With PHP 5.4 you can now easily add a callback function, using header_register_callback, to be called just before the headers are sent to the browser.

For example:

  header('Content-Type: text/plain');
  header('X-Test: test-header');

  header_register_callback( 'remove_XPoweredBy_header' );

  echo 'Testing';

This allows you to set a callback function, in this case, remove_XPoweredBy_header.

An example of something to do in this callback function:

  function remove_XPoweredBy_header()
  {
    header_remove('X-Test');
  }

This will prevent “X-Test” from showing up in the headers.

A new function were added to PHP 5.4 that make getting and setting HTTP response code easy.

To get the current HTTP code, all you have to do is call the http_response_code function

  echo http_response_code()  //If all is ok, this should echo 200

To set the HTTP response code, add a parameter to the http_response_code function

  http_response_code(404)
  echo http_response_code()  //This should echo 404 and return 404 in the header

Class members can now be accessed on instantiation in PHP 5.4. This is a very handy addition.
Before PHP 5.4 you had to create an object into a variable, and then access the class member/function:

  //The old way
  $object = new SomeClass();
  $object->someFunction();

With PHP 5.4 you can access the class member directly on instantiation:

  //The new way
  (new SomeClass)->someFunction();

PHP now supports array dereferencing directly from a function call. Before PHP 5.4 you had to store the returning value from a function into a variable, and then use the variable.
Eg:

  $cars = $explode(",", "ferrari,lamborghini,maserati,bugatti");
  echo $cars[3];  //bugatti

Now with PHP 5.4 you can do it like this:

  echo $explode(",", "ferrari,lamborghini,maserati,bugatti")[3];  //bugatti

Another example with your own function:

  function get_cars()
  {
    return ["ferrari","lamborghini","maserati","bugatti"];
  }
  echo get_cars()[3];  //bugatti

PHP 5.4 introduced a new shorter array syntax, similar to the syntax used in JavaScript.

The old, longer syntax:

  //The old way
  $cars = array("ferrari", "lamborghini", "maserati", "bugatti");

The new syntax is an alternative to the old syntax.

  //The short way
  $cars = ["ferrari", "lamborghini", "maserati", "bugatti"];

I had to come up with a way to check if PHP is running in SSL mode today. This will work on both Apache, Nginx and IIS

function is_ssl()
{
    $secure_connection = false;

    if (!empty($_SERVER['HTTPS']) && $_SERVER['HTTPS'] !== 'off'
        || $_SERVER['SERVER_PORT'] == 443) 
    {
        $secure_connection = true;
    }

    return $secure_connection;
}

I found this little nifty function on StackOverflow</a

I recently had to find a quick way to check if an array is a multi-dimensional array, only to find that there are no PHP built-in function to do this. Here is a quick and easy way to do it:

function is_multi_array( array $arr )
{
    return is_array($arr[key($arr)]);
}

This can easily be used in the following context:

$a = array("dimension1" => array("dimension2" => "I like it") );
if( is_multi_array( $a ) )
{
    echo $a['dimension1']['dimension2'];
}