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Minimal Perl for Unix and Linux People
Posted by
samzenpus
on Wed Feb 21, 2007 03:37 PM
from the easy-does-it dept.
from the easy-does-it dept.
Ravi writes "Perl (Practical Extraction and Report Language) — the language which was created by Larry Wall is arguably one of the greatest programming languages. But it has a reputation for taking an excessive cryptic nature which gives it an image especially among Perl novices as a language which is complex and hard to master. Minimal Perl: for Unix and Linux people, authored by Tim Maher and published by Manning Publications addresses the obstacles presented by Perl's complexity. This book which is divided into two parts comprising of a total of 12 chapters takes a unique methodology to explain the Perl syntax and its use. The author emphasizes on Perl's grep, awk and sed like features and relys on concepts such as inputs, filters and arguments to allow Unix users to directly apply their existing knowledge to the task of learning Perl." Read on for the rest of Ravi's review.
What I found while reading this book is that the "Minimal Perl" is a specially crafted subset of Perl language designed to be easily grasped by people who have a Unix background and who wish to use Perl to write their scripts. Its aim is to filter out the complex way of writing programs using Perl and whenever possible to accomplish tasks using just one or two lines of Perl. In the first part of the book, the author explains how Perl can be used to do the same tasks as accomplished by common Unix tools such as grep, awk, sed and find. He goes one step further by explaining how one can accomplish much more and in a much simpler way by using Perl techniques.
Throughout the book, the author makes sure that the learning curve in acquiring Perl skills remain gentle. Perl is a language whose syntax has a multitude of options, this book is peppered with numerous tables which provide excellent information at a glance. For example, in the third chapter titled "Perl as a (Better) grep command", the author lists and compares the fundamental capabilities of Perl and the different grep commands such as grep, egrep and fgrep which clearly shows the advantages that Perl has over grep. In another table, you get a birds eye view of the essential syntax of Perl's regular expressions and their meaning. This chapter alone has around 12 tables. This is a really nice feature because it doubles as a Perl reference where you can flip to the respective page and get the information you need.
The main strength and drawback of a language such as Perl is its dependence on regular expressions for accomplishing complex tasks. Once you master the regular expressions, the sky is the limit for ordering and segregating data using this language. In Perl, there is more than one way of doing the same thing. What is unique about this book is that the author specializes in explaining the easiest way of doing a particular task.
In many places, the author demonstrates complex tasks using just a few lines of Perl code. Many of the examples covered in this book are practical examples which give an idea of how the commands relate to the final outcome. For instance, while elaborating on the one line grep like commands in Perl, the author illustrates a web oriented application of pattern matching where he shows how to extract and list, the outline of slashdot.org site's front page. The surprising thing is this is accomplished using just a single line of Perl code. This book has lots of such one line examples which teache how to use Perl intelligently using minimal effort.
If part I of this book focuses on ways in which simple Perl programs can provide superior alternatives to standard Unix commands, the second part throws light on the other aspects of Perl concentrating on the syntax of the language and various built-in functions and modules available which do away with a lot of re-invention of the wheel, so to speak, and helps churn out code which is portable.
Chapter 7 titled "Built-in functions" introduces an eclectic mix of functions available in Perl. You have functions which are used to extract a list of fields from a string, functions to access the current date and time, generating random numbers, sorting lists, transforming lists, managing files with functions and so on. These functions are broadly classified into those which generate and process scalars and those that process lists.
In chapter 8 of this book, the author involves the reader on the numerous scripting techniques that can be used to write better Perl programs.
It was quite surprising that the author has chosen to discuss the variables, more specifically the list variables comprising of arrays and hashes, as well as the looping constructs only in the 9th and 10th chapters, when they should be somewhere up front. In hind sight, I feel it is a good decision. Once you execute the one liner Perl programs in the initial chapters, you will be fairly confident in using Perl by the time you reach the 9th chapter.
The last two chapters deal with creating sub-routines and modules. Over the years various Perl programmers have created modules which are used for diverse purposes. With an aim to share these modules, they are collected and stored at one central place known as CPAN, which is an acronym for Comprehensive Perl Archive Network. The final chapter, apart from teaching how to create modules in Perl and manage them, also introduces the CPAN and ways in which one can find the right module by searching on CPAN.
