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393fec97 GS |
1 | =head1 NAME |
2 | ||
3 | perlunicode - Unicode support in Perl | |
4 | ||
5 | =head1 DESCRIPTION | |
6 | ||
7 | WARNING: The implementation of Unicode support in Perl is incomplete. | |
8 | Expect sudden and unannounced changes! | |
9 | ||
10 | Beginning with version 5.6, Perl uses logically wide characters to | |
11 | represent strings internally. This internal representation of strings | |
12 | uses the UTF-8 encoding. | |
13 | ||
14 | In future, Perl-level operations will expect to work with characters | |
15 | rather than bytes, in general. | |
16 | ||
8cbd9a7a GS |
17 | However, as strictly an interim compatibility measure, Perl v5.6 aims to |
18 | provide a safe migration path from byte semantics to character semantics | |
19 | for programs. For operations where Perl can unambiguously decide that the | |
20 | input data is characters, Perl now switches to character semantics. | |
21 | For operations where this determination cannot be made without additional | |
22 | information from the user, Perl decides in favor of compatibility, and | |
23 | chooses to use byte semantics. | |
24 | ||
25 | This behavior preserves compatibility with earlier versions of Perl, | |
26 | which allowed byte semantics in Perl operations, but only as long as | |
27 | none of the program's inputs are marked as being as source of Unicode | |
28 | character data. Such data may come from filehandles, from calls to | |
29 | external programs, from information provided by the system (such as %ENV), | |
30 | or from literals and constants in the source text. Later, in | |
31 | L</Character encodings for input and output>, we'll see how such | |
32 | inputs may be marked as being Unicode character data sources. | |
33 | ||
46487f74 GS |
34 | If the C<-C> command line switch is used, (or the ${^WIDE_SYSTEM_CALLS} |
35 | global flag is set to C<1>), all system calls will use the | |
3969a896 | 36 | corresponding wide character APIs. This is currently only implemented |
46487f74 | 37 | on Windows. |
8cbd9a7a | 38 | |
8058d7ab GS |
39 | Regardless of the above, the C<bytes> pragma can always be used to force |
40 | byte semantics in a particular lexical scope. See L<bytes>. | |
8cbd9a7a GS |
41 | |
42 | The C<utf8> pragma is primarily a compatibility device that enables | |
43 | recognition of UTF-8 in literals encountered by the parser. It is also | |
44 | used for enabling some of the more experimental Unicode support features. | |
45 | Note that this pragma is only required until a future version of Perl | |
46 | in which character semantics will become the default. This pragma may | |
47 | then become a no-op. See L<utf8>. | |
48 | ||
49 | Unless mentioned otherwise, Perl operators will use character semantics | |
50 | when they are dealing with Unicode data, and byte semantics otherwise. | |
51 | Thus, character semantics for these operations apply transparently; if | |
52 | the input data came from a Unicode source (for example, by adding a | |
53 | character encoding discipline to the filehandle whence it came, or a | |
54 | literal UTF-8 string constant in the program), character semantics | |
55 | apply; otherwise, byte semantics are in effect. To force byte semantics | |
8058d7ab | 56 | on Unicode data, the C<bytes> pragma should be used. |
393fec97 GS |
57 | |
58 | Under character semantics, many operations that formerly operated on | |
59 | bytes change to operating on characters. For ASCII data this makes | |
60 | no difference, because UTF-8 stores ASCII in single bytes, but for | |
61 | any character greater than C<chr(127)>, the character is stored in | |
62 | a sequence of two or more bytes, all of which have the high bit set. | |
63 | But by and large, the user need not worry about this, because Perl | |
64 | hides it from the user. A character in Perl is logically just a number | |
