How php forces users to switch to www domain names

This article mainly introduces how php forces users to redirect to www domain names, which can simulate 301 redirection and output links when head redirection fails, for more information about how php forces users to switch to www domain names, see the example in this article. Share it with you for your reference. The specific analysis is as follows:

Sometimes the www domain name and non-www domain name of the website can access the website, but this is not conducive to the indexing of search engines, will spread the weight of the web page, therefore, if you want to permanently redirect a user to a www domain name through 301 when accessing a non-www domain name, for example, the user will directly redirect to www.jb51.net when accessing jb51.net. This php code considers that the user cannot redirect through head, the link will be output on the page for users to click.

// Install info.:// Copy and paste these lines into your default index.php or// the file that get's called if a visitor comes on your // website...// read the host from the server environment$host = $_SERVER["HTTP_HOST"];// fix host name - we never now... ;-)$host = strtolower($host);$host = trim($host);// This is important: // Webbrowsers like Firefox are doing their request without// the port number like "www.jb51.net" but some other // applications send host names like "www.jb51.net:80" $host = str_replace(':80', '', $host);$host = trim($host);// if the host is not starting with www. redirect the // user to the same URL but with www :-)if ($host != 'www.jb51.net'){  // You an also change the "!=" to "==", if you want to force   // the user to use the domain name without the www.   // send status header, so that search engines or other services  // detect that this is a permanent redirect and not a temporary  header('HTTP/1.1 301 Moved Permanently');  // read the URL the user requested:  $url = isset($_SERVER["REQUEST_URI"]) ? $_SERVER["REQUEST_URI"] : '';  // redirect the user to the new destination:  header('Location: http://www.jb51.net' . $url);  // Convert "special" chars -- cause we never now... ;-)  $url = htmlspecialchars($url);  // "fallback" link, if the browser is not supporting header redirects  print 'Please click here';  // stop the script execution here  exit;}// If the domain is www.jb51.net then go on with your PHP code // of with your website...// BTW: You need to replace jb51.net trough your own domain :-D

I hope this article will help you with php programming.