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 | |
75daf61c | 35 | The C<utf8> pragma implements the tables used for Unicode support. |
c349b1b9 JH |
36 | However, these tables are automatically loaded on demand, so the |
37 | C<utf8> pragma should not normally be used. | |
21bad921 | 38 | |
c349b1b9 JH |
39 | As a compatibility measure, this pragma must be explicitly used to |
40 | enable recognition of UTF-8 in the Perl scripts themselves on ASCII | |
41 | based machines or recognize UTF-EBCDIC on EBCDIC based machines. | |
42 | B<NOTE: this should be the only place where an explicit C<use utf8> | |
43 | is needed>. | |
21bad921 | 44 | |
1768d7eb | 45 | You can also use the C<encoding> pragma to change the default encoding |
6ec9efec | 46 | of the data in your script; see L<encoding>. |
1768d7eb | 47 | |
21bad921 GS |
48 | =back |
49 | ||
50 | =head2 Byte and Character semantics | |
393fec97 GS |
51 | |
52 | Beginning with version 5.6, Perl uses logically wide characters to | |
53 | represent strings internally. This internal representation of strings | |
b3419ed8 | 54 | uses either the UTF-8 or the UTF-EBCDIC encoding. |
393fec97 | 55 | |
75daf61c JH |
56 | In future, Perl-level operations can be expected to work with |
57 | characters rather than bytes, in general. | |
393fec97 | 58 | |
75daf61c JH |
59 | However, as strictly an interim compatibility measure, Perl aims to |
60 | provide a safe migration path from byte semantics to character | |
61 | semantics for programs. For operations where Perl can unambiguously | |
62 | decide that the input data is characters, Perl now switches to | |
63 | character semantics. For operations where this determination cannot | |
64 | be made without additional information from the user, Perl decides in | |
65 | favor of compatibility, and chooses to use byte semantics. | |
8cbd9a7a GS |
66 | |
67 | This behavior preserves compatibility with earlier versions of Perl, | |
68 | which allowed byte semantics in Perl operations, but only as long as | |
69 | none of the program's inputs are marked as being as source of Unicode | |
70 | character data. Such data may come from filehandles, from calls to | |
71 | external programs, from information provided by the system (such as %ENV), | |
21bad921 | 72 | or from literals and constants in the source text. |
8cbd9a7a | 73 | |
c349b1b9 | 74 | On Windows platforms, if the C<-C> command line switch is used, (or the |
75daf61c JH |
75 | ${^WIDE_SYSTEM_CALLS} global flag is set to C<1>), all system calls |
76 | will use the corresponding wide character APIs. Note that this is | |
c349b1b9 JH |
77 | currently only implemented on Windows since other platforms lack an |
78 | API standard on this area. | |
8cbd9a7a | 79 | |
75daf61c JH |
80 | Regardless of the above, the C<bytes> pragma can always be used to |
81 | force byte semantics in a particular lexical scope. See L<bytes>. | |
8cbd9a7a GS |
82 | |
83 | The C<utf8> pragma is primarily a compatibility device that enables | |
75daf61c | 84 | recognition of UTF-(8|EBCDIC) in literals encountered by the parser. |
7dedd01f JH |
85 | Note that this pragma is only required until a future version of Perl |
86 | in which character semantics will become the default. This pragma may | |
87 | then become a no-op. See L<utf8>. | |
8cbd9a7a GS |
88 | |
89 | Unless mentioned otherwise, Perl operators will use character semantics | |
90 | when they are dealing with Unicode data, and byte semantics otherwise. | |
91 | Thus, character semantics for these operations apply transparently; if | |
92 | the input data came from a Unicode source (for example, by adding a | |
93 | character encoding discipline to the filehandle whence it came, or a | |
94 | literal UTF-8 string constant in the program), character semantics | |
95 | apply; otherwise, byte semantics are in effect. To force byte semantics | |
8058d7ab | 96 | on Unicode data, the C<bytes> pragma should be used. |
393fec97 | 97 | |
0a378802 JH |
98 | Notice that if you concatenate strings with byte semantics and strings |
99 | with Unicode character data, the bytes will by default be upgraded | |