The special variables cheat-sheet and the guidelines for parenthesizing code provided in the two appendices are really useful as a quick reference while writing Perl programs.
This is not a comprehensive book on Perl, rather the author provides a slice of Perl which when mastered can accomplish most of the jobs which require Perl. You won't find object oriented concepts of Perl being mentioned in this book. In many ways the author has moved beyond explaining a subset of Perl by providing a section titled "Directions for further study" at the end of each chapter, where the author lists further material which can be used to learn more about the topic that is covered.
I really enjoyed going through this book, especially because of its focus on the practical side of using Perl and taking a minimal approach.
Ravi Kumar maintains a blog titled "All about Linux" where he shares his thoughts and experiences in using Linux, Open Source and Free software.
You can purchase Minimal Perl for Unix and Linux People from bn.com. Slashdot welcomes readers' book reviews -- to see your own review here, read the book review guidelines, then visit the submission page.
Throughout the book, the author makes sure that the learning curve in acquiring Perl skills remain gentle. Perl is a language whose syntax has a multitude of options, this book is peppered with numerous tables which provide excellent information at a glance. For example, in the third chapter titled "Perl as a (Better) grep command", the author lists and compares the fundamental capabilities of Perl and the different grep commands such as grep, egrep and fgrep which clearly shows the advantages that Perl has over grep. In another table, you get a birds eye view of the essential syntax of Perl's regular expressions and their meaning. This chapter alone has around 12 tables. This is a really nice feature because it doubles as a Perl reference where you can flip to the respective page and get the information you need.
The main strength and drawback of a language such as Perl is its dependence on regular expressions for accomplishing complex tasks. Once you master the regular expressions, the sky is the limit for ordering and segregating data using this language. In Perl, there is more than one way of doing the same thing. What is unique about this book is that the author specializes in explaining the easiest way of doing a particular task.
In many places, the author demonstrates complex tasks using just a few lines of Perl code. Many of the examples covered in this book are practical examples which give an idea of how the commands relate to the final outcome. For instance, while elaborating on the one line grep like commands in Perl, the author illustrates a web oriented application of pattern matching where he shows how to extract and list, the outline of slashdot.org site's front page. The surprising thing is this is accomplished using just a single line of Perl code. This book has lots of such one line examples which teache how to use Perl intelligently using minimal effort.
If part I of this book focuses on ways in which simple Perl programs can provide superior alternatives to standard Unix commands, the second part throws light on the other aspects of Perl concentrating on the syntax of the language and various built-in functions and modules available which do away with a lot of re-invention of the wheel, so to speak, and helps churn out code which is portable.
Chapter 7 titled "Built-in functions" introduces an eclectic mix of functions available in Perl. You have functions which are used to extract a list of fields from a string, functions to access the current date and time, generating random numbers, sorting lists, transforming lists, managing files with functions and so on. These functions are broadly classified into those which generate and process scalars and those that process lists.
In chapter 8 of this book, the author involves the reader on the numerous scripting techniques that can be used to write better Perl programs.
It was quite surprising that the author has chosen to discuss the variables, more specifically the list variables comprising of arrays and hashes, as well as the looping constructs only in the 9th and 10th chapters, when they should be somewhere up front. In hind sight, I feel it is a good decision. Once you execute the one liner Perl programs in the initial chapters, you will be fairly confident in using Perl by the time you reach the 9th chapter.
The last two chapters deal with creating sub-routines and modules. Over the years various Perl programmers have created modules which are used for diverse purposes. With an aim to share these modules, they are collected and stored at one central place known as CPAN, which is an acronym for Comprehensive Perl Archive Network. The final chapter, apart from teaching how to create modules in Perl and manage them, also introduces the CPAN and ways in which one can find the right module by searching on CPAN.
The special variables cheat-sheet and the guidelines for parenthesizing code provided in the two appendices are really useful as a quick reference while writing Perl programs.
