如何创建像这个网站的优惠券盒？

All the working coupon manager plugins in Wordpress are paid. So, I thought of creating a new one. I wanted to create a coupon box like one this site has: http://www.bestbigrockcoupons.com/

So far I've managed to create a Shortcode on Wordpress to generate the coupon box. Here's the code:

function couponbox_func($atts) {
  extract(shortcode_atts(array(
      'coupon' => '',
      'url' => '',
      'expires' => '',
   ), $atts));
if($expires)
{
$expires = "<span class=\"expires\">Expires: " . $expires . "</span><br>";
}
  if($name && $url)
{ 
  return "<div class=\"cbox\">
   " . $expires . "
   <a class=\"myButton\" href=\""
   . $url . "
   \" target=\"_blank\">" . $coupon . "</a>
   </div>";
}
}
add_shortcode( 'couponbox', 'couponbox_func' );

Now my question is that what should I do so that when a user clicks on the box, the coupon ($coupon) gets copied in user's clipboard similar to what happens in the above mentioned site.

Thanks.

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