#!/usr/bin/perl -w
use strict;

open WORDS, "/usr/dict/words" or die "no more words: $!";

for (@ARGV) {
  my @avoid = do {
    my @lits = /[a-z]/g;
    @lits ? "[" . join("", @lits) . "]" : ()
  };
  my %template;
  my $regex = "^";
  for (split //) {
    if (/[a-z]/) {
      $regex .= "$_";
    } elsif (/[A-Z]/) {
      if (exists $template{$_}) {
        $regex .= $template{$_};
      } else {
        my $id = 1 + keys %template;
        if (@avoid) {
          $regex .= "(?!" . join("|", @avoid) . ")";
        }
        $regex .= "(.)";
        push @avoid, $template{$_} = "\\$id";
      }
    } else {
      warn "ignoring $_";
    }
  }
  $regex .= "\$";
  print "$_ => $regex\n";
  seek WORDS, 0, 0;
  while (<WORDS>) {
    next unless /$regex/i;
    print;
  }
}
[download]