1=head1 NAME 2 3perlunicode - Unicode support in Perl 4 5=head1 DESCRIPTION 6 7=head2 Important Caveats 8 9Unicode support is an extensive requirement. While Perl does not 10implement the Unicode standard or the accompanying technical reports 11from cover to cover, Perl does support many Unicode features. 12 13=over 4 14 15=item Input and Output Layers 16 17Perl knows when a filehandle uses Perl's internal Unicode encodings 18(UTF-8, or UTF-EBCDIC if in EBCDIC) if the filehandle is opened with 19the ":utf8" layer. Other encodings can be converted to Perl's 20encoding on input or from Perl's encoding on output by use of the 21":encoding(...)" layer. See L<open>. 22 23To indicate that Perl source itself is using a particular encoding, 24see L<encoding>. 25 26=item Regular Expressions 27 28The regular expression compiler produces polymorphic opcodes. That is, 29the pattern adapts to the data and automatically switches to the Unicode 30character scheme when presented with Unicode data--or instead uses 31a traditional byte scheme when presented with byte data. 32 33=item C<use utf8> still needed to enable UTF-8/UTF-EBCDIC in scripts 34 35As a compatibility measure, the C<use utf8> pragma must be explicitly 36included to enable recognition of UTF-8 in the Perl scripts themselves 37(in string or regular expression literals, or in identifier names) on 38ASCII-based machines or to recognize UTF-EBCDIC on EBCDIC-based 39machines. B<These are the only times when an explicit C<use utf8> 40is needed.> See L<utf8>. 41 42You can also use the C<encoding> pragma to change the default encoding 43of the data in your script; see L<encoding>. 44 45=item BOM-marked scripts and UTF-16 scripts autodetected 46 47If a Perl script begins marked with the Unicode BOM (UTF-16LE, UTF16-BE, 48or UTF-8), or if the script looks like non-BOM-marked UTF-16 of either 49endianness, Perl will correctly read in the script as Unicode. 50(BOMless UTF-8 cannot be effectively recognized or differentiated from 51ISO 8859-1 or other eight-bit encodings.) 52 53=item C<use encoding> needed to upgrade non-Latin-1 byte strings 54 55By default, there is a fundamental asymmetry in Perl's unicode model: 56implicit upgrading from byte strings to Unicode strings assumes that 57they were encoded in I<ISO 8859-1 (Latin-1)>, but Unicode strings are 58downgraded with UTF-8 encoding. This happens because the first 256 59codepoints in Unicode happens to agree with Latin-1. 60 61If you wish to interpret byte strings as UTF-8 instead, use the 62C<encoding> pragma: 63 64 use encoding 'utf8'; 65 66See L</"Byte and Character Semantics"> for more details. 67 68=back 69 70=head2 Byte and Character Semantics 71 72Beginning with version 5.6, Perl uses logically-wide characters to 73represent strings internally. 74 75In future, Perl-level operations will be expected to work with 76characters rather than bytes. 77 78However, as an interim compatibility measure, Perl aims to 79provide a safe migration path from byte semantics to character 80semantics for programs. For operations where Perl can unambiguously 81decide that the input data are characters, Perl switches to 82character semantics. For operations where this determination cannot 83be made without additional information from the user, Perl decides in 84favor of compatibility and chooses to use byte semantics. 85 86This behavior preserves compatibility with earlier versions of Perl, 87which allowed byte semantics in Perl operations only if 88none of the program's inputs were marked as being as source of Unicode 89character data. Such data may come from filehandles, from calls to 90external programs, from information provided by the system (such as %ENV), 91or from literals and constants in the source text. 92 93The C<bytes> pragma will always, regardless of platform, force byte 94semantics in a particular lexical scope. See L<bytes>. 95 96The C<utf8> pragma is primarily a compatibility device that enables 97recognition of UTF-(8|EBCDIC) in literals encountered by the parser. 98Note that this pragma is only required while Perl defaults to byte 99semantics; when character semantics become the default, this pragma 100may become a no-op. See L<utf8>. 101 102Unless explicitly stated, Perl operators use character semantics 103for Unicode data and byte semantics for non-Unicode data. 104The decision to use character semantics is made transparently. If 105input data comes from a Unicode source--for example, if a character 106encoding layer is added to a filehandle or a literal Unicode 107string constant appears in a program--character semantics apply. 108Otherwise, byte semantics are in effect. The C<bytes> pragma should 109be used to force byte semantics on Unicode data. 110 111If strings operating under byte semantics and strings with Unicode 112character data are concatenated, the new string will be created by 113decoding the byte strings as I<ISO 8859-1 (Latin-1)>, even if the 114old Unicode string used EBCDIC. This translation is done without 115regard to the system's native 8-bit encoding. To change this for 116systems with non-Latin-1 and non-EBCDIC native encodings, use the 117C<encoding> pragma. See L<encoding>. 118 119Under character semantics, many operations that formerly operated on 120bytes now operate on characters. A character in Perl is 121logically just a number ranging from 0 to 2**31 or so. Larger 122characters may encode into longer sequences of bytes internally, but 123this internal detail is mostly hidden for Perl code. 124See L<perluniintro> for more. 125 126=head2 Effects of Character Semantics 127 128Character semantics have the following effects: 129 130=over 4 131 132=item * 133 134Strings--including hash keys--and regular expression patterns may 135contain characters that have an ordinal value larger than 255. 136 137If you use a Unicode editor to edit your program, Unicode characters 138may occur directly within the literal strings in one of the various 139Unicode encodings (UTF-8, UTF-EBCDIC, UCS-2, etc.), but will be recognized 140as such and converted to Perl's internal representation only if the 141appropriate L<encoding> is specified. 142 143Unicode characters can also be added to a string by using the 144C<\x{...}> notation. The Unicode code for the desired character, in 145hexadecimal, should be placed in the braces. For instance, a smiley 146face is C<\x{263A}>. This encoding scheme only works for characters 147with a code of 0x100 or above. 