SSI

A server-side include (SSI) is a variable value (for example, a file Last modified date) that a server can include in an HTML file before it sends it to the requestor. If you're creating a Web page, you can insert an include statement in the HTML file that looks like this:

     <!--#echo var="LAST_MODIFIED"-->

and the server will obtain the last-modified date for the file and insert it before the HTML file is sent to requestors.

LAST_MODIFIED is one of several environment variables that an operating system can keep track of and that can be accessible to a server program. The server administrator can make these environment variables usable when the system is set up.

A Web file that contains server-side include statements (such as the echo statement above) is usually defined by the administrator to be a file with an .shtml suffix. You can think of a server-side include as a limited form of Common Gateway Interface (CGI)  application. In fact, the CGI is not used. The server simply searches the server-side include file for CGI environment variables, and inserts the variable information in the places in the file where the include statements have been inserted.

When creating a Web site, a good idea is to ask your server administrator which environment variables can be used and whether the administrator can arrange to set the server up so that these can be handled. The administrator may be able to help you add the appropriate include statements to your HTML file.