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diff --git a/Master/tlpkg/tlperl/lib/pods/perlunicode.pod b/Master/tlpkg/tlperl/lib/pods/perlunicode.pod new file mode 100755 index 00000000000..5dbd3cd5232 --- /dev/null +++ b/Master/tlpkg/tlperl/lib/pods/perlunicode.pod @@ -0,0 +1,1659 @@ +=head1 NAME + +perlunicode - Unicode support in Perl + +=head1 DESCRIPTION + +=head2 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 +L<the Perl Unicode tutorial, perlunitut|perlunitut>, before reading +this reference document. + +=over 4 + +=item 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 L<open>. + +To indicate that Perl source itself is in UTF-8, use C<use utf8;>. + +=item 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. + +=item C<use utf8> still needed to enable UTF-8/UTF-EBCDIC in scripts + +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>. + +=item 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.) + +=item C<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 I<ISO 8859-1 (Latin-1)>, but Unicode strings are +downgraded with UTF-8 encoding. This happens because the first 256 +codepoints in Unicode happens to agree with Latin-1. + +See L</"Byte and Character Semantics"> for more details. + +=back + +=head2 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. + +Under byte semantics, when C<use locale> is in effect, Perl uses the +semantics associated with the current locale. Absent a C<use locale>, Perl +currently uses US-ASCII (or Basic Latin in Unicode terminology) byte semantics, +meaning that characters whose ordinal numbers are in the range 128 - 255 are +undefined except for their ordinal numbers. This means that none have case +(upper and lower), nor are any a member of character classes, like C<[:alpha:]> +or C<\w>. +(But all do belong to the C<\W> class or the Perl regular expression extension +C<[:^alpha:]>.) + +This behavior preserves compatibility with earlier versions of Perl, +which allowed byte semantics in Perl operations only if +none of the program's inputs were marked as being as source of Unicode +character data. Such data may come from filehandles, from calls to +external programs, from information provided by the system (such as %ENV), +or from literals and constants in the source text. + +The C<bytes> pragma will always, regardless of platform, force byte +semantics in a particular lexical scope. See L<bytes>. + +The C<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 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 have +character semantics. This can cause surprises: See L</BUGS>, below + +Under character semantics, many operations that formerly operated on +bytes now operate on characters. A character in Perl is +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 L<perluniintro> for more. + +=head2 Effects of Character Semantics + +Character semantics have the following effects: + +=over 4 + +=item * + +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 C<use utf8>, the latter requires a BOM.) + +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 works for all characters, but +for characters under 0x100, note that Perl may use an 8 bit encoding +internally, for optimization and/or backward compatibility. + +Additionally, if you + + use charnames ':full'; + +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. Perl does not currently attempt to canonicalize variable +names. + +=item * + +Regular expressions match characters instead of bytes. "." matches +a character instead of a byte. + +=item * + +Character classes in regular expressions match characters instead of +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, scripts, and block ranges may be used like +character classes via the C<\p{}> "matches property" construct and +the C<\P{}> negation, "doesn't match property". + +See L</"Unicode Character Properties"> for more details. + +You can define your own character properties and use them +in the regular expression with the C<\p{}> or C<\P{}> construct. + +See L</"User-Defined Character Properties"> for more details. + +=item * + +The special pattern C<\X> matches any extended Unicode +sequence--"a combining character sequence" in Standardese--where the +first character is a base character and subsequent characters are mark +characters that apply to the base character. C<\X> is equivalent to +C<< (?