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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
d66e1f56 32locally with C<(?s)>. (The C<L</\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
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96current locale might not have C<[0-9]> matched by C<\d>, and/or might match
97other characters whose code point is less than 256. The only such locale
98definitions that are legal would be to match C<[0-9]> plus another set of
9910 consecutive digit characters; anything else would be in violation of
100the C language standard, but Perl doesn't currently assume anything in
101regard to this.)
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102
103What this means is that unless the C</a> modifier is in effect C<\d> not
104only matches the digits '0' - '9', but also Arabic, Devanagari, and
105digits from other languages. This may cause some confusion, and some
106security issues.
107
108Some digits that C<\d> matches look like some of the [0-9] ones, but
109have different values. For example, BENGALI DIGIT FOUR (U+09EA) looks
110very much like an ASCII DIGIT EIGHT (U+0038). An application that
111is expecting only the ASCII digits might be misled, or if the match is
112C<\d+>, the matched string might contain a mixture of digits from
113different writing systems that look like they signify a number different
67592e11 114than they actually do. L<Unicode::UCD/num()> can
e397bccf 115be used to safely
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116calculate the value, returning C<undef> if the input string contains
117such a mixture.
118
119What C<\p{Digit}> means (and hence C<\d> except under the C</a>
120modifier) is C<\p{General_Category=Decimal_Number}>, or synonymously,
121C<\p{General_Category=Digit}>. Starting with Unicode version 4.1, this
122is the same set of characters matched by C<\p{Numeric_Type=Decimal}>.
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123But Unicode also has a different property with a similar name,
124C<\p{Numeric_Type=Digit}>, which matches a completely different set of
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125characters. These characters are things such as C<CIRCLED DIGIT ONE>
126or subscripts, or are from writing systems that lack all ten digits.
6b83a163 127
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128The design intent is for C<\d> to exactly match the set of characters
129that can safely be used with "normal" big-endian positional decimal
130syntax, where, for example 123 means one 'hundred', plus two 'tens',
131plus three 'ones'. This positional notation does not necessarily apply
132to characters that match the other type of "digit",
133C<\p{Numeric_Type=Digit}>, and so C<\d> doesn't match them.
6b83a163 134
e2cfb18c 135The Tamil digits (U+0BE6 - U+0BEF) can also legally be
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136used in old-style Tamil numbers in which they would appear no more than
137one in a row, separated by characters that mean "times 10", "times 100",
138etc. (See L<http://www.unicode.org/notes/tn21>.)
8a118206 139
b6538e4f 140Any character not matched by C<\d> is matched by C<\D>.
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141
142=head3 Word characters
143
ea449505 144A C<\w> matches a single alphanumeric character (an alphabetic character, or a
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145decimal digit); or a connecting punctuation character, such as an
146underscore ("_"); or a "mark" character (like some sort of accent) that
147attaches to one of those. It does not match a whole word. To match a
148whole word, use C<\w+>. This isn't the same thing as matching an
149English word, but in the ASCII range it is the same as a string of
150Perl-identifier characters.
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151
152=over
153
154=item If the C</a> modifier is in effect ...
155
156C<\w> matches the 63 characters [a-zA-Z0-9_].
157
158=item otherwise ...
159
160=over
161
162=item For code points above 255 ...
163
164C<\w> matches the same as C<\p{Word}> matches in this range. That is,
165it matches Thai letters, Greek letters, etc. This includes connector
d35dd6c6 166punctuation (like the underscore) which connect two words together, or
b6538e4f 167diacritics, such as a C<COMBINING TILDE> and the modifier letters, which
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168are generally used to add auxiliary markings to letters.
169
170=item For code points below 256 ...
171
172=over
173
174=item if locale rules are in effect ...
175
176C<\w> matches the platform's native underscore character plus whatever
177the locale considers to be alphanumeric.
178
4b9734bf 179=item if Unicode rules are in effect ...
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180
181C<\w> matches exactly what C<\p{Word}> matches.
182
183=item otherwise ...
184
185C<\w> matches [a-zA-Z0-9_].
186
187=back
188
189=back
190
191=back
192
193Which rules apply are determined as described in L<perlre/Which character set modifier is in effect?>.
8a118206 194
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195There are a number of security issues with the full Unicode list of word
196characters. See L<http://unicode.org/reports/tr36>.
197
198Also, for a somewhat finer-grained set of characters that are in programming
199language identifiers beyond the ASCII range, you may wish to instead use the
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200more customized L</Unicode Properties>, C<\p{ID_Start}>,
201C<\p{ID_Continue}>, C<\p{XID_Start}>, and C<\p{XID_Continue}>. See
202L<http://unicode.org/reports/tr31>.
6b83a163 203
b6538e4f 204Any character not matched by C<\w> is matched by C<\W>.
8a118206 205
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206=head3 Whitespace
207
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208C<\s> matches any single character considered whitespace.
209
210=over
211
212=item If the C</a> modifier is in effect ...
213
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214In all Perl versions, C<\s> matches the 5 characters [\t\n\f\r ]; that
215is, the horizontal tab,
216the newline, the form feed, the carriage return, and the space.
217Starting in Perl v5.18, experimentally, it also matches the vertical tab, C<\cK>.
218See note C<[1]> below for a discussion of this.
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219
220=item otherwise ...
221
222=over
223
224=item For code points above 255 ...
225
226C<\s> matches exactly the code points above 255 shown with an "s" column
227in the table below.
228
229=item For code points below 256 ...
