мета-данные страницы
  •  
Загрузка не удалась. Возможно, проблемы с правами доступа?

Различия

Показаны различия между двумя версиями страницы.

Ссылка на это сравнение

Предыдущая версия справа и слеваПредыдущая версия
Следующая версия		Предыдущая версия
perl:task3 [06/03/2010 17:16] – vlasovperl:task3 [23/10/2010 18:17] (текущий) – vlasov
Строка 1: Строка 1:
-<code>+<code html>
  
-<?xml version="1.0" ?> 
-<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> 
 <html> <html>
-<head> +<head><title>Simple test</title></head>
-<!-- saved from url=(0017)http://localhost/ --> +
-<script language="JavaScript" src="../../displayToc.js"></script> +
-<script language="JavaScript" src="../../tocParas.js"></script> +
-<script language="JavaScript" src="../../tocTab.js"></script> +
-<link rel="stylesheet" type="text/css" href="../../scineplex.css"> +
-<title>perlintro -- a brief introduction and overview of Perl</title> +
-<link rel="stylesheet" href="../../Active.css" type="text/css" /> +
-<meta http-equiv="content-type" content="text/html; charset=utf-8" /> +
-<link rev="made" href="mailto:" /> +
-</head> +
 <body> <body>
- +<p>Простой файл для удаления тэгов</p>
-<!-- INDEX BEGIN --> +
-<div name="index"> +
-<script>writelinks('__top__',2);</script> +
-<h1><a>perlintro -- a brief introduction and overview of Perl</a></h1> +
-<p><a name="__index__"></a></p> +
- +
- +
-<ul> +
- +
- <li><a href="#name">NAME</a></li> +
- <li><a href="#description">DESCRIPTION</a></li> +
- <ul> +
- +
- <li><a href="#what_is_perl">What is Perl?</a></li> +
- <li><a href="#running_perl_programs">Running Perl programs</a></li> +
- <li><a href="#safety_net">Safety net</a></li> +
- <li><a href="#basic_syntax_overview">Basic syntax overview</a></li> +
- <li><a href="#perl_variable_types">Perl variable types</a></li> +
- <li><a href="#variable_scoping">Variable scoping</a></li> +
- <li><a href="#conditional_and_looping_constructs">Conditional and looping constructs</a></li> +
- <li><a href="#builtin_operators_and_functions">Builtin operators and functions</a></li> +
- <li><a href="#files_and_i_o">Files and I/O</a></li> +
- <li><a href="#regular_expressions">Regular expressions</a></li> +
- <li><a href="#writing_subroutines">Writing subroutines</a></li> +
- <li><a href="#oo_perl">OO Perl</a></li> +
- <li><a href="#using_perl_modules">Using Perl modules</a></li> +
- </ul> +
- +
- <li><a href="#author">AUTHOR</a></li> +
-</ul> +
- +
-<hr name="index" /> +
-</div> +
-<!-- INDEX END --> +
- +
-<p> +
-</p> +
-<h1><a name="name">NAME</a></h1> +
-<p>perlintro -- a brief introduction and overview of Perl</p> +
-<p> +
-</p> +
-<hr /> +
-<h1><a name="description">DESCRIPTION</a></h1> +
-<p>This document is intended to give you a quick overview of the Perl +
-programming language, along with pointers to further documentation.  It +
-is intended as a &quot;bootstrap&quot; guide for those who are new to the +
-language, and provides just enough information for you to be able to +
-read other peoples' Perl and understand roughly what it's doing, or +
-write your own simple scripts.</p> +
-<p>This introductory document does not aim to be complete.  It does not +
-even aim to be entirely accurate.  In some cases perfection has been +
-sacrificed in the goal of getting the general idea across.  You are +
-<em>strongly</em> advised to follow this introduction with more information +
-from the full Perl manual, the table of contents to which can be found +
-in <a href="../../lib/pods/perltoc.html">the perltoc manpage</a>.</p> +
-<p>Throughout this document you'll see references to other parts of the +
-Perl documentation.  You can read that documentation using the <code>perldoc</code> +
-command or whatever method you're using to read this document.</p> +
-<p> +
-</p> +
-<h2><a name="what_is_perl">What is Perl?</a></h2> +
-<p>Perl is a general-purpose programming language originally developed for +
-text manipulation and now used for a wide range of tasks including +
-system administration, web development, network programming, GUI +
-development, and more.</p> +
-<p>The language is intended to be practical (easy to use, efficient, +
-complete) rather than beautiful (tiny, elegant, minimal).  Its major +
-features are that it's easy to use, supports both procedural and +
-object-oriented (OO) programming, has powerful built-in support for text +
-processing, and has one of the world's most impressive collections of +
-third-party modules.</p> +
-<p>Different definitions of Perl are given in <a href="../../lib/pods/perl.html">the perl manpage</a>, <a href="../../lib/pods/perlfaq1.html">the perlfaq1 manpage</a> and +
-no doubt other places.  From this we can determine that Perl is different +
-things to different people, but that lots of people think it's at least +
-worth writing about.</p> +
-<p> +
-</p> +
-<h2><a name="running_perl_programs">Running Perl programs</a></h2> +
-<p>To run a Perl program from the Unix command line:</p> +
-<pre> +
-    perl progname.pl</pre> +
-<p>Alternatively, put this as the first line of your script:</p> +
-<pre> +
-    <span class="comment">#!/usr/bin/env perl</span> +
-</pre> +
-<p>... and run the script as <code>/path/to/script.pl</code>.  Of course, it'll need +
-to be executable first, so <code>chmod 755 script.pl</code> (under Unix).</p> +
-<p>(This start line assumes you have the <strong>env</strong> program. You can also put +
-directly the path to your perl executable, like in <code>#!/usr/bin/perl</code>).</p> +
-<p>For more information, including instructions for other platforms such as +
-Windows and Mac OS, read <a href="../../lib/pods/perlrun.html">the perlrun manpage</a>.</p> +
-<p> +
-</p> +
-<h2><a name="safety_net">Safety net</a></h2> +
-<p>Perl by default is very forgiving. In order to make it more robust +
-it is recommended to start every program with the following lines:</p> +
-<pre> +
-    <span class="comment">#!/usr/bin/perl</span> +
-    <span class="keyword">use</span> <span class="variable">strict</span><span class="operator">;</span> +
-    <span class="keyword">use</span> <span class="variable">warnings</span><span class="operator">;</span> +
-</pre> +
-<p>The two additional lines request from perl to catch various common +
-problems in your code. They check different things so you need both. A +
-potential problem caught by <code>use strict;</code> will cause your code to stop +
-immediately when it is encountered, while <code>use warnings;</code> will merely +
-give a warning (like the command-line switch <strong>-w</strong>) and let your code run. +
-To read more about them check their respective manual pages at <a href="../../lib/strict.html">the strict manpage</a> +
-and <a href="../../lib/warnings.html">the warnings manpage</a>.</p> +
-<p> +
-</p> +
-<h2><a name="basic_syntax_overview">Basic syntax overview</a></h2> +
-<p>A Perl script or program consists of one or more statements.  These +
-statements are simply written in the script in a straightforward +
-fashion.  There is no need to have a <code>main()</code> function or anything of +
