re-direct a URL but maintain the same URL in browser

There are two ways to change the URL. The first is issuing a redirect to the client that tells the browser to make a new request to the new URL. This will update the browser's address bar with the new URL which isn't what you want.

The other option is to change the requested URI in the iRule before it's sent to the backend web server. This can be done with the HTTP::uri command. Something like this should do what you want

when HTTP_REQUEST {
  if { [HTTP::uri] eq "/eng/test.html" } {
    HTTP::uri "/global/eng/test.html"
  }
}

The backend server will think the request came in for "/global/eng/test.html" when it really came in as "/eng/test.html".

Hope this helps...

-Joe