A brief description about Perl
Perl is a high-level, general-purpose, interpreted, dynamic programming 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 and become widely popular amongst programmers. Larry Wall continues to oversee development of the core language, and its upcoming version, Perl 6. Perl borrows features from other programming languages including C, shell scripting (sh), AWK, and sed. The language provides powerful text processing facilities without the arbitrary data length limits of many contemporary Unix tools, facilitating easy manipulation of text files. Perl gained widespread popularity in the late 1990s as a CGI scripting language, in part due to its parsing abilities.
In addition to CGI, Perl is used for graphics programming, system administration, network programming, finance, bioinformatics, and other applications. Perl is nicknamed "the Swiss Army chainsaw of programming languages" due to its flexibility and power. It is also referred to as the "duct tape that holds the Internet together", in reference to its ubiquity and perceived inelegance.
Perl Name and Symbol
Name
Perl was originally named "Pearl", after the Parable of the Pearl from the Gospel of Matthew. Larry Wall wanted to give the language a short name with positive connotations; he claims that he considered (and rejected) every three- and four-letter word in the dictionary. He also considered naming it after his wife Gloria. Wall discovered the existing PEARL programming language before Perl's official release and changed the spelling of the name.
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.
There is some contention about the all-caps spelling "Perl", which the documentation declares incorrect and which some core community members consider a sign of outsiders. The name is occasionally backronymed as Practical Extraction and Report Language (which appears at the top of the documentation and in some printed literature). Several backronyms have been suggested as equally canonical, including Wall's own humorous Pathologically Eclectic Rubbish Lister. 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 camel on the cover and is commonly referred to as 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 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 pun on the pearl onion.
Perl History
Early Perl versions
Larry Wall began work on Perl in 1987, while working as a programmer at Unisys, and released version 1.0 to the comp.sources.misc newsgroup on December 18, 1987. The language expanded rapidly over the next few years.
Perl 2, released in 1988, featured a better regular expression engine. Perl 3, released in 1989, added support for binary data streams.
Originally the only documentation for Perl was a single (increasingly lengthy) man page. In 1991, Programming Perl (known to many Perl programmers as the "Camel Book" 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 documented by the book.
Early Perl 5
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 January 2011, it carries over 19,000 modules by more than 8,000 authors.
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 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.
[edit] 2000–present
Perl 5.6 was released on March 22, 2000. Major changes included 64 bit support, unicode string representation, large file support (e.g., files > 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, Larry Wall put forth a call for suggestions for a new version of Perl from the community. The process resulted in 361 RFCs (Request for Comments) documents which 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. The latest version of Perl 5.8 is 5.8.9, released December 14, 2008. Perl 5.8 improved unicode support, added a new IO implementation, added a new thread implementation, improved numeric accuracy, and added several new modules.
In 2004, work began on the Synopses – originally documents that 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, with planned release dates three months ahead.
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. The latest development release of Perl 5 is 5.13.9, released by Jesse Vincent on January 21, 2011.
Perl on Windows
Users of Microsoft Windows typically install one of the native binary distributions of Perl for Win32, most commonly Strawberry Perl or ActivePerl. Compiling Perl from source code under Windows is possible, but most installations lack the requisite C compiler and build tools. This also makes it difficult to install modules from the CPAN, particularly those that are partially written in C.
ActivePerl is a closed source distribution from ActiveState that has regular releases that track the core Perl releases. The distribution also includes the Perl package manager (PPM), a popular tool for installing, removing, upgrading, and managing the use of common Perl modules.
Strawberry Perl is an open source distribution for Windows. It has had regular, quarterly releases since January 2008, including new modules as feedback and requests come in. Strawberry Perl aims to be able to install modules like standard Perl distributions on other platforms, including compiling XS modules.
The Cygwin emulation layer is another way of running Perl under Windows. Cygwin provides a Unix-like environment on Windows, and both Perl and CPAN are available as standard pre-compiled packages in the Cygwin setup program. Because Cygwin also includes the gcc, compiling Perl from source is also possible.
