Match string that not containing a specific word (on Ruby)
===

I'm working on ruby with the class "match" and I want target a URL that not containing a certain string with a regular Expression:
ex:

    http://website1.com/url_with_some_words.html
    http://website2.com/url_with_some_other_words.html
    http://website3.com/url_with_the_word_dog.html

I want to target the URLs that not contains the word `dog`, so the 1st and the 2nd.

hope I was clear :)