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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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276Note that almost all properties are immune to case-insensitive matching.
277That is, adding a C</i> regular expression modifier does not change what
278they match. There are two sets that are affected. The first set is
279C<Uppercase_Letter>,
280C<Lowercase_Letter>,
281and C<Titlecase_Letter>,
282all of which match C<Cased_Letter> under C</i> matching.
283And the second set is
284C<Uppercase>,
285C<Lowercase>,
286and C<Titlecase>,
287all of which match C<Cased> under C</i> matching.
288(The difference between these sets is that some things, such as Roman
289Numerals come in both upper and lower case so they are C<Cased>, but
290aren't considered to be letters, so they aren't C<Cased_Letter>s.)
291This set also includes its subsets C<PosixUpper> and C<PosixLower> both
292of which under C</i> matching match C<PosixAlpha>.
293
294For more details on Unicode properties, see L<perlunicode/Unicode
295Character Properties>; for a
e1b711da 296complete list of possible properties, see
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297L<perluniprops/Properties accessible through \p{} and \P{}>,
298which notes all forms that have C</i> differences.
e1b711da 299It is also possible to define your own properties. This is discussed in
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300L<perlunicode/User-Defined Character Properties>.
301
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302=head4 Examples
303
304 "a" =~ /\w/ # Match, "a" is a 'word' character.
305 "7" =~ /\w/ # Match, "7" is a 'word' character as well.
306 "a" =~ /\d/ # No match, "a" isn't a digit.
307 "7" =~ /\d/ # Match, "7" is a digit.
ea449505 308 " " =~ /\s/ # Match, a space is whitespace.
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309 "a" =~ /\D/ # Match, "a" is a non-digit.
310 "7" =~ /\D/ # No match, "7" is not a non-digit.
ea449505 311 " " =~ /\S/ # No match, a space is not non-whitespace.
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313 " " =~ /\h/ # Match, space is horizontal whitespace.
314 " " =~ /\v/ # No match, space is not vertical whitespace.
315 "\r" =~ /\v/ # Match, a return is vertical whitespace.
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316
317 "a" =~ /\pL/ # Match, "a" is a letter.
318 "a" =~ /\p{Lu}/ # No match, /\p{Lu}/ matches upper case letters.
319
320 "\x{0e0b}" =~ /\p{Thai}/ # Match, \x{0e0b} is the character
321 # 'THAI CHARACTER SO SO', and that's in
322 # Thai Unicode class.
ea449505 323 "a" =~ /\P{Lao}/ # Match, as "a" is not a Laotian character.
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324
325
326=head2 Bracketed Character Classes
327
328The third form of character class you can use in Perl regular expressions
6b83a163 329is the bracketed character class. In its simplest form, it lists the characters
c1c4ae3a 330that may be matched, surrounded by square brackets, like this: C<[aeiou]>.
ea449505 331This matches one of C<a>, C<e>, C<i>, C<o> or C<u>. Like the other
8a118206 332character classes, exactly one character will be matched. To match
ea449505 333a longer string consisting of characters mentioned in the character
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334class, follow the character class with a L<quantifier|perlre/Quantifiers>. For
335instance, C<[aeiou]+> matches a string of one or more lowercase English vowels.
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336
337Repeating a character in a character class has no
338effect; it's considered to be in the set only once.
339
340Examples:
341
342 "e" =~ /[aeiou]/ # Match, as "e" is listed in the class.
343 "p" =~ /[aeiou]/ # No match, "p" is not listed in the class.
344 "ae" =~ /^[aeiou]$/ # No match, a character class only matches
345 # a single character.
346 "ae" =~ /^[aeiou]+$/ # Match, due to the quantifier.
347
348=head3 Special Characters Inside a Bracketed Character Class
349
350Most characters that are meta characters in regular expressions (that
df225385 351is, characters that carry a special meaning like C<.>, C<*>, or C<(>) lose
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352their special meaning and can be used inside a character class without
353the need to escape them. For instance, C<[()]> matches either an opening
354parenthesis, or a closing parenthesis, and the parens inside the character
355class don't group or capture.
