3 perlfaq1 - General Questions About Perl ($Revision: 1.23 $, $Date: 1999/05/23 16:08:30 $)
7 This section of the FAQ answers very general, high-level questions
12 Perl is a high-level programming language with an eclectic heritage
13 written by Larry Wall and a cast of thousands. It derives from the
14 ubiquitous C programming language and to a lesser extent from sed,
15 awk, the Unix shell, and at least a dozen other tools and languages.
16 Perl's process, file, and text manipulation facilities make it
17 particularly well-suited for tasks involving quick prototyping, system
18 utilities, software tools, system management tasks, database access,
19 graphical programming, networking, and world wide web programming.
20 These strengths make it especially popular with system administrators
21 and CGI script authors, but mathematicians, geneticists, journalists,
22 and even managers also use Perl. Maybe you should, too.
24 =head2 Who supports Perl? Who develops it? Why is it free?
26 The original culture of the pre-populist Internet and the deeply-held
27 beliefs of Perl's author, Larry Wall, gave rise to the free and open
28 distribution policy of perl. Perl is supported by its users. The
29 core, the standard Perl library, the optional modules, and the
30 documentation you're reading now were all written by volunteers. See
31 the personal note at the end of the README file in the perl source
32 distribution for more details. See L<perlhist> (new as of 5.005)
33 for Perl's milestone releases.
35 In particular, the core development team (known as the Perl Porters)
36 are a rag-tag band of highly altruistic individuals committed
37 to producing better software for free than you could hope to
38 purchase for money. You may snoop on pending developments via
39 nntp://news.perl.com/perl.porters-gw/ and the Deja archive at
40 http://www.deja.com/ using the perl.porters-gw newsgroup, or you can
41 subscribe to the mailing list by sending perl5-porters-request@perl.org
42 a subscription request.
44 While the GNU project includes Perl in its distributions, there's no
45 such thing as "GNU Perl". Perl is not produced nor maintained by the
46 Free Software Foundation. Perl's licensing terms are also more open
47 than GNU software's tend to be.
49 You can get commercial support of Perl if you wish, although for most
50 users the informal support will more than suffice. See the answer to
51 "Where can I buy a commercial version of perl?" for more information.
53 =head2 Which version of Perl should I use?
55 You should definitely use version 5. Version 4 is old, limited, and
56 no longer maintained; its last patch (4.036) was in 1992, long ago and
57 far away. Sure, it's stable, but so is anything that's dead; in fact,
58 perl4 had been called a dead, flea-bitten camel carcass. The most recent
59 production release is 5.6 (although 5.005_03 is still supported).
60 The most cutting-edge development release is 5.7. Further references
61 to the Perl language in this document refer to the production release
62 unless otherwise specified. There may be one or more official bug fixes
63 by the time you read this, and also perhaps some experimental versions
64 on the way to the next release. All releases prior to 5.004 were subject
65 to buffer overruns, a grave security issue.
67 =head2 What are perl4 and perl5?
69 Perl4 and perl5 are informal names for different versions of the Perl
70 programming 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
72 to mean there's a language called "perl5", which isn't the case.
73 Perl5 is merely the popular name for the fifth major release (October 1994),
74 while perl4 was the fourth major release (March 1991). There was also a
75 perl1 (in January 1988), a perl2 (June 1988), and a perl3 (October 1989).
77 The 5.0 release is, essentially, a ground-up rewrite of the original
78 perl source code from releases 1 through 4. It has been modularized,
79 object-oriented, tweaked, trimmed, and optimized until it almost doesn't
80 look like the old code. However, the interface is mostly the same, and
81 compatibility with previous releases is very high.
82 See L<perltrap/"Perl4 to Perl5 Traps">.
84 To avoid the "what language is perl5?" confusion, some people prefer to
85 simply 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.
88 See L<perlhist> for a history of Perl revisions.
92 At The Second O'Reilly Open Source Software Convention, Larry Wall
93 announced Perl6 development would begin in earnest. Perl6 was an oft
94 used term for Chip Salzenberg's project to rewrite Perl in C++ named
95 Topaz. However, Topaz should not be confused with the nisus to rewrite
96 Perl while keeping the lessons learned from other software, as well as
99 If you have a desire to help in the crusade to make Perl a better place
100 then peruse the Perl6 developers page at http://www.perl.org/perl6/ and
103 The first alpha release is expected by Summer 2001.
105 "We're really serious about reinventing everything that needs reinventing."
108 =head2 How stable is Perl?
110 Production releases, which incorporate bug fixes and new functionality,
111 are widely tested before release. Since the 5.000 release, we have
112 averaged only about one production release per year.
114 Larry and the Perl development team occasionally make changes to the
115 internal core of the language, but all possible efforts are made toward
116 backward compatibility. While not quite all perl4 scripts run flawlessly
117 under perl5, an update to perl should nearly never invalidate a program
118 written for an earlier version of perl (barring accidental bug fixes
119 and the rare new keyword).