100 | I<as if they were ISO 8859-1 (Latin-1)> (or if in EBCDIC, after a | |
101 | translation to ISO 8859-1). To change this, use the C<encoding> | |
102 | pragma, see L<encoding>. | |
7dedd01f | 103 | |
393fec97 | 104 | Under character semantics, many operations that formerly operated on |
75daf61c JH |
105 | bytes change to operating on characters. For ASCII data this makes no |
106 | difference, because UTF-8 stores ASCII in single bytes, but for any | |
107 | character greater than C<chr(127)>, the character B<may> be stored in | |
393fec97 | 108 | a sequence of two or more bytes, all of which have the high bit set. |
2796c109 JH |
109 | |
110 | For C1 controls or Latin 1 characters on an EBCDIC platform the | |
111 | character may be stored in a UTF-EBCDIC multi byte sequence. But by | |
112 | and large, the user need not worry about this, because Perl hides it | |
113 | from the user. A character in Perl is logically just a number ranging | |
114 | from 0 to 2**32 or so. Larger characters encode to longer sequences | |
115 | of bytes internally, but again, this is just an internal detail which | |
116 | is hidden at the Perl level. | |
393fec97 | 117 | |
8cbd9a7a | 118 | =head2 Effects of character semantics |
393fec97 GS |
119 | |
120 | Character semantics have the following effects: | |
121 | ||
122 | =over 4 | |
123 | ||
124 | =item * | |
125 | ||
126 | Strings and patterns may contain characters that have an ordinal value | |
21bad921 | 127 | larger than 255. |
393fec97 | 128 | |
75daf61c JH |
129 | Presuming you use a Unicode editor to edit your program, such |
130 | characters will typically occur directly within the literal strings as | |
131 | UTF-8 (or UTF-EBCDIC on EBCDIC platforms) characters, but you can also | |
132 | specify a particular character with an extension of the C<\x> | |
133 | notation. UTF-X characters are specified by putting the hexadecimal | |
134 | code within curlies after the C<\x>. For instance, a Unicode smiley | |
135 | face is C<\x{263A}>. | |
393fec97 GS |
136 | |
137 | =item * | |
138 | ||
139 | Identifiers within the Perl script may contain Unicode alphanumeric | |
140 | characters, including ideographs. (You are currently on your own when | |
75daf61c JH |
141 | it comes to using the canonical forms of characters--Perl doesn't |
142 | (yet) attempt to canonicalize variable names for you.) | |
393fec97 | 143 | |
393fec97 GS |
144 | =item * |
145 | ||
146 | Regular expressions match characters instead of bytes. For instance, | |
147 | "." matches a character instead of a byte. (However, the C<\C> pattern | |
75daf61c | 148 | is provided to force a match a single byte ("C<char>" in C, hence C<\C>).) |
393fec97 | 149 | |
393fec97 GS |
150 | =item * |
151 | ||
152 | Character classes in regular expressions match characters instead of | |
153 | bytes, and match against the character properties specified in the | |
75daf61c JH |
154 | Unicode properties database. So C<\w> can be used to match an |
155 | ideograph, for instance. | |
393fec97 | 156 | |
393fec97 GS |
157 | =item * |
158 | ||
159 | Named Unicode properties and block ranges make be used as character | |
160 | classes via the new C<\p{}> (matches property) and C<\P{}> (doesn't | |
161 | match property) constructs. For instance, C<\p{Lu}> matches any | |
162 | character with the Unicode uppercase property, while C<\p{M}> matches | |
9fdf68be JH |
163 | any mark character. Single letter properties may omit the brackets, |
164 | so that can be written C<\pM> also. Many predefined character classes | |
a1cc1cb1 | 165 | are available, such as C<\p{IsMirrored}> and C<\p{InTibetan}>. |
4193bef7 JH |
166 | |
167 | The C<\p{Is...}> test for "general properties" such as "letter", | |
168 | "digit", while the C<\p{In...}> test for Unicode scripts and blocks. | |
169 | ||
e150c829 JH |
170 | The official Unicode script and block names have spaces and dashes and |
171 | separators, but for convenience you can have dashes, spaces, and | |
172 | underbars at every word division, and you need not care about correct | |
173 | casing. It is recommended, however, that for consistency you use the | |
