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PERLUNICODE(1)                        Perl Programmers Reference Guide                        PERLUNICODE(1)



NAME
       perlunicode - Unicode support in Perl

DESCRIPTION
       Important Caveats

       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.

       People who want to learn to use Unicode in Perl, should probably read the Perl Unicode tutorial, per-lunitut, perlunitut,
       lunitut, before reading this reference document.

       Input and Output Layers
           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 open.

           To indicate that Perl source itself is in UTF-8, use "use utf8;".

       Regular Expressions
           The regular expression compiler produces polymorphic opcodes.  That is, the pattern adapts to the
           data and automatically switches to the Unicode character scheme when presented with data that is
           internally encoded in UTF-8 -- or instead uses a traditional byte scheme when presented with byte
           data.

       "use utf8" still needed to enable UTF-8/UTF-EBCDIC in scripts
           As a compatibility measure, the "use utf8" pragma must be explicitly included to enable recogni-tion recognition
           tion 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.
           These are the only times when an explicit "use utf8" is needed.  See utf8.

       BOM-marked scripts and UTF-16 scripts autodetected
           If a Perl script begins marked with the Unicode BOM (UTF-16LE, UTF16-BE, or UTF-8), or if the
           script looks like non-BOM-marked UTF-16 of either endianness, Perl will correctly read in the
           script as Unicode.  (BOMless UTF-8 cannot be effectively recognized or differentiated from ISO
           8859-1 or other eight-bit encodings.)

       "use encoding" needed to upgrade non-Latin-1 byte strings
           By default, there is a fundamental asymmetry in Perl's Unicode model: implicit upgrading from
           byte strings to Unicode strings assumes that they were encoded in ISO 8859-1 (Latin-1), but Uni-code Unicode
           code strings are downgraded with UTF-8 encoding.  This happens because the first 256 codepoints
           in Unicode happens to agree with Latin-1.

           See "Byte and Character Semantics" for more details.

       Byte and Character Semantics

       Beginning with version 5.6, Perl uses logically-wide characters to represent strings internally.

       In future, Perl-level operations will be expected to work with characters rather than bytes.

       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 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.

       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 char-acter character
       acter 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 "bytes" pragma will always, regardless of platform, force byte semantics in a particular lexical
       scope.  See bytes.

       The "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 semantics; when character semantics become the default, this pragma may become a no-op.  See
       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 "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 created by decoding the byte strings as 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.

       Under character semantics, many operations that formerly operated on 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 into longer sequences of bytes internally, but this internal detail is mostly hidden for Perl
       code.  See perluniintro for more.

       Effects of Character Semantics

       Character semantics have the following effects:

          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 UTF-8 encoding, or UTF-16.  (The former requires a BOM or "use utf8", the
           latter requires a BOM.)

           Unicode characters can also be added to a string by using the "\x{...}" notation.  The Unicode
           code for the desired character, in hexadecimal, should be placed in the braces. For instance, a
           smiley face is "\x{263A}".  This encoding scheme only works for all characters, but for charac-ters characters
           ters under 0x100, note that Perl may use an 8 bit encoding internally, for optimization and/or
           backward compatibility.

           Additionally, if you

              use charnames ':full';

           you can use the "\N{...}" notation and put the official Unicode character name within the braces,
           such as "\N{WHITE SMILING FACE}".

          If an appropriate encoding is specified, identifiers within the Perl script may contain Unicode
           alphanumeric characters, including ideographs.  Perl does not currently attempt to canonicalize
           variable names.

          Regular expressions match characters instead of bytes.  "." matches a character instead of a
           byte.

          Character classes in regular expressions match characters instead of bytes and match against the
           character properties specified in the Unicode properties database.  "\w" can be used to match a
           Japanese ideograph, for instance.

          Named Unicode properties, scripts, and block ranges may be used like character classes via the
           "\p{}" "matches property" construct and the "\P{}" negation, "doesn't match property".

           See "Unicode Character Properties" for more details.

