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 Disciplines
17 A filehandle can be marked as containing perl's internal Unicode
18 encoding (UTF-8 or UTF-EBCDIC) by opening it with the ":utf8" layer.
19 Other encodings can be converted to perl's encoding on input, or from
20 perl's encoding on output by use of the ":encoding(...)" layer.
23 To mark the Perl source itself as being in 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 switch to the Unicode
30 character scheme when presented with Unicode data, or a traditional
31 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, this pragma must be explicitly used to
36 enable recognition of UTF-8 in the Perl scripts themselves on ASCII
37 based machines, or to recognize UTF-EBCDIC on EBCDIC based machines.
38 B<NOTE: this should be the only place where an explicit C<use utf8>
41 You can also use the C<encoding> pragma to change the default encoding
42 of the data in your script; see L<encoding>.
46 =head2 Byte and Character semantics
48 Beginning with version 5.6, Perl uses logically wide characters to
49 represent strings internally.
51 In future, Perl-level operations can be expected to work with
52 characters rather than bytes, in general.
54 However, as strictly an interim compatibility measure, Perl aims to
55 provide a safe migration path from byte semantics to character
56 semantics for programs. For operations where Perl can unambiguously
57 decide that the input data is characters, Perl now switches to
58 character semantics. For operations where this determination cannot
59 be made without additional information from the user, Perl decides in
60 favor of compatibility, and chooses to use byte semantics.
62 This behavior preserves compatibility with earlier versions of Perl,
63 which allowed byte semantics in Perl operations, but only as long as
64 none of the program's inputs are marked as being as source of Unicode
65 character data. Such data may come from filehandles, from calls to
66 external programs, from information provided by the system (such as %ENV),
67 or from literals and constants in the source text.
69 On Windows platforms, if the C<-C> command line switch is used, (or the
70 ${^WIDE_SYSTEM_CALLS} global flag is set to C<1>), all system calls
71 will use the corresponding wide character APIs. Note that this is
72 currently only implemented on Windows since other platforms lack an
73 API standard on this area.
75 Regardless of the above, the C<bytes> pragma can always be used to
76 force byte semantics in a particular lexical scope. See L<bytes>.
78 The C<utf8> pragma is primarily a compatibility device that enables
79 recognition of UTF-(8|EBCDIC) in literals encountered by the parser.
80 Note that this pragma is only required until a future version of Perl
81 in which character semantics will become the default. This pragma may
82 then become a no-op. See L<utf8>.
84 Unless mentioned otherwise, Perl operators will use character semantics
85 when they are dealing with Unicode data, and byte semantics otherwise.
86 Thus, character semantics for these operations apply transparently; if
87 the input data came from a Unicode source (for example, by adding a
88 character encoding discipline to the filehandle whence it came, or a
89 literal Unicode string constant in the program), character semantics
90 apply; otherwise, byte semantics are in effect. To force byte semantics
91 on Unicode data, the C<bytes> pragma should be used.
93 Notice that if you concatenate strings with byte semantics and strings
94 with Unicode character data, the bytes will by default be upgraded
95 I<as if they were ISO 8859-1 (Latin-1)> (or if in EBCDIC, after a
96 translation to ISO 8859-1). This is done without regard to the
97 system's native 8-bit encoding, so to change this for systems with
98 non-Latin-1 (or non-EBCDIC) native encodings, use the C<encoding>
99 pragma, see L<encoding>.
101 Under character semantics, many operations that formerly operated on
102 bytes change to operating on characters. A character in Perl is
103 logically just a number ranging from 0 to 2**31 or so. Larger
104 characters may encode to longer sequences of bytes internally, but
105 this is just an internal detail which is hidden at the Perl level.
106 See L<perluniintro> for more on this.
108 =head2 Effects of character semantics
110 Character semantics have the following effects:
116 Strings (including hash keys) and regular expression patterns may
117 contain characters that have an ordinal value larger than 255.
119 If you use a Unicode editor to edit your program, Unicode characters
120 may occur directly within the literal strings in one of the various
121 Unicode encodings (UTF-8, UTF-EBCDIC, UCS-2, etc.), but are recognized
122 as such (and converted to Perl's internal representation) only if the
123 appropriate L<encoding> is specified.
