CGI Environment Variables

In order to pass data about the information request from the server to the script, the server uses command line arguments as well as environment variables. These environment variables are set when the server executes the gateway program.

Specification

The following environment variables are not request-specific and are set for all requests:

SERVER_SOFTWARE

The name and version of the information server software answering the request (and running the gateway). Format: name/version

SERVER_NAME

The server's hostname, DNS alias, or IP address as it would appear in self-referencing URLs.

GATEWAY_INTERFACE

The revision of the CGI specification to which this server complies. Format: CGI/revision

The following environment variables are specific to the request being fulfilled by the gateway program:

SERVER_PROTOCOL

The name and revision of the information protcol this request came in with. Format: protocol/revision

SERVER_PORT

The port number to which the request was sent.

REQUEST_METHOD

The method with which the request was made. For HTTP, this is "GET", "HEAD", "POST", etc.

PATH_INFO

The extra path information, as given by the client. In other words, scripts can be accessed by their virtual pathname, followed by extra information at the end of this path. The extra information is sent as PATH_INFO. This information should be decoded by the server if it comes from a URL before it is passed to the CGI script.

PATH_TRANSLATED

The server provides a translated version of PATH_INFO, which takes the path and does any virtual-to-physical mapping to it.

SCRIPT_NAME

A virtual path to the script being executed, used for self-referencing URLs.

QUERY_STRING

The information which follows the ? in the URL which referenced this script. This is the query information. It should not be decoded in any fashion. This variable should always be set when there is query information, regardless of command line decoding.

REMOTE_HOST

The hostname making the request. If the server does not have this information, it should set REMOTE_ADDR and leave this unset.

REMOTE_ADDR

The IP address of the remote host making the request.

AUTH_TYPE

If the server supports user authentication, and the script is protects, this is the protocol-specific authentication method used to validate the user.

REMOTE_USER

If the server supports user authentication, and the script is protected, this is the username they have authenticated as.

REMOTE_IDENT

If the HTTP server supports RFC 931 identification, then this variable will be set to the remote user name retrieved from the server. Usage of this variable should be limited to logging only.

CONTENT_TYPE

For queries which have attached information, such as HTTP POST and PUT, this is the content type of the data.

CONTENT_LENGTH

The length of the said content as given by the client.

In addition to these, the header lines received from the client, if any, are placed into the environment with the prefix HTTP_ followed by the header name. Any - characters in the header name are changed to _ characters. The server may exclude any headers which it has already processed, such as Authorization, Content-type, and Content-length. If necessary, the server may choose to exclude any or all of these headers if including them would exceed any system environment limits.

An example of this is the HTTP_ACCEPT variable which was defined in CGI/1.0. Another example is the header User-Agent.

HTTP_ACCEPT

The MIME types which the client will accept, as given by HTTP headers. Other protocols may need to get this information from elsewhere. Each item in this list should be separated by commas as per the HTTP spec.

Format: type/subtype, type/subtype

HTTP_USER_AGENT

The browser the client is using to send the request. General format: software/version library/version.

Examples

Examples of the setting of environment variables are really much better demonstrated than explained.

CGI - Common Gateway Interface