SSI is a great option if it is available to you, as already suggested, I always used PHP personally, but since PHP is not available, and if SSI is not available, there is also a JavaScript option.
The great thing about the JS option is that the server does not need support for it because include scripts are client-side. The bad thing is that if the client does not support JS in the browser, it will not work. Saying that the vast majority of website users have JS, and this is displayed by most websites in the world that use JS anyway.
Examples, the first one I found using the 2 second version of Google uses jQuery, see here . There are also some AJAX plugins that could potentially be used for this on the jQuery website, if that is the way you are interested.
Hope this helps you :-)
Ryan
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