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1 | =head1 NAME |
2 | |
3 | perlunicode - Unicode support in Perl |
4 | |
5 | =head1 DESCRIPTION |
6 | |
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7 | =head2 Important Caveats |
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8 | |
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9 | WARNING: While the implementation of Unicode support in Perl is now fairly |
10 | complete it is still evolving to some extent. |
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11 | |
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12 | In particular the way Unicode is handled on EBCDIC platforms is still |
13 | rather experimental. On such a platform references to UTF-8 encoding |
14 | in this document and elsewhere should be read as meaning UTF-EBCDIC as |
15 | specified in Unicode Technical Report 16 unless ASCII vs EBCDIC issues |
16 | are specifically discussed. There is no C<utfebcdic> pragma or |
17 | ":utfebcdic" layer, rather "utf8" and ":utf8" are re-used to mean |
18 | platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic> for |
19 | more discussion of the issues. |
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20 | |
21 | The following areas are still under development. |
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22 | |
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23 | =over 4 |
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24 | |
25 | =item Input and Output Disciplines |
26 | |
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27 | A filehandle can be marked as containing perl's internal Unicode |
28 | encoding (UTF-8 or UTF-EBCDIC) by opening it with the ":utf8" layer. |
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29 | Other encodings can be converted to perl's encoding on input, or from |
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30 | perl's encoding on output by use of the ":encoding()" layer. There is |
31 | not yet a clean way to mark the Perl source itself as being in an |
32 | particular encoding. |
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33 | |
34 | =item Regular Expressions |
35 | |
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36 | The regular expression compiler does now attempt to produce |
37 | polymorphic opcodes. That is the pattern should now adapt to the data |
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38 | and automatically switch to the Unicode character scheme when |
39 | presented with Unicode data, or a traditional byte scheme when |
40 | presented with byte data. The implementation is still new and |
41 | (particularly on EBCDIC platforms) may need further work. |
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42 | |
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43 | =item C<use utf8> still needed to enable UTF-8/UTF-EBCDIC in scripts |
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44 | |
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45 | The C<utf8> pragma implements the tables used for Unicode support. |
46 | These tables are automatically loaded on demand, so the C<utf8> pragma |
47 | need not normally be used. |
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48 | |
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49 | However, as a compatibility measure, this pragma must be explicitly |
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50 | used to enable recognition of UTF-8 in the Perl scripts themselves on |
51 | ASCII based machines or recognize UTF-EBCDIC on EBCDIC based machines. |
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52 | B<NOTE: this should be the only place where an explicit C<use utf8> is |
53 | needed>. |
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54 | |
55 | =back |
56 | |
57 | =head2 Byte and Character semantics |
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58 | |
59 | Beginning with version 5.6, Perl uses logically wide characters to |
60 | represent strings internally. This internal representation of strings |
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61 | uses either the UTF-8 or the UTF-EBCDIC encoding. |
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62 | |
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63 | In future, Perl-level operations can be expected to work with |
64 | characters rather than bytes, in general. |
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65 | |
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66 | However, as strictly an interim compatibility measure, Perl aims to |
67 | provide a safe migration path from byte semantics to character |
68 | semantics for programs. For operations where Perl can unambiguously |
69 | decide that the input data is characters, Perl now switches to |
70 | character semantics. For operations where this determination cannot |
71 | be made without additional information from the user, Perl decides in |
