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393fec97 GS |
1 | =head1 NAME |
2 | ||
3 | perlunicode - Unicode support in Perl | |
4 | ||
5 | =head1 DESCRIPTION | |
6 | ||
0a1f2d14 | 7 | =head2 Important Caveats |
21bad921 | 8 | |
376d9008 | 9 | Unicode support is an extensive requirement. While Perl does not |
c349b1b9 JH |
10 | implement the Unicode standard or the accompanying technical reports |
11 | from cover to cover, Perl does support many Unicode features. | |
21bad921 | 12 | |
2575c402 | 13 | People who want to learn to use Unicode in Perl, should probably read |
e4911a48 RS |
14 | L<the Perl Unicode tutorial, perlunitut|perlunitut>, before reading |
15 | this reference document. | |
2575c402 | 16 | |
13a2d996 | 17 | =over 4 |
21bad921 | 18 | |
fae2c0fb | 19 | =item Input and Output Layers |
21bad921 | 20 | |
376d9008 | 21 | Perl knows when a filehandle uses Perl's internal Unicode encodings |
1bfb14c4 JH |
22 | (UTF-8, or UTF-EBCDIC if in EBCDIC) if the filehandle is opened with |
23 | the ":utf8" layer. Other encodings can be converted to Perl's | |
24 | encoding on input or from Perl's encoding on output by use of the | |
25 | ":encoding(...)" layer. See L<open>. | |
c349b1b9 | 26 | |
2575c402 | 27 | To indicate that Perl source itself is in UTF-8, use C<use utf8;>. |
21bad921 GS |
28 | |
29 | =item Regular Expressions | |
30 | ||
c349b1b9 | 31 | The regular expression compiler produces polymorphic opcodes. That is, |
376d9008 | 32 | the pattern adapts to the data and automatically switches to the Unicode |
2575c402 | 33 | character scheme when presented with data that is internally encoded in |
ac036724 | 34 | UTF-8, or instead uses a traditional byte scheme when presented with |
2575c402 | 35 | byte data. |
21bad921 | 36 | |
ad0029c4 | 37 | =item C<use utf8> still needed to enable UTF-8/UTF-EBCDIC in scripts |
21bad921 | 38 | |
376d9008 JB |
39 | As a compatibility measure, the C<use utf8> pragma must be explicitly |
40 | included to enable recognition of UTF-8 in the Perl scripts themselves | |
1bfb14c4 JH |
41 | (in string or regular expression literals, or in identifier names) on |
42 | ASCII-based machines or to recognize UTF-EBCDIC on EBCDIC-based | |
376d9008 | 43 | machines. B<These are the only times when an explicit C<use utf8> |
8f8cf39c | 44 | is needed.> See L<utf8>. |
21bad921 | 45 | |
7aa207d6 JH |
46 | =item BOM-marked scripts and UTF-16 scripts autodetected |
47 | ||
48 | If a Perl script begins marked with the Unicode BOM (UTF-16LE, UTF16-BE, | |
49 | or UTF-8), or if the script looks like non-BOM-marked UTF-16 of either | |
50 | endianness, Perl will correctly read in the script as Unicode. | |
51 | (BOMless UTF-8 cannot be effectively recognized or differentiated from | |
52 | ISO 8859-1 or other eight-bit encodings.) | |
53 | ||
990e18f7 AT |
54 | =item C<use encoding> needed to upgrade non-Latin-1 byte strings |
55 | ||
38a44b82 | 56 | By default, there is a fundamental asymmetry in Perl's Unicode model: |
990e18f7 AT |
57 | implicit upgrading from byte strings to Unicode strings assumes that |
58 | they were encoded in I<ISO 8859-1 (Latin-1)>, but Unicode strings are | |
59 | downgraded with UTF-8 encoding. This happens because the first 256 | |
51f494cc | 60 | codepoints in Unicode happens to agree with Latin-1. |
990e18f7 | 61 | |
990e18f7 AT |
62 | See L</"Byte and Character Semantics"> for more details. |
63 | ||
21bad921 GS |
64 | =back |
65 | ||
376d9008 | 66 | =head2 Byte and Character Semantics |
393fec97 | 67 | |
376d9008 | 68 | Beginning with version 5.6, Perl uses logically-wide characters to |
3e4dbfed | 69 | represent strings internally. |
393fec97 | 70 | |
376d9008 JB |
71 | In future, Perl-level operations will be expected to work with |
72 | characters rather than bytes. | |
393fec97 | 73 | |
376d9008 | 74 | However, as an interim compatibility measure, Perl aims to |
75daf61c JH |
75 | provide a safe migration path from byte semantics to character |
76 | semantics for programs. For operations where Perl can unambiguously | |
376d9008 | 77 | decide that the input data are characters, Perl switches to |
75daf61c JH |
78 | character semantics. For operations where this determination cannot |
79 | be made without additional information from the user, Perl decides in | |
376d9008 | 80 | favor of compatibility and chooses to use byte semantics. |
8cbd9a7a | 81 | |
51f494cc | 82 | Under byte semantics, when C<use locale> is in effect, Perl uses the |
e1b711da KW |
83 | semantics associated with the current locale. Absent a C<use locale>, and |
84 | absent a C<use feature 'unicode_strings'> pragma, Perl currently uses US-ASCII | |
85 | (or Basic Latin in Unicode terminology) byte semantics, meaning that characters | |
86 | whose ordinal numbers are in the range 128 - 255 are undefined except for their | |
87 | ordinal numbers. This means that none have case (upper and lower), nor are any | |
88 | a member of character classes, like C<[:alpha:]> or C<\w>. (But all do belong | |
89 | to the C<\W> class or the Perl regular expression extension C<[:^alpha:]>.) | |
2bbc8d55 | 90 | |
8cbd9a7a | 91 | This behavior preserves compatibility with earlier versions of Perl, |
376d9008 | 92 | which allowed byte semantics in Perl operations only if |
e1b711da | 93 | none of the program's inputs were marked as being a source of Unicode |
8cbd9a7a GS |
94 | character data. Such data may come from filehandles, from calls to |
95 | external programs, from information provided by the system (such as %ENV), | |
21bad921 | 96 | or from literals and constants in the source text. |
8cbd9a7a | 97 | |
376d9008 JB |
98 | The C<bytes> pragma will always, regardless of platform, force byte |
99 | semantics in a particular lexical scope. See L<bytes>. | |
8cbd9a7a | 100 | |
e1b711da KW |
101 | The C<use feature 'unicode_strings'> pragma is intended to always, regardless |
102 | of platform, force Unicode semantics in a particular lexical scope. In | |
103 | release 5.12, it is partially implemented, applying only to case changes. | |
104 | See L</The "Unicode Bug"> below. | |
105 | ||
8cbd9a7a | 106 | The C<utf8> pragma is primarily a compatibility device that enables |
75daf61c | 107 | recognition of UTF-(8|EBCDIC) in literals encountered by the parser. |
376d9008 JB |
108 | Note that this pragma is only required while Perl defaults to byte |
109 | semantics; when character semantics become the default, this pragma | |
110 | may become a no-op. See L<utf8>. | |
111 | ||
112 | Unless explicitly stated, Perl operators use character semantics | |
113 | for Unicode data and byte semantics for non-Unicode data. | |
114 | The decision to use character semantics is made transparently. If | |
115 | input data comes from a Unicode source--for example, if a character | |
fae2c0fb | 116 | encoding layer is added to a filehandle or a literal Unicode |
376d9008 JB |
117 | string constant appears in a program--character semantics apply. |
118 | Otherwise, byte semantics are in effect. The C<bytes> pragma should | |
e1b711da KW |
119 | be 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 | |
121 | 5.12 it isn't fully implemented). | |
376d9008 JB |
122 | |
123 | If strings operating under byte semantics and strings with Unicode | |
51f494cc | 124 | character data are concatenated, the new string will have |
42bde815 | 125 | character semantics. This can cause surprises: See L</BUGS>, below |
7dedd01f | 126 | |
feda178f | 127 | Under character semantics, many operations that formerly operated on |
376d9008 | 128 | bytes now operate on characters. A character in Perl is |
feda178f | 129 | logically just a number ranging from 0 to 2**31 or so. Larger |
376d9008 JB |
130 | characters may encode into longer sequences of bytes internally, but |
131 | this internal detail is mostly hidden for Perl code. | |
132 | See L<perluniintro> for more. | |
393fec97 | 133 | |
376d9008 | 134 | =head2 Effects of Character Semantics |
393fec97 GS |
135 | |
136 | Character semantics have the following effects: | |
137 | ||
138 | =over 4 | |
139 | ||
140 | =item * | |
141 | ||
376d9008 | 142 | Strings--including hash keys--and regular expression patterns may |
574c8022 | 143 | contain characters that have an ordinal value larger than 255. |
393fec97 | 144 | |
2575c402 JW |
145 | If you use a Unicode editor to edit your program, Unicode characters may |
146 | occur 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 | |
2575c402 JW |
149 | Unicode characters can also be added to a string by using the C<\x{...}> |
150 | notation. The Unicode code for the desired character, in hexadecimal, | |
151 | should be placed in the braces. For instance, a smiley face is | |
2bbc8d55 | 152 | C<\x{263A}>. This encoding scheme works for all characters, but |
2575c402 JW |
153 | for characters under 0x100, note that Perl may use an 8 bit encoding |
154 | internally, for optimization and/or backward compatibility. | |
3e4dbfed JF |
155 | |
156 | Additionally, if you | |
574c8022 | 157 | |
3e4dbfed | 158 | use charnames ':full'; |
574c8022 | 159 | |
1bfb14c4 JH |
160 | you can use the C<\N{...}> notation and put the official Unicode |
161 | character name within the braces, such as C<\N{WHITE SMILING FACE}>. | |
376d9008 | 162 | |
393fec97 GS |
163 | =item * |
164 | ||
574c8022 JH |
165 | If an appropriate L<encoding> is specified, identifiers within the |
166 | Perl script may contain Unicode alphanumeric characters, including | |
376d9008 JB |
167 | ideographs. Perl does not currently attempt to canonicalize variable |
168 | names. | |
393fec97 | 169 | |
393fec97 GS |
170 | =item * |