-that kind.</p> +
-<p>Perl statements end in a semi-colon:</p> +
-<pre> +
-    <span class="keyword">print</span> <span class="string">"Hello, world"</span><span class="operator">;</span> +
-</pre> +
-<p>Comments start with a hash symbol and run to the end of the line</p> +
-<pre> +
-    <span class="comment"># This is a comment</span> +
-</pre> +
-<p>Whitespace is irrelevant:</p> +
-<pre> +
-    <span class="keyword">print</span> +
-        <span class="string">"Hello, world"</span> +
-        <span class="operator">;</span> +
-</pre> +
-<p>... except inside quoted strings:</p> +
-<pre> +
-    <span class="comment"># this would print with a linebreak in the middle</span> +
-    <span class="keyword">print</span> <span class="string">"Hello +
-    world"</span><span class="operator">;</span> +
-</pre> +
-<p>Double quotes or single quotes may be used around literal strings:</p> +
-<pre> +
-    <span class="keyword">print</span> <span class="string">"Hello, world"</span><span class="operator">;</span> +
-    <span class="keyword">print</span> <span class="string">'Hello, world'</span><span class="operator">;</span> +
-</pre> +
-<p>However, only double quotes &quot;interpolate&quot; variables and special +
-characters such as newlines (<a href="../../lib/pods/perlrun.html#n"><code>\n</code></a>):</p> +
-<pre> +
-    <span class="keyword">print</span> <span class="string">"Hello, </span><span class="variable">$name</span><span class="string">\n"</span><span class="operator">;</span>     <span class="comment"># works fine</span> +
-    <span class="keyword">print</span> <span class="string">'Hello, $name\n'</span><span class="operator">;</span>     <span class="comment"># prints $name\n literally</span> +
-</pre> +
-<p>Numbers don't need quotes around them:</p> +
-<pre> +
-    <span class="keyword">print</span> <span class="number">42</span><span class="operator">;</span> +
-</pre> +
-<p>You can use parentheses for functions' arguments or omit them +
-according to your personal taste.  They are only required +
-occasionally to clarify issues of precedence.</p> +
-<pre> +
-    <span class="keyword">print</span><span class="operator">(</span><span class="string">"Hello, world\n"</span><span class="operator">);</span> +
-    <span class="keyword">print</span> <span class="string">"Hello, world\n"</span><span class="operator">;</span> +
-</pre> +
-<p>More detailed information about Perl syntax can be found in <a href="../../lib/pods/perlsyn.html">the perlsyn manpage</a>.</p> +
-<p> +
-</p> +
-<h2><a name="perl_variable_types">Perl variable types</a></h2> +
-<p>Perl has three main variable types: scalars, arrays, and hashes.</p> +
-<dl> +
-<dt><strong><a name="scalars" class="item">Scalars</a></strong> +
- +
-<dd> +
-<p>A scalar represents a single value:</p> +
-</dd> +
-<dd> +
-<pre> +
-    <span class="keyword">my</span> <span class="variable">$animal</span> <span class="operator">=</span> <span class="string">"camel"</span><span class="operator">;</span> +
-    <span class="keyword">my</span> <span class="variable">$answer</span> <span class="operator">=</span> <span class="number">42</span><span class="operator">;</span> +
-</pre> +
-</dd> +
-<dd> +
-<p>Scalar values can be strings, integers or floating point numbers, and Perl +
-will automatically convert between them as required.  There is no need +
-to pre-declare your variable types, but you have to declare them using +
-the <a href="../../lib/pods/perlfunc.html#my"><code>my</code></a> keyword the first time you use them. (This is one of the +
-requirements of <code>use strict;</code>.)</p> +
-</dd> +
-<dd> +
-<p>Scalar values can be used in various ways:</p> +
-</dd> +
-<dd> +
-<pre> +
-    <span class="keyword">print</span> <span class="variable">$animal</span><span class="operator">;</span> +
-    <span class="keyword">print</span> <span class="string">"The animal is </span><span class="variable">$animal</span><span class="string">\n"</span><span class="operator">;</span> +
-    <span class="keyword">print</span> <span class="string">"The square of </span><span class="variable">$answer</span><span class="string"> is "</span><span class="operator">,</span> <span class="variable">$answer</span> <span class="operator">*</span> <span class="variable">$answer</span><span class="operator">,</span> <span class="string">"\n"</span><span class="operator">;</span> +
-</pre> +
-</dd> +
-<dd> +
-<p>There are a number of &quot;magic&quot; scalars with names that look like +
-punctuation or line noise.  These special variables are used for all +
-kinds of purposes, and are documented in <a href="../../lib/pods/perlvar.html">the perlvar manpage</a>.  The only one you +
-need to know about for now is <a href="../../lib/pods/perlvar.html#__"><code>$_</code></a> which is the &quot;default variable&quot;. +
-It's used as the default argument to a number of functions in Perl, and +
-it's set implicitly by certain looping constructs.</p> +
-</dd> +
-<dd> +
-<pre> +
-    <span class="keyword">print</span><span class="operator">;</span>          <span class="comment"># prints contents of $_ by default</span> +
-</pre> +
-</dd> +
-</li> +
-<dt><strong><a name="arrays" class="item">Arrays</a></strong> +
- +
-<dd> +
-<p>An array represents a list of values:</p> +
-</dd> +
-<dd> +
-<pre> +
-    <span class="keyword">my</span> <span class="variable">@animals</span> <span class="operator">=</span> <span class="operator">(</span><span class="string">"camel"</span><span class="operator">,</span> <span class="string">"llama"</span><span class="operator">,</span> <span class="string">"owl"</span><span class="operator">);</span> +
-    <span class="keyword">my</span> <span class="variable">@numbers</span> <span class="operator">=</span> <span class="operator">(</span><span class="number">23</span><span class="operator">,</span> <span class="number">42</span><span class="operator">,</span> <span class="number">69</span><span class="operator">);</span> +
-    <span class="keyword">my</span> <span class="variable">@mixed</span>   <span class="operator">=</span> <span class="operator">(</span><span class="string">"camel"</span><span class="operator">,</span> <span class="number">42</span><span class="operator">,</span> <span class="number">1.23</span><span class="operator">);</span> +
-</pre> +
-</dd> +
-<dd> +
-<p>Arrays are zero-indexed.  Here's how you get at elements in an array:</p> +
-</dd> +
-<dd> +
-<pre> +
-    <span class="keyword">print</span> <span class="variable">$animals</span><span class="operator">[</span><span class="number">0</span><span class="operator">]</span><span class="operator">;</span>              <span class="comment"># prints "camel"</span> +
-    <span class="keyword">print</span> <span class="variable">$animals</span><span class="operator">[</span><span class="number">1</span><span class="operator">]</span><span class="operator">;</span>              <span class="comment"># prints "llama"</span> +
-</pre> +
-</dd> +
-<dd> +
-<p>The special variable <code>$#array</code> tells you the index of the last element +
