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1 | =head1 NAME |
2 | ||
3 | perlunicode - Unicode support in Perl | |
4 | ||
5 | =head1 DESCRIPTION | |
6 | ||
7 | =head2 Important Caveats | |
8 | ||
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. | |
12 | ||
13 | =over 4 | |
14 | ||
15 | =item Input and Output Layers | |
16 | ||
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>. | |
22 | ||
23 | To indicate that Perl source itself is using a particular encoding, | |
24 | see L<encoding>. | |
25 | ||
26 | =item Regular Expressions | |
27 | ||
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. | |
32 | ||
33 | =item C<use utf8> still needed to enable UTF-8/UTF-EBCDIC in scripts | |
34 | ||
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>. | |
41 | ||
42 | You can also use the C<encoding> pragma to change the default encoding | |
43 | of the data in your script; see L<encoding>. | |
44 | ||
45 | =item BOM-marked scripts and UTF-16 scripts autodetected | |
46 | ||
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.) | |
52 | ||
53 | =item C<use encoding> needed to upgrade non-Latin-1 byte strings | |
54 | ||
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. | |
60 | ||
61 | If you wish to interpret byte strings as UTF-8 instead, use the | |
62 | C<encoding> pragma: | |
63 | ||
64 | use encoding 'utf8'; | |
65 | ||
66 | See L</"Byte and Character Semantics"> for more details. | |
67 | ||
68 | =back | |
69 | ||
70 | =head2 Byte and Character Semantics | |
71 | ||
72 | Beginning with version 5.6, Perl uses logically-wide characters to | |
73 | represent strings internally. | |
74 | ||
75 | In future, Perl-level operations will be expected to work with | |
76 | characters rather than bytes. | |
77 | ||
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. | |
85 | ||
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. | |
92 | ||
93 | The C<bytes> pragma will always, regardless of platform, force byte | |
94 | semantics in a particular lexical scope. See L<bytes>. | |
95 | ||
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>. | |
101 | ||
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. | |
110 | ||
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>. | |
118 | ||
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. | |
125 | ||
126 | =head2 Effects of Character Semantics | |
127 | ||
128 | Character semantics have the following effects: | |
129 | ||
130 | =over 4 | |
131 | ||
132 | =item * | |
133 | ||
134 | Strings--including hash keys--and regular expression patterns may | |
135 | contain characters that have an ordinal value larger than 255. | |
136 | ||
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. | |
142 | ||
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. | |
148 | ||
149 | Additionally, if you | |
150 | ||
151 | use charnames ':full'; | |
152 | ||
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}>. | |
155 | ||
156 | ||
157 | =item * | |
158 | ||
159 | If an appropriate L<encoding> is specified, identifiers within the | |
160 | Perl script may contain Unicode alphanumeric characters, including | |
161 | ideographs. Perl does not currently attempt to canonicalize variable | |
162 | names. | |
163 | ||
164 | =item * | |
165 | ||
166 | Regular expressions match characters instead of bytes. "." matches | |
167 | a character instead of a byte. The C<\C> pattern is provided to force | |
168 | a match a single byte--a C<char> in C, hence C<\C>. | |
169 | ||
170 | =item * | |
171 | ||
172 | Character classes in regular expressions match characters instead of | |
173 | bytes and match against the character properties specified in the | |
174 | Unicode properties database. C<\w> can be used to match a Japanese | |
175 | ideograph, for instance. | |
176 | ||
177 | (However, and as a limitation of the current implementation, using | |
178 | C<\w> or C<\W> I<inside> a C<[...]> character class will still match | |
179 | with byte semantics.) | |
180 | ||
181 | =item * | |
182 | ||
183 | Named Unicode properties, scripts, and block ranges may be used like | |
184 | character classes via the C<\p{}> "matches property" construct and | |
185 | the C<\P{}> negation, "doesn't match property". | |
186 | ||
187 | For instance, C<\p{Lu}> matches any character with the Unicode "Lu" | |
188 | (Letter, uppercase) property, while C<\p{M}> matches any character | |
189 | with an "M" (mark--accents and such) property. Brackets are not | |
190 | required for single letter properties, so C<\p{M}> is equivalent to | |
191 | C<\pM>. Many predefined properties are available, such as | |
192 | C<\p{Mirrored}> and C<\p{Tibetan}>. | |
193 | ||
194 | The official Unicode script and block names have spaces and dashes as | |
195 | separators, but for convenience you can use dashes, spaces, or | |
196 | underbars, and case is unimportant. It is recommended, however, that | |
197 | for consistency you use the following naming: the official Unicode | |
198 | script, property, or block name (see below for the additional rules | |
199 | that apply to block names) with whitespace and dashes removed, and the | |
200 | words "uppercase-first-lowercase-rest". C<Latin-1 Supplement> thus | |
201 | becomes C<Latin1Supplement>. | |
202 | ||
203 | You can also use negation in both C<\p{}> and C<\P{}> by introducing a caret | |
204 | (^) between the first brace and the property name: C<\p{^Tamil}> is | |
205 | equal to C<\P{Tamil}>. | |
206 | ||
207 | B<NOTE: the properties, scripts, and blocks listed here are as of | |
208 | Unicode 3.2.0, March 2002, or Perl 5.8.0, July 2002. Unicode 4.0.0 | |
209 | came out in April 2003, and Perl 5.8.1 in September 2003.> | |
210 | ||
211 | Here are the basic Unicode General Category properties, followed by their | |
212 | long form. You can use either; C<\p{Lu}> and C<\p{UppercaseLetter}>, | |
213 | for instance, are identical. | |
214 | ||
215 | Short Long | |
216 | ||
217 | L Letter | |
218 | LC CasedLetter | |
219 | Lu UppercaseLetter | |
220 | Ll LowercaseLetter | |
221 | Lt TitlecaseLetter | |
222 | Lm ModifierLetter | |
223 | Lo OtherLetter | |
224 | ||
225 | M Mark | |
226 | Mn NonspacingMark | |
227 | Mc SpacingMark | |
228 | Me EnclosingMark | |
229 | ||
230 | N Number | |
231 | Nd DecimalNumber | |
232 | Nl LetterNumber | |
233 | No OtherNumber | |
234 | ||
235 | P Punctuation | |
236 | Pc ConnectorPunctuation | |
237 | Pd DashPunctuation | |
238 | Ps OpenPunctuation | |
239 | Pe ClosePunctuation | |
240 | Pi InitialPunctuation | |
241 | (may behave like Ps or Pe depending on usage) | |
242 | Pf FinalPunctuation | |
243 | (may behave like Ps or Pe depending on usage) | |
244 | Po OtherPunctuation | |
245 | ||
246 | S Symbol | |
247 | Sm MathSymbol | |
248 | Sc CurrencySymbol | |
249 | Sk ModifierSymbol | |
250 | So OtherSymbol | |
251 | ||
252 | Z Separator | |
253 | Zs SpaceSeparator | |
254 | Zl LineSeparator | |
255 | Zp ParagraphSeparator | |
256 | ||
257 | C Other | |
258 | Cc Control | |
259 | Cf Format | |
260 | Cs Surrogate (not usable) | |
261 | Co PrivateUse | |
262 | Cn Unassigned | |
263 | ||
264 | Single-letter properties match all characters in any of the | |
