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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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Chapter 3: Perl Data Structures

Version 0.95

Contents

3.1. String operations

3.2 Numeric values and arithmetic operators

3.3. Operations on Arrays

3.4. Operations on Hashes

3.5. Typical errors

3.6. Summary

3.7. Exercises


Initially you can assume that like shell Perl has variables global to the script. this is OK assumptions if you scripts hover around 100 lines or so, which  is true for many Unix sysadmin.

If you need to write larger script the issue of namespaces became critical and  you should always use pragma strict in your scripts which help to segment  global namespace and detect many error that otherwise might go unnoticed into production version of the script. Actually you can benefit from pragma strict in small scripts too if they use nested loops and generally have complex logic.

Somewhat weaker but still useful version of pragma strict is

strict 'subs';

Which is highly recommended for all your scripts. Again, this is highly recommend option and you can omit it only at your own (and unnecessary) risk.

Uninitialized variables in Perl have a special value undef which is converted to zero in numeric comparisons and empty string in string comparisons. Memory allocation is automatic and unused variables can be garbage collected dynamically.

There are two major types of variables in Perl:

Each variable has several attributes, for example "is defined" attribute (which can be retrieved with defined built-in function) and as such internally is represented by a data structuresin interpreter identifier dictionary.

Perl provide a rich set of built-in operation for lists and associative arrays (hashes). It also provides some connections between these two data structures. Here Perl is really one of the top if not the top language in existence. If you task manipulating text files and  creating some forms of summaries or reports (or if the task in hand can be re-structured along these lines) you can benefit from using Perl.

At the same time multidimensional arrays are not natural to Perl and if your task is centered along the usage of multidimensional arrays you probably will be in disadvantage and should consider either using references or switch to other language that supports this abstraction better.

Like most programming language Perl also have several operating system specific data types. For example Perl supports the following data structures:

Overview of literature

Good introduction to Perl variables can be found in

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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

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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 DOSProgramming Languages History : PL/1 : Simula 67 : C : History of GCC developmentScripting 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-MonthHow to Solve It by George Polya : The Art of Computer Programming : The Elements of Programming Style : The Unix Haterís Handbook : The Jargon file : The True Believer : Programming Pearls : The Good Soldier Svejk : The Power Elite

Most popular humor pages:

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The Last but not Least


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