1PERLFAQ1(1) Perl Programmers Reference Guide PERLFAQ1(1)
2
6 perlfaq1 - General Questions About Perl ($Revision: 1.19 $, $Date:
7 2005/12/31 00:54:37 $)
8
10 This section of the FAQ answers very general, high-level questions
11 about Perl.
12 What is Perl?
14 Perl is a high-level programming language with an eclectic heritage
16 written by Larry Wall and a cast of thousands. It derives from the
17 ubiquitous C programming language and to a lesser extent from sed, awk,
18 the Unix shell, and at least a dozen other tools and languages. Perl's
19 process, file, and text manipulation facilities make it particularly
20 well-suited for tasks involving quick prototyping, system utilities,
21 software tools, system management tasks, database access, graphical
22 programming, networking, and world wide web programming. These
23 strengths make it especially popular with system administrators and CGI
24 script authors, but mathematicians, geneticists, journalists, and even
25 managers also use Perl. Maybe you should, too.
26 Who supports Perl? Who develops it? Why is it free?
28 The original culture of the pre-populist Internet and the deeply-held
30 beliefs of Perl's author, Larry Wall, gave rise to the free and open
31 distribution policy of perl. Perl is supported by its users. The
32 core, the standard Perl library, the optional modules, and the documen‐
33 tation you're reading now were all written by volunteers. See the per‐
34 sonal note at the end of the README file in the perl source distribu‐
35 tion for more details. See perlhist (new as of 5.005) for Perl's mile‐
36 stone releases.
37 In particular, the core development team (known as the Perl Porters)
39 are a rag-tag band of highly altruistic individuals committed to pro‐
40 ducing better software for free than you could hope to purchase for
41 money. You may snoop on pending developments via the archives at
42 http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/ and http://ar‐
43 chive.develooper.com/perl5-porters@perl.org/ or the news gateway
44 nntp://nntp.perl.org/perl.perl5.porters or its web interface at
45 http://nntp.perl.org/group/perl.perl5.porters , or read the faq at
46 http://simon-cozens.org/writings/p5p-faq , or you can subscribe to the
47 mailing list by sending perl5-porters-request@perl.org a subscription
48 request (an empty message with no subject is fine).
49 While the GNU project includes Perl in its distributions, there's no
51 such thing as "GNU Perl". Perl is not produced nor maintained by the
52 Free Software Foundation. Perl's licensing terms are also more open
53 than GNU software's tend to be.
54 You can get commercial support of Perl if you wish, although for most
56 users the informal support will more than suffice. See the answer to
57 "Where can I buy a commercial version of perl?" for more information.
58 Which version of Perl should I use?
60 (contributed by brian d foy)
62 There is often a matter of opinion and taste, and there isn't any one
64 answer that fits anyone. In general, you want to use either the cur‐
65 rent stable release, or the stable release immediately prior to that
66 one. Currently, those are perl5.8.x and perl5.6.x, respectively.
67 Beyond that, you have to consider several things and decide which is
69 best for you.
70 · If things aren't broken, upgrading perl may break them (or at least
72 issue new warnings).
73 · The latest versions of perl have more bug fixes.
75 · The Perl community is geared toward supporting the most recent
77 releases, so you'll have an easier time finding help for those.
78 · Versions prior to perl5.004 had serious security problems with buf‐
80 fer overflows, and in some cases have CERT advisories (for
81 instance, http://www.cert.org/advisories/CA-1997-17.html ).
82 · The latest versions are probably the least deployed and widely
84 tested, so you may want to wait a few months after their release
85 and see what problems others have if you are risk averse.
86 · The immediate, previous releases (i.e. perl5.6.x ) are usually
88 maintained for a while, although not at the same level as the cur‐
89 rent releases.
90 · No one is actively supporting perl4.x. Five years ago it was a
92 dead camel carcass (according to this document). Now it's barely a
93 skeleton as its whitewashed bones have fractured or eroded.
94 · There is no perl6.x for the next couple of years. Stay tuned, but
96 don't worry that you'll have to change major versions of Perl soon
97 (i.e. before 2006).
98 · There are really two tracks of perl development: a maintenance ver‐
100 sion and an experimental version. The maintenance versions are
101 stable, and have an even number as the minor release (i.e.