           You can define your own character properties and use them in the regular expression with the
           "\p{}" or "\P{}" construct.

           See "User-Defined Character Properties" for more details.

          The special pattern "\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.  "\X" is equivalent to "(?>\PM\pM*)".

          The "tr///" operator translates characters instead of bytes.  Note that the "tr///CU" functional-ity functionality
           ity has been removed.  For similar functionality see pack('U0', ...) and pack('C0', ...).

          Case translation operators use the Unicode case translation tables when character input is pro-vided. provided.
           vided.  Note that "uc()", or "\U" in interpolated strings, translates to uppercase, while
           "ucfirst", or "\u" in interpolated strings, translates to titlecase in languages that make the
           distinction.

          Most operators that deal with positions or lengths in a string will automatically switch to using
           character positions, including "chop()", "chomp()", "substr()", "pos()", "index()", "rindex()",
           "sprintf()", "write()", and "length()".  Operators that specifically do not switch include
           "vec()", "pack()", and "unpack()".  Operators that really don't care include operators that treat
           strings as a bucket of bits such as "sort()", and operators dealing with filenames.

          The "pack()"/"unpack()" letter "C" does not change, since it is often used for byte-oriented for-mats. formats.
           mats.  Again, think "char" in the C language.

           There is a new "U" specifier that converts between Unicode characters and code points. There is
           also a "W" specifier that is the equivalent of "chr"/"ord" and properly handles character values
           even if they are above 255.

          The "chr()" and "ord()" functions work on characters, similar to "pack("W")" and "unpack("W")",
           not "pack("C")" and "unpack("C")".  "pack("C")" and "unpack("C")" are methods for emulating byte-oriented byteoriented
           oriented "chr()" and "ord()" on Unicode strings.  While these methods reveal the internal encod-ing encoding
           ing of Unicode strings, that is not something one normally needs to care about at all.

          The bit string operators, "& | ^ ~", can operate on character data.  However, for backward com-patibility, compatibility,
           patibility, such as when using bit string operations when characters are all less than 256 in
           ordinal value, one should not use "~" (the bit complement) with characters of both values less
           than 256 and values greater than 256.  Most importantly, DeMorgan's laws ("~($x|$y) eq ~$x&~$y"
           and "~($x&$y) eq ~$x|~$y") will not hold.  The reason for this mathematical faux pas is that the
           complement cannot return both the 8-bit (byte-wide) bit complement and the full character-wide
           bit complement.

          lc(), uc(), lcfirst(), and ucfirst() work for the following cases:

                  the case mapping is from a single Unicode character to another single Unicode character,
                   or

                  the case mapping is from a single Unicode character to more than one Unicode character.

           Things to do with locales (Lithuanian, Turkish, Azeri) do 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(), lcfirst(), uc(), and ucfirst()
           (or their string-inlined versions).

           See "User-Defined Case Mappings" for more details.

          And finally, "scalar reverse()" reverses by character rather than by byte.

       Unicode Character Properties

       Named Unicode properties, scripts, and block ranges may be used like character classes via the "\p{}"
       "matches property" construct and the "\P{}" negation, "doesn't match property".

       For instance, "\p{Lu}" matches any character with the Unicode "Lu" (Letter, uppercase) property,
       while "\p{M}" matches any character with an "M" (mark--accents and such) property.  Brackets are not
       required for single letter properties, so "\p{M}" is equivalent to "\pM". Many predefined properties
       are available, such as "\p{Mirrored}" and "\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". "Latin-1 Supplement" thus becomes "Latin1Supplement".

       You can also use negation in both "\p{}" and "\P{}" by introducing a caret (^) between the first
       brace and the property name: "\p{^Tamil}" is equal to "\P{Tamil}".

       NOTE: the properties, scripts, and blocks listed here are as of Unicode 5.0.0 in July 2006.

       General Category
           Here are the basic Unicode General Category properties, followed by their long form.  You can use
           either; "\p{Lu}" and "\p{UppercaseLetter}", for instance, are identical.

