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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 |
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 | A filehandle can be marked as containing perl's internal Unicode |
18 | encoding (UTF-8 or UTF-EBCDIC) by opening it with the ":utf8" layer. |
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19 | Other encodings can be converted to perl's encoding on input, or from |
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20 | perl's encoding on output by use of the ":encoding(...)" layer. |
21 | See L<open>. |
22 | |
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23 | To mark the Perl source itself as being in 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, |
29 | the pattern adapts to the data and automatically switch to the Unicode |
30 | character scheme when presented with Unicode data, or a traditional |
31 | 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, this pragma must be explicitly used to |
36 | enable recognition of UTF-8 in the Perl scripts themselves on ASCII |
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37 | based machines, or to recognize UTF-EBCDIC on EBCDIC based machines. |
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38 | B<NOTE: this should be the only place where 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 | |
46 | =head2 Byte and Character semantics |
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47 | |
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 can be expected to work with |
52 | characters rather than bytes, in general. |
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53 | |
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54 | However, as strictly an interim compatibility measure, Perl aims to |
55 | provide a safe migration path from byte semantics to character |
56 | semantics for programs. For operations where Perl can unambiguously |
57 | decide that the input data is characters, Perl now switches to |
58 | character semantics. For operations where this determination cannot |
59 | be made without additional information from the user, Perl decides in |
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, |
63 | which allowed byte semantics in Perl operations, but only as long as |
64 | none of the program's inputs are marked as being as source of Unicode |
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 |
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70 | ${^WIDE_SYSTEM_CALLS} global flag is set to C<1>), all system calls |
71 | will use the corresponding wide character APIs. Note that this is |
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72 | currently only implemented on Windows since other platforms lack an |
73 | API standard on this area. |
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74 | |
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75 | Regardless of the above, the C<bytes> pragma can always be used to |
76 | force byte 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. |
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80 | Note that this pragma is only required until a future version of Perl |
81 | in which character semantics will become the default. This pragma may |
82 | then become a no-op. See L<utf8>. |
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83 | |
84 | Unless mentioned otherwise, Perl operators will use character semantics |
85 | when they are dealing with Unicode data, and byte semantics otherwise. |
86 | Thus, character semantics for these operations apply transparently; if |
87 | the input data came from a Unicode source (for example, by adding a |
88 | character encoding discipline to the filehandle whence it came, or a |
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89 | literal Unicode string constant in the program), character semantics |
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90 | apply; otherwise, byte semantics are in effect. To force byte semantics |
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91 | on Unicode data, the C<bytes> pragma should be used. |
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92 | |
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93 | Notice that if you concatenate strings with byte semantics and strings |
94 | with Unicode character data, the bytes will by default be upgraded |
95 | I<as if they were ISO 8859-1 (Latin-1)> (or if in EBCDIC, after a |
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96 | translation to ISO 8859-1). This is done without regard to the |
97 | system's native 8-bit encoding, so to change this for systems with |
98 | non-Latin-1 (or non-EBCDIC) native encodings, use the C<encoding> |
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99 | pragma, see L<encoding>. |
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100 | |
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101 | Under character semantics, many operations that formerly operated on |
102 | bytes change to operating on characters. A character in Perl is |
103 | logically just a number ranging from 0 to 2**31 or so. Larger |
104 | characters may encode to longer sequences of bytes internally, but |
105 | this is just an internal detail which is hidden at the Perl level. |
106 | See L<perluniintro> for more on this. |
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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 |
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 |
121 | Unicode encodings (UTF-8, UTF-EBCDIC, UCS-2, etc.), but are recognized |
122 | as such (and converted to Perl's internal representation) only if the |
123 | appropriate L<encoding> is specified. |
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124 | |
125 | You can also get Unicode characters into a string by using the C<\x{...}> |
126 | notation, putting the Unicode code for the desired character, in |
127 | hexadecimal, into the curlies. For instance, a smiley face is C<\x{263A}>. |
128 | This works only for characters with a code 0x100 and above. |
129 | |
130 | Additionally, if you |
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131 | |
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132 | use charnames ':full'; |
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133 | |
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134 | you can use the C<\N{...}> notation, putting the official Unicode character |
135 | name within the curlies. For example, C<\N{WHITE SMILING FACE}>. |
136 | This works for all characters that have names. |
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137 | |
138 | =item * |
139 | |
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140 | If an appropriate L<encoding> is specified, identifiers within the |
141 | Perl script may contain Unicode alphanumeric characters, including |
142 | ideographs. (You are currently on your own when it comes to using the |
143 | canonical forms of characters--Perl doesn't (yet) attempt to |
144 | canonicalize variable names for you.) |
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145 | |
