I have a requirement to insert a string between two markers.

Initially I get a sting (from a file stored on the server) between #DATA# and #END# using:

function getStringBetweenStrings($string,$start,$end){ 
    $startsAt=strpos($string,$start)+strlen($start);
 $endsAt=strpos($string,$end, $startsAt);
 return substr($string,$startsAt,$endsAt-$startsAt);
} 

I do some processing and based on the details of the string, query for some records. If there are records I need to be able to append them at the end of the string and then re-insert the string between #DATA# and #END# within the file on the server.

How can I best achieve this?

Is it possible to insert a record at a time in the file before #END# or is it best to manipulate the string on the server and just re-insert over the existing string in the file on the server?