Commit | Line | Data |
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393fec97 GS |
1 | =head1 NAME |
2 | ||
3 | perlunicode - Unicode support in Perl | |
4 | ||
5 | =head1 DESCRIPTION | |
6 | ||
0a1f2d14 | 7 | =head2 Important Caveats |
21bad921 | 8 | |
c349b1b9 JH |
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. | |
21bad921 | 12 | |
13a2d996 | 13 | =over 4 |
21bad921 GS |
14 | |
15 | =item Input and Output Disciplines | |
16 | ||
75daf61c JH |
17 | A filehandle can be marked as containing perl's internal Unicode |
18 | encoding (UTF-8 or UTF-EBCDIC) by opening it with the ":utf8" layer. | |
0a1f2d14 | 19 | Other encodings can be converted to perl's encoding on input, or from |
c349b1b9 JH |
20 | perl's encoding on output by use of the ":encoding(...)" layer. |
21 | See L<open>. | |
22 | ||
d1be9408 | 23 | To mark the Perl source itself as being in a particular encoding, |
c349b1b9 | 24 | see L<encoding>. |
21bad921 GS |
25 | |
26 | =item Regular Expressions | |
27 | ||
c349b1b9 JH |
28 | The regular expression compiler produces polymorphic opcodes. That is, |
29 | the pattern adapts to the data and automatically switch to the Unicode | |
30 | character scheme when presented with Unicode data, or a traditional | |
31 | byte scheme when presented with byte data. | |
21bad921 | 32 | |
ad0029c4 | 33 | =item C<use utf8> still needed to enable UTF-8/UTF-EBCDIC in scripts |
21bad921 | 34 | |
c349b1b9 JH |
35 | As a compatibility measure, this pragma must be explicitly used to |
36 | enable recognition of UTF-8 in the Perl scripts themselves on ASCII | |
3e4dbfed | 37 | based machines, or to recognize UTF-EBCDIC on EBCDIC based machines. |
c349b1b9 JH |
38 | B<NOTE: this should be the only place where an explicit C<use utf8> |
39 | is needed>. | |
21bad921 | 40 | |
1768d7eb | 41 | You can also use the C<encoding> pragma to change the default encoding |
6ec9efec | 42 | of the data in your script; see L<encoding>. |
1768d7eb | 43 | |
21bad921 GS |
44 | =back |
45 | ||
46 | =head2 Byte and Character semantics | |
393fec97 GS |
47 | |
48 | Beginning with version 5.6, Perl uses logically wide characters to | |
3e4dbfed | 49 | represent strings internally. |
393fec97 | 50 | |
75daf61c JH |
51 | In future, Perl-level operations can be expected to work with |
52 | characters rather than bytes, in general. | |
393fec97 | 53 | |
75daf61c JH |
54 | However, as strictly an interim compatibility measure, Perl aims to |
55 | provide a safe migration path from byte semantics to character | |
56 | semantics for programs. For operations where Perl can unambiguously | |
57 | decide that the input data is characters, Perl now switches to | |
58 | character semantics. For operations where this determination cannot | |
59 | be made without additional information from the user, Perl decides in | |
60 | favor of compatibility, and chooses to use byte semantics. | |
8cbd9a7a GS |
61 | |
62 | This behavior preserves compatibility with earlier versions of Perl, | |
63 | which allowed byte semantics in Perl operations, but only as long as | |
64 | none of the program's inputs are marked as being as source of Unicode | |
65 | character data. Such data may come from filehandles, from calls to | |
66 | external programs, from information provided by the system (such as %ENV), | |
21bad921 | 67 | or from literals and constants in the source text. |
8cbd9a7a | 68 | |
c349b1b9 | 69 | On Windows platforms, if the C<-C> command line switch is used, (or the |
75daf61c JH |
70 | ${^WIDE_SYSTEM_CALLS} global flag is set to C<1>), all system calls |
71 | will use the corresponding wide character APIs. Note that this is | |
c349b1b9 JH |
72 | currently only implemented on Windows since other platforms lack an |
73 | API standard on this area. | |
8cbd9a7a | 74 | |
75daf61c JH |
75 | Regardless of the above, the C<bytes> pragma can always be used to |
76 | force byte semantics in a particular lexical scope. See L<bytes>. | |
8cbd9a7a GS |
77 | |
78 | The C<utf8> pragma is primarily a compatibility device that enables | |
75daf61c | 79 | recognition of UTF-(8|EBCDIC) in literals encountered by the parser. |
7dedd01f JH |
80 | Note that this pragma is only required until a future version of Perl |
81 | in which character semantics will become the default. This pragma may | |
82 | then become a no-op. See L<utf8>. | |
8cbd9a7a GS |
83 | |
84 | Unless mentioned otherwise, Perl operators will use character semantics | |
85 | when they are dealing with Unicode data, and byte semantics otherwise. | |
86 | Thus, character semantics for these operations apply transparently; if | |
87 | the input data came from a Unicode source (for example, by adding a | |
88 | character encoding discipline to the filehandle whence it came, or a | |
3e4dbfed | 89 | literal Unicode string constant in the program), character semantics |
8cbd9a7a | 90 | apply; otherwise, byte semantics are in effect. To force byte semantics |
8058d7ab | 91 | on Unicode data, the C<bytes> pragma should be used. |
393fec97 | 92 | |
0a378802 JH |
93 | Notice that if you concatenate strings with byte semantics and strings |
94 | with Unicode character data, the bytes will by default be upgraded | |
95 | I<as if they were ISO 8859-1 (Latin-1)> (or if in EBCDIC, after a | |
3e4dbfed JF |
96 | translation to ISO 8859-1). This is done without regard to the |
97 | system's native 8-bit encoding, so to change this for systems with | |
98 | non-Latin-1 (or non-EBCDIC) native encodings, use the C<encoding> | |
0a378802 | 99 | pragma, see L<encoding>. |
7dedd01f | 100 | |
feda178f JH |
101 | Under character semantics, many operations that formerly operated on |
102 | bytes change to operating on characters. A character in Perl is | |
103 | logically just a number ranging from 0 to 2**31 or so. Larger | |
