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# 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('yargs-parser')('--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']}`.<br>
Indicate that keys should be parsed as an array and coerced to booleans / numbers:<br>
`{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:<br>
`{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:<br>
`{configObjects: [{'x': 5, 'y': 33}, {'z': 44}]}`.
* `opts.configuration`: provide configuration options to the yargs-parser (see: [configuration](#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.
* `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 positional argument? This is similar to how e.g. `ssh` parses its command line.
_If disabled:_
```sh
node example.js -a run b -x y
{ _: [ 'b' ], a: 'run', x: 'y' }
```
_If enabled:_
```sh
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:_
```sh
node example.js --test-field 1
{ _: [], 'test-field': 1, testField: 1, 'test-alias': 1, testAlias: 1 }
```
_If enabled:_
```sh
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:_
```sh
node example.js --test-field 1
{ _: [], 'test-field': 1, testField: 1 }
```
_If enabled:_
```sh
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_
```sh
node example.js --unknown-option --known-option 2 --string-option --unknown-option2
{ _: [], unknownOption: true, knownOption: 2, stringOption: '', unknownOption2: true }
```
_If enabled_
```sh
node example.js --unknown-option --known-option 2 --string-option --unknown-option2
{ _: ['--unknown-option'], knownOption: 2, stringOption: '--unknown-option2' }
```
## 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