1. Environment Variables

2. 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.

3. To see actual examples:

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

5. 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.

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

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

8. HTTP_ACCEPT
Media types the client accepts.

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

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

11. 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.

12. 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.

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

14. 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.

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

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

17. 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\

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

19. 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.

20. REMOTE_HOST
The remote hostname or IP of the requestor.

21. REQUEST_METHOD
I.e. GET or POST.

22. SCRIPT_NAME
The virtual path of the current script.

23. SERVER_NAME
Server hostname or IP

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

25. SERVER_PROTOCOL
SERVER_PROTOCOL = HTTP/1.1

26. SERVER_SOFTWARE
SERVER_SOFTWARE = Microsoft-IIS/5.0

27. URL
URL = /chat/servervariables.asp

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

29. 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.