perluniintro.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.

Mappings/SpecialCasing\fR is implemented.
.IP "\(bu" 4
String Collation
.Sp
People like to see their strings nicely sorted\*(--or as Unicode
parlance goes, collated.  But again, what do you mean by collate?
.Sp
(Does \f(CW\*(C`LATIN CAPITAL LETTER A WITH ACUTE\*(C'\fR come before or after
\&\f(CW\*(C`LATIN CAPITAL LETTER A WITH GRAVE\*(C'\fR?)
.Sp
The short answer is that by default, Perl compares strings (\f(CW\*(C`lt\*(C'\fR,
\&\f(CW\*(C`le\*(C'\fR, \f(CW\*(C`cmp\*(C'\fR, \f(CW\*(C`ge\*(C'\fR, \f(CW\*(C`gt\*(C'\fR) based only on the code points of the
characters.  In the above case, the answer is \*(L"after\*(R", since
\&\f(CW0x00C1\fR > \f(CW0x00C0\fR.
.Sp
The long answer is that \*(L"it depends\*(R", and a good answer cannot be
given without knowing (at the very least) the language context.
See Unicode::Collate, and \fIUnicode Collation Algorithm\fR
http://www.unicode.org/unicode/reports/tr10/
.Sh "Miscellaneous"
.IX Subsection "Miscellaneous"
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Character Ranges and Classes
.Sp
Character ranges in regular expression character classes (\f(CW\*(C`/[a\-z]/\*(C'\fR)
and in the \f(CW\*(C`tr///\*(C'\fR (also known as \f(CW\*(C`y///\*(C'\fR) operator are not magically
Unicode-aware.  What this means that \f(CW\*(C`[A\-Za\-z]\*(C'\fR will not magically start
to mean \*(L"all alphabetic letters\*(R"; not that it does mean that even for
8\-bit characters, you should be using \f(CW\*(C`/[[:alpha:]]/\*(C'\fR in that case.
.Sp
For specifying character classes like that in regular expressions,
you can use the various Unicode properties\*(--\f(CW\*(C`\epL\*(C'\fR, or perhaps
\&\f(CW\*(C`\ep{Alphabetic}\*(C'\fR, in this particular case.  You can use Unicode
code points as the end points of character ranges, but there is no
magic associated with specifying a certain range.  For further
information\*(--there are dozens of Unicode character classes\*(--see
perlunicode.
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String-To-Number Conversions
.Sp
Unicode does define several other decimal\*(--and numeric\*(--characters
besides the familiar 0 to 9, such as the Arabic and Indic digits.
Perl does not support string-to-number conversion for digits other
than \s-1ASCII\s0 0 to 9 (and \s-1ASCII\s0 a to f for hexadecimal).
.Sh "Questions With Answers"
.IX Subsection "Questions With Answers"
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Will My Old Scripts Break?
.Sp
Very probably not.  Unless you are generating Unicode characters
somehow, old behaviour should be preserved.  About the only behaviour
that has changed and which could start generating Unicode is the old
behaviour of \f(CW\*(C`chr()\*(C'\fR where supplying an argument more than 255
produced a character modulo 255.  \f(CW\*(C`chr(300)\*(C'\fR, for example, was equal
to \f(CW\*(C`chr(45)\*(C'\fR or \*(L"\-\*(R" (in \s-1ASCII\s0), now it is \s-1LATIN\s0 \s-1CAPITAL\s0 \s-1LETTER\s0 I \s-1WITH\s0
\&\s-1BREVE\s0.
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How Do I Make My Scripts Work With Unicode?
.Sp
Very little work should be needed since nothing changes until you
generate Unicode data.  The most important thing is getting input as
Unicode; for that, see the earlier I/O discussion.
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How Do I Know Whether My String Is In Unicode?
.Sp
You shouldn't care.  No, you really shouldn't.  No, really.  If you
have to care\*(--beyond the cases described above\*(--it means that we
didn't get the transparency of Unicode quite right.
