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NAME
perlfaq1 - General Questions About Perl ($Revision: 1.12 $, $Date:
1997/04/24 22:43:34 $)
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.
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.
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?
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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 Version 4 is old, limited, and no
longer maintained; its last patch (4.036) was in 1992.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. 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 by the
time you read this, and also perhaps some experimental versions on the
way to the next release.
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.
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?
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.
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
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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.
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 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.
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.
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.
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.
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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 multithreaded 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. :-)
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.
Is it a Perl program or a Perl script?
It doesn't matter.
In "standard terminology" a program has been compiled to physical machine
code once, and can then be be run multiple times, whereas a 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.
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 .
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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 .
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 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.
AUTHOR AND COPYRIGHT
Copyright (c) 1997 Tom Christiansen and Nathan Torkington. All rights
reserved. See the perlfaq manpage for distribution information.
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