3 perlunicode - Unicode support in Perl
7 =head2 Important Caveats
9 WARNING: While the implementation of Unicode support in Perl is now
10 fairly complete it is still evolving to some extent.
12 In particular the way Unicode is handled on EBCDIC platforms is still
13 rather experimental. On such a platform references to UTF-8 encoding
14 in this document and elsewhere should be read as meaning UTF-EBCDIC as
15 specified in Unicode Technical Report 16 unless ASCII vs EBCDIC issues
16 are specifically discussed. There is no C<utfebcdic> pragma or
17 ":utfebcdic" layer, rather "utf8" and ":utf8" are re-used to mean
18 platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic> for
19 more discussion of the issues.
21 The following areas are still under development.
25 =item Input and Output Disciplines
27 A filehandle can be marked as containing perl's internal Unicode
28 encoding (UTF-8 or UTF-EBCDIC) by opening it with the ":utf8" layer.
29 Other encodings can be converted to perl's encoding on input, or from
30 perl's encoding on output by use of the ":encoding()" layer. There is
31 not yet a clean way to mark the Perl source itself as being in an
34 =item Regular Expressions
36 The regular expression compiler does now attempt to produce
37 polymorphic opcodes. That is the pattern should now adapt to the data
38 and automatically switch to the Unicode character scheme when
39 presented with Unicode data, or a traditional byte scheme when
40 presented with byte data. The implementation is still new and
41 (particularly on EBCDIC platforms) may need further work.
43 =item C<use utf8> still needed to enable UTF-8/UTF-EBCDIC in scripts
45 The C<utf8> pragma implements the tables used for Unicode support.
46 These tables are automatically loaded on demand, so the C<utf8> pragma
47 need not normally be used.
49 However, as a compatibility measure, this pragma must be explicitly
50 used to enable recognition of UTF-8 in the Perl scripts themselves on
51 ASCII based machines or recognize UTF-EBCDIC on EBCDIC based machines.
52 B<NOTE: this should be the only place where an explicit C<use utf8> is
57 =head2 Byte and Character semantics
59 Beginning with version 5.6, Perl uses logically wide characters to
60 represent strings internally. This internal representation of strings
61 uses either the UTF-8 or the UTF-EBCDIC encoding.
63 In future, Perl-level operations can be expected to work with
64 characters rather than bytes, in general.
66 However, as strictly an interim compatibility measure, Perl aims to
67 provide a safe migration path from byte semantics to character
68 semantics for programs. For operations where Perl can unambiguously
69 decide that the input data is characters, Perl now switches to
70 character semantics. For operations where this determination cannot
71 be made without additional information from the user, Perl decides in
72 favor of compatibility, and chooses to use byte semantics.
74 This behavior preserves compatibility with earlier versions of Perl,
75 which allowed byte semantics in Perl operations, but only as long as
76 none of the program's inputs are marked as being as source of Unicode
77 character data. Such data may come from filehandles, from calls to
78 external programs, from information provided by the system (such as %ENV),
79 or from literals and constants in the source text.
81 If the C<-C> command line switch is used, (or the
82 ${^WIDE_SYSTEM_CALLS} global flag is set to C<1>), all system calls
83 will use the corresponding wide character APIs. Note that this is
84 currently only implemented on Windows since other platforms API
85 standard on this area.
87 Regardless of the above, the C<bytes> pragma can always be used to
88 force byte semantics in a particular lexical scope. See L<bytes>.
90 The C<utf8> pragma is primarily a compatibility device that enables
91 recognition of UTF-(8|EBCDIC) in literals encountered by the parser.
92 Note that this pragma is only required until a future version of Perl
93 in which character semantics will become the default. This pragma may
94 then become a no-op. See L<utf8>.
96 Unless mentioned otherwise, Perl operators will use character semantics
97 when they are dealing with Unicode data, and byte semantics otherwise.
98 Thus, character semantics for these operations apply transparently; if
99 the input data came from a Unicode source (for example, by adding a
100 character encoding discipline to the filehandle whence it came, or a
101 literal UTF-8 string constant in the program), character semantics
102 apply; otherwise, byte semantics are in effect. To force byte semantics
103 on Unicode data, the C<bytes> pragma should be used.
