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1 | =head1 NAME |
2 | |
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3 | perlfaq1 - General Questions About Perl ($Revision: 1.11 $, $Date: 1997/03/19 17:23:09 $) |
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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 |
53 | no longer maintained. Its last patch (4.036) was in 1992. The last |
54 | production release was 5.003, and the current experimental release for |
55 | those at the bleeding edge (as of 27/03/97) is 5.003_92, considered a beta |
56 | for production release 5.004, which will probably be out by the time |
57 | you read this. Further references to the Perl language in this document |
58 | refer to the current production release unless otherwise specified. |
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 | |
80 | =head2 How stable is Perl? |
81 | |
82 | Production releases, which incorporate bug fixes and new functionality, |
83 | are widely tested before release. Since the 5.000 release, we have |
84 | averaged only about one production release per year. |
85 | |
86 | Larry and the Perl development team occasionally make changes to the |
87 | internal core of the language, but all possible efforts are made toward |
88 | backward compatibility. While not quite all perl4 scripts run flawlessly |
89 | under perl5, an update to perl should nearly never invalidate a program |
90 | written for an earlier version of perl (barring accidental bug fixes |
91 | and the rare new keyword). |
92 | |
93 | =head2 Is Perl difficult to learn? |
94 | |
95 | Perl is easy to start learning -- and easy to keep learning. It looks |
96 | like most programming languages you're likely to have had experience |
97 | with, so if you've ever written an C program, an awk script, a shell |
98 | script, or even an Excel macro, you're already part way there. |
99 | |
100 | Most tasks only require a small subset of the Perl language. One of |
101 | the guiding mottos for Perl development is "there's more than one way |
102 | to do it" (TMTOWTDI, sometimes pronounced "tim toady"). Perl's |
103 | learning curve is therefore shallow (easy to learn) and long (there's |
104 | a whole lot you can do if you really want). |
105 | |
106 | Finally, Perl is (frequently) an interpreted language. This means |
107 | that you can write your programs and test them without an intermediate |
108 | compilation step, allowing you to experiment and test/debug quickly |
109 | and easily. This ease of experimentation flattens the learning curve |
110 | even more. |
111 | |
112 | Things that make Perl easier to learn: Unix experience, almost any kind |
113 | of programming experience, an understanding of regular expressions, and |
114 | the ability to understand other people's code. If there's something you |
115 | need to do, then it's probably already been done, and a working example is |
116 | usually available for free. Don't forget the new perl modules, either. |
117 | They're discussed in Part 3 of this FAQ, along with the CPAN, which is |
118 | discussed in Part 2. |
119 | |
120 | =head2 How does Perl compare with other languages like Java, Python, REXX, Scheme, or Tcl? |
121 | |
122 | Favorably in some areas, unfavorably in others. Precisely which areas |
123 | are good and bad is often a personal choice, so asking this question |
124 | on Usenet runs a strong risk of starting an unproductive Holy War. |
125 | |
126 | Probably the best thing to do is try to write equivalent code to do a |
127 | set of tasks. These languages have their own newsgroups in which you |
128 | can learn about (but hopefully not argue about) them. |
129 | |
130 | =head2 Can I do [task] in Perl? |
131 | |
132 | Perl is flexible and extensible enough for you to use on almost any |
133 | task, from one-line file-processing tasks to complex systems. For |
134 | many people, Perl serves as a great replacement for shell scripting. |
135 | For others, it serves as a convenient, high-level replacement for most |
136 | of what they'd program in low-level languages like C or C++. It's |
137 | ultimately up to you (and possibly your management ...) which tasks |
138 | you'll use Perl for and which you won't. |
139 | |
140 | If you have a library that provides an API, you can make any component |
141 | of it available as just another Perl function or variable using a Perl |
142 | extension written in C or C++ and dynamically linked into your main |
143 | perl interpreter. You can also go the other direction, and write your |
144 | main program in C or C++, and then link in some Perl code on the fly, |
145 | to create a powerful application. |
146 | |
147 | That said, there will always be small, focused, special-purpose |
148 | languages dedicated to a specific problem domain that are simply more |
149 | convenient for certain kinds of problems. Perl tries to be all things |
150 | to all people, but nothing special to anyone. Examples of specialized |
151 | languages that come to mind include prolog and matlab. |
152 | |
153 | =head2 When shouldn't I program in Perl? |
154 | |
155 | When your manager forbids it -- but do consider replacing them :-). |
156 | |
157 | Actually, one good reason is when you already have an existing |
158 | application written in another language that's all done (and done |
159 | well), or you have an application language specifically designed for a |
160 | certain task (e.g. prolog, make). |
161 | |
