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68dc0745 | 1 | =head1 NAME |
2 | ||
cf682770 | 3 | perlfaq1 - General Questions About Perl ($Revision: 1.4 $, $Date: 2002/01/18 21:00:17 $) |
68dc0745 | 4 | |
5 | =head1 DESCRIPTION | |
6 | ||
7 | This section of the FAQ answers very general, high-level questions | |
8 | about Perl. | |
9 | ||
10 | =head2 What is Perl? | |
11 | ||
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. | |
23 | ||
24 | =head2 Who supports Perl? Who develops it? Why is it free? | |
25 | ||
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 | |
5e3006a4 GS |
32 | distribution for more details. See L<perlhist> (new as of 5.005) |
33 | for Perl's milestone releases. | |
68dc0745 | 34 | |
65acb1b1 | 35 | In particular, the core development team (known as the Perl Porters) |
006d0b46 JH |
36 | are a rag-tag band of highly altruistic individuals committed to |
37 | producing better software for free than you could hope to purchase for | |
06a5f41f JH |
38 | money. You may snoop on pending developments via the archives at |
39 | http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/ | |
40 | and http://archive.develooper.com/perl5-porters@perl.org/ | |
cf682770 | 41 | or the news gateway nntp://nntp.perl.org/perl.perl5.porters or |
4915ea75 | 42 | its web interface at http://nntp.perl.org/group/perl.perl5.porters , |
06a5f41f | 43 | or read the faq at http://perlhacker.org/p5p-faq, |
006d0b46 JH |
44 | or you can subscribe to the mailing list by sending |
45 | perl5-porters-request@perl.org a subscription request | |
46 | (an empty message with no subject is fine). | |
68dc0745 | 47 | |
48 | While the GNU project includes Perl in its distributions, there's no | |
49 | such thing as "GNU Perl". Perl is not produced nor maintained by the | |
50 | Free Software Foundation. Perl's licensing terms are also more open | |
51 | than GNU software's tend to be. | |
52 | ||
53 | You can get commercial support of Perl if you wish, although for most | |
54 | users the informal support will more than suffice. See the answer to | |
55 | "Where can I buy a commercial version of perl?" for more information. | |
56 | ||
57 | =head2 Which version of Perl should I use? | |
58 | ||
59 | You should definitely use version 5. Version 4 is old, limited, and | |
65acb1b1 TC |
60 | no longer maintained; its last patch (4.036) was in 1992, long ago and |
61 | far away. Sure, it's stable, but so is anything that's dead; in fact, | |
62 | perl4 had been called a dead, flea-bitten camel carcass. The most recent | |
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63 | production release is 5.6 (although 5.005_03 is still supported). |
64 | The most cutting-edge development release is 5.7. Further references | |
65acb1b1 | 65 | to the Perl language in this document refer to the production release |
d92eb7b0 GS |
66 | unless otherwise specified. There may be one or more official bug fixes |
67 | by the time you read this, and also perhaps some experimental versions | |
68 | on the way to the next release. All releases prior to 5.004 were subject | |
69 | to buffer overruns, a grave security issue. | |
68dc0745 | 70 | |
71 | =head2 What are perl4 and perl5? | |
72 | ||
73 | Perl4 and perl5 are informal names for different versions of the Perl | |
74 | programming language. It's easier to say "perl5" than it is to say | |
75 | "the 5(.004) release of Perl", but some people have interpreted this | |
76 | to mean there's a language called "perl5", which isn't the case. | |
77 | Perl5 is merely the popular name for the fifth major release (October 1994), | |
78 | while perl4 was the fourth major release (March 1991). There was also a | |
79 | perl1 (in January 1988), a perl2 (June 1988), and a perl3 (October 1989). | |
80 | ||
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81 | The 5.0 release is, essentially, a ground-up rewrite of the original |
82 | perl source code from releases 1 through 4. It has been modularized, | |
83 | object-oriented, tweaked, trimmed, and optimized until it almost doesn't | |
84 | look like the old code. However, the interface is mostly the same, and | |
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85 | compatibility with previous releases is very high. |
86 | See L<perltrap/"Perl4 to Perl5 Traps">. | |
68dc0745 | 87 | |
88 | To avoid the "what language is perl5?" confusion, some people prefer to | |
89 | simply use "perl" to refer to the latest version of perl and avoid using | |
90 | "perl5" altogether. It's not really that big a deal, though. | |
