Perl
Paradigm	Multi-paradigm
Appeared in	1987
Designed by	Larry Wall
Latest release	5. A programming paradigm is a fundamental style of Computer programming. A multi-paradigm programming language is a Programming language that supports more than one Programming paradigm. Larry Wall (born September 27, 1954) is a Programmer and Author, most widely known for his creation of the Perl Programming A software release is the distribution whether public or private of an initial or new and upgraded version of a Computer software product 10. 0/ December 18, 2007 (2007-12-18); 179 days ago
Typing discipline	Dynamic
Influenced by	AWK, BASIC, BASIC-PLUS, C, C++, Lisp, Pascal, sed, Unix shell
Influenced	Python, PHP, Ruby, ECMAScript, Dao, Windows PowerShell
OS	Cross-platform
License	GNU General Public License, Artistic License
Website	http://www.perl.org/

Perl is a dynamic programming language created by Larry Wall and first released in 1987. Events 218 BC - Second Punic War: Battle of the Trebia - Hannibal 's Carthaginian forces defeat those of the Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. In Computer science, a type system defines how a Programming language classifies values and expressions into '''types''', how it can AWK is a general purpose Programming language that is designed for processing text-based data either in files or data streams and was created at Bell Labs in the 1970s In Computer programming, BASIC (an Acronym for Beginner's All-purpose Symbolic Instruction Code) is a family of High-level programming languages BASIC-PLUS was an extended dialect of the BASIC programming language developed by Digital Equipment Corporation (DEC for use on its RSTS/E time-sharing tags please moot on the talk page first! --> In Computing, C is a general-purpose cross-platform block structured C++ (" C Plus Plus " ˌsiːˌplʌsˈplʌs is a general-purpose Programming language. Lisp (or LISP) is a family of Computer Programming languages with a long history and a distinctive fully parenthesized syntax Pascal is an influential imperative and procedural Programming language, designed in 1968/9 and published in 1970 by Niklaus Wirth as a small sed ( S tream ED itor refers to a Unix utility which (a parses text files and (b implements a Programming language which can apply textual transformations A Unix shell, is a command line shell that provides the traditional User interface for the Unix Operating system and for Unix-like Python is a general-purpose High-level programming language. Its design philosophy emphasizes programmer productivity and code readability PHP is a computer Scripting language. Originally designed for producing Dynamic web pages it has evolved to include a Command line interface capability Ruby is a dynamic, reflective, general purpose Object-oriented programming language that combines syntax inspired by Perl with Smalltalk ECMAScript is a Scripting language, standardized by Ecma International in the ECMA-262 specification. Dao is an Object-oriented Scripting language with dynamically typed variables supporting complex Data structures. Windows PowerShell is an extensible command-line shell and associated Scripting language from Microsoft An operating system (commonly abbreviated OS and O/S) is the software component of a Computer system that is responsible for the management and coordination In computing cross-platform (also known as multi-platform) is a term used to refer to Computer software or computing methods and concepts that are implemented A software license (or software licence in commonwealth usage is a Legal instrument governing the usage or redistribution of copyright protected software Artistic license (also known as dramatic license, poetic license, narrative license, licentia poetica, or simply license) is a colloquial A website (alternatively web site or Web site, a back-construction from the Proper noun World Wide Web) is a collection of Web pages This article is about a class of programming languages for the method for reducing the runtime of algorithms see Dynamic programming. Larry Wall (born September 27, 1954) is a Programmer and Author, most widely known for his creation of the Perl Programming Perl borrows features from a variety of other languages including C, shell scripting (sh), AWK, sed and Lisp. tags please moot on the talk page first! --> In Computing, C is a general-purpose cross-platform block structured A shell script is a script written for the shell, or Command line interpreter, of an Operating system. The Bourne shell, or sh, was the default Unix shell of Unix Version 7, and replaced the Thompson shell, whose executable file had the same AWK is a general purpose Programming language that is designed for processing text-based data either in files or data streams and was created at Bell Labs in the 1970s sed ( S tream ED itor refers to a Unix utility which (a parses text files and (b implements a Programming language which can apply textual transformations Lisp (or LISP) is a family of Computer Programming languages with a long history and a distinctive fully parenthesized syntax ^[1] Perl was widely adopted because it provides powerful text processing facilities without arbitrary data length limits, as were present in many Unix tools at the time. ^[2]

History

Larry Wall began work on Perl in 1987, while working as a programmer at Unisys,^[3] and released version 1. Larry Wall (born September 27, 1954) is a Programmer and Author, most widely known for his creation of the Perl Programming Unisys Corporation ( based in Blue Bell, Pennsylvania, United States, and incorporated in Delaware, is a global provider of information technology 0 to the comp. sources. misc newsgroup on December 18, 1987^[4]. A newsgroup is a Repository usually within the Usenet system for messages posted from many users in different locations Events 218 BC - Second Punic War: Battle of the Trebia - Hannibal 's Carthaginian forces defeat those of the Year 1987 ( MCMLXXXVII) was a Common year starting on Thursday (link displays 1987 Gregorian calendar) The language expanded rapidly over the next few years. Perl 2, released in 1988, featured a better regular expression engine. In Computing, regular expressions provide a concise and flexible means for identifying strings of text of interest such as particular characters words or patterns of characters Perl 3, released in 1989, added support for binary data streams.

Originally the only documentation for Perl was a single (increasingly lengthy) man page. Almost all substantial UNIX and Unix-like Operating systems have extensive documentation known as man pages (short for "manual pages" In 1991, Programming perl (known to many Perl programmers as the "Camel Book") was published, and became the de facto reference for the language. Programming Perl,ISBN 0-596-00027-8best known as the Camel Book among Programmers is a book about writing programs using the Perl programming At the same time, the Perl version number was bumped to 4, not to mark a major change in the language, but to identify the version that was documented by the book.

Perl 4 went through a series of maintenance releases, culminating in Perl 4. 036 in 1993. At that point, Larry Wall abandoned Perl 4 to begin work on Perl 5.

Initial design of Perl 5 continued into 1994. The perl5-porters mailing list was established in May 1994 to coordinate work on porting Perl 5 to different platforms. A mailing list is a collection of names and addresses used by an individual or an organization to send material to multiple recipients It remains the primary forum for development, maintenance, and porting of Perl 5. ^[5]

Perl 5 was released on October 17, 1994. Events 539 BC - King Cyrus The Great of Persia marches into the city of Babylon, releasing the Jews from almost Year 1994 ( MCMXCIV) was a Common year starting on Saturday (link will display full 1994 Gregorian calendar) It was a nearly complete rewrite of the interpreter, and added many new features to the language, including objects, references, lexical (my) variables, and modules. In Computer science, an interpreter normally means a Computer program that executes, i In Computer science, a local variable is a Variable that is given local scope. Importantly, modules provided a mechanism for extending the language without modifying the interpreter. This allowed the core interpreter to stabilize, even as it enabled ordinary Perl programmers to add new language features.