265 | two-letter sub-properties starting with the same letter. | |
266 | C<LC> and C<L&> are special cases, which are aliases for the set of | |
267 | C<Ll>, C<Lu>, and C<Lt>. | |
268 | ||
269 | Because Perl hides the need for the user to understand the internal | |
270 | representation of Unicode characters, there is no need to implement | |
271 | the somewhat messy concept of surrogates. C<Cs> is therefore not | |
272 | supported. | |
273 | ||
274 | Because scripts differ in their directionality--Hebrew is | |
275 | written right to left, for example--Unicode supplies these properties in | |
276 | the BidiClass class: | |
277 | ||
278 | Property Meaning | |
279 | ||
280 | L Left-to-Right | |
281 | LRE Left-to-Right Embedding | |
282 | LRO Left-to-Right Override | |
283 | R Right-to-Left | |
284 | AL Right-to-Left Arabic | |
285 | RLE Right-to-Left Embedding | |
286 | RLO Right-to-Left Override | |
287 | PDF Pop Directional Format | |
288 | EN European Number | |
289 | ES European Number Separator | |
290 | ET European Number Terminator | |
291 | AN Arabic Number | |
292 | CS Common Number Separator | |
293 | NSM Non-Spacing Mark | |
294 | BN Boundary Neutral | |
295 | B Paragraph Separator | |
296 | S Segment Separator | |
297 | WS Whitespace | |
298 | ON Other Neutrals | |
299 | ||
300 | For example, C<\p{BidiClass:R}> matches characters that are normally | |
301 | written right to left. | |
302 | ||
303 | =back | |
304 | ||
305 | =head2 Scripts | |
306 | ||
307 | The script names which can be used by C<\p{...}> and C<\P{...}>, | |
308 | such as in C<\p{Latin}> or C<\p{Cyrillic}>, are as follows: | |
309 | ||
310 | Arabic | |
311 | Armenian | |
312 | Bengali | |
313 | Bopomofo | |
314 | Buhid | |
315 | CanadianAboriginal | |
316 | Cherokee | |
317 | Cyrillic | |
318 | Deseret | |
319 | Devanagari | |
320 | Ethiopic | |
321 | Georgian | |
322 | Gothic | |
323 | Greek | |
324 | Gujarati | |
325 | Gurmukhi | |
326 | Han | |
327 | Hangul | |
328 | Hanunoo | |
329 | Hebrew | |
330 | Hiragana | |
331 | Inherited | |
332 | Kannada | |
333 | Katakana | |
334 | Khmer | |
335 | Lao | |
336 | Latin | |
337 | Malayalam | |
338 | Mongolian | |
339 | Myanmar | |
340 | Ogham | |
341 | OldItalic | |
342 | Oriya | |
343 | Runic | |
344 | Sinhala | |
345 | Syriac | |
346 | Tagalog | |
347 | Tagbanwa | |
348 | Tamil | |
349 | Telugu | |
350 | Thaana | |
351 | Thai | |
352 | Tibetan | |
353 | Yi | |
354 | ||
355 | Extended property classes can supplement the basic | |
356 | properties, defined by the F<PropList> Unicode database: | |
357 | ||
358 | ASCIIHexDigit | |
359 | BidiControl | |
360 | Dash | |
361 | Deprecated | |
362 | Diacritic | |
363 | Extender | |
364 | GraphemeLink | |
365 | HexDigit | |
366 | Hyphen | |
367 | Ideographic | |
368 | IDSBinaryOperator | |
369 | IDSTrinaryOperator | |
370 | JoinControl | |
371 | LogicalOrderException | |
372 | NoncharacterCodePoint | |
373 | OtherAlphabetic | |
374 | OtherDefaultIgnorableCodePoint | |
375 | OtherGraphemeExtend | |
376 | OtherLowercase | |
377 | OtherMath | |
378 | OtherUppercase | |
379 | QuotationMark | |
380 | Radical | |
381 | SoftDotted | |
382 | TerminalPunctuation | |
383 | UnifiedIdeograph | |
384 | WhiteSpace | |
385 | ||
386 | and there are further derived properties: | |
387 | ||
388 | Alphabetic Lu + Ll + Lt + Lm + Lo + OtherAlphabetic | |
389 | Lowercase Ll + OtherLowercase | |
390 | Uppercase Lu + OtherUppercase | |
391 | Math Sm + OtherMath | |
392 | ||
393 | ID_Start Lu + Ll + Lt + Lm + Lo + Nl | |
394 | ID_Continue ID_Start + Mn + Mc + Nd + Pc | |
395 | ||
396 | Any Any character | |
397 | Assigned Any non-Cn character (i.e. synonym for \P{Cn}) | |
398 | Unassigned Synonym for \p{Cn} | |
399 | Common Any character (or unassigned code point) | |
400 | not explicitly assigned to a script | |
401 | ||
402 | For backward compatibility (with Perl 5.6), all properties mentioned | |
403 | so far may have C<Is> prepended to their name, so C<\P{IsLu}>, for | |
404 | example, is equal to C<\P{Lu}>. | |
405 | ||
406 | =head2 Blocks | |
407 | ||
408 | In addition to B<scripts>, Unicode also defines B<blocks> of | |
409 | characters. The difference between scripts and blocks is that the | |
410 | concept of scripts is closer to natural languages, while the concept | |
411 | of blocks is more of an artificial grouping based on groups of 256 | |
412 | Unicode characters. For example, the C<Latin> script contains letters | |
413 | from many blocks but does not contain all the characters from those | |
414 | blocks. It does not, for example, contain digits, because digits are | |
415 | shared across many scripts. Digits and similar groups, like | |
416 | punctuation, are in a category called C<Common>. | |
417 | ||
418 | For more about scripts, see the UTR #24: | |
419 | ||
420 | http://www.unicode.org/unicode/reports/tr24/ | |
421 | ||
422 | For more about blocks, see: | |
423 | ||
424 | http://www.unicode.org/Public/UNIDATA/Blocks.txt | |
425 | ||
426 | Block names are given with the C<In> prefix. For example, the | |
427 | Katakana block is referenced via C<\p{InKatakana}>. The C<In> | |
428 | prefix may be omitted if there is no naming conflict with a script | |
429 | or any other property, but it is recommended that C<In> always be used | |
430 | for block tests to avoid confusion. | |
431 | ||
432 | These block names are supported: | |
433 | ||
434 | InAlphabeticPresentationForms | |
435 | InArabic | |
436 | InArabicPresentationFormsA | |
437 | InArabicPresentationFormsB | |
438 | InArmenian | |
439 | InArrows | |
440 | InBasicLatin | |
441 | InBengali | |
442 | InBlockElements | |
443 | InBopomofo | |
444 | InBopomofoExtended | |
445 | InBoxDrawing | |
446 | InBraillePatterns | |
447 | InBuhid | |
448 | InByzantineMusicalSymbols | |
449 | InCJKCompatibility | |
450 | InCJKCompatibilityForms | |
451 | InCJKCompatibilityIdeographs | |
452 | InCJKCompatibilityIdeographsSupplement | |
453 | InCJKRadicalsSupplement | |
454 | InCJKSymbolsAndPunctuation | |
455 | InCJKUnifiedIdeographs | |
456 | InCJKUnifiedIdeographsExtensionA | |
457 | InCJKUnifiedIdeographsExtensionB | |
458 | InCherokee | |
459 | InCombiningDiacriticalMarks | |
460 | InCombiningDiacriticalMarksforSymbols | |
461 | InCombiningHalfMarks | |
462 | InControlPictures | |
463 | InCurrencySymbols | |
464 | InCyrillic | |
465 | InCyrillicSupplementary | |
466 | InDeseret | |
467 | InDevanagari | |
468 | InDingbats | |
469 | InEnclosedAlphanumerics | |
470 | InEnclosedCJKLettersAndMonths | |
471 | InEthiopic | |
472 | InGeneralPunctuation | |
473 | InGeometricShapes | |
474 | InGeorgian | |
475 | InGothic | |
476 | InGreekExtended | |
477 | InGreekAndCoptic | |
478 | InGujarati | |
479 | InGurmukhi | |
480 | InHalfwidthAndFullwidthForms | |
481 | InHangulCompatibilityJamo | |
482 | InHangulJamo | |
483 | InHangulSyllables | |
484 | InHanunoo | |
485 | InHebrew | |
486 | InHighPrivateUseSurrogates | |
487 | InHighSurrogates | |
488 | InHiragana | |
489 | InIPAExtensions | |
490 | InIdeographicDescriptionCharacters | |
491 | InKanbun | |
492 | InKangxiRadicals | |
493 | InKannada | |
494 | InKatakana | |
