Perl is a dynamic programming language created by Larry Wall and first released in 1987. Perl borrows features from a variety of other languages including C, shell scripting (sh), AWK, sed and Lisp. Perl was widely adopted because it provides powerful text processing facilities without arbitrary data length limits, as were present in many Unix tools at the time.
History
Larry Wall began work on Perl in 1987, while working as a programmer at Unisys, 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 streams.
Originally the only documentation for Perl was a single (increasingly lengthy) man page. In 1991, Programming perl (known to many Perl programmers as 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.
Initial design of Perl 5 continued into 1994. The perl5-portersmailing 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, lexical (my) variables, and modules. Importantly, modules provided a mechanism for extending the language without modifying the interpreter. This allowed the core interpreter to stabilize, even as it enabled ordinary Perl programmers to add new language features.
As of 2007, Perl 5 is still being actively maintained. Important features and some essential new language constructs have been added along the way, including Unicode support, threads, improved support for object oriented programming and many other enhancements.
On December 18, 2007, the 20th anniversary of Perl 1.0, Perl 5.10.0 was released. Perl 5.10.0 includes notable new features, which bring it closer to Perl 6, among them a new switch statement (called "given/when"), regular expressions updates, the "smart match operator" ~~, and more.
One of the most important events in Perl 5 history took place outside of the language proper, and was a consequence of its module support. On October 26, 1995, the Comprehensive Perl Archive Network (CPAN) was established as a repository for Perl modules and Perl itself. At the time of writing, it carries over 11,000 modules by over 5,000 authors. CPAN is widely regarded as one of the greatest strengths of Perl in practice.
Name
Perl was originally named "Pearl", after the Parable of the Pearl from the Gospel of Matthew. Larry Wall wanted to give the language a short name with positive connotations; he claims that he considered (and rejected) every three- and four-letter word in the dictionary. He also considered naming it after his wife Gloria. Wall discovered the existing PEARL programming language before Perl's official release 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 file systems are case-sensitive. Before the release of the first edition of Programming Perl, it was common to refer to the language as perl; Randal L. Schwartz, however, capitalised the language's name in the book to make it stand out better when typeset. The case distinction was subsequently adopted by the community.
The name is occasionally given as "PERL" (for Practical Extraction and Report Language). Although the expansion has prevailed in many of today's manuals, including the official Perl man page, it's merely a backronym. The name doesn't officially stand for anything, so spelling it in all caps is incorrect. Proper capitalisation is considered a shibboleth (label of insiders) in the Perl community. Several other expansions have been suggested, including Wall's own humorous Pathologically Eclectic Rubbish Lister. Indeed, Wall claims that the name was intended to inspire many different expansions.
The camel symbol
Programming Perl, published by O'Reilly Media, features a picture of a camel on the cover, and is commonly referred to as The Camel Book.
O'Reilly allows non-commercial use of the symbol, and provides Programming Republic of Perl logos and Powered by Perl buttons.
Overview
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 include support for multiple programming paradigms (procedural, object-oriented, and functional styles), reference countingmemory management (without a cycle detecting garbage collector), built-in support for text processing, and a large collection of third-party modules.
Features
The overall structure of Perl derives broadly from C. Perl is procedural in nature, with variables, expressions, assignment statements, brace-delimited code blocks, control structures, and subroutines.
Perl also takes features from shell programming. All variables are marked with leading sigils, which unambiguously identify the data type (scalar, array, hash, etc.) of the variable in context. Importantly, sigils allow variables to be interpolated directly into strings. Perl has many built-in functions which provide tools often used in shell programming (though many of these tools are implemented by programs external to the shell) like sorting, and calling on system facilities.
Perl takes lists from Lisp, associative arrays (hashes) from AWK, and regular expressions from sed. These simplify and facilitate many parsing, text handling, and data management tasks.
In Perl 5, features were added that support complex data structures, first-class functions (for example, closures as values), and an object-oriented programming model. These include references, packages, class-based method dispatch, and lexically scoped variables, along with compiler directives (for example, the strict pragma). A major additional feature introduced with Perl 5 was the ability to package code as reusable modules. Larry Wall later stated that "The whole intent of Perl 5's module system was to encourage the growth of Perl culture rather than the Perl core."
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 using reference counting (so it can't deallocate circular data structures without manual intervention). Legal type conversions—for example, conversions from number to string—are done automatically at run time; illegal type conversions are fatal errors.
