while(@fnames) {
  my $f = shift @fnames;

  for my $f2 (@fnames) {
    last if($size{$f} != $size{$f2});


##</code><code>##

my %filesets;
for ( @fnames ) {
  push @{ $filesets{ -s $_ } }, $_;
}

# filter out any lists that have only one element:

for ( keys %filesets ) {
  @{$filesets{$_}} <= 1 and delete $filesets{$_};
}

##</code><code>##

my %filesets;
for ( @fnames ) {
  my $size = -s $_;
  my $csum = `sum "$_"`;
  push @{ $filesets{$size.$csum} }, $_;
}