[mac-gs] how to use ghostscript through command line on OS X

[fabio]

I am graphic arts teacher on the SENAI University at Sao Paulo, Brasil.
I used to work with ghostscript on linux, invoking it from the shell and using x11 
and x11mono as the devices, to explain basic postscript and screening.

How do I use ghostscript from the unix shell from the MAC OS X and choose the 
display color and display mono as devices?

Fabio Bottura
Electronic Imaging Integration
SENAI University, BRA