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1 | =head1 NAME |
2 | |
3 | perlunicode - Unicode support in Perl |
4 | |
5 | =head1 DESCRIPTION |
6 | |
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7 | =head2 Important Caveats |
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8 | |
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9 | Unicode support is an extensive requirement. While Perl does not |
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10 | implement the Unicode standard or the accompanying technical reports |
11 | from cover to cover, Perl does support many Unicode features. |
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12 | |
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13 | People who want to learn to use Unicode in Perl, should probably read |
14 | L<the Perl Unicode tutorial|perlunitut> before reading this reference |
15 | document. |
16 | |
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17 | =over 4 |
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18 | |
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19 | =item Input and Output Layers |
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20 | |
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21 | Perl 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 |
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>. |
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26 | |
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27 | To indicate that Perl source itself is in UTF-8, use C<use utf8;>. |
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28 | |
29 | =item Regular Expressions |
30 | |
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31 | The regular expression compiler produces polymorphic opcodes. That is, |
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32 | the pattern adapts to the data and automatically switches to the Unicode |
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33 | character scheme when presented with data that is internally encoded in |
34 | UTF-8 -- or instead uses a traditional byte scheme when presented with |
35 | byte data. |
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36 | |
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37 | =item C<use utf8> still needed to enable UTF-8/UTF-EBCDIC in scripts |
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38 | |
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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 |
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41 | (in string or regular expression literals, or in identifier names) on |
42 | ASCII-based machines or to recognize UTF-EBCDIC on EBCDIC-based |
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43 | machines. B<These are the only times when an explicit C<use utf8> |
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44 | is needed.> See L<utf8>. |
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45 | |
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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 | |
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54 | =item C<use encoding> needed to upgrade non-Latin-1 byte strings |
55 | |
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56 | By default, there is a fundamental asymmetry in Perl's Unicode model: |
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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 |
60 | codepoints in Unicode happens to agree with Latin-1. |
61 | |
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62 | See L</"Byte and Character Semantics"> for more details. |
63 | |
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64 | =back |
65 | |
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66 | =head2 Byte and Character Semantics |
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67 | |
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68 | Beginning with version 5.6, Perl uses logically-wide characters to |
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69 | represent strings internally. |
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70 | |
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71 | In future, Perl-level operations will be expected to work with |
72 | characters rather than bytes. |
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73 | |
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74 | However, as an interim compatibility measure, Perl aims to |
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75 | provide a safe migration path from byte semantics to character |
76 | semantics for programs. For operations where Perl can unambiguously |
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77 | decide that the input data are characters, Perl switches to |
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78 | character semantics. For operations where this determination cannot |
79 | be made without additional information from the user, Perl decides in |
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80 | favor of compatibility and chooses to use byte semantics. |
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81 | |
82 | This behavior preserves compatibility with earlier versions of Perl, |
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83 | which allowed byte semantics in Perl operations only if |
84 | none of the program's inputs were marked as being as source of Unicode |
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85 | character data. Such data may come from filehandles, from calls to |
86 | external programs, from information provided by the system (such as %ENV), |
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87 | or from literals and constants in the source text. |
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88 | |
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89 | The C<bytes> pragma will always, regardless of platform, force byte |
90 | semantics in a particular lexical scope. See L<bytes>. |
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91 | |
92 | The C<utf8> pragma is primarily a compatibility device that enables |
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93 | recognition of UTF-(8|EBCDIC) in literals encountered by the parser. |
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94 | Note that this pragma is only required while Perl defaults to byte |
95 | semantics; when character semantics become the default, this pragma |
96 | may become a no-op. See L<utf8>. |
97 | |
98 | Unless explicitly stated, Perl operators use character semantics |
99 | for Unicode data and byte semantics for non-Unicode data. |
100 | The decision to use character semantics is made transparently. If |
101 | input data comes from a Unicode source--for example, if a character |
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102 | encoding layer is added to a filehandle or a literal Unicode |
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103 | string constant appears in a program--character semantics apply. |
104 | Otherwise, byte semantics are in effect. The C<bytes> pragma should |
105 | be used to force byte semantics on Unicode data. |
106 | |
107 | If strings operating under byte semantics and strings with Unicode |
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108 | character data are concatenated, the new string will be created by |
109 | decoding the byte strings as I<ISO 8859-1 (Latin-1)>, even if the |
110 | old Unicode string used EBCDIC. This translation is done without |
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111 | regard to the system's native 8-bit encoding. |
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112 | |
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113 | Under character semantics, many operations that formerly operated on |
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114 | bytes now operate on characters. A character in Perl is |
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115 | logically just a number ranging from 0 to 2**31 or so. Larger |
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116 | characters may encode into longer sequences of bytes internally, but |
117 | this internal detail is mostly hidden for Perl code. |
118 | See L<perluniintro> for more. |
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119 | |
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120 | =head2 Effects of Character Semantics |
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121 | |
122 | Character semantics have the following effects: |
123 | |
124 | =over 4 |
125 | |
126 | =item * |
127 | |
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128 | Strings--including hash keys--and regular expression patterns may |
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129 | contain characters that have an ordinal value larger than 255. |
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130 | |
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131 | If you use a Unicode editor to edit your program, Unicode characters may |
132 | occur directly within the literal strings in UTF-8 encoding, or UTF-16. |
133 | (The former requires a BOM or C<use utf8>, the latter requires a BOM.) |
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134 | |
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135 | Unicode characters can also be added to a string by using the C<\x{...}> |
136 | notation. The Unicode code for the desired character, in hexadecimal, |
137 | should be placed in the braces. For instance, a smiley face is |
138 | C<\x{263A}>. This encoding scheme only works for all characters, but |
139 | for characters under 0x100, note that Perl may use an 8 bit encoding |
140 | internally, for optimization and/or backward compatibility. |
