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1=head1 NAME
2
3perlunicode - Unicode support in Perl
4
5=head1 DESCRIPTION
6
0a1f2d14 7=head2 Important Caveats
21bad921 8
376d9008 9Unicode support is an extensive requirement. While Perl does not
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10implement the Unicode standard or the accompanying technical reports
11from cover to cover, Perl does support many Unicode features.
21bad921 12
2575c402 13People who want to learn to use Unicode in Perl, should probably read
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14L<the Perl Unicode tutorial, perlunitut|perlunitut>, before reading
15this reference document.
2575c402 16
13a2d996 17=over 4
21bad921 18
fae2c0fb 19=item Input and Output Layers
21bad921 20
376d9008 21Perl knows when a filehandle uses Perl's internal Unicode encodings
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22(UTF-8, or UTF-EBCDIC if in EBCDIC) if the filehandle is opened with
23the ":utf8" layer. Other encodings can be converted to Perl's
24encoding on input or from Perl's encoding on output by use of the
25":encoding(...)" layer. See L<open>.
c349b1b9 26
2575c402 27To indicate that Perl source itself is in UTF-8, use C<use utf8;>.
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28
29=item Regular Expressions
30
c349b1b9 31The regular expression compiler produces polymorphic opcodes. That is,
376d9008 32the pattern adapts to the data and automatically switches to the Unicode
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33character scheme when presented with data that is internally encoded in
34UTF-8 -- or instead uses a traditional byte scheme when presented with
35byte data.
21bad921 36
ad0029c4 37=item C<use utf8> still needed to enable UTF-8/UTF-EBCDIC in scripts
21bad921 38
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39As a compatibility measure, the C<use utf8> pragma must be explicitly
40included to enable recognition of UTF-8 in the Perl scripts themselves
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41(in string or regular expression literals, or in identifier names) on
42ASCII-based machines or to recognize UTF-EBCDIC on EBCDIC-based
376d9008 43machines. B<These are the only times when an explicit C<use utf8>
8f8cf39c 44is needed.> See L<utf8>.
21bad921 45
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46=item BOM-marked scripts and UTF-16 scripts autodetected
47
48If a Perl script begins marked with the Unicode BOM (UTF-16LE, UTF16-BE,
49or UTF-8), or if the script looks like non-BOM-marked UTF-16 of either
50endianness, Perl will correctly read in the script as Unicode.
51(BOMless UTF-8 cannot be effectively recognized or differentiated from
52ISO 8859-1 or other eight-bit encodings.)
53
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54=item C<use encoding> needed to upgrade non-Latin-1 byte strings
55
38a44b82 56By default, there is a fundamental asymmetry in Perl's Unicode model:
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57implicit upgrading from byte strings to Unicode strings assumes that
58they were encoded in I<ISO 8859-1 (Latin-1)>, but Unicode strings are
59downgraded with UTF-8 encoding. This happens because the first 256
60codepoints in Unicode happens to agree with Latin-1.
61
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62See L</"Byte and Character Semantics"> for more details.
63
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64=back
65
376d9008 66=head2 Byte and Character Semantics
393fec97 67
376d9008 68Beginning with version 5.6, Perl uses logically-wide characters to
3e4dbfed 69represent strings internally.
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71In future, Perl-level operations will be expected to work with
72characters rather than bytes.
393fec97 73
376d9008 74However, as an interim compatibility measure, Perl aims to
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75provide a safe migration path from byte semantics to character
76semantics for programs. For operations where Perl can unambiguously
376d9008 77decide that the input data are characters, Perl switches to
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78character semantics. For operations where this determination cannot
79be made without additional information from the user, Perl decides in
376d9008 80favor of compatibility and chooses to use byte semantics.
8cbd9a7a 81
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82Under byte semantics, when C<use locale> is in effect, Perl uses the
83semantics associated with the current locale. Absent a C<use locale>, Perl
84currently uses US-ASCII (or Basic Latin in Unicode terminology) byte semantics,
85meaning that characters whose ordinal numbers are in the range 128 - 255 are
86undefined except for their ordinal numbers. This means that none have case
87(upper and lower), nor are any a member of character classes, like C<[:alpha:]>
88or C<\w>.
89(But all do belong to the C<\W> class or the Perl regular expression extension
90C<[:^alpha:]>.)
91
8cbd9a7a 92This behavior preserves compatibility with earlier versions of Perl,
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93which allowed byte semantics in Perl operations only if
94none of the program's inputs were marked as being as source of Unicode
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95character data. Such data may come from filehandles, from calls to
96external programs, from information provided by the system (such as %ENV),
21bad921 97or from literals and constants in the source text.
8cbd9a7a 98
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99The C<bytes> pragma will always, regardless of platform, force byte
100semantics in a particular lexical scope. See L<bytes>.
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101
102The C<utf8> pragma is primarily a compatibility device that enables
75daf61c 103recognition of UTF-(8|EBCDIC) in literals encountered by the parser.
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104Note that this pragma is only required while Perl defaults to byte
105semantics; when character semantics become the default, this pragma
106may become a no-op. See L<utf8>.
107
108Unless explicitly stated, Perl operators use character semantics
109for Unicode data and byte semantics for non-Unicode data.
110The decision to use character semantics is made transparently. If
111input data comes from a Unicode source--for example, if a character
fae2c0fb 112encoding layer is added to a filehandle or a literal Unicode
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113string constant appears in a program--character semantics apply.
114Otherwise, byte semantics are in effect. The C<bytes> pragma should
115be used to force byte semantics on Unicode data.
116
117If strings operating under byte semantics and strings with Unicode
2bbc8d55 118character data are concatenated, the new string will have
42bde815 119character semantics. This can cause surprises: See L</BUGS>, below
7dedd01f 120
feda178f 121Under character semantics, many operations that formerly operated on
376d9008 122bytes now operate on characters. A character in Perl is
feda178f 123logically just a number ranging from 0 to 2**31 or so. Larger
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124characters may encode into longer sequences of bytes internally, but
125this internal detail is mostly hidden for Perl code.
126See L<perluniintro> for more.
393fec97 127
376d9008 128=head2 Effects of Character Semantics
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129
130Character semantics have the following effects:
131
132=over 4
133
134=item *
135
376d9008 136Strings--including hash keys--and regular expression patterns may
574c8022 137contain characters that have an ordinal value larger than 255.
393fec97 138
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139If you use a Unicode editor to edit your program, Unicode characters may
140occur directly within the literal strings in UTF-8 encoding, or UTF-16.
141(The former requires a BOM or C<use utf8>, the latter requires a BOM.)
3e4dbfed 142
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143Unicode characters can also be added to a string by using the C<\x{...}>
144notation. The Unicode code for the desired character, in hexadecimal,
145should be placed in the braces. For instance, a smiley face is
2bbc8d55 146C<\x{263A}>. This encoding scheme works for all characters, but
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147for characters under 0x100, note that Perl may use an 8 bit encoding
148internally, for optimization and/or backward compatibility.
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149
150Additionally, if you
574c8022 151
3e4dbfed 152 use charnames ':full';
574c8022 153
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154you can use the C<\N{...}> notation and put the official Unicode
155character name within the braces, such as C<\N{WHITE SMILING FACE}>.
376d9008 156
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157=item *
158
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159If an appropriate L<encoding> is specified, identifiers within the
160Perl script may contain Unicode alphanumeric characters, including
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161ideographs. Perl does not currently attempt to canonicalize variable
162names.
393fec97 163
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164=item *
165
1bfb14c4 166Regular expressions match characters instead of bytes. "." matches
2575c402 167a character instead of a byte.
393fec97 168
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169=item *
170
171Character classes in regular expressions match characters instead of
376d9008 172bytes and match against the character properties specified in the
1bfb14c4 173Unicode properties database. C<\w> can be used to match a Japanese
75daf61c 174ideograph, for instance.
393fec97 175
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176=item *
177
eb0cc9e3 178Named Unicode properties, scripts, and block ranges may be used like
376d9008 179character classes via the C<\p{}> "matches property" construct and
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180the C<\P{}> negation, "doesn't match property".
181
2575c402 182See L</"Unicode Character Properties"> for more details.
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183
184You can define your own character properties and use them
185in the regular expression with the C<\p{}> or C<\P{}> construct.
186
187See L</"User-Defined Character Properties"> for more details.
188
189=item *
190
191The special pattern C<\X> matches any extended Unicode
192sequence--"a combining character sequence" in Standardese--where the
193first character is a base character and subsequent characters are mark
194characters that apply to the base character. C<\X> is equivalent to
e1f17637 195C<< (?>\PM\pM*) >>.
