如果没有正确的话，正则表达式匹配

Question

I have a regex that's matching urls and converting them into html links. If the url is already part of a link I don't want to to match, for example:

http://stackoverflow.com/questions/ask

Should match, but:

<a href="http://stackoverflow.com/questions/ask">Stackoverflow</a>

Shouldn't match

How can I create a regex to do this?

Answer 1

If your url matching regular expression is $URL then you can use the following pattern

(?<!href[\"'])$URL

In PHP you'd write

preg_match("/(?<!href[\"'])$URL/", $text, $matches);