PHP has a large number of variable the are defined already.

PHP provide an additional set of predefined arrays containing variables from the web server.

PHP superglobal

1. $GLOBALS- It got the reference to every variable in the global scope.

<?php
$x = 75;
$y = 25;
 
function addition() {
    $GLOBALS['z'] = $GLOBALS['x'] + $GLOBALS['y'];
}
 
addition();
echo $z

2. $_SERVER- It is an array that has information about the header, path, script location.

<?php
echo $_SERVER['PHP_SELF'];
echo "<br>";
echo $_SERVER['SERVER_NAME'];
echo "<br>";
echo $_SERVER['HTTP_HOST'];
echo "<br>";
echo $_SERVER['HTTP_REFERER'];
echo "<br>";
echo $_SERVER['HTTP_USER_AGENT'];
echo "<br>";
echo $_SERVER['SCRIPT_NAME'];
?>

3. $_GET- It is an associative array of variable passed to the current script by HTTP GET method.

<?php
echo "Study " . $_GET['subject'] . " at " . $_GET['web'];
?>

4. $_POST- It is an associative array of variable passed to the current script by HTTP POST method.

<?php
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    // collect value of input field
    $name = $_POST['fname'];
    if (empty($name)) {
        echo "Name is empty";
    } else {
        echo $name;
    }
}
?>

5. $_FILES- It is an associative array of uploaded item by HTTP POST method.

6. $_REQUEST- It is an associative array of content by HTTP $_GET and $_POST method.

<?php
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    // collect value of input field
    $name = $_REQUEST['fname'];
    if (empty($name)) {
        echo "Name is empty";
    } else {
        echo $name;
    }
}
?>

7. $_COOKIE- It is an associative array of variable by HTTP cookies.

8. $_SESSION- It is an associative array of session variables.

9. $_PHP_SELF- It is a string that got the name of the script file which it is called.

10- $php_erromsg- It is the variable that got the last error message generated by php.

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