121 =head2 Is Perl difficult to learn?
123 No, Perl is easy to start learning--and easy to keep learning. It looks
124 like most programming languages you're likely to have experience
125 with, so if you've ever written a C program, an awk script, a shell
126 script, or even a BASIC program, you're already partway there.
128 Most tasks only require a small subset of the Perl language. One of
129 the guiding mottos for Perl development is "there's more than one way
130 to do it" (TMTOWTDI, sometimes pronounced "tim toady"). Perl's
131 learning curve is therefore shallow (easy to learn) and long (there's
132 a whole lot you can do if you really want).
134 Finally, because Perl is frequently (but not always, and certainly not by
135 definition) an interpreted language, you can write your programs and test
136 them without an intermediate compilation step, allowing you to experiment
137 and test/debug quickly and easily. This ease of experimentation flattens
138 the learning curve even more.
140 Things that make Perl easier to learn: Unix experience, almost any kind
141 of programming experience, an understanding of regular expressions, and
142 the ability to understand other people's code. If there's something you
143 need to do, then it's probably already been done, and a working example is
144 usually available for free. Don't forget the new perl modules, either.
145 They're discussed in Part 3 of this FAQ, along with CPAN, which is
148 =head2 How does Perl compare with other languages like Java, Python, REXX, Scheme, or Tcl?
150 Favorably in some areas, unfavorably in others. Precisely which areas
151 are good and bad is often a personal choice, so asking this question
152 on Usenet runs a strong risk of starting an unproductive Holy War.
154 Probably the best thing to do is try to write equivalent code to do a
155 set of tasks. These languages have their own newsgroups in which you
156 can learn about (but hopefully not argue about) them.
158 Some comparison documents can be found at http://language.perl.com/versus/
159 if you really can't stop yourself.
161 =head2 Can I do [task] in Perl?
163 Perl is flexible and extensible enough for you to use on virtually any
164 task, from one-line file-processing tasks to large, elaborate systems.
165 For many people, Perl serves as a great replacement for shell scripting.
166 For others, it serves as a convenient, high-level replacement for most of
167 what they'd program in low-level languages like C or C++. It's ultimately
168 up to you (and possibly your management) which tasks you'll use Perl
169 for and which you won't.
171 If you have a library that provides an API, you can make any component
172 of it available as just another Perl function or variable using a Perl
173 extension written in C or C++ and dynamically linked into your main
174 perl interpreter. You can also go the other direction, and write your
175 main program in C or C++, and then link in some Perl code on the fly,
176 to create a powerful application. See L<perlembed>.
178 That said, there will always be small, focused, special-purpose
179 languages dedicated to a specific problem domain that are simply more
180 convenient for certain kinds of problems. Perl tries to be all things
181 to all people, but nothing special to anyone. Examples of specialized
182 languages that come to mind include prolog and matlab.
184 =head2 When shouldn't I program in Perl?
186 When your manager forbids it--but do consider replacing them :-).
188 Actually, one good reason is when you already have an existing
189 application written in another language that's all done (and done
190 well), or you have an application language specifically designed for a
191 certain task (e.g. prolog, make).
193 For various reasons, Perl is probably not well-suited for real-time
194 embedded systems, low-level operating systems development work like
195 device drivers or context-switching code, complex multi-threaded
196 shared-memory applications, or extremely large applications. You'll
197 notice that perl is not itself written in Perl.
199 The new, native-code compiler for Perl may eventually reduce the
200 limitations given in the previous statement to some degree, but understand
201 that Perl remains fundamentally a dynamically typed language, not
202 a statically typed one. You certainly won't be chastised if you don't
203 trust nuclear-plant or brain-surgery monitoring code to it. And Larry
204 will sleep easier, too--Wall Street programs not withstanding. :-)
206 =head2 What's the difference between "perl" and "Perl"?
208 One bit. Oh, you weren't talking ASCII? :-) Larry now uses "Perl" to
209 signify the language proper and "perl" the implementation of it,
210 i.e. the current interpreter. Hence Tom's quip that "Nothing but perl
211 can parse Perl." You may or may not choose to follow this usage. For
212 example, parallelism means "awk and perl" and "Python and Perl" look
213 OK, while "awk and Perl" and "Python and perl" do not. But never
214 write "PERL", because perl isn't really an acronym, apocryphal
215 folklore and post-facto expansions notwithstanding.
217 =head2 Is it a Perl program or a Perl script?
219 Larry doesn't really care. He says (half in jest) that "a script is
220 what you give the actors. A program is what you give the audience."
222 Originally, a script was a canned sequence of normally interactive
223 commands--that is, a chat script. Something like a UUCP or PPP chat
224 script or an expect script fits the bill nicely, as do configuration
225 scripts run by a program at its start up, such F<.cshrc> or F<.ircrc>,
226 for example. Chat scripts were just drivers for existing programs,
227 not stand-alone programs in their own right.
