README.vms and related updates (from Peter Prymmer <pvhp@best.com>)
[p5sagit/p5-mst-13.2.git] / pod / perlfaq1.pod
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68dc0745 1=head1 NAME
2
d92eb7b0 3perlfaq1 - General Questions About Perl ($Revision: 1.23 $, $Date: 1999/05/23 16:08:30 $)
68dc0745 4
5=head1 DESCRIPTION
6
7This section of the FAQ answers very general, high-level questions
8about Perl.
9
10=head2 What is Perl?
11
12Perl is a high-level programming language with an eclectic heritage
13written by Larry Wall and a cast of thousands. It derives from the
14ubiquitous C programming language and to a lesser extent from sed,
15awk, the Unix shell, and at least a dozen other tools and languages.
16Perl's process, file, and text manipulation facilities make it
17particularly well-suited for tasks involving quick prototyping, system
18utilities, software tools, system management tasks, database access,
19graphical programming, networking, and world wide web programming.
20These strengths make it especially popular with system administrators
21and CGI script authors, but mathematicians, geneticists, journalists,
22and even managers also use Perl. Maybe you should, too.
23
24=head2 Who supports Perl? Who develops it? Why is it free?
25
26The original culture of the pre-populist Internet and the deeply-held
27beliefs of Perl's author, Larry Wall, gave rise to the free and open
28distribution policy of perl. Perl is supported by its users. The
29core, the standard Perl library, the optional modules, and the
30documentation you're reading now were all written by volunteers. See
31the personal note at the end of the README file in the perl source
5e3006a4 32distribution for more details. See L<perlhist> (new as of 5.005)
33for Perl's milestone releases.
68dc0745 34
65acb1b1 35In particular, the core development team (known as the Perl Porters)
36are a rag-tag band of highly altruistic individuals committed
37to producing better software for free than you could hope to
38purchase for money. You may snoop on pending developments via
87275199 39nntp://news.perl.com/perl.porters-gw/ and the Deja archive at
40http://www.deja.com/ using the perl.porters-gw newsgroup, or you can
65acb1b1 41subscribe to the mailing list by sending perl5-porters-request@perl.org
42a subscription request.
68dc0745 43
44While the GNU project includes Perl in its distributions, there's no
45such thing as "GNU Perl". Perl is not produced nor maintained by the
46Free Software Foundation. Perl's licensing terms are also more open
47than GNU software's tend to be.
48
49You can get commercial support of Perl if you wish, although for most
50users the informal support will more than suffice. See the answer to
51"Where can I buy a commercial version of perl?" for more information.
52
53=head2 Which version of Perl should I use?
54
55You should definitely use version 5. Version 4 is old, limited, and
65acb1b1 56no longer maintained; its last patch (4.036) was in 1992, long ago and
57far away. Sure, it's stable, but so is anything that's dead; in fact,
58perl4 had been called a dead, flea-bitten camel carcass. The most recent
d92eb7b0 59production release is 5.005_03 (although 5.004_05 is still supported).
60The most cutting-edge development release is 5.005_57. Further references
65acb1b1 61to the Perl language in this document refer to the production release
d92eb7b0 62unless otherwise specified. There may be one or more official bug fixes
63by the time you read this, and also perhaps some experimental versions
64on the way to the next release. All releases prior to 5.004 were subject
65to buffer overruns, a grave security issue.
68dc0745 66
67=head2 What are perl4 and perl5?
68
69Perl4 and perl5 are informal names for different versions of the Perl
70programming language. It's easier to say "perl5" than it is to say
71"the 5(.004) release of Perl", but some people have interpreted this
72to mean there's a language called "perl5", which isn't the case.
73Perl5 is merely the popular name for the fifth major release (October 1994),
74while perl4 was the fourth major release (March 1991). There was also a
75perl1 (in January 1988), a perl2 (June 1988), and a perl3 (October 1989).