105 Notice that if you have a string with byte semantics and you then
106 add character data into it, the bytes will be upgraded I<as if they
107 were ISO 8859-1 (Latin-1)> (or if in EBCDIC, after a translation
110 Under character semantics, many operations that formerly operated on
111 bytes change to operating on characters. For ASCII data this makes no
112 difference, because UTF-8 stores ASCII in single bytes, but for any
113 character greater than C<chr(127)>, the character B<may> be stored in
114 a sequence of two or more bytes, all of which have the high bit set.
116 For C1 controls or Latin 1 characters on an EBCDIC platform the
117 character may be stored in a UTF-EBCDIC multi byte sequence. But by
118 and large, the user need not worry about this, because Perl hides it
119 from the user. A character in Perl is logically just a number ranging
120 from 0 to 2**32 or so. Larger characters encode to longer sequences
121 of bytes internally, but again, this is just an internal detail which
122 is hidden at the Perl level.
124 =head2 Effects of character semantics
126 Character semantics have the following effects:
132 Strings and patterns may contain characters that have an ordinal value
135 Presuming you use a Unicode editor to edit your program, such
136 characters will typically occur directly within the literal strings as
137 UTF-8 (or UTF-EBCDIC on EBCDIC platforms) characters, but you can also
138 specify a particular character with an extension of the C<\x>
139 notation. UTF-X characters are specified by putting the hexadecimal
140 code within curlies after the C<\x>. For instance, a Unicode smiley
145 Identifiers within the Perl script may contain Unicode alphanumeric
146 characters, including ideographs. (You are currently on your own when
147 it comes to using the canonical forms of characters--Perl doesn't
148 (yet) attempt to canonicalize variable names for you.)
152 Regular expressions match characters instead of bytes. For instance,
153 "." matches a character instead of a byte. (However, the C<\C> pattern
154 is provided to force a match a single byte ("C<char>" in C, hence C<\C>).)
158 Character classes in regular expressions match characters instead of
159 bytes, and match against the character properties specified in the
160 Unicode properties database. So C<\w> can be used to match an
161 ideograph, for instance.
165 Named Unicode properties and block ranges make be used as character
166 classes via the new C<\p{}> (matches property) and C<\P{}> (doesn't
167 match property) constructs. For instance, C<\p{Lu}> matches any
168 character with the Unicode uppercase property, while C<\p{M}> matches
169 any mark character. Single letter properties may omit the brackets,
170 so that can be written C<\pM> also. Many predefined character classes
171 are available, such as C<\p{IsMirrored}> and C<\p{InTibetan}>.
173 The C<\p{Is...}> test for "general properties" such as "letter",
174 "digit", while the C<\p{In...}> test for Unicode scripts and blocks.
176 The official Unicode script and block names have spaces and
177 dashes and separators, but for convenience you can have
178 dashes, spaces, and underbars at every word division, and
179 you need not care about correct casing. It is recommended,
180 however, that for consistency you use the following naming:
181 the official Unicode script or block name (see below for
182 the additional rules that apply to block names), with the whitespace
183 and dashes removed, and the words "uppercase-first-lowercase-otherwise".
184 That is, "Latin-1 Supplement" becomes "Latin1Supplement".
186 You can also negate both C<\p{}> and C<\P{}> by introducing a caret
187 (^) between the first curly and the property name: C<\p{^InTamil}> is
188 equal to C<\P{InTamil}>.
190 The C<In> and C<Is> can be left out: C<\p{Greek}> is equal to
191 C<\p{InGreek}>, C<\P{Pd}> is equal to C<\P{Pd}>.
193 Here is the list as of Unicode 3.1.1 (the two-letter classes) and as
194 defined by Perl (the one-letter classes) (what Perl calls C<L> is
195 often in Unicode materials called C<L&>):
205 Mc Mark, Spacing Combining
208 Nd Number, Decimal Digit
212 Pc Punctuation, Connector
215 Pe Punctuation, Close
216 Pi Punctuation, Initial quote
217 (may behave like Ps or Pe depending on usage)
218 Pf Punctuation, Final quote
219 (may behave like Ps or Pe depending on usage)
220 Po Punctuation, Other
229 Zp Separator, Paragraph
234 Co Other, Private Use
235 Cn Other, Not Assigned (Unicode defines no Cn characters)
237 Additionally, because scripts differ in their directionality
238 (for example Hebrew is written right to left), all characters
239 have their directionality defined:
242 BidiLRE Left-to-Right Embedding
243 BidiLRO Left-to-Right Override
245 BidiAL Right-to-Left Arabic
246 BidiRLE Right-to-Left Embedding
247 BidiRLO Right-to-Left Override
248 BidiPDF Pop Directional Format
249 BidiEN European Number
250 BidiES European Number Separator
251 BidiET European Number Terminator
253 BidiCS Common Number Separator
254 BidiNSM Non-Spacing Mark
255 BidiBN Boundary Neutral
256 BidiB Paragraph Separator
257 BidiS Segment Separator
259 BidiON Other Neutrals
263 The scripts available for C<\p{In...}> and C<\P{In...}>, for example
264 \p{InCyrillic>, are as follows, for example C<\p{InLatin}> or C<\P{InHan}>:
309 In addition to B<scripts>, Unicode also defines B<blocks> of
310 characters. The difference between scripts and blocks is that the
311 former concept is closer to natural languages, while the latter
312 concept is more an artificial grouping based on groups of 256 Unicode
313 characters. For example, the C<Latin> script contains letters from
314 many blocks, but it does not contain all the characters from those
315 blocks, it does not for example contain digits.
