GNU m4

GNU m4 is an open source 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 includes built-in functions for adding files, running shell commands, doing arithmetic functions, and much more. It can copy its input to the output, expanding macros as it goes.

Macros are either user-defined or built-in, and can take any number of arguments. Besides just doing macro expansion the GNU m4 software can manipulate text in various ways.

GNU m4 can be used either as a macro processor or as a front-end to a compiler. It comes pre-installed in many popular Linux operating systems.