perlfaq1(1)
NAME
perlfaq1 - General Questions About Perl
VERSION
version 5.021010
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.
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 web programming.
Perl derives from the ubiquitous C programming language and to a lesser
extent from sed, awk, the Unix shell, and many other tools and
languages.
These strengths make it especially popular with web developers and
system administrators. Mathematicians, geneticists, journalists,
managers and many other people also use Perl.
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.
The core development team (known as the Perl Porters) are a group 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
<http://www.nntp.perl.org/group/perl.perl5.porters/> or read the faq
<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 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 perl5.18.x and perl5.16.x, respectively.
Beyond that, you have to consider several things and decide which is
best for you.
* If things aren't broken, upgrading perl may break them (or at least
issue new warnings).
* The latest versions of perl have more bug fixes.
* The Perl community is geared toward supporting the most recent
releases, so you'll have an easier time finding help for those.
* 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> ).
* 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.
* The immediate, previous releases (i.e. perl5.14.x ) are usually
maintained for a while, although not at the same level as the
current releases.
* No one is actively supporting Perl 4. Ten 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.
* The current leading implementation of Perl 6, Rakudo, released a
"useful, usable, 'early adopter'" distribution of Perl 6 (called
Rakudo Star) in July of 2010. Please see <http://rakudo.org/> for
more information.
* 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.
perl5.18.x, where 18 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.
perl5.19.x, where 19 is the minor release).
What are Perl 4, Perl 5, or Perl 6?
In short, Perl 4 is the parent to both Perl 5 and Perl 6. Perl 5 is the
older sibling, and though they are different languages, someone who
knows one will spot many similarities in the other.
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, first released in 1994. It
can run scripts from the previous major release, Perl 4 (March 1991),
but has significant differences.
Perl 6 is a reinvention of Perl, it is a language in the same lineage
but not compatible. The two are complementary, not mutually exclusive.
Perl 6 is not meant to replace Perl 5, and vice versa. See "What is
Perl 6?" below to find out more.
See perlhist for a history of Perl revisions.
What is Perl 6?
Perl 6 was originally described as the community's rewrite of Perl 5.
Development started in 2002; syntax and design work continue to this
day. As the language has evolved, it has become clear that it is a
separate language, incompatible with Perl 5 but in the same language
family.
Contrary to popular belief, Perl 6 and Perl 5 peacefully coexist with
one another. Perl 6 has proven to be a fascinating source of ideas for
those using Perl 5 (the Moose object system is a well-known example).
There is overlap in the communities, and this overlap fosters the
tradition of sharing and borrowing that have been instrumental to
Perl's success. The current leading implementation of Perl 6 is Rakudo,
and you can learn more about it at <http://rakudo.org>.
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://www.perl6.org/> and get involved.
"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 about one production release per year.
The Perl development team occasionally make changes to the internal
core of the language, but all possible efforts are made toward backward
compatibility.
How often are new versions of Perl released?
Recently, the plan has been to release a new version of Perl roughly
every April, but getting the release right is more important than
sticking rigidly to a calendar date, so the release date is somewhat
flexible. The historical release dates can be viewed at
<http://www.cpan.org/src/README.html>.
Even numbered minor versions (5.14, 5.16, 5.18) are production
versions, and odd numbered minor versions (5.15, 5.17, 5.19) are
development versions. Unless you want to try out an experimental
feature, you probably never want to install a development version of
Perl.
The Perl development team are called Perl 5 Porters, and their
organization is described at <http://perldoc.perl.org/perlpolicy.html>.
The organizational rules really just boil down to one: Larry is always
right, even when he was wrong.
Is Perl difficult to learn?
No, Perl is easy to start learning <http://learn.perl.org/> --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 Perl modules, either.
They're discussed in Part 3 of this FAQ, along with CPAN
<http://www.cpan.org/>, which is discussed in Part 2.
How does Perl compare with other languages like Java, Python, REXX, Scheme,
or Tcl?
Perl can be used for almost any coding problem, even ones which require
integrating specialist C code for extra speed. As with any tool it can
be used well or badly. Perl has many strengths, and a few weaknesses,
precisely which areas are good and bad is often a personal choice.
When choosing a language you should also be influenced by the resources
<http://www.cpan.org/>, testing culture <http://www.cpantesters.org/>
and community <http://www.perl.org/community.html> which surrounds it.
For comparisons to a specific language it is often best to create a
small project in both languages and compare the results, make sure to
use all the resources <http://www.cpan.org/> of each language, as a
language is far more than just it's syntax.
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?
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).
If you find that you need to speed up a specific part of a Perl
application (not something you often need) you may want to use C, but
you can access this from your Perl code with perlxs.
What's the difference between "perl" and "Perl"?
"Perl" is the name of the language. Only the "P" is capitalized. The
name of the interpreter (the program which runs the Perl script) is
"perl" with a lowercase "p".
You may or may not choose to follow this usage. But never write "PERL",
because perl is not an acronym.
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>.
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 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:
* <http://www.perl.org/about.html>
* <http://perltraining.com.au/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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