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I've started learning Perl but most of my former programming experience has been in languages that emphasize object oriented programming such as C# and Java. All the Perl examples I have found tend to be long single function programs and I find my self writing code the same way. Are there any resources or tutorials for writing maintainable well structured programs?
Firstly, regardless of what sort of Perl programming you're doing, you'll probably find Perl::Critic to be invaluable. The command-line tool is by far the most convenient for getting feedback on your code, but you there is also a web interface where you can upload your Perl code and receive instant, automated feedback. Note that Perl::Critic isn't going to teach you good structure, but it will help improve your style in general, and steer you away from some common mistakes.
To go with Perl::Critic, I'd recommend getting a copy of Perl Best Practices (PBP). It contains a lot of detailed information upon which Perl::Critic was based. Even if you disagree with particular guidelines in the book, it makes you think about how you code, and that's very, very valuable. You don't have to shell out money for a book, but the two compliment each other very nicely, and there are lengthy discussions you'll find in PBP that you won't get from Perl::Critic.
If you've already worked with other OO languages and OO design, the you'll probably find Moose to be a comfortable transition. Moose is very stable, very well supported, and has a huge and active community (especially via IRC). Moose supersedes almost all the existing OO Perl advice out there, including my own. Object Oriented design is common for a reason; it makes sense for a lot of projects, and there's no reason not to use it in Perl.
Personally, I found a massive improvement in my own program structure when I moved to a test-driven development model. Under such a model, breaking a problem down into small, easily tested units is essential. Start with Test::Tutorial if you're new to testing in Perl and then look at some other testing resources or books if you want to learn more. Use a tool like Devel::Cover or Devel::NYTProf to see what your test cases are hitting and what they're not. Having code that's hard to test is often a sign of poor structure.
Having said all this, the best teacher by far is to get involved with an existing Perl project with experienced contributors. See how they do things, and when you make contributions, think about their advice. If you want a real application with awesome cool value that seems to have sucked up the very best and brightest of the Perl community, then I'd recommend getting involved with Padre, the Perl editor.
If (for whatever reason) you can't get involved with another project, then consider posting code samples to communities such as Stack Overflow, or PerlMonks. Better still, if you can make your code open source, then do so, and solicit feedback. All programming languages are better learnt with others who are already familiar with them, and Perl is no exception here.
May you do Good Magic with Perl,
Paul
Perl Best Practices
If you're learning OO Perl you might as well move on to the next big thing and start learning Moose.
Moose is a postmodern object system for Perl 5 that takes the tedium out of writing object-oriented Perl. It borrows all the best features from Perl 6, CLOS (Lisp), Smalltalk, Java, BETA, OCaml, Ruby and more, while still keeping true to its Perl 5 roots.
Moose is 100% production ready and in heavy use in a number of systems and growing every day.
If you already know how to write well-structured programs and you want to write well-structured Perl, but the only impediment to that is the abundance of ancient, crufty, spaghetti-code examples that are scattered around the net and refuse to die...
Ignore the examples. Or at least ignore their poor structure and only pay attention to the small syntactic bits that you need to learn from.
There is nothing in Perl that pushes you to write bad code. If you already know how to write good code in other languages, then you can apply the exact same principles and practices in Perl. It's merely a matter of discipline, just like in any other language.
If you feel you already are learning the basics and want to improve program structure, then I'd suggest these books, probably best to read in this order:
Intermediate Perl -- this is probably the place to start for what you're asking about; covers developing and using Perl modules (essential for good structure), references, complex data structures, OO, and more
Perl Medic: Transforming Legacy Code -- demonstrates well-structured Perl by showing how to fix poorly-structured Perl
Effective Perl Programming: Writing Better Programs with Perl -- a classic, but still useful; full of Perl idioms that will help you write more Perl-ish Perl; not much on OO, but covers more fundamental coding structures to make your code more succinct and yet more expressive. I think of this as the book that got me from Perl literacy to Perl fluency
All three are best once you've comfortable with basic Perl syntax, but none of them get too far into esoteric advanced concepts that you can't follow if you're still starting out in Perl but have reasonable programming experience in other languages already.
Apart from the sources mentioned above I strongly recommend the book
"Higher-Order Perl" by Mark Jason Dominus.
If you can afford it buy it, otherwise the author has put the book on his website for free as in free beer, Free Higher Order Perl. For the PDF version: direct download URL (1.9 MB).
