How to debug a Mk-Script?

Mon Oct 19 08:50:06 UTC 2015

Hello,

after defining a USES pgsql:9.3+ in an port-update i stumbled over this 
error message:

the port wants postgresql-client version 9.3 9.4 and you have version 
9.4 installed.

This seems to be an error in Mk/Uses/pgsql.mk which i found to track 
down (in order to gather some more experience).

While i have already an idea what the case can be, i just want to add 
some output into the script. How is this possible? Can someone guide me 
please?

Thanks,
Torsten