    def extract_zip(work_dir)
      if File.directory?(@backup_path)
        Dir["#{@backup_path}/**/*"].each do |f_path|
          f_path=File.join(work_dir, f.name)
        end
      else
        Zip::File.open(@backup_path) do |zip_file|
          zip_file.each do |f|
            f_path=File.join(work_dir, f.name)
            FileUtils.mkdir_p(File.dirname(f_path))
            zip_file.extract(f, f_path) unless File.exist?(f_path)
          end
        end
      end
    end