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8a118206 1=head1 NAME
ea449505 2X<character class>
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3
4perlrecharclass - Perl Regular Expression Character Classes
5
6=head1 DESCRIPTION
7
8The top level documentation about Perl regular expressions
9is found in L<perlre>.
10
11This manual page discusses the syntax and use of character
6b83a163 12classes in Perl regular expressions.
8a118206 13
6b83a163 14A character class is a way of denoting a set of characters
8a118206 15in such a way that one character of the set is matched.
6b83a163 16It's important to remember that: matching a character class
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17consumes exactly one character in the source string. (The source
18string is the string the regular expression is matched against.)
19
20There are three types of character classes in Perl regular
6b83a163 21expressions: the dot, backslash sequences, and the form enclosed in square
ea449505 22brackets. Keep in mind, though, that often the term "character class" is used
6b83a163 23to mean just the bracketed form. Certainly, most Perl documentation does that.
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24
25=head2 The dot
26
27The dot (or period), C<.> is probably the most used, and certainly
28the most well-known character class. By default, a dot matches any
5db9882c 29character, except for the newline. That default can be changed to
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30add matching the newline by using the I<single line> modifier: either
31for the entire regular expression with the C</s> modifier, or
32locally with C<(?s)>. (The experimental C<\N> backslash sequence, described
33below, matches any character except newline without regard to the
34I<single line> modifier.)
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35
36Here are some examples:
37
38 "a" =~ /./ # Match
39 "." =~ /./ # Match
40 "" =~ /./ # No match (dot has to match a character)
41 "\n" =~ /./ # No match (dot does not match a newline)
42 "\n" =~ /./s # Match (global 'single line' modifier)
43 "\n" =~ /(?s:.)/ # Match (local 'single line' modifier)
44 "ab" =~ /^.$/ # No match (dot matches one character)
45
6b83a163 46=head2 Backslash sequences
82206b5e 47X<\w> X<\W> X<\s> X<\S> X<\d> X<\D> X<\p> X<\P>
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48X<\N> X<\v> X<\V> X<\h> X<\H>
49X<word> X<whitespace>
8a118206 50
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51A backslash sequence is a sequence of characters, the first one of which is a
52backslash. Perl ascribes special meaning to many such sequences, and some of
53these are character classes. That is, they match a single character each,
54provided that the character belongs to the specific set of characters defined
55by the sequence.
8a118206 56
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57Here's a list of the backslash sequences that are character classes. They
58are discussed in more detail below. (For the backslash sequences that aren't
59character classes, see L<perlrebackslash>.)
8a118206 60
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61 \d Match a decimal digit character.
62 \D Match a non-decimal-digit character.
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63 \w Match a "word" character.
64 \W Match a non-"word" character.
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65 \s Match a whitespace character.
66 \S Match a non-whitespace character.
67 \h Match a horizontal whitespace character.
68 \H Match a character that isn't horizontal whitespace.
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69 \v Match a vertical whitespace character.
70 \V Match a character that isn't vertical whitespace.
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71 \N Match a character that isn't a newline. Experimental.
72 \pP, \p{Prop} Match a character that has the given Unicode property.
6c5a041f 73 \PP, \P{Prop} Match a character that doesn't have the Unicode property
8a118206 74
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75=head3 \N
76
77C<\N> is new in 5.12, and is experimental. It, like the dot, matches any
78character that is not a newline. The difference is that C<\N> is not influenced
79by the I<single line> regular expression modifier (see L</The dot> above). Note
80that the form C<\N{...}> may mean something completely different. When the
81C<{...}> is a L<quantifier|perlre/Quantifiers>, it means to match a non-newline
82character that many times. For example, C<\N{3}> means to match 3
83non-newlines; C<\N{5,}> means to match 5 or more non-newlines. But if C<{...}>
84is not a legal quantifier, it is presumed to be a named character. See
85L<charnames> for those. For example, none of C<\N{COLON}>, C<\N{4F}>, and
86C<\N{F4}> contain legal quantifiers, so Perl will try to find characters whose
87names are respectively C<COLON>, C<4F>, and C<F4>.