Design
The design of Perl can be understood as a response to three broad trends in the computer industry: falling hardware costs, rising labor costs, and improvements in compiler technology. Many 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 memory management; dynamic typing; strings, lists, and hashes; regular expressions; introspection and an eval function.
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 concise and natural for humans to read and write, even where they complicate the Perl interpreter.
Perl syntax reflects the idea that "things that are different should look different". For example, scalars, arrays, and hashes have different leading sigils. Array indices and hash keys use different kinds of braces. Strings and regular expressions have different standard delimiters. This approach can be contrasted with languages like Lisp, where the same S-expression construct and basic syntax is used for many different purposes.
Perl doesn't enforce any particular programming paradigm (procedural, object-oriented, functional, etc.) 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." One consequence of this is that Perl isn't a tidy language. It includes many features, tolerates exceptions to its rules, and employs heuristics to resolve syntactical ambiguities. Because of the forgiving nature of the compiler, bugs can sometimes be hard to find. Discussing the variant behaviour of built-in functions in list and scalar contexts, the perlfunc(1) manual 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." (TIMTOWTDI, usually pronounced 'Tim Toady'). Others are "Perl: the Swiss Army Chainsaw of Programming Languages" and "No unnecessary limits". A stated design goal of Perl is to make easy tasks easy and difficult tasks possible. Perl has also been called "The Duct Tape of the Internet".
There is no written specification or standard for the Perl language, and no plans to create one for the current version of Perl. There has only been one implementation of the interpreter. That interpreter, together with its functional tests, stands as a de facto specification of the language.
Applications
Perl has many and varied applications, compounded by the availability of many standard and third-party modules.
Perl has been used since the early days of the Web to write CGI scripts. It is known as one of "the three Ps" (along with Python and PHP), the most popular dynamic languages for writing Web applications. It is also an integral component of the popular LAMPsolution stack for web development. Large projects written in Perl include Slash, Bugzilla, TWiki and Movable Type. Many high-traffic websites, such as bbc.co.uk, Amazon.com, LiveJournal.com, Ticketmaster.com and IMDb.com use Perl extensively.
Perl is often used as a glue language, tying together systems and interfaces that were not specifically designed to interoperate, and for "data munging", for example, converting or processing large amounts of data for tasks like creating reports. In fact, these strengths are intimately linked. The combination makes perl a popular all-purpose tool for system administrators, particularly as short programs can be entered and run on a single command line.
With a degree of care, Perl code can be made portable across Windows and Unix. Portable Perl code is often used by suppliers of software (both COTS and bespoke) to simplify packaging and maintenance of software build and deployment scripts.
Graphical user interfaces (GUI's) may be developed using Perl. In particular, Perl/Tk is commonly used to enable user interaction with Perl scripts. Such interaction may be synchronous or asynchronous using callbacks to update the GUI. For more information about the technologies involved see Tk,Tcl and WxPerl.
Perl is also widely used in finance and bioinformatics, where it's valued for rapid application development and deployment, and the ability to handle large data sets.
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, as of 2005, 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. Alternatively, 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 of 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 uninitiated, but 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: compile-time and run-time. At compile time, the interpreter parses the program text into a syntax tree. At run time, it executes the program by walking the tree. The text is parsed only once, and the syntax tree is subject to optimization before it's executed, so the execution phase is relatively efficient. Compile-time optimizations on the syntax tree include constant folding and context propagation, but peephole optimization is also performed. However, compile-time and run-time phases may nest: BEGIN code blocks execute at compile-time, while the eval function initiates compilation during runtime. Both operations are an implicit part of a number of others—most notably, the use clause that loads libraries, known in Perl as modules, implies a BEGIN block.
Perl has a context-sensitive grammar which can be affected by code executed during an intermittent run-time phase. Therefore Perl can't be parsed by a straight Lex/Yacc lexer/parser combination. Instead, the interpreter 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 (perl) can parse the Perl language (Perl). The truth of this is attested to by the persistent imperfections of other programs that undertake to parse Perl, such as source code analyzers and auto-indenters, which have to contend not only with the many ways to express unambiguous syntactic constructs, but also the fact that Perl can't be parsed in the general case without executing it. Though successful in creating a Perl parser for document-related purposes, the PPI project determined that parsing Perl code as a document (retaining its integrity) and as executable code simultaneously was, in fact, not possible. Specifically the author claimed that, "parsing Perl suffers from the 'Halting Problem.'"
Perl is distributed with some 120,000 functional tests. These run as part of the normal build process, and extensively exercise the interpreter and its core modules. Perl developers rely on the functional tests to ensure that changes to the interpreter don't 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's working properly.
