http redirect issue with $ character

Hi All

I have the following redirect setup and it seems to work aprt form when the $ character is inserted into the rule.

   when HTTP_REQUEST {
      if { [HTTP::host] equals "www.thiswebsite.com" and [HTTP::uri] starts_with "/t/$1" } {
                HTTP::redirect "http://www.thiswebsite2.com/www.thiswebsite.com/t/$1"
                            }
                     }

The problem however is that the virtual server responds with a receive failure. There is something about the $ that the F5 VS doesnt like.

Any pointers would be appreciated