=head1 NAME
-perlfaq1 - General Questions About Perl ($Revision: 1.14 $, $Date: 1998/06/14 22:15:25 $)
+perlfaq1 - General Questions About Perl ($Revision: 1.23 $, $Date: 1999/05/23 16:08:30 $)
=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
+nntp://news.perl.com/perl.porters-gw/ and the Deja archive at
+http://www.deja.com/ using the perl.porters-gw newsgroup, or you can
+subscribe to the mailing list by sending perl5-porters-request@perl.org
+a subscription request.
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-no longer maintained; its last patch (4.036) was in 1992.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 5.004_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
-5.004_01 by the time you read this, and also perhaps some experimental
-versions on the way to the next release.
+no longer maintained; its last patch (4.036) was in 1992, long ago and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 5.6 (although 5.005_03 is still supported).
+The most cutting-edge development release is 5.7. 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.
=head2 What are perl4 and perl5?
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.
+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 L<perltrap/"Perl4 to Perl5 Traps">.
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
See L<perlhist> for a history of Perl revisions.
+=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 should not be confused with the nisus to rewrite
+Perl while keeping the lessons learned from other software, as well as
+Perl5, in mind.
+
+If you have a desire to help in the crusade to make Perl a better place
+then peruse the Perl6 developers page at http://www.perl.org/perl6/ and
+get involved.
+
+The first alpha release is expected by Summer 2001.
+
+"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://language.perl.com/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 isn't really 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.perl.com/CPAN/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.perl.com/CPAN/misc/lwall-quotes.txt.gz .
-=head2 How can I convince my sysadmin/supervisor/employees to use version (5/5.004/Perl instead of some other language)?
+=head2 How can I convince my sysadmin/supervisor/employees to use version 5/5.005/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 5.004 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.
+the supported version. As of April 2001 that probably means
+running either of the releases 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 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.
+
+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/
=head1 AUTHOR AND COPYRIGHT
-Copyright (c) 1997, 1998 Tom Christiansen and Nathan Torkington.
-All rights reserved.
+Copyright (c) 1997, 1998, 1999, 2000, 2001 Tom Christiansen and Nathan
+Torkington. 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>.
-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
projects / p5sagit/p5-mst-13.2.git / blobdiff