| 1 | =head1 NAME |
| 2 | |
| 3 | perlfaq1 - General Questions About Perl ($Revision: 1.2 $, $Date: 2001/11/09 08:06:04 $) |
| 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 to |
| 37 | producing better software for free than you could hope to purchase for |
| 38 | money. You may snoop on pending developments via |
| 39 | nntp://news.perl.com/perl.porters-gw/ |
| 40 | or you can subscribe to the mailing list by sending |
| 41 | perl5-porters-request@perl.org a subscription request |
| 42 | (an empty message with no subject is fine). |
| 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 5.6 (although 5.005_03 is still supported). |
| 60 | The most cutting-edge development release is 5.7. 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. |
| 82 | See L<perltrap/"Perl4 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 | At The Second O'Reilly Open Source Software Convention, Larry Wall |
| 93 | announced Perl6 development would begin in earnest. Perl6 was an oft |
| 94 | used term for Chip Salzenberg's project to rewrite Perl in C++ named |
| 95 | Topaz. However, Topaz should not be confused with the nisus to rewrite |
| 96 | Perl while keeping the lessons learned from other software, as well as |
| 97 | Perl5, in mind. |
| 98 | |
| 99 | If you have a desire to help in the crusade to make Perl a better place |
| 100 | then peruse the Perl6 developers page at http://www.perl.org/perl6/ and |
| 101 | get involved. |
| 102 | |
| 103 | The first alpha release is expected by Summer 2001. |
| 104 | |
| 105 | "We're really serious about reinventing everything that needs reinventing." |
| 106 | --Larry Wall |
| 107 | |
| 108 | =head2 How stable is Perl? |
| 109 | |
| 110 | Production releases, which incorporate bug fixes and new functionality, |
| 111 | are widely tested before release. Since the 5.000 release, we have |
| 112 | averaged only about one production release per year. |
| 113 | |
| 114 | Larry and the Perl development team occasionally make changes to the |
| 115 | internal core of the language, but all possible efforts are made toward |
| 116 | backward compatibility. While not quite all perl4 scripts run flawlessly |
| 117 | under perl5, an update to perl should nearly never invalidate a program |
| 118 | written for an earlier version of perl (barring accidental bug fixes |
| 119 | and the rare new keyword). |
| 120 | |
| 121 | =head2 Is Perl difficult to learn? |
| 122 | |
| 123 | No, Perl is easy to start learning--and easy to keep learning. It looks |
| 124 | like most programming languages you're likely to have experience |
| 125 | with, so if you've ever written a C program, an awk script, a shell |
| 126 | script, or even a BASIC program, you're already partway there. |
| 127 | |
| 128 | Most tasks only require a small subset of the Perl language. One of |
| 129 | the guiding mottos for Perl development is "there's more than one way |
| 130 | to do it" (TMTOWTDI, sometimes pronounced "tim toady"). Perl's |
| 131 | learning curve is therefore shallow (easy to learn) and long (there's |
| 132 | a whole lot you can do if you really want). |
| 133 | |
| 134 | Finally, because Perl is frequently (but not always, and certainly not by |
| 135 | definition) an interpreted language, you can write your programs and test |
| 136 | them without an intermediate compilation step, allowing you to experiment |
| 137 | and test/debug quickly and easily. This ease of experimentation flattens |
| 138 | the learning curve even more. |
| 139 | |
| 140 | Things that make Perl easier to learn: Unix experience, almost any kind |
| 141 | of programming experience, an understanding of regular expressions, and |
| 142 | the ability to understand other people's code. If there's something you |
| 143 | need to do, then it's probably already been done, and a working example is |
| 144 | usually available for free. Don't forget the new perl modules, either. |
| 145 | They're discussed in Part 3 of this FAQ, along with CPAN, which is |
| 146 | discussed in Part 2. |
| 147 | |
| 148 | =head2 How does Perl compare with other languages like Java, Python, REXX, Scheme, or Tcl? |
| 149 | |
| 150 | Favorably in some areas, unfavorably in others. Precisely which areas |
| 151 | are good and bad is often a personal choice, so asking this question |
| 152 | on Usenet runs a strong risk of starting an unproductive Holy War. |
| 153 | |
| 154 | Probably the best thing to do is try to write equivalent code to do a |
| 155 | set of tasks. These languages have their own newsgroups in which you |
| 156 | can learn about (but hopefully not argue about) them. |
| 157 | |
| 158 | Some comparison documents can be found at http://language.perl.com/versus/ |
| 159 | if you really can't stop yourself. |
| 160 | |
| 161 | =head2 Can I do [task] in Perl? |
| 162 | |
| 163 | Perl is flexible and extensible enough for you to use on virtually any |
| 164 | task, from one-line file-processing tasks to large, elaborate systems. |
