m4

M4 or M-4 may refer to: In computers:m4 (computer language), a macro processing languageGNU m4, the GNU version of the m4 language In firearms and military equipment:Benelli M4 Super 90, a combat shotgun M4 Sherman, the primary tank used by the Allies in World War IIM4 Carbine, an assault rifleM2/M4 Selectable Light-weight Attack Munition (SLAM), a land mineM4 (cipher), a variant of the Enigma machineM4 flame fuel thickening compound, a substance used in fire bombs and incendiary weaponsMyasishchev M-4, a Soviet strategic bomberM4 SLBM, a French submarine-launched ballistic missileSpectre M4, a submachine gun
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GNU m4 is the GNU version of the m4 macro preprocessor. It is designed to avoid many kinds of limits found in traditional m4s: limits like maximum line lengths, maximum size of a macro, number of macros, etc. Removing such arbitrary limits is one of the stated goals of the GNU projects.The GNU Autoconf package makes extensive use of the features of GNU m4.GNU m4 is currently maintained by Gary V. Vaughan.
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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 by Francois Pinard pinard@iro.umontreal.ca and a public domain version by Ozan Yigit oz@sis.yorku.ca and Richard A. O'Keefe ok@goanna.cs.rmit.OZ.AU (FTP from any 386BSD, NetBSD or FreeBSD archive). A Macintosh version is here.
See also m3, m5.
["The M4 Macro Processor", Kernighan & Ritchie, Jul 1977].

See CTD (Common Technical Document).