The command line option
--share-single-file creates a single file sharing link that you can (for example) place in an email. Basic usage is:
The link expires after three days. The link contains random characters to make it hard to guess but (just as when created via the GUI) there is no password protection for single file sharing links. For password protection, create a ShareRoom.
After creating the single file sharing link, SpiderOak then runs --batchmode in order to synchronize the shared file with the server, and will return to a prompt when finished.