m4

from The Free On-line Dictionary of Computing (8 July 2008)
m4

   A {macro} processor for {Unix} and {GCOS} which is more
   flexible than {cpp}.  m4 copies its input to the output,
   expanding macros which can be either built-in or user-defined.
   m4 has built-in functions for including files, running {Unix}
   commands, doing integer arithmetic, manipulating text in
   various ways and recursing.  m4 can be used either as a
   {front-end} to a compiler or as a stand-alone tool.

   {sendmail}'s configuration file (/etc/sendmail.cf) is writen
   in m4 macros.

   There is a GNU m4 v1.1
   (ftp://gnu.org/pub/gnu/m4-1.0.tar.Z) by Francois
   Pinard <[email protected]> and a {public domain} version
   by Ozan Yigit <[email protected]> and Richard A. O'Keefe
   <[email protected]> (FTP from any {386BSD}, {NetBSD} or
   FreeBSD archive).  A Macintosh version is here
   (ftp://nic.switch.ch/pub/software/mac/src/mpw-c/).

   See also {m3}, {m5}.

   ["The M4 Macro Processor",
   Kernighan & Ritchie, Jul 1977].