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fix 2 environment handling bugs
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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
13a2d996 13=over 4
21bad921 14
fae2c0fb 15=item Input and Output Layers
21bad921 16
376d9008 17Perl knows when a filehandle uses Perl's internal Unicode encodings
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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>.
c349b1b9 22
376d9008 23To indicate that Perl source itself is using a particular encoding,
c349b1b9 24see L<encoding>.
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25
26=item Regular Expressions
27
c349b1b9 28The regular expression compiler produces polymorphic opcodes. That is,
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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.
21bad921 32
ad0029c4 33=item C<use utf8> still needed to enable UTF-8/UTF-EBCDIC in scripts
21bad921 34
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35As a compatibility measure, the C<use utf8> pragma must be explicitly
36included to enable recognition of UTF-8 in the Perl scripts themselves
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37(in string or regular expression literals, or in identifier names) on
38ASCII-based machines or to recognize UTF-EBCDIC on EBCDIC-based
376d9008 39machines. B<These are the only times when an explicit C<use utf8>
8f8cf39c 40is needed.> See L<utf8>.
21bad921 41
1768d7eb 42You can also use the C<encoding> pragma to change the default encoding
6ec9efec 43of the data in your script; see L<encoding>.
1768d7eb 44
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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
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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
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68=back
69
376d9008 70=head2 Byte and Character Semantics
393fec97 71
376d9008 72Beginning with version 5.6, Perl uses logically-wide characters to
3e4dbfed 73represent strings internally.
393fec97 74
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75In future, Perl-level operations will be expected to work with
76characters rather than bytes.
393fec97 77
376d9008 78However, as an interim compatibility measure, Perl aims to
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79provide a safe migration path from byte semantics to character
80semantics for programs. For operations where Perl can unambiguously
376d9008 81decide that the input data are characters, Perl switches to
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82character semantics. For operations where this determination cannot
83be made without additional information from the user, Perl decides in
376d9008 84favor of compatibility and chooses to use byte semantics.
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85
86This behavior preserves compatibility with earlier versions of Perl,
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87which allowed byte semantics in Perl operations only if
88none of the program's inputs were marked as being as source of Unicode
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89character data. Such data may come from filehandles, from calls to
90external programs, from information provided by the system (such as %ENV),
21bad921 91or from literals and constants in the source text.
8cbd9a7a 92
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93The C<bytes> pragma will always, regardless of platform, force byte
94semantics in a particular lexical scope. See L<bytes>.
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95
96The C<utf8> pragma is primarily a compatibility device that enables
75daf61c 97recognition of UTF-(8|EBCDIC) in literals encountered by the parser.
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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
fae2c0fb 106encoding layer is added to a filehandle or a literal Unicode
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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
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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>.
7dedd01f 118
feda178f 119Under character semantics, many operations that formerly operated on
376d9008 120bytes now operate on characters. A character in Perl is
feda178f 121logically just a number ranging from 0 to 2**31 or so. Larger
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122characters may encode into longer sequences of bytes internally, but
123this internal detail is mostly hidden for Perl code.
124See L<perluniintro> for more.
393fec97 125
376d9008 126=head2 Effects of Character Semantics
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127
128Character semantics have the following effects:
129
130=over 4
131
132=item *
133
376d9008 134Strings--including hash keys--and regular expression patterns may
574c8022 135contain characters that have an ordinal value larger than 255.
393fec97 136
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137If you use a Unicode editor to edit your program, Unicode characters
138may occur directly within the literal strings in one of the various
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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
feda178f 141appropriate L<encoding> is specified.
3e4dbfed 142
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143Unicode characters can also be added to a string by using the
144C<\x{...}> notation. The Unicode code for the desired character, in
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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.
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148
149Additionally, if you
574c8022 150
3e4dbfed 151 use charnames ':full';
574c8022 152
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153you can use the C<\N{...}> notation and put the official Unicode
154character name within the braces, such as C<\N{WHITE SMILING FACE}>.
376d9008 155
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156=item *
157
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158If an appropriate L<encoding> is specified, identifiers within the
159Perl script may contain Unicode alphanumeric characters, including
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160ideographs. Perl does not currently attempt to canonicalize variable
161names.
393fec97 162
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163=item *
164
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165Regular expressions match characters instead of bytes. "." matches
166a character instead of a byte. The C<\C> pattern is provided to force
167a match a single byte--a C<char> in C, hence C<\C>.
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(However, and as a limitation of the current implementation, using
177C<\w> or C<\W> I<inside> a C<[...]> character class will still match
178with byte semantics.)
179
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180=item *
181
eb0cc9e3 182Named Unicode properties, scripts, and block ranges may be used like
376d9008 183character classes via the C<\p{}> "matches property" construct and
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184the C<\P{}> negation, "doesn't match property".
185
186See L</"Unicode Character Properties"> for more details.
187
188You can define your own character properties and use them
189in the regular expression with the C<\p{}> or C<\P{}> construct.
190
191See L</"User-Defined Character Properties"> for more details.
192
193=item *
194
195The special pattern C<\X> matches any extended Unicode
196sequence--"a combining character sequence" in Standardese--where the
197first character is a base character and subsequent characters are mark
198characters that apply to the base character. C<\X> is equivalent to
199C<(?:\PM\pM*)>.
200
201=item *
202
203The C<tr///> operator translates characters instead of bytes. Note
204that the C<tr///CU> functionality has been removed. For similar
205functionality see pack('U0', ...) and pack('C0', ...).
206
207=item *
208
209Case translation operators use the Unicode case translation tables
210when character input is provided. Note that C<uc()>, or C<\U> in
211interpolated strings, translates to uppercase, while C<ucfirst>,
212or C<\u> in interpolated strings, translates to titlecase in languages
213that make the distinction.
214
215=item *
216
217Most operators that deal with positions or lengths in a string will
218automatically switch to using character positions, including
219C<chop()>, C<chomp()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>,
220C<sprintf()>, C<write()>, and C<length()>. An operator that
221specifically does not switch is C<vec()>. Operators that really don't
222care include operators that treat strings as a bucket of bits such as
223C<sort()>, and operators dealing with filenames.
224
225=item *
226
227The C<pack()>/C<unpack()> letter C<C> does I<not> change, since it is often
228used for byte-oriented formats. Again, think C<char> in the C language.
229
230There is a new C<U> specifier that converts between Unicode characters
231and code points. There is also a C<W> specifier that is the equivalent of
232C<chr>/C<ord> and properly handles character values even if they are above 255.
233
234=item *
235
236The C<chr()> and C<ord()> functions work on characters, similar to
237C<pack("W")> and C<unpack("W")>, I<not> C<pack("C")> and
238C<unpack("C")>. C<pack("C")> and C<unpack("C")> are methods for
239emulating byte-oriented C<chr()> and C<ord()> on Unicode strings.
240While these methods reveal the internal encoding of Unicode strings,
241that is not something one normally needs to care about at all.
242
243=item *
244
245The bit string operators, C<& | ^ ~>, can operate on character data.
246However, for backward compatibility, such as when using bit string
247operations when characters are all less than 256 in ordinal value, one
248should not use C<~> (the bit complement) with characters of both
249values less than 256 and values greater than 256. Most importantly,
250DeMorgan's laws (C<~($x|$y) eq ~$x&~$y> and C<~($x&$y) eq ~$x|~$y>)
251will not hold. The reason for this mathematical I<faux pas> is that
252the complement cannot return B<both> the 8-bit (byte-wide) bit
253complement B<and> the full character-wide bit complement.
