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68dc0745 | 1 | =head1 NAME |
2 | ||
109f0441 | 3 | perlfaq1 - General Questions About Perl |
68dc0745 | 4 | |
beb75a60 | 5 | =head1 DESCRIPTION |
68dc0745 | 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 | |
d12d61cf | 13 | written by Larry Wall and a cast of thousands. It derives from the |
68dc0745 | 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, | |
d12d61cf | 22 | and even managers also use Perl. Maybe you should, too. |
68dc0745 | 23 | |
d12d61cf | 24 | =head2 Who supports Perl? Who develops it? Why is it free? |
68dc0745 | 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 | |
d12d61cf | 28 | distribution policy of perl. Perl is supported by its users. The |
68dc0745 | 29 | core, the standard Perl library, the optional modules, and the |
d12d61cf | 30 | documentation you're reading now were all written by volunteers. See |
68dc0745 | 31 | the personal note at the end of the README file in the perl source |
d12d61cf | 32 | distribution for more details. See L<perlhist> (new as of 5.005) |
5e3006a4 | 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 | |
d12d61cf | 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 , |
ac9dac7f | 43 | or read the faq at http://dev.perl.org/perl5/docs/p5p-faq.html , |
006d0b46 | 44 | or you can subscribe to the mailing list by sending |
d12d61cf | 45 | perl5-porters-subscribe@perl.org a subscription request |
006d0b46 | 46 | (an empty message with no subject is fine). |
68dc0745 | 47 | |
48 | While the GNU project includes Perl in its distributions, there's no | |
d12d61cf | 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 | |
68dc0745 | 51 | than GNU software's tend to be. |
52 | ||
53 | You can get commercial support of Perl if you wish, although for most | |
d12d61cf | 54 | users the informal support will more than suffice. See the answer to |
68dc0745 | 55 | "Where can I buy a commercial version of perl?" for more information. |
56 | ||
57 | =head2 Which version of Perl should I use? | |
58 | ||
7678cced RGS |
59 | (contributed by brian d foy) |
60 | ||
500071f4 | 61 | There is often a matter of opinion and taste, and there isn't any one |
109f0441 | 62 | answer that fits everyone. In general, you want to use either the current |
ac9dac7f | 63 | stable release, or the stable release immediately prior to that one. |
733a5566 | 64 | Currently, those are perl5.14.x and perl5.12.x, respectively. |
7678cced | 65 | |
500071f4 RGS |
66 | Beyond that, you have to consider several things and decide which is best |
67 | for you. | |
7678cced RGS |
68 | |
69 | =over 4 | |
70 | ||
c234bec1 | 71 | =item * |
7678cced | 72 | |
500071f4 RGS |
73 | If things aren't broken, upgrading perl may break them (or at least issue |
74 | new warnings). | |
c234bec1 RGS |
75 | |
76 | =item * | |
7678cced RGS |
77 | |
78 | The latest versions of perl have more bug fixes. | |
79 | ||
c234bec1 | 80 | =item * |
7678cced | 81 | |
500071f4 RGS |
82 | The Perl community is geared toward supporting the most recent releases, |
83 | so you'll have an easier time finding help for those. | |
7678cced | 84 | |
c234bec1 RGS |
85 | =item * |
86 | ||
500071f4 RGS |
87 | Versions prior to perl5.004 had serious security problems with buffer |
88 | overflows, and in some cases have CERT advisories (for instance, | |
89 | http://www.cert.org/advisories/CA-1997-17.html ). | |
7678cced | 90 | |
c234bec1 | 91 | =item * |
7678cced | 92 | |
500071f4 RGS |
93 | The latest versions are probably the least deployed and widely tested, so |
94 | you may want to wait a few months after their release and see what | |
95 | problems others have if you are risk averse. | |
7678cced | 96 | |
c234bec1 | 97 | =item * |
7678cced | 98 | |
3cdbe49c | 99 | The immediate, previous releases (i.e. perl5.8.x ) are usually maintained |
500071f4 | 100 | for a while, although not at the same level as the current releases. |
7678cced | 101 | |
c234bec1 | 102 | =item * |
7678cced | 103 | |
beb75a60 | 104 | No one is actively supporting Perl 4. Ten years ago it was a dead |
d12d61cf | 105 | camel carcass (according to this document). Now it's barely a skeleton |
500071f4 | 106 | as its whitewashed bones have fractured or eroded. |
7678cced | 107 | |
c234bec1 | 108 | =item * |
7678cced | 109 | |
109f0441 | 110 | There is no Perl 6 release scheduled, but it will be available when |
