HOME

TheInfoList



OR:

Perl is a family of two
high-level High-level and low-level, as technical terms, are used to classify, describe and point to specific goals of a systematic operation; and are applied in a wide range of contexts, such as, for instance, in domains as widely varied as computer scienc ...
, general-purpose, interpreted,
dynamic programming language In computer science, a dynamic programming language is a class of high-level programming languages, which at runtime execute many common programming behaviours that static programming languages perform during compilation. These behaviors co ...
s. "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. Though Perl is not officially an acronym, there are various
backronym A backronym is an acronym formed from an already existing word by expanding its letters into the words of a phrase. Backronyms may be invented with either serious or humorous intent, or they may be a type of false etymology or folk etymology. The ...
s in use, including "Practical Extraction and Reporting Language". Perl was developed by
Larry Wall Larry Arnold Wall (born September 27, 1954) is an American computer programmer and author. He created the Perl programming language. Personal life Wall grew up in Los Angeles and then Bremerton, Washington, before starting higher education at ...
in 1987 as a general-purpose
Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and ot ...
scripting language A scripting language or script language is a programming language that is used to manipulate, customize, and automate the facilities of an existing system. Scripting languages are usually interpreted at runtime rather than compiled. A scripting ...
to make report processing easier. 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 AWK (''awk'') is a domain-specific language designed for text processing and typically used as a data extraction and reporting tool. Like sed and grep, it is a filter, and is a standard feature of most Unix-like operating systems. The AWK lang ...
, and
sed sed ("stream editor") is a Unix utility that parses and transforms text, using a simple, compact programming language. It was developed from 1973 to 1974 by Lee E. McMahon of Bell Labs, and is available today for most operating systems. sed w ...
; They provide text processing facilities without the arbitrary data-length limits of many contemporary Unix command line tools. Perl 5 gained widespread popularity in the late 1990s as a CGI scripting language, in part due to its powerful
regular expression A regular expression (shortened as regex or regexp; sometimes referred to as rational expression) is a sequence of characters that specifies a search pattern in text. Usually such patterns are used by string-searching algorithms for "find" ...
and string
parsing Parsing, syntax analysis, or syntactic analysis is the process of analyzing a string of symbols, either in natural language, computer languages or data structures, conforming to the rules of a formal grammar. The term ''parsing'' comes from L ...
abilities. In addition to CGI, Perl 5 is used for system administration, network programming, finance,
bioinformatics Bioinformatics () is an interdisciplinary field that develops methods and software tools for understanding biological data, in particular when the data sets are large and complex. As an interdisciplinary field of science, bioinformatics combi ...
, and other applications, such as for
GUI The GUI ( "UI" by itself is still usually pronounced . or ), graphical user interface, is a form of user interface that allows users to interact with electronic devices through graphical icons and audio indicator such as primary notation, inste ...
s. It has been nicknamed "the Swiss Army chainsaw of scripting languages" because of its flexibility and power, and also what some consider ugliness due to its utilization of more special characters than many other languages. In 1998, it was also referred to as the "
duct tape Duct tape (also called duck tape, from the cotton duck cloth it was originally made of) is cloth- or scrim-backed pressure-sensitive tape, often coated with polyethylene. There are a variety of constructions using different backings and adhesi ...
that holds the
Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, pub ...
together," in reference to both its ubiquitous use as a
glue language A scripting language or script language is a programming language that is used to manipulate, customize, and automate the facilities of an existing system. Scripting languages are usually interpreted at runtime rather than compiled. A scripting ...
and its perceived inelegance. Perl is a highly
expressive Expressivity, expressiveness, and expressive power may refer to: *Expressivity (genetics), variations in a phenotype among individuals carrying a particular genotype *Expressive loa, a type of loanword in phono-semantic matching *Expressive power ...
programming language: source code for a given algorithm can be short and highly compressible.


Name

Perl was originally named "Pearl". Wall wanted to give the language a short name with positive connotations. Wall discovered the existing
PEARL A pearl is a hard, glistening object produced within the soft tissue (specifically the mantle) of a living shelled mollusk or another animal, such as fossil conulariids. Just like the shell of a mollusk, a pearl is composed of calcium carb ...
programming language before Perl's official release and changed the spelling of the name. 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 ''Programming Perl'', best known as the Camel Book among programmers, is a book about writing programs using the Perl programming language, revised as several editions (1991-2012) to reflect major language changes since Perl version 4. Editions ...
'', 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. The name is occasionally expanded as a
backronym A backronym is an acronym formed from an already existing word by expanding its letters into the words of a phrase. Backronyms may be invented with either serious or humorous intent, or they may be a type of false etymology or folk etymology. The ...
: ''Practical Extraction and Report Language'' and Wall's own ''Pathologically Eclectic Rubbish Lister'' which is in the
manual page A man page (short for manual page) is a form of software documentation usually found on a Unix or Unix-like operating system. Topics covered include computer programs (including library and system calls), formal standards and conventions, and ev ...
for perl.


History


Early versions

Larry Wall Larry Arnold Wall (born September 27, 1954) is an American computer programmer and author. He created the Perl programming language. Personal life Wall grew up in Los Angeles and then Bremerton, Washington, before starting higher education at ...
began work on Perl in 1987, while working as a programmer at
Unisys Unisys Corporation is an American multinational information technology (IT) services and consulting company headquartered in Blue Bell, Pennsylvania. It provides digital workplace solutions, cloud, applications, and infrastructure solutions, ...
, and version 1.0 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 Binary data is data whose unit can take on only two possible states. These are often labelled as 0 and 1 in accordance with the binary numeral system and Boolean algebra. Binary data occurs in many different technical and scientific fields, wher ...
streams. Originally, the only documentation for Perl was a single lengthy
man page A man page (short for manual page) is a form of software documentation usually found on a Unix or Unix-like operating system. Topics covered include computer programs (including library and system calls), formal standards and conventions, and e ...
. 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.


