Perl Primer II: Basic CGI Scripts Troubleshooting
©by Dawn Rivers Baker
Simple scripts are simple to configure but sometimes things
do go wrong. Here are some basic tips for painlessly dealing
with perl problems
Last month, we took a look at the few basic bits of information
and procedures you'll need in order to configure and install
most simple CGI scripts on a Unix server ("Perl Primer:
A CGI Tutorial", The MicroEnterprise Monthly, July 2002).
Now, before you dive nose first into the wonderful world
of interactivity, I feel I ought to just mention that sometimes
these scripts can be a little touchy. Things can go wrong,
so that when you get the script uploaded and try to access
it, it don't work. So, this month, we'll go over a bit of
very basic troubleshooting tips.
Again, I caution you not to be nervous. Because they can
be touchy little scripts and nowhere near as forgiving as
hypertext markup language (HTML), they can refuse to work
because of some pretty minor errors. But those errors are
easy to fix and in the end, the effort will be worth it.
Assuming that the rest of your site design is crisp, clean
and clear, the features you can offer your site visitors
with these scripts can lift your business images into the
heights of professionalism just as fast as you can get those
"Hosted by Whatsit" graphics off your pages.
That said, if you are having trouble with a recalcitrant
script, here are a few basic things to look for.
Did you upload the script correctly?
Yes, this seems like a pretty brainless question, but
it's valid. Check to make sure the entire script uploaded.
Sometimes they get cut off during transfer, especially the
larger scripts and especially if you are on a dial-up connection
so that uploading is a slower process.
While you're at it, double-check to make sure that you
uploaded the file in ASCII rather than binary mode. Remember,
uploading in binary is for graphic images like .gif, .jpg
and .pdf files. For text files -- and perl scripts fall
under this category -- you need ASCII. If you are using
WS FTP-Pro, you need to be alert to this during all your
uploads because the program's default setting is binary.
Are all your system path configurations correct?
If you're getting those pesky 500 errors, you'll need
to check to make sure that you provided the correct system
path information to the program, starting with the path
to perl. As a matter of fact, errors in the path to perl
line are among the most common problems people have getting
their scripts to work. If you have to, go back to your web
host's control panel and look this up again but make sure
you have it right.
Once you're certain that you're script will be able to
find your server perl compilor, go back and make sure that
you have the rest of the system path information correctly
configured. Remember that system paths always start with
a slash ("/"). If you are pointing the program to a certain
directory, you will usually include a trailing slash but,
if you are specifically told not to include that trailing
slash then you should certainly follow directions.
These are system paths, too. Make sure you didn't inadvertently
input URLs into your configuration settings when the instructions
call for system paths. For that matter, also make sure you
do provide URLs and not system paths when the script asks
for URLs -- which they sometimes do. Follow directions.
And do be sure, when you are inputting those system paths,
that you are not giving your script bad directions. Correct
format for system paths aren't going to get your script
running if you tell it to go looking for a directory in
your cgi-bin that you the forget to create! Make sure that
everything you need to put into your directory structure
for the script to use is actually there. Create the directories
the script needs and upload the files the script needs to
find in those directories. Then give good path directions
to help the script find the files it needs to complete its
tasks.
Are your permissions set correctly?
This is one of those incredibly simple things that is
so easy to fix that it almost seems like getting the stubborn
script to finally work was nothing short of magic.
It's also something that is fairly easy to forget to do.
If you do your own webmastering, then the task of editing
and uploading files is no doubt pretty routine. In fact,
if that is the case, you may already be in the habit of
checking to make sure you upload text files in ASCII and
so are unlikely to make that particular novice mistake.
On the other hand, setting file permissions on your Unix
server is not a chore that you perform regularly as you
upload you files and because of that, you might forget to
do it. If you don't remember, just go back and do it again.
Make sure that you set file permissions as instructed on
directories as well as individual files. Particularly when
it comes to subdirectories in your cgi-bin, because these
files cannot ordinarily be accessed by anybody. So you have
to arrange the directory so that the web page that calls
the script is permitted access to that script. Don't forget
to set those permissions!
Most of the time, with the simpler scripts, these troubleshooting
tips will yield results. If you are still having trouble,
you can either scream for help from your web site hosting
tech support people or return to the source. If you have
paid for your script, you are entitled to a certain amount
of customer service and even if you are working with a freebie,
most sites that give away code have message boards where
you can bring your perl issues and get helpful hints from
the script's author and from other webmasters.
Copyright (c) 2003 by The
MicroEnterprise Monthly. All rights reserved. Reprinted
with permission.
PERL Primer part I CGI Tutorial