As of 2007, Perl 5 is still being actively maintained. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Important features and some essential new language constructs have been added along the way, including Unicode support, threads, improved support for object oriented programming and many other enhancements. In Computing, Unicode is an Industry standard allowing Computers to consistently represent and manipulate text expressed in most of the world's A thread in Computer science is short for a thread of execution. Object-oriented programming (OOP is a Programming paradigm that uses " objects " and their interactions to design applications and computer programs

On December 18, 2007, the 20th anniversary of Perl 1. Events 218 BC - Second Punic War: Battle of the Trebia - Hannibal 's Carthaginian forces defeat those of the Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. 0, Perl 5. 10. 0 was released. Perl 5. 10. 0 includes notable new features, which bring it closer to Perl 6, among them a new switch statement (called "given/when"), regular expressions updates, the "smart match operator" ~~, and more. Perl 6 is a planned major revision to the Perl Programming language. In Computer programming, a switch statement is a type of control statement that exists in most modern Imperative programming languages (e ^[6]

One of the most important events in Perl 5 history took place outside of the language proper, and was a consequence of its module support. On October 26, 1995, the Comprehensive Perl Archive Network (CPAN) was established as a repository for Perl modules and Perl itself. Events 740 - An Earthquake strikes Constantinople, causing much damage and death Year 1995 ( MCMXCV) was a Common year starting on Sunday. Events of 1995 CPAN is an Acronym standing for Comprehensive Perl Archive Network, an archive of over 12200 modules of software written in Perl, as well as documentation A repository is a place where Data or specimens are stored and maintained for future retrieval Modular programming is a software design technique that increases the extent to which software is composed from separate parts called modules At the time of writing, it carries over 13,500 modules by over 6,500 authors. CPAN is widely regarded as one of the greatest strengths of Perl in practice.

Name

Perl was originally named "Pearl", after the Parable of the Pearl from the Gospel of Matthew. The Parable of the Pearl or the Pearl of Great Price is a Parable told by Jesus in explaining the value of the Kingdom of Heaven, according The Gospel of Matthew (Gk Κατά Ματθαίον Ευαγγέλιον is one of the four Canonical gospels in the New Testament and is a Synoptic gospel Larry Wall wanted to give the language a short name with positive connotations; he claims that he considered (and rejected) every three- and four-letter word in the dictionary. He also considered naming it after his wife Gloria. Wall discovered the existing PEARL programming language before Perl's official release and changed the spelling of the name. PEARL, or Process and Experiment Automation Realtime Language is a Computer Programming language designed for multitasking and Real-time

The name is normally capitalized (Perl) when referring to the language and uncapitalized (perl) when referring to the interpreter program itself since Unix-like file systems are case-sensitive. Before the release of the first edition of Programming Perl, it was common to refer to the language as perl; Randal L. Schwartz, however, capitalised the language's name in the book to make it stand out better when typeset. Randal L Schwartz (born November 22, 1961) is an American author system administrator and programming consultant The case distinction was subsequently adopted by the community. ^[7]

The name is occasionally given as "PERL" (for Practical Extraction and Report Language). Although the expansion has prevailed in many of today's manuals, including the official Perl man page, it is merely a backronym. Almost all substantial UNIX and Unix-like Operating systems have extensive documentation known as man pages (short for "manual pages" A backronym (or bacronym) is a Phrase that is constructed "after the fact" from a previously existing word or Abbreviation, the abbreviation The name does not officially stand for anything, so spelling it in all caps is incorrect. Proper capitalisation is considered a shibboleth (label of insiders) in the Perl community. Shibboleth (ˈʃɪbəlɛθ or ˈʃɪbələθ is any practice which is indicative of one's social or regional origin ^[8] Several other expansions have been suggested, including Wall's own humorous Pathologically Eclectic Rubbish Lister. ^[9] Indeed, Wall claims that the name was intended to inspire many different expansions. ^[10]

The camel symbol

Programming Perl, published by O'Reilly Media, features a picture of a camel on the cover, and is commonly referred to as The Camel Book. Programming Perl,ISBN 0-596-00027-8best known as the Camel Book among Programmers is a book about writing programs using the Perl programming O'Reilly Media (formerly O'Reilly & Associates) is an American media company established by Tim O'Reilly Camels are Even-toed ungulates within the Genus Camelus. The Dromedary, one-humped or Arabian camel has a single hump and the ^[3] This image of a camel has become a general symbol of Perl.

It is also a hacker emblem, appearing on some T-shirts and other clothing items. The Hacker Emblem was first proposed in October 2003 by Eric S A T-shirt (or tee shirt) is a Shirt which is pulled on over the head to cover most of a person's Torso.

O'Reilly owns the image as a trademark, but claims to use their legal rights only to protect the "integrity and impact of that symbol". ^[11] O'Reilly allows non-commercial use of the symbol, and provides Programming Republic of Perl logos and Powered by Perl buttons. ^[12]

Overview

Perl is a general-purpose programming language originally developed for text manipulation and now used for a wide range of tasks including system administration, web development, network programming, GUI development, and more. A system administrator, systems administrator, or sysadmin, is a person employed to maintain and operate a Computer system and/or network. Web development is a broad term for any activity related to developing a Web site for the World Wide Web or an Intranet. In Computing, network programming, essentially identical to socket programming or Client-server programming, involves writing

The language is intended to be practical (easy to use, efficient, complete) rather than beautiful (tiny, elegant, minimal). ^[13] Its major features include support for multiple programming paradigms (procedural, object-oriented, and functional styles), reference counting memory management (without a cycle-detecting garbage collector), built-in support for text processing, and a large collection of third-party modules. Procedural programming can sometimes be used as a synonym for Imperative programming (specifying the steps the program must take to reach the desired state but can also Object-oriented programming (OOP is a Programming paradigm that uses " objects " and their interactions to design applications and computer programs In Computer science, functional programming is a Programming paradigm that treats Computation as the evaluation of mathematical functions and In Computer science, reference counting is a technique of storing the number of references pointers or handles to a resource such as an object or block of memory Memory management is the act of managing Computer memory. In its simpler forms this involves providing ways to allocate portions of memory to programs at their request Modular programming is a software design technique that increases the extent to which software is composed from separate parts called modules

Features

The overall structure of Perl derives broadly from C. Perl is procedural in nature, with variables, expressions, assignment statements, brace-delimited code blocks, control structures, and subroutines. A variable (ˈvɛərɪəbl is an Attribute of a physical or an abstract System which may change its Value while it is under Observation. An expression in a Programming language is a combination of values Variables operators and functions that are interpreted ( In Computer science the assignment statement sets or re-sets the value stored in the storage location(s denoted by a Variable Name. Brackets are Punctuation marks used in pairs to set apart or interject text within other text In Computer programming, a statement block (or code block) is a section of code which is grouped together much like a Paragraph; such blocks In Computer science control flow (or alternatively flow of control refers to the order in which the individual statements, instructions or Function In Computer science, a subroutine ( function, method, procedure, or subprogram) is a portion of code within a larger

Perl also takes features from shell programming. All variables are marked with leading sigils, which unambiguously identify the data type (scalar, array, hash, etc. In Computer programming, a sigil (pronounced /'sɪdʒɪl/ or /'sɪg ) of the variable in context. Importantly, sigils allow variables to be interpolated directly into strings. Perl has many built-in functions which provide tools often used in shell programming (though many of these tools are implemented by programs external to the shell) like sorting, and calling on system facilities.

Perl takes lists from Lisp, associative arrays (hashes) from AWK, and regular expressions from sed. In Computer science, a list is an ordered collection of entities / Items In the context of Object-oriented programming languages An associative array (also associative container, map, mapping, hash, dictionary, finite map, and in query-processing an In Computing, regular expressions provide a concise and flexible means for identifying strings of text of interest such as particular characters words or patterns of characters These simplify and facilitate many parsing, text handling, and data management tasks.

