I have a domain www.siteA.com, which uses Joomla, while the domain www.siteB.com is empty.
I would like to show the content of the domain www.siteA.com at www.siteB.com.
I tried to solve the problem first by making a domain redirection by .htaccess, but I could not show SiteA's content at SiteB.
How can you show the contents of mysiteA.com at mysiteB.com by domain masking in .htaccess?
You really should be doing this by CNAME-ing the domain, but if you really want to use .htaccess you can do what @Unkwntech suggests
Edit: It would just look like
www.siteB.com CNAME www.siteA.com
Whichever way you do it (CNAME or htaccess) you're probably going to get an SEO penalty for duplicate content.