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perlfaq1 (1)


perlfaq1 - General Questions About Perl


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Perl Programmers Reference Guide                      PERLFAQ1(1)

     perlfaq1 - General Questions About Perl

     This section of the FAQ answers very general, high-level
     questions about Perl.

  What is Perl?
     Perl is a high-level programming language with an eclectic
     heritage written by Larry Wall and a cast of thousands. It
     derives from the ubiquitous C programming language and to a
     lesser extent from sed, awk, the Unix shell, and at least a
     dozen other tools and languages.  Perl's process, file, and
     text manipulation facilities make it particularly well-
     suited for tasks involving quick prototyping, system
     utilities, software tools, system management tasks, database
     access, graphical programming, networking, and world wide
     web programming.  These strengths make it especially popular
     with system administrators and CGI script authors, but
     mathematicians, geneticists, journalists, and even managers
     also use Perl. Maybe you should, too.

  Who supports Perl? Who develops it? Why is it free?
     The original culture of the pre-populist Internet and the
     deeply-held beliefs of Perl's author, Larry Wall, gave rise
     to the free and open distribution policy of perl. Perl is
     supported by its users. The core, the standard Perl library,
     the optional modules, and the documentation you're reading
     now were all written by volunteers. See the personal note at
     the end of the README file in the perl source distribution
     for more details. See perlhist (new as of 5.005) for Perl's
     milestone releases.

     In particular, the core development team (known as the Perl
     Porters) are a rag-tag band of highly altruistic individuals
     committed to producing better software for free than you
     could hope to purchase for money. You may snoop on pending
     developments via the archives at and or the
     news gateway nntp:// or its
     web interface at , or read the
     faq at , or you
     can subscribe to the mailing list by sending a subscription request (an
     empty message with no subject is fine).

     While the GNU project includes Perl in its distributions,
     there's no such thing as "GNU Perl". Perl is not produced
     nor maintained by the Free Software Foundation. Perl's
     licensing terms are also more open than GNU software's tend

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     to be.

     You can get commercial support of Perl if you wish, although
     for most users the informal support will more than suffice.
     See the answer to "Where can I buy a commercial version of
     perl?" for more information.

  Which version of Perl should I use?
     (contributed by brian d foy)

     There is often a matter of opinion and taste, and there
     isn't any one answer that fits everyone. In general, you
     want to use either the current stable release, or the stable
     release immediately prior to that one.  Currently, those are
     perl5.10.x and perl5.8.x, respectively.

     Beyond that, you have to consider several things and decide
     which is best for you.

     o   If things aren't broken, upgrading perl may break them
         (or at least issue new warnings).

     o   The latest versions of perl have more bug fixes.

     o   The Perl community is geared toward supporting the most
         recent releases, so you'll have an easier time finding
         help for those.

     o   Versions prior to perl5.004 had serious security
         problems with buffer overflows, and in some cases have
         CERT advisories (for instance, ).

     o   The latest versions are probably the least deployed and
         widely tested, so you may want to wait a few months
         after their release and see what problems others have if
         you are risk averse.

     o   The immediate, previous releases (i.e. perl5.8.x ) are
         usually maintained for a while, although not at the same
         level as the current releases.

     o   No one is actively supporting Perl 4. Five years ago it
         was a dead camel carcass (according to this document).
         Now it's barely a skeleton as its whitewashed bones have
         fractured or eroded.

     o   There is no Perl 6 release scheduled, but it will be
         available when it's ready. Stay tuned, but don't worry
         that you'll have to change major versions of Perl; no
         one is going to take Perl 5 away from you.

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     o   There are really two tracks of perl development: a
         maintenance version and an experimental version. The
         maintenance versions are stable, and have an even number
         as the minor release (i.e. perl5.10.x, where 10 is the
         minor release). The experimental versions may include
         features that don't make it into the stable versions,
         and have an odd number as the minor release (i.e.
         perl5.9.x, where 9 is the minor release).

  What are Perl 4, Perl 5, or Perl 6?
     (contributed by brian d foy)

     In short, Perl 4 is the past, Perl 5 is the present, and
     Perl 6 is the future.

     The number after perl (i.e. the 5 after Perl 5) is the major
     release of the perl interpreter as well as the version of
     the language. Each major version has significant differences
     that earlier versions cannot support.

     The current major release of Perl is Perl 5, and was
     released in 1994.  It can run scripts from the previous
     major release, Perl 4 (March 1991), but has significant
     differences. It introduced the concept of references,
     complex data structures, and modules. The Perl 5 interpreter
     was a complete re-write of the previous perl sources.

     Perl 6 is the next major version of Perl, but it's still in
     development in both its syntax and design. The work started
     in 2002 and is still ongoing. Many of the most interesting
     features have shown up in the latest versions of Perl 5, and
     some Perl 5 modules allow you to use some Perl 6 syntax in
     your programs. You can learn more about Perl 6 at .

     See perlhist for a history of Perl revisions.

