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1 | =head1 NAME |
2 | ||
3 | perlunicode - Unicode support in Perl | |
4 | ||
5 | =head1 DESCRIPTION | |
6 | ||
0a1f2d14 | 7 | =head2 Important Caveats |
21bad921 | 8 | |
0a1f2d14 NIS |
9 | WARNING: While the implementation of Unicode support in Perl is now fairly |
10 | complete it is still evolving to some extent. | |
21bad921 | 11 | |
0a1f2d14 NIS |
12 | In particular the way Unicode is handled on EBCDIC platforms is still rather |
13 | experimental. On such a platform references to UTF-8 encoding in this | |
14 | document and elsewhere should be read as meaning UTF-EBCDIC as specified | |
15 | in Unicode Technical Report 16 unless ASCII vs EBCDIC issues are specifically | |
16 | discussed. There is no C<utfebcdic> pragma or ":utfebcdic" layer, rather | |
17 | "utf8" and ":utf8" are re-used to mean platform's "natural" 8-bit encoding | |
18 | of Unicode. See L<perlebcdic> for more discussion of the issues. | |
19 | ||
20 | The following areas are still under development. | |
21bad921 | 21 | |
13a2d996 | 22 | =over 4 |
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23 | |
24 | =item Input and Output Disciplines | |
25 | ||
0a1f2d14 NIS |
26 | A filehandle can be marked as containing perl's internal Unicode encoding |
27 | (UTF-8 or UTF-EBCDIC) by opening it with the ":utf8" layer. | |
28 | Other encodings can be converted to perl's encoding on input, or from | |
29 | perl's encoding on output by use of the ":encoding()" layer. | |
30 | There is not yet a clean way to mark the perl source itself as being | |
31 | in an particular encoding. | |
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32 | |
33 | =item Regular Expressions | |
34 | ||
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35 | The regular expression compiler does now attempt to produce |
36 | polymorphic opcodes. That is the pattern should now adapt to the data | |
37 | and automatically switch to the Unicode character scheme when presented | |
38 | with Unicode data, or a traditional byte scheme when presented with | |
39 | byte data. The implementation is still new and (particularly on | |
40 | EBCDIC platforms) may need further work. | |
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41 | |
42 | =item C<use utf8> still needed to enable a few features | |
43 | ||
44 | The C<utf8> pragma implements the tables used for Unicode support. These | |
45 | tables are automatically loaded on demand, so the C<utf8> pragma need not | |
46 | normally be used. | |
47 | ||
48 | However, as a compatibility measure, this pragma must be explicitly used | |
49 | to enable recognition of UTF-8 encoded literals and identifiers in the | |
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50 | source text on ASCII based machines or recognize UTF-EBCDIC encoded literals |
51 | and identifiers on EBCDIC based machines. | |
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52 | |
53 | =back | |
54 | ||
55 | =head2 Byte and Character semantics | |
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56 | |
57 | Beginning with version 5.6, Perl uses logically wide characters to | |
58 | represent strings internally. This internal representation of strings | |
b3419ed8 | 59 | uses either the UTF-8 or the UTF-EBCDIC encoding. |
393fec97 | 60 | |
21bad921 | 61 | In future, Perl-level operations can be expected to work with characters |
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62 | rather than bytes, in general. |
63 | ||
8cbd9a7a GS |
64 | However, as strictly an interim compatibility measure, Perl v5.6 aims to |
65 | provide a safe migration path from byte semantics to character semantics | |
66 | for programs. For operations where Perl can unambiguously decide that the | |
67 | input data is characters, Perl now switches to character semantics. | |
68 | For operations where this determination cannot be made without additional | |
69 | information from the user, Perl decides in favor of compatibility, and | |
70 | chooses to use byte semantics. | |
71 | ||
72 | This behavior preserves compatibility with earlier versions of Perl, | |
73 | which allowed byte semantics in Perl operations, but only as long as | |
74 | none of the program's inputs are marked as being as source of Unicode | |
75 | character data. Such data may come from filehandles, from calls to | |
76 | external programs, from information provided by the system (such as %ENV), | |
21bad921 | 77 | or from literals and constants in the source text. |
8cbd9a7a | 78 | |
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79 | If the C<-C> command line switch is used, (or the ${^WIDE_SYSTEM_CALLS} |
80 | global flag is set to C<1>), all system calls will use the | |
3969a896 | 81 | corresponding wide character APIs. This is currently only implemented |
e6739005 | 82 | on Windows since UNIXes lack API standard on this area. |
8cbd9a7a | 83 | |
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84 | Regardless of the above, the C<bytes> pragma can always be used to force |
