#!/usr/bin/perl -w

#declare all filenames
$filename1 = 'one.txt';
$filename2 = 'two.txt';
$filename3 = 'three.txt';

#open text file 1

open (FILE1, $filename1) or die "Unable to open $filename1 because $!\n";

while ($line = <FILE1>) {
	chomp ($line);
	($chrX, $chrpos, $value1, $value2) = split (/\t/, $line);
	$key1 = join ("_", $chrX, $chrpos);
	$hash{$key1}++;
};
close FILE1;

open (FILE2, $filename2) or die "Unable to open $filename2 because $!\n";

while ($line = <FILE2>) {
	chomp ($line);
	($chrX, $chrpos, $value11, $value22) = split (/\t/, $line);
	$key2 = join ("_", $chrX, $chrpos);
if (exists $hash{$key2} > 0) {
	$hash{key2} = $value11 + $value1;
	$hash{key2} = $value22 + $value2;
	$hash{key2}++
}
};
close FILE2;

open (FILE3, $filename3) or die "Unable to open $filename3 because $!\n";

while ($line = <FILE3>) {
	chomp ($line);
	($chrX, $chrpos, $value111, $value222) = split (/\t/, $line);
	$key3 = join ("_", $chrX, $chrpos);
if (exists $hash{$key3} > 0) {
	$hash{key3} = $value111 + $value11;
	$hash{key3} = $value222 + $value22;
	$hash{key3}++
}
};
print "$hash{key3} $value111 $value222";

close FILE2;