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68dc0745 | 1 | =head1 NAME |
2 | ||
793f5136 | 3 | perlfaq1 - General Questions About Perl ($Revision: 1.14 $, $Date: 2003/11/23 08:02:29 $) |
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 | 38 | money. You may snoop on pending developments via the archives at |
1577cd80 | 39 | http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/ |
f05bbc40 | 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 , |
49d635f9 | 43 | or read the faq at http://simon-cozens.org/writings/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, | |
36597cb9 | 62 | perl4 had been called a dead, flea-bitten camel carcass. The most |
793f5136 | 63 | recent production release is 5.8.2 (although 5.005_03 and 5.6.2 are |
36597cb9 JB |
64 | still supported). The most cutting-edge development release is 5.9. |
65 | Further references to the Perl language in this document refer to the | |
66 | production release unless otherwise specified. There may be one or | |
67 | more official bug fixes by the time you read this, and also perhaps | |
68 | some experimental versions on the way to the next release. | |
69 | All releases prior to 5.004 were subject to buffer overruns, a grave | |
70 | security issue. | |
68dc0745 | 71 | |
72 | =head2 What are perl4 and perl5? | |
73 | ||
74 | Perl4 and perl5 are informal names for different versions of the Perl | |
75 | programming language. It's easier to say "perl5" than it is to say | |
76 | "the 5(.004) release of Perl", but some people have interpreted this | |
77 | to mean there's a language called "perl5", which isn't the case. | |
78 | Perl5 is merely the popular name for the fifth major release (October 1994), | |
79 | while perl4 was the fourth major release (March 1991). There was also a | |
80 | perl1 (in January 1988), a perl2 (June 1988), and a perl3 (October 1989). | |
81 | ||
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82 | The 5.0 release is, essentially, a ground-up rewrite of the original |
83 | perl source code from releases 1 through 4. It has been modularized, | |
84 | object-oriented, tweaked, trimmed, and optimized until it almost doesn't | |
85 | look like the old code. However, the interface is mostly the same, and | |
197aec24 | 86 | compatibility with previous releases is very high. |
13a2d996 | 87 | See L<perltrap/"Perl4 to Perl5 Traps">. |
68dc0745 | 88 | |
89 | To avoid the "what language is perl5?" confusion, some people prefer to | |
90 | simply use "perl" to refer to the latest version of perl and avoid using | |
91 | "perl5" altogether. It's not really that big a deal, though. | |
92 | ||
5a964f20 TC |
93 | See L<perlhist> for a history of Perl revisions. |
94 | ||
d96a6f6b JH |
95 | =head2 What is Ponie? |
96 | ||
97 | At The O'Reilly Open Source Software Convention in 2003, Artur | |
98 | Bergman, Fotango, and The Perl Foundation announced a project to | |
99 | run perl5 on the Parrot virtual machine named Ponie. Ponie stands for | |
100 | Perl On New Internal Engine. The Perl 5.10 language implementation | |
101 | will be used for Ponie, and there will be no language level | |
102 | differences between perl5 and ponie. Ponie is not a complete rewrite | |
103 | of perl5. | |
104 | ||
793f5136 RGS |
105 | For more details, see http://www.poniecode.org/ |
106 | ||
65acb1b1 TC |
107 | =head2 What is perl6? |
108 | ||
197aec24 | 109 | At The Second O'Reilly Open Source Software Convention, Larry Wall |
4b29649f JH |
110 | announced Perl6 development would begin in earnest. Perl6 was an oft |
111 | used term for Chip Salzenberg's project to rewrite Perl in C++ named | |
0bc0ad85 | 112 | Topaz. However, Topaz provided valuable insights to the next version |
197aec24 | 113 | of Perl and its implementation, but was ultimately abandoned. |
7e14cdc9 | 114 | |
197aec24 RGS |
115 | If you want to learn more about Perl6, or have a desire to help in |
116 | the crusade to make Perl a better place then peruse the Perl6 developers | |
0bc0ad85 | 117 | page at http://dev.perl.org/perl6/ and get involved. |
7e14cdc9 | 118 | |
0bc0ad85 JH |
119 | Perl6 is not scheduled for release yet, and Perl5 will still be supported |
120 | for quite awhile after its release. Do not wait for Perl6 to do whatever | |
121 | you need to do. | |
7e14cdc9 EHA |
122 | |
123 | "We're really serious about reinventing everything that needs reinventing." | |
124 | --Larry Wall | |
65acb1b1 | 125 | |
68dc0745 | 126 | =head2 How stable is Perl? |
127 | ||
128 | Production releases, which incorporate bug fixes and new functionality, | |
129 | are widely tested before release. Since the 5.000 release, we have | |