>\PM\pM*) >>. + +=item * + +The C<tr///> operator translates characters instead of bytes. Note +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 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 a string will +automatically switch to using character positions, including +C<chop()>, C<chomp()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>, +C<sprintf()>, C<write()>, and C<length()>. An operator that +specifically does not switch is C<vec()>. Operators that really don't +care include operators that treat strings as a bucket of bits such as +C<sort()>, and operators dealing with filenames. + +=item * + +The C<pack()>/C<unpack()> letter C<C> does I<not> change, since it is often +used for byte-oriented formats. Again, think C<char> in the C language. + +There is a new C<U> specifier that converts between Unicode characters +and code points. There is also a C<W> specifier that is the equivalent of +C<chr>/C<ord> and properly handles character values even if they are above 255. + +=item * + +The C<chr()> and C<ord()> functions work on characters, similar to +C<pack("W")> and C<unpack("W")>, 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, 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 * + +lc(), uc(), lcfirst(), and ucfirst() work for the following cases: + +=over 8 + +=item * + +the case mapping is from a single Unicode character to another +single Unicode character, or + +=item * + +the case mapping is from a single Unicode character to more +than one Unicode character. + +=back + +Things to do with locales (Lithuanian, Turkish, Azeri) do B<not> work +since Perl does not understand the concept of Unicode locales. + +See the Unicode Technical Report #21, Case Mappings, for more details. + +But you can also define your own mappings to be used in the lc(), +lcfirst(), uc(), and ucfirst() (or their string-inlined versions). + +See L</"User-Defined Case Mappings"> for more details. + +=back + +=over 4 + +=item * + +And finally, C<scalar reverse()> reverses by character rather than by byte. + +=back + +=head2 Unicode Character Properties + +Named Unicode properties, scripts, and block ranges may be used like +character classes via the C<\p{}> "matches property" construct and +the C<\P{}> negation, "doesn't match property". + +For instance, C<\p{Lu}> matches any character with the Unicode "Lu" +(Letter, uppercase) property, while C<\p{M}> matches any character +with an "M" (mark--accents and such) property. Brackets are not +required for single letter properties, so C<\p{M}> is equivalent to +C<\pM>. Many predefined properties are available, such as +C<\p{Mirrored}> and C<\p{Tibetan}>. + +The official Unicode script and block names have spaces and dashes as +separators, but for convenience you can use dashes, spaces, or +underbars, and case is unimportant. It is recommended, however, that +for consistency you use the following naming: the official Unicode +script, property, or block name (see below for the additional rules +that apply to block names) with whitespace and dashes removed, and the +words "uppercase-first-lowercase-rest". C<Latin-1 Supplement> thus +becomes C<Latin1Supplement>. + +You can also use negation in both C<\p{}> and C<\P{}> by introducing a caret +(^) between the first brace and the property name: C<\p{^Tamil}> is +equal to C<\P{Tamil}>. + +B<NOTE: the properties, scripts, and blocks listed here are as of +Unicode 5.0.0 in July 2006.> + +=over 4 + +=item General Category + +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 + 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. +C<LC> and C<L&> are special cases, which are aliases for the set of +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. + +=item Bidirectional Character Types + +Because scripts differ in their directionality--Hebrew is +written right to left, for example--Unicode supplies these properties in +the BidiClass class: + + 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, C<\p{BidiClass:R}> matches characters that are normally +written right to left. + +=item Scripts + +The script names which can be used by C<\p{...}> and C<\P{...