Rational Developer for System z
PL/I for Windows, Version 8.0, Programming Guide

Specify description file (/F)

Syntax:/F filename

This option specifies filename as the name of the description file to use. If a dash (-) is entered instead of a file name, NMAKE reads a description file from the standard input device, typically the keyboard.

If a filename is not specified, it defaults to makefile.

Rational Developer for System z
PL/I for Windows, Version 8.0, Programming Guide