Edit:
I forgot to mention Perl Design Patterns. The PerlDesignPatterns site is a very good resource or reference for learning Perl design patterns.
Object-Oriented Perl
http://perl.about.com/od/objectorientedperl/Object_Oriented_Perl.htm
http://www.codeproject.com/KB/perl/camel_poop.aspx
http://www.tutorialspoint.com/perl/perl_oo_perl.htm
Personally, I didn't write good OO Perl until I started learning Java. I recommend you spend a small amount of time learning OO in a true OO language and apply what you learn to Perl.
For a place to be mentored, PerlMonks is GREAT.
Write Perl the way you would write C, although you should take advantage of some things BEGIN blocks and modules. It should be formatted so that it looks more or less like old style K&R C code.
As for structure, skip the OO stuff and style it as ADTs instead:
http://en.wikipedia.org/wiki/Abstract_data_type
Basically you do this by using data-structures where you would have used objects in OO (and separating out the algorithms into their own functions).
Then, pick only one way to do things and stick to it, consistency is vital to readability.
If you manage that, the code can be both readable and easy to understand.
Paul.
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I need to learn Perl for an academic research I am doing. I need to go through a lot of older perl scripts and run them, tweak some perl scripts from open source tools for my use and of course make some of my own.
I have a tight schedule so I needed to be comfortable with a perl code pretty quickly. I have previous coding experience from C and Java but not with any scripting languages as such. I found Perl to be quite difficult to get used to from the beginner tutorials I have gone across. I am more comfortable learning through screencasts rather than go through books when I start learning languages. Of course one always needs a good reference book or user manual but videos are more intuitive when learning something first especially because I can see the expert actually code stuff and explain it at the same time.
I've heard from other friends that there are great screencasts for other scripting languages like Ruby and Python. I was wondering is there any really good quality screencast for Perl out there. So, I ask for help from people who have good experience with Perl to point me to a good resource.
I don't think that screencasts are really that valuable in terms of learning fast and deep. There are some nice Perl 6 screencasts, but for Perl 5 I still think perldoc is the best thing you can find. Comprehensive and readable.
Also, Perl is a pretty big language, similar to natural languages in many cases: easy to get comfortable with simple things, and requiring more experience to get around the difficult/sophisticated syntax/concepts. Mastering Perl takes time, especially when you'll need to work with old Perl (it's pretty different to Modern Perl, written today).
This may not work for everyone,but personally, I find taking on small projects (or inventing my own) to be the only sufficient way of learning a language quickly.
One trick I use for high-speed, is to take stuff I've already written in other languages, and port it to the new one. I moved from Rexx to Perl this way a few years ago, then from Perl to Python recently, and now I'm moving from Python to Ruby in the same way. So, you could try taking something you've written in C, and porting it to Perl.
Frankly, being given a big pile of old code to comb through is a huge gift. You could try plugging the classes and functions into new short projects, to see how they behave. You could also try writing unit tests exercising them, to give you both familiarity with coding in Perl, and familiarity with the functionality of the codebase you're familiarizing yourself with.
One of the best ways of learning is:
Learn Perl debugger. If you are familiar with gdb, it should be a breeze
Run a few of those older scripts, and try to grok them, by looking up sercheable references on perldoc web site, tweaking/messing with them, and importantly, debugging them.
Whenever you run into some piece that you just don't get (especially feature/functionality that's not easily searcheable for like a keyword/built in function would be), come to SO with that specific thing and you'll get fairly reliably comprehensive answers.
Go through a decent set of books. O'Reilly are the best for Perl (Camel would be my recommendation) - they are actuially VERY quick/easy to skim through to get the main points of someone who already has C and Java experience. Couple that with the main perldoc tutorials (data structures, modules and OOP)
For doing new work of your own, get a hold of Perl Cookbook in addition to the above.
After having heard about new parts of the Perl ecosystem, such as Moose, DeclareX, and Catalyst, I thought that it'd be nice to take a look at Perl. Unfortunately, all of the introductory material I can find targets Perl 5.8 or 5.6, and knows nothing about these newer frameworks—let alone features introduced in recent Perl versions, such as the ~~ operator. What resources are available for someone interested in coming to Perl fresh, and wanting to learn the current best-practice way to do things right from the get-go?
