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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 | =back | |
46 | ||
47 | =head2 Byte and Character Semantics | |
48 | ||
49 | Beginning with version 5.6, Perl uses logically-wide characters to | |
50 | represent strings internally. | |
51 | ||
52 | In future, Perl-level operations will be expected to work with | |
53 | characters rather than bytes. | |
54 | ||
55 | However, as an interim compatibility measure, Perl aims to | |
56 | provide a safe migration path from byte semantics to character | |
57 | semantics for programs. For operations where Perl can unambiguously | |
58 | decide that the input data are characters, Perl switches to | |
59 | character semantics. For operations where this determination cannot | |
60 | be made without additional information from the user, Perl decides in | |
61 | favor of compatibility and chooses to use byte semantics. | |
62 | ||
63 | This behavior preserves compatibility with earlier versions of Perl, | |
64 | which allowed byte semantics in Perl operations only if | |
65 | none of the program's inputs were marked as being as source of Unicode | |
66 | character data. Such data may come from filehandles, from calls to | |
67 | external programs, from information provided by the system (such as %ENV), | |
68 | or from literals and constants in the source text. | |
69 | ||
70 | On Windows platforms, if the C<-C> command line switch is used or the | |
71 | ${^WIDE_SYSTEM_CALLS} global flag is set to C<1>, all system calls | |
72 | will use the corresponding wide-character APIs. This feature is | |
73 | available only on Windows to conform to the API standard already | |
74 | established for that platform--and there are very few non-Windows | |
75 | platforms that have Unicode-aware APIs. | |
76 | ||
77 | The C<bytes> pragma will always, regardless of platform, force byte | |
78 | semantics in a particular lexical scope. See L<bytes>. | |
79 | ||
80 | The C<utf8> pragma is primarily a compatibility device that enables | |
81 | recognition of UTF-(8|EBCDIC) in literals encountered by the parser. | |
82 | Note that this pragma is only required while Perl defaults to byte | |
83 | semantics; when character semantics become the default, this pragma | |
84 | may become a no-op. See L<utf8>. | |
85 | ||
86 | Unless explicitly stated, Perl operators use character semantics | |
87 | for Unicode data and byte semantics for non-Unicode data. | |
88 | The decision to use character semantics is made transparently. If | |
89 | input data comes from a Unicode source--for example, if a character | |
90 | encoding layer is added to a filehandle or a literal Unicode | |
91 | string constant appears in a program--character semantics apply. | |
92 | Otherwise, byte semantics are in effect. The C<bytes> pragma should | |
93 | be used to force byte semantics on Unicode data. | |
94 | ||
95 | If strings operating under byte semantics and strings with Unicode | |
96 | character data are concatenated, the new string will be upgraded to | |
97 | I<ISO 8859-1 (Latin-1)>, even if the old Unicode string used EBCDIC. | |
98 | This translation is done without regard to the system's native 8-bit | |
99 | encoding, so to change this for systems with non-Latin-1 and | |
100 | non-EBCDIC native encodings use the C<encoding> pragma. See | |
101 | L<encoding>. | |
102 | ||
103 | Under character semantics, many operations that formerly operated on | |
104 | bytes now operate on characters. A character in Perl is | |
105 | logically just a number ranging from 0 to 2**31 or so. Larger | |
106 | characters may encode into longer sequences of bytes internally, but | |
107 | this internal detail is mostly hidden for Perl code. | |
108 | See L<perluniintro> for more. | |
109 | ||
110 | =head2 Effects of Character Semantics | |
111 | ||
112 | Character semantics have the following effects: | |
113 | ||
114 | =over 4 | |
115 | ||
116 | =item * | |
117 | ||
118 | Strings--including hash keys--and regular expression patterns may | |
119 | contain characters that have an ordinal value larger than 255. | |
120 | ||
121 | If you use a Unicode editor to edit your program, Unicode characters | |
122 | may occur directly within the literal strings in one of the various | |
123 | Unicode encodings (UTF-8, UTF-EBCDIC, UCS-2, etc.), but will be recognized | |
124 | as such and converted to Perl's internal representation only if the | |
125 | appropriate L<encoding> is specified. | |
126 | ||
127 | Unicode characters can also be added to a string by using the | |
128 | C<\x{...}> notation. The Unicode code for the desired character, in | |
129 | hexadecimal, should be placed in the braces. For instance, a smiley | |
130 | face is C<\x{263A}>. This encoding scheme only works for characters | |
131 | with a code of 0x100 or above. | |
132 | ||
133 | Additionally, if you | |
134 | ||
135 | use charnames ':full'; | |
136 | ||
137 | you can use the C<\N{...}> notation and put the official Unicode | |
138 | character name within the braces, such as C<\N{WHITE SMILING FACE}>. | |
139 | ||
140 | ||
141 | =item * | |
142 | ||
143 | If an appropriate L<encoding> is specified, identifiers within the | |
144 | Perl script may contain Unicode alphanumeric characters, including | |
145 | ideographs. Perl does not currently attempt to canonicalize variable | |
146 | names. | |
147 | ||
148 | =item * | |
149 | ||
150 | Regular expressions match characters instead of bytes. "." matches | |
151 | a character instead of a byte. The C<\C> pattern is provided to force | |
152 | a match a single byte--a C<char> in C, hence C<\C>. | |
153 | ||
154 | =item * | |
155 | ||
156 | Character classes in regular expressions match characters instead of | |
157 | bytes and match against the character properties specified in the | |
158 | Unicode properties database. C<\w> can be used to match a Japanese | |
159 | ideograph, for instance. | |
160 | ||
161 | =item * | |
162 | ||
163 | Named Unicode properties, scripts, and block ranges may be used like | |
164 | character classes via the C<\p{}> "matches property" construct and | |
165 | the C<\P{}> negation, "doesn't match property". | |
166 | ||
167 | For instance, C<\p{Lu}> matches any character with the Unicode "Lu" | |