72 | favor of compatibility, and chooses to use byte semantics. |
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73 | |
74 | This behavior preserves compatibility with earlier versions of Perl, |
75 | which allowed byte semantics in Perl operations, but only as long as |
76 | none of the program's inputs are marked as being as source of Unicode |
77 | character data. Such data may come from filehandles, from calls to |
78 | external programs, from information provided by the system (such as %ENV), |
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79 | or from literals and constants in the source text. |
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80 | |
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81 | If the C<-C> command line switch is used, (or the |
82 | ${^WIDE_SYSTEM_CALLS} global flag is set to C<1>), all system calls |
83 | will use the corresponding wide character APIs. Note that this is |
84 | currently only implemented on Windows since other platforms API |
85 | standard on this area. |
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86 | |
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87 | Regardless of the above, the C<bytes> pragma can always be used to |
88 | force byte semantics in a particular lexical scope. See L<bytes>. |
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89 | |
90 | The C<utf8> pragma is primarily a compatibility device that enables |
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91 | recognition of UTF-(8|EBCDIC) in literals encountered by the parser. |
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92 | Note that this pragma is only required until a future version of Perl |
93 | in which character semantics will become the default. This pragma may |
94 | then become a no-op. See L<utf8>. |
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95 | |
96 | Unless mentioned otherwise, Perl operators will use character semantics |
97 | when they are dealing with Unicode data, and byte semantics otherwise. |
98 | Thus, character semantics for these operations apply transparently; if |
99 | the input data came from a Unicode source (for example, by adding a |
100 | character encoding discipline to the filehandle whence it came, or a |
101 | literal UTF-8 string constant in the program), character semantics |
102 | apply; otherwise, byte semantics are in effect. To force byte semantics |
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103 | on Unicode data, the C<bytes> pragma should be used. |
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104 | |
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105 | Notice that if you have a string with byte semantics and you then |
106 | add character data into it, the bytes will be upgraded I<as if they |
107 | were ISO 8859-1 (Latin-1)> (or if in EBCDIC, after a translation |
108 | to ISO 8859-1). |
109 | |
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110 | Under character semantics, many operations that formerly operated on |
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111 | bytes change to operating on characters. For ASCII data this makes no |
112 | difference, because UTF-8 stores ASCII in single bytes, but for any |
113 | character greater than C<chr(127)>, the character B<may> be stored in |
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114 | a sequence of two or more bytes, all of which have the high bit set. |
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115 | |
116 | For C1 controls or Latin 1 characters on an EBCDIC platform the |
117 | character may be stored in a UTF-EBCDIC multi byte sequence. But by |
118 | and large, the user need not worry about this, because Perl hides it |
119 | from the user. A character in Perl is logically just a number ranging |
120 | from 0 to 2**32 or so. Larger characters encode to longer sequences |
121 | of bytes internally, but again, this is just an internal detail which |
122 | is hidden at the Perl level. |
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123 | |
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124 | =head2 Effects of character semantics |
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125 | |
126 | Character semantics have the following effects: |
127 | |
128 | =over 4 |
129 | |
130 | =item * |
131 | |
132 | Strings and patterns may contain characters that have an ordinal value |
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133 | larger than 255. |
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134 | |
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135 | Presuming you use a Unicode editor to edit your program, such |
136 | characters will typically occur directly within the literal strings as |
137 | UTF-8 (or UTF-EBCDIC on EBCDIC platforms) characters, but you can also |
138 | specify a particular character with an extension of the C<\x> |
139 | notation. UTF-X characters are specified by putting the hexadecimal |
