"Linux Gazette...making Linux just a little more fun!"

1. References
2. Introduction
3. The Problem with Redirect
4. Using a Perl script
5. Using the mod_rewrite module for Apache
6. Using Redirect with Virtual Host
7. Conclusion

References

• Apache webserver
• Module mod_rewrite URL Rewriting Engine
• Perl programming language
• Mark's other articles
• The Apache/Perl Integration Project

  Introduction

  Apache has been a growing project for many years. It is personally amazing to me how Apache is so powerful, flexible, and easy to configure for a programmer. There is so much documentation about how to configure and do things in Apache, other commercial webservers just can't compare. Apache makes webserving fun for programmers. There are a lot of things you can test and tinker with.

  Along with the growing, comes new ways of doing things without getting rid of the old ways of doing things. I have a problem with my computer at gnujobs.com. Basically, I need to forward every request for 'http://www.tcu-inc.com/mark/articles' to 'http://www.gnujobs.com/Articles'. I tried the Apache Redirect directive, but it didn't work. So, I had to figure out why it didn't work and to see if there was any way around it.

  The Problem with Redirect

  The problem is, 'Redirect' didn't work for me when I tried to forward 'http://www.tcu-inc.com/mark/articles' to 'http://www.gnujobs.com/Articles' since both websites where running on the same webserver. However, I found out later, and it was obvious when I thought about it twice, I was using Redirect incorrectly. Nevertheless, it set me on a trip to get reacquainted with mod_rewrite. The solutions I had were
  1. Use a Perl script.
  2. Use mod_rewrite with Virtual Host
  3. Correctly use Redirect with Virtual Host

  Using a Perl script with Virtual Host

  This was my first solution after I couldn't get Redirect to work right. The only reason why I used it was because it was quick and dirty. It is actually fairly complex because you have to understand Perl programming, what "Location" does, and how to get a Perl script to execute with your Apache webserver. Besides that, it was simple for me to do because I have done similar things a million times over.

  The nice thing about using a Perl script, is that you don't have to recompile the Apache server. You do have to change the configuration slightly. You don't have to install mod_perl, but if you do, the configuration can be slightly different if you want to cache the perl script. Also, this can be done is any programming language, not just Perl.

  I had to change the httpd.conf file slightly:

  <VirtualHost 206.21.120.103>
  ServerAdmin info@gnujobs.com
  ServerName www.tcu-inc.com
  DocumentRoot /www/htdocs/
  
  ScriptAlias /mark/articles "/www2/TCU.pl"
  </VirtualHost>
  

  The ScriptAlias is the key part here. It redirects all requests from /mark/articles to the TCU.pl perl script.

  And the perl script looked like this,

  #!/usr/bin/perl
  
  
  print "Location: http://www.gnujobs.com$ENV{'REQUEST_URI'}";
  

  $ENV{'REQUEST_URI'} is the key part here. It is an environment variable that is equal to the file asked for on the www.tcu-inc.com webserver. The perl script takes the file asked for, and then redirects the browser to the new website. Also, I did a "chmod 755 TCU.pl" on the perl script to make sure it was executable.

  Using the mod_rewrite module for Apache

  Aaron Bush from COLUG is responsible for getting me to do it in mod_rewrite. I didn't like my Perl solution, and knew I could use mod_rewrite to do it, but I was being lazy. I knew I should do it in mod_rewrite, and Aaron asked me "Why don't you use mod_rewrite?". Feeling lazy, I was unhappy, for I knew that what separates the men from the boys can be issues like this, so I said to myself "screw it, I haven't used mod_rewrite in a long time, let me do it the right way".

  You have to have mod_rewrite compiled into Apache in order to use this option. Mod_rewrite is a nice module that "provides a rule-based rewriting engine to rewrite requested URLs on the fly". It is a very powerful module, and is essential to learn if you want to become a true webmaster or web programmer. It is not essential that you use it, but that you know what it can do so that you can present the options to your boss when you want to do weird things with your webserver.

  I compiled mod_rewrite into Apache and applied this configuration option to httpd.conf.

  <VirtualHost 206.21.120.103>
  ServerAdmin info@gnujobs.com
  ServerName www.tcu-inc.com
  DocumentRoot /www/htdocs/
  
  RewriteEngine on
  RewriteCond %{HTTP_HOST}  ^www\.tcu\-inc\.com$
  RewriteRule ^(/articles)(.*)  http://www.gnujobs.com/Articles$2 [R]
  </VirtualHost>
  

  RewriteCond sets the condition for which we are going to use mod_rewrite, which basically says pay attention to the webserver if www.tcu-inc.com is the base website name being used. RewriteRule takes the conditions (everything at www.tcu-inc.com) and says that if the requested file starts with "/articles" redirect it to www.gnujobs.com. The "$2" corresponds to "(.*)". The rest of the requested file after "/articles" is equal to "(.*)". [R] means "Take this match and redirect it".

  Using Redirect with Virtual Host

  After I figured out how to redirect www.tcu-inc.com to gnujobs.com with the other two methods, I realized I was doing a mistake with the standard "Redirect". I wasn't putting the Redirect command into the VirtualHost section. Once I did that, it worked fine.

  <VirtualHost 206.21.120.103>
  ServerAdmin info@gnujobs.com
  ServerName www.tcu-inc.com
  DocumentRoot /www/htdocs/
  
  Redirect /mark/articles http://www.gnujobs.com/Articles
  </VirtualHost>
  

  Conclusion

  I did a lot of work for nothing, but I made this nice article explaining different options for other people to learn from. Here are my suggestions about which of these 3 methods you should use:
  1. If you don't forsee ever having programmers work on your website, use the standard Redirect command.
  2. If you are a programmer or a true webmaster, then please use mod_rewrite. If you standardize on using mod_rewrite, you might find other uses for it as well which you might not realize unless you have had previous practice with mod_rewrite.
  3. I don't know why you would want to use a Perl script to do this, unless you want to record certain stats (which are possible in other ways) or do something else that is weird. Using a Perl script would just add more overhead. If you used it with mod_perl, you might end up using more memory because of caching. I wouldn't use a Perl script to do this, although that was my first working solution. Bad solutions are good only in the fact that you at least have something working.
  Mark works as an independent consultant donating time to causes like GNUJobs.com, writing articles, and writing free software.

  ---

  Copyright © 2000, Mark Nielsen.
  Copying license http://www.linuxgazette.net/copying.html
  Published in Issue 61 of Linux Gazette, January 2001

  ---