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Wikipedia

Perl

Perl is a family of two high-level, general-purpose, interpreted, dynamic programming languages. "Perl" refers to Perl 5, but from 2000 to 2019 it also referred to its redesigned "sister language", Perl 6, before the latter's name was officially changed to Raku in October 2019.[9][10]

Perl
ParadigmMulti-paradigm: functional, imperative, object-oriented (class-based), reflective
Designed byLarry Wall
DeveloperLarry Wall
First appearedDecember 18, 1987; 35 years ago (1987-12-18)[1]
Stable release
  • 5.36.0[2] / 28 May 2022; 7 months ago (2022-05-28)
  • 5.34.1[3] / 13 March 2022; 9 months ago (2022-03-13)
Preview release
5.37.6[4] / 21 November 2022; 52 days ago (2022-11-21)
Typing disciplineDynamic
Implementation languageC
OSCross-platform
LicenseArtistic License 1.0[5][6] or GNU General Public License[7]
Filename extensions.plx, .pl, .pm, .xs, .t, .pod, .cgi
Websiteperl.org
Influenced by
AWK, BASIC, C, C++, Lisp, sed, Unix shell[8]
Influenced
CoffeeScript,[citation needed] Groovy,[citation needed] JavaScript, Julia, LPC, PHP, Python, Raku, Ruby, PowerShell
  • Perl Programming at Wikibooks

Though Perl is not officially an acronym,[11] there are various backronyms in use, including "Practical Extraction and Reporting Language".[12] Perl was developed by Larry Wall in 1987 as a general-purpose Unix scripting language to make report processing easier.[13] Since then, it has undergone many changes and revisions. Raku, which began as a redesign of Perl 5 in 2000, eventually evolved into a separate language. Both languages continue to be developed independently by different development teams and liberally borrow ideas from each other.

The Perl languages borrow features from other programming languages including C, sh, AWK, and sed;[1] They provide text processing facilities without the arbitrary data-length limits of many contemporary Unix command line tools.[14] Perl 5 gained widespread popularity in the late 1990s as a CGI scripting language, in part due to its powerful regular expression and string parsing abilities.[15][16][17][18]

In addition to CGI, Perl 5 is used for system administration, network programming, finance, bioinformatics, and other applications, such as for GUIs. It has been nicknamed "the Swiss Army chainsaw of scripting languages" because of its flexibility and power,[19] and also what some consider ugliness[20] due to its utilization of more special characters than many other languages. In 1998, it was also referred to as the "duct tape that holds the Internet together," in reference to both its ubiquitous use as a glue language and its perceived inelegance.[21]

Perl is a highly expressive programming language: source code for a given algorithm can be short and highly compressible.[22][23]

Name

Perl was originally named "Pearl". Wall wanted to give the language a short name with positive connotations. Wall discovered the existing PEARL programming language before Perl's official release and changed the spelling of the name.[24]

When referring to the language, the name is capitalized: Perl. When referring to the program itself, the name is uncapitalized (perl) because most 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, capitalized the language's name in the book to make it stand out better when typeset. This case distinction was subsequently documented as canonical.[25]

The name is occasionally expanded as a backronym: Practical Extraction and Report Language[26] and Wall's own Pathologically Eclectic Rubbish Lister which is in the manual page for perl.[27]

History

Early versions

Larry Wall began work on Perl in 1987, while working as a programmer at Unisys,[14] and version 1.0 on December 18, 1987.[1] 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.[citation needed]

Originally, the only documentation for Perl was a single lengthy man page. In 1991, Programming Perl, known to many Perl programmers as the "Camel Book" because of its cover, 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 well documented by the book.[citation needed]

Early Perl 5

Perl 4 went through a series of maintenance releases, culminating in Perl 4.036 in 1993, whereupon Wall abandoned Perl 4 to begin work on Perl 5. Initial design 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.[28]

Perl 5.000 was released on October 17, 1994.[29] It was a nearly complete rewrite of the interpreter, and it 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. Perl 5 has been in active development since then.

Perl 5.001 was released on March 13, 1995. Perl 5.002 was released on February 29, 1996 with the new prototypes feature. This allowed module authors to make subroutines that behaved like Perl builtins. Perl 5.003 was released June 25, 1996, as a security release.[30]

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 the Perl language and Perl modules; as of December 2022, it carries over 211,850 modules in 43,865 distributions, written by more than 14,324 authors, and is mirrored worldwide at more than 245 locations.[31]

Perl 5.004 was released on May 15, 1997, and included, among other things, the UNIVERSAL package, giving Perl a base object from which all classes were automatically derived and the ability to require versions of modules. Another significant development was the inclusion of the CGI.pm module,[32] which contributed to Perl's popularity as a CGI scripting language.[33]

Perl 5.004 added support for Microsoft Windows, Plan 9, QNX, and AmigaOS.[32]

Perl 5.005 was released on July 22, 1998. This release included several enhancements to the regex engine, new hooks into the backend through the B::* modules, the qr// regex quote operator, a large selection of other new core modules, and added support for several more operating systems, including BeOS.[34]

2000–2020

Major version[29] Latest update[35]
Old version, no longer maintained: 5.4 1999-04-29
Old version, no longer maintained: 5.5 2004-02-23
Old version, no longer maintained: 5.6 2003-11-15
Old version, no longer maintained: 5.8 2008-12-14
Old version, no longer maintained: 5.10 2009-08-22
Old version, no longer maintained: 5.12 2012-11-10
Old version, no longer maintained: 5.14 2013-03-10
Old version, no longer maintained: 5.16 2013-03-11
Old version, no longer maintained: 5.18 2014-10-01
Old version, no longer maintained: 5.20 2015-09-12
Old version, no longer maintained: 5.22 2017-07-15
Old version, no longer maintained: 5.24 2018-04-14
Old version, no longer maintained: 5.26 2018-11-29
Old version, no longer maintained: 5.28 2020-06-01
Old version, no longer maintained: 5.30 2020-06-01
Old version, no longer maintained: 5.32 2021-01-23
Older version, yet still maintained: 5.34 2022-03-13
Current stable version: 5.36 2022-05-28
Latest preview version of a future release: 5.37 2022-10-20
Future release: 7.0 2023?
Legend:
Old version
Older version, still maintained
Current stable version
Latest preview version
Future release

Perl 5.6 was released on March 22, 2000. Major changes included 64-bit support, Unicode string representation, support for files over 2 GiB, and the "our" keyword.[36][37] When developing Perl 5.6, the decision was made to switch the versioning scheme to one more similar to other open source projects; after 5.005_63, the next version became 5.5.640, with plans for development versions to have odd numbers and stable versions to have even numbers.[38]

In 2000, Wall put forth a call for suggestions for a new version of Perl from the community. The process resulted in 361 RFC (request for comments) documents that were to be used in guiding development of Perl 6. In 2001,[39] work began on the "Apocalypses" for Perl 6, a series of documents meant to summarize the change requests and present the design of the next generation of Perl. They were presented as a digest of the RFCs, rather than a formal document. At this point, Perl 6 existed only as a description of a language.[citation needed]

Perl 5.8 was first released on July 18, 2002, and had nearly yearly updates since then. Perl 5.8 improved Unicode support, added a new I/O implementation, added a new thread implementation, improved numeric accuracy, and added several new modules.[40] As of 2013 this version still remains the most popular version of Perl and is used by Red Hat 5, Suse 10, Solaris 10, HP-UX 11.31 and AIX 5

In 2004, work began on the "Synopses" – documents that originally summarized the Apocalypses, but which became the specification for the Perl 6 language. In February 2005, Audrey Tang began work on Pugs, a Perl 6 interpreter written in Haskell.[41] This was the first concerted effort toward making Perl 6 a reality. This effort stalled in 2006.[42]

PONIE is an acronym for Perl On New Internal Engine. The PONIE Project existed from 2003 until 2006 and was to be a bridge between Perl 5 and Perl 6. It was an effort to rewrite the Perl 5 interpreter to run on Parrot, the Perl 6 virtual machine. The goal was to ensure the future of the millions of lines of Perl 5 code at thousands of companies around the world.[43] The PONIE project ended in 2006 and is no longer being actively developed. Some of the improvements made to the Perl 5 interpreter as part of PONIE were folded into that project.[44]

On December 18, 2007, the 20th anniversary of Perl 1.0, Perl 5.10.0 was released. Perl 5.10.0 included notable new features, which brought it closer to Perl 6. These included a switch statement (called "given"/"when"), regular expressions updates, and the smart match operator (~~).[45][46] Around this same time, development began in earnest on another implementation of Perl 6 known as Rakudo Perl, developed in tandem with the Parrot virtual machine. As of November 2009, Rakudo Perl has had regular monthly releases and now is the most complete implementation of Perl 6.

