Background
m4 is a macro processor, in the sense that it copies its input to the output, expanding macros as it goes
https://www.gnu.org/savannah-checkouts/gnu/m4/manual/m4-1.4.18/m4.html#Preliminaries
m4 is a core gnu utility, and is installed by default on most *nix systems. Every one that I’ve encountered, in fact. Including macOS.
I consider myself a pretty serious command line nerd and am familiar with
sed,awk,grep,cut,sort,tr, etc. But I had never heard of this macro processor. It seemed very mysterious and obscure when I first encountered it…
Read in full here:
https://chrisman.github.io/9.html
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