88
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89=head3 Digits
90
b6538e4f 91C<\d> matches a single character considered to be a decimal I<digit>.
5db9882c 92If the C</a> regular expression modifier is in effect, it matches [0-9].
582da942 93Otherwise, it
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94matches anything that is matched by C<\p{Digit}>, which includes [0-9].
95(An unlikely possible exception is that under locale matching rules, the
96current locale might not have [0-9] matched by C<\d>, and/or might match
97other characters whose code point is less than 256. Such a locale
98definition would be in violation of the C language standard, but Perl
99doesn't currently assume anything in regard to this.)
100
101What this means is that unless the C</a> modifier is in effect C<\d> not
102only matches the digits '0' - '9', but also Arabic, Devanagari, and
103digits from other languages. This may cause some confusion, and some
104security issues.
105
106Some digits that C<\d> matches look like some of the [0-9] ones, but
107have different values. For example, BENGALI DIGIT FOUR (U+09EA) looks
108very much like an ASCII DIGIT EIGHT (U+0038). An application that
109is expecting only the ASCII digits might be misled, or if the match is
110C<\d+>, the matched string might contain a mixture of digits from
111different writing systems that look like they signify a number different
67592e11 112than they actually do. L<Unicode::UCD/num()> can
e397bccf 113be used to safely
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114calculate the value, returning C<undef> if the input string contains
115such a mixture.
116
117What C<\p{Digit}> means (and hence C<\d> except under the C</a>
118modifier) is C<\p{General_Category=Decimal_Number}>, or synonymously,
119C<\p{General_Category=Digit}>. Starting with Unicode version 4.1, this
120is the same set of characters matched by C<\p{Numeric_Type=Decimal}>.
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121But Unicode also has a different property with a similar name,
122C<\p{Numeric_Type=Digit}>, which matches a completely different set of
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123characters. These characters are things such as C<CIRCLED DIGIT ONE>
124or subscripts, or are from writing systems that lack all ten digits.
6b83a163 125
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126The design intent is for C<\d> to exactly match the set of characters
127that can safely be used with "normal" big-endian positional decimal
128syntax, where, for example 123 means one 'hundred', plus two 'tens',
129plus three 'ones'. This positional notation does not necessarily apply
130to characters that match the other type of "digit",
131C<\p{Numeric_Type=Digit}>, and so C<\d> doesn't match them.
6b83a163 132
e2cfb18c 133The Tamil digits (U+0BE6 - U+0BEF) can also legally be
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134used in old-style Tamil numbers in which they would appear no more than
135one in a row, separated by characters that mean "times 10", "times 100",
136etc. (See L<http://www.unicode.org/notes/tn21>.)
8a118206 137
b6538e4f 138Any character not matched by C<\d> is matched by C<\D>.
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139
140=head3 Word characters
141
ea449505 142A C<\w> matches a single alphanumeric character (an alphabetic character, or a
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143decimal digit); or a connecting punctuation character, such as an
144underscore ("_"); or a "mark" character (like some sort of accent) that
145attaches to one of those. It does not match a whole word. To match a
146whole word, use C<\w+>. This isn't the same thing as matching an
147English word, but in the ASCII range it is the same as a string of
148Perl-identifier characters.
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149
150=over
151
152=item If the C</a> modifier is in effect ...
153
154C<\w> matches the 63 characters [a-zA-Z0-9_].
155
156=item otherwise ...
157
158=over
159
160=item For code points above 255 ...
161
162C<\w> matches the same as C<\p{Word}> matches in this range. That is,
163it matches Thai letters, Greek letters, etc. This includes connector
d35dd6c6 164punctuation (like the underscore) which connect two words together, or
b6538e4f 165diacritics, such as a C<COMBINING TILDE> and the modifier letters, which
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166are generally used to add auxiliary markings to letters.
167
168=item For code points below 256 ...
169
170=over
171
172=item if locale rules are in effect ...
173
174C<\w> matches the platform's native underscore character plus whatever
175the locale considers to be alphanumeric.
176
177=item if Unicode rules are in effect or if on an EBCDIC platform ...
178
179C<\w> matches exactly what C<\p{Word}> matches.
180
181=item otherwise ...
