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Perl automatically converts operands or the particular operator to strings or numbers depending on operation used (string context or numeric context). It is very important to remember that strings and numbers compare using different operators. Using for example "==" for string comparison is a nasty but very common bug in Perl scripts. It is common even for seasoned Perl programmers, especially if they also use the second language like C. This also bedevil novice Perl programmers who are still thinking in term of their previous language, such as Java or C.
That means that you need to put special efforts to avoid this. Remember that == is used for string equality and eq for number equality (letter operators are used for comparing strings). After writing script is make sense to browse it line by line trying to find this type of errors manually.
The most typical problem that lead to large number of errors in Perl scripts is that you need to use different comparison operators for numbers and strings. For example to compare numbers for equality "==" should be used while for comparison of strings "eq" should be used. This is the source of tremendous number of errors in Perl programs. In Perl 5.10 and later you can use ~~ to ask Perl to determine type of operation automatically, but in complex cases this "automatic" way produces errors too as compiler can guess wrong.
Accidentally omitting leading $ for scalar variables or using @ when accessing or assigning a value to array elements (which are considered to be scalars in Perl) is another frequent error
While in many way a very innovative language Perl suffers from some design decisions connected with using separate sets of build-in functions for strings and arrays:
The main problem with Perl that I see is the although it provides a rich set of functions for string and arrays they are not generalized in such a way that similar functions are applicable to both without renaming, although this is entirely possible. So instead of substr functions (that is defined on strings) you need to use splice function for arrays and remember idiosyncrasies of two functions instead of one. Here Larry Wall made a very bad decision, but we can do nothing about it. You will see the problem yourself after you will face the assortment of functions that are available in Perl for arrays and strings. Actually you are forced to use a subset as full assortment is beyond human capacities to master (starving in the food store effect ;-)
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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
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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 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
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 Haterís Handbook : The Jargon file : The True Believer : Programming Pearls : The Good Soldier Svejk : The Power Elite
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