148 149Additionally, if you 150 151 use charnames ':full'; 152 153you can use the C<\N{...}> notation and put the official Unicode 154character name within the braces, such as C<\N{WHITE SMILING FACE}>. 155 156 157=item * 158 159If an appropriate L<encoding> is specified, identifiers within the 160Perl script may contain Unicode alphanumeric characters, including 161ideographs. Perl does not currently attempt to canonicalize variable 162names. 163 164=item * 165 166Regular expressions match characters instead of bytes. "." matches 167a character instead of a byte. The C<\C> pattern is provided to force 168a match a single byte--a C<char> in C, hence C<\C>. 169 170=item * 171 172Character classes in regular expressions match characters instead of 173bytes and match against the character properties specified in the 174Unicode properties database. C<\w> can be used to match a Japanese 175ideograph, for instance. 176 177(However, and as a limitation of the current implementation, using 178C<\w> or C<\W> I<inside> a C<[...]> character class will still match 179with byte semantics.) 180 181=item * 182 183Named Unicode properties, scripts, and block ranges may be used like 184character classes via the C<\p{}> "matches property" construct and 185the C<\P{}> negation, "doesn't match property". 186 187For instance, C<\p{Lu}> matches any character with the Unicode "Lu" 188(Letter, uppercase) property, while C<\p{M}> matches any character 189with an "M" (mark--accents and such) property. Brackets are not 190required for single letter properties, so C<\p{M}> is equivalent to 191C<\pM>. Many predefined properties are available, such as 192C<\p{Mirrored}> and C<\p{Tibetan}>. 193 194The official Unicode script and block names have spaces and dashes as 195separators, but for convenience you can use dashes, spaces, or 196underbars, and case is unimportant. It is recommended, however, that 197for consistency you use the following naming: the official Unicode 198script, property, or block name (see below for the additional rules 199that apply to block names) with whitespace and dashes removed, and the 200words "uppercase-first-lowercase-rest". C<Latin-1 Supplement> thus 201becomes C<Latin1Supplement>. 202 203You can also use negation in both C<\p{}> and C<\P{}> by introducing a caret 204(^) between the first brace and the property name: C<\p{^Tamil}> is 205equal to C<\P{Tamil}>. 206 207B<NOTE: the properties, scripts, and blocks listed here are as of 208Unicode 3.2.0, March 2002, or Perl 5.8.0, July 2002. Unicode 4.0.0 209came out in April 2003, and Perl 5.8.1 in September 2003.> 210 211Here are the basic Unicode General Category properties, followed by their 212long form. You can use either; C<\p{Lu}> and C<\p{UppercaseLetter}>, 213for instance, are identical. 214 215 Short Long 216 217 L Letter 218 Lu UppercaseLetter 219 Ll LowercaseLetter 220 Lt TitlecaseLetter 221 Lm ModifierLetter 222 Lo OtherLetter 223 224 M Mark 225 Mn NonspacingMark 226 Mc SpacingMark 227 Me EnclosingMark 228 229 N Number 230 Nd DecimalNumber 231 Nl LetterNumber 232 No OtherNumber 233 234 P Punctuation 235 Pc ConnectorPunctuation 236 Pd DashPunctuation 237 Ps OpenPunctuation 238 Pe ClosePunctuation 239 Pi InitialPunctuation 240 (may behave like Ps or Pe depending on usage) 241 Pf FinalPunctuation 242 (may behave like Ps or Pe depending on usage) 243 Po OtherPunctuation 244 245 S Symbol 246 Sm MathSymbol 247 Sc CurrencySymbol 248 Sk ModifierSymbol 249 So OtherSymbol 250 251 Z Separator 252 Zs SpaceSeparator 253 Zl LineSeparator 254 Zp ParagraphSeparator 255 256 C Other 257 Cc Control 258 Cf Format 259 Cs Surrogate (not usable) 260 Co PrivateUse 261 Cn Unassigned 262 263Single-letter properties match all characters in any of the 264two-letter sub-properties starting with the same letter. 265C<L&> is a special case, which is an alias for C<Ll>, C<Lu>, and C<Lt>. 266 267Because Perl hides the need for the user to understand the internal 268representation of Unicode characters, there is no need to implement 269the somewhat messy concept of surrogates. C<Cs> is therefore not 270supported. 271 272Because scripts differ in their directionality--Hebrew is 273written right to left, for example--Unicode supplies these properties: 274 275 Property Meaning 276 277 BidiL Left-to-Right 278 BidiLRE Left-to-Right Embedding 279 BidiLRO Left-to-Right Override 280 BidiR Right-to-Left 281 BidiAL Right-to-Left Arabic 282 BidiRLE Right-to-Left Embedding 283 BidiRLO Right-to-Left Override 284 BidiPDF Pop Directional Format 285 BidiEN European Number 286 BidiES European Number Separator 287 BidiET European Number Terminator 288 BidiAN Arabic Number 289 BidiCS Common Number Separator 290 BidiNSM Non-Spacing Mark 291 BidiBN Boundary Neutral 292 BidiB Paragraph Separator 293 BidiS Segment Separator 294 BidiWS Whitespace 295 BidiON Other Neutrals 296 297For example, C<\p{BidiR}> matches characters that are normally 298written right to left. 299 300=back 301 302=head2 Scripts 303 304The script names which can be used by C<\p{...}> and C<\P{...}>, 305such as in C<\p{Latin}> or C<\p{Cyrillic}>, are as follows: 306 307 Arabic 308 Armenian 309 Bengali 310 Bopomofo 311 Buhid 312 CanadianAboriginal 313 Cherokee 314 Cyrillic 315 Deseret 316 Devanagari 317 Ethiopic 318 Georgian 319 Gothic 320 Greek 321 Gujarati 322 Gurmukhi 323 Han 324 Hangul 325 Hanunoo 326 Hebrew 327 Hiragana 328 Inherited 329 Kannada 330 Katakana 331 Khmer 332 Lao 333 Latin 334 Malayalam 335 Mongolian 336 Myanmar 337 Ogham 338 OldItalic 339 Oriya 340 Runic 341 Sinhala 342 Syriac 343 Tagalog 344 Tagbanwa 345 Tamil 346 Telugu 347 Thaana 348 Thai 349 Tibetan 350 Yi 351 352Extended property classes can supplement the basic 353properties, defined by the F<PropList> Unicode database: 354 355 ASCIIHexDigit 356 BidiControl 357 Dash 358 Deprecated 359 Diacritic 360 Extender 361 GraphemeLink 362 HexDigit 363 Hyphen 364 Ideographic 365 IDSBinaryOperator 366 IDSTrinaryOperator 367 JoinControl 368 LogicalOrderException 369 NoncharacterCodePoint 370 OtherAlphabetic 371 OtherDefaultIgnorableCodePoint 372 OtherGraphemeExtend 373 OtherLowercase 374 OtherMath 375 OtherUppercase 376 QuotationMark 377 Radical 378 SoftDotted 379 TerminalPunctuation 380 UnifiedIdeograph 381 WhiteSpace 382 383and there are further derived properties: 384 385 Alphabetic Lu + Ll + Lt + Lm + Lo + OtherAlphabetic 386 Lowercase Ll + OtherLowercase 387 Uppercase Lu + OtherUppercase 388 Math Sm + OtherMath 389 390 ID_Start Lu + Ll + Lt + Lm + Lo + Nl 391 ID_Continue ID_Start + Mn + Mc + Nd + Pc 392 393 Any Any character 394 Assigned Any non-Cn character (i.e. synonym for \P{Cn}) 395 Unassigned Synonym for \p{Cn} 396 Common Any character (or unassigned code point) 397 not explicitly assigned to a script 398 399For backward compatibility (with Perl 5.6), all properties mentioned 400so far may have C<Is> prepended to their name, so C<\P{IsLu}>, for 401example, is equal to C<\P{Lu}>. 