| 1 | =head1 NAME |
| 2 | |
| 3 | perlunicode - Unicode support in Perl |
| 4 | |
| 5 | =head1 DESCRIPTION |
| 6 | |
| 7 | =head2 Important Caveats |
| 8 | |
| 9 | WARNING: While the implementation of Unicode support in Perl is now |
| 10 | fairly complete it is still evolving to some extent. |
| 11 | |
| 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. |
| 20 | |
| 21 | The following areas are still under development. |
| 22 | |
| 23 | =over 4 |
| 24 | |
| 25 | =item Input and Output Disciplines |
| 26 | |
| 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. |
| 29 | Other encodings can be converted to perl's encoding on input, or from |
| 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. |
| 33 | |
| 34 | =item Regular Expressions |
| 35 | |
| 36 | The regular expression compiler does now attempt to produce |
| 37 | polymorphic opcodes. That is the pattern should now adapt to the data |
| 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. |
| 42 | |
| 43 | =item C<use utf8> still needed to enable UTF-8/UTF-EBCDIC in scripts |
| 44 | |
| 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. |
| 48 | |
| 49 | However, as a compatibility measure, this pragma must be explicitly |
| 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. |
| 52 | B<NOTE: this should be the only place where an explicit C<use utf8> is |
| 53 | needed>. |
| 54 | |
| 55 | =back |
| 56 | |
| 57 | =head2 Byte and Character semantics |
| 58 | |
| 59 | Beginning with version 5.6, Perl uses logically wide characters to |
| 60 | represent strings internally. This internal representation of strings |
| 61 | uses either the UTF-8 or the UTF-EBCDIC encoding. |
| 62 | |
| 63 | In future, Perl-level operations can be expected to work with |
| 64 | characters rather than bytes, in general. |
| 65 | |
| 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. |
| 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), |
| 79 | or from literals and constants in the source text. |
| 80 | |
| 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. |
| 86 | |
| 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>. |
| 89 | |
| 90 | The C<utf8> pragma is primarily a compatibility device that enables |
| 91 | recognition of UTF-(8|EBCDIC) in literals encountered by the parser. |
| 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>. |
| 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 |
| 103 | on Unicode data, the C<bytes> pragma should be used. |
| 104 | |
| 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 | |
| 110 | Under character semantics, many operations that formerly operated on |
| 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 |
| 114 | a sequence of two or more bytes, all of which have the high bit set. |
| 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. |
| 123 | |
| 124 | =head2 Effects of character semantics |
| 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 |
| 133 | larger than 255. |
| 134 | |
| 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}>. |
| 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 |
| 147 | it comes to using the canonical forms of characters--Perl doesn't |
| 148 | (yet) attempt to canonicalize variable names for you.) |
| 149 | |
| 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 |
| 154 | is provided to force a match a single byte ("C<char>" in C, hence C<\C>).) |
| 155 | |
| 156 | =item * |
| 157 | |
| 158 | Character classes in regular expressions match characters instead of |
