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perlrecharclass.pod: Add caveat about multi-char sequences
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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
87strings, C<\d> matches the same characters matched by
88C<\p{General_Category=Decimal_Number}>, or synonymously,
89C<\p{General_Category=Digit}>. Starting with Unicode version 4.1, this is the
90same set of characters matched by C<\p{Numeric_Type=Decimal}>.
91
92But Unicode also has a different property with a similar name,
93C<\p{Numeric_Type=Digit}>, which matches a completely different set of
94characters. These characters are things such as subscripts.
95
96The design intent is for C<\d> to match all the digits (and no other characters)
97that can be used with "normal" big-endian positional decimal syntax, whereby a
98sequence of such digits {N0, N1, N2, ...Nn} has the numeric value (...(N0 * 10
99+ N1) * 10 + N2) * 10 ... + Nn). In Unicode 5.2, the Tamil digits (U+0BE6 -
100U+0BEF) can also legally be used in old-style Tamil numbers in which they would
101appear no more than one in a row, separated by characters that mean "times 10",
102"times 100", etc. (See L<http://www.unicode.org/notes/tn21>.)
103
104Some of the non-European digits that C<\d> matches look like European ones, but
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105have different values. For example, BENGALI DIGIT FOUR (U+09EA) looks
106very much like an ASCII DIGIT EIGHT (U+0038).
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107
108It may be useful for security purposes for an application to require that all
109digits in a row be from the same script. See L<Unicode::UCD/charscript()>.
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110
111Any character that isn't matched by C<\d> will be matched by C<\D>.
112
113=head3 Word characters
114
ea449505 115A C<\w> matches a single alphanumeric character (an alphabetic character, or a
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116decimal digit) or an underscore (C<_>), not a whole word. To match a whole
117word, use C<\w+>. This isn't the same thing as matching an English word, but
118is the same as a string of Perl-identifier characters. What is considered a
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119word character depends on several factors, detailed below in L</Locale,
120EBCDIC, Unicode and UTF-8>. If those factors indicate a Unicode
121interpretation, C<\w> matches the characters that are considered word
ea449505 122characters in the Unicode database. That is, it not only matches ASCII letters,
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123but also Thai letters, Greek letters, etc. If a Unicode interpretation
124is not indicated, C<\w> matches those characters that are considered
125word characters by the current locale or EBCDIC code page. Without a
126locale or EBCDIC code page, C<\w> matches the ASCII letters, digits and
127the underscore.
8a118206 128
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129There are a number of security issues with the full Unicode list of word
130characters. See L<http://unicode.org/reports/tr36>.
131
132Also, for a somewhat finer-grained set of characters that are in programming
133language identifiers beyond the ASCII range, you may wish to instead use the
134more customized Unicode properties, "ID_Start", ID_Continue", "XID_Start", and
135"XID_Continue". See L<http://unicode.org/reports/tr31>.
136
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137Any character that isn't matched by C<\w> will be matched by C<\W>.
138
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139=head3 Whitespace
140
6b83a163 141C<\s> matches any single character that is considered whitespace. The exact
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142set of characters matched by C<\s> depends on several factors, detailed
143below in L</Locale, EBCDIC, Unicode and UTF-8>. If those factors
144indicate a Unicode interpretation, C<\s> matches what is considered
145whitespace in the Unicode database; the complete list is in the table
146below. Otherwise, if there is a locale or EBCDIC code page in effect,
147C<\s> matches whatever is considered whitespace by the current locale or
148EBCDIC code page. Without a locale or EBCDIC code page, C<\s> matches
149the horizontal tab (C<\t>), the newline (C<\n>), the form feed (C<\f>),
150the carriage return (C<\r>), and the space. (Note that it doesn't match
151the vertical tab, C<\cK>.) Perhaps the most notable possible surprise
152is that C<\s> matches a non-breaking space only if a Unicode
153interpretation is indicated, or the locale or EBCDIC code page that is
154in effect has that character.
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155
156Any character that isn't matched by C<\s> will be matched by C<\S>.
157
ea449505 158C<\h> will match any character that is considered horizontal whitespace;
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159this includes the space and the tab characters and a number other characters,
160all of which are listed in the table below. C<\H> will match any character
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161that is not considered horizontal whitespace.