174 | following naming: the official Unicode script, block, or property name | |
175 | (see below for the additional rules that apply to block names), | |
176 | with whitespace and dashes replaced with underbar, and the words | |
177 | "uppercase-first-lowercase-rest". That is, "Latin-1 Supplement" | |
178 | becomes "Latin_1_Supplement". | |
4193bef7 | 179 | |
a1cc1cb1 | 180 | You can also negate both C<\p{}> and C<\P{}> by introducing a caret |
e150c829 JH |
181 | (^) between the first curly and the property name: C<\p{^In_Tamil}> is |
182 | equal to C<\P{In_Tamil}>. | |
4193bef7 | 183 | |
61247495 | 184 | The C<In> and C<Is> can be left out: C<\p{Greek}> is equal to |
e150c829 | 185 | C<\p{In_Greek}>, C<\P{Pd}> is equal to C<\P{Pd}>. |
393fec97 | 186 | |
d73e5302 JH |
187 | Short Long |
188 | ||
189 | L Letter | |
e150c829 JH |
190 | Lu Uppercase_Letter |
191 | Ll Lowercase_Letter | |
192 | Lt Titlecase_Letter | |
193 | Lm Modifier_Letter | |
194 | Lo Other_Letter | |
d73e5302 JH |
195 | |
196 | M Mark | |
e150c829 JH |
197 | Mn Nonspacing_Mark |
198 | Mc Spacing_Mark | |
199 | Me Enclosing_Mark | |
d73e5302 JH |
200 | |
201 | N Number | |
e150c829 JH |
202 | Nd Decimal_Number |
203 | Nl Letter_Number | |
204 | No Other_Number | |
d73e5302 JH |
205 | |
206 | P Punctuation | |
e150c829 JH |
207 | Pc Connector_Punctuation |
208 | Pd Dash_Punctuation | |
209 | Ps Open_Punctuation | |
210 | Pe Close_Punctuation | |
211 | Pi Initial_Punctuation | |
d73e5302 | 212 | (may behave like Ps or Pe depending on usage) |
e150c829 | 213 | Pf Final_Punctuation |
d73e5302 | 214 | (may behave like Ps or Pe depending on usage) |
e150c829 | 215 | Po Other_Punctuation |
d73e5302 JH |
216 | |
217 | S Symbol | |
e150c829 JH |
218 | Sm Math_Symbol |
219 | Sc Currency_Symbol | |
220 | Sk Modifier_Symbol | |
221 | So Other_Symbol | |
d73e5302 JH |
222 | |
223 | Z Separator | |
e150c829 JH |
224 | Zs Space_Separator |
225 | Zl Line_Separator | |
226 | Zp Paragraph_Separator | |
d73e5302 JH |
227 | |
228 | C Other | |
e150c829 JH |
229 | Cc Control |
230 | Cf Format | |
231 | Cs Surrogate | |
232 | Co Private_Use | |
233 | Cn Unassigned | |
1ac13f9a JH |
234 | |
235 | There's also C<L&> which is an alias for C<Ll>, C<Lu>, and C<Lt>. | |
32293815 | 236 | |
d73e5302 JH |
237 | The following reserved ranges have C<In> tests: |
238 | ||
e150c829 JH |
239 | CJK_Ideograph_Extension_A |
240 | CJK_Ideograph | |
241 | Hangul_Syllable | |
242 | Non_Private_Use_High_Surrogate | |
243 | Private_Use_High_Surrogate | |
244 | Low_Surrogate | |
245 | Private_Surrogate | |
246 | CJK_Ideograph_Extension_B | |
247 | Plane_15_Private_Use | |
248 | Plane_16_Private_Use | |
d73e5302 JH |
249 | |
250 | For example C<"\x{AC00}" =~ \p{HangulSyllable}> will test true. | |
e9ad1727 JH |
251 | (Handling of surrogates is not implemented yet, because Perl |
252 | uses UTF-8 and not UTF-16 internally to represent Unicode.) | |
d73e5302 | 253 | |
32293815 JH |
254 | Additionally, because scripts differ in their directionality |
255 | (for example Hebrew is written right to left), all characters | |
256 | have their directionality defined: | |
257 | ||
d73e5302 JH |
258 | BidiL Left-to-Right |
259 | BidiLRE Left-to-Right Embedding | |
260 | BidiLRO Left-to-Right Override | |
261 | BidiR Right-to-Left | |
262 | BidiAL Right-to-Left Arabic | |
263 | BidiRLE Right-to-Left Embedding | |
264 | BidiRLO Right-to-Left Override | |
265 | BidiPDF Pop Directional Format | |
266 | BidiEN European Number | |
267 | BidiES European Number Separator | |
268 | BidiET European Number Terminator | |
269 | BidiAN Arabic Number | |
270 | BidiCS Common Number Separator | |
271 | BidiNSM Non-Spacing Mark | |
272 | BidiBN Boundary Neutral | |
273 | BidiB Paragraph Separator | |
274 | BidiS Segment Separator | |
275 | BidiWS Whitespace | |
276 | BidiON Other Neutrals | |
32293815 | 277 | |
210b36aa AMS |
278 | =back |
279 | ||
2796c109 JH |
280 | =head2 Scripts |
281 | ||
75daf61c JH |
282 | The scripts available for C<\p{In...}> and C<\P{In...}>, for example |
