The nms Project

Web programs written by experts

[General nms Questions] [Perl Questions] [Common Problems]

• I've heard that use strict; is gay ..
• Why don't the programs decode the parameters like other PERL programs?
• Why don't you use cgi-lib.pl like everyone else does?
• But isn't the CGI module terribly big and slow?
• What's with all this die stuff all over the programs?
• Isn't flock something that sheep do?
• Why don't the programs use Net::SMTP to send mail?
• Where can I learn more Perl?
• The programs keep crashing with flock unimplemented, why?

NAME

Frequently Asked Questions about the Perl used in the nms CGI programs.

<-- $Date: 2004/05/31 12:11:50 $ -->

DESCRIPTION

These are answers to some common questions about our Perl style and project usage of Perl.

I've heard that use strict; is gay ..

You shouldn't believe everything that bk tells you :)

use strict (together with -w) is a great way to keep a huge range of bugs out of your scripts. Even though the nms project team are all very experienced Perl programmers, we all insist on using them in all of our scripts. You should too.

Why don't the programs decode the parameters like other PERL programs?

Actually it's "Perl", not "PERL" :-)

The vast majority of Perl CGI programs seem to decode the CGI parameters using a buggy piece of code that probably originated in Matt's scripts. This code has a number of problems so we don't use it.

Fortunately, since Perl 5.004_04, the Perl distribution has included a library called CGI.pm which will do all your CGI parameter decoding for you. Why bother writing your own (potentially buggy) code when there's code right there that will do it for you?

Why don't you use cgi-lib.pl like everyone else does?

cgi-lib.pl was created for writing CGI programs back in the days of Perl 4, but we've come a long way since then. CGI.pm does all that cgi-lib.pl did... and much, much more.

But isn't the CGI module terribly big and slow?

It's certainly big! But because of the way it's written, only functions that you actually use will be loaded into memory. This means that it will have very little effect on the size or speed of your program.

What's with all this die stuff all over the programs?

This is another major problem with many other CGI programs. They always assume that everything they try to do will work. For example, if they open a file to read some data from it, they don't check that the file was opened successfully. We believe that it's vitally important to check for these things and in many cases the only appropriate action when things go wrong is to kill the program.

Isn't flock something that sheep do?

Yes, but it's also something that you should do every time that you access a file that can be accessed by other processes. If you're storing data from a web page in a file and your web page becomes popular, it is likely that two visitors can be saving data at the same time. If they both try to write to the file simultaneously, then the file can become corrupted. If they both try to flock (for "file lock") first, then only the first one will be successful. The second will be forced to wait until the first unlocks the file. This leads to far fewer corrupt files and is therefore a good idea.

Why don't the programs use Net::SMTP to send mail?

Firstly, because Net::SMTP is not available as part of the core Perl distribution except for in the development version leading to Perl 5.8.

Secondly, because the nms developers feel that it is better to use the queuing, MX lookup and retry capabilities of the local message transfer agent (MTA) to deliver mail messages - the Net::SMTP module does not do any of these things and the code to support them is likely to run into hundreds of lines and require several other modules. Also Net::SMTP requires an SMTP relay to be available on the local network.

Where can I learn more Perl?

If you wish to learn more Perl, you should look at Randal Schwartz's book Learning Perl, published by O'Reilly and Associates <http://www.oreilly.com/catalog/lperl3/>.

<http://www.perl.com/> is also a good starting point.

The programs keep crashing with flock unimplemented, why?

Hasn't anyone told you that Windows 98 is not a server operating system?

Unfortunately on Windows 95 and 98 there is no support whatsoever for advisory locking like flock, Perl does not try to emulate it because it would have to behave completely differently. You could try commenting out the lines in the affected programs with a '#', but you should be warned that this will lead to other side effects as these operating systems implement a 'mandatory non-blocking lock' on files open for writing: that is to say that if one process has a file open so it can write to it and a second process attempts to open the same file (whether for writing or reading only) then the second attempt will simply fail and there will be an error message. This is alright for testing or development purposes where you are unlikely to have more than one person using the program at the same time, but would be far from ideal for a public website.