125 You can also get Unicode characters into a string by using the C<\x{...}>
126 notation, putting the Unicode code for the desired character, in
127 hexadecimal, into the curlies. For instance, a smiley face is C<\x{263A}>.
128 This works only for characters with a code 0x100 and above.
132 use charnames ':full';
134 you can use the C<\N{...}> notation, putting the official Unicode character
135 name within the curlies. For example, C<\N{WHITE SMILING FACE}>.
136 This works for all characters that have names.
140 If Unicode is used in hash keys, there is a subtle effect on the hashes.
141 The hash becomes "Unicode-sticky" so that keys retrieved from the hash
142 (either by %hash, each %hash, or keys %hash) will be in Unicode, not
143 in bytes, even when the keys were bytes went they "went in". This
144 "stickiness" persists unless the hash is completely emptied, either by
145 using delete() or clearing the with undef() or assigning an empty list
146 to the hash. Most of the time this difference is negligible, but
147 there are few places where it matters: for example the regular
148 expression character classes like C<\w> behave differently for
149 bytes and characters.
153 If an appropriate L<encoding> is specified, identifiers within the
154 Perl script may contain Unicode alphanumeric characters, including
155 ideographs. (You are currently on your own when it comes to using the
156 canonical forms of characters--Perl doesn't (yet) attempt to
157 canonicalize variable names for you.)
161 Regular expressions match characters instead of bytes. For instance,
162 "." matches a character instead of a byte. (However, the C<\C> pattern
163 is provided to force a match a single byte ("C<char>" in C, hence C<\C>).)
167 Character classes in regular expressions match characters instead of
168 bytes, and match against the character properties specified in the
169 Unicode properties database. So C<\w> can be used to match an
170 ideograph, for instance.
174 Named Unicode properties, scripts, and block ranges may be used like
175 character classes via the new C<\p{}> (matches property) and C<\P{}>
176 (doesn't match property) constructs. For instance, C<\p{Lu}> matches any
177 character with the Unicode "Lu" (Letter, uppercase) property, while
178 C<\p{M}> matches any character with a "M" (mark -- accents and such)
179 property. Single letter properties may omit the brackets, so that can be
180 written C<\pM> also. Many predefined properties are available, such
181 as C<\p{Mirrored}> and C<\p{Tibetan}>.
183 The official Unicode script and block names have spaces and dashes as
184 separators, but for convenience you can have dashes, spaces, and underbars
185 at every word division, and you need not care about correct casing. It is
186 recommended, however, that for consistency you use the following naming:
187 the official Unicode script, block, or property name (see below for the
188 additional rules that apply to block names), with whitespace and dashes
189 removed, and the words "uppercase-first-lowercase-rest". That is, "Latin-1
190 Supplement" becomes "Latin1Supplement".
192 You can also negate both C<\p{}> and C<\P{}> by introducing a caret
193 (^) between the first curly and the property name: C<\p{^Tamil}> is
194 equal to C<\P{Tamil}>.
196 Here are the basic Unicode General Category properties, followed by their
197 long form (you can use either, e.g. C<\p{Lu}> and C<\p{LowercaseLetter}>
220 Pc ConnectorPunctuation
224 Pi InitialPunctuation
225 (may behave like Ps or Pe depending on usage)
227 (may behave like Ps or Pe depending on usage)
239 Zp ParagraphSeparator
244 Cs Surrogate (not usable)
248 The single-letter properties match all characters in any of the
249 two-letter sub-properties starting with the same letter.
