#!/usr/bin/perl
# file fusselkerl
use strict;
my $pat = shift;
my $p;
{
  my (%s, %i);
  my $d = my $c = 1; # our regexp will be inside parens, so first backref is 2
  $p = join (
    "",
    map {
      if($s{$_}++){
        "\\".$i{$_}
      }
      else{
        $i{$_}=++$c;
        $c>$d+1 ? '(?!'.join('|',map{"\\".abs}-$c+1..-$d-1).")(\\w)" : "(\\w)";
      }
    } split//,$pat
  );
}
print '(',$p,")\n";


open my $fh, '<', shift;
my %s;
while (<$fh>) {
    my @l = ();
    while (/\b($p)\b/g) {
      push @l, $1 unless $s{$1}++;
    }
    print join (", ",@l), $/ if @l;
}