redirect posts to new address

Question

I've change permalink of my wordpress site from

/%category%/%postname%/

to

%postname%

I've tested this code:

RedirectMatch 301 ^/([^/]+)/([^/]+)/([^/]+)/([^/]+)/$ site.com/$4
RedirectMatch 301 ^/([^/]+)/([^/]+)/([^/]+)/$ site.com/$3

and good work for redirect posts but this code redirect categories address too and show 404 not found page.

I need to only redirect old posts address to new address. Is it possible that only the posts be redirect?

Example:

site.com\cat1\subcat\post
redirect to:
site.com\post (no problem)

my site Categories in two or three level

two level not have problem but three level:

site.com\cat1\subcat\subcat2
(Categories should not be redirect)
but redirect to:
site.com\subcat2 (and Error 404 Not Found)

Answer 1

You can probably do this with PHP.

if (!empty($_POST)) {
        header('Location: ' . $url, true, 301); 
}