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196
197=item *
198
199The C<tr///> operator translates characters instead of bytes. Note
200that the C<tr///CU> functionality has been removed. For similar
201functionality see pack('U0', ...) and pack('C0', ...).
202
203=item *
204
205Case translation operators use the Unicode case translation tables
206when character input is provided. Note that C<uc()>, or C<\U> in
207interpolated strings, translates to uppercase, while C<ucfirst>,
208or C<\u> in interpolated strings, translates to titlecase in languages
209that make the distinction.
210
211=item *
212
213Most operators that deal with positions or lengths in a string will
214automatically switch to using character positions, including
215C<chop()>, C<chomp()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>,
216C<sprintf()>, C<write()>, and C<length()>. An operator that
217specifically does not switch is C<vec()>. Operators that really don't
218care include operators that treat strings as a bucket of bits such as
219C<sort()>, and operators dealing with filenames.
220
221=item *
222
223The C<pack()>/C<unpack()> letter C<C> does I<not> change, since it is often
224used for byte-oriented formats. Again, think C<char> in the C language.
225
226There is a new C<U> specifier that converts between Unicode characters
227and code points. There is also a C<W> specifier that is the equivalent of
228C<chr>/C<ord> and properly handles character values even if they are above 255.
229
230=item *
231
232The C<chr()> and C<ord()> functions work on characters, similar to
233C<pack("W")> and C<unpack("W")>, I<not> C<pack("C")> and
234C<unpack("C")>. C<pack("C")> and C<unpack("C")> are methods for
235emulating byte-oriented C<chr()> and C<ord()> on Unicode strings.
236While these methods reveal the internal encoding of Unicode strings,
237that is not something one normally needs to care about at all.
238
239=item *
240
241The bit string operators, C<& | ^ ~>, can operate on character data.
242However, for backward compatibility, such as when using bit string
243operations when characters are all less than 256 in ordinal value, one
244should not use C<~> (the bit complement) with characters of both
245values less than 256 and values greater than 256. Most importantly,
246DeMorgan's laws (C<~($x|$y) eq ~$x&~$y> and C<~($x&$y) eq ~$x|~$y>)
247will not hold. The reason for this mathematical I<faux pas> is that
248the complement cannot return B<both> the 8-bit (byte-wide) bit
249complement B<and> the full character-wide bit complement.
250
251=item *
252
253lc(), uc(), lcfirst(), and ucfirst() work for the following cases:
254
255=over 8
256
257=item *
258
259the case mapping is from a single Unicode character to another
260single Unicode character, or
261
262=item *
263
264the case mapping is from a single Unicode character to more
265than one Unicode character.
266
267=back
268
269Things to do with locales (Lithuanian, Turkish, Azeri) do B<not> work
270since Perl does not understand the concept of Unicode locales.
271
272See the Unicode Technical Report #21, Case Mappings, for more details.
273
274But you can also define your own mappings to be used in the lc(),
275lcfirst(), uc(), and ucfirst() (or their string-inlined versions).
276
277See L</"User-Defined Case Mappings"> for more details.
278
279=back
280
281=over 4
282
283=item *
284
285And finally, C<scalar reverse()> reverses by character rather than by byte.
286
287=back
288
289=head2 Unicode Character Properties
290
291Named Unicode properties, scripts, and block ranges may be used like
292character classes via the C<\p{}> "matches property" construct and
293the C<\P{}> negation, "doesn't match property".
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294
295For instance, C<\p{Lu}> matches any character with the Unicode "Lu"
296(Letter, uppercase) property, while C<\p{M}> matches any character
297with an "M" (mark--accents and such) property. Brackets are not
298required for single letter properties, so C<\p{M}> is equivalent to
299C<\pM>. Many predefined properties are available, such as
300C<\p{Mirrored}> and C<\p{Tibetan}>.
4193bef7 301
cfc01aea 302The official Unicode script and block names have spaces and dashes as
376d9008 303separators, but for convenience you can use dashes, spaces, or
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304underbars, and case is unimportant. It is recommended, however, that
305for consistency you use the following naming: the official Unicode
306script, property, or block name (see below for the additional rules
307that apply to block names) with whitespace and dashes removed, and the
308words "uppercase-first-lowercase-rest". C<Latin-1 Supplement> thus
309becomes C<Latin1Supplement>.
4193bef7 310
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311You can also use negation in both C<\p{}> and C<\P{}> by introducing a caret
312(^) between the first brace and the property name: C<\p{^Tamil}> is
eb0cc9e3 313equal to C<\P{Tamil}>.
4193bef7 314
14bb0a9a 315B<NOTE: the properties, scripts, and blocks listed here are as of
8158862b 316Unicode 5.0.0 in July 2006.>
14bb0a9a 317
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318=over 4
319
320=item General Category
321
eb0cc9e3 322Here are the basic Unicode General Category properties, followed by their
68cd2d32 323long form. You can use either; C<\p{Lu}> and C<\p{UppercaseLetter}>,
376d9008 324for instance, are identical.
393fec97 325
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326 Short Long
327
328 L Letter
12ac2576 329 LC CasedLetter
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330 Lu UppercaseLetter
331 Ll LowercaseLetter
332 Lt TitlecaseLetter
333 Lm ModifierLetter
334 Lo OtherLetter
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335
336 M Mark
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337 Mn NonspacingMark
338 Mc SpacingMark
339 Me EnclosingMark
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340
341 N Number
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342 Nd DecimalNumber
343 Nl LetterNumber
344 No OtherNumber
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345
346 P Punctuation
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347 Pc ConnectorPunctuation
348 Pd DashPunctuation
349 Ps OpenPunctuation
350 Pe ClosePunctuation
351 Pi InitialPunctuation
d73e5302 352 (may behave like Ps or Pe depending on usage)
eb0cc9e3 353 Pf FinalPunctuation
d73e5302 354 (may behave like Ps or Pe depending on usage)
eb0cc9e3 355 Po OtherPunctuation
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356
357 S Symbol
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358 Sm MathSymbol
359 Sc CurrencySymbol
360 Sk ModifierSymbol
361 So OtherSymbol
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362
363 Z Separator
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364 Zs SpaceSeparator
365 Zl LineSeparator
366 Zp ParagraphSeparator
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367
368 C Other
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369 Cc Control
370 Cf Format
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371 Cs Surrogate (not usable)
372 Co PrivateUse
e150c829 373 Cn Unassigned
1ac13f9a 374
376d9008 375Single-letter properties match all characters in any of the
3e4dbfed 376two-letter sub-properties starting with the same letter.
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377C<LC> and C<L&> are special cases, which are aliases for the set of
378C<Ll>, C<Lu>, and C<Lt>.
32293815 379
eb0cc9e3 380Because Perl hides the need for the user to understand the internal
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381representation of Unicode characters, there is no need to implement
382the somewhat messy concept of surrogates. C<Cs> is therefore not
eb0cc9e3 383supported.
d73e5302 384
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385=item Bidirectional Character Types
386
376d9008 387Because scripts differ in their directionality--Hebrew is
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388written right to left, for example--Unicode supplies these properties in
389the BidiClass class:
32293815 390
eb0cc9e3 391 Property Meaning
92e830a9 392
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393 L Left-to-Right
394 LRE Left-to-Right Embedding
395 LRO Left-to-Right Override
396 R Right-to-Left
397 AL Right-to-Left Arabic
398 RLE Right-to-Left Embedding
399 RLO Right-to-Left Override
400 PDF Pop Directional Format
401 EN European Number
402 ES European Number Separator
403 ET European Number Terminator
404 AN Arabic Number
405 CS Common Number Separator
406 NSM Non-Spacing Mark
407 BN Boundary Neutral
408 B Paragraph Separator
409 S Segment Separator
410 WS Whitespace
411 ON Other Neutrals
412
413For example, C<\p{BidiClass:R}> matches characters that are normally
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414written right to left.