Early Perl 5

Perl 4 went through a series of
maintenance release A maintenance release (also minor release or Maintenance Pack or MP) is a release of a product that does not add new features or content. For instance, in computer software, maintenance releases are typically intended to solve minor problems, typi ...
s, 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. Perl 5.000 was released on October 17, 1994. It was a nearly complete rewrite of the interpreter, and it added many new features to the language, including
objects Object may refer to: General meanings * Object (philosophy), a thing, being, or concept ** Object (abstract), an object which does not exist at any particular time or place ** Physical object, an identifiable collection of matter * Goal, an ...
, references, lexical (my) variables, and
modules Broadly speaking, modularity is the degree to which a system's components may be separated and recombined, often with the benefit of flexibility and variety in use. The concept of modularity is used primarily to reduce complexity by breaking a s ...
. 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
subroutine In computer programming, a function or subroutine is a sequence of program instructions that performs a specific task, packaged as a unit. This unit can then be used in programs wherever that particular task should be performed. Functions may ...
s that behaved like Perl builtins. Perl 5.003 was released June 25, 1996, as a security release. 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 The Comprehensive Perl Archive Network (CPAN) is a repository of over 250,000 software modules and accompanying documentation for 39,000 distributions, written in the Perl programming language by over 12,000 contributors. ''CPAN'' can denote eit ...
(CPAN) was established as a
repository Repository may refer to: Archives and online databases * Content repository, a database with an associated set of data management tools, allowing application-independent access to the content * Disciplinary repository (or subject repository), an ...
for the Perl language and
Perl module A Perl module is a discrete component of software for the Perl programming language. Technically, it is a particular set of conventions for using Perl's package mechanism that has become universally adopted. A module defines its source code to ...
s; 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. 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 CGI.pm is a large and once widely used Perl module for programming Common Gateway Interface (CGI) web applications, providing a consistent API for receiving and processing user input. There are also functions for producing HTML or XHTML output ...
module, which contributed to Perl's popularity as a CGI scripting language. Perl 5.004 added support for
Microsoft Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...
, Plan 9,
QNX QNX ( or ) is a commercial Unix-like real-time operating system, aimed primarily at the embedded systems market. QNX was one of the first commercially successful microkernel operating systems. The product was originally developed in the early ...
, and
AmigaOS AmigaOS is a family of proprietary native operating systems of the Amiga and AmigaOne personal computers. It was developed first by Commodore International and introduced with the launch of the first Amiga, the Amiga 1000, in 1985. Early versions ...
. Perl 5.005 was released on July 22, 1998. This release included several enhancements to the
regex A regular expression (shortened as regex or regexp; sometimes referred to as rational expression) is a sequence of characters that specifies a search pattern in text. Usually such patterns are used by string-searching algorithms for "find" or ...
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.


2000–2020

Perl 5.6 was released on March 22, 2000. Major changes included
64-bit In computer architecture, 64-bit integers, memory addresses, or other data units are those that are 64 bits wide. Also, 64-bit CPUs and ALUs are those that are based on processor registers, address buses, or data buses of that size. A compu ...
support,
Unicode Unicode, formally The Unicode Standard,The formal version reference is is an information technology Technical standard, standard for the consistent character encoding, encoding, representation, and handling of Character (computing), text expre ...
string representation, support for files over 2 GiB, and the "our" keyword. 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. 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, 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. 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. 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 The Pug is a breed of dog originally from China, with physically distinctive features of a wrinkly, short-muzzled face and curled tail. The breed has a fine, glossy coat that comes in a variety of colors, most often light brown (fawn) or bla ...
, a Perl 6 interpreter written in
Haskell Haskell () is a general-purpose, statically-typed, purely functional programming language with type inference and lazy evaluation. Designed for teaching, research and industrial applications, Haskell has pioneered a number of programming lan ...
. This was the first concerted effort toward making Perl 6 a reality. This effort stalled in 2006. 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 Parrots, also known as psittacines (), are birds of the roughly 398 species in 92 genera comprising the order Psittaciformes (), found mostly in tropical and subtropical regions. The order is subdivided into three superfamilies: the Psittacoide ...
, 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. 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. 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'' (~~). 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 Parrot was a register-based process virtual machine designed to run dynamic languages efficiently. It is possible to compile Parrot assembly language and Parrot intermediate representation (PIR, an intermediate language) to Parrot bytecode an ...
. 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. 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 The year 2038 problem (also known as Y2038, Y2K38, or the Epochalypse) is a time formatting bug in computer systems with representing times after 03:14:07 UTC on 19 January 2038. The problem exists in systems which measure Unix time â ...
compliance, regex conversion overloading,
DTrace DTrace is a comprehensive dynamic tracing framework originally created by Sun Microsystems for troubleshooting kernel and application problems on production systems in real time. Originally developed for Solaris, it has since been released und ...
support, and
Unicode Unicode, formally The Unicode Standard,The formal version reference is is an information technology Technical standard, standard for the consistent character encoding, encoding, representation, and handling of Character (computing), text expre ...
5.2. On May 14, 2011, Perl 5.14 was released with JSON support built-in. 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. Perl 5.16 also updates the core to support
Unicode Unicode, formally The Unicode Standard,The formal version reference is is an information technology Technical standard, standard for the consistent character encoding, encoding, representation, and handling of Character (computing), text expre ...
6.1. 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. 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, using consistent random number generator. Some observers credit the release of Perl 5.10 with the start of the Modern Perl movement. 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. While the book "Modern Perl" may be the most visible standard-bearer of this idea, other groups such as the Enlightened Perl Organization 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, ' by Stevan Little and friends, ' by the Perl11 team under Reini Urban, ' by , and '','' a Kickstarter project led by Will Braswell and affiliated with the Perll11 project.


2020 onward

In June 2020, Perl 7 was announced as the successor to Perl 5. Perl 7 was to initially be based on Perl 5.32 with a release expected in first half of 2021, and release candidates sooner. This plan was revised in May 2021, without any release timeframe or version of Perl 5 for use as a baseline specified. 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.


Symbols


Camel

''Programming Perl'', published by O'Reilly Media, features a picture of a
dromedary camel The dromedary (''Camelus dromedarius'' or ;), also known as the dromedary camel, Arabian camel, or one-humped camel, is a large even-toed ungulate, of the genus ''Camelus'', with one hump on its back. It is the tallest of the three species of ...
on the cover and is commonly called the "Camel Book". This image has become an unofficial symbol of Perl as well as a general
hacker A hacker is a person skilled in information technology who uses their technical knowledge to achieve a goal or overcome an obstacle, within a computerized system by non-standard means. Though the term ''hacker'' has become associated in popu ...
emblem, appearing on T-shirts and other clothing items. O'Reilly owns the image as a
trademark A trademark (also written trade mark or trade-mark) is a type of intellectual property consisting of a recognizable sign, design, or expression that identifies products or services from a particular source and distinguishes them from others ...
but licenses it for
non-commercial A non-commercial (also spelled noncommercial) activity is an activity that does not, in some sense, involve commerce, at least relative to similar activities that do have a commercial objective or emphasis. For example, advertising-free community ...
use, requiring only an acknowledgement and a link to www.perl.com. Licensing for commercial use is decided on a case-by-case basis. O'Reilly also provides "Programming Republic of Perl" logos for non-commercial sites and "Powered by Perl" buttons for any site that uses Perl.


