RBTools provides the post-review command:

post-review is a command line tool for Windows, Linux and MacOS X
that simplifies both creating and updating review requests.  It
can look at your source directory, generate a diff, and upload it
to a new or existing review request on an associated Review Board
server.  This saves a lot of time over the web UI, and for some
types of code repositories (such as Perforce), its actually required
in order to produce a compatible diff.

Homepage:
https://www.reviewboard.org/docs/rbtools/dev/
