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1=head1 NAME
2
3perlunicode - Unicode support in Perl
4
5=head1 DESCRIPTION
6
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7If you haven't already, before reading this document, you should become
8familiar with both L<perlunitut> and L<perluniintro>.
9
10Unicode aims to B<UNI>-fy the en-B<CODE>-ings of all the world's
11character sets into a single Standard. For quite a few of the various
12coding standards that existed when Unicode was first created, converting
13from each to Unicode essentially meant adding a constant to each code
14point in the original standard, and converting back meant just
15subtracting that same constant. For ASCII and ISO-8859-1, the constant
16is 0. For ISO-8859-5, (Cyrillic) the constant is 864; for Hebrew
17(ISO-8859-8), it's 1488; Thai (ISO-8859-11), 3424; and so forth. This
18made it easy to do the conversions, and facilitated the adoption of
19Unicode.
20
21And it worked; nowadays, those legacy standards are rarely used. Most
22everyone uses Unicode.
23
24Unicode is a comprehensive standard. It specifies many things outside
25the scope of Perl, such as how to display sequences of characters. For
26a full discussion of all aspects of Unicode, see
27L<http://www.unicode.org>.
28
0a1f2d14 29=head2 Important Caveats
21bad921 30
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31Even though some of this section may not be understandable to you on
32first reading, we think it's important enough to highlight some of the
33gotchas before delving further, so here goes:
34
376d9008 35Unicode support is an extensive requirement. While Perl does not
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36implement the Unicode standard or the accompanying technical reports
37from cover to cover, Perl does support many Unicode features.
21bad921 38
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39Also, the use of Unicode may present security issues that aren't obvious.
40Read L<Unicode Security Considerations|http://www.unicode.org/reports/tr36>.
41
13a2d996 42=over 4
21bad921 43
a9130ea9 44=item Safest if you C<use feature 'unicode_strings'>
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45
46In order to preserve backward compatibility, Perl does not turn
47on full internal Unicode support unless the pragma
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48L<S<C<use feature 'unicode_strings'>>|feature/The 'unicode_strings' feature>
49is specified. (This is automatically
50selected if you S<C<use 5.012>> or higher.) Failure to do this can
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51trigger unexpected surprises. See L</The "Unicode Bug"> below.
52
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53This pragma doesn't affect I/O. Nor does it change the internal
54representation of strings, only their interpretation. There are still
55several places where Unicode isn't fully supported, such as in
56filenames.
42581d5d 57
fae2c0fb 58=item Input and Output Layers
21bad921 59
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60Use the C<:encoding(...)> layer to read from and write to
61filehandles using the specified encoding. (See L<open>.)
c349b1b9 62
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63=item You should convert your non-ASCII, non-UTF-8 Perl scripts to be
64UTF-8.
21bad921 65
a6a7eedc 66See L<encoding>.
21bad921 67
a6a7eedc 68=item C<use utf8> still needed to enable L<UTF-8|/Unicode Encodings> in scripts
21bad921 69
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70If your Perl script is itself encoded in L<UTF-8|/Unicode Encodings>,
71the S<C<use utf8>> pragma must be explicitly included to enable
72recognition of that (in string or regular expression literals, or in
73identifier names). B<This is the only time when an explicit S<C<use
74utf8>> is needed.> (See L<utf8>).
7aa207d6 75
a6a7eedc 76=item C<BOM>-marked scripts and L<UTF-16|/Unicode Encodings> scripts autodetected
7aa207d6 77
fea12a3e 78If a Perl script begins with the Unicode C<BOM> (UTF-16LE,
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79UTF16-BE, or UTF-8), or if the script looks like non-C<BOM>-marked
80UTF-16 of either endianness, Perl will correctly read in the script as
81the appropriate Unicode encoding. (C<BOM>-less UTF-8 cannot be
82effectively recognized or differentiated from ISO 8859-1 or other
83eight-bit encodings.)
990e18f7 84
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85=back
86
376d9008 87=head2 Byte and Character Semantics
393fec97 88
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89Before Unicode, most encodings used 8 bits (a single byte) to encode
90each character. Thus a character was a byte, and a byte was a
91character, and there could be only 256 or fewer possible characters.
92"Byte Semantics" in the title of this section refers to
93this behavior. There was no need to distinguish between "Byte" and
94"Character".
95
96Then along comes Unicode which has room for over a million characters
97(and Perl allows for even more). This means that a character may
98require more than a single byte to represent it, and so the two terms
99are no longer equivalent. What matter are the characters as whole
100entities, and not usually the bytes that comprise them. That's what the
101term "Character Semantics" in the title of this section refers to.
102
103Perl had to change internally to decouple "bytes" from "characters".
104It is important that you too change your ideas, if you haven't already,
105so that "byte" and "character" no longer mean the same thing in your
106mind.
107
108The basic building block of Perl strings has always been a "character".
109The changes basically come down to that the implementation no longer
110thinks that a character is always just a single byte.
111
112There are various things to note:
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113
114=over 4
115
116=item *
117
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118String handling functions, for the most part, continue to operate in
119terms of characters. C<length()>, for example, returns the number of
120characters in a string, just as before. But that number no longer is
121necessarily the same as the number of bytes in the string (there may be
122more bytes than characters). The other such functions include
123C<chop()>, C<chomp()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>,
124C<sort()>, C<sprintf()>, and C<write()>.
125
126The exceptions are:
127
128=over 4
129
130=item *
131
132the bit-oriented C<vec>
133
134E<nbsp>
135
136=item *
137
138the byte-oriented C<pack>/C<unpack> C<"C"> format
139
140However, the C<W> specifier does operate on whole characters, as does the
141C<U> specifier.
142
143=item *
144
145some operators that interact with the platform's operating system
146
147Operators dealing with filenames are examples.
148
149=item *
150
151when the functions are called from within the scope of the
152S<C<L<use bytes|bytes>>> pragma
153
154Likely, you should use this only for debugging anyway.
155
156=back
157
158=item *
159
376d9008 160Strings--including hash keys--and regular expression patterns may
b65e6125 161contain characters that have ordinal values larger than 255.
393fec97 162
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163If you use a Unicode editor to edit your program, Unicode characters may
164occur directly within the literal strings in UTF-8 encoding, or UTF-16.
a9130ea9 165(The former requires a C<BOM> or C<use utf8>, the latter requires a C<BOM>.)
3e4dbfed 166
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167L<perluniintro/Creating Unicode> gives other ways to place non-ASCII
168characters in your strings.
6f335b04 169
a6a7eedc 170=item *
fbb93542 171
a6a7eedc 172The C<chr()> and C<ord()> functions work on whole characters.
376d9008 173
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174=item *
175
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176Regular expressions match whole characters. For example, C<"."> matches
177a whole character instead of only a single byte.
393fec97 178
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179=item *
180
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181The C<tr///> operator translates whole characters. (Note that the
182C<tr///CU> functionality has been removed. For similar functionality to
183that, see C<pack('U0', ...)> and C<pack('C0', ...)>).
393fec97 184
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185=item *
186
a6a7eedc 187C<scalar reverse()> reverses by character rather than by byte.
393fec97 188
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189=item *
190
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191The bit string operators, C<& | ^ ~> and (starting in v5.22)
192C<&. |. ^. ~.> can operate on characters that don't fit into a byte.
193However, the current behavior is likely to change. You should not use
194these operators on strings that are encoded in UTF-8. If you're not
195sure about the encoding of a string, downgrade it before using any of
196these operators; you can use
197L<C<utf8::utf8_downgrade()>|utf8/Utility functions>.
822502e5 198
a6a7eedc 199=back
822502e5 200
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201The bottom line is that Perl has always practiced "Character Semantics",
202but with the advent of Unicode, that is now different than "Byte
203Semantics".
204
205=head2 ASCII Rules versus Unicode Rules
206
207Before Unicode, when a character was a byte was a character,
208Perl knew only about the 128 characters defined by ASCII, code points 0
209through 127 (except for under S<C<use locale>>). That left the code
210points 128 to 255 as unassigned, and available for whatever use a
211program might want. The only semantics they have is their ordinal
212numbers, and that they are members of none of the non-negative character
213classes. None are considered to match C<\w> for example, but all match
214C<\W>.
822502e5 215
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216Unicode, of course, assigns each of those code points a particular
217meaning (along with ones above 255). To preserve backward
218compatibility, Perl only uses the Unicode meanings when there is some
219indication that Unicode is what is intended; otherwise the non-ASCII
220code points remain treated as if they are unassigned.
221
222Here are the ways that Perl knows that a string should be treated as
223Unicode:
224
225=over
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226
227=item *
228
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229Within the scope of S<C<use utf8>>
230
231If the whole program is Unicode (signified by using 8-bit B<U>nicode
232B<T>ransformation B<F>ormat), then all strings within it must be
233Unicode.
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234
235=item *
236
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237Within the scope of
238L<S<C<use feature 'unicode_strings'>>|feature/The 'unicode_strings' feature>
239
240This pragma was created so you can explicitly tell Perl that operations
241executed within its scope are to use Unicode rules. More operations are
242affected with newer perls. See L</The "Unicode Bug">.
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243
244=item *
245
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246Within the scope of S<C<use 5.012>> or higher
247
248This implicitly turns on S<C<use feature 'unicode_strings'>>.
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249
250=item *
251
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252Within the scope of
253L<S<C<use locale 'not_characters'>>|perllocale/Unicode and UTF-8>,
254or L<S<C<use locale>>|perllocale> and the current
255locale is a UTF-8 locale.
822502e5 256
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257The former is defined to imply Unicode handling; and the latter
258indicates a Unicode locale, hence a Unicode interpretation of all
259strings within it.
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260
261=item *
262
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263When the string contains a Unicode-only code point
264
265Perl has never accepted code points above 255 without them being
266Unicode, so their use implies Unicode for the whole string.
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267
268=item *
269
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270When the string contains a Unicode named code point C<\N{...}>
271
272The C<\N{...}> construct explicitly refers to a Unicode code point,
273even if it is one that is also in ASCII. Therefore the string
274containing it must be Unicode.
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275
276=item *
277
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278When the string has come from an external source marked as
279Unicode
280
281The L<C<-C>|perlrun/-C [numberE<sol>list]> command line option can
282specify that certain inputs to the program are Unicode, and the values
283of this can be read by your Perl code, see L<perlvar/"${^UNICODE}">.
284
285=item * When the string has been upgraded to UTF-8
286
287The function L<C<utf8::utf8_upgrade()>|utf8/Utility functions>
288can be explicitly used to permanently (unless a subsequent
289C<utf8::utf8_downgrade()> is called) cause a string to be treated as
290Unicode.
291
292=item * There are additional methods for regular expression patterns
293
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294A pattern that is compiled with the C<< /u >> or C<< /a >> modifiers is
295treated as Unicode (though there are some restrictions with C<< /a >>).
296Under the C<< /d >> and C<< /l >> modifiers, there are several other
297indications for Unicode; see L<perlre/Character set modifiers>.
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298
299=back
300
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301Note that all of the above are overridden within the scope of
302C<L<use bytes|bytes>>; but you should be using this pragma only for
303debugging.
304
305Note also that some interactions with the platform's operating system
306never use Unicode rules.
307
308When Unicode rules are in effect:
309
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310=over 4
311
312=item *
313
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314Case translation operators use the Unicode case translation tables.
315
316Note that C<uc()>, or C<\U> in interpolated strings, translates to
317uppercase, while C<ucfirst>, or C<\u> in interpolated strings,
318translates to titlecase in languages that make the distinction (which is
319equivalent to uppercase in languages without the distinction).
320
321There is a CPAN module, C<L<Unicode::Casing>>, which allows you to
322define your own mappings to be used in C<lc()>, C<lcfirst()>, C<uc()>,
323C<ucfirst()>, and C<fc> (or their double-quoted string inlined versions
324such as C<\U>). (Prior to Perl 5.16, this functionality was partially
325provided in the Perl core, but suffered from a number of insurmountable
326drawbacks, so the CPAN module was written instead.)
