每次重新加载页面时，如何逐个删除数组元素？

<?php
    session_start();    
    $_SESSION['del']=array("a1","a2","a3","a4","a5");
    unset($_SESSION['del'][0]);
    echo implode(" ",$_SESSION['del'])    
?>
<?php
    session_start();    
    $_SESSION['d