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141 | |
142 | Additionally, if you |
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143 | |
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144 | use charnames ':full'; |
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145 | |
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146 | you can use the C<\N{...}> notation and put the official Unicode |
147 | character name within the braces, such as C<\N{WHITE SMILING FACE}>. |
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148 | |
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149 | =item * |
150 | |
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151 | If an appropriate L<encoding> is specified, identifiers within the |
152 | Perl script may contain Unicode alphanumeric characters, including |
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153 | ideographs. Perl does not currently attempt to canonicalize variable |
154 | names. |
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155 | |
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156 | =item * |
157 | |
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158 | Regular expressions match characters instead of bytes. "." matches |
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159 | a character instead of a byte. |
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160 | |
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161 | =item * |
162 | |
163 | Character classes in regular expressions match characters instead of |
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164 | bytes and match against the character properties specified in the |
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165 | Unicode properties database. C<\w> can be used to match a Japanese |
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166 | ideograph, for instance. |
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167 | |
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168 | =item * |
169 | |
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170 | Named Unicode properties, scripts, and block ranges may be used like |
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171 | character classes via the C<\p{}> "matches property" construct and |
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172 | the C<\P{}> negation, "doesn't match property". |
173 | |
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174 | See L</"Unicode Character Properties"> for more details. |
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175 | |
176 | You can define your own character properties and use them |
177 | in the regular expression with the C<\p{}> or C<\P{}> construct. |
178 | |
179 | See L</"User-Defined Character Properties"> for more details. |
180 | |
181 | =item * |
182 | |
183 | The special pattern C<\X> matches any extended Unicode |
184 | sequence--"a combining character sequence" in Standardese--where the |
185 | first character is a base character and subsequent characters are mark |
186 | characters that apply to the base character. C<\X> is equivalent to |
187 | C<(?:\PM\pM*)>. |
188 | |
189 | =item * |
190 | |
191 | The C<tr///> operator translates characters instead of bytes. Note |
192 | that the C<tr///CU> functionality has been removed. For similar |
193 | functionality see pack('U0', ...) and pack('C0', ...). |
194 | |
195 | =item * |
196 | |
197 | Case translation operators use the Unicode case translation tables |
198 | when character input is provided. Note that C<uc()>, or C<\U> in |
199 | interpolated strings, translates to uppercase, while C<ucfirst>, |
200 | or C<\u> in interpolated strings, translates to titlecase in languages |
201 | that make the distinction. |
202 | |
203 | =item * |
204 | |
205 | Most operators that deal with positions or lengths in a string will |
206 | automatically switch to using character positions, including |
207 | C<chop()>, C<chomp()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>, |
208 | C<sprintf()>, C<write()>, and C<length()>. An operator that |
209 | specifically does not switch is C<vec()>. Operators that really don't |
210 | care include operators that treat strings as a bucket of bits such as |
211 | C<sort()>, and operators dealing with filenames. |
212 | |
213 | =item * |
214 | |
215 | The C<pack()>/C<unpack()> letter C<C> does I<not> change, since it is often |
216 | used for byte-oriented formats. Again, think C<char> in the C language. |
217 | |
218 | There is a new C<U> specifier that converts between Unicode characters |
219 | and code points. There is also a C<W> specifier that is the equivalent of |
220 | C<chr>/C<ord> and properly handles character values even if they are above 255. |
221 | |
222 | =item * |
223 | |
224 | The C<chr()> and C<ord()> functions work on characters, similar to |
225 | C<pack("W")> and C<unpack("W")>, I<not> C<pack("C")> and |
226 | C<unpack("C")>. C<pack("C")> and C<unpack("C")> are methods for |
227 | emulating byte-oriented C<chr()> and C<ord()> on Unicode strings. |
228 | While these methods reveal the internal encoding of Unicode strings, |
229 | that is not something one normally needs to care about at all. |
230 | |
231 | =item * |
232 | |
233 | The bit string operators, C<& | ^ ~>, can operate on character data. |
234 | However, for backward compatibility, such as when using bit string |
235 | operations when characters are all less than 256 in ordinal value, one |
236 | should not use C<~> (the bit complement) with characters of both |
237 | values less than 256 and values greater than 256. Most importantly, |
238 | DeMorgan's laws (C<~($x|$y) eq ~$x&~$y> and C<~($x&$y) eq ~$x|~$y>) |
239 | will not hold. The reason for this mathematical I<faux pas> is that |
240 | the complement cannot return B<both> the 8-bit (byte-wide) bit |
241 | complement B<and> the full character-wide bit complement. |
242 | |
243 | =item * |
244 | |
245 | lc(), uc(), lcfirst(), and ucfirst() work for the following cases: |
246 | |
247 | =over 8 |
248 | |
249 | =item * |
250 | |
251 | the case mapping is from a single Unicode character to another |
252 | single Unicode character, or |
253 | |
254 | =item * |
255 | |
256 | the case mapping is from a single Unicode character to more |
257 | than one Unicode character. |
258 | |
259 | =back |
260 | |
261 | Things to do with locales (Lithuanian, Turkish, Azeri) do B<not> work |
262 | since Perl does not understand the concept of Unicode locales. |
263 | |
264 | See the Unicode Technical Report #21, Case Mappings, for more details. |
265 | |
266 | But you can also define your own mappings to be used in the lc(), |
267 | lcfirst(), uc(), and ucfirst() (or their string-inlined versions). |
268 | |
269 | See L</"User-Defined Case Mappings"> for more details. |
270 | |
271 | =back |
272 | |
273 | =over 4 |
274 | |
275 | =item * |
276 | |
277 | And finally, C<scalar reverse()> reverses by character rather than by byte. |
278 | |
279 | =back |
280 | |
281 | =head2 Unicode Character Properties |
282 | |
283 | Named Unicode properties, scripts, and block ranges may be used like |
284 | character classes via the C<\p{}> "matches property" construct and |
285 | the C<\P{}> negation, "doesn't match property". |
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286 | |
287 | For instance, C<\p{Lu}> matches any character with the Unicode "Lu" |
288 | (Letter, uppercase) property, while C<\p{M}> matches any character |
289 | with an "M" (mark--accents and such) property. Brackets are not |
290 | required for single letter properties, so C<\p{M}> is equivalent to |
291 | C<\pM>. Many predefined properties are available, such as |
292 | C<\p{Mirrored}> and C<\p{Tibetan}>. |
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293 | |
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294 | The official Unicode script and block names have spaces and dashes as |
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295 | separators, but for convenience you can use dashes, spaces, or |
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296 | underbars, and case is unimportant. It is recommended, however, that |
297 | for consistency you use the following naming: the official Unicode |
298 | script, property, or block name (see below for the additional rules |
299 | that apply to block names) with whitespace and dashes removed, and the |
300 | words "uppercase-first-lowercase-rest". C<Latin-1 Supplement> thus |
301 | becomes C<Latin1Supplement>. |
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302 | |
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303 | You can also use negation in both C<\p{}> and C<\P{}> by introducing a caret |
304 | (^) between the first brace and the property name: C<\p{^Tamil}> is |
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305 | equal to C<\P{Tamil}>. |
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306 | |
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307 | B<NOTE: the properties, scripts, and blocks listed here are as of |
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308 | Unicode 5.0.0 in July 2006.> |
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309 | |
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310 | =over 4 |
311 | |
312 | =item General Category |
313 | |
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314 | Here are the basic Unicode General Category properties, followed by their |
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315 | long form. You can use either; C<\p{Lu}> and C<\p{UppercaseLetter}>, |
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316 | for instance, are identical. |
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317 | |