415
822502e5 416=item Scripts
2796c109 417
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418The script names which can be used by C<\p{...}> and C<\P{...}>,
419such as in C<\p{Latin}> or C<\p{Cyrillic}>, are as follows:
2796c109 420
1ac13f9a 421 Arabic
e9ad1727 422 Armenian
8158862b 423 Balinese
1ac13f9a 424 Bengali
e9ad1727 425 Bopomofo
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426 Braille
427 Buginese
1d81abf3 428 Buhid
eb0cc9e3 429 CanadianAboriginal
e9ad1727 430 Cherokee
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431 Coptic
432 Cuneiform
433 Cypriot
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434 Cyrillic
435 Deseret
436 Devanagari
437 Ethiopic
438 Georgian
8158862b 439 Glagolitic
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440 Gothic
441 Greek
1ac13f9a 442 Gujarati
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443 Gurmukhi
444 Han
445 Hangul
1d81abf3 446 Hanunoo
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447 Hebrew
448 Hiragana
449 Inherited
1ac13f9a 450 Kannada
e9ad1727 451 Katakana
8158862b 452 Kharoshthi
e9ad1727 453 Khmer
1ac13f9a 454 Lao
e9ad1727 455 Latin
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456 Limbu
457 LinearB
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458 Malayalam
459 Mongolian
1ac13f9a 460 Myanmar
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461 NewTaiLue
462 Nko
1ac13f9a 463 Ogham
eb0cc9e3 464 OldItalic
8158862b 465 OldPersian
e9ad1727 466 Oriya
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467 Osmanya
468 PhagsPa
469 Phoenician
1ac13f9a 470 Runic
8158862b 471 Shavian
e9ad1727 472 Sinhala
8158862b 473 SylotiNagri
e9ad1727 474 Syriac
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475 Tagalog
476 Tagbanwa
8158862b 477 TaiLe
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478 Tamil
479 Telugu
480 Thaana
481 Thai
482 Tibetan
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483 Tifinagh
484 Ugaritic
1ac13f9a 485 Yi
1ac13f9a 486
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487=item Extended property classes
488
376d9008 489Extended property classes can supplement the basic
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490properties, defined by the F<PropList> Unicode database:
491
1d81abf3 492 ASCIIHexDigit
eb0cc9e3 493 BidiControl
1ac13f9a 494 Dash
1d81abf3 495 Deprecated
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496 Diacritic
497 Extender
eb0cc9e3 498 HexDigit
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499 Hyphen
500 Ideographic
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501 IDSBinaryOperator
502 IDSTrinaryOperator
eb0cc9e3 503 JoinControl
1d81abf3 504 LogicalOrderException
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505 NoncharacterCodePoint
506 OtherAlphabetic
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507 OtherDefaultIgnorableCodePoint
508 OtherGraphemeExtend
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509 OtherIDStart
510 OtherIDContinue
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511 OtherLowercase
512 OtherMath
513 OtherUppercase
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514 PatternSyntax
515 PatternWhiteSpace
eb0cc9e3 516 QuotationMark
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517 Radical
518 SoftDotted
8158862b 519 STerm
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520 TerminalPunctuation
521 UnifiedIdeograph
8158862b 522 VariationSelector
eb0cc9e3 523 WhiteSpace
1ac13f9a 524
376d9008 525and there are further derived properties:
1ac13f9a 526
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527 Alphabetic = Lu + Ll + Lt + Lm + Lo + Nl + OtherAlphabetic
528 Lowercase = Ll + OtherLowercase
529 Uppercase = Lu + OtherUppercase
530 Math = Sm + OtherMath
1ac13f9a 531
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532 IDStart = Lu + Ll + Lt + Lm + Lo + Nl + OtherIDStart
533 IDContinue = IDStart + Mn + Mc + Nd + Pc + OtherIDContinue
1ac13f9a 534
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535 DefaultIgnorableCodePoint
536 = OtherDefaultIgnorableCodePoint
537 + Cf + Cc + Cs + Noncharacters + VariationSelector
538 - WhiteSpace - FFF9..FFFB (Annotation Characters)
539
540 Any = Any code points (i.e. U+0000 to U+10FFFF)
541 Assigned = Any non-Cn code points (i.e. synonym for \P{Cn})
542 Unassigned = Synonym for \p{Cn}
543 ASCII = ASCII (i.e. U+0000 to U+007F)
544
545 Common = Any character (or unassigned code point)
546 not explicitly assigned to a script
2796c109 547
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548=item Use of "Is" Prefix
549
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550For backward compatibility (with Perl 5.6), all properties mentioned
551so far may have C<Is> prepended to their name, so C<\P{IsLu}>, for
552example, is equal to C<\P{Lu}>.
eb0cc9e3 553
822502e5 554=item Blocks
2796c109 555
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556In addition to B<scripts>, Unicode also defines B<blocks> of
557characters. The difference between scripts and blocks is that the
558concept of scripts is closer to natural languages, while the concept
559of blocks is more of an artificial grouping based on groups of 256
376d9008 560Unicode characters. For example, the C<Latin> script contains letters
1bfb14c4 561from many blocks but does not contain all the characters from those
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562blocks. It does not, for example, contain digits, because digits are
563shared across many scripts. Digits and similar groups, like
564punctuation, are in a category called C<Common>.
2796c109 565
8158862b 566For more about scripts, see the UAX#24 "Script Names":
cfc01aea 567
8158862b 568 http://www.unicode.org/reports/tr24/
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569
570For more about blocks, see:
571
572 http://www.unicode.org/Public/UNIDATA/Blocks.txt
2796c109 573
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574Block names are given with the C<In> prefix. For example, the
575Katakana block is referenced via C<\p{InKatakana}>. The C<In>
7eabb34d 576prefix may be omitted if there is no naming conflict with a script
eb0cc9e3 577or any other property, but it is recommended that C<In> always be used
1bfb14c4 578for block tests to avoid confusion.
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579
580These block names are supported:
581
8158862b 582 InAegeanNumbers
1d81abf3 583 InAlphabeticPresentationForms
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584 InAncientGreekMusicalNotation
585 InAncientGreekNumbers
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586 InArabic
587 InArabicPresentationFormsA
588 InArabicPresentationFormsB
8158862b 589 InArabicSupplement
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590 InArmenian
591 InArrows
8158862b 592 InBalinese
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593 InBasicLatin
594 InBengali
595 InBlockElements
596 InBopomofo
597 InBopomofoExtended
598 InBoxDrawing
599 InBraillePatterns
8158862b 600 InBuginese
1d81abf3
JH
601 InBuhid
602 InByzantineMusicalSymbols
603 InCJKCompatibility
604 InCJKCompatibilityForms
605 InCJKCompatibilityIdeographs
606 InCJKCompatibilityIdeographsSupplement
607 InCJKRadicalsSupplement
8158862b 608 InCJKStrokes
1d81abf3
JH
609 InCJKSymbolsAndPunctuation
610 InCJKUnifiedIdeographs
611 InCJKUnifiedIdeographsExtensionA
612 InCJKUnifiedIdeographsExtensionB
613 InCherokee
614 InCombiningDiacriticalMarks
8158862b 615 InCombiningDiacriticalMarksSupplement
1d81abf3
JH
616 InCombiningDiacriticalMarksforSymbols
617 InCombiningHalfMarks
618 InControlPictures
8158862b
ST
619 InCoptic
620 InCountingRodNumerals
621 InCuneiform
622 InCuneiformNumbersAndPunctuation
1d81abf3 623 InCurrencySymbols
8158862b 624 InCypriotSyllabary
1d81abf3 625 InCyrillic
8158862b 626 InCyrillicSupplement
1d81abf3
JH
627 InDeseret
628 InDevanagari
629 InDingbats
630 InEnclosedAlphanumerics
631 InEnclosedCJKLettersAndMonths
632 InEthiopic
8158862b
ST
633 InEthiopicExtended
634 InEthiopicSupplement
1d81abf3
JH
635 InGeneralPunctuation
636 InGeometricShapes
637 InGeorgian
8158862b
ST
638 InGeorgianSupplement
639 InGlagolitic
1d81abf3
JH
640 InGothic
641 InGreekExtended
642 InGreekAndCoptic
643 InGujarati
644 InGurmukhi
645 InHalfwidthAndFullwidthForms
646 InHangulCompatibilityJamo
647 InHangulJamo
648 InHangulSyllables
649 InHanunoo
650 InHebrew
651 InHighPrivateUseSurrogates
652 InHighSurrogates
653 InHiragana
654 InIPAExtensions
655 InIdeographicDescriptionCharacters
656 InKanbun
657 InKangxiRadicals
658 InKannada
659 InKatakana
660 InKatakanaPhoneticExtensions
8158862b 661 InKharoshthi
1d81abf3 662 InKhmer
8158862b 663 InKhmerSymbols
1d81abf3
JH
664 InLao
665 InLatin1Supplement
666 InLatinExtendedA
667 InLatinExtendedAdditional
668 InLatinExtendedB
8158862b
ST
669 InLatinExtendedC
670 InLatinExtendedD
1d81abf3 671 InLetterlikeSymbols
8158862b
ST
672 InLimbu
673 InLinearBIdeograms
674 InLinearBSyllabary
1d81abf3
JH
675 InLowSurrogates
676 InMalayalam
677 InMathematicalAlphanumericSymbols
678 InMathematicalOperators
679 InMiscellaneousMathematicalSymbolsA
680 InMiscellaneousMathematicalSymbolsB
681 InMiscellaneousSymbols
8158862b 682 InMiscellaneousSymbolsAndArrows
1d81abf3 683 InMiscellaneousTechnical
8158862b 684 InModifierToneLetters
1d81abf3
JH
685 InMongolian
686 InMusicalSymbols
687 InMyanmar
8158862b
ST
688 InNKo
689 InNewTaiLue
1d81abf3
JH
690 InNumberForms
691 InOgham
692 InOldItalic
8158862b 693 InOldPersian
1d81abf3
JH
694 InOpticalCharacterRecognition
695 InOriya
8158862b
ST
696 InOsmanya
697 InPhagspa
698 InPhoenician
699 InPhoneticExtensions
700 InPhoneticExtensionsSupplement
1d81abf3
JH
701 InPrivateUseArea
702 InRunic
8158862b 703 InShavian
1d81abf3
JH
704 InSinhala
705 InSmallFormVariants
706 InSpacingModifierLetters
707 InSpecials
708 InSuperscriptsAndSubscripts
709 InSupplementalArrowsA
710 InSupplementalArrowsB
711 InSupplementalMathematicalOperators
8158862b 712 InSupplementalPunctuation
1d81abf3
JH
713 InSupplementaryPrivateUseAreaA
714 InSupplementaryPrivateUseAreaB
8158862b 715 InSylotiNagri
1d81abf3
JH
716 InSyriac
717 InTagalog
718 InTagbanwa
719 InTags
8158862b
ST
720 InTaiLe
721 InTaiXuanJingSymbols
1d81abf3
JH
722 InTamil
723 InTelugu
724 InThaana
725 InThai
726 InTibetan
8158862b
ST
727 InTifinagh
728 InUgaritic
1d81abf3
JH
729 InUnifiedCanadianAboriginalSyllabics
730 InVariationSelectors
8158862b
ST
731 InVariationSelectorsSupplement
732 InVerticalForms
1d81abf3
JH
733 InYiRadicals
734 InYiSyllables
8158862b 735 InYijingHexagramSymbols
32293815 736
393fec97
GS
737=back
738
376d9008 739=head2 User-Defined Character Properties
491fd90a
JH
740
741You can define your own character properties by defining subroutines
bac0b425
JP
742whose names begin with "In" or "Is". The subroutines can be defined in
743any package. The user-defined properties can be used in the regular
744expression C<\p> and C<\P> constructs; if you are using a user-defined
745property from a package other than the one you are in, you must specify
746its package in the C<\p> or C<\P> construct.
