# yargs-parser

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The mighty option parser used by [yargs](https://github.com/yargs/yargs).

visit the [yargs website](http://yargs.js.org/) for more examples, and thorough usage instructions.

<img width="250" src="https://raw.githubusercontent.com/yargs/yargs-parser/master/yargs-logo.png">

## Example

```sh
npm i yargs-parser --save
```

```js
var argv = require('yargs-parser')(process.argv.slice(2))
console.log(argv)
```

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

_or parse a string!_

```js
var argv = require('./')('--foo=99 --bar=33')
console.log(argv)
```

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

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

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

## API

### require('yargs-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.config`: indicate a key that represents a path to a configuration file (this file will be loaded and parsed).
  * `opts.coerce`: provide a custom synchronous function that returns a coerced value from the argument provided
    (or throws an error), e.g. `{coerce: {foo: function (arg) {return modifiedArg}}}`.
  * `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.string`: keys should be treated as strings (even if they resemble a number `-x 33`).
  * `opts.configuration`: provide configuration options to the yargs-parser (see: [configuration](#configuration)).
  * `opts.number`: keys should be treated as numbers.
  * `opts['--']`: arguments after the end-of-options flag `--` will be set to the `argv.['--']` array instead of being set to the `argv._` array.

**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.
* `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.
* `configuration`: the configuration loaded from the `yargs` stanza in package.json.

<a name="configuration"></a>

### 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`.

```js
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?

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

_if disabled:_

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

### camel-case expansion

* default: `true`.
* key: `camel-case-expansion`.

Should hyphenated arguments be expanded into camel-case aliases?

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

_if disabled:_

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

### dot-notation

* default: `true`
* key: `dot-notation`

Should keys that contain `.` be treated as objects?

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

_if disabled:_

```sh
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?

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

_if disabled:_

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

### boolean negation

* default: `true`
* key: `boolean-negation`

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

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

_if disabled:_

```sh
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:

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

_if disabled:_

```sh
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:

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

_if disabled:_

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

### negation prefix

* default: `no-`
* key: `negation-prefix`

The prefix to use for negated boolean variables.

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

_if set to `quux`:_

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

### populate --

* default: `false`.
* key: `populate--`

Should unparsed flags be stored in `--` or `_`.

_If disabled:_

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

_If enabled:_

```sh
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:_

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

_If enabled:_

```sh
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 text argument? This is similar to how e.g. `ssh` parses its command line.

_If disabled:_

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

_If enabled:_

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

## 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](https://github.com/substack) **beep** **boop** \o/

## License

ISC
