Irule redirect --> problem with character "#"

It looks like you're making this a lot more complicated than it needs to be, unless I'm missing something. If all you want to do is ensure there is always a www on the host, all you'd need is:

when HTTP_REQUEST {
  if{[HTTP::host] eq "mywebsite.com"] {
    HTTP::redirect "http://www.mywebsite.com[HTTP::uri]"
  }
}

That should take care of it for you regardless of the URI.

If there is something more complicated that you're trying to do, I missed it. Let me know what it is and I'll take a look.

Colin