In my first decade writing Makefiles, I developed the bad habit of
liberally using GNU Make’s extensions. I didn’t know the line between
GNU Make and the portable features guaranteed by POSIX. Usually it
didn’t matter much, but it would become an annoyance when building on
non-Linux systems, such as on the various BSDs. I’d have to specifically
install GNU Make, then remember to invoke it (i.e. as gmake) instead
of the system’s make.
I’ve since become familiar and comfortable with make’s official specification, and I’ve spend the last year writing strictly portable Makefiles. Not only has are my builds now portable across all unix-like systems, my Makefiles are cleaner and more robust. Many of the common make extensions — conditionals in particular — lead to fragile, complicated Makefiles and are best avoided anyway. It’s important to be able to trust your build system to do its job correctly.
This tutorial should be suitable for make beginners who have never written their own Makefiles before, as well as experienced developers who want to learn how to write portable Makefiles. Regardless, in order to understand the examples you must be familiar with the usual steps for building programs on the command line (compiler, linker, object files, etc.). I’m not going to suggest any fancy tricks nor provide any sort of standard starting template. Makefiles should be dead simple when the project is small, and grow in a predictable, clean fashion alongside the project.
I’m not going to cover every feature. You’ll need to read the specification for yourself to learn it all. This tutorial will go over the important features as well as the common conventions. It’s important to follow established conventions so that people using your Makefiles will know what to expect and how to accomplish the basic tasks.
If you’re running Debian, or a Debian derivative such as Ubuntu, the
bmake and freebsd-buildutils packages will provide the bmake and
fmake programs respectively. These alternative make implementations
are very useful for testing your Makefiles’ portability, should you
accidentally make use of a GNU Make feature. It’s not perfect since each
implements some of the same extensions as GNU Make, but it will catch
some common mistakes.
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