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68dc0745 | 1 | =head1 NAME |
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d92eb7b0 | 3 | perlfaq1 - General Questions About Perl ($Revision: 1.23 $, $Date: 1999/05/23 16:08:30 $) |
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 | |
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32 | distribution for more details. See L<perlhist> (new as of 5.005) |
33 | for Perl's milestone releases. | |
68dc0745 | 34 | |
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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 | |
6cecdcac | 39 | news://news.perl.com/perl.porters-gw/ and the Deja archive at |
87275199 | 40 | http://www.deja.com/ using the perl.porters-gw newsgroup, or you can |
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41 | subscribe to the mailing list by sending perl5-porters-request@perl.org |
42 | a subscription request. | |
68dc0745 | 43 | |
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. | |
48 | ||
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. | |
52 | ||
53 | =head2 Which version of Perl should I use? | |
54 | ||
55 | You should definitely use version 5. Version 4 is old, limited, and | |
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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 | |
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59 | production release is 5.005_03 (although 5.004_05 is still supported). |
60 | The most cutting-edge development release is 5.005_57. Further references | |
65acb1b1 | 61 | to the Perl language in this document refer to the production release |
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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. | |
68dc0745 | 66 | |
67 | =head2 What are perl4 and perl5? | |
68 | ||
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). | |
76 | ||
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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. See L<perltrap/"Perl4 | |
82 | to Perl5 Traps">. | |
68dc0745 | 83 | |
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. | |
87 | ||
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88 | See L<perlhist> for a history of Perl revisions. |
89 | ||
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90 | =head2 What is perl6? |
91 | ||
92 | Perl6 is a semi-jocular reference to the Topaz project. Headed by Chip | |
93 | Salzenberg, Topaz is yet-another ground-up rewrite of the current release | |
94 | of Perl, one whose major goal is to create a more maintainable core than | |
95 | found in release 5. Written in nominally portable C++, Topaz hopes to | |
96 | maintain 100% source-compatibility with previous releases of Perl but to | |
97 | run significantly faster and smaller. The Topaz team hopes to provide | |
98 | an XS compatibility interface to allow most XS modules to work unchanged, | |
d92eb7b0 | 99 | albeit perhaps without the efficiency that the new interface would allow. |
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100 | New features in Topaz are as yet undetermined, and will be addressed |
101 | once compatibility and performance goals are met. | |
102 | ||
103 | If you are a hard-working C++ wizard with a firm command of Perl's | |
104 | internals, and you would like to work on the project, send a request to | |
105 | perl6-porters-request@perl.org to subscribe to the Topaz mailing list. | |
106 | ||
107 | There is no ETA for Topaz. It is expected to be several years before it | |
108 | achieves enough robustness, compatibility, portability, and performance | |
109 | to replace perl5 for ordinary use by mere mortals. | |
110 | ||
68dc0745 | 111 | =head2 How stable is Perl? |
112 | ||
113 | Production releases, which incorporate bug fixes and new functionality, | |
114 | are widely tested before release. Since the 5.000 release, we have | |
115 | averaged only about one production release per year. | |
116 | ||
117 | Larry and the Perl development team occasionally make changes to the | |
118 | internal core of the language, but all possible efforts are made toward | |
119 | backward compatibility. While not quite all perl4 scripts run flawlessly | |
120 | under perl5, an update to perl should nearly never invalidate a program | |
121 | written for an earlier version of perl (barring accidental bug fixes | |
122 | and the rare new keyword). | |
123 | ||
124 | =head2 Is Perl difficult to learn? | |
125 | ||
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126 | No, Perl is easy to start learning -- and easy to keep learning. It looks |
127 | like most programming languages you're likely to have experience | |
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128 | with, so if you've ever written a C program, an awk script, a shell |
129 | script, or even a BASIC program, you're already part way there. | |
68dc0745 | 130 | |
131 | Most tasks only require a small subset of the Perl language. One of | |
132 | the guiding mottos for Perl development is "there's more than one way | |
133 | to do it" (TMTOWTDI, sometimes pronounced "tim toady"). Perl's | |
134 | learning curve is therefore shallow (easy to learn) and long (there's | |
135 | a whole lot you can do if you really want). | |
136 | ||
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137 | Finally, because Perl is frequently (but not always, and certainly not by |
138 | definition) an interpreted language, you can write your programs and test | |
139 | them without an intermediate compilation step, allowing you to experiment | |
140 | and test/debug quickly and easily. This ease of experimentation flattens | |
141 | the learning curve even more. | |
68dc0745 | 142 | |
143 | Things that make Perl easier to learn: Unix experience, almost any kind | |
