[john-tells-all]

I suggest using := as in `APP_URL := http://localhost` vs raw "=". The colon-equals format means "set value now", so it's easier to understand.

I've never used eval.

Make's use of Bash can lead to hairy quoting/escaping. I use Make as a "dumb high-level runner" and put any sort of intelligence, like conditionals or loops or networking, in lower-level scripts or programs.

Make is an orchestrator.