Redirect non-www to www in .htaccess

Question

I have this in my .htaccess file:

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

but whenever I

Answer 1

RewriteEngine On

RewriteCond %{HTTP_HOST} !^www\.

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

For Https

RewriteCond %{HTTPS}s ^on(s)|

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