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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 | =over 4 |
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14 | |
15 | =item Input and Output Disciplines |
16 | |
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17 | Perl knows when a filehandle uses Perl's internal Unicode encodings |
18 | (UTF-8 or UTF-EBCDIC) if the filehandle is opened with the ":utf8" |
19 | layer. Other encodings can be converted to Perl's encoding on input |
20 | or from Perl's encoding on output by use of the ":encoding(...)" |
21 | layer. See L<open>. |
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22 | |
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23 | To indicate that Perl source itself is using a particular encoding, |
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24 | see L<encoding>. |
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25 | |
26 | =item Regular Expressions |
27 | |
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28 | The regular expression compiler produces polymorphic opcodes. That is, |
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29 | the pattern adapts to the data and automatically switches to the Unicode |
30 | character scheme when presented with Unicode data--or instead uses |
31 | a traditional byte scheme when presented with byte data. |
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32 | |
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33 | =item C<use utf8> still needed to enable UTF-8/UTF-EBCDIC in scripts |
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34 | |
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35 | As a compatibility measure, the C<use utf8> pragma must be explicitly |
36 | included to enable recognition of UTF-8 in the Perl scripts themselves |
37 | on ASCII-based machines or to recognize UTF-EBCDIC on EBCDIC-based |
38 | machines. B<These are the only times when an explicit C<use utf8> |
39 | is needed.> |
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40 | |
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41 | You can also use the C<encoding> pragma to change the default encoding |
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42 | of the data in your script; see L<encoding>. |
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43 | |
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44 | =back |
45 | |
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46 | =head2 Byte and Character Semantics |
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47 | |
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48 | Beginning with version 5.6, Perl uses logically-wide characters to |
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49 | represent strings internally. |
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50 | |
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51 | In future, Perl-level operations will be expected to work with |
52 | characters rather than bytes. |
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53 | |
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54 | However, as an interim compatibility measure, Perl aims to |
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55 | provide a safe migration path from byte semantics to character |
56 | semantics for programs. For operations where Perl can unambiguously |
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57 | decide that the input data are characters, Perl switches to |
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58 | character semantics. For operations where this determination cannot |
59 | be made without additional information from the user, Perl decides in |
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60 | favor of compatibility and chooses to use byte semantics. |
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61 | |
62 | This behavior preserves compatibility with earlier versions of Perl, |
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63 | which allowed byte semantics in Perl operations only if |
64 | none of the program's inputs were marked as being as source of Unicode |
8cbd9a7a |
65 | character data. Such data may come from filehandles, from calls to |
66 | external programs, from information provided by the system (such as %ENV), |
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67 | or from literals and constants in the source text. |
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68 | |
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69 | On Windows platforms, if the C<-C> command line switch is used or the |
70 | ${^WIDE_SYSTEM_CALLS} global flag is set to C<1>, all system calls |
71 | will use the corresponding wide-character APIs. This feature is |
72 | available only on Windows to conform to the API standard already |
73 | established for that platform. |
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74 | |
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75 | The C<bytes> pragma will always, regardless of platform, force byte |
76 | semantics in a particular lexical scope. See L<bytes>. |
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77 | |
78 | The C<utf8> pragma is primarily a compatibility device that enables |
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79 | recognition of UTF-(8|EBCDIC) in literals encountered by the parser. |
376d9008 |
80 | Note that this pragma is only required while Perl defaults to byte |
81 | semantics; when character semantics become the default, this pragma |
82 | may become a no-op. See L<utf8>. |
83 | |
84 | Unless explicitly stated, Perl operators use character semantics |
85 | for Unicode data and byte semantics for non-Unicode data. |
86 | The decision to use character semantics is made transparently. If |
87 | input data comes from a Unicode source--for example, if a character |
88 | encoding discipline is added to a filehandle or a literal Unicode |
89 | string constant appears in a program--character semantics apply. |
90 | Otherwise, byte semantics are in effect. The C<bytes> pragma should |
91 | be used to force byte semantics on Unicode data. |
92 | |
93 | If strings operating under byte semantics and strings with Unicode |
94 | character data are concatenated, the new string will be upgraded to |
95 | I<ISO 8859-1 (Latin-1)>, even if the old Unicode string used EBCDIC. |
96 | This translation is done without regard to the system's native 8-bit |
97 | encoding, so to change this for systems with non-Latin-1 and |
98 | non-EBCDIC native encodings use the C<encoding> pragma. See |
99 | L<encoding>. |
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100 | |
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101 | Under character semantics, many operations that formerly operated on |
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102 | bytes now operate on characters. A character in Perl is |
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103 | logically just a number ranging from 0 to 2**31 or so. Larger |
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104 | characters may encode into longer sequences of bytes internally, but |
105 | this internal detail is mostly hidden for Perl code. |
106 | See L<perluniintro> for more. |
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107 | |
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108 | =head2 Effects of Character Semantics |
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109 | |
110 | Character semantics have the following effects: |
111 | |
112 | =over 4 |
113 | |
114 | =item * |
115 | |
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116 | Strings--including hash keys--and regular expression patterns may |
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117 | contain characters that have an ordinal value larger than 255. |