65 | ranging from 0 to 2**32 or so. Larger characters encode to longer | |
66 | sequences of bytes internally, but again, this is just an internal | |
67 | detail which is hidden at the Perl level. | |
68 | ||
8cbd9a7a | 69 | =head2 Effects of character semantics |
393fec97 GS |
70 | |
71 | Character semantics have the following effects: | |
72 | ||
73 | =over 4 | |
74 | ||
75 | =item * | |
76 | ||
77 | Strings and patterns may contain characters that have an ordinal value | |
78 | larger than 255. In Perl v5.6, this is only enabled if the lexical | |
79 | scope has a C<use utf8> declaration (due to compatibility needs) but | |
80 | future versions may enable this by default. | |
81 | ||
82 | Presuming you use a Unicode editor to edit your program, such characters | |
83 | will typically occur directly within the literal strings as UTF-8 | |
84 | characters, but you can also specify a particular character with an | |
85 | extension of the C<\x> notation. UTF-8 characters are specified by | |
86 | putting the hexadecimal code within curlies after the C<\x>. For instance, | |
87 | a Unicode smiley face is C<\x{263A}>. A character in the Latin-1 range | |
88 | (128..255) should be written C<\x{ab}> rather than C<\xab>, since the | |
89 | former will turn into a two-byte UTF-8 code, while the latter will | |
90 | continue to be interpreted as generating a 8-bit byte rather than a | |
91 | character. In fact, if C<-w> is turned on, it will produce a warning | |
92 | that you might be generating invalid UTF-8. | |
93 | ||
94 | =item * | |
95 | ||
96 | Identifiers within the Perl script may contain Unicode alphanumeric | |
97 | characters, including ideographs. (You are currently on your own when | |
98 | it comes to using the canonical forms of characters--Perl doesn't (yet) | |
99 | attempt to canonicalize variable names for you.) | |
100 | ||
8cbd9a7a | 101 | This also needs C<use utf8> currently. [XXX: Why?!? High-bit chars were |
393fec97 | 102 | syntax errors when they occurred within identifiers in previous versions, |
8cbd9a7a | 103 | so this should probably be enabled by default.] |
393fec97 GS |
104 | |
105 | =item * | |
106 | ||
107 | Regular expressions match characters instead of bytes. For instance, | |
108 | "." matches a character instead of a byte. (However, the C<\C> pattern | |
109 | is provided to force a match a single byte ("C<char>" in C, hence | |
110 | C<\C>).) | |
111 | ||
112 | Unicode support in regular expressions needs C<use utf8> currently. | |
113 | [XXX: Because the SWASH routines need to be loaded. And the RE engine | |
8cbd9a7a GS |
114 | appears to need an overhaul to dynamically match Unicode anyway--the |
115 | current RE compiler creates different nodes with and without C<use utf8>.] | |
393fec97 GS |
116 | |
117 | =item * | |
118 | ||
119 | Character classes in regular expressions match characters instead of | |
120 | bytes, and match against the character properties specified in the | |
121 | Unicode properties database. So C<\w> can be used to match an ideograph, | |
122 | for instance. | |
123 | ||
124 | C<use utf8> is needed to enable this. See above. | |
125 | ||
126 | =item * | |
127 | ||
128 | Named Unicode properties and block ranges make be used as character | |
129 | classes via the new C<\p{}> (matches property) and C<\P{}> (doesn't | |
130 | match property) constructs. For instance, C<\p{Lu}> matches any | |
131 | character with the Unicode uppercase property, while C<\p{M}> matches | |
132 | any mark character. Single letter properties may omit the brackets, so | |
133 | that can be written C<\pM> also. Many predefined character classes are | |
134 | available, such as C<\p{IsMirrored}> and C<\p{InTibetan}>. | |
135 | ||
136 | C<use utf8> is needed to enable this. See above. | |
137 | ||
138 | =item * | |
139 | ||
140 | The special pattern C<\X> match matches any extended Unicode sequence | |
141 | (a "combining character sequence" in Standardese), where the first | |
