Re: test z$foo = zbar (and Re: [PATCH 1/3] bisect: relax requirement for a working tree.)

Stefano Lattarini wrote:

  $ /usr/xpg4/bin/sh -c 'test -z ")"'; echo $?
  0

Yikes, thanks for pointing it out.  I wonder if we should introduce a
sane_test function, like this.

 empty_string () {
	case $* in
	?*)
		return 1 ;;
	*)
		return 0 ;;
	esac
 }

 # This is like "test", but:
 #  - it only implements a minimal subset of the functionality
 #  - it works around shells that cannot cope with parentheses as
 #    parameters to some operators, like ksh before 2008:
 #
 #	$ /usr/xpg4/bin/sh -c 'test -z ")"'; echo $?
 #	0
 sane_test () {
	# implied -n
	test "$#" = 0 && set -- -n ""
	test "$#" = 1 && set -- -n "$1"
	test "$#" = 2 && test "z$1" = z! && set -- -z "$2"

	test "$#" -le 4 || 

	case $# in
	2)
		case $1 in
		-z)
			empty_string "$2" ;;
		-n)
			! empty_string "$2" ;;
		-*)
			test "$@" ;;
		*)
			die "sane_test: unrecognized unary operator $1" ;;
		esac
		;;
	3)
		case $2 in
		= | !=)
			test "z$1" "$2" "z$3" ;;
		-eq | -lt | -gt | -le | -ge)
			test "$@" ;;
		*)
			die "sane_test: unrecognized binary operator $2" ;;
		esac
		;;
	4)
		test "z$1" = z! ||
		die "sane_test: unrecognized 4-argument test (not a negation)"

		shift
		! sane_test "$@"
		;;
	*)
		die 'sane_test: too many arguments'
		;;
	esac
 }