Is there a tirck in the get_xxxx function in the general_template.php file?

I’m a newbie in WordPress and I need a big help to understand how do-action works.

It seems there is a relationship between the instruction do_action and the code that follows it in the get_xxx function that I don’t understand. For example, in the following function :

function get_header( $name = null ) {

    do_action( 'get_header', $name );

        $templates = array();
        $name = (string) $name;
        if ( '' !== $name ) {
                $templates[] = "header-{$name}.php"; // instruction 1
        }

        $templates[] = 'header.php'; // instruction 2

        locate_template( $templates, true ); 
}

There is a do_action at the beginning to find header.php. Then afterwards, a series of codes are doing the same thing but with likely an issue because the content of the variable $templates of the line “instruction 1” is always overridden by the one in the line of “instruction 2” because it is not a “if then else”.

In every function get_xxxx we have the same structure. I guess there is a relationship between the do_action call and the series of codes that follow but I don’t get it.

I will be very grateful if somebody can help me to understand this issue.

The do_action:

do_action( 'get_header', $name );

its triggering the action get_header, so all actions attached using add_action to the action 'get_header' will be executed, its also passing the $name as parameter to the functions by example:

function my_function($name){
    echo "The Action sent me the name:".$name."!!";
}

add_action('get_header', 'my_function');

when the do_action( 'get_header', $name ); is executed my_function will be called with $name as a parameter, this way you can do “something” before the header template is loaded.

instruction 2 is not overriding instruction 1 its adding the default 'header.php' to the array as a fallback, if you are calling a custom header the $templates array will be like this (using get_header('custom');):

Array
(
    [0] => header-custom.php
    [1] => header.php
)

locate_template will try to find and load with require_once the first template, if it doesnt exist or it cant find it, it will fallback to header.php and try to load that one too.