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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
32locally with C<(?s)>. (The experimental C<\N> backslash sequence, described
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.
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71 \N Match a character that isn't a newline. Experimental.
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
77C<\N> is new in 5.12, and is experimental. It, like the dot, matches any
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 ("_"). It does not match a whole word. To match a whole
82206b5e 145word, use C<\w+>. This isn't the same thing as matching an English word, but
765fa144 146in the ASCII range it is the same as a string of Perl-identifier
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147characters.
148
149=over
150
151=item If the C</a> modifier is in effect ...
152
153C<\w> matches the 63 characters [a-zA-Z0-9_].
154
155=item otherwise ...
156
157=over
158
159=item For code points above 255 ...
160
161C<\w> matches the same as C<\p{Word}> matches in this range. That is,
162it matches Thai letters, Greek letters, etc. This includes connector
d35dd6c6 163punctuation (like the underscore) which connect two words together, or
b6538e4f 164diacritics, such as a C<COMBINING TILDE> and the modifier letters, which
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165are generally used to add auxiliary markings to letters.
166
167=item For code points below 256 ...
168
169=over
170
171=item if locale rules are in effect ...
172
173C<\w> matches the platform's native underscore character plus whatever
174the locale considers to be alphanumeric.
175
176=item if Unicode rules are in effect or if on an EBCDIC platform ...
177
178C<\w> matches exactly what C<\p{Word}> matches.
179
180=item otherwise ...
181
182C<\w> matches [a-zA-Z0-9_].
183
184=back
185
186=back
187
188=back
189
190Which rules apply are determined as described in L<perlre/Which character set modifier is in effect?>.
8a118206 191
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192There are a number of security issues with the full Unicode list of word
193characters. See L<http://unicode.org/reports/tr36>.
194
195Also, for a somewhat finer-grained set of characters that are in programming
196language identifiers beyond the ASCII range, you may wish to instead use the
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197more customized L</Unicode Properties>, C<\p{ID_Start}>,
198C<\p{ID_Continue}>, C<\p{XID_Start}>, and C<\p{XID_Continue}>. See
199L<http://unicode.org/reports/tr31>.
6b83a163 200
b6538e4f 201Any character not matched by C<\w> is matched by C<\W>.
8a118206 202
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203=head3 Whitespace
204
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205C<\s> matches any single character considered whitespace.
206
207=over
208
209=item If the C</a> modifier is in effect ...
210
211C<\s> matches the 5 characters [\t\n\f\r ]; that is, the horizontal tab,
212the newline, the form feed, the carriage return, and the space. (Note
213that it doesn't match the vertical tab, C<\cK> on ASCII platforms.)
214
215=item otherwise ...
216
217=over
218
219=item For code points above 255 ...
220
221C<\s> matches exactly the code points above 255 shown with an "s" column
222in the table below.
223
224=item For code points below 256 ...
225
226=over
227
228=item if locale rules are in effect ...
229
230C<\s> matches whatever the locale considers to be whitespace. Note that
231this is likely to include the vertical space, unlike non-locale C<\s>
232matching.
233
234=item if Unicode rules are in effect or if on an EBCDIC platform ...
235
236C<\s> matches exactly the characters shown with an "s" column in the
237table below.
238
239=item otherwise ...
240
241C<\s> matches [\t\n\f\r ].
242Note that this list doesn't include the non-breaking space.
243
244=back
245
246=back
247
248=back
249
250Which rules apply are determined as described in L<perlre/Which character set modifier is in effect?>.
8a118206 251
b6538e4f 252Any character not matched by C<\s> is matched by C<\S>.
8a118206 253
b6538e4f 254C<\h> matches any character considered horizontal whitespace;
8129baca 255this includes the platform's space and tab characters and several others
b6538e4f 256listed in the table below. C<\H> matches any character
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257not considered horizontal whitespace. They use the platform's native
258character set, and do not consider any locale that may otherwise be in
259use.
ea449505 260
b6538e4f 261C<\v> matches any character considered vertical whitespace;
8129baca 262this includes the platform's carriage return and line feed characters (newline)
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263plus several other characters, all listed in the table below.