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146 | =item * |
147 | |
148 | Regular expressions match characters instead of bytes. For instance, |
149 | "." matches a character instead of a byte. (However, the C<\C> pattern |
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150 | is provided to force a match a single byte ("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 |
155 | bytes, and match against the character properties specified in the |
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156 | Unicode properties database. So C<\w> can be used to match an |
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 |
162 | character classes via the new C<\p{}> (matches property) and C<\P{}> |
163 | (doesn't match property) constructs. For instance, C<\p{Lu}> matches any |
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164 | character with the Unicode "Lu" (Letter, uppercase) property, while |
165 | C<\p{M}> matches any character with a "M" (mark -- accents and such) |
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166 | property. Single letter properties may omit the brackets, so that can be |
167 | written C<\pM> also. Many predefined properties are available, such |
168 | as C<\p{Mirrored}> and C<\p{Tibetan}>. |
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169 | |
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170 | The official Unicode script and block names have spaces and dashes as |
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171 | separators, but for convenience you can have dashes, spaces, and underbars |
172 | at every word division, and you need not care about correct casing. It is |
173 | recommended, however, that for consistency you use the following naming: |
174 | the official Unicode script, block, or property name (see below for the |
175 | additional rules that apply to block names), with whitespace and dashes |
176 | removed, and the words "uppercase-first-lowercase-rest". That is, "Latin-1 |
177 | Supplement" becomes "Latin1Supplement". |
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178 | |
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179 | You can also negate both C<\p{}> and C<\P{}> by introducing a caret |
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180 | (^) between the first curly and the property name: C<\p{^Tamil}> is |
181 | equal to C<\P{Tamil}>. |
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182 | |
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183 | Here are the basic Unicode General Category properties, followed by their |
184 | long form (you can use either, e.g. C<\p{Lu}> and C<\p{LowercaseLetter}> |
185 | are identical). |
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186 | |
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187 | Short Long |
188 | |
189 | L Letter |
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190 | Lu UppercaseLetter |
191 | Ll LowercaseLetter |
192 | Lt TitlecaseLetter |
193 | Lm ModifierLetter |
194 | Lo OtherLetter |
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195 | |
196 | M Mark |
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197 | Mn NonspacingMark |
198 | Mc SpacingMark |
199 | Me EnclosingMark |
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200 | |
201 | N Number |
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202 | Nd DecimalNumber |
203 | Nl LetterNumber |
204 | No OtherNumber |
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205 | |
206 | P Punctuation |
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207 | Pc ConnectorPunctuation |
208 | Pd DashPunctuation |
209 | Ps OpenPunctuation |
210 | Pe ClosePunctuation |
211 | Pi InitialPunctuation |
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212 | (may behave like Ps or Pe depending on usage) |
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213 | Pf FinalPunctuation |
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214 | (may behave like Ps or Pe depending on usage) |
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215 | Po OtherPunctuation |
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216 | |
217 | S Symbol |
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218 | Sm MathSymbol |
219 | Sc CurrencySymbol |
220 | Sk ModifierSymbol |
221 | So OtherSymbol |
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222 | |
223 | Z Separator |
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224 | Zs SpaceSeparator |
225 | Zl LineSeparator |
226 | Zp ParagraphSeparator |
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227 | |
228 | C Other |
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229 | Cc Control |
230 | Cf Format |
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231 | Cs Surrogate (not usable) |
232 | Co PrivateUse |
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233 | Cn Unassigned |
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234 | |
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235 | The single-letter properties match all characters in any of the |
236 | two-letter sub-properties starting with the same letter. |
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237 | There's also C<L&> which is an alias for C<Ll>, C<Lu>, and C<Lt>. |
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238 | |
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239 | Because Perl hides the need for the user to understand the internal |
240 | representation of Unicode characters, it has no need to support the |
241 | somewhat messy concept of surrogates. Therefore, the C<Cs> property is not |
242 | supported. |
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243 | |
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244 | Because scripts differ in their directionality (for example Hebrew is |
245 | written right to left), Unicode supplies these properties: |
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246 | |
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247 | Property Meaning |
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248 | |
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249 | BidiL Left-to-Right |
250 | BidiLRE Left-to-Right Embedding |
251 | BidiLRO Left-to-Right Override |
252 | BidiR Right-to-Left |
253 | BidiAL Right-to-Left Arabic |
254 | BidiRLE Right-to-Left Embedding |
255 | BidiRLO Right-to-Left Override |
256 | BidiPDF Pop Directional Format |
257 | BidiEN European Number |
258 | BidiES European Number Separator |
259 | BidiET European Number Terminator |
260 | BidiAN Arabic Number |
261 | BidiCS Common Number Separator |
262 | BidiNSM Non-Spacing Mark |
263 | BidiBN Boundary Neutral |
264 | BidiB Paragraph Separator |
265 | BidiS Segment Separator |
266 | BidiWS Whitespace |
267 | BidiON Other Neutrals |
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268 | |
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269 | For example, C<\p{BidiR}> matches all characters that are normally |
270 | written right to left. |
271 | |
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272 | =back |
