And one more since it's Friday.

my @group = grep /\w/,
    split /(...)/, "ACTGACTGATGCATGCATGCATGCCGTACGTACGTACGT";
print join("+", @group), $/;

# ACT+GAC+TGA+TGC+ATG+CAT+GCA+TGC+CGT+ACG+TAC+GTA+CGT
[download]

Do not do it like that. :)