If you use the pseudo-two-dimensional index (using a comma):

 $hash{'a', 'b'}
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you only get a single key, that is, "a\034b" (unless you change $; ). This is like AWK's simulation of multi-dimensional arrays/hashes, right down to the use of SUBSEP ("\034") as a delimiter. Look at the following with Data::Dumper (I changed $; so you could see it):

use strict;
use Tie::Hash;
package Tie::HashNKeys;
use base 'Tie::StdHash';

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

sub STORE {
 $_[0]->{ join $;, sort split /$;/, $_[1] } = $_[2];
}

sub FETCH {
$_[0]->{ join $;, sort split /$;/, $_[1] };
}

package main;
use Data::Dumper;

$; = '~'; # so it can be seen
tie my %hash, 'Tie::HashNKeys';
$hash{'csUsers','csGroups'} = 'foo';
print $hash{'csGroups','csUsers'};   ## prints 'foo'
print Dumper(\%hash);
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