| 1 | =head1 NAME |
| 2 | |
| 3 | perlunicode - Unicode support in Perl |
| 4 | |
| 5 | =head1 DESCRIPTION |
| 6 | |
| 7 | =head2 Important Caveats |
| 8 | |
| 9 | Unicode support is an extensive requirement. While Perl does not |
| 10 | implement the Unicode standard or the accompanying technical reports |
| 11 | from cover to cover, Perl does support many Unicode features. |
| 12 | |
| 13 | People who want to learn to use Unicode in Perl, should probably read |
| 14 | the L<Perl Unicode tutorial, perlunitut|perlunitut> and |
| 15 | L<perluniintro>, before reading |
| 16 | this reference document. |
| 17 | |
| 18 | Also, the use of Unicode may present security issues that aren't obvious. |
| 19 | Read L<Unicode Security Considerations|http://www.unicode.org/reports/tr36>. |
| 20 | |
| 21 | =over 4 |
| 22 | |
| 23 | =item Safest if you "use feature 'unicode_strings'" |
| 24 | |
| 25 | In order to preserve backward compatibility, Perl does not turn |
| 26 | on full internal Unicode support unless the pragma |
| 27 | C<use feature 'unicode_strings'> is specified. (This is automatically |
| 28 | selected if you use C<use 5.012> or higher.) Failure to do this can |
| 29 | trigger unexpected surprises. See L</The "Unicode Bug"> below. |
| 30 | |
| 31 | This pragma doesn't affect I/O. Nor does it change the internal |
| 32 | representation of strings, only their interpretation. There are still |
| 33 | several places where Unicode isn't fully supported, such as in |
| 34 | filenames. |
| 35 | |
| 36 | =item Input and Output Layers |
| 37 | |
| 38 | Perl knows when a filehandle uses Perl's internal Unicode encodings |
| 39 | (UTF-8, or UTF-EBCDIC if in EBCDIC) if the filehandle is opened with |
| 40 | the ":encoding(utf8)" layer. Other encodings can be converted to Perl's |
| 41 | encoding on input or from Perl's encoding on output by use of the |
| 42 | ":encoding(...)" layer. See L<open>. |
| 43 | |
| 44 | To indicate that Perl source itself is in UTF-8, use C<use utf8;>. |
| 45 | |
| 46 | =item C<use utf8> still needed to enable UTF-8/UTF-EBCDIC in scripts |
| 47 | |
| 48 | As a compatibility measure, the C<use utf8> pragma must be explicitly |
| 49 | included to enable recognition of UTF-8 in the Perl scripts themselves |
| 50 | (in string or regular expression literals, or in identifier names) on |
| 51 | ASCII-based machines or to recognize UTF-EBCDIC on EBCDIC-based |
| 52 | machines. B<These are the only times when an explicit C<use utf8> |
| 53 | is needed.> See L<utf8>. |
| 54 | |
| 55 | =item BOM-marked scripts and UTF-16 scripts autodetected |
| 56 | |
| 57 | If a Perl script begins marked with the Unicode BOM (UTF-16LE, UTF16-BE, |
| 58 | or UTF-8), or if the script looks like non-BOM-marked UTF-16 of either |
| 59 | endianness, Perl will correctly read in the script as Unicode. |
| 60 | (BOMless UTF-8 cannot be effectively recognized or differentiated from |
| 61 | ISO 8859-1 or other eight-bit encodings.) |
| 62 | |
| 63 | =item C<use encoding> needed to upgrade non-Latin-1 byte strings |
| 64 | |
| 65 | By default, there is a fundamental asymmetry in Perl's Unicode model: |
| 66 | implicit upgrading from byte strings to Unicode strings assumes that |
| 67 | they were encoded in I<ISO 8859-1 (Latin-1)>, but Unicode strings are |
| 68 | downgraded with UTF-8 encoding. This happens because the first 256 |
| 69 | codepoints in Unicode happens to agree with Latin-1. |
| 70 | |
| 71 | See L</"Byte and Character Semantics"> for more details. |
| 72 | |
| 73 | =back |
| 74 | |
| 75 | =head2 Byte and Character Semantics |
| 76 | |
| 77 | Perl uses logically-wide characters to represent strings internally. |
| 78 | |
| 79 | Starting in Perl 5.14, Perl-level operations work with |
| 80 | characters rather than bytes within the scope of a |
| 81 | C<L<use feature 'unicode_strings'|feature>> (or equivalently |
| 82 | C<use 5.012> or higher). (This is not true if bytes have been |
| 83 | explicitly requested by C<L<use bytes|bytes>>, nor necessarily true |
| 84 | for interactions with the platform's operating system.) |
| 85 | |
| 86 | For earlier Perls, and when C<unicode_strings> is not in effect, Perl |
| 87 | provides a fairly safe environment that can handle both types of |
| 88 | semantics in programs. For operations where Perl can unambiguously |
| 89 | decide that the input data are characters, Perl switches to character |
| 90 | semantics. For operations where this determination cannot be made |
| 91 | without additional information from the user, Perl decides in favor of |
| 92 | compatibility and chooses to use byte semantics. |
| 93 | |
| 94 | When C<use locale> (but not C<use locale ':not_characters'>) is in |
| 95 | effect, Perl uses the semantics associated with the current locale. |
| 96 | (C<use locale> overrides C<use feature 'unicode_strings'> in the same scope; |
| 97 | while C<use locale ':not_characters'> effectively also selects |
| 98 | C<use feature 'unicode_strings'> in its scope; see L<perllocale>.) |
| 99 | Otherwise, Perl uses the platform's native |
| 100 | byte semantics for characters whose code points are less than 256, and |
| 101 | Unicode semantics for those greater than 255. That means that non-ASCII |
| 102 | characters are undefined except for their |
| 103 | ordinal numbers. This means that none have case (upper and lower), nor are any |
| 104 | a member of character classes, like C<[:alpha:]> or C<\w>. (But all do belong |
| 105 | to the C<\W> class or the Perl regular expression extension C<[:^alpha:]>.) |
| 106 | |
| 107 | This behavior preserves compatibility with earlier versions of Perl, |
| 108 | which allowed byte semantics in Perl operations only if |
| 109 | none of the program's inputs were marked as being a source of Unicode |
| 110 | character data. Such data may come from filehandles, from calls to |
| 111 | external programs, from information provided by the system (such as %ENV), |
| 112 | or from literals and constants in the source text. |
| 113 | |
| 114 | The C<utf8> pragma is primarily a compatibility device that enables |
| 115 | recognition of UTF-(8|EBCDIC) in literals encountered by the parser. |
| 116 | Note that this pragma is only required while Perl defaults to byte |
| 117 | semantics; when character semantics become the default, this pragma |
| 118 | may become a no-op. See L<utf8>. |
| 119 | |
| 120 | If strings operating under byte semantics and strings with Unicode |
| 121 | character data are concatenated, the new string will have |
| 122 | character semantics. This can cause surprises: See L</BUGS>, below. |
| 123 | You can choose to be warned when this happens. See L<encoding::warnings>. |
| 124 | |
| 125 | Under character semantics, many operations that formerly operated on |
| 126 | bytes now operate on characters. A character in Perl is |
| 127 | logically just a number ranging from 0 to 2**31 or so. Larger |
| 128 | characters may encode into longer sequences of bytes internally, but |
| 129 | this internal detail is mostly hidden for Perl code. |
| 130 | See L<perluniintro> for more. |
| 131 | |
| 132 | =head2 Effects of Character Semantics |
| 133 | |
| 134 | Character semantics have the following effects: |
| 135 | |
| 136 | =over 4 |
| 137 | |
| 138 | =item * |
| 139 | |
| 140 | Strings--including hash keys--and regular expression patterns may |
| 141 | contain characters that have an ordinal value larger than 255. |
| 142 | |
| 143 | If you use a Unicode editor to edit your program, Unicode characters may |
| 144 | occur directly within the literal strings in UTF-8 encoding, or UTF-16. |
| 145 | (The former requires a BOM or C<use utf8>, the latter requires a BOM.) |
| 146 | |
| 147 | Unicode characters can also be added to a string by using the C<\N{U+...}> |
| 148 | notation. The Unicode code for the desired character, in hexadecimal, |
| 149 | should be placed in the braces, after the C<U>. For instance, a smiley face is |
| 150 | C<\N{U+263A}>. |
| 151 | |
| 152 | Alternatively, you can use the C<\x{...}> notation for characters 0x100 and |
| 153 | above. For characters below 0x100 you may get byte semantics instead of |
| 154 | character semantics; see L</The "Unicode Bug">. On EBCDIC machines there is |
| 155 | the additional problem that the value for such characters gives the EBCDIC |
| 156 | character rather than the Unicode one, thus it is more portable to use |
| 157 | C<\N{U+...}> instead. |
| 158 | |
| 159 | Additionally, you can use the C<\N{...}> notation and put the official |
| 160 | Unicode character name within the braces, such as |
| 161 | C<\N{WHITE SMILING FACE}>. This automatically loads the L<charnames> |
| 162 | module with the C<:full> and C<:short> options. If you prefer different |
| 163 | options for this module, you can instead, before the C<\N{...}>, |
| 164 | explicitly load it with your desired options; for example, |
| 165 | |
| 166 | use charnames ':loose'; |
| 167 | |
| 168 | =item * |
| 169 | |
| 170 | If an appropriate L<encoding> is specified, identifiers within the |
| 171 | Perl script may contain Unicode alphanumeric characters, including |
| 172 | ideographs. Perl does not currently attempt to canonicalize variable |
| 173 | names. |
| 174 | |
| 175 | =item * |
| 176 | |
| 177 | Regular expressions match characters instead of bytes. "." matches |
| 178 | a character instead of a byte. |
| 179 | |
| 180 | =item * |
| 181 | |
| 182 | Bracketed character classes in regular expressions match characters instead of |
| 183 | bytes and match against the character properties specified in the |
| 184 | Unicode properties database. C<\w> can be used to match a Japanese |
| 185 | ideograph, for instance. |
| 186 | |
| 187 | =item * |
| 188 | |
| 189 | Named Unicode properties, scripts, and block ranges may be used (like bracketed |
| 190 | character classes) by using the C<\p{}> "matches property" construct and |
| 191 | the C<\P{}> negation, "doesn't match property". |
| 192 | See L</"Unicode Character Properties"> for more details. |
| 193 | |
| 194 | You can define your own character properties and use them |
| 195 | in the regular expression with the C<\p{}> or C<\P{}> construct. |
| 196 | See L</"User-Defined Character Properties"> for more details. |
| 197 | |
| 198 | =item * |
| 199 | |
| 200 | The special pattern C<\X> matches a logical character, an "extended grapheme |
| 201 | cluster" in Standardese. In Unicode what appears to the user to be a single |
| 202 | character, for example an accented C<G>, may in fact be composed of a sequence |
| 203 | of characters, in this case a C<G> followed by an accent character. C<\X> |
| 204 | will match the entire sequence. |
| 205 | |
| 206 | =item * |
| 207 | |
| 208 | The C<tr///> operator translates characters instead of bytes. Note |
| 209 | that the C<tr///CU> functionality has been removed. For similar |
| 210 | functionality see pack('U0', ...) and pack('C0', ...). |
| 211 | |
| 212 | =item * |
| 213 | |
| 214 | Case translation operators use the Unicode case translation tables |
| 215 | when character input is provided. Note that C<uc()>, or C<\U> in |