A major change in the development process of Perl 5 occurred with Perl 5.11; the development community has switched to a monthly release cycle of development releases, with a yearly schedule of stable releases. By that plan, bugfix point releases will follow the stable releases every three months.[citation needed]

On April 12, 2010, Perl 5.12.0 was released. Notable core enhancements include new package NAME VERSION syntax, the Yada Yada operator (intended to mark placeholder code that is not yet implemented), implicit strictures, full Y2038 compliance, regex conversion overloading, DTrace support, and Unicode 5.2.[47]

On May 14, 2011, Perl 5.14 was released with JSON support built-in.[48]

On May 20, 2012, Perl 5.16 was released. Notable new features include the ability to specify a given version of Perl that one wishes to emulate, allowing users to upgrade their version of Perl, but still run old scripts that would normally be incompatible.[49][failed verification] Perl 5.16 also updates the core to support Unicode 6.1.[49]

On May 18, 2013, Perl 5.18 was released. Notable new features include the new dtrace hooks, lexical subs, more CORE:: subs, overhaul of the hash for security reasons, support for Unicode 6.2.[50]

On May 27, 2014, Perl 5.20 was released. Notable new features include subroutine signatures, hash slices/new slice syntax, postfix dereferencing (experimental), Unicode 6.3, rand() using consistent random number generator.[51]

Some observers credit the release of Perl 5.10 with the start of the Modern Perl movement.[52] In particular, this phrase describes a style of development that embraces the use of the CPAN, takes advantage of recent developments in the language, and is rigorous about creating high quality code.[53] While the book "Modern Perl"[54] may be the most visible standard-bearer of this idea, other groups such as the Enlightened Perl Organization[55] have taken up the cause.

In late 2012 and 2013, several projects for alternative implementations for Perl 5 started: Perl5 in Perl6 by the Rakudo Perl team,[56] moe by Stevan Little and friends,[57] p2[58] by the Perl11 team under Reini Urban, gperl by goccy,[59] and rperl, a Kickstarter project led by Will Braswell and affiliated with the Perll11 project.[60]

2020 onward

In June 2020, Perl 7 was announced as the successor to Perl 5.[61] Perl 7 was to initially be based on Perl 5.32 with a release expected in first half of 2021, and release candidates sooner.[62] This plan was revised in May 2021, without any release timeframe or version of Perl 5 for use as a baseline specified.[63] When Perl 7 is released, Perl 5 will go into long term maintenance. Supported Perl 5 versions however will continue to get important security and bug fixes.[64]

Symbols

Camel

 
The Camel symbol used by O'Reilly Media

Programming Perl, published by O'Reilly Media, features a picture of a dromedary camel on the cover and is commonly called the "Camel Book".[65] This image has become an unofficial symbol of Perl as well as a general hacker emblem, appearing on T-shirts and other clothing items.[citation needed]

O'Reilly owns the image as a trademark but licenses it for non-commercial use, requiring only an acknowledgement and a link to www.perl.com. Licensing for commercial use is decided on a case-by-case basis.[66] O'Reilly also provides "Programming Republic of Perl" logos for non-commercial sites and "Powered by Perl" buttons for any site that uses Perl.[66]

Onion

 
The onion logo used by The Perl Foundation

The Perl Foundation owns an alternative symbol, an onion, which it licenses to its subsidiaries, Perl Mongers, PerlMonks, Perl.org, and others.[67] The symbol is a visual pun on pearl onion.[68]

Raptor

 
Alternative Perl 5 Logo

Sebastian Riedel, the creator of Mojolicious, created a logo depicting a raptor dinosaur, which is available under a CC-SA License, Version 4.0.[69] The analogue of the raptor comes from a series of talks given by Matt S Trout beginning in 2010.[70]

Overview

According to Wall, Perl has two slogans. The first is "There's more than one way to do it," commonly known as TMTOWTDI. The second slogan is "Easy things should be easy and hard things should be possible".[14]

Features

The overall structure of Perl derives broadly from C. Perl is procedural in nature, with variables, expressions, assignment statements, brace-delimited blocks, control structures, and subroutines.[71]

Perl also takes features from shell programming. All variables are marked with leading sigils, which allow variables to be interpolated directly into strings. However, unlike the shell, Perl uses sigils on all accesses to variables, and unlike most other programming languages that use sigils, the sigil doesn't denote the type of the variable but the type of the expression. So for example, while an array is denoted by the sigil "@" (for example @arrayname), an individual member of the array is denoted by the scalar sigil "$" (for example $arrayname[3]). Perl also has many built-in functions that provide tools often used in shell programming (although many of these tools are implemented by programs external to the shell) such as sorting, and calling operating system facilities.[citation needed]

Perl takes hashes ("associative arrays") from AWK and regular expressions from sed. These simplify many parsing, text-handling, and data-management tasks. Shared with Lisp is the implicit return of the last value in a block, and all statements are also expressions which can be used in larger expressions themselves.[citation needed]

Perl 5 added features that support complex data structures, first-class functions (that is, 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. 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."[72]

All versions of Perl do automatic data-typing and automatic 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 cannot 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.[citation needed]

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, aimed to make efficient use of expensive computer hardware. In contrast, Perl was designed so that computer programmers could write programs more quickly and easily.[73]

Perl has many features that ease the task of the programmer 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. Perl follows the theory of "no built-in limits,"[65] an idea similar to the Zero One Infinity rule.[citation needed]

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 write, even where they complicate the Perl interpreter.[74]

Perl's syntax reflects the idea that "things that are different should look different."[75] 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 a language such as Lisp, where the same basic syntax, composed of simple and universal symbolic expressions, is used for all purposes.[citation needed]

Perl does not enforce any particular programming paradigm (procedural, object-oriented, functional, or others) or even require the programmer to choose among them.[citation needed]

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."[14] One consequence of this is that Perl is not 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. Perl's function documentation remarks on the variant behavior of built-in functions in list and scalar contexts by saying, "In general, they do what you want, unless you want consistency."[76]

No written specification or standard for the Perl language exists for Perl versions through Perl 5, and there are no plans to create one for the current version of Perl. There has been only one implementation of the interpreter, and the language has evolved along with it. That interpreter, together with its functional tests, stands as a de facto specification of the language. Perl 6, however, started with a specification,[77] and several projects[78] aim to implement some or all of the specification.[citation needed]

Applications

Perl has many and varied applications, compounded by the availability of many standard and third-party modules.

Perl has chiefly been used to write CGI scripts: large projects written in Perl include cPanel, Slash, Bugzilla, RT, TWiki, and Movable Type; high-traffic websites that use Perl extensively include Priceline.com, Craigslist,[79] IMDb,[80] LiveJournal, DuckDuckGo,[81][82] Slashdot and Ticketmaster. It is also an optional component of the popular LAMP technology stack for Web development, in lieu of PHP or Python. Perl is used extensively as a system programming language in the Debian Linux distribution.[83]

Perl is often used as a glue language, tying together systems and interfaces that were not specifically designed to interoperate, and for "data munging,"[84] that is, converting or processing large amounts of data for tasks such as creating reports. In fact, these strengths are intimately linked. The combination makes Perl a popular all-purpose language for system administrators, particularly because short programs, often called "one-liner programs," can be entered and run on a single command line.[citation needed]

Perl code can be made portable across Windows and Unix; such code is often used by suppliers of software (both COTS and bespoke) to simplify packaging and maintenance of software build- and deployment-scripts.[citation needed]

Perl/Tk and wxPerl are commonly used to add graphical user interfaces to Perl scripts.

