Old story - maintenance page iRule

Thanks David! It really helped me to get into this. Just one more thing here - I'm trying to use a variable below (REDIRECTURL) to simplify future modifications, but when I try to use it within HTTP:respond code it doesn't return variable value and just prints it as a text "$REDIRECTURL".

when HTTP_REQUEST {
set REDIRECTURL "https://example.com"
switch [HTTP::uri] {
    "/we_have_moved.png" {
        HTTP::respond 200 content [ifile get we_have_moved.png] "Content-Type" "image/gif"
    }
    default {
        HTTP::respond 200 content {
            
            The site has been moved
            
            The webiste has moved to 
            Please update your bookmarks!
            You will be redirected in
            50 seconds 
            ![HTML5 Icon](we_have_moved.png)
            
            
            
            }
        }
    }
}

Is there any way to make this work?

Thanks!