In Perl 5, features were added that support complex data structures, first-class functions (i. A data structure in Computer science is a way of storing Data in a computer so that it can be used efficiently In Computer science, a Programming language is said to support first-class functions (or function literal) if it treats functions as e. , closures as values), and an object-oriented programming model. In Computer science, a closure is a function that is evaluated in an environment containing one or more Bound variables When called the function can access These include references, packages, class-based method dispatch, and lexically scoped variables, along with compiler directives (for example, the strict pragma). In Computer science, a reference is an object containing information which refers to data stored elsewhere as opposed to containing the data itself In Computer programming, scope is an enclosing context where values and expressions are associated In Computer programming, the term directive is applied in a variety of ways that are similar to the term command, it is also used to describe some Programming A major additional feature introduced with Perl 5 was the ability to package code as reusable modules. Larry Wall later stated that "The whole intent of Perl 5's module system was to encourage the growth of Perl culture rather than the Perl core. "^[14]

All versions of Perl do automatic data typing and memory management. The interpreter knows the type and storage requirements of every data object in the program; it allocates and frees storage for them as necessary using reference counting (so it cannot deallocate circular data structures without manual intervention). In Computer science, reference counting is a technique of storing the number of references pointers or handles to a resource such as an object or block of memory Legal type conversions—for example, conversions from number to string—are done automatically at run time; illegal type conversions are fatal errors.

Design

The design of Perl can be understood as a response to three broad trends in the computer industry: falling hardware costs, rising labor costs, and improvements in compiler technology. Many earlier computer languages, such as Fortran and C, were designed to make efficient use of expensive computer hardware. Fortran (previously FORTRAN) is a general-purpose, procedural, imperative Programming language that is especially suited to In contrast, Perl is designed to make efficient use of expensive computer programmers.

Perl has many features that ease the programmer's task at the expense of greater CPU and memory requirements. These include automatic memory management; dynamic typing; strings, lists, and hashes; regular expressions; introspection and an eval() function. In Computer science, a type system defines how a Programming language classifies values and expressions into '''types''', how it can

Wall was trained as a linguist, and the design of Perl is very much informed by linguistic principles. Examples include Huffman coding (common constructions should be short), good end-weighting (the important information should come first), and a large collection of language primitives. History In 1951 David A Huffman and his MIT information theory classmates were given Perl favors language constructs that are concise and natural for humans to read and write, even where they complicate the Perl interpreter.

Perl syntax reflects the idea that "things that are different should look different". For example, scalars, arrays, and hashes have different leading sigils. In Computer programming, a sigil (pronounced /'sɪdʒɪl/ or /'sɪg Array indices and hash keys use different kinds of braces. Strings and regular expressions have different standard delimiters. This approach can be contrasted with languages like Lisp, where the same S-expression construct and basic syntax is used for many different purposes. Lisp (or LISP) is a family of Computer Programming languages with a long history and a distinctive fully parenthesized syntax The term S-expression or sexp (where S stands for symbolic refers to a convention for representing Semi-structured data in human-readable textual form

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

There is a broad practical bent to both the Perl language and the community and culture that surround it. The preface to Programming Perl begins, "Perl is a language for getting your job done. " One consequence of this is that Perl is not a tidy language. It includes many features, tolerates exceptions to its rules, and employs heuristics to resolve syntactical ambiguities. Because of the forgiving nature of the compiler, bugs can sometimes be hard to find. Discussing the variant behaviour of built-in functions in list and scalar contexts, the perlfunc(1) manual page says "In general, they do what you want, unless you want consistency. "

Perl has several mottos that convey aspects of its design and use. One is "There's more than one way to do it. There is more than one way to do it ( TIMTOWTDI, usually pronounced "Tim Toady") is a Perl motto " (TIMTOWTDI, usually pronounced 'Tim Toady'). Others are "Perl: the Swiss Army Chainsaw of Programming Languages" and "No unnecessary limits". A stated design goal of Perl is to make easy tasks easy and difficult tasks possible. Perl has also been called "The Duct Tape of the Internet". ^[15]

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

Applications

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

Perl has been used since the early days of the Web to write CGI scripts. The Common Gateway Interface ( CGI) is a standard protocol for interfacing external Application software with an information server It is known as one of "the three Ps" (along with Python and PHP), the most popular dynamic languages for writing Web applications. Python is a general-purpose High-level programming language. Its design philosophy emphasizes programmer productivity and code readability PHP is a computer Scripting language. Originally designed for producing Dynamic web pages it has evolved to include a Command line interface capability It is also an integral component of the popular LAMP solution stack for web development. The Acronym LAMP refers to a Solution stack of software usually Free and open source software, used to run dynamic Web sites or servers In Computing, a solution stack is a set of Software subsystems or components needed to deliver a fully functional solution, e Large projects written in Perl include Slash, Bugzilla, TWiki and Movable Type. Slash (a Backronym for S lashdot- L ike A utomated S torytelling H omepage is the collection of Free software Bugzilla is a Web -based general-purpose Bugtracker tool originally developed and used by the Mozilla project and licensed under the Twiki is a Fictional character on the TV show Buck Rogers in the 25th Century. Movable type is the system of Printing and Typography that uses movable components to reproduce the elements of a document (usually individual letters or punctuation Many high-traffic websites, such as bbc.co.uk, Amazon.com, LiveJournal. Amazoncom Inc ( is an American electronic commerce ( E-commerce) company in Seattle Washington. LiveJournal (often abbreviated LJ) is a Virtual community where Internet users can keep a Blog, Journal or Diary. com, Ticketmaster. Ticketmaster is a ticket sales and distribution company based in West Hollywood California, USA, with operations in many countries around the world com and IMDb.com^[16] use Perl extensively.

Perl is often used as a glue language, tying together systems and interfaces that were not specifically designed to interoperate, and for "data munging", i. A glue language is a Programming language (usually a Scripting language) used for connecting Software components together e. , converting or processing large amounts of data for tasks like creating reports. In fact, these strengths are intimately linked. The combination makes perl a popular all-purpose tool for system administrators, particularly as short programs can be entered and run on a single command line. A system administrator, systems administrator, or sysadmin, is a person employed to maintain and operate a Computer system and/or network.

With a degree of care, Perl code can be made portable across Windows and Unix. Portable Perl code is often used by suppliers of software (both COTS and bespoke) to simplify packaging and maintenance of software build and deployment scripts.

Graphical user interfaces (GUI's) may be developed using Perl. In particular, Perl/Tk is commonly used to enable user interaction with Perl scripts. Such interaction may be synchronous or asynchronous using callbacks to update the GUI. For more information about the technologies involved see Tk,Tcl and WxPerl. Tk is an Open source, Cross-platform Widget toolkit, that is a library of basic elements for building a Graphical user interface (GUI Tcl (originally from "Tool Command Language" but nonetheless conventionally rendered as "Tcl" rather than "TCL" pronounced as " tickle " wxPerl is a Perl module by Mattia Barbon allowing the creation of Graphical user interface (GUI from Perl programming language.

