how to modify .htaccess file to always redirect to www

Question

I would like to modify my .htaccess file so that when someone comes into my site without typing www the site always redirects them to the www version. For example, if my url is www.abc.com and they just type abc.com, I want to redirect them to abc.com.

Here is my current htaccess file:

<IfModule mod_rewrite.c>
   RewriteBase /
   RewriteEngine on
   RewriteRule    ^$ app/webroot/    [L]
   RewriteRule    (.*) app/webroot/$1 [L]  
</IfModule>

Normally I know how to do the redirect, but im having issues since it already has those few lines in there.

Answer 1

I use the code below. It can be used for any domain name. You just need to enter it in your .htaccess file.

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

(edited to have all the code in the same block)