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Introduction to Perl 5.10 for Unix System Administrators

(Perl 5.10 without excessive complexity)

by Dr Nikolai Bezroukov

Contents : Foreword : Ch01 : Ch02 : Ch03 : Ch04 : Ch05 : Ch06 : Ch07 : Ch08 :

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Introduction

Scripting languages usually do not contain the concept of pointers (aka references). But Perl is an exclusion from this rule and surprisingly it proved that this concept is extremely, amazingly useful even for the class of very high languages that Perl belongs to. Actually Perl proved that references are fundamental notion in programming language and exclusion of them from the scripting language leads to substantial losses of expressive power and flexibility that are far greater then dangers connected with their misuse.

Initially Perl has very limited implementation of concept of references. Perl 4 permits only symbolic references (globs). For example, in Perl 4, you have to use names to index to an associative array called _main{} of symbol names for a package. Perl 5 introduced "hard references" in true C-style. This was done to solve several recurrent problems with the language:

One problem that came up all the time in Perl 4 was how to represent a hash whose values were lists. Perl 4 had hashes, of course, but the values had to be scalars; they couldn't be lists.
The second problem is multidimensional arrays. Arrays in Perl are one-dimensional and the easiest way to emulate multidimensional array is to use references.

Althouth references were "bolted-on" they proved to be extremely well designed and the way they were introduced in Perl 5 did provide the capability to create complex data structures like multidimensional arrays and nested hashes.

Perl 5 also allows references to subroutines. That makes subroutines more like a regular data type. This capability proved to be useful for extension of Perl with OO programming constructs.

Review of literature

Read perllol manual page along with perlref; it discusses lists of lists and multidimensional arrays in detail. After that, you should read the perldsc manual page; it's a Data Structure Cookbook that contains recipes for using and printing out arrays of hashes, hashes of arrays, and other kinds of data.

Chapter 9 from Programming Perl, Third Edition is available on O'Reilly site: http://oreilly.com/perl/excerpts/9780596000271/data-structures.html

There are several free ebooks that contain chapters about references.

A good introduction into references is contained in a sample chapter from Advanced Perl Programming by Sriram Srinivasan (August 1997) (see http://oreilly.com/catalog/advperl/excerpt/ch01.html )
Simon Cozin book chapter on references is pretty weak ( 3145_Chap07) but some examples are good. We will use a couple.
David Medinets Perl 5 by Example Ebook chapter on references can serve as a good reference. It is not a tutorial (see Perl 5 by Example/ chapter 8: References)

In addition to consulting Perl man pages and books it makes sense to look at the Perl source code for standard modules more information. Also the 't/op' directory in the Perl source tree has regression tests that should definitely get you thinking.

Some useful documents and informative posts are available at the Web sites www.perl.com and PerlMonks

Etc

Society

Groupthink : Two Party System as Polyarchy : Corruption of Regulators : Bureaucracies : Understanding Micromanagers and Control Freaks : Toxic Managers : Harvard Mafia : Diplomatic Communication : Surviving a Bad Performance Review : Insufficient Retirement Funds as Immanent Problem of Neoliberal Regime : PseudoScience : Who Rules America : Neoliberalism : The Iron Law of Oligarchy : Libertarian Philosophy

Quotes

War and Peace : Skeptical Finance : John Kenneth Galbraith :Talleyrand : Oscar Wilde : Otto Von Bismarck : Keynes : George Carlin : Skeptics : Propaganda : SE quotes : Language Design and Programming Quotes : Random IT-related quotes : Somerset Maugham : Marcus Aurelius : Kurt Vonnegut : Eric Hoffer : Winston Churchill : Napoleon Bonaparte : Ambrose Bierce : Bernard Shaw : Mark Twain Quotes

Bulletin:

Vol 25, No.12 (December, 2013) Rational Fools vs. Efficient Crooks The efficient markets hypothesis : Political Skeptic Bulletin, 2013 : Unemployment Bulletin, 2010 : Vol 23, No.10 (October, 2011) An observation about corporate security departments : Slightly Skeptical Euromaydan Chronicles, June 2014 : Greenspan legacy bulletin, 2008 : Vol 25, No.10 (October, 2013) Cryptolocker Trojan (Win32/Crilock.A) : Vol 25, No.08 (August, 2013) Cloud providers as intelligence collection hubs : Financial Humor Bulletin, 2010 : Inequality Bulletin, 2009 : Financial Humor Bulletin, 2008 : Copyleft Problems Bulletin, 2004 : Financial Humor Bulletin, 2011 : Energy Bulletin, 2010 : Malware Protection Bulletin, 2010 : Vol 26, No.1 (January, 2013) Object-Oriented Cult : Political Skeptic Bulletin, 2011 : Vol 23, No.11 (November, 2011) Softpanorama classification of sysadmin horror stories : Vol 25, No.05 (May, 2013) Corporate bullshit as a communication method : Vol 25, No.06 (June, 2013) A Note on the Relationship of Brooks Law and Conway Law

History:

Fifty glorious years (1950-2000): the triumph of the US computer engineering : Donald Knuth : TAoCP and its Influence of Computer Science : Richard Stallman : Linus Torvalds : Larry Wall : John K. Ousterhout : CTSS : Multix OS Unix History : Unix shell history : VI editor : History of pipes concept : Solaris : MS DOS : Programming Languages History : PL/1 : Simula 67 : C : History of GCC development : Scripting Languages : Perl history : OS History : Mail : DNS : SSH : CPU Instruction Sets : SPARC systems 1987-2006 : Norton Commander : Norton Utilities : Norton Ghost : Frontpage history : Malware Defense History : GNU Screen : OSS early history

Classic books:

The Peter Principle : Parkinson Law : 1984 : The Mythical Man-Month : How to Solve It by George Polya : The Art of Computer Programming : The Elements of Programming Style : The Unix Hater’s Handbook : The Jargon file : The True Believer : Programming Pearls : The Good Soldier Svejk : The Power Elite

Most popular humor pages:

Manifest of the Softpanorama IT Slacker Society : Ten Commandments of the IT Slackers Society : Computer Humor Collection : BSD Logo Story : The Cuckoo's Egg : IT Slang : C++ Humor : ARE YOU A BBS ADDICT? : The Perl Purity Test : Object oriented programmers of all nations : Financial Humor : Financial Humor Bulletin, 2008 : Financial Humor Bulletin, 2010 : The Most Comprehensive Collection of Editor-related Humor : Programming Language Humor : Goldman Sachs related humor : Greenspan humor : C Humor : Scripting Humor : Real Programmers Humor : Web Humor : GPL-related Humor : OFM Humor : Politically Incorrect Humor : IDS Humor : "Linux Sucks" Humor : Russian Musical Humor : Best Russian Programmer Humor : Microsoft plans to buy Catholic Church : Richard Stallman Related Humor : Admin Humor : Perl-related Humor : Linus Torvalds Related humor : PseudoScience Related Humor : Networking Humor : Shell Humor : Financial Humor Bulletin, 2011 : Financial Humor Bulletin, 2012 : Financial Humor Bulletin, 2013 : Java Humor : Software Engineering Humor : Sun Solaris Related Humor : Education Humor : IBM Humor : Assembler-related Humor : VIM Humor : Computer Viruses Humor : Bright tomorrow is rescheduled to a day after tomorrow : Classic Computer Humor

The Last but not Least Technology is dominated by two types of people: those who understand what they do not manage and those who manage what they do not understand ~Archibald Putt. Ph.D

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