Fix resolv.conf in Windows Subsystem for Linux, when WSL doesn't correctly generate it.

wsl-fix-resolvconf.sh

#!/bin/bash

TMP=`mktemp`
trap ctrlC INT

removeTempFiles() {
	rm -f $TMP
}

ctrlC() {
	echo
	echo "Trapped Ctrl-C, removing temporary files"
	removeTempFiles
	stty sane
}

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

echo
echo "Creating new resolv.conf"
echo "------------------------"

{ 
	head -1 /etc/resolv.conf | grep '^#.*generated'
	for i in `/mnt/c/Windows/System32/WindowsPowerShell/v1.0/powershell.exe -Command "Get-DnsClientServerAddress -AddressFamily ipv4 | Select-Object -ExpandProperty ServerAddresses"`; do 
		echo nameserver $i
	done
	tail -n+2 /etc/resolv.conf | grep -v '^nameserver'
} | tr -d '\r' | tee $TMP

(set -x; sudo cp -i $TMP /etc/resolv.conf)

removeTempFiles

Perfect! I still needed to run the following (Source: anyconnect WSL 2 - Windows Substem for Linux) to get enable the interface on the VPN

Get-NetAdapter | Where-Object {$_.InterfaceDescription -Match "Cisco AnyConnect"} | Set-NetIPInterface -InterfaceMetric 4000
Get-NetIPInterface -InterfaceAlias "vEthernet (WSL)" | Set-NetIPInterface -InterfaceMetric 1

But that doesn't provide the DNS resolution. The resolv.conf update was the missing piece.