in reply to Speed consideration
I would also recommend something like HTML::Template (or Template Toolkit) if you want to do some complex calculations/checking. But some of this can be done in SSI pretty simply. e.g.:
You can also use SSI to check to make sure that the query string matches a specific regular expression, etc. See http://httpd.apache.org/docs/mod/mod_include.html for more info.<A HREF='http://affiliateprogram.com?id=<!--#if expr="$QUERY_STRING" - +-><!--#echo var="QUERY_STRING" --><!--#else -->50<!--#endif -->">Link +</A>
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