- file_get_contents: documentation ( source)
- explode: documentation ( source)
<?php
$url = 'https://somedomain.com/somesite/';
$content = file_get_contents($url);
$first_step = explode( '<div id="thediv">' , $content );
$second_step = explode("</div>" , $first_step[1] );
echo $second_step[0];