| 216 | interpolated strings, translates to uppercase, while C<ucfirst>, |
| 217 | or C<\u> in interpolated strings, translates to titlecase in languages |
| 218 | that make the distinction (which is equivalent to uppercase in languages |
| 219 | without the distinction). |
| 220 | |
| 221 | =item * |
| 222 | |
| 223 | Most operators that deal with positions or lengths in a string will |
| 224 | automatically switch to using character positions, including |
| 225 | C<chop()>, C<chomp()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>, |
| 226 | C<sprintf()>, C<write()>, and C<length()>. An operator that |
| 227 | specifically does not switch is C<vec()>. Operators that really don't |
| 228 | care include operators that treat strings as a bucket of bits such as |
| 229 | C<sort()>, and operators dealing with filenames. |
| 230 | |
| 231 | =item * |
| 232 | |
| 233 | The C<pack()>/C<unpack()> letter C<C> does I<not> change, since it is often |
| 234 | used for byte-oriented formats. Again, think C<char> in the C language. |
| 235 | |
| 236 | There is a new C<U> specifier that converts between Unicode characters |
| 237 | and code points. There is also a C<W> specifier that is the equivalent of |
| 238 | C<chr>/C<ord> and properly handles character values even if they are above 255. |
| 239 | |
| 240 | =item * |
| 241 | |
| 242 | The C<chr()> and C<ord()> functions work on characters, similar to |
| 243 | C<pack("W")> and C<unpack("W")>, I<not> C<pack("C")> and |
| 244 | C<unpack("C")>. C<pack("C")> and C<unpack("C")> are methods for |
| 245 | emulating byte-oriented C<chr()> and C<ord()> on Unicode strings. |
| 246 | While these methods reveal the internal encoding of Unicode strings, |
| 247 | that is not something one normally needs to care about at all. |
| 248 | |
| 249 | =item * |
| 250 | |
| 251 | The bit string operators, C<& | ^ ~>, can operate on character data. |
| 252 | However, for backward compatibility, such as when using bit string |
| 253 | operations when characters are all less than 256 in ordinal value, one |
| 254 | should not use C<~> (the bit complement) with characters of both |
| 255 | values less than 256 and values greater than 256. Most importantly, |
| 256 | DeMorgan's laws (C<~($x|$y) eq ~$x&~$y> and C<~($x&$y) eq ~$x|~$y>) |
| 257 | will not hold. The reason for this mathematical I<faux pas> is that |
| 258 | the complement cannot return B<both> the 8-bit (byte-wide) bit |
| 259 | complement B<and> the full character-wide bit complement. |
| 260 | |
| 261 | =item * |
| 262 | |
| 263 | There is a CPAN module, L<Unicode::Casing>, which allows you to define |
| 264 | your own mappings to be used in C<lc()>, C<lcfirst()>, C<uc()>, |
| 265 | C<ucfirst()>, and C<fc> (or their double-quoted string inlined |
| 266 | versions such as C<\U>). |
| 267 | (Prior to Perl 5.16, this functionality was partially provided |
| 268 | in the Perl core, but suffered from a number of insurmountable |
| 269 | drawbacks, so the CPAN module was written instead.) |
| 270 | |
| 271 | =back |
| 272 | |
| 273 | =over 4 |
| 274 | |
| 275 | =item * |
| 276 | |
| 277 | And finally, C<scalar reverse()> reverses by character rather than by byte. |
| 278 | |
| 279 | =back |
| 280 | |
| 281 | =head2 Unicode Character Properties |
| 282 | |
| 283 | (The only time that Perl considers a sequence of individual code |
| 284 | points as a single logical character is in the C<\X> construct, already |
| 285 | mentioned above. Therefore "character" in this discussion means a single |
| 286 | Unicode code point.) |
| 287 | |
| 288 | Very nearly all Unicode character properties are accessible through |
| 289 | regular expressions by using the C<\p{}> "matches property" construct |
| 290 | and the C<\P{}> "doesn't match property" for its negation. |
| 291 | |
| 292 | For instance, C<\p{Uppercase}> matches any single character with the Unicode |
| 293 | "Uppercase" property, while C<\p{L}> matches any character with a |
| 294 | General_Category of "L" (letter) property. Brackets are not |
| 295 | required for single letter property names, so C<\p{L}> is equivalent to C<\pL>. |
| 296 | |
| 297 | More formally, C<\p{Uppercase}> matches any single character whose Unicode |
| 298 | Uppercase property value is True, and C<\P{Uppercase}> matches any character |
| 299 | whose Uppercase property value is False, and they could have been written as |
| 300 | C<\p{Uppercase=True}> and C<\p{Uppercase=False}>, respectively. |
| 301 | |
| 302 | This formality is needed when properties are not binary; that is, if they can |
| 303 | take on more values than just True and False. For example, the Bidi_Class (see |
| 304 | L</"Bidirectional Character Types"> below), can take on several different |
| 305 | values, such as Left, Right, Whitespace, and others. To match these, one needs |
| 306 | to specify both the property name (Bidi_Class), AND the value being |
| 307 | matched against |
| 308 | (Left, Right, etc.). This is done, as in the examples above, by having the |
| 309 | two components separated by an equal sign (or interchangeably, a colon), like |
| 310 | C<\p{Bidi_Class: Left}>. |
| 311 | |
| 312 | All Unicode-defined character properties may be written in these compound forms |
| 313 | of C<\p{property=value}> or C<\p{property:value}>, but Perl provides some |
| 314 | additional properties that are written only in the single form, as well as |
| 315 | single-form short-cuts for all binary properties and certain others described |
| 316 | below, in which you may omit the property name and the equals or colon |
| 317 | separator. |
| 318 | |
| 319 | Most Unicode character properties have at least two synonyms (or aliases if you |
| 320 | prefer): a short one that is easier to type and a longer one that is more |
| 321 | descriptive and hence easier to understand. Thus the "L" and "Letter" properties |
| 322 | above are equivalent and can be used interchangeably. Likewise, |
| 323 | "Upper" is a synonym for "Uppercase", and we could have written |
| 324 | C<\p{Uppercase}> equivalently as C<\p{Upper}>. Also, there are typically |
| 325 | various synonyms for the values the property can be. For binary properties, |
| 326 | "True" has 3 synonyms: "T", "Yes", and "Y"; and "False has correspondingly "F", |
| 327 | "No", and "N". But be careful. A short form of a value for one property may |
| 328 | not mean the same thing as the same short form for another. Thus, for the |
| 329 | General_Category property, "L" means "Letter", but for the Bidi_Class property, |
| 330 | "L" means "Left". A complete list of properties and synonyms is in |
| 331 | L<perluniprops>. |
| 332 | |
| 333 | Upper/lower case differences in property names and values are irrelevant; |
| 334 | thus C<\p{Upper}> means the same thing as C<\p{upper}> or even C<\p{UpPeR}>. |
| 335 | Similarly, you can add or subtract underscores anywhere in the middle of a |
| 336 | word, so that these are also equivalent to C<\p{U_p_p_e_r}>. And white space |
| 337 | is irrelevant adjacent to non-word characters, such as the braces and the equals |
| 338 | or colon separators, so C<\p{ Upper }> and C<\p{ Upper_case : Y }> are |
| 339 | equivalent to these as well. In fact, white space and even |
| 340 | hyphens can usually be added or deleted anywhere. So even C<\p{ Up-per case = Yes}> is |
| 341 | equivalent. All this is called "loose-matching" by Unicode. The few places |
| 342 | where stricter matching is used is in the middle of numbers, and in the Perl |
| 343 | extension properties that begin or end with an underscore. Stricter matching |
| 344 | cares about white space (except adjacent to non-word characters), |
| 345 | hyphens, and non-interior underscores. |
| 346 | |
| 347 | You can also use negation in both C<\p{}> and C<\P{}> by introducing a caret |
| 348 | (^) between the first brace and the property name: C<\p{^Tamil}> is |
| 349 | equal to C<\P{Tamil}>. |
| 350 | |
| 351 | Almost all properties are immune to case-insensitive matching. That is, |
| 352 | adding a C</i> regular expression modifier does not change what they |
| 353 | match. There are two sets that are affected. |
| 354 | The first set is |
| 355 | C<Uppercase_Letter>, |
| 356 | C<Lowercase_Letter>, |
| 357 | and C<Titlecase_Letter>, |
| 358 | all of which match C<Cased_Letter> under C</i> matching. |
| 359 | And the second set is |
| 360 | C<Uppercase>, |
| 361 | C<Lowercase>, |
| 362 | and C<Titlecase>, |
| 363 | all of which match C<Cased> under C</i> matching. |
| 364 | This set also includes its subsets C<PosixUpper> and C<PosixLower> both |
| 365 | of which under C</i> matching match C<PosixAlpha>. |
| 366 | (The difference between these sets is that some things, such as Roman |
| 367 | numerals, come in both upper and lower case so they are C<Cased>, but aren't considered |
| 368 | letters, so they aren't C<Cased_Letter>s.) |
| 369 | |
| 370 | The result is undefined if you try to match a non-Unicode code point |
| 371 | (that is, one above 0x10FFFF) against a Unicode property. Currently, a |
| 372 | warning is raised, and the match will fail. In some cases, this is |
| 373 | counterintuitive, as both these fail: |
| 374 | |
| 375 | chr(0x110000) =~ \p{ASCII_Hex_Digit=True} # Fails. |
| 376 | chr(0x110000) =~ \p{ASCII_Hex_Digit=False} # Fails! |
| 377 | |
| 378 | =head3 B<General_Category> |
| 379 | |
| 380 | Every Unicode character is assigned a general category, which is the "most |
| 381 | usual categorization of a character" (from |
| 382 | L<http://www.unicode.org/reports/tr44>). |
| 383 | |
| 384 | The compound way of writing these is like C<\p{General_Category=Number}> |
| 385 | (short, C<\p{gc:n}>). But Perl furnishes shortcuts in which everything up |
| 386 | through the equal or colon separator is omitted. So you can instead just write |
| 387 | C<\pN>. |
| 388 | |
| 389 | Here are the short and long forms of the General Category properties: |
| 390 | |
| 391 | Short Long |
| 392 | |
| 393 | L Letter |
| 394 | LC, L& Cased_Letter (that is: [\p{Ll}\p{Lu}\p{Lt}]) |
| 395 | Lu Uppercase_Letter |
| 396 | Ll Lowercase_Letter |
| 397 | Lt Titlecase_Letter |
| 398 | Lm Modifier_Letter |
| 399 | Lo Other_Letter |
| 400 | |
| 401 | M Mark |
| 402 | Mn Nonspacing_Mark |
| 403 | Mc Spacing_Mark |
| 404 | Me Enclosing_Mark |
| 405 | |
| 406 | N Number |
| 407 | Nd Decimal_Number (also Digit) |
| 408 | Nl Letter_Number |
| 409 | No Other_Number |
| 410 | |
| 411 | P Punctuation (also Punct) |
| 412 | Pc Connector_Punctuation |
| 413 | Pd Dash_Punctuation |
| 414 | Ps Open_Punctuation |
| 415 | Pe Close_Punctuation |
| 416 | Pi Initial_Punctuation |
| 417 | (may behave like Ps or Pe depending on usage) |
| 418 | Pf Final_Punctuation |
| 419 | (may behave like Ps or Pe depending on usage) |
| 420 | Po Other_Punctuation |
| 421 | |
| 422 | S Symbol |
| 423 | Sm Math_Symbol |
| 424 | Sc Currency_Symbol |
| 425 | Sk Modifier_Symbol |
| 426 | So Other_Symbol |
| 427 | |
| 428 | Z Separator |
| 429 | Zs Space_Separator |
| 430 | Zl Line_Separator |
| 431 | Zp Paragraph_Separator |
| 432 | |
| 433 | C Other |
| 434 | Cc Control (also Cntrl) |
| 435 | Cf Format |
| 436 | Cs Surrogate |