-of an array:</p> +
-</dd> +
-<dd> +
-<pre> +
-    <span class="keyword">print</span> <span class="variable">$mixed</span><span class="operator">[</span><span class="variable">$#mixed</span><span class="operator">]</span><span class="operator">;</span>       <span class="comment"># last element, prints 1.23</span> +
-</pre> +
-</dd> +
-<dd> +
-<p>You might be tempted to use <code>$#array + 1</code> to tell you how many items there +
-are in an array.  Don't bother.  As it happens, using <code>@array</code> where Perl +
-expects to find a scalar value (&quot;in scalar context&quot;) will give you the number +
-of elements in the array:</p> +
-</dd> +
-<dd> +
-<pre> +
-    <span class="keyword">if</span> <span class="operator">(</span><span class="variable">@animals</span> <span class="operator">&lt;</span> <span class="number">5</span><span class="operator">)</span> <span class="operator">{</span> <span class="operator">...</span> <span class="operator">}</span> +
-</pre> +
-</dd> +
-<dd> +
-<p>The elements we're getting from the array start with a <code>$</code> because +
-we're getting just a single value out of the array -- you ask for a scalar, +
-you get a scalar.</p> +
-</dd> +
-<dd> +
-<p>To get multiple values from an array:</p> +
-</dd> +
-<dd> +
-<pre> +
-    <span class="variable">@animals</span><span class="operator">[</span><span class="number">0</span><span class="operator">,</span><span class="number">1</span><span class="operator">]</span><span class="operator">;</span>                  <span class="comment"># gives ("camel", "llama");</span> +
-    <span class="variable">@animals</span><span class="operator">[</span><span class="number">0</span><span class="operator">..</span><span class="number">2</span><span class="operator">]</span><span class="operator">;</span>                 <span class="comment"># gives ("camel", "llama", "owl");</span> +
-    <span class="variable">@animals</span><span class="operator">[</span><span class="number">1</span><span class="operator">..</span><span class="variable">$#animals</span><span class="operator">]</span><span class="operator">;</span>         <span class="comment"># gives all except the first element</span> +
-</pre> +
-</dd> +
-<dd> +
-<p>This is called an &quot;array slice&quot;.</p> +
-</dd> +
-<dd> +
-<p>You can do various useful things to lists:</p> +
-</dd> +
-<dd> +
-<pre> +
-    <span class="keyword">my</span> <span class="variable">@sorted</span>    <span class="operator">=</span> <span class="keyword">sort</span> <span class="variable">@animals</span><span class="operator">;</span> +
-    <span class="keyword">my</span> <span class="variable">@backwards</span> <span class="operator">=</span> <span class="keyword">reverse</span> <span class="variable">@numbers</span><span class="operator">;</span> +
-</pre> +
-</dd> +
-<dd> +
-<p>There are a couple of special arrays too, such as <a href="../../lib/pods/perlvar.html#_argv"><code>@ARGV</code></a> (the command +
-line arguments to your script) and <a href="../../lib/pods/perlvar.html#__"><code>@_</code></a> (the arguments passed to a +
-subroutine).  These are documented in <a href="../../lib/pods/perlvar.html">the perlvar manpage</a>.</p> +
-</dd> +
-</li> +
-<dt><strong><a name="hashes" class="item">Hashes</a></strong> +
- +
-<dd> +
-<p>A hash represents a set of key/value pairs:</p> +
-</dd> +
-<dd> +
-<pre> +
-    <span class="keyword">my</span> <span class="variable">%fruit_color</span> <span class="operator">=</span> <span class="operator">(</span><span class="string">"apple"</span><span class="operator">,</span> <span class="string">"red"</span><span class="operator">,</span> <span class="string">"banana"</span><span class="operator">,</span> <span class="string">"yellow"</span><span class="operator">);</span> +
-</pre> +
-</dd> +
-<dd> +
-<p>You can use whitespace and the <code>=&gt;</code> operator to lay them out more +
-nicely:</p> +
-</dd> +
-<dd> +
-<pre> +
-    <span class="keyword">my</span> <span class="variable">%fruit_color</span> <span class="operator">=</span> <span class="operator">(</span> +
-        <span class="string">apple</span>  <span class="operator">=&gt;</span> <span class="string">"red"</span><span class="operator">,</span> +
-        <span class="string">banana</span> <span class="operator">=&gt;</span> <span class="string">"yellow"</span><span class="operator">,</span> +
-    <span class="operator">);</span> +
-</pre> +
-</dd> +
-<dd> +
-<p>To get at hash elements:</p> +
-</dd> +
-<dd> +
-<pre> +
-    <span class="variable">$fruit_color</span><span class="operator">{</span><span class="string">"apple"</span><span class="operator">}</span><span class="operator">;</span>           <span class="comment"># gives "red"</span> +
-</pre> +
-</dd> +
-<dd> +
-<p>You can get at lists of keys and values with <a href="../../lib/pods/perlfunc.html#keys"><code>keys()</code></a> and +
-<a href="../../lib/pods/perlfunc.html#values"><code>values()</code></a>.</p> +
-</dd> +
-<dd> +
-<pre> +
-    <span class="keyword">my</span> <span class="variable">@fruits</span> <span class="operator">=</span> <span class="keyword">keys</span> <span class="variable">%fruit_colors</span><span class="operator">;</span> +
-    <span class="keyword">my</span> <span class="variable">@colors</span> <span class="operator">=</span> <span class="keyword">values</span> <span class="variable">%fruit_colors</span><span class="operator">;</span> +
-</pre> +
-</dd> +
-<dd> +
-<p>Hashes have no particular internal order, though you can sort the keys +
-and loop through them.</p> +
-</dd> +
-<dd> +
-<p>Just like special scalars and arrays, there are also special hashes. +
-The most well known of these is <a href="../../lib/pods/perlvar.html#_env"><code>%ENV</code></a> which contains environment +
-variables.  Read all about it (and other special variables) in +
-<a href="../../lib/pods/perlvar.html">the perlvar manpage</a>.</p> +
-</dd> +
-</li> +
-</dl> +
-<p>Scalars, arrays and hashes are documented more fully in <a href="../../lib/pods/perldata.html">the perldata manpage</a>.</p> +
-<p>More complex data types can be constructed using references, which allow +
-you to build lists and hashes within lists and hashes.</p> +
-<p>A reference is a scalar value and can refer to any other Perl data +
-type. So by storing a reference as the value of an array or hash +
-element, you can easily create lists and hashes within lists and +
-hashes. The following example shows a 2 level hash of hash +
-structure using anonymous hash references.</p> +
-<pre> +
-    <span class="keyword">my</span> <span class="variable">$variables</span> <span class="operator">=</span> <span class="operator">{</span> +
-        <span class="string">scalar</span>  <span class="operator">=&gt;</span>  <span class="operator">{</span> +
-                     <span class="string">description</span> <span class="operator">=&gt;</span> <span class="string">"single item"</span><span class="operator">,</span> +
