PHP $_SERVER

$_SERVER is a superglobal that holds information regarding HTTP headers, path and script location etc. All the server and execution environment related information is available in this associative array. Most of the entries in this array are populated by web server.
PHP versions prior to 5.4.0 contained $HTTP_SERVER_VARS contained same information but has now been removed. Following are some prominent members of this array
PHP_SELF − stores filename of currently executing script. For example, a script in test folder of document root of a local server returns its path as follows −
<?php
echo $_SERVER['PHP_SELF'];
?>
This results in following output in browser with http://localhost/test/testscript.php URL
/test/testscript.php
SERVER_ADDR − This property of array returns The IP address of the server under which the current script is executing.
SERVER_NAME − Name of server hostunder which the current script is executing.In case of a erver running locally, localhost is returned
QUERY_STRING − A query string is the string of key=value pairs separated by & symbol and appended to URL after ? symbol. For example, http://localhost/testscript?name=xyz&age=20 URL returns trailing query string
REQUEST_METHOD − HTTP request method used for accessing a URL, such as POST, GET, POST, PUT or DELETE. In above query string example, a URL attached to query string wirh ? symbol requests the page with GET method
DOCUMENT_ROOT − returns name of directory on server that is configured as document root. On XAMPP apache server it returns htdocs as name of document root
C:/xampp/htdocs
DOCUMENT_ROOT − This is a string denoting the user agent (browser) being which is accessing the page.
Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/83.0.4103.116 Safari/537.36

REMOTE_ADDR − IP address of machine from which the user is viewing the current page.
SERVER_PORT − port number on which the web server is listening to incoming request. Default is 80
Following script invoked from document root of XAMPP server lists all server variables
<?php
foreach ($_SERVER as $k=>$v)
echo $k . "=>" . $v . "<br>";
?>
List of all server variables
MIBDIRS=>C:/xampp/php/extras/mibs
MYSQL_HOME=>\xampp\mysql\bin
OPENSSL_CONF=>C:/xampp/apache/bin/openssl.cnf
PHP_PEAR_SYSCONF_DIR=>\xampp\php
PHPRC=>\xampp\php
TMP=>\xampp\tmp
HTTP_HOST=>localhost
HTTP_CONNECTION=>keep-alive
HTTP_CACHE_CONTROL=>max-age=0
HTTP_DNT=>1
HTTP_UPGRADE_INSECURE_REQUESTS=>1
HTTP_USER_AGENT=>Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/84.0.4147.135 Safari/537.36
HTTP_ACCEPT=>text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9
HTTP_SEC_FETCH_SITE=>none
HTTP_SEC_FETCH_MODE=>navigate
HTTP_SEC_FETCH_USER=>?1
HTTP_SEC_FETCH_DEST=>document
HTTP_ACCEPT_ENCODING=>gzip, deflate, br
HTTP_ACCEPT_LANGUAGE=>en-US,en;q=0.9,mr;q=0.8
PATH=>C:\python37\Scripts\;C:\python37\;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;C:\Windows\System32\OpenSSH\;C:\Program Files (x86)\AMD\ATI.ACE\Core-Static;C:\python37\Scripts\;C:\python37\;C:\Users\User\AppData\Local\Microsoft\WindowsApps;C:\Users\User\AppData\Local\Programs\MiKTeX 2.9\miktex\bin\x64\;C:\MicrosoftVSCode\bin
SystemRoot=>C:\Windows
COMSPEC=>C:\Windows\system32\cmd.exe
PATHEXT=>.COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.MSC;.PY;.PYW
WINDIR=>C:\Windows
SERVER_SIGNATURE=>
Apache/2.4.41 (Win64) OpenSSL/1.0.2s PHP/7.1.32 Server at localhost Port 80

SERVER_SOFTWARE=>Apache/2.4.41 (Win64) OpenSSL/1.0.2s PHP/7.1.32
SERVER_NAME=>localhost
SERVER_ADDR=>::1
SERVER_PORT=>80
REMOTE_ADDR=>::1
DOCUMENT_ROOT=>C:/xampp/htdocs
REQUEST_SCHEME=>http
CONTEXT_PREFIX=>
CONTEXT_DOCUMENT_ROOT=>C:/xampp/htdocs
SERVER_ADMIN=>postmaster@localhost
SCRIPT_FILENAME=>C:/xampp/htdocs/testscript.php
REMOTE_PORT=>49475
GATEWAY_INTERFACE=>CGI/1.1
SERVER_PROTOCOL=>HTTP/1.1
REQUEST_METHOD=>GET
QUERY_STRING=>
REQUEST_URI=>/testscript.php
SCRIPT_NAME=>/testscript.php
PHP_SELF=>/testscript.php
REQUEST_TIME_FLOAT=>1599118525.327
REQUEST_TIME=>1599118525