X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperluniintro.pod;h=86360d4a726753bd72b551eddac85f8ed4e2ec1a;hb=98af1e142028dcf116f32636ea54f4c3e9494651;hp=92a6569eeb19692a6dd84de8b8d75753a2751882;hpb=a02b5feb1739f020578122f08572c084a84f6335;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perluniintro.pod b/pod/perluniintro.pod index 92a6569..86360d4 100644 --- a/pod/perluniintro.pod +++ b/pod/perluniintro.pod @@ -19,6 +19,7 @@ including all commercially-important modern languages. All characters in the largest Chinese, Japanese, and Korean dictionaries are also encoded. The standards will eventually cover almost all characters in more than 250 writing systems and thousands of languages. +Unicode 1.0 was released in October 1991, and 4.0 in April 2003. A Unicode I is an abstract entity. It is not bound to any particular integer width, especially not to the C language C. @@ -33,11 +34,10 @@ case 0x0041 and 0x03B1, respectively. These unique numbers are called I. The Unicode standard prefers using hexadecimal notation for the code -points. If numbers like C<0x0041> are unfamiliar to -you, take a peek at a later section, L. -The Unicode standard uses the notation C, -to give the hexadecimal code point and the normative name of -the character. +points. If numbers like C<0x0041> are unfamiliar to you, take a peek +at a later section, L. The Unicode standard +uses the notation C, to give the +hexadecimal code point and the normative name of the character. Unicode also defines various I for the characters, like "uppercase" or "lowercase", "decimal digit", or "punctuation"; @@ -86,12 +86,13 @@ characters that do not represent true characters. A common myth about Unicode is that it would be "16-bit", that is, Unicode is only represented as C<0x10000> (or 65536) characters from -C<0x0000> to C<0xFFFF>. B Since Unicode 2.0, Unicode -has been defined all the way up to 21 bits (C<0x10FFFF>), and since -Unicode 3.1, characters have been defined beyond C<0xFFFF>. The first -C<0x10000> characters are called the I, or the I (BMP). With Unicode 3.1, 17 planes in all are -defined--but nowhere near full of defined characters, yet. +C<0x0000> to C<0xFFFF>. B Since Unicode 2.0 (July +1996), Unicode has been defined all the way up to 21 bits (C<0x10FFFF>), +and since Unicode 3.1 (March 2001), characters have been defined +beyond C<0xFFFF>. The first C<0x10000> characters are called the +I, or the I (BMP). With Unicode +3.1, 17 (yes, seventeen) planes in all were defined--but they are +nowhere near full of defined characters, yet. Another myth is that the 256-character blocks have something to do with languages--that each block would define the characters used @@ -104,13 +105,14 @@ so on. Scripts usually span varied parts of several blocks. For further information see L. The Unicode code points are just abstract numbers. To input and -output these abstract numbers, the numbers must be I somehow. -Unicode defines several I, of which I -is perhaps the most popular. UTF-8 is a variable length encoding that -encodes Unicode characters as 1 to 6 bytes (only 4 with the currently -defined characters). Other encodings include UTF-16 and UTF-32 and their -big- and little-endian variants (UTF-8 is byte-order independent) -The ISO/IEC 10646 defines the UCS-2 and UCS-4 encoding forms. +output these abstract numbers, the numbers must be I or +I somehow. Unicode defines several I, of which I is perhaps the most popular. UTF-8 is a +variable length encoding that encodes Unicode characters as 1 to 6 +bytes (only 4 with the currently defined characters). Other encodings +include UTF-16 and UTF-32 and their big- and little-endian variants +(UTF-8 is byte-order independent) The ISO/IEC 10646 defines the UCS-2 +and UCS-4 encoding forms. For more information about encodings--for instance, to learn what I and I (BOMs) are--see L. @@ -158,14 +160,14 @@ strings contain a character beyond 0x00FF. For example, - perl -e 'print "\x{DF}\n", "\x{0100}\x{DF}\n"' + perl -e 'print "\x{DF}\n", "\x{0100}\x{DF}\n"' produces a fairly useless mixture of native bytes and UTF-8, as well as a warning: Wide character in print at ... -To output UTF-8, use the C<:utf8> output layer. Prepending +To output UTF-8, use the C<:encoding> or C<:utf8> output layer. Prepending binmode(STDOUT, ":utf8"); @@ -244,16 +246,14 @@ Note that both C<\x{...