264C<\V> matches any character not considered vertical whitespace.
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265They use the platform's native character set, and do not consider any
266locale that may otherwise be in use.
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267
268C<\R> matches anything that can be considered a newline under Unicode
269rules. It's not a character class, as it can match a multi-character
270sequence. Therefore, it cannot be used inside a bracketed character
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271class; use C<\v> instead (vertical whitespace). It uses the platform's
272native character set, and does not consider any locale that may
273otherwise be in use.
ea449505 274Details are discussed in L<perlrebackslash>.
8a118206 275
82206b5e 276Note that unlike C<\s> (and C<\d> and C<\w>), C<\h> and C<\v> always match
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277the same characters, without regard to other factors, such as the active
278locale or whether the source string is in UTF-8 format.
8a118206 279
82206b5e 280One might think that C<\s> is equivalent to C<[\h\v]>. This is not true.
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281The difference is that the vertical tab (C<"\x0b">) is not matched by
282C<\s>; it is however considered vertical whitespace.
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283
284The following table is a complete listing of characters matched by
82206b5e 285C<\s>, C<\h> and C<\v> as of Unicode 6.0.
8a118206 286
582da942 287The first column gives the Unicode code point of the character (in hex format),
8a118206 288the second column gives the (Unicode) name. The third column indicates
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289by which class(es) the character is matched (assuming no locale or EBCDIC code
290page is in effect that changes the C<\s> matching).
8a118206 291
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292 0x0009 CHARACTER TABULATION h s
293 0x000a LINE FEED (LF) vs
294 0x000b LINE TABULATION v
295 0x000c FORM FEED (FF) vs
296 0x000d CARRIAGE RETURN (CR) vs
297 0x0020 SPACE h s
298 0x0085 NEXT LINE (NEL) vs [1]
299 0x00a0 NO-BREAK SPACE h s [1]
300 0x1680 OGHAM SPACE MARK h s
301 0x180e MONGOLIAN VOWEL SEPARATOR h s
302 0x2000 EN QUAD h s
303 0x2001 EM QUAD h s
304 0x2002 EN SPACE h s
305 0x2003 EM SPACE h s
306 0x2004 THREE-PER-EM SPACE h s
307 0x2005 FOUR-PER-EM SPACE h s
308 0x2006 SIX-PER-EM SPACE h s
309 0x2007 FIGURE SPACE h s
310 0x2008 PUNCTUATION SPACE h s
311 0x2009 THIN SPACE h s
312 0x200a HAIR SPACE h s
313 0x2028 LINE SEPARATOR vs
314 0x2029 PARAGRAPH SEPARATOR vs
315 0x202f NARROW NO-BREAK SPACE h s
316 0x205f MEDIUM MATHEMATICAL SPACE h s
317 0x3000 IDEOGRAPHIC SPACE h s
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318
319=over 4
320
321=item [1]
322
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323NEXT LINE and NO-BREAK SPACE may or may not match C<\s> depending
324on the rules in effect. See
325L<the beginning of this section|/Whitespace>.
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326
327=back
328
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329=head3 Unicode Properties
330
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331C<\pP> and C<\p{Prop}> are character classes to match characters that fit given
332Unicode properties. One letter property names can be used in the C<\pP> form,
333with the property name following the C<\p>, otherwise, braces are required.
334When using braces, there is a single form, which is just the property name
335enclosed in the braces, and a compound form which looks like C<\p{name=value}>,
b6538e4f 336which means to match if the property "name" for the character has that particular
c1c4ae3a 337"value".
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338For instance, a match for a number can be written as C</\pN/> or as
339C</\p{Number}/>, or as C</\p{Number=True}/>.