317 For more about scripts see the UTR #24:
318 http://www.unicode.org/unicode/reports/tr24/
319 For more about blocks see
320 http://www.unicode.org/Public/UNIDATA/Blocks.txt
322 Because there are overlaps in naming (there are, for example, both
323 a script called C<Katakana> and a block called C<Katakana>, the block
324 version has C<Block> appended to its name, C<\p{InKatakanaBlock}>.
326 Notice that this definition was introduced in Perl 5.8.0: in Perl
327 5.6.0 only the blocks were used; in Perl 5.8.0 scripts became the
328 preferential Unicode character class definition; this meant that
329 the definitions of some character classes changed (the ones in the
330 below list that have the C<Block> appended).
337 SpacingModifierLetters
338 CombiningDiacriticalMarks
364 UnifiedCanadianAboriginalSyllabics
369 LatinExtendedAdditional
372 SuperscriptsandSubscripts
374 CombiningMarksforSymbols
378 MathematicalOperators
379 MiscellaneousTechnical
381 OpticalCharacterRecognition
382 EnclosedAlphanumerics
389 CJKRadicalsSupplement
391 IdeographicDescriptionCharacters
392 CJKSymbolsandPunctuation
396 HangulCompatibilityJamo
399 EnclosedCJKLettersandMonths
401 CJKUnifiedIdeographsExtensionA
407 HighPrivateUseSurrogates
410 CJKCompatibilityIdeographs
411 AlphabeticPresentationForms
412 ArabicPresentationFormsA
414 CJKCompatibilityForms
416 ArabicPresentationFormsB
418 HalfwidthandFullwidthForms
422 ByzantineMusicalSymbols
424 MathematicalAlphanumericSymbols
425 CJKUnifiedIdeographsExtensionB
426 CJKCompatibilityIdeographsSupplement
431 The special pattern C<\X> match matches any extended Unicode sequence
432 (a "combining character sequence" in Standardese), where the first
433 character is a base character and subsequent characters are mark
434 characters that apply to the base character. It is equivalent to
439 The C<tr///> operator translates characters instead of bytes. Note
440 that the C<tr///CU> functionality has been removed, as the interface
441 was a mistake. For similar functionality see pack('U0', ...) and
446 Case translation operators use the Unicode case translation tables
447 when provided character input. Note that C<uc()> translates to
448 uppercase, while C<ucfirst> translates to titlecase (for languages
449 that make the distinction). Naturally the corresponding backslash
450 sequences have the same semantics.
454 Most operators that deal with positions or lengths in the string will
455 automatically switch to using character positions, including
456 C<chop()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>,
457 C<sprintf()>, C<write()>, and C<length()>. Operators that
458 specifically don't switch include C<vec()>, C<pack()>, and
459 C<unpack()>. Operators that really don't care include C<chomp()>, as
460 well as any other operator that treats a string as a bucket of bits,
461 such as C<sort()>, and the operators dealing with filenames.
465 The C<pack()>/C<unpack()> letters "C<c>" and "C<C>" do I<not> change,
466 since they're often used for byte-oriented formats. (Again, think
467 "C<char>" in the C language.) However, there is a new "C<U>" specifier
468 that will convert between UTF-8 characters and integers. (It works
469 outside of the utf8 pragma too.)
473 The C<chr()> and C<ord()> functions work on characters. This is like
474 C<pack("U")> and C<unpack("U")>, not like C<pack("C")> and
475 C<unpack("C")>. In fact, the latter are how you now emulate
476 byte-oriented C<chr()> and C<ord()> for Unicode strings.
