3 perlunicode - Unicode support in Perl
7 =head2 Important Caveats
9 Unicode support is an extensive requirement. While Perl does not
10 implement the Unicode standard or the accompanying technical reports
11 from cover to cover, Perl does support many Unicode features.
15 =item Input and Output Layers
17 Perl knows when a filehandle uses Perl's internal Unicode encodings
18 (UTF-8, or UTF-EBCDIC if in EBCDIC) if the filehandle is opened with
19 the ":utf8" layer. Other encodings can be converted to Perl's
20 encoding on input or from Perl's encoding on output by use of the
21 ":encoding(...)" layer. See L<open>.
23 To indicate that Perl source itself is using a particular encoding,
26 =item Regular Expressions
28 The regular expression compiler produces polymorphic opcodes. That is,
29 the pattern adapts to the data and automatically switches to the Unicode
30 character scheme when presented with Unicode data--or instead uses
31 a traditional byte scheme when presented with byte data.
33 =item C<use utf8> still needed to enable UTF-8/UTF-EBCDIC in scripts
35 As a compatibility measure, the C<use utf8> pragma must be explicitly
36 included to enable recognition of UTF-8 in the Perl scripts themselves
37 (in string or regular expression literals, or in identifier names) on
38 ASCII-based machines or to recognize UTF-EBCDIC on EBCDIC-based
39 machines. B<These are the only times when an explicit C<use utf8>
40 is needed.> See L<utf8>.
42 You can also use the C<encoding> pragma to change the default encoding
43 of the data in your script; see L<encoding>.
45 =item BOM-marked scripts and UTF-16 scripts autodetected
47 If a Perl script begins marked with the Unicode BOM (UTF-16LE, UTF16-BE,
48 or UTF-8), or if the script looks like non-BOM-marked UTF-16 of either
49 endianness, Perl will correctly read in the script as Unicode.
50 (BOMless UTF-8 cannot be effectively recognized or differentiated from
51 ISO 8859-1 or other eight-bit encodings.)
53 =item C<use encoding> needed to upgrade non-Latin-1 byte strings
55 By default, there is a fundamental asymmetry in Perl's unicode model:
56 implicit upgrading from byte strings to Unicode strings assumes that
57 they were encoded in I<ISO 8859-1 (Latin-1)>, but Unicode strings are
58 downgraded with UTF-8 encoding. This happens because the first 256
59 codepoints in Unicode happens to agree with Latin-1.
61 If you wish to interpret byte strings as UTF-8 instead, use the
66 See L</"Byte and Character Semantics"> for more details.
70 =head2 Byte and Character Semantics
72 Beginning with version 5.6, Perl uses logically-wide characters to
73 represent strings internally.
75 In future, Perl-level operations will be expected to work with
76 characters rather than bytes.
78 However, as an interim compatibility measure, Perl aims to
79 provide a safe migration path from byte semantics to character
80 semantics for programs. For operations where Perl can unambiguously
81 decide that the input data are characters, Perl switches to
82 character semantics. For operations where this determination cannot
83 be made without additional information from the user, Perl decides in
84 favor of compatibility and chooses to use byte semantics.
86 This behavior preserves compatibility with earlier versions of Perl,
87 which allowed byte semantics in Perl operations only if
88 none of the program's inputs were marked as being as source of Unicode
89 character data. Such data may come from filehandles, from calls to
90 external programs, from information provided by the system (such as %ENV),
91 or from literals and constants in the source text.
93 The C<bytes> pragma will always, regardless of platform, force byte
94 semantics in a particular lexical scope. See L<bytes>.
96 The C<utf8> pragma is primarily a compatibility device that enables
97 recognition of UTF-(8|EBCDIC) in literals encountered by the parser.
98 Note that this pragma is only required while Perl defaults to byte
99 semantics; when character semantics become the default, this pragma
100 may become a no-op. See L<utf8>.
102 Unless explicitly stated, Perl operators use character semantics
103 for Unicode data and byte semantics for non-Unicode data.
104 The decision to use character semantics is made transparently. If
105 input data comes from a Unicode source--for example, if a character
106 encoding layer is added to a filehandle or a literal Unicode
107 string constant appears in a program--character semantics apply.
108 Otherwise, byte semantics are in effect. The C<bytes> pragma should
109 be used to force byte semantics on Unicode data.
111 If strings operating under byte semantics and strings with Unicode
112 character data are concatenated, the new string will be created by
113 decoding the byte strings as I<ISO 8859-1 (Latin-1)>, even if the
114 old Unicode string used EBCDIC. This translation is done without
115 regard to the system's native 8-bit encoding. To change this for
116 systems with non-Latin-1 and non-EBCDIC native encodings, use the
117 C<encoding> pragma. See L<encoding>.
119 Under character semantics, many operations that formerly operated on
120 bytes now operate on characters. A character in Perl is
121 logically just a number ranging from 0 to 2**31 or so. Larger
122 characters may encode into longer sequences of bytes internally, but
123 this internal detail is mostly hidden for Perl code.
124 See L<perluniintro> for more.
126 =head2 Effects of Character Semantics
128 Character semantics have the following effects:
134 Strings--including hash keys--and regular expression patterns may
135 contain characters that have an ordinal value larger than 255.
137 If you use a Unicode editor to edit your program, Unicode characters
138 may occur directly within the literal strings in one of the various
139 Unicode encodings (UTF-8, UTF-EBCDIC, UCS-2, etc.), but will be recognized
140 as such and converted to Perl's internal representation only if the
141 appropriate L<encoding> is specified.
143 Unicode characters can also be added to a string by using the
144 C<\x{...}> notation. The Unicode code for the desired character, in
145 hexadecimal, should be placed in the braces. For instance, a smiley
146 face is C<\x{263A}>. This encoding scheme only works for characters
147 with a code of 0x100 or above.
151 use charnames ':full';
153 you can use the C<\N{...}> notation and put the official Unicode
154 character name within the braces, such as C<\N{WHITE SMILING FACE}>.
