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8a118206 1=head1 NAME
ea449505 2X<character class>
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3
4perlrecharclass - Perl Regular Expression Character Classes
5
6=head1 DESCRIPTION
7
8The top level documentation about Perl regular expressions
9is found in L<perlre>.
10
11This manual page discusses the syntax and use of character
6b83a163 12classes in Perl regular expressions.
8a118206 13
6b83a163 14A character class is a way of denoting a set of characters
8a118206 15in such a way that one character of the set is matched.
6b83a163 16It's important to remember that: matching a character class
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17consumes exactly one character in the source string. (The source
18string is the string the regular expression is matched against.)
19
20There are three types of character classes in Perl regular
6b83a163 21expressions: the dot, backslash sequences, and the form enclosed in square
ea449505 22brackets. Keep in mind, though, that often the term "character class" is used
6b83a163 23to mean just the bracketed form. Certainly, most Perl documentation does that.
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24
25=head2 The dot
26
27The dot (or period), C<.> is probably the most used, and certainly
28the most well-known character class. By default, a dot matches any
5db9882c 29character, except for the newline. That default can be changed to
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30add matching the newline by using the I<single line> modifier: either
31for the entire regular expression with the C</s> modifier, or
2171640d 32locally with C<(?s)>. (The C<\N> backslash sequence, described
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33below, matches any character except newline without regard to the
34I<single line> modifier.)
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35
36Here are some examples:
37
38 "a" =~ /./ # Match
39 "." =~ /./ # Match
40 "" =~ /./ # No match (dot has to match a character)
41 "\n" =~ /./ # No match (dot does not match a newline)
42 "\n" =~ /./s # Match (global 'single line' modifier)
43 "\n" =~ /(?s:.)/ # Match (local 'single line' modifier)
44 "ab" =~ /^.$/ # No match (dot matches one character)
45
6b83a163 46=head2 Backslash sequences
82206b5e 47X<\w> X<\W> X<\s> X<\S> X<\d> X<\D> X<\p> X<\P>
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48X<\N> X<\v> X<\V> X<\h> X<\H>
49X<word> X<whitespace>
8a118206 50
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51A backslash sequence is a sequence of characters, the first one of which is a
52backslash. Perl ascribes special meaning to many such sequences, and some of
53these are character classes. That is, they match a single character each,
54provided that the character belongs to the specific set of characters defined
55by the sequence.
8a118206 56
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57Here's a list of the backslash sequences that are character classes. They
58are discussed in more detail below. (For the backslash sequences that aren't
59character classes, see L<perlrebackslash>.)
8a118206 60
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61 \d Match a decimal digit character.
62 \D Match a non-decimal-digit character.
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63 \w Match a "word" character.
64 \W Match a non-"word" character.
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65 \s Match a whitespace character.
66 \S Match a non-whitespace character.
67 \h Match a horizontal whitespace character.
68 \H Match a character that isn't horizontal whitespace.
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69 \v Match a vertical whitespace character.
70 \V Match a character that isn't vertical whitespace.
4e5e0888 71 \N Match a character that isn't a newline.
6b83a163 72 \pP, \p{Prop} Match a character that has the given Unicode property.
6c5a041f 73 \PP, \P{Prop} Match a character that doesn't have the Unicode property
8a118206 74
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75=head3 \N
76
2171640d 77C<\N>, available starting in v5.12, like the dot, matches any
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78character that is not a newline. The difference is that C<\N> is not influenced
79by the I<single line> regular expression modifier (see L</The dot> above). Note
80that the form C<\N{...}> may mean something completely different. When the
81C<{...}> is a L<quantifier|perlre/Quantifiers>, it means to match a non-newline
82character that many times. For example, C<\N{3}> means to match 3
83non-newlines; C<\N{5,}> means to match 5 or more non-newlines. But if C<{...}>
84is not a legal quantifier, it is presumed to be a named character. See
85L<charnames> for those. For example, none of C<\N{COLON}>, C<\N{4F}>, and
86C<\N{F4}> contain legal quantifiers, so Perl will try to find characters whose
87names are respectively C<COLON>, C<4F>, and C<F4>.
88
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89=head3 Digits
90
b6538e4f 91C<\d> matches a single character considered to be a decimal I<digit>.
5db9882c 92If the C</a> regular expression modifier is in effect, it matches [0-9].
582da942 93Otherwise, it
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94matches anything that is matched by C<\p{Digit}>, which includes [0-9].
95(An unlikely possible exception is that under locale matching rules, the
96current locale might not have [0-9] matched by C<\d>, and/or might match
97other characters whose code point is less than 256. Such a locale
98definition would be in violation of the C language standard, but Perl
99doesn't currently assume anything in regard to this.)
100
101What this means is that unless the C</a> modifier is in effect C<\d> not
102only matches the digits '0' - '9', but also Arabic, Devanagari, and
103digits from other languages. This may cause some confusion, and some
104security issues.
105
106Some digits that C<\d> matches look like some of the [0-9] ones, but
107have different values. For example, BENGALI DIGIT FOUR (U+09EA) looks
108very much like an ASCII DIGIT EIGHT (U+0038). An application that
109is expecting only the ASCII digits might be misled, or if the match is
110C<\d+>, the matched string might contain a mixture of digits from
111different writing systems that look like they signify a number different
67592e11 112than they actually do. L<Unicode::UCD/num()> can
e397bccf 113be used to safely
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114calculate the value, returning C<undef> if the input string contains
115such a mixture.
116
117What C<\p{Digit}> means (and hence C<\d> except under the C</a>
118modifier) is C<\p{General_Category=Decimal_Number}>, or synonymously,
119C<\p{General_Category=Digit}>. Starting with Unicode version 4.1, this
120is the same set of characters matched by C<\p{Numeric_Type=Decimal}>.
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121But Unicode also has a different property with a similar name,
122C<\p{Numeric_Type=Digit}>, which matches a completely different set of
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123characters. These characters are things such as C<CIRCLED DIGIT ONE>
124or subscripts, or are from writing systems that lack all ten digits.
