MirBSD manpage: perlfaq1(1)

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


     perlfaq1 - General Questions About Perl


     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 utili-
     ties, 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 per-
     sonal 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://simon-cozens.org/writings/p5p-faq , or you can
     subscribe to the mailing list by sending
     perl5-porters-request@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

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     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 anyone.  In general, you want
     to use either the current stable release, or the stable
     release immediately prior to that one.  Currently, those are
     perl5.8.x and perl5.6.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 prob-
         lems 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. perl5.6.x ) are
         usually maintained for a while, although not at the same
         level as the current releases.

     +   No one is actively supporting perl4.x.  Five years ago
         it was a dead camel carcass (according to this docu-
         ment).  Now it's barely a skeleton as its whitewashed
         bones have fractured or eroded.

     +   There is no perl6.x for the next couple of years.  Stay
         tuned, but don't worry that you'll have to change major

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         versions of Perl soon (i.e. before 2006).

     +   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. perl5.8.x, where 8 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 perl4, perl5, or perl6?

     (contributed by brian d foy)

     In short, perl4 is the past, perl5 is the present, and perl6
     is the future.

     The number after perl (i.e. the 5 after perl5) is the major
     release of the perl interpreter as well as the version of
     the language.  Each major version has significant differ-
     ences that earlier versions cannot support.

     The current major release of Perl is perl5, and was released
     in 1994. It can run scripts from the previous major release,
     perl4 (March 1991), but has significant differences. It
     introduced the concept of references, complex data struc-
     tures, and modules.  The perl5 interpreter was a complete
     re-write of the previous perl sources.

     Perl6 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 perl5, and
     some perl5 modules allow you to use some perl6 syntax in
     your programs.  You can learn more about perl6 at
     http://dev.perl.org/perl6/ .

     See perlhist for a history of Perl revisions.

     What is Ponie?

     At The O'Reilly Open Source Software Convention in 2003,
     Artur Bergman, Fotango, and The Perl Foundation announced a
     project to run perl5 on the Parrot virtual machine named
     Ponie. Ponie stands for Perl On New Internal Engine.  The
     Perl 5.10 language implementation will be used for Ponie,
     and there will be no language level differences between
     perl5 and ponie.  Ponie is not a complete rewrite of perl5.

     For more details, see http://www.poniecode.org/

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     What is perl6?

     At The Second O'Reilly Open Source Software Convention,
     Larry Wall announced Perl6 development would begin in ear-
     nest. Perl6 was an oft used term for Chip Salzenberg's pro-
     ject to rewrite Perl in C++ named Topaz. However, Topaz pro-
     vided valuable insights to the next version of Perl and its
     implementation, but was ultimately abandoned.

     If you want to learn more about Perl6, or have a desire to
     help in the crusade to make Perl a better place then peruse
     the Perl6 developers page at http://dev.perl.org/perl6/ and
     get involved.

     Perl6 is not scheduled for release yet, and Perl5 will still
     be supported for quite awhile after its release. Do not wait
     for Perl6 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 possi-
     ble 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).

     Is Perl difficult to learn?

     No, Perl is easy to start learning--and easy to keep learn-
     ing.  It looks like most programming languages you're likely
     to have experience with, so if you've ever written a C pro-
     gram, an awk script, a shell script, or even a BASIC pro-
     gram, 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).

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     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 intermedi-
     ate 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 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 start-
     ing 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.

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     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 prob-
     lems.  Perl tries to be all things to all people, but noth-
     ing 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 exist-
     ing application written in another language that's all done
     (and done well), or you have an application language specif-
     ically 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.

     The new, native-code compiler for Perl may eventually reduce
     the limitations given in the previous statement to some
     degree, but understand that 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 withstand-
     ing. :-)

     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 imple-
     mentation 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.  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."

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     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 pro-
     grams 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.

     Perl programs 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 at it 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.

     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?

     These are the "just another perl hacker" signatures that
     some people sign their postings with.  Randal Schwartz made
     these famous.  About 100 of the earlier ones are available
     from http://www.cpan.org/misc/japh .

     Where can I get a list of Larry Wall witticisms?

     Over a hundred quips by Larry, from postings of his or
     source code, can be found at
     http://www.cpan.org/misc/lwall-quotes.txt.gz .

     How can I convince my sysadmin/supervisor/employees to use
     version 5/5.6.1/Perl instead of some other language?

     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

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     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 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, 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
     hardware companies throughout the world.  In fact, many Unix
     vendors now ship Perl by default.  Support is usually just a
     news-posting away, if you can't find the answer in the
     comprehensive documentation, including this FAQ.

     See http://www.perl.org/advocacy/ for more information.

     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 ver-
     sion 5 of Perl is like the difference between awk and C++.
     (Well, OK, maybe it's 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.  As of
     December 2003 that means running either 5.8.2 (released in
     November 2003), or one of the older releases like 5.6.2
     (also released in November 2003; a maintenance release to
     let perl 5.6 compile on newer systems as 5.6.1 was released
     in April 2001) or 5.005_03 (released in March 1999),
     although 5.004_05 isn't that bad if you absolutely need such
     an old version (released in April 1999) for stability  rea-
     sons. Anything older than 5.004_05 shouldn't be used.

     Of particular note is the massive bug hunt for buffer over-
     flow problems that went into the 5.004 release.  All
     releases prior to that, including perl4, are considered
     insecure and should be upgraded as soon as possible.

     In August 2000 in all Linux distributions a new security
     problem was found in the optional 'suidperl' (not built or
     installed by default) in all the Perl branches 5.6, 5.005,
     and 5.004, see http://www.cpan.org/src/5.0/sperl-2000-08-05/
     Perl maintenance releases 5.6.1 and 5.8.0 have this security
     hole closed. Most, if not all, Linux distribution have
     patches for this vulnerability available, see
     http://www.linuxsecurity.com/advisories/ , but the most

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     recommendable way is to upgrade to at least Perl 5.6.1.
     Copyright (c) 1997-2006 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 pro-
     grams for fun or for profit as you see fit.  A simple com-
     ment in the code giving credit to the FAQ would be courteous
     but is not required.

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