X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperluniintro.pod;h=54ce2f0a1c6803ded1e19378fa015f2a14775736;hb=9e5bbba0de25c01ae9355c7a97e237602a37e9f3;hp=92a6569eeb19692a6dd84de8b8d75753a2751882;hpb=a02b5feb1739f020578122f08572c084a84f6335;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perluniintro.pod b/pod/perluniintro.pod index 92a6569..54ce2f0 100644 --- a/pod/perluniintro.pod +++ b/pod/perluniintro.pod @@ -19,11 +19,12 @@ 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. Unicode is language-neutral and display-neutral: it does not encode the -language of the text and it does not define fonts or other graphical +language of the text, and it does not generally define fonts or other graphical layout details. Unicode operates on characters and on text built from those characters. @@ -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"; @@ -45,25 +45,29 @@ these properties are independent of the names of the characters. Furthermore, various operations on the characters like uppercasing, lowercasing, and collating (sorting) are defined. -A Unicode character consists either of a single code point, or a -I (like C), followed by one or -more I (like C). This sequence of +A Unicode I "character" can actually consist of more than one internal +I "character" or code point. For Western languages, this is adequately +modelled by a I (like C) followed +by one or more I (like C). This sequence of base character and modifiers is called a I. - -Whether to call these combining character sequences "characters" -depends on your point of view. If you are a programmer, you probably -would tend towards seeing each element in the sequences as one unit, -or "character". The whole sequence could be seen as one "character", -however, from the user's point of view, since that's probably what it -looks like in the context of the user's language. +sequence>. Some non-western languages require more complicated +models, so Unicode created the I concept, and then the +I. For example, a Korean Hangul syllable is +considered a single logical character, but most often consists of three actual +Unicode characters: a leading consonant followed by an interior vowel followed +by a trailing consonant. + +Whether to call these extended grapheme clusters "characters" depends on your +point of view. If you are a programmer, you probably would tend towards seeing +each element in the sequences as one unit, or "character". The whole sequence +could be seen as one "character", however, from the user's point of view, since +that's probably what it looks like in the context of the user's language. With this "whole sequence" view of characters, the total number of characters is open-ended. But in the programmer's "one unit is one character" point of view, the concept of "characters" is more -deterministic. In this document, we take that second point of view: -one "character" is one Unicode code point, be it a base character or -a combining character. +deterministic. In this document, we take that second point of view: +one "character" is one Unicode code point. For some combinations, there are I characters. C, for example, is defined as @@ -84,33 +88,35 @@ character. Firstly, there are unallocated code points within otherwise used blocks. Secondly, there are special Unicode control characters that do not represent true characters. -A common myth about Unicode is that it would be "16-bit", that is, +A common myth about Unicode is that it is "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. - -Another myth is that the 256-character blocks have something to +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 about Unicode blocks--that they have something to do with languages--that each block would define the characters used by a language or a set of languages. B The division into blocks exists, but it is almost completely accidental--an artifact of how the characters have been and -still are allocated. Instead, there is a concept called I, -which is more useful: there is C script, C script, and -so on. Scripts usually span varied parts of several blocks. -For further information see L. +still are allocated. Instead, there is a concept called I, which is +more useful: there is C script, C script, and so on. Scripts +usually span varied parts of several blocks. For more information about +scripts, 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. 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. @@ -123,8 +129,7 @@ serious Unicode work. The maintenance release 5.6.1 fixed many of the problems of the initial Unicode implementation, but for example regular expressions still do not work with Unicode in 5.6.1. -B is no longer -necessary.> In earlier releases the C pragma was used to declare +B is needed only in much more restricted circumstances.> In earlier releases the C pragma was used to declare that operations in the current block or file would be Unicode-aware. This model was found to be wrong, or at least clumsy: the "Unicodeness" is now carried with the data, instead of being attached to the @@ -139,8 +144,8 @@ scripts with legacy 8-bit data in them would break. See L. Perl supports both pre-5.6 strings of eight-bit native bytes, and strings of Unicode characters. The principle is that Perl tries to keep its data as eight-bit bytes for as long as possible, but as soon -as Unicodeness cannot be avoided, the data is transparently upgraded -to Unicode. +as Unicodeness cannot be avoided, the data is (mostly) transparently upgraded +to Unicode. There are some problems--see L. Internally, Perl currently uses either whatever the native eight-bit character set of the platform (for example Latin-1) is, defaulting