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318 | Short Long |
319 | |
320 | L Letter |
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321 | LC CasedLetter |
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322 | Lu UppercaseLetter |
323 | Ll LowercaseLetter |
324 | Lt TitlecaseLetter |
325 | Lm ModifierLetter |
326 | Lo OtherLetter |
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327 | |
328 | M Mark |
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329 | Mn NonspacingMark |
330 | Mc SpacingMark |
331 | Me EnclosingMark |
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332 | |
333 | N Number |
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334 | Nd DecimalNumber |
335 | Nl LetterNumber |
336 | No OtherNumber |
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337 | |
338 | P Punctuation |
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339 | Pc ConnectorPunctuation |
340 | Pd DashPunctuation |
341 | Ps OpenPunctuation |
342 | Pe ClosePunctuation |
343 | Pi InitialPunctuation |
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344 | (may behave like Ps or Pe depending on usage) |
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345 | Pf FinalPunctuation |
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346 | (may behave like Ps or Pe depending on usage) |
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347 | Po OtherPunctuation |
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348 | |
349 | S Symbol |
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350 | Sm MathSymbol |
351 | Sc CurrencySymbol |
352 | Sk ModifierSymbol |
353 | So OtherSymbol |
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354 | |
355 | Z Separator |
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356 | Zs SpaceSeparator |
357 | Zl LineSeparator |
358 | Zp ParagraphSeparator |
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359 | |
360 | C Other |
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361 | Cc Control |
362 | Cf Format |
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363 | Cs Surrogate (not usable) |
364 | Co PrivateUse |
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365 | Cn Unassigned |
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366 | |
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367 | Single-letter properties match all characters in any of the |
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368 | two-letter sub-properties starting with the same letter. |
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369 | C<LC> and C<L&> are special cases, which are aliases for the set of |
370 | C<Ll>, C<Lu>, and C<Lt>. |
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371 | |
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372 | Because Perl hides the need for the user to understand the internal |
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373 | representation of Unicode characters, there is no need to implement |
374 | the somewhat messy concept of surrogates. C<Cs> is therefore not |
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375 | supported. |
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376 | |
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377 | =item Bidirectional Character Types |
378 | |
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379 | Because scripts differ in their directionality--Hebrew is |
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380 | written right to left, for example--Unicode supplies these properties in |
381 | the BidiClass class: |
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382 | |
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383 | Property Meaning |
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384 | |
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385 | L Left-to-Right |
386 | LRE Left-to-Right Embedding |
387 | LRO Left-to-Right Override |
388 | R Right-to-Left |
389 | AL Right-to-Left Arabic |
390 | RLE Right-to-Left Embedding |
391 | RLO Right-to-Left Override |
392 | PDF Pop Directional Format |
393 | EN European Number |
394 | ES European Number Separator |
395 | ET European Number Terminator |
396 | AN Arabic Number |
397 | CS Common Number Separator |
398 | NSM Non-Spacing Mark |
399 | BN Boundary Neutral |
400 | B Paragraph Separator |
401 | S Segment Separator |
402 | WS Whitespace |
403 | ON Other Neutrals |
404 | |
405 | For example, C<\p{BidiClass:R}> matches characters that are normally |
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406 | written right to left. |
407 | |
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408 | =item Scripts |
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409 | |
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410 | The script names which can be used by C<\p{...}> and C<\P{...}>, |
411 | such as in C<\p{Latin}> or C<\p{Cyrillic}>, are as follows: |
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412 | |
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413 | Arabic |
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414 | Armenian |
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415 | Balinese |
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416 | Bengali |
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417 | Bopomofo |
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418 | Braille |
419 | Buginese |
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420 | Buhid |
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421 | CanadianAboriginal |
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422 | Cherokee |
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423 | Coptic |
424 | Cuneiform |
425 | Cypriot |
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426 | Cyrillic |
427 | Deseret |
428 | Devanagari |
429 | Ethiopic |
430 | Georgian |
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431 | Glagolitic |
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432 | Gothic |
433 | Greek |
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434 | Gujarati |
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435 | Gurmukhi |
436 | Han |
437 | Hangul |
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438 | Hanunoo |
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439 | Hebrew |
440 | Hiragana |
441 | Inherited |
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442 | Kannada |
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443 | Katakana |
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444 | Kharoshthi |
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445 | Khmer |
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446 | Lao |
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447 | Latin |
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448 | Limbu |
449 | LinearB |
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450 | Malayalam |
451 | Mongolian |
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452 | Myanmar |
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453 | NewTaiLue |
454 | Nko |
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455 | Ogham |
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456 | OldItalic |
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457 | OldPersian |
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458 | Oriya |
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459 | Osmanya |
460 | PhagsPa |
461 | Phoenician |
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462 | Runic |
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463 | Shavian |
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464 | Sinhala |
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465 | SylotiNagri |
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466 | Syriac |
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467 | Tagalog |
468 | Tagbanwa |
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469 | TaiLe |
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470 | Tamil |
471 | Telugu |
472 | Thaana |
473 | Thai |
474 | Tibetan |
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475 | Tifinagh |
476 | Ugaritic |
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477 | Yi |
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478 | |
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479 | =item Extended property classes |
480 | |
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481 | Extended property classes can supplement the basic |
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482 | properties, defined by the F<PropList> Unicode database: |
483 | |
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484 | ASCIIHexDigit |
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485 | BidiControl |
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486 | Dash |
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487 | Deprecated |
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488 | Diacritic |
489 | Extender |
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490 | HexDigit |
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491 | Hyphen |
492 | Ideographic |
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493 | IDSBinaryOperator |
494 | IDSTrinaryOperator |
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495 | JoinControl |
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496 | LogicalOrderException |
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497 | NoncharacterCodePoint |
498 | OtherAlphabetic |
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499 | OtherDefaultIgnorableCodePoint |
500 | OtherGraphemeExtend |
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501 | OtherIDStart |
502 | OtherIDContinue |
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503 | OtherLowercase |
