htaccess problems with redirect for no www - apache

Question

I've been trying everything to manage a redirect from www.domain.com to domain.com,
but nothing seems to work for me. I always get a redirect loop - and I've tried various things I found here or on Google.
So here is my .htaccess, maybe someone could help me figure out what I can do to redirect correctly or if there is something wrong in here.
RewriteEngine On
RewriteCond %{HTTP_HOST} ^www\.example\.com [NC]
# Redirect all to .php
# Example: example.com/hello -> example.com/hello.php
RewriteRule ^(.*)$ $1.php [L,R=301]
# show example.com/index.php always as example.com/
RewriteCond %{THE_REQUEST} ^[A-Z]{3,9}\ /index\.php\ HTTP/
RewriteRule ^index\.php$ http://example.com/ [R=301,L]
Thank you so much!
I've already spent so much time trying to figure this out.

Answer 1

You have a rule that always matches, which is responsible for the infinite redirection. I've updated your ruleset below to fix that problem and perform the redirection you mentioned at the top of the answer. Let me know if this does what you expect.
RewriteEngine On
# Redirect www.example.com to example.com
RewriteCond %{HTTP_HOST} ^www [NC]
RewriteRule ^.*$ http://example.com/$0 [R=301,L]
# This performs an external redirection? Is that what you want?
# Don't do the rewrite if we're already pointing at a file, otherwise we'll
# just redirect over and over because .* matches what we redirect to, too
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} !\.php$
RewriteRule ^.+$ $0.php [L,R=301]
# show example.com/index.php always as example.com/
RewriteCond %{THE_REQUEST} ^[A-Z]{3,9}\ /index\.php\ HTTP/
RewriteRule ^index\.php$ http://example.com/ [R=301,L]

Answer 2

The answer is Apache documentation, the documentation tell how to force usage of www. You just have to reverse the example.
RewriteCond %{HTTP_HOST} !^example\.com [NC]
RewriteCond %{HTTP_HOST} !^$
RewriteRule ^/(.*) http://example.com/$1 [L,R]