docs:دليل_المبتدئين_إلى_بيرل

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دليل المبتدئين إلى بيرل

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Welcome to Perl.

Perl is the Swiss Army chainsaw of scripting languages: powerful and adaptable. It was first developed by Larry Wall, a linguist working as a systems administrator for NASA in the late 1980s, as a way to make report processing easier. Since then, it has moved into a large number of roles: automating system administration, acting as glue between different computer systems; and, of course, being one of the most popular languages for CGI programming on the Web.

Why did Perl become so popular when the Web came along? Two reasons: First, most of what is being done on the Web happens with text, and is best done with a language that's designed for text processing. More importantly, Perl was appreciably better than the alternatives at the time when people needed something to use. C is complex and can produce security problems (especially with untrusted data), Tcl can be awkward and Python didn't really have a foothold.

It also didn't hurt that Perl is a friendly language. It plays well with your personal programming style. The Perl slogan is “There's more than one way to do it”, and that lends itself well to large and small problems alike.

In this first part of our series, you'll learn a few basics about Perl and see a small sample program.

كلمة تخص نظم التشغيل

في هذه السلسلة, سأفترض أنك تستخدم نظام يونكس Unix حيث مفسر بيرل Perl interpreter موجود بالمسار usr/local/bin/perl/ . لا بأس إن كنت تستخدم ويندوز فمعظم الكود في بيرل مستقل عن نظام التشغيل platform-independent.

برنامجك الأول في بيرل

أكتب السطر البرمجي التالي و ضعه في ملف سمه first.pl

#!/usr/local/bin/perl
print "Hi there!\n";

(حسب التقاليد, أول برنامج يفترض أن يقول أهلا أيها العالم! (Hello world!), و لكني ثوري).

الأن, شغله بمفسر بيرل (Perl interpreter) الخاص بك. من سطر اﻷوامر, إذهب إلى المجلد المحتوي على الملف first.pl و أكتب perl first.pl من المفترض أن ترى:

Hi there!

\n تشير إلى “سطر جديد” و بدونها, بيرل لا تقفز إلى سطر جديد من النص لوحدها.

الدوال و الجمل

بيرل بها مكتبة غنية بالدوال.

Perl has a rich library of functions. They're the verbs of Perl, the commands that the interpreter runs. You can see a list of all the built-in functions on the perlfunc main page. Almost all functions can be given a list of parameters, which are separated by commas.

دالة الطباعة print function هي احد الاجزاء متكررة الاستخدام في بيرل. تستخدمها لعرض ما تريد على الشاشة أو لارسال معلومات لملف (و سنناقش هذا في المقالة القادمة). و هي تأخد مجموعة من العناصر للمخرجات كوسائط للدالة.

The print function is one of the most frequently used parts of Perl. You use it to display things on the screen or to send information to a file (which we'll discuss in the next article). It takes a list of things to output as its parameters.

print "This is a single statement.";
print "Look, ", "a ", "list!";

برنامج البيرل يحتوي على جمل, كل منها تنتهي بفاصلة منقوطة semicolon. الجمل لا يجب أن تكون في سطر منفصل; يمكن أن توجد عدة جمل في سطر واحد أو أن توزع جملة واحدة على عدة أسطر.

print "This is "; print "two statements.\n"; print "But this ",
"is only one statement.\n";

الأرقام و السلاسل و علامات الإقتباس

يوجد نوعين أساسيين من البيانات في بيرل: اﻷرقام و السلاسل strings.

التعامل مع الأرقام سهل, كلنا تعاملنا معهم. الشئ الوحيد الذي يجب عليك معرفته, أن لا تضع أبدا فاصلة أو فراغا للأرقام في بيرل. دائما أكتب 10000 و ليس 10,000 أو 000 10.

