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Echoing server information such as user IP, current date etc using SSI

Another common and practical usage of SSI is to display basic information about your server or your visitors, such as the last modified date of the webpage, current server time, visitor IP address etc. These are all tasks that client side languages such as JavaScript cannot accomplish, but can be done using the #echo command of SSI.. Here's a quick overview of some of variables you can use with SSI's #echo to display useful information:

DATE_GMT The current server date, in Greenwich mean time. Format using #config.
DATE_LOCAL The current server date. Format using #config.
DOCUMENT_NAME The file name of the current document.
DOCUMENT_URI The virtual path of the current document.
LAST_MODIFIED The last modified date of the document. Format using #config.
HTTP_REFERER URL of the document the client derived from to get to current document.
REMOTE_ADDR IP address of the visitor.
#flashmod Command to display last modified date/time of a document or file on the server. Format using #config.
#fsize Command to display file size of a document or file. Format using #config.

To echo something using SSI, the syntax is:

<!--#echo var="VARIABLE HERE" -->

Lets see how to use these variables exactly.

Echo current server date and time

To display the current server date and time, use either the "DATE_GMT" or "DATE_LOCAL" variable. In its simplest form:

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

Output: Wednesday, 19-Jun-2013 17:42:21 MDT

Not bad eh for one simple line of code.

Echo last modified date of current document or file

It's very useful at times to show the last modified date of a web page:

This document last modified: <!--#echo var="LAST_MODIFIED" -->

Output: This document last modified: Saturday, 04-Mar-2006 01:41:24 MST

Echo last modified date of any document or file

You can also display the last modified date of any document or file on your server besides the present, by using another command called #flastmod instead of #echo:

greenday.mp3 last modified: <!--#flastmod file="grenday.mp3"-->
Index page last modified: <!--#flastmod virtual="/index.html"-->

Sample output: greenday.mp3 last modified Thursday, 06-Jan-2005 05:35:27 EST.

Echoing visitor IP address

This is also a commonly requested question and answer- how to display the user's IP address:  

Your IP: <!--#echo var="REMOTE_ADDR" -->

Output: Your IP: 50.16.132.180

Displaying file size of a document

Finally, you can display the file size of any document on your server using #echo, by using a different command called #fsize.

This document's file size: <!--#fsize file="current.shtml" -->
The file size of main index page: <!--#fsize virtual="/index.shtml" -->

Sample output: This document's file size: 8.4K

Interesting Uses of SSI

The interesting thing to note about using the output commands of SSI is that they can be embedded anywhere inside your HTML source, even in unexpected places to do interesting things. For example, you can use SSI echo to populate a JavaScript variable with the visitor's IP address, then continue to use JavaScript to react accordingly:

<script type="text/javascript">
var userIP="<!--#echo var="REMOTE_ADDR" -->"
if (userIP=="list of bad IPs to check")
alert("You are not allowed on this site.")
</script>

Another unconventional usage is to pass the current server time to the JavaScript Date object, then use JavaScript to display the current live time of your server:

var currentime="<!--#echo var="DATE_LOCAL" -->"
var serverdate=new Date(currenttime)
//rest of script

Here's a completed example.