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1 | =head1 NAME |
2 | |
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3 | perlfaq1 - General Questions About Perl ($Revision: 1.19 $, $Date: 2005/12/31 00:54:37 $) |
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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. |
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34 | |
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35 | In particular, the core development team (known as the Perl Porters) |
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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 |
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38 | money. You may snoop on pending developments via the archives at |
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39 | http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/ |
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40 | and http://archive.develooper.com/perl5-porters@perl.org/ |
cf682770 |
41 | or the news gateway nntp://nntp.perl.org/perl.perl5.porters or |
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42 | its web interface at http://nntp.perl.org/group/perl.perl5.porters , |
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43 | or read the faq at http://simon-cozens.org/writings/p5p-faq , |
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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). |
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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 | |
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59 | (contributed by brian d foy) |
60 | |
61 | There is often a matter of opinion and taste, and there isn't any |
62 | one answer that fits anyone. In general, you want to use either |
63 | the current stable release, or the stable release immediately prior |
64 | to that one. Currently, those are perl5.8.x and perl5.6.x, respectively. |
65 | |
66 | Beyond that, you have to consider several things and decide which |
67 | is best for you. |
68 | |
69 | =over 4 |
70 | |
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71 | =item * |
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72 | |
73 | If things aren't broken, upgrading perl may break |
74 | them (or at least issue new warnings). |
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75 | |
76 | =item * |
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77 | |
78 | The latest versions of perl have more bug fixes. |
79 | |
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80 | =item * |
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81 | |
82 | The Perl community is geared toward supporting the most |
83 | recent releases, so you'll have an easier time finding help for |
84 | those. |
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85 | |
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86 | =item * |
87 | |
88 | Versions prior to perl5.004 had serious security problems with |
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89 | buffer overflows, and in some cases have CERT advisories (for |
90 | instance, http://www.cert.org/advisories/CA-1997-17.html ). |
91 | |
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92 | =item * |
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93 | |
94 | The latest versions are probably the least deployed and |
95 | widely tested, so you may want to wait a few months after their |
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96 | release and see what problems others have if you are risk averse. |
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97 | |
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98 | =item * |
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99 | |
100 | The immediate, previous releases (i.e. perl5.6.x ) are usually |
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101 | maintained for a while, although not at the same level as the |
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102 | current releases. |
103 | |
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104 | =item * |
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105 | |
106 | No one is actively supporting perl4.x. Five years ago it was |
107 | a dead camel carcass (according to this document). Now it's barely |
108 | a skeleton as its whitewashed bones have fractured or eroded. |
109 | |
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110 | =item * |
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111 | |
112 | There is no perl6.x for the next couple of years. Stay tuned, |
113 | but don't worry that you'll have to change major versions of Perl |
114 | soon (i.e. before 2006). |
115 | |
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116 | =item * |
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117 | |
118 | There are really two tracks of perl development: a |
119 | maintenance version and an experimental version. The |
120 | maintenance versions are stable, and have an even number |
121 | as the minor release (i.e. perl5.8.x, where 8 is the minor |
122 | release). The experimental versions may include features that |
123 | don't make it into the stable versions, and have an odd number |
124 | as the minor release (i.e. perl5.9.x, where 9 is the minor release). |
125 | |
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126 | =back |
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127 | |
128 | |
129 | =head2 What are perl4, perl5, or perl6? |
130 | |
131 | (contributed by brian d foy) |
132 | |
133 | In short, perl4 is the past, perl5 is the present, and perl6 is the |
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134 | future. |
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135 | |
136 | The number after perl (i.e. the 5 after perl5) is the major release |
137 | of the perl interpreter as well as the version of the language. Each |
138 | major version has significant differences that earlier versions cannot |
139 | support. |
140 | |
141 | The current major release of Perl is perl5, and was released in 1994. |
142 | It can run scripts from the previous major release, perl4 (March 1991), |
143 | but has significant differences. It introduced the concept of references, |
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144 | complex data structures, and modules. The perl5 interpreter was a |
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145 | complete re-write of the previous perl sources. |
146 | |
147 | Perl6 is the next major version of Perl, but it's still in development |
148 | in both its syntax and design. The work started in 2002 and is still |