327
328=item *
329
330Character classes in regular expressions match based on the character
331properties specified in the Unicode properties database.
332
333C<\w> can be used to match a Japanese ideograph, for instance; and
334C<[[:digit:]]> a Bengali number.
335
336=item *
337
338Named Unicode properties, scripts, and block ranges may be used (like
339bracketed character classes) by using the C<\p{}> "matches property"
340construct and the C<\P{}> negation, "doesn't match property".
341
342See L</"Unicode Character Properties"> for more details.
343
344You can define your own character properties and use them
345in the regular expression with the C<\p{}> or C<\P{}> construct.
346See L</"User-Defined Character Properties"> for more details.
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347
348=back
349
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350=head2 Extended Grapheme Clusters (Logical characters)
351
352Consider a character, say C<H>. It could appear with various marks around it,
353such as an acute accent, or a circumflex, or various hooks, circles, arrows,
354I<etc.>, above, below, to one side or the other, I<etc>. There are many
355possibilities among the world's languages. The number of combinations is
356astronomical, and if there were a character for each combination, it would
357soon exhaust Unicode's more than a million possible characters. So Unicode
358took a different approach: there is a character for the base C<H>, and a
359character for each of the possible marks, and these can be variously combined
360to get a final logical character. So a logical character--what appears to be a
361single character--can be a sequence of more than one individual characters.
362The Unicode standard calls these "extended grapheme clusters" (which
363is an improved version of the no-longer much used "grapheme cluster");
364Perl furnishes the C<\X> regular expression construct to match such
365sequences in their entirety.
366
367But Unicode's intent is to unify the existing character set standards and
368practices, and several pre-existing standards have single characters that
369mean the same thing as some of these combinations, like ISO-8859-1,
370which has quite a few of them. For example, C<"LATIN CAPITAL LETTER E
371WITH ACUTE"> was already in this standard when Unicode came along.
372Unicode therefore added it to its repertoire as that single character.
373But this character is considered by Unicode to be equivalent to the
374sequence consisting of the character C<"LATIN CAPITAL LETTER E">
375followed by the character C<"COMBINING ACUTE ACCENT">.
376
377C<"LATIN CAPITAL LETTER E WITH ACUTE"> is called a "pre-composed"
378character, and its equivalence with the "E" and the "COMBINING ACCENT"
379sequence is called canonical equivalence. All pre-composed characters
380are said to have a decomposition (into the equivalent sequence), and the
381decomposition type is also called canonical. A string may be comprised
382as much as possible of precomposed characters, or it may be comprised of
383entirely decomposed characters. Unicode calls these respectively,
384"Normalization Form Composed" (NFC) and "Normalization Form Decomposed".
385The C<L<Unicode::Normalize>> module contains functions that convert
386between the two. A string may also have both composed characters and
387decomposed characters; this module can be used to make it all one or the
388other.
389
390You may be presented with strings in any of these equivalent forms.
391There is currently nothing in Perl 5 that ignores the differences. So
392you'll have to specially hanlde it. The usual advice is to convert your
393inputs to C<NFD> before processing further.
394
395For more detailed information, see L<http://unicode.org/reports/tr15/>.
396
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397=head2 Unicode Character Properties
398
ee88f7b6 399(The only time that Perl considers a sequence of individual code
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400points as a single logical character is in the C<\X> construct, already
401mentioned above. Therefore "character" in this discussion means a single
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402Unicode code point.)
403
404Very nearly all Unicode character properties are accessible through
405regular expressions by using the C<\p{}> "matches property" construct
406and the C<\P{}> "doesn't match property" for its negation.
51f494cc 407
9d1c51c1 408For instance, C<\p{Uppercase}> matches any single character with the Unicode
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409C<"Uppercase"> property, while C<\p{L}> matches any character with a
410C<General_Category> of C<"L"> (letter) property (see
411L</General_Category> below). Brackets are not
9d1c51c1 412required for single letter property names, so C<\p{L}> is equivalent to C<\pL>.
51f494cc 413
9d1c51c1 414More formally, C<\p{Uppercase}> matches any single character whose Unicode
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415C<Uppercase> property value is C<True>, and C<\P{Uppercase}> matches any character
416whose C<Uppercase> property value is C<False>, and they could have been written as
9d1c51c1 417C<\p{Uppercase=True}> and C<\p{Uppercase=False}>, respectively.
51f494cc 418
b19eb496 419This formality is needed when properties are not binary; that is, if they can
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420take on more values than just C<True> and C<False>. For example, the
421C<Bidi_Class> property (see L</"Bidirectional Character Types"> below),
422can take on several different
423values, such as C<Left>, C<Right>, C<Whitespace>, and others. To match these, one needs
424to specify both the property name (C<Bidi_Class>), AND the value being
5bff2035 425matched against
b65e6125 426(C<Left>, C<Right>, I<etc.>). This is done, as in the examples above, by having the
9f815e24 427two components separated by an equal sign (or interchangeably, a colon), like
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428C<\p{Bidi_Class: Left}>.
429
430All Unicode-defined character properties may be written in these compound forms
a9130ea9 431of C<\p{I<property>=I<value>}> or C<\p{I<property>:I<value>}>, but Perl provides some
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432additional properties that are written only in the single form, as well as
433single-form short-cuts for all binary properties and certain others described
434below, in which you may omit the property name and the equals or colon
435separator.
436
437Most Unicode character properties have at least two synonyms (or aliases if you
b19eb496 438prefer): a short one that is easier to type and a longer one that is more
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439descriptive and hence easier to understand. Thus the C<"L"> and
440C<"Letter"> properties above are equivalent and can be used
441interchangeably. Likewise, C<"Upper"> is a synonym for C<"Uppercase">,
442and we could have written C<\p{Uppercase}> equivalently as C<\p{Upper}>.
443Also, there are typically various synonyms for the values the property
444can be. For binary properties, C<"True"> has 3 synonyms: C<"T">,
445C<"Yes">, and C<"Y">; and C<"False"> has correspondingly C<"F">,
446C<"No">, and C<"N">. But be careful. A short form of a value for one
447property may not mean the same thing as the same short form for another.
448Thus, for the C<L</General_Category>> property, C<"L"> means
449C<"Letter">, but for the L<C<Bidi_Class>|/Bidirectional Character Types>
450property, C<"L"> means C<"Left">. A complete list of properties and
451synonyms is in L<perluniprops>.
51f494cc 452
b19eb496 453Upper/lower case differences in property names and values are irrelevant;
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454thus C<\p{Upper}> means the same thing as C<\p{upper}> or even C<\p{UpPeR}>.
455Similarly, you can add or subtract underscores anywhere in the middle of a
456word, so that these are also equivalent to C<\p{U_p_p_e_r}>. And white space
457is irrelevant adjacent to non-word characters, such as the braces and the equals
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458or colon separators, so C<\p{ Upper }> and C<\p{ Upper_case : Y }> are
459equivalent to these as well. In fact, white space and even
460hyphens can usually be added or deleted anywhere. So even C<\p{ Up-per case = Yes}> is
51f494cc 461equivalent. All this is called "loose-matching" by Unicode. The few places
b19eb496 462where stricter matching is used is in the middle of numbers, and in the Perl
51f494cc 463extension properties that begin or end with an underscore. Stricter matching
b19eb496 464cares about white space (except adjacent to non-word characters),
51f494cc 465hyphens, and non-interior underscores.
4193bef7 466
376d9008 467You can also use negation in both C<\p{}> and C<\P{}> by introducing a caret
a9130ea9 468(C<^>) between the first brace and the property name: C<\p{^Tamil}> is
eb0cc9e3 469equal to C<\P{Tamil}>.
4193bef7 470
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471Almost all properties are immune to case-insensitive matching. That is,
472adding a C</i> regular expression modifier does not change what they
473match. There are two sets that are affected.
474The first set is
475C<Uppercase_Letter>,
476C<Lowercase_Letter>,
477and C<Titlecase_Letter>,
478all of which match C<Cased_Letter> under C</i> matching.
479And the second set is
480C<Uppercase>,
481C<Lowercase>,
482and C<Titlecase>,
483all of which match C<Cased> under C</i> matching.
484This set also includes its subsets C<PosixUpper> and C<PosixLower> both
a9130ea9 485of which under C</i> match C<PosixAlpha>.
56ca34ca 486(The difference between these sets is that some things, such as Roman
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487numerals, come in both upper and lower case so they are C<Cased>, but
488aren't considered letters, so they aren't C<Cased_Letter>'s.)
56ca34ca 489
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490See L</Beyond Unicode code points> for special considerations when
491matching Unicode properties against non-Unicode code points.
94b42e47 492
51f494cc 493=head3 B<General_Category>
14bb0a9a 494
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495Every Unicode character is assigned a general category, which is the "most
496usual categorization of a character" (from
497L<http://www.unicode.org/reports/tr44>).
822502e5 498
9f815e24 499The compound way of writing these is like C<\p{General_Category=Number}>
b65e6125 500(short: C<\p{gc:n}>). But Perl furnishes shortcuts in which everything up
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501through the equal or colon separator is omitted. So you can instead just write
502C<\pN>.
822502e5 503
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504Here are the short and long forms of the values the C<General Category> property
505can have:
393fec97 506
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507 Short Long
508
509 L Letter
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510 LC, L& Cased_Letter (that is: [\p{Ll}\p{Lu}\p{Lt}])
511 Lu Uppercase_Letter
512 Ll Lowercase_Letter
513 Lt Titlecase_Letter
514 Lm Modifier_Letter
515 Lo Other_Letter
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516
517 M Mark
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518 Mn Nonspacing_Mark
519 Mc Spacing_Mark
520 Me Enclosing_Mark
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521
522 N Number
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523 Nd Decimal_Number (also Digit)
524 Nl Letter_Number
525 No Other_Number
526
527 P Punctuation (also Punct)
528 Pc Connector_Punctuation
529 Pd Dash_Punctuation
530 Ps Open_Punctuation
531 Pe Close_Punctuation
532 Pi Initial_Punctuation
d73e5302 533 (may behave like Ps or Pe depending on usage)
51f494cc 534 Pf Final_Punctuation
d73e5302 535 (may behave like Ps or Pe depending on usage)
51f494cc 536 Po Other_Punctuation
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537
538 S Symbol
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539 Sm Math_Symbol
540 Sc Currency_Symbol
541 Sk Modifier_Symbol
542 So Other_Symbol
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543
544 Z Separator
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545 Zs Space_Separator
546 Zl Line_Separator
547 Zp Paragraph_Separator
d73e5302
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548
549 C Other
d88362ca 550 Cc Control (also Cntrl)
e150c829 551 Cf Format
6d4f9cf2 552 Cs Surrogate
51f494cc 553 Co Private_Use
e150c829 554 Cn Unassigned
1ac13f9a 555
376d9008 556Single-letter properties match all characters in any of the
3e4dbfed 557two-letter sub-properties starting with the same letter.
b19eb496 558C<LC> and C<L&> are special: both are aliases for the set consisting of everything matched by C<Ll>, C<Lu>, and C<Lt>.
32293815 559
51f494cc 560=head3 B<Bidirectional Character Types>
822502e5 561
b19eb496 562Because scripts differ in their directionality (Hebrew and Arabic are
a9130ea9 563written right to left, for example) Unicode supplies a C<Bidi_Class> property.
1850f57f 564Some of the values this property can have are:
32293815 565
88af3b93 566 Value Meaning
92e830a9 567
12ac2576
JP
568 L Left-to-Right
569 LRE Left-to-Right Embedding
570 LRO Left-to-Right Override
571 R Right-to-Left
51f494cc 572 AL Arabic Letter
12ac2576
JP
573 RLE Right-to-Left Embedding
574 RLO Right-to-Left Override
575 PDF Pop Directional Format
576 EN European Number
51f494cc
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577 ES European Separator
578 ET European Terminator
12ac2576 579 AN Arabic Number
51f494cc 580 CS Common Separator
12ac2576
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581 NSM Non-Spacing Mark
582 BN Boundary Neutral
583 B Paragraph Separator
584 S Segment Separator
585 WS Whitespace
586 ON Other Neutrals
587
51f494cc
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588This property is always written in the compound form.