85 | byte semantics in a particular lexical scope. See L<bytes>. | |
8cbd9a7a GS |
86 | |
87 | The C<utf8> pragma is primarily a compatibility device that enables | |
b3419ed8 | 88 | recognition of UTF-(8|EBCDIC) in literals encountered by the parser. It may also |
21bad921 | 89 | be used for enabling some of the more experimental Unicode support features. |
8cbd9a7a GS |
90 | Note that this pragma is only required until a future version of Perl |
91 | in which character semantics will become the default. This pragma may | |
92 | then become a no-op. See L<utf8>. | |
93 | ||
94 | Unless mentioned otherwise, Perl operators will use character semantics | |
95 | when they are dealing with Unicode data, and byte semantics otherwise. | |
96 | Thus, character semantics for these operations apply transparently; if | |
97 | the input data came from a Unicode source (for example, by adding a | |
98 | character encoding discipline to the filehandle whence it came, or a | |
99 | literal UTF-8 string constant in the program), character semantics | |
100 | apply; otherwise, byte semantics are in effect. To force byte semantics | |
8058d7ab | 101 | on Unicode data, the C<bytes> pragma should be used. |
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102 | |
103 | Under character semantics, many operations that formerly operated on | |
104 | bytes change to operating on characters. For ASCII data this makes | |
105 | no difference, because UTF-8 stores ASCII in single bytes, but for | |
21bad921 | 106 | any character greater than C<chr(127)>, the character may be stored in |
393fec97 | 107 | a sequence of two or more bytes, all of which have the high bit set. |
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108 | For C1 controls or Latin 1 characters on an EBCDIC platform the character |
109 | may be stored in a UTF-EBCDIC multi byte sequence. | |
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110 | But by and large, the user need not worry about this, because Perl |
111 | hides it from the user. A character in Perl is logically just a number | |
112 | ranging from 0 to 2**32 or so. Larger characters encode to longer | |
113 | sequences of bytes internally, but again, this is just an internal | |
114 | detail which is hidden at the Perl level. | |
115 | ||
8cbd9a7a | 116 | =head2 Effects of character semantics |
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117 | |
118 | Character semantics have the following effects: | |
119 | ||
120 | =over 4 | |
121 | ||
122 | =item * | |
123 | ||
124 | Strings and patterns may contain characters that have an ordinal value | |
21bad921 | 125 | larger than 255. |
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126 | |
127 | Presuming you use a Unicode editor to edit your program, such characters | |
b3419ed8 | 128 | will typically occur directly within the literal strings as UTF-(8|EBCDIC) |
393fec97 | 129 | characters, but you can also specify a particular character with an |
b3419ed8 | 130 | extension of the C<\x> notation. UTF-X characters are specified by |
393fec97 | 131 | putting the hexadecimal code within curlies after the C<\x>. For instance, |
4375e838 | 132 | a Unicode smiley face is C<\x{263A}>. |
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133 | |
134 | =item * | |
135 | ||
136 | Identifiers within the Perl script may contain Unicode alphanumeric | |
137 | characters, including ideographs. (You are currently on your own when | |
138 | it comes to using the canonical forms of characters--Perl doesn't (yet) | |
139 | attempt to canonicalize variable names for you.) | |
140 | ||
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141 | =item * |
142 | ||
143 | Regular expressions match characters instead of bytes. For instance, | |
144 | "." matches a character instead of a byte. (However, the C<\C> pattern | |
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145 | is provided to force a match a single byte ("C<char>" in C, hence |
146 | C<\C>).) | |
393fec97 | 147 | |
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148 | =item * |
149 | ||
150 | Character classes in regular expressions match characters instead of | |
151 | bytes, and match against the character properties specified in the | |
152 | Unicode properties database. So C<\w> can be used to match an ideograph, | |
153 | for instance. | |
154 | ||
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155 | =item * |
156 | ||
157 | Named Unicode properties and block ranges make be used as character | |
158 | classes via the new C<\p{}> (matches property) and C<\P{}> (doesn't | |
159 | match property) constructs. For instance, C<\p{Lu}> matches any | |
160 | character with the Unicode uppercase property, while C<\p{M}> matches | |
9fdf68be JH |
161 | any mark character. Single letter properties may omit the brackets, |
162 | so that can be written C<\pM> also. Many predefined character classes | |
163 | are available, such as C<\p{IsMirrored}> and C<\p{InTibetan}>. The | |