149 | ongoing. Many of the most interesting features have shown up in the |
150 | latest versions of perl5, and some perl5 modules allow you to use some |
151 | perl6 syntax in your programs. You can learn more about perl6 at |
152 | http://dev.perl.org/perl6/ . |
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153 | |
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154 | See L<perlhist> for a history of Perl revisions. |
155 | |
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156 | =head2 What is Ponie? |
157 | |
158 | At The O'Reilly Open Source Software Convention in 2003, Artur |
159 | Bergman, Fotango, and The Perl Foundation announced a project to |
160 | run perl5 on the Parrot virtual machine named Ponie. Ponie stands for |
161 | Perl On New Internal Engine. The Perl 5.10 language implementation |
162 | will be used for Ponie, and there will be no language level |
163 | differences between perl5 and ponie. Ponie is not a complete rewrite |
164 | of perl5. |
165 | |
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166 | For more details, see http://www.poniecode.org/ |
167 | |
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168 | =head2 What is perl6? |
169 | |
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170 | At The Second O'Reilly Open Source Software Convention, Larry Wall |
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171 | announced Perl6 development would begin in earnest. Perl6 was an oft |
172 | used term for Chip Salzenberg's project to rewrite Perl in C++ named |
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173 | Topaz. However, Topaz provided valuable insights to the next version |
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174 | of Perl and its implementation, but was ultimately abandoned. |
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175 | |
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176 | If you want to learn more about Perl6, or have a desire to help in |
177 | the crusade to make Perl a better place then peruse the Perl6 developers |
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178 | page at http://dev.perl.org/perl6/ and get involved. |
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179 | |
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180 | Perl6 is not scheduled for release yet, and Perl5 will still be supported |
181 | for quite awhile after its release. Do not wait for Perl6 to do whatever |
182 | you need to do. |
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183 | |
184 | "We're really serious about reinventing everything that needs reinventing." |
185 | --Larry Wall |
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186 | |
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187 | =head2 How stable is Perl? |
188 | |
189 | Production releases, which incorporate bug fixes and new functionality, |
190 | are widely tested before release. Since the 5.000 release, we have |
191 | averaged only about one production release per year. |
192 | |
193 | Larry and the Perl development team occasionally make changes to the |
194 | internal core of the language, but all possible efforts are made toward |
195 | backward compatibility. While not quite all perl4 scripts run flawlessly |
196 | under perl5, an update to perl should nearly never invalidate a program |
197 | written for an earlier version of perl (barring accidental bug fixes |
198 | and the rare new keyword). |
199 | |
200 | =head2 Is Perl difficult to learn? |
201 | |
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202 | No, Perl is easy to start learning--and easy to keep learning. It looks |
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203 | like most programming languages you're likely to have experience |
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204 | with, so if you've ever written a C program, an awk script, a shell |
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205 | script, or even a BASIC program, you're already partway there. |
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206 | |
207 | Most tasks only require a small subset of the Perl language. One of |
208 | the guiding mottos for Perl development is "there's more than one way |
209 | to do it" (TMTOWTDI, sometimes pronounced "tim toady"). Perl's |
210 | learning curve is therefore shallow (easy to learn) and long (there's |
211 | a whole lot you can do if you really want). |
212 | |
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213 | Finally, because Perl is frequently (but not always, and certainly not by |
214 | definition) an interpreted language, you can write your programs and test |
215 | them without an intermediate compilation step, allowing you to experiment |
216 | and test/debug quickly and easily. This ease of experimentation flattens |
217 | the learning curve even more. |
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218 | |
219 | Things that make Perl easier to learn: Unix experience, almost any kind |
220 | of programming experience, an understanding of regular expressions, and |
221 | the ability to understand other people's code. If there's something you |
222 | need to do, then it's probably already been done, and a working example is |
223 | usually available for free. Don't forget the new perl modules, either. |
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224 | They're discussed in Part 3 of this FAQ, along with CPAN, which is |
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225 | discussed in Part 2. |
226 | |
227 | =head2 How does Perl compare with other languages like Java, Python, REXX, Scheme, or Tcl? |
228 | |
229 | Favorably in some areas, unfavorably in others. Precisely which areas |
230 | are good and bad is often a personal choice, so asking this question |
231 | on Usenet runs a strong risk of starting an unproductive Holy War. |
232 | |
233 | Probably the best thing to do is try to write equivalent code to do a |
234 | set of tasks. These languages have their own newsgroups in which you |
235 | can learn about (but hopefully not argue about) them. |
236 | |
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237 | Some comparison documents can be found at http://www.perl.com/doc/FMTEYEWTK/versus/ |
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238 | if you really can't stop yourself. |
239 | |
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240 | =head2 Can I do [task] in Perl? |
241 | |
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242 | Perl is flexible and extensible enough for you to use on virtually any |