Implementation

Perl is implemented as a core interpreter, written in C, together with a large collection of modules, written in Perl and C. As of 2010, 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).[citation needed]

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.[citation needed]

The life of a Perl interpreter divides broadly into a compile phase and a run phase.[85] In Perl, the phases are the major stages in the interpreter's life-cycle. Each interpreter goes through each phase only once, and the phases follow in a fixed sequence.[citation needed]

Most of what happens in Perl's compile phase is compilation, and most of what happens in Perl's run phase is execution, but there are significant exceptions. Perl makes important use of its capability to execute Perl code during the compile phase. Perl will also delay compilation into the run phase. The terms that indicate the kind of processing that is actually occurring at any moment are compile time and run time. Perl is in compile time at most points during the compile phase, but compile time may also be entered during the run phase. The compile time for code in a string argument passed to the eval built-in occurs during the run phase. Perl is often in run time during the compile phase and spends most of the run phase in run time. Code in BEGIN blocks executes at run time but in the compile phase.

At compile time, the interpreter parses Perl code into a syntax tree. At run time, it executes the program by walking the tree. Text is parsed only once, and the syntax tree is subject to optimization before it is executed, so that execution is relatively efficient. Compile-time optimizations on the syntax tree include constant folding and context propagation, but peephole optimization is also performed.[86]

Perl has a Turing-complete grammar because parsing can be affected by run-time code executed during the compile phase.[87] Therefore, Perl cannot 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.[citation needed]

It is often said that "Only perl can parse Perl,"[88] meaning that only the Perl interpreter (perl) can parse the Perl language (Perl), but even this is not, in general, true. Because the Perl interpreter can simulate a Turing machine during its compile phase, it would need to decide the halting problem in order to complete parsing in every case. It is a longstanding result that the halting problem is undecidable, and therefore not even Perl can always parse Perl. Perl makes the unusual choice of giving the user access to its full programming power in its own compile phase. The cost in terms of theoretical purity is high, but practical inconvenience seems to be rare.[89]

Other programs that undertake to parse Perl, such as source-code analyzers and auto-indenters, have to contend not only with ambiguous syntactic constructs but also with the undecidability of Perl parsing in the general case. Adam Kennedy's PPI project focused on parsing Perl code as a document (retaining its integrity as a document), instead of parsing Perl as executable code (that not even Perl itself can always do). It was Kennedy who first conjectured that "parsing Perl suffers from the 'halting problem',"[90] which was later proved.[91]

Perl is distributed with over 250,000 functional tests for core Perl language and over 250,000 functional tests for core modules. 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 do not introduce software bugs; additionally, Perl users who see that the interpreter passes its functional tests on their system can have a high degree of confidence that it is working properly.[citation needed]

Availability

Perl is dual licensed under both the Artistic License 1.0[5][6] and the GNU General Public License.[7] 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[citation needed] reported exceptions, Perl can be compiled from source code on all POSIX-compliant, or otherwise-Unix-compatible, platforms.[92]

Because of unusual changes required for the classic Mac OS environment, a special port called MacPerl was shipped independently.[93]

The Comprehensive Perl Archive Network carries a complete list of supported platforms with links to the distributions available on each.[94] CPAN is also the source for publicly available Perl modules that are not part of the core Perl distribution.[citation needed]

Windows

Users of Microsoft Windows typically install one of the native binary distributions of Perl for Win32, most commonly Strawberry Perl or 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 difficult to install modules from the CPAN, particularly those that are partially written in C.[citation needed]

ActivePerl is a closed-source distribution from ActiveState that has regular releases that track the core Perl releases.[95] The distribution previously included the Perl package manager (PPM),[96] a popular tool for installing, removing, upgrading, and managing the use of common Perl modules; however, this tool was discontinued as of ActivePerl 5.28.[97] Included also is PerlScript, a Windows Script Host (WSH) engine implementing the Perl language. Visual Perl is an ActiveState tool that adds Perl to the Visual Studio .NET development suite. A VBScript-to-Perl converter, as well as a Perl compiler for Windows, and converters of awk and sed to Perl have also been produced by this company and included on the ActiveState CD for Windows, which includes all of their distributions plus the Komodo IDE and all but the first on the Unix/Linux/Posix variant thereof in 2002 and subsequently.[98]

Strawberry Perl is an open-source distribution for Windows. It has had regular, quarterly releases since January 2008, including new modules as feedback and requests come in. Strawberry Perl aims to be able to install modules like standard Perl distributions on other platforms, including compiling XS modules.[citation needed]

The Cygwin emulation layer is another way of running Perl under Windows. Cygwin provides a Unix-like environment on Windows, and both Perl and CPAN are available as standard pre-compiled packages in the Cygwin setup program. Since Cygwin also includes gcc, compiling Perl from source is also possible.[citation needed]

A Perl executable is included in several Windows Resource kits in the directory with other scripting tools.[citation needed]

Implementations of Perl come with the MKS Toolkit, Interix (the base of earlier implementations of Windows Services for Unix), and UWIN.[citation needed]

Database interfaces

Perl's text-handling capabilities can be used for generating SQL queries; arrays, hashes, and automatic memory management make it easy to collect and process the returned data. For example, in Tim Bunce's Perl DBI application programming interface (API), the arguments to the API can be the text of SQL queries; thus it is possible to program in multiple languages at the same time (e.g., for generating a Web page using HTML, JavaScript, and SQL in a here document). The use of Perl variable interpolation to programmatically customize each of the SQL queries, and the specification of Perl arrays or hashes as the structures to programmatically hold the resulting data sets from each SQL query, allows a high-level mechanism for handling large amounts of data for post-processing by a Perl subprogram.[99] 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 done for only a few of the most-important and most widely used databases, and it restricted the resulting perl executable to using just one database interface at a time.[100]

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 ANSI SQL databases.[101]

DBI provides caching for database handles and queries, which can greatly improve performance in long-lived execution environments such as mod_perl,[102] helping high-volume systems avert load spikes as in the Slashdot effect.[103]

In modern Perl applications, especially those written using web frameworks such as Catalyst, the DBI module is often used indirectly via object-relational mappers such as DBIx::Class, Class::DBI[104] or Rose::DB::Object[105] that generate SQL queries and handle data transparently to the application author.[106]

Comparative performance

The Computer Language Benchmarks Game compares the performance of implementations of typical programming problems in several programming languages.[107] The submitted Perl implementations typically perform toward the high end of the memory-usage spectrum and give varied speed results. Perl's performance in the benchmarks game is typical for interpreted languages.[108]

Large Perl programs start more slowly 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 expected because the perl interpreter spent significant time finding modules within his over-large include path.[109] Unlike Java, Python, and Ruby, Perl has only experimental support for pre-compiling.[110] Therefore, Perl programs pay this overhead penalty on every execution. The run phase of typical programs is long enough that amortized startup time is not substantial, but benchmarks that measure very short execution times are likely to be skewed due to this overhead.[111]

A number of tools have been introduced to improve this situation. The first such tool was Apache's mod_perl, which sought to address one of the most-common reasons that small Perl programs were invoked rapidly: CGI Web development. ActivePerl, via Microsoft ISAPI, provides similar performance improvements.[112]

Once Perl code is compiled, there is additional overhead during the execution phase that typically isn't present for programs written in compiled languages such as C or C++. Examples of such overhead include bytecode interpretation, reference-counting memory management, and dynamic type-checking.[113]

Optimizing

The most critical routines can be written in other languages (such as C), which can be connected to Perl via simple Inline modules or the more complex, but flexible, XS mechanism.[114]

