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NAME    [Toc]    [Back]

       perlfaq1 - General Questions About Perl ($Revision: 1.7 $,
       $Date: 2004/04/07 21:33:08 $)

DESCRIPTION    [Toc]    [Back]

       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 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://simon-cozens.org/writings/p5p-faq ,
       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?

       You should definitely use version 5.  Version 4 is old,
       limited, and no longer maintained; its last patch (4.036)
       was in 1992, long ago and far away.  Sure, it's stable,
       but so is anything that's dead; in fact, perl4 had been
       called a dead, flea-bitten camel carcass.  The most recent
       production release is 5.8.2 (although 5.005_03 and 5.6.2
       are still supported). The most cutting-edge development
       release is 5.9.  Further references to the Perl language
       in this document refer to the production release unless
       otherwise specified.  There may be one or more official
       bug fixes by the time you read this, and also perhaps some
       experimental versions on the way to the next release.  All
       releases prior to 5.004 were subject to buffer overruns, a
       grave security issue.

       What are perl4 and perl5?

       Perl4 and perl5 are informal names for different versions
       of the Perl programming language.  It's easier to say
       "perl5" than it is to say "the 5(.004) release of Perl",
       but some people have interpreted this to mean there's a
       language called "perl5", which isn't the case.  Perl5 is
       merely the popular name for the fifth major release (October
 1994), while perl4 was the fourth major release (March
       1991).  There was also a perl1 (in January 1988), a perl2
       (June 1988), and a perl3 (October 1989).

       The 5.0 release is, essentially, a ground-up rewrite of
       the original perl source code from releases 1 through 4.
       It has been modularized, object-oriented, tweaked,
       trimmed, and optimized until it almost doesn't look like
       the old code.  However, the interface is mostly the same,
       and compatibility with previous releases is very high.
       See "Perl4 to Perl5 Traps" in perltrap.

       To avoid the "what language is perl5?" confusion, some
       people prefer to simply use "perl" to refer to the latest
       version of perl and avoid using "perl5" altogether.  It's
       not really that big a deal, though.

       See perlhist for a history of Perl revisions.
       What is Ponie?

       At The O'Reilly Open Source Software Convention in 2003,
       Artur Bergman, Fotango, and The Perl Foundation announced
       a project to run perl5 on the Parrot virtual machine named
       Ponie. Ponie stands for Perl On New Internal Engine.  The
       Perl 5.10 language implementation will be used for Ponie,
       and there will be no language level differences between
       perl5 and ponie.  Ponie is not a complete rewrite of

       For more details, see http://www.poniecode.org/

       What is perl6?

       At The Second O'Reilly Open Source Software Convention,
       Larry Wall announced Perl6 development would begin in
       earnest. Perl6 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 Perl6, or have a desire to
       help in the crusade to make Perl a better place then
       peruse the Perl6 developers page at
       http://dev.perl.org/perl6/ and get involved.

       Perl6 is not scheduled for release yet, and Perl5 will
       still be supported for quite awhile after its release. Do
       not wait for Perl6 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 perl4 scripts run flawlessly under
       perl5, 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.

       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 the new
       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://language.perl.com/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

       That said, there will always be small, focused, specialpurpose
 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,

       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.

       The new, native-code compiler for Perl may eventually
       reduce the limitations given in the previous statement to
       some degree, but understand that 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."  You
       may or may not choose to follow this usage.  For example,
       parallelism means "awk and perl" and "Python and Perl"
       look OK, 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 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.

       Perl programs are (usually) neither strictly compiled nor
       strictly interpreted.  They can be compiled to a byte-code
       form (something of a Perl virtual machine) or to completely
  different languages, like C or assembly language.
       You can't tell just by looking at it whether the source is
       destined for a pure interpreter, a parse-tree interpreter,
       a byte-code interpreter, or a native-code compiler, so
       it's hard to give a definitive answer here.

       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?

       These are the "just another perl hacker" signatures that
       some people sign their postings with.  Randal Schwartz
       made these famous.  About 100 of the earlier ones are
       available from http://www.cpan.org/misc/japh .

       Where can I get a list of Larry Wall witticisms?

       Over a hundred quips by Larry, from postings of his or
       source code, can be found at
       http://www.cpan.org/misc/lwall-quotes.txt.gz .
       How can I convince my sysadmin/supervisor/employees to use
       version 5/5.6.1/Perl instead of some other language?

       If your manager or employees are wary of unsupported software,
 or software which doesn't officially ship with your
       operating system, you might try to appeal to their
       self-interest.  If programmers can be more productive
       using and utilizing Perl constructs, functionality, simplicity,
 and power, then the typical manager/supervisor/employee
 may be persuaded.  Regarding using Perl in
       general, it's also sometimes helpful to point out that
       delivery times may be reduced using Perl compared to other

       If you have a project which has a bottleneck, especially
       in terms of translation or testing, Perl almost certainly
       will provide a viable, quick solution.  In conjunction
       with any persuasion effort, you should not fail to point
       out that Perl is used, quite extensively, and with
       extremely reliable and valuable results, at many large
       computer software and hardware companies throughout the
       world.  In fact, many Unix vendors now ship Perl by
       default.  Support is usually just a news-posting away, if
       you can't find the answer in the comprehensive documentation,
 including this FAQ.

       See http://www.perl.org/advocacy/ for more information.

       If you face reluctance to upgrading from an older version
       of perl, then point out that version 4 is utterly unmaintained
 and unsupported by the Perl Development Team.
       Another big sell for Perl5 is the large number of modules
       and extensions which greatly reduce development time for
       any given task.  Also mention that the difference between
       version 4 and version 5 of Perl is like the difference
       between awk and C++.  (Well, OK, maybe it's not quite that
       distinct, but you get the idea.)  If you want support and
       a reasonable guarantee that what you're developing will
       continue to work in the future, then you have to run the
       supported version.  As of December 2003 that means running
       either 5.8.2 (released in November 2003), or one of the
       older releases like 5.6.2 (also released in November 2003;
       a maintenance release to let perl 5.6 compile on newer
       systems as 5.6.1 was released in April 2001) or 5.005_03
       (released in March 1999), although 5.004_05 isn't that bad
       if you absolutely need such an old version (released in
       April 1999) for stability  reasons.  Anything older than
       5.004_05 shouldn't be used.

       Of particular note is the massive bug hunt for buffer
       overflow problems that went into the 5.004 release.  All
       releases prior to that, including perl4, are considered
       insecure and should be upgraded as soon as possible.
       In August 2000 in all Linux distributions a new security
       problem was found in the optional 'suidperl' (not built or
       installed by default) in all the Perl branches 5.6, 5.005,
       and 5.004, see
       http://www.cpan.org/src/5.0/sperl-2000-08-05/ Perl maintenance
 releases 5.6.1 and 5.8.0 have this security hole
       closed.  Most, if not all, Linux distribution have patches
       for this vulnerability available, see http://www.linuxse-
       curity.com/advisories/ , but the most recommendable way is
       to upgrade to at least Perl 5.6.1.


       Copyright (c) 1997, 1998, 1999, 2000, 2001 Tom Christiansen
 and Nathan Torkington.  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 v5.8.5                 2002-11-06                          8
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