<?php
//Store your html into $html variable.
$html="<html>
<head>
<title>Rakesh Verma</title>
</head>
<body>
    <a href='http://example.com'>Example</a>
    <a href='http://google.com'>Google</a>
    <a href='http://www.yahoo.com'>Yahoo</a>
</body>
</html>";
$dom = new DOMDocument();
$dom->loadHTML($html);
//Evaluate Anchor tag in HTML
$xpath = new DOMXPath($dom);
$hrefs = $xpath->evaluate("/html/body//a");
for ($i = 0; $i < $hrefs->length; $i++) {
        $href = $hrefs->item($i);
        $url = $href->getAttribute('href');
        //remove and set target attribute        
        $href->removeAttribute('target');
        $href->setAttribute("target", "_blank");
        $newURL=$url.".au";
        //remove and set href attribute        
        $href->removeAttribute('href');
        $href->setAttribute("href", $newURL);
}
// save html
$html=$dom->saveHTML();
echo $html;
?>
