mach - the generic command line dispatching tool that powers the mach command to aid Firefox development - now has support for sub-commands.

You can now create simple and intuitive user interfaces involving sub-actions. e.g.

mach device sync
mach device run
mach device delete

Before, to do something like this would require a universal argument parser or separate mach commands. Both constitute a poor user experience (confusing array of available arguments or proliferation of top-level commands). Both result in mach help being difficult to comprehend. And that's not good for usability and approachability.

Nothing in Firefox currently uses this feature. Although there is an in-progress patch in bug 1108293 for providing a mach command to analyze C/C++ build dependencies. It is my hope that others write useful commands and functionality on top of this feature.

The documentation for mach has also been rewritten. It is now exposed as part of the in-tree Sphinx documentation.

Everyone should thank Andrew Halberstadt for promptly reviewing the changes!

http://gregoryszorc.com/blog/2014/12/18/mach-sub-commands