ArgParser
- Dart course
- Advanced
- Lesson 56/83
- 5 min
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.
Practice 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']}').
Starter code
// import the args package
void main() {
// parse --verbose flag and --file option with ArgParser
}Sample 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"]}');
}Expected output
Verbose: true File: notlar.txt
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 The addFlag call
parser.____('verbose', abbr: 'v');parser.addFlag('verbose', abbr: 'v');Explanation: addFlag('verbose', abbr: 'v') adds a boolean flag.
2 What does addFlag add?
- List
- Boolean flag Correct answer
- Number
- Text option
Explanation: addFlag adds a boolean flag.
3 Match the ArgResults parts
| Term | Meaning |
|---|---|
results['name'] |
Option value |
results['verbose'] |
Boolean flag |
results.rest |
Positional args |
wasParsed |
Was-given check |