This is not a comprehensive book on Perl, rather the author provides a slice of Perl which when mastered can accomplish most of the jobs which require Perl. You won't find object oriented concepts of Perl being mentioned in this book. In many ways the author has moved beyond explaining a subset of Perl by providing a section titled "Directions for further study" at the end of each chapter, where the author lists further material which can be used to learn more about the topic that is covered.
I really enjoyed going through this book, especially because of its focus on the practical side of using Perl and taking a minimal approach.
Ravi Kumar maintains a blog titled "All about Linux" where he shares his thoughts and experiences in using Linux, Open Source and Free software.
You can purchase Minimal Perl for Unix and Linux People 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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Minimal Perl for Unix and Linux People (Score:3, Funny)
Very Minimal Perl for Unix People (Score:3, Informative)
Very useful if you need to use text files from DOS/Windows and DOX2UNIX is not installed:
perl -e "while(<>){s/\r//;print;}"
This strips carriage returns out of a file, and does it pretty quickly.
Re:Very Minimal Perl for Unix People (Score:5, Informative)
No, it's horrendously slow. The traditional Unix way of doing it (tr -d '\015') is around twice as fast on files that are sufficiently large that startup costs are lost in the noise, and even faster on smaller files.
Parent
Re: (Score:3, Informative)
*sigh* (Score:5, Funny)
Re:*sigh* (Score:4, Insightful)
Parent
Re: (Score:3, Informative)
Remeber that a "Backronym" (hate that word!) is a subtype of acronym.
Re:*sigh* (Score:4, Interesting)
Parent
I've got a question about subtypes of acronym (Score:4, Funny)
Would Muhammad Ali's GOAT (Greatest Of All Time) line of food products [bakeryandsnacks.com] be considered a snackronym or a blackronym?
Parent
Re:*sigh* (Score:5, Funny)
ITYM 'Poorly Hung Perl'. 8^)
Parent
Re: (Score:3, Interesting)
Cryptic? Complex!? (Score:5, Funny)
So wrong! Just look at the following example:
#!/usr/bin/perl -w
length q caller vec and print chr oct ord q qx eq and print chr ord q ref or and print chr ord q or no and print chr ord q else and print chr ord qq q q and print chr ord q tie gt and print chr ord qw q sin q and print chr ord q q eq and print chr ord qw q sin q and print chr ord q sin s and print chr ord q cmp lc and print chr ord q split s and print chr ord qw q lc q and print chr ord q ne sin and print chr hex length q q bless localtime ref q
Run that. Nothing cryptic or complex at all.
(BTW, it prints "Perl is simple!")
Re:Cryptic? Complex!? (Score:5, Interesting)
I used Perl for fun and profit (wrote many Perl scripts for a speech software company) for many years, hanging on past the point where others started using Python, PHP, and Ruby instead. I knew Perl and could practically think in it. But one of the main problems with Perl is it's so easy to right totally unmaintainable, totally unreadable code. I read a Perl program I wrote a few years ago and I can never figure it out. The object-oriented part of Perl is a ridiculous kludge with so many little details that I can't remember them all. There are about 100 subtly different ways to write a constructor for your object:
sub new() {
my ($class) = @_;
my $self = {}
return bless $self, $class
}
sub new() { return bless {} }
sub new() {
my ($class) = @_
my $self = {}
bless $self, (ref $class || $class)
}
All of these, of course, have subtly different behaviors. The second will break inheritance. The third will allow you to use the constructor as an instance method, not just a class method. There are no enforced function prototypes or standard way to get parameters... and if you do use the *optional* prototype mechanism, you will subtly change the precedence of calls to your function.
I thought that having 1000 ways to do something was great, but it turns out to be a nightmare for non-trivial programs. Every time I try to use a cute fancy shortcut in Perl, it bites me in the ass. As a result of the over-flexibility, people have tried to impose "standards" on Perl. There are "standard" techniques for named parameters, "standard" techniques for accessor functions, etc. And that's nice, but Perl has 10,000+ available modules to do everything from screen-scrape Google news to access Oracle databases (it's greatest strength!!!). And not all those modules use the standard techniques.
About a year ago I decided to give Python a try. And I haven't looked back. It can do everything Perl can do, and then some. Everything is clearer and having a "standard" way to do most things makes learning new modules immensely easier. Having slightly more verbose syntax and strict type-checking is slightly annoying at first, but keeps me sane in the long run.
