#!/bin/bash

shopt -s extglob

declare -a stack
while read line; do
	[[ "$line" ]] || exit 0
	stack=( )
	line=${line//\\*/×}
	for token in ${line//\//÷}; do
		case $token in
		[÷×+-])
			if [[ ${#stack[@]} -gt 1 ]]; then
				op=${token/÷//}; op=${op/×/*}
				result=$((${stack[1]} $op ${stack[0]}))
				stack=( $result ${stack[@]:2} )
			else
				echo "Stack underflow"
			fi
			;;
		?(-)+([[:digit:]]))
			stack=( $token ${stack[@]} )
			;;
		*)
			echo "Bad operator: $token"
		esac
	done
	[[ ${#stack[@]} -gt 0 ]] \
		&& echo ${stack[$((${#stack[@]}-1))]}
done