These are useful directives you can use in 'htaccess' files.

Also see

• http://httpd.apache.org/docs/2.0/howto/htaccess.html
• http://www.javascriptkit.com/howto/htaccess.shtml

Turn off url filtering if it interferes with executing your script

SecFilterEngine Off

Also see http://help.joyent.com/index.php?pg=kb.page&id=85

Source: http://www.techiecorner.com/106/how-to-disable-directory-browsing-using-htaccess-apache-web-server/

# Below allows browsing of directories
Options Indexes

Tells Apache how to handle files with specific extensions.

AddHandler x-httpd-php5 .php
AddHandler x-httpd-php .php4
# Also parse dhtml files by php?
AddHandler x-httpd-php .dhtml

Source: http://www.besthostratings.com/articles/force-ssl-htaccess.html
Source: http://www.forum.psoft.net/archive/index.php/t-16393.html
Source: http://www.addedbytes.com/articles/for-beginners/url-rewriting-for-beginners/
Source: https://www.cheatography.com/davechild/cheat-sheets/mod-rewrite/

## Force https secure connection.
## See https://www.cheatography.com/davechild/cheat-sheets/mod-rewrite/
RewriteEngine On
RewriteCond %{HTTPS} !=on
## HTTP_HOST is from HTTP Header (provided by client browser, can be less secure), 
## SERVER_NAME is from server internal variable (can be more secure, but make sure it is configured properly or it might not work well.
#RewriteRule ^ https://%{HTTP_HOST}%{REQUEST_URI} [NS,L,R=301] 
RewriteRule ^ https://%{SERVER_NAME}%{REQUEST_URI} [NS,L,R=301]

For explanation, see http://httpd.apache.org/docs/1.3/mod/mod_rewrite.html#RewriteRule

Alternatively, use following RewriteCond for checking port 443 instead of HTTPS

 RewriteCond %{SERVER_PORT} !=443 

Do you wish to the same by PHP?
https://secure.php.net/manual/en/function.header.php
https://www.w3schools.com/php/func_http_header.asp

<?php
if ($_SERVER[HTTPS]!="on") {
  //$strURIName=$_SERVER['SERVER_NAME'] . getenv("REQUEST_URI"); 
  // The function 'getenv' does not work if your Server API is ASAPI (IIS).
  // So, try to don't use getenv('REMOTE_ADDR'), but $_SERVER["REMOTE_ADDR"].
  $strURIName= $_SERVER['SERVER_NAME'] . $_SERVER['REQUEST_URI'];
  header ("Location: https://$strURIName");
  exit;
}

To troubleshoot your PHP code

<?php
echo "<b>_SERVER Variables from $_SERVER</b><br><br>";
reset($_SERVER);
while (list ($key, $val) = each ($_SERVER)) {
  print $key . " = " . $val . "<br>";
}

Preserves url, works for both http and https.

http://stackoverflow.com/questions/20307621/redirect-subdomain-to-folder-without-changing-url

# see http://stackoverflow.com/questions/20307621/redirect-subdomain-to-folder-without-changing-url
RewriteEngine on
RewriteBase /
RewriteCond %{HTTP_HOST} ^(www)\.domain\.com$ [NC]
RewriteRule !^www/ /www%{REQUEST_URI} [L,NC]
# L = last rule, 
# NC = No Case, case insensitive,