code: func Serve(helper Helper) {
  	var err error
  	if len(os.Args) != 2 {
  		err = fmt.Errorf("Usage: %s <store|get|erase|list|version>", os.Args[0])
  	}
  
  	if err == nil {
  		err = HandleCommand(helper, os.Args[1], os.Stdin, os.Stdout)
  	}
  
  	if err != nil {
  		fmt.Fprintf(os.Stdout, "%v\n", err)
  		os.Exit(1)
  	}
  }
docs: // Serve initializes the credentials helper and parses the action argument.
  // This function is designed to be called from a command line interface.
  // It uses os.Args[1] as the key for the action.
  // It uses os.Stdin as input and os.Stdout as output.
  // This function terminates the program with os.Exit(1) if there is an error.