.Sp
Okay, if you insist:
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.Vb 1
\&    print utf8::is_utf8($string) ? 1 : 0, "\en";
.Ve
.Sp
But note that this doesn't mean that any of the characters in the
string are necessary \s-1UTF\-8\s0 encoded, or that any of the characters have
code points greater than 0xFF (255) or even 0x80 (128), or that the
string has any characters at all.  All the \f(CW\*(C`is_utf8()\*(C'\fR does is to
return the value of the internal \*(L"utf8ness\*(R" flag attached to the
\&\f(CW$string\fR.  If the flag is off, the bytes in the scalar are interpreted
as a single byte encoding.  If the flag is on, the bytes in the scalar
are interpreted as the (multi-byte, variable-length) \s-1UTF\-8\s0 encoded code
points of the characters.  Bytes added to an \s-1UTF\-8\s0 encoded string are
automatically upgraded to \s-1UTF\-8\s0.  If mixed non\-UTF\-8 and \s-1UTF\-8\s0 scalars
are merged (double-quoted interpolation, explicit concatenation, and
printf/sprintf parameter substitution), the result will be \s-1UTF\-8\s0 encoded
as if copies of the byte strings were upgraded to \s-1UTF\-8:\s0 for example,
.Sp
.Vb 3
\&    $a = "ab\ex80c";
\&    $b = "\ex{100}";
\&    print "$a = $b\en";
.Ve
.Sp
the output string will be UTF\-8\-encoded \f(CW\*(C`ab\ex80c = \ex{100}\en\*(C'\fR, but
\&\f(CW$a\fR will stay byte-encoded.
.Sp
Sometimes you might really need to know the byte length of a string
instead of the character length. For that use either the
\&\f(CW\*(C`Encode::encode_utf8()\*(C'\fR function or the \f(CW\*(C`bytes\*(C'\fR pragma and its only
defined function \f(CW\*(C`length()\*(C'\fR:
.Sp
.Vb 7
\&    my $unicode = chr(0x100);
\&    print length($unicode), "\en"; # will print 1
\&    require Encode;
\&    print length(Encode::encode_utf8($unicode)), "\en"; # will print 2
\&    use bytes;
\&    print length($unicode), "\en"; # will also print 2
\&                                  # (the 0xC4 0x80 of the UTF\-8)
.Ve
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How Do I Detect Data That's Not Valid In a Particular Encoding?
.Sp
Use the \f(CW\*(C`Encode\*(C'\fR package to try converting it.
For example,
.Sp
.Vb 7
\&    use Encode \*(Aqdecode_utf8\*(Aq;
\&    eval { decode_utf8($string, Encode::FB_CROAK) };
\&    if ($@) {
\&        # $string is valid utf8
\&    } else {
\&        # $string is not valid utf8
\&    }
.Ve
.Sp
Or use \f(CW\*(C`unpack\*(C'\fR to try decoding it:
.Sp
.Vb 2
\&    use warnings;
\&    @chars = unpack("C0U*", $string_of_bytes_that_I_think_is_utf8);
.Ve
.Sp
If invalid, a \f(CW\*(C`Malformed UTF\-8 character\*(C'\fR warning is produced. The \*(L"C0\*(R" means
\&\*(L"process the string character per character\*(R".  Without that, the
\&\f(CW\*(C`unpack("U*", ...)\*(C'\fR would work in \f(CW\*(C`U0\*(C'\fR mode (the default if the format
string starts with \f(CW\*(C`U\*(C'\fR) and it would return the bytes making up the \s-1UTF\-8\s0
encoding of the target string, something that will always work.
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How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa?
.Sp
This probably isn't as useful as you might think.
Normally, you shouldn't need to.
.Sp
In one sense, what you are asking doesn't make much sense: encodings
are for characters, and binary data are not \*(L"characters\*(R", so converting
\&\*(L"data\*(R" into some encoding isn't meaningful unless you know in what
character set and encoding the binary data is in, in which case it's
not just binary data, now is it?