250 There's also C<L&> which is an alias for C<Ll>, C<Lu>, and C<Lt>.
252 Because Perl hides the need for the user to understand the internal
253 representation of Unicode characters, it has no need to support the
254 somewhat messy concept of surrogates. Therefore, the C<Cs> property is not
257 Because scripts differ in their directionality (for example Hebrew is
258 written right to left), Unicode supplies these properties:
263 BidiLRE Left-to-Right Embedding
264 BidiLRO Left-to-Right Override
266 BidiAL Right-to-Left Arabic
267 BidiRLE Right-to-Left Embedding
268 BidiRLO Right-to-Left Override
269 BidiPDF Pop Directional Format
270 BidiEN European Number
271 BidiES European Number Separator
272 BidiET European Number Terminator
274 BidiCS Common Number Separator
275 BidiNSM Non-Spacing Mark
276 BidiBN Boundary Neutral
277 BidiB Paragraph Separator
278 BidiS Segment Separator
280 BidiON Other Neutrals
282 For example, C<\p{BidiR}> matches all characters that are normally
283 written right to left.
289 The scripts available via C<\p{...}> and C<\P{...}>, for example
290 C<\p{Latin}> or \p{Cyrillic>, are as follows:
337 There are also extended property classes that supplement the basic
338 properties, defined by the F<PropList> Unicode database:
353 LogicalOrderException
354 NoncharacterCodePoint
356 OtherDefaultIgnorableCodePoint
368 and further derived properties:
370 Alphabetic Lu + Ll + Lt + Lm + Lo + OtherAlphabetic
371 Lowercase Ll + OtherLowercase
372 Uppercase Lu + OtherUppercase
375 ID_Start Lu + Ll + Lt + Lm + Lo + Nl
376 ID_Continue ID_Start + Mn + Mc + Nd + Pc
379 Assigned Any non-Cn character (i.e. synonym for C<\P{Cn}>)
380 Unassigned Synonym for C<\p{Cn}>
381 Common Any character (or unassigned code point)
382 not explicitly assigned to a script
384 For backward compatability, all properties mentioned so far may have C<Is>
385 prepended to their name (e.g. C<\P{IsLu}> is equal to C<\P{Lu}>).
389 In addition to B<scripts>, Unicode also defines B<blocks> of characters.
390 The difference between scripts and blocks is that the scripts concept is
391 closer to natural languages, while the blocks concept is more an artificial
392 grouping based on groups of mostly 256 Unicode characters. For example, the
393 C<Latin> script contains letters from many blocks. On the other hand, the
394 C<Latin> script does not contain all the characters from those blocks. It
395 does not, for example, contain digits because digits are shared across many
396 scripts. Digits and other similar groups, like punctuation, are in a
397 category called C<Common>.
399 For more about scripts, see the UTR #24:
401 http://www.unicode.org/unicode/reports/tr24/
403 For more about blocks, see:
405 http://www.unicode.org/Public/UNIDATA/Blocks.txt
407 Blocks names are given with the C<In> prefix. For example, the
408 Katakana block is referenced via C<\p{InKatakana}>. The C<In>
409 prefix may be omitted if there is no nameing conflict with a script
410 or any other property, but it is recommended that C<In> always be used
413 These block names are supported:
415 InAlphabeticPresentationForms
417 InArabicPresentationFormsA
418 InArabicPresentationFormsB
429 InByzantineMusicalSymbols
431 InCJKCompatibilityForms
432 InCJKCompatibilityIdeographs
433 InCJKCompatibilityIdeographsSupplement
434 InCJKRadicalsSupplement
435 InCJKSymbolsAndPunctuation
436 InCJKUnifiedIdeographs
437 InCJKUnifiedIdeographsExtensionA
438 InCJKUnifiedIdeographsExtensionB
440 InCombiningDiacriticalMarks
441 InCombiningDiacriticalMarksforSymbols
446 InCyrillicSupplementary
450 InEnclosedAlphanumerics
451 InEnclosedCJKLettersAndMonths
461 InHalfwidthAndFullwidthForms
462 InHangulCompatibilityJamo
467 InHighPrivateUseSurrogates
471 InIdeographicDescriptionCharacters
476 InKatakanaPhoneticExtensions
481 InLatinExtendedAdditional
486 InMathematicalAlphanumericSymbols
487 InMathematicalOperators
488 InMiscellaneousMathematicalSymbolsA
489 InMiscellaneousMathematicalSymbolsB
490 InMiscellaneousSymbols
491 InMiscellaneousTechnical
498 InOpticalCharacterRecognition
504 InSpacingModifierLetters
506 InSuperscriptsAndSubscripts
507 InSupplementalArrowsA
508 InSupplementalArrowsB
509 InSupplementalMathematicalOperators
510 InSupplementaryPrivateUseAreaA
511 InSupplementaryPrivateUseAreaB
521 InUnifiedCanadianAboriginalSyllabics
530 The special pattern C<\X> matches any extended Unicode sequence
531 (a "combining character sequence" in Standardese), where the first
532 character is a base character and subsequent characters are mark
533 characters that apply to the base character. It is equivalent to
538 The C<tr///> operator translates characters instead of bytes. Note
539 that the C<tr///CU> functionality has been removed, as the interface
540 was a mistake. For similar functionality see pack('U0', ...) and
545 Case translation operators use the Unicode case translation tables
546 when provided character input. Note that C<uc()> (also known as C<\U>
547 in doublequoted strings) translates to uppercase, while C<ucfirst>
548 (also known as C<\u> in doublequoted strings) translates to titlecase
549 (for languages that make the distinction). Naturally the
550 corresponding backslash sequences have the same semantics.