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118 | |
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119 | If you use a Unicode editor to edit your program, Unicode characters |
120 | may occur directly within the literal strings in one of the various |
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121 | Unicode encodings (UTF-8, UTF-EBCDIC, UCS-2, etc.), but will be recognized |
122 | as such and converted to Perl's internal representation only if the |
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123 | appropriate L<encoding> is specified. |
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124 | |
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125 | Unicode characters can also be added to a string by using the C<\x{...}> |
126 | notation. The Unicode code for the desired character, in |
127 | hexadecimal, should be placed in the braces. For instance, a smiley |
128 | face is C<\x{263A}>. This encoding scheme only works for characters |
129 | with a code of 0x100 or above. |
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130 | |
131 | Additionally, if you |
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132 | |
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133 | use charnames ':full'; |
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134 | |
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135 | you can use the C<\N{...}> notation and put the official Unicode character |
136 | name within the braces, such as C<\N{WHITE SMILING FACE}>. |
137 | |
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138 | |
139 | =item * |
140 | |
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141 | If an appropriate L<encoding> is specified, identifiers within the |
142 | Perl script may contain Unicode alphanumeric characters, including |
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143 | ideographs. Perl does not currently attempt to canonicalize variable |
144 | names. |
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145 | |
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146 | =item * |
147 | |
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148 | Regular expressions match characters instead of bytes. |
149 | "." matches a character instead of a byte. The C<\C> pattern |
150 | is provided to force a match a single byte--a "C<char>" in C, hence C<\C>. |
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151 | |
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152 | =item * |
153 | |
154 | Character classes in regular expressions match characters instead of |
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155 | bytes and match against the character properties specified in the |
156 | Unicode properties database. C<\w> can be used to match an |
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157 | ideograph, for instance. |
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158 | |
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159 | =item * |
160 | |
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161 | Named Unicode properties, scripts, and block ranges may be used like |
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162 | character classes via the C<\p{}> "matches property" construct and |
163 | the C<\P{}> negation, "doesn't match property". |
164 | For instance, C<\p{Lu}> matches any |
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165 | character with the Unicode "Lu" (Letter, uppercase) property, while |
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166 | C<\p{M}> matches any character with an "M" (mark--accents and such) |
167 | property. Brackets are not required for single letter properties, so |
168 | C<\p{M}> is equivalent to C<\pM>. Many predefined properties are |
169 | available, such as C<\p{Mirrored}> and C<\p{Tibetan}>. |
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170 | |
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171 | The official Unicode script and block names have spaces and dashes as |
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172 | separators, but for convenience you can use dashes, spaces, or |
173 | underbars, and case is unimportant. It is |
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174 | recommended, however, that for consistency you use the following naming: |
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175 | the official Unicode script, property, or block name (see below for the |
176 | additional rules that apply to block names) with whitespace and dashes |
177 | removed, and the words "uppercase-first-lowercase-rest". "C<Latin-1 |
178 | Supplement>" thus becomes "C<Latin1Supplement>". |
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179 | |
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180 | You can also use negation in both C<\p{}> and C<\P{}> by introducing a caret |
181 | (^) between the first brace and the property name: C<\p{^Tamil}> is |
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182 | equal to C<\P{Tamil}>. |
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183 | |
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184 | Here are the basic Unicode General Category properties, followed by their |
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185 | long form. You can use either; C<\p{Lu}> and C<\p{LowercaseLetter}>, |
186 | for instance, are identical. |
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187 | |
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188 | Short Long |
189 | |
190 | L Letter |
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191 | Lu UppercaseLetter |
192 | Ll LowercaseLetter |
193 | Lt TitlecaseLetter |
194 | Lm ModifierLetter |
195 | Lo OtherLetter |
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196 | |
197 | M Mark |
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198 | Mn NonspacingMark |
199 | Mc SpacingMark |
200 | Me EnclosingMark |
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201 | |
202 | N Number |
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203 | Nd DecimalNumber |
204 | Nl LetterNumber |
205 | No OtherNumber |
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206 | |
207 | P Punctuation |
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208 | Pc ConnectorPunctuation |
209 | Pd DashPunctuation |
210 | Ps OpenPunctuation |
211 | Pe ClosePunctuation |
212 | Pi InitialPunctuation |
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213 | (may behave like Ps or Pe depending on usage) |
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214 | Pf FinalPunctuation |
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215 | (may behave like Ps or Pe depending on usage) |
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216 | Po OtherPunctuation |
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217 | |
218 | S Symbol |
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219 | Sm MathSymbol |
220 | Sc CurrencySymbol |
221 | Sk ModifierSymbol |
222 | So OtherSymbol |
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223 | |
224 | Z Separator |
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225 | Zs SpaceSeparator |
226 | Zl LineSeparator |
227 | Zp ParagraphSeparator |
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228 | |
229 | C Other |
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230 | Cc Control |
231 | Cf Format |
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232 | Cs Surrogate (not usable) |
233 | Co PrivateUse |
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234 | Cn Unassigned |
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235 | |
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236 | Single-letter properties match all characters in any of the |
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237 | two-letter sub-properties starting with the same letter. |