| 159 | bytes, and match against the character properties specified in the |
| 160 | Unicode properties database. So C<\w> can be used to match an |
| 161 | ideograph, for instance. |
| 162 | |
| 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 |
| 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}>. |
| 172 | |
| 173 | The C<\p{Is...}> test for "general properties" such as "letter", |
| 174 | "digit", while the C<\p{In...}> test for Unicode scripts and blocks. |
| 175 | |
| 176 | The official Unicode script and block names have spaces and |
| 177 | dashes and separators, but for convenience you can have |
| 178 | dashes, spaces, and underbars at every word division, and |
| 179 | you need not care about correct casing. It is recommended, |
| 180 | however, that for consistency you use the following naming: |
| 181 | the official Unicode script or block name (see below for |
| 182 | the additional rules that apply to block names), with the whitespace |
| 183 | and dashes removed, and the words "uppercase-first-lowercase-otherwise". |
| 184 | That is, "Latin-1 Supplement" becomes "Latin1Supplement". |
| 185 | |
| 186 | You can also negate both C<\p{}> and C<\P{}> by introducing a caret |
| 187 | (^) between the first curly and the property name: C<\p{^InTamil}> is |
| 188 | equal to C<\P{InTamil}>. |
| 189 | |
| 190 | The C<In> and C<Is> can be left out: C<\p{Greek}> is equal to |
| 191 | C<\p{InGreek}>, C<\P{Pd}> is equal to C<\P{Pd}>. |
| 192 | |
| 193 | Short Long |
| 194 | |
| 195 | L Letter |
| 196 | Lu Uppercase Letter |
| 197 | Ll Lowercase Letter |
| 198 | Lt Titlecase Letter |
| 199 | Lm Modifier Letter |
| 200 | Lo Other Letter |
| 201 | |
| 202 | M Mark |
| 203 | Mn Non-Spacing Mark |
| 204 | Mc Spacing Combining Mark |
| 205 | Me Enclosing Mark |
| 206 | |
| 207 | N Number |
| 208 | Nd Decimal Digit Number |
| 209 | Nl Letter Number |
| 210 | No Other Number |
| 211 | |
| 212 | P Punctuation |
| 213 | Pc Connector Punctuation |
| 214 | Pd Dash Punctuation |
| 215 | Ps Open Punctuation |
| 216 | Pe Close Punctuation |
| 217 | Pi Initial Punctuation |
| 218 | (may behave like Ps or Pe depending on usage) |
| 219 | Pf Final Punctuation |
| 220 | (may behave like Ps or Pe depending on usage) |
| 221 | Po Other Punctuation |
| 222 | |
| 223 | S Symbol |
| 224 | Sm Math Symbol |
| 225 | Sc Currency Symbol |
| 226 | Sk Modifier Symbol |
| 227 | So Other Symbol |
| 228 | |
| 229 | Z Separator |
| 230 | Zs Space Separator |
| 231 | Zl Line Separator |
| 232 | Zp Paragraph Separator |
| 233 | |
| 234 | C Other |
| 235 | Cc (Other) Control |
| 236 | Cf (Other) Format |
| 237 | Cs (Other) Surrogate |
| 238 | Co (Other) Private Use |
| 239 | Cn (Other) Not Assigned |
| 240 | |
| 241 | There's also C<L&> which is an alias for C<Ll>, C<Lu>, and C<Lt>. |
| 242 | |
| 243 | The following reserved ranges have C<In> tests: |
| 244 | |
| 245 | CJK Ideograph Extension A |
| 246 | CJK Ideograph |
| 247 | Hangul Syllable |
| 248 | Non Private Use High Surrogate |
| 249 | Private Use High Surrogate |
| 250 | Low Surrogate |
| 251 | Private Surrogate |
| 252 | CJK Ideograph Extension B |
| 253 | Plane 15 Private Use |
| 254 | Plane 16 Private Use |
| 255 | |
| 256 | For example C<"\x{AC00}" =~ \p{HangulSyllable}> will test true. |
| 257 | (Handling of surrogates is not implemented yet.) |
| 258 | |
| 259 | Additionally, because scripts differ in their directionality |
