Use 'nslookup' to query one or more domains, using a pre-defined list of nameservers

dns_check.sh

#!/bin/bash

# what's this all about then?
description="Use 'nslookup' to query one or more domains, using a pre-defined list of nameservers"

# set nameservers as associative arrays
declare -A primary_nameservers
primary_nameservers['Google']='8.8.8.8'
primary_nameservers['CloudFlare']='1.1.1.1'
primary_nameservers['Quad9']='9.9.9.9'
primary_nameservers['Control D']='76.76.2.0'
primary_nameservers['OpenDNS']='208.67.222.222'
primary_nameservers['Yandex Basic DNS']='77.88.8.8'

declare -A additional_nameservers
additional_nameservers['AdGuard DNS']='94.140.14.14'
additional_nameservers['Digital Ocean SG']='139.59.219.245'
additional_nameservers['Orcon NZ']='121.98.0.1'
additional_nameservers['SiteHost NZ']='223.165.64.97'
additional_nameservers['Telstra AU']='139.130.4.4'
additional_nameservers['Yandex Safe DNS']='77.88.8.88'

# final list used in the loop (populated after parsing options)
declare -A nameservers

# misc. vars / settings / default
lookup_type="A"
this_script=$(basename "${BASH_SOURCE[0]}")
use_all_nameservers=false
watch_seconds=""

# colors, cos we like colours!
clr_default="\e[0m"
clr_white="\e[1m"
clr_dim="\e[2m"
clr_inverse="\e[7m"
clr_red="\e[31m"
clr_green="\e[32m"
clr_yellow="\e[33m"
clr_cyan="\e[36m"

# help text
help() {
    echo "$description"
    echo -e "${clr_yellow}Either pass in a list of domains: \n\t${clr_default}${this_script} domain.com\n\t${this_script} 'domain.com domain2.com domain3.com'\n\t${this_script} -d domain.com \n\t${this_script} --domains='domain.com domain2.com'\e[0m"
    echo -e "${clr_yellow}Or export a ENV variable 'domains': \n\t${clr_default}export domains=\"domain.com domain2.com\"\e[0m"
    echo -e "${clr_yellow}OPTIONS:${clr_default}"
    echo -e "\t -d | --domains \tDomain(s) to query"
    echo -e "\t -t | --type \t\tSet query type [ A = default | AAAA | NS | MX ]"
    echo -e "\t -e | --expected \tHighlight result RED if doesn't match 'expected'"
    echo -e "\t -a | --all \t\tQuery additional nameservers as well"
    echo -e "\t -w | --watch=SECONDS \tRun repeatedly, sleeping SECONDS between runs"
    echo -e "\t -h | --help \t\tDisplay this help"
    echo -e "${clr_yellow}EXAMPLES:${clr_default}"
    echo -e "\t${this_script} -t NS domain.com"
    echo -e "\t${this_script} -d domain.com -e 123.123.123.123"
    echo -e "\t${this_script} --domains='domain.com domain2.com' --type=NS"
    echo -e "${clr_yellow}NOTES:${clr_default} \n\tWhen passing domains without a preceding option (-d | --domains), it must be the last argument."
    echo
    exit
}

# write error to STDERR and exit
die() {
    echo -e "${clr_red}ERROR:${clr_default} $1 ${clr_dim}${2}${clr_default}" >&2; exit 2;
}

# getopts required arg fallback
option_needs_arg() {
    if [ -z "$OPTARG" ] ; then
        die "Missing argument for --$OPT" "[ERR1:long-option-missing-arg]"
    fi
}

while getopts :d:ht:e:aw:-: OPT; do

    # support long options: https://stackoverflow.com/a/28466267/519360
    if [ "$OPT" = "-" ]; then  # long option: reformulate OPT and OPTARG
        OPT="${OPTARG%%=*}"        # extract long option name
        OPTARG="${OPTARG#$OPT}"    # extract long option argument (may be empty)
        OPTARG="${OPTARG#=}"       # if long option argument, remove assigning "="
    fi

