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

Override environment variables (/E)

Syntax:/E

This option disables inherited macro redefinition.

NMAKE inherits all current environment variables as macros, which can be redefined in a description file. The /E option disables any redefinition -- the inherited macro always has the value of the environment variable.

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