Perl 5

Perl 5, the language usually referred to as "Perl", continues to be actively developed. Perl 5.12.0 was released in April 2010 with some new features influenced by the design of Perl 6,[47][115] followed by Perl 5.14.1 (released on June 17, 2011), Perl 5.16.1 (released on August 9, 2012.[116]), and Perl 5.18.0 (released on May 18, 2013). Perl 5 development versions are released on a monthly basis, with major releases coming out once per year.[117]

The relative proportion of Internet searches for "Perl programming", as compared with similar searches for other programming languages, steadily declined from about 10% in 2005 to about 2% in 2011, and to about 0.7% in 2020.[118]

Raku (Perl 6)

 
Camelia, the logo for the Perl 6 project[119]

At the 2000 Perl Conference, Jon Orwant made a case for a major new language-initiative.[120] 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, which submitted more than 300 RFCs.[121]

Wall spent the next few years digesting the RFCs and synthesizing them into a coherent framework for Perl 6. He presented his design for Perl 6 in a series of documents called "apocalypses" – numbered to correspond to chapters in Programming Perl. As of January 2011, the developing specification of Perl 6 was encapsulated in design documents called Synopses – numbered to correspond to Apocalypses.[122]

Thesis work by Bradley M. Kuhn, overseen by Wall, considered the possible use of the Java virtual machine as a runtime for Perl.[123] Kuhn's thesis showed this approach to be problematic. 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.[citation needed]

In 2005, Audrey Tang created the Pugs project, an implementation of Perl 6 in Haskell. This acted as, 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 Libera Chat #raku IRC channel. Many functional programming influences were absorbed by the Perl 6 design team.[124]

In 2012, Perl 6 development was centered primarily on two compilers:[125]

  1. Rakudo, an implementation running on the Parrot virtual machine and the Java virtual machine.[126]
  2. Niecza, which targets the Common Language Runtime.

In 2013, MoarVM (“Metamodel On A Runtime”), a C language-based virtual machine designed primarily for Rakudo was announced.[127]

In October 2019, Perl 6 was renamed to Raku.[128]

As of 2017 only the Rakudo implementation and MoarVM are under active development, and other virtual machines, such as the Java Virtual Machine and JavaScript, are supported.[129]

Perl 7

Perl 7 was announced on 24 June 2020 at "The Perl Conference in the Cloud" as the successor to Perl 5.[62][61] Based on Perl 5.32, Perl 7 was planned to be backward compatible with modern Perl 5 code; Perl 5 code, without boilerplate (pragma) header needs adding use compat::perl5; to stay compatible, but modern code can drop some of the boilerplate.

The plan to go to Perl 7 brought up more discussion, however, and the Perl Steering Committee canceled it to avoid issues with backward compatibility for scripts that were not written to the pragmas and modules that would become the default in Perl 7. Perl 7 will only come out when the developers add enough features to warrant a major release upgrade.[130]

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 Wall's first "State of the Onion" talk.[131]

State of the Onion

State of the Onion is the name for 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 culture, the wider hacker culture, Wall's linguistic background, sometimes his family life, and occasionally even his Christian background.[132]

Each talk is first given at various Perl conferences and is eventually also published online.

Perl pastimes

JAPHs

In email, Usenet, and message board postings, "Just another Perl hacker" (JAPH) programs are a common trend, originated by Randal L. Schwartz, one of the earliest professional Perl trainers.[133] 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 as developed by Schwartz includes the comma at the end, although this is often omitted.[134]

Perl golf

Perl "golf" is the pastime of reducing the number of characters (key "strokes") used in a Perl program to the bare minimum, much in the same way that golf players seek to take as few shots as possible in a round. The phrase's first use[135] emphasized the difference between pedestrian code meant to teach a newcomer and terse hacks likely to amuse experienced Perl programmers, an example of the latter being JAPHs that were already used in signatures in Usenet postings and elsewhere. Similar stunts had been an unnamed pastime in the language APL in previous decades. The use of Perl to write a program that performed RSA encryption prompted a widespread and practical interest in this pastime.[136] In subsequent years, the term "code golf" has been applied to the pastime in other languages.[137] A Perl Golf Apocalypse was held at Perl Conference 4.0 in Monterey, California in July 2000.

Obfuscation

As with C, obfuscated code competitions were a well known pastime in the late 1990s. The Obfuscated Perl Contest was a competition held by The Perl Journal from 1996 to 2000 that made an arch virtue of Perl's syntactic flexibility. Awards were given for categories such as "most powerful"—programs that made efficient use of space—and "best four-line signature" for programs that fit into four lines of 76 characters in the style of a Usenet signature block.[138]

Poetry

Perl poetry is the practice of writing poems that can be compiled as legal Perl code, for example the piece known as Black Perl. Perl poetry is made possible by the large number of English words that are used in the Perl language. New poems are regularly submitted to the community at PerlMonks.[139]

Perl on IRC

A number of IRC channels offer support for Perl and some of its modules.

IRC Network Channels
irc.libera.chat #perl #raku
irc.perl.org #moose #poe #catalyst #dbix-class #perl-help #distzilla #epo #corehackers #sdl #win32 #toolchain #padre #dancer
irc.slashnet.org #perlmonks
irc.oftc.net #perl #debian-perl (packaging Perl modules for Debian)
irc.efnet.net #perlhelp
irc.rizon.net #perl

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.[140] Upon execution of such a program, the module translates its source code into regular Perl and runs it.[citation needed]

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 is not 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,[141] which allows the program's source code to be "whitened" (i.e., all characters replaced with whitespace) and yet still work.[citation needed]

Example code

In older versions of Perl, one would write the Hello World program as:

print "Hello, World!\n"; 

Here is a more complex Perl program, that counts down seconds from a given starting value:

#!/usr/bin/perl use strict; use warnings; my ( $remaining, $total ); $remaining = $total = shift(@ARGV); STDOUT->autoflush(1); while ( $remaining ) { printf ( "Remaining %s/%s \r", $remaining--, $total ); sleep 1; } print "\n"; 

The Perl interpreter can also be used for one-off scripts on the command line. The following example (as invoked from an sh-compatible shell, such as Bash) translates the string "Bob" in all files ending with .txt in the current directory to "Robert":

$ perl -i.bak -lp -e 's/Bob/Robert/g' *.txt 

Criticism

Perl has been referred to as "line noise" and a write-only language by its critics. The earliest such mention was in the first edition of the book Learning Perl, a Perl 4 tutorial book written by Randal L. Schwartz,[142] in the first chapter of which he states: "Yes, sometimes Perl looks like line noise to the uninitiated, but to the seasoned Perl programmer, it looks like checksummed line noise with a mission in life."[143] He also stated that the accusation that Perl is a write-only language could be avoided by coding with "proper care".[143] The Perl overview document perlintro states that the names of built-in "magic" scalar variables "look like punctuation or line noise".[144] However, the English module provides both long and short English alternatives. perlstyle document states that line noise in regular expressions could be mitigated using the /x modifier to add whitespace.[145]

According to the Perl 6 FAQ, Perl 6 was designed to mitigate "the usual suspects" that elicit the "line noise" claim from Perl 5 critics, including the removal of "the majority of the punctuation variables" and the sanitization of the regex syntax.[146] The Perl 6 FAQ also states that what is sometimes referred to as Perl's line noise is "the actual syntax of the language" just as gerunds and prepositions are a part of the English language.[146] In a December 2012 blog posting, despite claiming that "Rakudo Perl 6 has failed and will continue to fail unless it gets some adult supervision", chromatic stated that the design of Perl 6 has a "well-defined grammar" as well as an "improved type system, a unified object system with an intelligent metamodel, metaoperators, and a clearer system of context that provides for such niceties as pervasive laziness".[147] He also stated that "Perl 6 has a coherence and a consistency that Perl 5 lacks."[147]

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Further reading

  • Learning Perl 6th Edition (2011), O'Reilly. Beginner-level introduction to Perl.
  • Beginning Perl 1st Edition (2012), Wrox. A beginner's tutorial for those new to programming or just new to Perl.
  • Modern Perl December 22, 2011, at the Wayback Machine 2nd Edition (2012), Onyx Neon. Describes Modern Perl programming techniques.
  • Programming Perl 4th Edition (2012), O'Reilly. The definitive Perl reference.
  • Effective Perl Programming 2nd Edition (2010), Addison-Wesley. Intermediate- to advanced-level guide to writing idiomatic Perl.
  • Perl Cookbook, ISBN 0-596-00313-7. Practical Perl programming examples.
  • Dominus, Mark Jason (2005). Higher Order Perl. Morgan Kaufmann. ISBN 978-1-55860-701-9. Functional programming techniques in Perl.

