Redirect all urls
 

I recently moved a clients site from one domain to another one (let's say www.myfirstdomain.com moved to www.myseconddomain.com). Both domains are still active.
Now the first site is found by Google and some people have shortcuts.
Can I redirect all urls from the first domain to the second one?
That is* if someone types www.myfirstdomain.com/blog/id/4 it should be redirected to www.myseconddomain.com/blog/id/4
I suppose its something in .htaccess but what lines of code do this?

EDIT: it's a little more complicated. The old domain was in www.myfristdomain.com/site2
The new one is in www.myseconddomain.com/site