229 A computer scientist will correctly explain that all programs are
230 interpreted and that the only question is at what level. But if you
231 ask this question of someone who isn't a computer scientist, they might
232 tell you that a I<program> has been compiled to physical machine code
233 once and can then be run multiple times, whereas a I<script> must be
234 translated by a program each time it's used.
236 Perl programs are (usually) neither strictly compiled nor strictly
237 interpreted. They can be compiled to a byte-code form (something of a
238 Perl virtual machine) or to completely different languages, like C or
239 assembly language. You can't tell just by looking at it whether the
240 source is destined for a pure interpreter, a parse-tree interpreter,
241 a byte-code interpreter, or a native-code compiler, so it's hard to give
242 a definitive answer here.
244 Now that "script" and "scripting" are terms that have been seized by
245 unscrupulous or unknowing marketeers for their own nefarious purposes,
246 they have begun to take on strange and often pejorative meanings,
247 like "non serious" or "not real programming". Consequently, some Perl
248 programmers prefer to avoid them altogether.
250 =head2 What is a JAPH?
252 These are the "just another perl hacker" signatures that some people
253 sign their postings with. Randal Schwartz made these famous. About
254 100 of the earlier ones are available from
255 http://www.perl.com/CPAN/misc/japh .
257 =head2 Where can I get a list of Larry Wall witticisms?
259 Over a hundred quips by Larry, from postings of his or source code,
260 can be found at http://www.perl.com/CPAN/misc/lwall-quotes.txt.gz .
262 Newer examples can be found by perusing Larry's postings:
264 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=
266 =head2 How can I convince my sysadmin/supervisor/employees to use version 5/5.005/Perl instead of some other language?
268 If your manager or employees are wary of unsupported software, or
269 software which doesn't officially ship with your operating system, you
270 might try to appeal to their self-interest. If programmers can be
271 more productive using and utilizing Perl constructs, functionality,
272 simplicity, and power, then the typical manager/supervisor/employee
273 may be persuaded. Regarding using Perl in general, it's also
274 sometimes helpful to point out that delivery times may be reduced
275 using Perl compared to other languages.
277 If you have a project which has a bottleneck, especially in terms of
278 translation or testing, Perl almost certainly will provide a viable,
279 quick solution. In conjunction with any persuasion effort, you
280 should not fail to point out that Perl is used, quite extensively, and
281 with extremely reliable and valuable results, at many large computer
282 software and hardware companies throughout the world. In fact,
283 many Unix vendors now ship Perl by default. Support is usually
284 just a news-posting away, if you can't find the answer in the
285 I<comprehensive> documentation, including this FAQ.
287 See http://www.perl.org/advocacy/ for more information.
289 If you face reluctance to upgrading from an older version of perl,
290 then point out that version 4 is utterly unmaintained and unsupported
291 by the Perl Development Team. Another big sell for Perl5 is the large
292 number of modules and extensions which greatly reduce development time
293 for any given task. Also mention that the difference between version
294 4 and version 5 of Perl is like the difference between awk and C++.
295 (Well, OK, maybe it's not quite that distinct, but you get the idea.)
296 If you want support and a reasonable guarantee that what you're
297 developing will continue to work in the future, then you have to run
298 the supported version. As of April 2001 that probably means
299 running either of the releases 5.6.1 (released in April 2001) or
300 5.005_03 (released in March 1999), although 5.004_05 isn't that bad
301 if you B<absolutely> need such an old version (released in April 1999)
302 for stability reasons. Anything older than 5.004_05 shouldn't be used.
304 Of particular note is the massive bug hunt for buffer overflow
305 problems that went into the 5.004 release. All releases prior to
306 that, including perl4, are considered insecure and should be upgraded
309 In August 2000 in all Linux distributions a new security problem was
310 found in the optional 'suidperl' (not built or installed by default)
311 in all the Perl branches 5.6, 5.005, and 5.004, see
312 http://www.cpan.org/src/5.0/sperl-2000-08-05/
314 =head1 AUTHOR AND COPYRIGHT
316 Copyright (c) 1997, 1998, 1999, 2000, 2001 Tom Christiansen and Nathan
317 Torkington. All rights reserved.
319 When included as an integrated part of the Standard Distribution
320 of Perl or of its documentation (printed or otherwise), this works is
321 covered under Perl's Artistic Licence. For separate distributions of
322 all or part of this FAQ outside of that, see L<perlfaq>.
324 Irrespective of its distribution, all code examples here are in the public
325 domain. You are permitted and encouraged to use this code and any
326 derivatives thereof in your own programs for fun or for profit as you
327 see fit. A simple comment in the code giving credit to the FAQ would
328 be courteous but is not required.