How to write script to update the ip address

Question

Hi all,
I need a help to write a script write on my Mac OS 10.10.1
I have a dynamic DNS that need to update through a URL for the new  public IP address.
The script to get the current external IP address
curl -s checkip.dyndns.org|sed -e 's/.*Current IP Address: //' -e 's/<.*$//' 
This is the URL need to update everything 5 minutes with the output of the current public Ip address or it can detect the change if change then do update if no then do nothing,
https://domain.com/update?host=ab&domain=abc.com&password=xx&ip=1.1.1.1
Thanks for the help

Answer 1

Storing passwords in a shell script is an EXTREMELY bad idea. The following will get the current IP address, validate the IP address, test whether the IP address has change by reading the file /var/tmp/stored_ip or create the file if it doesn't exits- DO YOUR COMMAND HERE is the line that I am going to let you figure out.
#!/bin/ksh
new_ip="$(/usr/bin/curl -s https://icanhazip.com/)"
if [ -f /var/tmp/stored_ip ]; then
    if /usr/bin/host $new_ip > /dev/null 2>&1; then
        printf "%s\n" "Valid IP address found"
    else
        printf "%s\n" "Invalid IP address"
        exit 1   
    fi
else
    printf "%s\n" "$new_ip" > /var/tmp/stored_ip
    exit 1
fi
read -r stored_ip < /var/tmp/stored_ip
if [ "$new_ip" = "$stored_ip" ]; then
    printf "%s\n" "IP address has not changed"
else
    DO YOUR COMMAND HERE
fi
printf "%s\n" "$new_ip" > /var/tmp/stored_ip
exit 0