my @strings = qw( aaabbbb ab abb aabb aaabb aabbb );

{
  my ($a_counter, $b_counter);
  for my $string ( @strings )
  {
    $a_counter = 0;
    $b_counter = 0;
    print "In $string there were $a_counter 'a's and $b_counter 'b's. \n" if ( $string =~ /(a(?{$a_counter ++;}))+(b(?{$b_counter ++;}))+/ );
  }
}