.Sp
If you have a raw sequence of bytes that you know should be
interpreted via a particular encoding, you can use \f(CW\*(C`Encode\*(C'\fR:
.Sp
.Vb 2
\&    use Encode \*(Aqfrom_to\*(Aq;
\&    from_to($data, "iso\-8859\-1", "utf\-8"); # from latin\-1 to utf\-8
.Ve
.Sp
The call to \f(CW\*(C`from_to()\*(C'\fR changes the bytes in \f(CW$data\fR, but nothing
material about the nature of the string has changed as far as Perl is
concerned.  Both before and after the call, the string \f(CW$data\fR
contains just a bunch of 8\-bit bytes. As far as Perl is concerned,
the encoding of the string remains as \*(L"system-native 8\-bit bytes\*(R".
.Sp
You might relate this to a fictional 'Translate' module:
.Sp
.Vb 4
\&   use Translate;
\&   my $phrase = "Yes";
\&   Translate::from_to($phrase, \*(Aqenglish\*(Aq, \*(Aqdeutsch\*(Aq);
\&   ## phrase now contains "Ja"
.Ve
.Sp
The contents of the string changes, but not the nature of the string.
Perl doesn't know any more after the call than before that the
contents of the string indicates the affirmative.
.Sp
Back to converting data.  If you have (or want) data in your system's
native 8\-bit encoding (e.g. Latin\-1, \s-1EBCDIC\s0, etc.), you can use
pack/unpack to convert to/from Unicode.
.Sp
.Vb 2
\&    $native_string  = pack("W*", unpack("U*", $Unicode_string));
\&    $Unicode_string = pack("U*", unpack("W*", $native_string));
.Ve
.Sp
If you have a sequence of bytes you \fBknow\fR is valid \s-1UTF\-8\s0,
but Perl doesn't know it yet, you can make Perl a believer, too:
.Sp
.Vb 2
\&    use Encode \*(Aqdecode_utf8\*(Aq;
\&    $Unicode = decode_utf8($bytes);
.Ve
.Sp
or:
.Sp
.Vb 1
\&    $Unicode = pack("U0a*", $bytes);
.Ve
.Sp
You can convert well-formed \s-1UTF\-8\s0 to a sequence of bytes, but if
you just want to convert random binary data into \s-1UTF\-8\s0, you can't.
\&\fBAny random collection of bytes isn't well-formed \s-1UTF\-8\s0\fR.  You can
use \f(CW\*(C`unpack("C*", $string)\*(C'\fR for the former, and you can create
well-formed Unicode data by \f(CW\*(C`pack("U*", 0xff, ...)\*(C'\fR.
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How Do I Display Unicode?  How Do I Input Unicode?
.Sp
See http://www.alanwood.net/unicode/ and
http://www.cl.cam.ac.uk/~mgk25/unicode.html
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How Does Unicode Work With Traditional Locales?
.Sp
In Perl, not very well.  Avoid using locales through the \f(CW\*(C`locale\*(C'\fR
pragma.  Use only one or the other.  But see perlrun for the
description of the \f(CW\*(C`\-C\*(C'\fR switch and its environment counterpart,
\&\f(CW$ENV{PERL_UNICODE}\fR to see how to enable various Unicode features,
for example by using locale settings.
.Sh "Hexadecimal Notation"
.IX Subsection "Hexadecimal Notation"
The Unicode standard prefers using hexadecimal notation because
that more clearly shows the division of Unicode into blocks of 256 characters.
Hexadecimal is also simply shorter than decimal.  You can use decimal
notation, too, but learning to use hexadecimal just makes life easier
with the Unicode standard.  The \f(CW\*(C`U+HHHH\*(C'\fR notation uses hexadecimal,
for example.
.PP
The \f(CW\*(C`0x\*(C'\fR prefix means a hexadecimal number, the digits are 0\-9 \fIand\fR
a\-f (or A\-F, case doesn't matter).  Each hexadecimal digit represents
four bits, or half a byte.  \f(CW\*(C`print 0x..., "\en"\*(C'\fR will show a
hexadecimal number in decimal, and \f(CW\*(C`printf "%x\en", $decimal\*(C'\fR will
show a decimal number in hexadecimal.  If you have just the
\&\*(L"hex digits\*(R" of a hexadecimal number, you can use the \f(CW\*(C`hex()\*(C'\fR function.
