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   1  =head1 NAME
   2  
   3  perlfaq1 - General Questions About Perl ($Revision: 10427 $)
   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 the archives at
  39  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/
  40  and http://archive.develooper.com/perl5-porters@perl.org/
  41  or the news gateway nntp://nntp.perl.org/perl.perl5.porters or
  42  its web interface at http://nntp.perl.org/group/perl.perl5.porters ,
  43  or read the faq at http://dev.perl.org/perl5/docs/p5p-faq.html ,
  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
  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
  51  than GNU software's tend to be.
  52  
  53  You can get commercial support of Perl if you wish, although for most
  54  users the informal support will more than suffice.  See the answer to
  55  "Where can I buy a commercial version of perl?" for more information.
  56  
  57  =head2 Which version of Perl should I use?
  58  
  59  (contributed by brian d foy)
  60  
  61  There is often a matter of opinion and taste, and there isn't any one
  62  answer that fits anyone.  In general, you want to use either the current
  63  stable release, or the stable release immediately prior to that one.
  64  Currently, those are perl5.10.x and perl5.8.x, respectively.
  65  
  66  Beyond that, you have to consider several things and decide which is best
  67  for you.
  68  
  69  =over 4
  70  
  71  =item *
  72  
  73  If things aren't broken, upgrading perl may break them (or at least issue
  74  new warnings).
  75  
  76  =item *
  77  
  78  The latest versions of perl have more bug fixes.
  79  
  80  =item *
  81  
  82  The Perl community is geared toward supporting the most recent releases,
  83  so you'll have an easier time finding help for those.
  84  
  85  =item *
  86  
  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 ).
  90  
  91  =item *
  92  
  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.
  96  
  97  =item *
  98  
  99  The immediate, previous releases (i.e. perl5.8.x ) are usually maintained
 100  for a while, although not at the same level as the current releases.
 101  
 102  =item *
 103  
 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
 106  as its whitewashed bones have fractured or eroded.
 107  
 108  =item *
 109  
 110  There is no Perl 6 release scheduled, but it will be available when 
 111  it's ready.  Stay tuned, but don't worry that you'll have to change 
 112  major versions of Perl; no one is going to take Perl 5 away from you.
 113  
 114  =item *
 115  
 116  There are really two tracks of perl development: a maintenance version
 117  and an experimental version.  The maintenance versions are stable, and
 118  have an even number as the minor release (i.e. perl5.10.x, where 10 is the
 119  minor release).  The experimental versions may include features that
 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).
 122  
 123  =back
 124  
 125  
 126  =head2 What are Perl 4, Perl 5, or Perl 6?
 127  
 128  (contributed by brian d foy)
 129  
 130  In short, Perl 4 is the past, Perl 5 is the present, and Perl 6 is the
 131  future.
 132  
 133  The number after perl (i.e. the 5 after Perl 5) is the major release
 134  of the perl interpreter as well as the version of the language.  Each
 135  major version has significant differences that earlier versions cannot
 136  support.
 137  
 138  The current major release of Perl is Perl 5, and was released in 1994.
 139  It can run scripts from the previous major release, Perl 4 (March 1991),
 140  but has significant differences. It introduced the concept of references,
 141  complex data structures, and modules.  The Perl 5 interpreter was a
 142  complete re-write of the previous perl sources.
 143  
 144  Perl 6 is the next major version of Perl, but it's still in development
 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
 147  latest versions of Perl 5, and some Perl 5 modules allow you to use some
 148  Perl 6 syntax in your programs.  You can learn more about Perl 6 at
 149  http://dev.perl.org/perl6/ .
 150  
 151  See L<perlhist> for a history of Perl revisions.
 152  
 153  =head2 What was Ponie?
 154  
 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
 159  Perl Foundation. It was abandoned in 2006
 160  ( http://www.nntp.perl.org/group/perl.ponie.dev/487 ).
 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.
 167  
 168  =head2 What is Perl 6?
 169  
 170  At The Second O'Reilly Open Source Software Convention, Larry Wall
 171  announced Perl 6 development would begin in earnest. Perl 6 was an oft
 172  used term for Chip Salzenberg's project to rewrite Perl in C++ named
 173  Topaz. However, Topaz provided valuable insights to the next version
 174  of Perl and its implementation, but was ultimately abandoned.
 175  
 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
 178  page at http://dev.perl.org/perl6/ and get involved.
 179  
 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
 182  you need to do.
 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,
 190  are widely tested before release.  Since the 5.000 release, we have
 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
 195  backward compatibility.  While not quite all Perl 4 scripts run flawlessly
 196  under Perl 5, an update to perl should nearly never invalidate a program
 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  
 202  No, Perl is easy to start learning--and easy to keep learning.  It looks
 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  
 207  Most tasks only require a small subset of the Perl language.  One of
 208  the guiding mottos for Perl development is "there's more than one way
 209  to do it" (TMTOWTDI, sometimes pronounced "tim toady").  Perl's
 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
 216  and test/debug quickly and easily.  This ease of experimentation flattens
 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
 221  the ability to understand other people's code.  If there's something you
 222  need to do, then it's probably already been done, and a working example is
 223  usually available for free.  Don't forget Perl modules, either.
 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  
 229  Favorably in some areas, unfavorably in others.  Precisely which areas
 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
 234  set of tasks.  These languages have their own newsgroups in which you
 235  can learn about (but hopefully not argue about) them.