340Lowercase letters are matched by the property I<Lowercase_Letter> which
e2cfb18c 341has the short form I<Ll>. They need the braces, so are written as C</\p{Ll}/> or
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342C</\p{Lowercase_Letter}/>, or C</\p{General_Category=Lowercase_Letter}/>
343(the underscores are optional).
344C</\pLl/> is valid, but means something different.
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345It matches a two character string: a letter (Unicode property C<\pL>),
346followed by a lowercase C<l>.
347
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348If neither the C</a> modifier nor locale rules are in effect, the use of
349a Unicode property will force the regular expression into using Unicode
350rules.
351
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352Note that almost all properties are immune to case-insensitive matching.
353That is, adding a C</i> regular expression modifier does not change what
82206b5e 354they match. There are two sets that are affected. The first set is
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355C<Uppercase_Letter>,
356C<Lowercase_Letter>,
357and C<Titlecase_Letter>,
358all of which match C<Cased_Letter> under C</i> matching.
b6538e4f 359The second set is
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360C<Uppercase>,
361C<Lowercase>,
362and C<Titlecase>,
363all of which match C<Cased> under C</i> matching.
364(The difference between these sets is that some things, such as Roman
e2cfb18c 365numerals, come in both upper and lower case, so they are C<Cased>, but
b6538e4f 366aren't considered to be letters, so they aren't C<Cased_Letter>s. They're
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367actually C<Letter_Number>s.)
368This set also includes its subsets C<PosixUpper> and C<PosixLower>, both
e2cfb18c 369of which under C</i> match C<PosixAlpha>.
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370
371For more details on Unicode properties, see L<perlunicode/Unicode
372Character Properties>; for a
e1b711da 373complete list of possible properties, see
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374L<perluniprops/Properties accessible through \p{} and \P{}>,
375which notes all forms that have C</i> differences.
e1b711da 376It is also possible to define your own properties. This is discussed in
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377L<perlunicode/User-Defined Character Properties>.
378
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379Unicode properties are defined (surprise!) only on Unicode code points.
380A warning is raised and all matches fail on non-Unicode code points
381(those above the legal Unicode maximum of 0x10FFFF). This can be
382somewhat surprising,
383
384 chr(0x110000) =~ \p{ASCII_Hex_Digit=True} # Fails.
385 chr(0x110000) =~ \p{ASCII_Hex_Digit=False} # Also fails!
386
387Even though these two matches might be thought of as complements, they
388are so only on Unicode code points.
389
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390=head4 Examples
391
392 "a" =~ /\w/ # Match, "a" is a 'word' character.
393 "7" =~ /\w/ # Match, "7" is a 'word' character as well.
394 "a" =~ /\d/ # No match, "a" isn't a digit.
395 "7" =~ /\d/ # Match, "7" is a digit.
ea449505 396 " " =~ /\s/ # Match, a space is whitespace.
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397 "a" =~ /\D/ # Match, "a" is a non-digit.
398 "7" =~ /\D/ # No match, "7" is not a non-digit.
ea449505 399 " " =~ /\S/ # No match, a space is not non-whitespace.
8a118206 400
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401 " " =~ /\h/ # Match, space is horizontal whitespace.
402 " " =~ /\v/ # No match, space is not vertical whitespace.
403 "\r" =~ /\v/ # Match, a return is vertical whitespace.
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404
405 "a" =~ /\pL/ # Match, "a" is a letter.
406 "a" =~ /\p{Lu}/ # No match, /\p{Lu}/ matches upper case letters.
407
408 "\x{0e0b}" =~ /\p{Thai}/ # Match, \x{0e0b} is the character
409 # 'THAI CHARACTER SO SO', and that's in
410 # Thai Unicode class.
ea449505 411 "a" =~ /\P{Lao}/ # Match, as "a" is not a Laotian character.
8a118206 412
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413It is worth emphasizing that C<\d>, C<\w>, etc, match single characters, not
414complete numbers or words. To match a number (that consists of digits),
415use C<\d+>; to match a word, use C<\w+>. But be aware of the security
416considerations in doing so, as mentioned above.
