I'd say it depends on the type of URL you wish to process. you could get the regex to look for 'http://' or 'www.'. But it is not necessary to use regex per se. Once you've worked out what regex should search for, it shouldn't be to hard.
Why not just use:
if (*http://* isin $1-) || (*www.* isin $1-) { Do something here }
The regex i got is:
$regex(test, $1-, http://.+|www\..+)
The regex will not work for only 'www.' or 'http://' it needs to have 'www.somethingmorehere' or 'http://this could be a web address'