how to get href value of anchor tag in jquery in list

<ul class="sub_menu">
    <li><a href="caps">Caps</a></li>
    <li><a href="jeans">Jeans</a></li>
    <li><a href="shorts">Shorts</a></li>
    <li><a href="foootwear">Footwear</a></li>
</ul>


$('ul.sub_menu li a').click(function() {
    event.preventDefault();
    var txt = $(this).attr('href');
    alert(txt);    
});