182
183C<\w> matches [a-zA-Z0-9_].
184
185=back
186
187=back
188
189=back
190
191Which rules apply are determined as described in L<perlre/Which character set modifier is in effect?>.
8a118206 192
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193There are a number of security issues with the full Unicode list of word
194characters. See L<http://unicode.org/reports/tr36>.
195
196Also, for a somewhat finer-grained set of characters that are in programming
197language identifiers beyond the ASCII range, you may wish to instead use the
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198more customized L</Unicode Properties>, C<\p{ID_Start}>,
199C<\p{ID_Continue}>, C<\p{XID_Start}>, and C<\p{XID_Continue}>. See
200L<http://unicode.org/reports/tr31>.
6b83a163 201
b6538e4f 202Any character not matched by C<\w> is matched by C<\W>.
8a118206 203
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204=head3 Whitespace
205
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206C<\s> matches any single character considered whitespace.
207
208=over
209
210=item If the C</a> modifier is in effect ...
211
212C<\s> matches the 5 characters [\t\n\f\r ]; that is, the horizontal tab,
213the newline, the form feed, the carriage return, and the space. (Note
214that it doesn't match the vertical tab, C<\cK> on ASCII platforms.)
215
216=item otherwise ...
217
218=over
219
220=item For code points above 255 ...
221
222C<\s> matches exactly the code points above 255 shown with an "s" column
223in the table below.
224
225=item For code points below 256 ...
226
227=over
228
229=item if locale rules are in effect ...
230
231C<\s> matches whatever the locale considers to be whitespace. Note that
232this is likely to include the vertical space, unlike non-locale C<\s>
233matching.
234
235=item if Unicode rules are in effect or if on an EBCDIC platform ...
236
237C<\s> matches exactly the characters shown with an "s" column in the
238table below.
239
240=item otherwise ...
241
242C<\s> matches [\t\n\f\r ].
243Note that this list doesn't include the non-breaking space.
244
245=back
246
247=back
248
249=back
250
251Which rules apply are determined as described in L<perlre/Which character set modifier is in effect?>.
8a118206 252
b6538e4f 253Any character not matched by C<\s> is matched by C<\S>.
8a118206 254
b6538e4f 255C<\h> matches any character considered horizontal whitespace;
8129baca 256this includes the platform's space and tab characters and several others
b6538e4f 257listed in the table below. C<\H> matches any character
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258not considered horizontal whitespace. They use the platform's native
259character set, and do not consider any locale that may otherwise be in
260use.
ea449505 261
b6538e4f 262C<\v> matches any character considered vertical whitespace;
8129baca 263this includes the platform's carriage return and line feed characters (newline)
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264plus several other characters, all listed in the table below.
265C<\V> matches any character not considered vertical whitespace.
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266They use the platform's native character set, and do not consider any
267locale that may otherwise be in use.
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268
269C<\R> matches anything that can be considered a newline under Unicode
270rules. It's not a character class, as it can match a multi-character
271sequence. Therefore, it cannot be used inside a bracketed character
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272class; use C<\v> instead (vertical whitespace). It uses the platform's
273native character set, and does not consider any locale that may
274otherwise be in use.
ea449505 275Details are discussed in L<perlrebackslash>.
8a118206 276
82206b5e 277Note that unlike C<\s> (and C<\d> and C<\w>), C<\h> and C<\v> always match
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278the same characters, without regard to other factors, such as the active
279locale or whether the source string is in UTF-8 format.
8a118206 280
82206b5e 281One might think that C<\s> is equivalent to C<[\h\v]>. This is not true.
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282The difference is that the vertical tab (C<"\x0b">) is not matched by
283C<\s>; it is however considered vertical whitespace.
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284
285The following table is a complete listing of characters matched by
82206b5e 286C<\s>, C<\h> and C<\v> as of Unicode 6.0.
8a118206 287
582da942 288The first column gives the Unicode code point of the character (in hex format),
8a118206 289the second column gives the (Unicode) name. The third column indicates
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290by which class(es) the character is matched (assuming no locale or EBCDIC code
291page is in effect that changes the C<\s> matching).
