Wrt: https://twitter.com/jcoglan/status/458219405273759744

Makefile

PATH := ./foo:$(PATH)
export PATH

foo:
	mkdir -vp $@

foo/bar: foo
	printf "#!/bin/echo Hello\n" > $@.tmp && chmod +x $@.tmp && mv -v $@.tmp $@

runit_okay: foo/bar
	echo $$PATH
	sh -c 'bar'

runit_fail: foo/bar
	echo $$PATH
	bar

runit_env: foo/bar
	echo $$PATH
	env bar

transcript.txt

:; make runit_fail
mkdir -vp foo
printf "#!/bin/echo Hello\n" > foo/bar.tmp && chmod +x foo/bar.tmp && mv -v foo/bar.tmp foo/bar
foo/bar.tmp -> foo/bar
echo $PATH
./foo:/usr/bin:/opt/pkg/sbin:/opt/pkg/bin:/Users/cez/Library/Haskell/bin:/usr/local/heroku/bin:/usr/local/git/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/X11/bin:/opt/local/bin:/Users/cez/bin
bar
make: bar: No such file or directory
make: *** [runit_fail] Error 1
:; make runit_okay
echo $PATH
./foo:/usr/bin:/opt/pkg/sbin:/opt/pkg/bin:/Users/cez/Library/Haskell/bin:/usr/local/heroku/bin:/usr/local/git/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/X11/bin:/opt/local/bin:/Users/cez/bin
sh -c 'bar'
Hello ./foo/bar
:; make runit_env
echo $PATH
./foo:/usr/bin:/opt/pkg/sbin:/opt/pkg/bin:/Users/cez/Library/Haskell/bin:/usr/local/heroku/bin:/usr/local/git/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/X11/bin:/opt/local/bin:/Users/cez/bin
env bar
Hello ./foo/bar
:;