use File::Find;

find(sub {
    my ($mode) = (stat)[2] & 0777;  # see perldoc -f stat
    my $new_mode = 0664;
    if ( -d _ or ($mode | 0111) ) {
        $new_mode |= 0111;
    }
    if ($new_mode != $mode) {
        chmod($new_mode, $_)
            or warn("Failed to set permissions on "
                    ."$File::Find::name; $!");
    }
}, "dir");