104 | characters may encode to longer sequences of bytes internally, but | |
105 | this is just an internal detail which is hidden at the Perl level. | |
106 | See L<perluniintro> for more on this. | |
393fec97 | 107 | |
8cbd9a7a | 108 | =head2 Effects of character semantics |
393fec97 GS |
109 | |
110 | Character semantics have the following effects: | |
111 | ||
112 | =over 4 | |
113 | ||
114 | =item * | |
115 | ||
574c8022 JH |
116 | Strings (including hash keys) and regular expression patterns may |
117 | contain characters that have an ordinal value larger than 255. | |
393fec97 | 118 | |
feda178f JH |
119 | If you use a Unicode editor to edit your program, Unicode characters |
120 | may occur directly within the literal strings in one of the various | |
121 | Unicode encodings (UTF-8, UTF-EBCDIC, UCS-2, etc.), but are recognized | |
122 | as such (and converted to Perl's internal representation) only if the | |
123 | appropriate L<encoding> is specified. | |
3e4dbfed JF |
124 | |
125 | You can also get Unicode characters into a string by using the C<\x{...}> | |
126 | notation, putting the Unicode code for the desired character, in | |
127 | hexadecimal, into the curlies. For instance, a smiley face is C<\x{263A}>. | |
128 | This works only for characters with a code 0x100 and above. | |
129 | ||
130 | Additionally, if you | |
574c8022 | 131 | |
3e4dbfed | 132 | use charnames ':full'; |
574c8022 | 133 | |
3e4dbfed JF |
134 | you can use the C<\N{...}> notation, putting the official Unicode character |
135 | name within the curlies. For example, C<\N{WHITE SMILING FACE}>. | |
136 | This works for all characters that have names. | |
393fec97 GS |
137 | |
138 | =item * | |
139 | ||
3990cdf5 JH |
140 | If Unicode is used in hash keys, there is a subtle effect on the hashes. |
141 | The hash becomes "Unicode-sticky" so that keys retrieved from the hash | |
142 | (either by %hash, each %hash, or keys %hash) will be in Unicode, not | |
143 | in bytes, even when the keys were bytes went they "went in". This | |
144 | "stickiness" persists unless the hash is completely emptied, either by | |
145 | using delete() or clearing the with undef() or assigning an empty list | |
146 | to the hash. Most of the time this difference is negligible, but | |
147 | there are few places where it matters: for example the regular | |
148 | expression character classes like C<\w> behave differently for | |
149 | bytes and characters. | |
150 | ||
151 | =item * | |
152 | ||
574c8022 JH |
153 | If an appropriate L<encoding> is specified, identifiers within the |
154 | Perl script may contain Unicode alphanumeric characters, including | |
155 | ideographs. (You are currently on your own when it comes to using the | |
156 | canonical forms of characters--Perl doesn't (yet) attempt to | |
157 | canonicalize variable names for you.) | |
393fec97 | 158 | |
393fec97 GS |
159 | =item * |
160 | ||
161 | Regular expressions match characters instead of bytes. For instance, | |
162 | "." matches a character instead of a byte. (However, the C<\C> pattern | |
75daf61c | 163 | is provided to force a match a single byte ("C<char>" in C, hence C<\C>).) |
393fec97 | 164 | |
393fec97 GS |
165 | =item * |
166 | ||
167 | Character classes in regular expressions match characters instead of | |
168 | bytes, and match against the character properties specified in the | |
75daf61c JH |
169 | Unicode properties database. So C<\w> can be used to match an |
170 | ideograph, for instance. | |
393fec97 | 171 | |
393fec97 GS |
172 | =item * |
173 | ||
eb0cc9e3 JH |
174 | Named Unicode properties, scripts, and block ranges may be used like |
175 | character classes via the new C<\p{}> (matches property) and C<\P{}> | |
176 | (doesn't match property) constructs. For instance, C<\p{Lu}> matches any | |
feda178f JH |
177 | character with the Unicode "Lu" (Letter, uppercase) property, while |
178 | C<\p{M}> matches any character with a "M" (mark -- accents and such) | |
eb0cc9e3 JH |
179 | property. Single letter properties may omit the brackets, so that can be |
180 | written C<\pM> also. Many predefined properties are available, such | |
181 | as C<\p{Mirrored}> and C<\p{Tibetan}>. | |
4193bef7 | 182 | |
cfc01aea | 183 | The official Unicode script and block names have spaces and dashes as |
eb0cc9e3 JH |
184 | separators, but for convenience you can have dashes, spaces, and underbars |
185 | at every word division, and you need not care about correct casing. It is | |
186 | recommended, however, that for consistency you use the following naming: | |
187 | the official Unicode script, block, or property name (see below for the | |
188 | additional rules that apply to block names), with whitespace and dashes | |
189 | removed, and the words "uppercase-first-lowercase-rest". That is, "Latin-1 | |
190 | Supplement" becomes "Latin1Supplement". | |
4193bef7 | 191 | |
a1cc1cb1 | 192 | You can also negate both C<\p{}> and C<\P{}> by introducing a caret |
eb0cc9e3 JH |
193 | (^) between the first curly and the property name: C<\p{^Tamil}> is |
194 | equal to C<\P{Tamil}>. | |
4193bef7 | 195 | |
eb0cc9e3 JH |
196 | Here are the basic Unicode General Category properties, followed by their |
197 | long form (you can use either, e.g. C<\p{Lu}> and C<\p{LowercaseLetter}> | |
198 | are identical). | |
393fec97 | 199 | |
d73e5302 JH |
200 | Short Long |
201 | ||
202 | L Letter | |
eb0cc9e3 JH |
203 | Lu UppercaseLetter |
204 | Ll LowercaseLetter | |
205 | Lt TitlecaseLetter | |
206 | Lm ModifierLetter | |
207 | Lo OtherLetter | |
d73e5302 JH |
208 | |
209 | M Mark | |
eb0cc9e3 JH |
210 | Mn NonspacingMark |
211 | Mc SpacingMark | |
212 | Me EnclosingMark | |
d73e5302 JH |
213 | |
214 | N Number | |
eb0cc9e3 JH |
215 | Nd DecimalNumber |