Basically I don't use perl for anything other than one-liner regexp tricks anymore. Stuff like perl -i -pe 's/FOO/BAR/g' *, which will change the string FOO to BAR in all the files in the current directory.
Parent
Re: (Score:3, Funny)
Re:Cryptic? Complex!? (Score:5, Insightful)
Parent
Re: (Score:3, Informative)
Re:Cryptic? Complex!? (Score:5, Informative)
Sed will do that too:
sed -i 's/FOO/BAR/g' *
The review says that the book uses the reader's knowledge of sed, awk, and grep. I figure: why not just use sed, awk, and grep...however, one advantage for Perl here is that (I presume) that line works with any Perl; '-i' is a GNU sed extension and may not work on non-GNU seds...
Parent
Re: (Score:3, Insightful)
I was a Python afficionado, although most of my professional experience was with Java. Then I joined a Perl project. I was open minded, any language can be good in the right hands. Now, two and a half years later, I'm pretty good at it.
As the team grows, we find ourselves relying more and more on standard techniques. They're not your standard techniques, they're just what we came up with as our standard way. They work well. We have a beautiful object oriented mod_perl/Template Toolkit system, unit tests, R
Strategies for complex perl code bases (Score:4, Insightful)
That's a pretty common way of implementing objects in perl, but it is, of course, not the only way... The current thinking seems to be we should all switch to using "Inside-Out Objects" (briefly: object data is moved to class data, and the object only needs to be a unique id to pick out the correct values from the class data -- so you bless a scalar ref, and get a lightweight object which stringifies to a unique id). The point being that if you do things this way, you really *have* to use the accessors, you can't cheat and treat the object as a hash reference any more. Unfortunately, last I looked there was some argument about what precisely was the right way to do this (there's some issue with thread support), though the best publicized way of doing it certainly the one recommended by Damien Conway in his newish book "Perl Best Practices".
If you're not interested in re-writing your entire code-base to conform to someone's notion of "Best Practices", myself I might suggest looking into "lock_keys" in the Hash::Util module. You could adopt the practice of doing a lock_keys on the hashref at the end of the object/creation initialization stage, and then if anyone accidentally tries to create a new hash field later, it will throw an error. A simple, effective trick, and I wish it were better publicized...
On occasion I wonder how hard it would be to write an automated test that would look for cases where someone has done a "$obj->{hash_field}"...
In general, coding standards are important, and where the language is really flexible, they arguably become even more important -- but I think a lot of that problem can be solved with some good automated testing. For example, there's a CPAN module called Perl::Critic that will do things for you like check to make sure your code matches a given set of coding standards (it defaults to Conway's "Best Practices", as I remember it).
Parent
Re: (Score:3, Informative)
Hey, that's Perl Hack [oreilly.com] #87!
Re: (Score:3, Interesting)
This was one of the things I noticed immediately when poking around in the Python standard library... it's quite easy to find where functions are called and defined. Just grep for "function\s*(" or "def function". It's always on one line. The parentheses are always there. It jumps out visually. Nice.
Re:Cryptic? Complex!? (Score:4, Insightful)
Parent
Re:Cryptic? Complex!? (Score:4, Insightful)
You know, it seems like *everyone* is put off by this aspect of Python at first. The first time I looked at it, it drove me nuts, and then I ignored Python for another two years.
But once I actually tried to write a program in Python, I found I didn't mind it one bit. Within a few hours my eyes didn't get confused by the lack of braces. I think it's actually easier on the eyes once you get used to it.
So I can't say, "don't knock it", because I've done that myself for sure. But do give Python another look, maybe play around with the tutorial for an hour or two.
Parent
Re: (Score:3, Interesting)
But once I actually tried to write a program in Python, I found I didn't mind it one bit. Within a few hours my eyes didn't get confused by the lack of braces. I think it's actually easier on the eyes once you get used to it.
Python was one of my first programming languages, and the whitespace thing made sense to me from the beginning. In most C-style code, people use both braces and indentation to denote blocks; isn't that redundant? It seems braces are for the compiler and indentation is for human readers. Shouldn't higher level languages be designed for humans rather than machines?
