Страницы справочника OS X

Эта страница руководства для  версии 10.9 Mac OS X

Читать страницы руководства

PERLFAQ1(1)                           Perl Programmers Reference Guide                           PERLFAQ1(1)



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 perl5.10.x and perl5.8.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. Five 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. 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 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, but it's still in development in both its syntax and
       design. The work started in 2002 and is still ongoing. Many 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. You can learn more about Perl 6 at http://dev.perl.org/perl6/ .

       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 fileprocessing
       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 multithreaded
       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 more 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.



perl v5.12.5                                     2012-11-03                                      PERLFAQ1(1)