in reply to regex problem

It is unclear what you are looking for. Are you looking for .jpg files under http://b.thumbs.redditmedia.com/ that do not have png in their names?

Replies are listed 'Best First'.
Re^2: regex problem
by ExReg (Priest) on Nov 03, 2015 at 23:36 UTC

    If indeed you are looking for .jpg files under http://b.thumbs.redditmedia.com/ that do not have png in their names, it might be easiest to just get rid of your lookaheads and lookbehinds

    my @urls=$response_body =~ m{(http://b.thumbs.redditmedia.com/.+?\.jpg)}gi;

    and then add another line to get rid of the lines in the just created @urls that have png in them. Writing regexes that must match one thing but cannot match another are prone to caveats or are not blazingly intuitive.