216 | Nl LetterNumber | |
217 | No OtherNumber | |
d73e5302 JH |
218 | |
219 | P Punctuation | |
eb0cc9e3 JH |
220 | Pc ConnectorPunctuation |
221 | Pd DashPunctuation | |
222 | Ps OpenPunctuation | |
223 | Pe ClosePunctuation | |
224 | Pi InitialPunctuation | |
d73e5302 | 225 | (may behave like Ps or Pe depending on usage) |
eb0cc9e3 | 226 | Pf FinalPunctuation |
d73e5302 | 227 | (may behave like Ps or Pe depending on usage) |
eb0cc9e3 | 228 | Po OtherPunctuation |
d73e5302 JH |
229 | |
230 | S Symbol | |
eb0cc9e3 JH |
231 | Sm MathSymbol |
232 | Sc CurrencySymbol | |
233 | Sk ModifierSymbol | |
234 | So OtherSymbol | |
d73e5302 JH |
235 | |
236 | Z Separator | |
eb0cc9e3 JH |
237 | Zs SpaceSeparator |
238 | Zl LineSeparator | |
239 | Zp ParagraphSeparator | |
d73e5302 JH |
240 | |
241 | C Other | |
e150c829 JH |
242 | Cc Control |
243 | Cf Format | |
eb0cc9e3 JH |
244 | Cs Surrogate (not usable) |
245 | Co PrivateUse | |
e150c829 | 246 | Cn Unassigned |
1ac13f9a | 247 | |
3e4dbfed JF |
248 | The single-letter properties match all characters in any of the |
249 | two-letter sub-properties starting with the same letter. | |
1ac13f9a | 250 | There's also C<L&> which is an alias for C<Ll>, C<Lu>, and C<Lt>. |
32293815 | 251 | |
eb0cc9e3 JH |
252 | Because Perl hides the need for the user to understand the internal |
253 | representation of Unicode characters, it has no need to support the | |
254 | somewhat messy concept of surrogates. Therefore, the C<Cs> property is not | |
255 | supported. | |
d73e5302 | 256 | |
eb0cc9e3 JH |
257 | Because scripts differ in their directionality (for example Hebrew is |
258 | written right to left), Unicode supplies these properties: | |
32293815 | 259 | |
eb0cc9e3 | 260 | Property Meaning |
92e830a9 | 261 | |
d73e5302 JH |
262 | BidiL Left-to-Right |
263 | BidiLRE Left-to-Right Embedding | |
264 | BidiLRO Left-to-Right Override | |
265 | BidiR Right-to-Left | |
266 | BidiAL Right-to-Left Arabic | |
267 | BidiRLE Right-to-Left Embedding | |
268 | BidiRLO Right-to-Left Override | |
269 | BidiPDF Pop Directional Format | |
270 | BidiEN European Number | |
271 | BidiES European Number Separator | |
272 | BidiET European Number Terminator | |
273 | BidiAN Arabic Number | |
274 | BidiCS Common Number Separator | |
275 | BidiNSM Non-Spacing Mark | |
276 | BidiBN Boundary Neutral | |
277 | BidiB Paragraph Separator | |
278 | BidiS Segment Separator | |
279 | BidiWS Whitespace | |
280 | BidiON Other Neutrals | |
32293815 | 281 | |
eb0cc9e3 JH |
282 | For example, C<\p{BidiR}> matches all characters that are normally |
283 | written right to left. | |
284 | ||
210b36aa AMS |
285 | =back |
286 | ||
2796c109 JH |
287 | =head2 Scripts |
288 | ||
eb0cc9e3 JH |
289 | The scripts available via C<\p{...}> and C<\P{...}>, for example |
290 | C<\p{Latin}> or \p{Cyrillic>, are as follows: | |
2796c109 | 291 | |
1ac13f9a | 292 | Arabic |
e9ad1727 | 293 | Armenian |
1ac13f9a | 294 | Bengali |
e9ad1727 | 295 | Bopomofo |
eb0cc9e3 | 296 | CanadianAboriginal |
e9ad1727 JH |
297 | Cherokee |
298 | Cyrillic | |
299 | Deseret | |
300 | Devanagari | |
301 | Ethiopic | |
302 | Georgian | |
303 | Gothic | |
304 | Greek | |
1ac13f9a | 305 | Gujarati |
e9ad1727 JH |
306 | Gurmukhi |
307 | Han | |
308 | Hangul | |
309 | Hebrew | |
310 | Hiragana | |
311 | Inherited | |
1ac13f9a | 312 | Kannada |
e9ad1727 JH |
313 | Katakana |
314 | Khmer | |
1ac13f9a | 315 | Lao |
e9ad1727 JH |
316 | Latin |
317 | Malayalam | |
318 | Mongolian | |
1ac13f9a | 319 | Myanmar |
1ac13f9a | 320 | Ogham |
eb0cc9e3 | 321 | OldItalic |
e9ad1727 | 322 | Oriya |
1ac13f9a | 323 | Runic |
e9ad1727 JH |
324 | Sinhala |
325 | Syriac | |
326 | Tamil | |
327 | Telugu | |
328 | Thaana | |
329 | Thai | |
330 | Tibetan | |
1ac13f9a | 331 | Yi |
1ac13f9a JH |
332 | |
333 | There are also extended property classes that supplement the basic | |
334 | properties, defined by the F<PropList> Unicode database: | |
335 | ||
e9ad1727 | 336 | ASCII_Hex_Digit |
eb0cc9e3 | 337 | BidiControl |
1ac13f9a | 338 | Dash |
1ac13f9a JH |
339 | Diacritic |
340 | Extender | |
eb0cc9e3 | 341 | HexDigit |
e9ad1727 JH |
342 | Hyphen |
343 | Ideographic | |
eb0cc9e3 JH |
344 | JoinControl |
345 | NoncharacterCodePoint | |
346 | OtherAlphabetic | |
347 | OtherLowercase | |
348 | OtherMath | |
349 | OtherUppercase | |
350 | QuotationMark | |
351 | WhiteSpace | |
1ac13f9a JH |
352 | |
353 | and further derived properties: | |
354 | ||
eb0cc9e3 JH |
355 | Alphabetic Lu + Ll + Lt + Lm + Lo + OtherAlphabetic |
356 | Lowercase Ll + OtherLowercase | |
357 | Uppercase Lu + OtherUppercase | |
358 | Math Sm + OtherMath | |
1ac13f9a JH |
359 | |
360 | ID_Start Lu + Ll + Lt + Lm + Lo + Nl | |
361 | ID_Continue ID_Start + Mn + Mc + Nd + Pc | |
362 | ||
363 | Any Any character | |
eb0cc9e3 JH |
364 | Assigned Any non-Cn character (i.e. synonym for C<\P{Cn}>) |
365 | Unassigned Synonym for C<\p{Cn}> | |
1ac13f9a | 366 | Common Any character (or unassigned code point) |
e150c829 | 367 | not explicitly assigned to a script |
2796c109 | 368 | |
eb0cc9e3 JH |
369 | For backward compatability, all properties mentioned so far may have C<Is> |
370 | prepended to their name (e.g. C<\P{IsLu}> is equal to C<\P{Lu}>). | |
371 | ||
2796c109 JH |
372 | =head2 Blocks |
373 | ||
eb0cc9e3 JH |
374 | In addition to B<scripts>, Unicode also defines B<blocks> of characters. |
375 | The difference between scripts and blocks is that the scripts concept is | |
376 | closer to natural languages, while the blocks concept is more an artificial | |
377 | grouping based on groups of mostly 256 Unicode characters. For example, the | |
378 | C<Latin> script contains letters from many blocks. On the other hand, the | |
379 | C<Latin> script does not contain all the characters from those blocks. It | |
