create superglobal variables in php?

is there a way to create my own custom superglobal variables like $_POST and $_GET?

Static class variables can be referenced globally, e.g.:

class myGlobals {

   static $myVariable;

}

function a() {

  print myGlobals::$myVariable;

}

Yes, it is possible, but not with the so-called "core" PHP functionalities. You have to install an extension called runkit7: Installation

After that, you can set your custom superglobals in php.ini as documented here: ini.runkit.superglobal

I think you already have it - every variable you create in global space can be accessed using the $GLOBALS superglobal like this:

// in global space
$myVar = "hello";

// inside a function
function foo() {
    echo $GLOBALS['myVar'];
}

   Class Registry {
 private $vars = array();
 public function __set($index, $value){$this->vars[$index] = $value;}
 public function __get($index){return $this->vars[$index];}
}
$registry = new Registry;

function _REGISTRY(){
    global $registry;
    return $registry;
}

_REGISTRY()->sampleArray=array(1,2,'red','white');

//_REGISTRY()->someOtherClassName = new className;
//_REGISTRY()->someOtherClassName->dosomething();

class sampleClass {
    public function sampleMethod(){
        print_r(_REGISTRY()->sampleArray); echo '<br/>';
        _REGISTRY()->sampleVar='value';
        echo _REGISTRY()->sampleVar.'<br/>';
        
    }
}

$whatever = new sampleClass;

$whatever->sampleMethod();

One other way to get around this issue is to use a static class method or variable.

For example:

class myGlobals {

   public static $myVariable;

}

Then, in your functions you can simply refer to your global variable like this:

function Test()
{
 echo myGlobals::$myVariable;
}

Not as clean as some other languages, but at least you don't have to keep declaring it global all the time.

No

There are only built-in superglobals listed in this manual

Not really. though you can just abuse the ones that are there if you don't mind the ugliness of it.

You can also use the Environment variables of the server, and access these in PHP This is a good way to maybe store global database access if you own and exclusively use the server.

possible workaround with $GLOBALS:

file.php:

$GLOBALS['xyz'] = "hello";

any_included_file.php:

echo $GLOBALS['xyz'];

One solution is to create your superglobal variable in a separate php file and then auto load that file with every php call using the auto_prepend_file directive.

something like this should work after restarting your php server (your ini file location might be different):

/usr/local/etc/php/conf.d/load-my-custom-superglobals.ini

auto_prepend_file=/var/www/html/superglobals.php

/var/www/html/superglobals.php

<?php
  $_GLOBALS['_MY_SUPER_GLOBAL'] = 'example';

/var/www/html/index.php

<?php
  echo $_MY_SUPER_GLOBAL;