Perl Medic

Craig Maloney writes "Anyone who codes in Perl can relate to working on other people's code. Sometimes the code will thankfully include "use warnings" and be a joy to maintain. More likely, though, the code will have so many warnings that the useful output is long gone in the stratosphere of your scroll buffer. Even good code written for earlier versions of Perl can become aged and decrepit, requiring elderly modules that may or may not work with newer versions of Perl. Maintaining this code can be a hassle, but fortunately Perl Medic: Transforming Legacy Code (referred to for the duration of the review as Perl Medic) provides some very useful tips for getting through these migrations, and will help the next person maintaining your code." Read on for the rest of Maloney's review. Perl Medic author Peter J. Scott pages 312 publisher Addison Wesley rating 8 reviewer Craig Maloney ISBN 0201795264 summary A great collection of Perl wisdom and tips for experts and other patient Perl acolytes.

One of the goals of Perl Medic is to transform code from stylistically poor and unmaintainable into stylistically sound, maintainable and testable code. The format of Perl Medic is very similar to books like The Pragmatic Programmer or The Practice of Programming. Perl Medic shows the reader best practices by example. Some of the chapters are checklists of practices that will help improve your ability to manage and wrangle the code, while others are lists of patterns and practices you should avoid, and should replace with the examples provided. This format very readable, and provides an excellent forum for gleaning what ways to improve the code.

Perl Medic is designed with experienced coders in mind. Topics are presented as if the reader may be using these ideas already in their code, whether good or not. While the advice is good, the presentation may be confusing for beginner and intermediate programmers who aren't intimately familiar with the concepts. I found myself re-reading several topics to try and grasp what the author was trying to convey. After several readings of the section on test harnesses, I still needed help, and ran to the Perl documentation to better understand what the author was saying. Certain advice is also presented, only to have it countered in the next section. Most Perl programmers are familiar with the '-w' switch, which turns on warnings in a Perl program. The pragma 'use warnings' is introduced as a way to turn on warnings for just the code being worked on without displaying the warnings of the modules included in the program. In the next section, the author points out that it might be a good idea to put '-w' in there to see if there are any issues in the modules you may be including. While this advice may be intuitive for experienced Perl coders, the beginner may be confused. "Should I use '-w', or should I use 'use warnings'" she may ask herself.

The book also suffers from a case of being too brief in some sections. In section 2.3.1 (Gobbledygook) the reader is directed for help on how to turn a partially obfuscated program into more intelligible code; a very useful skill indeed. The author redirects the reader to section 4.5 where the utility perltidy is discussed with further detail, but before ending the section, the author also introduces the module 'B::Deobfuscate' along with a URL. No mention of how to use it is provided. In section 6.4 (Debugging Strategies) the author gives advice on how to debug a program. His advice: "Divide and Conquer". While there is debugging advice throughout the book, it's a little frustrating to see a section specifically designated "Debugging", with only one subheading under it. The organization of some of the topics feels artificial, and perhaps should be reorganized in future editions.

Underneath these faults, though, Perl Medic is a great book. Chapter 11 (A Case Study) should be required reading for coders inheriting Perl projects. This chapter is a blow-by-blow account of the author's work in transforming a simple LDAP application from Perl 4 into a robust Perl 5.8 application. The author is very candid about what decisions were made in the code transformation, and why certain elements were addressed in the way they were addressed. One particular element is an elderly module used for the LDAP lookups themselves. The author details the process used to determine a better module to replace this module, and guides the reader through each of the steps required to change the code to use this new module. The decisions the author uses to make this code work under the new environment are enlightening for anyone planning a migration of Perl code into a newer environment. Chapter 7 contains the versions of Perl from Perl 4 up until 5.8.3, and elaborates on what changed between the versions (very helpful for those who are planning an upgrade from 5.003 to a more recent version of Perl). Chapter 9 (Analysis) has very useful tips for not only debugging you program, but for using the Perl Debugger and getting the most out of your debugging session.

Perl Medic is recommended for anyone who is tasked with maintaining or writing Perl Code. While the examples are written with experienced coders in mind, beginners will do well to use this book for areas to focus on while they learn the language. Inheriting code can be a daunting task, but with a book like Perl Medic, you'll have the tools at hand to help ease the work ahead into a more manageable task. And you'll make it easier for "the next guy".

You can purchase Perl Medic: Transforming Legacy Code from bn.com. Slashdot welcomes readers' book reviews -- to see your own review here, read the book review guidelines, then visit the submission page.

Comments

not just for legacy code

[consumer]

This is the best book I've ever read about how to write clear and maintainable Perl code. The advice is solid and up-to-date with discussions of perltidy, modern web techniques, etc. I would recommend this book to anyone who writes Perl, just as a style guide.

Using a new language is usually not an option

[winkydink]

In most cases, refreshing an existing program will take less time than rewriting it in a diffferent language, as in both cases you need to have a firm understanding of what the program does before proceeding.

In many corporate cases, you don't have the luxury of writing in any language you please and, even if you do, in most cases you'll have an uphill challenge convincing a PHB that rewriting from scratch in a new language is the better proposition.

No problem.

[jspoon]

More likely, though, the code will have so many warnings that the useful output is long gone in the stratosphere of your scroll buffer.

When this happens, just write a Perl script to sort out the parts you need to know and print out a nice little summary.

Re:nice perl is possible

[abulafia]

Perl has always been a write only language that is only readable by the author.

Funny. I'm supporting an app initially written about 8 years ago entirely in perl. It is about 80K lines. Outputs PDF by writing postscript directly (don't ask, but there are reasons for this). I came in about 3 years ago on it. None of the original developers (nor the original company) are around. Somehow, we still maintain an improve it. Maybe it isn't such a write-only language.

I've lost track of the number of modules on cpan.org that are stuck at version y.xx and have not been updated in a long time and only work with versions of Perl *OLDER* than 5.3 because no one is able to correct the module to work with perl v5.3+

I assume you've also lost count of all the C, Fortran, PHP, Pascal and Java projects that don't work in modern environments, too.

Bottom line: If you can write good code in any language, you can write quality perl. Bad perl is easier to write than some languages, and I think that is a sign of utility. And don't get me started on some of the _bloody fucking awful_ Java I'm also supporting...