curl http://username:password@dynupdate.no-ip.com/nic/update?hostname=mytest.example.com&myip=1.2.3.4

#!/bin/bash

IP=$(/sbin/ip -4 a l wwan0 | grep 'inet ' | grep -oP '(?<=inets)d+(.d+){3}')

curl "http://username:password@dynupdate.no-ip.com/nic/update?hostname=mytest.example.com&myip=${IP}"

chmod 755 /home/user/update_noip.sh
crontab -e
# Add:
*/10 * * * * /home/user/update_noip.sh >/dev/null 2>&1