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

my $file = $ARGV[0] || 'words.txt';
open(my $fh, '<', $file) or die "Unable to open '$file' for reading: $
+!";

my %freq;
while (<$fh>) {
    tr/a-z//cd;
    ++$freq{$_} for split //;
}

while (%freq) {
    my ($small) = sort {$freq{$a} <=> $freq{$b}} keys %freq;
    seek $fh, 0, 0;
    my ($max, $word) = (-1, '');
    while (<$fh>) {
        last if $max == keys %freq;
        next if index($_, $small) == -1; 
        tr/a-z//cd;
        my %uniq = map {$_ => undef} split //;
        delete $uniq{$small};
        my $cnt = grep defined $freq{$_}, keys %uniq;
        ($max, $word) = ($cnt, $_) if $cnt > $max;
    }
    print "$word\n";
    delete @freq{split //, $word};
}
__END__
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