=head1 DESCRIPTION
-WARNING: The implementation of Unicode support in Perl is incomplete.
-Expect sudden and unannounced changes!
+=head2 Important Caveats
+
+WARNING: While the implementation of Unicode support in Perl is now fairly
+complete it is still evolving to some extent.
+
+In particular the way Unicode is handled on EBCDIC platforms is still
+rather experimental. On such a platform references to UTF-8 encoding
+in this document and elsewhere should be read as meaning UTF-EBCDIC as
+specified in Unicode Technical Report 16 unless ASCII vs EBCDIC issues
+are specifically discussed. There is no C<utfebcdic> pragma or
+":utfebcdic" layer, rather "utf8" and ":utf8" are re-used to mean
+platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic> for
+more discussion of the issues.
+
+The following areas are still under development.
+
+=over 4
+
+=item Input and Output Disciplines
+
+A filehandle can be marked as containing perl's internal Unicode
+encoding (UTF-8 or UTF-EBCDIC) by opening it with the ":utf8" layer.
+Other encodings can be converted to perl's encoding on input, or from
+perl's encoding on output by use of the ":encoding()" layer. There is
+not yet a clean way to mark the Perl source itself as being in an
+particular encoding.
+
+=item Regular Expressions
+
+The regular expression compiler does now attempt to produce
+polymorphic opcodes. That is the pattern should now adapt to the data
+and automatically switch to the Unicode character scheme when
+presented with Unicode data, or a traditional byte scheme when
+presented with byte data. The implementation is still new and
+(particularly on EBCDIC platforms) may need further work.
+
+=item C<use utf8> still needed to enable UTF-8/UTF-EBCDIC in scripts
+
+The C<utf8> pragma implements the tables used for Unicode support.
+These tables are automatically loaded on demand, so the C<utf8> pragma
+need not normally be used.
+
+However, as a compatibility measure, this pragma must be explicitly
+used to enable recognition of UTF-8 in the Perl scripts themselves on
+ASCII based machines or recognize UTF-EBCDIC on EBCDIC based machines.
+B<This should be the only place where an explicit C<use utf8> is needed>.
+
+=back
+
+=head2 Byte and Character semantics
Beginning with version 5.6, Perl uses logically wide characters to
represent strings internally. This internal representation of strings
-uses the UTF-8 encoding.
+uses either the UTF-8 or the UTF-EBCDIC encoding.
-In future, Perl-level operations will expect to work with characters
-rather than bytes, in general.
+In future, Perl-level operations can be expected to work with
+characters rather than bytes, in general.
-However, as strictly an interim compatibility measure, Perl v5.6 aims to
-provide a safe migration path from byte semantics to character semantics
-for programs. For operations where Perl can unambiguously decide that the
-input data is characters, Perl now switches to character semantics.
-For operations where this determination cannot be made without additional
-information from the user, Perl decides in favor of compatibility, and
-chooses to use byte semantics.
+However, as strictly an interim compatibility measure, Perl aims to
+provide a safe migration path from byte semantics to character
+semantics for programs. For operations where Perl can unambiguously
+decide that the input data is characters, Perl now switches to
+character semantics. For operations where this determination cannot
+be made without additional information from the user, Perl decides in
+favor of compatibility, and chooses to use byte semantics.
This behavior preserves compatibility with earlier versions of Perl,
which allowed byte semantics in Perl operations, but only as long as
none of the program's inputs are marked as being as source of Unicode
character data. Such data may come from filehandles, from calls to
external programs, from information provided by the system (such as %ENV),
-or from literals and constants in the source text. Later, in
-L</Character encodings for input and output>, we'll see how such
-inputs may be marked as being Unicode character data sources.
+or from literals and constants in the source text.
-One particular condition will enable character semantics on the entire
-program, bypassing the compatibility mode: if the C<$^U> global flag is
-set to C<1>, nearly all operations will use character semantics by
-default. As an added convenience, if the C<utf8> pragma is used in the
-C<main> package, C<$^U> is enabled automatically. [XXX: Should there
-be a -C switch to enable $^U?]
+If the C<-C> command line switch is used, (or the
+${^WIDE_SYSTEM_CALLS} global flag is set to C<1>), all system calls
+will use the corresponding wide character APIs. Note that this is
+currently only implemented on Windows since other platforms API
+standard on this area.
