Update script for dynv6.com to set your IPv4 address and IPv6 prefix

dynv6.sh

#!/bin/sh -e
hostname=$1
device=$2
file=$HOME/.dynv6.addr6
[ -e $file ] && old=`cat $file`

if [ -z "$hostname" -o -z "$token" ]; then
  echo "Usage: token=<your-authentication-token> [netmask=64] $0 your-name.dynv6.net [device]"
  exit 1
fi

if [ -z "$netmask" ]; then
  netmask=128
fi

if [ -n "$device" ]; then
  device="dev $device"
fi
address=$(ip -6 addr list scope global $device | grep -v " fd" | sed -n 's/.*inet6 \([0-9a-f:]\+\).*/\1/p' | head -n 1)

if [ -e /usr/bin/curl ]; then
  bin="curl -fsS"
elif [ -e /usr/bin/wget ]; then
  bin="wget -O-"
else
  echo "neither curl nor wget found"
  exit 1
fi

if [ -z "$address" ]; then
  echo "no IPv6 address found"
  exit 1
fi

# address with netmask
current=$address/$netmask

if [ "$old" = "$current" ]; then
  echo "IPv6 address unchanged"
  exit
fi

# send addresses to dynv6
$bin "http://dynv6.com/api/update?hostname=$hostname&ipv6=$current&token=$token"
$bin "http://ipv4.dynv6.com/api/update?hostname=$hostname&ipv4=auto&token=$token"

# save current address
echo $current > $file

from @bertenvdb

Click on the 'raw' button on the top right-hand side of the above script, and copy/paste the entire code to a file dynv6.sh in your home directory.
Make the script executable
chmod +x dynv6.sh
Execute the script using the link found on the 'instructions' tab of your host on dynv6.net
token=Q-4pOEg4UyAuq8mySeWgAJfiGWXHtQ ./dynv6.sh test123x.dynv6.net
Optionally have cron execute the script every 5 mins or so. Nothing will be sent if your IP hasn't changed.

crontab -e to open your editor
Add the line */5 * * * * token=Q-4pOEg4UyAuq8mySeWgAJfiGWXHtQ ./dynv6.sh test123x.dynv6.net
save and close editor