External links

  • Official website  

perl, this, article, about, programming, language, other, uses, disambiguation, confused, with, pearl, programming, language, family, high, level, general, purpose, interpreted, dynamic, programming, languages, refers, from, 2000, 2019, also, referred, redesig. This article is about the programming language For other uses see Perl disambiguation Not to be confused with PEARL programming language Perl is a family of two high level general purpose interpreted dynamic programming languages Perl refers to Perl 5 but from 2000 to 2019 it also referred to its redesigned sister language Perl 6 before the latter s name was officially changed to Raku in October 2019 9 10 PerlParadigmMulti paradigm functional imperative object oriented class based reflectiveDesigned byLarry WallDeveloperLarry WallFirst appearedDecember 18 1987 35 years ago 1987 12 18 1 Stable release5 36 0 2 28 May 2022 7 months ago 2022 05 28 5 34 1 3 13 March 2022 9 months ago 2022 03 13 Preview release5 37 6 4 21 November 2022 52 days ago 2022 11 21 Typing disciplineDynamicImplementation languageCOSCross platformLicenseArtistic License 1 0 5 6 or GNU General Public License 7 Filename extensions plx pl pm xs t pod cgiWebsiteperl orgInfluenced byAWK BASIC C C Lisp sed Unix shell 8 InfluencedCoffeeScript citation needed Groovy citation needed JavaScript Julia LPC PHP Python Raku Ruby PowerShellPerl Programming at WikibooksThough Perl is not officially an acronym 11 there are various backronyms in use including Practical Extraction and Reporting Language 12 Perl was developed by Larry Wall in 1987 as a general purpose Unix scripting language to make report processing easier 13 Since then it has undergone many changes and revisions Raku which began as a redesign of Perl 5 in 2000 eventually evolved into a separate language Both languages continue to be developed independently by different development teams and liberally borrow ideas from each other The Perl languages borrow features from other programming languages including C sh AWK and sed 1 They provide text processing facilities without the arbitrary data length limits of many contemporary Unix command line tools 14 Perl 5 gained widespread popularity in the late 1990s as a CGI scripting language in part due to its powerful regular expression and string parsing abilities 15 16 17 18 In addition to CGI Perl 5 is used for system administration network programming finance bioinformatics and other applications such as for GUIs It has been nicknamed the Swiss Army chainsaw of scripting languages because of its flexibility and power 19 and also what some consider ugliness 20 due to its utilization of more special characters than many other languages In 1998 it was also referred to as the duct tape that holds the Internet together in reference to both its ubiquitous use as a glue language and its perceived inelegance 21 Perl is a highly expressive programming language source code for a given algorithm can be short and highly compressible 22 23 Contents 1 Name 2 History 2 1 Early versions 2 2 Early Perl 5 2 3 2000 2020 2 4 2020 onward 3 Symbols 3 1 Camel 3 2 Onion 3 3 Raptor 4 Overview 4 1 Features 4 2 Design 4 3 Applications 4 4 Implementation 4 5 Availability 4 5 1 Windows 5 Database interfaces 6 Comparative performance 6 1 Optimizing 7 Perl 5 8 Raku Perl 6 9 Perl 7 10 Perl community 10 1 State of the Onion 10 2 Perl pastimes 10 2 1 JAPHs 10 2 2 Perl golf 10 2 3 Obfuscation 10 2 4 Poetry 10 3 Perl on IRC 10 4 CPAN Acme 11 Example code 12 Criticism 13 See also 14 References 15 Further reading 16 External linksName EditPerl was originally named Pearl Wall wanted to give the language a short name with positive connotations Wall discovered the existing PEARL programming language before Perl s official release and changed the spelling of the name 24 When referring to the language the name is capitalized Perl When referring to the program itself the name is uncapitalized perl because most 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 capitalized the language s name in the book to make it stand out better when typeset This case distinction was subsequently documented as canonical 25 The name is occasionally expanded as a backronym Practical Extraction and Report Language 26 and Wall s own Pathologically Eclectic Rubbish Lister which is in the manual page for perl 27 History EditEarly versions Edit Larry Wall began work on Perl in 1987 while working as a programmer at Unisys 14 and version 1 0 on December 18 1987 1 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 citation needed Originally the only documentation for Perl was a single lengthy man page In 1991 Programming Perl known to many Perl programmers as the Camel Book because of its cover 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 well documented by the book citation needed Early Perl 5 Edit Main article Perl 5 version history Perl 4 went through a series of maintenance releases culminating in Perl 4 036 in 1993 whereupon Wall abandoned Perl 4 to begin work on Perl 5 Initial design 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 28 Perl 5 000 was released on October 17 1994 29 It was a nearly complete rewrite of the interpreter and it 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 Perl 5 has been in active development since then Perl 5 001 was released on March 13 1995 Perl 5 002 was released on February 29 1996 with the new prototypes feature This allowed module authors to make subroutines that behaved like Perl builtins Perl 5 003 was released June 25 1996 as a security release 30 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 the Perl language and Perl modules as of December 2022 it carries over 211 850 modules in 43 865 distributions written by more than 14 324 authors and is mirrored worldwide at more than 245 locations 31 Perl 5 004 was released on May 15 1997 and included among other things the UNIVERSAL package giving Perl a base object from which all classes were automatically derived and the ability to require versions of modules Another significant development was the inclusion of the CGI pm module 32 which contributed to Perl s popularity as a CGI scripting language 33 Perl 5 004 added support for Microsoft Windows Plan 9 QNX and AmigaOS 32 Perl 5 005 was released on July 22 1998 This release included several enhancements to the regex engine new hooks into the backend through the B modules the qr regex quote operator a large selection of other new core modules and added support for several more operating systems including BeOS 34 2000 2020 Edit Major version 29 Latest update 35 Old version no longer maintained 5 4 1999 04 29Old version no longer maintained 5 5 2004 02 23Old version no longer maintained 5 6 2003 11 15Old version no longer maintained 5 8 2008 12 14Old version no longer maintained 5 10 2009 08 22Old version no longer maintained 5 12 2012 11 10Old version no longer maintained 5 14 2013 03 10Old version no longer maintained 5 16 2013 03 11Old version no longer maintained 5 18 2014 10 01Old version no longer maintained 5 20 2015 09 12Old version no longer maintained 5 22 2017 07 15Old version no longer maintained 5 24 2018 04 14Old version no longer maintained 5 26 2018 11 29Old version no longer maintained 5 28 2020 06 01Old version no longer maintained 5 30 2020 06 01Old version no longer maintained 5 32 2021 01 23Older version yet still maintained 5 34 2022 03 13Current stable version 5 36 2022 05 28Latest preview version of a future release 5 37 2022 10 20Future release 7 0 2023 Legend Old version Older version still maintained Current stable version Latest preview version Future releasePerl 5 6 was released on March 22 2000 Major changes included 64 bit support Unicode string representation support for files over 2 GiB and the our keyword 36 37 When developing Perl 5 6 the decision was made to switch the versioning scheme to one more similar to other open source projects after 5 005 63 the next version became 5 5 640 with plans for development versions to have odd numbers and stable versions to have even numbers 38 In 2000 Wall put forth a call for suggestions for a new version of Perl from the community The process resulted in 361 RFC request for comments documents that were to be used in guiding development of Perl 6 In 2001 39 work began on the Apocalypses for Perl 6 a series of documents meant to summarize the change requests and present the design of the next generation of Perl They were presented as a digest of the RFCs rather than a formal document At this point Perl 6 existed only as a description of a language citation needed Perl 5 8 was first released on July 18 2002 and had nearly yearly updates since then Perl 5 8 improved Unicode support added a new I O implementation added a new thread implementation improved numeric accuracy and added several new modules 40 As of 2013 this version still remains the most popular version of Perl and is used by Red Hat 5 Suse 10 Solaris 10 HP UX 11 31 and AIX 5In 2004 work began on the Synopses documents that originally summarized the Apocalypses but which became the specification for the Perl 6 language In February 2005 Audrey Tang began work on Pugs a Perl 6 interpreter written in Haskell 41 This was the first concerted effort toward making Perl 6 a reality This effort stalled in 2006 42 PONIE is an acronym for Perl On New Internal Engine The PONIE Project existed from 2003 until 2006 and was to be a bridge between Perl 5 and Perl 6 It was an effort to rewrite the Perl 5 interpreter to run on Parrot the Perl 6 virtual machine The goal was to ensure the future of the millions of lines of Perl 5 code at thousands of companies around the world 43 The PONIE project ended in 2006 and is no longer being actively developed Some of the improvements made to the Perl 5 interpreter as part of PONIE were folded into that project 44 On December 18 2007 the 20th anniversary