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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 | |
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15 | =item Input and Output Layers |
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16 | |
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17 | Perl knows when a filehandle uses Perl's internal Unicode encodings |
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18 | (UTF-8, or UTF-EBCDIC if in EBCDIC) if the filehandle is opened with |
19 | the ":utf8" layer. Other encodings can be converted to Perl's |
20 | encoding on input or from Perl's encoding on output by use of the |
21 | ":encoding(...)" 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 |
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37 | (in string or regular expression literals, or in identifier names) on |
38 | ASCII-based machines or to recognize UTF-EBCDIC on EBCDIC-based |
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39 | machines. B<These are the only times when an explicit C<use utf8> |
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40 | is needed.> See L<utf8>. |
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41 | |
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42 | You can also use the C<encoding> pragma to change the default encoding |
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43 | of the data in your script; see L<encoding>. |
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44 | |
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45 | =item BOM-marked scripts and UTF-16 scripts autodetected |
46 | |
47 | If a Perl script begins marked with the Unicode BOM (UTF-16LE, UTF16-BE, |
48 | or UTF-8), or if the script looks like non-BOM-marked UTF-16 of either |
49 | endianness, Perl will correctly read in the script as Unicode. |
50 | (BOMless UTF-8 cannot be effectively recognized or differentiated from |
51 | ISO 8859-1 or other eight-bit encodings.) |
52 | |
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53 | =item C<use encoding> needed to upgrade non-Latin-1 byte strings |
54 | |
55 | By default, there is a fundamental asymmetry in Perl's unicode model: |
56 | implicit upgrading from byte strings to Unicode strings assumes that |
57 | they were encoded in I<ISO 8859-1 (Latin-1)>, but Unicode strings are |
58 | downgraded with UTF-8 encoding. This happens because the first 256 |
59 | codepoints in Unicode happens to agree with Latin-1. |
60 | |
61 | If you wish to interpret byte strings as UTF-8 instead, use the |
62 | C<encoding> pragma: |
63 | |
64 | use encoding 'utf8'; |
65 | |
66 | See L</"Byte and Character Semantics"> for more details. |
67 | |
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68 | =back |
69 | |
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70 | =head2 Byte and Character Semantics |
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71 | |
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72 | Beginning with version 5.6, Perl uses logically-wide characters to |
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73 | represent strings internally. |
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74 | |
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75 | In future, Perl-level operations will be expected to work with |
76 | characters rather than bytes. |
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77 | |
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78 | However, as an interim compatibility measure, Perl aims to |
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79 | provide a safe migration path from byte semantics to character |
80 | semantics for programs. For operations where Perl can unambiguously |
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81 | decide that the input data are characters, Perl switches to |
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82 | character semantics. For operations where this determination cannot |
83 | be made without additional information from the user, Perl decides in |
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84 | favor of compatibility and chooses to use byte semantics. |
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85 | |
86 | This behavior preserves compatibility with earlier versions of Perl, |
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87 | which allowed byte semantics in Perl operations only if |
88 | none of the program's inputs were marked as being as source of Unicode |
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89 | character data. Such data may come from filehandles, from calls to |
90 | external programs, from information provided by the system (such as %ENV), |
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91 | or from literals and constants in the source text. |
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92 | |
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93 | The C<bytes> pragma will always, regardless of platform, force byte |
94 | semantics in a particular lexical scope. See L<bytes>. |
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95 | |
96 | The C<utf8> pragma is primarily a compatibility device that enables |
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97 | recognition of UTF-(8|EBCDIC) in literals encountered by the parser. |
376d9008 |
98 | Note that this pragma is only required while Perl defaults to byte |
99 | semantics; when character semantics become the default, this pragma |
100 | may become a no-op. See L<utf8>. |
101 | |
102 | Unless explicitly stated, Perl operators use character semantics |
103 | for Unicode data and byte semantics for non-Unicode data. |
104 | The decision to use character semantics is made transparently. If |
105 | input data comes from a Unicode source--for example, if a character |
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106 | encoding layer is added to a filehandle or a literal Unicode |
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107 | string constant appears in a program--character semantics apply. |
108 | Otherwise, byte semantics are in effect. The C<bytes> pragma should |
109 | be used to force byte semantics on Unicode data. |
110 | |
111 | If strings operating under byte semantics and strings with Unicode |
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112 | character data are concatenated, the new string will be created by |
113 | decoding the byte strings as I<ISO 8859-1 (Latin-1)>, even if the |
114 | old Unicode string used EBCDIC. This translation is done without |
115 | regard to the system's native 8-bit encoding. To change this for |
116 | systems with non-Latin-1 and non-EBCDIC native encodings, use the |
117 | C<encoding> pragma. See L<encoding>. |
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118 | |
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119 | Under character semantics, many operations that formerly operated on |
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120 | bytes now operate on characters. A character in Perl is |
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121 | logically just a number ranging from 0 to 2**31 or so. Larger |
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122 | characters may encode into longer sequences of bytes internally, but |
123 | this internal detail is mostly hidden for Perl code. |
124 | See L<perluniintro> for more. |
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125 | |
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126 | =head2 Effects of Character Semantics |
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127 | |
128 | Character semantics have the following effects: |
129 | |
130 | =over 4 |
131 | |
132 | =item * |
133 | |
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134 | Strings--including hash keys--and regular expression patterns may |
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135 | contain characters that have an ordinal value larger than 255. |
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136 | |
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137 | If you use a Unicode editor to edit your program, Unicode characters |
138 | may occur directly within the literal strings in one of the various |
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139 | Unicode encodings (UTF-8, UTF-EBCDIC, UCS-2, etc.), but will be recognized |
140 | as such and converted to Perl's internal representation only if the |
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141 | appropriate L<encoding> is specified. |
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142 | |
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143 | Unicode characters can also be added to a string by using the |
144 | C<\x{...}> notation. The Unicode code for the desired character, in |
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145 | hexadecimal, should be placed in the braces. For instance, a smiley |
146 | face is C<\x{263A}>. This encoding scheme only works for characters |
