Need Assistance for this Htaccess Rewrite Rule - .htaccess

Question

I have a problem with my .htaccess, a short explanation I would like to set http://example.com/newest on my website. However, it always redirects to http://example.com/postname. Where I just need the exact "newest" page. Here is my code:
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteBase /
RewriteRule ^[^/]+$ %{REQUEST_URI}/ [L,R=301]
RewriteRule ^/category/(.*)$ page.php?f=$1
RewriteRule ^/search/(.*)$ search.php?f=$1
RewriteRule ^(.*)/$ post.php?f=$1 <- If this is removed, my post htaccess will not work
RewriteRule ^newest/$ index.php?f=newest <- I want to execute this code
I really don't know what this is called, I have been looking for the whole stackoverflow but I did not get any answer. Please remain me if this is a duplicate question.

Answer 1

As Mohammed implied in comments, your directives are in the wrong order. The line above your "newest" rewrite is a catch-all and rewrites all requests, so the last line will never match.
http://example.com/newest
Note that your rules imply that your URLs should end in a trailing slash. So, you should be linking to http://example.com/newest/ (with a trailing slash), not http://example.com/newest, otherwise your users will get a lot of unnecessary redirects.
However, you appear to be under the belief that the RewriteCond directive applies to all the directives that follow. This is not the case. It only applies to the first RewriteCond directive. You also need some L flags to prevent further processing.
You also have a slash prefix on the "category" and "search" rewrite patterns, so these would never match in a .htaccess context.
Try something like the following instead:
RewriteEngine On
RewriteBase /
# Don't process the request further if it maps to an existing file
RewriteCond %{REQUEST_FILENAME} -f
RewriteRule ^ - [L]
# Append trailing if omitted
# Although strictly speaking this only redirects if there are no slashes at all in the URL
RewriteRule ^[^/]+$ %{REQUEST_URI}/ [L,R=301]
RewriteRule ^category/(.*)$ page.php?f=$1 [L]
RewriteRule ^search/(.*)$ search.php?f=$1 [L]
RewriteRule ^newest/$ index.php?f=newest [L]
RewriteRule ^(.*)/$ post.php?f=$1 [L]