402 403=head2 Blocks 404 405In addition to B<scripts>, Unicode also defines B<blocks> of 406characters. The difference between scripts and blocks is that the 407concept of scripts is closer to natural languages, while the concept 408of blocks is more of an artificial grouping based on groups of 256 409Unicode characters. For example, the C<Latin> script contains letters 410from many blocks but does not contain all the characters from those 411blocks. It does not, for example, contain digits, because digits are 412shared across many scripts. Digits and similar groups, like 413punctuation, are in a category called C<Common>. 414 415For more about scripts, see the UTR #24: 416 417 http://www.unicode.org/unicode/reports/tr24/ 418 419For more about blocks, see: 420 421 http://www.unicode.org/Public/UNIDATA/Blocks.txt 422 423Block names are given with the C<In> prefix. For example, the 424Katakana block is referenced via C<\p{InKatakana}>. The C<In> 425prefix may be omitted if there is no naming conflict with a script 426or any other property, but it is recommended that C<In> always be used 427for block tests to avoid confusion. 428 429These block names are supported: 430 431 InAlphabeticPresentationForms 432 InArabic 433 InArabicPresentationFormsA 434 InArabicPresentationFormsB 435 InArmenian 436 InArrows 437 InBasicLatin 438 InBengali 439 InBlockElements 440 InBopomofo 441 InBopomofoExtended 442 InBoxDrawing 443 InBraillePatterns 444 InBuhid 445 InByzantineMusicalSymbols 446 InCJKCompatibility 447 InCJKCompatibilityForms 448 InCJKCompatibilityIdeographs 449 InCJKCompatibilityIdeographsSupplement 450 InCJKRadicalsSupplement 451 InCJKSymbolsAndPunctuation 452 InCJKUnifiedIdeographs 453 InCJKUnifiedIdeographsExtensionA 454 InCJKUnifiedIdeographsExtensionB 455 InCherokee 456 InCombiningDiacriticalMarks 457 InCombiningDiacriticalMarksforSymbols 458 InCombiningHalfMarks 459 InControlPictures 460 InCurrencySymbols 461 InCyrillic 462 InCyrillicSupplementary 463 InDeseret 464 InDevanagari 465 InDingbats 466 InEnclosedAlphanumerics 467 InEnclosedCJKLettersAndMonths 468 InEthiopic 469 InGeneralPunctuation 470 InGeometricShapes 471 InGeorgian 472 InGothic 473 InGreekExtended 474 InGreekAndCoptic 475 InGujarati 476 InGurmukhi 477 InHalfwidthAndFullwidthForms 478 InHangulCompatibilityJamo 479 InHangulJamo 480 InHangulSyllables 481 InHanunoo 482 InHebrew 483 InHighPrivateUseSurrogates 484 InHighSurrogates 485 InHiragana 486 InIPAExtensions 487 InIdeographicDescriptionCharacters 488 InKanbun 489 InKangxiRadicals 490 InKannada 491 InKatakana 492 InKatakanaPhoneticExtensions 493 InKhmer 494 InLao 495 InLatin1Supplement 496 InLatinExtendedA 497 InLatinExtendedAdditional 498 InLatinExtendedB 499 InLetterlikeSymbols 500 InLowSurrogates 501 InMalayalam 502 InMathematicalAlphanumericSymbols 503 InMathematicalOperators 504 InMiscellaneousMathematicalSymbolsA 505 InMiscellaneousMathematicalSymbolsB 506 InMiscellaneousSymbols 507 InMiscellaneousTechnical 508 InMongolian 509 InMusicalSymbols 510 InMyanmar 511 InNumberForms 512 InOgham 513 InOldItalic 514 InOpticalCharacterRecognition 515 InOriya 516 InPrivateUseArea 517 InRunic 518 InSinhala 519 InSmallFormVariants 520 InSpacingModifierLetters 521 InSpecials 522 InSuperscriptsAndSubscripts 523 InSupplementalArrowsA 524 InSupplementalArrowsB 525 InSupplementalMathematicalOperators 526 InSupplementaryPrivateUseAreaA 527 InSupplementaryPrivateUseAreaB 528 InSyriac 529 InTagalog 530 InTagbanwa 531 InTags 532 InTamil 533 InTelugu 534 InThaana 535 InThai 536 InTibetan 537 InUnifiedCanadianAboriginalSyllabics 538 InVariationSelectors 539 InYiRadicals 540 InYiSyllables 541 542=over 4 543 544=item * 545 546The special pattern C<\X> matches any extended Unicode 547sequence--"a combining character sequence" in Standardese--where the 548first character is a base character and subsequent characters are mark 549characters that apply to the base character. C<\X> is equivalent to 550C<(?:\PM\pM*)>. 551 552=item * 553 554The C<tr///> operator translates characters instead of bytes. Note 555that the C<tr///CU> functionality has been removed. For similar 556functionality see pack('U0', ...) and pack('C0', ...). 557 558=item * 559 560Case translation operators use the Unicode case translation tables 561when character input is provided. Note that C<uc()>, or C<\U> in 562interpolated strings, translates to uppercase, while C<ucfirst>, 563or C<\u> in interpolated strings, translates to titlecase in languages 564that make the distinction. 565 566=item * 567 568Most operators that deal with positions or lengths in a string will 569automatically switch to using character positions, including 570C<chop()>, C<chomp()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>, 571C<sprintf()>, C<write()>, and C<length()>. Operators that 572specifically do not switch include C<vec()>, C<pack()>, and 573C<unpack()>. Operators that really don't care include 574operators that treats strings as a bucket of bits such as C<sort()>, 575and operators dealing with filenames. 576 577=item * 578 579The C<pack()>/C<unpack()> letters C<c> and C<C> do I<not> change, 580since they are often used for byte-oriented formats. Again, think 581C<char> in the C language. 582 583There is a new C<U> specifier that converts between Unicode characters 584and code points. 585 586=item * 587 588The C<chr()> and C<ord()> functions work on characters, similar to 589C<pack("U")> and C<unpack("U")>, I<not> C<pack("C")> and 590C<unpack("C")>. C<pack("C")> and C<unpack("C")> are methods for 591emulating byte-oriented C<chr()> and C<ord()> on Unicode strings. 