I am loading a perl script that creates 2 arrays - 1 with a list of id's for classes offered and another with # of students already registered for each class (from a flat file that already exists)

How can I reference the array values generated by the cgi scipt in javascript?

Overall task:
I have shopping cart function that uses a value called classid
I want to read the classid array genereated by perl script
If classid value in shopping cart function matches a classid value in classid array
get matching element in # of students already registered" array
When I say matching, I mean element number or index.
Message user that "nn" students have already registered for this class...

If javascript could open and read a file on my server... I probably would not need cgi script?

No, javascript on the client machine can't and is not made to read files on the server. It's a client side language though it can be very well used on your server (that would be something rare).

To pass values from your server variables to javascript, you would need to dynamically generate the javascript content. In Java, we can do something like this:

/* Greet.jsp */

  /* Here I am fetching the user name from the session variable which
   * I set on the server. There has to be a similar API offered by Perl for
   * accessing server side variables. Since only plain HTML pages are served
   * to the client / user by the server after processing the server side
   * constructs, you get to see the value of the username assigned to 
   * the javascript variable.
  myName = '<%= session.getAttribute("username") %>';
  function greet() { alert('Hello ' + myName); }
  <input type="button" value="Click" onclick="greet();" />
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