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238 | C<L&> is a special case, which is an alias for C<Ll>, C<Lu>, and C<Lt>. |
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239 | |
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240 | Because Perl hides the need for the user to understand the internal |
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241 | representation of Unicode characters, there is no need to implement the |
242 | somewhat messy concept of surrogates. C<Cs> is therefore not |
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243 | supported. |
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244 | |
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245 | Because scripts differ in their directionality--Hebrew is |
246 | written right to left, for example--Unicode supplies these properties: |
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247 | |
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248 | Property Meaning |
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249 | |
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250 | BidiL Left-to-Right |
251 | BidiLRE Left-to-Right Embedding |
252 | BidiLRO Left-to-Right Override |
253 | BidiR Right-to-Left |
254 | BidiAL Right-to-Left Arabic |
255 | BidiRLE Right-to-Left Embedding |
256 | BidiRLO Right-to-Left Override |
257 | BidiPDF Pop Directional Format |
258 | BidiEN European Number |
259 | BidiES European Number Separator |
260 | BidiET European Number Terminator |
261 | BidiAN Arabic Number |
262 | BidiCS Common Number Separator |
263 | BidiNSM Non-Spacing Mark |
264 | BidiBN Boundary Neutral |
265 | BidiB Paragraph Separator |
266 | BidiS Segment Separator |
267 | BidiWS Whitespace |
268 | BidiON Other Neutrals |
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269 | |
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270 | For example, C<\p{BidiR}> matches characters that are normally |
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271 | written right to left. |
272 | |
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273 | =back |
274 | |
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275 | =head2 Scripts |
276 | |
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277 | The script names which can be used by C<\p{...}> and C<\P{...}>, |
278 | such as in C<\p{Latin}> or C<\p{Cyrillic}>, are as follows: |
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279 | |
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280 | Arabic |
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281 | Armenian |
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282 | Bengali |
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283 | Bopomofo |
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284 | Buhid |
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285 | CanadianAboriginal |
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286 | Cherokee |
287 | Cyrillic |
288 | Deseret |
289 | Devanagari |
290 | Ethiopic |
291 | Georgian |
292 | Gothic |
293 | Greek |
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294 | Gujarati |
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295 | Gurmukhi |
296 | Han |
297 | Hangul |
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298 | Hanunoo |
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299 | Hebrew |
300 | Hiragana |
301 | Inherited |
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302 | Kannada |
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303 | Katakana |
304 | Khmer |
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305 | Lao |
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306 | Latin |
307 | Malayalam |
308 | Mongolian |
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309 | Myanmar |
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310 | Ogham |
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311 | OldItalic |
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312 | Oriya |
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313 | Runic |
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314 | Sinhala |
315 | Syriac |
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316 | Tagalog |
317 | Tagbanwa |
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318 | Tamil |
319 | Telugu |
320 | Thaana |
321 | Thai |
322 | Tibetan |
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323 | Yi |
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324 | |
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325 | Extended property classes can supplement the basic |
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326 | properties, defined by the F<PropList> Unicode database: |
327 | |
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328 | ASCIIHexDigit |
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329 | BidiControl |
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330 | Dash |
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331 | Deprecated |
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332 | Diacritic |
333 | Extender |
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334 | GraphemeLink |
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335 | HexDigit |
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336 | Hyphen |
337 | Ideographic |
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338 | IDSBinaryOperator |
339 | IDSTrinaryOperator |
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340 | JoinControl |
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341 | LogicalOrderException |
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342 | NoncharacterCodePoint |
343 | OtherAlphabetic |
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344 | OtherDefaultIgnorableCodePoint |
345 | OtherGraphemeExtend |
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346 | OtherLowercase |
347 | OtherMath |
348 | OtherUppercase |
349 | QuotationMark |
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350 | Radical |
351 | SoftDotted |
352 | TerminalPunctuation |
353 | UnifiedIdeograph |
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354 | WhiteSpace |
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355 | |
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356 | and there are further derived properties: |
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357 | |
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358 | Alphabetic Lu + Ll + Lt + Lm + Lo + OtherAlphabetic |
359 | Lowercase Ll + OtherLowercase |
360 | Uppercase Lu + OtherUppercase |
361 | Math Sm + OtherMath |
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362 | |
363 | ID_Start Lu + Ll + Lt + Lm + Lo + Nl |
364 | ID_Continue ID_Start + Mn + Mc + Nd + Pc |
365 | |
366 | Any Any character |
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367 | Assigned Any non-Cn character (i.e. synonym for \P{Cn}) |
368 | Unassigned Synonym for \p{Cn} |
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369 | Common Any character (or unassigned code point) |
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370 | not explicitly assigned to a script |
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371 | |
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372 | For backward compatibility, all properties mentioned so far may have C<Is> |
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373 | prepended to their name, so C<\P{IsLu}>, for example, is equal to C<\P{Lu}>. |
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374 | |
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375 | =head2 Blocks |
376 | |
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377 | In addition to B<scripts>, Unicode also defines B<blocks> of characters. |
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378 | The difference between scripts and blocks is that the concept of |