6b83a163 125
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126The design intent is for C<\d> to exactly match the set of characters
127that can safely be used with "normal" big-endian positional decimal
128syntax, where, for example 123 means one 'hundred', plus two 'tens',
129plus three 'ones'. This positional notation does not necessarily apply
130to characters that match the other type of "digit",
131C<\p{Numeric_Type=Digit}>, and so C<\d> doesn't match them.
6b83a163 132
e2cfb18c 133The Tamil digits (U+0BE6 - U+0BEF) can also legally be
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134used in old-style Tamil numbers in which they would appear no more than
135one in a row, separated by characters that mean "times 10", "times 100",
136etc. (See L<http://www.unicode.org/notes/tn21>.)
8a118206 137
b6538e4f 138Any character not matched by C<\d> is matched by C<\D>.
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139
140=head3 Word characters
141
ea449505 142A C<\w> matches a single alphanumeric character (an alphabetic character, or a
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143decimal digit); or a connecting punctuation character, such as an
144underscore ("_"); or a "mark" character (like some sort of accent) that
145attaches to one of those. It does not match a whole word. To match a
146whole word, use C<\w+>. This isn't the same thing as matching an
147English word, but in the ASCII range it is the same as a string of
148Perl-identifier characters.
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149
150=over
151
152=item If the C</a> modifier is in effect ...
153
154C<\w> matches the 63 characters [a-zA-Z0-9_].
155
156=item otherwise ...
157
158=over
159
160=item For code points above 255 ...
161
162C<\w> matches the same as C<\p{Word}> matches in this range. That is,
163it matches Thai letters, Greek letters, etc. This includes connector
d35dd6c6 164punctuation (like the underscore) which connect two words together, or
b6538e4f 165diacritics, such as a C<COMBINING TILDE> and the modifier letters, which
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166are generally used to add auxiliary markings to letters.
167
168=item For code points below 256 ...
169
170=over
171
172=item if locale rules are in effect ...
173
174C<\w> matches the platform's native underscore character plus whatever
175the locale considers to be alphanumeric.
176
4b9734bf 177=item if Unicode rules are in effect ...
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178
179C<\w> matches exactly what C<\p{Word}> matches.
180
181=item otherwise ...
182
183C<\w> matches [a-zA-Z0-9_].
184
185=back
186
187=back
188
189=back
190
191Which rules apply are determined as described in L<perlre/Which character set modifier is in effect?>.
8a118206 192
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193There are a number of security issues with the full Unicode list of word
194characters. See L<http://unicode.org/reports/tr36>.
195
196Also, for a somewhat finer-grained set of characters that are in programming
197language identifiers beyond the ASCII range, you may wish to instead use the
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198more customized L</Unicode Properties>, C<\p{ID_Start}>,
199C<\p{ID_Continue}>, C<\p{XID_Start}>, and C<\p{XID_Continue}>. See
200L<http://unicode.org/reports/tr31>.
6b83a163 201
b6538e4f 202Any character not matched by C<\w> is matched by C<\W>.
8a118206 203
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204=head3 Whitespace
205
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206C<\s> matches any single character considered whitespace.
207
208=over
209
210=item If the C</a> modifier is in effect ...
211
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212In all Perl versions, C<\s> matches the 5 characters [\t\n\f\r ]; that
213is, the horizontal tab,
214the newline, the form feed, the carriage return, and the space.
215Starting in Perl v5.18, experimentally, it also matches the vertical tab, C<\cK>.
216See note C<[1]> below for a discussion of this.
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217
218=item otherwise ...
219
220=over
221
222=item For code points above 255 ...
223
224C<\s> matches exactly the code points above 255 shown with an "s" column
225in the table below.
226
227=item For code points below 256 ...
228
229=over
230
231=item if locale rules are in effect ...
232
d28d8023 233C<\s> matches whatever the locale considers to be whitespace.
82206b5e 234
4b9734bf 235=item if Unicode rules are in effect ...
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236
237C<\s> matches exactly the characters shown with an "s" column in the
238table below.
239
240=item otherwise ...
241
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242C<\s> matches [\t\n\f\r\cK ] and, starting, experimentally in Perl
243v5.18, the vertical tab, C<\cK>.
244(See note C<[1]> below for a discussion of this.)
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245Note that this list doesn't include the non-breaking space.
246
247=back
248
249=back
250
251=back
252
253Which rules apply are determined as described in L<perlre/Which character set modifier is in effect?>.
8a118206 254
b6538e4f 255Any character not matched by C<\s> is matched by C<\S>.
8a118206 256
b6538e4f 257C<\h> matches any character considered horizontal whitespace;
8129baca 258this includes the platform's space and tab characters and several others
b6538e4f 259listed in the table below. C<\H> matches any character
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260not considered horizontal whitespace. They use the platform's native
261character set, and do not consider any locale that may otherwise be in
262use.
ea449505 263
b6538e4f 264C<\v> matches any character considered vertical whitespace;
8129baca 265this includes the platform's carriage return and line feed characters (newline)
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266plus several other characters, all listed in the table below.
267C<\V> matches any character not considered vertical whitespace.
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268They use the platform's native character set, and do not consider any
269locale that may otherwise be in use.
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270
271C<\R> matches anything that can be considered a newline under Unicode
272rules. It's not a character class, as it can match a multi-character
273sequence. Therefore, it cannot be used inside a bracketed character
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274class; use C<\v> instead (vertical whitespace). It uses the platform's
275native character set, and does not consider any locale that may
276otherwise be in use.
ea449505 277Details are discussed in L<perlrebackslash>.
8a118206 278
82206b5e 279Note that unlike C<\s> (and C<\d> and C<\w>), C<\h> and C<\v> always match
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280the same characters, without regard to other factors, such as the active
281locale or whether the source string is in UTF-8 format.
8a118206 282
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283One might think that C<\s> is equivalent to C<[\h\v]>. This is indeed true
284starting in Perl v5.18, but prior to that, the sole difference was that the
285vertical tab (C<"\cK">) was not matched by C<\s>.