140 | code within curlies after the C<\x>. For instance, a Unicode smiley |
141 | face is C<\x{263A}>. |
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142 | |
143 | =item * |
144 | |
145 | Identifiers within the Perl script may contain Unicode alphanumeric |
146 | characters, including ideographs. (You are currently on your own when |
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147 | it comes to using the canonical forms of characters--Perl doesn't |
148 | (yet) attempt to canonicalize variable names for you.) |
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149 | |
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150 | =item * |
151 | |
152 | Regular expressions match characters instead of bytes. For instance, |
153 | "." matches a character instead of a byte. (However, the C<\C> pattern |
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154 | is provided to force a match a single byte ("C<char>" in C, hence C<\C>).) |
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155 | |
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156 | =item * |
157 | |
158 | Character classes in regular expressions match characters instead of |
159 | bytes, and match against the character properties specified in the |
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160 | Unicode properties database. So C<\w> can be used to match an |
161 | ideograph, for instance. |
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162 | |
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163 | =item * |
164 | |
165 | Named Unicode properties and block ranges make be used as character |
166 | classes via the new C<\p{}> (matches property) and C<\P{}> (doesn't |
167 | match property) constructs. For instance, C<\p{Lu}> matches any |
168 | character with the Unicode uppercase property, while C<\p{M}> matches |
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169 | any mark character. Single letter properties may omit the brackets, |
170 | so that can be written C<\pM> also. Many predefined character classes |
171 | are available, such as C<\p{IsMirrored}> and C<\p{InTibetan}>. The |
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172 | names of the C<In> classes are the official Unicode script and block |
173 | names but with all non-alphanumeric characters removed, for example |
174 | the block name C<"Latin-1 Supplement"> becomes C<\p{InLatin1Supplement}>. |
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175 | |
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176 | Here is the list as of Unicode 3.1.0 (the two-letter classes) and |
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177 | as defined by Perl (the one-letter classes) (in Unicode materials |
178 | what Perl calls C<L> is often called C<L&>): |
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179 | |
180 | L Letter |
181 | Lu Letter, Uppercase |
182 | Ll Letter, Lowercase |
183 | Lt Letter, Titlecase |
184 | Lm Letter, Modifier |
185 | Lo Letter, Other |
186 | M Mark |
187 | Mn Mark, Non-Spacing |
188 | Mc Mark, Spacing Combining |
189 | Me Mark, Enclosing |
190 | N Number |
191 | Nd Number, Decimal Digit |
192 | Nl Number, Letter |
193 | No Number, Other |
194 | P Punctuation |
195 | Pc Punctuation, Connector |
196 | Pd Punctuation, Dash |
197 | Ps Punctuation, Open |
198 | Pe Punctuation, Close |
199 | Pi Punctuation, Initial quote |
200 | (may behave like Ps or Pe depending on usage) |
201 | Pf Punctuation, Final quote |
202 | (may behave like Ps or Pe depending on usage) |
203 | Po Punctuation, Other |
204 | S Symbol |
205 | Sm Symbol, Math |
206 | Sc Symbol, Currency |
207 | Sk Symbol, Modifier |
208 | So Symbol, Other |
209 | Z Separator |
210 | Zs Separator, Space |
211 | Zl Separator, Line |
212 | Zp Separator, Paragraph |
213 | C Other |
214 | Cc Other, Control |
215 | Cf Other, Format |
216 | Cs Other, Surrogate |
217 | Co Other, Private Use |
218 | Cn Other, Not Assigned (Unicode defines no Cn characters) |
219 | |
220 | Additionally, because scripts differ in their directionality |
221 | (for example Hebrew is written right to left), all characters |
222 | have their directionality defined: |
223 | |
224 | BidiL Left-to-Right |
225 | BidiLRE Left-to-Right Embedding |
226 | BidiLRO Left-to-Right Override |
227 | BidiR Right-to-Left |
228 | BidiAL Right-to-Left Arabic |
229 | BidiRLE Right-to-Left Embedding |
230 | BidiRLO Right-to-Left Override |
231 | BidiPDF Pop Directional Format |
232 | BidiEN European Number |
233 | BidiES European Number Separator |
234 | BidiET European Number Terminator |
235 | BidiAN Arabic Number |
236 | BidiCS Common Number Separator |
237 | BidiNSM Non-Spacing Mark |
238 | BidiBN Boundary Neutral |
239 | BidiB Paragraph Separator |
240 | BidiS Segment Separator |
241 | BidiWS Whitespace |
242 | BidiON Other Neutrals |
243 | |
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244 | =head2 Scripts |
245 | |
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246 | The scripts available for C<\p{In...}> and C<\P{In...}>, for example |
