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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"> modifier is specified, C<\d> matches the same
88characters 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
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120in the ASCII range is the same as a string of Perl-identifier
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>
190respectively. If the source string is in UTF-8 format, both the next line and
191the no-break space are matched by C<\s>.
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192
193The following table is a complete listing of characters matched by
ea449505 194C<\s>, C<\h> and C<\v> as of Unicode 5.2.
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195
196The first column gives the code point of the character (in hex format),
197the second column gives the (Unicode) name. The third column indicates
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198by which class(es) the character is matched (assuming no locale or EBCDIC code
199page is in effect that changes the C<\s> matching).
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200
201 0x00009 CHARACTER TABULATION h s
202 0x0000a LINE FEED (LF) vs
203 0x0000b LINE TABULATION v
204 0x0000c FORM FEED (FF) vs
205 0x0000d CARRIAGE RETURN (CR) vs
206 0x00020 SPACE h s
207 0x00085 NEXT LINE (NEL) vs [1]
208 0x000a0 NO-BREAK SPACE h s [1]
209 0x01680 OGHAM SPACE MARK h s
210 0x0180e MONGOLIAN VOWEL SEPARATOR h s
211 0x02000 EN QUAD h s
212 0x02001 EM QUAD h s
213 0x02002 EN SPACE h s
214 0x02003 EM SPACE h s
215 0x02004 THREE-PER-EM SPACE h s
216 0x02005 FOUR-PER-EM SPACE h s
217 0x02006 SIX-PER-EM SPACE h s
218 0x02007 FIGURE SPACE h s
219 0x02008 PUNCTUATION SPACE h s
220 0x02009 THIN SPACE h s
221 0x0200a HAIR SPACE h s
222 0x02028 LINE SEPARATOR vs
223 0x02029 PARAGRAPH SEPARATOR vs
224 0x0202f NARROW NO-BREAK SPACE h s
225 0x0205f MEDIUM MATHEMATICAL SPACE h s
226 0x03000 IDEOGRAPHIC SPACE h s
227
228=over 4
229
230=item [1]
231
232NEXT LINE and NO-BREAK SPACE only match C<\s> if the source string is in
ea449505 233UTF-8 format, or the locale or EBCDIC code page that is in effect includes them.
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234
235=back
236
237It is worth noting that C<\d>, C<\w>, etc, match single characters, not
e486b3cc 238complete numbers or words. To match a number (that consists of digits),
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239use C<\d+>; to match a word, use C<\w+>.
240
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241=head3 \N
242
243C<\N> is new in 5.12, and is experimental. It, like the dot, will match any
244character that is not a newline. The difference is that C<\N> is not influenced
245by the I<single line> regular expression modifier (see L</The dot> above). Note
246that the form C<\N{...}> may mean something completely different. When the
247C<{...}> is a L<quantifier|perlre/Quantifiers>, it means to match a non-newline
248character that many times. For example, C<\N{3}> means to match 3
249non-newlines; C<\N{5,}> means to match 5 or more non-newlines. But if C<{...}>
250is not a legal quantifier, it is presumed to be a named character. See
251L<charnames> for those. For example, none of C<\N{COLON}>, C<\N{4F}>, and
252C<\N{F4}> contain legal quantifiers, so Perl will try to find characters whose
253names are, respectively, C<COLON>, C<4F>, and C<F4>.
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254
255=head3 Unicode Properties
256
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257C<\pP> and C<\p{Prop}> are character classes to match characters that fit given
258Unicode properties. One letter property names can be used in the C<\pP> form,
259with the property name following the C<\p>, otherwise, braces are required.
260When using braces, there is a single form, which is just the property name
261enclosed in the braces, and a compound form which looks like C<\p{name=value}>,
262which means to match if the property "name" for the character has the particular
263"value".
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264For instance, a match for a number can be written as C</\pN/> or as
265C</\p{Number}/>, or as C</\p{Number=True}/>.
266Lowercase letters are matched by the property I<Lowercase_Letter> which
267has as short form I<Ll>. They need the braces, so are written as C</\p{Ll}/> or
268C</\p{Lowercase_Letter}/>, or C</\p{General_Category=Lowercase_Letter}/>
269(the underscores are optional).
270C</\pLl/> is valid, but means something different.
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271It matches a two character string: a letter (Unicode property C<\pL>),
272followed by a lowercase C<l>.
