$content = <<<EOS
Link_1: [code]This is a textual line.
www.google.com
This is a textual line.[/code]

Link_2: [php]This is a textual line.
www.google.com
This is a textual line.[/php]
EOS;
$needle = '~(?:https?://)?(?:www.)(?:[^.s]+)(?:.[^.ns]+)*.w{2,4}(?=(?:(?![/?(?:code|php)])[Ss])*[/(?:code|php)])~m';
echo preg_replace($needle,'LINK HIDDEN',$content);