Start a PiHole docker container with the appropriate upstream DNS and server IPs autodetected.

pihole_docker.sh

#!/bin/bash

docker run --rm -d --name pihole \
  -p 53:53/tcp -p 53:53/udp -p 80:80 \
  -v /home/pihole/etc/pihole:/etc/pihole/ \
  -v /home/pihole/etc/dnsmasq.d:/etc/dnsmasq.d/ \
  --dns $(nslookup 1.1.1.1 | \
    grep Server: | tr -s '\t' | \
    cut -f2) \
  -e DNS1=$(nslookup 1.1.1.1 | \
    grep Server: | tr -s '\t' | cut -f2) \
  -e DNS2=no \
  -e ServerIP=$(ip route list | \
    grep "^default" | cut -d ' ' -f7,9 | sort -t ' ' -k2 | \
    head -n1 | cut -d ' ' -f1) \
  pihole/pihole:latest