Onion

The Perl Foundation The Perl Foundation (TPF) is a non-profit, 501(c)(3) organization based in Holland, Michigan. It is dedicated to the advancement of the Perl and Raku (programming language) programming languages through open discussion, collaboration, design, a ...
owns an alternative symbol, an onion, which it licenses to its subsidiaries, Perl Mongers,
PerlMonks ''PerlMonks'' is a community website covering all aspects of Perl programming and other related topics such as web applications and system administration. It is often referred to by users as 'The Monastery'. The name PerlMonks, and the general sty ...
, Perl.org, and others. The symbol is a
visual pun A visual pun is a pun involving an image or images (in addition to or instead of language), often based on a rebus. Visual puns in which the image is at odds with the inscription are common in cartoons such as ''Lost Consonants'' or ''The Far ...
on
pearl onion The pearl onion (''Allium ampeloprasum'' var. ''sectivum'' or ''A. ampeloprasum'' 'Pearl-Onion Group'), also known as button, baby or silverskin onions in the UK, is a close relative of the leek (''A. ampeloprasum'' var. ''porrum''), and may be d ...
.


Raptor

Sebastian Riedel, the creator of
Mojolicious Mojolicious is a real-time web application framework, written by Sebastian Riedel, creator of the web application framework Catalyst. Licensed as free software under the Artistic License v 2.0, it is written in the Perl programming language, and is ...
, created a logo depicting a raptor dinosaur, which is available under a CC-SA License, Version 4.0. The analogue of the raptor comes from a series of talks given by Matt S Trout beginning in 2010.


Overview

According to Wall, Perl has two slogans. The first is "
There's more than one way to do it There's more than one way to do it (TMTOWTDI or TIMTOWTDI, pronounced ''Tim Toady'') is a Perl programming motto. The language was designed with this idea in mind, in that it “doesn't try to tell the programmer how to program.” As proponents of ...
," commonly known as TMTOWTDI. The second slogan is "Easy things should be easy and hard things should be possible".


Features

The overall structure of Perl derives broadly from C. Perl is procedural in nature, with
variable Variable may refer to: * Variable (computer science), a symbolic name associated with a value and whose associated value may be changed * Variable (mathematics), a symbol that represents a quantity in a mathematical expression, as used in many ...
s, expressions,
assignment statement In computer programming, an assignment statement sets and/or re-sets the value stored in the storage location(s) denoted by a variable name; in other words, it copies a value into the variable. In most imperative programming languages, the assi ...
s,
brace Brace(s) or bracing may refer to: Medical * Orthopaedic brace, a device used to restrict or assist body movement ** Back brace, a device limiting motion of the spine *** Milwaukee brace, a kind of back brace used in the treatment of spinal cur ...
-delimited
block Block or blocked may refer to: Arts, entertainment and media Broadcasting * Block programming, the result of a programming strategy in broadcasting * W242BX, a radio station licensed to Greenville, South Carolina, United States known as ''96.3 ...
s,
control structure In computer science, control flow (or flow of control) is the order in which individual statements, instructions or function calls of an imperative program are executed or evaluated. The emphasis on explicit control flow distinguishes an ''imp ...
s, and
subroutine In computer programming, a function or subroutine is a sequence of program instructions that performs a specific task, packaged as a unit. This unit can then be used in programs wherever that particular task should be performed. Functions may ...
s. Perl also takes features from shell programming. All variables are marked with leading
sigils A sigil () is a type of symbol used in magic. The term has usually referred to a pictorial signature of a deity or spirit. In modern usage, especially in the context of chaos magic, sigil refers to a symbolic representation of the practitione ...
, which allow variables to be
interpolated In the mathematical field of numerical analysis, interpolation is a type of estimation, a method of constructing (finding) new data points based on the range of a discrete set of known data points. In engineering and science, one often has a n ...
directly into
strings String or strings may refer to: *String (structure), a long flexible structure made from threads twisted together, which is used to tie, bind, or hang other objects Arts, entertainment, and media Films * ''Strings'' (1991 film), a Canadian anim ...
. 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 /code>). 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 An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...
facilities. Perl takes hashes ("associative arrays") from
AWK AWK (''awk'') is a domain-specific language designed for text processing and typically used as a data extraction and reporting tool. Like sed and grep, it is a filter, and is a standard feature of most Unix-like operating systems. The AWK lang ...
and
regular expression A regular expression (shortened as regex or regexp; sometimes referred to as rational expression) is a sequence of characters that specifies a search pattern in text. Usually such patterns are used by string-searching algorithms for "find" ...
s from
sed sed ("stream editor") is a Unix utility that parses and transforms text, using a simple, compact programming language. It was developed from 1973 to 1974 by Lee E. McMahon of Bell Labs, and is available today for most operating systems. sed w ...
. These simplify many parsing, text-handling, and data-management tasks. Shared with Lisp is the implicit
return Return may refer to: In business, economics, and finance * Return on investment (ROI), the financial gain after an expense. * Rate of return, the financial term for the profit or loss derived from an investment * Tax return, a blank document or t ...
of the last value in a block, and all statements are also expressions which can be used in larger expressions themselves. Perl 5 added features that support complex
data structure In computer science, a data structure is a data organization, management, and storage format that is usually chosen for efficient access to data. More precisely, a data structure is a collection of data values, the relationships among them, a ...
s,
first-class function In computer science, a programming language is said to have first-class functions if it treats functions as first-class citizens. This means the language supports passing functions as arguments to other functions, returning them as the values from ...
s (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 directive In computer programming, a directive or pragma (from "pragmatic") is a language construct that specifies how a compiler (or other translator) should process its input. Directives are not part of the grammar of a programming language, and may vary ...
s (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." All versions of Perl do automatic data-typing and automatic
memory management Memory management is a form of resource management applied to computer memory. The essential requirement of memory management is to provide ways to dynamically allocate portions of memory to programs at their request, and free it for reuse when ...
. 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 conversion In computer science, type conversion, type casting, type coercion, and type juggling are different ways of changing an expression from one data type to another. An example would be the conversion of an integer value into a floating point valu ...
s — for example, conversions from number to string — are done automatically at
run time Run(s) or RUN may refer to: Places * Run (island), one of the Banda Islands in Indonesia * Run (stream), a stream in the Dutch province of North Brabant People * Run (rapper), Joseph Simmons, now known as "Reverend Run", from the hip-hop group ...
; 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 In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs that ...
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. 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 In computer programming, a type system is a logical system comprising a set of rules that assigns a property called a type to every "term" (a word, phrase, or other set of symbols). Usually the terms are various constructs of a computer progra ...
; strings, lists, and hashes; regular expressions;
introspection Introspection is the examination of one's own conscious thoughts and feelings. In psychology, the process of introspection relies on the observation of one's mental state, while in a spiritual context it may refer to the examination of one's s ...
; and an eval() function. Perl follows the theory of "no built-in limits," an idea similar to the Zero One Infinity rule. Wall was trained as a linguist, and the design of Perl is very much informed by
linguistic Linguistics is the scientific study of human language. It is called a scientific study because it entails a comprehensive, systematic, objective, and precise analysis of all aspects of language, particularly its nature and structure. Linguis ...
principles. Examples include
Huffman coding In computer science and information theory, a Huffman code is a particular type of optimal prefix code that is commonly used for lossless data compression. The process of finding or using such a code proceeds by means of Huffman coding, an algo ...
(common constructions should be short), good end-weighting (the important information should come first), and a large collection of
language primitive In computing, language primitives are the simplest elements available in a programming language. A primitive is the smallest 'unit of processing' available to a programmer of a given machine, or can be an atomic element of an expression in a la ...
s. Perl favors language constructs that are concise and natural for humans to write, even where they complicate the Perl interpreter. Perl's
syntax In linguistics, syntax () is the study of how words and morphemes combine to form larger units such as phrases and sentences. Central concerns of syntax include word order, grammatical relations, hierarchical sentence structure ( constituency) ...
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 a language such as Lisp, where the same basic syntax, composed of simple and universal symbolic expressions, is used for all purposes. Perl does not enforce any particular
programming paradigm Programming paradigms are a way to classify programming languages based on their features. Languages can be classified into multiple paradigms. Some paradigms are concerned mainly with implications for the execution model of the language, suc ...
( procedural,
object-oriented Object-oriented programming (OOP) is a programming paradigm based on the concept of " objects", which can contain data and code. The data is in the form of fields (often known as attributes or ''properties''), and the code is in the form of p ...
, functional, or others) 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 is not a tidy language. It includes many features, tolerates exceptions to its rules, and employs
heuristics A heuristic (; ), or heuristic technique, is any approach to problem solving or self-discovery that employs a practical method that is not guaranteed to be optimal, perfect, or rational, but is nevertheless sufficient for reaching an immediate, ...
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." No written
specification A specification often refers to a set of documented requirements to be satisfied by a material, design, product, or service. A specification is often a type of technical standard. There are different types of technical or engineering specificati ...
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, and several projects aim to implement some or all of the specification.