283 | \p{InCyrillic>, are as follows, for example C<\p{InLatin}> or C<\P{InHan}>: | |
2796c109 | 284 | |
1ac13f9a | 285 | Arabic |
e9ad1727 | 286 | Armenian |
1ac13f9a | 287 | Bengali |
e9ad1727 JH |
288 | Bopomofo |
289 | Canadian-Aboriginal | |
290 | Cherokee | |
291 | Cyrillic | |
292 | Deseret | |
293 | Devanagari | |
294 | Ethiopic | |
295 | Georgian | |
296 | Gothic | |
297 | Greek | |
1ac13f9a | 298 | Gujarati |
e9ad1727 JH |
299 | Gurmukhi |
300 | Han | |
301 | Hangul | |
302 | Hebrew | |
303 | Hiragana | |
304 | Inherited | |
1ac13f9a | 305 | Kannada |
e9ad1727 JH |
306 | Katakana |
307 | Khmer | |
1ac13f9a | 308 | Lao |
e9ad1727 JH |
309 | Latin |
310 | Malayalam | |
311 | Mongolian | |
1ac13f9a | 312 | Myanmar |
1ac13f9a | 313 | Ogham |
e9ad1727 JH |
314 | Old-Italic |
315 | Oriya | |
1ac13f9a | 316 | Runic |
e9ad1727 JH |
317 | Sinhala |
318 | Syriac | |
319 | Tamil | |
320 | Telugu | |
321 | Thaana | |
322 | Thai | |
323 | Tibetan | |
1ac13f9a | 324 | Yi |
1ac13f9a JH |
325 | |
326 | There are also extended property classes that supplement the basic | |
327 | properties, defined by the F<PropList> Unicode database: | |
328 | ||
e9ad1727 | 329 | ASCII_Hex_Digit |
1ac13f9a | 330 | Bidi_Control |
1ac13f9a | 331 | Dash |
1ac13f9a JH |
332 | Diacritic |
333 | Extender | |
e9ad1727 JH |
334 | Hex_Digit |
335 | Hyphen | |
336 | Ideographic | |
337 | Join_Control | |
338 | Noncharacter_Code_Point | |
339 | Other_Alphabetic | |
1ac13f9a | 340 | Other_Lowercase |
e9ad1727 | 341 | Other_Math |
1ac13f9a | 342 | Other_Uppercase |
e9ad1727 | 343 | Quotation_Mark |
e150c829 | 344 | White_Space |
1ac13f9a JH |
345 | |
346 | and further derived properties: | |
347 | ||
348 | Alphabetic Lu + Ll + Lt + Lm + Lo + Other_Alphabetic | |
349 | Lowercase Ll + Other_Lowercase | |
350 | Uppercase Lu + Other_Uppercase | |
351 | Math Sm + Other_Math | |
352 | ||
353 | ID_Start Lu + Ll + Lt + Lm + Lo + Nl | |
354 | ID_Continue ID_Start + Mn + Mc + Nd + Pc | |
355 | ||
356 | Any Any character | |
357 | Assigned Any non-Cn character | |
358 | Common Any character (or unassigned code point) | |
e150c829 | 359 | not explicitly assigned to a script |
2796c109 JH |
360 | |
361 | =head2 Blocks | |
362 | ||
363 | In addition to B<scripts>, Unicode also defines B<blocks> of | |
364 | characters. The difference between scripts and blocks is that the | |
e9ad1727 | 365 | scripts concept is closer to natural languages, while the blocks |
2796c109 JH |
366 | concept is more an artificial grouping based on groups of 256 Unicode |
367 | characters. For example, the C<Latin> script contains letters from | |
e9ad1727 JH |
368 | many blocks. On the other hand, the C<Latin> script does not contain |
369 | all the characters from those blocks, it does not for example contain | |
370 | digits because digits are shared across many scripts. Digits and | |
371 | other similar groups, like punctuation, are in a category called | |
372 | C<Common>. | |
2796c109 JH |
373 | |
374 | For more about scripts see the UTR #24: | |
375 | http://www.unicode.org/unicode/reports/tr24/ | |
376 | For more about blocks see | |
377 | http://www.unicode.org/Public/UNIDATA/Blocks.txt | |
378 | ||
379 | Because there are overlaps in naming (there are, for example, both | |
380 | a script called C<Katakana> and a block called C<Katakana>, the block | |
381 | version has C<Block> appended to its name, C<\p{InKatakanaBlock}>. | |
382 | ||
383 | Notice that this definition was introduced in Perl 5.8.0: in Perl | |
e150c829 | 384 | 5.6 only the blocks were used; in Perl 5.8.0 scripts became the |
61247495 JH |
385 | preferential Unicode character class definition; this meant that |
386 | the definitions of some character classes changed (the ones in the | |
2796c109 JH |
387 | below list that have the C<Block> appended). |
388 | ||
e9ad1727 JH |
389 | Alphabetic Presentation Forms |
390 | Arabic Block | |
391 | Arabic Presentation Forms-A | |
392 | Arabic Presentation Forms-B | |
393 | Armenian Block | |
394 | Arrows | |
71d929cb | 395 | Basic Latin |
e9ad1727 JH |
396 | Bengali Block |
397 | Block Elements | |
398 | Bopomofo Block | |
399 | Bopomofo Extended | |
