from cover to cover, Perl does support many Unicode features.
People who want to learn to use Unicode in Perl, should probably read
-L<the Perl Unicode tutorial|perlunitut> before reading this reference
-document.
+L<the Perl Unicode tutorial, perlunitut|perlunitut>, before reading
+this reference document.
=over 4
implicit upgrading from byte strings to Unicode strings assumes that
they were encoded in I<ISO 8859-1 (Latin-1)>, but Unicode strings are
downgraded with UTF-8 encoding. This happens because the first 256
-codepoints in Unicode happens to agree with Latin-1.
+codepoints in Unicode happens to agree with Latin-1.
See L</"Byte and Character Semantics"> for more details.
be made without additional information from the user, Perl decides in
favor of compatibility and chooses to use byte semantics.
+Under byte semantics, when C<use locale> is in effect, Perl uses the
+semantics associated with the current locale. Absent a C<use locale>, and
+absent a C<use feature 'unicode_strings'> pragma, Perl currently uses US-ASCII
+(or Basic Latin in Unicode terminology) byte semantics, meaning that characters
+whose ordinal numbers are in the range 128 - 255 are undefined except for their
+ordinal numbers. This means that none have case (upper and lower), nor are any
+a member of character classes, like C<[:alpha:]> or C<\w>. (But all do belong
+to the C<\W> class or the Perl regular expression extension C<[:^alpha:]>.)
+
This behavior preserves compatibility with earlier versions of Perl,
which allowed byte semantics in Perl operations only if
-none of the program's inputs were marked as being as source of Unicode
+none of the program's inputs were marked as being a 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.
The C<bytes> pragma will always, regardless of platform, force byte
semantics in a particular lexical scope. See L<bytes>.
+The C<use feature 'unicode_strings'> pragma is intended to always, regardless
+of platform, force Unicode semantics in a particular lexical scope. In
+release 5.12, it is partially implemented, applying only to case changes.
+See L</The "Unicode Bug"> below.
+
The C<utf8> pragma is primarily a compatibility device that enables
recognition of UTF-(8|EBCDIC) in literals encountered by the parser.
Note that this pragma is only required while Perl defaults to byte
encoding layer is added to a filehandle or a literal Unicode
string constant appears in a program--character semantics apply.
Otherwise, byte semantics are in effect. The C<bytes> pragma should
-be used to force byte semantics on Unicode data.
+be used to force byte semantics on Unicode data, and the C<use feature
+'unicode_strings'> pragma to force Unicode semantics on byte data (though in
+5.12 it isn't fully implemented).
If strings operating under byte semantics and strings with Unicode
-character data are concatenated, the new string will be created by
-decoding the byte strings as I<ISO 8859-1 (Latin-1)>, even if the
-old Unicode string used EBCDIC. This translation is done without
-regard to the system's native 8-bit encoding.
+character data are concatenated, the new string will have
+character semantics. This can cause surprises: See L</BUGS>, below
Under character semantics, many operations that formerly operated on
bytes now operate on characters. A character in Perl is
Unicode characters can also be added to a string by using the C<\x{...}>
notation. The Unicode code for the desired character, in hexadecimal,
should be placed in the braces. For instance, a smiley face is
-C<\x{263A}>. This encoding scheme only works for all characters, but
+C<\x{263A}>. This encoding scheme works for all characters, but
for characters under 0x100, note that Perl may use an 8 bit encoding
internally, for optimization and/or backward compatibility.
Named Unicode properties, scripts, and block ranges may be used like
character classes via the C<\p{}> "matches property" construct and
the C<\P{}> negation, "doesn't match property".
-
See L</"Unicode Character Properties"> for more details.
You can define your own character properties and use them
in the regular expression with the C<\p{}> or C<\P{}> construct.
-
See L</"User-Defined Character Properties"> for more details.
=item *
-The special pattern C<\X> matches any extended Unicode
-sequence--"a combining character sequence" in Standardese--where the
-first character is a base character and subsequent characters are mark
-characters that apply to the base character. C<\X> is equivalent to
-C<(?:\PM\pM*)>.
+The special pattern C<\X> matches a logical character, an "extended grapheme
+cluster" in Standardese. In Unicode what appears to the user to be a single
+character, for example an accented C<G>, may in fact be composed of a sequence
+of characters, in this case a C<G> followed by an accent character. C<\X>
+will match the entire sequence.
=item *
when character input is provided. Note that C<uc()>, or C<\U> in
interpolated strings, translates to uppercase, while C<ucfirst>,
or C<\u> in interpolated strings, translates to titlecase in languages
-that make the distinction.
+that make the distinction (which is equivalent to uppercase in languages
+without the distinction).
=item *
automatically switch to using character positions, including
C<chop()>, C<chomp()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>,
C<sprintf()>, C<write()>, and C<length()>. An operator that
-specifically does not switch is C<vec()>. Operators that really don't
-care include operators that treat strings as a bucket of bits such as
+specifically does not switch is C<vec()>. Operators that really don't
+care include operators that treat strings as a bucket of bits such as
C<sort()>, and operators dealing with filenames.
=item *
-The C<pack()>/C<unpack()> letter C<C> does I<not> change, since it is often
+The C<pack()>/C<unpack()> letter C<C> does I<not> change, since it is often
used for byte-oriented formats. Again, think C<char> in the C language.
There is a new C<U> specifier that converts between Unicode characters
=item *
-lc(), uc(), lcfirst(), and ucfirst() work for the following cases:
-
-=over 8
-
-=item *
-
-the case mapping is from a single Unicode character to another
-single Unicode character, or
-
-=item *
-
-the case mapping is from a single Unicode character to more
-than one Unicode character.
-
-=back
-
-Things to do with locales (Lithuanian, Turkish, Azeri) do B<not> work
-since Perl does not understand the concept of Unicode locales.
-
-See the Unicode Technical Report #21, Case Mappings, for more details.
-
-But you can also define your own mappings to be used in the lc(),
+You can define your own mappings to be used in lc(),
lcfirst(), uc(), and ucfirst() (or their string-inlined versions).
-
See L</"User-Defined Case Mappings"> for more details.
=back
=head2 Unicode Character Properties
-Named Unicode properties, scripts, and block ranges may be used like
-character classes via the C<\p{}> "matches property" construct and
-the C<\P{}> negation, "doesn't match property".
-
-For instance, C<\p{Lu}> matches any character with the Unicode "Lu"
-(Letter, uppercase) property, while C<\p{M}> matches any character
-with an "M" (mark--accents and such) property. Brackets are not
-required for single letter properties, so C<\p{M}> is equivalent to
-C<\pM>. Many predefined properties are available, such as
-C<\p{Mirrored}> and C<\p{Tibetan}>.
-
-The official Unicode script and block names have spaces and dashes as
-separators, but for convenience you can use dashes, spaces, or
-underbars, and case is unimportant. It is recommended, however, that
-for consistency you use the following naming: the official Unicode
-script, property, or block name (see below for the additional rules
-that apply to block names) with whitespace and dashes removed, and the
-words "uppercase-first-lowercase-rest". C<Latin-1 Supplement> thus
-becomes C<Latin1Supplement>.
