3 perlunicode - Unicode support in Perl
7 =head2 Important Caveats
9 WARNING: While the implementation of Unicode support in Perl is now fairly
10 complete it is still evolving to some extent.
12 In particular the way Unicode is handled on EBCDIC platforms is still
13 rather experimental. On such a platform references to UTF-8 encoding
14 in this document and elsewhere should be read as meaning UTF-EBCDIC as
15 specified in Unicode Technical Report 16 unless ASCII vs EBCDIC issues
16 are specifically discussed. There is no C<utfebcdic> pragma or
17 ":utfebcdic" layer, rather "utf8" and ":utf8" are re-used to mean
18 platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic> for
19 more discussion of the issues.
21 The following areas are still under development.
25 =item Input and Output Disciplines
27 A filehandle can be marked as containing perl's internal Unicode
28 encoding (UTF-8 or UTF-EBCDIC) by opening it with the ":utf8" layer.
29 Other encodings can be converted to perl's encoding on input, or from
30 perl's encoding on output by use of the ":encoding()" layer. There is
31 not yet a clean way to mark the Perl source itself as being in an
34 =item Regular Expressions
36 The regular expression compiler does now attempt to produce
37 polymorphic opcodes. That is the pattern should now adapt to the data
38 and automatically switch to the Unicode character scheme when
39 presented with Unicode data, or a traditional byte scheme when
40 presented with byte data. The implementation is still new and
41 (particularly on EBCDIC platforms) may need further work.
43 =item C<use utf8> still needed to enable UTF-8/UTF-EBCDIC in scripts
45 The C<utf8> pragma implements the tables used for Unicode support.
46 These tables are automatically loaded on demand, so the C<utf8> pragma
47 need not normally be used.
49 However, as a compatibility measure, this pragma must be explicitly
50 used to enable recognition of UTF-8 in the Perl scripts themselves on
51 ASCII based machines or recognize UTF-EBCDIC on EBCDIC based machines.
52 B<NOTE: this should be the only place where an explicit C<use utf8> is
57 =head2 Byte and Character semantics
59 Beginning with version 5.6, Perl uses logically wide characters to
60 represent strings internally. This internal representation of strings
61 uses either the UTF-8 or the UTF-EBCDIC encoding.
63 In future, Perl-level operations can be expected to work with
64 characters rather than bytes, in general.
66 However, as strictly an interim compatibility measure, Perl aims to
67 provide a safe migration path from byte semantics to character
68 semantics for programs. For operations where Perl can unambiguously
69 decide that the input data is characters, Perl now switches to
70 character semantics. For operations where this determination cannot
71 be made without additional information from the user, Perl decides in
72 favor of compatibility, and chooses to use byte semantics.
74 This behavior preserves compatibility with earlier versions of Perl,
75 which allowed byte semantics in Perl operations, but only as long as
76 none of the program's inputs are marked as being as source of Unicode
77 character data. Such data may come from filehandles, from calls to
78 external programs, from information provided by the system (such as %ENV),
79 or from literals and constants in the source text.
81 If the C<-C> command line switch is used, (or the
82 ${^WIDE_SYSTEM_CALLS} global flag is set to C<1>), all system calls
83 will use the corresponding wide character APIs. Note that this is
84 currently only implemented on Windows since other platforms API
85 standard on this area.
87 Regardless of the above, the C<bytes> pragma can always be used to
88 force byte semantics in a particular lexical scope. See L<bytes>.
90 The C<utf8> pragma is primarily a compatibility device that enables
91 recognition of UTF-(8|EBCDIC) in literals encountered by the parser.
92 Note that this pragma is only required until a future version of Perl
93 in which character semantics will become the default. This pragma may
94 then become a no-op. See L<utf8>.
96 Unless mentioned otherwise, Perl operators will use character semantics
97 when they are dealing with Unicode data, and byte semantics otherwise.
98 Thus, character semantics for these operations apply transparently; if
99 the input data came from a Unicode source (for example, by adding a
100 character encoding discipline to the filehandle whence it came, or a
101 literal UTF-8 string constant in the program), character semantics
102 apply; otherwise, byte semantics are in effect. To force byte semantics
103 on Unicode data, the C<bytes> pragma should be used.
105 Notice that if you have a string with byte semantics and you then
106 add character data into it, the bytes will be upgraded I<as if they
107 were ISO 8859-1 (Latin-1)> (or if in EBCDIC, after a translation
110 Under character semantics, many operations that formerly operated on
111 bytes change to operating on characters. For ASCII data this makes no
112 difference, because UTF-8 stores ASCII in single bytes, but for any
113 character greater than C<chr(127)>, the character B<may> be stored in
114 a sequence of two or more bytes, all of which have the high bit set.