400 | Box Drawing | |
401 | Braille Patterns | |
402 | Byzantine Musical Symbols | |
403 | CJK Compatibility | |
404 | CJK Compatibility Forms | |
405 | CJK Compatibility Ideographs | |
406 | CJK Compatibility Ideographs Supplement | |
407 | CJK Radicals Supplement | |
408 | CJK Symbols and Punctuation | |
409 | CJK Unified Ideographs | |
410 | CJK Unified Ideographs Extension A | |
411 | CJK Unified Ideographs Extension B | |
412 | Cherokee Block | |
71d929cb | 413 | Combining Diacritical Marks |
e9ad1727 JH |
414 | Combining Half Marks |
415 | Combining Marks for Symbols | |
416 | Control Pictures | |
417 | Currency Symbols | |
71d929cb | 418 | Cyrillic Block |
e9ad1727 | 419 | Deseret Block |
71d929cb | 420 | Devanagari Block |
e9ad1727 JH |
421 | Dingbats |
422 | Enclosed Alphanumerics | |
423 | Enclosed CJK Letters and Months | |
424 | Ethiopic Block | |
425 | General Punctuation | |
426 | Geometric Shapes | |
71d929cb | 427 | Georgian Block |
e9ad1727 JH |
428 | Gothic Block |
429 | Greek Block | |
430 | Greek Extended | |
431 | Gujarati Block | |
432 | Gurmukhi Block | |
433 | Halfwidth and Fullwidth Forms | |
434 | Hangul Compatibility Jamo | |
71d929cb | 435 | Hangul Jamo |
e9ad1727 JH |
436 | Hangul Syllables |
437 | Hebrew Block | |
438 | High Private Use Surrogates | |
439 | High Surrogates | |
440 | Hiragana Block | |
441 | IPA Extensions | |
442 | Ideographic Description Characters | |
443 | Kanbun | |
444 | Kangxi Radicals | |
445 | Kannada Block | |
446 | Katakana Block | |
71d929cb | 447 | Khmer Block |
e9ad1727 JH |
448 | Lao Block |
449 | Latin 1 Supplement | |
71d929cb | 450 | Latin Extended Additional |
e9ad1727 JH |
451 | Latin Extended-A |
452 | Latin Extended-B | |
71d929cb | 453 | Letterlike Symbols |
e9ad1727 JH |
454 | Low Surrogates |
455 | Malayalam Block | |
456 | Mathematical Alphanumeric Symbols | |
71d929cb | 457 | Mathematical Operators |
e9ad1727 | 458 | Miscellaneous Symbols |
71d929cb | 459 | Miscellaneous Technical |
e9ad1727 JH |
460 | Mongolian Block |
461 | Musical Symbols | |
462 | Myanmar Block | |
463 | Number Forms | |
464 | Ogham Block | |
465 | Old Italic Block | |
71d929cb | 466 | Optical Character Recognition |
e9ad1727 | 467 | Oriya Block |
71d929cb | 468 | Private Use |
e9ad1727 JH |
469 | Runic Block |
470 | Sinhala Block | |
71d929cb | 471 | Small Form Variants |
e9ad1727 | 472 | Spacing Modifier Letters |
2796c109 | 473 | Specials |
e9ad1727 JH |
474 | Superscripts and Subscripts |
475 | Syriac Block | |
2796c109 | 476 | Tags |
e9ad1727 JH |
477 | Tamil Block |
478 | Telugu Block | |
479 | Thaana Block | |
480 | Thai Block | |
481 | Tibetan Block | |
482 | Unified Canadian Aboriginal Syllabics | |
483 | Yi Radicals | |
484 | Yi Syllables | |
32293815 | 485 | |
210b36aa AMS |
486 | =over 4 |
487 | ||
393fec97 GS |
488 | =item * |
489 | ||
490 | The special pattern C<\X> match matches any extended Unicode sequence | |
491 | (a "combining character sequence" in Standardese), where the first | |
492 | character is a base character and subsequent characters are mark | |
493 | characters that apply to the base character. It is equivalent to | |
494 | C<(?:\PM\pM*)>. | |
495 | ||
393fec97 GS |
496 | =item * |
497 | ||
383e7cdd JH |
498 | The C<tr///> operator translates characters instead of bytes. Note |
499 | that the C<tr///CU> functionality has been removed, as the interface | |
500 | was a mistake. For similar functionality see pack('U0', ...) and | |
501 | pack('C0', ...). | |
393fec97 | 502 | |
393fec97 GS |
503 | =item * |
504 | ||
505 | Case translation operators use the Unicode case translation tables | |
44bc797b JH |
506 | when provided character input. Note that C<uc()> (also known as C<\U> |
507 | in doublequoted strings) translates to uppercase, while C<ucfirst> | |
508 | (also known as C<\u> in doublequoted strings) translates to titlecase | |
509 | (for languages that make the distinction). Naturally the | |
510 | corresponding backslash sequences have the same semantics. | |
393fec97 GS |
511 | |
512 | =item * | |
513 | ||
514 | Most operators that deal with positions or lengths in the string will | |
