AFAIK the function file_get_contents() loads all the contents of a file into a string.
If you know the exact position of the content you want, you can use the offset and maxlength parameters to read only a section.
Or, if it's not too much of a performance hit, maybe you could get the whole file as a string, then simply remove everything before and after the markers using substr().
// Read 14 characters starting from the 21st character
$section = file_get_contents('./yourFile.php', NULL, NULL, 20, 14);