               Short       Long

               L           Letter
               LC          CasedLetter
               Lu          UppercaseLetter
               Ll          LowercaseLetter
               Lt          TitlecaseLetter
               Lm          ModifierLetter
               Lo          OtherLetter

               M           Mark
               Mn          NonspacingMark
               Mc          SpacingMark
               Me          EnclosingMark

               N           Number
               Nd          DecimalNumber
               Nl          LetterNumber
               No          OtherNumber

               P           Punctuation
               Pc          ConnectorPunctuation
               Pd          DashPunctuation
               Ps          OpenPunctuation
               Pe          ClosePunctuation
               Pi          InitialPunctuation
                           (may behave like Ps or Pe depending on usage)
               Pf          FinalPunctuation
                           (may behave like Ps or Pe depending on usage)
               Po          OtherPunctuation

               S           Symbol
               Sm          MathSymbol
               Sc          CurrencySymbol
               Sk          ModifierSymbol
               So          OtherSymbol

               Z           Separator
               Zs          SpaceSeparator
               Zl          LineSeparator
               Zp          ParagraphSeparator

               C           Other
               Cc          Control
               Cf          Format
               Cs          Surrogate   (not usable)
               Co          PrivateUse
               Cn          Unassigned

           Single-letter properties match all characters in any of the two-letter sub-properties starting
           with the same letter.  "LC" and "L&" are special cases, which are aliases for the set of "Ll",
           "Lu", and "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. "Cs" is
           therefore not supported.

       Bidirectional Character Types
           Because scripts differ in their directionality--Hebrew is written right to left, for exam-ple--Unicode example--Unicode
           ple--Unicode supplies these properties in the BidiClass class:

               Property    Meaning

               L           Left-to-Right
               LRE         Left-to-Right Embedding
               LRO         Left-to-Right Override
               R           Right-to-Left
               AL          Right-to-Left Arabic
               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
               AN          Arabic Number
               CS          Common Number Separator
               NSM         Non-Spacing Mark
               BN          Boundary Neutral
               B           Paragraph Separator
               S           Segment Separator
               WS          Whitespace
               ON          Other Neutrals

           For example, "\p{BidiClass:R}" matches characters that are normally written right to left.

       Scripts
           The script names which can be used by "\p{...}" and "\P{...}", such as in "\p{Latin}" or
           "\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

       Extended property classes
           Extended property classes can supplement the basic properties, defined by the 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

       Use of "Is" Prefix
           For backward compatibility (with Perl 5.6), all properties mentioned so far may have "Is"
           prepended to their name, so "\P{IsLu}", for example, is equal to "\P{Lu}".

       Blocks
           In addition to scripts, Unicode also defines blocks of characters.  The difference between
           scripts and blocks is that the concept of scripts is closer to natural languages, while the con-cept concept
           cept of blocks is more of an artificial grouping based on groups of 256 Unicode characters. For
           example, the "Latin" script contains letters from many blocks but does not contain all the char-acters characters
           acters 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 "Com-mon". "Common".
           mon".

           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 "In" prefix. For example, the Katakana block is referenced via
           "\p{InKatakana}".  The "In" prefix may be omitted if there is no naming conflict with a script or
           any other property, but it is recommended that "In" always be used for block tests to avoid con-fusion. confusion.
           fusion.

           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

       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 "\p" and "\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 "\p" or "\P" construct.

           # assuming property IsForeign defined in Lang::
           package main;  # property package name required
           if ($txt =~ /\p{Lang::IsForeign}+/) { ... }

           package Lang;  # property package name not required
           if ($txt =~ /\p{IsForeign}+/) { ... }

       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:

          A single hexadecimal number denoting a Unicode code point to include.

          Two hexadecimal numbers separated by horizontal whitespace (space or tabular characters) denoting
           a range of Unicode code points to include.

