Domain Redirect iRule

The equals operator doesn't support a wildcard match. But nevertheless:

} elseif { not ( [HTTP::uri] equals "/" ) } { 
    HTTP::respond 301 Location "http://www.blah.com[HTTP::uri]" 
} 

would create an infinite loop for any traffic that wasn't just "/". Important to observe of course that in the absence of a URI path in the browser, HTTP::uri will still return "/". So the first iRule didn't work?

when HTTP_REQUEST {
    if { [HTTP::uri] equals "/" } {
        HTTP::redirect ...
    }
}

This explicitly states that if the URI path is nothing/empty, then redirect, and implies that anything else be allowed through. You may otherwise not be meeting the HTTP::host qualifications.