You could also do it with a regexp.

Which would look something like:

my $dna = 'accatgagctgtacgtagcatctgagcgcgcatgactgtgactgacgtaggcagca';
my $increment = 3;
my $substr = 10;
my @windows = $dna=~/(?=(.{$substr})).{$increment}/gs;
print "$_\n" for @windows;
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