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286
287The following table is a complete listing of characters matched by
a9c9e371 288C<\s>, C<\h> and C<\v> as of Unicode 6.3.
8a118206 289
582da942 290The first column gives the Unicode code point of the character (in hex format),
8a118206 291the second column gives the (Unicode) name. The third column indicates
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292by which class(es) the character is matched (assuming no locale is in
293effect that changes the C<\s> matching).
8a118206 294
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295 0x0009 CHARACTER TABULATION h s
296 0x000a LINE FEED (LF) vs
d28d8023 297 0x000b LINE TABULATION vs [1]
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298 0x000c FORM FEED (FF) vs
299 0x000d CARRIAGE RETURN (CR) vs
300 0x0020 SPACE h s
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301 0x0085 NEXT LINE (NEL) vs [2]
302 0x00a0 NO-BREAK SPACE h s [2]
fc28d2a3 303 0x1680 OGHAM SPACE MARK h s
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304 0x2000 EN QUAD h s
305 0x2001 EM QUAD h s
306 0x2002 EN SPACE h s
307 0x2003 EM SPACE h s
308 0x2004 THREE-PER-EM SPACE h s
309 0x2005 FOUR-PER-EM SPACE h s
310 0x2006 SIX-PER-EM SPACE h s
311 0x2007 FIGURE SPACE h s
312 0x2008 PUNCTUATION SPACE h s
313 0x2009 THIN SPACE h s
314 0x200a HAIR SPACE h s
315 0x2028 LINE SEPARATOR vs
316 0x2029 PARAGRAPH SEPARATOR vs
317 0x202f NARROW NO-BREAK SPACE h s
318 0x205f MEDIUM MATHEMATICAL SPACE h s
319 0x3000 IDEOGRAPHIC SPACE h s
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320
321=over 4
322
323=item [1]
324
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325Prior to Perl v5.18, C<\s> did not match the vertical tab. The change
326in v5.18 is considered an experiment, which means it could be backed out
327in v5.20 or v5.22 if experience indicates that it breaks too much
328existing code. If this change adversely affects you, send email to
329C<perlbug@perl.org>; if it affects you positively, email
330C<perlthanks@perl.org>. In the meantime, C<[^\S\cK]> (obscurely)
331matches what C<\s> traditionally did.
332
333=item [2]
334
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335NEXT LINE and NO-BREAK SPACE may or may not match C<\s> depending
336on the rules in effect. See
337L<the beginning of this section|/Whitespace>.
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338
339=back
340
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341=head3 Unicode Properties
342
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343C<\pP> and C<\p{Prop}> are character classes to match characters that fit given
344Unicode properties. One letter property names can be used in the C<\pP> form,
345with the property name following the C<\p>, otherwise, braces are required.
346When using braces, there is a single form, which is just the property name
347enclosed in the braces, and a compound form which looks like C<\p{name=value}>,
b6538e4f 348which means to match if the property "name" for the character has that particular
c1c4ae3a 349"value".
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350For instance, a match for a number can be written as C</\pN/> or as
351C</\p{Number}/>, or as C</\p{Number=True}/>.
352Lowercase letters are matched by the property I<Lowercase_Letter> which
e2cfb18c 353has the short form I<Ll>. They need the braces, so are written as C</\p{Ll}/> or
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354C</\p{Lowercase_Letter}/>, or C</\p{General_Category=Lowercase_Letter}/>
355(the underscores are optional).
356C</\pLl/> is valid, but means something different.
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357It matches a two character string: a letter (Unicode property C<\pL>),
358followed by a lowercase C<l>.
359
bc943be5 360If locale rules are not in effect, the use of
82206b5e 361a Unicode property will force the regular expression into using Unicode
bc943be5 362rules, if it isn't already.
82206b5e 363
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364Note that almost all properties are immune to case-insensitive matching.
365That is, adding a C</i> regular expression modifier does not change what
82206b5e 366they match. There are two sets that are affected. The first set is
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367C<Uppercase_Letter>,
368C<Lowercase_Letter>,
369and C<Titlecase_Letter>,
370all of which match C<Cased_Letter> under C</i> matching.
b6538e4f 371The second set is
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372C<Uppercase>,
373C<Lowercase>,
374and C<Titlecase>,
375all of which match C<Cased> under C</i> matching.
376(The difference between these sets is that some things, such as Roman
e2cfb18c 377numerals, come in both upper and lower case, so they are C<Cased>, but
b6538e4f 378aren't considered to be letters, so they aren't C<Cased_Letter>s. They're
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379actually C<Letter_Number>s.)
380This set also includes its subsets C<PosixUpper> and C<PosixLower>, both
e2cfb18c 381of which under C</i> match C<PosixAlpha>.
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382
383For more details on Unicode properties, see L<perlunicode/Unicode
384Character Properties>; for a
e1b711da 385complete list of possible properties, see
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386L<perluniprops/Properties accessible through \p{} and \P{}>,
387which notes all forms that have C</i> differences.
e1b711da 388It is also possible to define your own properties. This is discussed in
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389L<perlunicode/User-Defined Character Properties>.
390
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391Unicode properties are defined (surprise!) only on Unicode code points.
392A warning is raised and all matches fail on non-Unicode code points
393(those above the legal Unicode maximum of 0x10FFFF). This can be
394somewhat surprising,
395
396 chr(0x110000) =~ \p{ASCII_Hex_Digit=True} # Fails.
397 chr(0x110000) =~ \p{ASCII_Hex_Digit=False} # Also fails!
398
399Even though these two matches might be thought of as complements, they
400are so only on Unicode code points.
401
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402=head4 Examples
403
404 "a" =~ /\w/ # Match, "a" is a 'word' character.
405 "7" =~ /\w/ # Match, "7" is a 'word' character as well.
406 "a" =~ /\d/ # No match, "a" isn't a digit.
407 "7" =~ /\d/ # Match, "7" is a digit.
ea449505 408 " " =~ /\s/ # Match, a space is whitespace.