102 perl5.8.x, where 8 is the minor release). The experimental ver‐
103 sions may include features that don't make it into the stable ver‐
104 sions, and have an odd number as the minor release (i.e. perl5.9.x,
105 where 9 is the minor release).
106 What are perl4, perl5, or perl6?
108 (contributed by brian d foy)
110 In short, perl4 is the past, perl5 is the present, and perl6 is the
112 future.
113 The number after perl (i.e. the 5 after perl5) is the major release of
115 the perl interpreter as well as the version of the language. Each
116 major version has significant differences that earlier versions cannot
117 support.
118 The current major release of Perl is perl5, and was released in 1994.
120 It can run scripts from the previous major release, perl4 (March 1991),
121 but has significant differences. It introduced the concept of refer‐
122 ences, complex data structures, and modules. The perl5 interpreter was
123 a complete re-write of the previous perl sources.
124 Perl6 is the next major version of Perl, but it's still in development
126 in both its syntax and design. The work started in 2002 and is still
127 ongoing. Many of the most interesting features have shown up in the
128 latest versions of perl5, and some perl5 modules allow you to use some
129 perl6 syntax in your programs. You can learn more about perl6 at
130 http://dev.perl.org/perl6/ .
131 See perlhist for a history of Perl revisions.
133 What is Ponie?
135 At The O'Reilly Open Source Software Convention in 2003, Artur Bergman,
137 Fotango, and The Perl Foundation announced a project to run perl5 on
138 the Parrot virtual machine named Ponie. Ponie stands for Perl On New
139 Internal Engine. The Perl 5.10 language implementation will be used
140 for Ponie, and there will be no language level differences between
141 perl5 and ponie. Ponie is not a complete rewrite of perl5.
142 For more details, see http://www.poniecode.org/
144 What is perl6?
146 At The Second O'Reilly Open Source Software Convention, Larry Wall
148 announced Perl6 development would begin in earnest. Perl6 was an oft
149 used term for Chip Salzenberg's project to rewrite Perl in C++ named
150 Topaz. However, Topaz provided valuable insights to the next version of
151 Perl and its implementation, but was ultimately abandoned.
152 If you want to learn more about Perl6, or have a desire to help in the
154 crusade to make Perl a better place then peruse the Perl6 developers
155 page at http://dev.perl.org/perl6/ and get involved.
156 Perl6 is not scheduled for release yet, and Perl5 will still be sup‐
158 ported for quite awhile after its release. Do not wait for Perl6 to do
159 whatever you need to do.
160 "We're really serious about reinventing everything that needs reinvent‐
162 ing." --Larry Wall
163 How stable is Perl?
165 Production releases, which incorporate bug fixes and new functionality,
167 are widely tested before release. Since the 5.000 release, we have
168 averaged only about one production release per year.
169 Larry and the Perl development team occasionally make changes to the
171 internal core of the language, but all possible efforts are made toward
172 backward compatibility. While not quite all perl4 scripts run flaw‐
173 lessly under perl5, an update to perl should nearly never invalidate a
174 program written for an earlier version of perl (barring accidental bug
175 fixes and the rare new keyword).
176 Is Perl difficult to learn?
178 No, Perl is easy to start learning--and easy to keep learning. It
180 looks like most programming languages you're likely to have experience
181 with, so if you've ever written a C program, an awk script, a shell
182 script, or even a BASIC program, you're already partway there.
183 Most tasks only require a small subset of the Perl language. One of
185 the guiding mottos for Perl development is "there's more than one way
186 to do it" (TMTOWTDI, sometimes pronounced "tim toady"). Perl's learn‐
187 ing curve is therefore shallow (easy to learn) and long (there's a
188 whole lot you can do if you really want).
189 Finally, because Perl is frequently (but not always, and certainly not
191 by definition) an interpreted language, you can write your programs and
192 test them without an intermediate compilation step, allowing you to
193 experiment and test/debug quickly and easily. This ease of experimen‐
194 tation flattens the learning curve even more.