230
231=over
232
233=item if locale rules are in effect ...
234
d28d8023 235C<\s> matches whatever the locale considers to be whitespace.
82206b5e 236
4b9734bf 237=item if Unicode rules are in effect ...
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238
239C<\s> matches exactly the characters shown with an "s" column in the
240table below.
241
242=item otherwise ...
243
2941e8b2 244C<\s> matches [\t\n\f\r ] and, starting, experimentally in Perl
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245v5.18, the vertical tab, C<\cK>.
246(See note C<[1]> below for a discussion of this.)
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247Note that this list doesn't include the non-breaking space.
248
249=back
250
251=back
252
253=back
254
255Which rules apply are determined as described in L<perlre/Which character set modifier is in effect?>.
8a118206 256
b6538e4f 257Any character not matched by C<\s> is matched by C<\S>.
8a118206 258
b6538e4f 259C<\h> matches any character considered horizontal whitespace;
8129baca 260this includes the platform's space and tab characters and several others
b6538e4f 261listed in the table below. C<\H> matches any character
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262not considered horizontal whitespace. They use the platform's native
263character set, and do not consider any locale that may otherwise be in
264use.
ea449505 265
b6538e4f 266C<\v> matches any character considered vertical whitespace;
8129baca 267this includes the platform's carriage return and line feed characters (newline)
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268plus several other characters, all listed in the table below.
269C<\V> matches any character not considered vertical whitespace.
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270They use the platform's native character set, and do not consider any
271locale that may otherwise be in use.
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272
273C<\R> matches anything that can be considered a newline under Unicode
274rules. It's not a character class, as it can match a multi-character
275sequence. Therefore, it cannot be used inside a bracketed character
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276class; use C<\v> instead (vertical whitespace). It uses the platform's
277native character set, and does not consider any locale that may
278otherwise be in use.
ea449505 279Details are discussed in L<perlrebackslash>.
8a118206 280
82206b5e 281Note that unlike C<\s> (and C<\d> and C<\w>), C<\h> and C<\v> always match
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282the same characters, without regard to other factors, such as the active
283locale or whether the source string is in UTF-8 format.
8a118206 284
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285One might think that C<\s> is equivalent to C<[\h\v]>. This is indeed true
286starting in Perl v5.18, but prior to that, the sole difference was that the
287vertical tab (C<"\cK">) was not matched by C<\s>.
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288
289The following table is a complete listing of characters matched by
a9c9e371 290C<\s>, C<\h> and C<\v> as of Unicode 6.3.
8a118206 291
582da942 292The first column gives the Unicode code point of the character (in hex format),
8a118206 293the second column gives the (Unicode) name. The third column indicates
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294by which class(es) the character is matched (assuming no locale is in
295effect that changes the C<\s> matching).
8a118206 296
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297 0x0009 CHARACTER TABULATION h s
298 0x000a LINE FEED (LF) vs
d28d8023 299 0x000b LINE TABULATION vs [1]
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300 0x000c FORM FEED (FF) vs
301 0x000d CARRIAGE RETURN (CR) vs
302 0x0020 SPACE h s
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303 0x0085 NEXT LINE (NEL) vs [2]
304 0x00a0 NO-BREAK SPACE h s [2]
fc28d2a3 305 0x1680 OGHAM SPACE MARK h s
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306 0x2000 EN QUAD h s
307 0x2001 EM QUAD h s
308 0x2002 EN SPACE h s
309 0x2003 EM SPACE h s
310 0x2004 THREE-PER-EM SPACE h s
311 0x2005 FOUR-PER-EM SPACE h s
312 0x2006 SIX-PER-EM SPACE h s
313 0x2007 FIGURE SPACE h s
314 0x2008 PUNCTUATION SPACE h s
315 0x2009 THIN SPACE h s
316 0x200a HAIR SPACE h s
317 0x2028 LINE SEPARATOR vs
318 0x2029 PARAGRAPH SEPARATOR vs
319 0x202f NARROW NO-BREAK SPACE h s
320 0x205f MEDIUM MATHEMATICAL SPACE h s
321 0x3000 IDEOGRAPHIC SPACE h s
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322
323=over 4
324
325=item [1]
326
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327Prior to Perl v5.18, C<\s> did not match the vertical tab. The change
328in v5.18 is considered an experiment, which means it could be backed out
a04e6aad 329in v5.22 if experience indicates that it breaks too much
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330existing code. If this change adversely affects you, send email to
331C<perlbug@perl.org>; if it affects you positively, email
332C<perlthanks@perl.org>. In the meantime, C<[^\S\cK]> (obscurely)
333matches what C<\s> traditionally did.
334
335=item [2]
336
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337NEXT LINE and NO-BREAK SPACE may or may not match C<\s> depending
338on the rules in effect. See
339L<the beginning of this section|/Whitespace>.
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340
341=back
342
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343=head3 Unicode Properties
344
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345C<\pP> and C<\p{Prop}> are character classes to match characters that fit given
346Unicode properties. One letter property names can be used in the C<\pP> form,
347with the property name following the C<\p>, otherwise, braces are required.
348When using braces, there is a single form, which is just the property name
349enclosed in the braces, and a compound form which looks like C<\p{name=value}>,
b6538e4f 350which means to match if the property "name" for the character has that particular
c1c4ae3a 351"value".
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352For instance, a match for a number can be written as C</\pN/> or as
353C</\p{Number}/>, or as C</\p{Number=True}/>.
