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1 =head1 NAME
2
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3 perlfaq1 - General Questions About Perl
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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
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13 written by Larry Wall and a cast of thousands. It derives from the
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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,
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22 and even managers also use Perl. Maybe you should, too.
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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
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28 distribution policy of perl. Perl is supported by its users. The
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29 core, the standard Perl library, the optional modules, and the
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30 documentation you're reading now were all written by volunteers. See
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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)
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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 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/
40 and http://archive.develooper.com/perl5-porters@perl.org/
36eeb21 From: Philip Newton <Philip.Newton@gmx.net>
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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://dev.perl.org/perl5/docs/p5p-faq.html ,
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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).
47
48 While the GNU project includes Perl in its distributions, there's no
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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
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51 than GNU software's tend to be.
52
53 You can get commercial support of Perl if you wish, although for most
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54 users the informal support will more than suffice. See the answer to
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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
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61 There is often a matter of opinion and taste, and there isn't any one
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62 answer that fits everyone. In general, you want to use either the current
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63 stable release, or the stable release immediately prior to that one.
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64 Currently, those are perl5.10.x and perl5.8.x, respectively.
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65
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66 Beyond that, you have to consider several things and decide which is best
67 for you.
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68
69 =over 4
70
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71 =item *
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72
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73 If things aren't broken, upgrading perl may break them (or at least issue
74 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
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82 The Perl community is geared toward supporting the most recent releases,
83 so you'll have an easier time finding help for those.
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84
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85 =item *
86
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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 ).
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90
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91 =item *
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92
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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.
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96
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97 =item *
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98
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99 The immediate, previous releases (i.e. perl5.8.x ) are usually maintained
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100 for a while, although not at the same level as the current releases.
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101
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102 =item *
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103
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104 No one is actively supporting Perl 4. Five years ago it was a dead
105 camel carcass (according to this document). Now it's barely a skeleton
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106 as its whitewashed bones have fractured or eroded.
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107
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108 =item *
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109
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110 There is no Perl 6 release scheduled, but it will be available when
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111 it's ready. Stay tuned, but don't worry that you'll have to change
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112 major versions of Perl; no one is going to take Perl 5 away from you.
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113
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114 =item *
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115
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116 There are really two tracks of perl development: a maintenance version
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117 and an experimental version. The maintenance versions are stable, and
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118 have an even number as the minor release (i.e. perl5.10.x, where 10 is the
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119 minor release). The experimental versions may include features that
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120 don't make it into the stable versions, and have an odd number as the
121 minor release (i.e. perl5.9.x, where 9 is the minor release).
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122
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123 =back
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124
125
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126 =head2 What are Perl 4, Perl 5, or Perl 6?
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127
128 (contributed by brian d foy)
129
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130 In short, Perl 4 is the past, Perl 5 is the present, and Perl 6 is the
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131 future.
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132
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133 The number after perl (i.e. the 5 after Perl 5) is the major release
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134 of the perl interpreter as well as the version of the language. Each
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135 major version has significant differences that earlier versions cannot
136 support.
137
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138 The current major release of Perl is Perl 5, and was released in 1994.
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139 It can run scripts from the previous major release, Perl 4 (March 1991),
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140 but has significant differences. It introduced the concept of references,
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141 complex data structures, and modules. The Perl 5 interpreter was a
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142 complete re-write of the previous perl sources.
143
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144 Perl 6 is the next major version of Perl, but it's still in development
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145 in both its syntax and design. The work started in 2002 and is still
146 ongoing. Many of the most interesting features have shown up in the
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147 latest versions of Perl 5, and some Perl 5 modules allow you to use some
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148 Perl 6 syntax in your programs. You can learn more about Perl 6 at
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149 http://dev.perl.org/perl6/ .
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150
151 See L<perlhist> for a history of Perl revisions.
152
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153 =head2 What was Ponie?
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154
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155 (contributed by brian d foy)
156
157 Ponie stands for "Perl On the New Internal Engine", started by Arthur
158 Bergman from Fotango in 2003, and subsequently run as a project of The
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159 Perl Foundation. It was abandoned in 2006
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160 ( http://www.nntp.perl.org/group/perl.ponie.dev/487 ).
