Permanent Redirection through HTACCESS

Redirect Home Page
RedirectMatch 301 ^/$ http://mynewsite.com/

Redirect a single page
redirect 301 /old/old.html http://mynewsite.com/new.html

Redirect a entire website
Redirect 301 / http://mynewsite.com/

Redirect htm pages to php pages

RewriteEngine on
RewriteBase /
RewriteRule (.*).htm$ /$1.php 

Redirect all 404 errors
ErrorDocument 404 /404.php or ErrorDocument 404 http://mynewsite.com

Redirect the entire sub-folder
RedirectMatch 301 ^/folder/ http://mynewsite.com/