356
357Characters that may carry a special meaning inside a character class are:
358C<\>, C<^>, C<->, C<[> and C<]>, and are discussed below. They can be
359escaped with a backslash, although this is sometimes not needed, in which
360case the backslash may be omitted.
361
362The sequence C<\b> is special inside a bracketed character class. While
6b83a163 363outside the character class, C<\b> is an assertion indicating a point
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364that does not have either two word characters or two non-word characters
365on either side, inside a bracketed character class, C<\b> matches a
366backspace character.
367
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368The sequences
369C<\a>,
370C<\c>,
371C<\e>,
372C<\f>,
373C<\n>,
e526e8bb 374C<\N{I<NAME>}>,
765fa144 375C<\N{U+I<hex char>}>,
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376C<\r>,
377C<\t>,
378and
379C<\x>
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380are also special and have the same meanings as they do outside a
381bracketed character class. (However, inside a bracketed character
382class, if C<\N{I<NAME>}> expands to a sequence of characters, only the first
383one in the sequence is used, with a warning.)
df225385 384
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385Also, a backslash followed by two or three octal digits is considered an octal
386number.
df225385 387
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388A C<[> is not special inside a character class, unless it's the start of a
389POSIX character class (see L</POSIX Character Classes> below). It normally does
390not need escaping.
8a118206 391
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392A C<]> is normally either the end of a POSIX character class (see
393L</POSIX Character Classes> below), or it signals the end of the bracketed
394character class. If you want to include a C<]> in the set of characters, you
395must generally escape it.
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396However, if the C<]> is the I<first> (or the second if the first
397character is a caret) character of a bracketed character class, it
398does not denote the end of the class (as you cannot have an empty class)
399and is considered part of the set of characters that can be matched without
400escaping.
401
402Examples:
403
404 "+" =~ /[+?*]/ # Match, "+" in a character class is not special.
405 "\cH" =~ /[\b]/ # Match, \b inside in a character class
c1c4ae3a 406 # is equivalent to a backspace.
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407 "]" =~ /[][]/ # Match, as the character class contains.
408 # both [ and ].
409 "[]" =~ /[[]]/ # Match, the pattern contains a character class
410 # containing just ], and the character class is
411 # followed by a ].
412
413=head3 Character Ranges
414
415It is not uncommon to want to match a range of characters. Luckily, instead
416of listing all the characters in the range, one may use the hyphen (C<->).
417If inside a bracketed character class you have two characters separated
418by a hyphen, it's treated as if all the characters between the two are in
419the class. For instance, C<[0-9]> matches any ASCII digit, and C<[a-m]>
420matches any lowercase letter from the first half of the ASCII alphabet.
421
422Note that the two characters on either side of the hyphen are not
765fa144 423necessarily both letters or both digits. Any character is possible,
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424although not advisable. C<['-?]> contains a range of characters, but
425most people will not know which characters that will be. Furthermore,
426such ranges may lead to portability problems if the code has to run on
427a platform that uses a different character set, such as EBCDIC.
428
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429If a hyphen in a character class cannot syntactically be part of a range, for
430instance because it is the first or the last character of the character class,
8a118206 431or if it immediately follows a range, the hyphen isn't special, and will be
6b83a163 432considered a character that is to be matched literally. You have to escape the
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433hyphen with a backslash if you want to have a hyphen in your set of characters
434to be matched, and its position in the class is such that it could be
435considered part of a range.
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436
437Examples:
438
439 [a-z] # Matches a character that is a lower case ASCII letter.
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440 [a-fz] # Matches any letter between 'a' and 'f' (inclusive) or
441 # the letter 'z'.
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442 [-z] # Matches either a hyphen ('-') or the letter 'z'.
443 [a-f-m] # Matches any letter between 'a' and 'f' (inclusive), the
444 # hyphen ('-'), or the letter 'm'.
