Using Server Side Includes (SSI)

Server Side Includes applied to a HTML document, provide for interactive real-time features such as echoing current time, conditional execution based on logical comparisons, querying or updating a database, sending and email, without programming or CGI scripts.  An SSI consists of a special sequence of characters or 'tokens' embedded within a HTML page.  As the page is sent by the server, the page is scanned for special these tokens.  When a token is found the server interprets the data in the token and performs an action based on the token data.

All documents containing SSI's must have the file extension .shtml - this is necessary so that the server knows to parse through the document, find the SSIs and send the appropriate information back to the client.

The format of a SSI token is as follows:

<!--#'<tag><variable set>'--> where

• <!-- is the opening identifier

• <tag> is one of the following: echo, include, fsize, flastmod, exec, config, odbc, email, if, goto, label, break.

• <variable set> is a set of one or more variables and their values and are dependent on the tag

• -->  is the closing identifier

However, having the server parse documents is a double edged sword. It can be costly for servers to perform parsing of files while sending them and should therefore only be used where necessary such as having a last modified date or a text counter.

Further information on SSIs can be found at the NCSA and the ApacheWeek web sites.

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