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### The Variable `MAKEFILES`

If the environment variable `MAKEFILES` is defined, `make` considers its value as a list of names (separated by whitespace) of additional makefiles to be read before the others. This works much like the `include` directive: various directories are searched for those files (see Including Other Makefiles). In addition, the default goal is never taken from one of these makefiles and it is not an error if the files listed in `MAKEFILES` are not found.

The main use of `MAKEFILES` is in communication between recursive invocations of `make` (see Recursive Use of `make`). It usually is not desirable to set the environment variable before a top-level invocation of `make`, because it is usually better not to mess with a makefile from outside. However, if you are running `make` without a specific makefile, a makefile in `MAKEFILES` can do useful things to help the built-in implicit rules work better, such as defining search paths (see Directory Search).

Some users are tempted to set `MAKEFILES` in the environment automatically on login, and program makefiles to expect this to be done. This is a very bad idea, because such makefiles will fail to work if run by anyone else. It is much better to write explicit `include` directives in the makefiles. See Including Other Makefiles.