anchor.diff:    var command = result.command;
   
     if (command == null) {
  +    print("Specify a command: ${parser.commands.keys.join(', ')}");
       _printUsage(parser);
       return;
     }
  
positive.code: ArgParser _getParser() => new ArgParser()
    ..addOption(_formatOption,
        abbr: 'f',
        allowed: _FORMAT_ALLOWED,
        defaultsTo: 'html',
        allowedHelp: _FORMAT_HELP)
    ..addOption(_ignoreOption,
  
negative.code:       help: 'Check pub.dartlang.org for lasted packages and flag those that '
        'are outdated.');
  
  const _FORMAT_HELP = const {
    'dot': 'Generate a GraphViz dot file',
    'html': 'Wrap the GraphViz dot format in an HTML template which renders it.'
  