| Index: mojo/public/dart/third_party/args/README.md
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| +Parses raw command-line arguments into a set of options and values.
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| +
|
| +This library supports [GNU][] and [POSIX][] style options, and it works
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| +in both server-side and client-side apps.
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| +
|
| +## Defining options
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| +
|
| +First create an [ArgParser][]:
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| +
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| + var parser = new ArgParser();
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| +
|
| +Then define a set of options on that parser using [addOption()][addOption] and
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| +[addFlag()][addFlag]. Here's the minimal way to create an option named "name":
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| +
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| + parser.addOption('name');
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| +
|
| +When an option can only be set or unset (as opposed to taking a string value),
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| +use a flag:
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| +
|
| +```dart
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| +parser.addFlag('name');
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| +```
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| +
|
| +Flag options, by default, accept a 'no-' prefix to negate the option. You can
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| +disable the 'no-' prefix using the `negatable` parameter:
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| +
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| +```dart
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| +parser.addFlag('name', negatable: false);
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| +```
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| +
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| +*Note:* From here on out, "option" refers to both regular options and flags. In
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| +cases where the distinction matters, we'll use "non-flag option."
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| +
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| +Options can have an optional single-character abbreviation, specified with the
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| +`abbr` parameter:
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| +
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| +```dart
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| +parser.addOption('mode', abbr: 'm');
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| +parser.addFlag('verbose', abbr: 'v');
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| +```
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| +
|
| +Options can also have a default value, specified with the `defaultsTo`
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| +parameter. The default value is used when arguments don't specify the option.
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| +
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| +```dart
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| +parser.addOption('mode', defaultsTo: 'debug');
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| +parser.addFlag('verbose', defaultsTo: false);
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| +```
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| +
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| +The default value for non-flag options can be any string. For flags, it must
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| +be a `bool`.
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| +
|
| +To validate a non-flag option, you can use the `allowed` parameter to provide an
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| +allowed set of values. When you do, the parser throws a [FormatException] if the
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| +value for an option is not in the allowed set. Here's an example of specifying
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| +allowed values:
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| +
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| +```dart
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| +parser.addOption('mode', allowed: ['debug', 'release']);
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| +```
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| +
|
| +You can use the `callback` parameter to associate a function with an option.
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| +Later, when parsing occurs, the callback function is invoked with the value of
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| +the option:
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| +
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| +```dart
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| +parser.addOption('mode', callback: (mode) => print('Got mode $mode'));
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| +parser.addFlag('verbose', callback: (verbose) {
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| + if (verbose) print('Verbose');
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| +});
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| +```
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| +
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| +The callbacks for all options are called whenever a set of arguments is parsed.
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| +If an option isn't provided in the args, its callback is passed the default
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| +value, or `null` if no default value is set.
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| +
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| +## Parsing arguments
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| +
|
| +Once you have an [ArgParser][] set up with some options and flags, you use it by
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| +calling [ArgParser.parse()][parse] with a set of arguments:
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| +
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| +```dart
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| +var results = parser.parse(['some', 'command', 'line', 'args']);
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| +```
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| +
|
| +These arguments usually come from the arguments to `main()`. For example:
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| +
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| + main(List<String> args) {
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| + // ...
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| + var results = parser.parse(args);
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| + }
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| +
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| +However, you can pass in any list of strings. The `parse()` method returns an
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| +instance of [ArgResults][], a map-like object that contains the values of the
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| +parsed options.
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| +
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| +```dart
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| +var parser = new ArgParser();
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| +parser.addOption('mode');
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| +parser.addFlag('verbose', defaultsTo: true);
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| +var results = parser.parse(['--mode', 'debug', 'something', 'else']);
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| +
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| +print(results['mode']); // debug
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| +print(results['verbose']); // true
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| +```
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| +
|
| +By default, the `parse()` method stops as soon as it reaches `--` by itself or
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| +anything that the parser doesn't recognize as an option, flag, or option value.
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| +If arguments still remain, they go into [ArgResults.rest][rest].
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| +
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| +```dart
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| +print(results.rest); // ['something', 'else']
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| +```
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| +
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| +To continue to parse options found after non-option arguments, pass
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| +`allowTrailingOptions: true` when creating the [ArgParser][].
