perlfaq1
(1)
Name
perlfaq1 - General Questions About Perl
Synopsis
Please see following description for synopsis
Description
Perl Programmers Reference Guide PERLFAQ1(1)
NAME
perlfaq1 - General Questions About Perl
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://dev.perl.org/perl5/docs/p5p-faq.html , or you
can subscribe to the mailing list by sending
perl5-porters-subscribe@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
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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?
(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.
o If things aren't broken, upgrading perl may break them
(or at least issue new warnings).
o The latest versions of perl have more bug fixes.
o The Perl community is geared toward supporting the most
recent releases, so you'll have an easier time finding
help for those.
o 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 ).
o 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.
o 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.
o 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.
o 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.
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o 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).
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 perlhist for a history of Perl revisions.
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.
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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 read
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
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 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).
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
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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 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://www.perl.com/doc/FMTEYEWTK/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.
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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 multi-threaded shared-memory applications, or
extremely large applications. You'll notice that perl is not
itself written in Perl.
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."
Before the first edition of 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 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.
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
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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.
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?
(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 .
Where can I get a list of Larry Wall witticisms?
(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 .
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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:
o http://perltraining.com.au/whyperl.html
o http://www.perl.org/advocacy/whyperl.html
AUTHOR AND COPYRIGHT
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.
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ATTRIBUTES
See attributes(5) for descriptions of the following
attributes:
+---------------+------------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+------------------+
|Availability | runtime/perl-512 |
+---------------+------------------+
|Stability | Uncommitted |
+---------------+------------------+
NOTES
This software was built from source available at
https://java.net/projects/solaris-userland. The original
community source was downloaded from
http://www.cpan.org/src/5.0/perl-5.12.5.tar.bz2
Further information about this software can be found on the
open source community website at http://www.perl.org/.
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