[Users] merging string and pseudo-variable in avp_write

[Benko]

Hello!

I'd like to implement an avpops serial forking solution as described in
http://www.voice-sistem.ro/docs/avpops/ar01s08.html#ex_serial_forking

However, i would like to define the adresses as "$rU at mydomain.org".
What is the correct syntax to merge the string and the variable in
avp_write? I would like to do something like this:

avp_write("sip:$rU at mydomain1.org", "$serial_fork");
avp_write("sip:$rU at mydomain2.org", "$serial_fork");

where $rU should be parsed. $serial_fork would have a value of e.g.
"12632421 at mydomain1.org" then. Or does this not work at all? How else
could i define it?

Can someone point me to a fundamental doc where the openser.cfg-syntax
is described? My well-tried trial-and-error method doesn't seem to work
here...

thx
Christian