perlfaq1.1

视频监控网络部分的协议ddns,的模块的实现代码,请大家大胆指正.

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See perlhist for a history of Perl revisions.
.Sh "What was Ponie?"
.IX Subsection "What was Ponie?"
(contributed by brian d foy)
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Ponie stands for \*(L"Perl On the New Internal Engine\*(R", started by Arthur
Bergman from Fotango in 2003, and subsequently run as a project of The
Perl Foundation. It was abandoned in 2006
( http://www.nntp.perl.org/group/perl.ponie.dev/487 ).
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Instead of using the current Perl internals, Ponie aimed to create a
new one that would provide a translation path from Perl 5 to Perl 6
(or anything else that targets Parrot, actually). You would have been
able  to just keep using Perl 5 with Parrot, the virtual machine which
will compile and run Perl 6 bytecode.
.Sh "What is Perl 6?"
.IX Subsection "What is Perl 6?"
At The Second O'Reilly Open Source Software Convention, Larry Wall
announced Perl 6 development would begin in earnest. Perl 6 was an oft
used term for Chip Salzenberg's project to rewrite Perl in \*(C+ named
Topaz. However, Topaz provided valuable insights to the next version
of Perl and its implementation, but was ultimately abandoned.
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If you want to learn more about Perl 6, or have a desire to help in
the crusade to make Perl a better place then peruse the Perl 6 developers
page at http://dev.perl.org/perl6/ and get involved.
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Perl 6 is not scheduled for release yet, and Perl 5 will still be supported
for quite awhile after its release. Do not wait for Perl 6 to do whatever
you need to do.
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\&\*(L"We're really serious about reinventing everything that needs reinventing.\*(R"
\&\-\-Larry Wall
.Sh "How stable is Perl?"
.IX Subsection "How stable is Perl?"
Production releases, which incorporate bug fixes and new functionality,
are widely tested before release.  Since the 5.000 release, we have
averaged only about one production release per year.
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Larry and the Perl development team occasionally make changes to the
internal core of the language, but all possible efforts are made toward
backward compatibility.  While not quite all Perl 4 scripts run flawlessly
under Perl 5, an update to perl should nearly never invalidate a program
written for an earlier version of perl (barring accidental bug fixes
and the rare new keyword).
.Sh "Is Perl difficult to learn?"
.IX Subsection "Is Perl difficult to learn?"
No, Perl is easy to start learning\*(--and easy to keep learning.  It looks
like most programming languages you're likely to have experience
with, so if you've ever written a C program, an awk script, a shell
script, or even a \s-1BASIC\s0 program, you're already partway there.
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Most tasks only require a small subset of the Perl language.  One of
the guiding mottos for Perl development is \*(L"there's more than one way
to do it\*(R" (\s-1TMTOWTDI\s0, sometimes pronounced \*(L"tim toady\*(R").  Perl's
learning curve is therefore shallow (easy to learn) and long (there's
a whole lot you can do if you really want).
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Finally, because Perl is frequently (but not always, and certainly not by
definition) an interpreted language, you can write your programs and test
them without an intermediate compilation step, allowing you to experiment
and test/debug quickly and easily.  This ease of experimentation flattens
the learning curve even more.
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Things that make Perl easier to learn: Unix experience, almost any kind
of programming experience, an understanding of regular expressions, and
the ability to understand other people's code.  If there's something you
need to do, then it's probably already been done, and a working example is
usually available for free.  Don't forget Perl modules, either.
They're discussed in Part 3 of this \s-1FAQ\s0, along with \s-1CPAN\s0, which is
discussed in Part 2.
.Sh "How does Perl compare with other languages like Java, Python, \s-1REXX\s0, Scheme, or Tcl?"
.IX Subsection "How does Perl compare with other languages like Java, Python, REXX, Scheme, or Tcl?"
Favorably in some areas, unfavorably in others.  Precisely which areas
are good and bad is often a personal choice, so asking this question
on Usenet runs a strong risk of starting an unproductive Holy War.
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Probably the best thing to do is try to write equivalent code to do a
set of tasks.  These languages have their own newsgroups in which you
can learn about (but hopefully not argue about) them.