147 | with a code of 0x100 or above. |
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148 | |
149 | Additionally, if you |
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150 | |
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151 | use charnames ':full'; |
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152 | |
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153 | you can use the C<\N{...}> notation and put the official Unicode |
154 | character name within the braces, such as C<\N{WHITE SMILING FACE}>. |
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155 | |
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156 | |
157 | =item * |
158 | |
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159 | If an appropriate L<encoding> is specified, identifiers within the |
160 | Perl script may contain Unicode alphanumeric characters, including |
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161 | ideographs. Perl does not currently attempt to canonicalize variable |
162 | names. |
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163 | |
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164 | =item * |
165 | |
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166 | Regular expressions match characters instead of bytes. "." matches |
167 | a character instead of a byte. The C<\C> pattern is provided to force |
168 | a match a single byte--a C<char> in C, hence C<\C>. |
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169 | |
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170 | =item * |
171 | |
172 | Character classes in regular expressions match characters instead of |
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173 | bytes and match against the character properties specified in the |
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174 | Unicode properties database. C<\w> can be used to match a Japanese |
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175 | ideograph, for instance. |
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176 | |
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177 | (However, and as a limitation of the current implementation, using |
178 | C<\w> or C<\W> I<inside> a C<[...]> character class will still match |
179 | with byte semantics.) |
180 | |
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181 | =item * |
182 | |
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183 | Named Unicode properties, scripts, and block ranges may be used like |
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184 | character classes via the C<\p{}> "matches property" construct and |
185 | the C<\P{}> negation, "doesn't match property". |
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186 | |
187 | For instance, C<\p{Lu}> matches any character with the Unicode "Lu" |
188 | (Letter, uppercase) property, while C<\p{M}> matches any character |
189 | with an "M" (mark--accents and such) property. Brackets are not |
190 | required for single letter properties, so C<\p{M}> is equivalent to |
191 | C<\pM>. Many predefined properties are available, such as |
192 | C<\p{Mirrored}> and C<\p{Tibetan}>. |
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193 | |
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194 | The official Unicode script and block names have spaces and dashes as |
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195 | separators, but for convenience you can use dashes, spaces, or |
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196 | underbars, and case is unimportant. It is recommended, however, that |
197 | for consistency you use the following naming: the official Unicode |
198 | script, property, or block name (see below for the additional rules |
199 | that apply to block names) with whitespace and dashes removed, and the |
200 | words "uppercase-first-lowercase-rest". C<Latin-1 Supplement> thus |
201 | becomes C<Latin1Supplement>. |
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202 | |
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203 | You can also use negation in both C<\p{}> and C<\P{}> by introducing a caret |
204 | (^) between the first brace and the property name: C<\p{^Tamil}> is |
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205 | equal to C<\P{Tamil}>. |
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206 | |
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207 | B<NOTE: the properties, scripts, and blocks listed here are as of |
208 | Unicode 3.2.0, March 2002, or Perl 5.8.0, July 2002. Unicode 4.0.0 |
209 | came out in April 2003, and Perl 5.8.1 in September 2003.> |
210 | |
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211 | Here are the basic Unicode General Category properties, followed by their |
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212 | long form. You can use either; C<\p{Lu}> and C<\p{UppercaseLetter}>, |
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213 | for instance, are identical. |
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214 | |
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215 | Short Long |
216 | |
217 | L Letter |
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218 | LC CasedLetter |
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219 | Lu UppercaseLetter |
220 | Ll LowercaseLetter |
221 | Lt TitlecaseLetter |
222 | Lm ModifierLetter |
223 | Lo OtherLetter |
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224 | |
225 | M Mark |
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226 | Mn NonspacingMark |
227 | Mc SpacingMark |
228 | Me EnclosingMark |
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229 | |
230 | N Number |
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231 | Nd DecimalNumber |
232 | Nl LetterNumber |
233 | No OtherNumber |
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234 | |
235 | P Punctuation |
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236 | Pc ConnectorPunctuation |
237 | Pd DashPunctuation |
238 | Ps OpenPunctuation |
239 | Pe ClosePunctuation |
240 | Pi InitialPunctuation |
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241 | (may behave like Ps or Pe depending on usage) |
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242 | Pf FinalPunctuation |
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243 | (may behave like Ps or Pe depending on usage) |
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244 | Po OtherPunctuation |
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245 | |
246 | S Symbol |
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247 | Sm MathSymbol |
248 | Sc CurrencySymbol |
249 | Sk ModifierSymbol |
250 | So OtherSymbol |
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251 | |
252 | Z Separator |
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253 | Zs SpaceSeparator |
254 | Zl LineSeparator |
255 | Zp ParagraphSeparator |
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256 | |
257 | C Other |
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258 | Cc Control |
259 | Cf Format |
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260 | Cs Surrogate (not usable) |
261 | Co PrivateUse |
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262 | Cn Unassigned |
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263 | |
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264 | Single-letter properties match all characters in any of the |
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265 | two-letter sub-properties starting with the same letter. |
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266 | C<LC> and C<L&> are special cases, which are aliases for the set of |
267 | C<Ll>, C<Lu>, and C<Lt>. |
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268 | |
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269 | Because Perl hides the need for the user to understand the internal |
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270 | representation of Unicode characters, there is no need to implement |
271 | the somewhat messy concept of surrogates. C<Cs> is therefore not |
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272 | supported. |
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273 | |
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274 | Because scripts differ in their directionality--Hebrew is |
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275 | written right to left, for example--Unicode supplies these properties in |
276 | the BidiClass class: |
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277 | |
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278 | Property Meaning |
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279 | |
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280 | L Left-to-Right |
281 | LRE Left-to-Right Embedding |
282 | LRO Left-to-Right Override |
283 | R Right-to-Left |
284 | AL Right-to-Left Arabic |
285 | RLE Right-to-Left Embedding |
286 | RLO Right-to-Left Override |