168 | (Letter, uppercase) property, while C<\p{M}> matches any character | |
169 | with an "M" (mark--accents and such) property. Brackets are not | |
170 | required for single letter properties, so C<\p{M}> is equivalent to | |
171 | C<\pM>. Many predefined properties are available, such as | |
172 | C<\p{Mirrored}> and C<\p{Tibetan}>. | |
173 | ||
174 | The official Unicode script and block names have spaces and dashes as | |
175 | separators, but for convenience you can use dashes, spaces, or | |
176 | underbars, and case is unimportant. It is recommended, however, that | |
177 | for consistency you use the following naming: the official Unicode | |
178 | script, property, or block name (see below for the additional rules | |
179 | that apply to block names) with whitespace and dashes removed, and the | |
180 | words "uppercase-first-lowercase-rest". C<Latin-1 Supplement> thus | |
181 | becomes C<Latin1Supplement>. | |
182 | ||
183 | You can also use negation in both C<\p{}> and C<\P{}> by introducing a caret | |
184 | (^) between the first brace and the property name: C<\p{^Tamil}> is | |
185 | equal to C<\P{Tamil}>. | |
186 | ||
187 | Here are the basic Unicode General Category properties, followed by their | |
188 | long form. You can use either; C<\p{Lu}> and C<\p{LowercaseLetter}>, | |
189 | for instance, are identical. | |
190 | ||
191 | Short Long | |
192 | ||
193 | L Letter | |
194 | Lu UppercaseLetter | |
195 | Ll LowercaseLetter | |
196 | Lt TitlecaseLetter | |
197 | Lm ModifierLetter | |
198 | Lo OtherLetter | |
199 | ||
200 | M Mark | |
201 | Mn NonspacingMark | |
202 | Mc SpacingMark | |
203 | Me EnclosingMark | |
204 | ||
205 | N Number | |
206 | Nd DecimalNumber | |
207 | Nl LetterNumber | |
208 | No OtherNumber | |
209 | ||
210 | P Punctuation | |
211 | Pc ConnectorPunctuation | |
212 | Pd DashPunctuation | |
213 | Ps OpenPunctuation | |
214 | Pe ClosePunctuation | |
215 | Pi InitialPunctuation | |
216 | (may behave like Ps or Pe depending on usage) | |
217 | Pf FinalPunctuation | |
218 | (may behave like Ps or Pe depending on usage) | |
219 | Po OtherPunctuation | |
220 | ||
221 | S Symbol | |
222 | Sm MathSymbol | |
223 | Sc CurrencySymbol | |
224 | Sk ModifierSymbol | |
225 | So OtherSymbol | |
226 | ||
227 | Z Separator | |
228 | Zs SpaceSeparator | |
229 | Zl LineSeparator | |
230 | Zp ParagraphSeparator | |
231 | ||
232 | C Other | |
233 | Cc Control | |
234 | Cf Format | |
235 | Cs Surrogate (not usable) | |
236 | Co PrivateUse | |
237 | Cn Unassigned | |
238 | ||
239 | Single-letter properties match all characters in any of the | |
240 | two-letter sub-properties starting with the same letter. | |
241 | C<L&> is a special case, which is an alias for C<Ll>, C<Lu>, and C<Lt>. | |
242 | ||
243 | Because Perl hides the need for the user to understand the internal | |
244 | representation of Unicode characters, there is no need to implement | |
245 | the somewhat messy concept of surrogates. C<Cs> is therefore not | |
246 | supported. | |
247 | ||
248 | Because scripts differ in their directionality--Hebrew is | |
249 | written right to left, for example--Unicode supplies these properties: | |
250 | ||
251 | Property Meaning | |
252 | ||
253 | BidiL Left-to-Right | |
254 | BidiLRE Left-to-Right Embedding | |
255 | BidiLRO Left-to-Right Override | |
256 | BidiR Right-to-Left | |
257 | BidiAL Right-to-Left Arabic | |
258 | BidiRLE Right-to-Left Embedding | |
259 | BidiRLO Right-to-Left Override | |
260 | BidiPDF Pop Directional Format | |
261 | BidiEN European Number | |
262 | BidiES European Number Separator | |
263 | BidiET European Number Terminator | |
264 | BidiAN Arabic Number | |
265 | BidiCS Common Number Separator | |
266 | BidiNSM Non-Spacing Mark | |
267 | BidiBN Boundary Neutral | |
268 | BidiB Paragraph Separator | |
269 | BidiS Segment Separator | |
270 | BidiWS Whitespace | |
271 | BidiON Other Neutrals | |
272 | ||
273 | For example, C<\p{BidiR}> matches characters that are normally | |
274 | written right to left. | |
275 | ||
276 | =back | |
277 | ||
278 | =head2 Scripts | |
279 | ||
280 | The script names which can be used by C<\p{...}> and C<\P{...}>, | |
281 | such as in C<\p{Latin}> or C<\p{Cyrillic}>, are as follows: | |
282 | ||
283 | Arabic | |
284 | Armenian | |
285 | Bengali | |
286 | Bopomofo | |
287 | Buhid | |
288 | CanadianAboriginal | |
289 | Cherokee | |
290 | Cyrillic | |
291 | Deseret | |
292 | Devanagari | |
293 | Ethiopic | |
294 | Georgian | |
295 | Gothic | |
296 | Greek | |
297 | Gujarati | |
298 | Gurmukhi | |
299 | Han | |
300 | Hangul | |
301 | Hanunoo | |
302 | Hebrew | |
303 | Hiragana | |
304 | Inherited | |
305 | Kannada | |
306 | Katakana | |
307 | Khmer | |
308 | Lao | |
309 | Latin | |
310 | Malayalam | |
311 | Mongolian | |
312 | Myanmar | |
313 | Ogham | |
314 | OldItalic | |
315 | Oriya | |
316 | Runic | |
317 | Sinhala | |
318 | Syriac | |
319 | Tagalog | |
320 | Tagbanwa | |
321 | Tamil | |
322 | Telugu | |
323 | Thaana | |
324 | Thai | |
325 | Tibetan | |
326 | Yi | |
327 | ||
328 | Extended property classes can supplement the basic | |
329 | properties, defined by the F<PropList> Unicode database: | |
330 | ||
331 | ASCIIHexDigit | |
332 | BidiControl | |
333 | Dash | |
334 | Deprecated | |
335 | Diacritic | |
336 | Extender | |
337 | GraphemeLink | |
338 | HexDigit | |
339 | Hyphen | |
340 | Ideographic | |
341 | IDSBinaryOperator | |
342 | IDSTrinaryOperator | |
343 | JoinControl | |
344 | LogicalOrderException | |
345 | NoncharacterCodePoint | |
346 | OtherAlphabetic | |
347 | OtherDefaultIgnorableCodePoint | |
348 | OtherGraphemeExtend | |
349 | OtherLowercase | |
350 | OtherMath | |
351 | OtherUppercase | |
352 | QuotationMark | |
353 | Radical | |
354 | SoftDotted | |
355 | TerminalPunctuation | |
356 | UnifiedIdeograph | |
357 | WhiteSpace | |
358 | ||
359 | and there are further derived properties: | |
360 | ||
361 | Alphabetic Lu + Ll + Lt + Lm + Lo + OtherAlphabetic | |
362 | Lowercase Ll + OtherLowercase | |
363 | Uppercase Lu + OtherUppercase | |
364 | Math Sm + OtherMath | |
365 | ||
366 | ID_Start Lu + Ll + Lt + Lm + Lo + Nl | |
367 | ID_Continue ID_Start + Mn + Mc + Nd + Pc | |
368 | ||
369 | Any Any character | |
