use strict; use warnings; use Data::Dumper;

sub kv1{ 
	my @flds=split(/\s+/, $_[0]);
	return( $flds[2], $flds[3] );
}
sub kv2{ 
	my @flds=split(/\s+/, $_[0]);
	return( $flds[1] . $flds[2], $flds[3] );
}

my ($line,$fname, %data,%all, %kv_func);
%kv_func=(                             #dispatch table
	'file 1' => \&kv1, 
	'file 2' => \&kv1, 
	'file 3' => \&kv1, 
	'file 4' => \&kv1, 
	'file 5' => \&kv2, 
);
while( <DATA> ){
	if (my $num = /^file/ .. /^\n/ ){ # test them with flip-flop 
		chomp($line=$_);
		if( /^(file\s*\d+)/ ){   #begin of block 
			$fname = $1;
		}elsif ($num =~ /E0/ ){  #end of block
			$all{$fname}={%data};
			%data=();
		} else {			     ##data lines
			my ($k,$v) = $kv_func{$fname}->($line);
			$data{$k}= exists($data{$k}) ? $data{$k}+$v : $v;
		}
	}
}

print Dumper \%all;

__DATA__
file 1  
2 1 AB 1.0 
2 2 AB-1 2.0 
4 1 AB-4 1.0 
4 2 AB-6 2.0

a never comes here...
file 2 
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

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

file 4
56 01 AB 4.0 
56 12 AB-1 6.0
65 44 AB-4 9.0
65 46 AB-6 4.0

file 5
1 A B 12.00
2 C D 13.00
3 E F 11.00
4 G H 22.00