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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 | =back |
46 | |
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47 | =head2 Byte and Character Semantics |
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48 | |
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49 | Beginning with version 5.6, Perl uses logically-wide characters to |
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50 | represent strings internally. |
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51 | |
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52 | In future, Perl-level operations will be expected to work with |
53 | characters rather than bytes. |
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54 | |
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55 | However, as an interim compatibility measure, Perl aims to |
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56 | provide a safe migration path from byte semantics to character |
57 | semantics for programs. For operations where Perl can unambiguously |
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58 | decide that the input data are characters, Perl switches to |
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59 | character semantics. For operations where this determination cannot |
60 | be made without additional information from the user, Perl decides in |
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61 | favor of compatibility and chooses to use byte semantics. |
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62 | |
63 | This behavior preserves compatibility with earlier versions of Perl, |
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64 | which allowed byte semantics in Perl operations only if |
65 | none of the program's inputs were marked as being as source of Unicode |
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66 | character data. Such data may come from filehandles, from calls to |
67 | external programs, from information provided by the system (such as %ENV), |
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68 | or from literals and constants in the source text. |
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69 | |
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70 | The C<bytes> pragma will always, regardless of platform, force byte |
71 | semantics in a particular lexical scope. See L<bytes>. |
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72 | |
73 | The C<utf8> pragma is primarily a compatibility device that enables |
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74 | recognition of UTF-(8|EBCDIC) in literals encountered by the parser. |
376d9008 |
75 | Note that this pragma is only required while Perl defaults to byte |
76 | semantics; when character semantics become the default, this pragma |
77 | may become a no-op. See L<utf8>. |
78 | |
79 | Unless explicitly stated, Perl operators use character semantics |
80 | for Unicode data and byte semantics for non-Unicode data. |
81 | The decision to use character semantics is made transparently. If |
82 | input data comes from a Unicode source--for example, if a character |
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83 | encoding layer is added to a filehandle or a literal Unicode |
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84 | string constant appears in a program--character semantics apply. |
85 | Otherwise, byte semantics are in effect. The C<bytes> pragma should |
86 | be used to force byte semantics on Unicode data. |
87 | |
88 | If strings operating under byte semantics and strings with Unicode |
89 | character data are concatenated, the new string will be upgraded to |
90 | I<ISO 8859-1 (Latin-1)>, even if the old Unicode string used EBCDIC. |
91 | This translation is done without regard to the system's native 8-bit |
92 | encoding, so to change this for systems with non-Latin-1 and |
93 | non-EBCDIC native encodings use the C<encoding> pragma. See |
94 | L<encoding>. |
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95 | |
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96 | Under character semantics, many operations that formerly operated on |
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97 | bytes now operate on characters. A character in Perl is |
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98 | logically just a number ranging from 0 to 2**31 or so. Larger |
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99 | characters may encode into longer sequences of bytes internally, but |
100 | this internal detail is mostly hidden for Perl code. |
101 | See L<perluniintro> for more. |
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102 | |
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103 | =head2 Effects of Character Semantics |
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104 | |
105 | Character semantics have the following effects: |
106 | |
107 | =over 4 |
108 | |
109 | =item * |
110 | |
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111 | Strings--including hash keys--and regular expression patterns may |
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112 | contain characters that have an ordinal value larger than 255. |
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113 | |
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114 | If you use a Unicode editor to edit your program, Unicode characters |
115 | may occur directly within the literal strings in one of the various |
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116 | Unicode encodings (UTF-8, UTF-EBCDIC, UCS-2, etc.), but will be recognized |
117 | as such and converted to Perl's internal representation only if the |
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118 | appropriate L<encoding> is specified. |
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119 | |
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120 | Unicode characters can also be added to a string by using the |
121 | C<\x{...}> notation. The Unicode code for the desired character, in |
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122 | hexadecimal, should be placed in the braces. For instance, a smiley |
123 | face is C<\x{263A}>. This encoding scheme only works for characters |
124 | with a code of 0x100 or above. |
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125 | |
126 | Additionally, if you |
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127 | |
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128 | use charnames ':full'; |
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129 | |
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130 | you can use the C<\N{...}> notation and put the official Unicode |
131 | character name within the braces, such as C<\N{WHITE SMILING FACE}>. |
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132 | |
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133 | |
134 | =item * |
135 | |
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136 | If an appropriate L<encoding> is specified, identifiers within the |
137 | Perl script may contain Unicode alphanumeric characters, including |
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138 | ideographs. Perl does not currently attempt to canonicalize variable |
139 | names. |
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140 | |
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141 | =item * |
142 | |
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143 | Regular expressions match characters instead of bytes. "." matches |
144 | a character instead of a byte. The C<\C> pattern is provided to force |
145 | a match a single byte--a C<char> in C, hence C<\C>. |
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146 | |
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147 | =item * |
148 | |
149 | Character classes in regular expressions match characters instead of |
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150 | bytes and match against the character properties specified in the |
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151 | Unicode properties database. C<\w> can be used to match a Japanese |
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152 | ideograph, for instance. |
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153 | |
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154 | =item * |
155 | |