254
255=item *
256
257lc(), uc(), lcfirst(), and ucfirst() work for the following cases:
258
259=over 8
260
261=item *
262
263the case mapping is from a single Unicode character to another
264single Unicode character, or
265
266=item *
267
268the case mapping is from a single Unicode character to more
269than one Unicode character.
270
271=back
272
273Things to do with locales (Lithuanian, Turkish, Azeri) do B<not> work
274since Perl does not understand the concept of Unicode locales.
275
276See the Unicode Technical Report #21, Case Mappings, for more details.
277
278But you can also define your own mappings to be used in the lc(),
279lcfirst(), uc(), and ucfirst() (or their string-inlined versions).
280
281See L</"User-Defined Case Mappings"> for more details.
282
283=back
284
285=over 4
286
287=item *
288
289And finally, C<scalar reverse()> reverses by character rather than by byte.
290
291=back
292
293=head2 Unicode Character Properties
294
295Named Unicode properties, scripts, and block ranges may be used like
296character classes via the C<\p{}> "matches property" construct and
297the C<\P{}> negation, "doesn't match property".
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298
299For instance, C<\p{Lu}> matches any character with the Unicode "Lu"
300(Letter, uppercase) property, while C<\p{M}> matches any character
301with an "M" (mark--accents and such) property. Brackets are not
302required for single letter properties, so C<\p{M}> is equivalent to
303C<\pM>. Many predefined properties are available, such as
304C<\p{Mirrored}> and C<\p{Tibetan}>.
4193bef7 305
cfc01aea 306The official Unicode script and block names have spaces and dashes as
376d9008 307separators, but for convenience you can use dashes, spaces, or
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308underbars, and case is unimportant. It is recommended, however, that
309for consistency you use the following naming: the official Unicode
310script, property, or block name (see below for the additional rules
311that apply to block names) with whitespace and dashes removed, and the
312words "uppercase-first-lowercase-rest". C<Latin-1 Supplement> thus
313becomes C<Latin1Supplement>.
4193bef7 314
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315You can also use negation in both C<\p{}> and C<\P{}> by introducing a caret
316(^) between the first brace and the property name: C<\p{^Tamil}> is
eb0cc9e3 317equal to C<\P{Tamil}>.
4193bef7 318
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319B<NOTE: the properties, scripts, and blocks listed here are as of
320Unicode 3.2.0, March 2002, or Perl 5.8.0, July 2002. Unicode 4.0.0
321came out in April 2003, and Perl 5.8.1 in September 2003.>
322
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323=over 4
324
325=item General Category
326
eb0cc9e3 327Here are the basic Unicode General Category properties, followed by their
68cd2d32 328long form. You can use either; C<\p{Lu}> and C<\p{UppercaseLetter}>,
376d9008 329for instance, are identical.
393fec97 330
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331 Short Long
332
333 L Letter
12ac2576 334 LC CasedLetter
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335 Lu UppercaseLetter
336 Ll LowercaseLetter
337 Lt TitlecaseLetter
338 Lm ModifierLetter
339 Lo OtherLetter
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340
341 M Mark
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342 Mn NonspacingMark
343 Mc SpacingMark
344 Me EnclosingMark
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345
346 N Number
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347 Nd DecimalNumber
348 Nl LetterNumber
349 No OtherNumber
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350
351 P Punctuation
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352 Pc ConnectorPunctuation
353 Pd DashPunctuation
354 Ps OpenPunctuation
355 Pe ClosePunctuation
356 Pi InitialPunctuation
d73e5302 357 (may behave like Ps or Pe depending on usage)
eb0cc9e3 358 Pf FinalPunctuation
d73e5302 359 (may behave like Ps or Pe depending on usage)
eb0cc9e3 360 Po OtherPunctuation
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361
362 S Symbol
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363 Sm MathSymbol
364 Sc CurrencySymbol
365 Sk ModifierSymbol
366 So OtherSymbol
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367
368 Z Separator
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369 Zs SpaceSeparator
370 Zl LineSeparator
371 Zp ParagraphSeparator
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372
373 C Other
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374 Cc Control
375 Cf Format
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376 Cs Surrogate (not usable)
377 Co PrivateUse
e150c829 378 Cn Unassigned
1ac13f9a 379
376d9008 380Single-letter properties match all characters in any of the
3e4dbfed 381two-letter sub-properties starting with the same letter.
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382C<LC> and C<L&> are special cases, which are aliases for the set of
383C<Ll>, C<Lu>, and C<Lt>.
32293815 384
eb0cc9e3 385Because Perl hides the need for the user to understand the internal
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386representation of Unicode characters, there is no need to implement
387the somewhat messy concept of surrogates. C<Cs> is therefore not
eb0cc9e3 388supported.
d73e5302 389
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390=item Bidirectional Character Types
391
376d9008 392Because scripts differ in their directionality--Hebrew is
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393written right to left, for example--Unicode supplies these properties in
394the BidiClass class:
32293815 395
eb0cc9e3 396 Property Meaning
92e830a9 397
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398 L Left-to-Right
399 LRE Left-to-Right Embedding
400 LRO Left-to-Right Override
401 R Right-to-Left
402 AL Right-to-Left Arabic
403 RLE Right-to-Left Embedding
404 RLO Right-to-Left Override
405 PDF Pop Directional Format
406 EN European Number
407 ES European Number Separator
408 ET European Number Terminator
409 AN Arabic Number
410 CS Common Number Separator
411 NSM Non-Spacing Mark
412 BN Boundary Neutral
413 B Paragraph Separator
414 S Segment Separator
415 WS Whitespace
416 ON Other Neutrals
417
418For example, C<\p{BidiClass:R}> matches characters that are normally
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419written right to left.
