matching data!

<?php$data = "date: ".$_POST['date'];$file = file('filename');//i need to match $data in to any particular line, then after that matching line, it would display next 40 line, how can i do it//this is showing me the first 40 line of the filefor($i=0,$end=(sizeof($file)<40?sizeof($file):40);$i<$end;$i++)print "$file[$i]<br/>";?>