Perl Applications
Perl has many and varied applications, compounded by the availability of many standard and third-party modules.
Ever since the early days of the Web, programmers have used Perl to write CGI scripts. Perl is known as one of "the three Ps" (along with Python and PHP), the most popular dynamic languages for writing Web applications. It is also an integral component of the popular LAMP solution stack for web development. Large projects written in Perl include cPanel, Slash, Bugzilla, RT, TWiki, and Movable Type. Many high-traffic websites use Perl extensively. Examples include Amazon.com, bbc.co.uk, Priceline.com, Craigslist, IMDb, LiveJournal, Slashdot and Ticketmaster.
Perl is often used as a glue language, tying together systems and interfaces that were not specifically designed to interoperate, and for "data munging", that is, converting or processing large amounts of data for tasks such as creating reports. In fact, these strengths are intimately linked. The combination makes Perl a popular all-purpose language for system administrators, particularly because short programs can be entered and run on a single command line.
With a degree of care, Perl code can be made portable across Windows and Unix. Portable Perl code is often used by suppliers of software (both COTS and bespoke) to simplify packaging and maintenance of software build- and deployment-scripts.
Graphical user interfaces (GUIs) may be developed using Perl. For example, Perl/Tk is commonly used to enable user interaction with Perl scripts. Such interaction may be synchronous or asynchronous, using callbacks to update the GUI. For more information about the technologies involved, see Tk, Tcl and WxPerl.
Perl is also widely used in finance and in bioinformatics, where it is valued for rapid application development and deployment and for its capability to handle large data-sets.
Perl Design
The design of Perl can be understood as a response to three broad trends in the computer industry: falling hardware costs, rising labor costs, and improvements in compiler technology. Many earlier computer languages, such as Fortran and C, aimed to make efficient use of expensive computer hardware. In contrast, Perl is designed to make efficient use of expensive computer-programmers.
Perl has many features that ease the task of the programmer at the expense of greater CPU and memory requirements. These include automatic memory management; dynamic typing; strings, lists, and hashes; regular expressions; introspection; and an eval() function. Perl follows the theory of "no built-in limits", an idea similar to the Zero One Infinity rule.
Perl syntax reflects the idea that "things that are different should look different". For example, scalars, arrays, and hashes have different leading sigils. Array indices and hash keys use different kinds of braces. Strings and regular expressions have different standard delimiters. This approach can be contrasted with languages such as Lisp, where the same S-expression construct and basic syntax are used for many different purposes.
Perl does not enforce any particular programming paradigm (procedural, object-oriented, functional, or others) or even require the programmer to choose among them.
No written specification or standard for the Perl language exists for Perl versions through Perl 5, and there are no plans to create one for the current version of Perl. There has been only one implementation of the interpreter, and the language has evolved along with it. That interpreter, together with its functional tests, stands as a de facto specification of the language. Perl 6, however, started with a specification, and several projects aim to implement some or all of the specification
Perl Feature
The overall structure of Perl derives broadly from C. Perl is procedural in nature, with variables, expressions, assignment statements, brace-delimited blocks, control structures, and subroutines.
Perl also takes features from shell programming. All variables are marked with leading sigils, which unambiguously identify the data type (for example, scalar, array, hash) of the variable in context. Importantly, sigils allow variables to be interpolated directly into strings. Perl has many built-in functions that provide tools often used in shell programming (although many of these tools are implemented by programs external to the shell) such as sorting, and calling on system facilities.
Perl takes lists from Lisp, hashes ("associative arrays") from AWK, and regular expressions from sed. These simplify and facilitate many parsing, text-handling, and data-management tasks.
Perl 5 added features that support complex data structures, first-class functions (that is, closures as values), and an object-oriented programming model. These include references, packages, class-based method dispatch, and lexically scoped variables, along with compiler directives (for example, the strict pragma). A major additional feature introduced with Perl 5 was the ability to package code as reusable modules. Larry Wall later stated that "The whole intent of Perl 5's module system was to encourage the growth of Perl culture rather than the Perl core."