Re: (Score:3, Informative)
>>> if True: a = 0; b = 1; c = 2; print a, b, c
0 1 2
>>>
Re: (Score:3, Informative)
Hmm, that seems a round-about way to do things. I presume you never happened to run into some of the nice features in Emacs python-mode, specifically python-shift-left and python-shift-right which will mov
Re: (Score:3, Interesting)
I {} Perl (Score:5, Interesting)
That is all...
Re:I {} Perl (Score:5, Funny)
Parent
Should I read this or continue with sed/awk? (Score:3, Insightful)
I'm currently going through http://www.oreilly.com/catalog/sed2/ [oreilly.com], but I can see my using perl the more I do website programming. Would an experience scripter suggest that I switch to perl (for it seems it can perform similar text manipulation functions conveniently in a programming lanuage), or spend more time with sed/awk?
I'll probably do both incidentally, but opinions would be appreciated. It seems everyone rates perl.
I was going to switch to Python, but apparently Perl is better for smaller/one line regexp manipulation in scripts, and python for building large applications.
Re:Should I read this or continue with sed/awk? (Score:4, Informative)
I don't want to put Perl down, but I think that its day is past except for those who, because they learnt it when it was the only thing around, are willing to tolerate its eccentricities. While switching from sed/awk to a general-purpose programming language with good text manipulation abilities can certain improve the possibilities of what you can accomplish with a single chuck of code and processor (as opposed to the old-time Unix way of piping), I'd recommend Python for that, getting started with a guide like Mertz's Text Processing in Python [amazon.com] (Addison-Wesley, 2003). Python is now as mature, if not more, in the realm of text processing as Perl was when its won its accolades a decade ago. (Heck, the treatment of Unicode is enormously forward-thinking compared to any other scripting language on the market.) And so you get the same power as you would with Perl, but much, much more readable.
I fear I'm starting a holy war by recommending Python in a Perl discussion. That's certainly not my intention. For those who already know and love Perl I say, great, keep on trucking. But I just can't see the point in steering newbies towards it.
Parent
Re:Should I read this or continue with sed/awk? (Score:4, Funny)
Well, I didn't mean that to be taken personally... but consider the fact that ESR is on your side.
Parent
Re: (Score:3, Interesting)
I don't have much experience with sed and awk so I'm not sure what you plan on using perl for. The basic answer is you need to use the right tool for the job but I don't know what job you have so I can't directly answer your question.
Perl is pretty good with text manipulation due to it's built-in and extensive support of regular expressions. It's also got most programming language features so you can extend it and use it for larger tasks or even create real software all in perl. Perl also has a v
Re: (Score:3, Interesting)
Perl's greatest strength is CPAN, which is a library of perl modules that handle just about any programming task that you can think of, and then some. Sometimes, it's uncanny how well certain modules fit your problem -- you can almost guess the names based on what you want. (need to find the size of
Why not for Windows people? (Score:5, Interesting)
Just remembering by boss's jaw drop when he asked me if I could do a quick analysis of a couple thousand lines of logs and asked how long it would take. "10 minutes." And I delivered. He thought I'd have to fire up VS and write some C code.
He borrowed my Camel book during his next vacation.
Re:Why not for Windows people? (Score:4, Informative)
Parent
Re: (Score:3, Interesting)
Cryptic? (Score:4, Insightful)
Is it just me, or is it possible to create perfectly legible code in Perl if you use good technique, just like in any other language?
The cryptic/convoluted stuff only comes out when you try to be too cute.
Re:Cryptic? (Score:4, Informative)
Of course. The thing that people complain about is that perl allows you to write code that only a fellow perl-head can understand. It's harder to accomplish that with C, for example. But perl doesn't automatically mean you won't understand it. It just makes it more likely :)
Parent
Re: (Score:3, Insightful)
Whenever I come across code that just looks like `an explosion at an ascii factory', I first indent it (which usually fixes the readability). If that doesn't work, I try to figure out what it's trying to do (likely developer didn't know any better, and used some clunky code to do something trivial; usually code that can easily be `clarified' by replacing whole sections of it with a single regex).
