my $string = 'AAABCDAAADCBAAABBDAAA';
my @matches = $string =~ /AAA\w+AAA/g;

##</code><code>##

AAABCDAAA
AAADCBAAA
AAABBDAAA
AAABCDAAADCBAAA
AAADCBAAABBDAAA
AAABCDAAADCBAAABBDAAA