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 cPanel is a web hosting control panel software developed by cPanel, LLC. It provides a graphical interface (GUI) and automation tools designed to simplify the process of hosting a web site to the website owner or the "end user". It enables admin ...
,
Slash Slash may refer to: * Slash (punctuation), the "/" character Arts and entertainment Fictional characters * Slash (Marvel Comics) * Slash (''Teenage Mutant Ninja Turtles'') Music * Harry Slash & The Slashtones, an American rock band * Nash ...
,
Bugzilla Bugzilla is a web-based general-purpose bug tracking system and testing tool originally developed and used by the Mozilla project, and licensed under the Mozilla Public License. Released as open-source software by Netscape Communications in 199 ...
, RT,
TWiki TWiki is a Perl-based structured wiki application, typically used to run a collaboration platform, knowledge or document management system, a knowledge base, or team portal. Users can create wiki pages using the TWiki Markup Language, and dev ...
, and
Movable Type Movable type (US English; moveable type in British English) is the system and technology of printing and typography that uses movable components to reproduce the elements of a document (usually individual alphanumeric characters or punctuatio ...
; high-traffic websites that use Perl extensively include
Priceline.com Priceline.com is an online travel agency for finding discount rates for travel-related purchases such as airline tickets and hotel stays. The company facilitates the provision of travel services from its suppliers to its clients. Priceline.com ...
,
Craigslist Craigslist (stylized as craigslist) is an American classified advertisements website with sections devoted to jobs, housing, for sale, items wanted, services, community service, gigs, résumés, and discussion forums. Craig Newmark began the ...
,
IMDb IMDb (an abbreviation of Internet Movie Database) is an online database of information related to films, television series, home videos, video games, and streaming content online – including cast, production crew and personal biographies, ...
,
LiveJournal LiveJournal (russian: Живой Đ–Ńрнал), stylised as LiVEJOURNAL, is a Russian-owned social networking service where users can keep a blog, journal, or diary. American programmer Brad Fitzpatrick started LiveJournal on April 15, 1999, a ...
,
DuckDuckGo DuckDuckGo (DDG) is an internet search engine that emphasizes protecting searchers' privacy and avoiding the filter bubble of personalized search results. DuckDuckGo does not show search results from content farms. It uses various APIs o ...
,
Slashdot ''Slashdot'' (sometimes abbreviated as ''/.'') is a social news website that originally advertised itself as "News for Nerds. Stuff that Matters". It features news stories concerning science, technology, and politics that are submitted and eval ...
and
Ticketmaster Ticketmaster Entertainment, Inc. is an American ticket sales and distribution company based in Beverly Hills, California with operations in many countries around the world. In 2010, it merged with Live Nation under the name Live Nation Enter ...
. It is also an optional component of the popular
LAMP Lamp, Lamps or LAMP may refer to: Lighting * Oil lamp, using an oil-based fuel source * Kerosene lamp, using kerosene as a fuel * Electric lamp, or light bulb, a replaceable component that produces light from electricity * Light fixture, or li ...
technology stack for
Web development Web development is the work involved in developing a website for the Internet (World Wide Web) or an intranet (a private network). Web development can range from developing a simple single static page of plain text to complex web applications ...
, in lieu of
PHP PHP is a general-purpose scripting language geared toward web development. It was originally created by Danish-Canadian programmer Rasmus Lerdorf in 1993 and released in 1995. The PHP reference implementation is now produced by The PHP Group. ...
or
Python Python may refer to: Snakes * Pythonidae, a family of nonvenomous snakes found in Africa, Asia, and Australia ** ''Python'' (genus), a genus of Pythonidae found in Africa and Asia * Python (mythology), a mythical serpent Computing * Python (pro ...
. Perl is used extensively as a
system programming language A system programming language is a programming language used for system programming; such languages are designed for writing system software, which usually requires different development approaches when compared with application software. Edsger W ...
in the Debian
Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which ...
distribution. Perl is often used as a
glue language A scripting language or script language is a programming language that is used to manipulate, customize, and automate the facilities of an existing system. Scripting languages are usually interpreted at runtime rather than compiled. A scripting ...
, tying together systems and interfaces that were not specifically designed to interoperate, and for "
data munging Data wrangling, sometimes referred to as data munging, is the process of transforming and mapping data from one " raw" data form into another format with the intent of making it more appropriate and valuable for a variety of downstream purposes ...
," 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 administrator A system administrator, or sysadmin, or admin is a person who is responsible for the upkeep, configuration, and reliable operation of computer systems, especially multi-user computers, such as servers. The system administrator seeks to en ...
s, particularly because short programs, often called "
one-liner program In computer programming, a one-liner program originally was textual input to the command-line of an operating system shell that performed some function in just one line of input. In the present day, a one-liner can be * an expression written in t ...
s," can be entered and run on a single
command line A command-line interpreter or command-line processor uses a command-line interface (CLI) to receive commands from a user in the form of lines of text. This provides a means of setting parameters for the environment, invoking executables and pro ...
. Perl code can be made portable across
Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...
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. Perl/Tk and
wxPerl As shown in the table below, wxWidgets has a range of bindings for various programming language A programming language is a system of notation for writing computer programs. Most programming languages are text-based formal languages, but the ...
are commonly used to add
graphical user interface The GUI ( "UI" by itself is still usually pronounced . or ), graphical user interface, is a form of user interface that allows users to interact with electronic devices through graphical icons and audio indicator such as primary notation, inste ...
s 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. , 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 Character encoding is the process of assigning numbers to Graphics, graphical character (computing), characters, especially the written characters of Language, human language, allowing them to be Data storage, stored, Data communication, transmi ...
tables). The interpreter has an object-oriented architecture. All of the elements of the Perl language—scalars, arrays, hashes, coderefs,
file handle In Unix and Unix-like computer operating systems, a file descriptor (FD, less frequently fildes) is a process-unique identifier ( handle) for a file or other input/output resource, such as a pipe or network socket. File descriptors typically hav ...
s—are represented in the interpreter by C structs. Operations on these structs are defined by a large collection of macros,
typedef typedef is a reserved keyword in the programming languages C, C++, and Objective-C. It is used to create an additional name (''alias'') for another data type, but does not create a new type, except in the obscure case of a qualified typedef of ...
s, and functions; these constitute the Perl C
API An application programming interface (API) is a way for two or more computer programs to communicate with each other. It is a type of software interface, offering a service to other pieces of software. A document or standard that describes how ...
. The Perl API can be bewildering to the uninitiated, but its entry points follow a consistent
naming scheme In computing, naming schemes are often used for objects connected into computer networks. Naming schemes in computing Server naming is a common tradition. It makes it more convenient to refer to a machine by name than by its IP address. The CIA n ...
, which provides guidance to those who use it. The life of a Perl interpreter divides broadly into a compile phase and a run phase. 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. 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 In some programming languages, eval , short for the English evaluate, is a function which evaluates a string as though it were an expression in the language, and returns a result; in others, it executes multiple lines of code as though they had ...
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 Syntax tree may refer to: * Abstract syntax tree, used in computer science * Concrete syntax tree A parse tree or parsing tree or derivation tree or concrete syntax tree is an ordered, rooted tree that represents the syntactic structure of a str ...
. 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 Peephole optimization is an optimization technique performed on a small set of compiler-generated instructions; the small set is known as the peephole or window. Peephole optimization involves changing the small set of instructions to an equiva ...
is also performed. Perl has a
Turing-complete In computability theory, a system of data-manipulation rules (such as a computer's instruction set, a programming language, or a cellular automaton) is said to be Turing-complete or computationally universal if it can be used to simulate any ...
grammar In linguistics, the grammar of a natural language is its set of structure, structural constraints on speakers' or writers' composition of clause (linguistics), clauses, phrases, and words. The term can also refer to the study of such constraint ...
because parsing can be affected by run-time code executed during the compile phase. Therefore, Perl cannot be parsed by a straight
Lex Lex or LEX may refer to: Arts and entertainment * ''Lex'', a daily featured column in the ''Financial Times'' Games * Lex, the mascot of the word-forming puzzle video game ''Bookworm'' * Lex, the protagonist of the word-forming puzzle video ga ...
/
Yacc Yacc (Yet Another Compiler-Compiler) is a computer program for the Unix operating system developed by Stephen C. Johnson. It is a Look Ahead Left-to-Right Rightmost Derivation (LALR) parser generator, generating a LALR parser (the part of a co ...
lexer/
parser Parsing, syntax analysis, or syntactic analysis is the process of analyzing a string of symbols, either in natural language, computer languages or data structures, conforming to the rules of a formal grammar. The term ''parsing'' comes from Lat ...
combination. Instead, the interpreter implements its own lexer, which coordinates with a modified GNU bison parser to resolve ambiguities in the language. It is often said that "Only perl can parse Perl," 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 computability theory, the halting problem is the problem of determining, from a description of an arbitrary computer program and an input, whether the program will finish running, or continue to run forever. Alan Turing proved in 1936 that a ...
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. 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 Adam Thomas Kennedy (born January 10, 1976) is an American former professional baseball second baseman. He played in Major League Baseball (MLB) for the St. Louis Cardinals, Oakland Athletics, Los Angeles Angels of Anaheim, Washington National ...
'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'," which was later proved. 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 bug A software bug is an error, flaw or fault in the design, development, or operation of computer software that causes it to produce an incorrect or unexpected result, or to behave in unintended ways. The process of finding and correcting bugs i ...
s; 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.


