#! perl -slw
use strict;

our $LEN ||= 10;

my $s = 'A' x $LEN;
print $s;

for my $p1 ( 0 .. $LEN -1 ) {
	for my $c1 ( qw[ C G T ] ) {
		for my $p2 ( $p1 .. $LEN -1 ) {
			next if $p1 == $p2;
			for my $c2 ( qw[ C G T ] ) {
				my $t = $s;
				substr $t, $p1, 1, $c1;
				substr $t, $p2, 1, $c2;
				print $t;
			}
		}
	}
}
__END__
P:\test\demerphq>keyGen -LEN=10 >test.words

P:\test\demerphq>wc -l test.words
    406 test.words