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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
29character, except for the newline. The 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
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47X<\w> X<\W> X<\s> X<\S> X<\d> X<\D> X<\p> X<\P>
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
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74
75=head3 Digits
76
6b83a163 77C<\d> matches a single character that is considered to be a decimal I<digit>.
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78What is considered a decimal digit depends on several factors, detailed
79below in L</Locale, EBCDIC, Unicode and UTF-8>. If those factors
80indicate a Unicode interpretation, C<\d> not only matches the digits
81'0' - '9', but also Arabic, Devanagari and digits from other languages.
82Otherwise, if there is a locale in effect, it will match whatever
83characters the locale considers decimal digits. Without a locale, C<\d>
84matches just the digits '0' to '9'.
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85
86Unicode digits may cause some confusion, and some security issues. In UTF-8
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87strings, unless the C<"a"> regular expression modifier is specified,
88C<\d> matches the same characters matched by
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89C<\p{General_Category=Decimal_Number}>, or synonymously,
90C<\p{General_Category=Digit}>. Starting with Unicode version 4.1, this is the
91same set of characters matched by C<\p{Numeric_Type=Decimal}>.
92
93But Unicode also has a different property with a similar name,
94C<\p{Numeric_Type=Digit}>, which matches a completely different set of
95characters. These characters are things such as subscripts.
96
97The design intent is for C<\d> to match all the digits (and no other characters)
98that can be used with "normal" big-endian positional decimal syntax, whereby a
99sequence of such digits {N0, N1, N2, ...Nn} has the numeric value (...(N0 * 10
100+ N1) * 10 + N2) * 10 ... + Nn). In Unicode 5.2, the Tamil digits (U+0BE6 -
101U+0BEF) can also legally be used in old-style Tamil numbers in which they would
102appear no more than one in a row, separated by characters that mean "times 10",
103"times 100", etc. (See L<http://www.unicode.org/notes/tn21>.)
104
105Some of the non-European digits that C<\d> matches look like European ones, but
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106have different values. For example, BENGALI DIGIT FOUR (U+09EA) looks
107very much like an ASCII DIGIT EIGHT (U+0038).
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108
109It may be useful for security purposes for an application to require that all
110digits in a row be from the same script. See L<Unicode::UCD/charscript()>.
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111
112Any character that isn't matched by C<\d> will be matched by C<\D>.
113
114=head3 Word characters
115
ea449505 116A C<\w> matches a single alphanumeric character (an alphabetic character, or a
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117decimal digit) or a connecting punctuation character, such as an
118underscore ("_"). It does not match a whole word. To match a whole
6b83a163 119word, use C<\w+>. This isn't the same thing as matching an English word, but
765fa144 120in the ASCII range it is the same as a string of Perl-identifier
d35dd6c6 121characters. What is considered a
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122word character depends on several factors, detailed below in L</Locale,
123EBCDIC, Unicode and UTF-8>. If those factors indicate a Unicode
124interpretation, C<\w> matches the characters that are considered word
ea449505 125characters in the Unicode database. That is, it not only matches ASCII letters,
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126but also Thai letters, Greek letters, etc. This includes connector
127punctuation (like the underscore) which connect two words together, or
128marks, such as a C<COMBINING TILDE>, which are generally used to add
129diacritical marks to letters. If a Unicode interpretation
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130is not indicated, C<\w> matches those characters that are considered
131word characters by the current locale or EBCDIC code page. Without a
132locale or EBCDIC code page, C<\w> matches the ASCII letters, digits and
133the underscore.
8a118206 134
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135There are a number of security issues with the full Unicode list of word
136characters. See L<http://unicode.org/reports/tr36>.
137
138Also, for a somewhat finer-grained set of characters that are in programming
139language identifiers beyond the ASCII range, you may wish to instead use the
140more customized Unicode properties, "ID_Start", ID_Continue", "XID_Start", and
141"XID_Continue". See L<http://unicode.org/reports/tr31>.
142
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143Any character that isn't matched by C<\w> will be matched by C<\W>.