420
822502e5 421=item Scripts
2796c109 422
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423The script names which can be used by C<\p{...}> and C<\P{...}>,
424such as in C<\p{Latin}> or C<\p{Cyrillic}>, are as follows:
2796c109 425
1ac13f9a 426 Arabic
e9ad1727 427 Armenian
1ac13f9a 428 Bengali
e9ad1727 429 Bopomofo
1d81abf3 430 Buhid
eb0cc9e3 431 CanadianAboriginal
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432 Cherokee
433 Cyrillic
434 Deseret
435 Devanagari
436 Ethiopic
437 Georgian
438 Gothic
439 Greek
1ac13f9a 440 Gujarati
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441 Gurmukhi
442 Han
443 Hangul
1d81abf3 444 Hanunoo
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445 Hebrew
446 Hiragana
447 Inherited
1ac13f9a 448 Kannada
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449 Katakana
450 Khmer
1ac13f9a 451 Lao
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452 Latin
453 Malayalam
454 Mongolian
1ac13f9a 455 Myanmar
1ac13f9a 456 Ogham
eb0cc9e3 457 OldItalic
e9ad1727 458 Oriya
1ac13f9a 459 Runic
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460 Sinhala
461 Syriac
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462 Tagalog
463 Tagbanwa
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464 Tamil
465 Telugu
466 Thaana
467 Thai
468 Tibetan
1ac13f9a 469 Yi
1ac13f9a 470
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471=item Extended property classes
472
376d9008 473Extended property classes can supplement the basic
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474properties, defined by the F<PropList> Unicode database:
475
1d81abf3 476 ASCIIHexDigit
eb0cc9e3 477 BidiControl
1ac13f9a 478 Dash
1d81abf3 479 Deprecated
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480 Diacritic
481 Extender
1d81abf3 482 GraphemeLink
eb0cc9e3 483 HexDigit
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484 Hyphen
485 Ideographic
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486 IDSBinaryOperator
487 IDSTrinaryOperator
eb0cc9e3 488 JoinControl
1d81abf3 489 LogicalOrderException
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490 NoncharacterCodePoint
491 OtherAlphabetic
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492 OtherDefaultIgnorableCodePoint
493 OtherGraphemeExtend
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494 OtherLowercase
495 OtherMath
496 OtherUppercase
497 QuotationMark
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498 Radical
499 SoftDotted
500 TerminalPunctuation
501 UnifiedIdeograph
eb0cc9e3 502 WhiteSpace
1ac13f9a 503
376d9008 504and there are further derived properties:
1ac13f9a 505
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506 Alphabetic Lu + Ll + Lt + Lm + Lo + OtherAlphabetic
507 Lowercase Ll + OtherLowercase
508 Uppercase Lu + OtherUppercase
509 Math Sm + OtherMath
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510
511 ID_Start Lu + Ll + Lt + Lm + Lo + Nl
512 ID_Continue ID_Start + Mn + Mc + Nd + Pc
513
514 Any Any character
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515 Assigned Any non-Cn character (i.e. synonym for \P{Cn})
516 Unassigned Synonym for \p{Cn}
1ac13f9a 517 Common Any character (or unassigned code point)
e150c829 518 not explicitly assigned to a script
2796c109 519
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520=item Use of "Is" Prefix
521
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522For backward compatibility (with Perl 5.6), all properties mentioned
523so far may have C<Is> prepended to their name, so C<\P{IsLu}>, for
524example, is equal to C<\P{Lu}>.
eb0cc9e3 525
822502e5 526=item Blocks
2796c109 527
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528In addition to B<scripts>, Unicode also defines B<blocks> of
529characters. The difference between scripts and blocks is that the
530concept of scripts is closer to natural languages, while the concept
531of blocks is more of an artificial grouping based on groups of 256
376d9008 532Unicode characters. For example, the C<Latin> script contains letters
1bfb14c4 533from many blocks but does not contain all the characters from those
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534blocks. It does not, for example, contain digits, because digits are
535shared across many scripts. Digits and similar groups, like
536punctuation, are in a category called C<Common>.
2796c109 537
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538For more about scripts, see the UTR #24:
539
540 http://www.unicode.org/unicode/reports/tr24/
541
542For more about blocks, see:
543
544 http://www.unicode.org/Public/UNIDATA/Blocks.txt
2796c109 545
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546Block names are given with the C<In> prefix. For example, the
547Katakana block is referenced via C<\p{InKatakana}>. The C<In>
7eabb34d 548prefix may be omitted if there is no naming conflict with a script
eb0cc9e3 549or any other property, but it is recommended that C<In> always be used
1bfb14c4 550for block tests to avoid confusion.
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551
552These block names are supported:
553
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554 InAlphabeticPresentationForms
555 InArabic
556 InArabicPresentationFormsA
557 InArabicPresentationFormsB
558 InArmenian
559 InArrows
560 InBasicLatin
561 InBengali
562 InBlockElements
563 InBopomofo
564 InBopomofoExtended
565 InBoxDrawing
566 InBraillePatterns
567 InBuhid
568 InByzantineMusicalSymbols
569 InCJKCompatibility
570 InCJKCompatibilityForms
571 InCJKCompatibilityIdeographs
572 InCJKCompatibilityIdeographsSupplement
573 InCJKRadicalsSupplement
574 InCJKSymbolsAndPunctuation
575 InCJKUnifiedIdeographs
576 InCJKUnifiedIdeographsExtensionA
577 InCJKUnifiedIdeographsExtensionB
578 InCherokee
579 InCombiningDiacriticalMarks
580 InCombiningDiacriticalMarksforSymbols
581 InCombiningHalfMarks
582 InControlPictures
583 InCurrencySymbols
584 InCyrillic
585 InCyrillicSupplementary
586 InDeseret
587 InDevanagari
588 InDingbats
589 InEnclosedAlphanumerics
590 InEnclosedCJKLettersAndMonths
591 InEthiopic
592 InGeneralPunctuation
593 InGeometricShapes
594 InGeorgian
595 InGothic
596 InGreekExtended
597 InGreekAndCoptic
598 InGujarati
599 InGurmukhi
600 InHalfwidthAndFullwidthForms
601 InHangulCompatibilityJamo
602 InHangulJamo
603 InHangulSyllables
604 InHanunoo
605 InHebrew
606 InHighPrivateUseSurrogates
607 InHighSurrogates
608 InHiragana
609 InIPAExtensions
610 InIdeographicDescriptionCharacters
611 InKanbun
612 InKangxiRadicals
613 InKannada
614 InKatakana
615 InKatakanaPhoneticExtensions
616 InKhmer
617 InLao
618 InLatin1Supplement
619 InLatinExtendedA
620 InLatinExtendedAdditional
621 InLatinExtendedB
622 InLetterlikeSymbols
623 InLowSurrogates
624 InMalayalam
625 InMathematicalAlphanumericSymbols
626 InMathematicalOperators
627 InMiscellaneousMathematicalSymbolsA
628 InMiscellaneousMathematicalSymbolsB
629 InMiscellaneousSymbols
630 InMiscellaneousTechnical
631 InMongolian
632 InMusicalSymbols
633 InMyanmar
634 InNumberForms
635 InOgham
636 InOldItalic
637 InOpticalCharacterRecognition
638 InOriya
639 InPrivateUseArea
640 InRunic
641 InSinhala
642 InSmallFormVariants
643 InSpacingModifierLetters
644 InSpecials
645 InSuperscriptsAndSubscripts
646 InSupplementalArrowsA
647 InSupplementalArrowsB
648 InSupplementalMathematicalOperators
649 InSupplementaryPrivateUseAreaA
650 InSupplementaryPrivateUseAreaB
651 InSyriac
652 InTagalog
653 InTagbanwa
654 InTags
655 InTamil
656 InTelugu
657 InThaana
658 InThai
659 InTibetan
660 InUnifiedCanadianAboriginalSyllabics
661 InVariationSelectors
662 InYiRadicals
663 InYiSyllables
32293815 664
393fec97
GS
665=back
666
376d9008 667=head2 User-Defined Character Properties
491fd90a
JH
668
669You can define your own character properties by defining subroutines
bac0b425
JP
670whose names begin with "In" or "Is". The subroutines can be defined in
671any package. The user-defined properties can be used in the regular
672expression C<\p> and C<\P> constructs; if you are using a user-defined
673property from a package other than the one you are in, you must specify
674its package in the C<\p> or C<\P> construct.
675
676 # assuming property IsForeign defined in Lang::
677 package main; # property package name required
678 if ($txt =~ /\p{Lang::IsForeign}+/) { ... }
679
680 package Lang; # property package name not required
681 if ($txt =~ /\p{IsForeign}+/) { ... }
682
683
684Note that the effect is compile-time and immutable once defined.
491fd90a 685
376d9008
JB
686The subroutines must return a specially-formatted string, with one
687or more newline-separated lines. Each line must be one of the following:
491fd90a
JH
688
689=over 4
690
691=item *
692
99a6b1f0 693Two hexadecimal numbers separated by horizontal whitespace (space or
376d9008 694tabular characters) denoting a range of Unicode code points to include.