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Some comparison documents can be found at http://www.perl.com/doc/FMTEYEWTK/versus/
if you really can't stop yourself.
.Sh "Can I do [task] in Perl?"
.IX Subsection "Can I do [task] in Perl?"
Perl is flexible and extensible enough for you to use on virtually any
task, from one-line file-processing tasks to large, elaborate systems.
For many people, Perl serves as a great replacement for shell scripting.
For others, it serves as a convenient, high-level replacement for most of
what they'd program in low-level languages like C or \*(C+.  It's ultimately
up to you (and possibly your management) which tasks you'll use Perl
for and which you won't.
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If you have a library that provides an \s-1API\s0, you can make any component
of it available as just another Perl function or variable using a Perl
extension written in C or \*(C+ and dynamically linked into your main
perl interpreter.  You can also go the other direction, and write your
main program in C or \*(C+, and then link in some Perl code on the fly,
to create a powerful application.  See perlembed.
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That said, there will always be small, focused, special-purpose
languages dedicated to a specific problem domain that are simply more
convenient for certain kinds of problems.  Perl tries to be all things
to all people, but nothing special to anyone.  Examples of specialized
languages that come to mind include prolog and matlab.
.Sh "When shouldn't I program in Perl?"
.IX Subsection "When shouldn't I program in Perl?"
When your manager forbids it\*(--but do consider replacing them :\-).
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Actually, one good reason is when you already have an existing
application written in another language that's all done (and done
well), or you have an application language specifically designed for a
certain task (e.g. prolog, make).
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For various reasons, Perl is probably not well-suited for real-time
embedded systems, low-level operating systems development work like
device drivers or context-switching code, complex multi-threaded
shared-memory applications, or extremely large applications.  You'll
notice that perl is not itself written in Perl.
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Perl remains fundamentally a dynamically typed language, not
a statically typed one.  You certainly won't be chastised if you don't
trust nuclear-plant or brain-surgery monitoring code to it.  And Larry
will sleep easier, too\*(--Wall Street programs not withstanding. :\-)
.ie n .Sh "What's the difference between ""perl"" and ""Perl""?"
.el .Sh "What's the difference between ``perl'' and ``Perl''?"
.IX Subsection "What's the difference between perl and Perl?"
One bit.  Oh, you weren't talking \s-1ASCII\s0? :\-) Larry now uses \*(L"Perl\*(R" to
signify the language proper and \*(L"perl\*(R" the implementation of it, i.e.
the current interpreter.  Hence Tom's quip that \*(L"Nothing but perl can
parse Perl.\*(R"
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Before the first edition of \fIProgramming perl\fR, people commonly
referred to the language as \*(L"perl\*(R", and its name appeared that way in
the title because it referred to the interpreter. In the book, Randal
Schwartz capitalised the language's name to make it stand out better
when typeset. This convention was adopted by the community, and the
second edition became \fIProgramming Perl\fR, using the capitalized
version of the name to refer to the language.
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You may or may not choose to follow this usage.  For example,
parallelism means \*(L"awk and perl\*(R" and \*(L"Python and Perl\*(R" look good, while
\&\*(L"awk and Perl\*(R" and \*(L"Python and perl\*(R" do not.  But never write \*(L"\s-1PERL\s0\*(R",
because perl is not an acronym, apocryphal folklore and post-facto
expansions notwithstanding.
.Sh "Is it a Perl program or a Perl script?"
.IX Subsection "Is it a Perl program or a Perl script?"
Larry doesn't really care.  He says (half in jest) that \*(L"a script is
what you give the actors.  A program is what you give the audience.\*(R"
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Originally, a script was a canned sequence of normally interactive
commands\*(--that is, a chat script.  Something like a \s-1UUCP\s0 or \s-1PPP\s0 chat
script or an expect script fits the bill nicely, as do configuration
scripts run by a program at its start up, such \fI.cshrc\fR or \fI.ircrc\fR,
for example.  Chat scripts were just drivers for existing programs,
not stand-alone programs in their own right.
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A computer scientist will correctly explain that all programs are
interpreted and that the only question is at what level.  But if you
ask this question of someone who isn't a computer scientist, they might
tell you that a \fIprogram\fR has been compiled to physical machine code
once and can then be run multiple times, whereas a \fIscript\fR must be
translated by a program each time it's used.
