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Perl Books Media Programming Book Reviews

Perl Medic 194

Posted by timothy from the triage dept.
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.
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Perl Medic

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  • The thing about Perl... (Score:3, Insightful)

    by Sheetrock ( 152993 ) on Tuesday May 10, 2005 @03:17PM (#12491414) Homepage Journal
    While its ubiquitiousness and relative ease of use as far as banging together a CGI script in an hour goes, it does not seem designed for maintainability.

    Preventative and maintainance coding is difficult enough when a language has a particular idiom you can follow. Perl gives you an unparallelled freedom of expression and with it several confusingly different ways to achieve the same task.

    I used to be a believer, but now it seems Python is ready to take the yoke, at least with those of us who wonder how can you build a complex yet maintainable script without static typing.

    • I used to be a believer, but now it seems Python is ready to take the yoke, at least with those of us who wonder how can you build a complex yet maintainable script without static typing.

      Some kind of optional static typing is a recent Python design teapot-tempest [artima.com], but Python is most definitely not statically checked as of this writing.
      Of course, how you edit [slashdot.org] really matters most...

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

    You can inherit shit in any language.

    • Re:Comments to come: blah, Perl hard to read/maint (Score:5, Insightful)

      by Uruk ( 4907 ) on Tuesday May 10, 2005 @03:32PM (#12491597)
      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.

      • Ask any VB developer about the 'Option explicit declaration' (I think thats the name? Its been years since I touched it)?

        It forces the compiler to treat code without explicit declarations of types to be treated as errors. It also prevents undeclared variables from being used due to spelling errors.

        For example in C++ you have to do
        int test1 =0 or
        int test1

        before you can use it in code. Earlier versions of C did not do this and created alot of hassles.

        Also many gnu C++ programs were not that well written b
        • Ask any VB developer about the 'Option explicit declaration' (I think thats the name? Its been years since I touched it)?

          It forces the compiler to treat code without explicit declarations of types to be treated as errors. It also prevents undeclared variables from being used due to spelling errors.

          use strict qw(vars);
          • Why stop with just the vars? I think it makes more sense just to "use strict" until those rare occasions when you need to turn something off.

            If I recall correctly (and as you would expect) the book discusses using strict.

            • True. In practice, if I'm using strict, I use it without qualifiers. In this specific case, however, I was just pointing out the particular Perl answer to gp's "strong typing" issue.

              "strict refs" sometimes bites me in old code that I've inherited and don't have time or permission to rewrite, though.

      • Just because you can write:

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

        Doesn't mean that you should.

        Totally right! No need for ():es when you have a suffix 'if'. You should end it .. if $foo;

        Only joking.

        Seriously, I second your position; Perl breaks all the rules but works anyway, given some discipline. It is both powerful and fun.

        If I get a choice, I use it for everything.

      • One of the brilliant aspects of perl is that it allows you to write code like you think about code.

        While that point of view does have some merit, it also points out the worst failure of Perl. Far to many people do almost no thinking about their code and then get to live with just what they bargained for. Sadly, any later maintainers didn't bargain at all but still have to survive the mess created in the mean time. In se, this "why would I need to think" attitude is not a problem of Perl, but Perl does i

    • Re:Comments to come: blah, Perl hard to read/maint (Score:4, Insightful)

      by Coryoth ( 254751 ) on Tuesday May 10, 2005 @03:32PM (#12491601) Homepage Journal
      s/shitty perl code/shitty code in any language/;

      You can inherit shit in any language.

      That is true, but perl does provide easy ways to write sloppy or unmaintainable code. That's not necessarily a bad thing, because it is exactly that looseness that makes perl a very fast language to develop quick scripts in - there aren't anywhere near as many hoops to jump through and TIMTOWTDI makes it very easy to just write whatever you're thinking. For the niche of a language that lets you knock together something to do the job quickly perl is fine.

      If you want anything maintainable you need to forget all of that and make use strict and use warnings mandatory, and enforce some coding style standards. That can be done, and if you do that it is easy enough to write maintainable perl - it's just that you can't expect the language to help you with it much: you have to enforce and police the standards yourself.

      Jedidiah.

  • not just for legacy code (Score:5, Informative)

    by consumer ( 9588 ) on Tuesday May 10, 2005 @03:18PM (#12491439)
    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.
    • Hear, hear! I have had this book in my desktop library since i bought it eight months ago. While it's certainly too short to truly cover the topic completely, this book has remarkable depth, and is still quite easy to grok. You can read it cover-to-cover or flip around and always find some useful advice. Don't make the mistake of thinking this book is too short to be useful... It's filled with hints and links to more information. Heck, nowadays, all books should be filled with links and references; printed materials too often become obsolete too quickly!