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409 "a" =~ /\D/ # Match, "a" is a non-digit.
410 "7" =~ /\D/ # No match, "7" is not a non-digit.
ea449505 411 " " =~ /\S/ # No match, a space is not non-whitespace.
8a118206 412
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413 " " =~ /\h/ # Match, space is horizontal whitespace.
414 " " =~ /\v/ # No match, space is not vertical whitespace.
415 "\r" =~ /\v/ # Match, a return is vertical whitespace.
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416
417 "a" =~ /\pL/ # Match, "a" is a letter.
418 "a" =~ /\p{Lu}/ # No match, /\p{Lu}/ matches upper case letters.
419
420 "\x{0e0b}" =~ /\p{Thai}/ # Match, \x{0e0b} is the character
421 # 'THAI CHARACTER SO SO', and that's in
422 # Thai Unicode class.
ea449505 423 "a" =~ /\P{Lao}/ # Match, as "a" is not a Laotian character.
8a118206 424
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425It is worth emphasizing that C<\d>, C<\w>, etc, match single characters, not
426complete numbers or words. To match a number (that consists of digits),
427use C<\d+>; to match a word, use C<\w+>. But be aware of the security
428considerations in doing so, as mentioned above.
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429
430=head2 Bracketed Character Classes
431
432The third form of character class you can use in Perl regular expressions
6b83a163 433is the bracketed character class. In its simplest form, it lists the characters
c1c4ae3a 434that may be matched, surrounded by square brackets, like this: C<[aeiou]>.
ea449505 435This matches one of C<a>, C<e>, C<i>, C<o> or C<u>. Like the other
1f59b283 436character classes, exactly one character is matched.* To match
ea449505 437a longer string consisting of characters mentioned in the character
6b83a163 438class, follow the character class with a L<quantifier|perlre/Quantifiers>. For
b6538e4f 439instance, C<[aeiou]+> matches one or more lowercase English vowels.
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440
441Repeating a character in a character class has no
442effect; it's considered to be in the set only once.
443
444Examples:
445
446 "e" =~ /[aeiou]/ # Match, as "e" is listed in the class.
447 "p" =~ /[aeiou]/ # No match, "p" is not listed in the class.
448 "ae" =~ /^[aeiou]$/ # No match, a character class only matches
449 # a single character.
450 "ae" =~ /^[aeiou]+$/ # Match, due to the quantifier.
451
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452 -------
453
df0e3973 454* There is an exception to a bracketed character class matching a
1cecf2c0 455single character only. When the class is to match caselessly under C</i>
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456matching rules, and a character that is explicitly mentioned inside the
457class matches a
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458multiple-character sequence caselessly under Unicode rules, the class
459(when not L<inverted|/Negation>) will also match that sequence. For
460example, Unicode says that the letter C<LATIN SMALL LETTER SHARP S>
461should match the sequence C<ss> under C</i> rules. Thus,
462
463 'ss' =~ /\A\N{LATIN SMALL LETTER SHARP S}\z/i # Matches
464 'ss' =~ /\A[aeioust\N{LATIN SMALL LETTER SHARP S}]\z/i # Matches
465
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466For this to happen, the character must be explicitly specified, and not
467be part of a multi-character range (not even as one of its endpoints).
468(L</Character Ranges> will be explained shortly.) Therefore,
469
470 'ss' =~ /\A[\0-\x{ff}]\z/i # Doesn't match
471 'ss' =~ /\A[\0-\N{LATIN SMALL LETTER SHARP S}]\z/i # No match
472 'ss' =~ /\A[\xDF-\xDF]\z/i # Matches on ASCII platforms, since \XDF
473 # is LATIN SMALL LETTER SHARP S, and the
474 # range is just a single element
475
476Note that it isn't a good idea to specify these types of ranges anyway.
477
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478=head3 Special Characters Inside a Bracketed Character Class
479
480Most characters that are meta characters in regular expressions (that
df225385 481is, characters that carry a special meaning like C<.>, C<*>, or C<(>) lose
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482their special meaning and can be used inside a character class without
483the need to escape them. For instance, C<[()]> matches either an opening
484parenthesis, or a closing parenthesis, and the parens inside the character
485class don't group or capture.
486
487Characters that may carry a special meaning inside a character class are:
488C<\>, C<^>, C<->, C<[> and C<]>, and are discussed below. They can be
489escaped with a backslash, although this is sometimes not needed, in which
490case the backslash may be omitted.
491
492The sequence C<\b> is special inside a bracketed character class. While
6b83a163 493outside the character class, C<\b> is an assertion indicating a point
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494that does not have either two word characters or two non-word characters
495on either side, inside a bracketed character class, C<\b> matches a
496backspace character.
497
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498The sequences
499C<\a>,
500C<\c>,
501C<\e>,
502C<\f>,
503C<\n>,
e526e8bb 504C<\N{I<NAME>}>,
765fa144 505C<\N{U+I<hex char>}>,
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506C<\r>,
507C<\t>,
508and
509C<\x>
06ee63cd
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510are also special and have the same meanings as they do outside a
511bracketed character class. (However, inside a bracketed character
512class, if C<\N{I<NAME>}> expands to a sequence of characters, only the first
513one in the sequence is used, with a warning.)
df225385 514
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515Also, a backslash followed by two or three octal digits is considered an octal
516number.
df225385 517
6b83a163
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518A C<[> is not special inside a character class, unless it's the start of a
519POSIX character class (see L</POSIX Character Classes> below). It normally does
520not need escaping.
8a118206 521
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522A C<]> is normally either the end of a POSIX character class (see
523L</POSIX Character Classes> below), or it signals the end of the bracketed
524character class. If you want to include a C<]> in the set of characters, you
525must generally escape it.
b6538e4f 526
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527However, if the C<]> is the I<first> (or the second if the first
528character is a caret) character of a bracketed character class, it
529does not denote the end of the class (as you cannot have an empty class)
530and is considered part of the set of characters that can be matched without
531escaping.
