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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
51f494cc 60codepoints in Unicode happens to agree with Latin-1.
990e18f7 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.
393fec97 70
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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
51f494cc 82Under byte semantics, when C<use locale> is in effect, Perl uses the
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83semantics associated with the current locale. Absent a C<use locale>, and
84absent a C<use feature 'unicode_strings'> pragma, Perl currently uses US-ASCII
85(or Basic Latin in Unicode terminology) byte semantics, meaning that characters
86whose ordinal numbers are in the range 128 - 255 are undefined except for their
87ordinal numbers. This means that none have case (upper and lower), nor are any
88a member of character classes, like C<[:alpha:]> or C<\w>. (But all do belong
89to the C<\W> class or the Perl regular expression extension C<[:^alpha:]>.)
2bbc8d55 90
8cbd9a7a 91This behavior preserves compatibility with earlier versions of Perl,
376d9008 92which allowed byte semantics in Perl operations only if
e1b711da 93none of the program's inputs were marked as being a source of Unicode
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94character data. Such data may come from filehandles, from calls to
95external programs, from information provided by the system (such as %ENV),
21bad921 96or from literals and constants in the source text.
8cbd9a7a 97
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98The C<bytes> pragma will always, regardless of platform, force byte
99semantics in a particular lexical scope. See L<bytes>.
8cbd9a7a 100
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101The C<use feature 'unicode_strings'> pragma is intended to always, regardless
102of platform, force Unicode semantics in a particular lexical scope. In
103release 5.12, it is partially implemented, applying only to case changes.
104See L</The "Unicode Bug"> below.
105
8cbd9a7a 106The C<utf8> pragma is primarily a compatibility device that enables
75daf61c 107recognition of UTF-(8|EBCDIC) in literals encountered by the parser.
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108Note that this pragma is only required while Perl defaults to byte
109semantics; when character semantics become the default, this pragma
110may become a no-op. See L<utf8>.
111
112Unless explicitly stated, Perl operators use character semantics
113for Unicode data and byte semantics for non-Unicode data.
114The decision to use character semantics is made transparently. If
115input data comes from a Unicode source--for example, if a character
fae2c0fb 116encoding layer is added to a filehandle or a literal Unicode
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117string constant appears in a program--character semantics apply.
118Otherwise, byte semantics are in effect. The C<bytes> pragma should
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119be used to force byte semantics on Unicode data, and the C<use feature
120'unicode_strings'> pragma to force Unicode semantics on byte data (though in
1215.12 it isn't fully implemented).
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122
123If strings operating under byte semantics and strings with Unicode
51f494cc 124character data are concatenated, the new string will have
42bde815 125character semantics. This can cause surprises: See L</BUGS>, below
7dedd01f 126
feda178f 127Under character semantics, many operations that formerly operated on
376d9008 128bytes now operate on characters. A character in Perl is
feda178f 129logically just a number ranging from 0 to 2**31 or so. Larger
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130characters may encode into longer sequences of bytes internally, but
131this internal detail is mostly hidden for Perl code.
132See L<perluniintro> for more.
393fec97 133
376d9008 134=head2 Effects of Character Semantics
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135
136Character semantics have the following effects:
137
138=over 4
139
140=item *
141
376d9008 142Strings--including hash keys--and regular expression patterns may
574c8022 143contain characters that have an ordinal value larger than 255.
393fec97 144
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145If you use a Unicode editor to edit your program, Unicode characters may
146occur directly within the literal strings in UTF-8 encoding, or UTF-16.
147(The former requires a BOM or C<use utf8>, the latter requires a BOM.)
3e4dbfed 148
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149Unicode characters can also be added to a string by using the C<\x{...}>
150notation. The Unicode code for the desired character, in hexadecimal,
151should be placed in the braces. For instance, a smiley face is
2bbc8d55 152C<\x{263A}>. This encoding scheme works for all characters, but
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153for characters under 0x100, note that Perl may use an 8 bit encoding
154internally, for optimization and/or backward compatibility.
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155
156Additionally, if you
574c8022 157
3e4dbfed 158 use charnames ':full';
574c8022 159
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160you can use the C<\N{...}> notation and put the official Unicode
161character name within the braces, such as C<\N{WHITE SMILING FACE}>.
376d9008 162
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163=item *
164
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165If an appropriate L<encoding> is specified, identifiers within the
166Perl script may contain Unicode alphanumeric characters, including
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167ideographs. Perl does not currently attempt to canonicalize variable
168names.
393fec97 169
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170=item *
171
1bfb14c4 172Regular expressions match characters instead of bytes. "." matches
2575c402 173a character instead of a byte.
393fec97 174
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175=item *
176
177Character classes in regular expressions match characters instead of
376d9008 178bytes and match against the character properties specified in the
1bfb14c4 179Unicode properties database. C<\w> can be used to match a Japanese
75daf61c 180ideograph, for instance.
393fec97 181
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182=item *
183
eb0cc9e3 184Named Unicode properties, scripts, and block ranges may be used like
376d9008 185character classes via the C<\p{}> "matches property" construct and
822502e5 186the C<\P{}> negation, "doesn't match property".
2575c402 187See L</"Unicode Character Properties"> for more details.
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188
189You can define your own character properties and use them
190in the regular expression with the C<\p{}> or C<\P{}> construct.
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191See L</"User-Defined Character Properties"> for more details.
192
193=item *
194
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195The special pattern C<\X> matches a logical character, an "extended grapheme
196cluster" in Standardese. In Unicode what appears to the user to be a single
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197character, for example an accented C<G>, may in fact be composed of a sequence
198of characters, in this case a C<G> followed by an accent character. C<\X>
199will match the entire sequence.
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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
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213that make the distinction (which is equivalent to uppercase in languages
214without the distinction).
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215
216=item *
217
218Most operators that deal with positions or lengths in a string will
219automatically switch to using character positions, including
220C<chop()>, C<chomp()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>,
221C<sprintf()>, C<write()>, and C<length()>. An operator that
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222specifically does not switch is C<vec()>. Operators that really don't
223care include operators that treat strings as a bucket of bits such as
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224C<sort()>, and operators dealing with filenames.
225
226=item *
227
51f494cc 228The C<pack()>/C<unpack()> letter C<C> does I<not> change, since it is often
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229used for byte-oriented formats. Again, think C<char> in the C language.
230
231There is a new C<U> specifier that converts between Unicode characters
232and code points. There is also a C<W> specifier that is the equivalent of
233C<chr>/C<ord> and properly handles character values even if they are above 255.
234
235=item *
236
237The C<chr()> and C<ord()> functions work on characters, similar to
238C<pack("W")> and C<unpack("W")>, I<not> C<pack("C")> and
239C<unpack("C")>. C<pack("C")> and C<unpack("C")> are methods for
240emulating byte-oriented C<chr()> and C<ord()> on Unicode strings.
241While these methods reveal the internal encoding of Unicode strings,
242that is not something one normally needs to care about at all.
243
244=item *
245
246The bit string operators, C<& | ^ ~>, can operate on character data.
247However, for backward compatibility, such as when using bit string
248operations when characters are all less than 256 in ordinal value, one
249should not use C<~> (the bit complement) with characters of both
250values less than 256 and values greater than 256. Most importantly,
251DeMorgan's laws (C<~($x|$y) eq ~$x&~$y> and C<~($x&$y) eq ~$x|~$y>)
252will not hold. The reason for this mathematical I<faux pas> is that
253the complement cannot return B<both> the 8-bit (byte-wide) bit
254complement B<and> the full character-wide bit complement.
255
256=item *
257
e1b711da 258You can define your own mappings to be used in lc(),
822502e5 259lcfirst(), uc(), and ucfirst() (or their string-inlined versions).
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260See L</"User-Defined Case Mappings"> for more details.
261
262=back
263
264=over 4
265
266=item *
267
268And finally, C<scalar reverse()> reverses by character rather than by byte.
269
270=back
271
272=head2 Unicode Character Properties
273
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274Most Unicode character properties are accessible by using regular expressions.
275They are used like character classes via the C<\p{}> "matches property"
276construct and the C<\P{}> negation, "doesn't match property".
277
278For instance, C<\p{Uppercase}> matches any character with the Unicode
279"Uppercase" property, while C<\p{L}> matches any character with a
280General_Category of "L" (letter) property. Brackets are not
281required for single letter properties, so C<\p{L}> is equivalent to C<\pL>.
282
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283More formally, C<\p{Uppercase}> matches any character whose Unicode Uppercase
284property value is True, and C<\P{Uppercase}> matches any character whose
285Uppercase property value is False, and they could have been written as
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286C<\p{Uppercase=True}> and C<\p{Uppercase=False}>, respectively
287
288This formality is needed when properties are not binary, that is if they can
289take on more values than just True and False. For example, the Bidi_Class (see
290L</"Bidirectional Character Types"> below), can take on a number of different
291values, such as Left, Right, Whitespace, and others. To match these, one needs
e1b711da 292to specify the property name (Bidi_Class), and the value being matched against
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293(Left, Right, I<etc.>). This is done, as in the examples above, by having the
294two components separated by an equal sign (or interchangeably, a colon), like
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295C<\p{Bidi_Class: Left}>.
