Introduction to the Perl language, Issue#1

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<h4><code>What Will I Learn? <p dir="auto">Introductory training support for programming with the Perl language. <ul> <li>Perl Language Introduction <li>PERL Overview <li>PERL Language Data types <h4><code>Requirements <p dir="auto">Basic Knowledge of programming and software concept. <h4><code>Difficulty <ul> <li>Basic <h4><code>Tutorial Contents <hr /> <h5><code>1 .INTRODUCTION <hr /> <p dir="auto"><code>A .What is Perl? <hr /> <p dir="auto">P.E.R.L. means Practical Extraction and Report Language. What we could (try to) translate as "practical language of extraction and editing".<br /> Created in 1986 by Larry Wall (System Engineer). Initially to manage a "News" system between two networks. <p dir="auto"><code>It is :<br /> _________,<br /> • A programming language<br /> • Free software (which can be obtained on the Internet in particular)<br /> • An interpreted language:<br /> no compilation<br /> slower than a compiled program<br /> each "script" requires the Perl interpreter on the machine to run. <p dir="auto"><code>Why Perl became popular:<br /> ________________________________,<br /> • portability: Perl exists on most platforms today (Unix, NT, Windows, Mac,VMS, Amiga, Atari ...)<br /> • free: available on the Internet (as well as an impressive number of bookstores and utilities)<br /> • Simplicity: Some commands allow to do what a program of 500 lines in Cor in Pascal did.<br /> • robustness: No memory allocation to handle, strings, stacks, variable names Unlimited ... <p dir="auto"><code>B. What use of Perl? <hr /> <p dir="auto"><code>Originally Perl was created for:<br /> _______________________________________, <ol> <li>manipulate files (especially to manage several files at the same time), <li>manipulate texts (search, substitution), <li>manipulate processes (especially through the network). <p dir="auto">Perl was mainly for the UNIX world <p dir="auto"><code>Why are you using Perl today?<br /> ____________________________________, <ol> <li>generate, update, analyze HTML files (especially for writing CGI), <li>"universal" access to databases, <li>file format conversion. <p dir="auto">Perl is no longer tied to the UNIX world <p dir="auto"><code>Perl is not made for:<br /> _______________________________,<br /> • write interactive interfaces (but there is now the Tk module, which allows it, on Unix or Windows),<br /> • scientific computing (Perl is not compiled: performance problem if we want by example do multiplications of matrices, but again there is the module PDL). <h2><code>C . versions <p dir="auto"><code>Three main versions of Perl:<br /> • Perl 4: The old version that did not integrate object programming (sometimes still used)<br /> • Perl 5.6: The old version<br /> • Perl 5.8: The new version that incorporates Unicode (international character encoding) <hr /> <h5><code>2 .PERL Overview <hr /> <p dir="auto"><code>Little polite program -<br /> ------------------------------, <pre><code>#!/bin/perl print "Bonjour"; <p dir="auto"><code>Display the number of lines in a file:<br /> ------------------------------------------------, <pre><code>#! / Bin / perl open (F, '<myfile') || die "Opening problem: $!" ; my $ i = 0; while (my $ line = <F>) { $ I ++; } close F; print "Number of lines: $ i"; <p dir="auto"><code>F is a file descriptor, which we can call as we want (the use is that we note the file descriptors in uppercase).