162
ea449505 163C<\v> will match any character that is considered vertical whitespace;
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164this includes the carriage return and line feed characters (newline) plus several
165other characters, all listed in the table below.
ea449505 166C<\V> will match any character that is not considered vertical whitespace.
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167
168C<\R> matches anything that can be considered a newline under Unicode
169rules. It's not a character class, as it can match a multi-character
170sequence. Therefore, it cannot be used inside a bracketed character
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171class; use C<\v> instead (vertical whitespace).
172Details are discussed in L<perlrebackslash>.
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173
174Note that unlike C<\s>, C<\d> and C<\w>, C<\h> and C<\v> always match
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175the same characters, without regard to other factors, such as if the
176source string is in UTF-8 format or not.
8a118206 177
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178One might think that C<\s> is equivalent to C<[\h\v]>. This is not true. The
179vertical tab (C<"\x0b">) is not matched by C<\s>, it is however considered
180vertical whitespace. Furthermore, if the source string is not in UTF-8 format,
181and any locale or EBCDIC code page that is in effect doesn't include them, the
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182next line (ASCII-platform C<"\x85">) and the no-break space (ASCII-platform
183C<"\xA0">) characters are not matched by C<\s>, but are by C<\v> and C<\h>
184respectively. If the source string is in UTF-8 format, both the next line and
185the no-break space are matched by C<\s>.
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186
187The following table is a complete listing of characters matched by
ea449505 188C<\s>, C<\h> and C<\v> as of Unicode 5.2.
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189
190The first column gives the code point of the character (in hex format),
191the second column gives the (Unicode) name. The third column indicates
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192by which class(es) the character is matched (assuming no locale or EBCDIC code
193page is in effect that changes the C<\s> matching).
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194
195 0x00009 CHARACTER TABULATION h s
196 0x0000a LINE FEED (LF) vs
197 0x0000b LINE TABULATION v
198 0x0000c FORM FEED (FF) vs
199 0x0000d CARRIAGE RETURN (CR) vs
200 0x00020 SPACE h s
201 0x00085 NEXT LINE (NEL) vs [1]
202 0x000a0 NO-BREAK SPACE h s [1]
203 0x01680 OGHAM SPACE MARK h s
204 0x0180e MONGOLIAN VOWEL SEPARATOR h s
205 0x02000 EN QUAD h s
206 0x02001 EM QUAD h s
207 0x02002 EN SPACE h s
208 0x02003 EM SPACE h s
209 0x02004 THREE-PER-EM SPACE h s
210 0x02005 FOUR-PER-EM SPACE h s
211 0x02006 SIX-PER-EM SPACE h s
212 0x02007 FIGURE SPACE h s
213 0x02008 PUNCTUATION SPACE h s
214 0x02009 THIN SPACE h s
215 0x0200a HAIR SPACE h s
216 0x02028 LINE SEPARATOR vs
217 0x02029 PARAGRAPH SEPARATOR vs
218 0x0202f NARROW NO-BREAK SPACE h s
219 0x0205f MEDIUM MATHEMATICAL SPACE h s
220 0x03000 IDEOGRAPHIC SPACE h s
221
222=over 4
223
224=item [1]
225
226NEXT LINE and NO-BREAK SPACE only match C<\s> if the source string is in
ea449505 227UTF-8 format, or the locale or EBCDIC code page that is in effect includes them.
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228
229=back
230
231It is worth noting that C<\d>, C<\w>, etc, match single characters, not
232complete numbers or words. To match a number (that consists of integers),
233use C<\d+>; to match a word, use C<\w+>.
234
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235=head3 \N
236
237C<\N> is new in 5.12, and is experimental. It, like the dot, will match any
238character that is not a newline. The difference is that C<\N> is not influenced
239by the I<single line> regular expression modifier (see L</The dot> above). Note
240that the form C<\N{...}> may mean something completely different. When the
241C<{...}> is a L<quantifier|perlre/Quantifiers>, it means to match a non-newline
242character that many times. For example, C<\N{3}> means to match 3
243non-newlines; C<\N{5,}> means to match 5 or more non-newlines. But if C<{...}>
244is not a legal quantifier, it is presumed to be a named character. See
245L<charnames> for those. For example, none of C<\N{COLON}>, C<\N{4F}>, and
246C<\N{F4}> contain legal quantifiers, so Perl will try to find characters whose
247names are, respectively, C<COLON>, C<4F>, and C<F4>.
