Don't write until user saves

[kousu]

journal/journal

Lines 100 to 103 in 9687728

	if [ ! -e "$TODAY" ]; then
	mkdir -p "$(dirname "$TODAY")"
	(header; echo; echo) >> "$TODAY"
	fi

makes the journal get created on its first access, but what if the user makes a mistake (journal thursday when they meant friday) or wants to use a clever hack by setting $EDITOR to something that does data processing (e.g. EDITOR=head, EDITOR="wc -w" as in https://github.com/kousu/journal/blob/96877287c3da842cccc86847a80636e4281161d6/README.md#tips-and-tricks). It would be nice if non-existent files didn't get created just for looking at them -- reading shouldn't cause a write!. But I don't know how.

pass(1) solves this by a layer of indirection -- they first write to a tmp file, and after $EDITOR quits check what, if anything, was saved to it, and then only move it back in place if they want; they also have to use a tmpfile anyway because they need to temporarily decrypt the contents somewhere.