map $uri $match {
~^/common/file/dachui/(.*) /dachui/;
}
$match 为 /dachui/
$uri nginx内置变量
假如 $uri 为 /common/file/dachui/20170427160407.jpg
正则匹配后 $1 为 20170427160407.jpg
$match$1 为 dachui/20170427160407.jpg 要放一起用,否则$1不生效
http://www.ttlsa.com/nginx/using-nginx-map-method/