It’s quite easy. Make sure you have RubyGems and Ruby installed first, of course.
$ sudo gem install hpricot Building native extensions. This could take a while... ERROR: Error installing hpricot: ERROR: Failed to build gem native extension. /usr/bin/ruby1.8 extconf.rb extconf.rb:1:in `require': no such file to load -- mkmf (LoadError) from extconf.rb:1
sudo apt-get install ruby1.8-dev build-essential sudo gem install hpricot