445 ['-?] # Matches any of the characters '()*+,-./0123456789:;<=>?
446 # (But not on an EBCDIC platform).
447
448
449=head3 Negation
450
451It is also possible to instead list the characters you do not want to
452match. You can do so by using a caret (C<^>) as the first character in the
453character class. For instance, C<[^a-z]> matches a character that is not a
454lowercase ASCII letter.
455
456This syntax make the caret a special character inside a bracketed character
457class, but only if it is the first character of the class. So if you want
458to have the caret as one of the characters you want to match, you either
459have to escape the caret, or not list it first.
460
461Examples:
462
463 "e" =~ /[^aeiou]/ # No match, the 'e' is listed.
464 "x" =~ /[^aeiou]/ # Match, as 'x' isn't a lowercase vowel.
465 "^" =~ /[^^]/ # No match, matches anything that isn't a caret.
466 "^" =~ /[x^]/ # Match, caret is not special here.
467
468=head3 Backslash Sequences
469
ea449505 470You can put any backslash sequence character class (with the exception of
765fa144 471C<\N> and C<\R>) inside a bracketed character class, and it will act just
df225385 472as if you put all the characters matched by the backslash sequence inside the
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473character class. For instance, C<[a-f\d]> will match any decimal digit, or any
474of the lowercase letters between 'a' and 'f' inclusive.
475
476C<\N> within a bracketed character class must be of the forms C<\N{I<name>}>
765fa144 477or C<\N{U+I<hex char>}>, and NOT be the form that matches non-newlines,
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478for the same reason that a dot C<.> inside a bracketed character class loses
479its special meaning: it matches nearly anything, which generally isn't what you
480want to happen.
df225385 481
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482
483Examples:
484
485 /[\p{Thai}\d]/ # Matches a character that is either a Thai
486 # character, or a digit.
487 /[^\p{Arabic}()]/ # Matches a character that is neither an Arabic
488 # character, nor a parenthesis.
489
490Backslash sequence character classes cannot form one of the endpoints
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491of a range. Thus, you can't say:
492
493 /[\p{Thai}-\d]/ # Wrong!
8a118206 494
6b83a163 495=head3 POSIX Character Classes
ea449505 496X<character class> X<\p> X<\p{}>
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497X<alpha> X<alnum> X<ascii> X<blank> X<cntrl> X<digit> X<graph>
498X<lower> X<print> X<punct> X<space> X<upper> X<word> X<xdigit>
8a118206 499
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500POSIX character classes have the form C<[:class:]>, where I<class> is
501name, and the C<[:> and C<:]> delimiters. POSIX character classes only appear
8a118206 502I<inside> bracketed character classes, and are a convenient and descriptive
f7d1198f 503way of listing a group of characters, though they can suffer from
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504portability issues (see below and L<Locale, EBCDIC, Unicode and UTF-8>).
505
506Be careful about the syntax,
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507
508 # Correct:
509 $string =~ /[[:alpha:]]/
510
511 # Incorrect (will warn):
512 $string =~ /[:alpha:]/
513
514The latter pattern would be a character class consisting of a colon,
515and the letters C<a>, C<l>, C<p> and C<h>.
6b83a163 516POSIX character classes can be part of a larger bracketed character class. For
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517example,
518
519 [01[:alpha:]%]
520
521is valid and matches '0', '1', any alphabetic character, and the percent sign.
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522
523Perl recognizes the following POSIX character classes:
524
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525 alpha Any alphabetical character ("[A-Za-z]").
526 alnum Any alphanumerical character. ("[A-Za-z0-9]")
527 ascii Any character in the ASCII character set.
ea8b8ad2 528 blank A GNU extension, equal to a space or a horizontal tab ("\t").
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529 cntrl Any control character. See Note [2] below.
530 digit Any decimal digit ("[0-9]"), equivalent to "\d".
531 graph Any printable character, excluding a space. See Note [3] below.
