Storing output of here-string BC calculation into a variable for error-checking

Question

I have an assignment for school which is to create a script that can calculate a math equation any length using order of operations. I had some trouble with this and ended up finding out about here-strings. The biggest problem with the script seems to be error-checking. I tried to check the output of bc using $?, however it is 0 whether it is success or fail. In response to that I am now attempting to store the output of the here-string into a variable, and then I will use regex to check if output begins with a number. Here is the piece of code I wish to store in a variable, followed by the rest of my script.

#!/bin/bash
set -f
#the here-string bc command I wish to store output into variable
cat << EOF | bc
scale=2
$*
EOF


read -p "Make another calculation?" response
while [ $response = "y" ];do
    read -p "Enter NUMBER OPERATOR NUMBER" calc1
cat << EOF | bc
scale=2
$calc1
EOF
read -p "Make another calculation?" response
done
~

Answer 1

This should do the trick:

#!/bin/sh

while read -p "Make another calculation? " response; [ "$response" = y ]; do
    read -p "Enter NUMBER OPERATOR NUMBER: " calc1
    result=$(bc << EOF 2>&1
scale=2
$calc1
EOF
)
    case $result in
    ([0-9]*)
         printf '%s\n' "$calc1 = $result";;
    (*)
         printf '%s\n' "Error, exiting"; break;;
    esac
done

Sample run:

$ ./x.sh
Make another calculation? y
Enter NUMBER OPERATOR NUMBER: 5+5
5+5 = 10
Make another calculation? y
Enter NUMBER OPERATOR NUMBER: 1/0
Error, exiting

Note that you might do this without a here-document like this:

result=$(echo "scale=2; $calc1" | bc 2>&1)