296
297All Unicode-defined character properties may be written in these compound forms
298of C<\p{property=value}> or C<\p{property:value}>, but Perl provides some
299additional properties that are written only in the single form, as well as
300single-form short-cuts for all binary properties and certain others described
301below, in which you may omit the property name and the equals or colon
302separator.
303
304Most Unicode character properties have at least two synonyms (or aliases if you
305prefer), a short one that is easier to type, and a longer one which is more
306descriptive and hence it is easier to understand what it means. Thus the "L"
307and "Letter" above are equivalent and can be used interchangeably. Likewise,
308"Upper" is a synonym for "Uppercase", and we could have written
309C<\p{Uppercase}> equivalently as C<\p{Upper}>. Also, there are typically
310various synonyms for the values the property can be. For binary properties,
311"True" has 3 synonyms: "T", "Yes", and "Y"; and "False has correspondingly "F",
312"No", and "N". But be careful. A short form of a value for one property may
e1b711da 313not mean the same thing as the same short form for another. Thus, for the
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314General_Category property, "L" means "Letter", but for the Bidi_Class property,
315"L" means "Left". A complete list of properties and synonyms is in
316L<perluniprops>.
317
318Upper/lower case differences in the property names and values are irrelevant,
319thus C<\p{Upper}> means the same thing as C<\p{upper}> or even C<\p{UpPeR}>.
320Similarly, you can add or subtract underscores anywhere in the middle of a
321word, so that these are also equivalent to C<\p{U_p_p_e_r}>. And white space
322is irrelevant adjacent to non-word characters, such as the braces and the equals
323or colon separators so C<\p{ Upper }> and C<\p{ Upper_case : Y }> are
324equivalent to these as well. In fact, in most cases, white space and even
325hyphens can be added or deleted anywhere. So even C<\p{ Up-per case = Yes}> is
326equivalent. All this is called "loose-matching" by Unicode. The few places
327where stricter matching is employed is in the middle of numbers, and the Perl
328extension properties that begin or end with an underscore. Stricter matching
329cares about white space (except adjacent to the non-word characters) and
330hyphens, and non-interior underscores.
4193bef7 331
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332You can also use negation in both C<\p{}> and C<\P{}> by introducing a caret
333(^) between the first brace and the property name: C<\p{^Tamil}> is
eb0cc9e3 334equal to C<\P{Tamil}>.
4193bef7 335
51f494cc 336=head3 B<General_Category>
14bb0a9a 337
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338Every Unicode character is assigned a general category, which is the "most
339usual categorization of a character" (from
340L<http://www.unicode.org/reports/tr44>).
822502e5 341
9f815e24 342The compound way of writing these is like C<\p{General_Category=Number}>
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343(short, C<\p{gc:n}>). But Perl furnishes shortcuts in which everything up
344through the equal or colon separator is omitted. So you can instead just write
345C<\pN>.
822502e5 346
51f494cc 347Here are the short and long forms of the General Category properties:
393fec97 348
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349 Short Long
350
351 L Letter
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352 LC, L& Cased_Letter (that is: [\p{Ll}\p{Lu}\p{Lt}])
353 Lu Uppercase_Letter
354 Ll Lowercase_Letter
355 Lt Titlecase_Letter
356 Lm Modifier_Letter
357 Lo Other_Letter
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358
359 M Mark
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360 Mn Nonspacing_Mark
361 Mc Spacing_Mark
362 Me Enclosing_Mark
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363
364 N Number
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365 Nd Decimal_Number (also Digit)
366 Nl Letter_Number
367 No Other_Number
368
369 P Punctuation (also Punct)
370 Pc Connector_Punctuation
371 Pd Dash_Punctuation
372 Ps Open_Punctuation
373 Pe Close_Punctuation
374 Pi Initial_Punctuation
d73e5302 375 (may behave like Ps or Pe depending on usage)
51f494cc 376 Pf Final_Punctuation
d73e5302 377 (may behave like Ps or Pe depending on usage)
51f494cc 378 Po Other_Punctuation
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379
380 S Symbol
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381 Sm Math_Symbol
382 Sc Currency_Symbol
383 Sk Modifier_Symbol
384 So Other_Symbol
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385
386 Z Separator
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387 Zs Space_Separator
388 Zl Line_Separator
389 Zp Paragraph_Separator
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390
391 C Other
51f494cc 392 Cc Control (also Cntrl)
e150c829 393 Cf Format
eb0cc9e3 394 Cs Surrogate (not usable)
51f494cc 395 Co Private_Use
e150c829 396 Cn Unassigned
1ac13f9a 397
376d9008 398Single-letter properties match all characters in any of the
3e4dbfed 399two-letter sub-properties starting with the same letter.
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400C<LC> and C<L&> are special cases, which are aliases for the set of
401C<Ll>, C<Lu>, and C<Lt>.
32293815 402
eb0cc9e3 403Because Perl hides the need for the user to understand the internal
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404representation of Unicode characters, there is no need to implement
405the somewhat messy concept of surrogates. C<Cs> is therefore not
eb0cc9e3 406supported.
d73e5302 407
51f494cc 408=head3 B<Bidirectional Character Types>
822502e5 409
376d9008 410Because scripts differ in their directionality--Hebrew is
12ac2576 411written right to left, for example--Unicode supplies these properties in
51f494cc 412the Bidi_Class class:
32293815 413
eb0cc9e3 414 Property Meaning
92e830a9 415
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416 L Left-to-Right
417 LRE Left-to-Right Embedding
418 LRO Left-to-Right Override
419 R Right-to-Left
51f494cc 420 AL Arabic Letter
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421 RLE Right-to-Left Embedding
422 RLO Right-to-Left Override
423 PDF Pop Directional Format
424 EN European Number
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425 ES European Separator
426 ET European Terminator
12ac2576 427 AN Arabic Number
51f494cc 428 CS Common Separator
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429 NSM Non-Spacing Mark
430 BN Boundary Neutral
431 B Paragraph Separator
432 S Segment Separator
433 WS Whitespace
434 ON Other Neutrals
435
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436This property is always written in the compound form.
437For example, C<\p{Bidi_Class:R}> matches characters that are normally
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438written right to left.
439
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440=head3 B<Scripts>
441
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442The world's languages are written in a number of scripts. This sentence
443(unless you're reading it in translation) is written in Latin, while Russian is
444written in Cyrllic, and Greek is written in, well, Greek; Japanese mainly in
445Hiragana or Katakana. There are many more.
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446
447The Unicode Script property gives what script a given character is in,
448and can be matched with the compound form like C<\p{Script=Hebrew}> (short:
449C<\p{sc=hebr}>). Perl furnishes shortcuts for all script names. You can omit
450everything up through the equals (or colon), and simply write C<\p{Latin}> or
451C<\P{Cyrillic}>.
452
453A complete list of scripts and their shortcuts is in L<perluniprops>.
454
51f494cc 455=head3 B<Use of "Is" Prefix>
822502e5 456
1bfb14c4 457For backward compatibility (with Perl 5.6), all properties mentioned
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458so far may have C<Is> or C<Is_> prepended to their name, so C<\P{Is_Lu}>, for
459example, is equal to C<\P{Lu}>, and C<\p{IsScript:Arabic}> is equal to
460C<\p{Arabic}>.
eb0cc9e3 461
51f494cc 462=head3 B<Blocks>
2796c109 463
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464In addition to B<scripts>, Unicode also defines B<blocks> of
465characters. The difference between scripts and blocks is that the
466concept of scripts is closer to natural languages, while the concept
51f494cc 467of blocks is more of an artificial grouping based on groups of Unicode
9f815e24 468characters with consecutive ordinal values. For example, the "Basic Latin"
51f494cc 469block is all characters whose ordinals are between 0 and 127, inclusive, in
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470other words, the ASCII characters. The "Latin" script contains some letters
471from this block as well as several more, like "Latin-1 Supplement",
472"Latin Extended-A", I<etc.>, but it does not contain all the characters from
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473those blocks. It does not, for example, contain digits, because digits are
474shared across many scripts. Digits and similar groups, like punctuation, are in
475the script called C<Common>. There is also a script called C<Inherited> for
476characters that modify other characters, and inherit the script value of the
477controlling character.
478
479For more about scripts versus blocks, see UAX#24 "Unicode Script Property":
480L<http://www.unicode.org/reports/tr24>
481
482The Script property is likely to be the one you want to use when processing
483natural language; the Block property may be useful in working with the nuts and
484bolts of Unicode.
485
486Block names are matched in the compound form, like C<\p{Block: Arrows}> or
487C<\p{Blk=Hebrew}>. Unlike most other properties only a few block names have a
488Unicode-defined short name. But Perl does provide a (slight) shortcut: You
489can say, for example C<\p{In_Arrows}> or C<\p{In_Hebrew}>. For backwards
490compatibility, the C<In> prefix may be omitted if there is no naming conflict
491with a script or any other property, and you can even use an C<Is> prefix
492instead in those cases. But it is not a good idea to do this, for a couple
493reasons:
494
495=over 4
496
497=item 1
498
499It is confusing. There are many naming conflicts, and you may forget some.
9f815e24 500For example, C<\p{Hebrew}> means the I<script> Hebrew, and NOT the I<block>
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501Hebrew. But would you remember that 6 months from now?