592While these methods reveal the internal encoding of Unicode strings, 593that is not something one normally needs to care about at all. 594 595=item * 596 597The bit string operators, C<& | ^ ~>, can operate on character data. 598However, for backward compatibility, such as when using bit string 599operations when characters are all less than 256 in ordinal value, one 600should not use C<~> (the bit complement) with characters of both 601values less than 256 and values greater than 256. Most importantly, 602DeMorgan's laws (C<~($x|$y) eq ~$x&~$y> and C<~($x&$y) eq ~$x|~$y>) 603will not hold. The reason for this mathematical I<faux pas> is that 604the complement cannot return B<both> the 8-bit (byte-wide) bit 605complement B<and> the full character-wide bit complement. 606 607=item * 608 609lc(), uc(), lcfirst(), and ucfirst() work for the following cases: 610 611=over 8 612 613=item * 614 615the case mapping is from a single Unicode character to another 616single Unicode character, or 617 618=item * 619 620the case mapping is from a single Unicode character to more 621than one Unicode character. 622 623=back 624 625Things to do with locales (Lithuanian, Turkish, Azeri) do B<not> work 626since Perl does not understand the concept of Unicode locales. 627 628See the Unicode Technical Report #21, Case Mappings, for more details. 629 630=back 631 632=over 4 633 634=item * 635 636And finally, C<scalar reverse()> reverses by character rather than by byte. 637 638=back 639 640=head2 User-Defined Character Properties 641 642You can define your own character properties by defining subroutines 643whose names begin with "In" or "Is". The subroutines must be defined 644in the C<main> package. The user-defined properties can be used in the 645regular expression C<\p> and C<\P> constructs. Note that the effect 646is compile-time and immutable once defined. 647 648The subroutines must return a specially-formatted string, with one 649or more newline-separated lines. Each line must be one of the following: 650 651=over 4 652 653=item * 654 655Two hexadecimal numbers separated by horizontal whitespace (space or 656tabular characters) denoting a range of Unicode code points to include. 657 658=item * 659 660Something to include, prefixed by "+": a built-in character 661property (prefixed by "utf8::"), to represent all the characters in that 662property; two hexadecimal code points for a range; or a single 663hexadecimal code point. 664 665=item * 666 667Something to exclude, prefixed by "-": an existing character 668property (prefixed by "utf8::"), for all the characters in that 669property; two hexadecimal code points for a range; or a single 670hexadecimal code point. 671 672=item * 673 674Something to negate, prefixed "!": an existing character 675property (prefixed by "utf8::") for all the characters except the 676characters in the property; two hexadecimal code points for a range; 677or a single hexadecimal code point. 678 679=back 680 681For example, to define a property that covers both the Japanese 682syllabaries (hiragana and katakana), you can define 683 684 sub InKana { 685 return <<END; 686 3040\t309F 687 30A0\t30FF 688 END 689 } 690 691Imagine that the here-doc end marker is at the beginning of the line. 692Now you can use C<\p{InKana}> and C<\P{InKana}>. 693 694You could also have used the existing block property names: 695 696 sub InKana { 697 return <<'END'; 698 +utf8::InHiragana 699 +utf8::InKatakana 700 END 701 } 702 703Suppose you wanted to match only the allocated characters, 704not the raw block ranges: in other words, you want to remove 705the non-characters: 706 707 sub InKana { 708 return <<'END'; 709 +utf8::InHiragana 710 +utf8::InKatakana 711 -utf8::IsCn 712 END 713 } 714 715The negation is useful for defining (surprise!) negated classes. 716 717 sub InNotKana { 718 return <<'END'; 719 !utf8::InHiragana 720 -utf8::InKatakana 721 +utf8::IsCn 722 END 723 } 724 725You can also define your own mappings to be used in the lc(), 726lcfirst(), uc(), and ucfirst() (or their string-inlined versions). 727The principle is the same: define subroutines in the C<main> package 728with names like C<ToLower> (for lc() and lcfirst()), C<ToTitle> (for 729the first character in ucfirst()), and C<ToUpper> (for uc(), and the 730rest of the characters in ucfirst()). 731 732The string returned by the subroutines needs now to be three 733hexadecimal numbers separated by tabulators: start of the source 734range, end of the source range, and start of the destination range. 735For example: 736 737 sub ToUpper { 738 return <<END; 739 0061\t0063\t0041 740 END 741 } 742 743defines an uc() mapping that causes only the characters "a", "b", and 744"c" to be mapped to "A", "B", "C", all other characters will remain 745unchanged. 746 747If there is no source range to speak of, that is, the mapping is from 748a single character to another single character, leave the end of the 749source range empty, but the two tabulator characters are still needed. 750For example: 751 752 sub ToLower { 753 return <<END; 754 0041\t\t0061 755 END 756 } 757 758defines a lc() mapping that causes only "A" to be mapped to "a", all 759other characters will remain unchanged. 760 761(For serious hackers only) If you want to introspect the default 762mappings, you can find the data in the directory 763C<$Config{privlib}>/F<unicore/To/>. The mapping data is returned as 764the here-document, and the C<utf8::ToSpecFoo> are special exception 765mappings derived from <$Config{privlib}>/F<unicore/SpecialCasing.txt>. 766The C<Digit> and C<Fold> mappings that one can see in the directory 767are not directly user-accessible, one can use either the 768C<Unicode::UCD> module, or just match case-insensitively (that's when 769the C<Fold> mapping is used). 770 771A final note on the user-defined property tests and mappings: they 772will be used only if the scalar has been marked as having Unicode 773characters. Old byte-style strings will not be affected. 774 775=head2 Character Encodings for Input and Output 776 777See L<Encode>. 778 779=head2 Unicode Regular Expression Support Level 780 781The following list of Unicode support for regular expressions describes 782all the features currently supported. The references to "Level N" 783and the section numbers refer to the Unicode Technical Report 18, 784"Unicode Regular Expression Guidelines", version 6 (Unicode 3.2.0, 785Perl 5.8.0). 786 787=over 4 788 789=item * 790 791Level 1 - Basic Unicode Support 792 793 2.1 Hex Notation - done [1] 794 Named Notation - done [2] 795 2.2 Categories - done [3][4] 796 2.3 Subtraction - MISSING [5][6] 797 2.4 Simple Word Boundaries - done [7] 798 2.5 Simple Loose Matches - done [8] 799 2.6 End of Line - MISSING [9][10] 800 801 [ 1] \x{...