M4

The term M4 has several meanings:
The M4 motorway is a major British motorway which runs from Chiswick, west of London, into Wales.
The M4 is also a motorway in Sydney, Australia, running from the western suburb of Emu Plains to the inner western suburb of Strathfield.
The M4 Carbine is also a carbine version of the M16 rifle.
M4 is also Messier object M4, or Messier 4, also known as NGC 6121, a globular cluster in the constellation of Scorpius.

This article is about the M4 macro processing language.

M4 is a macro processing language.

A list of M4 resources may be found at " class="external">http://www.m4site.com

A macro processor is a text-replacement tool. Its chief use is to re-use text templates, typically in programming applications, but also in text editing, text processing applications.

Macro processors were prevalent when assembly language programming was the common tool of programmers. In these early days of programming, the programmers noted that much of their program was repeated text. Simple means to re-use this text were invented. Programmers soon discovered it easy to not only reuse entire blocks of text, but, on occasion, substitute different values for similar parameters. This defined the usage range of macro processors.

M4 offers these facilities:

text replacement
parameter substitution
file inclusion
string manipulation
conditional evaluation
arithmetic expressions
system interface
programmer diagnostics

Unlike most earlier macro processors, it is not targeted at any particular computer or human language.

An example:

define(`Name', `A very very long name')
printf("Name\\n");

After being processed with m4:

m4 inputfile >outputfile

The outputfile will look like

printf("A very very long name\\n")

There is a GNU version of m4.

M4

External links