GUI menus in bash shell script

#!/bin/bash
#menu driven program to display memoryinfo and cpuinfo
while true
do
dialog --menu "Choose one:" 10 30 3 1 MemoryInfo 2 CPUInfo 3 exit 2>op
o=`cat op`
   case $o in
   1)cat /proc/meminfo>tmp
      dialog --title "Memory Info" --textbox tmp 22 70;;
 
   2)cat /proc/cpuinfo>tmp
       dialog --title "CPU Info" --textbox tmp 22 70;;
   3)clear
       exit;;
     esac
done

 #example 2
while true
do
 dialog --menu "Enter choice" 12 30 4 1 date 2 cal  3 ls 4 exit  2>op
  o=`cat op`
  case $o in
  1)date >t
    dialog --title "date" --textbox t 10 30;;
  2) cal 01 2020 >t
      dialog --title "calendar" --textbox t 15 40;;
  3)ls >t
      dialog --title "list of files" --textbox t 30 40;;
  4)clear
     exit;;
  esac
done