158 If an appropriate L<encoding> is specified, identifiers within the
159 Perl script may contain Unicode alphanumeric characters, including
160 ideographs. Perl does not currently attempt to canonicalize variable
165 Regular expressions match characters instead of bytes. "." matches
166 a character instead of a byte. The C<\C> pattern is provided to force
167 a match a single byte--a C<char> in C, hence C<\C>.
171 Character classes in regular expressions match characters instead of
172 bytes and match against the character properties specified in the
173 Unicode properties database. C<\w> can be used to match a Japanese
174 ideograph, for instance.
176 (However, and as a limitation of the current implementation, using
177 C<\w> or C<\W> I<inside> a C<[...]> character class will still match
178 with byte semantics.)
182 Named Unicode properties, scripts, and block ranges may be used like
183 character classes via the C<\p{}> "matches property" construct and
184 the C<\P{}> negation, "doesn't match property".
186 See L</"Unicode Character Properties"> for more details.
188 You can define your own character properties and use them
189 in the regular expression with the C<\p{}> or C<\P{}> construct.
191 See L</"User-Defined Character Properties"> for more details.
195 The special pattern C<\X> matches any extended Unicode
196 sequence--"a combining character sequence" in Standardese--where the
197 first character is a base character and subsequent characters are mark
198 characters that apply to the base character. C<\X> is equivalent to
203 The C<tr///> operator translates characters instead of bytes. Note
204 that the C<tr///CU> functionality has been removed. For similar
205 functionality see pack('U0', ...) and pack('C0', ...).
209 Case translation operators use the Unicode case translation tables
210 when character input is provided. Note that C<uc()>, or C<\U> in
211 interpolated strings, translates to uppercase, while C<ucfirst>,
212 or C<\u> in interpolated strings, translates to titlecase in languages
213 that make the distinction.
217 Most operators that deal with positions or lengths in a string will
218 automatically switch to using character positions, including
219 C<chop()>, C<chomp()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>,
220 C<sprintf()>, C<write()>, and C<length()>. An operator that
221 specifically does not switch is C<vec()>. Operators that really don't
222 care include operators that treat strings as a bucket of bits such as
223 C<sort()>, and operators dealing with filenames.
227 The C<pack()>/C<unpack()> letter C<C> does I<not> change, since it is often
228 used for byte-oriented formats. Again, think C<char> in the C language.
230 There is a new C<U> specifier that converts between Unicode characters
231 and code points. There is also a C<W> specifier that is the equivalent of
232 C<chr>/C<ord> and properly handles character values even if they are above 255.
236 The C<chr()> and C<ord()> functions work on characters, similar to
237 C<pack("W")> and C<unpack("W")>, I<not> C<pack("C")> and
238 C<unpack("C")>. C<pack("C")> and C<unpack("C")> are methods for
239 emulating byte-oriented C<chr()> and C<ord()> on Unicode strings.
240 While these methods reveal the internal encoding of Unicode strings,
241 that is not something one normally needs to care about at all.
245 The bit string operators, C<& | ^ ~>, can operate on character data.
246 However, for backward compatibility, such as when using bit string
247 operations when characters are all less than 256 in ordinal value, one
248 should not use C<~> (the bit complement) with characters of both
249 values less than 256 and values greater than 256. Most importantly,
250 DeMorgan's laws (C<~($x|$y) eq ~$x&~$y> and C<~($x&$y) eq ~$x|~$y>)
251 will not hold. The reason for this mathematical I<faux pas> is that
252 the complement cannot return B<both> the 8-bit (byte-wide) bit
253 complement B<and> the full character-wide bit complement.
257 lc(), uc(), lcfirst(), and ucfirst() work for the following cases:
263 the case mapping is from a single Unicode character to another
264 single Unicode character, or
268 the case mapping is from a single Unicode character to more
269 than one Unicode character.
273 Things to do with locales (Lithuanian, Turkish, Azeri) do B<not> work
274 since Perl does not understand the concept of Unicode locales.
276 See the Unicode Technical Report #21, Case Mappings, for more details.
278 But you can also define your own mappings to be used in the lc(),
279 lcfirst(), uc(), and ucfirst() (or their string-inlined versions).
281 See L</"User-Defined Case Mappings"> for more details.
289 And finally, C<scalar reverse()> reverses by character rather than by byte.
293 =head2 Unicode Character Properties
295 Named Unicode properties, scripts, and block ranges may be used like
296 character classes via the C<\p{}> "matches property" construct and
297 the C<\P{}> negation, "doesn't match property".
299 For instance, C<\p{Lu}> matches any character with the Unicode "Lu"
300 (Letter, uppercase) property, while C<\p{M}> matches any character
301 with an "M" (mark--accents and such) property. Brackets are not
302 required for single letter properties, so C<\p{M}> is equivalent to
303 C<\pM>. Many predefined properties are available, such as
304 C<\p{Mirrored}> and C<\p{Tibetan}>.
306 The official Unicode script and block names have spaces and dashes as
307 separators, but for convenience you can use dashes, spaces, or
308 underbars, and case is unimportant. It is recommended, however, that
309 for consistency you use the following naming: the official Unicode
310 script, property, or block name (see below for the additional rules
311 that apply to block names) with whitespace and dashes removed, and the
312 words "uppercase-first-lowercase-rest". C<Latin-1 Supplement> thus
313 becomes C<Latin1Supplement>.
315 You can also use negation in both C<\p{}> and C<\P{}> by introducing a caret
316 (^) between the first brace and the property name: C<\p{^Tamil}> is
317 equal to C<\P{Tamil}>.
319 B<NOTE: the properties, scripts, and blocks listed here are as of
320 Unicode 5.0.0 in July 2006.>
324 =item General Category
326 Here are the basic Unicode General Category properties, followed by their
327 long form. You can use either; C<\p{Lu}> and C<\p{UppercaseLetter}>,
328 for instance, are identical.
351 Pc ConnectorPunctuation
355 Pi InitialPunctuation
356 (may behave like Ps or Pe depending on usage)
358 (may behave like Ps or Pe depending on usage)
370 Zp ParagraphSeparator
375 Cs Surrogate (not usable)
379 Single-letter properties match all characters in any of the
380 two-letter sub-properties starting with the same letter.