144
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145=head3 Whitespace
146
6b83a163 147C<\s> matches any single character that is considered whitespace. The exact
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148set of characters matched by C<\s> depends on several factors, detailed
149below in L</Locale, EBCDIC, Unicode and UTF-8>. If those factors
150indicate a Unicode interpretation, C<\s> matches what is considered
151whitespace in the Unicode database; the complete list is in the table
152below. Otherwise, if there is a locale or EBCDIC code page in effect,
153C<\s> matches whatever is considered whitespace by the current locale or
154EBCDIC code page. Without a locale or EBCDIC code page, C<\s> matches
155the horizontal tab (C<\t>), the newline (C<\n>), the form feed (C<\f>),
156the carriage return (C<\r>), and the space. (Note that it doesn't match
157the vertical tab, C<\cK>.) Perhaps the most notable possible surprise
158is that C<\s> matches a non-breaking space only if a Unicode
159interpretation is indicated, or the locale or EBCDIC code page that is
160in effect has that character.
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161
162Any character that isn't matched by C<\s> will be matched by C<\S>.
163
ea449505 164C<\h> will match any character that is considered horizontal whitespace;
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165this includes the space and the tab characters and a number other characters,
166all of which are listed in the table below. C<\H> will match any character
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167that is not considered horizontal whitespace.
168
ea449505 169C<\v> will match any character that is considered vertical whitespace;
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170this includes the carriage return and line feed characters (newline) plus several
171other characters, all listed in the table below.
ea449505 172C<\V> will match any character that is not considered vertical whitespace.
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173
174C<\R> matches anything that can be considered a newline under Unicode
175rules. It's not a character class, as it can match a multi-character
176sequence. Therefore, it cannot be used inside a bracketed character
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177class; use C<\v> instead (vertical whitespace).
178Details are discussed in L<perlrebackslash>.
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179
180Note that unlike C<\s>, C<\d> and C<\w>, C<\h> and C<\v> always match
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181the same characters, without regard to other factors, such as if the
182source string is in UTF-8 format or not.
8a118206 183
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184One might think that C<\s> is equivalent to C<[\h\v]>. This is not true. The
185vertical tab (C<"\x0b">) is not matched by C<\s>, it is however considered
186vertical whitespace. Furthermore, if the source string is not in UTF-8 format,
187and any locale or EBCDIC code page that is in effect doesn't include them, the
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188next line (ASCII-platform C<"\x85">) and the no-break space (ASCII-platform
189C<"\xA0">) characters are not matched by C<\s>, but are by C<\v> and C<\h>
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190respectively. If the C<"a"> modifier is not in effect, and the source
191string is in UTF-8 format, both the next line and
6b83a163 192the no-break space are matched by C<\s>.
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193
194The following table is a complete listing of characters matched by
ea449505 195C<\s>, C<\h> and C<\v> as of Unicode 5.2.
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196
197The first column gives the code point of the character (in hex format),
198the second column gives the (Unicode) name. The third column indicates
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199by which class(es) the character is matched (assuming no locale or EBCDIC code
200page is in effect that changes the C<\s> matching).
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201
202 0x00009 CHARACTER TABULATION h s
203 0x0000a LINE FEED (LF) vs
204 0x0000b LINE TABULATION v
205 0x0000c FORM FEED (FF) vs
206 0x0000d CARRIAGE RETURN (CR) vs
207 0x00020 SPACE h s
208 0x00085 NEXT LINE (NEL) vs [1]
209 0x000a0 NO-BREAK SPACE h s [1]
210 0x01680 OGHAM SPACE MARK h s
211 0x0180e MONGOLIAN VOWEL SEPARATOR h s
212 0x02000 EN QUAD h s
213 0x02001 EM QUAD h s
214 0x02002 EN SPACE h s
215 0x02003 EM SPACE h s
216 0x02004 THREE-PER-EM SPACE h s
217 0x02005 FOUR-PER-EM SPACE h s
218 0x02006 SIX-PER-EM SPACE h s
219 0x02007 FIGURE SPACE h s
220 0x02008 PUNCTUATION SPACE h s
221 0x02009 THIN SPACE h s
222 0x0200a HAIR SPACE h s
223 0x02028 LINE SEPARATOR vs
224 0x02029 PARAGRAPH SEPARATOR vs
225 0x0202f NARROW NO-BREAK SPACE h s
226 0x0205f MEDIUM MATHEMATICAL SPACE h s
227 0x03000 IDEOGRAPHIC SPACE h s
228
229=over 4
230
231=item [1]
232
233NEXT LINE and NO-BREAK SPACE only match C<\s> if the source string is in
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234UTF-8 format and the C<"a"> modifier is not in effect; or the locale or
235EBCDIC code page that is in effect includes them.