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156 | Named Unicode properties, scripts, and block ranges may be used like |
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157 | character classes via the C<\p{}> "matches property" construct and |
158 | the C<\P{}> negation, "doesn't match property". |
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159 | |
160 | For instance, C<\p{Lu}> matches any character with the Unicode "Lu" |
161 | (Letter, uppercase) property, while C<\p{M}> matches any character |
162 | with an "M" (mark--accents and such) property. Brackets are not |
163 | required for single letter properties, so C<\p{M}> is equivalent to |
164 | C<\pM>. Many predefined properties are available, such as |
165 | C<\p{Mirrored}> and C<\p{Tibetan}>. |
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166 | |
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167 | The official Unicode script and block names have spaces and dashes as |
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168 | separators, but for convenience you can use dashes, spaces, or |
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169 | underbars, and case is unimportant. It is recommended, however, that |
170 | for consistency you use the following naming: the official Unicode |
171 | script, property, or block name (see below for the additional rules |
172 | that apply to block names) with whitespace and dashes removed, and the |
173 | words "uppercase-first-lowercase-rest". C<Latin-1 Supplement> thus |
174 | becomes C<Latin1Supplement>. |
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175 | |
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176 | You can also use negation in both C<\p{}> and C<\P{}> by introducing a caret |
177 | (^) between the first brace and the property name: C<\p{^Tamil}> is |
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178 | equal to C<\P{Tamil}>. |
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179 | |
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180 | B<NOTE: the properties, scripts, and blocks listed here are as of |
181 | Unicode 3.2.0, March 2002, or Perl 5.8.0, July 2002. Unicode 4.0.0 |
182 | came out in April 2003, and Perl 5.8.1 in September 2003.> |
183 | |
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184 | Here are the basic Unicode General Category properties, followed by their |
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185 | long form. You can use either; C<\p{Lu}> and C<\p{UppercaseLetter}>, |
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186 | for instance, are identical. |
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187 | |
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188 | Short Long |
189 | |
190 | L Letter |
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191 | Lu UppercaseLetter |
192 | Ll LowercaseLetter |
193 | Lt TitlecaseLetter |
194 | Lm ModifierLetter |
195 | Lo OtherLetter |
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196 | |
197 | M Mark |
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198 | Mn NonspacingMark |
199 | Mc SpacingMark |
200 | Me EnclosingMark |
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201 | |
202 | N Number |
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203 | Nd DecimalNumber |
204 | Nl LetterNumber |
205 | No OtherNumber |
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206 | |
207 | P Punctuation |
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208 | Pc ConnectorPunctuation |
209 | Pd DashPunctuation |
210 | Ps OpenPunctuation |
211 | Pe ClosePunctuation |
212 | Pi InitialPunctuation |
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213 | (may behave like Ps or Pe depending on usage) |
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214 | Pf FinalPunctuation |
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215 | (may behave like Ps or Pe depending on usage) |
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216 | Po OtherPunctuation |
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217 | |
218 | S Symbol |
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219 | Sm MathSymbol |
220 | Sc CurrencySymbol |
221 | Sk ModifierSymbol |
222 | So OtherSymbol |
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223 | |
224 | Z Separator |
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225 | Zs SpaceSeparator |
226 | Zl LineSeparator |
227 | Zp ParagraphSeparator |
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228 | |
229 | C Other |
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230 | Cc Control |
231 | Cf Format |
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232 | Cs Surrogate (not usable) |
233 | Co PrivateUse |
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234 | Cn Unassigned |
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235 | |
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236 | Single-letter properties match all characters in any of the |
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237 | two-letter sub-properties starting with the same letter. |
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238 | C<L&> is a special case, which is an alias for C<Ll>, C<Lu>, and C<Lt>. |
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239 | |
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240 | Because Perl hides the need for the user to understand the internal |
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241 | representation of Unicode characters, there is no need to implement |
242 | the somewhat messy concept of surrogates. C<Cs> is therefore not |
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243 | supported. |
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244 | |
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245 | Because scripts differ in their directionality--Hebrew is |
246 | written right to left, for example--Unicode supplies these properties: |
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247 | |
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248 | Property Meaning |
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249 | |
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250 | BidiL Left-to-Right |
251 | BidiLRE Left-to-Right Embedding |
252 | BidiLRO Left-to-Right Override |
253 | BidiR Right-to-Left |
254 | BidiAL Right-to-Left Arabic |
255 | BidiRLE Right-to-Left Embedding |
256 | BidiRLO Right-to-Left Override |
257 | BidiPDF Pop Directional Format |
258 | BidiEN European Number |
259 | BidiES European Number Separator |
260 | BidiET European Number Terminator |
261 | BidiAN Arabic Number |
262 | BidiCS Common Number Separator |
263 | BidiNSM Non-Spacing Mark |
264 | BidiBN Boundary Neutral |
265 | BidiB Paragraph Separator |
266 | BidiS Segment Separator |
267 | BidiWS Whitespace |
268 | BidiON Other Neutrals |
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269 | |
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270 | For example, C<\p{BidiR}> matches characters that are normally |
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271 | written right to left. |
272 | |
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273 | =back |
274 | |
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275 | =head2 Scripts |
276 | |
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277 | The script names which can be used by C<\p{...}> and C<\P{...}>, |
278 | such as in C<\p{Latin}> or C<\p{Cyrillic}>, are as follows: |
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279 | |
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280 | Arabic |
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281 | Armenian |
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282 | Bengali |
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283 | Bopomofo |
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284 | Buhid |
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285 | CanadianAboriginal |
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286 | Cherokee |
287 | Cyrillic |
288 | Deseret |
289 | Devanagari |
290 | Ethiopic |
291 | Georgian |
292 | Gothic |
293 | Greek |
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294 | Gujarati |
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295 | Gurmukhi |
296 | Han |
297 | Hangul |
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298 | Hanunoo |
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299 | Hebrew |