Perl
Re:Cryptic? (Score:4, Funny)
Cryptic 32-character hexadecimal MD5 hashes are a myth. It's only cryptic if you don't understand it.
Parent
Cryptic whitespace (Score:4, Insightful)
A language which makes a semantic distinction between tabs and spaces may give the appearance of enforcing legibility but in fact does little useful to help legibility.
A programming language should not make a distinction on meaning based on whether tabs or spaces are used; all whitespace should be regarded equaly (except, understandably, end of line characters).
Otherwise, python seems ok. I just wish it had a whitespace-agnostic mode.
*I* cannot visualy tell the difference between tabs and spaces, why should the programming language?
Parent
Not hard to learn, very easy to remember (Score:5, Insightful)
The thing I've noticed, as a Perl programmer, is that it is the *only* language I've ever used (amongst bash, c, c++, java, rexx, fortran, basic) that I can take a break from for a year, come back, and be able to write a simple script without the need to refer to any books or online manuals. That is VERY useful for those of us who are more sysadmins than programmers. This power is partly due to the "more than one way to do it" philosophy, that lets you program in a style that works for you, hence allowing you to remember *how* to write in that language.
Then again, that's what most anti-Perl folks bitch about. Any language can be obfuscated. If you write hard to decipher code in Perl, you'll write it that way in any language.
Picking Up Perl (Score:5, Informative)
http://downloads.activestate.com/ActivePerl/Windo
http://www.crimsoneditor.com/ [crimsoneditor.com]
After you install perl open a command prompt and run ppm, this is your simple GUI gateway to CPAN packages (make a mental note). After you get a handle on basic perl checkout Perl/Tk (GUI Toolkit for Perl). The Tk packages are included and installed with ActivePerl... Here's your first Perl/TK program:
use Tk;
my $top = new MainWindow;
$top->configure(-title=>"My First Perl GUI Program");
my $lab = $top->Label(-textvariable=>\$labelText);
my $b = $top->Button(-text=>'Click Me!', -command=>sub {$labelText="Congratulations! it worked!" });
$lab->grid(-row=>0, -column=>0);
$b->grid(-row=>1, -column=>0);
MainLoop;
perl5 has run it's course (Score:4, Insightful)
I've been programming perl for 10 years. I've written enough XS modules to be sadly familiar with perlguts and perlapi. I've used perl for a huge array of applications, not excluding some pretty twisted apache hacks using mod_perl. I write perl code every day in my job.
Lately however, I've grown more and more frustrated with this language. Here's some reasons why:
Re:PERL backronym (Score:5, Funny)
Stands for Python'll Eventually Replace this Language.
or, optionally:
Perl Eats Ruby for Lunch
Parent
Re:So you like the book (Score:5, Funny)
IGN scoring works like this:
5/10 - The game runs
6/10 - The game is an FPS
7/10 - The game has team-based mulitplayer online play
8/10 - The game runs at 190 frames-per-second
9/10 - The game is made by a publisher that buys advertising on IGN
10/10 - The game is made by a publisher that buys A LOT of advertising on IGN
Parent
Re: (Score:3, Funny)
You just type on Slashdot all day long.
Re:oh come on, you're not even trying now (Score:5, Interesting)
KISS is hard. Very hard. It's different in different places. Sometimes keeping it simple means writing less code. Sometimes it means creating a new sub-language that better describes your problem.
In perl, you can change the nature of the language itself. *Everything* can be changed. The idea is that if there is more than one way to do it, then you can do it the simplest way for whatever definition of simple is required.
Maintaining consistency is up to the developer himself. Obviously, those tempted to succumb to the lure of sloppiness (which, unfortunately, in my experience, is every perl programmer I've ever met including myself) shouldn't use perl for really big projects.
You can't blame the language for giving you that freedom, though.
Perl is where it is because you don't have to change the way that you think in order to program in it. Perl will change how it works to match how you think, which makes it more convenient than almost any other language.
That particular behavior is what makes it possible to have so many perl modules in existane, which in turn is responsible for the popularity. It's also why about half of those modules have bugs so horrible that they're unusable. It's certainly a tradeoff.
Parent
Re: (Score:3, Insightful)