This method should be a bit more efficient that either substr in a loop or using the regex engine.

#! perl -slw
use strict;

my $dna = 'accatgagctgtacgtagcatctgagcgcgcatgactgtgactgacgtaggcagca';

my $n = int( ( length( $dna ) - ( 10 - 3 ) ) / 3 );

print for unpack "(A10 X7)$n", $dna;

__END__
C:\Perl\test>test
accatgagct
atgagctgta
agctgtacgt
tgtacgtagc
acgtagcatc
tagcatctga
catctgagcg
ctgagcgcgc
agcgcgcatg
gcgcatgact
catgactgtg
gactgtgact
tgtgactgac
gactgacgta
tgacgtaggc
cgtaggcagc
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