}>, +such as in C<\p{Latin}> or C<\p{Cyrillic}>, are as follows: + + Arabic + Armenian + Balinese + Bengali + Bopomofo + Braille + Buginese + Buhid + CanadianAboriginal + Cherokee + Coptic + Cuneiform + Cypriot + Cyrillic + Deseret + Devanagari + Ethiopic + Georgian + Glagolitic + Gothic + Greek + Gujarati + Gurmukhi + Han + Hangul + Hanunoo + Hebrew + Hiragana + Inherited + Kannada + Katakana + Kharoshthi + Khmer + Lao + Latin + Limbu + LinearB + Malayalam + Mongolian + Myanmar + NewTaiLue + Nko + Ogham + OldItalic + OldPersian + Oriya + Osmanya + PhagsPa + Phoenician + Runic + Shavian + Sinhala + SylotiNagri + Syriac + Tagalog + Tagbanwa + TaiLe + Tamil + Telugu + Thaana + Thai + Tibetan + Tifinagh + Ugaritic + Yi + +=item Extended property classes + +Extended property classes can supplement the basic +properties, defined by the F<PropList> Unicode database: + + ASCIIHexDigit + BidiControl + Dash + Deprecated + Diacritic + Extender + HexDigit + Hyphen + Ideographic + IDSBinaryOperator + IDSTrinaryOperator + JoinControl + LogicalOrderException + NoncharacterCodePoint + OtherAlphabetic + OtherDefaultIgnorableCodePoint + OtherGraphemeExtend + OtherIDStart + OtherIDContinue + OtherLowercase + OtherMath + OtherUppercase + PatternSyntax + PatternWhiteSpace + QuotationMark + Radical + SoftDotted + STerm + TerminalPunctuation + UnifiedIdeograph + VariationSelector + WhiteSpace + +and there are further derived properties: + + Alphabetic = Lu + Ll + Lt + Lm + Lo + Nl + OtherAlphabetic + Lowercase = Ll + OtherLowercase + Uppercase = Lu + OtherUppercase + Math = Sm + OtherMath + + IDStart = Lu + Ll + Lt + Lm + Lo + Nl + OtherIDStart + IDContinue = IDStart + Mn + Mc + Nd + Pc + OtherIDContinue + + DefaultIgnorableCodePoint + = OtherDefaultIgnorableCodePoint + + Cf + Cc + Cs + Noncharacters + VariationSelector + - WhiteSpace - FFF9..FFFB (Annotation Characters) + + Any = Any code points (i.e. U+0000 to U+10FFFF) + Assigned = Any non-Cn code points (i.e. synonym for \P{Cn}) + Unassigned = Synonym for \p{Cn} + ASCII = ASCII (i.e. U+0000 to U+007F) + + Common = Any character (or unassigned code point) + not explicitly assigned to a script + +=item Use of "Is" Prefix + +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}>. + +=item Blocks + +In addition to B<scripts>, Unicode also defines B<blocks> of +characters. The difference between scripts and blocks is that the +concept of scripts is closer to natural languages, while the concept +of blocks is more of an artificial grouping based on groups of 256 +Unicode characters. For example, the C<Latin> script contains letters +from many blocks but does not contain all the characters from those +blocks. It does not, for example, contain digits, because digits are +shared across many scripts. Digits and similar groups, like +punctuation, are in a category called C<Common>. + +For more about scripts, see the UAX#24 "Script Names": + + http://www.unicode.org/reports/tr24/ + +For more about blocks, see: + + http://www.unicode.org/Public/UNIDATA/Blocks.txt + +Block names are given with the C<In> prefix. For example, the +Katakana block is referenced via C<\p{InKatakana}>. The C<In> +prefix may be omitted if there is no naming conflict with a script +or any other property, but it is recommended that C<In> always be used +for block tests to avoid confusion. + +These block names are supported: + + InAegeanNumbers + InAlphabeticPresentationForms + InAncientGreekMusicalNotation + InAncientGreekNumbers + InArabic + InArabicPresentationFormsA + InArabicPresentationFormsB + InArabicSupplement + InArmenian + InArrows + InBalinese + InBasicLatin + InBengali + InBlockElements + InBopomofo + InBopomofoExtended + InBoxDrawing + InBraillePatterns + InBuginese + InBuhid + InByzantineMusicalSymbols + InCJKCompatibility + InCJKCompatibilityForms + InCJKCompatibilityIdeographs + InCJKCompatibilityIdeographsSupplement + InCJKRadicalsSupplement + InCJKStrokes + InCJKSymbolsAndPunctuation + InCJKUnifiedIdeographs + InCJKUnifiedIdeographsExtensionA + InCJKUnifiedIdeographsExtensionB + InCherokee + InCombiningDiacriticalMarks + InCombiningDiacriticalMarksSupplement + InCombiningDiacriticalMarksforSymbols + InCombiningHalfMarks + InControlPictures + InCoptic + InCountingRodNumerals + InCuneiform + InCuneiformNumbersAndPunctuation + InCurrencySymbols + InCypriotSyllabary + InCyrillic + InCyrillicSupplement + InDeseret + InDevanagari + InDingbats + InEnclosedAlphanumerics + InEnclosedCJKLettersAndMonths + InEthiopic + InEthiopicExtended + InEthiopicSupplement + InGeneralPunctuation + InGeometricShapes + InGeorgian + InGeorgianSupplement + InGlagolitic + InGothic + InGreekExtended + InGreekAndCoptic + InGujarati + InGurmukhi + InHalfwidthAndFullwidthForms + InHangulCompatibilityJamo + InHangulJamo + InHangulSyllables + InHanunoo + InHebrew + InHighPrivateUseSurrogates + InHighSurrogates + InHiragana + InIPAExtensions + InIdeographicDescriptionCharacters + InKanbun + InKangxiRadicals + InKannada + InKatakana + InKatakanaPhoneticExtensions + InKharoshthi + InKhmer + InKhmerSymbols + InLao + InLatin1Supplement + InLatinExtendedA + InLatinExtendedAdditional + InLatinExtendedB + InLatinExtendedC + InLatinExtendedD + InLetterlikeSymbols + InLimbu + InLinearBIdeograms + InLinearBSyllabary + InLowSurrogates + InMalayalam + InMathematicalAlphanumericSymbols + InMathematicalOperators + InMiscellaneousMathematicalSymbolsA + InMiscellaneousMathematicalSymbolsB + InMiscellaneousSymbols + InMiscellaneousSymbolsAndArrows + InMiscellaneousTechnical + InModifierToneLetters + InMongolian + InMusicalSymbols + InMyanmar + InNKo + InNewTaiLue + InNumberForms + InOgham + InOldItalic + InOldPersian + InOpticalCharacterRecognition + InOriya + InOsmanya + InPhagspa + InPhoenician + InPhoneticExtensions + InPhoneticExtensionsSupplement + InPrivateUseArea + InRunic + InShavian + InSinhala + InSmallFormVariants + InSpacingModifierLetters + InSpecials + InSuperscriptsAndSubscripts + InSupplementalArrowsA + InSupplementalArrowsB + InSupplementalMathematicalOperators + InSupplementalPunctuation + InSupplementaryPrivateUseAreaA + InSupplementaryPrivateUseAreaB + InSylotiNagri + InSyriac + InTagalog + InTagbanwa + InTags + InTaiLe + InTaiXuanJingSymbols + InTamil + InTelugu + InThaana + InThai + InTibetan + InTifinagh + InUgaritic + InUnifiedCanadianAboriginalSyllabics + InVariationSelectors + InVariationSelectorsSupplement + InVerticalForms + InYiRadicals + InYiSyllables + InYijingHexagramSymbols + +=back + +=head2 User-Defined Character Properties + +You can define your own character properties by defining subroutines +whose names begin with "In" or "Is". The subroutines can be defined in +any package. The user-defined properties can be used in the regular +expression C<\p> and C<\P> constructs; if you are using a user-defined +property from a package other than the one you are in, you must specify +its package in the C<\p> or C<\P> construct. + + # 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: + +=over 4 + +=item * + +A single hexadecimal number denoting a Unicode code point to include. + +=item * + +Two hexadecimal numbers separated by horizontal whitespace (space or +tabular characters) denoting a range of Unicode code points to include. + +=item * + +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 hexadecimal code +points for a range; or a single hexadecimal code point. + +=item * + +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 hexadecimal code +points for a range; or a single hexadecimal code point. + +=item * + +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 hexadecimal code +points for a range; or a single hexadecimal code point. + +=item * + +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. + +=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 + } + +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 nothing (resulting in an empty set). + +=head2 User-Defined Case Mappings + +You can also define your own mappings to be used in the lc(), +lcfirst(), uc(), and ucfirst() (or their string-inlined versions). +The principle is similar to that of user-defined character +properties: to define subroutines in the C<main> package +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 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. + +=head2 Character Encodings for Input and Output + +See L<Encode>. + +=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 Standard #18, +"Unicode Regular Expressions", version 11, in May 2005. + +=over 4 + +=item * + +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 "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 to U+1F00 U+03B9, + not with 1F80. This difference matters mainly for certain Greek + capital letters with certain modifiers: the Full case-folding + decomposes the letter, while the Simple case-folding would map + it to a single character. + [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, intersection, union, and removal (subtraction) syntax. + +[b] '+' for union, '-' for removal (set-difference), '&' for intersection +(see L</"User-Defined Character Properties">) + +[c] Try the C<:crlf> layer (see L<PerlIO>). + +[d] Avoid C<use warning 'utf8';> (or say C<no warning 'utf8';>) to allow +U+FFFF (C<\x{FFFF}>). + +=item * + +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] C<\N{...