PHP5 get http response body using CURL library

get response body of specified web page using php5, such as google homepage.

<?php
ob_start();

$ch = curl_init("http://www.google.com/");
curl_exec($ch);
curl_close($ch);
$retrievedhtml = ob_get_contents();
ob_end_clean();
// ob_end_flush();

echo $retrievedhtml;
?>