php - Change a relative URL to absolute URL

Question

for example i've got a string like this:

$html = '
            <a href="test.html">test</a>
            <a href="http://mydomain.com/test.html">test</a>
            <a href="http://otherdomain.com/test.html">test</a>
            <a href="someothertest/otherdir/hi.html">hi</a>
        ';

and i want to append the absolute url to all hrefs where no abolute domain is given.

$html = '
            <a href="http://mydomain.com/test.html">test</a>
            <a href="http://mydomain.com/test.html">test</a>
            <a href="http://otherdomain.com/test.html">test</a>
            <a href="http://mydomain.com/someothertest/otherdir/hi.html">hi</a>
        ';  

whats the best way to do that? i guess something with RegEx, but my RegEx skills are ** ;)

thanks in advance!

Answer 1

found a good way :

$html = preg_replace("#(<s*as+[^>]*hrefs*=s*["'])(?!http)([^"'>]+)(["'>]+)#", '$1http://mydomain.com/$2$3', $html);

you can use (?!http|mailto) if you have also mailto links in your $html