495 | InKatakanaPhoneticExtensions | |
496 | InKhmer | |
497 | InLao | |
498 | InLatin1Supplement | |
499 | InLatinExtendedA | |
500 | InLatinExtendedAdditional | |
501 | InLatinExtendedB | |
502 | InLetterlikeSymbols | |
503 | InLowSurrogates | |
504 | InMalayalam | |
505 | InMathematicalAlphanumericSymbols | |
506 | InMathematicalOperators | |
507 | InMiscellaneousMathematicalSymbolsA | |
508 | InMiscellaneousMathematicalSymbolsB | |
509 | InMiscellaneousSymbols | |
510 | InMiscellaneousTechnical | |
511 | InMongolian | |
512 | InMusicalSymbols | |
513 | InMyanmar | |
514 | InNumberForms | |
515 | InOgham | |
516 | InOldItalic | |
517 | InOpticalCharacterRecognition | |
518 | InOriya | |
519 | InPrivateUseArea | |
520 | InRunic | |
521 | InSinhala | |
522 | InSmallFormVariants | |
523 | InSpacingModifierLetters | |
524 | InSpecials | |
525 | InSuperscriptsAndSubscripts | |
526 | InSupplementalArrowsA | |
527 | InSupplementalArrowsB | |
528 | InSupplementalMathematicalOperators | |
529 | InSupplementaryPrivateUseAreaA | |
530 | InSupplementaryPrivateUseAreaB | |
531 | InSyriac | |
532 | InTagalog | |
533 | InTagbanwa | |
534 | InTags | |
535 | InTamil | |
536 | InTelugu | |
537 | InThaana | |
538 | InThai | |
539 | InTibetan | |
540 | InUnifiedCanadianAboriginalSyllabics | |
541 | InVariationSelectors | |
542 | InYiRadicals | |
543 | InYiSyllables | |
544 | ||
545 | =over 4 | |
546 | ||
547 | =item * | |
548 | ||
549 | The special pattern C<\X> matches any extended Unicode | |
550 | sequence--"a combining character sequence" in Standardese--where the | |
551 | first character is a base character and subsequent characters are mark | |
552 | characters that apply to the base character. C<\X> is equivalent to | |
553 | C<(?:\PM\pM*)>. | |
554 | ||
555 | =item * | |
556 | ||
557 | The C<tr///> operator translates characters instead of bytes. Note | |
558 | that the C<tr///CU> functionality has been removed. For similar | |
559 | functionality see pack('U0', ...) and pack('C0', ...). | |
560 | ||
561 | =item * | |
562 | ||
563 | Case translation operators use the Unicode case translation tables | |
564 | when character input is provided. Note that C<uc()>, or C<\U> in | |
565 | interpolated strings, translates to uppercase, while C<ucfirst>, | |
566 | or C<\u> in interpolated strings, translates to titlecase in languages | |
567 | that make the distinction. | |
568 | ||
569 | =item * | |
570 | ||
571 | Most operators that deal with positions or lengths in a string will | |
572 | automatically switch to using character positions, including | |
573 | C<chop()>, C<chomp()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>, | |
574 | C<sprintf()>, C<write()>, and C<length()>. Operators that | |
575 | specifically do not switch include C<vec()>, C<pack()>, and | |
576 | C<unpack()>. Operators that really don't care include | |
577 | operators that treats strings as a bucket of bits such as C<sort()>, | |
578 | and operators dealing with filenames. | |
579 | ||
580 | =item * | |
581 | ||
582 | The C<pack()>/C<unpack()> letters C<c> and C<C> do I<not> change, | |
583 | since they are often used for byte-oriented formats. Again, think | |
584 | C<char> in the C language. | |
585 | ||
586 | There is a new C<U> specifier that converts between Unicode characters | |
587 | and code points. | |
588 | ||
589 | =item * | |
590 | ||
591 | The C<chr()> and C<ord()> functions work on characters, similar to | |
592 | C<pack("U")> and C<unpack("U")>, I<not> C<pack("C")> and | |
593 | C<unpack("C")>. C<pack("C")> and C<unpack("C")> are methods for | |
594 | emulating byte-oriented C<chr()> and C<ord()> on Unicode strings. | |
595 | While these methods reveal the internal encoding of Unicode strings, | |
596 | that is not something one normally needs to care about at all. | |
597 | ||
598 | =item * | |
599 | ||
600 | The bit string operators, C<& | ^ ~>, can operate on character data. | |
601 | However, for backward compatibility, such as when using bit string | |
602 | operations when characters are all less than 256 in ordinal value, one | |
603 | should not use C<~> (the bit complement) with characters of both | |
604 | values less than 256 and values greater than 256. Most importantly, | |
605 | DeMorgan's laws (C<~($x|$y) eq ~$x&~$y> and C<~($x&$y) eq ~$x|~$y>) | |
606 | will not hold. The reason for this mathematical I<faux pas> is that | |
607 | the complement cannot return B<both> the 8-bit (byte-wide) bit | |
608 | complement B<and> the full character-wide bit complement. | |
609 | ||
610 | =item * | |
611 | ||
612 | lc(), uc(), lcfirst(), and ucfirst() work for the following cases: | |
613 | ||
614 | =over 8 | |
615 | ||
616 | =item * | |
617 | ||
618 | the case mapping is from a single Unicode character to another | |
619 | single Unicode character, or | |
620 | ||
621 | =item * | |
622 | ||
623 | the case mapping is from a single Unicode character to more | |
624 | than one Unicode character. | |
625 | ||
626 | =back | |
627 | ||
628 | Things to do with locales (Lithuanian, Turkish, Azeri) do B<not> work | |
629 | since Perl does not understand the concept of Unicode locales. | |
630 | ||
631 | See the Unicode Technical Report #21, Case Mappings, for more details. | |
632 | ||
633 | =back | |
634 | ||
635 | =over 4 | |
636 | ||
637 | =item * | |
638 | ||
639 | And finally, C<scalar reverse()> reverses by character rather than by byte. | |
640 | ||
641 | =back | |
642 | ||
643 | =head2 User-Defined Character Properties | |
644 | ||
645 | You can define your own character properties by defining subroutines | |
646 | whose names begin with "In" or "Is". The subroutines can be defined in | |
647 | any package. The user-defined properties can be used in the regular | |
648 | expression C<\p> and C<\P> constructs; if you are using a user-defined | |
649 | property from a package other than the one you are in, you must specify | |
650 | its package in the C<\p> or C<\P> construct. | |
651 | ||
652 | # assuming property IsForeign defined in Lang:: | |
653 | package main; # property package name required | |
654 | if ($txt =~ /\p{Lang::IsForeign}+/) { ... } | |
655 | ||
656 | package Lang; # property package name not required | |
657 | if ($txt =~ /\p{IsForeign}+/) { ... } | |
658 | ||
659 | ||
660 | Note that the effect is compile-time and immutable once defined. | |
661 | ||
662 | The subroutines must return a specially-formatted string, with one | |
663 | or more newline-separated lines. Each line must be one of the following: | |
664 | ||
665 | =over 4 | |
666 | ||
667 | =item * | |
668 | ||
669 | Two hexadecimal numbers separated by horizontal whitespace (space or | |
670 | tabular characters) denoting a range of Unicode code points to include. | |
671 | ||
672 | =item * | |
673 | ||
674 | Something to include, prefixed by "+": a built-in character | |
675 | property (prefixed by "utf8::") or a user-defined character property, | |
676 | to represent all the characters in that property; two hexadecimal code | |
677 | points for a range; or a single hexadecimal code point. | |
678 | ||
679 | =item * | |
680 | ||