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248
249=head3 Unicode Properties
250
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251C<\pP> and C<\p{Prop}> are character classes to match characters that fit given
252Unicode properties. One letter property names can be used in the C<\pP> form,
253with the property name following the C<\p>, otherwise, braces are required.
254When using braces, there is a single form, which is just the property name
255enclosed in the braces, and a compound form which looks like C<\p{name=value}>,
256which means to match if the property "name" for the character has the particular
257"value".
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258For instance, a match for a number can be written as C</\pN/> or as
259C</\p{Number}/>, or as C</\p{Number=True}/>.
260Lowercase letters are matched by the property I<Lowercase_Letter> which
261has as short form I<Ll>. They need the braces, so are written as C</\p{Ll}/> or
262C</\p{Lowercase_Letter}/>, or C</\p{General_Category=Lowercase_Letter}/>
263(the underscores are optional).
264C</\pLl/> is valid, but means something different.
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265It matches a two character string: a letter (Unicode property C<\pL>),
266followed by a lowercase C<l>.
267
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268For more details, see L<perlunicode/Unicode Character Properties>; for a
269complete list of possible properties, see
270L<perluniprops/Properties accessible through \p{} and \P{}>.
271It is also possible to define your own properties. This is discussed in
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272L<perlunicode/User-Defined Character Properties>.
273
274
275=head4 Examples
276
277 "a" =~ /\w/ # Match, "a" is a 'word' character.
278 "7" =~ /\w/ # Match, "7" is a 'word' character as well.
279 "a" =~ /\d/ # No match, "a" isn't a digit.
280 "7" =~ /\d/ # Match, "7" is a digit.
ea449505 281 " " =~ /\s/ # Match, a space is whitespace.
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282 "a" =~ /\D/ # Match, "a" is a non-digit.
283 "7" =~ /\D/ # No match, "7" is not a non-digit.
ea449505 284 " " =~ /\S/ # No match, a space is not non-whitespace.
8a118206 285
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286 " " =~ /\h/ # Match, space is horizontal whitespace.
287 " " =~ /\v/ # No match, space is not vertical whitespace.
288 "\r" =~ /\v/ # Match, a return is vertical whitespace.
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289
290 "a" =~ /\pL/ # Match, "a" is a letter.
291 "a" =~ /\p{Lu}/ # No match, /\p{Lu}/ matches upper case letters.
292
293 "\x{0e0b}" =~ /\p{Thai}/ # Match, \x{0e0b} is the character
294 # 'THAI CHARACTER SO SO', and that's in
295 # Thai Unicode class.
ea449505 296 "a" =~ /\P{Lao}/ # Match, as "a" is not a Laotian character.
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297
298
299=head2 Bracketed Character Classes
300
301The third form of character class you can use in Perl regular expressions
6b83a163 302is the bracketed character class. In its simplest form, it lists the characters
c1c4ae3a 303that may be matched, surrounded by square brackets, like this: C<[aeiou]>.
ea449505 304This matches one of C<a>, C<e>, C<i>, C<o> or C<u>. Like the other
8a118206 305character classes, exactly one character will be matched. To match
ea449505 306a longer string consisting of characters mentioned in the character
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307class, follow the character class with a L<quantifier|perlre/Quantifiers>. For
308instance, C<[aeiou]+> matches a string of one or more lowercase English vowels.
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309
310Repeating a character in a character class has no
311effect; it's considered to be in the set only once.
312
313Examples:
314
315 "e" =~ /[aeiou]/ # Match, as "e" is listed in the class.
316 "p" =~ /[aeiou]/ # No match, "p" is not listed in the class.
317 "ae" =~ /^[aeiou]$/ # No match, a character class only matches
318 # a single character.
319 "ae" =~ /^[aeiou]+$/ # Match, due to the quantifier.
320
321=head3 Special Characters Inside a Bracketed Character Class
322
323Most characters that are meta characters in regular expressions (that
df225385 324is, characters that carry a special meaning like C<.>, C<*>, or C<(>) lose
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325their special meaning and can be used inside a character class without
326the need to escape them. For instance, C<[()]> matches either an opening
327parenthesis, or a closing parenthesis, and the parens inside the character
328class don't group or capture.
329
330Characters that may carry a special meaning inside a character class are:
331C<\>, C<^>, C<->, C<[> and C<]>, and are discussed below. They can be
332escaped with a backslash, although this is sometimes not needed, in which
333case the backslash may be omitted.
