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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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3.6. Summary of data structures in Perl

Despite the fact the scripting languages are VHL( very high level languages), most data structures in them exist because of speed. That's why we have both strings and lists. Semantically, strings are more or less a subset of lists in which the elements are characters. So why do you need a separate data type? You don't, really. Strings only exist for efficiency. But it's lame to make corresponding functions different, the trap into which Perl had fallen. It clutter up the semantics of the language.

You can create and initialize arrays in hashes

    my @array = (1,3,5,12,37,42);
    my %hash  = ( alpha => 4, beta => 6 );

Scalars are often used for representing and manipulating strings. Perl provides five classic PL/1-style operations on strings (length, concatenation (denoted as . -dot), substr, index and tr -- translate) and a lot of minor, Unix inspired primitives like chop, chomp, uc, lc.

Perl preserves the possibility of using substr on the left side of assignment statement -- the possibility pioneered in PL/1. A very useful string function is split.

 Summary of String Functions

Function Description
chomp(scalar) chomp(array) Intelligent chop. By default removes a newline. Can remove any tail that is specified in a special  variable $/.  Removal is performed only if tail matched $/. Can operate on all elements of an array.
chop(scalar)  chop(array) Removes and return the last character from a string. Can operate on arrays. In this case will remove the last character from every element in an array.
chr(scalar) Scalar should a number between 0 and 255. Returns the character that in ASCII code has internal representation (converted to decimal) equal to the NUMBER.  For example, chr(65) returns the letter A.
crypt(scalar1, scalar2) Encrypts STRING1.
index(string, substring, start_position) Search for a substring in string. Returns the position of the first occurrence of the substring in string at or after start_position. If you don't specify start_position, it assumed to be 0 (the beginning of the string). See also rindex
join(string, array_to_join) Opposite to the split function. Concatenate all element of the array and returns the resulting string. The first argument specifies delimiter to be used in the concatenation. For example,
join('.', ('131', '10', '10'))
will return "131.10.10".
lc(scalar) Opposite to uc. Returns a string with every letter of scalar in lowercase.
For example, lc("YAHOO") returns "yahoo".
lcfirst(scalar) Returns a string with the first letter of  scalar in lowercase. For example, lcfirst("Yahoo") returns "yahoo".
length(scalar) A classic string operation function. Returns the length of the scalar. Not applicable to arrays and hashes.
rindex(scalar, substring, start_position) Similar to index but return the position of the last occurrence of the substring in string at or after start_position. If you don't specify start_position, it assumed to be 0 (the beginning of the string).
split(regex, string, limit) A very important function. Breaks up a string based on some delimiter (can be a regex). In an array context, it returns a list of substrings that match regex. In a scalar context, returns the number of matches found.
substr(string, offset, length) A very important function. Returns a portion of string starting from the position specified by the offset and length determined by the length parameters. If length is not specified returns tail of the string, starting from the offset position. A negative offset can be used and will count characters from the end of the string.
tr/fromset/toset/ The tr function allows character-by-character translation.  Has several important options discussed in the text.
uc(string) Opposite to lc. Returns a string with every letter of the string in uppercase. For example, uc("abba") returns "ABBA".
ucfirst(string) Opposite to lcfirst. Returns a string with the first letter of the string in uppercase. For example, ucfirst("nick") returns "Nick".

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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


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 quotesSomerset Maugham : Marcus Aurelius : Kurt Vonnegut : Eric Hoffer : Winston Churchill : Napoleon Bonaparte : Ambrose BierceBernard Shaw : Mark Twain Quotes


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


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:

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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