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.
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 email@example.com 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.
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.
Beyond that, you have to consider several things and decide which is best for you.
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.
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.
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.
If you want to learn more about Perl 6 read the Perl 6 developers page at <http://www.perl6.org/> and get involved.
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.
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.
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.
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.
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>.
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:
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.