273
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274For more details, see L<perlunicode/Unicode Character Properties>; for a
275complete list of possible properties, see
276L<perluniprops/Properties accessible through \p{} and \P{}>.
277It is also possible to define your own properties. This is discussed in
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278L<perlunicode/User-Defined Character Properties>.
279
280
281=head4 Examples
282
283 "a" =~ /\w/ # Match, "a" is a 'word' character.
284 "7" =~ /\w/ # Match, "7" is a 'word' character as well.
285 "a" =~ /\d/ # No match, "a" isn't a digit.
286 "7" =~ /\d/ # Match, "7" is a digit.
ea449505 287 " " =~ /\s/ # Match, a space is whitespace.
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288 "a" =~ /\D/ # Match, "a" is a non-digit.
289 "7" =~ /\D/ # No match, "7" is not a non-digit.
ea449505 290 " " =~ /\S/ # No match, a space is not non-whitespace.
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292 " " =~ /\h/ # Match, space is horizontal whitespace.
293 " " =~ /\v/ # No match, space is not vertical whitespace.
294 "\r" =~ /\v/ # Match, a return is vertical whitespace.
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295
296 "a" =~ /\pL/ # Match, "a" is a letter.
297 "a" =~ /\p{Lu}/ # No match, /\p{Lu}/ matches upper case letters.
298
299 "\x{0e0b}" =~ /\p{Thai}/ # Match, \x{0e0b} is the character
300 # 'THAI CHARACTER SO SO', and that's in
301 # Thai Unicode class.
ea449505 302 "a" =~ /\P{Lao}/ # Match, as "a" is not a Laotian character.
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303
304
305=head2 Bracketed Character Classes
306
307The third form of character class you can use in Perl regular expressions
6b83a163 308is the bracketed character class. In its simplest form, it lists the characters
c1c4ae3a 309that may be matched, surrounded by square brackets, like this: C<[aeiou]>.
ea449505 310This matches one of C<a>, C<e>, C<i>, C<o> or C<u>. Like the other
8a118206 311character classes, exactly one character will be matched. To match
ea449505 312a longer string consisting of characters mentioned in the character
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313class, follow the character class with a L<quantifier|perlre/Quantifiers>. For
314instance, C<[aeiou]+> matches a string of one or more lowercase English vowels.
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315
316Repeating a character in a character class has no
317effect; it's considered to be in the set only once.
318
319Examples:
320
321 "e" =~ /[aeiou]/ # Match, as "e" is listed in the class.
322 "p" =~ /[aeiou]/ # No match, "p" is not listed in the class.
323 "ae" =~ /^[aeiou]$/ # No match, a character class only matches
324 # a single character.
325 "ae" =~ /^[aeiou]+$/ # Match, due to the quantifier.
326
327=head3 Special Characters Inside a Bracketed Character Class
328
329Most characters that are meta characters in regular expressions (that
df225385 330is, characters that carry a special meaning like C<.>, C<*>, or C<(>) lose
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331their special meaning and can be used inside a character class without
332the need to escape them. For instance, C<[()]> matches either an opening
333parenthesis, or a closing parenthesis, and the parens inside the character
334class don't group or capture.
335
336Characters that may carry a special meaning inside a character class are:
337C<\>, C<^>, C<->, C<[> and C<]>, and are discussed below. They can be
338escaped with a backslash, although this is sometimes not needed, in which
339case the backslash may be omitted.
340
341The sequence C<\b> is special inside a bracketed character class. While
6b83a163 342outside the character class, C<\b> is an assertion indicating a point
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343that does not have either two word characters or two non-word characters
344on either side, inside a bracketed character class, C<\b> matches a
345backspace character.
346
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347The sequences
348C<\a>,
349C<\c>,
350C<\e>,
351C<\f>,
352C<\n>,
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353C<\N{I<NAME>}>,
354C<\N{U+I<wide hex char>}>,
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355C<\r>,
356C<\t>,
357and
358C<\x>
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359are also special and have the same meanings as they do outside a
360bracketed character class. (However, inside a bracketed character
361class, if C<\N{I<NAME>}> expands to a sequence of characters, only the first
362one in the sequence is used, with a warning.)
df225385 363
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364Also, a backslash followed by two or three octal digits is considered an octal
365number.
df225385 366
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367A C<[> is not special inside a character class, unless it's the start of a
368POSIX character class (see L</POSIX Character Classes> below). It normally does
369not need escaping.