502
503=item 2
504
505It is unstable. A new version of Unicode may pre-empt the current meaning by
506creating a property with the same name. There was a time in very early Unicode
9f815e24 507releases when C<\p{Hebrew}> would have matched the I<block> Hebrew; now it
51f494cc 508doesn't.
32293815 509
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510=back
511
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512Some people just prefer to always use C<\p{Block: foo}> and C<\p{Script: bar}>
513instead of the shortcuts, for clarity, and because they can't remember the
514difference between 'In' and 'Is' anyway (or aren't confident that those who
515eventually will read their code will know).
516
517A complete list of blocks and their shortcuts is in L<perluniprops>.
518
9f815e24
KW
519=head3 B<Other Properties>
520
521There are many more properties than the very basic ones described here.
522A complete list is in L<perluniprops>.
523
524Unicode defines all its properties in the compound form, so all single-form
525properties are Perl extensions. A number of these are just synonyms for the
526Unicode ones, but some are genunine extensions, including a couple that are in
527the compound form. And quite a few of these are actually recommended by Unicode
528(in L<http://www.unicode.org/reports/tr18>).
529
530This section gives some details on all the extensions that aren't synonyms for
531compound-form Unicode properties (for those, you'll have to refer to the
532L<Unicode Standard|http://www.unicode.org/reports/tr44>.
533
534=over
535
536=item B<C<\p{All}>>
537
538This matches any of the 1_114_112 Unicode code points. It is a synonym for
539C<\p{Any}>.
540
541=item B<C<\p{Alnum}>>
542
543This matches any C<\p{Alphabetic}> or C<\p{Decimal_Number}> character.
544
545=item B<C<\p{Any}>>
546
547This matches any of the 1_114_112 Unicode code points. It is a synonym for
548C<\p{All}>.
549
550=item B<C<\p{Assigned}>>
551
552This matches any assigned code point; that is, any code point whose general
553category is not Unassigned (or equivalently, not Cn).
554
555=item B<C<\p{Blank}>>
556
557This is the same as C<\h> and C<\p{HorizSpace}>: A character that changes the
558spacing horizontally.
559
560=item B<C<\p{Decomposition_Type: Non_Canonical}>> (Short: C<\p{Dt=NonCanon}>)
561
562Matches a character that has a non-canonical decomposition.
563
564To understand the use of this rarely used property=value combination, it is
565necessary to know some basics about decomposition.
566Consider a character, say H. It could appear with various marks around it,
567such as an acute accent, or a circumflex, or various hooks, circles, arrows,
568I<etc.>, above, below, to one side and/or the other, I<etc.> There are many
569possibilities among the world's languages. The number of combinations is
570astronomical, and if there were a character for each combination, it would
571soon exhaust Unicode's more than a million possible characters. So Unicode
572took a different approach: there is a character for the base H, and a
573character for each of the possible marks, and they can be combined variously
574to get a final logical character. So a logical character--what appears to be a
575single character--can be a sequence of more than one individual characters.
576This is called an "extended grapheme cluster". (Perl furnishes the C<\X>
577construct to match such sequences.)
578
579But Unicode's intent is to unify the existing character set standards and
580practices, and a number of pre-existing standards have single characters that
581mean the same thing as some of these combinations. An example is ISO-8859-1,
582which has quite a few of these in the Latin-1 range, an example being "LATIN
583CAPITAL LETTER E WITH ACUTE". Because this character was in this pre-existing
584standard, Unicode added it to its repertoire. But this character is considered
585by Unicode to be equivalent to the sequence consisting of first the character
586"LATIN CAPITAL LETTER E", then the character "COMBINING ACUTE ACCENT".
587
588"LATIN CAPITAL LETTER E WITH ACUTE" is called a "pre-composed" character, and
589the equivalence with the sequence is called canonical equivalence. All
590pre-composed characters are said to have a decomposition (into the equivalent
591sequence) and the decomposition type is also called canonical.
592
593However, many more characters have a different type of decomposition, a
594"compatible" or "non-canonical" decomposition. The sequences that form these
595decompositions are not considered canonically equivalent to the pre-composed
596character. An example, again in the Latin-1 range, is the "SUPERSCRIPT ONE".
597It is kind of like a regular digit 1, but not exactly; its decomposition
598into the digit 1 is called a "compatible" decomposition, specifically a
599"super" decomposition. There are several such compatibility
600decompositions (see L<http://www.unicode.org/reports/tr44>), including one
601called "compat" which means some miscellaneous type of decomposition
602that doesn't fit into the decomposition categories that Unicode has chosen.
603
604Note that most Unicode characters don't have a decomposition, so their
605decomposition type is "None".
606
607Perl has added the C<Non_Canonical> type, for your convenience, to mean any of
608the compatibility decompositions.
609
610=item B<C<\p{Graph}>>
611
612Matches any character that is graphic. Theoretically, this means a character
613that on a printer would cause ink to be used.
614
615=item B<C<\p{HorizSpace}>>
616
617This is the same as C<\h> and C<\p{Blank}>: A character that changes the
618spacing horizontally.
619
620=item B<C<\p{In=*}>>
621
622This is a synonym for C<\p{Present_In=*}>
623
624=item B<C<\p{PerlSpace}>>
625
626This is the same as C<\s>, restricted to ASCII, namely C<S<[ \f\n\r\t]>>.
627
628Mnemonic: Perl's (original) space
629
630=item B<C<\p{PerlWord}>>
631
632This is the same as C<\w>, restricted to ASCII, namely C<[A-Za-z0-9_]>
633
634Mnemonic: Perl's (original) word.
635
636=item B<C<\p{PosixAlnum}>>
637
638This matches any alphanumeric character in the ASCII range, namely
639C<[A-Za-z0-9]>.
640
641=item B<C<\p{PosixAlpha}>>
642
643This matches any alphabetic character in the ASCII range, namely C<[A-Za-z]>.
644
645=item B<C<\p{PosixBlank}>>
646
647This matches any blank character in the ASCII range, namely C<S<[ \t]>>.
648
649=item B<C<\p{PosixCntrl}>>
650
651This matches any control character in the ASCII range, namely C<[\x00-\x1F\x7F]>
652
653=item B<C<\p{PosixDigit}>>
654
655This matches any digit character in the ASCII range, namely C<[0-9]>.
656
657=item B<C<\p{PosixGraph}>>
658
659This matches any graphical character in the ASCII range, namely C<[\x21-\x7E]>.
660
661=item B<C<\p{PosixLower}>>
662
663This matches any lowercase character in the ASCII range, namely C<[a-z]>.
664
665=item B<C<\p{PosixPrint}>>
666
667This matches any printable character in the ASCII range, namely C<[\x20-\x7E]>.
668These are the graphical characters plus SPACE.
669
670=item B<C<\p{PosixPunct}>>
671
672This matches any punctuation character in the ASCII range, namely
673C<[\x21-\x2F\x3A-\x40\x5B-\x60\x7B-\x7E]>. These are the
674graphical characters that aren't word characters. Note that the Posix standard
675includes in its definition of punctuation, those characters that Unicode calls
676"symbols."
677
678=item B<C<\p{PosixSpace}>>
679
680This matches any space character in the ASCII range, namely
681C<S<[ \f\n\r\t\x0B]>> (the last being a vertical tab).
682
683=item B<C<\p{PosixUpper}>>
684
685This matches any uppercase character in the ASCII range, namely C<[A-Z]>.
686
687=item B<C<\p{Present_In: *}>> (Short: C<\p{In=*}>)
688
689This property is used when you need to know in what Unicode version(s) a
690character is.
691
692The "*" above stands for some two digit Unicode version number, such as
693C<1.1> or C<4.0>; or the "*" can also be C<Unassigned>. This property will
694match the code points whose final disposition has been settled as of the
695Unicode release given by the version number; C<\p{Present_In: Unassigned}>
696will match those code points whose meaning has yet to be assigned.
697
698For example, C<U+0041> "LATIN CAPITAL LETTER A" was present in the very first
699Unicode release available, which is C<1.1>, so this property is true for all
700valid "*" versions. On the other hand, C<U+1EFF> was not assigned until version
7015.1 when it became "LATIN SMALL LETTER Y WITH LOOP", so the only "*" that
702would match it are 5.1, 5.2, and later.
703
704Unicode furnishes the C<Age> property from which this is derived. The problem
705with Age is that a strict interpretation of it (which Perl takes) has it
706matching the precise release a code point's meaning is introduced in. Thus
707C<U+0041> would match only 1.1; and C<U+1EFF> only 5.1. This is not usually what
708you want.
709
710Some non-Perl implementations of the Age property may change its meaning to be
711the same as the Perl Present_In property; just be aware of that.
712
713Another confusion with both these properties is that the definition is not
714that the code point has been assigned, but that the meaning of the code point
715has been determined. This is because 66 code points will always be
716unassigned, and, so the Age for them is the Unicode version the decision to
717make them so was made in. For example, C<U+FDD0> is to be permanently
718unassigned to a character, and the decision to do that was made in version 3.1,
719so C<\p{Age=3.1}> matches this character and C<\p{Present_In: 3.1}> and up
720matches as well.
721
722=item B<C<\p{Print}>>
723
724This matches any character that is graphical or is space, but not a control.