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236
237=back
238
239It is worth noting that C<\d>, C<\w>, etc, match single characters, not
e486b3cc 240complete numbers or words. To match a number (that consists of digits),
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241use C<\d+>; to match a word, use C<\w+>.
242
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243=head3 \N
244
245C<\N> is new in 5.12, and is experimental. It, like the dot, will match any
246character that is not a newline. The difference is that C<\N> is not influenced
247by the I<single line> regular expression modifier (see L</The dot> above). Note
248that the form C<\N{...}> may mean something completely different. When the
249C<{...}> is a L<quantifier|perlre/Quantifiers>, it means to match a non-newline
250character that many times. For example, C<\N{3}> means to match 3
251non-newlines; C<\N{5,}> means to match 5 or more non-newlines. But if C<{...}>
252is not a legal quantifier, it is presumed to be a named character. See
253L<charnames> for those. For example, none of C<\N{COLON}>, C<\N{4F}>, and
254C<\N{F4}> contain legal quantifiers, so Perl will try to find characters whose
255names are, respectively, C<COLON>, C<4F>, and C<F4>.
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256
257=head3 Unicode Properties
258
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259C<\pP> and C<\p{Prop}> are character classes to match characters that fit given
260Unicode properties. One letter property names can be used in the C<\pP> form,
261with the property name following the C<\p>, otherwise, braces are required.
262When using braces, there is a single form, which is just the property name
263enclosed in the braces, and a compound form which looks like C<\p{name=value}>,
264which means to match if the property "name" for the character has the particular
265"value".
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266For instance, a match for a number can be written as C</\pN/> or as
267C</\p{Number}/>, or as C</\p{Number=True}/>.
268Lowercase letters are matched by the property I<Lowercase_Letter> which
269has as short form I<Ll>. They need the braces, so are written as C</\p{Ll}/> or
270C</\p{Lowercase_Letter}/>, or C</\p{General_Category=Lowercase_Letter}/>
271(the underscores are optional).
272C</\pLl/> is valid, but means something different.
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273It matches a two character string: a letter (Unicode property C<\pL>),
274followed by a lowercase C<l>.
275
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276For more details, see L<perlunicode/Unicode Character Properties>; for a
277complete list of possible properties, see
278L<perluniprops/Properties accessible through \p{} and \P{}>.
279It is also possible to define your own properties. This is discussed in
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280L<perlunicode/User-Defined Character Properties>.
281
282
283=head4 Examples
284
285 "a" =~ /\w/ # Match, "a" is a 'word' character.
286 "7" =~ /\w/ # Match, "7" is a 'word' character as well.
287 "a" =~ /\d/ # No match, "a" isn't a digit.
288 "7" =~ /\d/ # Match, "7" is a digit.
ea449505 289 " " =~ /\s/ # Match, a space is whitespace.
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290 "a" =~ /\D/ # Match, "a" is a non-digit.
291 "7" =~ /\D/ # No match, "7" is not a non-digit.
ea449505 292 " " =~ /\S/ # No match, a space is not non-whitespace.
8a118206 293
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294 " " =~ /\h/ # Match, space is horizontal whitespace.
295 " " =~ /\v/ # No match, space is not vertical whitespace.
296 "\r" =~ /\v/ # Match, a return is vertical whitespace.
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297
298 "a" =~ /\pL/ # Match, "a" is a letter.
299 "a" =~ /\p{Lu}/ # No match, /\p{Lu}/ matches upper case letters.
300
301 "\x{0e0b}" =~ /\p{Thai}/ # Match, \x{0e0b} is the character
302 # 'THAI CHARACTER SO SO', and that's in
303 # Thai Unicode class.
ea449505 304 "a" =~ /\P{Lao}/ # Match, as "a" is not a Laotian character.
