I seem to remember a blog post about this regex issue here on HN a few months ago. It definitely surprised me to learn that Ruby doesn't treat $ as end-of-string by default.

I blogged in http://advogato.org/person/fxn/diary/498.html some key differences between Perl and Ruby regexp flags (which includes this gotcha).

http://homakov.blogspot.com/2012/05/saferweb-injects-in-vari... it is usual mistake in url validators