Can global variables be created with the keyword global and through a superglobal variable within a function in PHP?

I have heard using global variables is not good, however I am just trying to understand how the PHP language works. I am a beginner in the coding world.

Why can global variables be created within functions? Whether it is through the use of the global keyword or through a superglobal variable. I thought these two actions were used to access global variables in a function. I thought the only way you can create a global variable is to create it outside a function; in the global scope. I have looked at many different websites including w3schools.com and php.net

This is just some simple code I created to try and understand the way global variables work with functions:

<?php

function sample1() {
    global $a;
    echo $a = "this ";
}

sample1();

function sample2() {
    echo $GLOBALS['$b'] = "is ";
}

sample2();

function sample3() {
    global $c;
    $c = "an ";
}

sample3();
echo $c;

function sample4() {
    $GLOBALS['$d'] = "example ";
}

sample4();
echo $GLOBALS['$d'];

?>

This is the result of the code:

this is an example

All of the code works, but I don't understand how I created a global variable on any of these blocks of code? The global variables were not created outside of the functions. How can they be created inside of a function? What am I missing? Any response is appreciated - If possible, please keep the answer simple - I would like to discuss this further in the comment section, because I'm sure I will have follow up questions - Thank you

Variables can be created in the global scope in the two ways you just did - there's nothing saying that a function can't create (or change) a variable in the global scope - WHEN you explicitly ask for it through $GLOBALS or the global keyword.

The issue is that your belief "I thought the only way you can create a global variable is to create it outside a function; in the global scope." is not an exact statement. When you're using $GLOBALS and global, you're referring to the global scope. You're introducing a reference to the global scope inside your function.

With global you're in effect linking the local reference to the global reference, while with $GLOBALS you're explicitly referencing the global scope (which internally inside PHP can be introduced to the local scope in the same way).

In that case you're explicitly saying "I want this variable to be available in the global scope, make it so!" and PHP does what you're asking it to. This behaviour differ between languages, but as you've discovered for PHP, it's allowed.

It's not something I would recommend using in any way - it makes your code very hard to follow and argue around, so consider it an esoteric detail.