All versions of Perl do automatic data-typing and automatic memory-management. The interpreter knows the type and storage requirements of every data object in the program; it allocates and frees storage for them as necessary using reference counting (so it cannot deallocate circular data structures without manual intervention). Legal type-conversions — for example, conversions from number to string — are done automatically at run time; illegal type conversions are fatal errors.
Perl Overview
Perl is a general-purpose programming language originally developed for text manipulation, but as of 2010[update] is used for a wide range of tasks including system administration, web development, network programming, games, bioinformatics, and GUI development.
The language is intended to be practical (easy to use, efficient, complete) rather than beautiful (tiny, elegant, minimal). Its major features include support for multiple programming paradigms (procedural, object-oriented, and functional styles), reference counting memory management (without a cycle-detecting garbage collector), built-in support for text processing, and a large collection of third-party modules.
According to Larry Wall, Perl has two slogans. The first is "There's more than one way to do it", commonly known as TMTOWTDI. The second slogan is "Easy things should be easy and hard things should be possible".
Perl Database Interaction
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 done for only a few of the most-important and most widely used databases, and it restricted the resulting perl executable to using just one database interface at a time.
In Perl 5, database interfaces are implemented by Perl DBI modules. The DBI (Database Interface) module presents a single, database-independent interface to Perl applications, while the DBD (Database Driver) modules handle the details of accessing some 50 different databases; there are DBD drivers for most ANSI SQL databases.
DBI provides caching for database handles and queries, which can greatly improve performance in long-lived execution environments such as mod_perl, helping high-volume systems avert load spikes as in the Slashdot effect.
In modern Perl applications, especially those written using Web application frameworks such as Catalyst, the DBI module is often used indirectly via object-relational mappers such as DBIx::Class, Class::DBI or Rose::DB::Object which generate SQL queries and handle data transparently to the application author.
Perl is a high-level, general-purpose, interpreted, dynamic programming 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 and become widely popular amongst programmers. Larry Wall continues to oversee development of the core language, and its upcoming version, Perl 6. Perl borrows features from other programming languages including C, shell scripting (sh), AWK, and sed. The language provides powerful text processing facilities without the arbitrary data length limits of many contemporary Unix tools, facilitating easy manipulation of text files. Perl gained widespread popularity in the late 1990s as a CGI scripting language, in part due to its parsing abilities.
In addition to CGI, Perl is used for graphics programming, system administration, network programming, finance, bioinformatics, and other applications. Perl is nicknamed "the Swiss Army chainsaw of programming languages" due to its flexibility and power. It is also referred to as the "duct tape that holds the Internet together", in reference to its ubiquity and perceived inelegance.
Perl Name and Symbol
Name
Perl was originally named "Pearl", after the Parable of the Pearl from the Gospel of Matthew. Larry Wall wanted to give the language a short name with positive connotations; he claims that he considered (and rejected) every three- and four-letter word in the dictionary. He also considered naming it after his wife Gloria. Wall discovered the existing PEARL programming language before Perl's official release and changed the spelling of the name.
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.
There is some contention about the all-caps spelling "Perl", which the documentation declares incorrect and which some core community members consider a sign of outsiders. The name is occasionally backronymed as Practical Extraction and Report Language (which appears at the top of the documentation and in some printed literature). Several backronyms have been suggested as equally canonical, including Wall's own humorous Pathologically Eclectic Rubbish Lister. Indeed, Wall claims that the name was intended to inspire many different expansions.
Camel symbol
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.
Onion symbol
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 pun on the pearl onion.
Perl History
Early Perl versions
Larry Wall began work on Perl in 1987, while working as a programmer at Unisys, and released version 1.0 to the comp.sources.misc newsgroup on December 18, 1987. The language expanded rapidly over the next few years.
Perl 2, released in 1988, featured a better regular expression engine. Perl 3, released in 1989, added support for binary data streams.