381 C<LC> and C<L&> are special cases, which are aliases for the set of
382 C<Ll>, C<Lu>, and C<Lt>.
384 Because Perl hides the need for the user to understand the internal
385 representation of Unicode characters, there is no need to implement
386 the somewhat messy concept of surrogates. C<Cs> is therefore not
389 =item Bidirectional Character Types
391 Because scripts differ in their directionality--Hebrew is
392 written right to left, for example--Unicode supplies these properties in
398 LRE Left-to-Right Embedding
399 LRO Left-to-Right Override
401 AL Right-to-Left Arabic
402 RLE Right-to-Left Embedding
403 RLO Right-to-Left Override
404 PDF Pop Directional Format
406 ES European Number Separator
407 ET European Number Terminator
409 CS Common Number Separator
412 B Paragraph Separator
417 For example, C<\p{BidiClass:R}> matches characters that are normally
418 written right to left.
422 The script names which can be used by C<\p{...}> and C<\P{...}>,
423 such as in C<\p{Latin}> or C<\p{Cyrillic}>, are as follows:
491 =item Extended property classes
493 Extended property classes can supplement the basic
494 properties, defined by the F<PropList> Unicode database:
508 LogicalOrderException
509 NoncharacterCodePoint
511 OtherDefaultIgnorableCodePoint
529 and there are further derived properties:
531 Alphabetic = Lu + Ll + Lt + Lm + Lo + Nl + OtherAlphabetic
532 Lowercase = Ll + OtherLowercase
533 Uppercase = Lu + OtherUppercase
534 Math = Sm + OtherMath
536 IDStart = Lu + Ll + Lt + Lm + Lo + Nl + OtherIDStart
537 IDContinue = IDStart + Mn + Mc + Nd + Pc + OtherIDContinue
539 DefaultIgnorableCodePoint
540 = OtherDefaultIgnorableCodePoint
541 + Cf + Cc + Cs + Noncharacters + VariationSelector
542 - WhiteSpace - FFF9..FFFB (Annotation Characters)
544 Any = Any code points (i.e. U+0000 to U+10FFFF)
545 Assigned = Any non-Cn code points (i.e. synonym for \P{Cn})
546 Unassigned = Synonym for \p{Cn}
547 ASCII = ASCII (i.e. U+0000 to U+007F)
549 Common = Any character (or unassigned code point)
550 not explicitly assigned to a script
552 =item Use of "Is" Prefix
554 For backward compatibility (with Perl 5.6), all properties mentioned
555 so far may have C<Is> prepended to their name, so C<\P{IsLu}>, for
556 example, is equal to C<\P{Lu}>.
560 In addition to B<scripts>, Unicode also defines B<blocks> of
561 characters. The difference between scripts and blocks is that the
562 concept of scripts is closer to natural languages, while the concept
563 of blocks is more of an artificial grouping based on groups of 256
564 Unicode characters. For example, the C<Latin> script contains letters
565 from many blocks but does not contain all the characters from those
566 blocks. It does not, for example, contain digits, because digits are
567 shared across many scripts. Digits and similar groups, like
568 punctuation, are in a category called C<Common>.
570 For more about scripts, see the UAX#24 "Script Names":
572 http://www.unicode.org/reports/tr24/
574 For more about blocks, see:
576 http://www.unicode.org/Public/UNIDATA/Blocks.txt
578 Block names are given with the C<In> prefix. For example, the
579 Katakana block is referenced via C<\p{InKatakana}>. The C<In>
580 prefix may be omitted if there is no naming conflict with a script
581 or any other property, but it is recommended that C<In> always be used
582 for block tests to avoid confusion.
584 These block names are supported:
587 InAlphabeticPresentationForms
588 InAncientGreekMusicalNotation
589 InAncientGreekNumbers
591 InArabicPresentationFormsA
592 InArabicPresentationFormsB
606 InByzantineMusicalSymbols
608 InCJKCompatibilityForms
609 InCJKCompatibilityIdeographs
610 InCJKCompatibilityIdeographsSupplement
611 InCJKRadicalsSupplement
613 InCJKSymbolsAndPunctuation
614 InCJKUnifiedIdeographs
615 InCJKUnifiedIdeographsExtensionA
616 InCJKUnifiedIdeographsExtensionB
618 InCombiningDiacriticalMarks
619 InCombiningDiacriticalMarksSupplement
620 InCombiningDiacriticalMarksforSymbols
624 InCountingRodNumerals
626 InCuneiformNumbersAndPunctuation
634 InEnclosedAlphanumerics
635 InEnclosedCJKLettersAndMonths
649 InHalfwidthAndFullwidthForms
650 InHangulCompatibilityJamo
655 InHighPrivateUseSurrogates
659 InIdeographicDescriptionCharacters
664 InKatakanaPhoneticExtensions
671 InLatinExtendedAdditional
681 InMathematicalAlphanumericSymbols
682 InMathematicalOperators
683 InMiscellaneousMathematicalSymbolsA
684 InMiscellaneousMathematicalSymbolsB
685 InMiscellaneousSymbols
686 InMiscellaneousSymbolsAndArrows
687 InMiscellaneousTechnical
688 InModifierToneLetters
698 InOpticalCharacterRecognition
704 InPhoneticExtensionsSupplement
710 InSpacingModifierLetters
712 InSuperscriptsAndSubscripts
713 InSupplementalArrowsA
714 InSupplementalArrowsB
715 InSupplementalMathematicalOperators
716 InSupplementalPunctuation
717 InSupplementaryPrivateUseAreaA
718 InSupplementaryPrivateUseAreaB
733 InUnifiedCanadianAboriginalSyllabics
735 InVariationSelectorsSupplement
739 InYijingHexagramSymbols
743 =head2 User-Defined Character Properties
745 You can define your own character properties by defining subroutines
746 whose names begin with "In" or "Is". The subroutines can be defined in
747 any package. The user-defined properties can be used in the regular
748 expression C<\p> and C<\P> constructs; if you are using a user-defined
749 property from a package other than the one you are in, you must specify
750 its package in the C<\p> or C<\P> construct.