      (Normally I'm a grammar/spelling nazi for myself... but I've been coding in PHP all day and I've lost the will to fight for correctness.)
  • 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. (Score:5, Funny)

    by jspoon ( 585173 ) on Tuesday May 10, 2005 @03:19PM (#12491453)
    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.

  • Maintainability of Perl code? (Score:4, Insightful)

    by Sv-Manowar ( 772313 ) on Tuesday May 10, 2005 @03:24PM (#12491512) Homepage Journal

    Cue the flood of 'Perl is hard to maintain/read' and counterflood of 'You can write hard to maintain/read code in any language' posts.

    I think it can be generally agreed that due to the TMTOWTDI philosophy behind Perl, there can be complications involved when inheriting code from others who use a different style and different approach. (Obviously due to the many ways any given task can be approached).

    One (common?) approach to dealing with this seems to be to use different languages such as Python or Ruby. Arguably, however, if more coders stuck to code style guidelines and used best practices instead of quick hacks, the problem would be minimal, or at least no worse than other scripting languages.

    • Re:Maintainability of Perl code? (Score:1, Insightful)

      by Anonymous Coward
      Perl is hard to maintain because:

      1) too much punctuation .. make things hard to read

      2) too much "magic" .. makes things hard to read

      3) too much scaffolding to do object-oriented programming .. makes things hard to read

      4) just a shitty data model .. why are there arrays AND arrayrefs? Why not just arrays? That means the programmer always has to make a decision between crisp readability (arrays) and performance/lack of aliasing issues (arrayrefs).

      5) shitty object model. Do you want to do some setup to yo

      • Really I have tried writing clear Perl code, but it's always "not quite there"...

        And you blame the language for that? How convenient.

      • Not going to intersperse your points with mine, since I really hate that style, so I'll just go in order.

        1. No one will argue against perl having too much punctuation. It's a hell of a noisy language, and you can really play some perl golf with sigils if you try. Sometimes you even have to, but rarely.

        2. The "magic" also makes things easier to read. "open $file or die" anyone? Sure beats checking whether it returns nonzero, don't it?

        3. Then use one of the Class:: modules. Personally, I rather LIKE t

        • Re:Maintainability of Perl code? (Score:1, Funny)

          by Anonymous Coward
          Not going to intersperse your points with mine, since I really hate that style, so I'll just go in order.

          That's being a true Perl programmer. Never make it easy for someone to read your stuff.
        • re #2:

          IF the only magic I had do deal with was 'open or die' I would be jumping with joy. There is plenty of other magic, for example the whole context changes meaning of operators significantly.

          I value consistency in a language... Larry's whole 'postmodern' thing aside.
    • I'd like to argue that Perl is very maintainable. Many studies show a correlation between LOC and number of defects. So the important thing is reducing the LOC written. The differences accountable to language syntax is negligable when you can reduce the amount of code you write by order(s) of magnitude. With Perl, you have CPAN (http://search.cpan.org/ [cpan.org]), a repository of pre-written, tested code, the vast majority of which are classes ready to use in object-oriented fashion. Now, I'm not going to say that Pe
    • TMTOWTDI?

      That doesn't spell "Don't do what I say, do what Larry thinks I mean"
    • ok.

      Tell me, between those two programs (that do exactly the same thing), which is easier to read ?
      (I had a mycat.c file to show too, but it didn't pass the filters ...)

      /**** MyCat.java ****/
      package net.beuarh.lasher;

      import java.io.BufferedReader;
      import java.io.File;
      import java.io.IOException;
      import java.io.FileNotFoundException;
      import java.io.FileReader;

      public class MyCat {
      public static void main(String[] args) {
      if (args.length != 1) {
      System.err.println("Usage : " + MyCat.class + " <file_
    • It's not only the TMTOWTDI that makes Perl inherently more "abuseable" than most other languages. It's the "default variable" ($_, etc) thing, where actually using the variable in syntax is optional.

      These features are really, really, nice to have, when you're hacking, or writing up quick little scripts to do some administrative task. It's nice to have the option of brevity when you have a high level of comfort with the language. But these options ARE a detriment to maintaining stylistic conformity.