beb75a60 | 111 | it's ready. The joke is that it's scheduled for Christmas, but that we |
112 | just don't know which one. Stay tuned, but don't worry that you'll | |
113 | have to change major versions of Perl; no one is going to take Perl 5 | |
114 | away from you. | |
7678cced | 115 | |
c234bec1 | 116 | =item * |
7678cced | 117 | |
500071f4 | 118 | There are really two tracks of perl development: a maintenance version |
d12d61cf | 119 | and an experimental version. The maintenance versions are stable, and |
3cdbe49c | 120 | have an even number as the minor release (i.e. perl5.10.x, where 10 is the |
d12d61cf | 121 | minor release). The experimental versions may include features that |
500071f4 RGS |
122 | don't make it into the stable versions, and have an odd number as the |
123 | minor release (i.e. perl5.9.x, where 9 is the minor release). | |
7678cced | 124 | |
c234bec1 | 125 | =back |
7678cced RGS |
126 | |
127 | ||
e9d185f8 | 128 | =head2 What are Perl 4, Perl 5, or Perl 6? |
7678cced RGS |
129 | |
130 | (contributed by brian d foy) | |
131 | ||
c195e131 | 132 | In short, Perl 4 is the past, Perl 5 is the present, and Perl 6 is the |
c234bec1 | 133 | future. |
7678cced | 134 | |
beb75a60 | 135 | The number after Perl (i.e. the 5 after Perl 5) is the major release |
d12d61cf | 136 | of the perl interpreter as well as the version of the language. Each |
7678cced RGS |
137 | major version has significant differences that earlier versions cannot |
138 | support. | |
139 | ||
beb75a60 | 140 | The current major release of Perl is Perl 5, and was first released in |
141 | 1994. It can run scripts from the previous major release, Perl 4 | |
142 | (March 1991), but has significant differences. It introduced the | |
143 | concept of references, complex data structures, and modules. The Perl | |
144 | 5 interpreter was a complete re-write of the previous perl sources. | |
145 | ||
146 | Perl 6 is the next major version of Perl, although it's not intended to | |
147 | replace Perl 5. It's still in development in both its syntax and | |
148 | design. The work started in 2002 and is still ongoing. Some of the | |
149 | most interesting features have shown up in the latest versions of Perl | |
150 | 5, and some Perl 5 modules allow you to use some Perl 6 syntax in your | |
151 | programs. The current leading implementation of Perl 6 is Rakudo ( | |
152 | http://rakudo.org ). | |
68dc0745 | 153 | |
5a964f20 TC |
154 | See L<perlhist> for a history of Perl revisions. |
155 | ||
322be77c | 156 | =head2 What was Ponie? |
d96a6f6b | 157 | |
500071f4 RGS |
158 | (contributed by brian d foy) |
159 | ||
160 | Ponie stands for "Perl On the New Internal Engine", started by Arthur | |
161 | Bergman from Fotango in 2003, and subsequently run as a project of The | |
322be77c | 162 | Perl Foundation. It was abandoned in 2006 |
c195e131 | 163 | ( http://www.nntp.perl.org/group/perl.ponie.dev/487 ). |
d96a6f6b | 164 | |
322be77c RGS |
165 | Instead of using the current Perl internals, Ponie aimed to create a |
166 | new one that would provide a translation path from Perl 5 to Perl 6 | |
167 | (or anything else that targets Parrot, actually). You would have been | |
d12d61cf | 168 | able to just keep using Perl 5 with Parrot, the virtual machine which |
322be77c | 169 | will compile and run Perl 6 bytecode. |
793f5136 | 170 | |
e9d185f8 | 171 | =head2 What is Perl 6? |
65acb1b1 | 172 | |
197aec24 | 173 | At The Second O'Reilly Open Source Software Convention, Larry Wall |
e9d185f8 | 174 | announced Perl 6 development would begin in earnest. Perl 6 was an oft |
4b29649f | 175 | used term for Chip Salzenberg's project to rewrite Perl in C++ named |
0bc0ad85 | 176 | Topaz. However, Topaz provided valuable insights to the next version |
197aec24 | 177 | of Perl and its implementation, but was ultimately abandoned. |
7e14cdc9 | 178 | |
e9d185f8 | 179 | If you want to learn more about Perl 6, or have a desire to help in |
04c2c53e | 180 | the crusade to make Perl a better place then read the Perl 6 developers |
0bc0ad85 | 181 | page at http://dev.perl.org/perl6/ and get involved. |
7e14cdc9 | 182 | |
e9d185f8 RGS |
183 | Perl 6 is not scheduled for release yet, and Perl 5 will still be supported |
184 | for quite awhile after its release. Do not wait for Perl 6 to do whatever | |
0bc0ad85 | 185 | you need to do. |
7e14cdc9 EHA |
186 | |
187 | "We're really serious about reinventing everything that needs reinventing." | |