}> allows namespaces (see L<charnames>). + +=item * + +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") + +=back + +=head2 Unicode Encodings + +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 + +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 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 + + 0aaaaaaa 0aaaaaaa + 00000bbbbbaaaaaa 110bbbbb 10aaaaaa + ccccbbbbbbaaaaaa 1110cccc 10bbbbbb 10aaaaaa + 00000dddccccccbbbbbbaaaaaa 11110ddd 10cccccc 10bbbbbb 10aaaaaa + +As you can see, the continuation bytes all begin with C<10>, and the +leading bits of the start byte tell how many bytes the are in the +encoded character. + +=item * + +UTF-EBCDIC + +Like UTF-8 but EBCDIC-safe, in the way that UTF-8 is ASCII-safe. + +=item * + +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 +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 C<U+10000..U+10FFFF> +range of Unicode code points in pairs of 16-bit units. The I<high +surrogates> are the range C<U+D800..U+DBFF>, and the I<low surrogates> +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 - 0xD800) * 0x400 + ($lo - 0xDC00); + +If you try to generate surrogates (for example by using chr()), you +will get a warning if warnings are turned on, because those code +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-memory 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 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 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 +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, 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 C<0x00 0x00 0xFE 0xFF> for BE and +C<0xFF 0xFE 0x00 0x00> for LE. + +=item * + +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 C<U+FFFF>, +because it does not use surrogates. UCS-4 is a 32-bit encoding, +functionally identical to UTF-32. + +=item * + +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. + +=back + +=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, 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 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 +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 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 interfaces Perl +currently (as of 5.8.3) simply assumes byte strings both as arguments +and results, or UTF-8 strings if the C<encoding> pragma has been used. + +One reason why Perl does not attempt to resolve the role of Unicode in +this cases is that the answers are highly dependent on the operating +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 * + +chdir, chmod, chown, chroot, exec, link, lstat, mkdir, +rename, rmdir, stat, symlink, truncate, unlink, utime, -X + +=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 a byte +string into UTF-8, or vice versa. The low-level calls +utf8::upgrade($bytestring) and utf8::downgrade($utf8string[, FAIL_OK]) are +the answers. + +Note that utf8::downgrade() can fail if the string contains characters +that don't fit into a byte. + +=head2 Using Unicode in XS + +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 * + +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 if the C<UTF8> +flag is on; the bytes pragma is ignored. The C<UTF8> flag being on +does B<not> mean that there are any characters of code points greater +than 255 (or 127) in the scalar or that there are even any characters +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 * + +C<uvchr_to_utf8(buf, chr)> writes a Unicode character code point into +a buffer encoding the code point as UTF-8, and returns a pointer +pointing after the UTF-8 bytes. It works appropriately on EBCDIC machines. + +=item * + +C<utf8_to_uvchr(buf, lenp)> reads UTF-8 encoded bytes from a buffer and +returns the Unicode character code point and, optionally, the length of +the UTF-8 byte sequence. It works appropriately on EBCDIC machines. + +=item * + +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 * + +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 * + +C<is_utf8_char(s)> returns true if the pointer points to a valid UTF-8 +character. + +=item * + +C<is_utf8_string(buf, len)> returns true if C<len> bytes of the buffer +are valid UTF-8. + +=item * + +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 * + +C<utf8_distance(a, b)> will tell the distance in characters between the +two pointers pointing to the same UTF-8 encoded buffer. + +=item * + +C<utf8_hop(s, off)> will return a pointer to a UTF-8 encoded buffer +that is C<off> (positive or negative) Unicode characters displaced +from the UTF-8 buffer C<s>. Be careful not to overstep the buffer: +C<utf8_hop()> will merrily run off the end or the beginning of the +buffer if told to do so. + +=item * + +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 * + +C<ibcmp_utf8(s1, pe1, l1, u1, s2, pe2, l2, u2)> can be used to +compare two strings case-insensitively in Unicode. For case-sensitive +comparisons you can just use C<memEQ()> and C<memNE()> as usual. + +=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 Problems with characters whose ordinal numbers are in the range 128 - 255 with no Locale specified + +Without a locale specified, unlike all other characters or code points, +these characters have very different semantics in byte semantics versus +character semantics. +In character semantics they are interpreted as Unicode code points, which means +they are viewed as Latin-1 (ISO-8859-1). +In byte semantics, they are considered to be unassigned characters, +meaning that the only semantics they have is their +ordinal numbers, and that they are not members of various character classes. +None are considered to match C<\w> for example, but all match C<\W>. +Besides these class matches, +the known operations that this affects are those that change the case, +regular expression matching while ignoring case, +and B<quotemeta()>. +This can lead to unexpected results in which a string's semantics suddenly +change if a code point above 255 is appended to or removed from it, +which changes the string's semantics from byte to character or vice versa. +This behavior is scheduled to change in version 5.12, but in the meantime, +a workaround is to always call utf8::upgrade($string), or to use the +standard modules L<Encode> or L<charnames>. + +=head2 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. 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, at least for some operations. In general, +operations with UTF-8 encoded strings are still slower. As an example, +the Unicode properties (character classes) like C<\p{Nd}> are known to +be quite a bit slower (5-20 times) than their simpler counterparts +like C<\d> (then again, there 268 Unicode characters matching C<Nd> +compared with the 10 ASCII characters matching C<d>). + +=head2 Possible problems on EBCDIC platforms + +In earlier versions, when byte and character data were concatenated, +the new string was sometimes created by +decoding the byte strings as I<ISO 8859-1 (Latin-1)>, even if the +old Unicode string used EBCDIC. + +If you find any of these, please report them as bugs. + +=head2 Porting code from perl-5.6.X + +Perl 5.8 has a different Unicode model from 5.6. In 5.6 the programmer +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 $fh, ":encoding(utf8)"; + } + +=item * + +A scalar that is going to be passed to some extension + +Be it Compress::Zlib, Apache::Request or any extension that has no +mention of Unicode in the manpage, you need to make sure that the +UTF8 flag is stripped off. Note that at the time of this writing +(October 2002) the mentioned modules are not UTF-8-aware. Please +check the documentation to verify if this is still true. + + if ($] > 5.007) { + require Encode; + $val = Encode::encode_utf8($val); # make octets + } + +=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 UTF8 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 $ret; + } + } + } + } + + +=item * + +A large scalar that you know can only contain ASCII + +Scalars that contain only ASCII and are marked as UTF-8 are sometimes +a drag to your program. If you recognize such a situation, just remove +the UTF8 flag: + + utf8::downgrade($val) if $] > 5.007; + +=back + +=head1 SEE ALSO + +L<perlunitut>, L<perluniintro>, L<Encode>, L<open>, L<utf8>, L<bytes>, +L<perlretut>, L<perlvar/"${^UNICODE}"> + +=cut |