752 # assuming property IsForeign defined in Lang::
753 package main; # property package name required
754 if ($txt =~ /\p{Lang::IsForeign}+/) { ... }
756 package Lang; # property package name not required
757 if ($txt =~ /\p{IsForeign}+/) { ... }
760 Note that the effect is compile-time and immutable once defined.
762 The subroutines must return a specially-formatted string, with one
763 or more newline-separated lines. Each line must be one of the following:
769 Two hexadecimal numbers separated by horizontal whitespace (space or
770 tabular characters) denoting a range of Unicode code points to include.
774 Something to include, prefixed by "+": a built-in character
775 property (prefixed by "utf8::") or a user-defined character property,
776 to represent all the characters in that property; two hexadecimal code
777 points for a range; or a single hexadecimal code point.
781 Something to exclude, prefixed by "-": an existing character
782 property (prefixed by "utf8::") or a user-defined character property,
783 to represent all the characters in that property; two hexadecimal code
784 points for a range; or a single hexadecimal code point.
788 Something to negate, prefixed "!": an existing character
789 property (prefixed by "utf8::") or a user-defined character property,
790 to represent all the characters in that property; two hexadecimal code
791 points for a range; or a single hexadecimal code point.
795 Something to intersect with, prefixed by "&": an existing character
796 property (prefixed by "utf8::") or a user-defined character property,
797 for all the characters except the characters in the property; two
798 hexadecimal code points for a range; or a single hexadecimal code point.
802 For example, to define a property that covers both the Japanese
803 syllabaries (hiragana and katakana), you can define
812 Imagine that the here-doc end marker is at the beginning of the line.
813 Now you can use C<\p{InKana}> and C<\P{InKana}>.
815 You could also have used the existing block property names:
824 Suppose you wanted to match only the allocated characters,
825 not the raw block ranges: in other words, you want to remove
836 The negation is useful for defining (surprise!) negated classes.
846 Intersection is useful for getting the common characters matched by
847 two (or more) classes.
856 It's important to remember not to use "&" for the first set -- that
857 would be intersecting with nothing (resulting in an empty set).
859 A final note on the user-defined property tests: they will be used
860 only if the scalar has been marked as having Unicode characters.
861 Old byte-style strings will not be affected.
863 =head2 User-Defined Case Mappings
865 You can also define your own mappings to be used in the lc(),
866 lcfirst(), uc(), and ucfirst() (or their string-inlined versions).
867 The principle is similar to that of user-defined character
868 properties: to define subroutines in the C<main> package
869 with names like C<ToLower> (for lc() and lcfirst()), C<ToTitle> (for
870 the first character in ucfirst()), and C<ToUpper> (for uc(), and the
871 rest of the characters in ucfirst()).
873 The string returned by the subroutines needs now to be three
874 hexadecimal numbers separated by tabulators: start of the source
875 range, end of the source range, and start of the destination range.
884 defines an uc() mapping that causes only the characters "a", "b", and
885 "c" to be mapped to "A", "B", "C", all other characters will remain
888 If there is no source range to speak of, that is, the mapping is from
889 a single character to another single character, leave the end of the
890 source range empty, but the two tabulator characters are still needed.
899 defines a lc() mapping that causes only "A" to be mapped to "a", all
900 other characters will remain unchanged.
902 (For serious hackers only) If you want to introspect the default
903 mappings, you can find the data in the directory
904 C<$Config{privlib}>/F<unicore/To/>. The mapping data is returned as
905 the here-document, and the C<utf8::ToSpecFoo> are special exception
906 mappings derived from <$Config{privlib}>/F<unicore/SpecialCasing.txt>.
907 The C<Digit> and C<Fold> mappings that one can see in the directory
908 are not directly user-accessible, one can use either the
909 C<Unicode::UCD> module, or just match case-insensitively (that's when
910 the C<Fold> mapping is used).
912 A final note on the user-defined case mappings: they will be used
913 only if the scalar has been marked as having Unicode characters.
914 Old byte-style strings will not be affected.
916 =head2 Character Encodings for Input and Output
920 =head2 Unicode Regular Expression Support Level
922 The following list of Unicode support for regular expressions describes
923 all the features currently supported. The references to "Level N"
924 and the section numbers refer to the Unicode Technical Standard #18,
925 "Unicode Regular Expressions", version 11, in May 2005.
931 Level 1 - Basic Unicode Support
933 RL1.1 Hex Notation - done [1]
934 RL1.2 Properties - done [2][3]
935 RL1.2a Compatibility Properties - done [4]
936 RL1.3 Subtraction and Intersection - MISSING [5]
937 RL1.4 Simple Word Boundaries - done [6]
938 RL1.5 Simple Loose Matches - done [7]
939 RL1.6 Line Boundaries - MISSING [8]
940 RL1.7 Supplementary Code Points - done [9]
944 [3] supports not only minimal list (general category, scripts,
945 Alphabetic, Lowercase, Uppercase, WhiteSpace,
946 NoncharacterCodePoint, DefaultIgnorableCodePoint, Any,
947 ASCII, Assigned), but also bidirectional types, blocks, etc.
948 (see L</"Unicode Character Properties">)
949 [4] \d \D \s \S \w \W \X [:prop:] [:^prop:]
950 [5] can use regular expression look-ahead [a] or
951 user-defined character properties [b] to emulate set operations
953 [7] note that Perl does Full case-folding in matching, not Simple:
954 for example U+1F88 is equivalent with U+1F00 U+03B9,
955 not with 1F80. This difference matters for certain Greek
956 capital letters with certain modifiers: the Full case-folding
957 decomposes the letter, while the Simple case-folding would map
958 it to a single character.
959 [8] should do ^ and $ also on U+000B (\v in C), FF (\f), CR (\r),
960 CRLF (\r\n), NEL (U+0085), LS (U+2028), and PS (U+2029);
961 should also affect <>, $., and script line numbers;
962 should not split lines within CRLF [c] (i.e. there is no empty
963 line between \r and \n)
964 [9] UTF-8/UTF-EBDDIC used in perl allows not only U+10000 to U+10FFFF
965 but also beyond U+10FFFF [d]
967 [a] You can mimic class subtraction using lookahead.