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305
306
307=head2 Bracketed Character Classes
308
309The third form of character class you can use in Perl regular expressions
6b83a163 310is the bracketed character class. In its simplest form, it lists the characters
c1c4ae3a 311that may be matched, surrounded by square brackets, like this: C<[aeiou]>.
ea449505 312This matches one of C<a>, C<e>, C<i>, C<o> or C<u>. Like the other
8a118206 313character classes, exactly one character will be matched. To match
ea449505 314a longer string consisting of characters mentioned in the character
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315class, follow the character class with a L<quantifier|perlre/Quantifiers>. For
316instance, C<[aeiou]+> matches a string of one or more lowercase English vowels.
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317
318Repeating a character in a character class has no
319effect; it's considered to be in the set only once.
320
321Examples:
322
323 "e" =~ /[aeiou]/ # Match, as "e" is listed in the class.
324 "p" =~ /[aeiou]/ # No match, "p" is not listed in the class.
325 "ae" =~ /^[aeiou]$/ # No match, a character class only matches
326 # a single character.
327 "ae" =~ /^[aeiou]+$/ # Match, due to the quantifier.
328
329=head3 Special Characters Inside a Bracketed Character Class
330
331Most characters that are meta characters in regular expressions (that
df225385 332is, characters that carry a special meaning like C<.>, C<*>, or C<(>) lose
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333their special meaning and can be used inside a character class without
334the need to escape them. For instance, C<[()]> matches either an opening
335parenthesis, or a closing parenthesis, and the parens inside the character
336class don't group or capture.
337
338Characters that may carry a special meaning inside a character class are:
339C<\>, C<^>, C<->, C<[> and C<]>, and are discussed below. They can be
340escaped with a backslash, although this is sometimes not needed, in which
341case the backslash may be omitted.
342
343The sequence C<\b> is special inside a bracketed character class. While
6b83a163 344outside the character class, C<\b> is an assertion indicating a point
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345that does not have either two word characters or two non-word characters
346on either side, inside a bracketed character class, C<\b> matches a
347backspace character.
348
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349The sequences
350C<\a>,
351C<\c>,
352C<\e>,
353C<\f>,
354C<\n>,
e526e8bb 355C<\N{I<NAME>}>,
765fa144 356C<\N{U+I<hex char>}>,
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357C<\r>,
358C<\t>,
359and
360C<\x>
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361are also special and have the same meanings as they do outside a
362bracketed character class. (However, inside a bracketed character
363class, if C<\N{I<NAME>}> expands to a sequence of characters, only the first
364one in the sequence is used, with a warning.)
df225385 365
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366Also, a backslash followed by two or three octal digits is considered an octal
367number.
df225385 368
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369A C<[> is not special inside a character class, unless it's the start of a
370POSIX character class (see L</POSIX Character Classes> below). It normally does
371not need escaping.
8a118206 372
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373A C<]> is normally either the end of a POSIX character class (see
374L</POSIX Character Classes> below), or it signals the end of the bracketed
375character class. If you want to include a C<]> in the set of characters, you
376must generally escape it.
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377However, if the C<]> is the I<first> (or the second if the first
378character is a caret) character of a bracketed character class, it
379does not denote the end of the class (as you cannot have an empty class)
380and is considered part of the set of characters that can be matched without
381escaping.
382
383Examples:
384
385 "+" =~ /[+?*]/ # Match, "+" in a character class is not special.
386 "\cH" =~ /[\b]/ # Match, \b inside in a character class
c1c4ae3a 387 # is equivalent to a backspace.
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388 "]" =~ /[][]/ # Match, as the character class contains.
389 # both [ and ].
390 "[]" =~ /[[]]/ # Match, the pattern contains a character class
391 # containing just ], and the character class is
392 # followed by a ].
393
394=head3 Character Ranges
395
396It is not uncommon to want to match a range of characters. Luckily, instead
397of listing all the characters in the range, one may use the hyphen (C<->).
398If inside a bracketed character class you have two characters separated
399by a hyphen, it's treated as if all the characters between the two are in
400the class. For instance, C<[0-9]> matches any ASCII digit, and C<[a-m]>
401matches any lowercase letter from the first half of the ASCII alphabet.