287 | PDF Pop Directional Format |
288 | EN European Number |
289 | ES European Number Separator |
290 | ET European Number Terminator |
291 | AN Arabic Number |
292 | CS Common Number Separator |
293 | NSM Non-Spacing Mark |
294 | BN Boundary Neutral |
295 | B Paragraph Separator |
296 | S Segment Separator |
297 | WS Whitespace |
298 | ON Other Neutrals |
299 | |
300 | For example, C<\p{BidiClass:R}> matches characters that are normally |
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301 | written right to left. |
302 | |
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303 | =back |
304 | |
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305 | =head2 Scripts |
306 | |
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307 | The script names which can be used by C<\p{...}> and C<\P{...}>, |
308 | such as in C<\p{Latin}> or C<\p{Cyrillic}>, are as follows: |
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309 | |
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310 | Arabic |
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311 | Armenian |
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312 | Bengali |
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313 | Bopomofo |
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314 | Buhid |
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315 | CanadianAboriginal |
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316 | Cherokee |
317 | Cyrillic |
318 | Deseret |
319 | Devanagari |
320 | Ethiopic |
321 | Georgian |
322 | Gothic |
323 | Greek |
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324 | Gujarati |
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325 | Gurmukhi |
326 | Han |
327 | Hangul |
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328 | Hanunoo |
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329 | Hebrew |
330 | Hiragana |
331 | Inherited |
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332 | Kannada |
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333 | Katakana |
334 | Khmer |
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335 | Lao |
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336 | Latin |
337 | Malayalam |
338 | Mongolian |
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339 | Myanmar |
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340 | Ogham |
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341 | OldItalic |
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342 | Oriya |
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343 | Runic |
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344 | Sinhala |
345 | Syriac |
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346 | Tagalog |
347 | Tagbanwa |
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348 | Tamil |
349 | Telugu |
350 | Thaana |
351 | Thai |
352 | Tibetan |
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353 | Yi |
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354 | |
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355 | Extended property classes can supplement the basic |
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356 | properties, defined by the F<PropList> Unicode database: |
357 | |
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358 | ASCIIHexDigit |
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359 | BidiControl |
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360 | Dash |
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361 | Deprecated |
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362 | Diacritic |
363 | Extender |
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364 | GraphemeLink |
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365 | HexDigit |
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366 | Hyphen |
367 | Ideographic |
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368 | IDSBinaryOperator |
369 | IDSTrinaryOperator |
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370 | JoinControl |
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371 | LogicalOrderException |
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372 | NoncharacterCodePoint |
373 | OtherAlphabetic |
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374 | OtherDefaultIgnorableCodePoint |
375 | OtherGraphemeExtend |
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376 | OtherLowercase |
377 | OtherMath |
378 | OtherUppercase |
379 | QuotationMark |
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380 | Radical |
381 | SoftDotted |
382 | TerminalPunctuation |
383 | UnifiedIdeograph |
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384 | WhiteSpace |
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385 | |
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386 | and there are further derived properties: |
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387 | |
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388 | Alphabetic Lu + Ll + Lt + Lm + Lo + OtherAlphabetic |
389 | Lowercase Ll + OtherLowercase |
390 | Uppercase Lu + OtherUppercase |
391 | Math Sm + OtherMath |
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392 | |
393 | ID_Start Lu + Ll + Lt + Lm + Lo + Nl |
394 | ID_Continue ID_Start + Mn + Mc + Nd + Pc |
395 | |
396 | Any Any character |
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397 | Assigned Any non-Cn character (i.e. synonym for \P{Cn}) |
398 | Unassigned Synonym for \p{Cn} |
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399 | Common Any character (or unassigned code point) |
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400 | not explicitly assigned to a script |
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401 | |
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402 | For backward compatibility (with Perl 5.6), all properties mentioned |
403 | so far may have C<Is> prepended to their name, so C<\P{IsLu}>, for |
404 | example, is equal to C<\P{Lu}>. |
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405 | |
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406 | =head2 Blocks |
407 | |
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408 | In addition to B<scripts>, Unicode also defines B<blocks> of |
409 | characters. The difference between scripts and blocks is that the |
410 | concept of scripts is closer to natural languages, while the concept |
411 | of blocks is more of an artificial grouping based on groups of 256 |
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412 | Unicode characters. For example, the C<Latin> script contains letters |
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413 | from many blocks but does not contain all the characters from those |
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414 | blocks. It does not, for example, contain digits, because digits are |
415 | shared across many scripts. Digits and similar groups, like |
416 | punctuation, are in a category called C<Common>. |
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417 | |
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418 | For more about scripts, see the UTR #24: |
419 | |
420 | http://www.unicode.org/unicode/reports/tr24/ |
421 | |
422 | For more about blocks, see: |
423 | |
424 | http://www.unicode.org/Public/UNIDATA/Blocks.txt |
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425 | |
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426 | Block names are given with the C<In> prefix. For example, the |
427 | Katakana block is referenced via C<\p{InKatakana}>. The C<In> |
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428 | prefix may be omitted if there is no naming conflict with a script |
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429 | or any other property, but it is recommended that C<In> always be used |
1bfb14c4 |
430 | for block tests to avoid confusion. |
eb0cc9e3 |
431 | |
432 | These block names are supported: |
433 | |
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434 | InAlphabeticPresentationForms |
435 | InArabic |
436 | InArabicPresentationFormsA |
437 | InArabicPresentationFormsB |
438 | InArmenian |
439 | InArrows |
440 | InBasicLatin |
441 | InBengali |
442 | InBlockElements |
443 | InBopomofo |
444 | InBopomofoExtended |
445 | InBoxDrawing |
446 | InBraillePatterns |
447 | InBuhid |
448 | InByzantineMusicalSymbols |
449 | InCJKCompatibility |
450 | InCJKCompatibilityForms |
451 | InCJKCompatibilityIdeographs |
452 | InCJKCompatibilityIdeographsSupplement |
453 | InCJKRadicalsSupplement |
454 | InCJKSymbolsAndPunctuation |
455 | InCJKUnifiedIdeographs |
456 | InCJKUnifiedIdeographsExtensionA |
457 | InCJKUnifiedIdeographsExtensionB |
458 | InCherokee |
459 | InCombiningDiacriticalMarks |
460 | InCombiningDiacriticalMarksforSymbols |
461 | InCombiningHalfMarks |
462 | InControlPictures |
463 | InCurrencySymbols |
464 | InCyrillic |
465 | InCyrillicSupplementary |
466 | InDeseret |
467 | InDevanagari |
468 | InDingbats |
469 | InEnclosedAlphanumerics |
470 | InEnclosedCJKLettersAndMonths |