142 | character is a base character and subsequent characters are mark | |
143 | characters that apply to the base character. It is equivalent to | |
144 | C<(?:\PM\pM*)>. | |
145 | ||
146 | C<use utf8> is needed to enable this. See above. | |
147 | ||
148 | =item * | |
149 | ||
150 | The C<tr///> operator translates characters instead of bytes. It can also | |
151 | be forced to translate between 8-bit codes and UTF-8 regardless of the | |
152 | surrounding utf8 state. For instance, if you know your input in Latin-1, | |
153 | you can say: | |
154 | ||
155 | use utf8; | |
156 | while (<>) { | |
157 | tr/\0-\xff//CU; # latin1 char to utf8 | |
158 | ... | |
159 | } | |
160 | ||
161 | Similarly you could translate your output with | |
162 | ||
163 | tr/\0-\x{ff}//UC; # utf8 to latin1 char | |
164 | ||
165 | No, C<s///> doesn't take /U or /C (yet?). | |
166 | ||
167 | C<use utf8> is needed to enable this. See above. | |
168 | ||
169 | =item * | |
170 | ||
171 | Case translation operators use the Unicode case translation tables | |
172 | when provided character input. Note that C<uc()> translates to | |
173 | uppercase, while C<ucfirst> translates to titlecase (for languages | |
174 | that make the distinction). Naturally the corresponding backslash | |
175 | sequences have the same semantics. | |
176 | ||
177 | =item * | |
178 | ||
179 | Most operators that deal with positions or lengths in the string will | |
180 | automatically switch to using character positions, including C<chop()>, | |
181 | C<substr()>, C<pos()>, C<index()>, C<rindex()>, C<sprintf()>, | |
182 | C<write()>, and C<length()>. Operators that specifically don't switch | |
183 | include C<vec()>, C<pack()>, and C<unpack()>. Operators that really | |
184 | don't care include C<chomp()>, as well as any other operator that | |
185 | treats a string as a bucket of bits, such as C<sort()>, and the | |
186 | operators dealing with filenames. | |
187 | ||
188 | =item * | |
189 | ||
190 | The C<pack()>/C<unpack()> letters "C<c>" and "C<C>" do I<not> change, | |
191 | since they're often used for byte-oriented formats. (Again, think | |
192 | "C<char>" in the C language.) However, there is a new "C<U>" specifier | |
193 | that will convert between UTF-8 characters and integers. (It works | |
194 | outside of the utf8 pragma too.) | |
195 | ||
196 | =item * | |
197 | ||
198 | The C<chr()> and C<ord()> functions work on characters. This is like | |
199 | C<pack("U")> and C<unpack("U")>, not like C<pack("C")> and | |
200 | C<unpack("C")>. In fact, the latter are how you now emulate | |
201 | byte-oriented C<chr()> and C<ord()> under utf8. | |
202 | ||
203 | =item * | |
204 | ||
205 | And finally, C<scalar reverse()> reverses by character rather than by byte. | |
206 | ||
207 | =back | |
208 | ||
8cbd9a7a GS |
209 | =head2 Character encodings for input and output |
210 | ||
211 | [XXX: This feature is not yet implemented.] | |
212 | ||
393fec97 GS |
213 | =head1 CAVEATS |
214 | ||
215 | As of yet, there is no method for automatically coercing input and | |
216 | output to some encoding other than UTF-8. This is planned in the near | |
217 | future, however. | |
218 | ||
8cbd9a7a GS |
219 | Whether an arbitrary piece of data will be treated as "characters" or |
220 | "bytes" by internal operations cannot be divined at the current time. | |
393fec97 GS |
221 | |
222 | Use of locales with utf8 may lead to odd results. Currently there is | |
223 | some attempt to apply 8-bit locale info to characters in the range | |
224 | 0..255, but this is demonstrably incorrect for locales that use | |
225 | characters above that range (when mapped into Unicode). It will also | |
226 | tend to run slower. Avoidance of locales is strongly encouraged. | |
227 | ||
228 | =head1 SEE ALSO | |
229 | ||
8058d7ab | 230 | L<bytes>, L<utf8>, L<perlvar/"${^WIDE_SYSTEM_CALLS}"> |
393fec97 GS |
231 | |
232 | =cut |