75daf61c JH |
515 | automatically switch to using character positions, including |
516 | C<chop()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>, | |
517 | C<sprintf()>, C<write()>, and C<length()>. Operators that | |
518 | specifically don't switch include C<vec()>, C<pack()>, and | |
519 | C<unpack()>. Operators that really don't care include C<chomp()>, as | |
520 | well as any other operator that treats a string as a bucket of bits, | |
521 | such as C<sort()>, and the operators dealing with filenames. | |
393fec97 GS |
522 | |
523 | =item * | |
524 | ||
525 | The C<pack()>/C<unpack()> letters "C<c>" and "C<C>" do I<not> change, | |
526 | since they're often used for byte-oriented formats. (Again, think | |
527 | "C<char>" in the C language.) However, there is a new "C<U>" specifier | |
528 | that will convert between UTF-8 characters and integers. (It works | |
529 | outside of the utf8 pragma too.) | |
530 | ||
531 | =item * | |
532 | ||
533 | The C<chr()> and C<ord()> functions work on characters. This is like | |
534 | C<pack("U")> and C<unpack("U")>, not like C<pack("C")> and | |
535 | C<unpack("C")>. In fact, the latter are how you now emulate | |
35bcd338 JH |
536 | byte-oriented C<chr()> and C<ord()> for Unicode strings. |
537 | (Note that this reveals the internal UTF-8 encoding of strings and | |
538 | you are not supposed to do that unless you know what you are doing.) | |
393fec97 GS |
539 | |
540 | =item * | |
541 | ||
a1ca4561 YST |
542 | The bit string operators C<& | ^ ~> can operate on character data. |
543 | However, for backward compatibility reasons (bit string operations | |
75daf61c JH |
544 | when the characters all are less than 256 in ordinal value) one should |
545 | not mix C<~> (the bit complement) and characters both less than 256 and | |
a1ca4561 YST |
546 | equal or greater than 256. Most importantly, the DeMorgan's laws |
547 | (C<~($x|$y) eq ~$x&~$y>, C<~($x&$y) eq ~$x|~$y>) won't hold. | |
548 | Another way to look at this is that the complement cannot return | |
75daf61c | 549 | B<both> the 8-bit (byte) wide bit complement B<and> the full character |
a1ca4561 YST |
550 | wide bit complement. |
551 | ||
552 | =item * | |
553 | ||
983ffd37 JH |
554 | lc(), uc(), lcfirst(), and ucfirst() work for the following cases: |
555 | ||
556 | =over 8 | |
557 | ||
558 | =item * | |
559 | ||
560 | the case mapping is from a single Unicode character to another | |
561 | single Unicode character | |
562 | ||
563 | =item * | |
564 | ||
565 | the case mapping is from a single Unicode character to more | |
566 | than one Unicode character | |
567 | ||
568 | =back | |
569 | ||
210b36aa | 570 | What doesn't yet work are the following cases: |
983ffd37 JH |
571 | |
572 | =over 8 | |
573 | ||
574 | =item * | |
575 | ||
576 | the "final sigma" (Greek) | |
577 | ||
578 | =item * | |
579 | ||
580 | anything to with locales (Lithuanian, Turkish, Azeri) | |
581 | ||
582 | =back | |
583 | ||
584 | See the Unicode Technical Report #21, Case Mappings, for more details. | |
ac1256e8 JH |
585 | |
586 | =item * | |
587 | ||
393fec97 GS |
588 | And finally, C<scalar reverse()> reverses by character rather than by byte. |
589 | ||
590 | =back | |
591 | ||
8cbd9a7a GS |
592 | =head2 Character encodings for input and output |
593 | ||
7221edc9 | 594 | See L<Encode>. |
8cbd9a7a | 595 | |
393fec97 GS |
596 | =head1 CAVEATS |
597 | ||
598 | As of yet, there is no method for automatically coercing input and | |
b3419ed8 PK |
599 | output to some encoding other than UTF-8 or UTF-EBCDIC. This is planned |
600 | in the near future, however. | |
393fec97 | 601 | |
8cbd9a7a GS |
602 | Whether an arbitrary piece of data will be treated as "characters" or |
603 | "bytes" by internal operations cannot be divined at the current time. | |
393fec97 GS |
604 | |
605 | Use of locales with utf8 may lead to odd results. Currently there is | |
606 | some attempt to apply 8-bit locale info to characters in the range | |
607 | 0..255, but this is demonstrably incorrect for locales that use | |
608 | characters above that range (when mapped into Unicode). It will also | |
