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 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 perl5.14.x and perl5.12.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. perl5.8.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.
- •
- There is no Perl 6 release scheduled, but it will be
available when it's ready. The joke is that it's scheduled for Christmas,
but that we just don't know which one. 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.
- •
- 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 first 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, although it's not intended to replace
Perl 5. It's still in development in both its syntax and design. The work
started in 2002 and is still ongoing. Some 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. The current leading
implementation of Perl 6 is Rakudo (
http://rakudo.org ).
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.
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 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.
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 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
.
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://perltraining.com.au/whyperl.html
- •
- 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.