471 | InEthiopic |
472 | InGeneralPunctuation |
473 | InGeometricShapes |
474 | InGeorgian |
475 | InGothic |
476 | InGreekExtended |
477 | InGreekAndCoptic |
478 | InGujarati |
479 | InGurmukhi |
480 | InHalfwidthAndFullwidthForms |
481 | InHangulCompatibilityJamo |
482 | InHangulJamo |
483 | InHangulSyllables |
484 | InHanunoo |
485 | InHebrew |
486 | InHighPrivateUseSurrogates |
487 | InHighSurrogates |
488 | InHiragana |
489 | InIPAExtensions |
490 | InIdeographicDescriptionCharacters |
491 | InKanbun |
492 | InKangxiRadicals |
493 | InKannada |
494 | InKatakana |
495 | InKatakanaPhoneticExtensions |
496 | InKhmer |
497 | InLao |
498 | InLatin1Supplement |
499 | InLatinExtendedA |
500 | InLatinExtendedAdditional |
501 | InLatinExtendedB |
502 | InLetterlikeSymbols |
503 | InLowSurrogates |
504 | InMalayalam |
505 | InMathematicalAlphanumericSymbols |
506 | InMathematicalOperators |
507 | InMiscellaneousMathematicalSymbolsA |
508 | InMiscellaneousMathematicalSymbolsB |
509 | InMiscellaneousSymbols |
510 | InMiscellaneousTechnical |
511 | InMongolian |
512 | InMusicalSymbols |
513 | InMyanmar |
514 | InNumberForms |
515 | InOgham |
516 | InOldItalic |
517 | InOpticalCharacterRecognition |
518 | InOriya |
519 | InPrivateUseArea |
520 | InRunic |
521 | InSinhala |
522 | InSmallFormVariants |
523 | InSpacingModifierLetters |
524 | InSpecials |
525 | InSuperscriptsAndSubscripts |
526 | InSupplementalArrowsA |
527 | InSupplementalArrowsB |
528 | InSupplementalMathematicalOperators |
529 | InSupplementaryPrivateUseAreaA |
530 | InSupplementaryPrivateUseAreaB |
531 | InSyriac |
532 | InTagalog |
533 | InTagbanwa |
534 | InTags |
535 | InTamil |
536 | InTelugu |
537 | InThaana |
538 | InThai |
539 | InTibetan |
540 | InUnifiedCanadianAboriginalSyllabics |
541 | InVariationSelectors |
542 | InYiRadicals |
543 | InYiSyllables |
32293815 |
544 | |
210b36aa |
545 | =over 4 |
546 | |
393fec97 |
547 | =item * |
548 | |
376d9008 |
549 | The special pattern C<\X> matches any extended Unicode |
550 | sequence--"a combining character sequence" in Standardese--where the |
551 | first character is a base character and subsequent characters are mark |
552 | characters that apply to the base character. C<\X> is equivalent to |
393fec97 |
553 | C<(?:\PM\pM*)>. |
554 | |
393fec97 |
555 | =item * |
556 | |
383e7cdd |
557 | The C<tr///> operator translates characters instead of bytes. Note |
376d9008 |
558 | that the C<tr///CU> functionality has been removed. For similar |
559 | functionality see pack('U0', ...) and pack('C0', ...). |
393fec97 |
560 | |
393fec97 |
561 | =item * |
562 | |
563 | Case translation operators use the Unicode case translation tables |
376d9008 |
564 | when character input is provided. Note that C<uc()>, or C<\U> in |
565 | interpolated strings, translates to uppercase, while C<ucfirst>, |
566 | or C<\u> in interpolated strings, translates to titlecase in languages |
567 | that make the distinction. |
393fec97 |
568 | |
569 | =item * |
570 | |
376d9008 |
571 | Most operators that deal with positions or lengths in a string will |
75daf61c |
572 | automatically switch to using character positions, including |
f5b005ca |
573 | C<chop()>, C<chomp()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>, |
75daf61c |
574 | C<sprintf()>, C<write()>, and C<length()>. Operators that |
376d9008 |
575 | specifically do not switch include C<vec()>, C<pack()>, and |
f5b005ca |
576 | C<unpack()>. Operators that really don't care include |
376d9008 |
577 | operators that treats strings as a bucket of bits such as C<sort()>, |
578 | and operators dealing with filenames. |
393fec97 |
579 | |
580 | =item * |
581 | |
1bfb14c4 |
582 | The C<pack()>/C<unpack()> letters C<c> and C<C> do I<not> change, |
376d9008 |
583 | since they are often used for byte-oriented formats. Again, think |
1bfb14c4 |
584 | C<char> in the C language. |
585 | |
586 | There is a new C<U> specifier that converts between Unicode characters |
587 | and code points. |
393fec97 |
588 | |
589 | =item * |
590 | |
376d9008 |
591 | The C<chr()> and C<ord()> functions work on characters, similar to |
592 | C<pack("U")> and C<unpack("U")>, I<not> C<pack("C")> and |
593 | C<unpack("C")>. C<pack("C")> and C<unpack("C")> are methods for |
594 | emulating byte-oriented C<chr()> and C<ord()> on Unicode strings. |
595 | While these methods reveal the internal encoding of Unicode strings, |
596 | that is not something one normally needs to care about at all. |
393fec97 |
597 | |
598 | =item * |
599 | |
376d9008 |
600 | The bit string operators, C<& | ^ ~>, can operate on character data. |
601 | However, for backward compatibility, such as when using bit string |
602 | operations when characters are all less than 256 in ordinal value, one |
603 | should not use C<~> (the bit complement) with characters of both |
604 | values less than 256 and values greater than 256. Most importantly, |
605 | DeMorgan's laws (C<~($x|$y) eq ~$x&~$y> and C<~($x&$y) eq ~$x|~$y>) |
606 | will not hold. The reason for this mathematical I<faux pas> is that |
607 | the complement cannot return B<both> the 8-bit (byte-wide) bit |
608 | complement B<and> the full character-wide bit complement. |
a1ca4561 |
609 | |
610 | =item * |
611 | |
983ffd37 |
612 | lc(), uc(), lcfirst(), and ucfirst() work for the following cases: |
613 | |
614 | =over 8 |
615 | |
616 | =item * |
617 | |
618 | the case mapping is from a single Unicode character to another |
376d9008 |
619 | single Unicode character, or |
983ffd37 |
620 | |
621 | =item * |
622 | |
623 | the case mapping is from a single Unicode character to more |
376d9008 |
624 | than one Unicode character. |
983ffd37 |
625 | |
626 | =back |
627 | |
63de3cb2 |
628 | Things to do with locales (Lithuanian, Turkish, Azeri) do B<not> work |
629 | since Perl does not understand the concept of Unicode locales. |
983ffd37 |
630 | |
dc33ebcf |
631 | See the Unicode Technical Report #21, Case Mappings, for more details. |
632 | |
983ffd37 |
633 | =back |
634 | |
dc33ebcf |
635 | =over 4 |
ac1256e8 |
636 | |
637 | =item * |
638 | |
393fec97 |
639 | And finally, C<scalar reverse()> reverses by character rather than by byte. |
640 | |
641 | =back |
642 | |
376d9008 |
643 | =head2 User-Defined Character Properties |
491fd90a |
644 | |
645 | You can define your own character properties by defining subroutines |
bac0b425 |
646 | whose names begin with "In" or "Is". The subroutines can be defined in |
647 | any package. The user-defined properties can be used in the regular |
648 | expression C<\p> and C<\P> constructs; if you are using a user-defined |
649 | property from a package other than the one you are in, you must specify |
650 | its package in the C<\p> or C<\P> construct. |
651 | |
652 | # assuming property IsForeign defined in Lang:: |
653 | package main; # property package name required |
654 | if ($txt =~ /\p{Lang::IsForeign}+/) { ... } |
655 | |
656 | package Lang; # property package name not required |
657 | if ($txt =~ /\p{IsForeign}+/) { ... } |
658 | |
659 | |
660 | Note that the effect is compile-time and immutable once defined. |
491fd90a |
661 | |
376d9008 |
662 | The subroutines must return a specially-formatted string, with one |
663 | or more newline-separated lines. Each line must be one of the following: |
491fd90a |
664 | |
665 | =over 4 |
666 | |
667 | =item * |
668 | |
99a6b1f0 |
669 | Two hexadecimal numbers separated by horizontal whitespace (space or |
376d9008 |
670 | tabular characters) denoting a range of Unicode code points to include. |
491fd90a |
671 | |
672 | =item * |
673 | |
376d9008 |
674 | Something to include, prefixed by "+": a built-in character |
bac0b425 |
675 | property (prefixed by "utf8::") or a user-defined character property, |
676 | to represent all the characters in that property; two hexadecimal code |
677 | points for a range; or a single hexadecimal code point. |
491fd90a |
678 | |
679 | =item * |
680 | |
376d9008 |
681 | Something to exclude, prefixed by "-": an existing character |
bac0b425 |
682 | property (prefixed by "utf8::") or a user-defined character property, |
683 | to represent all the characters in that property; two hexadecimal code |
684 | points for a range; or a single hexadecimal code point. |
491fd90a |
685 | |
686 | =item * |
687 | |
376d9008 |
688 | Something to negate, prefixed "!": an existing character |
bac0b425 |
689 | property (prefixed by "utf8::") or a user-defined character property, |
690 | to represent all the characters in that property; two hexadecimal code |
691 | points for a range; or a single hexadecimal code point. |
692 | |
693 | =item * |
694 | |
695 | Something to intersect with, prefixed by "&": an existing character |
696 | property (prefixed by "utf8::") or a user-defined character property, |
697 | for all the characters except the characters in the property; two |
698 | hexadecimal code points for a range; or a single hexadecimal code point. |
491fd90a |
699 | |
700 | =back |
701 | |
702 | For example, to define a property that covers both the Japanese |