354Lowercase letters are matched by the property I<Lowercase_Letter> which
e2cfb18c 355has the short form I<Ll>. They need the braces, so are written as C</\p{Ll}/> or
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356C</\p{Lowercase_Letter}/>, or C</\p{General_Category=Lowercase_Letter}/>
357(the underscores are optional).
358C</\pLl/> is valid, but means something different.
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359It matches a two character string: a letter (Unicode property C<\pL>),
360followed by a lowercase C<l>.
361
bc943be5 362If locale rules are not in effect, the use of
82206b5e 363a Unicode property will force the regular expression into using Unicode
bc943be5 364rules, if it isn't already.
82206b5e 365
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366Note that almost all properties are immune to case-insensitive matching.
367That is, adding a C</i> regular expression modifier does not change what
82206b5e 368they match. There are two sets that are affected. The first set is
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369C<Uppercase_Letter>,
370C<Lowercase_Letter>,
371and C<Titlecase_Letter>,
372all of which match C<Cased_Letter> under C</i> matching.
b6538e4f 373The second set is
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374C<Uppercase>,
375C<Lowercase>,
376and C<Titlecase>,
377all of which match C<Cased> under C</i> matching.
378(The difference between these sets is that some things, such as Roman
e2cfb18c 379numerals, come in both upper and lower case, so they are C<Cased>, but
b6538e4f 380aren't considered to be letters, so they aren't C<Cased_Letter>s. They're
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381actually C<Letter_Number>s.)
382This set also includes its subsets C<PosixUpper> and C<PosixLower>, both
e2cfb18c 383of which under C</i> match C<PosixAlpha>.
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384
385For more details on Unicode properties, see L<perlunicode/Unicode
386Character Properties>; for a
e1b711da 387complete list of possible properties, see
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388L<perluniprops/Properties accessible through \p{} and \P{}>,
389which notes all forms that have C</i> differences.
e1b711da 390It is also possible to define your own properties. This is discussed in
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391L<perlunicode/User-Defined Character Properties>.
392
94b42e47 393Unicode properties are defined (surprise!) only on Unicode code points.
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394Starting in v5.20, when matching against C<\p> and C<\P>, Perl treats
395non-Unicode code points (those above the legal Unicode maximum of
3960x10FFFF) as if they were typical unassigned Unicode code points.
94b42e47 397
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398Prior to v5.20, Perl raised a warning and made all matches fail on
399non-Unicode code points. This could be somewhat surprising:
94b42e47 400
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401 chr(0x110000) =~ \p{ASCII_Hex_Digit=True} # Fails on Perls < v5.20.
402 chr(0x110000) =~ \p{ASCII_Hex_Digit=False} # Also fails on Perls
403 # < v5.20
404
405Even though these two matches might be thought of as complements, until
406v5.20 they were so only on Unicode code points.
94b42e47 407
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408=head4 Examples
409
410 "a" =~ /\w/ # Match, "a" is a 'word' character.
411 "7" =~ /\w/ # Match, "7" is a 'word' character as well.
412 "a" =~ /\d/ # No match, "a" isn't a digit.
413 "7" =~ /\d/ # Match, "7" is a digit.
ea449505 414 " " =~ /\s/ # Match, a space is whitespace.
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415 "a" =~ /\D/ # Match, "a" is a non-digit.
416 "7" =~ /\D/ # No match, "7" is not a non-digit.
ea449505 417 " " =~ /\S/ # No match, a space is not non-whitespace.
8a118206 418
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419 " " =~ /\h/ # Match, space is horizontal whitespace.
420 " " =~ /\v/ # No match, space is not vertical whitespace.
421 "\r" =~ /\v/ # Match, a return is vertical whitespace.
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422
423 "a" =~ /\pL/ # Match, "a" is a letter.
424 "a" =~ /\p{Lu}/ # No match, /\p{Lu}/ matches upper case letters.
425
426 "\x{0e0b}" =~ /\p{Thai}/ # Match, \x{0e0b} is the character
427 # 'THAI CHARACTER SO SO', and that's in
428 # Thai Unicode class.
ea449505 429 "a" =~ /\P{Lao}/ # Match, as "a" is not a Laotian character.
8a118206 430
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431It is worth emphasizing that C<\d>, C<\w>, etc, match single characters, not
432complete numbers or words. To match a number (that consists of digits),
433use C<\d+>; to match a word, use C<\w+>. But be aware of the security
434considerations in doing so, as mentioned above.
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435
436=head2 Bracketed Character Classes
437
438The third form of character class you can use in Perl regular expressions
6b83a163 439is the bracketed character class. In its simplest form, it lists the characters
c1c4ae3a 440that may be matched, surrounded by square brackets, like this: C<[aeiou]>.
ea449505 441This matches one of C<a>, C<e>, C<i>, C<o> or C<u>. Like the other
1f59b283 442character classes, exactly one character is matched.* To match
ea449505 443a longer string consisting of characters mentioned in the character
6b83a163 444class, follow the character class with a L<quantifier|perlre/Quantifiers>. For
b6538e4f 445instance, C<[aeiou]+> matches one or more lowercase English vowels.
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446
447Repeating a character in a character class has no
448effect; it's considered to be in the set only once.
449
450Examples:
451
452 "e" =~ /[aeiou]/ # Match, as "e" is listed in the class.
453 "p" =~ /[aeiou]/ # No match, "p" is not listed in the class.
454 "ae" =~ /^[aeiou]$/ # No match, a character class only matches
455 # a single character.
456 "ae" =~ /^[aeiou]+$/ # Match, due to the quantifier.
