public static function realPath(/*string*/ $filePath = '') {
    if('' === $filePath) {
      $filePath = '.';
    }
    $filePath = @realpath($filePath);
    if(false !== $filePath) {
      $filePath = str_replace('\\', '/', $filePath);
      if('/' !== $filePath) {
        $filePath = rtrim($filePath, '/');
      }
    }
    return $filePath;
  }