Perl Program Repair Shop and Red Flags

Length: 3-6 hours

Prerequisites: Basic familiarity with Perl is required.


You've probably been working too hard when you program, writing twenty lines of code when you only needed ten. But there is a better way, and I will show it to you. You'll learn how to improve your own code and the code of others, making it cleaner, more readable, more reusable, and more efficient, while at the same time making it 30-50% smaller. Smaller code contains fewer bugs and takes less time to maintain.

All the bad code in this class is guaranteed 100% genuine and typical. We will examine several real code examples in detail and see how to improve them. We'll focus on 'red flags', which are obvious warning signs in your code that are plainly visible once you know what to look for, and on techniques that require little complex thought or ingenuity.

Participants are encouraged to submit their own code for anonymous review in the class. Class content varies depending on submissions, but is sure to include some of the topics listed below.

Sample Topics

Sample Slides

Detailed preview, including several sample slides


The class is different every time I give it---I am always replacing old sections with new ones. Three-hour versions of the class typically consider two to four examples; six-hour versions consider five to eight examples. The best Red Flags classes happen when some of the examples have been contributed by people in the audience.

Six-hour hands-on versions cover two to four examples, and include a development lab, in which the students all write the same program, then a maintenance lab, in which the students exchange their lab programs at random and then extend and debug the once they receive, and discussion sections, in which the students analyze and critique the code.


Usually I like to provide a class outline on my web site. But a detailed outline doesn't represent this class well because the class is not hierarchically organized. It is structured around a series of examples; the examples suggest certain themes, which I then develop in more or less detail.

I typically cover two to four real programs and work them over in detail, pointing out the problems and showing how to fix them. Some problems appear early on and then recur in other programs so that the class builds up several themes simultaneously. Major themes include:

Course content changes every time I give the class. At present, the class covers:

Other code I've discussed in the past has included:

I'm presently preparing new material that analyzes code written by a well-known Perl expert.

All code is guaranteed genuine---this class contains no contrived or fake examples. Even trivial one-line examples are taken from real code. I don't want to stand up and expound a lot of principles that have nothing to do with the real world. If I couldn't find lots of real examples of the problems I wanted to talk about, I wouldn't put them in the class. The problems I discuss are all problems you will see in real code, because I see them over and over in real code.

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