402
403Note that the two characters on either side of the hyphen are not
765fa144 404necessarily both letters or both digits. Any character is possible,
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405although not advisable. C<['-?]> contains a range of characters, but
406most people will not know which characters that will be. Furthermore,
407such ranges may lead to portability problems if the code has to run on
408a platform that uses a different character set, such as EBCDIC.
409
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410If a hyphen in a character class cannot syntactically be part of a range, for
411instance because it is the first or the last character of the character class,
8a118206 412or if it immediately follows a range, the hyphen isn't special, and will be
6b83a163 413considered a character that is to be matched literally. You have to escape the
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414hyphen with a backslash if you want to have a hyphen in your set of characters
415to be matched, and its position in the class is such that it could be
416considered part of a range.
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417
418Examples:
419
420 [a-z] # Matches a character that is a lower case ASCII letter.
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421 [a-fz] # Matches any letter between 'a' and 'f' (inclusive) or
422 # the letter 'z'.
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423 [-z] # Matches either a hyphen ('-') or the letter 'z'.
424 [a-f-m] # Matches any letter between 'a' and 'f' (inclusive), the
425 # hyphen ('-'), or the letter 'm'.
426 ['-?] # Matches any of the characters '()*+,-./0123456789:;<=>?
427 # (But not on an EBCDIC platform).
428
429
430=head3 Negation
431
432It is also possible to instead list the characters you do not want to
433match. You can do so by using a caret (C<^>) as the first character in the
434character class. For instance, C<[^a-z]> matches a character that is not a
435lowercase ASCII letter.
436
437This syntax make the caret a special character inside a bracketed character
438class, but only if it is the first character of the class. So if you want
439to have the caret as one of the characters you want to match, you either
440have to escape the caret, or not list it first.
441
442Examples:
443
444 "e" =~ /[^aeiou]/ # No match, the 'e' is listed.
445 "x" =~ /[^aeiou]/ # Match, as 'x' isn't a lowercase vowel.
446 "^" =~ /[^^]/ # No match, matches anything that isn't a caret.
447 "^" =~ /[x^]/ # Match, caret is not special here.
448
449=head3 Backslash Sequences
450
ea449505 451You can put any backslash sequence character class (with the exception of
765fa144 452C<\N> and C<\R>) inside a bracketed character class, and it will act just
df225385 453as if you put all the characters matched by the backslash sequence inside the
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454character class. For instance, C<[a-f\d]> will match any decimal digit, or any
455of the lowercase letters between 'a' and 'f' inclusive.
456
457C<\N> within a bracketed character class must be of the forms C<\N{I<name>}>
765fa144 458or C<\N{U+I<hex char>}>, and NOT be the form that matches non-newlines,
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459for the same reason that a dot C<.> inside a bracketed character class loses
460its special meaning: it matches nearly anything, which generally isn't what you
461want to happen.
df225385 462
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463
464Examples:
465
466 /[\p{Thai}\d]/ # Matches a character that is either a Thai
467 # character, or a digit.
468 /[^\p{Arabic}()]/ # Matches a character that is neither an Arabic
469 # character, nor a parenthesis.
470
471Backslash sequence character classes cannot form one of the endpoints
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472of a range. Thus, you can't say:
473
474 /[\p{Thai}-\d]/ # Wrong!
8a118206 475
6b83a163 476=head3 POSIX Character Classes
ea449505 477X<character class> X<\p> X<\p{}>
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478X<alpha> X<alnum> X<ascii> X<blank> X<cntrl> X<digit> X<graph>
479X<lower> X<print> X<punct> X<space> X<upper> X<word> X<xdigit>
8a118206 480
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481POSIX character classes have the form C<[:class:]>, where I<class> is
482name, and the C<[:> and C<:]> delimiters. POSIX character classes only appear
8a118206 483I<inside> bracketed character classes, and are a convenient and descriptive
f7d1198f 484way of listing a group of characters, though they can suffer from
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485portability issues (see below and L<Locale, EBCDIC, Unicode and UTF-8>).
486
487Be careful about the syntax,
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488
489 # Correct:
490 $string =~ /[[:alpha:]]/
491
492 # Incorrect (will warn):
493 $string =~ /[:alpha:]/
494
495The latter pattern would be a character class consisting of a colon,
496and the letters C<a>, C<l>, C<p> and C<h>.