188 | --Larry Wall | |
65acb1b1 | 189 | |
68dc0745 | 190 | =head2 How stable is Perl? |
191 | ||
192 | Production releases, which incorporate bug fixes and new functionality, | |
d12d61cf | 193 | are widely tested before release. Since the 5.000 release, we have |
68dc0745 | 194 | averaged only about one production release per year. |
195 | ||
196 | Larry and the Perl development team occasionally make changes to the | |
197 | internal core of the language, but all possible efforts are made toward | |
d12d61cf | 198 | backward compatibility. While not quite all Perl 4 scripts run flawlessly |
e9d185f8 | 199 | under Perl 5, an update to perl should nearly never invalidate a program |
68dc0745 | 200 | written for an earlier version of perl (barring accidental bug fixes |
201 | and the rare new keyword). | |
202 | ||
203 | =head2 Is Perl difficult to learn? | |
204 | ||
d12d61cf | 205 | No, Perl is easy to start learning--and easy to keep learning. It looks |
5a964f20 | 206 | like most programming languages you're likely to have experience |
87275199 | 207 | with, so if you've ever written a C program, an awk script, a shell |
a6dd486b | 208 | script, or even a BASIC program, you're already partway there. |
68dc0745 | 209 | |
d12d61cf | 210 | Most tasks only require a small subset of the Perl language. One of |
68dc0745 | 211 | the guiding mottos for Perl development is "there's more than one way |
d12d61cf | 212 | to do it" (TMTOWTDI, sometimes pronounced "tim toady"). Perl's |
68dc0745 | 213 | learning curve is therefore shallow (easy to learn) and long (there's |
214 | a whole lot you can do if you really want). | |
215 | ||
65acb1b1 TC |
216 | Finally, because Perl is frequently (but not always, and certainly not by |
217 | definition) an interpreted language, you can write your programs and test | |
218 | them without an intermediate compilation step, allowing you to experiment | |
d12d61cf | 219 | and test/debug quickly and easily. This ease of experimentation flattens |
65acb1b1 | 220 | the learning curve even more. |
68dc0745 | 221 | |
222 | Things that make Perl easier to learn: Unix experience, almost any kind | |
223 | of programming experience, an understanding of regular expressions, and | |
d12d61cf | 224 | the ability to understand other people's code. If there's something you |
68dc0745 | 225 | need to do, then it's probably already been done, and a working example is |
d12d61cf | 226 | usually available for free. Don't forget Perl modules, either. |
65acb1b1 | 227 | They're discussed in Part 3 of this FAQ, along with CPAN, which is |
68dc0745 | 228 | discussed in Part 2. |
229 | ||
230 | =head2 How does Perl compare with other languages like Java, Python, REXX, Scheme, or Tcl? | |
231 | ||
d12d61cf | 232 | Favorably in some areas, unfavorably in others. Precisely which areas |
68dc0745 | 233 | are good and bad is often a personal choice, so asking this question |
234 | on Usenet runs a strong risk of starting an unproductive Holy War. | |
235 | ||
236 | Probably the best thing to do is try to write equivalent code to do a | |
d12d61cf | 237 | set of tasks. These languages have their own newsgroups in which you |
68dc0745 | 238 | can learn about (but hopefully not argue about) them. |
239 | ||
c98c5709 | 240 | Some comparison documents can be found at http://www.perl.com/doc/FMTEYEWTK/versus/ |
65acb1b1 TC |
241 | if you really can't stop yourself. |
242 | ||
68dc0745 | 243 | =head2 Can I do [task] in Perl? |
244 | ||
65acb1b1 TC |
245 | Perl is flexible and extensible enough for you to use on virtually any |
246 | task, from one-line file-processing tasks to large, elaborate systems. | |
247 | For many people, Perl serves as a great replacement for shell scripting. | |
248 | For others, it serves as a convenient, high-level replacement for most of | |
d12d61cf | 249 | what they'd program in low-level languages like C or C++. It's ultimately |
65acb1b1 TC |
250 | up to you (and possibly your management) which tasks you'll use Perl |
251 | for and which you won't. | |
68dc0745 | 252 | |
253 | If you have a library that provides an API, you can make any component | |
254 | of it available as just another Perl function or variable using a Perl | |
255 | extension written in C or C++ and dynamically linked into your main | |
d12d61cf | 256 | perl interpreter. You can also go the other direction, and write your |
68dc0745 | 257 | main program in C or C++, and then link in some Perl code on the fly, |
