Here's part 1:

#! /usr/bin/perl -w
 
use strict;
 
open WORDS,"</usr/dict/words";
my @words = (<WORDS>);
close WORDS;
 
my @guessed = qw(a b c r l);
my @matches = f("__rl",\@words,\@guessed);
print foreach (@matches);
 
#--------------------------------------
 
sub f{
  my ($guess,$wordref,$letterref) = @_;
  my @m = ();
  my $alphabet = join"|",('a'..'z');
  my $guessed  = join"|",@$letterref;
  $alphabet =~ s/$guessed//g;
  $guess =~ s!_![$alphabet]!g;
  foreach (@$wordref) {
    push @m,$_ if (/\b$guess\b/)
  }
  return @m;
}
 
#--------------------------------------
[download]

OK, it's not very short but it does the job. I'll have a go at part 2 this evening.

JJ