8a118206 292
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293 0x0009 CHARACTER TABULATION h s
294 0x000a LINE FEED (LF) vs
295 0x000b LINE TABULATION v
296 0x000c FORM FEED (FF) vs
297 0x000d CARRIAGE RETURN (CR) vs
298 0x0020 SPACE h s
299 0x0085 NEXT LINE (NEL) vs [1]
300 0x00a0 NO-BREAK SPACE h s [1]
301 0x1680 OGHAM SPACE MARK h s
302 0x180e MONGOLIAN VOWEL SEPARATOR h s
303 0x2000 EN QUAD h s
304 0x2001 EM QUAD h s
305 0x2002 EN SPACE h s
306 0x2003 EM SPACE h s
307 0x2004 THREE-PER-EM SPACE h s
308 0x2005 FOUR-PER-EM SPACE h s
309 0x2006 SIX-PER-EM SPACE h s
310 0x2007 FIGURE SPACE h s
311 0x2008 PUNCTUATION SPACE h s
312 0x2009 THIN SPACE h s
313 0x200a HAIR SPACE h s
314 0x2028 LINE SEPARATOR vs
315 0x2029 PARAGRAPH SEPARATOR vs
316 0x202f NARROW NO-BREAK SPACE h s
317 0x205f MEDIUM MATHEMATICAL SPACE h s
318 0x3000 IDEOGRAPHIC SPACE h s
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319
320=over 4
321
322=item [1]
323
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324NEXT LINE and NO-BREAK SPACE may or may not match C<\s> depending
325on the rules in effect. See
326L<the beginning of this section|/Whitespace>.
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327
328=back
329
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330=head3 Unicode Properties
331
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332C<\pP> and C<\p{Prop}> are character classes to match characters that fit given
333Unicode properties. One letter property names can be used in the C<\pP> form,
334with the property name following the C<\p>, otherwise, braces are required.
335When using braces, there is a single form, which is just the property name
336enclosed in the braces, and a compound form which looks like C<\p{name=value}>,
b6538e4f 337which means to match if the property "name" for the character has that particular
c1c4ae3a 338"value".
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339For instance, a match for a number can be written as C</\pN/> or as
340C</\p{Number}/>, or as C</\p{Number=True}/>.
341Lowercase letters are matched by the property I<Lowercase_Letter> which
e2cfb18c 342has the short form I<Ll>. They need the braces, so are written as C</\p{Ll}/> or
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343C</\p{Lowercase_Letter}/>, or C</\p{General_Category=Lowercase_Letter}/>
344(the underscores are optional).
345C</\pLl/> is valid, but means something different.
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346It matches a two character string: a letter (Unicode property C<\pL>),
347followed by a lowercase C<l>.
348
bc943be5 349If locale rules are not in effect, the use of
82206b5e 350a Unicode property will force the regular expression into using Unicode
bc943be5 351rules, if it isn't already.
82206b5e 352
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353Note that almost all properties are immune to case-insensitive matching.
354That is, adding a C</i> regular expression modifier does not change what
82206b5e 355they match. There are two sets that are affected. The first set is
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356C<Uppercase_Letter>,
357C<Lowercase_Letter>,
358and C<Titlecase_Letter>,
359all of which match C<Cased_Letter> under C</i> matching.
b6538e4f 360The second set is
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361C<Uppercase>,
362C<Lowercase>,
363and C<Titlecase>,
364all of which match C<Cased> under C</i> matching.
365(The difference between these sets is that some things, such as Roman
e2cfb18c 366numerals, come in both upper and lower case, so they are C<Cased>, but
b6538e4f 367aren't considered to be letters, so they aren't C<Cased_Letter>s. They're
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368actually C<Letter_Number>s.)
369This set also includes its subsets C<PosixUpper> and C<PosixLower>, both
e2cfb18c 370of which under C</i> match C<PosixAlpha>.
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371
372For more details on Unicode properties, see L<perlunicode/Unicode
373Character Properties>; for a
e1b711da 374complete list of possible properties, see
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375L<perluniprops/Properties accessible through \p{} and \P{}>,
376which notes all forms that have C</i> differences.
e1b711da 377It is also possible to define your own properties. This is discussed in
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378L<perlunicode/User-Defined Character Properties>.