554 Most operators that deal with positions or lengths in the string will
555 automatically switch to using character positions, including
556 C<chop()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>,
557 C<sprintf()>, C<write()>, and C<length()>. Operators that
558 specifically don't switch include C<vec()>, C<pack()>, and
559 C<unpack()>. Operators that really don't care include C<chomp()>, as
560 well as any other operator that treats a string as a bucket of bits,
561 such as C<sort()>, and the operators dealing with filenames.
565 The C<pack()>/C<unpack()> letters "C<c>" and "C<C>" do I<not> change,
566 since they're often used for byte-oriented formats. (Again, think
567 "C<char>" in the C language.) However, there is a new "C<U>" specifier
568 that will convert between Unicode characters and integers.
572 The C<chr()> and C<ord()> functions work on characters. This is like
573 C<pack("U")> and C<unpack("U")>, not like C<pack("C")> and
574 C<unpack("C")>. In fact, the latter are how you now emulate
575 byte-oriented C<chr()> and C<ord()> for Unicode strings.
576 (Note that this reveals the internal encoding of Unicode strings,
577 which is not something one normally needs to care about at all.)
581 The bit string operators C<& | ^ ~> can operate on character data.
582 However, for backward compatibility reasons (bit string operations
583 when the characters all are less than 256 in ordinal value) one should
584 not mix C<~> (the bit complement) and characters both less than 256 and
585 equal or greater than 256. Most importantly, the DeMorgan's laws
586 (C<~($x|$y) eq ~$x&~$y>, C<~($x&$y) eq ~$x|~$y>) won't hold.
587 Another way to look at this is that the complement cannot return
588 B<both> the 8-bit (byte) wide bit complement B<and> the full character
593 lc(), uc(), lcfirst(), and ucfirst() work for the following cases:
599 the case mapping is from a single Unicode character to another
600 single Unicode character
604 the case mapping is from a single Unicode character to more
605 than one Unicode character
609 What doesn't yet work are the following cases:
615 the "final sigma" (Greek)
619 anything to with locales (Lithuanian, Turkish, Azeri)
623 See the Unicode Technical Report #21, Case Mappings, for more details.
627 And finally, C<scalar reverse()> reverses by character rather than by byte.
631 =head2 Character encodings for input and output
635 =head2 Unicode Regular Expression Support Level
637 The following list of Unicode regular expression support describes
638 feature by feature the Unicode support implemented in Perl as of Perl
639 5.8.0. The "Level N" and the section numbers refer to the Unicode
640 Technical Report 18, "Unicode Regular Expression Guidelines".
646 Level 1 - Basic Unicode Support
648 2.1 Hex Notation - done [1]
649 Named Notation - done [2]
650 2.2 Categories - done [3][4]
651 2.3 Subtraction - MISSING [5][6]
652 2.4 Simple Word Boundaries - done [7]
653 2.5 Simple Loose Matches - done [8]
654 2.6 End of Line - MISSING [9][10]
658 [ 3] . \p{...} \P{...}
659 [ 4] now scripts (see UTR#24 Script Names) in addition to blocks
661 [ 6] can use look-ahead to emulate subtraction (*)
662 [ 7] include Letters in word characters
663 [ 8] note that perl does Full casefolding in matching, not Simple:
664 for example U+1F88 is equivalent with U+1F000 U+03B9,
665 not with 1F80. This difference matters for certain Greek
666 capital letters with certain modifiers: the Full casefolding
667 decomposes the letter, while the Simple casefolding would map
668 it to a single character.
