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1 | =head1 NAME |
2 | |
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3 | perlfaq1 - General Questions About Perl ($Revision: 1.12 $, $Date: 1997/04/24 22:43:34 $) |
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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 |
32 | distribution for more details. |
33 | |
34 | In particular, the core development team (known as the Perl |
35 | Porters) are a rag-tag band of highly altruistic individuals |
36 | committed to producing better software for free than you |
37 | could hope to purchase for money. You may snoop on pending |
38 | developments via news://genetics.upenn.edu/perl.porters-gw/ and |
39 | http://www.frii.com/~gnat/perl/porters/summary.html. |
40 | |
41 | While the GNU project includes Perl in its distributions, there's no |
42 | such thing as "GNU Perl". Perl is not produced nor maintained by the |
43 | Free Software Foundation. Perl's licensing terms are also more open |
44 | than GNU software's tend to be. |
45 | |
46 | You can get commercial support of Perl if you wish, although for most |
47 | users the informal support will more than suffice. See the answer to |
48 | "Where can I buy a commercial version of perl?" for more information. |
49 | |
50 | =head2 Which version of Perl should I use? |
51 | |
52 | You should definitely use version 5. Version 4 is old, limited, and |
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53 | no longer maintained; its last patch (4.036) was in 1992. The most |
54 | recent production release is 5.004. Further references to the Perl |
55 | language in this document refer to this production release unless |
56 | otherwise specified. There may be one or more official bug fixes for |
57 | 5.004 by the time you read this, and also perhaps some experimental |
58 | versions on the way to the next release. |
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59 | |
60 | =head2 What are perl4 and perl5? |
61 | |
62 | Perl4 and perl5 are informal names for different versions of the Perl |
63 | programming language. It's easier to say "perl5" than it is to say |
64 | "the 5(.004) release of Perl", but some people have interpreted this |
65 | to mean there's a language called "perl5", which isn't the case. |
66 | Perl5 is merely the popular name for the fifth major release (October 1994), |
67 | while perl4 was the fourth major release (March 1991). There was also a |
68 | perl1 (in January 1988), a perl2 (June 1988), and a perl3 (October 1989). |
69 | |
70 | The 5.0 release is, essentially, a complete rewrite of the perl source |
71 | code from the ground up. It has been modularized, object-oriented, |
72 | tweaked, trimmed, and optimized until it almost doesn't look like the |
73 | old code. However, the interface is mostly the same, and compatibility |
74 | with previous releases is very high. |
75 | |
76 | To avoid the "what language is perl5?" confusion, some people prefer to |
77 | simply use "perl" to refer to the latest version of perl and avoid using |
78 | "perl5" altogether. It's not really that big a deal, though. |
79 | |
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80 | See L<perlhist> for a history of Perl revisions. |
81 | |
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82 | =head2 How stable is Perl? |
83 | |
84 | Production releases, which incorporate bug fixes and new functionality, |
85 | are widely tested before release. Since the 5.000 release, we have |
86 | averaged only about one production release per year. |
87 | |
88 | Larry and the Perl development team occasionally make changes to the |
89 | internal core of the language, but all possible efforts are made toward |
90 | backward compatibility. While not quite all perl4 scripts run flawlessly |
91 | under perl5, an update to perl should nearly never invalidate a program |
92 | written for an earlier version of perl (barring accidental bug fixes |
93 | and the rare new keyword). |
94 | |
95 | =head2 Is Perl difficult to learn? |
96 | |
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97 | No, Perl is easy to start learning -- and easy to keep learning. It looks |
98 | like most programming languages you're likely to have experience |
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99 | with, so if you've ever written an C program, an awk script, a shell |
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100 | script, or even BASIC program, you're already part way there. |
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101 | |
102 | Most tasks only require a small subset of the Perl language. One of |
103 | the guiding mottos for Perl development is "there's more than one way |
104 | to do it" (TMTOWTDI, sometimes pronounced "tim toady"). Perl's |
105 | learning curve is therefore shallow (easy to learn) and long (there's |