273 | |
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274 | =head2 Scripts |
275 | |
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276 | The scripts available via C<\p{...}> and C<\P{...}>, for example |
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277 | C<\p{Latin}> or C<\p{Cyrillic}>, are as follows: |
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278 | |
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279 | Arabic |
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280 | Armenian |
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281 | Bengali |
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282 | Bopomofo |
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283 | Buhid |
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284 | CanadianAboriginal |
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285 | Cherokee |
286 | Cyrillic |
287 | Deseret |
288 | Devanagari |
289 | Ethiopic |
290 | Georgian |
291 | Gothic |
292 | Greek |
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293 | Gujarati |
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294 | Gurmukhi |
295 | Han |
296 | Hangul |
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297 | Hanunoo |
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298 | Hebrew |
299 | Hiragana |
300 | Inherited |
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301 | Kannada |
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302 | Katakana |
303 | Khmer |
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304 | Lao |
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305 | Latin |
306 | Malayalam |
307 | Mongolian |
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308 | Myanmar |
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309 | Ogham |
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310 | OldItalic |
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311 | Oriya |
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312 | Runic |
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313 | Sinhala |
314 | Syriac |
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315 | Tagalog |
316 | Tagbanwa |
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317 | Tamil |
318 | Telugu |
319 | Thaana |
320 | Thai |
321 | Tibetan |
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322 | Yi |
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323 | |
324 | There are also extended property classes that supplement the basic |
325 | properties, defined by the F<PropList> Unicode database: |
326 | |
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327 | ASCIIHexDigit |
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328 | BidiControl |
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329 | Dash |
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330 | Deprecated |
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331 | Diacritic |
332 | Extender |
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333 | GraphemeLink |
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334 | HexDigit |
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335 | Hyphen |
336 | Ideographic |
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337 | IDSBinaryOperator |
338 | IDSTrinaryOperator |
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339 | JoinControl |
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340 | LogicalOrderException |
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341 | NoncharacterCodePoint |
342 | OtherAlphabetic |
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343 | OtherDefaultIgnorableCodePoint |
344 | OtherGraphemeExtend |
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345 | OtherLowercase |
346 | OtherMath |
347 | OtherUppercase |
348 | QuotationMark |
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349 | Radical |
350 | SoftDotted |
351 | TerminalPunctuation |
352 | UnifiedIdeograph |
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353 | WhiteSpace |
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354 | |
355 | and further derived properties: |
356 | |
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357 | Alphabetic Lu + Ll + Lt + Lm + Lo + OtherAlphabetic |
358 | Lowercase Ll + OtherLowercase |
359 | Uppercase Lu + OtherUppercase |
360 | Math Sm + OtherMath |
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361 | |
362 | ID_Start Lu + Ll + Lt + Lm + Lo + Nl |
363 | ID_Continue ID_Start + Mn + Mc + Nd + Pc |
364 | |
365 | Any Any character |
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366 | Assigned Any non-Cn character (i.e. synonym for \P{Cn}) |
367 | Unassigned Synonym for \p{Cn} |
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368 | Common Any character (or unassigned code point) |
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369 | not explicitly assigned to a script |
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370 | |
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371 | For backward compatibility, all properties mentioned so far may have C<Is> |
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372 | prepended to their name (e.g. C<\P{IsLu}> is equal to C<\P{Lu}>). |
373 | |
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374 | =head2 Blocks |
375 | |
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376 | In addition to B<scripts>, Unicode also defines B<blocks> of characters. |
377 | The difference between scripts and blocks is that the scripts concept is |
378 | closer to natural languages, while the blocks concept is more an artificial |
379 | grouping based on groups of mostly 256 Unicode characters. For example, the |
380 | C<Latin> script contains letters from many blocks. On the other hand, the |
381 | C<Latin> script does not contain all the characters from those blocks. It |
382 | does not, for example, contain digits because digits are shared across many |
383 | scripts. Digits and other similar groups, like punctuation, are in a |
384 | category called C<Common>. |
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385 | |
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386 | For more about scripts, see the UTR #24: |
387 | |
388 | http://www.unicode.org/unicode/reports/tr24/ |
389 | |
390 | For more about blocks, see: |
391 | |
392 | http://www.unicode.org/Public/UNIDATA/Blocks.txt |
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393 | |
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394 | Blocks names are given with the C<In> prefix. For example, the |
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395 | Katakana block is referenced via C<\p{InKatakana}>. The C<In> |
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396 | prefix may be omitted if there is no naming conflict with a script |
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397 | or any other property, but it is recommended that C<In> always be used |
398 | to avoid confusion. |
399 | |
400 | These block names are supported: |
401 | |
