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 The C<utf8> pragma implements the tables used for Unicode support.
36 However, these tables are automatically loaded on demand, so the
37 C<utf8> pragma should not normally be used.
39 As a compatibility measure, this pragma must be explicitly used to
40 enable recognition of UTF-8 in the Perl scripts themselves on ASCII
41 based machines or recognize UTF-EBCDIC on EBCDIC based machines.
42 B<NOTE: this should be the only place where an explicit C<use utf8>
45 You can also use the C<encoding> pragma to change the default encoding
46 of the data in your script; see L<encoding>.
50 =head2 Byte and Character semantics
52 Beginning with version 5.6, Perl uses logically wide characters to
53 represent strings internally. This internal representation of strings
54 uses either the UTF-8 or the UTF-EBCDIC encoding.
56 In future, Perl-level operations can be expected to work with
57 characters rather than bytes, in general.
59 However, as strictly an interim compatibility measure, Perl aims to
60 provide a safe migration path from byte semantics to character
61 semantics for programs. For operations where Perl can unambiguously
62 decide that the input data is characters, Perl now switches to
63 character semantics. For operations where this determination cannot
64 be made without additional information from the user, Perl decides in
65 favor of compatibility, and chooses to use byte semantics.
67 This behavior preserves compatibility with earlier versions of Perl,
68 which allowed byte semantics in Perl operations, but only as long as
69 none of the program's inputs are marked as being as source of Unicode
70 character data. Such data may come from filehandles, from calls to
71 external programs, from information provided by the system (such as %ENV),
72 or from literals and constants in the source text.
74 On Windows platforms, if the C<-C> command line switch is used, (or the
75 ${^WIDE_SYSTEM_CALLS} global flag is set to C<1>), all system calls
76 will use the corresponding wide character APIs. Note that this is
77 currently only implemented on Windows since other platforms lack an
78 API standard on this area.
80 Regardless of the above, the C<bytes> pragma can always be used to
81 force byte semantics in a particular lexical scope. See L<bytes>.
83 The C<utf8> pragma is primarily a compatibility device that enables
84 recognition of UTF-(8|EBCDIC) in literals encountered by the parser.
85 Note that this pragma is only required until a future version of Perl
86 in which character semantics will become the default. This pragma may
87 then become a no-op. See L<utf8>.
89 Unless mentioned otherwise, Perl operators will use character semantics
90 when they are dealing with Unicode data, and byte semantics otherwise.
91 Thus, character semantics for these operations apply transparently; if
92 the input data came from a Unicode source (for example, by adding a
93 character encoding discipline to the filehandle whence it came, or a
94 literal UTF-8 string constant in the program), character semantics
95 apply; otherwise, byte semantics are in effect. To force byte semantics
96 on Unicode data, the C<bytes> pragma should be used.
98 Notice that if you concatenate strings with byte semantics and strings
99 with Unicode character data, the bytes will by default be upgraded
100 I<as if they were ISO 8859-1 (Latin-1)> (or if in EBCDIC, after a
101 translation to ISO 8859-1). To change this, use the C<encoding>
102 pragma, see L<encoding>.
104 Under character semantics, many operations that formerly operated on
105 bytes change to operating on characters. For ASCII data this makes no
106 difference, because UTF-8 stores ASCII in single bytes, but for any
107 character greater than C<chr(127)>, the character B<may> be stored in
108 a sequence of two or more bytes, all of which have the high bit set.
110 For C1 controls or Latin 1 characters on an EBCDIC platform the
111 character may be stored in a UTF-EBCDIC multi byte sequence. But by
112 and large, the user need not worry about this, because Perl hides it
113 from the user. A character in Perl is logically just a number ranging
114 from 0 to 2**32 or so. Larger characters encode to longer sequences
115 of bytes internally, but again, this is just an internal detail which
116 is hidden at the Perl level.
118 =head2 Effects of character semantics
120 Character semantics have the following effects:
126 Strings and patterns may contain characters that have an ordinal value
129 Presuming you use a Unicode editor to edit your program, such
130 characters will typically occur directly within the literal strings as
131 UTF-8 (or UTF-EBCDIC on EBCDIC platforms) characters, but you can also
132 specify a particular character with an extension of the C<\x>
133 notation. UTF-X characters are specified by putting the hexadecimal
134 code within curlies after the C<\x>. For instance, a Unicode smiley
139 Identifiers within the Perl script may contain Unicode alphanumeric
140 characters, including ideographs. (You are currently on your own when
141 it comes to using the canonical forms of characters--Perl doesn't
142 (yet) attempt to canonicalize variable names for you.)