370 | Assigned Any non-Cn character (i.e. synonym for \P{Cn}) | |
371 | Unassigned Synonym for \p{Cn} | |
372 | Common Any character (or unassigned code point) | |
373 | not explicitly assigned to a script | |
374 | ||
375 | For backward compatibility (with Perl 5.6), all properties mentioned | |
376 | so far may have C<Is> prepended to their name, so C<\P{IsLu}>, for | |
377 | example, is equal to C<\P{Lu}>. | |
378 | ||
379 | =head2 Blocks | |
380 | ||
381 | In addition to B<scripts>, Unicode also defines B<blocks> of | |
382 | characters. The difference between scripts and blocks is that the | |
383 | concept of scripts is closer to natural languages, while the concept | |
384 | of blocks is more of an artificial grouping based on groups of 256 | |
385 | Unicode characters. For example, the C<Latin> script contains letters | |
386 | from many blocks but does not contain all the characters from those | |
387 | blocks. It does not, for example, contain digits, because digits are | |
388 | shared across many scripts. Digits and similar groups, like | |
389 | punctuation, are in a category called C<Common>. | |
390 | ||
391 | For more about scripts, see the UTR #24: | |
392 | ||
393 | http://www.unicode.org/unicode/reports/tr24/ | |
394 | ||
395 | For more about blocks, see: | |
396 | ||
397 | http://www.unicode.org/Public/UNIDATA/Blocks.txt | |
398 | ||
399 | Block names are given with the C<In> prefix. For example, the | |
400 | Katakana block is referenced via C<\p{InKatakana}>. The C<In> | |
401 | prefix may be omitted if there is no naming conflict with a script | |
402 | or any other property, but it is recommended that C<In> always be used | |
403 | for block tests to avoid confusion. | |
404 | ||
405 | These block names are supported: | |
406 | ||
407 | InAlphabeticPresentationForms | |
408 | InArabic | |
409 | InArabicPresentationFormsA | |
410 | InArabicPresentationFormsB | |
411 | InArmenian | |
412 | InArrows | |
413 | InBasicLatin | |
414 | InBengali | |
415 | InBlockElements | |
416 | InBopomofo | |
417 | InBopomofoExtended | |
418 | InBoxDrawing | |
419 | InBraillePatterns | |
420 | InBuhid | |
421 | InByzantineMusicalSymbols | |
422 | InCJKCompatibility | |
423 | InCJKCompatibilityForms | |
424 | InCJKCompatibilityIdeographs | |
425 | InCJKCompatibilityIdeographsSupplement | |
426 | InCJKRadicalsSupplement | |
427 | InCJKSymbolsAndPunctuation | |
428 | InCJKUnifiedIdeographs | |
429 | InCJKUnifiedIdeographsExtensionA | |
430 | InCJKUnifiedIdeographsExtensionB | |
431 | InCherokee | |
432 | InCombiningDiacriticalMarks | |
433 | InCombiningDiacriticalMarksforSymbols | |
434 | InCombiningHalfMarks | |
435 | InControlPictures | |
436 | InCurrencySymbols | |
437 | InCyrillic | |
438 | InCyrillicSupplementary | |
439 | InDeseret | |
440 | InDevanagari | |
441 | InDingbats | |
442 | InEnclosedAlphanumerics | |
443 | InEnclosedCJKLettersAndMonths | |
444 | InEthiopic | |
445 | InGeneralPunctuation | |
446 | InGeometricShapes | |
447 | InGeorgian | |
448 | InGothic | |
449 | InGreekExtended | |
450 | InGreekAndCoptic | |
451 | InGujarati | |
452 | InGurmukhi | |
453 | InHalfwidthAndFullwidthForms | |
454 | InHangulCompatibilityJamo | |
455 | InHangulJamo | |
456 | InHangulSyllables | |
457 | InHanunoo | |
458 | InHebrew | |
459 | InHighPrivateUseSurrogates | |
460 | InHighSurrogates | |
461 | InHiragana | |
462 | InIPAExtensions | |
463 | InIdeographicDescriptionCharacters | |
464 | InKanbun | |
465 | InKangxiRadicals | |
466 | InKannada | |
467 | InKatakana | |
468 | InKatakanaPhoneticExtensions | |
469 | InKhmer | |
470 | InLao | |
471 | InLatin1Supplement | |
472 | InLatinExtendedA | |
473 | InLatinExtendedAdditional | |
474 | InLatinExtendedB | |
475 | InLetterlikeSymbols | |
476 | InLowSurrogates | |
477 | InMalayalam | |
478 | InMathematicalAlphanumericSymbols | |
479 | InMathematicalOperators | |
480 | InMiscellaneousMathematicalSymbolsA | |
481 | InMiscellaneousMathematicalSymbolsB | |
482 | InMiscellaneousSymbols | |
483 | InMiscellaneousTechnical | |
484 | InMongolian | |
485 | InMusicalSymbols | |
486 | InMyanmar | |
487 | InNumberForms | |
488 | InOgham | |
489 | InOldItalic | |
490 | InOpticalCharacterRecognition | |
491 | InOriya | |
492 | InPrivateUseArea | |
493 | InRunic | |
494 | InSinhala | |
495 | InSmallFormVariants | |
496 | InSpacingModifierLetters | |
497 | InSpecials | |
498 | InSuperscriptsAndSubscripts | |
499 | InSupplementalArrowsA | |
500 | InSupplementalArrowsB | |
501 | InSupplementalMathematicalOperators | |
502 | InSupplementaryPrivateUseAreaA | |
503 | InSupplementaryPrivateUseAreaB | |
504 | InSyriac | |
505 | InTagalog | |
506 | InTagbanwa | |
507 | InTags | |
508 | InTamil | |
509 | InTelugu | |
510 | InThaana | |
511 | InThai | |
512 | InTibetan | |
513 | InUnifiedCanadianAboriginalSyllabics | |
514 | InVariationSelectors | |
515 | InYiRadicals | |
516 | InYiSyllables | |
517 | ||
518 | =over 4 | |
519 | ||
520 | =item * | |
521 | ||
522 | The special pattern C<\X> matches any extended Unicode | |
523 | sequence--"a combining character sequence" in Standardese--where the | |
524 | first character is a base character and subsequent characters are mark | |
525 | characters that apply to the base character. C<\X> is equivalent to | |
526 | C<(?:\PM\pM*)>. | |
527 | ||
528 | =item * | |
529 | ||
530 | The C<tr///> operator translates characters instead of bytes. Note | |
531 | that the C<tr///CU> functionality has been removed. For similar | |
532 | functionality see pack('U0', ...) and pack('C0', ...). | |
533 | ||
534 | =item * | |
535 | ||
536 | Case translation operators use the Unicode case translation tables | |
537 | when character input is provided. Note that C<uc()>, or C<\U> in | |
538 | interpolated strings, translates to uppercase, while C<ucfirst>, | |
539 | or C<\u> in interpolated strings, translates to titlecase in languages | |
540 | that make the distinction. | |
541 | ||
542 | =item * | |
543 | ||
544 | Most operators that deal with positions or lengths in a string will | |
545 | automatically switch to using character positions, including | |
546 | C<chop()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>, | |
547 | C<sprintf()>, C<write()>, and C<length()>. Operators that | |
