The module ngx_http_core_module supports the built-in variables, whose names correspond with the names of variables in Apache.

First of all, these are the variables, which represent the lines of the title of the client request, for example, $http_user_agent, $http_cookie and so forth.

Furthermore, there are other variables:

$arg_PARAMETER, this variable contains the value of the GET request variable PARAMETER if present in the query string

$args, this variable is equal to arguments in the line of request;

$content_length, this variable is equal to line “Content-Length” in the header of request;

$content_type, this variable is equal to line “Content-Type” in the header of request;

$document_root, this variable is equal to the value of directive root for the current request;

$document_uri, the same as $uri;

$host, this variable is equal to line “Host” in the header of request or name of the server, to whom the request arrived, if there is no this line;

$is_args evaluates to “?” if $args is set, “” otherwise.

$limit_rate, the variable allows to limit connection rate;

$query_string, the same as $args;

$request_method, this variable is equal to the method of request, usually this “GET” or “POST”;

$remote_addr, this variable is equal to the address of client;

$remote_port, this variable is equal to the port of client;

$remote_user, this variable is equal to the name of user, authenticated by ngx_http_auth_basic_module;

$request_filename, this variable is equal to path to the file for the current request, formed from directives root or alias and URI request;

$request_body_file, client request body temporary filename;

$request_uri, this variable is equal to the complete initial URI together with the arguments;

$scheme, the HTTP scheme (http, https). Evaluated only on demand, for example:

rewrite  ^(.+)$  $scheme://example.com$1  redirect;

$server_protocol, this variable is equal to the protocol of request, usually this “HTTP/1.0″ or “HTTP/1.1″;

$server_addr, the variable is equal to the server address, to whom arrived the request. As a rule, for obtaining the value of this variable is done one system call. In order to avoid system call, it is necessary to indicate addresses in directives listen and to use parameter bind;

$server_name, this variable is equal to the name of the server, to whom arrived the request;

$server_port, this variable is equal to the port of the server, to which the request arrived;

$uri, this variable is equal to current URI in the request, it can differ from initial, for example by internal redirects, or with the use of index it is file with internal redirects.