my @strings = qw( acaabbbb );

for ( @strings )
{
    local our $a_counter = 0;
    local our $b_counter = 0;
    /
        (?: a (?{ $a_counter++ }) )+
        (?: b (?{ $b_counter++ }) )+
    /x;
    print("a: $a_counter\n");  # a: 3
    print("b: $b_counter\n");  # b: 4
}