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Perl

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Programming Republic of Perl logo

Perl, also Practical Extraction and Report Language (a backronym, see below), is an interpreted procedural programming language designed by Larry Wall. Perl borrows features from C, shell scripting (sh), awk, sed, and (to a lesser extent) many other programming languages.

Contents

Overview

The perlintro(1) man page says

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.

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. </blockquote>

Language features

The overall structure of Perl derives broadly from C. Perl is a procedural programming language, with variables, expressions, assignment statements, brace-delimited code blocks, control structures, and subroutines.

Perl also takes features from shell programming. Perl programs are interpreted. All variables are marked with leading sigils. Sigils unambiguously identify variable names, thus allowing Perl to have a rich syntax. Importantly, sigils allow variables to be interpolated directly into strings. Like the Unix shells, Perl has many built-in functions for common tasks, like sorting, and for accessing system facilities.

Perl takes associative arrays from awk and regular expressions from sed. These simplify and facilitate all manner of parsing, text handling, and data management tasks.

In Perl 5, features were added that support complex data structures and an object oriented programming model. These include references, packages, and class-based method dispatch. Perl 5 also saw the introduction of lexically scoped variables, which make it easier to write robust code, and modules, which make it practical to write and distribute libraries of Perl code.

All versions of Perl do automatic data typing and memory management. The interpreter knows the type and storage requirements of every data object in the program; it allocates and frees storage for them as necessary. Legal type conversions are done automatically at run time; illegal type conversions are fatal errors. It is not possible, within the language, to leak memory, crash the interpreter, or corrupt its internal data representation.

Applications

Perl has many and varied applications.

Perl has been used since the early days of the web to write CGI scripts, and is a component of the popular LAMP (Linux/Apache/MySQL/(Perl/PHP/Python)) platform for web development. Perl has been called "the glue that holds the web together". Large systems written in Perl include Slashdot and early implementations of PHP [1] (http://www.php.net/history) and Wikipedia.

Perl finds many applications as a "glue language", tying together systems and interfaces that were not specifically designed to interoperate. Systems administrators use Perl as an all-purpose tool; short Perl programs can be entered and run on a single command line.

Perl is widely used in finance and bioinformatics, where it is valued for rapid application development, ability to handle large data sets, and the availability of many standard and 3rd-party modules.

Implementation

Perl is implemented as a core interpreter, written in C, together with a large collection of modules, written in Perl and C. The source distribution is currently 12 MB when packaged in a tar file and compressed. The interpreter is 150,000 lines of C code and compiles to a 1 MB executable on typical machine architectures. Alternately, the interpreter can be compiled to a link library and embedded in other programs. There are nearly 500 modules in the distribution, comprising 200,000 lines of Perl and an additional 350,000 lines of C code. Much of the C code in the modules consists of character encoding tables.

The interpreter has an object-oriented architecture. All the elements of the Perl language—scalars, arrays, hashes, coderefs, file handles—are represented in the interpreter by C structs. Operations on these structs are defined by a large collection of macros, typedefs and functions; these constitute the Perl C API. The Perl API can be bewildering to the uninitiate; however, its entry points follow a consistent naming scheme, which provides guidance to those who use it.

The execution of a Perl program divides broadly into two phases. First, the interpreter parses the program text into a syntax tree. Then, it executes the program by walking the tree. The text is parsed only once, and the syntax tree is subject to optimization before it is executed, so the execution phase is relatively efficient.

Perl has a context-free grammar; however, it cannot be parsed by a straight Yacc/Lex parser/lexer combination. Instead, it implements its own lexer, which coordinates with a modified GNU bison parser to resolve ambiguities in the language. It is said that "only perl can parse Perl", meaning that only the Perl interpreter can parse the Perl language. The truth of this is attested by the imperfections of other programs that undertake to parse Perl, such as source code analyzers and auto-indenters.

Maintenance of the Perl interpreter has become increasingly difficult over the years. The code base has been in continuous development since 1994. The code has been optimized for performance at the expense of simplicity, clarity, and strong internal interfaces. New features have been added, yet virtually complete backwards compatibility with earlier versions is maintained. The size and complexity of the interpreter is a barrier to developers who wish to work on it.

Perl is distributed with some 90,000 functional tests. These run as part of the normal build process, and extensively exercise the interperter and its core modules. Perl developers rely on the functional tests to ensure that changes to the interpreter do not introduce bugs; conversely, Perl users who see the interpreter pass its functional tests on their system can have a high degree of confidence that it is working properly.