| 437 | Co Private_Use |
| 438 | Cn Unassigned |
| 439 | |
| 440 | Single-letter properties match all characters in any of the |
| 441 | two-letter sub-properties starting with the same letter. |
| 442 | C<LC> and C<L&> are special: both are aliases for the set consisting of everything matched by C<Ll>, C<Lu>, and C<Lt>. |
| 443 | |
| 444 | =head3 B<Bidirectional Character Types> |
| 445 | |
| 446 | Because scripts differ in their directionality (Hebrew and Arabic are |
| 447 | written right to left, for example) Unicode supplies a Bidi_Class property. |
| 448 | Some of the values this property can have are: |
| 449 | |
| 450 | Value Meaning |
| 451 | |
| 452 | L Left-to-Right |
| 453 | LRE Left-to-Right Embedding |
| 454 | LRO Left-to-Right Override |
| 455 | R Right-to-Left |
| 456 | AL Arabic Letter |
| 457 | RLE Right-to-Left Embedding |
| 458 | RLO Right-to-Left Override |
| 459 | PDF Pop Directional Format |
| 460 | EN European Number |
| 461 | ES European Separator |
| 462 | ET European Terminator |
| 463 | AN Arabic Number |
| 464 | CS Common Separator |
| 465 | NSM Non-Spacing Mark |
| 466 | BN Boundary Neutral |
| 467 | B Paragraph Separator |
| 468 | S Segment Separator |
| 469 | WS Whitespace |
| 470 | ON Other Neutrals |
| 471 | |
| 472 | This property is always written in the compound form. |
| 473 | For example, C<\p{Bidi_Class:R}> matches characters that are normally |
| 474 | written right to left. Unlike the |
| 475 | General_Category property, this |
| 476 | property can have more values added in a future Unicode release. Those |
| 477 | listed above comprised the complete set for many Unicode releases, but |
| 478 | others were added in Unicode 6.3; you can always find what the |
| 479 | current ones are in in L<perluniprops>. And |
| 480 | L<http://www.unicode.org/reports/tr9/> describes how to use them. |
| 481 | |
| 482 | =head3 B<Scripts> |
| 483 | |
| 484 | The world's languages are written in many different scripts. This sentence |
| 485 | (unless you're reading it in translation) is written in Latin, while Russian is |
| 486 | written in Cyrillic, and Greek is written in, well, Greek; Japanese mainly in |
| 487 | Hiragana or Katakana. There are many more. |
| 488 | |
| 489 | The Unicode Script and Script_Extensions properties give what script a |
| 490 | given character is in. Either property can be specified with the |
| 491 | compound form like |
| 492 | C<\p{Script=Hebrew}> (short: C<\p{sc=hebr}>), or |
| 493 | C<\p{Script_Extensions=Javanese}> (short: C<\p{scx=java}>). |
| 494 | In addition, Perl furnishes shortcuts for all |
| 495 | C<Script> property names. You can omit everything up through the equals |
| 496 | (or colon), and simply write C<\p{Latin}> or C<\P{Cyrillic}>. |
| 497 | (This is not true for C<Script_Extensions>, which is required to be |
| 498 | written in the compound form.) |
| 499 | |
| 500 | The difference between these two properties involves characters that are |
| 501 | used in multiple scripts. For example the digits '0' through '9' are |
| 502 | used in many parts of the world. These are placed in a script named |
| 503 | C<Common>. Other characters are used in just a few scripts. For |
| 504 | example, the "KATAKANA-HIRAGANA DOUBLE HYPHEN" is used in both Japanese |
| 505 | scripts, Katakana and Hiragana, but nowhere else. The C<Script> |
| 506 | property places all characters that are used in multiple scripts in the |
| 507 | C<Common> script, while the C<Script_Extensions> property places those |
| 508 | that are used in only a few scripts into each of those scripts; while |
| 509 | still using C<Common> for those used in many scripts. Thus both these |
| 510 | match: |
| 511 | |
| 512 | "0" =~ /\p{sc=Common}/ # Matches |
| 513 | "0" =~ /\p{scx=Common}/ # Matches |
| 514 | |
| 515 | and only the first of these match: |
| 516 | |
| 517 | "\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{sc=Common} # Matches |
| 518 | "\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{scx=Common} # No match |
| 519 | |
| 520 | And only the last two of these match: |
| 521 | |
| 522 | "\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{sc=Hiragana} # No match |
| 523 | "\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{sc=Katakana} # No match |
| 524 | "\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{scx=Hiragana} # Matches |
| 525 | "\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{scx=Katakana} # Matches |
| 526 | |
| 527 | C<Script_Extensions> is thus an improved C<Script>, in which there are |
| 528 | fewer characters in the C<Common> script, and correspondingly more in |
| 529 | other scripts. It is new in Unicode version 6.0, and its data are likely |
| 530 | to change significantly in later releases, as things get sorted out. |
| 531 | |
| 532 | (Actually, besides C<Common>, the C<Inherited> script, contains |
| 533 | characters that are used in multiple scripts. These are modifier |
| 534 | characters which modify other characters, and inherit the script value |
| 535 | of the controlling character. Some of these are used in many scripts, |
| 536 | and so go into C<Inherited> in both C<Script> and C<Script_Extensions>. |
| 537 | Others are used in just a few scripts, so are in C<Inherited> in |
| 538 | C<Script>, but not in C<Script_Extensions>.) |
| 539 | |
| 540 | It is worth stressing that there are several different sets of digits in |
| 541 | Unicode that are equivalent to 0-9 and are matchable by C<\d> in a |
| 542 | regular expression. If they are used in a single language only, they |
| 543 | are in that language's C<Script> and C<Script_Extension>. If they are |
| 544 | used in more than one script, they will be in C<sc=Common>, but only |
| 545 | if they are used in many scripts should they be in C<scx=Common>. |
| 546 | |
| 547 | A complete list of scripts and their shortcuts is in L<perluniprops>. |
| 548 | |
| 549 | =head3 B<Use of "Is" Prefix> |
| 550 | |
| 551 | For backward compatibility (with Perl 5.6), all properties mentioned |
| 552 | so far may have C<Is> or C<Is_> prepended to their name, so C<\P{Is_Lu}>, for |
| 553 | example, is equal to C<\P{Lu}>, and C<\p{IsScript:Arabic}> is equal to |
| 554 | C<\p{Arabic}>. |
| 555 | |
| 556 | =head3 B<Blocks> |
| 557 | |
| 558 | In addition to B<scripts>, Unicode also defines B<blocks> of |
| 559 | characters. The difference between scripts and blocks is that the |
| 560 | concept of scripts is closer to natural languages, while the concept |
| 561 | of blocks is more of an artificial grouping based on groups of Unicode |
| 562 | characters with consecutive ordinal values. For example, the "Basic Latin" |
| 563 | block is all characters whose ordinals are between 0 and 127, inclusive; in |
| 564 | other words, the ASCII characters. The "Latin" script contains some letters |
| 565 | from this as well as several other blocks, like "Latin-1 Supplement", |
| 566 | "Latin Extended-A", etc., but it does not contain all the characters from |
| 567 | those blocks. It does not, for example, contain the digits 0-9, because |
| 568 | those digits are shared across many scripts, and hence are in the |
| 569 | C<Common> script. |
| 570 | |
| 571 | For more about scripts versus blocks, see UAX#24 "Unicode Script Property": |
| 572 | L<http://www.unicode.org/reports/tr24> |
| 573 | |
| 574 | The C<Script> or C<Script_Extensions> properties are likely to be the |
| 575 | ones you want to use when processing |
| 576 | natural language; the Block property may occasionally be useful in working |
| 577 | with the nuts and bolts of Unicode. |
| 578 | |
| 579 | Block names are matched in the compound form, like C<\p{Block: Arrows}> or |
| 580 | C<\p{Blk=Hebrew}>. Unlike most other properties, only a few block names have a |
| 581 | Unicode-defined short name. But Perl does provide a (slight) shortcut: You |
| 582 | can say, for example C<\p{In_Arrows}> or C<\p{In_Hebrew}>. For backwards |
| 583 | compatibility, the C<In> prefix may be omitted if there is no naming conflict |
| 584 | with a script or any other property, and you can even use an C<Is> prefix |
| 585 | instead in those cases. But it is not a good idea to do this, for a couple |
| 586 | reasons: |
| 587 | |
| 588 | =over 4 |
| 589 | |
| 590 | =item 1 |
| 591 | |
| 592 | It is confusing. There are many naming conflicts, and you may forget some. |
| 593 | For example, C<\p{Hebrew}> means the I<script> Hebrew, and NOT the I<block> |
| 594 | Hebrew. But would you remember that 6 months from now? |
| 595 | |
| 596 | =item 2 |
| 597 | |
| 598 | It is unstable. A new version of Unicode may preempt the current meaning by |
| 599 | creating a property with the same name. There was a time in very early Unicode |
| 600 | releases when C<\p{Hebrew}> would have matched the I<block> Hebrew; now it |
| 601 | doesn't. |
| 602 | |
| 603 | =back |
| 604 | |
| 605 | Some people prefer to always use C<\p{Block: foo}> and C<\p{Script: bar}> |
| 606 | instead of the shortcuts, whether for clarity, because they can't remember the |
| 607 | difference between 'In' and 'Is' anyway, or they aren't confident that those who |
| 608 | eventually will read their code will know that difference. |
| 609 | |
| 610 | A complete list of blocks and their shortcuts is in L<perluniprops>. |
| 611 | |
| 612 | =head3 B<Other Properties> |
| 613 | |
| 614 | There are many more properties than the very basic ones described here. |
| 615 | A complete list is in L<perluniprops>. |
| 616 | |
| 617 | Unicode defines all its properties in the compound form, so all single-form |
| 618 | properties are Perl extensions. Most of these are just synonyms for the |
| 619 | Unicode ones, but some are genuine extensions, including several that are in |
| 620 | the compound form. And quite a few of these are actually recommended by Unicode |
| 621 | (in L<http://www.unicode.org/reports/tr18>). |
| 622 | |
| 623 | This section gives some details on all extensions that aren't just |
| 624 | synonyms for compound-form Unicode properties |
| 625 | (for those properties, you'll have to refer to the |
| 626 | L<Unicode Standard|http://www.unicode.org/reports/tr44>. |
| 627 | |
| 628 | =over |
| 629 | |
| 630 | =item B<C<\p{All}>> |
| 631 | |
| 632 | This matches any of the 1_114_112 Unicode code points. It is a synonym for |
| 633 | C<\p{Any}>. |
| 634 | |
| 635 | =item B<C<\p{Alnum}>> |
| 636 | |
| 637 | This matches any C<\p{Alphabetic}> or C<\p{Decimal_Number}> character. |
| 638 | |
| 639 | =item B<C<\p{Any}>> |
| 640 | |
| 641 | This matches any of the 1_114_112 Unicode code points. It is a synonym for |
| 642 | C<\p{All}>. |
| 643 | |
| 644 | =item B<C<\p{ASCII}>> |
| 645 | |
| 646 | This matches any of the 128 characters in the US-ASCII character set, |
| 647 | which is a subset of Unicode. |
| 648 | |
| 649 | =item B<C<\p{Assigned}>> |
| 650 | |
| 651 | This matches any assigned code point; that is, any code point whose general |
| 652 | category is not Unassigned (or equivalently, not Cn). |
| 653 | |
| 654 | =item B<C<\p{Blank}>> |
| 655 | |
| 656 | This is the same as C<\h> and C<\p{HorizSpace}>: A character that changes the |