243 | task, from one-line file-processing tasks to large, elaborate systems. |
244 | For many people, Perl serves as a great replacement for shell scripting. |
245 | For others, it serves as a convenient, high-level replacement for most of |
246 | what they'd program in low-level languages like C or C++. It's ultimately |
247 | up to you (and possibly your management) which tasks you'll use Perl |
248 | for and which you won't. |
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249 | |
250 | If you have a library that provides an API, you can make any component |
251 | of it available as just another Perl function or variable using a Perl |
252 | extension written in C or C++ and dynamically linked into your main |
253 | perl interpreter. You can also go the other direction, and write your |
254 | main program in C or C++, and then link in some Perl code on the fly, |
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255 | to create a powerful application. See L<perlembed>. |
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256 | |
257 | That said, there will always be small, focused, special-purpose |
258 | languages dedicated to a specific problem domain that are simply more |
259 | convenient for certain kinds of problems. Perl tries to be all things |
260 | to all people, but nothing special to anyone. Examples of specialized |
261 | languages that come to mind include prolog and matlab. |
262 | |
263 | =head2 When shouldn't I program in Perl? |
264 | |
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265 | When your manager forbids it--but do consider replacing them :-). |
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266 | |
267 | Actually, one good reason is when you already have an existing |
268 | application written in another language that's all done (and done |
269 | well), or you have an application language specifically designed for a |
270 | certain task (e.g. prolog, make). |
271 | |
272 | For various reasons, Perl is probably not well-suited for real-time |
273 | embedded systems, low-level operating systems development work like |
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274 | device drivers or context-switching code, complex multi-threaded |
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275 | shared-memory applications, or extremely large applications. You'll |
276 | notice that perl is not itself written in Perl. |
277 | |
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278 | The new, native-code compiler for Perl may eventually reduce the |
279 | limitations given in the previous statement to some degree, but understand |
280 | that Perl remains fundamentally a dynamically typed language, not |
281 | a statically typed one. You certainly won't be chastised if you don't |
282 | trust nuclear-plant or brain-surgery monitoring code to it. And Larry |
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283 | will sleep easier, too--Wall Street programs not withstanding. :-) |
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284 | |
285 | =head2 What's the difference between "perl" and "Perl"? |
286 | |
287 | One bit. Oh, you weren't talking ASCII? :-) Larry now uses "Perl" to |
288 | signify the language proper and "perl" the implementation of it, |
289 | i.e. the current interpreter. Hence Tom's quip that "Nothing but perl |
290 | can parse Perl." You may or may not choose to follow this usage. For |
291 | example, parallelism means "awk and perl" and "Python and Perl" look |
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292 | OK, while "awk and Perl" and "Python and perl" do not. But never |
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293 | write "PERL", because perl is not an acronym, apocryphal |
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294 | folklore and post-facto expansions notwithstanding. |
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295 | |
296 | =head2 Is it a Perl program or a Perl script? |
297 | |
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298 | Larry doesn't really care. He says (half in jest) that "a script is |
299 | what you give the actors. A program is what you give the audience." |
300 | |
301 | Originally, a script was a canned sequence of normally interactive |
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302 | commands--that is, a chat script. Something like a UUCP or PPP chat |
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303 | script or an expect script fits the bill nicely, as do configuration |
304 | scripts run by a program at its start up, such F<.cshrc> or F<.ircrc>, |
305 | for example. Chat scripts were just drivers for existing programs, |
306 | not stand-alone programs in their own right. |
307 | |
308 | A computer scientist will correctly explain that all programs are |
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309 | interpreted and that the only question is at what level. But if you |
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310 | ask this question of someone who isn't a computer scientist, they might |
311 | tell you that a I<program> has been compiled to physical machine code |
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312 | once and can then be run multiple times, whereas a I<script> must be |
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313 | translated by a program each time it's used. |
314 | |
315 | Perl programs are (usually) neither strictly compiled nor strictly |
316 | interpreted. They can be compiled to a byte-code form (something of a |
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317 | Perl virtual machine) or to completely different languages, like C or |
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318 | assembly language. You can't tell just by looking at it whether the |
319 | source is destined for a pure interpreter, a parse-tree interpreter, |
320 | a byte-code interpreter, or a native-code compiler, so it's hard to give |
321 | a definitive answer here. |
322 | |
323 | Now that "script" and "scripting" are terms that have been seized by |
324 | unscrupulous or unknowing marketeers for their own nefarious purposes, |
325 | they have begun to take on strange and often pejorative meanings, |
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326 | like "non serious" or "not real programming". Consequently, some Perl |
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327 | programmers prefer to avoid them altogether. |
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328 | |
329 | =head2 What is a JAPH? |
330 | |
331 | These are the "just another perl hacker" signatures that some people |