    case "$OPT" in
        h | help )
            help;;
        e | expected )
            option_needs_arg
            expected_result="$OPTARG";;
        t | type )
            option_needs_arg
            lookup_type="${OPTARG^^}";; # convert to uppercase "^^"
        d | domains )
            option_needs_arg
            domains="$OPTARG";;
        a | all )
            use_all_nameservers=true;;
        w | watch )
            option_needs_arg
            watch_seconds="$OPTARG";;
        : )
            die "Missing argument for -$OPTARG" "[ERR2:missing-arg]";;
        ??* )
            die "Unrecognised option --$OPT" "[ERR3:bad-long-option]";;
        ? )
            die "Unrecognised option -$OPTARG" "[ERR4:bad-short-option]";;
    esac

done

shift $((OPTIND-1)) # remove parsed options and args from $@ list

# if there is a remaining argument, consider it as a list of domains to query
if [[ $1 != '' ]]; then
    domains="${1}"
elif [[ $domains == '' ]]; then
    echo -e "\e[31mNo domains to query!\e[0m"
    help
fi

# check 'lookup_type' for accepted values
case "$lookup_type" in
    NS | A | AAAA | MX ) ;;
    * ) die "Unsupported lookup type";;
esac

# validate watch interval (if provided)
if [[ -n $watch_seconds ]] && [[ ! $watch_seconds =~ ^[0-9]+$ ]]; then
    die "Watch value must be a positive integer number of seconds" "[ERR5:bad-watch-value]"
fi

build_nameserver_list() {
    # start with primary nameservers
    nameservers=()
    for key in "${!primary_nameservers[@]}"; do
        nameservers[$key]="${primary_nameservers[$key]}"
    done

    # optionally include additional nameservers
    if [[ $use_all_nameservers == true ]]; then
        for key in "${!additional_nameservers[@]}"; do
            nameservers[$key]="${additional_nameservers[$key]}"
        done
    fi
}

do_nslookup_loop() {

    for this_domain in $domains; do

        echo -e "${clr_cyan}+ $this_domain ...${clr_default}"
        echo -e "  ${clr_yellow}Nameserver:\t\t\t\t\tResult:${clr_default}"

        for key in "${!nameservers[@]}"; do

            # run nslookup
            local nslookup_result=$( nslookup -type="${lookup_type}" $this_domain ${nameservers[$key]} )

            # check for failure
            local failed="$( echo "$nslookup_result" | egrep "NXDOMAIN|No answer" )"

            if [[ $failed != '' ]]; then
                local result_output="NOT FOUND!"
            else
                # check if this is a canonical lookup
                local canonical="$( echo "$nslookup_result" | grep "canonical name" | cut -f2 )"
                # format result_output according to lookup type, i.e. NS, A
                if [[ $lookup_type == "NS" ]]; then
                    local result_output=$( echo "${nslookup_result}" | grep "nameserver =" | cut -f2 -d'=' | sed 's/^ //' | sed 's/.$//' | sort )
                elif [[ $lookup_type == "MX" ]]; then
                    local result_output="$( echo "$nslookup_result" | tail -4 | grep "mail exchanger =" | cut -f2 -d'=' | cut -f3 -d' ' | sed 's/.$//' | sort )"
                else # default for 'A' or 'AAAA' lookup
                    local result_output="$( echo "$nslookup_result" | tail -3 | grep "Address:" | cut -f2 -d' ' )"
                fi
            fi

            # output 
            echo -e -n "${clr_white}  ${key} ${clr_dim}[${nameservers[$key]}]${clr_default}"

            # hacky method faking column layout (pad spaces based on length of col 1 )
            loops="$(( 42 - (( ${#key} + ${#nameservers[$key]} )) ))"
            for i in $( seq 0 $loops ); do echo -n " "; done

            if [[ $result_output == *"$expected_result"* ]] || [[ $expected_result == '' ]] && [[ $failed == '' ]]; then
                echo -en "${clr_green}"
            else
                echo -en "${clr_red}"
            fi
    
            echo -en ${result_output}${clr_default}

            if [[ $canonical != '' ]] && [[ $failed == '' ]] ; then
                canonical="CNAME: $( echo $canonical | cut -f2 -d '=' | sed 's/^ //' )"
                echo -en " ${clr_dim}${canonical}${clr_default}"
            fi

            echo # newline

        done

    done

}

build_nameserver_list

while true; do
    clear
    # run the nslookup loop
    do_nslookup_loop

    # if not watching, exit after first run
    if [[ -z $watch_seconds ]]; then
        break
    fi

    sleep "$watch_seconds"
done

# tidy up
unset domains
unset nameservers
exit

Added support for A, AAAA, NS and MX query types