$_SERVER['REQUEST_URI'] - It return the URL in to access the page which is executing the script. If you need to type
http://www.example.com/product.php?id=5 to access the page then
$_SERVER['DOCUMENT_ROOT'] – Returns the root directory of the server which is specified in the configuration file of server. This variable usually returns the path like
/usr/yoursite/www in Linux and
D:/xamps/xampp/htdocs in windows.
$_SERVER['HTTP_HOST'] – Returns the host’s name as found in the http header. This variable usually returns the path like
example.com when the you find
http://example.com in browser’s address-bar and return
www.example.com when you see
http://www.example.com in the address-bar. This is quite useful when you’ve to preserve session while making online payment using PHP since session stored for
http://example.com is not same as for the
$_SERVER['HTTP_USER_AGENT'] - Returns the user agent’s (browser) detail accessing the web page. We can use
strpos($_SERVER["HTTP_USER_AGENT"],”MSIE”) to detect Microsoft Internet explorer or you can use
strpos($_SERVER["HTTP_USER_AGENT"],”Firefox”) to detect firefox browser in PHP.
$_SERVER['PHP_SELF'] - Returns the file-name of the currently executing script. Let’s suppose that you’re accessing the URL
/product.php in your script.
$_SERVER['QUERY_STRING'] – Returns the query string if query string is used to access the script currently executing. Query strings are those string which is available after “?” sign.if you use
$_SERVER['QUERY_STRING'] in the script executing the following URL
http://www.example.com/index.php?id=5&page=product then it returns
id=5&page=product in your script.
$_SERVER['REMOTE_ADDR'] – Returns the IP address of remote machine accessing the current page. But you can’t relie on
$_SERVER['REMOTE_ADDR'] to get the real IP address of client’s machine. See this article to know how to get real IP addrees in PHP.
$_SERVER['SCRIPT_FILENAME'] - Returns the absolute path of the file which is currently executing. It returns path like
var/example.com/www/product.php in Linux and path like
D:/xampp/xampp/htdocs/test/example.php in windows.