"a" =~ /((a)*)*/ and
  printf("1:%s, 2:%s\n",
    defined($1) ? "'$1'" : "undef",
    defined($2) ? "'$2'" : "undef",
  );

"ab" =~ /((a)|(b))*/ and
  printf("1:%s, 2:%s, 3:%s\n",
    defined($1) ? "'$1'" : "undef",
    defined($2) ? "'$2'" : "undef",
    defined($3) ? "'$3'" : "undef",
  );