968 For example, what UTS#18 might write as
970 [{Greek}-[{UNASSIGNED}]]
972 in Perl can be written as:
974 (?!\p{Unassigned})\p{InGreekAndCoptic}
975 (?=\p{Assigned})\p{InGreekAndCoptic}
977 But in this particular example, you probably really want
981 which will match assigned characters known to be part of the Greek script.
983 Also see the Unicode::Regex::Set module, it does implement the full
984 UTS#18 grouping, intersection, union, and removal (subtraction) syntax.
986 [b] '+' for union, '-' for removal (set-difference), '&' for intersection
987 (see L</"User-Defined Character Properties">)
989 [c] Try the C<:crlf> layer (see L<PerlIO>).
991 [d] Avoid C<use warning 'utf8';> (or say C<no warning 'utf8';>) to allow
992 U+FFFF (C<\x{FFFF}>).
996 Level 2 - Extended Unicode Support
998 RL2.1 Canonical Equivalents - MISSING [10][11]
999 RL2.2 Default Grapheme Clusters - MISSING [12][13]
1000 RL2.3 Default Word Boundaries - MISSING [14]
1001 RL2.4 Default Loose Matches - MISSING [15]
1002 RL2.5 Name Properties - MISSING [16]
1003 RL2.6 Wildcard Properties - MISSING
1005 [10] see UAX#15 "Unicode Normalization Forms"
1006 [11] have Unicode::Normalize but not integrated to regexes
1007 [12] have \X but at this level . should equal that
1008 [13] UAX#29 "Text Boundaries" considers CRLF and Hangul syllable
1009 clusters as a single grapheme cluster.
1010 [14] see UAX#29, Word Boundaries
1011 [15] see UAX#21 "Case Mappings"
1012 [16] have \N{...} but neither compute names of CJK Ideographs
1013 and Hangul Syllables nor use a loose match [e]
1015 [e] C<\N{...}> allows namespaces (see L<charnames>).
1019 Level 3 - Tailored Support
1021 RL3.1 Tailored Punctuation - MISSING
1022 RL3.2 Tailored Grapheme Clusters - MISSING [17][18]
1023 RL3.3 Tailored Word Boundaries - MISSING
1024 RL3.4 Tailored Loose Matches - MISSING
1025 RL3.5 Tailored Ranges - MISSING
1026 RL3.6 Context Matching - MISSING [19]
1027 RL3.7 Incremental Matches - MISSING
1028 ( RL3.8 Unicode Set Sharing )
1029 RL3.9 Possible Match Sets - MISSING
1030 RL3.10 Folded Matching - MISSING [20]
1031 RL3.11 Submatchers - MISSING
1033 [17] see UAX#10 "Unicode Collation Algorithms"
1034 [18] have Unicode::Collate but not integrated to regexes
1035 [19] have (?<=x) and (?=x), but look-aheads or look-behinds should see
1036 outside of the target substring
1037 [20] need insensitive matching for linguistic features other than case;
1038 for example, hiragana to katakana, wide and narrow, simplified Han
1039 to traditional Han (see UTR#30 "Character Foldings")
1043 =head2 Unicode Encodings
1045 Unicode characters are assigned to I<code points>, which are abstract
1046 numbers. To use these numbers, various encodings are needed.
1054 UTF-8 is a variable-length (1 to 6 bytes, current character allocations
1055 require 4 bytes), byte-order independent encoding. For ASCII (and we
1056 really do mean 7-bit ASCII, not another 8-bit encoding), UTF-8 is
1059 The following table is from Unicode 3.2.
1061 Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
1063 U+0000..U+007F 00..7F
1064 U+0080..U+07FF C2..DF 80..BF
1065 U+0800..U+0FFF E0 A0..BF 80..BF
1066 U+1000..U+CFFF E1..EC 80..BF 80..BF
1067 U+D000..U+D7FF ED 80..9F 80..BF
1068 U+D800..U+DFFF ******* ill-formed *******
1069 U+E000..U+FFFF EE..EF 80..BF 80..BF
1070 U+10000..U+3FFFF F0 90..BF 80..BF 80..BF
1071 U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF
1072 U+100000..U+10FFFF F4 80..8F 80..BF 80..BF
1074 Note the C<A0..BF> in C<U+0800..U+0FFF>, the C<80..9F> in
1075 C<U+D000...U+D7FF>, the C<90..B>F in C<U+10000..U+3FFFF>, and the
1076 C<80...8F> in C<U+100000..U+10FFFF>. The "gaps" are caused by legal
1077 UTF-8 avoiding non-shortest encodings: it is technically possible to
1078 UTF-8-encode a single code point in different ways, but that is
1079 explicitly forbidden, and the shortest possible encoding should always
1080 be used. So that's what Perl does.
1082 Another way to look at it is via bits:
1084 Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
1087 00000bbbbbaaaaaa 110bbbbb 10aaaaaa
1088 ccccbbbbbbaaaaaa 1110cccc 10bbbbbb 10aaaaaa
1089 00000dddccccccbbbbbbaaaaaa 11110ddd 10cccccc 10bbbbbb 10aaaaaa
1091 As you can see, the continuation bytes all begin with C<10>, and the
1092 leading bits of the start byte tell how many bytes the are in the
1099 Like UTF-8 but EBCDIC-safe, in the way that UTF-8 is ASCII-safe.
1103 UTF-16, UTF-16BE, UTF-16LE, Surrogates, and BOMs (Byte Order Marks)
1105 The followings items are mostly for reference and general Unicode
1106 knowledge, Perl doesn't use these constructs internally.
1108 UTF-16 is a 2 or 4 byte encoding. The Unicode code points
1109 C<U+0000..U+FFFF> are stored in a single 16-bit unit, and the code
1110 points C<U+10000..U+10FFFF> in two 16-bit units. The latter case is
1111 using I<surrogates>, the first 16-bit unit being the I<high
1112 surrogate>, and the second being the I<low surrogate>.