While I can read the 3rd edition of the camel book, then work the rest of my way through piles of CPAN documentation and the like, I'd tremendously appreciate a tutorial that doesn't force me to learn a bunch of deprecated ways to do things, just to turn around and unlearn them again when I read a reference manual. Real-world code that's well-documented and uses some of these newer corners of Perl would also be wonderful.
chromatic is in the process of writing a Modern Perl book which is available for preview in his Github account. The recent Catalyst book by Kieren Diment and Matt Trout covers several modern perl practices and the current "Enlightened Stack" as Matt I believe calls it.
There is also work going on for a Moose book, but I doubt it will be available before next summer even if the authors were able to focus on it full time. For learning Best Practices, as long as you take it with a huge grain of salt the discussion in Damian's Perl Best Practices is worth reading. I wouldn't recommend his practices are best, but they illuminate where the conversation points are and you can google around for people's comments on it. The biggest problem I personally had was the OO suggestions it had, and it led me to find Moose which I adore.
Finally, interact with the community. Join a mailing list or three, an irc channel or two, and blog regularly about what you're learning. The Perl community is generally supportive of helping people who really are interested in learning find the tools they need.
Learning Perl, 5th Edition is current up to 5.10. There's even a chapter for the smart match operator, just like you want, in addition to the other new features that a beginner will want. If you want to start learning Perl, that's the book to use. Once you get through it, move onto whatever else you want to do. I'll have Effective Perl Programming, 2nd Edition out around the start of spring too. That will be current up to 5.10.1 (and maybe a little farther since we use at least one 5.12 feature in some code).
You really don't want a book on Catalyst or Moose. Anything you read will be out of date because those projects have a high velocity and the practices change pretty quickly. You're going to need to learn the basics before you dive into the advanced topics, anyway.
To continue as a programmer, you're going to have to get used to not depending on books. I can't write them as fast as stuff changes, so you have to learn from the documentation too. That's just how life is.
There was an excellent talk at OSCON by Paul Fenwick on "Awesome Things You've Missed in Perl" where he gives several code examples and usage tips for using Modern Perl.
The talk was recorded, but it's not on the list of recordings yet:
http://www.oscon.com/oscon2010/public/schedule/proceedings
Here are some other great talks worth checking out that also provide examples of Modern Perl:
Top 10 Perl Performance Tips
Understanding and Optimizing your Code with Devel::NYTProf
Moose is Perl: A Guide to the New Revolution
And finally (not from OSCON):
Larry Wall speaking at Google
Even if this answer is very late, a new book about Modern Perl has came out on 2012. It's called Beginning Perl and is written by Curtis 'Ovid' Poe. It focuses on learning the Perl skills employers are looking for and is for both programming beginners or for experimented programmers who want to learn a new language.
After introduce the language itself, Ovid continue on DBIx::Class, Moose, Catalyst, and more CPAN tools and community's best practices with a lot of real-world examples, demonstrating how you actually use Perl in the workplace, for web development, data processing or system administration. The book was first available for free on the O'Reilly website, but has been removed now (you have to pay for a printed or electronic version).
Hope it will be useful for future readers of this QA.
I would recommend the mentioned Learning Perl 5th Edition followed by Damian Conway's Perl Best Practices (also previously mentioned).
I would like also point you to the PBP Module Recommendation Commentary that discusses the current "community view" of the modules discussed in Perl Best Practices.
Despite what is discussed (or not) at this site, two of my favorite Perl Best Practice recommendations are Data::Alias and Smart::Comments (Even though Smart::Comments is a source filter, you can easily remove it before sending your code to production. It is great for debugging.).
Is it feasible to learn Perl and Catalyst at the same time? If so, what would be the typical path?
I am experienced .Net/C#/C++ developer but fairly new to Perl
Catalyst is a web framework in Perl which does use some advanced concepts in Perl like attributes, references, et cetera. Perl should be learnt first. When you are comfortable with Perl, you can dive into Catalyst.
For learning Perl, you can check out http://learn.perl.org/. There are lots of Perl Mongers websites as well. You may be able to find a community near your area too!
Also do surf on to Perl Monks.
Start right away with a gentle Catalyst tutorial, with some beginner's Perl tutorials/references handy. Coming from C#/C++ you will have a few surprises with Perl, but not enough to worry about. Perl is typically distributed with much documentation, and it's invaluable. So I feel you can pick up on Perl as you learn Catalyst, and then learn deeper Perl skills later.
In the book, coming out on the 12th of july 2009, we recommend that you're familiar with Perl data types, references, and objects. The best free sources I came up with for learning about this stuff are the Perlmonks tutorials, especially the one on references.