491fd90a
JH
695
696=item *
697
376d9008 698Something to include, prefixed by "+": a built-in character
bac0b425
JP
699property (prefixed by "utf8::") or a user-defined character property,
700to represent all the characters in that property; two hexadecimal code
701points for a range; or a single hexadecimal code point.
491fd90a
JH
702
703=item *
704
376d9008 705Something to exclude, prefixed by "-": an existing character
bac0b425
JP
706property (prefixed by "utf8::") or a user-defined character property,
707to represent all the characters in that property; two hexadecimal code
708points for a range; or a single hexadecimal code point.
491fd90a
JH
709
710=item *
711
376d9008 712Something to negate, prefixed "!": an existing character
bac0b425
JP
713property (prefixed by "utf8::") or a user-defined character property,
714to represent all the characters in that property; two hexadecimal code
715points for a range; or a single hexadecimal code point.
716
717=item *
718
719Something to intersect with, prefixed by "&": an existing character
720property (prefixed by "utf8::") or a user-defined character property,
721for all the characters except the characters in the property; two
722hexadecimal code points for a range; or a single hexadecimal code point.
491fd90a
JH
723
724=back
725
726For example, to define a property that covers both the Japanese
727syllabaries (hiragana and katakana), you can define
728
729 sub InKana {
d5822f25
A
730 return <<END;
731 3040\t309F
732 30A0\t30FF
491fd90a
JH
733 END
734 }
735
d5822f25
A
736Imagine that the here-doc end marker is at the beginning of the line.
737Now you can use C<\p{InKana}> and C<\P{InKana}>.
491fd90a
JH
738
739You could also have used the existing block property names:
740
741 sub InKana {
742 return <<'END';
743 +utf8::InHiragana
744 +utf8::InKatakana
745 END
746 }
747
748Suppose you wanted to match only the allocated characters,
d5822f25 749not the raw block ranges: in other words, you want to remove
491fd90a
JH
750the non-characters:
751
752 sub InKana {
753 return <<'END';
754 +utf8::InHiragana
755 +utf8::InKatakana
756 -utf8::IsCn
757 END
758 }
759
760The negation is useful for defining (surprise!) negated classes.
761
762 sub InNotKana {
763 return <<'END';
764 !utf8::InHiragana
765 -utf8::InKatakana
766 +utf8::IsCn
767 END
768 }
769
bac0b425
JP
770Intersection is useful for getting the common characters matched by
771two (or more) classes.
772
773 sub InFooAndBar {
774 return <<'END';
775 +main::Foo
776 &main::Bar
777 END
778 }
779
780It's important to remember not to use "&" for the first set -- that
781would be intersecting with nothing (resulting in an empty set).
782
822502e5
ST
783A final note on the user-defined property tests: they will be used
784only if the scalar has been marked as having Unicode characters.
785Old byte-style strings will not be affected.
786
787=head2 User-Defined Case Mappings
788
3a2263fe
RGS
789You can also define your own mappings to be used in the lc(),
790lcfirst(), uc(), and ucfirst() (or their string-inlined versions).
822502e5
ST
791The principle is similar to that of user-defined character
792properties: to define subroutines in the C<main> package
3a2263fe
RGS
793with names like C<ToLower> (for lc() and lcfirst()), C<ToTitle> (for
794the first character in ucfirst()), and C<ToUpper> (for uc(), and the
795rest of the characters in ucfirst()).
796
797The string returned by the subroutines needs now to be three
798hexadecimal numbers separated by tabulators: start of the source
799range, end of the source range, and start of the destination range.
800For example:
801
802 sub ToUpper {
803 return <<END;
804 0061\t0063\t0041
805 END
806 }
807
808defines an uc() mapping that causes only the characters "a", "b", and
809"c" to be mapped to "A", "B", "C", all other characters will remain
810unchanged.
811
812If there is no source range to speak of, that is, the mapping is from
813a single character to another single character, leave the end of the
814source range empty, but the two tabulator characters are still needed.
815For example:
816
817 sub ToLower {
818 return <<END;
819 0041\t\t0061
820 END
821 }
822
823defines a lc() mapping that causes only "A" to be mapped to "a", all
824other characters will remain unchanged.
825
826(For serious hackers only) If you want to introspect the default
827mappings, you can find the data in the directory
828C<$Config{privlib}>/F<unicore/To/>. The mapping data is returned as
829the here-document, and the C<utf8::ToSpecFoo> are special exception
830mappings derived from <$Config{privlib}>/F<unicore/SpecialCasing.txt>.
831The C<Digit> and C<Fold> mappings that one can see in the directory
832are not directly user-accessible, one can use either the
833C<Unicode::UCD> module, or just match case-insensitively (that's when
834the C<Fold> mapping is used).
835
822502e5
ST
836A final note on the user-defined case mappings: they will be used
837only if the scalar has been marked as having Unicode characters.
838Old byte-style strings will not be affected.
3a2263fe 839
376d9008 840=head2 Character Encodings for Input and Output
8cbd9a7a 841
7221edc9 842See L<Encode>.
8cbd9a7a 843
c29a771d 844=head2 Unicode Regular Expression Support Level
776f8809 845
376d9008
JB
846The following list of Unicode support for regular expressions describes
847all the features currently supported. The references to "Level N"
848and the section numbers refer to the Unicode Technical Report 18,
965cd703
JH
849"Unicode Regular Expression Guidelines", version 6 (Unicode 3.2.0,
850Perl 5.8.0).
776f8809
JH
851
852=over 4
853
854=item *
855
856Level 1 - Basic Unicode Support
857
858 2.1 Hex Notation - done [1]
3bfdc84c 859 Named Notation - done [2]
776f8809
JH
860 2.2 Categories - done [3][4]
861 2.3 Subtraction - MISSING [5][6]
862 2.4 Simple Word Boundaries - done [7]
78d3e1bf 863 2.5 Simple Loose Matches - done [8]
776f8809
JH
864 2.6 End of Line - MISSING [9][10]
865
866 [ 1] \x{...}
867 [ 2] \N{...}
eb0cc9e3 868 [ 3] . \p{...} \P{...}
12ac2576
JP
869 [ 4] support for scripts (see UTR#24 Script Names), blocks,
870 binary properties, enumerated non-binary properties, and
871 numeric properties (as listed in UTR#18 Other Properties)
776f8809 872 [ 5] have negation
237bad5b
JH
873 [ 6] can use regular expression look-ahead [a]
874 or user-defined character properties [b] to emulate subtraction
776f8809 875 [ 7] include Letters in word characters
376d9008 876 [ 8] note that Perl does Full case-folding in matching, not Simple:
835863de 877 for example U+1F88 is equivalent with U+1F00 U+03B9,
e0f9d4a8 878 not with 1F80. This difference matters for certain Greek
376d9008
JB
879 capital letters with certain modifiers: the Full case-folding
880 decomposes the letter, while the Simple case-folding would map
e0f9d4a8 881 it to a single character.
5ca1ac52 882 [ 9] see UTR #13 Unicode Newline Guidelines
835863de 883 [10] should do ^ and $ also on \x{85}, \x{2028} and \x{2029}
ec83e909 884 (should also affect <>, $., and script line numbers)
3bfdc84c 885 (the \x{85}, \x{2028} and \x{2029} do match \s)
7207e29d 886
237bad5b 887[a] You can mimic class subtraction using lookahead.