Originally the only documentation for Perl was a single (increasingly lengthy) man page. In 1991, Programming Perl (known to many Perl programmers as the "Camel Book" 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 documented by the book.
Early Perl 5
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 January 2011, it carries over 19,000 modules by more than 8,000 authors.
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 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.
[edit] 2000–present
Perl 5.6 was released on March 22, 2000. Major changes included 64 bit support, unicode string representation, large file support (e.g., files > 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, Larry Wall put forth a call for suggestions for a new version of Perl from the community. The process resulted in 361 RFCs (Request for Comments) documents which 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. The latest version of Perl 5.8 is 5.8.9, released December 14, 2008. Perl 5.8 improved unicode support, added a new IO implementation, added a new thread implementation, improved numeric accuracy, and added several new modules.
In 2004, work began on the Synopses – originally documents that 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, with planned release dates three months ahead.
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. The latest development release of Perl 5 is 5.13.9, released by Jesse Vincent on January 21, 2011.
Perl on Windows
Users of Microsoft Windows typically install one of the native binary distributions of Perl for Win32, most commonly Strawberry Perl or ActivePerl. Compiling Perl from source code under Windows is possible, but most installations lack the requisite C compiler and build tools. This also makes it difficult to install modules from the CPAN, particularly those that are partially written in C.
ActivePerl is a closed source distribution from ActiveState that has regular releases that track the core Perl releases. The distribution also includes the Perl package manager (PPM), a popular tool for installing, removing, upgrading, and managing the use of common Perl modules.
Strawberry Perl is an open source distribution for Windows. It has had regular, quarterly releases since January 2008, including new modules as feedback and requests come in. Strawberry Perl aims to be able to install modules like standard Perl distributions on other platforms, including compiling XS modules.
The Cygwin emulation layer is another way of running Perl under Windows. Cygwin provides a Unix-like environment on Windows, and both Perl and CPAN are available as standard pre-compiled packages in the Cygwin setup program. Because Cygwin also includes the gcc, compiling Perl from source is also possible.
Perl Applications
Perl has many and varied applications, compounded by the availability of many standard and third-party modules.
Ever since the early days of the Web, programmers have used Perl to write CGI scripts. Perl is known as one of "the three Ps" (along with Python and PHP), the most popular dynamic languages for writing Web applications. It is also an integral component of the popular LAMP solution stack for web development. Large projects written in Perl include cPanel, Slash, Bugzilla, RT, TWiki, and Movable Type. Many high-traffic websites use Perl extensively. Examples include Amazon.com, bbc.co.uk, Priceline.com, Craigslist, IMDb, LiveJournal, Slashdot and Ticketmaster.
Perl is often used as a glue language, tying together systems and interfaces that were not specifically designed to interoperate, and for "data munging", that is, converting or processing large amounts of data for tasks such as creating reports. In fact, these strengths are intimately linked. The combination makes Perl a popular all-purpose language for system administrators, particularly because short programs can be entered and run on a single command line.
With a degree of care, Perl code can be made portable across Windows and Unix. Portable Perl code is often used by suppliers of software (both COTS and bespoke) to simplify packaging and maintenance of software build- and deployment-scripts.
Graphical user interfaces (GUIs) may be developed using Perl. For example, Perl/Tk is commonly used to enable user interaction with Perl scripts. Such interaction may be synchronous or asynchronous, using callbacks to update the GUI. For more information about the technologies involved, see Tk, Tcl and WxPerl.
Perl is also widely used in finance and in bioinformatics, where it is valued for rapid application development and deployment and for its capability to handle large data-sets.
Perl Design
The design of Perl can be understood as a response to three broad trends in the computer industry: falling hardware costs, rising labor costs, and improvements in compiler technology. Many earlier computer languages, such as Fortran and C, aimed to make efficient use of expensive computer hardware. In contrast, Perl is designed to make efficient use of expensive computer-programmers.
