code: func MustRun(cmd *exec.Cmd) {
  	fmt.Println(">>>", strings.Join(cmd.Args, " "))
  	if !*DryRunFlag {
  		cmd.Stderr = os.Stderr
  		cmd.Stdout = os.Stdout
  		if err := cmd.Run(); err != nil {
  			log.Fatal(err)
  		}
  	}
  }
docs: // MustRun executes the given command and exits the host process for
  // any error.