          Something to include, prefixed by "+": a built-in character property (prefixed by "utf8::") or a
           user-defined character property, to represent all the characters in that property; two hexadeci-mal hexadecimal
           mal code points for a range; or a single hexadecimal code point.

          Something to exclude, prefixed by "-": an existing character property (prefixed by "utf8::") or a
           user-defined character property, to represent all the characters in that property; two hexadeci-mal hexadecimal
           mal code points for a range; or a single hexadecimal code point.

          Something to negate, prefixed "!": an existing character property (prefixed by "utf8::") or a
           user-defined character property, to represent all the characters in that property; two hexadeci-mal hexadecimal
           mal code points for a range; or a single hexadecimal code point.

          Something to intersect with, prefixed by "&": an existing character property (prefixed by
           "utf8::") or a user-defined character property, for all the characters except the characters in
           the property; two hexadecimal code points for a range; or a single hexadecimal code point.

       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 "\p{InKana}"
       and "\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
           }

       Intersection is useful for getting the common characters matched by two (or more) classes.

           sub InFooAndBar {
               return <<'END';
           +main::Foo
           &main::Bar
           END
           }

       It's important to remember not to use "&" for the first set -- that would be intersecting with noth-
       ing (resulting in an empty set).

       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 proper-ties: properties:
       ties: to define subroutines in the "main" package with names like "ToLower" (for lc() and lcfirst()),
       "ToTitle" (for the first character in ucfirst()), and "ToUpper" (for uc(), and the rest of the char-acters characters
       acters in ucfirst()).

       The string returned by the subroutines needs now to be three hexadecimal numbers separated by tabula-tors: tabulators:
       tors: 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 $Config{privlib}/unicore/To/.  The mapping data is returned as the here-document, and
       the "utf8::ToSpecFoo" are special exception mappings derived from <$Config{privlib}>/unicore/Special-Casing.txt. <$Config{privlib}>/unicore/SpecialCasing.txt.
       Casing.txt.  The "Digit" and "Fold" mappings that one can see in the directory are not directly
       user-accessible, one can use either the "Unicode::UCD" module, or just match case-insensitively
       (that's when the "Fold" mapping is used).

       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.

       Character Encodings for Input and Output

       See Encode.

       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 Stan-dard Standard
       dard #18, "Unicode Regular Expressions", version 11, in May 2005.

          Level 1 - Basic Unicode Support

                   RL1.1   Hex Notation                        - done          [1]
                   RL1.2   Properties                          - done          [2][3]
                   RL1.2a  Compatibility Properties            - done          [4]
                   RL1.3   Subtraction and Intersection        - MISSING       [5]
                   RL1.4   Simple Word Boundaries              - done          [6]
                   RL1.5   Simple Loose Matches                - done          [7]
                   RL1.6   Line Boundaries                     - MISSING       [8]
                   RL1.7   Supplementary Code Points           - done          [9]

                   [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">)
                   [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
                        capital letters with certain modifiers: the Full case-folding
                        decomposes the letter, while the Simple case-folding would map
                        it to a single character.
                   [8]  should do ^ and $ also on U+000B (\v in C), FF (\f), CR (\r),
                        CRLF (\r\n), NEL (U+0085), LS (U+2028), and PS (U+2029);
                        should also affect <>, $., and script line numbers;
                        should not split lines within CRLF [c] (i.e. there is no empty
                        line between \r and \n)
                   [9]  UTF-8/UTF-EBDDIC used in perl allows not only U+10000 to U+10FFFF
                        but also beyond U+10FFFF [d]

           [a] You can mimic class subtraction using lookahead.  For example, what UTS#18 might write as

               [{Greek}-[{UNASSIGNED}]]

           in Perl can be written as:

               (?!\p{Unassigned})\p{InGreekAndCoptic}
               (?=\p{Assigned})\p{InGreekAndCoptic}

           But in this particular example, you probably really want

               \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 UTS#18 grouping, intersec-tion, intersection,
           tion, union, and removal (subtraction) syntax.