589For example, C<\p{Bidi_Class:R}> matches characters that are normally
1850f57f 590written right to left. Unlike the
a9130ea9 591C<L</General_Category>> property, this
1850f57f
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592property can have more values added in a future Unicode release. Those
593listed above comprised the complete set for many Unicode releases, but
594others were added in Unicode 6.3; you can always find what the
20ada7da 595current ones are in L<perluniprops>. And
1850f57f 596L<http://www.unicode.org/reports/tr9/> describes how to use them.
eb0cc9e3 597
51f494cc
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598=head3 B<Scripts>
599
b19eb496 600The world's languages are written in many different scripts. This sentence
e1b711da 601(unless you're reading it in translation) is written in Latin, while Russian is
c69ca1d4 602written in Cyrillic, and Greek is written in, well, Greek; Japanese mainly in
e1b711da 603Hiragana or Katakana. There are many more.
51f494cc 604
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605The Unicode C<Script> and C<Script_Extensions> properties give what
606script a given character is in. The C<Script_Extensions> property is an
607improved version of C<Script>, as demonstrated below. Either property
608can be specified with the compound form like
82aed44a
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609C<\p{Script=Hebrew}> (short: C<\p{sc=hebr}>), or
610C<\p{Script_Extensions=Javanese}> (short: C<\p{scx=java}>).
611In addition, Perl furnishes shortcuts for all
48791bf1
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612C<Script_Extensions> property names. You can omit everything up through
613the equals (or colon), and simply write C<\p{Latin}> or C<\P{Cyrillic}>.
614(This is not true for C<Script>, which is required to be
615written in the compound form. Prior to Perl v5.26, the single form
616returned the plain old C<Script> version, but was changed because
617C<Script_Extensions> gives better results.)
82aed44a
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618
619The difference between these two properties involves characters that are
620used in multiple scripts. For example the digits '0' through '9' are
621used in many parts of the world. These are placed in a script named
622C<Common>. Other characters are used in just a few scripts. For
a9130ea9 623example, the C<"KATAKANA-HIRAGANA DOUBLE HYPHEN"> is used in both Japanese
82aed44a
KW
624scripts, Katakana and Hiragana, but nowhere else. The C<Script>
625property places all characters that are used in multiple scripts in the
626C<Common> script, while the C<Script_Extensions> property places those
627that are used in only a few scripts into each of those scripts; while
628still using C<Common> for those used in many scripts. Thus both these
629match:
630
631 "0" =~ /\p{sc=Common}/ # Matches
632 "0" =~ /\p{scx=Common}/ # Matches
633
634and only the first of these match:
635
636 "\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{sc=Common} # Matches
637 "\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{scx=Common} # No match
638
639And only the last two of these match:
640
641 "\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{sc=Hiragana} # No match
642 "\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{sc=Katakana} # No match
643 "\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{scx=Hiragana} # Matches
644 "\N{KATAKANA-HIRAGANA DOUBLE HYPHEN}" =~ /\p{scx=Katakana} # Matches
645
646C<Script_Extensions> is thus an improved C<Script>, in which there are
647fewer characters in the C<Common> script, and correspondingly more in
648other scripts. It is new in Unicode version 6.0, and its data are likely
649to change significantly in later releases, as things get sorted out.
b65e6125 650New code should probably be using C<Script_Extensions> and not plain
48791bf1
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651C<Script>. If you compile perl with a Unicode release that doesn't have
652C<Script_Extensions>, the single form Perl extensions will instead refer
653to the plain C<Script> property. If you compile with a version of
654Unicode that doesn't have the C<Script> property, these extensions will
655not be defined at all.
82aed44a
KW
656
657(Actually, besides C<Common>, the C<Inherited> script, contains
658characters that are used in multiple scripts. These are modifier
b65e6125 659characters which inherit the script value
82aed44a
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660of the controlling character. Some of these are used in many scripts,
661and so go into C<Inherited> in both C<Script> and C<Script_Extensions>.
662Others are used in just a few scripts, so are in C<Inherited> in
663C<Script>, but not in C<Script_Extensions>.)
664
665It is worth stressing that there are several different sets of digits in
666Unicode that are equivalent to 0-9 and are matchable by C<\d> in a
667regular expression. If they are used in a single language only, they
48791bf1 668are in that language's C<Script> and C<Script_Extensions>. If they are
82aed44a
KW
669used in more than one script, they will be in C<sc=Common>, but only
670if they are used in many scripts should they be in C<scx=Common>.
51f494cc 671
48791bf1
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672The explanation above has omitted some detail; refer to UAX#24 "Unicode
673Script Property": L<http://www.unicode.org/reports/tr24>.
674
51f494cc
KW
675A complete list of scripts and their shortcuts is in L<perluniprops>.
676
a9130ea9 677=head3 B<Use of the C<"Is"> Prefix>
822502e5 678
b65e6125
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679For backward compatibility (with Perl 5.6), all properties writable
680without using the compound form mentioned
51f494cc
KW
681so far may have C<Is> or C<Is_> prepended to their name, so C<\P{Is_Lu}>, for
682example, is equal to C<\P{Lu}>, and C<\p{IsScript:Arabic}> is equal to
683C<\p{Arabic}>.
eb0cc9e3 684
51f494cc 685=head3 B<Blocks>
2796c109 686
1bfb14c4
JH
687In addition to B<scripts>, Unicode also defines B<blocks> of
688characters. The difference between scripts and blocks is that the
689concept of scripts is closer to natural languages, while the concept
51f494cc 690of blocks is more of an artificial grouping based on groups of Unicode
a9130ea9 691characters with consecutive ordinal values. For example, the C<"Basic Latin">
b65e6125 692block is all the characters whose ordinals are between 0 and 127, inclusive; in
a9130ea9
KW
693other words, the ASCII characters. The C<"Latin"> script contains some letters
694from this as well as several other blocks, like C<"Latin-1 Supplement">,
b65e6125 695C<"Latin Extended-A">, I<etc.>, but it does not contain all the characters from
7be67b37 696those blocks. It does not, for example, contain the digits 0-9, because
82aed44a
KW
697those digits are shared across many scripts, and hence are in the
698C<Common> script.
51f494cc
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699
700For more about scripts versus blocks, see UAX#24 "Unicode Script Property":
701L<http://www.unicode.org/reports/tr24>
702
48791bf1 703The C<Script_Extensions> or C<Script> properties are likely to be the
82aed44a 704ones you want to use when processing
a9130ea9 705natural language; the C<Block> property may occasionally be useful in working
b19eb496 706with the nuts and bolts of Unicode.
51f494cc
KW
707
708Block names are matched in the compound form, like C<\p{Block: Arrows}> or
b19eb496 709C<\p{Blk=Hebrew}>. Unlike most other properties, only a few block names have a
6b5cf123
KW
710Unicode-defined short name.
711
712Perl also defines single form synonyms for the block property in cases
713where these do not conflict with something else. But don't use any of
714these, because they are unstable. Since these are Perl extensions, they
715are subordinate to official Unicode property names; Unicode doesn't know
716nor care about Perl's extensions. It may happen that a name that
717currently means the Perl extension will later be changed without warning
718to mean a different Unicode property in a future version of the perl
719interpreter that uses a later Unicode release, and your code would no
720longer work. The extensions are mentioned here for completeness: Take
721the block name and prefix it with one of: C<In> (for example
722C<\p{Blk=Arrows}> can currently be written as C<\p{In_Arrows}>); or
723sometimes C<Is> (like C<\p{Is_Arrows}>); or sometimes no prefix at all
48791bf1 724(C<\p{Arrows}>). As of this writing (Unicode 9.0) there are no
6b5cf123
KW
725conflicts with using the C<In_> prefix, but there are plenty with the
726other two forms. For example, C<\p{Is_Hebrew}> and C<\p{Hebrew}> mean
48791bf1
KW
727C<\p{Script_Extensions=Hebrew}> which is NOT the same thing as
728C<\p{Blk=Hebrew}>. Our
6b5cf123
KW
729advice used to be to use the C<In_> prefix as a single form way of
730specifying a block. But Unicode 8.0 added properties whose names begin
731with C<In>, and it's now clear that it's only luck that's so far
732prevented a conflict. Using C<In> is only marginally less typing than
733C<Blk:>, and the latter's meaning is clearer anyway, and guaranteed to
734never conflict. So don't take chances. Use C<\p{Blk=foo}> for new
735code. And be sure that block is what you really really want to do. In
736most cases scripts are what you want instead.
737
738A complete list of blocks is in L<perluniprops>.
51f494cc 739
9f815e24
KW
740=head3 B<Other Properties>
741
742There are many more properties than the very basic ones described here.
743A complete list is in L<perluniprops>.
744
745Unicode defines all its properties in the compound form, so all single-form
b19eb496
TC
746properties are Perl extensions. Most of these are just synonyms for the
747Unicode ones, but some are genuine extensions, including several that are in
9f815e24
KW
748the compound form. And quite a few of these are actually recommended by Unicode
749(in L<http://www.unicode.org/reports/tr18>).
750
5bff2035
KW
751This section gives some details on all extensions that aren't just
752synonyms for compound-form Unicode properties
753(for those properties, you'll have to refer to the
9f815e24
KW
754L<Unicode Standard|http://www.unicode.org/reports/tr44>.
755
756=over
757
758=item B<C<\p{All}>>
759
2d88a86a
KW
760This matches every possible code point. It is equivalent to C<qr/./s>.
761Unlike all the other non-user-defined C<\p{}> property matches, no
762warning is ever generated if this is property is matched against a
763non-Unicode code point (see L</Beyond Unicode code points> below).
9f815e24
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764
765=item B<C<\p{Alnum}>>
766
767This matches any C<\p{Alphabetic}> or C<\p{Decimal_Number}> character.
768
769=item B<C<\p{Any}>>
770
2d88a86a
KW
771This matches any of the 1_114_112 Unicode code points. It is a synonym
772for C<\p{Unicode}>.
9f815e24 773
42581d5d
KW
774=item B<C<\p{ASCII}>>
775
776This matches any of the 128 characters in the US-ASCII character set,
777which is a subset of Unicode.
778
9f815e24
KW
779=item B<C<\p{Assigned}>>
780
a9130ea9
KW
781This matches any assigned code point; that is, any code point whose L<general
782category|/General_Category> is not C<Unassigned> (or equivalently, not C<Cn>).
9f815e24
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783
784=item B<C<\p{Blank}>>
785
786This is the same as C<\h> and C<\p{HorizSpace}>: A character that changes the
787spacing horizontally.
788
789=item B<C<\p{Decomposition_Type: Non_Canonical}>> (Short: C<\p{Dt=NonCanon}>)
790
791Matches a character that has a non-canonical decomposition.
792
a6a7eedc
KW
793The L</Extended Grapheme Clusters (Logical characters)> section above
794talked about canonical decompositions. However, many more characters
795have a different type of decomposition, a "compatible" or
796"non-canonical" decomposition. The sequences that form these
797decompositions are not considered canonically equivalent to the
798pre-composed character. An example is the C<"SUPERSCRIPT ONE">. It is
799somewhat like a regular digit 1, but not exactly; its decomposition into
800the digit 1 is called a "compatible" decomposition, specifically a
9f815e24 801"super" decomposition. There are several such compatibility
b65e6125
KW
802decompositions (see L<http://www.unicode.org/reports/tr44>), including
803one called "compat", which means some miscellaneous type of
804decomposition that doesn't fit into the other decomposition categories
805that Unicode has chosen.
9f815e24
KW
806
807Note that most Unicode characters don't have a decomposition, so their
a9130ea9 808decomposition type is C<"None">.
9f815e24 809
b19eb496
TC
810For your convenience, Perl has added the C<Non_Canonical> decomposition
811type to mean any of the several compatibility decompositions.
