package Tie::Hash::MultiVal;

use strict; 
use warnings;

use Tie::Hash;
use base qw(Tie::StdHash);

sub TIEHASH {
   my $class = shift;
   return bless {@_}, $class;
}

sub STORE {
   my ($hash,$k,$v) = @_;
   if (exists $hash->{$k}) {
      if (ref $hash->{$k}) {
         push @{$hash->{$k}}, $v;
      } else {
         $hash->{$k} = [$hash->{$k},$v];
      }
   } else {
      $hash->{$k} = $v;
   }
}

sub DELETE {
   my ($hash,$k) = @_;
   if (ref $hash->{$k}) {
      pop @{$hash->{$k}};
      $hash->{$k} = $hash->{$k}[0] if @{$hash->{$k}} == 1;
   } else {
      delete $hash->{$k};
   }
}

1;
[download]

use strict; 
use warnings;
use URI;
use Data::Dumper;
use Tie::Hash::MultiVal;

my $uri = URI->new('http://foo.com/bar.cgi?foo=bar&foo=baz&bar=qux&baz
+=qux');
my %hash;
tie %hash, 'MyHash';

%hash = $uri->query_form();
@hash{qw(foo bar baz qux)} = qw(one two three four);

delete $hash{foo};
print Dumper \%hash;
[download]

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)