use strict;
use warnings FATAL => 'all';
 
my $string = "aacbbbcac";
 
my $re1 = qr/((a+)?(b+)?(c))*/;
if ($string =~ $re1) {
  foreach (0..$#-) {
    printf "Group %d: <%s>\n", $_, substr($string, $-[$_], $+[$_] - $-[$_]);
  }
}

##</code><code>##

Group 0: <aacbbbcac>
Group 1: <ac>
Group 2: <a>
Group 3: <bbb>
Group 4: <c>