I'm not sure that you can read in an external source via the system's 'open' (or perl's for that matter) function. You may want to see the LWP module (LWP module at CPAN, if the link didn't come out correctly).
There are some examples of its use at TPJ, and on this site. I suggest the tutorial section, or the HTML docs at cpan.
(I assume the URL is linking outside your machine... is that correct?)