You have an option when you start gs to use a file as input. So if you have saved some commands in a file called square.ps, you could execute them with gs square.ps. When gs is done interpreting your file, it will return you to the gscommand prompt so you can continue your session. If you made a mistake, all you have to fix is the input file.
Even better, gs has a run command which you
can use to run a file from the gs prompt. If you
want to read a file called square.ps from the
gs command line, you would type (square.ps) run.
The parentheses around the filename act like quotes do in many programming
languages - they delimit a string.
David Maxwell,
who is still writing this, would like to
hear your comments and suggestions.
And remember, parts of this manual are based on
P.J. Weingartner's work:
A First Guide to PostScript.