| 165 | For many people, Perl serves as a great replacement for shell scripting. |
| 166 | For others, it serves as a convenient, high-level replacement for most of |
| 167 | what they'd program in low-level languages like C or C++. It's ultimately |
| 168 | up to you (and possibly your management) which tasks you'll use Perl |
| 169 | for and which you won't. |
| 170 | |
| 171 | If you have a library that provides an API, you can make any component |
| 172 | of it available as just another Perl function or variable using a Perl |
| 173 | extension written in C or C++ and dynamically linked into your main |
| 174 | perl interpreter. You can also go the other direction, and write your |
| 175 | main program in C or C++, and then link in some Perl code on the fly, |
| 176 | to create a powerful application. See L<perlembed>. |
| 177 | |
| 178 | That said, there will always be small, focused, special-purpose |
| 179 | languages dedicated to a specific problem domain that are simply more |
| 180 | convenient for certain kinds of problems. Perl tries to be all things |
| 181 | to all people, but nothing special to anyone. Examples of specialized |
| 182 | languages that come to mind include prolog and matlab. |
| 183 | |
| 184 | =head2 When shouldn't I program in Perl? |
| 185 | |
| 186 | When your manager forbids it--but do consider replacing them :-). |
| 187 | |
| 188 | Actually, one good reason is when you already have an existing |
| 189 | application written in another language that's all done (and done |
| 190 | well), or you have an application language specifically designed for a |
| 191 | certain task (e.g. prolog, make). |
| 192 | |
| 193 | For various reasons, Perl is probably not well-suited for real-time |
| 194 | embedded systems, low-level operating systems development work like |
| 195 | device drivers or context-switching code, complex multi-threaded |
| 196 | shared-memory applications, or extremely large applications. You'll |
| 197 | notice that perl is not itself written in Perl. |
| 198 | |
| 199 | The new, native-code compiler for Perl may eventually reduce the |
| 200 | limitations given in the previous statement to some degree, but understand |
| 201 | that Perl remains fundamentally a dynamically typed language, not |
| 202 | a statically typed one. You certainly won't be chastised if you don't |
| 203 | trust nuclear-plant or brain-surgery monitoring code to it. And Larry |
| 204 | will sleep easier, too--Wall Street programs not withstanding. :-) |
| 205 | |
| 206 | =head2 What's the difference between "perl" and "Perl"? |
| 207 | |
| 208 | One bit. Oh, you weren't talking ASCII? :-) Larry now uses "Perl" to |
| 209 | signify the language proper and "perl" the implementation of it, |
| 210 | i.e. the current interpreter. Hence Tom's quip that "Nothing but perl |
| 211 | can parse Perl." You may or may not choose to follow this usage. For |
| 212 | example, parallelism means "awk and perl" and "Python and Perl" look |
| 213 | OK, while "awk and Perl" and "Python and perl" do not. But never |
| 214 | write "PERL", because perl isn't really an acronym, apocryphal |
| 215 | folklore and post-facto expansions notwithstanding. |
| 216 | |
| 217 | =head2 Is it a Perl program or a Perl script? |
| 218 | |
| 219 | Larry doesn't really care. He says (half in jest) that "a script is |
| 220 | what you give the actors. A program is what you give the audience." |
| 221 | |
| 222 | Originally, a script was a canned sequence of normally interactive |
| 223 | commands--that is, a chat script. Something like a UUCP or PPP chat |
| 224 | script or an expect script fits the bill nicely, as do configuration |
| 225 | scripts run by a program at its start up, such F<.cshrc> or F<.ircrc>, |
| 226 | for example. Chat scripts were just drivers for existing programs, |
| 227 | not stand-alone programs in their own right. |
| 228 | |
| 229 | A computer scientist will correctly explain that all programs are |
| 230 | interpreted and that the only question is at what level. But if you |
| 231 | ask this question of someone who isn't a computer scientist, they might |
| 232 | tell you that a I<program> has been compiled to physical machine code |
| 233 | once and can then be run multiple times, whereas a I<script> must be |
| 234 | translated by a program each time it's used. |
| 235 | |
| 236 | Perl programs are (usually) neither strictly compiled nor strictly |
| 237 | interpreted. They can be compiled to a byte-code form (something of a |
| 238 | Perl virtual machine) or to completely different languages, like C or |
| 239 | assembly language. You can't tell just by looking at it whether the |
| 240 | source is destined for a pure interpreter, a parse-tree interpreter, |
| 241 | a byte-code interpreter, or a native-code compiler, so it's hard to give |
| 242 | a definitive answer here. |
| 243 | |
| 244 | Now that "script" and "scripting" are terms that have been seized by |
