ArgParser

Learn option processing with ArgParser.

ArgParser option types

ArgParser adds options with three methods. addOption('name') is a text option; the user gives --name=value. addFlag('verbose') is a boolean flag; --verbose means true, absence means false. addMultiOption('files') is a multi-value list.

Each method takes abbr (abbreviation) and help (help text). Example: addFlag('verbose', abbr: 'v', help: 'Verbose output'). After parsing results['verbose'] returns true or false.

ArgResults

parser.parse(arguments) returns an ArgResults object. You access option values with results['name']. Flags return boolean, options return text, multi-options return lists.

Positional arguments are in the results.rest list. You check whether an option was given with results.wasParsed('name'). This is the core way to trigger different behaviors in a CLI tool. For example if the --verbose flag was given you turn on verbose output; otherwise you run silently.

Exercise Parse a flag and a file

Add import 'package:args/args.dart';. In main create final parser = ArgParser()..addFlag('verbose', abbr: 'v')..addOption('file');. Parse with final results = parser.parse(['--verbose', '--file=notlar.txt']);. Print with print('Verbose: ${results['verbose']}') and print('File: ${results['file']}').

Show example solution

import 'package:args/args.dart';

void main() {
  final parser = ArgParser()
    ..addFlag('verbose', abbr: 'v')
    ..addOption('file');
  final results = parser.parse(['--verbose', '--file=notlar.txt']);
  print('Verbose: ${results["verbose"]}');
  print('File: ${results["file"]}');
}

Test yourself

The addFlag call

parser.____('verbose', abbr: 'v');

Show answer

parser.addFlag('verbose', abbr: 'v');

What does addFlag add?
- List
- Boolean flag
- Number
- Text option
Show answer

Boolean flag — addFlag adds a boolean flag.
Match the ArgResults parts

results['name']

Option value
results['verbose']

Boolean flag
results.rest

Positional args
wasParsed

Was-given check

Next lesson: stdin/stdout

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