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.
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 9 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.