| 657 | spacing horizontally. |
| 658 | |
| 659 | =item B<C<\p{Decomposition_Type: Non_Canonical}>> (Short: C<\p{Dt=NonCanon}>) |
| 660 | |
| 661 | Matches a character that has a non-canonical decomposition. |
| 662 | |
| 663 | To understand the use of this rarely used property=value combination, it is |
| 664 | necessary to know some basics about decomposition. |
| 665 | Consider a character, say H. It could appear with various marks around it, |
| 666 | such as an acute accent, or a circumflex, or various hooks, circles, arrows, |
| 667 | I<etc.>, above, below, to one side or the other, etc. There are many |
| 668 | possibilities among the world's languages. The number of combinations is |
| 669 | astronomical, and if there were a character for each combination, it would |
| 670 | soon exhaust Unicode's more than a million possible characters. So Unicode |
| 671 | took a different approach: there is a character for the base H, and a |
| 672 | character for each of the possible marks, and these can be variously combined |
| 673 | to get a final logical character. So a logical character--what appears to be a |
| 674 | single character--can be a sequence of more than one individual characters. |
| 675 | This is called an "extended grapheme cluster"; Perl furnishes the C<\X> |
| 676 | regular expression construct to match such sequences. |
| 677 | |
| 678 | But Unicode's intent is to unify the existing character set standards and |
| 679 | practices, and several pre-existing standards have single characters that |
| 680 | mean the same thing as some of these combinations. An example is ISO-8859-1, |
| 681 | which has quite a few of these in the Latin-1 range, an example being "LATIN |
| 682 | CAPITAL LETTER E WITH ACUTE". Because this character was in this pre-existing |
| 683 | standard, Unicode added it to its repertoire. But this character is considered |
| 684 | by Unicode to be equivalent to the sequence consisting of the character |
| 685 | "LATIN CAPITAL LETTER E" followed by the character "COMBINING ACUTE ACCENT". |
| 686 | |
| 687 | "LATIN CAPITAL LETTER E WITH ACUTE" is called a "pre-composed" character, and |
| 688 | its equivalence with the sequence is called canonical equivalence. All |
| 689 | pre-composed characters are said to have a decomposition (into the equivalent |
| 690 | sequence), and the decomposition type is also called canonical. |
| 691 | |
| 692 | However, many more characters have a different type of decomposition, a |
| 693 | "compatible" or "non-canonical" decomposition. The sequences that form these |
| 694 | decompositions are not considered canonically equivalent to the pre-composed |
| 695 | character. An example, again in the Latin-1 range, is the "SUPERSCRIPT ONE". |
| 696 | It is somewhat like a regular digit 1, but not exactly; its decomposition |
| 697 | into the digit 1 is called a "compatible" decomposition, specifically a |
| 698 | "super" decomposition. There are several such compatibility |
| 699 | decompositions (see L<http://www.unicode.org/reports/tr44>), including one |
| 700 | called "compat", which means some miscellaneous type of decomposition |
| 701 | that doesn't fit into the decomposition categories that Unicode has chosen. |
| 702 | |
| 703 | Note that most Unicode characters don't have a decomposition, so their |
| 704 | decomposition type is "None". |
| 705 | |
| 706 | For your convenience, Perl has added the C<Non_Canonical> decomposition |
| 707 | type to mean any of the several compatibility decompositions. |
| 708 | |
| 709 | =item B<C<\p{Graph}>> |
| 710 | |
| 711 | Matches any character that is graphic. Theoretically, this means a character |
| 712 | that on a printer would cause ink to be used. |
| 713 | |
| 714 | =item B<C<\p{HorizSpace}>> |
| 715 | |
| 716 | This is the same as C<\h> and C<\p{Blank}>: a character that changes the |
| 717 | spacing horizontally. |
| 718 | |
| 719 | =item B<C<\p{In=*}>> |
| 720 | |
| 721 | This is a synonym for C<\p{Present_In=*}> |
| 722 | |
| 723 | =item B<C<\p{PerlSpace}>> |
| 724 | |
| 725 | This is the same as C<\s>, restricted to ASCII, namely C<S<[ \f\n\r\t]>> |
| 726 | and starting in Perl v5.18, experimentally, a vertical tab. |
| 727 | |
| 728 | Mnemonic: Perl's (original) space |
| 729 | |
| 730 | =item B<C<\p{PerlWord}>> |
| 731 | |
| 732 | This is the same as C<\w>, restricted to ASCII, namely C<[A-Za-z0-9_]> |
| 733 | |
| 734 | Mnemonic: Perl's (original) word. |
| 735 | |
| 736 | =item B<C<\p{Posix...}>> |
| 737 | |
| 738 | There are several of these, which are equivalents using the C<\p> |
| 739 | notation for Posix classes and are described in |
| 740 | L<perlrecharclass/POSIX Character Classes>. |
| 741 | |
| 742 | =item B<C<\p{Present_In: *}>> (Short: C<\p{In=*}>) |
| 743 | |
| 744 | This property is used when you need to know in what Unicode version(s) a |
| 745 | character is. |
| 746 | |
| 747 | The "*" above stands for some two digit Unicode version number, such as |
| 748 | C<1.1> or C<4.0>; or the "*" can also be C<Unassigned>. This property will |
| 749 | match the code points whose final disposition has been settled as of the |
| 750 | Unicode release given by the version number; C<\p{Present_In: Unassigned}> |
| 751 | will match those code points whose meaning has yet to be assigned. |
| 752 | |
| 753 | For example, C<U+0041> "LATIN CAPITAL LETTER A" was present in the very first |
| 754 | Unicode release available, which is C<1.1>, so this property is true for all |
| 755 | valid "*" versions. On the other hand, C<U+1EFF> was not assigned until version |
| 756 | 5.1 when it became "LATIN SMALL LETTER Y WITH LOOP", so the only "*" that |
| 757 | would match it are 5.1, 5.2, and later. |
| 758 | |
| 759 | Unicode furnishes the C<Age> property from which this is derived. The problem |
| 760 | with Age is that a strict interpretation of it (which Perl takes) has it |
| 761 | matching the precise release a code point's meaning is introduced in. Thus |
| 762 | C<U+0041> would match only 1.1; and C<U+1EFF> only 5.1. This is not usually what |
| 763 | you want. |
| 764 | |
| 765 | Some non-Perl implementations of the Age property may change its meaning to be |
| 766 | the same as the Perl Present_In property; just be aware of that. |
| 767 | |
| 768 | Another confusion with both these properties is that the definition is not |
| 769 | that the code point has been I<assigned>, but that the meaning of the code point |
| 770 | has been I<determined>. This is because 66 code points will always be |
| 771 | unassigned, and so the Age for them is the Unicode version in which the decision |
| 772 | to make them so was made. For example, C<U+FDD0> is to be permanently |
| 773 | unassigned to a character, and the decision to do that was made in version 3.1, |
| 774 | so C<\p{Age=3.1}> matches this character, as also does C<\p{Present_In: 3.1}> and up. |
| 775 | |
| 776 | =item B<C<\p{Print}>> |
| 777 | |
| 778 | This matches any character that is graphical or blank, except controls. |
| 779 | |
| 780 | =item B<C<\p{SpacePerl}>> |
| 781 | |
| 782 | This is the same as C<\s>, including beyond ASCII. |
| 783 | |
| 784 | Mnemonic: Space, as modified by Perl. (It doesn't include the vertical tab |
| 785 | which both the Posix standard and Unicode consider white space.) |
| 786 | |
| 787 | =item B<C<\p{Title}>> and B<C<\p{Titlecase}>> |
| 788 | |
| 789 | Under case-sensitive matching, these both match the same code points as |
| 790 | C<\p{General Category=Titlecase_Letter}> (C<\p{gc=lt}>). The difference |
| 791 | is that under C</i> caseless matching, these match the same as |
| 792 | C<\p{Cased}>, whereas C<\p{gc=lt}> matches C<\p{Cased_Letter>). |
| 793 | |
| 794 | =item B<C<\p{VertSpace}>> |
| 795 | |
| 796 | This is the same as C<\v>: A character that changes the spacing vertically. |
| 797 | |
| 798 | =item B<C<\p{Word}>> |
| 799 | |
| 800 | This is the same as C<\w>, including over 100_000 characters beyond ASCII. |
| 801 | |
| 802 | =item B<C<\p{XPosix...}>> |
| 803 | |
| 804 | There are several of these, which are the standard Posix classes |
| 805 | extended to the full Unicode range. They are described in |
| 806 | L<perlrecharclass/POSIX Character Classes>. |
| 807 | |
| 808 | =back |
| 809 | |
| 810 | =head2 User-Defined Character Properties |
| 811 | |
| 812 | You can define your own binary character properties by defining subroutines |
| 813 | whose names begin with "In" or "Is". (The experimental feature |
| 814 | L<perlre/(?[ ])> provides an alternative which allows more complex |
| 815 | definitions.) The subroutines can be defined in any |
| 816 | package. The user-defined properties can be used in the regular expression |
| 817 | C<\p> and C<\P> constructs; if you are using a user-defined property from a |
| 818 | package other than the one you are in, you must specify its package in the |
| 819 | C<\p> or C<\P> construct. |
| 820 | |
| 821 | # assuming property Is_Foreign defined in Lang:: |
| 822 | package main; # property package name required |
| 823 | if ($txt =~ /\p{Lang::IsForeign}+/) { ... } |
| 824 | |
| 825 | package Lang; # property package name not required |
| 826 | if ($txt =~ /\p{IsForeign}+/) { ... } |
| 827 | |
| 828 | |
| 829 | Note that the effect is compile-time and immutable once defined. |
| 830 | However, the subroutines are passed a single parameter, which is 0 if |
| 831 | case-sensitive matching is in effect and non-zero if caseless matching |
| 832 | is in effect. The subroutine may return different values depending on |
| 833 | the value of the flag, and one set of values will immutably be in effect |
| 834 | for all case-sensitive matches, and the other set for all case-insensitive |
| 835 | matches. |
| 836 | |
| 837 | Note that if the regular expression is tainted, then Perl will die rather |
| 838 | than calling the subroutine, where the name of the subroutine is |
| 839 | determined by the tainted data. |
| 840 | |
| 841 | The subroutines must return a specially-formatted string, with one |
| 842 | or more newline-separated lines. Each line must be one of the following: |
| 843 | |
| 844 | =over 4 |
| 845 | |
| 846 | =item * |
| 847 | |
| 848 | A single hexadecimal number denoting a code point to include. |
| 849 | |
| 850 | =item * |
| 851 | |
| 852 | Two hexadecimal numbers separated by horizontal whitespace (space or |
| 853 | tabular characters) denoting a range of code points to include. |
| 854 | |
| 855 | =item * |
| 856 | |
| 857 | Something to include, prefixed by "+": a built-in character |
| 858 | property (prefixed by "utf8::") or a fully qualified (including package |
| 859 | name) user-defined character property, |
| 860 | to represent all the characters in that property; two hexadecimal code |
| 861 | points for a range; or a single hexadecimal code point. |
| 862 | |
| 863 | =item * |
| 864 | |
| 865 | Something to exclude, prefixed by "-": an existing character |
| 866 | property (prefixed by "utf8::") or a fully qualified (including package |
| 867 | name) user-defined character property, |
| 868 | to represent all the characters in that property; two hexadecimal code |