380 | does not, for example, contain digits because digits are shared across many | |
381 | scripts. Digits and other similar groups, like punctuation, are in a | |
382 | category called C<Common>. | |
2796c109 | 383 | |
cfc01aea JF |
384 | For more about scripts, see the UTR #24: |
385 | ||
386 | http://www.unicode.org/unicode/reports/tr24/ | |
387 | ||
388 | For more about blocks, see: | |
389 | ||
390 | http://www.unicode.org/Public/UNIDATA/Blocks.txt | |
2796c109 | 391 | |
eb0cc9e3 | 392 | Blocks names are given with the C<In> prefix. For example, the |
92e830a9 | 393 | Katakana block is referenced via C<\p{InKatakana}>. The C<In> |
eb0cc9e3 JH |
394 | prefix may be omitted if there is no nameing conflict with a script |
395 | or any other property, but it is recommended that C<In> always be used | |
396 | to avoid confusion. | |
397 | ||
398 | These block names are supported: | |
399 | ||
400 | InAlphabeticPresentationForms | |
401 | InArabicBlock | |
402 | InArabicPresentationFormsA | |
403 | InArabicPresentationFormsB | |
404 | InArmenianBlock | |
405 | InArrows | |
406 | InBasicLatin | |
407 | InBengaliBlock | |
408 | InBlockElements | |
409 | InBopomofoBlock | |
410 | InBopomofoExtended | |
411 | InBoxDrawing | |
412 | InBraillePatterns | |
413 | InByzantineMusicalSymbols | |
414 | InCJKCompatibility | |
415 | InCJKCompatibilityForms | |
416 | InCJKCompatibilityIdeographs | |
417 | InCJKCompatibilityIdeographsSupplement | |
418 | InCJKRadicalsSupplement | |
419 | InCJKSymbolsAndPunctuation | |
420 | InCJKUnifiedIdeographs | |
421 | InCJKUnifiedIdeographsExtensionA | |
422 | InCJKUnifiedIdeographsExtensionB | |
423 | InCherokeeBlock | |
424 | InCombiningDiacriticalMarks | |
425 | InCombiningHalfMarks | |
426 | InCombiningMarksForSymbols | |
427 | InControlPictures | |
428 | InCurrencySymbols | |
429 | InCyrillicBlock | |
430 | InDeseretBlock | |
431 | InDevanagariBlock | |
432 | InDingbats | |
433 | InEnclosedAlphanumerics | |
434 | InEnclosedCJKLettersAndMonths | |
435 | InEthiopicBlock | |
436 | InGeneralPunctuation | |
437 | InGeometricShapes | |
438 | InGeorgianBlock | |
439 | InGothicBlock | |
440 | InGreekBlock | |
441 | InGreekExtended | |
442 | InGujaratiBlock | |
443 | InGurmukhiBlock | |
444 | InHalfwidthAndFullwidthForms | |
445 | InHangulCompatibilityJamo | |
446 | InHangulJamo | |
447 | InHangulSyllables | |
448 | InHebrewBlock | |
449 | InHighPrivateUseSurrogates | |
450 | InHighSurrogates | |
451 | InHiraganaBlock | |
452 | InIPAExtensions | |
453 | InIdeographicDescriptionCharacters | |
454 | InKanbun | |
455 | InKangxiRadicals | |
456 | InKannadaBlock | |
457 | InKatakanaBlock | |
458 | InKhmerBlock | |
459 | InLaoBlock | |
460 | InLatin1Supplement | |
461 | InLatinExtendedAdditional | |
462 | InLatinExtended-A | |
463 | InLatinExtended-B | |
464 | InLetterlikeSymbols | |
465 | InLowSurrogates | |
466 | InMalayalamBlock | |
467 | InMathematicalAlphanumericSymbols | |
468 | InMathematicalOperators | |
469 | InMiscellaneousSymbols | |
470 | InMiscellaneousTechnical | |
471 | InMongolianBlock | |
472 | InMusicalSymbols | |
473 | InMyanmarBlock | |
474 | InNumberForms | |
475 | InOghamBlock | |
476 | InOldItalicBlock | |
477 | InOpticalCharacterRecognition | |
478 | InOriyaBlock | |
479 | InPrivateUse | |
480 | InRunicBlock | |
481 | InSinhalaBlock | |
482 | InSmallFormVariants | |
483 | InSpacingModifierLetters | |
484 | InSpecials | |
485 | InSuperscriptsAndSubscripts | |
486 | InSyriacBlock | |
487 | InTags | |
488 | InTamilBlock | |
489 | InTeluguBlock | |
490 | InThaanaBlock | |
491 | InThaiBlock | |
492 | InTibetanBlock | |
493 | InUnifiedCanadianAboriginalSyllabics | |
494 | InYiRadicals | |
495 | InYiSyllables | |
32293815 | 496 | |
210b36aa AMS |
497 | =over 4 |
498 | ||
393fec97 GS |
499 | =item * |
500 | ||
c29a771d | 501 | The special pattern C<\X> matches any extended Unicode sequence |
393fec97 GS |
502 | (a "combining character sequence" in Standardese), where the first |
503 | character is a base character and subsequent characters are mark | |
504 | characters that apply to the base character. It is equivalent to | |
505 | C<(?:\PM\pM*)>. | |
506 | ||
393fec97 GS |
507 | =item * |
508 | ||
383e7cdd JH |
509 | The C<tr///> operator translates characters instead of bytes. Note |
510 | that the C<tr///CU> functionality has been removed, as the interface | |
511 | was a mistake. For similar functionality see pack('U0', ...) and | |
512 | pack('C0', ...). | |
393fec97 | 513 | |
393fec97 GS |
514 | =item * |
515 | ||
516 | Case translation operators use the Unicode case translation tables | |
44bc797b JH |
517 | when provided character input. Note that C<uc()> (also known as C<\U> |
518 | in doublequoted strings) translates to uppercase, while C<ucfirst> | |
519 | (also known as C<\u> in doublequoted strings) translates to titlecase | |
520 | (for languages that make the distinction). Naturally the | |
521 | corresponding backslash sequences have the same semantics. | |
393fec97 GS |
522 | |
523 | =item * | |
524 | ||
525 | Most operators that deal with positions or lengths in the string will | |
75daf61c JH |
526 | automatically switch to using character positions, including |
527 | C<chop()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>, | |
528 | C<sprintf()>, C<write()>, and C<length()>. Operators that | |
529 | specifically don't switch include C<vec()>, C<pack()>, and | |
530 | C<unpack()>. Operators that really don't care include C<chomp()>, as | |
531 | well as any other operator that treats a string as a bucket of bits, | |
532 | such as C<sort()>, and the operators dealing with filenames. | |
393fec97 GS |
533 | |
534 | =item * | |
535 | ||
536 | The C<pack()>/C<unpack()> letters "C<c>" and "C<C>" do I<not> change, | |
