Read and rewrite a custom field

Hello,

weird question:
Currently I’m fetching something from a custom field to show it up on the post.

Example: Custom field “URL”:

<p>URL:<a href="<?php echo get_post_meta($post->ID, "url", $single = true);?>"><?php echo get_post_meta($post->ID, "url", $single = true);?></a></p>

So when I enter http://www.domain.com as a custom field, it shows up as http://www.domain.com on the published post. Perfect.

But what if the URL is long and if I don’t want to use some tiny url creator?

I would like to enter some long address (http://www.domain.com/directory/someaddress.html) in a custom field and it should shop up as “http://www.domain.com” (but the a href should be the real address).

Is that possible? I sure know that I can truncate the address, but then it’s not usable…

Anyone?
Thanks!