116 For C1 controls or Latin 1 characters on an EBCDIC platform the
117 character may be stored in a UTF-EBCDIC multi byte sequence. But by
118 and large, the user need not worry about this, because Perl hides it
119 from the user. A character in Perl is logically just a number ranging
120 from 0 to 2**32 or so. Larger characters encode to longer sequences
121 of bytes internally, but again, this is just an internal detail which
122 is hidden at the Perl level.
124 =head2 Effects of character semantics
126 Character semantics have the following effects:
132 Strings and patterns may contain characters that have an ordinal value
135 Presuming you use a Unicode editor to edit your program, such
136 characters will typically occur directly within the literal strings as
137 UTF-8 (or UTF-EBCDIC on EBCDIC platforms) characters, but you can also
138 specify a particular character with an extension of the C<\x>
139 notation. UTF-X characters are specified by putting the hexadecimal
140 code within curlies after the C<\x>. For instance, a Unicode smiley
145 Identifiers within the Perl script may contain Unicode alphanumeric
146 characters, including ideographs. (You are currently on your own when
147 it comes to using the canonical forms of characters--Perl doesn't
148 (yet) attempt to canonicalize variable names for you.)
152 Regular expressions match characters instead of bytes. For instance,
153 "." matches a character instead of a byte. (However, the C<\C> pattern
154 is provided to force a match a single byte ("C<char>" in C, hence C<\C>).)
158 Character classes in regular expressions match characters instead of
159 bytes, and match against the character properties specified in the
160 Unicode properties database. So C<\w> can be used to match an
161 ideograph, for instance.
165 Named Unicode properties and block ranges make be used as character
166 classes via the new C<\p{}> (matches property) and C<\P{}> (doesn't
167 match property) constructs. For instance, C<\p{Lu}> matches any
168 character with the Unicode uppercase property, while C<\p{M}> matches
169 any mark character. Single letter properties may omit the brackets,
170 so that can be written C<\pM> also. Many predefined character classes
171 are available, such as C<\p{IsMirrored}> and C<\p{InTibetan}>. The
172 names of the C<In> classes are the official Unicode script and block
173 names but with all non-alphanumeric characters removed, for example
174 the block name C<"Latin-1 Supplement"> becomes C<\p{InLatin1Supplement}>.
176 Here is the list as of Unicode 3.1.0 (the two-letter classes) and
177 as defined by Perl (the one-letter classes) (in Unicode materials
178 what Perl calls C<L> is often called C<L&>):
188 Mc Mark, Spacing Combining
191 Nd Number, Decimal Digit
195 Pc Punctuation, Connector
198 Pe Punctuation, Close
199 Pi Punctuation, Initial quote
200 (may behave like Ps or Pe depending on usage)
201 Pf Punctuation, Final quote
202 (may behave like Ps or Pe depending on usage)
203 Po Punctuation, Other
212 Zp Separator, Paragraph
217 Co Other, Private Use
218 Cn Other, Not Assigned (Unicode defines no Cn characters)
220 Additionally, because scripts differ in their directionality
221 (for example Hebrew is written right to left), all characters
222 have their directionality defined:
225 BidiLRE Left-to-Right Embedding
226 BidiLRO Left-to-Right Override
228 BidiAL Right-to-Left Arabic
229 BidiRLE Right-to-Left Embedding
230 BidiRLO Right-to-Left Override
231 BidiPDF Pop Directional Format
232 BidiEN European Number
233 BidiES European Number Separator
234 BidiET European Number Terminator
236 BidiCS Common Number Separator
237 BidiNSM Non-Spacing Mark
238 BidiBN Boundary Neutral
239 BidiB Paragraph Separator
240 BidiS Segment Separator
242 BidiON Other Neutrals
246 The scripts available for C<\p{In...}> and C<\P{In...}>, for example
247 \p{InCyrillic>, are as follows, for example C<\p{InLatin}> or C<\P{InHan}>:
292 In addition to B<scripts>, Unicode also defines B<blocks> of
293 characters. The difference between scripts and blocks is that the
294 former concept is closer to natural languages, while the latter
295 concept is more an artificial grouping based on groups of 256 Unicode
296 characters. For example, the C<Latin> script contains letters from
297 many blocks, but it does not contain all the characters from those
298 blocks, it does not for example contain digits.
300 For more about scripts see the UTR #24:
301 http://www.unicode.org/unicode/reports/tr24/
302 For more about blocks see
303 http://www.unicode.org/Public/UNIDATA/Blocks.txt
305 Because there are overlaps in naming (there are, for example, both
306 a script called C<Katakana> and a block called C<Katakana>, the block
307 version has C<Block> appended to its name, C<\p{InKatakanaBlock}>.