144 | of programming experience, an understanding of regular expressions, and | |
145 | the ability to understand other people's code. If there's something you | |
146 | need to do, then it's probably already been done, and a working example is | |
147 | usually available for free. Don't forget the new perl modules, either. | |
65acb1b1 | 148 | They're discussed in Part 3 of this FAQ, along with CPAN, which is |
68dc0745 | 149 | discussed in Part 2. |
150 | ||
151 | =head2 How does Perl compare with other languages like Java, Python, REXX, Scheme, or Tcl? | |
152 | ||
153 | Favorably in some areas, unfavorably in others. Precisely which areas | |
154 | are good and bad is often a personal choice, so asking this question | |
155 | on Usenet runs a strong risk of starting an unproductive Holy War. | |
156 | ||
157 | Probably the best thing to do is try to write equivalent code to do a | |
158 | set of tasks. These languages have their own newsgroups in which you | |
159 | can learn about (but hopefully not argue about) them. | |
160 | ||
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161 | Some comparison documents can be found at http://language.perl.com/versus/ |
162 | if you really can't stop yourself. | |
163 | ||
68dc0745 | 164 | =head2 Can I do [task] in Perl? |
165 | ||
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166 | Perl is flexible and extensible enough for you to use on virtually any |
167 | task, from one-line file-processing tasks to large, elaborate systems. | |
168 | For many people, Perl serves as a great replacement for shell scripting. | |
169 | For others, it serves as a convenient, high-level replacement for most of | |
170 | what they'd program in low-level languages like C or C++. It's ultimately | |
171 | up to you (and possibly your management) which tasks you'll use Perl | |
172 | for and which you won't. | |
68dc0745 | 173 | |
174 | If you have a library that provides an API, you can make any component | |
175 | of it available as just another Perl function or variable using a Perl | |
176 | extension written in C or C++ and dynamically linked into your main | |
177 | perl interpreter. You can also go the other direction, and write your | |
178 | main program in C or C++, and then link in some Perl code on the fly, | |
65acb1b1 | 179 | to create a powerful application. See L<perlembed>. |
68dc0745 | 180 | |
181 | That said, there will always be small, focused, special-purpose | |
182 | languages dedicated to a specific problem domain that are simply more | |
183 | convenient for certain kinds of problems. Perl tries to be all things | |
184 | to all people, but nothing special to anyone. Examples of specialized | |
185 | languages that come to mind include prolog and matlab. | |
186 | ||
187 | =head2 When shouldn't I program in Perl? | |
188 | ||
189 | When your manager forbids it -- but do consider replacing them :-). | |
190 | ||
191 | Actually, one good reason is when you already have an existing | |
192 | application written in another language that's all done (and done | |
193 | well), or you have an application language specifically designed for a | |
194 | certain task (e.g. prolog, make). | |
195 | ||
196 | For various reasons, Perl is probably not well-suited for real-time | |
197 | embedded systems, low-level operating systems development work like | |
65acb1b1 | 198 | device drivers or context-switching code, complex multi-threaded |
68dc0745 | 199 | shared-memory applications, or extremely large applications. You'll |
200 | notice that perl is not itself written in Perl. | |
201 | ||
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202 | The new, native-code compiler for Perl may eventually reduce the |
203 | limitations given in the previous statement to some degree, but understand | |
204 | that Perl remains fundamentally a dynamically typed language, not | |
205 | a statically typed one. You certainly won't be chastised if you don't | |
206 | trust nuclear-plant or brain-surgery monitoring code to it. And Larry | |
207 | will sleep easier, too -- Wall Street programs not withstanding. :-) | |
68dc0745 | 208 | |
209 | =head2 What's the difference between "perl" and "Perl"? | |
210 | ||
211 | One bit. Oh, you weren't talking ASCII? :-) Larry now uses "Perl" to | |
212 | signify the language proper and "perl" the implementation of it, | |
213 | i.e. the current interpreter. Hence Tom's quip that "Nothing but perl | |
214 | can parse Perl." You may or may not choose to follow this usage. For | |
215 | example, parallelism means "awk and perl" and "Python and Perl" look | |
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216 | OK, while "awk and Perl" and "Python and perl" do not. But never |
217 | write "PERL", because perl isn't really an acronym, apocryphal | |
65acb1b1 | 218 | folklore and post-facto expansions notwithstanding. |
68dc0745 | 219 | |
220 | =head2 Is it a Perl program or a Perl script? | |
221 | ||
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222 | Larry doesn't really care. He says (half in jest) that "a script is |
223 | what you give the actors. A program is what you give the audience." | |
224 | ||
225 | Originally, a script was a canned sequence of normally interactive | |
87275199 | 226 | commands, that is, a chat script. Something like a UUCP or PPP chat |
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227 | script or an expect script fits the bill nicely, as do configuration |
228 | scripts run by a program at its start up, such F<.cshrc> or F<.ircrc>, | |
229 | for example. Chat scripts were just drivers for existing programs, | |
230 | not stand-alone programs in their own right. | |
231 | ||
232 | A computer scientist will correctly explain that all programs are | |
233 | interpreted, and that the only question is at what level. But if you | |