379
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380Unicode properties are defined (surprise!) only on Unicode code points.
381A warning is raised and all matches fail on non-Unicode code points
382(those above the legal Unicode maximum of 0x10FFFF). This can be
383somewhat surprising,
384
385 chr(0x110000) =~ \p{ASCII_Hex_Digit=True} # Fails.
386 chr(0x110000) =~ \p{ASCII_Hex_Digit=False} # Also fails!
387
388Even though these two matches might be thought of as complements, they
389are so only on Unicode code points.
390
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391=head4 Examples
392
393 "a" =~ /\w/ # Match, "a" is a 'word' character.
394 "7" =~ /\w/ # Match, "7" is a 'word' character as well.
395 "a" =~ /\d/ # No match, "a" isn't a digit.
396 "7" =~ /\d/ # Match, "7" is a digit.
ea449505 397 " " =~ /\s/ # Match, a space is whitespace.
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398 "a" =~ /\D/ # Match, "a" is a non-digit.
399 "7" =~ /\D/ # No match, "7" is not a non-digit.
ea449505 400 " " =~ /\S/ # No match, a space is not non-whitespace.
8a118206 401
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402 " " =~ /\h/ # Match, space is horizontal whitespace.
403 " " =~ /\v/ # No match, space is not vertical whitespace.
404 "\r" =~ /\v/ # Match, a return is vertical whitespace.
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405
406 "a" =~ /\pL/ # Match, "a" is a letter.
407 "a" =~ /\p{Lu}/ # No match, /\p{Lu}/ matches upper case letters.
408
409 "\x{0e0b}" =~ /\p{Thai}/ # Match, \x{0e0b} is the character
410 # 'THAI CHARACTER SO SO', and that's in
411 # Thai Unicode class.
ea449505 412 "a" =~ /\P{Lao}/ # Match, as "a" is not a Laotian character.
8a118206 413
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414It is worth emphasizing that C<\d>, C<\w>, etc, match single characters, not
415complete numbers or words. To match a number (that consists of digits),
416use C<\d+>; to match a word, use C<\w+>. But be aware of the security
417considerations in doing so, as mentioned above.
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418
419=head2 Bracketed Character Classes
420
421The third form of character class you can use in Perl regular expressions
6b83a163 422is the bracketed character class. In its simplest form, it lists the characters
c1c4ae3a 423that may be matched, surrounded by square brackets, like this: C<[aeiou]>.
ea449505 424This matches one of C<a>, C<e>, C<i>, C<o> or C<u>. Like the other
1f59b283 425character classes, exactly one character is matched.* To match
ea449505 426a longer string consisting of characters mentioned in the character
6b83a163 427class, follow the character class with a L<quantifier|perlre/Quantifiers>. For
b6538e4f 428instance, C<[aeiou]+> matches one or more lowercase English vowels.
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429
430Repeating a character in a character class has no
431effect; it's considered to be in the set only once.
432
433Examples:
434
435 "e" =~ /[aeiou]/ # Match, as "e" is listed in the class.
436 "p" =~ /[aeiou]/ # No match, "p" is not listed in the class.
437 "ae" =~ /^[aeiou]$/ # No match, a character class only matches
438 # a single character.
439 "ae" =~ /^[aeiou]+$/ # Match, due to the quantifier.
440
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441 -------
442
df0e3973 443* There is an exception to a bracketed character class matching a
1cecf2c0 444single character only. When the class is to match caselessly under C</i>
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445matching rules, and a character that is explicitly mentioned inside the
446class matches a
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447multiple-character sequence caselessly under Unicode rules, the class
448(when not L<inverted|/Negation>) will also match that sequence. For
449example, Unicode says that the letter C<LATIN SMALL LETTER SHARP S>
450should match the sequence C<ss> under C</i> rules. Thus,
451
452 'ss' =~ /\A\N{LATIN SMALL LETTER SHARP S}\z/i # Matches
453 'ss' =~ /\A[aeioust\N{LATIN SMALL LETTER SHARP S}]\z/i # Matches
454
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455For this to happen, the character must be explicitly specified, and not
456be part of a multi-character range (not even as one of its endpoints).