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417
418=head2 Bracketed Character Classes
419
420The third form of character class you can use in Perl regular expressions
6b83a163 421is the bracketed character class. In its simplest form, it lists the characters
c1c4ae3a 422that may be matched, surrounded by square brackets, like this: C<[aeiou]>.
ea449505 423This matches one of C<a>, C<e>, C<i>, C<o> or C<u>. Like the other
1f59b283 424character classes, exactly one character is matched.* To match
ea449505 425a longer string consisting of characters mentioned in the character
6b83a163 426class, follow the character class with a L<quantifier|perlre/Quantifiers>. For
b6538e4f 427instance, C<[aeiou]+> matches one or more lowercase English vowels.
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428
429Repeating a character in a character class has no
430effect; it's considered to be in the set only once.
431
432Examples:
433
434 "e" =~ /[aeiou]/ # Match, as "e" is listed in the class.
435 "p" =~ /[aeiou]/ # No match, "p" is not listed in the class.
436 "ae" =~ /^[aeiou]$/ # No match, a character class only matches
437 # a single character.
438 "ae" =~ /^[aeiou]+$/ # Match, due to the quantifier.
439
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440 -------
441
df0e3973 442* There is an exception to a bracketed character class matching a
1cecf2c0 443single character only. When the class is to match caselessly under C</i>
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444matching rules, and a character inside the class matches a
445multiple-character sequence caselessly under Unicode rules, the class
446(when not L<inverted|/Negation>) will also match that sequence. For
447example, Unicode says that the letter C<LATIN SMALL LETTER SHARP S>
448should match the sequence C<ss> under C</i> rules. Thus,
449
450 'ss' =~ /\A\N{LATIN SMALL LETTER SHARP S}\z/i # Matches
451 'ss' =~ /\A[aeioust\N{LATIN SMALL LETTER SHARP S}]\z/i # Matches
452
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453=head3 Special Characters Inside a Bracketed Character Class
454
455Most characters that are meta characters in regular expressions (that
df225385 456is, characters that carry a special meaning like C<.>, C<*>, or C<(>) lose
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457their special meaning and can be used inside a character class without
458the need to escape them. For instance, C<[()]> matches either an opening
459parenthesis, or a closing parenthesis, and the parens inside the character
460class don't group or capture.
461
462Characters that may carry a special meaning inside a character class are:
463C<\>, C<^>, C<->, C<[> and C<]>, and are discussed below. They can be
464escaped with a backslash, although this is sometimes not needed, in which
465case the backslash may be omitted.
466
467The sequence C<\b> is special inside a bracketed character class. While
6b83a163 468outside the character class, C<\b> is an assertion indicating a point
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469that does not have either two word characters or two non-word characters
470on either side, inside a bracketed character class, C<\b> matches a
471backspace character.
472
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473The sequences
474C<\a>,
475C<\c>,
476C<\e>,
477C<\f>,
478C<\n>,
e526e8bb 479C<\N{I<NAME>}>,
765fa144 480C<\N{U+I<hex char>}>,
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481C<\r>,
482C<\t>,
483and
484C<\x>
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485are also special and have the same meanings as they do outside a
486bracketed character class. (However, inside a bracketed character
487class, if C<\N{I<NAME>}> expands to a sequence of characters, only the first
488one in the sequence is used, with a warning.)
df225385 489
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490Also, a backslash followed by two or three octal digits is considered an octal
491number.
df225385 492
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493A C<[> is not special inside a character class, unless it's the start of a
494POSIX character class (see L</POSIX Character Classes> below). It normally does
495not need escaping.
8a118206 496
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497A C<]> is normally either the end of a POSIX character class (see
498L</POSIX Character Classes> below), or it signals the end of the bracketed
499character class. If you want to include a C<]> in the set of characters, you
500must generally escape it.
b6538e4f 501
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502However, if the C<]> is the I<first> (or the second if the first
503character is a caret) character of a bracketed character class, it
504does not denote the end of the class (as you cannot have an empty class)
505and is considered part of the set of characters that can be matched without
506escaping.
