The problem:

You have a running backup or logging, that creates the same type of files in a given timeframe.
In my example, it was a mysql-backup, that created ".sql.gz" files periodically.
Those files are written on tape, so there is no need to keep them longer than necessary.

The solution:

A little "one-liner", that can be added to a existing backup-script. In my case, I decided to run it in a separate script and all folders, where I have old files, that can be deleted.

The one-liner:

find /backup-folder -name '*.sql.gz' -mtime +5 -exec rm {} \;

If you want to run a test and verify the results first, you can run the first part without erasing files:

find /backup-folder -name '*.sql.gz' -mtime +5

How it works:

"find" creates a list of all files, that end on ".sql.gz" in the folder "/backup-folder", that are older than 5 days. The results are passed on to the "rm" command. The curly brackets ("{}") are a placeholder for these results.
It works like a loop, where every result of find, that fits the conditions, will be sent to rm, where it will be deleted.

Little hint for the time-preiod definition:

Numeric arguments(... for the -mtime) can be specified as

+n for greater than n,
-n for less than n,
n for exactly n.

So, you can change values to keep old files and only delete new ones ...

Hope it helps ...