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161
162 Instead of using the current Perl internals, Ponie aimed to create a
163 new one that would provide a translation path from Perl 5 to Perl 6
164 (or anything else that targets Parrot, actually). You would have been
165 able to just keep using Perl 5 with Parrot, the virtual machine which
166 will compile and run Perl 6 bytecode.
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167
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168 =head2 What is Perl 6?
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169
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170 At The Second O'Reilly Open Source Software Convention, Larry Wall
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171 announced Perl 6 development would begin in earnest. Perl 6 was an oft
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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 Perl 6, or have a desire to help in
177 the crusade to make Perl a better place then peruse the Perl 6 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 Perl 6 is not scheduled for release yet, and Perl 5 will still be supported
181 for quite awhile after its release. Do not wait for Perl 6 to do whatever
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182 you need to do.
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183
184 "We're really serious about reinventing everything that needs reinventing."
185 --Larry Wall
186
187 =head2 How stable is Perl?
188
189 Production releases, which incorporate bug fixes and new functionality,
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190 are widely tested before release. Since the 5.000 release, we have
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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
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195 backward compatibility. While not quite all Perl 4 scripts run flawlessly
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196 under Perl 5, an update to perl should nearly never invalidate a program
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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
204 with, so if you've ever written a C program, an awk script, a shell
205 script, or even a BASIC program, you're already partway there.
206
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207 Most tasks only require a small subset of the Perl language. One of
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208 the guiding mottos for Perl development is "there's more than one way
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209 to do it" (TMTOWTDI, sometimes pronounced "tim toady"). Perl's
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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
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
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216 and test/debug quickly and easily. This ease of experimentation flattens
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217 the learning curve even more.
218
219 Things that make Perl easier to learn: Unix experience, almost any kind
220 of programming experience, an understanding of regular expressions, and
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221 the ability to understand other people's code. If there's something you
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222 need to do, then it's probably already been done, and a working example is
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223 usually available for free. Don't forget Perl modules, either.
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224 They're discussed in Part 3 of this FAQ, along with CPAN, which is
225 discussed in Part 2.
226
227 =head2 How does Perl compare with other languages like Java, Python, REXX, Scheme, or Tcl?
228
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229 Favorably in some areas, unfavorably in others. Precisely which areas
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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
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234 set of tasks. These languages have their own newsgroups in which you
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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
240 =head2 Can I do [task] in Perl?
241
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
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246 what they'd program in low-level languages like C or C++. It's ultimately
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247 up to you (and possibly your management) which tasks you'll use Perl
248 for and which you won't.
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
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253 perl interpreter. You can also go the other direction, and write your
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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
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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
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261 languages that come to mind include prolog and matlab.
262
263 =head2 When shouldn't I program in Perl?
264
265 When your manager forbids it--but do consider replacing them :-).
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
274 device drivers or context-switching code, complex multi-threaded
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275 shared-memory applications, or extremely large applications. You'll
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276 notice that perl is not itself written in Perl.
277
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278 Perl remains fundamentally a dynamically typed language, not
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279 a statically typed one. You certainly won't be chastised if you don't
280 trust nuclear-plant or brain-surgery monitoring code to it. And Larry
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281 will sleep easier, too--Wall Street programs not withstanding. :-)
282
283 =head2 What's the difference between "perl" and "Perl"?
284
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285 One bit. Oh, you weren't talking ASCII? :-) Larry now uses "Perl" to
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286 signify the language proper and "perl" the implementation of it, i.e.
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287 the current interpreter. Hence Tom's quip that "Nothing but perl can
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288 parse Perl."
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289
aa37d38 T<> is not valid in our pod.
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290 Before the first edition of I<Programming perl>, people commonly
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291 referred to the language as "perl", and its name appeared that way in
292 the title because it referred to the interpreter. In the book, Randal
293 Schwartz capitalised the language's name to make it stand out better
294 when typeset. This convention was adopted by the community, and the
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295 second edition became I<Programming Perl>, using the capitalized
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296 version of the name to refer to the language.
297
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298 You may or may not choose to follow this usage. For example,
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299 parallelism means "awk and perl" and "Python and Perl" look good, while
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300 "awk and Perl" and "Python and perl" do not. But never write "PERL",
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301 because perl is not an acronym, apocryphal folklore and post-facto
302 expansions notwithstanding.
