anchor.diff:  const OPTION_COMMUNITY_PAGE = 'community_page';
   const OPTION_API_KEY = 'api_key';
   const OPTION_MAX_USERS = 'max_users';
  -const OPTION_OUTPUT_FILE = 'output';
   const FLAG_HELP = 'help';
   
   main(List<String> args) async {
  
positive.code:   var maxCount = int.parse(params[OPTION_MAX_USERS], onError: (s) => 0);
    var users = await getGplusUsers(communityFile, apiKey, maxCount);
  
    var output = stdout;
    if (params.options.contains(OPTION_OUTPUT_FILE)) {
      output = new File(params[OPTION_OUTPUT_FILE]).openWrite();
    }
    users.forEach((user) {
      output.writeln(user);
    });
    output.writeln('${users.length} members.');
    output.close();
  }
  
negative.code:       ..addOption(OPTION_COMMUNITY_PAGE, abbr: 'c')
        ..addOption(OPTION_API_KEY, abbr: 'a')
        ..addOption(OPTION_MAX_USERS, abbr: 'm', defaultsTo: '0')
        ..addFlag(FLAG_HELP, negatable: false, abbr: 'h');
    var params = parser.parse(args);
    if (params[FLAG_HELP] ||
  