532
533Examples:
534
535 "+" =~ /[+?*]/ # Match, "+" in a character class is not special.
f321be7e 536 "\cH" =~ /[\b]/ # Match, \b inside in a character class.
c1c4ae3a 537 # is equivalent to a backspace.
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538 "]" =~ /[][]/ # Match, as the character class contains.
539 # both [ and ].
540 "[]" =~ /[[]]/ # Match, the pattern contains a character class
541 # containing just ], and the character class is
542 # followed by a ].
543
544=head3 Character Ranges
545
546It is not uncommon to want to match a range of characters. Luckily, instead
b6538e4f 547of listing all characters in the range, one may use the hyphen (C<->).
8a118206 548If inside a bracketed character class you have two characters separated
b6538e4f 549by a hyphen, it's treated as if all characters between the two were in
8a118206 550the class. For instance, C<[0-9]> matches any ASCII digit, and C<[a-m]>
e2cfb18c 551matches any lowercase letter from the first half of the ASCII alphabet.
8a118206
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552
553Note that the two characters on either side of the hyphen are not
765fa144 554necessarily both letters or both digits. Any character is possible,
8a118206 555although not advisable. C<['-?]> contains a range of characters, but
b6538e4f 556most people will not know which characters that means. Furthermore,
8a118206
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557such ranges may lead to portability problems if the code has to run on
558a platform that uses a different character set, such as EBCDIC.
559
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560If a hyphen in a character class cannot syntactically be part of a range, for
561instance because it is the first or the last character of the character class,
b6538e4f
TC
562or if it immediately follows a range, the hyphen isn't special, and so is
563considered a character to be matched literally. If you want a hyphen in
564your set of characters to be matched and its position in the class is such
565that it could be considered part of a range, you must escape that hyphen
566with a backslash.
8a118206
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567
568Examples:
569
570 [a-z] # Matches a character that is a lower case ASCII letter.
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571 [a-fz] # Matches any letter between 'a' and 'f' (inclusive) or
572 # the letter 'z'.
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573 [-z] # Matches either a hyphen ('-') or the letter 'z'.
574 [a-f-m] # Matches any letter between 'a' and 'f' (inclusive), the
575 # hyphen ('-'), or the letter 'm'.
576 ['-?] # Matches any of the characters '()*+,-./0123456789:;<=>?
577 # (But not on an EBCDIC platform).
578
579
580=head3 Negation
581
582It is also possible to instead list the characters you do not want to
583match. You can do so by using a caret (C<^>) as the first character in the
b6538e4f 584character class. For instance, C<[^a-z]> matches any character that is not a
e2cfb18c
KW
585lowercase ASCII letter, which therefore includes more than a million
586Unicode code points. The class is said to be "negated" or "inverted".
8a118206
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587
588This syntax make the caret a special character inside a bracketed character
589class, but only if it is the first character of the class. So if you want
82206b5e 590the caret as one of the characters to match, either escape the caret or
e2cfb18c 591else don't list it first.
8a118206 592
1f59b283 593In inverted bracketed character classes, Perl ignores the Unicode rules
56e1c5aa
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594that normally say that certain characters should match a sequence of
595multiple characters under caseless C</i> matching. Following those
596rules could lead to highly confusing situations:
1f59b283 597
582da942 598 "ss" =~ /^[^\xDF]+$/ui; # Matches!
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599
600This should match any sequences of characters that aren't C<\xDF> nor
601what C<\xDF> matches under C</i>. C<"s"> isn't C<\xDF>, but Unicode
602says that C<"ss"> is what C<\xDF> matches under C</i>. So which one
603"wins"? Do you fail the match because the string has C<ss> or accept it
582da942
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604because it has an C<s> followed by another C<s>? Perl has chosen the
605latter.
1f59b283 606
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607Examples:
608
609 "e" =~ /[^aeiou]/ # No match, the 'e' is listed.
610 "x" =~ /[^aeiou]/ # Match, as 'x' isn't a lowercase vowel.
611 "^" =~ /[^^]/ # No match, matches anything that isn't a caret.
612 "^" =~ /[x^]/ # Match, caret is not special here.
613
614=head3 Backslash Sequences
615
ea449505 616You can put any backslash sequence character class (with the exception of
765fa144 617C<\N> and C<\R>) inside a bracketed character class, and it will act just
b6538e4f
TC
618as if you had put all characters matched by the backslash sequence inside the
619character class. For instance, C<[a-f\d]> matches any decimal digit, or any
6b83a163
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620of the lowercase letters between 'a' and 'f' inclusive.
621
622C<\N> within a bracketed character class must be of the forms C<\N{I<name>}>
765fa144 623or C<\N{U+I<hex char>}>, and NOT be the form that matches non-newlines,
6b83a163
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624for the same reason that a dot C<.> inside a bracketed character class loses
625its special meaning: it matches nearly anything, which generally isn't what you
626want to happen.
df225385 627
8a118206
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628
629Examples:
630
631 /[\p{Thai}\d]/ # Matches a character that is either a Thai
632 # character, or a digit.
633 /[^\p{Arabic}()]/ # Matches a character that is neither an Arabic
634 # character, nor a parenthesis.
635
636Backslash sequence character classes cannot form one of the endpoints
6b83a163
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637of a range. Thus, you can't say:
638
639 /[\p{Thai}-\d]/ # Wrong!
8a118206 640
6b83a163 641=head3 POSIX Character Classes
ea449505 642X<character class> X<\p> X<\p{}>
ea449505
KW
643X<alpha> X<alnum> X<ascii> X<blank> X<cntrl> X<digit> X<graph>
644X<lower> X<print> X<punct> X<space> X<upper> X<word> X<xdigit>
8a118206 645
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646POSIX character classes have the form C<[:class:]>, where I<class> is
647name, and the C<[:> and C<:]> delimiters. POSIX character classes only appear
8a118206 648I<inside> bracketed character classes, and are a convenient and descriptive
82206b5e 649way of listing a group of characters.