1114 Surrogates are code points set aside to encode the C<U+10000..U+10FFFF>
1115 range of Unicode code points in pairs of 16-bit units. The I<high
1116 surrogates> are the range C<U+D800..U+DBFF>, and the I<low surrogates>
1117 are the range C<U+DC00..U+DFFF>. The surrogate encoding is
1119 $hi = ($uni - 0x10000) / 0x400 + 0xD800;
1120 $lo = ($uni - 0x10000) % 0x400 + 0xDC00;
1124 $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00);
1126 If you try to generate surrogates (for example by using chr()), you
1127 will get a warning if warnings are turned on, because those code
1128 points are not valid for a Unicode character.
1130 Because of the 16-bitness, UTF-16 is byte-order dependent. UTF-16
1131 itself can be used for in-memory computations, but if storage or
1132 transfer is required either UTF-16BE (big-endian) or UTF-16LE
1133 (little-endian) encodings must be chosen.
1135 This introduces another problem: what if you just know that your data
1136 is UTF-16, but you don't know which endianness? Byte Order Marks, or
1137 BOMs, are a solution to this. A special character has been reserved
1138 in Unicode to function as a byte order marker: the character with the
1139 code point C<U+FEFF> is the BOM.
1141 The trick is that if you read a BOM, you will know the byte order,
1142 since if it was written on a big-endian platform, you will read the
1143 bytes C<0xFE 0xFF>, but if it was written on a little-endian platform,
1144 you will read the bytes C<0xFF 0xFE>. (And if the originating platform
1145 was writing in UTF-8, you will read the bytes C<0xEF 0xBB 0xBF>.)
1147 The way this trick works is that the character with the code point
1148 C<U+FFFE> is guaranteed not to be a valid Unicode character, so the
1149 sequence of bytes C<0xFF 0xFE> is unambiguously "BOM, represented in
1150 little-endian format" and cannot be C<U+FFFE>, represented in big-endian
1155 UTF-32, UTF-32BE, UTF-32LE
1157 The UTF-32 family is pretty much like the UTF-16 family, expect that
1158 the units are 32-bit, and therefore the surrogate scheme is not
1159 needed. The BOM signatures will be C<0x00 0x00 0xFE 0xFF> for BE and
1160 C<0xFF 0xFE 0x00 0x00> for LE.
1166 Encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit
1167 encoding. Unlike UTF-16, UCS-2 is not extensible beyond C<U+FFFF>,
1168 because it does not use surrogates. UCS-4 is a 32-bit encoding,
1169 functionally identical to UTF-32.
1175 A seven-bit safe (non-eight-bit) encoding, which is useful if the
1176 transport or storage is not eight-bit safe. Defined by RFC 2152.
1180 =head2 Security Implications of Unicode
1188 Unfortunately, the specification of UTF-8 leaves some room for
1189 interpretation of how many bytes of encoded output one should generate
1190 from one input Unicode character. Strictly speaking, the shortest
1191 possible sequence of UTF-8 bytes should be generated,
1192 because otherwise there is potential for an input buffer overflow at
1193 the receiving end of a UTF-8 connection. Perl always generates the
1194 shortest length UTF-8, and with warnings on Perl will warn about
1195 non-shortest length UTF-8 along with other malformations, such as the
1196 surrogates, which are not real Unicode code points.
1200 Regular expressions behave slightly differently between byte data and
1201 character (Unicode) data. For example, the "word character" character
1202 class C<\w> will work differently depending on if data is eight-bit bytes
1205 In the first case, the set of C<\w> characters is either small--the
1206 default set of alphabetic characters, digits, and the "_"--or, if you
1207 are using a locale (see L<perllocale>), the C<\w> might contain a few
1208 more letters according to your language and country.
1210 In the second case, the C<\w> set of characters is much, much larger.
1211 Most importantly, even in the set of the first 256 characters, it will
1212 probably match different characters: unlike most locales, which are
1213 specific to a language and country pair, Unicode classifies all the
1214 characters that are letters I<somewhere> as C<\w>. For example, your
1215 locale might not think that LATIN SMALL LETTER ETH is a letter (unless
1216 you happen to speak Icelandic), but Unicode does.
1218 As discussed elsewhere, Perl has one foot (two hooves?) planted in
1219 each of two worlds: the old world of bytes and the new world of
1220 characters, upgrading from bytes to characters when necessary.
1221 If your legacy code does not explicitly use Unicode, no automatic
1222 switch-over to characters should happen. Characters shouldn't get
1223 downgraded to bytes, either. It is possible to accidentally mix bytes
1224 and characters, however (see L<perluniintro>), in which case C<\w> in
1225 regular expressions might start behaving differently. Review your
1226 code. Use warnings and the C<strict> pragma.
1230 =head2 Unicode in Perl on EBCDIC
1232 The way Unicode is handled on EBCDIC platforms is still
1233 experimental. On such platforms, references to UTF-8 encoding in this
1234 document and elsewhere should be read as meaning the UTF-EBCDIC
1235 specified in Unicode Technical Report 16, unless ASCII vs. EBCDIC issues
1236 are specifically discussed. There is no C<utfebcdic> pragma or
1237 ":utfebcdic" layer; rather, "utf8" and ":utf8" are reused to mean
1238 the platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic>
1239 for more discussion of the issues.
1243 Usually locale settings and Unicode do not affect each other, but
1244 there are a couple of exceptions:
1250 You can enable automatic UTF-8-ification of your standard file
1251 handles, default C<open()> layer, and C<@ARGV> by using either
1252 the C<-C> command line switch or the C<PERL_UNICODE> environment
1253 variable, see L<perlrun> for the documentation of the C<-C> switch.
1257 Perl tries really hard to work both with Unicode and the old
1258 byte-oriented world. Most often this is nice, but sometimes Perl's
1259 straddling of the proverbial fence causes problems.
1263 =head2 When Unicode Does Not Happen
1265 While Perl does have extensive ways to input and output in Unicode,
1266 and few other 'entry points' like the @ARGV which can be interpreted
1267 as Unicode (UTF-8), there still are many places where Unicode (in some
1268 encoding or another) could be given as arguments or received as
1269 results, or both, but it is not.
