#!/bin/bash

IFS="|" # Split menus on |, so we can have spaces in titles

# Use parameters as a stack.  $1 is the current menu.
# we can add with set -- again, or remove with 'shift'.
set -- main

while [ "$#" -gt 0 ]
do
        case "$1" in    # Look up the right options for the menu
        main)           OPTIONS="CH1|CH2|CH3|Q" ;;
        submenu1)       OPTIONS="A|B|C|Q"       ;;
        submenu2)       OPTIONS="D|E|F|Q"       ;;
        submenu3)       OPTIONS="X|Y|Z|Q"       ;;
        esac

        PS3=$'\n'"$1 menu: "    # Special variable controlling select prompt

        # Print menu, get reply
        select X in $OPTIONS
        do
                [ -z "$X" ] || break
        done

        # We treat Q specially, it returns to the previous menu.
        if [ "$X" = "Q" ]
        then
                shift           # Return to previous menu
                continue        # Go to top of loop
        fi

        case "$1" in
        main)
                case "$X" in
                CH1)    set -- submenu1 "$*"    ;;
                CH2)    set -- submenu2 "$*"    ;;
                CH3)    set -- submenu3 "$*"    ;;
                esac
                ;;

        submenu1)
                case "$X" in
                A)     # Switch to submenu2 by removing submenu1 before adding
                        shift
                        set -- submenu2 "$*"
                        ;;
                B)      ;;
                C)      ;;
                esac
                ;;

        submenu2)
                case "$X" in
                A)      ;;
                B)      ;;
                C)      ;;
                esac
                ;;

        submenu3)
                case "$X" in
                A)      ;;
                B)      ;;
                C)      ;;
                esac
                ;;

        *)      echo "Unknown menu $1, removing"
                shift
                ;;
        esac
done

echo "Menu list is empty, quitting" >&2