opennic munin script

#!/bin/bash

domain=example.geek  # domain name to resolve
n_nameservers=2      # /etc/resolv.conf must list 2 OpenNIC resolvers at the top of the file
timeout=1            # seconds
n_iterations=2       # n samples to average

action=$1
nss=()

# read only first n_nameservers
function get_nameservers {
    local re='^nameserver[[:space:]]+(.+)'
    local n=0

    while read -r line; [ $n -lt $n_nameservers ]; do
        [[ "$line" =~ $re ]]

        if [ -n "${BASH_REMATCH[1]}" ]; then
            let ++n
            echo "${BASH_REMATCH[1]}"
        fi
    done </etc/resolv.conf
}

nss=( $(get_nameservers) )

case "$action" in
    config)
        echo "graph_title OpenNIC DNS response time"
        echo "graph_category network"
        echo "graph_vlabel % fail (-) / time (ms) (+)"
        echo "graph_info This plugin monitors OpenNIC DNS response time. A single look-up for the target domain" \
             "is sent and the time to get a valid response is shown in milliseconds. The query is sent" \
             "to the first $n_nameservers resolvers in /etc/resolv.conf. The query timeout is $timeout seconds."

        for i in $(eval echo {0..$((${#nss[@]} - 1))}); do
            ns=${nss[$i]}

            echo "time${i}.label $ns time"
            echo "time${i}.min 0"
            echo "time${i}.max $((1000 * timeout))"
            echo "time${i}.warning 250"
            echo "time${i}.info DNS response time for $ns"
            echo "loss${i}.label $ns fail"
            echo "loss${i}.min -100"
            echo "loss${i}.max 0"
            echo "loss${i}.warning -50:"
            echo "loss${i}.info Failed requests for $ns (percent)"
        done
        ;;

    "")
        for i_ns in $(eval echo {0..$((${#nss[@]} - 1))}); do
            ns=${nss[$i_ns]}
            time=0
            lost=0

            for i_it in $(eval echo {0..$((n_iterations - 1))}); do
                out=$(dig +notcp +ignore +noall +stats +time=$timeout +tries=1 +retry=0 +fail @${ns} ${domain}. A)

                re='Query time: ([[:digit:]]+) msec'
                if [[ "$out" =~ $re ]]; then
                    let time+=${BASH_REMATCH[1]}
                fi

                re='no servers could be reached'
                if [[ "$out" =~ $re ]]; then
                    let ++lost
                fi
            done

            let time/=n_iterations
            let lost=-100*lost/n_iterations

            echo "time${i_ns}.value ${time}"
            echo "loss${i_ns}.value ${lost}"
        done
        ;;
    *)
        echo "unrecognized action: '$action'"
        exit 1
        ;;
esac