Introducing Commandant

12Jun10

I’ve been meaning to write about Commandant for ages. I started it last year because I wanted to write command driven applications with a user experience just like Bazaar. There are several things that I like about Bazaar’s user interface:

  • You only have to know that the program is called bzr to start discovering it, because its default behaviour is to teach you how to use the builtin help system.
  • Each command has a clear name that makes its purpose easy to discern.
  • Each command has a succinct summary and a well written long description, along with clear information about the arguments and options the command accepts.
  • Help topics provide general information about the program that isn’t command-specific. The topics describe conceptual and technical aspects of the program that help the user better understand how to use it.
  • The interface conventions are very simple. It doesn’t take long to figure out how things work.

I wanted, as much as possible, to start writing application logic without having to do much work to get a working user interface. With that in mind, the basic goal for Commandant is to provide a Bazaar-like user interface with the least effort possible. I started by trying to extend Bazaar but I ran into tricky integration problems that made it hard to make progress, so I switched gears and started implementing the logic from scratch. Reinventing the wheel got me further than trying to integrate, but I quickly reached a point where progress slowed down because I had to deal with tricky problems that Bazaar had already solved. In the meantime, Robert landed changes in Bazaar that removed the integration hurdles that I’d run into.

With the integration problems out of the way, I stopped wasting time reinventing the wheel, and Commandant is now a thin layer on top of bzrlib itself. Being able to take advantage of the work that has been done in Bazaar has been a blessing. There’s more that can be done to improve Commandant, but it is very usable in its current state. If you’re interested in learning more, the README file should get you started.

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2 Responses to “Introducing Commandant”

  1. I’ve seen a couple of frameworks for building command line interfaces, and one thing I always wished they did was to auto-generate completion scripts for zsh (and bash I suppose), so that these don’t need to be maintained manually.

    • 2 Jamu

      I agree that auto-completion is important. An auto-complete script template is included with Commandant, so that authors of Commandant-based programs don’t have to figure it out for themselves. I should add one for zsh too, but I’m not a zsh user so it hasn’t been a priority. Anyway, once the initial script is created nothing special needs to be done to keep it up-to-date. Including a tool to generate the final result automatically, instead of requiring users to copy and edit a template, would be nice. I’ve filed bug #597306 to track the issue. Thanks for the suggestion!


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