<?php
$re = '/\(link\)(.*?)\(\/link\)/';
$str = "(link)there is link1(/link), (link)there is link2(/link)";
$subst = "<a href='$1'>$1</a>";
echo $result;
PD9waHAKCiRyZSA9ICcvXChsaW5rXCkoLio/KVwoXC9saW5rXCkvJzsgCiRzdHIgPSAiKGxpbmspdGhlcmUgaXMgbGluazEoL2xpbmspLCAobGluayl0aGVyZSBpcyBsaW5rMigvbGluaykiOyAKJHN1YnN0ID0gIjxhIGhyZWY9JyQxJz4kMTwvYT4iOyAKJHJlc3VsdCA9IHByZWdfcmVwbGFjZSgkcmUsICRzdWJzdCwgJHN0cik7CmVjaG8gJHJlc3VsdDs=