I'm confused, are you looking to split the string into arbitrary-length sets of contiguous repeated characters, or just into n-length strings, regardless of whether or not the characters in them repeat? Your choice of strings, 'aabbcccddee', makes this somewhat ambiguous. If you want the former, HAWTDI:

$string='aabbbbbbcccccaaaddeefghhhh';
my @l;

push @l, $1.$2 while $string =~ /(\w)(\1*)/g;

print join ',', @l;

# outputs

aa,bbbbbb,ccccc,aaa,dd,ee,f,g,hhhh
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Of course, this uses a regex and a while, etc...