The third edition of Programming Perl is impressive from the start. It has almost double the page count of the second edition. The cover is the same, except for the discreet banner in the top right corner, the TMTOWTDI ("There's More Than One Way To Do It") slogan at the top, and the list of authors. The similarity is only skin deep, however, as a look at the table of contents will quickly dispel any illusions that this book is only a revision. The third edition covers a multitude of changes made in the Perl language since version 5.003. It has extended or created many sections, while preserving cohesiveness and consistency.
Larry Wall and Tom Christiansen are back in this edition, while Randal L. Schwartz has been replaced by Jon Orwant. Larry Wall is the creator of the Perl language. Tom Christiansen is known as the caretaker of the Perl online documentation, and is the principal author of The Perl Cookbook (an indispensable resource for the Perl programmer). Jon Orwant is the Chief Technology Officer of O'Reilly & Associates and editor-in-chief of The Perl Journal, the best-known and perhaps most highly regarded Perl magazine. The style of the previous editions has been preserved. Lucid exposition interspersed with good examples and many jokes that will strike a chord with programmers are prevalent in the text.
The editor, Linda Mui, and the technical editor, Nathan Torkington, have done an excellent job as well. There were very few errors in the book, which is impressive considering the page count. The O'Reilly Web site (see Resources) has a link to the updated errata.
This review will have two key elements. It is a review of the book, but also a review (though in a much more cursory fashion) of the changes in Perl since version 5.003. The third edition of Programming Perl incorporates those changes, but does not distinguish between features from 5.004, 5.005, and 5.6.0. This is unfortunate, because there are major differences between the two versions, and many Perl sites running 5.005, for example, need to know what has changed with 5.6.0, compared with the changes from 5.003 to 5.005.
The "perldoc perldelta" command will show the changes made since the last version, so in a 5.6.0 installation you can see what has changed since 5.005. Similarly, "perldoc perl5004delta" will show what changes were made for 5.004. The information is also available on the Web at Perl.com (see Resources), but it is sufficiently technical that a more gentle summary should have been in the book.
There are many things new with Perl since the 5.003 release. New language constructs, modules, pragmas, and capabilities abound. The following is a summary of changes on the user side, using the relevant perldoc pages. You should consult them yourself, since this summary omits many minor but possibly significant changes.
| 5.003 to 5.004 | 5.004 to 5.005 | 5.005 to 5.6.0 |
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Overview and some gory details
The overview sections have changed little from the second edition, but they still provide an adequate introduction to the Perl language, mixed with "the appropriate amount of fun."
A more detailed overview of the language is given in Chapters 2 through 4. The content is updated in all the right places, including the invaluable "use constant" pragma. Again, there is little different so far from the second edition.
The chapter on pattern matching is new. The second edition had no more than 35 pages dedicated to this complicated topic, while the third edition has nearly 80. There are examples for all the features, and all the advanced and new ones are explained in depth. Where to start? Lookahead, cloistered modifiers, conditional sections, named characters, they're all there. The named characters and character classes are Unicode-enabled, and examples are shown for them. POSIX character classes are also listed.
The pattern matching chapter is sufficient for learning about this fascinating side of Perl. It carries a wise warning ("Don't try to do everything with regular expressions"), and that is something every Perl novice should avoid. It is impossible to capture in a chapter all the applications of regular expressions, however, and for those interested in further information Mastering Regular Expressions (see Resources) by Jeffrey E. F. Friedl is a good bet.
Subroutines, references, and data structures
The subroutines chapter covers new syntax (prototypes and attributes), plus the brand new lvalue attribute (as of 5.6.0). Imagine being able to modify the return value of your subroutine! Until now, special care had to be taken to allow modification of object attributes, for example. With lvalue subroutines, you can directly affect scalars returned by subroutines. Prototypes are another important feature, and should be used whenever possible (but not to "retrofit prototypes onto [old functions]"). This is a short but important chapter.
The chapter on references is important for those who need to learn about data structures and passing values with Perl. Anonymous data (arrays, hashes, and subroutines), closures, pseudohashes, hash slices, and weak references are covered in detail. The examples are good, as usual. The coverage of pseudohashes is particularly useful for anyone writing classes with named fields that need speed.
The data structures chapter is complete and useful, though Mastering Algorithms with Perl (see Resources) by Jon Orwant, Jarkko Hietaniemi, and John Macdonald is necessary for anyone trying to implement complicated data structures with Perl. The chapter in Programming Perl is, nevertheless, a good introduction with many examples. It also mentions the indispensable Data::Dumper module, used here for saving and restoring data.
