gistfile1.txt

#!/usr/bin/env ruby

require 'rubygems'
require 'nokogiri'

doc = Nokogiri::HTML.parse(open('input.html'), nil, 'utf-8')

meta_content_type = Nokogiri::XML::Node.new 'meta', doc
meta_content_type['http-equiv'] = 'Content-Type'
meta_content_type['content'] = 'text/html; charset=utf-8'

doc.search('head').first << meta_content_type

puts doc.to_html