130 | averaged only about one production release per year. | |
131 | ||
132 | Larry and the Perl development team occasionally make changes to the | |
133 | internal core of the language, but all possible efforts are made toward | |
134 | backward compatibility. While not quite all perl4 scripts run flawlessly | |
135 | under perl5, an update to perl should nearly never invalidate a program | |
136 | written for an earlier version of perl (barring accidental bug fixes | |
137 | and the rare new keyword). | |
138 | ||
139 | =head2 Is Perl difficult to learn? | |
140 | ||
a6dd486b | 141 | No, Perl is easy to start learning--and easy to keep learning. It looks |
5a964f20 | 142 | like most programming languages you're likely to have experience |
87275199 | 143 | with, so if you've ever written a C program, an awk script, a shell |
a6dd486b | 144 | script, or even a BASIC program, you're already partway there. |
68dc0745 | 145 | |
146 | Most tasks only require a small subset of the Perl language. One of | |
147 | the guiding mottos for Perl development is "there's more than one way | |
148 | to do it" (TMTOWTDI, sometimes pronounced "tim toady"). Perl's | |
149 | learning curve is therefore shallow (easy to learn) and long (there's | |
150 | a whole lot you can do if you really want). | |
151 | ||
65acb1b1 TC |
152 | Finally, because Perl is frequently (but not always, and certainly not by |
153 | definition) an interpreted language, you can write your programs and test | |
154 | them without an intermediate compilation step, allowing you to experiment | |
155 | and test/debug quickly and easily. This ease of experimentation flattens | |
156 | the learning curve even more. | |
68dc0745 | 157 | |
158 | Things that make Perl easier to learn: Unix experience, almost any kind | |
159 | of programming experience, an understanding of regular expressions, and | |
160 | the ability to understand other people's code. If there's something you | |
161 | need to do, then it's probably already been done, and a working example is | |
162 | usually available for free. Don't forget the new perl modules, either. | |
65acb1b1 | 163 | They're discussed in Part 3 of this FAQ, along with CPAN, which is |
68dc0745 | 164 | discussed in Part 2. |
165 | ||
166 | =head2 How does Perl compare with other languages like Java, Python, REXX, Scheme, or Tcl? | |
167 | ||
168 | Favorably in some areas, unfavorably in others. Precisely which areas | |
169 | are good and bad is often a personal choice, so asking this question | |
170 | on Usenet runs a strong risk of starting an unproductive Holy War. | |
171 | ||
172 | Probably the best thing to do is try to write equivalent code to do a | |
173 | set of tasks. These languages have their own newsgroups in which you | |
174 | can learn about (but hopefully not argue about) them. | |
175 | ||
65acb1b1 TC |
176 | Some comparison documents can be found at http://language.perl.com/versus/ |
177 | if you really can't stop yourself. | |
178 | ||
68dc0745 | 179 | =head2 Can I do [task] in Perl? |
180 | ||
65acb1b1 TC |
181 | Perl is flexible and extensible enough for you to use on virtually any |
182 | task, from one-line file-processing tasks to large, elaborate systems. | |
183 | For many people, Perl serves as a great replacement for shell scripting. | |
184 | For others, it serves as a convenient, high-level replacement for most of | |
185 | what they'd program in low-level languages like C or C++. It's ultimately | |
186 | up to you (and possibly your management) which tasks you'll use Perl | |
187 | for and which you won't. | |
68dc0745 | 188 | |
189 | If you have a library that provides an API, you can make any component | |
190 | of it available as just another Perl function or variable using a Perl | |
191 | extension written in C or C++ and dynamically linked into your main | |
192 | perl interpreter. You can also go the other direction, and write your | |
193 | main program in C or C++, and then link in some Perl code on the fly, | |
65acb1b1 | 194 | to create a powerful application. See L<perlembed>. |
68dc0745 | 195 | |
196 | That said, there will always be small, focused, special-purpose | |
197 | languages dedicated to a specific problem domain that are simply more | |
198 | convenient for certain kinds of problems. Perl tries to be all things | |
199 | to all people, but nothing special to anyone. Examples of specialized | |
200 | languages that come to mind include prolog and matlab. | |
201 | ||
202 | =head2 When shouldn't I program in Perl? | |
203 | ||
a6dd486b | 204 | When your manager forbids it--but do consider replacing them :-). |
