Revonzy Mini Shell

=head1 NAME

perlfaq1 - General Questions About Perl

=head1 DESCRIPTION

This section of the FAQ answers very general, high-level questions
about Perl.

=head2 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.

=head2 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
L<archives|http://www.nntp.perl.org/group/perl.perl5.porters/>
or read the L<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.

=head2 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 perl5.14.x and perl5.12.x, respectively.

Beyond that, you have to consider several things and decide which is best
for you.

=over 4

=item *

If things aren't broken, upgrading perl may break them (or at least issue
new warnings).

=item *

The latest versions of perl have more bug fixes.

=item *

The Perl community is geared toward supporting the most recent releases,
so you'll have an easier time finding help for those.

=item *

Versions prior to perl5.004 had serious security problems with buffer
overflows, and in some cases have CERT advisories (for instance,
L<http://www.cert.org/advisories/CA-1997-17.html> ).

=item *

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.

=item *

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.

=item *

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.

=item *

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 L<http://rakudo.org/> for more information.

=item *

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).

=back

=head2 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 L</"What is Perl 6?"> below
to find out more.

See L<perlhist> for a history of Perl revisions.

=head2 What is Perl 6?

Perl 6 was I<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 L<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 L<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 L<http://www.perl6.org/> and get involved.

"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,
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.

=head2 Is Perl difficult to learn?

No, Perl is easy to start L<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 L<CPAN|http://www.cpan.org/>, which is
discussed in Part 2.

=head2 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
L<resources|http://www.cpan.org/>, L<testing culture|http://www.cpantesters.org/>
and L<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 L<resources|http://www.cpan.org/> of each language,
as a language is far more than just it's syntax.

=head2 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 L<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.

=head2 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 L<perlxs>.

=head2 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.

=head2 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 L<http://www.cpan.org/misc/japh>.

=head2 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 ( L<http://www.perlmonks.com> )
and the various Perl mailing lists ( L<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:

=over 4

=item * L<http://www.perl.org/about.html>

=item * L<http://perltraining.com.au/whyperl.html>

=back

=head1 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.