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402 | InAlphabeticPresentationForms |
403 | InArabic |
404 | InArabicPresentationFormsA |
405 | InArabicPresentationFormsB |
406 | InArmenian |
407 | InArrows |
408 | InBasicLatin |
409 | InBengali |
410 | InBlockElements |
411 | InBopomofo |
412 | InBopomofoExtended |
413 | InBoxDrawing |
414 | InBraillePatterns |
415 | InBuhid |
416 | InByzantineMusicalSymbols |
417 | InCJKCompatibility |
418 | InCJKCompatibilityForms |
419 | InCJKCompatibilityIdeographs |
420 | InCJKCompatibilityIdeographsSupplement |
421 | InCJKRadicalsSupplement |
422 | InCJKSymbolsAndPunctuation |
423 | InCJKUnifiedIdeographs |
424 | InCJKUnifiedIdeographsExtensionA |
425 | InCJKUnifiedIdeographsExtensionB |
426 | InCherokee |
427 | InCombiningDiacriticalMarks |
428 | InCombiningDiacriticalMarksforSymbols |
429 | InCombiningHalfMarks |
430 | InControlPictures |
431 | InCurrencySymbols |
432 | InCyrillic |
433 | InCyrillicSupplementary |
434 | InDeseret |
435 | InDevanagari |
436 | InDingbats |
437 | InEnclosedAlphanumerics |
438 | InEnclosedCJKLettersAndMonths |
439 | InEthiopic |
440 | InGeneralPunctuation |
441 | InGeometricShapes |
442 | InGeorgian |
443 | InGothic |
444 | InGreekExtended |
445 | InGreekAndCoptic |
446 | InGujarati |
447 | InGurmukhi |
448 | InHalfwidthAndFullwidthForms |
449 | InHangulCompatibilityJamo |
450 | InHangulJamo |
451 | InHangulSyllables |
452 | InHanunoo |
453 | InHebrew |
454 | InHighPrivateUseSurrogates |
455 | InHighSurrogates |
456 | InHiragana |
457 | InIPAExtensions |
458 | InIdeographicDescriptionCharacters |
459 | InKanbun |
460 | InKangxiRadicals |
461 | InKannada |
462 | InKatakana |
463 | InKatakanaPhoneticExtensions |
464 | InKhmer |
465 | InLao |
466 | InLatin1Supplement |
467 | InLatinExtendedA |
468 | InLatinExtendedAdditional |
469 | InLatinExtendedB |
470 | InLetterlikeSymbols |
471 | InLowSurrogates |
472 | InMalayalam |
473 | InMathematicalAlphanumericSymbols |
474 | InMathematicalOperators |
475 | InMiscellaneousMathematicalSymbolsA |
476 | InMiscellaneousMathematicalSymbolsB |
477 | InMiscellaneousSymbols |
478 | InMiscellaneousTechnical |
479 | InMongolian |
480 | InMusicalSymbols |
481 | InMyanmar |
482 | InNumberForms |
483 | InOgham |
484 | InOldItalic |
485 | InOpticalCharacterRecognition |
486 | InOriya |
487 | InPrivateUseArea |
488 | InRunic |
489 | InSinhala |
490 | InSmallFormVariants |
491 | InSpacingModifierLetters |
492 | InSpecials |
493 | InSuperscriptsAndSubscripts |
494 | InSupplementalArrowsA |
495 | InSupplementalArrowsB |
496 | InSupplementalMathematicalOperators |
497 | InSupplementaryPrivateUseAreaA |
498 | InSupplementaryPrivateUseAreaB |
499 | InSyriac |
500 | InTagalog |
501 | InTagbanwa |
502 | InTags |
503 | InTamil |
504 | InTelugu |
505 | InThaana |
506 | InThai |
507 | InTibetan |
508 | InUnifiedCanadianAboriginalSyllabics |
509 | InVariationSelectors |
510 | InYiRadicals |
511 | InYiSyllables |
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512 | |
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513 | =over 4 |
514 | |
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515 | =item * |
516 | |
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517 | The special pattern C<\X> matches any extended Unicode sequence |
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518 | (a "combining character sequence" in Standardese), where the first |
519 | character is a base character and subsequent characters are mark |
520 | characters that apply to the base character. It is equivalent to |
521 | C<(?:\PM\pM*)>. |
522 | |
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523 | =item * |
524 | |
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525 | The C<tr///> operator translates characters instead of bytes. Note |
526 | that the C<tr///CU> functionality has been removed, as the interface |
527 | was a mistake. For similar functionality see pack('U0', ...) and |
528 | pack('C0', ...). |
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529 | |
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530 | =item * |
531 | |
532 | Case translation operators use the Unicode case translation tables |
44bc797b |
533 | when provided character input. Note that C<uc()> (also known as C<\U> |
534 | in doublequoted strings) translates to uppercase, while C<ucfirst> |
535 | (also known as C<\u> in doublequoted strings) translates to titlecase |
536 | (for languages that make the distinction). Naturally the |
537 | corresponding backslash sequences have the same semantics. |
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538 | |
539 | =item * |
540 | |
541 | Most operators that deal with positions or lengths in the string will |
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542 | automatically switch to using character positions, including |
543 | C<chop()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>, |
544 | C<sprintf()>, C<write()>, and C<length()>. Operators that |
545 | specifically don't switch include C<vec()>, C<pack()>, and |
546 | C<unpack()>. Operators that really don't care include C<chomp()>, as |
547 | well as any other operator that treats a string as a bucket of bits, |
548 | such as C<sort()>, and the operators dealing with filenames. |
393fec97 |
549 | |
550 | =item * |
551 | |
552 | The C<pack()>/C<unpack()> letters "C<c>" and "C<C>" do I<not> change, |
553 | since they're often used for byte-oriented formats. (Again, think |
554 | "C<char>" in the C language.) However, there is a new "C<U>" specifier |
3e4dbfed |
555 | that will convert between Unicode characters and integers. |
393fec97 |
556 | |
557 | =item * |
558 | |
559 | The C<chr()> and C<ord()> functions work on characters. This is like |
560 | C<pack("U")> and C<unpack("U")>, not like C<pack("C")> and |
561 | C<unpack("C")>. In fact, the latter are how you now emulate |
35bcd338 |
562 | byte-oriented C<chr()> and C<ord()> for Unicode strings. |
3e4dbfed |
563 | (Note that this reveals the internal encoding of Unicode strings, |
564 | which is not something one normally needs to care about at all.) |
393fec97 |
565 | |
566 | =item * |
567 | |
a1ca4561 |
568 | The bit string operators C<& | ^ ~> can operate on character data. |
569 | However, for backward compatibility reasons (bit string operations |
75daf61c |
570 | when the characters all are less than 256 in ordinal value) one should |
571 | not mix C<~> (the bit complement) and characters both less than 256 and |
a1ca4561 |
572 | equal or greater than 256. Most importantly, the DeMorgan's laws |
573 | (C<~($x|$y) eq ~$x&~$y>, C<~($x&$y) eq ~$x|~$y>) won't hold. |
574 | Another way to look at this is that the complement cannot return |
75daf61c |
575 | B<both> the 8-bit (byte) wide bit complement B<and> the full character |
a1ca4561 |
576 | wide bit complement. |
577 | |
578 | =item * |
579 | |
983ffd37 |
580 | lc(), uc(), lcfirst(), and ucfirst() work for the following cases: |
581 | |
582 | =over 8 |
583 | |
584 | =item * |
585 | |
586 | the case mapping is from a single Unicode character to another |
587 | single Unicode character |
