View source for Creating a Plugin for Joomla

=== Creating the Installation File ===
As with all extensions in Joomla!, plugins are easily installed as a .zip file (.tar.gz is also supported) but a correctly formatted XML file must be included. As an example, here is the XML installation file for the categories search plugin.
<source lang="xml">
<?xml version="1.0" encoding="utf-8"?>
<extension version="2.5" type="plugin" group="search">
	<name>plg_search_categories</name>
	<author>Joomla! Project</author>
	<creationDate>November 2005</creationDate>
	<copyright>Copyright (C) 2005 - 2013 Open Source Matters. All rights reserved.</copyright>
	<license>GNU General Public License version 2 or later; see LICENSE.txt</license>
	<authorEmail>admin@joomla.org</authorEmail>
	<authorUrl>www.joomla.org</authorUrl>
	<version>2.5.0</version>
	<description>PLG_SEARCH_CATEGORIES_XML_DESCRIPTION</description>
	<files>
		<filename plugin="categories">categories.php</filename>
		<filename>index.html</filename>
	</files>
	<languages>
		<language tag="en-GB">en-GB.plg_search_categories.ini</language>
		<language tag="en-GB">en-GB.plg_search_categories.sys.ini</language>
	</languages>
	<config>
		<fields name="params">

			<fieldset name="basic">
				<field name="search_limit" type="text"
					default="50"
					description="JFIELD_PLG_SEARCH_SEARCHLIMIT_DESC"
					label="JFIELD_PLG_SEARCH_SEARCHLIMIT_LABEL"
					size="5"
				/>

				<field name="search_content" type="radio"
					default="0"
					description="JFIELD_PLG_SEARCH_ALL_DESC"
					label="JFIELD_PLG_SEARCH_ALL_LABEL"
				>
					<option value="0">JOFF</option>
					<option value="1">JON</option>
				</field>

				<field name="search_archived" type="radio"
					default="0"
					description="JFIELD_PLG_SEARCH_ARCHIVED_DESC"
					label="JFIELD_PLG_SEARCH_ARCHIVED_LABEL"
				>
					<option value="0">JOFF</option>
					<option value="1">JON</option>
				</field>
			</fieldset>

		</fields>
	</config>
</extension>
</source>

As you can see, the system is similar to other Joomla! XML installation files. You only have to look out for the <code>group="xxx"</code> entry in the <code><extension></code> tag and the extended information in the <code><filename></code> tag. This information tells Joomla! into which folder to copy the file and to which group the plugin should be added.

If you are creating a plugin that responds to existing core events, the <code>group="xxx"</code> attribute would be changed to reflect the name of existing plugin folder for the event type you wish to augment. e.g. <code>group="authentication"</code> or <code>group="user"</code>. See [[Plugin/Events]] for a complete list of existing core event categories. In creating a new plugin to respond to core events it is important that your plugin's name is unique and does not conflict with any of the other plugins that may also be responding to the core event you wish to service as well.

If you are creating a plugin to respond to non-core system events your choice for the <code>group="xxx"</code> tag should be different than any of the existing core categories.

'''Tip''' If you add the attribute <code>method="upgrade"</code> to the tag <code>extension</code>, this plugin can be installed without uninstalling an earlier version. All existing files will be overwritten, but old files will not be deleted.