السلاسل أعقد قليلا. السلاسل هي مجموعة من الحروف داخل علامتي إقتباس مفردتين أو مزدوجتين:

   'This is a test.'
   "Hi there!\n"

الفرق بين علامات الإقتباس المفردة و علامات الإقتباس المزدوجة هو أن علامات الإقتباس المفردة تعني وجود محتوى يجب أن يؤخد كنص بينما علامات الإقباس المزدوجة تعني وجود محتوى يجب أن يفسر interpreted. على سبيل المثال, (ترجمة لم تكتمل)

The difference between single quotes and double quotes is that single quotes mean that their contents should be taken literally, while double quotes mean that their contents should be interpreted. For example, the character sequence \n is a newline character when it appears in a string with double quotes, but is literally the two characters, backslash and n, when it appears in single quotes.

    print "This string\nshows up on two lines.";
    print 'This string \n shows up on only one.';

(Two other useful backslash sequences are \t to insert a tab character, and
to insert a backslash into a double-quoted string.)

Variables

If functions are Perl's verbs, then variables are its nouns. Perl has three types of variables: scalars, arrays and hashes. Think of them as “things,” “lists,” and “dictionaries.” In Perl, all variable names are a punctuation character, a letter or underscore, and one or more alphanumeric characters or underscores.

Scalars are single things. This might be a number or a string. The name of a scalar begins with a dollar sign, such as $i or $abacus. You assign a value to a scalar by telling Perl what it equals, like so:

    $i = 5;
    $pie_flavor = 'apple';
    $constitution1776 = "We the People, etc.";

You don't need to specify whether a scalar is a number or a string. It doesn't matter, because when Perl needs to treat a scalar as a string, it does; when it needs to treat it as a number, it does. The conversion happens automatically. (This is different from many other languages, where strings and numbers are two separate data types.)

If you use a double-quoted string, Perl will insert the value of any scalar variables you name in the string. This is often used to fill in strings on the fly:

    $apple_count = 5; 
    $count_report = "There are $apple_count apples.";
    print "The report is: $count_report\n";

The final output from this code is The report is: There are 5 apples..

Numbers in Perl can be manipulated with the usual mathematical operations: addition, multiplication, division and subtraction. (Multiplication and division are indicated in Perl with the * and / symbols, by the way.)

    $a = 5;
    $b = $a + 10;       # $b is now equal to 15.
    $c = $b * 10;       # $c is now equal to 150.
    $a = $a - 1;        # $a is now 4, and algebra teachers are cringing.

You can also use special operators like ++, –, +=, -=, /= and *=. These manipulate a scalar's value without needing two elements in an equation. Some people like them, some don't. I like the fact that they can make code clearer.

   $a = 5;
   $a++;        # $a is now 6; we added 1 to it.
   $a += 10;    # Now it's 16; we added 10.
   $a /= 2;     # And divided it by 2, so it's 8.

Strings in Perl don't have quite as much flexibility. About the only basic operator that you can use on strings is concatenation, which is a $10 way of saying “put together.” The concatenation operator is the period. Concatenation and addition are two different things:

   $a = "8";    # Note the quotes.  $a is a string.
   $b = $a + "1";   # "1" is a string too.
   $c = $a . "1";   # But $b and $c have different values!

Remember that Perl converts strings to numbers transparently whenever it's needed, so to get the value of $b, the Perl interpreter converted the two strings “8” and “1” to numbers, then added them. The value of $b is the number 9. However, $c used concatenation, so its value is the string “81”.

Just remember, the plus sign adds numbers and the period puts strings together.

Arrays are lists of scalars. Array names begin with @. You define arrays by listing their contents in parentheses, separated by commas:

    @lotto_numbers = (1, 2, 3, 4, 5, 6);  # Hey, it could happen.
    @months = ("July", "August", "September");

The contents of an array are indexed beginning with 0. (Why not 1? Because. It's a computer thing.) To retrieve the elements of an array, you replace the @ sign with a $ sign, and follow that with the index position of the element you want. (It begins with a dollar sign because you're getting a scalar value.) You can also modify it in place, just like any other scalar.

