Redirect both host and path via iRules

If it's just a few conditions you could reasonably nest switch statements:

when HTTP_REQUEST {
    switch -glob [string tolower [HTTP::host]] {
        "abc.com" - 
        "www.abc.com" {
            HTTP::redirect http://abc.123.com
        }
        "def.com" -
        "www.def.com" {
            switch -glob [string tolower [HTTP::uri]] {
                "/example*" {
                    HTTP::redirect "https://www.def.com/site1/example"
                }
                default { 
                    HTTP::redirect https://www.def.com[HTTP::uri]
                }
            }
        } 
        default {
            reject
        }     
    }
}