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14 GNU make

Only after it has tried to ﬁnd a way to remake a makeﬁle and failed, will make diagnose the

missing makeﬁle as a fatal error.

If you want make to simply ignore a makeﬁle which does not exist or cannot be remade,

with no error message, use the -include directive instead of include, like this:

-include filenames...

This acts like include in every way except that there is no error (not even a warning)

if any of the ﬁlenames (or any prerequisites of any of the ﬁlenames) do not exist or cannot

be remade.

For compatibility with some other make implementations, sinclude is another name for

-include.

3.4 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

Section 3.3 [Including Other Makeﬁles], page 13). In addition, the default goal is never

taken from one of these makeﬁles (or any makeﬁle included by them) 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 Section 5.7 [Recursive Use of make], page 50). 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 Section 4.4 [Directory Search], page 25).

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 Section 3.3 [Including Other Makeﬁles], page 13.

3.5 How Makeﬁles Are Remade

Sometimes makeﬁles can be remade from other ﬁles, such as RCS or SCCS ﬁles. If a makeﬁle

can be remade from other ﬁles, you probably want make to get an up-to-date version of the

makeﬁle to read in.

To this end, after reading in all makeﬁles, make will consider each as a goal target and

attempt to update it. If a makeﬁle has a rule which says how to update it (found either

in that very makeﬁle or in another one) or if an implicit rule applies to it (see Chapter 10

[Using Implicit Rules], page 111), it will be updated if necessary. After all makeﬁles have

been checked, if any have actually been changed, make starts with a clean slate and reads

all the makeﬁles over again. (It will also attempt to update each of them over again, but

normally this will not change them again, since they are already up to date.)

If you know that one or more of your makeﬁles cannot be remade and you want to keep

make from performing an implicit rule search on them, perhaps for eﬃciency reasons, you

can use any normal method of preventing implicit rule look-up to do so. For example,

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Roland Ver. 4.5 Informações Técnicas Página 24