If you're an experienced programmer just getting into perl then Catalyst is quite a good way to learn how to program disciplined, structured, object oriented Perl.
Other than that, as dwc says the tutorial is pretty good.
The most important thing to remember to always:
use strict;
use warnings;
at the beginning of all Perl files.
(at least until you know why)
I think its only natural to know about the material that goes into building before constructing one. and framework is precisely that.
Natural transition is from the basics and if you think you have less time, you should probably start with small books like Beginning perl by simon cozens or learn.perl.org etc
to know what it is like to write programs what are differences in procedural and object oriented lingo when it comes to perl etc.
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I got into Perl years ago and always found it a fun and expressive language to work with.
I found that programming in Perl makes me quite productive thanks to its low overhead and the outstanding amount of ready-made solutions to common problems on CPAN.
If you're new to Perl, what got you into it?
I was coding PHP for a living, and then heard of their change from :: to \ as a name-space separator. I'm really not joking or being spiteful, but that is really what got the ball rolling.
Not to be elitist, but I suddenly realised that the people I had to collaborate with whom knew PHP understood very little in programming concepts in ways that frustrated me how they could be so blind, the people in the IRC rooms for it were no longer a source of help for my questions, and I usually spent more time answering questions and waiting for somebody to turn up whom could answer mine. Usually I ended up solving it myself.
Most the time I realised was people re-solving the same problems over and over again in increasingly bad ways.
I discovered problematic behaviours in PHP which defied logic and reasoning (like the array_merge_recursive family), and discovered functions that were undocumented in how to use them, and when I reported a bug in the functions, my bug was marked as "Bogus" and I was expected to be psychic.
I had a friend whom was constantly proclaiming the goodness of Perl, so I basically gave it a shot and now am hooked like an addict.
Additionally, my experience in other higher-order dynamically typed languages (JavaScript and Ruby, yes, JavaScript is a more powerful language than PHP in terms of language features) left me a knowledge with many ways to solve types of problems easily, but being restricted in such a way I had no way to use these powerful features. Perl satisfied this need.
Why Perl and not Ruby? I've played with Ruby a bit, but my experience taught me the support and documentation is sparse, the language is slow and immature. Nice it may be, but its still in diminished in capacity against Perl from what I've seen. And it shared PHPs major flaw that it has a huge user base comprised of total novices all doing things the wrong way, and I really wanted to not have to deal with that so much.
It's not nice to be elitist, but once you have tried to explain the same thing to 30 people (and taken an hour to get a simple concept into their heads every time) it reaches a point of frustration. (I can't cope with the 'There is somebody on the internet who is wrong' situation, If I can't SEE it, it doesn't happen)
I started doing Perl during my third year in computer science as a part of 'Scripting languages' course. I have a friend studying biotechnology and I helped her with some data mining scripts for dealing with protein databases (parsing text files, regexps, simple integrity checks). It was all very natural to do in Perl.
Then I got my first part-time job and had to use it professionally. I was responsible for developing set of batch scripts that handled some part of business logic in the company. And it was the task where Perl revealed all its potential. Need to get data from DB? - no problem, just go to CPAN. Need to automate wiki - no problem, go to CPAN. The amount of already created modules is overwhelming and you can be sure you will always find what you need in CPAN.
To sum up. For me, Perl is a swiss army knife of scripting languages. Everything can be done in it and it has huge number of additional modules even for very exotic tasks. And by the way, did I mention REGEXPS?
With Perl (and the expressive power behind TMTOWTDI), programming becomes a creative task. I can write if($expr) { $statement; } if I plan on having many else statements, or I can write $statement if $expr; if that makes more sense (for example, I'm fond of writing:
sub doSomething {
my($toObject, $argument) = #_;
die "No object specified" unless defined($toObject);
die "Object invalid: $toObject" unless $toObject->ISA('Example');
# Do stuff
}
but of course that's not always the easiest, and most expressive way of doing it; so I come up with a better way for the task at hand!). People complain because Perl lets you write horrible looking code; I love Perl because it lets me write code which looks pretty to me (and yes, I can see the downside of having a dozen different programmers writing in their own styles; I'll hold to the idea that good writers can be pretty expressive and understandable no matter how different the subject matter).
With other programming languages, I end up having to think my way through abstraction layers (how will this Map give me Collections whose Iterators I can use to ... and so on). With Perl, I'm usually only one abstraction level above basic Perl. For instance, DBI will give me database results as ordinary, everyday Perl scalars, lists and hashes, so everything I know about these simple, core data structures carries over to every task I put DBI to (Complicated data structures? That's what PostgreSQL is for!).
