Commit | Line | Data |
393fec97 |
1 | =head1 NAME |
2 | |
3 | perlunicode - Unicode support in Perl |
4 | |
5 | =head1 DESCRIPTION |
6 | |
0a1f2d14 |
7 | =head2 Important Caveats |
21bad921 |
8 | |
0a1f2d14 |
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 |
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 |
21bad921 |
23 | |
24 | =item Input and Output Disciplines |
25 | |
0a1f2d14 |
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. |
21bad921 |
32 | |
33 | =item Regular Expressions |
34 | |
e6739005 |
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. |
21bad921 |
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 |
50 | source text. |
51 | |
52 | =back |
53 | |
54 | =head2 Byte and Character semantics |
393fec97 |
55 | |
56 | Beginning with version 5.6, Perl uses logically wide characters to |
57 | represent strings internally. This internal representation of strings |
58 | uses the UTF-8 encoding. |
59 | |
21bad921 |
60 | In future, Perl-level operations can be expected to work with characters |
393fec97 |
61 | rather than bytes, in general. |
62 | |
8cbd9a7a |
63 | However, as strictly an interim compatibility measure, Perl v5.6 aims to |
64 | provide a safe migration path from byte semantics to character semantics |
65 | for programs. For operations where Perl can unambiguously decide that the |
66 | input data is characters, Perl now switches to character semantics. |
67 | For operations where this determination cannot be made without additional |
68 | information from the user, Perl decides in favor of compatibility, and |
69 | chooses to use byte semantics. |
70 | |
71 | This behavior preserves compatibility with earlier versions of Perl, |
72 | which allowed byte semantics in Perl operations, but only as long as |
73 | none of the program's inputs are marked as being as source of Unicode |
74 | character data. Such data may come from filehandles, from calls to |
75 | external programs, from information provided by the system (such as %ENV), |
21bad921 |
76 | or from literals and constants in the source text. |
8cbd9a7a |
77 | |
46487f74 |
78 | If the C<-C> command line switch is used, (or the ${^WIDE_SYSTEM_CALLS} |
79 | global flag is set to C<1>), all system calls will use the |
3969a896 |
80 | corresponding wide character APIs. This is currently only implemented |
e6739005 |
81 | on Windows since UNIXes lack API standard on this area. |
8cbd9a7a |
82 | |
8058d7ab |
83 | Regardless of the above, the C<bytes> pragma can always be used to force |
84 | byte semantics in a particular lexical scope. See L<bytes>. |
8cbd9a7a |
85 | |
86 | The C<utf8> pragma is primarily a compatibility device that enables |
21bad921 |
87 | recognition of UTF-8 in literals encountered by the parser. It may also |
88 | be used for enabling some of the more experimental Unicode support features. |
8cbd9a7a |
89 | Note that this pragma is only required until a future version of Perl |
90 | in which character semantics will become the default. This pragma may |
91 | then become a no-op. See L<utf8>. |
92 | |
93 | Unless mentioned otherwise, Perl operators will use character semantics |
94 | when they are dealing with Unicode data, and byte semantics otherwise. |
95 | Thus, character semantics for these operations apply transparently; if |
96 | the input data came from a Unicode source (for example, by adding a |
97 | character encoding discipline to the filehandle whence it came, or a |
98 | literal UTF-8 string constant in the program), character semantics |
99 | apply; otherwise, byte semantics are in effect. To force byte semantics |
8058d7ab |
100 | on Unicode data, the C<bytes> pragma should be used. |
393fec97 |
101 | |
102 | Under character semantics, many operations that formerly operated on |
103 | bytes change to operating on characters. For ASCII data this makes |
104 | no difference, because UTF-8 stores ASCII in single bytes, but for |
21bad921 |
105 | any character greater than C<chr(127)>, the character may be stored in |
393fec97 |
106 | a sequence of two or more bytes, all of which have the high bit set. |
107 | But by and large, the user need not worry about this, because Perl |
108 | hides it from the user. A character in Perl is logically just a number |
109 | ranging from 0 to 2**32 or so. Larger characters encode to longer |
110 | sequences of bytes internally, but again, this is just an internal |
111 | detail which is hidden at the Perl level. |
112 | |
8cbd9a7a |
113 | =head2 Effects of character semantics |
393fec97 |
114 | |
115 | Character semantics have the following effects: |
116 | |
117 | =over 4 |
118 | |
119 | =item * |
120 | |
121 | Strings and patterns may contain characters that have an ordinal value |
21bad921 |
122 | larger than 255. |
393fec97 |
123 | |
124 | Presuming you use a Unicode editor to edit your program, such characters |
125 | will typically occur directly within the literal strings as UTF-8 |
126 | characters, but you can also specify a particular character with an |
127 | extension of the C<\x> notation. UTF-8 characters are specified by |
128 | putting the hexadecimal code within curlies after the C<\x>. For instance, |
4375e838 |
129 | a Unicode smiley face is C<\x{263A}>. |
393fec97 |
130 | |
131 | =item * |
132 | |
133 | Identifiers within the Perl script may contain Unicode alphanumeric |
134 | characters, including ideographs. (You are currently on your own when |
135 | it comes to using the canonical forms of characters--Perl doesn't (yet) |