}> and C<\N{...}> are compile-time string constants: you cannot use variables in them. if you want similar run-time functionality, use C and C. -Also note that if all the code points for pack "U" are below 0x100, -bytes will be generated, just like if you were using C. - - my $bytes = pack("U*", 0x80, 0xFF); - If you want to force the result to Unicode characters, use the special -C<"U0"> prefix. It consumes no arguments but forces the result to be -in Unicode characters, instead of bytes. +C<"U0"> prefix. It consumes no arguments but causes the following bytes +to be interpreted as the UTF-8 encoding of Unicode characters: - my $chars = pack("U0U*", 0x80, 0xFF); + my $chars = pack("U0W*", 0x80, 0x42); + +Likewise, you can stop such UTF-8 interpretation by using the special +C<"C0"> prefix. =head2 Handling Unicode @@ -263,7 +263,7 @@ C will work on the Unicode characters; regular expressions will work on the Unicode characters (see L and L). Note that Perl considers combining character sequences to be -characters, so for example +separate characters, so for example use charnames ':full'; print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"), "\n"; @@ -278,27 +278,13 @@ encodings, I/O, and certain special cases: When you combine legacy data and Unicode the legacy data needs to be upgraded to Unicode. Normally ISO 8859-1 (or EBCDIC, if -applicable) is assumed. You can override this assumption by -using the C pragma, for example - - use encoding 'latin2'; # ISO 8859-2 - -in which case literals (string or regular expressions), C, -and C in your whole script are assumed to produce Unicode -characters from ISO 8859-2 code points. Note that the matching for -encoding names is forgiving: instead of C you could have -said C, or C, or other variations. With just - - use encoding; - -the environment variable C will be consulted. -If that variable isn't set, the encoding pragma will fail. +applicable) is assumed. The C module knows about many encodings and has interfaces for doing conversions between those encodings: - use Encode 'from_to'; - from_to($data, "iso-8859-3", "utf-8"); # from legacy to utf-8 + use Encode 'decode'; + $data = decode("iso-8859-3", $data); # convert from legacy to utf-8 =head2 Unicode I/O @@ -331,7 +317,9 @@ and on already open streams, use C: The matching of encoding names is loose: case does not matter, and many encodings have several aliases. Note that the C<:utf8> layer must always be specified exactly like that; it is I subject to -the loose matching of encoding names. +the loose matching of encoding names. Also note that C<:utf8> is unsafe for +input, because it accepts the data without validating that it is indeed valid +UTF8. See L for the C<:utf8> layer, L and L for the C<:encoding()> layer, and @@ -343,7 +331,7 @@ Unicode or legacy encodings does not magically turn the data into Unicode in Perl's eyes. To do that, specify the appropriate layer when opening files - open(my $fh,'<:utf8', 'anything'); + open(my $fh,'<:encoding(utf8)', 'anything'); my $line_of_unicode = <$fh>; open(my $fh,'<:encoding(Big5)', 'anything'); @@ -352,7 +340,7 @@ layer when opening files The I/O layers can also be specified more flexibly with the C pragma. See L, or look at the following example. - use open ':utf8'; # input and output default layer will be UTF-8 + use open ':encoding(utf8)'; # input/output default encoding will be UTF-8 open X, ">file"; print X chr(0x100), "\n"; close X; @@ -372,11 +360,6 @@ With the C pragma you can use the C<:locale> layer printf "%#x\n", ord(), "\n"; # this should print 0xc1 close I; -or you can also use the C<':encoding(...)'