457
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458 -------
459
df0e3973 460* There is an exception to a bracketed character class matching a
1cecf2c0 461single character only. When the class is to match caselessly under C</i>
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462matching rules, and a character that is explicitly mentioned inside the
463class matches a
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464multiple-character sequence caselessly under Unicode rules, the class
465(when not L<inverted|/Negation>) will also match that sequence. For
466example, Unicode says that the letter C<LATIN SMALL LETTER SHARP S>
467should match the sequence C<ss> under C</i> rules. Thus,
468
469 'ss' =~ /\A\N{LATIN SMALL LETTER SHARP S}\z/i # Matches
470 'ss' =~ /\A[aeioust\N{LATIN SMALL LETTER SHARP S}]\z/i # Matches
471
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472For this to happen, the character must be explicitly specified, and not
473be part of a multi-character range (not even as one of its endpoints).
474(L</Character Ranges> will be explained shortly.) Therefore,
475
476 'ss' =~ /\A[\0-\x{ff}]\z/i # Doesn't match
477 'ss' =~ /\A[\0-\N{LATIN SMALL LETTER SHARP S}]\z/i # No match
478 'ss' =~ /\A[\xDF-\xDF]\z/i # Matches on ASCII platforms, since \XDF
479 # is LATIN SMALL LETTER SHARP S, and the
480 # range is just a single element
481
482Note that it isn't a good idea to specify these types of ranges anyway.
483
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484=head3 Special Characters Inside a Bracketed Character Class
485
486Most characters that are meta characters in regular expressions (that
df225385 487is, characters that carry a special meaning like C<.>, C<*>, or C<(>) lose
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488their special meaning and can be used inside a character class without
489the need to escape them. For instance, C<[()]> matches either an opening
490parenthesis, or a closing parenthesis, and the parens inside the character
491class don't group or capture.
492
493Characters that may carry a special meaning inside a character class are:
494C<\>, C<^>, C<->, C<[> and C<]>, and are discussed below. They can be
495escaped with a backslash, although this is sometimes not needed, in which
496case the backslash may be omitted.
497
498The sequence C<\b> is special inside a bracketed character class. While
6b83a163 499outside the character class, C<\b> is an assertion indicating a point
8a118206
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500that does not have either two word characters or two non-word characters
501on either side, inside a bracketed character class, C<\b> matches a
502backspace character.
503
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504The sequences
505C<\a>,
506C<\c>,
507C<\e>,
508C<\f>,
509C<\n>,
e526e8bb 510C<\N{I<NAME>}>,
765fa144 511C<\N{U+I<hex char>}>,
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512C<\r>,
513C<\t>,
514and
515C<\x>
06ee63cd
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516are also special and have the same meanings as they do outside a
517bracketed character class. (However, inside a bracketed character
518class, if C<\N{I<NAME>}> expands to a sequence of characters, only the first
519one in the sequence is used, with a warning.)
df225385 520
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521Also, a backslash followed by two or three octal digits is considered an octal
522number.
df225385 523
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524A C<[> is not special inside a character class, unless it's the start of a
525POSIX character class (see L</POSIX Character Classes> below). It normally does
526not need escaping.
8a118206 527
6b83a163
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528A C<]> is normally either the end of a POSIX character class (see
529L</POSIX Character Classes> below), or it signals the end of the bracketed
530character class. If you want to include a C<]> in the set of characters, you
531must generally escape it.
b6538e4f 532
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533However, if the C<]> is the I<first> (or the second if the first
534character is a caret) character of a bracketed character class, it
535does not denote the end of the class (as you cannot have an empty class)
536and is considered part of the set of characters that can be matched without
537escaping.
538
539Examples:
540
541 "+" =~ /[+?*]/ # Match, "+" in a character class is not special.
f321be7e 542 "\cH" =~ /[\b]/ # Match, \b inside in a character class.
c1c4ae3a 543 # is equivalent to a backspace.
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544 "]" =~ /[][]/ # Match, as the character class contains.
545 # both [ and ].
546 "[]" =~ /[[]]/ # Match, the pattern contains a character class
547 # containing just ], and the character class is
548 # followed by a ].
549
550=head3 Character Ranges
551
552It is not uncommon to want to match a range of characters. Luckily, instead
b6538e4f 553of listing all characters in the range, one may use the hyphen (C<->).
8a118206 554If inside a bracketed character class you have two characters separated
b6538e4f 555by a hyphen, it's treated as if all characters between the two were in
8a118206 556the class. For instance, C<[0-9]> matches any ASCII digit, and C<[a-m]>
e2cfb18c 557matches any lowercase letter from the first half of the ASCII alphabet.
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558
559Note that the two characters on either side of the hyphen are not
765fa144 560necessarily both letters or both digits. Any character is possible,
8a118206 561although not advisable. C<['-?]> contains a range of characters, but
b6538e4f 562most people will not know which characters that means. Furthermore,
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563such ranges may lead to portability problems if the code has to run on
564a platform that uses a different character set, such as EBCDIC.
565
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566If a hyphen in a character class cannot syntactically be part of a range, for
567instance because it is the first or the last character of the character class,
b6538e4f
TC
568or if it immediately follows a range, the hyphen isn't special, and so is
569considered a character to be matched literally. If you want a hyphen in
570your set of characters to be matched and its position in the class is such
571that it could be considered part of a range, you must escape that hyphen
572with a backslash.
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573
574Examples:
575
576 [a-z] # Matches a character that is a lower case ASCII letter.