171 | ||
1bfb14c4 | 172 | Regular expressions match characters instead of bytes. "." matches |
2575c402 | 173 | a character instead of a byte. |
393fec97 | 174 | |
393fec97 GS |
175 | =item * |
176 | ||
177 | Character classes in regular expressions match characters instead of | |
376d9008 | 178 | bytes and match against the character properties specified in the |
1bfb14c4 | 179 | Unicode properties database. C<\w> can be used to match a Japanese |
75daf61c | 180 | ideograph, for instance. |
393fec97 | 181 | |
393fec97 GS |
182 | =item * |
183 | ||
eb0cc9e3 | 184 | Named Unicode properties, scripts, and block ranges may be used like |
376d9008 | 185 | character classes via the C<\p{}> "matches property" construct and |
822502e5 | 186 | the C<\P{}> negation, "doesn't match property". |
2575c402 | 187 | See L</"Unicode Character Properties"> for more details. |
822502e5 TS |
188 | |
189 | You can define your own character properties and use them | |
190 | in the regular expression with the C<\p{}> or C<\P{}> construct. | |
822502e5 TS |
191 | See L</"User-Defined Character Properties"> for more details. |
192 | ||
193 | =item * | |
194 | ||
9f815e24 KW |
195 | The special pattern C<\X> matches a logical character, an "extended grapheme |
196 | cluster" in Standardese. In Unicode what appears to the user to be a single | |
51f494cc KW |
197 | character, for example an accented C<G>, may in fact be composed of a sequence |
198 | of characters, in this case a C<G> followed by an accent character. C<\X> | |
199 | will match the entire sequence. | |
822502e5 TS |
200 | |
201 | =item * | |
202 | ||
203 | The C<tr///> operator translates characters instead of bytes. Note | |
204 | that the C<tr///CU> functionality has been removed. For similar | |
205 | functionality see pack('U0', ...) and pack('C0', ...). | |
206 | ||
207 | =item * | |
208 | ||
209 | Case translation operators use the Unicode case translation tables | |
210 | when character input is provided. Note that C<uc()>, or C<\U> in | |
211 | interpolated strings, translates to uppercase, while C<ucfirst>, | |
212 | or C<\u> in interpolated strings, translates to titlecase in languages | |
e1b711da KW |
213 | that make the distinction (which is equivalent to uppercase in languages |
214 | without the distinction). | |
822502e5 TS |
215 | |
216 | =item * | |
217 | ||
218 | Most operators that deal with positions or lengths in a string will | |
219 | automatically switch to using character positions, including | |
220 | C<chop()>, C<chomp()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>, | |
221 | C<sprintf()>, C<write()>, and C<length()>. An operator that | |
51f494cc KW |
222 | specifically does not switch is C<vec()>. Operators that really don't |
223 | care include operators that treat strings as a bucket of bits such as | |
822502e5 TS |
224 | C<sort()>, and operators dealing with filenames. |
225 | ||
226 | =item * | |
227 | ||
51f494cc | 228 | The C<pack()>/C<unpack()> letter C<C> does I<not> change, since it is often |
822502e5 TS |
229 | used for byte-oriented formats. Again, think C<char> in the C language. |
230 | ||
231 | There is a new C<U> specifier that converts between Unicode characters | |
232 | and code points. There is also a C<W> specifier that is the equivalent of | |
233 | C<chr>/C<ord> and properly handles character values even if they are above 255. | |
234 | ||
235 | =item * | |
236 | ||
237 | The C<chr()> and C<ord()> functions work on characters, similar to | |
238 | C<pack("W")> and C<unpack("W")>, I<not> C<pack("C")> and | |
239 | C<unpack("C")>. C<pack("C")> and C<unpack("C")> are methods for | |
240 | emulating byte-oriented C<chr()> and C<ord()> on Unicode strings. | |
241 | While these methods reveal the internal encoding of Unicode strings, | |
242 | that is not something one normally needs to care about at all. | |
243 | ||
244 | =item * | |
245 | ||
246 | The bit string operators, C<& | ^ ~>, can operate on character data. | |
247 | However, for backward compatibility, such as when using bit string | |
248 | operations when characters are all less than 256 in ordinal value, one | |
249 | should not use C<~> (the bit complement) with characters of both | |
250 | values less than 256 and values greater than 256. Most importantly, | |
251 | DeMorgan's laws (C<~($x|$y) eq ~$x&~$y> and C<~($x&$y) eq ~$x|~$y>) | |
252 | will not hold. The reason for this mathematical I<faux pas> is that | |
253 | the complement cannot return B<both> the 8-bit (byte-wide) bit | |
254 | complement B<and> the full character-wide bit complement. | |
255 | ||
256 | =item * | |
257 | ||
e1b711da | 258 | You can define your own mappings to be used in lc(), |
822502e5 | 259 | lcfirst(), uc(), and ucfirst() (or their string-inlined versions). |
822502e5 TS |
260 | See L</"User-Defined Case Mappings"> for more details. |
261 | ||
262 | =back | |
263 | ||
264 | =over 4 | |
265 | ||
266 | =item * | |
267 | ||
268 | And finally, C<scalar reverse()> reverses by character rather than by byte. | |
269 | ||
270 | =back | |
271 | ||
272 | =head2 Unicode Character Properties | |
273 | ||
51f494cc KW |
274 | Most Unicode character properties are accessible by using regular expressions. |
275 | They are used like character classes via the C<\p{}> "matches property" | |
276 | construct and the C<\P{}> negation, "doesn't match property". | |
277 | ||
278 | For instance, C<\p{Uppercase}> matches any character with the Unicode | |
279 | "Uppercase" property, while C<\p{L}> matches any character with a | |
280 | General_Category of "L" (letter) property. Brackets are not | |
281 | required for single letter properties, so C<\p{L}> is equivalent to C<\pL>. | |
282 | ||
e1b711da KW |
283 | More formally, C<\p{Uppercase}> matches any character whose Unicode Uppercase |
284 | property value is True, and C<\P{Uppercase}> matches any character whose | |
285 | Uppercase property value is False, and they could have been written as | |
51f494cc KW |
286 | C<\p{Uppercase=True}> and C<\p{Uppercase=False}>, respectively |
287 | ||
288 | This formality is needed when properties are not binary, that is if they can | |
289 | take on more values than just True and False. For example, the Bidi_Class (see | |
290 | L</"Bidirectional Character Types"> below), can take on a number of different | |
291 | values, such as Left, Right, Whitespace, and others. To match these, one needs | |
e1b711da | 292 | to specify the property name (Bidi_Class), and the value being matched against |
9f815e24 KW |
293 | (Left, Right, I<etc.>). This is done, as in the examples above, by having the |
294 | two components separated by an equal sign (or interchangeably, a colon), like | |
51f494cc KW |
295 | C<\p{Bidi_Class: Left}>. |
296 | ||
297 | All Unicode-defined character properties may be written in these compound forms | |
298 | of C<\p{property=value}> or C<\p{property:value}>, but Perl provides some | |
299 | additional properties that are written only in the single form, as well as | |
300 | single-form short-cuts for all binary properties and certain others described | |
301 | below, in which you may omit the property name and the equals or colon | |
302 | separator. | |
303 | ||
304 | Most Unicode character properties have at least two synonyms (or aliases if you | |
305 | prefer), a short one that is easier to type, and a longer one which is more | |
306 | descriptive and hence it is easier to understand what it means. Thus the "L" | |
307 | and "Letter" above are equivalent and can be used interchangeably. Likewise, | |
308 | "Upper" is a synonym for "Uppercase", and we could have written | |
309 | C<\p{Uppercase}> equivalently as C<\p{Upper}>. Also, there are typically | |
310 | various 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 | 313 | not mean the same thing as the same short form for another. Thus, for the |
51f494cc KW |
314 | General_Category property, "L" means "Letter", but for the Bidi_Class property, |
315 | "L" means "Left". A complete list of properties and synonyms is in | |
316 | L<perluniprops>. | |
317 | ||
318 | Upper/lower case differences in the property names and values are irrelevant, | |
319 | thus C<\p{Upper}> means the same thing as C<\p{upper}> or even C<\p{UpPeR}>. | |
320 | Similarly, you can add or subtract underscores anywhere in the middle of a | |
321 | word, so that these are also equivalent to C<\p{U_p_p_e_r}>. And white space | |
322 | is irrelevant adjacent to non-word characters, such as the braces and the equals | |
323 | or colon separators so C<\p{ Upper }> and C<\p{ Upper_case : Y }> are | |
324 | equivalent to these as well. In fact, in most cases, white space and even | |
325 | hyphens can be added or deleted anywhere. So even C<\p{ Up-per case = Yes}> is | |
326 | equivalent. All this is called "loose-matching" by Unicode. The few places | |
327 | where stricter matching is employed is in the middle of numbers, and the Perl | |
328 | extension properties that begin or end with an underscore. Stricter matching | |
329 | cares about white space (except adjacent to the non-word characters) and | |
330 | hyphens, and non-interior underscores. | |
4193bef7 | 331 | |
376d9008 JB |
332 | You 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 | 334 | equal to C<\P{Tamil}>. |
4193bef7 | 335 | |
51f494cc | 336 | =head3 B<General_Category> |
14bb0a9a | 337 | |
51f494cc KW |
338 | Every Unicode character is assigned a general category, which is the "most |
339 | usual categorization of a character" (from | |
340 | L<http://www.unicode.org/reports/tr44>). | |
822502e5 | 341 | |