76
65acb1b1 77The 5.0 release is, essentially, a ground-up rewrite of the original
78perl source code from releases 1 through 4. It has been modularized,
79object-oriented, tweaked, trimmed, and optimized until it almost doesn't
80look like the old code. However, the interface is mostly the same, and
81compatibility with previous releases is very high. See L<perltrap/"Perl4
82to Perl5 Traps">.
68dc0745 83
84To avoid the "what language is perl5?" confusion, some people prefer to
85simply use "perl" to refer to the latest version of perl and avoid using
86"perl5" altogether. It's not really that big a deal, though.
87
5a964f20 88See L<perlhist> for a history of Perl revisions.
89
65acb1b1 90=head2 What is perl6?
91
92Perl6 is a semi-jocular reference to the Topaz project. Headed by Chip
93Salzenberg, Topaz is yet-another ground-up rewrite of the current release
94of Perl, one whose major goal is to create a more maintainable core than
95found in release 5. Written in nominally portable C++, Topaz hopes to
96maintain 100% source-compatibility with previous releases of Perl but to
97run significantly faster and smaller. The Topaz team hopes to provide
98an XS compatibility interface to allow most XS modules to work unchanged,
d92eb7b0 99albeit perhaps without the efficiency that the new interface would allow.
65acb1b1 100New features in Topaz are as yet undetermined, and will be addressed
101once compatibility and performance goals are met.
102
103If you are a hard-working C++ wizard with a firm command of Perl's
104internals, and you would like to work on the project, send a request to
105perl6-porters-request@perl.org to subscribe to the Topaz mailing list.
106
107There is no ETA for Topaz. It is expected to be several years before it
108achieves enough robustness, compatibility, portability, and performance
109to replace perl5 for ordinary use by mere mortals.
110
68dc0745 111=head2 How stable is Perl?
112
113Production releases, which incorporate bug fixes and new functionality,
114are widely tested before release. Since the 5.000 release, we have
115averaged only about one production release per year.
116
117Larry and the Perl development team occasionally make changes to the
118internal core of the language, but all possible efforts are made toward
119backward compatibility. While not quite all perl4 scripts run flawlessly
120under perl5, an update to perl should nearly never invalidate a program
121written for an earlier version of perl (barring accidental bug fixes
122and the rare new keyword).
123
124=head2 Is Perl difficult to learn?
125
5a964f20 126No, Perl is easy to start learning -- and easy to keep learning. It looks
127like most programming languages you're likely to have experience
87275199 128with, so if you've ever written a C program, an awk script, a shell
129script, or even a BASIC program, you're already part way there.
68dc0745 130
131Most tasks only require a small subset of the Perl language. One of
132the guiding mottos for Perl development is "there's more than one way
133to do it" (TMTOWTDI, sometimes pronounced "tim toady"). Perl's
134learning curve is therefore shallow (easy to learn) and long (there's
135a whole lot you can do if you really want).
136
65acb1b1 137Finally, because Perl is frequently (but not always, and certainly not by
138definition) an interpreted language, you can write your programs and test
139them without an intermediate compilation step, allowing you to experiment
140and test/debug quickly and easily. This ease of experimentation flattens
141the learning curve even more.
68dc0745 142
143Things that make Perl easier to learn: Unix experience, almost any kind
144of programming experience, an understanding of regular expressions, and
145the ability to understand other people's code. If there's something you
146need to do, then it's probably already been done, and a working example is
147usually available for free. Don't forget the new perl modules, either.
65acb1b1 148They're discussed in Part 3 of this FAQ, along with CPAN, which is
68dc0745 149discussed in Part 2.
150
151=head2 How does Perl compare with other languages like Java, Python, REXX, Scheme, or Tcl?
152
153Favorably in some areas, unfavorably in others. Precisely which areas
154are good and bad is often a personal choice, so asking this question
155on Usenet runs a strong risk of starting an unproductive Holy War.
156
157Probably the best thing to do is try to write equivalent code to do a
158set of tasks. These languages have their own newsgroups in which you
159can learn about (but hopefully not argue about) them.
160
65acb1b1 161Some comparison documents can be found at http://language.perl.com/versus/
162if you really can't stop yourself.
