Spool the current plot to the printer.
This command takes whatever is the current display in you plot window, writes
it to a postscript file, and then sends it to a printer using the unix
lpr command. It will thus be printed on whatever printer lpr
uses as your default printer. If a filename is specified, the postscript
file will be saved (e.g. hardcopy dataplot.ps color will produce a
color plot saved in the file dataplot.ps). If mono or
color is not given, the hardcopy will be monochrome.