=head1 NAME
-perlfaq1 - General Questions About Perl ($Revision: 1.12 $, $Date: 1997/04/24 22:43:34 $)
+perlfaq1 - General Questions About Perl
=head1 DESCRIPTION
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.
-
-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.
+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 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-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-no longer maintained.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 last
-production release was 5.003, and the current experimental release for
-those at the bleeding edge (as of 27/03/97) is 5.003_92, considered a beta
-for production release 5.004, which will probably be out by the time
-you read this. Further references to the Perl language in this document
-refer to the current production release unless otherwise specified.
-
-=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 everyone. 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, 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. perl5.8.x ) are usually maintained
+for a while, although not at the same level as the current releases.
+
+=item *
+
+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.
+
+=item *
+
+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.
+
+=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. perl5.10.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).
+
+=back
+
+
+=head2 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 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 L<perlhist> for a history of Perl revisions.
+
+=head2 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.
+
+=head2 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 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
=head2 How stable is Perl?
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
+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).
=head2 Is Perl difficult to learn?
-Perl is easy to start learning -- and easy to keep learning. It looks
-like most programming languages you're likely to have had experience
-with, so if you've ever written an C program, an awk script, a shell
-script, or even an Excel macro, you're already part way there.
+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
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
+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.
=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. :-)
+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"?
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.
+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 I<Programming perl>, people commonly
+referred to the language as "perl", and its name appeared that way in
+the title because it referred to the interpreter. 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 I<Programming Perl>, using the capitalized
+version of the name to refer to the language.
+
+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.
=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
-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.
+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.
+
+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 .
+(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 .
=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 .
-
-=head2 How can I convince my sysadmin/supervisor/employees to use version (5/5.004/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, as 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
-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
-just a news-posting away, if you can't find the answer in the
-I<comprehensive> documentation, including this FAQ.
-
-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
-developing will continue to work in the future, then you have to run
-the supported version. That probably means running the 5.004 release,
-although 5.003 isn't that bad (it's just one year and one release
-behind). Several important bugs were fixed from the 5.000 through
-5.002 versions, though, so try upgrading past them if possible.
+(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 .
+
+=head2 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, 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 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 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:
+
+=over 4
+
+=item * http://perltraining.com.au/whyperl.html
+
+=item * http://www.perl.org/advocacy/whyperl.html
+
+=back
=head1 AUTHOR AND COPYRIGHT
-Copyright (c) 1997 Tom Christiansen and Nathan Torkington.
-All rights reserved. See L<perlfaq> for distribution information.
+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.
https://perl5.git.perl.org / perl5.git / blobdiff