  What was Ponie?
     (contributed by brian d foy)

     Ponie stands for "Perl On the New Internal Engine", started
     by Arthur Bergman from Fotango in 2003, and subsequently run
     as a project of The Perl Foundation. It was abandoned in
     2006 ( ).

     Instead of using the current Perl internals, Ponie aimed to
     create a new one that would provide a translation path from
     Perl 5 to Perl 6 (or anything else that targets Parrot,
     actually). You would have been able to just keep using Perl
     5 with Parrot, the virtual machine which will compile and
     run Perl 6 bytecode.

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  What is Perl 6?
     At The Second O'Reilly Open Source Software Convention,
     Larry Wall announced Perl 6 development would begin in
     earnest. Perl 6 was an oft used term for Chip Salzenberg's
     project to rewrite Perl in C++ named Topaz. However, Topaz
     provided valuable insights to the next version of Perl and
     its implementation, but was ultimately abandoned.

     If you want to learn more about Perl 6, or have a desire to
     help in the crusade to make Perl a better place then read
     the Perl 6 developers page at and
     get involved.

     Perl 6 is not scheduled for release yet, and Perl 5 will
     still be supported for quite awhile after its release. Do
     not wait for Perl 6 to do whatever you need to do.

     "We're really serious about reinventing everything that
     needs reinventing."  --Larry Wall

  How stable is Perl?
     Production releases, which incorporate bug fixes and new
     functionality, are widely tested before release. Since the
     5.000 release, we have averaged only about one production
     release per year.

     Larry and the Perl development team occasionally make
     changes to the internal core of the language, but all
     possible efforts are made toward backward compatibility.
     While not quite all Perl 4 scripts run flawlessly under Perl
     5, an update to perl should nearly never invalidate a
     program written for an earlier version of perl (barring
     accidental bug fixes and the rare new keyword).

  Is Perl difficult to learn?
     No, Perl is easy to start learning--and easy to keep
     learning. It looks like most programming languages you're
     likely to have experience with, so if you've ever written a
     C program, an awk script, a shell script, or even a BASIC
     program, you're already partway there.

     Most tasks only require a small subset of the Perl language.
     One of the guiding mottos for Perl development is "there's
     more than one way to do it" (TMTOWTDI, sometimes pronounced
     "tim toady"). Perl's learning curve is therefore shallow
     (easy to learn) and long (there's a whole lot you can do if
     you really want).

     Finally, because Perl is frequently (but not always, and
     certainly not by definition) an interpreted language, you
     can write your programs and test them without an
     intermediate compilation step, allowing you to experiment

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     and test/debug quickly and easily. This ease of
     experimentation flattens the learning curve even more.

     Things that make Perl easier to learn: Unix experience,
     almost any kind of programming experience, an understanding
     of regular expressions, and the ability to understand other
     people's code. If there's something you need to do, then
     it's probably already been done, and a working example is
     usually available for free. Don't forget Perl modules,
     either.  They're discussed in Part 3 of this FAQ, along with
     CPAN, which is discussed in Part 2.

  How does Perl compare with other languages like Java, Python,
     REXX, Scheme, or Tcl?
     Favorably in some areas, unfavorably in others. Precisely
     which areas are good and bad is often a personal choice, so
     asking this question on Usenet runs a strong risk of
     starting an unproductive Holy War.

     Probably the best thing to do is try to write equivalent
     code to do a set of tasks. These languages have their own
     newsgroups in which you can learn about (but hopefully not
     argue about) them.

     Some comparison documents can be found at if you really
     can't stop yourself.

  Can I do [task] in Perl?
     Perl is flexible and extensible enough for you to use on
     virtually any task, from one-line file-processing tasks to
     large, elaborate systems.  For many people, Perl serves as a
     great replacement for shell scripting.  For others, it
     serves as a convenient, high-level replacement for most of
     what they'd program in low-level languages like C or C++.
     It's ultimately up to you (and possibly your management)
     which tasks you'll use Perl for and which you won't.

     If you have a library that provides an API, you can make any
     component of it available as just another Perl function or
     variable using a Perl extension written in C or C++ and
     dynamically linked into your main perl interpreter. You can
     also go the other direction, and write your main program in
     C or C++, and then link in some Perl code on the fly, to
     create a powerful application. See perlembed.

     That said, there will always be small, focused, special-
     purpose languages dedicated to a specific problem domain
     that are simply more convenient for certain kinds of
     problems. Perl tries to be all things to all people, but
     nothing special to anyone. Examples of specialized languages
     that come to mind include prolog and matlab.

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  When shouldn't I program in Perl?
     When your manager forbids it--but do consider replacing them

     Actually, one good reason is when you already have an
     existing application written in another language that's all
     done (and done well), or you have an application language
     specifically designed for a certain task (e.g. prolog,

     For various reasons, Perl is probably not well-suited for
     real-time embedded systems, low-level operating systems
     development work like device drivers or context-switching
     code, complex multi-threaded shared-memory applications, or
     extremely large applications. You'll notice that perl is not
     itself written in Perl.