I've only been using Perl full-time for about a year, but these are the big wins for me, and the reason I first went full-time onto Perl after a year suffering at the hands of Java 1.4's Collections model (don't ask). Other programming languages make me feel like I'm putting together a jigsaw puzzle, as you line up all the modules and packages just right; Perl feels like a box full of Legos, with some "special" bricks (like DBI, CGI.pm and Test::*) thrown in for good measure. There are tons of different ways to solve any problem, and Perl lets you try any of them you like, in any way you like.
I'm still not that long time in the Perl community and what me first brought in was Larry Wall's humor and wisdom. True, Perl has it quirks but the language comes from an understanding of things that is very close to mine so I'm much less comfortable with Python and to a lesser degree Ruby.
I don't do web app's more GUI with WxPerl and it works just fine. I'm very interested in languages also in lesser known like factor, boo, rebol and so on but all in all is Perl my choice. and it's because a mixture of powerful syntax (can be very functional if you like it), the community, CPAN of course, and, like I said before, due to the cosy feeling being in the right place.
Perl is its community, which is the reason to use it both on a social and practical level. (See CPAN and Perlmonks, which likely inspired SO.)
There's a lot of freedom when coding in Perl; you can write some wicked-crazy unreadable hacks, but it doesn't take long once you've gotten a feel for the language (and learned how to use perltidy :-) ) before you realize that well-written perl code can look downright pretty.
It's interesting; I ended up as a full-time Perl programmer after learning it for my sysadmin-type job in college; and now it's my strongest skill. I'm going to stick with Perl for a while because so far the language has been versatile to grow with me. I write a lot of systems software in Perl, and decided to pick up web programming for fun, and Catalyst was there waiting for me. Do I want to try out a new language paradigm? Perl will probably support it. In contrast, when I was coding in PHP for a time, I immediately felt like I was pressing against a glass ceiling.
I work as a technological troubleshooter for a big organization in southern OH. I had to learn Perl to keep some automated network text manipulation systems up and running and eventually got a little excited about it. I eventually thought of myself as a developer and wrote some programs that parsed some database data and made some people’s lives a little easier. But after reading some of the posts on this website and listening to the stackoverflow podcast and even starting to read the book Code Complete from someone’s suggested reading list I no longer have any delusions that I was a developer of Perl or any other language for that matter. However, maybe someday I could be.
I had used awk a few time for shell scripts way, way back in the days. In one ancient project we needed to implement the a TELNET protocol connection, so I wrote a quick version in Perl 4. It worked really well, and I started to really like the language.
Later, I wrote a big full commercial web application in Perl 5, complete with it's own framework and database. I was careful not to use to many of Perl's more esoteric features, so the code looked more like C than Perl. It worked really well, performance was good and the code was easily extended.
Recently I've been working in Java, but I often find myself missing the Perl's loose typing, and its ability to encapsulate things way better than Java. My favorite features were being able to put Perl datastructures (arrays and hashes) and code directly in config files and execute them, and the ability to tie code to syntax like arrays. Both lead to some really slick code.
Paul.
simple syntax, powerful scripting capabilities for win32 and unix systems, and totally powerful regex!
I pickup Perl on my first job where I had to write plenty of automation script for electrical engineers to mine datalogs and format them to Excel and sometimes deal with sql server too. With Perl I could usually get something working rather quickly, so all is good in the manufacturing land. :P
I started using Perl as an enhancement to our build process for embedded development. We needed to develop diverse outputs based on our cross compiled payload and Perl was a great fit.
Our enhancements included floating-point to hexadecimal conversion, S-record post-processing, and checksum modifications.
Not that this kind of work can't be done with many other tools, but I would definitely recommend Perl for build-related work.
What brought me to Perl was when I saw the DBI and realized that I could write the ESQL/C programs I was writing at the time in one fifth the time.
What has kept me using Perl is that the two other languages likely to unseat it are both strongly typed. That is
print "10" + 5;
is a type error rather than 15.
I'm not taking it up. I had to work on a project in Perl a few years ago, and I came to really dislike the language. It has a sometimes-awkward syntax and a lot of crazy gotchas that I found hard to work with. Honestly, I think Ruby has superseded Perl in many respects: it's good at roughly the same things, but has much nicer features and is easier to use.