d12d61cf | 258 | to create a powerful application. See L<perlembed>. |
68dc0745 | 259 | |
260 | That said, there will always be small, focused, special-purpose | |
261 | languages dedicated to a specific problem domain that are simply more | |
d12d61cf | 262 | convenient for certain kinds of problems. Perl tries to be all things |
263 | to all people, but nothing special to anyone. Examples of specialized | |
68dc0745 | 264 | languages that come to mind include prolog and matlab. |
265 | ||
266 | =head2 When shouldn't I program in Perl? | |
267 | ||
a6dd486b | 268 | When your manager forbids it--but do consider replacing them :-). |
68dc0745 | 269 | |
270 | Actually, one good reason is when you already have an existing | |
271 | application written in another language that's all done (and done | |
272 | well), or you have an application language specifically designed for a | |
273 | certain task (e.g. prolog, make). | |
274 | ||
275 | For various reasons, Perl is probably not well-suited for real-time | |
276 | embedded systems, low-level operating systems development work like | |
65acb1b1 | 277 | device drivers or context-switching code, complex multi-threaded |
d12d61cf | 278 | shared-memory applications, or extremely large applications. You'll |
68dc0745 | 279 | notice that perl is not itself written in Perl. |
280 | ||
ac9dac7f | 281 | Perl remains fundamentally a dynamically typed language, not |
d12d61cf | 282 | a statically typed one. You certainly won't be chastised if you don't |
283 | trust nuclear-plant or brain-surgery monitoring code to it. And Larry | |
a6dd486b | 284 | will sleep easier, too--Wall Street programs not withstanding. :-) |
68dc0745 | 285 | |
286 | =head2 What's the difference between "perl" and "Perl"? | |
287 | ||
d12d61cf | 288 | One bit. Oh, you weren't talking ASCII? :-) Larry now uses "Perl" to |
c195e131 | 289 | signify the language proper and "perl" the implementation of it, i.e. |
d12d61cf | 290 | the current interpreter. Hence Tom's quip that "Nothing but perl can |
109f0441 | 291 | parse Perl." |
c195e131 RGS |
292 | |
293 | Before the first edition of I<Programming perl>, people commonly | |
294 | referred to the language as "perl", and its name appeared that way in | |
295 | the title because it referred to the interpreter. In the book, Randal | |
296 | Schwartz capitalised the language's name to make it stand out better | |
297 | when typeset. This convention was adopted by the community, and the | |
298 | second edition became I<Programming Perl>, using the capitalized | |
299 | version of the name to refer to the language. | |
300 | ||
d12d61cf | 301 | You may or may not choose to follow this usage. For example, |
c195e131 | 302 | parallelism means "awk and perl" and "Python and Perl" look good, while |
d12d61cf | 303 | "awk and Perl" and "Python and perl" do not. But never write "PERL", |
c195e131 RGS |
304 | because perl is not an acronym, apocryphal folklore and post-facto |
305 | expansions notwithstanding. | |
68dc0745 | 306 | |
307 | =head2 Is it a Perl program or a Perl script? | |
308 | ||
d12d61cf | 309 | Larry doesn't really care. He says (half in jest) that "a script is |
310 | what you give the actors. A program is what you give the audience." | |
65acb1b1 TC |
311 | |
312 | Originally, a script was a canned sequence of normally interactive | |
d12d61cf | 313 | commands--that is, a chat script. Something like a UUCP or PPP chat |
65acb1b1 TC |
314 | script or an expect script fits the bill nicely, as do configuration |
315 | scripts run by a program at its start up, such F<.cshrc> or F<.ircrc>, | |
d12d61cf | 316 | for example. Chat scripts were just drivers for existing programs, |
65acb1b1 TC |
317 | not stand-alone programs in their own right. |
318 | ||
319 | A computer scientist will correctly explain that all programs are | |
d12d61cf | 320 | interpreted and that the only question is at what level. But if you |
65acb1b1 TC |
321 | ask this question of someone who isn't a computer scientist, they might |
322 | tell you that a I<program> has been compiled to physical machine code | |
a6dd486b | 323 | once and can then be run multiple times, whereas a I<script> must be |
65acb1b1 TC |
324 | translated by a program each time it's used. |
325 | ||
65acb1b1 TC |
326 | Now that "script" and "scripting" are terms that have been seized by |