504 | OtherMath |
505 | OtherUppercase |
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506 | PatternSyntax |
507 | PatternWhiteSpace |
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508 | QuotationMark |
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509 | Radical |
510 | SoftDotted |
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511 | STerm |
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512 | TerminalPunctuation |
513 | UnifiedIdeograph |
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514 | VariationSelector |
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515 | WhiteSpace |
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516 | |
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517 | and there are further derived properties: |
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518 | |
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519 | Alphabetic = Lu + Ll + Lt + Lm + Lo + Nl + OtherAlphabetic |
520 | Lowercase = Ll + OtherLowercase |
521 | Uppercase = Lu + OtherUppercase |
522 | Math = Sm + OtherMath |
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523 | |
8158862b |
524 | IDStart = Lu + Ll + Lt + Lm + Lo + Nl + OtherIDStart |
525 | IDContinue = IDStart + Mn + Mc + Nd + Pc + OtherIDContinue |
1ac13f9a |
526 | |
8158862b |
527 | DefaultIgnorableCodePoint |
528 | = OtherDefaultIgnorableCodePoint |
529 | + Cf + Cc + Cs + Noncharacters + VariationSelector |
530 | - WhiteSpace - FFF9..FFFB (Annotation Characters) |
531 | |
532 | Any = Any code points (i.e. U+0000 to U+10FFFF) |
533 | Assigned = Any non-Cn code points (i.e. synonym for \P{Cn}) |
534 | Unassigned = Synonym for \p{Cn} |
535 | ASCII = ASCII (i.e. U+0000 to U+007F) |
536 | |
537 | Common = Any character (or unassigned code point) |
538 | not explicitly assigned to a script |
2796c109 |
539 | |
822502e5 |
540 | =item Use of "Is" Prefix |
541 | |
1bfb14c4 |
542 | For backward compatibility (with Perl 5.6), all properties mentioned |
543 | so far may have C<Is> prepended to their name, so C<\P{IsLu}>, for |
544 | example, is equal to C<\P{Lu}>. |
eb0cc9e3 |
545 | |
822502e5 |
546 | =item Blocks |
2796c109 |
547 | |
1bfb14c4 |
548 | In addition to B<scripts>, Unicode also defines B<blocks> of |
549 | characters. The difference between scripts and blocks is that the |
550 | concept of scripts is closer to natural languages, while the concept |
551 | of blocks is more of an artificial grouping based on groups of 256 |
376d9008 |
552 | Unicode characters. For example, the C<Latin> script contains letters |
1bfb14c4 |
553 | from many blocks but does not contain all the characters from those |
376d9008 |
554 | blocks. It does not, for example, contain digits, because digits are |
555 | shared across many scripts. Digits and similar groups, like |
556 | punctuation, are in a category called C<Common>. |
2796c109 |
557 | |
8158862b |
558 | For more about scripts, see the UAX#24 "Script Names": |
cfc01aea |
559 | |
8158862b |
560 | http://www.unicode.org/reports/tr24/ |
cfc01aea |
561 | |
562 | For more about blocks, see: |
563 | |
564 | http://www.unicode.org/Public/UNIDATA/Blocks.txt |
2796c109 |
565 | |
376d9008 |
566 | Block names are given with the C<In> prefix. For example, the |
567 | Katakana block is referenced via C<\p{InKatakana}>. The C<In> |
7eabb34d |
568 | prefix may be omitted if there is no naming conflict with a script |
eb0cc9e3 |
569 | or any other property, but it is recommended that C<In> always be used |
1bfb14c4 |
570 | for block tests to avoid confusion. |
eb0cc9e3 |
571 | |
572 | These block names are supported: |
573 | |
8158862b |
574 | InAegeanNumbers |
1d81abf3 |
575 | InAlphabeticPresentationForms |
8158862b |
576 | InAncientGreekMusicalNotation |
577 | InAncientGreekNumbers |
1d81abf3 |
578 | InArabic |
579 | InArabicPresentationFormsA |
580 | InArabicPresentationFormsB |
8158862b |
581 | InArabicSupplement |
1d81abf3 |
582 | InArmenian |
583 | InArrows |
8158862b |
584 | InBalinese |
1d81abf3 |
585 | InBasicLatin |
586 | InBengali |
587 | InBlockElements |
588 | InBopomofo |
589 | InBopomofoExtended |
590 | InBoxDrawing |
591 | InBraillePatterns |
8158862b |
592 | InBuginese |
1d81abf3 |
593 | InBuhid |
594 | InByzantineMusicalSymbols |
595 | InCJKCompatibility |
596 | InCJKCompatibilityForms |
597 | InCJKCompatibilityIdeographs |
598 | InCJKCompatibilityIdeographsSupplement |
599 | InCJKRadicalsSupplement |
8158862b |
600 | InCJKStrokes |
1d81abf3 |
601 | InCJKSymbolsAndPunctuation |
602 | InCJKUnifiedIdeographs |
603 | InCJKUnifiedIdeographsExtensionA |
604 | InCJKUnifiedIdeographsExtensionB |
605 | InCherokee |
606 | InCombiningDiacriticalMarks |
8158862b |
607 | InCombiningDiacriticalMarksSupplement |
1d81abf3 |
608 | InCombiningDiacriticalMarksforSymbols |
609 | InCombiningHalfMarks |
610 | InControlPictures |
8158862b |
611 | InCoptic |
612 | InCountingRodNumerals |
613 | InCuneiform |
614 | InCuneiformNumbersAndPunctuation |
1d81abf3 |
615 | InCurrencySymbols |
8158862b |
616 | InCypriotSyllabary |
1d81abf3 |
617 | InCyrillic |
8158862b |
618 | InCyrillicSupplement |
1d81abf3 |
619 | InDeseret |
620 | InDevanagari |
621 | InDingbats |
622 | InEnclosedAlphanumerics |
623 | InEnclosedCJKLettersAndMonths |
624 | InEthiopic |
8158862b |
625 | InEthiopicExtended |
626 | InEthiopicSupplement |
1d81abf3 |
627 | InGeneralPunctuation |
628 | InGeometricShapes |
629 | InGeorgian |
8158862b |
630 | InGeorgianSupplement |
631 | InGlagolitic |
1d81abf3 |
632 | InGothic |
633 | InGreekExtended |
634 | InGreekAndCoptic |
635 | InGujarati |
636 | InGurmukhi |
637 | InHalfwidthAndFullwidthForms |
638 | InHangulCompatibilityJamo |
639 | InHangulJamo |
640 | InHangulSyllables |
641 | InHanunoo |
642 | InHebrew |
643 | InHighPrivateUseSurrogates |
644 | InHighSurrogates |
645 | InHiragana |
646 | InIPAExtensions |
647 | InIdeographicDescriptionCharacters |
648 | InKanbun |
649 | InKangxiRadicals |
650 | InKannada |
651 | InKatakana |
652 | InKatakanaPhoneticExtensions |
8158862b |
653 | InKharoshthi |
1d81abf3 |
654 | InKhmer |
8158862b |
655 | InKhmerSymbols |
1d81abf3 |
656 | InLao |
657 | InLatin1Supplement |
658 | InLatinExtendedA |
659 | InLatinExtendedAdditional |
660 | InLatinExtendedB |
8158862b |
661 | InLatinExtendedC |
662 | InLatinExtendedD |
1d81abf3 |
663 | InLetterlikeSymbols |
8158862b |
664 | InLimbu |
665 | InLinearBIdeograms |
666 | InLinearBSyllabary |
1d81abf3 |
667 | InLowSurrogates |
668 | InMalayalam |
669 | InMathematicalAlphanumericSymbols |
670 | InMathematicalOperators |
671 | InMiscellaneousMathematicalSymbolsA |
672 | InMiscellaneousMathematicalSymbolsB |
673 | InMiscellaneousSymbols |
8158862b |
674 | InMiscellaneousSymbolsAndArrows |
1d81abf3 |
675 | InMiscellaneousTechnical |
8158862b |
676 | InModifierToneLetters |
1d81abf3 |
677 | InMongolian |
678 | InMusicalSymbols |
679 | InMyanmar |
8158862b |
680 | InNKo |
681 | InNewTaiLue |
1d81abf3 |
682 | InNumberForms |
683 | InOgham |
684 | InOldItalic |
8158862b |
685 | InOldPersian |
1d81abf3 |
686 | InOpticalCharacterRecognition |
687 | InOriya |
8158862b |
688 | InOsmanya |
689 | InPhagspa |
690 | InPhoenician |
691 | InPhoneticExtensions |
692 | InPhoneticExtensionsSupplement |
1d81abf3 |
693 | InPrivateUseArea |
694 | InRunic |
8158862b |
695 | InShavian |
1d81abf3 |
696 | InSinhala |
697 | InSmallFormVariants |
698 | InSpacingModifierLetters |
699 | InSpecials |
700 | InSuperscriptsAndSubscripts |
701 | InSupplementalArrowsA |
702 | InSupplementalArrowsB |
703 | InSupplementalMathematicalOperators |
8158862b |
704 | InSupplementalPunctuation |
1d81abf3 |
705 | InSupplementaryPrivateUseAreaA |
706 | InSupplementaryPrivateUseAreaB |
8158862b |
707 | InSylotiNagri |
1d81abf3 |
708 | InSyriac |
709 | InTagalog |
710 | InTagbanwa |
711 | InTags |
8158862b |
712 | InTaiLe |
713 | InTaiXuanJingSymbols |
1d81abf3 |
714 | InTamil |
715 | InTelugu |
716 | InThaana |
717 | InThai |
718 | InTibetan |
8158862b |
719 | InTifinagh |
720 | InUgaritic |
1d81abf3 |
721 | InUnifiedCanadianAboriginalSyllabics |
722 | InVariationSelectors |
8158862b |
723 | InVariationSelectorsSupplement |
724 | InVerticalForms |
1d81abf3 |
725 | InYiRadicals |
726 | InYiSyllables |
8158862b |
727 | InYijingHexagramSymbols |
32293815 |
728 | |
393fec97 |
729 | =back |
730 | |
376d9008 |
731 | =head2 User-Defined Character Properties |
491fd90a |
732 | |
733 | You can define your own character properties by defining subroutines |
bac0b425 |
734 | whose names begin with "In" or "Is". The subroutines can be defined in |
735 | any package. The user-defined properties can be used in the regular |
736 | expression C<\p> and C<\P> constructs; if you are using a user-defined |
737 | property from a package other than the one you are in, you must specify |
738 | its package in the C<\p> or C<\P> construct. |
739 | |
740 | # assuming property IsForeign defined in Lang:: |
741 | package main; # property package name required |
742 | if ($txt =~ /\p{Lang::IsForeign}+/) { ... } |
743 | |
744 | package Lang; # property package name not required |
745 | if ($txt =~ /\p{IsForeign}+/) { ... } |
746 | |
747 | |
748 | Note that the effect is compile-time and immutable once defined. |
491fd90a |
749 | |
376d9008 |
750 | The subroutines must return a specially-formatted string, with one |
751 | or more newline-separated lines. Each line must be one of the following: |
491fd90a |
752 | |
753 | =over 4 |
754 | |
755 | =item * |
756 | |
510254c9 |
757 | A single hexadecimal number denoting a Unicode code point to include. |
758 | |
759 | =item * |
760 | |
99a6b1f0 |
761 | Two hexadecimal numbers separated by horizontal whitespace (space or |
376d9008 |
762 | tabular characters) denoting a range of Unicode code points to include. |
491fd90a |
763 | |
764 | =item * |