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577 [a-fz] # Matches any letter between 'a' and 'f' (inclusive) or
578 # the letter 'z'.
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579 [-z] # Matches either a hyphen ('-') or the letter 'z'.
580 [a-f-m] # Matches any letter between 'a' and 'f' (inclusive), the
581 # hyphen ('-'), or the letter 'm'.
582 ['-?] # Matches any of the characters '()*+,-./0123456789:;<=>?
583 # (But not on an EBCDIC platform).
584
585
586=head3 Negation
587
588It is also possible to instead list the characters you do not want to
589match. You can do so by using a caret (C<^>) as the first character in the
b6538e4f 590character class. For instance, C<[^a-z]> matches any character that is not a
e2cfb18c
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591lowercase ASCII letter, which therefore includes more than a million
592Unicode code points. The class is said to be "negated" or "inverted".
8a118206
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593
594This syntax make the caret a special character inside a bracketed character
595class, but only if it is the first character of the class. So if you want
82206b5e 596the caret as one of the characters to match, either escape the caret or
e2cfb18c 597else don't list it first.
8a118206 598
1f59b283 599In inverted bracketed character classes, Perl ignores the Unicode rules
56e1c5aa
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600that normally say that certain characters should match a sequence of
601multiple characters under caseless C</i> matching. Following those
602rules could lead to highly confusing situations:
1f59b283 603
582da942 604 "ss" =~ /^[^\xDF]+$/ui; # Matches!
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605
606This should match any sequences of characters that aren't C<\xDF> nor
607what C<\xDF> matches under C</i>. C<"s"> isn't C<\xDF>, but Unicode
608says that C<"ss"> is what C<\xDF> matches under C</i>. So which one
609"wins"? Do you fail the match because the string has C<ss> or accept it
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610because it has an C<s> followed by another C<s>? Perl has chosen the
611latter.
1f59b283 612
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613Examples:
614
615 "e" =~ /[^aeiou]/ # No match, the 'e' is listed.
616 "x" =~ /[^aeiou]/ # Match, as 'x' isn't a lowercase vowel.
617 "^" =~ /[^^]/ # No match, matches anything that isn't a caret.
618 "^" =~ /[x^]/ # Match, caret is not special here.
619
620=head3 Backslash Sequences
621
ea449505 622You can put any backslash sequence character class (with the exception of
765fa144 623C<\N> and C<\R>) inside a bracketed character class, and it will act just
b6538e4f
TC
624as if you had put all characters matched by the backslash sequence inside the
625character class. For instance, C<[a-f\d]> matches any decimal digit, or any
6b83a163
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626of the lowercase letters between 'a' and 'f' inclusive.
627
628C<\N> within a bracketed character class must be of the forms C<\N{I<name>}>
765fa144 629or C<\N{U+I<hex char>}>, and NOT be the form that matches non-newlines,
6b83a163
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630for the same reason that a dot C<.> inside a bracketed character class loses
631its special meaning: it matches nearly anything, which generally isn't what you
632want to happen.
df225385 633
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634
635Examples:
636
637 /[\p{Thai}\d]/ # Matches a character that is either a Thai
638 # character, or a digit.
639 /[^\p{Arabic}()]/ # Matches a character that is neither an Arabic
640 # character, nor a parenthesis.
641
642Backslash sequence character classes cannot form one of the endpoints
6b83a163
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643of a range. Thus, you can't say:
644
645 /[\p{Thai}-\d]/ # Wrong!
8a118206 646
6b83a163 647=head3 POSIX Character Classes
ea449505 648X<character class> X<\p> X<\p{}>
ea449505
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649X<alpha> X<alnum> X<ascii> X<blank> X<cntrl> X<digit> X<graph>
650X<lower> X<print> X<punct> X<space> X<upper> X<word> X<xdigit>
8a118206 651
d66e1f56 652POSIX character classes have the form C<[:class:]>, where I<class> is the
6b83a163 653name, and the C<[:> and C<:]> delimiters. POSIX character classes only appear
8a118206 654I<inside> bracketed character classes, and are a convenient and descriptive
82206b5e 655way of listing a group of characters.
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656
657Be careful about the syntax,
8a118206
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658
659 # Correct:
660 $string =~ /[[:alpha:]]/
661
662 # Incorrect (will warn):
663 $string =~ /[:alpha:]/
664
665The latter pattern would be a character class consisting of a colon,
666and the letters C<a>, C<l>, C<p> and C<h>.
d66e1f56 667
82206b5e 668POSIX character classes can be part of a larger bracketed character class.
b6538e4f 669For example,
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670
671 [01[:alpha:]%]
672
673is valid and matches '0', '1', any alphabetic character, and the percent sign.
8a118206
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674
675Perl recognizes the following POSIX character classes:
676
ea449505 677 alpha Any alphabetical character ("[A-Za-z]").
48cbae4f 678 alnum Any alphanumeric character ("[A-Za-z0-9]").
ea449505 679 ascii Any character in the ASCII character set.
ea8b8ad2 680 blank A GNU extension, equal to a space or a horizontal tab ("\t").
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681 cntrl Any control character. See Note [2] below.
682 digit Any decimal digit ("[0-9]"), equivalent to "\d".
683 graph Any printable character, excluding a space. See Note [3] below.
684 lower Any lowercase character ("[a-z]").
685 print Any printable character, including a space. See Note [4] below.
c1c4ae3a 686 punct Any graphical character excluding "word" characters. Note [5].
d28d8023
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687 space Any whitespace character. "\s" including the vertical tab
688 ("\cK").
