To build for Windows:
/Applications/Unity/Unity.app/Contents/MacOS/Unity -batchmode -nographics -silent-crashes -projectPath <siriusPath> -buildWindowsPlayer "<userHome>/Build/windows/sirius.exe" -quit
To build for Mac:
/Applications/Unity/Unity.app/Contents/MacOS/Unity -batchmode -nographics -silent-crashes -projectPath <siriusPath> -buildOSXPlayer "<userHome>/Build/osx/sirius.app" -quit
To build for Linux:
/Applications/Unity/Unity.app/Contents/MacOS/Unity -batchmode -nographics -silent-crashes -projectPath <siriusPath> -buildOSXPlayer "<userHome>/Build/linux/sirius.exe" -quit