The formats chapter covers a feature of Perl that is not widely used today. It is a combination of FORTRAN's output formatting keywords, BASIC's output layout, and nroff's ideology. If you have used any of those three, you may find formats convenient and useful. There is nothing noticeably new in this chapter, except that it's a chapter now where it used to be a section. At 6 pages, it's hard to see a reason for making it a chapter.
Packages, modules, objects, overloading, and tied variables
In the second edition of Programming Perl, object-oriented programming was not emphasized. The section on objects was small and offered little help with intensive OO methodology in Perl. This has changed with the third edition. The chapter on objects is a longer, more detailed exposition of OO in Perl, though it is still somewhat neglected in the book as a whole. Features like the UNIVERSAL class's isa() and can() methods, Class::Struct, and lvalue class methods are gently explained.
Packages and modules are important to any Perl programmer. The new chapters on those features are slightly longer than in the second edition, but probably should have been merged into one chapter as they are only a few pages each. They are important reading to anyone concerned with reuse of their Perl code (and this should be everyone), but there's little new since the second edition, other than new examples and updates for new features. Required module versions, for example, are covered (use MODULE VERSION).
The chapter on operator overloading is lengthy and useful. Moreover, it is completely new, because in the second edition there was no way to overload operators in Perl. This is a significant language shift, and the chapter documents it well. There are many examples covering the range from simple (addition/subtraction overloading) to the complex (overloading numeric constants and run-time overloading).
The chapter on tied variables covers the essentials of this useful technique, and is updated with methods for tying a filehandle, and a list of Tie modules on CPAN. There are also more examples and detail for the standard scalar, array, and hash tying methods.
It is difficult to support Unicode, and the chapter on that topic explains why. The UTF-8 encoding is the one that Perl implements best. There are others (UTF-16 and UTF-32, for example) defined by the Unicode consortium, but UTF-8 is the best supported encoding for international character sets. The Unicode resources at the end of this chapter, particularly the Perl, Unicode, and I18N FAQ will provide a more complete picture of what made it into the 5.6.0 release of Perl, and what didn't. The book does not distinguish well between Unicode as a character mapping and the UTF-8 encoding.
A neat example shows a Perl program written in UTF-8 encoding, so the variable names can use non-ASCII letters. Bringing more people into the Perl community should be easier when Perl is flexible enough to speak their language.
Unicode support in Perl as of 5.6.0 is a step in the right direction. It is not complete, however, and caution should be used. There are CPAN Unicode modules that work correctly with older versions of Perl as well as 5.6.0, and they should be used if appropriate. As an aside, getting simple applications like xterm and mutt on Linux to support UTF-8 encodings can be quite challenging as well. UTF-8 is a fairly new standard, and support for it is just starting to percolate into software. Perl loses out to Java in Unicode support for now, which is not surprising since Java was designed to support Unicode from its inception.
The chapter on IPC (inter-process communications) is an expanded version of the IPC section in the second edition. New and better examples are provided, and it is remarkable how a module like IO::Socket::INET can simplify the chore of writing a network server. Also, a neat example of the use of the new v-strings to send CR/LF is shown.
Threads are finally a stable (sort of) feature in Perl 5.6.0, and the chapter on them is a good resource for the beginning threads programmer. There is a brief description of threading as an algorithmic approach, a justification for the UNIX fork-based threading model we all love and hate, and some pretty good examples, including the use of the lock function and subroutine attribute. Unfortunately, you still have to build your Perl to support threads explicitly, because the threaded Perl interpreter is "pretty much guaranteed" to run slower than the plain non-threaded one.
The CLI (command-line interface) chapter is a must-read. All the information in it is guaranteed to save you time at some point in the future, whether through clever use of the -p switch, or through the PERL5LIB variable. Learn it thoroughly. This chapter is updated from the related section in the second edition, most notably by including more information about the environment variables that affect the Perl interpreter, and which were not mentioned at all in the second edition.
The saddest thing about the chapter on debugging is what neglects to mention. Despite all of its power and elegance, the built-in Perl debugger does not come close to the ptkdb debugger available from CPAN. Check ptkdb out on CPAN, and you will probably agree that it is a very good tool, at the very least. ptkdb may have been omitted because it does not run on every platform (it requires the Tk module, for one), but for a tool this powerful and useful, a simple mention would have been more than welcome. If you like the built-in debugger, or you have to use it because ptkdb does not run on your platform, the chapter will be undoubtedly useful. There's 10 more pages from the second edition, full of technical information and examples. Interoperability with Emacs is mentioned as well, though without specifics on setup and use. The Profiler section is last, pending any NBC lawsuits. Who knew Larry Wall watched so much TV?