} 802 [ 2] \N{...} 803 [ 3] . \p{...} \P{...} 804 [ 4] now scripts (see UTR#24 Script Names) in addition to blocks 805 [ 5] have negation 806 [ 6] can use regular expression look-ahead [a] 807 or user-defined character properties [b] to emulate subtraction 808 [ 7] include Letters in word characters 809 [ 8] note that Perl does Full case-folding in matching, not Simple: 810 for example U+1F88 is equivalent with U+1F00 U+03B9, 811 not with 1F80. This difference matters for certain Greek 812 capital letters with certain modifiers: the Full case-folding 813 decomposes the letter, while the Simple case-folding would map 814 it to a single character. 815 [ 9] see UTR #13 Unicode Newline Guidelines 816 [10] should do ^ and $ also on \x{85}, \x{2028} and \x{2029} 817 (should also affect <>, $., and script line numbers) 818 (the \x{85}, \x{2028} and \x{2029} do match \s) 819 820[a] You can mimic class subtraction using lookahead. 821For example, what UTR #18 might write as 822 823 [{Greek}-[{UNASSIGNED}]] 824 825in Perl can be written as: 826 827 (?!\p{Unassigned})\p{InGreekAndCoptic} 828 (?=\p{Assigned})\p{InGreekAndCoptic} 829 830But in this particular example, you probably really want 831 832 \p{GreekAndCoptic} 833 834which will match assigned characters known to be part of the Greek script. 835 836Also see the Unicode::Regex::Set module, it does implement the full 837UTR #18 grouping, intersection, union, and removal (subtraction) syntax. 838 839[b] See L</"User-Defined Character Properties">. 840 841=item * 842 843Level 2 - Extended Unicode Support 844 845 3.1 Surrogates - MISSING [11] 846 3.2 Canonical Equivalents - MISSING [12][13] 847 3.3 Locale-Independent Graphemes - MISSING [14] 848 3.4 Locale-Independent Words - MISSING [15] 849 3.5 Locale-Independent Loose Matches - MISSING [16] 850 851 [11] Surrogates are solely a UTF-16 concept and Perl's internal 852 representation is UTF-8. The Encode module does UTF-16, though. 853 [12] see UTR#15 Unicode Normalization 854 [13] have Unicode::Normalize but not integrated to regexes 855 [14] have \X but at this level . should equal that 856 [15] need three classes, not just \w and \W 857 [16] see UTR#21 Case Mappings 858 859=item * 860 861Level 3 - Locale-Sensitive Support 862 863 4.1 Locale-Dependent Categories - MISSING 864 4.2 Locale-Dependent Graphemes - MISSING [16][17] 865 4.3 Locale-Dependent Words - MISSING 866 4.4 Locale-Dependent Loose Matches - MISSING 867 4.5 Locale-Dependent Ranges - MISSING 868 869 [16] see UTR#10 Unicode Collation Algorithms 870 [17] have Unicode::Collate but not integrated to regexes 871 872=back 873 874=head2 Unicode Encodings 875 876Unicode characters are assigned to I<code points>, which are abstract 877numbers. To use these numbers, various encodings are needed. 878 879=over 4 880 881=item * 882 883UTF-8 884 885UTF-8 is a variable-length (1 to 6 bytes, current character allocations 886require 4 bytes), byte-order independent encoding. For ASCII (and we 887really do mean 7-bit ASCII, not another 8-bit encoding), UTF-8 is 888transparent. 889 890The following table is from Unicode 3.2. 891 892 Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte 893 894 U+0000..U+007F 00..7F 895 U+0080..U+07FF C2..DF 80..BF 896 U+0800..U+0FFF E0 A0..BF 80..BF 897 U+1000..U+CFFF E1..EC 80..BF 80..BF 898 U+D000..U+D7FF ED 80..9F 80..BF 899 U+D800..U+DFFF ******* ill-formed ******* 900 U+E000..U+FFFF EE..EF 80..BF 80..BF 901 U+10000..U+3FFFF F0 90..BF 80..BF 80..BF 902 U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF 903 U+100000..U+10FFFF F4 80..8F 80..BF 80..BF 904 905Note the C<A0..BF> in C<U+0800..U+0FFF>, the C<80..9F> in 906C<U+D000...U+D7FF>, the C<90..B>F in C<U+10000..U+3FFFF>, and the 907C<80...8F> in C<U+100000..U+10FFFF>. The "gaps" are caused by legal 908UTF-8 avoiding non-shortest encodings: it is technically possible to 909UTF-8-encode a single code point in different ways, but that is 910explicitly forbidden, and the shortest possible encoding should always 911be used. So that's what Perl does. 912 913Another way to look at it is via bits: 914 915 Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte 916 917 0aaaaaaa 0aaaaaaa 918 00000bbbbbaaaaaa 110bbbbb 10aaaaaa 919 ccccbbbbbbaaaaaa 1110cccc 10bbbbbb 10aaaaaa 920 00000dddccccccbbbbbbaaaaaa 11110ddd 10cccccc 10bbbbbb 10aaaaaa 921 922As you can see, the continuation bytes all begin with C<10>, and the 923leading bits of the start byte tell how many bytes the are in the 924encoded character. 925 926=item * 927 928UTF-EBCDIC 929 930Like UTF-8 but EBCDIC-safe, in the way that UTF-8 is ASCII-safe. 931 932=item * 933 934UTF-16, UTF-16BE, UTF-16LE, Surrogates, and BOMs (Byte Order Marks) 935 936The followings items are mostly for reference and general Unicode 937knowledge, Perl doesn't use these constructs internally. 938 939UTF-16 is a 2 or 4 byte encoding. The Unicode code points 940C<U+0000..U+FFFF> are stored in a single 16-bit unit, and the code 941points C<U+10000..U+10FFFF> in two 16-bit units. The latter case is 942using I<surrogates>, the first 16-bit unit being the I<high 943surrogate>, and the second being the I<low surrogate>. 944 945Surrogates are code points set aside to encode the C<U+10000..U+10FFFF> 946range of Unicode code points in pairs of 16-bit units. The I<high 947surrogates> are the range C<U+D800..U+DBFF>, and the I<low surrogates> 948are the range C<U+DC00..U+DFFF>. The surrogate encoding is 949 950 $hi = ($uni - 0x10000) / 0x400 + 0xD800; 951 $lo = ($uni - 0x10000) % 0x400 + 0xDC00; 952 953and the decoding is 954 955 $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00); 956 957If you try to generate surrogates (for example by using chr()), you 958will get a warning if warnings are turned on, because those code 959points are not valid for a Unicode character. 960 961Because of the 16-bitness, UTF-16 is byte-order dependent. UTF-16 962itself can be used for in-memory computations, but if storage or 963transfer is required either UTF-16BE (big-endian) or UTF-16LE 964(little-endian) encodings must be chosen. 