9f815e24
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812
813=item B<C<\p{Graph}>>
814
815Matches any character that is graphic. Theoretically, this means a character
816that on a printer would cause ink to be used.
817
818=item B<C<\p{HorizSpace}>>
819
b19eb496 820This is the same as C<\h> and C<\p{Blank}>: a character that changes the
9f815e24
KW
821spacing horizontally.
822
42581d5d 823=item B<C<\p{In=*}>>
9f815e24
KW
824
825This is a synonym for C<\p{Present_In=*}>
826
827=item B<C<\p{PerlSpace}>>
828
d28d8023 829This is the same as C<\s>, restricted to ASCII, namely C<S<[ \f\n\r\t]>>
779cf272 830and starting in Perl v5.18, a vertical tab.
9f815e24
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831
832Mnemonic: Perl's (original) space
833
834=item B<C<\p{PerlWord}>>
835
836This is the same as C<\w>, restricted to ASCII, namely C<[A-Za-z0-9_]>
837
838Mnemonic: Perl's (original) word.
839
42581d5d 840=item B<C<\p{Posix...}>>
9f815e24 841
b65e6125
KW
842There are several of these, which are equivalents, using the C<\p{}>
843notation, for Posix classes and are described in
42581d5d 844L<perlrecharclass/POSIX Character Classes>.
9f815e24
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845
846=item B<C<\p{Present_In: *}>> (Short: C<\p{In=*}>)
847
848This property is used when you need to know in what Unicode version(s) a
849character is.
850
851The "*" above stands for some two digit Unicode version number, such as
852C<1.1> or C<4.0>; or the "*" can also be C<Unassigned>. This property will
853match the code points whose final disposition has been settled as of the
854Unicode release given by the version number; C<\p{Present_In: Unassigned}>
855will match those code points whose meaning has yet to be assigned.
856
a9130ea9 857For example, C<U+0041> C<"LATIN CAPITAL LETTER A"> was present in the very first
9f815e24
KW
858Unicode release available, which is C<1.1>, so this property is true for all
859valid "*" versions. On the other hand, C<U+1EFF> was not assigned until version
a9130ea9 8605.1 when it became C<"LATIN SMALL LETTER Y WITH LOOP">, so the only "*" that
9f815e24
KW
861would match it are 5.1, 5.2, and later.
862
863Unicode furnishes the C<Age> property from which this is derived. The problem
864with Age is that a strict interpretation of it (which Perl takes) has it
865matching the precise release a code point's meaning is introduced in. Thus
866C<U+0041> would match only 1.1; and C<U+1EFF> only 5.1. This is not usually what
867you want.
868
869Some non-Perl implementations of the Age property may change its meaning to be
a9130ea9 870the same as the Perl C<Present_In> property; just be aware of that.
9f815e24
KW
871
872Another confusion with both these properties is that the definition is not
b19eb496
TC
873that the code point has been I<assigned>, but that the meaning of the code point
874has been I<determined>. This is because 66 code points will always be
a9130ea9 875unassigned, and so the C<Age> for them is the Unicode version in which the decision
b19eb496 876to make them so was made. For example, C<U+FDD0> is to be permanently
9f815e24 877unassigned to a character, and the decision to do that was made in version 3.1,
b19eb496 878so C<\p{Age=3.1}> matches this character, as also does C<\p{Present_In: 3.1}> and up.
9f815e24
KW
879
880=item B<C<\p{Print}>>
881
ae5b72c8 882This matches any character that is graphical or blank, except controls.
9f815e24
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883
884=item B<C<\p{SpacePerl}>>
885
886This is the same as C<\s>, including beyond ASCII.
887
4d4acfba 888Mnemonic: Space, as modified by Perl. (It doesn't include the vertical tab
779cf272 889until v5.18, which both the Posix standard and Unicode consider white space.)
9f815e24 890
4364919a
KW
891=item B<C<\p{Title}>> and B<C<\p{Titlecase}>>
892
893Under case-sensitive matching, these both match the same code points as
894C<\p{General Category=Titlecase_Letter}> (C<\p{gc=lt}>). The difference
895is that under C</i> caseless matching, these match the same as
896C<\p{Cased}>, whereas C<\p{gc=lt}> matches C<\p{Cased_Letter>).
897
2d88a86a
KW
898=item B<C<\p{Unicode}>>
899
900This matches any of the 1_114_112 Unicode code points.
901C<\p{Any}>.
902
9f815e24
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903=item B<C<\p{VertSpace}>>
904
905This is the same as C<\v>: A character that changes the spacing vertically.
906
907=item B<C<\p{Word}>>
908
b19eb496 909This is the same as C<\w>, including over 100_000 characters beyond ASCII.
9f815e24 910
42581d5d
KW
911=item B<C<\p{XPosix...}>>
912
b19eb496 913There are several of these, which are the standard Posix classes
42581d5d
KW
914extended to the full Unicode range. They are described in
915L<perlrecharclass/POSIX Character Classes>.
916
9f815e24
KW
917=back
918
a9130ea9 919
376d9008 920=head2 User-Defined Character Properties
491fd90a 921
51f494cc 922You can define your own binary character properties by defining subroutines
a9130ea9 923whose names begin with C<"In"> or C<"Is">. (The experimental feature
9d1a5160
KW
924L<perlre/(?[ ])> provides an alternative which allows more complex
925definitions.) The subroutines can be defined in any
51f494cc 926package. The user-defined properties can be used in the regular expression
a9130ea9 927C<\p{}> and C<\P{}> constructs; if you are using a user-defined property from a
51f494cc 928package other than the one you are in, you must specify its package in the
a9130ea9 929C<\p{}> or C<\P{}> construct.
bac0b425 930
51f494cc 931 # assuming property Is_Foreign defined in Lang::
bac0b425
JP
932 package main; # property package name required
933 if ($txt =~ /\p{Lang::IsForeign}+/) { ... }
934
935 package Lang; # property package name not required
936 if ($txt =~ /\p{IsForeign}+/) { ... }
937
938
939Note that the effect is compile-time and immutable once defined.
b19eb496
TC
940However, the subroutines are passed a single parameter, which is 0 if
941case-sensitive matching is in effect and non-zero if caseless matching
56ca34ca
KW
942is in effect. The subroutine may return different values depending on
943the value of the flag, and one set of values will immutably be in effect
b19eb496 944for all case-sensitive matches, and the other set for all case-insensitive
56ca34ca 945matches.
491fd90a 946
b19eb496 947Note that if the regular expression is tainted, then Perl will die rather
a9130ea9 948than calling the subroutine when the name of the subroutine is
0e9be77f
DM
949determined by the tainted data.
950
376d9008
JB
951The subroutines must return a specially-formatted string, with one
952or more newline-separated lines. Each line must be one of the following:
491fd90a
JH
953
954=over 4
955
956=item *
957
df9e1087 958A single hexadecimal number denoting a code point to include.
510254c9
A
959
960=item *
961
99a6b1f0 962Two hexadecimal numbers separated by horizontal whitespace (space or
df9e1087 963tabular characters) denoting a range of code points to include.
491fd90a
JH
964
965=item *
966
a9130ea9
KW
967Something to include, prefixed by C<"+">: a built-in character
968property (prefixed by C<"utf8::">) or a fully qualified (including package
830137a2 969name) user-defined character property,
bac0b425
JP
970to represent all the characters in that property; two hexadecimal code
971points for a range; or a single hexadecimal code point.
491fd90a
JH
972
973=item *
974
a9130ea9
KW
975Something to exclude, prefixed by C<"-">: an existing character
976property (prefixed by C<"utf8::">) or a fully qualified (including package
830137a2 977name) user-defined character property,
bac0b425
JP
978to represent all the characters in that property; two hexadecimal code
979points for a range; or a single hexadecimal code point.
491fd90a
JH
980
981=item *
982
a9130ea9
KW
983Something to negate, prefixed C<"!">: an existing character
984property (prefixed by C<"utf8::">) or a fully qualified (including package
830137a2 985name) user-defined character property,
bac0b425
JP
986to represent all the characters in that property; two hexadecimal code
987points for a range; or a single hexadecimal code point.
988
989=item *
990
a9130ea9
KW
991Something to intersect with, prefixed by C<"&">: an existing character
992property (prefixed by C<"utf8::">) or a fully qualified (including package
830137a2 993name) user-defined character property,
bac0b425
JP
994for all the characters except the characters in the property; two
995hexadecimal code points for a range; or a single hexadecimal code point.
491fd90a
JH
996
997=back
998
999For example, to define a property that covers both the Japanese
1000syllabaries (hiragana and katakana), you can define
1001
1002 sub InKana {
d88362ca 1003 return <<END;
d5822f25
A
1004 3040\t309F
1005 30A0\t30FF
491fd90a
JH
1006 END
1007 }
1008
d5822f25
A
1009Imagine that the here-doc end marker is at the beginning of the line.
1010Now you can use C<\p{InKana}> and C<\P{InKana}>.
491fd90a
JH
1011
1012You could also have used the existing block property names:
1013
1014 sub InKana {
d88362ca 1015 return <<'END';
491fd90a
JH
1016 +utf8::InHiragana
1017 +utf8::InKatakana
1018 END
1019 }
1020
1021Suppose you wanted to match only the allocated characters,
d5822f25 1022not the raw block ranges: in other words, you want to remove
b65e6125 1023the unassigned characters:
491fd90a
JH
1024
1025 sub InKana {
d88362ca 1026 return <<'END';
491fd90a
JH
1027 +utf8::InHiragana
1028 +utf8::InKatakana
1029 -utf8::IsCn
1030 END
1031 }
1032
1033The negation is useful for defining (surprise!) negated classes.
1034
1035 sub InNotKana {
d88362ca 1036 return <<'END';
491fd90a
JH
1037 !utf8::InHiragana
1038 -utf8::InKatakana
1039 +utf8::IsCn
1040 END
1041 }
1042
461020ad
KW
1043This will match all non-Unicode code points, since every one of them is
1044not in Kana. You can use intersection to exclude these, if desired, as
1045this modified example shows:
bac0b425 1046
461020ad 1047 sub InNotKana {
bac0b425 1048 return <<'END';
461020ad
KW
1049 !utf8::InHiragana
1050 -utf8::InKatakana
1051 +utf8::IsCn
1052 &utf8::Any
bac0b425
JP
1053 END
1054 }
1055
461020ad
KW
1056C<&utf8::Any> must be the last line in the definition.
1057
1058Intersection is used generally for getting the common characters matched
a9130ea9 1059by two (or more) classes. It's important to remember not to use C<"&"> for
461020ad
KW
1060the first set; that would be intersecting with nothing, resulting in an
1061empty set.
1062
2d88a86a
KW
1063Unlike non-user-defined C<\p{}> property matches, no warning is ever
1064generated if these properties are matched against a non-Unicode code
1065point (see L</Beyond Unicode code points> below).
bac0b425 1066
68585b5e 1067=head2 User-Defined Case Mappings (for serious hackers only)
822502e5 1068
5d1892be 1069B<This feature has been removed as of Perl 5.16.>
a9130ea9 1070The CPAN module C<L<Unicode::Casing>> provides better functionality without
5d1892be
KW
1071the drawbacks that this feature had. If you are using a Perl earlier
1072than 5.16, this feature was most fully documented in the 5.14 version of
1073this pod:
1074L<http://perldoc.perl.org/5.14.0/perlunicode.html#User-Defined-Case-Mappings-%28for-serious-hackers-only%29>
3a2263fe 1075
376d9008 1076=head2 Character Encodings for Input and Output
8cbd9a7a 1077
7221edc9 1078See L<Encode>.
8cbd9a7a 1079
c29a771d 1080=head2 Unicode Regular Expression Support Level
776f8809 1081
b19eb496 1082The following list of Unicode supported features for regular expressions describes
fea12a3e
KW
1083all features currently directly supported by core Perl. The references
1084to "Level I<N>" and the section numbers refer to
1085L<UTS#18 "Unicode Regular Expressions"|http://www.unicode.org/reports/tr18>,
1086version 13, November 2013.
