Thanks for the cron details,
But how can i schedule Backup for Sunday and Wednesday night , Sunday full backup level=0 and wat about wednesday shall i go with incremental ?
So write two shell scripts*. One to take a level 0 backup, the second to take a level 1 backup.
Use cron to schedule the level 0 on Sunday
Make another cron entry to schedule the level 1 on the other days.
Your question is about two distinct tasks ... 1) write shell scripts, and 2) scheduling with cron. But from the questions you ask it appears that you haven't yet made that distinction in your own mind .. that you don't understand that cron is nothing but a scheduler. It schedules whatever.
So is your problem in knowing how to write the script to run the backup, or is it in knowing how to use cron to schedule it?
* Actually the two scripts will be nearly identical, so much so that you could just write one script and use a command line parm to determine if it is a level 0 or a level 1 backup. That's what I do.