588 | |
589 | =item * |
590 | |
591 | the case mapping is from a single Unicode character to more |
592 | than one Unicode character |
593 | |
594 | =back |
595 | |
210b36aa |
596 | What doesn't yet work are the following cases: |
983ffd37 |
597 | |
598 | =over 8 |
599 | |
600 | =item * |
601 | |
602 | the "final sigma" (Greek) |
603 | |
604 | =item * |
605 | |
606 | anything to with locales (Lithuanian, Turkish, Azeri) |
607 | |
608 | =back |
609 | |
610 | See the Unicode Technical Report #21, Case Mappings, for more details. |
ac1256e8 |
611 | |
612 | =item * |
613 | |
393fec97 |
614 | And finally, C<scalar reverse()> reverses by character rather than by byte. |
615 | |
616 | =back |
617 | |
237bad5b |
618 | =head2 User-defined Character Properties |
491fd90a |
619 | |
620 | You can define your own character properties by defining subroutines |
621 | that have names beginning with "In" or "Is". The subroutines must be |
622 | visible in the package that uses the properties. The user-defined |
623 | properties can be used in the regular expression C<\p> and C<\P> |
624 | constructs. |
625 | |
626 | The subroutines must return a specially formatted string: one or more |
627 | newline-separated lines. Each line must be one of the following: |
628 | |
629 | =over 4 |
630 | |
631 | =item * |
632 | |
633 | Two hexadecimal numbers separated by a tabulator denoting a range |
11ef8fdd |
634 | of Unicode codepoints to include. |
491fd90a |
635 | |
636 | =item * |
637 | |
11ef8fdd |
638 | Something to include, prefixed by "+": either an built-in character |
639 | property (prefixed by "utf8::"), for all the characters in that |
640 | property; or two hexadecimal codepoints for a range; or a single |
641 | hexadecimal codepoint. |
491fd90a |
642 | |
643 | =item * |
644 | |
11ef8fdd |
645 | Something to exclude, prefixed by "-": either an existing character |
646 | property (prefixed by "utf8::"), for all the characters in that |
647 | property; or two hexadecimal codepoints for a range; or a single |
648 | hexadecimal codepoint. |
491fd90a |
649 | |
650 | =item * |
651 | |
11ef8fdd |
652 | Something to negate, prefixed "!": either an existing character |
653 | property (prefixed by "utf8::") for all the characters except the |
654 | characters in the property; or two hexadecimal codepoints for a range; |
655 | or a single hexadecimal codepoint. |
491fd90a |
656 | |
657 | =back |
658 | |
659 | For example, to define a property that covers both the Japanese |
660 | syllabaries (hiragana and katakana), you can define |
661 | |
662 | sub InKana { |
d5822f25 |
663 | return <<END; |
664 | 3040\t309F |
665 | 30A0\t30FF |
491fd90a |
666 | END |
667 | } |
668 | |
d5822f25 |
669 | Imagine that the here-doc end marker is at the beginning of the line. |
670 | Now you can use C<\p{InKana}> and C<\P{InKana}>. |
491fd90a |
671 | |
672 | You could also have used the existing block property names: |
673 | |
674 | sub InKana { |
675 | return <<'END'; |
676 | +utf8::InHiragana |
677 | +utf8::InKatakana |
678 | END |
679 | } |
680 | |
681 | Suppose you wanted to match only the allocated characters, |
d5822f25 |
682 | not the raw block ranges: in other words, you want to remove |
491fd90a |
683 | the non-characters: |
684 | |
685 | sub InKana { |
686 | return <<'END'; |
687 | +utf8::InHiragana |
688 | +utf8::InKatakana |
689 | -utf8::IsCn |
690 | END |
691 | } |
692 | |
693 | The negation is useful for defining (surprise!) negated classes. |
694 | |
695 | sub InNotKana { |
696 | return <<'END'; |
697 | !utf8::InHiragana |
698 | -utf8::InKatakana |
699 | +utf8::IsCn |
700 | END |
701 | } |
702 | |
8cbd9a7a |
703 | =head2 Character encodings for input and output |
704 | |
7221edc9 |
705 | See L<Encode>. |
8cbd9a7a |
706 | |
c29a771d |
707 | =head2 Unicode Regular Expression Support Level |
776f8809 |
708 | |
709 | The following list of Unicode regular expression support describes |
710 | feature by feature the Unicode support implemented in Perl as of Perl |
711 | 5.8.0. The "Level N" and the section numbers refer to the Unicode |
712 | Technical Report 18, "Unicode Regular Expression Guidelines". |
713 | |
714 | =over 4 |
715 | |
716 | =item * |
717 | |
718 | Level 1 - Basic Unicode Support |
719 | |
720 | 2.1 Hex Notation - done [1] |
3bfdc84c |
721 | Named Notation - done [2] |
776f8809 |
722 | 2.2 Categories - done [3][4] |
723 | 2.3 Subtraction - MISSING [5][6] |
724 | 2.4 Simple Word Boundaries - done [7] |
78d3e1bf |
725 | 2.5 Simple Loose Matches - done [8] |
776f8809 |
726 | 2.6 End of Line - MISSING [9][10] |
727 | |
728 | [ 1] \x{...} |
729 | [ 2] \N{...} |
eb0cc9e3 |
730 | [ 3] . \p{...} \P{...} |
29bdacb8 |
731 | [ 4] now scripts (see UTR#24 Script Names) in addition to blocks |
776f8809 |
732 | [ 5] have negation |
237bad5b |
733 | [ 6] can use regular expression look-ahead [a] |
734 | or user-defined character properties [b] to emulate subtraction |
776f8809 |
735 | [ 7] include Letters in word characters |
e0f9d4a8 |
736 | [ 8] note that perl does Full casefolding in matching, not Simple: |
737 | for example U+1F88 is equivalent with U+1F000 U+03B9, |
738 | not with 1F80. This difference matters for certain Greek |
739 | capital letters with certain modifiers: the Full casefolding |
740 | decomposes the letter, while the Simple casefolding would map |
741 | it to a single character. |
776f8809 |
742 | [ 9] see UTR#13 Unicode Newline Guidelines |
ec83e909 |
743 | [10] should do ^ and $ also on \x{85}, \x{2028} and \x{2029}) |
744 | (should also affect <>, $., and script line numbers) |
3bfdc84c |
745 | (the \x{85}, \x{2028} and \x{2029} do match \s) |
7207e29d |
746 | |
237bad5b |
747 | [a] You can mimic class subtraction using lookahead. |
dbe420b4 |
748 | For example, what TR18 might write as |
29bdacb8 |
749 | |
dbe420b4 |
750 | [{Greek}-[{UNASSIGNED}]] |
751 | |
752 | in Perl can be written as: |
753 | |
1d81abf3 |
754 | (?!\p{Unassigned})\p{InGreekAndCoptic} |
755 | (?=\p{Assigned})\p{InGreekAndCoptic} |
dbe420b4 |
756 | |
757 | But in this particular example, you probably really want |
758 | |
759 | \p{Greek} |
760 | |
761 | which will match assigned characters known to be part of the Greek script. |
29bdacb8 |
762 | |
237bad5b |
763 | [b] See L</User-defined Character Properties>. |
764 | |
776f8809 |
765 | =item * |
766 | |
767 | Level 2 - Extended Unicode Support |
768 | |
769 | 3.1 Surrogates - MISSING |
770 | 3.2 Canonical Equivalents - MISSING [11][12] |
771 | 3.3 Locale-Independent Graphemes - MISSING [13] |
772 | 3.4 Locale-Independent Words - MISSING [14] |
773 | 3.5 Locale-Independent Loose Matches - MISSING [15] |
774 | |
775 | [11] see UTR#15 Unicode Normalization |
776 | [12] have Unicode::Normalize but not integrated to regexes |
777 | [13] have \X but at this level . should equal that |
778 | [14] need three classes, not just \w and \W |
779 | [15] see UTR#21 Case Mappings |
780 | |
781 | =item * |
782 | |
783 | Level 3 - Locale-Sensitive Support |
784 | |
785 | 4.1 Locale-Dependent Categories - MISSING |
786 | 4.2 Locale-Dependent Graphemes - MISSING [16][17] |
