=head2 Important Caveats
-Unicode support is an extensive requirement. While perl does not
+Unicode support is an extensive requirement. While Perl does not
implement the Unicode standard or the accompanying technical reports
from cover to cover, Perl does support many Unicode features.
=over 4
-=item Input and Output Disciplines
+=item Input and Output Layers
-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.
-See L<open>.
+Perl knows when a filehandle uses Perl's internal Unicode encodings
+(UTF-8, or UTF-EBCDIC if in EBCDIC) if the filehandle is opened 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. See L<open>.
-To mark the Perl source itself as being in a particular encoding,
+To indicate that Perl source itself is using a particular encoding,
see L<encoding>.
=item Regular Expressions
The regular expression compiler produces polymorphic opcodes. That is,
-the pattern adapts 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 pattern adapts to the data and automatically switches to the Unicode
+character scheme when presented with Unicode data--or instead uses
+a traditional byte scheme when presented with byte data.
=item C<use utf8> still needed to enable UTF-8/UTF-EBCDIC in scripts
-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 to recognize UTF-EBCDIC on EBCDIC based machines.
-B<NOTE: this should be the only place where an explicit C<use utf8>
-is needed>.
+As a compatibility measure, the C<use utf8> pragma must be explicitly
+included to enable recognition of UTF-8 in the Perl scripts themselves
+(in string or regular expression literals, or in identifier names) on
+ASCII-based machines or to recognize UTF-EBCDIC on EBCDIC-based
+machines. B<These are the only times when an explicit C<use utf8>
+is needed.> See L<utf8>.
You can also use the C<encoding> pragma to change the default encoding
of the data in your script; see L<encoding>.
=back
-=head2 Byte and Character semantics
+=head2 Byte and Character Semantics
-Beginning with version 5.6, Perl uses logically wide characters to
+Beginning with version 5.6, Perl uses logically-wide characters to
represent strings internally.
-In future, Perl-level operations can be expected to work with
-characters rather than bytes, in general.
+In future, Perl-level operations will be expected to work with
+characters rather than bytes.
-However, as strictly an interim compatibility measure, Perl aims to
+However, as 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
+decide that the input data are characters, Perl 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.
+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
+which allowed byte semantics in Perl operations only if
+none of the program's inputs were 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.
-On Windows platforms, 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 lack an
-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<bytes> pragma will always, regardless of platform, 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|EBCDIC) in literals encountered by the parser.
-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.
-Thus, character semantics for these operations apply transparently; if
-the input data came from a Unicode source (for example, by adding a
-character encoding discipline to the filehandle whence it came, or a
-literal Unicode string constant in the program), character semantics
-apply; otherwise, byte semantics are in effect. To force byte semantics
-on Unicode data, the C<bytes> pragma should be used.
-
-Notice that if you concatenate strings with byte semantics and strings
-with Unicode character data, the bytes will by default be upgraded
-I<as if they were ISO 8859-1 (Latin-1)> (or if in EBCDIC, after a
-translation to ISO 8859-1). This is done without regard to the
-system's native 8-bit encoding, so to change this for systems with
-non-Latin-1 (or non-EBCDIC) native encodings, use the C<encoding>
-pragma, see L<encoding>.
+Note that this pragma is only required while Perl defaults to byte
+semantics; when character semantics become the default, this pragma
+may become a no-op. See L<utf8>.
+
+Unless explicitly stated, Perl operators use character semantics
+for Unicode data and byte semantics for non-Unicode data.
+The decision to use character semantics is made transparently. If
+input data comes from a Unicode source--for example, if a character
+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.
+
+If strings operating under byte semantics and strings with Unicode
+character data are concatenated, the new string will be upgraded to
+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, so to change this for systems with non-Latin-1 and
+non-EBCDIC native encodings use the C<encoding> pragma. See
+L<encoding>.
Under character semantics, many operations that formerly operated on
-bytes change to operating on characters. A character in Perl is
+bytes now operate on characters. A character in Perl is
logically just a number ranging from 0 to 2**31 or so. Larger
-characters may encode to longer sequences of bytes internally, but
-this is just an internal detail which is hidden at the Perl level.
-See L<perluniintro> for more on this.
+characters may encode into longer sequences of bytes internally, but
+this internal detail is mostly hidden for Perl code.
+See L<perluniintro> for more.
-=head2 Effects of character semantics
+=head2 Effects of Character Semantics
Character semantics have the following effects:
=item *
-Strings and patterns may contain characters that have an ordinal value
-larger than 255.
+Strings--including hash keys--and regular expression patterns may
+contain characters that have an ordinal value larger than 255.
If you use a Unicode editor to edit your program, Unicode characters
may occur directly within the literal strings in one of the various
-Unicode encodings (UTF-8, UTF-EBCDIC, UCS-2, etc.), but are recognized
-as such (and converted to Perl's internal representation) only if the
+Unicode encodings (UTF-8, UTF-EBCDIC, UCS-2, etc.), but will be recognized
+as such and converted to Perl's internal representation only if the
appropriate L<encoding> is specified.
-You can also get Unicode characters into a string by using the C<\x{...}>
-notation, putting the Unicode code for the desired character, in
-hexadecimal, into the curlies. For instance, a smiley face is C<\x{263A}>.
-This works only for characters with a code 0x100 and above.
+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 characters
+with a code of 0x100 or above.
Additionally, if you
+
use charnames ':full';
-you can use the C<\N{...}> notation, putting the official Unicode character
-name within the curlies. For example, C<\N{WHITE SMILING FACE}>.
-This works for all characters that have names.
+
+you can use the C<\N{...}> notation and put the official Unicode
+character name within the braces, such as C<\N{WHITE SMILING FACE}>.
+
=item *
-If an appropriate L<encoding> is specified,
-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.)
+If an appropriate L<encoding> is specified, identifiers within the
+Perl script may contain Unicode alphanumeric characters, including
+ideographs. Perl does not currently attempt to canonicalize variable
+names.
=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>).)
+Regular expressions match characters instead of bytes. "." matches
+a character instead of a byte. The C<\C> pattern is provided to force
+a match a single byte--a 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
+bytes and match against the character properties specified in the
+Unicode properties database. C<\w> can be used to match a Japanese
ideograph, for instance.
=item *
-Named Unicode properties and block ranges may be used as character
-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 "Lu" (Letter, uppercase) property, while
-C<\p{M}> matches any character with a "M" (mark -- accents and such)
-property. 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}>.
+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".
-The C<\p{Is...}> test for "general properties" such as "letter",
-"digit", while the C<\p{In...}> test for Unicode scripts and blocks.