747
748 # assuming property IsForeign defined in Lang::
749 package main; # property package name required
750 if ($txt =~ /\p{Lang::IsForeign}+/) { ... }
751
752 package Lang; # property package name not required
753 if ($txt =~ /\p{IsForeign}+/) { ... }
754
755
756Note that the effect is compile-time and immutable once defined.
491fd90a 757
376d9008
JB
758The subroutines must return a specially-formatted string, with one
759or more newline-separated lines. Each line must be one of the following:
491fd90a
JH
760
761=over 4
762
763=item *
764
510254c9
A
765A single hexadecimal number denoting a Unicode code point to include.
766
767=item *
768
99a6b1f0 769Two hexadecimal numbers separated by horizontal whitespace (space or
376d9008 770tabular characters) denoting a range of Unicode code points to include.
491fd90a
JH
771
772=item *
773
376d9008 774Something to include, prefixed by "+": a built-in character
bac0b425
JP
775property (prefixed by "utf8::") or a user-defined character property,
776to represent all the characters in that property; two hexadecimal code
777points for a range; or a single hexadecimal code point.
491fd90a
JH
778
779=item *
780
376d9008 781Something to exclude, prefixed by "-": an existing character
bac0b425
JP
782property (prefixed by "utf8::") or a user-defined character property,
783to represent all the characters in that property; two hexadecimal code
784points for a range; or a single hexadecimal code point.
491fd90a
JH
785
786=item *
787
376d9008 788Something to negate, prefixed "!": an existing character
bac0b425
JP
789property (prefixed by "utf8::") or a user-defined character property,
790to represent all the characters in that property; two hexadecimal code
791points for a range; or a single hexadecimal code point.
792
793=item *
794
795Something to intersect with, prefixed by "&": an existing character
796property (prefixed by "utf8::") or a user-defined character property,
797for all the characters except the characters in the property; two
798hexadecimal code points for a range; or a single hexadecimal code point.
491fd90a
JH
799
800=back
801
802For example, to define a property that covers both the Japanese
803syllabaries (hiragana and katakana), you can define
804
805 sub InKana {
d5822f25
A
806 return <<END;
807 3040\t309F
808 30A0\t30FF
491fd90a
JH
809 END
810 }
811
d5822f25
A
812Imagine that the here-doc end marker is at the beginning of the line.
813Now you can use C<\p{InKana}> and C<\P{InKana}>.
491fd90a
JH
814
815You could also have used the existing block property names:
816
817 sub InKana {
818 return <<'END';
819 +utf8::InHiragana
820 +utf8::InKatakana
821 END
822 }
823
824Suppose you wanted to match only the allocated characters,
d5822f25 825not the raw block ranges: in other words, you want to remove
491fd90a
JH
826the non-characters:
827
828 sub InKana {
829 return <<'END';
830 +utf8::InHiragana
831 +utf8::InKatakana
832 -utf8::IsCn
833 END
834 }
835
836The negation is useful for defining (surprise!) negated classes.
837
838 sub InNotKana {
839 return <<'END';
840 !utf8::InHiragana
841 -utf8::InKatakana
842 +utf8::IsCn
843 END
844 }
845
bac0b425
JP
846Intersection is useful for getting the common characters matched by
847two (or more) classes.
848
849 sub InFooAndBar {
850 return <<'END';
851 +main::Foo
852 &main::Bar
853 END
854 }
855
856It's important to remember not to use "&" for the first set -- that
857would be intersecting with nothing (resulting in an empty set).
858
822502e5
ST
859=head2 User-Defined Case Mappings
860
3a2263fe
RGS
861You can also define your own mappings to be used in the lc(),
862lcfirst(), uc(), and ucfirst() (or their string-inlined versions).
822502e5
ST
863The principle is similar to that of user-defined character
864properties: to define subroutines in the C<main> package
3a2263fe
RGS
865with names like C<ToLower> (for lc() and lcfirst()), C<ToTitle> (for
866the first character in ucfirst()), and C<ToUpper> (for uc(), and the
867rest of the characters in ucfirst()).
868
869The string returned by the subroutines needs now to be three
870hexadecimal numbers separated by tabulators: start of the source
871range, end of the source range, and start of the destination range.
872For example:
873
874 sub ToUpper {
875 return <<END;
876 0061\t0063\t0041
877 END
878 }
879
880defines an uc() mapping that causes only the characters "a", "b", and
881"c" to be mapped to "A", "B", "C", all other characters will remain
882unchanged.
883
884If there is no source range to speak of, that is, the mapping is from
885a single character to another single character, leave the end of the
886source range empty, but the two tabulator characters are still needed.
887For example:
888
889 sub ToLower {
890 return <<END;
891 0041\t\t0061
892 END
893 }
894
895defines a lc() mapping that causes only "A" to be mapped to "a", all
896other characters will remain unchanged.
897
898(For serious hackers only) If you want to introspect the default
899mappings, you can find the data in the directory
900C<$Config{privlib}>/F<unicore/To/>. The mapping data is returned as
901the here-document, and the C<utf8::ToSpecFoo> are special exception
902mappings derived from <$Config{privlib}>/F<unicore/SpecialCasing.txt>.
903The C<Digit> and C<Fold> mappings that one can see in the directory
904are not directly user-accessible, one can use either the
905C<Unicode::UCD> module, or just match case-insensitively (that's when
906the C<Fold> mapping is used).
907
822502e5
ST
908A final note on the user-defined case mappings: they will be used
909only if the scalar has been marked as having Unicode characters.
910Old byte-style strings will not be affected.
3a2263fe 911
376d9008 912=head2 Character Encodings for Input and Output
8cbd9a7a 913
7221edc9 914See L<Encode>.
8cbd9a7a 915
c29a771d 916=head2 Unicode Regular Expression Support Level
776f8809 917
376d9008
JB
918The following list of Unicode support for regular expressions describes
919all the features currently supported. The references to "Level N"
8158862b
ST
920and the section numbers refer to the Unicode Technical Standard #18,
921"Unicode Regular Expressions", version 11, in May 2005.
