perlfaq1


DESCRIPTION
       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
       http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/ and
       http://archive.develooper.com/perl5-porters@perl.org/ or the news
       gateway nntp://nntp.perl.org/perl.perl5.porters or its web interface at
       http://nntp.perl.org/group/perl.perl5.porters , or read the faq at
       http://dev.perl.org/perl5/docs/p5p-faq.html , or you can subscribe to
       the mailing list by sending perl5-porters-subscribe@perl.org 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 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
           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, http://www.cert.org/advisories/CA-1997-17.html ).

       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. Ten 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. The joke is that it's scheduled for Christmas, but that
           we just don't know which one. 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.

       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 first 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, although it's not intended to
       replace Perl 5. It's still in development in both its syntax and
       design. The work started in 2002 and is still ongoing. Some 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

       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.

   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 http://dev.perl.org/perl6/ 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 and test/debug quickly and easily. This ease of
       experimentation flattens the learning curve even more.
       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
       http://www.perl.com/doc/FMTEYEWTK/versus/ 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.

   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, make).

       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
       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 notwithstanding.

   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 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 http://www.cpan.org/misc/japh .

   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.  :)

       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 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 (
       http://www.perlmonks.com ) and the various Perl mailing lists (
       http://lists.perl.org ) 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:

       o   http://perltraining.com.au/whyperl.html

       o   http://www.perl.org/advocacy/whyperl.html

AUTHOR AND COPYRIGHT
       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.



perl v5.14.2                      2011-09-26                       PERLFAQ1(1)
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