| 260 | (for example Hebrew is written right to left), all characters |
| 261 | have their directionality defined: |
| 262 | |
| 263 | BidiL Left-to-Right |
| 264 | BidiLRE Left-to-Right Embedding |
| 265 | BidiLRO Left-to-Right Override |
| 266 | BidiR Right-to-Left |
| 267 | BidiAL Right-to-Left Arabic |
| 268 | BidiRLE Right-to-Left Embedding |
| 269 | BidiRLO Right-to-Left Override |
| 270 | BidiPDF Pop Directional Format |
| 271 | BidiEN European Number |
| 272 | BidiES European Number Separator |
| 273 | BidiET European Number Terminator |
| 274 | BidiAN Arabic Number |
| 275 | BidiCS Common Number Separator |
| 276 | BidiNSM Non-Spacing Mark |
| 277 | BidiBN Boundary Neutral |
| 278 | BidiB Paragraph Separator |
| 279 | BidiS Segment Separator |
| 280 | BidiWS Whitespace |
| 281 | BidiON Other Neutrals |
| 282 | |
| 283 | =head2 Scripts |
| 284 | |
| 285 | The scripts available for C<\p{In...}> and C<\P{In...}>, for example |
| 286 | \p{InCyrillic>, are as follows, for example C<\p{InLatin}> or C<\P{InHan}>: |
| 287 | |
| 288 | Latin |
| 289 | Greek |
| 290 | Cyrillic |
| 291 | Armenian |
| 292 | Hebrew |
| 293 | Arabic |
| 294 | Syriac |
| 295 | Thaana |
| 296 | Devanagari |
| 297 | Bengali |
| 298 | Gurmukhi |
| 299 | Gujarati |
| 300 | Oriya |
| 301 | Tamil |
| 302 | Telugu |
| 303 | Kannada |
| 304 | Malayalam |
| 305 | Sinhala |
| 306 | Thai |
| 307 | Lao |
| 308 | Tibetan |
| 309 | Myanmar |
| 310 | Georgian |
| 311 | Hangul |
| 312 | Ethiopic |
| 313 | Cherokee |
| 314 | CanadianAboriginal |
| 315 | Ogham |
| 316 | Runic |
| 317 | Khmer |
| 318 | Mongolian |
| 319 | Hiragana |
| 320 | Katakana |
| 321 | Bopomofo |
| 322 | Han |
| 323 | Yi |
| 324 | OldItalic |
| 325 | Gothic |
| 326 | Deseret |
| 327 | Inherited |
| 328 | |
| 329 | There are also extended property classes that supplement the basic |
| 330 | properties, defined by the F<PropList> Unicode database: |
| 331 | |
| 332 | White_space |
| 333 | Bidi_Control |
| 334 | Join_Control |
| 335 | Dash |
| 336 | Hyphen |
| 337 | Quotation_Mark |
| 338 | Other_Math |
| 339 | Hex_Digit |
| 340 | ASCII_Hex_Digit |
| 341 | Other_Alphabetic |
| 342 | Ideographic |
| 343 | Diacritic |
| 344 | Extender |
| 345 | Other_Lowercase |
| 346 | Other_Uppercase |
| 347 | Noncharacter_Code_Point |
| 348 | |
| 349 | and further derived properties: |
| 350 | |
| 351 | Alphabetic Lu + Ll + Lt + Lm + Lo + Other_Alphabetic |
| 352 | Lowercase Ll + Other_Lowercase |
| 353 | Uppercase Lu + Other_Uppercase |
| 354 | Math Sm + Other_Math |
| 355 | |
| 356 | ID_Start Lu + Ll + Lt + Lm + Lo + Nl |
| 357 | ID_Continue ID_Start + Mn + Mc + Nd + Pc |
| 358 | |
| 359 | Any Any character |
| 360 | Assigned Any non-Cn character |
| 361 | Common Any character (or unassigned code point) |
| 362 | not explicitly assigned to a script. |
| 363 | |
| 364 | =head2 Blocks |
| 365 | |
| 366 | In addition to B<scripts>, Unicode also defines B<blocks> of |
| 367 | characters. The difference between scripts and blocks is that the |
| 368 | former concept is closer to natural languages, while the latter |
| 369 | concept is more an artificial grouping based on groups of 256 Unicode |
| 370 | characters. For example, the C<Latin> script contains letters from |
| 371 | many blocks, but it does not contain all the characters from those |
| 372 | blocks, it does not for example contain digits. |
| 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 |
| 384 | 5.6.0 only the blocks were used; in Perl 5.8.0 scripts became the |
