Bash script to update a dnsdynamic.org domain with your machine's current external IP.

dnsdynamic_update.sh

#!/bin/bash

# script name
SC=`basename $0`

############### CONFIG ################
user="<<DNSDYNAMIC-ACCOUNT-EMAIL>>"
pw="<<DNSDYNAMIC-ACCOUNT-PASSWD>>"
domain="<<DNSDYNAMIC-DOMAIN-TO-UPDATE>>"

log="/home/<<USER-NAME>>/bin/last_ext_ip"
#######################################

# external IP services
read -d '' urls << 'END'
http://myip.dnsdynamic.org/
http://whatismyip.akamai.com/
https://ident.me/
https://ip.tyk.nu/
https://tnx.nl/ip
https://wgetip.com/
END

function check_network {
  ping -q -c 1 -w 3 8.8.8.8 > /dev/null 2>&1
  if [ "$?" -ne 0 ]; then
    echo "[$(date '+%x %X')] [$SC] No network connection. Exiting"
    exit 1
  fi
}

function update_dnsdynamic {
    # check URLs until first IP is found
    for url in $urls; do
        ext_ip=$(curl -m 5 -L -s $url)
        if [ ! -z $ext_ip ]; then
            echo -e "[$(date '+%x %X')] [$SC] $url -> $ext_ip"
            break
        fi
    done
    
    # check if the found IP has been already logged/updated
    if [ -f $log ]; then
        last_ext_ip=$(cat $log)
    fi
    
    # if IP has not been logged, update the dnsdynamic.org domain
    if [ "$ext_ip" != "$last_ext_ip" ]; then
        echo -e "[$(date '+%x %X')] [$SC] Running curl to upgrade dnsdynamic.org"
        out=$(curl -s --user "$user:$pw" "https://www.dnsdynamic.org/api/?hostname=$domain&myip=$ext_ip")
        response=$(echo $out | cut -d " " -f1)
        echo -e "[$(date '+%x %X')] [$SC] -> $out"

        if [ $? -eq 0 ]; then
            if [ "$response" == "good" ]; then
                echo -e "[$(date '+%x %X')] [$SC] dnsdynamic.org successfully updated"
            elif [ "$response" == "nochg" ]; then
                echo -e "[$(date '+%x %X')] [$SC] no change at dnsdynamic.org"
            fi

            # store IP for later reference
            echo $ext_ip > $log
        else
            echo -e "[$(date '+%x %X')] [$SC] dnsdynamic.org IP upgrade *failed*"
        fi
    else
        echo -e "[$(date '+%x %X')] [$SC] external IP unchanged"
    fi
}

check_network
update_dnsdynamic