379 | scripts is closer to natural languages, while the concept of blocks |
380 | is more of an artificial grouping based on groups of around 256 |
381 | Unicode characters. For example, the C<Latin> script contains letters |
382 | from many blocks but does not contain all the characters from those |
383 | blocks. It does not, for example, contain digits, because digits are |
384 | shared across many scripts. Digits and similar groups, like |
385 | punctuation, are in a category called C<Common>. |
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386 | |
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387 | For more about scripts, see the UTR #24: |
388 | |
389 | http://www.unicode.org/unicode/reports/tr24/ |
390 | |
391 | For more about blocks, see: |
392 | |
393 | http://www.unicode.org/Public/UNIDATA/Blocks.txt |
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394 | |
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395 | Block names are given with the C<In> prefix. For example, the |
396 | Katakana block is referenced via C<\p{InKatakana}>. The C<In> |
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397 | prefix may be omitted if there is no naming conflict with a script |
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398 | or any other property, but it is recommended that C<In> always be used |
399 | to avoid confusion. |
400 | |
401 | These block names are supported: |
402 | |
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403 | InAlphabeticPresentationForms |
404 | InArabic |
405 | InArabicPresentationFormsA |
406 | InArabicPresentationFormsB |
407 | InArmenian |
408 | InArrows |
409 | InBasicLatin |
410 | InBengali |
411 | InBlockElements |
412 | InBopomofo |
413 | InBopomofoExtended |
414 | InBoxDrawing |
415 | InBraillePatterns |
416 | InBuhid |
417 | InByzantineMusicalSymbols |
418 | InCJKCompatibility |
419 | InCJKCompatibilityForms |
420 | InCJKCompatibilityIdeographs |
421 | InCJKCompatibilityIdeographsSupplement |
422 | InCJKRadicalsSupplement |
423 | InCJKSymbolsAndPunctuation |
424 | InCJKUnifiedIdeographs |
425 | InCJKUnifiedIdeographsExtensionA |
426 | InCJKUnifiedIdeographsExtensionB |
427 | InCherokee |
428 | InCombiningDiacriticalMarks |
429 | InCombiningDiacriticalMarksforSymbols |
430 | InCombiningHalfMarks |
431 | InControlPictures |
432 | InCurrencySymbols |
433 | InCyrillic |
434 | InCyrillicSupplementary |
435 | InDeseret |
436 | InDevanagari |
437 | InDingbats |
438 | InEnclosedAlphanumerics |
439 | InEnclosedCJKLettersAndMonths |
440 | InEthiopic |
441 | InGeneralPunctuation |
442 | InGeometricShapes |
443 | InGeorgian |
444 | InGothic |
445 | InGreekExtended |
446 | InGreekAndCoptic |
447 | InGujarati |
448 | InGurmukhi |
449 | InHalfwidthAndFullwidthForms |
450 | InHangulCompatibilityJamo |
451 | InHangulJamo |
452 | InHangulSyllables |
453 | InHanunoo |
454 | InHebrew |
455 | InHighPrivateUseSurrogates |
456 | InHighSurrogates |
457 | InHiragana |
458 | InIPAExtensions |
459 | InIdeographicDescriptionCharacters |
460 | InKanbun |
461 | InKangxiRadicals |
462 | InKannada |
463 | InKatakana |
464 | InKatakanaPhoneticExtensions |
465 | InKhmer |
466 | InLao |
467 | InLatin1Supplement |
468 | InLatinExtendedA |
469 | InLatinExtendedAdditional |
470 | InLatinExtendedB |
471 | InLetterlikeSymbols |
472 | InLowSurrogates |
473 | InMalayalam |
474 | InMathematicalAlphanumericSymbols |
475 | InMathematicalOperators |
476 | InMiscellaneousMathematicalSymbolsA |
477 | InMiscellaneousMathematicalSymbolsB |
478 | InMiscellaneousSymbols |
479 | InMiscellaneousTechnical |
480 | InMongolian |
481 | InMusicalSymbols |
482 | InMyanmar |
483 | InNumberForms |
484 | InOgham |
485 | InOldItalic |
486 | InOpticalCharacterRecognition |
487 | InOriya |
488 | InPrivateUseArea |
489 | InRunic |
490 | InSinhala |
491 | InSmallFormVariants |
492 | InSpacingModifierLetters |
493 | InSpecials |
494 | InSuperscriptsAndSubscripts |
495 | InSupplementalArrowsA |
496 | InSupplementalArrowsB |
497 | InSupplementalMathematicalOperators |
498 | InSupplementaryPrivateUseAreaA |
499 | InSupplementaryPrivateUseAreaB |
500 | InSyriac |
501 | InTagalog |
502 | InTagbanwa |
503 | InTags |
504 | InTamil |
505 | InTelugu |
506 | InThaana |
507 | InThai |
508 | InTibetan |
509 | InUnifiedCanadianAboriginalSyllabics |
510 | InVariationSelectors |
511 | InYiRadicals |
512 | InYiSyllables |
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513 | |
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514 | =over 4 |
515 | |
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516 | =item * |
517 | |
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518 | The special pattern C<\X> matches any extended Unicode |
519 | sequence--"a combining character sequence" in Standardese--where the |
520 | first character is a base character and subsequent characters are mark |
521 | characters that apply to the base character. C<\X> is equivalent to |
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522 | C<(?:\PM\pM*)>. |
523 | |
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524 | =item * |
525 | |
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526 | The C<tr///> operator translates characters instead of bytes. Note |
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527 | that the C<tr///CU> functionality has been removed. For similar |
528 | functionality see pack('U0', ...) and pack('C0', ...). |
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529 | |
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530 | =item * |
531 | |
532 | Case translation operators use the Unicode case translation tables |
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533 | when character input is provided. Note that C<uc()>, or C<\U> in |
534 | interpolated strings, translates to uppercase, while C<ucfirst>, |
535 | or C<\u> in interpolated strings, translates to titlecase in languages |
536 | that make the distinction. |
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537 | |
538 | =item * |
539 | |
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540 | Most operators that deal with positions or lengths in a string will |
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541 | automatically switch to using character positions, including |
542 | C<chop()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>, |
543 | C<sprintf()>, C<write()>, and C<length()>. Operators that |
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544 | specifically do not switch include C<vec()>, C<pack()>, and |
545 | C<unpack()>. Operators that really don't care include C<chomp()>, |
546 | operators that treats strings as a bucket of bits such as C<sort()>, |
547 | and operators dealing with filenames. |
393fec97 |
548 | |
549 | =item * |
550 | |
551 | The C<pack()>/C<unpack()> letters "C<c>" and "C<C>" do I<not> change, |
376d9008 |
552 | since they are often used for byte-oriented formats. Again, think |
553 | "C<char>" in the C language. There is a new "C<U>" specifier |
554 | that converts between Unicode characters and integers. |
393fec97 |
555 | |
556 | =item * |
557 | |
376d9008 |
558 | The C<chr()> and C<ord()> functions work on characters, similar to |
559 | C<pack("U")> and C<unpack("U")>, I<not> C<pack("C")> and |
560 | C<unpack("C")>. C<pack("C")> and C<unpack("C")> are methods for |
561 | emulating byte-oriented C<chr()> and C<ord()> on Unicode strings. |
562 | While these methods reveal the internal encoding of Unicode strings, |
563 | that is not something one normally needs to care about at all. |
393fec97 |
564 | |
565 | =item * |
566 | |
376d9008 |
567 | The bit string operators, C<& | ^ ~>, can operate on character data. |
568 | However, for backward compatibility, such as when using bit string |
569 | operations when characters are all less than 256 in ordinal value, one |