| 385 | preferential Unicode character class definition; this meant that |
| 386 | the definitions of some character classes changed (the ones in the |
| 387 | below list that have the C<Block> appended). |
| 388 | |
| 389 | BasicLatin |
| 390 | Latin1Supplement |
| 391 | LatinExtendedA |
| 392 | LatinExtendedB |
| 393 | IPAExtensions |
| 394 | SpacingModifierLetters |
| 395 | CombiningDiacriticalMarks |
| 396 | GreekBlock |
| 397 | CyrillicBlock |
| 398 | ArmenianBlock |
| 399 | HebrewBlock |
| 400 | ArabicBlock |
| 401 | SyriacBlock |
| 402 | ThaanaBlock |
| 403 | DevanagariBlock |
| 404 | BengaliBlock |
| 405 | GurmukhiBlock |
| 406 | GujaratiBlock |
| 407 | OriyaBlock |
| 408 | TamilBlock |
| 409 | TeluguBlock |
| 410 | KannadaBlock |
| 411 | MalayalamBlock |
| 412 | SinhalaBlock |
| 413 | ThaiBlock |
| 414 | LaoBlock |
| 415 | TibetanBlock |
| 416 | MyanmarBlock |
| 417 | GeorgianBlock |
| 418 | HangulJamo |
| 419 | EthiopicBlock |
| 420 | CherokeeBlock |
| 421 | UnifiedCanadianAboriginalSyllabics |
| 422 | OghamBlock |
| 423 | RunicBlock |
| 424 | KhmerBlock |
| 425 | MongolianBlock |
| 426 | LatinExtendedAdditional |
| 427 | GreekExtended |
| 428 | GeneralPunctuation |
| 429 | SuperscriptsandSubscripts |
| 430 | CurrencySymbols |
| 431 | CombiningMarksforSymbols |
| 432 | LetterlikeSymbols |
| 433 | NumberForms |
| 434 | Arrows |
| 435 | MathematicalOperators |
| 436 | MiscellaneousTechnical |
| 437 | ControlPictures |
| 438 | OpticalCharacterRecognition |
| 439 | EnclosedAlphanumerics |
| 440 | BoxDrawing |
| 441 | BlockElements |
| 442 | GeometricShapes |
| 443 | MiscellaneousSymbols |
| 444 | Dingbats |
| 445 | BraillePatterns |
| 446 | CJKRadicalsSupplement |
| 447 | KangxiRadicals |
| 448 | IdeographicDescriptionCharacters |
| 449 | CJKSymbolsandPunctuation |
| 450 | HiraganaBlock |
| 451 | KatakanaBlock |
| 452 | BopomofoBlock |
| 453 | HangulCompatibilityJamo |
| 454 | Kanbun |
| 455 | BopomofoExtended |
| 456 | EnclosedCJKLettersandMonths |
| 457 | CJKCompatibility |
| 458 | CJKUnifiedIdeographsExtensionA |
| 459 | CJKUnifiedIdeographs |
| 460 | YiSyllables |
| 461 | YiRadicals |
| 462 | HangulSyllables |
| 463 | HighSurrogates |
| 464 | HighPrivateUseSurrogates |
| 465 | LowSurrogates |
| 466 | PrivateUse |
| 467 | CJKCompatibilityIdeographs |
| 468 | AlphabeticPresentationForms |
| 469 | ArabicPresentationFormsA |
| 470 | CombiningHalfMarks |
| 471 | CJKCompatibilityForms |
| 472 | SmallFormVariants |
| 473 | ArabicPresentationFormsB |
| 474 | Specials |
| 475 | HalfwidthandFullwidthForms |
| 476 | OldItalicBlock |
| 477 | GothicBlock |
| 478 | DeseretBlock |
| 479 | ByzantineMusicalSymbols |
| 480 | MusicalSymbols |
| 481 | MathematicalAlphanumericSymbols |
| 482 | CJKUnifiedIdeographsExtensionB |
| 483 | CJKCompatibilityIdeographsSupplement |
| 484 | Tags |
| 485 | |
| 486 | =item * |
| 487 | |
| 488 | The special pattern C<\X> match matches any extended Unicode sequence |
| 489 | (a "combining character sequence" in Standardese), where the first |
| 490 | character is a base character and subsequent characters are mark |
| 491 | characters that apply to the base character. It is equivalent to |
| 492 | C<(?:\PM\pM*)>. |
| 493 | |
| 494 | =item * |
| 495 | |
| 496 | The C<tr///> operator translates characters instead of bytes. Note |
| 497 | that the C<tr///CU> functionality has been removed, as the interface |
| 498 | was a mistake. For similar functionality see pack('U0', ...) and |