5ca1ac52 888For example, what UTR #18 might write as
29bdacb8 889
dbe420b4
JH
890 [{Greek}-[{UNASSIGNED}]]
891
892in Perl can be written as:
893
1d81abf3
JH
894 (?!\p{Unassigned})\p{InGreekAndCoptic}
895 (?=\p{Assigned})\p{InGreekAndCoptic}
dbe420b4
JH
896
897But in this particular example, you probably really want
898
1bfb14c4 899 \p{GreekAndCoptic}
dbe420b4
JH
900
901which will match assigned characters known to be part of the Greek script.
29bdacb8 902
5ca1ac52
JH
903Also see the Unicode::Regex::Set module, it does implement the full
904UTR #18 grouping, intersection, union, and removal (subtraction) syntax.
905
818c4caa 906[b] See L</"User-Defined Character Properties">.
237bad5b 907
776f8809
JH
908=item *
909
910Level 2 - Extended Unicode Support
911
63de3cb2
JH
912 3.1 Surrogates - MISSING [11]
913 3.2 Canonical Equivalents - MISSING [12][13]
914 3.3 Locale-Independent Graphemes - MISSING [14]
915 3.4 Locale-Independent Words - MISSING [15]
916 3.5 Locale-Independent Loose Matches - MISSING [16]
917
918 [11] Surrogates are solely a UTF-16 concept and Perl's internal
919 representation is UTF-8. The Encode module does UTF-16, though.
920 [12] see UTR#15 Unicode Normalization
921 [13] have Unicode::Normalize but not integrated to regexes
922 [14] have \X but at this level . should equal that
923 [15] need three classes, not just \w and \W
924 [16] see UTR#21 Case Mappings
776f8809
JH
925
926=item *
927
928Level 3 - Locale-Sensitive Support
929
930 4.1 Locale-Dependent Categories - MISSING
931 4.2 Locale-Dependent Graphemes - MISSING [16][17]
932 4.3 Locale-Dependent Words - MISSING
933 4.4 Locale-Dependent Loose Matches - MISSING
934 4.5 Locale-Dependent Ranges - MISSING
935
936 [16] see UTR#10 Unicode Collation Algorithms
937 [17] have Unicode::Collate but not integrated to regexes
938
939=back
940
c349b1b9
JH
941=head2 Unicode Encodings
942
376d9008
JB
943Unicode characters are assigned to I<code points>, which are abstract
944numbers. To use these numbers, various encodings are needed.
c349b1b9
JH
945
946=over 4
947
c29a771d 948=item *
5cb3728c
RB
949
950UTF-8
c349b1b9 951
3e4dbfed 952UTF-8 is a variable-length (1 to 6 bytes, current character allocations
376d9008
JB
953require 4 bytes), byte-order independent encoding. For ASCII (and we
954really do mean 7-bit ASCII, not another 8-bit encoding), UTF-8 is
955transparent.
c349b1b9 956
8c007b5a 957The following table is from Unicode 3.2.
05632f9a
JH
958
959 Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
960
8c007b5a
JH
961 U+0000..U+007F 00..7F
962 U+0080..U+07FF C2..DF 80..BF
ec90690f
ST
963 U+0800..U+0FFF E0 A0..BF 80..BF
964 U+1000..U+CFFF E1..EC 80..BF 80..BF
965 U+D000..U+D7FF ED 80..9F 80..BF
8c007b5a 966 U+D800..U+DFFF ******* ill-formed *******
ec90690f 967 U+E000..U+FFFF EE..EF 80..BF 80..BF
05632f9a
JH
968 U+10000..U+3FFFF F0 90..BF 80..BF 80..BF
969 U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF
970 U+100000..U+10FFFF F4 80..8F 80..BF 80..BF
971
376d9008
JB
972Note the C<A0..BF> in C<U+0800..U+0FFF>, the C<80..9F> in
973C<U+D000...U+D7FF>, the C<90..B>F in C<U+10000..U+3FFFF>, and the
974C<80...8F> in C<U+100000..U+10FFFF>. The "gaps" are caused by legal
975UTF-8 avoiding non-shortest encodings: it is technically possible to
976UTF-8-encode a single code point in different ways, but that is
977explicitly forbidden, and the shortest possible encoding should always
978be used. So that's what Perl does.
37361303 979
376d9008 980Another way to look at it is via bits:
05632f9a
JH
981
982 Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
983
984 0aaaaaaa 0aaaaaaa
985 00000bbbbbaaaaaa 110bbbbb 10aaaaaa
986 ccccbbbbbbaaaaaa 1110cccc 10bbbbbb 10aaaaaa
987 00000dddccccccbbbbbbaaaaaa 11110ddd 10cccccc 10bbbbbb 10aaaaaa
988
989As you can see, the continuation bytes all begin with C<10>, and the
8c007b5a 990leading bits of the start byte tell how many bytes the are in the
05632f9a
JH
991encoded character.
992
c29a771d 993=item *
5cb3728c
RB
994
995UTF-EBCDIC
dbe420b4 996
376d9008 997Like UTF-8 but EBCDIC-safe, in the way that UTF-8 is ASCII-safe.
dbe420b4 998
c29a771d 999=item *
5cb3728c 1000
1e54db1a 1001UTF-16, UTF-16BE, UTF-16LE, Surrogates, and BOMs (Byte Order Marks)
c349b1b9 1002
1bfb14c4
JH
1003The followings items are mostly for reference and general Unicode
1004knowledge, Perl doesn't use these constructs internally.
dbe420b4 1005
c349b1b9 1006UTF-16 is a 2 or 4 byte encoding. The Unicode code points
1bfb14c4
JH
1007C<U+0000..U+FFFF> are stored in a single 16-bit unit, and the code
1008points C<U+10000..U+10FFFF> in two 16-bit units. The latter case is
c349b1b9
JH
1009using I<surrogates>, the first 16-bit unit being the I<high
1010surrogate>, and the second being the I<low surrogate>.
1011
376d9008 1012Surrogates are code points set aside to encode the C<U+10000..U+10FFFF>
c349b1b9 1013range of Unicode code points in pairs of 16-bit units. The I<high
376d9008
JB
1014surrogates> are the range C<U+D800..U+DBFF>, and the I<low surrogates>
1015are the range C<U+DC00..U+DFFF>. The surrogate encoding is
c349b1b9
JH
1016
1017 $hi = ($uni - 0x10000) / 0x400 + 0xD800;
1018 $lo = ($uni - 0x10000) % 0x400 + 0xDC00;
1019
1020and the decoding is
1021
1a3fa709 1022 $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00);
c349b1b9 1023
feda178f 1024If you try to generate surrogates (for example by using chr()), you
376d9008
JB
1025will get a warning if warnings are turned on, because those code
1026points are not valid for a Unicode character.
9466bab6 1027
376d9008 1028Because of the 16-bitness, UTF-16 is byte-order dependent. UTF-16
c349b1b9 1029itself can be used for in-memory computations, but if storage or
376d9008
JB
1030transfer is required either UTF-16BE (big-endian) or UTF-16LE
1031(little-endian) encodings must be chosen.
c349b1b9
JH
1032
1033This introduces another problem: what if you just know that your data
376d9008
JB
1034is UTF-16, but you don't know which endianness? Byte Order Marks, or
1035BOMs, are a solution to this. A special character has been reserved
86bbd6d1 1036in Unicode to function as a byte order marker: the character with the
376d9008 1037code point C<U+FEFF> is the BOM.