1087
1088=head3 Level 1 - Basic Unicode Support
1089
1090 RL1.1 Hex Notation - Done [1]
1091 RL1.2 Properties - Done [2]
1092 RL1.2a Compatibility Properties - Done [3]
1093 RL1.3 Subtraction and Intersection - Experimental [4]
1094 RL1.4 Simple Word Boundaries - Done [5]
1095 RL1.5 Simple Loose Matches - Done [6]
1096 RL1.6 Line Boundaries - Partial [7]
1097 RL1.7 Supplementary Code Points - Done [8]
755789c0 1098
6f33e417
KW
1099=over 4
1100
a6a7eedc 1101=item [1] C<\N{U+...}> and C<\x{...}>
6f33e417 1102
fea12a3e
KW
1103=item [2]
1104C<\p{...}> C<\P{...}>. This requirement is for a minimal list of
1105properties. Perl supports these and all other Unicode character
1106properties, as R2.7 asks (see L</"Unicode Character Properties"> above).
6f33e417 1107
fea12a3e
KW
1108=item [3]
1109Perl has C<\d> C<\D> C<\s> C<\S> C<\w> C<\W> C<\X> C<[:I<prop>:]>
1110C<[:^I<prop>:]>, plus all the properties specified by
1111L<http://www.unicode.org/reports/tr18/#Compatibility_Properties>. These
1112are described above in L</Other Properties>
6f33e417 1113
fea12a3e 1114=item [4]
6f33e417 1115
fea12a3e 1116The experimental feature C<"(?[...])"> starting in v5.18 accomplishes
a6a7eedc 1117this.
6f33e417 1118
a6a7eedc
KW
1119See L<perlre/(?[ ])>. If you don't want to use an experimental
1120feature, you can use one of the following:
6f33e417
KW
1121
1122=over 4
1123
a6a7eedc 1124=item *
f67a5002 1125Regular expression lookahead
6f33e417
KW
1126
1127You can mimic class subtraction using lookahead.
8158862b 1128For example, what UTS#18 might write as
29bdacb8 1129
209c9685 1130 [{Block=Greek}-[{UNASSIGNED}]]
dbe420b4
JH
1131
1132in Perl can be written as:
1133
209c9685
KW
1134 (?!\p{Unassigned})\p{Block=Greek}
1135 (?=\p{Assigned})\p{Block=Greek}
dbe420b4
JH
1136
1137But in this particular example, you probably really want
1138
209c9685 1139 \p{Greek}
dbe420b4
JH
1140
1141which will match assigned characters known to be part of the Greek script.
29bdacb8 1142
a6a7eedc
KW
1143=item *
1144
1145CPAN module C<L<Unicode::Regex::Set>>
8158862b 1146
6f33e417
KW
1147It does implement the full UTS#18 grouping, intersection, union, and
1148removal (subtraction) syntax.
8158862b 1149
a6a7eedc
KW
1150=item *
1151
1152L</"User-Defined Character Properties">
6f33e417 1153
a9130ea9 1154C<"+"> for union, C<"-"> for removal (set-difference), C<"&"> for intersection
6f33e417
KW
1155
1156=back
1157
fea12a3e
KW
1158=item [5]
1159C<\b> C<\B> meet most, but not all, the details of this requirement, but
1160C<\b{wb}> and C<\B{wb}> do, as well as the stricter R2.3.
1161
1162=item [6]
6f33e417 1163
a6a7eedc 1164Note that Perl does Full case-folding in matching, not Simple:
6f33e417 1165
a6a7eedc
KW
1166For example C<U+1F88> is equivalent to C<U+1F00 U+03B9>, instead of just
1167C<U+1F80>. This difference matters mainly for certain Greek capital
a9130ea9
KW
1168letters with certain modifiers: the Full case-folding decomposes the
1169letter, while the Simple case-folding would map it to a single
1170character.
6f33e417 1171
fea12a3e
KW
1172=item [7]
1173
1174The reason this is considered to be only partially implemented is that
1175Perl has L<C<qrE<sol>\b{lb}E<sol>>|perlrebackslash/\b{lb}> and
1176C<L<Unicode::LineBreak>> that are conformant with
1177L<UAX#14 "Unicode Line Breaking Algorithm"|http://www.unicode.org/reports/tr14>.
1178The regular expression construct provides default behavior, while the
1179heavier-weight module provides customizable line breaking.
1180
1181But Perl treats C<\n> as the start- and end-line
1182delimiter, whereas Unicode specifies more characters that should be
1183so-interpreted.
6f33e417 1184
a6a7eedc 1185These are:
6f33e417 1186
a6a7eedc
KW
1187 VT U+000B (\v in C)
1188 FF U+000C (\f)
1189 CR U+000D (\r)
1190 NEL U+0085
1191 LS U+2028
1192 PS U+2029
6f33e417 1193
a6a7eedc
KW
1194C<^> and C<$> in regular expression patterns are supposed to match all
1195these, but don't.
1196These characters also don't, but should, affect C<< <> >> C<$.>, and
1197script line numbers.
6f33e417 1198
a6a7eedc
KW
1199Also, lines should not be split within C<CRLF> (i.e. there is no
1200empty line between C<\r> and C<\n>). For C<CRLF>, try the C<:crlf>
1201layer (see L<PerlIO>).
1202
fea12a3e 1203=item [8]
a9130ea9
KW
1204UTF-8/UTF-EBDDIC used in Perl allows not only C<U+10000> to
1205C<U+10FFFF> but also beyond C<U+10FFFF>
6f33e417
KW
1206
1207=back
5ca1ac52 1208
fea12a3e 1209=head3 Level 2 - Extended Unicode Support
776f8809 1210
fea12a3e
KW
1211 RL2.1 Canonical Equivalents - Retracted [9]
1212 by Unicode
1213 RL2.2 Extended Grapheme Clusters - Partial [10]
1214 RL2.3 Default Word Boundaries - Done [11]
1215 RL2.4 Default Case Conversion - Done
1216 RL2.5 Name Properties - Done
1217 RL2.6 Wildcard Properties - Missing
1218 RL2.7 Full Properties - Done
776f8809 1219
fea12a3e 1220=over 4
8158862b 1221
fea12a3e
KW
1222=item [9]
1223Unicode has rewritten this portion of UTS#18 to say that getting
1224canonical equivalence (see UAX#15
1225L<"Unicode Normalization Forms"|http://www.unicode.org/reports/tr15>)
1226is basically to be done at the programmer level. Use NFD to write
1227both your regular expressions and text to match them against (you
1228can use L<Unicode::Normalize>).
776f8809 1229
fea12a3e
KW
1230=item [10]
1231Perl has C<\X> and C<\b{gcb}> but we don't have a "Grapheme Cluster Mode".
1232
1233=item [11] see
1234L<UAX#29 "Unicode Text Segmentation"|http://www.unicode.org/reports/tr29>,
1235
1236=back
1237
1238=head3 Level 3 - Tailored Support
1239
1240 RL3.1 Tailored Punctuation - Missing
1241 RL3.2 Tailored Grapheme Clusters - Missing [12]
1242 RL3.3 Tailored Word Boundaries - Missing
1243 RL3.4 Tailored Loose Matches - Retracted by Unicode
1244 RL3.5 Tailored Ranges - Retracted by Unicode
1245 RL3.6 Context Matching - Missing [13]
1246 RL3.7 Incremental Matches - Missing
1247 RL3.8 Unicode Set Sharing - Unicode is proposing
1248 to retract this
1249 RL3.9 Possible Match Sets - Missing
1250 RL3.10 Folded Matching - Retracted by Unicode
1251 RL3.11 Submatchers - Missing
1252
1253=over 4
1254
1255=item [12]
1256Perl has L<Unicode::Collate>, but it isn't integrated with regular
1257expressions. See
1258L<UTS#10 "Unicode Collation Algorithms"|http://www.unicode.org/reports/tr10>.
776f8809 1259
fea12a3e
KW
1260=item [13]
1261Perl has C<(?<=x)> and C<(?=x)>, but lookaheads or lookbehinds should
1262see outside of the target substring
776f8809
JH
1263
1264=back
1265
c349b1b9
JH
1266=head2 Unicode Encodings
1267
376d9008
JB
1268Unicode characters are assigned to I<code points>, which are abstract
1269numbers. To use these numbers, various encodings are needed.
c349b1b9
JH
1270
1271=over 4
1272
c29a771d 1273=item *
5cb3728c
RB
1274
1275UTF-8
c349b1b9 1276
6d4f9cf2 1277UTF-8 is a variable-length (1 to 4 bytes), byte-order independent
a6a7eedc
KW
1278encoding. In most of Perl's documentation, including elsewhere in this
1279document, the term "UTF-8" means also "UTF-EBCDIC". But in this section,
1280"UTF-8" refers only to the encoding used on ASCII platforms. It is a
1281superset of 7-bit US-ASCII, so anything encoded in ASCII has the
1282identical representation when encoded in UTF-8.
c349b1b9 1283
8c007b5a 1284The following table is from Unicode 3.2.
05632f9a 1285
755789c0 1286 Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
05632f9a 1287
d88362ca 1288 U+0000..U+007F 00..7F
e1b711da 1289 U+0080..U+07FF * C2..DF 80..BF
d88362ca 1290 U+0800..U+0FFF E0 * A0..BF 80..BF
ec90690f
ST
1291 U+1000..U+CFFF E1..EC 80..BF 80..BF
1292 U+D000..U+D7FF ED 80..9F 80..BF
755789c0 1293 U+D800..U+DFFF +++++ utf16 surrogates, not legal utf8 +++++
ec90690f 1294 U+E000..U+FFFF EE..EF 80..BF 80..BF
d88362ca
KW
1295 U+10000..U+3FFFF F0 * 90..BF 80..BF 80..BF
1296 U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF
1297 U+100000..U+10FFFF F4 80..8F 80..BF 80..BF
e1b711da 1298
b19eb496 1299Note the gaps marked by "*" before several of the byte entries above. These are
e1b711da
KW
1300caused by legal UTF-8 avoiding non-shortest encodings: it is technically
1301possible to UTF-8-encode a single code point in different ways, but that is
1302explicitly forbidden, and the shortest possible encoding should always be used
1303(and that is what Perl does).
37361303 1304
376d9008 1305Another way to look at it is via bits:
05632f9a 1306
755789c0 1307 Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
05632f9a 1308
755789c0
KW
1309 0aaaaaaa 0aaaaaaa
1310 00000bbbbbaaaaaa 110bbbbb 10aaaaaa
1311 ccccbbbbbbaaaaaa 1110cccc 10bbbbbb 10aaaaaa
1312 00000dddccccccbbbbbbaaaaaa 11110ddd 10cccccc 10bbbbbb 10aaaaaa
05632f9a 1313
a9130ea9 1314As you can see, the continuation bytes all begin with C<"10">, and the
e1b711da 1315leading bits of the start byte tell how many bytes there are in the
05632f9a
JH
1316encoded character.
1317
6d4f9cf2 1318The original UTF-8 specification allowed up to 6 bytes, to allow
a9130ea9 1319encoding of numbers up to C<0x7FFF_FFFF>. Perl continues to allow those,
6d4f9cf2
KW
1320and has extended that up to 13 bytes to encode code points up to what
1321can fit in a 64-bit word. However, Perl will warn if you output any of
b19eb496 1322these as being non-portable; and under strict UTF-8 input protocols,
760c7c2f
KW
1323they are forbidden. In addition, it is deprecated to use a code point
1324larger than what a signed integer variable on your system can hold. On
132532-bit ASCII systems, this means C<0x7FFF_FFFF> is the legal maximum
1326going forward (much higher on 64-bit systems).