of Perl 1 0 Perl 5 10 0 was released Perl 5 10 0 included notable new features which brought it closer to Perl 6 These included a switch statement called given when regular expressions updates and the smart match operator 45 46 Around this same time development began in earnest on another implementation of Perl 6 known as Rakudo Perl developed in tandem with the Parrot virtual machine As of November 2009 Rakudo Perl has had regular monthly releases and now is the most complete implementation of Perl 6 A major change in the development process of Perl 5 occurred with Perl 5 11 the development community has switched to a monthly release cycle of development releases with a yearly schedule of stable releases By that plan bugfix point releases will follow the stable releases every three months citation needed On April 12 2010 Perl 5 12 0 was released Notable core enhancements include new package NAME VERSION syntax the Yada Yada operator intended to mark placeholder code that is not yet implemented implicit strictures full Y2038 compliance regex conversion overloading DTrace support and Unicode 5 2 47 On May 14 2011 Perl 5 14 was released with JSON support built in 48 On May 20 2012 Perl 5 16 was released Notable new features include the ability to specify a given version of Perl that one wishes to emulate allowing users to upgrade their version of Perl but still run old scripts that would normally be incompatible 49 failed verification Perl 5 16 also updates the core to support Unicode 6 1 49 On May 18 2013 Perl 5 18 was released Notable new features include the new dtrace hooks lexical subs more CORE subs overhaul of the hash for security reasons support for Unicode 6 2 50 On May 27 2014 Perl 5 20 was released Notable new features include subroutine signatures hash slices new slice syntax postfix dereferencing experimental Unicode 6 3 rand using consistent random number generator 51 Some observers credit the release of Perl 5 10 with the start of the Modern Perl movement 52 In particular this phrase describes a style of development that embraces the use of the CPAN takes advantage of recent developments in the language and is rigorous about creating high quality code 53 While the book Modern Perl 54 may be the most visible standard bearer of this idea other groups such as the Enlightened Perl Organization 55 have taken up the cause In late 2012 and 2013 several projects for alternative implementations for Perl 5 started Perl5 in Perl6 by the Rakudo Perl team 56 moe by Stevan Little and friends 57 p2 58 by the Perl11 team under Reini Urban gperl by goccy 59 and rperl a Kickstarter project led by Will Braswell and affiliated with the Perll11 project 60 2020 onward Edit In June 2020 Perl 7 was announced as the successor to Perl 5 61 Perl 7 was to initially be based on Perl 5 32 with a release expected in first half of 2021 and release candidates sooner 62 This plan was revised in May 2021 without any release timeframe or version of Perl 5 for use as a baseline specified 63 When Perl 7 is released Perl 5 will go into long term maintenance Supported Perl 5 versions however will continue to get important security and bug fixes 64 Symbols EditCamel Edit The Camel symbol used by O Reilly Media Programming Perl published by O Reilly Media features a picture of a dromedary camel on the cover and is commonly called the Camel Book 65 This image has become an unofficial symbol of Perl as well as a general hacker emblem appearing on T shirts and other clothing items citation needed O Reilly owns the image as a trademark but licenses it for non commercial use requiring only an acknowledgement and a link to www perl com Licensing for commercial use is decided on a case by case basis 66 O Reilly also provides Programming Republic of Perl logos for non commercial sites and Powered by Perl buttons for any site that uses Perl 66 Onion Edit The onion logo used by The Perl Foundation The Perl Foundation owns an alternative symbol an onion which it licenses to its subsidiaries Perl Mongers PerlMonks Perl org and others 67 The symbol is a visual pun on pearl onion 68 Raptor Edit Alternative Perl 5 Logo Sebastian Riedel the creator of Mojolicious created a logo depicting a raptor dinosaur which is available under a CC SA License Version 4 0 69 The analogue of the raptor comes from a series of talks given by Matt S Trout beginning in 2010 70 Overview EditMain article Perl language structure According to Wall Perl has two slogans The first is There s more than one way to do it commonly known as TMTOWTDI The second slogan is Easy things should be easy and hard things should be possible 14 Features Edit The overall structure of Perl derives broadly from C Perl is procedural in nature with variables expressions assignment statements brace delimited blocks control structures and subroutines 71 Perl also takes features from shell programming All variables are marked with leading sigils which allow variables to be interpolated directly into strings However unlike the shell Perl uses sigils on all accesses to variables and unlike most other programming languages that use sigils the sigil doesn t denote the type of the variable but the type of the expression So for example while an array is denoted by the sigil for example arrayname an individual member of the array is denoted by the scalar sigil for example arrayname 3 Perl also has many built in functions that provide tools often used in shell programming although many of these tools are implemented by programs external to the shell such as sorting and calling operating system facilities citation needed Perl takes hashes associative arrays from AWK and regular expressions from sed These simplify many parsing text handling and data management tasks Shared with Lisp is the implicit return of the last value in a block and all statements are also expressions which can be used in larger expressions themselves citation needed Perl 5 added features that support complex data structures first class functions that is 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 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 72 All versions of Perl do automatic data typing and automatic 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 cannot 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 citation needed Design Edit 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 aimed to make efficient use of expensive computer hardware In contrast Perl was designed so that computer programmers could write programs more quickly and easily 73 Perl has many features that ease the task of the programmer 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 Perl follows the theory of no built in limits 65 an idea similar to the Zero One Infinity rule citation needed 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 write even where they complicate the Perl interpreter 74 Perl s syntax reflects the idea that things that are different should look different 75 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 a language such as Lisp where the same basic syntax composed of simple and universal symbolic expressions is used for all purposes citation needed Perl does not enforce any particular programming paradigm procedural object oriented functional or others or even require the programmer to choose among them citation needed 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 14 One consequence of this is that Perl is not 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 Perl s function documentation remarks on the variant behavior of built in functions in list and scalar contexts by saying In general they do what you want unless you want consistency 76 No written specification or standard for the Perl language exists for Perl versions through Perl 5 and there are no plans to create one for the current version of Perl There has been only one implementation of the interpreter and the language has evolved along with it That interpreter together with its functional tests stands as a de facto specification of the language Perl 6 however started with a specification 77 and several projects 78 aim to implement some or all of the specification citation needed Applications Edit Perl has many and varied applications compounded by the availability of many standard and third party modules Perl has chiefly been used to write CGI scripts large projects written in Perl include cPanel Slash Bugzilla RT TWiki and Movable Type high traffic websites that use Perl extensively include Priceline com Craigslist 79 IMDb 80 LiveJournal DuckDuckGo 81 82 Slashdot and Ticketmaster It is also an optional component of the popular LAMP technology stack for Web development in lieu of PHP or Python Perl is used extensively as a system programming language in the Debian Linux distribution 83 Perl is often used as a glue language tying together systems and interfaces that were not specifically designed to interoperate and for data munging 84 that is converting or processing large amounts of data for tasks such as creating reports In fact these strengths are intimately linked The combination makes Perl a popular all purpose language for system administrators particularly because short programs often called one liner programs can be entered and run on a single command line citation needed Perl code can be made portable across Windows and Unix such code is often used by suppliers of software both COTS and bespoke to simplify packaging and maintenance of software build and deployment scripts citation needed Perl Tk and wxPerl are commonly used to add graphical user interfaces to Perl scripts Implementation Edit Perl is implemented as a core interpreter written in C together with a large collection of modules written in Perl and C As of 2010 update 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 citation needed 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 citation needed