
{ _: [ 'a' ], '--': [ 'x', 'y' ], b: true }

set placeholder key

• default: false.
• key: set-placeholder-key.

Should a placeholder be added for keys not set via the corresponding CLI argument?

If disabled:

$ node example.js -a 1 -c 2
{ _: [], a: 1, c: 2 }

If enabled:

$ node example.js -a 1 -c 2
{ _: [], a: 1, b: undefined, c: 2 }

halt at non-option

• default: false.
• key: halt-at-non-option.

Should parsing stop at the first positional argument? This is similar to how e.g. ssh parses its command line.

If disabled:

$ node example.js -a run b -x y
{ _: [ 'b' ], a: 'run', x: 'y' }

If enabled:

$ node example.js -a run b -x y
{ _: [ 'b', '-x', 'y' ], a: 'run' }

strip aliased

• default: false
• key: strip-aliased

Should aliases be removed before returning results?

If disabled:

$ node example.js --test-field 1
{ _: [], 'test-field': 1, testField: 1, 'test-alias': 1, testAlias: 1 }

If enabled:

$ node example.js --test-field 1
{ _: [], 'test-field': 1, testField: 1 }

strip dashed

• default: false
• key: strip-dashed

Should dashed keys be removed before returning results? This option has no effect if camel-case-expansion is disabled.

If disabled:

$ node example.js --test-field 1
{ _: [], 'test-field': 1, testField: 1 }

If enabled:

$ node example.js --test-field 1
{ _: [], testField: 1 }

unknown options as args

• default: false
• key: unknown-options-as-args

Should unknown options be treated like regular arguments? An unknown option is one that is not configured in opts.

If disabled

$ node example.js --unknown-option --known-option 2 --string-option --unknown-option2
{ _: [], unknownOption: true, knownOption: 2, stringOption: '', unknownOption2: true }

If enabled

$ node example.js --unknown-option --known-option 2 --string-option --unknown-option2
{ _: ['--unknown-option'], knownOption: 2, stringOption: '--unknown-option2' }

Supported Node.js Versions

Libraries in this ecosystem make a best effort to track Node.js' release schedule. Here's a post on why we think this is important.

Special Thanks

The yargs project evolves from optimist and minimist. It owes its existence to a lot of James Halliday's hard work. Thanks substack beep boop \o/

License

ISC