RewriteRule: ^ vs ^(.*)$ vs ^.*$ Is there a Difference? - regex

Question

What is the difference in using ^ vs ^(.*)$ vs ^.*$ as wildcards in a RewriteRule?
My goal is to redirect http://carnarianism.com/ (anything) to the landing (default) page of http://carnarian.com/. I have found the following solutions, which all seem to work, so I wonder which is better for performance?
RewriteRule ^ http://carnarian.com/ [R=301,L]
RewriteRule ^.*$ http://carnarian.com/ [R=301,L]
RewriteRule ^(.*)$ http://carnarian.com/ [R=301,L]
All of these seem to work okay. This is my very first post on StackOverflow, most of the time I can find an answer just searching for it.
To be clear: ABOVE the questioned RewriteRule in my .htaccess is a RewriteCond and WWW Handler as follows:
RewriteEngine On
RewriteBase /
# FROM www. --TO-- NO www. See no-www.org
RewriteCond %{HTTP_HOST} ^www\.(.+)$ [NC]
RewriteRule ^(.*)$ http://%1/$1 [R=301,L]
RewriteCond %{HTTP_HOST} carnarianism\.com$ [NC]
########## The Above Questioned RewriteRule ??? ##########
RewriteRule ^ http://carnarian.com/ [R=301,L]
Note: I started this search with the following, but I did not want the following because the path was also passed, and I want it to go to the landing page only. Therefore, I know you need the parentheses to be able to use the $1 variable. I do not want the $1 variable.
RewriteRule ^(.*)$ http://carnarian.com/$1 [R=301,L]

Answer 1

^ makes none of the original URL accessible as backreferences. $0 is an empty string.
^.*$ makes the entire original URL accessible as the $0 backreference (so you can do e.g. http://example.com/oldurl.php?url=$0)
^(.*) makes the entire original URL accessible as both the $0 and $1 backreferences; it's usually used when you want to actually use the old URL in the replacement since it's more explicit about the use.
All of them match the same thing, but produce different backreference groups.

Answer 2

The one that is better performance wise is the one you have benchmarked yourself.
But since you are using a .htaccess file rather than having this configuration in the server directly (maybe via a VirtualHost?) which is parsed only once, it really doesn't matter. Parsing .htaccess files at every single request is much more time consuming than performing the regular expression by a factor of thousands.
If you care about performance you should never ever use .htaccess files and even disable their parsing with: AllowOverride None. Not disabling them, and having a request like: http://example.com/sites/css/theme/main.css Apache will still try to load all the following files:
.htaccess
sites/.htaccess
sites/css/.htaccess
sites/css/theme/.htaccess
It will generate system calls even if those file does not exist.
Trying therefore to improve your RewriteRule in an .htaccess file is like sneezing in the ocean in the hope of making it less salty. :)
Now, if you improved your setup to use server configuration and to answer your original question: ^.*$ might be more efficient than ^(.*)$ as less references needs to be created. Chance is high, however, that you can't measure it.