537 | since they're often used for byte-oriented formats. (Again, think | |
538 | "C<char>" in the C language.) However, there is a new "C<U>" specifier | |
3e4dbfed | 539 | that will convert between Unicode characters and integers. |
393fec97 GS |
540 | |
541 | =item * | |
542 | ||
543 | The C<chr()> and C<ord()> functions work on characters. This is like | |
544 | C<pack("U")> and C<unpack("U")>, not like C<pack("C")> and | |
545 | C<unpack("C")>. In fact, the latter are how you now emulate | |
35bcd338 | 546 | byte-oriented C<chr()> and C<ord()> for Unicode strings. |
3e4dbfed JF |
547 | (Note that this reveals the internal encoding of Unicode strings, |
548 | which is not something one normally needs to care about at all.) | |
393fec97 GS |
549 | |
550 | =item * | |
551 | ||
a1ca4561 YST |
552 | The bit string operators C<& | ^ ~> can operate on character data. |
553 | However, for backward compatibility reasons (bit string operations | |
75daf61c JH |
554 | when the characters all are less than 256 in ordinal value) one should |
555 | not mix C<~> (the bit complement) and characters both less than 256 and | |
a1ca4561 YST |
556 | equal or greater than 256. Most importantly, the DeMorgan's laws |
557 | (C<~($x|$y) eq ~$x&~$y>, C<~($x&$y) eq ~$x|~$y>) won't hold. | |
558 | Another way to look at this is that the complement cannot return | |
75daf61c | 559 | B<both> the 8-bit (byte) wide bit complement B<and> the full character |
a1ca4561 YST |
560 | wide bit complement. |
561 | ||
562 | =item * | |
563 | ||
983ffd37 JH |
564 | lc(), uc(), lcfirst(), and ucfirst() work for the following cases: |
565 | ||
566 | =over 8 | |
567 | ||
568 | =item * | |
569 | ||
570 | the case mapping is from a single Unicode character to another | |
571 | single Unicode character | |
572 | ||
573 | =item * | |
574 | ||
575 | the case mapping is from a single Unicode character to more | |
576 | than one Unicode character | |
577 | ||
578 | =back | |
579 | ||
210b36aa | 580 | What doesn't yet work are the following cases: |
983ffd37 JH |
581 | |
582 | =over 8 | |
583 | ||
584 | =item * | |
585 | ||
586 | the "final sigma" (Greek) | |
587 | ||
588 | =item * | |
589 | ||
590 | anything to with locales (Lithuanian, Turkish, Azeri) | |
591 | ||
592 | =back | |
593 | ||
594 | See the Unicode Technical Report #21, Case Mappings, for more details. | |
ac1256e8 JH |
595 | |
596 | =item * | |
597 | ||
393fec97 GS |
598 | And finally, C<scalar reverse()> reverses by character rather than by byte. |
599 | ||
600 | =back | |
601 | ||
8cbd9a7a GS |
602 | =head2 Character encodings for input and output |
603 | ||
7221edc9 | 604 | See L<Encode>. |
8cbd9a7a | 605 | |
c29a771d | 606 | =head2 Unicode Regular Expression Support Level |
776f8809 JH |
607 | |
608 | The following list of Unicode regular expression support describes | |
609 | feature by feature the Unicode support implemented in Perl as of Perl | |
610 | 5.8.0. The "Level N" and the section numbers refer to the Unicode | |
611 | Technical Report 18, "Unicode Regular Expression Guidelines". | |
612 | ||
613 | =over 4 | |
614 | ||
615 | =item * | |
616 | ||
617 | Level 1 - Basic Unicode Support | |
618 | ||
619 | 2.1 Hex Notation - done [1] | |
3bfdc84c | 620 | Named Notation - done [2] |
776f8809 JH |
621 | 2.2 Categories - done [3][4] |
622 | 2.3 Subtraction - MISSING [5][6] | |
623 | 2.4 Simple Word Boundaries - done [7] | |
78d3e1bf | 624 | 2.5 Simple Loose Matches - done [8] |
776f8809 JH |
625 | 2.6 End of Line - MISSING [9][10] |
626 | ||
627 | [ 1] \x{...} | |
628 | [ 2] \N{...} | |
eb0cc9e3 | 629 | [ 3] . \p{...} \P{...} |
29bdacb8 | 630 | [ 4] now scripts (see UTR#24 Script Names) in addition to blocks |
776f8809 | 631 | [ 5] have negation |
29bdacb8 | 632 | [ 6] can use look-ahead to emulate subtraction (*) |
776f8809 | 633 | [ 7] include Letters in word characters |
e0f9d4a8 JH |
634 | [ 8] note that perl does Full casefolding in matching, not Simple: |
635 | for example U+1F88 is equivalent with U+1F000 U+03B9, | |
636 | not with 1F80. This difference matters for certain Greek | |
637 | capital letters with certain modifiers: the Full casefolding | |
638 | decomposes the letter, while the Simple casefolding would map | |
639 | it to a single character. | |
776f8809 | 640 | [ 9] see UTR#13 Unicode Newline Guidelines |
ec83e909 JH |
641 | [10] should do ^ and $ also on \x{85}, \x{2028} and \x{2029}) |
642 | (should also affect <>, $., and script line numbers) | |
3bfdc84c | 643 | (the \x{85}, \x{2028} and \x{2029} do match \s) |
7207e29d | 644 | |
dbe420b4 JH |
645 | (*) You can mimic class subtraction using lookahead. |
646 | For example, what TR18 might write as | |
29bdacb8 | 647 | |
dbe420b4 JH |
648 | [{Greek}-[{UNASSIGNED}]] |
649 | ||
650 | in Perl can be written as: | |
651 | ||
eb0cc9e3 JH |
652 | (?!\p{Unassigned})\p{InGreek} |
653 | (?=\p{Assigned})\p{InGreek} | |
dbe420b4 JH |
654 | |
655 | But in this particular example, you probably really want | |
656 | ||
657 | \p{Greek} | |
658 | ||
659 | which will match assigned characters known to be part of the Greek script. | |
29bdacb8 | 660 | |
776f8809 JH |
661 | =item * |
662 | ||
663 | Level 2 - Extended Unicode Support | |
664 | ||
665 | 3.1 Surrogates - MISSING | |
666 | 3.2 Canonical Equivalents - MISSING [11][12] | |
667 | 3.3 Locale-Independent Graphemes - MISSING [13] | |
668 | 3.4 Locale-Independent Words - MISSING [14] | |
669 | 3.5 Locale-Independent Loose Matches - MISSING [15] | |
670 | ||
671 | [11] see UTR#15 Unicode Normalization | |
672 | [12] have Unicode::Normalize but not integrated to regexes | |
673 | [13] have \X but at this level . should equal that | |
674 | [14] need three classes, not just \w and \W | |
675 | [15] see UTR#21 Case Mappings | |
676 | ||
677 | =item * | |