68dc0745 | 205 | |
206 | Actually, one good reason is when you already have an existing | |
207 | application written in another language that's all done (and done | |
208 | well), or you have an application language specifically designed for a | |
209 | certain task (e.g. prolog, make). | |
210 | ||
211 | For various reasons, Perl is probably not well-suited for real-time | |
212 | embedded systems, low-level operating systems development work like | |
65acb1b1 | 213 | device drivers or context-switching code, complex multi-threaded |
68dc0745 | 214 | shared-memory applications, or extremely large applications. You'll |
215 | notice that perl is not itself written in Perl. | |
216 | ||
65acb1b1 TC |
217 | The new, native-code compiler for Perl may eventually reduce the |
218 | limitations given in the previous statement to some degree, but understand | |
219 | that Perl remains fundamentally a dynamically typed language, not | |
220 | a statically typed one. You certainly won't be chastised if you don't | |
221 | trust nuclear-plant or brain-surgery monitoring code to it. And Larry | |
a6dd486b | 222 | will sleep easier, too--Wall Street programs not withstanding. :-) |
68dc0745 | 223 | |
224 | =head2 What's the difference between "perl" and "Perl"? | |
225 | ||
226 | One bit. Oh, you weren't talking ASCII? :-) Larry now uses "Perl" to | |
227 | signify the language proper and "perl" the implementation of it, | |
228 | i.e. the current interpreter. Hence Tom's quip that "Nothing but perl | |
229 | can parse Perl." You may or may not choose to follow this usage. For | |
230 | example, parallelism means "awk and perl" and "Python and Perl" look | |
87275199 | 231 | OK, while "awk and Perl" and "Python and perl" do not. But never |
881bdbd4 | 232 | write "PERL", because perl is not an acronym, apocryphal |
65acb1b1 | 233 | folklore and post-facto expansions notwithstanding. |
68dc0745 | 234 | |
235 | =head2 Is it a Perl program or a Perl script? | |
236 | ||
65acb1b1 TC |
237 | Larry doesn't really care. He says (half in jest) that "a script is |
238 | what you give the actors. A program is what you give the audience." | |
239 | ||
240 | Originally, a script was a canned sequence of normally interactive | |
a6dd486b | 241 | commands--that is, a chat script. Something like a UUCP or PPP chat |
65acb1b1 TC |
242 | script or an expect script fits the bill nicely, as do configuration |
243 | scripts run by a program at its start up, such F<.cshrc> or F<.ircrc>, | |
244 | for example. Chat scripts were just drivers for existing programs, | |
245 | not stand-alone programs in their own right. | |
246 | ||
247 | A computer scientist will correctly explain that all programs are | |
a6dd486b | 248 | interpreted and that the only question is at what level. But if you |
65acb1b1 TC |
249 | ask this question of someone who isn't a computer scientist, they might |
250 | tell you that a I<program> has been compiled to physical machine code | |
a6dd486b | 251 | once and can then be run multiple times, whereas a I<script> must be |
65acb1b1 TC |
252 | translated by a program each time it's used. |
253 | ||
254 | Perl programs are (usually) neither strictly compiled nor strictly | |
255 | interpreted. They can be compiled to a byte-code form (something of a | |
fc36a67e | 256 | Perl virtual machine) or to completely different languages, like C or |
65acb1b1 TC |
257 | assembly language. You can't tell just by looking at it whether the |
258 | source is destined for a pure interpreter, a parse-tree interpreter, | |
259 | a byte-code interpreter, or a native-code compiler, so it's hard to give | |
260 | a definitive answer here. | |
261 | ||
262 | Now that "script" and "scripting" are terms that have been seized by | |
263 | unscrupulous or unknowing marketeers for their own nefarious purposes, | |
264 | they have begun to take on strange and often pejorative meanings, | |
87275199 | 265 | like "non serious" or "not real programming". Consequently, some Perl |
65acb1b1 | 266 | programmers prefer to avoid them altogether. |
68dc0745 | 267 | |
268 | =head2 What is a JAPH? | |
269 | ||
270 | These are the "just another perl hacker" signatures that some people | |
65acb1b1 TC |
271 | sign their postings with. Randal Schwartz made these famous. About |
272 | 100 of the earlier ones are available from | |
a93751fa | 273 | http://www.cpan.org/misc/japh . |
68dc0745 | 274 | |
275 | =head2 Where can I get a list of Larry Wall witticisms? | |
276 | ||
277 | Over a hundred quips by Larry, from postings of his or source code, | |
a93751fa | 278 | can be found at http://www.cpan.org/misc/lwall-quotes.txt.gz . |
