Session count from table

There is no direct access (yet) to the session table from the CLI. My one recommendation would be to add a service URI to your above iRule to respond to local cURL requests:

when RULE_INIT { 
    set static::total_active_clients 0 
    set static::sessionCookiePrefix "session" 
    set static::max_active_clients 5 
    set static::sessionTimeout 120 
} 
when HTTP_REQUEST { 
    set subtableName "sessionLimit-shopMaintainence" 
    set sessionCookieName "$static::sessionCookiePrefix-Maintainence" 
    set need_cookie 0

     service function to return session table count
    if { ( [HTTP::uri] equals "/getcount" ) and ( [class match [IP::client_addr] equals my_allowed_clients] ) } {
        HTTP::respond 200 content [table keys -subtable $subtableName -count]
    }

    if { [HTTP::cookie exists $sessionCookieName] } {
        set client_id [HTTP::cookie $sessionCookieName]
        set sessiondata [table lookup -subtable $subtableName $client_id]

        if { $sessiondata != "" } {
            return
        }
    }

    set sessionCount [table keys -subtable $subtableName -count]
    log local0. sessionCount
    if {$sessionCount < $static::max_active_clients} {
        set need_cookie 1
        set client_id [format "%08d" [expr { int(100000000 * rand()) }]]
        set sessionValue [IP::client_addr]

        table add -subtable $subtableName $client_id $sessionValue $static::sessionTimeout
        log local0. "[HTTP::cookie names] [IP::client_addr]      NEW"
    } else {
        HTTP::redirect "http://www.xyz.com/"
    }
}
when HTTP_RESPONSE { 
    if { $need_cookie == 1 } { 
        HTTP::cookie insert name $sessionCookieName value $client_id path "/" 
    } 
}

From the command line you can now issue a cURL request:

curl http://VIP/getcount

which should return the current table count. I also added a data group address match so that you could lock it down to a defined set of client source addresses.