There is no written specification or standard for the Perl language, and no plans to create one. There has only ever been one implementation of the interpreter. That interpreter, together with its functional tests, stands as a de facto specification of the language.

Availability

Perl is free software, and may be distributed under either the Artistic License or the GNU General Public License. It is available for most operating systems. It is particularly prevalent on Unix and Unix-like systems (such as Linux, FreeBSD, and Mac OS X), and is growing in popularity on Microsoft Windows systems.

Perl has been ported to over a hundred different platforms. Perl can, with only six reported exceptions, be compiled from source on all Unix-like, POSIX-compliant or otherwise Unix-compatible platforms, including AmigaOS, BeOS, Cygwin, and Mac OS X. It can be compiled from source on Windows; however, many Windows installations lack a C compiler, so Windows users typically install a binary distribution, such as ActivePerl (http://www.activestate.com/Products/ActivePerl/) or IndigoPerl (http://www.indigostar.com/indigoperl.htm). A custom port, MacPerl (http://www.ptf.com/macperl/), is also available for Mac OS Classic. [2] (http://www.perl.com/CPAN/ports/)

Language structure

Data types

Perl has three fundamental data types: scalars, lists, and hashes. A scalar is a single value; it may be a number, a string, or a reference. A list is an ordered collection of scalars. A variable that holds a list is called an array. A hash, or associative array, is a map from strings to scalars; the strings are called keys and the scalars are called values.

All variables are marked by a leading sigil, which identifies the data type. The same name may be used for variables of different types, without conflict.

 $foo   # a scalar
 @foo   # a list
 %foo   # a hash

Numbers are written in the usual way; strings are enclosed by quotes of various kinds.

 $n     = 42;
 $name  = "joe";
 $color = 'red';

A list may be written by listing its elements, separated by commas, and enclosed by parentheses where required by operator precedence.

 @scores = (32, 45, 16, 5);

A hash may be initialized from a list of key/value pairs.

 %favorite = (joe => 'red',
              sam => 'blue');

Individual elements of a list are accessed by providing a numerical index, in square brackets. Individual values in a hash are accessed by providing the corresponding key, in curly braces. The $ sigil identifies the accessed element as a scalar.

 $scores[2]      # an element of @scores
 $favorite{joe}  # a value in %favorite

The number of elements in an array can be obtained by evalulating the array in scalar context.

 $count = @friends;

There are a few functions that operate on entire hashes.

 @names     = keys   %address;
 @addresses = values %address;

Control structures

Main article: Perl control structures

Perl has several kinds of control structures.

It has block-oriented control structures, similar to those in the C and Java programming languages. Conditions are surrounded by parentheses, and controlled blocks are surrounded by braces.

label while ( cond ) { ... }
label while ( cond ) { ... } continue { ... }
label for ( init-expr ; cond-expr ; incr-expr ) { ... }
label foreach var ( list ) { ... }
label foreach var ( list ) { ... } continue { ... }
if ( cond ) { ... }
if ( cond ) { ... } else { ... } 
if ( cond ) { ... } elsif ( cond ) { ... } else { ... } 

Where only a single statement is being controlled, statement modifiers provide a lighter syntax.

statement if      cond ;
statement unless  cond ;
statement while   cond ;
statement until   cond ;
statement foreach list ;

Short-circuit logical operators are commonly used to effect control flow at the expression level.

expr and expr
expr or  expr

Perl has two implicit looping constructs.

 results = grep { ... } list
 results = map  { ... } list

grep<code> returns all elements of list for which the controlled block evaulates to true. <code>map<code> evaluates the controlled block for each element of list and returns a list of the resulting values. These constructs enable a simple functional programming style.

There is no switch (multi-way branch) statement in Perl 5. The Perl documentation describes a half-dozen ways to achieve the same effect by using other control structures, none entirely satisfactory. A very general and flexible switch statement has been designed for Perl 6. The <code>Switch module makes most of the functionality of the Perl 6 switch available to Perl 5 programs.

Perl includes a goto label statement, but it is virtually never used. It is considered poor form, the implementation is slow, and situations where a goto is called for in other languages either tend not to occur in Perl or are better handled with other control structures, such as labeled loops.

There is also a goto &sub statement that performs a tail call. It terminates the current subroutine and immediately calls the specified sub. Use of this form is culturally accepted but unusual because it is rarely needed.

