rotate files, keeping the last x

rotate.sh

# bad, if the recent backups failed, this can end up removing everything
find . -type f -name 'test-*' -mtime +5 -delete

# good, keeps 5 files at all time
keep=5
find . -type f -name 'test-*' -printf '%T@\0%p\n' \
  | sort -rn \
  | cut -d $'\0' -f2 \
  | tail -n +$(( keep + 1 ) \
  | xargs rm