code: func LookupUidFromFile(userName, passwdFile string) (uid int, err error) {
  	users, err := parsePasswdFile(passwdFile)
  	if err != nil {
  		return -1, errwrap.Wrap(fmt.Errorf("error parsing %q file", passwdFile), err)
  	}
  
  	user, ok := users[userName]
  	if !ok {
  		return -1, fmt.Errorf("%q user not found", userName)
  	}
  
  	return user.Uid, nil
  }
docs: // LookupUidFromFile reads the passwd file specified by passwdFile, and returns the
  // uid of the user specified by userName.