Subroutines

Subroutines are defined with the sub keyword, and invoked simply by naming them. Subroutine definitions may appear anywhere in the program. Parentheses are required for calls that precede the definion.

foo();
sub foo { ... }
foo;

A list of arguments may be provided after the subroutine name. Arguments may be scalars, lists, or hashes.

foo $a, @b, %c;

The parameters to a subroutine need not be declared as to either number or type; in fact, they may vary from call to call. Arrays are expanded to their elements, hashes are expanded to a list of key/value pairs, and the whole lot is passed into the subroutine as one undifferentiated list of scalars.

Whatever arguments are passed are available to the subroutine in the special array @_. The elements of @_ are aliased to the actual arguments; changing an element of @_ changes the corresponding argument.

Elements of @_ may be accessed by subscripting it in the usual way.

$_[0], $_[1]

However, the resulting code can be difficult to read, and the parameters have pass-by-reference semantics, which may be undesirable.

One common idiom is to assign @_ to a list of named variables.

($a, $b, $c) = @_;

This effects both mnemonic parameter names and pass-by-value sematics. Another idiom is to shift parameters off of @_. This is especially common when the subroutine takes only one argument.

$a = shift;

Subroutines may return values.

return 42, $x, @y, %z;

If the subroutine does not exit via a return statement, then it returns the last expression evaluated within the subroutine body. Arrays and hashes in the return value are expanded to lists of scalars, just as they are for arguments.

The returned expression is evaluated in the calling context of the subroutine; this can surprise the unwary.

sub list  {      (4, 5, 6)     }
sub array { @a = (4, 5, 6); @a }

$a = list   # returns 6 - last element of list
$a = array  # returns 3 - number of elements in list
@a = list   # returns (4, 5, 6)
@a = array  # returns (4, 5, 6)

Regular expressions

The Perl language includes a specialized syntax for writing regular expressions (REs), and the interpreter contains an engine for matching strings to REs. The RE engine uses a backtracking algorithm; this extends its capabilities from simple pattern matching to string capture and substitution.

The Perl regular expression syntax was originally taken from Unix Version 8 regular expressions. However, it diverged before the first release of Perl, and has since grown to include many more features.

The m// (match) operator introduces a regular expression match. (The leading m may be omitted for brevity.) In the simplest case, an expression like

 $x =~ m/abc/

evaluates to true iff the string $x matches the regular expression abc. To capture a matched string, surround the part of the RE that you want with parentheses and evaluate it in list context. This is more interesting for patterns that can match multiple strings

 ($matched) = $x =~ m/a(.)c/;   # capture the character between 'a' and 'c'

The s// (substitute) operator specifies a search and replace operation

 $x =~ s/abc/aBc/;   # upcase the b

Perl regular expressions can take modifiers. These are single-letter suffixes that modify the meaning of the expression

 $x =~ m/abc/i;      # case-insensitive pattern match
 $x =~ s/abc/aBc/g;  # global search and replace

Perl regular expressions can be dense and cryptic. Partly, this is because regular expression matching is an inherently complex operation, and partly it is because the RE syntax is extremely compact. Some relief from the second problem is afforded by the /x modifer, which allows programmers to place whitespace and comments inside regular expressions

 $x =~ m/a     # match 'a'
         .     # match any character
         c     # match 'c'
          /x;

One common use of regular expressions is to specify delimiters for the split operator.

 @words = split m/,/, $line;   # divide $line into comma-separated values

The split operator complements string capture. String capture returns strings that match the RE; split returns strings that don't match the RE.

See also Perl regular expression examples

Database interfaces

Perl is widely favored for database applications. Its text handling facilities are good for generating SQL queries; arrays, hashes and automatic memory management make it easy to collect and process the returned data.

In early versions of Perl, database interfaces were created by relinking the interpreter with a client-side database library. This was somewhat clumsy; a particular problem was that the resulting perl executable was restricted to using just the one database interface that it was linked to. Also, relinking the interpreter was sufficiently difficult that it was only done for a few of the most important and widely used databases.

In Perl 5, database interfaces are implemented by modules. The DBI (Database Interface) module presents a single, database-independent interface to Perl applications, while the DBD:: (Database Driver) modules handle the details of accessing some 50 different databases. There are DBD:: drivers for most ANSI SQL databases.

Language design

The design of Perl can be understood as a natural response to three broad trends in the computer industry: falling hardware costs, rising labor costs, and advancing compiler technology. Earlier computer languages, such as Fortran and C, were designed to make efficient use of expensive computer hardware. In contrast, Perl is designed to make efficient use of expensive computer programmers.