9f815e24 | 342 | The compound way of writing these is like C<\p{General_Category=Number}> |
51f494cc KW |
343 | (short, C<\p{gc:n}>). But Perl furnishes shortcuts in which everything up |
344 | through the equal or colon separator is omitted. So you can instead just write | |
345 | C<\pN>. | |
822502e5 | 346 | |
51f494cc | 347 | Here are the short and long forms of the General Category properties: |
393fec97 | 348 | |
d73e5302 JH |
349 | Short Long |
350 | ||
351 | L Letter | |
51f494cc KW |
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 | |
d73e5302 JH |
358 | |
359 | M Mark | |
51f494cc KW |
360 | Mn Nonspacing_Mark |
361 | Mc Spacing_Mark | |
362 | Me Enclosing_Mark | |
d73e5302 JH |
363 | |
364 | N Number | |
51f494cc KW |
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 |
d73e5302 JH |
379 | |
380 | S Symbol | |
51f494cc KW |
381 | Sm Math_Symbol |
382 | Sc Currency_Symbol | |
383 | Sk Modifier_Symbol | |
384 | So Other_Symbol | |
d73e5302 JH |
385 | |
386 | Z Separator | |
51f494cc KW |
387 | Zs Space_Separator |
388 | Zl Line_Separator | |
389 | Zp Paragraph_Separator | |
d73e5302 JH |
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 | 398 | Single-letter properties match all characters in any of the |
3e4dbfed | 399 | two-letter sub-properties starting with the same letter. |
12ac2576 JP |
400 | C<LC> and C<L&> are special cases, which are aliases for the set of |
401 | C<Ll>, C<Lu>, and C<Lt>. | |
32293815 | 402 | |
eb0cc9e3 | 403 | Because Perl hides the need for the user to understand the internal |
1bfb14c4 JH |
404 | representation of Unicode characters, there is no need to implement |
405 | the somewhat messy concept of surrogates. C<Cs> is therefore not | |
eb0cc9e3 | 406 | supported. |
d73e5302 | 407 | |
51f494cc | 408 | =head3 B<Bidirectional Character Types> |
822502e5 | 409 | |
376d9008 | 410 | Because scripts differ in their directionality--Hebrew is |
12ac2576 | 411 | written right to left, for example--Unicode supplies these properties in |
51f494cc | 412 | the Bidi_Class class: |
32293815 | 413 | |
eb0cc9e3 | 414 | Property Meaning |
92e830a9 | 415 | |
12ac2576 JP |
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 |
12ac2576 JP |
421 | RLE Right-to-Left Embedding |
422 | RLO Right-to-Left Override | |
423 | PDF Pop Directional Format | |
424 | EN European Number | |
51f494cc KW |
425 | ES European Separator |
426 | ET European Terminator | |
12ac2576 | 427 | AN Arabic Number |
51f494cc | 428 | CS Common Separator |
12ac2576 JP |
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 | ||
51f494cc KW |
436 | This property is always written in the compound form. |
437 | For example, C<\p{Bidi_Class:R}> matches characters that are normally | |
eb0cc9e3 JH |
438 | written right to left. |
439 | ||
51f494cc KW |
440 | =head3 B<Scripts> |
441 | ||
e1b711da KW |
442 | The 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 | |
444 | written in Cyrllic, and Greek is written in, well, Greek; Japanese mainly in | |
445 | Hiragana or Katakana. There are many more. | |
51f494cc KW |
446 | |
447 | The Unicode Script property gives what script a given character is in, | |
448 | and can be matched with the compound form like C<\p{Script=Hebrew}> (short: | |
449 | C<\p{sc=hebr}>). Perl furnishes shortcuts for all script names. You can omit | |
450 | everything up through the equals (or colon), and simply write C<\p{Latin}> or | |
451 | C<\P{Cyrillic}>. | |
452 | ||
453 | A complete list of scripts and their shortcuts is in L<perluniprops>. | |
454 | ||
51f494cc | 455 | =head3 B<Use of "Is" Prefix> |
822502e5 | 456 | |
1bfb14c4 | 457 | For backward compatibility (with Perl 5.6), all properties mentioned |
51f494cc KW |
458 | so far may have C<Is> or C<Is_> prepended to their name, so C<\P{Is_Lu}>, for |
459 | example, is equal to C<\P{Lu}>, and C<\p{IsScript:Arabic}> is equal to | |
460 | C<\p{Arabic}>. | |
eb0cc9e3 | 461 | |
51f494cc | 462 | =head3 B<Blocks> |
2796c109 | 463 | |
1bfb14c4 JH |
464 | In addition to B<scripts>, Unicode also defines B<blocks> of |
465 | characters. The difference between scripts and blocks is that the | |
466 | concept of scripts is closer to natural languages, while the concept | |
51f494cc | 467 | of blocks is more of an artificial grouping based on groups of Unicode |
9f815e24 | 468 | characters with consecutive ordinal values. For example, the "Basic Latin" |
51f494cc | 469 | block is all characters whose ordinals are between 0 and 127, inclusive, in |
9f815e24 KW |
470 | other words, the ASCII characters. The "Latin" script contains some letters |
471 | from 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 | |
51f494cc KW |
473 | those blocks. It does not, for example, contain digits, because digits are |
474 | shared across many scripts. Digits and similar groups, like punctuation, are in | |
475 | the script called C<Common>. There is also a script called C<Inherited> for | |
476 | characters that modify other characters, and inherit the script value of the | |
477 | controlling character. | |
478 | ||
479 | For more about scripts versus blocks, see UAX#24 "Unicode Script Property": | |
480 | L<http://www.unicode.org/reports/tr24> | |
481 | ||
482 | The Script property is likely to be the one you want to use when processing | |
483 | natural language; the Block property may be useful in working with the nuts and | |
484 | bolts of Unicode. | |
485 | ||
486 | Block names are matched in the compound form, like C<\p{Block: Arrows}> or | |
487 | C<\p{Blk=Hebrew}>. Unlike most other properties only a few block names have a | |
488 | Unicode-defined short name. But Perl does provide a (slight) shortcut: You | |
489 | can say, for example C<\p{In_Arrows}> or C<\p{In_Hebrew}>. For backwards | |
490 | compatibility, the C<In> prefix may be omitted if there is no naming conflict | |
491 | with a script or any other property, and you can even use an C<Is> prefix | |
492 | instead in those cases. But it is not a good idea to do this, for a couple | |
493 | reasons: | |
494 | ||
495 | =over 4 | |
496 | ||
497 | =item 1 | |
498 | ||
499 | It is confusing. There are many naming conflicts, and you may forget some. | |
9f815e24 | 500 | For example, C<\p{Hebrew}> means the I<script> Hebrew, and NOT the I<block> |
51f494cc KW |
501 | Hebrew. But would you remember that 6 months from now? |
502 | ||
503 | =item 2 | |
504 | ||
505 | It is unstable. A new version of Unicode may pre-empt the current meaning by | |
506 | creating a property with the same name. There was a time in very early Unicode | |
9f815e24 | 507 | releases when C<\p{Hebrew}> would have matched the I<block> Hebrew; now it |
51f494cc | 508 | doesn't. |
32293815 | 509 | |
393fec97 GS |
510 | =back |
511 | ||
51f494cc KW |
512 | Some people just prefer to always use C<\p{Block: foo}> and C<\p{Script: bar}> |
513 | instead of the shortcuts, for clarity, and because they can't remember the | |
514 | difference between 'In' and 'Is' anyway (or aren't confident that those who | |
515 | eventually will read their code will know). | |
516 | ||
517 | A complete list of blocks and their shortcuts is in L<perluniprops>. | |
518 | ||
9f815e24 KW |
519 | =head3 B<Other Properties> |
520 | ||
521 | There are many more properties than the very basic ones described here. | |
522 | A complete list is in L<perluniprops>. | |
523 | ||
524 | Unicode defines all its properties in the compound form, so all single-form | |
525 | properties are Perl extensions. A number of these are just synonyms for the | |
526 | Unicode ones, but some are genunine extensions, including a couple that are in | |
527 | the compound form. And quite a few of these are actually recommended by Unicode | |
528 | (in L<http://www.unicode.org/reports/tr18>). | |
529 | ||
530 | This section gives some details on all the extensions that aren't synonyms for | |
531 | compound-form Unicode properties (for those, you'll have to refer to the | |
532 | L<Unicode Standard|http://www.unicode.org/reports/tr44>. | |
533 | ||
534 | =over | |
535 | ||
536 | =item B<C<\p{All}>> | |
537 | ||
538 | This matches any of the 1_114_112 Unicode code points. It is a synonym for | |
539 | C<\p{Any}>. | |
540 | ||
541 | =item B<C<\p{Alnum}>> | |
542 | ||
543 | This matches any C<\p{Alphabetic}> or C<\p{Decimal_Number}> character. | |
544 | ||
545 | =item B<C<\p{Any}>> | |
546 | ||
547 | This matches any of the 1_114_112 Unicode code points. It is a synonym for | |
548 | C<\p{All}>. | |
549 | ||
550 | =item B<C<\p{Assigned}>> | |
551 | ||
552 | This matches any assigned code point; that is, any code point whose general | |
553 | category is not Unassigned (or equivalently, not Cn). | |
554 | ||
555 | =item B<C<\p{Blank}>> | |
556 | ||
557 | This is the same as C<\h> and C<\p{HorizSpace}>: A character that changes the | |
558 | spacing horizontally. | |
559 | ||
560 | =item B<C<\p{Decomposition_Type: Non_Canonical}>> (Short: C<\p{Dt=NonCanon}>) | |
561 | ||
562 | Matches a character that has a non-canonical decomposition. | |
563 | ||
564 | To understand the use of this rarely used property=value combination, it is | |
565 | necessary to know some basics about decomposition. | |
566 | Consider a character, say H. It could appear with various marks around it, | |
567 | such as an acute accent, or a circumflex, or various hooks, circles, arrows, | |
568 | I<etc.>, above, below, to one side and/or the other, I<etc.> There are many | |
569 | possibilities among the world's languages. The number of combinations is | |
570 | astronomical, and if there were a character for each combination, it would | |