-                     <span class="string">sigil</span> <span class="operator">=&gt;</span> <span class="string">'$'</span><span class="operator">,</span> +
-                    <span class="operator">}</span><span class="operator">,</span> +
-        <span class="string">array</span>   <span class="operator">=&gt;</span>  <span class="operator">{</span> +
-                     <span class="string">description</span> <span class="operator">=&gt;</span> <span class="string">"ordered list of items"</span><span class="operator">,</span> +
-                     <span class="string">sigil</span> <span class="operator">=&gt;</span> <span class="string">'@'</span><span class="operator">,</span> +
-                    <span class="operator">}</span><span class="operator">,</span> +
-        <span class="string">hash</span>    <span class="operator">=&gt;</span>  <span class="operator">{</span> +
-                     <span class="string">description</span> <span class="operator">=&gt;</span> <span class="string">"key/value pairs"</span><span class="operator">,</span> +
-                     <span class="string">sigil</span> <span class="operator">=&gt;</span> <span class="string">'%'</span><span class="operator">,</span> +
-                    <span class="operator">}</span><span class="operator">,</span> +
-    <span class="operator">}</span><span class="operator">;</span> +
-</pre> +
-<pre> +
-    <span class="keyword">print</span> <span class="string">"Scalars begin with a </span><span class="variable">$variables</span><span class="string">-&gt;{'scalar'}-&gt;{'sigil'}\n"</span><span class="operator">;</span> +
-</pre> +
-<p>Exhaustive information on the topic of references can be found in +
-<a href="../../lib/pods/perlreftut.html">the perlreftut manpage</a>, <a href="../../lib/pods/perllol.html">the perllol manpage</a>, <a href="../../lib/pods/perlref.html">the perlref manpage</a> and <a href="../../lib/pods/perldsc.html">the perldsc manpage</a>.</p> +
-<p> +
-</p> +
-<h2><a name="variable_scoping">Variable scoping</a></h2> +
-<p>Throughout the previous section all the examples have used the syntax:</p> +
-<pre> +
-    <span class="keyword">my</span> <span class="variable">$var</span> <span class="operator">=</span> <span class="string">"value"</span><span class="operator">;</span> +
-</pre> +
-<p>The <a href="../../lib/pods/perlfunc.html#my"><code>my</code></a> is actually not required; you could just use:</p> +
-<pre> +
-    <span class="variable">$var</span> <span class="operator">=</span> <span class="string">"value"</span><span class="operator">;</span> +
-</pre> +
-<p>However, the above usage will create global variables throughout your +
-program, which is bad programming practice.  <a href="../../lib/pods/perlfunc.html#my"><code>my</code></a> creates lexically +
-scoped variables instead.  The variables are scoped to the block +
-(i.e. a bunch of statements surrounded by curly-braces) in which they +
-are defined.</p> +
-<pre> +
-    <span class="keyword">my</span> <span class="variable">$x</span> <span class="operator">=</span> <span class="string">"foo"</span><span class="operator">;</span> +
-    <span class="keyword">my</span> <span class="variable">$some_condition</span> <span class="operator">=</span> <span class="number">1</span><span class="operator">;</span> +
-    <span class="keyword">if</span> <span class="operator">(</span><span class="variable">$some_condition</span><span class="operator">)</span> <span class="operator">{</span> +
-        <span class="keyword">my</span> <span class="variable">$y</span> <span class="operator">=</span> <span class="string">"bar"</span><span class="operator">;</span> +
-        <span class="keyword">print</span> <span class="variable">$x</span><span class="operator">;</span>           <span class="comment"># prints "foo"</span> +
-        <span class="keyword">print</span> <span class="variable">$y</span><span class="operator">;</span>           <span class="comment"># prints "bar"</span> +
-    <span class="operator">}</span> +
-    <span class="keyword">print</span> <span class="variable">$x</span><span class="operator">;</span>               <span class="comment"># prints "foo"</span> +
-    <span class="keyword">print</span> <span class="variable">$y</span><span class="operator">;</span>               <span class="comment"># prints nothing; $y has fallen out of scope</span> +
-</pre> +
-<p>Using <a href="../../lib/pods/perlfunc.html#my"><code>my</code></a> in combination with a <code>use strict;</code> at the top of +
-your Perl scripts means that the interpreter will pick up certain common +
-programming errors.  For instance, in the example above, the final +
-<code>print $b</code> would cause a compile-time error and prevent you from +
-running the program.  Using <code>strict</code> is highly recommended.</p> +
-<p> +
-</p> +
-<h2><a name="conditional_and_looping_constructs">Conditional and looping constructs</a></h2> +
-<p>Perl has most of the usual conditional and looping constructs except for +
-case/switch (but if you really want it, there is a Switch module in Perl +
-5.8 and newer, and on CPAN. See the section on modules, below, for more +
-information about modules and CPAN).</p> +
-<p>The conditions can be any Perl expression.  See the list of operators in +
-the next section for information on comparison and boolean logic operators, +
-which are commonly used in conditional statements.</p> +
-<dl> +
-<dt><strong><a name="if" class="item">if</a></strong> +
- +
-<dd> +
-<pre> +
-    <span class="keyword">if</span> <span class="operator">(</span> <span class="variable">condition</span> <span class="operator">)</span> <span class="operator">{</span> +
-        <span class="operator">...</span> +
-    <span class="operator">}</span> <span class="keyword">elsif</span> <span class="operator">(</span> <span class="variable">other</span> <span class="variable">condition</span> <span class="operator">)</span> <span class="operator">{</span> +
-        <span class="operator">...</span> +
-    <span class="operator">}</span> <span class="keyword">else</span> <span class="operator">{</span> +
-        <span class="operator">...</span> +
-    <span class="operator">}</span> +
-</pre> +
-</dd> +
-<dd> +
-<p>There's also a negated version of it:</p> +
-</dd> +
-<dd> +
-<pre> +
-    <span class="keyword">unless</span> <span class="operator">(</span> <span class="variable">condition</span> <span class="operator">)</span> <span class="operator">{</span> +
-        <span class="operator">...</span> +
-    <span class="operator">}</span> +
-</pre> +
-</dd> +
-<dd> +
-<p>This is provided as a more readable version of <a href="#if"><code>if (!condition)</code></a>.</p> +
-</dd> +
-<dd> +
-<p>Note that the braces are required in Perl, even if you've only got one +
-line in the block.  However, there is a clever way of making your one-line +
-conditional blocks more English like:</p> +
-</dd> +
-<dd> +
-<pre> +
-    <span class="comment"># the traditional way</span> +
-    <span class="keyword">if</span> <span class="operator">(</span><span class="variable">$zippy</span><span class="operator">)</span> <span class="operator">{</span> +
