code: func RunGit(args ...string) string {
  	cmd := exec.Command("git", args...)
  	var stdout, stderr bytes.Buffer
  	cmd.Stdout, cmd.Stderr = &stdout, &stderr
  	if err := cmd.Run(); err == exec.ErrNotFound {
  		if !warnedAboutGit {
  			log.Println("Warning: can't find 'git' in PATH")
  			warnedAboutGit = true
  		}
  		return ""
  	} else if err != nil {
  		log.Fatal(strings.Join(cmd.Args, " "), ": ", err, "\n", stderr.String())
  	}
  	return strings.TrimSpace(stdout.String())
  }
docs: // RunGit runs a git subcommand and returns its output.
  // The command must complete successfully.