How do I scan multiple upper or lower cases in string variables.

Hello Im trying to develop my first custom event handler on a SMS message that will scan incoming text with different cases of string "KEY", "key" or "Key". This project is running on a linux machine and using a simple bash script only.  How do I scan or trigger any one of the string returning TEXT="Your Good!". Should i convert scanned string all to uppercase(lowercase) or should i declared all strings in arrays or should i use a conditional loop?Start Free Trial

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#!/bin/sh
#
#Search the code Key, KEY or key inside the message.
#
#CODE that we want to search
SEARCH= Key | key | KEY
#
#Text message that we want to send
TEXT="Your Good!"
#
#
CODE=`/bin/cat $FILE | grep "$SEARCH"`
#
#if code is not empty reply with the message "Your Good!"
if [ "$CODE" == "$SEARCH" ]; then
        echo "$TEXT"
fi