~ # ls /etc/local.d/

README insecure.start resolv.start

#!/bin/sh
# shellcheck shell=dash

tmp=$(mktemp)
powershell="/mnt/c/Windows/System32/WindowsPowerShell/v1.0/powershell.exe"

removeTempFiles() {
    rm -f "$tmp"
}

echo "Current resolv.conf"
echo "-------------------"
cat /etc/resolv.conf
echo
echo "Creating new resolv.conf"
echo "------------------------"

initial=$(cat /etc/resolv.conf | grep '^nameserver')
added=$($powershell -Command "Get-DnsClientServerAddress -AddressFamily ipv4 | Select-Object -ExpandProperty ServerAddresses")

{
    echo "search mydomain.cpy.local"
    for i in $initial; do
        [ "$i" = "nameserver" ] && continue
        echo nameserver "$i"
    done
    for a in $added; do
        item=$(echo $a | sed -e 's/^[[:space:]]*//' | sed -e 's/\r//g')
        [ "$item" = "nameserver" ] && continue
        contains=0
        for j in $initial; do
            [ "$j" = "nameserver" ] && continue
            [ "$item" = "$j" ] && contains=1 && break
        done
        [ $contains = 0 ] && echo nameserver "$item"
    done
} | tr -d '\r' | tee "$tmp"
(set -x; cp -r "$tmp" /etc/resolv.conf)

removeTempFiles