Perl has many features that ease the programmer's task at the expense of greater CPU and memory requirements. These include automatic data typing and memory management; strings, lists, and hashes; regular expressions, and interpreted execution.

Larry Wall was trained as a linguist, and the design of Perl is very much informed by linguistic principles. Examples include Huffman coding (common constructions should be short), good end-weighting (the important information should come first), and a large collection of language primitives. Perl favors language constructs that are natural for humans to read and write, even where they complicate the Perl interpreter.

Perl has features that support a variety of programming paradigms, such as procedural, functional, and object-oriented. At the same time, Perl does not enforce any particular paradigm, or even require the programmer to choose among them.

There is a broad practical bent to both the Perl language and the community and culture that surround it. The preface to Programming Perl begins, "Perl is a language for getting your job done" [3] (http://www.unix.org.ua/orelly/perl/prog3/ch00_01.htm). One consequence of this is that Perl is not a tidy language. It includes features if people use them, tolerates exceptions to its rules, and employs heuristics to resolve syntactical ambiguities. Discussing the variant behaviour of built-in functions in list and scalar context, the perlfunc(1) man page says,

In general, they do what you want, unless you want consistency.

Perl has several mottos that convey aspects of its design and use. One is There's more than one way to do it (TMTOWTDI - usually pronounced 'Tim Toady'). Another is Perl: the Swiss Army Chainsaw of Programming Languages. A stated design goal of Perl is to make easy tasks easy and difficult tasks possible.

Opinion

Perl engenders strong feelings among both its proponents and its detractors.

Pro

Programmers who like Perl typically cite its power, expressiveness, and ease of use. Perl provides infrastructure for many common programming tasks, such as string and list processing. Other tasks, such as memory management, are handled automatically and transparently. Programmers coming from other languages to Perl often find that whole classes of problems that they have struggled with in the past just don't arise in Perl. As Larry Wall put it,

What is the sound of Perl? Is it not the sound of a wall that people have stopped banging their heads against?

Besides its practical benefits, many programmers simply seem to enjoy working in Perl. Early issues of The Perl Journal (http://www.tpj.com) had a page titled "What is Perl?" that concluded

Perl is fun. In these days of self-serving jargon, conflicting and unpredictable standards, and proprietary systems that discourage peeking under the hood, people have forgotten that programming is supposed to be fun. I don't mean the satisfaction of seeing our well-tuned programs do our bidding, but the literary act of creative writing that yields those programs. With Perl, the journey is as enjoyable as the destination ...

Whatever the reasons, there is clearly a broad community of people who are passionate about Perl, as evidenced by the thousands of modules that have been contributed to CPAN, and the hundreds of design proposals that were submitted as RFCs for Perl 6.

Con

People who dislike Perl voice a variety of objections, some substantive and some less so.

One common complaint is that Perl is ugly. In particular, its prodigious use of punctuation seems to put people off; Perl source code is sometimes likened to "line noise". In The Python Paradox (http://www.paulgraham.com/pypar.html), Paul Graham both acknowledges and responds to this:

At the mention of ugly source code, people will of course think of Perl. But the superficial ugliness of Perl is not the sort I mean. Real ugliness is not harsh-looking syntax, but having to build programs out of the wrong concepts.

Another criticism is that Perl is excessively complex and compact, and that it leads to "write-only" code, that is, to code that is virtually impossible to understand after it has been written. It is, of course, possible to write obscure code in any language, but Perl has perhaps more than the usual share of terse, complex and arcane language constructs to exacerbate the problem. Perl supports many such features for backwards compatibility, and for use where maintainability is expressly not a concern, such as programs that are entered and run directly on the command line.

The freewheeling language style that delights some Perl programmers concerns others. For example, Perl has a relatively weak object model. Access to private data is restricted only by convention, not the language itself. An object created in one place may easily be modified in another; there may not be any single place where its state is definitively established. There are techniques for addressing these issues, but they are complex and seldom used. On a different level, one of the early Unix engineers from Bell Labs has expressed surprise that anyone could write important applications in a language for which there is no published specification.

Some worry that Perl is licensed under terms that are incompatible with commercial use. However, Perl is used successfully by many businesses, so this would seem to be either ignorance or FUD. Some worry that Perl uses too much RAM or CPU. In fact, Perl is not a good language for applications that are truly processor-bound; however, there are many, many others for which it is perfectly adequate.

