Logs your public IP address and respective hostname into a file

publicip.sh

#!/usr/bin/env bash

# Public IP logger r2 (2012/04/10)
# Filipe Rodrigues <shello@shello.org>
# Logs your public IP address into a file

LC_TIME=C # Deactivate for the system time locale
LOGFILE="${HOME}/publicip/publicip.log" # Logfile

CURR_DATE=`date`

# IP address lookup using OpenDNS
CURR_IP=`dig @208.67.222.220 +short myip.opendns.com`
if [[ $? != 0 ]]; then
  exit 1
fi

# Reverse lookup, to get the hostname
CURR_HOST=`dig -x ${CURR_IP} +short`

# Format the log line to have the date and IP address and hostname separated by
# a tab character; don't print the hostname if it has no useful information
LOGLINE="$(printf "${CURR_DATE}\t${CURR_IP}")"
if [[ "${CURR_HOST}" != "${CURR_IP}" ]]; then
  LOGLINE="$(printf "${LOGLINE}\t${CURR_HOST}")"
fi

# Update the access time for the log file, and create it if it's missing;
touch -a ${LOGFILE}

# If the log isn't zero-size, check the last IP address
if [[ -s "${LOGFILE}" ]]; then
  LAST_IP=`tail -n 1 "${LOGFILE}" | cut -f 2`
  
  if [[ "${LAST_IP}" == "${CURR_IP}" ]]; then
    exit 0
  fi
fi

printf "${LOGLINE}\n" >> ${LOGFILE}

exit 0