mechanize：GUIDE：Filling Out Forms

まんま

require 'mechanize'

agent = Mechanize.new
page = agent.get('http://google.com/')
google_form = page.form('f')
google_form.q = 'ruby mechanize'
page = agent.submit(google_form)
pp page

で、

#<Mechanize::Page
 {url
  #<URI::HTTP:0xb7628bdc URL:http://www.google.co.jp/search?hl=ja&source=hp&ie=Shift_JIS&q=ruby+mechanize>}
  ...