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650
651Be careful about the syntax,
8a118206
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652
653 # Correct:
654 $string =~ /[[:alpha:]]/
655
656 # Incorrect (will warn):
657 $string =~ /[:alpha:]/
658
659The latter pattern would be a character class consisting of a colon,
660and the letters C<a>, C<l>, C<p> and C<h>.
82206b5e 661POSIX character classes can be part of a larger bracketed character class.
b6538e4f 662For example,
ea449505
KW
663
664 [01[:alpha:]%]
665
666is valid and matches '0', '1', any alphabetic character, and the percent sign.
8a118206
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667
668Perl recognizes the following POSIX character classes:
669
ea449505 670 alpha Any alphabetical character ("[A-Za-z]").
48cbae4f 671 alnum Any alphanumeric character ("[A-Za-z0-9]").
ea449505 672 ascii Any character in the ASCII character set.
ea8b8ad2 673 blank A GNU extension, equal to a space or a horizontal tab ("\t").
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674 cntrl Any control character. See Note [2] below.
675 digit Any decimal digit ("[0-9]"), equivalent to "\d".
676 graph Any printable character, excluding a space. See Note [3] below.
677 lower Any lowercase character ("[a-z]").
678 print Any printable character, including a space. See Note [4] below.
c1c4ae3a 679 punct Any graphical character excluding "word" characters. Note [5].
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680 space Any whitespace character. "\s" including the vertical tab
681 ("\cK").
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682 upper Any uppercase character ("[A-Z]").
683 word A Perl extension ("[A-Za-z0-9_]"), equivalent to "\w".
684 xdigit Any hexadecimal digit ("[0-9a-fA-F]").
685
686Most POSIX character classes have two Unicode-style C<\p> property
687counterparts. (They are not official Unicode properties, but Perl extensions
688derived from official Unicode properties.) The table below shows the relation
689between POSIX character classes and these counterparts.
690
691One counterpart, in the column labelled "ASCII-range Unicode" in
b6538e4f 692the table, matches only characters in the ASCII character set.
ea449505
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693
694The other counterpart, in the column labelled "Full-range Unicode", matches any
695appropriate characters in the full Unicode character set. For example,
b6538e4f 696C<\p{Alpha}> matches not just the ASCII alphabetic characters, but any
82206b5e 697character in the entire Unicode character set considered alphabetic.
582da942 698An entry in the column labelled "backslash sequence" is a (short)
5db9882c 699equivalent.
ea449505 700
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701 [[:...:]] ASCII-range Full-range backslash Note
702 Unicode Unicode sequence
ea449505 703 -----------------------------------------------------
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704 alpha \p{PosixAlpha} \p{XPosixAlpha}
705 alnum \p{PosixAlnum} \p{XPosixAlnum}
82206b5e 706 ascii \p{ASCII}
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707 blank \p{PosixBlank} \p{XPosixBlank} \h [1]
708 or \p{HorizSpace} [1]
709 cntrl \p{PosixCntrl} \p{XPosixCntrl} [2]
710 digit \p{PosixDigit} \p{XPosixDigit} \d
711 graph \p{PosixGraph} \p{XPosixGraph} [3]
712 lower \p{PosixLower} \p{XPosixLower}
713 print \p{PosixPrint} \p{XPosixPrint} [4]
714 punct \p{PosixPunct} \p{XPosixPunct} [5]
715 \p{PerlSpace} \p{XPerlSpace} \s [6]
716 space \p{PosixSpace} \p{XPosixSpace} [6]
717 upper \p{PosixUpper} \p{XPosixUpper}
718 word \p{PosixWord} \p{XPosixWord} \w
82206b5e 719 xdigit \p{PosixXDigit} \p{XPosixXDigit}
8a118206
RGS
720
721=over 4
722
ea449505
KW
723=item [1]
724
725C<\p{Blank}> and C<\p{HorizSpace}> are synonyms.
726
727=item [2]
8a118206 728
ea449505 729Control characters don't produce output as such, but instead usually control
b6538e4f 730the terminal somehow: for example, newline and backspace are control characters.
82206b5e 731In the ASCII range, characters whose code points are between 0 and 31 inclusive,
ea449505 732plus 127 (C<DEL>) are control characters.
8a118206 733
ea449505 734=item [3]
8a118206
RGS
735
736Any character that is I<graphical>, that is, visible. This class consists
b6538e4f 737of all alphanumeric characters and all punctuation characters.
8a118206 738
ea449505 739=item [4]
8a118206 740
b6538e4f
TC
741All printable characters, which is the set of all graphical characters
742plus those whitespace characters which are not also controls.
ea449505 743
b6dac59a 744=item [5]
ea449505 745
b6538e4f 746C<\p{PosixPunct}> and C<[[:punct:]]> in the ASCII range match all
ea449505
KW
747non-controls, non-alphanumeric, non-space characters:
748C<[-!"#$%&'()*+,./:;<=E<gt>?@[\\\]^_`{|}~]> (although if a locale is in effect,
749it could alter the behavior of C<[[:punct:]]>).
750
cbc24f92
KW
751The similarly named property, C<\p{Punct}>, matches a somewhat different
752set in the ASCII range, namely
0be9b861
KW
753C<[-!"#%&'()*,./:;?@[\\\]_{}]>. That is, it is missing the nine
754characters C<[$+E<lt>=E<gt>^`|~]>.
6c5a041f
KW
755This is because Unicode splits what POSIX considers to be punctuation into two
756categories, Punctuation and Symbols.
757
e2cfb18c 758C<\p{XPosixPunct}> and (under Unicode rules) C<[[:punct:]]>, match what
765fa144
KW
759C<\p{PosixPunct}> matches in the ASCII range, plus what C<\p{Punct}>
760matches. This is different than strictly matching according to
761C<\p{Punct}>. Another way to say it is that
82206b5e
KW
762if Unicode rules are in effect, C<[[:punct:]]> matches all characters
763that Unicode considers punctuation, plus all ASCII-range characters that
764Unicode considers symbols.
