3 perlunicode - Unicode support in Perl
7 =head2 Important Caveats
9 WARNING: While the implementation of Unicode support in Perl is now
10 fairly 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 concatenate strings with byte semantics and strings
106 with Unicode character data, the bytes will by default be upgraded
107 I<as if they were ISO 8859-1 (Latin-1)> (or if in EBCDIC, after a
108 translation to ISO 8859-1). To change this, use the C<encoding>
109 pragma, see L<encoding>.
111 Under character semantics, many operations that formerly operated on
112 bytes change to operating on characters. For ASCII data this makes no
113 difference, because UTF-8 stores ASCII in single bytes, but for any
114 character greater than C<chr(127)>, the character B<may> be stored in
115 a sequence of two or more bytes, all of which have the high bit set.
117 For C1 controls or Latin 1 characters on an EBCDIC platform the
118 character may be stored in a UTF-EBCDIC multi byte sequence. But by
119 and large, the user need not worry about this, because Perl hides it
120 from the user. A character in Perl is logically just a number ranging
121 from 0 to 2**32 or so. Larger characters encode to longer sequences
122 of bytes internally, but again, this is just an internal detail which
123 is hidden at the Perl level.
125 =head2 Effects of character semantics
127 Character semantics have the following effects:
133 Strings and patterns may contain characters that have an ordinal value
136 Presuming you use a Unicode editor to edit your program, such
137 characters will typically occur directly within the literal strings as
138 UTF-8 (or UTF-EBCDIC on EBCDIC platforms) characters, but you can also
139 specify a particular character with an extension of the C<\x>
140 notation. UTF-X characters are specified by putting the hexadecimal
141 code within curlies after the C<\x>. For instance, a Unicode smiley
146 Identifiers within the Perl script may contain Unicode alphanumeric
147 characters, including ideographs. (You are currently on your own when
148 it comes to using the canonical forms of characters--Perl doesn't
149 (yet) attempt to canonicalize variable names for you.)
153 Regular expressions match characters instead of bytes. For instance,
154 "." matches a character instead of a byte. (However, the C<\C> pattern
155 is provided to force a match a single byte ("C<char>" in C, hence C<\C>).)
159 Character classes in regular expressions match characters instead of
160 bytes, and match against the character properties specified in the
161 Unicode properties database. So C<\w> can be used to match an
162 ideograph, for instance.
166 Named Unicode properties and block ranges make be used as character
167 classes via the new C<\p{}> (matches property) and C<\P{}> (doesn't
168 match property) constructs. For instance, C<\p{Lu}> matches any
169 character with the Unicode uppercase property, while C<\p{M}> matches
170 any mark character. Single letter properties may omit the brackets,
171 so that can be written C<\pM> also. Many predefined character classes
172 are available, such as C<\p{IsMirrored}> and C<\p{InTibetan}>.
174 The C<\p{Is...}> test for "general properties" such as "letter",
175 "digit", while the C<\p{In...}> test for Unicode scripts and blocks.
177 The official Unicode script and block names have spaces and dashes and
178 separators, but for convenience you can have dashes, spaces, and
179 underbars at every word division, and you need not care about correct
180 casing. It is recommended, however, that for consistency you use the
181 following naming: the official Unicode script, block, or property name
182 (see below for the additional rules that apply to block names),
183 with whitespace and dashes replaced with underbar, and the words
184 "uppercase-first-lowercase-rest". That is, "Latin-1 Supplement"
185 becomes "Latin_1_Supplement".
187 You can also negate both C<\p{}> and C<\P{}> by introducing a caret
188 (^) between the first curly and the property name: C<\p{^In_Tamil}> is
189 equal to C<\P{In_Tamil}>.
191 The C<In> and C<Is> can be left out: C<\p{Greek}> is equal to
192 C<\p{In_Greek}>, C<\P{Pd}> is equal to C<\P{Pd}>.
214 Pc Connector_Punctuation
218 Pi Initial_Punctuation
219 (may behave like Ps or Pe depending on usage)
221 (may behave like Ps or Pe depending on usage)
233 Zp Paragraph_Separator
242 There's also C<L&> which is an alias for C<Ll>, C<Lu>, and C<Lt>.
244 The following reserved ranges have C<In> tests:
246 CJK_Ideograph_Extension_A
249 Non_Private_Use_High_Surrogate
250 Private_Use_High_Surrogate
253 CJK_Ideograph_Extension_B
257 For example C<"\x{AC00}" =~ \p{HangulSyllable}> will test true.
258 (Handling of surrogates is not implemented yet, because Perl
259 uses UTF-8 and not UTF-16 internally to represent Unicode.)