    @months = ("July", "August", "September");
    print $months[0];   # This prints "July".
    $months[2] = "Smarch";  # We just renamed September!

If an array doesn't exist, by the way, you'll create it when you try to assign a value to one of its elements.

    $winter_months[0] = "December";  # This implicitly creates @winter_months.

Arrays always return their contents in the same order; if you go through @months from beginning to end, no matter how many times you do it, you'll get back July, August and September in that order. If you want to find the length of an array, use the value $#array_name. This is one less than the number of elements in the array. If the array just doesn't exist or is empty, $#array_name is -1. If you want to resize an array, just change the value of $#array_name.

    @months = ("July", "August", "September");
    print $#months;         # This prints 2.
    $a1 = $#autumn_months;  # We don't have an @autumn_months, so this is -1.
    $#months = 0;           # Now @months only contains "July".

Hashes are called ``dictionaries'' in some programming languages, and that's what they are: a term and a definition, or in more correct language a key and a value. Each key in a hash has one and only one corresponding value. The name of a hash begins with a percentage sign, like %parents. You define hashes by comma-separated pairs of key and value, like so:

    %days_in_month = ( "July" => 31, "August" => 31, "September" => 30 );

You can fetch any value from a hash by referring to $hashname{key}, or modify it in place just like any other scalar.

    print $days_in_month{"September"}; # 30, of course.
    $days_in_month{"February"} = 29;   # It's a leap year.

If you want to see what keys are in a hash, you can use the keys function with the name of the hash. This returns a list containing all of the keys in the hash. The list isn't always in the same order, though; while we could count on @months to always return July, August, September in that order, keys %days_in_summer might return them in any order whatsoever.

    @month_list = keys %days_in_summer;
    # @month_list is now ('July', 'September', 'August') !

The three types of variables have three separate namespaces. That means that $abacus and @abacus are two different variables, and $abacus[0] (the first element of @abacus) is not the same as $abacus{0} (the value in abacus that has the key 0).

التعليقات

لاحظ, في بعض نماذج الأكواد السابقة في القسم السابق, علقت على الكود. و التعليقات مفيدة لشرح عمل جزء معين من الكود, و التعليق حيوي لأي جزء من الكود تخطط لتعديله أو تحسينه أو إصلاحه أو حتى للإطلاع عليه لاحقا. (و هذا يعني أن التعليقات حيوية لكل الأكواد.)

Notice that in some of the code samples from the previous section, I've used code comments. These are useful for explaining what a particular piece of code does, and vital for any piece of code you plan to modify, enhance, fix, or just look at again. (That is to say, comments are vital for all code.)

أي شئ في سطر من كود بيرل يتبع إشارة # فهو تعليق. (بالتأكيد, بإستتناء, إن كانت إشارة # تظهر في سلسلة string.)

   print "Hello world!\n";  # That's more like it.
   # This entire line is a comment.

الحلقات

غالبا في كل مرة تكتب فيها برنامج, ستحتاج لاستخدام الحلقات. فهي تسمح لك بتكرار عمل كود معين مرة بعد مرة. هذا جزء من مفهوم عام في البرمجة يسمى التحكم بالدفق flow control.

Perl has several different functions that are useful for flow control, the most basic of which is for. When you use the for function, you specify a variable that will be used for the loop index, and a list of values to loop over. Inside a pair of curly brackets, you put any code you want to run during the loop:

     for $i (1, 2, 3, 4, 5) {
         print "$i\n";
     }

This loop prints the numbers 1 through 5, each on a separate line.

