1 | =head1 NAME |
---|
2 | |
---|
3 | perlfaq1 - General Questions About Perl ($Revision: 1.1.1.2 $, $Date: 2000-04-07 20:44:19 $) |
---|
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 |
---|
32 | distribution for more details. See L<perlhist> (new as of 5.005) |
---|
33 | for Perl's milestone releases. |
---|
34 | |
---|
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 |
---|
39 | news://news.perl.com/perl.porters-gw/ and the Deja archive at |
---|
40 | http://www.deja.com/ using the perl.porters-gw newsgroup, or you can |
---|
41 | subscribe to the mailing list by sending perl5-porters-request@perl.org |
---|
42 | a subscription request. |
---|
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 |
---|
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 |
---|
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 |
---|
61 | to the Perl language in this document refer to the production release |
---|
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. |
---|
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 | |
---|
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">. |
---|
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 | |
---|
88 | See L<perlhist> for a history of Perl revisions. |
---|
89 | |
---|
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, |
---|
99 | albeit perhaps without the efficiency that the new interface would allow. |
---|
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 | |
---|
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 | |
---|
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 |
---|
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. |
---|
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 | |
---|
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. |
---|
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. |
---|
148 | They're discussed in Part 3 of this FAQ, along with CPAN, which is |
---|
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 | |
---|
161 | Some comparison documents can be found at http://language.perl.com/versus/ |
---|
162 | if you really can't stop yourself. |
---|
163 | |
---|
164 | =head2 Can I do [task] in Perl? |
---|
165 | |
---|
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. |
---|
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, |
---|
179 | to create a powerful application. See L<perlembed>. |
---|
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 |
---|
198 | device drivers or context-switching code, complex multi-threaded |
---|
199 | shared-memory applications, or extremely large applications. You'll |
---|
200 | notice that perl is not itself written in Perl. |
---|
201 | |
---|
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. :-) |
---|
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 |
---|
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 |
---|
218 | folklore and post-facto expansions notwithstanding. |
---|
219 | |
---|
220 | =head2 Is it a Perl program or a Perl script? |
---|
221 | |
---|
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 |
---|
226 | commands, that is, a chat script. Something like a UUCP or PPP chat |
---|
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 |
---|
241 | Perl virtual machine) or to completely different languages, like C or |
---|
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, |
---|
250 | like "non serious" or "not real programming". Consequently, some Perl |
---|
251 | programmers prefer to avoid them altogether. |
---|
252 | |
---|
253 | =head2 What is a JAPH? |
---|
254 | |
---|
255 | These are the "just another perl hacker" signatures that some people |
---|
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 . |
---|
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, |
---|
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= |
---|
268 | |
---|
269 | =head2 How can I convince my sysadmin/supervisor/employees to use version (5/5.005/Perl instead of some other language)? |
---|
270 | |
---|
271 | If your manager or employees are wary of unsupported software, or |
---|
272 | software which doesn't officially ship with your operating system, you |
---|
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 |
---|
281 | translation or testing, Perl almost certainly will provide a viable, |
---|
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 | |
---|
290 | See http://www.perl.org/advocacy/ for more information. |
---|
291 | |
---|
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++. |
---|
298 | (Well, OK, maybe not quite that distinct, but you get the idea.) If you |
---|
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 |
---|
303 | 5.003 versions, though, so try upgrading past them if possible. |
---|
304 | |
---|
305 | Of particular note is the massive bug hunt for buffer overflow |
---|
306 | problems that went into the 5.004 release. All releases prior to |
---|
307 | that, including perl4, are considered insecure and should be upgraded |
---|
308 | as soon as possible. |
---|
309 | |
---|
310 | =head1 AUTHOR AND COPYRIGHT |
---|
311 | |
---|
312 | Copyright (c) 1997, 1998, 1999 Tom Christiansen and Nathan Torkington. |
---|
313 | All rights reserved. |
---|
314 | |
---|
315 | When included as an integrated part of the Standard Distribution |
---|
316 | of Perl or of its documentation (printed or otherwise), this works is |
---|
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 | |
---|
320 | Irrespective of its distribution, all code examples here are in the public |
---|
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. |
---|