Php undefinierter Offset
If preg_match did not find a match, $matches is an empty array. So you should check if preg_match found an match before accessing $matches[0], for example:
function get_match($regex,$content)
{
if (preg_match($regex,$content,$matches)) {
return $matches[0];
} else {
return null;
}
}
Ankur