RewriteRule subtle differences - one in the same? - .htaccess

Question

I'm trying to better understand mod_rewrite and I've come across some differences, which I think do the same thing? In this case, no existing files or directories and rewriting to an index.php page.
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule .+ - [L]
Do I need the [OR] or can I leave it off?
What are the differences or advantages of the following rules? I'm currently using the first one, but I've come across the last four in places like WordPress:
#currently using
RewriteRule ^(.+)$ index\.php?$1 [L]
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]

Answer 1

Do I need the [OR] or can I leave it off?
In this case you need the [OR] because RewriteCond's are inherently ANDed, and it's not the case that a request is both a file and a directory (as far as mod_rewrite is concerned).
RewriteRule ^(.+)$ index\.php?$1 [L]
This rewrites all requests that aren't for the document root (e.g. http://domain.com/) as a query string for index.php, thus a request for http://domain.com/some/path/file.html gets internally rewritten to index.php?some/path/file.html
RewriteRule ^index\.php$ - [L]
This is a rule to prevent rewrite looping. The rewrite engine will continue to loop through all the rules until the URI is the same before the rewrite iteration and after (without the query string). If the URI starts with index.php simply stop the current rewrite iteration (what the - does). The rewrite engine sees that the URI before sending it through the rules was index.php and after the rules was index.php, thus the rewrite engine stops and all rewriting is done. This prevents mod_rewrite from rewriting things to index.php?index.php which the first rule would do upon the 2nd pass through the rewrite engine if it isn't for this rule.
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
This is the catch-all. If the first rule never gets applied, and the request isn't for an existing file or directory, send the request to index.php. Though in this case, it looks like this rule will never get applied.
EDIT:
is there a way to ignore a certain rule if a condition is true? For example, www.domain.com/some/path > index.php?some/path, but if the URI is www.domain.com/this/path > no rewrite?
You'd have to add 2 conditions, one that checks to make sure the requested host isn't "www.domain.com" and one to check that the URI isn't "/this/path":
RewriteCond %{HTTP_HOST} !^(www\.)?domain\.com$ [NC,OR]
RewriteCond %{REQUEST_URI} !^/some/path
The [NC] indicates that the condition's match should ignore case, so when someone enters the URL http://WWW.domain.com/ in their address bar, it will match (or in this case, not match). The second condition matches when the URI starts with "/some/path", which means requests for http://domain.com/some/path/file.html will match and NOT get rewritten. If you want to match exactly "/some/path", then the regular expression needs to be !^/some/path$.
Why not use [OR] in the final block between !-f and !-d?
This is the logical negation of -f OR -d: "if the file exists, don't rewrite, OR if the directory exists, don't rewrite" turns into "if the file doesn't exist, AND if the directory doesn't exist, then rewrite"