> layer - - open(my $epic,'<:encoding(iso-8859-7)','iliad.greek'); - my $line_of_unicode = <$epic>; - These methods install a transparent filter on the I/O stream that converts data from the specified encoding when it is read in from the stream. The result is always Unicode. @@ -404,8 +387,8 @@ the file "text.utf8", encoded as UTF-8: while (<$nihongo>) { print $unicode $_ } The naming of encodings, both by the C and by the C -pragma, is similar to the C pragma in that it allows for -flexible names: C and C will both be understood. +pragma allows for flexible names: C and C will both be +understood. Common encodings recognized by ISO, MIME, IANA, and various other standardisation organisations are recognised; for a more detailed @@ -425,13 +408,13 @@ by repeatedly encoding the data: local $/; ## read in the whole file of 8-bit characters $t = ; close F; - open F, ">:utf8", "file"; + open F, ">:encoding(utf8)", "file"; print F $t; ## convert to UTF-8 on output close F; If you run this code twice, the contents of the F will be twice -UTF-8 encoded. A C would have avoided the bug, or -explicitly opening also the F for input as UTF-8. +UTF-8 encoded. A C would have avoided the +bug, or explicitly opening also the F for input as UTF-8. B: the C<:utf8> and C<:encoding> features work only if your Perl has been built with the new PerlIO feature (which is the default @@ -452,7 +435,7 @@ displayed as C<\x..>, and the rest of the characters as themselves: chr($_) =~ /[[:cntrl:]]/ ? # else if control character ... sprintf("\\x%02X", $_) : # \x.. quotemeta(chr($_)) # else quoted or as themselves - } unpack("U*", $_[0])); # unpack Unicode characters + } unpack("W*", $_[0])); # unpack Unicode characters } For example, @@ -492,17 +475,18 @@ explicitly-defined I/O layers). But if you must, there are two ways of looking behind the scenes. One way of peeking inside the internal encoding of Unicode characters -is to use C to get the bytes or C -to display the bytes: +is to use C to get the bytes of whatever the string +encoding happens to be, or C to get the bytes of the +UTF-8 encoding: # this prints c4 80 for the UTF-8 bytes 0xc4 0x80 - print join(" ", unpack("H*", pack("U", 0x100))), "\n"; + print join(" ", unpack("U0(H2)*", pack("U", 0x100))), "\n"; Yet another way would be to use the Devel::Peek module: perl -MDevel::Peek -e 'Dump(chr(0x100))' -That shows the UTF8 flag in FLAGS and both the UTF-8 bytes +That shows the C flag in FLAGS and both the UTF-8 bytes and Unicode characters in C. See also later in this document the discussion about the C function. @@ -530,8 +514,8 @@ CAPITAL LETTER As should be considered equal, or even As of any case. The long answer is that you need to consider character normalization and casing issues: see L, Unicode Technical Reports #15 and #21, I and I, http://www.unicode.org/unicode/reports/tr15/ and -http://www.unicode.org/unicode/reports/tr21/ +Mappings>, http://www.unicode.org/unicode/reports/tr15/ and +http://www.unicode.org/unicode/reports/tr21/ As of Perl 5.8.0, the "Full" case-folding of I is implemented. @@ -636,7 +620,7 @@ C<$string>. 