725
726=item B<C<\p{SpacePerl}>>
727
728This is the same as C<\s>, including beyond ASCII.
729
4d4acfba
KW
730Mnemonic: Space, as modified by Perl. (It doesn't include the vertical tab
731which both the Posix standard and Unicode consider to be space.)
9f815e24
KW
732
733=item B<C<\p{VertSpace}>>
734
735This is the same as C<\v>: A character that changes the spacing vertically.
736
737=item B<C<\p{Word}>>
738
739This is the same as C<\w>, including beyond ASCII.
740
741=back
742
376d9008 743=head2 User-Defined Character Properties
491fd90a 744
51f494cc
KW
745You can define your own binary character properties by defining subroutines
746whose names begin with "In" or "Is". The subroutines can be defined in any
747package. The user-defined properties can be used in the regular expression
748C<\p> and C<\P> constructs; if you are using a user-defined property from a
749package other than the one you are in, you must specify its package in the
750C<\p> or C<\P> construct.
bac0b425 751
51f494cc 752 # assuming property Is_Foreign defined in Lang::
bac0b425
JP
753 package main; # property package name required
754 if ($txt =~ /\p{Lang::IsForeign}+/) { ... }
755
756 package Lang; # property package name not required
757 if ($txt =~ /\p{IsForeign}+/) { ... }
758
759
760Note that the effect is compile-time and immutable once defined.
491fd90a 761
376d9008
JB
762The subroutines must return a specially-formatted string, with one
763or more newline-separated lines. Each line must be one of the following:
491fd90a
JH
764
765=over 4
766
767=item *
768
510254c9
A
769A single hexadecimal number denoting a Unicode code point to include.
770
771=item *
772
99a6b1f0 773Two hexadecimal numbers separated by horizontal whitespace (space or
376d9008 774tabular characters) denoting a range of Unicode code points to include.
491fd90a
JH
775
776=item *
777
376d9008 778Something to include, prefixed by "+": a built-in character
bac0b425
JP
779property (prefixed by "utf8::") or a user-defined character property,
780to represent all the characters in that property; two hexadecimal code
781points for a range; or a single hexadecimal code point.
491fd90a
JH
782
783=item *
784
376d9008 785Something to exclude, prefixed by "-": an existing character
bac0b425
JP
786property (prefixed by "utf8::") or a user-defined character property,
787to represent all the characters in that property; two hexadecimal code
788points for a range; or a single hexadecimal code point.
491fd90a
JH
789
790=item *
791
376d9008 792Something to negate, prefixed "!": an existing character
bac0b425
JP
793property (prefixed by "utf8::") or a user-defined character property,
794to represent all the characters in that property; two hexadecimal code
795points for a range; or a single hexadecimal code point.
796
797=item *
798
799Something to intersect with, prefixed by "&": an existing character
800property (prefixed by "utf8::") or a user-defined character property,
801for all the characters except the characters in the property; two
802hexadecimal code points for a range; or a single hexadecimal code point.
491fd90a
JH
803
804=back
805
806For example, to define a property that covers both the Japanese
807syllabaries (hiragana and katakana), you can define
808
809 sub InKana {
d5822f25
A
810 return <<END;
811 3040\t309F
812 30A0\t30FF
491fd90a
JH
813 END
814 }
815
d5822f25
A
816Imagine that the here-doc end marker is at the beginning of the line.
817Now you can use C<\p{InKana}> and C<\P{InKana}>.
491fd90a
JH
818
819You could also have used the existing block property names:
820
821 sub InKana {
822 return <<'END';
823 +utf8::InHiragana
824 +utf8::InKatakana
825 END
826 }
827
828Suppose you wanted to match only the allocated characters,
d5822f25 829not the raw block ranges: in other words, you want to remove
491fd90a
JH
830the non-characters:
831
832 sub InKana {
833 return <<'END';
834 +utf8::InHiragana
835 +utf8::InKatakana
836 -utf8::IsCn
837 END
838 }
839
840The negation is useful for defining (surprise!) negated classes.
841
842 sub InNotKana {
843 return <<'END';
844 !utf8::InHiragana
845 -utf8::InKatakana
846 +utf8::IsCn
847 END
848 }
849
bac0b425
JP
850Intersection is useful for getting the common characters matched by
851two (or more) classes.
852
853 sub InFooAndBar {
854 return <<'END';
855 +main::Foo
856 &main::Bar
857 END
858 }
859
860It's important to remember not to use "&" for the first set -- that
861would be intersecting with nothing (resulting in an empty set).
862
822502e5
ST
863=head2 User-Defined Case Mappings
864
3a2263fe
RGS
865You can also define your own mappings to be used in the lc(),
866lcfirst(), uc(), and ucfirst() (or their string-inlined versions).
822502e5 867The principle is similar to that of user-defined character
51f494cc 868properties: to define subroutines
3a2263fe
RGS
869with names like C<ToLower> (for lc() and lcfirst()), C<ToTitle> (for
870the first character in ucfirst()), and C<ToUpper> (for uc(), and the
871rest of the characters in ucfirst()).
872
51f494cc 873The string returned by the subroutines needs to be two hexadecimal numbers
e1b711da
KW
874separated by two tabulators: the two numbers being, respectively, the source
875code point and the destination code point. For example:
3a2263fe
RGS
876
877 sub ToUpper {
878 return <<END;
51f494cc 879 0061\t\t0041
3a2263fe
RGS
880 END
881 }
882
51f494cc
KW
883defines an uc() mapping that causes only the character "a"
884to be mapped to "A"; all other characters will remain unchanged.
3a2263fe 885
51f494cc
KW
886(For serious hackers only) The above means you have to furnish a complete
887mapping; you can't just override a couple of characters and leave the rest
888unchanged. You can find all the mappings in the directory
889C<$Config{privlib}>/F<unicore/To/>. The mapping data is returned as the
890here-document, and the C<utf8::ToSpecFoo> are special exception mappings
9f815e24
KW
891derived from <$Config{privlib}>/F<unicore/SpecialCasing.txt>. The "Digit" and
892"Fold" mappings that one can see in the directory are not directly
51f494cc 893user-accessible, one can use either the C<Unicode::UCD> module, or just match
9f815e24 894case-insensitively (that's when the "Fold" mapping is used).
3a2263fe 895
51f494cc
KW
896The mappings will only take effect on scalars that have been marked as having
897Unicode characters, for example by using C<utf8::upgrade()>.
898Old byte-style strings are not affected.
3a2263fe 899
51f494cc 900The mappings are in effect for the package they are defined in.
3a2263fe 901
376d9008 902=head2 Character Encodings for Input and Output
8cbd9a7a 903
7221edc9 904See L<Encode>.
8cbd9a7a 905
c29a771d 906=head2 Unicode Regular Expression Support Level
776f8809 907
376d9008
JB
908The following list of Unicode support for regular expressions describes
909all the features currently supported. The references to "Level N"
8158862b
ST
910and the section numbers refer to the Unicode Technical Standard #18,
911"Unicode Regular Expressions", version 11, in May 2005.
776f8809
JH
912
913=over 4
914
915=item *
916
917Level 1 - Basic Unicode Support
918
8158862b
ST
919 RL1.1 Hex Notation - done [1]
920 RL1.2 Properties - done [2][3]
921 RL1.2a Compatibility Properties - done [4]
922 RL1.3 Subtraction and Intersection - MISSING [5]
923 RL1.4 Simple Word Boundaries - done [6]
924 RL1.5 Simple Loose Matches - done [7]
925 RL1.6 Line Boundaries - MISSING [8]
926 RL1.7 Supplementary Code Points - done [9]
927
928 [1] \x{...}
929 [2] \p{...} \P{...}
e1b711da
KW
930 [3] supports not only minimal list, but all Unicode character
931 properties (see L</Unicode Character Properties>)
8158862b
ST
932 [4] \d \D \s \S \w \W \X [:prop:] [:^prop:]
933 [5] can use regular expression look-ahead [a] or
934 user-defined character properties [b] to emulate set operations
935 [6] \b \B
e1b711da
KW
936 [7] note that Perl does Full case-folding in matching (but with bugs),
937 not Simple: for example U+1F88 is equivalent to U+1F00 U+03B9,
2bbc8d55 938 not with 1F80. This difference matters mainly for certain Greek
376d9008
JB
939 capital letters with certain modifiers: the Full case-folding
940 decomposes the letter, while the Simple case-folding would map
e0f9d4a8 941 it to a single character.
8158862b
ST
942 [8] should do ^ and $ also on U+000B (\v in C), FF (\f), CR (\r),
943 CRLF (\r\n), NEL (U+0085), LS (U+2028), and PS (U+2029);
944 should also affect <>, $., and script line numbers;
945 should not split lines within CRLF [c] (i.e. there is no empty
946 line between \r and \n)
947 [9] UTF-8/UTF-EBDDIC used in perl allows not only U+10000 to U+10FFFF
948 but also beyond U+10FFFF [d]
7207e29d 949
237bad5b 950[a] You can mimic class subtraction using lookahead.
