Get Value from Key:Value Pair with variable as input and output

I have an array of Department Names and Department Codes in a script. A user will select a Department Name which is then assigned to a variable; I need to

read the array (deptCodeArray)
find the Department Name selected by the user (departmentName)
get the Department Code matched to the Department Name from the array and set to a variable (deptCode) that will be used later. This script is run on remote macOS computers (macOS Big Sur or later) using an MDM tool (Jamf).

# This is an array of Department Namse and matching Department Codes embedded 
# in the script. I have full control over this array.

deptCodeArray="
Information Technology=IT,
Marketing=MA,
Finance=FI
"

# The Department Name will be selected by the user when the script runs 
# (The full script includes a user dialog with a menu of department 3 names 
# to select from.)

departmentName="Information Technology"

# The Department Code is the desired output, to be used later in the script.
# In this case it should be deptCode=IT

deptCode=""

I've tried a couple of different ways to get this working. Apparently macOS does not support associative arrays? I started with "declare -A deptCodeArray" but apparently this requires bash 4, which does not come with macOS, and installing is not an option.

I was trying awk, but I have some trouble understanding how to make that work, and I am not sure if something else would work. I am also not sure if I have the correct syntax for the array.

Solution

Here is a way how to do it with bash's =~ operator, which considers the string to the right of it as a regular expression. This example doesn't use arrays, except the BASH_REMATCH (a builtin array whose members are assigned by the =~ operator), and should work in macOS' bash:

#!/bin/bash

# The variable name is misleading. This isn't a bash array
deptCodeArray="
Information Technology=IT,
Marketing=MA,
Finance=FI
"

departmentName="Information Technology"

[[ $deptCodeArray =~ $'\n'"$departmentName"=([^$'\n',]*) ]]
deptCode=${BASH_REMATCH[1]}

echo "$deptCode"

For more information about =~ operator, see Conditional Constructs, the section starting with [[…]]. For the $'…' construct, see ANSI-C Quoting