146 Regular expressions match characters instead of bytes. For instance,
147 "." matches a character instead of a byte. (However, the C<\C> pattern
148 is provided to force a match a single byte ("C<char>" in C, hence C<\C>).)
152 Character classes in regular expressions match characters instead of
153 bytes, and match against the character properties specified in the
154 Unicode properties database. So C<\w> can be used to match an
155 ideograph, for instance.
159 Named Unicode properties and block ranges make be used as character
160 classes via the new C<\p{}> (matches property) and C<\P{}> (doesn't
161 match property) constructs. For instance, C<\p{Lu}> matches any
162 character with the Unicode uppercase property, while C<\p{M}> matches
163 any mark character. Single letter properties may omit the brackets,
164 so that can be written C<\pM> also. Many predefined character classes
165 are available, such as C<\p{IsMirrored}> and C<\p{InTibetan}>.
167 The C<\p{Is...}> test for "general properties" such as "letter",
168 "digit", while the C<\p{In...}> test for Unicode scripts and blocks.
170 The official Unicode script and block names have spaces and dashes and
171 separators, but for convenience you can have dashes, spaces, and
172 underbars at every word division, and you need not care about correct
173 casing. It is recommended, however, that for consistency you use the
174 following naming: the official Unicode script, block, or property name
175 (see below for the additional rules that apply to block names),
176 with whitespace and dashes replaced with underbar, and the words
177 "uppercase-first-lowercase-rest". That is, "Latin-1 Supplement"
178 becomes "Latin_1_Supplement".
180 You can also negate both C<\p{}> and C<\P{}> by introducing a caret
181 (^) between the first curly and the property name: C<\p{^In_Tamil}> is
182 equal to C<\P{In_Tamil}>.
184 The C<In> and C<Is> can be left out: C<\p{Greek}> is equal to
185 C<\p{In_Greek}>, C<\P{Pd}> is equal to C<\P{Pd}>.
207 Pc Connector_Punctuation
211 Pi Initial_Punctuation
212 (may behave like Ps or Pe depending on usage)
214 (may behave like Ps or Pe depending on usage)
226 Zp Paragraph_Separator
235 There's also C<L&> which is an alias for C<Ll>, C<Lu>, and C<Lt>.
237 The following reserved ranges have C<In> tests:
239 CJK_Ideograph_Extension_A
242 Non_Private_Use_High_Surrogate
243 Private_Use_High_Surrogate
246 CJK_Ideograph_Extension_B
250 For example C<"\x{AC00}" =~ \p{HangulSyllable}> will test true.
251 (Handling of surrogates is not implemented yet, because Perl
252 uses UTF-8 and not UTF-16 internally to represent Unicode.)
254 Additionally, because scripts differ in their directionality
255 (for example Hebrew is written right to left), all characters
256 have their directionality defined:
259 BidiLRE Left-to-Right Embedding
260 BidiLRO Left-to-Right Override
262 BidiAL Right-to-Left Arabic
263 BidiRLE Right-to-Left Embedding
264 BidiRLO Right-to-Left Override
265 BidiPDF Pop Directional Format
266 BidiEN European Number
267 BidiES European Number Separator
268 BidiET European Number Terminator
270 BidiCS Common Number Separator
271 BidiNSM Non-Spacing Mark
272 BidiBN Boundary Neutral
273 BidiB Paragraph Separator
274 BidiS Segment Separator
276 BidiON Other Neutrals
280 The scripts available for C<\p{In...}> and C<\P{In...}>, for example
281 \p{InCyrillic>, are as follows, for example C<\p{InLatin}> or C<\P{InHan}>:
324 There are also extended property classes that supplement the basic
325 properties, defined by the F<PropList> Unicode database:
336 Noncharacter_Code_Point
344 and further derived properties:
346 Alphabetic Lu + Ll + Lt + Lm + Lo + Other_Alphabetic
347 Lowercase Ll + Other_Lowercase
348 Uppercase Lu + Other_Uppercase
351 ID_Start Lu + Ll + Lt + Lm + Lo + Nl
352 ID_Continue ID_Start + Mn + Mc + Nd + Pc
355 Assigned Any non-Cn character
356 Common Any character (or unassigned code point)
357 not explicitly assigned to a script
361 In addition to B<scripts>, Unicode also defines B<blocks> of
362 characters. The difference between scripts and blocks is that the
363 scripts concept is closer to natural languages, while the blocks
364 concept is more an artificial grouping based on groups of 256 Unicode
365 characters. For example, the C<Latin> script contains letters from
366 many blocks. On the other hand, the C<Latin> script does not contain
367 all the characters from those blocks, it does not for example contain
368 digits because digits are shared across many scripts. Digits and
369 other similar groups, like punctuation, are in a category called
372 For more about scripts see the UTR #24:
373 http://www.unicode.org/unicode/reports/tr24/
374 For more about blocks see
375 http://www.unicode.org/Public/UNIDATA/Blocks.txt
377 Because there are overlaps in naming (there are, for example, both
378 a script called C<Katakana> and a block called C<Katakana>, the block
379 version has C<Block> appended to its name, C<\p{InKatakanaBlock}>.
