Let's say every Makefile you've read looked like noise. There's one shape underneath: target, colon, prerequisites, recipe.

The target is usually a file the recipe builds. The prerequisites are the files it's built from. The recipe is shell commands, and the manual is blunt about the catch: you need a tab at the beginning of every recipe line. That one obscurity, the manual's own word, catches the unwary.

Three lines and a tab. Every Makefile you'll ever read is made of these.

Let's say you run make twice and the second time says 'up to date'. What was checked?

Times, nothing else. A target is out of date when it doesn't exist, or when any prerequisite is newer, compared by last-modified time. make never reads the contents to decide. The reasoning in the manual: the target is computed from the prerequisites, so a changed prerequisite makes the existing target's contents no longer necessarily valid.

It compares labels on the boxes, not what's inside them.

Let's say make refuses with 'missing separator'. Count your editor's indent characters.

Every recipe line must begin with a real tab. Eight spaces look identical to you and are a different byte to make, and modern versions even guess at your mistake in the error. The one escape is setting .RECIPEPREFIX to another character, for the editors and the stubborn. Fix the editor to emit tabs, once, and this error never comes back.

The most famous wart in the tool, and it's one settings screen.

Let's say a file named clean ever lands in the directory. make clean now refuses: it sees the file, no prerequisites, up to date.

The fix is declaring the name: .PHONY: clean makes it a prerequisite of a special target, and the recipe runs regardless of any file. Phony means not-a-file, an action wearing a target's clothes. It's also a small speedup, the manual notes: implicit rule search is skipped for phony targets.

If the recipe doesn't build a file with the target's name, that target is phony. Say so.

Let's say the build might delete or overwrite something you care about. Read the plan first.

-n prints every recipe it would run, executing nothing, the same rehearsal habit as rsync's dry run. Its siblings: -t marks targets fresh by touching times, and -q says nothing and answers by exit code, 0 up to date, 1 needs work, 2 error, made for scripts. One caveat the manual flags: lines involving $(MAKE) still run under -n, recursion must recurse.

Destructive target, or borrowed Makefile? -n before enter.