A script to check which of your network interfaces is up

check-internet.sh

#!/bin/bash

# Built only to support macOS, almost certainly doesn't work on Linux

lan_mac='<your LAN MAC address>'
wifi_mac='<your Wi-Fi MAC address>'

test_url='<some test URL, which should fully support both IPv4 and IPv6>'

interfaces=$(ifconfig | grep -E '^[A-z0-9]+: ' | sed 's/: .*$//g')

reset=0
if [ "$1" == "--reset" ]; then
  reset=1
fi

matches_mac() {
  interface=$1
  mac=$2

  ifconfig "$interface" | grep 'ether' | grep "$mac" > /dev/null
}

check_url() {
  interface=$1
  ipv=$2

  curl --interface "$interface" $ipv -m 2 -I -s "$test_url" > /dev/null

  if [ $? -eq 0 ]; then
    echo "UP"
  else
    echo "DOWN"
  fi
}

reset_interface() {
  interface=$1

  sudo ifconfig "$interface" down
  sudo ifconfig "$interface" up
}

lan_interface=''
wifi_interface=''

for interface in $interfaces; do
  if matches_mac "$interface" "$lan_mac"; then
    lan_interface=$interface
  fi

  if matches_mac "$interface" "$wifi_mac"; then
    wifi_interface=$interface
  fi
done

if [ ! -z "$lan_interface" ]; then
  if [ $reset -eq 1 ]; then
    echo "Resetting LAN interface..."
    reset_interface "$lan_interface"
    echo "Done"
  else
    echo ""
    echo "LAN status:"
    echo "    IPv4: $(check_url "$lan_interface" "-4")"
    echo "    IPv6: $(check_url "$lan_interface" "-6")"
  fi
fi

if [ ! -z "$wifi_interface" ]; then
  if [ $reset -eq 1 ]; then
    echo "Resetting Wi-Fi interface..."
    reset_interface "$wifi_interface"
    echo "Done"
  else
    echo ""
    echo "Wi-Fi status:"
    echo "    IPv4: $(check_url "$wifi_interface" "-4")"
    echo "    IPv6: $(check_url "$wifi_interface" "-6")"
  fi
fi