106 | a whole lot you can do if you really want). |
107 | |
108 | Finally, Perl is (frequently) an interpreted language. This means |
109 | that you can write your programs and test them without an intermediate |
110 | compilation step, allowing you to experiment and test/debug quickly |
111 | and easily. This ease of experimentation flattens the learning curve |
112 | even more. |
113 | |
114 | Things that make Perl easier to learn: Unix experience, almost any kind |
115 | of programming experience, an understanding of regular expressions, and |
116 | the ability to understand other people's code. If there's something you |
117 | need to do, then it's probably already been done, and a working example is |
118 | usually available for free. Don't forget the new perl modules, either. |
119 | They're discussed in Part 3 of this FAQ, along with the CPAN, which is |
120 | discussed in Part 2. |
121 | |
122 | =head2 How does Perl compare with other languages like Java, Python, REXX, Scheme, or Tcl? |
123 | |
124 | Favorably in some areas, unfavorably in others. Precisely which areas |
125 | are good and bad is often a personal choice, so asking this question |
126 | on Usenet runs a strong risk of starting an unproductive Holy War. |
127 | |
128 | Probably the best thing to do is try to write equivalent code to do a |
129 | set of tasks. These languages have their own newsgroups in which you |
130 | can learn about (but hopefully not argue about) them. |
131 | |
132 | =head2 Can I do [task] in Perl? |
133 | |
134 | Perl is flexible and extensible enough for you to use on almost any |
135 | task, from one-line file-processing tasks to complex systems. For |
136 | many people, Perl serves as a great replacement for shell scripting. |
137 | For others, it serves as a convenient, high-level replacement for most |
138 | of what they'd program in low-level languages like C or C++. It's |
139 | ultimately up to you (and possibly your management ...) which tasks |
140 | you'll use Perl for and which you won't. |
141 | |
142 | If you have a library that provides an API, you can make any component |
143 | of it available as just another Perl function or variable using a Perl |
144 | extension written in C or C++ and dynamically linked into your main |
145 | perl interpreter. You can also go the other direction, and write your |
146 | main program in C or C++, and then link in some Perl code on the fly, |
147 | to create a powerful application. |
148 | |
149 | That said, there will always be small, focused, special-purpose |
150 | languages dedicated to a specific problem domain that are simply more |
151 | convenient for certain kinds of problems. Perl tries to be all things |
152 | to all people, but nothing special to anyone. Examples of specialized |
153 | languages that come to mind include prolog and matlab. |
154 | |
155 | =head2 When shouldn't I program in Perl? |
156 | |
157 | When your manager forbids it -- but do consider replacing them :-). |
158 | |
159 | Actually, one good reason is when you already have an existing |
160 | application written in another language that's all done (and done |
161 | well), or you have an application language specifically designed for a |
162 | certain task (e.g. prolog, make). |
163 | |
164 | For various reasons, Perl is probably not well-suited for real-time |
165 | embedded systems, low-level operating systems development work like |
166 | device drivers or context-switching code, complex multithreaded |
167 | shared-memory applications, or extremely large applications. You'll |
168 | notice that perl is not itself written in Perl. |
169 | |
170 | The new native-code compiler for Perl may reduce the limitations given |
171 | in the previous statement to some degree, but understand that Perl |
172 | remains fundamentally a dynamically typed language, and not a |
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173 | statically typed one. You certainly won't be chastized if you don't |
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174 | trust nuclear-plant or brain-surgery monitoring code to it. And |
175 | Larry will sleep easier, too -- Wall Street programs not |
176 | withstanding. :-) |
177 | |
178 | =head2 What's the difference between "perl" and "Perl"? |
179 | |
180 | One bit. Oh, you weren't talking ASCII? :-) Larry now uses "Perl" to |
181 | signify the language proper and "perl" the implementation of it, |
182 | i.e. the current interpreter. Hence Tom's quip that "Nothing but perl |
183 | can parse Perl." You may or may not choose to follow this usage. For |
184 | example, parallelism means "awk and perl" and "Python and Perl" look |
185 | ok, while "awk and Perl" and "Python and perl" do not. |
186 | |
187 | =head2 Is it a Perl program or a Perl script? |
188 | |
189 | It doesn't matter. |
190 | |