Availability

Perl is
dual licensed Multi-licensing is the practice of distributing software under two or more different sets of terms and conditions. This may mean multiple different software licenses or sets of licenses. Prefixes may be used to indicate the number of licenses ...
under both the
Artistic License Artistic license (alongside more contextually-specific derivative terms such as poetic license, historical license, dramatic license, and narrative license) refers to deviation from fact or form for artistic purposes. It can include the alterat ...
1.0Artistic
- file on the Perl 5 git repository
and the
GNU General Public License The GNU General Public License (GNU GPL or simply GPL) is a series of widely used free software licenses that guarantee end users the Four Freedoms (Free software), four freedoms to run, study, share, and modify the software. The license was th ...
. Distributions are available for most
operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...
s. It is particularly prevalent on
Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and ot ...
and
Unix-like A Unix-like (sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-li ...
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 In computing, source code, or simply code, is any collection of code, with or without comments, written using a human-readable programming language, usually as plain text. The source code of a program is specially designed to facilitate the wo ...
on all
POSIX The Portable Operating System Interface (POSIX) is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems. POSIX defines both the system- and user-level application programming inter ...
-compliant, or otherwise-Unix-compatible, platforms. Because of unusual changes required for the classic Mac OS environment, a special port called MacPerl was shipped independently. The
Comprehensive Perl Archive Network The Comprehensive Perl Archive Network (CPAN) is a repository of over 250,000 software modules and accompanying documentation for 39,000 distributions, written in the Perl programming language by over 12,000 contributors. ''CPAN'' can denote eit ...
carries a complete list of supported platforms with links to the distributions available on each. CPAN is also the source for publicly available Perl modules that are not part of the core Perl distribution.