+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 have dashes, spaces, and
-underbars at every word division, and you need not care about correct
-casing. It is recommended, however, that for consistency you use the
-following naming: the official Unicode script, block, or property name
-(see below for the additional rules that apply to block names), with
-whitespace and dashes replaced with underbar, and the words
-"uppercase-first-lowercase-rest". That is, "Latin-1 Supplement"
-becomes "Latin_1_Supplement".
-
-You can also negate both C<\p{}> and C<\P{}> by introducing a caret
-(^) between the first curly and the property name: C<\p{^In_Tamil}> is
-equal to C<\P{In_Tamil}>.
-
-The C<In> and C<Is> can be left out: C<\p{Greek}> is equal to
-C<\p{In_Greek}>, C<\P{Pd}> is equal to C<\P{Pd}>.
+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>.
+
+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}>.
+
+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.
Short Long
L Letter
- Lu Uppercase_Letter
- Ll Lowercase_Letter
- Lt Titlecase_Letter
- Lm Modifier_Letter
- Lo Other_Letter
+ Lu UppercaseLetter
+ Ll LowercaseLetter
+ Lt TitlecaseLetter
+ Lm ModifierLetter
+ Lo OtherLetter
M Mark
- Mn Nonspacing_Mark
- Mc Spacing_Mark
- Me Enclosing_Mark
+ Mn NonspacingMark
+ Mc SpacingMark
+ Me EnclosingMark
N Number
- Nd Decimal_Number
- Nl Letter_Number
- No Other_Number
+ Nd DecimalNumber
+ Nl LetterNumber
+ No OtherNumber
P Punctuation
- Pc Connector_Punctuation
- Pd Dash_Punctuation
- Ps Open_Punctuation
- Pe Close_Punctuation
- Pi Initial_Punctuation
+ Pc ConnectorPunctuation
+ Pd DashPunctuation
+ Ps OpenPunctuation
+ Pe ClosePunctuation
+ Pi InitialPunctuation
(may behave like Ps or Pe depending on usage)
- Pf Final_Punctuation
+ Pf FinalPunctuation
(may behave like Ps or Pe depending on usage)
- Po Other_Punctuation
+ Po OtherPunctuation
S Symbol
- Sm Math_Symbol
- Sc Currency_Symbol
- Sk Modifier_Symbol
- So Other_Symbol
+ Sm MathSymbol
+ Sc CurrencySymbol
+ Sk ModifierSymbol
+ So OtherSymbol
Z Separator
- Zs Space_Separator
- Zl Line_Separator
- Zp Paragraph_Separator
+ Zs SpaceSeparator
+ Zl LineSeparator
+ Zp ParagraphSeparator
C Other
Cc Control
Cf Format
- Cs Surrogate
- Co Private_Use
+ Cs Surrogate (not usable)
+ Co PrivateUse
Cn Unassigned
-The single-letter properties match all characters in any of the
+Single-letter properties match all characters in any of the
two-letter sub-properties starting with the same letter.
-There's also C<L&> which is an alias for C<Ll>, C<Lu>, and C<Lt>.
-
-The following reserved ranges have C<In> tests:
-
- CJK_Ideograph_Extension_A
- CJK_Ideograph
- Hangul_Syllable
- Non_Private_Use_High_Surrogate
- Private_Use_High_Surrogate
- Low_Surrogate
- Private_Surrogate
- CJK_Ideograph_Extension_B
- Plane_15_Private_Use
- Plane_16_Private_Use
-
-For example C<"\x{AC00}" =~ \p{HangulSyllable}> will test true.
-(Handling of surrogates is not implemented yet, because Perl
-uses UTF-8 and not UTF-16 internally to represent Unicode.
-So you really can't use the "Cs" category.)
-
-Additionally, because scripts differ in their directionality
-(for example Hebrew is written right to left), all characters
-have their directionality defined:
+C<L&> is a special case, which is an alias for C<Ll>, C<Lu>, and C<Lt>.
+
+Because Perl hides the need for the user to understand the internal
+representation of Unicode characters, there is no need to implement
+the somewhat messy concept of surrogates. C<Cs> is therefore not
+supported.
+
+Because scripts differ in their directionality--Hebrew is
+written right to left, for example--Unicode supplies these properties:
+
+ Property Meaning
BidiL Left-to-Right
BidiLRE Left-to-Right Embedding
BidiWS Whitespace
BidiON Other Neutrals
+For example, C<\p{BidiR}> matches characters that are normally
+written right to left.
+
=back
=head2 Scripts
-The scripts available for C<\p{In...}> and C<\P{In...}>, for example
-C<\p{InLatin}> or \p{InCyrillic>, are as follows:
+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
Bengali
Bopomofo
- Canadian-Aboriginal
+ Buhid
+ CanadianAboriginal
Cherokee
Cyrillic
Deseret
Gurmukhi
Han
Hangul
+ Hanunoo
Hebrew
Hiragana
Inherited
Mongolian
Myanmar
Ogham
- Old-Italic
+ OldItalic
Oriya
Runic
Sinhala
Syriac
+ Tagalog
+ Tagbanwa
Tamil
Telugu
Thaana
Tibetan
Yi
-There are also extended property classes that supplement the basic
+Extended property classes can supplement the basic
properties, defined by the F<PropList> Unicode database:
- ASCII_Hex_Digit
- Bidi_Control
+ ASCIIHexDigit
+ BidiControl
Dash
+ Deprecated
Diacritic
Extender
- Hex_Digit
+ GraphemeLink
+ HexDigit
Hyphen
Ideographic
- Join_Control
- Noncharacter_Code_Point
- Other_Alphabetic
- Other_Lowercase
- Other_Math
- Other_Uppercase
- Quotation_Mark
- White_Space
-
-and further derived properties:
-
- Alphabetic Lu + Ll + Lt + Lm + Lo + Other_Alphabetic
- Lowercase Ll + Other_Lowercase
- Uppercase Lu + Other_Uppercase
- Math Sm + Other_Math
+ IDSBinaryOperator
+ IDSTrinaryOperator
+ JoinControl
+ LogicalOrderException
+ NoncharacterCodePoint
+ OtherAlphabetic
+ OtherDefaultIgnorableCodePoint
+ OtherGraphemeExtend
+ OtherLowercase
+ OtherMath
+ OtherUppercase
+ QuotationMark
+ Radical
+ SoftDotted
+ TerminalPunctuation
+ UnifiedIdeograph
+ WhiteSpace
+
+and there are further derived properties:
+
+ Alphabetic Lu + Ll + Lt + Lm + Lo + OtherAlphabetic
+ Lowercase Ll + OtherLowercase
+ Uppercase Lu + OtherUppercase
+ Math Sm + OtherMath
ID_Start Lu + Ll + Lt + Lm + Lo + Nl
ID_Continue ID_Start + Mn + Mc + Nd + Pc
Any Any character
- Assigned Any non-Cn character
+ Assigned Any non-Cn character (i.e. synonym for \P{Cn})
+ Unassigned Synonym for \p{Cn}
Common Any character (or unassigned code point)
not explicitly assigned to a script
+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}>.
