Backup specific directories to external disk

backup.sh

#!/bin/bash
# Backup specific directories to external disk
# Created by Natan Felles

# Install rsync to do this script work. Execute "apt-get install rsync" in Debian distros
# To discover the UUID of the external disk, use gnome-disks ou execute "blkid"
# Do not forget to configure the variables LOGDIR, LOGFILE, DIRS and UUID

# Local log dir path
LOGDIR=/var/log/backup/

# Local log file name
LOGFILE="`date +%Y%m%d`-`date +%H%M%S`".log

# Local log location
LOG=$LOGDIR$LOGFILE

# Directories to backup without bars. Use "" if you want backup the / dir
DIRS=("etc" "home")

# The hard disk UUID to save the backup files
UUID=166cb153-c1ba-4d6c-acf0-2fffb1bb1bbf

# Message

echo "Backup started at `date`. Please wait."
echo "If you wants to see logs, open the file $LOG"

# Actions
sudo echo "/--------------------------------------------------------------------------------" >> $LOG
sudo echo "| Sync started at `date`" >> $LOG

for d in "${DIRS[@]}"
do
	sudo echo "|--------------------------------------------------------------------------------" >> $LOG
	sudo echo "| /$d status:" >> $LOG
	echo "- Sync from /$d to /mnt/$UUID/$d/ is running"
	sudo echo "|--------------------------------------------------------------------------------" >> $LOG
	sudo rsync -Cravzp /$d/ /mnt/$UUID/$d/ >> $LOG
done

sudo echo "|--------------------------------------------------------------------------------" >> $LOG
sudo echo "| Sync finished at `date`" >> $LOG
sudo echo "\--------------------------------------------------------------------------------" >> $LOG
sudo echo "Backup was finished at `date`. Bye!"

To backup automatically you can use a cron job.
Edit /etc/crontab and add this line:
0 12 * * * root /root/backup.sh
It says that the file localized in /root will be executed every day at 12 hours.