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 backward compatibility with earlier versions is maintained. The size and complexity of the interpreter is a barrier to developers who wish to work on it.
Availability
Perl is free software, and is licensed under both the Artistic License and the GNU General Public License. Distributions are available for most operating systems. It is particularly prevalent on Unix and Unix-like systems, but it has been ported to most modern (and many obsolete) platforms. With only six reported exceptions, Perl can be compiled from source code on all Unix-like, POSIX-compliant or otherwise Unix-compatible platforms. However, this is rarely necessary, as Perl is included in the default installation of many popular operating systems.
Because of unusual changes required for the Mac OS Classic environment, a special port called MacPerl was shipped independently.
The CPAN carries a complete list of supported platforms with links to the distributions available on each.
Windows
Users of Microsoft Windows typically install one of the native binary distributions of Perl for Win32, most commonly ActivePerl. Compiling Perl from source code under Windows is possible, but most installations lack the requisite C compiler and build tools. This also makes it hard to install modules from the CPAN, particularly those that are partially written in C.
Users of the ActivePerl binary distribution are therefore dependent on the repackaged modules provided in ActiveState’s module repository, which are precompiled and can be installed with PPM. Limited resources to maintain this repository have been cause for various long-standing problems.
To address this and other problems of Perl on the Windows platform, win32.perl.org was launched by Adam Kennedy on behalf of The Perl Foundation in June 2006. This is a community website for "all things Windows and Perl." A major aim of this project is to provide production-quality alternative Perl distributions that include an embedded C compiler and build tools, so as to enable Windows users to install modules directly from the CPAN. The production distribution in the family is known as Strawberry Perl, with research and experimental work done in a related Vanilla Perl distribution.
Another popular way of running Perl under Windows is provided by the Cygwin emulation layer. Cygwin provides a Unix-like environment on Windows and both perl and cpan are conveniently available as standard pre-compiled packages in the Cygwin setup program. Since Cygwin also includes the gcc, compiling Perl from source is also possible.
Language structure
In Perl, the minimal Hello world program may be written as follows:
print "Hello, world!
"
This prints the stringHello, world! and a newline, symbolically expressed by an n character whose interpretation is altered by the preceding escape character (a backslash).
The canonical form of the program is slightly more verbose:
!/usr/bin/perl
print "Hello, world!
";
The hash mark character introduces a comment in Perl, which runs up to the end of the line of code and is ignored by the compiler. The comment used here's of a special kind: it’s called the shebang line. This tells Unix-like operating systems where to find the Perl interpreter, making it possible to invoke the program without explicitly mentioning perl. (Note that on Microsoft Windows systems, Perl programs are typically invoked by associating the .plextension with the Perl interpreter. In order to deal with such circumstances, perl detects the shebang line and parses it for switches, so it isn't strictly true that the shebang line is ignored by the compiler.)
The second line in the canonical form includes a semicolon, which is used to separate statements in Perl. With only a single statement in a block or file, a separator is unnecessary, so it can be omitted from the minimal form of the program—or more generally from the final statement in any block or file. The canonical form includes it because it's common to terminate every statement even when it's unnecessary to do so, as this makes editing easier: code can be added to or moved away from the end of a block or file without having to adjust semicolons.
Version 5.10 of Perl introduces a say function that implicitly appends a newline character to its output, making the minimal "Hello world" program even shorter:
say 'Hello, world!'
A hash, or associative array, is a map from strings to scalars; the strings are called keys and the scalars are called values.
A file handle is a map to a file, device, or pipe which is open for reading, writing, or both.
A subroutine is a piece of code that may be passed arguments, be executed, and return data
Most variables are marked by a leading sigil, which identifies the data type being accessed (not the type of the variable itself), except filehandles, which don't have a sigil. The same name may be used for variables of different data types, without conflict.
$foo # a scalar
@foo # an array
%foo # a hash
FOO # a file handle or constant
&foo # a subroutine. (The & is optional)
File handles and constants need not be uppercase, but it's a common convention owing to the fact that there's no sigil to denote them. Both are global in scope, but file handles are interchangeable with references to file handles, which can be stored in scalars, which in turn permit lexical scoping. Doing so is encouraged in Damian Conway's Perl Best Practices. As a convenience, the open function in Perl 5.6 and newer will autovivify undefined scalars to file handle references.
Numbers are written in the bare form; strings are enclosed by quotes of various kinds.