787 | 4.3 Locale-Dependent Words - MISSING |
788 | 4.4 Locale-Dependent Loose Matches - MISSING |
789 | 4.5 Locale-Dependent Ranges - MISSING |
790 | |
791 | [16] see UTR#10 Unicode Collation Algorithms |
792 | [17] have Unicode::Collate but not integrated to regexes |
793 | |
794 | =back |
795 | |
c349b1b9 |
796 | =head2 Unicode Encodings |
797 | |
798 | Unicode characters are assigned to I<code points> which are abstract |
86bbd6d1 |
799 | numbers. To use these numbers various encodings are needed. |
c349b1b9 |
800 | |
801 | =over 4 |
802 | |
c29a771d |
803 | =item * |
5cb3728c |
804 | |
805 | UTF-8 |
c349b1b9 |
806 | |
3e4dbfed |
807 | UTF-8 is a variable-length (1 to 6 bytes, current character allocations |
808 | require 4 bytes), byteorder independent encoding. For ASCII, UTF-8 is |
809 | transparent (and we really do mean 7-bit ASCII, not another 8-bit encoding). |
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 |
05632f9a |
817 | U+0800..U+0FFF E0 A0..BF 80..BF |
8c007b5a |
818 | U+1000..U+CFFF E1..EC 80..BF 80..BF |
819 | U+D000..U+D7FF ED 80..9F 80..BF |
820 | U+D800..U+DFFF ******* ill-formed ******* |
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 | |
8c007b5a |
826 | Note the A0..BF in U+0800..U+0FFF, the 80..9F in U+D000...U+D7FF, |
827 | the 90..BF in U+10000..U+3FFFF, and the 80...8F in U+100000..U+10FFFF. |
37361303 |
828 | The "gaps" are caused by legal UTF-8 avoiding non-shortest encodings: |
829 | it is technically possible to UTF-8-encode a single code point in different |
830 | ways, but that is explicitly forbidden, and the shortest possible encoding |
831 | should always be used (and that is what Perl does). |
832 | |
05632f9a |
833 | Or, another way to look at it, as bits: |
834 | |
835 | Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte |
836 | |
837 | 0aaaaaaa 0aaaaaaa |
838 | 00000bbbbbaaaaaa 110bbbbb 10aaaaaa |
839 | ccccbbbbbbaaaaaa 1110cccc 10bbbbbb 10aaaaaa |
840 | 00000dddccccccbbbbbbaaaaaa 11110ddd 10cccccc 10bbbbbb 10aaaaaa |
841 | |
842 | As you can see, the continuation bytes all begin with C<10>, and the |
8c007b5a |
843 | leading bits of the start byte tell how many bytes the are in the |
05632f9a |
844 | encoded character. |
845 | |
c29a771d |
846 | =item * |
5cb3728c |
847 | |
848 | UTF-EBCDIC |
dbe420b4 |
849 | |
fe854a6f |
850 | Like UTF-8, but EBCDIC-safe, as UTF-8 is ASCII-safe. |
dbe420b4 |
851 | |
c29a771d |
852 | =item * |
5cb3728c |
853 | |
854 | UTF-16, UTF-16BE, UTF16-LE, Surrogates, and BOMs (Byte Order Marks) |
c349b1b9 |
855 | |
dbe420b4 |
856 | (The followings items are mostly for reference, Perl doesn't |
857 | use them internally.) |
858 | |
c349b1b9 |
859 | UTF-16 is a 2 or 4 byte encoding. The Unicode code points |
860 | 0x0000..0xFFFF are stored in two 16-bit units, and the code points |
dbe420b4 |
861 | 0x010000..0x10FFFF in two 16-bit units. The latter case is |
c349b1b9 |
862 | using I<surrogates>, the first 16-bit unit being the I<high |
863 | surrogate>, and the second being the I<low surrogate>. |
864 | |
865 | Surrogates are code points set aside to encode the 0x01000..0x10FFFF |
866 | range of Unicode code points in pairs of 16-bit units. The I<high |
867 | surrogates> are the range 0xD800..0xDBFF, and the I<low surrogates> |
868 | are the range 0xDC00..0xDFFFF. The surrogate encoding is |
869 | |
870 | $hi = ($uni - 0x10000) / 0x400 + 0xD800; |
871 | $lo = ($uni - 0x10000) % 0x400 + 0xDC00; |
872 | |
873 | and the decoding is |
874 | |
1a3fa709 |
875 | $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00); |
c349b1b9 |
876 | |
feda178f |
877 | If you try to generate surrogates (for example by using chr()), you |
878 | will get a warning if warnings are turned on (C<-w> or C<use |
879 | warnings;>) because those code points are not valid for a Unicode |
880 | character. |
9466bab6 |
881 | |
86bbd6d1 |
882 | Because of the 16-bitness, UTF-16 is byteorder dependent. UTF-16 |
c349b1b9 |
883 | itself can be used for in-memory computations, but if storage or |
86bbd6d1 |
884 | transfer is required, either UTF-16BE (Big Endian) or UTF-16LE |
c349b1b9 |
885 | (Little Endian) must be chosen. |
886 | |
887 | This introduces another problem: what if you just know that your data |
888 | is UTF-16, but you don't know which endianness? Byte Order Marks |
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 |
891 | code point 0xFEFF is the BOM. |
042da322 |
892 | |
c349b1b9 |
893 | The trick is that if you read a BOM, you will know the byte order, |
894 | since if it was written on a big endian platform, you will read the |
86bbd6d1 |
895 | bytes 0xFE 0xFF, but if it was written on a little endian platform, |
896 | you will read the bytes 0xFF 0xFE. (And if the originating platform |
897 | was writing in UTF-8, you will read the bytes 0xEF 0xBB 0xBF.) |
042da322 |
898 | |
86bbd6d1 |
899 | The way this trick works is that the character with the code point |
900 | 0xFFFE is guaranteed not to be a valid Unicode character, so the |
901 | sequence of bytes 0xFF 0xFE is unambiguously "BOM, represented in |
042da322 |
902 | little-endian format" and cannot be "0xFFFE, represented in big-endian |
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 |
911 | needed. The BOM signatures will be 0x00 0x00 0xFE 0xFF for BE and |
912 | 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 |
919 | encoding, UCS-4 is a 32-bit encoding. Unlike UTF-16, UCS-2 |
920 | is not extensible beyond 0xFFFF, because it does not use surrogates. |
c349b1b9 |
921 | |
c29a771d |
922 | =item * |
5cb3728c |
923 | |
924 | UTF-7 |
c349b1b9 |
925 | |
926 | A seven-bit safe (non-eight-bit) encoding, useful if the |
927 | transport/storage is not eight-bit safe. Defined by RFC 2152. |
928 | |
95a1a48b |
929 | =back |
930 | |
0d7c09bb |
931 | =head2 Security Implications of Unicode |
932 | |
933 | =over 4 |
934 | |
935 | =item * |
936 | |
937 | Malformed UTF-8 |
bf0fa0b2 |
938 | |
939 | Unfortunately, the specification of UTF-8 leaves some room for |
940 | interpretation of how many bytes of encoded output one should generate |
941 | from one input Unicode character. Strictly speaking, one is supposed |
942 | to always generate the shortest possible sequence of UTF-8 bytes, |
feda178f |
943 | because otherwise there is potential for input buffer overflow at |
944 | the receiving end of a UTF-8 connection. Perl always generates the |
945 | shortest length UTF-8, and with warnings on (C<-w> or C<use |
946 | warnings;>) Perl will warn about non-shortest length UTF-8 (and other |
947 | malformations, too, such as the surrogates, which are not real |
948 | Unicode code points.) |
bf0fa0b2 |
949 | |
0d7c09bb |
950 | =item * |
951 | |
952 | Regular expressions behave slightly differently between byte data and |
953 | character (Unicode data). For example, the "word character" character |
954 | class C<\w> will work differently when the data is all eight-bit bytes |
955 | or when the data is Unicode. |
956 | |
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 |
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 | |
