USERNAME=myusername
PASSWORD=mypassword
HOSTNAME=myhostname.dyndns.org

cd /root/
if [ -f /root/ipcheck.dat ]; then
  ipcheck -r checkip.dyndns.org:8245 $USERNAME $PASSWORD $HOSTNAME
else
  ipcheck --makedat -r checkip.dyndns.org:8245 $USERNAME $PASSWORD $HOSTNAME
fi