681 | Something to exclude, prefixed by "-": an existing character | |
682 | property (prefixed by "utf8::") or a user-defined character property, | |
683 | to represent all the characters in that property; two hexadecimal code | |
684 | points for a range; or a single hexadecimal code point. | |
685 | ||
686 | =item * | |
687 | ||
688 | Something to negate, prefixed "!": an existing character | |
689 | property (prefixed by "utf8::") or a user-defined character property, | |
690 | to represent all the characters in that property; two hexadecimal code | |
691 | points for a range; or a single hexadecimal code point. | |
692 | ||
693 | =item * | |
694 | ||
695 | Something to intersect with, prefixed by "&": an existing character | |
696 | property (prefixed by "utf8::") or a user-defined character property, | |
697 | for all the characters except the characters in the property; two | |
698 | hexadecimal code points for a range; or a single hexadecimal code point. | |
699 | ||
700 | =back | |
701 | ||
702 | For example, to define a property that covers both the Japanese | |
703 | syllabaries (hiragana and katakana), you can define | |
704 | ||
705 | sub InKana { | |
706 | return <<END; | |
707 | 3040\t309F | |
708 | 30A0\t30FF | |
709 | END | |
710 | } | |
711 | ||
712 | Imagine that the here-doc end marker is at the beginning of the line. | |
713 | Now you can use C<\p{InKana}> and C<\P{InKana}>. | |
714 | ||
715 | You could also have used the existing block property names: | |
716 | ||
717 | sub InKana { | |
718 | return <<'END'; | |
719 | +utf8::InHiragana | |
720 | +utf8::InKatakana | |
721 | END | |
722 | } | |
723 | ||
724 | Suppose you wanted to match only the allocated characters, | |
725 | not the raw block ranges: in other words, you want to remove | |
726 | the non-characters: | |
727 | ||
728 | sub InKana { | |
729 | return <<'END'; | |
730 | +utf8::InHiragana | |
731 | +utf8::InKatakana | |
732 | -utf8::IsCn | |
733 | END | |
734 | } | |
735 | ||
736 | The negation is useful for defining (surprise!) negated classes. | |
737 | ||
738 | sub InNotKana { | |
739 | return <<'END'; | |
740 | !utf8::InHiragana | |
741 | -utf8::InKatakana | |
742 | +utf8::IsCn | |
743 | END | |
744 | } | |
745 | ||
746 | Intersection is useful for getting the common characters matched by | |
747 | two (or more) classes. | |
748 | ||
749 | sub InFooAndBar { | |
750 | return <<'END'; | |
751 | +main::Foo | |
752 | &main::Bar | |
753 | END | |
754 | } | |
755 | ||
756 | It's important to remember not to use "&" for the first set -- that | |
757 | would be intersecting with nothing (resulting in an empty set). | |
758 | ||
759 | You can also define your own mappings to be used in the lc(), | |
760 | lcfirst(), uc(), and ucfirst() (or their string-inlined versions). | |
761 | The principle is the same: define subroutines in the C<main> package | |
762 | with names like C<ToLower> (for lc() and lcfirst()), C<ToTitle> (for | |
763 | the first character in ucfirst()), and C<ToUpper> (for uc(), and the | |
764 | rest of the characters in ucfirst()). | |
765 | ||
766 | The string returned by the subroutines needs now to be three | |
767 | hexadecimal numbers separated by tabulators: start of the source | |
768 | range, end of the source range, and start of the destination range. | |
769 | For example: | |
770 | ||
771 | sub ToUpper { | |
772 | return <<END; | |
773 | 0061\t0063\t0041 | |
774 | END | |
775 | } | |
776 | ||
777 | defines an uc() mapping that causes only the characters "a", "b", and | |
778 | "c" to be mapped to "A", "B", "C", all other characters will remain | |
779 | unchanged. | |
780 | ||
781 | If there is no source range to speak of, that is, the mapping is from | |
782 | a single character to another single character, leave the end of the | |
783 | source range empty, but the two tabulator characters are still needed. | |
784 | For example: | |
785 | ||
786 | sub ToLower { | |
787 | return <<END; | |
788 | 0041\t\t0061 | |
789 | END | |
790 | } | |
791 | ||
792 | defines a lc() mapping that causes only "A" to be mapped to "a", all | |
793 | other characters will remain unchanged. | |
794 | ||
795 | (For serious hackers only) If you want to introspect the default | |
796 | mappings, you can find the data in the directory | |
797 | C<$Config{privlib}>/F<unicore/To/>. The mapping data is returned as | |
798 | the here-document, and the C<utf8::ToSpecFoo> are special exception | |
799 | mappings derived from <$Config{privlib}>/F<unicore/SpecialCasing.txt>. | |
800 | The C<Digit> and C<Fold> mappings that one can see in the directory | |
801 | are not directly user-accessible, one can use either the | |
802 | C<Unicode::UCD> module, or just match case-insensitively (that's when | |
803 | the C<Fold> mapping is used). | |
804 | ||
805 | A final note on the user-defined property tests and mappings: they | |
806 | will be used only if the scalar has been marked as having Unicode | |
807 | characters. Old byte-style strings will not be affected. | |
808 | ||
809 | =head2 Character Encodings for Input and Output | |
810 | ||
811 | See L<Encode>. | |
812 | ||
813 | =head2 Unicode Regular Expression Support Level | |
814 | ||
815 | The following list of Unicode support for regular expressions describes | |
816 | all the features currently supported. The references to "Level N" | |
817 | and the section numbers refer to the Unicode Technical Report 18, | |
818 | "Unicode Regular Expression Guidelines", version 6 (Unicode 3.2.0, | |
819 | Perl 5.8.0). | |
820 | ||
821 | =over 4 | |
822 | ||
823 | =item * | |
824 | ||
825 | Level 1 - Basic Unicode Support | |
826 | ||
827 | 2.1 Hex Notation - done [1] | |
828 | Named Notation - done [2] | |
829 | 2.2 Categories - done [3][4] | |
830 | 2.3 Subtraction - MISSING [5][6] | |
831 | 2.4 Simple Word Boundaries - done [7] | |
832 | 2.5 Simple Loose Matches - done [8] | |
833 | 2.6 End of Line - MISSING [9][10] | |
834 | ||
835 | [ 1] \x{...} | |
836 | [ 2] \N{...} | |
837 | [ 3] . \p{...} \P{...} | |
838 | [ 4] support for scripts (see UTR#24 Script Names), blocks, | |
839 | binary properties, enumerated non-binary properties, and | |
840 | numeric properties (as listed in UTR#18 Other Properties) | |
841 | [ 5] have negation | |
842 | [ 6] can use regular expression look-ahead [a] | |
843 | or user-defined character properties [b] to emulate subtraction | |
844 | [ 7] include Letters in word characters | |
845 | [ 8] note that Perl does Full case-folding in matching, not Simple: | |
846 | for example U+1F88 is equivalent with U+1F00 U+03B9, | |
847 | not with 1F80. This difference matters for certain Greek | |
848 | capital letters with certain modifiers: the Full case-folding | |
849 | decomposes the letter, while the Simple case-folding would map | |
850 | it to a single character. | |
851 | [ 9] see UTR #13 Unicode Newline Guidelines | |
852 | [10] should do ^ and $ also on \x{85}, \x{2028} and \x{2029} | |
853 | (should also affect <>, $., and script line numbers) | |
854 | (the \x{85}, \x{2028} and \x{2029} do match \s) | |
855 | ||
856 | [a] You can mimic class subtraction using lookahead. | |