| 869 | points for a range; or a single hexadecimal code point. |
| 870 | |
| 871 | =item * |
| 872 | |
| 873 | Something to negate, prefixed "!": an existing character |
| 874 | property (prefixed by "utf8::") or a fully qualified (including package |
| 875 | name) user-defined character property, |
| 876 | to represent all the characters in that property; two hexadecimal code |
| 877 | points for a range; or a single hexadecimal code point. |
| 878 | |
| 879 | =item * |
| 880 | |
| 881 | Something to intersect with, prefixed by "&": an existing character |
| 882 | property (prefixed by "utf8::") or a fully qualified (including package |
| 883 | name) user-defined character property, |
| 884 | for all the characters except the characters in the property; two |
| 885 | hexadecimal code points for a range; or a single hexadecimal code point. |
| 886 | |
| 887 | =back |
| 888 | |
| 889 | For example, to define a property that covers both the Japanese |
| 890 | syllabaries (hiragana and katakana), you can define |
| 891 | |
| 892 | sub InKana { |
| 893 | return <<END; |
| 894 | 3040\t309F |
| 895 | 30A0\t30FF |
| 896 | END |
| 897 | } |
| 898 | |
| 899 | Imagine that the here-doc end marker is at the beginning of the line. |
| 900 | Now you can use C<\p{InKana}> and C<\P{InKana}>. |
| 901 | |
| 902 | You could also have used the existing block property names: |
| 903 | |
| 904 | sub InKana { |
| 905 | return <<'END'; |
| 906 | +utf8::InHiragana |
| 907 | +utf8::InKatakana |
| 908 | END |
| 909 | } |
| 910 | |
| 911 | Suppose you wanted to match only the allocated characters, |
| 912 | not the raw block ranges: in other words, you want to remove |
| 913 | the non-characters: |
| 914 | |
| 915 | sub InKana { |
| 916 | return <<'END'; |
| 917 | +utf8::InHiragana |
| 918 | +utf8::InKatakana |
| 919 | -utf8::IsCn |
| 920 | END |
| 921 | } |
| 922 | |
| 923 | The negation is useful for defining (surprise!) negated classes. |
| 924 | |
| 925 | sub InNotKana { |
| 926 | return <<'END'; |
| 927 | !utf8::InHiragana |
| 928 | -utf8::InKatakana |
| 929 | +utf8::IsCn |
| 930 | END |
| 931 | } |
| 932 | |
| 933 | This will match all non-Unicode code points, since every one of them is |
| 934 | not in Kana. You can use intersection to exclude these, if desired, as |
| 935 | this modified example shows: |
| 936 | |
| 937 | sub InNotKana { |
| 938 | return <<'END'; |
| 939 | !utf8::InHiragana |
| 940 | -utf8::InKatakana |
| 941 | +utf8::IsCn |
| 942 | &utf8::Any |
| 943 | END |
| 944 | } |
| 945 | |
| 946 | C<&utf8::Any> must be the last line in the definition. |
| 947 | |
| 948 | Intersection is used generally for getting the common characters matched |
| 949 | by two (or more) classes. It's important to remember not to use "&" for |
| 950 | the first set; that would be intersecting with nothing, resulting in an |
| 951 | empty set. |
| 952 | |
| 953 | (Note that official Unicode properties differ from these in that they |
| 954 | automatically exclude non-Unicode code points and a warning is raised if |
| 955 | a match is attempted on one of those.) |
| 956 | |
| 957 | =head2 User-Defined Case Mappings (for serious hackers only) |
| 958 | |
| 959 | B<This feature has been removed as of Perl 5.16.> |
| 960 | The CPAN module L<Unicode::Casing> provides better functionality without |
| 961 | the drawbacks that this feature had. If you are using a Perl earlier |
| 962 | than 5.16, this feature was most fully documented in the 5.14 version of |
| 963 | this pod: |
| 964 | L<http://perldoc.perl.org/5.14.0/perlunicode.html#User-Defined-Case-Mappings-%28for-serious-hackers-only%29> |
| 965 | |
| 966 | =head2 Character Encodings for Input and Output |
| 967 | |
| 968 | See L<Encode>. |
| 969 | |
| 970 | =head2 Unicode Regular Expression Support Level |
| 971 | |
| 972 | The following list of Unicode supported features for regular expressions describes |
| 973 | all features currently directly supported by core Perl. The references to "Level N" |
| 974 | and the section numbers refer to the Unicode Technical Standard #18, |
| 975 | "Unicode Regular Expressions", version 13, from August 2008. |
| 976 | |
| 977 | =over 4 |
| 978 | |
| 979 | =item * |
| 980 | |
| 981 | Level 1 - Basic Unicode Support |
| 982 | |
| 983 | RL1.1 Hex Notation - done [1] |
| 984 | RL1.2 Properties - done [2][3] |
| 985 | RL1.2a Compatibility Properties - done [4] |
| 986 | RL1.3 Subtraction and Intersection - experimental [5] |
| 987 | RL1.4 Simple Word Boundaries - done [6] |
| 988 | RL1.5 Simple Loose Matches - done [7] |
| 989 | RL1.6 Line Boundaries - MISSING [8][9] |
| 990 | RL1.7 Supplementary Code Points - done [10] |
| 991 | |
| 992 | =over 4 |
| 993 | |
| 994 | =item [1] |
| 995 | |
| 996 | \x{...} |
| 997 | |
| 998 | =item [2] |
| 999 | |
| 1000 | \p{...} \P{...} |
| 1001 | |
| 1002 | =item [3] |
| 1003 | |
| 1004 | supports not only minimal list, but all Unicode character properties (see Unicode Character Properties above) |
| 1005 | |
| 1006 | =item [4] |
| 1007 | |
| 1008 | \d \D \s \S \w \W \X [:prop:] [:^prop:] |
| 1009 | |
| 1010 | =item [5] |
| 1011 | |
| 1012 | The experimental feature in v5.18 C<"(?[...])"> accomplishes this. See |
| 1013 | L<perlre/(?[ ])>. If you don't want to use an experimental feature, |
| 1014 | you can use one of the following: |
| 1015 | |
| 1016 | =over 4 |
| 1017 | |
| 1018 | =item * Regular expression look-ahead |
| 1019 | |
| 1020 | You can mimic class subtraction using lookahead. |
| 1021 | For example, what UTS#18 might write as |
| 1022 | |
| 1023 | [{Block=Greek}-[{UNASSIGNED}]] |
| 1024 | |
| 1025 | in Perl can be written as: |
| 1026 | |
| 1027 | (?!\p{Unassigned})\p{Block=Greek} |
| 1028 | (?=\p{Assigned})\p{Block=Greek} |
| 1029 | |
| 1030 | But in this particular example, you probably really want |
| 1031 | |
| 1032 | \p{Greek} |
| 1033 | |
| 1034 | which will match assigned characters known to be part of the Greek script. |
| 1035 | |
| 1036 | =item * CPAN module L<Unicode::Regex::Set> |
| 1037 | |
| 1038 | It does implement the full UTS#18 grouping, intersection, union, and |
| 1039 | removal (subtraction) syntax. |
| 1040 | |
| 1041 | =item * L</"User-Defined Character Properties"> |
| 1042 | |
| 1043 | '+' for union, '-' for removal (set-difference), '&' for intersection |
| 1044 | |
| 1045 | =back |
| 1046 | |
| 1047 | =item [6] |
| 1048 | |
| 1049 | \b \B |
| 1050 | |
| 1051 | =item [7] |
| 1052 | |
| 1053 | Note that Perl does Full case-folding in matching (but with bugs), not Simple: for example U+1F88 is equivalent to U+1F00 U+03B9, instead of just U+1F80. This difference matters mainly for certain Greek capital letters with certain modifiers: the Full case-folding decomposes the letter, while the Simple case-folding would map it to a single character. |
| 1054 | |
| 1055 | =item [8] |
| 1056 | |
| 1057 | Should do ^ and $ also on U+000B (\v in C), FF (\f), CR (\r), CRLF |
| 1058 | (\r\n), NEL (U+0085), LS (U+2028), and PS (U+2029); should also affect |
| 1059 | <>, $., and script line numbers; should not split lines within CRLF |
| 1060 | (i.e. there is no empty line between \r and \n). For CRLF, try the |
| 1061 | C<:crlf> layer (see L<PerlIO>). |
| 1062 | |
| 1063 | =item [9] |
| 1064 | |
| 1065 | Linebreaking conformant with UAX#14 "Unicode Line Breaking Algorithm" is available through the Unicode::LineBreaking module. |
| 1066 | |
| 1067 | =item [10] |
| 1068 | |
| 1069 | UTF-8/UTF-EBDDIC used in Perl allows not only U+10000 to |
| 1070 | U+10FFFF but also beyond U+10FFFF |
| 1071 | |
| 1072 | =back |
| 1073 | |
| 1074 | =item * |
| 1075 | |
| 1076 | Level 2 - Extended Unicode Support |
| 1077 | |
| 1078 | RL2.1 Canonical Equivalents - MISSING [10][11] |
| 1079 | RL2.2 Default Grapheme Clusters - MISSING [12] |
| 1080 | RL2.3 Default Word Boundaries - MISSING [14] |
| 1081 | RL2.4 Default Loose Matches - MISSING [15] |
| 1082 | RL2.5 Name Properties - DONE |
| 1083 | RL2.6 Wildcard Properties - MISSING |
| 1084 | |
| 1085 | [10] see UAX#15 "Unicode Normalization Forms" |
| 1086 | [11] have Unicode::Normalize but not integrated to regexes |
| 1087 | [12] have \X but we don't have a "Grapheme Cluster Mode" |
| 1088 | [14] see UAX#29, Word Boundaries |
| 1089 | [15] This is covered in Chapter 3.13 (in Unicode 6.0) |
| 1090 | |
| 1091 | =item * |
| 1092 | |
| 1093 | Level 3 - Tailored Support |
| 1094 | |
| 1095 | RL3.1 Tailored Punctuation - MISSING |
| 1096 | RL3.2 Tailored Grapheme Clusters - MISSING [17][18] |
| 1097 | RL3.3 Tailored Word Boundaries - MISSING |
| 1098 | RL3.4 Tailored Loose Matches - MISSING |
| 1099 | RL3.5 Tailored Ranges - MISSING |
| 1100 | RL3.6 Context Matching - MISSING [19] |
| 1101 | RL3.7 Incremental Matches - MISSING |
| 1102 | ( RL3.8 Unicode Set Sharing ) |
| 1103 | RL3.9 Possible Match Sets - MISSING |
| 1104 | RL3.10 Folded Matching - MISSING [20] |
| 1105 | RL3.11 Submatchers - MISSING |
| 1106 | |
| 1107 | [17] see UAX#10 "Unicode Collation Algorithms" |
| 1108 | [18] have Unicode::Collate but not integrated to regexes |
| 1109 | [19] have (?<=x) and (?=x), but look-aheads or look-behinds |
| 1110 | should see outside of the target substring |
| 1111 | [20] need insensitive matching for linguistic features other |
| 1112 | than case; for example, hiragana to katakana, wide and |
| 1113 | narrow, simplified Han to traditional Han (see UTR#30 |
| 1114 | "Character Foldings") |
| 1115 | |
| 1116 | =back |
| 1117 | |
| 1118 | =head2 Unicode Encodings |
| 1119 | |
| 1120 | Unicode characters are assigned to I<code points>, which are abstract |
| 1121 | numbers. To use these numbers, various encodings are needed. |
| 1122 | |
| 1123 | =over 4 |
| 1124 | |
| 1125 | =item * |
| 1126 | |
| 1127 | UTF-8 |
| 1128 | |
| 1129 | UTF-8 is a variable-length (1 to 4 bytes), byte-order independent |
| 1130 | encoding. For ASCII (and we really do mean 7-bit ASCII, not another |
| 1131 | 8-bit encoding), UTF-8 is transparent. |
| 1132 | |
| 1133 | The following table is from Unicode 3.2. |
| 1134 | |
| 1135 | Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte |
| 1136 | |
| 1137 | U+0000..U+007F 00..7F |
| 1138 | U+0080..U+07FF * C2..DF 80..BF |
| 1139 | U+0800..U+0FFF E0 * A0..BF 80..BF |
| 1140 | U+1000..U+CFFF E1..EC 80..BF 80..BF |
| 1141 | U+D000..U+D7FF ED 80..9F 80..BF |
| 1142 | U+D800..U+DFFF +++++ utf16 surrogates, not legal utf8 +++++ |
| 1143 | U+E000..U+FFFF EE..EF 80..BF 80..BF |
| 1144 | U+10000..U+3FFFF F0 * 90..BF 80..BF 80..BF |
| 1145 | U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF |
| 1146 | U+100000..U+10FFFF F4 80..8F 80..BF 80..BF |
| 1147 | |
| 1148 | Note the gaps marked by "*" before several of the byte entries above. These are |
| 1149 | caused by legal UTF-8 avoiding non-shortest encodings: it is technically |
| 1150 | possible to UTF-8-encode a single code point in different ways, but that is |
| 1151 | explicitly forbidden, and the shortest possible encoding should always be used |
| 1152 | (and that is what Perl does). |
| 1153 | |
| 1154 | Another way to look at it is via bits: |
| 1155 | |
| 1156 | Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte |
| 1157 | |
