file 1
STD	Area	Name	Amount
2	1	AB	1.0	
2	2	AB-1	2.0
4	1	AB-4	1.0	
4	2	AB-6	2.0

##</code><code>##

file 2
STD	Area	Name	Amount
21	01	AB	4.0	
22	12	AB-1	6.0
41	44	AB-4	9.0	
42	46	AB-6	4.0
42	46	AB-6	4.0

##</code><code>##

file 3
STD	Area	Name	Amount
01	10	AB	4.0	
20	02	AB-1	6.0
40	04	AB-4	9.0	
02	26	AB-6	4.0

##</code><code>##

file 4
STD	Area	Name	Amount
56	01	AB	4.0	
56	12	AB-1	6.0
65	44	AB-4	9.0	
65	46	AB-6	4.0

##</code><code>##

Output:
	file 1 file 2 file 3	file 4 
AB	 1.0	4.0	4.0	4.0
AB-1	 2.0	6.0	6.0	6.0
AB-4	 1.0	9.0	9.0	9.0
AB-6	 2.0	8.0	4.0	4.0

##</code><code>##

my %result;
my %hash = ( '2.1','AB',
'2.2','AB-1',
'4.1','AB-4',
'4.2','AB-6',
'21.01','AB',
'22.12','AB-1',
'41.44','AB-4',
'42.46','AB-6',
'42.46','AB-6',
'01.10','AB',
'20.02','AB-1',
'40.04','AB-4',
'02.26','AB-6',
'56.01','AB',
'56.12','AB-1',
'65.44','AB-4',
'65.46','AB-6');

foreach my $file (@files) {
open FILE, "<$dir/$file" or warn "Couldn't open file ($!) or file ($!) not found\n";
while (chomp ( my @fields = split /\t/, <FILE>) ) {	
my $key = "$fields[0].$fields[1]";

if (exists $hash{$key})
{
$key = $hash{$key};

if (exists($result{$key}))
{
$result{$key} += $fields[03];
}
else { 
$result{$key} += $fields[03];
}
}
}
}
close FILE;