65acb1b1 | 279 | |
ae3d0b9f | 280 | =head2 How can I convince my sysadmin/supervisor/employees to use version 5/5.6.1/Perl instead of some other language? |
68dc0745 | 281 | |
282 | If your manager or employees are wary of unsupported software, or | |
87275199 | 283 | software which doesn't officially ship with your operating system, you |
68dc0745 | 284 | might try to appeal to their self-interest. If programmers can be |
285 | more productive using and utilizing Perl constructs, functionality, | |
286 | simplicity, and power, then the typical manager/supervisor/employee | |
287 | may be persuaded. Regarding using Perl in general, it's also | |
288 | sometimes helpful to point out that delivery times may be reduced | |
a6dd486b | 289 | using Perl compared to other languages. |
68dc0745 | 290 | |
291 | If you have a project which has a bottleneck, especially in terms of | |
5a964f20 | 292 | translation or testing, Perl almost certainly will provide a viable, |
a6dd486b | 293 | quick solution. In conjunction with any persuasion effort, you |
68dc0745 | 294 | should not fail to point out that Perl is used, quite extensively, and |
295 | with extremely reliable and valuable results, at many large computer | |
a6dd486b JB |
296 | software and hardware companies throughout the world. In fact, |
297 | many Unix vendors now ship Perl by default. Support is usually | |
68dc0745 | 298 | just a news-posting away, if you can't find the answer in the |
299 | I<comprehensive> documentation, including this FAQ. | |
300 | ||
65acb1b1 TC |
301 | See http://www.perl.org/advocacy/ for more information. |
302 | ||
68dc0745 | 303 | If you face reluctance to upgrading from an older version of perl, |
304 | then point out that version 4 is utterly unmaintained and unsupported | |
305 | by the Perl Development Team. Another big sell for Perl5 is the large | |
306 | number of modules and extensions which greatly reduce development time | |
307 | for any given task. Also mention that the difference between version | |
308 | 4 and version 5 of Perl is like the difference between awk and C++. | |
f4c2dd42 JA |
309 | (Well, OK, maybe it's not quite that distinct, but you get the idea.) |
310 | If you want support and a reasonable guarantee that what you're | |
311 | developing will continue to work in the future, then you have to run | |
793f5136 RGS |
312 | the supported version. As of December 2003 that means running either |
313 | 5.8.2 (released in November 2003), or one of the older releases like | |
314 | 5.6.2 (also released in November 2003; a maintenance release to let perl | |
315 | 5.6 compile on newer systems as 5.6.1 was released in April 2001) or | |
316 | 5.005_03 (released in March 1999), | |
36597cb9 JB |
317 | although 5.004_05 isn't that bad if you B<absolutely> need such an old |
318 | version (released in April 1999) for stability reasons. | |
319 | Anything older than 5.004_05 shouldn't be used. | |
5e3006a4 | 320 | |
87275199 | 321 | Of particular note is the massive bug hunt for buffer overflow |
5e3006a4 GS |
322 | problems that went into the 5.004 release. All releases prior to |
323 | that, including perl4, are considered insecure and should be upgraded | |
65acb1b1 | 324 | as soon as possible. |
68dc0745 | 325 | |
cb4d4ad7 | 326 | In August 2000 in all Linux distributions a new security problem was |
f4c2dd42 JA |
327 | found in the optional 'suidperl' (not built or installed by default) |
328 | in all the Perl branches 5.6, 5.005, and 5.004, see | |
329 | http://www.cpan.org/src/5.0/sperl-2000-08-05/ | |
03739d21 JH |
330 | Perl maintenance releases 5.6.1 and 5.8.0 have this security hole closed. |
331 | Most, if not all, Linux distribution have patches for this | |
332 | vulnerability available, see http://www.linuxsecurity.com/advisories/ , | |
333 | but the most recommendable way is to upgrade to at least Perl 5.6.1. | |
f4c2dd42 | 334 | |
68dc0745 | 335 | =head1 AUTHOR AND COPYRIGHT |
336 | ||
0bc0ad85 JH |
337 | Copyright (c) 1997, 1998, 1999, 2000, 2001 Tom Christiansen and Nathan |
338 | Torkington. All rights reserved. | |
5a964f20 | 339 | |
5a7beb56 JH |
340 | This documentation is free; you can redistribute it and/or modify it |
341 | under the same terms as Perl itself. | |
c8db1d39 | 342 | |
87275199 | 343 | Irrespective of its distribution, all code examples here are in the public |
c8db1d39 TC |
344 | domain. You are permitted and encouraged to use this code and any |
345 | derivatives thereof in your own programs for fun or for profit as you | |
346 | see fit. A simple comment in the code giving credit to the FAQ would | |
347 | be courteous but is not required. |