+
=head2 Blocks
In addition to B<scripts>, Unicode also defines B<blocks> of
characters. The difference between scripts and blocks is that the
-scripts concept is closer to natural languages, while the blocks
-concept is more an artificial grouping based on groups of 256 Unicode
-characters. For example, the C<Latin> script contains letters from
-many blocks. On the other hand, the C<Latin> script 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 other similar groups, like punctuation, are in a category called
-C<Common>.
+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 UTR #24:
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 only the blocks were used; in Perl 5.8.0 scripts became the
-preferential Unicode character class definition (prompted by
-recommendations from the Unicode consortium); this meant that
-the definitions of some character classes changed (the ones in
-the below list that have the C<Block> appended).
-
- Alphabetic Presentation Forms
- Arabic Block
- Arabic Presentation Forms-A
- Arabic Presentation Forms-B
- Armenian Block
- Arrows
- Basic Latin
- Bengali Block
- Block Elements
- Bopomofo Block
- Bopomofo Extended
- Box Drawing
- Braille Patterns
- Byzantine Musical Symbols
- CJK Compatibility
- CJK Compatibility Forms
- CJK Compatibility Ideographs
- CJK Compatibility Ideographs Supplement
- CJK Radicals Supplement
- CJK Symbols and Punctuation
- CJK Unified Ideographs
- CJK Unified Ideographs Extension A
- CJK Unified Ideographs Extension B
- Cherokee Block
- Combining Diacritical Marks
- Combining Half Marks
- Combining Marks for Symbols
- Control Pictures
- Currency Symbols
- Cyrillic Block
- Deseret Block
- Devanagari Block
- Dingbats
- Enclosed Alphanumerics
- Enclosed CJK Letters and Months
- Ethiopic Block
- General Punctuation
- Geometric Shapes
- Georgian Block
- Gothic Block
- Greek Block
- Greek Extended
- Gujarati Block
- Gurmukhi Block
- Halfwidth and Fullwidth Forms
- Hangul Compatibility Jamo
- Hangul Jamo
- Hangul Syllables
- Hebrew Block
- High Private Use Surrogates
- High Surrogates
- Hiragana Block
- IPA Extensions
- Ideographic Description Characters
- Kanbun
- Kangxi Radicals
- Kannada Block
- Katakana Block
- Khmer Block
- Lao Block
- Latin 1 Supplement
- Latin Extended Additional
- Latin Extended-A
- Latin Extended-B
- Letterlike Symbols
- Low Surrogates
- Malayalam Block
- Mathematical Alphanumeric Symbols
- Mathematical Operators
- Miscellaneous Symbols
- Miscellaneous Technical
- Mongolian Block
- Musical Symbols
- Myanmar Block
- Number Forms
- Ogham Block
- Old Italic Block
- Optical Character Recognition
- Oriya Block
- Private Use
- Runic Block
- Sinhala Block
- Small Form Variants
- Spacing Modifier Letters
- Specials
- Superscripts and Subscripts
- Syriac Block
- Tags
- Tamil Block
- Telugu Block
- Thaana Block
- Thai Block
- Tibetan Block
- Unified Canadian Aboriginal Syllabics
- Yi Radicals
- Yi Syllables
+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:
+
+ InAlphabeticPresentationForms
+ InArabic
+ InArabicPresentationFormsA
+ InArabicPresentationFormsB
+ InArmenian
+ InArrows
+ InBasicLatin
+ InBengali
+ InBlockElements
+ InBopomofo
+ InBopomofoExtended
+ InBoxDrawing
+ InBraillePatterns
+ InBuhid
+ InByzantineMusicalSymbols
+ InCJKCompatibility
+ InCJKCompatibilityForms
+ InCJKCompatibilityIdeographs
+ InCJKCompatibilityIdeographsSupplement
+ InCJKRadicalsSupplement
+ InCJKSymbolsAndPunctuation
+ InCJKUnifiedIdeographs
+ InCJKUnifiedIdeographsExtensionA
+ InCJKUnifiedIdeographsExtensionB
+ InCherokee
+ InCombiningDiacriticalMarks
+ InCombiningDiacriticalMarksforSymbols
+ InCombiningHalfMarks
+ InControlPictures
+ InCurrencySymbols
+ InCyrillic
+ InCyrillicSupplementary
+ InDeseret
+ InDevanagari
+ InDingbats
+ InEnclosedAlphanumerics
+ InEnclosedCJKLettersAndMonths
+ InEthiopic
+ InGeneralPunctuation
+ InGeometricShapes
+ InGeorgian
+ InGothic
+ InGreekExtended
+ InGreekAndCoptic
+ InGujarati
+ InGurmukhi
+ InHalfwidthAndFullwidthForms
+ InHangulCompatibilityJamo
+ InHangulJamo
+ InHangulSyllables
+ InHanunoo
+ InHebrew
+ InHighPrivateUseSurrogates
+ InHighSurrogates
+ InHiragana
+ InIPAExtensions
+ InIdeographicDescriptionCharacters
+ InKanbun
+ InKangxiRadicals
+ InKannada
+ InKatakana
+ InKatakanaPhoneticExtensions
+ InKhmer
+ InLao
+ InLatin1Supplement
+ InLatinExtendedA
+ InLatinExtendedAdditional
+ InLatinExtendedB
+ InLetterlikeSymbols
+ InLowSurrogates
+ InMalayalam
+ InMathematicalAlphanumericSymbols
+ InMathematicalOperators
+ InMiscellaneousMathematicalSymbolsA
+ InMiscellaneousMathematicalSymbolsB
+ InMiscellaneousSymbols
+ InMiscellaneousTechnical
+ InMongolian
+ InMusicalSymbols
+ InMyanmar
+ InNumberForms
+ InOgham
+ InOldItalic
+ InOpticalCharacterRecognition
+ InOriya
+ InPrivateUseArea
+ InRunic
+ InSinhala
+ InSmallFormVariants
+ InSpacingModifierLetters
+ InSpecials
+ InSuperscriptsAndSubscripts
+ InSupplementalArrowsA
+ InSupplementalArrowsB
+ InSupplementalMathematicalOperators
+ InSupplementaryPrivateUseAreaA
+ InSupplementaryPrivateUseAreaB
+ InSyriac
+ InTagalog
+ InTagbanwa
+ InTags
+ InTamil
+ InTelugu
+ InThaana
+ InThai
+ InTibetan
+ InUnifiedCanadianAboriginalSyllabics
+ InVariationSelectors
+ InYiRadicals
+ InYiSyllables
=over 4
=item *
-The special pattern C<\X> match 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. It is equivalent to
+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*)>.
