while (@ARGV) {
    $_ = $ARGV[0];
    last unless s/^-//;
    shift;
    last if /^-$/;
    while (length) {
        if (s/^a//)        { ++$aflag }
        elsif (s/^b(.*)//) { $bflag = length($1) ? $1 : shift }
        else { die "Unknown flag(s): -$_\n" }
    }
}