8a118206 765
ea449505 766=item [6]
8a118206 767
d28d8023
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768C<\p{SpacePerl}> and C<\p{Space}> match identically starting with Perl
769v5.18. In earlier versions, these differ only in that in non-locale
770matching, C<\p{SpacePerl}> does not match the vertical tab, C<\cK>.
771Same for the two ASCII-only range forms.
8a118206
RGS
772
773=back
774
ab6199be
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775There are various other synonyms that can be used besides the names
776listed in the table. For example, C<\p{PosixAlpha}> can be written as
777C<\p{Alpha}>. All are listed in
778L<perluniprops/Properties accessible through \p{} and \P{}>,
779plus all characters matched by each ASCII-range property.
780
781Both the C<\p> counterparts always assume Unicode rules are in effect.
782On ASCII platforms, this means they assume that the code points from 128
783to 255 are Latin-1, and that means that using them under locale rules is
784unwise unless the locale is guaranteed to be Latin-1 or UTF-8. In contrast, the
785POSIX character classes are useful under locale rules. They are
786affected by the actual rules in effect, as follows:
787
788=over
789
790=item If the C</a> modifier, is in effect ...
791
792Each of the POSIX classes matches exactly the same as their ASCII-range
793counterparts.
794
795=item otherwise ...
796
797=over
798
799=item For code points above 255 ...
800
801The POSIX class matches the same as its Full-range counterpart.
802
803=item For code points below 256 ...
804
805=over
806
807=item if locale rules are in effect ...
808
8129baca
KW
809The POSIX class matches according to the locale, except that
810C<word> uses the platform's native underscore character, no matter what
811the locale is.
ab6199be 812
4b9734bf 813=item if Unicode rules are in effect ...
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814
815The POSIX class matches the same as the Full-range counterpart.
816
817=item otherwise ...
818
819The POSIX class matches the same as the ASCII range counterpart.
820
821=back
822
823=back
824
825=back
826
827Which rules apply are determined as described in
828L<perlre/Which character set modifier is in effect?>.
829
830It is proposed to change this behavior in a future release of Perl so that
831whether or not Unicode rules are in effect would not change the
4b9734bf 832behavior: Outside of locale, the POSIX classes
ab6199be
KW
833would behave like their ASCII-range counterparts. If you wish to
834comment on this proposal, send email to C<perl5-porters@perl.org>.
cbc24f92 835
1f59b283 836=head4 Negation of POSIX character classes
ea449505 837X<character class, negation>
8a118206
RGS
838
839A Perl extension to the POSIX character class is the ability to
840negate it. This is done by prefixing the class name with a caret (C<^>).
841Some examples:
842
ea449505
KW
843 POSIX ASCII-range Full-range backslash
844 Unicode Unicode sequence
845 -----------------------------------------------------
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KW
846 [[:^digit:]] \P{PosixDigit} \P{XPosixDigit} \D
847 [[:^space:]] \P{PosixSpace} \P{XPosixSpace}
848 \P{PerlSpace} \P{XPerlSpace} \S
849 [[:^word:]] \P{PerlWord} \P{XPosixWord} \W
850
765fa144 851The backslash sequence can mean either ASCII- or Full-range Unicode,
82206b5e 852depending on various factors as described in L<perlre/Which character set modifier is in effect?>.
8a118206
RGS
853
854=head4 [= =] and [. .]
855
b6538e4f 856Perl recognizes the POSIX character classes C<[=class=]> and
82206b5e 857C<[.class.]>, but does not (yet?) support them. Any attempt to use
b6538e4f 858either construct raises an exception.
8a118206
RGS
859
860=head4 Examples
861
862 /[[:digit:]]/ # Matches a character that is a digit.
863 /[01[:lower:]]/ # Matches a character that is either a
864 # lowercase letter, or '0' or '1'.
c1c4ae3a 865 /[[:digit:][:^xdigit:]]/ # Matches a character that can be anything
bc943be5
KW
866 # except the letters 'a' to 'f' and 'A' to
867 # 'F'. This is because the main character
868 # class is composed of two POSIX character
869 # classes that are ORed together, one that
870 # matches any digit, and the other that
871 # matches anything that isn't a hex digit.
872 # The OR adds the digits, leaving only the
873 # letters 'a' to 'f' and 'A' to 'F' excluded.
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KW
874
875=head3 Extended Bracketed Character Classes
876X<character class>
877X<set operations>
878
879This is a fancy bracketed character class that can be used for more
880readable and less error-prone classes, and to perform set operations,
881such as intersection. An example is
882
883 /(?[ \p{Thai} & \p{Digit} ])/
884
885This will match all the digit characters that are in the Thai script.
886
887This is an experimental feature available starting in 5.18, and is
888subject to change as we gain field experience with it. Any attempt to
889use it will raise a warning, unless disabled via
890
891 no warnings "experimental::regex_sets";
892
893Comments on this feature are welcome; send email to
894C<perl5-porters@perl.org>.
895
896We can extend the example above:
897
898 /(?[ ( \p{Thai} + \p{Lao} ) & \p{Digit} ])/
899
900This matches digits that are in either the Thai or Laotian scripts.
901
902Notice the white space in these examples. This construct always has
903the C<E<sol>x> modifier turned on.
904
905The available binary operators are:
906
907 & intersection
908 + union
909 | another name for '+', hence means union
910 - subtraction (the result matches the set consisting of those
911 code points matched by the first operand, excluding any that
912 are also matched by the second operand)
913 ^ symmetric difference (the union minus the intersection). This
914 is like an exclusive or, in that the result is the set of code
915 points that are matched by either, but not both, of the
916 operands.
917
918There is one unary operator:
919
920 ! complement
921
922All the binary operators left associate, and are of equal precedence.
923The unary operator right associates, and has higher precedence. Use
924parentheses to override the default associations. Some feedback we've
925received indicates a desire for intersection to have higher precedence
926than union. This is something that feedback from the field may cause us
927to change in future releases; you may want to parenthesize copiously to
928avoid such changes affecting your code, until this feature is no longer
929considered experimental.