=item *
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', ...).
+that the C<tr///CU> functionality has been removed. For similar
+functionality see pack('U0', ...) and pack('C0', ...).
=item *
Case translation operators use the Unicode case translation tables
-when provided character input. Note that C<uc()> (also known as C<\U>
-in doublequoted strings) translates to uppercase, while C<ucfirst>
-(also known as C<\u> in doublequoted strings) translates to titlecase
-(for languages that make the distinction). Naturally the
-corresponding backslash sequences have the same semantics.
+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.
=item *
-Most operators that deal with positions or lengths in the string will
+Most operators that deal with positions or lengths in a 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 do
n'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.
+specifically do
not switch include C<vec()>, C<pack()>, and
+C<unpack()>. Operators that really don't care include C<chomp()>,
+operators that treats strings as a bucket of bits such as C<sort()>,
+and operators dealing with filenames.
=item *
-The C<pack()>/C<unpack()> letters "C<c>" and "C<C>" do I<not> change,
-since they're often used for byte-oriented formats. (Again, think
-"C<char>" in the C language.) However, there is a new "C<U>" specifier
-that will convert between Unicode characters and integers.
+The C<pack()>/C<unpack()> letters C<c> and C<C> do I<not> change,
+since they are 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
+and code points.
=item *
-The C<chr()> and C<ord()> functions work on characters. This is like
-C<pack("U")> and C<unpack("U")>,
not like C<pack("C")> and
-C<unpack("C")>. In fact, the latter are how you now emulate
-byte-oriented C<chr()> and C<ord()> for Unicode strings.
-(Note that this reveals the internal encoding of Unicode strings,
-which is not something one normally needs to care about at all.)
+The C<chr()> and C<ord()> functions work on characters, similar to
+C<pack("U")> and C<unpack("U")>,
I<not> C<pack("C")> and
+C<unpack("C")>. C<pack("C")> and C<unpack("C")> are methods for
+emulating byte-oriented C<chr()> and C<ord()> on Unicode strings.
+While these methods reveal the internal encoding of Unicode strings,
+that is not something one normally needs to care about at all.
=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|~$y>) won't hold.
-Another way to look at this is that the complement cannot return
-B<both> the 8-bit (byte) wide bit complement B<and> the full character
-wide bit complement.
+The bit string operators, C<& | ^ ~>, can operate on character data.
+However, for backward compatibility, such as when using bit string
+operations when characters are all less than 256 in ordinal value, one
+should not use C<~> (the bit complement) with characters of both
+values less than 256 and values greater than 256. Most importantly,
+DeMorgan's laws (C<~($x|$y) eq ~$x&~$y> and C<~($x&$y) eq ~$x|~$y>)
+will not hold. The reason for this mathematical I<faux pas> is that
+the complement cannot return B<both> the 8-bit (byte-wide) bit
+complement B<and> the full character-wide bit complement.
=item *
=item *
the case mapping is from a single Unicode character to another
-single Unicode character
+single Unicode character, or
=item *
the case mapping is from a single Unicode character to more
-than one Unicode character
+than one Unicode character.
=back
-What doesn't yet work are the following cases:
+Things to do with locales (Lithuanian, Turkish, Azeri) do B<not> work
+since Perl does not understand the concept of Unicode locales.
-=over 8
+See the Unicode Technical Report #21, Case Mappings, for more details.
-=item *
+=back
-the "final sigma" (Greek)
+=over 4
=item *
-anything to with locales (Lithuanian, Turkish, Azeri)
+And finally, C<scalar reverse()> reverses by character rather than by byte.
=back
-See the Unicode Technical Report #21, Case Mappings, for more details.
+=head2 User-Defined Character Properties
+
+You can define your own character properties by defining subroutines
+whose names begin with "In" or "Is". The subroutines must be defined
+in the C<main> package. The user-defined properties can be used in the
+regular expression C<\p> and C<\P> constructs. Note that the effect
+is compile-time and immutable once defined.
+
+The subroutines must return a specially-formatted string, with one
+or more newline-separated lines. Each line must be one of the following:
+
+=over 4
=item *
-And finally, C<scalar reverse()> reverses by character rather than by byte.
+Two hexadecimal numbers separated by horizontal whitespace (space or
+tabular characters) denoting a range of Unicode code points to include.
-=back
+=item *
-=head2 Character encodings for input and output
+Something to include, prefixed by "+": a built-in character
+property (prefixed by "utf8::"), to represent all the characters in that
+property; two hexadecimal code points for a range; or a single
+hexadecimal code point.
-See L<Encode>.
+=item *
-=head1 CAVEATS
+Something to exclude, prefixed by "-": an existing character
+property (prefixed by "utf8::"), for all the characters in that
+property; two hexadecimal code points for a range; or a single
+hexadecimal code point.
-Whether an arbitrary piece of data will be treated as "characters" or
-"bytes" by internal operations cannot be divined at the current time.
+=item *
-Use of locales with Unicode data may lead to odd results. Currently
-there is some attempt to apply 8-bit locale info to characters in the
-range 0..255, but this is demonstrably incorrect for locales that use
-characters above that range when mapped into Unicode. It will also
-tend to run slower. Avoidance of locales is strongly encouraged.
+Something to negate, prefixed "!": an existing character
+property (prefixed by "utf8::") for all the characters except the
+characters in the property; two hexadecimal code points for a range;
+or a single hexadecimal code point.
-=head1 UNICODE REGULAR EXPRESSION SUPPORT LEVEL
+=back
+
+For example, to define a property that covers both the Japanese
+syllabaries (hiragana and katakana), you can define
+
+ sub InKana {
+ return <<END;
+ 3040\t309F
+ 30A0\t30FF
+ END
+ }
+
+Imagine that the here-doc end marker is at the beginning of the line.
+Now you can use C<\p{InKana}> and C<\P{InKana}>.
+
+You could also have used the existing block property names:
+
+ sub InKana {
+ return <<'END';
+ +utf8::InHiragana
+ +utf8::InKatakana
+ END
+ }
+
+Suppose you wanted to match only the allocated characters,
+not the raw block ranges: in other words, you want to remove
+the non-characters:
+
+ sub InKana {
+ return <<'END';
+ +utf8::InHiragana
+ +utf8::InKatakana
+ -utf8::IsCn
+ END
+ }
+
+The negation is useful for defining (surprise!) negated classes.
+
+ sub InNotKana {
+ return <<'END';
+ !utf8::InHiragana
+ -utf8::InKatakana
+ +utf8::IsCn
+ END
+ }
+
+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 the same: define subroutines in the C<main> package
+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:
+
+ sub ToUpper {
+ return <<END;
+ 0061\t0063\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 a lc() mapping that causes only "A" to be mapped to "a", all
+other characters will remain unchanged.
+
+(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).
