Create a menu driven script with do loop and case statement in bash

Question

I am trying to create a bash script to create json files from a txt file in AWS. The script below is failing (I think) at the first case option. I think it's because I have the $opt variable which is a catch all. Basically I want it to exit if you input the exit number. Create the files for any other valid number, and with an invalid number, ask you for another option.

#!/bin/bash

clear

# define variables
NOW=$(date +%F-%a-%H.%M) # year-month-date-day-hour.minute format

# display region list menu
region=($(aws ec2 describe-regions | jq -r '.Regions[].RegionName'))
aws ec2 describe-security-groups --region $region | jq -r '.SecurityGroups[].GroupId' > $region.txt
PS3="Select Region number: "
select opt in "${region[@]}" "exit"
do
   case $opt in
       $opt)
          aws ec2 describe-security-groups --region $region | jq -r '.SecurityGroups[].GroupId' > $region.txt
       # read security groups file into array and create individual json files
       mkdir -p "$region"
       while read group; do
         echo "Processing group: $group"
          aws ec2 describe-security-groups --region $region --group-ids "$group" > "$region"/"$group-"$DATE".json"
       done < $region.txt
           break
          ;;
          "exit")
       echo "Exiting..."
          exit
          ;;
          *)
       echo "Invalid option, try again..."
   esac
done

# cleanup security group text file
rm $region.txt

The expected behaviour is that you enter a number from 1-14 and Security Group json files are created into a directory of the region name. This part works. However if you enter 15 to exit this happens;

Select Region number: 15
Processing group: sg-4fec0526

Also if you enter an incorrect number e.g. 16 the same things happens as with 15;

Select Region number: 16
Processing group: sg-4fec0526

Numer 15 should exit and anything not 1-15 should echo out Invalid... and ask you to enter another number.

As for why it's a menu? I want granular control just now

Answer 1

The problem is your case statement, as you said. This is always going to be true since any variable, by definition, always matches itself:

case $opt in
   $opt)
     . . . 

So no matter what value you give it, it will always execute the same case block. I am really not sure what you're trying to do but I think you were aiming for something like this:

#!/bin/bash

## Enable extended globbing for the +(...) pattern
shopt -s extglob
clear
# define variables
NOW=$(date +%F-%a-%H.%M) # year-month-date-day-hour.minute format

# display region list menu
region=($(aws ec2 describe-regions | 
    jq -r '.Regions[].RegionName'))
aws ec2 describe-security-groups --region "$region" | jq -r '.SecurityGroups[].GroupId' > "$region.txt"
PS3="Select Region number: "

## make a dummy array which includes the values
validOptions=${region[0]};
for ((i=1; i<${#region[@]}; i++)); do
        validOptions="$validOptions|${region[i]}"
done

select opt in "${region[@]}" "exit"
do
   case $opt in
        ## This uses bash's +(pat1|pat2) syntax which matches
        ## one or more of the |-separated strings.
        +($validOptions))
            echo "Valid!"
            aws ec2 describe-security-groups --region "$region" | 
                jq -r '.SecurityGroups[].GroupId' > "$region.txt"
        # read security groups file into array and create
        # individual json files
        mkdir -p "$region"
        while read group; do
            echo "Processing group: $group"
            aws ec2 describe-security-groups --region "$region" --group-ids "$group" > "${region}/${group}-${DATE}.json"
        done < "$region.txt"
        break
        ;;
    "exit")
        echo "Exiting..."
        exit
        ;;
    *)
        echo "Invalid option $opt, try again..."
   esac
done