857 | For example, what UTR #18 might write as | |
858 | ||
859 | [{Greek}-[{UNASSIGNED}]] | |
860 | ||
861 | in Perl can be written as: | |
862 | ||
863 | (?!\p{Unassigned})\p{InGreekAndCoptic} | |
864 | (?=\p{Assigned})\p{InGreekAndCoptic} | |
865 | ||
866 | But in this particular example, you probably really want | |
867 | ||
868 | \p{GreekAndCoptic} | |
869 | ||
870 | which will match assigned characters known to be part of the Greek script. | |
871 | ||
872 | Also see the Unicode::Regex::Set module, it does implement the full | |
873 | UTR #18 grouping, intersection, union, and removal (subtraction) syntax. | |
874 | ||
875 | [b] See L</"User-Defined Character Properties">. | |
876 | ||
877 | =item * | |
878 | ||
879 | Level 2 - Extended Unicode Support | |
880 | ||
881 | 3.1 Surrogates - MISSING [11] | |
882 | 3.2 Canonical Equivalents - MISSING [12][13] | |
883 | 3.3 Locale-Independent Graphemes - MISSING [14] | |
884 | 3.4 Locale-Independent Words - MISSING [15] | |
885 | 3.5 Locale-Independent Loose Matches - MISSING [16] | |
886 | ||
887 | [11] Surrogates are solely a UTF-16 concept and Perl's internal | |
888 | representation is UTF-8. The Encode module does UTF-16, though. | |
889 | [12] see UTR#15 Unicode Normalization | |
890 | [13] have Unicode::Normalize but not integrated to regexes | |
891 | [14] have \X but at this level . should equal that | |
892 | [15] need three classes, not just \w and \W | |
893 | [16] see UTR#21 Case Mappings | |
894 | ||
895 | =item * | |
896 | ||
897 | Level 3 - Locale-Sensitive Support | |
898 | ||
899 | 4.1 Locale-Dependent Categories - MISSING | |
900 | 4.2 Locale-Dependent Graphemes - MISSING [16][17] | |
901 | 4.3 Locale-Dependent Words - MISSING | |
902 | 4.4 Locale-Dependent Loose Matches - MISSING | |
903 | 4.5 Locale-Dependent Ranges - MISSING | |
904 | ||
905 | [16] see UTR#10 Unicode Collation Algorithms | |
906 | [17] have Unicode::Collate but not integrated to regexes | |
907 | ||
908 | =back | |
909 | ||
910 | =head2 Unicode Encodings | |
911 | ||
912 | Unicode characters are assigned to I<code points>, which are abstract | |
913 | numbers. To use these numbers, various encodings are needed. | |
914 | ||
915 | =over 4 | |
916 | ||
917 | =item * | |
918 | ||
919 | UTF-8 | |
920 | ||
921 | UTF-8 is a variable-length (1 to 6 bytes, current character allocations | |
922 | require 4 bytes), byte-order independent encoding. For ASCII (and we | |
923 | really do mean 7-bit ASCII, not another 8-bit encoding), UTF-8 is | |
924 | transparent. | |
925 | ||
926 | The following table is from Unicode 3.2. | |
927 | ||
928 | Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte | |
929 | ||
930 | U+0000..U+007F 00..7F | |
931 | U+0080..U+07FF C2..DF 80..BF | |
932 | U+0800..U+0FFF E0 A0..BF 80..BF | |
933 | U+1000..U+CFFF E1..EC 80..BF 80..BF | |
934 | U+D000..U+D7FF ED 80..9F 80..BF | |
935 | U+D800..U+DFFF ******* ill-formed ******* | |
936 | U+E000..U+FFFF EE..EF 80..BF 80..BF | |
937 | U+10000..U+3FFFF F0 90..BF 80..BF 80..BF | |
938 | U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF | |
939 | U+100000..U+10FFFF F4 80..8F 80..BF 80..BF | |
940 | ||
941 | Note the C<A0..BF> in C<U+0800..U+0FFF>, the C<80..9F> in | |
942 | C<U+D000...U+D7FF>, the C<90..B>F in C<U+10000..U+3FFFF>, and the | |
943 | C<80...8F> in C<U+100000..U+10FFFF>. The "gaps" are caused by legal | |
944 | UTF-8 avoiding non-shortest encodings: it is technically possible to | |
945 | UTF-8-encode a single code point in different ways, but that is | |
946 | explicitly forbidden, and the shortest possible encoding should always | |
947 | be used. So that's what Perl does. | |
948 | ||
949 | Another way to look at it is via bits: | |
950 | ||
951 | Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte | |
952 | ||
953 | 0aaaaaaa 0aaaaaaa | |
954 | 00000bbbbbaaaaaa 110bbbbb 10aaaaaa | |
955 | ccccbbbbbbaaaaaa 1110cccc 10bbbbbb 10aaaaaa | |
956 | 00000dddccccccbbbbbbaaaaaa 11110ddd 10cccccc 10bbbbbb 10aaaaaa | |
957 | ||
958 | As you can see, the continuation bytes all begin with C<10>, and the | |
959 | leading bits of the start byte tell how many bytes the are in the | |
960 | encoded character. | |
961 | ||
962 | =item * | |
963 | ||
964 | UTF-EBCDIC | |
965 | ||
966 | Like UTF-8 but EBCDIC-safe, in the way that UTF-8 is ASCII-safe. | |
967 | ||
968 | =item * | |
969 | ||
970 | UTF-16, UTF-16BE, UTF-16LE, Surrogates, and BOMs (Byte Order Marks) | |
971 | ||
972 | The followings items are mostly for reference and general Unicode | |
973 | knowledge, Perl doesn't use these constructs internally. | |
974 | ||
975 | UTF-16 is a 2 or 4 byte encoding. The Unicode code points | |
976 | C<U+0000..U+FFFF> are stored in a single 16-bit unit, and the code | |
977 | points C<U+10000..U+10FFFF> in two 16-bit units. The latter case is | |
978 | using I<surrogates>, the first 16-bit unit being the I<high | |
979 | surrogate>, and the second being the I<low surrogate>. | |
980 | ||
981 | Surrogates are code points set aside to encode the C<U+10000..U+10FFFF> | |
982 | range of Unicode code points in pairs of 16-bit units. The I<high | |
983 | surrogates> are the range C<U+D800..U+DBFF>, and the I<low surrogates> | |
984 | are the range C<U+DC00..U+DFFF>. The surrogate encoding is | |
985 | ||
986 | $hi = ($uni - 0x10000) / 0x400 + 0xD800; | |
987 | $lo = ($uni - 0x10000) % 0x400 + 0xDC00; | |
988 | ||
989 | and the decoding is | |
990 | ||
991 | $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00); | |
992 | ||
993 | If you try to generate surrogates (for example by using chr()), you | |
994 | will get a warning if warnings are turned on, because those code | |
995 | points are not valid for a Unicode character. | |
996 | ||
997 | Because of the 16-bitness, UTF-16 is byte-order dependent. UTF-16 | |
998 | itself can be used for in-memory computations, but if storage or | |
999 | transfer is required either UTF-16BE (big-endian) or UTF-16LE | |
1000 | (little-endian) encodings must be chosen. | |
1001 | ||
1002 | This introduces another problem: what if you just know that your data | |
1003 | is UTF-16, but you don't know which endianness? Byte Order Marks, or | |
1004 | BOMs, are a solution to this. A special character has been reserved | |
1005 | in Unicode to function as a byte order marker: the character with the | |
1006 | code point C<U+FEFF> is the BOM. | |
1007 | ||
1008 | The trick is that if you read a BOM, you will know the byte order, | |
1009 | since if it was written on a big-endian platform, you will read the | |
1010 | bytes C<0xFE 0xFF>, but if it was written on a little-endian platform, | |
1011 | you will read the bytes C<0xFF 0xFE>. (And if the originating platform | |
1012 | was writing in UTF-8, you will read the bytes C<0xEF 0xBB 0xBF>.) | |
1013 | ||
1014 | The way this trick works is that the character with the code point | |
1015 | C<U+FFFE> is guaranteed not to be a valid Unicode character, so the | |
1016 | sequence of bytes C<0xFF 0xFE> is unambiguously "BOM, represented in | |
1017 | little-endian format" and cannot be C<U+FFFE>, represented in big-endian | |
1018 | format". | |
1019 | ||
1020 | =item * | |
