nginx用正则表达式实现泛域名自动匹配目录的方法

最基本的写法是server{
listen 80;
server_name www.a.com;
root /html/a;
…
}
server{
listen 80;
server_name www.b.com;
root /html/b;
…
}

server {
 listen 80;
 # $subdomain 将匹配到二级域名级以上
 # $domain 将匹配到一级域名
 # $tld 将匹配到根节点名
 server_name ~^((?<subdomain>.*)\.)?(?<domain>[^.]+)\.(?<tld>[a-zA-Z]+)$;
 #如果没有$subdomain，则跳转到www
 if ($subdomain = "") {
  # set $subdomain "_";
  set $subdomain "www";
  return 301 $scheme://www.$domain.$tld$request_uri;
 }
 root /usr/share/nginx/html/${domain}.${tld}/${subdomain};
}