=head1 DESCRIPTION
-=head2 Important Caveat
+=head2 Important Caveats
-WARNING: The implementation of Unicode support in Perl is incomplete.
+WARNING: While the implementation of Unicode support in Perl is now fairly
+complete it is still evolving to some extent.
-The following areas need further work.
+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.
-=over
+The following areas are still under development.
+
+=over 4
=item Input and Output Disciplines
-There is currently no easy way to mark data read from a file or other
-external source as being utf8. This will be one of the major areas of
-focus in the near future.
+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 existing regular expression compiler does not produce polymorphic
-opcodes. This means that the determination on whether to match Unicode
-characters is made when the pattern is compiled, based on whether the
-pattern contains Unicode characters, and not when the matching happens
-at run time. This needs to be changed to adaptively match Unicode if
-the string to be matched is Unicode.
+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 a few features
However, as a compatibility measure, this pragma must be explicitly used
to enable recognition of UTF-8 encoded literals and identifiers in the
-source text.
+source text on ASCII based machines or recognize UTF-EBCDIC encoded literals
+and identifiers on EBCDIC based machines.
=back
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 can be expected to work with characters
rather than bytes, in general.
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. This is currently only implemented
-on Windows.
+on Windows since UNIXes lack API standard on this area.
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 may also
+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
no difference, because UTF-8 stores ASCII in single bytes, but for
any character greater than C<chr(127)>, the character may be stored in
a sequence of two or more bytes, all of which have the high bit set.
+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
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
+will typically occur directly within the literal strings as UTF-(8|EBCDIC)
characters, but you can also specify a particular character with an
-extension of the C<\x> notation. UTF-8 characters are specified by
+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}>. 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 the C<use warnings> pragma of the C<-w> switch
-is turned on, it will produce a warning
-that you might be generating invalid UTF-8.
+a Unicode smiley face is C<\x{263A}>.
=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}>.
+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 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
+Perl 5.8.0 (the one-letter classes):
+
+ 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
+
+The blocks available for C<\p{InBlock}> and C<\P{InBlock}>, for
+example \p{InCyrillic>, are as follows:
+
+ BasicLatin
+ Latin1Supplement
+ LatinExtendedA
+ LatinExtendedB
+ IPAExtensions
+ SpacingModifierLetters
+ CombiningDiacriticalMarks
+ Greek
+ Cyrillic
+ Armenian
+ Hebrew
+ Arabic
+ Syriac
+ Thaana
+ Devanagari
+ Bengali
+ Gurmukhi
+ Gujarati
+ Oriya
+ Tamil
+ Telugu
+ Kannada
+ Malayalam
+ Sinhala
+ Thai
+ Lao
+ Tibetan
+ Myanmar
+ Georgian
+ HangulJamo
+ Ethiopic
+ Cherokee
+ UnifiedCanadianAboriginalSyllabics
+ Ogham
+ Runic
+ Khmer
+ Mongolian
+ LatinExtendedAdditional
+ GreekExtended
+ GeneralPunctuation
+ SuperscriptsandSubscripts
+ CurrencySymbols
+ CombiningMarksforSymbols
+ LetterlikeSymbols
+ NumberForms
+ Arrows
+ MathematicalOperators
+ MiscellaneousTechnical
+ ControlPictures
+ OpticalCharacterRecognition
+ EnclosedAlphanumerics
+ BoxDrawing
+ BlockElements
+ GeometricShapes
+ MiscellaneousSymbols
+ Dingbats
+ BraillePatterns
+ CJKRadicalsSupplement
+ KangxiRadicals
+ IdeographicDescriptionCharacters
+ CJKSymbolsandPunctuation
+ Hiragana
+ Katakana
+ Bopomofo
+ HangulCompatibilityJamo
+ Kanbun
+ BopomofoExtended
+ EnclosedCJKLettersandMonths
+ CJKCompatibility
+ CJKUnifiedIdeographsExtensionA
+ CJKUnifiedIdeographs
+ YiSyllables
+ YiRadicals
+ HangulSyllables
+ HighSurrogates
+ HighPrivateUseSurrogates
+ LowSurrogates
+ PrivateUse
+ CJKCompatibilityIdeographs
+ AlphabeticPresentationForms
+ ArabicPresentationFormsA
+ CombiningHalfMarks
+ CJKCompatibilityForms
+ SmallFormVariants
+ ArabicPresentationFormsB
+ Specials
+ HalfwidthandFullwidthForms
+ OldItalic
+ Gothic
+ Deseret
+ ByzantineMusicalSymbols
+ MusicalSymbols
+ MathematicalAlphanumericSymbols
+ CJKUnifiedIdeographsExtensionB
+ CJKCompatibilityIdeographsSupplement
+ Tags
=item *
=item *
-The C<tr///> operator translates characters instead of bytes. It can also
-be forced to translate between 8-bit codes and UTF-8. For instance, if you
-know your input in Latin-1, you can say:
-
- 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?).
+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 *
+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 cannot
+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|~$y>) won't hold.
+Another way to look at this is that the complement cannot return
+B<both> the 8-bit (byte) wide bit complement, and the full character
+wide bit complement.
+
+=item *
+
And finally, C<scalar reverse()> reverses by character rather than by byte.
=back
=head2 Character encodings for input and output
-[XXX: This feature is not yet implemented.]
+See L<Encode>.
=head1 CAVEATS
As of yet, there is no method for automatically coercing input and
-output to some encoding other than UTF-8. This is planned in the near
-future, however.
+output to some encoding other than UTF-8 or UTF-EBCDIC. This is planned
+in the near future, however.
Whether an arbitrary piece of data will be treated as "characters" or
"bytes" by internal operations cannot be divined at the current time.
=head1 SEE ALSO
-L<bytes>, L<utf8>, L<perlvar/"${^WIDE_SYSTEM_CALLS}">
+L<bytes>, L<utf8>, L<perlretut>, L<perlvar/"${^WIDE_SYSTEM_CALLS}">
=cut
projects / p5sagit/p5-mst-13.2.git / blobdiff