WordPress filter hooks and how to define them in example

In WordPress, a filter is a function. Developers can create custom filters by using the Filter API.

This process is called “hooking” and the place where we apply the filter is called a hook.

Here you can find some more examples of using filters and actions in general and some explanation about the differences between these two.

The most important part is to create a hook.

Actually we create a hook by using the apply_filters special WordPress function. Somewhere if our theme files we may have this code:

echo apply_filters( 'my_custom_filter_hook', 'Copyright 2013 by programming-review' );

Please note the most important code sequence in here echo apply_filters actually this is what defines hook entry point. Here is our replace_copyright() function being set to my_custom_filter_hook hook

function replace_copyright( $copyright ) {
// do something to $copyright
return $copyright;
}
add_filter( 'my_custom_filter_hook', 'replace_copyright' );