571 | soon exhaust Unicode's more than a million possible characters. So Unicode | |
572 | took a different approach: there is a character for the base H, and a | |
573 | character for each of the possible marks, and they can be combined variously | |
574 | to get a final logical character. So a logical character--what appears to be a | |
575 | single character--can be a sequence of more than one individual characters. | |
576 | This is called an "extended grapheme cluster". (Perl furnishes the C<\X> | |
577 | construct to match such sequences.) | |
578 | ||
579 | But Unicode's intent is to unify the existing character set standards and | |
580 | practices, and a number of pre-existing standards have single characters that | |
581 | mean the same thing as some of these combinations. An example is ISO-8859-1, | |
582 | which has quite a few of these in the Latin-1 range, an example being "LATIN | |
583 | CAPITAL LETTER E WITH ACUTE". Because this character was in this pre-existing | |
584 | standard, Unicode added it to its repertoire. But this character is considered | |
585 | by 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 | |
589 | the equivalence with the sequence is called canonical equivalence. All | |
590 | pre-composed characters are said to have a decomposition (into the equivalent | |
591 | sequence) and the decomposition type is also called canonical. | |
592 | ||
593 | However, many more characters have a different type of decomposition, a | |
594 | "compatible" or "non-canonical" decomposition. The sequences that form these | |
595 | decompositions are not considered canonically equivalent to the pre-composed | |
596 | character. An example, again in the Latin-1 range, is the "SUPERSCRIPT ONE". | |
597 | It is kind of like a regular digit 1, but not exactly; its decomposition | |
598 | into the digit 1 is called a "compatible" decomposition, specifically a | |
599 | "super" decomposition. There are several such compatibility | |
600 | decompositions (see L<http://www.unicode.org/reports/tr44>), including one | |
601 | called "compat" which means some miscellaneous type of decomposition | |
602 | that doesn't fit into the decomposition categories that Unicode has chosen. | |
603 | ||
604 | Note that most Unicode characters don't have a decomposition, so their | |
605 | decomposition type is "None". | |
606 | ||
607 | Perl has added the C<Non_Canonical> type, for your convenience, to mean any of | |
608 | the compatibility decompositions. | |
609 | ||
610 | =item B<C<\p{Graph}>> | |
611 | ||
612 | Matches any character that is graphic. Theoretically, this means a character | |
613 | that on a printer would cause ink to be used. | |
614 | ||
615 | =item B<C<\p{HorizSpace}>> | |
616 | ||
617 | This is the same as C<\h> and C<\p{Blank}>: A character that changes the | |
618 | spacing horizontally. | |
619 | ||
620 | =item B<C<\p{In=*}>> | |
621 | ||
622 | This is a synonym for C<\p{Present_In=*}> | |
623 | ||
624 | =item B<C<\p{PerlSpace}>> | |
625 | ||
626 | This is the same as C<\s>, restricted to ASCII, namely C<S<[ \f\n\r\t]>>. | |
627 | ||
628 | Mnemonic: Perl's (original) space | |
629 | ||
630 | =item B<C<\p{PerlWord}>> | |
631 | ||
632 | This is the same as C<\w>, restricted to ASCII, namely C<[A-Za-z0-9_]> | |
633 | ||
634 | Mnemonic: Perl's (original) word. | |
635 | ||
636 | =item B<C<\p{PosixAlnum}>> | |
637 | ||
638 | This matches any alphanumeric character in the ASCII range, namely | |
639 | C<[A-Za-z0-9]>. | |
640 | ||
641 | =item B<C<\p{PosixAlpha}>> | |
642 | ||
643 | This matches any alphabetic character in the ASCII range, namely C<[A-Za-z]>. | |
644 | ||
645 | =item B<C<\p{PosixBlank}>> | |
646 | ||
647 | This matches any blank character in the ASCII range, namely C<S<[ \t]>>. | |
648 | ||
649 | =item B<C<\p{PosixCntrl}>> | |
650 | ||
651 | This matches any control character in the ASCII range, namely C<[\x00-\x1F\x7F]> | |
652 | ||
653 | =item B<C<\p{PosixDigit}>> | |
654 | ||
655 | This matches any digit character in the ASCII range, namely C<[0-9]>. | |
656 | ||
657 | =item B<C<\p{PosixGraph}>> | |
658 | ||
659 | This matches any graphical character in the ASCII range, namely C<[\x21-\x7E]>. | |
660 | ||
661 | =item B<C<\p{PosixLower}>> | |
662 | ||
663 | This matches any lowercase character in the ASCII range, namely C<[a-z]>. | |
664 | ||
665 | =item B<C<\p{PosixPrint}>> | |
666 | ||
667 | This matches any printable character in the ASCII range, namely C<[\x20-\x7E]>. | |
668 | These are the graphical characters plus SPACE. | |
669 | ||
670 | =item B<C<\p{PosixPunct}>> | |
671 | ||
672 | This matches any punctuation character in the ASCII range, namely | |
673 | C<[\x21-\x2F\x3A-\x40\x5B-\x60\x7B-\x7E]>. These are the | |
674 | graphical characters that aren't word characters. Note that the Posix standard | |
675 | includes in its definition of punctuation, those characters that Unicode calls | |
676 | "symbols." | |
677 | ||
678 | =item B<C<\p{PosixSpace}>> | |
679 | ||
680 | This matches any space character in the ASCII range, namely | |
681 | C<S<[ \f\n\r\t\x0B]>> (the last being a vertical tab). | |
682 | ||
683 | =item B<C<\p{PosixUpper}>> | |
684 | ||
685 | This 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 | ||
689 | This property is used when you need to know in what Unicode version(s) a | |
690 | character is. | |
691 | ||
692 | The "*" above stands for some two digit Unicode version number, such as | |
693 | C<1.1> or C<4.0>; or the "*" can also be C<Unassigned>. This property will | |
694 | match the code points whose final disposition has been settled as of the | |
695 | Unicode release given by the version number; C<\p{Present_In: Unassigned}> | |
696 | will match those code points whose meaning has yet to be assigned. | |
697 | ||
698 | For example, C<U+0041> "LATIN CAPITAL LETTER A" was present in the very first | |
699 | Unicode release available, which is C<1.1>, so this property is true for all | |
700 | valid "*" versions. On the other hand, C<U+1EFF> was not assigned until version | |
701 | 5.1 when it became "LATIN SMALL LETTER Y WITH LOOP", so the only "*" that | |
702 | would match it are 5.1, 5.2, and later. | |
703 | ||
704 | Unicode furnishes the C<Age> property from which this is derived. The problem | |
705 | with Age is that a strict interpretation of it (which Perl takes) has it | |
706 | matching the precise release a code point's meaning is introduced in. Thus | |
707 | C<U+0041> would match only 1.1; and C<U+1EFF> only 5.1. This is not usually what | |
708 | you want. | |
709 | ||
710 | Some non-Perl implementations of the Age property may change its meaning to be | |
711 | the same as the Perl Present_In property; just be aware of that. | |
712 | ||
713 | Another confusion with both these properties is that the definition is not | |
714 | that the code point has been assigned, but that the meaning of the code point | |
715 | has been determined. This is because 66 code points will always be | |
716 | unassigned, and, so the Age for them is the Unicode version the decision to | |
717 | make them so was made in. For example, C<U+FDD0> is to be permanently | |
718 | unassigned to a character, and the decision to do that was made in version 3.1, | |
719 | so C<\p{Age=3.1}> matches this character and C<\p{Present_In: 3.1}> and up | |
720 | matches as well. | |
721 | ||
722 | =item B<C<\p{Print}>> | |
723 | ||
ae5b72c8 | 724 | This matches any character that is graphical or blank, except controls. |
9f815e24 KW |
725 | |
726 | =item B<C<\p{SpacePerl}>> | |
727 | ||
728 | This is the same as C<\s>, including beyond ASCII. | |
729 | ||
4d4acfba KW |
730 | Mnemonic: Space, as modified by Perl. (It doesn't include the vertical tab |
731 | which both the Posix standard and Unicode consider to be space.) | |
9f815e24 KW |
732 | |
733 | =item B<C<\p{VertSpace}>> | |
734 | ||
735 | This is the same as C<\v>: A character that changes the spacing vertically. | |
736 | ||
737 | =item B<C<\p{Word}>> | |
738 | ||
739 | This is the same as C<\w>, including beyond ASCII. | |
740 | ||
741 | =back | |
742 | ||
376d9008 | 743 | =head2 User-Defined Character Properties |
491fd90a | 744 | |
51f494cc KW |
745 | You can define your own binary character properties by defining subroutines |
746 | whose names begin with "In" or "Is". The subroutines can be defined in any | |
747 | package. The user-defined properties can be used in the regular expression | |
748 | C<\p> and C<\P> constructs; if you are using a user-defined property from a | |
749 | package other than the one you are in, you must specify its package in the | |
750 | C<\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 | ||
760 | Note that the effect is compile-time and immutable once defined. | |
491fd90a | 761 | |
376d9008 JB |
762 | The subroutines must return a specially-formatted string, with one |
763 | or more newline-separated lines. Each line must be one of the following: | |
491fd90a JH |
764 | |
765 | =over 4 | |
766 | ||
767 | =item * | |
768 | ||
510254c9 A |
769 | A single hexadecimal number denoting a Unicode code point to include. |
770 | ||
771 | =item * | |
772 | ||
99a6b1f0 | 773 | Two hexadecimal numbers separated by horizontal whitespace (space or |
376d9008 | 774 | tabular characters) denoting a range of Unicode code points to include. |
491fd90a JH |
775 | |
776 | =item * | |
777 | ||
376d9008 | 778 | Something to include, prefixed by "+": a built-in character |
bac0b425 JP |
779 | property (prefixed by "utf8::") or a user-defined character property, |
780 | to represent all the characters in that property; two hexadecimal code | |