678 | ||
679 | Level 3 - Locale-Sensitive Support | |
680 | ||
681 | 4.1 Locale-Dependent Categories - MISSING | |
682 | 4.2 Locale-Dependent Graphemes - MISSING [16][17] | |
683 | 4.3 Locale-Dependent Words - MISSING | |
684 | 4.4 Locale-Dependent Loose Matches - MISSING | |
685 | 4.5 Locale-Dependent Ranges - MISSING | |
686 | ||
687 | [16] see UTR#10 Unicode Collation Algorithms | |
688 | [17] have Unicode::Collate but not integrated to regexes | |
689 | ||
690 | =back | |
691 | ||
c349b1b9 JH |
692 | =head2 Unicode Encodings |
693 | ||
694 | Unicode characters are assigned to I<code points> which are abstract | |
86bbd6d1 | 695 | numbers. To use these numbers various encodings are needed. |
c349b1b9 JH |
696 | |
697 | =over 4 | |
698 | ||
c29a771d | 699 | =item * |
5cb3728c RB |
700 | |
701 | UTF-8 | |
c349b1b9 | 702 | |
3e4dbfed JF |
703 | UTF-8 is a variable-length (1 to 6 bytes, current character allocations |
704 | require 4 bytes), byteorder independent encoding. For ASCII, UTF-8 is | |
705 | transparent (and we really do mean 7-bit ASCII, not another 8-bit encoding). | |
c349b1b9 | 706 | |
8c007b5a | 707 | The following table is from Unicode 3.2. |
05632f9a JH |
708 | |
709 | Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte | |
710 | ||
8c007b5a JH |
711 | U+0000..U+007F 00..7F |
712 | U+0080..U+07FF C2..DF 80..BF | |
05632f9a | 713 | U+0800..U+0FFF E0 A0..BF 80..BFÂ Â |
8c007b5a JH |
714 | U+1000..U+CFFF E1..EC 80..BF 80..BFÂ Â |
715 | U+D000..U+D7FF ED 80..9F 80..BFÂ Â | |
716 | U+D800..U+DFFF ******* ill-formed ******* | |
717 | U+E000..U+FFFF EE..EF 80..BF 80..BFÂ Â | |
05632f9a JH |
718 | U+10000..U+3FFFF F0 90..BF 80..BF 80..BF |
719 | U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF | |
720 | U+100000..U+10FFFF F4 80..8F 80..BF 80..BF | |
721 | ||
8c007b5a JH |
722 | Note the A0..BF in U+0800..U+0FFF, the 80..9F in U+D000...U+D7FF, |
723 | the 90..BF in U+10000..U+3FFFF, and the 80...8F in U+100000..U+10FFFF. | |
05632f9a JH |
724 | Or, another way to look at it, as bits: |
725 | ||
726 | Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte | |
727 | ||
728 | 0aaaaaaa 0aaaaaaa | |
729 | 00000bbbbbaaaaaa 110bbbbb 10aaaaaa | |
730 | ccccbbbbbbaaaaaa 1110cccc 10bbbbbb 10aaaaaa | |
731 | 00000dddccccccbbbbbbaaaaaa 11110ddd 10cccccc 10bbbbbb 10aaaaaa | |
732 | ||
733 | As you can see, the continuation bytes all begin with C<10>, and the | |
8c007b5a | 734 | leading bits of the start byte tell how many bytes the are in the |
05632f9a JH |
735 | encoded character. |
736 | ||
c29a771d | 737 | =item * |
5cb3728c RB |
738 | |
739 | UTF-EBCDIC | |
dbe420b4 | 740 | |
fe854a6f | 741 | Like UTF-8, but EBCDIC-safe, as UTF-8 is ASCII-safe. |
dbe420b4 | 742 | |
c29a771d | 743 | =item * |
5cb3728c RB |
744 | |
745 | UTF-16, UTF-16BE, UTF16-LE, Surrogates, and BOMs (Byte Order Marks) | |
c349b1b9 | 746 | |
dbe420b4 JH |
747 | (The followings items are mostly for reference, Perl doesn't |
748 | use them internally.) | |
749 | ||
c349b1b9 JH |
750 | UTF-16 is a 2 or 4 byte encoding. The Unicode code points |
751 | 0x0000..0xFFFF are stored in two 16-bit units, and the code points | |
dbe420b4 | 752 | 0x010000..0x10FFFF in two 16-bit units. The latter case is |
c349b1b9 JH |
753 | using I<surrogates>, the first 16-bit unit being the I<high |
754 | surrogate>, and the second being the I<low surrogate>. | |
755 | ||
756 | Surrogates are code points set aside to encode the 0x01000..0x10FFFF | |
757 | range of Unicode code points in pairs of 16-bit units. The I<high | |
758 | surrogates> are the range 0xD800..0xDBFF, and the I<low surrogates> | |
759 | are the range 0xDC00..0xDFFFF. The surrogate encoding is | |
760 | ||
761 | $hi = ($uni - 0x10000) / 0x400 + 0xD800; | |
762 | $lo = ($uni - 0x10000) % 0x400 + 0xDC00; | |
763 | ||
764 | and the decoding is | |
765 | ||
766 | $uni = 0x10000 + ($hi - 0xD8000) * 0x400 + ($lo - 0xDC00); | |
767 | ||
feda178f JH |
768 | If you try to generate surrogates (for example by using chr()), you |
769 | will get a warning if warnings are turned on (C<-w> or C<use | |
770 | warnings;>) because those code points are not valid for a Unicode | |
771 | character. | |
9466bab6 | 772 | |
86bbd6d1 | 773 | Because of the 16-bitness, UTF-16 is byteorder dependent. UTF-16 |
c349b1b9 | 774 | itself can be used for in-memory computations, but if storage or |
86bbd6d1 | 775 | transfer is required, either UTF-16BE (Big Endian) or UTF-16LE |
c349b1b9 JH |
776 | (Little Endian) must be chosen. |
777 | ||
778 | This introduces another problem: what if you just know that your data | |
779 | is UTF-16, but you don't know which endianness? Byte Order Marks | |
780 | (BOMs) are a solution to this. A special character has been reserved | |
86bbd6d1 PN |
781 | in Unicode to function as a byte order marker: the character with the |
782 | code point 0xFEFF is the BOM. | |
042da322 | 783 | |
c349b1b9 JH |
784 | The trick is that if you read a BOM, you will know the byte order, |
785 | since if it was written on a big endian platform, you will read the | |
86bbd6d1 PN |
786 | bytes 0xFE 0xFF, but if it was written on a little endian platform, |
787 | you will read the bytes 0xFF 0xFE. (And if the originating platform | |
788 | was writing in UTF-8, you will read the bytes 0xEF 0xBB 0xBF.) | |
042da322 | 789 | |
86bbd6d1 PN |
790 | The way this trick works is that the character with the code point |
791 | 0xFFFE is guaranteed not to be a valid Unicode character, so the | |
792 | sequence of bytes 0xFF 0xFE is unambiguously "BOM, represented in | |
042da322 JH |
793 | little-endian format" and cannot be "0xFFFE, represented in big-endian |
794 | format". | |
c349b1b9 | 795 | |
c29a771d | 796 | =item * |
5cb3728c RB |
797 | |
798 | UTF-32, UTF-32BE, UTF32-LE | |
c349b1b9 JH |