| 1158 | 0aaaaaaa 0aaaaaaa |
| 1159 | 00000bbbbbaaaaaa 110bbbbb 10aaaaaa |
| 1160 | ccccbbbbbbaaaaaa 1110cccc 10bbbbbb 10aaaaaa |
| 1161 | 00000dddccccccbbbbbbaaaaaa 11110ddd 10cccccc 10bbbbbb 10aaaaaa |
| 1162 | |
| 1163 | As you can see, the continuation bytes all begin with "10", and the |
| 1164 | leading bits of the start byte tell how many bytes there are in the |
| 1165 | encoded character. |
| 1166 | |
| 1167 | The original UTF-8 specification allowed up to 6 bytes, to allow |
| 1168 | encoding of numbers up to 0x7FFF_FFFF. Perl continues to allow those, |
| 1169 | and has extended that up to 13 bytes to encode code points up to what |
| 1170 | can fit in a 64-bit word. However, Perl will warn if you output any of |
| 1171 | these as being non-portable; and under strict UTF-8 input protocols, |
| 1172 | they are forbidden. |
| 1173 | |
| 1174 | The Unicode non-character code points are also disallowed in UTF-8 in |
| 1175 | "open interchange". See L</Non-character code points>. |
| 1176 | |
| 1177 | =item * |
| 1178 | |
| 1179 | UTF-EBCDIC |
| 1180 | |
| 1181 | Like UTF-8 but EBCDIC-safe, in the way that UTF-8 is ASCII-safe. |
| 1182 | |
| 1183 | =item * |
| 1184 | |
| 1185 | UTF-16, UTF-16BE, UTF-16LE, Surrogates, and BOMs (Byte Order Marks) |
| 1186 | |
| 1187 | The followings items are mostly for reference and general Unicode |
| 1188 | knowledge, Perl doesn't use these constructs internally. |
| 1189 | |
| 1190 | Like UTF-8, UTF-16 is a variable-width encoding, but where |
| 1191 | UTF-8 uses 8-bit code units, UTF-16 uses 16-bit code units. |
| 1192 | All code points occupy either 2 or 4 bytes in UTF-16: code points |
| 1193 | C<U+0000..U+FFFF> are stored in a single 16-bit unit, and code |
| 1194 | points C<U+10000..U+10FFFF> in two 16-bit units. The latter case is |
| 1195 | using I<surrogates>, the first 16-bit unit being the I<high |
| 1196 | surrogate>, and the second being the I<low surrogate>. |
| 1197 | |
| 1198 | Surrogates are code points set aside to encode the C<U+10000..U+10FFFF> |
| 1199 | range of Unicode code points in pairs of 16-bit units. The I<high |
| 1200 | surrogates> are the range C<U+D800..U+DBFF> and the I<low surrogates> |
| 1201 | are the range C<U+DC00..U+DFFF>. The surrogate encoding is |
| 1202 | |
| 1203 | $hi = ($uni - 0x10000) / 0x400 + 0xD800; |
| 1204 | $lo = ($uni - 0x10000) % 0x400 + 0xDC00; |
| 1205 | |
| 1206 | and the decoding is |
| 1207 | |
| 1208 | $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00); |
| 1209 | |
| 1210 | Because of the 16-bitness, UTF-16 is byte-order dependent. UTF-16 |
| 1211 | itself can be used for in-memory computations, but if storage or |
| 1212 | transfer is required either UTF-16BE (big-endian) or UTF-16LE |
| 1213 | (little-endian) encodings must be chosen. |
| 1214 | |
| 1215 | This introduces another problem: what if you just know that your data |
| 1216 | is UTF-16, but you don't know which endianness? Byte Order Marks, or |
| 1217 | BOMs, are a solution to this. A special character has been reserved |
| 1218 | in Unicode to function as a byte order marker: the character with the |
| 1219 | code point C<U+FEFF> is the BOM. |
| 1220 | |
| 1221 | The trick is that if you read a BOM, you will know the byte order, |
| 1222 | since if it was written on a big-endian platform, you will read the |
| 1223 | bytes C<0xFE 0xFF>, but if it was written on a little-endian platform, |
| 1224 | you will read the bytes C<0xFF 0xFE>. (And if the originating platform |
| 1225 | was writing in UTF-8, you will read the bytes C<0xEF 0xBB 0xBF>.) |
| 1226 | |
| 1227 | The way this trick works is that the character with the code point |
| 1228 | C<U+FFFE> is not supposed to be in input streams, so the |
| 1229 | sequence of bytes C<0xFF 0xFE> is unambiguously "BOM, represented in |
| 1230 | little-endian format" and cannot be C<U+FFFE>, represented in big-endian |
| 1231 | format". |
| 1232 | |
| 1233 | Surrogates have no meaning in Unicode outside their use in pairs to |
| 1234 | represent other code points. However, Perl allows them to be |
| 1235 | represented individually internally, for example by saying |
| 1236 | C<chr(0xD801)>, so that all code points, not just those valid for open |
| 1237 | interchange, are |
| 1238 | representable. Unicode does define semantics for them, such as their |
| 1239 | General Category is "Cs". But because their use is somewhat dangerous, |
| 1240 | Perl will warn (using the warning category "surrogate", which is a |
| 1241 | sub-category of "utf8") if an attempt is made |
| 1242 | to do things like take the lower case of one, or match |
| 1243 | case-insensitively, or to output them. (But don't try this on Perls |
| 1244 | before 5.14.) |
| 1245 | |
| 1246 | =item * |
| 1247 | |
| 1248 | UTF-32, UTF-32BE, UTF-32LE |
| 1249 | |
| 1250 | The UTF-32 family is pretty much like the UTF-16 family, expect that |
| 1251 | the units are 32-bit, and therefore the surrogate scheme is not |
| 1252 | needed. UTF-32 is a fixed-width encoding. The BOM signatures are |
| 1253 | C<0x00 0x00 0xFE 0xFF> for BE and C<0xFF 0xFE 0x00 0x00> for LE. |
| 1254 | |
| 1255 | =item * |
| 1256 | |
| 1257 | UCS-2, UCS-4 |
| 1258 | |
| 1259 | Legacy, fixed-width encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit |
| 1260 | encoding. Unlike UTF-16, UCS-2 is not extensible beyond C<U+FFFF>, |
| 1261 | because it does not use surrogates. UCS-4 is a 32-bit encoding, |
| 1262 | functionally identical to UTF-32 (the difference being that |
| 1263 | UCS-4 forbids neither surrogates nor code points larger than 0x10_FFFF). |
| 1264 | |
| 1265 | =item * |
| 1266 | |
| 1267 | UTF-7 |
| 1268 | |
| 1269 | A seven-bit safe (non-eight-bit) encoding, which is useful if the |
| 1270 | transport or storage is not eight-bit safe. Defined by RFC 2152. |
| 1271 | |
| 1272 | =back |
| 1273 | |
| 1274 | =head2 Non-character code points |
| 1275 | |
| 1276 | 66 code points are set aside in Unicode as "non-character code points". |
| 1277 | These all have the Unassigned (Cn) General Category, and they never will |
| 1278 | be assigned. These are never supposed to be in legal Unicode input |
| 1279 | streams, so that code can use them as sentinels that can be mixed in |
| 1280 | with character data, and they always will be distinguishable from that data. |
| 1281 | To keep them out of Perl input streams, strict UTF-8 should be |
| 1282 | specified, such as by using the layer C<:encoding('UTF-8')>. The |
| 1283 | non-character code points are the 32 between U+FDD0 and U+FDEF, and the |
| 1284 | 34 code points U+FFFE, U+FFFF, U+1FFFE, U+1FFFF, ... U+10FFFE, U+10FFFF. |
| 1285 | Some people are under the mistaken impression that these are "illegal", |
| 1286 | but that is not true. An application or cooperating set of applications |
| 1287 | can legally use them at will internally; but these code points are |
| 1288 | "illegal for open interchange". Therefore, Perl will not accept these |
| 1289 | from input streams unless lax rules are being used, and will warn |
| 1290 | (using the warning category "nonchar", which is a sub-category of "utf8") if |
| 1291 | an attempt is made to output them. |
| 1292 | |
| 1293 | =head2 Beyond Unicode code points |
| 1294 | |
| 1295 | The maximum Unicode code point is U+10FFFF. But Perl accepts code |
| 1296 | points up to the maximum permissible unsigned number available on the |
| 1297 | platform. However, Perl will not accept these from input streams unless |
| 1298 | lax rules are being used, and will warn (using the warning category |
| 1299 | "non_unicode", which is a sub-category of "utf8") if an attempt is made to |
| 1300 | operate on or output them. For example, C<uc(0x11_0000)> will generate |
| 1301 | this warning, returning the input parameter as its result, as the upper |
| 1302 | case of every non-Unicode code point is the code point itself. |
| 1303 | |
| 1304 | =head2 Security Implications of Unicode |
| 1305 | |
| 1306 | Read L<Unicode Security Considerations|http://www.unicode.org/reports/tr36>. |
| 1307 | Also, note the following: |
| 1308 | |
| 1309 | =over 4 |
| 1310 | |
| 1311 | =item * |
| 1312 | |
| 1313 | Malformed UTF-8 |
| 1314 | |
| 1315 | Unfortunately, the original specification of UTF-8 leaves some room for |
| 1316 | interpretation of how many bytes of encoded output one should generate |
| 1317 | from one input Unicode character. Strictly speaking, the shortest |
| 1318 | possible sequence of UTF-8 bytes should be generated, |
| 1319 | because otherwise there is potential for an input buffer overflow at |
| 1320 | the receiving end of a UTF-8 connection. Perl always generates the |
| 1321 | shortest length UTF-8, and with warnings on, Perl will warn about |
| 1322 | non-shortest length UTF-8 along with other malformations, such as the |
| 1323 | surrogates, which are not Unicode code points valid for interchange. |
| 1324 | |
| 1325 | =item * |
| 1326 | |
| 1327 | Regular expression pattern matching may surprise you if you're not |
| 1328 | accustomed to Unicode. Starting in Perl 5.14, several pattern |
| 1329 | modifiers are available to control this, called the character set |
| 1330 | modifiers. Details are given in L<perlre/Character set modifiers>. |
| 1331 | |
| 1332 | =back |
| 1333 | |
| 1334 | As discussed elsewhere, Perl has one foot (two hooves?) planted in |
| 1335 | each of two worlds: the old world of bytes and the new world of |
| 1336 | characters, upgrading from bytes to characters when necessary. |
| 1337 | If your legacy code does not explicitly use Unicode, no automatic |
| 1338 | switch-over to characters should happen. Characters shouldn't get |
| 1339 | downgraded to bytes, either. It is possible to accidentally mix bytes |
| 1340 | and characters, however (see L<perluniintro>), in which case C<\w> in |
| 1341 | regular expressions might start behaving differently (unless the C</a> |
| 1342 | modifier is in effect). Review your code. Use warnings and the C<strict> pragma. |
| 1343 | |
| 1344 | =head2 Unicode in Perl on EBCDIC |
| 1345 | |
| 1346 | The way Unicode is handled on EBCDIC platforms is still |
| 1347 | experimental. On such platforms, references to UTF-8 encoding in this |
| 1348 | document and elsewhere should be read as meaning the UTF-EBCDIC |
| 1349 | specified in Unicode Technical Report 16, unless ASCII vs. EBCDIC issues |
| 1350 | are specifically discussed. There is no C<utfebcdic> pragma or |
| 1351 | ":utfebcdic" layer; rather, "utf8" and ":utf8" are reused to mean |
| 1352 | the platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic> |
| 1353 | for more discussion of the issues. |
| 1354 | |
| 1355 | =head2 Locales |
| 1356 | |
| 1357 | See L<perllocale/Unicode and UTF-8> |
| 1358 | |
| 1359 | =head2 When Unicode Does Not Happen |
| 1360 | |
| 1361 | While Perl does have extensive ways to input and output in Unicode, |
| 1362 | and a few other "entry points" like the @ARGV array (which can sometimes be |
| 1363 | interpreted as UTF-8), there are still many places where Unicode |
| 1364 | (in some encoding or another) could be given as arguments or received as |