261 Additionally, because scripts differ in their directionality
262 (for example Hebrew is written right to left), all characters
263 have their directionality defined:
266 BidiLRE Left-to-Right Embedding
267 BidiLRO Left-to-Right Override
269 BidiAL Right-to-Left Arabic
270 BidiRLE Right-to-Left Embedding
271 BidiRLO Right-to-Left Override
272 BidiPDF Pop Directional Format
273 BidiEN European Number
274 BidiES European Number Separator
275 BidiET European Number Terminator
277 BidiCS Common Number Separator
278 BidiNSM Non-Spacing Mark
279 BidiBN Boundary Neutral
280 BidiB Paragraph Separator
281 BidiS Segment Separator
283 BidiON Other Neutrals
287 The scripts available for C<\p{In...}> and C<\P{In...}>, for example
288 \p{InCyrillic>, are as follows, for example C<\p{InLatin}> or C<\P{InHan}>:
331 There are also extended property classes that supplement the basic
332 properties, defined by the F<PropList> Unicode database:
343 Noncharacter_Code_Point
351 and further derived properties:
353 Alphabetic Lu + Ll + Lt + Lm + Lo + Other_Alphabetic
354 Lowercase Ll + Other_Lowercase
355 Uppercase Lu + Other_Uppercase
358 ID_Start Lu + Ll + Lt + Lm + Lo + Nl
359 ID_Continue ID_Start + Mn + Mc + Nd + Pc
362 Assigned Any non-Cn character
363 Common Any character (or unassigned code point)
364 not explicitly assigned to a script
368 In addition to B<scripts>, Unicode also defines B<blocks> of
369 characters. The difference between scripts and blocks is that the
370 scripts concept is closer to natural languages, while the blocks
371 concept is more an artificial grouping based on groups of 256 Unicode
372 characters. For example, the C<Latin> script contains letters from
373 many blocks. On the other hand, the C<Latin> script does not contain
374 all the characters from those blocks, it does not for example contain
375 digits because digits are shared across many scripts. Digits and
376 other similar groups, like punctuation, are in a category called
379 For more about scripts see the UTR #24:
380 http://www.unicode.org/unicode/reports/tr24/
381 For more about blocks see
382 http://www.unicode.org/Public/UNIDATA/Blocks.txt
384 Because there are overlaps in naming (there are, for example, both
385 a script called C<Katakana> and a block called C<Katakana>, the block
386 version has C<Block> appended to its name, C<\p{InKatakanaBlock}>.
388 Notice that this definition was introduced in Perl 5.8.0: in Perl
389 5.6 only the blocks were used; in Perl 5.8.0 scripts became the
390 preferential Unicode character class definition; this meant that
391 the definitions of some character classes changed (the ones in the
392 below list that have the C<Block> appended).
394 Alphabetic Presentation Forms
396 Arabic Presentation Forms-A
397 Arabic Presentation Forms-B
407 Byzantine Musical Symbols
409 CJK Compatibility Forms
410 CJK Compatibility Ideographs
411 CJK Compatibility Ideographs Supplement
412 CJK Radicals Supplement
413 CJK Symbols and Punctuation
414 CJK Unified Ideographs
415 CJK Unified Ideographs Extension A
416 CJK Unified Ideographs Extension B
418 Combining Diacritical Marks
420 Combining Marks for Symbols
427 Enclosed Alphanumerics
428 Enclosed CJK Letters and Months
438 Halfwidth and Fullwidth Forms
439 Hangul Compatibility Jamo
443 High Private Use Surrogates
447 Ideographic Description Characters
455 Latin Extended Additional
461 Mathematical Alphanumeric Symbols
462 Mathematical Operators
463 Miscellaneous Symbols
464 Miscellaneous Technical
471 Optical Character Recognition
477 Spacing Modifier Letters
479 Superscripts and Subscripts
487 Unified Canadian Aboriginal Syllabics
493 The special pattern C<\X> match matches any extended Unicode sequence
494 (a "combining character sequence" in Standardese), where the first
495 character is a base character and subsequent characters are mark
496 characters that apply to the base character. It is equivalent to
501 The C<tr///> operator translates characters instead of bytes. Note
502 that the C<tr///CU> functionality has been removed, as the interface
503 was a mistake. For similar functionality see pack('U0', ...) and
508 Case translation operators use the Unicode case translation tables
509 when provided character input. Note that C<uc()> (also known as C<\U>
510 in doublequoted strings) translates to uppercase, while C<ucfirst>
511 (also known as C<\u> in doublequoted strings) translates to titlecase
512 (for languages that make the distinction). Naturally the
513 corresponding backslash sequences have the same semantics.
517 Most operators that deal with positions or lengths in the string will
518 automatically switch to using character positions, including
519 C<chop()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>,
520 C<sprintf()>, C<write()>, and C<length()>. Operators that
521 specifically don't switch include C<vec()>, C<pack()>, and
522 C<unpack()>. Operators that really don't care include C<chomp()>, as
523 well as any other operator that treats a string as a bucket of bits,
524 such as C<sort()>, and the operators dealing with filenames.