| 245 | unscrupulous or unknowing marketeers for their own nefarious purposes, |
| 246 | they have begun to take on strange and often pejorative meanings, |
| 247 | like "non serious" or "not real programming". Consequently, some Perl |
| 248 | programmers prefer to avoid them altogether. |
| 249 | |
| 250 | =head2 What is a JAPH? |
| 251 | |
| 252 | These are the "just another perl hacker" signatures that some people |
| 253 | sign their postings with. Randal Schwartz made these famous. About |
| 254 | 100 of the earlier ones are available from |
| 255 | http://www.cpan.org/misc/japh . |
| 256 | |
| 257 | =head2 Where can I get a list of Larry Wall witticisms? |
| 258 | |
| 259 | Over a hundred quips by Larry, from postings of his or source code, |
| 260 | can be found at http://www.cpan.org/misc/lwall-quotes.txt.gz . |
| 261 | |
| 262 | =head2 How can I convince my sysadmin/supervisor/employees to use version 5/5.005/Perl instead of some other language? |
| 263 | |
| 264 | If your manager or employees are wary of unsupported software, or |
| 265 | software which doesn't officially ship with your operating system, you |
| 266 | might try to appeal to their self-interest. If programmers can be |
| 267 | more productive using and utilizing Perl constructs, functionality, |
| 268 | simplicity, and power, then the typical manager/supervisor/employee |
| 269 | may be persuaded. Regarding using Perl in general, it's also |
| 270 | sometimes helpful to point out that delivery times may be reduced |
| 271 | using Perl compared to other languages. |
| 272 | |
| 273 | If you have a project which has a bottleneck, especially in terms of |
| 274 | translation or testing, Perl almost certainly will provide a viable, |
| 275 | quick solution. In conjunction with any persuasion effort, you |
| 276 | should not fail to point out that Perl is used, quite extensively, and |
| 277 | with extremely reliable and valuable results, at many large computer |
| 278 | software and hardware companies throughout the world. In fact, |
| 279 | many Unix vendors now ship Perl by default. Support is usually |
| 280 | just a news-posting away, if you can't find the answer in the |
| 281 | I<comprehensive> documentation, including this FAQ. |
| 282 | |
| 283 | See http://www.perl.org/advocacy/ for more information. |
| 284 | |
| 285 | If you face reluctance to upgrading from an older version of perl, |
| 286 | then point out that version 4 is utterly unmaintained and unsupported |
| 287 | by the Perl Development Team. Another big sell for Perl5 is the large |
| 288 | number of modules and extensions which greatly reduce development time |
| 289 | for any given task. Also mention that the difference between version |
| 290 | 4 and version 5 of Perl is like the difference between awk and C++. |
| 291 | (Well, OK, maybe it's not quite that distinct, but you get the idea.) |
| 292 | If you want support and a reasonable guarantee that what you're |
| 293 | developing will continue to work in the future, then you have to run |
| 294 | the supported version. As of April 2001 that probably means |
| 295 | running either of the releases 5.6.1 (released in April 2001) or |
| 296 | 5.005_03 (released in March 1999), although 5.004_05 isn't that bad |
| 297 | if you B<absolutely> need such an old version (released in April 1999) |
| 298 | for stability reasons. Anything older than 5.004_05 shouldn't be used. |
| 299 | |
| 300 | Of particular note is the massive bug hunt for buffer overflow |
| 301 | problems that went into the 5.004 release. All releases prior to |
| 302 | that, including perl4, are considered insecure and should be upgraded |
| 303 | as soon as possible. |
| 304 | |
| 305 | In August 2000 in all Linux distributions a new security problem was |
| 306 | found in the optional 'suidperl' (not built or installed by default) |
| 307 | in all the Perl branches 5.6, 5.005, and 5.004, see |
| 308 | http://www.cpan.org/src/5.0/sperl-2000-08-05/ |
| 309 | Perl maintenance releases 5.6.1 and 5.8.0 have this security hole closed. |
| 310 | Most, if not all, Linux distribution have patches for this |
| 311 | vulnerability available, see http://www.linuxsecurity.com/advisories/ , |
| 312 | but the most recommendable way is to upgrade to at least Perl 5.6.1. |
| 313 | |
| 314 | =head1 AUTHOR AND COPYRIGHT |
| 315 | |
| 316 | Copyright (c) 1997, 1998, 1999, 2000, 2001 Tom Christiansen and Nathan |
| 317 | Torkington. All rights reserved. |
| 318 | |
| 319 | This documentation is free; you can redistribute it and/or modify it |
| 320 | under the same terms as Perl itself. |
| 321 | |
| 322 | Irrespective of its distribution, all code examples here are in the public |
| 323 | domain. You are permitted and encouraged to use this code and any |
| 324 | derivatives thereof in your own programs for fun or for profit as you |
| 325 | see fit. A simple comment in the code giving credit to the FAQ would |
| 326 | be courteous but is not required. |