This script updates the DNS records of DNS Stock.

It generates an URL http://dyndns.dns-stock.com/?hostname=<domain>&username=<username>&password=<pass>&myip=<ipaddr>, which is eventually passed to the DNS Stock server. The code is basically about parsing, validating, checking and formatting the returned WAN IP <ipaddr>. Two URLs are configured to check WAN IP. If the first one returns an error, the second one is queried. If that one fails as well, the script abandons. The logfile dnsstock_update.log reveals relevant details about what happened.

Configured passwords can either be plain text (depreciated) or MD5 crypted (preferred), as visible on DNS Stock site. The DNS Stock server accepts both formats.

Code and logfile entries should be self-explanatory.

Download: dnsstock_update.sh

Comments are desired.

Thanks,

#!/bin/sh

# dnsstock_update.sh
#
# dns stock DDNS update script
# forIPv4 only
# by geohei 
# created : 28.03.2016
# revised : 02.04.2016 - added 'dyndns.dns-stock.com/my-ip.php' as primary check ip url
#
# dns stock update url syntax
# http://dyndns.dns-stock.com/?hostname=&username=&password=&myip=
#
# use cron to trigger (suggested every minute) e.g. '* * * * * ~/dnsstock_update.sh'
#
# $tmpdir
# is used for 'dnsstock_update.cache' and 'dnsstock_update.log' files
# omit trailing '/'

domain=''
username=''
password=''
checkipurl_1='dyndns.dns-stock.com/my-ip.php'
checkipurl_2='ipv4.whatismyv6.com'
tmpdir='/tmp'

# parse IPv4 for $checkipurl_1
ipaddr=$(wget -q -O - $checkipurl_1)
# check if wget returned != 0
if [ $? != 0 ]; then
  # parse IPv4 for 'ipv4.whatismyv6.com'
  ipaddr=$(wget -q -O - $checkipurl_2 | grep -iohP '(?<=\x3e)([0-9]+\.){3}[0-9]+(?=\x3c)')
  # check if wget returned != 0
  if [ $? != 0 ]; then
    exit 1
  else
    checkipurl_use='(2)'
  fi
else
  checkipurl_use='(1)'
fi

# exit 0 if $ipaddr is cached (= didn't change)
if [ -e $tmpdir/dnsstock_update.cache ] && [ $(cat $tmpdir/dnsstock_update.cache) = $ipaddr ]; then
  exit 0
fi

# check if IP valid (>255 check and IP syntax check)
if expr "$ipaddr" : '[0-9][0-9]*\.[0-9][0-9]*\.[0-9][0-9]*\.[0-9][0-9]*$' >/dev/null; then
  for i in 1 2 3 4; do
    # >255 check
    if [ $(echo "$ipaddr" | cut -d. -f$i) -gt 255 ]; then
      # write log entry
      echo "$(date '+%Y-%m-%d %H:%M:%S')   FAIL$checkipurl_use: IPv4 invalid: $ipaddr (>255 check failed)." >> $tmpdir/dnsstock_update.log
      exit 1
    fi
  done
  # update dns
  success=$(wget -q -O - "http://dyndns.dns-stock.com/?hostname=$domain&username=$username&password=$password&myip=$ipaddr")
  if [ ! -z $update ]; then
    # write log entry
    echo "$(date '+%Y-%m-%d %H:%M:%S')   FAIL$checkipurl_use: dns stock server returned error." >> $tmpdir/dnsstock_update.log
    exit 1
  fi
  # update dnsstock_update.cache
  echo $ipaddr > $tmpdir/dnsstock_update.cache
  # write log entry
  echo "$(date '+%Y-%m-%d %H:%M:%S')   SUCCESS$checkipurl_use: IPv4 valid and updated: '$ipaddr'." >> $tmpdir/dnsstock_update.log
  exit 0
else
  # write log entry
  echo "$(date '+%Y-%m-%d %H:%M:%S')   FAIL$checkipurl_use: IPv4 invalid: '$ipaddr' (IP syntax check failed)." >> $tmpdir/dnsstock_update.log
  exit 1
fi

exit 0