anchor.diff:        final file = "channels/$channel/release/$revision/${files[key]}";
         buffer.writeln('  ${key}_FILE = "$file"');
         buffer.writeln('  ${key}_HASH = "$hash"');
  -    })
  +    });
     })
       .then((_) => getVersion(channel, revision))
       .then((version) {
  
positive.code:       .then((_) => runGit(
            ['clone', 'git@github.com:dart-lang/homebrew-dart.git', '.']))
        .then((_) => writeHomebrewInfo(channel, revision))
        .then((_) => runGit(['add', '${channel}_info.rb']))
        .then((_) => runGit(['commit', '-a', '-m',
                             'Updated $channel branch to revision $revision']))
        .then((_) => runGit(['push']))
  
negative.code:   final options = parser.parse(args);
    final revision = options['revision'];
    final channel = options['channel'];
    if ([revision, channel, options['key']].contains(null)) {
      print("Usage: update_homebrew.dart -r revision -c channel -k ssh_key\n"
            "  ssh_key should allow pushes to dart-lang/homebrew-dart on github");
      return;
    }
    final sshWrapper = Platform.script.resolve('ssh_with_key').toFilePath();
    gitEnvironment = {'GIT_SSH': sshWrapper,
                      'SSH_KEY_PATH': options['key']};
  