Original versions of https://github.com/sahal/auto_verify_dns

auto_verify_dns-v1.sh

#!/bin/bash
# ./auto_verify_dns.sh
# _very_ dumb way to verify that a list of dns servers work...
# by sahal
#
# use: ./auto_verify_dns.sh /full/path/to/dns/servers  > ~/output
# requires timeout3 (set $W_TOUT) by Dimitry V Golovashkin (see Google)

# path to timeout3 - written by Dmitry V Golovashkin - via google
W_TOUT=/home/sahal/scripts/others/timeout3

fullpath_to_list_of_dns_servers=$1
#output=$2

a=($(cat $fullpath_to_list_of_dns_servers))
for i in $(seq 0 $((${#a[@]} - 1)))
do
	$W_TOUT -t 5 nslookup baidu.com ${a[$i]} | grep answer\: > /dev/null 2>&1
	if [ $? -eq 0 ]; then
		echo ${a[$i]} #>> $output
	fi
done

auto_verify_dns.sh

#!/bin/bash
# ./auto_verify_dns.sh [server 10.0.0.12]
# desc: a quick test to see if a list (or one) of nameservers (IP/domains)
# are able to resolve a particular $domain within a set $timeoutsec
# by: Sahal Ansari (github@sahal.info)
# todo: check if nameserver given is a valid IP, print timeout lengths

#pick a domain to resolve (e.g. yahoo.com or google.com) and put it here:
domain=change.this.to.something.local
# full path to timeout3
# https://github.com/jeuneS2/lemberg/blob/master/timeout3
timeout3=/home/user/timeout3.sh
timeoutsec=5
# a list of potential dns servers
dns=/home/user/listodnsservers

if [ ! -e $timeout3 ]; then
	echo "OOps, You don't have timeout3"
	echo "Get it: https://github.com/jeuneS2/lemberg/blob/master/timeout3"
	exit 1
fi

function checkdns {
	$timeout3 -t $timeoutsec nslookup $domain $1 > /dev/null 2>&1 && echo $1
}

function breaklist {
	if [ ! -e "$dns" ]; then
		echo "OOps, Cannot find your list of DNS servers!?"
		exit 1
	fi

	# you can mess with the input file (or not)
	# for server in $(cut -d, -f2 < $dns)
	for server in $(cat $dns)
	do
		checkdns $server
        done
}

case $1 in
server*)
	checkdns $2
;;

*)
	breaklist
;;
esac

See the updated version on my github: https://github.com/sahal/auto_verify_dns