You can use the PHP Document Object Model (DOM), an example:
<?php
$f = '
<html>
<head>
<title>test</title>
</head>
<body>
<div id="aaa">apples</div>
<div id="bbb">oranges</div>
</body>
</html>
';
$dom = new domDocument;
$dom->loadHTML($f);
$dom->preserveWhiteSpace = false;
$t = $dom->getElementsByTagName('div');
$newElement = $t->item(0)->nodeValue; // 0 to display #aaa, 1 for #bbb
echo $newElement . "\n";
?>