532 lower Any lowercase character ("[a-z]").
533 print Any printable character, including a space. See Note [4] below.
c1c4ae3a 534 punct Any graphical character excluding "word" characters. Note [5].
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535 space Any whitespace character. "\s" plus the vertical tab ("\cK").
536 upper Any uppercase character ("[A-Z]").
537 word A Perl extension ("[A-Za-z0-9_]"), equivalent to "\w".
538 xdigit Any hexadecimal digit ("[0-9a-fA-F]").
539
540Most POSIX character classes have two Unicode-style C<\p> property
541counterparts. (They are not official Unicode properties, but Perl extensions
542derived from official Unicode properties.) The table below shows the relation
543between POSIX character classes and these counterparts.
544
545One counterpart, in the column labelled "ASCII-range Unicode" in
6b83a163 546the table, will only match characters in the ASCII character set.
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547
548The other counterpart, in the column labelled "Full-range Unicode", matches any
549appropriate characters in the full Unicode character set. For example,
550C<\p{Alpha}> will match not just the ASCII alphabetic characters, but any
551character in the entire Unicode character set that is considered to be
765fa144 552alphabetic. The column labelled "backslash sequence" is a (short) synonym for
cbc24f92 553the Full-range Unicode form.
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554
555(Each of the counterparts has various synonyms as well.
556L<perluniprops/Properties accessible through \p{} and \P{}> lists all the
557synonyms, plus all the characters matched by each of the ASCII-range
558properties. For example C<\p{AHex}> is a synonym for C<\p{ASCII_Hex_Digit}>,
559and any C<\p> property name can be prefixed with "Is" such as C<\p{IsAlpha}>.)
560
561Both the C<\p> forms are unaffected by any locale that is in effect, or whether
562the string is in UTF-8 format or not, or whether the platform is EBCDIC or not.
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563In contrast, the POSIX character classes are affected, unless the
564regular expression is compiled with the C<"a"> modifier. If the C<"a">
565modifier is not in effect, and the source string is in UTF-8 format, the
566POSIX classes behave like their "Full-range" Unicode counterparts. If
567C<"a"> modifier is in effect; or the source string is not in UTF-8
568format, and no locale is in effect, and the platform is not EBCDIC, all
569the POSIX classes behave like their ASCII-range counterparts.
570Otherwise, they behave based on the rules of the locale or EBCDIC code
571page.
6b83a163 572
ea449505 573It is proposed to change this behavior in a future release of Perl so that the
765fa144 574the UTF-8-ness of the source string will be irrelevant to the behavior of the
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575POSIX character classes. This means they will always behave in strict
576accordance with the official POSIX standard. That is, if either locale or
577EBCDIC code page is present, they will behave in accordance with those; if
578absent, the classes will match only their ASCII-range counterparts. If you
765fa144 579wish to comment on this proposal, send email to C<perl5-porters@perl.org>.
ea449505 580
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581 [[:...:]] ASCII-range Full-range backslash Note
582 Unicode Unicode sequence
ea449505 583 -----------------------------------------------------
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584 alpha \p{PosixAlpha} \p{XPosixAlpha}
585 alnum \p{PosixAlnum} \p{XPosixAlnum}
ea449505 586 ascii \p{ASCII}
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587 blank \p{PosixBlank} \p{XPosixBlank} \h [1]
588 or \p{HorizSpace} [1]
589 cntrl \p{PosixCntrl} \p{XPosixCntrl} [2]
590 digit \p{PosixDigit} \p{XPosixDigit} \d
591 graph \p{PosixGraph} \p{XPosixGraph} [3]
592 lower \p{PosixLower} \p{XPosixLower}
593 print \p{PosixPrint} \p{XPosixPrint} [4]
594 punct \p{PosixPunct} \p{XPosixPunct} [5]
595 \p{PerlSpace} \p{XPerlSpace} \s [6]
596 space \p{PosixSpace} \p{XPosixSpace} [6]
597 upper \p{PosixUpper} \p{XPosixUpper}
598 word \p{PosixWord} \p{XPosixWord} \w
599 xdigit \p{ASCII_Hex_Digit} \p{XPosixXDigit}
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600
601=over 4
602
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603=item [1]
604
605C<\p{Blank}> and C<\p{HorizSpace}> are synonyms.
