Input:
  @FileNames : A list of candidate files

Step 1: Build a hash to group potentially similar strings
  {
    local $/ = \32;
    for my $curFile (@FileNames) {
      open INF, '<', $curFile or die...
      my $key = <INF>;
      close INF or die...

      # list of files matching the first 32 chars
      push @{$Candidates{$key}{LIST}}, $curFile;

      # regex for matching similar groups
      my $tmp = $key;
      $tmp =~ s/N/./;
      $Candidates{$key}{REGEX} = qr/$r/;
    }
  }

Step 2: Merge compatible groups
  for my $key (keys %Candidates) {
    $Candidates{$key}{SIMILAR} = 
        grep { /$Candidates{$key}{REGEX}/ && ($_ ne $key) }
        keys %Candidates;
  }

Step 3: Remove unmatchable items
  my %UnmatchableKeys;
  for my $key (keys %Candidates) {
    next if exists $Candidates{$key}{SIMILAR};
    next if scalar @{$Candidates}{$key}{LIST}} > 1;
    $UnmatchableKeys{$key} = 1;
  }

Step 4: Generate lists of items needing to be compared
  for my $key (keys %Candidates} {
    next if exists $UnmatchableKeys{$key};
    my @similarFiles = (@{$Candidates}{$key}{LIST}});
    for my $others (keys %{$Candidates{$key}{SIMILAR}}) {
      push @similarFiles, @{$Candidates{$key}{LIST}};
    }
    print "GROUP: ", join(", ", sort @similarFiles), "\n";
  }