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

my %hash;
while( my $line = <DATA> ) {
	chomp $line;
	push @{ $hash{ $_ } }, substr $line, $_, 2 
		for 0 .. length( $line ) -2;
}
print Dumper \%hash;

__DATA__
ABCDEFGHIJKLM
abcdefghijklm
NOPQRSTUVWXYZ
nopqrstuvwxyz