+
+A final note on the user-defined property tests and mappings: they
+will be used only if the scalar has been marked as having Unicode
+characters. Old byte-style strings will not be affected.
+
+=head2 Character Encodings for Input and Output
+
+See L<Encode>.
-The following list of Unicode regular expression support describes
-feature by feature the Unicode support implemented in Perl as of Perl
-5.8.0. The "Level N" and the section numbers refer to the Unicode
-Technical Report 18, "Unicode Regular Expression Guidelines".
+=head2 Unicode Regular Expression Support Level
+
+The following list of Unicode support for regular expressions describes
+all the features currently supported. The references to "Level N"
+and the section numbers refer to the Unicode Technical Report 18,
+"Unicode Regular Expression Guidelines".
=over 4
Level 1 - Basic Unicode Support
2.1 Hex Notation - done [1]
- Named Notation - done [2]
+ Named Notation - done [2]
2.2 Categories - done [3][4]
2.3 Subtraction - MISSING [5][6]
2.4 Simple Word Boundaries - done [7]
- 2.5 Simple Loose Matches - MISSING [8]
+ 2.5 Simple Loose Matches - done [8]
2.6 End of Line - MISSING [9][10]
[ 1] \x{...}
[ 2] \N{...}
- [ 3] . \p{Is...} \P{Is...}
+ [ 3] . \p{...} \P{...}
[ 4] now scripts (see UTR#24 Script Names) in addition to blocks
[ 5] have negation
- [ 6] can use look-ahead to emulate subtraction (*)
+ [ 6] can use regular expression look-ahead [a]
+ or user-defined character properties [b] to emulate subtraction
[ 7] include Letters in word characters
- [ 8] see UTR#21 Case Mappings: Perl implements most mappings,
- but not yet special cases like the SIGMA example.
- [ 9] see UTR#13 Unicode Newline Guidelines
- [10] should do ^ and $ also on \x{85}, \x{2028} and \x{2029})
+ [ 8] 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
+ capital letters with certain modifiers: the Full case-folding
+ decomposes the letter, while the Simple case-folding would map
+ it to a single character.
+ [ 9] see UTR #13 Unicode Newline Guidelines
+ [10] should do ^ and $ also on \x{85}, \x{2028} and \x{2029}
(should also affect <>, $., and script line numbers)
-
-(*) You can mimic class subtraction using lookahead.
-For example, what TR18 might write as
+ (the \x{85}, \x{2028} and \x{2029} do match \s)
+
+[a] You can mimic class subtraction using lookahead.
+For example, what UTR #18 might write as
[{Greek}-[{UNASSIGNED}]]
in Perl can be written as:
- (?!\p{UNASSIGNED})\p{GreekBlock}
- (?=\p{ASSIGNED})\p{GreekBlock}
+ (?!\p{Unassigned})\p{InGreekAndCoptic}
+ (?=\p{Assigned})\p{InGreekAndCoptic}
But in this particular example, you probably really want
- \p{Greek}
+ \p{GreekAndCoptic}
which will match assigned characters known to be part of the Greek script.
+Also see the Unicode::Regex::Set module, it does implement the full
+UTR #18 grouping, intersection, union, and removal (subtraction) syntax.
+
+[b] See L</"User-Defined Character Properties">.
+
=item *
Level 2 - Extended Unicode Support
- 3.1 Surrogates - MISSING
- 3.2 Canonical Equivalents - MISSING [11][12]
- 3.3 Locale-Independent Graphemes - MISSING [13]
- 3.4 Locale-Independent Words - MISSING [14]
- 3.5 Locale-Independent Loose Matches - MISSING [15]
+ 3.1 Surrogates - MISSING [11]
+ 3.2 Canonical Equivalents - MISSING [12][13]
+ 3.3 Locale-Independent Graphemes - MISSING [14]
+ 3.4 Locale-Independent Words - MISSING [15]
+ 3.5 Locale-Independent Loose Matches - MISSING [16]
- [11] see UTR#15 Unicode Normalization
- [12] have Unicode::Normalize but not integrated to regexes
- [13] have \X but at this level . should equal that
- [14] need three classes, not just \w and \W
- [15] see UTR#21 Case Mappings
+ [11] Surrogates are solely a UTF-16 concept and Perl's internal
+ representation is UTF-8. The Encode module does UTF-16, though.
+ [12] see UTR#15 Unicode Normalization
+ [13] have Unicode::Normalize but not integrated to regexes
+ [14] have \X but at this level . should equal that
+ [15] need three classes, not just \w and \W
+ [16] see UTR#21 Case Mappings
=item *
=head2 Unicode Encodings
-Unicode characters are assigned to I<code points> which are abstract
-numbers. To use these numbers various encodings are needed.
+Unicode characters are assigned to I<code points>, which are abstract
+numbers. To use these numbers, various encodings are needed.
=over 4
-=item UTF-8
+=item *
+
+UTF-8
UTF-8 is a variable-length (1 to 6 bytes, current character allocations
-require 4 bytes), byteorder independent encoding. For ASCII, UTF-8 is
-transparent (and we really do mean 7-bit ASCII, not another 8-bit encoding).
+require 4 bytes), byte-order independent encoding. For ASCII (and we
+really do mean 7-bit ASCII, not another 8-bit encoding), UTF-8 is
+transparent.
-The following table is from Unicode 3.1.
+The following table is from Unicode 3.2.
Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
- U+0000..U+007F 00..7FÂ Â Â
- U+0080..U+07FF C2..DF 80..BFÂ Â Â
- U+0800..U+0FFF E0 A0..BF 80..BFÂ Â
- U+1000..U+FFFF E1..EF 80..BF 80..BFÂ Â
+ 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+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
-Or, another way to look at it, as bits:
+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.
+
+Another way to look at it is via bits:
Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
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 tells how many bytes the are in the
+leading bits of the start byte tell how many bytes the are in the
encoded character.
-=item UTF-EBCDIC
+=item *
-Like UTF-8, but EBCDIC-safe, as UTF-8 is ASCII-safe.
+UTF-EBCDIC
-=item UTF-16, UTF-16BE, UTF16-LE, Surrogates, and BOMs (Byte Order Marks)
+Like UTF-8 but EBCDIC-safe, in the way that UTF-8 is ASCII-safe.
-(The followings items are mostly for reference, Perl doesn't
-use them internally.)
+=item *
+
+UTF-16, UTF-16BE, UTF16-LE, Surrogates, and BOMs (Byte Order Marks)
+
+The followings items are mostly for reference and general Unicode
+knowledge, Perl doesn't use these constructs internally.