8158862b 951For example, what UTS#18 might write as
29bdacb8 952
dbe420b4
JH
953 [{Greek}-[{UNASSIGNED}]]
954
955in Perl can be written as:
956
1d81abf3
JH
957 (?!\p{Unassigned})\p{InGreekAndCoptic}
958 (?=\p{Assigned})\p{InGreekAndCoptic}
dbe420b4
JH
959
960But in this particular example, you probably really want
961
1bfb14c4 962 \p{GreekAndCoptic}
dbe420b4
JH
963
964which will match assigned characters known to be part of the Greek script.
29bdacb8 965
5ca1ac52 966Also see the Unicode::Regex::Set module, it does implement the full
8158862b
ST
967UTS#18 grouping, intersection, union, and removal (subtraction) syntax.
968
969[b] '+' for union, '-' for removal (set-difference), '&' for intersection
970(see L</"User-Defined Character Properties">)
971
972[c] Try the C<:crlf> layer (see L<PerlIO>).
5ca1ac52 973
c670e63a
KW
974[d] U+FFFF will currently generate a warning message if 'utf8' warnings are
975 enabled
237bad5b 976
776f8809
JH
977=item *
978
979Level 2 - Extended Unicode Support
980
8158862b 981 RL2.1 Canonical Equivalents - MISSING [10][11]
c670e63a 982 RL2.2 Default Grapheme Clusters - MISSING [12]
8158862b
ST
983 RL2.3 Default Word Boundaries - MISSING [14]
984 RL2.4 Default Loose Matches - MISSING [15]
985 RL2.5 Name Properties - MISSING [16]
986 RL2.6 Wildcard Properties - MISSING
987
988 [10] see UAX#15 "Unicode Normalization Forms"
989 [11] have Unicode::Normalize but not integrated to regexes
e1b711da 990 [12] have \X but we don't have a "Grapheme Cluster Mode"
8158862b
ST
991 [14] see UAX#29, Word Boundaries
992 [15] see UAX#21 "Case Mappings"
993 [16] have \N{...} but neither compute names of CJK Ideographs
994 and Hangul Syllables nor use a loose match [e]
995
996[e] C<\N{...}> allows namespaces (see L<charnames>).
776f8809
JH
997
998=item *
999
8158862b
ST
1000Level 3 - Tailored Support
1001
1002 RL3.1 Tailored Punctuation - MISSING
1003 RL3.2 Tailored Grapheme Clusters - MISSING [17][18]
1004 RL3.3 Tailored Word Boundaries - MISSING
1005 RL3.4 Tailored Loose Matches - MISSING
1006 RL3.5 Tailored Ranges - MISSING
1007 RL3.6 Context Matching - MISSING [19]
1008 RL3.7 Incremental Matches - MISSING
1009 ( RL3.8 Unicode Set Sharing )
1010 RL3.9 Possible Match Sets - MISSING
1011 RL3.10 Folded Matching - MISSING [20]
1012 RL3.11 Submatchers - MISSING
1013
1014 [17] see UAX#10 "Unicode Collation Algorithms"
1015 [18] have Unicode::Collate but not integrated to regexes
1016 [19] have (?<=x) and (?=x), but look-aheads or look-behinds should see
1017 outside of the target substring
1018 [20] need insensitive matching for linguistic features other than case;
1019 for example, hiragana to katakana, wide and narrow, simplified Han
1020 to traditional Han (see UTR#30 "Character Foldings")
776f8809
JH
1021
1022=back
1023
c349b1b9
JH
1024=head2 Unicode Encodings
1025
376d9008
JB
1026Unicode characters are assigned to I<code points>, which are abstract
1027numbers. To use these numbers, various encodings are needed.
c349b1b9
JH
1028
1029=over 4
1030
c29a771d 1031=item *
5cb3728c
RB
1032
1033UTF-8
c349b1b9 1034
3e4dbfed 1035UTF-8 is a variable-length (1 to 6 bytes, current character allocations
376d9008
JB
1036require 4 bytes), byte-order independent encoding. For ASCII (and we
1037really do mean 7-bit ASCII, not another 8-bit encoding), UTF-8 is
1038transparent.
c349b1b9 1039
8c007b5a 1040The following table is from Unicode 3.2.
05632f9a 1041
e1b711da 1042 Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
05632f9a 1043
e1b711da
KW
1044 U+0000..U+007F 00..7F
1045 U+0080..U+07FF * C2..DF 80..BF
1046 U+0800..U+0FFF E0 * A0..BF 80..BF
ec90690f
ST
1047 U+1000..U+CFFF E1..EC 80..BF 80..BF
1048 U+D000..U+D7FF ED 80..9F 80..BF
e1b711da 1049 U+D800..U+DFFF +++++++ utf16 surrogates, not legal utf8 +++++++
ec90690f 1050 U+E000..U+FFFF EE..EF 80..BF 80..BF
e1b711da
KW
1051 U+10000..U+3FFFF F0 * 90..BF 80..BF 80..BF
1052 U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF
1053 U+100000..U+10FFFF F4 80..8F 80..BF 80..BF
1054
1055Note the gaps before several of the byte entries above marked by '*'. These are
1056caused by legal UTF-8 avoiding non-shortest encodings: it is technically
1057possible to UTF-8-encode a single code point in different ways, but that is
1058explicitly forbidden, and the shortest possible encoding should always be used
1059(and that is what Perl does).
37361303 1060
376d9008 1061Another way to look at it is via bits:
05632f9a
JH
1062
1063 Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
1064
1065 0aaaaaaa 0aaaaaaa
1066 00000bbbbbaaaaaa 110bbbbb 10aaaaaa
1067 ccccbbbbbbaaaaaa 1110cccc 10bbbbbb 10aaaaaa
1068 00000dddccccccbbbbbbaaaaaa 11110ddd 10cccccc 10bbbbbb 10aaaaaa
1069
9f815e24 1070As you can see, the continuation bytes all begin with "10", and the
e1b711da 1071leading bits of the start byte tell how many bytes there are in the
05632f9a
JH
1072encoded character.
1073
c29a771d 1074=item *
5cb3728c
RB
1075
1076UTF-EBCDIC
dbe420b4 1077
376d9008 1078Like UTF-8 but EBCDIC-safe, in the way that UTF-8 is ASCII-safe.
dbe420b4 1079
c29a771d 1080=item *
5cb3728c 1081
1e54db1a 1082UTF-16, UTF-16BE, UTF-16LE, Surrogates, and BOMs (Byte Order Marks)
c349b1b9 1083
1bfb14c4
JH
1084The followings items are mostly for reference and general Unicode
1085knowledge, Perl doesn't use these constructs internally.
dbe420b4 1086
c349b1b9 1087UTF-16 is a 2 or 4 byte encoding. The Unicode code points
1bfb14c4
JH
1088C<U+0000..U+FFFF> are stored in a single 16-bit unit, and the code
1089points C<U+10000..U+10FFFF> in two 16-bit units. The latter case is
c349b1b9
JH
1090using I<surrogates>, the first 16-bit unit being the I<high
1091surrogate>, and the second being the I<low surrogate>.
1092
376d9008 1093Surrogates are code points set aside to encode the C<U+10000..U+10FFFF>
c349b1b9 1094range of Unicode code points in pairs of 16-bit units. The I<high
9f815e24 1095surrogates> are the range C<U+D800..U+DBFF> and the I<low surrogates>
376d9008 1096are the range C<U+DC00..U+DFFF>. The surrogate encoding is
c349b1b9
JH
1097
1098 $hi = ($uni - 0x10000) / 0x400 + 0xD800;
1099 $lo = ($uni - 0x10000) % 0x400 + 0xDC00;
1100
1101and the decoding is
1102
1a3fa709 1103 $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00);
c349b1b9 1104
feda178f 1105If you try to generate surrogates (for example by using chr()), you
e1b711da 1106will get a warning, if warnings are turned on, because those code
376d9008 1107points are not valid for a Unicode character.
9466bab6 1108
376d9008 1109Because of the 16-bitness, UTF-16 is byte-order dependent. UTF-16
c349b1b9 1110itself can be used for in-memory computations, but if storage or
376d9008
JB
1111transfer is required either UTF-16BE (big-endian) or UTF-16LE
1112(little-endian) encodings must be chosen.
c349b1b9
JH
1113
1114This introduces another problem: what if you just know that your data
376d9008
JB
1115is UTF-16, but you don't know which endianness? Byte Order Marks, or
1116BOMs, are a solution to this. A special character has been reserved
86bbd6d1 1117in Unicode to function as a byte order marker: the character with the
376d9008 1118code point C<U+FEFF> is the BOM.
042da322 1119
c349b1b9 1120The trick is that if you read a BOM, you will know the byte order,
376d9008
JB
1121since if it was written on a big-endian platform, you will read the
1122bytes C<0xFE 0xFF>, but if it was written on a little-endian platform,
1123you will read the bytes C<0xFF 0xFE>. (And if the originating platform
1124was writing in UTF-8, you will read the bytes C<0xEF 0xBB 0xBF>.)
