I suspect that it's the nature of having options with optional arguments.

I think that there are two or three problems here.

One is that we should probably announce when we're expecting data on standard in with some sort of "reading archive from standard input" log message.

Two is that mongorestore takes a positional argument specifying a directory or file to restore from. Archive mode precludes the use of those files, and we should actually emit an error when one specified both archive mode, and a positional file or directory argument.

And, a third possibility is that we try to make the option parsing better and make the archive argument pick up the following option if it doesn't start with --'s

Lastly, I think this same problem effects mongodump albeit in a different way.