How to Redirect Subdomains to Other Domain

What I'm trying to accomplish with htaccess mod-rewrite:

Redirect all sub-domains to new domain name w rewrite rule.

e.g.

test1.olddomain.com ===> test1.newdomain.com

test2.olddomain.com ===> test2.newdomain.com

test3.olddomain.com ===>开发者_运维知识库 test3.newdomain.com

This is what I have so far which of course is wrong:

Options +FollowSymLinks
RewriteEngine on
RewriteCond %{HTTP_HOST} ^olddomain\.com$ [NC]
RewriteRule ^(.*)$ http://www.newdomain.com/$1 [R=301,L]

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

RewriteRule [a-zA-Z]+\.olddomain.com$ http://$1.newdomain.com/ [R=301,L]

Since I'm not a Regular Expression junkie just yet, I need your help... Thanks for any help you can give here. I know also we can compile these first two conditions into one.

Note: The reason I don't redirect all domain using DNS is that a lot of directories need special rewrite rules in order to maintain positions on SEO.

In .htaccess files, the "URL" that RewriteRules match has been stripped of the domain name and any directories that led to the current directory. (Using mod_rewrite in .htaccess files is a huge pain; if you have access to the server conf do it there instead!!)

So, assuming that your .htaccess is in your DocumentRoot, try something like this:

RewriteEngine on
RewriteCond %{HTTP_HOST} ^(.*)olddomain\.com$ [NC]
RewriteRule ^(.*)$ http://%1newdomain.com/$1 [R=301,L]

The %1 is supposed to match the first group in the RewriteCond and the $1 is supposed to match the URL part.

RewriteRule ^(.+)\.olddomain\.com$ http://$1.newdomain.com/ [R=301,L]

You need to specify the ^ at the beginning to ask the regex engine to match a line beginning there. Next, you match anything before ".olddomain.com" and assign that to the first matched pattern (which will later be accessible in $1). You need to surround with parentheses (.+) in order for the match to be assigned to $1.