6b83a163 497POSIX character classes can be part of a larger bracketed character class. For
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498example,
499
500 [01[:alpha:]%]
501
502is valid and matches '0', '1', any alphabetic character, and the percent sign.
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503
504Perl recognizes the following POSIX character classes:
505
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506 alpha Any alphabetical character ("[A-Za-z]").
507 alnum Any alphanumerical character. ("[A-Za-z0-9]")
508 ascii Any character in the ASCII character set.
ea8b8ad2 509 blank A GNU extension, equal to a space or a horizontal tab ("\t").
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510 cntrl Any control character. See Note [2] below.
511 digit Any decimal digit ("[0-9]"), equivalent to "\d".
512 graph Any printable character, excluding a space. See Note [3] below.
513 lower Any lowercase character ("[a-z]").
514 print Any printable character, including a space. See Note [4] below.
c1c4ae3a 515 punct Any graphical character excluding "word" characters. Note [5].
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516 space Any whitespace character. "\s" plus the vertical tab ("\cK").
517 upper Any uppercase character ("[A-Z]").
518 word A Perl extension ("[A-Za-z0-9_]"), equivalent to "\w".
519 xdigit Any hexadecimal digit ("[0-9a-fA-F]").
520
521Most POSIX character classes have two Unicode-style C<\p> property
522counterparts. (They are not official Unicode properties, but Perl extensions
523derived from official Unicode properties.) The table below shows the relation
524between POSIX character classes and these counterparts.
525
526One counterpart, in the column labelled "ASCII-range Unicode" in
6b83a163 527the table, will only match characters in the ASCII character set.
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528
529The other counterpart, in the column labelled "Full-range Unicode", matches any
530appropriate characters in the full Unicode character set. For example,
531C<\p{Alpha}> will match not just the ASCII alphabetic characters, but any
532character in the entire Unicode character set that is considered to be
765fa144 533alphabetic. The column labelled "backslash sequence" is a (short) synonym for
cbc24f92 534the Full-range Unicode form.
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535
536(Each of the counterparts has various synonyms as well.
537L<perluniprops/Properties accessible through \p{} and \P{}> lists all the
538synonyms, plus all the characters matched by each of the ASCII-range
539properties. For example C<\p{AHex}> is a synonym for C<\p{ASCII_Hex_Digit}>,
540and any C<\p> property name can be prefixed with "Is" such as C<\p{IsAlpha}>.)
541
542Both the C<\p> forms are unaffected by any locale that is in effect, or whether
543the string is in UTF-8 format or not, or whether the platform is EBCDIC or not.
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544In contrast, the POSIX character classes are affected, unless the
545regular expression is compiled with the C<"a"> modifier. If the C<"a">
546modifier is not in effect, and the source string is in UTF-8 format, the
547POSIX classes behave like their "Full-range" Unicode counterparts. If
548C<"a"> modifier is in effect; or the source string is not in UTF-8
549format, and no locale is in effect, and the platform is not EBCDIC, all
550the POSIX classes behave like their ASCII-range counterparts.
551Otherwise, they behave based on the rules of the locale or EBCDIC code
552page.
6b83a163 553
ea449505 554It is proposed to change this behavior in a future release of Perl so that the
765fa144 555the UTF-8-ness of the source string will be irrelevant to the behavior of the
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556POSIX character classes. This means they will always behave in strict
557accordance with the official POSIX standard. That is, if either locale or
558EBCDIC code page is present, they will behave in accordance with those; if
559absent, the classes will match only their ASCII-range counterparts. If you
765fa144 560wish to comment on this proposal, send email to C<perl5-porters@perl.org>.
