Trouble in getting user input while using CASE statement in UNIX

i want to get user input like this

please tell which option to chose

  1. mango 2. tango 3. rango

if user chooses mango

then it should execute a set of statements and again ask like this

what do you want to do
1.add 2.subtract 3.exit

when i choose exit it should goto my previous menu asking again (please tell which option to chose

  1. mango 2. tango 3. rango )

i have did coding to an extent like this

#!/usr/bin/ksh
#

echo -e -n "choose names as listed in the below format 1. mango 2. tango 3. rango 4.exit"
read answer
echo "$answer"

while true
do
   case $answer in
   mango) DT=$(date)
   echo "******************* $DT ***********************" 
   echo -e "Specify what options 1.add 2.subtract 3.exit"
   read input
   #
   if [ "add" = "$input" ]
   then
         echo "add"
   elif [ "exit" = "$input" ]
   then
        exit 0;;          
                        #iam getting error at the place exit 0;;
   elif [ "subtract" = "$input" ]
           echo "sub"
   else
           echo "!! must specify add or subtract"
   fi
 
   #
   tango) echo "tango"
   break;;
   #
   rango) echo "rango"
   break;;
   exit) exit 0;
   break;;
   #
   *) echo "please enter correct value" read ;;
   break;;
   # --- VBE --- adding missing done...--- #
done

As you can see first it will ask me to choose from 6 options

  1. mango 2. tango 3. rango 4.exit

. If for example if i chose 1. mango
then it will ask
1.add 2.subtract 3.exit
now if i chose exit . it should go back to main menu (THIS IS WHAT IAM NOT ABLE TO DO) and ask

  1. mango 2. tango 3. rango 4.exit
    if i give exit here then only script should exit.

Please help how to do this one in the existing scrit. if not possible then modify and do in whicvere way u wish to do to to get the final result. I have just put an skeleton overview of the script. If anyone have any better approach on this then please advice as to how to arrive to this solution.

The ;; are in the wrong place, they should be after the fi which terminates your if statement. In a case statement the ;; terminates each separate condition.

The last two lines are a bit iffy. Probably best to just output an error message because the script is going to ask the question again on the next iteration of the "while true" loop (if you move the question to within the loop). Also, lose the break;; line because it is totally out of context.
Add the "esac" to complement the original "case".
Add the "done" to complement the original "do".

*) echo "please enter correct value" ;;
esac
done

The initial question to populate $answer should probably be inside the do-done loop or the users will neve get the chance to change the value.

Consider using the ksh's built-in "select" construct for constructing menus. This shows a nested example that does what you are looking for:

#!/usr/bin/ksh

#  Set select construct prompts for each menu level.
typeset -r MAINPROMPT="Select a main option: "
typeset -r MANGOPROMPT="Select mango option: "

#  Loop main menu until user exits explicitly.
while :
do
  print "\nMenu Title Goes Here\n"
  PS3=$MAINPROMPT  # PS3 is the prompt for the select construct.

  select option in mango tango rango exit
  do
    case $REPLY in   # REPLY is set by the select construct, and is the number of the selection.
      1) # mango
         #  Loop mango menu until user exits explicitly.
         while :
         do
           print "\nmango sub-menu title\n"
           PS3=$MANGOPROMPT
           select option1 in add substract exit
           do
             case $REPLY in
               1) # add
                  print "\nYou picked [add]"
                  break  #  Breaks out of the select, back to the mango loop.
                  ;;
               2) # subtract
                  print "\nYou picked [subtract]"
                  break  #  Breaks out of the select, back to the mango loop.
                  ;;
               3) # exit
                  break 2  # Breaks out 2 levels, the select loop plus the mango while loop, back to the main loop.
                  ;;
               *) # always allow for the unexpected
                  print "\nUnknown mango operation [${REPLY}]"
                  break
                  ;;
             esac
           done
         done
         break
         ;;
      2) # tango
         ;&  # Fall through to #3
      3) #rango
         print "\nYou picked $option"
         break
         ;;
      4) # exit
         break 2  #  Break out 2 levels, out of the select and the main loop.
         ;;
      *) # Always code for the unexpected.
         print "\nUnknown option [${REPLY}]"
         break
         ;;
    esac
  done
done

exit 0
 

not the most efficient way but it works in showing user input with case statement.