-Regardless of the above, the C<byte> pragma can always be used to force
-byte semantics in a particular lexical scope. See L<byte>.
+Regardless of the above, the C<bytes> pragma can always be used to
+force byte semantics in a particular lexical scope. See L<bytes>.
The C<utf8> pragma is primarily a compatibility device that enables
-recognition of UTF-8 in literals encountered by the parser. It is also
-used for enabling some of the more experimental Unicode support features.
-Note that this pragma is only required until a future version of Perl
-in which character semantics will become the default. This pragma may
-then become a no-op. See L<utf8>.
+recognition of UTF-(8|EBCDIC) in literals encountered by the parser.
+It may also be used for enabling some of the more experimental Unicode
+support features. Note that this pragma is only required until a
+future version of Perl in which character semantics will become the
+default. This pragma may then become a no-op. See L<utf8>.
Unless mentioned otherwise, Perl operators will use character semantics
when they are dealing with Unicode data, and byte semantics otherwise.
character encoding discipline to the filehandle whence it came, or a
literal UTF-8 string constant in the program), character semantics
apply; otherwise, byte semantics are in effect. To force byte semantics
-on Unicode data, the C<byte> pragma should be used.
+on Unicode data, the C<bytes> pragma should be used.
Under character semantics, many operations that formerly operated on
-bytes change to operating on characters. For ASCII data this makes
-no difference, because UTF-8 stores ASCII in single bytes, but for
-any character greater than C<chr(127)>, the character is stored in
+bytes change to operating on characters. For ASCII data this makes no
+difference, because UTF-8 stores ASCII in single bytes, but for any
+character greater than C<chr(127)>, the character B<may> be stored in
a sequence of two or more bytes, all of which have the high bit set.
-But by and large, the user need not worry about this, because Perl
-hides it from the user. A character in Perl is logically just a number
-ranging from 0 to 2**32 or so. Larger characters encode to longer
-sequences of bytes internally, but again, this is just an internal
-detail which is hidden at the Perl level.
+
+For C1 controls or Latin 1 characters on an EBCDIC platform the
+character may be stored in a UTF-EBCDIC multi byte sequence. But by
+and large, the user need not worry about this, because Perl hides it
+from the user. A character in Perl is logically just a number ranging
+from 0 to 2**32 or so. Larger characters encode to longer sequences
+of bytes internally, but again, this is just an internal detail which
+is hidden at the Perl level.
=head2 Effects of character semantics
=item *
Strings and patterns may contain characters that have an ordinal value
-larger than 255. In Perl v5.6, this is only enabled if the lexical
-scope has a C<use utf8> declaration (due to compatibility needs) but
-future versions may enable this by default.
-
-Presuming you use a Unicode editor to edit your program, such characters
-will typically occur directly within the literal strings as UTF-8
-characters, but you can also specify a particular character with an
-extension of the C<\x> notation. UTF-8 characters are specified by
-putting the hexadecimal code within curlies after the C<\x>. For instance,
-a Unicode smiley face is C<\x{263A}>. A character in the Latin-1 range
-(128..255) should be written C<\x{ab}> rather than C<\xab>, since the
-former will turn into a two-byte UTF-8 code, while the latter will
-continue to be interpreted as generating a 8-bit byte rather than a
-character. In fact, if C<-w> is turned on, it will produce a warning
-that you might be generating invalid UTF-8.
+larger than 255.
+
+Presuming you use a Unicode editor to edit your program, such
+characters will typically occur directly within the literal strings as
+UTF-8 (or UTF-EBCDIC on EBCDIC platforms) characters, but you can also
+specify a particular character with an extension of the C<\x>
+notation. UTF-X characters are specified by putting the hexadecimal
+code within curlies after the C<\x>. For instance, a Unicode smiley
+face is C<\x{263A}>.
=item *
Identifiers within the Perl script may contain Unicode alphanumeric
characters, including ideographs. (You are currently on your own when
-it comes to using the canonical forms of characters--Perl doesn't (yet)
-attempt to canonicalize variable names for you.)
