PHP/HTML/HTTP REFERER

HTTP_REFERER and HTTP_USER_AGENT

 
<?php
            if (isset($_SERVER["HTTP_REFERER"])) {
                    print "The page you were on previously was {$_SERVER["HTTP_REFERER"]}<br />";
            } else {
                    print "You didn"t click any links to get here<br />";
            }
    ?>
    <a href="refer.php">Click me!</a>