to @@ -150,22 +155,22 @@ character set. Otherwise, it uses UTF-8. A user of Perl does not normally need to know nor care how Perl happens to encode its internal strings, but it becomes relevant when -outputting Unicode strings to a stream without a PerlIO layer -- one with -the "default" encoding. In such a case, the raw bytes used internally +outputting Unicode strings to a stream without a PerlIO layer (one with +the "default" encoding). In such a case, the raw bytes used internally (the native character set or UTF-8, as appropriate for each string) will be used, and a "Wide character" warning will be issued if those 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"); @@ -191,11 +196,12 @@ C. Perl 5.8.0 also supports Unicode on EBCDIC platforms. There, Unicode support is somewhat more complex to implement since -additional conversions are needed at every step. Some problems -remain, see L for details. +additional conversions are needed at every step. + +Later Perl releases have added code that will not work on EBCDIC platforms, and +no one has complained, so the divergence has continued. If you want to run +Perl on an EBCDIC platform, send email to perlbug@perl.org -In any case, the Unicode support on EBCDIC platforms is better than -in the 5.6 series, which didn't work much at all for EBCDIC platform. On EBCDIC platforms, the internal Unicode encoding form is UTF-EBCDIC instead of UTF-8. The difference is that as UTF-8 is "ASCII-safe" in that ASCII characters encode to UTF-8 as-is, while UTF-EBCDIC is @@ -244,16 +250,14 @@ 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("U0W*", 0x80, 0x42); - my $chars = pack("U0U*", 0x80, 0xFF); +Likewise, you can stop such UTF-8 interpretation by using the special +C<"C0"> prefix. =head2 Handling Unicode @@ -262,14 +266,14 @@ strings as usual. Functions like C, C, and C will work on the Unicode characters; regular expressions will work on the Unicode characters (see L and L). -Note that Perl considers combining character sequences to be -characters, so for example +Note that Perl considers grapheme clusters to be separate characters, so for +example use charnames ':full'; print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"), "\n"; will print 2, not 1. The only exception is that regular expressions -have C<\X> for matching a combining character sequence. +have C<\X> for matching an extended grapheme cluster. Life is not quite so transparent, however, when working with legacy encodings, I/O, and certain special cases: @@ -278,27 +282,13 @@ encodings, I/O, and certain special cases: When you combine legacy data and Unicode the legacy data needs to be upgraded to Unicode. Normally ISO 8859-1 (or EBCDIC, if -applicable) is assumed. You can override this assumption by -using the C pragma, for example - - use encoding 'latin2'; # ISO 8859-2 - -in which case literals (string or regular expressions), C, -and C in your whole script are assumed to produce Unicode -characters from ISO 8859-2 code points. Note that the matching for -encoding names is forgiving: instead of C you could have -said C, or C, or other variations. With just - - use encoding; - -the environment variable C will be consulted. -If that variable isn't set, the encoding pragma will fail. +applicable) is assumed. The C module knows about many encodings and has interfaces for doing conversions between those encodings: - use Encode 'from_to'; - from_to($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 +321,9 @@ 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 +335,7 @@ 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 +344,8 @@ 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; @@ -363,7 +356,8 @@ the C pragma. See L, or look at the following example. With the C pragma you can use the C<:locale> layer BEGIN { $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R' } - # the :locale will probe the locale environment variables like LC_ALL + # the :locale will probe the locale environment variables like + # LC_ALL use open OUT => ':locale'; # russki parusski open(O, ">koi8"); print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1 @@ -372,11 +366,6 @@ 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 +393,8 @@ 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 +414,13 @@ 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 @@ -445,14 +434,14 @@ its argument so that Unicode characters with code points greater than 255 are displayed as C<\x{...}>, control characters (like C<\n>) are displayed as C<\x..>, and the rest of the characters as themselves: - sub nice_string { - join("", - map { $_ > 255 ? # if wide character... - sprintf("\\x{%04X}", $_) : # \x{...} - chr($_) =~ /[[:cntrl:]]/ ? # else if control character ... - sprintf("\\x%02X", $_) : # \x.. - quotemeta(chr($_)) # else quoted or as themselves - } unpack("U*", $_[0])); # unpack Unicode characters + sub nice_string { + join("", + map { $_ > 255 ? # if wide character... + sprintf("\\x{%04X}", $_) : # \x{...