[Chapter 5] 5.3 Environment Variables

5.3 Environment Variables

As I mentioned before, you can insert the values of environment variables in an otherwise static HTML document. Here is an example of a document that contains a few SSI directives:

<HTML>
<HEAD><TITLE>Welcome!</TITLE></HEAD>
<BODY>
<H1>Welcome to my server at <!--#echo var="SERVER_NAME"-->...</H1>
<HR>
Dear user from <!--#echo var="REMOTE_HOST"-->,
<P>
There are many links to various CGI documents throughout the Web,
so feel free to explore.
    .
    .
    .
<HR>
<ADDRESS>Shishir Gundavaram (<!--#echo var="DATE_LOCAL"-->)</ADDRESS>
</BODY></HTML>

SSI directives have the following format:

<!--#command parameter="argument"-->

In this example, the echo SSI command with the var parameter is used to display the IP name or address of the serving machine, the remote host name, and the local time. Of course, we could have written a CGI program to perform the same function, but this approach is much quicker and easier, as you can see.

All environment variables that are available to CGI programs are also available to SSI directives. There are also a few variables that are exclusively available for use in SSI directives, such as DATE_LOCAL, which contains the current local time. Another is DATE_GMT:

The current GMT time is: <!--#echo var="DATE_GMT"-->

which contains the Greenwich Mean Time.

Here is another example that uses some of these exclusive SSI environment variables to output information about the current document:

<H2>File Summary</H2>
<HR>
The document you are viewing is titled:  <!--#echo var="DOCUMENT_NAME"-->,
and you can access it a later time by opening the URL to:
<!--#echo var="DOCUMENT_URI"-->. Please add this to your bookmark list.
<HR>
Document last modified on <!--#echo var="LAST_MODIFIED"-->.

This will display the name, URL (although the variable is titled DOCUMENT_URI), and modification time for the current HTML document.

For a listing of CGI environment variables, see Table 2.1. Table 5.2 shows additional SSI environment variables.

Table 5.2: Additional SSI Environment Variables
Environment Variable	Description
DOCUMENT_NAME	The current file
DOCUMENT_URI	Virtual path to the file
QUERY_STRING_UNESCAPED	Undecoded query string with all shell metacharacters escaped with "\"
DATE_LOCAL	Current date and time in the local time zone
DATE_GMT	Current date and time in GMT
LAST_MODIFIED	Last modification date and time for current file