669 [ 9] see UTR#13 Unicode Newline Guidelines
670 [10] should do ^ and $ also on \x{85}, \x{2028} and \x{2029})
671 (should also affect <>, $., and script line numbers)
672 (the \x{85}, \x{2028} and \x{2029} do match \s)
674 (*) You can mimic class subtraction using lookahead.
675 For example, what TR18 might write as
677 [{Greek}-[{UNASSIGNED}]]
679 in Perl can be written as:
681 (?!\p{Unassigned})\p{InGreekAndCoptic}
682 (?=\p{Assigned})\p{InGreekAndCoptic}
684 But in this particular example, you probably really want
688 which will match assigned characters known to be part of the Greek script.
692 Level 2 - Extended Unicode Support
694 3.1 Surrogates - MISSING
695 3.2 Canonical Equivalents - MISSING [11][12]
696 3.3 Locale-Independent Graphemes - MISSING [13]
697 3.4 Locale-Independent Words - MISSING [14]
698 3.5 Locale-Independent Loose Matches - MISSING [15]
700 [11] see UTR#15 Unicode Normalization
701 [12] have Unicode::Normalize but not integrated to regexes
702 [13] have \X but at this level . should equal that
703 [14] need three classes, not just \w and \W
704 [15] see UTR#21 Case Mappings
708 Level 3 - Locale-Sensitive Support
710 4.1 Locale-Dependent Categories - MISSING
711 4.2 Locale-Dependent Graphemes - MISSING [16][17]
712 4.3 Locale-Dependent Words - MISSING
713 4.4 Locale-Dependent Loose Matches - MISSING
714 4.5 Locale-Dependent Ranges - MISSING
716 [16] see UTR#10 Unicode Collation Algorithms
717 [17] have Unicode::Collate but not integrated to regexes
721 =head2 Unicode Encodings
723 Unicode characters are assigned to I<code points> which are abstract
724 numbers. To use these numbers various encodings are needed.
732 UTF-8 is a variable-length (1 to 6 bytes, current character allocations
733 require 4 bytes), byteorder independent encoding. For ASCII, UTF-8 is
734 transparent (and we really do mean 7-bit ASCII, not another 8-bit encoding).
736 The following table is from Unicode 3.2.
738 Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
740 U+0000..U+007F 00..7F
741 U+0080..U+07FF C2..DF 80..BF
742 U+0800..U+0FFF E0 A0..BF 80..BF
743 U+1000..U+CFFF E1..EC 80..BF 80..BF
744 U+D000..U+D7FF ED 80..9F 80..BF
745 U+D800..U+DFFF ******* ill-formed *******
746 U+E000..U+FFFF EE..EF 80..BF 80..BF
747 U+10000..U+3FFFF F0 90..BF 80..BF 80..BF
748 U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF
749 U+100000..U+10FFFF F4 80..8F 80..BF 80..BF
751 Note the A0..BF in U+0800..U+0FFF, the 80..9F in U+D000...U+D7FF,
752 the 90..BF in U+10000..U+3FFFF, and the 80...8F in U+100000..U+10FFFF.
753 Or, another way to look at it, as bits:
755 Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
758 00000bbbbbaaaaaa 110bbbbb 10aaaaaa
759 ccccbbbbbbaaaaaa 1110cccc 10bbbbbb 10aaaaaa
760 00000dddccccccbbbbbbaaaaaa 11110ddd 10cccccc 10bbbbbb 10aaaaaa
762 As you can see, the continuation bytes all begin with C<10>, and the
763 leading bits of the start byte tell how many bytes the are in the
770 Like UTF-8, but EBCDIC-safe, as UTF-8 is ASCII-safe.
774 UTF-16, UTF-16BE, UTF16-LE, Surrogates, and BOMs (Byte Order Marks)
776 (The followings items are mostly for reference, Perl doesn't
777 use them internally.)