381 Notice that this definition was introduced in Perl 5.8.0: in Perl
382 5.6 only the blocks were used; in Perl 5.8.0 scripts became the
383 preferential Unicode character class definition; this meant that
384 the definitions of some character classes changed (the ones in the
385 below list that have the C<Block> appended).
387 Alphabetic Presentation Forms
389 Arabic Presentation Forms-A
390 Arabic Presentation Forms-B
400 Byzantine Musical Symbols
402 CJK Compatibility Forms
403 CJK Compatibility Ideographs
404 CJK Compatibility Ideographs Supplement
405 CJK Radicals Supplement
406 CJK Symbols and Punctuation
407 CJK Unified Ideographs
408 CJK Unified Ideographs Extension A
409 CJK Unified Ideographs Extension B
411 Combining Diacritical Marks
413 Combining Marks for Symbols
420 Enclosed Alphanumerics
421 Enclosed CJK Letters and Months
431 Halfwidth and Fullwidth Forms
432 Hangul Compatibility Jamo
436 High Private Use Surrogates
440 Ideographic Description Characters
448 Latin Extended Additional
454 Mathematical Alphanumeric Symbols
455 Mathematical Operators
456 Miscellaneous Symbols
457 Miscellaneous Technical
464 Optical Character Recognition
470 Spacing Modifier Letters
472 Superscripts and Subscripts
480 Unified Canadian Aboriginal Syllabics
486 The special pattern C<\X> match matches any extended Unicode sequence
487 (a "combining character sequence" in Standardese), where the first
488 character is a base character and subsequent characters are mark
489 characters that apply to the base character. It is equivalent to
494 The C<tr///> operator translates characters instead of bytes. Note
495 that the C<tr///CU> functionality has been removed, as the interface
496 was a mistake. For similar functionality see pack('U0', ...) and
501 Case translation operators use the Unicode case translation tables
502 when provided character input. Note that C<uc()> (also known as C<\U>
503 in doublequoted strings) translates to uppercase, while C<ucfirst>
504 (also known as C<\u> in doublequoted strings) translates to titlecase
505 (for languages that make the distinction). Naturally the
506 corresponding backslash sequences have the same semantics.
510 Most operators that deal with positions or lengths in the string will
511 automatically switch to using character positions, including
512 C<chop()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>,
513 C<sprintf()>, C<write()>, and C<length()>. Operators that
514 specifically don't switch include C<vec()>, C<pack()>, and
515 C<unpack()>. Operators that really don't care include C<chomp()>, as
516 well as any other operator that treats a string as a bucket of bits,
517 such as C<sort()>, and the operators dealing with filenames.
521 The C<pack()>/C<unpack()> letters "C<c>" and "C<C>" do I<not> change,
522 since they're often used for byte-oriented formats. (Again, think
523 "C<char>" in the C language.) However, there is a new "C<U>" specifier
524 that will convert between UTF-8 characters and integers. (It works
525 outside of the utf8 pragma too.)
529 The C<chr()> and C<ord()> functions work on characters. This is like
530 C<pack("U")> and C<unpack("U")>, not like C<pack("C")> and
531 C<unpack("C")>. In fact, the latter are how you now emulate
532 byte-oriented C<chr()> and C<ord()> for Unicode strings.
533 (Note that this reveals the internal UTF-8 encoding of strings and
534 you are not supposed to do that unless you know what you are doing.)