91 | ||
5a964f20 TC |
92 | See L<perlhist> for a history of Perl revisions. |
93 | ||
65acb1b1 TC |
94 | =head2 What is perl6? |
95 | ||
4b29649f JH |
96 | At The Second O'Reilly Open Source Software Convention, Larry Wall |
97 | announced Perl6 development would begin in earnest. Perl6 was an oft | |
98 | used term for Chip Salzenberg's project to rewrite Perl in C++ named | |
99 | Topaz. However, Topaz should not be confused with the nisus to rewrite | |
100 | Perl while keeping the lessons learned from other software, as well as | |
101 | Perl5, in mind. | |
7e14cdc9 EHA |
102 | |
103 | If you have a desire to help in the crusade to make Perl a better place | |
104 | then peruse the Perl6 developers page at http://www.perl.org/perl6/ and | |
105 | get involved. | |
106 | ||
107 | The first alpha release is expected by Summer 2001. | |
108 | ||
109 | "We're really serious about reinventing everything that needs reinventing." | |
110 | --Larry Wall | |
65acb1b1 | 111 | |
68dc0745 | 112 | =head2 How stable is Perl? |
113 | ||
114 | Production releases, which incorporate bug fixes and new functionality, | |
115 | are widely tested before release. Since the 5.000 release, we have | |
116 | averaged only about one production release per year. | |
117 | ||
118 | Larry and the Perl development team occasionally make changes to the | |
119 | internal core of the language, but all possible efforts are made toward | |
120 | backward compatibility. While not quite all perl4 scripts run flawlessly | |
121 | under perl5, an update to perl should nearly never invalidate a program | |
122 | written for an earlier version of perl (barring accidental bug fixes | |
123 | and the rare new keyword). | |
124 | ||
125 | =head2 Is Perl difficult to learn? | |
126 | ||
a6dd486b | 127 | No, Perl is easy to start learning--and easy to keep learning. It looks |
5a964f20 | 128 | like most programming languages you're likely to have experience |
87275199 | 129 | with, so if you've ever written a C program, an awk script, a shell |
a6dd486b | 130 | script, or even a BASIC program, you're already partway there. |
68dc0745 | 131 | |
132 | Most tasks only require a small subset of the Perl language. One of | |
133 | the guiding mottos for Perl development is "there's more than one way | |
134 | to do it" (TMTOWTDI, sometimes pronounced "tim toady"). Perl's | |
135 | learning curve is therefore shallow (easy to learn) and long (there's | |
136 | a whole lot you can do if you really want). | |
137 | ||
65acb1b1 TC |
138 | Finally, because Perl is frequently (but not always, and certainly not by |
139 | definition) an interpreted language, you can write your programs and test | |
140 | them without an intermediate compilation step, allowing you to experiment | |
141 | and test/debug quickly and easily. This ease of experimentation flattens | |
142 | the learning curve even more. | |
68dc0745 | 143 | |
144 | Things that make Perl easier to learn: Unix experience, almost any kind | |
145 | of programming experience, an understanding of regular expressions, and | |
146 | the ability to understand other people's code. If there's something you | |
147 | need to do, then it's probably already been done, and a working example is | |
148 | usually available for free. Don't forget the new perl modules, either. | |
65acb1b1 | 149 | They're discussed in Part 3 of this FAQ, along with CPAN, which is |
68dc0745 | 150 | discussed in Part 2. |
151 | ||
152 | =head2 How does Perl compare with other languages like Java, Python, REXX, Scheme, or Tcl? | |
153 | ||
154 | Favorably in some areas, unfavorably in others. Precisely which areas | |
155 | are good and bad is often a personal choice, so asking this question | |
156 | on Usenet runs a strong risk of starting an unproductive Holy War. | |
157 | ||
158 | Probably the best thing to do is try to write equivalent code to do a | |
159 | set of tasks. These languages have their own newsgroups in which you | |
160 | can learn about (but hopefully not argue about) them. | |
161 | ||
65acb1b1 TC |
162 | Some comparison documents can be found at http://language.perl.com/versus/ |
163 | if you really can't stop yourself. | |
164 | ||
68dc0745 | 165 | =head2 Can I do [task] in Perl? |
166 | ||
65acb1b1 TC |
167 | Perl is flexible and extensible enough for you to use on virtually any |
168 | task, from one-line file-processing tasks to large, elaborate systems. | |
169 | For many people, Perl serves as a great replacement for shell scripting. | |
