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Apache SSI - Server-side includes (SHTML) as a templating language

Tutorial Introduction
  https://httpd.apache.org/docs/2.4/howto/ssi.html
SSI Expressions
  https://httpd.apache.org/docs/2.4/expr.html

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WARNING: accessing variables in a #if changed in apache 2.4 making this
incompatible with all other implementations of SSI!

That is this
  <!-- #if expr="${var_name}" -->
produced errors in the server error log
  Could not parse expr "${var_name} in ...: Parse error near '$'

Specifically to make this work you need to replace ${var_name}
with  v(var_name)    Arrgghhhhh....

It is recommended you use  the directive
  SSILegacyExprParser on
in either <Directory> or ".htaccess" files.

Preferable the former as it only works with Apache v2.4

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I have used SHTML as a templating system for static web sites.

Basically I run a local only Apache web server, and then use curl to
convert specific SHTML pages into static HTML before uploading to the
web service provider.

This also lets me use the apache 'Fancy Directory Indexes' to generate
directory "index.html" files, for the same static web server site.

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Templated Includes

Set variables before including a template file allows you to change the
resulting HTML output.  This could be used for make a template of an array of
items in your HTML, allowing you to edit a single copy of the SHTML include.


<!--#set var="class" value="archimedean_duals" -->

<!--#set var="object" value="triakis_tetrahedron" -->
<!--#include file="object.shtml" -->

<!--#set var="object" value="triakis_octahedron" -->
<!--#set var="hart_obj" value="triakisoctahedron" -->
<!--#include file="object.shtml" -->

and so on.

Inside the "object.shtml" file I can then use these variables...

For example here is a small sub-section...

  <!--#set var="image" value="$class/$object" -->
  <TD ALIGN=center><NOBR>
  <A HREF="<!--#echo var="image" -->.jpg"
        ><IMG SRC="<!--#echo var="image" -->.gif"  WIDTH=120 HEIGHT=90
              ALIGN=middle ALT="[photo]"></A><BR>
  <!--#echo var="object" --><BR>

The "object.shtml" file include also unsets any optional variables such as
"image" and "hart_obj" at the end, so it does not effect later file template
includes.

Such optional variables can, when not defined, 'fall back' to some built-in
value if unset, such as a fixed value, or based on some other variable such as
"object".

See example of the HTML output of the above code usage in
   https://antofthy.gitlab.io/graphics/polyhedra/

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Comment your HTML, such that it is NOT included in HTML output

That is adding a comment to a SHTML document but not including
that comment in the generated HTML sent to clients.

Note   <!-- .... -->  comments are sent out, just not displayed in the HTML
displayed document.  But they ARE SENT OUT in the HTML source.

Best solution so far...

<!--#set var="comment" value="
   This is a SSI comment that is not included in the resulting
   HTML source sent to the client.  However you can NOT include
   un-escaped \" in the comment!
"-->

And optionally add, though it is not really needed.

<!--#set var="comment" value="" -->

Alturnative wrapp it in a SSI if construct

<!--#if expr="false" -->
   Everything here is NOT included in the SSI templated file
<!--#endif -->

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Test if variable is set (fall backs)

<!--#if expr="!${hart_obj}"
--><!--#set var="hart_obj" value="$object"
--><!--#endif
-->

ASIDE: Note the way we avoid including lots of empty lines in the
resulting HTML file. This extra blank lines are a pain of SSI
but not really a problem.

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Query Strings or Dynamic Web pages using SSI
https://web.archive.org/web/20091125091246/http://www.daveoncode.com/2009/10/29/

You can extract things from query strings to determine
what content to serve using something like...

<!--#if expr="$QUERY_STRING = /year=([0-9]{4})/" -->
    <!--ssi-comment: year found -->
    <!--#set var="year" value="$1" -->
<!--#else -->
    <!--ssi-comment: year NOT found -->
    <!--#set var="year" value="$DATE_LOCAL" -->
<!--#endif -->

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