$name = "joe";
$color = 'red';
$number1 = 42;
$number2 = '42';
This evaluates to true
if ($number1 == $number2)
$x = either; # returns "Oranges"
@x = either; # returns (1, 2)
Regular expressions
The Perl language includes a specialized syntax for writing regular expressions (RE, or regexes), and the interpreter contains an engine for matching strings to regular expressions. The regular expression engine uses a backtracking algorithm, extending its capabilities from simple pattern matching to string capture and substitution. The regular expression engine is derived from regex written by Henry Spencer.
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. Other languages and applications are now adopting Perl compatible regular expressions over POSIX regular expressions including PHP, Ruby, Java, Microsoft's .NET Framework, and the Apache HTTP server.
Regular expression syntax is extremely compact, owing to history. The first regular expression dialects were only slightly more expressive than globs, and the syntax was designed so that an expression would resemble the text it matches. This meant using no more than a single punctuation character or a pair of delimiting characters to express the few supported assertions. Over time, the expressiveness of regular expressions grew tremendously, but the syntax design was never revised and continues to rely on punctuation. As a result, regular expressions can be cryptic and extremely dense.
Uses
The m// (match) operator introduces a regular expression match. (If it's delimited by slashes, as in all the examples here, then the leading m may be omitted for brevity. If the m is present, as in all the following examples, other delimiters can be used in place of slashes.) In the simplest case, an expression like
$x =~ m/abc/
evaluates to true if and only if the string $x matches the regular expression abc.
The s/// (substitute) operator, on the other hand, specifies a search and replace operation:
$x =~ s/abc/aBc/; # upcase the b
Another use of regular expressions is to specify delimiters for the split function:
@words = split m/,/, $line;
The split function creates a list of the parts of the string separated by matches of the regular expression. In this example, a line is divided into a list of its comma-separated parts, and this list is then assigned to the @words array.
Syntax
Portions of a regular expression may be enclosed in parentheses; corresponding portions of a matching string are captured. Captured strings are assigned to the sequential built-in variables $1, $2, $3, ..., and a list of captured strings is returned as the value of the match.
$x =~ m/a(.)c/; # capture the character between 'a' and 'c'
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
Since regular expressions can be dense and cryptic because of their compact syntax, the /x modifier was added in Perl to help programmers write more legible regular expressions. It allows programmers to place whitespace and comments inside regular expressions:
$x =~ m/a # match 'a'
. # followed by any character
c # then followed by the 'c'character
/x;
Database interfaces
Perl is widely favored for database applications. Its text handling facilities are useful 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 sufficiently difficult that it was only done for a few of the most important and widely used databases, and restricted the resulting perl executable to using just one database interface at a time.
In Perl 5, database interfaces are implemented by Perl DBI 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 ANSISQL databases.
DBI provides caching for database handles and queries, which can greatly improve performance in long-lived execution environments such as mod_perl, helping high-volume systems avert load spikes as in the Slashdot effect.
Comparative performance
The Computer Language Benchmarks Game compare the performance of implementations of typical programming problems in several programming languages. The submitted Perl implementations were typically towards the high end of the memory usage spectrum, and had varied speed results. Perl's performance in the benchmarks game is similar to other interpreted languages such as Python, faster than PHP, and significantly faster than Ruby, but slower than most compiled languages.
Perl programs can start slower than similar programs in compiled languages because perl has to compile the source every time it runs. In a talk at the YAPC::Europe 2005 conference and subsequent article, "A Timely Start", Jean-Louis Leroy found that his Perl programs took much longer to run than he expected because the perl interpreter spent much of the time finding modules because of his over-large include path. Because pre-compiling is still an experimental part of Perl—unlike that of Java, Python, and Ruby—Perl programs pay this overhead penalty on every execution. When amortized over a long run phase, startup time isn't typically substantial, but measurement of very short execution times can often be skewed as is often found in benchmarks.
A number of tools have been introduced to improve this situation, the first of which was Apache's mod_perl, which sought to address one of the most common reasons that small Perl programs were invoked rapidly: CGIWeb development. ActivePerl, via Microsoft ISAPI provides similar performance improvements.
Once Perl code is compiled, there's additional overhead during the execution phase that typically isn't present for programs written in compiled languages like C or C++, including, among many other things, overhead due to bytecode interpretation, reference-counting memory management, and dynamic type checking.
Optimizing
Perl programs, like any code, can be tuned for performance using benchmarks and profiles after a readable and correct implementation is finished. In part because of Perl's interpreted nature, writing more-efficient Perl won't always be enough to meet one's performance goals for a program.