| 499 | pack('C0', ...). |
| 500 | |
| 501 | =item * |
| 502 | |
| 503 | Case translation operators use the Unicode case translation tables |
| 504 | when provided character input. Note that C<uc()> translates to |
| 505 | uppercase, while C<ucfirst> translates to titlecase (for languages |
| 506 | that make the distinction). Naturally the corresponding backslash |
| 507 | sequences have the same semantics. |
| 508 | |
| 509 | =item * |
| 510 | |
| 511 | Most operators that deal with positions or lengths in the string will |
| 512 | automatically switch to using character positions, including |
| 513 | C<chop()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>, |
| 514 | C<sprintf()>, C<write()>, and C<length()>. Operators that |
| 515 | specifically don't switch include C<vec()>, C<pack()>, and |
| 516 | C<unpack()>. Operators that really don't care include C<chomp()>, as |
| 517 | well as any other operator that treats a string as a bucket of bits, |
| 518 | such as C<sort()>, and the operators dealing with filenames. |
| 519 | |
| 520 | =item * |
| 521 | |
| 522 | The C<pack()>/C<unpack()> letters "C<c>" and "C<C>" do I<not> change, |
| 523 | since they're often used for byte-oriented formats. (Again, think |
| 524 | "C<char>" in the C language.) However, there is a new "C<U>" specifier |
| 525 | that will convert between UTF-8 characters and integers. (It works |
| 526 | outside of the utf8 pragma too.) |
| 527 | |
| 528 | =item * |
| 529 | |
| 530 | The C<chr()> and C<ord()> functions work on characters. This is like |
| 531 | C<pack("U")> and C<unpack("U")>, not like C<pack("C")> and |
| 532 | C<unpack("C")>. In fact, the latter are how you now emulate |
| 533 | byte-oriented C<chr()> and C<ord()> for Unicode strings. |
| 534 | (Note that this reveals the internal UTF-8 encoding of strings and |
| 535 | you are not supposed to do that unless you know what you are doing.) |
| 536 | |
| 537 | =item * |
| 538 | |
| 539 | The bit string operators C<& | ^ ~> can operate on character data. |
| 540 | However, for backward compatibility reasons (bit string operations |
| 541 | when the characters all are less than 256 in ordinal value) one should |
| 542 | not mix C<~> (the bit complement) and characters both less than 256 and |
| 543 | equal or greater than 256. Most importantly, the DeMorgan's laws |
| 544 | (C<~($x|$y) eq ~$x&~$y>, C<~($x&$y) eq ~$x|~$y>) won't hold. |
| 545 | Another way to look at this is that the complement cannot return |
| 546 | B<both> the 8-bit (byte) wide bit complement B<and> the full character |
| 547 | wide bit complement. |
| 548 | |
| 549 | =item * |
| 550 | |
| 551 | lc(), uc(), lcfirst(), and ucfirst() work only for some of the |
| 552 | simplest cases, where the mapping goes from a single Unicode character |
| 553 | to another single Unicode character, and where the mapping does not |
| 554 | depend on surrounding characters, or on locales. More complex cases, |
| 555 | where for example one character maps into several, are not yet |
| 556 | implemented. See the Unicode Technical Report #21, Case Mappings, |
| 557 | for more details. The Unicode::UCD module (part of Perl since 5.8.0) |
| 558 | casespec() and casefold() interfaces supply information about the more |
| 559 | complex cases. |
| 560 | |
| 561 | =item * |
| 562 | |
| 563 | And finally, C<scalar reverse()> reverses by character rather than by byte. |
| 564 | |
| 565 | =back |