309 Notice that this definition was introduced in Perl 5.8.0: in Perl
310 5.6.0 only the blocks were used; in Perl 5.8.0 scripts became the
311 preferential character class definition; this meant that the
312 definitions of some character classes changed (the ones in the
313 below list that have the C<Block> appended).
320 SpacingModifierLetters
321 CombiningDiacriticalMarks
347 UnifiedCanadianAboriginalSyllabics
352 LatinExtendedAdditional
355 SuperscriptsandSubscripts
357 CombiningMarksforSymbols
361 MathematicalOperators
362 MiscellaneousTechnical
364 OpticalCharacterRecognition
365 EnclosedAlphanumerics
372 CJKRadicalsSupplement
374 IdeographicDescriptionCharacters
375 CJKSymbolsandPunctuation
379 HangulCompatibilityJamo
382 EnclosedCJKLettersandMonths
384 CJKUnifiedIdeographsExtensionA
390 HighPrivateUseSurrogates
393 CJKCompatibilityIdeographs
394 AlphabeticPresentationForms
395 ArabicPresentationFormsA
397 CJKCompatibilityForms
399 ArabicPresentationFormsB
401 HalfwidthandFullwidthForms
405 ByzantineMusicalSymbols
407 MathematicalAlphanumericSymbols
408 CJKUnifiedIdeographsExtensionB
409 CJKCompatibilityIdeographsSupplement
414 The special pattern C<\X> match matches any extended Unicode sequence
415 (a "combining character sequence" in Standardese), where the first
416 character is a base character and subsequent characters are mark
417 characters that apply to the base character. It is equivalent to
422 The C<tr///> operator translates characters instead of bytes. Note
423 that the C<tr///CU> functionality has been removed, as the interface
424 was a mistake. For similar functionality see pack('U0', ...) and
429 Case translation operators use the Unicode case translation tables
430 when provided character input. Note that C<uc()> translates to
431 uppercase, while C<ucfirst> translates to titlecase (for languages
432 that make the distinction). Naturally the corresponding backslash
433 sequences have the same semantics.
437 Most operators that deal with positions or lengths in the string will
438 automatically switch to using character positions, including
439 C<chop()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>,
440 C<sprintf()>, C<write()>, and C<length()>. Operators that
441 specifically don't switch include C<vec()>, C<pack()>, and
442 C<unpack()>. Operators that really don't care include C<chomp()>, as
443 well as any other operator that treats a string as a bucket of bits,
444 such as C<sort()>, and the operators dealing with filenames.
448 The C<pack()>/C<unpack()> letters "C<c>" and "C<C>" do I<not> change,
449 since they're often used for byte-oriented formats. (Again, think
450 "C<char>" in the C language.) However, there is a new "C<U>" specifier
451 that will convert between UTF-8 characters and integers. (It works
452 outside of the utf8 pragma too.)
456 The C<chr()> and C<ord()> functions work on characters. This is like
457 C<pack("U")> and C<unpack("U")>, not like C<pack("C")> and
458 C<unpack("C")>. In fact, the latter are how you now emulate
459 byte-oriented C<chr()> and C<ord()> under utf8.
463 The bit string operators C<& | ^ ~> can operate on character data.
464 However, for backward compatibility reasons (bit string operations
465 when the characters all are less than 256 in ordinal value) one should
466 not mix C<~> (the bit complement) and characters both less than 256 and
467 equal or greater than 256. Most importantly, the DeMorgan's laws
468 (C<~($x|$y) eq ~$x&~$y>, C<~($x&$y) eq ~$x|~$y>) won't hold.
469 Another way to look at this is that the complement cannot return
470 B<both> the 8-bit (byte) wide bit complement B<and> the full character
475 And finally, C<scalar reverse()> reverses by character rather than by byte.
479 =head2 Character encodings for input and output
485 As of yet, there is no method for automatically coercing input and
486 output to some encoding other than UTF-8 or UTF-EBCDIC. This is planned
487 in the near future, however.
489 Whether an arbitrary piece of data will be treated as "characters" or
490 "bytes" by internal operations cannot be divined at the current time.
492 Use of locales with utf8 may lead to odd results. Currently there is
493 some attempt to apply 8-bit locale info to characters in the range
494 0..255, but this is demonstrably incorrect for locales that use
495 characters above that range (when mapped into Unicode). It will also
496 tend to run slower. Avoidance of locales is strongly encouraged.
500 L<bytes>, L<utf8>, L<perlretut>, L<perlvar/"${^WIDE_SYSTEM_CALLS}">