703 | syllabaries (hiragana and katakana), you can define |
704 | |
705 | sub InKana { |
d5822f25 |
706 | return <<END; |
707 | 3040\t309F |
708 | 30A0\t30FF |
491fd90a |
709 | END |
710 | } |
711 | |
d5822f25 |
712 | Imagine that the here-doc end marker is at the beginning of the line. |
713 | Now you can use C<\p{InKana}> and C<\P{InKana}>. |
491fd90a |
714 | |
715 | You could also have used the existing block property names: |
716 | |
717 | sub InKana { |
718 | return <<'END'; |
719 | +utf8::InHiragana |
720 | +utf8::InKatakana |
721 | END |
722 | } |
723 | |
724 | Suppose you wanted to match only the allocated characters, |
d5822f25 |
725 | not the raw block ranges: in other words, you want to remove |
491fd90a |
726 | the non-characters: |
727 | |
728 | sub InKana { |
729 | return <<'END'; |
730 | +utf8::InHiragana |
731 | +utf8::InKatakana |
732 | -utf8::IsCn |
733 | END |
734 | } |
735 | |
736 | The negation is useful for defining (surprise!) negated classes. |
737 | |
738 | sub InNotKana { |
739 | return <<'END'; |
740 | !utf8::InHiragana |
741 | -utf8::InKatakana |
742 | +utf8::IsCn |
743 | END |
744 | } |
745 | |
bac0b425 |
746 | Intersection is useful for getting the common characters matched by |
747 | two (or more) classes. |
748 | |
749 | sub InFooAndBar { |
750 | return <<'END'; |
751 | +main::Foo |
752 | &main::Bar |
753 | END |
754 | } |
755 | |
756 | It's important to remember not to use "&" for the first set -- that |
757 | would be intersecting with nothing (resulting in an empty set). |
758 | |
3a2263fe |
759 | You can also define your own mappings to be used in the lc(), |
760 | lcfirst(), uc(), and ucfirst() (or their string-inlined versions). |
761 | The principle is the same: define subroutines in the C<main> package |
762 | with names like C<ToLower> (for lc() and lcfirst()), C<ToTitle> (for |
763 | the first character in ucfirst()), and C<ToUpper> (for uc(), and the |
764 | rest of the characters in ucfirst()). |
765 | |
766 | The string returned by the subroutines needs now to be three |
767 | hexadecimal numbers separated by tabulators: start of the source |
768 | range, end of the source range, and start of the destination range. |
769 | For example: |
770 | |
771 | sub ToUpper { |
772 | return <<END; |
773 | 0061\t0063\t0041 |
774 | END |
775 | } |
776 | |
777 | defines an uc() mapping that causes only the characters "a", "b", and |
778 | "c" to be mapped to "A", "B", "C", all other characters will remain |
779 | unchanged. |
780 | |
781 | If there is no source range to speak of, that is, the mapping is from |
782 | a single character to another single character, leave the end of the |
783 | source range empty, but the two tabulator characters are still needed. |
784 | For example: |
785 | |
786 | sub ToLower { |
787 | return <<END; |
788 | 0041\t\t0061 |
789 | END |
790 | } |
791 | |
792 | defines a lc() mapping that causes only "A" to be mapped to "a", all |
793 | other characters will remain unchanged. |
794 | |
795 | (For serious hackers only) If you want to introspect the default |
796 | mappings, you can find the data in the directory |
797 | C<$Config{privlib}>/F<unicore/To/>. The mapping data is returned as |
798 | the here-document, and the C<utf8::ToSpecFoo> are special exception |
799 | mappings derived from <$Config{privlib}>/F<unicore/SpecialCasing.txt>. |
800 | The C<Digit> and C<Fold> mappings that one can see in the directory |
801 | are not directly user-accessible, one can use either the |
802 | C<Unicode::UCD> module, or just match case-insensitively (that's when |
803 | the C<Fold> mapping is used). |
804 | |
805 | A final note on the user-defined property tests and mappings: they |
806 | will be used only if the scalar has been marked as having Unicode |
807 | characters. Old byte-style strings will not be affected. |
808 | |
376d9008 |
809 | =head2 Character Encodings for Input and Output |
8cbd9a7a |
810 | |
7221edc9 |
811 | See L<Encode>. |
8cbd9a7a |
812 | |
c29a771d |
813 | =head2 Unicode Regular Expression Support Level |
776f8809 |
814 | |
376d9008 |
815 | The following list of Unicode support for regular expressions describes |
816 | all the features currently supported. The references to "Level N" |
817 | and the section numbers refer to the Unicode Technical Report 18, |
965cd703 |
818 | "Unicode Regular Expression Guidelines", version 6 (Unicode 3.2.0, |
819 | Perl 5.8.0). |
776f8809 |
820 | |
821 | =over 4 |
822 | |
823 | =item * |
824 | |
825 | Level 1 - Basic Unicode Support |
826 | |
827 | 2.1 Hex Notation - done [1] |
3bfdc84c |
828 | Named Notation - done [2] |
776f8809 |
829 | 2.2 Categories - done [3][4] |
830 | 2.3 Subtraction - MISSING [5][6] |
831 | 2.4 Simple Word Boundaries - done [7] |
78d3e1bf |
832 | 2.5 Simple Loose Matches - done [8] |
776f8809 |
833 | 2.6 End of Line - MISSING [9][10] |
834 | |
835 | [ 1] \x{...} |
836 | [ 2] \N{...} |
eb0cc9e3 |
837 | [ 3] . \p{...} \P{...} |
12ac2576 |
838 | [ 4] support for scripts (see UTR#24 Script Names), blocks, |
839 | binary properties, enumerated non-binary properties, and |
840 | numeric properties (as listed in UTR#18 Other Properties) |
776f8809 |
841 | [ 5] have negation |
237bad5b |
842 | [ 6] can use regular expression look-ahead [a] |
843 | or user-defined character properties [b] to emulate subtraction |
776f8809 |
844 | [ 7] include Letters in word characters |
376d9008 |
845 | [ 8] note that Perl does Full case-folding in matching, not Simple: |
835863de |
846 | for example U+1F88 is equivalent with U+1F00 U+03B9, |
e0f9d4a8 |
847 | not with 1F80. This difference matters for certain Greek |
376d9008 |
848 | capital letters with certain modifiers: the Full case-folding |
849 | decomposes the letter, while the Simple case-folding would map |
e0f9d4a8 |
850 | it to a single character. |
5ca1ac52 |
851 | [ 9] see UTR #13 Unicode Newline Guidelines |
835863de |
852 | [10] should do ^ and $ also on \x{85}, \x{2028} and \x{2029} |
ec83e909 |
853 | (should also affect <>, $., and script line numbers) |
3bfdc84c |
854 | (the \x{85}, \x{2028} and \x{2029} do match \s) |
7207e29d |
855 | |
237bad5b |
856 | [a] You can mimic class subtraction using lookahead. |
5ca1ac52 |
857 | For example, what UTR #18 might write as |
29bdacb8 |
858 | |
dbe420b4 |
859 | [{Greek}-[{UNASSIGNED}]] |
860 | |
861 | in Perl can be written as: |
862 | |
1d81abf3 |
863 | (?!\p{Unassigned})\p{InGreekAndCoptic} |
864 | (?=\p{Assigned})\p{InGreekAndCoptic} |
dbe420b4 |
865 | |
866 | But in this particular example, you probably really want |
867 | |
1bfb14c4 |
868 | \p{GreekAndCoptic} |
dbe420b4 |
869 | |
870 | which will match assigned characters known to be part of the Greek script. |
29bdacb8 |
871 | |
5ca1ac52 |
872 | Also see the Unicode::Regex::Set module, it does implement the full |
873 | UTR #18 grouping, intersection, union, and removal (subtraction) syntax. |
874 | |
818c4caa |
875 | [b] See L</"User-Defined Character Properties">. |
237bad5b |
876 | |
776f8809 |
877 | =item * |
878 | |
879 | Level 2 - Extended Unicode Support |
880 | |
63de3cb2 |
881 | 3.1 Surrogates - MISSING [11] |
882 | 3.2 Canonical Equivalents - MISSING [12][13] |
883 | 3.3 Locale-Independent Graphemes - MISSING [14] |
884 | 3.4 Locale-Independent Words - MISSING [15] |
885 | 3.5 Locale-Independent Loose Matches - MISSING [16] |
886 | |
887 | [11] Surrogates are solely a UTF-16 concept and Perl's internal |
888 | representation is UTF-8. The Encode module does UTF-16, though. |
889 | [12] see UTR#15 Unicode Normalization |
890 | [13] have Unicode::Normalize but not integrated to regexes |
891 | [14] have \X but at this level . should equal that |
892 | [15] need three classes, not just \w and \W |
893 | [16] see UTR#21 Case Mappings |
776f8809 |
894 | |
895 | =item * |
896 | |
897 | Level 3 - Locale-Sensitive Support |
898 | |
899 | 4.1 Locale-Dependent Categories - MISSING |
900 | 4.2 Locale-Dependent Graphemes - MISSING [16][17] |
901 | 4.3 Locale-Dependent Words - MISSING |
902 | 4.4 Locale-Dependent Loose Matches - MISSING |
903 | 4.5 Locale-Dependent Ranges - MISSING |
904 | |
905 | [16] see UTR#10 Unicode Collation Algorithms |
906 | [17] have Unicode::Collate but not integrated to regexes |
907 | |
908 | =back |
909 | |
c349b1b9 |
910 | =head2 Unicode Encodings |
911 | |
376d9008 |
912 | Unicode characters are assigned to I<code points>, which are abstract |
913 | numbers. To use these numbers, various encodings are needed. |
c349b1b9 |
914 | |
915 | =over 4 |
916 | |
c29a771d |
917 | =item * |
5cb3728c |
918 | |
919 | UTF-8 |
c349b1b9 |
920 | |
3e4dbfed |
921 | UTF-8 is a variable-length (1 to 6 bytes, current character allocations |
376d9008 |
922 | require 4 bytes), byte-order independent encoding. For ASCII (and we |
923 | really do mean 7-bit ASCII, not another 8-bit encoding), UTF-8 is |
924 | transparent. |
c349b1b9 |
925 | |
8c007b5a |
926 | The following table is from Unicode 3.2. |
05632f9a |
927 | |
928 | Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte |
929 | |
8c007b5a |
930 | U+0000..U+007F 00..7F |
931 | U+0080..U+07FF C2..DF 80..BF |
ec90690f |
932 | U+0800..U+0FFF E0 A0..BF 80..BF |
933 | U+1000..U+CFFF E1..EC 80..BF 80..BF |
934 | U+D000..U+D7FF ED 80..9F 80..BF |
8c007b5a |
935 | U+D800..U+DFFF ******* ill-formed ******* |
ec90690f |
936 | U+E000..U+FFFF EE..EF 80..BF 80..BF |
05632f9a |
937 | U+10000..U+3FFFF F0 90..BF 80..BF 80..BF |
938 | U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF |
939 | U+100000..U+10FFFF F4 80..8F 80..BF 80..BF |
940 | |
376d9008 |
941 | Note the C<A0..BF> in C<U+0800..U+0FFF>, the C<80..9F> in |
942 | C<U+D000...U+D7FF>, the C<90..B>F in C<U+10000..U+3FFFF>, and the |
943 | C<80...8F> in C<U+100000..U+10FFFF>. The "gaps" are caused by legal |
944 | UTF-8 avoiding non-shortest encodings: it is technically possible to |
945 | UTF-8-encode a single code point in different ways, but that is |
946 | explicitly forbidden, and the shortest possible encoding should always |
947 | be used. So that's what Perl does. |
37361303 |
948 | |
376d9008 |
949 | Another way to look at it is via bits: |
05632f9a |
950 | |
951 | Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte |
952 | |
953 | 0aaaaaaa 0aaaaaaa |
954 | 00000bbbbbaaaaaa 110bbbbb 10aaaaaa |
955 | ccccbbbbbbaaaaaa 1110cccc 10bbbbbb 10aaaaaa |
956 | 00000dddccccccbbbbbbaaaaaa 11110ddd 10cccccc 10bbbbbb 10aaaaaa |
957 | |
958 | As you can see, the continuation bytes all begin with C<10>, and the |
8c007b5a |
959 | leading bits of the start byte tell how many bytes the are in the |
05632f9a |
960 | encoded character. |
961 | |
c29a771d |
962 | =item * |
5cb3728c |
963 | |
964 | UTF-EBCDIC |
dbe420b4 |
965 | |
376d9008 |
966 | Like UTF-8 but EBCDIC-safe, in the way that UTF-8 is ASCII-safe. |
dbe420b4 |
967 | |
c29a771d |
968 | =item * |
5cb3728c |
969 | |
1e54db1a |
970 | UTF-16, UTF-16BE, UTF-16LE, Surrogates, and BOMs (Byte Order Marks) |
c349b1b9 |
971 | |
1bfb14c4 |
972 | The followings items are mostly for reference and general Unicode |
973 | knowledge, Perl doesn't use these constructs internally. |
dbe420b4 |
974 | |
c349b1b9 |
975 | UTF-16 is a 2 or 4 byte encoding. The Unicode code points |
1bfb14c4 |
976 | C<U+0000..U+FFFF> are stored in a single 16-bit unit, and the code |
977 | points C<U+10000..U+10FFFF> in two 16-bit units. The latter case is |
c349b1b9 |
978 | using I<surrogates>, the first 16-bit unit being the I<high |
979 | surrogate>, and the second being the I<low surrogate>. |
980 | |
376d9008 |
981 | Surrogates are code points set aside to encode the C<U+10000..U+10FFFF> |
c349b1b9 |
982 | range of Unicode code points in pairs of 16-bit units. The I<high |
376d9008 |
983 | surrogates> are the range C<U+D800..U+DBFF>, and the I<low surrogates> |
984 | are the range C<U+DC00..U+DFFF>. The surrogate encoding is |
c349b1b9 |
985 | |
986 | $hi = ($uni - 0x10000) / 0x400 + 0xD800; |
987 | $lo = ($uni - 0x10000) % 0x400 + 0xDC00; |
988 | |
989 | and the decoding is |
990 | |
1a3fa709 |
991 | $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00); |
c349b1b9 |
992 | |
feda178f |
993 | If you try to generate surrogates (for example by using chr()), you |
376d9008 |
994 | will get a warning if warnings are turned on, because those code |
995 | points are not valid for a Unicode character. |
9466bab6 |
996 | |
376d9008 |
997 | Because of the 16-bitness, UTF-16 is byte-order dependent. UTF-16 |
c349b1b9 |
998 | itself can be used for in-memory computations, but if storage or |
376d9008 |
999 | transfer is required either UTF-16BE (big-endian) or UTF-16LE |
1000 | (little-endian) encodings must be chosen. |
c349b1b9 |
1001 | |
1002 | This introduces another problem: what if you just know that your data |
376d9008 |
1003 | is UTF-16, but you don't know which endianness? Byte Order Marks, or |
1004 | BOMs, are a solution to this. A special character has been reserved |
86bbd6d1 |
1005 | in Unicode to function as a byte order marker: the character with the |
376d9008 |
1006 | code point C<U+FEFF> is the BOM. |
042da322 |
1007 | |
c349b1b9 |
1008 | The trick is that if you read a BOM, you will know the byte order, |
376d9008 |
1009 | since if it was written on a big-endian platform, you will read the |
1010 | bytes C<0xFE 0xFF>, but if it was written on a little-endian platform, |
1011 | you will read the bytes C<0xFF 0xFE>. (And if the originating platform |
1012 | was writing in UTF-8, you will read the bytes C<0xEF 0xBB 0xBF>.) |
042da322 |
1013 | |
86bbd6d1 |
1014 | The way this trick works is that the character with the code point |
376d9008 |
1015 | C<U+FFFE> is guaranteed not to be a valid Unicode character, so the |
1016 | sequence of bytes C<0xFF 0xFE> is unambiguously "BOM, represented in |
1bfb14c4 |
1017 | little-endian format" and cannot be C<U+FFFE>, represented in big-endian |
042da322 |
1018 | format". |
c349b1b9 |
1019 | |
c29a771d |
1020 | =item * |
5cb3728c |
1021 | |
1e54db1a |
1022 | UTF-32, UTF-32BE, UTF-32LE |
c349b1b9 |
1023 | |
1024 | The UTF-32 family is pretty much like the UTF-16 family, expect that |
042da322 |
1025 | the units are 32-bit, and therefore the surrogate scheme is not |
376d9008 |
1026 | needed. The BOM signatures will be C<0x00 0x00 0xFE 0xFF> for BE and |
1027 | C<0xFF 0xFE 0x00 0x00> for LE. |
c349b1b9 |
1028 | |
c29a771d |
1029 | =item * |
5cb3728c |
1030 | |
1031 | UCS-2, UCS-4 |
c349b1b9 |
1032 | |
86bbd6d1 |
1033 | Encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit |
376d9008 |
1034 | encoding. Unlike UTF-16, UCS-2 is not extensible beyond C<U+FFFF>, |
339cfa0e |
1035 | because it does not use surrogates. UCS-4 is a 32-bit encoding, |
1036 | functionally identical to UTF-32. |
c349b1b9 |
1037 | |
c29a771d |
1038 | =item * |
5cb3728c |
1039 | |
1040 | UTF-7 |
c349b1b9 |
1041 | |
376d9008 |
1042 | A seven-bit safe (non-eight-bit) encoding, which is useful if the |
1043 | transport or storage is not eight-bit safe. Defined by RFC 2152. |
c349b1b9 |
1044 | |
95a1a48b |
1045 | =back |
1046 | |
0d7c09bb |
1047 | =head2 Security Implications of Unicode |
1048 | |
1049 | =over 4 |
1050 | |
1051 | =item * |
1052 | |
1053 | Malformed UTF-8 |
bf0fa0b2 |
1054 | |
1055 | Unfortunately, the specification of UTF-8 leaves some room for |
1056 | interpretation of how many bytes of encoded output one should generate |
376d9008 |
1057 | from one input Unicode character. Strictly speaking, the shortest |
1058 | possible sequence of UTF-8 bytes should be generated, |
1059 | because otherwise there is potential for an input buffer overflow at |
feda178f |
1060 | the receiving end of a UTF-8 connection. Perl always generates the |
376d9008 |
1061 | shortest length UTF-8, and with warnings on Perl will warn about |
1062 | non-shortest length UTF-8 along with other malformations, such as the |
1063 | surrogates, which are not real Unicode code points. |
bf0fa0b2 |
1064 | |
0d7c09bb |
1065 | =item * |
1066 | |
1067 | Regular expressions behave slightly differently between byte data and |
376d9008 |
1068 | character (Unicode) data. For example, the "word character" character |
1069 | class C<\w> will work differently depending on if data is eight-bit bytes |
1070 | or Unicode. |
0d7c09bb |
1071 | |
376d9008 |
1072 | In the first case, the set of C<\w> characters is either small--the |
1073 | default set of alphabetic characters, digits, and the "_"--or, if you |
0d7c09bb |
1074 | are using a locale (see L<perllocale>), the C<\w> might contain a few |
1075 | more letters according to your language and country. |
1076 | |
376d9008 |
1077 | In the second case, the C<\w> set of characters is much, much larger. |
1bfb14c4 |
1078 | Most importantly, even in the set of the first 256 characters, it will |
1079 | probably match different characters: unlike most locales, which are |
1080 | specific to a language and country pair, Unicode classifies all the |
1081 | characters that are letters I<somewhere> as C<\w>. For example, your |
1082 | locale might not think that LATIN SMALL LETTER ETH is a letter (unless |
1083 | you happen to speak Icelandic), but Unicode does. |
0d7c09bb |
1084 | |
376d9008 |
1085 | As discussed elsewhere, Perl has one foot (two hooves?) planted in |
1bfb14c4 |
1086 | each of two worlds: the old world of bytes and the new world of |
1087 | characters, upgrading from bytes to characters when necessary. |
376d9008 |
1088 | If your legacy code does not explicitly use Unicode, no automatic |
1089 | switch-over to characters should happen. Characters shouldn't get |
1bfb14c4 |
1090 | downgraded to bytes, either. It is possible to accidentally mix bytes |
1091 | and characters, however (see L<perluniintro>), in which case C<\w> in |
1092 | regular expressions might start behaving differently. Review your |
1093 | code. Use warnings and the C<strict> pragma. |
0d7c09bb |
1094 | |
1095 | =back |
1096 | |
c349b1b9 |
1097 | =head2 Unicode in Perl on EBCDIC |
1098 | |
376d9008 |
1099 | The way Unicode is handled on EBCDIC platforms is still |
1100 | experimental. On such platforms, references to UTF-8 encoding in this |
