When I flashed OSE image with reference flashing guide (Flashing webOS OSE | webOS Open Source Edition) on macOS, I got following error message.
sudo dd bs=4M if=./webos-image-raspberrypi3-master-20180822064009.rpi-sdimg of=/dev/rdisk4
dd: bs: illegal numeric value
This option of bb command is wrong, it should be fixed such as below.
4M -> 4m
$ sudo dd bs=4m if=./**.rpi-sdimg of=/dev/rdisk n