Nginx: conditional "expires" directive

[somebi]

I like your solution. But i'm getting error:

nginx: [emerg] "expires" directive invalid value in
/usr/local/nginx/conf/nginx.conf:131
nginx: configuration file /usr/local/nginx/conf/nginx.conf test failed

When using expires 							$caching_expires;

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,213841,213844#msg-213844