Adding www to your domain with htaccess

The script below adds www to all the requests without the prefix www e.g. example.com and converts it to www.example.com

RewriteEngine On
RewriteCond %{HTTP_HOST} !^www\.
RewriteRule ^(.*)$ http://www.%{HTTP_HOST}/$1 [R=301,L]

Line one -> Switch on Rewrite Engine
Line two -> Looks for url without www and captures the rest of url
Line three -> Add the www to previous captured url and forwards the request