765 | |
376d9008 |
766 | Something to include, prefixed by "+": a built-in character |
bac0b425 |
767 | property (prefixed by "utf8::") or a user-defined character property, |
768 | to represent all the characters in that property; two hexadecimal code |
769 | points for a range; or a single hexadecimal code point. |
491fd90a |
770 | |
771 | =item * |
772 | |
376d9008 |
773 | Something to exclude, prefixed by "-": an existing character |
bac0b425 |
774 | property (prefixed by "utf8::") or a user-defined character property, |
775 | to represent all the characters in that property; two hexadecimal code |
776 | points for a range; or a single hexadecimal code point. |
491fd90a |
777 | |
778 | =item * |
779 | |
376d9008 |
780 | Something to negate, prefixed "!": an existing character |
bac0b425 |
781 | property (prefixed by "utf8::") or a user-defined character property, |
782 | to represent all the characters in that property; two hexadecimal code |
783 | points for a range; or a single hexadecimal code point. |
784 | |
785 | =item * |
786 | |
787 | Something to intersect with, prefixed by "&": an existing character |
788 | property (prefixed by "utf8::") or a user-defined character property, |
789 | for all the characters except the characters in the property; two |
790 | hexadecimal code points for a range; or a single hexadecimal code point. |
491fd90a |
791 | |
792 | =back |
793 | |
794 | For example, to define a property that covers both the Japanese |
795 | syllabaries (hiragana and katakana), you can define |
796 | |
797 | sub InKana { |
d5822f25 |
798 | return <<END; |
799 | 3040\t309F |
800 | 30A0\t30FF |
491fd90a |
801 | END |
802 | } |
803 | |
d5822f25 |
804 | Imagine that the here-doc end marker is at the beginning of the line. |
805 | Now you can use C<\p{InKana}> and C<\P{InKana}>. |
491fd90a |
806 | |
807 | You could also have used the existing block property names: |
808 | |
809 | sub InKana { |
810 | return <<'END'; |
811 | +utf8::InHiragana |
812 | +utf8::InKatakana |
813 | END |
814 | } |
815 | |
816 | Suppose you wanted to match only the allocated characters, |
d5822f25 |
817 | not the raw block ranges: in other words, you want to remove |
491fd90a |
818 | the non-characters: |
819 | |
820 | sub InKana { |
821 | return <<'END'; |
822 | +utf8::InHiragana |
823 | +utf8::InKatakana |
824 | -utf8::IsCn |
825 | END |
826 | } |
827 | |
828 | The negation is useful for defining (surprise!) negated classes. |
829 | |
830 | sub InNotKana { |
831 | return <<'END'; |
832 | !utf8::InHiragana |
833 | -utf8::InKatakana |
834 | +utf8::IsCn |
835 | END |
836 | } |
837 | |
bac0b425 |
838 | Intersection is useful for getting the common characters matched by |
839 | two (or more) classes. |
840 | |
841 | sub InFooAndBar { |
842 | return <<'END'; |
843 | +main::Foo |
844 | &main::Bar |
845 | END |
846 | } |
847 | |
848 | It's important to remember not to use "&" for the first set -- that |
849 | would be intersecting with nothing (resulting in an empty set). |
850 | |
822502e5 |
851 | =head2 User-Defined Case Mappings |
852 | |
3a2263fe |
853 | You can also define your own mappings to be used in the lc(), |
854 | lcfirst(), uc(), and ucfirst() (or their string-inlined versions). |
822502e5 |
855 | The principle is similar to that of user-defined character |
856 | properties: to define subroutines in the C<main> package |
3a2263fe |
857 | with names like C<ToLower> (for lc() and lcfirst()), C<ToTitle> (for |
858 | the first character in ucfirst()), and C<ToUpper> (for uc(), and the |
859 | rest of the characters in ucfirst()). |
860 | |
861 | The string returned by the subroutines needs now to be three |
862 | hexadecimal numbers separated by tabulators: start of the source |
863 | range, end of the source range, and start of the destination range. |
864 | For example: |
865 | |
866 | sub ToUpper { |
867 | return <<END; |
868 | 0061\t0063\t0041 |
869 | END |
870 | } |
871 | |
872 | defines an uc() mapping that causes only the characters "a", "b", and |
873 | "c" to be mapped to "A", "B", "C", all other characters will remain |
874 | unchanged. |
875 | |
876 | If there is no source range to speak of, that is, the mapping is from |
877 | a single character to another single character, leave the end of the |
878 | source range empty, but the two tabulator characters are still needed. |
879 | For example: |
880 | |
881 | sub ToLower { |
882 | return <<END; |
883 | 0041\t\t0061 |
884 | END |
885 | } |
886 | |
887 | defines a lc() mapping that causes only "A" to be mapped to "a", all |
888 | other characters will remain unchanged. |
889 | |
890 | (For serious hackers only) If you want to introspect the default |
891 | mappings, you can find the data in the directory |
892 | C<$Config{privlib}>/F<unicore/To/>. The mapping data is returned as |
893 | the here-document, and the C<utf8::ToSpecFoo> are special exception |
894 | mappings derived from <$Config{privlib}>/F<unicore/SpecialCasing.txt>. |
895 | The C<Digit> and C<Fold> mappings that one can see in the directory |
896 | are not directly user-accessible, one can use either the |
897 | C<Unicode::UCD> module, or just match case-insensitively (that's when |
898 | the C<Fold> mapping is used). |
899 | |
822502e5 |
900 | A final note on the user-defined case mappings: they will be used |
901 | only if the scalar has been marked as having Unicode characters. |
902 | Old byte-style strings will not be affected. |
3a2263fe |
903 | |
376d9008 |
904 | =head2 Character Encodings for Input and Output |
8cbd9a7a |
905 | |
7221edc9 |
906 | See L<Encode>. |
8cbd9a7a |
907 | |
c29a771d |
908 | =head2 Unicode Regular Expression Support Level |
776f8809 |
909 | |
376d9008 |
910 | The following list of Unicode support for regular expressions describes |
911 | all the features currently supported. The references to "Level N" |
8158862b |
912 | and the section numbers refer to the Unicode Technical Standard #18, |
913 | "Unicode Regular Expressions", version 11, in May 2005. |
776f8809 |
914 | |
915 | =over 4 |
916 | |
917 | =item * |
918 | |
919 | Level 1 - Basic Unicode Support |
920 | |
8158862b |
921 | RL1.1 Hex Notation - done [1] |
922 | RL1.2 Properties - done [2][3] |
923 | RL1.2a Compatibility Properties - done [4] |
924 | RL1.3 Subtraction and Intersection - MISSING [5] |
925 | RL1.4 Simple Word Boundaries - done [6] |
926 | RL1.5 Simple Loose Matches - done [7] |
927 | RL1.6 Line Boundaries - MISSING [8] |
928 | RL1.7 Supplementary Code Points - done [9] |
929 | |
930 | [1] \x{...} |
931 | [2] \p{...} \P{...} |
932 | [3] supports not only minimal list (general category, scripts, |
933 | Alphabetic, Lowercase, Uppercase, WhiteSpace, |
934 | NoncharacterCodePoint, DefaultIgnorableCodePoint, Any, |
935 | ASCII, Assigned), but also bidirectional types, blocks, etc. |
936 | (see L</"Unicode Character Properties">) |
937 | [4] \d \D \s \S \w \W \X [:prop:] [:^prop:] |
938 | [5] can use regular expression look-ahead [a] or |
939 | user-defined character properties [b] to emulate set operations |
940 | [6] \b \B |
941 | [7] note that Perl does Full case-folding in matching, not Simple: |
835863de |
942 | for example U+1F88 is equivalent with U+1F00 U+03B9, |
e0f9d4a8 |
943 | not with 1F80. This difference matters for certain Greek |
376d9008 |
944 | capital letters with certain modifiers: the Full case-folding |
945 | decomposes the letter, while the Simple case-folding would map |
e0f9d4a8 |
946 | it to a single character. |
8158862b |
947 | [8] should do ^ and $ also on U+000B (\v in C), FF (\f), CR (\r), |
948 | CRLF (\r\n), NEL (U+0085), LS (U+2028), and PS (U+2029); |
949 | should also affect <>, $., and script line numbers; |
950 | should not split lines within CRLF [c] (i.e. there is no empty |
951 | line between \r and \n) |
952 | [9] UTF-8/UTF-EBDDIC used in perl allows not only U+10000 to U+10FFFF |
953 | but also beyond U+10FFFF [d] |
7207e29d |
954 | |
237bad5b |
955 | [a] You can mimic class subtraction using lookahead. |
8158862b |
956 | For example, what UTS#18 might write as |
29bdacb8 |
957 | |
dbe420b4 |
958 | [{Greek}-[{UNASSIGNED}]] |
959 | |
960 | in Perl can be written as: |
961 | |
1d81abf3 |
962 | (?!\p{Unassigned})\p{InGreekAndCoptic} |
963 | (?=\p{Assigned})\p{InGreekAndCoptic} |
dbe420b4 |
964 | |
965 | But in this particular example, you probably really want |
966 | |
1bfb14c4 |
967 | \p{GreekAndCoptic} |
dbe420b4 |
968 | |
969 | which will match assigned characters known to be part of the Greek script. |
29bdacb8 |
970 | |
5ca1ac52 |
971 | Also see the Unicode::Regex::Set module, it does implement the full |
8158862b |
972 | UTS#18 grouping, intersection, union, and removal (subtraction) syntax. |
973 | |
974 | [b] '+' for union, '-' for removal (set-difference), '&' for intersection |
975 | (see L</"User-Defined Character Properties">) |
976 | |
977 | [c] Try the C<:crlf> layer (see L<PerlIO>). |
5ca1ac52 |
978 | |
8158862b |
979 | [d] Avoid C<use warning 'utf8';> (or say C<no warning 'utf8';>) to allow |
980 | U+FFFF (C<\x{FFFF}>). |
237bad5b |
981 | |
776f8809 |
982 | =item * |
983 | |
984 | Level 2 - Extended Unicode Support |
985 | |
8158862b |
986 | RL2.1 Canonical Equivalents - MISSING [10][11] |
987 | RL2.2 Default Grapheme Clusters - MISSING [12][13] |
988 | RL2.3 Default Word Boundaries - MISSING [14] |
989 | RL2.4 Default Loose Matches - MISSING [15] |
990 | RL2.5 Name Properties - MISSING [16] |
991 | RL2.6 Wildcard Properties - MISSING |
992 | |
993 | [10] see UAX#15 "Unicode Normalization Forms" |
994 | [11] have Unicode::Normalize but not integrated to regexes |
995 | [12] have \X but at this level . should equal that |
996 | [13] UAX#29 "Text Boundaries" considers CRLF and Hangul syllable |
997 | clusters as a single grapheme cluster. |
998 | [14] see UAX#29, Word Boundaries |
