htaccess - redirect only non-subdomain requests - apache

Question

...except www, which is a subdomain too, of course.
This is my current htaccess rule with added comments:
RewriteEngine On
#redirect non-www to www
RewriteCond %{HTTP_HOST} !^www\.
RewriteRule ^(.*)$ http://www.%{HTTP_HOST}/$1 [R=301,L]
#what does this do?
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_URI} !^/login/
#rewrite /a/1 to /index.php?action=a&urlId=1
RewriteRule ^([^/]+)/([^/]+)/?$ index.php?action=$1&urlId=$2 [L,QSA]
#rewrite /a to /index.php?action=a
RewriteRule ^([^/]+)/?$ index.php?action=$1 [L,QSA]
Now my problem is, I added two subdomains a.domain.com and b.domain.com that point to the same directory and therefor go through the same htaccess - but they are used for direct static file-access. How can I prevent a.example.com and b.example.com to use the above rules completely?
And maybe someone could explain what this does:
#what does this do?
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_URI} !^/login/
Thanks!

Answer 1

the solution is to add a condition that check if the host is domain.com before executing the RewriteRule
RewriteCond %{HTTP_HOST} ^(www\.)?domain\.com$
regarding your second question, one or more RewriteCond directives are not seperate instructions but associated with a RewriteRule, they are conditions that must be valid to execute the RewriteRule.
in your case :
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_URI} !^/login/
RewriteRule ^([^/]+)/([^/]+)/?$ index.php?action=$1&urlId=$2 [L,QSA]
the rewriteRule is executed only if the requested uri does not point to a file, and does not begin with /login/.