776f8809
JH
922
923=over 4
924
925=item *
926
927Level 1 - Basic Unicode Support
928
8158862b
ST
929 RL1.1 Hex Notation - done [1]
930 RL1.2 Properties - done [2][3]
931 RL1.2a Compatibility Properties - done [4]
932 RL1.3 Subtraction and Intersection - MISSING [5]
933 RL1.4 Simple Word Boundaries - done [6]
934 RL1.5 Simple Loose Matches - done [7]
935 RL1.6 Line Boundaries - MISSING [8]
936 RL1.7 Supplementary Code Points - done [9]
937
938 [1] \x{...}
939 [2] \p{...} \P{...}
940 [3] supports not only minimal list (general category, scripts,
941 Alphabetic, Lowercase, Uppercase, WhiteSpace,
942 NoncharacterCodePoint, DefaultIgnorableCodePoint, Any,
943 ASCII, Assigned), but also bidirectional types, blocks, etc.
ea8b8ad2 944 (see "Unicode Character Properties")
8158862b
ST
945 [4] \d \D \s \S \w \W \X [:prop:] [:^prop:]
946 [5] can use regular expression look-ahead [a] or
947 user-defined character properties [b] to emulate set operations
948 [6] \b \B
949 [7] note that Perl does Full case-folding in matching, not Simple:
2bbc8d55
SP
950 for example U+1F88 is equivalent to U+1F00 U+03B9,
951 not with 1F80. This difference matters mainly for certain Greek
376d9008
JB
952 capital letters with certain modifiers: the Full case-folding
953 decomposes the letter, while the Simple case-folding would map
e0f9d4a8 954 it to a single character.
8158862b
ST
955 [8] should do ^ and $ also on U+000B (\v in C), FF (\f), CR (\r),
956 CRLF (\r\n), NEL (U+0085), LS (U+2028), and PS (U+2029);
957 should also affect <>, $., and script line numbers;
958 should not split lines within CRLF [c] (i.e. there is no empty
959 line between \r and \n)
960 [9] UTF-8/UTF-EBDDIC used in perl allows not only U+10000 to U+10FFFF
961 but also beyond U+10FFFF [d]
7207e29d 962
237bad5b 963[a] You can mimic class subtraction using lookahead.
8158862b 964For example, what UTS#18 might write as
29bdacb8 965
dbe420b4
JH
966 [{Greek}-[{UNASSIGNED}]]
967
968in Perl can be written as:
969
1d81abf3
JH
970 (?!\p{Unassigned})\p{InGreekAndCoptic}
971 (?=\p{Assigned})\p{InGreekAndCoptic}
dbe420b4
JH
972
973But in this particular example, you probably really want
974
1bfb14c4 975 \p{GreekAndCoptic}
dbe420b4
JH
976
977which will match assigned characters known to be part of the Greek script.
29bdacb8 978
5ca1ac52 979Also see the Unicode::Regex::Set module, it does implement the full
8158862b
ST
980UTS#18 grouping, intersection, union, and removal (subtraction) syntax.
981
982[b] '+' for union, '-' for removal (set-difference), '&' for intersection
983(see L</"User-Defined Character Properties">)
984
985[c] Try the C<:crlf> layer (see L<PerlIO>).
5ca1ac52 986
8158862b
ST
987[d] Avoid C<use warning 'utf8';> (or say C<no warning 'utf8';>) to allow
988U+FFFF (C<\x{FFFF}>).
237bad5b 989
776f8809
JH
990=item *
991
992Level 2 - Extended Unicode Support
993
8158862b
ST
994 RL2.1 Canonical Equivalents - MISSING [10][11]
995 RL2.2 Default Grapheme Clusters - MISSING [12][13]
996 RL2.3 Default Word Boundaries - MISSING [14]
997 RL2.4 Default Loose Matches - MISSING [15]
998 RL2.5 Name Properties - MISSING [16]
999 RL2.6 Wildcard Properties - MISSING
1000
1001 [10] see UAX#15 "Unicode Normalization Forms"
1002 [11] have Unicode::Normalize but not integrated to regexes
1003 [12] have \X but at this level . should equal that
1004 [13] UAX#29 "Text Boundaries" considers CRLF and Hangul syllable
1005 clusters as a single grapheme cluster.
1006 [14] see UAX#29, Word Boundaries
1007 [15] see UAX#21 "Case Mappings"
1008 [16] have \N{...} but neither compute names of CJK Ideographs
1009 and Hangul Syllables nor use a loose match [e]
1010
1011[e] C<\N{...}> allows namespaces (see L<charnames>).
776f8809
JH
1012
1013=item *
1014
8158862b
ST
1015Level 3 - Tailored Support
1016
1017 RL3.1 Tailored Punctuation - MISSING
1018 RL3.2 Tailored Grapheme Clusters - MISSING [17][18]
1019 RL3.3 Tailored Word Boundaries - MISSING
1020 RL3.4 Tailored Loose Matches - MISSING
1021 RL3.5 Tailored Ranges - MISSING
1022 RL3.6 Context Matching - MISSING [19]
1023 RL3.7 Incremental Matches - MISSING
1024 ( RL3.8 Unicode Set Sharing )
1025 RL3.9 Possible Match Sets - MISSING
1026 RL3.10 Folded Matching - MISSING [20]
1027 RL3.11 Submatchers - MISSING
1028
1029 [17] see UAX#10 "Unicode Collation Algorithms"
1030 [18] have Unicode::Collate but not integrated to regexes
1031 [19] have (?<=x) and (?=x), but look-aheads or look-behinds should see
1032 outside of the target substring
1033 [20] need insensitive matching for linguistic features other than case;
1034 for example, hiragana to katakana, wide and narrow, simplified Han
1035 to traditional Han (see UTR#30 "Character Foldings")
776f8809
JH
1036
1037=back
1038
c349b1b9
JH
1039=head2 Unicode Encodings
1040
376d9008
JB
1041Unicode characters are assigned to I<code points>, which are abstract
1042numbers. To use these numbers, various encodings are needed.
c349b1b9
JH
1043
1044=over 4
1045
c29a771d 1046=item *
5cb3728c
RB
1047
1048UTF-8
c349b1b9 1049
3e4dbfed 1050UTF-8 is a variable-length (1 to 6 bytes, current character allocations
376d9008
JB
1051require 4 bytes), byte-order independent encoding. For ASCII (and we
1052really do mean 7-bit ASCII, not another 8-bit encoding), UTF-8 is
1053transparent.
c349b1b9 1054
8c007b5a 1055The following table is from Unicode 3.2.
05632f9a
JH
1056
1057 Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
1058
8c007b5a
JH
1059 U+0000..U+007F 00..7F
1060 U+0080..U+07FF C2..DF 80..BF
ec90690f
ST
1061 U+0800..U+0FFF E0 A0..BF 80..BF
1062 U+1000..U+CFFF E1..EC 80..BF 80..BF
1063 U+D000..U+D7FF ED 80..9F 80..BF
8c007b5a 1064 U+D800..U+DFFF ******* ill-formed *******
ec90690f 1065 U+E000..U+FFFF EE..EF 80..BF 80..BF
05632f9a
JH
1066 U+10000..U+3FFFF F0 90..BF 80..BF 80..BF
1067 U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF
1068 U+100000..U+10FFFF F4 80..8F 80..BF 80..BF
1069
376d9008
JB
1070Note the C<A0..BF> in C<U+0800..U+0FFF>, the C<80..9F> in
1071C<U+D000...U+D7FF>, the C<90..B>F in C<U+10000..U+3FFFF>, and the
1072C<80...8F> in C<U+100000..U+10FFFF>. The "gaps" are caused by legal
1073UTF-8 avoiding non-shortest encodings: it is technically possible to
1074UTF-8-encode a single code point in different ways, but that is
1075explicitly forbidden, and the shortest possible encoding should always
1076be used. So that's what Perl does.
37361303 1077
376d9008 1078Another way to look at it is via bits:
05632f9a
JH
1079
1080 Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
1081
1082 0aaaaaaa 0aaaaaaa
1083 00000bbbbbaaaaaa 110bbbbb 10aaaaaa
1084 ccccbbbbbbaaaaaa 1110cccc 10bbbbbb 10aaaaaa
1085 00000dddccccccbbbbbbaaaaaa 11110ddd 10cccccc 10bbbbbb 10aaaaaa
1086
1087As you can see, the continuation bytes all begin with C<10>, and the
8c007b5a 1088leading bits of the start byte tell how many bytes the are in the
05632f9a
JH
1089encoded character.
1090
c29a771d 1091=item *
5cb3728c
RB
1092
1093UTF-EBCDIC
dbe420b4 1094
376d9008 1095Like UTF-8 but EBCDIC-safe, in the way that UTF-8 is ASCII-safe.
dbe420b4 1096
c29a771d 1097=item *
5cb3728c 1098
1e54db1a 1099UTF-16, UTF-16BE, UTF-16LE, Surrogates, and BOMs (Byte Order Marks)
c349b1b9 1100
1bfb14c4
JH
1101The followings items are mostly for reference and general Unicode
1102knowledge, Perl doesn't use these constructs internally.
dbe420b4 1103
c349b1b9 1104UTF-16 is a 2 or 4 byte encoding. The Unicode code points
1bfb14c4
JH
1105C<U+0000..U+FFFF> are stored in a single 16-bit unit, and the code
1106points C<U+10000..U+10FFFF> in two 16-bit units. The latter case is
c349b1b9
JH
1107using I<surrogates>, the first 16-bit unit being the I<high
1108surrogate>, and the second being the I<low surrogate>.