Perl is also widely used in finance and bioinformatics, where it is valued for rapid application development and deployment, and the ability to handle large data sets. Bioinformatics is the application of information technology to the field of molecular biology

Implementation

Perl is implemented as a core interpreter, written in C, together with a large collection of modules, written in Perl and C. The source distribution is, as of 2005, 12 MB when packaged in a tar file and compressed. Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. A megabyte is a unit of Information or Computer storage equal to either 106 (1000000 Bytes or 220 (1048576 bytes depending on In Computing, tar (derived from tape archive) is both a File format (in the form of a type of archive Bitstream) and the name The interpreter is 150,000 lines of C code and compiles to a 1 MB executable on typical machine architectures. Alternatively, the interpreter can be compiled to a link library and embedded in other programs. There are nearly 500 modules in the distribution, comprising 200,000 lines of Perl and an additional 350,000 lines of C code. (Much of the C code in the modules consists of character encoding tables. )

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

The execution of a Perl program divides broadly into two phases: compile-time and run-time. ^[17] At compile time, the interpreter parses the program text into a syntax tree. At run time, it executes the program by walking the tree. The text is parsed only once, and the syntax tree is subject to optimization before it is executed, so the execution phase is relatively efficient. Compile-time optimizations on the syntax tree include constant folding and context propagation, but peephole optimization is also performed. In Compiler theory, constant folding and constant propagation are related optimization techniques used by many modern compilers In Compiler theory, peephole optimization is a kind of optimization performed over a very small set of instructions in a segment of generated code However, compile-time and run-time phases may nest: BEGIN code blocks execute at compile-time, while the eval function initiates compilation during runtime. In some Programming languages eval is a function which eval uates a string as though it were an expression and returns a result in others it executes Both operations are an implicit part of a number of others—most notably, the use clause that loads libraries, known in Perl as modules, implies a BEGIN block.

Perl has a context-sensitive grammar which can be affected by code executed during an intermittent run-time phase. Grammar is the field of Linguistics that covers the Rules governing the use of any given natural language. ^[18] Therefore Perl cannot be parsed by a straight Lex/Yacc lexer/parser combination. In Computer science, lex is a program that generates lexical analyzers ("scanners" or "lexers" The Computer program yacc is a Parser generator developed by Stephen C Instead, the interpreter implements its own lexer, which coordinates with a modified GNU bison parser to resolve ambiguities in the language. GNU bison is a Parser generator that is part of the GNU project. It is said that "only perl can parse Perl", meaning that only the Perl interpreter (perl) can parse the Perl language (Perl). NOTES FOR EDITORS "Perl" is not an acronym (read the "Name" section below The truth of this is attested to by the persistent imperfections of other programs that undertake to parse Perl, such as source code analyzers and auto-indenters, which have to contend not only with the many ways to express unambiguous syntactic constructs, but also the fact that Perl cannot be parsed in the general case without executing it. Though successful in creating a Perl parser for document-related purposes, the PPI project determined that parsing Perl code as a document (retaining its integrity) and as executable code simultaneously was, in fact, not possible. Specifically the author claimed that, "parsing Perl suffers from the 'Halting Problem. In computability theory, the halting problem is a Decision problem which can be stated as follows given a description of a program and a finite input '"^[19]

Perl is distributed with some 120,000 functional tests. These run as part of the normal build process, and extensively exercise the interpreter and its core modules. Perl developers rely on the functional tests to ensure that changes to the interpreter do not introduce bugs; conversely, Perl users who see the interpreter pass its functional tests on their system can have a high degree of confidence that it is working properly.

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

Availability

Perl is free software, and is licensed under both the Artistic License and the GNU General Public License. Free software or software libre is Software that can be used studied and modified without restriction and which can be copied and redistributed in modified or unmodified Artistic license (also known as dramatic license, poetic license, narrative license, licentia poetica, or simply license) is a colloquial Distributions are available for most operating systems. NOTES FOR EDITORS "Perl" is not an acronym (read the "Name" section below An operating system (commonly abbreviated OS and O/S) is the software component of a Computer system that is responsible for the management and coordination It is particularly prevalent on Unix and Unix-like systems, but it has been ported to most modern (and many obsolete) platforms. Unix (officially trademarked as UNIX, sometimes also written as Unix with Small caps) is a computer A Unix-like (sometimes shortened to *nix) Operating system is one that behaves in a manner similar to a Unix system while not necessarily conforming With only six reported exceptions, Perl can be compiled from source code on all Unix-like, POSIX-compliant or otherwise Unix-compatible platforms. In Computer science, source code (commonly just source or code) is any sequence of statements or declarations written in some Human-readable POSIX (ˈpɒzɪks or "Portable Operating System Interface" is the collective name of a family of related standards specified by the IEEE to define ^[20] However, this is rarely necessary, as Perl is included in the default installation of many popular operating systems.

Because of unusual changes required for the Mac OS Classic environment, a special port called MacPerl was shipped independently. On January 24, 1984, Apple Computer Inc (now Apple Inc) introduced the Apple Macintosh Personal computer, with the Macintosh 128K ^[21]

The CPAN carries a complete list of supported platforms with links to the distributions available on each. ^[22]

Windows

Users of Microsoft Windows typically install one of the native binary distributions of Perl for Win32^[23], most commonly ActivePerl. Microsoft Windows is a series of Software Operating systems and Graphical user interfaces produced by Microsoft. ActiveState is a Canadian Proprietary software company headquartered in Vancouver, British Columbia that develops sells and supports Cross-platform Compiling Perl from source code under Windows is possible, but most installations lack the requisite C compiler and build tools. In Computer science, source code (commonly just source or code) is any sequence of statements or declarations written in some Human-readable This also makes it hard to install modules from the CPAN, particularly those that are partially written in C.

Users of the ActivePerl binary distribution are therefore dependent on the repackaged modules provided in ActiveState’s module repository, which are precompiled and can be installed with PPM. ActiveState is a Canadian Proprietary software company headquartered in Vancouver, British Columbia that develops sells and supports Cross-platform Perl Package Manager ( PPM) is a Perl utility intended to simplify the tasks of locating installing upgrading and removing software packages Limited resources to maintain this repository have been cause for various long-standing problems^[24][25].

To address this and other problems of Perl on the Windows platform, win32.perl.org was launched by Adam Kennedy on behalf of The Perl Foundation in June 2006. The Perl Foundation (TPF is dedicated to the advancement of the Perl programming language through open discussion collaboration design and code This is a community website for "all things Windows and Perl. " A major aim of this project is to provide production-quality alternative Perl distributions that include an embedded C compiler and build tools, so as to enable Windows users to install modules directly from the CPAN. The production distribution in the family is known as Strawberry Perl, with research and experimental work done in a related Vanilla Perl distribution.

Another popular way of running Perl under Windows is provided by the Cygwin emulation layer. Cygwin (ˈsɪɡwɪn is a collection of tools originally developed by Cygnus Solutions to provide in Microsoft Windows a command line and programming interface familiar Cygwin provides a Unix-like environment on Windows and both perl and cpan are conveniently available as standard pre-compiled packages in the Cygwin setup program. Since Cygwin also includes the gcc, compiling Perl from source is also possible. The GNU Compiler Collection (usually shortened to GCC) is a set of Compilers produced for various Programming languages by the GNU Project

Language structure

In Perl, the minimal Hello world program may be written as follows:

print "Hello, world!\n"

This prints the string Hello, world! and a newline, symbolically expressed by an n character whose interpretation is altered by the preceding escape character (a backslash). A "Hello World" program is a Computer program that prints out "Hello world!" on a Display device. In Computing, input/output, or I/O, refers to the communication between an Information processing system (such as a Computer) and the outside In Computer programming and some branches of Mathematics, a string is an ordered Sequence of Symbols. In Computing, a newline (also known as a line break or end-of-line / EOL character is a special character or sequence of characters In Computing and Telecommunication, an escape character is a single character which in a sequence of characters signifies that what is to follow takes an alternative