042da322 1125
86bbd6d1 1126The way this trick works is that the character with the code point
376d9008
JB
1127C<U+FFFE> is guaranteed not to be a valid Unicode character, so the
1128sequence of bytes C<0xFF 0xFE> is unambiguously "BOM, represented in
1bfb14c4 1129little-endian format" and cannot be C<U+FFFE>, represented in big-endian
e1b711da
KW
1130format". (Actually, C<U+FFFE> is legal for use by your program, even for
1131input/output, but better not use it if you need a BOM. But it is "illegal for
1132interchange", so that an unsuspecting program won't get confused.)
c349b1b9 1133
c29a771d 1134=item *
5cb3728c 1135
1e54db1a 1136UTF-32, UTF-32BE, UTF-32LE
c349b1b9
JH
1137
1138The UTF-32 family is pretty much like the UTF-16 family, expect that
042da322 1139the units are 32-bit, and therefore the surrogate scheme is not
376d9008
JB
1140needed. The BOM signatures will be C<0x00 0x00 0xFE 0xFF> for BE and
1141C<0xFF 0xFE 0x00 0x00> for LE.
c349b1b9 1142
c29a771d 1143=item *
5cb3728c
RB
1144
1145UCS-2, UCS-4
c349b1b9 1146
86bbd6d1 1147Encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit
376d9008 1148encoding. Unlike UTF-16, UCS-2 is not extensible beyond C<U+FFFF>,
339cfa0e
JH
1149because it does not use surrogates. UCS-4 is a 32-bit encoding,
1150functionally identical to UTF-32.
c349b1b9 1151
c29a771d 1152=item *
5cb3728c
RB
1153
1154UTF-7
c349b1b9 1155
376d9008
JB
1156A seven-bit safe (non-eight-bit) encoding, which is useful if the
1157transport or storage is not eight-bit safe. Defined by RFC 2152.
c349b1b9 1158
95a1a48b
JH
1159=back
1160
0d7c09bb
JH
1161=head2 Security Implications of Unicode
1162
e1b711da
KW
1163Read L<Unicode Security Considerations|http://www.unicode.org/reports/tr36>.
1164Also, note the following:
1165
0d7c09bb
JH
1166=over 4
1167
1168=item *
1169
1170Malformed UTF-8
bf0fa0b2
JH
1171
1172Unfortunately, the specification of UTF-8 leaves some room for
1173interpretation of how many bytes of encoded output one should generate
376d9008
JB
1174from one input Unicode character. Strictly speaking, the shortest
1175possible sequence of UTF-8 bytes should be generated,
1176because otherwise there is potential for an input buffer overflow at
feda178f 1177the receiving end of a UTF-8 connection. Perl always generates the
e1b711da 1178shortest length UTF-8, and with warnings on, Perl will warn about
376d9008
JB
1179non-shortest length UTF-8 along with other malformations, such as the
1180surrogates, which are not real Unicode code points.
bf0fa0b2 1181
0d7c09bb
JH
1182=item *
1183
1184Regular expressions behave slightly differently between byte data and
376d9008
JB
1185character (Unicode) data. For example, the "word character" character
1186class C<\w> will work differently depending on if data is eight-bit bytes
1187or Unicode.
0d7c09bb 1188
376d9008
JB
1189In the first case, the set of C<\w> characters is either small--the
1190default set of alphabetic characters, digits, and the "_"--or, if you
0d7c09bb
JH
1191are using a locale (see L<perllocale>), the C<\w> might contain a few
1192more letters according to your language and country.
1193
376d9008 1194In the second case, the C<\w> set of characters is much, much larger.
1bfb14c4
JH
1195Most importantly, even in the set of the first 256 characters, it will
1196probably match different characters: unlike most locales, which are
1197specific to a language and country pair, Unicode classifies all the
1198characters that are letters I<somewhere> as C<\w>. For example, your
1199locale might not think that LATIN SMALL LETTER ETH is a letter (unless
1200you happen to speak Icelandic), but Unicode does.
0d7c09bb 1201
376d9008 1202As discussed elsewhere, Perl has one foot (two hooves?) planted in
1bfb14c4
JH
1203each of two worlds: the old world of bytes and the new world of
1204characters, upgrading from bytes to characters when necessary.
376d9008
JB
1205If your legacy code does not explicitly use Unicode, no automatic
1206switch-over to characters should happen. Characters shouldn't get
1bfb14c4
JH
1207downgraded to bytes, either. It is possible to accidentally mix bytes
1208and characters, however (see L<perluniintro>), in which case C<\w> in
1209regular expressions might start behaving differently. Review your
1210code. Use warnings and the C<strict> pragma.
0d7c09bb
JH
1211
1212=back
1213
c349b1b9
JH
1214=head2 Unicode in Perl on EBCDIC
1215
376d9008
JB
1216The way Unicode is handled on EBCDIC platforms is still
1217experimental. On such platforms, references to UTF-8 encoding in this
1218document and elsewhere should be read as meaning the UTF-EBCDIC
1219specified in Unicode Technical Report 16, unless ASCII vs. EBCDIC issues
c349b1b9 1220are specifically discussed. There is no C<utfebcdic> pragma or
376d9008 1221":utfebcdic" layer; rather, "utf8" and ":utf8" are reused to mean
86bbd6d1
PN
1222the platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic>
1223for more discussion of the issues.
c349b1b9 1224
b310b053
JH
1225=head2 Locales
1226
4616122b 1227Usually locale settings and Unicode do not affect each other, but
b310b053
JH
1228there are a couple of exceptions:
1229
1230=over 4
1231
1232=item *
1233
8aa8f774
JH
1234You can enable automatic UTF-8-ification of your standard file
1235handles, default C<open()> layer, and C<@ARGV> by using either
1236the C<-C> command line switch or the C<PERL_UNICODE> environment
1237variable, see L<perlrun> for the documentation of the C<-C> switch.
b310b053
JH
1238
1239=item *
1240
376d9008
JB
1241Perl tries really hard to work both with Unicode and the old
1242byte-oriented world. Most often this is nice, but sometimes Perl's
1243straddling of the proverbial fence causes problems.
b310b053
JH
1244
1245=back
1246
1aad1664
JH
1247=head2 When Unicode Does Not Happen
1248
1249While Perl does have extensive ways to input and output in Unicode,
1250and few other 'entry points' like the @ARGV which can be interpreted
1251as Unicode (UTF-8), there still are many places where Unicode (in some
1252encoding or another) could be given as arguments or received as
1253results, or both, but it is not.
1254
e1b711da
KW
1255The following are such interfaces. Also, see L</The "Unicode Bug">.
1256For all of these interfaces Perl
6cd4dd6c
JH
1257currently (as of 5.8.3) simply assumes byte strings both as arguments
1258and results, or UTF-8 strings if the C<encoding> pragma has been used.
1aad1664
JH
1259
1260One reason why Perl does not attempt to resolve the role of Unicode in
e1b711da 1261these cases is that the answers are highly dependent on the operating
1aad1664
JH
1262system and the file system(s). For example, whether filenames can be
1263in Unicode, and in exactly what kind of encoding, is not exactly a
1264portable concept. Similarly for the qx and system: how well will the
1265'command line interface' (and which of them?) handle Unicode?
1266
1267=over 4
1268
557a2462
RB
1269=item *
1270
51f494cc 1271chdir, chmod, chown, chroot, exec, link, lstat, mkdir,
1e8e8236 1272rename, rmdir, stat, symlink, truncate, unlink, utime, -X
557a2462
RB
1273
1274=item *
1275
1276%ENV
1277
1278=item *
1279
1280glob (aka the <*>)
1281
1282=item *
1aad1664 1283
557a2462 1284open, opendir, sysopen
1aad1664 1285
557a2462 1286=item *
1aad1664 1287
557a2462 1288qx (aka the backtick operator), system
1aad1664 1289
557a2462 1290=item *
1aad1664 1291
557a2462 1292readdir, readlink
1aad1664
JH
1293
1294=back
1295
e1b711da
KW
1296=head2 The "Unicode Bug"
1297
1298The term, the "Unicode bug" has been applied to an inconsistency with the
1299Unicode characters whose code points are in the Latin-1 Supplement block, that
1300is, between 128 and 255. Without a locale specified, unlike all other
1301characters or code points, these characters have very different semantics in
1302byte semantics versus character semantics.
1303
1304In character semantics they are interpreted as Unicode code points, which means
1305they have the same semantics as Latin-1 (ISO-8859-1).
1306
1307In byte semantics, they are considered to be unassigned characters, meaning
1308that the only semantics they have is their ordinal numbers, and that they are
1309not members of various character classes. None are considered to match C<\w>
1310for example, but all match C<\W>. (On EBCDIC platforms, the behavior may
1311be different from this, depending on the underlying C language library
1312functions.)
1313
1314The behavior is known to have effects on these areas:
1315
1316=over 4
1317
1318=item *
1319
1320Changing the case of a scalar, that is, using C<uc()>, C<ucfirst()>, C<lc()>,
1321and C<lcfirst()>, or C<\L>, C<\U>, C<\u> and C<\l> in regular expression
1322substitutions.
1323
1324=item *
1325
1326Using caseless (C</i>) regular expression matching
1327
1328=item *
1329
1330Matching a number of properties in regular expressions, such as C<\w>
1331
1332=item *
1333
1334User-defined case change mappings. You can create a C<ToUpper()> function, for
1335example, which overrides Perl's built-in case mappings. The scalar must be
1336encoded in utf8 for your function to actually be invoked.