781 | points for a range; or a single hexadecimal code point. | |
491fd90a JH |
782 | |
783 | =item * | |
784 | ||
376d9008 | 785 | Something to exclude, prefixed by "-": an existing character |
bac0b425 JP |
786 | property (prefixed by "utf8::") or a user-defined character property, |
787 | to represent all the characters in that property; two hexadecimal code | |
788 | points for a range; or a single hexadecimal code point. | |
491fd90a JH |
789 | |
790 | =item * | |
791 | ||
376d9008 | 792 | Something to negate, prefixed "!": an existing character |
bac0b425 JP |
793 | property (prefixed by "utf8::") or a user-defined character property, |
794 | to represent all the characters in that property; two hexadecimal code | |
795 | points for a range; or a single hexadecimal code point. | |
796 | ||
797 | =item * | |
798 | ||
799 | Something to intersect with, prefixed by "&": an existing character | |
800 | property (prefixed by "utf8::") or a user-defined character property, | |
801 | for all the characters except the characters in the property; two | |
802 | hexadecimal code points for a range; or a single hexadecimal code point. | |
491fd90a JH |
803 | |
804 | =back | |
805 | ||
806 | For example, to define a property that covers both the Japanese | |
807 | syllabaries (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 |
816 | Imagine that the here-doc end marker is at the beginning of the line. |
817 | Now you can use C<\p{InKana}> and C<\P{InKana}>. | |
491fd90a JH |
818 | |
819 | You 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 | ||
828 | Suppose you wanted to match only the allocated characters, | |
d5822f25 | 829 | not the raw block ranges: in other words, you want to remove |
491fd90a JH |
830 | the non-characters: |
831 | ||
832 | sub InKana { | |
833 | return <<'END'; | |
834 | +utf8::InHiragana | |
835 | +utf8::InKatakana | |
836 | -utf8::IsCn | |
837 | END | |
838 | } | |
839 | ||
840 | The 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 |
850 | Intersection is useful for getting the common characters matched by |
851 | two (or more) classes. | |
852 | ||
853 | sub InFooAndBar { | |
854 | return <<'END'; | |
855 | +main::Foo | |
856 | &main::Bar | |
857 | END | |
858 | } | |
859 | ||
ac036724 | 860 | It's important to remember not to use "&" for the first set; that |
bac0b425 JP |
861 | would be intersecting with nothing (resulting in an empty set). |
862 | ||
822502e5 TS |
863 | =head2 User-Defined Case Mappings |
864 | ||
3a2263fe RGS |
865 | You can also define your own mappings to be used in the lc(), |
866 | lcfirst(), uc(), and ucfirst() (or their string-inlined versions). | |
822502e5 | 867 | The principle is similar to that of user-defined character |
51f494cc | 868 | properties: to define subroutines |
3a2263fe RGS |
869 | with names like C<ToLower> (for lc() and lcfirst()), C<ToTitle> (for |
870 | the first character in ucfirst()), and C<ToUpper> (for uc(), and the | |
871 | rest of the characters in ucfirst()). | |
872 | ||
51f494cc | 873 | The string returned by the subroutines needs to be two hexadecimal numbers |
e1b711da KW |
874 | separated by two tabulators: the two numbers being, respectively, the source |
875 | code 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 |
883 | defines an uc() mapping that causes only the character "a" |
884 | to 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 |
887 | mapping; you can't just override a couple of characters and leave the rest | |
888 | unchanged. You can find all the mappings in the directory | |
889 | C<$Config{privlib}>/F<unicore/To/>. The mapping data is returned as the | |
890 | here-document, and the C<utf8::ToSpecFoo> are special exception mappings | |
9f815e24 KW |
891 | derived from <$Config{privlib}>/F<unicore/SpecialCasing.txt>. The "Digit" and |
892 | "Fold" mappings that one can see in the directory are not directly | |
51f494cc | 893 | user-accessible, one can use either the C<Unicode::UCD> module, or just match |
9f815e24 | 894 | case-insensitively (that's when the "Fold" mapping is used). |
3a2263fe | 895 | |
51f494cc KW |
896 | The mappings will only take effect on scalars that have been marked as having |
897 | Unicode characters, for example by using C<utf8::upgrade()>. | |
898 | Old byte-style strings are not affected. | |
3a2263fe | 899 | |
51f494cc | 900 | The 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 | 904 | See L<Encode>. |
8cbd9a7a | 905 | |
c29a771d | 906 | =head2 Unicode Regular Expression Support Level |
776f8809 | 907 | |
376d9008 JB |
908 | The following list of Unicode support for regular expressions describes |
909 | all the features currently supported. The references to "Level N" | |
8158862b TS |
910 | and 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 | ||
917 | Level 1 - Basic Unicode Support | |
918 | ||
8158862b TS |
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 TS |
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 TS |
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 | 951 | For example, what UTS#18 might write as |
29bdacb8 | 952 | |
dbe420b4 JH |
953 | [{Greek}-[{UNASSIGNED}]] |
954 | ||
955 | in Perl can be written as: | |
956 | ||
1d81abf3 JH |
957 | (?!\p{Unassigned})\p{InGreekAndCoptic} |
958 | (?=\p{Assigned})\p{InGreekAndCoptic} | |
dbe420b4 JH |
959 | |
960 | But in this particular example, you probably really want | |
961 | ||
1bfb14c4 | 962 | \p{GreekAndCoptic} |
dbe420b4 JH |
963 | |
964 | which will match assigned characters known to be part of the Greek script. | |
29bdacb8 | 965 | |
5ca1ac52 | 966 | Also see the Unicode::Regex::Set module, it does implement the full |
8158862b TS |
967 | UTS#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 | ||
979 | Level 2 - Extended Unicode Support | |
980 | ||
8158862b | 981 | RL2.1 Canonical Equivalents - MISSING [10][11] |
c670e63a | 982 | RL2.2 Default Grapheme Clusters - MISSING [12] |
8158862b TS |
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 TS |
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 TS |
1000 | Level 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 |
1026 | Unicode characters are assigned to I<code points>, which are abstract |
1027 | numbers. To use these numbers, various encodings are needed. | |
c349b1b9 JH |
1028 | |
1029 | =over 4 | |
1030 | ||
c29a771d | 1031 | =item * |
5cb3728c RB |
1032 | |
1033 | UTF-8 | |
c349b1b9 | 1034 | |
3e4dbfed | 1035 | UTF-8 is a variable-length (1 to 6 bytes, current character allocations |
376d9008 JB |
1036 | require 4 bytes), byte-order independent encoding. For ASCII (and we |
1037 | really do mean 7-bit ASCII, not another 8-bit encoding), UTF-8 is | |
1038 | transparent. | |
c349b1b9 | 1039 | |
8c007b5a | 1040 | The 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 TS |
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 | ||
1055 | Note the gaps before several of the byte entries above marked by '*'. These are | |
1056 | caused by legal UTF-8 avoiding non-shortest encodings: it is technically | |
1057 | possible to UTF-8-encode a single code point in different ways, but that is | |
1058 | explicitly forbidden, and the shortest possible encoding should always be used | |
1059 | (and that is what Perl does). | |
37361303 | 1060 | |
376d9008 | 1061 | Another 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 | 1070 | As you can see, the continuation bytes all begin with "10", and the |
e1b711da | 1071 | leading bits of the start byte tell how many bytes there are in the |
05632f9a JH |
1072 | encoded character. |
1073 | ||
c29a771d | 1074 | =item * |
5cb3728c RB |
1075 | |
1076 | UTF-EBCDIC | |
dbe420b4 | 1077 | |
376d9008 | 1078 | Like UTF-8 but EBCDIC-safe, in the way that UTF-8 is ASCII-safe. |
dbe420b4 | 1079 | |
c29a771d | 1080 | =item * |
5cb3728c | 1081 | |
1e54db1a | 1082 | UTF-16, UTF-16BE, UTF-16LE, Surrogates, and BOMs (Byte Order Marks) |
c349b1b9 | 1083 | |
1bfb14c4 JH |
1084 | The followings items are mostly for reference and general Unicode |
1085 | knowledge, Perl doesn't use these constructs internally. | |
dbe420b4 | 1086 | |
c349b1b9 | 1087 | UTF-16 is a 2 or 4 byte encoding. The Unicode code points |
1bfb14c4 JH |
1088 | C<U+0000..U+FFFF> are stored in a single 16-bit unit, and the code |
1089 | points C<U+10000..U+10FFFF> in two 16-bit units. The latter case is | |
c349b1b9 JH |
1090 | using I<surrogates>, the first 16-bit unit being the I<high |
1091 | surrogate>, and the second being the I<low surrogate>. | |
1092 | ||
376d9008 | 1093 | Surrogates are code points set aside to encode the C<U+10000..U+10FFFF> |
c349b1b9 | 1094 | range of Unicode code points in pairs of 16-bit units. The I<high |
9f815e24 | 1095 | surrogates> are the range C<U+D800..U+DBFF> and the I<low surrogates> |
376d9008 | 1096 | are 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 | ||
1101 | and the decoding is | |
1102 | ||
1a3fa709 | 1103 | $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00); |
c349b1b9 | 1104 | |
feda178f | 1105 | If you try to generate surrogates (for example by using chr()), you |
e1b711da | 1106 | will get a warning, if warnings are turned on, because those code |
376d9008 | 1107 | points are not valid for a Unicode character. |
9466bab6 | 1108 | |
376d9008 | 1109 | Because of the 16-bitness, UTF-16 is byte-order dependent. UTF-16 |
c349b1b9 | 1110 | itself can be used for in-memory computations, but if storage or |
376d9008 JB |
1111 | transfer is required either UTF-16BE (big-endian) or UTF-16LE |
1112 | (little-endian) encodings must be chosen. | |
c349b1b9 JH |
1113 | |
1114 | This introduces another problem: what if you just know that your data | |
