Precedence in Macro Definitions

If a macro is multiply defined, NMAKE uses the highest-precedence definition. The following list shows the order of precedence, from highest to lowest:

1. A macro defined on the command line
2. A macro defined in a makefile or include file
3. An inherited environment-variable macro
4. A predefined macro, such as FOR and RC

Use the /E option to cause macros inherited from environment variables to override makefile macros with the same name. Use !UNDEF to override a command line.