+Most Unicode character properties are accessible by using regular expressions.
+They are used like character classes via the C<\p{}> "matches property"
+construct and the C<\P{}> negation, "doesn't match property".
+
+For instance, C<\p{Uppercase}> matches any character with the Unicode
+"Uppercase" property, while C<\p{L}> matches any character with a
+General_Category of "L" (letter) property. Brackets are not
+required for single letter properties, so C<\p{L}> is equivalent to C<\pL>.
+
+More formally, C<\p{Uppercase}> matches any character whose Unicode Uppercase
+property value is True, and C<\P{Uppercase}> matches any character whose
+Uppercase property value is False, and they could have been written as
+C<\p{Uppercase=True}> and C<\p{Uppercase=False}>, respectively
+
+This formality is needed when properties are not binary, that is if they can
+take on more values than just True and False. For example, the Bidi_Class (see
+L</"Bidirectional Character Types"> below), can take on a number of different
+values, such as Left, Right, Whitespace, and others. To match these, one needs
+to specify the property name (Bidi_Class), and the value being matched against
+(Left, Right, I<etc.>). This is done, as in the examples above, by having the
+two components separated by an equal sign (or interchangeably, a colon), like
+C<\p{Bidi_Class: Left}>.
+
+All Unicode-defined character properties may be written in these compound forms
+of C<\p{property=value}> or C<\p{property:value}>, but Perl provides some
+additional properties that are written only in the single form, as well as
+single-form short-cuts for all binary properties and certain others described
+below, in which you may omit the property name and the equals or colon
+separator.
+
+Most Unicode character properties have at least two synonyms (or aliases if you
+prefer), a short one that is easier to type, and a longer one which is more
+descriptive and hence it is easier to understand what it means. Thus the "L"
+and "Letter" above are equivalent and can be used interchangeably. Likewise,
+"Upper" is a synonym for "Uppercase", and we could have written
+C<\p{Uppercase}> equivalently as C<\p{Upper}>. Also, there are typically
+various synonyms for the values the property can be. For binary properties,
+"True" has 3 synonyms: "T", "Yes", and "Y"; and "False has correspondingly "F",
+"No", and "N". But be careful. A short form of a value for one property may
+not mean the same thing as the same short form for another. Thus, for the
+General_Category property, "L" means "Letter", but for the Bidi_Class property,
+"L" means "Left". A complete list of properties and synonyms is in
+L<perluniprops>.
+
+Upper/lower case differences in the property names and values are irrelevant,
+thus C<\p{Upper}> means the same thing as C<\p{upper}> or even C<\p{UpPeR}>.
+Similarly, you can add or subtract underscores anywhere in the middle of a
+word, so that these are also equivalent to C<\p{U_p_p_e_r}>. And white space
+is irrelevant adjacent to non-word characters, such as the braces and the equals
+or colon separators so C<\p{ Upper }> and C<\p{ Upper_case : Y }> are
+equivalent to these as well. In fact, in most cases, white space and even
+hyphens can be added or deleted anywhere. So even C<\p{ Up-per case = Yes}> is
+equivalent. All this is called "loose-matching" by Unicode. The few places
+where stricter matching is employed is in the middle of numbers, and the Perl
+extension properties that begin or end with an underscore. Stricter matching
+cares about white space (except adjacent to the non-word characters) and
+hyphens, and non-interior underscores.
You can also use negation in both C<\p{}> and C<\P{}> by introducing a caret
(^) between the first brace and the property name: C<\p{^Tamil}> is
equal to C<\P{Tamil}>.
-B<NOTE: the properties, scripts, and blocks listed here are as of
-Unicode 5.0.0 in July 2006.>
+=head3 B<General_Category>
-=over 4
+Every Unicode character is assigned a general category, which is the "most
+usual categorization of a character" (from
+L<http://www.unicode.org/reports/tr44>).
-=item General Category
+The compound way of writing these is like C<\p{General_Category=Number}>
+(short, C<\p{gc:n}>). But Perl furnishes shortcuts in which everything up
+through the equal or colon separator is omitted. So you can instead just write
+C<\pN>.
-Here are the basic Unicode General Category properties, followed by their
-long form. You can use either; C<\p{Lu}> and C<\p{UppercaseLetter}>,
-for instance, are identical.
+Here are the short and long forms of the General Category properties:
Short Long
L Letter
- LC CasedLetter
- Lu UppercaseLetter
- Ll LowercaseLetter
- Lt TitlecaseLetter
- Lm ModifierLetter
- Lo OtherLetter
+ LC, L& Cased_Letter (that is: [\p{Ll}\p{Lu}\p{Lt}])
+ Lu Uppercase_Letter
+ Ll Lowercase_Letter
+ Lt Titlecase_Letter
+ Lm Modifier_Letter
+ Lo Other_Letter
M Mark
- Mn NonspacingMark
- Mc SpacingMark
- Me EnclosingMark
+ Mn Nonspacing_Mark
+ Mc Spacing_Mark
+ Me Enclosing_Mark
N Number
- Nd DecimalNumber
- Nl LetterNumber
- No OtherNumber
-
- P Punctuation
- Pc ConnectorPunctuation
- Pd DashPunctuation
- Ps OpenPunctuation
- Pe ClosePunctuation
- Pi InitialPunctuation
+ Nd Decimal_Number (also Digit)
+ Nl Letter_Number
+ No Other_Number
+
+ P Punctuation (also Punct)
+ Pc Connector_Punctuation
+ Pd Dash_Punctuation
+ Ps Open_Punctuation
+ Pe Close_Punctuation
+ Pi Initial_Punctuation
(may behave like Ps or Pe depending on usage)
- Pf FinalPunctuation
+ Pf Final_Punctuation
(may behave like Ps or Pe depending on usage)
- Po OtherPunctuation
+ Po Other_Punctuation
S Symbol
- Sm MathSymbol
- Sc CurrencySymbol
- Sk ModifierSymbol
- So OtherSymbol
+ Sm Math_Symbol
+ Sc Currency_Symbol
+ Sk Modifier_Symbol
+ So Other_Symbol
Z Separator
- Zs SpaceSeparator
- Zl LineSeparator
- Zp ParagraphSeparator
+ Zs Space_Separator
+ Zl Line_Separator
+ Zp Paragraph_Separator
C Other
- Cc Control
+ Cc Control (also Cntrl)
Cf Format
Cs Surrogate (not usable)
- Co PrivateUse
+ Co Private_Use
Cn Unassigned
Single-letter properties match all characters in any of the
the somewhat messy concept of surrogates. C<Cs> is therefore not
supported.
-=item Bidirectional Character Types
+=head3 B<Bidirectional Character Types>
Because scripts differ in their directionality--Hebrew is
written right to left, for example--Unicode supplies these properties in
-the BidiClass class:
+the Bidi_Class class:
Property Meaning
LRE Left-to-Right Embedding
LRO Left-to-Right Override
R Right-to-Left
- AL Right-to-Left Arabic
+ AL Arabic Letter
RLE Right-to-Left Embedding
RLO Right-to-Left Override
PDF Pop Directional Format
EN European Number
- ES European Number Separator
- ET European Number Terminator
+ ES European Separator
+ ET European Terminator
AN Arabic Number
- CS Common Number Separator
+ CS Common Separator
NSM Non-Spacing Mark
BN Boundary Neutral
B Paragraph Separator
WS Whitespace
ON Other Neutrals
-For example, C<\p{BidiClass:R}> matches characters that are normally
+This property is always written in the compound form.
