my ( $ac, $ag, $at, $cc, $cg, $ga, $gc, $ta, $tg, $tt ) = ( 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 ); my %seq = ( aa => \$tt, ag => \$ag, ac => \$ac, at => \$at, ta => \$ta, tg => \$tg, tc => \$ga, tt => \$tt, ca => \$tg, cg => \$cg, cc => \$cc, ct => \$ag, ga => \$ga, gg => \$cc, gc => \$gc, gt => \$ac ); # do some stuff ... ${$seq{$1}}++ while $genome =~ m/(..)/g;