History

Larry Wall began work on Perl in 1987, and released version 1.0 to the comp.sources.misc newsgroup on December 18, 1987. The language expanded rapidly over the next few years. Perl 2, released in 1988, featured a better regular expression engine. Perl 3, released in 1989, added support for binary data.

Until 1991, the only documentation for Perl was a single (increasingly lengthy) man page. In 1991, Programming Perl (the Camel Book) was published, and became the de facto reference for the language. At the same time, the Perl version number was bumped to 4, not to mark a major change in the language, but to identify the version that was documented by the book.

Perl 4 went through a series of maintenance releases, culminating in Perl 4.036 in 1993. At that point, Larry Wall abandoned Perl 4 to begin work on Perl 5. Perl 4 remains at version 4.036 to this day.

Development of Perl 5 continued into 1994. The perl5-porters mailing list was established in May 1994 to coordinate work on porting Perl 5 to different platforms. It remains the primary forum for development, maintenance, and porting of Perl 5.

Perl 5 was released on October 17, 1994. It was a nearly complete rewrite of the interpreter, and added many new features to the language, including objects, references, packages, and modules. Importantly, modules provided a mechanism for extending the language without modifying the interpreter. This allowed the core interpreter to stablize, even as it enabled ordinary Perl programmers to add new language features.

On October 26, 1995, the Comprehensive Perl Archive Network (CPAN) was established. CPAN is a collection of web sites that archive and distribute Perl sources, binary distributions, documentation, scripts, and modules. Originally, each CPAN site had to be accessed through its own URL; today, the single URL http://www.cpan.org automatically redirects to a CPAN site.

As of 2005, Perl 5 is still being actively maintained. It now includes Unicode support. The latest production release is Perl 5.8.7.

At the 2000 Perl Conference Jon Orwant made a case for a major new language initiative. This led to a decision to begin work on a redesign of the language, to be called Perl 6. Proposals for new language features were solicited from the Perl community at large, and over 300 RFCs were submitted.

Larry Wall spent the next few years digesting the RFCs and synthesizing them into a coherent framework for Perl 6. He has presented his design for Perl 6 in a series of documents called apocalypses.

In 2001, it was decided that Perl 6 would run on a cross-language virtual machine called Parrot. As of 2005, both Perl 6 and Parrot are under active development.

CPAN

Main article: CPAN

CPAN (http://www.cpan.org) is the Comprehensive Perl Archive Network. It is a collection of mirrored web sites that serve as a primary archive and distribution channel for Perl sources, distributions, documentation, scripts, and—especially—modules.

Essentially everything on CPAN is freely available; much of the software is licensed under either the Artistic License, the GPL, or both. Anyone can upload software to CPAN via PAUSE (http://pause.perl.org), the Perl Authors Upload Server.

There are currently over 7,000 modules available on CPAN, contributed by nearly 4,000 authors. Modules are available for a wide variety of tasks, including advanced mathematics, database connectivity, and networking.

Modules on CPAN can be downloaded and installed by hand. However, it is common for modules to depend on other modules, and following module dependencies by hand can be tedious. The CPAN.pm module understands module dependencies; it can be configured to automatically download and install a module and, recursively, all modules that it requires.

Code samples

In Perl, the canonical "hello world" program is:

#!/usr/bin/perl -w

print "Hello, world!\n";

The first line is the shebang, which indicates the interpreter for Unix-like operating systems. (It is the most common, but not the only way of ensuring that the perl interpreter runs the program.) The second line prints the string 'Hello world' and a newline (like a person pressing 'Return' or 'Enter').

Here is a one-line, throw-away perl program that does rot-13 encoding/decoding. It is entered and run directly on the command line

perl -pe 'tr/A-Za-z/N-ZA-Mn-za-m/' < input_file > output_file

Name

Perl was originally named "Pearl", after "the pearl of great price" of Matthew 13:46. Larry Wall wanted to give the language a short name with positive connotations, and claims he looked at (and rejected) every three- and four-letter word in the dictionary. He even thought of naming it after his wife Gloria. Before the language's official release, Wall discovered that there was already a programming language named Pearl, and changed the spelling of the name.

