lua 获取环境变量 os.getenv

来源：https://ketzacoatl.github.io/posts/2017-03-04-lua-and-openresty-part-4-using-envvars.html

• os.getenv("ABC")

worker_processes  1;
env DB_HOST;
env DB_USER;
env DB_PASS;
env DB_NAME;
error_log error.log;
events {
    worker_connections 1024;
}
http {
    server {
        listen        8000;
        charset       utf-8;
        charset_types application/json;
        default_type  application/json;
        location / {
            content_by_lua '
                local cjson = require "cjson"
                local pgmoon = require("pgmoon")
                local pg = pgmoon.new({
                  host     = os.getenv("DB_HOST"),
                  port     = "5432",
                  user     = os.getenv("DB_USER"),
                  password = os.getenv("DB_PASS"),
                  database = os.getenv("DB_NAME")
                })
                assert(pg:connect())
                local encode_json = require("pgmoon.json").encode_json
                local get, post, files = require "resty.reqargs"()
                assert(pg:query("INSERT INTO posts (data) VALUES(" .. encode_json(post) .. ");"))
                pg:keepalive()
                pg = nil   
                ngx.status  = ngx.HTTP_OK
                ngx.say(cjson.encode({status = "saved", msg=post}))
                return ngx.exit(ngx.HTTP_OK)
            ';
        }
    }
}