} + chr($_) =~ /[[:cntrl:]]/ ? # else if control character ... + sprintf("\\x%02X", $_) : # \x.. + quotemeta(chr($_)) # else quoted or as themselves + } unpack("W*", $_[0])); # unpack Unicode characters } For example, @@ -492,17 +481,18 @@ 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. @@ -528,13 +518,12 @@ case, the answer is no (because 0x00C1 != 0x0041). But sometimes, any 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/ +and casing issues: see L, Unicode Technical Report #15, +L and +sections on case mapping in the L. As of Perl 5.8.0, the "Full" case-folding of I is implemented. +Mappings/SpecialCasing> is implemented, but bugs remain in C with them. =item * @@ -554,7 +543,7 @@ C<0x00C1> > C<0x00C0>. The long answer is that "it depends", and a good answer cannot be given without knowing (at the very least) the language context. See L, and I -http://www.unicode.org/unicode/reports/tr10/ +L =back @@ -566,19 +555,19 @@ http://www.unicode.org/unicode/reports/tr10/ Character Ranges and Classes -Character ranges in regular expression character classes (C) -and in the C (also known as C) operator are not magically -Unicode-aware. What this means that C<[A-Za-z]> will not magically start -to mean "all alphabetic letters"; not that it does mean that even for -8-bit characters, you should be using C in that case. +Character ranges in regular expression bracketed character classes ( e.g., +C) and in the C (also known as C) operator are not +magically Unicode-aware. What this means is that C<[A-Za-z]> will not +magically start to mean "all alphabetic letters" (not that it does mean that +even for 8-bit characters; for those, if you are using locales (L), +use C; and if not, use the 8-bit-aware property C<\p{alpha}>). + +All the properties that begin with C<\p> (and its inverse C<\P>) are actually +character classes that are Unicode-aware. There are dozens of them, see +L. -For specifying character classes like that in regular expressions, -you can use the various Unicode properties--C<\pL>, or perhaps -C<\p{Alphabetic}>, 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 -L. +You can use Unicode code points as the end points of character ranges, and the +range will include all Unicode code points that lie between those end points. =item * @@ -619,11 +608,12 @@ Unicode; for that, see the earlier I/O discussion. How Do I Know Whether My String Is In Unicode? -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. +You shouldn't have to care. But you may, because currently the semantics of the +characters whose ordinals are in the range 128 to 255 are different depending on +whether the string they are contained within is in Unicode or not. +(See L.) -Okay, if you insist: +To determine if a string is in Unicode, use: print utf8::is_utf8($string) ? 1 : 0, "\n"; @@ -634,9 +624,9 @@ string has any characters at all. All the C does is to return the value of the internal "utf8ness" flag attached to the C<$string>. If the flag is off, the bytes in the scalar are interpreted as a single byte encoding. If the flag is on, the bytes in the scalar -are interpreted as the (multi-byte, variable-length) UTF-8 encoded code -points of the characters. Bytes added to an UTF-8 encoded string are -automatically upgraded to UTF-8. If mixed non-UTF8 and UTF-8 scalars +are interpreted as the (variable-length, potentially multi-byte) UTF-8 encoded +code points of the characters. Bytes added to a UTF-8 encoded string are +automatically upgraded to UTF-8. If mixed non-UTF-8 and UTF-8 scalars are merged (double-quoted interpolation, explicit concatenation, and printf/sprintf parameter substitution), the result will be UTF-8 encoded as if copies of the byte strings were upgraded to UTF-8: for example, @@ -650,8 +640,8 @@ C<$a> will stay byte-encoded. Sometimes you might really need to know the byte length of a string instead of the character length. For that use either the -C function or the C pragma and its only -defined function C: +C function or the C pragma and +the C function: my $unicode = chr(0x100); print length($unicode), "\n"; # will print 1 @@ -660,6 +650,7 @@ defined function C: use bytes; print length($unicode), "\n"; # will also print 2 # (the 0xC4 0x80 of the UTF-8) + no bytes; =item * @@ -668,22 +659,24 @@ How Do I Detect Data That's Not Valid In a Particular Encoding? Use the C package to try converting it. For example, - use Encode 'encode_utf8'; - if (encode_utf8($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 +718,8 @@ 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: @@ -734,25 +727,34 @@ but Perl doesn't know it yet, you can make Perl a believer, too: use Encode 'decode_utf8'; $Unicode = decode_utf8($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 -use C for the former, and you can create -well-formed Unicode data by C. +or: + + $Unicode = pack("U0a*", $bytes); + +You can find the bytes that make up a UTF-8 sequence with + + @bytes = unpack("C*", $Unicode_string) + +and you can create well-formed Unicode with + + $Unicode_string = pack("U*", 0xff, ...) =item * How Do I Display Unicode? How Do I Input Unicode? -See http://www.alanwood.net/unicode/ and -http://www.cl.cam.ac.uk/~mgk25/unicode.html +See L and +L =item * How Does Unicode Work With Traditional Locales? In Perl, not very well. Avoid using locales through the C -pragma. Use only one or the other. +pragma. Use only one or the other. But see L for the +description of the C<-C> switch and its environment counterpart, +C<$ENV{PERL_UNICODE}> to see how to enable various Unicode features, +for example by using locale settings. =back @@ -794,44 +796,44 @@ show a decimal number in hexadecimal. If you have just the Unicode Consortium - http://www.unicode.org/ +L =item * Unicode FAQ - http://www.unicode.org/unicode/faq/ +L =item * Unicode Glossary - http://www.unicode.org/glossary/ +L =item * Unicode Useful Resources - http://www.unicode.org/unicode/onlinedat/resources.html +L =item * Unicode and Multilingual Support in HTML, Fonts, Web Browsers and Other Applications - http://www.alanwood.net/unicode/ +L =item * UTF-8 and Unicode FAQ for Unix/Linux - http://www.cl.cam.ac.uk/~mgk25/unicode.html +L =item * Legacy Character Sets - http://www.czyborra.com/ - http://www.eki.ee/letter/ +L +L =item * @@ -840,7 +842,7 @@ 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 +877,9 @@ 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