300 | Hiragana |
301 | Inherited |
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302 | Kannada |
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303 | Katakana |
304 | Khmer |
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305 | Lao |
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306 | Latin |
307 | Malayalam |
308 | Mongolian |
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309 | Myanmar |
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310 | Ogham |
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311 | OldItalic |
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312 | Oriya |
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313 | Runic |
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314 | Sinhala |
315 | Syriac |
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316 | Tagalog |
317 | Tagbanwa |
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318 | Tamil |
319 | Telugu |
320 | Thaana |
321 | Thai |
322 | Tibetan |
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323 | Yi |
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324 | |
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325 | Extended property classes can supplement the basic |
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326 | properties, defined by the F<PropList> Unicode database: |
327 | |
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328 | ASCIIHexDigit |
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329 | BidiControl |
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330 | Dash |
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331 | Deprecated |
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332 | Diacritic |
333 | Extender |
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334 | GraphemeLink |
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335 | HexDigit |
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336 | Hyphen |
337 | Ideographic |
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338 | IDSBinaryOperator |
339 | IDSTrinaryOperator |
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340 | JoinControl |
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341 | LogicalOrderException |
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342 | NoncharacterCodePoint |
343 | OtherAlphabetic |
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344 | OtherDefaultIgnorableCodePoint |
345 | OtherGraphemeExtend |
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346 | OtherLowercase |
347 | OtherMath |
348 | OtherUppercase |
349 | QuotationMark |
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350 | Radical |
351 | SoftDotted |
352 | TerminalPunctuation |
353 | UnifiedIdeograph |
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354 | WhiteSpace |
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355 | |
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356 | and there are further derived properties: |
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357 | |
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358 | Alphabetic Lu + Ll + Lt + Lm + Lo + OtherAlphabetic |
359 | Lowercase Ll + OtherLowercase |
360 | Uppercase Lu + OtherUppercase |
361 | Math Sm + OtherMath |
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362 | |
363 | ID_Start Lu + Ll + Lt + Lm + Lo + Nl |
364 | ID_Continue ID_Start + Mn + Mc + Nd + Pc |
365 | |
366 | Any Any character |
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367 | Assigned Any non-Cn character (i.e. synonym for \P{Cn}) |
368 | Unassigned Synonym for \p{Cn} |
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369 | Common Any character (or unassigned code point) |
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370 | not explicitly assigned to a script |
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371 | |
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372 | For backward compatibility (with Perl 5.6), all properties mentioned |
373 | so far may have C<Is> prepended to their name, so C<\P{IsLu}>, for |
374 | example, is equal to C<\P{Lu}>. |
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375 | |
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376 | =head2 Blocks |
377 | |
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378 | In addition to B<scripts>, Unicode also defines B<blocks> of |
379 | characters. The difference between scripts and blocks is that the |
380 | concept of scripts is closer to natural languages, while the concept |
381 | of blocks is more of an artificial grouping based on groups of 256 |
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382 | Unicode characters. For example, the C<Latin> script contains letters |
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383 | from many blocks but does not contain all the characters from those |
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384 | blocks. It does not, for example, contain digits, because digits are |
385 | shared across many scripts. Digits and similar groups, like |
386 | punctuation, are in a category called C<Common>. |
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387 | |
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388 | For more about scripts, see the UTR #24: |
389 | |
390 | http://www.unicode.org/unicode/reports/tr24/ |
391 | |
392 | For more about blocks, see: |
393 | |
394 | http://www.unicode.org/Public/UNIDATA/Blocks.txt |
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395 | |
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396 | Block names are given with the C<In> prefix. For example, the |
397 | Katakana block is referenced via C<\p{InKatakana}>. The C<In> |
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398 | prefix may be omitted if there is no naming conflict with a script |
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399 | or any other property, but it is recommended that C<In> always be used |
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400 | for block tests to avoid confusion. |
eb0cc9e3 |
401 | |
402 | These block names are supported: |
403 | |
1d81abf3 |
404 | InAlphabeticPresentationForms |
405 | InArabic |
406 | InArabicPresentationFormsA |
407 | InArabicPresentationFormsB |
408 | InArmenian |
409 | InArrows |
410 | InBasicLatin |
411 | InBengali |
412 | InBlockElements |
413 | InBopomofo |
414 | InBopomofoExtended |
415 | InBoxDrawing |
416 | InBraillePatterns |
417 | InBuhid |
418 | InByzantineMusicalSymbols |
419 | InCJKCompatibility |
420 | InCJKCompatibilityForms |
421 | InCJKCompatibilityIdeographs |
422 | InCJKCompatibilityIdeographsSupplement |
423 | InCJKRadicalsSupplement |
424 | InCJKSymbolsAndPunctuation |
425 | InCJKUnifiedIdeographs |
426 | InCJKUnifiedIdeographsExtensionA |
427 | InCJKUnifiedIdeographsExtensionB |
428 | InCherokee |
429 | InCombiningDiacriticalMarks |
430 | InCombiningDiacriticalMarksforSymbols |
431 | InCombiningHalfMarks |
432 | InControlPictures |
433 | InCurrencySymbols |
434 | InCyrillic |
435 | InCyrillicSupplementary |
436 | InDeseret |
437 | InDevanagari |
438 | InDingbats |
439 | InEnclosedAlphanumerics |
440 | InEnclosedCJKLettersAndMonths |
441 | InEthiopic |
442 | InGeneralPunctuation |
443 | InGeometricShapes |
444 | InGeorgian |
445 | InGothic |
446 | InGreekExtended |
447 | InGreekAndCoptic |
448 | InGujarati |
449 | InGurmukhi |
450 | InHalfwidthAndFullwidthForms |
451 | InHangulCompatibilityJamo |
452 | InHangulJamo |
453 | InHangulSyllables |
454 | InHanunoo |
455 | InHebrew |
456 | InHighPrivateUseSurrogates |
457 | InHighSurrogates |
458 | InHiragana |
459 | InIPAExtensions |
460 | InIdeographicDescriptionCharacters |
461 | InKanbun |
462 | InKangxiRadicals |
463 | InKannada |
464 | InKatakana |
465 | InKatakanaPhoneticExtensions |
466 | InKhmer |
467 | InLao |
468 | InLatin1Supplement |
469 | InLatinExtendedA |
470 | InLatinExtendedAdditional |
471 | InLatinExtendedB |
472 | InLetterlikeSymbols |
473 | InLowSurrogates |
474 | InMalayalam |
475 | InMathematicalAlphanumericSymbols |
476 | InMathematicalOperators |
477 | InMiscellaneousMathematicalSymbolsA |
478 | InMiscellaneousMathematicalSymbolsB |
479 | InMiscellaneousSymbols |
480 | InMiscellaneousTechnical |
481 | InMongolian |
482 | InMusicalSymbols |
483 | InMyanmar |
484 | InNumberForms |
485 | InOgham |
486 | InOldItalic |
487 | InOpticalCharacterRecognition |
488 | InOriya |
489 | InPrivateUseArea |
