Predefined Variables
PHP's superglobal variables are
$_SERVER, $GLOBALS, $_REQUEST, $_POST, $_GET, $_FILES, $_ENV, $_COOKIE, $_SESSION.
They are available anywhere withoutscope that is accessible from anywhere.
$_SESSION
session_start();
//use session
$_SESSION["name"] = "session stored";
session_unset();
session_destroy();
COOKIE
Cookies are often used to identify the user. A cookie is a small file that the server embeds on the user's computer. Each time the same computer requests a page through a browser, it will send the cookie, too. With PHP, you can both create and retrieve cookie values.
setcookie(name, value, expire, path, domain, secure, httponly);
we retrieve cookie with
$_COOKIE["name"];
Working with Files
PHP offers a number of functions to use when creating, reading, uploading, and editing files.
$mode = r; // r,w,a,x, r+, w+, a+,x+;
$file = fopen("filename", $mode);
fwrite($file, "data");
fclose(); //return true onsuccess and false on failure
REF: https://www.sololearn.com/Play/PHP