A handy shortcut for defining loops is using .. to specify a range of numbers. You can write (1, 2, 3, 4, 5) as (1 .. 5). You can also use arrays and scalars in your loop list. Try this code and see what happens:

    @one_to_ten = (1 .. 10);
    $top_limit = 25;
    for $i (@one_to_ten, 15, 20 .. $top_limit) {
        print "$i\n";
    }

The items in your loop list don't have to be numbers; you can use strings just as easily. If the hash %month_has contains names of months and the number of days in each month, you can use the keys function to step through them.

    for $i (keys %month_has) {
        print "$i has $month_has{$i} days.\n";
    }
 
    for $marx ('Groucho', 'Harpo', 'Zeppo', 'Karl') {
        print "$marx is my favorite Marx brother.\n";
    }

The Miracle of Compound Interest

You now know enough about Perl - variables, print, and for() - to write a small, useful program. Everyone loves money, so the first sample program is a compound-interest calculator. It will print a (somewhat) nicely formatted table showing the value of an investment over a number of years. (You can see the program at compound_interest.pl)

The single most complex line in the program is this one:

    $interest = int (($apr / 100) * $nest_egg * 100) / 100;

$apr / 100 is the interest rate, and ($apr / 100) * $nest_egg is the amount of interest earned in one year. This line uses the int() function, which returns the integer value of a scalar (its value after any fractional part has been stripped off). We use int() here because when you multiply, for example, 10925 by 9.25%, the result is 1010.5625, which we must round off to 1010.56. To do this, we multiply by 100, yielding 101056.25, use int() to throw away the leftover fraction, yielding 101056, and then divide by 100 again, so that the final result is 1010.56. Try stepping through this statement yourself to see just how we end up with the correct result, rounded to cents.

Play Around!

At this point you have some basic knowledge of Perl syntax and a few simple toys to play with - print, for(), keys(), and int(). Try writing some simple programs with them. Here are two suggestions, one simple and the other a little more complex:

  • A word frequency counter. How often does each word show up in an array of words? Print out a report. (Hint: Use a hash to count of the number of appearances of each word.)
  • Given a month and the day of the week that's the first of that month, print a calendar for the month. (Remember, you need \n to go to a new line.)

نقاش

الصادق الشريدي, 2008/05/07 14:51

المقطع باللغة الإنجليزية الذي لم يزل من القسم (التعليقات) ترجمته فوقه من يرى أن الترجمة جيدة يمكنه أن يزيله

الصادق الشريدي, 2008/05/07 15:09

\n بماذا يشار إليها في الترجمة و the character sequence ما ترجمتها

مؤيد السعدي, 2008/05/07 15:49

سلسلة المحارف character sequence أما \n فهو سطر جديد new line

مؤيد السعدي, 2008/05/07 16:01

تم التلوين لتمييز التعليقات من خلال حصر الكود ب <code perl>

الصادق الشريدي, 2008/05/08 10:05

يعني \n أعرف أنه سطر جديد و لكن هل يسمى الامر \n أم ماذا ؟

مؤيد السعدي, 2008/05/08 15:40

علامة السطر الجديد أو محرف السطر الجديد لأنه ليس أمراً

IncLudEr, 2008/12/02 12:17

السلام عليكم

ملاحظة فقط في القائمات Arrays

يمكنك استعمال qw() أفضل بكثير

@months = (“July”, “August”, “September”);

@months = qw(July August September);

و في الـ Hashes

%days_in_month = ( “July” ⇒ 31, “August” ⇒ 31, “September” ⇒ 30 );

%days_in_month = qw(July 31

August 31

September 30);

فقط

تحياتي

مؤيد السعدي, 2008/12/03 20:37

هذا مقال مترجمة تستطيع وضع تعليقك في الهوامش باستخدام زوجان من الأقواس الهلاية ثم الهامش ثم الاقتباس

أو عمل مقال أصيل

إذا لم تكن تملك صلاحيات التحرير قم بالتسجيل ثم راسلني لإعطائك الصلاحيات

Sugeng, 2012/08/10 04:13

No quetsion this is the place to get this info, thanks y'all.

Jenay, 2013/06/14 16:05

Last one to utliize this is a rotten egg!

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آخر تعديل:: 23 نيسان 2015 الساعة 00:19 (تحرير خارجي)