I am not a linux expert, so I always tried to be very very safe on this. More than once my backups did not get rotated, filling up my data-disk in Moodle 1.9 so I tried to search/find the backup* and in german the sicherung* files:
/moodle/data # find -type f -name backup*
./3022/backupdata/backup-unterrichtsevaluation_s_2010_todelete-20120730-0513.zip
./1878/backupdata/backup-microeconomics_of_competitiveness_porter_harvard_as10_-20120817-1849.zip
I redirected the output to a file, e.g.
/moodle/data # find -type f -name backup* > backupFiles.txt
Then I opened the backupFiles.txt file with a text editor and did a global find/replace of the trailing ./ with rm ./ and finally stored the whole thing to a bash/shell script like this
/moodle/data # head removeAllBackupZipFiles.sh
rm ./22/backupdata/backup-*.zip
rm ./24/backupdata/backup-*.zip
rm ./37/backupdata/backup-*.zip
Then I simply run the above script being sure that only the explicitely mentioned files would be removed/deleted. Of course you can do such things also with find -type f -name backup* -exec command, but I never risked. If I would I would have done an -exec cp to copy or later mv to move the backup-zip-files to a given directory where I would have safely removed them with rm backup*
But if you lack space, as I did, copying or moving was not an option, I had to delete them in place.
Rosario