- preg_match: documentation ( source)
- print_r: documentation ( source)
<?php
// Positive numbers:
preg_match("/tag/","tag1,tag10,tag11,tag13,tag15,tag17,tag19,tag20,tag4,tag9,tag8,tag7,tag6,tag5,tag3,tag2,tag18,tag16,tag14,tag12",$matches);
print_r($matches);
?>