490 | InRunic |
491 | InSinhala |
492 | InSmallFormVariants |
493 | InSpacingModifierLetters |
494 | InSpecials |
495 | InSuperscriptsAndSubscripts |
496 | InSupplementalArrowsA |
497 | InSupplementalArrowsB |
498 | InSupplementalMathematicalOperators |
499 | InSupplementaryPrivateUseAreaA |
500 | InSupplementaryPrivateUseAreaB |
501 | InSyriac |
502 | InTagalog |
503 | InTagbanwa |
504 | InTags |
505 | InTamil |
506 | InTelugu |
507 | InThaana |
508 | InThai |
509 | InTibetan |
510 | InUnifiedCanadianAboriginalSyllabics |
511 | InVariationSelectors |
512 | InYiRadicals |
513 | InYiSyllables |
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514 | |
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515 | =over 4 |
516 | |
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517 | =item * |
518 | |
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519 | The special pattern C<\X> matches any extended Unicode |
520 | sequence--"a combining character sequence" in Standardese--where the |
521 | first character is a base character and subsequent characters are mark |
522 | characters that apply to the base character. C<\X> is equivalent to |
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523 | C<(?:\PM\pM*)>. |
524 | |
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525 | =item * |
526 | |
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527 | The C<tr///> operator translates characters instead of bytes. Note |
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528 | that the C<tr///CU> functionality has been removed. For similar |
529 | functionality see pack('U0', ...) and pack('C0', ...). |
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530 | |
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531 | =item * |
532 | |
533 | Case translation operators use the Unicode case translation tables |
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534 | when character input is provided. Note that C<uc()>, or C<\U> in |
535 | interpolated strings, translates to uppercase, while C<ucfirst>, |
536 | or C<\u> in interpolated strings, translates to titlecase in languages |
537 | that make the distinction. |
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538 | |
539 | =item * |
540 | |
376d9008 |
541 | Most operators that deal with positions or lengths in a string will |
75daf61c |
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 |
376d9008 |
545 | specifically do not switch include C<vec()>, C<pack()>, and |
546 | C<unpack()>. Operators that really don't care include C<chomp()>, |
547 | operators that treats strings as a bucket of bits such as C<sort()>, |
548 | and operators dealing with filenames. |
393fec97 |
549 | |
550 | =item * |
551 | |
1bfb14c4 |
552 | The C<pack()>/C<unpack()> letters C<c> and C<C> do I<not> change, |
376d9008 |
553 | since they are often used for byte-oriented formats. Again, think |
1bfb14c4 |
554 | C<char> in the C language. |
555 | |
556 | There is a new C<U> specifier that converts between Unicode characters |
557 | and code points. |
393fec97 |
558 | |
559 | =item * |
560 | |
376d9008 |
561 | The C<chr()> and C<ord()> functions work on characters, similar to |
562 | C<pack("U")> and C<unpack("U")>, I<not> C<pack("C")> and |
563 | C<unpack("C")>. C<pack("C")> and C<unpack("C")> are methods for |
564 | emulating byte-oriented C<chr()> and C<ord()> on Unicode strings. |
565 | While these methods reveal the internal encoding of Unicode strings, |
566 | that is not something one normally needs to care about at all. |
393fec97 |
567 | |
568 | =item * |
569 | |
376d9008 |
570 | The bit string operators, C<& | ^ ~>, can operate on character data. |
571 | However, for backward compatibility, such as when using bit string |
572 | operations when characters are all less than 256 in ordinal value, one |
573 | should not use C<~> (the bit complement) with characters of both |
574 | values less than 256 and values greater than 256. Most importantly, |
575 | DeMorgan's laws (C<~($x|$y) eq ~$x&~$y> and C<~($x&$y) eq ~$x|~$y>) |
576 | will not hold. The reason for this mathematical I<faux pas> is that |
577 | the complement cannot return B<both> the 8-bit (byte-wide) bit |
578 | complement B<and> the full character-wide bit complement. |
a1ca4561 |
579 | |
580 | =item * |
581 | |
983ffd37 |
582 | lc(), uc(), lcfirst(), and ucfirst() work for the following cases: |
583 | |
584 | =over 8 |
585 | |
586 | =item * |
587 | |
588 | the case mapping is from a single Unicode character to another |
376d9008 |
589 | single Unicode character, or |
983ffd37 |
590 | |
591 | =item * |
592 | |
593 | the case mapping is from a single Unicode character to more |
376d9008 |
594 | than one Unicode character. |
983ffd37 |
595 | |
596 | =back |
597 | |
63de3cb2 |
598 | Things to do with locales (Lithuanian, Turkish, Azeri) do B<not> work |
599 | since Perl does not understand the concept of Unicode locales. |
983ffd37 |
600 | |
dc33ebcf |
601 | See the Unicode Technical Report #21, Case Mappings, for more details. |
602 | |
983ffd37 |
603 | =back |
604 | |
dc33ebcf |
605 | =over 4 |
ac1256e8 |
606 | |
607 | =item * |
608 | |
393fec97 |
609 | And finally, C<scalar reverse()> reverses by character rather than by byte. |
610 | |
611 | =back |
612 | |
376d9008 |
613 | =head2 User-Defined Character Properties |
491fd90a |
614 | |
615 | You can define your own character properties by defining subroutines |
3a2263fe |
616 | whose names begin with "In" or "Is". The subroutines must be defined |
617 | in the C<main> package. The user-defined properties can be used in the |
618 | regular expression C<\p> and C<\P> constructs. Note that the effect |
619 | is compile-time and immutable once defined. |
491fd90a |
620 | |
376d9008 |
621 | The subroutines must return a specially-formatted string, with one |
622 | or more newline-separated lines. Each line must be one of the following: |
491fd90a |
623 | |
624 | =over 4 |
625 | |
626 | =item * |
627 | |
99a6b1f0 |
628 | Two hexadecimal numbers separated by horizontal whitespace (space or |
376d9008 |
629 | tabular characters) denoting a range of Unicode code points to include. |
491fd90a |
630 | |
631 | =item * |
632 | |
376d9008 |
633 | Something to include, prefixed by "+": a built-in character |
634 | property (prefixed by "utf8::"), to represent all the characters in that |
635 | property; two hexadecimal code points for a range; or a single |
636 | hexadecimal code point. |
491fd90a |
637 | |
638 | =item * |
639 | |
376d9008 |
640 | Something to exclude, prefixed by "-": an existing character |
11ef8fdd |
641 | property (prefixed by "utf8::"), for all the characters in that |
376d9008 |
642 | property; two hexadecimal code points for a range; or a single |
643 | hexadecimal code point. |
491fd90a |
644 | |
645 | =item * |
646 | |
376d9008 |
647 | Something to negate, prefixed "!": an existing character |
11ef8fdd |
648 | property (prefixed by "utf8::") for all the characters except the |
376d9008 |
649 | characters in the property; two hexadecimal code points for a range; |
650 | or a single hexadecimal code point. |
491fd90a |
651 | |
652 | =back |
653 | |
654 | For example, to define a property that covers both the Japanese |
655 | syllabaries (hiragana and katakana), you can define |
656 | |
657 | sub InKana { |
d5822f25 |
658 | return <<END; |
659 | 3040\t309F |
660 | 30A0\t30FF |
491fd90a |
661 | END |
662 | } |
663 | |
d5822f25 |
664 | Imagine that the here-doc end marker is at the beginning of the line. |
665 | Now you can use C<\p{InKana}> and C<\P{InKana}>. |
491fd90a |
666 | |
667 | You could also have used the existing block property names: |
668 | |
669 | sub InKana { |
670 | return <<'END'; |
671 | +utf8::InHiragana |
672 | +utf8::InKatakana |
673 | END |
674 | } |
675 | |
676 | Suppose you wanted to match only the allocated characters, |
d5822f25 |
677 | not the raw block ranges: in other words, you want to remove |
491fd90a |
678 | the non-characters: |
679 | |
680 | sub InKana { |
681 | return <<'END'; |
682 | +utf8::InHiragana |
683 | +utf8::InKatakana |
684 | -utf8::IsCn |
685 | END |
686 | } |
687 | |
688 | The negation is useful for defining (surprise!) negated classes. |
689 | |
690 | sub InNotKana { |
691 | return <<'END'; |
692 | !utf8::InHiragana |
693 | -utf8::InKatakana |
694 | +utf8::IsCn |
695 | END |
696 | } |
697 | |
3a2263fe |
698 | You can also define your own mappings to be used in the lc(), |
