File TieHashCI.pm:

package TieHashCI;
use Tie::Hash;
use vars qw (@ISA);

@ISA = qw(Tie::StdHash);
#my $exists = 0;

sub STORE {
    my ($self, $key, $value) = @_;
    return( $self->{ lc $key } = $value );
}

sub FETCH {
    my ($self, $key) = @_;
#    print ("Fetch $key\n");
    return( $self->{ lc $key } );
}

sub EXISTS {
    my ($self, $key) = @_;
#    $exists++;
#    print STDOUT (".");
    return( exists $self->{ lc $key } );
}

sub DEFINED {
    my ($self, $key) = @_;
#    print ("Defined $key\n");
    return( defined $self->{ lc $key } );
}

sub DELETE {
    my ($self, $key) = @_;
#    print ("Delete $key\n");
    return (delete $self->{ lc $key } );
}

#  sub CLEAR {}
#  sub FIRSTKEY{};
#  sub NEXTKEY{};

END {
#    print ("Exists: $exists\n");
}

1;
[download]

use TieHashCI;
my %data = (); tie (%data, 'TieHashCI');
[download]

If TieHashCI.pm is not in your @INC, try something like:

BEGIN {
  use FindBin qw($Bin);
  use lib "$Bin/lib"; # if TieHashCI is in ./lib
} # BEGIN
use TieHashCI;
[download]

But it wastes lots of ressources...

Best regards,
perl -e "s>>*F>e=>y)\*martinF)stronat)=>print,print v8.8.8.32.11.32"