6d4f9cf2 1327
c29a771d 1328=item *
5cb3728c
RB
1329
1330UTF-EBCDIC
dbe420b4 1331
b65e6125 1332Like UTF-8, but EBCDIC-safe, in the way that UTF-8 is ASCII-safe.
a6a7eedc
KW
1333This means that all the basic characters (which includes all
1334those that have ASCII equivalents (like C<"A">, C<"0">, C<"%">, I<etc.>)
1335are the same in both EBCDIC and UTF-EBCDIC.)
1336
c0236afe
KW
1337UTF-EBCDIC is used on EBCDIC platforms. It generally requires more
1338bytes to represent a given code point than UTF-8 does; the largest
1339Unicode code points take 5 bytes to represent (instead of 4 in UTF-8),
1340and, extended for 64-bit words, it uses 14 bytes instead of 13 bytes in
1341UTF-8.
dbe420b4 1342
c29a771d 1343=item *
5cb3728c 1344
b65e6125 1345UTF-16, UTF-16BE, UTF-16LE, Surrogates, and C<BOM>'s (Byte Order Marks)
c349b1b9 1346
1bfb14c4
JH
1347The followings items are mostly for reference and general Unicode
1348knowledge, Perl doesn't use these constructs internally.
dbe420b4 1349
b19eb496
TC
1350Like UTF-8, UTF-16 is a variable-width encoding, but where
1351UTF-8 uses 8-bit code units, UTF-16 uses 16-bit code units.
1352All code points occupy either 2 or 4 bytes in UTF-16: code points
1353C<U+0000..U+FFFF> are stored in a single 16-bit unit, and code
1bfb14c4 1354points C<U+10000..U+10FFFF> in two 16-bit units. The latter case is
c349b1b9
JH
1355using I<surrogates>, the first 16-bit unit being the I<high
1356surrogate>, and the second being the I<low surrogate>.
1357
376d9008 1358Surrogates are code points set aside to encode the C<U+10000..U+10FFFF>
c349b1b9 1359range of Unicode code points in pairs of 16-bit units. The I<high
9f815e24 1360surrogates> are the range C<U+D800..U+DBFF> and the I<low surrogates>
376d9008 1361are the range C<U+DC00..U+DFFF>. The surrogate encoding is
c349b1b9 1362
d88362ca
KW
1363 $hi = ($uni - 0x10000) / 0x400 + 0xD800;
1364 $lo = ($uni - 0x10000) % 0x400 + 0xDC00;
c349b1b9
JH
1365
1366and the decoding is
1367
d88362ca 1368 $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00);
c349b1b9 1369
376d9008 1370Because of the 16-bitness, UTF-16 is byte-order dependent. UTF-16
c349b1b9 1371itself can be used for in-memory computations, but if storage or
376d9008
JB
1372transfer is required either UTF-16BE (big-endian) or UTF-16LE
1373(little-endian) encodings must be chosen.
c349b1b9
JH
1374
1375This introduces another problem: what if you just know that your data
376d9008 1376is UTF-16, but you don't know which endianness? Byte Order Marks, or
b65e6125 1377C<BOM>'s, are a solution to this. A special character has been reserved
86bbd6d1 1378in Unicode to function as a byte order marker: the character with the
a9130ea9 1379code point C<U+FEFF> is the C<BOM>.
042da322 1380
a9130ea9 1381The trick is that if you read a C<BOM>, you will know the byte order,
376d9008
JB
1382since if it was written on a big-endian platform, you will read the
1383bytes C<0xFE 0xFF>, but if it was written on a little-endian platform,
1384you will read the bytes C<0xFF 0xFE>. (And if the originating platform
b65e6125
KW
1385was writing in ASCII platform UTF-8, you will read the bytes
1386C<0xEF 0xBB 0xBF>.)
042da322 1387
86bbd6d1 1388The way this trick works is that the character with the code point
6d4f9cf2 1389C<U+FFFE> is not supposed to be in input streams, so the
a9130ea9 1390sequence of bytes C<0xFF 0xFE> is unambiguously "C<BOM>, represented in
1bfb14c4 1391little-endian format" and cannot be C<U+FFFE>, represented in big-endian
6d4f9cf2
KW
1392format".
1393
1394Surrogates have no meaning in Unicode outside their use in pairs to
1395represent other code points. However, Perl allows them to be
1396represented individually internally, for example by saying
f651977e
TC
1397C<chr(0xD801)>, so that all code points, not just those valid for open
1398interchange, are
6d4f9cf2 1399representable. Unicode does define semantics for them, such as their
a9130ea9
KW
1400C<L</General_Category>> is C<"Cs">. But because their use is somewhat dangerous,
1401Perl will warn (using the warning category C<"surrogate">, which is a
1402sub-category of C<"utf8">) if an attempt is made
6d4f9cf2
KW
1403to do things like take the lower case of one, or match
1404case-insensitively, or to output them. (But don't try this on Perls
1405before 5.14.)
c349b1b9 1406
c29a771d 1407=item *
5cb3728c 1408
1e54db1a 1409UTF-32, UTF-32BE, UTF-32LE
c349b1b9 1410
b65e6125 1411The UTF-32 family is pretty much like the UTF-16 family, except that
042da322 1412the units are 32-bit, and therefore the surrogate scheme is not
a9130ea9 1413needed. UTF-32 is a fixed-width encoding. The C<BOM> signatures are
b19eb496 1414C<0x00 0x00 0xFE 0xFF> for BE and C<0xFF 0xFE 0x00 0x00> for LE.
c349b1b9 1415
c29a771d 1416=item *
5cb3728c
RB
1417
1418UCS-2, UCS-4
c349b1b9 1419
b19eb496 1420Legacy, fixed-width encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit
376d9008 1421encoding. Unlike UTF-16, UCS-2 is not extensible beyond C<U+FFFF>,
339cfa0e 1422because it does not use surrogates. UCS-4 is a 32-bit encoding,
b19eb496 1423functionally identical to UTF-32 (the difference being that
a9130ea9 1424UCS-4 forbids neither surrogates nor code points larger than C<0x10_FFFF>).
c349b1b9 1425
c29a771d 1426=item *
5cb3728c
RB
1427
1428UTF-7
c349b1b9 1429
376d9008
JB
1430A seven-bit safe (non-eight-bit) encoding, which is useful if the
1431transport or storage is not eight-bit safe. Defined by RFC 2152.
c349b1b9 1432
95a1a48b
JH
1433=back
1434
57e88091 1435=head2 Noncharacter code points
6d4f9cf2 1436
57e88091 143766 code points are set aside in Unicode as "noncharacter code points".
a9130ea9 1438These all have the C<Unassigned> (C<Cn>) C<L</General_Category>>, and
57e88091
KW
1439no character will ever be assigned to any of them. They are the 32 code
1440points between C<U+FDD0> and C<U+FDEF> inclusive, and the 34 code
1441points:
1442
1443 U+FFFE U+FFFF
1444 U+1FFFE U+1FFFF
1445 U+2FFFE U+2FFFF
1446 ...
1447 U+EFFFE U+EFFFF
1448 U+FFFFE U+FFFFF
1449 U+10FFFE U+10FFFF
1450
1451Until Unicode 7.0, the noncharacters were "B<forbidden> for use in open
1452interchange of Unicode text data", so that code that processed those
1453streams could use these code points as sentinels that could be mixed in
1454with character data, and would always be distinguishable from that data.
1455(Emphasis above and in the next paragraph are added in this document.)
1456
1457Unicode 7.0 changed the wording so that they are "B<not recommended> for
1458use in open interchange of Unicode text data". The 7.0 Standard goes on
1459to say:
1460
1461=over 4
1462
1463"If a noncharacter is received in open interchange, an application is
1464not required to interpret it in any way. It is good practice, however,
1465to recognize it as a noncharacter and to take appropriate action, such
1466as replacing it with C<U+FFFD> replacement character, to indicate the
1467problem in the text. It is not recommended to simply delete
1468noncharacter code points from such text, because of the potential
1469security issues caused by deleting uninterpreted characters. (See
1470conformance clause C7 in Section 3.2, Conformance Requirements, and
1471L<Unicode Technical Report #36, "Unicode Security
1472Considerations"|http://www.unicode.org/reports/tr36/#Substituting_for_Ill_Formed_Subsequences>)."
1473
1474=back
1475
1476This change was made because it was found that various commercial tools
1477like editors, or for things like source code control, had been written
1478so that they would not handle program files that used these code points,
1479effectively precluding their use almost entirely! And that was never
1480the intent. They've always been meant to be usable within an
1481application, or cooperating set of applications, at will.
1482
1483If you're writing code, such as an editor, that is supposed to be able
1484to handle any Unicode text data, then you shouldn't be using these code
1485points yourself, and instead allow them in the input. If you need
1486sentinels, they should instead be something that isn't legal Unicode.
1487For UTF-8 data, you can use the bytes 0xC1 and 0xC2 as sentinels, as
1488they never appear in well-formed UTF-8. (There are equivalents for
1489UTF-EBCDIC). You can also store your Unicode code points in integer
1490variables and use negative values as sentinels.
1491
1492If you're not writing such a tool, then whether you accept noncharacters
1493as input is up to you (though the Standard recommends that you not). If
1494you do strict input stream checking with Perl, these code points
1495continue to be forbidden. This is to maintain backward compatibility
1496(otherwise potential security holes could open up, as an unsuspecting
1497application that was written assuming the noncharacters would be
1498filtered out before getting to it, could now, without warning, start
1499getting them). To do strict checking, you can use the layer
1500C<:encoding('UTF-8')>.
1501
1502Perl continues to warn (using the warning category C<"nonchar">, which
1503is a sub-category of C<"utf8">) if an attempt is made to output
1504noncharacters.
42581d5d
KW
1505
1506=head2 Beyond Unicode code points
1507
a9130ea9
KW
1508The maximum Unicode code point is C<U+10FFFF>, and Unicode only defines
1509operations on code points up through that. But Perl works on code
42581d5d
KW
1510points up to the maximum permissible unsigned number available on the
1511platform. However, Perl will not accept these from input streams unless
1512lax rules are being used, and will warn (using the warning category
2d88a86a
KW
1513C<"non_unicode">, which is a sub-category of C<"utf8">) if any are output.
1514
1515Since Unicode rules are not defined on these code points, if a
1516Unicode-defined operation is done on them, Perl uses what we believe are
1517sensible rules, while generally warning, using the C<"non_unicode">
1518category. For example, C<uc("\x{11_0000}")> will generate such a
1519warning, returning the input parameter as its result, since Perl defines
1520the uppercase of every non-Unicode code point to be the code point
b65e6125
KW
1521itself. (All the case changing operations, not just uppercasing, work
1522this way.)
2d88a86a
KW
1523
1524The situation with matching Unicode properties in regular expressions,
1525the C<\p{}> and C<\P{}> constructs, against these code points is not as
1526clear cut, and how these are handled has changed as we've gained
1527experience.
1528
1529One possibility is to treat any match against these code points as
1530undefined. But since Perl doesn't have the concept of a match being
1531undefined, it converts this to failing or C<FALSE>. This is almost, but
1532not quite, what Perl did from v5.14 (when use of these code points
1533became generally reliable) through v5.18. The difference is that Perl
1534treated all C<\p{}> matches as failing, but all C<\P{}> matches as
1535succeeding.
1536
1537One problem with this is that it leads to unexpected, and confusting
1538results in some cases:
1539
1540 chr(0x110000) =~ \p{ASCII_Hex_Digit=True} # Failed on <= v5.18
1541 chr(0x110000) =~ \p{ASCII_Hex_Digit=False} # Failed! on <= v5.18
1542
1543That is, it treated both matches as undefined, and converted that to
1544false (raising a warning on each). The first case is the expected
1545result, but the second is likely counterintuitive: "How could both be
1546false when they are complements?" Another problem was that the
1547implementation optimized many Unicode property matches down to already
1548existing simpler, faster operations, which don't raise the warning. We
1549chose to not forgo those optimizations, which help the vast majority of
1550matches, just to generate a warning for the unlikely event that an
1551above-Unicode code point is being matched against.
