htaccess redirection to particular folder - wordpress

Question

I have installed word press in the public html folder of my hosting. I have put my old codeigniter site files into "oldsite\codeigniter". But i am unable to access this code igniter website always getting page not found error from word press
Sample URL : example.com/oldsite/codeigniter
How can i redirect to sub folder if the URL contains "oldsite" or oldsite/codeigniter
RewriteEngine On
RewriteRule ^oldsite/codeigniter/(.*)$ example.com/oldsite/codeigniter/$1 [NC,R=301,L]
codeigniter htaccess file
RewriteEngine on
RewriteCond %{REQUEST_URI} !(.gif|.jpg|.png)$
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php/$1 [L]
RewriteRule codeigniter/home$
example.com/oldsite/codeigniter[L,R=301]

Answer 1

This should be a comment, but is a bit too long.
To reiterate the initial setup: Wordpress is installed in the document root, public_html. And there's an old CodeIgniter website, which is installed in public_html/oldsite/codeigniter.
There should be just two .htaccess files necessary, one for Wordpress and one for CodeIgniter. Both are taken from their respective websites, https://codex.wordpress.org/htaccess and https://codeigniter.com/user_guide/general/urls.html
# /public_html/.htaccess
# Wordpress
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
# /public_html/oldsite/codeigniter
# CodeIgniter
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php/$1 [L]
If this fails for some reason, it might be that Apache is confused because of the relative path index.php. If this is the reason, you can fix it by using an absolute path, e.g.
RewriteRule ^(.*)$ /oldsite/codeigniter/index.php/$1 [L]
or add a RewriteBase directive
RewriteBase /oldsite/codeigniter