$re = '/part(0*[2-9][0-9]*|0*1[0-9]+)\.rar/';
$str = 'S01.rar
S23.part1.rar
s4.part01.rar
Movie.rar
Youtube Movie.part1.rar
123Mov Ddaa.part01.rar
123Mov Ddaa.part001.rar
S01.part11.rar
S01.part010.rar
S01.part100.rar
S01.part02.rar
S2.part4.rar
Movie.part3.rar
Youtube Movie.part08.rar
123Mov Ddaa.part002.rar';
preg_match_all($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