548 | specifically do not switch include C<vec()>, C<pack()>, and | |
549 | C<unpack()>. Operators that really don't care include C<chomp()>, | |
550 | operators that treats strings as a bucket of bits such as C<sort()>, | |
551 | and operators dealing with filenames. | |
552 | ||
553 | =item * | |
554 | ||
555 | The C<pack()>/C<unpack()> letters C<c> and C<C> do I<not> change, | |
556 | since they are often used for byte-oriented formats. Again, think | |
557 | C<char> in the C language. | |
558 | ||
559 | There is a new C<U> specifier that converts between Unicode characters | |
560 | and code points. | |
561 | ||
562 | =item * | |
563 | ||
564 | The C<chr()> and C<ord()> functions work on characters, similar to | |
565 | C<pack("U")> and C<unpack("U")>, I<not> C<pack("C")> and | |
566 | C<unpack("C")>. C<pack("C")> and C<unpack("C")> are methods for | |
567 | emulating byte-oriented C<chr()> and C<ord()> on Unicode strings. | |
568 | While these methods reveal the internal encoding of Unicode strings, | |
569 | that is not something one normally needs to care about at all. | |
570 | ||
571 | =item * | |
572 | ||
573 | The bit string operators, C<& | ^ ~>, can operate on character data. | |
574 | However, for backward compatibility, such as when using bit string | |
575 | operations when characters are all less than 256 in ordinal value, one | |
576 | should not use C<~> (the bit complement) with characters of both | |
577 | values less than 256 and values greater than 256. Most importantly, | |
578 | DeMorgan's laws (C<~($x|$y) eq ~$x&~$y> and C<~($x&$y) eq ~$x|~$y>) | |
579 | will not hold. The reason for this mathematical I<faux pas> is that | |
580 | the complement cannot return B<both> the 8-bit (byte-wide) bit | |
581 | complement B<and> the full character-wide bit complement. | |
582 | ||
583 | =item * | |
584 | ||
585 | lc(), uc(), lcfirst(), and ucfirst() work for the following cases: | |
586 | ||
587 | =over 8 | |
588 | ||
589 | =item * | |
590 | ||
591 | the case mapping is from a single Unicode character to another | |
592 | single Unicode character, or | |
593 | ||
594 | =item * | |
595 | ||
596 | the case mapping is from a single Unicode character to more | |
597 | than one Unicode character. | |
598 | ||
599 | =back | |
600 | ||
601 | The following cases do not yet work: | |
602 | ||
603 | =over 8 | |
604 | ||
605 | =item * | |
606 | ||
607 | the "final sigma" (Greek), and | |
608 | ||
609 | =item * | |
610 | ||
611 | anything to with locales (Lithuanian, Turkish, Azeri). | |
612 | ||
613 | =back | |
614 | ||
615 | See the Unicode Technical Report #21, Case Mappings, for more details. | |
616 | ||
617 | =item * | |
618 | ||
619 | And finally, C<scalar reverse()> reverses by character rather than by byte. | |
620 | ||
621 | =back | |
622 | ||
623 | =head2 User-Defined Character Properties | |
624 | ||
625 | You can define your own character properties by defining subroutines | |
626 | whose names begin with "In" or "Is". The subroutines must be | |
627 | visible in the package that uses the properties. The user-defined | |
628 | properties can be used in the regular expression C<\p> and C<\P> | |
629 | constructs. | |
630 | ||
631 | The subroutines must return a specially-formatted string, with one | |
632 | or more newline-separated lines. Each line must be one of the following: | |
633 | ||
634 | =over 4 | |
635 | ||
636 | =item * | |
637 | ||
638 | Two hexadecimal numbers separated by horizontal whitespace (space or | |
639 | tabular characters) denoting a range of Unicode code points to include. | |
640 | ||
641 | =item * | |
642 | ||
643 | Something to include, prefixed by "+": a built-in character | |
644 | property (prefixed by "utf8::"), to represent all the characters in that | |
645 | property; two hexadecimal code points for a range; or a single | |
646 | hexadecimal code point. | |
647 | ||
648 | =item * | |
649 | ||
650 | Something to exclude, prefixed by "-": an existing character | |
651 | property (prefixed by "utf8::"), for all the characters in that | |
652 | property; two hexadecimal code points for a range; or a single | |
653 | hexadecimal code point. | |
654 | ||
655 | =item * | |
656 | ||
657 | Something to negate, prefixed "!": an existing character | |
658 | property (prefixed by "utf8::") for all the characters except the | |
659 | characters in the property; two hexadecimal code points for a range; | |
660 | or a single hexadecimal code point. | |
661 | ||
662 | =back | |
663 | ||
664 | For example, to define a property that covers both the Japanese | |
665 | syllabaries (hiragana and katakana), you can define | |
666 | ||
667 | sub InKana { | |
668 | return <<END; | |
669 | 3040\t309F | |
670 | 30A0\t30FF | |
671 | END | |
672 | } | |
673 | ||
674 | Imagine that the here-doc end marker is at the beginning of the line. | |
675 | Now you can use C<\p{InKana}> and C<\P{InKana}>. | |
676 | ||
677 | You could also have used the existing block property names: | |
678 | ||
679 | sub InKana { | |
680 | return <<'END'; | |
681 | +utf8::InHiragana | |
682 | +utf8::InKatakana | |
683 | END | |
684 | } | |
685 | ||
686 | Suppose you wanted to match only the allocated characters, | |
687 | not the raw block ranges: in other words, you want to remove | |
688 | the non-characters: | |
689 | ||
690 | sub InKana { | |
691 | return <<'END'; | |
692 | +utf8::InHiragana | |
693 | +utf8::InKatakana | |
694 | -utf8::IsCn | |
695 | END | |
696 | } | |
697 | ||
698 | The negation is useful for defining (surprise!) negated classes. | |
699 | ||
700 | sub InNotKana { | |
701 | return <<'END'; | |
702 | !utf8::InHiragana | |
703 | -utf8::InKatakana | |
704 | +utf8::IsCn | |
705 | END | |
706 | } | |
707 | ||
708 | =head2 Character Encodings for Input and Output | |
709 | ||
710 | See L<Encode>. | |
711 | ||
712 | =head2 Unicode Regular Expression Support Level | |
713 | ||
714 | The following list of Unicode support for regular expressions describes | |
715 | all the features currently supported. The references to "Level N" | |
716 | and the section numbers refer to the Unicode Technical Report 18, | |
717 | "Unicode Regular Expression Guidelines". | |
718 | ||
719 | =over 4 | |
720 | ||
721 | =item * | |
722 | ||