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689 upper Any uppercase character ("[A-Z]").
690 word A Perl extension ("[A-Za-z0-9_]"), equivalent to "\w".
691 xdigit Any hexadecimal digit ("[0-9a-fA-F]").
692
693Most POSIX character classes have two Unicode-style C<\p> property
694counterparts. (They are not official Unicode properties, but Perl extensions
695derived from official Unicode properties.) The table below shows the relation
696between POSIX character classes and these counterparts.
697
698One counterpart, in the column labelled "ASCII-range Unicode" in
b6538e4f 699the table, matches only characters in the ASCII character set.
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700
701The other counterpart, in the column labelled "Full-range Unicode", matches any
702appropriate characters in the full Unicode character set. For example,
b6538e4f 703C<\p{Alpha}> matches not just the ASCII alphabetic characters, but any
82206b5e 704character in the entire Unicode character set considered alphabetic.
582da942 705An entry in the column labelled "backslash sequence" is a (short)
5db9882c 706equivalent.
ea449505 707
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708 [[:...:]] ASCII-range Full-range backslash Note
709 Unicode Unicode sequence
ea449505 710 -----------------------------------------------------
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711 alpha \p{PosixAlpha} \p{XPosixAlpha}
712 alnum \p{PosixAlnum} \p{XPosixAlnum}
82206b5e 713 ascii \p{ASCII}
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714 blank \p{PosixBlank} \p{XPosixBlank} \h [1]
715 or \p{HorizSpace} [1]
716 cntrl \p{PosixCntrl} \p{XPosixCntrl} [2]
717 digit \p{PosixDigit} \p{XPosixDigit} \d
718 graph \p{PosixGraph} \p{XPosixGraph} [3]
719 lower \p{PosixLower} \p{XPosixLower}
720 print \p{PosixPrint} \p{XPosixPrint} [4]
721 punct \p{PosixPunct} \p{XPosixPunct} [5]
722 \p{PerlSpace} \p{XPerlSpace} \s [6]
723 space \p{PosixSpace} \p{XPosixSpace} [6]
724 upper \p{PosixUpper} \p{XPosixUpper}
725 word \p{PosixWord} \p{XPosixWord} \w
82206b5e 726 xdigit \p{PosixXDigit} \p{XPosixXDigit}
8a118206
RGS
727
728=over 4
729
ea449505
KW
730=item [1]
731
732C<\p{Blank}> and C<\p{HorizSpace}> are synonyms.
733
734=item [2]
8a118206 735
ea449505 736Control characters don't produce output as such, but instead usually control
b6538e4f 737the terminal somehow: for example, newline and backspace are control characters.
82206b5e 738In the ASCII range, characters whose code points are between 0 and 31 inclusive,
ea449505 739plus 127 (C<DEL>) are control characters.
8a118206 740
ea449505 741=item [3]
8a118206
RGS
742
743Any character that is I<graphical>, that is, visible. This class consists
b6538e4f 744of all alphanumeric characters and all punctuation characters.
8a118206 745
ea449505 746=item [4]
8a118206 747
b6538e4f
TC
748All printable characters, which is the set of all graphical characters
749plus those whitespace characters which are not also controls.
ea449505 750
b6dac59a 751=item [5]
ea449505 752
b6538e4f 753C<\p{PosixPunct}> and C<[[:punct:]]> in the ASCII range match all
ea449505
KW
754non-controls, non-alphanumeric, non-space characters:
755C<[-!"#$%&'()*+,./:;<=E<gt>?@[\\\]^_`{|}~]> (although if a locale is in effect,
756it could alter the behavior of C<[[:punct:]]>).
757
cbc24f92
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758The similarly named property, C<\p{Punct}>, matches a somewhat different
759set in the ASCII range, namely
0be9b861
KW
760C<[-!"#%&'()*,./:;?@[\\\]_{}]>. That is, it is missing the nine
761characters C<[$+E<lt>=E<gt>^`|~]>.
6c5a041f
KW
762This is because Unicode splits what POSIX considers to be punctuation into two
763categories, Punctuation and Symbols.
764
e2cfb18c 765C<\p{XPosixPunct}> and (under Unicode rules) C<[[:punct:]]>, match what
765fa144
KW
766C<\p{PosixPunct}> matches in the ASCII range, plus what C<\p{Punct}>
767matches. This is different than strictly matching according to
768C<\p{Punct}>. Another way to say it is that
82206b5e
KW
769if Unicode rules are in effect, C<[[:punct:]]> matches all characters
770that Unicode considers punctuation, plus all ASCII-range characters that
771Unicode considers symbols.
8a118206 772
ea449505 773=item [6]
8a118206 774
d28d8023
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775C<\p{SpacePerl}> and C<\p{Space}> match identically starting with Perl
776v5.18. In earlier versions, these differ only in that in non-locale
777matching, C<\p{SpacePerl}> does not match the vertical tab, C<\cK>.
778Same for the two ASCII-only range forms.
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779
780=back
781
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782There are various other synonyms that can be used besides the names
783listed in the table. For example, C<\p{PosixAlpha}> can be written as
784C<\p{Alpha}>. All are listed in
d66e1f56 785L<perluniprops/Properties accessible through \p{} and \P{}>.
ab6199be
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786
787Both the C<\p> counterparts always assume Unicode rules are in effect.