1337
1338=back
1339
1340This behavior can lead to unexpected results in which a string's semantics
1341suddenly change if a code point above 255 is appended to or removed from it,
1342which changes the string's semantics from byte to character or vice versa. As
1343an example, consider the following program and its output:
1344
1345 $ perl -le'
1346 $s1 = "\xC2";
1347 $s2 = "\x{2660}";
1348 for ($s1, $s2, $s1.$s2) {
1349 print /\w/ || 0;
1350 }
1351 '
1352 0
1353 0
1354 1
1355
9f815e24 1356If there's no C<\w> in C<s1> or in C<s2>, why does their concatenation have one?
e1b711da
KW
1357
1358This anomaly stems from Perl's attempt to not disturb older programs that
1359didn't use Unicode, and hence had no semantics for characters outside of the
1360ASCII range (except in a locale), along with Perl's desire to add Unicode
1361support seamlessly. The result wasn't seamless: these characters were
1362orphaned.
1363
1364Work is being done to correct this, but only some of it was complete in time
1365for the 5.12 release. What has been finished is the important part of the case
1366changing component. Due to concerns, and some evidence, that older code might
1367have come to rely on the existing behavior, the new behavior must be explicitly
1368enabled by the feature C<unicode_strings> in the L<feature> pragma, even though
1369no new syntax is involved.
1370
1371See L<perlfunc/lc> for details on how this pragma works in combination with
1372various others for casing. Even though the pragma only affects casing
1373operations in the 5.12 release, it is planned to have it affect all the
1374problematic behaviors in later releases: you can't have one without them all.
1375
1376In the meantime, a workaround is to always call utf8::upgrade($string), or to
1377use the standard modules L<Encode> or L<charnames>.
1378
1aad1664
JH
1379=head2 Forcing Unicode in Perl (Or Unforcing Unicode in Perl)
1380
e1b711da
KW
1381Sometimes (see L</"When Unicode Does Not Happen"> or L</The "Unicode Bug">)
1382there are situations where you simply need to force a byte
2bbc8d55
SP
1383string into UTF-8, or vice versa. The low-level calls
1384utf8::upgrade($bytestring) and utf8::downgrade($utf8string[, FAIL_OK]) are
1aad1664
JH
1385the answers.
1386
2bbc8d55
SP
1387Note that utf8::downgrade() can fail if the string contains characters
1388that don't fit into a byte.
1aad1664 1389
e1b711da
KW
1390Calling either function on a string that already is in the desired state is a
1391no-op.
1392
95a1a48b
JH
1393=head2 Using Unicode in XS
1394
3a2263fe
RGS
1395If you want to handle Perl Unicode in XS extensions, you may find the
1396following C APIs useful. See also L<perlguts/"Unicode Support"> for an
1397explanation about Unicode at the XS level, and L<perlapi> for the API
1398details.
95a1a48b
JH
1399
1400=over 4
1401
1402=item *
1403
1bfb14c4 1404C<DO_UTF8(sv)> returns true if the C<UTF8> flag is on and the bytes
2bbc8d55 1405pragma is not in effect. C<SvUTF8(sv)> returns true if the C<UTF8>
1bfb14c4
JH
1406flag is on; the bytes pragma is ignored. The C<UTF8> flag being on
1407does B<not> mean that there are any characters of code points greater
1408than 255 (or 127) in the scalar or that there are even any characters
1409in the scalar. What the C<UTF8> flag means is that the sequence of
1410octets in the representation of the scalar is the sequence of UTF-8
1411encoded code points of the characters of a string. The C<UTF8> flag
1412being off means that each octet in this representation encodes a
1413single character with code point 0..255 within the string. Perl's
1414Unicode model is not to use UTF-8 until it is absolutely necessary.
95a1a48b
JH
1415
1416=item *
1417
2bbc8d55 1418C<uvchr_to_utf8(buf, chr)> writes a Unicode character code point into
1bfb14c4 1419a buffer encoding the code point as UTF-8, and returns a pointer
2bbc8d55 1420pointing after the UTF-8 bytes. It works appropriately on EBCDIC machines.
95a1a48b
JH
1421
1422=item *
1423
2bbc8d55 1424C<utf8_to_uvchr(buf, lenp)> reads UTF-8 encoded bytes from a buffer and
376d9008 1425returns the Unicode character code point and, optionally, the length of
2bbc8d55 1426the UTF-8 byte sequence. It works appropriately on EBCDIC machines.
95a1a48b
JH
1427
1428=item *
1429
376d9008
JB
1430C<utf8_length(start, end)> returns the length of the UTF-8 encoded buffer
1431in characters. C<sv_len_utf8(sv)> returns the length of the UTF-8 encoded
95a1a48b
JH
1432scalar.
1433
1434=item *
1435
376d9008
JB
1436C<sv_utf8_upgrade(sv)> converts the string of the scalar to its UTF-8
1437encoded form. C<sv_utf8_downgrade(sv)> does the opposite, if
1438possible. C<sv_utf8_encode(sv)> is like sv_utf8_upgrade except that
1439it does not set the C<UTF8> flag. C<sv_utf8_decode()> does the
1440opposite of C<sv_utf8_encode()>. Note that none of these are to be
1441used as general-purpose encoding or decoding interfaces: C<use Encode>
1442for that. C<sv_utf8_upgrade()> is affected by the encoding pragma
1443but C<sv_utf8_downgrade()> is not (since the encoding pragma is
1444designed to be a one-way street).
95a1a48b
JH
1445
1446=item *
1447
376d9008 1448C<is_utf8_char(s)> returns true if the pointer points to a valid UTF-8
90f968e0 1449character.
95a1a48b
JH
1450
1451=item *
1452
376d9008 1453C<is_utf8_string(buf, len)> returns true if C<len> bytes of the buffer
95a1a48b
JH
1454are valid UTF-8.
1455
1456=item *
1457
376d9008
JB
1458C<UTF8SKIP(buf)> will return the number of bytes in the UTF-8 encoded
1459character in the buffer. C<UNISKIP(chr)> will return the number of bytes
1460required to UTF-8-encode the Unicode character code point. C<UTF8SKIP()>
90f968e0 1461is useful for example for iterating over the characters of a UTF-8
376d9008 1462encoded buffer; C<UNISKIP()> is useful, for example, in computing
90f968e0 1463the size required for a UTF-8 encoded buffer.
95a1a48b
JH
1464
1465=item *
1466
376d9008 1467C<utf8_distance(a, b)> will tell the distance in characters between the
95a1a48b
JH
1468two pointers pointing to the same UTF-8 encoded buffer.
1469
1470=item *
1471
2bbc8d55 1472C<utf8_hop(s, off)> will return a pointer to a UTF-8 encoded buffer
376d9008
JB
1473that is C<off> (positive or negative) Unicode characters displaced
1474from the UTF-8 buffer C<s>. Be careful not to overstep the buffer:
1475C<utf8_hop()> will merrily run off the end or the beginning of the
1476buffer if told to do so.
95a1a48b 1477
d2cc3551
JH
1478=item *
1479
376d9008
JB
1480C<pv_uni_display(dsv, spv, len, pvlim, flags)> and
1481C<sv_uni_display(dsv, ssv, pvlim, flags)> are useful for debugging the
1482output of Unicode strings and scalars. By default they are useful
1483only for debugging--they display B<all> characters as hexadecimal code
1bfb14c4
JH
1484points--but with the flags C<UNI_DISPLAY_ISPRINT>,
1485C<UNI_DISPLAY_BACKSLASH>, and C<UNI_DISPLAY_QQ> you can make the
1486output more readable.
d2cc3551
JH
1487
1488=item *
1489
2bbc8d55 1490C<ibcmp_utf8(s1, pe1, l1, u1, s2, pe2, l2, u2)> can be used to
376d9008
JB
1491compare two strings case-insensitively in Unicode. For case-sensitive
1492comparisons you can just use C<memEQ()> and C<memNE()> as usual.
d2cc3551 1493
c349b1b9
JH
1494=back
1495
95a1a48b
JH
1496For more information, see L<perlapi>, and F<utf8.c> and F<utf8.h>
1497in the Perl source code distribution.
1498
e1b711da
KW
1499=head2 Hacking Perl to work on earlier Unicode versions (for very serious hackers only)
1500
1501Perl by default comes with the latest supported Unicode version built in, but
1502you can change to use any earlier one.
1503
1504Download the files in the version of Unicode that you want from the Unicode web
1505site L<http://www.unicode.org>). These should replace the existing files in
1506C<\$Config{privlib}>/F<unicore>. (C<\%Config> is available from the Config
1507module.) Follow the instructions in F<README.perl> in that directory to change
1508some of their names, and then run F<make>.
1509
1510It is even possible to download them to a different directory, and then change
1511F<utf8_heavy.pl> in the directory C<\$Config{privlib}> to point to the new
1512directory, or maybe make a copy of that directory before making the change, and
1513using C<@INC> or the C<-I> run-time flag to switch between versions at will
1514(but because of caching, not in the middle of a process), but all this is
1515beyond the scope of these instructions.