136 | attempt to canonicalize variable names for you.) |
137 | |
393fec97 |
138 | =item * |
139 | |
140 | Regular expressions match characters instead of bytes. For instance, |
141 | "." matches a character instead of a byte. (However, the C<\C> pattern |
945c54fd |
142 | is provided to force a match a single byte ("C<char>" in C, hence |
143 | C<\C>).) |
393fec97 |
144 | |
393fec97 |
145 | =item * |
146 | |
147 | Character classes in regular expressions match characters instead of |
148 | bytes, and match against the character properties specified in the |
149 | Unicode properties database. So C<\w> can be used to match an ideograph, |
150 | for instance. |
151 | |
393fec97 |
152 | =item * |
153 | |
154 | Named Unicode properties and block ranges make be used as character |
155 | classes via the new C<\p{}> (matches property) and C<\P{}> (doesn't |
156 | match property) constructs. For instance, C<\p{Lu}> matches any |
157 | character with the Unicode uppercase property, while C<\p{M}> matches |
158 | any mark character. Single letter properties may omit the brackets, so |
159 | that can be written C<\pM> also. Many predefined character classes are |
160 | available, such as C<\p{IsMirrored}> and C<\p{InTibetan}>. |
161 | |
393fec97 |
162 | =item * |
163 | |
164 | The special pattern C<\X> match matches any extended Unicode sequence |
165 | (a "combining character sequence" in Standardese), where the first |
166 | character is a base character and subsequent characters are mark |
167 | characters that apply to the base character. It is equivalent to |
168 | C<(?:\PM\pM*)>. |
169 | |
393fec97 |
170 | =item * |
171 | |
383e7cdd |
172 | The C<tr///> operator translates characters instead of bytes. Note |
173 | that the C<tr///CU> functionality has been removed, as the interface |
174 | was a mistake. For similar functionality see pack('U0', ...) and |
175 | pack('C0', ...). |
393fec97 |
176 | |
393fec97 |
177 | =item * |
178 | |
179 | Case translation operators use the Unicode case translation tables |
180 | when provided character input. Note that C<uc()> translates to |
181 | uppercase, while C<ucfirst> translates to titlecase (for languages |
182 | that make the distinction). Naturally the corresponding backslash |
183 | sequences have the same semantics. |
184 | |
185 | =item * |
186 | |
187 | Most operators that deal with positions or lengths in the string will |
188 | automatically switch to using character positions, including C<chop()>, |
189 | C<substr()>, C<pos()>, C<index()>, C<rindex()>, C<sprintf()>, |
190 | C<write()>, and C<length()>. Operators that specifically don't switch |
191 | include C<vec()>, C<pack()>, and C<unpack()>. Operators that really |
192 | don't care include C<chomp()>, as well as any other operator that |
193 | treats a string as a bucket of bits, such as C<sort()>, and the |
194 | operators dealing with filenames. |
195 | |
196 | =item * |
197 | |
198 | The C<pack()>/C<unpack()> letters "C<c>" and "C<C>" do I<not> change, |
199 | since they're often used for byte-oriented formats. (Again, think |
200 | "C<char>" in the C language.) However, there is a new "C<U>" specifier |
201 | that will convert between UTF-8 characters and integers. (It works |
202 | outside of the utf8 pragma too.) |
203 | |
204 | =item * |
205 | |
206 | The C<chr()> and C<ord()> functions work on characters. This is like |
207 | C<pack("U")> and C<unpack("U")>, not like C<pack("C")> and |
208 | C<unpack("C")>. In fact, the latter are how you now emulate |
209 | byte-oriented C<chr()> and C<ord()> under utf8. |
210 | |
211 | =item * |
212 | |
a1ca4561 |
213 | The bit string operators C<& | ^ ~> can operate on character data. |
214 | However, for backward compatibility reasons (bit string operations |
215 | when the characters all are less than 256 in ordinal value) one cannot |
216 | mix C<~> (the bit complement) and characters both less than 256 and |
217 | equal or greater than 256. Most importantly, the DeMorgan's laws |
218 | (C<~($x|$y) eq ~$x&~$y>, C<~($x&$y) eq ~$x|~$y>) won't hold. |
219 | Another way to look at this is that the complement cannot return |
220 | B<both> the 8-bit (byte) wide bit complement, and the full character |
221 | wide bit complement. |
222 | |
223 | =item * |
224 | |
393fec97 |
225 | And finally, C<scalar reverse()> reverses by character rather than by byte. |
226 | |
227 | =back |
228 | |
8cbd9a7a |
229 | =head2 Character encodings for input and output |
230 | |
945c54fd |
231 | [XXX: This feature is not yet implemented.] |
8cbd9a7a |
232 | |
393fec97 |
233 | =head1 CAVEATS |
234 | |
235 | As of yet, there is no method for automatically coercing input and |
236 | output to some encoding other than UTF-8. This is planned in the near |
237 | future, however. |
238 | |
8cbd9a7a |
239 | Whether an arbitrary piece of data will be treated as "characters" or |
240 | "bytes" by internal operations cannot be divined at the current time. |
393fec97 |
241 | |
242 | Use of locales with utf8 may lead to odd results. Currently there is |
243 | some attempt to apply 8-bit locale info to characters in the range |
244 | 0..255, but this is demonstrably incorrect for locales that use |
245 | characters above that range (when mapped into Unicode). It will also |
246 | tend to run slower. Avoidance of locales is strongly encouraged. |
247 | |
248 | =head1 SEE ALSO |
249 | |
8058d7ab |
250 | L<bytes>, L<utf8>, L<perlvar/"${^WIDE_SYSTEM_CALLS}"> |
393fec97 |
251 | |
252 | =cut |