723 | Level 1 - Basic Unicode Support | |
724 | ||
725 | 2.1 Hex Notation - done [1] | |
726 | Named Notation - done [2] | |
727 | 2.2 Categories - done [3][4] | |
728 | 2.3 Subtraction - MISSING [5][6] | |
729 | 2.4 Simple Word Boundaries - done [7] | |
730 | 2.5 Simple Loose Matches - done [8] | |
731 | 2.6 End of Line - MISSING [9][10] | |
732 | ||
733 | [ 1] \x{...} | |
734 | [ 2] \N{...} | |
735 | [ 3] . \p{...} \P{...} | |
736 | [ 4] now scripts (see UTR#24 Script Names) in addition to blocks | |
737 | [ 5] have negation | |
738 | [ 6] can use regular expression look-ahead [a] | |
739 | or user-defined character properties [b] to emulate subtraction | |
740 | [ 7] include Letters in word characters | |
741 | [ 8] note that Perl does Full case-folding in matching, not Simple: | |
742 | for example U+1F88 is equivalent with U+1F000 U+03B9, | |
743 | not with 1F80. This difference matters for certain Greek | |
744 | capital letters with certain modifiers: the Full case-folding | |
745 | decomposes the letter, while the Simple case-folding would map | |
746 | it to a single character. | |
747 | [ 9] see UTR#13 Unicode Newline Guidelines | |
748 | [10] should do ^ and $ also on \x{85}, \x{2028} and \x{2029}) | |
749 | (should also affect <>, $., and script line numbers) | |
750 | (the \x{85}, \x{2028} and \x{2029} do match \s) | |
751 | ||
752 | [a] You can mimic class subtraction using lookahead. | |
753 | For example, what TR18 might write as | |
754 | ||
755 | [{Greek}-[{UNASSIGNED}]] | |
756 | ||
757 | in Perl can be written as: | |
758 | ||
759 | (?!\p{Unassigned})\p{InGreekAndCoptic} | |
760 | (?=\p{Assigned})\p{InGreekAndCoptic} | |
761 | ||
762 | But in this particular example, you probably really want | |
763 | ||
764 | \p{GreekAndCoptic} | |
765 | ||
766 | which will match assigned characters known to be part of the Greek script. | |
767 | ||
768 | [b] See L</"User-Defined Character Properties">. | |
769 | ||
770 | =item * | |
771 | ||
772 | Level 2 - Extended Unicode Support | |
773 | ||
774 | 3.1 Surrogates - MISSING | |
775 | 3.2 Canonical Equivalents - MISSING [11][12] | |
776 | 3.3 Locale-Independent Graphemes - MISSING [13] | |
777 | 3.4 Locale-Independent Words - MISSING [14] | |
778 | 3.5 Locale-Independent Loose Matches - MISSING [15] | |
779 | ||
780 | [11] see UTR#15 Unicode Normalization | |
781 | [12] have Unicode::Normalize but not integrated to regexes | |
782 | [13] have \X but at this level . should equal that | |
783 | [14] need three classes, not just \w and \W | |
784 | [15] see UTR#21 Case Mappings | |
785 | ||
786 | =item * | |
787 | ||
788 | Level 3 - Locale-Sensitive Support | |
789 | ||
790 | 4.1 Locale-Dependent Categories - MISSING | |
791 | 4.2 Locale-Dependent Graphemes - MISSING [16][17] | |
792 | 4.3 Locale-Dependent Words - MISSING | |
793 | 4.4 Locale-Dependent Loose Matches - MISSING | |
794 | 4.5 Locale-Dependent Ranges - MISSING | |
795 | ||
796 | [16] see UTR#10 Unicode Collation Algorithms | |
797 | [17] have Unicode::Collate but not integrated to regexes | |
798 | ||
799 | =back | |
800 | ||
801 | =head2 Unicode Encodings | |
802 | ||
803 | Unicode characters are assigned to I<code points>, which are abstract | |
804 | numbers. To use these numbers, various encodings are needed. | |
805 | ||
806 | =over 4 | |
807 | ||
808 | =item * | |
809 | ||
810 | UTF-8 | |
811 | ||
812 | UTF-8 is a variable-length (1 to 6 bytes, current character allocations | |
813 | require 4 bytes), byte-order independent encoding. For ASCII (and we | |
814 | really do mean 7-bit ASCII, not another 8-bit encoding), UTF-8 is | |
815 | transparent. | |
816 | ||
817 | The following table is from Unicode 3.2. | |
818 | ||
819 | Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte | |
820 | ||
821 | U+0000..U+007F 00..7F | |
822 | U+0080..U+07FF C2..DF 80..BF | |
823 | U+0800..U+0FFF E0 A0..BF 80..BF | |
824 | U+1000..U+CFFF E1..EC 80..BF 80..BF | |
825 | U+D000..U+D7FF ED 80..9F 80..BF | |
826 | U+D800..U+DFFF ******* ill-formed ******* | |
827 | U+E000..U+FFFF EE..EF 80..BF 80..BF | |
828 | U+10000..U+3FFFF F0 90..BF 80..BF 80..BF | |
829 | U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF | |
830 | U+100000..U+10FFFF F4 80..8F 80..BF 80..BF | |
831 | ||
832 | Note the C<A0..BF> in C<U+0800..U+0FFF>, the C<80..9F> in | |
833 | C<U+D000...U+D7FF>, the C<90..B>F in C<U+10000..U+3FFFF>, and the | |
834 | C<80...8F> in C<U+100000..U+10FFFF>. The "gaps" are caused by legal | |
835 | UTF-8 avoiding non-shortest encodings: it is technically possible to | |
836 | UTF-8-encode a single code point in different ways, but that is | |
837 | explicitly forbidden, and the shortest possible encoding should always | |
838 | be used. So that's what Perl does. | |
839 | ||
840 | Another way to look at it is via bits: | |
841 | ||
842 | Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte | |
843 | ||
844 | 0aaaaaaa 0aaaaaaa | |
845 | 00000bbbbbaaaaaa 110bbbbb 10aaaaaa | |
846 | ccccbbbbbbaaaaaa 1110cccc 10bbbbbb 10aaaaaa | |
847 | 00000dddccccccbbbbbbaaaaaa 11110ddd 10cccccc 10bbbbbb 10aaaaaa | |
848 | ||
849 | As you can see, the continuation bytes all begin with C<10>, and the | |
850 | leading bits of the start byte tell how many bytes the are in the | |
851 | encoded character. | |
852 | ||
853 | =item * | |
854 | ||
855 | UTF-EBCDIC | |
856 | ||
857 | Like UTF-8 but EBCDIC-safe, in the way that UTF-8 is ASCII-safe. | |
858 | ||
859 | =item * | |
860 | ||
861 | UTF-16, UTF-16BE, UTF16-LE, Surrogates, and BOMs (Byte Order Marks) | |
862 | ||
863 | The followings items are mostly for reference and general Unicode | |
864 | knowledge, Perl doesn't use these constructs internally. | |
865 | ||
866 | UTF-16 is a 2 or 4 byte encoding. The Unicode code points | |
867 | C<U+0000..U+FFFF> are stored in a single 16-bit unit, and the code | |
868 | points C<U+10000..U+10FFFF> in two 16-bit units. The latter case is | |
869 | using I<surrogates>, the first 16-bit unit being the I<high | |
870 | surrogate>, and the second being the I<low surrogate>. | |
871 | ||
872 | Surrogates are code points set aside to encode the C<U+10000..U+10FFFF> | |
873 | range of Unicode code points in pairs of 16-bit units. The I<high | |
