rsync Shell Script Incremental Backup

write the Shell Script rsync Incremental Backup

#!/bin/bash

#rsync -avz --delete /boot /backup/

save as backup.sh

#vi /etc/crontab

12 15 * * * root sh backup.sh /tmp/backup.log 2>&1
It will store there output into the /tmp/backup.log file

it will run these backup.sh command at 3:12 PM
it will make the as rsync backup as  automated process.

--delete option if the destination has any extra file if it is not per sent in the source then it will delete the document form the destination.
--log-file=/backup/$(DOM)/rsync_log >> it will maintain the log file
--exclude-from=/root/exclude-data >> what are files & direction mention here It will not copy or Transfer the data while synchronize.
How to write the Shell script for rsync Incremental Backup.