Writing a plugin
================

Introduction
------------

Plugins are very similar to bzr core functionality.  They can import
anything in bzrlib.  A plugin may simply override standard functionality,
but most plugins supply new commands.

Creating a new command
----------------------

To create a command, make a new object that derives from
``bzrlib.commands.Command``, and name it ``cmd_foo``, where foo is the name of
your command.  If you create a command whose name contains an underscore,
it will appear in the UI with the underscore turned into a hyphen.  For
example, `cmd_baz_import` will appear as `baz-import`.  For examples of how
to write commands, please see ``builtins.py``.

Once you've created a command you must register the command with
``bzrlib.commands.register_command(cmd_foo)``.  You must register the
command when your file is imported, otherwise bzr will not see it.

Installing a hook
-----------------

See `Using hooks`_.

 .. _Using hooks: hooks.txt


Specifying a plugin version number
----------------------------------
Simply define ``version_info`` to be a tuple defining the current version
number of your plugin. eg.
``version_info = (0, 9, 0)``
``version_info = (0, 9, 0, 'dev', 0)``

Plugin searching rules
----------------------

Bzr will scan ``~/.bazaar/plugins``  and ``bzrlib/plugins`` for plugins
by default.  You can override this with  ``BZR_PLUGIN_PATH``
(see `User Reference 
<../user-reference/configuration-help.html#bzr-plugin-path>`_ for details).

Plugins may be either modules or packages.  If your plugin is a single
file, you can structure it as a module.  If it has multiple files, or if
you want to distribute it as a bzr branch, you should structure it as a
package, i.e. a directory with an ``__init__.py`` file.

More information
----------------

Please feel free to contribute your plugin to BzrTools, if you think it
would be useful to other people.

See the `Bazaar Developer Guide`_ for details on Bazaar's development
guidelines and policies.

.. _Bazaar Developer Guide: ../developer-guide/HACKING.html