799 | |
800 | The UTF-32 family is pretty much like the UTF-16 family, expect that | |
042da322 JH |
801 | the units are 32-bit, and therefore the surrogate scheme is not |
802 | needed. The BOM signatures will be 0x00 0x00 0xFE 0xFF for BE and | |
803 | 0xFF 0xFE 0x00 0x00 for LE. | |
c349b1b9 | 804 | |
c29a771d | 805 | =item * |
5cb3728c RB |
806 | |
807 | UCS-2, UCS-4 | |
c349b1b9 | 808 | |
86bbd6d1 PN |
809 | Encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit |
810 | encoding, UCS-4 is a 32-bit encoding. Unlike UTF-16, UCS-2 | |
811 | is not extensible beyond 0xFFFF, because it does not use surrogates. | |
c349b1b9 | 812 | |
c29a771d | 813 | =item * |
5cb3728c RB |
814 | |
815 | UTF-7 | |
c349b1b9 JH |
816 | |
817 | A seven-bit safe (non-eight-bit) encoding, useful if the | |
818 | transport/storage is not eight-bit safe. Defined by RFC 2152. | |
819 | ||
95a1a48b JH |
820 | =back |
821 | ||
bf0fa0b2 JH |
822 | =head2 Security Implications of Malformed UTF-8 |
823 | ||
824 | Unfortunately, the specification of UTF-8 leaves some room for | |
825 | interpretation of how many bytes of encoded output one should generate | |
826 | from one input Unicode character. Strictly speaking, one is supposed | |
827 | to always generate the shortest possible sequence of UTF-8 bytes, | |
feda178f JH |
828 | because otherwise there is potential for input buffer overflow at |
829 | the receiving end of a UTF-8 connection. Perl always generates the | |
830 | shortest length UTF-8, and with warnings on (C<-w> or C<use | |
831 | warnings;>) Perl will warn about non-shortest length UTF-8 (and other | |
832 | malformations, too, such as the surrogates, which are not real | |
833 | Unicode code points.) | |
bf0fa0b2 | 834 | |
c349b1b9 JH |
835 | =head2 Unicode in Perl on EBCDIC |
836 | ||
837 | The way Unicode is handled on EBCDIC platforms is still rather | |
86bbd6d1 | 838 | experimental. On such a platform, references to UTF-8 encoding in this |
c349b1b9 JH |
839 | document and elsewhere should be read as meaning UTF-EBCDIC as |
840 | specified in Unicode Technical Report 16 unless ASCII vs EBCDIC issues | |
841 | are specifically discussed. There is no C<utfebcdic> pragma or | |
86bbd6d1 PN |
842 | ":utfebcdic" layer, rather, "utf8" and ":utf8" are re-used to mean |
843 | the platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic> | |
844 | for more discussion of the issues. | |
c349b1b9 | 845 | |
b310b053 JH |
846 | =head2 Locales |
847 | ||
4616122b | 848 | Usually locale settings and Unicode do not affect each other, but |
b310b053 JH |
849 | there are a couple of exceptions: |
850 | ||
851 | =over 4 | |
852 | ||
853 | =item * | |
854 | ||
855 | If your locale environment variables (LANGUAGE, LC_ALL, LC_CTYPE, LANG) | |
856 | contain the strings 'UTF-8' or 'UTF8' (case-insensitive matching), | |
857 | the default encoding of your STDIN, STDOUT, and STDERR, and of | |
858 | B<any subsequent file open>, is UTF-8. | |
859 | ||
860 | =item * | |
861 | ||
862 | Perl tries really hard to work both with Unicode and the old byte | |
863 | oriented world: most often this is nice, but sometimes this causes | |
574c8022 | 864 | problems. |
b310b053 JH |
865 | |
866 | =back | |
867 | ||
95a1a48b JH |
868 | =head2 Using Unicode in XS |
869 | ||
870 | If you want to handle Perl Unicode in XS extensions, you may find | |
90f968e0 | 871 | the following C APIs useful (see perlapi for details): |
95a1a48b JH |
872 | |
873 | =over 4 | |
874 | ||
875 | =item * | |
876 | ||
f1e62f77 AT |
877 | DO_UTF8(sv) returns true if the UTF8 flag is on and the bytes pragma |
878 | is not in effect. SvUTF8(sv) returns true is the UTF8 flag is on, the | |
879 | bytes pragma is ignored. The UTF8 flag being on does B<not> mean that | |
b31c5e31 AT |
880 | there are any characters of code points greater than 255 (or 127) in |
881 | the scalar, or that there even are any characters in the scalar. | |
882 | What the UTF8 flag means is that the sequence of octets in the | |
883 | representation of the scalar is the sequence of UTF-8 encoded | |
884 | code points of the characters of a string. The UTF8 flag being | |
885 | off means that each octet in this representation encodes a single | |
886 | character with codepoint 0..255 within the string. Perl's Unicode | |
887 | model is not to use UTF-8 until it's really necessary. | |
95a1a48b JH |
888 | |
889 | =item * | |
890 | ||
891 | uvuni_to_utf8(buf, chr) writes a Unicode character code point into a | |
cfc01aea | 892 | buffer encoding the code point as UTF-8, and returns a pointer |
95a1a48b JH |
893 | pointing after the UTF-8 bytes. |
894 | ||
895 | =item * | |
896 | ||
897 | utf8_to_uvuni(buf, lenp) reads UTF-8 encoded bytes from a buffer and | |
898 | returns the Unicode character code point (and optionally the length of | |
899 | the UTF-8 byte sequence). | |
900 | ||
901 | =item * | |
902 | ||
90f968e0 JH |
903 | utf8_length(start, end) returns the length of the UTF-8 encoded buffer |
904 | in characters. sv_len_utf8(sv) returns the length of the UTF-8 encoded | |
95a1a48b JH |
905 | scalar. |
906 | ||
907 | =item * | |
908 | ||
909 | sv_utf8_upgrade(sv) converts the string of the scalar to its UTF-8 | |
910 | encoded form. sv_utf8_downgrade(sv) does the opposite (if possible). | |
911 | sv_utf8_encode(sv) is like sv_utf8_upgrade but the UTF8 flag does not | |
912 | get turned on. sv_utf8_decode() does the opposite of sv_utf8_encode(). | |
13a6c0e0 JH |
913 | Note that none of these are to be used as general purpose encoding/decoding |
914 | interfaces: use Encode for that. sv_utf8_upgrade() is affected by the | |
915 | encoding pragma, but sv_utf8_downgrade() is not (since the encoding | |
916 | pragma is designed to be a one-way street). | |
95a1a48b JH |
917 | |