+For example, C<\p{Bidi_Class:R}> matches characters that are normally
written right to left.
-=item Scripts
-
-The script names which can be used by C<\p{...}> and C<\P{...}>,
-such as in C<\p{Latin}> or C<\p{Cyrillic}>, are as follows:
-
- Arabic
- Armenian
- Balinese
- Bengali
- Bopomofo
- Braille
- Buginese
- Buhid
- CanadianAboriginal
- Cherokee
- Coptic
- Cuneiform
- Cypriot
- Cyrillic
- Deseret
- Devanagari
- Ethiopic
- Georgian
- Glagolitic
- Gothic
- Greek
- Gujarati
- Gurmukhi
- Han
- Hangul
- Hanunoo
- Hebrew
- Hiragana
- Inherited
- Kannada
- Katakana
- Kharoshthi
- Khmer
- Lao
- Latin
- Limbu
- LinearB
- Malayalam
- Mongolian
- Myanmar
- NewTaiLue
- Nko
- Ogham
- OldItalic
- OldPersian
- Oriya
- Osmanya
- PhagsPa
- Phoenician
- Runic
- Shavian
- Sinhala
- SylotiNagri
- Syriac
- Tagalog
- Tagbanwa
- TaiLe
- Tamil
- Telugu
- Thaana
- Thai
- Tibetan
- Tifinagh
- Ugaritic
- Yi
-
-=item Extended property classes
-
-Extended property classes can supplement the basic
-properties, defined by the F<PropList> Unicode database:
-
- ASCIIHexDigit
- BidiControl
- Dash
- Deprecated
- Diacritic
- Extender
- HexDigit
- Hyphen
- Ideographic
- IDSBinaryOperator
- IDSTrinaryOperator
- JoinControl
- LogicalOrderException
- NoncharacterCodePoint
- OtherAlphabetic
- OtherDefaultIgnorableCodePoint
- OtherGraphemeExtend
- OtherIDStart
- OtherIDContinue
- OtherLowercase
- OtherMath
- OtherUppercase
- PatternSyntax
- PatternWhiteSpace
- QuotationMark
- Radical
- SoftDotted
- STerm
- TerminalPunctuation
- UnifiedIdeograph
- VariationSelector
- WhiteSpace
-
-and there are further derived properties:
-
- Alphabetic = Lu + Ll + Lt + Lm + Lo + Nl + OtherAlphabetic
- Lowercase = Ll + OtherLowercase
- Uppercase = Lu + OtherUppercase
- Math = Sm + OtherMath
-
- IDStart = Lu + Ll + Lt + Lm + Lo + Nl + OtherIDStart
- IDContinue = IDStart + Mn + Mc + Nd + Pc + OtherIDContinue
-
- DefaultIgnorableCodePoint
- = OtherDefaultIgnorableCodePoint
- + Cf + Cc + Cs + Noncharacters + VariationSelector
- - WhiteSpace - FFF9..FFFB (Annotation Characters)
-
- Any = Any code points (i.e. U+0000 to U+10FFFF)
- Assigned = Any non-Cn code points (i.e. synonym for \P{Cn})
- Unassigned = Synonym for \p{Cn}
- ASCII = ASCII (i.e. U+0000 to U+007F)
-
- Common = Any character (or unassigned code point)
- not explicitly assigned to a script
-
-=item Use of "Is" Prefix
+=head3 B<Scripts>
+
+The world's languages are written in a number of scripts. This sentence
+(unless you're reading it in translation) is written in Latin, while Russian is
+written in Cyrllic, and Greek is written in, well, Greek; Japanese mainly in
+Hiragana or Katakana. There are many more.
+
+The Unicode Script property gives what script a given character is in,
+and can be matched with the compound form like C<\p{Script=Hebrew}> (short:
+C<\p{sc=hebr}>). Perl furnishes shortcuts for all script names. You can omit
+everything up through the equals (or colon), and simply write C<\p{Latin}> or
+C<\P{Cyrillic}>.
+
+A complete list of scripts and their shortcuts is in L<perluniprops>.
+
+=head3 B<Use of "Is" Prefix>
For backward compatibility (with Perl 5.6), all properties mentioned
-so far may have C<Is> prepended to their name, so C<\P{IsLu}>, for
-example, is equal to C<\P{Lu}>.
+so far may have C<Is> or C<Is_> prepended to their name, so C<\P{Is_Lu}>, for
+example, is equal to C<\P{Lu}>, and C<\p{IsScript:Arabic}> is equal to
+C<\p{Arabic}>.
-=item Blocks
+=head3 B<Blocks>
In addition to B<scripts>, Unicode also defines B<blocks> of
characters. The difference between scripts and blocks is that the
concept of scripts is closer to natural languages, while the concept
-of blocks is more of an artificial grouping based on groups of 256
-Unicode characters. For example, the C<Latin> script contains letters
-from many blocks but does not contain all the characters from those
-blocks. It does not, for example, contain digits, because digits are
-shared across many scripts. Digits and similar groups, like
-punctuation, are in a category called C<Common>.
-
-For more about scripts, see the UAX#24 "Script Names":
-
- http://www.unicode.org/reports/tr24/
-
-For more about blocks, see:
-
- http://www.unicode.org/Public/UNIDATA/Blocks.txt
-
-Block names are given with the C<In> prefix. For example, the
-Katakana block is referenced via C<\p{InKatakana}>. The C<In>
-prefix may be omitted if there is no naming conflict with a script
-or any other property, but it is recommended that C<In> always be used
-for block tests to avoid confusion.