In such situations, the most critical routines of a Perl program can be written in other languages such as C or Assembler, which can be connected to Perl via simple Inline modules or the more complex but flexible XS mechanism. Nicholas Clark, a Perl core developer, discusses some Perl design trade-offs and some solutions in When perl isn't quite fast enough.
In extreme cases, optimizing Perl can require intimate knowledge of the interpreter's workings rather than skill with algorithms, the Perl language, or general principles of optimization.
Future
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", which are numbered to correspond to chapters in Programming Perl ("The Camel Book"). The current, not yet finalized specification of Perl 6 is encapsulated in design documents called Synopses, which are numbered to correspond to Apocalypses.
Perl 6 isn't intended to be backward compatible, though there will be a compatibility mode.
In 2001, it was decided that Perl 6 would run on a cross-language virtual machine called Parrot. This will mean that other languages targeting the Parrot will gain native access to CPAN, allowing some level of cross-language development.
In 2005 Audrey Tang created the pugs project, an implementation of Perl 6 in Haskell. This was and continues to act as a test platform for the Perl 6 language (separate from the development of the actual implementation) allowing the language designers to explore. The pugs project spawned an active Perl/Haskell cross-language community centered around the freenode #perl6 irc channel.
A number of features in the Perl 6 language now show similarities with Haskell, and Perl 6 has been embraced by the Haskell community as a potential scripting language.
As of 2006, Perl 6, Parrot, and pugs are under active development, and a new module for Perl 5 called v6 allows some Perl 6 code to run directly on top of Perl 5.
Development of Perl 5 is also continuing. Perl 5.10 was released in December of 2007, with some new features influenced by the design of Perl 6.
The Perl community
Perl's culture and community has developed alongside the language itself. Usenet was the first public venue in which Perl was introduced, but over the course of its evolution, Perl's community was shaped by the growth of broadening Internet-based services including the introduction of the World Wide Web. The community that surrounds Perl was, in fact, the topic of Larry Wall's first "State of the Onion" talk.
State of the Onion
State of the Onion is the name for Larry Wall’s yearly keynote-style summaries on the progress of Perl and its community. They are characterized by his hallmark humor, employing references to Perl’s and the wider hacker culture, as well as Wall’s linguistic and sometimes his Christian background.
Each talk is first given at various Perl conferences and eventually also published online.
Pastimes
Perl's pastimes have become a defining element of the community. Included among them are trivial and complex uses of the language.
JAPHs
In email, Usenet and message board postings, "Just another Perl hacker" (JAPH) programs have become a common trend, originated by Randal L. Schwartz, one of the earliest professional Perl trainers.
In the parlance of Perl culture, Perl programmers are known as Perl hackers, and from this derives the practice of writing short programs to print out the phrase "Just another Perl hacker,". In the spirit of the original concept, these programs are moderately obfuscated and short enough to fit into the signature of an email or Usenet message. The "canonical" JAPH includes the comma at the end, although this is often omitted.
Perl golf
Perl "golf" is the pastime of reducing the number of characters used in a Perl program to the bare minimum, much as how golf players seek to take as few shots as possible in a round. This use of the word "golf" originally focused on the JAPHs used in signatures in Usenet postings and elsewhere, though the same stunts had been an unnamed pastime in the language APL in previous decades. The use of Perl to write a program which performed RSA encryption prompted a widespread and practical interest in this pastime. In subsequent years, code golf has been taken up as a pastime in other languages besides Perl.
Obfuscation
As with C, obfuscated code competitions are a well-known pastime. The annual Obfuscated Perl contest made an arch virtue of Perl's syntactic flexibility.
Poetry
Similar to obfuscated code and golf, but with a different purpose, Perl poetry is the practice of writing poems that can actually be compiled as legal (although generally non-sensical) Perl code. 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 section.
CPAN Acme
There are also many examples of code written purely for entertainment on the CPAN. Lingua::Romana::Perligata, for example, allows writing programs in Latin. Upon execution of such a program, the module translates its source code into regular Perl and runs it.
The Perl community has set aside the "Acme" namespace for modules that are fun in nature (but its scope has widened to include exploratory or experimental code or any other module that isn't meant to ever be used in production). Some of the Acme modules are deliberately implemented in amusing ways. This includes Acme::Bleach, one of the first modules in the Acme:: namespace, which allows the program's source code to be "whitened" (for example, all characters replaced with whitespace) and yet still work.
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