get_wan_ip

#!/bin/bash
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
################################################################################
#
# This script can be used to obtain the WAN ip address from a SMCD3GNV router.
# Software version:  eMTA & DOCSIS Software Version: 3.1.5.3.3_NCS 
#
# Home page: https://github.com/samiam/ddclient-SMCD3GNV
#
# ddclient example setup:
#  use=cmd, cmd=/etc/ddclient/get_wan_ip
#  protocol=freedns
#  server=freedns.afraid.org
#  login=<your_login>
#  password=<your_password>
#  <your_ddns_hostname>
#
################################################################################

## Start config
ROUTER_IP="10.0.0.1"         # default
ROUTER_PASSWORD="password"   # default
## End config

export PATH=/bin:/usr/bin:$PATH

COOKIE_JAR=/var/tmp/cookie_jar    # for curl to store cookies
TEMPFILE=$(tempfile)              # downloaded file

################################################################################  
# Login to router and add cookie
function router_login () {
  curl --silent \
       --cookie-jar $COOKIE_JAR \
       --output /dev/null \
       --form "usernamehaha=admin&passwordhaha=$ROUTER_PASSWORD" \
       --referer http://$ROUTER_IP/goform/login \
       http://$ROUTER_IP/goform/login
}

# Get connection status page
# --location will follow redirect to home_loggedout.asp
# if cookie doesn't work
function fetch_connection_status () {
  curl --silent \
       --cookie $COOKIE_JAR \
       --output $TEMPFILE \
       --referer http://$ROUTER_IP/goform/login \
       --location \
       http://$ROUTER_IP/user/connection_status.asp
}

# Sanity check that we got page
function check_connection_status () {
  grep -q connection_status.asp $TEMPFILE
}

function print_wan_ip () {
  perl -ne '/^var wan_ipAddress = \"(.*)\"/ && print "$1\n";' $TEMPFILE
}

function cleanup () {
  rm $TEMPFILE
  exit 0
}

################################################################################
## Mainline

# Try old cookie...
if [ -s $COOKIE_JAR ]; then
  #echo "Using cached cookie..."
  fetch_connection_status
  check_connection_status && print_wan_ip && cleanup  # success!
fi

# Cached cookie unsuccessful... reset
router_login
fetch_connection_status
check_connection_status && print_wan_ip && cleanup  # success!

echo "Error: Unable to obtain WAN connection ip address: see $TEMPFILE"
exit 1