public function copy($sourceUrl, $destinationUrl)
 {
     $sourcePath = self::urlToPath($sourceUrl);
     $destinationPath = self::urlToPath($destinationUrl);
     $res = copy($sourcePath, $destinationPath);
     if (function_exists('exec')) {
         if (!$res && !(Lms_Text::uppercase(Lms_Text::substring(PHP_OS, 0, 3)) === 'WIN')) {
             exec("cp -r " . escapeshellarg($sourcePath) . " " . escapeshellarg($destinationPath));
             return true;
         }
     } else {
         throw new Exception("Can't perform shell command. Probably 'exec' is disabled in your php.ini file");
     }
     return $res;
 }