874 | surrogates> are the range C<U+D800..U+DBFF>, and the I<low surrogates> | |
875 | are the range C<U+DC00..U+DFFF>. The surrogate encoding is | |
876 | ||
877 | $hi = ($uni - 0x10000) / 0x400 + 0xD800; | |
878 | $lo = ($uni - 0x10000) % 0x400 + 0xDC00; | |
879 | ||
880 | and the decoding is | |
881 | ||
882 | $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00); | |
883 | ||
884 | If you try to generate surrogates (for example by using chr()), you | |
885 | will get a warning if warnings are turned on, because those code | |
886 | points are not valid for a Unicode character. | |
887 | ||
888 | Because of the 16-bitness, UTF-16 is byte-order dependent. UTF-16 | |
889 | itself can be used for in-memory computations, but if storage or | |
890 | transfer is required either UTF-16BE (big-endian) or UTF-16LE | |
891 | (little-endian) encodings must be chosen. | |
892 | ||
893 | This introduces another problem: what if you just know that your data | |
894 | is UTF-16, but you don't know which endianness? Byte Order Marks, or | |
895 | BOMs, are a solution to this. A special character has been reserved | |
896 | in Unicode to function as a byte order marker: the character with the | |
897 | code point C<U+FEFF> is the BOM. | |
898 | ||
899 | The trick is that if you read a BOM, you will know the byte order, | |
900 | since if it was written on a big-endian platform, you will read the | |
901 | bytes C<0xFE 0xFF>, but if it was written on a little-endian platform, | |
902 | you will read the bytes C<0xFF 0xFE>. (And if the originating platform | |
903 | was writing in UTF-8, you will read the bytes C<0xEF 0xBB 0xBF>.) | |
904 | ||
905 | The way this trick works is that the character with the code point | |
906 | C<U+FFFE> is guaranteed not to be a valid Unicode character, so the | |
907 | sequence of bytes C<0xFF 0xFE> is unambiguously "BOM, represented in | |
908 | little-endian format" and cannot be C<U+FFFE>, represented in big-endian | |
909 | format". | |
910 | ||
911 | =item * | |
912 | ||
913 | UTF-32, UTF-32BE, UTF32-LE | |
914 | ||
915 | The UTF-32 family is pretty much like the UTF-16 family, expect that | |
916 | the units are 32-bit, and therefore the surrogate scheme is not | |
917 | needed. The BOM signatures will be C<0x00 0x00 0xFE 0xFF> for BE and | |
918 | C<0xFF 0xFE 0x00 0x00> for LE. | |
919 | ||
920 | =item * | |
921 | ||
922 | UCS-2, UCS-4 | |
923 | ||
924 | Encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit | |
925 | encoding. Unlike UTF-16, UCS-2 is not extensible beyond C<U+FFFF>, | |
926 | because it does not use surrogates. UCS-4 is a 32-bit encoding, | |
927 | functionally identical to UTF-32. | |
928 | ||
929 | =item * | |
930 | ||
931 | UTF-7 | |
932 | ||
933 | A seven-bit safe (non-eight-bit) encoding, which is useful if the | |
934 | transport or storage is not eight-bit safe. Defined by RFC 2152. | |
935 | ||
936 | =back | |
937 | ||
938 | =head2 Security Implications of Unicode | |
939 | ||
940 | =over 4 | |
941 | ||
942 | =item * | |
943 | ||
944 | Malformed UTF-8 | |
945 | ||
946 | Unfortunately, the specification of UTF-8 leaves some room for | |
947 | interpretation of how many bytes of encoded output one should generate | |
948 | from one input Unicode character. Strictly speaking, the shortest | |
949 | possible sequence of UTF-8 bytes should be generated, | |
950 | because otherwise there is potential for an input buffer overflow at | |
951 | the receiving end of a UTF-8 connection. Perl always generates the | |
952 | shortest length UTF-8, and with warnings on Perl will warn about | |
953 | non-shortest length UTF-8 along with other malformations, such as the | |
954 | surrogates, which are not real Unicode code points. | |
955 | ||
956 | =item * | |
957 | ||
958 | Regular expressions behave slightly differently between byte data and | |
959 | character (Unicode) data. For example, the "word character" character | |
960 | class C<\w> will work differently depending on if data is eight-bit bytes | |
961 | or Unicode. | |
962 | ||
963 | In the first case, the set of C<\w> characters is either small--the | |
964 | default set of alphabetic characters, digits, and the "_"--or, if you | |
965 | are using a locale (see L<perllocale>), the C<\w> might contain a few | |
966 | more letters according to your language and country. | |
967 | ||
968 | In the second case, the C<\w> set of characters is much, much larger. | |
969 | Most importantly, even in the set of the first 256 characters, it will | |
970 | probably match different characters: unlike most locales, which are | |
971 | specific to a language and country pair, Unicode classifies all the | |
972 | characters that are letters I<somewhere> as C<\w>. For example, your | |
973 | locale might not think that LATIN SMALL LETTER ETH is a letter (unless | |
974 | you happen to speak Icelandic), but Unicode does. | |
975 | ||
976 | As discussed elsewhere, Perl has one foot (two hooves?) planted in | |
977 | each of two worlds: the old world of bytes and the new world of | |
978 | characters, upgrading from bytes to characters when necessary. | |
979 | If your legacy code does not explicitly use Unicode, no automatic | |
980 | switch-over to characters should happen. Characters shouldn't get | |
981 | downgraded to bytes, either. It is possible to accidentally mix bytes | |
982 | and characters, however (see L<perluniintro>), in which case C<\w> in | |
983 | regular expressions might start behaving differently. Review your | |
984 | code. Use warnings and the C<strict> pragma. | |
985 | ||
986 | =back | |
987 | ||
988 | =head2 Unicode in Perl on EBCDIC | |
989 | ||
990 | The way Unicode is handled on EBCDIC platforms is still | |
991 | experimental. On such platforms, references to UTF-8 encoding in this | |
992 | document and elsewhere should be read as meaning the UTF-EBCDIC | |
993 | specified in Unicode Technical Report 16, unless ASCII vs. EBCDIC issues | |
994 | are specifically discussed. There is no C<utfebcdic> pragma or | |
995 | ":utfebcdic" layer; rather, "utf8" and ":utf8" are reused to mean | |
996 | the platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic> | |
997 | for more discussion of the issues. | |
998 | ||
999 | =head2 Locales | |
1000 | ||