918 | =item * | |
919 | ||
90f968e0 JH |
920 | is_utf8_char(s) returns true if the pointer points to a valid UTF-8 |
921 | character. | |
95a1a48b JH |
922 | |
923 | =item * | |
924 | ||
925 | is_utf8_string(buf, len) returns true if the len bytes of the buffer | |
926 | are valid UTF-8. | |
927 | ||
928 | =item * | |
929 | ||
930 | UTF8SKIP(buf) will return the number of bytes in the UTF-8 encoded | |
931 | character in the buffer. UNISKIP(chr) will return the number of bytes | |
90f968e0 JH |
932 | required to UTF-8-encode the Unicode character code point. UTF8SKIP() |
933 | is useful for example for iterating over the characters of a UTF-8 | |
934 | encoded buffer; UNISKIP() is useful for example in computing | |
935 | the size required for a UTF-8 encoded buffer. | |
95a1a48b JH |
936 | |
937 | =item * | |
938 | ||
939 | utf8_distance(a, b) will tell the distance in characters between the | |
940 | two pointers pointing to the same UTF-8 encoded buffer. | |
941 | ||
942 | =item * | |
943 | ||
944 | utf8_hop(s, off) will return a pointer to an UTF-8 encoded buffer that | |
945 | is C<off> (positive or negative) Unicode characters displaced from the | |
90f968e0 JH |
946 | UTF-8 buffer C<s>. Be careful not to overstep the buffer: utf8_hop() |
947 | will merrily run off the end or the beginning if told to do so. | |
95a1a48b | 948 | |
d2cc3551 JH |
949 | =item * |
950 | ||
951 | pv_uni_display(dsv, spv, len, pvlim, flags) and sv_uni_display(dsv, | |
952 | ssv, pvlim, flags) are useful for debug output of Unicode strings and | |
90f968e0 JH |
953 | scalars. By default they are useful only for debug: they display |
954 | B<all> characters as hexadecimal code points, but with the flags | |
955 | UNI_DISPLAY_ISPRINT and UNI_DISPLAY_BACKSLASH you can make the output | |
956 | more readable. | |
d2cc3551 JH |
957 | |
958 | =item * | |
959 | ||
90f968e0 JH |
960 | ibcmp_utf8(s1, pe1, u1, l1, u1, s2, pe2, l2, u2) can be used to |
961 | compare two strings case-insensitively in Unicode. | |
962 | (For case-sensitive comparisons you can just use memEQ() and memNE() | |
963 | as usual.) | |
d2cc3551 | 964 | |
c349b1b9 JH |
965 | =back |
966 | ||
95a1a48b JH |
967 | For more information, see L<perlapi>, and F<utf8.c> and F<utf8.h> |
968 | in the Perl source code distribution. | |
969 | ||
c29a771d JH |
970 | =head1 BUGS |
971 | ||
972 | Use of locales with Unicode data may lead to odd results. Currently | |
973 | there is some attempt to apply 8-bit locale info to characters in the | |
974 | range 0..255, but this is demonstrably incorrect for locales that use | |
975 | characters above that range when mapped into Unicode. It will also | |
574c8022 | 976 | tend to run slower. Use of locales with Unicode is discouraged. |
c29a771d JH |
977 | |
978 | Some functions are slower when working on UTF-8 encoded strings than | |
574c8022 | 979 | on byte encoded strings. All functions that need to hop over |
c29a771d JH |
980 | characters such as length(), substr() or index() can work B<much> |
981 | faster when the underlying data are byte-encoded. Witness the | |
982 | following benchmark: | |
666f95b9 | 983 | |
c29a771d JH |
984 | % perl -e ' |
985 | use Benchmark; | |
986 | use strict; | |
987 | our $l = 10000; | |
988 | our $u = our $b = "x" x $l; | |
989 | substr($u,0,1) = "\x{100}"; | |
990 | timethese(-2,{ | |
991 | LENGTH_B => q{ length($b) }, | |
992 | LENGTH_U => q{ length($u) }, | |
993 | SUBSTR_B => q{ substr($b, $l/4, $l/2) }, | |
994 | SUBSTR_U => q{ substr($u, $l/4, $l/2) }, | |
995 | }); | |
996 | ' | |
997 | Benchmark: running LENGTH_B, LENGTH_U, SUBSTR_B, SUBSTR_U for at least 2 CPU seconds... | |
998 | LENGTH_B: 2 wallclock secs ( 2.36 usr + 0.00 sys = 2.36 CPU) @ 5649983.05/s (n=13333960) | |
999 | LENGTH_U: 2 wallclock secs ( 2.11 usr + 0.00 sys = 2.11 CPU) @ 12155.45/s (n=25648) | |
1000 | SUBSTR_B: 3 wallclock secs ( 2.16 usr + 0.00 sys = 2.16 CPU) @ 374480.09/s (n=808877) | |
1001 | SUBSTR_U: 2 wallclock secs ( 2.11 usr + 0.00 sys = 2.11 CPU) @ 6791.00/s (n=14329) | |
666f95b9 | 1002 | |
c29a771d JH |
1003 | The numbers show an incredible slowness on long UTF-8 strings and you |
1004 | should carefully avoid to use these functions within tight loops. For | |
1005 | example if you want to iterate over characters, it is infinitely | |
1006 | better to split into an array than to use substr, as the following | |
1007 | benchmark shows: | |
1008 | ||
1009 | % perl -e ' | |
1010 | use Benchmark; | |
1011 | use strict; | |
1012 | our $l = 10000; | |
1013 | our $u = our $b = "x" x $l; | |
1014 | substr($u,0,1) = "\x{100}"; | |
1015 | timethese(-5,{ | |
1016 | SPLIT_B => q{ for my $c (split //, $b){} }, | |
1017 | SPLIT_U => q{ for my $c (split //, $u){} }, | |
1018 | SUBSTR_B => q{ for my $i (0..length($b)-1){my $c = substr($b,$i,1);} }, | |
1019 | SUBSTR_U => q{ for my $i (0..length($u)-1){my $c = substr($u,$i,1);} }, | |
1020 | }); | |
1021 | ' | |
1022 | Benchmark: running SPLIT_B, SPLIT_U, SUBSTR_B, SUBSTR_U for at least 5 CPU seconds... | |
1023 | SPLIT_B: 6 wallclock secs ( 5.29 usr + 0.00 sys = 5.29 CPU) @ 56.14/s (n=297) | |
1024 | SPLIT_U: 5 wallclock secs ( 5.17 usr + 0.01 sys = 5.18 CPU) @ 55.21/s (n=286) | |
1025 | SUBSTR_B: 5 wallclock secs ( 5.34 usr + 0.00 sys = 5.34 CPU) @ 123.22/s (n=658) | |
1026 | SUBSTR_U: 7 wallclock secs ( 6.20 usr + 0.00 sys = 6.20 CPU) @ 0.81/s (n=5) | |
1027 | ||
1028 | You see, the algorithm based on substr() was faster with byte encoded | |
1029 | data but it is pathologically slow with UTF-8 data. | |
666f95b9 | 1030 | |
393fec97 GS |
1031 | =head1 SEE ALSO |
1032 | ||
72ff2908 JH |
1033 | L<perluniintro>, L<encoding>, L<Encode>, L<open>, L<utf8>, L<bytes>, |
1034 | L<perlretut>, L<perlvar/"${^WIDE_SYSTEM_CALLS}"> | |
393fec97 GS |
1035 | |
1036 | =cut |