 236  
 237  Some comparison documents can be found at http://www.perl.com/doc/FMTEYEWTK/versus/
 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
 246  what they'd program in low-level languages like C or C++.  It's ultimately
 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
 253  perl interpreter.  You can also go the other direction, and write your
 254  main program in C or C++, and then link in some Perl code on the fly,
 255  to create a powerful application.  See L<perlembed>.
 256  
 257  That said, there will always be small, focused, special-purpose
 258  languages dedicated to a specific problem domain that are simply more
 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
 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
 275  shared-memory applications, or extremely large applications.  You'll
 276  notice that perl is not itself written in Perl.
 277  
 278  Perl remains fundamentally a dynamically typed language, not
 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
 281  will sleep easier, too--Wall Street programs not withstanding. :-)
 282  
 283  =head2 What's the difference between "perl" and "Perl"?
 284  
 285  One bit.  Oh, you weren't talking ASCII? :-) Larry now uses "Perl" to
 286  signify the language proper and "perl" the implementation of it, i.e.
 287  the current interpreter.  Hence Tom's quip that "Nothing but perl can
 288  parse Perl."  
 289  
 290  Before the first edition of I<Programming perl>, people commonly
 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
 295  second edition became I<Programming Perl>, using the capitalized
 296  version of the name to refer to the language.
 297  
 298  You may or may not choose to follow this usage.  For example,
 299  parallelism means "awk and perl" and "Python and Perl" look good, while
 300  "awk and Perl" and "Python and perl" do not.  But never write "PERL",
 301  because perl is not an acronym, apocryphal folklore and post-facto
 302  expansions notwithstanding.
 303  
 304  =head2 Is it a Perl program or a Perl script?
 305  
 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."
 308  
 309  Originally, a script was a canned sequence of normally interactive
 310  commands--that is, a chat script.  Something like a UUCP or PPP chat
 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>,
 313  for example.  Chat scripts were just drivers for existing programs,
 314  not stand-alone programs in their own right.
 315  
 316  A computer scientist will correctly explain that all programs are
 317  interpreted and that the only question is at what level.  But if you
 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,
 326  like "non serious" or "not real programming".  Consequently, some Perl
 327  programmers prefer to avoid them altogether.
 328  
 329  =head2 What is a JAPH?
 330  
 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  
 338      print "Just another Perl hacker, ";
 339  
 340  Note the trailing comma and space, which allows the addition of other
 341  JAxH clauses for his many other interests.
 342  
 343  Other people picked up on this and started to write clever or obfuscated
 344  programs to produce the same output, spinning things quickly out of
 345  control while still providing hours of amusement for their creators and
 346  readers.
 347  
 348  CPAN has several JAPH programs at http://www.cpan.org/misc/japh .
 349  
 350  =head2 Where can I get a list of Larry Wall witticisms?
 351  
 352  (contributed by brian d foy)
 353  
 354  Google "larry wall quotes"! You might even try the "I feel lucky" button.
 355  :)
 356  
 357  Wikiquote has the witticisms from Larry along with their source,
 358  including his usenet postings and source code comments.
 359  
 360  If you want a plain text file, try
 361  http://www.cpan.org/misc/lwall-quotes.txt.gz .
 362  
 363  =head2 How can I convince others to use Perl?
 364  
 365  (contributed by brian d foy)
 366  
 367  Appeal to their self interest! If Perl is new (and thus scary) to them,
 368  find something that Perl can do to solve one of their problems. That
 369  might mean that Perl either saves them something (time, headaches, money)
 370  or gives them something (flexibility, power, testability).
 371  
 372  In general, the benefit of a language is closely related to the skill of
 373  the people using that language. If you or your team can be more faster,
 374  better, and stronger through Perl, you'll deliver more value. Remember,
 375  people often respond better to what they get out of it. If you run
 376  into resistance, figure out what those people get out of the other
 377  choice and how Perl might satisfy that requirement.
 378  
 379  You don't have to worry about finding or paying for Perl; it's freely
 380  available and several popular operating systems come with Perl. Community
 381  support in places such as Perlmonks ( http://www.perlmonks.com )
 382  and the various Perl mailing lists ( http://lists.perl.org ) means that
 383  you can usually get quick answers to your problems.
 384  
 385  Finally, keep in mind that Perl might not be the right tool for every
 386  job. You're a much better advocate if your claims are reasonable and
 387  grounded in reality. Dogmatically advocating anything tends to make
 388  people discount your message. Be honest about possible disadvantages
 389  to your choice of Perl since any choice has trade-offs.
 390  
 391  You might find these links useful:
 392  
 393  =over 4
 394  
 395  =item * http://perltraining.com.au/whyperl.html
 396  
 397  =item * http://www.perl.org/advocacy/whyperl.html
 398  
 399  =back
 400  
 401  =head1 REVISION
 402  
 403  Revision: $Revision: 10427 $
 404  
 405  Date: $Date: 2007-12-14 00:39:01 +0100 (Fri, 14 Dec 2007) $
 406  
 407  See L<perlfaq> for source control details and availability.
 408  
 409  =head1 AUTHOR AND COPYRIGHT
 410  
 411  Copyright (c) 1997-2007 Tom Christiansen, Nathan Torkington, and
 412  other authors as noted. All rights reserved.
 413  
 414  This documentation is free; you can redistribute it and/or modify it
 415  under the same terms as Perl itself.
 416  
 417  Irrespective of its distribution, all code examples here are in the public
 418  domain.  You are permitted and encouraged to use this code and any
 419  derivatives thereof in your own programs for fun or for profit as you
 420  see fit.  A simple comment in the code giving credit to the FAQ would
 421  be courteous but is not required.