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332 | sign their postings with. Randal Schwartz made these famous. About |
333 | 100 of the earlier ones are available from |
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334 | http://www.cpan.org/misc/japh . |
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335 | |
336 | =head2 Where can I get a list of Larry Wall witticisms? |
337 | |
338 | Over a hundred quips by Larry, from postings of his or source code, |
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339 | can be found at http://www.cpan.org/misc/lwall-quotes.txt.gz . |
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340 | |
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341 | =head2 How can I convince my sysadmin/supervisor/employees to use version 5/5.6.1/Perl instead of some other language? |
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342 | |
343 | If your manager or employees are wary of unsupported software, or |
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344 | software which doesn't officially ship with your operating system, you |
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345 | might try to appeal to their self-interest. If programmers can be |
346 | more productive using and utilizing Perl constructs, functionality, |
347 | simplicity, and power, then the typical manager/supervisor/employee |
348 | may be persuaded. Regarding using Perl in general, it's also |
349 | sometimes helpful to point out that delivery times may be reduced |
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350 | using Perl compared to other languages. |
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351 | |
352 | If you have a project which has a bottleneck, especially in terms of |
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353 | translation or testing, Perl almost certainly will provide a viable, |
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354 | quick solution. In conjunction with any persuasion effort, you |
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355 | should not fail to point out that Perl is used, quite extensively, and |
356 | with extremely reliable and valuable results, at many large computer |
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357 | software and hardware companies throughout the world. In fact, |
358 | many Unix vendors now ship Perl by default. Support is usually |
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359 | just a news-posting away, if you can't find the answer in the |
360 | I<comprehensive> documentation, including this FAQ. |
361 | |
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362 | See http://www.perl.org/advocacy/ for more information. |
363 | |
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364 | If you face reluctance to upgrading from an older version of perl, |
365 | then point out that version 4 is utterly unmaintained and unsupported |
366 | by the Perl Development Team. Another big sell for Perl5 is the large |
367 | number of modules and extensions which greatly reduce development time |
368 | for any given task. Also mention that the difference between version |
369 | 4 and version 5 of Perl is like the difference between awk and C++. |
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370 | (Well, OK, maybe it's not quite that distinct, but you get the idea.) |
371 | If you want support and a reasonable guarantee that what you're |
372 | developing will continue to work in the future, then you have to run |
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373 | the supported version. As of December 2003 that means running either |
374 | 5.8.2 (released in November 2003), or one of the older releases like |
375 | 5.6.2 (also released in November 2003; a maintenance release to let perl |
376 | 5.6 compile on newer systems as 5.6.1 was released in April 2001) or |
377 | 5.005_03 (released in March 1999), |
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378 | although 5.004_05 isn't that bad if you B<absolutely> need such an old |
379 | version (released in April 1999) for stability reasons. |
380 | Anything older than 5.004_05 shouldn't be used. |
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381 | |
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382 | Of particular note is the massive bug hunt for buffer overflow |
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383 | problems that went into the 5.004 release. All releases prior to |
384 | that, including perl4, are considered insecure and should be upgraded |
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385 | as soon as possible. |
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386 | |
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387 | In August 2000 in all Linux distributions a new security problem was |
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388 | found in the optional 'suidperl' (not built or installed by default) |
389 | in all the Perl branches 5.6, 5.005, and 5.004, see |
390 | http://www.cpan.org/src/5.0/sperl-2000-08-05/ |
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391 | Perl maintenance releases 5.6.1 and 5.8.0 have this security hole closed. |
392 | Most, if not all, Linux distribution have patches for this |
393 | vulnerability available, see http://www.linuxsecurity.com/advisories/ , |
394 | but the most recommendable way is to upgrade to at least Perl 5.6.1. |
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395 | |
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396 | =head1 AUTHOR AND COPYRIGHT |
397 | |
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398 | Copyright (c) 1997-2006 Tom Christiansen, Nathan Torkington, and |
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399 | other authors as noted. All rights reserved. |
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400 | |
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401 | This documentation is free; you can redistribute it and/or modify it |
402 | under the same terms as Perl itself. |
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403 | |
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404 | Irrespective of its distribution, all code examples here are in the public |
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405 | domain. You are permitted and encouraged to use this code and any |
406 | derivatives thereof in your own programs for fun or for profit as you |
407 | see fit. A simple comment in the code giving credit to the FAQ would |
408 | be courteous but is not required. |