609 | tend to run slower. Avoidance of locales is strongly encouraged. | |
610 | ||
776f8809 JH |
611 | =head1 UNICODE REGULAR EXPRESSION SUPPORT LEVEL |
612 | ||
613 | The following list of Unicode regular expression support describes | |
614 | feature by feature the Unicode support implemented in Perl as of Perl | |
615 | 5.8.0. The "Level N" and the section numbers refer to the Unicode | |
616 | Technical Report 18, "Unicode Regular Expression Guidelines". | |
617 | ||
618 | =over 4 | |
619 | ||
620 | =item * | |
621 | ||
622 | Level 1 - Basic Unicode Support | |
623 | ||
624 | 2.1 Hex Notation - done [1] | |
625 | Named Notation - done [2] | |
626 | 2.2 Categories - done [3][4] | |
627 | 2.3 Subtraction - MISSING [5][6] | |
628 | 2.4 Simple Word Boundaries - done [7] | |
90a59240 | 629 | 2.5 Simple Loose Matches - done [8] |
776f8809 JH |
630 | 2.6 End of Line - MISSING [9][10] |
631 | ||
632 | [ 1] \x{...} | |
633 | [ 2] \N{...} | |
634 | [ 3] . \p{Is...} \P{Is...} | |
635 | [ 4] now scripts (see UTR#24 Script Names) in addition to blocks | |
636 | [ 5] have negation | |
637 | [ 6] can use look-ahead to emulate subtracion | |
638 | [ 7] include Letters in word characters | |
90a59240 | 639 | [ 8] see UTR#21 Case Mappings: Perl implements 1:1 mappings |
776f8809 JH |
640 | [ 9] see UTR#13 Unicode Newline Guidelines |
641 | [10] should do ^ and $ also on \x{2028} and \x{2029} | |
642 | ||
643 | =item * | |
644 | ||
645 | Level 2 - Extended Unicode Support | |
646 | ||
647 | 3.1 Surrogates - MISSING | |
648 | 3.2 Canonical Equivalents - MISSING [11][12] | |
649 | 3.3 Locale-Independent Graphemes - MISSING [13] | |
650 | 3.4 Locale-Independent Words - MISSING [14] | |
651 | 3.5 Locale-Independent Loose Matches - MISSING [15] | |
652 | ||
653 | [11] see UTR#15 Unicode Normalization | |
654 | [12] have Unicode::Normalize but not integrated to regexes | |
655 | [13] have \X but at this level . should equal that | |
656 | [14] need three classes, not just \w and \W | |
657 | [15] see UTR#21 Case Mappings | |
658 | ||
659 | =item * | |
660 | ||
661 | Level 3 - Locale-Sensitive Support | |
662 | ||
663 | 4.1 Locale-Dependent Categories - MISSING | |
664 | 4.2 Locale-Dependent Graphemes - MISSING [16][17] | |
665 | 4.3 Locale-Dependent Words - MISSING | |
666 | 4.4 Locale-Dependent Loose Matches - MISSING | |
667 | 4.5 Locale-Dependent Ranges - MISSING | |
668 | ||
669 | [16] see UTR#10 Unicode Collation Algorithms | |
670 | [17] have Unicode::Collate but not integrated to regexes | |
671 | ||
672 | =back | |
673 | ||
c349b1b9 JH |
674 | =head2 Unicode Encodings |
675 | ||
676 | Unicode characters are assigned to I<code points> which are abstract | |
86bbd6d1 | 677 | numbers. To use these numbers various encodings are needed. |
c349b1b9 JH |
678 | |
679 | =over 4 | |
680 | ||
681 | =item UTF-8 | |
682 | ||
86bbd6d1 | 683 | UTF-8 is the encoding used internally by Perl. UTF-8 is a variable |
c349b1b9 | 684 | length (1 to 6 bytes, current character allocations require 4 bytes), |
86bbd6d1 PN |
685 | byteorder independent encoding. For ASCII, UTF-8 is transparent |
686 | (and we really do mean 7-bit ASCII, not any 8-bit encoding). | |
c349b1b9 JH |
687 | |
688 | =item UTF-16, UTF-16BE, UTF16-LE, Surrogates, and BOMs (Byte Order Marks) | |
689 | ||
690 | UTF-16 is a 2 or 4 byte encoding. The Unicode code points | |
691 | 0x0000..0xFFFF are stored in two 16-bit units, and the code points | |
692 | 0x010000..0x10FFFF in four 16-bit units. The latter case is | |
693 | using I<surrogates>, the first 16-bit unit being the I<high | |
694 | surrogate>, and the second being the I<low surrogate>. | |
695 | ||
696 | Surrogates are code points set aside to encode the 0x01000..0x10FFFF | |
697 | range of Unicode code points in pairs of 16-bit units. The I<high | |
698 | surrogates> are the range 0xD800..0xDBFF, and the I<low surrogates> | |
699 | are the range 0xDC00..0xDFFFF. The surrogate encoding is | |
700 | ||
701 | $hi = ($uni - 0x10000) / 0x400 + 0xD800; | |
702 | $lo = ($uni - 0x10000) % 0x400 + 0xDC00; | |
703 | ||
704 | and the decoding is | |
705 | ||
