I am sure there are many excellent answers to this question. But I decided to write a piece of code that demonstrates various ways to add multiple values to a single hash key:

#!/usr/bin/perl
use warnings;
use strict;

#
# There are a lot of ways to associate a single hash key
# With multiple values. We will demonstrate some of
# these in this code:
#

my %hash = ();

#
# Using a hash element to store an (anonymous) array.
#

$hash{array_key} = [ 1,2,3,4,5 ];

#
# using a hash element as a stack.
#

push @{$hash{array_key}}, 6;

print "Array values are: ", join(' ',@{$hash{array_key}}), "\n";

#
# Using a hash element to store a reference to an array
#

my @array = ( 2,3,4,5,6 );

$hash{array_ref} = \@array;

#
# Using a hash element to store an anonymous hash.
#(Hash of hashes)
#
$hash{anon_hash} = { first_name => "Fred" , last_name => "Flintstone" 
+};

print_hash(\%{$hash{anon_hash}});

#
# Using a hash element to store a reference to a hash.
#(Hash of hashes)
#
my %neighbor = (
    first_name => "Barney",
    last_name  => "Rubble",
);
$hash{hash_ref} = \%neighbor;

print_hash(\%{$hash{hash_ref}});
#
# Using a hash element to store an anonymous copy of a hash.
#(hash of hashes)
#
my %wife = (
    first_name => "Wilma",
    last_name  => "Flintstone",
);

$hash{hash_copy} = { %wife };

$hash{hash_copy}{first_name} = "Betty";
$hash{hash_copy}{last_name} = "Rubble";

print_hash(\%wife);
print_hash(\%{$hash{hash_copy}});

sub print_hash {
    my $hashref = shift;
    print "Hash values: ";
    for ( sort keys %{$hashref} ) {
    print $$hashref{$_}, " ";
    }
    print "\n";
}
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And the output is:

C:\Code>perl hash_examples.pl
Array values are: 1 2 3 4 5 6
Hash values: Fred Flintstone
Hash values: Barney Rubble
Hash values: Wilma Flintstone
Hash values: Betty Rubble
[download]