Data group redirection or trim the hostname?

Updating an external data group (class) is cumbersome; you're better off using an internal class. You mentioned "hundreds" of entries, which really isn't much at all.

However, as you already suspected it would be much easier to simply manipulate the string.

However, I'm not entire sure what you're looking for. Is the first folder name (e.g. www.foo.com) always the hostname you want to redirect to? Are there any requests to www.site.com that should not be redirected?

If the answer to the first question is "yes" and the answer to the second question is "no" you should be able to use this:

 when HTTP_REQUEST {

     extract the string between the first and second slash, 
     assuming that this is always the hostname to redirect to.
     Use a skip count of 1 to strip the first slash.
    set hostname [findstr [string tolower [HTTP::path]] "/" 1 "/"]

     Remove the hostname part of the uri. Using "string map" 
     because it retains the case of the URI 
     (important for Linux/Apache, and also to retain the case 
     of any query strings)
    set uri [string map -nocase {"/$hostname" ""} [HTTP::uri]]

    HTTP::respond 301 Location "http://$hostname$uri"

}

Note: I don't have a BIG-IP handy right now so I didn't test the iRule.

This should do it. Just create a class (type: string) with the name "class_exceptionList" and populate it with the folder names (in lower case) that shouldn't be redirected.

 when HTTP_REQUEST {

     extract the string between the first and second slash, 
     assuming that this is always the hostname to redirect to.
     Use a skip count of 1 to strip the first slash.
    set firstFolder [findstr [string tolower [HTTP::path]] "/" 1 "/"]

     Remove the first folder from the uri unless it's listed in the class.
     Using "string map" because it retains the case of the URI.
     (important for Linux/Apache, and also to retain the case 
     of any query strings)

    if { [class match $firstFolder equals class_exceptionList } {

        set uri [string map -nocase {"/$hostname" ""} [HTTP::uri]]

        HTTP::respond 301 Location "http://$firstFolder$uri"

    }

}

Ah - I didn't notice that my update hadn't been saved (looks like the forum is having problems). For other members, here's the correct code:

 when HTTP_REQUEST {

     extract the string between the first and second slash, 
     assuming that this is always the hostname to redirect to.
     Use a skip count of 1 to strip the first slash.
    set firstFolder [findstr [string tolower [HTTP::path]] "/" 1 "/"]

     Remove the first folder from the uri unless it's listed in the class.
     Using "string map" because it retains the case of the URI.
     (important for Linux/Apache, and also to retain the case 
     of any query strings)

    if { not [class match $firstFolder equals class_exceptionList] } {

        set uri [string map -nocase {"/$hostname" ""} [HTTP::uri]]

        HTTP::respond 301 Location "http://$firstFolder$uri"

    }

}

Thanks for all your help. I made a few more changes, but it looks like it is working as needed. Feel free to critique if there are any areas of improvements.

when CLIENT_ACCEPTED {

    Check the VS port to determine if connection is SSL or not
   switch [TCP::local_port] {
      "443" {
         set proto "https"
      }
      default {
         set proto "http"
      }
   }

log local0.  "This is the new protocol - ${proto}"

}


when HTTP_REQUEST {

     extract the string between the first and second slash, 
     assuming that this is always the hostname to redirect to.
     Use a skip count of 1 to strip the first slash.
    set firstFolder [findstr [string tolower [HTTP::path]] "/" 1 "/"]

    log local0.  "This is the domain - $firstFolder" 

     Remove the first folder from the uri unless it's listed in the class.
     Using "string map" because it retains the case of the URI.
     (important for Linux/Apache, and also to retain the case 
     of any query strings)

    if { not [class match $firstFolder redirect.data.group] } {

        set uri [string map -nocase {"/$hostname" ""} [HTTP::uri]]

        log local0.  "This is the new uri - $uri"

        HTTP::respond 301 Location "${proto}:/$uri"

        log local0.  "This is the new url - ${proto}:/$uri"

    }

}