#!/usr/bin/perl

# http://perlmonks.org/?node_id=1201500

use strict;
use warnings;

my $file = '/usr/share/dict/words'; # YMMV

open my $fh, '<', $file or die "$! opening $file";
while(<$fh>)
  {
  /^[a-z]{6,}$/i or next;
  my $word = $_;
  my @counts;
  $counts[ s/$&//gi ] .= $& while s/.//;
  grep(!$_ || /../, @counts) or print $word;
  }