I have used it recently. I have a similar attitude towards m4 as shell scripts: they are good for quick hacks, proofs of concept, and very simple systems. When

I have used it recently. I have a similar attitude towards m4 as shell scripts: they are good for quick hacks, proofs of concept, and very simple systems. When I need to sprinkle just a bit of macros on something, m4 is great. For example, a one-off piece of technical documentation I wrote is markdown interspersed with code examples. I wanted to make sure the code passed its unit tests, so it lives in separate files and I use m4 to include it into the bigger document. This is nicer than catting separate file chunks together because the text can all be contiguous, but if I needed to do anything more sophisticated I would probably switch to purpose-built templating or static site system.