不多介绍，直接看实例

<?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 this!</a>