PERLFAQ1(1)

NNAAMMEE
perlfaq1 - General Questions About Perl ($Revision: 1.12
$, $Date: 1997/04/24 22:43:34 $)

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

WWhhaatt iiss PPeerrll??

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.

WWhhoo ssuuppppoorrttss PPeerrll?? WWhhoo ddeevveellooppss iitt?? WWhhyy iiss iitt ffrreeee??

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.

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
news://genetics.upenn.edu/perl.porters-gw/ and
http://www.frii.com/~gnat/perl/porters/summary.html.

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.

WWhhiicchh vveerrssiioonn ooff PPeerrll sshhoouulldd II uussee??

You should definitely use version 5. Version 4 is old,
limited, and no longer maintained; its last patch (4.036)
was in 1992. The most recent production release is 5.004.
Further references to the Perl language in this document
refer to this production release unless otherwise
specified. There may be one or more official bug fixes
for 5.004 by the time you read this, and also perhaps some
experimental versions on the way to the next release.

WWhhaatt aarree ppeerrll44 aanndd ppeerrll55??

Perl4 and perl5 are informal names for different versions
of the Perl programming language. It's easier to say
"perl5" than it is to say "the 5(.004) release of Perl",
but some people have interpreted this to mean there's a
language called "perl5", which isn't the case. Perl5 is
merely the popular name for the fifth major release
(October 1994), while perl4 was the fourth major release
(March 1991). There was also a perl1 (in January 1988), a
perl2 (June 1988), and a perl3 (October 1989).

The 5.0 release is, essentially, a complete rewrite of the
perl source code from the ground up. It has been
modularized, object-oriented, tweaked, trimmed, and
optimized until it almost doesn't look like the old code.
However, the interface is mostly the same, and
compatibility with previous releases is very high.

To avoid the "what language is perl5?" confusion, some
people prefer to simply use "perl" to refer to the latest
version of perl and avoid using "perl5" altogether. It's
not really that big a deal, though.

HHooww ssttaabbllee iiss PPeerrll??

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 perl4 scripts run flawlessly under
perl5, 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).

IIss PPeerrll ddiiffffiiccuulltt ttoo lleeaarrnn??

Perl is easy to start learning -- and easy to keep
learning. It looks like most programming languages you're

likely to have had experience with, so if you've ever
written an C program, an awk script, a shell script, or
even an Excel macro, you're already part way 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, Perl is (frequently) an interpreted language.
This means that 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 the new perl modules, either. They're discussed in
Part 3 of this FAQ, along with the CPAN, which is
discussed in Part 2.

HHooww ddooeess PPeerrll ccoommppaarree wwiitthh ootthheerr llaanngguuaaggeess lliikkee JJaavvaa,,
PPyytthhoonn,, RREEXXXX,, SScchheemmee,, oorr TTccll??

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.

CCaann II ddoo [[ttaasskk]] iinn PPeerrll??

Perl is flexible and extensible enough for you to use on
almost any task, from one-line file-processing tasks to
complex 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.

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.

WWhheenn sshhoouullddnn''tt II pprrooggrraamm iinn PPeerrll??

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 multithreaded shared-memory applications, or
extremely large applications. You'll notice that perl is
not itself written in Perl.

The new native-code compiler for Perl may reduce the
limitations given in the previous statement to some
degree, but understand that Perl remains fundamentally a
dynamically typed language, and not a statically typed
one. You certainly won't be chastized 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. :-)

WWhhaatt''ss tthhee ddiiffffeerreennccee bbeettwweeeenn """"ppeerrll"""" aanndd """"PPeerrll""""??

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." You
may or may not choose to follow this usage. For example,
parallelism means "awk and perl" and "Python and Perl"
look ok, while "awk and Perl" and "Python and perl" do
not.

IIss iitt aa PPeerrll pprrooggrraamm oorr aa PPeerrll ssccrriipptt??

It doesn't matter.

In "standard terminology" a program has been compiled to
physical machine code once, and can then be be run
multiple times, whereas a script must be translated by a
program each time it's used. Perl programs, however, are
usually neither strictly compiled nor strictly
interpreted. They can be compiled to a byte code form
(something of a Perl virtual machine) or to completely
different languages, like C or assembly language. You
can't tell just by looking whether the source is destined
for a pure interpreter, a parse-tree interpreter, a byte
code interpreter, or a native-code compiler, so it's hard
to give a definitive answer here.

WWhhaatt iiss aa JJAAPPHH??

These are the "just another perl hacker" signatures that
some people sign their postings with. About 100 of the of
the earlier ones are available from
http://www.perl.com/CPAN/misc/japh .

WWhheerree ccaann II ggeett aa lliisstt ooff LLaarrrryy WWaallll wwiittttiicciissmmss??

Over a hundred quips by Larry, from postings of his or
source code, can be found at
http://www.perl.com/CPAN/misc/lwall-quotes .

HHooww ccaann II ccoonnvviinnccee mmyy ssyyssaaddmmiinn//ssuuppeerrvviissoorr//eemmppllooyyeeeess ttoo uussee
vveerrssiioonn ((55//55..000044//PPeerrll iinnsstteeaadd ooff ssoommee ootthheerr llaanngguuaaggee))??

If your manager or employees are wary of unsupported
software, or software which doesn't officially ship with
your Operating System, you might try to appeal to their
self-interest. If programmers can be more productive
using and utilizing Perl constructs, functionality,
simplicity, and power, then the typical
manager/supervisor/employee may be persuaded. Regarding
using Perl in general, it's also sometimes helpful to
point out that delivery times may be reduced using Perl,
as compared to other languages.

If you have a project which has a bottleneck, especially
in terms of translation, or testing, Perl almost certainly
will provide a viable, and quick solution. In conjunction
with any persuasion effort, you should not fail to point
out that Perl is used, quite extensively, and with
extremely reliable and valuable results, at many large
computer software and/or hardware companies throughout the
world. In fact, many Unix vendors now ship Perl by
default, and support is usually just a news-posting away,
if you can't find the answer in the comprehensive
documentation, including this FAQ.

If you face reluctance to upgrading from an older version
of perl, then point out that version 4 is utterly

unmaintained and unsupported by the Perl Development Team.
Another big sell for Perl5 is the large number of modules
and extensions which greatly reduce development time for
any given task. Also mention that the difference between
version 4 and version 5 of Perl is like the difference
between awk and C++. (Well, ok, maybe not quite that
distinct, but you get the idea.) If you want support and
a reasonable guarantee that what you're developing will
continue to work in the future, then you have to run the
supported version. That probably means running the 5.004
release, although 5.003 isn't that bad (it's just one year
and one release behind). Several important bugs were
fixed from the 5.000 through 5.002 versions, though, so
try upgrading past them if possible.