can someone explain what this php code is doing or its purpose

Question

here is the snippit

$thisFile = str_replace('\\', '/', __FILE__);
$docRoot = $_SERVER['DOCUMENT_ROOT'];

$webRoot  = str_replace(array($docRoot, 'library/config.php'), '', $thisFile);
$srvRoot  = str_replace('library/config.php', '', $thisFile);

if i save this into test.php as a file. the section that im getting confused on is how the str_replace is makeing the $webRoot value come out to test.php

Answer 1

The variable __FILE__ is the name of the current source file, or "test.php".

Answer 2

That code will compute the absolute filesystem path ($srvRoot) and absolute URL path ($webRoot) to an application directory, I suppose, from where the current file can be addressed relatively with library/config.php.

__FILE__ is a magic constant and contains the absolute filesystem path to the file the constant is used in. $thisFile will contain that filesystem path where back-slashes are replaced by forward-slashes. $docRoot is the absolute filesystem path to the root directory that is accessible from the web.

So, for example, if __FILE__ is /var/www/htdocs/apps/foobar/library/config.php and $_SERVER['DOCUMENT_ROOT'] is /var/www/htdocs, $webRoot is /apps/foobar/ and $srvRoot is /var/www/htdocs/apps/foobar/.