Using plugins
=============

.. Information on how to use plugins in Bazaar.

What is a plugin?
-----------------

A plugin is an external component for Bazaar that is typically made by
third parties. A plugin is capable of augmenting Bazaar by adding new
functionality.  A plugin can also change current Bazaar behavior by
replacing current functionality. Sample applications of plugins are:

* overriding commands
* adding new commands
* providing additional network transports
* customizing log output.
  
The sky is the limit for the customization that can be done through plugins.
In fact, plugins often work as a way for developers to test new features for
Bazaar prior to inclusion in the official codebase. Plugins are helpful
at feature retirement time as well, e.g. deprecated file formats may one
day be removed from the Bazaar core and be made available as a plugin instead.

Plugins are good for users, good for external developers and good for
Bazaar itself.

Where to find plugins 
---------------------

We keep our list of plugins on the http://bazaar-vcs.org/BzrPlugins page.

How to install a plugin 
-----------------------

Installing a plugin is very easy! If not already created, create a
``plugins`` directory under your Bazaar configuration directory,
``~/.bazaar/`` on Linux and
``C:\Documents and Settings\<username>\Application Data\Bazaar\2.0\``
on Windows. Within this directory (referred to as $BZR_HOME below),
each plugin is placed in its own subdirectory.

Plugins work particularly well with Bazaar branches. For example, to
install the bzrtools plugins for your main user account on Linux,
one can perform the following:: 

    bzr branch http://panoramicfeedback.com/opensource/bzr/bzrtools
    ~/.bazaar/plugins/bzrtools

When installing plugins, the directories that you install them in must
be valid python identifiers. This means that they can only contain
certain characters, notably they cannot contain hyphens (``-``). Rather
than installing ``bzr-gtk`` to ``$BZR_HOME/plugins/bzr-gtk``, install it
to ``$BZR_HOME/plugins/gtk``.

Alternative plugin locations
----------------------------

If you have the necessary permissions, plugins can also be installed on
a system-wide basis. Two locations are currently checked for plugins:

 1. the system location - bzrlib/plugins
 2. the personal location - $BZR_HOME/plugins.

On a Linux installation, these locations are typically
``/usr/lib/python2.4/site-packages/bzrlib/plugins/`` and
``$HOME/.bazaar/plugins/``.
On a Windows installation, the system location might be
``C:\\Program Files\\Bazaar\\plugins``
while the personal location might be
``C:\Documents and Settings\<username>\Application Data\Bazaar\2.0\plugins``.

One can additionally override the personal plugins location
by setting the environment variable ``BZR_PLUGIN_PATH``
to a directory that contains plugins.

Listing the installed plugins
-----------------------------

To do this, use the plugins command like this::

    bzr plugins

The name, location and version of each plugin installed will be displayed.

New commands added by plugins can be seen by running ``bzr help commands``.
The commands provided by a plugin are shown followed by the name of the
plugin in brackets.

Popular plugins
---------------

Here is a sample of some of the more popular plugins.

  ================ ================= ==================================
  Category         Name              Description
  ================ ================= ==================================
  GUI              QBzr              Qt-based GUI tools
  GUI              bzr-gtk           GTK-based GUI tools
  GUI              bzr-eclipse       Eclipse integration
  General          bzrtools          misc. enhancements including shelf
  General          difftools         external diff tool helper
  General          extmerge          external merge tool helper
  Integration      bzr-svn           use Subversion as a repository
  Migration        cvsps             migrate CVS patch-sets
  ================ ================= ==================================

If you wish to write your own plugins, it is not difficult to do.
See `Writing a plugin`_ in the appendices to get started.