1101 | document and elsewhere should be read as meaning the UTF-EBCDIC |
1102 | specified in Unicode Technical Report 16, unless ASCII vs. EBCDIC issues |
c349b1b9 |
1103 | are specifically discussed. There is no C<utfebcdic> pragma or |
376d9008 |
1104 | ":utfebcdic" layer; rather, "utf8" and ":utf8" are reused to mean |
86bbd6d1 |
1105 | the platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic> |
1106 | for more discussion of the issues. |
c349b1b9 |
1107 | |
b310b053 |
1108 | =head2 Locales |
1109 | |
4616122b |
1110 | Usually locale settings and Unicode do not affect each other, but |
b310b053 |
1111 | there are a couple of exceptions: |
1112 | |
1113 | =over 4 |
1114 | |
1115 | =item * |
1116 | |
8aa8f774 |
1117 | You can enable automatic UTF-8-ification of your standard file |
1118 | handles, default C<open()> layer, and C<@ARGV> by using either |
1119 | the C<-C> command line switch or the C<PERL_UNICODE> environment |
1120 | variable, see L<perlrun> for the documentation of the C<-C> switch. |
b310b053 |
1121 | |
1122 | =item * |
1123 | |
376d9008 |
1124 | Perl tries really hard to work both with Unicode and the old |
1125 | byte-oriented world. Most often this is nice, but sometimes Perl's |
1126 | straddling of the proverbial fence causes problems. |
b310b053 |
1127 | |
1128 | =back |
1129 | |
1aad1664 |
1130 | =head2 When Unicode Does Not Happen |
1131 | |
1132 | While Perl does have extensive ways to input and output in Unicode, |
1133 | and few other 'entry points' like the @ARGV which can be interpreted |
1134 | as Unicode (UTF-8), there still are many places where Unicode (in some |
1135 | encoding or another) could be given as arguments or received as |
1136 | results, or both, but it is not. |
1137 | |
6cd4dd6c |
1138 | The following are such interfaces. For all of these interfaces Perl |
1139 | currently (as of 5.8.3) simply assumes byte strings both as arguments |
1140 | and results, or UTF-8 strings if the C<encoding> pragma has been used. |
1aad1664 |
1141 | |
1142 | One reason why Perl does not attempt to resolve the role of Unicode in |
1143 | this cases is that the answers are highly dependent on the operating |
1144 | system and the file system(s). For example, whether filenames can be |
1145 | in Unicode, and in exactly what kind of encoding, is not exactly a |
1146 | portable concept. Similarly for the qx and system: how well will the |
1147 | 'command line interface' (and which of them?) handle Unicode? |
1148 | |
1149 | =over 4 |
1150 | |
557a2462 |
1151 | =item * |
1152 | |
1e8e8236 |
1153 | chmod, chmod, chown, chroot, exec, link, lstat, mkdir, |
1154 | rename, rmdir, stat, symlink, truncate, unlink, utime, -X |
557a2462 |
1155 | |
1156 | =item * |
1157 | |
1158 | %ENV |
1159 | |
1160 | =item * |
1161 | |
1162 | glob (aka the <*>) |
1163 | |
1164 | =item * |
1aad1664 |
1165 | |
557a2462 |
1166 | open, opendir, sysopen |
1aad1664 |
1167 | |
557a2462 |
1168 | =item * |
1aad1664 |
1169 | |
557a2462 |
1170 | qx (aka the backtick operator), system |
1aad1664 |
1171 | |
557a2462 |
1172 | =item * |
1aad1664 |
1173 | |
557a2462 |
1174 | readdir, readlink |
1aad1664 |
1175 | |
1176 | =back |
1177 | |
1178 | =head2 Forcing Unicode in Perl (Or Unforcing Unicode in Perl) |
1179 | |
1180 | Sometimes (see L</"When Unicode Does Not Happen">) there are |
1181 | situations where you simply need to force Perl to believe that a byte |
1182 | string is UTF-8, or vice versa. The low-level calls |
1183 | utf8::upgrade($bytestring) and utf8::downgrade($utf8string) are |
1184 | the answers. |
1185 | |
1186 | Do not use them without careful thought, though: Perl may easily get |
1187 | very confused, angry, or even crash, if you suddenly change the 'nature' |
1188 | of scalar like that. Especially careful you have to be if you use the |
1189 | utf8::upgrade(): any random byte string is not valid UTF-8. |
1190 | |
95a1a48b |
1191 | =head2 Using Unicode in XS |
1192 | |
3a2263fe |
1193 | If you want to handle Perl Unicode in XS extensions, you may find the |
1194 | following C APIs useful. See also L<perlguts/"Unicode Support"> for an |
1195 | explanation about Unicode at the XS level, and L<perlapi> for the API |
1196 | details. |
95a1a48b |
1197 | |
1198 | =over 4 |
1199 | |
1200 | =item * |
1201 | |
1bfb14c4 |
1202 | C<DO_UTF8(sv)> returns true if the C<UTF8> flag is on and the bytes |
1203 | pragma is not in effect. C<SvUTF8(sv)> returns true is the C<UTF8> |
1204 | flag is on; the bytes pragma is ignored. The C<UTF8> flag being on |
1205 | does B<not> mean that there are any characters of code points greater |
1206 | than 255 (or 127) in the scalar or that there are even any characters |
1207 | in the scalar. What the C<UTF8> flag means is that the sequence of |
1208 | octets in the representation of the scalar is the sequence of UTF-8 |
1209 | encoded code points of the characters of a string. The C<UTF8> flag |
1210 | being off means that each octet in this representation encodes a |
1211 | single character with code point 0..255 within the string. Perl's |
1212 | Unicode model is not to use UTF-8 until it is absolutely necessary. |
95a1a48b |
1213 | |
1214 | =item * |
1215 | |
fb9cc174 |
1216 | C<uvuni_to_utf8(buf, chr)> writes a Unicode character code point into |
1bfb14c4 |
1217 | a buffer encoding the code point as UTF-8, and returns a pointer |
95a1a48b |
1218 | pointing after the UTF-8 bytes. |
1219 | |
1220 | =item * |
1221 | |
376d9008 |
1222 | C<utf8_to_uvuni(buf, lenp)> reads UTF-8 encoded bytes from a buffer and |
1223 | returns the Unicode character code point and, optionally, the length of |
1224 | the UTF-8 byte sequence. |
95a1a48b |
1225 | |
1226 | =item * |
1227 | |
376d9008 |
1228 | C<utf8_length(start, end)> returns the length of the UTF-8 encoded buffer |
1229 | in characters. C<sv_len_utf8(sv)> returns the length of the UTF-8 encoded |
95a1a48b |
1230 | scalar. |
1231 | |
1232 | =item * |
1233 | |
376d9008 |
1234 | C<sv_utf8_upgrade(sv)> converts the string of the scalar to its UTF-8 |
1235 | encoded form. C<sv_utf8_downgrade(sv)> does the opposite, if |
1236 | possible. C<sv_utf8_encode(sv)> is like sv_utf8_upgrade except that |
1237 | it does not set the C<UTF8> flag. C<sv_utf8_decode()> does the |
1238 | opposite of C<sv_utf8_encode()>. Note that none of these are to be |
1239 | used as general-purpose encoding or decoding interfaces: C<use Encode> |
1240 | for that. C<sv_utf8_upgrade()> is affected by the encoding pragma |
1241 | but C<sv_utf8_downgrade()> is not (since the encoding pragma is |
1242 | designed to be a one-way street). |
95a1a48b |
1243 | |
1244 | =item * |
1245 | |
376d9008 |
1246 | C<is_utf8_char(s)> returns true if the pointer points to a valid UTF-8 |
90f968e0 |
1247 | character. |
95a1a48b |
1248 | |
1249 | =item * |
1250 | |
376d9008 |
1251 | C<is_utf8_string(buf, len)> returns true if C<len> bytes of the buffer |
95a1a48b |
1252 | are valid UTF-8. |
1253 | |
1254 | =item * |
1255 | |
376d9008 |
1256 | C<UTF8SKIP(buf)> will return the number of bytes in the UTF-8 encoded |
1257 | character in the buffer. C<UNISKIP(chr)> will return the number of bytes |
1258 | required to UTF-8-encode the Unicode character code point. C<UTF8SKIP()> |
90f968e0 |
1259 | is useful for example for iterating over the characters of a UTF-8 |
376d9008 |
1260 | encoded buffer; C<UNISKIP()> is useful, for example, in computing |
90f968e0 |
1261 | the size required for a UTF-8 encoded buffer. |
95a1a48b |
1262 | |
1263 | =item * |
1264 | |
376d9008 |
1265 | C<utf8_distance(a, b)> will tell the distance in characters between the |
95a1a48b |
1266 | two pointers pointing to the same UTF-8 encoded buffer. |
1267 | |
1268 | =item * |
1269 | |
376d9008 |
1270 | C<utf8_hop(s, off)> will return a pointer to an UTF-8 encoded buffer |
1271 | that is C<off> (positive or negative) Unicode characters displaced |
1272 | from the UTF-8 buffer C<s>. Be careful not to overstep the buffer: |
1273 | C<utf8_hop()> will merrily run off the end or the beginning of the |
1274 | buffer if told to do so. |
95a1a48b |
1275 | |
d2cc3551 |
1276 | =item * |
1277 | |
376d9008 |
1278 | C<pv_uni_display(dsv, spv, len, pvlim, flags)> and |
1279 | C<sv_uni_display(dsv, ssv, pvlim, flags)> are useful for debugging the |
1280 | output of Unicode strings and scalars. By default they are useful |
1281 | only for debugging--they display B<all> characters as hexadecimal code |
1bfb14c4 |
1282 | points--but with the flags C<UNI_DISPLAY_ISPRINT>, |
1283 | C<UNI_DISPLAY_BACKSLASH>, and C<UNI_DISPLAY_QQ> you can make the |
1284 | output more readable. |
d2cc3551 |
1285 | |
1286 | =item * |
1287 | |
376d9008 |
1288 | C<ibcmp_utf8(s1, pe1, u1, l1, u1, s2, pe2, l2, u2)> can be used to |
1289 | compare two strings case-insensitively in Unicode. For case-sensitive |
1290 | comparisons you can just use C<memEQ()> and C<memNE()> as usual. |
d2cc3551 |
1291 | |
c349b1b9 |
1292 | =back |
1293 | |
95a1a48b |
1294 | For more information, see L<perlapi>, and F<utf8.c> and F<utf8.h> |
