语法: prefix = ngx.config.prefix()
环境: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua*, body_filter_by_lua*, log_by_lua*, ngx.timer., init_by_lua, init_worker_by_lua**
返回 Nginx 服务的 "prefix" 路径，它可能是由 Nginx 启动时通过可选 -p 命令行确定的，也可能是由编译 Nginx 的 ./configure 脚本中可选的 --prefix 命令行参数确定的。
该 API 在 0.9.2 版本首次引入。
English source:
syntax: prefix = ngx.config.prefix()
context: set_by_lua, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua*, body_filter_by_lua*, log_by_lua*, ngx.timer., init_by_lua, init_worker_by_lua**
Returns the Nginx server "prefix" path, as determined by the -p command-line option when running the nginx executable, or the path specified by the --prefix command-line option when building Nginx with the ./configure script.
This function was first introduced in the 0.9.2.