| 1365 | results, or both, but it is not. |
| 1366 | |
| 1367 | The following are such interfaces. Also, see L</The "Unicode Bug">. |
| 1368 | For all of these interfaces Perl |
| 1369 | currently (as of v5.16.0) simply assumes byte strings both as arguments |
| 1370 | and results, or UTF-8 strings if the (problematic) C<encoding> pragma has been used. |
| 1371 | |
| 1372 | One reason that Perl does not attempt to resolve the role of Unicode in |
| 1373 | these situations is that the answers are highly dependent on the operating |
| 1374 | system and the file system(s). For example, whether filenames can be |
| 1375 | in Unicode and in exactly what kind of encoding, is not exactly a |
| 1376 | portable concept. Similarly for C<qx> and C<system>: how well will the |
| 1377 | "command-line interface" (and which of them?) handle Unicode? |
| 1378 | |
| 1379 | =over 4 |
| 1380 | |
| 1381 | =item * |
| 1382 | |
| 1383 | chdir, chmod, chown, chroot, exec, link, lstat, mkdir, |
| 1384 | rename, rmdir, stat, symlink, truncate, unlink, utime, -X |
| 1385 | |
| 1386 | =item * |
| 1387 | |
| 1388 | %ENV |
| 1389 | |
| 1390 | =item * |
| 1391 | |
| 1392 | glob (aka the <*>) |
| 1393 | |
| 1394 | =item * |
| 1395 | |
| 1396 | open, opendir, sysopen |
| 1397 | |
| 1398 | =item * |
| 1399 | |
| 1400 | qx (aka the backtick operator), system |
| 1401 | |
| 1402 | =item * |
| 1403 | |
| 1404 | readdir, readlink |
| 1405 | |
| 1406 | =back |
| 1407 | |
| 1408 | =head2 The "Unicode Bug" |
| 1409 | |
| 1410 | The term, "Unicode bug" has been applied to an inconsistency |
| 1411 | on ASCII platforms with the |
| 1412 | Unicode code points in the Latin-1 Supplement block, that |
| 1413 | is, between 128 and 255. Without a locale specified, unlike all other |
| 1414 | characters or code points, these characters have very different semantics in |
| 1415 | byte semantics versus character semantics, unless |
| 1416 | C<use feature 'unicode_strings'> is specified, directly or indirectly. |
| 1417 | (It is indirectly specified by a C<use v5.12> or higher.) |
| 1418 | |
| 1419 | In character semantics these upper-Latin1 characters are interpreted as |
| 1420 | Unicode code points, which means |
| 1421 | they have the same semantics as Latin-1 (ISO-8859-1). |
| 1422 | |
| 1423 | In byte semantics (without C<unicode_strings>), they are considered to |
| 1424 | be unassigned characters, meaning that the only semantics they have is |
| 1425 | their ordinal numbers, and that they are |
| 1426 | not members of various character classes. None are considered to match C<\w> |
| 1427 | for example, but all match C<\W>. |
| 1428 | |
| 1429 | Perl 5.12.0 added C<unicode_strings> to force character semantics on |
| 1430 | these code points in some circumstances, which fixed portions of the |
| 1431 | bug; Perl 5.14.0 fixed almost all of it; and Perl 5.16.0 fixed the |
| 1432 | remainder (so far as we know, anyway). The lesson here is to enable |
| 1433 | C<unicode_strings> to avoid the headaches described below. |
| 1434 | |
| 1435 | The old, problematic behavior affects these areas: |
| 1436 | |
| 1437 | =over 4 |
| 1438 | |
| 1439 | =item * |
| 1440 | |
| 1441 | Changing the case of a scalar, that is, using C<uc()>, C<ucfirst()>, C<lc()>, |
| 1442 | and C<lcfirst()>, or C<\L>, C<\U>, C<\u> and C<\l> in double-quotish |
| 1443 | contexts, such as regular expression substitutions. |
| 1444 | Under C<unicode_strings> starting in Perl 5.12.0, character semantics are |
| 1445 | generally used. See L<perlfunc/lc> for details on how this works |
| 1446 | in combination with various other pragmas. |
| 1447 | |
| 1448 | =item * |
| 1449 | |
| 1450 | Using caseless (C</i>) regular expression matching. |
| 1451 | Starting in Perl 5.14.0, regular expressions compiled within |
| 1452 | the scope of C<unicode_strings> use character semantics |
| 1453 | even when executed or compiled into larger |
| 1454 | regular expressions outside the scope. |
| 1455 | |
| 1456 | =item * |
| 1457 | |
| 1458 | Matching any of several properties in regular expressions, namely C<\b>, |
| 1459 | C<\B>, C<\s>, C<\S>, C<\w>, C<\W>, and all the Posix character classes |
| 1460 | I<except> C<[[:ascii:]]>. |
| 1461 | Starting in Perl 5.14.0, regular expressions compiled within |
| 1462 | the scope of C<unicode_strings> use character semantics |
| 1463 | even when executed or compiled into larger |
| 1464 | regular expressions outside the scope. |
| 1465 | |
| 1466 | =item * |
| 1467 | |
| 1468 | In C<quotemeta> or its inline equivalent C<\Q>, no code points above 127 |
| 1469 | are quoted in UTF-8 encoded strings, but in byte encoded strings, code |
| 1470 | points between 128-255 are always quoted. |
| 1471 | Starting in Perl 5.16.0, consistent quoting rules are used within the |
| 1472 | scope of C<unicode_strings>, as described in L<perlfunc/quotemeta>. |
| 1473 | |
| 1474 | =back |
| 1475 | |
| 1476 | This behavior can lead to unexpected results in which a string's semantics |
| 1477 | suddenly change if a code point above 255 is appended to or removed from it, |
| 1478 | which changes the string's semantics from byte to character or vice versa. As |
| 1479 | an example, consider the following program and its output: |
| 1480 | |
| 1481 | $ perl -le' |
| 1482 | no feature 'unicode_strings'; |
| 1483 | $s1 = "\xC2"; |
| 1484 | $s2 = "\x{2660}"; |
| 1485 | for ($s1, $s2, $s1.$s2) { |
| 1486 | print /\w/ || 0; |
| 1487 | } |
| 1488 | ' |
| 1489 | 0 |
| 1490 | 0 |
| 1491 | 1 |
| 1492 | |
| 1493 | If there's no C<\w> in C<s1> or in C<s2>, why does their concatenation have one? |
| 1494 | |
| 1495 | This anomaly stems from Perl's attempt to not disturb older programs that |
| 1496 | didn't use Unicode, and hence had no semantics for characters outside of the |
| 1497 | ASCII range (except in a locale), along with Perl's desire to add Unicode |
| 1498 | support seamlessly. The result wasn't seamless: these characters were |
| 1499 | orphaned. |
| 1500 | |
| 1501 | For Perls earlier than those described above, or when a string is passed |
| 1502 | to a function outside the subpragma's scope, a workaround is to always |
| 1503 | call C<utf8::upgrade($string)>, |
| 1504 | or to use the standard module L<Encode>. Also, a scalar that has any characters |
| 1505 | whose ordinal is 0x100 or above, or which were specified using either of the |
| 1506 | C<\N{...}> notations, will automatically have character semantics. |
| 1507 | |
| 1508 | =head2 Forcing Unicode in Perl (Or Unforcing Unicode in Perl) |
| 1509 | |
| 1510 | Sometimes (see L</"When Unicode Does Not Happen"> or L</The "Unicode Bug">) |
| 1511 | there are situations where you simply need to force a byte |
| 1512 | string into UTF-8, or vice versa. The low-level calls |
| 1513 | utf8::upgrade($bytestring) and utf8::downgrade($utf8string[, FAIL_OK]) are |
| 1514 | the answers. |
| 1515 | |
| 1516 | Note that utf8::downgrade() can fail if the string contains characters |
| 1517 | that don't fit into a byte. |
| 1518 | |
| 1519 | Calling either function on a string that already is in the desired state is a |
| 1520 | no-op. |
| 1521 | |
| 1522 | =head2 Using Unicode in XS |
| 1523 | |
| 1524 | If you want to handle Perl Unicode in XS extensions, you may find the |
| 1525 | following C APIs useful. See also L<perlguts/"Unicode Support"> for an |
| 1526 | explanation about Unicode at the XS level, and L<perlapi> for the API |
| 1527 | details. |
| 1528 | |
| 1529 | =over 4 |
| 1530 | |
| 1531 | =item * |
| 1532 | |
| 1533 | C<DO_UTF8(sv)> returns true if the C<UTF8> flag is on and the bytes |
| 1534 | pragma is not in effect. C<SvUTF8(sv)> returns true if the C<UTF8> |
| 1535 | flag is on; the bytes pragma is ignored. The C<UTF8> flag being on |
| 1536 | does B<not> mean that there are any characters of code points greater |
| 1537 | than 255 (or 127) in the scalar or that there are even any characters |
| 1538 | in the scalar. What the C<UTF8> flag means is that the sequence of |
| 1539 | octets in the representation of the scalar is the sequence of UTF-8 |
| 1540 | encoded code points of the characters of a string. The C<UTF8> flag |
| 1541 | being off means that each octet in this representation encodes a |
| 1542 | single character with code point 0..255 within the string. Perl's |
| 1543 | Unicode model is not to use UTF-8 until it is absolutely necessary. |
| 1544 | |
| 1545 | =item * |
| 1546 | |
| 1547 | C<uvchr_to_utf8(buf, chr)> writes a Unicode character code point into |
| 1548 | a buffer encoding the code point as UTF-8, and returns a pointer |
| 1549 | pointing after the UTF-8 bytes. It works appropriately on EBCDIC machines. |
| 1550 | |
| 1551 | =item * |
| 1552 | |
| 1553 | C<utf8_to_uvchr_buf(buf, bufend, lenp)> reads UTF-8 encoded bytes from a |
| 1554 | buffer and |
| 1555 | returns the Unicode character code point and, optionally, the length of |
| 1556 | the UTF-8 byte sequence. It works appropriately on EBCDIC machines. |
| 1557 | |
| 1558 | =item * |
| 1559 | |
| 1560 | C<utf8_length(start, end)> returns the length of the UTF-8 encoded buffer |
| 1561 | in characters. C<sv_len_utf8(sv)> returns the length of the UTF-8 encoded |
| 1562 | scalar. |
| 1563 | |
| 1564 | =item * |
| 1565 | |
| 1566 | C<sv_utf8_upgrade(sv)> converts the string of the scalar to its UTF-8 |
| 1567 | encoded form. C<sv_utf8_downgrade(sv)> does the opposite, if |
| 1568 | possible. C<sv_utf8_encode(sv)> is like sv_utf8_upgrade except that |
| 1569 | it does not set the C<UTF8> flag. C<sv_utf8_decode()> does the |
| 1570 | opposite of C<sv_utf8_encode()>. Note that none of these are to be |
| 1571 | used as general-purpose encoding or decoding interfaces: C<use Encode> |
| 1572 | for that. C<sv_utf8_upgrade()> is affected by the encoding pragma |
| 1573 | but C<sv_utf8_downgrade()> is not (since the encoding pragma is |
| 1574 | designed to be a one-way street). |
| 1575 | |
| 1576 | =item * |
| 1577 | |
| 1578 | C<is_utf8_string(buf, len)> returns true if C<len> bytes of the buffer |
| 1579 | are valid UTF-8. |
| 1580 | |
| 1581 | =item * |
| 1582 | |
| 1583 | C<is_utf8_char_buf(buf, buf_end)> returns true if the pointer points to |
| 1584 | a valid UTF-8 character. |
| 1585 | |
| 1586 | =item * |
| 1587 | |
| 1588 | C<UTF8SKIP(buf)> will return the number of bytes in the UTF-8 encoded |
| 1589 | character in the buffer. C<UNISKIP(chr)> will return the number of bytes |
| 1590 | required to UTF-8-encode the Unicode character code point. C<UTF8SKIP()> |
| 1591 | is useful for example for iterating over the characters of a UTF-8 |
| 1592 | encoded buffer; C<UNISKIP()> is useful, for example, in computing |
| 1593 | the size required for a UTF-8 encoded buffer. |
| 1594 | |
| 1595 | =item * |
| 1596 | |
| 1597 | C<utf8_distance(a, b)> will tell the distance in characters between the |
| 1598 | two pointers pointing to the same UTF-8 encoded buffer. |
| 1599 | |
| 1600 | =item * |
| 1601 | |
| 1602 | C<utf8_hop(s, off)> will return a pointer to a UTF-8 encoded buffer |
| 1603 | that is C<off> (positive or negative) Unicode characters displaced |
| 1604 | from the UTF-8 buffer C<s>. Be careful not to overstep the buffer: |