1109
376d9008 1110Surrogates are code points set aside to encode the C<U+10000..U+10FFFF>
c349b1b9 1111range of Unicode code points in pairs of 16-bit units. The I<high
376d9008
JB
1112surrogates> are the range C<U+D800..U+DBFF>, and the I<low surrogates>
1113are the range C<U+DC00..U+DFFF>. The surrogate encoding is
c349b1b9
JH
1114
1115 $hi = ($uni - 0x10000) / 0x400 + 0xD800;
1116 $lo = ($uni - 0x10000) % 0x400 + 0xDC00;
1117
1118and the decoding is
1119
1a3fa709 1120 $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00);
c349b1b9 1121
feda178f 1122If you try to generate surrogates (for example by using chr()), you
376d9008
JB
1123will get a warning if warnings are turned on, because those code
1124points are not valid for a Unicode character.
9466bab6 1125
376d9008 1126Because of the 16-bitness, UTF-16 is byte-order dependent. UTF-16
c349b1b9 1127itself can be used for in-memory computations, but if storage or
376d9008
JB
1128transfer is required either UTF-16BE (big-endian) or UTF-16LE
1129(little-endian) encodings must be chosen.
c349b1b9
JH
1130
1131This introduces another problem: what if you just know that your data
376d9008
JB
1132is UTF-16, but you don't know which endianness? Byte Order Marks, or
1133BOMs, are a solution to this. A special character has been reserved
86bbd6d1 1134in Unicode to function as a byte order marker: the character with the
376d9008 1135code point C<U+FEFF> is the BOM.
042da322 1136
c349b1b9 1137The trick is that if you read a BOM, you will know the byte order,
376d9008
JB
1138since if it was written on a big-endian platform, you will read the
1139bytes C<0xFE 0xFF>, but if it was written on a little-endian platform,
1140you will read the bytes C<0xFF 0xFE>. (And if the originating platform
1141was writing in UTF-8, you will read the bytes C<0xEF 0xBB 0xBF>.)
042da322 1142
86bbd6d1 1143The way this trick works is that the character with the code point
376d9008
JB
1144C<U+FFFE> is guaranteed not to be a valid Unicode character, so the
1145sequence of bytes C<0xFF 0xFE> is unambiguously "BOM, represented in
1bfb14c4 1146little-endian format" and cannot be C<U+FFFE>, represented in big-endian
042da322 1147format".
c349b1b9 1148
c29a771d 1149=item *
5cb3728c 1150
1e54db1a 1151UTF-32, UTF-32BE, UTF-32LE
c349b1b9
JH
1152
1153The UTF-32 family is pretty much like the UTF-16 family, expect that
042da322 1154the units are 32-bit, and therefore the surrogate scheme is not
376d9008
JB
1155needed. The BOM signatures will be C<0x00 0x00 0xFE 0xFF> for BE and
1156C<0xFF 0xFE 0x00 0x00> for LE.
c349b1b9 1157
c29a771d 1158=item *
5cb3728c
RB
1159
1160UCS-2, UCS-4
c349b1b9 1161
86bbd6d1 1162Encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit
376d9008 1163encoding. Unlike UTF-16, UCS-2 is not extensible beyond C<U+FFFF>,
339cfa0e
JH
1164because it does not use surrogates. UCS-4 is a 32-bit encoding,
1165functionally identical to UTF-32.
c349b1b9 1166
c29a771d 1167=item *
5cb3728c
RB
1168
1169UTF-7
c349b1b9 1170
376d9008
JB
1171A seven-bit safe (non-eight-bit) encoding, which is useful if the
1172transport or storage is not eight-bit safe. Defined by RFC 2152.
c349b1b9 1173
95a1a48b
JH
1174=back
1175
0d7c09bb
JH
1176=head2 Security Implications of Unicode
1177
1178=over 4
1179
1180=item *
1181
1182Malformed UTF-8
bf0fa0b2
JH
1183
1184Unfortunately, the specification of UTF-8 leaves some room for
1185interpretation of how many bytes of encoded output one should generate
376d9008
JB
1186from one input Unicode character. Strictly speaking, the shortest
1187possible sequence of UTF-8 bytes should be generated,
1188because otherwise there is potential for an input buffer overflow at
feda178f 1189the receiving end of a UTF-8 connection. Perl always generates the
376d9008
JB
1190shortest length UTF-8, and with warnings on Perl will warn about
1191non-shortest length UTF-8 along with other malformations, such as the
1192surrogates, which are not real Unicode code points.
bf0fa0b2 1193
0d7c09bb
JH
1194=item *
1195
1196Regular expressions behave slightly differently between byte data and
376d9008
JB
1197character (Unicode) data. For example, the "word character" character
1198class C<\w> will work differently depending on if data is eight-bit bytes
1199or Unicode.
0d7c09bb 1200
376d9008
JB
1201In the first case, the set of C<\w> characters is either small--the
1202default set of alphabetic characters, digits, and the "_"--or, if you
0d7c09bb
JH
1203are using a locale (see L<perllocale>), the C<\w> might contain a few
1204more letters according to your language and country.
1205
376d9008 1206In the second case, the C<\w> set of characters is much, much larger.
1bfb14c4
JH
1207Most importantly, even in the set of the first 256 characters, it will
1208probably match different characters: unlike most locales, which are
1209specific to a language and country pair, Unicode classifies all the
1210characters that are letters I<somewhere> as C<\w>. For example, your
1211locale might not think that LATIN SMALL LETTER ETH is a letter (unless
1212you happen to speak Icelandic), but Unicode does.
0d7c09bb 1213
376d9008 1214As discussed elsewhere, Perl has one foot (two hooves?) planted in
1bfb14c4
JH
1215each of two worlds: the old world of bytes and the new world of
1216characters, upgrading from bytes to characters when necessary.
376d9008
JB
1217If your legacy code does not explicitly use Unicode, no automatic
1218switch-over to characters should happen. Characters shouldn't get
1bfb14c4
JH
1219downgraded to bytes, either. It is possible to accidentally mix bytes
1220and characters, however (see L<perluniintro>), in which case C<\w> in
1221regular expressions might start behaving differently. Review your
1222code. Use warnings and the C<strict> pragma.
0d7c09bb
JH
1223
1224=back
1225
c349b1b9
JH
1226=head2 Unicode in Perl on EBCDIC
1227
376d9008
JB
1228The way Unicode is handled on EBCDIC platforms is still
1229experimental. On such platforms, references to UTF-8 encoding in this
1230document and elsewhere should be read as meaning the UTF-EBCDIC
1231specified in Unicode Technical Report 16, unless ASCII vs. EBCDIC issues
c349b1b9 1232are specifically discussed. There is no C<utfebcdic> pragma or
376d9008 1233":utfebcdic" layer; rather, "utf8" and ":utf8" are reused to mean
86bbd6d1
PN
1234the platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic>
1235for more discussion of the issues.
c349b1b9 1236
b310b053
JH
1237=head2 Locales
1238
4616122b 1239Usually locale settings and Unicode do not affect each other, but
b310b053
JH
1240there are a couple of exceptions:
1241
1242=over 4
1243
1244=item *
1245
8aa8f774
JH
1246You can enable automatic UTF-8-ification of your standard file
1247handles, default C<open()> layer, and C<@ARGV> by using either
1248the C<-C> command line switch or the C<PERL_UNICODE> environment
1249variable, see L<perlrun> for the documentation of the C<-C> switch.
b310b053
JH
1250
1251=item *
1252
376d9008
JB
1253Perl tries really hard to work both with Unicode and the old
1254byte-oriented world. Most often this is nice, but sometimes Perl's
1255straddling of the proverbial fence causes problems.
b310b053
JH
1256
1257=back
1258
1aad1664
JH
1259=head2 When Unicode Does Not Happen
1260
1261While Perl does have extensive ways to input and output in Unicode,
1262and few other 'entry points' like the @ARGV which can be interpreted
1263as Unicode (UTF-8), there still are many places where Unicode (in some
1264encoding or another) could be given as arguments or received as
1265results, or both, but it is not.
1266
6cd4dd6c
JH
1267The following are such interfaces. For all of these interfaces Perl
1268currently (as of 5.8.3) simply assumes byte strings both as arguments
1269and results, or UTF-8 strings if the C<encoding> pragma has been used.