-        <span class="keyword">print</span> <span class="string">"Yow!"</span><span class="operator">;</span> +
-    <span class="operator">}</span> +
-</pre> +
-</dd> +
-<dd> +
-<pre> +
-    <span class="comment"># the Perlish post-condition way</span> +
-    <span class="keyword">print</span> <span class="string">"Yow!"</span> <span class="keyword">if</span> <span class="variable">$zippy</span><span class="operator">;</span> +
-    <span class="keyword">print</span> <span class="string">"We have no bananas"</span> <span class="keyword">unless</span> <span class="variable">$bananas</span><span class="operator">;</span> +
-</pre> +
-</dd> +
-<dt><strong><a name="while" class="item">while</a></strong> +
- +
-<dd> +
-<pre> +
-    <span class="keyword">while</span> <span class="operator">(</span> <span class="variable">condition</span> <span class="operator">)</span> <span class="operator">{</span> +
-        <span class="operator">...</span> +
-    <span class="operator">}</span> +
-</pre> +
-</dd> +
-<dd> +
-<p>There's also a negated version, for the same reason we have <code>unless</code>:</p> +
-</dd> +
-<dd> +
-<pre> +
-    <span class="keyword">until</span> <span class="operator">(</span> <span class="variable">condition</span> <span class="operator">)</span> <span class="operator">{</span> +
-        <span class="operator">...</span> +
-    <span class="operator">}</span> +
-</pre> +
-</dd> +
-<dd> +
-<p>You can also use <a href="#while"><code>while</code></a> in a post-condition:</p> +
-</dd> +
-<dd> +
-<pre> +
-    <span class="keyword">print</span> <span class="string">"LA LA LA\n"</span> <span class="keyword">while</span> <span class="number">1</span><span class="operator">;</span>          <span class="comment"># loops forever</span> +
-</pre> +
-</dd> +
-<dt><strong><a name="for" class="item">for</a></strong> +
- +
-<dd> +
-<p>Exactly like C:</p> +
-</dd> +
-<dd> +
-<pre> +
-    <span class="keyword">for</span> <span class="operator">(</span><span class="variable">$i</span> <span class="operator">=</span> <span class="number">0</span><span class="operator">;</span> <span class="variable">$i</span> <span class="operator">&lt;=</span> <span class="variable">$max</span><span class="operator">;</span> <span class="variable">$i</span><span class="operator">++)</span> <span class="operator">{</span> +
-        <span class="operator">...</span> +
-    <span class="operator">}</span> +
-</pre> +
-</dd> +
-<dd> +
-<p>The C style for loop is rarely needed in Perl since Perl provides +
-the more friendly list scanning <a href="#foreach"><code>foreach</code></a> loop.</p> +
-</dd> +
-</li> +
-<dt><strong><a name="foreach" class="item">foreach</a></strong> +
- +
-<dd> +
-<pre> +
-    <span class="keyword">foreach</span> <span class="operator">(</span><span class="variable">@array</span><span class="operator">)</span> <span class="operator">{</span> +
-        <span class="keyword">print</span> <span class="string">"This element is </span><span class="variable">$_</span><span class="string">\n"</span><span class="operator">;</span> +
-    <span class="operator">}</span> +
-</pre> +
-</dd> +
-<dd> +
-<pre> +
-    <span class="keyword">print</span> <span class="variable">$list</span><span class="operator">[</span><span class="variable">$_</span><span class="operator">]</span> <span class="keyword">foreach</span> <span class="number">0</span> <span class="operator">..</span> <span class="variable">$max</span><span class="operator">;</span> +
-</pre> +
-</dd> +
-<dd> +
-<pre> +
-    <span class="comment"># you don't have to use the default $_ either...</span> +
-    <span class="keyword">foreach</span> <span class="keyword">my</span> <span class="variable">$key</span> <span class="operator">(</span><span class="keyword">keys</span> <span class="variable">%hash</span><span class="operator">)</span> <span class="operator">{</span> +
-        <span class="keyword">print</span> <span class="string">"The value of </span><span class="variable">$key</span><span class="string"> is </span><span class="variable">$hash</span><span class="string">{</span><span class="variable">$key</span><span class="string">}\n"</span><span class="operator">;</span> +
-    <span class="operator">}</span> +
-</pre> +
-</dd> +
-</dl> +
-<p>For more detail on looping constructs (and some that weren't mentioned in +
-this overview) see <a href="../../lib/pods/perlsyn.html">the perlsyn manpage</a>.</p> +
-<p> +
-</p> +
-<h2><a name="builtin_operators_and_functions">Builtin operators and functions</a></h2> +
-<p>Perl comes with a wide selection of builtin functions.  Some of the ones +
-we've already seen include <a href="../../lib/pods/perlfunc.html#print"><code>print</code></a>, <a href="../../lib/pods/perlfunc.html#sort"><code>sort</code></a> and <a href="../../lib/pods/perlfunc.html#reverse"><code>reverse</code></a>.  A list of +
-them is given at the start of <a href="../../lib/pods/perlfunc.html">the perlfunc manpage</a> and you can easily read +
-about any given function by using <code>perldoc -f functionname</code>.</p> +
-<p>Perl operators are documented in full in <a href="../../lib/pods/perlop.html">the perlop manpage</a>, but here are a few +
-of the most common ones:</p> +
-<dl> +
-<dt><strong><a name="arithmetic" class="item">Arithmetic</a></strong> +
- +
-<dd> +
-<pre> +
-    +   addition +
-    -   subtraction +
-    *   multiplication +
-    /   division</pre> +
-</dd> +
-<dt><strong><a name="numeric_comparison" class="item">Numeric comparison</a></strong> +
- +
-<dd> +
-<pre> +
-    ==  equality +
-    !=  inequality +
-    &lt;   less than +
-    &gt;   greater than +
-    &lt;=  less than or equal +
-    &gt;=  greater than or equal</pre> +
-</dd> +
-<dt><strong><a name="string_comparison" class="item">String comparison</a></strong> +
- +
-<dd> +
-<pre> +
-    eq  equality +
-    ne  inequality +
-    lt  less than +
-    gt  greater than +
-    le  less than or equal +
-    ge  greater than or equal</pre> +
-</dd> +
-<dd> +
-<p>(Why do we have separate numeric and string comparisons?  Because we don't +
-have special variable types, and Perl needs to know whether to sort +
-numerically (where 99 is less than 100) or alphabetically (where 100 comes +
-before 99).</p> +
-</dd> +
-<dt><strong><a name="boolean_logic" class="item">Boolean logic</a></strong> +
- +
-<dd> +
-<pre> +
-    &amp;&amp;  and +
-    ||  or +
-    !   not</pre> +
-</dd> +
-<dd> +
-<p>(<code>and</code>, <code>or</code> and <code>not</code> aren't just in the above table as descriptions +
-of the operators -- they're also supported as operators in their own +
-right.  They're more readable than the C-style operators, but have +
-different precedence to <code>&amp;&amp;</code> and friends.  Check <a href="../../lib/pods/perlop.html">the perlop manpage</a> for more +
-detail.)</p> +
-</dd> +
-<dt><strong><a name="miscellaneous2" class="item">Miscellaneous</a></strong> +
- +
-<dd> +
-<pre> +
-    =   assignment +
-    .   string concatenation +
