Rules of Makefiles

A somewhat tongue-in-cheek title, but this page lists a few very important rules you should always keep in mind when creating makefiles. Following these rules will allow your makefiles to be both pithy and beautiful. And they will make maintaining and modifying them, and thus your entire life, a much more pleasant experience.

  1. Use GNU make.

    Don’t hassle with writing portable makefiles, use a portable make instead!

  2. Every non-.PHONY rule must update a file with the exact name of its target.

    Make sure every command script touches the file “$@“–not “../$@“, or “$(notdir $@)“, but exactly $@. That way you and GNU make always agree.

  3. Life is simplest if the targets are built in the current working directory.

    Use VPATH to locate the sources from the objects directory, not to locate the objects from the sources directory.

  4. Follow the Principle of Least Repetition.

    Try to never write a filename more than once. Do this through a combination of make variables, pattern rules, automatic variables, and GNU make functions.

  5. Every non-continued line that starts with a TAB is part of a command script–and vice versa.

    If a non-continued line does not begin with a TAB character, it is never part of a command script: it is always interpreted as makefile syntax. If a non-continued line does begin with a TAB character, it is always part of a command script: it is never interpreted as makefile syntax.

    Continued lines are always of the same type as their predecessor, regardless of what characters they start with.

Yes, that’s all of them… so far. It’s not that that’s all I have to say on the subject, but coming up with points which are both truly fundamental and expressible in a succinct rule format, ain’t easy.

Let me know if you have suggestions.

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