root@er-x:~# cat /root/parse-set.sh
parse_ipset() {
	if [ -x /sbin/fw4 ]; then
		local domainlist=${1%/*}
		local setlist=${1##*/}
		local nftsets=""

		IFS=,
		for set in $setlist; do
			local family=$(nft -t list set inet fw4 "$set" 2>&1 | sed -nre 's#^.+ipv([46])_addr.*$#\1#p')
			nftsets="${nftsets:+$nftsets,}${family:+$family#}inet#fw4#$set"
		done
		IFS=$' \t\n'

		echo "--nftset=$domainlist/$nftsets"
	else
		echo "--ipset=$1"
	fi
}

parse_ipset "/example.org/yahoo.com/google.com/set1,set2,set3"
root@er-x:~# sh /root/parse-set.sh
--nftset=/example.org/yahoo.com/google.com/4#inet#fw4#set1,6#inet#fw4#set2,inet#fw4#set3
root@er-x:~#