170 | For others, it serves as a convenient, high-level replacement for most of | |
171 | what they'd program in low-level languages like C or C++. It's ultimately | |
172 | up to you (and possibly your management) which tasks you'll use Perl | |
173 | for and which you won't. | |
68dc0745 | 174 | |
175 | If you have a library that provides an API, you can make any component | |
176 | of it available as just another Perl function or variable using a Perl | |
177 | extension written in C or C++ and dynamically linked into your main | |
178 | perl interpreter. You can also go the other direction, and write your | |
179 | main program in C or C++, and then link in some Perl code on the fly, | |
65acb1b1 | 180 | to create a powerful application. See L<perlembed>. |
68dc0745 | 181 | |
182 | That said, there will always be small, focused, special-purpose | |
183 | languages dedicated to a specific problem domain that are simply more | |
184 | convenient for certain kinds of problems. Perl tries to be all things | |
185 | to all people, but nothing special to anyone. Examples of specialized | |
186 | languages that come to mind include prolog and matlab. | |
187 | ||
188 | =head2 When shouldn't I program in Perl? | |
189 | ||
a6dd486b | 190 | When your manager forbids it--but do consider replacing them :-). |
68dc0745 | 191 | |
192 | Actually, one good reason is when you already have an existing | |
193 | application written in another language that's all done (and done | |
194 | well), or you have an application language specifically designed for a | |
195 | certain task (e.g. prolog, make). | |
196 | ||
197 | For various reasons, Perl is probably not well-suited for real-time | |
198 | embedded systems, low-level operating systems development work like | |
65acb1b1 | 199 | device drivers or context-switching code, complex multi-threaded |
68dc0745 | 200 | shared-memory applications, or extremely large applications. You'll |
201 | notice that perl is not itself written in Perl. | |
202 | ||
65acb1b1 TC |
203 | The new, native-code compiler for Perl may eventually reduce the |
204 | limitations given in the previous statement to some degree, but understand | |
205 | that Perl remains fundamentally a dynamically typed language, not | |
206 | a statically typed one. You certainly won't be chastised if you don't | |
207 | trust nuclear-plant or brain-surgery monitoring code to it. And Larry | |
a6dd486b | 208 | will sleep easier, too--Wall Street programs not withstanding. :-) |
68dc0745 | 209 | |
210 | =head2 What's the difference between "perl" and "Perl"? | |
211 | ||
212 | One bit. Oh, you weren't talking ASCII? :-) Larry now uses "Perl" to | |
213 | signify the language proper and "perl" the implementation of it, | |
214 | i.e. the current interpreter. Hence Tom's quip that "Nothing but perl | |
215 | can parse Perl." You may or may not choose to follow this usage. For | |
216 | example, parallelism means "awk and perl" and "Python and Perl" look | |
87275199 GS |
217 | OK, while "awk and Perl" and "Python and perl" do not. But never |
218 | write "PERL", because perl isn't really an acronym, apocryphal | |
65acb1b1 | 219 | folklore and post-facto expansions notwithstanding. |
68dc0745 | 220 | |
221 | =head2 Is it a Perl program or a Perl script? | |
222 | ||
65acb1b1 TC |
223 | Larry doesn't really care. He says (half in jest) that "a script is |
224 | what you give the actors. A program is what you give the audience." | |
225 | ||
226 | Originally, a script was a canned sequence of normally interactive | |
a6dd486b | 227 | commands--that is, a chat script. Something like a UUCP or PPP chat |
65acb1b1 TC |
228 | script or an expect script fits the bill nicely, as do configuration |
229 | scripts run by a program at its start up, such F<.cshrc> or F<.ircrc>, | |
230 | for example. Chat scripts were just drivers for existing programs, | |
231 | not stand-alone programs in their own right. | |
232 | ||
233 | A computer scientist will correctly explain that all programs are | |
a6dd486b | 234 | interpreted and that the only question is at what level. But if you |
65acb1b1 TC |
235 | ask this question of someone who isn't a computer scientist, they might |
236 | tell you that a I<program> has been compiled to physical machine code | |
a6dd486b | 237 | once and can then be run multiple times, whereas a I<script> must be |
65acb1b1 TC |
238 | translated by a program each time it's used. |
239 | ||
240 | Perl programs are (usually) neither strictly compiled nor strictly | |