195 Things that make Perl easier to learn: Unix experience, almost any kind
197 of programming experience, an understanding of regular expressions, and
198 the ability to understand other people's code. If there's something
199 you need to do, then it's probably already been done, and a working
200 example is usually available for free. Don't forget the new perl mod‐
201 ules, either. They're discussed in Part 3 of this FAQ, along with
202 CPAN, which is discussed in Part 2.
203 How does Perl compare with other languages like Java, Python, REXX,
205 Scheme, or Tcl?
206 Favorably in some areas, unfavorably in others. Precisely which areas
208 are good and bad is often a personal choice, so asking this question on
209 Usenet runs a strong risk of starting an unproductive Holy War.
210 Probably the best thing to do is try to write equivalent code to do a
212 set of tasks. These languages have their own newsgroups in which you
213 can learn about (but hopefully not argue about) them.
214 Some comparison documents can be found at
216 http://www.perl.com/doc/FMTEYEWTK/versus/ if you really can't stop
217 yourself.
218 Can I do [task] in Perl?
220 Perl is flexible and extensible enough for you to use on virtually any
222 task, from one-line file-processing tasks to large, elaborate systems.
223 For many people, Perl serves as a great replacement for shell script‐
224 ing. For others, it serves as a convenient, high-level replacement for
225 most of what they'd program in low-level languages like C or C++. It's
226 ultimately up to you (and possibly your management) which tasks you'll
227 use Perl for and which you won't.
228 If you have a library that provides an API, you can make any component
230 of it available as just another Perl function or variable using a Perl
231 extension written in C or C++ and dynamically linked into your main
232 perl interpreter. You can also go the other direction, and write your
233 main program in C or C++, and then link in some Perl code on the fly,
234 to create a powerful application. See perlembed.
235 That said, there will always be small, focused, special-purpose lan‐
237 guages dedicated to a specific problem domain that are simply more con‐
238 venient for certain kinds of problems. Perl tries to be all things to
239 all people, but nothing special to anyone. Examples of specialized
240 languages that come to mind include prolog and matlab.
241 When shouldn't I program in Perl?
243 When your manager forbids it--but do consider replacing them :-).
245 Actually, one good reason is when you already have an existing applica‐
247 tion written in another language that's all done (and done well), or
248 you have an application language specifically designed for a certain
249 task (e.g. prolog, make).
250 For various reasons, Perl is probably not well-suited for real-time
252 embedded systems, low-level operating systems development work like
253 device drivers or context-switching code, complex multi-threaded
254 shared-memory applications, or extremely large applications. You'll
255 notice that perl is not itself written in Perl.
256 The new, native-code compiler for Perl may eventually reduce the limi‐
258 tations given in the previous statement to some degree, but understand
259 that Perl remains fundamentally a dynamically typed language, not a
260 statically typed one. You certainly won't be chastised if you don't
261 trust nuclear-plant or brain-surgery monitoring code to it. And Larry
262 will sleep easier, too--Wall Street programs not withstanding. :-)
263 What's the difference between "perl" and "Perl"?
265 One bit. Oh, you weren't talking ASCII? :-) Larry now uses "Perl" to
267 signify the language proper and "perl" the implementation of it, i.e.
268 the current interpreter. Hence Tom's quip that "Nothing but perl can
269 parse Perl." You may or may not choose to follow this usage. For
270 example, parallelism means "awk and perl" and "Python and Perl" look
271 OK, while "awk and Perl" and "Python and perl" do not. But never write
272 "PERL", because perl is not an acronym, apocryphal folklore and post-
273 facto expansions notwithstanding.
274 Is it a Perl program or a Perl script?
276 Larry doesn't really care. He says (half in jest) that "a script is
278 what you give the actors. A program is what you give the audience."
279 Originally, a script was a canned sequence of normally interactive com‐
281 mands--that is, a chat script. Something like a UUCP or PPP chat
282 script or an expect script fits the bill nicely, as do configuration
283 scripts run by a program at its start up, such .cshrc or .ircrc, for
284 example. Chat scripts were just drivers for existing programs, not
285 stand-alone programs in their own right.
286 A computer scientist will correctly explain that all programs are
288 interpreted and that the only question is at what level. But if you
289 ask this question of someone who isn't a computer scientist, they might
290 tell you that a program has been compiled to physical machine code once
291 and can then be run multiple times, whereas a script must be translated
292 by a program each time it's used.
293 Perl programs are (usually) neither strictly compiled nor strictly
295 interpreted. They can be compiled to a byte-code form (something of a
296 Perl virtual machine) or to completely different languages, like C or
297 assembly language. You can't tell just by looking at it whether the
298 source is destined for a pure interpreter, a parse-tree interpreter, a
299 byte-code interpreter, or a native-code compiler, so it's hard to give
300 a definitive answer here.