8a118206 370
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371A C<]> is normally either the end of a POSIX character class (see
372L</POSIX Character Classes> below), or it signals the end of the bracketed
373character class. If you want to include a C<]> in the set of characters, you
374must generally escape it.
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375However, if the C<]> is the I<first> (or the second if the first
376character is a caret) character of a bracketed character class, it
377does not denote the end of the class (as you cannot have an empty class)
378and is considered part of the set of characters that can be matched without
379escaping.
380
381Examples:
382
383 "+" =~ /[+?*]/ # Match, "+" in a character class is not special.
384 "\cH" =~ /[\b]/ # Match, \b inside in a character class
c1c4ae3a 385 # is equivalent to a backspace.
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386 "]" =~ /[][]/ # Match, as the character class contains.
387 # both [ and ].
388 "[]" =~ /[[]]/ # Match, the pattern contains a character class
389 # containing just ], and the character class is
390 # followed by a ].
391
392=head3 Character Ranges
393
394It is not uncommon to want to match a range of characters. Luckily, instead
395of listing all the characters in the range, one may use the hyphen (C<->).
396If inside a bracketed character class you have two characters separated
397by a hyphen, it's treated as if all the characters between the two are in
398the class. For instance, C<[0-9]> matches any ASCII digit, and C<[a-m]>
399matches any lowercase letter from the first half of the ASCII alphabet.
400
401Note that the two characters on either side of the hyphen are not
402necessary both letters or both digits. Any character is possible,
403although not advisable. C<['-?]> contains a range of characters, but
404most people will not know which characters that will be. Furthermore,
405such ranges may lead to portability problems if the code has to run on
406a platform that uses a different character set, such as EBCDIC.
407
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408If a hyphen in a character class cannot syntactically be part of a range, for
409instance because it is the first or the last character of the character class,
8a118206 410or if it immediately follows a range, the hyphen isn't special, and will be
6b83a163 411considered a character that is to be matched literally. You have to escape the
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412hyphen with a backslash if you want to have a hyphen in your set of characters
413to be matched, and its position in the class is such that it could be
414considered part of a range.
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415
416Examples:
417
418 [a-z] # Matches a character that is a lower case ASCII letter.
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419 [a-fz] # Matches any letter between 'a' and 'f' (inclusive) or
420 # the letter 'z'.
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421 [-z] # Matches either a hyphen ('-') or the letter 'z'.
422 [a-f-m] # Matches any letter between 'a' and 'f' (inclusive), the
423 # hyphen ('-'), or the letter 'm'.
424 ['-?] # Matches any of the characters '()*+,-./0123456789:;<=>?
425 # (But not on an EBCDIC platform).
426
427
428=head3 Negation
429
430It is also possible to instead list the characters you do not want to
431match. You can do so by using a caret (C<^>) as the first character in the
432character class. For instance, C<[^a-z]> matches a character that is not a
433lowercase ASCII letter.
434
435This syntax make the caret a special character inside a bracketed character
436class, but only if it is the first character of the class. So if you want
437to have the caret as one of the characters you want to match, you either
438have to escape the caret, or not list it first.
439
440Examples:
441
442 "e" =~ /[^aeiou]/ # No match, the 'e' is listed.
443 "x" =~ /[^aeiou]/ # Match, as 'x' isn't a lowercase vowel.
444 "^" =~ /[^^]/ # No match, matches anything that isn't a caret.
445 "^" =~ /[x^]/ # Match, caret is not special here.
446
447=head3 Backslash Sequences
448
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449You can put any backslash sequence character class (with the exception of
450C<\N>) inside a bracketed character class, and it will act just
df225385 451as if you put all the characters matched by the backslash sequence inside the
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452character class. For instance, C<[a-f\d]> will match any decimal digit, or any
453of the lowercase letters between 'a' and 'f' inclusive.
454
455C<\N> within a bracketed character class must be of the forms C<\N{I<name>}>
456or C<\N{U+I<wide hex char>}>, and NOT be the form that matches non-newlines,
457for the same reason that a dot C<.> inside a bracketed character class loses
458its special meaning: it matches nearly anything, which generally isn't what you
459want to happen.
df225385 460
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461
462Examples:
463
464 /[\p{Thai}\d]/ # Matches a character that is either a Thai
465 # character, or a digit.