1271 The following are such interfaces. For all of these interfaces Perl
1272 currently (as of 5.8.3) simply assumes byte strings both as arguments
1273 and results, or UTF-8 strings if the C<encoding> pragma has been used.
1275 One reason why Perl does not attempt to resolve the role of Unicode in
1276 this cases is that the answers are highly dependent on the operating
1277 system and the file system(s). For example, whether filenames can be
1278 in Unicode, and in exactly what kind of encoding, is not exactly a
1279 portable concept. Similarly for the qx and system: how well will the
1280 'command line interface' (and which of them?) handle Unicode?
1286 chdir, chmod, chown, chroot, exec, link, lstat, mkdir,
1287 rename, rmdir, stat, symlink, truncate, unlink, utime, -X
1299 open, opendir, sysopen
1303 qx (aka the backtick operator), system
1311 =head2 Forcing Unicode in Perl (Or Unforcing Unicode in Perl)
1313 Sometimes (see L</"When Unicode Does Not Happen">) there are
1314 situations where you simply need to force Perl to believe that a byte
1315 string is UTF-8, or vice versa. The low-level calls
1316 utf8::upgrade($bytestring) and utf8::downgrade($utf8string) are
1319 Do not use them without careful thought, though: Perl may easily get
1320 very confused, angry, or even crash, if you suddenly change the 'nature'
1321 of scalar like that. Especially careful you have to be if you use the
1322 utf8::upgrade(): any random byte string is not valid UTF-8.
1324 =head2 Using Unicode in XS
1326 If you want to handle Perl Unicode in XS extensions, you may find the
1327 following C APIs useful. See also L<perlguts/"Unicode Support"> for an
1328 explanation about Unicode at the XS level, and L<perlapi> for the API
1335 C<DO_UTF8(sv)> returns true if the C<UTF8> flag is on and the bytes
1336 pragma is not in effect. C<SvUTF8(sv)> returns true is the C<UTF8>
1337 flag is on; the bytes pragma is ignored. The C<UTF8> flag being on
1338 does B<not> mean that there are any characters of code points greater
1339 than 255 (or 127) in the scalar or that there are even any characters
1340 in the scalar. What the C<UTF8> flag means is that the sequence of
1341 octets in the representation of the scalar is the sequence of UTF-8
1342 encoded code points of the characters of a string. The C<UTF8> flag
1343 being off means that each octet in this representation encodes a
1344 single character with code point 0..255 within the string. Perl's
1345 Unicode model is not to use UTF-8 until it is absolutely necessary.
1349 C<uvuni_to_utf8(buf, chr)> writes a Unicode character code point into
1350 a buffer encoding the code point as UTF-8, and returns a pointer
1351 pointing after the UTF-8 bytes.
1355 C<utf8_to_uvuni(buf, lenp)> reads UTF-8 encoded bytes from a buffer and
1356 returns the Unicode character code point and, optionally, the length of
1357 the UTF-8 byte sequence.
1361 C<utf8_length(start, end)> returns the length of the UTF-8 encoded buffer
1362 in characters. C<sv_len_utf8(sv)> returns the length of the UTF-8 encoded
1367 C<sv_utf8_upgrade(sv)> converts the string of the scalar to its UTF-8
1368 encoded form. C<sv_utf8_downgrade(sv)> does the opposite, if
1369 possible. C<sv_utf8_encode(sv)> is like sv_utf8_upgrade except that
1370 it does not set the C<UTF8> flag. C<sv_utf8_decode()> does the
1371 opposite of C<sv_utf8_encode()>. Note that none of these are to be
1372 used as general-purpose encoding or decoding interfaces: C<use Encode>
1373 for that. C<sv_utf8_upgrade()> is affected by the encoding pragma
1374 but C<sv_utf8_downgrade()> is not (since the encoding pragma is
1375 designed to be a one-way street).
1379 C<is_utf8_char(s)> returns true if the pointer points to a valid UTF-8
1384 C<is_utf8_string(buf, len)> returns true if C<len> bytes of the buffer
1389 C<UTF8SKIP(buf)> will return the number of bytes in the UTF-8 encoded
1390 character in the buffer. C<UNISKIP(chr)> will return the number of bytes
1391 required to UTF-8-encode the Unicode character code point. C<UTF8SKIP()>
1392 is useful for example for iterating over the characters of a UTF-8
1393 encoded buffer; C<UNISKIP()> is useful, for example, in computing
1394 the size required for a UTF-8 encoded buffer.
1398 C<utf8_distance(a, b)> will tell the distance in characters between the
1399 two pointers pointing to the same UTF-8 encoded buffer.
1403 C<utf8_hop(s, off)> will return a pointer to an UTF-8 encoded buffer
1404 that is C<off> (positive or negative) Unicode characters displaced
1405 from the UTF-8 buffer C<s>. Be careful not to overstep the buffer:
1406 C<utf8_hop()> will merrily run off the end or the beginning of the
1407 buffer if told to do so.
1411 C<pv_uni_display(dsv, spv, len, pvlim, flags)> and
1412 C<sv_uni_display(dsv, ssv, pvlim, flags)> are useful for debugging the
1413 output of Unicode strings and scalars. By default they are useful
1414 only for debugging--they display B<all> characters as hexadecimal code
1415 points--but with the flags C<UNI_DISPLAY_ISPRINT>,
1416 C<UNI_DISPLAY_BACKSLASH>, and C<UNI_DISPLAY_QQ> you can make the
1417 output more readable.
1421 C<ibcmp_utf8(s1, pe1, u1, l1, u1, s2, pe2, l2, u2)> can be used to
1422 compare two strings case-insensitively in Unicode. For case-sensitive
1423 comparisons you can just use C<memEQ()> and C<memNE()> as usual.
1427 For more information, see L<perlapi>, and F<utf8.c> and F<utf8.h>
1428 in the Perl source code distribution.
