Environment Variables

Overview Your CGI or ASP Programs may make use of a “Collection” of variables, variously called ENVIRONMENT or SERVER VARIABLES. Different variables may be set on different servers. Your server logs may be set to record these variables.

To see actual examples: http://parana.ecs.csus.edu/fall02/servervariables.asp http://sequoia.ecs.csus.edu/~harville/cgi-bin/environment.cgi

CONTENT_LENGTH The length in bytes of the returned document. USE: Perhaps the programmer wants to limit the size of the response.

CONTENT_TYPE The type of information returned. Ex: text/html USE: Perhaps the programmer wants to have different parts of the program activate depending on the content type.

DOCUMENT_ROOT The main site directory. USE: Setting up paths for dynamically generated URLs.

GATEWAY_INTERFACE The CGI version number. USE: Perhaps certain program features require a certain CGI version.

HTTP_ACCEPT Media types the client accepts.

HTTP_ACCEPT_ENCODING Methods of compression the browser understands. HTTP_ACCEPT_ENCODING = gzip, deflate

HTTP_ACCEPT_LANGUAGE HTTP_ACCEPT_LANGUAGE = en-us USE: Perhaps different files are to be served up depending on the language of the user.

HTTP_CONNECTION HTTP_CONNECTION = Keep-Alive Every request made requires that the server and client re-introduce each other. Keep-Alive is a switch that allows requests sent within a very short time to avoid this server-client bureaucracy.

HTTP_COOKIE A list of cookies the particular site (or advertising group) has control over. USE: Customer tracking, customization and other honorable or questionable activities.

HTTP_HOST The name of the machine on which the script resides. HTTP_HOST = parana

HTTP_REFERER The page that requested the current document or program. Note the correct misspelling. Referrer would be more correct, but the mistake was made and not corrected. USE: Redirection to a previous page.

HTTP_USER_AGENT The client browser version. Use: Customization or redirection based on browser type (and thus capabilities).

PATH_INFO The current virtual path. PATH_INFO = /chat/servervariables.asp Use: Recording a page name for redirection.

PATH_TRANSLATED The full absolute path on the server. PATH_INFO = /chat/servervariables.asp PATH_TRANSLATED = C:\csc123\chat\servervariables.asp ALSO: APPL_PHYSICAL_PATH = C:\csc123\chat\

QUERY_STRING This variable returns the query string: ?example=Kevin%20Harville USE: Using form or Querystring information.

REMOTE_ADDR The remote IP making the request. USE: Serving up unique pages based on the user. Companies have actually served different pages to their competitors than to their clients.

REMOTE_HOST The remote hostname or IP of the requestor.

REQUEST_METHOD I.e. GET or POST.

SCRIPT_NAME The virtual path of the current script.

SERVER_NAME Server hostname or IP

SERVER_PORT Usually 80 The “channel” incoming requests come in on.

SERVER_PROTOCOL SERVER_PROTOCOL = HTTP/1.1

SERVER_SOFTWARE SERVER_SOFTWARE = Microsoft-IIS/5.0

URL URL = /chat/servervariables.asp

Others Numerous ones exist for SSL HTTP_RAW and ALL_HTTP give long lists of the variables.

Summary Server or Environment Variables are a useful means of site customization. They allow for customers to be tracked, which may or may not be in the customer’s best interest. The allow logging of information.