           [b] '+' for union, '-' for removal (set-difference), '&' for intersection (see "User-Defined
           Character Properties")

           [c] Try the ":crlf" layer (see PerlIO).

           [d] Avoid "use warning 'utf8';" (or say "no warning 'utf8';") to allow U+FFFF ("\x{FFFF}").

          Level 2 - Extended Unicode Support

                   RL2.1   Canonical Equivalents           - MISSING       [10][11]
                   RL2.2   Default Grapheme Clusters       - MISSING       [12][13]
                   RL2.3   Default Word Boundaries         - MISSING       [14]
                   RL2.4   Default Loose Matches           - MISSING       [15]
                   RL2.5   Name Properties                 - MISSING       [16]
                   RL2.6   Wildcard Properties             - MISSING

                   [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.
                   [14] see UAX#29, Word Boundaries
                   [15] see UAX#21 "Case Mappings"
                   [16] have \N{...} but neither compute names of CJK Ideographs
                        and Hangul Syllables nor use a loose match [e]

           [e] "\N{...}" allows namespaces (see charnames).

          Level 3 - Tailored Support

                   RL3.1   Tailored Punctuation            - MISSING
                   RL3.2   Tailored Grapheme Clusters      - MISSING       [17][18]
                   RL3.3   Tailored Word Boundaries        - MISSING
                   RL3.4   Tailored Loose Matches          - MISSING
                   RL3.5   Tailored Ranges                 - MISSING
                   RL3.6   Context Matching                - MISSING       [19]
                   RL3.7   Incremental Matches             - MISSING
                 ( RL3.8   Unicode Set Sharing )
                   RL3.9   Possible Match Sets             - MISSING
                   RL3.10  Folded Matching                 - MISSING       [20]
                   RL3.11  Submatchers                     - MISSING

                   [17] see UAX#10 "Unicode Collation Algorithms"
                   [18] have Unicode::Collate but not integrated to regexes
                   [19] have (?<=x) and (?=x), but look-aheads or look-behinds should see
                        outside of the target substring
                   [20] need insensitive matching for linguistic features other than case;
                        for example, hiragana to katakana, wide and narrow, simplified Han
                        to traditional Han (see UTR#30 "Character Foldings")

       Unicode Encodings

       Unicode characters are assigned to code points, which are abstract numbers.  To use these numbers,
       various encodings are needed.

          UTF-8

           UTF-8 is a variable-length (1 to 6 bytes, current character allocations 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 3.2.

            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+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

           Note the "A0..BF" in "U+0800..U+0FFF", the "80..9F" in "U+D000...U+D7FF", the "90..B"F in
           "U+10000..U+3FFFF", and the "80...8F" in "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

                               0aaaaaaa     0aaaaaaa
                       00000bbbbbaaaaaa     110bbbbb  10aaaaaa
                       ccccbbbbbbaaaaaa     1110cccc  10bbbbbb  10aaaaaa
             00000dddccccccbbbbbbaaaaaa     11110ddd  10cccccc  10bbbbbb  10aaaaaa

           As you can see, the continuation bytes all begin with 10, and the leading bits of the start byte
           tell how many bytes the are in the encoded character.

          UTF-EBCDIC

           Like UTF-8 but EBCDIC-safe, in the way that UTF-8 is ASCII-safe.

          UTF-16, UTF-16BE, UTF-16LE, 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 "U+0000..U+FFFF" are stored in a sin-gle single
           gle 16-bit unit, and the code points "U+10000..U+10FFFF" in two 16-bit units.  The latter case is
           using surrogates, the first 16-bit unit being the high surrogate, and the second being the low
           surrogate.

           Surrogates are code points set aside to encode the "U+10000..U+10FFFF" range of Unicode code
           points in pairs of 16-bit units.  The high surrogates are the range "U+D800..U+DBFF", and the low
           surrogates are the range "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 - 0xD800) * 0x400 + ($lo - 0xDC00);

           If you try to generate surrogates (for example by using chr()), you will get a warning if warn-ings warnings
           ings 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 itself can be used for in-mem-ory in-memory
           ory computations, but if storage or 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, 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 "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 littleendian
           endian platform, you will read the bytes "0xFF 0xFE".  (And if the originating platform was writ-ing writing
           ing in UTF-8, you will read the bytes "0xEF 0xBB 0xBF".)