538 The bit string operators C<& | ^ ~> can operate on character data.
539 However, for backward compatibility reasons (bit string operations
540 when the characters all are less than 256 in ordinal value) one should
541 not mix C<~> (the bit complement) and characters both less than 256 and
542 equal or greater than 256. Most importantly, the DeMorgan's laws
543 (C<~($x|$y) eq ~$x&~$y>, C<~($x&$y) eq ~$x|~$y>) won't hold.
544 Another way to look at this is that the complement cannot return
545 B<both> the 8-bit (byte) wide bit complement B<and> the full character
550 lc(), uc(), lcfirst(), and ucfirst() work for the following cases:
556 the case mapping is from a single Unicode character to another
557 single Unicode character
561 the case mapping is from a single Unicode character to more
562 than one Unicode character
566 What doesn't yet work are the followng cases:
572 the "final sigma" (Greek)
576 anything to with locales (Lithuanian, Turkish, Azeri)
580 See the Unicode Technical Report #21, Case Mappings, for more details.
584 And finally, C<scalar reverse()> reverses by character rather than by byte.
588 =head2 Character encodings for input and output
594 As of yet, there is no method for automatically coercing input and
595 output to some encoding other than UTF-8 or UTF-EBCDIC. This is planned
596 in the near future, however.
598 Whether an arbitrary piece of data will be treated as "characters" or
599 "bytes" by internal operations cannot be divined at the current time.
601 Use of locales with utf8 may lead to odd results. Currently there is
602 some attempt to apply 8-bit locale info to characters in the range
603 0..255, but this is demonstrably incorrect for locales that use
604 characters above that range (when mapped into Unicode). It will also
605 tend to run slower. Avoidance of locales is strongly encouraged.
607 =head1 UNICODE REGULAR EXPRESSION SUPPORT LEVEL
609 The following list of Unicode regular expression support describes
610 feature by feature the Unicode support implemented in Perl as of Perl
611 5.8.0. The "Level N" and the section numbers refer to the Unicode
612 Technical Report 18, "Unicode Regular Expression Guidelines".
618 Level 1 - Basic Unicode Support
620 2.1 Hex Notation - done [1]
621 Named Notation - done [2]
622 2.2 Categories - done [3][4]
623 2.3 Subtraction - MISSING [5][6]
624 2.4 Simple Word Boundaries - done [7]
625 2.5 Simple Loose Matches - done [8]
626 2.6 End of Line - MISSING [9][10]
630 [ 3] . \p{Is...} \P{Is...}
631 [ 4] now scripts (see UTR#24 Script Names) in addition to blocks
633 [ 6] can use look-ahead to emulate subtracion
634 [ 7] include Letters in word characters
635 [ 8] see UTR#21 Case Mappings: Perl implements 1:1 mappings
636 [ 9] see UTR#13 Unicode Newline Guidelines
637 [10] should do ^ and $ also on \x{2028} and \x{2029}
641 Level 2 - Extended Unicode Support
643 3.1 Surrogates - MISSING
644 3.2 Canonical Equivalents - MISSING [11][12]
645 3.3 Locale-Independent Graphemes - MISSING [13]
646 3.4 Locale-Independent Words - MISSING [14]
647 3.5 Locale-Independent Loose Matches - MISSING [15]
649 [11] see UTR#15 Unicode Normalization
650 [12] have Unicode::Normalize but not integrated to regexes
651 [13] have \X but at this level . should equal that
652 [14] need three classes, not just \w and \W
653 [15] see UTR#21 Case Mappings
657 Level 3 - Locale-Sensitive Support
659 4.1 Locale-Dependent Categories - MISSING
660 4.2 Locale-Dependent Graphemes - MISSING [16][17]
661 4.3 Locale-Dependent Words - MISSING
662 4.4 Locale-Dependent Loose Matches - MISSING
663 4.5 Locale-Dependent Ranges - MISSING
665 [16] see UTR#10 Unicode Collation Algorithms
666 [17] have Unicode::Collate but not integrated to regexes
670 =head2 Unicode Encodings
672 Unicode characters are assigned to I<code points> which are abstract
673 numbers. To use these numbers various encodings are needed.
679 UTF-8 is the encoding used internally by Perl. UTF-8 is a variable
680 length (1 to 6 bytes, current character allocations require 4 bytes),
681 byteorder independent encoding. For ASCII, UTF-8 is transparent
682 (and we really do mean 7-bit ASCII, not any 8-bit encoding).
