Variable: lpr-command

Name of program for printing a file.

On MS-DOS and MS-Windows systems, if the value is an empty string then
Emacs will write directly to the printer port named by `printer-name'.
The programs `print' and `nprint' (the standard print programs on
Windows NT and Novell Netware respectively) are handled specially, using
`printer-name' as the destination for output; any other program is
treated like `lpr' except that an explicit filename is given as the last argument.