The life of a Perl interpreter divides broadly into a compile phase and a run phase 85 In Perl the phases are the major stages in the interpreter s life cycle Each interpreter goes through each phase only once and the phases follow in a fixed sequence citation needed Most of what happens in Perl s compile phase is compilation and most of what happens in Perl s run phase is execution but there are significant exceptions Perl makes important use of its capability to execute Perl code during the compile phase Perl will also delay compilation into the run phase The terms that indicate the kind of processing that is actually occurring at any moment are compile time and run time Perl is in compile time at most points during the compile phase but compile time may also be entered during the run phase The compile time for code in a string argument passed to the a href Eval html title Eval eval a built in occurs during the run phase Perl is often in run time during the compile phase and spends most of the run phase in run time Code in BEGIN blocks executes at run time but in the compile phase At compile time the interpreter parses Perl code into a syntax tree At run time it executes the program by walking the tree Text is parsed only once and the syntax tree is subject to optimization before it is executed so that execution is relatively efficient Compile time optimizations on the syntax tree include constant folding and context propagation but peephole optimization is also performed 86 Perl has a Turing complete grammar because parsing can be affected by run time code executed during the compile phase 87 Therefore Perl cannot 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 citation needed It is often said that Only perl can parse Perl 88 meaning that only the Perl interpreter perl can parse the Perl language Perl but even this is not in general true Because the Perl interpreter can simulate a Turing machine during its compile phase it would need to decide the halting problem in order to complete parsing in every case It is a longstanding result that the halting problem is undecidable and therefore not even Perl can always parse Perl Perl makes the unusual choice of giving the user access to its full programming power in its own compile phase The cost in terms of theoretical purity is high but practical inconvenience seems to be rare 89 Other programs that undertake to parse Perl such as source code analyzers and auto indenters have to contend not only with ambiguous syntactic constructs but also with the undecidability of Perl parsing in the general case Adam Kennedy s PPI project focused on parsing Perl code as a document retaining its integrity as a document instead of parsing Perl as executable code that not even Perl itself can always do It was Kennedy who first conjectured that parsing Perl suffers from the halting problem 90 which was later proved 91 Perl is distributed with over 250 000 functional tests for core Perl language and over 250 000 functional tests for core modules 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 do not introduce software bugs additionally Perl users who see that the interpreter passes its functional tests on their system can have a high degree of confidence that it is working properly citation needed Availability Edit Perl is dual licensed under both the Artistic License 1 0 5 6 and the GNU General Public License 7 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 citation needed reported exceptions Perl can be compiled from source code on all POSIX compliant or otherwise Unix compatible platforms 92 Because of unusual changes required for the classic Mac OS environment a special port called MacPerl was shipped independently 93 The Comprehensive Perl Archive Network carries a complete list of supported platforms with links to the distributions available on each 94 CPAN is also the source for publicly available Perl modules that are not part of the core Perl distribution citation needed Windows Edit Users of Microsoft Windows typically install one of the native binary distributions of Perl for Win32 most commonly Strawberry Perl or 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 difficult to install modules from the CPAN particularly those that are partially written in C citation needed ActivePerl is a closed source distribution from ActiveState that has regular releases that track the core Perl releases 95 The distribution previously included the Perl package manager PPM 96 a popular tool for installing removing upgrading and managing the use of common Perl modules however this tool was discontinued as of ActivePerl 5 28 97 Included also is PerlScript a Windows Script Host WSH engine implementing the Perl language Visual Perl is an ActiveState tool that adds Perl to the Visual Studio NET development suite A VBScript to Perl converter as well as a Perl compiler for Windows and converters of awk and sed to Perl have also been produced by this company and included on the ActiveState CD for Windows which includes all of their distributions plus the Komodo IDE and all but the first on the Unix Linux Posix variant thereof in 2002 and subsequently 98 Strawberry Perl is an open source distribution for Windows It has had regular quarterly releases since January 2008 including new modules as feedback and requests come in Strawberry Perl aims to be able to install modules like standard Perl distributions on other platforms including compiling XS modules citation needed The Cygwin emulation layer is another way of running Perl under Windows Cygwin provides a Unix like environment on Windows and both Perl and CPAN are available as standard pre compiled packages in the Cygwin setup program Since Cygwin also includes gcc compiling Perl from source is also possible citation needed A Perl executable is included in several Windows Resource kits in the directory with other scripting tools citation needed Implementations of Perl come with the MKS Toolkit Interix the base of earlier implementations of Windows Services for Unix and UWIN citation needed Database interfaces EditPerl s text handling capabilities can be used for generating SQL queries arrays hashes and automatic memory management make it easy to collect and process the returned data For example in Tim Bunce s Perl DBI application programming interface API the arguments to the API can be the text of SQL queries thus it is possible to program in multiple languages at the same time e g for generating a Web page using HTML JavaScript and SQL in a here document The use of Perl variable interpolation to programmatically customize each of the SQL queries and the specification of Perl arrays or hashes as the structures to programmatically hold the resulting data sets from each SQL query allows a high level mechanism for handling large amounts of data for post processing by a Perl subprogram 99 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 done for only a few of the most important and most widely used databases and it restricted the resulting perl executable to using just one database interface at a time 100 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 ANSI SQL databases 101 DBI provides caching for database handles and queries which can greatly improve performance in long lived execution environments such as mod perl 102 helping high volume systems avert load spikes as in the Slashdot effect 103 In modern Perl applications especially those written using web frameworks such as Catalyst the DBI module is often used indirectly via object relational mappers such as DBIx Class Class DBI 104 or Rose DB Object 105 that generate SQL queries and handle data transparently to the application author 106 Comparative performance EditThe Computer Language Benchmarks Game compares the performance of implementations of typical programming problems in several programming languages 107 The submitted Perl implementations typically perform toward the high end of the memory usage spectrum and give varied speed results Perl s performance in the benchmarks game is typical for interpreted languages 108 Large Perl programs start more slowly 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 expected because the perl interpreter spent significant time finding modules within his over large include path 109 Unlike Java Python and Ruby Perl has only experimental support for pre compiling 110 Therefore Perl programs pay this overhead penalty on every execution The run phase of typical programs is long enough that amortized startup time is not substantial but benchmarks that measure very short execution times are likely to be skewed due to this overhead 111 A number of tools have been introduced to improve this situation The first such tool was Apache s mod perl which sought to address one of the most common reasons that small Perl programs were invoked rapidly CGI Web development ActivePerl via Microsoft ISAPI provides similar performance improvements 112 Once Perl code is compiled there is additional overhead during the execution phase that typically isn t present for programs written in compiled languages such as C or C Examples of such overhead include bytecode interpretation reference counting memory management and dynamic type checking 113 Optimizing Edit The most critical routines can be written in other languages such as C which can be connected to Perl via simple Inline modules or the more complex but flexible XS mechanism 114 Perl 5 EditPerl 5 the language usually referred to as Perl continues to be actively developed Perl 5 12 0 was released in April 2010 with some new features influenced by the design of Perl 6 47 115 followed by Perl 5 14 1 released on June 17 2011 Perl 5 16 1 released on August 9 2012 116 and Perl 5 18 0 released on May 18 2013 Perl 5 development versions are released on a monthly basis with major releases coming out once per year 117 The relative proportion of