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A tool I first encountered in the pages of the seminal book "Software Tools", years before I had so much as seen a Unix command prompt,
It never quite "took off" the way some other Unix tools did.
The lack of an escape character — a surprising omission — makes it less handy to use than it might be.
It can be thought of as where you go when sed won't do, or do easily, what you want.
Years ago, I wrote an article on using M4, perhaps still worth a read.
This page was brought to you by ksh, vi, m4, sed & make,
courtesy of openbsd.
Last changed: Sun Mar 3 11:54:02 CET 2019