1432 =head2 Interaction with Locales
1434 Use of locales with Unicode data may lead to odd results. Currently,
1435 Perl attempts to attach 8-bit locale info to characters in the range
1436 0..255, but this technique is demonstrably incorrect for locales that
1437 use characters above that range when mapped into Unicode. Perl's
1438 Unicode support will also tend to run slower. Use of locales with
1439 Unicode is discouraged.
1441 =head2 Interaction with Extensions
1443 When Perl exchanges data with an extension, the extension should be
1444 able to understand the UTF-8 flag and act accordingly. If the
1445 extension doesn't know about the flag, it's likely that the extension
1446 will return incorrectly-flagged data.
1448 So if you're working with Unicode data, consult the documentation of
1449 every module you're using if there are any issues with Unicode data
1450 exchange. If the documentation does not talk about Unicode at all,
1451 suspect the worst and probably look at the source to learn how the
1452 module is implemented. Modules written completely in Perl shouldn't
1453 cause problems. Modules that directly or indirectly access code written
1454 in other programming languages are at risk.
1456 For affected functions, the simple strategy to avoid data corruption is
1457 to always make the encoding of the exchanged data explicit. Choose an
1458 encoding that you know the extension can handle. Convert arguments passed
1459 to the extensions to that encoding and convert results back from that
1460 encoding. Write wrapper functions that do the conversions for you, so
1461 you can later change the functions when the extension catches up.
1463 To provide an example, let's say the popular Foo::Bar::escape_html
1464 function doesn't deal with Unicode data yet. The wrapper function
1465 would convert the argument to raw UTF-8 and convert the result back to
1466 Perl's internal representation like so:
1468 sub my_escape_html ($) {
1470 return unless defined $what;
1471 Encode::decode_utf8(Foo::Bar::escape_html(Encode::encode_utf8($what)));
1474 Sometimes, when the extension does not convert data but just stores
1475 and retrieves them, you will be in a position to use the otherwise
1476 dangerous Encode::_utf8_on() function. Let's say the popular
1477 C<Foo::Bar> extension, written in C, provides a C<param> method that
1478 lets you store and retrieve data according to these prototypes:
1480 $self->param($name, $value); # set a scalar
1481 $value = $self->param($name); # retrieve a scalar
1483 If it does not yet provide support for any encoding, one could write a
1484 derived class with such a C<param> method:
1487 my($self,$name,$value) = @_;
1488 utf8::upgrade($name); # make sure it is UTF-8 encoded
1490 utf8::upgrade($value); # make sure it is UTF-8 encoded
1491 return $self->SUPER::param($name,$value);
1493 my $ret = $self->SUPER::param($name);
1494 Encode::_utf8_on($ret); # we know, it is UTF-8 encoded
1499 Some extensions provide filters on data entry/exit points, such as
1500 DB_File::filter_store_key and family. Look out for such filters in
1501 the documentation of your extensions, they can make the transition to
1502 Unicode data much easier.
1506 Some functions are slower when working on UTF-8 encoded strings than
1507 on byte encoded strings. All functions that need to hop over
1508 characters such as length(), substr() or index(), or matching regular
1509 expressions can work B<much> faster when the underlying data are
1512 In Perl 5.8.0 the slowness was often quite spectacular; in Perl 5.8.1
1513 a caching scheme was introduced which will hopefully make the slowness
1514 somewhat less spectacular, at least for some operations. In general,
1515 operations with UTF-8 encoded strings are still slower. As an example,
1516 the Unicode properties (character classes) like C<\p{Nd}> are known to
1517 be quite a bit slower (5-20 times) than their simpler counterparts
1518 like C<\d> (then again, there 268 Unicode characters matching C<Nd>
1519 compared with the 10 ASCII characters matching C<d>).
1521 =head2 Porting code from perl-5.6.X
1523 Perl 5.8 has a different Unicode model from 5.6. In 5.6 the programmer
1524 was required to use the C<utf8> pragma to declare that a given scope
1525 expected to deal with Unicode data and had to make sure that only
1526 Unicode data were reaching that scope. If you have code that is
1527 working with 5.6, you will need some of the following adjustments to
1528 your code. The examples are written such that the code will continue
1529 to work under 5.6, so you should be safe to try them out.
1535 A filehandle that should read or write UTF-8
1538 binmode $fh, ":utf8";
1543 A scalar that is going to be passed to some extension
1545 Be it Compress::Zlib, Apache::Request or any extension that has no
1546 mention of Unicode in the manpage, you need to make sure that the
1547 UTF-8 flag is stripped off. Note that at the time of this writing
1548 (October 2002) the mentioned modules are not UTF-8-aware. Please
1549 check the documentation to verify if this is still true.
1553 $val = Encode::encode_utf8($val); # make octets
1558 A scalar we got back from an extension
1560 If you believe the scalar comes back as UTF-8, you will most likely
1561 want the UTF-8 flag restored:
1565 $val = Encode::decode_utf8($val);
1570 Same thing, if you are really sure it is UTF-8
1574 Encode::_utf8_on($val);
1579 A wrapper for fetchrow_array and fetchrow_hashref
1581 When the database contains only UTF-8, a wrapper function or method is
1582 a convenient way to replace all your fetchrow_array and
1583 fetchrow_hashref calls. A wrapper function will also make it easier to
1584 adapt to future enhancements in your database driver. Note that at the
1585 time of this writing (October 2002), the DBI has no standardized way
1586 to deal with UTF-8 data. Please check the documentation to verify if
1590 my($self, $sth, $what) = @_; # $what is one of fetchrow_{array,hashref}
1596 my @arr = $sth->$what;
1598 defined && /[^\000-\177]/ && Encode::_utf8_on($_);
1602 my $ret = $sth->$what;
1604 for my $k (keys %$ret) {
1605 defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret->{$k};
1609 defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret;
1619 A large scalar that you know can only contain ASCII
1621 Scalars that contain only ASCII and are marked as UTF-8 are sometimes
1622 a drag to your program. If you recognize such a situation, just remove
1625 utf8::downgrade($val) if $] > 5.007;
1631 L<perluniintro>, L<encoding>, L<Encode>, L<open>, L<utf8>, L<bytes>,
1632 L<perlretut>, L<perlvar/"${^UNICODE}">