protected function selectBuilder()
    {
        if (PHP_OS === 'Darwin') {
            if (exec('which growlnotify')) {
                return new GrowlNotifyBuilder;
            }
            if (exec('which terminal-notifier')) {
                return new TerminalNotifierBuilder;
            }
        }
        if (PHP_OS === 'Linux') {
            if (exec('which notify-send')) {
                return new NotifySendBuilder;
            }
        }
        if (PHP_OS === 'WINNT') {
            if (exec('where growlnotify')) {
                return new GrowlNotifyWindowsBuilder;
            }
        }
    }