1aad1664
JH
1270
1271One reason why Perl does not attempt to resolve the role of Unicode in
1272this cases is that the answers are highly dependent on the operating
1273system and the file system(s). For example, whether filenames can be
1274in Unicode, and in exactly what kind of encoding, is not exactly a
1275portable concept. Similarly for the qx and system: how well will the
1276'command line interface' (and which of them?) handle Unicode?
1277
1278=over 4
1279
557a2462
RB
1280=item *
1281
254c2b64 1282chdir, chmod, chown, chroot, exec, link, lstat, mkdir,
1e8e8236 1283rename, rmdir, stat, symlink, truncate, unlink, utime, -X
557a2462
RB
1284
1285=item *
1286
1287%ENV
1288
1289=item *
1290
1291glob (aka the <*>)
1292
1293=item *
1aad1664 1294
557a2462 1295open, opendir, sysopen
1aad1664 1296
557a2462 1297=item *
1aad1664 1298
557a2462 1299qx (aka the backtick operator), system
1aad1664 1300
557a2462 1301=item *
1aad1664 1302
557a2462 1303readdir, readlink
1aad1664
JH
1304
1305=back
1306
1307=head2 Forcing Unicode in Perl (Or Unforcing Unicode in Perl)
1308
1309Sometimes (see L</"When Unicode Does Not Happen">) there are
2bbc8d55
SP
1310situations where you simply need to force a byte
1311string into UTF-8, or vice versa. The low-level calls
1312utf8::upgrade($bytestring) and utf8::downgrade($utf8string[, FAIL_OK]) are
1aad1664
JH
1313the answers.
1314
2bbc8d55
SP
1315Note that utf8::downgrade() can fail if the string contains characters
1316that don't fit into a byte.
1aad1664 1317
95a1a48b
JH
1318=head2 Using Unicode in XS
1319
3a2263fe
RGS
1320If you want to handle Perl Unicode in XS extensions, you may find the
1321following C APIs useful. See also L<perlguts/"Unicode Support"> for an
1322explanation about Unicode at the XS level, and L<perlapi> for the API
1323details.
95a1a48b
JH
1324
1325=over 4
1326
1327=item *
1328
1bfb14c4 1329C<DO_UTF8(sv)> returns true if the C<UTF8> flag is on and the bytes
2bbc8d55 1330pragma is not in effect. C<SvUTF8(sv)> returns true if the C<UTF8>
1bfb14c4
JH
1331flag is on; the bytes pragma is ignored. The C<UTF8> flag being on
1332does B<not> mean that there are any characters of code points greater
1333than 255 (or 127) in the scalar or that there are even any characters
1334in the scalar. What the C<UTF8> flag means is that the sequence of
1335octets in the representation of the scalar is the sequence of UTF-8
1336encoded code points of the characters of a string. The C<UTF8> flag
1337being off means that each octet in this representation encodes a
1338single character with code point 0..255 within the string. Perl's
1339Unicode model is not to use UTF-8 until it is absolutely necessary.
95a1a48b
JH
1340
1341=item *
1342
2bbc8d55 1343C<uvchr_to_utf8(buf, chr)> writes a Unicode character code point into
1bfb14c4 1344a buffer encoding the code point as UTF-8, and returns a pointer
2bbc8d55 1345pointing after the UTF-8 bytes. It works appropriately on EBCDIC machines.
95a1a48b
JH
1346
1347=item *
1348
2bbc8d55 1349C<utf8_to_uvchr(buf, lenp)> reads UTF-8 encoded bytes from a buffer and
376d9008 1350returns the Unicode character code point and, optionally, the length of
2bbc8d55 1351the UTF-8 byte sequence. It works appropriately on EBCDIC machines.
95a1a48b
JH
1352
1353=item *
1354
376d9008
JB
1355C<utf8_length(start, end)> returns the length of the UTF-8 encoded buffer
1356in characters. C<sv_len_utf8(sv)> returns the length of the UTF-8 encoded
95a1a48b
JH
1357scalar.
1358
1359=item *
1360
376d9008
JB
1361C<sv_utf8_upgrade(sv)> converts the string of the scalar to its UTF-8
1362encoded form. C<sv_utf8_downgrade(sv)> does the opposite, if
1363possible. C<sv_utf8_encode(sv)> is like sv_utf8_upgrade except that
1364it does not set the C<UTF8> flag. C<sv_utf8_decode()> does the
1365opposite of C<sv_utf8_encode()>. Note that none of these are to be
1366used as general-purpose encoding or decoding interfaces: C<use Encode>
1367for that. C<sv_utf8_upgrade()> is affected by the encoding pragma
1368but C<sv_utf8_downgrade()> is not (since the encoding pragma is
1369designed to be a one-way street).
95a1a48b
JH
1370
1371=item *
1372
376d9008 1373C<is_utf8_char(s)> returns true if the pointer points to a valid UTF-8
90f968e0 1374character.
95a1a48b
JH
1375
1376=item *
1377
376d9008 1378C<is_utf8_string(buf, len)> returns true if C<len> bytes of the buffer
95a1a48b
JH
1379are valid UTF-8.
1380
1381=item *
1382
376d9008
JB
1383C<UTF8SKIP(buf)> will return the number of bytes in the UTF-8 encoded
1384character in the buffer. C<UNISKIP(chr)> will return the number of bytes
1385required to UTF-8-encode the Unicode character code point. C<UTF8SKIP()>
90f968e0 1386is useful for example for iterating over the characters of a UTF-8
376d9008 1387encoded buffer; C<UNISKIP()> is useful, for example, in computing
90f968e0 1388the size required for a UTF-8 encoded buffer.
95a1a48b
JH
1389
1390=item *
1391
376d9008 1392C<utf8_distance(a, b)> will tell the distance in characters between the
95a1a48b
JH
1393two pointers pointing to the same UTF-8 encoded buffer.
1394
1395=item *
1396
2bbc8d55 1397C<utf8_hop(s, off)> will return a pointer to a UTF-8 encoded buffer
376d9008
JB
1398that is C<off> (positive or negative) Unicode characters displaced
1399from the UTF-8 buffer C<s>. Be careful not to overstep the buffer:
1400C<utf8_hop()> will merrily run off the end or the beginning of the
1401buffer if told to do so.
95a1a48b 1402
d2cc3551
JH
1403=item *
1404
376d9008
JB
1405C<pv_uni_display(dsv, spv, len, pvlim, flags)> and
1406C<sv_uni_display(dsv, ssv, pvlim, flags)> are useful for debugging the
1407output of Unicode strings and scalars. By default they are useful
1408only for debugging--they display B<all> characters as hexadecimal code
1bfb14c4
JH
1409points--but with the flags C<UNI_DISPLAY_ISPRINT>,
1410C<UNI_DISPLAY_BACKSLASH>, and C<UNI_DISPLAY_QQ> you can make the
1411output more readable.
d2cc3551
JH
1412
1413=item *
1414
2bbc8d55 1415C<ibcmp_utf8(s1, pe1, l1, u1, s2, pe2, l2, u2)> can be used to
376d9008
JB
1416compare two strings case-insensitively in Unicode. For case-sensitive
1417comparisons you can just use C<memEQ()> and C<memNE()> as usual.
d2cc3551 1418
c349b1b9
JH
1419=back
1420
95a1a48b
JH
1421For more information, see L<perlapi>, and F<utf8.c> and F<utf8.h>
1422in the Perl source code distribution.
1423
c29a771d
JH
1424=head1 BUGS
1425
376d9008 1426=head2 Interaction with Locales
7eabb34d 1427
376d9008
JB
1428Use of locales with Unicode data may lead to odd results. Currently,
1429Perl attempts to attach 8-bit locale info to characters in the range
14300..255, but this technique is demonstrably incorrect for locales that
1431use characters above that range when mapped into Unicode. Perl's
1432Unicode support will also tend to run slower. Use of locales with
1433Unicode is discouraged.
c29a771d 1434
2bbc8d55
SP
1435=head2 Problems with characters whose ordinal numbers are in the range 128 - 255 with no Locale specified
1436
1437Without a locale specified, unlike all other characters or code points,
1438these characters have very different semantics in byte semantics versus
1439character semantics.
1440In character semantics they are interpreted as Unicode code points, which means
1441they are viewed as Latin-1 (ISO-8859-1).
1442In byte semantics, they are considered to be unassigned characters,
1443meaning that the only semantics they have is their
1444ordinal numbers, and that they are not members of various character classes.
1445None are considered to match C<\w> for example, but all match C<\W>.