042da322 1038
c349b1b9 1039The trick is that if you read a BOM, you will know the byte order,
376d9008
JB
1040since if it was written on a big-endian platform, you will read the
1041bytes C<0xFE 0xFF>, but if it was written on a little-endian platform,
1042you will read the bytes C<0xFF 0xFE>. (And if the originating platform
1043was writing in UTF-8, you will read the bytes C<0xEF 0xBB 0xBF>.)
042da322 1044
86bbd6d1 1045The way this trick works is that the character with the code point
376d9008
JB
1046C<U+FFFE> is guaranteed not to be a valid Unicode character, so the
1047sequence of bytes C<0xFF 0xFE> is unambiguously "BOM, represented in
1bfb14c4 1048little-endian format" and cannot be C<U+FFFE>, represented in big-endian
042da322 1049format".
c349b1b9 1050
c29a771d 1051=item *
5cb3728c 1052
1e54db1a 1053UTF-32, UTF-32BE, UTF-32LE
c349b1b9
JH
1054
1055The UTF-32 family is pretty much like the UTF-16 family, expect that
042da322 1056the units are 32-bit, and therefore the surrogate scheme is not
376d9008
JB
1057needed. The BOM signatures will be C<0x00 0x00 0xFE 0xFF> for BE and
1058C<0xFF 0xFE 0x00 0x00> for LE.
c349b1b9 1059
c29a771d 1060=item *
5cb3728c
RB
1061
1062UCS-2, UCS-4
c349b1b9 1063
86bbd6d1 1064Encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit
376d9008 1065encoding. Unlike UTF-16, UCS-2 is not extensible beyond C<U+FFFF>,
339cfa0e
JH
1066because it does not use surrogates. UCS-4 is a 32-bit encoding,
1067functionally identical to UTF-32.
c349b1b9 1068
c29a771d 1069=item *
5cb3728c
RB
1070
1071UTF-7
c349b1b9 1072
376d9008
JB
1073A seven-bit safe (non-eight-bit) encoding, which is useful if the
1074transport or storage is not eight-bit safe. Defined by RFC 2152.
c349b1b9 1075
95a1a48b
JH
1076=back
1077
0d7c09bb
JH
1078=head2 Security Implications of Unicode
1079
1080=over 4
1081
1082=item *
1083
1084Malformed UTF-8
bf0fa0b2
JH
1085
1086Unfortunately, the specification of UTF-8 leaves some room for
1087interpretation of how many bytes of encoded output one should generate
376d9008
JB
1088from one input Unicode character. Strictly speaking, the shortest
1089possible sequence of UTF-8 bytes should be generated,
1090because otherwise there is potential for an input buffer overflow at
feda178f 1091the receiving end of a UTF-8 connection. Perl always generates the
376d9008
JB
1092shortest length UTF-8, and with warnings on Perl will warn about
1093non-shortest length UTF-8 along with other malformations, such as the
1094surrogates, which are not real Unicode code points.
bf0fa0b2 1095
0d7c09bb
JH
1096=item *
1097
1098Regular expressions behave slightly differently between byte data and
376d9008
JB
1099character (Unicode) data. For example, the "word character" character
1100class C<\w> will work differently depending on if data is eight-bit bytes
1101or Unicode.
0d7c09bb 1102
376d9008
JB
1103In the first case, the set of C<\w> characters is either small--the
1104default set of alphabetic characters, digits, and the "_"--or, if you
0d7c09bb
JH
1105are using a locale (see L<perllocale>), the C<\w> might contain a few
1106more letters according to your language and country.
1107
376d9008 1108In the second case, the C<\w> set of characters is much, much larger.
1bfb14c4
JH
1109Most importantly, even in the set of the first 256 characters, it will
1110probably match different characters: unlike most locales, which are
1111specific to a language and country pair, Unicode classifies all the
1112characters that are letters I<somewhere> as C<\w>. For example, your
1113locale might not think that LATIN SMALL LETTER ETH is a letter (unless
1114you happen to speak Icelandic), but Unicode does.
0d7c09bb 1115
376d9008 1116As discussed elsewhere, Perl has one foot (two hooves?) planted in
1bfb14c4
JH
1117each of two worlds: the old world of bytes and the new world of
1118characters, upgrading from bytes to characters when necessary.
376d9008
JB
1119If your legacy code does not explicitly use Unicode, no automatic
1120switch-over to characters should happen. Characters shouldn't get
1bfb14c4
JH
1121downgraded to bytes, either. It is possible to accidentally mix bytes
1122and characters, however (see L<perluniintro>), in which case C<\w> in
1123regular expressions might start behaving differently. Review your
1124code. Use warnings and the C<strict> pragma.
0d7c09bb
JH
1125
1126=back
1127
c349b1b9
JH
1128=head2 Unicode in Perl on EBCDIC
1129
376d9008
JB
1130The way Unicode is handled on EBCDIC platforms is still
1131experimental. On such platforms, references to UTF-8 encoding in this
1132document and elsewhere should be read as meaning the UTF-EBCDIC
1133specified in Unicode Technical Report 16, unless ASCII vs. EBCDIC issues
c349b1b9 1134are specifically discussed. There is no C<utfebcdic> pragma or
376d9008 1135":utfebcdic" layer; rather, "utf8" and ":utf8" are reused to mean
86bbd6d1
PN
1136the platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic>
1137for more discussion of the issues.
c349b1b9 1138
b310b053
JH
1139=head2 Locales
1140
4616122b 1141Usually locale settings and Unicode do not affect each other, but
b310b053
JH
1142there are a couple of exceptions:
1143
1144=over 4
1145
1146=item *
1147
8aa8f774
JH
1148You can enable automatic UTF-8-ification of your standard file
1149handles, default C<open()> layer, and C<@ARGV> by using either
1150the C<-C> command line switch or the C<PERL_UNICODE> environment
1151variable, see L<perlrun> for the documentation of the C<-C> switch.
b310b053
JH
1152
1153=item *
1154
376d9008
JB
1155Perl tries really hard to work both with Unicode and the old
1156byte-oriented world. Most often this is nice, but sometimes Perl's
1157straddling of the proverbial fence causes problems.
b310b053
JH
1158
1159=back
1160
1aad1664
JH
1161=head2 When Unicode Does Not Happen
1162
1163While Perl does have extensive ways to input and output in Unicode,
1164and few other 'entry points' like the @ARGV which can be interpreted
1165as Unicode (UTF-8), there still are many places where Unicode (in some
1166encoding or another) could be given as arguments or received as
1167results, or both, but it is not.
1168
6cd4dd6c
JH
1169The following are such interfaces. For all of these interfaces Perl
1170currently (as of 5.8.3) simply assumes byte strings both as arguments
1171and results, or UTF-8 strings if the C<encoding> pragma has been used.
1aad1664
JH
1172
1173One reason why Perl does not attempt to resolve the role of Unicode in
1174this cases is that the answers are highly dependent on the operating
1175system and the file system(s). For example, whether filenames can be
1176in Unicode, and in exactly what kind of encoding, is not exactly a
1177portable concept. Similarly for the qx and system: how well will the
1178'command line interface' (and which of them?) handle Unicode?
