$re = '/.*?<pre>.*\s?((<br\s*?\/?>\s?).*?){1,}<\/pre>/m';
$str = '<pre>Match<br /></pre>
<pre>Match<br />Match again<br /></pre>DONT MATCH<br />blablabla
<pre>
<br />
Hard mode : U should have been matched aswell</pre>
';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
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