965 966This introduces another problem: what if you just know that your data 967is UTF-16, but you don't know which endianness? Byte Order Marks, or 968BOMs, are a solution to this. A special character has been reserved 969in Unicode to function as a byte order marker: the character with the 970code point C<U+FEFF> is the BOM. 971 972The trick is that if you read a BOM, you will know the byte order, 973since if it was written on a big-endian platform, you will read the 974bytes C<0xFE 0xFF>, but if it was written on a little-endian platform, 975you will read the bytes C<0xFF 0xFE>. (And if the originating platform 976was writing in UTF-8, you will read the bytes C<0xEF 0xBB 0xBF>.) 977 978The way this trick works is that the character with the code point 979C<U+FFFE> is guaranteed not to be a valid Unicode character, so the 980sequence of bytes C<0xFF 0xFE> is unambiguously "BOM, represented in 981little-endian format" and cannot be C<U+FFFE>, represented in big-endian 982format". 983 984=item * 985 986UTF-32, UTF-32BE, UTF-32LE 987 988The UTF-32 family is pretty much like the UTF-16 family, expect that 989the units are 32-bit, and therefore the surrogate scheme is not 990needed. The BOM signatures will be C<0x00 0x00 0xFE 0xFF> for BE and 991C<0xFF 0xFE 0x00 0x00> for LE. 992 993=item * 994 995UCS-2, UCS-4 996 997Encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit 998encoding. Unlike UTF-16, UCS-2 is not extensible beyond C<U+FFFF>, 999because it does not use surrogates. UCS-4 is a 32-bit encoding, 1000functionally identical to UTF-32. 1001 1002=item * 1003 1004UTF-7 1005 1006A seven-bit safe (non-eight-bit) encoding, which is useful if the 1007transport or storage is not eight-bit safe. Defined by RFC 2152. 1008 1009=back 1010 1011=head2 Security Implications of Unicode 1012 1013=over 4 1014 1015=item * 1016 1017Malformed UTF-8 1018 1019Unfortunately, the specification of UTF-8 leaves some room for 1020interpretation of how many bytes of encoded output one should generate 1021from one input Unicode character. Strictly speaking, the shortest 1022possible sequence of UTF-8 bytes should be generated, 1023because otherwise there is potential for an input buffer overflow at 1024the receiving end of a UTF-8 connection. Perl always generates the 1025shortest length UTF-8, and with warnings on Perl will warn about 1026non-shortest length UTF-8 along with other malformations, such as the 1027surrogates, which are not real Unicode code points. 1028 1029=item * 1030 1031Regular expressions behave slightly differently between byte data and 1032character (Unicode) data. For example, the "word character" character 1033class C<\w> will work differently depending on if data is eight-bit bytes 1034or Unicode. 1035 1036In the first case, the set of C<\w> characters is either small--the 1037default set of alphabetic characters, digits, and the "_"--or, if you 1038are using a locale (see L<perllocale>), the C<\w> might contain a few 1039more letters according to your language and country. 1040 1041In the second case, the C<\w> set of characters is much, much larger. 1042Most importantly, even in the set of the first 256 characters, it will 1043probably match different characters: unlike most locales, which are 1044specific to a language and country pair, Unicode classifies all the 1045characters that are letters I<somewhere> as C<\w>. For example, your 1046locale might not think that LATIN SMALL LETTER ETH is a letter (unless 1047you happen to speak Icelandic), but Unicode does. 1048 1049As discussed elsewhere, Perl has one foot (two hooves?) planted in 1050each of two worlds: the old world of bytes and the new world of 1051characters, upgrading from bytes to characters when necessary. 1052If your legacy code does not explicitly use Unicode, no automatic 1053switch-over to characters should happen. Characters shouldn't get 1054downgraded to bytes, either. It is possible to accidentally mix bytes 1055and characters, however (see L<perluniintro>), in which case C<\w> in 1056regular expressions might start behaving differently. Review your 1057code. Use warnings and the C<strict> pragma. 1058 1059=back 1060 1061=head2 Unicode in Perl on EBCDIC 1062 1063The way Unicode is handled on EBCDIC platforms is still 1064experimental. On such platforms, references to UTF-8 encoding in this 1065document and elsewhere should be read as meaning the UTF-EBCDIC 1066specified in Unicode Technical Report 16, unless ASCII vs. EBCDIC issues 1067are specifically discussed. There is no C<utfebcdic> pragma or 1068":utfebcdic" layer; rather, "utf8" and ":utf8" are reused to mean 1069the platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic> 1070for more discussion of the issues. 1071 1072=head2 Locales 1073 1074Usually locale settings and Unicode do not affect each other, but 1075there are a couple of exceptions: 1076 1077=over 4 1078 1079=item * 1080 1081You can enable automatic UTF-8-ification of your standard file 1082handles, default C<open()> layer, and C<@ARGV> by using either 1083the C<-C> command line switch or the C<PERL_UNICODE> environment 1084variable, see L<perlrun> for the documentation of the C<-C> switch. 1085 1086=item * 1087 1088Perl tries really hard to work both with Unicode and the old 1089byte-oriented world. Most often this is nice, but sometimes Perl's 1090straddling of the proverbial fence causes problems. 1091 1092=back 1093 1094=head2 When Unicode Does Not Happen 1095 1096While Perl does have extensive ways to input and output in Unicode, 1097and few other 'entry points' like the @ARGV which can be interpreted 1098as Unicode (UTF-8), there still are many places where Unicode (in some 1099encoding or another) could be given as arguments or received as 1100results, or both, but it is not. 1101 1102The following are such interfaces. For all of these interfaces Perl 1103currently (as of 5.8.3) simply assumes byte strings both as arguments 1104and results, or UTF-8 strings if the C<encoding> pragma has been used. 1105 1106One reason why Perl does not attempt to resolve the role of Unicode in 1107this cases is that the answers are highly dependent on the operating 1108system and the file system(s). For example, whether filenames can be 1109in Unicode, and in exactly what kind of encoding, is not exactly a 1110portable concept. Similarly for the qx and system: how well will the 1111'command line interface' (and which of them?) handle Unicode? 