How To Prevent Duplicate Content

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How To Prevent Duplicate Content?

Example:

http://codeigniter.com/index.php

no redirect to:

http://codeigniter.com/

My .htaccess:

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /

#remove www. from the uri and redirect with a 301 code.
RewriteCond %{HTTP_HOST} .
RewriteCond %{HTTP_HOST} !^example\.com
RewriteRule ^(.*)$ http://example.com/$1 [R=301,L]

#rewrite uri if its not a file to index.php
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.+)$ /index.php/$1

</IfModule>