1021 | ||
1022 | UTF-32, UTF-32BE, UTF-32LE | |
1023 | ||
1024 | The UTF-32 family is pretty much like the UTF-16 family, expect that | |
1025 | the units are 32-bit, and therefore the surrogate scheme is not | |
1026 | needed. The BOM signatures will be C<0x00 0x00 0xFE 0xFF> for BE and | |
1027 | C<0xFF 0xFE 0x00 0x00> for LE. | |
1028 | ||
1029 | =item * | |
1030 | ||
1031 | UCS-2, UCS-4 | |
1032 | ||
1033 | Encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit | |
1034 | encoding. Unlike UTF-16, UCS-2 is not extensible beyond C<U+FFFF>, | |
1035 | because it does not use surrogates. UCS-4 is a 32-bit encoding, | |
1036 | functionally identical to UTF-32. | |
1037 | ||
1038 | =item * | |
1039 | ||
1040 | UTF-7 | |
1041 | ||
1042 | A seven-bit safe (non-eight-bit) encoding, which is useful if the | |
1043 | transport or storage is not eight-bit safe. Defined by RFC 2152. | |
1044 | ||
1045 | =back | |
1046 | ||
1047 | =head2 Security Implications of Unicode | |
1048 | ||
1049 | =over 4 | |
1050 | ||
1051 | =item * | |
1052 | ||
1053 | Malformed UTF-8 | |
1054 | ||
1055 | Unfortunately, the specification of UTF-8 leaves some room for | |
1056 | interpretation of how many bytes of encoded output one should generate | |
1057 | from one input Unicode character. Strictly speaking, the shortest | |
1058 | possible sequence of UTF-8 bytes should be generated, | |
1059 | because otherwise there is potential for an input buffer overflow at | |
1060 | the receiving end of a UTF-8 connection. Perl always generates the | |
1061 | shortest length UTF-8, and with warnings on Perl will warn about | |
1062 | non-shortest length UTF-8 along with other malformations, such as the | |
1063 | surrogates, which are not real Unicode code points. | |
1064 | ||
1065 | =item * | |
1066 | ||
1067 | Regular expressions behave slightly differently between byte data and | |
1068 | character (Unicode) data. For example, the "word character" character | |
1069 | class C<\w> will work differently depending on if data is eight-bit bytes | |
1070 | or Unicode. | |
1071 | ||
1072 | In the first case, the set of C<\w> characters is either small--the | |
1073 | default set of alphabetic characters, digits, and the "_"--or, if you | |
1074 | are using a locale (see L<perllocale>), the C<\w> might contain a few | |
1075 | more letters according to your language and country. | |
1076 | ||
1077 | In the second case, the C<\w> set of characters is much, much larger. | |
1078 | Most importantly, even in the set of the first 256 characters, it will | |
1079 | probably match different characters: unlike most locales, which are | |
1080 | specific to a language and country pair, Unicode classifies all the | |
1081 | characters that are letters I<somewhere> as C<\w>. For example, your | |
1082 | locale might not think that LATIN SMALL LETTER ETH is a letter (unless | |
1083 | you happen to speak Icelandic), but Unicode does. | |
1084 | ||
1085 | As discussed elsewhere, Perl has one foot (two hooves?) planted in | |
1086 | each of two worlds: the old world of bytes and the new world of | |
1087 | characters, upgrading from bytes to characters when necessary. | |
1088 | If your legacy code does not explicitly use Unicode, no automatic | |
1089 | switch-over to characters should happen. Characters shouldn't get | |
1090 | downgraded to bytes, either. It is possible to accidentally mix bytes | |
1091 | and characters, however (see L<perluniintro>), in which case C<\w> in | |
1092 | regular expressions might start behaving differently. Review your | |
1093 | code. Use warnings and the C<strict> pragma. | |
1094 | ||
1095 | =back | |
1096 | ||
1097 | =head2 Unicode in Perl on EBCDIC | |
1098 | ||
1099 | The way Unicode is handled on EBCDIC platforms is still | |
1100 | experimental. On such platforms, references to UTF-8 encoding in this | |
1101 | document and elsewhere should be read as meaning the UTF-EBCDIC | |
1102 | specified in Unicode Technical Report 16, unless ASCII vs. EBCDIC issues | |
1103 | are specifically discussed. There is no C<utfebcdic> pragma or | |
1104 | ":utfebcdic" layer; rather, "utf8" and ":utf8" are reused to mean | |
1105 | the platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic> | |
1106 | for more discussion of the issues. | |
1107 | ||
1108 | =head2 Locales | |
1109 | ||
1110 | Usually locale settings and Unicode do not affect each other, but | |
1111 | there are a couple of exceptions: | |
1112 | ||
1113 | =over 4 | |
1114 | ||
1115 | =item * | |
1116 | ||
1117 | You can enable automatic UTF-8-ification of your standard file | |
1118 | handles, default C<open()> layer, and C<@ARGV> by using either | |
1119 | the C<-C> command line switch or the C<PERL_UNICODE> environment | |
1120 | variable, see L<perlrun> for the documentation of the C<-C> switch. | |
1121 | ||
1122 | =item * | |
1123 | ||
1124 | Perl tries really hard to work both with Unicode and the old | |
1125 | byte-oriented world. Most often this is nice, but sometimes Perl's | |
1126 | straddling of the proverbial fence causes problems. | |
1127 | ||
1128 | =back | |
1129 | ||
1130 | =head2 When Unicode Does Not Happen | |
1131 | ||
1132 | While Perl does have extensive ways to input and output in Unicode, | |
1133 | and few other 'entry points' like the @ARGV which can be interpreted | |
1134 | as Unicode (UTF-8), there still are many places where Unicode (in some | |
1135 | encoding or another) could be given as arguments or received as | |
1136 | results, or both, but it is not. | |
1137 | ||
1138 | The following are such interfaces. For all of these interfaces Perl | |
1139 | currently (as of 5.8.3) simply assumes byte strings both as arguments | |
1140 | and results, or UTF-8 strings if the C<encoding> pragma has been used. | |
1141 | ||
1142 | One reason why Perl does not attempt to resolve the role of Unicode in | |
1143 | this cases is that the answers are highly dependent on the operating | |
1144 | system and the file system(s). For example, whether filenames can be | |
1145 | in Unicode, and in exactly what kind of encoding, is not exactly a | |
1146 | portable concept. Similarly for the qx and system: how well will the | |
1147 | 'command line interface' (and which of them?) handle Unicode? | |
1148 | ||
1149 | =over 4 | |
1150 | ||
1151 | =item * | |
1152 | ||
1153 | chdir, chmod, chown, chroot, exec, link, lstat, mkdir, | |
1154 | rename, rmdir, stat, symlink, truncate, unlink, utime, -X | |
1155 | ||
1156 | =item * | |
1157 | ||
1158 | %ENV | |
1159 | ||
1160 | =item * | |
1161 | ||
1162 | glob (aka the <*>) | |
1163 | ||
1164 | =item * | |
1165 | ||
1166 | open, opendir, sysopen | |
1167 | ||
1168 | =item * | |
1169 | ||
1170 | qx (aka the backtick operator), system | |
1171 | ||
1172 | =item * | |
1173 | ||
1174 | readdir, readlink | |
1175 | ||
1176 | =back | |
1177 | ||
1178 | =head2 Forcing Unicode in Perl (Or Unforcing Unicode in Perl) | |
1179 | ||
1180 | Sometimes (see L</"When Unicode Does Not Happen">) there are | |
1181 | situations where you simply need to force Perl to believe that a byte | |
1182 | string is UTF-8, or vice versa. The low-level calls | |
