zsh script to compare macOS Versions - see https://rhymeswithdiploma.com/2020/07/10/macos-is-at-least/ for full explanation

macos-is-at-least.sh

#!/bin/zsh -f
# Purpose: Check to see if we are running on Big Sur
#
# From:	Timothy J. Luoma
# Mail:	luomat at gmail dot com
# Date:	2020-07-10

PATH="/usr/local/bin:/usr/bin:/usr/sbin:/sbin:/bin"

	# this will check to make sure `sw_vers` exists
	# if it does not, this is probably not macOS
if ((! $+commands[sw_vers] ))
then
	echo "$NAME: 'sw_vers' is required but not found in $PATH" >>/dev/stderr
	exit 2
fi

	## First we get the value for this Mac and save it to `$ACTUAL`
ACTUAL=$(sw_vers -productVersion)

	## load 'is-at-least' so we can use it
autoload is-at-least

	## "Is the version of macOS that we are using _at least_ 10.16?"
is-at-least "10.16" "$ACTUAL"

	## EXIT will be '0' if ACTUAL is at least 10.16
	## EXIT will be '1' if ACTUAL is _less than_ 10.16
EXIT="$?"

if [[ "$EXIT" == "0" ]]
then
		# This is Big Sur (or later)
	echo "YES"

elif [[ "$EXIT" == "1" ]]
then
		# This is BEFORE Big Sur
	echo "NO"

else
		# we should never get here
	echo "This should not have happened. EXIT = $EXIT"

fi

exit 0