make: MAKEFILES Variable

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1 3.4 The Variable 'MAKEFILES'
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1 If the environment variable 'MAKEFILES' is defined, 'make' considers its
1 value as a list of names (separated by whitespace) of additional
1 makefiles to be read before the others.  This works much like the
1 'include' directive: various directories are searched for those files
1 (⇒Including Other Makefiles Include.).  In addition, the default
1 goal is never taken from one of these makefiles (or any makefile
1 included by them) and it is not an error if the files listed in
1 'MAKEFILES' are not found.
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1    The main use of 'MAKEFILES' is in communication between recursive
1 invocations of 'make' (⇒Recursive Use of 'make' Recursion.).  It
1 usually is not desirable to set the environment variable before a
1 top-level invocation of 'make', because it is usually better not to mess
1 with a makefile from outside.  However, if you are running 'make'
1 without a specific makefile, a makefile in 'MAKEFILES' can do useful
1 things to help the built-in implicit rules work better, such as defining
1 search paths (⇒Directory Search).
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1    Some users are tempted to set 'MAKEFILES' in the environment
1 automatically on login, and program makefiles to expect this to be done.
1 This is a very bad idea, because such makefiles will fail to work if run
1 by anyone else.  It is much better to write explicit 'include'
1 directives in the makefiles.  ⇒Including Other Makefiles Include.
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