8 Useful server variables available in PHP

Set your Server Variable name in Dreamweaver as the part between the square brackets.
e.g. $_SERVER['HTTP_HOST'] you need to set as HTTP_HOST

When you use it as a dynamic variable it will be entered into your script or email as {SERVER.HTTP_HOST}

1. $_SERVER['REQUEST_URI']
   It returns 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['REQUEST_URI'] returns /product.php?id=5″.
2. $_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.
3. $_SERVER['HTTP_HOST']
   Returns the host’s name as found in the http header.
   This variable usually returns the path like example.com when you find http://example.com in browsers 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 an online payment using PHP since session stored for http://example.com is not same as for the http://www.example.com.
4. $_SERVER['HTTP_USER_AGENT']
   Returns the user agents (browser) detail accessing the web page.
   We can use strpos($_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.
5. $_SERVER['PHP_SELF']
   Returns the file-name of the currently executing script.
   Let’s suppose that you’re accessing the URL http://www.example.com/product.php?id=5 then $_SERVER['PHP_SELF'] returns /product.php in your script.
6. $_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 the ? 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.
7. $_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.
8. $_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.