162 | For various reasons, Perl is probably not well-suited for real-time |
163 | embedded systems, low-level operating systems development work like |
164 | device drivers or context-switching code, complex multithreaded |
165 | shared-memory applications, or extremely large applications. You'll |
166 | notice that perl is not itself written in Perl. |
167 | |
168 | The new native-code compiler for Perl may reduce the limitations given |
169 | in the previous statement to some degree, but understand that Perl |
170 | remains fundamentally a dynamically typed language, and not a |
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171 | statically typed one. You certainly won't be chastised if you don't |
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172 | trust nuclear-plant or brain-surgery monitoring code to it. And |
173 | Larry will sleep easier, too -- Wall Street programs not |
174 | withstanding. :-) |
175 | |
176 | =head2 What's the difference between "perl" and "Perl"? |
177 | |
178 | One bit. Oh, you weren't talking ASCII? :-) Larry now uses "Perl" to |
179 | signify the language proper and "perl" the implementation of it, |
180 | i.e. the current interpreter. Hence Tom's quip that "Nothing but perl |
181 | can parse Perl." You may or may not choose to follow this usage. For |
182 | example, parallelism means "awk and perl" and "Python and Perl" look |
183 | ok, while "awk and Perl" and "Python and perl" do not. |
184 | |
185 | =head2 Is it a Perl program or a Perl script? |
186 | |
187 | It doesn't matter. |
188 | |
189 | In "standard terminology" a I<program> has been compiled to physical |
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190 | machine code once, and can then be run multiple times, whereas a |
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191 | I<script> must be translated by a program each time it's used. Perl |
192 | programs, however, are usually neither strictly compiled nor strictly |
193 | interpreted. They can be compiled to a bytecode form (something of a Perl |
194 | virtual machine) or to completely different languages, like C or assembly |
195 | language. You can't tell just by looking whether the source is destined |
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196 | for a pure interpreter, a parse-tree interpreter, a byte code interpreter, |
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197 | or a native-code compiler, so it's hard to give a definitive answer here. |
198 | |
199 | =head2 What is a JAPH? |
200 | |
201 | These are the "just another perl hacker" signatures that some people |
202 | sign their postings with. About 100 of the of the earlier ones are |
203 | available from http://www.perl.com/CPAN/misc/japh . |
204 | |
205 | =head2 Where can I get a list of Larry Wall witticisms? |
206 | |
207 | Over a hundred quips by Larry, from postings of his or source code, |
208 | can be found at http://www.perl.com/CPAN/misc/lwall-quotes . |
209 | |
210 | =head2 How can I convince my sysadmin/supervisor/employees to use version (5/5.004/Perl instead of some other language)? |
211 | |
212 | If your manager or employees are wary of unsupported software, or |
213 | software which doesn't officially ship with your Operating System, you |
214 | might try to appeal to their self-interest. If programmers can be |
215 | more productive using and utilizing Perl constructs, functionality, |
216 | simplicity, and power, then the typical manager/supervisor/employee |
217 | may be persuaded. Regarding using Perl in general, it's also |
218 | sometimes helpful to point out that delivery times may be reduced |
219 | using Perl, as compared to other languages. |
220 | |
221 | If you have a project which has a bottleneck, especially in terms of |
222 | translation, or testing, Perl almost certainly will provide a viable, |
223 | and quick solution. In conjunction with any persuasion effort, you |
224 | should not fail to point out that Perl is used, quite extensively, and |
225 | with extremely reliable and valuable results, at many large computer |
226 | software and/or hardware companies throughout the world. In fact, |
227 | many Unix vendors now ship Perl by default, and support is usually |
228 | just a news-posting away, if you can't find the answer in the |
229 | I<comprehensive> documentation, including this FAQ. |
230 | |
231 | If you face reluctance to upgrading from an older version of perl, |
232 | then point out that version 4 is utterly unmaintained and unsupported |
233 | by the Perl Development Team. Another big sell for Perl5 is the large |
234 | number of modules and extensions which greatly reduce development time |
235 | for any given task. Also mention that the difference between version |
236 | 4 and version 5 of Perl is like the difference between awk and C++. |
237 | (Well, ok, maybe not quite that distinct, but you get the idea.) If |
238 | you want support and a reasonable guarantee that what you're |
239 | developing will continue to work in the future, then you have to run |
240 | the supported version. That probably means running the 5.004 release, |
241 | although 5.003 isn't that bad (it's just one year and one release |
242 | behind). Several important bugs were fixed from the 5.000 through |
243 | 5.002 versions, though, so try upgrading past them if possible. |
244 | |
245 | =head1 AUTHOR AND COPYRIGHT |
246 | |
247 | Copyright (c) 1997 Tom Christiansen and Nathan Torkington. |
248 | All rights reserved. See L<perlfaq> for distribution information. |