Fileprune will delete files from the specified set targeting a given
distribution of the files within time as well as size, number, and
age constraints.  Its main purpose is to keep a set of daily-created
backup files in manageable size, while still providing reasonable
access to older versions.  Specifying a size, file number, or age
constraint will simply remove files starting from the oldest, until
the constraint is met.  The distribution specification (exponential,
Gaussian (normal), or Fibonacci) provides finer control of the files
to delete, allowing the retention of recent copies and the increasingly
aggressive pruning of the older files.  The retention schedule
specifies the age intervals for which files will be retained.  As
an example, an exponential retention schedule for 10 files with a
base of 2 will be

1 2 4 8 16 32 64 128 256 512 1024

The above schedule specifies that for the interval of 65 to 128
days there should be (at least) one retained file (unless constraints
and options override this setting).

WWW: http://www.spinellis.gr/sw/unix/fileprune/