457(L</Character Ranges> will be explained shortly.) Therefore,
458
459 'ss' =~ /\A[\0-\x{ff}]\z/i # Doesn't match
460 'ss' =~ /\A[\0-\N{LATIN SMALL LETTER SHARP S}]\z/i # No match
461 'ss' =~ /\A[\xDF-\xDF]\z/i # Matches on ASCII platforms, since \XDF
462 # is LATIN SMALL LETTER SHARP S, and the
463 # range is just a single element
464
465Note that it isn't a good idea to specify these types of ranges anyway.
466
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467=head3 Special Characters Inside a Bracketed Character Class
468
469Most characters that are meta characters in regular expressions (that
df225385 470is, characters that carry a special meaning like C<.>, C<*>, or C<(>) lose
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471their special meaning and can be used inside a character class without
472the need to escape them. For instance, C<[()]> matches either an opening
473parenthesis, or a closing parenthesis, and the parens inside the character
474class don't group or capture.
475
476Characters that may carry a special meaning inside a character class are:
477C<\>, C<^>, C<->, C<[> and C<]>, and are discussed below. They can be
478escaped with a backslash, although this is sometimes not needed, in which
479case the backslash may be omitted.
480
481The sequence C<\b> is special inside a bracketed character class. While
6b83a163 482outside the character class, C<\b> is an assertion indicating a point
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483that does not have either two word characters or two non-word characters
484on either side, inside a bracketed character class, C<\b> matches a
485backspace character.
486
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487The sequences
488C<\a>,
489C<\c>,
490C<\e>,
491C<\f>,
492C<\n>,
e526e8bb 493C<\N{I<NAME>}>,
765fa144 494C<\N{U+I<hex char>}>,
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495C<\r>,
496C<\t>,
497and
498C<\x>
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499are also special and have the same meanings as they do outside a
500bracketed character class. (However, inside a bracketed character
501class, if C<\N{I<NAME>}> expands to a sequence of characters, only the first
502one in the sequence is used, with a warning.)
df225385 503
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504Also, a backslash followed by two or three octal digits is considered an octal
505number.
df225385 506
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507A C<[> is not special inside a character class, unless it's the start of a
508POSIX character class (see L</POSIX Character Classes> below). It normally does
509not need escaping.
8a118206 510
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511A C<]> is normally either the end of a POSIX character class (see
512L</POSIX Character Classes> below), or it signals the end of the bracketed
513character class. If you want to include a C<]> in the set of characters, you
514must generally escape it.
b6538e4f 515
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516However, if the C<]> is the I<first> (or the second if the first
517character is a caret) character of a bracketed character class, it
518does not denote the end of the class (as you cannot have an empty class)
519and is considered part of the set of characters that can be matched without
520escaping.
521
522Examples:
523
524 "+" =~ /[+?*]/ # Match, "+" in a character class is not special.
525 "\cH" =~ /[\b]/ # Match, \b inside in a character class
c1c4ae3a 526 # is equivalent to a backspace.
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527 "]" =~ /[][]/ # Match, as the character class contains.
528 # both [ and ].
529 "[]" =~ /[[]]/ # Match, the pattern contains a character class
530 # containing just ], and the character class is
531 # followed by a ].
532
533=head3 Character Ranges
534
535It is not uncommon to want to match a range of characters. Luckily, instead
b6538e4f 536of listing all characters in the range, one may use the hyphen (C<->).
8a118206 537If inside a bracketed character class you have two characters separated
b6538e4f 538by a hyphen, it's treated as if all characters between the two were in
8a118206 539the class. For instance, C<[0-9]> matches any ASCII digit, and C<[a-m]>
e2cfb18c 540matches any lowercase letter from the first half of the ASCII alphabet.
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541
542Note that the two characters on either side of the hyphen are not
765fa144 543necessarily both letters or both digits. Any character is possible,
8a118206 544although not advisable. C<['-?]> contains a range of characters, but
b6538e4f 545most people will not know which characters that means. Furthermore,
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546such ranges may lead to portability problems if the code has to run on
547a platform that uses a different character set, such as EBCDIC.