788On ASCII platforms, this means they assume that the code points from 128
789to 255 are Latin-1, and that means that using them under locale rules is
790unwise unless the locale is guaranteed to be Latin-1 or UTF-8. In contrast, the
791POSIX character classes are useful under locale rules. They are
792affected by the actual rules in effect, as follows:
793
794=over
795
796=item If the C</a> modifier, is in effect ...
797
798Each of the POSIX classes matches exactly the same as their ASCII-range
799counterparts.
800
801=item otherwise ...
802
803=over
804
805=item For code points above 255 ...
806
807The POSIX class matches the same as its Full-range counterpart.
808
809=item For code points below 256 ...
810
811=over
812
813=item if locale rules are in effect ...
814
a145a423
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815The POSIX class matches according to the locale, except:
816
817=over
818
819=item C<word>
820
821also includes the platform's native underscore character, no matter what
8129baca 822the locale is.
ab6199be 823
a145a423
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824=item C<ascii>
825
826on platforms that don't have the POSIX C<ascii> extension, this matches
827just the platform's native ASCII-range characters.
828
829=item C<blank>
830
831on platforms that don't have the POSIX C<blank> extension, this matches
832just the platform's native tab and space characters.
833
834=back
835
4b9734bf 836=item if Unicode rules are in effect ...
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837
838The POSIX class matches the same as the Full-range counterpart.
839
840=item otherwise ...
841
842The POSIX class matches the same as the ASCII range counterpart.
843
844=back
845
846=back
847
848=back
849
850Which rules apply are determined as described in
851L<perlre/Which character set modifier is in effect?>.
852
853It is proposed to change this behavior in a future release of Perl so that
854whether or not Unicode rules are in effect would not change the
4b9734bf 855behavior: Outside of locale, the POSIX classes
ab6199be
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856would behave like their ASCII-range counterparts. If you wish to
857comment on this proposal, send email to C<perl5-porters@perl.org>.
cbc24f92 858
1f59b283 859=head4 Negation of POSIX character classes
ea449505 860X<character class, negation>
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861
862A Perl extension to the POSIX character class is the ability to
863negate it. This is done by prefixing the class name with a caret (C<^>).
864Some examples:
865
ea449505
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866 POSIX ASCII-range Full-range backslash
867 Unicode Unicode sequence
868 -----------------------------------------------------
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869 [[:^digit:]] \P{PosixDigit} \P{XPosixDigit} \D
870 [[:^space:]] \P{PosixSpace} \P{XPosixSpace}
871 \P{PerlSpace} \P{XPerlSpace} \S
872 [[:^word:]] \P{PerlWord} \P{XPosixWord} \W
873
765fa144 874The backslash sequence can mean either ASCII- or Full-range Unicode,
82206b5e 875depending on various factors as described in L<perlre/Which character set modifier is in effect?>.
8a118206
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876
877=head4 [= =] and [. .]
878
b6538e4f 879Perl recognizes the POSIX character classes C<[=class=]> and
82206b5e 880C<[.class.]>, but does not (yet?) support them. Any attempt to use
b6538e4f 881either construct raises an exception.
8a118206
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882
883=head4 Examples
884
885 /[[:digit:]]/ # Matches a character that is a digit.
886 /[01[:lower:]]/ # Matches a character that is either a
887 # lowercase letter, or '0' or '1'.
c1c4ae3a 888 /[[:digit:][:^xdigit:]]/ # Matches a character that can be anything
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889 # except the letters 'a' to 'f' and 'A' to
890 # 'F'. This is because the main character
891 # class is composed of two POSIX character
892 # classes that are ORed together, one that
893 # matches any digit, and the other that
894 # matches anything that isn't a hex digit.
895 # The OR adds the digits, leaving only the
896 # letters 'a' to 'f' and 'A' to 'F' excluded.
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897
898=head3 Extended Bracketed Character Classes
899X<character class>
900X<set operations>
901
902This is a fancy bracketed character class that can be used for more
903readable and less error-prone classes, and to perform set operations,
904such as intersection. An example is
905
906 /(?[ \p{Thai} & \p{Digit} ])/
907
908This will match all the digit characters that are in the Thai script.
909
910This is an experimental feature available starting in 5.18, and is
911subject to change as we gain field experience with it. Any attempt to
912use it will raise a warning, unless disabled via
913
914 no warnings "experimental::regex_sets";
915
916Comments on this feature are welcome; send email to
917C<perl5-porters@perl.org>.
918
919We can extend the example above:
920
921 /(?[ ( \p{Thai} + \p{Lao} ) & \p{Digit} ])/
922
923This matches digits that are in either the Thai or Laotian scripts.
924
925Notice the white space in these examples. This construct always has
d66e1f56 926the C<E<sol>x> modifier turned on within it.
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927
928The available binary operators are:
929
930 & intersection
931 + union
932 | another name for '+', hence means union
933 - subtraction (the result matches the set consisting of those
934 code points matched by the first operand, excluding any that
935 are also matched by the second operand)
936 ^ symmetric difference (the union minus the intersection). This
937 is like an exclusive or, in that the result is the set of code
938 points that are matched by either, but not both, of the
939 operands.
940
941There is one unary operator:
942
943 ! complement
944
945All the binary operators left associate, and are of equal precedence.
946The unary operator right associates, and has higher precedence. Use
947parentheses to override the default associations. Some feedback we've
948received indicates a desire for intersection to have higher precedence
949than union. This is something that feedback from the field may cause us
950to change in future releases; you may want to parenthesize copiously to
951avoid such changes affecting your code, until this feature is no longer
952considered experimental.