247 | \p{InCyrillic>, are as follows, for example C<\p{InLatin}> or C<\P{InHan}>: |
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248 | |
249 | Latin |
250 | Greek |
251 | Cyrillic |
252 | Armenian |
253 | Hebrew |
254 | Arabic |
255 | Syriac |
256 | Thaana |
257 | Devanagari |
258 | Bengali |
259 | Gurmukhi |
260 | Gujarati |
261 | Oriya |
262 | Tamil |
263 | Telugu |
264 | Kannada |
265 | Malayalam |
266 | Sinhala |
267 | Thai |
268 | Lao |
269 | Tibetan |
270 | Myanmar |
271 | Georgian |
272 | Hangul |
273 | Ethiopic |
274 | Cherokee |
275 | CanadianAboriginal |
276 | Ogham |
277 | Runic |
278 | Khmer |
279 | Mongolian |
280 | Hiragana |
281 | Katakana |
282 | Bopomofo |
283 | Han |
284 | Yi |
285 | OldItalic |
286 | Gothic |
287 | Deseret |
288 | Inherited |
289 | |
290 | =head2 Blocks |
291 | |
292 | In addition to B<scripts>, Unicode also defines B<blocks> of |
293 | characters. The difference between scripts and blocks is that the |
294 | former concept is closer to natural languages, while the latter |
295 | concept is more an artificial grouping based on groups of 256 Unicode |
296 | characters. For example, the C<Latin> script contains letters from |
297 | many blocks, but it does not contain all the characters from those |
298 | blocks, it does not for example contain digits. |
299 | |
300 | For more about scripts see the UTR #24: |
301 | http://www.unicode.org/unicode/reports/tr24/ |
302 | For more about blocks see |
303 | http://www.unicode.org/Public/UNIDATA/Blocks.txt |
304 | |
305 | Because there are overlaps in naming (there are, for example, both |
306 | a script called C<Katakana> and a block called C<Katakana>, the block |
307 | version has C<Block> appended to its name, C<\p{InKatakanaBlock}>. |
308 | |
309 | Notice that this definition was introduced in Perl 5.8.0: in Perl |
310 | 5.6.0 only the blocks were used; in Perl 5.8.0 scripts became the |
311 | preferential character class definition; this meant that the |
312 | definitions of some character classes changed (the ones in the |
313 | below list that have the C<Block> appended). |
314 | |
315 | BasicLatin |
316 | Latin1Supplement |
317 | LatinExtendedA |
318 | LatinExtendedB |
319 | IPAExtensions |
320 | SpacingModifierLetters |
321 | CombiningDiacriticalMarks |
322 | GreekBlock |
323 | CyrillicBlock |
324 | ArmenianBlock |
325 | HebrewBlock |
326 | ArabicBlock |
327 | SyriacBlock |
328 | ThaanaBlock |
329 | DevanagariBlock |
330 | BengaliBlock |
331 | GurmukhiBlock |
332 | GujaratiBlock |
333 | OriyaBlock |
334 | TamilBlock |
335 | TeluguBlock |
336 | KannadaBlock |
337 | MalayalamBlock |
338 | SinhalaBlock |
339 | ThaiBlock |
340 | LaoBlock |
341 | TibetanBlock |
342 | MyanmarBlock |
343 | GeorgianBlock |
344 | HangulJamo |
345 | EthiopicBlock |
346 | CherokeeBlock |
347 | UnifiedCanadianAboriginalSyllabics |
348 | OghamBlock |
349 | RunicBlock |
350 | KhmerBlock |
351 | MongolianBlock |
352 | LatinExtendedAdditional |
353 | GreekExtended |
354 | GeneralPunctuation |
355 | SuperscriptsandSubscripts |
356 | CurrencySymbols |
357 | CombiningMarksforSymbols |
358 | LetterlikeSymbols |
359 | NumberForms |
360 | Arrows |
361 | MathematicalOperators |
362 | MiscellaneousTechnical |
363 | ControlPictures |
364 | OpticalCharacterRecognition |
365 | EnclosedAlphanumerics |
366 | BoxDrawing |
367 | BlockElements |
368 | GeometricShapes |
369 | MiscellaneousSymbols |
370 | Dingbats |
371 | BraillePatterns |
372 | CJKRadicalsSupplement |
373 | KangxiRadicals |
374 | IdeographicDescriptionCharacters |
375 | CJKSymbolsandPunctuation |
376 | HiraganaBlock |
377 | KatakanaBlock |
378 | BopomofoBlock |
379 | HangulCompatibilityJamo |
380 | Kanbun |
381 | BopomofoExtended |
382 | EnclosedCJKLettersandMonths |
383 | CJKCompatibility |
384 | CJKUnifiedIdeographsExtensionA |
385 | CJKUnifiedIdeographs |
386 | YiSyllables |
387 | YiRadicals |
388 | HangulSyllables |
389 | HighSurrogates |
390 | HighPrivateUseSurrogates |
391 | LowSurrogates |
392 | PrivateUse |
393 | CJKCompatibilityIdeographs |
394 | AlphabeticPresentationForms |
395 | ArabicPresentationFormsA |
396 | CombiningHalfMarks |
397 | CJKCompatibilityForms |
398 | SmallFormVariants |
399 | ArabicPresentationFormsB |
400 | Specials |
401 | HalfwidthandFullwidthForms |
402 | OldItalicBlock |
403 | GothicBlock |
404 | DeseretBlock |
405 | ByzantineMusicalSymbols |
406 | MusicalSymbols |
407 | MathematicalAlphanumericSymbols |
408 | CJKUnifiedIdeographsExtensionB |
409 | CJKCompatibilityIdeographsSupplement |
410 | Tags |
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411 | |
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412 | =item * |
413 | |
414 | The special pattern C<\X> match matches any extended Unicode sequence |
415 | (a "combining character sequence" in Standardese), where the first |
416 | character is a base character and subsequent characters are mark |
