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


NAME
       perlfaq1 - General Questions About Perl ($Revision: 1.2 $,
       $Date: 1999/04/29 22:52:10 $)



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 the
       perlhist manpage (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
       nntp://news.perl.com/perl.porters-gw/ and the Deja News
       archive at http://www.dejanews.com/ using the
       perl.porters-gw newsgroup, or you can subscribe to the
       mailing list by sending perl5-porters-request@perl.org a
       subscription request.

       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.



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       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?

       You should definitely use version 5.  Version 4 is old,
       limited, and no longer maintained; its last patch (4.036)
       was in 1992, long ago and far away.  Sure, it's stable,
       but so is anything that's dead; in fact, perl4 had been
       called a dead, flea-bitten camel carcass.  The most recent
       production release is 5.005_02 (although 5.004_04 is still
       supported).  The most cutting-edge development release is
       5.005_54.  Further references to the Perl language in this
       document refer to the production release unless otherwise
       specified.  There may be one or more official bug fixes
       for 5.005_02 by the time you read this, and also perhaps
       some experimental versions on the way to the next release.
       All releases prior to 5.004 were subject to buffer
       overruns, a grave security issue.

       What are perl4 and perl5?

       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 ground-up rewrite of
       the original perl source code from releases 1 through 4.
       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. See
       the section on Perl4 to Perl5 Traps in the perltrap
       manpage.

       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.

       See the perlhist manpage for a history of Perl revisions.

       What is perl6?

       Perl6 is a semi-jocular reference to the Topaz project.
       Headed by Chip Salzenberg, Topaz is yet-another ground-up



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       rewrite of the current release of Perl, one whose major
       goal is to create a more maintainable core than found in
       release 5.  Written in nominally portable C++, Topaz hopes
       to maintain 100% source-compatibility with previous
       releases of Perl but to run significantly faster and
       smaller.  The Topaz team hopes to provide an XS
       compatibility interface to allow most XS modules to work
       unchanged, albeit perhaps without the efficiency that the
       new interface uowld allow.  New features in Topaz are as
       yet undetermined, and will be addressed once compatibility
       and performance goals are met.

       If you are a hard-working C++ wizard with a firm command
       of Perl's internals, and you would like to work on the
       project, send a request to perl6-porters-request@perl.org
       to subscribe to the Topaz mailing list.

       There is no ETA for Topaz.  It is expected to be several
       years before it achieves enough robustness, compatibility,
       portability, and performance to replace perl5 for ordinary
       use by mere mortals.

       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 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
       learning.  It looks like most programming languages you're
       likely to have experience with, so if you've ever written
       an C program, an awk script, a shell script, or even BASIC
       program, 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, because Perl is frequently (but not always, and
       certainly not by definition) an interpreted language, you



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       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 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://language.perl.com/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 the perlembed manpage.

       That said, there will always be small, focused, special-
       purpose languages dedicated to a specific problem domain



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       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 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 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."  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 isn't really an
       acronym, aprocryphal 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



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       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.

       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.perl.com/CPAN/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.perl.com/CPAN/misc/lwall-quotes.txt.gz .

       Newer examples can be found by perusing Larry's postings:

           http://x1.dejanews.com/dnquery.xp?QRY=*&DBS=2&ST=PS&defaultOp=AND&LNG=ALL&format=terse&showsort=date&maxhits=100&subjects=&groups=&authors=larry@*wall.org&fromdate=&todate=


       How can I convince my sysadmin/supervisor/employees to use
       version (5/5.005/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



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       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.

       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 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 5.005
       release, although 5.004 isn't that bad.  Several important
       bugs were fixed from the 5.000 through 5.003 versions,
       though, so try upgrading past them if possible.

       Of particular note is the massive bughunt for buffer
       overflow 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.

AUTHOR AND COPYRIGHT
       Copyright (c) 1997-1999 Tom Christiansen and Nathan
       Torkington.  All rights reserved.

       When included as an integrated part of the Standard
       Distribution of Perl or of its documentation (printed or
       otherwise), this work is covered under Perl's Artistic
       Licence.  For separate distributions of all or part of
       this FAQ outside of that, see the perlfaq manpage.

       Irrespective of its distribution, all code examples here



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       are 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.




















































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