-    x   string multiplication +
-    ..  range operator (creates a list of numbers)</pre> +
-</dd> +
-</dl> +
-<p>Many operators can be combined with a <code>=</code> as follows:</p> +
-<pre> +
-    <span class="variable">$a</span> <span class="operator">+=</span> <span class="number">1</span><span class="operator">;</span>        <span class="comment"># same as $a = $a + 1</span> +
-    <span class="variable">$a</span> <span class="operator">-=</span> <span class="number">1</span><span class="operator">;</span>        <span class="comment"># same as $a = $a - 1</span> +
-    <span class="variable">$a</span> <span class="operator">.=</span> <span class="string">"\n"</span><span class="operator">;</span>     <span class="comment"># same as $a = $a . "\n";</span> +
-</pre> +
-<p> +
-</p> +
-<h2><a name="files_and_i_o">Files and I/O</a></h2> +
-<p>You can open a file for input or output using the <a href="../../lib/pods/perlfunc.html#open"><code>open()</code></a> function. +
-It's documented in extravagant detail in <a href="../../lib/pods/perlfunc.html">the perlfunc manpage</a> and <a href="../../lib/pods/perlopentut.html">the perlopentut manpage</a>, +
-but in short:</p> +
-<pre> +
-    <span class="keyword">open</span><span class="operator">(</span><span class="keyword">my</span> <span class="variable">$in</span><span class="operator">,</span>  <span class="string">"&lt;"</span><span class="operator">,</span>  <span class="string">"input.txt"</span><span class="operator">)</span>  <span class="keyword">or</span> <span class="keyword">die</span> <span class="string">"Can't open input.txt: $!"</span><span class="operator">;</span> +
-    <span class="keyword">open</span><span class="operator">(</span><span class="keyword">my</span> <span class="variable">$out</span><span class="operator">,</span> <span class="string">"&gt;"</span><span class="operator">,</span>  <span class="string">"output.txt"</span><span class="operator">)</span> <span class="keyword">or</span> <span class="keyword">die</span> <span class="string">"Can't open output.txt: $!"</span><span class="operator">;</span> +
-    <span class="keyword">open</span><span class="operator">(</span><span class="keyword">my</span> <span class="variable">$log</span><span class="operator">,</span> <span class="string">"&gt;&gt;"</span><span class="operator">,</span> <span class="string">"my.log"</span><span class="operator">)</span>     <span class="keyword">or</span> <span class="keyword">die</span> <span class="string">"Can't open my.log: $!"</span><span class="operator">;</span> +
-</pre> +
-<p>You can read from an open filehandle using the <code>&lt;&gt;</code> operator.  In +
-scalar context it reads a single line from the filehandle, and in list +
-context it reads the whole file in, assigning each line to an element of +
-the list:</p> +
-<pre> +
-    <span class="keyword">my</span> <span class="variable">$line</span>  <span class="operator">=</span> <span class="operator">&lt;</span><span class="variable">$in</span><span class="operator">&gt;;</span> +
-    <span class="keyword">my</span> <span class="variable">@lines</span> <span class="operator">=</span> <span class="operator">&lt;</span><span class="variable">$in</span><span class="operator">&gt;;</span> +
-</pre> +
-<p>Reading in the whole file at one time is called slurping. It can +
-be useful but it may be a memory hog. Most text file processing +
-can be done a line at a time with Perl's looping constructs.</p> +
-<p>The <code>&lt;&gt;</code> operator is most often seen in a <a href="#while"><code>while</code></a> loop:</p> +
-<pre> +
-    <span class="keyword">while</span> <span class="operator">(&lt;</span><span class="variable">$in</span><span class="operator">&gt;)</span> <span class="operator">{</span>     <span class="comment"># assigns each line in turn to $_</span> +
-        <span class="keyword">print</span> <span class="string">"Just read in this line: </span><span class="variable">$_</span><span class="string">"</span><span class="operator">;</span> +
-    <span class="operator">}</span> +
-</pre> +
-<p>We've already seen how to print to standard output using <a href="../../lib/pods/perlfunc.html#print"><code>print()</code></a>. +
-However, <a href="../../lib/pods/perlfunc.html#print"><code>print()</code></a> can also take an optional first argument specifying +
-which filehandle to print to:</p> +
-<pre> +
-    <span class="keyword">print</span> <span class="variable">STDERR</span> <span class="string">"This is your final warning.\n"</span><span class="operator">;</span> +
-    <span class="keyword">print</span> <span class="variable">$out</span> <span class="variable">$record</span><span class="operator">;</span> +
-    <span class="keyword">print</span> <span class="variable">$log</span> <span class="variable">$logmessage</span><span class="operator">;</span> +
-</pre> +
-<p>When you're done with your filehandles, you should <a href="../../lib/pods/perlfunc.html#close"><code>close()</code></a> them +
-(though to be honest, Perl will clean up after you if you forget):</p> +
-<pre> +
-    <span class="keyword">close</span> <span class="variable">$in</span> <span class="keyword">or</span> <span class="keyword">die</span> <span class="string">"</span><span class="variable">$in</span><span class="string">: $!"</span><span class="operator">;</span> +
-</pre> +
-<p> +
-</p> +
-<h2><a name="regular_expressions">Regular expressions</a></h2> +
-<p>Perl's regular expression support is both broad and deep, and is the +
-subject of lengthy documentation in <a href="../../lib/pods/perlrequick.html">the perlrequick manpage</a>, <a href="../../lib/pods/perlretut.html">the perlretut manpage</a>, and +
-elsewhere.  However, in short:</p> +
-<dl> +
-<dt><strong><a name="simple_matching" class="item">Simple matching</a></strong> +
- +
-<dd> +
-<pre> +
-    <span class="keyword">if</span> <span class="operator">(</span><span class="regex">/foo/</span><span class="operator">)</span>       <span class="operator">{</span> <span class="operator">...</span> <span class="operator">}</span>  <span class="comment"># true if $_ contains "foo"</span> +
-    <span class="keyword">if</span> <span class="operator">(</span><span class="variable">$a</span> <span class="operator">=~</span> <span class="regex">/foo/</span><span class="operator">)</span> <span class="operator">{</span> <span class="operator">...</span> <span class="operator">}</span>  <span class="comment"># true if $a contains "foo"</span> +
-</pre> +
-</dd> +
-<dd> +
-<p>The <code>//</code> matching operator is documented in <a href="../../lib/pods/perlop.html">the perlop manpage</a>.  It operates on +
-<a href="../../lib/pods/perlvar.html#__"><code>$_</code></a> by default, or can be bound to another variable using the <code>=~</code> +
-binding operator (also documented in <a href="../../lib/pods/perlop.html">the perlop manpage</a>).</p> +
-</dd> +
-<dt><strong><a name="simple_substitution" class="item">Simple substitution</a></strong> +
- +
-<dd> +
-<pre> +
