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.\" ========================================================================
.\"
.IX Title "PERLFAQ1 1"
.TH PERLFAQ1 1 "2019-10-24" "perl v5.30.2" "Perl Programmers Reference Guide"
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.SH "NAME"
perlfaq1 \- General Questions About Perl
.SH "VERSION"
.IX Header "VERSION"
version 5.20190126
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This section of the \s-1FAQ\s0 answers very general, high-level questions
about Perl.
.SS "What is Perl?"
.IX Subsection "What is Perl?"
Perl is a high-level programming language with an eclectic heritage
written by Larry Wall and a cast of thousands.
.PP
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.
.PP
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.
.PP
These strengths make it especially popular with web developers
and system administrators. Mathematicians, geneticists, journalists,
managers and many other people also use Perl.
.SS "Who supports Perl? Who develops it? Why is it free?"
.IX Subsection "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.
.PP
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 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).
.PP
While the \s-1GNU\s0 project includes Perl in its distributions, there's no
such thing as \*(L"\s-1GNU\s0 Perl\*(R". Perl is not produced nor maintained by the
Free Software Foundation. Perl's licensing terms are also more open
than \s-1GNU\s0 software's tend to be.
.PP
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
\&\*(L"Where can I buy a commercial version of Perl?\*(R" for more information.
.SS "Which version of Perl should I use?"
.IX Subsection "Which version of Perl should I use?"
(contributed by brian d foy with updates from others)
.PP
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.
.PP
Beyond that, you have to consider several things and decide which is best
for you.
.IP "\(bu" 4
If things aren't broken, upgrading perl may break them (or at least issue
new warnings).
.IP "\(bu" 4
The latest versions of perl have more bug fixes.
.IP "\(bu" 4
The latest versions of perl may contain performance improvements and
features not present in older versions.  There have been many changes
in perl since perl5 was first introduced.
.IP "\(bu" 4
The Perl community is geared toward supporting the most recent releases,
so you'll have an easier time finding help for those.
.IP "\(bu" 4
Older versions of perl may have security vulnerabilities, some of which
are serious (see perlsec and search
CVEs <https://cve.mitre.org/cgi-bin/cvekey.cgi?keyword=Perl> for more
information).
.IP "\(bu" 4
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.
.IP "\(bu" 4
The immediate, in addition to the current stable release, the previous
stable release is maintained.  See
\&\*(L"\s-1MAINTENANCE AND SUPPORT\*(R"\s0 in perlpolicy for more information.
.IP "\(bu" 4
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. perl5.24.x, where 24 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. perl5.25.x, where 25 is the minor release).
.IP "\(bu" 4
You can consult releases <http://dev.perl.org/perl5> to determine the
current stable release of Perl.
.SS "What are Perl 4, Perl 5, or Perl 6?"
.IX Subsection "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.
.PP
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.
.PP
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.
.PP
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?\*(R" below
to find out more.
.PP
See perlhist for a history of Perl revisions.
.SS "What is Perl 6?"
.IX Subsection "What is Perl 6?"
Perl 6 was \fIoriginally\fR described as the community's rewrite of Perl 5,
however as the language evolved, it became clear that it is a separate
language, but in the same language family as Perl 5.
.PP
Perl 6 is not intended primarily as a replacement for Perl 5, but as its
own thing \- and libraries exist to allow you to call Perl 5 code from Perl
6 programs and vice versa.
.PP
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.
.PP
If you want to learn more about Perl 6 read the Perl 6 developers
page at <http://www.perl6.org/> and get involved.
.PP
\&\*(L"We're really serious about reinventing everything that needs reinventing.\*(R"
\&\-\-Larry Wall
.SS "How stable is Perl?"
.IX Subsection "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.
.PP
The Perl development team occasionally make changes to the
internal core of the language, but all possible efforts are made toward
backward compatibility.
.SS "How often are new versions of Perl released?"
.IX Subsection "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>.
.PP
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.
.PP
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.
.SS "Is Perl difficult to learn?"
.IX Subsection "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 \s-1BASIC\s0 program, you're already partway there.
.PP
Most tasks only require a small subset of the Perl language. One of
the guiding mottos for Perl development is \*(L"there's more than one way
to do it\*(R" (\s-1TMTOWTDI,\s0 sometimes pronounced \*(L"tim toady\*(R"). Perl's
learning curve is therefore shallow (easy to learn) and long (there's
a whole lot you can do if you really want).
.PP
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.
.PP
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 \s-1FAQ,\s0 along with \s-1CPAN\s0 <http://www.cpan.org/>, which is
discussed in Part 2.
.SS "How does Perl compare with other languages like Java, Python, \s-1REXX,\s0 Scheme, or Tcl?"
.IX Subsection "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.
.PP
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.
.PP
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.
.SS "Can I do [task] in Perl?"
.IX Subsection "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.
.PP
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.
.PP
If you have a library that provides an \s-1API,\s0 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.
.PP
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.
.SS "When shouldn't I program in Perl?"
.IX Subsection "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).
.PP
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.
.ie n .SS "What's the difference between ""perl"" and ""Perl""?"
.el .SS "What's the difference between ``perl'' and ``Perl''?"
.IX Subsection "What's the difference between perl and Perl?"
\&\*(L"Perl\*(R" is the name of the language. Only the \*(L"P\*(R" is capitalized.
The name of the interpreter (the program which runs the Perl script)
is \*(L"perl\*(R" with a lowercase \*(L"p\*(R".
.PP
You may or may not choose to follow this usage. But never write \*(L"\s-1PERL\*(R",\s0
because perl is not an acronym.
.SS "What is a \s-1JAPH\s0?"
.IX Subsection "What is a JAPH?"
(contributed by brian d foy)
.PP
\&\s-1JAPH\s0 stands for \*(L"Just another Perl hacker,\*(R", which Randal Schwartz used
to sign email and usenet messages starting in the late 1980s. He
previously used the phrase with many subjects (\*(L"Just another x hacker,\*(R"),
so to distinguish his \s-1JAPH,\s0 he started to write them as Perl programs:
.PP
.Vb 1
\&    print "Just another Perl hacker,";
.Ve
.PP
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.
.PP
\&\s-1CPAN\s0 has several \s-1JAPH\s0 programs at <http://www.cpan.org/misc/japh>.
.SS "How can I convince others to use Perl?"
.IX Subsection "How can I convince others to use Perl?"
(contributed by brian d foy)
.PP
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).
.PP
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.
.PP
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.
.PP
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.
.PP
You might find these links useful:
.IP "\(bu" 4
<http://www.perl.org/about.html>
.IP "\(bu" 4
<http://perltraining.com.au/whyperl.html>
.SH "AUTHOR AND COPYRIGHT"
.IX Header "AUTHOR AND COPYRIGHT"
Copyright (c) 1997\-2010 Tom Christiansen, Nathan Torkington, and
other authors as noted. All rights reserved.
.PP
This documentation is free; you can redistribute it and/or modify it
under the same terms as Perl itself.
.PP
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 \s-1FAQ\s0 would
be courteous but is not required.