779 UTF-16 is a 2 or 4 byte encoding. The Unicode code points
780 0x0000..0xFFFF are stored in two 16-bit units, and the code points
781 0x010000..0x10FFFF in two 16-bit units. The latter case is
782 using I<surrogates>, the first 16-bit unit being the I<high
783 surrogate>, and the second being the I<low surrogate>.
785 Surrogates are code points set aside to encode the 0x01000..0x10FFFF
786 range of Unicode code points in pairs of 16-bit units. The I<high
787 surrogates> are the range 0xD800..0xDBFF, and the I<low surrogates>
788 are the range 0xDC00..0xDFFFF. The surrogate encoding is
790 $hi = ($uni - 0x10000) / 0x400 + 0xD800;
791 $lo = ($uni - 0x10000) % 0x400 + 0xDC00;
795 $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00);
797 If you try to generate surrogates (for example by using chr()), you
798 will get a warning if warnings are turned on (C<-w> or C<use
799 warnings;>) because those code points are not valid for a Unicode
802 Because of the 16-bitness, UTF-16 is byteorder dependent. UTF-16
803 itself can be used for in-memory computations, but if storage or
804 transfer is required, either UTF-16BE (Big Endian) or UTF-16LE
805 (Little Endian) must be chosen.
807 This introduces another problem: what if you just know that your data
808 is UTF-16, but you don't know which endianness? Byte Order Marks
809 (BOMs) are a solution to this. A special character has been reserved
810 in Unicode to function as a byte order marker: the character with the
811 code point 0xFEFF is the BOM.
813 The trick is that if you read a BOM, you will know the byte order,
814 since if it was written on a big endian platform, you will read the
815 bytes 0xFE 0xFF, but if it was written on a little endian platform,
816 you will read the bytes 0xFF 0xFE. (And if the originating platform
817 was writing in UTF-8, you will read the bytes 0xEF 0xBB 0xBF.)
819 The way this trick works is that the character with the code point
820 0xFFFE is guaranteed not to be a valid Unicode character, so the
821 sequence of bytes 0xFF 0xFE is unambiguously "BOM, represented in
822 little-endian format" and cannot be "0xFFFE, represented in big-endian
827 UTF-32, UTF-32BE, UTF32-LE
829 The UTF-32 family is pretty much like the UTF-16 family, expect that
830 the units are 32-bit, and therefore the surrogate scheme is not
831 needed. The BOM signatures will be 0x00 0x00 0xFE 0xFF for BE and
832 0xFF 0xFE 0x00 0x00 for LE.
838 Encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit
839 encoding, UCS-4 is a 32-bit encoding. Unlike UTF-16, UCS-2
840 is not extensible beyond 0xFFFF, because it does not use surrogates.
846 A seven-bit safe (non-eight-bit) encoding, useful if the
847 transport/storage is not eight-bit safe. Defined by RFC 2152.
851 =head2 Security Implications of Malformed UTF-8
853 Unfortunately, the specification of UTF-8 leaves some room for
854 interpretation of how many bytes of encoded output one should generate
855 from one input Unicode character. Strictly speaking, one is supposed
856 to always generate the shortest possible sequence of UTF-8 bytes,
857 because otherwise there is potential for input buffer overflow at
858 the receiving end of a UTF-8 connection. Perl always generates the
859 shortest length UTF-8, and with warnings on (C<-w> or C<use
860 warnings;>) Perl will warn about non-shortest length UTF-8 (and other
861 malformations, too, such as the surrogates, which are not real
862 Unicode code points.)
864 =head2 Unicode in Perl on EBCDIC
866 The way Unicode is handled on EBCDIC platforms is still rather
867 experimental. On such a platform, references to UTF-8 encoding in this
868 document and elsewhere should be read as meaning UTF-EBCDIC as
869 specified in Unicode Technical Report 16 unless ASCII vs EBCDIC issues
870 are specifically discussed. There is no C<utfebcdic> pragma or
871 ":utfebcdic" layer, rather, "utf8" and ":utf8" are re-used to mean
872 the platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic>
873 for more discussion of the issues.