684 =item UTF-16, UTF-16BE, UTF16-LE, Surrogates, and BOMs (Byte Order Marks)
686 UTF-16 is a 2 or 4 byte encoding. The Unicode code points
687 0x0000..0xFFFF are stored in two 16-bit units, and the code points
688 0x010000..0x10FFFF in four 16-bit units. The latter case is
689 using I<surrogates>, the first 16-bit unit being the I<high
690 surrogate>, and the second being the I<low surrogate>.
692 Surrogates are code points set aside to encode the 0x01000..0x10FFFF
693 range of Unicode code points in pairs of 16-bit units. The I<high
694 surrogates> are the range 0xD800..0xDBFF, and the I<low surrogates>
695 are the range 0xDC00..0xDFFFF. The surrogate encoding is
697 $hi = ($uni - 0x10000) / 0x400 + 0xD800;
698 $lo = ($uni - 0x10000) % 0x400 + 0xDC00;
702 $uni = 0x10000 + ($hi - 0xD8000) * 0x400 + ($lo - 0xDC00);
704 Because of the 16-bitness, UTF-16 is byteorder dependent. UTF-16
705 itself can be used for in-memory computations, but if storage or
706 transfer is required, either UTF-16BE (Big Endian) or UTF-16LE
707 (Little Endian) must be chosen.
709 This introduces another problem: what if you just know that your data
710 is UTF-16, but you don't know which endianness? Byte Order Marks
711 (BOMs) are a solution to this. A special character has been reserved
712 in Unicode to function as a byte order marker: the character with the
713 code point 0xFEFF is the BOM.
715 The trick is that if you read a BOM, you will know the byte order,
716 since if it was written on a big endian platform, you will read the
717 bytes 0xFE 0xFF, but if it was written on a little endian platform,
718 you will read the bytes 0xFF 0xFE. (And if the originating platform
719 was writing in UTF-8, you will read the bytes 0xEF 0xBB 0xBF.)
721 The way this trick works is that the character with the code point
722 0xFFFE is guaranteed not to be a valid Unicode character, so the
723 sequence of bytes 0xFF 0xFE is unambiguously "BOM, represented in
724 little-endian format" and cannot be "0xFFFE, represented in big-endian
727 =item UTF-32, UTF-32BE, UTF32-LE
729 The UTF-32 family is pretty much like the UTF-16 family, expect that
730 the units are 32-bit, and therefore the surrogate scheme is not
731 needed. The BOM signatures will be 0x00 0x00 0xFE 0xFF for BE and
732 0xFF 0xFE 0x00 0x00 for LE.
736 Encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit
737 encoding, UCS-4 is a 32-bit encoding. Unlike UTF-16, UCS-2
738 is not extensible beyond 0xFFFF, because it does not use surrogates.
742 A seven-bit safe (non-eight-bit) encoding, useful if the
743 transport/storage is not eight-bit safe. Defined by RFC 2152.
745 =head2 Security Implications of Malformed UTF-8
747 Unfortunately, the specification of UTF-8 leaves some room for
748 interpretation of how many bytes of encoded output one should generate
749 from one input Unicode character. Strictly speaking, one is supposed
750 to always generate the shortest possible sequence of UTF-8 bytes,
751 because otherwise there is potential for input buffer overflow at the
752 receiving end of a UTF-8 connection. Perl always generates the shortest
753 length UTF-8, and with warnings on (C<-w> or C<use warnings;>) Perl will
754 warn about non-shortest length UTF-8 (and other malformations, too,
755 such as the surrogates, which are not real character code points.)
757 =head2 Unicode in Perl on EBCDIC
759 The way Unicode is handled on EBCDIC platforms is still rather
760 experimental. On such a platform, references to UTF-8 encoding in this
761 document and elsewhere should be read as meaning UTF-EBCDIC as
762 specified in Unicode Technical Report 16 unless ASCII vs EBCDIC issues
763 are specifically discussed. There is no C<utfebcdic> pragma or
764 ":utfebcdic" layer, rather, "utf8" and ":utf8" are re-used to mean
765 the platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic>
766 for more discussion of the issues.
772 L<encoding>, L<Encode>, L<open>, L<bytes>, L<utf8>, L<perlretut>,
773 L<perlvar/"${^WIDE_SYSTEM_CALLS}">
projects / p5sagit/p5-mst-13.2.git / blob