507
508Examples:
509
510 "+" =~ /[+?*]/ # Match, "+" in a character class is not special.
511 "\cH" =~ /[\b]/ # Match, \b inside in a character class
c1c4ae3a 512 # is equivalent to a backspace.
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513 "]" =~ /[][]/ # Match, as the character class contains.
514 # both [ and ].
515 "[]" =~ /[[]]/ # Match, the pattern contains a character class
516 # containing just ], and the character class is
517 # followed by a ].
518
519=head3 Character Ranges
520
521It is not uncommon to want to match a range of characters. Luckily, instead
b6538e4f 522of listing all characters in the range, one may use the hyphen (C<->).
8a118206 523If inside a bracketed character class you have two characters separated
b6538e4f 524by a hyphen, it's treated as if all characters between the two were in
8a118206 525the class. For instance, C<[0-9]> matches any ASCII digit, and C<[a-m]>
e2cfb18c 526matches any lowercase letter from the first half of the ASCII alphabet.
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527
528Note that the two characters on either side of the hyphen are not
765fa144 529necessarily both letters or both digits. Any character is possible,
8a118206 530although not advisable. C<['-?]> contains a range of characters, but
b6538e4f 531most people will not know which characters that means. Furthermore,
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532such ranges may lead to portability problems if the code has to run on
533a platform that uses a different character set, such as EBCDIC.
534
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535If a hyphen in a character class cannot syntactically be part of a range, for
536instance because it is the first or the last character of the character class,
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537or if it immediately follows a range, the hyphen isn't special, and so is
538considered a character to be matched literally. If you want a hyphen in
539your set of characters to be matched and its position in the class is such
540that it could be considered part of a range, you must escape that hyphen
541with a backslash.
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542
543Examples:
544
545 [a-z] # Matches a character that is a lower case ASCII letter.
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546 [a-fz] # Matches any letter between 'a' and 'f' (inclusive) or
547 # the letter 'z'.
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548 [-z] # Matches either a hyphen ('-') or the letter 'z'.
549 [a-f-m] # Matches any letter between 'a' and 'f' (inclusive), the
550 # hyphen ('-'), or the letter 'm'.
551 ['-?] # Matches any of the characters '()*+,-./0123456789:;<=>?
552 # (But not on an EBCDIC platform).
553
554
555=head3 Negation
556
557It is also possible to instead list the characters you do not want to
558match. You can do so by using a caret (C<^>) as the first character in the
b6538e4f 559character class. For instance, C<[^a-z]> matches any character that is not a
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560lowercase ASCII letter, which therefore includes more than a million
561Unicode code points. The class is said to be "negated" or "inverted".
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562
563This syntax make the caret a special character inside a bracketed character
564class, but only if it is the first character of the class. So if you want
82206b5e 565the caret as one of the characters to match, either escape the caret or
e2cfb18c 566else don't list it first.
8a118206 567
1f59b283 568In inverted bracketed character classes, Perl ignores the Unicode rules
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569that normally say that certain characters should match a sequence of
570multiple characters under caseless C</i> matching. Following those
571rules could lead to highly confusing situations:
1f59b283 572
582da942 573 "ss" =~ /^[^\xDF]+$/ui; # Matches!
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574
575This should match any sequences of characters that aren't C<\xDF> nor
576what C<\xDF> matches under C</i>. C<"s"> isn't C<\xDF>, but Unicode
577says that C<"ss"> is what C<\xDF> matches under C</i>. So which one
578"wins"? Do you fail the match because the string has C<ss> or accept it
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579because it has an C<s> followed by another C<s>? Perl has chosen the
580latter.
1f59b283 581
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582Examples:
583
584 "e" =~ /[^aeiou]/ # No match, the 'e' is listed.
585 "x" =~ /[^aeiou]/ # Match, as 'x' isn't a lowercase vowel.
586 "^" =~ /[^^]/ # No match, matches anything that isn't a caret.
