I\'m trying to match the highlighted parts of this string:
maybe something here src=\"http://some.random.url.com/\" and the string continues.
You should use a DOM parser, but this regex would get you started if there is a reason you must use regexes
.*(?]*(?src=['"][^>'"]+['"]?).*
It uses named capture groups by the way, here's how they work
preg_match('/.*(?]*src=[\'"](?[^>\'"])+[\'"]?.*/', $searchText, $groups); print_r($groups['iframeSrc']);