code: public function getKeys($keys = [])
      {
          $allKeys = $this->reader->keys();
  
          return array_filter($allKeys, function ($key) use ($keys) {
              if (!empty($keys)) {
                  return in_array($key, $keys);
              }
              return true;
          }, ARRAY_FILTER_USE_KEY);
      }
docs: Get all or exists given keys in file content
  
  @param  array  $keys
  
  @return array