Retrieve Your Public IP with Shell Commands and a Robust Bash Script

Why Detecting Your Public IP Matters

Home broadband connections often receive dynamic IP addresses from ISPs, which can change on each dial‑up or at scheduled intervals. This variability disrupts services that rely on a stable external address, such as monitoring tools or network storage, making automatic public‑IP detection essential for DDNS updates.

Simple Methods to Get the Public IP

Browser‑Based Lookup

Visiting a service like https://checkip.amazonaws.com returns the client’s public IP in plain text. Many similar endpoints exist, for example:

https://api.ipify.org
https://ifconfig.me/ip
https://icanhazip.com
https://ipinfo.io/ip
https://ipecho.net/plain
https://checkipv4.dedyn.io

cURL Command

From the terminal, curl https://checkip.amazonaws.com fetches the same information without opening a browser. The generic form is:

curl <url>

dig Query

The dig utility can query OpenDNS to resolve myip.opendns.com via the resolver resolver1.opendns.com:

dig +short myip.opendns.com @resolver1.opendns.com

This method sends a minimal DNS request, avoiding HTTP headers and TLS overhead, but it may be blocked or cached by some ISPs.

Robust Bash Script with Fallback Logic

The script below first tries the dig approach; if it fails, it falls back to a list of HTTP services accessed with curl -4s. Hosts are selected randomly, and the script repeats until a valid IPv4 address is obtained or the list is exhausted.

#!/bin/bash
# This script tries to obtain the current public IPv4 address using OpenDNS first,
# then falls back to several online services.

hosts=("checkip.amazonaws.com" "api.ipify.org" "ifconfig.me/ip" "icanhazip.com" "ipinfo.io/ip" "ipecho.net/plain" "checkipv4.dedyn.io")

CURL=$(which curl)
DIG=$(which dig)

# Try OpenDNS via dig
check=$($DIG +short myip.opendns.com @resolver1.opendns.com A)

if [ ! $? -eq 0 ] || [ -z "$check" ] || [[ ! $check =~ ^[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+$ ]]; then
    echo "Unable to get your public IP address by OpenDNS service, trying other methods."
    count=${#hosts[@]}
    while [ -z "$check" ] && [ $count -ne 0 ]; do
        selectedhost=${hosts[$RANDOM % ${#hosts[@]}]}
        check=$($CURL -4s https://$selectedhost | grep -v '^$')
        if [[ $check =~ ^[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+$ ]]; then
            break
        else
            echo "The host $selectedhost returned an invalid IP address."
            check=""
            ((count--))
        fi
    done
fi

if [ -z "$check" ]; then
    echo "Unable to get your public IP address. Please check your internet connection."
    exit 1
fi

echo "Your public IP address is $check"
exit 0

The script uses curl -4s to force IPv4 and silence progress output. Random selection spreads the load across services, reducing the chance of being rate‑limited or banned.

Key Takeaways

Relying on a single external service is fragile; combining multiple providers with intelligent fallback logic ensures higher reliability for DDNS updates and other network‑dependent applications. Randomized selection also provides a simple form of load balancing, preventing excessive requests to any one endpoint.