UTF-16 is a 2 or 4 byte encoding. The Unicode code points
-0x0000..0xFFFF are stored in two 16-bit units, and the code points
-0x010000..0x10FFFF in two 16-bit units. The latter case is
+C<U+0000..U+FFFF> are stored in a single 16-bit unit, and the code
+points C<U+10000..U+10FFFF> in two 16-bit units. The latter case is
using I<surrogates>, the first 16-bit unit being the I<high
surrogate>, and the second being the I<low surrogate>.
-Surrogates are code points set aside to encode the 0x01000..0x10FFFF
+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 0xD800..0xDBFF, and the I<low surrogates>
-are the range 0xDC00..0xDFFFF. The surrogate encoding is
+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;
$lo = ($uni - 0x10000) % 0x400 + 0xDC00;
and the decoding is
- $uni = 0x10000 + ($hi - 0xD8000) * 0x400 + ($lo - 0xDC00);
+ $uni = 0x10000 + ($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 (C<-w> or C<use
-warnings;>) because those code points are not valid for a Unicode
-character.
+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 byteorder dependent. UTF-16
+Because of the 16-bitness, UTF-16 is byte-order dependent. UTF-16
itself can be used for in-memory computations, but if storage or
-transfer is required, either UTF-16BE (Big Endian) or UTF-16LE
-(Little Endian) must be chosen.
+transfer is required either UTF-16BE (big-endian) or UTF-16LE
+(little-endian) encodings must be chosen.
This introduces another problem: what if you just know that your data
-is UTF-16, but you don't know which endianness? Byte Order Marks
-(BOMs) are a solution to this. A special character has been reserved
+is UTF-16, but you don't know which endianness? Byte Order Marks, or
+BOMs, are a solution to this. A special character has been reserved
in Unicode to function as a byte order marker: the character with the
-code point 0xFEFF is the BOM.
+code point C<U+FEFF> is the BOM.
The trick is that if you read a BOM, you will know the byte order,
-since if it was written on a big endian platform, you will read the
-bytes 0xFE 0xFF, but if it was written on a little endian platform,
-you will read the bytes 0xFF 0xFE. (And if the originating platform
-was writing in UTF-8, you will read the bytes 0xEF 0xBB 0xBF.)
+since if it was written on a big-endian platform, you will read the
+bytes C<0xFE 0xFF>, but if it was written on a little-endian platform,
+you will read the bytes C<0xFF 0xFE>. (And if the originating platform
+was writing in UTF-8, you will read the bytes C<0xEF 0xBB 0xBF>.)
The way this trick works is that the character with the code point
-0xFFFE is guaranteed not to be a valid Unicode character, so the
-sequence of bytes 0xFF 0xFE is unambiguously "BOM, represented in
-little-endian format" and cannot be "0xFFFE, represented in big-endian
+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".
-=item UTF-32, UTF-32BE, UTF32-LE
+=item *
+
+UTF-32, UTF-32BE, UTF32-LE
The UTF-32 family is pretty much like the UTF-16 family, expect that
the units are 32-bit, and therefore the surrogate scheme is not
-needed. The BOM signatures will be 0x00 0x00 0xFE 0xFF for BE and
-0xFF 0xFE 0x00 0x00 for LE.
+needed. The BOM signatures will be C<0x00 0x00 0xFE 0xFF> for BE and
+C<0xFF 0xFE 0x00 0x00> for LE.
+
+=item *
-=item UCS-2, UCS-4
+UCS-2, UCS-4
Encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit
-encoding, UCS-4 is a 32-bit encoding. Unlike UTF-16, UCS-2
-is not extensible beyond 0xFFFF, because it does not use surrogates.
+encoding. Unlike UTF-16, UCS-2 is not extensible beyond C<U+FFFF>,
+because it does not use surrogates. UCS-4 is a 32-bit encoding,
+functionally identical to UTF-32.
+
+=item *
-=item UTF-7
+UTF-7
-A seven-bit safe (non-eight-bit) encoding, useful if the
-transport/storage is not eight-bit safe. Defined by RFC 2152.
+A seven-bit safe (non-eight-bit) encoding, which is useful if the
+transport or storage is not eight-bit safe. Defined by RFC 2152.
=back
-=head2 Security Implications of Malformed UTF-8
+=head2 Security Implications of Unicode
+
+=over 4
+
+=item *
+
+Malformed UTF-8
Unfortunately, the specification of UTF-8 leaves some room for
interpretation of how many bytes of encoded output one should generate
-from one input Unicode character. Strictly speaking, one is supposed
-to always generate the shortest possible sequence of UTF-8 bytes,
-because otherwise there is potential for input buffer overflow at
+from one input Unicode character. Strictly speaking, the shortest
+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 (C<-w> or C<use
-warnings;>) Perl will warn about non-shortest length UTF-8 (and other
-malformations, too, such as the surrogates, which are not real
-Unicode code points.)
+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.
+
+=item *
+
+Regular expressions behave slightly differently between byte data and
+character (Unicode) data. For example, the "word character" character
+class C<\w> will work differently depending on if data is eight-bit bytes
+or Unicode.
+
+In the first case, the set of C<\w> characters is either small--the
+default set of alphabetic characters, digits, and the "_"--or, if you
+are using a locale (see L<perllocale>), the C<\w> might contain a few
+more letters according to your language and country.
+
+In the second case, the C<\w> set of characters is much, much larger.
+Most importantly, even in the set of the first 256 characters, it will
+probably match different characters: unlike most locales, which are
+specific to a language and country pair, Unicode classifies all the
+characters that are letters I<somewhere> as C<\w>. For example, your
+locale might not think that LATIN SMALL LETTER ETH is a letter (unless
+you happen to speak Icelandic), but Unicode does.
+
+As discussed elsewhere, Perl has one foot (two hooves?) planted in
+each of two worlds: the old world of bytes and the new world of
+characters, upgrading from bytes to characters when necessary.
+If your legacy code does not explicitly use Unicode, no automatic
+switch-over to characters should happen. Characters shouldn't get
+downgraded to bytes, either. It is possible to accidentally mix bytes
+and characters, however (see L<perluniintro>), in which case C<\w> in
+regular expressions might start behaving differently. Review your
+code. Use warnings and the C<strict> pragma.
+
+=back
=head2 Unicode in Perl on EBCDIC
-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
+The way Unicode is handled on EBCDIC platforms is still
+experimental. On such platforms, references to UTF-8 encoding in this
+document and elsewhere should be read as meaning the UTF-EBCDIC
+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
+":utfebcdic" layer; rather, "utf8" and ":utf8" are reused to mean
the platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic>
for more discussion of the issues.
+=head2 Locales
+
+Usually locale settings and Unicode do not affect each other, but
+there are a couple of exceptions:
+
+=over 4
+
+=item *
+
+You can enable automatic UTF-8-ification of your standard file
+handles, default C<open()> layer, and C<@ARGV> by using either
+the C<-C> command line switch or the C<PERL_UNICODE> environment
+variable, see L<perlrun> for the documentation of the C<-C> switch.
