~bzr-pqm/bzr/bzr.dev

Using hooks

===========

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

<../user-reference/bzr_man.html#hooks>`_ in the User Reference.

Most hooks are run on the client, but a few are run on the server.  (Also

see the `bzr-push-and-update`_ plugin that handles one special case of

server-side operations.)

.. _bzr-push-and-update: https://launchpad.net/bzr-push-and-update/

Using hooks

-----------

To use a hook, you should `write a plugin <#writing-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