164 | names of the C<In> classes are the official Unicode block names but | |
165 | with all non-alphanumeric characters removed, for example the block | |
166 | name C<"Latin-1 Supplement"> becomes C<\p{InLatin1Supplement}>. | |
393fec97 | 167 | |
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168 | =item * |
169 | ||
170 | The special pattern C<\X> match matches any extended Unicode sequence | |
171 | (a "combining character sequence" in Standardese), where the first | |
172 | character is a base character and subsequent characters are mark | |
173 | characters that apply to the base character. It is equivalent to | |
174 | C<(?:\PM\pM*)>. | |
175 | ||
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176 | =item * |
177 | ||
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178 | The C<tr///> operator translates characters instead of bytes. Note |
179 | that the C<tr///CU> functionality has been removed, as the interface | |
180 | was a mistake. For similar functionality see pack('U0', ...) and | |
181 | pack('C0', ...). | |
393fec97 | 182 | |
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183 | =item * |
184 | ||
185 | Case translation operators use the Unicode case translation tables | |
186 | when provided character input. Note that C<uc()> translates to | |
187 | uppercase, while C<ucfirst> translates to titlecase (for languages | |
188 | that make the distinction). Naturally the corresponding backslash | |
189 | sequences have the same semantics. | |
190 | ||
191 | =item * | |
192 | ||
193 | Most operators that deal with positions or lengths in the string will | |
194 | automatically switch to using character positions, including C<chop()>, | |
195 | C<substr()>, C<pos()>, C<index()>, C<rindex()>, C<sprintf()>, | |
196 | C<write()>, and C<length()>. Operators that specifically don't switch | |
197 | include C<vec()>, C<pack()>, and C<unpack()>. Operators that really | |
198 | don't care include C<chomp()>, as well as any other operator that | |
199 | treats a string as a bucket of bits, such as C<sort()>, and the | |
200 | operators dealing with filenames. | |
201 | ||
202 | =item * | |
203 | ||
204 | The C<pack()>/C<unpack()> letters "C<c>" and "C<C>" do I<not> change, | |
205 | since they're often used for byte-oriented formats. (Again, think | |
206 | "C<char>" in the C language.) However, there is a new "C<U>" specifier | |
207 | that will convert between UTF-8 characters and integers. (It works | |
208 | outside of the utf8 pragma too.) | |
209 | ||
210 | =item * | |
211 | ||
212 | The C<chr()> and C<ord()> functions work on characters. This is like | |
213 | C<pack("U")> and C<unpack("U")>, not like C<pack("C")> and | |
214 | C<unpack("C")>. In fact, the latter are how you now emulate | |
215 | byte-oriented C<chr()> and C<ord()> under utf8. | |
216 | ||
217 | =item * | |
218 | ||
a1ca4561 YST |
219 | The bit string operators C<& | ^ ~> can operate on character data. |
220 | However, for backward compatibility reasons (bit string operations | |
221 | when the characters all are less than 256 in ordinal value) one cannot | |
222 | mix C<~> (the bit complement) and characters both less than 256 and | |
223 | equal or greater than 256. Most importantly, the DeMorgan's laws | |
224 | (C<~($x|$y) eq ~$x&~$y>, C<~($x&$y) eq ~$x|~$y>) won't hold. | |
225 | Another way to look at this is that the complement cannot return | |
226 | B<both> the 8-bit (byte) wide bit complement, and the full character | |
227 | wide bit complement. | |
228 | ||
229 | =item * | |
230 | ||
393fec97 GS |
231 | And finally, C<scalar reverse()> reverses by character rather than by byte. |
232 | ||
233 | =back | |
234 | ||
8cbd9a7a GS |
235 | =head2 Character encodings for input and output |
236 | ||
7221edc9 | 237 | See L<Encode>. |
8cbd9a7a | 238 | |
393fec97 GS |
239 | =head1 CAVEATS |
240 | ||
241 | As of yet, there is no method for automatically coercing input and | |
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242 | output to some encoding other than UTF-8 or UTF-EBCDIC. This is planned |
243 | in the near future, however. | |
393fec97 | 244 | |
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245 | Whether an arbitrary piece of data will be treated as "characters" or |
246 | "bytes" by internal operations cannot be divined at the current time. | |
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247 | |
248 | Use of locales with utf8 may lead to odd results. Currently there is | |
249 | some attempt to apply 8-bit locale info to characters in the range | |
250 | 0..255, but this is demonstrably incorrect for locales that use | |
251 | characters above that range (when mapped into Unicode). It will also | |
252 | tend to run slower. Avoidance of locales is strongly encouraged. | |
253 | ||
254 | =head1 SEE ALSO | |
255 | ||
8058d7ab | 256 | L<bytes>, L<utf8>, L<perlvar/"${^WIDE_SYSTEM_CALLS}"> |
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257 | |
258 | =cut |