[PyMOL] Accessing PyMol's commands from outside (or without viewer)

[Shu-Hsien S. <sheu@BU.EDU>]

Hi,

This should be a trial question though I cannot find a way of doing it.
I have a simple script that looks like this:
(the original commands, rather than cmd.select......)
select ligand, resn XYZ
select protein, ! ligand
select box, protein within 8 of ligand
select box, box or byres box
save box as box.pdb

I don't need the viewer at all and would be even more efficient if I can 
call the PyMol API from the shell. Or, in a python script.
For example, I would like to have something like:
./pymol select_box.py

thanks!