466 /[^\p{Arabic}()]/ # Matches a character that is neither an Arabic
467 # character, nor a parenthesis.
468
469Backslash sequence character classes cannot form one of the endpoints
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470of a range. Thus, you can't say:
471
472 /[\p{Thai}-\d]/ # Wrong!
8a118206 473
6b83a163 474=head3 POSIX Character Classes
ea449505 475X<character class> X<\p> X<\p{}>
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476X<alpha> X<alnum> X<ascii> X<blank> X<cntrl> X<digit> X<graph>
477X<lower> X<print> X<punct> X<space> X<upper> X<word> X<xdigit>
8a118206 478
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479POSIX character classes have the form C<[:class:]>, where I<class> is
480name, and the C<[:> and C<:]> delimiters. POSIX character classes only appear
8a118206 481I<inside> bracketed character classes, and are a convenient and descriptive
c1c4ae3a 482way of listing a group of characters, though they currently suffer from
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483portability issues (see below and L<Locale, EBCDIC, Unicode and UTF-8>).
484
485Be careful about the syntax,
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486
487 # Correct:
488 $string =~ /[[:alpha:]]/
489
490 # Incorrect (will warn):
491 $string =~ /[:alpha:]/
492
493The latter pattern would be a character class consisting of a colon,
494and the letters C<a>, C<l>, C<p> and C<h>.
6b83a163 495POSIX character classes can be part of a larger bracketed character class. For
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496example,
497
498 [01[:alpha:]%]
499
500is valid and matches '0', '1', any alphabetic character, and the percent sign.
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501
502Perl recognizes the following POSIX character classes:
503
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504 alpha Any alphabetical character ("[A-Za-z]").
505 alnum Any alphanumerical character. ("[A-Za-z0-9]")
506 ascii Any character in the ASCII character set.
ea8b8ad2 507 blank A GNU extension, equal to a space or a horizontal tab ("\t").
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508 cntrl Any control character. See Note [2] below.
509 digit Any decimal digit ("[0-9]"), equivalent to "\d".
510 graph Any printable character, excluding a space. See Note [3] below.
511 lower Any lowercase character ("[a-z]").
512 print Any printable character, including a space. See Note [4] below.
c1c4ae3a 513 punct Any graphical character excluding "word" characters. Note [5].
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514 space Any whitespace character. "\s" plus the vertical tab ("\cK").
515 upper Any uppercase character ("[A-Z]").
516 word A Perl extension ("[A-Za-z0-9_]"), equivalent to "\w".
517 xdigit Any hexadecimal digit ("[0-9a-fA-F]").
518
519Most POSIX character classes have two Unicode-style C<\p> property
520counterparts. (They are not official Unicode properties, but Perl extensions
521derived from official Unicode properties.) The table below shows the relation
522between POSIX character classes and these counterparts.
523
524One counterpart, in the column labelled "ASCII-range Unicode" in
6b83a163 525the table, will only match characters in the ASCII character set.
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526
527The other counterpart, in the column labelled "Full-range Unicode", matches any
528appropriate characters in the full Unicode character set. For example,
529C<\p{Alpha}> will match not just the ASCII alphabetic characters, but any
530character in the entire Unicode character set that is considered to be
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531alphabetic. The backslash sequence column is a (short) synonym for
532the Full-range Unicode form.
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533
534(Each of the counterparts has various synonyms as well.
535L<perluniprops/Properties accessible through \p{} and \P{}> lists all the
536synonyms, plus all the characters matched by each of the ASCII-range
537properties. For example C<\p{AHex}> is a synonym for C<\p{ASCII_Hex_Digit}>,
538and any C<\p> property name can be prefixed with "Is" such as C<\p{IsAlpha}>.)
539
540Both the C<\p> forms are unaffected by any locale that is in effect, or whether
541the string is in UTF-8 format or not, or whether the platform is EBCDIC or not.
542In contrast, the POSIX character classes are affected. If the source string is
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543in UTF-8 format, the POSIX classes behave like their "Full-range"
544Unicode counterparts. If the
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545source string is not in UTF-8 format, and no locale is in effect, and the
546platform is not EBCDIC, all the POSIX classes behave like their ASCII-range
547counterparts. Otherwise, they behave based on the rules of the locale or
548EBCDIC code page.