1183 | utf8::upgrade($bytestring) and utf8::downgrade($utf8string) are | |
1184 | the answers. | |
1185 | ||
1186 | Do not use them without careful thought, though: Perl may easily get | |
1187 | very confused, angry, or even crash, if you suddenly change the 'nature' | |
1188 | of scalar like that. Especially careful you have to be if you use the | |
1189 | utf8::upgrade(): any random byte string is not valid UTF-8. | |
1190 | ||
1191 | =head2 Using Unicode in XS | |
1192 | ||
1193 | If you want to handle Perl Unicode in XS extensions, you may find the | |
1194 | following C APIs useful. See also L<perlguts/"Unicode Support"> for an | |
1195 | explanation about Unicode at the XS level, and L<perlapi> for the API | |
1196 | details. | |
1197 | ||
1198 | =over 4 | |
1199 | ||
1200 | =item * | |
1201 | ||
1202 | C<DO_UTF8(sv)> returns true if the C<UTF8> flag is on and the bytes | |
1203 | pragma is not in effect. C<SvUTF8(sv)> returns true is the C<UTF8> | |
1204 | flag is on; the bytes pragma is ignored. The C<UTF8> flag being on | |
1205 | does B<not> mean that there are any characters of code points greater | |
1206 | than 255 (or 127) in the scalar or that there are even any characters | |
1207 | in the scalar. What the C<UTF8> flag means is that the sequence of | |
1208 | octets in the representation of the scalar is the sequence of UTF-8 | |
1209 | encoded code points of the characters of a string. The C<UTF8> flag | |
1210 | being off means that each octet in this representation encodes a | |
1211 | single character with code point 0..255 within the string. Perl's | |
1212 | Unicode model is not to use UTF-8 until it is absolutely necessary. | |
1213 | ||
1214 | =item * | |
1215 | ||
1216 | C<uvuni_to_utf8(buf, chr)> writes a Unicode character code point into | |
1217 | a buffer encoding the code point as UTF-8, and returns a pointer | |
1218 | pointing after the UTF-8 bytes. | |
1219 | ||
1220 | =item * | |
1221 | ||
1222 | C<utf8_to_uvuni(buf, lenp)> reads UTF-8 encoded bytes from a buffer and | |
1223 | returns the Unicode character code point and, optionally, the length of | |
1224 | the UTF-8 byte sequence. | |
1225 | ||
1226 | =item * | |
1227 | ||
1228 | C<utf8_length(start, end)> returns the length of the UTF-8 encoded buffer | |
1229 | in characters. C<sv_len_utf8(sv)> returns the length of the UTF-8 encoded | |
1230 | scalar. | |
1231 | ||
1232 | =item * | |
1233 | ||
1234 | C<sv_utf8_upgrade(sv)> converts the string of the scalar to its UTF-8 | |
1235 | encoded form. C<sv_utf8_downgrade(sv)> does the opposite, if | |
1236 | possible. C<sv_utf8_encode(sv)> is like sv_utf8_upgrade except that | |
1237 | it does not set the C<UTF8> flag. C<sv_utf8_decode()> does the | |
1238 | opposite of C<sv_utf8_encode()>. Note that none of these are to be | |
1239 | used as general-purpose encoding or decoding interfaces: C<use Encode> | |
1240 | for that. C<sv_utf8_upgrade()> is affected by the encoding pragma | |
1241 | but C<sv_utf8_downgrade()> is not (since the encoding pragma is | |
1242 | designed to be a one-way street). | |
1243 | ||
1244 | =item * | |
1245 | ||
1246 | C<is_utf8_char(s)> returns true if the pointer points to a valid UTF-8 | |
1247 | character. | |
1248 | ||
1249 | =item * | |
1250 | ||
1251 | C<is_utf8_string(buf, len)> returns true if C<len> bytes of the buffer | |
1252 | are valid UTF-8. | |
1253 | ||
1254 | =item * | |
1255 | ||
1256 | C<UTF8SKIP(buf)> will return the number of bytes in the UTF-8 encoded | |
1257 | character in the buffer. C<UNISKIP(chr)> will return the number of bytes | |
1258 | required to UTF-8-encode the Unicode character code point. C<UTF8SKIP()> | |
1259 | is useful for example for iterating over the characters of a UTF-8 | |
1260 | encoded buffer; C<UNISKIP()> is useful, for example, in computing | |
1261 | the size required for a UTF-8 encoded buffer. | |
1262 | ||
1263 | =item * | |
1264 | ||
1265 | C<utf8_distance(a, b)> will tell the distance in characters between the | |
1266 | two pointers pointing to the same UTF-8 encoded buffer. | |
1267 | ||
1268 | =item * | |
1269 | ||
1270 | C<utf8_hop(s, off)> will return a pointer to an UTF-8 encoded buffer | |
1271 | that is C<off> (positive or negative) Unicode characters displaced | |
1272 | from the UTF-8 buffer C<s>. Be careful not to overstep the buffer: | |
1273 | C<utf8_hop()> will merrily run off the end or the beginning of the | |
1274 | buffer if told to do so. | |
1275 | ||
1276 | =item * | |
1277 | ||
1278 | C<pv_uni_display(dsv, spv, len, pvlim, flags)> and | |
1279 | C<sv_uni_display(dsv, ssv, pvlim, flags)> are useful for debugging the | |
1280 | output of Unicode strings and scalars. By default they are useful | |
1281 | only for debugging--they display B<all> characters as hexadecimal code | |
1282 | points--but with the flags C<UNI_DISPLAY_ISPRINT>, | |
1283 | C<UNI_DISPLAY_BACKSLASH>, and C<UNI_DISPLAY_QQ> you can make the | |
1284 | output more readable. | |
1285 | ||
1286 | =item * | |
1287 | ||
1288 | C<ibcmp_utf8(s1, pe1, u1, l1, u1, s2, pe2, l2, u2)> can be used to | |
1289 | compare two strings case-insensitively in Unicode. For case-sensitive | |
1290 | comparisons you can just use C<memEQ()> and C<memNE()> as usual. | |
1291 | ||
1292 | =back | |
1293 | ||
1294 | For more information, see L<perlapi>, and F<utf8.c> and F<utf8.h> | |
1295 | in the Perl source code distribution. | |
1296 | ||
1297 | =head1 BUGS | |
1298 | ||
1299 | =head2 Interaction with Locales | |
1300 | ||
1301 | Use of locales with Unicode data may lead to odd results. Currently, | |
1302 | Perl attempts to attach 8-bit locale info to characters in the range | |
1303 | 0..255, but this technique is demonstrably incorrect for locales that | |
1304 | use characters above that range when mapped into Unicode. Perl's | |
1305 | Unicode support will also tend to run slower. Use of locales with | |
1306 | Unicode is discouraged. | |
1307 | ||
1308 | =head2 Interaction with Extensions | |
1309 | ||
1310 | When Perl exchanges data with an extension, the extension should be | |
1311 | able to understand the UTF-8 flag and act accordingly. If the | |
1312 | extension doesn't know about the flag, it's likely that the extension | |
1313 | will return incorrectly-flagged data. | |
1314 | ||
1315 | So if you're working with Unicode data, consult the documentation of | |
1316 | every module you're using if there are any issues with Unicode data | |
1317 | exchange. If the documentation does not talk about Unicode at all, | |
1318 | suspect the worst and probably look at the source to learn how the | |
1319 | module is implemented. Modules written completely in Perl shouldn't | |
1320 | cause problems. Modules that directly or indirectly access code written | |
1321 | in other programming languages are at risk. | |
1322 | ||
1323 | For affected functions, the simple strategy to avoid data corruption is | |
1324 | to always make the encoding of the exchanged data explicit. Choose an | |
1325 | encoding that you know the extension can handle. Convert arguments passed | |
1326 | to the extensions to that encoding and convert results back from that | |
