[Unit]
Description=Run script to update CloudFlare DNS
After=network.target

[Service]
Type=oneshot
ExecStart=/usr/local/bin/cfddns.sh -c /path/to/account.details -r server.domain.tld -l /var/log/cfddns.log
ExecStart=/usr/local/bin/cfddns.sh -6 -c /path/to/account.details -r server.domain.tld -l /var/log/cfddns.log

[Install]
WantedBy=multi-user.target