           The way this trick works is that the character with the code point "U+FFFE" is guaranteed not to
           be a valid Unicode character, so the sequence of bytes "0xFF 0xFE" is unambiguously "BOM, repre-sented represented
           sented in little-endian format" and cannot be "U+FFFE", represented in big-endian format".

          UTF-32, UTF-32BE, UTF-32LE

           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.

          UCS-2, UCS-4

           Encodings defined by the ISO 10646 standard.  UCS-2 is a 16-bit encoding.  Unlike UTF-16, UCS-2
           is not extensible beyond "U+FFFF", because it does not use surrogates.  UCS-4 is a 32-bit encod-ing, encoding,
           ing, functionally identical to UTF-32.

          UTF-7

           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.

       Security Implications of Unicode


          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, the
           shortest possible sequence of UTF-8 bytes should be generated, because otherwise there is poten-tial potential
           tial for an input buffer overflow at the receiving end of a UTF-8 connection.  Perl always gener-ates generates
           ates the 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.

          Regular expressions behave slightly differently between byte data and character (Unicode) data.
           For example, the "word character" character class "\w" will work differently depending on if data
           is eight-bit bytes or Unicode.

           In the first case, the set of "\w" characters is either small--the default set of alphabetic
           characters, digits, and the "_"--or, if you are using a locale (see perllocale), the "\w" might
           contain a few more letters according to your language and country.

           In the second case, the "\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 somewhere as "\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 neces-sary. necessary.
           sary.  If your legacy code does not explicitly use Unicode, no automatic switch-over to charac-ters characters
           ters should happen.  Characters shouldn't get downgraded to bytes, either.  It is possible to
           accidentally mix bytes and characters, however (see perluniintro), in which case "\w" in regular
           expressions might start behaving differently.  Review your code.  Use warnings and the "strict"
           pragma.

       Unicode in Perl on EBCDIC

       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 "utfebcdic" pragma or ":utfebcdic" layer; rather, "utf8" and ":utf8" are reused to mean the plat-form's platform's
       form's "natural" 8-bit encoding of Unicode. See perlebcdic for more discussion of the issues.

       Locales

       Usually locale settings and Unicode do not affect each other, but there are a couple of exceptions:

          You can enable automatic UTF-8-ification of your standard file handles, default "open()" layer,
           and @ARGV by using either the "-C" command line switch or the "PERL_UNICODE" environment vari-able, variable,
           able, see perlrun for the documentation of the "-C" switch.

          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.

       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 interfaces Perl currently (as of 5.8.3) simply
       assumes byte strings both as arguments and results, or UTF-8 strings if the "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 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.  Simi-larly Similarly
       larly for the qx and system: how well will the 'command line interface' (and which of them?) handle
       Unicode?

          chdir, chmod, chown, chroot, exec, link, lstat, mkdir, rename, rmdir, stat, symlink, truncate,
           unlink, utime, -X

          %ENV

          glob (aka the <*>)

          open, opendir, sysopen

          qx (aka the backtick operator), system

          readdir, readlink

       Forcing Unicode in Perl (Or Unforcing Unicode in Perl)

       Sometimes (see "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.

       Using Unicode in XS

       If you want to handle Perl Unicode in XS extensions, you may find the following C APIs useful.  See
       also "Unicode Support" in perlguts for an explanation about Unicode at the XS level, and perlapi for
       the API details.

          "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.  The "UTF8" flag
           being on does 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 "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 "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.

          "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.

          "utf8_to_uvuni(buf, lenp)" reads UTF-8 encoded bytes from a buffer and returns the Unicode char-acter character
           acter code point and, optionally, the length of the UTF-8 byte sequence.

