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Chapter 12. CGI Overview > CGI Environment Variables

12.4. CGI Environment Variables

Much of the information needed by CGI programs is made available via Unix environment variables. Programs can access this information as they would any environment variable (e.g., via the %ENV associative array in Perl). Table 12.1 lists the environment variables commonly available through CGI. However, since servers occasionally vary on the names of environment variables they assign, check with your own server documentation for more information.

Table 12.1. CGI Environment Variables
Environment VariableContent Returned
AUTH_TYPEThe authentication method used to validate a user. See REMOTE_IDENT and REMOTE_USER.
CONTENT_LENGTHThe length of the query data (in bytes or the number of characters) passed to the CGI program through standard input.
CONTENT_TYPEThe media type of the query data, such as text/html. See Chapter 17 for a listing of commonly used content types.
DOCUMENT_ROOTThe directory from which web documents are served.
GATEWAY_INTERFACEThe revision of the Common Gateway Interface the server uses.
HTTP_ACCEPTA list of the media types the client can accept.
HTTP_COOKIEA list of cookies defined for that URL. (See Chapter 17 for more information.)
HTTP_FROMThe email address of the user making the query (many browsers do not support this variable).
HTTP_REFERERThe URL of the document the client points to before accessing the CGI program.
PATH_INFOExtra path information passed to a CGI program.
PATH_TRANSLATEDThe translated version of the path given by the variable PATH_INFO.
QUERY_STRINGThe query information passed to the program. It is appended to the URL following a question mark (?).
REMOTE_ADDRThe remote IP address from which the user is making the request.
REMOTE_HOSTThe remote hostname from which the user is making the request.
REMOTE_IDENTThe user making the request.
REMOTE_USERThe authenticated name of the user making the query.
REQUEST_METHODThe method with which the information request was issued (e.g., GET, POST, HEAD). See Chapter 17 for more information on request methods.
SCRIPT_NAMEThe virtual path (e.g., /cgi-bin/program.pl) of the script being executed.
SERVER_NAMEThe server's hostname or IP address.
SERVER_PORTThe port number of the host on which the server is running.
SERVER_PROTOCOLThe name and revision of the information protocol the request came in with.
SERVER_SOFTWAREThe name and version of the server software that is answering the client request.



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