+
+=item *
+
+Perl tries really hard to work both with Unicode and the old
+byte-oriented world. Most often this is nice, but sometimes Perl's
+straddling of the proverbial fence causes problems.
+
+=back
+
+=head2 When Unicode Does Not Happen
+
+While Perl does have extensive ways to input and output in Unicode,
+and few other 'entry points' like the @ARGV which can be interpreted
+as Unicode (UTF-8), there still are many places where Unicode (in some
+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 Perl currently
+(as of 5.8.1) simply assumes byte strings both as arguments and results.
+
+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
+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
+'command line interface' (and which of them?) handle Unicode?
+
+=over 4
+
+=item chmod, chmod, chown, chroot, exec, link, mkdir, rename, rmdir, stat, symlink, truncate, unlink, utime
+
+=item %ENV
+
+=item glob (aka the <*>)
+
+=item open, opendir, sysopen
+
+=item qx (aka the backtick operator), system
+
+=item readdir, readlink
+
+=back
+
+=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
+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.
+
=head2 Using Unicode in XS
-If you want to handle Perl Unicode in XS extensions, you may find
-the following C APIs useful:
+If you want to handle Perl Unicode in XS extensions, you may find the
+following C APIs useful. See also L<perlguts/"Unicode Support"> for an
+explanation about Unicode at the XS level, and L<perlapi> for the API
+details.
=over 4
=item *
-DO_UTF8(sv) returns true if the UTF8 flag is on and the bytes
-pragma is not in effect. SvUTF8(sv) returns true is the UTF8
-flag is on, the bytes pragma is ignored. Remember that UTF8
-flag being on does not mean that there would be any characters
-of code points greater than 255 or 127 in the scalar, or that
-there even are any characters in the scalar. The UTF8 flag
-means that any characters added to the string will be encoded
-in UTF8 if the code points of the characters are greater than
-255. Not "if greater than 127", since Perl's Unicode model
-is not to use UTF-8 until it's really necessary.
+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>
+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
+in the scalar. What the C<UTF8> flag means is that the sequence of
+octets in the representation of the scalar is the sequence of UTF-8
+encoded code points of the characters of a string. The C<UTF8> flag
+being off means that each octet in this representation encodes a
+single character with code point 0..255 within the string. Perl's
+Unicode model is not to use UTF-8 until it is absolutely necessary.
=item *
-uvuni_to_utf8(buf, chr) writes a Unicode character code point into a
-buffer encoding the code point as UTF-8, and returns a pointer
+C<uvuni_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.
=item *
-utf8_to_uvuni(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).
+C<utf8_to_uvuni(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.
=item *
-utf8_length(s, len) returns the length of the UTF-8 encoded buffer in
-characters. sv_len_utf8(sv) returns the length of the UTF-8 encoded
+C<utf8_length(start, end)> returns the length of the UTF-8 encoded buffer
+in characters. C<sv_len_utf8(sv)> returns the length of the UTF-8 encoded
scalar.
=item *
-sv_utf8_upgrade(sv) converts the string of the scalar to its UTF-8
-encoded form. sv_utf8_downgrade(sv) does the opposite (if possible).
-sv_utf8_encode(sv) is like sv_utf8_upgrade but the UTF8 flag does not
-get turned on. sv_utf8_decode() does the opposite of sv_utf8_encode().
+C<sv_utf8_upgrade(sv)> converts the string of the scalar to its UTF-8
+encoded form. C<sv_utf8_downgrade(sv)> does the opposite, if
+possible. C<sv_utf8_encode(sv)> is like sv_utf8_upgrade except that
+it does not set the C<UTF8> flag. C<sv_utf8_decode()> does the
+opposite of C<sv_utf8_encode()>. Note that none of these are to be
+used as general-purpose encoding or decoding interfaces: C<use Encode>
+for that. C<sv_utf8_upgrade()> is affected by the encoding pragma
+but C<sv_utf8_downgrade()> is not (since the encoding pragma is
+designed to be a one-way street).
=item *
-is_utf8_char(buf) returns true if the buffer points to valid UTF-8.
+C<is_utf8_char(s)> returns true if the pointer points to a valid UTF-8
+character.
=item *
-is_utf8_string(buf, len) returns true if the len bytes of the buffer
+C<is_utf8_string(buf, len)> returns true if C<len> bytes of the buffer
are valid UTF-8.
=item *
-UTF8SKIP(buf) will return the number of bytes in the UTF-8 encoded
-character in the buffer. UNISKIP(chr) will return the number of bytes
-required to UTF-8-encode the Unicode character code point.
+C<UTF8SKIP(buf)> will return the number of bytes in the UTF-8 encoded
+character in the buffer. C<UNISKIP(chr)> will return the number of bytes
+required to UTF-8-encode the Unicode character code point. C<UTF8SKIP()>
+is useful for example for iterating over the characters of a UTF-8
+encoded buffer; C<UNISKIP()> is useful, for example, in computing
+the size required for a UTF-8 encoded buffer.
=item *
-utf8_distance(a, b) will tell the distance in characters between the
+C<utf8_distance(a, b)> will tell the distance in characters between the
two pointers pointing to the same UTF-8 encoded buffer.
=item *
-utf8_hop(s, off) will return a pointer to an UTF-8 encoded buffer that
-is C<off> (positive or negative) Unicode characters displaced from the
-UTF-8 buffer C<s>.
+C<utf8_hop(s, off)> will return a pointer to an 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
+buffer if told to do so.
=item *
-pv_uni_display(dsv, spv, len, pvlim, flags) and sv_uni_display(dsv,
-ssv, pvlim, flags) are useful for debug output of Unicode strings and
-scalars (only for debug: they display B<all> characters as hexadecimal
-code points).
+C<pv_uni_display(dsv, spv, len, pvlim, flags)> and
+C<sv_uni_display(dsv, ssv, pvlim, flags)> are useful for debugging the
+output of Unicode strings and scalars. By default they are useful
+only for debugging--they display B<all> characters as hexadecimal code
+points--but with the flags C<UNI_DISPLAY_ISPRINT>,
+C<UNI_DISPLAY_BACKSLASH>, and C<UNI_DISPLAY_QQ> you can make the
+output more readable.
=item *
-ibcmp_utf8(s1, u1, len1, s2, u2, len2) can be used to compare two
-strings case-insensitively in Unicode. (For case-sensitive
-comparisons you can just use memEQ() and memNE() as usual.)
+C<ibcmp_utf8(s1, pe1, u1, 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.
=back
For more information, see L<perlapi>, and F<utf8.c> and F<utf8.h>
in the Perl source code distribution.
