<?php
$string = 'Writing to tell you that var MyCode = "dentline"; Learn it.';
preg_match('/var MyCode = "(.*?)";/', $string, $matches); echo $matches[1];
?>
PD9waHAKJHN0cmluZyA9ICdXcml0aW5nIHRvIHRlbGwgeW91IHRoYXQgdmFyIE15Q29kZSA9ICJkZW50bGluZSI7IExlYXJuIGl0Lic7CiRtYXRjaGVzID0gYXJyYXkoKTsKcHJlZ19tYXRjaCgnL3ZhciBNeUNvZGUgPSAiKC4qPykiOy8nLCAkc3RyaW5nLCAkbWF0Y2hlcyk7CmVjaG8gJG1hdGNoZXNbMV07Cj8+