In checker mode, the environment variable HATCOM is modified and points at your local version of the COMMON block in your current working directory. During observing (obs@hat) it is /tmp/hatcomsol. Normally you want to do this in the directory where you test the script (be sure nobody else is in checker mode in that directory too, since you would share the same COMMON block, LST clock etc.). In addition, an environment variable HATCHK is set (to the shell process id, the PID) to be able for scripts to permit to detect that they're running in checker mode. An example would be
if ($?HATCHK) then echo "You are now in checker mode" endif
which would inform you when you are in checker mode. In observing mode the echo command would be ignored.
Since the checker does nothing more than modify your UNIX environment, support for other shells than the C-shell should be straightforward.