code: func (c *cipdSubcommand) printError(err error) {
  	if _, ok := err.(commandLineError); ok {
  		fmt.Fprintf(os.Stderr, "Bad command line: %s.\n\n", err)
  		c.Flags.Usage()
  		return
  	}
  
  	if merr, _ := err.(errors.MultiError); len(merr) != 0 {
  		fmt.Fprintln(os.Stderr, "Errors:")
  		for _, err := range merr {
  			fmt.Fprintf(os.Stderr, "  %s\n", err)
  		}
  		return
  	}
  
  	fmt.Fprintf(os.Stderr, "Error: %s.\n", err)
  }
docs: // printError prints error to stderr (recognizing commandLineError).