m4

GNU m4

GNU m4 is an implementation of the traditional Unix macro processor. It is mostly SVR4 compatible, although it has some extensions (for example, handling more than 9 positional parameters to macros). GNU m4 also has built-in functions for including files, running shell commands, doing arithmetic, etc. GNU m4 is a macro processor, in the sense that it copies its input to the output, expanding macros as it goes.