Windows

Users of
Microsoft Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...
typically install one of the native binary distributions of Perl for Win32, most commonly
Strawberry Perl Strawberry Perl is a distribution of the Perl programming language for the Microsoft Windows platform. Additionally, strawberry contains a fully featured Mingw-w64 C/C++ compiler with many libraries included. While most other distributions rely o ...
or
ActivePerl ActivePerl is a distribution of Perl from ActiveState (formerly part of Sophos) for Windows, macOS, Linux, Solaris, AIX and HP-UX. A few main editions are available, including: Community (free, for development use only), and several paid tiers u ...
. 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. ActivePerl is a closed-source distribution from
ActiveState ActiveState Software Inc is a Canadian software company headquartered in Vancouver, British Columbia. It develops, sells, and supports cross-platform development tools for dynamic languages such as Perl, PHP, Python, Ruby, and Tcl, as well ...
that has regular releases that track the core Perl releases. The distribution previously included the Perl package manager (PPM), 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. Included also is
PerlScript ActivePerl is a distribution of Perl from ActiveState (formerly part of Sophos) for Windows, macOS, Linux, Solaris, AIX and HP-UX. A few main editions are available, including: Community (free, for development use only), and several paid tier ...
, a
Windows Script Host The Microsoft Windows Script Host (WSH) (formerly named Windows Scripting Host) is an automation technology for Microsoft Windows operating systems that provides scripting abilities comparable to batch files, but with a wider range of supported fe ...
(WSH) engine implementing the Perl language. Visual Perl is an ActiveState tool that adds Perl to the Visual Studio .NET development suite. A
VBScript VBScript (''"Microsoft Visual Basic Scripting Edition"'') is an Active Scripting language developed by Microsoft that is modeled on Visual Basic. It allows Microsoft Windows system administrators to generate powerful tools for managing computers ...
-to-Perl converter, as well as a Perl compiler for Windows, and converters of
awk AWK (''awk'') is a domain-specific language designed for text processing and typically used as a data extraction and reporting tool. Like sed and grep, it is a filter, and is a standard feature of most Unix-like operating systems. The AWK lang ...
and
sed sed ("stream editor") is a Unix utility that parses and transforms text, using a simple, compact programming language. It was developed from 1973 to 1974 by Lee E. McMahon of Bell Labs, and is available today for most operating systems. sed w ...
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 Komodo IDE is an integrated development environment (IDE) for dynamic programming languages. It was introduced in May 2000. Many of Komodo's features are derived from an embedded Python interpreter. Komodo IDE uses the Mozilla and Scintilla cod ...
and all but the first on the Unix/Linux/Posix variant thereof in 2002 and subsequently. 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. 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. A Perl executable is included in several Windows Resource kits in the directory with other scripting tools. Implementations of Perl come with the
MKS Toolkit MKS Toolkit is a software package produced and maintained by PTC that provides a Unix-like environment for scripting, connectivity and porting Unix and Linux software to Microsoft Windows. It was originally created for MS-DOS, and OS/2 versions ...
,
Interix Interix was an optional, POSIX-conformant Unix subsystem for Windows NT operating systems. Interix was a component of Windows Services for UNIX, and a superset of the Microsoft POSIX subsystem. Like the POSIX subsystem, Interix was an environment ...
(the base of earlier implementations of
Windows Services for Unix Windows Services for UNIX (SFU) is a discontinued software package produced by Microsoft which provided a Unix environment on Windows NT and some of its immediate successor operating-systems. SFU 1.0 and 2.0 used the MKS Toolkit; starting with ...
), and
UWIN UWIN is a computer software package created by David Korn which allows programs written for the operating system Unix to be built and run on Microsoft Windows with few, if any, changes. Some of the software development was subcontracted to Wipro ...
.


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 In computing, the Perl DBI (Perl Database Interface) offers a standardized way for programmers using the Perl programming language to embed database communication within their programs. The latest DBI module for Perl from CPAN can run on a range o ...
application programming interface An application programming interface (API) is a way for two or more computer programs to communicate with each other. It is a type of software interface, offering a service to other pieces of software. A document or standard that describes how t ...
(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 The HyperText Markup Language or HTML is the standard markup language for documents designed to be displayed in a web browser. It can be assisted by technologies such as Cascading Style Sheets (CSS) and scripting languages such as JavaSc ...
,
JavaScript JavaScript (), often abbreviated as JS, is a programming language that is one of the core technologies of the World Wide Web, alongside HTML and CSS. As of 2022, 98% of websites use JavaScript on the client side for webpage behavior, of ...
, and SQL in a
here document In computing, a here document (here-document, here-text, heredoc, hereis, here-string or here-script) is a file literal or input stream literal: it is a section of a source code file that is treated as if it were a separate file. The term is also ...
). The use of Perl
variable interpolation In computer programming, string interpolation (or variable interpolation, variable substitution, or variable expansion) is the process of evaluating a string literal containing one or more placeholders, yielding a result in which the placeholders ...
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 set A data set (or dataset) is a collection of data. In the case of tabular data, a data set corresponds to one or more database tables, where every column of a table represents a particular variable, and each row corresponds to a given record of the ...
s from each SQL query, allows a high-level mechanism for handling large amounts of data for post-processing by a Perl subprogram. In early versions of Perl, database interfaces were created by relinking the interpreter with a
client-side Client-side refers to operations that are performed by the client in a client–server relationship in a computer network. General concepts Typically, a client is a computer application, such as a web browser, that runs on a user's local comput ...
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. 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 The American National Standards Institute (ANSI ) is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organi ...
SQL databases. DBI provides caching for database handles and queries, which can greatly improve performance in long-lived execution environments such as
mod_perl Mod, MOD or mods may refer to: Places * Modesto City–County Airport, Stanislaus County, California, US Arts, entertainment, and media Music * Mods (band), a Norwegian rock band * M.O.D. (Method of Destruction), a band from New York City, US ...
, helping high-volume systems avert load spikes as in the
Slashdot effect The Slashdot effect, also known as slashdotting, occurs when a popular website links to a smaller website, causing a massive increase in traffic. This overloads the smaller site, causing it to slow down or even temporarily become unavailable. Thi ...
. In modern Perl applications, especially those written using
web framework A web framework (WF) or web application framework (WAF) is a software framework that is designed to support the development of web applications including web services, web resources, and web APIs. Web frameworks provide a standard way to build and ...
s such as
Catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
, the DBI module is often used indirectly via object-relational mappers such as DBIx::Class, Class::DBI or Rose::DB::Object that generate SQL queries and handle data transparently to the application author.