699 | lcfirst(), uc(), and ucfirst() (or their string-inlined versions). |
700 | The principle is the same: define subroutines in the C<main> package |
701 | with names like C<ToLower> (for lc() and lcfirst()), C<ToTitle> (for |
702 | the first character in ucfirst()), and C<ToUpper> (for uc(), and the |
703 | rest of the characters in ucfirst()). |
704 | |
705 | The string returned by the subroutines needs now to be three |
706 | hexadecimal numbers separated by tabulators: start of the source |
707 | range, end of the source range, and start of the destination range. |
708 | For example: |
709 | |
710 | sub ToUpper { |
711 | return <<END; |
712 | 0061\t0063\t0041 |
713 | END |
714 | } |
715 | |
716 | defines an uc() mapping that causes only the characters "a", "b", and |
717 | "c" to be mapped to "A", "B", "C", all other characters will remain |
718 | unchanged. |
719 | |
720 | If there is no source range to speak of, that is, the mapping is from |
721 | a single character to another single character, leave the end of the |
722 | source range empty, but the two tabulator characters are still needed. |
723 | For example: |
724 | |
725 | sub ToLower { |
726 | return <<END; |
727 | 0041\t\t0061 |
728 | END |
729 | } |
730 | |
731 | defines a lc() mapping that causes only "A" to be mapped to "a", all |
732 | other characters will remain unchanged. |
733 | |
734 | (For serious hackers only) If you want to introspect the default |
735 | mappings, you can find the data in the directory |
736 | C<$Config{privlib}>/F<unicore/To/>. The mapping data is returned as |
737 | the here-document, and the C<utf8::ToSpecFoo> are special exception |
738 | mappings derived from <$Config{privlib}>/F<unicore/SpecialCasing.txt>. |
739 | The C<Digit> and C<Fold> mappings that one can see in the directory |
740 | are not directly user-accessible, one can use either the |
741 | C<Unicode::UCD> module, or just match case-insensitively (that's when |
742 | the C<Fold> mapping is used). |
743 | |
744 | A final note on the user-defined property tests and mappings: they |
745 | will be used only if the scalar has been marked as having Unicode |
746 | characters. Old byte-style strings will not be affected. |
747 | |
376d9008 |
748 | =head2 Character Encodings for Input and Output |
8cbd9a7a |
749 | |
7221edc9 |
750 | See L<Encode>. |
8cbd9a7a |
751 | |
c29a771d |
752 | =head2 Unicode Regular Expression Support Level |
776f8809 |
753 | |
376d9008 |
754 | The following list of Unicode support for regular expressions describes |
755 | all the features currently supported. The references to "Level N" |
756 | and the section numbers refer to the Unicode Technical Report 18, |
965cd703 |
757 | "Unicode Regular Expression Guidelines", version 6 (Unicode 3.2.0, |
758 | Perl 5.8.0). |
776f8809 |
759 | |
760 | =over 4 |
761 | |
762 | =item * |
763 | |
764 | Level 1 - Basic Unicode Support |
765 | |
766 | 2.1 Hex Notation - done [1] |
3bfdc84c |
767 | Named Notation - done [2] |
776f8809 |
768 | 2.2 Categories - done [3][4] |
769 | 2.3 Subtraction - MISSING [5][6] |
770 | 2.4 Simple Word Boundaries - done [7] |
78d3e1bf |
771 | 2.5 Simple Loose Matches - done [8] |
776f8809 |
772 | 2.6 End of Line - MISSING [9][10] |
773 | |
774 | [ 1] \x{...} |
775 | [ 2] \N{...} |
eb0cc9e3 |
776 | [ 3] . \p{...} \P{...} |
29bdacb8 |
777 | [ 4] now scripts (see UTR#24 Script Names) in addition to blocks |
776f8809 |
778 | [ 5] have negation |
237bad5b |
779 | [ 6] can use regular expression look-ahead [a] |
780 | or user-defined character properties [b] to emulate subtraction |
776f8809 |
781 | [ 7] include Letters in word characters |
376d9008 |
782 | [ 8] note that Perl does Full case-folding in matching, not Simple: |
835863de |
783 | for example U+1F88 is equivalent with U+1F00 U+03B9, |
e0f9d4a8 |
784 | not with 1F80. This difference matters for certain Greek |
376d9008 |
785 | capital letters with certain modifiers: the Full case-folding |
786 | decomposes the letter, while the Simple case-folding would map |
e0f9d4a8 |
787 | it to a single character. |
5ca1ac52 |
788 | [ 9] see UTR #13 Unicode Newline Guidelines |
835863de |
789 | [10] should do ^ and $ also on \x{85}, \x{2028} and \x{2029} |
ec83e909 |
790 | (should also affect <>, $., and script line numbers) |
3bfdc84c |
791 | (the \x{85}, \x{2028} and \x{2029} do match \s) |
7207e29d |
792 | |
237bad5b |
793 | [a] You can mimic class subtraction using lookahead. |
5ca1ac52 |
794 | For example, what UTR #18 might write as |
29bdacb8 |
795 | |
dbe420b4 |
796 | [{Greek}-[{UNASSIGNED}]] |
797 | |
798 | in Perl can be written as: |
799 | |
1d81abf3 |
800 | (?!\p{Unassigned})\p{InGreekAndCoptic} |
801 | (?=\p{Assigned})\p{InGreekAndCoptic} |
dbe420b4 |
802 | |
803 | But in this particular example, you probably really want |
804 | |
1bfb14c4 |
805 | \p{GreekAndCoptic} |
dbe420b4 |
806 | |
807 | which will match assigned characters known to be part of the Greek script. |
29bdacb8 |
808 | |
5ca1ac52 |
809 | Also see the Unicode::Regex::Set module, it does implement the full |
810 | UTR #18 grouping, intersection, union, and removal (subtraction) syntax. |
811 | |
818c4caa |
812 | [b] See L</"User-Defined Character Properties">. |
237bad5b |
813 | |
776f8809 |
814 | =item * |
815 | |
816 | Level 2 - Extended Unicode Support |
817 | |
63de3cb2 |
818 | 3.1 Surrogates - MISSING [11] |
819 | 3.2 Canonical Equivalents - MISSING [12][13] |
820 | 3.3 Locale-Independent Graphemes - MISSING [14] |
821 | 3.4 Locale-Independent Words - MISSING [15] |
822 | 3.5 Locale-Independent Loose Matches - MISSING [16] |
823 | |
824 | [11] Surrogates are solely a UTF-16 concept and Perl's internal |
825 | representation is UTF-8. The Encode module does UTF-16, though. |
826 | [12] see UTR#15 Unicode Normalization |
827 | [13] have Unicode::Normalize but not integrated to regexes |
828 | [14] have \X but at this level . should equal that |
829 | [15] need three classes, not just \w and \W |
830 | [16] see UTR#21 Case Mappings |
776f8809 |
831 | |
832 | =item * |
833 | |
834 | Level 3 - Locale-Sensitive Support |
835 | |
836 | 4.1 Locale-Dependent Categories - MISSING |
837 | 4.2 Locale-Dependent Graphemes - MISSING [16][17] |
838 | 4.3 Locale-Dependent Words - MISSING |
839 | 4.4 Locale-Dependent Loose Matches - MISSING |
840 | 4.5 Locale-Dependent Ranges - MISSING |
841 | |
842 | [16] see UTR#10 Unicode Collation Algorithms |
843 | [17] have Unicode::Collate but not integrated to regexes |
844 | |
845 | =back |
846 | |
c349b1b9 |
847 | =head2 Unicode Encodings |
848 | |
376d9008 |
849 | Unicode characters are assigned to I<code points>, which are abstract |
850 | numbers. To use these numbers, various encodings are needed. |
c349b1b9 |
851 | |
852 | =over 4 |
853 | |
c29a771d |
854 | =item * |
5cb3728c |
855 | |
856 | UTF-8 |
c349b1b9 |
857 | |
3e4dbfed |
858 | UTF-8 is a variable-length (1 to 6 bytes, current character allocations |
376d9008 |
859 | require 4 bytes), byte-order independent encoding. For ASCII (and we |
860 | really do mean 7-bit ASCII, not another 8-bit encoding), UTF-8 is |
861 | transparent. |
c349b1b9 |
862 | |
8c007b5a |
863 | The following table is from Unicode 3.2. |
05632f9a |
864 | |
865 | Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte |
866 | |
8c007b5a |
867 | U+0000..U+007F 00..7F |
868 | U+0080..U+07FF C2..DF 80..BF |
ec90690f |
869 | U+0800..U+0FFF E0 A0..BF 80..BF |
870 | U+1000..U+CFFF E1..EC 80..BF 80..BF |
871 | U+D000..U+D7FF ED 80..9F 80..BF |
8c007b5a |
872 | U+D800..U+DFFF ******* ill-formed ******* |
ec90690f |
873 | U+E000..U+FFFF EE..EF 80..BF 80..BF |
05632f9a |
874 | U+10000..U+3FFFF F0 90..BF 80..BF 80..BF |
875 | U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF |
876 | U+100000..U+10FFFF F4 80..8F 80..BF 80..BF |
877 | |
376d9008 |
878 | Note the C<A0..BF> in C<U+0800..U+0FFF>, the C<80..9F> in |
879 | C<U+D000...U+D7FF>, the C<90..B>F in C<U+10000..U+3FFFF>, and the |
880 | C<80...8F> in C<U+100000..U+10FFFF>. The "gaps" are caused by legal |
881 | UTF-8 avoiding non-shortest encodings: it is technically possible to |
882 | UTF-8-encode a single code point in different ways, but that is |
883 | explicitly forbidden, and the shortest possible encoding should always |
884 | be used. So that's what Perl does. |
37361303 |
885 | |
376d9008 |
886 | Another way to look at it is via bits: |
05632f9a |
887 | |
888 | Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte |
889 | |
890 | 0aaaaaaa 0aaaaaaa |
891 | 00000bbbbbaaaaaa 110bbbbb 10aaaaaa |
892 | ccccbbbbbbaaaaaa 1110cccc 10bbbbbb 10aaaaaa |
893 | 00000dddccccccbbbbbbaaaaaa 11110ddd 10cccccc 10bbbbbb 10aaaaaa |
894 | |
895 | As you can see, the continuation bytes all begin with C<10>, and the |
8c007b5a |
896 | leading bits of the start byte tell how many bytes the are in the |
05632f9a |
897 | encoded character. |
898 | |
c29a771d |
899 | =item * |
5cb3728c |
900 | |
901 | UTF-EBCDIC |
dbe420b4 |
902 | |
376d9008 |
903 | Like UTF-8 but EBCDIC-safe, in the way that UTF-8 is ASCII-safe. |
dbe420b4 |
904 | |
c29a771d |
905 | =item * |
5cb3728c |
906 | |
907 | UTF-16, UTF-16BE, UTF16-LE, Surrogates, and BOMs (Byte Order Marks) |
c349b1b9 |
908 | |
1bfb14c4 |
909 | The followings items are mostly for reference and general Unicode |
910 | knowledge, Perl doesn't use these constructs internally. |
dbe420b4 |
911 | |
c349b1b9 |
912 | UTF-16 is a 2 or 4 byte encoding. The Unicode code points |
1bfb14c4 |
913 | C<U+0000..U+FFFF> are stored in a single 16-bit unit, and the code |
914 | points C<U+10000..U+10FFFF> in two 16-bit units. The latter case is |
c349b1b9 |
915 | using I<surrogates>, the first 16-bit unit being the I<high |
916 | surrogate>, and the second being the I<low surrogate>. |
917 | |
376d9008 |
918 | Surrogates are code points set aside to encode the C<U+10000..U+10FFFF> |
c349b1b9 |
919 | range of Unicode code points in pairs of 16-bit units. The I<high |
376d9008 |
920 | surrogates> are the range C<U+D800..U+DBFF>, and the I<low surrogates> |
921 | are the range C<U+DC00..U+DFFF>. The surrogate encoding is |
c349b1b9 |
922 | |
923 | $hi = ($uni - 0x10000) / 0x400 + 0xD800; |
924 | $lo = ($uni - 0x10000) % 0x400 + 0xDC00; |
925 | |
926 | and the decoding is |
927 | |
1a3fa709 |
928 | $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00); |
c349b1b9 |
929 | |
feda178f |
930 | If you try to generate surrogates (for example by using chr()), you |
376d9008 |
931 | will get a warning if warnings are turned on, because those code |
932 | points are not valid for a Unicode character. |
9466bab6 |
933 | |
376d9008 |
934 | Because of the 16-bitness, UTF-16 is byte-order dependent. UTF-16 |
c349b1b9 |
935 | itself can be used for in-memory computations, but if storage or |
376d9008 |
936 | transfer is required either UTF-16BE (big-endian) or UTF-16LE |
937 | (little-endian) encodings must be chosen. |
c349b1b9 |
938 | |
939 | This introduces another problem: what if you just know that your data |
376d9008 |
940 | is UTF-16, but you don't know which endianness? Byte Order Marks, or |
941 | BOMs, are a solution to this. A special character has been reserved |
86bbd6d1 |
942 | in Unicode to function as a byte order marker: the character with the |
376d9008 |
943 | code point C<U+FEFF> is the BOM. |
042da322 |
944 | |
c349b1b9 |
945 | The trick is that if you read a BOM, you will know the byte order, |
376d9008 |
946 | since if it was written on a big-endian platform, you will read the |
947 | bytes C<0xFE 0xFF>, but if it was written on a little-endian platform, |
948 | you will read the bytes C<0xFF 0xFE>. (And if the originating platform |
949 | was writing in UTF-8, you will read the bytes C<0xEF 0xBB 0xBF>.) |
042da322 |
950 | |
86bbd6d1 |
951 | The way this trick works is that the character with the code point |
376d9008 |
952 | C<U+FFFE> is guaranteed not to be a valid Unicode character, so the |
953 | sequence of bytes C<0xFF 0xFE> is unambiguously "BOM, represented in |
1bfb14c4 |
954 | little-endian format" and cannot be C<U+FFFE>, represented in big-endian |
042da322 |
955 | format". |
c349b1b9 |
956 | |
c29a771d |
957 | =item * |
5cb3728c |
958 | |
959 | UTF-32, UTF-32BE, UTF32-LE |
c349b1b9 |
960 | |
961 | The UTF-32 family is pretty much like the UTF-16 family, expect that |
042da322 |
962 | the units are 32-bit, and therefore the surrogate scheme is not |
376d9008 |
963 | needed. The BOM signatures will be C<0x00 0x00 0xFE 0xFF> for BE and |
964 | C<0xFF 0xFE 0x00 0x00> for LE. |
c349b1b9 |
965 | |
c29a771d |
966 | =item * |
5cb3728c |
967 | |
968 | UCS-2, UCS-4 |
c349b1b9 |
969 | |
86bbd6d1 |
970 | Encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit |
376d9008 |
971 | encoding. Unlike UTF-16, UCS-2 is not extensible beyond C<U+FFFF>, |
339cfa0e |
972 | because it does not use surrogates. UCS-4 is a 32-bit encoding, |
973 | functionally identical to UTF-32. |
c349b1b9 |
974 | |
c29a771d |
975 | =item * |
5cb3728c |
976 | |
977 | UTF-7 |
c349b1b9 |
978 | |
376d9008 |
979 | A seven-bit safe (non-eight-bit) encoding, which is useful if the |
980 | transport or storage is not eight-bit safe. Defined by RFC 2152. |
c349b1b9 |
981 | |
95a1a48b |
982 | =back |
983 | |
0d7c09bb |
984 | =head2 Security Implications of Unicode |
985 | |
986 | =over 4 |
987 | |
988 | =item * |
989 | |
990 | Malformed UTF-8 |
bf0fa0b2 |
991 | |
992 | Unfortunately, the specification of UTF-8 leaves some room for |
993 | interpretation of how many bytes of encoded output one should generate |
376d9008 |
994 | from one input Unicode character. Strictly speaking, the shortest |
995 | possible sequence of UTF-8 bytes should be generated, |
996 | because otherwise there is potential for an input buffer overflow at |
feda178f |
997 | the receiving end of a UTF-8 connection. Perl always generates the |
376d9008 |
998 | shortest length UTF-8, and with warnings on Perl will warn about |
999 | non-shortest length UTF-8 along with other malformations, such as the |
1000 | surrogates, which are not real Unicode code points. |
bf0fa0b2 |
1001 | |
0d7c09bb |
1002 | =item * |
1003 | |
1004 | Regular expressions behave slightly differently between byte data and |
376d9008 |
1005 | character (Unicode) data. For example, the "word character" character |
1006 | class C<\w> will work differently depending on if data is eight-bit bytes |
1007 | or Unicode. |
0d7c09bb |
1008 | |
376d9008 |
1009 | In the first case, the set of C<\w> characters is either small--the |
1010 | default set of alphabetic characters, digits, and the "_"--or, if you |
0d7c09bb |
1011 | are using a locale (see L<perllocale>), the C<\w> might contain a few |
1012 | more letters according to your language and country. |
1013 | |
376d9008 |
1014 | In the second case, the C<\w> set of characters is much, much larger. |
1bfb14c4 |
1015 | Most importantly, even in the set of the first 256 characters, it will |
1016 | probably match different characters: unlike most locales, which are |
1017 | specific to a language and country pair, Unicode classifies all the |
1018 | characters that are letters I<somewhere> as C<\w>. For example, your |
1019 | locale might not think that LATIN SMALL LETTER ETH is a letter (unless |
1020 | you happen to speak Icelandic), but Unicode does. |
0d7c09bb |
1021 | |
376d9008 |
1022 | As discussed elsewhere, Perl has one foot (two hooves?) planted in |
1bfb14c4 |
1023 | each of two worlds: the old world of bytes and the new world of |
1024 | characters, upgrading from bytes to characters when necessary. |
376d9008 |
1025 | If your legacy code does not explicitly use Unicode, no automatic |
1026 | switch-over to characters should happen. Characters shouldn't get |
1bfb14c4 |
1027 | downgraded to bytes, either. It is possible to accidentally mix bytes |
1028 | and characters, however (see L<perluniintro>), in which case C<\w> in |
1029 | regular expressions might start behaving differently. Review your |
1030 | code. Use warnings and the C<strict> pragma. |
0d7c09bb |
1031 | |
1032 | =back |
1033 | |
c349b1b9 |
1034 | =head2 Unicode in Perl on EBCDIC |
1035 | |
376d9008 |
1036 | The way Unicode is handled on EBCDIC platforms is still |
1037 | experimental. On such platforms, references to UTF-8 encoding in this |
1038 | document and elsewhere should be read as meaning the UTF-EBCDIC |
1039 | specified in Unicode Technical Report 16, unless ASCII vs. EBCDIC issues |
c349b1b9 |
1040 | are specifically discussed. There is no C<utfebcdic> pragma or |
376d9008 |
1041 | ":utfebcdic" layer; rather, "utf8" and ":utf8" are reused to mean |
86bbd6d1 |
1042 | the platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic> |
1043 | for more discussion of the issues. |
c349b1b9 |
1044 | |
b310b053 |
1045 | =head2 Locales |
1046 | |
4616122b |
1047 | Usually locale settings and Unicode do not affect each other, but |
b310b053 |
1048 | there are a couple of exceptions: |