1001 | Usually locale settings and Unicode do not affect each other, but | |
1002 | there are a couple of exceptions: | |
1003 | ||
1004 | =over 4 | |
1005 | ||
1006 | =item * | |
1007 | ||
1008 | If your locale environment variables (LANGUAGE, LC_ALL, LC_CTYPE, LANG) | |
1009 | contain the strings 'UTF-8' or 'UTF8' (case-insensitive matching), | |
1010 | the default encodings of your STDIN, STDOUT, and STDERR, and of | |
1011 | B<any subsequent file open>, are considered to be UTF-8. | |
1012 | ||
1013 | =item * | |
1014 | ||
1015 | Perl tries really hard to work both with Unicode and the old | |
1016 | byte-oriented world. Most often this is nice, but sometimes Perl's | |
1017 | straddling of the proverbial fence causes problems. | |
1018 | ||
1019 | =back | |
1020 | ||
1021 | =head2 Using Unicode in XS | |
1022 | ||
1023 | If you want to handle Perl Unicode in XS extensions, you may find | |
1024 | the following C APIs useful. See L<perlapi> for details. | |
1025 | ||
1026 | =over 4 | |
1027 | ||
1028 | =item * | |
1029 | ||
1030 | C<DO_UTF8(sv)> returns true if the C<UTF8> flag is on and the bytes | |
1031 | pragma is not in effect. C<SvUTF8(sv)> returns true is the C<UTF8> | |
1032 | flag is on; the bytes pragma is ignored. The C<UTF8> flag being on | |
1033 | does B<not> mean that there are any characters of code points greater | |
1034 | than 255 (or 127) in the scalar or that there are even any characters | |
1035 | in the scalar. What the C<UTF8> flag means is that the sequence of | |
1036 | octets in the representation of the scalar is the sequence of UTF-8 | |
1037 | encoded code points of the characters of a string. The C<UTF8> flag | |
1038 | being off means that each octet in this representation encodes a | |
1039 | single character with code point 0..255 within the string. Perl's | |
1040 | Unicode model is not to use UTF-8 until it is absolutely necessary. | |
1041 | ||
1042 | =item * | |
1043 | ||
1044 | C<uvuni_to_utf8(buf, chr>) writes a Unicode character code point into | |
1045 | a buffer encoding the code point as UTF-8, and returns a pointer | |
1046 | pointing after the UTF-8 bytes. | |
1047 | ||
1048 | =item * | |
1049 | ||
1050 | C<utf8_to_uvuni(buf, lenp)> reads UTF-8 encoded bytes from a buffer and | |
1051 | returns the Unicode character code point and, optionally, the length of | |
1052 | the UTF-8 byte sequence. | |
1053 | ||
1054 | =item * | |
1055 | ||
1056 | C<utf8_length(start, end)> returns the length of the UTF-8 encoded buffer | |
1057 | in characters. C<sv_len_utf8(sv)> returns the length of the UTF-8 encoded | |
1058 | scalar. | |
1059 | ||
1060 | =item * | |
1061 | ||
1062 | C<sv_utf8_upgrade(sv)> converts the string of the scalar to its UTF-8 | |
1063 | encoded form. C<sv_utf8_downgrade(sv)> does the opposite, if | |
1064 | possible. C<sv_utf8_encode(sv)> is like sv_utf8_upgrade except that | |
1065 | it does not set the C<UTF8> flag. C<sv_utf8_decode()> does the | |
1066 | opposite of C<sv_utf8_encode()>. Note that none of these are to be | |
1067 | used as general-purpose encoding or decoding interfaces: C<use Encode> | |
1068 | for that. C<sv_utf8_upgrade()> is affected by the encoding pragma | |
1069 | but C<sv_utf8_downgrade()> is not (since the encoding pragma is | |
1070 | designed to be a one-way street). | |
1071 | ||
1072 | =item * | |
1073 | ||
1074 | C<is_utf8_char(s)> returns true if the pointer points to a valid UTF-8 | |
1075 | character. | |
1076 | ||
1077 | =item * | |
1078 | ||
1079 | C<is_utf8_string(buf, len)> returns true if C<len> bytes of the buffer | |
1080 | are valid UTF-8. | |
1081 | ||
1082 | =item * | |
1083 | ||
1084 | C<UTF8SKIP(buf)> will return the number of bytes in the UTF-8 encoded | |
1085 | character in the buffer. C<UNISKIP(chr)> will return the number of bytes | |
1086 | required to UTF-8-encode the Unicode character code point. C<UTF8SKIP()> | |
1087 | is useful for example for iterating over the characters of a UTF-8 | |
1088 | encoded buffer; C<UNISKIP()> is useful, for example, in computing | |
1089 | the size required for a UTF-8 encoded buffer. | |
1090 | ||
1091 | =item * | |
1092 | ||
1093 | C<utf8_distance(a, b)> will tell the distance in characters between the | |
1094 | two pointers pointing to the same UTF-8 encoded buffer. | |
1095 | ||
1096 | =item * | |
1097 | ||
1098 | C<utf8_hop(s, off)> will return a pointer to an UTF-8 encoded buffer | |
1099 | that is C<off> (positive or negative) Unicode characters displaced | |
1100 | from the UTF-8 buffer C<s>. Be careful not to overstep the buffer: | |
1101 | C<utf8_hop()> will merrily run off the end or the beginning of the | |
1102 | buffer if told to do so. | |
1103 | ||
1104 | =item * | |
1105 | ||
1106 | C<pv_uni_display(dsv, spv, len, pvlim, flags)> and | |
1107 | C<sv_uni_display(dsv, ssv, pvlim, flags)> are useful for debugging the | |
1108 | output of Unicode strings and scalars. By default they are useful | |
1109 | only for debugging--they display B<all> characters as hexadecimal code | |
1110 | points--but with the flags C<UNI_DISPLAY_ISPRINT>, | |
1111 | C<UNI_DISPLAY_BACKSLASH>, and C<UNI_DISPLAY_QQ> you can make the | |
1112 | output more readable. | |
1113 | ||
1114 | =item * | |
1115 | ||
1116 | C<ibcmp_utf8(s1, pe1, u1, l1, u1, s2, pe2, l2, u2)> can be used to | |
1117 | compare two strings case-insensitively in Unicode. For case-sensitive | |
1118 | comparisons you can just use C<memEQ()> and C<memNE()> as usual. | |
1119 | ||
1120 | =back | |
1121 | ||
1122 | For more information, see L<perlapi>, and F<utf8.c> and F<utf8.h> | |
1123 | in the Perl source code distribution. | |
1124 | ||
1125 | =head1 BUGS | |
1126 | ||
1127 | =head2 Interaction with Locales | |
1128 | ||
1129 | Use of locales with Unicode data may lead to odd results. Currently, | |
1130 | Perl attempts to attach 8-bit locale info to characters in the range | |
1131 | 0..255, but this technique is demonstrably incorrect for locales that | |
1132 | use characters above that range when mapped into Unicode. Perl's | |
1133 | Unicode support will also tend to run slower. Use of locales with | |
1134 | Unicode is discouraged. | |
1135 | ||
1136 | =head2 Interaction with Extensions | |
1137 | ||
1138 | When Perl exchanges data with an extension, the extension should be | |
