Introduction to PHP superglobal variables

Superglobal variables, introduced in PHP 4.1.0, are built-in variables that are always available in all scopes.

Super global variables — Super global variables are built-in variables that are always available in all scopes.

Many of the predefined variables in PHP are "superglobal," meaning they are available throughout the entire scope of a script. They can be accessed within a function or method without executing global $variable; .

These super global variables are:

##$GLOBALS — Reference all variables available in the global scope

A global combination array that contains all variables. The name of the variable is the key of the array.

##

<?php

function test(){
    $foo = "local variable";
    echo &#39;$foo in global scope:&#39;.$GLOBALS[&#39;foo&#39;].&#39;<br />&#39;;//$foo in global scope:Example content
    echo &#39;$foo in current scope:&#39;.$foo.&#39;<br />&#39;;//$foo in current scope:local variable
    $GLOBALS[&#39;foo&#39;] = &#39;1111&#39;;
    echo &#39;$foo in global scope:&#39;.$GLOBALS[&#39;foo&#39;].&#39;<br />&#39;;//$foo in global scope:1111}
$foo = "Example content";
test();
echo $foo.&#39;<br />&#39;;//1111

<?= = ] = $GLOBALS[] + $GLOBALS[];.$b.;

global is used to define global variables, but This global variable does not apply to the entire website, but to the current page, including all files in include or require. However, global variables defined within the function body can be used within the function body, while global variables defined outside the function body cannot be used within the function body. See the example below for details.

(1) Define global variables within the function body, which can be used within the function body.

<?php

$a = 1;
$b = 2;
function sum(){    global $a,$b;//在函数内声明为全局变量
    $b = $a + $b;
}
sum();
echo $a.&#39;---&#39;.$b.&#39;<br />&#39;;//1---3

(2) Define global variables outside the function body and cannot use them inside the function body.

$a = 1;global $a;//在函数体外把$a定义为global变量function aa(){
    echo $a;
}
aa();//会报错，不能输出变量

##$_SERVER --

$HTTP_SERVER_VARS [Deleted] — Server and execution environment information is a file containing information such as header, path, and script locations. Array of information etc. The items in this array are created by the web server. There is no guarantee that every server will offer all items; servers may ignore some, or serve items not listed here.

The following table lists the most important elements you can access in $_SERVER:

Element/Code	Description
$_SERVER['PHP_SELF']	Return the current execution The file name of the script.
$_SERVER['GATEWAY_INTERFACE']	Returns the version of the CGI specification used by the server.
$_SERVER['SERVER_ADDR']	Returns the IP address of the server where the script is currently running.
$_SERVER['SERVER_NAME']	Returns the host name of the server where the script is currently running.
$_SERVER['SERVER_SOFTWARE']	Returns the server identification string (such as Apache/2.2.24).
$_SERVER['SERVER_PROTOCOL']	Returns the name and version of the communication protocol when the page was requested (for example, "HTTP/1.0").
$_SERVER['REQUEST_METHOD']	Returns the request method used to access the page (such as POST).
$_SERVER['REQUEST_TIME']	Returns the timestamp when the request started (for example, 1577687494).
$_SERVER['QUERY_STRING']	Returns the query string, if this page is accessed through the query string.
$_SERVER['HTTP_ACCEPT']	Returns the request headers from the current request.
$_SERVER['HTTP_ACCEPT_CHARSET']	Return the Accept_Charset header from the current request (such as utf-8, ISO-8859-1)
$_SERVER['HTTP_HOST']	Return the Host header from the current request.
$_SERVER['HTTP_REFERER']	Returns the full URL of the current page (not reliable as not supported by all user agents).
$_SERVER['HTTPS']	Whether to query the script through the secure HTTP protocol.
$_SERVER['REMOTE_ADDR']	Returns the IP address of the user browsing the current page.
$_SERVER['REMOTE_HOST']	Returns the host name of the user browsing the current page.
$_SERVER['REMOTE_PORT']	Returns the port number used to connect to the web server on the user's machine.
$_SERVER['SCRIPT_FILENAME']	Returns the absolute path of the currently executing script.
$_SERVER['SERVER_ADMIN']	This value specifies the SERVER_ADMIN parameter in the Apache server configuration file.
$_SERVER['SERVER_PORT']	The port used by the Web server. The default value is "80".
$_SERVER['SERVER_SIGNATURE']	Returns the server version and virtual host name.
$_SERVER['PATH_TRANSLATED']	The base path of the file system (not the document root directory) where the current script is located.
$_SERVER['SCRIPT_NAME']	Returns the path of the current script.
$_SERVER['SCRIPT_URI']	Returns the URI of the current page.

<?php

echo &#39;<pre class="brush:php;toolbar:false">&#39;;
print_r($_SERVER);

$_GET -- $HTTP_GET_VARS [已弃用] — HTTP GET 变量

通过 URL 参数传递给当前脚本的变量的数组。

$_POST -- $HTTP_POST_VARS [已弃用] — HTTP POST 变量

当 HTTP POST 请求的 Content-Type 是 application/x-www-form-urlencoded 或 multipart/form-data 时，会将变量以关联数组形式传入当前脚本。

$_FILES -- $HTTP_POST_FILES [已弃用] — HTTP 文件上传变量

通过 HTTP POST 方式上传到当前脚本的项目的数组。

$_COOKIE -- $HTTP_COOKIE_VARS [已弃用] — HTTP Cookies

通过 HTTP Cookies 方式传递给当前脚本的变量的数组。

$_SESSION -- $HTTP_SESSION_VARS [已弃用] — Session 变量

当前脚本可用 SESSION 变量的数组

$_REQUEST — HTTP Request 变量

$_ENV -- $HTTP_ENV_VARS [已弃用] — 环境变量

通过环境方式传递给当前脚本的变量的数组。

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