code: func GenNewFleetService(newFile, oldFile, newVal, oldVal string) error {
  	input, err := ioutil.ReadFile(oldFile)
  	if err != nil {
  		return err
  	}
  	lines := strings.Split(string(input), "\n")
  
  	for i, line := range lines {
  		if strings.Contains(line, oldVal) {
  			lines[i] = strings.Replace(line, oldVal, newVal, len(oldVal))
  		}
  	}
  	output := strings.Join(lines, "\n")
  	err = ioutil.WriteFile(newFile, []byte(output), 0644)
  	if err != nil {
  		return err
  	}
  	return nil
  }
docs: // GenNewFleetService() is a helper for generating a temporary fleet service
  // that reads from oldFile, replaces oldVal with newVal, and stores the result
  // to newFile.