Script to diagnose network connectivity

check-online

#!/usr/bin/env bash
set -eu
case `uname` in
    Linux)
        gateway=`ip route | awk '$1~/default/ && $2~/via/ {print $3}'`
        ping_opts="-c1 -W2"
        ;;
    OpenBSD)
        gateway=`route -n show | awk '$1~/default/ {print $2}'`
        ping_opts="-c1 -w2"
        ;;
    *)
        echo "E: Which OS are you running, smartass?"
        exit 111
        ;;
esac

nss=`awk '$1~/nameserver/ {print $2}' /etc/resolv.conf`

monitor="google.com google.pl google.de"

verbose=0

quiet() {
    if [ "$verbose" -eq 0 ]
    then
        $@ >/dev/null
    else
        $@
    fi
}

err() {
    echo $@ >&2
}

for arg in "${@}"
do
    case $arg in
        --debug|-d)
            err "D: gateway:"  $gateway
            err "D: nss:"      $nss
            err "D: monitor:"  $monitor
            verbose=1
            ;;
    esac
done

if test -z "$gateway"
then
    err "E: No gateway"
    echo "nogw"
    exit 2
else
    err "I: gateway OK"
fi

if test -z "$nss"
then
    err "E: No configured nameservers"
    echo "nonss"
    exit 2
else
    err "I: nss OK"
fi

for host in $gateway $nss
do
    if echo "$host" | grep -q :
    then
        ping=ping6
    else
        ping=ping
    fi
    if ! quiet $ping $ping_opts "$host"
    then
        err "E: No response from $host"
        echo "$host"
        exit 2
    else
        err "I: host OK: $host"
    fi
    sleep 0.1
done

for host in $monitor
do
    if ! quiet ping $ping_opts "$host"
    then
        err "E: No response from $host"
        echo "$host"
        exit 2
    else
        err "I: host OK: $host"
    fi
    sleep 0.1
done