-
-This also needs C<use utf8> currently. [XXX: Why?!? High-bit chars were
-syntax errors when they occurred within identifiers in previous versions,
-so this should probably be enabled by default.]
+it comes to using the canonical forms of characters--Perl doesn't
+(yet) attempt to canonicalize variable names for you.)
=item *
Regular expressions match characters instead of bytes. For instance,
"." matches a character instead of a byte. (However, the C<\C> pattern
-is provided to force a match a single byte ("C<char>" in C, hence
-C<\C>).)
-
-Unicode support in regular expressions needs C<use utf8> currently.
-[XXX: Because the SWASH routines need to be loaded. And the RE engine
-appears to need an overhaul to dynamically match Unicode anyway--the
-current RE compiler creates different nodes with and without C<use utf8>.]
+is provided to force a match a single byte ("C<char>" in C, hence C<\C>).)
=item *
Character classes in regular expressions match characters instead of
bytes, and match against the character properties specified in the
-Unicode properties database. So C<\w> can be used to match an ideograph,
-for instance.
-
-C<use utf8> is needed to enable this. See above.
+Unicode properties database. So C<\w> can be used to match an
+ideograph, for instance.
=item *
classes via the new C<\p{}> (matches property) and C<\P{}> (doesn't
match property) constructs. For instance, C<\p{Lu}> matches any
character with the Unicode uppercase property, while C<\p{M}> matches
-any mark character. Single letter properties may omit the brackets, so
-that can be written C<\pM> also. Many predefined character classes are
-available, such as C<\p{IsMirrored}> and C<\p{InTibetan}>.
-
-C<use utf8> is needed to enable this. See above.
+any mark character. Single letter properties may omit the brackets,
+so that can be written C<\pM> also. Many predefined character classes
+are available, such as C<\p{IsMirrored}> and C<\p{InTibetan}>. The
+names of the C<In> classes are the official Unicode script and block
+names but with all non-alphanumeric characters removed, for example
+the block name C<"Latin-1 Supplement"> becomes C<\p{InLatin1Supplement}>.
+
+Here is the list as of Unicode 3.1.0 (the two-letter classes) and
+as defined by Perl (the one-letter classes) (in Unicode materials
+what Perl calls C<L> is often called C<L&>):
+
+ L Letter
+ Lu Letter, Uppercase
+ Ll Letter, Lowercase
+ Lt Letter, Titlecase
+ Lm Letter, Modifier
+ Lo Letter, Other
+ M Mark
+ Mn Mark, Non-Spacing
+ Mc Mark, Spacing Combining
+ Me Mark, Enclosing
+ N Number
+ Nd Number, Decimal Digit
+ Nl Number, Letter
+ No Number, Other
+ P Punctuation
+ Pc Punctuation, Connector
+ Pd Punctuation, Dash
+ Ps Punctuation, Open
+ Pe Punctuation, Close
+ Pi Punctuation, Initial quote
+ (may behave like Ps or Pe depending on usage)
+ Pf Punctuation, Final quote
+ (may behave like Ps or Pe depending on usage)
+ Po Punctuation, Other
+ S Symbol
+ Sm Symbol, Math
+ Sc Symbol, Currency
+ Sk Symbol, Modifier
+ So Symbol, Other
+ Z Separator
+ Zs Separator, Space
+ Zl Separator, Line
+ Zp Separator, Paragraph
+ C Other
+ Cc Other, Control
+ Cf Other, Format
+ Cs Other, Surrogate
+ Co Other, Private Use
+ Cn Other, Not Assigned (Unicode defines no Cn characters)
+
+Additionally, because scripts differ in their directionality
+(for example Hebrew is written right to left), all characters
+have their directionality defined:
+
+ BidiL Left-to-Right
+ BidiLRE Left-to-Right Embedding
+ BidiLRO Left-to-Right Override
+ BidiR Right-to-Left
+ BidiAL Right-to-Left Arabic
+ BidiRLE Right-to-Left Embedding
+ BidiRLO Right-to-Left Override
+ BidiPDF Pop Directional Format
+ BidiEN European Number
+ BidiES European Number Separator
+ BidiET European Number Terminator
+ BidiAN Arabic Number
+ BidiCS Common Number Separator