|
| +
|
| +## Specifying options
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| +
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| +To actually pass in options and flags on the command line, use GNU or POSIX
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| +style. Consider this option:
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| +
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| +```dart
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| +parser.addOption('name', abbr: 'n');
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| +```
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| +
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| +You can specify its value on the command line using any of the following:
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| +
|
| +```
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| +--name=somevalue
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| +--name somevalue
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| +-nsomevalue
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| +-n somevalue
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| +```
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| +
|
| +Consider this flag:
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| +
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| +```dart
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| +parser.addFlag('name', abbr: 'n');
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| +```
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| +
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| +You can set it to true using one of the following:
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| +
|
| +```
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| +--name
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| +-n
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| +```
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| +
|
| +You can set it to false using the following:
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| +
|
| +```
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| +--no-name
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| +```
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| +
|
| +Multiple flag abbreviations can be collapsed into a single argument. Say you
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| +define these flags:
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| +
|
| +```dart
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| +parser
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| + ..addFlag('verbose', abbr: 'v')
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| + ..addFlag('french', abbr: 'f')
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| + ..addFlag('iambic-pentameter', abbr: 'i');
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| +```
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| +
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| +You can set all three flags at once:
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| +
|
| +```
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| +-vfi
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| +```
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| +
|
| +By default, an option has only a single value, with later option values
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| +overriding earlier ones; for example:
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| +
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| +```dart
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| +var parser = new ArgParser();
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| +parser.addOption('mode');
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| +var results = parser.parse(['--mode', 'on', '--mode', 'off']);
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| +print(results['mode']); // prints 'off'
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| +```
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| +
|
| +If you need multiple values, set the `allowMultiple` parameter. In that case the
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| +option can occur multiple times, and the `parse()` method returns a list of
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| +values:
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| +
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| +```dart
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| +var parser = new ArgParser();
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| +parser.addOption('mode', allowMultiple: true);
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| +var results = parser.parse(['--mode', 'on', '--mode', 'off']);
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| +print(results['mode']); // prints '[on, off]'
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| +```
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| +
|
| +By default, values for a multi-valued option may also be separated with commas:
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| +
|
| +```dart
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| +var parser = new ArgParser();
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| +parser.addOption('mode', allowMultiple: true);
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| +var results = parser.parse(['--mode', 'on,off']);
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| +print(results['mode']); // prints '[on, off]'
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| +```
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| +
|
| +This can be disabled by passing `splitCommas: false`.
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| +
|
| +## Defining commands ##
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| +
|
| +In addition to *options*, you can also define *commands*. A command is a named
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| +argument that has its own set of options. For example, consider this shell
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| +command:
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| +
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| +```
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| +$ git commit -a
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| +```
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| +
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| +The executable is `git`, the command is `commit`, and the `-a` option is an
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| +option passed to the command. You can add a command using the [addCommand][]
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| +method:
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| +
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| +```dart
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| +var parser = new ArgParser();
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| +var command = parser.addCommand('commit');
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| +```
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| +
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| +It returns another [ArgParser][], which you can then use to define options
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| +specific to that command. If you already have an [ArgParser][] for the command's
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| +options, you can pass it in:
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| +
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| +```dart
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| +var parser = new ArgParser();
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| +var command = new ArgParser();
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| +parser.addCommand('commit', command);
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| +```
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| +
|
| +The [ArgParser][] for a command can then define options or flags:
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| +
|
| +```dart
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| +command.addFlag('all', abbr: 'a');
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| +```
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| +
|
| +You can add multiple commands to the same parser so that a user can select one
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| +from a range of possible commands. When parsing an argument list, you can then
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| +determine which command was entered and what options were provided for it.
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| +
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| +```dart
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| +var results = parser.parse(['commit', '-a']);
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| +print(results.command.name); // "commit"
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| +print(results.command['all']); // true
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| +```
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| +
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| +Options for a command must appear after the command in the argument list. For
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| +example, given the above parser, `"git -a commit"` is *not* valid. The parser
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| +tries to find the right-most command that accepts an option. For example:
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| +
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| +```dart
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| +var parser = new ArgParser();
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| +parser.addFlag('all', abbr: 'a');
|
| +var command = parser.addCommand('commit');
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| +command.addFlag('all', abbr: 'a');
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| +
|
| +var results = parser.parse(['commit', '-a']);
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| +print(results.command['all']); // true
|
| +```
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| +
|
| +Here, both the top-level parser and the `"commit"` command can accept a `"-a"`
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| +(which is probably a bad command line interface, admittedly). In that case, when
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| +`"-a"` appears after `"commit"`, it is applied to that command. If it appears to
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| +the left of `"commit"`, it is given to the top-level parser.
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| +
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| +## Dispatching Commands
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| +
|
| +If you're writing a command-based application, you can use the [CommandRunner][]
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| +and [Command][] classes to help structure it. [CommandRunner][] has built-in
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| +support for dispatching to [Command][]s based on command-line arguments, as well
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| +as handling `--help` flags and invalid arguments. For example:
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| +
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| +```dart
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| +var runner = new CommandRunner("git", "Distributed version control.")
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| + ..addCommand(new CommitCommand())
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| + ..addCommand(new StashCommand())
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| + ..run(['commit', '-a']); // Calls [CommitCommand.run()]
|
| +```
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| +
|
| +Custom commands are defined by extending the [Command][] class. For example:
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| +
|
| +```dart
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| +class CommitCommand extends Command {
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| + // The [name] and [description] properties must be defined by every
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| + // subclass.