477 (Note that this reveals the internal UTF-8 encoding of strings and
478 you are not supposed to do that unless you know what you are doing.)
482 The bit string operators C<& | ^ ~> can operate on character data.
483 However, for backward compatibility reasons (bit string operations
484 when the characters all are less than 256 in ordinal value) one should
485 not mix C<~> (the bit complement) and characters both less than 256 and
486 equal or greater than 256. Most importantly, the DeMorgan's laws
487 (C<~($x|$y) eq ~$x&~$y>, C<~($x&$y) eq ~$x|~$y>) won't hold.
488 Another way to look at this is that the complement cannot return
489 B<both> the 8-bit (byte) wide bit complement B<and> the full character
494 lc(), uc(), lcfirst(), and ucfirst() work only for some of the
495 simplest cases, where the mapping goes from a single Unicode character
496 to another single Unicode character, and where the mapping does not
497 depend on surrounding characters, or on locales. More complex cases,
498 where for example one character maps into several, are not yet
499 implemented. See the Unicode Technical Report #21, Case Mappings,
500 for more details. The Unicode::UCD module (part of Perl since 5.8.0)
501 casespec() and casefold() interfaces supply information about the more
506 And finally, C<scalar reverse()> reverses by character rather than by byte.
510 =head2 Character encodings for input and output
516 As of yet, there is no method for automatically coercing input and
517 output to some encoding other than UTF-8 or UTF-EBCDIC. This is planned
518 in the near future, however.
520 Whether an arbitrary piece of data will be treated as "characters" or
521 "bytes" by internal operations cannot be divined at the current time.
523 Use of locales with utf8 may lead to odd results. Currently there is
524 some attempt to apply 8-bit locale info to characters in the range
525 0..255, but this is demonstrably incorrect for locales that use
526 characters above that range (when mapped into Unicode). It will also
527 tend to run slower. Avoidance of locales is strongly encouraged.
529 =head1 UNICODE REGULAR EXPRESSION SUPPORT LEVEL
531 The following list of Unicode regular expression support describes
532 feature by feature the Unicode support implemented in Perl as of Perl
533 5.8.0. The "Level N" and the section numbers refer to the Unicode
534 Technical Report 18, "Unicode Regular Expression Guidelines".
540 Level 1 - Basic Unicode Support
542 2.1 Hex Notation - done [1]
543 Named Notation - done [2]
544 2.2 Categories - done [3][4]
545 2.3 Subtraction - MISSING [5][6]
546 2.4 Simple Word Boundaries - done [7]
547 2.5 Simple Loose Matches - MISSING [8]
548 2.6 End of Line - MISSING [9][10]
552 [ 3] . \p{Is...} \P{Is...}
553 [ 4] now scripts (see UTR#24 Script Names) in addition to blocks
555 [ 6] can use look-ahead to emulate subtracion
556 [ 7] include Letters in word characters
557 [ 8] see UTR#21 Case Mappings
558 [ 9] see UTR#13 Unicode Newline Guidelines
559 [10] should do ^ and $ also on \x{2028} and \x{2029}
563 Level 2 - Extended Unicode Support
565 3.1 Surrogates - MISSING
566 3.2 Canonical Equivalents - MISSING [11][12]
567 3.3 Locale-Independent Graphemes - MISSING [13]
568 3.4 Locale-Independent Words - MISSING [14]
569 3.5 Locale-Independent Loose Matches - MISSING [15]
571 [11] see UTR#15 Unicode Normalization
572 [12] have Unicode::Normalize but not integrated to regexes
573 [13] have \X but at this level . should equal that
574 [14] need three classes, not just \w and \W
575 [15] see UTR#21 Case Mappings
579 Level 3 - Locale-Sensitive Support
581 4.1 Locale-Dependent Categories - MISSING
582 4.2 Locale-Dependent Graphemes - MISSING [16][17]
583 4.3 Locale-Dependent Words - MISSING
584 4.4 Locale-Dependent Loose Matches - MISSING
585 4.5 Locale-Dependent Ranges - MISSING
587 [16] see UTR#10 Unicode Collation Algorithms
588 [17] have Unicode::Collate but not integrated to regexes
594 L<bytes>, L<utf8>, L<perlretut>, L<perlvar/"${^WIDE_SYSTEM_CALLS}">