How to redirect traffic from one post to same post on another domain?

Ok, i have an old domain using wordpress with some posts on it. Those posts are indexed very well by google but now i want to direct all the traffic from search engine to those posts to the same posts on another domain which is a bit new.

I have been searching on internet and everywhere they are talking about redirecting traffic from old domain to new domain, but i don’t want to direct an entire traffic for the domain, but only for those specific posts from old domain.

Also i am a bit newbie to .htaccess code thing. So looking for some help here.

For example
http://www.old.com/cat1/page4 to http://www.new/cat1/cat2/page7
http://www.old.com/cat3/page5 to http://www.new/cat1/cat2/page4
and so on