#!/bin/sh
# This script uses the ip utility to monitor all the ipv6 addresses. Any change
# that occurs will trigger an echo to stdout or the file received as argument,
# if there is any

if [ $# -gt 1 ]; then
  echo "Usage: $("basename $0") [output_filename]"
  exit 1
fi

ip -oneline monitor address |
while read line; do
  if [ $# = 1 ]; then
    echo >"$1"
  else
    echo "ip monitor triggered"
  fi
done