587 "^" =~ /[x^]/ # Match, caret is not special here.
588
589=head3 Backslash Sequences
590
ea449505 591You can put any backslash sequence character class (with the exception of
765fa144 592C<\N> and C<\R>) inside a bracketed character class, and it will act just
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593as if you had put all characters matched by the backslash sequence inside the
594character class. For instance, C<[a-f\d]> matches any decimal digit, or any
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595of the lowercase letters between 'a' and 'f' inclusive.
596
597C<\N> within a bracketed character class must be of the forms C<\N{I<name>}>
765fa144 598or C<\N{U+I<hex char>}>, and NOT be the form that matches non-newlines,
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599for the same reason that a dot C<.> inside a bracketed character class loses
600its special meaning: it matches nearly anything, which generally isn't what you
601want to happen.
df225385 602
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603
604Examples:
605
606 /[\p{Thai}\d]/ # Matches a character that is either a Thai
607 # character, or a digit.
608 /[^\p{Arabic}()]/ # Matches a character that is neither an Arabic
609 # character, nor a parenthesis.
610
611Backslash sequence character classes cannot form one of the endpoints
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612of a range. Thus, you can't say:
613
614 /[\p{Thai}-\d]/ # Wrong!
8a118206 615
6b83a163 616=head3 POSIX Character Classes
ea449505 617X<character class> X<\p> X<\p{}>
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618X<alpha> X<alnum> X<ascii> X<blank> X<cntrl> X<digit> X<graph>
619X<lower> X<print> X<punct> X<space> X<upper> X<word> X<xdigit>
8a118206 620
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621POSIX character classes have the form C<[:class:]>, where I<class> is
622name, and the C<[:> and C<:]> delimiters. POSIX character classes only appear
8a118206 623I<inside> bracketed character classes, and are a convenient and descriptive
82206b5e 624way of listing a group of characters.
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625
626Be careful about the syntax,
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627
628 # Correct:
629 $string =~ /[[:alpha:]]/
630
631 # Incorrect (will warn):
632 $string =~ /[:alpha:]/
633
634The latter pattern would be a character class consisting of a colon,
635and the letters C<a>, C<l>, C<p> and C<h>.
82206b5e 636POSIX character classes can be part of a larger bracketed character class.
b6538e4f 637For example,
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638
639 [01[:alpha:]%]
640
641is valid and matches '0', '1', any alphabetic character, and the percent sign.
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642
643Perl recognizes the following POSIX character classes:
644
ea449505 645 alpha Any alphabetical character ("[A-Za-z]").
b6538e4f 646 alnum Any alphanumeric character. ("[A-Za-z0-9]")
ea449505 647 ascii Any character in the ASCII character set.
ea8b8ad2 648 blank A GNU extension, equal to a space or a horizontal tab ("\t").
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649 cntrl Any control character. See Note [2] below.
650 digit Any decimal digit ("[0-9]"), equivalent to "\d".
651 graph Any printable character, excluding a space. See Note [3] below.
652 lower Any lowercase character ("[a-z]").
653 print Any printable character, including a space. See Note [4] below.
c1c4ae3a 654 punct Any graphical character excluding "word" characters. Note [5].
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655 space Any whitespace character. "\s" plus the vertical tab ("\cK").
656 upper Any uppercase character ("[A-Z]").
657 word A Perl extension ("[A-Za-z0-9_]"), equivalent to "\w".
658 xdigit Any hexadecimal digit ("[0-9a-fA-F]").
659
660Most POSIX character classes have two Unicode-style C<\p> property
661counterparts. (They are not official Unicode properties, but Perl extensions
662derived from official Unicode properties.) The table below shows the relation
663between POSIX character classes and these counterparts.
664
665One counterpart, in the column labelled "ASCII-range Unicode" in
b6538e4f 666the table, matches only characters in the ASCII character set.
