How to open white night on a mac?

[Urkle]

Look at the contents of the ".bat". Most l likely it is launching Amnesia with a specific command line parameter..

You simply need to "Recreate" that on the mac, so, probably something like this. (from the "Terminal" application)

./Launcher.app/Contents/MacOS/Launcher config/whitenight_main_init.cfg

Since you are running the Steam release you need to actually run Launcher first, and not Amnesia.
another "slightly easier" option is to edit the properties of Amnesia in Steam (right click properties) and change the command line "launch arguments" that steam passes in.