From: Junegunn Choi <junegunn.c@...>
Date: 2011-11-24T13:58:19+09:00
Subject: Re: Create Excel Sheet(.xls/.xlsx)

Are you sure you want to write your own code for handling Excel binary format?
I suggest you try  'spreadsheet' gem.

require 'spreadsheet'
book = Spreadsheet::Workbook.new
sheet = book.create_worksheet
book.write 'test.xls'

-- 
cheers,
junegunn choi.