+ BidiNSM Non-Spacing Mark
+ BidiBN Boundary Neutral
+ BidiB Paragraph Separator
+ BidiS Segment Separator
+ BidiWS Whitespace
+ BidiON Other Neutrals
+
+=head2 Scripts
+
+The scripts available for C<\p{In...}> and C<\P{In...}>, for example
+\p{InCyrillic>, are as follows, for example C<\p{InLatin}> or C<\P{InHan}>:
+
+ Latin
+ Greek
+ Cyrillic
+ Armenian
+ Hebrew
+ Arabic
+ Syriac
+ Thaana
+ Devanagari
+ Bengali
+ Gurmukhi
+ Gujarati
+ Oriya
+ Tamil
+ Telugu
+ Kannada
+ Malayalam
+ Sinhala
+ Thai
+ Lao
+ Tibetan
+ Myanmar
+ Georgian
+ Hangul
+ Ethiopic
+ Cherokee
+ CanadianAboriginal
+ Ogham
+ Runic
+ Khmer
+ Mongolian
+ Hiragana
+ Katakana
+ Bopomofo
+ Han
+ Yi
+ OldItalic
+ Gothic
+ Deseret
+ Inherited
+
+=head2 Blocks
+
+In addition to B<scripts>, Unicode also defines B<blocks> of
+characters. The difference between scripts and blocks is that the
+former concept is closer to natural languages, while the latter
+concept is more an artificial grouping based on groups of 256 Unicode
+characters. For example, the C<Latin> script contains letters from
+many blocks, but it does not contain all the characters from those
+blocks, it does not for example contain digits.
+
+For more about scripts see the UTR #24:
+http://www.unicode.org/unicode/reports/tr24/
+For more about blocks see
+http://www.unicode.org/Public/UNIDATA/Blocks.txt
+
+Because there are overlaps in naming (there are, for example, both
+a script called C<Katakana> and a block called C<Katakana>, the block
+version has C<Block> appended to its name, C<\p{InKatakanaBlock}>.
+
+Notice that this definition was introduced in Perl 5.8.0: in Perl
+5.6.0 only the blocks were used; in Perl 5.8.0 scripts became the
+preferential character class definition; this meant that the
+definitions of some character classes changed (the ones in the
+below list that have the C<Block> appended).
+
+ BasicLatin
+ Latin1Supplement
+ LatinExtendedA
+ LatinExtendedB
+ IPAExtensions
+ SpacingModifierLetters
+ CombiningDiacriticalMarks
+ GreekBlock
+ CyrillicBlock
+ ArmenianBlock
+ HebrewBlock
+ ArabicBlock
+ SyriacBlock
+ ThaanaBlock
+ DevanagariBlock
+ BengaliBlock
+ GurmukhiBlock
+ GujaratiBlock
+ OriyaBlock
+ TamilBlock
+ TeluguBlock
+ KannadaBlock
+ MalayalamBlock
+ SinhalaBlock
+ ThaiBlock
+ LaoBlock
+ TibetanBlock
+ MyanmarBlock
+ GeorgianBlock
+ HangulJamo
+ EthiopicBlock
+ CherokeeBlock
+ UnifiedCanadianAboriginalSyllabics
+ OghamBlock
+ RunicBlock
+ KhmerBlock
+ MongolianBlock
+ LatinExtendedAdditional
+ GreekExtended
+ GeneralPunctuation
+ SuperscriptsandSubscripts
+ CurrencySymbols
+ CombiningMarksforSymbols
+ LetterlikeSymbols
+ NumberForms
+ Arrows
+ MathematicalOperators
+ MiscellaneousTechnical
+ ControlPictures
+ OpticalCharacterRecognition
+ EnclosedAlphanumerics
+ BoxDrawing
+ BlockElements
+ GeometricShapes
+ MiscellaneousSymbols
+ Dingbats
+ BraillePatterns
+ CJKRadicalsSupplement
+ KangxiRadicals
+ IdeographicDescriptionCharacters
+ CJKSymbolsandPunctuation
+ HiraganaBlock
+ KatakanaBlock
+ BopomofoBlock
+ HangulCompatibilityJamo
+ Kanbun
+ BopomofoExtended
+ EnclosedCJKLettersandMonths
+ CJKCompatibility
+ CJKUnifiedIdeographsExtensionA
+ CJKUnifiedIdeographs
+ YiSyllables
+ YiRadicals
+ HangulSyllables
+ HighSurrogates
+ HighPrivateUseSurrogates
+ LowSurrogates
+ PrivateUse
+ CJKCompatibilityIdeographs
+ AlphabeticPresentationForms
+ ArabicPresentationFormsA
+ CombiningHalfMarks
+ CJKCompatibilityForms
+ SmallFormVariants
+ ArabicPresentationFormsB
+ Specials
+ HalfwidthandFullwidthForms
+ OldItalicBlock
+ GothicBlock
+ DeseretBlock
+ ByzantineMusicalSymbols
+ MusicalSymbols
+ MathematicalAlphanumericSymbols
+ CJKUnifiedIdeographsExtensionB
+ CJKCompatibilityIdeographsSupplement
+ Tags
=item *
characters that apply to the base character. It is equivalent to
C<(?:\PM\pM*)>.