334
335The sequence C<\b> is special inside a bracketed character class. While
6b83a163 336outside the character class, C<\b> is an assertion indicating a point
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337that does not have either two word characters or two non-word characters
338on either side, inside a bracketed character class, C<\b> matches a
339backspace character.
340
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341The sequences
342C<\a>,
343C<\c>,
344C<\e>,
345C<\f>,
346C<\n>,
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347C<\N{I<NAME>}>,
348C<\N{U+I<wide hex char>}>,
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349C<\r>,
350C<\t>,
351and
352C<\x>
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353are also special and have the same meanings as they do outside a
354bracketed character class. (However, inside a bracketed character
355class, if C<\N{I<NAME>}> expands to a sequence of characters, only the first
356one in the sequence is used, with a warning.)
df225385 357
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358Also, a backslash followed by two or three octal digits is considered an octal
359number.
df225385 360
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361A C<[> is not special inside a character class, unless it's the start of a
362POSIX character class (see L</POSIX Character Classes> below). It normally does
363not need escaping.
8a118206 364
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365A C<]> is normally either the end of a POSIX character class (see
366L</POSIX Character Classes> below), or it signals the end of the bracketed
367character class. If you want to include a C<]> in the set of characters, you
368must generally escape it.
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369However, if the C<]> is the I<first> (or the second if the first
370character is a caret) character of a bracketed character class, it
371does not denote the end of the class (as you cannot have an empty class)
372and is considered part of the set of characters that can be matched without
373escaping.
374
375Examples:
376
377 "+" =~ /[+?*]/ # Match, "+" in a character class is not special.
378 "\cH" =~ /[\b]/ # Match, \b inside in a character class
c1c4ae3a 379 # is equivalent to a backspace.
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380 "]" =~ /[][]/ # Match, as the character class contains.
381 # both [ and ].
382 "[]" =~ /[[]]/ # Match, the pattern contains a character class
383 # containing just ], and the character class is
384 # followed by a ].
385
386=head3 Character Ranges
387
388It is not uncommon to want to match a range of characters. Luckily, instead
389of listing all the characters in the range, one may use the hyphen (C<->).
390If inside a bracketed character class you have two characters separated
391by a hyphen, it's treated as if all the characters between the two are in
392the class. For instance, C<[0-9]> matches any ASCII digit, and C<[a-m]>
393matches any lowercase letter from the first half of the ASCII alphabet.
394
395Note that the two characters on either side of the hyphen are not
396necessary both letters or both digits. Any character is possible,
397although not advisable. C<['-?]> contains a range of characters, but
398most people will not know which characters that will be. Furthermore,
399such ranges may lead to portability problems if the code has to run on
400a platform that uses a different character set, such as EBCDIC.
401
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402If a hyphen in a character class cannot syntactically be part of a range, for
403instance because it is the first or the last character of the character class,
8a118206 404or if it immediately follows a range, the hyphen isn't special, and will be
6b83a163 405considered a character that is to be matched literally. You have to escape the
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406hyphen with a backslash if you want to have a hyphen in your set of characters
407to be matched, and its position in the class is such that it could be
408considered part of a range.
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409
410Examples:
411
412 [a-z] # Matches a character that is a lower case ASCII letter.
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413 [a-fz] # Matches any letter between 'a' and 'f' (inclusive) or
414 # the letter 'z'.
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415 [-z] # Matches either a hyphen ('-') or the letter 'z'.
416 [a-f-m] # Matches any letter between 'a' and 'f' (inclusive), the
417 # hyphen ('-'), or the letter 'm'.
418 ['-?] # Matches any of the characters '()*+,-./0123456789:;<=>?
419 # (But not on an EBCDIC platform).
420
421
422=head3 Negation
423
424It is also possible to instead list the characters you do not want to
425match. You can do so by using a caret (C<^>) as the first character in the
426character class. For instance, C<[^a-z]> matches a character that is not a
427lowercase ASCII letter.
428
429This syntax make the caret a special character inside a bracketed character
430class, but only if it is the first character of the class. So if you want
431to have the caret as one of the characters you want to match, you either
432have to escape the caret, or not list it first.
433
434Examples:
435
436 "e" =~ /[^aeiou]/ # No match, the 'e' is listed.