<code>Each Perl statement ends with a semicolon. <hr /> <h5><code>3 .PERL Data types <hr /> <p dir="auto"><code>A. Constants<br /> -------------------,<br /> <code>1, -12345, 0.1415, 1.6E16 (means 160,000,000,000,000,000), 'cherry', 'a','the fruits of the palm are the dates' <p dir="auto"><code>B. Scalars<br /> -------------------,<br /> <code>Scalars are preceded by the $ character - <pre><code>$ i = 0; $ c = 'a'; $ my_fruit_prefere = 'kiwi'; $ root__read_of_2 = 1.41421; $ string = '100 grams of $ my_fruit_prefere'; => '100 grams of $ my_fruit_prefere' $ string = "100 grams of $ my_fruit_prefere"; => '100 grams of kiwi' <p dir="auto"><code>Caution: Do not put spaces in variable names. A name can be as long we want it in the latest version, <p dir="auto"><code>C. Table lists<br /> ---------------------,<br /> <code>In Perl, arrays can be used as sets or lists.<br /> Always preceded by the<code>"@" character <pre><code>@ digits = (1,2,3,4,5,6,7,8,9,0); @fruits = ('almond', 'strawberry', 'cherry'); @alphabet = ('a' .. 'z'); Both points mean "so much to so much" @a = ('a'); @nul = (); @cartes = ('01' .. '10', 'Valet', 'Lady', 'King'); <p dir="auto"><code>we refer to an element of the table according to its index by: <pre><code>$ digits [1] (=> 2) $ fruits [0] (=> 'almond') <p dir="auto"><code>NOTE: In Perl (as in C) arrays start at index 0 <p dir="auto"><code>You can assign a table to another table: <pre><code>@ch = @ digits; @alphanum = (@alphabet, '_', @ digits); ## EQU1 ## ',' 8 ',' 9 ',' 0 ') @ set = (@ digits, 'date', 'kiwi', 12.45); <p dir="auto"><code>Notes:<br /> We have a special scalar: $ # array that indicates the last array index (and therefore its size - 1): $ fruits [$ # fruits] (=> 'cherry')<br /> <code>Ability to reference a part of a table <pre><code>@cards [6 .. $ # cards] => ('07', '08', '09', '10', 'Valet', 'Lady', 'King') @fruits [0..1] => ('almond', 'strawberry') <p dir="auto"><code>D. Indexed (or associative) tables<br /> ---------------------------------------------,<br /> <code>They are always preceded by the% character: <pre><code>% price = ('almond' => 30, 'strawberry' => 9, 'cherry' => 25); `or :` % price = (kernel => 30, strawberry => 9, cherry => 25); <p dir="auto"><code>We then refer to an element of the array as: <pre><code>$ price {'cherry'} (=> 25) `(or $ price {cherry}` `Examples:` % digit = (); $ digit {'a'} = 1; => or $ digit {a} = 1; print $ digit {'one'}; $ var = 'one'; print $ digit {$ var}; <p dir="auto"><code>E. Remarks<br /> -------------------,<br /> 1 . <code>Perl5 allows combinations, like a table of tables: <pre><code>% seasons = ( Apricot '=> [' been '], 'strawberry' => ['spring', 'summer'], 'apple' => ['autumn', 'winter'], 'orange' => ['winter'], 'cherry' => ['spring'], 'almond' => ['spring', 'summer', 'autumn', 'winter']); `or` @departements = ( ['Ain', 'Bourg-en-Bresse', 'Rhône-Alpes'], ['Aisne', 'Laon', 'Picardie'], ['Yonne', 'Auxerre', 'Burgundy']); <p dir="auto">2 . <code>No Booleans (as in C language)<br /> We use integers knowing that 0 is evaluated as false (in fact it is the chain of empty character) and 1 as true. <pre><code>my $ two_greater_what_un = (2> 1); if ($ two_more_large_one) { print "Ok!"; } <p dir="auto">3 . <code>Two-dimensional tables<br /> <code>Indexed tables can be used to simulate 2 (or n) dimensional tables: <pre><code>% table_multiplication = ('1,1' => 1, '1,2' => 2, ..., '9.8' => 72, '9.9' => 81); $ translation {'almond', 'english'} = 'almond'; $ translation {'almond', 'italian'} = 'amoria'; $ translation {'cherry', 'english'} = 'cherry'; You can also use Perl 5's table tables to do this: @table_multiplication = ( [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], # Multiplied by 0 [0, 1, 2, 3, 4, 5, 6, 7, 8, 9], # Multiplied by 1 [0, 2, 4, 6, 8,10,12,14,16,18], # Multiplied by 2 ... [0, 9,18,27,36,45,54,63,72,81]); # Multiplied by 9 <p dir="auto">We will then refer to 2 * 6 by $ table_mult [6] [2] <p dir="auto"><br /><hr /><em>Posted on <a href="https://utopian.io/utopian-io/@meblogger/introduction-to-the-perl-language-issue-1" target="_blank" rel="nofollow noreferrer noopener" title="This link will take you away from hive.blog" class="external_link">Utopian.io - Rewarding Open Source Contributors<hr /><p>