ea449505 561
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562 [[:...:]] ASCII-range Full-range backslash Note
563 Unicode Unicode sequence
ea449505 564 -----------------------------------------------------
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565 alpha \p{PosixAlpha} \p{XPosixAlpha}
566 alnum \p{PosixAlnum} \p{XPosixAlnum}
ea449505 567 ascii \p{ASCII}
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568 blank \p{PosixBlank} \p{XPosixBlank} \h [1]
569 or \p{HorizSpace} [1]
570 cntrl \p{PosixCntrl} \p{XPosixCntrl} [2]
571 digit \p{PosixDigit} \p{XPosixDigit} \d
572 graph \p{PosixGraph} \p{XPosixGraph} [3]
573 lower \p{PosixLower} \p{XPosixLower}
574 print \p{PosixPrint} \p{XPosixPrint} [4]
575 punct \p{PosixPunct} \p{XPosixPunct} [5]
576 \p{PerlSpace} \p{XPerlSpace} \s [6]
577 space \p{PosixSpace} \p{XPosixSpace} [6]
578 upper \p{PosixUpper} \p{XPosixUpper}
579 word \p{PosixWord} \p{XPosixWord} \w
580 xdigit \p{ASCII_Hex_Digit} \p{XPosixXDigit}
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581
582=over 4
583
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584=item [1]
585
586C<\p{Blank}> and C<\p{HorizSpace}> are synonyms.
587
588=item [2]
8a118206 589
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590Control characters don't produce output as such, but instead usually control
591the terminal somehow: for example newline and backspace are control characters.
592In the ASCII range, characters whose ordinals are between 0 and 31 inclusive,
593plus 127 (C<DEL>) are control characters.
8a118206 594
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595On EBCDIC platforms, it is likely that the code page will define C<[[:cntrl:]]>
596to be the EBCDIC equivalents of the ASCII controls, plus the controls
6b83a163 597that in Unicode have ordinals from 128 through 159.
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598
599=item [3]
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600
601Any character that is I<graphical>, that is, visible. This class consists
602of all the alphanumerical characters and all punctuation characters.
603
ea449505 604=item [4]
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605
606All printable characters, which is the set of all the graphical characters
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607plus whitespace characters that are not also controls.
608
b6dac59a 609=item [5]
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610
611C<\p{PosixPunct}> and C<[[:punct:]]> in the ASCII range match all the
612non-controls, non-alphanumeric, non-space characters:
613C<[-!"#$%&'()*+,./:;<=E<gt>?@[\\\]^_`{|}~]> (although if a locale is in effect,
614it could alter the behavior of C<[[:punct:]]>).
615
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616The similarly named property, C<\p{Punct}>, matches a somewhat different
617set in the ASCII range, namely
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618C<[-!"#%&'()*,./:;?@[\\\]_{}]>. That is, it is missing C<[$+E<lt>=E<gt>^`|~]>.
619This is because Unicode splits what POSIX considers to be punctuation into two
620categories, Punctuation and Symbols.
621
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622C<\p{XPosixPunct}> and (in Unicode mode) C<[[:punct:]]>, match what
623C<\p{PosixPunct}> matches in the ASCII range, plus what C<\p{Punct}>
624matches. This is different than strictly matching according to
625C<\p{Punct}>. Another way to say it is that
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626for a UTF-8 string, C<[[:punct:]]> matches all the characters that Unicode
627considers to be punctuation, plus all the ASCII-range characters that Unicode
628considers to be symbols.
8a118206 629
ea449505 630=item [6]
8a118206 631
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632C<\p{SpacePerl}> and C<\p{Space}> differ only in that C<\p{Space}> additionally
633matches the vertical tab, C<\cK>. Same for the two ASCII-only range forms.
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634
635=back
636
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637There are various other synonyms that can be used for these besides
638C<\p{HorizSpace}> and \C<\p{XPosixBlank}>. For example
639C<\p{PosixAlpha}> can be written as C<\p{Alpha}>. All are listed
640in L<perluniprops/Properties accessible through \p{} and \P{}>.
641
8a118206 642=head4 Negation
ea449505 643X<character class, negation>
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644
645A Perl extension to the POSIX character class is the ability to
646negate it. This is done by prefixing the class name with a caret (C<^>).
647Some examples:
648
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649 POSIX ASCII-range Full-range backslash
650 Unicode Unicode sequence
651 -----------------------------------------------------
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652 [[:^digit:]] \P{PosixDigit} \P{XPosixDigit} \D
653 [[:^space:]] \P{PosixSpace} \P{XPosixSpace}
654 \P{PerlSpace} \P{XPerlSpace} \S
655 [[:^word:]] \P{PerlWord} \P{XPosixWord} \W
656
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657The backslash sequence can mean either ASCII- or Full-range Unicode,
658depending on various factors. See L</Locale, EBCDIC, Unicode and UTF-8>
659below.