437 "x" =~ /[^aeiou]/ # Match, as 'x' isn't a lowercase vowel.
438 "^" =~ /[^^]/ # No match, matches anything that isn't a caret.
439 "^" =~ /[x^]/ # Match, caret is not special here.
440
441=head3 Backslash Sequences
442
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443You can put any backslash sequence character class (with the exception of
444C<\N>) inside a bracketed character class, and it will act just
df225385 445as if you put all the characters matched by the backslash sequence inside the
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446character class. For instance, C<[a-f\d]> will match any decimal digit, or any
447of the lowercase letters between 'a' and 'f' inclusive.
448
449C<\N> within a bracketed character class must be of the forms C<\N{I<name>}>
450or C<\N{U+I<wide hex char>}>, and NOT be the form that matches non-newlines,
451for the same reason that a dot C<.> inside a bracketed character class loses
452its special meaning: it matches nearly anything, which generally isn't what you
453want to happen.
df225385 454
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455
456Examples:
457
458 /[\p{Thai}\d]/ # Matches a character that is either a Thai
459 # character, or a digit.
460 /[^\p{Arabic}()]/ # Matches a character that is neither an Arabic
461 # character, nor a parenthesis.
462
463Backslash sequence character classes cannot form one of the endpoints
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464of a range. Thus, you can't say:
465
466 /[\p{Thai}-\d]/ # Wrong!
8a118206 467
6b83a163 468=head3 POSIX Character Classes
ea449505 469X<character class> X<\p> X<\p{}>
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470X<alpha> X<alnum> X<ascii> X<blank> X<cntrl> X<digit> X<graph>
471X<lower> X<print> X<punct> X<space> X<upper> X<word> X<xdigit>
8a118206 472
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473POSIX character classes have the form C<[:class:]>, where I<class> is
474name, and the C<[:> and C<:]> delimiters. POSIX character classes only appear
8a118206 475I<inside> bracketed character classes, and are a convenient and descriptive
c1c4ae3a 476way of listing a group of characters, though they currently suffer from
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477portability issues (see below and L<Locale, EBCDIC, Unicode and UTF-8>).
478
479Be careful about the syntax,
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480
481 # Correct:
482 $string =~ /[[:alpha:]]/
483
484 # Incorrect (will warn):
485 $string =~ /[:alpha:]/
486
487The latter pattern would be a character class consisting of a colon,
488and the letters C<a>, C<l>, C<p> and C<h>.
6b83a163 489POSIX character classes can be part of a larger bracketed character class. For
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490example,
491
492 [01[:alpha:]%]
493
494is valid and matches '0', '1', any alphabetic character, and the percent sign.
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495
496Perl recognizes the following POSIX character classes:
497
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498 alpha Any alphabetical character ("[A-Za-z]").
499 alnum Any alphanumerical character. ("[A-Za-z0-9]")
500 ascii Any character in the ASCII character set.
ea8b8ad2 501 blank A GNU extension, equal to a space or a horizontal tab ("\t").
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502 cntrl Any control character. See Note [2] below.
503 digit Any decimal digit ("[0-9]"), equivalent to "\d".
504 graph Any printable character, excluding a space. See Note [3] below.
505 lower Any lowercase character ("[a-z]").
506 print Any printable character, including a space. See Note [4] below.
c1c4ae3a 507 punct Any graphical character excluding "word" characters. Note [5].
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508 space Any whitespace character. "\s" plus the vertical tab ("\cK").
509 upper Any uppercase character ("[A-Z]").
510 word A Perl extension ("[A-Za-z0-9_]"), equivalent to "\w".
511 xdigit Any hexadecimal digit ("[0-9a-fA-F]").
512
513Most POSIX character classes have two Unicode-style C<\p> property
514counterparts. (They are not official Unicode properties, but Perl extensions
515derived from official Unicode properties.) The table below shows the relation
516between POSIX character classes and these counterparts.
517
518One counterpart, in the column labelled "ASCII-range Unicode" in
6b83a163 519the table, will only match characters in the ASCII character set.
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520
521The other counterpart, in the column labelled "Full-range Unicode", matches any
522appropriate characters in the full Unicode character set. For example,
523C<\p{Alpha}> will match not just the ASCII alphabetic characters, but any
524character in the entire Unicode character set that is considered to be
525alphabetic.
526
527(Each of the counterparts has various synonyms as well.