241 | interpreted. They can be compiled to a byte-code form (something of a | |
fc36a67e | 242 | Perl virtual machine) or to completely different languages, like C or |
65acb1b1 TC |
243 | assembly language. You can't tell just by looking at it whether the |
244 | source is destined for a pure interpreter, a parse-tree interpreter, | |
245 | a byte-code interpreter, or a native-code compiler, so it's hard to give | |
246 | a definitive answer here. | |
247 | ||
248 | Now that "script" and "scripting" are terms that have been seized by | |
249 | unscrupulous or unknowing marketeers for their own nefarious purposes, | |
250 | they have begun to take on strange and often pejorative meanings, | |
87275199 | 251 | like "non serious" or "not real programming". Consequently, some Perl |
65acb1b1 | 252 | programmers prefer to avoid them altogether. |
68dc0745 | 253 | |
254 | =head2 What is a JAPH? | |
255 | ||
256 | These are the "just another perl hacker" signatures that some people | |
65acb1b1 TC |
257 | sign their postings with. Randal Schwartz made these famous. About |
258 | 100 of the earlier ones are available from | |
a93751fa | 259 | http://www.cpan.org/misc/japh . |
68dc0745 | 260 | |
261 | =head2 Where can I get a list of Larry Wall witticisms? | |
262 | ||
263 | Over a hundred quips by Larry, from postings of his or source code, | |
a93751fa | 264 | can be found at http://www.cpan.org/misc/lwall-quotes.txt.gz . |
65acb1b1 | 265 | |
f9ac83b8 | 266 | =head2 How can I convince my sysadmin/supervisor/employees to use version 5/5.005/Perl instead of some other language? |
68dc0745 | 267 | |
268 | If your manager or employees are wary of unsupported software, or | |
87275199 | 269 | software which doesn't officially ship with your operating system, you |
68dc0745 | 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 | |
a6dd486b | 275 | using Perl compared to other languages. |
68dc0745 | 276 | |
277 | If you have a project which has a bottleneck, especially in terms of | |
5a964f20 | 278 | translation or testing, Perl almost certainly will provide a viable, |
a6dd486b | 279 | quick solution. In conjunction with any persuasion effort, you |
68dc0745 | 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 | |
a6dd486b JB |
282 | software and hardware companies throughout the world. In fact, |
283 | many Unix vendors now ship Perl by default. Support is usually | |
68dc0745 | 284 | just a news-posting away, if you can't find the answer in the |
285 | I<comprehensive> documentation, including this FAQ. | |
286 | ||
65acb1b1 TC |
287 | See http://www.perl.org/advocacy/ for more information. |
288 | ||
68dc0745 | 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++. | |
f4c2dd42 JA |
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 | |
bd15af9d JH |
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 | |
f4c2dd42 JA |
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. | |
5e3006a4 | 303 | |
87275199 | 304 | Of particular note is the massive bug hunt for buffer overflow |
5e3006a4 GS |
305 | problems that went into the 5.004 release. All releases prior to |
306 | that, including perl4, are considered insecure and should be upgraded | |
65acb1b1 | 307 | as soon as possible. |
68dc0745 | 308 | |
cb4d4ad7 | 309 | In August 2000 in all Linux distributions a new security problem was |
f4c2dd42 JA |
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/ | |
03739d21 JH |
313 | Perl maintenance releases 5.6.1 and 5.8.0 have this security hole closed. |
314 | Most, if not all, Linux distribution have patches for this | |
315 | vulnerability available, see http://www.linuxsecurity.com/advisories/ , | |
316 | but the most recommendable way is to upgrade to at least Perl 5.6.1. | |
f4c2dd42 | 317 | |
68dc0745 | 318 | =head1 AUTHOR AND COPYRIGHT |
319 | ||
be3c0a43 JH |
320 | Copyright (c) 1997, 1998, 1999, 2000, 2001, 2002 Tom Christiansen and |
321 | Nathan Torkington. All rights reserved. | |
5a964f20 | 322 | |
5a7beb56 JH |
323 | This documentation is free; you can redistribute it and/or modify it |
324 | under the same terms as Perl itself. | |
c8db1d39 | 325 | |
87275199 | 326 | Irrespective of its distribution, all code examples here are in the public |
c8db1d39 TC |
327 | domain. You are permitted and encouraged to use this code and any |
328 | derivatives thereof in your own programs for fun or for profit as you | |
329 | see fit. A simple comment in the code giving credit to the FAQ would | |
330 | be courteous but is not required. |