Perl still has CPAN, though, which even Ruby can't match (although Ruby has a lot of useful libraries, too).
I considered learning Perl last year.
It was the only technologies that I actively decided not to learn. This is nothing directly against the language itself, it just seemed that I would be coming to the party 10 years too late. It is very useful for the shell scripting tasks that it was designed for but for me personally I prefer languages with a stronger coherence.
Perl 6 seems like it's on indefinite hiatus and even when it arrives I don't believe that it will make the language profoundly more compelling.
Also, Larry Wall scares me.
For my situation Perl wasn't the right choice and thats why.
Perl is not as bad as I thought. I used to use it in a couple customer scripts about one year ago, and even grew to like it a bit. Then again, I've never ever missed it since.
The reason? It's mostly a write-only language. Going above a 100 line solution made me be wary of my own code, which is definately not a good outcome. With other languages that bar is considerably higher (maybe 1000 or 10000 lines).
I see no reason to go for Perl in new projects, for new users, in -soon- 2009.
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I am a bioinformatics student and am in the process of learning perl. I don't have a strong programming background but would like for that to change.
Right now I am in the process of reading/following and coding from this book
I want to know is this the best way to go about learning perl? Should I be experimenting with regular expressions more? Should I keep trying writing sample perl scripts?
Related: what are good books for learning perl
The definitive learning Perl book is aptly called "Learning Perl". Get it.
I cannot recommend writing sample scripts. Try to write something that you need. It doesn't have to be a big endeavor; everyone needs a little tool now and then. Writing sample scripts is boring; always was, always will be.
This seems like a potential duplicate as here are some related questions:
What are the best resources to starting learning Perl?
What’s the best online source to learn Perl?
Like most other answers on this post I can't disagree with the choice of "Learning Perl" as your first Perl text. Keep a copy of the perldoc documentation available for quick reference(I prefer using the html/pdf format which is available as a download from the main page).
In order to keep things from getting boring, especially in the initial stages I started converting my shell scripts to Perl, hacking away at it until I had three or more different versions of the same program with decreasing file size(not great for maintenance though). But then you know what they say - TMTOWTDI. Now I don't bother with shell scripts any more, writing it in Perl results in smaller turnaround times and the code can be easily reused and enhanced.
Once you are familiar with the more advanced concepts and are approaching a level of comfortability with using it for your day-to-day work or just simple one-liners you might want to have a look at Mark Jason Dominus' Higher-Order Perl which, according to me, takes the language and the reader's understanding of it to an entirely new level. The chapter on "Recursion and Callbacks" was a real eye-opener and changed my style completely from that of writing C-programs in Perl to actually writing "Perl" programs in Perl.
I use the online book "Learning Perl the Hard Way" to teach my coworkers about Perl.
Don't be intimidated by the title, it's just that it's directed at programmers who are already fluent in another language and therefore it doesn't focus on the programming part, but mostly on the Perl part, so it may apply better to your case (or not).
You really can't go wrong with the Lama book
Learning Perl
There's quite a library of O'Reilly books on Perl. Programming Perl is also excellent and probably worth having to complement the Lama book - I have both on my shelves and although I haven't needed to code in Perl for quite some time I found these books together a solid enough combination. The Perl Cookbook came in useful too (yes, this is one of those areas that O'Reilly has pretty much sew up :-).
As to practical exercises, Perl does have something of a reputation as a 'Write Only' language, so look for clear examples and if you are confused by anything don't necessarily assume that the problem is you - there's always more than one way to do it.
You also might want to look for examples of good code to study.
My experience is that there's nothing better for learning than doing. But you need someone to provide feedback, especially when you hit roadblocks that you can't get past. Stackoverflow is good for that, but, IME, Perlmonks is better in that there is a chatterbox for immediate feedback, as well as their question-and-answer posts for longer questions, combined with a more specialised environment. (And Larry Wall has been rumoured to hang out there, too, as well as a number of the authors of the above-referred-to books.)
Learn by doing. Get the books mentioned by others, but the real way to learn is to start a simple project. Mine was a Gtk based SQL editor. If you run into problems ask questions here and on the Perl Beginners list.
The choice of book is can be vary from person to person. So, as bioinformatics student who use perl, don't get any book that called "(X Programming language) for bioinformatics". Usually this kind of book is either.
They only give very basic of that programming language. You gonna to miss all the power from that language.
Wasting its space on how to use API, which you can find information easily via google.