<?php
$id = $_GET['id'];
if ($id)
{
header("Location: http://example.com/structure/auction_detail.asp?id=$id");
exit;
}
else
{
?>
<form method="get" action="<?=$SERVER['PHP_SELF']?>">
<input type="text" name="id">
<input type="submit" value="Submit">
</form>
<?}?>