Environment Variables with SSI.

author: jim.cerny@unh.edu

This illustrates a complete list of environment variables.

Background.

Environment variables are used to exchange information between a Web server and browser. There is a standardized list of these developed for CGI (Common Gateway Interface) scripting. SSI supports those plus a few additional ones. Some of the CGI environment variables provide information about the server, but most provide information about the browser. Ways that this information is commonly used include the activity logging done by Web servers (captures browser IP address, browser id string, etc.) and by Web authors who use JavaScript to make decisions (type of browser, plug-ins available, or to read-write cookies).

Environment Variables.

You can get a block of reported environment variables with the directive.

   <!--#printenv -->

SCRIPT_URL=/NIS/Courses/SSI/environ-vars.html SCRIPT_URI=http://unhinfo.unh.edu/NIS/Courses/SSI/environ-vars.html HTTP_HOST=unhinfo.unh.edu HTTP_USER_AGENT=CCBot/1.0 (+http://www.commoncrawl.org/bot.html) HTTP_ACCEPT=Accept: application/xhtml+xml,text/html;q=0.9,text/plain; HTTP_ACCEPT_LANGUAGE=en-us,en;q=0.5 HTTP_ACCEPT_ENCODING=gzip HTTP_ACCEPT_CHARSET=ISO-8859-1,utf-8;q=0.7,*;q=0.7 HTTP_CONNECTION=close HTTP_CACHE_CONTROL=no-cache HTTP_PRAGMA=no-cache PATH=/sbin:/usr/sbin:/bin:/usr/bin:/usr/X11R6/bin SERVER_SIGNATURE=<address>Apache/2.0.52 (Red Hat) Server at unhinfo.unh.edu Port 80</address> SERVER_SOFTWARE=Apache/2.0.52 (Red Hat) SERVER_NAME=unhinfo.unh.edu SERVER_ADDR=132.177.132.98 SERVER_PORT=80 REMOTE_ADDR=38.103.63.61 DOCUMENT_ROOT=/usr/local/web/data SERVER_ADMIN=cwis.admin@unh.edu SCRIPT_FILENAME=/usr/local/web/data/NIS/Courses/SSI/environ-vars.html REMOTE_PORT=52939 GATEWAY_INTERFACE=CGI/1.1 SERVER_PROTOCOL=HTTP/1.1 REQUEST_METHOD=GET QUERY_STRING= REQUEST_URI=/NIS/Courses/SSI/environ-vars.html SCRIPT_NAME=/NIS/Courses/SSI/environ-vars.html DATE_LOCAL=August 28, 2008 DATE_GMT=August 28, 2008 LAST_MODIFIED=August 17, 1999 DOCUMENT_URI=/NIS/Courses/SSI/environ-vars.html USER_NAME=unhinfo DOCUMENT_NAME=environ-vars.html

Instead you would probably use one or a few environment variables selectively, integrated in your overall page design. One way is just for annotation to automatically include date, URL, or other information on your pages, probably in the headers or footers. Another way is in some simple kinds of flow control (see source in flow-auth.txt) to customize the material presented.

This alphabetic list of SSI environment variables is assembled from an NCSA CGI list, plus the Apache extensions as documented and inferred from the "printenv" directive (see above). When reading any discussions of SSI, remember that while many servers support many variables, the specific list is dependent on the server and its release version. Remember, too, that these variables were developed for a programming environment and we've disabled the SSI "exec" directive for calling scripts. Detailed discussion of that kind of environment is available in books such as CGI Programming by Shishir Gundavaram.

• AUTH_TYPE
  If the server supports user authentication, and the script is protected, this is the protocol-specific authetnication method used to validate the user.
  (none)

• CONTENT_LENGTH
  Length of the content as given by the client.
  (none)

• CONTENT_TYPE
  For queries which have attached information (e.g., POST and PUT), this is the content type of the data.
  (none)

• DATE_GMT
  The current date in Greenwich Mean Time.
  August 28, 2008

• DATE_LOCAL
  The current date in the local time zone.
  August 28, 2008

• DOCUMENT_NAME
  The filename (excl. directories) of requested document.
  environ-vars.html

• DOCUMENT_ROOT
  Directory on the server in which Web documents are located or "rooted".
  /usr/local/web/data

• DOCUMENT_URI
  The URL path of the requested document. Affected by nesting of SSIs.
  /NIS/Courses/SSI/environ-vars.html

• GATEWAY_INTERFACE
  Revision of the CGI specification to which the server complies.
  CGI/1.1

• HTTP_ACCEPT
  The MIME types which the client will accept.
  Accept: application/xhtml+xml,text/html;q=0.9,text/plain;

• HTTP_ACCEPT_ENCODING
  
  gzip

• HTTP_ACCEPT_LANGUAGE
  Language setting for the browser.
  en-us,en;q=0.5

• HTTP_CONNECTION
  
  close

• HTTP_HOST
  
  unhinfo.unh.edu

• HTTP_REFERER
  The URL of the document that the client points to before accessing this page or script.
  (none)

• HTTP_USER_AGENT
  The browser identification string.
  CCBot/1.0 (+http://www.commoncrawl.org/bot.html)

• LAST_MODIFIED
  Last modification date of the requested document.
  August 17, 1999

• PATH
  
  /sbin:/usr/sbin:/bin:/usr/bin:/usr/X11R6/bin

• PATH_INFO
  Extra path information, as given by the client, for decoding by the server before passing to a CGI script.
  (none)

• PATH_TRANSLATED
  The PATH_INFO after the server does any virtual to physical mapping of it.
  (none)

• QUERY_STRING
  Information which follows the "?" in the URL referencing a script.

• REMOTE_ADDR
  The IP adddress of the remote host making the request.
  38.103.63.61

• REMOTE_PORT
  
  52939

• REMOTE_HOST
  Host name making the request to the server.
  (none)

• REMOTE_IDENT
  If the HTTP server supports RFC 931 identification then this variable will be set to the remote user name retrieved from the server.
  (none)

• REMOTE_USER
  If the server supports user authentication, and the script is protected, this is the username they have authenticated as.
  (none)

• REQUEST_URI
  The file identifier requested.
  /NIS/Courses/SSI/environ-vars.html

• REQUEST_METHOD
  Method of request, which for HTTP is GET, HEAD, or POST.
  GET

• SCRIPT_FILE_NAME
  
  (none)

• SCRIPT_NAME
  Virtual path to the script being executed, used for self-referencing URLs.
  /NIS/Courses/SSI/environ-vars.html

• SCRIPT_URI
  
  http://unhinfo.unh.edu/NIS/Courses/SSI/environ-vars.html

• SCRIPT_URL
  
  /NIS/Courses/SSI/environ-vars.html

• SERVER_ADMIN
  E-mail address of the server sysadmin.
  cwis.admin@unh.edu

• SERVER_NAME
  Server's hostname, DNS alias, or IP address as appearing in self-referencing URLs.
  unhinfo.unh.edu

• SERVER_PORT
  Server port for Web traffic (default=80).
  80

• SERVER_PROTOCOL
  Name and revision of the information protocol this request came in with.
  HTTP/1.1

• SERVER_SOFTWARE
  Name and version of the server software.
  Apache/2.0.52 (Red Hat)

• USER_NAME
  Process uname nder which the server software runs.
  unhinfo