1552
1553As a result of these problems, starting in v5.20, what Perl does is
1554to treat non-Unicode code points as just typical unassigned Unicode
1555characters, and matches accordingly. (Note: Unicode has atypical
57e88091 1556unassigned code points. For example, it has noncharacter code points,
2d88a86a
KW
1557and ones that, when they do get assigned, are destined to be written
1558Right-to-left, as Arabic and Hebrew are. Perl assumes that no
1559non-Unicode code point has any atypical properties.)
1560
1561Perl, in most cases, will raise a warning when matching an above-Unicode
1562code point against a Unicode property when the result is C<TRUE> for
1563C<\p{}>, and C<FALSE> for C<\P{}>. For example:
1564
1565 chr(0x110000) =~ \p{ASCII_Hex_Digit=True} # Fails, no warning
1566 chr(0x110000) =~ \p{ASCII_Hex_Digit=False} # Succeeds, with warning
1567
1568In both these examples, the character being matched is non-Unicode, so
1569Unicode doesn't define how it should match. It clearly isn't an ASCII
1570hex digit, so the first example clearly should fail, and so it does,
1571with no warning. But it is arguable that the second example should have
1572an undefined, hence C<FALSE>, result. So a warning is raised for it.
1573
1574Thus the warning is raised for many fewer cases than in earlier Perls,
1575and only when what the result is could be arguable. It turns out that
1576none of the optimizations made by Perl (or are ever likely to be made)
1577cause the warning to be skipped, so it solves both problems of Perl's
1578earlier approach. The most commonly used property that is affected by
1579this change is C<\p{Unassigned}> which is a short form for
1580C<\p{General_Category=Unassigned}>. Starting in v5.20, all non-Unicode
1581code points are considered C<Unassigned>. In earlier releases the
1582matches failed because the result was considered undefined.
1583
1584The only place where the warning is not raised when it might ought to
1585have been is if optimizations cause the whole pattern match to not even
1586be attempted. For example, Perl may figure out that for a string to
1587match a certain regular expression pattern, the string has to contain
1588the substring C<"foobar">. Before attempting the match, Perl may look
1589for that substring, and if not found, immediately fail the match without
1590actually trying it; so no warning gets generated even if the string
1591contains an above-Unicode code point.
1592
1593This behavior is more "Do what I mean" than in earlier Perls for most
1594applications. But it catches fewer issues for code that needs to be
1595strictly Unicode compliant. Therefore there is an additional mode of
1596operation available to accommodate such code. This mode is enabled if a
1597regular expression pattern is compiled within the lexical scope where
1598the C<"non_unicode"> warning class has been made fatal, say by:
1599
1600 use warnings FATAL => "non_unicode"
1601
44ecbbd8 1602(see L<warnings>). In this mode of operation, Perl will raise the
2d88a86a
KW
1603warning for all matches against a non-Unicode code point (not just the
1604arguable ones), and it skips the optimizations that might cause the
1605warning to not be output. (It currently still won't warn if the match
1606isn't even attempted, like in the C<"foobar"> example above.)
1607
1608In summary, Perl now normally treats non-Unicode code points as typical
1609Unicode unassigned code points for regular expression matches, raising a
1610warning only when it is arguable what the result should be. However, if
1611this warning has been made fatal, it isn't skipped.
1612
1613There is one exception to all this. C<\p{All}> looks like a Unicode
1614property, but it is a Perl extension that is defined to be true for all
1615possible code points, Unicode or not, so no warning is ever generated
1616when matching this against a non-Unicode code point. (Prior to v5.20,
1617it was an exact synonym for C<\p{Any}>, matching code points C<0>
1618through C<0x10FFFF>.)
6d4f9cf2 1619
0d7c09bb
JH
1620=head2 Security Implications of Unicode
1621
b65e6125
KW
1622First, read
1623L<Unicode Security Considerations|http://www.unicode.org/reports/tr36>.
1624
e1b711da
KW
1625Also, note the following:
1626
0d7c09bb
JH
1627=over 4
1628
1629=item *
1630
1631Malformed UTF-8
bf0fa0b2 1632
42581d5d 1633Unfortunately, the original specification of UTF-8 leaves some room for
bf0fa0b2 1634interpretation of how many bytes of encoded output one should generate
376d9008
JB
1635from one input Unicode character. Strictly speaking, the shortest
1636possible sequence of UTF-8 bytes should be generated,
1637because otherwise there is potential for an input buffer overflow at
feda178f 1638the receiving end of a UTF-8 connection. Perl always generates the
e1b711da 1639shortest length UTF-8, and with warnings on, Perl will warn about
376d9008 1640non-shortest length UTF-8 along with other malformations, such as the
b19eb496 1641surrogates, which are not Unicode code points valid for interchange.
bf0fa0b2 1642
0d7c09bb
JH
1643=item *
1644
68693f9e 1645Regular expression pattern matching may surprise you if you're not
b19eb496
TC
1646accustomed to Unicode. Starting in Perl 5.14, several pattern
1647modifiers are available to control this, called the character set
42581d5d
KW
1648modifiers. Details are given in L<perlre/Character set modifiers>.
1649
1650=back
0d7c09bb 1651
376d9008 1652As discussed elsewhere, Perl has one foot (two hooves?) planted in
a6a7eedc
KW
1653each of two worlds: the old world of ASCII and single-byte locales, and
1654the new world of Unicode, upgrading when necessary.
376d9008 1655If your legacy code does not explicitly use Unicode, no automatic
a6a7eedc 1656switch-over to Unicode should happen.
0d7c09bb 1657
c349b1b9
JH
1658=head2 Unicode in Perl on EBCDIC
1659
a6a7eedc
KW
1660Unicode is supported on EBCDIC platforms. See L<perlebcdic>.
1661
1662Unless ASCII vs. EBCDIC issues are specifically being discussed,
1663references to UTF-8 encoding in this document and elsewhere should be
1664read as meaning UTF-EBCDIC on EBCDIC platforms.
1665See L<perlebcdic/Unicode and UTF>.
1666
1667Because UTF-EBCDIC is so similar to UTF-8, the differences are mostly
1668hidden from you; S<C<use utf8>> (and NOT something like
1669S<C<use utfebcdic>>) declares the the script is in the platform's
1670"native" 8-bit encoding of Unicode. (Similarly for the C<":utf8">
1671layer.)
c349b1b9 1672
b310b053
JH
1673=head2 Locales
1674
42581d5d 1675See L<perllocale/Unicode and UTF-8>
b310b053 1676
1aad1664
JH
1677=head2 When Unicode Does Not Happen
1678
b65e6125
KW
1679There are still many places where Unicode (in some encoding or
1680another) could be given as arguments or received as results, or both in
1681Perl, but it is not, in spite of Perl having extensive ways to input and
1682output in Unicode, and a few other "entry points" like the C<@ARGV>
1683array (which can sometimes be interpreted as UTF-8).
1aad1664 1684
e1b711da
KW
1685The following are such interfaces. Also, see L</The "Unicode Bug">.
1686For all of these interfaces Perl
b9cedb1b 1687currently (as of v5.16.0) simply assumes byte strings both as arguments
b65e6125 1688and results, or UTF-8 strings if the (deprecated) C<encoding> pragma has been used.
1aad1664 1689
b19eb496
TC
1690One reason that Perl does not attempt to resolve the role of Unicode in
1691these situations is that the answers are highly dependent on the operating
1aad1664 1692system and the file system(s). For example, whether filenames can be
b19eb496
TC
1693in Unicode and in exactly what kind of encoding, is not exactly a
1694portable concept. Similarly for C<qx> and C<system>: how well will the
1695"command-line interface" (and which of them?) handle Unicode?
1aad1664
JH
1696
1697=over 4
1698
557a2462
RB
1699=item *
1700
a9130ea9
KW
1701C<chdir>, C<chmod>, C<chown>, C<chroot>, C<exec>, C<link>, C<lstat>, C<mkdir>,
1702C<rename>, C<rmdir>, C<stat>, C<symlink>, C<truncate>, C<unlink>, C<utime>, C<-X>
557a2462
RB
1703
1704=item *
1705
a9130ea9 1706C<%ENV>
557a2462
RB
1707
1708=item *
1709
a9130ea9 1710C<glob> (aka the C<E<lt>*E<gt>>)
557a2462
RB
1711
1712=item *
1aad1664 1713
a9130ea9 1714C<open>, C<opendir>, C<sysopen>
1aad1664 1715
557a2462 1716=item *
1aad1664 1717
a9130ea9 1718C<qx> (aka the backtick operator), C<system>
1aad1664 1719
557a2462 1720=item *
1aad1664 1721
a9130ea9 1722C<readdir>, C<readlink>
1aad1664
JH
1723
1724=back
1725
e1b711da
KW
1726=head2 The "Unicode Bug"
1727
a6a7eedc
KW
1728The term, "Unicode bug" has been applied to an inconsistency with the
1729code points in the C<Latin-1 Supplement> block, that is, between
1730128 and 255. Without a locale specified, unlike all other characters or
1731code points, these characters can have very different semantics
1732depending on the rules in effect. (Characters whose code points are
1733above 255 force Unicode rules; whereas the rules for ASCII characters
1734are the same under both ASCII and Unicode rules.)
1735
1736Under Unicode rules, these upper-Latin1 characters are interpreted as
1737Unicode code points, which means they have the same semantics as Latin-1
1738(ISO-8859-1) and C1 controls.
1739
1740As explained in L</ASCII Rules versus Unicode Rules>, under ASCII rules,
1741they are considered to be unassigned characters.
1742
1743This can lead to unexpected results. For example, a string's
1744semantics can suddenly change if a code point above 255 is appended to
1745it, which changes the rules from ASCII to Unicode. As an
1746example, consider the following program and its output:
1747
1748 $ perl -le'
f434f357 1749 no feature "unicode_strings";
a6a7eedc
KW
1750 $s1 = "\xC2";
1751 $s2 = "\x{2660}";
1752 for ($s1, $s2, $s1.$s2) {
1753 print /\w/ || 0;
1754 }
1755 '
1756 0
1757 0
1758 1
1759
1760If there's no C<\w> in C<s1> nor in C<s2>, why does their concatenation
1761have one?
1762
1763This anomaly stems from Perl's attempt to not disturb older programs that
1764didn't use Unicode, along with Perl's desire to add Unicode support
1765seamlessly. But the result turned out to not be seamless. (By the way,
1766you can choose to be warned when things like this happen. See
1767C<L<encoding::warnings>>.)
1768
1769L<S<C<use feature 'unicode_strings'>>|feature/The 'unicode_strings' feature>
1770was added, starting in Perl v5.12, to address this problem. It affects
1771these things:
e1b711da
KW
1772
1773=over 4
1774
1775=item *
1776
1777Changing the case of a scalar, that is, using C<uc()>, C<ucfirst()>, C<lc()>,
2e2b2571
KW
1778and C<lcfirst()>, or C<\L>, C<\U>, C<\u> and C<\l> in double-quotish
1779contexts, such as regular expression substitutions.
a6a7eedc
KW
1780
1781Under C<unicode_strings> starting in Perl 5.12.0, Unicode rules are
2e2b2571
KW
1782generally used. See L<perlfunc/lc> for details on how this works
1783in combination with various other pragmas.
e1b711da
KW
1784
1785=item *
1786
2e2b2571 1787Using caseless (C</i>) regular expression matching.
a6a7eedc 1788
2e2b2571 1789Starting in Perl 5.14.0, regular expressions compiled within
a6a7eedc 1790the scope of C<unicode_strings> use Unicode rules
2e2b2571
KW
1791even when executed or compiled into larger
1792regular expressions outside the scope.
e1b711da
KW
1793
1794=item *
1795
a6a7eedc
KW
1796Matching any of several properties in regular expressions.