301 Now that "script" and "scripting" are terms that have been seized by
303 unscrupulous or unknowing marketeers for their own nefarious purposes,
304 they have begun to take on strange and often pejorative meanings, like
305 "non serious" or "not real programming". Consequently, some Perl pro‐
306 grammers prefer to avoid them altogether.
307 What is a JAPH?
309 These are the "just another perl hacker" signatures that some people
311 sign their postings with. Randal Schwartz made these famous. About
312 100 of the earlier ones are available from
313 http://www.cpan.org/misc/japh .
314 Where can I get a list of Larry Wall witticisms?
316 Over a hundred quips by Larry, from postings of his or source code, can
318 be found at http://www.cpan.org/misc/lwall-quotes.txt.gz .
319 How can I convince my sysadmin/supervisor/employees to use version
321 5/5.6.1/Perl instead of some other language?
322 If your manager or employees are wary of unsupported software, or soft‐
324 ware which doesn't officially ship with your operating system, you
325 might try to appeal to their self-interest. If programmers can be more
326 productive using and utilizing Perl constructs, functionality, simplic‐
327 ity, and power, then the typical manager/supervisor/employee may be
328 persuaded. Regarding using Perl in general, it's also sometimes help‐
329 ful to point out that delivery times may be reduced using Perl compared
330 to other languages.
331 If you have a project which has a bottleneck, especially in terms of
333 translation or testing, Perl almost certainly will provide a viable,
334 quick solution. In conjunction with any persuasion effort, you should
335 not fail to point out that Perl is used, quite extensively, and with
336 extremely reliable and valuable results, at many large computer soft‐
337 ware and hardware companies throughout the world. In fact, many Unix
338 vendors now ship Perl by default. Support is usually just a news-post‐
339 ing away, if you can't find the answer in the comprehensive documenta‐
340 tion, including this FAQ.
341 See http://www.perl.org/advocacy/ for more information.
343 If you face reluctance to upgrading from an older version of perl, then
345 point out that version 4 is utterly unmaintained and unsupported by the
346 Perl Development Team. Another big sell for Perl5 is the large number
347 of modules and extensions which greatly reduce development time for any
348 given task. Also mention that the difference between version 4 and
349 version 5 of Perl is like the difference between awk and C++. (Well,
350 OK, maybe it's not quite that distinct, but you get the idea.) If you
351 want support and a reasonable guarantee that what you're developing
352 will continue to work in the future, then you have to run the supported
353 version. As of December 2003 that means running either 5.8.2 (released
354 in November 2003), or one of the older releases like 5.6.2 (also
355 released in November 2003; a maintenance release to let perl 5.6 com‐
356 pile on newer systems as 5.6.1 was released in April 2001) or 5.005_03
357 (released in March 1999), although 5.004_05 isn't that bad if you abso‐
358 lutely need such an old version (released in April 1999) for stability
359 reasons. Anything older than 5.004_05 shouldn't be used.
360 Of particular note is the massive bug hunt for buffer overflow problems
362 that went into the 5.004 release. All releases prior to that, includ‐
363 ing perl4, are considered insecure and should be upgraded as soon as
364 possible.
365 In August 2000 in all Linux distributions a new security problem was
367 found in the optional 'suidperl' (not built or installed by default) in
368 all the Perl branches 5.6, 5.005, and 5.004, see
369 http://www.cpan.org/src/5.0/sperl-2000-08-05/ Perl maintenance releases
370 5.6.1 and 5.8.0 have this security hole closed. Most, if not all,
371 Linux distribution have patches for this vulnerability available, see
372 http://www.linuxsecurity.com/advisories/ , but the most recommendable
373 way is to upgrade to at least Perl 5.6.1.
374
376 Copyright (c) 1997-2006 Tom Christiansen, Nathan Torkington, and other
377 authors as noted. All rights reserved.
378 This documentation is free; you can redistribute it and/or modify it
380 under the same terms as Perl itself.
381 Irrespective of its distribution, all code examples here are in the
383 public domain. You are permitted and encouraged to use this code and
384 any derivatives thereof in your own programs for fun or for profit as
385 you see fit. A simple comment in the code giving credit to the FAQ
386 would be courteous but is not required.
387perl v5.8.8 2006-01-07 PERLFAQ1(1)