528L<perluniprops/Properties accessible through \p{} and \P{}> lists all the
529synonyms, plus all the characters matched by each of the ASCII-range
530properties. For example C<\p{AHex}> is a synonym for C<\p{ASCII_Hex_Digit}>,
531and any C<\p> property name can be prefixed with "Is" such as C<\p{IsAlpha}>.)
532
533Both the C<\p> forms are unaffected by any locale that is in effect, or whether
534the string is in UTF-8 format or not, or whether the platform is EBCDIC or not.
535In contrast, the POSIX character classes are affected. If the source string is
536in UTF-8 format, the POSIX classes (with the exception of C<[[:punct:]]>, see
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537Note [5] below) behave like their "Full-range" Unicode counterparts. If the
538source string is not in UTF-8 format, and no locale is in effect, and the
539platform is not EBCDIC, all the POSIX classes behave like their ASCII-range
540counterparts. Otherwise, they behave based on the rules of the locale or
541EBCDIC code page.
542
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543It is proposed to change this behavior in a future release of Perl so that the
544the UTF8ness of the source string will be irrelevant to the behavior of the
545POSIX character classes. This means they will always behave in strict
546accordance with the official POSIX standard. That is, if either locale or
547EBCDIC code page is present, they will behave in accordance with those; if
548absent, the classes will match only their ASCII-range counterparts. If you
549disagree with this proposal, send email to C<perl5-porters@perl.org>.
550
551 [[:...:]] ASCII-range Full-range backslash Note
552 Unicode Unicode sequence
553 -----------------------------------------------------
554 alpha \p{PosixAlpha} \p{Alpha}
555 alnum \p{PosixAlnum} \p{Alnum}
556 ascii \p{ASCII}
c1c4ae3a 557 blank \p{PosixBlank} \p{Blank} = [1]
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558 \p{HorizSpace} \h [1]
559 cntrl \p{PosixCntrl} \p{Cntrl} [2]
560 digit \p{PosixDigit} \p{Digit} \d
561 graph \p{PosixGraph} \p{Graph} [3]
562 lower \p{PosixLower} \p{Lower}
563 print \p{PosixPrint} \p{Print} [4]
564 punct \p{PosixPunct} \p{Punct} [5]
565 \p{PerlSpace} \p{SpacePerl} \s [6]
566 space \p{PosixSpace} \p{Space} [6]
567 upper \p{PosixUpper} \p{Upper}
568 word \p{PerlWord} \p{Word} \w
569 xdigit \p{ASCII_Hex_Digit} \p{XDigit}
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570
571=over 4
572
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573=item [1]
574
575C<\p{Blank}> and C<\p{HorizSpace}> are synonyms.
576
577=item [2]
8a118206 578
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579Control characters don't produce output as such, but instead usually control
580the terminal somehow: for example newline and backspace are control characters.
581In the ASCII range, characters whose ordinals are between 0 and 31 inclusive,
582plus 127 (C<DEL>) are control characters.
8a118206 583
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584On EBCDIC platforms, it is likely that the code page will define C<[[:cntrl:]]>
585to be the EBCDIC equivalents of the ASCII controls, plus the controls
6b83a163 586that in Unicode have ordinals from 128 through 159.
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587
588=item [3]
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589
590Any character that is I<graphical>, that is, visible. This class consists
591of all the alphanumerical characters and all punctuation characters.
592
ea449505 593=item [4]
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594
595All printable characters, which is the set of all the graphical characters
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596plus whitespace characters that are not also controls.
597
6c5a041f 598=item [5] (punct)
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599
600C<\p{PosixPunct}> and C<[[:punct:]]> in the ASCII range match all the
601non-controls, non-alphanumeric, non-space characters:
602C<[-!"#$%&'()*+,./:;<=E<gt>?@[\\\]^_`{|}~]> (although if a locale is in effect,
603it could alter the behavior of C<[[:punct:]]>).
604
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605C<\p{Punct}> matches a somewhat different set in the ASCII range, namely
606C<[-!"#%&'()*,./:;?@[\\\]_{}]>. That is, it is missing C<[$+E<lt>=E<gt>^`|~]>.
607This is because Unicode splits what POSIX considers to be punctuation into two
608categories, Punctuation and Symbols.