930
931The main restriction is that everything is a metacharacter. Thus,
932you cannot refer to single characters by doing something like this:
933
934 /(?[ a + b ])/ # Syntax error!
935
936The easiest way to specify an individual typable character is to enclose
937it in brackets:
938
939 /(?[ [a] + [b] ])/
940
941(This is the same thing as C<[ab]>.) You could also have said the
942equivalent:
943
944 /(?[[ a b ]])/
945
de36fb2e
KW
946(You can, of course, specify single characters by using, C<\x{...}>,
947C<\N{...}>, etc.)
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KW
948
949This last example shows the use of this construct to specify an ordinary
950bracketed character class without additional set operations. Note the
951white space within it; C<E<sol>x> is turned on even within bracketed
952character classes, except you can't have comments inside them. Hence,
953
954 (?[ [#] ])
955
956matches the literal character "#". To specify a literal white space character,
957you can escape it with a backslash, like:
958
959 /(?[ [ a e i o u \ ] ])/
960
961This matches the English vowels plus the SPACE character.
962All the other escapes accepted by normal bracketed character classes are
963accepted here as well; but unrecognized escapes that generate warnings
964in normal classes are fatal errors here.
965
966All warnings from these class elements are fatal, as well as some
967practices that don't currently warn. For example you cannot say
968
969 /(?[ [ \xF ] ])/ # Syntax error!
970
971You have to have two hex digits after a braceless C<\x> (use a leading
972zero to make two). These restrictions are to lower the incidence of
973typos causing the class to not match what you thought it would.
974
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KW
975If a regular bracketed character class contains a C<\p{}> or C<\P{}> and
976is matched against a non-Unicode code point, a warning may be
977raised, as the result is not Unicode-defined. No such warning will come
978when using this extended form.
979
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980The final difference between regular bracketed character classes and
981these, is that it is not possible to get these to match a
982multi-character fold. Thus,
983
984 /(?[ [\xDF] ])/iu
985
986does not match the string C<ss>.
987
988You don't have to enclose POSIX class names inside double brackets,
989hence both of the following work:
990
991 /(?[ [:word:] - [:lower:] ])/
992 /(?[ [[:word:]] - [[:lower:]] ])/
993
994Any contained POSIX character classes, including things like C<\w> and C<\D>
995respect the C<E<sol>a> (and C<E<sol>aa>) modifiers.
996
997C<< (?[ ]) >> is a regex-compile-time construct. Any attempt to use
998something which isn't knowable at the time the containing regular
999expression is compiled is a fatal error. In practice, this means
11a9b3e0 1000just three limitations:
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1001
1002=over 4
1003
1004=item 1
1005
1006This construct cannot be used within the scope of
1007C<use locale> (or the C<E<sol>l> regex modifier).
1008
1009=item 2
1010
1011Any
1012L<user-defined property|perlunicode/"User-Defined Character Properties">
1013used must be already defined by the time the regular expression is
1014compiled (but note that this construct can be used instead of such
1015properties).
1016
1017=item 3
1018
1019A regular expression that otherwise would compile
1020using C<E<sol>d> rules, and which uses this construct will instead
1021use C<E<sol>u>. Thus this construct tells Perl that you don't want
1022C<E<sol>d> rules for the entire regular expression containing it.
1023
1024=back
1025
1026The C<E<sol>x> processing within this class is an extended form.
1027Besides the characters that are considered white space in normal C</x>
1028processing, there are 5 others, recommended by the Unicode standard:
1029
1030 U+0085 NEXT LINE
1031 U+200E LEFT-TO-RIGHT MARK
1032 U+200F RIGHT-TO-LEFT MARK
1033 U+2028 LINE SEPARATOR
1034 U+2029 PARAGRAPH SEPARATOR
1035
1036Note that skipping white space applies only to the interior of this
1037construct. There must not be any space between any of the characters
1038that form the initial C<(?[>. Nor may there be space between the
1039closing C<])> characters.
1040
11a9b3e0 1041Just as in all regular expressions, the pattern can be built up by
572224ce
KW
1042including variables that are interpolated at regex compilation time.
1043Care must be taken to ensure that you are getting what you expect. For
1044example:
1045
1046 my $thai_or_lao = '\p{Thai} + \p{Lao}';
1047 ...
1048 qr/(?[ \p{Digit} & $thai_or_lao ])/;
1049
1050compiles to
1051
1052 qr/(?[ \p{Digit} & \p{Thai} + \p{Lao} ])/;
1053
1054But this does not have the effect that someone reading the code would
1055likely expect, as the intersection applies just to C<\p{Thai}>,
1056excluding the Laotian. Pitfalls like this can be avoided by
1057parenthesizing the component pieces:
1058
1059 my $thai_or_lao = '( \p{Thai} + \p{Lao} )';
1060
1061But any modifiers will still apply to all the components:
1062
1063 my $lower = '\p{Lower} + \p{Digit}';
1064 qr/(?[ \p{Greek} & $lower ])/i;
1065
1066matches upper case things. You can avoid surprises by making the
1067components into instances of this construct by compiling them:
1068
1069 my $thai_or_lao = qr/(?[ \p{Thai} + \p{Lao} ])/;
1070 my $lower = qr/(?[ \p{Lower} + \p{Digit} ])/;
1071
1072When these are embedded in another pattern, what they match does not
1073change, regardless of parenthesization or what modifiers are in effect
1074in that outer pattern.
1075
1076Due to the way that Perl parses things, your parentheses and brackets
1077may need to be balanced, even including comments. If you run into any
1078examples, please send them to C<perlbug@perl.org>, so that we can have a
1079concrete example for this man page.
1080
1081We may change it so that things that remain legal uses in normal bracketed
1082character classes might become illegal within this experimental
1083construct. One proposal, for example, is to forbid adjacent uses of the
1084same character, as in C<(?[ [aa] ])>. The motivation for such a change
1085is that this usage is likely a typo, as the second "a" adds nothing.