706 | $uni = 0x10000 + ($hi - 0xD8000) * 0x400 + ($lo - 0xDC00); | |
707 | ||
86bbd6d1 | 708 | Because of the 16-bitness, UTF-16 is byteorder dependent. UTF-16 |
c349b1b9 | 709 | itself can be used for in-memory computations, but if storage or |
86bbd6d1 | 710 | transfer is required, either UTF-16BE (Big Endian) or UTF-16LE |
c349b1b9 JH |
711 | (Little Endian) must be chosen. |
712 | ||
713 | This introduces another problem: what if you just know that your data | |
714 | is UTF-16, but you don't know which endianness? Byte Order Marks | |
715 | (BOMs) are a solution to this. A special character has been reserved | |
86bbd6d1 PN |
716 | in Unicode to function as a byte order marker: the character with the |
717 | code point 0xFEFF is the BOM. | |
042da322 | 718 | |
c349b1b9 JH |
719 | The trick is that if you read a BOM, you will know the byte order, |
720 | since if it was written on a big endian platform, you will read the | |
86bbd6d1 PN |
721 | bytes 0xFE 0xFF, but if it was written on a little endian platform, |
722 | you will read the bytes 0xFF 0xFE. (And if the originating platform | |
723 | was writing in UTF-8, you will read the bytes 0xEF 0xBB 0xBF.) | |
042da322 | 724 | |
86bbd6d1 PN |
725 | The way this trick works is that the character with the code point |
726 | 0xFFFE is guaranteed not to be a valid Unicode character, so the | |
727 | sequence of bytes 0xFF 0xFE is unambiguously "BOM, represented in | |
042da322 JH |
728 | little-endian format" and cannot be "0xFFFE, represented in big-endian |
729 | format". | |
c349b1b9 JH |
730 | |
731 | =item UTF-32, UTF-32BE, UTF32-LE | |
732 | ||
733 | The UTF-32 family is pretty much like the UTF-16 family, expect that | |
042da322 JH |
734 | the units are 32-bit, and therefore the surrogate scheme is not |
735 | needed. The BOM signatures will be 0x00 0x00 0xFE 0xFF for BE and | |
736 | 0xFF 0xFE 0x00 0x00 for LE. | |
c349b1b9 JH |
737 | |
738 | =item UCS-2, UCS-4 | |
739 | ||
86bbd6d1 PN |
740 | Encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit |
741 | encoding, UCS-4 is a 32-bit encoding. Unlike UTF-16, UCS-2 | |
742 | is not extensible beyond 0xFFFF, because it does not use surrogates. | |
c349b1b9 JH |
743 | |
744 | =item UTF-7 | |
745 | ||
746 | A seven-bit safe (non-eight-bit) encoding, useful if the | |
747 | transport/storage is not eight-bit safe. Defined by RFC 2152. | |
748 | ||
bf0fa0b2 JH |
749 | =head2 Security Implications of Malformed UTF-8 |
750 | ||
751 | Unfortunately, the specification of UTF-8 leaves some room for | |
752 | interpretation of how many bytes of encoded output one should generate | |
753 | from one input Unicode character. Strictly speaking, one is supposed | |
754 | to always generate the shortest possible sequence of UTF-8 bytes, | |
755 | because otherwise there is potential for input buffer overflow at the | |
756 | receiving end of a UTF-8 connection. Perl always generates the shortest | |
757 | length UTF-8, and with warnings on (C<-w> or C<use warnings;>) Perl will | |
758 | warn about non-shortest length UTF-8 (and other malformations, too, | |
759 | such as the surrogates, which are not real character code points.) | |
760 | ||
c349b1b9 JH |
761 | =head2 Unicode in Perl on EBCDIC |
762 | ||
763 | The way Unicode is handled on EBCDIC platforms is still rather | |
86bbd6d1 | 764 | experimental. On such a platform, references to UTF-8 encoding in this |
c349b1b9 JH |
765 | document and elsewhere should be read as meaning UTF-EBCDIC as |
766 | specified in Unicode Technical Report 16 unless ASCII vs EBCDIC issues | |
767 | are specifically discussed. There is no C<utfebcdic> pragma or | |
86bbd6d1 PN |
768 | ":utfebcdic" layer, rather, "utf8" and ":utf8" are re-used to mean |
769 | the platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic> | |
770 | for more discussion of the issues. | |
c349b1b9 JH |
771 | |
772 | =back | |
773 | ||
393fec97 GS |
774 | =head1 SEE ALSO |
775 | ||
c349b1b9 JH |
776 | L<encoding>, L<Encode>, L<open>, L<bytes>, L<utf8>, L<perlretut>, |
777 | L<perlvar/"${^WIDE_SYSTEM_CALLS}"> | |
393fec97 GS |
778 | |
779 | =cut |