What is a hook?

One way to customize Bazaar’s behaviour is with hooks. Hooks allow you to perform actions before or after certain Bazaar operations. The operations include commit, push, pull, and uncommit. For a complete list of hooks and their parameters, see Hooks in the User Reference.

Most hooks are run on the client, but a few are run on the server. (Also see the push-and-update plugin that handles one special case of server-side operations.)

Using hooks

To use a hook, you should write a plugin. Instead of creating a new command, this plugin will define and install the hook. Here’s an example:

from bzrlib import branch


def post_push_hook(push_result):
    print "The new revno is %d" % push_result.new_revno


branch.Branch.hooks.install_named_hook('post_push', post_push_hook,
                                 'My post_push hook')

To use this example, create a file named push_hook.py, and stick it in plugins subdirectory of your configuration directory. (If you have never installed any plugins, you may need to create the plugins directory).

That’s it! The next time you push, it should show “The new revno is...”. Of course, hooks can be much more elaborate than this, because you have the full power of Python at your disposal. Now that you know how to use hooks, what you do with them is up to you.

The plugin code does two things. First, it defines a function that will be run after push completes. (It could instead use an instance method or a callable object.) All push hooks take a single argument, the push_result.

Second, the plugin installs the hook. The first argument 'post_push' identifies where to install the hook. The second argument is the hook itself. The third argument is a name 'My post_push hook', which can be used in progress messages and error messages.

Debugging hooks

To get a list of installed hooks, use the hidden hooks command:

bzr hooks