What/When would this regular expression match?

Question

I was reading about regular expressions (I'm a regex newbie, but want to learn them) and came across this regex:

/^(?!http:\/\/www.google.com).*/

and I didn't know what or when it would match...so my question is just that, what/when would this regex match?

Thanks for helping out a regex padawan!

Answer 1

That's a negative lookahead. It matches anything that doesn't start with:

http://www.google.com

(where the dots can be any character, which is probably not intended).