| 566 | |
| 567 | =head2 Character encodings for input and output |
| 568 | |
| 569 | See L<Encode>. |
| 570 | |
| 571 | =head1 CAVEATS |
| 572 | |
| 573 | As of yet, there is no method for automatically coercing input and |
| 574 | output to some encoding other than UTF-8 or UTF-EBCDIC. This is planned |
| 575 | in the near future, however. |
| 576 | |
| 577 | Whether an arbitrary piece of data will be treated as "characters" or |
| 578 | "bytes" by internal operations cannot be divined at the current time. |
| 579 | |
| 580 | Use of locales with utf8 may lead to odd results. Currently there is |
| 581 | some attempt to apply 8-bit locale info to characters in the range |
| 582 | 0..255, but this is demonstrably incorrect for locales that use |
| 583 | characters above that range (when mapped into Unicode). It will also |
| 584 | tend to run slower. Avoidance of locales is strongly encouraged. |
| 585 | |
| 586 | =head1 UNICODE REGULAR EXPRESSION SUPPORT LEVEL |
| 587 | |
| 588 | The following list of Unicode regular expression support describes |
| 589 | feature by feature the Unicode support implemented in Perl as of Perl |
| 590 | 5.8.0. The "Level N" and the section numbers refer to the Unicode |
| 591 | Technical Report 18, "Unicode Regular Expression Guidelines". |
| 592 | |
| 593 | =over 4 |
| 594 | |
| 595 | =item * |
| 596 | |
| 597 | Level 1 - Basic Unicode Support |
| 598 | |
| 599 | 2.1 Hex Notation - done [1] |
| 600 | Named Notation - done [2] |
| 601 | 2.2 Categories - done [3][4] |
| 602 | 2.3 Subtraction - MISSING [5][6] |
| 603 | 2.4 Simple Word Boundaries - done [7] |
| 604 | 2.5 Simple Loose Matches - MISSING [8] |
| 605 | 2.6 End of Line - MISSING [9][10] |
| 606 | |
| 607 | [ 1] \x{...} |
| 608 | [ 2] \N{...} |
| 609 | [ 3] . \p{Is...} \P{Is...} |
| 610 | [ 4] now scripts (see UTR#24 Script Names) in addition to blocks |
| 611 | [ 5] have negation |
| 612 | [ 6] can use look-ahead to emulate subtracion |
| 613 | [ 7] include Letters in word characters |
| 614 | [ 8] see UTR#21 Case Mappings |
| 615 | [ 9] see UTR#13 Unicode Newline Guidelines |
| 616 | [10] should do ^ and $ also on \x{2028} and \x{2029} |
| 617 | |
| 618 | =item * |
| 619 | |
| 620 | Level 2 - Extended Unicode Support |
| 621 | |
| 622 | 3.1 Surrogates - MISSING |
| 623 | 3.2 Canonical Equivalents - MISSING [11][12] |
| 624 | 3.3 Locale-Independent Graphemes - MISSING [13] |
| 625 | 3.4 Locale-Independent Words - MISSING [14] |
| 626 | 3.5 Locale-Independent Loose Matches - MISSING [15] |
| 627 | |
| 628 | [11] see UTR#15 Unicode Normalization |
| 629 | [12] have Unicode::Normalize but not integrated to regexes |
| 630 | [13] have \X but at this level . should equal that |
| 631 | [14] need three classes, not just \w and \W |
| 632 | [15] see UTR#21 Case Mappings |
| 633 | |
| 634 | =item * |
| 635 | |
| 636 | Level 3 - Locale-Sensitive Support |
| 637 | |
| 638 | 4.1 Locale-Dependent Categories - MISSING |
| 639 | 4.2 Locale-Dependent Graphemes - MISSING [16][17] |
| 640 | 4.3 Locale-Dependent Words - MISSING |
| 641 | 4.4 Locale-Dependent Loose Matches - MISSING |
| 642 | 4.5 Locale-Dependent Ranges - MISSING |
| 643 | |
| 644 | [16] see UTR#10 Unicode Collation Algorithms |
| 645 | [17] have Unicode::Collate but not integrated to regexes |
| 646 | |
| 647 | =back |
| 648 | |
| 649 | =head1 SEE ALSO |
| 650 | |
| 651 | L<bytes>, L<utf8>, L<perlretut>, L<perlvar/"${^WIDE_SYSTEM_CALLS}"> |
| 652 | |
| 653 | =cut |