$re = '/Showing\s+(?:\d+\s+of\s+)?([\d,.]+)\s+\(search/';
$str = '<div class="center">Showing 25 of 2,343,098 (search took 1.245 seconds)</div>
<div class="center">Showing 2343098 (search took 1.245 seconds)</div>
<div class="center">
Showing 125
of 2,343,098
(search took 1.245 seconds)</div>';
preg_match_all($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