public function list() : String
    {
        $list = '';

        if( is_file($this->crontabCommands) )
        {
            $jobs  = $this->listArray();
            $list  = '<pre>';
            $list .= '[ID] CRON JOB<br><br>';

            foreach( $jobs as $key => $job )
            {
                $list .= '[' . $key . ']: '. $job . '<br>';
            }

            $list .= '</pre>';
        }

        return $list;
    }