If you want to redirect your domain name to sub-directory but the url shows only domain name
For example :
http://yourdomain.com redirect to
http://yourdomain.com/blog but the URL shows only
http://yourdomain.comThen add the following rules in your .htaccess file.
<IfModule mod_rewrite.c>
RewriteEngine on
RewriteCond %{HTTP_HOST} ^yourdomain.com
RewriteRule ^(.*)$ http://www.yourdomain.com/$1 [R=301,L]
RewriteRule ^$ blog/ [L]
RewriteRule (.*) blog/$1 [L]
</IfModule>