327 | unscrupulous or unknowing marketeers for their own nefarious purposes, | |
328 | they have begun to take on strange and often pejorative meanings, | |
d12d61cf | 329 | like "non serious" or "not real programming". Consequently, some Perl |
65acb1b1 | 330 | programmers prefer to avoid them altogether. |
68dc0745 | 331 | |
332 | =head2 What is a JAPH? | |
333 | ||
500071f4 RGS |
334 | (contributed by brian d foy) |
335 | ||
336 | JAPH stands for "Just another Perl hacker,", which Randal Schwartz used | |
337 | to sign email and usenet messages starting in the late 1980s. He | |
338 | previously used the phrase with many subjects ("Just another x hacker,"), | |
339 | so to distinguish his JAPH, he started to write them as Perl programs: | |
340 | ||
109f0441 | 341 | print "Just another Perl hacker,"; |
500071f4 RGS |
342 | |
343 | Other people picked up on this and started to write clever or obfuscated | |
344 | programs to produce the same output, spinning things quickly out of | |
345 | control while still providing hours of amusement for their creators and | |
346 | readers. | |
347 | ||
348 | CPAN has several JAPH programs at http://www.cpan.org/misc/japh . | |
68dc0745 | 349 | |
350 | =head2 Where can I get a list of Larry Wall witticisms? | |
351 | ||
500071f4 RGS |
352 | (contributed by brian d foy) |
353 | ||
354 | Google "larry wall quotes"! You might even try the "I feel lucky" button. | |
355 | :) | |
356 | ||
357 | Wikiquote has the witticisms from Larry along with their source, | |
358 | including his usenet postings and source code comments. | |
359 | ||
360 | If you want a plain text file, try | |
361 | http://www.cpan.org/misc/lwall-quotes.txt.gz . | |
362 | ||
363 | =head2 How can I convince others to use Perl? | |
364 | ||
365 | (contributed by brian d foy) | |
366 | ||
367 | Appeal to their self interest! If Perl is new (and thus scary) to them, | |
368 | find something that Perl can do to solve one of their problems. That | |
369 | might mean that Perl either saves them something (time, headaches, money) | |
370 | or gives them something (flexibility, power, testability). | |
371 | ||
372 | In general, the benefit of a language is closely related to the skill of | |
fd74a741 | 373 | the people using that language. If you or your team can be faster, |
500071f4 RGS |
374 | better, and stronger through Perl, you'll deliver more value. Remember, |
375 | people often respond better to what they get out of it. If you run | |
ac9dac7f | 376 | into resistance, figure out what those people get out of the other |
500071f4 RGS |
377 | choice and how Perl might satisfy that requirement. |
378 | ||
379 | You don't have to worry about finding or paying for Perl; it's freely | |
380 | available and several popular operating systems come with Perl. Community | |
381 | support in places such as Perlmonks ( http://www.perlmonks.com ) | |
382 | and the various Perl mailing lists ( http://lists.perl.org ) means that | |
383 | you can usually get quick answers to your problems. | |
384 | ||
385 | Finally, keep in mind that Perl might not be the right tool for every | |
386 | job. You're a much better advocate if your claims are reasonable and | |
387 | grounded in reality. Dogmatically advocating anything tends to make | |
388 | people discount your message. Be honest about possible disadvantages | |
389 | to your choice of Perl since any choice has trade-offs. | |
390 | ||
391 | You might find these links useful: | |
392 | ||
393 | =over 4 | |
394 | ||
395 | =item * http://perltraining.com.au/whyperl.html | |
396 | ||
397 | =item * http://www.perl.org/advocacy/whyperl.html | |
398 | ||
399 | =back | |
400 | ||
68dc0745 | 401 | =head1 AUTHOR AND COPYRIGHT |
402 | ||
8d2e243f | 403 | Copyright (c) 1997-2010 Tom Christiansen, Nathan Torkington, and |
7678cced | 404 | other authors as noted. All rights reserved. |
5a964f20 | 405 | |
5a7beb56 JH |
406 | This documentation is free; you can redistribute it and/or modify it |
407 | under the same terms as Perl itself. | |
c8db1d39 | 408 | |
87275199 | 409 | Irrespective of its distribution, all code examples here are in the public |
d12d61cf | 410 | domain. You are permitted and encouraged to use this code and any |
c8db1d39 | 411 | derivatives thereof in your own programs for fun or for profit as you |
d12d61cf | 412 | see fit. A simple comment in the code giving credit to the FAQ would |
c8db1d39 | 413 | be courteous but is not required. |