          "utf8_length(start, end)" returns the length of the UTF-8 encoded buffer in characters.
           "sv_len_utf8(sv)" returns the length of the UTF-8 encoded scalar.

          "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 except that it does not set the "UTF8" flag.  "sv_utf8_decode()" does the oppo-site opposite
           site of "sv_utf8_encode()".  Note that none of these are to be used as general-purpose encoding
           or decoding interfaces: "use Encode" for that.  "sv_utf8_upgrade()" is affected by the encoding
           pragma but "sv_utf8_downgrade()" is not (since the encoding pragma is designed to be a one-way
           street).

          is_utf8_char(s) returns true if the pointer points to a valid UTF-8 character.

          "is_utf8_string(buf, len)" returns true if "len" bytes of the buffer are valid UTF-8.

          "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.  "UTF8SKIP()" is useful for example for iterating over the characters of a UTF-8
           encoded buffer; "UNISKIP()" is useful, for example, in computing the size required for a UTF-8
           encoded buffer.

          "utf8_distance(a, b)" will tell the distance in characters between the two pointers pointing to
           the same UTF-8 encoded buffer.

          "utf8_hop(s, off)" will return a pointer to an UTF-8 encoded buffer that is "off" (positive or
           negative) Unicode characters displaced from the UTF-8 buffer "s".  Be careful not to overstep the
           buffer: "utf8_hop()" will merrily run off the end or the beginning of the buffer if told to do
           so.

          "pv_uni_display(dsv, spv, len, pvlim, flags)" and "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 all characters as hexadecimal code points--but with the flags
           "UNI_DISPLAY_ISPRINT", "UNI_DISPLAY_BACKSLASH", and "UNI_DISPLAY_QQ" you can make the output more
           readable.

          "ibcmp_utf8(s1, pe1, u1, l1, u1, s2, pe2, l2, u2)" can be used to compare two strings case-insen-sitively case-insensitively
           sitively in Unicode.  For case-sensitive comparisons you can just use "memEQ()" and "memNE()" as
           usual.

       For more information, see perlapi, and utf8.c and utf8.h in the Perl source code distribution.

BUGS
       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.

       Interaction with Extensions

       When Perl exchanges data with an extension, the extension should be able to understand the UTF8 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. Mod-ules Modules
       ules 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
       "Foo::Bar" extension, written in C, provides a "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
       "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 fam-ily. family.
       ily. Look out for such filters in the documentation of your extensions, they can make the transition
       to Unicode data much easier.

       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 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, at least for some operations.  In
       general, operations with UTF-8 encoded strings are still slower. As an example, the Unicode proper-ties properties
       ties (character classes) like "\p{Nd}" are known to be quite a bit slower (5-20 times) than their
       simpler counterparts like "\d" (then again, there 268 Unicode characters matching "Nd" compared with
       the 10 ASCII characters matching "d").

       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 "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 con-tinue continue
       tinue to work under 5.6, so you should be safe to try them out.

          A filehandle that should read or write UTF-8

             if ($] > 5.007) {
               binmode $fh, ":encoding(utf8)";
             }

          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 man-page, manpage,
           page, you need to make sure that the UTF8 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
             }

          A scalar we got back from an extension

           If you believe the scalar comes back as UTF-8, you will most likely want the UTF8 flag restored:

             if ($] > 5.007) {
               require Encode;
               $val = Encode::decode_utf8($val);
             }

          Same thing, if you are really sure it is UTF-8

             if ($] > 5.007) {
               require Encode;
               Encode::_utf8_on($val);
             }

          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;
                   }
                 }
               }
             }

          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 UTF8 flag:

             utf8::downgrade($val) if $] > 5.007;

SEE ALSO
       perlunitut, perluniintro, Encode, open, utf8, bytes, perlretut, "${^UNICODE}" in perlvar



perl v5.8.9                                      2007-11-17                                   PERLUNICODE(1)

Reporting Problems

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