234 | ask this question of someone who isn't a computer scientist, they might | |
235 | tell you that a I<program> has been compiled to physical machine code | |
236 | once, and can then be run multiple times, whereas a I<script> must be | |
237 | translated by a program each time it's used. | |
238 | ||
239 | Perl programs are (usually) neither strictly compiled nor strictly | |
240 | interpreted. They can be compiled to a byte-code form (something of a | |
fc36a67e | 241 | Perl virtual machine) or to completely different languages, like C or |
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242 | assembly language. You can't tell just by looking at it whether the |
243 | source is destined for a pure interpreter, a parse-tree interpreter, | |
244 | a byte-code interpreter, or a native-code compiler, so it's hard to give | |
245 | a definitive answer here. | |
246 | ||
247 | Now that "script" and "scripting" are terms that have been seized by | |
248 | unscrupulous or unknowing marketeers for their own nefarious purposes, | |
249 | they have begun to take on strange and often pejorative meanings, | |
87275199 | 250 | like "non serious" or "not real programming". Consequently, some Perl |
65acb1b1 | 251 | programmers prefer to avoid them altogether. |
68dc0745 | 252 | |
253 | =head2 What is a JAPH? | |
254 | ||
255 | These are the "just another perl hacker" signatures that some people | |
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256 | sign their postings with. Randal Schwartz made these famous. About |
257 | 100 of the earlier ones are available from | |
258 | http://www.perl.com/CPAN/misc/japh . | |
68dc0745 | 259 | |
260 | =head2 Where can I get a list of Larry Wall witticisms? | |
261 | ||
262 | Over a hundred quips by Larry, from postings of his or source code, | |
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263 | can be found at http://www.perl.com/CPAN/misc/lwall-quotes.txt.gz . |
264 | ||
265 | Newer 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 | |
271 | If your manager or employees are wary of unsupported software, or | |
87275199 | 272 | software which doesn't officially ship with your operating system, you |
68dc0745 | 273 | might try to appeal to their self-interest. If programmers can be |
274 | more productive using and utilizing Perl constructs, functionality, | |
275 | simplicity, and power, then the typical manager/supervisor/employee | |
276 | may be persuaded. Regarding using Perl in general, it's also | |
277 | sometimes helpful to point out that delivery times may be reduced | |
278 | using Perl, as compared to other languages. | |
279 | ||
280 | If you have a project which has a bottleneck, especially in terms of | |
5a964f20 | 281 | translation or testing, Perl almost certainly will provide a viable, |
68dc0745 | 282 | and quick solution. In conjunction with any persuasion effort, you |
283 | should not fail to point out that Perl is used, quite extensively, and | |
284 | with extremely reliable and valuable results, at many large computer | |
285 | software and/or hardware companies throughout the world. In fact, | |
286 | many Unix vendors now ship Perl by default, and support is usually | |
287 | just a news-posting away, if you can't find the answer in the | |
288 | I<comprehensive> documentation, including this FAQ. | |
289 | ||
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290 | See http://www.perl.org/advocacy/ for more information. |
291 | ||
68dc0745 | 292 | If you face reluctance to upgrading from an older version of perl, |
293 | then point out that version 4 is utterly unmaintained and unsupported | |
294 | by the Perl Development Team. Another big sell for Perl5 is the large | |
295 | number of modules and extensions which greatly reduce development time | |
296 | for any given task. Also mention that the difference between version | |
297 | 4 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 |
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299 | want support and a reasonable guarantee that what you're developing |
300 | will continue to work in the future, then you have to run the supported | |
301 | version. That probably means running the 5.005 release, although 5.004 | |
302 | isn't that bad. Several important bugs were fixed from the 5.000 through | |
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303 | 5.003 versions, though, so try upgrading past them if possible. |
304 | ||
87275199 | 305 | Of particular note is the massive bug hunt for buffer overflow |
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306 | problems that went into the 5.004 release. All releases prior to |
307 | that, including perl4, are considered insecure and should be upgraded | |
65acb1b1 | 308 | as soon as possible. |
68dc0745 | 309 | |
310 | =head1 AUTHOR AND COPYRIGHT | |
311 | ||
87275199 | 312 | Copyright (c) 1997, 1998, 1999 Tom Christiansen and Nathan Torkington. |
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313 | All rights reserved. |
314 | ||
c8db1d39 | 315 | When included as an integrated part of the Standard Distribution |
d92eb7b0 | 316 | of Perl or of its documentation (printed or otherwise), this works is |
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317 | covered under Perl's Artistic Licence. For separate distributions of |
318 | all or part of this FAQ outside of that, see L<perlfaq>. | |
319 | ||
87275199 | 320 | Irrespective of its distribution, all code examples here are in the public |
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321 | domain. You are permitted and encouraged to use this code and any |
322 | derivatives thereof in your own programs for fun or for profit as you | |
323 | see fit. A simple comment in the code giving credit to the FAQ would | |
324 | be courteous but is not required. |