I call it Macript, a portmanteau of "macro" and "script". It's a short Perl program that reads a source file, scans it for anything that looks like a macro invocation, tests for whether a script by that name exists in the directory where Macript was invoked, and, if it does, expands the invocation to the standard output result of running that script with whatever arguments happen to be given via the macro.
That's pretty much it. And let me say, as a preprocessing step, it's much too useful. I would say that it's entirely changed my build process, but that would be a lie, because I'm pretty stuck in tradition. However, I suspect that a lot of people stand to benefit from a tool like this.
Say you want to perform some text-based program translation for which the ordinary C preprocessor is insufficient, or for which you simply don't want to resort to hairy macros or x-macros. Want to produce forward declarations for all of the functions in a source file? Easy. Want to perform conditional compilation based on the results of a configuration script? Piece of cake. Want to generate compile-time warnings about uses of functions that are marked
// DEPRECATEDin the source? Trivial.
All kinds of code generation and static analysis tasks become a breeze by adding this one simple preprocessing step to your build. I strongly encourage you to try it out, and I suspect you'll be pleased with the results. The best part is that it's not an enormous investment. Even software that relies heavily on Macript can almost certainly be rewritten to avoid it, but it just happens to automate a few things that can make life a whole heck (or at least a fourth of a heck) of a lot easier.
I promise you'll be able to find it on Sourceforge very soon. Stay tuned!