Thanks to Valdez, I have a good working script:

# inside finalorderpage.shtml
<!--#include virtual="/cgi-bin/intercept.cgi">

# intercept.cgi
#!/usr/bin/perl

use CGI;

# scripts executed via SSI don't get usual informations,
# so we must rebuild the query passed to our calling page
# using %ENV (it's a dirty trick)

my $req_uri = $ENV{REQUEST_URI};
my $query_string = substr($req_uri, index($req_uri, '?')+1);
my $q = new CGI($query_string);

print $q->header('text/html');
print $q->param('VendorTxCode');
[download]

How do I manage to get the script to print the output into the actual code, for example, if VendorTxCode = 3746887345, how can I insert the result into my SHTML page instead of just outputting the result onto the screen? This probably isn't the right way of doing it, but to get my point across, here is what I want to do:

<INPUT type="hidden" name="VendorTxCode" value="<!--#include virtual="
+/cgi-bin/joyfultoys/order/bin/intercept.cgi">">
[download]

So my HTML will look something like:

<INPUT type="hidden" name="VendorTxCode" value="3746887345">
[download]

Please excuse my lack of knowledge. I am learning fast...

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