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Now that \*(L"script\*(R" and \*(L"scripting\*(R" are terms that have been seized by
unscrupulous or unknowing marketeers for their own nefarious purposes,
they have begun to take on strange and often pejorative meanings,
like \*(L"non serious\*(R" or \*(L"not real programming\*(R".  Consequently, some Perl
programmers prefer to avoid them altogether.
.Sh "What is a \s-1JAPH\s0?"
.IX Subsection "What is a JAPH?"
(contributed by brian d foy)
.PP
\&\s-1JAPH\s0 stands for \*(L"Just another Perl hacker,\*(R", which Randal Schwartz used
to sign email and usenet messages starting in the late 1980s. He
previously used the phrase with many subjects (\*(L"Just another x hacker,\*(R"),
so to distinguish his \s-1JAPH\s0, he started to write them as Perl programs:
.PP
.Vb 1
\&        print "Just another Perl hacker, ";
.Ve
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Note the trailing comma and space, which allows the addition of other
JAxH clauses for his many other interests.
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Other people picked up on this and started to write clever or obfuscated
programs to produce the same output, spinning things quickly out of
control while still providing hours of amusement for their creators and
readers.
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\&\s-1CPAN\s0 has several \s-1JAPH\s0 programs at http://www.cpan.org/misc/japh .
.Sh "Where can I get a list of Larry Wall witticisms?"
.IX Subsection "Where can I get a list of Larry Wall witticisms?"
(contributed by brian d foy)
.PP
Google \*(L"larry wall quotes\*(R"! You might even try the \*(L"I feel lucky\*(R" button.
:)
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Wikiquote has the witticisms from Larry along with their source,
including his usenet postings and source code comments.
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If you want a plain text file, try
http://www.cpan.org/misc/lwall\-quotes.txt.gz .
.Sh "How can I convince others to use Perl?"
.IX Subsection "How can I convince others to use Perl?"
(contributed by brian d foy)
.PP
Appeal to their self interest! If Perl is new (and thus scary) to them,
find something that Perl can do to solve one of their problems. That
might mean that Perl either saves them something (time, headaches, money)
or gives them something (flexibility, power, testability).
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In general, the benefit of a language is closely related to the skill of
the people using that language. If you or your team can be more faster,
better, and stronger through Perl, you'll deliver more value. Remember,
people often respond better to what they get out of it. If you run
into resistance, figure out what those people get out of the other
choice and how Perl might satisfy that requirement.
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You don't have to worry about finding or paying for Perl; it's freely
available and several popular operating systems come with Perl. Community
support in places such as Perlmonks ( http://www.perlmonks.com )
and the various Perl mailing lists ( http://lists.perl.org ) means that
you can usually get quick answers to your problems.
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Finally, keep in mind that Perl might not be the right tool for every
job. You're a much better advocate if your claims are reasonable and
grounded in reality. Dogmatically advocating anything tends to make
people discount your message. Be honest about possible disadvantages
to your choice of Perl since any choice has trade-offs.
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You might find these links useful:
.IP "\(bu" 4
http://perltraining.com.au/whyperl.html
.IP "\(bu" 4
http://www.perl.org/advocacy/whyperl.html
.SH "REVISION"
.IX Header "REVISION"
Revision: \f(CW$Revision:\fR 10427 $
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Date: \f(CW$Date:\fR 2007\-12\-14 00:39:01 +0100 (Fri, 14 Dec 2007) $
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See perlfaq for source control details and availability.
.SH "AUTHOR AND COPYRIGHT"
.IX Header "AUTHOR AND COPYRIGHT"
Copyright (c) 1997\-2007 Tom Christiansen, Nathan Torkington, and
other authors as noted. All rights reserved.
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This documentation is free; you can redistribute it and/or modify it
under the same terms as Perl itself.
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Irrespective of its distribution, all code examples here are in the public
domain.  You are permitted and encouraged to use this code and any
derivatives thereof in your own programs for fun or for profit as you
see fit.  A simple comment in the code giving credit to the \s-1FAQ\s0 would
be courteous but is not required.