376d9008 JB |
1115 | is UTF-16, but you don't know which endianness? Byte Order Marks, or |
1116 | BOMs, are a solution to this. A special character has been reserved | |
86bbd6d1 | 1117 | in Unicode to function as a byte order marker: the character with the |
376d9008 | 1118 | code point C<U+FEFF> is the BOM. |
042da322 | 1119 | |
c349b1b9 | 1120 | The trick is that if you read a BOM, you will know the byte order, |
376d9008 JB |
1121 | since if it was written on a big-endian platform, you will read the |
1122 | bytes C<0xFE 0xFF>, but if it was written on a little-endian platform, | |
1123 | you will read the bytes C<0xFF 0xFE>. (And if the originating platform | |
1124 | was writing in UTF-8, you will read the bytes C<0xEF 0xBB 0xBF>.) | |
042da322 | 1125 | |
86bbd6d1 | 1126 | The way this trick works is that the character with the code point |
376d9008 JB |
1127 | C<U+FFFE> is guaranteed not to be a valid Unicode character, so the |
1128 | sequence of bytes C<0xFF 0xFE> is unambiguously "BOM, represented in | |
1bfb14c4 | 1129 | little-endian format" and cannot be C<U+FFFE>, represented in big-endian |
e1b711da KW |
1130 | format". (Actually, C<U+FFFE> is legal for use by your program, even for |
1131 | input/output, but better not use it if you need a BOM. But it is "illegal for | |
1132 | interchange", so that an unsuspecting program won't get confused.) | |
c349b1b9 | 1133 | |
c29a771d | 1134 | =item * |
5cb3728c | 1135 | |
1e54db1a | 1136 | UTF-32, UTF-32BE, UTF-32LE |
c349b1b9 JH |
1137 | |
1138 | The UTF-32 family is pretty much like the UTF-16 family, expect that | |
042da322 | 1139 | the units are 32-bit, and therefore the surrogate scheme is not |
376d9008 JB |
1140 | needed. The BOM signatures will be C<0x00 0x00 0xFE 0xFF> for BE and |
1141 | C<0xFF 0xFE 0x00 0x00> for LE. | |
c349b1b9 | 1142 | |
c29a771d | 1143 | =item * |
5cb3728c RB |
1144 | |
1145 | UCS-2, UCS-4 | |
c349b1b9 | 1146 | |
86bbd6d1 | 1147 | Encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit |
376d9008 | 1148 | encoding. Unlike UTF-16, UCS-2 is not extensible beyond C<U+FFFF>, |
339cfa0e JH |
1149 | because it does not use surrogates. UCS-4 is a 32-bit encoding, |
1150 | functionally identical to UTF-32. | |
c349b1b9 | 1151 | |
c29a771d | 1152 | =item * |
5cb3728c RB |
1153 | |
1154 | UTF-7 | |
c349b1b9 | 1155 | |
376d9008 JB |
1156 | A seven-bit safe (non-eight-bit) encoding, which is useful if the |
1157 | transport 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 |
1163 | Read L<Unicode Security Considerations|http://www.unicode.org/reports/tr36>. |
1164 | Also, note the following: | |
1165 | ||
0d7c09bb JH |
1166 | =over 4 |
1167 | ||
1168 | =item * | |
1169 | ||
1170 | Malformed UTF-8 | |
bf0fa0b2 JH |
1171 | |
1172 | Unfortunately, the specification of UTF-8 leaves some room for | |
1173 | interpretation of how many bytes of encoded output one should generate | |
376d9008 JB |
1174 | from one input Unicode character. Strictly speaking, the shortest |
1175 | possible sequence of UTF-8 bytes should be generated, | |
1176 | because otherwise there is potential for an input buffer overflow at | |
feda178f | 1177 | the receiving end of a UTF-8 connection. Perl always generates the |
e1b711da | 1178 | shortest length UTF-8, and with warnings on, Perl will warn about |
376d9008 JB |
1179 | non-shortest length UTF-8 along with other malformations, such as the |
1180 | surrogates, which are not real Unicode code points. | |
bf0fa0b2 | 1181 | |
0d7c09bb JH |
1182 | =item * |
1183 | ||
1184 | Regular expressions behave slightly differently between byte data and | |
376d9008 JB |
1185 | character (Unicode) data. For example, the "word character" character |
1186 | class C<\w> will work differently depending on if data is eight-bit bytes | |
1187 | or Unicode. | |
0d7c09bb | 1188 | |
376d9008 JB |
1189 | In the first case, the set of C<\w> characters is either small--the |
1190 | default set of alphabetic characters, digits, and the "_"--or, if you | |
0d7c09bb JH |
1191 | are using a locale (see L<perllocale>), the C<\w> might contain a few |
1192 | more letters according to your language and country. | |
1193 | ||
376d9008 | 1194 | In the second case, the C<\w> set of characters is much, much larger. |
1bfb14c4 JH |
1195 | Most importantly, even in the set of the first 256 characters, it will |
1196 | probably match different characters: unlike most locales, which are | |
1197 | specific to a language and country pair, Unicode classifies all the | |
1198 | characters that are letters I<somewhere> as C<\w>. For example, your | |
1199 | locale might not think that LATIN SMALL LETTER ETH is a letter (unless | |
1200 | you happen to speak Icelandic), but Unicode does. | |
0d7c09bb | 1201 | |
376d9008 | 1202 | As discussed elsewhere, Perl has one foot (two hooves?) planted in |
1bfb14c4 JH |
1203 | each of two worlds: the old world of bytes and the new world of |
1204 | characters, upgrading from bytes to characters when necessary. | |
376d9008 JB |
1205 | If your legacy code does not explicitly use Unicode, no automatic |
1206 | switch-over to characters should happen. Characters shouldn't get | |
1bfb14c4 JH |
1207 | downgraded to bytes, either. It is possible to accidentally mix bytes |
1208 | and characters, however (see L<perluniintro>), in which case C<\w> in | |
1209 | regular expressions might start behaving differently. Review your | |
1210 | code. 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 |
1216 | The way Unicode is handled on EBCDIC platforms is still |
1217 | experimental. On such platforms, references to UTF-8 encoding in this | |
1218 | document and elsewhere should be read as meaning the UTF-EBCDIC | |
1219 | specified in Unicode Technical Report 16, unless ASCII vs. EBCDIC issues | |
c349b1b9 | 1220 | are specifically discussed. There is no C<utfebcdic> pragma or |
376d9008 | 1221 | ":utfebcdic" layer; rather, "utf8" and ":utf8" are reused to mean |
86bbd6d1 PN |
1222 | the platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic> |
1223 | for more discussion of the issues. | |
c349b1b9 | 1224 | |
b310b053 JH |
1225 | =head2 Locales |
1226 | ||
4616122b | 1227 | Usually locale settings and Unicode do not affect each other, but |
b310b053 JH |
1228 | there are a couple of exceptions: |
1229 | ||
1230 | =over 4 | |
1231 | ||
1232 | =item * | |
1233 | ||
8aa8f774 JH |
1234 | You can enable automatic UTF-8-ification of your standard file |
1235 | handles, default C<open()> layer, and C<@ARGV> by using either | |
1236 | the C<-C> command line switch or the C<PERL_UNICODE> environment | |
1237 | variable, see L<perlrun> for the documentation of the C<-C> switch. | |
b310b053 JH |
1238 | |
1239 | =item * | |
1240 | ||
376d9008 JB |
1241 | Perl tries really hard to work both with Unicode and the old |
1242 | byte-oriented world. Most often this is nice, but sometimes Perl's | |
1243 | straddling of the proverbial fence causes problems. | |
b310b053 JH |
1244 | |
1245 | =back | |
1246 | ||
1aad1664 JH |
1247 | =head2 When Unicode Does Not Happen |
1248 | ||
1249 | While Perl does have extensive ways to input and output in Unicode, | |
1250 | and few other 'entry points' like the @ARGV which can be interpreted | |
1251 | as Unicode (UTF-8), there still are many places where Unicode (in some | |
1252 | encoding or another) could be given as arguments or received as | |
1253 | results, or both, but it is not. | |
1254 | ||
e1b711da KW |
1255 | The following are such interfaces. Also, see L</The "Unicode Bug">. |
1256 | For all of these interfaces Perl | |
6cd4dd6c JH |
1257 | currently (as of 5.8.3) simply assumes byte strings both as arguments |
1258 | and results, or UTF-8 strings if the C<encoding> pragma has been used. | |
1aad1664 JH |
1259 | |
1260 | One reason why Perl does not attempt to resolve the role of Unicode in | |
e1b711da | 1261 | these cases is that the answers are highly dependent on the operating |
1aad1664 JH |
1262 | system and the file system(s). For example, whether filenames can be |
1263 | in Unicode, and in exactly what kind of encoding, is not exactly a | |
1264 | portable 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 | 1271 | chdir, chmod, chown, chroot, exec, link, lstat, mkdir, |
1e8e8236 | 1272 | rename, rmdir, stat, symlink, truncate, unlink, utime, -X |
557a2462 RB |
1273 | |
1274 | =item * | |
1275 | ||
1276 | %ENV | |
1277 | ||
1278 | =item * | |
1279 | ||
1280 | glob (aka the <*>) | |
1281 | ||
1282 | =item * | |
1aad1664 | 1283 | |
557a2462 | 1284 | open, opendir, sysopen |
1aad1664 | 1285 | |
557a2462 | 1286 | =item * |
1aad1664 | 1287 | |
557a2462 | 1288 | qx (aka the backtick operator), system |
1aad1664 | 1289 | |
557a2462 | 1290 | =item * |
1aad1664 | 1291 | |
557a2462 | 1292 | readdir, readlink |
1aad1664 JH |
1293 | |
1294 | =back | |
1295 | ||
e1b711da KW |
1296 | =head2 The "Unicode Bug" |
1297 | ||
1298 | The term, the "Unicode bug" has been applied to an inconsistency with the | |
1299 | Unicode characters whose code points are in the Latin-1 Supplement block, that | |
1300 | is, between 128 and 255. Without a locale specified, unlike all other | |
1301 | characters or code points, these characters have very different semantics in | |
1302 | byte semantics versus character semantics. | |
1303 | ||
1304 | In character semantics they are interpreted as Unicode code points, which means | |
1305 | they have the same semantics as Latin-1 (ISO-8859-1). | |
1306 | ||
1307 | In byte semantics, they are considered to be unassigned characters, meaning | |