549
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550It is proposed to change this behavior in a future release of Perl so that the
551the UTF8ness of the source string will be irrelevant to the behavior of the
552POSIX character classes. This means they will always behave in strict
553accordance with the official POSIX standard. That is, if either locale or
554EBCDIC code page is present, they will behave in accordance with those; if
555absent, the classes will match only their ASCII-range counterparts. If you
556disagree with this proposal, send email to C<perl5-porters@perl.org>.
557
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558 [[:...:]] ASCII-range Full-range backslash Note
559 Unicode Unicode sequence
ea449505 560 -----------------------------------------------------
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561 alpha \p{PosixAlpha} \p{XPosixAlpha}
562 alnum \p{PosixAlnum} \p{XPosixAlnum}
ea449505 563 ascii \p{ASCII}
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564 blank \p{PosixBlank} \p{XPosixBlank} \h [1]
565 or \p{HorizSpace} [1]
566 cntrl \p{PosixCntrl} \p{XPosixCntrl} [2]
567 digit \p{PosixDigit} \p{XPosixDigit} \d
568 graph \p{PosixGraph} \p{XPosixGraph} [3]
569 lower \p{PosixLower} \p{XPosixLower}
570 print \p{PosixPrint} \p{XPosixPrint} [4]
571 punct \p{PosixPunct} \p{XPosixPunct} [5]
572 \p{PerlSpace} \p{XPerlSpace} \s [6]
573 space \p{PosixSpace} \p{XPosixSpace} [6]
574 upper \p{PosixUpper} \p{XPosixUpper}
575 word \p{PosixWord} \p{XPosixWord} \w
576 xdigit \p{ASCII_Hex_Digit} \p{XPosixXDigit}
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577
578=over 4
579
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580=item [1]
581
582C<\p{Blank}> and C<\p{HorizSpace}> are synonyms.
583
584=item [2]
8a118206 585
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586Control characters don't produce output as such, but instead usually control
587the terminal somehow: for example newline and backspace are control characters.
588In the ASCII range, characters whose ordinals are between 0 and 31 inclusive,
589plus 127 (C<DEL>) are control characters.
8a118206 590
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591On EBCDIC platforms, it is likely that the code page will define C<[[:cntrl:]]>
592to be the EBCDIC equivalents of the ASCII controls, plus the controls
6b83a163 593that in Unicode have ordinals from 128 through 159.
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594
595=item [3]
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596
597Any character that is I<graphical>, that is, visible. This class consists
598of all the alphanumerical characters and all punctuation characters.
599
ea449505 600=item [4]
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601
602All printable characters, which is the set of all the graphical characters
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603plus whitespace characters that are not also controls.
604
b6dac59a 605=item [5]
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606
607C<\p{PosixPunct}> and C<[[:punct:]]> in the ASCII range match all the
608non-controls, non-alphanumeric, non-space characters:
609C<[-!"#$%&'()*+,./:;<=E<gt>?@[\\\]^_`{|}~]> (although if a locale is in effect,
610it could alter the behavior of C<[[:punct:]]>).
611
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612The similarly named property, C<\p{Punct}>, matches a somewhat different
613set in the ASCII range, namely
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614C<[-!"#%&'()*,./:;?@[\\\]_{}]>. That is, it is missing C<[$+E<lt>=E<gt>^`|~]>.
615This is because Unicode splits what POSIX considers to be punctuation into two
616categories, Punctuation and Symbols.
617
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618C<\p{PosixPunct>, and when the matching string is in UTF-8 format,
619C<[[:punct:]]>, match what they match in the ASCII range, plus what
620C<\p{Punct}> matches. This is different
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621than strictly matching according to C<\p{Punct}>. Another way to say it is that
622for a UTF-8 string, C<[[:punct:]]> matches all the characters that Unicode
623considers to be punctuation, plus all the ASCII-range characters that Unicode
624considers to be symbols.
8a118206 625
ea449505 626=item [6]
8a118206 627
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628C<\p{SpacePerl}> and C<\p{Space}> differ only in that C<\p{Space}> additionally
629matches the vertical tab, C<\cK>. Same for the two ASCII-only range forms.
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630
631=back
632
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633There are various other synonyms that can be used for these besides
634C<\p{HorizSpace}> and \C<\p{XPosixBlank}>. For example
635C<\p{PosixAlpha}> can be written as C<\p{Alpha}>. All are listed
636in L<perluniprops/Properties accessible through \p{} and \P{}>.