1327 | encoding. Write wrapper functions that do the conversions for you, so | |
1328 | you can later change the functions when the extension catches up. | |
1329 | ||
1330 | To provide an example, let's say the popular Foo::Bar::escape_html | |
1331 | function doesn't deal with Unicode data yet. The wrapper function | |
1332 | would convert the argument to raw UTF-8 and convert the result back to | |
1333 | Perl's internal representation like so: | |
1334 | ||
1335 | sub my_escape_html ($) { | |
1336 | my($what) = shift; | |
1337 | return unless defined $what; | |
1338 | Encode::decode_utf8(Foo::Bar::escape_html(Encode::encode_utf8($what))); | |
1339 | } | |
1340 | ||
1341 | Sometimes, when the extension does not convert data but just stores | |
1342 | and retrieves them, you will be in a position to use the otherwise | |
1343 | dangerous Encode::_utf8_on() function. Let's say the popular | |
1344 | C<Foo::Bar> extension, written in C, provides a C<param> method that | |
1345 | lets you store and retrieve data according to these prototypes: | |
1346 | ||
1347 | $self->param($name, $value); # set a scalar | |
1348 | $value = $self->param($name); # retrieve a scalar | |
1349 | ||
1350 | If it does not yet provide support for any encoding, one could write a | |
1351 | derived class with such a C<param> method: | |
1352 | ||
1353 | sub param { | |
1354 | my($self,$name,$value) = @_; | |
1355 | utf8::upgrade($name); # make sure it is UTF-8 encoded | |
1356 | if (defined $value) | |
1357 | utf8::upgrade($value); # make sure it is UTF-8 encoded | |
1358 | return $self->SUPER::param($name,$value); | |
1359 | } else { | |
1360 | my $ret = $self->SUPER::param($name); | |
1361 | Encode::_utf8_on($ret); # we know, it is UTF-8 encoded | |
1362 | return $ret; | |
1363 | } | |
1364 | } | |
1365 | ||
1366 | Some extensions provide filters on data entry/exit points, such as | |
1367 | DB_File::filter_store_key and family. Look out for such filters in | |
1368 | the documentation of your extensions, they can make the transition to | |
1369 | Unicode data much easier. | |
1370 | ||
1371 | =head2 Speed | |
1372 | ||
1373 | Some functions are slower when working on UTF-8 encoded strings than | |
1374 | on byte encoded strings. All functions that need to hop over | |
1375 | characters such as length(), substr() or index(), or matching regular | |
1376 | expressions can work B<much> faster when the underlying data are | |
1377 | byte-encoded. | |
1378 | ||
1379 | In Perl 5.8.0 the slowness was often quite spectacular; in Perl 5.8.1 | |
1380 | a caching scheme was introduced which will hopefully make the slowness | |
1381 | somewhat less spectacular, at least for some operations. In general, | |
1382 | operations with UTF-8 encoded strings are still slower. As an example, | |
1383 | the Unicode properties (character classes) like C<\p{Nd}> are known to | |
1384 | be quite a bit slower (5-20 times) than their simpler counterparts | |
1385 | like C<\d> (then again, there 268 Unicode characters matching C<Nd> | |
1386 | compared with the 10 ASCII characters matching C<d>). | |
1387 | ||
1388 | =head2 Porting code from perl-5.6.X | |
1389 | ||
1390 | Perl 5.8 has a different Unicode model from 5.6. In 5.6 the programmer | |
1391 | was required to use the C<utf8> pragma to declare that a given scope | |
1392 | expected to deal with Unicode data and had to make sure that only | |
1393 | Unicode data were reaching that scope. If you have code that is | |
1394 | working with 5.6, you will need some of the following adjustments to | |
1395 | your code. The examples are written such that the code will continue | |
1396 | to work under 5.6, so you should be safe to try them out. | |
1397 | ||
1398 | =over 4 | |
1399 | ||
1400 | =item * | |
1401 | ||
1402 | A filehandle that should read or write UTF-8 | |
1403 | ||
1404 | if ($] > 5.007) { | |
1405 | binmode $fh, ":utf8"; | |
1406 | } | |
1407 | ||
1408 | =item * | |
1409 | ||
1410 | A scalar that is going to be passed to some extension | |
1411 | ||
1412 | Be it Compress::Zlib, Apache::Request or any extension that has no | |
1413 | mention of Unicode in the manpage, you need to make sure that the | |
1414 | UTF-8 flag is stripped off. Note that at the time of this writing | |
1415 | (October 2002) the mentioned modules are not UTF-8-aware. Please | |
1416 | check the documentation to verify if this is still true. | |
1417 | ||
1418 | if ($] > 5.007) { | |
1419 | require Encode; | |
1420 | $val = Encode::encode_utf8($val); # make octets | |
1421 | } | |
1422 | ||
1423 | =item * | |
1424 | ||
1425 | A scalar we got back from an extension | |
1426 | ||
1427 | If you believe the scalar comes back as UTF-8, you will most likely | |
1428 | want the UTF-8 flag restored: | |
1429 | ||
1430 | if ($] > 5.007) { | |
1431 | require Encode; | |
1432 | $val = Encode::decode_utf8($val); | |
1433 | } | |
1434 | ||
1435 | =item * | |
1436 | ||
1437 | Same thing, if you are really sure it is UTF-8 | |
1438 | ||
1439 | if ($] > 5.007) { | |
1440 | require Encode; | |
1441 | Encode::_utf8_on($val); | |
1442 | } | |
1443 | ||
1444 | =item * | |
1445 | ||
1446 | A wrapper for fetchrow_array and fetchrow_hashref | |
1447 | ||
1448 | When the database contains only UTF-8, a wrapper function or method is | |
1449 | a convenient way to replace all your fetchrow_array and | |
1450 | fetchrow_hashref calls. A wrapper function will also make it easier to | |
1451 | adapt to future enhancements in your database driver. Note that at the | |
1452 | time of this writing (October 2002), the DBI has no standardized way | |
1453 | to deal with UTF-8 data. Please check the documentation to verify if | |
1454 | that is still true. | |
1455 | ||
1456 | sub fetchrow { | |
1457 | my($self, $sth, $what) = @_; # $what is one of fetchrow_{array,hashref} | |
1458 | if ($] < 5.007) { | |
1459 | return $sth->$what; | |
1460 | } else { | |
1461 | require Encode; | |
1462 | if (wantarray) { | |
1463 | my @arr = $sth->$what; | |
1464 | for (@arr) { | |
1465 | defined && /[^\000-\177]/ && Encode::_utf8_on($_); | |
1466 | } | |
1467 | return @arr; | |
1468 | } else { | |
1469 | my $ret = $sth->$what; | |
1470 | if (ref $ret) { | |
1471 | for my $k (keys %$ret) { | |
1472 | defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret->{$k}; | |
1473 | } | |
1474 | return $ret; | |
1475 | } else { | |
1476 | defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret; | |
1477 | return $ret; | |
1478 | } | |
1479 | } | |
1480 | } | |
1481 | } | |
1482 | ||
1483 | ||
1484 | =item * | |
1485 | ||
1486 | A large scalar that you know can only contain ASCII | |
1487 | ||
1488 | Scalars that contain only ASCII and are marked as UTF-8 are sometimes | |
1489 | a drag to your program. If you recognize such a situation, just remove | |
1490 | the UTF-8 flag: | |
1491 | ||
1492 | utf8::downgrade($val) if $] > 5.007; | |
1493 | ||
1494 | =back | |
1495 | ||
1496 | =head1 SEE ALSO | |
1497 | ||
1498 | L<perluniintro>, L<encoding>, L<Encode>, L<open>, L<utf8>, L<bytes>, | |
1499 | L<perlretut>, L<perlvar/"${^UNICODE}"> | |
1500 | ||
1501 | =cut |