1797
1798These properties are C<\b> (without braces), C<\B> (without braces),
1799C<\s>, C<\S>, C<\w>, C<\W>, and all the Posix character classes
630d17dc 1800I<except> C<[[:ascii:]]>.
a6a7eedc 1801
2e2b2571 1802Starting in Perl 5.14.0, regular expressions compiled within
a6a7eedc 1803the scope of C<unicode_strings> use Unicode rules
2e2b2571
KW
1804even when executed or compiled into larger
1805regular expressions outside the scope.
e1b711da
KW
1806
1807=item *
1808
a6a7eedc
KW
1809In C<quotemeta> or its inline equivalent C<\Q>.
1810
2e2b2571
KW
1811Starting in Perl 5.16.0, consistent quoting rules are used within the
1812scope of C<unicode_strings>, as described in L<perlfunc/quotemeta>.
a6a7eedc
KW
1813Prior to that, or outside its scope, no code points above 127 are quoted
1814in UTF-8 encoded strings, but in byte encoded strings, code points
1815between 128-255 are always quoted.
eb88ed9e 1816
e1b711da
KW
1817=back
1818
a6a7eedc
KW
1819You can see from the above that the effect of C<unicode_strings>
1820increased over several Perl releases. (And Perl's support for Unicode
1821continues to improve; it's best to use the latest available release in
1822order to get the most complete and accurate results possible.) Note that
1823C<unicode_strings> is automatically chosen if you S<C<use 5.012>> or
1824higher.
e1b711da 1825
2e2b2571 1826For Perls earlier than those described above, or when a string is passed
a6a7eedc 1827to a function outside the scope of C<unicode_strings>, see the next section.
e1b711da 1828
1aad1664
JH
1829=head2 Forcing Unicode in Perl (Or Unforcing Unicode in Perl)
1830
e1b711da
KW
1831Sometimes (see L</"When Unicode Does Not Happen"> or L</The "Unicode Bug">)
1832there are situations where you simply need to force a byte
a6a7eedc
KW
1833string into UTF-8, or vice versa. The standard module L<Encode> can be
1834used for this, or the low-level calls
a9130ea9 1835L<C<utf8::upgrade($bytestring)>|utf8/Utility functions> and
a6a7eedc 1836L<C<utf8::downgrade($utf8string[, FAIL_OK])>|utf8/Utility functions>.
1aad1664 1837
a9130ea9 1838Note that C<utf8::downgrade()> can fail if the string contains characters
2bbc8d55 1839that don't fit into a byte.
1aad1664 1840
e1b711da
KW
1841Calling either function on a string that already is in the desired state is a
1842no-op.
1843
a6a7eedc
KW
1844L</ASCII Rules versus Unicode Rules> gives all the ways that a string is
1845made to use Unicode rules.
95a1a48b 1846
37b3b608 1847=head2 Using Unicode in XS
c349b1b9 1848
37b3b608
KW
1849See L<perlguts/"Unicode Support"> for an introduction to Unicode at
1850the XS level, and L<perlapi/Unicode Support> for the API details.
95a1a48b 1851
e1b711da
KW
1852=head2 Hacking Perl to work on earlier Unicode versions (for very serious hackers only)
1853
a6a7eedc
KW
1854Perl by default comes with the latest supported Unicode version built-in, but
1855the goal is to allow you to change to use any earlier one. In Perls
1856v5.20 and v5.22, however, the earliest usable version is Unicode 5.1.
c55dd03d 1857Perl v5.18 and v5.24 are able to handle all earlier versions.
e1b711da 1858
42581d5d 1859Download the files in the desired version of Unicode from the Unicode web
e1b711da 1860site L<http://www.unicode.org>). These should replace the existing files in
b19eb496 1861F<lib/unicore> in the Perl source tree. Follow the instructions in
116693e8 1862F<README.perl> in that directory to change some of their names, and then build
26e391dd 1863perl (see L<INSTALL>).
116693e8 1864
c8d992ba
A
1865=head2 Porting code from perl-5.6.X
1866
a6a7eedc
KW
1867Perls starting in 5.8 have a different Unicode model from 5.6. In 5.6 the
1868programmer was required to use the C<utf8> pragma to declare that a
1869given scope expected to deal with Unicode data and had to make sure that
1870only Unicode data were reaching that scope. If you have code that is
c8d992ba 1871working with 5.6, you will need some of the following adjustments to
a6a7eedc
KW
1872your code. The examples are written such that the code will continue to
1873work under 5.6, so you should be safe to try them out.
c8d992ba 1874
755789c0 1875=over 3
c8d992ba
A
1876
1877=item *
1878
1879A filehandle that should read or write UTF-8
1880
b9cedb1b 1881 if ($] > 5.008) {
740d4bb2 1882 binmode $fh, ":encoding(utf8)";
c8d992ba
A
1883 }
1884
1885=item *
1886
1887A scalar that is going to be passed to some extension
1888
a9130ea9 1889Be it C<Compress::Zlib>, C<Apache::Request> or any extension that has no
c8d992ba 1890mention of Unicode in the manpage, you need to make sure that the
2575c402 1891UTF8 flag is stripped off. Note that at the time of this writing
b9cedb1b 1892(January 2012) the mentioned modules are not UTF-8-aware. Please
c8d992ba
A
1893check the documentation to verify if this is still true.
1894
b9cedb1b 1895 if ($] > 5.008) {
c8d992ba
A
1896 require Encode;
1897 $val = Encode::encode_utf8($val); # make octets
1898 }
1899
1900=item *
1901
1902A scalar we got back from an extension
1903
1904If you believe the scalar comes back as UTF-8, you will most likely
2575c402 1905want the UTF8 flag restored:
c8d992ba 1906
b9cedb1b 1907 if ($] > 5.008) {
c8d992ba
A
1908 require Encode;
1909 $val = Encode::decode_utf8($val);
1910 }
1911
1912=item *
1913
1914Same thing, if you are really sure it is UTF-8
1915
b9cedb1b 1916 if ($] > 5.008) {
c8d992ba
A
1917 require Encode;
1918 Encode::_utf8_on($val);
1919 }
1920
1921=item *
1922
a9130ea9 1923A wrapper for L<DBI> C<fetchrow_array> and C<fetchrow_hashref>
c8d992ba
A
1924
1925When the database contains only UTF-8, a wrapper function or method is
a9130ea9
KW
1926a convenient way to replace all your C<fetchrow_array> and
1927C<fetchrow_hashref> calls. A wrapper function will also make it easier to
c8d992ba 1928adapt to future enhancements in your database driver. Note that at the
b9cedb1b 1929time of this writing (January 2012), the DBI has no standardized way
a9130ea9 1930to deal with UTF-8 data. Please check the L<DBI documentation|DBI> to verify if
c8d992ba
A
1931that is still true.
1932
1933 sub fetchrow {
d88362ca
KW
1934 # $what is one of fetchrow_{array,hashref}
1935 my($self, $sth, $what) = @_;
b9cedb1b 1936 if ($] < 5.008) {
c8d992ba
A
1937 return $sth->$what;
1938 } else {
1939 require Encode;
1940 if (wantarray) {
1941 my @arr = $sth->$what;
1942 for (@arr) {
1943 defined && /[^\000-\177]/ && Encode::_utf8_on($_);
1944 }
1945 return @arr;
1946 } else {
1947 my $ret = $sth->$what;
1948 if (ref $ret) {
1949 for my $k (keys %$ret) {
d88362ca
KW
1950 defined
1951 && /[^\000-\177]/
1952 && Encode::_utf8_on($_) for $ret->{$k};
c8d992ba
A
1953 }
1954 return $ret;
1955 } else {
1956 defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret;
1957 return $ret;
1958 }
1959 }
1960 }
1961 }
1962
1963
1964=item *
1965
1966A large scalar that you know can only contain ASCII
1967
1968Scalars that contain only ASCII and are marked as UTF-8 are sometimes
1969a drag to your program. If you recognize such a situation, just remove
2575c402 1970the UTF8 flag:
c8d992ba 1971
b9cedb1b 1972 utf8::downgrade($val) if $] > 5.008;
c8d992ba
A
1973
1974=back
1975
a6a7eedc
KW
1976=head1 BUGS
1977
1978See also L</The "Unicode Bug"> above.
1979
1980=head2 Interaction with Extensions
1981
1982When Perl exchanges data with an extension, the extension should be
1983able to understand the UTF8 flag and act accordingly. If the
1984extension doesn't recognize that flag, it's likely that the extension
1985will return incorrectly-flagged data.
1986
1987So if you're working with Unicode data, consult the documentation of
1988every module you're using if there are any issues with Unicode data
1989exchange. If the documentation does not talk about Unicode at all,
1990suspect the worst and probably look at the source to learn how the
1991module is implemented. Modules written completely in Perl shouldn't
1992cause problems. Modules that directly or indirectly access code written
1993in other programming languages are at risk.
1994
1995For affected functions, the simple strategy to avoid data corruption is
1996to always make the encoding of the exchanged data explicit. Choose an
1997encoding that you know the extension can handle. Convert arguments passed
1998to the extensions to that encoding and convert results back from that
1999encoding. Write wrapper functions that do the conversions for you, so
2000you can later change the functions when the extension catches up.
2001
2002To provide an example, let's say the popular C<Foo::Bar::escape_html>
2003function doesn't deal with Unicode data yet. The wrapper function
2004would convert the argument to raw UTF-8 and convert the result back to
2005Perl's internal representation like so:
2006
2007 sub my_escape_html ($) {
2008 my($what) = shift;
2009 return unless defined $what;
2010 Encode::decode_utf8(Foo::Bar::escape_html(
2011 Encode::encode_utf8($what)));
2012 }
2013
2014Sometimes, when the extension does not convert data but just stores
2015and retrieves it, you will be able to use the otherwise
2016dangerous L<C<Encode::_utf8_on()>|Encode/_utf8_on> function. Let's say
2017the popular C<Foo::Bar> extension, written in C, provides a C<param>
2018method that lets you store and retrieve data according to these prototypes:
2019
2020 $self->param($name, $value); # set a scalar
2021 $value = $self->param($name); # retrieve a scalar
2022
2023If it does not yet provide support for any encoding, one could write a
2024derived class with such a C<param> method:
2025
2026 sub param {
2027 my($self,$name,$value) = @_;
2028 utf8::upgrade($name); # make sure it is UTF-8 encoded
2029 if (defined $value) {
2030 utf8::upgrade($value); # make sure it is UTF-8 encoded
2031 return $self->SUPER::param($name,$value);
2032 } else {
2033 my $ret = $self->SUPER::param($name);
2034 Encode::_utf8_on($ret); # we know, it is UTF-8 encoded
2035 return $ret;
2036 }
2037 }
2038
2039Some extensions provide filters on data entry/exit points, such as
2040C<DB_File::filter_store_key> and family. Look out for such filters in
2041the documentation of your extensions; they can make the transition to
2042Unicode data much easier.
2043
2044=head2 Speed
2045
2046Some functions are slower when working on UTF-8 encoded strings than
2047on byte encoded strings. All functions that need to hop over
2048characters such as C<length()>, C<substr()> or C<index()>, or matching
2049regular expressions can work B<much> faster when the underlying data are
2050byte-encoded.
2051
2052In Perl 5.8.0 the slowness was often quite spectacular; in Perl 5.8.1
2053a caching scheme was introduced which improved the situation. In general,
2054operations with UTF-8 encoded strings are still slower. As an example,
2055the Unicode properties (character classes) like C<\p{Nd}> are known to
2056be quite a bit slower (5-20 times) than their simpler counterparts
2057like C<[0-9]> (then again, there are hundreds of Unicode characters matching
2058C<Nd> compared with the 10 ASCII characters matching C<[0-9]>).
2059
393fec97
GS
2060=head1 SEE ALSO
2061
51f494cc 2062L<perlunitut>, L<perluniintro>, L<perluniprops>, L<Encode>, L<open>, L<utf8>, L<bytes>,
b65e6125 2063L<perlretut>, L<perlvar/"${^UNICODE}">,
51f494cc 2064L<http://www.unicode.org/reports/tr44>).
393fec97
GS
2065
2066=cut