570 | should not use C<~> (the bit complement) with characters of both |
571 | values less than 256 and values greater than 256. Most importantly, |
572 | DeMorgan's laws (C<~($x|$y) eq ~$x&~$y> and C<~($x&$y) eq ~$x|~$y>) |
573 | will not hold. The reason for this mathematical I<faux pas> is that |
574 | the complement cannot return B<both> the 8-bit (byte-wide) bit |
575 | complement B<and> the full character-wide bit complement. |
a1ca4561 |
576 | |
577 | =item * |
578 | |
983ffd37 |
579 | lc(), uc(), lcfirst(), and ucfirst() work for the following cases: |
580 | |
581 | =over 8 |
582 | |
583 | =item * |
584 | |
585 | the case mapping is from a single Unicode character to another |
376d9008 |
586 | single Unicode character, or |
983ffd37 |
587 | |
588 | =item * |
589 | |
590 | the case mapping is from a single Unicode character to more |
376d9008 |
591 | than one Unicode character. |
983ffd37 |
592 | |
593 | =back |
594 | |
376d9008 |
595 | The following cases do not yet work: |
983ffd37 |
596 | |
597 | =over 8 |
598 | |
599 | =item * |
600 | |
376d9008 |
601 | the "final sigma" (Greek), and |
983ffd37 |
602 | |
603 | =item * |
604 | |
376d9008 |
605 | anything to with locales (Lithuanian, Turkish, Azeri). |
983ffd37 |
606 | |
607 | =back |
608 | |
609 | See the Unicode Technical Report #21, Case Mappings, for more details. |
ac1256e8 |
610 | |
611 | =item * |
612 | |
393fec97 |
613 | And finally, C<scalar reverse()> reverses by character rather than by byte. |
614 | |
615 | =back |
616 | |
376d9008 |
617 | =head2 User-Defined Character Properties |
491fd90a |
618 | |
619 | You can define your own character properties by defining subroutines |
376d9008 |
620 | whose names begin with "In" or "Is". The subroutines must be |
491fd90a |
621 | visible in the package that uses the properties. The user-defined |
622 | properties can be used in the regular expression C<\p> and C<\P> |
623 | constructs. |
624 | |
376d9008 |
625 | The subroutines must return a specially-formatted string, with one |
626 | or more newline-separated lines. Each line must be one of the following: |
491fd90a |
627 | |
628 | =over 4 |
629 | |
630 | =item * |
631 | |
99a6b1f0 |
632 | Two hexadecimal numbers separated by horizontal whitespace (space or |
376d9008 |
633 | tabular characters) denoting a range of Unicode code points to include. |
491fd90a |
634 | |
635 | =item * |
636 | |
376d9008 |
637 | Something to include, prefixed by "+": a built-in character |
638 | property (prefixed by "utf8::"), to represent all the characters in that |
639 | property; two hexadecimal code points for a range; or a single |
640 | hexadecimal code point. |
491fd90a |
641 | |
642 | =item * |
643 | |
376d9008 |
644 | Something to exclude, prefixed by "-": an existing character |
11ef8fdd |
645 | property (prefixed by "utf8::"), for all the characters in that |
376d9008 |
646 | property; two hexadecimal code points for a range; or a single |
647 | hexadecimal code point. |
491fd90a |
648 | |
649 | =item * |
650 | |
376d9008 |
651 | Something to negate, prefixed "!": an existing character |
11ef8fdd |
652 | property (prefixed by "utf8::") for all the characters except the |
376d9008 |
653 | characters in the property; two hexadecimal code points for a range; |
654 | or a single hexadecimal code point. |
491fd90a |
655 | |
656 | =back |
657 | |
658 | For example, to define a property that covers both the Japanese |
659 | syllabaries (hiragana and katakana), you can define |
660 | |
661 | sub InKana { |
d5822f25 |
662 | return <<END; |
663 | 3040\t309F |
664 | 30A0\t30FF |
491fd90a |
665 | END |
666 | } |
667 | |
d5822f25 |
668 | Imagine that the here-doc end marker is at the beginning of the line. |
669 | Now you can use C<\p{InKana}> and C<\P{InKana}>. |
491fd90a |
670 | |
671 | You could also have used the existing block property names: |
672 | |
673 | sub InKana { |
674 | return <<'END'; |
675 | +utf8::InHiragana |
676 | +utf8::InKatakana |
677 | END |
678 | } |
679 | |
680 | Suppose you wanted to match only the allocated characters, |
d5822f25 |
681 | not the raw block ranges: in other words, you want to remove |
491fd90a |
682 | the non-characters: |
683 | |
684 | sub InKana { |
685 | return <<'END'; |
686 | +utf8::InHiragana |
687 | +utf8::InKatakana |
688 | -utf8::IsCn |
689 | END |
690 | } |
691 | |
692 | The negation is useful for defining (surprise!) negated classes. |
693 | |
694 | sub InNotKana { |
695 | return <<'END'; |
696 | !utf8::InHiragana |
697 | -utf8::InKatakana |
698 | +utf8::IsCn |
699 | END |
700 | } |
701 | |
376d9008 |
702 | =head2 Character Encodings for Input and Output |
8cbd9a7a |
703 | |
7221edc9 |
704 | See L<Encode>. |
8cbd9a7a |
705 | |
c29a771d |
706 | =head2 Unicode Regular Expression Support Level |
776f8809 |
707 | |
376d9008 |
708 | The following list of Unicode support for regular expressions describes |
709 | all the features currently supported. The references to "Level N" |
710 | and the section numbers refer to the Unicode Technical Report 18, |
711 | "Unicode Regular Expression Guidelines". |
776f8809 |
712 | |
713 | =over 4 |
714 | |
715 | =item * |
716 | |
717 | Level 1 - Basic Unicode Support |
718 | |
719 | 2.1 Hex Notation - done [1] |
3bfdc84c |
720 | Named Notation - done [2] |
776f8809 |
721 | 2.2 Categories - done [3][4] |
722 | 2.3 Subtraction - MISSING [5][6] |
723 | 2.4 Simple Word Boundaries - done [7] |
78d3e1bf |
724 | 2.5 Simple Loose Matches - done [8] |
776f8809 |
725 | 2.6 End of Line - MISSING [9][10] |
726 | |
727 | [ 1] \x{...} |
728 | [ 2] \N{...} |
eb0cc9e3 |
729 | [ 3] . \p{...} \P{...} |
29bdacb8 |
730 | [ 4] now scripts (see UTR#24 Script Names) in addition to blocks |
776f8809 |
731 | [ 5] have negation |
237bad5b |
732 | [ 6] can use regular expression look-ahead [a] |
733 | or user-defined character properties [b] to emulate subtraction |
776f8809 |
734 | [ 7] include Letters in word characters |
376d9008 |
735 | [ 8] note that Perl does Full case-folding in matching, not Simple: |
e0f9d4a8 |
736 | for example U+1F88 is equivalent with U+1F000 U+03B9, |
737 | not with 1F80. This difference matters for certain Greek |
376d9008 |
738 | capital letters with certain modifiers: the Full case-folding |
739 | decomposes the letter, while the Simple case-folding would map |
e0f9d4a8 |
740 | it to a single character. |
776f8809 |
741 | [ 9] see UTR#13 Unicode Newline Guidelines |
ec83e909 |
742 | [10] should do ^ and $ also on \x{85}, \x{2028} and \x{2029}) |
743 | (should also affect <>, $., and script line numbers) |
3bfdc84c |
744 | (the \x{85}, \x{2028} and \x{2029} do match \s) |
7207e29d |
745 | |
237bad5b |
746 | [a] You can mimic class subtraction using lookahead. |
dbe420b4 |
747 | For example, what TR18 might write as |
29bdacb8 |
748 | |
dbe420b4 |
749 | [{Greek}-[{UNASSIGNED}]] |
750 | |
751 | in Perl can be written as: |
752 | |
1d81abf3 |
753 | (?!\p{Unassigned})\p{InGreekAndCoptic} |
754 | (?=\p{Assigned})\p{InGreekAndCoptic} |
dbe420b4 |
755 | |
756 | But in this particular example, you probably really want |
757 | |
758 | \p{Greek} |
759 | |
760 | which will match assigned characters known to be part of the Greek script. |
29bdacb8 |
761 | |
237bad5b |
762 | [b] See L</User-defined Character Properties>. |
763 | |
776f8809 |
764 | =item * |
765 | |
766 | Level 2 - Extended Unicode Support |
767 | |
768 | 3.1 Surrogates - MISSING |
769 | 3.2 Canonical Equivalents - MISSING [11][12] |
770 | 3.3 Locale-Independent Graphemes - MISSING [13] |
771 | 3.4 Locale-Independent Words - MISSING [14] |
772 | 3.5 Locale-Independent Loose Matches - MISSING [15] |
773 | |
774 | [11] see UTR#15 Unicode Normalization |
775 | [12] have Unicode::Normalize but not integrated to regexes |
776 | [13] have \X but at this level . should equal that |
777 | [14] need three classes, not just \w and \W |