-C<use utf8> is needed to enable this. See above.
-
=item *
-The C<tr///> operator translates characters instead of bytes. It can also
-be forced to translate between 8-bit codes and UTF-8 regardless of the
-surrounding utf8 state. For instance, if you know your input in Latin-1,
-you can say:
-
- use utf8;
- while (<>) {
- tr/\0-\xff//CU; # latin1 char to utf8
- ...
- }
-
-Similarly you could translate your output with
-
- tr/\0-\x{ff}//UC; # utf8 to latin1 char
-
-No, C<s///> doesn't take /U or /C (yet?).
-
-C<use utf8> is needed to enable this. See above.
+The C<tr///> operator translates characters instead of bytes. Note
+that the C<tr///CU> functionality has been removed, as the interface
+was a mistake. For similar functionality see pack('U0', ...) and
+pack('C0', ...).
=item *
=item *
Most operators that deal with positions or lengths in the string will
-automatically switch to using character positions, including C<chop()>,
-C<substr()>, C<pos()>, C<index()>, C<rindex()>, C<sprintf()>,
-C<write()>, and C<length()>. Operators that specifically don't switch
-include C<vec()>, C<pack()>, and C<unpack()>. Operators that really
-don't care include C<chomp()>, as well as any other operator that
-treats a string as a bucket of bits, such as C<sort()>, and the
-operators dealing with filenames.
+automatically switch to using character positions, including
+C<chop()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>,
+C<sprintf()>, C<write()>, and C<length()>. Operators that
+specifically don't switch include C<vec()>, C<pack()>, and
+C<unpack()>. Operators that really don't care include C<chomp()>, as
+well as any other operator that treats a string as a bucket of bits,
+such as C<sort()>, and the operators dealing with filenames.
=item *
=item *
+The bit string operators C<& | ^ ~> can operate on character data.
+However, for backward compatibility reasons (bit string operations
+when the characters all are less than 256 in ordinal value) one should
+not mix C<~> (the bit complement) and characters both less than 256 and
+equal or greater than 256. Most importantly, the DeMorgan's laws
+(C<~($x|$y) eq ~$x&~$y>, C<~($x&$y) eq ~$x|~$y>) won't hold.
+Another way to look at this is that the complement cannot return
+B<both> the 8-bit (byte) wide bit complement B<and> the full character
+wide bit complement.
+
+=item *
+
And finally, C<scalar reverse()> reverses by character rather than by byte.
=back
=head2 Character encodings for input and output
-[XXX: This feature is not yet implemented.]
+See L<Encode>.
=head1 CAVEATS
As of yet, there is no method for automatically coercing input and
-output to some encoding other than UTF-8. This is planned in the near
-future, however.
+output to some encoding other than UTF-8 or UTF-EBCDIC. This is planned
+in the near future, however.
Whether an arbitrary piece of data will be treated as "characters" or
"bytes" by internal operations cannot be divined at the current time.
=head1 SEE ALSO
-L<byte>, L<utf8>, L<perlvar/"$^U">
+L<bytes>, L<utf8>, L<perlretut>, L<perlvar/"${^WIDE_SYSTEM_CALLS}">
=cut
projects / p5sagit/p5-mst-13.2.git / blobdiff