877 Usually locale settings and Unicode do not affect each other, but
878 there are a couple of exceptions:
884 If your locale environment variables (LANGUAGE, LC_ALL, LC_CTYPE, LANG)
885 contain the strings 'UTF-8' or 'UTF8' (case-insensitive matching),
886 the default encoding of your STDIN, STDOUT, and STDERR, and of
887 B<any subsequent file open>, is UTF-8.
891 Perl tries really hard to work both with Unicode and the old byte
892 oriented world: most often this is nice, but sometimes this causes
897 =head2 Using Unicode in XS
899 If you want to handle Perl Unicode in XS extensions, you may find
900 the following C APIs useful (see perlapi for details):
906 DO_UTF8(sv) returns true if the UTF8 flag is on and the bytes pragma
907 is not in effect. SvUTF8(sv) returns true is the UTF8 flag is on, the
908 bytes pragma is ignored. The UTF8 flag being on does B<not> mean that
909 there are any characters of code points greater than 255 (or 127) in
910 the scalar, or that there even are any characters in the scalar.
911 What the UTF8 flag means is that the sequence of octets in the
912 representation of the scalar is the sequence of UTF-8 encoded
913 code points of the characters of a string. The UTF8 flag being
914 off means that each octet in this representation encodes a single
915 character with codepoint 0..255 within the string. Perl's Unicode
916 model is not to use UTF-8 until it's really necessary.
920 uvuni_to_utf8(buf, chr) writes a Unicode character code point into a
921 buffer encoding the code point as UTF-8, and returns a pointer
922 pointing after the UTF-8 bytes.
926 utf8_to_uvuni(buf, lenp) reads UTF-8 encoded bytes from a buffer and
927 returns the Unicode character code point (and optionally the length of
928 the UTF-8 byte sequence).
932 utf8_length(start, end) returns the length of the UTF-8 encoded buffer
933 in characters. sv_len_utf8(sv) returns the length of the UTF-8 encoded
938 sv_utf8_upgrade(sv) converts the string of the scalar to its UTF-8
939 encoded form. sv_utf8_downgrade(sv) does the opposite (if possible).
940 sv_utf8_encode(sv) is like sv_utf8_upgrade but the UTF8 flag does not
941 get turned on. sv_utf8_decode() does the opposite of sv_utf8_encode().
942 Note that none of these are to be used as general purpose encoding/decoding
943 interfaces: use Encode for that. sv_utf8_upgrade() is affected by the
944 encoding pragma, but sv_utf8_downgrade() is not (since the encoding
945 pragma is designed to be a one-way street).
949 is_utf8_char(s) returns true if the pointer points to a valid UTF-8
954 is_utf8_string(buf, len) returns true if the len bytes of the buffer
959 UTF8SKIP(buf) will return the number of bytes in the UTF-8 encoded
960 character in the buffer. UNISKIP(chr) will return the number of bytes
961 required to UTF-8-encode the Unicode character code point. UTF8SKIP()
962 is useful for example for iterating over the characters of a UTF-8
963 encoded buffer; UNISKIP() is useful for example in computing
964 the size required for a UTF-8 encoded buffer.
968 utf8_distance(a, b) will tell the distance in characters between the
969 two pointers pointing to the same UTF-8 encoded buffer.
973 utf8_hop(s, off) will return a pointer to an UTF-8 encoded buffer that
974 is C<off> (positive or negative) Unicode characters displaced from the
975 UTF-8 buffer C<s>. Be careful not to overstep the buffer: utf8_hop()
976 will merrily run off the end or the beginning if told to do so.