.PP
.Vb 6
\&    print 0x0009, "\en";    # 9
\&    print 0x000a, "\en";    # 10
\&    print 0x000f, "\en";    # 15
\&    print 0x0010, "\en";    # 16
\&    print 0x0011, "\en";    # 17
\&    print 0x0100, "\en";    # 256
\&
\&    print 0x0041, "\en";    # 65
\&
\&    printf "%x\en",  65;    # 41
\&    printf "%#x\en", 65;    # 0x41
\&
\&    print hex("41"), "\en"; # 65
.Ve
.Sh "Further Resources"
.IX Subsection "Further Resources"
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Unicode Consortium
.Sp
http://www.unicode.org/
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Unicode \s-1FAQ\s0
.Sp
http://www.unicode.org/unicode/faq/
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Unicode Glossary
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http://www.unicode.org/glossary/
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Unicode Useful Resources
.Sp
http://www.unicode.org/unicode/onlinedat/resources.html
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Unicode and Multilingual Support in \s-1HTML\s0, Fonts, Web Browsers and Other Applications
.Sp
http://www.alanwood.net/unicode/
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\&\s-1UTF\-8\s0 and Unicode \s-1FAQ\s0 for Unix/Linux
.Sp
http://www.cl.cam.ac.uk/~mgk25/unicode.html
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Legacy Character Sets
.Sp
http://www.czyborra.com/
http://www.eki.ee/letter/
.IP "\(bu" 4
The Unicode support files live within the Perl installation in the
directory
.Sp
.Vb 1
\&    $Config{installprivlib}/unicore
.Ve
.Sp
in Perl 5.8.0 or newer, and
.Sp
.Vb 1
\&    $Config{installprivlib}/unicode
.Ve
.Sp
in the Perl 5.6 series.  (The renaming to \fIlib/unicore\fR was done to
avoid naming conflicts with lib/Unicode in case-insensitive filesystems.)
The main Unicode data file is \fIUnicodeData.txt\fR (or \fIUnicode.301\fR in
Perl 5.6.1.)  You can find the \f(CW$Config{installprivlib}\fR by
.Sp
.Vb 1
\&    perl "\-V:installprivlib"
.Ve
.Sp
You can explore various information from the Unicode data files using
the \f(CW\*(C`Unicode::UCD\*(C'\fR module.
.SH "UNICODE IN OLDER PERLS"
.IX Header "UNICODE IN OLDER PERLS"
If you cannot upgrade your Perl to 5.8.0 or later, you can still
do some Unicode processing by using the modules \f(CW\*(C`Unicode::String\*(C'\fR,
\&\f(CW\*(C`Unicode::Map8\*(C'\fR, and \f(CW\*(C`Unicode::Map\*(C'\fR, available from \s-1CPAN\s0.
If you have the \s-1GNU\s0 recode installed, you can also use the
Perl front-end \f(CW\*(C`Convert::Recode\*(C'\fR for character conversions.
.PP
The following are fast conversions from \s-1ISO\s0 8859\-1 (Latin\-1) bytes
to \s-1UTF\-8\s0 bytes and back, the code works even with older Perl 5 versions.
.PP
.Vb 2
\&    # ISO 8859\-1 to UTF\-8
\&    s/([\ex80\-\exFF])/chr(0xC0|ord($1)>>6).chr(0x80|ord($1)&0x3F)/eg;
\&
\&    # UTF\-8 to ISO 8859\-1
\&    s/([\exC2\exC3])([\ex80\-\exBF])/chr(ord($1)<<6&0xC0|ord($2)&0x3F)/eg;
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
perlunitut, perlunicode, Encode, open, utf8, bytes,
perlretut, perlrun, Unicode::Collate, Unicode::Normalize,
Unicode::UCD
.SH "ACKNOWLEDGMENTS"
.IX Header "ACKNOWLEDGMENTS"
Thanks to the kind readers of the perl5\[e-mail],
perl\[e-mail], linux\[e-mail], and [e-mail]
mailing lists for their valuable feedback.
.SH "AUTHOR, COPYRIGHT, AND LICENSE"
.IX Header "AUTHOR, COPYRIGHT, AND LICENSE"
Copyright 2001\-2002 Jarkko Hietaniemi <[e-mail]>
.PP
This document may be distributed under the same terms as Perl itself.