=head1 NAME
-perlfaq1 - General Questions About Perl ($Revision: 1.15 $, $Date: 1998/08/05 11:52:24 $)
+perlfaq1 - General Questions About Perl ($Revision: 1.19 $, $Date: 2005/12/31 00:54:37 $)
=head1 DESCRIPTION
distribution for more details. See L<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 news://genetics.upenn.edu/perl.porters-gw/ and
-http://www.frii.com/~gnat/perl/porters/summary.html.
+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://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
=head2 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-no longer maintained; its last patch (4.036) was in 1992. The most
-recent production release is 5.005_01. Further references to the Perl
-language in this document refer to this production release unless
-otherwise specified. There may be one or more official bug fixes for
-5.005_01 by the time you read this, and also perhaps some experimental
-versions on the way to the next release.
-
-=head2 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 complete rewrite of the perl source
-code from the ground up. 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.
-
-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.
+(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 perl5.8.x and perl5.6.x, respectively.
+
+Beyond that, you have to consider several things and decide which
+is best for you.
+
+=over 4
+
+=item *
+
+If things aren't broken, upgrading perl may break
+them (or at least issue new warnings).
+
+=item *
+
+The latest versions of perl have more bug fixes.
+
+=item *
+
+The Perl community is geared toward supporting the most
+recent releases, so you'll have an easier time finding help for
+those.
+
+=item *
+
+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 ).
+
+=item *
+
+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.
+
+=item *
+
+The immediate, previous releases (i.e. perl5.6.x ) are usually
+maintained for a while, although not at the same level as the
+current releases.
+
+=item *
+
+No one is actively supporting perl4.x. 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.
+
+=item *
+
+There is no perl6.x for the next couple of years. Stay tuned,
+but don't worry that you'll have to change major versions of Perl
+soon (i.e. before 2006).
+
+=item *
+
+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. perl5.8.x, where 8 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).
+
+=back
+
+
+=head2 What are perl4, perl5, or perl6?
+
+(contributed by brian d foy)
+
+In short, perl4 is the past, perl5 is the present, and perl6 is the
+future.
+
+The number after perl (i.e. the 5 after perl5) 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 perl5, and was released in 1994.
+It can run scripts from the previous major release, perl4 (March 1991),
+but has significant differences. It introduced the concept of references,
+complex data structures, and modules. The perl5 interpreter was a
+complete re-write of the previous perl sources.
+
+Perl6 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 perl5, and some perl5 modules allow you to use some
+perl6 syntax in your programs. You can learn more about perl6 at
+http://dev.perl.org/perl6/ .
See L<perlhist> for a history of Perl revisions.
+=head2 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.
+
+For more details, see http://www.poniecode.org/
+
+=head2 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
+
=head2 How stable is Perl?
Production releases, which incorporate bug fixes and new functionality,
=head2 Is Perl difficult to learn?
-No, Perl is easy to start learning -- and easy to keep learning. It looks
+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 an C program, an awk script, a shell
-script, or even BASIC program, you're already part way there.
+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
learning curve is therefore shallow (easy to learn) and long (there's
a whole lot you can do if you really want).
-Finally, Perl is (frequently) an interpreted language. This means
-that 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.
+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 the CPAN, which is
+They're discussed in Part 3 of this FAQ, along with CPAN, which is
discussed in Part 2.
=head2 How does Perl compare with other languages like Java, Python, REXX, Scheme, or Tcl?
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.
+
=head2 Can I do [task] in Perl?
-Perl is flexible and extensible enough for you to use on almost any
-task, from one-line file-processing tasks to complex 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.
+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.
+to create a powerful application. See L<perlembed>.
That said, there will always be small, focused, special-purpose
languages dedicated to a specific problem domain that are simply more
=head2 When shouldn't I program in Perl?
-When your manager forbids it -- but do consider replacing them :-).
+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
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 multithreaded
+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 reduce the limitations given
-in the previous statement to some degree, but understand that Perl
-remains fundamentally a dynamically typed language, and not a
-statically typed one. You certainly won't be chastized 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. :-)
+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. :-)
=head2 What's the difference between "perl" and "Perl"?
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.
+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 notwithstanding.
=head2 Is it a Perl program or a Perl script?
-It doesn't matter.
-
-In "standard terminology" a I<program> has been compiled to physical
-machine code once, and can then be be run multiple times, whereas a
-I<script> must be translated by a program each time it's used. Perl
-programs, however, are usually neither strictly compiled nor strictly
-interpreted. They can be compiled to a byte code form (something of a
+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 F<.cshrc> or F<.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 I<program> has been compiled to physical machine code
+once and can then be run multiple times, whereas a I<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 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.
+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.
=head2 What is a JAPH?
These are the "just another perl hacker" signatures that some people
-sign their postings with. About 100 of the of the earlier ones are
-available from http://www.perl.com/CPAN/misc/japh .
+sign their postings with. Randal Schwartz made these famous. About
+100 of the earlier ones are available from
+http://www.cpan.org/misc/japh .
=head2 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.perl.com/CPAN/misc/lwall-quotes .
+can be found at http://www.cpan.org/misc/lwall-quotes.txt.gz .
-=head2 How can I convince my sysadmin/supervisor/employees to use version (5/5.005/Perl instead of some other language)?
+=head2 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
+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, as compared to other languages.
+using Perl compared to other languages.
If you have a project which has a bottleneck, especially in terms of
translation or testing, Perl almost certainly will provide a viable,
-and quick solution. In conjunction with any persuasion effort, you
+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/or hardware companies throughout the world. In fact,
-many Unix vendors now ship Perl by default, and support is usually
+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
I<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 not quite that distinct, but you get the idea.) If
-you want support and a reasonable guarantee that what you're
+(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. That probably means running the 5.005 release,
-although 5.004 isn't that bad (it's just one year and one release
-behind). Several important bugs were fixed from the 5.000 through
-5.003 versions, though, so try upgrading past them if possible.
-
-Of particular note is the massive bughunt for buffer overflow
+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 B<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.
+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.linuxsecurity.com/advisories/ ,
+but the most recommendable way is to upgrade to at least Perl 5.6.1.
=head1 AUTHOR AND COPYRIGHT
-Copyright (c) 1997, 1998 Tom Christiansen and Nathan Torkington.
-All rights reserved.
+Copyright (c) 1997-2006 Tom Christiansen, Nathan Torkington, and
+other authors as noted. All rights reserved.
-When included as an integrated part of the Standard Distribution
-of Perl or of its documentation (printed or otherwise), this works is
-covered under Perl's Artistic Licence. For separate distributions of
-all or part of this FAQ outside of that, see L<perlfaq>.
+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 public
+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
https://perl5.git.perl.org / perl5.git / blobdiff