     Perl remains fundamentally a dynamically typed language, not
     a statically typed one. You certainly won't be chastised if
     you don't trust nuclear-plant or brain-surgery monitoring
     code to it. And Larry will sleep easier, too--Wall Street
     programs not withstanding. :-)

  What's the difference between "perl" and "Perl"?
     One bit. Oh, you weren't talking ASCII? :-) Larry now uses
     "Perl" to signify the language proper and "perl" the
     implementation of it, i.e.  the current interpreter. Hence
     Tom's quip that "Nothing but perl can parse Perl."

     Before the first edition of Programming perl, people
     commonly referred to the language as "perl", and its name
     appeared that way in the title because it referred to the
     interpreter. In the book, Randal Schwartz capitalised the
     language's name to make it stand out better when typeset.
     This convention was adopted by the community, and the second
     edition became Programming Perl, using the capitalized
     version of the name to refer to the language.

     You may or may not choose to follow this usage. For example,
     parallelism means "awk and perl" and "Python and Perl" look
     good, while "awk and Perl" and "Python and perl" do not. But
     never write "PERL", because perl is not an acronym,
     apocryphal folklore and post-facto expansions

  Is it a Perl program or a Perl script?
     Larry doesn't really care. He says (half in jest) that "a
     script is what you give the actors. A program is what you
     give the audience."

     Originally, a script was a canned sequence of normally
     interactive commands--that is, a chat script. Something like

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     a UUCP or PPP chat script or an expect script fits the bill
     nicely, as do configuration scripts run by a program at its
     start up, such .cshrc or .ircrc, for example. Chat scripts
     were just drivers for existing programs, not stand-alone
     programs in their own right.

     A computer scientist will correctly explain that all
     programs are interpreted and that the only question is at
     what level. But if you ask this question of someone who
     isn't a computer scientist, they might tell you that a
     program has been compiled to physical machine code once and
     can then be run multiple times, whereas a script must be
     translated by a program each time it's used.

     Now that "script" and "scripting" are terms that have been
     seized by unscrupulous or unknowing marketeers for their own
     nefarious purposes, they have begun to take on strange and
     often pejorative meanings, like "non serious" or "not real
     programming". Consequently, some Perl programmers prefer to
     avoid them altogether.

  What is a JAPH?
     (contributed by brian d foy)

     JAPH stands for "Just another Perl hacker,", which Randal
     Schwartz used to sign email and usenet messages starting in
     the late 1980s. He previously used the phrase with many
     subjects ("Just another x hacker,"), so to distinguish his
     JAPH, he started to write them as Perl programs:

             print "Just another Perl hacker,";

     Other people picked up on this and started to write clever
     or obfuscated programs to produce the same output, spinning
     things quickly out of control while still providing hours of
     amusement for their creators and readers.

     CPAN has several JAPH programs at .

  Where can I get a list of Larry Wall witticisms?
     (contributed by brian d foy)

     Google "larry wall quotes"! You might even try the "I feel
     lucky" button.  :)

     Wikiquote has the witticisms from Larry along with their
     source, including his usenet postings and source code

     If you want a plain text file, try .

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  How can I convince others to use Perl?
     (contributed by brian d foy)

     Appeal to their self interest! If Perl is new (and thus
     scary) to them, find something that Perl can do to solve one
     of their problems. That might mean that Perl either saves
     them something (time, headaches, money) or gives them
     something (flexibility, power, testability).

     In general, the benefit of a language is closely related to
     the skill of the people using that language. If you or your
     team can be more faster, better, and stronger through Perl,
     you'll deliver more value. Remember, people often respond
     better to what they get out of it. If you run into
     resistance, figure out what those people get out of the
     other choice and how Perl might satisfy that requirement.

     You don't have to worry about finding or paying for Perl;
     it's freely available and several popular operating systems
     come with Perl. Community support in places such as
     Perlmonks ( ) and the various Perl
     mailing lists ( ) means that you can
     usually get quick answers to your problems.

     Finally, keep in mind that Perl might not be the right tool
     for every job. You're a much better advocate if your claims
     are reasonable and grounded in reality. Dogmatically
     advocating anything tends to make people discount your
     message. Be honest about possible disadvantages to your
     choice of Perl since any choice has trade-offs.

     You might find these links useful:



     Copyright (c) 1997-2010 Tom Christiansen, Nathan Torkington,
     and other authors as noted. All rights reserved.

     This documentation is free; you can redistribute it and/or
     modify it under the same terms as Perl itself.

     Irrespective of its distribution, all code examples here are
     in the public domain. You are permitted and encouraged to
     use this code and any derivatives thereof in your own
     programs for fun or for profit as you see fit. A simple
     comment in the code giving credit to the FAQ would be
     courteous but is not required.

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     See attributes(5) for descriptions of the following

     |Availability   | runtime/perl-512 |
     |Stability      | Uncommitted      |
     This software was built from source available at  The original
     community source was downloaded from

     Further information about this software can be found on the
     open source community website at

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