606
607=item [2]
8a118206 608
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609Control characters don't produce output as such, but instead usually control
610the terminal somehow: for example newline and backspace are control characters.
611In the ASCII range, characters whose ordinals are between 0 and 31 inclusive,
612plus 127 (C<DEL>) are control characters.
8a118206 613
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614On EBCDIC platforms, it is likely that the code page will define C<[[:cntrl:]]>
615to be the EBCDIC equivalents of the ASCII controls, plus the controls
6b83a163 616that in Unicode have ordinals from 128 through 159.
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617
618=item [3]
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619
620Any character that is I<graphical>, that is, visible. This class consists
621of all the alphanumerical characters and all punctuation characters.
622
ea449505 623=item [4]
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624
625All printable characters, which is the set of all the graphical characters
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626plus whitespace characters that are not also controls.
627
b6dac59a 628=item [5]
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629
630C<\p{PosixPunct}> and C<[[:punct:]]> in the ASCII range match all the
631non-controls, non-alphanumeric, non-space characters:
632C<[-!"#$%&'()*+,./:;<=E<gt>?@[\\\]^_`{|}~]> (although if a locale is in effect,
633it could alter the behavior of C<[[:punct:]]>).
634
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635The similarly named property, C<\p{Punct}>, matches a somewhat different
636set in the ASCII range, namely
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637C<[-!"#%&'()*,./:;?@[\\\]_{}]>. That is, it is missing C<[$+E<lt>=E<gt>^`|~]>.
638This is because Unicode splits what POSIX considers to be punctuation into two
639categories, Punctuation and Symbols.
640
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641C<\p{XPosixPunct}> and (in Unicode mode) C<[[:punct:]]>, match what
642C<\p{PosixPunct}> matches in the ASCII range, plus what C<\p{Punct}>
643matches. This is different than strictly matching according to
644C<\p{Punct}>. Another way to say it is that
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645for a UTF-8 string, C<[[:punct:]]> matches all the characters that Unicode
646considers to be punctuation, plus all the ASCII-range characters that Unicode
647considers to be symbols.
8a118206 648
ea449505 649=item [6]
8a118206 650
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651C<\p{SpacePerl}> and C<\p{Space}> differ only in that C<\p{Space}> additionally
652matches the vertical tab, C<\cK>. Same for the two ASCII-only range forms.
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653
654=back
655
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656There are various other synonyms that can be used for these besides
657C<\p{HorizSpace}> and \C<\p{XPosixBlank}>. For example
658C<\p{PosixAlpha}> can be written as C<\p{Alpha}>. All are listed
659in L<perluniprops/Properties accessible through \p{} and \P{}>.
660
8a118206 661=head4 Negation
ea449505 662X<character class, negation>
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663
664A Perl extension to the POSIX character class is the ability to
665negate it. This is done by prefixing the class name with a caret (C<^>).
666Some examples:
667
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668 POSIX ASCII-range Full-range backslash
669 Unicode Unicode sequence
670 -----------------------------------------------------
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671 [[:^digit:]] \P{PosixDigit} \P{XPosixDigit} \D
672 [[:^space:]] \P{PosixSpace} \P{XPosixSpace}
673 \P{PerlSpace} \P{XPerlSpace} \S
674 [[:^word:]] \P{PerlWord} \P{XPosixWord} \W
675
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676The backslash sequence can mean either ASCII- or Full-range Unicode,
677depending on various factors. See L</Locale, EBCDIC, Unicode and UTF-8>
678below.
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679
680=head4 [= =] and [. .]