609
610When the matching string is in UTF-8 format, C<[[:punct:]]> matches what it
611matches in the ASCII range, plus what C<\p{Punct}> matches. This is different
612than strictly matching according to C<\p{Punct}>. Another way to say it is that
613for a UTF-8 string, C<[[:punct:]]> matches all the characters that Unicode
614considers to be punctuation, plus all the ASCII-range characters that Unicode
615considers to be symbols.
8a118206 616
ea449505 617=item [6]
8a118206 618
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619C<\p{SpacePerl}> and C<\p{Space}> differ only in that C<\p{Space}> additionally
620matches the vertical tab, C<\cK>. Same for the two ASCII-only range forms.
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621
622=back
623
624=head4 Negation
ea449505 625X<character class, negation>
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626
627A Perl extension to the POSIX character class is the ability to
628negate it. This is done by prefixing the class name with a caret (C<^>).
629Some examples:
630
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631 POSIX ASCII-range Full-range backslash
632 Unicode Unicode sequence
633 -----------------------------------------------------
c1c4ae3a 634 [[:^digit:]] \P{PosixDigit} \P{Digit} \D
ea449505 635 [[:^space:]] \P{PosixSpace} \P{Space}
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636 \P{PerlSpace} \P{SpacePerl} \S
637 [[:^word:]] \P{PerlWord} \P{Word} \W
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638
639=head4 [= =] and [. .]
640
641Perl will recognize the POSIX character classes C<[=class=]>, and
ea449505 642C<[.class.]>, but does not (yet?) support them. Use of
740bae87 643such a construct will lead to an error.
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644
645
646=head4 Examples
647
648 /[[:digit:]]/ # Matches a character that is a digit.
649 /[01[:lower:]]/ # Matches a character that is either a
650 # lowercase letter, or '0' or '1'.
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651 /[[:digit:][:^xdigit:]]/ # Matches a character that can be anything
652 # except the letters 'a' to 'f'. This is
653 # because the main character class is composed
654 # of two POSIX character classes that are ORed
655 # together, one that matches any digit, and
656 # the other that matches anything that isn't a
657 # hex digit. The result matches all
658 # characters except the letters 'a' to 'f' and
659 # 'A' to 'F'.
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660
661
ea449505 662=head2 Locale, EBCDIC, Unicode and UTF-8
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663
664Some of the character classes have a somewhat different behaviour depending
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665on the internal encoding of the source string, if the regular expression
666is marked as having Unicode semantics, the locale that is in effect,
667and if the program is running on an EBCDIC platform.
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668
669C<\w>, C<\d>, C<\s> and the POSIX character classes (and their negations,
17657a39 670including C<\W>, C<\D>, C<\S>) have this behaviour. (Since the backslash
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671sequences C<\b> and C<\B> are defined in terms of C<\w> and C<\W>, they also are
672affected.)
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674The rule is that if the source string is in UTF-8 format or the regular
675expression is marked as indicating Unicode semantics (see the next
676paragraph), the character classes match according to the Unicode
677properties. Otherwise, the character classes match according to
678whatever locale or EBCDIC code page is in effect. If there is no locale
679nor EBCDIC, they match the ASCII defaults (0 to 9 for C<\d>; 52 letters,
68010 digits and underscore for C<\w>; etc.).
681
682A regular expression is marked for Unicode semantics if it is encoded in
683utf8 (usually as a result of including a literal character whose code
684point is above 255), or if it contains a C<\N{U+...}> or C<\N{I<name>}>
685construct.
686
687The differences in behavior between locale and non-locale semantics
688can affect any character whose code point is 255 or less. The
689differences in behavior between Unicode and non-Unicode semantics
690affects only ASCII platforms, and only when matching against characters
691whose code points are between 128 and 255 inclusive. See
692L<perlunicode/The "Unicode Bug">.
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693
694For portability reasons, it may be better to not use C<\w>, C<\d>, C<\s>
695or the POSIX character classes, and use the Unicode properties instead.
696
697=head4 Examples
698
699 $str = "\xDF"; # $str is not in UTF-8 format.
700 $str =~ /^\w/; # No match, as $str isn't in UTF-8 format.
701 $str .= "\x{0e0b}"; # Now $str is in UTF-8 format.
702 $str =~ /^\w/; # Match! $str is now in UTF-8 format.
703 chop $str;
704 $str =~ /^\w/; # Still a match! $str remains in UTF-8 format.
705
706=cut