def copy_truncate
      return unless ::File.exist?(@fn)
      FileUtils.concat @fn, @fn_copy
      @io.truncate 0

      # touch the age file if needed
      if @age
        FileUtils.touch @age_fn
        @age_fn_mtime = nil
      end

      @roller.roll = true
    end
def copy_truncate
      return unless ::File.exist?(@fn)
      FileUtils.concat @fn, @fn_copy
      @io.truncate 0

      # touch the age file if needed
      if @age
        FileUtils.touch @age_fn
        @age_fn_mtime = nil
      end

      @roller.roll = true
    end
Copy the contents of the logfile to another file. Truncate the logfile
 to zero length. This method will set the roll flag so that all the
 current logfiles will be rolled along with the copied file.