$re = '/^&[^-]+-(?<pagination>\d+)&?$/m';
$str = '&sot-4
&dorer-56&
&sot-281&
&dorer-0
sot-5
&dorer-
&sot-&
dorer-34&';
preg_match_all($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