#! perl -slw
use strict;
use Data::Dumper;
use Tie::IxHash;

my %login;

{
	tie my %csv, 'Tie::IxHash';
	@csv{ qw[one two three four five] } = qw[11 12 13 14 15];
	$login{1} = \%csv;
}

{
	tie my %csv, 'Tie::IxHash';
	@csv{ qw[one two three four five] } = qw[11 12 23 undef 25];
	$login{2} = \%csv;
}

print Dumper \%login;

my %union = (%{$login{1}}, %{$login{2}});

print Dumper \%union;

my %union = (%{$login{2}}, %{$login{1}});

print Dumper \%union;