1112 1113=over 4 1114 1115=item * 1116 1117chmod, chmod, chown, chroot, exec, link, lstat, mkdir, 1118rename, rmdir, stat, symlink, truncate, unlink, utime, -X 1119 1120=item * 1121 1122%ENV 1123 1124=item * 1125 1126glob (aka the <*>) 1127 1128=item * 1129 1130open, opendir, sysopen 1131 1132=item * 1133 1134qx (aka the backtick operator), system 1135 1136=item * 1137 1138readdir, readlink 1139 1140=back 1141 1142=head2 Forcing Unicode in Perl (Or Unforcing Unicode in Perl) 1143 1144Sometimes (see L</"When Unicode Does Not Happen">) there are 1145situations where you simply need to force Perl to believe that a byte 1146string is UTF-8, or vice versa. The low-level calls 1147utf8::upgrade($bytestring) and utf8::downgrade($utf8string) are 1148the answers. 1149 1150Do not use them without careful thought, though: Perl may easily get 1151very confused, angry, or even crash, if you suddenly change the 'nature' 1152of scalar like that. Especially careful you have to be if you use the 1153utf8::upgrade(): any random byte string is not valid UTF-8. 1154 1155=head2 Using Unicode in XS 1156 1157If you want to handle Perl Unicode in XS extensions, you may find the 1158following C APIs useful. See also L<perlguts/"Unicode Support"> for an 1159explanation about Unicode at the XS level, and L<perlapi> for the API 1160details. 1161 1162=over 4 1163 1164=item * 1165 1166C<DO_UTF8(sv)> returns true if the C<UTF8> flag is on and the bytes 1167pragma is not in effect. C<SvUTF8(sv)> returns true is the C<UTF8> 1168flag is on; the bytes pragma is ignored. The C<UTF8> flag being on 1169does B<not> mean that there are any characters of code points greater 1170than 255 (or 127) in the scalar or that there are even any characters 1171in the scalar. What the C<UTF8> flag means is that the sequence of 1172octets in the representation of the scalar is the sequence of UTF-8 1173encoded code points of the characters of a string. The C<UTF8> flag 1174being off means that each octet in this representation encodes a 1175single character with code point 0..255 within the string. Perl's 1176Unicode model is not to use UTF-8 until it is absolutely necessary. 1177 1178=item * 1179 1180C<uvuni_to_utf8(buf, chr)> writes a Unicode character code point into 1181a buffer encoding the code point as UTF-8, and returns a pointer 1182pointing after the UTF-8 bytes. 1183 1184=item * 1185 1186C<utf8_to_uvuni(buf, lenp)> reads UTF-8 encoded bytes from a buffer and 1187returns the Unicode character code point and, optionally, the length of 1188the UTF-8 byte sequence. 1189 1190=item * 1191 1192C<utf8_length(start, end)> returns the length of the UTF-8 encoded buffer 1193in characters. C<sv_len_utf8(sv)> returns the length of the UTF-8 encoded 1194scalar. 1195 1196=item * 1197 1198C<sv_utf8_upgrade(sv)> converts the string of the scalar to its UTF-8 1199encoded form. C<sv_utf8_downgrade(sv)> does the opposite, if 1200possible. C<sv_utf8_encode(sv)> is like sv_utf8_upgrade except that 1201it does not set the C<UTF8> flag. C<sv_utf8_decode()> does the 1202opposite of C<sv_utf8_encode()>. Note that none of these are to be 1203used as general-purpose encoding or decoding interfaces: C<use Encode> 1204for that. C<sv_utf8_upgrade()> is affected by the encoding pragma 1205but C<sv_utf8_downgrade()> is not (since the encoding pragma is 1206designed to be a one-way street). 1207 1208=item * 1209 1210C<is_utf8_char(s)> returns true if the pointer points to a valid UTF-8 1211character. 1212 1213=item * 1214 1215C<is_utf8_string(buf, len)> returns true if C<len> bytes of the buffer 1216are valid UTF-8. 1217 1218=item * 1219 1220C<UTF8SKIP(buf)> will return the number of bytes in the UTF-8 encoded 1221character in the buffer. C<UNISKIP(chr)> will return the number of bytes 1222required to UTF-8-encode the Unicode character code point. C<UTF8SKIP()> 1223is useful for example for iterating over the characters of a UTF-8 1224encoded buffer; C<UNISKIP()> is useful, for example, in computing 1225the size required for a UTF-8 encoded buffer. 1226 1227=item * 1228 1229C<utf8_distance(a, b)> will tell the distance in characters between the 1230two pointers pointing to the same UTF-8 encoded buffer. 1231 1232=item * 1233 1234C<utf8_hop(s, off)> will return a pointer to an UTF-8 encoded buffer 1235that is C<off> (positive or negative) Unicode characters displaced 1236from the UTF-8 buffer C<s>. Be careful not to overstep the buffer: 1237C<utf8_hop()> will merrily run off the end or the beginning of the 1238buffer if told to do so. 1239 1240=item * 1241 1242C<pv_uni_display(dsv, spv, len, pvlim, flags)> and 1243C<sv_uni_display(dsv, ssv, pvlim, flags)> are useful for debugging the 1244output of Unicode strings and scalars. By default they are useful 1245only for debugging--they display B<all> characters as hexadecimal code 1246points--but with the flags C<UNI_DISPLAY_ISPRINT>, 1247C<UNI_DISPLAY_BACKSLASH>, and C<UNI_DISPLAY_QQ> you can make the 1248output more readable. 1249 1250=item * 1251 1252C<ibcmp_utf8(s1, pe1, u1, l1, u1, s2, pe2, l2, u2)> can be used to 1253compare two strings case-insensitively in Unicode. For case-sensitive 1254comparisons you can just use C<memEQ()> and C<memNE()> as usual. 1255 1256=back 1257 1258For more information, see L<perlapi>, and F<utf8.c> and F<utf8.h> 1259in the Perl source code distribution. 1260 1261=head1 BUGS 1262 1263=head2 Interaction with Locales 1264 1265Use of locales with Unicode data may lead to odd results. Currently, 1266Perl attempts to attach 8-bit locale info to characters in the range 12670..255, but this technique is demonstrably incorrect for locales that 1268use characters above that range when mapped into Unicode. Perl's 1269Unicode support will also tend to run slower. Use of locales with 1270Unicode is discouraged. 