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 variable

Content returned


The authentication method used to validate a user. See REMOTE_IDENT and REMOTE_USER.


The length of the query data (in bytes or the number of characters) passed to the CGI program through standard input.


The media type of the query data, such as text/html. See Chapter 17 for a listing of commonly used content types.


The directory from which web documents are served.


The revision of the Common Gateway Interface the server uses.


A list of the media types the client can accept.


A list of cookies defined for that URL. (See Chapter 17 for more information.)


The email address of the user making the query (many browsers do not support this variable).


The URL of the document the client points to before accessing the CGI program.


Extra path information passed to a CGI program.


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