-
-These block names are supported:
-
- InAegeanNumbers
- InAlphabeticPresentationForms
- InAncientGreekMusicalNotation
- InAncientGreekNumbers
- InArabic
- InArabicPresentationFormsA
- InArabicPresentationFormsB
- InArabicSupplement
- InArmenian
- InArrows
- InBalinese
- InBasicLatin
- InBengali
- InBlockElements
- InBopomofo
- InBopomofoExtended
- InBoxDrawing
- InBraillePatterns
- InBuginese
- InBuhid
- InByzantineMusicalSymbols
- InCJKCompatibility
- InCJKCompatibilityForms
- InCJKCompatibilityIdeographs
- InCJKCompatibilityIdeographsSupplement
- InCJKRadicalsSupplement
- InCJKStrokes
- InCJKSymbolsAndPunctuation
- InCJKUnifiedIdeographs
- InCJKUnifiedIdeographsExtensionA
- InCJKUnifiedIdeographsExtensionB
- InCherokee
- InCombiningDiacriticalMarks
- InCombiningDiacriticalMarksSupplement
- InCombiningDiacriticalMarksforSymbols
- InCombiningHalfMarks
- InControlPictures
- InCoptic
- InCountingRodNumerals
- InCuneiform
- InCuneiformNumbersAndPunctuation
- InCurrencySymbols
- InCypriotSyllabary
- InCyrillic
- InCyrillicSupplement
- InDeseret
- InDevanagari
- InDingbats
- InEnclosedAlphanumerics
- InEnclosedCJKLettersAndMonths
- InEthiopic
- InEthiopicExtended
- InEthiopicSupplement
- InGeneralPunctuation
- InGeometricShapes
- InGeorgian
- InGeorgianSupplement
- InGlagolitic
- InGothic
- InGreekExtended
- InGreekAndCoptic
- InGujarati
- InGurmukhi
- InHalfwidthAndFullwidthForms
- InHangulCompatibilityJamo
- InHangulJamo
- InHangulSyllables
- InHanunoo
- InHebrew
- InHighPrivateUseSurrogates
- InHighSurrogates
- InHiragana
- InIPAExtensions
- InIdeographicDescriptionCharacters
- InKanbun
- InKangxiRadicals
- InKannada
- InKatakana
- InKatakanaPhoneticExtensions
- InKharoshthi
- InKhmer
- InKhmerSymbols
- InLao
- InLatin1Supplement
- InLatinExtendedA
- InLatinExtendedAdditional
- InLatinExtendedB
- InLatinExtendedC
- InLatinExtendedD
- InLetterlikeSymbols
- InLimbu
- InLinearBIdeograms
- InLinearBSyllabary
- InLowSurrogates
- InMalayalam
- InMathematicalAlphanumericSymbols
- InMathematicalOperators
- InMiscellaneousMathematicalSymbolsA
- InMiscellaneousMathematicalSymbolsB
- InMiscellaneousSymbols
- InMiscellaneousSymbolsAndArrows
- InMiscellaneousTechnical
- InModifierToneLetters
- InMongolian
- InMusicalSymbols
- InMyanmar
- InNKo
- InNewTaiLue
- InNumberForms
- InOgham
- InOldItalic
- InOldPersian
- InOpticalCharacterRecognition
- InOriya
- InOsmanya
- InPhagspa
- InPhoenician
- InPhoneticExtensions
- InPhoneticExtensionsSupplement
- InPrivateUseArea
- InRunic
- InShavian
- InSinhala
- InSmallFormVariants
- InSpacingModifierLetters
- InSpecials
- InSuperscriptsAndSubscripts
- InSupplementalArrowsA
- InSupplementalArrowsB
- InSupplementalMathematicalOperators
- InSupplementalPunctuation
- InSupplementaryPrivateUseAreaA
- InSupplementaryPrivateUseAreaB
- InSylotiNagri
- InSyriac
- InTagalog
- InTagbanwa
- InTags
- InTaiLe
- InTaiXuanJingSymbols
- InTamil
- InTelugu
- InThaana
- InThai
- InTibetan
- InTifinagh
- InUgaritic
- InUnifiedCanadianAboriginalSyllabics
- InVariationSelectors
- InVariationSelectorsSupplement
- InVerticalForms
- InYiRadicals
- InYiSyllables
- InYijingHexagramSymbols
+of blocks is more of an artificial grouping based on groups of Unicode
+characters with consecutive ordinal values. For example, the "Basic Latin"
+block is all characters whose ordinals are between 0 and 127, inclusive, in
+other words, the ASCII characters. The "Latin" script contains some letters
+from this block as well as several more, like "Latin-1 Supplement",
+"Latin Extended-A", I<etc.>, but it does not contain all the characters from
+those blocks. It does not, for example, contain digits, because digits are
+shared across many scripts. Digits and similar groups, like punctuation, are in
+the script called C<Common>. There is also a script called C<Inherited> for
+characters that modify other characters, and inherit the script value of the
+controlling character.
+
+For more about scripts versus blocks, see UAX#24 "Unicode Script Property":
+L<http://www.unicode.org/reports/tr24>
+
+The Script property is likely to be the one you want to use when processing
+natural language; the Block property may be useful in working with the nuts and
+bolts of Unicode.
+
+Block names are matched in the compound form, like C<\p{Block: Arrows}> or
+C<\p{Blk=Hebrew}>. Unlike most other properties only a few block names have a
+Unicode-defined short name. But Perl does provide a (slight) shortcut: You
+can say, for example C<\p{In_Arrows}> or C<\p{In_Hebrew}>. For backwards
+compatibility, the C<In> prefix may be omitted if there is no naming conflict
+with a script or any other property, and you can even use an C<Is> prefix
+instead in those cases. But it is not a good idea to do this, for a couple
+reasons:
+
+=over 4
+
+=item 1
+
+It is confusing. There are many naming conflicts, and you may forget some.
+For example, C<\p{Hebrew}> means the I<script> Hebrew, and NOT the I<block>
+Hebrew. But would you remember that 6 months from now?
+
+=item 2
+
+It is unstable. A new version of Unicode may pre-empt the current meaning by
+creating a property with the same name. There was a time in very early Unicode
+releases when C<\p{Hebrew}> would have matched the I<block> Hebrew; now it
+doesn't.
+
+=back
+
+Some people just prefer to always use C<\p{Block: foo}> and C<\p{Script: bar}>
+instead of the shortcuts, for clarity, and because they can't remember the
+difference between 'In' and 'Is' anyway (or aren't confident that those who
+eventually will read their code will know).
+
+A complete list of blocks and their shortcuts is in L<perluniprops>.
+
+=head3 B<Other Properties>
+
+There are many more properties than the very basic ones described here.
+A complete list is in L<perluniprops>.
+
+Unicode defines all its properties in the compound form, so all single-form
+properties are Perl extensions. A number of these are just synonyms for the
+Unicode ones, but some are genunine extensions, including a couple that are in
+the compound form. And quite a few of these are actually recommended by Unicode
+(in L<http://www.unicode.org/reports/tr18>).
+
+This section gives some details on all the extensions that aren't synonyms for
+compound-form Unicode properties (for those, you'll have to refer to the
+L<Unicode Standard|http://www.unicode.org/reports/tr44>.
+
+=over
+
+=item B<C<\p{All}>>
+
+This matches any of the 1_114_112 Unicode code points. It is a synonym for
+C<\p{Any}>.
+
+=item B<C<\p{Alnum}>>
+
+This matches any C<\p{Alphabetic}> or C<\p{Decimal_Number}> character.
+
+=item B<C<\p{Any}>>
+
+This matches any of the 1_114_112 Unicode code points. It is a synonym for
+C<\p{All}>.
+
+=item B<C<\p{Assigned}>>
+
+This matches any assigned code point; that is, any code point whose general
+category is not Unassigned (or equivalently, not Cn).
+
+=item B<C<\p{Blank}>>
+
+This is the same as C<\h> and C<\p{HorizSpace}>: A character that changes the
+spacing horizontally.
+
+=item B<C<\p{Decomposition_Type: Non_Canonical}>> (Short: C<\p{Dt=NonCanon}>)
+
+Matches a character that has a non-canonical decomposition.
