Replace relative urls to absolute with regex if url is does not exist

Question

I have database with many news items and I have relative urls like this

/index.php?news etc...

I need to convert these urls to absolute, like this:

http(or - s)//example.com/index.php?news etc..

Also I have this code and it works

$regex = '~<a([^>]*)href=["\']([^"\']*)["\']([^>]*)>~';
$replace = '<a$1href="'. $absolute_url .'/$2"$3>';
$data->introtext = preg_replace($regex, $replace, $news->introtext); 

where $news->introtext is my text with many links eg:

<a href="/index.php">some text</a> some text here <a href="https://facebook.com/etc">

code works like this:

<a href="http://example.com/index.php">some text</a> some text here <a href="http://example.com/https://facebook.com/etc">

and I don't want to add http://example.com/ if link is like https://facebook.com/etc

Answer 1

Found good way:

$data->introtext = preg_replace("#(<\s*a\s+[^>]*href\s*=\s*[\"'])(?!http)([^\"'>]+)([\"'>]+)#", '$1http://example.com/$2$3', $news->introtext);

if urls not exits then add url