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PERLFAQ1(1)			 Perl Programmers Reference Guide		      PERLFAQ1(1)

       perlfaq1 - General Questions About Perl ($Revision: 10427 $)

       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 lan-
       guages.	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.devel-
       ooper.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-request@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
       anyone.	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,

       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 warn-

       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, http://www.cert.org/advi-
	   sories/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.  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.

       o   There are really two tracks of perl development: a maintenance version and an experi-
	   mental 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 ver-
	   sions 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 inter-
       preter as well as the version of the language.  Each major version has significant differ-
       ences 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
       http://dev.perl.org/perl6/ .

       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 ( http://www.nntp.perl.org/group/perl.ponie.dev/487 ).

       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 devel-
       opment 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 peruse 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 pro-
       gramming 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

       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 pro-
       nounced "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.

       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 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 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 inter-
       preter. 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 lan-

       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 com-
       puter 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".  Conse-
       quently, 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 sub-
       jects ("Just another x hacker,"), so to distinguish his JAPH, he started to write them as
       Perl programs:

	       print "Just another Perl hacker, ";

       Note the trailing comma and space, which allows the addition of other JAxH clauses for his
       many other interests.

       Other people picked up on this and started to write clever or obfuscated programs to pro-
       duce 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.  :)

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

       If you want a plain text file, try http://www.cpan.org/misc/lwall-quotes.txt.gz .

       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,

       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 sev-
       eral popular operating systems come with Perl. Community support in places such as Perl-
       monks ( 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 advo-
       cating anything tends to make people discount your message. Be honest about possible dis-
       advantages to your choice of Perl since any choice has trade-offs.

       You might find these links useful:

       * http://perltraining.com.au/whyperl.html
       * http://www.perl.org/advocacy/whyperl.html

       Revision: $Revision: 10427 $

       Date: $Date: 2007-12-14 00:39:01 +0100 (Fri, 14 Dec 2007) $

       See perlfaq for source control details and availability.

       Copyright (c) 1997-2007 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 pro-
       grams 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 v5.8.9				    2007-11-17				      PERLFAQ1(1)
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