1446Besides these class matches,
1447the known operations that this affects are those that change the case,
1448regular expression matching while ignoring case,
1449and B<quotemeta()>.
1450This can lead to unexpected results in which a string's semantics suddenly
1451change if a code point above 255 is appended to or removed from it,
1452which changes the string's semantics from byte to character or vice versa.
1453This behavior is scheduled to change in version 5.12, but in the meantime,
fe749c9a
KW
1454a workaround is to always call utf8::upgrade($string), or to use the
1455standard modules L<Encode> or L<charnames>.
2bbc8d55 1456
376d9008 1457=head2 Interaction with Extensions
7eabb34d 1458
376d9008 1459When Perl exchanges data with an extension, the extension should be
2575c402 1460able to understand the UTF8 flag and act accordingly. If the
376d9008
JB
1461extension doesn't know about the flag, it's likely that the extension
1462will return incorrectly-flagged data.
7eabb34d
A
1463
1464So if you're working with Unicode data, consult the documentation of
1465every module you're using if there are any issues with Unicode data
1466exchange. If the documentation does not talk about Unicode at all,
a73d23f6 1467suspect the worst and probably look at the source to learn how the
376d9008 1468module is implemented. Modules written completely in Perl shouldn't
a73d23f6
RGS
1469cause problems. Modules that directly or indirectly access code written
1470in other programming languages are at risk.
7eabb34d 1471
376d9008 1472For affected functions, the simple strategy to avoid data corruption is
7eabb34d 1473to always make the encoding of the exchanged data explicit. Choose an
376d9008 1474encoding that you know the extension can handle. Convert arguments passed
7eabb34d
A
1475to the extensions to that encoding and convert results back from that
1476encoding. Write wrapper functions that do the conversions for you, so
1477you can later change the functions when the extension catches up.
1478
376d9008 1479To provide an example, let's say the popular Foo::Bar::escape_html
7eabb34d
A
1480function doesn't deal with Unicode data yet. The wrapper function
1481would convert the argument to raw UTF-8 and convert the result back to
376d9008 1482Perl's internal representation like so:
7eabb34d
A
1483
1484 sub my_escape_html ($) {
1485 my($what) = shift;
1486 return unless defined $what;
1487 Encode::decode_utf8(Foo::Bar::escape_html(Encode::encode_utf8($what)));
1488 }
1489
1490Sometimes, when the extension does not convert data but just stores
1491and retrieves them, you will be in a position to use the otherwise
1492dangerous Encode::_utf8_on() function. Let's say the popular
66b79f27 1493C<Foo::Bar> extension, written in C, provides a C<param> method that
7eabb34d
A
1494lets you store and retrieve data according to these prototypes:
1495
1496 $self->param($name, $value); # set a scalar
1497 $value = $self->param($name); # retrieve a scalar
1498
1499If it does not yet provide support for any encoding, one could write a
1500derived class with such a C<param> method:
1501
1502 sub param {
1503 my($self,$name,$value) = @_;
1504 utf8::upgrade($name); # make sure it is UTF-8 encoded
af55fc6a 1505 if (defined $value) {
7eabb34d
A
1506 utf8::upgrade($value); # make sure it is UTF-8 encoded
1507 return $self->SUPER::param($name,$value);
1508 } else {
1509 my $ret = $self->SUPER::param($name);
1510 Encode::_utf8_on($ret); # we know, it is UTF-8 encoded
1511 return $ret;
1512 }
1513 }
1514
a73d23f6
RGS
1515Some extensions provide filters on data entry/exit points, such as
1516DB_File::filter_store_key and family. Look out for such filters in
66b79f27 1517the documentation of your extensions, they can make the transition to
7eabb34d
A
1518Unicode data much easier.
1519
376d9008 1520=head2 Speed
7eabb34d 1521
c29a771d 1522Some functions are slower when working on UTF-8 encoded strings than
574c8022 1523on byte encoded strings. All functions that need to hop over
7c17141f
JH
1524characters such as length(), substr() or index(), or matching regular
1525expressions can work B<much> faster when the underlying data are
1526byte-encoded.
1527
1528In Perl 5.8.0 the slowness was often quite spectacular; in Perl 5.8.1
1529a caching scheme was introduced which will hopefully make the slowness
a104b433
JH
1530somewhat less spectacular, at least for some operations. In general,
1531operations with UTF-8 encoded strings are still slower. As an example,
1532the Unicode properties (character classes) like C<\p{Nd}> are known to
1533be quite a bit slower (5-20 times) than their simpler counterparts
1534like C<\d> (then again, there 268 Unicode characters matching C<Nd>
1535compared with the 10 ASCII characters matching C<d>).
666f95b9 1536
fe749c9a
KW
1537=head2 Possible problems on EBCDIC platforms
1538
1539In earlier versions, when byte and character data were concatenated,
1540the new string was sometimes created by
1541decoding the byte strings as I<ISO 8859-1 (Latin-1)>, even if the
1542old Unicode string used EBCDIC.
1543
1544If you find any of these, please report them as bugs.
1545
c8d992ba
A
1546=head2 Porting code from perl-5.6.X
1547
1548Perl 5.8 has a different Unicode model from 5.6. In 5.6 the programmer
1549was required to use the C<utf8> pragma to declare that a given scope
1550expected to deal with Unicode data and had to make sure that only
1551Unicode data were reaching that scope. If you have code that is
1552working with 5.6, you will need some of the following adjustments to
1553your code. The examples are written such that the code will continue
1554to work under 5.6, so you should be safe to try them out.
1555
1556=over 4
1557
1558=item *
1559
1560A filehandle that should read or write UTF-8
1561
1562 if ($] > 5.007) {
740d4bb2 1563 binmode $fh, ":encoding(utf8)";
c8d992ba
A
1564 }
1565
1566=item *
1567
1568A scalar that is going to be passed to some extension
1569
1570Be it Compress::Zlib, Apache::Request or any extension that has no
1571mention of Unicode in the manpage, you need to make sure that the
2575c402 1572UTF8 flag is stripped off. Note that at the time of this writing
c8d992ba
A
1573(October 2002) the mentioned modules are not UTF-8-aware. Please
1574check the documentation to verify if this is still true.
1575
1576 if ($] > 5.007) {
1577 require Encode;
1578 $val = Encode::encode_utf8($val); # make octets
1579 }
1580
1581=item *
1582
1583A scalar we got back from an extension
1584
1585If you believe the scalar comes back as UTF-8, you will most likely
2575c402 1586want the UTF8 flag restored:
c8d992ba
A
1587
1588 if ($] > 5.007) {
1589 require Encode;
1590 $val = Encode::decode_utf8($val);
1591 }
1592
1593=item *
1594
1595Same thing, if you are really sure it is UTF-8
1596
1597 if ($] > 5.007) {
1598 require Encode;
1599 Encode::_utf8_on($val);
1600 }
1601
1602=item *
1603
1604A wrapper for fetchrow_array and fetchrow_hashref
1605
1606When the database contains only UTF-8, a wrapper function or method is
1607a convenient way to replace all your fetchrow_array and
1608fetchrow_hashref calls. A wrapper function will also make it easier to
1609adapt to future enhancements in your database driver. Note that at the
1610time of this writing (October 2002), the DBI has no standardized way
1611to deal with UTF-8 data. Please check the documentation to verify if
1612that is still true.
1613
1614 sub fetchrow {
1615 my($self, $sth, $what) = @_; # $what is one of fetchrow_{array,hashref}
1616 if ($] < 5.007) {
1617 return $sth->$what;
1618 } else {
1619 require Encode;
1620 if (wantarray) {
1621 my @arr = $sth->$what;
1622 for (@arr) {
1623 defined && /[^\000-\177]/ && Encode::_utf8_on($_);
1624 }
1625 return @arr;
1626 } else {
1627 my $ret = $sth->$what;
1628 if (ref $ret) {
1629 for my $k (keys %$ret) {
1630 defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret->{$k};
1631 }
1632 return $ret;
1633 } else {
1634 defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret;
1635 return $ret;
1636 }
1637 }
1638 }
1639 }
1640
1641
1642=item *
1643
1644A large scalar that you know can only contain ASCII
1645
1646Scalars that contain only ASCII and are marked as UTF-8 are sometimes
1647a drag to your program. If you recognize such a situation, just remove
2575c402 1648the UTF8 flag:
c8d992ba
A
1649
1650 utf8::downgrade($val) if $] > 5.007;
1651
1652=back
1653
393fec97
GS
1654=head1 SEE ALSO
1655
2575c402 1656L<perlunitut>, L<perluniintro>, L<Encode>, L<open>, L<utf8>, L<bytes>,
a05d7ebb 1657L<perlretut>, L<perlvar/"${^UNICODE}">
393fec97
GS
1658
1659=cut