+
+To understand the use of this rarely used property=value combination, it is
+necessary to know some basics about decomposition.
+Consider a character, say H. It could appear with various marks around it,
+such as an acute accent, or a circumflex, or various hooks, circles, arrows,
+I<etc.>, above, below, to one side and/or the other, I<etc.> There are many
+possibilities among the world's languages. The number of combinations is
+astronomical, and if there were a character for each combination, it would
+soon exhaust Unicode's more than a million possible characters. So Unicode
+took a different approach: there is a character for the base H, and a
+character for each of the possible marks, and they can be combined variously
+to get a final logical character. So a logical character--what appears to be a
+single character--can be a sequence of more than one individual characters.
+This is called an "extended grapheme cluster". (Perl furnishes the C<\X>
+construct to match such sequences.)
+
+But Unicode's intent is to unify the existing character set standards and
+practices, and a number of pre-existing standards have single characters that
+mean the same thing as some of these combinations. An example is ISO-8859-1,
+which has quite a few of these in the Latin-1 range, an example being "LATIN
+CAPITAL LETTER E WITH ACUTE". Because this character was in this pre-existing
+standard, Unicode added it to its repertoire. But this character is considered
+by Unicode to be equivalent to the sequence consisting of first the character
+"LATIN CAPITAL LETTER E", then the character "COMBINING ACUTE ACCENT".
+
+"LATIN CAPITAL LETTER E WITH ACUTE" is called a "pre-composed" character, and
+the equivalence with the sequence is called canonical equivalence. All
+pre-composed characters are said to have a decomposition (into the equivalent
+sequence) and the decomposition type is also called canonical.
+
+However, many more characters have a different type of decomposition, a
+"compatible" or "non-canonical" decomposition. The sequences that form these
+decompositions are not considered canonically equivalent to the pre-composed
+character. An example, again in the Latin-1 range, is the "SUPERSCRIPT ONE".
+It is kind of like a regular digit 1, but not exactly; its decomposition
+into the digit 1 is called a "compatible" decomposition, specifically a
+"super" decomposition. There are several such compatibility
+decompositions (see L<http://www.unicode.org/reports/tr44>), including one
+called "compat" which means some miscellaneous type of decomposition
+that doesn't fit into the decomposition categories that Unicode has chosen.
+
+Note that most Unicode characters don't have a decomposition, so their
+decomposition type is "None".
+
+Perl has added the C<Non_Canonical> type, for your convenience, to mean any of
+the compatibility decompositions.
+
+=item B<C<\p{Graph}>>
+
+Matches any character that is graphic. Theoretically, this means a character
+that on a printer would cause ink to be used.
+
+=item B<C<\p{HorizSpace}>>
+
+This is the same as C<\h> and C<\p{Blank}>: A character that changes the
+spacing horizontally.
+
+=item B<C<\p{In=*}>>
+
+This is a synonym for C<\p{Present_In=*}>
+
+=item B<C<\p{PerlSpace}>>
+
+This is the same as C<\s>, restricted to ASCII, namely C<S<[ \f\n\r\t]>>.
+
+Mnemonic: Perl's (original) space
+
+=item B<C<\p{PerlWord}>>
+
+This is the same as C<\w>, restricted to ASCII, namely C<[A-Za-z0-9_]>
+
+Mnemonic: Perl's (original) word.
+
+=item B<C<\p{PosixAlnum}>>
+
+This matches any alphanumeric character in the ASCII range, namely
+C<[A-Za-z0-9]>.
+
+=item B<C<\p{PosixAlpha}>>
+
+This matches any alphabetic character in the ASCII range, namely C<[A-Za-z]>.
+
+=item B<C<\p{PosixBlank}>>
+
+This matches any blank character in the ASCII range, namely C<S<[ \t]>>.
+
+=item B<C<\p{PosixCntrl}>>
+
+This matches any control character in the ASCII range, namely C<[\x00-\x1F\x7F]>
+
+=item B<C<\p{PosixDigit}>>
+
+This matches any digit character in the ASCII range, namely C<[0-9]>.
+
+=item B<C<\p{PosixGraph}>>
+
+This matches any graphical character in the ASCII range, namely C<[\x21-\x7E]>.
+
+=item B<C<\p{PosixLower}>>
+
+This matches any lowercase character in the ASCII range, namely C<[a-z]>.
+
+=item B<C<\p{PosixPrint}>>
+
+This matches any printable character in the ASCII range, namely C<[\x20-\x7E]>.
+These are the graphical characters plus SPACE.
+
+=item B<C<\p{PosixPunct}>>
+
+This matches any punctuation character in the ASCII range, namely
+C<[\x21-\x2F\x3A-\x40\x5B-\x60\x7B-\x7E]>. These are the
+graphical characters that aren't word characters. Note that the Posix standard
+includes in its definition of punctuation, those characters that Unicode calls
+"symbols."
+
+=item B<C<\p{PosixSpace}>>
+
+This matches any space character in the ASCII range, namely
+C<S<[ \f\n\r\t\x0B]>> (the last being a vertical tab).
+
+=item B<C<\p{PosixUpper}>>
+
+This matches any uppercase character in the ASCII range, namely C<[A-Z]>.
+
+=item B<C<\p{Present_In: *}>> (Short: C<\p{In=*}>)
+
+This property is used when you need to know in what Unicode version(s) a
+character is.
+
+The "*" above stands for some two digit Unicode version number, such as
+C<1.1> or C<4.0>; or the "*" can also be C<Unassigned>. This property will
+match the code points whose final disposition has been settled as of the
+Unicode release given by the version number; C<\p{Present_In: Unassigned}>
+will match those code points whose meaning has yet to be assigned.
+
+For example, C<U+0041> "LATIN CAPITAL LETTER A" was present in the very first
+Unicode release available, which is C<1.1>, so this property is true for all
+valid "*" versions. On the other hand, C<U+1EFF> was not assigned until version
+5.1 when it became "LATIN SMALL LETTER Y WITH LOOP", so the only "*" that
+would match it are 5.1, 5.2, and later.
+
+Unicode furnishes the C<Age> property from which this is derived. The problem
+with Age is that a strict interpretation of it (which Perl takes) has it
+matching the precise release a code point's meaning is introduced in. Thus
+C<U+0041> would match only 1.1; and C<U+1EFF> only 5.1. This is not usually what
+you want.
+
+Some non-Perl implementations of the Age property may change its meaning to be
+the same as the Perl Present_In property; just be aware of that.
+
+Another confusion with both these properties is that the definition is not
+that the code point has been assigned, but that the meaning of the code point
+has been determined. This is because 66 code points will always be
+unassigned, and, so the Age for them is the Unicode version the decision to
+make them so was made in. For example, C<U+FDD0> is to be permanently
+unassigned to a character, and the decision to do that was made in version 3.1,
+so C<\p{Age=3.1}> matches this character and C<\p{Present_In: 3.1}> and up
+matches as well.
+
+=item B<C<\p{Print}>>
+
+This matches any character that is graphical or is space, but not a control.
+
+=item B<C<\p{SpacePerl}>>
+
+This is the same as C<\s>, including beyond ASCII.
