How to I interpret these htaccess rewrite rules

Question

I was given a set or re-write rules for a new website. I've never used them before and I'm trying to understand what we are doing here

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

RewriteCond $1 !^(CCSFG|images|fonts|themes|robots\.txt|index\.php) [NC]  
RewriteRule ^(.*)$ /index.php/$1 [L]

If I understand this, the first ruleset

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

says:
If HTTP_HOST is anything AND
if HTTP_HOST doesn't start with www.myco.com
then
rewrite any page request to start with http://www.myco.com/, return a 301 redirect and stop processing more rules

The next ruleset

RewriteCond $1 !^(CCSFG|images|fonts|ee-system|themes|robots\.txt|index\.php) [NC]  
RewriteRule ^(.*)$ /index.php/$1 [L]

says: If the request doesn't start with CCSFG,image or fonts or, etc (non-case sensitive) then rewrite the whole request to prepend /index.php/ and stop processing more rules

Is my interpretation correct?

If so, what would be the purpose of the second ruleset? Why would I want to prepend /index.php/ to these entries?

Answer 1

Yup, pretty much exactly.

The first RewriteCond %{HTTP_HOST} . exists so as to not redirect loop someone who isn't sending a host header - it's verifying that the host header variable contains at least one character.

The prepending behavior exists to force page requests to be handled by index.php, likely for pretty URLs - the exceptions are for locations that need to be served by a physically present file.

So, for /images/image2.jpg, it's letting Apache serve the file at that location, but for /contentpage/1/2/3 it's rewriting to /index.php/contentpage/1/2/3, letting the PHP app do its thing.

Actually, it's technically rewriting to //index.php/contentpage/1/2/3; it's clear that it has a changed base (from being in an htaccess file), and it's not taking that into account for its destination.