163
68dc0745 164=head2 Can I do [task] in Perl?
165
65acb1b1 166Perl is flexible and extensible enough for you to use on virtually any
167task, from one-line file-processing tasks to large, elaborate systems.
168For many people, Perl serves as a great replacement for shell scripting.
169For others, it serves as a convenient, high-level replacement for most of
170what they'd program in low-level languages like C or C++. It's ultimately
171up to you (and possibly your management) which tasks you'll use Perl
172for and which you won't.
68dc0745 173
174If you have a library that provides an API, you can make any component
175of it available as just another Perl function or variable using a Perl
176extension written in C or C++ and dynamically linked into your main
177perl interpreter. You can also go the other direction, and write your
178main program in C or C++, and then link in some Perl code on the fly,
65acb1b1 179to create a powerful application. See L<perlembed>.
68dc0745 180
181That said, there will always be small, focused, special-purpose
182languages dedicated to a specific problem domain that are simply more
183convenient for certain kinds of problems. Perl tries to be all things
184to all people, but nothing special to anyone. Examples of specialized
185languages that come to mind include prolog and matlab.
186
187=head2 When shouldn't I program in Perl?
188
189When your manager forbids it -- but do consider replacing them :-).
190
191Actually, one good reason is when you already have an existing
192application written in another language that's all done (and done
193well), or you have an application language specifically designed for a
194certain task (e.g. prolog, make).
195
196For various reasons, Perl is probably not well-suited for real-time
197embedded systems, low-level operating systems development work like
65acb1b1 198device drivers or context-switching code, complex multi-threaded
68dc0745 199shared-memory applications, or extremely large applications. You'll
200notice that perl is not itself written in Perl.
201
65acb1b1 202The new, native-code compiler for Perl may eventually reduce the
203limitations given in the previous statement to some degree, but understand
204that Perl remains fundamentally a dynamically typed language, not
205a statically typed one. You certainly won't be chastised if you don't
206trust nuclear-plant or brain-surgery monitoring code to it. And Larry
207will sleep easier, too -- Wall Street programs not withstanding. :-)
68dc0745 208
209=head2 What's the difference between "perl" and "Perl"?
210
211One bit. Oh, you weren't talking ASCII? :-) Larry now uses "Perl" to
212signify the language proper and "perl" the implementation of it,
213i.e. the current interpreter. Hence Tom's quip that "Nothing but perl
214can parse Perl." You may or may not choose to follow this usage. For
215example, parallelism means "awk and perl" and "Python and Perl" look
87275199 216OK, while "awk and Perl" and "Python and perl" do not. But never
217write "PERL", because perl isn't really an acronym, apocryphal
65acb1b1 218folklore and post-facto expansions notwithstanding.
68dc0745 219
220=head2 Is it a Perl program or a Perl script?
221
65acb1b1 222Larry doesn't really care. He says (half in jest) that "a script is
223what you give the actors. A program is what you give the audience."
224
225Originally, a script was a canned sequence of normally interactive
87275199 226commands, that is, a chat script. Something like a UUCP or PPP chat
65acb1b1 227script or an expect script fits the bill nicely, as do configuration
228scripts run by a program at its start up, such F<.cshrc> or F<.ircrc>,
229for example. Chat scripts were just drivers for existing programs,
230not stand-alone programs in their own right.
231
232A computer scientist will correctly explain that all programs are
233interpreted, and that the only question is at what level. But if you
234ask this question of someone who isn't a computer scientist, they might
235tell you that a I<program> has been compiled to physical machine code
236once, and can then be run multiple times, whereas a I<script> must be
237translated by a program each time it's used.
238
239Perl programs are (usually) neither strictly compiled nor strictly
240interpreted. They can be compiled to a byte-code form (something of a
fc36a67e 241Perl virtual machine) or to completely different languages, like C or
65acb1b1 242assembly language. You can't tell just by looking at it whether the
243source is destined for a pure interpreter, a parse-tree interpreter,
244a byte-code interpreter, or a native-code compiler, so it's hard to give
245a definitive answer here.
