From WikiPaul - Paul Swanson's wiki
sudo crontab -e
0 3 * * * /home/username/scripts/update/update.sh
#!/bin/bash
LOGPATH=/home/username/scripts/update
echo "Starting at " | tee -a $LOGPATH/logupdate.txt
echo `date` | tee -a $LOGPATH/logupdate.txt
apt-get -y update | tee -a $LOGPATH/logupdate.txt
apt-get -y upgrade | tee -a $LOGPATH/logupdate.txt
apt-get -y autoclean | tee -a $LOGPATH/logupdate.txt
echo "Ended at " | tee -a $LOGPATH/logupdate.txt
echo `date` | tee -a $LOGPATH/logupdate.txt
echo `date` >> $LOGPATH/logdate.txt