code: func pidPath(dir, id string) string {
  	// If no directory is given we do not write a pid
  	if dir == "" {
  		return ""
  	}
  
  	return filepath.Join(dir, fmt.Sprintf("%s.pid", id))
  }
docs: // pidPath is a helper to return the path to the pid file for the given
  // directory and service ID.