      The

  • nice perl is possible (Score:5, Insightful)

    by hey ( 83763 ) on Tuesday May 10, 2005 @03:26PM (#12491533) Journal
    For example:
    sub main()
    {
    init();
    work();
    cleanup();
    }

    • Re:nice perl is possible (Score:1, Funny)

      by Anonymous Coward
      I guess you can write COBOL in Perl too!
    • Sorry dude, but that is the c style of writing code on unix/linux systems.

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

      • Re:nice perl is possible (Score:5, Insightful)

        by abulafia ( 7826 ) on Tuesday May 10, 2005 @04:32PM (#12492204)
        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:nice perl is possible (Score:1, Insightful)

      by Anonymous Coward
      You didn't just go there! You did!

      I have just inherited code that resembles just that: function calls with no arguments. They don't use strict, so all variables are global. The subroutines are little more than macros, and you have to refresh yourself on what variables are affected each time you see a function call.

      I think Perl's major flaws stem from not having "use strict" on by default. If it doesn't need strict, it can probably work just fine in shell script!

  • Maintainability (Score:5, Insightful)

    by XanC ( 644172 ) on Tuesday May 10, 2005 @03:27PM (#12491552)
    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:Maintainability (Score:1, Insightful)

      by Anonymous Coward
      Many big, inherited apps started life as quick n' dirty 'never gonna touch this again' hacks... I am tempted to say most of them do. Many large apps have sections written by less experienced programmers and/or someone who was under the gun.

    • As explained above, many perl programs are no longer maintainable because of the extensibility of the language. As some perl modules rise in popularity, some fall - an example is the old LDAP library mentioned above that is no longer usable on new perl versions.

      For quick hacks, if it can be done with awk, I will do so. If it requires date processing, I will use gawk. I am not above shelling out to ldapsearch from awk because I will have to maintain fewer complex package installations.

      I will only fall ba


  • #!perl -w
    use strict

    Those are the two guidelines required by our methodology.

    • Re:no perl scripts should forget... (Score:1, Insightful)

      by Anonymous Coward
      Where I work, use of $_ in any form is punishable by death. If you use it in the implied form, you get tortured first.
      • implied $_ has a five line limit. beyond that, out comes the wet-noodle whacker. ;-)
      • So, you gave up grep and map? How sad.

        After all, you can't use them without $_.

        And defaulting regex to $_ is a very natural thing to do.

        I think a rule like this is like saying "Don't shift the car out of first gear! Higher gears kill!". That's not responsible. The responsible thing to do is to create guidelines for clarity. Banishing $_ is not one of them in any sane Perl shop.

        • Ok, so we do use it with grep. We frown on map because it can lead to resource hogging if you

          my @results = map { }
          map { }
          map { } @a_very_big_array;

          (which can be hard to deciper as well as inefficient speed wise when compared to other loops)

          Also, if you have a series of regexes, it's nice to have some clue what you are searching through once the assignment to $_ is off the page.

          As I said here [slashdot.org], I think for serious projects, you have to really strict with guidelines when usin
  • Sorry, can't resist...

    For other languages there is -Wall -Werror. On a better OS use ${BDECFLAGS} instead of -Wall :-)

  • If you liked Peter's book, attend Peter's workshop (Score:3, Informative)

    by TomDLux ( 28486 ) on Tuesday May 10, 2005 @03:59PM (#12491853)

    I agree, perl medic is a great book, influential in encouraging and developing good habits.



    Peter will be speaking, though not on the same topic, at YAPC:2005, June 27, 28, 29 in Toronto. There's a whole day's worth of workshops on perl6, including PUGS, most of a day on testing, as well as threads on DBI, CGI, and lots of other workshops. Register now! [yapc.org] At $85US for registration, it's the best bargain you'll find this year.


    If you are planning to attend, Book your hotel room soon. The host hotel is only guaranteeing room availability till next weekend. There's a huge conference coming to Toronto a few days after YAPC, so the hotel wants to start making rooms available for early arrivals. Not that all the rooms will disappear the first day, but you wouldn't want to be disappointed, would you?



  • Some of the code I've been forced to maintain needed Dr Kevorkian.

  • Perl is too clever (Score:1, Insightful)

    by COBOL/MVS ( 196516 )
    Having written code in Perl and other languages (COBOL, C++, Java, VB, TCL), I have come to the conclusion that Perl as a language is more concerned with being clever than getting the job done. The language has some of the most untechnical keywords (e.g. bless, chomp and others) and it makes it completely laughable (like a toy almost). Also, just look at any of the books and or documention written about perl. They all read like Tom Baker scripts from the 1970s Dr. Who episodes.

    While the TIMTOWTDI philos

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