While you can work around this limitation by using <(command) as the input filename, it would be more idiomatic if you could just use bsondump in a normal pipeline as a filter. I see three options

• Read from stdin automatically if no filename is specified. Maybe still display help if stdin isatty(stdin).
• Use '-' as a magic filename like mongodump (users can still do './-' if they really want to use a file named '-')
• Add a --stdin option