#! perl -slw
use strict;

package Tie::Hashi;
use Tie::Hash;
our @ISA = 'Tie::ExtraHash';

sub TIEHASH{ bless [{}], $_[ 0 ]; }
sub STORE { $_[ 0 ][ 0 ]{ lc $_[ 1 ] } = $_[ 2 ]; }
sub FETCH { $_[ 0 ][ 0 ]{ lc $_[ 1 ] }; }
sub EXISTS{ exists $_[ 0 ][ 0 ]{ lc $_[ 1 ] }; }
sub DELETE{ delete $_[ 0 ][ 0 ]{ lc $_[ 1 ] }; }
1;
package main;

tie my %hashi, 'Tie::Hashi';

$hashi{ TheKey } = 12345;

print $hashi{ tHeKeY };

print keys %hashi, $/, values %hashi;
__END__
P:\test>tiehashi.pl
12345
thekey
12345