1179
1180=over 4
1181
557a2462
RB
1182=item *
1183
254c2b64 1184chdir, chmod, chown, chroot, exec, link, lstat, mkdir,
1e8e8236 1185rename, rmdir, stat, symlink, truncate, unlink, utime, -X
557a2462
RB
1186
1187=item *
1188
1189%ENV
1190
1191=item *
1192
1193glob (aka the <*>)
1194
1195=item *
1aad1664 1196
557a2462 1197open, opendir, sysopen
1aad1664 1198
557a2462 1199=item *
1aad1664 1200
557a2462 1201qx (aka the backtick operator), system
1aad1664 1202
557a2462 1203=item *
1aad1664 1204
557a2462 1205readdir, readlink
1aad1664
JH
1206
1207=back
1208
1209=head2 Forcing Unicode in Perl (Or Unforcing Unicode in Perl)
1210
1211Sometimes (see L</"When Unicode Does Not Happen">) there are
1212situations where you simply need to force Perl to believe that a byte
1213string is UTF-8, or vice versa. The low-level calls
1214utf8::upgrade($bytestring) and utf8::downgrade($utf8string) are
1215the answers.
1216
1217Do not use them without careful thought, though: Perl may easily get
1218very confused, angry, or even crash, if you suddenly change the 'nature'
1219of scalar like that. Especially careful you have to be if you use the
1220utf8::upgrade(): any random byte string is not valid UTF-8.
1221
95a1a48b
JH
1222=head2 Using Unicode in XS
1223
3a2263fe
RGS
1224If you want to handle Perl Unicode in XS extensions, you may find the
1225following C APIs useful. See also L<perlguts/"Unicode Support"> for an
1226explanation about Unicode at the XS level, and L<perlapi> for the API
1227details.
95a1a48b
JH
1228
1229=over 4
1230
1231=item *
1232
1bfb14c4
JH
1233C<DO_UTF8(sv)> returns true if the C<UTF8> flag is on and the bytes
1234pragma is not in effect. C<SvUTF8(sv)> returns true is the C<UTF8>
1235flag is on; the bytes pragma is ignored. The C<UTF8> flag being on
1236does B<not> mean that there are any characters of code points greater
1237than 255 (or 127) in the scalar or that there are even any characters
1238in the scalar. What the C<UTF8> flag means is that the sequence of
1239octets in the representation of the scalar is the sequence of UTF-8
1240encoded code points of the characters of a string. The C<UTF8> flag
1241being off means that each octet in this representation encodes a
1242single character with code point 0..255 within the string. Perl's
1243Unicode model is not to use UTF-8 until it is absolutely necessary.
95a1a48b
JH
1244
1245=item *
1246
fb9cc174 1247C<uvuni_to_utf8(buf, chr)> writes a Unicode character code point into
1bfb14c4 1248a buffer encoding the code point as UTF-8, and returns a pointer
95a1a48b
JH
1249pointing after the UTF-8 bytes.
1250
1251=item *
1252
376d9008
JB
1253C<utf8_to_uvuni(buf, lenp)> reads UTF-8 encoded bytes from a buffer and
1254returns the Unicode character code point and, optionally, the length of
1255the UTF-8 byte sequence.
95a1a48b
JH
1256
1257=item *
1258
376d9008
JB
1259C<utf8_length(start, end)> returns the length of the UTF-8 encoded buffer
1260in characters. C<sv_len_utf8(sv)> returns the length of the UTF-8 encoded
95a1a48b
JH
1261scalar.
1262
1263=item *
1264
376d9008
JB
1265C<sv_utf8_upgrade(sv)> converts the string of the scalar to its UTF-8
1266encoded form. C<sv_utf8_downgrade(sv)> does the opposite, if
1267possible. C<sv_utf8_encode(sv)> is like sv_utf8_upgrade except that
1268it does not set the C<UTF8> flag. C<sv_utf8_decode()> does the
1269opposite of C<sv_utf8_encode()>. Note that none of these are to be
1270used as general-purpose encoding or decoding interfaces: C<use Encode>
1271for that. C<sv_utf8_upgrade()> is affected by the encoding pragma
1272but C<sv_utf8_downgrade()> is not (since the encoding pragma is
1273designed to be a one-way street).
95a1a48b
JH
1274
1275=item *
1276
376d9008 1277C<is_utf8_char(s)> returns true if the pointer points to a valid UTF-8
90f968e0 1278character.
95a1a48b
JH
1279
1280=item *
1281
376d9008 1282C<is_utf8_string(buf, len)> returns true if C<len> bytes of the buffer
95a1a48b
JH
1283are valid UTF-8.
1284
1285=item *
1286
376d9008
JB
1287C<UTF8SKIP(buf)> will return the number of bytes in the UTF-8 encoded
1288character in the buffer. C<UNISKIP(chr)> will return the number of bytes
1289required to UTF-8-encode the Unicode character code point. C<UTF8SKIP()>
90f968e0 1290is useful for example for iterating over the characters of a UTF-8
376d9008 1291encoded buffer; C<UNISKIP()> is useful, for example, in computing
90f968e0 1292the size required for a UTF-8 encoded buffer.
95a1a48b
JH
1293
1294=item *
1295
376d9008 1296C<utf8_distance(a, b)> will tell the distance in characters between the
95a1a48b
JH
1297two pointers pointing to the same UTF-8 encoded buffer.
1298
1299=item *
1300
376d9008
JB
1301C<utf8_hop(s, off)> will return a pointer to an UTF-8 encoded buffer
1302that is C<off> (positive or negative) Unicode characters displaced
1303from the UTF-8 buffer C<s>. Be careful not to overstep the buffer:
1304C<utf8_hop()> will merrily run off the end or the beginning of the
1305buffer if told to do so.
95a1a48b 1306
d2cc3551
JH
1307=item *
1308
376d9008
JB
1309C<pv_uni_display(dsv, spv, len, pvlim, flags)> and
1310C<sv_uni_display(dsv, ssv, pvlim, flags)> are useful for debugging the
1311output of Unicode strings and scalars. By default they are useful
1312only for debugging--they display B<all> characters as hexadecimal code
1bfb14c4
JH
1313points--but with the flags C<UNI_DISPLAY_ISPRINT>,
1314C<UNI_DISPLAY_BACKSLASH>, and C<UNI_DISPLAY_QQ> you can make the
1315output more readable.
d2cc3551
JH
1316
1317=item *
1318
376d9008
JB
1319C<ibcmp_utf8(s1, pe1, u1, l1, u1, s2, pe2, l2, u2)> can be used to
1320compare two strings case-insensitively in Unicode. For case-sensitive
1321comparisons you can just use C<memEQ()> and C<memNE()> as usual.
d2cc3551 1322
c349b1b9
JH
1323=back
1324
95a1a48b
JH
1325For more information, see L<perlapi>, and F<utf8.c> and F<utf8.h>
1326in the Perl source code distribution.
1327
c29a771d
JH
1328=head1 BUGS
1329
376d9008 1330=head2 Interaction with Locales
7eabb34d 1331
376d9008
JB
1332Use of locales with Unicode data may lead to odd results. Currently,
1333Perl attempts to attach 8-bit locale info to characters in the range
13340..255, but this technique is demonstrably incorrect for locales that
1335use characters above that range when mapped into Unicode. Perl's
1336Unicode support will also tend to run slower. Use of locales with
1337Unicode is discouraged.
c29a771d 1338
376d9008 1339=head2 Interaction with Extensions
7eabb34d 1340
376d9008 1341When Perl exchanges data with an extension, the extension should be
7eabb34d 1342able to understand the UTF-8 flag and act accordingly. If the
376d9008
JB
1343extension doesn't know about the flag, it's likely that the extension
1344will return incorrectly-flagged data.
