package Tie::CaseInsensitive;
use strict;
use Tie::Hash;
use vars qw(@ISA);
@ISA = qw(Tie::StdHash);
sub STORE {
    my ($self, $key, $value) = @_;
    return $self->{lc $key} = $value;
    } 
sub FETCH {
    my ($self, $key) = @_;
    return $self->{lc $key};
} 
sub EXISTS {
    my ($self, $key) = @_;
    return exists $self->{lc $key};
} 
sub DEFINED {
    my ($self, $key) = @_;
    return defined $self->{lc $key};
} 
1;

##</code><code>##

#!/usr/bin/perl 

use Tie::CaseInsensitive;
tie %HASH, 'Tie::CaseInsensitive';

$HASH{BoB}  = 1; 
$HASH{bob}  = 2;
$HASH{BOb}  = 3;   

print "Here are all the key value pairs\n";
foreach(keys %HASH){
   print "$_,$HASH{$_}\n";
}