$re = '/^(.*)((<img|<script|<link)(.*) (src|href))\=(\"|\')(?!cdn|https|https|\/\/)(\/)?(<\/script>|\>)?(.*)$/m';
$str = '';
$subst = "$1$2=$6http:\/\/test.com\/$8$9";
$result = preg_replace($re, $subst, $str, 1);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php