The canonical form of the program is slightly more verbose:

#!/usr/bin/perl
print "Hello, world!\n";

The hash mark character introduces a comment in Perl, which runs up to the end of the line of code and is ignored by the compiler. In Computer programming, a comment is a Programming language construct used to embed Information in the Source code of a computer program The comment used here is of a special kind: it’s called the shebang line. In Computing, a shebang (also called a hashbang, hashpling, or pound bang) refers to the characters "#!" when they are the This tells Unix-like operating systems where to find the Perl interpreter, making it possible to invoke the program without explicitly mentioning perl. (Note that on Microsoft Windows systems, Perl programs are typically invoked by associating the . Microsoft Windows is a series of Software Operating systems and Graphical user interfaces produced by Microsoft. pl extension with the Perl interpreter. A filename extension is a suffix to the name of a Computer file applied to indicate the encoding convention ( File format) of its contents In order to deal with such circumstances, perl detects the shebang line and parses it for switches,^[20] so it is not strictly true that the shebang line is ignored by the compiler. )

The second line in the canonical form includes a semicolon, which is used to separate statements in Perl. With only a single statement in a block or file, a separator is unnecessary, so it can be omitted from the minimal form of the program—or more generally from the final statement in any block or file. The canonical form includes it because it is common to terminate every statement even when it is unnecessary to do so, as this makes editing easier: code can be added to or moved away from the end of a block or file without having to adjust semicolons.

Version 5. 10 of Perl introduces a say function that implicitly appends a newline character to its output, making the minimal "Hello world" program even shorter:

say 'Hello, world!'

Data types

Perl has a number of fundamental data types, the most commonly used and discussed being: scalars, arrays, hashes, filehandles and subroutines:

• A scalar is a single value; it may be a number, a string or a reference
• An array is an ordered collection of scalars
• A hash, or associative array, is a map from strings to scalars; the strings are called keys and the scalars are called values. A data type in Programming languages is an attribute of a datum which tells the computer (and the programmer something about the kind of datum it is In computing a scalar is a Variable or field that can hold only one value at a time as opposed to composite variables like Array, list In Computer science an array is a Data structure consisting of a group of elements that are accessed by indexing. In Computer science, a hash table, or a hash map, is a Data structure that associates keys with values. In computer programming a file descriptor is an abstract key for accessing a file In Computer science, a subroutine ( function, method, procedure, or subprogram) is a portion of code within a larger In computing a scalar is a Variable or field that can hold only one value at a time as opposed to composite variables like Array, list In Computer programming and some branches of Mathematics, a string is an ordered Sequence of Symbols. In Computer science, a reference is an object containing information which refers to data stored elsewhere as opposed to containing the data itself In Computer science an array is a Data structure consisting of a group of elements that are accessed by indexing. An associative array (also associative container, map, mapping, hash, dictionary, finite map, and in query-processing an
• A file handle is a map to a file, device, or pipe which is open for reading, writing, or both. In computer programming a file descriptor is an abstract key for accessing a file
• A subroutine is a piece of code that may be passed arguments, be executed, and return data

Most variables are marked by a leading sigil, which identifies the data type being accessed (not the type of the variable itself), except filehandles, which don't have a sigil. In Computer programming, a sigil (pronounced /'sɪdʒɪl/ or /'sɪg The same name may be used for variables of different data types, without conflict.

$foo # a scalar
@foo # an array
%foo # a hash
FOO # a file handle or constant
&foo # a subroutine.  (The & is optional)

File handles and constants need not be uppercase, but it is a common convention owing to the fact that there is no sigil to denote them. In computer programming a file descriptor is an abstract key for accessing a file Both are global in scope, but file handles are interchangeable with references to file handles, which can be stored in scalars, which in turn permit lexical scoping. Doing so is encouraged in Damian Conway's Perl Best Practices. Damian Conway (born 1964 is a prominent member of the Perl community a proponent of Object-oriented programming, and the author of several books. As a convenience, the open function in Perl 5. 6 and newer will autovivify undefined scalars to file handle references.

Numbers are written in the bare form; strings are enclosed by quotes of various kinds.

$name = "joe";
$color = 'red';
 
$number1 = 42;
$number2 = '42';
 
# This evaluates to true
if ($number1 == $number2) { print "Numbers and strings of numbers are the same!"; }
 
$answer = "The answer is $number1"; # Variable interpolation: The answer is 42
$price = 'This device costs $42'; # No interpolation in single quotes
 
$album = "It's David Bowie's \"Heroes\""; # literal quotes inside a string;
$album = 'It\'s David Bowie\'s "Heroes"'; # same as above with single quotes;
$album = q(It's David Bowie's "Heroes"); # the quote-like operators q() and qq() allow
 # almost any delimiter instead of quotes, to
 # avoid excessive backslashing
 
$multilined_string =<<EOF;
This is my multilined string
note that I am terminating it with the "EOF" word. 
EOF

Perl will convert strings into numbers and vice versa depending on the context in which they are used. In the following example the strings $n and $m are treated as numbers when they are the arguments to the addition operator. This code prints the number '5', discarding non numeric information for the operation, although the variable values remain the same. (The string concatenation operator is the period, not the + symbol. )

$n = '3 apples';
$m = '2 oranges';
print $n + $m;

Perl also has a boolean context that it uses in evaluating conditional statements. The following values all evaluate as false in Perl:

$false = 0; # the number zero
$false = 0. 0; # the number zero as a float
$false = 0b0; # the number zero in binary
$false = 0x0; # the number zero in hexadecimal
$false = '0'; # the string zero
$false = ""; # the empty string
$false = undef; # the return value from undef

All other values are evaluated to true. This includes the odd self-describing literal string of "0 but true", which in fact is 0 as a number, but true when used as a boolean. (Any non-numeric string would also have this property, but this particular string is ignored by Perl with respect to numeric warnings. ) A less explicit but more conceptually portable version of this string is '0E0' or '0e0', which does not rely on characters being evaluated as 0, as '0E0' is literally "zero times ten to the zeroth power. "

Evaluated boolean expressions also return scalar values. Although the documentation does not promise which particular true or false is returned (and thus cannot be relied on), many boolean operators return 1 for true and the empty-string for false (which evaluates to zero in a numeric context). The defined() function tells if the variable has any value set. In the above examples defined($false) is true for every value except undef.

If a specifically 1 or 0 result (as in C) is needed, an explicit conversion is thought by some authors to be required:

my $real_result = $boolean_result ? 1 : 0;

However, if it's known that the value is either 1 or undef, an implicit conversion can be used instead:

my $real_result = $boolean_result + 0;

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

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

It can be written many other ways as well, some straightforward and some less so:

# An explicit and straightforward way
@scores = ('32', '45', '16', '5');
 
# Equivalent to the above, but the qw() quote-like operator saves typing of
# quotes and commas and reduces visual clutter; almost any delimiter can be
# used instead of parentheses
@scores = qw(32 45 16 5);
 
# The split function returns a list of strings, which are extracted
# from the expression using a regex template. 
# This may be useful for reading from a file of comma-separated values (CSV)
@scores = split /,/, '32,45,16,5';
 
# It's also possible to use a postfix for operator and aliasing of
# the $_ magic variable to the next value of the list during each
# iteration; this is pointless here, but similar idioms are widely used
# in some circumstances. 
push @scores, $_ foreach 32, 45, 16, 5;

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

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

The => operator is equivalent to a comma, except that it assumes quotes around the preceding token if it is a bare identifier: (joe => 'red') is the same as ('joe' => 'red'). It can therefore be used to elide quote marks, improving readability.

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

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

Thus, a hash can also be specified by setting its keys individually:

$favorite{joe} = 'red';
$favorite{sam} = 'blue';

Multiple elements may be accessed by using the @ sigil instead (identifying the result as a list).

@scores[2, 3, 1] # three elements of @scores
@favorite{'joe', 'sam'} # two values in %favorite
@favorite{qw(joe sam)} # same as above

The number of elements in an array can be obtained by evaluating the array in scalar context or with the help of the $# sigil. The latter gives the index of the last element in the array, not the number of elements.

$count = @friends; # Assigning to a scalar forces scalar context
 
# This notation is sometimes discouraged, because it tends
# to be confused with comments. 
 
$#friends; # The index of the last element in @friends
$#friends+1; # Usually the number of elements in @friends is one more
 # than $#friends because the first element is at index 0,
 # not 1, unless the programmer reset this to a different
 # value, which most Perl manuals discourage. 

There are a few functions that operate on entire hashes.

@names = keys %addressbook;
@addresses = values %addressbook;
 
# Every call to each returns the next key/value pair. 
# All values will be eventually returned, but their order
# cannot be predicted. 
while (($name, $address) = each %addressbook) {
 print "$name lives at $address\n";
}
 
# Similar to the above, but sorted alphabetically
foreach my $next_name (sort keys %addressbook) {
 print "$next_name lives at $addressbook{$next_name}\n";
}

Control structures

Main article: Perl control structures

Perl has several kinds of control structures. The basic control structures of Perl are similar to those used in C and Java, but they have been extended in several ways

It has block-oriented control structures, similar to those in the C, Javascript, and Java programming languages. JavaScript is a Scripting language most often used for Client-side web development Conditions are surrounded by parentheses, and controlled blocks are surrounded by braces:

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

Where only a single statement is being controlled, statement modifiers provide a more concise syntax:

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

Short-circuit logical operators are commonly used to affect control flow at the expression level:

expr and expr
expr && expr
expr or expr
expr || expr

(The "and" and "or" operators are similar to && and || but have lower precedence, which makes it easier to use them to control entire statements. Short-circuit evaluation or minimal evaluation denotes the semantics of some Boolean operators in some Programming languages in which the second argument )

The flow control keywords next (corresponding to C's continue), last (corresponding to C's break), return, and redo are expressions, so they can be used with short-circuit operators.

Perl also has two implicit looping constructs, each of which has two forms:

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

grep returns all elements of list for which the controlled block or expression evaluates to true. map evaluates the controlled block or expression for each element of list and returns a list of the resulting values. These constructs enable a simple functional programming style. In Computer science, functional programming is a Programming paradigm that treats Computation as the evaluation of mathematical functions and

Up until the 5. 10. 0 release, there was no switch statement in Perl 5. In Computer programming, a switch statement is a type of control statement that exists in most modern Imperative programming languages (e From 5. 10. 0 onwards, a multi-way branch statement called given/when is available, which takes the following form:

given ( expr ) { when ( cond ) { . . .  } default { . . .  } }

Syntactically, this structure behaves similarly to switch statement's found in other languages, but with a few important differences. In Computer programming, a switch statement is a type of control statement that exists in most modern Imperative programming languages (e The largest is that unlike switch/case structures, given/when statements break execution after the first successful branch, rather than waiting for explicitly defined break commands. Conversely, explicit continues are instead necessary to emulate switch behavior.

For those not using the 5. 10. 0 release, the Perl documentation describes a half-dozen ways to achieve the same effect by using other control structures. There is also a Switch module, which provides functionality modeled on the forthcoming Perl 6 re-design. Perl 6 is a planned major revision to the Perl Programming language. It is implemented using a source filter, so its use is unofficially discouraged. ^[26]

Perl includes a goto label statement, but it is rarely used. Situations where a goto is called for in other languages don't occur as often in Perl due to its breadth of flow control options.

There is also a goto &sub statement that performs a tail call. A tail call is a Subroutine call just before the end of a subroutine It terminates the current subroutine and immediately calls the specified sub. This is used in situations where a caller can perform more efficient stack management than Perl itself (typically because no change to the current stack is required), and in deep recursion tail calling can have substantial positive impact on performance because it avoids the overhead of scope/stack management on return. In Computer science, a call stack is a dynamic stack data structure which stores information about the active Subroutines of a Computer program

Subroutines

Subroutines are defined with the sub keyword, and invoked simply by naming them. In Computer science, a subroutine ( function, method, procedure, or subprogram) is a portion of code within a larger If the subroutine in question has not yet been declared, invocation requires either parentheses after the function name or an ampersand (&) before it. But using & without parentheses will also implicitly pass the arguments of the current subroutine to the one called, and using & with parentheses will bypass prototypes.

# Calling a subroutine
 
# Parentheses are required here if the subroutine is defined later in the code
foo();
&foo; # (this also works, but has other consequences regarding arguments passed to the subroutine)
 
# Defining a subroutine
sub foo { . . .  }
 
foo; # Here parentheses are not required

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

foo $x, @y, %z;

The parameters to a subroutine do not need to be declared as to either number or type; in fact, they may vary from call to call. Any validation of parameters must be performed explicitly inside the subroutine.

Arrays are expanded to their elements, hashes are expanded to a list of key/value pairs, and the whole lot is passed into the subroutine as one flat list of scalars.

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

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

$_[0], $_[1]

However, the resulting code can be difficult to read, and the parameters have pass-by-reference semantics, which may be undesirable. In Computer science, an evaluation strategy is a set of (usually deterministic rules for determining the evaluation of expressions in a Programming language

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

my ($x, $y, $z) = @_;

This provides mnemonic parameter names and implements pass-by-value semantics. In Computer science, an evaluation strategy is a set of (usually deterministic rules for determining the evaluation of expressions in a Programming language The my keyword indicates that the following variables are lexically scoped to the containing block.

Another idiom is to shift parameters off of @_. This is especially common when the subroutine takes only one argument, or for handling the $self argument in object-oriented modules.

my $x = shift;

Subroutines may assign @_ to a hash to simulate named arguments; this is recommended in Perl Best Practices for subroutines that are likely ever to have more than three parameters. ^[27]

sub function1 {
 my %args = @_;
 print "'x' argument was '$args{x}'\n";
}
function1( x => 23 );

Subroutines may return values.

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

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

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

sub list { (4, 5, 6) }
sub array { @x = (4, 5, 6); @x }
 
$x = list; # returns 6 - last element of list
$x = array; # returns 3 - number of elements in list
@x = list; # returns (4, 5, 6)
@x = array; # returns (4, 5, 6)

A subroutine can discover its calling context with the wantarray function.

sub either {
 return wantarray ? (1, 2) : 'Oranges';
}
 
$x = either; # returns "Oranges"
@x = either; # returns (1, 2)

Regular expressions

The Perl language includes a specialized syntax for writing regular expressions (RE, or regexes), and the interpreter contains an engine for matching strings to regular expressions. In Computing, regular expressions provide a concise and flexible means for identifying strings of text of interest such as particular characters words or patterns of characters The regular expression engine uses a backtracking algorithm, extending its capabilities from simple pattern matching to string capture and substitution. Backtracking is a type of Algorithm that is a refinement of Brute force search. The regular expression engine is derived from regex written by Henry Spencer. Henry Spencer is a Canadian Computer programmer and space enthusiast

The Perl regular expression syntax was originally taken from Unix Version 8 regular expressions. However, it diverged before the first release of Perl, and has since grown to include many more features. Other languages and applications are now adopting Perl compatible regular expressions over POSIX regular expressions including PHP, Ruby, Java, Microsoft's .NET Framework^[28], and the Apache HTTP server. Perl Compatible Regular Expressions ( PCRE) is a Regular expression C library inspired by Perl 's external interface written by POSIX (ˈpɒzɪks or "Portable Operating System Interface" is the collective name of a family of related standards specified by the IEEE to define PHP is a computer Scripting language. Originally designed for producing Dynamic web pages it has evolved to include a Command line interface capability Ruby is a dynamic, reflective, general purpose Object-oriented programming language that combines syntax inspired by Perl with Smalltalk

Regular expression syntax is extremely compact, owing to history. The first regular expression dialects were only slightly more expressive than globs, and the syntax was designed so that an expression would resemble the text it matches. In Computer programming, the verb glob or globbing is used to refer to an instance of Pattern matching behavior This meant using no more than a single punctuation character or a pair of delimiting characters to express the few supported assertions. Over time, the expressiveness of regular expressions grew tremendously, but the syntax design was never revised and continues to rely on punctuation. As a result, regular expressions can be cryptic and extremely dense.

Uses

The m// (match) operator introduces a regular expression match. (If it is delimited by slashes, as in all the examples here, then the leading m may be omitted for brevity. If the m is present, as in all the following examples, other delimiters can be used in place of slashes. ) In the simplest case, an expression like

$x =~ m/abc/

evaluates to true if and only if the string $x matches the regular expression abc. ↔

The s/// (substitute) operator, on the other hand, specifies a search and replace operation:

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

Another use of regular expressions is to specify delimiters for the split function:

@words = split m/,/, $line;

The split function creates a list of the parts of the string separated by matches of the regular expression. In this example, a line is divided into a list of its comma-separated parts, and this list is then assigned to the @words array.

Syntax

Portions of a regular expression may be enclosed in parentheses; corresponding portions of a matching string are captured. Captured strings are assigned to the sequential built-in variables $1, $2, $3, . . . , and a list of captured strings is returned as the value of the match.

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

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

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

Since regular expressions can be dense and cryptic because of their compact syntax, the /x modifier was added in Perl to help programmers write more legible regular expressions. It allows programmers to place whitespace and comments inside regular expressions:

$x =~ m/a # match 'a'
 .  # followed by any character
 c # then followed by the 'c'character
 /x;

Database interfaces

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

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

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

DBI provides caching for database handles and queries, which can greatly improve performance in long-lived execution environments such as mod_perl^[29], helping high-volume systems avert load spikes as in the Slashdot effect. mod_perl is an optional module for the Apache HTTP server. It embeds a Perl interpreter into the Apache server so that dynamic content produced by Perl The Slashdot effect, also known as slashdotting, is the phenomenon of a popular Website linking to a smaller site causing the smaller site to slow down or even temporarily

Comparative performance

The Computer Language Benchmarks Game^[30] compare the performance of implementations of typical programming problems in several programming languages. The submitted Perl implementations were typically towards the high end of the memory usage spectrum, and had varied speed results. Perl's performance in the benchmarks game is similar to other interpreted languages such as Python, faster than PHP, and significantly faster than Ruby, but slower than most compiled languages.

Perl programs can start slower than similar programs in compiled languages because perl has to compile the source every time it runs. In a talk at the YAPC::Europe 2005 conference and subsequent article, "A Timely Start", Jean-Louis Leroy found that his Perl programs took much longer to run than he expected because the perl interpreter spent much of the time finding modules because of his over-large include path. Yet Another Perl Conference, usually given as the abbreviation YAPC, is a series of conferences discussing the Perl computer programming language usually organised ^[31] Because pre-compiling is still an experimental part of Perl^[32]—unlike that of Java, Python, and Ruby—Perl programs pay this overhead penalty on every execution. When amortized over a long run phase, startup time is not typically substantial, but measurement of very short execution times can often be skewed as is often found in benchmarks. In Computer science, especially Analysis of algorithms, amortized analysis refers to finding the average running time per operation over a Worst-case

A number of tools have been introduced to improve this situation, the first of which was Apache's mod_perl, which sought to address one of the most common reasons that small Perl programs were invoked rapidly: CGI Web development. mod_perl is an optional module for the Apache HTTP server. It embeds a Perl interpreter into the Apache server so that dynamic content produced by Perl The Common Gateway Interface ( CGI) is a standard protocol for interfacing external Application software with an information server The World Wide Web (commonly shortened to the Web) is a system of interlinked Hypertext documents accessed via the Internet. ActivePerl, via Microsoft ISAPI provides similar performance improvements. ActiveState is a Canadian Proprietary software company headquartered in Vancouver, British Columbia that develops sells and supports Cross-platform The Internet Server Application Programming Interface ( ISAPI) is an N-tier API of Internet Information Services (IIS Microsoft 's

Once Perl code is compiled, there is additional overhead during the execution phase that typically isn't present for programs written in compiled languages like C or C++, including, among many other things, overhead due to bytecode interpretation, reference-counting memory management, and dynamic type checking.

Optimizing

Perl programs, like any code, can be tuned for performance using benchmarks and profiles after a readable and correct implementation is finished. In Computing, optimization is the process of modifying a system to make some aspect of it work more efficiently or use fewer resources This article is about the use of benchmarks in computing for other uses see Benchmark. In Software engineering, performance analysis, more commonly today known as profiling, is the investigation of a program's behavior using information gathered as the In part because of Perl's interpreted nature, writing more-efficient Perl will not always be enough to meet one's performance goals for a program.

In such situations, the most critical routines of a Perl program can be written in other languages such as C or Assembler, which can be connected to Perl via simple Inline modules or the more complex but flexible XS mechanism. tags please moot on the talk page first! --> In Computing, C is a general-purpose cross-platform block structured See the terminology section below for information regarding inconsistent use of the terms assembly and assembler XS is an interface through which a Perl program can call a C or C++ language Subroutine. ^[33] Nicholas Clark, a Perl core developer, discusses some Perl design trade-offs and some solutions in When perl is not quite fast enough. ^[34]

In extreme cases, optimizing Perl can require intimate knowledge of the interpreter's workings rather than skill with algorithms, the Perl language, or general principles of optimization.

Future

Main article: Perl 6

At the 2000 Perl Conference, Jon Orwant made a case for a major new language initiative. Perl 6 is a planned major revision to the Perl Programming language. ^[35] This led to a decision to begin work on a redesign of the language, to be called Perl 6. Proposals for new language features were solicited from the Perl community at large, and over 300 RFCs were submitted. In Computer network Engineering, a Request for Comments (RFC is a Memorandum published by the Internet Engineering Task Force (IETF describing

Larry Wall spent the next few years digesting the RFCs and synthesizing them into a coherent framework for Perl 6. Larry Wall (born September 27, 1954) is a Programmer and Author, most widely known for his creation of the Perl Programming He has presented his design for Perl 6 in a series of documents called "apocalypses", which are numbered to correspond to chapters in Programming Perl ("The Camel Book"). Programming Perl,ISBN 0-596-00027-8best known as the Camel Book among Programmers is a book about writing programs using the Perl programming The current, not yet finalized specification of Perl 6 is encapsulated in design documents called Synopses, which are numbered to correspond to Apocalypses.

Perl 6 is not intended to be backward compatible, though there will be a compatibility mode.

In 2001, it was decided that Perl 6 would run on a cross-language virtual machine called Parrot. In Computer science, a virtual machine (VM is a Software implementation of a machine (computer that executes programs like a real machine Parrot is a register -based Virtual machine being developed using the C programming language and intended to run Dynamic languages efficiently This will mean that other languages targeting the Parrot will gain native access to CPAN, allowing some level of cross-language development. CPAN is an Acronym standing for Comprehensive Perl Archive Network, an archive of over 12200 modules of software written in Perl, as well as documentation

In 2005 Audrey Tang created the pugs project, an implementation of Perl 6 in Haskell. Audrey Tang (born April 18, 1981; formerly known as Autrijus Tang) is a Taiwanese Free software Programmer, who has been Pugs is a Compiler and interpreter for the Perl 6 Programming language, started on February 1 2005 by Audrey Tang Haskell is a standardized Purely functional Programming language with non-strict semantics, named after the Logician Haskell Curry This was and continues to act as a test platform for the Perl 6 language (separate from the development of the actual implementation) allowing the language designers to explore. The pugs project spawned an active Perl/Haskell cross-language community centered around the freenode #perl6 irc channel. freenode, formerly known as Open Projects Network, is a popular IRC network used to discuss peer-directed projects

A number of features in the Perl 6 language now show similarities with Haskell, and Perl 6 has been embraced by the Haskell community as a potential scripting language.

As of 2006, Perl 6, Parrot, and pugs are under active development, and a new module for Perl 5 called v6 allows some Perl 6 code to run directly on top of Perl 5. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. v6 is a Perl module which runs under Perl version 5 and transforms Perl 6 code into Perl 5 code on the fly

Development of Perl 5 is also continuing. Perl 5. 10 was released in December of 2007, with some new features influenced by the design of Perl 6.

The Perl community

Perl's culture and community has developed alongside the language itself. Usenet was the first public venue in which Perl was introduced, but over the course of its evolution, Perl's community was shaped by the growth of broadening Internet-based services including the introduction of the World Wide Web. Usenet, a Portmanteau of "user" and "network" is a world-wide distributed Internet discussion system The community that surrounds Perl was, in fact, the topic of Larry Wall's first "State of the Onion" talk. ^[36]

State of the Onion

State of the Onion is the name for Larry Wall’s yearly keynote-style summaries on the progress of Perl and its community. A keynote in Literature, Music or Public speaking is the principal underlying theme They are characterized by his hallmark humor, employing references to Perl’s and the wider hacker culture, as well as Wall’s linguistic and sometimes his Christian background.

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

Pastimes

Perl's pastimes have become a defining element of the community. Included among them are trivial and complex uses of the language.

JAPHs

In email, Usenet and message board postings, "Just another Perl hacker" (JAPH) programs have become a common trend, originated by Randal L. Schwartz, one of the earliest professional Perl trainers. Just another Perl hacker, or JAPH, typically refers to a Perl program which prints "Just another Perl hacker" (the comma is Canonical but is Randal L Schwartz (born November 22, 1961) is an American author system administrator and programming consultant ^[37]

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,". Just another Perl hacker, or JAPH, typically refers to a Perl program which prints "Just another Perl hacker" (the comma is Canonical but is In the spirit of the original concept, these programs are moderately obfuscated and short enough to fit into the signature of an email or Usenet message. The "canonical" JAPH includes the comma at the end, although this is often omitted.

Perl golf

Perl "golf" is the pastime of reducing the number of characters used in a Perl program to the bare minimum, much as how golf players seek to take as few shots as possible in a round. This use of the word "golf" originally focused on the JAPHs used in signatures in Usenet postings and elsewhere, though the same stunts had been an unnamed pastime in the language APL in previous decades. The use of Perl to write a program which performed RSA encryption prompted a widespread and practical interest in this pastime. In Cryptography, RSA is an Algorithm for Public-key cryptography. ^[38] In subsequent years, code golf has been taken up as a pastime in other languages besides Perl. ^[39]

Obfuscation

As with C, obfuscated code competitions are a well-known pastime. Obfuscated code is Source code or Intermediate language that is very hard to read and understand often intentionally The annual Obfuscated Perl contest made an arch virtue of Perl's syntactic flexibility. The Obfuscated Perl Contest was a competition for programmers of Perl which was held annually between 1996 and 2000.

Poetry

Similar to obfuscated code and golf, but with a different purpose, Perl poetry is the practice of writing poems that can actually be compiled as legal (although generally non-sensical) Perl code. This hobby is more or less unique to Perl due to the large number of regular English words used in the language. New poems are regularly published in the Perl Monks site's Perl Poetry section. PerlMonks is a community Website covering all aspects of Perl Programming and other related topics such as Web applications and ^[40]

CPAN Acme

There are also many examples of code written purely for entertainment on the CPAN. CPAN is an Acronym standing for Comprehensive Perl Archive Network, an archive of over 12200 modules of software written in Perl, as well as documentation Lingua::Romana::Perligata, for example, allows writing programs in Latin. Latin ( lingua Latīna, laˈtiːna is an Italic language, historically spoken in Latium and Ancient Rome. ^[41] 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). The Acme Corporation is a fictional corporation that exists in several Cartoons, Films and TV series, most significantly in the Looney Tunes universe Some of the Acme modules are deliberately implemented in amusing ways. This includes Acme::Bleach, one of the first modules in the Acme:: namespace,^[42] which allows the program's source code to be "whitened" (i. e. , all characters replaced with whitespace) and yet still work.

Further reading

• Learning Perl, Fourth Edition (the Llama book), ISBN 0-596-10105-8
• Perl Cookbook, ISBN 0-596-00313-7
• Programming Perl, (the Camel book), ISBN 0-596-00027-8

See also

• The Perl Foundation
• Perl instruction at Wikiversity—you can use the training and/or help add to it
• Perl Object Environment (POE)—a framework for writing persistent object-oriented environments with event loops. Learning Perl, also known as the llama book, is a tutorial book for the Perl programming language and is published by O'Reilly. The Perl Cookbook, ISBN 0-596-00313-7 is a book containing solutions to common short tasks in Perl Programming Perl,ISBN 0-596-00027-8best known as the Camel Book among Programmers is a book about writing programs using the Perl programming The Perl Foundation (TPF is dedicated to the advancement of the Perl programming language through open discussion collaboration design and code For the Mach variant see Mach kernel The Perl Object Environment or POE In Computer science, the event loop, message dispatcher, message loop or message pump is a programming construct that waits for and dispatches
• Perl Data Language (PDL)—a Perl module which allows extending Perl for higher-order scientific processing. PDL (short for P erl D ata L anguage is a set of Array programming extensions to the Perl programming language.
• Plain Old Documentation (POD)—a documentation tool for Perl. Plain Old Documentation, abbreviated pod, is a simple Markup language used to document the Perl programming language
• Just another Perl hacker (JAPH)
• Perl Monks
• Perl Mongers
• PerlScript
• Perl 6
• Comparison of programming languages
• Autovivification

References

External links

• Perl.org—Official Perl website
• Perl documentation
• The Perl Foundation
• Official Perl 5 Wiki
• Perl at the Open Directory Project