Comparative performance

The Computer Language Benchmarks Game The Computer Language Benchmarks Game (formerly called The Great Computer Language Shootout) is a free software project for comparing how a given subset of simple algorithms can be implemented in various popular programming languages. The project ...
compares the performance of implementations of typical programming problems in several programming languages. 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. 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. Unlike Java, Python, and Ruby, Perl has only experimental support for pre-compiling. Therefore, Perl programs pay this overhead penalty on every execution. The run phase of typical programs is long enough that
amortized In computer science, amortized analysis is a method for analyzing a given algorithm's complexity, or how much of a resource, especially time or memory, it takes to execute. The motivation for amortized analysis is that looking at the worst-case ...
startup time is not substantial, but benchmarks that measure very short execution times are likely to be skewed due to this overhead. A number of tools have been introduced to improve this situation. The first such tool was Apache's
mod_perl Mod, MOD or mods may refer to: Places * Modesto City–County Airport, Stanislaus County, California, US Arts, entertainment, and media Music * Mods (band), a Norwegian rock band * M.O.D. (Method of Destruction), a band from New York City, US ...
, which sought to address one of the most-common reasons that small Perl programs were invoked rapidly: CGI Web development.
ActivePerl ActivePerl is a distribution of Perl from ActiveState (formerly part of Sophos) for Windows, macOS, Linux, Solaris, AIX and HP-UX. A few main editions are available, including: Community (free, for development use only), and several paid tiers u ...
, via Microsoft
ISAPI The Internet Server Application Programming Interface (ISAPI) is an N-tier API of Internet Information Services (IIS), Microsoft's collection of Windows-based web server services. The most prominent application of IIS and ISAPI is Microsoft's we ...
, provides similar performance improvements. 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 Bytecode (also called portable code or p-code) is a form of instruction set designed for efficient execution by a software interpreter. Unlike human-readable source code, bytecodes are compact numeric codes, constants, and references (norma ...
interpretation, reference-counting memory management, and dynamic type-checking.


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.


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, followed by Perl 5.14.1 (released on June 17, 2011), Perl 5.16.1 (released on August 9, 2012.), 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. 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.


Raku (Perl 6)

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, which submitted more than 300 RFCs. 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''. , the developing specification of Perl 6 was encapsulated in design documents called Synopsesnumbered to correspond to Apocalypses. Thesis work by
Bradley M. Kuhn Bradley M. Kuhn (born 1973) is a free software activist from the United States. Kuhn is currently Policy Fellow and Hacker-in-Residence of the Software Freedom Conservancy, having previously been executive director. Until 2010 he was the FLOSS C ...
, overseen by Wall, considered the possible use of the Java virtual machine as a runtime for Perl. 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 In computing, a virtual machine (VM) is the virtualization/emulation of a computer system. Virtual machines are based on computer architectures and provide functionality of a physical computer. Their implementations may involve specialized hardw ...
called
Parrot Parrots, also known as psittacines (), are birds of the roughly 398 species in 92 genera comprising the order Psittaciformes (), found mostly in tropical and subtropical regions. The order is subdivided into three superfamilies: the Psittacoide ...
. This will mean that other languages targeting the Parrot will gain native access to
CPAN The Comprehensive Perl Archive Network (CPAN) is a repository of over 250,000 software modules and accompanying documentation for 39,000 distributions, written in the Perl programming language by over 12,000 contributors. ''CPAN'' can denote eit ...
, allowing some level of cross-language development. In 2005, Audrey Tang created the
Pugs The Pug is a breed of dog originally from China, with physically distinctive features of a wrinkly, short-muzzled face and curled tail. The breed has a fine, glossy coat that comes in a variety of colors, most often light brown (fawn) or bla ...
project, an implementation of Perl 6 in
Haskell Haskell () is a general-purpose, statically-typed, purely functional programming language with type inference and lazy evaluation. Designed for teaching, research and industrial applications, Haskell has pioneered a number of programming lan ...
. 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 Libera Chat, stylized Libera.Chat, is an IRC network for free and open source software projects. It was founded on 19 May 2021 by former Freenode staff members, after Freenode was taken over by Andrew Lee, founder of Private Internet Access ...
#raku IRC channel. Many
functional programming In computer science, functional programming is a programming paradigm where programs are constructed by applying and composing functions. It is a declarative programming paradigm in which function definitions are trees of expressions that ...
influences were absorbed by the Perl 6 design team. In 2012, Perl 6 development was centered primarily on two compilers: #
Rakudo Rakudo is a Raku compiler targeting MoarVM, and the Java Virtual Machine, that implements the Raku specification. It is currently the only major Raku compiler in active development. Originally developed within the Parrot project, the Rakudo sour ...
, an implementation running on the Parrot virtual machine and the Java virtual machine. # Niecza, which targets the Common Language Runtime. In 2013,
MoarVM MoarVM (''Metamodel On A Runtime Virtual Machine'') is a virtual machine built for the 6model object system. It is being built to serve as yet another VM backend for Raku. MoarVM was created to allow for greater efficiency than Parrot by havin ...
(“Metamodel On A Runtime”), a C language-based
virtual machine In computing, a virtual machine (VM) is the virtualization/emulation of a computer system. Virtual machines are based on computer architectures and provide functionality of a physical computer. Their implementations may involve specialized hardw ...
designed primarily for Rakudo was announced. In October 2019, Perl 6 was renamed to Raku. only the Rakudo implementation and MoarVM are under active development, and other virtual machines, such as the Java Virtual Machine and
JavaScript JavaScript (), often abbreviated as JS, is a programming language that is one of the core technologies of the World Wide Web, alongside HTML and CSS. As of 2022, 98% of websites use JavaScript on the client side for webpage behavior, of ...
, are supported.


Perl 7

Perl 7 was announced on 24 June 2020 at "The Perl Conference in the Cloud" as the successor to Perl 5. Based on Perl 5.32, Perl 7 was planned to be
backward compatible Backward compatibility (sometimes known as backwards compatibility) is a property of an operating system, product, or technology that allows for interoperability with an older legacy system, or with input designed for such a system, especially in ...
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.


Perl community

Perl's culture and community has developed alongside the language itself.
Usenet Usenet () is a worldwide distributed discussion system available on computers. It was developed from the general-purpose Unix-to-Unix Copy (UUCP) dial-up network architecture. Tom Truscott and Jim Ellis conceived the idea in 1979, and it was ...
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.


