function mainmenu {
echo "--------------- MAIN MENU -------------------"
echo " 1. CH1 "
echo " 2. CH2 "
echo " 3. CH3 "
echo "Choose 1-3"
read choice
case $choice in
1)
    while :
    do
    submenu # calling another menu here
    case $subchoice in
        1)
               do something
               ;;
        2) 
              do something
              ;;
        3)
              do something
              ;;
        4)
              do something
             ;;
        5)
             mainmenu
             ;;
        6)
             uexit                    #  calling the function to exit
             exit 1 
             ;;
        esac
       done
       ;;
2)
     while :
     do
               submenu2 # calling another menu here
            case $subchoice2 in
            1)
                   do something
                   ;;
           2)
                  do something
                  ;;
           3)
                 while :
                 do
                                submenu3 # calling another menu here
                         case $subchoice3 in
                         1)
                                  do something
                                  ;;
                        2)
                                 do something
                                 ;;
                       3)
                                do something
                                ;;
                      4)
                               do something
                               ;;
                      5)
                                      submenu2
                              ;;
                     6)
                              uexit
                              exit 1 
                             ;;
                     esac
                    done
                    ;;
          4)
                    do something
                     ;;
          5) 
                    mainmenu
                     ;;
          6)
                     uexit
                    exit 1  
                     ;;
          esac
        done 
       ;;
3)
      do something
       ;;
4)
      uexit
      exit 1
    ;;
esac
return
}
mainmenu