980 pv_uni_display(dsv, spv, len, pvlim, flags) and sv_uni_display(dsv,
981 ssv, pvlim, flags) are useful for debug output of Unicode strings and
982 scalars. By default they are useful only for debug: they display
983 B<all> characters as hexadecimal code points, but with the flags
984 UNI_DISPLAY_ISPRINT and UNI_DISPLAY_BACKSLASH you can make the output
989 ibcmp_utf8(s1, pe1, u1, l1, u1, s2, pe2, l2, u2) can be used to
990 compare two strings case-insensitively in Unicode.
991 (For case-sensitive comparisons you can just use memEQ() and memNE()
996 For more information, see L<perlapi>, and F<utf8.c> and F<utf8.h>
997 in the Perl source code distribution.
1001 Use of locales with Unicode data may lead to odd results. Currently
1002 there is some attempt to apply 8-bit locale info to characters in the
1003 range 0..255, but this is demonstrably incorrect for locales that use
1004 characters above that range when mapped into Unicode. It will also
1005 tend to run slower. Use of locales with Unicode is discouraged.
1007 Some functions are slower when working on UTF-8 encoded strings than
1008 on byte encoded strings. All functions that need to hop over
1009 characters such as length(), substr() or index() can work B<much>
1010 faster when the underlying data are byte-encoded. Witness the
1011 following benchmark:
1017 our $u = our $b = "x" x $l;
1018 substr($u,0,1) = "\x{100}";
1020 LENGTH_B => q{ length($b) },
1021 LENGTH_U => q{ length($u) },
1022 SUBSTR_B => q{ substr($b, $l/4, $l/2) },
1023 SUBSTR_U => q{ substr($u, $l/4, $l/2) },
1026 Benchmark: running LENGTH_B, LENGTH_U, SUBSTR_B, SUBSTR_U for at least 2 CPU seconds...
1027 LENGTH_B: 2 wallclock secs ( 2.36 usr + 0.00 sys = 2.36 CPU) @ 5649983.05/s (n=13333960)
1028 LENGTH_U: 2 wallclock secs ( 2.11 usr + 0.00 sys = 2.11 CPU) @ 12155.45/s (n=25648)
1029 SUBSTR_B: 3 wallclock secs ( 2.16 usr + 0.00 sys = 2.16 CPU) @ 374480.09/s (n=808877)
1030 SUBSTR_U: 2 wallclock secs ( 2.11 usr + 0.00 sys = 2.11 CPU) @ 6791.00/s (n=14329)
1032 The numbers show an incredible slowness on long UTF-8 strings and you
1033 should carefully avoid to use these functions within tight loops. For
1034 example if you want to iterate over characters, it is infinitely
1035 better to split into an array than to use substr, as the following
1042 our $u = our $b = "x" x $l;
1043 substr($u,0,1) = "\x{100}";
1045 SPLIT_B => q{ for my $c (split //, $b){} },
1046 SPLIT_U => q{ for my $c (split //, $u){} },
1047 SUBSTR_B => q{ for my $i (0..length($b)-1){my $c = substr($b,$i,1);} },
1048 SUBSTR_U => q{ for my $i (0..length($u)-1){my $c = substr($u,$i,1);} },
1051 Benchmark: running SPLIT_B, SPLIT_U, SUBSTR_B, SUBSTR_U for at least 5 CPU seconds...
1052 SPLIT_B: 6 wallclock secs ( 5.29 usr + 0.00 sys = 5.29 CPU) @ 56.14/s (n=297)
1053 SPLIT_U: 5 wallclock secs ( 5.17 usr + 0.01 sys = 5.18 CPU) @ 55.21/s (n=286)
1054 SUBSTR_B: 5 wallclock secs ( 5.34 usr + 0.00 sys = 5.34 CPU) @ 123.22/s (n=658)
1055 SUBSTR_U: 7 wallclock secs ( 6.20 usr + 0.00 sys = 6.20 CPU) @ 0.81/s (n=5)
1057 You see, the algorithm based on substr() was faster with byte encoded
1058 data but it is pathologically slow with UTF-8 data.
1062 L<perluniintro>, L<encoding>, L<Encode>, L<open>, L<utf8>, L<bytes>,
1063 L<perlretut>, L<perlvar/"${^WIDE_SYSTEM_CALLS}">