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

Comments to come: blah, Perl hard to read/maintain

[Neil Blender]

s/shitty perl code/shitty code in any language/;

You can inherit shit in any language.

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.

nice perl is possible

[hey]

For example:

sub main()
{
init();
work();
cleanup();
}

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...

Re:Use a real language.

[Camel Pilot]

on what test? Take a fairly common task - word counting

Perl 1.0 cpu time 11 lines of code.
gcc 0.3 cpu time 182 lines of code.

So i can distort reality also and say while C can sometimes be as fast as 3 times faster it will take 1700% more lines of code.

Maintainability

[XanC]

A lot of posts are complaining about Perl being unmaintainable, and suited to banging out a quick script in a half hour but not for anything more complex than that.

Baloney. The advantage of Perl is that you have the option to write maintainably if you want to!

If I just need a quick solution to a problem, I can very quickly write gibberish that does the job and then forget about it.

If I'm writing a big app which someone will inherit from me, I can avoid confusing constructs for something easier to follow. I can pass variables in Perl style, C-style, I can use objects if I want. Whatever I think will be most maintainable for somebody else.

Just because you can write gibberish in Perl doesn't mean you can't write good stuff too.

Re:Nay

[shobadobs]

PHP? Are you kidding me? There is nothing worse than PHP. PHP looks strewn together without thought. Just consider the system by which PHP's built-in functions are named. Except that there is no such system; the names follow all sorts of different casing rules.

PHP was made by taking a cute language for embedding a broken imitation of Perl-esque syntax in-between HTML and extending it with bajillions of functions that badly needed to be namespaced. It never provided anything useful that Perl couldn't, except that it made newbies comfortable by making them feel like they're in "HTML land" instead of "Programming language land."

Re:Comments to come: blah, Perl hard to read/maint

[Uruk]

Yeah, but perl makes it easier to write shit. I happen to love perl and use it all the time, but I also have to be very disciplined about the aspects and particularly syntax conventions of the language that I use, in order to write readable perl. Just because you can write:

do { thirty(); things(); in(); a(); list(); unformatted(); } if($foo);

Doesn't mean that you should.

One of the brilliant aspects of perl is that it allows you to write code like you think about code. Well doesn't that presuppose that other people are going to think about code the same way you do? Ooops.

Books and books have been written on the need for code formatting, syntax, and variable naming conventions in languages that are twice as rigorous and disciplined as perl. In perl, the need is double.

So I guess what I'm saying is that although shitty code is shitty code in any language, perl provides the possibility for a certain depth and richness of shit that just isn't accomodated in other languages. Kudos to the authors for addressing what is a real problem with a powerful and widely used programming language.

Re:Nay

[Just Some Guy]

My favorite bit of PHP idiocy is mysql_query() versus pg_query(). Given that the functions are basically identical except for the databases they access:

1. Why is the first's prototype:

   resource mysql_query ( string query [, resource link_identifier] )

   while the second has its arguments reversed:

   resource pg_query ( resource connection, string query )

   ?
2. Why is "mysql" spelled out, but "postgresql" or even "pgsql" abbreviated to just "pg"?

I hate the language for its utter lack of consistency. People talk about how great the php.net documentation is but I think they have the causality reversed: those docs have to be excellent or the language would be unnavigable. I have no desire to remember 3500 core language functions with similar (but inconsistent) naming systems and a randomized argument list. Seriously, what were they thinking?

I don't think PHP is inherently bad, but the current implementation certainly is.