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660
661=head4 [= =] and [. .]
662
663Perl will recognize the POSIX character classes C<[=class=]>, and
ea449505 664C<[.class.]>, but does not (yet?) support them. Use of
740bae87 665such a construct will lead to an error.
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666
667
668=head4 Examples
669
670 /[[:digit:]]/ # Matches a character that is a digit.
671 /[01[:lower:]]/ # Matches a character that is either a
672 # lowercase letter, or '0' or '1'.
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673 /[[:digit:][:^xdigit:]]/ # Matches a character that can be anything
674 # except the letters 'a' to 'f'. This is
675 # because the main character class is composed
676 # of two POSIX character classes that are ORed
677 # together, one that matches any digit, and
678 # the other that matches anything that isn't a
679 # hex digit. The result matches all
680 # characters except the letters 'a' to 'f' and
681 # 'A' to 'F'.
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682
683
ea449505 684=head2 Locale, EBCDIC, Unicode and UTF-8
8a118206 685
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686Some of the character classes have a somewhat different behaviour
687depending on the internal encoding of the source string, if the regular
688expression is marked as having Unicode semantics, the locale that is in
689effect, and if the program is running on an EBCDIC platform.
690
691C<\w>, C<\d>, C<\s> and the POSIX character classes (and their
692negations, including C<\W>, C<\D>, C<\S>) have this behaviour. (Since
693the backslash sequences C<\b> and C<\B> are defined in terms of C<\w>
694and C<\W>, they also are affected.)
695
696Starting in Perl 5.14, if the regular expression is compiled with the
697C<"a"> modifier, the behavior doesn't differ regardless of any other
698factors. C<\d> matches the 10 digits 0-9; C<\D> any character but those
69910; C<\s>, exactly the five characters "[ \f\n\r\t]"; C<\w> only the 63
700characters "[A-Za-z0-9_]"; and the C<"[[:posix:]]"> classes only the
701appropriate ASCII characters, the same characters as are matched by the
702corresponding C<\p{}> property given in the "ASCII-range Unicode" column
703in the table above. (The behavior of all of their complements follows
704the same paradigm.)
705
706Otherwise, a regular expression is marked for Unicode semantics if it is
707encoded in utf8 (usually as a result of including a literal character
708whose code point is above 255), or if it contains a C<\N{U+...}> or
709C<\N{I<name>}> construct, or (starting in Perl 5.14) if it was compiled
710in the scope of a C<S<use feature "unicode_strings">> pragma and not in
711the scope of a C<S<use locale>> pragma, or has the C<"u"> regular
b6dac59a 712expression modifier.
17657a39 713
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714Note that one can specify C<"use re '/l'"> for example, for any regular
715expression modifier, and this has precedence over either of the
716C<S<use feature "unicode_strings">> or C<S<use locale>> pragmas.
717
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718The differences in behavior between locale and non-locale semantics
719can affect any character whose code point is 255 or less. The
720differences in behavior between Unicode and non-Unicode semantics
721affects only ASCII platforms, and only when matching against characters
722whose code points are between 128 and 255 inclusive. See
723L<perlunicode/The "Unicode Bug">.
8a118206 724
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725For portability reasons, unless the C<"a"> modifier is specified,
726it may be better to not use C<\w>, C<\d>, C<\s> or the POSIX character
727classes and use the Unicode properties instead.
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728That way you can control whether you want matching of just characters in
729the ASCII character set, or any Unicode characters.
730C<S<use feature "unicode_strings">> will allow seamless Unicode behavior
731no matter what the internal encodings are, but won't allow restricting
732to just the ASCII characters.
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733
734=head4 Examples
735
736 $str = "\xDF"; # $str is not in UTF-8 format.
737 $str =~ /^\w/; # No match, as $str isn't in UTF-8 format.
738 $str .= "\x{0e0b}"; # Now $str is in UTF-8 format.
739 $str =~ /^\w/; # Match! $str is now in UTF-8 format.
740 chop $str;
741 $str =~ /^\w/; # Still a match! $str remains in UTF-8 format.
742
743=cut