246
247Now that "script" and "scripting" are terms that have been seized by
248unscrupulous or unknowing marketeers for their own nefarious purposes,
249they have begun to take on strange and often pejorative meanings,
87275199 250like "non serious" or "not real programming". Consequently, some Perl
65acb1b1 251programmers prefer to avoid them altogether.
68dc0745 252
253=head2 What is a JAPH?
254
255These are the "just another perl hacker" signatures that some people
65acb1b1 256sign their postings with. Randal Schwartz made these famous. About
257100 of the earlier ones are available from
258http://www.perl.com/CPAN/misc/japh .
68dc0745 259
260=head2 Where can I get a list of Larry Wall witticisms?
261
262Over a hundred quips by Larry, from postings of his or source code,
65acb1b1 263can be found at http://www.perl.com/CPAN/misc/lwall-quotes.txt.gz .
264
265Newer examples can be found by perusing Larry's postings:
266
267 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=
68dc0745 268
5e3006a4 269=head2 How can I convince my sysadmin/supervisor/employees to use version (5/5.005/Perl instead of some other language)?
68dc0745 270
271If your manager or employees are wary of unsupported software, or
87275199 272software which doesn't officially ship with your operating system, you
68dc0745 273might try to appeal to their self-interest. If programmers can be
274more productive using and utilizing Perl constructs, functionality,
275simplicity, and power, then the typical manager/supervisor/employee
276may be persuaded. Regarding using Perl in general, it's also
277sometimes helpful to point out that delivery times may be reduced
278using Perl, as compared to other languages.
279
280If you have a project which has a bottleneck, especially in terms of
5a964f20 281translation or testing, Perl almost certainly will provide a viable,
68dc0745 282and quick solution. In conjunction with any persuasion effort, you
283should not fail to point out that Perl is used, quite extensively, and
284with extremely reliable and valuable results, at many large computer
285software and/or hardware companies throughout the world. In fact,
286many Unix vendors now ship Perl by default, and support is usually
287just a news-posting away, if you can't find the answer in the
288I<comprehensive> documentation, including this FAQ.
289
65acb1b1 290See http://www.perl.org/advocacy/ for more information.
291
68dc0745 292If you face reluctance to upgrading from an older version of perl,
293then point out that version 4 is utterly unmaintained and unsupported
294by the Perl Development Team. Another big sell for Perl5 is the large
295number of modules and extensions which greatly reduce development time
296for any given task. Also mention that the difference between version
2974 and version 5 of Perl is like the difference between awk and C++.
87275199 298(Well, OK, maybe not quite that distinct, but you get the idea.) If you
65acb1b1 299want support and a reasonable guarantee that what you're developing
300will continue to work in the future, then you have to run the supported
301version. That probably means running the 5.005 release, although 5.004
302isn't that bad. Several important bugs were fixed from the 5.000 through
5e3006a4 3035.003 versions, though, so try upgrading past them if possible.
304
87275199 305Of particular note is the massive bug hunt for buffer overflow
5e3006a4 306problems that went into the 5.004 release. All releases prior to
307that, including perl4, are considered insecure and should be upgraded
65acb1b1 308as soon as possible.
68dc0745 309
310=head1 AUTHOR AND COPYRIGHT
311
87275199 312Copyright (c) 1997, 1998, 1999 Tom Christiansen and Nathan Torkington.
5a964f20 313All rights reserved.
314
c8db1d39 315When included as an integrated part of the Standard Distribution
d92eb7b0 316of Perl or of its documentation (printed or otherwise), this works is
c8db1d39 317covered under Perl's Artistic Licence. For separate distributions of
318all or part of this FAQ outside of that, see L<perlfaq>.
319
87275199 320Irrespective of its distribution, all code examples here are in the public
c8db1d39 321domain. You are permitted and encouraged to use this code and any
322derivatives thereof in your own programs for fun or for profit as you
323see fit. A simple comment in the code giving credit to the FAQ would
324be courteous but is not required.