The name is normally capitalized (Perl) when referring to the language, and uncapitalized (perl) when referring to the interpreter program itself since Unix-like filesystems are case sensitive. (There is a saying in the Perl community: "Only perl can parse Perl.") It is not appropriate to write "PERL" as it is not really an acronym, although several backronyms have been suggested, including the humorous Pathologically Eclectic Rubbish Lister. Practical Extraction and Report Language has prevailed in many of today's manuals, including the official Perl man page. It is also consistent with the old name "Pearl": Practical Extraction And Report Language.

Fun with Perl

In common with C, obfuscated code competitions are a popular feature of Perl culture. The annual Obfuscated Perl contest makes an arch virtue of Perl's syntactic flexibility. The following program prints the text "Just another Perl / Unix hacker", using 32 concurrent processes coordinated by pipes. A complete explanation is available on the author's Web site (http://perl.plover.com/obfuscated/).

 @P=split//,".URRUU\c8R";@d=split//,"\nrekcah xinU / lreP rehtona tsuJ";sub p{
 @p{"r$p","u$p"}=(P,P);pipe"r$p","u$p";++$p;($q*=2)+=$f=!fork;map{$P=$P[$f^ord
 ($p{$_})&6];$p{$_}=/ ^$P/ix?$P:close$_}keys%p}p;p;p;p;p;map{$p{$_}=~/^[P.]/&&
 close$_}%p;wait until$?;map{/^r/&&<$_>}%p;$_=$d[$q];sleep rand(2)if/\S/;print

Similar to obfuscated code but with a different purpose, Perl Poetry is the practice of writing poems that can actually be compiled by perl. This hobby is more or less unique to Perl, due to the large number of regular English words used in the language. New poems are regularly published in the Perl Monks site's Perl Poetry (http://www.perlmonks.org/index.pl?node=Perl%20Poetry) section.

Another popular pastime is Perl golf. As with the physical sport, the objective is to reduce the number of strokes that it takes to complete a particular objective, but here "strokes" refers to keystrokes rather than swings of a golf club. A task, such as "scan an input string and return the longest palindrome that it contains", is proposed, and participants try to outdo each other by writing solutions that require fewer and fewer characters of Perl source code.

Another tradition among Perl hackers is writing JAPHs, which are short obfuscated programs that print out the phrase "Just another Perl hacker,". The "canonical" JAPH includes the comma at the end, although this is often omitted, and many variants on the theme have been created (example: [4] (http://www.perlmonks.org/index.pl?node_id=292135), which prints "Just Another Perl Pirate!").

One interesting Perl module is Lingua::Romana::Perligata. This module translates the source code of a script that uses it from Latin into Perl, allowing the programmer to write executable programs in Latin.

The Perl community has set aside the "Acme" namespace for modules that are fun or experimental in nature. Some of the Acme modules are deliberately implemented in amusing ways. Some examples:

  • Acme::Hello (http://search.cpan.org/dist/Acme-Hello/) simplifies the process of writing a "Hello, World!" program
  • Acme::Currency (http://search.cpan.org/dist/Acme-Currency/) allows you to change the "$" prefix for scalar variables to some other character
  • Acme::ProgressBar (http://search.cpan.org/dist/Acme-ProgressBar/) is a horribly inefficient way to indicate progress for a task
  • Acme::VerySign (http://search.cpan.org/dist/Acme-VerySign/) satirizes the widely-criticized Verisign SiteFinder service
  • Acme::Don't (http://search.cpan.org/~dconway/Acme-Don-t-1.01/t.pm) implements the logical opposite of the do keyword—don't, which does not execute the provided block.

See also

See also

External links

User groups

  • Perl Mongers (http://www.pm.org/) – local user groups in cities worldwide
  • PerlMonks (http://www.perlmonks.org/) – an active and popular online user group and discussion forum
  • use Perl; (http://use.perl.org/) – Perl news and community discussion

Distributions

  • CPAN (http://www.cpan.org/) – Comprehensive Perl Archive Network, Perl source distribution
  • ActiveState (http://www.activestate.com/) – Perl for Microsoft Windows platforms
  • IndigoPerl (http://www.indigostar.com/indigoperl.htm) – another distribution of Perl for Microsoft Windows

Development

History

Miscellaneous

Books

Template:Book

References

Perl man pages

The Perl man pages are included in the Perl source distribution (http://www.cpan.org/src/stable.tar.gz). They have no "official" location on the web, but are often available at the sites listed above under #External links

  • perlintro - a brief introduction and overview of Perl
  • perlsyn - Perl syntax
  • perlre - Perl regular expressions
  • perl5xydelta - what is new for perl v5.x.y

Web pages

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