637
8a118206 638=head4 Negation
ea449505 639X<character class, negation>
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640
641A Perl extension to the POSIX character class is the ability to
642negate it. This is done by prefixing the class name with a caret (C<^>).
643Some examples:
644
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645 POSIX ASCII-range Full-range backslash
646 Unicode Unicode sequence
647 -----------------------------------------------------
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648 [[:^digit:]] \P{PosixDigit} \P{XPosixDigit} \D
649 [[:^space:]] \P{PosixSpace} \P{XPosixSpace}
650 \P{PerlSpace} \P{XPerlSpace} \S
651 [[:^word:]] \P{PerlWord} \P{XPosixWord} \W
652
653Again, the backslash sequence means Full-range Unicode.
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654
655=head4 [= =] and [. .]
656
657Perl will recognize the POSIX character classes C<[=class=]>, and
ea449505 658C<[.class.]>, but does not (yet?) support them. Use of
740bae87 659such a construct will lead to an error.
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660
661
662=head4 Examples
663
664 /[[:digit:]]/ # Matches a character that is a digit.
665 /[01[:lower:]]/ # Matches a character that is either a
666 # lowercase letter, or '0' or '1'.
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667 /[[:digit:][:^xdigit:]]/ # Matches a character that can be anything
668 # except the letters 'a' to 'f'. This is
669 # because the main character class is composed
670 # of two POSIX character classes that are ORed
671 # together, one that matches any digit, and
672 # the other that matches anything that isn't a
673 # hex digit. The result matches all
674 # characters except the letters 'a' to 'f' and
675 # 'A' to 'F'.
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676
677
ea449505 678=head2 Locale, EBCDIC, Unicode and UTF-8
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679
680Some of the character classes have a somewhat different behaviour depending
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681on the internal encoding of the source string, if the regular expression
682is marked as having Unicode semantics, the locale that is in effect,
683and if the program is running on an EBCDIC platform.
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684
685C<\w>, C<\d>, C<\s> and the POSIX character classes (and their negations,
17657a39 686including C<\W>, C<\D>, C<\S>) have this behaviour. (Since the backslash
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687sequences C<\b> and C<\B> are defined in terms of C<\w> and C<\W>, they also are
688affected.)
8a118206 689
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690The rule is that if the source string is in UTF-8 format or the regular
691expression is marked as indicating Unicode semantics (see the next
692paragraph), the character classes match according to the Unicode
693properties. Otherwise, the character classes match according to
694whatever locale or EBCDIC code page is in effect. If there is no locale
695nor EBCDIC, they match the ASCII defaults (0 to 9 for C<\d>; 52 letters,
69610 digits and underscore for C<\w>; etc.).
697
698A regular expression is marked for Unicode semantics if it is encoded in
699utf8 (usually as a result of including a literal character whose code
700point is above 255), or if it contains a C<\N{U+...}> or C<\N{I<name>}>
a12cf05f 701construct, or (starting in Perl 5.14) if it was compiled in the scope of a
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702C<S<use feature "unicode_strings">> pragma, or has the C<"u"> regular
703expression modifier.
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704
705The differences in behavior between locale and non-locale semantics
706can affect any character whose code point is 255 or less. The
707differences in behavior between Unicode and non-Unicode semantics
708affects only ASCII platforms, and only when matching against characters
709whose code points are between 128 and 255 inclusive. See
710L<perlunicode/The "Unicode Bug">.
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711
712For portability reasons, it may be better to not use C<\w>, C<\d>, C<\s>
713or the POSIX character classes, and use the Unicode properties instead.
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714That way you can control whether you want matching of just characters in
715the ASCII character set, or any Unicode characters.
716C<S<use feature "unicode_strings">> will allow seamless Unicode behavior
717no matter what the internal encodings are, but won't allow restricting
718to just the ASCII characters.
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719
720=head4 Examples
721
722 $str = "\xDF"; # $str is not in UTF-8 format.
723 $str =~ /^\w/; # No match, as $str isn't in UTF-8 format.
724 $str .= "\x{0e0b}"; # Now $str is in UTF-8 format.
725 $str =~ /^\w/; # Match! $str is now in UTF-8 format.
726 chop $str;
727 $str =~ /^\w/; # Still a match! $str remains in UTF-8 format.
728
729=cut