+
+Mnemonic: Space, as modified by Perl. (It doesn't include the vertical tab
+which both the Posix standard and Unicode consider to be space.)
+
+=item B<C<\p{VertSpace}>>
+
+This is the same as C<\v>: A character that changes the spacing vertically.
+
+=item B<C<\p{Word}>>
+
+This is the same as C<\w>, including beyond ASCII.
=back
=head2 User-Defined Character Properties
-You can define your own character properties by defining subroutines
-whose names begin with "In" or "Is". The subroutines can be defined in
-any package. The user-defined properties can be used in the regular
-expression C<\p> and C<\P> constructs; if you are using a user-defined
-property from a package other than the one you are in, you must specify
-its package in the C<\p> or C<\P> construct.
+You can define your own binary character properties by defining subroutines
+whose names begin with "In" or "Is". The subroutines can be defined in any
+package. The user-defined properties can be used in the regular expression
+C<\p> and C<\P> constructs; if you are using a user-defined property from a
+package other than the one you are in, you must specify its package in the
+C<\p> or C<\P> construct.
- # assuming property IsForeign defined in Lang::
+ # assuming property Is_Foreign defined in Lang::
package main; # property package name required
if ($txt =~ /\p{Lang::IsForeign}+/) { ... }
=item *
+A single hexadecimal number denoting a Unicode code point to include.
+
+=item *
+
Two hexadecimal numbers separated by horizontal whitespace (space or
tabular characters) denoting a range of Unicode code points to include.
It's important to remember not to use "&" for the first set -- that
would be intersecting with nothing (resulting in an empty set).
-A final note on the user-defined property tests: they will be used
-only if the scalar has been marked as having Unicode characters.
-Old byte-style strings will not be affected.
-
=head2 User-Defined Case Mappings
You can also define your own mappings to be used in the lc(),
lcfirst(), uc(), and ucfirst() (or their string-inlined versions).
The principle is similar to that of user-defined character
-properties: to define subroutines in the C<main> package
+properties: to define subroutines
with names like C<ToLower> (for lc() and lcfirst()), C<ToTitle> (for
the first character in ucfirst()), and C<ToUpper> (for uc(), and the
rest of the characters in ucfirst()).
-The string returned by the subroutines needs now to be three
-hexadecimal numbers separated by tabulators: start of the source
-range, end of the source range, and start of the destination range.
-For example:
+The string returned by the subroutines needs to be two hexadecimal numbers
+separated by two tabulators: the two numbers being, respectively, the source
+code point and the destination code point. For example:
sub ToUpper {
return <<END;
- 0061\t0063\t0041
+ 0061\t\t0041
END
}
-defines an uc() mapping that causes only the characters "a", "b", and
-"c" to be mapped to "A", "B", "C", all other characters will remain
-unchanged.
-
-If there is no source range to speak of, that is, the mapping is from
-a single character to another single character, leave the end of the
-source range empty, but the two tabulator characters are still needed.
-For example:
-
- sub ToLower {
- return <<END;
- 0041\t\t0061
- END
- }
+defines an uc() mapping that causes only the character "a"
+to be mapped to "A"; all other characters will remain unchanged.
-defines a lc() mapping that causes only "A" to be mapped to "a", all
-other characters will remain unchanged.
+(For serious hackers only) The above means you have to furnish a complete
+mapping; you can't just override a couple of characters and leave the rest
+unchanged. You can find all the mappings in the directory
+C<$Config{privlib}>/F<unicore/To/>. The mapping data is returned as the
+here-document, and the C<utf8::ToSpecFoo> are special exception mappings
+derived from <$Config{privlib}>/F<unicore/SpecialCasing.txt>. The "Digit" and
+"Fold" mappings that one can see in the directory are not directly
+user-accessible, one can use either the C<Unicode::UCD> module, or just match
+case-insensitively (that's when the "Fold" mapping is used).
-(For serious hackers only) If you want to introspect the default
-mappings, you can find the data in the directory
-C<$Config{privlib}>/F<unicore/To/>. The mapping data is returned as
-the here-document, and the C<utf8::ToSpecFoo> are special exception
-mappings derived from <$Config{privlib}>/F<unicore/SpecialCasing.txt>.
-The C<Digit> and C<Fold> mappings that one can see in the directory
-are not directly user-accessible, one can use either the
-C<Unicode::UCD> module, or just match case-insensitively (that's when
-the C<Fold> mapping is used).
+The mappings will only take effect on scalars that have been marked as having
+Unicode characters, for example by using C<utf8::upgrade()>.
+Old byte-style strings are not affected.
-A final note on the user-defined case mappings: they will be used
-only if the scalar has been marked as having Unicode characters.
-Old byte-style strings will not be affected.
+The mappings are in effect for the package they are defined in.
=head2 Character Encodings for Input and Output
[1] \x{...}
[2] \p{...} \P{...}
- [3] supports not only minimal list (general category, scripts,
- Alphabetic, Lowercase, Uppercase, WhiteSpace,
- NoncharacterCodePoint, DefaultIgnorableCodePoint, Any,
- ASCII, Assigned), but also bidirectional types, blocks, etc.
- (see L</"Unicode Character Properties">)
+ [3] supports not only minimal list, but all Unicode character
+ properties (see L</Unicode Character Properties>)
[4] \d \D \s \S \w \W \X [:prop:] [:^prop:]
[5] can use regular expression look-ahead [a] or
user-defined character properties [b] to emulate set operations
[6] \b \B
- [7] note that Perl does Full case-folding in matching, not Simple:
- for example U+1F88 is equivalent with U+1F00 U+03B9,
- not with 1F80. This difference matters for certain Greek
+ [7] note that Perl does Full case-folding in matching (but with bugs),
+ not Simple: for example U+1F88 is equivalent to U+1F00 U+03B9,
+ not with 1F80. This difference matters mainly for certain Greek
capital letters with certain modifiers: the Full case-folding
decomposes the letter, while the Simple case-folding would map
it to a single character.
[c] Try the C<:crlf> layer (see L<PerlIO>).
-[d] Avoid C<use warning 'utf8';> (or say C<no warning 'utf8';>) to allow
-U+FFFF (C<\x{FFFF}>).
+[d] U+FFFF will currently generate a warning message if 'utf8' warnings are
+ enabled
=item *
Level 2 - Extended Unicode Support
RL2.1 Canonical Equivalents - MISSING [10][11]
- RL2.2 Default Grapheme Clusters - MISSING [12][13]
+ RL2.2 Default Grapheme Clusters - MISSING [12]
RL2.3 Default Word Boundaries - MISSING [14]
RL2.4 Default Loose Matches - MISSING [15]
RL2.5 Name Properties - MISSING [16]
[10] see UAX#15 "Unicode Normalization Forms"
[11] have Unicode::Normalize but not integrated to regexes
- [12] have \X but at this level . should equal that
- [13] UAX#29 "Text Boundaries" considers CRLF and Hangul syllable
- clusters as a single grapheme cluster.
+ [12] have \X but we don't have a "Grapheme Cluster Mode"
[14] see UAX#29, Word Boundaries
[15] see UAX#21 "Case Mappings"
[16] have \N{...} but neither compute names of CJK Ideographs
The following table is from Unicode 3.2.
- Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
+ Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
- U+0000..U+007F 00..7F
- U+0080..U+07FF C2..DF 80..BF
- U+0800..U+0FFF E0 A0..BF 80..BF
+ U+0000..U+007F 00..7F
+ U+0080..U+07FF * C2..DF 80..BF
+ U+0800..U+0FFF E0 * A0..BF 80..BF
U+1000..U+CFFF E1..EC 80..BF 80..BF
U+D000..U+D7FF ED 80..9F 80..BF
- U+D800..U+DFFF ******* ill-formed *******
+ U+D800..U+DFFF +++++++ utf16 surrogates, not legal utf8 +++++++
U+E000..U+FFFF EE..EF 80..BF 80..BF
- U+10000..U+3FFFF F0 90..BF 80..BF 80..BF
- U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF
- U+100000..U+10FFFF F4 80..8F 80..BF 80..BF
-
-Note the C<A0..BF> in C<U+0800..U+0FFF>, the C<80..9F> in
-C<U+D000...U+D7FF>, the C<90..B>F in C<U+10000..U+3FFFF>, and the
-C<80...8F> in C<U+100000..U+10FFFF>. The "gaps" are caused by legal
-UTF-8 avoiding non-shortest encodings: it is technically possible to
-UTF-8-encode a single code point in different ways, but that is
-explicitly forbidden, and the shortest possible encoding should always
-be used. So that's what Perl does.
+ U+10000..U+3FFFF F0 * 90..BF 80..BF 80..BF
+ U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF
+ U+100000..U+10FFFF F4 80..8F 80..BF 80..BF
+
+Note the gaps before several of the byte entries above marked by '*'. These are
+caused by legal UTF-8 avoiding non-shortest encodings: it is technically
+possible to UTF-8-encode a single code point in different ways, but that is
+explicitly forbidden, and the shortest possible encoding should always be used
+(and that is what Perl does).
Another way to look at it is via bits:
ccccbbbbbbaaaaaa 1110cccc 10bbbbbb 10aaaaaa
00000dddccccccbbbbbbaaaaaa 11110ddd 10cccccc 10bbbbbb 10aaaaaa
-As you can see, the continuation bytes all begin with C<10>, and the
-leading bits of the start byte tell how many bytes the are in the
+As you can see, the continuation bytes all begin with "10", and the
+leading bits of the start byte tell how many bytes there are in the
encoded character.
=item *
Surrogates are code points set aside to encode the C<U+10000..U+10FFFF>
range of Unicode code points in pairs of 16-bit units. The I<high
-surrogates> are the range C<U+D800..U+DBFF>, and the I<low surrogates>
+surrogates> are the range C<U+D800..U+DBFF> and the I<low surrogates>
are the range C<U+DC00..U+DFFF>. The surrogate encoding is
$hi = ($uni - 0x10000) / 0x400 + 0xD800;
$uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00);
If you try to generate surrogates (for example by using chr()), you
-will get a warning if warnings are turned on, because those code
+will get a warning, if warnings are turned on, because those code
points are not valid for a Unicode character.
Because of the 16-bitness, UTF-16 is byte-order dependent. UTF-16
C<U+FFFE> is guaranteed not to be a valid Unicode character, so the
sequence of bytes C<0xFF 0xFE> is unambiguously "BOM, represented in
little-endian format" and cannot be C<U+FFFE>, represented in big-endian
-format".
+format". (Actually, C<U+FFFE> is legal for use by your program, even for
+input/output, but better not use it if you need a BOM. But it is "illegal for
+interchange", so that an unsuspecting program won't get confused.)
=item *
=head2 Security Implications of Unicode
+Read L<Unicode Security Considerations|http://www.unicode.org/reports/tr36>.
+Also, note the following:
+
=over 4
=item *
possible sequence of UTF-8 bytes should be generated,
because otherwise there is potential for an input buffer overflow at
the receiving end of a UTF-8 connection. Perl always generates the
-shortest length UTF-8, and with warnings on Perl will warn about
+shortest length UTF-8, and with warnings on, Perl will warn about
non-shortest length UTF-8 along with other malformations, such as the
surrogates, which are not real Unicode code points.
encoding or another) could be given as arguments or received as
results, or both, but it is not.
-The following are such interfaces. For all of these interfaces Perl
+The following are such interfaces. Also, see L</The "Unicode Bug">.
+For all of these interfaces Perl
currently (as of 5.8.3) simply assumes byte strings both as arguments
and results, or UTF-8 strings if the C<encoding> pragma has been used.
One reason why Perl does not attempt to resolve the role of Unicode in
-this cases is that the answers are highly dependent on the operating
+these cases is that the answers are highly dependent on the operating
system and the file system(s). For example, whether filenames can be
in Unicode, and in exactly what kind of encoding, is not exactly a
portable concept. Similarly for the qx and system: how well will the
=item *
-chdir, chmod, chown, chroot, exec, link, lstat, mkdir,
+chdir, chmod, chown, chroot, exec, link, lstat, mkdir,
rename, rmdir, stat, symlink, truncate, unlink, utime, -X
=item *
=back
+=head2 The "Unicode Bug"
+
+The term, the "Unicode bug" has been applied to an inconsistency with the
+Unicode characters whose code points are in the Latin-1 Supplement block, that
+is, between 128 and 255. Without a locale specified, unlike all other
+characters or code points, these characters have very different semantics in
+byte semantics versus character semantics.
+
+In character semantics they are interpreted as Unicode code points, which means
+they have the same semantics as Latin-1 (ISO-8859-1).
+
+In byte semantics, they are considered to be unassigned characters, meaning
+that the only semantics they have is their ordinal numbers, and that they are
+not members of various character classes. None are considered to match C<\w>
+for example, but all match C<\W>. (On EBCDIC platforms, the behavior may
+be different from this, depending on the underlying C language library
+functions.)
+
+The behavior is known to have effects on these areas:
+
+=over 4
+
+=item *
+
+Changing the case of a scalar, that is, using C<uc()>, C<ucfirst()>, C<lc()>,
+and C<lcfirst()>, or C<\L>, C<\U>, C<\u> and C<\l> in regular expression
+substitutions.
+
+=item *
+
+Using caseless (C</i>) regular expression matching
+
+=item *
+
+Matching a number of properties in regular expressions, such as C<\w>
+
+=item *
+
+User-defined case change mappings. You can create a C<ToUpper()> function, for
+example, which overrides Perl's built-in case mappings. The scalar must be
+encoded in utf8 for your function to actually be invoked.
+
+=back
+
+This behavior can lead to unexpected results in which a string's semantics
+suddenly change if a code point above 255 is appended to or removed from it,
+which changes the string's semantics from byte to character or vice versa. As
+an example, consider the following program and its output:
+
+ $ perl -le'
+ $s1 = "\xC2";
+ $s2 = "\x{2660}";
+ for ($s1, $s2, $s1.$s2) {
+ print /\w/ || 0;
+ }
+ '
+ 0
+ 0
+ 1
+
+If there's no C<\w> in C<s1> or in C<s2>, why does their concatenation have one?