778 | [15] see UTR#21 Case Mappings |
779 | |
780 | =item * |
781 | |
782 | Level 3 - Locale-Sensitive Support |
783 | |
784 | 4.1 Locale-Dependent Categories - MISSING |
785 | 4.2 Locale-Dependent Graphemes - MISSING [16][17] |
786 | 4.3 Locale-Dependent Words - MISSING |
787 | 4.4 Locale-Dependent Loose Matches - MISSING |
788 | 4.5 Locale-Dependent Ranges - MISSING |
789 | |
790 | [16] see UTR#10 Unicode Collation Algorithms |
791 | [17] have Unicode::Collate but not integrated to regexes |
792 | |
793 | =back |
794 | |
c349b1b9 |
795 | =head2 Unicode Encodings |
796 | |
376d9008 |
797 | Unicode characters are assigned to I<code points>, which are abstract |
798 | numbers. To use these numbers, various encodings are needed. |
c349b1b9 |
799 | |
800 | =over 4 |
801 | |
c29a771d |
802 | =item * |
5cb3728c |
803 | |
804 | UTF-8 |
c349b1b9 |
805 | |
3e4dbfed |
806 | UTF-8 is a variable-length (1 to 6 bytes, current character allocations |
376d9008 |
807 | require 4 bytes), byte-order independent encoding. For ASCII (and we |
808 | really do mean 7-bit ASCII, not another 8-bit encoding), UTF-8 is |
809 | transparent. |
c349b1b9 |
810 | |
8c007b5a |
811 | The following table is from Unicode 3.2. |
05632f9a |
812 | |
813 | Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte |
814 | |
8c007b5a |
815 | U+0000..U+007F 00..7F |
816 | U+0080..U+07FF C2..DF 80..BF |
ec90690f |
817 | U+0800..U+0FFF E0 A0..BF 80..BF |
818 | U+1000..U+CFFF E1..EC 80..BF 80..BF |
819 | U+D000..U+D7FF ED 80..9F 80..BF |
8c007b5a |
820 | U+D800..U+DFFF ******* ill-formed ******* |
ec90690f |
821 | U+E000..U+FFFF EE..EF 80..BF 80..BF |
05632f9a |
822 | U+10000..U+3FFFF F0 90..BF 80..BF 80..BF |
823 | U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF |
824 | U+100000..U+10FFFF F4 80..8F 80..BF 80..BF |
825 | |
376d9008 |
826 | Note the C<A0..BF> in C<U+0800..U+0FFF>, the C<80..9F> in |
827 | C<U+D000...U+D7FF>, the C<90..B>F in C<U+10000..U+3FFFF>, and the |
828 | C<80...8F> in C<U+100000..U+10FFFF>. The "gaps" are caused by legal |
829 | UTF-8 avoiding non-shortest encodings: it is technically possible to |
830 | UTF-8-encode a single code point in different ways, but that is |
831 | explicitly forbidden, and the shortest possible encoding should always |
832 | be used. So that's what Perl does. |
37361303 |
833 | |
376d9008 |
834 | Another way to look at it is via bits: |
05632f9a |
835 | |
836 | Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte |
837 | |
838 | 0aaaaaaa 0aaaaaaa |
839 | 00000bbbbbaaaaaa 110bbbbb 10aaaaaa |
840 | ccccbbbbbbaaaaaa 1110cccc 10bbbbbb 10aaaaaa |
841 | 00000dddccccccbbbbbbaaaaaa 11110ddd 10cccccc 10bbbbbb 10aaaaaa |
842 | |
843 | As you can see, the continuation bytes all begin with C<10>, and the |
8c007b5a |
844 | leading bits of the start byte tell how many bytes the are in the |
05632f9a |
845 | encoded character. |
846 | |
c29a771d |
847 | =item * |
5cb3728c |
848 | |
849 | UTF-EBCDIC |
dbe420b4 |
850 | |
376d9008 |
851 | Like UTF-8 but EBCDIC-safe, in the way that UTF-8 is ASCII-safe. |
dbe420b4 |
852 | |
c29a771d |
853 | =item * |
5cb3728c |
854 | |
855 | UTF-16, UTF-16BE, UTF16-LE, Surrogates, and BOMs (Byte Order Marks) |
c349b1b9 |
856 | |
376d9008 |
857 | The followings items are mostly for reference, Perl doesn't |
858 | use them internally. |
dbe420b4 |
859 | |
c349b1b9 |
860 | UTF-16 is a 2 or 4 byte encoding. The Unicode code points |
376d9008 |
861 | C<U+0000..U+FFFF> are stored in a single 16-bit unit, and the code points |
862 | C<U+10000..U+10FFFF> in two 16-bit units. The latter case is |
c349b1b9 |
863 | using I<surrogates>, the first 16-bit unit being the I<high |
864 | surrogate>, and the second being the I<low surrogate>. |
865 | |
376d9008 |
866 | Surrogates are code points set aside to encode the C<U+10000..U+10FFFF> |
c349b1b9 |
867 | range of Unicode code points in pairs of 16-bit units. The I<high |
376d9008 |
868 | surrogates> are the range C<U+D800..U+DBFF>, and the I<low surrogates> |
869 | are the range C<U+DC00..U+DFFF>. The surrogate encoding is |
c349b1b9 |
870 | |
871 | $hi = ($uni - 0x10000) / 0x400 + 0xD800; |
872 | $lo = ($uni - 0x10000) % 0x400 + 0xDC00; |
873 | |
874 | and the decoding is |
875 | |
1a3fa709 |
876 | $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00); |
c349b1b9 |
877 | |
feda178f |
878 | If you try to generate surrogates (for example by using chr()), you |
376d9008 |
879 | will get a warning if warnings are turned on, because those code |
880 | points are not valid for a Unicode character. |
9466bab6 |
881 | |
376d9008 |
882 | Because of the 16-bitness, UTF-16 is byte-order dependent. UTF-16 |
c349b1b9 |
883 | itself can be used for in-memory computations, but if storage or |
376d9008 |
884 | transfer is required either UTF-16BE (big-endian) or UTF-16LE |
885 | (little-endian) encodings must be chosen. |
c349b1b9 |
886 | |
887 | This introduces another problem: what if you just know that your data |
376d9008 |
888 | is UTF-16, but you don't know which endianness? Byte Order Marks, or |
889 | BOMs, are a solution to this. A special character has been reserved |
86bbd6d1 |
890 | in Unicode to function as a byte order marker: the character with the |
376d9008 |
891 | code point C<U+FEFF> is the BOM. |
042da322 |
892 | |
c349b1b9 |
893 | The trick is that if you read a BOM, you will know the byte order, |
376d9008 |
894 | since if it was written on a big-endian platform, you will read the |
895 | bytes C<0xFE 0xFF>, but if it was written on a little-endian platform, |
896 | you will read the bytes C<0xFF 0xFE>. (And if the originating platform |
897 | was writing in UTF-8, you will read the bytes C<0xEF 0xBB 0xBF>.) |
042da322 |
898 | |
86bbd6d1 |
899 | The way this trick works is that the character with the code point |
376d9008 |
900 | C<U+FFFE> is guaranteed not to be a valid Unicode character, so the |
901 | sequence of bytes C<0xFF 0xFE> is unambiguously "BOM, represented in |
902 | little-endian format" and cannot be "C<U+FFFE>, represented in big-endian |
042da322 |
903 | format". |
c349b1b9 |
904 | |
c29a771d |
905 | =item * |
5cb3728c |
906 | |
907 | UTF-32, UTF-32BE, UTF32-LE |
c349b1b9 |
908 | |
909 | The UTF-32 family is pretty much like the UTF-16 family, expect that |
042da322 |
910 | the units are 32-bit, and therefore the surrogate scheme is not |
376d9008 |
911 | needed. The BOM signatures will be C<0x00 0x00 0xFE 0xFF> for BE and |
912 | C<0xFF 0xFE 0x00 0x00> for LE. |
c349b1b9 |
913 | |
c29a771d |
914 | =item * |
5cb3728c |
915 | |
916 | UCS-2, UCS-4 |
c349b1b9 |
917 | |
86bbd6d1 |
918 | Encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit |
376d9008 |
919 | encoding. Unlike UTF-16, UCS-2 is not extensible beyond C<U+FFFF>, |
339cfa0e |
920 | because it does not use surrogates. UCS-4 is a 32-bit encoding, |
921 | functionally identical to UTF-32. |
c349b1b9 |
922 | |
c29a771d |
923 | =item * |
5cb3728c |
924 | |
925 | UTF-7 |
c349b1b9 |
926 | |
376d9008 |
927 | A seven-bit safe (non-eight-bit) encoding, which is useful if the |
928 | transport or storage is not eight-bit safe. Defined by RFC 2152. |
c349b1b9 |
929 | |
95a1a48b |
930 | =back |
931 | |
0d7c09bb |
932 | =head2 Security Implications of Unicode |
933 | |
934 | =over 4 |
935 | |
936 | =item * |
937 | |
938 | Malformed UTF-8 |
bf0fa0b2 |
939 | |
940 | Unfortunately, the specification of UTF-8 leaves some room for |
941 | interpretation of how many bytes of encoded output one should generate |
376d9008 |
942 | from one input Unicode character. Strictly speaking, the shortest |
943 | possible sequence of UTF-8 bytes should be generated, |
944 | because otherwise there is potential for an input buffer overflow at |
feda178f |
945 | the receiving end of a UTF-8 connection. Perl always generates the |
376d9008 |
946 | shortest length UTF-8, and with warnings on Perl will warn about |
