Nginx 这些变量非常有用， refer to: http://wiki.nginx.org/HttpCoreModule#.24args
The core module supports built-in variables, whose names correspond with the names of variables in Apache.
First of all, there are variables which represent header lines in the client request, for example, $http_user_agent, $http_cookie, and so forth. Note that because these correspond to what the client actually sends, they are not guaranteed to exist and their meaning is defined elsewhere (e.g. in relevant standards).
Furthermore, there are other variables:
This variable contains the value of the GET request variable PARAMETER if present in the query string
This variable is the GET parameters in request line, e.g. foo=123&bar=blahblah; This variable could be changed.
The address of the client in binary form;
The amount of bytes sent as part of the body of the response. Is accurate even when connections are aborted or interrupted.
This variable is equal to line Content-Length in the header of request;
This variable is equal to line Content-Type in the header of request;
The value of the cookie COOKIE;
This variable is equal to the value of directive root for the current request;
The same as $uri.
This variable is equal to line Host in the header of request or name of the server processing the request if the Host header is not available.
This variable may have a different value from $http_host in such cases: 1) when the Host input header is absent or has an empty value, $host equals to the value of server_name directive; 2)when the value of Host contains port number, $host doesn't include that port number. $host's value is always lowercase since 0.8.17.
Set to the machine's hostname as returned by gethostname
The value of the HTTP request header HEADER when converted to lowercase and with 'dashes' converted to 'underscores', e.g. $http_user_agent, $http_referer...;
Evaluates to "?" if $args is set, "" otherwise.
This variable allows limiting the connection rate.
The version of Nginx that the server is currently running;
The same as $args except that this variable is readonly.
The address of the client.
The port of the client;
This variable is equal to the name of user, authenticated by the Auth Basic Module;
This variable is equal to path to the file for the current request, formed from directives root or alias and URI request;
This variable(0.7.58+) contains the body of the request. The significance of this variable appears in locations with directives proxy_pass or fastcgi_pass.
Client request body temporary filename;
Set to "OK" if request was completed successfully. Empty if request was not completed or if request was not the last part of a series of range requests.
This variable is equal to the method of request, usually GET or POST.
This variable always evaluates to the method name of the main request, not the current request, when the current request is a subrequest.
This variable is equal to the *original* request URI as received from the client including the args. It cannot be modified. Look at $uri for the post-rewrite/altered URI. Does not include host name. Example: "/foo/bar.php?arg=baz"
The HTTP scheme (i.e. http, https). Evaluated only on demand, for example:
rewrite ^ $scheme://example.com$uri redirect;
The value of the HTTP response header HEADER when converted to lowercase and with 'dashes' converted to 'underscores', e.g. $sent_http_cache_control, $sent_http_content_type... .
The server address. Generally nginx makes a system call to obtain this value. To improve efficiency and avoid this system call, specify an address with the listen directive and to use the bind parameter.
The name of the server.
This variable is equal to the port of the server, to which the request arrived;
This variable is the protocol of the request. Common examples are: HTTP/1.0 or HTTP/1.1
This variable is the current request URI, without any arguments (see $args for those). This variable will reflect any modifications done so far by internal redirects or the index module. Note this may be different from $request_uri, as $request_uri is what was originally sent by the browser before any such modifications. Does not include the protocol or host name. Example: /foo/bar.html