Dart CLI Applications

Project Setup

# Create a CLI app:
dart create --template=console my_cli

# Structure:
# my_cli/
#   bin/my_cli.dart    ← entry point
#   lib/               ← library code
#   pubspec.yaml

Command-line Arguments

// bin/my_cli.dart
import 'dart:io';

void main(List<String> args) {
  if (args.isEmpty) {
    print('Usage: my_cli <command> [options]');
    exit(1);
  }

  switch (args[0]) {
    case 'hello':
      var name = args.length > 1 ? args[1] : 'World';
      print('Hello, $name!');
    case 'add':
      if (args.length < 3) {
        stderr.writeln('Usage: add <num1> <num2>');
        exit(1);
      }
      var a = double.parse(args[1]);
      var b = double.parse(args[2]);
      print('$${args[1]} + $${args[2]} = $${a + b}');
    default:
      stderr.writeln('Unknown command: $${args[0]}');
      exit(1);
  }
}

// Or use the 'args' package for structured parsing:
// dart pub add args

Reading stdin

import 'dart:io';

void main() {
  stdout.write('Enter your name: ');
  var name = stdin.readLineSync();

  stdout.write('Enter your age: ');
  var ageStr = stdin.readLineSync() ?? '0';
  var age = int.tryParse(ageStr) ?? 0;

  print('Hello, $name! You are $age years old.');

  // Read multiple lines until EOF:
  print('Enter text (Ctrl+D to finish):');
  String? line;
  var lines = <String>[];
  while ((line = stdin.readLineSync()) != null) {
    lines.add(line!);
  }
  print('You entered $${lines.length} lines');
}

Colored Output

// ANSI color codes for terminal output
class Colors {
  static const reset = '\x1B[0m';
  static const red = '\x1B[31m';
  static const green = '\x1B[32m';
  static const yellow = '\x1B[33m';
  static const blue = '\x1B[34m';
  static const bold = '\x1B[1m';

  static String colorize(String text, String color) => '$color$text$reset';
  static String error(String text) => colorize('[ERROR] $text', red);
  static String success(String text) => colorize('[OK] $text', green);
  static String warning(String text) => colorize('[WARN] $text', yellow);
  static String info(String text) => colorize('[INFO] $text', blue);
}

void main() {
  print(Colors.success('Server started'));
  print(Colors.warning('Low disk space'));
  print(Colors.error('Connection refused'));
  print(Colors.info('Processing 100 items'));
}

CLI App Example: Task Manager

import 'dart:io';
import 'dart:convert';

class TaskManager {
  final String _file = 'tasks.json';
  List<Map<String, dynamic>> _tasks = [];

  void load() {
    var f = File(_file);
    if (f.existsSync()) {
      _tasks = List.from(jsonDecode(f.readAsStringSync()));
    }
  }

  void save() => File(_file).writeAsStringSync(jsonEncode(_tasks));

  void add(String title) {
    _tasks.add({'id': DateTime.now().millisecondsSinceEpoch, 'title': title, 'done': false});
    save();
    print('Added: $title');
  }

  void list() {
    if (_tasks.isEmpty) { print('No tasks'); return; }
    for (var t in _tasks) {
      print('[$${t['done'] ? 'x' : ' '}] $${t['id']}: $${t['title']}');
    }
  }

  void complete(int id) {
    var task = _tasks.firstWhere((t) => t['id'] == id, orElse: () => {});
    if (task.isEmpty) { print('Task not found'); return; }
    task['done'] = true;
    save();
    print('Completed: $${task['title']}');
  }
}

void main(List<String> args) {
  var manager = TaskManager()..load();
  switch (args.isEmpty ? 'list' : args[0]) {
    case 'add':
      manager.add(args.skip(1).join(' '));
    case 'done':
      manager.complete(int.parse(args[1]));
    default:
      manager.list();
  }
}

🧠 Quiz

Summary

Dart CLI apps start with void main(List<String> args). Read stdin with stdin.readLineSync(), write to stdout/stderr, and exit with exit(code). Use the args package for complex argument parsing. Use ANSI codes for colored terminal output. Dart CLI apps compile to native binaries with dart compile exe.