999 | [15] see UAX#21 "Case Mappings" |
1000 | [16] have \N{...} but neither compute names of CJK Ideographs |
1001 | and Hangul Syllables nor use a loose match [e] |
1002 | |
1003 | [e] C<\N{...}> allows namespaces (see L<charnames>). |
776f8809 |
1004 | |
1005 | =item * |
1006 | |
8158862b |
1007 | Level 3 - Tailored Support |
1008 | |
1009 | RL3.1 Tailored Punctuation - MISSING |
1010 | RL3.2 Tailored Grapheme Clusters - MISSING [17][18] |
1011 | RL3.3 Tailored Word Boundaries - MISSING |
1012 | RL3.4 Tailored Loose Matches - MISSING |
1013 | RL3.5 Tailored Ranges - MISSING |
1014 | RL3.6 Context Matching - MISSING [19] |
1015 | RL3.7 Incremental Matches - MISSING |
1016 | ( RL3.8 Unicode Set Sharing ) |
1017 | RL3.9 Possible Match Sets - MISSING |
1018 | RL3.10 Folded Matching - MISSING [20] |
1019 | RL3.11 Submatchers - MISSING |
1020 | |
1021 | [17] see UAX#10 "Unicode Collation Algorithms" |
1022 | [18] have Unicode::Collate but not integrated to regexes |
1023 | [19] have (?<=x) and (?=x), but look-aheads or look-behinds should see |
1024 | outside of the target substring |
1025 | [20] need insensitive matching for linguistic features other than case; |
1026 | for example, hiragana to katakana, wide and narrow, simplified Han |
1027 | to traditional Han (see UTR#30 "Character Foldings") |
776f8809 |
1028 | |
1029 | =back |
1030 | |
c349b1b9 |
1031 | =head2 Unicode Encodings |
1032 | |
376d9008 |
1033 | Unicode characters are assigned to I<code points>, which are abstract |
1034 | numbers. To use these numbers, various encodings are needed. |
c349b1b9 |
1035 | |
1036 | =over 4 |
1037 | |
c29a771d |
1038 | =item * |
5cb3728c |
1039 | |
1040 | UTF-8 |
c349b1b9 |
1041 | |
3e4dbfed |
1042 | UTF-8 is a variable-length (1 to 6 bytes, current character allocations |
376d9008 |
1043 | require 4 bytes), byte-order independent encoding. For ASCII (and we |
1044 | really do mean 7-bit ASCII, not another 8-bit encoding), UTF-8 is |
1045 | transparent. |
c349b1b9 |
1046 | |
8c007b5a |
1047 | The following table is from Unicode 3.2. |
05632f9a |
1048 | |
1049 | Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte |
1050 | |
8c007b5a |
1051 | U+0000..U+007F 00..7F |
1052 | U+0080..U+07FF C2..DF 80..BF |
ec90690f |
1053 | U+0800..U+0FFF E0 A0..BF 80..BF |
1054 | U+1000..U+CFFF E1..EC 80..BF 80..BF |
1055 | U+D000..U+D7FF ED 80..9F 80..BF |
8c007b5a |
1056 | U+D800..U+DFFF ******* ill-formed ******* |
ec90690f |
1057 | U+E000..U+FFFF EE..EF 80..BF 80..BF |
05632f9a |
1058 | U+10000..U+3FFFF F0 90..BF 80..BF 80..BF |
1059 | U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF |
1060 | U+100000..U+10FFFF F4 80..8F 80..BF 80..BF |
1061 | |
376d9008 |
1062 | Note the C<A0..BF> in C<U+0800..U+0FFF>, the C<80..9F> in |
1063 | C<U+D000...U+D7FF>, the C<90..B>F in C<U+10000..U+3FFFF>, and the |
1064 | C<80...8F> in C<U+100000..U+10FFFF>. The "gaps" are caused by legal |
1065 | UTF-8 avoiding non-shortest encodings: it is technically possible to |
1066 | UTF-8-encode a single code point in different ways, but that is |
1067 | explicitly forbidden, and the shortest possible encoding should always |
1068 | be used. So that's what Perl does. |
37361303 |
1069 | |
376d9008 |
1070 | Another way to look at it is via bits: |
05632f9a |
1071 | |
1072 | Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte |
1073 | |
1074 | 0aaaaaaa 0aaaaaaa |
1075 | 00000bbbbbaaaaaa 110bbbbb 10aaaaaa |
1076 | ccccbbbbbbaaaaaa 1110cccc 10bbbbbb 10aaaaaa |
1077 | 00000dddccccccbbbbbbaaaaaa 11110ddd 10cccccc 10bbbbbb 10aaaaaa |
1078 | |
1079 | As you can see, the continuation bytes all begin with C<10>, and the |
8c007b5a |
1080 | leading bits of the start byte tell how many bytes the are in the |
05632f9a |
1081 | encoded character. |
1082 | |
c29a771d |
1083 | =item * |
5cb3728c |
1084 | |
1085 | UTF-EBCDIC |
dbe420b4 |
1086 | |
376d9008 |
1087 | Like UTF-8 but EBCDIC-safe, in the way that UTF-8 is ASCII-safe. |
dbe420b4 |
1088 | |
c29a771d |
1089 | =item * |
5cb3728c |
1090 | |
1e54db1a |
1091 | UTF-16, UTF-16BE, UTF-16LE, Surrogates, and BOMs (Byte Order Marks) |
c349b1b9 |
1092 | |
1bfb14c4 |
1093 | The followings items are mostly for reference and general Unicode |
1094 | knowledge, Perl doesn't use these constructs internally. |
dbe420b4 |
1095 | |
c349b1b9 |
1096 | UTF-16 is a 2 or 4 byte encoding. The Unicode code points |
1bfb14c4 |
1097 | C<U+0000..U+FFFF> are stored in a single 16-bit unit, and the code |
1098 | points C<U+10000..U+10FFFF> in two 16-bit units. The latter case is |
c349b1b9 |
1099 | using I<surrogates>, the first 16-bit unit being the I<high |
1100 | surrogate>, and the second being the I<low surrogate>. |
1101 | |
376d9008 |
1102 | Surrogates are code points set aside to encode the C<U+10000..U+10FFFF> |
c349b1b9 |
1103 | range of Unicode code points in pairs of 16-bit units. The I<high |
376d9008 |
1104 | surrogates> are the range C<U+D800..U+DBFF>, and the I<low surrogates> |
1105 | are the range C<U+DC00..U+DFFF>. The surrogate encoding is |
c349b1b9 |
1106 | |
1107 | $hi = ($uni - 0x10000) / 0x400 + 0xD800; |
1108 | $lo = ($uni - 0x10000) % 0x400 + 0xDC00; |
1109 | |
1110 | and the decoding is |
1111 | |
1a3fa709 |
1112 | $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00); |
c349b1b9 |
1113 | |
feda178f |
1114 | If you try to generate surrogates (for example by using chr()), you |
376d9008 |
1115 | will get a warning if warnings are turned on, because those code |
1116 | points are not valid for a Unicode character. |
9466bab6 |
1117 | |
376d9008 |
1118 | Because of the 16-bitness, UTF-16 is byte-order dependent. UTF-16 |
c349b1b9 |
1119 | itself can be used for in-memory computations, but if storage or |
376d9008 |
1120 | transfer is required either UTF-16BE (big-endian) or UTF-16LE |
1121 | (little-endian) encodings must be chosen. |
c349b1b9 |
1122 | |
1123 | This introduces another problem: what if you just know that your data |
376d9008 |
1124 | is UTF-16, but you don't know which endianness? Byte Order Marks, or |
1125 | BOMs, are a solution to this. A special character has been reserved |
86bbd6d1 |
1126 | in Unicode to function as a byte order marker: the character with the |
376d9008 |
1127 | code point C<U+FEFF> is the BOM. |
042da322 |
1128 | |
c349b1b9 |
1129 | The trick is that if you read a BOM, you will know the byte order, |
376d9008 |
1130 | since if it was written on a big-endian platform, you will read the |
1131 | bytes C<0xFE 0xFF>, but if it was written on a little-endian platform, |
1132 | you will read the bytes C<0xFF 0xFE>. (And if the originating platform |
1133 | was writing in UTF-8, you will read the bytes C<0xEF 0xBB 0xBF>.) |
042da322 |
1134 | |
86bbd6d1 |
1135 | The way this trick works is that the character with the code point |
376d9008 |
1136 | C<U+FFFE> is guaranteed not to be a valid Unicode character, so the |
1137 | sequence of bytes C<0xFF 0xFE> is unambiguously "BOM, represented in |
1bfb14c4 |
1138 | little-endian format" and cannot be C<U+FFFE>, represented in big-endian |
042da322 |
1139 | format". |
c349b1b9 |
1140 | |
c29a771d |
1141 | =item * |
5cb3728c |
1142 | |
1e54db1a |
1143 | UTF-32, UTF-32BE, UTF-32LE |
c349b1b9 |
1144 | |
1145 | The UTF-32 family is pretty much like the UTF-16 family, expect that |
042da322 |
1146 | the units are 32-bit, and therefore the surrogate scheme is not |
376d9008 |
1147 | needed. The BOM signatures will be C<0x00 0x00 0xFE 0xFF> for BE and |
1148 | C<0xFF 0xFE 0x00 0x00> for LE. |
c349b1b9 |
1149 | |
c29a771d |
1150 | =item * |
5cb3728c |
1151 | |
1152 | UCS-2, UCS-4 |
c349b1b9 |
1153 | |
86bbd6d1 |
1154 | Encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit |
376d9008 |
1155 | encoding. Unlike UTF-16, UCS-2 is not extensible beyond C<U+FFFF>, |
339cfa0e |
1156 | because it does not use surrogates. UCS-4 is a 32-bit encoding, |
1157 | functionally identical to UTF-32. |
c349b1b9 |
1158 | |
c29a771d |
1159 | =item * |
5cb3728c |
1160 | |
1161 | UTF-7 |
c349b1b9 |
1162 | |
376d9008 |
1163 | A seven-bit safe (non-eight-bit) encoding, which is useful if the |
1164 | transport or storage is not eight-bit safe. Defined by RFC 2152. |
c349b1b9 |
1165 | |
95a1a48b |
1166 | =back |
1167 | |
0d7c09bb |
1168 | =head2 Security Implications of Unicode |
1169 | |
1170 | =over 4 |
1171 | |
1172 | =item * |
1173 | |
1174 | Malformed UTF-8 |
bf0fa0b2 |
1175 | |
1176 | Unfortunately, the specification of UTF-8 leaves some room for |
1177 | interpretation of how many bytes of encoded output one should generate |
376d9008 |
1178 | from one input Unicode character. Strictly speaking, the shortest |
1179 | possible sequence of UTF-8 bytes should be generated, |
1180 | because otherwise there is potential for an input buffer overflow at |
feda178f |
1181 | the receiving end of a UTF-8 connection. Perl always generates the |
376d9008 |
1182 | shortest length UTF-8, and with warnings on Perl will warn about |
1183 | non-shortest length UTF-8 along with other malformations, such as the |
1184 | surrogates, which are not real Unicode code points. |
bf0fa0b2 |
1185 | |
0d7c09bb |
1186 | =item * |
1187 | |
1188 | Regular expressions behave slightly differently between byte data and |
376d9008 |
1189 | character (Unicode) data. For example, the "word character" character |
1190 | class C<\w> will work differently depending on if data is eight-bit bytes |
1191 | or Unicode. |
0d7c09bb |
1192 | |
376d9008 |
1193 | In the first case, the set of C<\w> characters is either small--the |
1194 | default set of alphabetic characters, digits, and the "_"--or, if you |
0d7c09bb |
1195 | are using a locale (see L<perllocale>), the C<\w> might contain a few |
1196 | more letters according to your language and country. |
1197 | |
376d9008 |
