rewrite witch to be compatible with more shells

sh/witch

@@ -1,67 +1,54 @@
 #!/usr/bin/env sh
-# NO_ZSH NO_BASH YES_DASH YES_ASH
-# this is `which` from Debian. the only changes are superficial (formatting).
-# this does not work as-is with zsh.
+# YES_ZSH YES_BASH YES_DASH YES_ASH
+### @ witch
+### this is a personal rewrite of `which` from Debian.
+### the original version didn't run on certain shells,
+### and inherited inconsistent behaviors from getopts.
 
 set -ef
 
-if test -n "$KSH_VERSION"; then
-	puts() {
-		print -r -- "$*"
-	}
-else
-	puts() {
-		printf '%s\n' "$*"
-	}
-fi
-
-ALLMATCHES=0
-
-while getopts a whichopts
-do
-	case "$whichopts" in
-		a) ALLMATCHES=1 ;;
-		?) puts "Usage: $0 [-a] args"; exit 2 ;;
+all=0
+for flag; do
+	case "$flag" in
+	(--) shift; break;;
+	(-?*)
+		shift
+		while flag="${flag#?}"; [ -n "$flag" ]; do
+			case "$flag" in
+			(a*) all=1;;
+			(*)
+				printf >&2 'Illegal option: -%.1s\n' "$flag"
+				printf 'Usage: %s\n' "$0 [-a] args"
+				exit 2;;
+			esac
+		done;;
+	(*) break
 	esac
 done
-shift $(($OPTIND - 1))
 
-if [ "$#" -eq 0 ]; then
-	ALLRET=1
-else
-	ALLRET=0
-fi
-case $PATH in
-	(*[!:]:) PATH="$PATH:" ;;
-esac
-for PROGRAM in "$@"; do
-	RET=1
-	IFS_SAVE="$IFS"
-	IFS=:
-	case $PROGRAM in
-		*/*)
-			if [ -f "$PROGRAM" ] && [ -x "$PROGRAM" ]; then
-				puts "$PROGRAM"
-				RET=0
+[ "$#" != 0 ] && res=1 || res=0
+
+IFS=:
+for prog; do
+	err=1
+	case "$prog" in
+	(*/*)
+		if [ -f "$prog" ] && [ -x "$prog" ]; then
+			printf %s\\n "$prog"
+			err=0
+		fi;;
+	(*)
+		set -- $(printf %s: "$PATH")
+		for sub; do
+			[ -n "$sub" ] || sub=.
+			if [ -f "$sub/$prog" ] && [ -x "$sub/$prog" ]; then
+				printf %s\\n "$sub/$prog"
+				err=0
+				[ "$all" = 1 ] || break
 			fi
-			;;
-		*)
-			for ELEMENT in $PATH; do
-				if [ -z "$ELEMENT" ]; then
-					ELEMENT=.
-				fi
-				if [ -f "$ELEMENT/$PROGRAM" ] && [ -x "$ELEMENT/$PROGRAM" ]; then
-					puts "$ELEMENT/$PROGRAM"
-					RET=0
-					[ "$ALLMATCHES" -eq 1 ] || break
-				fi
-			done
-			;;
+		done;;
 	esac
-	IFS="$IFS_SAVE"
-	if [ "$RET" -ne 0 ]; then
-		ALLRET=1
-	fi
+	[ "$err" = 0 ] || res=1
 done
 
-exit "$ALLRET"
+exit "$res"