681
682Perl will recognize the POSIX character classes C<[=class=]>, and
ea449505 683C<[.class.]>, but does not (yet?) support them. Use of
740bae87 684such a construct will lead to an error.
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685
686
687=head4 Examples
688
689 /[[:digit:]]/ # Matches a character that is a digit.
690 /[01[:lower:]]/ # Matches a character that is either a
691 # lowercase letter, or '0' or '1'.
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692 /[[:digit:][:^xdigit:]]/ # Matches a character that can be anything
693 # except the letters 'a' to 'f'. This is
694 # because the main character class is composed
695 # of two POSIX character classes that are ORed
696 # together, one that matches any digit, and
697 # the other that matches anything that isn't a
698 # hex digit. The result matches all
699 # characters except the letters 'a' to 'f' and
700 # 'A' to 'F'.
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701
702
ea449505 703=head2 Locale, EBCDIC, Unicode and UTF-8
8a118206 704
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705Some of the character classes have a somewhat different behaviour
706depending on the internal encoding of the source string, if the regular
707expression is marked as having Unicode semantics, the locale that is in
708effect, and if the program is running on an EBCDIC platform.
709
710C<\w>, C<\d>, C<\s> and the POSIX character classes (and their
711negations, including C<\W>, C<\D>, C<\S>) have this behaviour. (Since
712the backslash sequences C<\b> and C<\B> are defined in terms of C<\w>
713and C<\W>, they also are affected.)
714
715Starting in Perl 5.14, if the regular expression is compiled with the
716C<"a"> modifier, the behavior doesn't differ regardless of any other
717factors. C<\d> matches the 10 digits 0-9; C<\D> any character but those
71810; C<\s>, exactly the five characters "[ \f\n\r\t]"; C<\w> only the 63
719characters "[A-Za-z0-9_]"; and the C<"[[:posix:]]"> classes only the
720appropriate ASCII characters, the same characters as are matched by the
721corresponding C<\p{}> property given in the "ASCII-range Unicode" column
722in the table above. (The behavior of all of their complements follows
723the same paradigm.)
724
725Otherwise, a regular expression is marked for Unicode semantics if it is
726encoded in utf8 (usually as a result of including a literal character
727whose code point is above 255), or if it contains a C<\N{U+...}> or
728C<\N{I<name>}> construct, or (starting in Perl 5.14) if it was compiled
729in the scope of a C<S<use feature "unicode_strings">> pragma and not in
730the scope of a C<S<use locale>> pragma, or has the C<"u"> regular
b6dac59a 731expression modifier.
17657a39 732
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733Note that one can specify C<"use re '/l'"> for example, for any regular
734expression modifier, and this has precedence over either of the
735C<S<use feature "unicode_strings">> or C<S<use locale>> pragmas.
736
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737The differences in behavior between locale and non-locale semantics
738can affect any character whose code point is 255 or less. The
739differences in behavior between Unicode and non-Unicode semantics
740affects only ASCII platforms, and only when matching against characters
741whose code points are between 128 and 255 inclusive. See
742L<perlunicode/The "Unicode Bug">.
8a118206 743
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744For portability reasons, unless the C<"a"> modifier is specified,
745it may be better to not use C<\w>, C<\d>, C<\s> or the POSIX character
746classes and use the Unicode properties instead.
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747That way you can control whether you want matching of just characters in
748the ASCII character set, or any Unicode characters.
749C<S<use feature "unicode_strings">> will allow seamless Unicode behavior
750no matter what the internal encodings are, but won't allow restricting
751to just the ASCII characters.
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752
753=head4 Examples
754
755 $str = "\xDF"; # $str is not in UTF-8 format.
756 $str =~ /^\w/; # No match, as $str isn't in UTF-8 format.
757 $str .= "\x{0e0b}"; # Now $str is in UTF-8 format.
758 $str =~ /^\w/; # Match! $str is now in UTF-8 format.
759 chop $str;
760 $str =~ /^\w/; # Still a match! $str remains in UTF-8 format.
761
762=cut