- preg_match: documentation ( source)
<?php
//modify instagram embed code.
$code = '<iframe src="//instagram.com/p/mJ1-QxtlVg/embed/" width="600" height="696" frameborder="0" scrolling="no" allowtransparency="true"></iframe>';
$instagramEmbedPattern = "/instagram\.com\/p\/(.*)\/embed\/?/";
preg_match($instagramEmbedPattern, $code, $matches);
if (2 === count($matches)) {
echo $matches[1];
}