+
+This anomaly stems from Perl's attempt to not disturb older programs that
+didn't use Unicode, and hence had no semantics for characters outside of the
+ASCII range (except in a locale), along with Perl's desire to add Unicode
+support seamlessly. The result wasn't seamless: these characters were
+orphaned.
+
+Work is being done to correct this, but only some of it was complete in time
+for the 5.12 release. What has been finished is the important part of the case
+changing component. Due to concerns, and some evidence, that older code might
+have come to rely on the existing behavior, the new behavior must be explicitly
+enabled by the feature C<unicode_strings> in the L<feature> pragma, even though
+no new syntax is involved.
+
+See L<perlfunc/lc> for details on how this pragma works in combination with
+various others for casing. Even though the pragma only affects casing
+operations in the 5.12 release, it is planned to have it affect all the
+problematic behaviors in later releases: you can't have one without them all.
+
+In the meantime, a workaround is to always call utf8::upgrade($string), or to
+use the standard modules L<Encode> or L<charnames>.
+
=head2 Forcing Unicode in Perl (Or Unforcing Unicode in Perl)
-Sometimes (see L</"When Unicode Does Not Happen">) there are
-situations where you simply need to force Perl to believe that a byte
-string is UTF-8, or vice versa. The low-level calls
-utf8::upgrade($bytestring) and utf8::downgrade($utf8string) are
+Sometimes (see L</"When Unicode Does Not Happen"> or L</The "Unicode Bug">)
+there are situations where you simply need to force a byte
+string into UTF-8, or vice versa. The low-level calls
+utf8::upgrade($bytestring) and utf8::downgrade($utf8string[, FAIL_OK]) are
the answers.
-Do not use them without careful thought, though: Perl may easily get
-very confused, angry, or even crash, if you suddenly change the 'nature'
-of scalar like that. Especially careful you have to be if you use the
-utf8::upgrade(): any random byte string is not valid UTF-8.
+Note that utf8::downgrade() can fail if the string contains characters
+that don't fit into a byte.
+
+Calling either function on a string that already is in the desired state is a
+no-op.
=head2 Using Unicode in XS
=item *
C<DO_UTF8(sv)> returns true if the C<UTF8> flag is on and the bytes
-pragma is not in effect. C<SvUTF8(sv)> returns true is the C<UTF8>
+pragma is not in effect. C<SvUTF8(sv)> returns true if the C<UTF8>
flag is on; the bytes pragma is ignored. The C<UTF8> flag being on
does B<not> mean that there are any characters of code points greater
than 255 (or 127) in the scalar or that there are even any characters
=item *
-C<uvuni_to_utf8(buf, chr)> writes a Unicode character code point into
+C<uvchr_to_utf8(buf, chr)> writes a Unicode character code point into
a buffer encoding the code point as UTF-8, and returns a pointer
-pointing after the UTF-8 bytes.
+pointing after the UTF-8 bytes. It works appropriately on EBCDIC machines.
=item *
-C<utf8_to_uvuni(buf, lenp)> reads UTF-8 encoded bytes from a buffer and
+C<utf8_to_uvchr(buf, lenp)> reads UTF-8 encoded bytes from a buffer and
returns the Unicode character code point and, optionally, the length of
-the UTF-8 byte sequence.
+the UTF-8 byte sequence. It works appropriately on EBCDIC machines.
=item *
=item *
-C<utf8_hop(s, off)> will return a pointer to an UTF-8 encoded buffer
+C<utf8_hop(s, off)> will return a pointer to a UTF-8 encoded buffer
that is C<off> (positive or negative) Unicode characters displaced
from the UTF-8 buffer C<s>. Be careful not to overstep the buffer:
C<utf8_hop()> will merrily run off the end or the beginning of the
=item *
-C<ibcmp_utf8(s1, pe1, u1, l1, u1, s2, pe2, l2, u2)> can be used to
+C<ibcmp_utf8(s1, pe1, l1, u1, s2, pe2, l2, u2)> can be used to
compare two strings case-insensitively in Unicode. For case-sensitive
comparisons you can just use C<memEQ()> and C<memNE()> as usual.
For more information, see L<perlapi>, and F<utf8.c> and F<utf8.h>
in the Perl source code distribution.
+=head2 Hacking Perl to work on earlier Unicode versions (for very serious hackers only)
+
+Perl by default comes with the latest supported Unicode version built in, but
+you can change to use any earlier one.
+
+Download the files in the version of Unicode that you want from the Unicode web
+site L<http://www.unicode.org>). These should replace the existing files in
+C<\$Config{privlib}>/F<unicore>. (C<\%Config> is available from the Config
+module.) Follow the instructions in F<README.perl> in that directory to change
+some of their names, and then run F<make>.
+
+It is even possible to download them to a different directory, and then change
+F<utf8_heavy.pl> in the directory C<\$Config{privlib}> to point to the new
+directory, or maybe make a copy of that directory before making the change, and
+using C<@INC> or the C<-I> run-time flag to switch between versions at will
+(but because of caching, not in the middle of a process), but all this is
+beyond the scope of these instructions.
+
=head1 BUGS
=head2 Interaction with Locales
Unicode support will also tend to run slower. Use of locales with
Unicode is discouraged.
+=head2 Problems with characters in the Latin-1 Supplement range
+
+See L</The "Unicode Bug">
+
+=head2 Problems with case-insensitive regular expression matching
+
+There are problems with case-insensitive matches, including those involving
+character classes (enclosed in [square brackets]), characters whose fold
+is to multiple characters (such as the single character LATIN SMALL LIGATURE
+FFL matches case-insensitively with the 3-character string C<ffl>), and
+characters in the Latin-1 Supplement.
+
=head2 Interaction with Extensions
When Perl exchanges data with an extension, the extension should be
like C<\d> (then again, there 268 Unicode characters matching C<Nd>
compared with the 10 ASCII characters matching C<d>).
+=head2 Problems on EBCDIC platforms
+
+There are a number of known problems with Perl on EBCDIC platforms. If you
+want to use Perl there, send email to perlbug@perl.org.
+
+In earlier versions, when byte and character data were concatenated,
+the new string was sometimes created by
+decoding the byte strings as I<ISO 8859-1 (Latin-1)>, even if the
+old Unicode string used EBCDIC.
+
+If you find any of these, please report them as bugs.
+
=head2 Porting code from perl-5.6.X
Perl 5.8 has a different Unicode model from 5.6. In 5.6 the programmer
A filehandle that should read or write UTF-8
if ($] > 5.007) {
- binmode $fh, ":utf8";
+ binmode $fh, ":encoding(utf8)";
}
=item *
=head1 SEE ALSO
-L<perlunitut>, L<perluniintro>, L<Encode>, L<open>, L<utf8>, L<bytes>,
+L<perlunitut>, L<perluniintro>, L<perluniprops>, L<Encode>, L<open>, L<utf8>, L<bytes>,
L<perlretut>, L<perlvar/"${^UNICODE}">
+L<http://www.unicode.org/reports/tr44>).
=cut
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