528 The C<pack()>/C<unpack()> letters "C<c>" and "C<C>" do I<not> change,
529 since they're often used for byte-oriented formats. (Again, think
530 "C<char>" in the C language.) However, there is a new "C<U>" specifier
531 that will convert between UTF-8 characters and integers. (It works
532 outside of the utf8 pragma too.)
536 The C<chr()> and C<ord()> functions work on characters. This is like
537 C<pack("U")> and C<unpack("U")>, not like C<pack("C")> and
538 C<unpack("C")>. In fact, the latter are how you now emulate
539 byte-oriented C<chr()> and C<ord()> for Unicode strings.
540 (Note that this reveals the internal UTF-8 encoding of strings and
541 you are not supposed to do that unless you know what you are doing.)
545 The bit string operators C<& | ^ ~> can operate on character data.
546 However, for backward compatibility reasons (bit string operations
547 when the characters all are less than 256 in ordinal value) one should
548 not mix C<~> (the bit complement) and characters both less than 256 and
549 equal or greater than 256. Most importantly, the DeMorgan's laws
550 (C<~($x|$y) eq ~$x&~$y>, C<~($x&$y) eq ~$x|~$y>) won't hold.
551 Another way to look at this is that the complement cannot return
552 B<both> the 8-bit (byte) wide bit complement B<and> the full character
557 lc(), uc(), lcfirst(), and ucfirst() work for the following cases:
563 the case mapping is from a single Unicode character to another
564 single Unicode character
568 the case mapping is from a single Unicode character to more
569 than one Unicode character
573 What doesn't yet work are the followng cases:
579 the "final sigma" (Greek)
583 anything to with locales (Lithuanian, Turkish, Azeri)
587 See the Unicode Technical Report #21, Case Mappings, for more details.
591 And finally, C<scalar reverse()> reverses by character rather than by byte.
595 =head2 Character encodings for input and output
601 As of yet, there is no method for automatically coercing input and
602 output to some encoding other than UTF-8 or UTF-EBCDIC. This is planned
603 in the near future, however.
605 Whether an arbitrary piece of data will be treated as "characters" or
606 "bytes" by internal operations cannot be divined at the current time.
608 Use of locales with utf8 may lead to odd results. Currently there is
609 some attempt to apply 8-bit locale info to characters in the range
610 0..255, but this is demonstrably incorrect for locales that use
611 characters above that range (when mapped into Unicode). It will also
612 tend to run slower. Avoidance of locales is strongly encouraged.
614 =head1 UNICODE REGULAR EXPRESSION SUPPORT LEVEL
616 The following list of Unicode regular expression support describes
617 feature by feature the Unicode support implemented in Perl as of Perl
618 5.8.0. The "Level N" and the section numbers refer to the Unicode
619 Technical Report 18, "Unicode Regular Expression Guidelines".
625 Level 1 - Basic Unicode Support
627 2.1 Hex Notation - done [1]
628 Named Notation - done [2]
629 2.2 Categories - done [3][4]
630 2.3 Subtraction - MISSING [5][6]
631 2.4 Simple Word Boundaries - done [7]
632 2.5 Simple Loose Matches - MISSING [8]
633 2.6 End of Line - MISSING [9][10]
637 [ 3] . \p{Is...} \P{Is...}
638 [ 4] now scripts (see UTR#24 Script Names) in addition to blocks
640 [ 6] can use look-ahead to emulate subtracion
641 [ 7] include Letters in word characters
642 [ 8] see UTR#21 Case Mappings
643 [ 9] see UTR#13 Unicode Newline Guidelines
644 [10] should do ^ and $ also on \x{2028} and \x{2029}
648 Level 2 - Extended Unicode Support
650 3.1 Surrogates - MISSING
651 3.2 Canonical Equivalents - MISSING [11][12]
652 3.3 Locale-Independent Graphemes - MISSING [13]
653 3.4 Locale-Independent Words - MISSING [14]
654 3.5 Locale-Independent Loose Matches - MISSING [15]
656 [11] see UTR#15 Unicode Normalization
657 [12] have Unicode::Normalize but not integrated to regexes
658 [13] have \X but at this level . should equal that
659 [14] need three classes, not just \w and \W
660 [15] see UTR#21 Case Mappings
664 Level 3 - Locale-Sensitive Support
666 4.1 Locale-Dependent Categories - MISSING
667 4.2 Locale-Dependent Graphemes - MISSING [16][17]
668 4.3 Locale-Dependent Words - MISSING
669 4.4 Locale-Dependent Loose Matches - MISSING
670 4.5 Locale-Dependent Ranges - MISSING
672 [16] see UTR#10 Unicode Collation Algorithms
673 [17] have Unicode::Collate but not integrated to regexes
679 L<bytes>, L<utf8>, L<perlretut>, L<perlvar/"${^WIDE_SYSTEM_CALLS}">
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