foo.rb

#!/usr/bin/env ruby
env = {
  "HTTP_ACCEPT"=>"text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8",
  "HTTP_ACCEPT_ENCODING"=>"gzip, deflate",
  "HTTP_ACCEPT_LANGUAGE"=>"en-us",
  "HTTP_CONNECTION"=>"keep-alive",
  "HTTP_HOST"=>"localhost:9292",
  "HTTP_USER_AGENT"=>"Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_1) AppleWebKit/536.25 (KHTML, like Gecko) Version/6.0 Safari/536.25",
  "HTTP_VERSION"=>"HTTP/1.1",
  'deleteme'=>1,
}

expected_env = {
  "accept"=>"text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8",
  "accept_encoding"=>"gzip, deflate",
  "accept_language"=>"en-us",
  #???# "cache_control"=>"max-age=0",
  "connection"=>"keep-alive",
  "host"=>"localhost:9292",
  "user_agent"=>"Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_1) AppleWebKit/536.25 (KHTML, like Gecko) Version/6.0 Safari/536.25",
  "version"=>"HTTP/1.1"
}

def clean_headers env
  Hash[env.map { |k,v| k[/^HTTP_(.+)/] ? [ $1.downcase , v ] : nil }.compact ]
end

require 'yaml'
puts expected_env.to_yaml, clean_headers(env).to_yaml
puts expected_env == clean_headers(env)