962 | In the second case, the C<\w> set of characters is much, much larger, |
963 | and most importantly, even in the set of the first 256 characters, it |
964 | will most probably be different: as opposed to most locales (which are |
965 | specific to a language and country pair) Unicode classifies all the |
966 | characters that are letters as C<\w>. For example: your locale might |
967 | not think that LATIN SMALL LETTER ETH is a letter (unless you happen |
968 | to speak Icelandic), but Unicode does. |
969 | |
a73d23f6 |
970 | As discussed elsewhere, Perl tries to stand one leg (two legs, as |
0746c07b |
971 | camels are quadrupeds?) in two worlds: the old world of bytes and the new |
0d7c09bb |
972 | world of characters, upgrading from bytes to characters when necessary. |
973 | If your legacy code is not explicitly using Unicode, no automatic |
974 | switchover to characters should happen, and characters shouldn't get |
975 | downgraded back to bytes, either. It is possible to accidentally mix |
976 | bytes and characters, however (see L<perluniintro>), in which case the |
977 | C<\w> might start behaving differently. Review your code. |
978 | |
979 | =back |
980 | |
c349b1b9 |
981 | =head2 Unicode in Perl on EBCDIC |
982 | |
983 | The way Unicode is handled on EBCDIC platforms is still rather |
86bbd6d1 |
984 | experimental. On such a platform, references to UTF-8 encoding in this |
c349b1b9 |
985 | document and elsewhere should be read as meaning UTF-EBCDIC as |
986 | specified in Unicode Technical Report 16 unless ASCII vs EBCDIC issues |
987 | are specifically discussed. There is no C<utfebcdic> pragma or |
86bbd6d1 |
988 | ":utfebcdic" layer, rather, "utf8" and ":utf8" are re-used to mean |
989 | the platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic> |
990 | for more discussion of the issues. |
c349b1b9 |
991 | |
b310b053 |
992 | =head2 Locales |
993 | |
4616122b |
994 | Usually locale settings and Unicode do not affect each other, but |
b310b053 |
995 | there are a couple of exceptions: |
996 | |
997 | =over 4 |
998 | |
999 | =item * |
1000 | |
1001 | If your locale environment variables (LANGUAGE, LC_ALL, LC_CTYPE, LANG) |
1002 | contain the strings 'UTF-8' or 'UTF8' (case-insensitive matching), |
1003 | the default encoding of your STDIN, STDOUT, and STDERR, and of |
1004 | B<any subsequent file open>, is UTF-8. |
1005 | |
1006 | =item * |
1007 | |
1008 | Perl tries really hard to work both with Unicode and the old byte |
1009 | oriented world: most often this is nice, but sometimes this causes |
574c8022 |
1010 | problems. |
b310b053 |
1011 | |
1012 | =back |
1013 | |
95a1a48b |
1014 | =head2 Using Unicode in XS |
1015 | |
1016 | If you want to handle Perl Unicode in XS extensions, you may find |
90f968e0 |
1017 | the following C APIs useful (see perlapi for details): |
95a1a48b |
1018 | |
1019 | =over 4 |
1020 | |
1021 | =item * |
1022 | |
f1e62f77 |
1023 | DO_UTF8(sv) returns true if the UTF8 flag is on and the bytes pragma |
1024 | is not in effect. SvUTF8(sv) returns true is the UTF8 flag is on, the |
1025 | bytes pragma is ignored. The UTF8 flag being on does B<not> mean that |
b31c5e31 |
1026 | there are any characters of code points greater than 255 (or 127) in |
1027 | the scalar, or that there even are any characters in the scalar. |
1028 | What the UTF8 flag means is that the sequence of octets in the |
1029 | representation of the scalar is the sequence of UTF-8 encoded |
1030 | code points of the characters of a string. The UTF8 flag being |
1031 | off means that each octet in this representation encodes a single |
1032 | character with codepoint 0..255 within the string. Perl's Unicode |
1033 | model is not to use UTF-8 until it's really necessary. |
95a1a48b |
1034 | |
1035 | =item * |
1036 | |
1037 | uvuni_to_utf8(buf, chr) writes a Unicode character code point into a |
cfc01aea |
1038 | buffer encoding the code point as UTF-8, and returns a pointer |
95a1a48b |
1039 | pointing after the UTF-8 bytes. |
1040 | |
1041 | =item * |
1042 | |
1043 | utf8_to_uvuni(buf, lenp) reads UTF-8 encoded bytes from a buffer and |
1044 | returns the Unicode character code point (and optionally the length of |
1045 | the UTF-8 byte sequence). |
1046 | |
1047 | =item * |
1048 | |
90f968e0 |
1049 | utf8_length(start, end) returns the length of the UTF-8 encoded buffer |
1050 | in characters. sv_len_utf8(sv) returns the length of the UTF-8 encoded |
95a1a48b |
1051 | scalar. |
1052 | |
1053 | =item * |
1054 | |
1055 | sv_utf8_upgrade(sv) converts the string of the scalar to its UTF-8 |
1056 | encoded form. sv_utf8_downgrade(sv) does the opposite (if possible). |
1057 | sv_utf8_encode(sv) is like sv_utf8_upgrade but the UTF8 flag does not |
1058 | get turned on. sv_utf8_decode() does the opposite of sv_utf8_encode(). |
13a6c0e0 |
1059 | Note that none of these are to be used as general purpose encoding/decoding |
1060 | interfaces: use Encode for that. sv_utf8_upgrade() is affected by the |
1061 | encoding pragma, but sv_utf8_downgrade() is not (since the encoding |
1062 | pragma is designed to be a one-way street). |
95a1a48b |
1063 | |
1064 | =item * |
1065 | |
90f968e0 |
1066 | is_utf8_char(s) returns true if the pointer points to a valid UTF-8 |
1067 | character. |
95a1a48b |
1068 | |
1069 | =item * |
1070 | |
1071 | is_utf8_string(buf, len) returns true if the len bytes of the buffer |
1072 | are valid UTF-8. |
1073 | |
1074 | =item * |
1075 | |
1076 | UTF8SKIP(buf) will return the number of bytes in the UTF-8 encoded |
1077 | character in the buffer. UNISKIP(chr) will return the number of bytes |
90f968e0 |
1078 | required to UTF-8-encode the Unicode character code point. UTF8SKIP() |
1079 | is useful for example for iterating over the characters of a UTF-8 |
1080 | encoded buffer; UNISKIP() is useful for example in computing |
1081 | the size required for a UTF-8 encoded buffer. |
95a1a48b |
1082 | |
1083 | =item * |
1084 | |
1085 | utf8_distance(a, b) will tell the distance in characters between the |
1086 | two pointers pointing to the same UTF-8 encoded buffer. |
1087 | |
1088 | =item * |
1089 | |
1090 | utf8_hop(s, off) will return a pointer to an UTF-8 encoded buffer that |
1091 | is C<off> (positive or negative) Unicode characters displaced from the |
90f968e0 |
1092 | UTF-8 buffer C<s>. Be careful not to overstep the buffer: utf8_hop() |
1093 | will merrily run off the end or the beginning if told to do so. |
95a1a48b |
1094 | |
d2cc3551 |
1095 | =item * |
1096 | |
1097 | pv_uni_display(dsv, spv, len, pvlim, flags) and sv_uni_display(dsv, |
1098 | ssv, pvlim, flags) are useful for debug output of Unicode strings and |
90f968e0 |
1099 | scalars. By default they are useful only for debug: they display |
1100 | B<all> characters as hexadecimal code points, but with the flags |
1101 | UNI_DISPLAY_ISPRINT and UNI_DISPLAY_BACKSLASH you can make the output |
1102 | more readable. |
d2cc3551 |
1103 | |
1104 | =item * |
1105 | |
90f968e0 |
1106 | ibcmp_utf8(s1, pe1, u1, l1, u1, s2, pe2, l2, u2) can be used to |
1107 | compare two strings case-insensitively in Unicode. |