The chapter on compiling is all about the internals of Perl. It is a fascinating read for the technically minded, and is helpful in understanding how the BEGIN/END/CHECK/INIT subroutines work, and how modules are used.
The internals chapter should probably have been merged with the compiling chapter. It is an excellent introduction to arcane (for most Perl users) subjects like embedding Perl in your programs or extending Perl with C code. It is too brief, unfortunately, but perhaps that is consistent with the overall beginner-to-intermediate level of the book.
The most pleasant surprise in the third edition are the "Perl as Culture" chapters. They are an excellent introduction to all the things that make Perl more than a language, a community. These chapters are greatly expanded versions of a few sections in the second edition, and a fascinating read.
The CPAN chapter is the starting point for anyone seriously interested in Perl development. CPAN is the best resource for Perl modules, and a chapter devoted to it is greatly appreciated.
The security chapter is also expanded significantly from the second edition. This is practical advice, and contains many useful examples. The original 4 pages have become 25 or so, and there isn't a single line you should miss. There is information specific to security with CGI programs (including, but not restricted to, the CGI module).
The chapters on common practices, writing portable Perl, POD (Plain Old Documentation), and Perl culture are well written and updated, and the examples are very good. These chapters should be read by anyone interested in participating in the Perl community, actively or passively. There's a lot to be learned from gems like "Black Perl."
Special names, functions, pragmas, and standard modules
The special names, functions, pragmas, and standard modules chapters are complete and well illustrated. Updates on new features are especially welcome, and the examples do a good job of bringing Perl 5.6.0 to life. It is nice that the technical reference section is really at the end of the book, where in the second edition it lay before the chapter on other oddments (called "Perl as Culture" and split into several chapters in the third edition).
A small discussion of Unicode compliance of modules and functions would have been useful for those interested in per-function and per-module compliance, but the hope expressed in the Unicode chapter is that everything in Perl can be magically made Unicode-compliant with the "use utf8" pragma.
All in all, the third edition of this very popular book is a major event in Perl's history. The release of version 5.6.0 brought many software improvements to the Perl community, but it also made the second edition significantly outdated. This gap is remedied by the third edition. Still, this book is no mere upgrade. Several sections are completely new, and others are more than twice their original size in the second edition. New modules, pragmas, functions, and capabilities are shown in action with great examples. Perl programmers should consider purchasing the third edition of Programming Perl for all these reasons, but most of all because this is now the definite and best reference for the Perl language.
- Read Ted's other Perl articles in the "Cultured Perl" series on developerWorks.
- CPAN has all the Perl modules you ever wanted.
- Perl.com offers Perl information and related resources.
- Programming Perl Third Edition by Larry Wall, Tom Christiansen, and
Jon Orwant (O'Reilly & Associates, 2000) is the best guide to Perl
today, up-to-date with 5.005 and 5.6.0 now.
- Mastering Regular Expressions by Jeffrey E. F. Friedl (O'Reilly & Associates, 1997) is a standard and definitive reference on regular expressions.
- O'Reilly & Associates are the publishers of Programming Perl and many other books mentioned in this article.
- Unicode resources:
- The Unicode Consortium Home Page is the place to start for Unicode.
- Read the UTF-8 and Unicode FAQ for UNIX/Linux (Linux-specific). Or go to the ftp site for The Unicode HOWTO.
- Read the Perl, Unicode and I18N FAQ
Teodor Zlatanov graduated with an M.S. in computer engineering from Boston University in 1999. He has worked as a programmer since 1992, using Perl, Java, C, and C++. His interests are in open source work on text parsing, 3-tier client-server database architectures, UNIX system administration, CORBA, and project management. He can be contacted at tzz@bu.edu.
Table of contents
- The authors
- What's new
- Overview and some gory details
- Pattern matching
- Subroutines, references, and data structures
- Formats
- Packages, modules, objects, overloading, and tied variables
- Unicode
- IPC and threads
- CLI and debugging
- Compiling and internals
- Perl culture
- Special names, functions, pragmas, and standard modules
- Conclusion
- Resources
- About the author
- Comments
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