1308 | that the only semantics they have is their ordinal numbers, and that they are | |
1309 | not members of various character classes. None are considered to match C<\w> | |
1310 | for example, but all match C<\W>. (On EBCDIC platforms, the behavior may | |
1311 | be different from this, depending on the underlying C language library | |
1312 | functions.) | |
1313 | ||
1314 | The behavior is known to have effects on these areas: | |
1315 | ||
1316 | =over 4 | |
1317 | ||
1318 | =item * | |
1319 | ||
1320 | Changing the case of a scalar, that is, using C<uc()>, C<ucfirst()>, C<lc()>, | |
1321 | and C<lcfirst()>, or C<\L>, C<\U>, C<\u> and C<\l> in regular expression | |
1322 | substitutions. | |
1323 | ||
1324 | =item * | |
1325 | ||
1326 | Using caseless (C</i>) regular expression matching | |
1327 | ||
1328 | =item * | |
1329 | ||
1330 | Matching a number of properties in regular expressions, such as C<\w> | |
1331 | ||
1332 | =item * | |
1333 | ||
1334 | User-defined case change mappings. You can create a C<ToUpper()> function, for | |
1335 | example, which overrides Perl's built-in case mappings. The scalar must be | |
1336 | encoded in utf8 for your function to actually be invoked. | |
1337 | ||
1338 | =back | |
1339 | ||
1340 | This behavior can lead to unexpected results in which a string's semantics | |
1341 | suddenly change if a code point above 255 is appended to or removed from it, | |
1342 | which changes the string's semantics from byte to character or vice versa. As | |
1343 | an 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 | 1356 | If there's no C<\w> in C<s1> or in C<s2>, why does their concatenation have one? |
e1b711da KW |
1357 | |
1358 | This anomaly stems from Perl's attempt to not disturb older programs that | |
1359 | didn't use Unicode, and hence had no semantics for characters outside of the | |
1360 | ASCII range (except in a locale), along with Perl's desire to add Unicode | |
1361 | support seamlessly. The result wasn't seamless: these characters were | |
1362 | orphaned. | |
1363 | ||
1364 | Work is being done to correct this, but only some of it was complete in time | |
1365 | for the 5.12 release. What has been finished is the important part of the case | |
1366 | changing component. Due to concerns, and some evidence, that older code might | |
1367 | have come to rely on the existing behavior, the new behavior must be explicitly | |
1368 | enabled by the feature C<unicode_strings> in the L<feature> pragma, even though | |
1369 | no new syntax is involved. | |
1370 | ||
1371 | See L<perlfunc/lc> for details on how this pragma works in combination with | |
1372 | various others for casing. Even though the pragma only affects casing | |
1373 | operations in the 5.12 release, it is planned to have it affect all the | |
1374 | problematic behaviors in later releases: you can't have one without them all. | |
1375 | ||
1376 | In the meantime, a workaround is to always call utf8::upgrade($string), or to | |
1377 | use the standard modules L<Encode> or L<charnames>. | |
1378 | ||
1aad1664 JH |
1379 | =head2 Forcing Unicode in Perl (Or Unforcing Unicode in Perl) |
1380 | ||
e1b711da KW |
1381 | Sometimes (see L</"When Unicode Does Not Happen"> or L</The "Unicode Bug">) |
1382 | there are situations where you simply need to force a byte | |
2bbc8d55 SP |
1383 | string into UTF-8, or vice versa. The low-level calls |
1384 | utf8::upgrade($bytestring) and utf8::downgrade($utf8string[, FAIL_OK]) are | |
1aad1664 JH |
1385 | the answers. |
1386 | ||
2bbc8d55 SP |
1387 | Note that utf8::downgrade() can fail if the string contains characters |
1388 | that don't fit into a byte. | |
1aad1664 | 1389 | |
e1b711da KW |
1390 | Calling either function on a string that already is in the desired state is a |
1391 | no-op. | |
1392 | ||
95a1a48b JH |
1393 | =head2 Using Unicode in XS |
1394 | ||
3a2263fe RGS |
1395 | If you want to handle Perl Unicode in XS extensions, you may find the |
1396 | following C APIs useful. See also L<perlguts/"Unicode Support"> for an | |
1397 | explanation about Unicode at the XS level, and L<perlapi> for the API | |
1398 | details. | |
95a1a48b JH |
1399 | |
1400 | =over 4 | |
1401 | ||
1402 | =item * | |
1403 | ||
1bfb14c4 | 1404 | C<DO_UTF8(sv)> returns true if the C<UTF8> flag is on and the bytes |
2bbc8d55 | 1405 | pragma is not in effect. C<SvUTF8(sv)> returns true if the C<UTF8> |
1bfb14c4 JH |
1406 | flag is on; the bytes pragma is ignored. The C<UTF8> flag being on |
1407 | does B<not> mean that there are any characters of code points greater | |
1408 | than 255 (or 127) in the scalar or that there are even any characters | |
1409 | in the scalar. What the C<UTF8> flag means is that the sequence of | |
1410 | octets in the representation of the scalar is the sequence of UTF-8 | |
1411 | encoded code points of the characters of a string. The C<UTF8> flag | |
1412 | being off means that each octet in this representation encodes a | |
1413 | single character with code point 0..255 within the string. Perl's | |
1414 | Unicode model is not to use UTF-8 until it is absolutely necessary. | |
95a1a48b JH |
1415 | |
1416 | =item * | |
1417 | ||
2bbc8d55 | 1418 | C<uvchr_to_utf8(buf, chr)> writes a Unicode character code point into |
1bfb14c4 | 1419 | a buffer encoding the code point as UTF-8, and returns a pointer |
2bbc8d55 | 1420 | pointing after the UTF-8 bytes. It works appropriately on EBCDIC machines. |
95a1a48b JH |
1421 | |
1422 | =item * | |
1423 | ||
2bbc8d55 | 1424 | C<utf8_to_uvchr(buf, lenp)> reads UTF-8 encoded bytes from a buffer and |
376d9008 | 1425 | returns the Unicode character code point and, optionally, the length of |
2bbc8d55 | 1426 | the UTF-8 byte sequence. It works appropriately on EBCDIC machines. |
95a1a48b JH |
1427 | |
1428 | =item * | |
1429 | ||
376d9008 JB |
1430 | C<utf8_length(start, end)> returns the length of the UTF-8 encoded buffer |
1431 | in characters. C<sv_len_utf8(sv)> returns the length of the UTF-8 encoded | |
95a1a48b JH |
1432 | scalar. |
1433 | ||
1434 | =item * | |
1435 | ||
376d9008 JB |
1436 | C<sv_utf8_upgrade(sv)> converts the string of the scalar to its UTF-8 |
1437 | encoded form. C<sv_utf8_downgrade(sv)> does the opposite, if | |
1438 | possible. C<sv_utf8_encode(sv)> is like sv_utf8_upgrade except that | |
1439 | it does not set the C<UTF8> flag. C<sv_utf8_decode()> does the | |
1440 | opposite of C<sv_utf8_encode()>. Note that none of these are to be | |
1441 | used as general-purpose encoding or decoding interfaces: C<use Encode> | |
1442 | for that. C<sv_utf8_upgrade()> is affected by the encoding pragma | |
1443 | but C<sv_utf8_downgrade()> is not (since the encoding pragma is | |
1444 | designed to be a one-way street). | |
95a1a48b JH |
1445 | |
1446 | =item * | |
1447 | ||
376d9008 | 1448 | C<is_utf8_char(s)> returns true if the pointer points to a valid UTF-8 |
90f968e0 | 1449 | character. |
95a1a48b JH |
1450 | |
1451 | =item * | |
1452 | ||
376d9008 | 1453 | C<is_utf8_string(buf, len)> returns true if C<len> bytes of the buffer |
95a1a48b JH |
1454 | are valid UTF-8. |
1455 | ||
1456 | =item * | |
1457 | ||
376d9008 JB |
1458 | C<UTF8SKIP(buf)> will return the number of bytes in the UTF-8 encoded |
1459 | character in the buffer. C<UNISKIP(chr)> will return the number of bytes | |
1460 | required to UTF-8-encode the Unicode character code point. C<UTF8SKIP()> | |
90f968e0 | 1461 | is useful for example for iterating over the characters of a UTF-8 |
376d9008 | 1462 | encoded buffer; C<UNISKIP()> is useful, for example, in computing |
90f968e0 | 1463 | the size required for a UTF-8 encoded buffer. |
95a1a48b JH |
1464 | |
1465 | =item * | |
1466 | ||
376d9008 | 1467 | C<utf8_distance(a, b)> will tell the distance in characters between the |
95a1a48b JH |
1468 | two pointers pointing to the same UTF-8 encoded buffer. |
1469 | ||
1470 | =item * | |
1471 | ||
2bbc8d55 | 1472 | C<utf8_hop(s, off)> will return a pointer to a UTF-8 encoded buffer |
376d9008 JB |
1473 | that is C<off> (positive or negative) Unicode characters displaced |
1474 | from the UTF-8 buffer C<s>. Be careful not to overstep the buffer: | |
1475 | C<utf8_hop()> will merrily run off the end or the beginning of the | |
1476 | buffer if told to do so. | |
95a1a48b | 1477 | |
d2cc3551 JH |
1478 | =item * |
1479 | ||
376d9008 JB |
1480 | C<pv_uni_display(dsv, spv, len, pvlim, flags)> and |
1481 | C<sv_uni_display(dsv, ssv, pvlim, flags)> are useful for debugging the | |
1482 | output of Unicode strings and scalars. By default they are useful | |
1483 | only for debugging--they display B<all> characters as hexadecimal code | |
1bfb14c4 JH |
1484 | points--but with the flags C<UNI_DISPLAY_ISPRINT>, |
1485 | C<UNI_DISPLAY_BACKSLASH>, and C<UNI_DISPLAY_QQ> you can make the | |
1486 | output more readable. | |
d2cc3551 JH |
1487 | |
1488 | =item * | |
1489 | ||
2bbc8d55 | 1490 | C<ibcmp_utf8(s1, pe1, l1, u1, s2, pe2, l2, u2)> can be used to |
376d9008 JB |
1491 | compare two strings case-insensitively in Unicode. For case-sensitive |
1492 | comparisons you can just use C<memEQ()> and C<memNE()> as usual. | |
d2cc3551 | 1493 | |
c349b1b9 JH |
1494 | =back |
1495 | ||
95a1a48b JH |
1496 | For more information, see L<perlapi>, and F<utf8.c> and F<utf8.h> |
1497 | in the Perl source code distribution. | |
1498 | ||
e1b711da KW |
1499 | =head2 Hacking Perl to work on earlier Unicode versions (for very serious hackers only) |
1500 | ||
1501 | Perl by default comes with the latest supported Unicode version built in, but | |
1502 | you can change to use any earlier one. | |
1503 | ||
1504 | Download the files in the version of Unicode that you want from the Unicode web | |