-    <span class="regex">s/foo/bar/</span><span class="operator">;</span>               <span class="comment"># replaces foo with bar in $_</span> +
-    <span class="variable">$a</span> <span class="operator">=~</span> <span class="regex">s/foo/bar/</span><span class="operator">;</span>         <span class="comment"># replaces foo with bar in $a</span> +
-    <span class="variable">$a</span> <span class="operator">=~</span> <span class="regex">s/foo/bar/g</span><span class="operator">;</span>        <span class="comment"># replaces ALL INSTANCES of foo with bar in $a</span> +
-</pre> +
-</dd> +
-<dd> +
-<p>The <a href="../../lib/pods/perlfunc.html#s_"><code>s///</code></a> substitution operator is documented in <a href="../../lib/pods/perlop.html">the perlop manpage</a>.</p> +
-</dd> +
-<dt><strong><a name="more_complex_regular_expressions" class="item">More complex regular expressions</a></strong> +
- +
-<dd> +
-<p>You don't just have to match on fixed strings.  In fact, you can match +
-on just about anything you could dream of by using more complex regular +
-expressions.  These are documented at great length in <a href="../../lib/pods/perlre.html">the perlre manpage</a>, but for +
-the meantime, here's a quick cheat sheet:</p> +
-</dd> +
-<dd> +
-<pre> +
-    .                   a single character +
-    \s                  a whitespace character (space, tab, newline, ...) +
-    \S                  non-whitespace character +
-    \d                  a digit (0-9) +
-    \D                  a non-digit +
-    \w                  a word character (a-z, A-Z, 0-9, _) +
-    \W                  a non-word character +
-    [aeiou]             matches a single character in the given set +
-    [^aeiou]            matches a single character outside the given set +
-    (foo|bar|baz)       matches any of the alternatives specified</pre> +
-</dd> +
-<dd> +
-<pre> +
-    ^                   start of string +
-    $                   end of string</pre> +
-</dd> +
-<dd> +
-<p>Quantifiers can be used to specify how many of the previous thing you +
-want to match on, where &quot;thing&quot; means either a literal character, one +
-of the metacharacters listed above, or a group of characters or +
-metacharacters in parentheses.</p> +
-</dd> +
-<dd> +
-<pre> +
-    <span class="operator">*</span>                   <span class="variable">zero</span> <span class="keyword">or</span> <span class="variable">more</span> <span class="variable">of</span> <span class="variable">the</span> <span class="variable">previous</span> <span class="variable">thing</span> +
-    <span class="operator">+</span>                   <span class="variable">one</span> <span class="keyword">or</span> <span class="variable">more</span> <span class="variable">of</span> <span class="variable">the</span> <span class="variable">previous</span> <span class="variable">thing</span> +
-    <span class="operator">?</span>                   <span class="variable">zero</span> <span class="keyword">or</span> <span class="variable">one</span> <span class="variable">of</span> <span class="variable">the</span> <span class="variable">previous</span> <span class="variable">thing</span> +
-    <span class="operator">{</span><span class="number">3</span><span class="operator">}</span>                 <span class="variable">matches</span> <span class="variable">exactly</span> <span class="number">3</span> <span class="variable">of</span> <span class="variable">the</span> <span class="variable">previous</span> <span class="variable">thing</span> +
-    <span class="operator">{</span><span class="number">3</span><span class="operator">,</span><span class="number">6</span><span class="operator">}</span>               <span class="variable">matches</span> <span class="variable">between</span> <span class="number">3</span> <span class="keyword">and</span> <span class="number">6</span> <span class="variable">of</span> <span class="variable">the</span> <span class="variable">previous</span> <span class="variable">thing</span> +
-    <span class="operator">{</span><span class="number">3</span><span class="operator">,}</span>                <span class="variable">matches</span> <span class="number">3</span> <span class="keyword">or</span> <span class="variable">more</span> <span class="variable">of</span> <span class="variable">the</span> <span class="variable">previous</span> <span class="variable">thing</span> +
-</pre> +
-</dd> +
-<dd> +
-<p>Some brief examples:</p> +
-</dd> +
-<dd> +
-<pre> +
-    <span class="regex">/^\d+/</span>              <span class="variable">string</span> <span class="variable">starts</span> <span class="variable">with</span> <span class="variable">one</span> <span class="keyword">or</span> <span class="variable">more</span> <span class="variable">digits</span> +
-    <span class="operator">/^</span><span class="variable">$/</span>                <span class="variable">nothing</span> <span class="variable">in</span> <span class="variable">the</span> <span class="variable">string</span> <span class="operator">(</span><span class="variable">start</span> <span class="keyword">and</span> <span class="variable">end</span> <span class="variable">are</span> <span class="variable">adjacent</span><span class="operator">)</span> +
-    <span class="operator">/(\</span><span class="variable">d</span><span class="operator">\</span><span class="regex">s){3}/         a three digits, each followed by a whitespace +
-                        character (eg "3 4 5 ") +
-    /(a.)</span><span class="operator">+</span><span class="regex">/             matches a string in which every odd-numbered letter +
-                        is a (eg "abacadaf") +
-    </span> +
-</pre> +
-</dd> +
-<dd> +
-<pre> +
-    <span class="comment"># This loop reads from STDIN, and prints non-blank lines:</span> +
-    <span class="keyword">while</span> <span class="operator">(&lt;&gt;)</span> <span class="operator">{</span> +
-        <span class="keyword">next</span> <span class="keyword">if</span> <span class="regex">/^$/</span><span class="operator">;</span> +
-        <span class="keyword">print</span><span class="operator">;</span> +
-    <span class="operator">}</span> +
-</pre> +
-</dd> +
-</li> +
-<dt><strong><a name="parentheses_for_capturing" class="item">Parentheses for capturing</a></strong> +
- +
-<dd> +
-<p>As well as grouping, parentheses serve a second purpose.  They can be +
-used to capture the results of parts of the regexp match for later use. +
-The results end up in <code>$1</code>, <code>$2</code> and so on.</p> +
-</dd> +
-<dd> +
-<pre> +
-    <span class="comment"># a cheap and nasty way to break an email address up into parts</span> +
-</pre> +
-</dd> +
-<dd> +
-<pre> +
-    <span class="keyword">if</span> <span class="operator">(</span><span class="variable">$email</span> <span class="operator">=~</span> <span class="regex">/([^@]+)@(.+)/</span><span class="operator">)</span> <span class="operator">{</span> +
-        <span class="keyword">print</span> <span class="string">"Username is </span><span class="variable">$1</span><span class="string">\n"</span><span class="operator">;</span> +