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| + final name = "commit";
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| + final description = "Record changes to the repository.";
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| +
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| + CommitCommand() {
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| + // [argParser] is automatically created by the parent class.
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| + argParser.addFlag('all', abbr: 'a');
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| + }
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| +
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| + // [run] may also return a Future.
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| + void run() {
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| + // [options] is set before [run()] is called and contains the options
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| + // passed to this command.
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| + print(options['all']);
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| + }
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| +}
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| +```
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| +
|
| +Commands can also have subcommands, which are added with [addSubcommand][]. A
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| +command with subcommands can't run its own code, so [run][] doesn't need to be
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| +implemented. For example:
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| +
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| +```dart
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| +class StashCommand extends Command {
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| + final String name = "stash";
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| + final String description = "Stash changes in the working directory.";
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| +
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| + StashCommand() {
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| + addSubcommand(new StashSaveCommand());
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| + addSubcommand(new StashListCommand());
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| + }
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| +}
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| +```
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| +
|
| +[CommandRunner][] automatically adds a `help` command that displays usage
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| +information for commands, as well as support for the `--help` flag for all
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| +commands. If it encounters an error parsing the arguments or processing a
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| +command, it throws a [UsageError][]; your `main()` method should catch these and
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| +print them appropriately. For example:
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| +
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| +```dart
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| +runner.run(arguments).catchError((error) {
|
| + if (error is! UsageError) throw error;
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| + print(error);
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| + exit(64); // Exit code 64 indicates a usage error.
|
| +});
|
| +```
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| +
|
| +## Displaying usage
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| +
|
| +You can automatically generate nice help text, suitable for use as the output of
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| +`--help`. To display good usage information, you should provide some help text
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| +when you create your options.
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| +
|
| +To define help text for an entire option, use the `help:` parameter:
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| +
|
| +```dart
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| +parser.addOption('mode', help: 'The compiler configuration',
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| + allowed: ['debug', 'release']);
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| +parser.addFlag('verbose', help: 'Show additional diagnostic info');
|
| +```
|
| +
|
| +For non-flag options, you can also provide a help string for the parameter:
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| +
|
| +```dart
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| +parser.addOption('out', help: 'The output path', valueHelp: 'path',
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| + allowed: ['debug', 'release']);
|
| +```
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| +
|
| +For non-flag options, you can also provide detailed help for each expected value
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| +by using the `allowedHelp:` parameter:
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| +
|
| +```dart
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| +parser.addOption('arch', help: 'The architecture to compile for',
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| + allowedHelp: {
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| + 'ia32': 'Intel x86',
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| + 'arm': 'ARM Holding 32-bit chip'
|
| + });
|
| +```
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| +
|
| +To display the help, use the [getUsage()][getUsage] method:
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| +
|
| +```dart
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| +print(parser.getUsage());
|
| +```
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| +
|
| +The resulting string looks something like this:
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| +
|
| +```
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| +--mode The compiler configuration
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| + [debug, release]
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| +
|
| +--out=<path> The output path
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| +--[no-]verbose Show additional diagnostic info
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| +--arch The architecture to compile for
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| + [arm] ARM Holding 32-bit chip
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| + [ia32] Intel x86
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| +```
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| +
|
| +[posix]: http://pubs.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap12.html#tag_12_02
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| +[gnu]: http://www.gnu.org/prep/standards/standards.html#Command_002dLine-Interfaces
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| +[ArgParser]: http://www.dartdocs.org/documentation/args/latest/index.html#args/args.ArgParser
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| +[ArgResults]: http://www.dartdocs.org/documentation/args/latest/index.html#args/args.ArgResults
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| +[CommandRunner]: http://www.dartdocs.org/documentation/args/latest/index.html#args/args.CommandRunner
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| +[Command]: http://www.dartdocs.org/documentation/args/latest/index.html#args/args.Command
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| +[UsageError]: http://www.dartdocs.org/documentation/args/latest/index.html#args/args.UsageError
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| +[addOption]: http://www.dartdocs.org/documentation/args/latest/index.html#args/args.ArgParser@id_addOption
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| +[addFlag]: http://www.dartdocs.org/documentation/args/latest/index.html#args/args.ArgParser@id_addFlag
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| +[parse]: http://www.dartdocs.org/documentation/args/latest/index.html#args/args.ArgParser@id_parse
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| +[rest]: http://www.dartdocs.org/documentation/args/latest/index.html#args/args.ArgResults@id_rest
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| +[addCommand]: http://www.dartdocs.org/documentation/args/latest/index.html#args/args.ArgParser@id_addCommand
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| +[getUsage]: http://www.dartdocs.org/documentation/args/latest/index.html#args/args.ArgParser@id_getUsage
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| +[addSubcommand]: http://www.dartdocs.org/documentation/args/latest/index.html#args/args.Command@id_addSubcommand
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| +[run]: http://www.dartdocs.org/documentation/args/latest/index.html#args/args.Command@id_run
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|
|