1516
c29a771d
JH
1517=head1 BUGS
1518
376d9008 1519=head2 Interaction with Locales
7eabb34d 1520
376d9008
JB
1521Use of locales with Unicode data may lead to odd results. Currently,
1522Perl attempts to attach 8-bit locale info to characters in the range
15230..255, but this technique is demonstrably incorrect for locales that
1524use characters above that range when mapped into Unicode. Perl's
1525Unicode support will also tend to run slower. Use of locales with
1526Unicode is discouraged.
c29a771d 1527
9f815e24 1528=head2 Problems with characters in the Latin-1 Supplement range
2bbc8d55 1529
e1b711da
KW
1530See L</The "Unicode Bug">
1531
1532=head2 Problems with case-insensitive regular expression matching
1533
1534There are problems with case-insensitive matches, including those involving
1535character classes (enclosed in [square brackets]), characters whose fold
9f815e24
KW
1536is to multiple characters (such as the single character LATIN SMALL LIGATURE
1537FFL matches case-insensitively with the 3-character string C<ffl>), and
1538characters in the Latin-1 Supplement.
2bbc8d55 1539
376d9008 1540=head2 Interaction with Extensions
7eabb34d 1541
376d9008 1542When Perl exchanges data with an extension, the extension should be
2575c402 1543able to understand the UTF8 flag and act accordingly. If the
376d9008
JB
1544extension doesn't know about the flag, it's likely that the extension
1545will return incorrectly-flagged data.
7eabb34d
A
1546
1547So if you're working with Unicode data, consult the documentation of
1548every module you're using if there are any issues with Unicode data
1549exchange. If the documentation does not talk about Unicode at all,
a73d23f6 1550suspect the worst and probably look at the source to learn how the
376d9008 1551module is implemented. Modules written completely in Perl shouldn't
a73d23f6
RGS
1552cause problems. Modules that directly or indirectly access code written
1553in other programming languages are at risk.
7eabb34d 1554
376d9008 1555For affected functions, the simple strategy to avoid data corruption is
7eabb34d 1556to always make the encoding of the exchanged data explicit. Choose an
376d9008 1557encoding that you know the extension can handle. Convert arguments passed
7eabb34d
A
1558to the extensions to that encoding and convert results back from that
1559encoding. Write wrapper functions that do the conversions for you, so
1560you can later change the functions when the extension catches up.
1561
376d9008 1562To provide an example, let's say the popular Foo::Bar::escape_html
7eabb34d
A
1563function doesn't deal with Unicode data yet. The wrapper function
1564would convert the argument to raw UTF-8 and convert the result back to
376d9008 1565Perl's internal representation like so:
7eabb34d
A
1566
1567 sub my_escape_html ($) {
1568 my($what) = shift;
1569 return unless defined $what;
1570 Encode::decode_utf8(Foo::Bar::escape_html(Encode::encode_utf8($what)));
1571 }
1572
1573Sometimes, when the extension does not convert data but just stores
1574and retrieves them, you will be in a position to use the otherwise
1575dangerous Encode::_utf8_on() function. Let's say the popular
66b79f27 1576C<Foo::Bar> extension, written in C, provides a C<param> method that
7eabb34d
A
1577lets you store and retrieve data according to these prototypes:
1578
1579 $self->param($name, $value); # set a scalar
1580 $value = $self->param($name); # retrieve a scalar
1581
1582If it does not yet provide support for any encoding, one could write a
1583derived class with such a C<param> method:
1584
1585 sub param {
1586 my($self,$name,$value) = @_;
1587 utf8::upgrade($name); # make sure it is UTF-8 encoded
af55fc6a 1588 if (defined $value) {
7eabb34d
A
1589 utf8::upgrade($value); # make sure it is UTF-8 encoded
1590 return $self->SUPER::param($name,$value);
1591 } else {
1592 my $ret = $self->SUPER::param($name);
1593 Encode::_utf8_on($ret); # we know, it is UTF-8 encoded
1594 return $ret;
1595 }
1596 }
1597
a73d23f6
RGS
1598Some extensions provide filters on data entry/exit points, such as
1599DB_File::filter_store_key and family. Look out for such filters in
66b79f27 1600the documentation of your extensions, they can make the transition to
7eabb34d
A
1601Unicode data much easier.
1602
376d9008 1603=head2 Speed
7eabb34d 1604
c29a771d 1605Some functions are slower when working on UTF-8 encoded strings than
574c8022 1606on byte encoded strings. All functions that need to hop over
7c17141f
JH
1607characters such as length(), substr() or index(), or matching regular
1608expressions can work B<much> faster when the underlying data are
1609byte-encoded.
1610
1611In Perl 5.8.0 the slowness was often quite spectacular; in Perl 5.8.1
1612a caching scheme was introduced which will hopefully make the slowness
a104b433
JH
1613somewhat less spectacular, at least for some operations. In general,
1614operations with UTF-8 encoded strings are still slower. As an example,
1615the Unicode properties (character classes) like C<\p{Nd}> are known to
1616be quite a bit slower (5-20 times) than their simpler counterparts
1617like C<\d> (then again, there 268 Unicode characters matching C<Nd>
1618compared with the 10 ASCII characters matching C<d>).
666f95b9 1619
e1b711da
KW
1620=head2 Problems on EBCDIC platforms
1621
1622There are a number of known problems with Perl on EBCDIC platforms. If you
1623want to use Perl there, send email to perlbug@perl.org.
fe749c9a
KW
1624
1625In earlier versions, when byte and character data were concatenated,
1626the new string was sometimes created by
1627decoding the byte strings as I<ISO 8859-1 (Latin-1)>, even if the
1628old Unicode string used EBCDIC.
1629
1630If you find any of these, please report them as bugs.
1631
c8d992ba
A
1632=head2 Porting code from perl-5.6.X
1633
1634Perl 5.8 has a different Unicode model from 5.6. In 5.6 the programmer
1635was required to use the C<utf8> pragma to declare that a given scope
1636expected to deal with Unicode data and had to make sure that only
1637Unicode data were reaching that scope. If you have code that is
1638working with 5.6, you will need some of the following adjustments to
1639your code. The examples are written such that the code will continue
1640to work under 5.6, so you should be safe to try them out.
1641
1642=over 4
1643
1644=item *
1645
1646A filehandle that should read or write UTF-8
1647
1648 if ($] > 5.007) {
740d4bb2 1649 binmode $fh, ":encoding(utf8)";
c8d992ba
A
1650 }
1651
1652=item *
1653
1654A scalar that is going to be passed to some extension
1655
1656Be it Compress::Zlib, Apache::Request or any extension that has no
1657mention of Unicode in the manpage, you need to make sure that the
2575c402 1658UTF8 flag is stripped off. Note that at the time of this writing
c8d992ba
A
1659(October 2002) the mentioned modules are not UTF-8-aware. Please
1660check the documentation to verify if this is still true.
1661
1662 if ($] > 5.007) {
1663 require Encode;
1664 $val = Encode::encode_utf8($val); # make octets
1665 }
1666
1667=item *
1668
1669A scalar we got back from an extension
1670
1671If you believe the scalar comes back as UTF-8, you will most likely
2575c402 1672want the UTF8 flag restored:
c8d992ba
A
1673
1674 if ($] > 5.007) {
1675 require Encode;
1676 $val = Encode::decode_utf8($val);
1677 }
1678
1679=item *
1680
1681Same thing, if you are really sure it is UTF-8
1682
1683 if ($] > 5.007) {
1684 require Encode;
1685 Encode::_utf8_on($val);
1686 }
1687
1688=item *
1689
1690A wrapper for fetchrow_array and fetchrow_hashref
1691
1692When the database contains only UTF-8, a wrapper function or method is
1693a convenient way to replace all your fetchrow_array and
1694fetchrow_hashref calls. A wrapper function will also make it easier to
1695adapt to future enhancements in your database driver. Note that at the
1696time of this writing (October 2002), the DBI has no standardized way
1697to deal with UTF-8 data. Please check the documentation to verify if
1698that is still true.
1699
1700 sub fetchrow {
1701 my($self, $sth, $what) = @_; # $what is one of fetchrow_{array,hashref}
1702 if ($] < 5.007) {
1703 return $sth->$what;
1704 } else {
1705 require Encode;
1706 if (wantarray) {
1707 my @arr = $sth->$what;
1708 for (@arr) {
1709 defined && /[^\000-\177]/ && Encode::_utf8_on($_);
1710 }
1711 return @arr;
1712 } else {
1713 my $ret = $sth->$what;
1714 if (ref $ret) {
1715 for my $k (keys %$ret) {
1716 defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret->{$k};
1717 }
1718 return $ret;
1719 } else {
1720 defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret;
1721 return $ret;
1722 }
1723 }
1724 }
1725 }
1726
1727
1728=item *
1729
1730A large scalar that you know can only contain ASCII
1731
1732Scalars that contain only ASCII and are marked as UTF-8 are sometimes
1733a drag to your program. If you recognize such a situation, just remove
2575c402 1734the UTF8 flag:
c8d992ba
A
1735
1736 utf8::downgrade($val) if $] > 5.007;
1737
1738=back
1739
393fec97
GS
1740=head1 SEE ALSO
1741
51f494cc 1742L<perlunitut>, L<perluniintro>, L<perluniprops>, L<Encode>, L<open>, L<utf8>, L<bytes>,
a05d7ebb 1743L<perlretut>, L<perlvar/"${^UNICODE}">
51f494cc 1744L<http://www.unicode.org/reports/tr44>).
393fec97
GS
1745
1746=cut