1108 | (For case-sensitive comparisons you can just use memEQ() and memNE() |
1109 | as usual.) |
d2cc3551 |
1110 | |
c349b1b9 |
1111 | =back |
1112 | |
95a1a48b |
1113 | For more information, see L<perlapi>, and F<utf8.c> and F<utf8.h> |
1114 | in the Perl source code distribution. |
1115 | |
c29a771d |
1116 | =head1 BUGS |
1117 | |
7eabb34d |
1118 | =head2 Interaction with locales |
1119 | |
c29a771d |
1120 | Use of locales with Unicode data may lead to odd results. Currently |
1121 | there is some attempt to apply 8-bit locale info to characters in the |
1122 | range 0..255, but this is demonstrably incorrect for locales that use |
1123 | characters above that range when mapped into Unicode. It will also |
574c8022 |
1124 | tend to run slower. Use of locales with Unicode is discouraged. |
c29a771d |
1125 | |
7eabb34d |
1126 | =head2 Interaction with extensions |
1127 | |
1128 | When perl exchanges data with an extension, the extension should be |
1129 | able to understand the UTF-8 flag and act accordingly. If the |
1130 | extension doesn't know about the flag, the risk is high that it will |
1131 | return data that are incorrectly flagged. |
1132 | |
1133 | So if you're working with Unicode data, consult the documentation of |
1134 | every module you're using if there are any issues with Unicode data |
1135 | exchange. If the documentation does not talk about Unicode at all, |
a73d23f6 |
1136 | suspect the worst and probably look at the source to learn how the |
1137 | module is implemented. Modules written completely in perl shouldn't |
1138 | cause problems. Modules that directly or indirectly access code written |
1139 | in other programming languages are at risk. |
7eabb34d |
1140 | |
1141 | For affected functions the simple strategy to avoid data corruption is |
1142 | to always make the encoding of the exchanged data explicit. Choose an |
1143 | encoding you know the extension can handle. Convert arguments passed |
1144 | to the extensions to that encoding and convert results back from that |
1145 | encoding. Write wrapper functions that do the conversions for you, so |
1146 | you can later change the functions when the extension catches up. |
1147 | |
1148 | To provide an example let's say the popular Foo::Bar::escape_html |
1149 | function doesn't deal with Unicode data yet. The wrapper function |
1150 | would convert the argument to raw UTF-8 and convert the result back to |
1151 | perl's internal representation like so: |
1152 | |
1153 | sub my_escape_html ($) { |
1154 | my($what) = shift; |
1155 | return unless defined $what; |
1156 | Encode::decode_utf8(Foo::Bar::escape_html(Encode::encode_utf8($what))); |
1157 | } |
1158 | |
1159 | Sometimes, when the extension does not convert data but just stores |
1160 | and retrieves them, you will be in a position to use the otherwise |
1161 | dangerous Encode::_utf8_on() function. Let's say the popular |
66b79f27 |
1162 | C<Foo::Bar> extension, written in C, provides a C<param> method that |
7eabb34d |
1163 | lets you store and retrieve data according to these prototypes: |
1164 | |
1165 | $self->param($name, $value); # set a scalar |
1166 | $value = $self->param($name); # retrieve a scalar |
1167 | |
1168 | If it does not yet provide support for any encoding, one could write a |
1169 | derived class with such a C<param> method: |
1170 | |
1171 | sub param { |
1172 | my($self,$name,$value) = @_; |
1173 | utf8::upgrade($name); # make sure it is UTF-8 encoded |
1174 | if (defined $value) |
1175 | utf8::upgrade($value); # make sure it is UTF-8 encoded |
1176 | return $self->SUPER::param($name,$value); |
1177 | } else { |
1178 | my $ret = $self->SUPER::param($name); |
1179 | Encode::_utf8_on($ret); # we know, it is UTF-8 encoded |
1180 | return $ret; |
1181 | } |
1182 | } |
1183 | |
a73d23f6 |
1184 | Some extensions provide filters on data entry/exit points, such as |
1185 | DB_File::filter_store_key and family. Look out for such filters in |
66b79f27 |
1186 | the documentation of your extensions, they can make the transition to |
7eabb34d |
1187 | Unicode data much easier. |
1188 | |
1189 | =head2 speed |
1190 | |
c29a771d |
1191 | Some functions are slower when working on UTF-8 encoded strings than |
574c8022 |
1192 | on byte encoded strings. All functions that need to hop over |
c29a771d |
1193 | characters such as length(), substr() or index() can work B<much> |
1194 | faster when the underlying data are byte-encoded. Witness the |
1195 | following benchmark: |
666f95b9 |
1196 | |
c29a771d |
1197 | % perl -e ' |
1198 | use Benchmark; |
1199 | use strict; |
1200 | our $l = 10000; |
1201 | our $u = our $b = "x" x $l; |
1202 | substr($u,0,1) = "\x{100}"; |
1203 | timethese(-2,{ |
1204 | LENGTH_B => q{ length($b) }, |
1205 | LENGTH_U => q{ length($u) }, |
1206 | SUBSTR_B => q{ substr($b, $l/4, $l/2) }, |
1207 | SUBSTR_U => q{ substr($u, $l/4, $l/2) }, |
1208 | }); |
1209 | ' |
1210 | Benchmark: running LENGTH_B, LENGTH_U, SUBSTR_B, SUBSTR_U for at least 2 CPU seconds... |
1211 | LENGTH_B: 2 wallclock secs ( 2.36 usr + 0.00 sys = 2.36 CPU) @ 5649983.05/s (n=13333960) |
1212 | LENGTH_U: 2 wallclock secs ( 2.11 usr + 0.00 sys = 2.11 CPU) @ 12155.45/s (n=25648) |
1213 | SUBSTR_B: 3 wallclock secs ( 2.16 usr + 0.00 sys = 2.16 CPU) @ 374480.09/s (n=808877) |
1214 | SUBSTR_U: 2 wallclock secs ( 2.11 usr + 0.00 sys = 2.11 CPU) @ 6791.00/s (n=14329) |
666f95b9 |
1215 | |
c29a771d |
1216 | The numbers show an incredible slowness on long UTF-8 strings and you |
1217 | should carefully avoid to use these functions within tight loops. For |
1218 | example if you want to iterate over characters, it is infinitely |
1219 | better to split into an array than to use substr, as the following |
1220 | benchmark shows: |
1221 | |
1222 | % perl -e ' |
1223 | use Benchmark; |
1224 | use strict; |
1225 | our $l = 10000; |
1226 | our $u = our $b = "x" x $l; |
1227 | substr($u,0,1) = "\x{100}"; |
1228 | timethese(-5,{ |
1229 | SPLIT_B => q{ for my $c (split //, $b){} }, |
1230 | SPLIT_U => q{ for my $c (split //, $u){} }, |
1231 | SUBSTR_B => q{ for my $i (0..length($b)-1){my $c = substr($b,$i,1);} }, |
1232 | SUBSTR_U => q{ for my $i (0..length($u)-1){my $c = substr($u,$i,1);} }, |
1233 | }); |
1234 | ' |
1235 | Benchmark: running SPLIT_B, SPLIT_U, SUBSTR_B, SUBSTR_U for at least 5 CPU seconds... |
1236 | SPLIT_B: 6 wallclock secs ( 5.29 usr + 0.00 sys = 5.29 CPU) @ 56.14/s (n=297) |
1237 | SPLIT_U: 5 wallclock secs ( 5.17 usr + 0.01 sys = 5.18 CPU) @ 55.21/s (n=286) |
1238 | SUBSTR_B: 5 wallclock secs ( 5.34 usr + 0.00 sys = 5.34 CPU) @ 123.22/s (n=658) |
1239 | SUBSTR_U: 7 wallclock secs ( 6.20 usr + 0.00 sys = 6.20 CPU) @ 0.81/s (n=5) |
1240 | |
1241 | You see, the algorithm based on substr() was faster with byte encoded |
1242 | data but it is pathologically slow with UTF-8 data. |
666f95b9 |
1243 | |
393fec97 |
1244 | =head1 SEE ALSO |
1245 | |
72ff2908 |
1246 | L<perluniintro>, L<encoding>, L<Encode>, L<open>, L<utf8>, L<bytes>, |
1247 | L<perlretut>, L<perlvar/"${^WIDE_SYSTEM_CALLS}"> |
393fec97 |
1248 | |
1249 | =cut |