WordPress Plugins

By:- Mr. Ashok Negi

What is Plugin?

A plugin in WordPress is a PHP script that extends or alters the core functionality ofWordPress. Quite simply plugins are files installed in WordPress to add a feature, or

set of features, to WordPress

Plugin provides a set of hooks that enable plugins access to specific parts of WordPress. WordPress contains two different types of hooks: Actions and Filters. The Action hook enables you to trigger custom plugin code at specific points during execution. For example, you can trigger a custom function to run after a user registers a user account in WordPress.

The Filter hook to modifies text before adding or after retrieving from the database.

How to install any plugin in wordpress?

Following are the different ways to install any plugin1: Unzip the zipped plugin and then copy and paste folder inside the plugin

folder the path to plugin folder is \wp-content\plugins2: Go to Admin > Plugins > Add New, You can search the plugin by keyword, author

or tag then you will get the list of plugin for the keyword you have entered.3: The second link in Add New Plugin is “Upload” If you have a plugin in a .zip

format, you may install it by uploading it here.

How to create a custom plugin?

CREATING A PLUGIN FILEA plugin in WordPress can be a single PHP file or a group of files inside a folder. You need to consider many things when creating a new plugin in WordPress such as the plugin name and proper folder usage.

NAMING YOUR PLUGINWhen choosing a name for your plugin, it’s good practice to consider a name based on what your plugin actually does. For example, if you create an SEO - focused plugin, you wouldn’t want to name it Bob’s Plugin. Your audience would have no idea what your plugin actually does based on the plugin name. Your plugin name should be unique to your plugin and should also be descriptive of your plugin’s purpose.

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HEADER REQUIREMENTSThe plugin header is the only requirement for a plugin to function in WordPress. The plugin header is a PHP comment block located at the top of your primary plugin PHP file. This comment block tells WordPress that this is a valid WordPress plugin.Following is an example of a plugin header:< ?php/*Plugin Name: My PluginPlugin URI: http://example.com/wordpress-plugins/my-pluginDescription: A brief description of my pluginVersion: 1.0Author: OpensourcetechnologiesAuthor URI: http://www.opensourcetechnologies.comLicense: GPLv2*/? >

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As you can see, the plugin header is straightforward. The only required line for WordPress to recognize your plugin is the plugin name, but it’s good practice to fill in the entire header as shown.

Hooks, Actions and Filters

Hooks are provided by WordPress to allow your plugin to 'hook into' the rest of WordPress; that is, to call functions in your plugin at specific times, and thereby set your plugin in motion. There are two kinds of hooks:

1. Actions: Actions are triggered by specific events that take place in WordPress, such as publishing a post, changing themes, or displaying a page of the admin panel.You can check all actions list at http://codex.wordpress.org/Plugin_API/Action_ReferenceCommon actions functions are has_action(), add_action(), do_action(), do_action_ref_array(), did_action(), remove_action(), remove_all_actions()

2. Filters: Filters are the hooks that WordPress launches to modify text of various types before adding it to the database or sending it to the browser screen. Your plugin can specify that one or more of its PHP functions is executed to modify specific types of text at these times, using the Filter API. You can check all filters list at: http://codex.wordpress.org/Plugin_API/Filter_ReferenceCommon filter funtions are has_filter(), add_filter(), apply_filters(), current_filter(), merge_filters(), remove_filter(), remove_all_filters()

Example Action

To email some friends whenever an entry is posted on your blog

function email_friends( $post_ID ) { $friends = 'bob@example.org, susie@example.org'; wp_mail( $friends, "sally's blog updated", 'I just put something on my blog: http://blog.example.com' ); return $post_ID; } add_action('publish_post', 'email_friends');

publish_post: This action hook runs when a post is published, or if it is edited and its status is "published". Action function arguments: post IDemail_friends: This is the function, get called on publishing a post and accepting a parameter post ID.

Example Filter

This filter function adds an image before the post on the post page. It assumes an image named post_icon.png exists in the theme images folder. It runs at a lower priority (20) which runs later than most other filters (default is 10). function my_the_content_filter( $content ) { if ( is_single() ) // Add image to the beginning of each page $content = sprintf( '<img class="post-icon" src="%s/images/post_icon.png" alt="Post icon" title=""/>%s', get_bloginfo( 'stylesheet_directory' ), $content ); // Returns the content. return $content; }

add_filter( 'the_content', 'my_the_content_filter', 20 );

Example Plugins

Now I am going to show three sample plugin that I have made to make you more clear about the plugin-Helloworld : In this example I have created very simple function call and no hook.-simple-add-to-footer: In this example I have used two hooks ‘wp_footer’ and ‘the_content’.-Myplugin: In this example I have used two hooks ‘the_content’ and ‘the_title’

Thanks