1295 | in the Perl source code distribution. |
1296 | |
c29a771d |
1297 | =head1 BUGS |
1298 | |
376d9008 |
1299 | =head2 Interaction with Locales |
7eabb34d |
1300 | |
376d9008 |
1301 | Use of locales with Unicode data may lead to odd results. Currently, |
1302 | Perl attempts to attach 8-bit locale info to characters in the range |
1303 | 0..255, but this technique is demonstrably incorrect for locales that |
1304 | use characters above that range when mapped into Unicode. Perl's |
1305 | Unicode support will also tend to run slower. Use of locales with |
1306 | Unicode is discouraged. |
c29a771d |
1307 | |
376d9008 |
1308 | =head2 Interaction with Extensions |
7eabb34d |
1309 | |
376d9008 |
1310 | When Perl exchanges data with an extension, the extension should be |
7eabb34d |
1311 | able to understand the UTF-8 flag and act accordingly. If the |
376d9008 |
1312 | extension doesn't know about the flag, it's likely that the extension |
1313 | will return incorrectly-flagged data. |
7eabb34d |
1314 | |
1315 | So if you're working with Unicode data, consult the documentation of |
1316 | every module you're using if there are any issues with Unicode data |
1317 | exchange. If the documentation does not talk about Unicode at all, |
a73d23f6 |
1318 | suspect the worst and probably look at the source to learn how the |
376d9008 |
1319 | module is implemented. Modules written completely in Perl shouldn't |
a73d23f6 |
1320 | cause problems. Modules that directly or indirectly access code written |
1321 | in other programming languages are at risk. |
7eabb34d |
1322 | |
376d9008 |
1323 | For affected functions, the simple strategy to avoid data corruption is |
7eabb34d |
1324 | to always make the encoding of the exchanged data explicit. Choose an |
376d9008 |
1325 | encoding that you know the extension can handle. Convert arguments passed |
7eabb34d |
1326 | to the extensions to that encoding and convert results back from that |
1327 | encoding. Write wrapper functions that do the conversions for you, so |
1328 | you can later change the functions when the extension catches up. |
1329 | |
376d9008 |
1330 | To provide an example, let's say the popular Foo::Bar::escape_html |
7eabb34d |
1331 | function doesn't deal with Unicode data yet. The wrapper function |
1332 | would convert the argument to raw UTF-8 and convert the result back to |
376d9008 |
1333 | Perl's internal representation like so: |
7eabb34d |
1334 | |
1335 | sub my_escape_html ($) { |
1336 | my($what) = shift; |
1337 | return unless defined $what; |
1338 | Encode::decode_utf8(Foo::Bar::escape_html(Encode::encode_utf8($what))); |
1339 | } |
1340 | |
1341 | Sometimes, when the extension does not convert data but just stores |
1342 | and retrieves them, you will be in a position to use the otherwise |
1343 | dangerous Encode::_utf8_on() function. Let's say the popular |
66b79f27 |
1344 | C<Foo::Bar> extension, written in C, provides a C<param> method that |
7eabb34d |
1345 | lets you store and retrieve data according to these prototypes: |
1346 | |
1347 | $self->param($name, $value); # set a scalar |
1348 | $value = $self->param($name); # retrieve a scalar |
1349 | |
1350 | If it does not yet provide support for any encoding, one could write a |
1351 | derived class with such a C<param> method: |
1352 | |
1353 | sub param { |
1354 | my($self,$name,$value) = @_; |
1355 | utf8::upgrade($name); # make sure it is UTF-8 encoded |
1356 | if (defined $value) |
1357 | utf8::upgrade($value); # make sure it is UTF-8 encoded |
1358 | return $self->SUPER::param($name,$value); |
1359 | } else { |
1360 | my $ret = $self->SUPER::param($name); |
1361 | Encode::_utf8_on($ret); # we know, it is UTF-8 encoded |
1362 | return $ret; |
1363 | } |
1364 | } |
1365 | |
a73d23f6 |
1366 | Some extensions provide filters on data entry/exit points, such as |
1367 | DB_File::filter_store_key and family. Look out for such filters in |
66b79f27 |
1368 | the documentation of your extensions, they can make the transition to |
7eabb34d |
1369 | Unicode data much easier. |
1370 | |
376d9008 |
1371 | =head2 Speed |
7eabb34d |
1372 | |
c29a771d |
1373 | Some functions are slower when working on UTF-8 encoded strings than |
574c8022 |
1374 | on byte encoded strings. All functions that need to hop over |
7c17141f |
1375 | characters such as length(), substr() or index(), or matching regular |
1376 | expressions can work B<much> faster when the underlying data are |
1377 | byte-encoded. |
1378 | |
1379 | In Perl 5.8.0 the slowness was often quite spectacular; in Perl 5.8.1 |
1380 | a caching scheme was introduced which will hopefully make the slowness |
a104b433 |
1381 | somewhat less spectacular, at least for some operations. In general, |
1382 | operations with UTF-8 encoded strings are still slower. As an example, |
1383 | the Unicode properties (character classes) like C<\p{Nd}> are known to |
1384 | be quite a bit slower (5-20 times) than their simpler counterparts |
1385 | like C<\d> (then again, there 268 Unicode characters matching C<Nd> |
1386 | compared with the 10 ASCII characters matching C<d>). |
666f95b9 |
1387 | |
c8d992ba |
1388 | =head2 Porting code from perl-5.6.X |
1389 | |
1390 | Perl 5.8 has a different Unicode model from 5.6. In 5.6 the programmer |
1391 | was required to use the C<utf8> pragma to declare that a given scope |
1392 | expected to deal with Unicode data and had to make sure that only |
1393 | Unicode data were reaching that scope. If you have code that is |
1394 | working with 5.6, you will need some of the following adjustments to |
1395 | your code. The examples are written such that the code will continue |
1396 | to work under 5.6, so you should be safe to try them out. |
1397 | |
1398 | =over 4 |
1399 | |
1400 | =item * |
1401 | |
1402 | A filehandle that should read or write UTF-8 |
1403 | |
1404 | if ($] > 5.007) { |
1405 | binmode $fh, ":utf8"; |
1406 | } |
1407 | |
1408 | =item * |
1409 | |
1410 | A scalar that is going to be passed to some extension |
1411 | |
1412 | Be it Compress::Zlib, Apache::Request or any extension that has no |
1413 | mention of Unicode in the manpage, you need to make sure that the |
1414 | UTF-8 flag is stripped off. Note that at the time of this writing |
1415 | (October 2002) the mentioned modules are not UTF-8-aware. Please |
1416 | check the documentation to verify if this is still true. |
1417 | |
1418 | if ($] > 5.007) { |
1419 | require Encode; |
1420 | $val = Encode::encode_utf8($val); # make octets |
1421 | } |
1422 | |
1423 | =item * |
1424 | |
1425 | A scalar we got back from an extension |
1426 | |
1427 | If you believe the scalar comes back as UTF-8, you will most likely |
1428 | want the UTF-8 flag restored: |
1429 | |
1430 | if ($] > 5.007) { |
1431 | require Encode; |
1432 | $val = Encode::decode_utf8($val); |
1433 | } |
1434 | |
1435 | =item * |
1436 | |
1437 | Same thing, if you are really sure it is UTF-8 |
1438 | |
1439 | if ($] > 5.007) { |
1440 | require Encode; |
1441 | Encode::_utf8_on($val); |
1442 | } |
1443 | |
1444 | =item * |
1445 | |
1446 | A wrapper for fetchrow_array and fetchrow_hashref |
1447 | |
1448 | When the database contains only UTF-8, a wrapper function or method is |
1449 | a convenient way to replace all your fetchrow_array and |
1450 | fetchrow_hashref calls. A wrapper function will also make it easier to |
1451 | adapt to future enhancements in your database driver. Note that at the |
1452 | time of this writing (October 2002), the DBI has no standardized way |
1453 | to deal with UTF-8 data. Please check the documentation to verify if |
1454 | that is still true. |
1455 | |
1456 | sub fetchrow { |
1457 | my($self, $sth, $what) = @_; # $what is one of fetchrow_{array,hashref} |
1458 | if ($] < 5.007) { |
1459 | return $sth->$what; |
1460 | } else { |
1461 | require Encode; |
1462 | if (wantarray) { |
1463 | my @arr = $sth->$what; |
1464 | for (@arr) { |
1465 | defined && /[^\000-\177]/ && Encode::_utf8_on($_); |
1466 | } |
1467 | return @arr; |
1468 | } else { |
1469 | my $ret = $sth->$what; |
1470 | if (ref $ret) { |
1471 | for my $k (keys %$ret) { |
1472 | defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret->{$k}; |
1473 | } |
1474 | return $ret; |
1475 | } else { |
1476 | defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret; |
1477 | return $ret; |
1478 | } |
1479 | } |
1480 | } |
1481 | } |
1482 | |
1483 | |
1484 | =item * |
1485 | |
1486 | A large scalar that you know can only contain ASCII |
1487 | |
1488 | Scalars that contain only ASCII and are marked as UTF-8 are sometimes |
1489 | a drag to your program. If you recognize such a situation, just remove |
1490 | the UTF-8 flag: |
1491 | |
1492 | utf8::downgrade($val) if $] > 5.007; |
1493 | |
1494 | =back |
1495 | |
393fec97 |
1496 | =head1 SEE ALSO |
1497 | |
72ff2908 |
1498 | L<perluniintro>, L<encoding>, L<Encode>, L<open>, L<utf8>, L<bytes>, |
a05d7ebb |
1499 | L<perlretut>, L<perlvar/"${^UNICODE}"> |
393fec97 |
1500 | |
1501 | =cut |