To generate a .spine file using the Spine CLI, you can use the import command. This involves specifying the input file, which can be a .skel or other supported format, and the output file, which will be the .spine file. The command looks like this:

spine -i input.skel -o output.spine --import

You can also use the short form -r instead of --import, as they perform the same function. This command will convert the input skeleton file into a Spine project file.