Internet searches for Perl programming as compared with similar searches for other programming languages steadily declined from about 10 in 2005 to about 2 in 2011 and to about 0 7 in 2020 118 Raku Perl 6 EditMain article Raku programming language Camelia the logo for the Perl 6 project 119 At the 2000 Perl Conference Jon Orwant made a case for a major new language initiative 120 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 which submitted more than 300 RFCs 121 Wall spent the next few years digesting the RFCs and synthesizing them into a coherent framework for Perl 6 He presented his design for Perl 6 in a series of documents called apocalypses numbered to correspond to chapters in Programming Perl As of January 2011 update the developing specification of Perl 6 was encapsulated in design documents called Synopses numbered to correspond to Apocalypses 122 Thesis work by Bradley M Kuhn overseen by Wall considered the possible use of the Java virtual machine as a runtime for Perl 123 Kuhn s thesis showed this approach to be problematic 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 citation needed In 2005 Audrey Tang created the Pugs project an implementation of Perl 6 in Haskell This acted as 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 Libera Chat raku IRC channel Many functional programming influences were absorbed by the Perl 6 design team 124 In 2012 Perl 6 development was centered primarily on two compilers 125 Rakudo an implementation running on the Parrot virtual machine and the Java virtual machine 126 Niecza which targets the Common Language Runtime In 2013 MoarVM Metamodel On A Runtime a C language based virtual machine designed primarily for Rakudo was announced 127 In October 2019 Perl 6 was renamed to Raku 128 As of 2017 update only the Rakudo implementation and MoarVM are under active development and other virtual machines such as the Java Virtual Machine and JavaScript are supported 129 Perl 7 EditPerl 7 was announced on 24 June 2020 at The Perl Conference in the Cloud as the successor to Perl 5 62 61 Based on Perl 5 32 Perl 7 was planned to be backward compatible with modern Perl 5 code Perl 5 code without boilerplate pragma header needs adding use compat perl5 to stay compatible but modern code can drop some of the boilerplate The plan to go to Perl 7 brought up more discussion however and the Perl Steering Committee canceled it to avoid issues with backward compatibility for scripts that were not written to the pragmas and modules that would become the default in Perl 7 Perl 7 will only come out when the developers add enough features to warrant a major release upgrade 130 Perl community EditPerl 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 Wall s first State of the Onion talk 131 State of the Onion Edit State of the Onion is the name for 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 culture the wider hacker culture Wall s linguistic background sometimes his family life and occasionally even his Christian background 132 Each talk is first given at various Perl conferences and is eventually also published online Perl pastimes Edit JAPHs Edit In email Usenet and message board postings Just another Perl hacker JAPH programs are a common trend originated by Randal L Schwartz one of the earliest professional Perl trainers 133 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 as developed by Schwartz includes the comma at the end although this is often omitted 134 Perl golf Edit Perl golf is the pastime of reducing the number of characters key strokes used in a Perl program to the bare minimum much in the same way that golf players seek to take as few shots as possible in a round The phrase s first use 135 emphasized the difference between pedestrian code meant to teach a newcomer and terse hacks likely to amuse experienced Perl programmers an example of the latter being JAPHs that were already used in signatures in Usenet postings and elsewhere Similar stunts had been an unnamed pastime in the language APL in previous decades The use of Perl to write a program that performed RSA encryption prompted a widespread and practical interest in this pastime 136 In subsequent years the term code golf has been applied to the pastime in other languages 137 A Perl Golf Apocalypse was held at Perl Conference 4 0 in Monterey California in July 2000 Obfuscation Edit As with C obfuscated code competitions were a well known pastime in the late 1990s The Obfuscated Perl Contest was a competition held by The Perl Journal from 1996 to 2000 that made an arch virtue of Perl s syntactic flexibility Awards were given for categories such as most powerful programs that made efficient use of space and best four line signature for programs that fit into four lines of 76 characters in the style of a Usenet signature block 138 Poetry Edit Perl poetry is the practice of writing poems that can be compiled as legal Perl code for example the piece known as Black Perl Perl poetry is made possible by the large number of English words that are used in the Perl language New poems are regularly submitted to the community at PerlMonks 139 Perl on IRC Edit A number of IRC channels offer support for Perl and some of its modules IRC Network Channelsirc libera chat perl rakuirc perl org moose poe catalyst dbix class perl help distzilla epo corehackers sdl win32 toolchain padre dancerirc slashnet org perlmonksirc oftc net perl debian perl packaging Perl modules for Debian irc efnet net perlhelpirc rizon net perlCPAN Acme Edit There are also many examples of code written purely for entertainment on the CPAN Lingua Romana Perligata for example allows writing programs in Latin 140 Upon execution of such a program the module translates its source code into regular Perl and runs it citation needed 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 is not 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 141 which allows the program s source code to be whitened i e all characters replaced with whitespace and yet still work citation needed Example code EditIn older versions of Perl one would write the Hello World program as print Hello World n Here is a more complex Perl program that counts down seconds from a given starting value usr bin perl use strict use warnings my remaining total remaining total shift ARGV STDOUT gt autoflush 1 while remaining printf Remaining s s r remaining total sleep 1 print n The Perl interpreter can also be used for one off scripts on the command line The following example as invoked from an sh compatible shell such as Bash translates the string Bob in all files ending with txt in the current directory to Robert perl i bak lp e s Bob Robert g txtCriticism EditPerl has been referred to as line noise and a write only language by its critics The earliest such mention was in the first edition of the book Learning Perl a Perl 4 tutorial book written by Randal L Schwartz 142 in the first chapter of which he states Yes sometimes Perl looks like line noise to the uninitiated but to the seasoned Perl programmer it looks like checksummed line noise with a mission in life 143 He also stated that the accusation that Perl is a write only language could be avoided by coding with proper care 143 The Perl overview document perlintro states that the names of built in magic scalar variables look like punctuation or line noise 144 However the English module provides both long and short English alternatives perlstyle document states that line noise in regular expressions could be mitigated using the x modifier to add whitespace 145 According to the Perl 6 FAQ Perl 6 was designed to mitigate the usual suspects that elicit the line noise claim from Perl 5 critics including the removal of the majority of the punctuation variables and the sanitization of the regex syntax 146 The Perl 6 FAQ also states that what is sometimes referred to as Perl s line noise is the actual syntax of the language just as gerunds and prepositions are a part of the English language 146 In a December 2012 blog posting despite claiming that Rakudo Perl 6 has failed and will continue to fail unless it gets some adult supervision chromatic stated that the design of Perl 6 has a well defined grammar as well as an improved type system a unified object system with an intelligent metamodel metaoperators and a clearer system of context that provides for such niceties as pervasive laziness 147 He also stated that Perl 6 has a coherence and a consistency that Perl 5 lacks 147 See also Edit Free and open source software portal Computer programming portalOutline of Perl Perl Data Language Perl Object Environment Plain Old DocumentationReferences Edit a b c Ashton Elaine 1999 The Timeline of Perl and its Culture v3 0 0505 Archived from the original on January 11 2013 Retrieved March 12 2004 perl 5 36 0 is now available www nntp perl org Retrieved May 30 2022 Perl 5 34 1 is now available www nntp perl org Retrieved March 13 2022 perl 5 37 6 is now available www nntp perl org Retrieved November 21 2022 a b The Artistic License dev perl org dev perl org Archived from the original on July 24 2018 Retrieved June 24 2016 a b Artistic Archived July 25 2018 at the Wayback Machine file on the Perl 5 git repository a b 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Wesley Intermediate to advanced level guide to writing idiomatic Perl Perl Cookbook ISBN 0 596 00313 7 Practical Perl programming examples Dominus Mark Jason 2005 Higher Order Perl Morgan Kaufmann ISBN 978 1 55860 701 9 Functional programming techniques in Perl External links EditPerl at Wikipedia s sister projects Definitions from Wiktionary Media from Commons Quotations from Wikiquote Textbooks from Wikibooks Resources from Wikiversity Official website Retrieved from https en wikipedia org w index php title Perl amp oldid 1128606718, wikipedia, wiki, book, books, library,

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