Server-side includes are a simple way of generating documents that are the same apart from a small dynamic part (such as a page access counter). The HTTP server needs to be configured to accept them.
A tutorial is at
http://www.onlinecomputersciencedegree.com/ .
Most commonly used is the exec
command
<!--#exec cmd="..." -->
The command in "..." will be given to /bin/sh
to execute. e.g.
<!--#exec cmd="/bin/date" -->
will include today's date in the document.