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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 particu­
       larly 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 espe­
       cially 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 inter­
       face 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
       called a dead, flea-bitten camel carcass.  The most recent
       production release is 5.8.0 (although 5.005_03 and 5.6.1
       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 (Octo­
       ber 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
       perl5.

       What is perl6?

       At The Second O'Reilly Open Source Software Convention,

       "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 produc­
       tion release per year.

       Larry and the Perl development team occasionally make
       changes to the internal core of the language, but all pos­
       sible 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 lan­
       guage.  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 there­
       fore 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 interme­
       diate compilation step, allowing you to experiment and
       test/debug quickly and easily.  This ease of experimenta­
       tion flattens the learning curve even more.

       Things that make Perl easier to learn: Unix experience,
       almost any kind of programming experience, an understand­
       ing 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 exam­
       ple 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?
       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 func­
       tion or variable using a Perl extension written in C or
       C++ and dynamically linked into your main perl inter­
       preter.  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 prob­
       lems.  Perl tries to be all things to all people, but
       nothing special to anyone.  Examples of specialized lan­
       guages 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 lan­
       guage specifically designed for a certain task (e.g. pro­
       log, 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.

       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 fundamen­
       tally 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

       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 pro­
       gram 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 pro­
       grams 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 com­
       pletely 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 .

       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 documenta­
       tion, 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 unmain­
       tained 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 August 2002 that means running
       either 5.8.0 (released in July 2002), or one of the older
       releases like 5.6.1 (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 mainte­
       nance 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.


AUTHOR AND COPYRIGHT

       Copyright (c) 1997, 1998, 1999, 2000, 2001 Tom Chris­
       tiansen and Nathan Torkington.  All rights reserved.

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