Shell script which checks whether the public ip address has changed and updates myaddr.tools DynDNS

update-myaddr-dns.sh

#!/bin/bash
# insert your myaddr data and ntfy push topic
myAddrApiKey="***"
myAddrUrl="replace-me.myaddr.io"
ntfyUrl="https://ntfy.sh/***"
publicDnsResolver="86.54.11.100" # use DNS4EU

# function to validate IPv4 address (format + range)
is_ipv4() {
    local ip="$1"
    local IFS=.
    local o1 o2 o3 o4

    # Split into 4 octets
    read -r o1 o2 o3 o4 <<< "$ip"

    # Must have 4 numeric fields
    [[ "$o1" =~ ^[0-9]+$ && "$o2" =~ ^[0-9]+$ && "$o3" =~ ^[0-9]+$ && "$o4" =~ ^[0-9]+$ ]] || return 1

    # Range check 0–255
    (( o1 >= 0 && o1 <= 255 )) || return 1
    (( o2 >= 0 && o2 <= 255 )) || return 1
    (( o3 >= 0 && o3 <= 255 )) || return 1
    (( o4 >= 0 && o4 <= 255 )) || return 1

    return 0
}

# max 6 tries every 5 seconds (if connection is currently offline)
if ! currentDynDns=$(dig +time=5 +tries=6 +short $myAddrUrl @"$publicDnsResolver"); then
    echo "Problem: dig network error or timeout."
    exit 1
fi

# validate dyndns IPv4
if ! is_ipv4 "$currentDynDns"; then
    echo "Fehler: '$currentDynDns' ist keine gültige IPv4-Adresse."
    exit 1
fi
echo "myaddr dyndns ip address: $currentDynDns"

# check public ip address using ipify.org
currentIp=$(curl -s https://api.ipify.org)

# validate public IPv4
if ! is_ipv4 "$currentIp"; then
    echo "Fehler: '$currentIp' ist keine gültige IPv4-Adresse."
    exit 1
fi
echo "Public ip address: $currentIp"

# update dyndns only if ip address has changed
if [ "$currentIp" != "$currentDynDns" ]; then
    echo "IP changed, updating myaddr dns..."
    # update ipv4
    curl -s "https://ipv4.myaddr.tools/update?ip=$currentIp&key=$myAddrApiKey"
    # update ipv6
    currentIpV6=$(curl -s 'https://api64.ipify.org')
    curl -s "https://ipv6.myaddr.tools/update?ip=$currentIpV6&key=$myAddrApiKey"
    # send push notification
    ntfyResult=$(curl -s -X POST -H "Title: DDNS Update" -H "Tags: ballot_box_with_check" -d "$myAddrUrl mit IP-Adresse $currentIp aktualisiert!" $ntfyUrl)
else
    echo "Nothing to do, ip hasn't changed."
fi

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