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667
668The other counterpart, in the column labelled "Full-range Unicode", matches any
669appropriate characters in the full Unicode character set. For example,
b6538e4f 670C<\p{Alpha}> matches not just the ASCII alphabetic characters, but any
82206b5e 671character in the entire Unicode character set considered alphabetic.
582da942 672An entry in the column labelled "backslash sequence" is a (short)
5db9882c 673equivalent.
ea449505 674
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675 [[:...:]] ASCII-range Full-range backslash Note
676 Unicode Unicode sequence
ea449505 677 -----------------------------------------------------
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678 alpha \p{PosixAlpha} \p{XPosixAlpha}
679 alnum \p{PosixAlnum} \p{XPosixAlnum}
82206b5e 680 ascii \p{ASCII}
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681 blank \p{PosixBlank} \p{XPosixBlank} \h [1]
682 or \p{HorizSpace} [1]
683 cntrl \p{PosixCntrl} \p{XPosixCntrl} [2]
684 digit \p{PosixDigit} \p{XPosixDigit} \d
685 graph \p{PosixGraph} \p{XPosixGraph} [3]
686 lower \p{PosixLower} \p{XPosixLower}
687 print \p{PosixPrint} \p{XPosixPrint} [4]
688 punct \p{PosixPunct} \p{XPosixPunct} [5]
689 \p{PerlSpace} \p{XPerlSpace} \s [6]
690 space \p{PosixSpace} \p{XPosixSpace} [6]
691 upper \p{PosixUpper} \p{XPosixUpper}
692 word \p{PosixWord} \p{XPosixWord} \w
82206b5e 693 xdigit \p{PosixXDigit} \p{XPosixXDigit}
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694
695=over 4
696
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697=item [1]
698
699C<\p{Blank}> and C<\p{HorizSpace}> are synonyms.
700
701=item [2]
8a118206 702
ea449505 703Control characters don't produce output as such, but instead usually control
b6538e4f 704the terminal somehow: for example, newline and backspace are control characters.
82206b5e 705In the ASCII range, characters whose code points are between 0 and 31 inclusive,
ea449505 706plus 127 (C<DEL>) are control characters.
8a118206 707
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708On EBCDIC platforms, it is likely that the code page will define C<[[:cntrl:]]>
709to be the EBCDIC equivalents of the ASCII controls, plus the controls
82206b5e 710that in Unicode have code pointss from 128 through 159.
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711
712=item [3]
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713
714Any character that is I<graphical>, that is, visible. This class consists
b6538e4f 715of all alphanumeric characters and all punctuation characters.
8a118206 716
ea449505 717=item [4]
8a118206 718
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TC
719All printable characters, which is the set of all graphical characters
720plus those whitespace characters which are not also controls.
ea449505 721
b6dac59a 722=item [5]
ea449505 723
b6538e4f 724C<\p{PosixPunct}> and C<[[:punct:]]> in the ASCII range match all
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725non-controls, non-alphanumeric, non-space characters:
726C<[-!"#$%&'()*+,./:;<=E<gt>?@[\\\]^_`{|}~]> (although if a locale is in effect,
727it could alter the behavior of C<[[:punct:]]>).
728
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729The similarly named property, C<\p{Punct}>, matches a somewhat different
730set in the ASCII range, namely
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731C<[-!"#%&'()*,./:;?@[\\\]_{}]>. That is, it is missing the nine
732characters C<[$+E<lt>=E<gt>^`|~]>.
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733This is because Unicode splits what POSIX considers to be punctuation into two
734categories, Punctuation and Symbols.
735
e2cfb18c 736C<\p{XPosixPunct}> and (under Unicode rules) C<[[:punct:]]>, match what
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737C<\p{PosixPunct}> matches in the ASCII range, plus what C<\p{Punct}>
738matches. This is different than strictly matching according to
739C<\p{Punct}>. Another way to say it is that
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740if Unicode rules are in effect, C<[[:punct:]]> matches all characters
741that Unicode considers punctuation, plus all ASCII-range characters that
742Unicode considers symbols.
