Filtering RSS Feeds/News

So, I need to build an application which will grab some news from some
sources, but only news containing an specific query such as “Iraq war”,
and display in my main page.

I tried using Scrapi, Nokogiri, Scrubyt, Mechanize, but with no success
(maybe cause I’m a RoR newbie?). So I went to Feedzirra and the likes,
but I couldn’t find a way to filter the feeds results for a specific

So, what is the best/easiest/cleaner way to do this?