Q:

PHP How to create simple hook?

I already tried to Google how to do this, but I still can't figure it out. How do I create a simple hook inside PHP? Here is what I've tried so far: 
wrapper.php (application starts here)
<?php   require 'core.php';   ?>
<?php   require 'view.php';   ?>

core.php
<?php

$hooks['hook_head'] = array();

//supposed to insert action in $hooks
function addHook($hookName, $funct){
    global $hooks;
    array_push($hooks[$hookName], $funct);
}

//supposed to execute specific hook
function executeHook($hookname){
    global $hooks;
    foreach($hooks[$hookname] as $funct){
        call_user_func( $funct );
    }
}

//supposed to execute action in $hooks when array key = hook_head
function hook_head(){
    global $hooks;
    if (array_key_exists('hook_head', $hooks)) {
        executeHook( 'hook_head' );
    }
}

//supposed to execute action in $hooks when array key == hook_footer
function hook_footer(){
    global $hooks;
    if (array_key_exists('hook_footer', $hooks)) {
        executeHook( 'hook_footer' );
    }
}

?>

view.php
<!DOCTYPE HTML>
<html>
<head>
    <?php   hook_head();  ?>
</head>
<body>
    <hr />

    <?php
        //add action to hook start here
        $test = function(){    echo "test succeds";    };
        addHook('hook_head', $test);
    ?>

    <?php  hook_footer();  ?>
</body>
</html>

The code works fine if I insert an action inside $hooks['hook_head'], before I call hook_head(). What I actually am trying to do though, is insert the action after I called hook_head(). How do I do this? 

A:

Move the addHook call to before the hook_head call (preferably to the beginning of the file).
I did notice that you "want to start coding (insert action in hook head) after it call hook_head()", but that's very cumbersome. It would look something like that:

Change hook_head() to insert some kind of token into the output.
At the end of the script,

call ob_get_clean() to get the output buffer of the page.
For each hook:

Execute the hook.
Call ob_get_clean() again to get the output buffer of the hook.
Replace the appropriate token in the oputput buffer of the page with the output buffer of the hook.

Print the output buffer of the page.

As I said: cumbersome. I strongly advice against it. I only mentioned it because you asked specifically. It contradicts the intuitive control flow of

Input
Processing
Output 

