#!/bin/bash

ERROR_NO_NETWORK_CONTROLLER=1
ERROR_NO_NETWORK_INTERFACE=2

# check for network controller

dev_installed() { lspci -v | grep -q "Network controller\|Ethernet controller"; }
if ! dev_installed; then echo "No network controller detected."; exit $ERROR_NO_NETWORK_CONTROLLER; fi

# check for non virtual devices

physical_network_devices() {

    # /sys/class/net contains symlinks for all available network devices

    DEVICES=$(
        for SYMLINK in /sys/class/net/*; do
            readlink -e "$SYMLINK"
        done
    )

    # physical device: /sys/devices/pci0000:00/0000:00:1c.0/0000:01:00.0/net/wlp1s0
    # virtual device: /sys/devices/virtual/net/lo

    echo "$DEVICES" |
    grep -v virtual | #keep those not virtual
    sed -E 's/.*\/([^\/]+)$/\1/' # keep just the name
}

PHYSICAL_NETWORK_INTERFACES=$(physical_network_devices)

if [ -z "$PHYSICAL_NETWORK_INTERFACES" ]; then echo "No physical network interface found."; exit $ERROR_NO_NETWORK_INTERFACE; fi

# check interfaces are up

for INTERFACE in $PHYSICAL_NETWORK_INTERFACES; do
    UP=$(ip link show up "$INTERFACE")
    [[ -z $UP ]] && echo "$INTERFACE is DOWN"
done