URL branching in pre request access policy

Hi

I have an access policy that is shared amongst a few VS in their own partitions.

the AP and per request policy exist in /common

and VS's in their own partitions utilise this.

I have URL branch object and I would like branch on the URL

i use the dialogue boxes and end up with something like this

expr {[mcget {perflow.branching.url}] contains "abc.com/diag-sso"}

This is mean to capture

https://<??>.abc.com/diag-sso 

But it might also capture something like

https://<??>.abc.com/Some/OtherURI/abc.com/diag-sso 

which is not what I want. Now as this is a shared policy how can I get the hostname associated with the VS

or how can I change it to match something like this regex

https://[^.]*.abc.com/diag-sso 

it would actually be nice if you could actually access just the URI - path of  {perflow.branching.url} if I could guarantee it was at the first /

so for completeness if

{perflow.branching.url} => https://<??>.abc.com/diag-sso 

???? => /diag-sso