1049 | |
1050 | =over 4 |
1051 | |
1052 | =item * |
1053 | |
8aa8f774 |
1054 | You can enable automatic UTF-8-ification of your standard file |
1055 | handles, default C<open()> layer, and C<@ARGV> by using either |
1056 | the C<-C> command line switch or the C<PERL_UNICODE> environment |
1057 | variable, see L<perlrun> for the documentation of the C<-C> switch. |
b310b053 |
1058 | |
1059 | =item * |
1060 | |
376d9008 |
1061 | Perl tries really hard to work both with Unicode and the old |
1062 | byte-oriented world. Most often this is nice, but sometimes Perl's |
1063 | straddling of the proverbial fence causes problems. |
b310b053 |
1064 | |
1065 | =back |
1066 | |
1aad1664 |
1067 | =head2 When Unicode Does Not Happen |
1068 | |
1069 | While Perl does have extensive ways to input and output in Unicode, |
1070 | and few other 'entry points' like the @ARGV which can be interpreted |
1071 | as Unicode (UTF-8), there still are many places where Unicode (in some |
1072 | encoding or another) could be given as arguments or received as |
1073 | results, or both, but it is not. |
1074 | |
1075 | The following are such interfaces. For all of these Perl currently |
1076 | (as of 5.8.1) simply assumes byte strings both as arguments and results. |
1077 | |
1078 | One reason why Perl does not attempt to resolve the role of Unicode in |
1079 | this cases is that the answers are highly dependent on the operating |
1080 | system and the file system(s). For example, whether filenames can be |
1081 | in Unicode, and in exactly what kind of encoding, is not exactly a |
1082 | portable concept. Similarly for the qx and system: how well will the |
1083 | 'command line interface' (and which of them?) handle Unicode? |
1084 | |
1085 | =over 4 |
1086 | |
557a2462 |
1087 | =item * |
1088 | |
1089 | chmod, chmod, chown, chroot, exec, link, mkdir |
1090 | rename, rmdir stat, symlink, truncate, unlink, utime |
1091 | |
1092 | =item * |
1093 | |
1094 | %ENV |
1095 | |
1096 | =item * |
1097 | |
1098 | glob (aka the <*>) |
1099 | |
1100 | =item * |
1aad1664 |
1101 | |
557a2462 |
1102 | open, opendir, sysopen |
1aad1664 |
1103 | |
557a2462 |
1104 | =item * |
1aad1664 |
1105 | |
557a2462 |
1106 | qx (aka the backtick operator), system |
1aad1664 |
1107 | |
557a2462 |
1108 | =item * |
1aad1664 |
1109 | |
557a2462 |
1110 | readdir, readlink |
1aad1664 |
1111 | |
1112 | =back |
1113 | |
1114 | =head2 Forcing Unicode in Perl (Or Unforcing Unicode in Perl) |
1115 | |
1116 | Sometimes (see L</"When Unicode Does Not Happen">) there are |
1117 | situations where you simply need to force Perl to believe that a byte |
1118 | string is UTF-8, or vice versa. The low-level calls |
1119 | utf8::upgrade($bytestring) and utf8::downgrade($utf8string) are |
1120 | the answers. |
1121 | |
1122 | Do not use them without careful thought, though: Perl may easily get |
1123 | very confused, angry, or even crash, if you suddenly change the 'nature' |
1124 | of scalar like that. Especially careful you have to be if you use the |
1125 | utf8::upgrade(): any random byte string is not valid UTF-8. |
1126 | |
95a1a48b |
1127 | =head2 Using Unicode in XS |
1128 | |
3a2263fe |
1129 | If you want to handle Perl Unicode in XS extensions, you may find the |
1130 | following C APIs useful. See also L<perlguts/"Unicode Support"> for an |
1131 | explanation about Unicode at the XS level, and L<perlapi> for the API |
1132 | details. |
95a1a48b |
1133 | |
1134 | =over 4 |
1135 | |
1136 | =item * |
1137 | |
1bfb14c4 |
1138 | C<DO_UTF8(sv)> returns true if the C<UTF8> flag is on and the bytes |
1139 | pragma is not in effect. C<SvUTF8(sv)> returns true is the C<UTF8> |
1140 | flag is on; the bytes pragma is ignored. The C<UTF8> flag being on |
1141 | does B<not> mean that there are any characters of code points greater |
1142 | than 255 (or 127) in the scalar or that there are even any characters |
1143 | in the scalar. What the C<UTF8> flag means is that the sequence of |
1144 | octets in the representation of the scalar is the sequence of UTF-8 |
1145 | encoded code points of the characters of a string. The C<UTF8> flag |
1146 | being off means that each octet in this representation encodes a |
1147 | single character with code point 0..255 within the string. Perl's |
1148 | Unicode model is not to use UTF-8 until it is absolutely necessary. |
95a1a48b |
1149 | |
1150 | =item * |
1151 | |
1bfb14c4 |
1152 | C<uvuni_to_utf8(buf, chr>) writes a Unicode character code point into |
1153 | a buffer encoding the code point as UTF-8, and returns a pointer |
95a1a48b |
1154 | pointing after the UTF-8 bytes. |
1155 | |
1156 | =item * |
1157 | |
376d9008 |
1158 | C<utf8_to_uvuni(buf, lenp)> reads UTF-8 encoded bytes from a buffer and |
1159 | returns the Unicode character code point and, optionally, the length of |
1160 | the UTF-8 byte sequence. |
95a1a48b |
1161 | |
1162 | =item * |
1163 | |
376d9008 |
1164 | C<utf8_length(start, end)> returns the length of the UTF-8 encoded buffer |
1165 | in characters. C<sv_len_utf8(sv)> returns the length of the UTF-8 encoded |
95a1a48b |
1166 | scalar. |
1167 | |
1168 | =item * |
1169 | |
376d9008 |
1170 | C<sv_utf8_upgrade(sv)> converts the string of the scalar to its UTF-8 |
1171 | encoded form. C<sv_utf8_downgrade(sv)> does the opposite, if |
1172 | possible. C<sv_utf8_encode(sv)> is like sv_utf8_upgrade except that |
1173 | it does not set the C<UTF8> flag. C<sv_utf8_decode()> does the |
1174 | opposite of C<sv_utf8_encode()>. Note that none of these are to be |
1175 | used as general-purpose encoding or decoding interfaces: C<use Encode> |
1176 | for that. C<sv_utf8_upgrade()> is affected by the encoding pragma |
1177 | but C<sv_utf8_downgrade()> is not (since the encoding pragma is |
1178 | designed to be a one-way street). |
95a1a48b |
1179 | |
1180 | =item * |
1181 | |
376d9008 |
1182 | C<is_utf8_char(s)> returns true if the pointer points to a valid UTF-8 |
90f968e0 |
1183 | character. |
95a1a48b |
1184 | |
1185 | =item * |
1186 | |
376d9008 |
1187 | C<is_utf8_string(buf, len)> returns true if C<len> bytes of the buffer |
95a1a48b |
1188 | are valid UTF-8. |
1189 | |
1190 | =item * |
1191 | |
376d9008 |
1192 | C<UTF8SKIP(buf)> will return the number of bytes in the UTF-8 encoded |
1193 | character in the buffer. C<UNISKIP(chr)> will return the number of bytes |
1194 | required to UTF-8-encode the Unicode character code point. C<UTF8SKIP()> |
90f968e0 |
1195 | is useful for example for iterating over the characters of a UTF-8 |
376d9008 |
1196 | encoded buffer; C<UNISKIP()> is useful, for example, in computing |
90f968e0 |
1197 | the size required for a UTF-8 encoded buffer. |
95a1a48b |
1198 | |
1199 | =item * |
1200 | |
376d9008 |
1201 | C<utf8_distance(a, b)> will tell the distance in characters between the |
95a1a48b |
1202 | two pointers pointing to the same UTF-8 encoded buffer. |
1203 | |
1204 | =item * |
1205 | |
376d9008 |
1206 | C<utf8_hop(s, off)> will return a pointer to an UTF-8 encoded buffer |
1207 | that is C<off> (positive or negative) Unicode characters displaced |
1208 | from the UTF-8 buffer C<s>. Be careful not to overstep the buffer: |
1209 | C<utf8_hop()> will merrily run off the end or the beginning of the |
1210 | buffer if told to do so. |
95a1a48b |
1211 | |
d2cc3551 |
1212 | =item * |
1213 | |
376d9008 |
1214 | C<pv_uni_display(dsv, spv, len, pvlim, flags)> and |
1215 | C<sv_uni_display(dsv, ssv, pvlim, flags)> are useful for debugging the |
1216 | output of Unicode strings and scalars. By default they are useful |
1217 | only for debugging--they display B<all> characters as hexadecimal code |
1bfb14c4 |
1218 | points--but with the flags C<UNI_DISPLAY_ISPRINT>, |
1219 | C<UNI_DISPLAY_BACKSLASH>, and C<UNI_DISPLAY_QQ> you can make the |
1220 | output more readable. |
d2cc3551 |
1221 | |
1222 | =item * |
1223 | |
376d9008 |
1224 | C<ibcmp_utf8(s1, pe1, u1, l1, u1, s2, pe2, l2, u2)> can be used to |
1225 | compare two strings case-insensitively in Unicode. For case-sensitive |
1226 | comparisons you can just use C<memEQ()> and C<memNE()> as usual. |
d2cc3551 |
1227 | |
c349b1b9 |
1228 | =back |
1229 | |
95a1a48b |
1230 | For more information, see L<perlapi>, and F<utf8.c> and F<utf8.h> |
1231 | in the Perl source code distribution. |
1232 | |
c29a771d |
1233 | =head1 BUGS |
1234 | |
376d9008 |
1235 | =head2 Interaction with Locales |
7eabb34d |
1236 | |
376d9008 |