Perl has many features that ease the task of the programmer at the expense of greater CPU and memory requirements. These include automatic memory management; dynamic typing; strings, lists, and hashes; regular expressions; introspection; and an eval() function. Perl follows the theory of "no built-in limits", an idea similar to the Zero One Infinity rule.
Perl syntax reflects the idea that "things that are different should look different". For example, scalars, arrays, and hashes have different leading sigils. Array indices and hash keys use different kinds of braces. Strings and regular expressions have different standard delimiters. This approach can be contrasted with languages such as Lisp, where the same S-expression construct and basic syntax are used for many different purposes.
Perl does not enforce any particular programming paradigm (procedural, object-oriented, functional, or others) or even require the programmer to choose among them.
No written specification or standard for the Perl language exists for Perl versions through Perl 5, and there are no plans to create one for the current version of Perl. There has been only one implementation of the interpreter, and the language has evolved along with it. That interpreter, together with its functional tests, stands as a de facto specification of the language. Perl 6, however, started with a specification, and several projects aim to implement some or all of the specification
Perl Feature
The overall structure of Perl derives broadly from C. Perl is procedural in nature, with variables, expressions, assignment statements, brace-delimited blocks, control structures, and subroutines.
Perl also takes features from shell programming. All variables are marked with leading sigils, which unambiguously identify the data type (for example, scalar, array, hash) of the variable in context. Importantly, sigils allow variables to be interpolated directly into strings. Perl has many built-in functions that provide tools often used in shell programming (although many of these tools are implemented by programs external to the shell) such as sorting, and calling on system facilities.
Perl takes lists from Lisp, hashes ("associative arrays") from AWK, and regular expressions from sed. These simplify and facilitate many parsing, text-handling, and data-management tasks.
Perl 5 added features that support complex data structures, first-class functions (that is, closures as values), and an object-oriented programming model. These include references, packages, class-based method dispatch, and lexically scoped variables, along with compiler directives (for example, the strict pragma). A major additional feature introduced with Perl 5 was the ability to package code as reusable modules. Larry Wall later stated that "The whole intent of Perl 5's module system was to encourage the growth of Perl culture rather than the Perl core."
All versions of Perl do automatic data-typing and automatic memory-management. The interpreter knows the type and storage requirements of every data object in the program; it allocates and frees storage for them as necessary using reference counting (so it cannot deallocate circular data structures without manual intervention). Legal type-conversions — for example, conversions from number to string — are done automatically at run time; illegal type conversions are fatal errors.
Perl Overview
Perl is a general-purpose programming language originally developed for text manipulation, but as of 2010[update] is used for a wide range of tasks including system administration, web development, network programming, games, bioinformatics, and GUI development.
The language is intended to be practical (easy to use, efficient, complete) rather than beautiful (tiny, elegant, minimal). Its major features include support for multiple programming paradigms (procedural, object-oriented, and functional styles), reference counting memory management (without a cycle-detecting garbage collector), built-in support for text processing, and a large collection of third-party modules.
According to Larry Wall, Perl has two slogans. The first is "There's more than one way to do it", commonly known as TMTOWTDI. The second slogan is "Easy things should be easy and hard things should be possible".
Perl Database Interaction
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 done for only a few of the most-important and most widely used databases, and it restricted the resulting perl executable to using just one database interface at a time.
In Perl 5, database interfaces are implemented by Perl DBI modules. The DBI (Database Interface) module presents a single, database-independent interface to Perl applications, while the DBD (Database Driver) modules handle the details of accessing some 50 different databases; there are DBD drivers for most ANSI SQL databases.
DBI provides caching for database handles and queries, which can greatly improve performance in long-lived execution environments such as mod_perl, helping high-volume systems avert load spikes as in the Slashdot effect.
In modern Perl applications, especially those written using Web application frameworks such as Catalyst, the DBI module is often used indirectly via object-relational mappers such as DBIx::Class, Class::DBI or Rose::DB::Object which generate SQL queries and handle data transparently to the application author.
