#!/bin/sh -eu
# A target must not be rebuilt when a non-existence dependency does not exist.

>all.do printf 'redo-ifchange a\n'
>a.do printf 'test -e b || redo-ifcreate b\ndate +%s\n'

redo
<a read -r timestamp_a1

sleep 1

redo
<a read -r timestamp_a2

test ${timestamp_a2} -eq ${timestamp_a1}