Redirect non-www to www in .htaccess

Below snippet shows how to redirect a site from non-www to www

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

or

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

or

Here’s the correct solution which supports https and http:

RewriteEngine on
RewriteCond %{HTTP_HOST} !^www\.
RewriteCond %{HTTPS}s on(s)|offs()
RewriteRule ^ http%1://www.%{HTTP_HOST}%{REQUEST_URI} [NE,L,R]