You can use split: 
my $string= 'AAABBBCCCDD';
my $i=0;
my @words= grep $i=!$i,split /(?<=(.))(?!\1)/,$string;
print join "\n",@words,'';

[download]
s$$([},&%#}/&/]+}%&{})*;#$&&s&&$^X.($'^"%]=\&(|?*{%
+.+=%;.#_}\&"^"-+%*).}%:##%}={~=~:.")&e&&s""`$''`"e

In reply to Re^2: Split a string based on change of character by Skeeve
in thread Split a string based on change of character by eyepopslikeamosquito

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