#!/usr/bin/perl -Tw

use strict;
print "Content-type: text/plain\n\n",
  qq{We regret that the service is temporarily 
     unavailable while essential maintenance is undertaken.
     It is expected to be back online from 12:20 GMT.
     Please, bear with us. Thank you!};

Let's say you now want to disable the /home/httpd/perl/chat.pl script. Just do this:

panic% mv /home/httpd/perl/chat.pl /home/httpd/perl/chat.pl.orig
panic% ln -s /home/httpd/perl/down4maintenance.pl /home/httpd/perl/chat.pl

Of course, the server configuration must allow symbolic links for this trick to work. Make sure that the directive:

Options FollowSymLinks

is in the <Location> or <Directory>section of httpd.conf.

Alternatively, you can just back up the real script and then copy the file over it:

panic% cp /home/httpd/perl/chat.pl /home/httpd/perl/chat.pl.orig
panic% cp /home/httpd/perl/down4maintenance.pl /home/httpd/perl/chat.pl

Once the maintenance work has been completed, restoring the previous setup is easy. Simply overwrite the symbolic link or the file:

panic% mv /home/httpd/perl/chat.pl.orig /home/httpd/perl/chat.pl

Now make sure that the script has the current timestamp:

panic% touch /home/httpd/perl/chat.pl

Apache::Registry will automatically detect the change and use the new script from now on.

This scenario is possible because Apache::Registry checks the modification time of the script before each invocation. If the script's file is more recent than the version already loaded in memory, Apache::Registry reloads the script from disk.