Check if device is landscape via ADB

This can be done through the following command:

adb shell dumpsys | grep 'SurfaceOrientation' | awk '{ print $2 }'

The output will be an integer ranging from 0 to 3 for each of the four possible orientations. 0 and 2 are landscapes while 1 and 3 are portraits. As the dumpsys output is very large, the command might take a few seconds to complete.

Update: dgmltn's modification is likely much faster:

adb shell dumpsys input | grep 'SurfaceOrientation' | awk '{ print $2 }'