#!/bin/sh

export STACKCD

stackcd()
{
	local action="$1"	# e.g. 'push' or 'pop' or 'dirs' or ~3
	local i

	case "$action" in
		'~'[0-9])
			i=0
			for _ in $STACKCD; do {
				case "$action" in
					'~'$i)
						cd $_
						return $?
					;;
				esac
				i=$((i+1))
			} done
		;;
		dirs)
			i=0
			for _ in $STACKCD; do {
				printf '%i  %s\n' "$i" "$_"
			} done
		;;
		push)
			STACKCD="$PWD $STACKCD"
		;;
		pop)
			set -- $STACKCD
			cd "$1" || return 1
			shift
			STACKCD="$*"
		;;
	esac
}

stackcd push .
cd /tmp
stackcd push .
stackcd dirs
stackcd ~1
stackcd pop