1237 | Use of locales with Unicode data may lead to odd results. Currently, |
1238 | Perl attempts to attach 8-bit locale info to characters in the range |
1239 | 0..255, but this technique is demonstrably incorrect for locales that |
1240 | use characters above that range when mapped into Unicode. Perl's |
1241 | Unicode support will also tend to run slower. Use of locales with |
1242 | Unicode is discouraged. |
c29a771d |
1243 | |
376d9008 |
1244 | =head2 Interaction with Extensions |
7eabb34d |
1245 | |
376d9008 |
1246 | When Perl exchanges data with an extension, the extension should be |
7eabb34d |
1247 | able to understand the UTF-8 flag and act accordingly. If the |
376d9008 |
1248 | extension doesn't know about the flag, it's likely that the extension |
1249 | will return incorrectly-flagged data. |
7eabb34d |
1250 | |
1251 | So if you're working with Unicode data, consult the documentation of |
1252 | every module you're using if there are any issues with Unicode data |
1253 | exchange. If the documentation does not talk about Unicode at all, |
a73d23f6 |
1254 | suspect the worst and probably look at the source to learn how the |
376d9008 |
1255 | module is implemented. Modules written completely in Perl shouldn't |
a73d23f6 |
1256 | cause problems. Modules that directly or indirectly access code written |
1257 | in other programming languages are at risk. |
7eabb34d |
1258 | |
376d9008 |
1259 | For affected functions, the simple strategy to avoid data corruption is |
7eabb34d |
1260 | to always make the encoding of the exchanged data explicit. Choose an |
376d9008 |
1261 | encoding that you know the extension can handle. Convert arguments passed |
7eabb34d |
1262 | to the extensions to that encoding and convert results back from that |
1263 | encoding. Write wrapper functions that do the conversions for you, so |
1264 | you can later change the functions when the extension catches up. |
1265 | |
376d9008 |
1266 | To provide an example, let's say the popular Foo::Bar::escape_html |
7eabb34d |
1267 | function doesn't deal with Unicode data yet. The wrapper function |
1268 | would convert the argument to raw UTF-8 and convert the result back to |
376d9008 |
1269 | Perl's internal representation like so: |
7eabb34d |
1270 | |
1271 | sub my_escape_html ($) { |
1272 | my($what) = shift; |
1273 | return unless defined $what; |
1274 | Encode::decode_utf8(Foo::Bar::escape_html(Encode::encode_utf8($what))); |
1275 | } |
1276 | |
1277 | Sometimes, when the extension does not convert data but just stores |
1278 | and retrieves them, you will be in a position to use the otherwise |
1279 | dangerous Encode::_utf8_on() function. Let's say the popular |
66b79f27 |
1280 | C<Foo::Bar> extension, written in C, provides a C<param> method that |
7eabb34d |
1281 | lets you store and retrieve data according to these prototypes: |
1282 | |
1283 | $self->param($name, $value); # set a scalar |
1284 | $value = $self->param($name); # retrieve a scalar |
1285 | |
1286 | If it does not yet provide support for any encoding, one could write a |
1287 | derived class with such a C<param> method: |
1288 | |
1289 | sub param { |
1290 | my($self,$name,$value) = @_; |
1291 | utf8::upgrade($name); # make sure it is UTF-8 encoded |
1292 | if (defined $value) |
1293 | utf8::upgrade($value); # make sure it is UTF-8 encoded |
1294 | return $self->SUPER::param($name,$value); |
1295 | } else { |
1296 | my $ret = $self->SUPER::param($name); |
1297 | Encode::_utf8_on($ret); # we know, it is UTF-8 encoded |
1298 | return $ret; |
1299 | } |
1300 | } |
1301 | |
a73d23f6 |
1302 | Some extensions provide filters on data entry/exit points, such as |
1303 | DB_File::filter_store_key and family. Look out for such filters in |
66b79f27 |
1304 | the documentation of your extensions, they can make the transition to |
7eabb34d |
1305 | Unicode data much easier. |
1306 | |
376d9008 |
1307 | =head2 Speed |
7eabb34d |
1308 | |
c29a771d |
1309 | Some functions are slower when working on UTF-8 encoded strings than |
574c8022 |
1310 | on byte encoded strings. All functions that need to hop over |
7c17141f |
1311 | characters such as length(), substr() or index(), or matching regular |
1312 | expressions can work B<much> faster when the underlying data are |
1313 | byte-encoded. |
1314 | |
1315 | In Perl 5.8.0 the slowness was often quite spectacular; in Perl 5.8.1 |
1316 | a caching scheme was introduced which will hopefully make the slowness |
1317 | somewhat less spectacular. Operations with UTF-8 encoded strings are |
1318 | still slower, though. |
666f95b9 |
1319 | |
c8d992ba |
1320 | =head2 Porting code from perl-5.6.X |
1321 | |
1322 | Perl 5.8 has a different Unicode model from 5.6. In 5.6 the programmer |
1323 | was required to use the C<utf8> pragma to declare that a given scope |
1324 | expected to deal with Unicode data and had to make sure that only |
1325 | Unicode data were reaching that scope. If you have code that is |
1326 | working with 5.6, you will need some of the following adjustments to |
1327 | your code. The examples are written such that the code will continue |
1328 | to work under 5.6, so you should be safe to try them out. |
1329 | |
1330 | =over 4 |
1331 | |
1332 | =item * |
1333 | |
1334 | A filehandle that should read or write UTF-8 |
1335 | |
1336 | if ($] > 5.007) { |
1337 | binmode $fh, ":utf8"; |
1338 | } |
1339 | |
1340 | =item * |
1341 | |
1342 | A scalar that is going to be passed to some extension |
1343 | |
1344 | Be it Compress::Zlib, Apache::Request or any extension that has no |
1345 | mention of Unicode in the manpage, you need to make sure that the |
1346 | UTF-8 flag is stripped off. Note that at the time of this writing |
1347 | (October 2002) the mentioned modules are not UTF-8-aware. Please |
1348 | check the documentation to verify if this is still true. |
1349 | |
1350 | if ($] > 5.007) { |
1351 | require Encode; |
1352 | $val = Encode::encode_utf8($val); # make octets |
1353 | } |
1354 | |
1355 | =item * |
1356 | |
1357 | A scalar we got back from an extension |
1358 | |
1359 | If you believe the scalar comes back as UTF-8, you will most likely |
1360 | want the UTF-8 flag restored: |
1361 | |
1362 | if ($] > 5.007) { |
1363 | require Encode; |
1364 | $val = Encode::decode_utf8($val); |
1365 | } |
1366 | |
1367 | =item * |
1368 | |
1369 | Same thing, if you are really sure it is UTF-8 |
1370 | |
1371 | if ($] > 5.007) { |
1372 | require Encode; |
1373 | Encode::_utf8_on($val); |
1374 | } |
1375 | |
1376 | =item * |
1377 | |
1378 | A wrapper for fetchrow_array and fetchrow_hashref |
1379 | |
1380 | When the database contains only UTF-8, a wrapper function or method is |
1381 | a convenient way to replace all your fetchrow_array and |
1382 | fetchrow_hashref calls. A wrapper function will also make it easier to |
1383 | adapt to future enhancements in your database driver. Note that at the |
1384 | time of this writing (October 2002), the DBI has no standardized way |
1385 | to deal with UTF-8 data. Please check the documentation to verify if |
1386 | that is still true. |
1387 | |
1388 | sub fetchrow { |
1389 | my($self, $sth, $what) = @_; # $what is one of fetchrow_{array,hashref} |
1390 | if ($] < 5.007) { |
1391 | return $sth->$what; |
1392 | } else { |
1393 | require Encode; |
1394 | if (wantarray) { |
1395 | my @arr = $sth->$what; |
1396 | for (@arr) { |
1397 | defined && /[^\000-\177]/ && Encode::_utf8_on($_); |
1398 | } |
1399 | return @arr; |
1400 | } else { |
1401 | my $ret = $sth->$what; |
1402 | if (ref $ret) { |
1403 | for my $k (keys %$ret) { |
1404 | defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret->{$k}; |
1405 | } |
1406 | return $ret; |
1407 | } else { |
1408 | defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret; |
1409 | return $ret; |
1410 | } |
1411 | } |
1412 | } |
1413 | } |
1414 | |
1415 | |
1416 | =item * |
1417 | |
1418 | A large scalar that you know can only contain ASCII |
1419 | |
1420 | Scalars that contain only ASCII and are marked as UTF-8 are sometimes |
1421 | a drag to your program. If you recognize such a situation, just remove |
1422 | the UTF-8 flag: |
1423 | |
1424 | utf8::downgrade($val) if $] > 5.007; |
1425 | |
1426 | =back |
1427 | |
393fec97 |
1428 | =head1 SEE ALSO |
1429 | |
72ff2908 |
1430 | L<perluniintro>, L<encoding>, L<Encode>, L<open>, L<utf8>, L<bytes>, |
a05d7ebb |
1431 | L<perlretut>, L<perlvar/"${^UNICODE}"> |
393fec97 |
1432 | |
1433 | =cut |