7eabb34d
A
1345
1346So if you're working with Unicode data, consult the documentation of
1347every module you're using if there are any issues with Unicode data
1348exchange. If the documentation does not talk about Unicode at all,
a73d23f6 1349suspect the worst and probably look at the source to learn how the
376d9008 1350module is implemented. Modules written completely in Perl shouldn't
a73d23f6
RGS
1351cause problems. Modules that directly or indirectly access code written
1352in other programming languages are at risk.
7eabb34d 1353
376d9008 1354For affected functions, the simple strategy to avoid data corruption is
7eabb34d 1355to always make the encoding of the exchanged data explicit. Choose an
376d9008 1356encoding that you know the extension can handle. Convert arguments passed
7eabb34d
A
1357to the extensions to that encoding and convert results back from that
1358encoding. Write wrapper functions that do the conversions for you, so
1359you can later change the functions when the extension catches up.
1360
376d9008 1361To provide an example, let's say the popular Foo::Bar::escape_html
7eabb34d
A
1362function doesn't deal with Unicode data yet. The wrapper function
1363would convert the argument to raw UTF-8 and convert the result back to
376d9008 1364Perl's internal representation like so:
7eabb34d
A
1365
1366 sub my_escape_html ($) {
1367 my($what) = shift;
1368 return unless defined $what;
1369 Encode::decode_utf8(Foo::Bar::escape_html(Encode::encode_utf8($what)));
1370 }
1371
1372Sometimes, when the extension does not convert data but just stores
1373and retrieves them, you will be in a position to use the otherwise
1374dangerous Encode::_utf8_on() function. Let's say the popular
66b79f27 1375C<Foo::Bar> extension, written in C, provides a C<param> method that
7eabb34d
A
1376lets you store and retrieve data according to these prototypes:
1377
1378 $self->param($name, $value); # set a scalar
1379 $value = $self->param($name); # retrieve a scalar
1380
1381If it does not yet provide support for any encoding, one could write a
1382derived class with such a C<param> method:
1383
1384 sub param {
1385 my($self,$name,$value) = @_;
1386 utf8::upgrade($name); # make sure it is UTF-8 encoded
1387 if (defined $value)
1388 utf8::upgrade($value); # make sure it is UTF-8 encoded
1389 return $self->SUPER::param($name,$value);
1390 } else {
1391 my $ret = $self->SUPER::param($name);
1392 Encode::_utf8_on($ret); # we know, it is UTF-8 encoded
1393 return $ret;
1394 }
1395 }
1396
a73d23f6
RGS
1397Some extensions provide filters on data entry/exit points, such as
1398DB_File::filter_store_key and family. Look out for such filters in
66b79f27 1399the documentation of your extensions, they can make the transition to
7eabb34d
A
1400Unicode data much easier.
1401
376d9008 1402=head2 Speed
7eabb34d 1403
c29a771d 1404Some functions are slower when working on UTF-8 encoded strings than
574c8022 1405on byte encoded strings. All functions that need to hop over
7c17141f
JH
1406characters such as length(), substr() or index(), or matching regular
1407expressions can work B<much> faster when the underlying data are
1408byte-encoded.
1409
1410In Perl 5.8.0 the slowness was often quite spectacular; in Perl 5.8.1
1411a caching scheme was introduced which will hopefully make the slowness
a104b433
JH
1412somewhat less spectacular, at least for some operations. In general,
1413operations with UTF-8 encoded strings are still slower. As an example,
1414the Unicode properties (character classes) like C<\p{Nd}> are known to
1415be quite a bit slower (5-20 times) than their simpler counterparts
1416like C<\d> (then again, there 268 Unicode characters matching C<Nd>
1417compared with the 10 ASCII characters matching C<d>).
666f95b9 1418
c8d992ba
A
1419=head2 Porting code from perl-5.6.X
1420
1421Perl 5.8 has a different Unicode model from 5.6. In 5.6 the programmer
1422was required to use the C<utf8> pragma to declare that a given scope
1423expected to deal with Unicode data and had to make sure that only
1424Unicode data were reaching that scope. If you have code that is
1425working with 5.6, you will need some of the following adjustments to
1426your code. The examples are written such that the code will continue
1427to work under 5.6, so you should be safe to try them out.
1428
1429=over 4
1430
1431=item *
1432
1433A filehandle that should read or write UTF-8
1434
1435 if ($] > 5.007) {
1436 binmode $fh, ":utf8";
1437 }
1438
1439=item *
1440
1441A scalar that is going to be passed to some extension
1442
1443Be it Compress::Zlib, Apache::Request or any extension that has no
1444mention of Unicode in the manpage, you need to make sure that the
1445UTF-8 flag is stripped off. Note that at the time of this writing
1446(October 2002) the mentioned modules are not UTF-8-aware. Please
1447check the documentation to verify if this is still true.
1448
1449 if ($] > 5.007) {
1450 require Encode;
1451 $val = Encode::encode_utf8($val); # make octets
1452 }
1453
1454=item *
1455
1456A scalar we got back from an extension
1457
1458If you believe the scalar comes back as UTF-8, you will most likely
1459want the UTF-8 flag restored:
1460
1461 if ($] > 5.007) {
1462 require Encode;
1463 $val = Encode::decode_utf8($val);
1464 }
1465
1466=item *
1467
1468Same thing, if you are really sure it is UTF-8
1469
1470 if ($] > 5.007) {
1471 require Encode;
1472 Encode::_utf8_on($val);
1473 }
1474
1475=item *
1476
1477A wrapper for fetchrow_array and fetchrow_hashref
1478
1479When the database contains only UTF-8, a wrapper function or method is
1480a convenient way to replace all your fetchrow_array and
1481fetchrow_hashref calls. A wrapper function will also make it easier to
1482adapt to future enhancements in your database driver. Note that at the
1483time of this writing (October 2002), the DBI has no standardized way
1484to deal with UTF-8 data. Please check the documentation to verify if
1485that is still true.
1486
1487 sub fetchrow {
1488 my($self, $sth, $what) = @_; # $what is one of fetchrow_{array,hashref}
1489 if ($] < 5.007) {
1490 return $sth->$what;
1491 } else {
1492 require Encode;
1493 if (wantarray) {
1494 my @arr = $sth->$what;
1495 for (@arr) {
1496 defined && /[^\000-\177]/ && Encode::_utf8_on($_);
1497 }
1498 return @arr;
1499 } else {
1500 my $ret = $sth->$what;
1501 if (ref $ret) {
1502 for my $k (keys %$ret) {
1503 defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret->{$k};
1504 }
1505 return $ret;
1506 } else {
1507 defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret;
1508 return $ret;
1509 }
1510 }
1511 }
1512 }
1513
1514
1515=item *
1516
1517A large scalar that you know can only contain ASCII
1518
1519Scalars that contain only ASCII and are marked as UTF-8 are sometimes
1520a drag to your program. If you recognize such a situation, just remove
1521the UTF-8 flag:
1522
1523 utf8::downgrade($val) if $] > 5.007;
1524
1525=back
1526
393fec97
GS
1527=head1 SEE ALSO
1528
72ff2908 1529L<perluniintro>, L<encoding>, L<Encode>, L<open>, L<utf8>, L<bytes>,
a05d7ebb 1530L<perlretut>, L<perlvar/"${^UNICODE}">
393fec97
GS
1531
1532=cut