Returns a multidimensional ARRAY containing a list of all defined variables, be them environment, server or user-defined variables, within the scope that is called.
Want to know more?
Language - Variables 
Want to know more?
Language - Variables
<?php
arr get_defined_vars ( )
?>
EXERCISE
<?php
$arr01 = get_defined_vars();
echo '<pre>';
print_r($arr01);
echo '</pre>';
?>
EXERCISE
<?php
$arr02a = [ 1, '2', 3, 'four'];
$vr02 = 'This is one more string!';
$arr02b = get_defined_vars();
echo '<pre>';
print_r($arr02b);
echo '</pre>';
?>
EXERCISE
<?php
// The result of this exercise will depend
// of the configuration of your system
$vr03 = $_SERVER;
$arr03 = get_defined_vars();
echo '<pre>';
print_r($arr03);
echo '</pre>';
?>
EXERCISE
<?php
$a = $b = $c = "anything call me";
$abc = get_defined_vars();
echo '<pre>';
print_r($abc);
echo '</pre>';
?>