1271 1272=head2 Interaction with Extensions 1273 1274When Perl exchanges data with an extension, the extension should be 1275able to understand the UTF-8 flag and act accordingly. If the 1276extension doesn't know about the flag, it's likely that the extension 1277will return incorrectly-flagged data. 1278 1279So if you're working with Unicode data, consult the documentation of 1280every module you're using if there are any issues with Unicode data 1281exchange. If the documentation does not talk about Unicode at all, 1282suspect the worst and probably look at the source to learn how the 1283module is implemented. Modules written completely in Perl shouldn't 1284cause problems. Modules that directly or indirectly access code written 1285in other programming languages are at risk. 1286 1287For affected functions, the simple strategy to avoid data corruption is 1288to always make the encoding of the exchanged data explicit. Choose an 1289encoding that you know the extension can handle. Convert arguments passed 1290to the extensions to that encoding and convert results back from that 1291encoding. Write wrapper functions that do the conversions for you, so 1292you can later change the functions when the extension catches up. 1293 1294To provide an example, let's say the popular Foo::Bar::escape_html 1295function doesn't deal with Unicode data yet. The wrapper function 1296would convert the argument to raw UTF-8 and convert the result back to 1297Perl's internal representation like so: 1298 1299 sub my_escape_html ($) { 1300 my($what) = shift; 1301 return unless defined $what; 1302 Encode::decode_utf8(Foo::Bar::escape_html(Encode::encode_utf8($what))); 1303 } 1304 1305Sometimes, when the extension does not convert data but just stores 1306and retrieves them, you will be in a position to use the otherwise 1307dangerous Encode::_utf8_on() function. Let's say the popular 1308C<Foo::Bar> extension, written in C, provides a C<param> method that 1309lets you store and retrieve data according to these prototypes: 1310 1311 $self->param($name, $value); # set a scalar 1312 $value = $self->param($name); # retrieve a scalar 1313 1314If it does not yet provide support for any encoding, one could write a 1315derived class with such a C<param> method: 1316 1317 sub param { 1318 my($self,$name,$value) = @_; 1319 utf8::upgrade($name); # make sure it is UTF-8 encoded 1320 if (defined $value) 1321 utf8::upgrade($value); # make sure it is UTF-8 encoded 1322 return $self->SUPER::param($name,$value); 1323 } else { 1324 my $ret = $self->SUPER::param($name); 1325 Encode::_utf8_on($ret); # we know, it is UTF-8 encoded 1326 return $ret; 1327 } 1328 } 1329 1330Some extensions provide filters on data entry/exit points, such as 1331DB_File::filter_store_key and family. Look out for such filters in 1332the documentation of your extensions, they can make the transition to 1333Unicode data much easier. 1334 1335=head2 Speed 1336 1337Some functions are slower when working on UTF-8 encoded strings than 1338on byte encoded strings. All functions that need to hop over 1339characters such as length(), substr() or index(), or matching regular 1340expressions can work B<much> faster when the underlying data are 1341byte-encoded. 1342 1343In Perl 5.8.0 the slowness was often quite spectacular; in Perl 5.8.1 1344a caching scheme was introduced which will hopefully make the slowness 1345somewhat less spectacular, at least for some operations. In general, 1346operations with UTF-8 encoded strings are still slower. As an example, 1347the Unicode properties (character classes) like C<\p{Nd}> are known to 1348be quite a bit slower (5-20 times) than their simpler counterparts 1349like C<\d> (then again, there 268 Unicode characters matching C<Nd> 1350compared with the 10 ASCII characters matching C<d>). 1351 1352=head2 Porting code from perl-5.6.X 1353 1354Perl 5.8 has a different Unicode model from 5.6. In 5.6 the programmer 1355was required to use the C<utf8> pragma to declare that a given scope 1356expected to deal with Unicode data and had to make sure that only 1357Unicode data were reaching that scope. If you have code that is 1358working with 5.6, you will need some of the following adjustments to 1359your code. The examples are written such that the code will continue 1360to work under 5.6, so you should be safe to try them out. 1361 1362=over 4 1363 1364=item * 1365 1366A filehandle that should read or write UTF-8 1367 1368 if ($] > 5.007) { 1369 binmode $fh, ":utf8"; 1370 } 1371 1372=item * 1373 1374A scalar that is going to be passed to some extension 1375 1376Be it Compress::Zlib, Apache::Request or any extension that has no 1377mention of Unicode in the manpage, you need to make sure that the 1378UTF-8 flag is stripped off. Note that at the time of this writing 1379(October 2002) the mentioned modules are not UTF-8-aware. Please 1380check the documentation to verify if this is still true. 1381 1382 if ($] > 5.007) { 1383 require Encode; 1384 $val = Encode::encode_utf8($val); # make octets 1385 } 1386 1387=item * 1388 1389A scalar we got back from an extension 1390 1391If you believe the scalar comes back as UTF-8, you will most likely 1392want the UTF-8 flag restored: 1393 1394 if ($] > 5.007) { 1395 require Encode; 1396 $val = Encode::decode_utf8($val); 1397 } 1398 1399=item * 1400 1401Same thing, if you are really sure it is UTF-8 1402 1403 if ($] > 5.007) { 1404 require Encode; 1405 Encode::_utf8_on($val); 1406 } 1407 1408=item * 1409 1410A wrapper for fetchrow_array and fetchrow_hashref 1411 1412When the database contains only UTF-8, a wrapper function or method is 1413a convenient way to replace all your fetchrow_array and 1414fetchrow_hashref calls. A wrapper function will also make it easier to 1415adapt to future enhancements in your database driver. Note that at the 1416time of this writing (October 2002), the DBI has no standardized way 1417to deal with UTF-8 data. Please check the documentation to verify if 1418that is still true. 1419 1420 sub fetchrow { 1421 my($self, $sth, $what) = @_; # $what is one of fetchrow_{array,hashref} 1422 if ($] < 5.007) { 1423 return $sth->$what; 1424 } else { 1425 require Encode; 1426 if (wantarray) { 1427 my @arr = $sth->$what; 1428 for (@arr) { 1429 defined && /[^\000-\177]/ && Encode::_utf8_on($_); 1430 } 1431 return @arr; 1432 } else { 1433 my $ret = $sth->$what; 1434 if (ref $ret) { 1435 for my $k (keys %$ret) { 1436 defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret->{$k}; 1437 } 1438 return $ret; 1439 } else { 1440 defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret; 1441 return $ret; 1442 } 1443 } 1444 } 1445 } 1446 1447 1448=item * 1449 1450A large scalar that you know can only contain ASCII 1451 1452Scalars that contain only ASCII and are marked as UTF-8 are sometimes 1453a drag to your program. If you recognize such a situation, just remove 1454the UTF-8 flag: 1455 1456 utf8::downgrade($val) if $] > 5.007; 1457 1458=back 1459 1460=head1 SEE ALSO 1461 1462L<perluniintro>, L<encoding>, L<Encode>, L<open>, L<utf8>, L<bytes>, 1463L<perlretut>, L<perlvar/"${^UNICODE}"> 1464 1465=cut 1466