m4 - Traditional Unix macro processor.

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.

For more information, visit:  http://www.gnu.org/software/m4