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PERLFAQ1(1)
NAME
perlfaq1 - General Questions About Perl ($Revision: 1.14 $, $Date:
2003/11/23 08:02:29 $)
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 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
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 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 perl5.
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 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 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,
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 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
notwithstanding.
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 languages.
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.linuxsecurity.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 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.
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