proxy_cache_bypass and proxy_no_cache

[amodpandey]

I want to proxy_cache responses only with a specific cookie in request.

I thought to use

proxy_cache_bypass    ! $cookie_cache;
proxy_no_cache            ! $cookie_cache;

That ( ! ) does not work. 

One more question, why we need to have proxy_cache_bypass and proxy_no_cache
else
nginx: [warn] "proxy_no_cache" functionality has been changed in 0.8.46, now
it should be used together with "proxy_cache_bypass"

Help Please!

Regards
Amod

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,233778,233778#msg-233778