Rewrite Custom Fields url

I use custom fields named ‘url’ to add another website url (like http://www.youtube.com), I want to rewrite the ‘url’ as http://www.mysite.com/go/123.

I tried all rewrite plugins, no one could do this.

I want set post id as 123

I want to auto rewrite link when I add it in custom fields named “url”.

For example:

I named a “url” in custom fields add http://www.yahoo.com as value, I use <?php echo get_post_meta($post->ID, ‘url’, true); ?> to get it, I don’t want to show the link http://www.yahoo.com, I want to rewrite it as http://www.mysite.com/29382 with post id automatically generated.