191 | In "standard terminology" a I<program> has been compiled to physical |
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192 | machine code once, and can then be be run multiple times, whereas a |
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193 | I<script> must be translated by a program each time it's used. Perl |
194 | programs, however, are usually neither strictly compiled nor strictly |
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195 | interpreted. They can be compiled to a byte code form (something of a |
196 | Perl virtual machine) or to completely different languages, like C or |
197 | assembly language. You can't tell just by looking whether the source |
198 | is destined for a pure interpreter, a parse-tree interpreter, a byte |
199 | code interpreter, or a native-code compiler, so it's hard to give a |
200 | definitive answer here. |
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201 | |
202 | =head2 What is a JAPH? |
203 | |
204 | These are the "just another perl hacker" signatures that some people |
205 | sign their postings with. About 100 of the of the earlier ones are |
206 | available from http://www.perl.com/CPAN/misc/japh . |
207 | |
208 | =head2 Where can I get a list of Larry Wall witticisms? |
209 | |
210 | Over a hundred quips by Larry, from postings of his or source code, |
211 | can be found at http://www.perl.com/CPAN/misc/lwall-quotes . |
212 | |
213 | =head2 How can I convince my sysadmin/supervisor/employees to use version (5/5.004/Perl instead of some other language)? |
214 | |
215 | If your manager or employees are wary of unsupported software, or |
216 | software which doesn't officially ship with your Operating System, you |
217 | might try to appeal to their self-interest. If programmers can be |
218 | more productive using and utilizing Perl constructs, functionality, |
219 | simplicity, and power, then the typical manager/supervisor/employee |
220 | may be persuaded. Regarding using Perl in general, it's also |
221 | sometimes helpful to point out that delivery times may be reduced |
222 | using Perl, as compared to other languages. |
223 | |
224 | If you have a project which has a bottleneck, especially in terms of |
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225 | translation or testing, Perl almost certainly will provide a viable, |
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226 | and quick solution. In conjunction with any persuasion effort, you |
227 | should not fail to point out that Perl is used, quite extensively, and |
228 | with extremely reliable and valuable results, at many large computer |
229 | software and/or hardware companies throughout the world. In fact, |
230 | many Unix vendors now ship Perl by default, and support is usually |
231 | just a news-posting away, if you can't find the answer in the |
232 | I<comprehensive> documentation, including this FAQ. |
233 | |
234 | If you face reluctance to upgrading from an older version of perl, |
235 | then point out that version 4 is utterly unmaintained and unsupported |
236 | by the Perl Development Team. Another big sell for Perl5 is the large |
237 | number of modules and extensions which greatly reduce development time |
238 | for any given task. Also mention that the difference between version |
239 | 4 and version 5 of Perl is like the difference between awk and C++. |
240 | (Well, ok, maybe not quite that distinct, but you get the idea.) If |
241 | you want support and a reasonable guarantee that what you're |
242 | developing will continue to work in the future, then you have to run |
243 | the supported version. That probably means running the 5.004 release, |
244 | although 5.003 isn't that bad (it's just one year and one release |
245 | behind). Several important bugs were fixed from the 5.000 through |
246 | 5.002 versions, though, so try upgrading past them if possible. |
247 | |
248 | =head1 AUTHOR AND COPYRIGHT |
249 | |
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250 | Copyright (c) 1997, 1998 Tom Christiansen and Nathan Torkington. |
251 | All rights reserved. |
252 | |
253 | When included as part of the Standard Version of Perl, or as part of |
254 | its complete documentation whether printed or otherwise, this work |
255 | may be distributed only under the terms of Perl's Artistic License. |
256 | Any distribution of this file or derivatives thereof I<outside> |
257 | of that package require that special arrangements be made with |
258 | copyright holder. |
259 | |
260 | Irrespective of its distribution, all code examples in this file |
261 | are hereby placed into the public domain. You are permitted and |
262 | encouraged to use this code in your own programs for fun |
263 | or for profit as you see fit. A simple comment in the code giving |
264 | credit would be courteous but is not required. |