8a118206 743
ea449505 744=item [6]
8a118206 745
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746C<\p{SpacePerl}> and C<\p{Space}> differ only in that in non-locale
747matching, C<\p{Space}> additionally
ea449505 748matches the vertical tab, C<\cK>. Same for the two ASCII-only range forms.
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749
750=back
751
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752There are various other synonyms that can be used besides the names
753listed in the table. For example, C<\p{PosixAlpha}> can be written as
754C<\p{Alpha}>. All are listed in
755L<perluniprops/Properties accessible through \p{} and \P{}>,
756plus all characters matched by each ASCII-range property.
757
758Both the C<\p> counterparts always assume Unicode rules are in effect.
759On ASCII platforms, this means they assume that the code points from 128
760to 255 are Latin-1, and that means that using them under locale rules is
761unwise unless the locale is guaranteed to be Latin-1 or UTF-8. In contrast, the
762POSIX character classes are useful under locale rules. They are
763affected by the actual rules in effect, as follows:
764
765=over
766
767=item If the C</a> modifier, is in effect ...
768
769Each of the POSIX classes matches exactly the same as their ASCII-range
770counterparts.
771
772=item otherwise ...
773
774=over
775
776=item For code points above 255 ...
777
778The POSIX class matches the same as its Full-range counterpart.
779
780=item For code points below 256 ...
781
782=over
783
784=item if locale rules are in effect ...
785
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786The POSIX class matches according to the locale, except that
787C<word> uses the platform's native underscore character, no matter what
788the locale is.
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789
790=item if Unicode rules are in effect or if on an EBCDIC platform ...
791
792The POSIX class matches the same as the Full-range counterpart.
793
794=item otherwise ...
795
796The POSIX class matches the same as the ASCII range counterpart.
797
798=back
799
800=back
801
802=back
803
804Which rules apply are determined as described in
805L<perlre/Which character set modifier is in effect?>.
806
807It is proposed to change this behavior in a future release of Perl so that
808whether or not Unicode rules are in effect would not change the
809behavior: Outside of locale or an EBCDIC code page, the POSIX classes
810would behave like their ASCII-range counterparts. If you wish to
811comment on this proposal, send email to C<perl5-porters@perl.org>.
cbc24f92 812
1f59b283 813=head4 Negation of POSIX character classes
ea449505 814X<character class, negation>
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815
816A Perl extension to the POSIX character class is the ability to
817negate it. This is done by prefixing the class name with a caret (C<^>).
818Some examples:
819
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820 POSIX ASCII-range Full-range backslash
821 Unicode Unicode sequence
822 -----------------------------------------------------
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823 [[:^digit:]] \P{PosixDigit} \P{XPosixDigit} \D
824 [[:^space:]] \P{PosixSpace} \P{XPosixSpace}
825 \P{PerlSpace} \P{XPerlSpace} \S
826 [[:^word:]] \P{PerlWord} \P{XPosixWord} \W
827
765fa144 828The backslash sequence can mean either ASCII- or Full-range Unicode,
82206b5e 829depending on various factors as described in L<perlre/Which character set modifier is in effect?>.
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830
831=head4 [= =] and [. .]
832
b6538e4f 833Perl recognizes the POSIX character classes C<[=class=]> and
82206b5e 834C<[.class.]>, but does not (yet?) support them. Any attempt to use
b6538e4f 835either construct raises an exception.
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836
837=head4 Examples
838
839 /[[:digit:]]/ # Matches a character that is a digit.
840 /[01[:lower:]]/ # Matches a character that is either a
841 # lowercase letter, or '0' or '1'.
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842 /[[:digit:][:^xdigit:]]/ # Matches a character that can be anything
843 # except the letters 'a' to 'f'. This is
844 # because the main character class is composed
845 # of two POSIX character classes that are ORed
846 # together, one that matches any digit, and
847 # the other that matches anything that isn't a
848 # hex digit. The result matches all
849 # characters except the letters 'a' to 'f' and
850 # 'A' to 'F'.