iRule to redirect a URL but replace only a portion of the variable length URI??

Hi, I don't know if I clearly understood, so I would try another way:

1) Single string pattern for documents path (no regsub)

when HTTP_REQUEST {
    if { [string tolower [getfield [HTTP::host] ":" 1]] equals "oldsharepoint.uk" } {
        if { [string match -nocase "/*/*/documents/*" [HTTP::path]] } {
            set uri [string range [HTTP::uri] [string first /documents [string tolower [HTTP::uri]]] end]
            HTTP::respond 301 noserver Location "http://newsharepoint.uk/new${uri}"
            unset uri
        }
    }
}

2) data group rewrite (I'd recommend for large list):

ltm data-group internal dg_redirect_shpt_paths {
    records {
        /a/1234/ {
            data /new/
        }
        /b/1/ {
            data /new2/
        }
    }
    type string
}

when HTTP_REQUEST {
    if { [string tolower [getfield [HTTP::host] ":" 1]] equals "oldsharepoint.uk" } {
        set p [URI::path [string tolower [HTTP::uri]] 1 2]
        set m [class match -value $p equals dg_redirect_shpt_paths]
        if { $m ne "" } {
            HTTP::respond 301 noserver Location "http://newsharepoint.uk[string map -nocase "$p $m" [HTTP::uri]]"
        }
        unset -nocomplain p m
    }
}

3) rewrite with array list:

when CLIENT_ACCEPTED {
     I don't like using statics variables, so here it is and not in RULE_INIT
    array set redirect_shpt_paths {
        /a/1234/    /new/
        /b/1/       /new2/
    }
}
when HTTP_REQUEST {
    if { [string tolower [getfield [HTTP::host] ":" 1]] equals "oldsharepoint.uk" } {
        set p [URI::path [string tolower [HTTP::uri]] 1 2]
        foreach m [array names redirect_shpt_paths] {
            if { $m eq $p } {
                set uri [string map -nocase "$p $redirect_shpt_paths($m)" [HTTP::uri]]
                HTTP::respond 301 noserver Location "http://newsharepoint.uk$uri"
            }
        }
        unset -nocomplain p m uri
    }
}
when CLIENT_CLOSED {
    unset -nocomplain redirect_shpt_paths
}

If I'm wrong, I apologize,

Respectfully.