#!/usr/bin/perl
use strict;
use warnings;

chomp(my @list = `du -kh /mnt/edi/si51/documents`);
my $dltd = 0;
foreach my $line (@list) {
  my ($size,$path) = split /\t/, $line;
  $size =~ s/\D//g;
  if ($size == 0) {
    rmdir $path && $dltd++
  }
}

printf "%d directories deleted.\n",$dltd;
[download]

UPDATE: There are several things that were in an earlier version of this script that didn't make the second cut, but only because I got lazy. My original got deleted somehow, and I had foolishly not kept a copy, so I wrote the above quickly.

The directory structure is documents/4digityear/abbreviatedcardinalmonth/2digitday/hour/minute. At first I restricted deletions to directories above some number of days old, but rmdir updates the directory time information, meaning a directory that was now empty because all its empty constituent directories were gone looked like it was brand new. This made it useless to run consecutively. I came up with a calculation that used the directory tree to come up with the age, and that worked. I just didn't bother with it when I rewrote the script this time. Some of the alternate solutions don't have that limitation.