func backup(filename string) error {
	if DO_BACKUP {
		if _, ok := _FILES_BACKUPED[filename]; !ok {
			if err := file.Backup(filename); err != nil {
				return err
			}
			_FILES_BACKUPED[filename] = struct{}{}
		}
	}
	return nil
}
func backup(filename string) error {
	if DO_BACKUP {
		if _, ok := _FILES_BACKUPED[filename]; !ok {
			if err := file.Backup(filename); err != nil {
				return err
			}
			_FILES_BACKUPED[filename] = struct{}{}
		}
	}
	return nil
}
// backup does a backup of a file.