| 1605 | C<utf8_hop()> will merrily run off the end or the beginning of the |
| 1606 | buffer if told to do so. |
| 1607 | |
| 1608 | =item * |
| 1609 | |
| 1610 | C<pv_uni_display(dsv, spv, len, pvlim, flags)> and |
| 1611 | C<sv_uni_display(dsv, ssv, pvlim, flags)> are useful for debugging the |
| 1612 | output of Unicode strings and scalars. By default they are useful |
| 1613 | only for debugging--they display B<all> characters as hexadecimal code |
| 1614 | points--but with the flags C<UNI_DISPLAY_ISPRINT>, |
| 1615 | C<UNI_DISPLAY_BACKSLASH>, and C<UNI_DISPLAY_QQ> you can make the |
| 1616 | output more readable. |
| 1617 | |
| 1618 | =item * |
| 1619 | |
| 1620 | C<foldEQ_utf8(s1, pe1, l1, u1, s2, pe2, l2, u2)> can be used to |
| 1621 | compare two strings case-insensitively in Unicode. For case-sensitive |
| 1622 | comparisons you can just use C<memEQ()> and C<memNE()> as usual, except |
| 1623 | if one string is in utf8 and the other isn't. |
| 1624 | |
| 1625 | =back |
| 1626 | |
| 1627 | For more information, see L<perlapi>, and F<utf8.c> and F<utf8.h> |
| 1628 | in the Perl source code distribution. |
| 1629 | |
| 1630 | =head2 Hacking Perl to work on earlier Unicode versions (for very serious hackers only) |
| 1631 | |
| 1632 | Perl by default comes with the latest supported Unicode version built in, but |
| 1633 | you can change to use any earlier one. |
| 1634 | |
| 1635 | Download the files in the desired version of Unicode from the Unicode web |
| 1636 | site L<http://www.unicode.org>). These should replace the existing files in |
| 1637 | F<lib/unicore> in the Perl source tree. Follow the instructions in |
| 1638 | F<README.perl> in that directory to change some of their names, and then build |
| 1639 | perl (see L<INSTALL>). |
| 1640 | |
| 1641 | =head1 BUGS |
| 1642 | |
| 1643 | =head2 Interaction with Locales |
| 1644 | |
| 1645 | See L<perllocale/Unicode and UTF-8> |
| 1646 | |
| 1647 | =head2 Problems with characters in the Latin-1 Supplement range |
| 1648 | |
| 1649 | See L</The "Unicode Bug"> |
| 1650 | |
| 1651 | =head2 Interaction with Extensions |
| 1652 | |
| 1653 | When Perl exchanges data with an extension, the extension should be |
| 1654 | able to understand the UTF8 flag and act accordingly. If the |
| 1655 | extension doesn't recognize that flag, it's likely that the extension |
| 1656 | will return incorrectly-flagged data. |
| 1657 | |
| 1658 | So if you're working with Unicode data, consult the documentation of |
| 1659 | every module you're using if there are any issues with Unicode data |
| 1660 | exchange. If the documentation does not talk about Unicode at all, |
| 1661 | suspect the worst and probably look at the source to learn how the |
| 1662 | module is implemented. Modules written completely in Perl shouldn't |
| 1663 | cause problems. Modules that directly or indirectly access code written |
| 1664 | in other programming languages are at risk. |
| 1665 | |
| 1666 | For affected functions, the simple strategy to avoid data corruption is |
| 1667 | to always make the encoding of the exchanged data explicit. Choose an |
| 1668 | encoding that you know the extension can handle. Convert arguments passed |
| 1669 | to the extensions to that encoding and convert results back from that |
| 1670 | encoding. Write wrapper functions that do the conversions for you, so |
| 1671 | you can later change the functions when the extension catches up. |
| 1672 | |
| 1673 | To provide an example, let's say the popular Foo::Bar::escape_html |
| 1674 | function doesn't deal with Unicode data yet. The wrapper function |
| 1675 | would convert the argument to raw UTF-8 and convert the result back to |
| 1676 | Perl's internal representation like so: |
| 1677 | |
| 1678 | sub my_escape_html ($) { |
| 1679 | my($what) = shift; |
| 1680 | return unless defined $what; |
| 1681 | Encode::decode_utf8(Foo::Bar::escape_html( |
| 1682 | Encode::encode_utf8($what))); |
| 1683 | } |
| 1684 | |
| 1685 | Sometimes, when the extension does not convert data but just stores |
| 1686 | and retrieves them, you will be able to use the otherwise |
| 1687 | dangerous Encode::_utf8_on() function. Let's say the popular |
| 1688 | C<Foo::Bar> extension, written in C, provides a C<param> method that |
| 1689 | lets you store and retrieve data according to these prototypes: |
| 1690 | |
| 1691 | $self->param($name, $value); # set a scalar |
| 1692 | $value = $self->param($name); # retrieve a scalar |
| 1693 | |
| 1694 | If it does not yet provide support for any encoding, one could write a |
| 1695 | derived class with such a C<param> method: |
| 1696 | |
| 1697 | sub param { |
| 1698 | my($self,$name,$value) = @_; |
| 1699 | utf8::upgrade($name); # make sure it is UTF-8 encoded |
| 1700 | if (defined $value) { |
| 1701 | utf8::upgrade($value); # make sure it is UTF-8 encoded |
| 1702 | return $self->SUPER::param($name,$value); |
| 1703 | } else { |
| 1704 | my $ret = $self->SUPER::param($name); |
| 1705 | Encode::_utf8_on($ret); # we know, it is UTF-8 encoded |
| 1706 | return $ret; |
| 1707 | } |
| 1708 | } |
| 1709 | |
| 1710 | Some extensions provide filters on data entry/exit points, such as |
| 1711 | DB_File::filter_store_key and family. Look out for such filters in |
| 1712 | the documentation of your extensions, they can make the transition to |
| 1713 | Unicode data much easier. |
| 1714 | |
| 1715 | =head2 Speed |
| 1716 | |
| 1717 | Some functions are slower when working on UTF-8 encoded strings than |
| 1718 | on byte encoded strings. All functions that need to hop over |
| 1719 | characters such as length(), substr() or index(), or matching regular |
| 1720 | expressions can work B<much> faster when the underlying data are |
| 1721 | byte-encoded. |
| 1722 | |
| 1723 | In Perl 5.8.0 the slowness was often quite spectacular; in Perl 5.8.1 |
| 1724 | a caching scheme was introduced which will hopefully make the slowness |
| 1725 | somewhat less spectacular, at least for some operations. In general, |
| 1726 | operations with UTF-8 encoded strings are still slower. As an example, |
| 1727 | the Unicode properties (character classes) like C<\p{Nd}> are known to |
| 1728 | be quite a bit slower (5-20 times) than their simpler counterparts |
| 1729 | like C<\d> (then again, there are hundreds of Unicode characters matching C<Nd> |
| 1730 | compared with the 10 ASCII characters matching C<d>). |
| 1731 | |
| 1732 | =head2 Problems on EBCDIC platforms |
| 1733 | |
| 1734 | There are several known problems with Perl on EBCDIC platforms. If you |
| 1735 | want to use Perl there, send email to perlbug@perl.org. |
| 1736 | |
| 1737 | In earlier versions, when byte and character data were concatenated, |
| 1738 | the new string was sometimes created by |
| 1739 | decoding the byte strings as I<ISO 8859-1 (Latin-1)>, even if the |
| 1740 | old Unicode string used EBCDIC. |
| 1741 | |
| 1742 | If you find any of these, please report them as bugs. |
| 1743 | |
| 1744 | =head2 Porting code from perl-5.6.X |
| 1745 | |
| 1746 | Perl 5.8 has a different Unicode model from 5.6. In 5.6 the programmer |
| 1747 | was required to use the C<utf8> pragma to declare that a given scope |
| 1748 | expected to deal with Unicode data and had to make sure that only |
| 1749 | Unicode data were reaching that scope. If you have code that is |
| 1750 | working with 5.6, you will need some of the following adjustments to |
| 1751 | your code. The examples are written such that the code will continue |
| 1752 | to work under 5.6, so you should be safe to try them out. |
| 1753 | |
| 1754 | =over 3 |
| 1755 | |
| 1756 | =item * |
| 1757 | |
| 1758 | A filehandle that should read or write UTF-8 |
| 1759 | |
| 1760 | if ($] > 5.008) { |
| 1761 | binmode $fh, ":encoding(utf8)"; |
| 1762 | } |
| 1763 | |
| 1764 | =item * |
| 1765 | |
| 1766 | A scalar that is going to be passed to some extension |
| 1767 | |
| 1768 | Be it Compress::Zlib, Apache::Request or any extension that has no |
| 1769 | mention of Unicode in the manpage, you need to make sure that the |
| 1770 | UTF8 flag is stripped off. Note that at the time of this writing |
| 1771 | (January 2012) the mentioned modules are not UTF-8-aware. Please |
| 1772 | check the documentation to verify if this is still true. |
| 1773 | |
| 1774 | if ($] > 5.008) { |
| 1775 | require Encode; |
| 1776 | $val = Encode::encode_utf8($val); # make octets |
| 1777 | } |
| 1778 | |
| 1779 | =item * |
| 1780 | |
| 1781 | A scalar we got back from an extension |
| 1782 | |
| 1783 | If you believe the scalar comes back as UTF-8, you will most likely |
| 1784 | want the UTF8 flag restored: |
| 1785 | |
| 1786 | if ($] > 5.008) { |
| 1787 | require Encode; |
| 1788 | $val = Encode::decode_utf8($val); |
| 1789 | } |
| 1790 | |
| 1791 | =item * |
| 1792 | |
| 1793 | Same thing, if you are really sure it is UTF-8 |
| 1794 | |
| 1795 | if ($] > 5.008) { |
| 1796 | require Encode; |
| 1797 | Encode::_utf8_on($val); |
| 1798 | } |
| 1799 | |
| 1800 | =item * |
| 1801 | |
| 1802 | A wrapper for fetchrow_array and fetchrow_hashref |
| 1803 | |
| 1804 | When the database contains only UTF-8, a wrapper function or method is |
| 1805 | a convenient way to replace all your fetchrow_array and |
| 1806 | fetchrow_hashref calls. A wrapper function will also make it easier to |
| 1807 | adapt to future enhancements in your database driver. Note that at the |
| 1808 | time of this writing (January 2012), the DBI has no standardized way |
| 1809 | to deal with UTF-8 data. Please check the documentation to verify if |
| 1810 | that is still true. |
| 1811 | |
| 1812 | sub fetchrow { |
| 1813 | # $what is one of fetchrow_{array,hashref} |
| 1814 | my($self, $sth, $what) = @_; |
| 1815 | if ($] < 5.008) { |
| 1816 | return $sth->$what; |
| 1817 | } else { |
| 1818 | require Encode; |
| 1819 | if (wantarray) { |
| 1820 | my @arr = $sth->$what; |
| 1821 | for (@arr) { |
| 1822 | defined && /[^\000-\177]/ && Encode::_utf8_on($_); |
| 1823 | } |
| 1824 | return @arr; |
| 1825 | } else { |
| 1826 | my $ret = $sth->$what; |
| 1827 | if (ref $ret) { |
| 1828 | for my $k (keys %$ret) { |
| 1829 | defined |
| 1830 | && /[^\000-\177]/ |
| 1831 | && Encode::_utf8_on($_) for $ret->{$k}; |
| 1832 | } |
| 1833 | return $ret; |
| 1834 | } else { |
| 1835 | defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret; |
| 1836 | return $ret; |
| 1837 | } |
| 1838 | } |
| 1839 | } |
| 1840 | } |
| 1841 | |
| 1842 | |
| 1843 | =item * |
| 1844 | |
| 1845 | A large scalar that you know can only contain ASCII |
| 1846 | |
| 1847 | Scalars that contain only ASCII and are marked as UTF-8 are sometimes |
| 1848 | a drag to your program. If you recognize such a situation, just remove |
| 1849 | the UTF8 flag: |
| 1850 | |
| 1851 | utf8::downgrade($val) if $] > 5.008; |
| 1852 | |
| 1853 | =back |
| 1854 | |
| 1855 | =head1 SEE ALSO |
| 1856 | |
| 1857 | L<perlunitut>, L<perluniintro>, L<perluniprops>, L<Encode>, L<open>, L<utf8>, L<bytes>, |
| 1858 | L<perlretut>, L<perlvar/"${^UNICODE}"> |
| 1859 | L<http://www.unicode.org/reports/tr44>). |
| 1860 | |
| 1861 | =cut |