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303
304 =head2 Is it a Perl program or a Perl script?
305
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306 Larry doesn't really care. He says (half in jest) that "a script is
307 what you give the actors. A program is what you give the audience."
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308
309 Originally, a script was a canned sequence of normally interactive
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310 commands--that is, a chat script. Something like a UUCP or PPP chat
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311 script or an expect script fits the bill nicely, as do configuration
312 scripts run by a program at its start up, such F<.cshrc> or F<.ircrc>,
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313 for example. Chat scripts were just drivers for existing programs,
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314 not stand-alone programs in their own right.
315
316 A computer scientist will correctly explain that all programs are
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317 interpreted and that the only question is at what level. But if you
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318 ask this question of someone who isn't a computer scientist, they might
319 tell you that a I<program> has been compiled to physical machine code
320 once and can then be run multiple times, whereas a I<script> must be
321 translated by a program each time it's used.
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.
328
329 =head2 What is a JAPH?
330
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331 (contributed by brian d foy)
332
333 JAPH stands for "Just another Perl hacker,", which Randal Schwartz used
334 to sign email and usenet messages starting in the late 1980s. He
335 previously used the phrase with many subjects ("Just another x hacker,"),
336 so to distinguish his JAPH, he started to write them as Perl programs:
337
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338 print "Just another Perl hacker,";
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339
340 Other people picked up on this and started to write clever or obfuscated
341 programs to produce the same output, spinning things quickly out of
342 control while still providing hours of amusement for their creators and
343 readers.
344
345 CPAN has several JAPH programs at http://www.cpan.org/misc/japh .
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346
347 =head2 Where can I get a list of Larry Wall witticisms?
348
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349 (contributed by brian d foy)
350
351 Google "larry wall quotes"! You might even try the "I feel lucky" button.
352 :)
353
354 Wikiquote has the witticisms from Larry along with their source,
355 including his usenet postings and source code comments.
356
357 If you want a plain text file, try
358 http://www.cpan.org/misc/lwall-quotes.txt.gz .
359
360 =head2 How can I convince others to use Perl?
361
362 (contributed by brian d foy)
363
364 Appeal to their self interest! If Perl is new (and thus scary) to them,
365 find something that Perl can do to solve one of their problems. That
366 might mean that Perl either saves them something (time, headaches, money)
367 or gives them something (flexibility, power, testability).
368
369 In general, the benefit of a language is closely related to the skill of
370 the people using that language. If you or your team can be more faster,
371 better, and stronger through Perl, you'll deliver more value. Remember,
372 people often respond better to what they get out of it. If you run
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373 into resistance, figure out what those people get out of the other
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374 choice and how Perl might satisfy that requirement.
375
376 You don't have to worry about finding or paying for Perl; it's freely
377 available and several popular operating systems come with Perl. Community
378 support in places such as Perlmonks ( http://www.perlmonks.com )
379 and the various Perl mailing lists ( http://lists.perl.org ) means that
380 you can usually get quick answers to your problems.
381
382 Finally, keep in mind that Perl might not be the right tool for every
383 job. You're a much better advocate if your claims are reasonable and
384 grounded in reality. Dogmatically advocating anything tends to make
385 people discount your message. Be honest about possible disadvantages
386 to your choice of Perl since any choice has trade-offs.
387
388 You might find these links useful:
389
390 =over 4
391
392 =item * http://perltraining.com.au/whyperl.html
393
394 =item * http://www.perl.org/advocacy/whyperl.html
395
396 =back
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397
398 =head1 AUTHOR AND COPYRIGHT
399
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400 Copyright (c) 1997-2010 Tom Christiansen, Nathan Torkington, and
bf227cc * Updated the year of copyright and note in each COPYRIGHT section
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401 other authors as noted. All rights reserved.
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402
403 This documentation is free; you can redistribute it and/or modify it
404 under the same terms as Perl itself.
405
406 Irrespective of its distribution, all code examples here are in the public
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407 domain. You are permitted and encouraged to use this code and any
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408 derivatives thereof in your own programs for fun or for profit as you
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409 see fit. A simple comment in the code giving credit to the FAQ would
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410 be courteous but is not required.
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