.CD "m4 \(en macro processor"
.SX "m4\fR [\fB\(enD \fIname\fR = \fIvalue\fR]\fR [\fB\(enU \fIname\fR] 
.FL "\(enD" "Define a symbol"
.FL "\(enU" "Undefine a symbol"
.EY "m4 <m4test" "Run M4"
.PP
\fIM4\fR is a general-purpose macro processor.
It is described in Chap. 9.
It has been used to implement programming languages, such as RATFOR.