Can someone recommend a way to extract the user part of a Contact header URI?

Right now I'm just trying to pass it to xlog().  I have tried:

- xlog("L_NOTICE", "$(ct{uri.user})");

This gives me an error starting Kamailio: "function xlog: parameter 2 is not constant".  Note, I can't seem to get any select working, for example, @ruri gives me the same error.

Any suggestions?

Thanks,

Marc