def normal_iterator(first_line, next_lines, &block)
      Enumerator.new do |y|
        y << first_line
        loop do
          y << next_lines.next
        end
      end.each_slice(batch_size).with_index(&block)
    end
def normal_iterator(first_line, next_lines, &block)
      Enumerator.new do |y|
        y << first_line
        loop do
          y << next_lines.next
        end
      end.each_slice(batch_size).with_index(&block)
    end
Splits the input lines into slices, based on the batch_size of the current
 command. Executes the given block for each of the batches.