1505 | site L<http://www.unicode.org>). These should replace the existing files in | |
1506 | C<\$Config{privlib}>/F<unicore>. (C<\%Config> is available from the Config | |
1507 | module.) Follow the instructions in F<README.perl> in that directory to change | |
1508 | some of their names, and then run F<make>. | |
1509 | ||
1510 | It is even possible to download them to a different directory, and then change | |
1511 | F<utf8_heavy.pl> in the directory C<\$Config{privlib}> to point to the new | |
1512 | directory, or maybe make a copy of that directory before making the change, and | |
1513 | using 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 | |
1515 | beyond the scope of these instructions. | |
1516 | ||
c29a771d JH |
1517 | =head1 BUGS |
1518 | ||
376d9008 | 1519 | =head2 Interaction with Locales |
7eabb34d | 1520 | |
376d9008 JB |
1521 | Use of locales with Unicode data may lead to odd results. Currently, |
1522 | Perl attempts to attach 8-bit locale info to characters in the range | |
1523 | 0..255, but this technique is demonstrably incorrect for locales that | |
1524 | use characters above that range when mapped into Unicode. Perl's | |
1525 | Unicode support will also tend to run slower. Use of locales with | |
1526 | Unicode is discouraged. | |
c29a771d | 1527 | |
9f815e24 | 1528 | =head2 Problems with characters in the Latin-1 Supplement range |
2bbc8d55 | 1529 | |
e1b711da KW |
1530 | See L</The "Unicode Bug"> |
1531 | ||
1532 | =head2 Problems with case-insensitive regular expression matching | |
1533 | ||
1534 | There are problems with case-insensitive matches, including those involving | |
1535 | character classes (enclosed in [square brackets]), characters whose fold | |
9f815e24 KW |
1536 | is to multiple characters (such as the single character LATIN SMALL LIGATURE |
1537 | FFL matches case-insensitively with the 3-character string C<ffl>), and | |
1538 | characters in the Latin-1 Supplement. | |
2bbc8d55 | 1539 | |
376d9008 | 1540 | =head2 Interaction with Extensions |
7eabb34d | 1541 | |
376d9008 | 1542 | When Perl exchanges data with an extension, the extension should be |
2575c402 | 1543 | able to understand the UTF8 flag and act accordingly. If the |
376d9008 JB |
1544 | extension doesn't know about the flag, it's likely that the extension |
1545 | will return incorrectly-flagged data. | |
7eabb34d A |
1546 | |
1547 | So if you're working with Unicode data, consult the documentation of | |
1548 | every module you're using if there are any issues with Unicode data | |
1549 | exchange. If the documentation does not talk about Unicode at all, | |
a73d23f6 | 1550 | suspect the worst and probably look at the source to learn how the |
376d9008 | 1551 | module is implemented. Modules written completely in Perl shouldn't |
a73d23f6 RGS |
1552 | cause problems. Modules that directly or indirectly access code written |
1553 | in other programming languages are at risk. | |
7eabb34d | 1554 | |
376d9008 | 1555 | For affected functions, the simple strategy to avoid data corruption is |
7eabb34d | 1556 | to always make the encoding of the exchanged data explicit. Choose an |
376d9008 | 1557 | encoding that you know the extension can handle. Convert arguments passed |
7eabb34d A |
1558 | to the extensions to that encoding and convert results back from that |
1559 | encoding. Write wrapper functions that do the conversions for you, so | |
1560 | you can later change the functions when the extension catches up. | |
1561 | ||
376d9008 | 1562 | To provide an example, let's say the popular Foo::Bar::escape_html |
7eabb34d A |
1563 | function doesn't deal with Unicode data yet. The wrapper function |
1564 | would convert the argument to raw UTF-8 and convert the result back to | |
376d9008 | 1565 | Perl'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 | ||
1573 | Sometimes, when the extension does not convert data but just stores | |
1574 | and retrieves them, you will be in a position to use the otherwise | |
1575 | dangerous Encode::_utf8_on() function. Let's say the popular | |
66b79f27 | 1576 | C<Foo::Bar> extension, written in C, provides a C<param> method that |
7eabb34d A |
1577 | lets 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 | ||
1582 | If it does not yet provide support for any encoding, one could write a | |
1583 | derived 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 |
1598 | Some extensions provide filters on data entry/exit points, such as |
1599 | DB_File::filter_store_key and family. Look out for such filters in | |
66b79f27 | 1600 | the documentation of your extensions, they can make the transition to |
7eabb34d A |
1601 | Unicode data much easier. |
1602 | ||
376d9008 | 1603 | =head2 Speed |
7eabb34d | 1604 | |
c29a771d | 1605 | Some functions are slower when working on UTF-8 encoded strings than |
574c8022 | 1606 | on byte encoded strings. All functions that need to hop over |
7c17141f JH |
1607 | characters such as length(), substr() or index(), or matching regular |
1608 | expressions can work B<much> faster when the underlying data are | |
1609 | byte-encoded. | |
1610 | ||
1611 | In Perl 5.8.0 the slowness was often quite spectacular; in Perl 5.8.1 | |
1612 | a caching scheme was introduced which will hopefully make the slowness | |
a104b433 JH |
1613 | somewhat less spectacular, at least for some operations. In general, |
1614 | operations with UTF-8 encoded strings are still slower. As an example, | |
1615 | the Unicode properties (character classes) like C<\p{Nd}> are known to | |
1616 | be quite a bit slower (5-20 times) than their simpler counterparts | |
1617 | like C<\d> (then again, there 268 Unicode characters matching C<Nd> | |
1618 | compared with the 10 ASCII characters matching C<d>). | |
666f95b9 | 1619 | |
e1b711da KW |
1620 | =head2 Problems on EBCDIC platforms |
1621 | ||
1622 | There are a number of known problems with Perl on EBCDIC platforms. If you | |
1623 | want to use Perl there, send email to perlbug@perl.org. | |
fe749c9a KW |
1624 | |
1625 | In earlier versions, when byte and character data were concatenated, | |
1626 | the new string was sometimes created by | |
1627 | decoding the byte strings as I<ISO 8859-1 (Latin-1)>, even if the | |
1628 | old Unicode string used EBCDIC. | |
1629 | ||
1630 | If you find any of these, please report them as bugs. | |
1631 | ||
c8d992ba A |
1632 | =head2 Porting code from perl-5.6.X |
1633 | ||
1634 | Perl 5.8 has a different Unicode model from 5.6. In 5.6 the programmer | |
1635 | was required to use the C<utf8> pragma to declare that a given scope | |
1636 | expected to deal with Unicode data and had to make sure that only | |
1637 | Unicode data were reaching that scope. If you have code that is | |
1638 | working with 5.6, you will need some of the following adjustments to | |
1639 | your code. The examples are written such that the code will continue | |
1640 | to work under 5.6, so you should be safe to try them out. | |
1641 | ||
1642 | =over 4 | |
1643 | ||
1644 | =item * | |
1645 | ||
1646 | A filehandle that should read or write UTF-8 | |
1647 | ||
1648 | if ($] > 5.007) { | |
740d4bb2 | 1649 | binmode $fh, ":encoding(utf8)"; |
c8d992ba A |
1650 | } |
1651 | ||
1652 | =item * | |
1653 | ||
1654 | A scalar that is going to be passed to some extension | |
1655 | ||
1656 | Be it Compress::Zlib, Apache::Request or any extension that has no | |
1657 | mention of Unicode in the manpage, you need to make sure that the | |
2575c402 | 1658 | UTF8 flag is stripped off. Note that at the time of this writing |
c8d992ba A |
1659 | (October 2002) the mentioned modules are not UTF-8-aware. Please |
1660 | check the documentation to verify if this is still true. | |
1661 | ||
1662 | if ($] > 5.007) { | |
1663 | require Encode; | |
1664 | $val = Encode::encode_utf8($val); # make octets | |
1665 | } | |
1666 | ||
1667 | =item * | |
1668 | ||
1669 | A scalar we got back from an extension | |
1670 | ||
1671 | If you believe the scalar comes back as UTF-8, you will most likely | |
2575c402 | 1672 | want 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 | ||
1681 | Same 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 | ||
1690 | A wrapper for fetchrow_array and fetchrow_hashref | |
1691 | ||
1692 | When the database contains only UTF-8, a wrapper function or method is | |
1693 | a convenient way to replace all your fetchrow_array and | |
1694 | fetchrow_hashref calls. A wrapper function will also make it easier to | |
1695 | adapt to future enhancements in your database driver. Note that at the | |
1696 | time of this writing (October 2002), the DBI has no standardized way | |
1697 | to deal with UTF-8 data. Please check the documentation to verify if | |
1698 | that 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 $ret; | |
1722 | } | |
1723 | } | |
1724 | } | |
1725 | } | |
1726 | ||
1727 | ||
1728 | =item * | |
1729 | ||
1730 | A large scalar that you know can only contain ASCII | |
1731 | ||
1732 | Scalars that contain only ASCII and are marked as UTF-8 are sometimes | |
1733 | a drag to your program. If you recognize such a situation, just remove | |
2575c402 | 1734 | the UTF8 flag: |
c8d992ba A |
1735 | |
1736 | utf8::downgrade($val) if $] > 5.007; | |
1737 | ||
1738 | =back | |
1739 | ||
393fec97 GS |
1740 | =head1 SEE ALSO |
1741 | ||
51f494cc | 1742 | L<perlunitut>, L<perluniintro>, L<perluniprops>, L<Encode>, L<open>, L<utf8>, L<bytes>, |
a05d7ebb | 1743 | L<perlretut>, L<perlvar/"${^UNICODE}"> |
51f494cc | 1744 | L<http://www.unicode.org/reports/tr44>). |
393fec97 GS |
1745 | |
1746 | =cut |