Function: ps-despool

Send the spooled PostScript to the printer.

Interactively, when you use a prefix argument (C-u), the command prompts the
user for a file name, and saves the spooled PostScript image in that file
instead of sending it to the printer.

Noninteractively, the argument FILENAME is treated as follows: if it is nil,
send the image to the printer. If FILENAME is a string, save the PostScript
image in a file with that name. (fn &optional FILENAME)