Glyph Designer 1 provided the ability to run a binary included within the Glyph Designer app bundle called GDCL. This allowed you to generate font output from the command line by providing GDCL with a Glyph Designer project and options on what you want to have happen e.g. the size you want the font to be output.
For Glyph Designer 2 this is still the case except GDCL is no longer a separate application. To perform the actions of GDCL you need to run the Glyph Designer.app file from the command line passing in the parameters you want to use of -h to get help as shown below:
If you don't provide one of the recognised command line options then Glyph Designer will start in GUI mode and open in the desktop.
If Glyph Designer were installed in your Applications folder then the following command would cause Glyph Designer to output its help information.
./Applications/Glyph\ Designer.app/Contents/MacOS/Glyph\ Designer -h