947 | non-shortest length UTF-8 along with other malformations, such as the |
948 | surrogates, which are not real Unicode code points. |
bf0fa0b2 |
949 | |
0d7c09bb |
950 | =item * |
951 | |
952 | Regular expressions behave slightly differently between byte data and |
376d9008 |
953 | character (Unicode) data. For example, the "word character" character |
954 | class C<\w> will work differently depending on if data is eight-bit bytes |
955 | or Unicode. |
0d7c09bb |
956 | |
376d9008 |
957 | In the first case, the set of C<\w> characters is either small--the |
958 | default set of alphabetic characters, digits, and the "_"--or, if you |
0d7c09bb |
959 | are using a locale (see L<perllocale>), the C<\w> might contain a few |
960 | more letters according to your language and country. |
961 | |
376d9008 |
962 | In the second case, the C<\w> set of characters is much, much larger. |
963 | Most importantly, even in the set of the first 256 characters, it |
964 | will probably match different characters: unlike most locales, |
965 | which are specific to a language and country pair, Unicode classifies all |
966 | the characters that are letters as C<\w>. For example, your locale might |
0d7c09bb |
967 | not think that LATIN SMALL LETTER ETH is a letter (unless you happen |
968 | to speak Icelandic), but Unicode does. |
969 | |
376d9008 |
970 | As discussed elsewhere, Perl has one foot (two hooves?) planted in |
971 | each of two worlds: the old world of bytes and the new |
0d7c09bb |
972 | world of characters, upgrading from bytes to characters when necessary. |
376d9008 |
973 | If your legacy code does not explicitly use Unicode, no automatic |
974 | switch-over to characters should happen. Characters shouldn't get |
975 | downgraded to bytes, either. It is possible to accidentally mix |
976 | bytes and characters, however (see L<perluniintro>), in which case |
977 | C<\w> in regular expressions might start behaving differently. Review |
978 | your code. |
0d7c09bb |
979 | |
980 | =back |
981 | |
c349b1b9 |
982 | =head2 Unicode in Perl on EBCDIC |
983 | |
376d9008 |
984 | The way Unicode is handled on EBCDIC platforms is still |
985 | experimental. On such platforms, references to UTF-8 encoding in this |
986 | document and elsewhere should be read as meaning the UTF-EBCDIC |
987 | specified in Unicode Technical Report 16, unless ASCII vs. EBCDIC issues |
c349b1b9 |
988 | are specifically discussed. There is no C<utfebcdic> pragma or |
376d9008 |
989 | ":utfebcdic" layer; rather, "utf8" and ":utf8" are reused to mean |
86bbd6d1 |
990 | the platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic> |
991 | for more discussion of the issues. |
c349b1b9 |
992 | |
b310b053 |
993 | =head2 Locales |
994 | |
4616122b |
995 | Usually locale settings and Unicode do not affect each other, but |
b310b053 |
996 | there are a couple of exceptions: |
997 | |
998 | =over 4 |
999 | |
1000 | =item * |
1001 | |
1002 | If your locale environment variables (LANGUAGE, LC_ALL, LC_CTYPE, LANG) |
1003 | contain the strings 'UTF-8' or 'UTF8' (case-insensitive matching), |
376d9008 |
1004 | the default encodings of your STDIN, STDOUT, and STDERR, and of |
1005 | B<any subsequent file open>, are considered to be UTF-8. |
b310b053 |
1006 | |
1007 | =item * |
1008 | |
376d9008 |
1009 | Perl tries really hard to work both with Unicode and the old |
1010 | byte-oriented world. Most often this is nice, but sometimes Perl's |
1011 | straddling of the proverbial fence causes problems. |
b310b053 |
1012 | |
1013 | =back |
1014 | |
95a1a48b |
1015 | =head2 Using Unicode in XS |
1016 | |
1017 | If you want to handle Perl Unicode in XS extensions, you may find |
376d9008 |
1018 | the following C APIs useful. See L<perlapi> for details. |
95a1a48b |
1019 | |
1020 | =over 4 |
1021 | |
1022 | =item * |
1023 | |
376d9008 |
1024 | C<DO_UTF8(sv)> returns true if the C<UTF8> flag is on and the bytes pragma |
1025 | is not in effect. C<SvUTF8(sv)> returns true is the C<UTF8> flag is on; the |
1026 | bytes pragma is ignored. The C<UTF8> flag being on does B<not> mean that |
b31c5e31 |
1027 | there are any characters of code points greater than 255 (or 127) in |
376d9008 |
1028 | the scalar or that there are even any characters in the scalar. |
1029 | What the C<UTF8> flag means is that the sequence of octets in the |
b31c5e31 |
1030 | representation of the scalar is the sequence of UTF-8 encoded |
376d9008 |
1031 | code points of the characters of a string. The C<UTF8> flag being |
b31c5e31 |
1032 | off means that each octet in this representation encodes a single |
376d9008 |
1033 | character with code point 0..255 within the string. Perl's Unicode |
1034 | model is not to use UTF-8 until it is absolutely necessary. |
95a1a48b |
1035 | |
1036 | =item * |
1037 | |
376d9008 |
1038 | C<uvuni_to_utf8(buf, chr>) writes a Unicode character code point into a |
cfc01aea |
1039 | buffer encoding the code point as UTF-8, and returns a pointer |
95a1a48b |
1040 | pointing after the UTF-8 bytes. |
1041 | |
1042 | =item * |
1043 | |
376d9008 |
1044 | C<utf8_to_uvuni(buf, lenp)> reads UTF-8 encoded bytes from a buffer and |
1045 | returns the Unicode character code point and, optionally, the length of |
1046 | the UTF-8 byte sequence. |
95a1a48b |
1047 | |
1048 | =item * |
1049 | |
376d9008 |
1050 | C<utf8_length(start, end)> returns the length of the UTF-8 encoded buffer |
1051 | in characters. C<sv_len_utf8(sv)> returns the length of the UTF-8 encoded |
95a1a48b |
1052 | scalar. |
1053 | |
1054 | =item * |
1055 | |
376d9008 |
1056 | C<sv_utf8_upgrade(sv)> converts the string of the scalar to its UTF-8 |
1057 | encoded form. C<sv_utf8_downgrade(sv)> does the opposite, if |
1058 | possible. C<sv_utf8_encode(sv)> is like sv_utf8_upgrade except that |
1059 | it does not set the C<UTF8> flag. C<sv_utf8_decode()> does the |
1060 | opposite of C<sv_utf8_encode()>. Note that none of these are to be |
1061 | used as general-purpose encoding or decoding interfaces: C<use Encode> |
1062 | for that. C<sv_utf8_upgrade()> is affected by the encoding pragma |
1063 | but C<sv_utf8_downgrade()> is not (since the encoding pragma is |
1064 | designed to be a one-way street). |
95a1a48b |
1065 | |
1066 | =item * |
1067 | |
376d9008 |
1068 | C<is_utf8_char(s)> returns true if the pointer points to a valid UTF-8 |
90f968e0 |
1069 | character. |
95a1a48b |
1070 | |
1071 | =item * |
1072 | |
376d9008 |
1073 | C<is_utf8_string(buf, len)> returns true if C<len> bytes of the buffer |
95a1a48b |
1074 | are valid UTF-8. |
1075 | |
1076 | =item * |
1077 | |
376d9008 |
1078 | C<UTF8SKIP(buf)> will return the number of bytes in the UTF-8 encoded |
1079 | character in the buffer. C<UNISKIP(chr)> will return the number of bytes |
1080 | required to UTF-8-encode the Unicode character code point. C<UTF8SKIP()> |
90f968e0 |
1081 | is useful for example for iterating over the characters of a UTF-8 |
376d9008 |
1082 | encoded buffer; C<UNISKIP()> is useful, for example, in computing |
90f968e0 |
1083 | the size required for a UTF-8 encoded buffer. |
95a1a48b |
1084 | |
1085 | =item * |
1086 | |
376d9008 |
1087 | C<utf8_distance(a, b)> will tell the distance in characters between the |
95a1a48b |
1088 | two pointers pointing to the same UTF-8 encoded buffer. |
1089 | |
1090 | =item * |
1091 | |
376d9008 |
1092 | C<utf8_hop(s, off)> will return a pointer to an UTF-8 encoded buffer |
1093 | that is C<off> (positive or negative) Unicode characters displaced |
1094 | from the UTF-8 buffer C<s>. Be careful not to overstep the buffer: |
1095 | C<utf8_hop()> will merrily run off the end or the beginning of the |
1096 | buffer if told to do so. |
95a1a48b |
1097 | |
d2cc3551 |
1098 | =item * |
1099 | |
376d9008 |
1100 | C<pv_uni_display(dsv, spv, len, pvlim, flags)> and |
1101 | C<sv_uni_display(dsv, ssv, pvlim, flags)> are useful for debugging the |