417 | characters that apply to the base character. It is equivalent to |
418 | C<(?:\PM\pM*)>. |
419 | |
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420 | =item * |
421 | |
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422 | The C<tr///> operator translates characters instead of bytes. Note |
423 | that the C<tr///CU> functionality has been removed, as the interface |
424 | was a mistake. For similar functionality see pack('U0', ...) and |
425 | pack('C0', ...). |
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426 | |
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427 | =item * |
428 | |
429 | Case translation operators use the Unicode case translation tables |
430 | when provided character input. Note that C<uc()> translates to |
431 | uppercase, while C<ucfirst> translates to titlecase (for languages |
432 | that make the distinction). Naturally the corresponding backslash |
433 | sequences have the same semantics. |
434 | |
435 | =item * |
436 | |
437 | Most operators that deal with positions or lengths in the string will |
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438 | automatically switch to using character positions, including |
439 | C<chop()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>, |
440 | C<sprintf()>, C<write()>, and C<length()>. Operators that |
441 | specifically don't switch include C<vec()>, C<pack()>, and |
442 | C<unpack()>. Operators that really don't care include C<chomp()>, as |
443 | well as any other operator that treats a string as a bucket of bits, |
444 | such as C<sort()>, and the operators dealing with filenames. |
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445 | |
446 | =item * |
447 | |
448 | The C<pack()>/C<unpack()> letters "C<c>" and "C<C>" do I<not> change, |
449 | since they're often used for byte-oriented formats. (Again, think |
450 | "C<char>" in the C language.) However, there is a new "C<U>" specifier |
451 | that will convert between UTF-8 characters and integers. (It works |
452 | outside of the utf8 pragma too.) |
453 | |
454 | =item * |
455 | |
456 | The C<chr()> and C<ord()> functions work on characters. This is like |
457 | C<pack("U")> and C<unpack("U")>, not like C<pack("C")> and |
458 | C<unpack("C")>. In fact, the latter are how you now emulate |
459 | byte-oriented C<chr()> and C<ord()> under utf8. |
460 | |
461 | =item * |
462 | |
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463 | The bit string operators C<& | ^ ~> can operate on character data. |
464 | However, for backward compatibility reasons (bit string operations |
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465 | when the characters all are less than 256 in ordinal value) one should |
466 | not mix C<~> (the bit complement) and characters both less than 256 and |
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467 | equal or greater than 256. Most importantly, the DeMorgan's laws |
468 | (C<~($x|$y) eq ~$x&~$y>, C<~($x&$y) eq ~$x|~$y>) won't hold. |
469 | Another way to look at this is that the complement cannot return |
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470 | B<both> the 8-bit (byte) wide bit complement B<and> the full character |
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471 | wide bit complement. |
472 | |
473 | =item * |
474 | |
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475 | And finally, C<scalar reverse()> reverses by character rather than by byte. |
476 | |
477 | =back |
478 | |
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479 | =head2 Character encodings for input and output |
480 | |
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481 | See L<Encode>. |
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482 | |
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483 | =head1 CAVEATS |
484 | |
485 | As of yet, there is no method for automatically coercing input and |
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486 | output to some encoding other than UTF-8 or UTF-EBCDIC. This is planned |
487 | in the near future, however. |
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488 | |
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489 | Whether an arbitrary piece of data will be treated as "characters" or |
490 | "bytes" by internal operations cannot be divined at the current time. |
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491 | |
492 | Use of locales with utf8 may lead to odd results. Currently there is |
493 | some attempt to apply 8-bit locale info to characters in the range |
494 | 0..255, but this is demonstrably incorrect for locales that use |
495 | characters above that range (when mapped into Unicode). It will also |
496 | tend to run slower. Avoidance of locales is strongly encouraged. |
497 | |
498 | =head1 SEE ALSO |
499 | |
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500 | L<bytes>, L<utf8>, L<perlretut>, L<perlvar/"${^WIDE_SYSTEM_CALLS}"> |
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501 | |
502 | =cut |