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

# Set up
my @charsets = (
                [ "b", "h" ],
                [ "e" ],
                [ "l", "p", "i" ],
                [ "l" ],
                [ "o" ],
               );

# Do it
my @words = ("");
for my $char_ref (@charsets) {
   my @temp_words;
   for my $word_part (@words) {
      for my $char (@$char_ref) {
         push @temp_words, $word_part . $char;
      }
   }
   @words = @temp_words;
}

# Show it
print "$_\n" for @words;