If you need to check for if an specific file exists:

if _, err := os.Stat("/path/to/whatever"); os.IsNotExist(err) {
  // path/to/whatever does not exist
}

You can make a helper function:

func exists(path string) (bool, error) {
	_, err := os.Stat(path)
	if err == nil {
		return true, nil
	}
	if os.IsNotExist(err) {
		return false, nil
	}
	return true, err
}