Tvheadend

The regular expression is indeed missing both a bracket and a +, but the ^ character in this case indicates that the string should start with whatever comes next to it. It only functions as a negator inside brackets, e.g. [^b] matches everything without a "b".

I can't get this regex to work with some common regex testing tools, I assume it's because it uses Perl functions. Has this ever worked?

Oh, I found one missing character('@') from my correction.

#define URL_RE "([A-Za-z]+)://(("UC"+)(:("PC"+))?@)?("HC"+)(:([0-9]+))?(/.*)?"

In my case, it is work. I think, if you want to test with regex tool, you need to replace "UC", "PC" and "HC" with their regex definitions in url.c.