Shell script for updating resolv.dnsmasq.conf in OS X

dnsmasqresolv.sh

#!/bin/bash

# updates resolv.dnsmasq.conf with DHCP provided DNS servers for the
# currently active network interface on OS X

# the location of the dnsmasq resolv file
RESOLV=/etc/resolv.dnsmasq.conf

# get the list of active services from scutil
SERVICES=$(echo 'show Setup:/Network/Global/IPv4' | scutil | grep -e '[[:digit:]] :' | awk '{print $3}')

#echo "$SERVICES"

for service in $SERVICES
do
    interface=$(echo "show Setup:/Network/Service/$service/Interface" | scutil | grep -e ^[[:space:]])
    interfaceName=$(echo $interface | awk '{print $12 "(" $3 ")"}')

    echo "Checking Interface $interfaceName"

    # get dns info for this service from scutil.  the dns info provided here appears
    # to be from dhcp as its not affected by the dns setting in network preferences
    # this is what we want to use for our resolv file.  there will only be an entry
    # in scutil for this service if the interface is active
    nameservers=$(echo "show State:/Network/Service/$service/DNS" | scutil | grep -e '[[:digit:]] :' | awk '{print $3}')

    if [ $nameservers ]
    then
        echo "Found DNS on Interface $interfaceName"

        # empty out the RESOLV file
        cat /dev/null > $RESOLV

        for nameserver in $nameservers
        do
            echo "adding nameserver $nameserver to $RESOLV"

            # append nameserver entry to RESOLV
            echo "nameserver $nameserver" >> $RESOLV
        done

        # SERVICES is listed in active order, so we can break after the first hit
        break
    fi
done

exit 0