1198 | In the second case, the C<\w> set of characters is much, much larger. |
1bfb14c4 |
1199 | Most importantly, even in the set of the first 256 characters, it will |
1200 | probably match different characters: unlike most locales, which are |
1201 | specific to a language and country pair, Unicode classifies all the |
1202 | characters that are letters I<somewhere> as C<\w>. For example, your |
1203 | locale might not think that LATIN SMALL LETTER ETH is a letter (unless |
1204 | you happen to speak Icelandic), but Unicode does. |
0d7c09bb |
1205 | |
376d9008 |
1206 | As discussed elsewhere, Perl has one foot (two hooves?) planted in |
1bfb14c4 |
1207 | each of two worlds: the old world of bytes and the new world of |
1208 | characters, upgrading from bytes to characters when necessary. |
376d9008 |
1209 | If your legacy code does not explicitly use Unicode, no automatic |
1210 | switch-over to characters should happen. Characters shouldn't get |
1bfb14c4 |
1211 | downgraded to bytes, either. It is possible to accidentally mix bytes |
1212 | and characters, however (see L<perluniintro>), in which case C<\w> in |
1213 | regular expressions might start behaving differently. Review your |
1214 | code. Use warnings and the C<strict> pragma. |
0d7c09bb |
1215 | |
1216 | =back |
1217 | |
c349b1b9 |
1218 | =head2 Unicode in Perl on EBCDIC |
1219 | |
376d9008 |
1220 | The way Unicode is handled on EBCDIC platforms is still |
1221 | experimental. On such platforms, references to UTF-8 encoding in this |
1222 | document and elsewhere should be read as meaning the UTF-EBCDIC |
1223 | specified in Unicode Technical Report 16, unless ASCII vs. EBCDIC issues |
c349b1b9 |
1224 | are specifically discussed. There is no C<utfebcdic> pragma or |
376d9008 |
1225 | ":utfebcdic" layer; rather, "utf8" and ":utf8" are reused to mean |
86bbd6d1 |
1226 | the platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic> |
1227 | for more discussion of the issues. |
c349b1b9 |
1228 | |
b310b053 |
1229 | =head2 Locales |
1230 | |
4616122b |
1231 | Usually locale settings and Unicode do not affect each other, but |
b310b053 |
1232 | there are a couple of exceptions: |
1233 | |
1234 | =over 4 |
1235 | |
1236 | =item * |
1237 | |
8aa8f774 |
1238 | You can enable automatic UTF-8-ification of your standard file |
1239 | handles, default C<open()> layer, and C<@ARGV> by using either |
1240 | the C<-C> command line switch or the C<PERL_UNICODE> environment |
1241 | variable, see L<perlrun> for the documentation of the C<-C> switch. |
b310b053 |
1242 | |
1243 | =item * |
1244 | |
376d9008 |
1245 | Perl tries really hard to work both with Unicode and the old |
1246 | byte-oriented world. Most often this is nice, but sometimes Perl's |
1247 | straddling of the proverbial fence causes problems. |
b310b053 |
1248 | |
1249 | =back |
1250 | |
1aad1664 |
1251 | =head2 When Unicode Does Not Happen |
1252 | |
1253 | While Perl does have extensive ways to input and output in Unicode, |
1254 | and few other 'entry points' like the @ARGV which can be interpreted |
1255 | as Unicode (UTF-8), there still are many places where Unicode (in some |
1256 | encoding or another) could be given as arguments or received as |
1257 | results, or both, but it is not. |
1258 | |
6cd4dd6c |
1259 | The following are such interfaces. For all of these interfaces Perl |
1260 | currently (as of 5.8.3) simply assumes byte strings both as arguments |
1261 | and results, or UTF-8 strings if the C<encoding> pragma has been used. |
1aad1664 |
1262 | |
1263 | One reason why Perl does not attempt to resolve the role of Unicode in |
1264 | this cases is that the answers are highly dependent on the operating |
1265 | system and the file system(s). For example, whether filenames can be |
1266 | in Unicode, and in exactly what kind of encoding, is not exactly a |
1267 | portable concept. Similarly for the qx and system: how well will the |
1268 | 'command line interface' (and which of them?) handle Unicode? |
1269 | |
1270 | =over 4 |
1271 | |
557a2462 |
1272 | =item * |
1273 | |
254c2b64 |
1274 | chdir, chmod, chown, chroot, exec, link, lstat, mkdir, |
1e8e8236 |
1275 | rename, rmdir, stat, symlink, truncate, unlink, utime, -X |
557a2462 |
1276 | |
1277 | =item * |
1278 | |
1279 | %ENV |
1280 | |
1281 | =item * |
1282 | |
1283 | glob (aka the <*>) |
1284 | |
1285 | =item * |
1aad1664 |
1286 | |
557a2462 |
1287 | open, opendir, sysopen |
1aad1664 |
1288 | |
557a2462 |
1289 | =item * |
1aad1664 |
1290 | |
557a2462 |
1291 | qx (aka the backtick operator), system |
1aad1664 |
1292 | |
557a2462 |
1293 | =item * |
1aad1664 |
1294 | |
557a2462 |
1295 | readdir, readlink |
1aad1664 |
1296 | |
1297 | =back |
1298 | |
1299 | =head2 Forcing Unicode in Perl (Or Unforcing Unicode in Perl) |
1300 | |
1301 | Sometimes (see L</"When Unicode Does Not Happen">) there are |
1302 | situations where you simply need to force Perl to believe that a byte |
1303 | string is UTF-8, or vice versa. The low-level calls |
1304 | utf8::upgrade($bytestring) and utf8::downgrade($utf8string) are |
1305 | the answers. |
1306 | |
1307 | Do not use them without careful thought, though: Perl may easily get |
1308 | very confused, angry, or even crash, if you suddenly change the 'nature' |
1309 | of scalar like that. Especially careful you have to be if you use the |
1310 | utf8::upgrade(): any random byte string is not valid UTF-8. |
1311 | |
95a1a48b |
1312 | =head2 Using Unicode in XS |
1313 | |
3a2263fe |
1314 | If you want to handle Perl Unicode in XS extensions, you may find the |
1315 | following C APIs useful. See also L<perlguts/"Unicode Support"> for an |
1316 | explanation about Unicode at the XS level, and L<perlapi> for the API |
1317 | details. |
95a1a48b |
1318 | |
1319 | =over 4 |
1320 | |
1321 | =item * |
1322 | |
1bfb14c4 |
1323 | C<DO_UTF8(sv)> returns true if the C<UTF8> flag is on and the bytes |
1324 | pragma is not in effect. C<SvUTF8(sv)> returns true is the C<UTF8> |
1325 | flag is on; the bytes pragma is ignored. The C<UTF8> flag being on |
1326 | does B<not> mean that there are any characters of code points greater |
1327 | than 255 (or 127) in the scalar or that there are even any characters |
1328 | in the scalar. What the C<UTF8> flag means is that the sequence of |
1329 | octets in the representation of the scalar is the sequence of UTF-8 |
1330 | encoded code points of the characters of a string. The C<UTF8> flag |
1331 | being off means that each octet in this representation encodes a |
1332 | single character with code point 0..255 within the string. Perl's |
1333 | Unicode model is not to use UTF-8 until it is absolutely necessary. |
95a1a48b |
1334 | |
1335 | =item * |
1336 | |
fb9cc174 |
1337 | C<uvuni_to_utf8(buf, chr)> writes a Unicode character code point into |
1bfb14c4 |
1338 | a buffer encoding the code point as UTF-8, and returns a pointer |
95a1a48b |
1339 | pointing after the UTF-8 bytes. |
1340 | |
1341 | =item * |
1342 | |
376d9008 |
1343 | C<utf8_to_uvuni(buf, lenp)> reads UTF-8 encoded bytes from a buffer and |
1344 | returns the Unicode character code point and, optionally, the length of |
1345 | the UTF-8 byte sequence. |
95a1a48b |
1346 | |
1347 | =item * |
1348 | |
376d9008 |
1349 | C<utf8_length(start, end)> returns the length of the UTF-8 encoded buffer |
1350 | in characters. C<sv_len_utf8(sv)> returns the length of the UTF-8 encoded |
95a1a48b |
1351 | scalar. |
1352 | |
1353 | =item * |
1354 | |
376d9008 |
1355 | C<sv_utf8_upgrade(sv)> converts the string of the scalar to its UTF-8 |
1356 | encoded form. C<sv_utf8_downgrade(sv)> does the opposite, if |
1357 | possible. C<sv_utf8_encode(sv)> is like sv_utf8_upgrade except that |
1358 | it does not set the C<UTF8> flag. C<sv_utf8_decode()> does the |
1359 | opposite of C<sv_utf8_encode()>. Note that none of these are to be |
1360 | used as general-purpose encoding or decoding interfaces: C<use Encode> |
1361 | for that. C<sv_utf8_upgrade()> is affected by the encoding pragma |
1362 | but C<sv_utf8_downgrade()> is not (since the encoding pragma is |
1363 | designed to be a one-way street). |
95a1a48b |
1364 | |
1365 | =item * |
1366 | |
376d9008 |
1367 | C<is_utf8_char(s)> returns true if the pointer points to a valid UTF-8 |
90f968e0 |
1368 | character. |
95a1a48b |
1369 | |
1370 | =item * |
1371 | |
376d9008 |
1372 | C<is_utf8_string(buf, len)> returns true if C<len> bytes of the buffer |
95a1a48b |
1373 | are valid UTF-8. |
1374 | |
1375 | =item * |
1376 | |
376d9008 |
1377 | C<UTF8SKIP(buf)> will return the number of bytes in the UTF-8 encoded |
1378 | character in the buffer. C<UNISKIP(chr)> will return the number of bytes |
1379 | required to UTF-8-encode the Unicode character code point. C<UTF8SKIP()> |
90f968e0 |
1380 | is useful for example for iterating over the characters of a UTF-8 |
376d9008 |
1381 | encoded buffer; C<UNISKIP()> is useful, for example, in computing |
90f968e0 |
1382 | the size required for a UTF-8 encoded buffer. |
95a1a48b |
1383 | |
1384 | =item * |
1385 | |
376d9008 |
1386 | C<utf8_distance(a, b)> will tell the distance in characters between the |
95a1a48b |
1387 | two pointers pointing to the same UTF-8 encoded buffer. |
1388 | |
1389 | =item * |
1390 | |
376d9008 |
1391 | C<utf8_hop(s, off)> will return a pointer to an UTF-8 encoded buffer |
1392 | that is C<off> (positive or negative) Unicode characters displaced |
1393 | from the UTF-8 buffer C<s>. Be careful not to overstep the buffer: |
1394 | C<utf8_hop()> will merrily run off the end or the beginning of the |
1395 | buffer if told to do so. |
95a1a48b |
1396 | |
d2cc3551 |
1397 | =item * |
1398 | |
376d9008 |
1399 | C<pv_uni_display(dsv, spv, len, pvlim, flags)> and |
1400 | C<sv_uni_display(dsv, ssv, pvlim, flags)> are useful for debugging the |
