#!/bin/bash

# Find the interface used for the default route (e.g., to reach 8.8.8.8)
INTERFACE=$(ip route get 8.8.8.8 | awk '{for(i=1;i<=NF;i++) if ($i=="dev") {print $(i+1); exit}}')

if [ -z "$INTERFACE" ] || [ "$INTERFACE" = "lo" ]; then
    echo "No valid default route found." >/dev/stderr
    exit 1
fi

# Extract the primary IPv4 address from the interface (excluding loopback)
IP=$(ip -4 addr show dev "$INTERFACE" scope global | grep -oP '(?<=inet\s)\d{1,3}(\.\d{1,3}){3}(?=/)' | head -n1)

if [ -z "$IP" ]; then
    echo "No global IPv4 address found on $INTERFACE." >/dev/stderr
    exit 1
fi

echo "$IP"