If you use a cell name that doesn't exist, then we still get to see the gds file header information but no comparison will actually happen. You could see just the first part of the information by piping to the head command like this:
% compare_gds layout.gds dummyname layout.gds dummyname dummyout | head -32
Because the cellname doesn't exist, the utility stops after looking at the first gds file. I wonder if this process will still take too long on a large file. will you have a chance to test it?
Thanks a lot, its not taking more time to print the version.