-        <span class="keyword">print</span> <span class="string">"Hostname is </span><span class="variable">$2</span><span class="string">\n"</span><span class="operator">;</span> +
-    <span class="operator">}</span> +
-</pre> +
-</dd> +
-</li> +
-<dt><strong><a name="other_regexp_features" class="item">Other regexp features</a></strong> +
- +
-<dd> +
-<p>Perl regexps also support backreferences, lookaheads, and all kinds of +
-other complex details.  Read all about them in <a href="../../lib/pods/perlrequick.html">the perlrequick manpage</a>, +
-<a href="../../lib/pods/perlretut.html">the perlretut manpage</a>, and <a href="../../lib/pods/perlre.html">the perlre manpage</a>.</p> +
-</dd> +
-</li> +
-</dl> +
-<p> +
-</p> +
-<h2><a name="writing_subroutines">Writing subroutines</a></h2> +
-<p>Writing subroutines is easy:</p> +
-<pre> +
-    <span class="keyword">sub</span><span class="variable"> logger </span><span class="operator">{</span> +
-        <span class="keyword">my</span> <span class="variable">$logmessage</span> <span class="operator">=</span> <span class="keyword">shift</span><span class="operator">;</span> +
-        <span class="keyword">open</span> <span class="keyword">my</span> <span class="variable">$logfile</span><span class="operator">,</span> <span class="string">"&gt;&gt;"</span><span class="operator">,</span> <span class="string">"my.log"</span> <span class="keyword">or</span> <span class="keyword">die</span> <span class="string">"Could not open my.log: $!"</span><span class="operator">;</span> +
-        <span class="keyword">print</span> <span class="variable">$logfile</span> <span class="variable">$logmessage</span><span class="operator">;</span> +
-    <span class="operator">}</span> +
-</pre> +
-<p>Now we can use the subroutine just as any other built-in function:</p> +
-<pre> +
-    <span class="variable">logger</span><span class="operator">(</span><span class="string">"We have a logger subroutine!"</span><span class="operator">);</span> +
-</pre> +
-<p>What's that <a href="../../lib/pods/perlfunc.html#shift"><code>shift</code></a>?  Well, the arguments to a subroutine are available +
-to us as a special array called <a href="../../lib/pods/perlvar.html#__"><code>@_</code></a> (see <a href="../../lib/pods/perlvar.html">the perlvar manpage</a> for more on that). +
-The default argument to the <a href="../../lib/pods/perlfunc.html#shift"><code>shift</code></a> function just happens to be <a href="../../lib/pods/perlvar.html#__"><code>@_</code></a>. +
-So <code>my $logmessage = shift;</code> shifts the first item off the list of +
-arguments and assigns it to <code>$logmessage</code>.</p> +
-<p>We can manipulate <a href="../../lib/pods/perlvar.html#__"><code>@_</code></a> in other ways too:</p> +
-<pre> +
-    <span class="keyword">my</span> <span class="operator">(</span><span class="variable">$logmessage</span><span class="operator">,</span> <span class="variable">$priority</span><span class="operator">)</span> <span class="operator">=</span> <span class="variable">@_</span><span class="operator">;</span>       <span class="comment"># common</span> +
-    <span class="keyword">my</span> <span class="variable">$logmessage</span> <span class="operator">=</span> <span class="variable">$_</span><span class="operator">[</span><span class="number">0</span><span class="operator">]</span><span class="operator">;</span>                 <span class="comment"># uncommon, and ugly</span> +
-</pre> +
-<p>Subroutines can also return values:</p> +
-<pre> +
-    <span class="keyword">sub</span><span class="variable"> square </span><span class="operator">{</span> +
-        <span class="keyword">my</span> <span class="variable">$num</span> <span class="operator">=</span> <span class="keyword">shift</span><span class="operator">;</span> +
-        <span class="keyword">my</span> <span class="variable">$result</span> <span class="operator">=</span> <span class="variable">$num</span> <span class="operator">*</span> <span class="variable">$num</span><span class="operator">;</span> +
-        <span class="keyword">return</span> <span class="variable">$result</span><span class="operator">;</span> +
-    <span class="operator">}</span> +
-</pre> +
-<p>Then use it like:</p> +
-<pre> +
-    <span class="variable">$sq</span> <span class="operator">=</span> <span class="variable">square</span><span class="operator">(</span><span class="number">8</span><span class="operator">);</span> +
-</pre> +
-<p>For more information on writing subroutines, see <a href="../../lib/pods/perlsub.html">the perlsub manpage</a>.</p> +
-<p> +
-</p> +
-<h2><a name="oo_perl">OO Perl</a></h2> +
-<p>OO Perl is relatively simple and is implemented using references which +
-know what sort of object they are based on Perl's concept of packages. +
-However, OO Perl is largely beyond the scope of this document. +
-Read <a href="../../lib/pods/perlboot.html">the perlboot manpage</a>, <a href="../../lib/pods/perltoot.html">the perltoot manpage</a>, <a href="../../lib/pods/perltooc.html">the perltooc manpage</a> and <a href="../../lib/pods/perlobj.html">the perlobj manpage</a>.</p> +
-<p>As a beginning Perl programmer, your most common use of OO Perl will be +
-in using third-party modules, which are documented below.</p> +
-<p> +
-</p> +
-<h2><a name="using_perl_modules">Using Perl modules</a></h2> +
-<p>Perl modules provide a range of features to help you avoid reinventing +
-the wheel, and can be downloaded from CPAN ( <a href="http://www.cpan.org/">http://www.cpan.org/</a> ).  A +
-number of popular modules are included with the Perl distribution +
-itself.</p> +
-<p>Categories of modules range from text manipulation to network protocols +
-to database integration to graphics.  A categorized list of modules is +
-also available from CPAN.</p> +
-<p>To learn how to install modules you download from CPAN, read +
-<a href="../../lib/pods/perlmodinstall.html">the perlmodinstall manpage</a></p> +
-<p>To learn how to use a particular module, use <code>perldoc Module::Name</code>. +
-Typically you will want to <code>use Module::Name</code>, which will then give +
-you access to exported functions or an OO interface to the module.</p> +
-<p><a href="../../lib/pods/perlfaq.html">the perlfaq manpage</a> contains questions and answers related to many common +
-tasks, and often provides suggestions for good CPAN modules to use.</p> +
-<p><a href="../../lib/pods/perlmod.html">the perlmod manpage</a> describes Perl modules in general.  <a href="../../lib/pods/perlmodlib.html">the perlmodlib manpage</a> lists the +
-modules which came with your Perl installation.</p> +
-<p>If you feel the urge to write Perl modules, <a href="../../lib/pods/perlnewmod.html">the perlnewmod manpage</a> will give you +
-good advice.</p> +
-<p> +
-</p> +
-<hr /> +
-<h1><a name="author">AUTHOR</a></h1> +
-<p>Kirrily &quot;Skud&quot; Robert &lt;<a href="mailto:skud@cpan.org">skud@cpan.org</a>&gt;</p> +
 </body> </body>
 +</html>
  
-</html> 
 </code> </code>
- 
-