What are the predefined variables in php?

php has predefined variables such as "$_SERVER", "$_GET and $_POST", "$_COOKIE", "$_SESSION" and "$_FILES". 1. $_SERVER, an array containing information about the server and operating environment; 2. $_GET and $_POST, are arrays used to obtain data submitted through the GET and POST methods. 3. $_COOKIE, used to obtain the value of the cookie variable stored on the client browser.

The operating environment of this tutorial: windows10 system, php8.1.3 version, DELL G3 computer.

PHP is a server-side scripting language widely used in website development. It has many built-in functions and features, including some predefined variables that are used to store data about servers, requests, and other environmental information. In this article, we will explore some commonly used predefined variables in PHP.

1. $_SERVER

$_SERVER is an array containing information about the server and operating environment. It contains many subkeys, such as the server's name, host address, client IP address, current script path, etc. The following are some commonly used $_SERVER subkeys:

- $_SERVER['SERVER_NAME']: The host name of the server currently running the script.

- $_SERVER['HTTP_HOST']: The host name of the current request.

- $_SERVER['REQUEST_METHOD']: The method of the current request (GET, POST, etc.).

- $_SERVER['SCRIPT_FILENAME']: The absolute path and file name of the currently executing script.

- $_SERVER['HTTP_USER_AGENT']: User agent information (browser information) of the current request.

2. $_GET and $_POST

$_GET and $_POST are arrays used to obtain data submitted through the GET and POST methods. The GET method passes data through the URL, while the POST method passes data through the request body. For example, if the URL contains `?name=John`, you can use $_GET['name'] to get the value of a variable named John. Similarly, if your form has an input field named `name`, you can use $_POST['name'] to access its value.

3. $_COOKIE

$_COOKIE is used to obtain the value of the cookie variable stored on the client browser. A cookie is a mechanism that stores small pieces of data on a user's computer for the purpose of tracking and identifying the user. In PHP, you can set a cookie using the setcookie() function and access its value using $_COOKIE.

4. $_SESSION

$_SESSION variable is used to store user information between different pages. It can be used to track a user's login status, store shopping cart contents, etc. Before using $_SESSION, the session must be started through the session_start() function.

5. The $_FILES

$_FILES variable is used to obtain information about files uploaded through the file upload form fields. It is an array containing the attributes of the uploaded file (such as file name, file type, file size, etc.). $_FILES allows you to move uploaded files to a target location on the server.

In addition to the predefined variables mentioned above, PHP also provides many other predefined variables, such as $_ENV, $_REQUEST, etc. Each predefined variable has its specific purpose and functionality and can be used according to development needs.

When developing PHP applications, it is very important to understand and correctly use these predefined variables. They provide convenient and accessible ways to obtain and process data about servers, requests, and other environmental information, thereby improving development efficiency and functionality. .

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