Bash functions to change DNS from terminal.

change-dns.sh

function setGoogleDNS() {
  CHANNEL=`route get google.com | grep interface | sed -n -e 's/^.*interface: //p'`
  NETWORK=`networksetup -listnetworkserviceorder | grep $CHANNEL | sed -n -e 's/^.*Port: //p' | sed -n -e 's/,.*//p'`
  echo "Setting Google's DNS on channel '$CHANNEL' for network '$NETWORK'."
  sudo networksetup -setdnsservers $NETWORK 8.8.8.8 8.8.4.4 2001:4860:4860::8888 2001:4860:4860::8844
}

function setCloudflareDNS() {
  CHANNEL=`route get google.com | grep interface | sed -n -e 's/^.*interface: //p'`
  NETWORK=`networksetup -listnetworkserviceorder | grep $CHANNEL | sed -n -e 's/^.*Port: //p' | sed -n -e 's/,.*//p'`
  echo "Setting Cloudflare's DNS on channel '$CHANNEL' for network '$NETWORK'."
  sudo networksetup -setdnsservers $NETWORK 1.1.1.1 1.0.0.1 2606:4700:4700::1111 2606:4700:4700::1001
}

function resetDNS() {
  CHANNEL=`route get google.com | grep interface | sed -n -e 's/^.*interface: //p'`
  NETWORK=`networksetup -listnetworkserviceorder | grep $CHANNEL | sed -n -e 's/^.*Port: //p' | sed -n -e 's/,.*//p'`
  echo "Resetting DNS on channel '$CHANNEL' for network '$NETWORK'."
  sudo networksetup -setdnsservers $NETWORK empty
}

function showDNS() {
  CHANNEL=`route get google.com | grep interface | sed -n -e 's/^.*interface: //p'`
  NETWORK=`networksetup -listnetworkserviceorder | grep $CHANNEL | sed -n -e 's/^.*Port: //p' | sed -n -e 's/,.*//p'`
  networksetup -getdnsservers $NETWORK
}