tips to hooks in wordpress

Below is a simple example of using an action hook by creating an action:

<?php
add_action( 'wp_head', 'my_actionhook_example' );
function my_actionhook_example() {
echo '<meta name="description" content="Hello world. This meta description was created using my action hook example." />' . "\n";
} // The end of my_actionhook_example()
?>
The above code is something which you might place in your theme or child-theme’s functions.php file and when it is executed it will simply echo a meta tag inside the head portion of a WordPess page.

The add_action line registers (or hooks) your action (called my_actionhook_example) to the action hook which is called wp_head.

If you recall from earlier we said that an action is a customized function which you create and in the example above you can see the function definition and the code for the function which simply adds some meta data.

Filter Hooks
Filter hooks are another type of WordPress hook and these deal with the manipulation of text and other output.
A filter hook can be identified by either of the following pieces of code:

apply_filters( $tag, $value );
apply_filters_ref_array( $tag, $args );
For example in the WordPress core you will find a line of code like the following:

$title = apply_filters('wp_title', $title, $sep, $seplocation);

The above example shows the creation of the wp_title filter hook. This hook allows you to manipulate a page’s title before it is displayed in the browser.

As for the action hooks, filter hooks follow a similar pattern. The $tag represents the name of the hook and there are also parameters which are passed to filters which are registered to the hook.

Unlike the do_action hook, the apply_filters hook will always pass a parameter to the filter (which is the customized function you write) and your filter in turn must always return the $value parameter back to WordPress.

To create and register a filter you will use a similar approach to creating an action. For example you will write a function (known as the filter) which does something and you will also register your filter to a particular hook using a command such as:

add_filter ( 'hook_name', 'your_filter', [priority], [accepted_args] );

where:

hook_name = name of the hook you want register to
your_filter = the name of your filter (or function)
priority = (optional) integer which represents the order your filter should be applied. If no value is added, it defaults to 10.
accepted_args = (optional) integer argument defining how many arguments your function can accept (default 1) because your filter must accpet at least one parameter which will be returned.
Let’s look at a simple example of creating and registering a filter.
The code below shows something you might add in your customized theme functions.php file to append the site name to a page’s title:

<?php

add_filter( ‘wp_title’, ‘mytest_add_sitename_to_title’, 10, 2 );

mytest_add_sitename_to_title( $title, $sep ) {

/* Retrieve site name. */

$name = get_bloginfo( ‘name’ );

/* Append site name to $title. */

$title .= $sep . ‘ ‘ . $name;

/* Return the title. */

return $title;

}

?>

We can see from this example that we are registering our filter which is called mytest_add_sitename_to_title to the wp_title filter hook and we are assigning a priority of 10 and specifying that our filter function will accept 2 arguments.

link : https://www.tipsandtricks-hq.com/wordpress-action-hooks-and-filter-hooks-an-introduction-4163