+=head1 BUGS
+
+=head2 Interaction with Locales
+
+Use of locales with Unicode data may lead to odd results. Currently,
+Perl attempts to attach 8-bit locale info to characters in the range
+0..255, but this technique is demonstrably incorrect for locales that
+use characters above that range when mapped into Unicode. Perl's
+Unicode support will also tend to run slower. Use of locales with
+Unicode is discouraged.
+
+=head2 Interaction with Extensions
+
+When Perl exchanges data with an extension, the extension should be
+able to understand the UTF-8 flag and act accordingly. If the
+extension doesn't know about the flag, it's likely that the extension
+will return incorrectly-flagged data.
+
+So if you're working with Unicode data, consult the documentation of
+every module you're using if there are any issues with Unicode data
+exchange. If the documentation does not talk about Unicode at all,
+suspect the worst and probably look at the source to learn how the
+module is implemented. Modules written completely in Perl shouldn't
+cause problems. Modules that directly or indirectly access code written
+in other programming languages are at risk.
+
+For affected functions, the simple strategy to avoid data corruption is
+to always make the encoding of the exchanged data explicit. Choose an
+encoding that you know the extension can handle. Convert arguments passed
+to the extensions to that encoding and convert results back from that
+encoding. Write wrapper functions that do the conversions for you, so
+you can later change the functions when the extension catches up.
+
+To provide an example, let's say the popular Foo::Bar::escape_html
+function doesn't deal with Unicode data yet. The wrapper function
+would convert the argument to raw UTF-8 and convert the result back to
+Perl's internal representation like so:
+
+ sub my_escape_html ($) {
+ my($what) = shift;
+ return unless defined $what;
+ Encode::decode_utf8(Foo::Bar::escape_html(Encode::encode_utf8($what)));
+ }
+
+Sometimes, when the extension does not convert data but just stores
+and retrieves them, you will be in a position to use the otherwise
+dangerous Encode::_utf8_on() function. Let's say the popular
+C<Foo::Bar> extension, written in C, provides a C<param> method that
+lets you store and retrieve data according to these prototypes:
+
+ $self->param($name, $value); # set a scalar
+ $value = $self->param($name); # retrieve a scalar
+
+If it does not yet provide support for any encoding, one could write a
+derived class with such a C<param> method:
+
+ sub param {
+ my($self,$name,$value) = @_;
+ utf8::upgrade($name); # make sure it is UTF-8 encoded
+ if (defined $value)
+ utf8::upgrade($value); # make sure it is UTF-8 encoded
+ return $self->SUPER::param($name,$value);
+ } else {
+ my $ret = $self->SUPER::param($name);
+ Encode::_utf8_on($ret); # we know, it is UTF-8 encoded
+ return $ret;
+ }
+ }
+
+Some extensions provide filters on data entry/exit points, such as
+DB_File::filter_store_key and family. Look out for such filters in
+the documentation of your extensions, they can make the transition to
+Unicode data much easier.
+
+=head2 Speed
+
+Some functions are slower when working on UTF-8 encoded strings than
+on byte encoded strings. All functions that need to hop over
+characters such as length(), substr() or index(), or matching regular
+expressions can work B<much> faster when the underlying data are
+byte-encoded.
+
+In Perl 5.8.0 the slowness was often quite spectacular; in Perl 5.8.1
+a caching scheme was introduced which will hopefully make the slowness
+somewhat less spectacular. Operations with UTF-8 encoded strings are
+still slower, though.
+
+=head2 Porting code from perl-5.6.X
+
+Perl 5.8 has a different Unicode model from 5.6. In 5.6 the programmer
+was required to use the C<utf8> pragma to declare that a given scope
+expected to deal with Unicode data and had to make sure that only
+Unicode data were reaching that scope. If you have code that is
+working with 5.6, you will need some of the following adjustments to
+your code. The examples are written such that the code will continue
+to work under 5.6, so you should be safe to try them out.
+
+=over 4
+
+=item *
+
+A filehandle that should read or write UTF-8
+
+ if ($] > 5.007) {
+ binmode $fh, ":utf8";
+ }
+
+=item *
+
+A scalar that is going to be passed to some extension
+
+Be it Compress::Zlib, Apache::Request or any extension that has no
+mention of Unicode in the manpage, you need to make sure that the
+UTF-8 flag is stripped off. Note that at the time of this writing
+(October 2002) the mentioned modules are not UTF-8-aware. Please
+check the documentation to verify if this is still true.
+
+ if ($] > 5.007) {
+ require Encode;
+ $val = Encode::encode_utf8($val); # make octets
+ }
+
+=item *
+
+A scalar we got back from an extension
+
+If you believe the scalar comes back as UTF-8, you will most likely
+want the UTF-8 flag restored:
+
+ if ($] > 5.007) {
+ require Encode;
+ $val = Encode::decode_utf8($val);
+ }
+
+=item *
+
+Same thing, if you are really sure it is UTF-8
+
+ if ($] > 5.007) {
+ require Encode;
+ Encode::_utf8_on($val);
+ }
+
+=item *
+
+A wrapper for fetchrow_array and fetchrow_hashref
+
+When the database contains only UTF-8, a wrapper function or method is
+a convenient way to replace all your fetchrow_array and
+fetchrow_hashref calls. A wrapper function will also make it easier to
+adapt to future enhancements in your database driver. Note that at the
+time of this writing (October 2002), the DBI has no standardized way
+to deal with UTF-8 data. Please check the documentation to verify if
+that is still true.
+
+ sub fetchrow {
+ my($self, $sth, $what) = @_; # $what is one of fetchrow_{array,hashref}
+ if ($] < 5.007) {
+ return $sth->$what;
+ } else {
+ require Encode;
+ if (wantarray) {
+ my @arr = $sth->$what;
+ for (@arr) {
+ defined && /[^\000-\177]/ && Encode::_utf8_on($_);
+ }
+ return @arr;
+ } else {
+ my $ret = $sth->$what;
+ if (ref $ret) {
+ for my $k (keys %$ret) {
+ defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret->{$k};
+ }
+ return $ret;
+ } else {
+ defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret;
+ return $ret;
+ }
+ }
+ }
+ }
+
+
+=item *
+
+A large scalar that you know can only contain ASCII
+
+Scalars that contain only ASCII and are marked as UTF-8 are sometimes
+a drag to your program. If you recognize such a situation, just remove
+the UTF-8 flag:
+
+ utf8::downgrade($val) if $] > 5.007;
+
+=back
+
=head1 SEE ALSO
L<perluniintro>, L<encoding>, L<Encode>, L<open>, L<utf8>, L<bytes>,
-L<perlretut>, L<perlvar/"${^WIDE_SYSTEM_CALLS}">
+L<perlretut>, L<perlvar/"${^UNICODE}">
=cut
https://perl5.git.perl.org / perl5.git / blobdiff