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

I believe the top answer successfully redirects non-www to www (ex: mysite.com -> www.mysite.com), but doesn't take into account wildcard subdomains, which results in:

random.mysite.com -> www.random.mysite.com

Here's a solution with/without HTTPS

HTTP

RewriteEngine On

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

HTTP/HTTPS

RewriteEngine On

RewriteCond %{HTTPS} =on
RewriteRule ^(.*)$ - [env=protocol:https]

RewriteCond %{HTTPS} !=on
RewriteRule ^(.*)$ - [env=protocol:http]

RewriteCond %{HTTP_HOST} !www.mysite.com$ [NC]
RewriteRule ^(.*)$ %{ENV:protocol}://www.mysite.com/$1 [L,R=301]

*note: I haven't tested https because I don't currently have a cert to test, but if someone can verify or optimize what I have that would be awesome.