1102 | output of Unicode strings and scalars. By default they are useful |
1103 | only for debugging--they display B<all> characters as hexadecimal code |
1104 | points--but with the flags C<UNI_DISPLAY_ISPRINT> and |
1105 | C<UNI_DISPLAY_BACKSLASH> you can make the output more readable. |
d2cc3551 |
1106 | |
1107 | =item * |
1108 | |
376d9008 |
1109 | C<ibcmp_utf8(s1, pe1, u1, l1, u1, s2, pe2, l2, u2)> can be used to |
1110 | compare two strings case-insensitively in Unicode. For case-sensitive |
1111 | comparisons you can just use C<memEQ()> and C<memNE()> as usual. |
d2cc3551 |
1112 | |
c349b1b9 |
1113 | =back |
1114 | |
95a1a48b |
1115 | For more information, see L<perlapi>, and F<utf8.c> and F<utf8.h> |
1116 | in the Perl source code distribution. |
1117 | |
c29a771d |
1118 | =head1 BUGS |
1119 | |
376d9008 |
1120 | =head2 Interaction with Locales |
7eabb34d |
1121 | |
376d9008 |
1122 | Use of locales with Unicode data may lead to odd results. Currently, |
1123 | Perl attempts to attach 8-bit locale info to characters in the range |
1124 | 0..255, but this technique is demonstrably incorrect for locales that |
1125 | use characters above that range when mapped into Unicode. Perl's |
1126 | Unicode support will also tend to run slower. Use of locales with |
1127 | Unicode is discouraged. |
c29a771d |
1128 | |
376d9008 |
1129 | =head2 Interaction with Extensions |
7eabb34d |
1130 | |
376d9008 |
1131 | When Perl exchanges data with an extension, the extension should be |
7eabb34d |
1132 | able to understand the UTF-8 flag and act accordingly. If the |
376d9008 |
1133 | extension doesn't know about the flag, it's likely that the extension |
1134 | will return incorrectly-flagged data. |
7eabb34d |
1135 | |
1136 | So if you're working with Unicode data, consult the documentation of |
1137 | every module you're using if there are any issues with Unicode data |
1138 | exchange. If the documentation does not talk about Unicode at all, |
a73d23f6 |
1139 | suspect the worst and probably look at the source to learn how the |
376d9008 |
1140 | module is implemented. Modules written completely in Perl shouldn't |
a73d23f6 |
1141 | cause problems. Modules that directly or indirectly access code written |
1142 | in other programming languages are at risk. |
7eabb34d |
1143 | |
376d9008 |
1144 | For affected functions, the simple strategy to avoid data corruption is |
7eabb34d |
1145 | to always make the encoding of the exchanged data explicit. Choose an |
376d9008 |
1146 | encoding that you know the extension can handle. Convert arguments passed |
7eabb34d |
1147 | to the extensions to that encoding and convert results back from that |
1148 | encoding. Write wrapper functions that do the conversions for you, so |
1149 | you can later change the functions when the extension catches up. |
1150 | |
376d9008 |
1151 | To provide an example, let's say the popular Foo::Bar::escape_html |
7eabb34d |
1152 | function doesn't deal with Unicode data yet. The wrapper function |
1153 | would convert the argument to raw UTF-8 and convert the result back to |
376d9008 |
1154 | Perl's internal representation like so: |
7eabb34d |
1155 | |
1156 | sub my_escape_html ($) { |
1157 | my($what) = shift; |
1158 | return unless defined $what; |
1159 | Encode::decode_utf8(Foo::Bar::escape_html(Encode::encode_utf8($what))); |
1160 | } |
1161 | |
1162 | Sometimes, when the extension does not convert data but just stores |
1163 | and retrieves them, you will be in a position to use the otherwise |
1164 | dangerous Encode::_utf8_on() function. Let's say the popular |
66b79f27 |
1165 | C<Foo::Bar> extension, written in C, provides a C<param> method that |
7eabb34d |
1166 | lets you store and retrieve data according to these prototypes: |
1167 | |
1168 | $self->param($name, $value); # set a scalar |
1169 | $value = $self->param($name); # retrieve a scalar |
1170 | |
1171 | If it does not yet provide support for any encoding, one could write a |
1172 | derived class with such a C<param> method: |
1173 | |
1174 | sub param { |
1175 | my($self,$name,$value) = @_; |
1176 | utf8::upgrade($name); # make sure it is UTF-8 encoded |
1177 | if (defined $value) |
1178 | utf8::upgrade($value); # make sure it is UTF-8 encoded |
1179 | return $self->SUPER::param($name,$value); |
1180 | } else { |
1181 | my $ret = $self->SUPER::param($name); |
1182 | Encode::_utf8_on($ret); # we know, it is UTF-8 encoded |
1183 | return $ret; |
1184 | } |
1185 | } |
1186 | |
a73d23f6 |
1187 | Some extensions provide filters on data entry/exit points, such as |
1188 | DB_File::filter_store_key and family. Look out for such filters in |
66b79f27 |
1189 | the documentation of your extensions, they can make the transition to |
7eabb34d |
1190 | Unicode data much easier. |
1191 | |
376d9008 |
1192 | =head2 Speed |
7eabb34d |
1193 | |
c29a771d |
1194 | Some functions are slower when working on UTF-8 encoded strings than |
574c8022 |
1195 | on byte encoded strings. All functions that need to hop over |
c29a771d |
1196 | characters such as length(), substr() or index() can work B<much> |
1197 | faster when the underlying data are byte-encoded. Witness the |
1198 | following benchmark: |
666f95b9 |
1199 | |
c29a771d |
1200 | % perl -e ' |
1201 | use Benchmark; |
1202 | use strict; |
1203 | our $l = 10000; |
1204 | our $u = our $b = "x" x $l; |
1205 | substr($u,0,1) = "\x{100}"; |
1206 | timethese(-2,{ |
1207 | LENGTH_B => q{ length($b) }, |
1208 | LENGTH_U => q{ length($u) }, |
1209 | SUBSTR_B => q{ substr($b, $l/4, $l/2) }, |
1210 | SUBSTR_U => q{ substr($u, $l/4, $l/2) }, |
1211 | }); |
1212 | ' |
1213 | Benchmark: running LENGTH_B, LENGTH_U, SUBSTR_B, SUBSTR_U for at least 2 CPU seconds... |
1214 | LENGTH_B: 2 wallclock secs ( 2.36 usr + 0.00 sys = 2.36 CPU) @ 5649983.05/s (n=13333960) |
1215 | LENGTH_U: 2 wallclock secs ( 2.11 usr + 0.00 sys = 2.11 CPU) @ 12155.45/s (n=25648) |
1216 | SUBSTR_B: 3 wallclock secs ( 2.16 usr + 0.00 sys = 2.16 CPU) @ 374480.09/s (n=808877) |
1217 | SUBSTR_U: 2 wallclock secs ( 2.11 usr + 0.00 sys = 2.11 CPU) @ 6791.00/s (n=14329) |
666f95b9 |
1218 | |
376d9008 |
1219 | The numbers show an incredible slowness on long UTF-8 strings. You |
1220 | should carefully avoid using these functions in tight loops. If you |
1221 | want to iterate over characters, the superior coding technique would |
1222 | split the characters into an array instead of using substr, as the following |
c29a771d |
1223 | benchmark shows: |
1224 | |
1225 | % perl -e ' |
1226 | use Benchmark; |
1227 | use strict; |
1228 | our $l = 10000; |
1229 | our $u = our $b = "x" x $l; |
1230 | substr($u,0,1) = "\x{100}"; |
1231 | timethese(-5,{ |
1232 | SPLIT_B => q{ for my $c (split //, $b){} }, |
1233 | SPLIT_U => q{ for my $c (split //, $u){} }, |
1234 | SUBSTR_B => q{ for my $i (0..length($b)-1){my $c = substr($b,$i,1);} }, |
1235 | SUBSTR_U => q{ for my $i (0..length($u)-1){my $c = substr($u,$i,1);} }, |
1236 | }); |
1237 | ' |
1238 | Benchmark: running SPLIT_B, SPLIT_U, SUBSTR_B, SUBSTR_U for at least 5 CPU seconds... |
1239 | SPLIT_B: 6 wallclock secs ( 5.29 usr + 0.00 sys = 5.29 CPU) @ 56.14/s (n=297) |
1240 | SPLIT_U: 5 wallclock secs ( 5.17 usr + 0.01 sys = 5.18 CPU) @ 55.21/s (n=286) |
1241 | SUBSTR_B: 5 wallclock secs ( 5.34 usr + 0.00 sys = 5.34 CPU) @ 123.22/s (n=658) |
1242 | SUBSTR_U: 7 wallclock secs ( 6.20 usr + 0.00 sys = 6.20 CPU) @ 0.81/s (n=5) |
1243 | |
376d9008 |
1244 | Even though the algorithm based on C<substr()> is faster than |
1245 | C<split()> for byte-encoded data, it pales in comparison to the speed |
1246 | of C<split()> when used with UTF-8 data. |
666f95b9 |
1247 | |
393fec97 |
1248 | =head1 SEE ALSO |
1249 | |
72ff2908 |
1250 | L<perluniintro>, L<encoding>, L<Encode>, L<open>, L<utf8>, L<bytes>, |
1251 | L<perlretut>, L<perlvar/"${^WIDE_SYSTEM_CALLS}"> |
393fec97 |
1252 | |
1253 | =cut |