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) UTF-8 encoded code points of the characters. Bytes added to an UTF-8 encoded string are -automatically upgraded to UTF-8. If mixed non-UTF8 and UTF-8 scalars +automatically upgraded to UTF-8. If mixed non-UTF-8 and UTF-8 scalars are merged (double-quoted interpolation, explicit concatenation, and printf/sprintf parameter substitution), the result will be UTF-8 encoded as if copies of the byte strings were upgraded to UTF-8: for example, @@ -668,22 +652,24 @@ How Do I Detect Data That's Not Valid In a Particular Encoding? Use the C package to try converting it. For example, - use Encode 'encode_utf8'; - if (encode_utf8($string_of_bytes_that_I_think_is_utf8)) { - # valid + use Encode 'decode_utf8'; + + if (eval { decode_utf8($string, Encode::FB_CROAK); 1 }) { + # $string is valid utf8 } else { - # invalid + # $string is not valid utf8 } -For UTF-8 only, you can use: +Or use C to try decoding it: use warnings; - @chars = unpack("U0U*", $string_of_bytes_that_I_think_is_utf8); + @chars = unpack("C0U*", $string_of_bytes_that_I_think_is_utf8); -If invalid, a C -warning is produced. The "U0" means "expect strictly UTF-8 encoded -Unicode". Without that the C would accept also -data like C), similarly to the C as we saw earlier. +If invalid, a C warning is produced. The "C0" means +"process the string character per character". Without that, the +C would work in C mode (the default if the format +string starts with C) and it would return the bytes making up the UTF-8 +encoding of the target string, something that will always work. =item * @@ -725,8 +711,8 @@ Back to converting data. If you have (or want) data in your system's native 8-bit encoding (e.g. Latin-1, EBCDIC, etc.), you can use pack/unpack to convert to/from Unicode. - $native_string = pack("C*", unpack("U*", $Unicode_string)); - $Unicode_string = pack("U*", unpack("C*", $native_string)); + $native_string = pack("W*", unpack("U*", $Unicode_string)); + $Unicode_string = pack("U*", unpack("W*", $native_string)); If you have a sequence of bytes you B is valid UTF-8, but Perl doesn't know it yet, you can make Perl a believer, too: @@ -734,6 +720,10 @@ but Perl doesn't know it yet, you can make Perl a believer, too: use Encode 'decode_utf8'; $Unicode = decode_utf8($bytes); +or: + + $Unicode = pack("U0a*", $bytes); + You can convert well-formed UTF-8 to a sequence of bytes, but if you just want to convert random binary data into UTF-8, you can't. B. You can @@ -752,7 +742,10 @@ http://www.cl.cam.ac.uk/~mgk25/unicode.html How Does Unicode Work With Traditional Locales? In Perl, not very well. Avoid using locales through the C -pragma. Use only one or the other. +pragma. Use only one or the other. But see L for the +description of the C<-C> switch and its environment counterpart, +C<$ENV{PERL_UNICODE}> to see how to enable various Unicode features, +for example by using locale settings. =back @@ -794,44 +787,44 @@ show a decimal number in hexadecimal. If you have just the Unicode Consortium - http://www.unicode.org/ +http://www.unicode.org/ =item * Unicode FAQ - http://www.unicode.org/unicode/faq/ +http://www.unicode.org/unicode/faq/ =item * Unicode Glossary - http://www.unicode.org/glossary/ +http://www.unicode.org/glossary/ =item * Unicode Useful Resources - http://www.unicode.org/unicode/onlinedat/resources.html +http://www.unicode.org/unicode/onlinedat/resources.html =item * Unicode and Multilingual Support in HTML, Fonts, Web Browsers and Other Applications - http://www.alanwood.net/unicode/ +http://www.alanwood.net/unicode/ =item * UTF-8 and Unicode FAQ for Unix/Linux - http://www.cl.cam.ac.uk/~mgk25/unicode.html +http://www.cl.cam.ac.uk/~mgk25/unicode.html =item * Legacy Character Sets - http://www.czyborra.com/ - http://www.eki.ee/letter/ +http://www.czyborra.com/ +http://www.eki.ee/letter/ =item * @@ -840,7 +833,7 @@ directory $Config{installprivlib}/unicore -in Perl 5.8.0 or newer, and +in Perl 5.8.0 or newer, and $Config{installprivlib}/unicode @@ -875,8 +868,9 @@ to UTF-8 bytes and back, the code works even with older Perl 5 versions. =head1 SEE ALSO -L, L, L, L, L, L, -L, L, L, L +L, L, L, L, L, L, +L, L, L, L, +L =head1 ACKNOWLEDGMENTS