1139 | able to understand the UTF-8 flag and act accordingly. If the | |
1140 | extension doesn't know about the flag, it's likely that the extension | |
1141 | will return incorrectly-flagged data. | |
1142 | ||
1143 | So if you're working with Unicode data, consult the documentation of | |
1144 | every module you're using if there are any issues with Unicode data | |
1145 | exchange. If the documentation does not talk about Unicode at all, | |
1146 | suspect the worst and probably look at the source to learn how the | |
1147 | module is implemented. Modules written completely in Perl shouldn't | |
1148 | cause problems. Modules that directly or indirectly access code written | |
1149 | in other programming languages are at risk. | |
1150 | ||
1151 | For affected functions, the simple strategy to avoid data corruption is | |
1152 | to always make the encoding of the exchanged data explicit. Choose an | |
1153 | encoding that you know the extension can handle. Convert arguments passed | |
1154 | to the extensions to that encoding and convert results back from that | |
1155 | encoding. Write wrapper functions that do the conversions for you, so | |
1156 | you can later change the functions when the extension catches up. | |
1157 | ||
1158 | To provide an example, let's say the popular Foo::Bar::escape_html | |
1159 | function doesn't deal with Unicode data yet. The wrapper function | |
1160 | would convert the argument to raw UTF-8 and convert the result back to | |
1161 | Perl's internal representation like so: | |
1162 | ||
1163 | sub my_escape_html ($) { | |
1164 | my($what) = shift; | |
1165 | return unless defined $what; | |
1166 | Encode::decode_utf8(Foo::Bar::escape_html(Encode::encode_utf8($what))); | |
1167 | } | |
1168 | ||
1169 | Sometimes, when the extension does not convert data but just stores | |
1170 | and retrieves them, you will be in a position to use the otherwise | |
1171 | dangerous Encode::_utf8_on() function. Let's say the popular | |
1172 | C<Foo::Bar> extension, written in C, provides a C<param> method that | |
1173 | lets you store and retrieve data according to these prototypes: | |
1174 | ||
1175 | $self->param($name, $value); # set a scalar | |
1176 | $value = $self->param($name); # retrieve a scalar | |
1177 | ||
1178 | If it does not yet provide support for any encoding, one could write a | |
1179 | derived class with such a C<param> method: | |
1180 | ||
1181 | sub param { | |
1182 | my($self,$name,$value) = @_; | |
1183 | utf8::upgrade($name); # make sure it is UTF-8 encoded | |
1184 | if (defined $value) | |
1185 | utf8::upgrade($value); # make sure it is UTF-8 encoded | |
1186 | return $self->SUPER::param($name,$value); | |
1187 | } else { | |
1188 | my $ret = $self->SUPER::param($name); | |
1189 | Encode::_utf8_on($ret); # we know, it is UTF-8 encoded | |
1190 | return $ret; | |
1191 | } | |
1192 | } | |
1193 | ||
1194 | Some extensions provide filters on data entry/exit points, such as | |
1195 | DB_File::filter_store_key and family. Look out for such filters in | |
1196 | the documentation of your extensions, they can make the transition to | |
1197 | Unicode data much easier. | |
1198 | ||
1199 | =head2 Speed | |
1200 | ||
1201 | Some functions are slower when working on UTF-8 encoded strings than | |
1202 | on byte encoded strings. All functions that need to hop over | |
1203 | characters such as length(), substr() or index() can work B<much> | |
1204 | faster when the underlying data are byte-encoded. Witness the | |
1205 | following benchmark: | |
1206 | ||
1207 | % perl -e ' | |
1208 | use Benchmark; | |
1209 | use strict; | |
1210 | our $l = 10000; | |
1211 | our $u = our $b = "x" x $l; | |
1212 | substr($u,0,1) = "\x{100}"; | |
1213 | timethese(-2,{ | |
1214 | LENGTH_B => q{ length($b) }, | |
1215 | LENGTH_U => q{ length($u) }, | |
1216 | SUBSTR_B => q{ substr($b, $l/4, $l/2) }, | |
1217 | SUBSTR_U => q{ substr($u, $l/4, $l/2) }, | |
1218 | }); | |
1219 | ' | |
1220 | Benchmark: running LENGTH_B, LENGTH_U, SUBSTR_B, SUBSTR_U for at least 2 CPU seconds... | |
1221 | LENGTH_B: 2 wallclock secs ( 2.36 usr + 0.00 sys = 2.36 CPU) @ 5649983.05/s (n=13333960) | |
1222 | LENGTH_U: 2 wallclock secs ( 2.11 usr + 0.00 sys = 2.11 CPU) @ 12155.45/s (n=25648) | |
1223 | SUBSTR_B: 3 wallclock secs ( 2.16 usr + 0.00 sys = 2.16 CPU) @ 374480.09/s (n=808877) | |
1224 | SUBSTR_U: 2 wallclock secs ( 2.11 usr + 0.00 sys = 2.11 CPU) @ 6791.00/s (n=14329) | |
1225 | ||
1226 | The numbers show an incredible slowness on long UTF-8 strings. You | |
1227 | should carefully avoid using these functions in tight loops. If you | |
1228 | want to iterate over characters, the superior coding technique would | |
1229 | split the characters into an array instead of using substr, as the following | |
1230 | benchmark shows: | |
1231 | ||
1232 | % perl -e ' | |
1233 | use Benchmark; | |
1234 | use strict; | |
1235 | our $l = 10000; | |
1236 | our $u = our $b = "x" x $l; | |
1237 | substr($u,0,1) = "\x{100}"; | |
1238 | timethese(-5,{ | |
1239 | SPLIT_B => q{ for my $c (split //, $b){} }, | |
1240 | SPLIT_U => q{ for my $c (split //, $u){} }, | |
1241 | SUBSTR_B => q{ for my $i (0..length($b)-1){my $c = substr($b,$i,1);} }, | |
1242 | SUBSTR_U => q{ for my $i (0..length($u)-1){my $c = substr($u,$i,1);} }, | |
1243 | }); | |
1244 | ' | |
1245 | Benchmark: running SPLIT_B, SPLIT_U, SUBSTR_B, SUBSTR_U for at least 5 CPU seconds... | |
1246 | SPLIT_B: 6 wallclock secs ( 5.29 usr + 0.00 sys = 5.29 CPU) @ 56.14/s (n=297) | |
1247 | SPLIT_U: 5 wallclock secs ( 5.17 usr + 0.01 sys = 5.18 CPU) @ 55.21/s (n=286) | |
1248 | SUBSTR_B: 5 wallclock secs ( 5.34 usr + 0.00 sys = 5.34 CPU) @ 123.22/s (n=658) | |
1249 | SUBSTR_U: 7 wallclock secs ( 6.20 usr + 0.00 sys = 6.20 CPU) @ 0.81/s (n=5) | |
1250 | ||
1251 | Even though the algorithm based on C<substr()> is faster than | |
1252 | C<split()> for byte-encoded data, it pales in comparison to the speed | |
1253 | of C<split()> when used with UTF-8 data. | |
1254 | ||
1255 | =head1 SEE ALSO | |
1256 | ||
1257 | L<perluniintro>, L<encoding>, L<Encode>, L<open>, L<utf8>, L<bytes>, | |
1258 | L<perlretut>, L<perlvar/"${^WIDE_SYSTEM_CALLS}"> | |
1259 | ||
1260 | =cut |