Bash Script for backing up files

I'm using a shopping cart solution that has a backup feature. This backup feature relies on 3 .sh scripts to interact with linux to backup the necessary files (1 of the .sh scripts is used for restoring the files in the event that it is needed) The problem is that when the backup feature is turned on, it backs up the files every night. That's just fine with me, except after a while it starts hogging up my bandwidth and I have to delete old backups. What I'd like to do is have the scripts modified so that there is a variable labeled "days_to_backup" (or something similar) that I can enter in a number (say, 7 here), and then the backup script would only save the last 7 days of backups. So when a new backup is created the next day, the oldest backup is deleted. It would have to know that if there were fewer than 7 backups not to delete anything (like when the backup feature is first turned on) This script has to be FLAWLESS because if the backup fails or files are improperly deleted this could cause huge problems. This should not be a huge deal for someone well-versed in writing bash scripts.