Perl in a Nutshell, 2nd Edition

CGI Environment Variables

Most 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 (via the %ENV hash in Perl). The table below lists 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.

Environment variable	Content returned
AUTH_TYPE	The authentication method used to validate a user. See REMOTE_IDENT and REMOTE_USER.
CONTENT_LENGTH	The length of the query data (in bytes or the number of characters)passed to the CGI program through standard input.
CONTENT_TYPE	The media type of the query data, such as text/html.
DOCUMENT_ROOT	The directory from which web documents are served.
GATEWAY_INTERFACE	The revision of the Common Gateway Interface that the server uses.
HTTP_ACCEPT	A list of the media types that the client can accept.
HTTP_COOKIE	A list of cookies defined for that URL.
HTTP_FROM	The email address of the user making the query (many browsers do not support this variable).
HTTP_REFERER	The URL of the document the client read before accessing the CGI program.
HTTP_USER_AGENT	The browser the client is using to issue the request.
PATH_INFO	Extra path information passed to a CGI program.
PATH_TRANSLATED	The translated version of the path given by the variable PATH_INFO.
QUERY_STRING	The query information passed to the program. It is appended ...