require 'cgi'

# escape
name = "ruby?"
value = "yes"
url = "http://example.com/?" + CGI.escape(name) + '=' + CGI.escape(value) + "&var=T"
# url: http://example.com/?ruby%3F=yes&var=T
html = %(<a href="#{CGI.escapeHTML(url)}">example</a>)
# html: <a href="http://example.com/?ruby%3F=yes&amp;var=T">example</a>

# unescape
name_encoded = html.match(/http:([^"]+)/)[0]
# name_encoded: http://example.com/?ruby%3F=yes&amp;var=T
href = CGI.unescapeHTML(name_encoded)
# href: http://example.com/?ruby%3F=yes&var=T
query = href.match(/\?(.*)$/)[1]
# query: ruby%3F=yes&var=T
pairs = query.split('&')
# pairs: ["ruby%3F=yes", "var=T"]
name, value = pairs[0].split('=').map{|v| CGI.unescape(v)}
# name, value: ["ruby?", "yes"]