The full command line that comes after the executable. Typically something like:

-quit -batchmode -executeMethod YourEditorScript.YourBuildMethod [-nographic] or
-quit -batchmode -buildWindowsPlayer path/to/your/build.exe or
-quit -batchmode -buildOSXPlayer path/to/your/build.app

Note: we make little to no attempt to detect conflicting arguments or arguments not suitable to the platform neither at configuration nor at runtime.

If the specified command line contains no -projectpath argument, the plugin automatically adds one with the proper parameter (the workspace of the project on the target machine). This is to make sure unity builds the proper project. Otherwise unity would reuse the last opened project. You can override it, but this hasn't been thoroughly tested.

See the official Editor command line arguments documentation.