953
954The main restriction is that everything is a metacharacter. Thus,
955you cannot refer to single characters by doing something like this:
956
957 /(?[ a + b ])/ # Syntax error!
958
959The easiest way to specify an individual typable character is to enclose
960it in brackets:
961
962 /(?[ [a] + [b] ])/
963
964(This is the same thing as C<[ab]>.) You could also have said the
965equivalent:
966
967 /(?[[ a b ]])/
968
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969(You can, of course, specify single characters by using, C<\x{...}>,
970C<\N{...}>, etc.)
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971
972This last example shows the use of this construct to specify an ordinary
973bracketed character class without additional set operations. Note the
974white space within it; C<E<sol>x> is turned on even within bracketed
975character classes, except you can't have comments inside them. Hence,
976
977 (?[ [#] ])
978
979matches the literal character "#". To specify a literal white space character,
980you can escape it with a backslash, like:
981
982 /(?[ [ a e i o u \ ] ])/
983
984This matches the English vowels plus the SPACE character.
985All the other escapes accepted by normal bracketed character classes are
986accepted here as well; but unrecognized escapes that generate warnings
987in normal classes are fatal errors here.
988
989All warnings from these class elements are fatal, as well as some
990practices that don't currently warn. For example you cannot say
991
992 /(?[ [ \xF ] ])/ # Syntax error!
993
994You have to have two hex digits after a braceless C<\x> (use a leading
995zero to make two). These restrictions are to lower the incidence of
996typos causing the class to not match what you thought it would.
997
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998If a regular bracketed character class contains a C<\p{}> or C<\P{}> and
999is matched against a non-Unicode code point, a warning may be
1000raised, as the result is not Unicode-defined. No such warning will come
1001when using this extended form.
1002
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1003The final difference between regular bracketed character classes and
1004these, is that it is not possible to get these to match a
1005multi-character fold. Thus,
1006
1007 /(?[ [\xDF] ])/iu
1008
1009does not match the string C<ss>.
1010
1011You don't have to enclose POSIX class names inside double brackets,
1012hence both of the following work:
1013
1014 /(?[ [:word:] - [:lower:] ])/
1015 /(?[ [[:word:]] - [[:lower:]] ])/
1016
1017Any contained POSIX character classes, including things like C<\w> and C<\D>
1018respect the C<E<sol>a> (and C<E<sol>aa>) modifiers.
1019
1020C<< (?[ ]) >> is a regex-compile-time construct. Any attempt to use
1021something which isn't knowable at the time the containing regular
1022expression is compiled is a fatal error. In practice, this means
11a9b3e0 1023just three limitations:
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1024
1025=over 4
1026
1027=item 1
1028
1029This construct cannot be used within the scope of
1030C<use locale> (or the C<E<sol>l> regex modifier).
1031
1032=item 2
1033
1034Any
1035L<user-defined property|perlunicode/"User-Defined Character Properties">
1036used must be already defined by the time the regular expression is
1037compiled (but note that this construct can be used instead of such
1038properties).
1039
1040=item 3
1041
1042A regular expression that otherwise would compile
1043using C<E<sol>d> rules, and which uses this construct will instead
1044use C<E<sol>u>. Thus this construct tells Perl that you don't want
1045C<E<sol>d> rules for the entire regular expression containing it.
1046
1047=back
1048
572224ce
KW
1049Note that skipping white space applies only to the interior of this
1050construct. There must not be any space between any of the characters
1051that form the initial C<(?[>. Nor may there be space between the
1052closing C<])> characters.
1053
11a9b3e0 1054Just as in all regular expressions, the pattern can be built up by
572224ce
KW
1055including variables that are interpolated at regex compilation time.
1056Care must be taken to ensure that you are getting what you expect. For
1057example:
1058
1059 my $thai_or_lao = '\p{Thai} + \p{Lao}';
1060 ...
1061 qr/(?[ \p{Digit} & $thai_or_lao ])/;
1062
1063compiles to
1064
1065 qr/(?[ \p{Digit} & \p{Thai} + \p{Lao} ])/;
1066
1067But this does not have the effect that someone reading the code would
1068likely expect, as the intersection applies just to C<\p{Thai}>,
1069excluding the Laotian. Pitfalls like this can be avoided by
1070parenthesizing the component pieces:
1071
1072 my $thai_or_lao = '( \p{Thai} + \p{Lao} )';
1073
1074But any modifiers will still apply to all the components:
1075
1076 my $lower = '\p{Lower} + \p{Digit}';
1077 qr/(?[ \p{Greek} & $lower ])/i;
1078
1079matches upper case things. You can avoid surprises by making the
1080components into instances of this construct by compiling them:
1081
1082 my $thai_or_lao = qr/(?[ \p{Thai} + \p{Lao} ])/;
1083 my $lower = qr/(?[ \p{Lower} + \p{Digit} ])/;
1084
1085When these are embedded in another pattern, what they match does not
1086change, regardless of parenthesization or what modifiers are in effect
1087in that outer pattern.
1088
1089Due to the way that Perl parses things, your parentheses and brackets
1090may need to be balanced, even including comments. If you run into any
1091examples, please send them to C<perlbug@perl.org>, so that we can have a
1092concrete example for this man page.
1093
1094We may change it so that things that remain legal uses in normal bracketed
1095character classes might become illegal within this experimental
1096construct. One proposal, for example, is to forbid adjacent uses of the
1097same character, as in C<(?[ [aa] ])>. The motivation for such a change
1098is that this usage is likely a typo, as the second "a" adds nothing.