1401 | output of Unicode strings and scalars. By default they are useful |
1402 | only for debugging--they display B<all> characters as hexadecimal code |
1bfb14c4 |
1403 | points--but with the flags C<UNI_DISPLAY_ISPRINT>, |
1404 | C<UNI_DISPLAY_BACKSLASH>, and C<UNI_DISPLAY_QQ> you can make the |
1405 | output more readable. |
d2cc3551 |
1406 | |
1407 | =item * |
1408 | |
376d9008 |
1409 | C<ibcmp_utf8(s1, pe1, u1, l1, u1, s2, pe2, l2, u2)> can be used to |
1410 | compare two strings case-insensitively in Unicode. For case-sensitive |
1411 | comparisons you can just use C<memEQ()> and C<memNE()> as usual. |
d2cc3551 |
1412 | |
c349b1b9 |
1413 | =back |
1414 | |
95a1a48b |
1415 | For more information, see L<perlapi>, and F<utf8.c> and F<utf8.h> |
1416 | in the Perl source code distribution. |
1417 | |
c29a771d |
1418 | =head1 BUGS |
1419 | |
376d9008 |
1420 | =head2 Interaction with Locales |
7eabb34d |
1421 | |
376d9008 |
1422 | Use of locales with Unicode data may lead to odd results. Currently, |
1423 | Perl attempts to attach 8-bit locale info to characters in the range |
1424 | 0..255, but this technique is demonstrably incorrect for locales that |
1425 | use characters above that range when mapped into Unicode. Perl's |
1426 | Unicode support will also tend to run slower. Use of locales with |
1427 | Unicode is discouraged. |
c29a771d |
1428 | |
376d9008 |
1429 | =head2 Interaction with Extensions |
7eabb34d |
1430 | |
376d9008 |
1431 | When Perl exchanges data with an extension, the extension should be |
2575c402 |
1432 | able to understand the UTF8 flag and act accordingly. If the |
376d9008 |
1433 | extension doesn't know about the flag, it's likely that the extension |
1434 | will return incorrectly-flagged data. |
7eabb34d |
1435 | |
1436 | So if you're working with Unicode data, consult the documentation of |
1437 | every module you're using if there are any issues with Unicode data |
1438 | exchange. If the documentation does not talk about Unicode at all, |
a73d23f6 |
1439 | suspect the worst and probably look at the source to learn how the |
376d9008 |
1440 | module is implemented. Modules written completely in Perl shouldn't |
a73d23f6 |
1441 | cause problems. Modules that directly or indirectly access code written |
1442 | in other programming languages are at risk. |
7eabb34d |
1443 | |
376d9008 |
1444 | For affected functions, the simple strategy to avoid data corruption is |
7eabb34d |
1445 | to always make the encoding of the exchanged data explicit. Choose an |
376d9008 |
1446 | encoding that you know the extension can handle. Convert arguments passed |
7eabb34d |
1447 | to the extensions to that encoding and convert results back from that |
1448 | encoding. Write wrapper functions that do the conversions for you, so |
1449 | you can later change the functions when the extension catches up. |
1450 | |
376d9008 |
1451 | To provide an example, let's say the popular Foo::Bar::escape_html |
7eabb34d |
1452 | function doesn't deal with Unicode data yet. The wrapper function |
1453 | would convert the argument to raw UTF-8 and convert the result back to |
376d9008 |
1454 | Perl's internal representation like so: |
7eabb34d |
1455 | |
1456 | sub my_escape_html ($) { |
1457 | my($what) = shift; |
1458 | return unless defined $what; |
1459 | Encode::decode_utf8(Foo::Bar::escape_html(Encode::encode_utf8($what))); |
1460 | } |
1461 | |
1462 | Sometimes, when the extension does not convert data but just stores |
1463 | and retrieves them, you will be in a position to use the otherwise |
1464 | dangerous Encode::_utf8_on() function. Let's say the popular |
66b79f27 |
1465 | C<Foo::Bar> extension, written in C, provides a C<param> method that |
7eabb34d |
1466 | lets you store and retrieve data according to these prototypes: |
1467 | |
1468 | $self->param($name, $value); # set a scalar |
1469 | $value = $self->param($name); # retrieve a scalar |
1470 | |
1471 | If it does not yet provide support for any encoding, one could write a |
1472 | derived class with such a C<param> method: |
1473 | |
1474 | sub param { |
1475 | my($self,$name,$value) = @_; |
1476 | utf8::upgrade($name); # make sure it is UTF-8 encoded |
af55fc6a |
1477 | if (defined $value) { |
7eabb34d |
1478 | utf8::upgrade($value); # make sure it is UTF-8 encoded |
1479 | return $self->SUPER::param($name,$value); |
1480 | } else { |
1481 | my $ret = $self->SUPER::param($name); |
1482 | Encode::_utf8_on($ret); # we know, it is UTF-8 encoded |
1483 | return $ret; |
1484 | } |
1485 | } |
1486 | |
a73d23f6 |
1487 | Some extensions provide filters on data entry/exit points, such as |
1488 | DB_File::filter_store_key and family. Look out for such filters in |
66b79f27 |
1489 | the documentation of your extensions, they can make the transition to |
7eabb34d |
1490 | Unicode data much easier. |
1491 | |
376d9008 |
1492 | =head2 Speed |
7eabb34d |
1493 | |
c29a771d |
1494 | Some functions are slower when working on UTF-8 encoded strings than |
574c8022 |
1495 | on byte encoded strings. All functions that need to hop over |
7c17141f |
1496 | characters such as length(), substr() or index(), or matching regular |
1497 | expressions can work B<much> faster when the underlying data are |
1498 | byte-encoded. |
1499 | |
1500 | In Perl 5.8.0 the slowness was often quite spectacular; in Perl 5.8.1 |
1501 | a caching scheme was introduced which will hopefully make the slowness |
a104b433 |
1502 | somewhat less spectacular, at least for some operations. In general, |
1503 | operations with UTF-8 encoded strings are still slower. As an example, |
1504 | the Unicode properties (character classes) like C<\p{Nd}> are known to |
1505 | be quite a bit slower (5-20 times) than their simpler counterparts |
1506 | like C<\d> (then again, there 268 Unicode characters matching C<Nd> |
1507 | compared with the 10 ASCII characters matching C<d>). |
666f95b9 |
1508 | |
c8d992ba |
1509 | =head2 Porting code from perl-5.6.X |
1510 | |
1511 | Perl 5.8 has a different Unicode model from 5.6. In 5.6 the programmer |
1512 | was required to use the C<utf8> pragma to declare that a given scope |
1513 | expected to deal with Unicode data and had to make sure that only |
1514 | Unicode data were reaching that scope. If you have code that is |
1515 | working with 5.6, you will need some of the following adjustments to |
1516 | your code. The examples are written such that the code will continue |
1517 | to work under 5.6, so you should be safe to try them out. |
1518 | |
1519 | =over 4 |
1520 | |
1521 | =item * |
1522 | |
1523 | A filehandle that should read or write UTF-8 |
1524 | |
1525 | if ($] > 5.007) { |
1526 | binmode $fh, ":utf8"; |
1527 | } |
1528 | |
1529 | =item * |
1530 | |
1531 | A scalar that is going to be passed to some extension |
1532 | |
1533 | Be it Compress::Zlib, Apache::Request or any extension that has no |
1534 | mention of Unicode in the manpage, you need to make sure that the |
2575c402 |
1535 | UTF8 flag is stripped off. Note that at the time of this writing |
c8d992ba |
1536 | (October 2002) the mentioned modules are not UTF-8-aware. Please |
1537 | check the documentation to verify if this is still true. |
1538 | |
1539 | if ($] > 5.007) { |
1540 | require Encode; |
1541 | $val = Encode::encode_utf8($val); # make octets |
1542 | } |
1543 | |
1544 | =item * |
1545 | |
1546 | A scalar we got back from an extension |
1547 | |
1548 | If you believe the scalar comes back as UTF-8, you will most likely |
2575c402 |
1549 | want the UTF8 flag restored: |
c8d992ba |
1550 | |
1551 | if ($] > 5.007) { |
1552 | require Encode; |
1553 | $val = Encode::decode_utf8($val); |
1554 | } |
1555 | |
1556 | =item * |
1557 | |
1558 | Same thing, if you are really sure it is UTF-8 |
1559 | |
1560 | if ($] > 5.007) { |
1561 | require Encode; |
1562 | Encode::_utf8_on($val); |
1563 | } |
1564 | |
1565 | =item * |
1566 | |
1567 | A wrapper for fetchrow_array and fetchrow_hashref |
1568 | |
1569 | When the database contains only UTF-8, a wrapper function or method is |
1570 | a convenient way to replace all your fetchrow_array and |
1571 | fetchrow_hashref calls. A wrapper function will also make it easier to |
1572 | adapt to future enhancements in your database driver. Note that at the |
1573 | time of this writing (October 2002), the DBI has no standardized way |
1574 | to deal with UTF-8 data. Please check the documentation to verify if |
1575 | that is still true. |
1576 | |
1577 | sub fetchrow { |
1578 | my($self, $sth, $what) = @_; # $what is one of fetchrow_{array,hashref} |
1579 | if ($] < 5.007) { |
1580 | return $sth->$what; |
1581 | } else { |
1582 | require Encode; |
1583 | if (wantarray) { |
1584 | my @arr = $sth->$what; |
1585 | for (@arr) { |
1586 | defined && /[^\000-\177]/ && Encode::_utf8_on($_); |
1587 | } |
1588 | return @arr; |
1589 | } else { |
1590 | my $ret = $sth->$what; |
1591 | if (ref $ret) { |
1592 | for my $k (keys %$ret) { |
1593 | defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret->{$k}; |
1594 | } |
1595 | return $ret; |
1596 | } else { |
1597 | defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret; |
1598 | return $ret; |
1599 | } |
1600 | } |
1601 | } |
1602 | } |
1603 | |
1604 | |
1605 | =item * |
1606 | |
1607 | A large scalar that you know can only contain ASCII |
1608 | |
1609 | Scalars that contain only ASCII and are marked as UTF-8 are sometimes |
1610 | a drag to your program. If you recognize such a situation, just remove |
2575c402 |
1611 | the UTF8 flag: |
c8d992ba |
1612 | |
1613 | utf8::downgrade($val) if $] > 5.007; |
1614 | |
1615 | =back |
1616 | |
393fec97 |
1617 | =head1 SEE ALSO |
1618 | |
2575c402 |
1619 | L<perlunitut>, L<perluniintro>, L<Encode>, L<open>, L<utf8>, L<bytes>, |
a05d7ebb |
1620 | L<perlretut>, L<perlvar/"${^UNICODE}"> |
393fec97 |
1621 | |
1622 | =cut |