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. 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 Just another Perl hacker, or JAPH, typically refers to a Perl program that prints "Just another Perl hacker," (the comma is canonical but is occasionally omitted). Short JAPH programs are often used as signatures in online forums, or as T-shirt ...
" (JAPH) programs are 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 as developed by Schwartz includes the comma at the end, although this is often omitted.


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 Golf is a club-and-ball sport in which players use various clubs to hit balls into a series of holes on a course in as few strokes as possible. Golf, unlike most ball games, cannot and does not use a standardized playing area, and coping wi ...
players seek to take as few shots as possible in a round. The phrase's first use 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
JAPH Just another Perl hacker, or JAPH, typically refers to a Perl program that prints "Just another Perl hacker," (the comma is canonical but is occasionally omitted). Short JAPH programs are often used as signature block, signatures in online Intern ...
s 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. In subsequent years, the term "
code golf Code golf is a type of recreational computer programming competition in which participants strive to achieve the shortest possible source code that solves a certain problem.Code Golf Stack ExchangeAbout code-golf Retrieved 2021-12-21. Code golf ch ...
" has been applied to the pastime in other languages. A Perl Golf Apocalypse was held at Perl Conference 4.0 in Monterey, California in July 2000.


Obfuscation

As with C,
obfuscated code In software development, obfuscation is the act of creating source or machine code that is difficult for humans or computers to understand. Like obfuscation in natural language, it may use needlessly roundabout expressions to compose statemen ...
competitions were a well known pastime in the late 1990s. The
Obfuscated Perl Contest The Obfuscated Perl Contest was a competition for programmers of Perl which was held annually between 1996 and 2000. Entrants to the competition aimed to write "devious, inhuman, disgusting, amusing, amazing, and bizarre Perl code". It was run by ...
was a competition held by
The Perl Journal ''The'' () is a grammatical Article (grammar), article in English language, English, denoting persons or things already mentioned, under discussion, implied or otherwise presumed familiar to listeners, readers, or speakers. It is the definite ...
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.


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 "Black Perl" is a code poem written using the Perl programming language. It was posted anonymously to Usenet on April 1, 1990, and is popular among Perl programmers as a piece of Perl poetry. Written in Perl 3, the poem is able to be executed as ...
. 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 ''PerlMonks'' is a community website covering all aspects of Perl programming and other related topics such as web applications and system administration. It is often referred to by users as 'The Monastery'. The name PerlMonks, and the general sty ...
.


Perl on IRC

A number of
IRC Internet Relay Chat (IRC) is a text-based chat system for instant messaging. IRC is designed for group communication in discussion forums, called '' channels'', but also allows one-on-one communication via private messages as well as chat an ...
channels offer support for Perl and some of its modules.


CPAN Acme

There are also many examples of code written purely for entertainment on the
CPAN The Comprehensive Perl Archive Network (CPAN) is a repository of over 250,000 software modules and accompanying documentation for 39,000 distributions, written in the Perl programming language by over 12,000 contributors. ''CPAN'' can denote eit ...
. Lingua::Romana::Perligata, for example, allows writing programs in
Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
. 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 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, which allows the program's source code to be "whitened" (i.e., all characters replaced with whitespace) and yet still work.


Example code

In older versions of Perl, one would write the
Hello World ''Hello'' is a salutation or greeting in the English language. It is first attested in writing from 1826. Early uses ''Hello'', with that spelling, was used in publications in the U.S. as early as the 18 October 1826 edition of the '' Norwich ...
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 ) 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 In electronics, noise is an unwanted disturbance in an electrical signal. Noise generated by electronic devices varies greatly as it is produced by several different effects. In particular, noise is inherent in physics, and central to the ...
" and a
write-only language In computer humor, a write-only language is a pejorative term for a programming language alleged to have syntax or semantics sufficiently dense and bizarre that any routine of significant size is too difficult to understand by other programmers an ...
by its critics. The earliest such mention was in the first edition of the book ''
Learning Perl ''Learning Perl'', also known as the llama book, is a tutorial book for the Perl programming language, and is published by O'Reilly Media. The first edition (1993) was authored solely by Randal L. Schwartz, and covered Perl 4. All subsequent edi ...
'', a Perl 4 tutorial book written by Randal L. Schwartz, 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
checksum A checksum is a small-sized block of data derived from another block of digital data for the purpose of detecting errors that may have been introduced during its transmission or storage. By themselves, checksums are often used to verify data ...
med line noise with a mission in life." He also stated that the accusation that Perl is a write-only language could be avoided by coding with "proper care". The Perl overview document ' states that the names of built-in "magic" scalar variables "look like punctuation or line noise". However, the English module provides both long and short English alternatives. ' document states that line noise in regular expressions could be mitigated using the /x modifier to add whitespace. 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. 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
gerund In linguistics, a gerund ( abbreviated ) is any of various nonfinite verb forms in various languages; most often, but not exclusively, one that functions as a noun. In English, it has the properties of both verb and noun, such as being modifiable ...
s and
prepositions Prepositions and postpositions, together called adpositions (or broadly, in traditional grammar, simply prepositions), are a class of words used to express spatial or temporal relations (''in'', ''under'', ''towards'', ''before'') or mark various ...
are a part of the
English language English is a West Germanic language of the Indo-European language family, with its earliest forms spoken by the inhabitants of early medieval England. It is named after the Angles, one of the ancient Germanic peoples that migrated to the is ...
. 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". He also stated that "Perl 6 has a coherence and a consistency that Perl 5 lacks."


See also

* Outline of Perl *
Perl Data Language Perl Data Language (abbreviated PDL) is a set of free software array programming extensions to the Perl programming language. PDL extends the data structures built into Perl, to include large multidimensional arrays, and adds functionality to m ...
* Perl Object Environment *
Plain Old Documentation Plain Old Documentation (pod) is a lightweight markup language used to document the Perl programming language as well as Perl modules and programs. Design Pod is designed to be a simple, clean language with just enough syntax to be useful. It pur ...


References


Further reading


Learning Perl
6th Edition (2011), O'Reilly. Beginner-level introduction to Perl.

1st Edition (2012), Wrox. A beginner's tutorial for those new to programming or just new to Perl.
Modern Perl
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'', . Practical Perl programming examples. * Functional programming techniques in Perl.


External links

* {{Authority control Perl, American inventions Programming languages C programming language family Cross-platform software Dynamic programming languages Dynamically typed programming languages Free compilers and interpreters Free software programmed in C High-level programming languages Multi-paradigm programming languages Object-oriented programming languages Procedural programming languages Programming languages created in 1987 Scripting languages Software using the Artistic license Text-oriented programming languages Unix programming tools Articles with example Perl code