#!/bin/bash

y=1
echo -e "Choose Names as listed in the format below.\n \
1. mango\t2. tango\t3. rango\t4. exit"
read answer


while [ $y=1 ]; do
    case ${answer} in
    "[Mm][Aa][Nn][Gg][Oo]"|1)
        echo "mango"
        mode="mango"
        echo -e "Specify an Option\n1. add\t2. sub\t3. exit"
        read option
        case ${option} in
            "[Aa][Dd][Dd]"|1)
                echo "you chose add"
                ;;
            "[Ss][Uu][Bb]"|2)
                echo "you chose sub"
                ;;
            "[Ee][Xx][Ii][Tt]"|3)
                echo "goodbye"
                exit 0
                ;;
        esac
        ;;
    "[Tt][Aa][Nn][Gg][Oo]"|2)
        echo "tango"
        mode="tango"
            echo -e "Specify an Option\n1. add\t2. sub\t3. exit"
            read option
            case ${option} in
                    "[Aa][Dd][Dd]"|1)
                            echo "you chose add"
                            ;;
                    "[Ss][Uu][Bb]"|2)
                            echo "you chose sub"
                            ;;
                    "[Ee][Xx][Ii][Tt]"|3)
                            echo "goodbye"
                            exit 0
                            ;;
        esac
        ;;
    "[Rr][Aa][Nn][Gg][Oo]"|3)
        echo "rango"
        mode="rango"
                echo -e "Specify an Option\n1. add\t2. sub\t3. exit"
                read option
                    case ${option} in
                    "[Aa][Dd][Dd]"|1)
                                echo "you chose add"
                                ;;
                    "[Ss][Uu][Bb]"|2)
                            echo "you chose sub"
                            ;;
                    "[Ee][Xx][Ii][Tt]"|3)
                            echo "goodbye"
                            exit 0
                            ;;
        esac
        ;;
    "[Ee][Xx][Ii][Tt]"|4)
        echo "goodbye"
        exit 0
        ;;
    *)
        echo"Please enter a valid answer"
        ;;
    esac
    echo "would you like to continue?"
    read reply 
    if [ "$reply"="y" ]; then
        y=1
    else
        y=0
    fi
done

New, improved version that clears the screen before displaying the menu:

#!/usr/dt/bin/dtksh

# set select construct prompts for each menu level.
typeset -r MAINPROMPT="Select a main option: "
typeset -r MANGOPROMPT="Select mango option: "

#  Loop main menu until user exits explicitly.
while :
do
   clear
  print "\nMenu Title Goes Here\n"
  PS3=$MAINPROMPT  # PS3 is the prompt for the select construct.

  select option in mango tango rango exit
  do
    case $REPLY in   # REPLY is set by the select construct,
                     # and is the number of the selection.
      1) # mango
         #  Loop mango menu until user exits explicitly.
         while :
         do
           clear
           print "\nmango sub-menu title\n"
           PS3=$MANGOPROMPT
           select option1 in add substract exit
           do
             case $REPLY in
               1) # add
                  print "\nYou picked [add]"
                  break  #  Breaks out of the select, back to the mango loop.
                  ;;
               2) # subtract
                  print "\nYou picked [subtract]"
                  break  #  Breaks out of the select, back to the mango loop.
                  ;;
               3) # exit
                  break 2  # Breaks out 2 levels, the select loop plus
                           # the mango while loop, back to the main loop.
                  ;;
               *) # always allow for the unexpected
                  print "\nUnknown mango operation [${REPLY}]"
                  break
                  ;;
             esac
           done
         sleep 2
         done
         break
         ;;
      2) # tango
         ;&  # Fall through to #3
      3) #rango
         print "\nYou picked $option"
         break
         ;;
      4) # exit
         break 2  #  Break out 2 levels, out of the select and the main loop.
         ;;
      *) # Always code for the unexpected.
         print "\nUnknown option [${REPLY}]"
         break
         ;;
    esac
  done
sleep 2
done

exit 0