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Server-Side Include Redirector

Page Last Updated: 21 July 1996
Latest Software: Version 1.0

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1. General Information & Package Overview

Redirector is a simple CGI+Server-Side Include package for displaying redirection information for moved files. The purpose of the package is threefold:

The package consists of two components. The first part is an HTML document template that contains the outline of an HTML document, and that uses SSI (Server-Side Includes) to inlcude the output of the forwarding program. The second part is the forwarding gateway program, forward.pl, which provides the content for the returned HTML document (via the SSI mechanism) and which returns the correct URL for the moved document. This is a Perl, Version 4 script, but it is simple enough that it should work properly under Perl, verison 5.

2. The Server-Side Include Document

Each document is replaced by a server-side include document of the form:
 <TITLE> This Document has Moved !!</TITLE> 
 <META HTTP-EQUIV="Expires" CONTENT="Mon, 01 Apr 1996 09:00:00 GMT">
 <META HTTP-EQUIV="Pragma" CONTENT="no-cache">
 <!--#exec cgi="/cgi-bin/forward.pl" -->
 </BODY> </HTML>
where forward.pl is the gateway program that does all the work. This document must be parsed by the server as a server-side include document. With NCSA, Apache or Netscape servers, this means that the document must have the execute bit set. An example procedure for doing this is shown below.

Note that the path to forward.pl must be correct: if you have this CGI program in another CGI program directory, or if you change the name of the program, you must modify the referring HTML documents.

2.1 If Moving a Single Document

Suppose the document that is moved is named duckling.html, and that the forwarding document is named forward.html. What we need to do is (i) move the duckling out of the way; (2) copy forward.html in place of duckling.html, and (3) mark the file as executable. The UNIX commands for doing these three things are:
  mv duckling.html duckling.html.orig #move duckling.html out of way
  cp forward.html duckling.html       #copy forward.html into place
  chmod +x duckling.html              #mark duckling.html executable

2.2 If Moving a Group of Document

This is similar to moving a bunch of single document, except that you do not need to make multiple copies of the forwarding document -- you can just make links from a generic forwarding document to a single copy. We will assume that the single file is forward.html The general format is (here file refers to all the files you want to redirect):
  chmod +x forward.html          #mark forward.html executable
  mv file.html file.html.orig    #move files out of way
  ln forward.html file.html      #link all files to forward.html

3. Gateway Program forward.pl

The gateway program is very simple, and requires that you specify two things: the base URL for the new location of the documents, $new_base_url, and the base URL of the old location of the documents, $orig_base_url. Consequently, with the current version of the program, you need a different program for each moved directory hierarchy.

The program gets the URL of the document being accessed from the environment variable DOCUMENT_URI -- this will simply be the path to the document, as seen by the server. The original URL of the document is then the combination of this variable and the original base URL ($orig_base_url+DOCUMENT_URI), and the new URL can be similarly constructed.

3.1 Referer Information

Some browsers send referer information, to indicate the document from which the current link was accessed. This is passed to the gateway program through the environment variable HTTP_REFERER. If this variable is present, the program also prints this information out, and includes text that asks the user to fix this referring page, or to send mail to the manager of the page so it can be fixed.

3.2 Database Version forward-dbm.pl

For some pages, you may wish to maintain a database of all the referring pages: that way, you can yourself access these pages, check for feedback mail addresses, and send them mail asking that they fix the links. The second program forward-dbm.pl is identical to forward.pl, except that it uses DBM to create and update this database.

4. Downloading The Programs

You can access the files by themselves, or as a UNIX tar archive. Here are the links: