Perl is a family of high-level, general-purpose, interpreted, dynamic programming languages. The languages in this family include Perl 5 and Perl 6.
Though Perl is not officially an acronym, there are various backronyms in use, including “Practical Extraction and Reporting Language”. Perl was originally developed by Larry Wall in 1987 as a general-purpose Unix scripting language to make report processing easier. Since then, it has undergone many changes and revisions. Perl 6, 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 one another.
The Perl languages borrow features from other programming languages including C, shell script (sh), AWK, and sed. They provide powerful text processing facilities without the arbitrary data-length limits of many contemporary Unix commandline tools, facilitating easy manipulation of text files. Perl 5 gained widespread popularity in the late 1990s as a CGI scripting language, in part due to its then unsurpassed regular expression and string parsing abilities.
In addition to CGI, Perl 5 is used for system administration, network programming, finance, bioinformatics, and other applications, such as for GUIs. It has been nicknamed “the Swiss Army chainsaw of scripting languages” because of its flexibility and power, and also its ugliness. In 1998, it was also referred to as the “duct tape that holds the Internet together”, in reference to both its ubiquitous use as a glue language and its perceived inelegance.
Larry Wall began work on Perl in 1987, while working as a programmer at Unisys, and released version 1.0 to the comp.sources.misc newsgroup on December 18, 1987. The language expanded rapidly over the next few years.
Perl 2, released in 1988, featured a better regular expression engine. Perl 3, released in 1989, added support for binary data streams.
Originally, the only documentation for Perl was a single lengthy man page. In 1991, Programming Perl, known to many Perl programmers as the “Camel Book” because of its cover, was published and became the de facto reference for the language. At the same time, the Perl version number was bumped to 4, not to mark a major change in the language but to identify the version that was well documented by the book.
Early Perl 5
Main article: Perl 5 version history
Perl 4 went through a series of maintenance releases, culminating in Perl 4.036 in 1993. At that point, 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, references, lexical (my) variables, and modules. Importantly, modules provided a mechanism for extending the language without modifying the interpreter. This allowed the core interpreter to stabilize, even as it enabled ordinary Perl programmers to add new language features. Perl 5 has been in active development since then.
Perl 5.001 was released on March 13, 1995. Perl 5.002 was released on February 29, 1996 with the new prototypes feature. This allowed module authors to make subroutines that behaved like Perl builtins. Perl 5.003 was released June 25, 1996, as a security release.
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; as of May 2017, it carries over 185,178 modules in 35,190 distributions, written by more than 13,071 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 to which all classes were automatically derived and the ability to require versions of modules. Another significant development was the inclusion of the CGI.pm module, which contributed to Perl’s popularity as a CGI scripting language.
Perl is also now supported running under Microsoft Windows and several other operating systems.
Perl 5.005 was released on July 22, 1998. This release included several enhancements to the regex engine, new hooks into the backend through the B::* modules, the qr// regex quote operator, a large selection of other new core modules, and added support for several more operating systems, including BeOS.
Perl 5.6 was released on March 22, 2000. Major changes included 64-bit support, Unicode string representation, support for files over 2 GiB, and the “our” keyword. 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, a Perl 6 interpreter written in Haskell. This was the first concerted effort towards making Perl 6 a reality. This effort stalled in 2006.
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. 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 compliance, regex conversion overloading, DTrace support, and Unicode 5.2. On January 21, 2011, Perl 5.12.3 was released; it contains updated modules and some documentation changes. Version 5.12.4 was released on June 20, 2011. The latest version of that branch, 5.12.5, was released on November 10, 2012.
On May 14, 2011, Perl 5.14 was released. JSON support is built-in as of 5.14.0. The latest version of that branch, 5.14.4, was released on March 10, 2013.
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 6.1.
On May 18, 2013, Perl 5.18 was released. Notable new features include the new d trace 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, rand() 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, moe by Stevan Little and friends, p2 by the Perl11 team under Reini Urban, gperl by goccy, and rperl a kickstarter project led by Will Braswell and affiliated with the Perll11 project.
PONIE is an acronym for Perl On New Internal Engine. The PONIE Project existed from 2003 until 2006 and was to be a bridge between Perl 5 and Perl 6. It was an effort to rewrite the Perl 5 interpreter to run on Parrot, the Perl 6 virtual machine. The goal was to ensure the future of the millions of lines of Perl 5 code at thousands of companies around the world.
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.
Perl was originally named “Pearl”. Wall wanted to give the language a short name with positive connotations; he claims that he considered 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.
When referring to the language, the name is normally capitalized (Perl) as a proper noun. When referring to the interpreter program itself, the name is often uncapitalized (perl) because most Unix-like file systems are case-sensitive. Before the release of the first edition of Programming Perl, it was common to refer to the language as perl; Randal L. Schwartz, however, capitalized the language’s name in the book to make it stand out better when typeset. This case distinction was subsequently documented as canonical.
The name is occasionally expanded as Practical Extraction and Report Language, but this is a backronym. Other expansions have been suggested as equally canonical, including Wall’s own Pathologically Eclectic Rubbish Lister which is in the manual page for perl. Indeed, Wall claims that the name was intended to inspire many different expansions.
Programming Perl, published by O’Reilly Media, features a picture of a dromedary camel on the cover and is commonly called the “Camel Book”. This image of a camel has become an unofficial symbol of Perl as well as a general hacker emblem, appearing on T-shirts and other clothing items.
O’Reilly owns the image as a trademark but licenses it for non-commercial use, requiring only an acknowledgement and a link to www.perl.com. Licensing for commercial use is decided on a case by case basis. O’Reilly also provides “Programming Republic of Perl” logos for non-commercial sites and “Powered by Perl” buttons for any site that uses Perl.
The onion logo used by The Perl Foundation
The Perl Foundation owns an alternative symbol, an onion, which it licenses to its subsidiaries, Perl Mongers, PerlMonks, Perl.org, and others. The symbol is a visual pun on pearl onion
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