548
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549If a hyphen in a character class cannot syntactically be part of a range, for
550instance because it is the first or the last character of the character class,
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551or if it immediately follows a range, the hyphen isn't special, and so is
552considered a character to be matched literally. If you want a hyphen in
553your set of characters to be matched and its position in the class is such
554that it could be considered part of a range, you must escape that hyphen
555with a backslash.
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556
557Examples:
558
559 [a-z] # Matches a character that is a lower case ASCII letter.
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560 [a-fz] # Matches any letter between 'a' and 'f' (inclusive) or
561 # the letter 'z'.
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562 [-z] # Matches either a hyphen ('-') or the letter 'z'.
563 [a-f-m] # Matches any letter between 'a' and 'f' (inclusive), the
564 # hyphen ('-'), or the letter 'm'.
565 ['-?] # Matches any of the characters '()*+,-./0123456789:;<=>?
566 # (But not on an EBCDIC platform).
567
568
569=head3 Negation
570
571It is also possible to instead list the characters you do not want to
572match. You can do so by using a caret (C<^>) as the first character in the
b6538e4f 573character class. For instance, C<[^a-z]> matches any character that is not a
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574lowercase ASCII letter, which therefore includes more than a million
575Unicode code points. The class is said to be "negated" or "inverted".
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576
577This syntax make the caret a special character inside a bracketed character
578class, but only if it is the first character of the class. So if you want
82206b5e 579the caret as one of the characters to match, either escape the caret or
e2cfb18c 580else don't list it first.
8a118206 581
1f59b283 582In inverted bracketed character classes, Perl ignores the Unicode rules
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583that normally say that certain characters should match a sequence of
584multiple characters under caseless C</i> matching. Following those
585rules could lead to highly confusing situations:
1f59b283 586
582da942 587 "ss" =~ /^[^\xDF]+$/ui; # Matches!
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588
589This should match any sequences of characters that aren't C<\xDF> nor
590what C<\xDF> matches under C</i>. C<"s"> isn't C<\xDF>, but Unicode
591says that C<"ss"> is what C<\xDF> matches under C</i>. So which one
592"wins"? Do you fail the match because the string has C<ss> or accept it
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593because it has an C<s> followed by another C<s>? Perl has chosen the
594latter.
1f59b283 595
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596Examples:
597
598 "e" =~ /[^aeiou]/ # No match, the 'e' is listed.
599 "x" =~ /[^aeiou]/ # Match, as 'x' isn't a lowercase vowel.
600 "^" =~ /[^^]/ # No match, matches anything that isn't a caret.
601 "^" =~ /[x^]/ # Match, caret is not special here.
602
603=head3 Backslash Sequences
604
ea449505 605You can put any backslash sequence character class (with the exception of
765fa144 606C<\N> and C<\R>) inside a bracketed character class, and it will act just
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607as if you had put all characters matched by the backslash sequence inside the
608character class. For instance, C<[a-f\d]> matches any decimal digit, or any
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609of the lowercase letters between 'a' and 'f' inclusive.
610
611C<\N> within a bracketed character class must be of the forms C<\N{I<name>}>
765fa144 612or C<\N{U+I<hex char>}>, and NOT be the form that matches non-newlines,
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613for the same reason that a dot C<.> inside a bracketed character class loses
614its special meaning: it matches nearly anything, which generally isn't what you
615want to happen.
df225385 616
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617
618Examples:
619
620 /[\p{Thai}\d]/ # Matches a character that is either a Thai
621 # character, or a digit.
622 /[^\p{Arabic}()]/ # Matches a character that is neither an Arabic
623 # character, nor a parenthesis.
624
625Backslash sequence character classes cannot form one of the endpoints
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626of a range. Thus, you can't say:
627
628 /[\p{Thai}-\d]/ # Wrong!
8a118206 629
6b83a163 630=head3 POSIX Character Classes
ea449505 631X<character class> X<\p> X<\p{}>
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632X<alpha> X<alnum> X<ascii> X<blank> X<cntrl> X<digit> X<graph>
633X<lower> X<print> X<punct> X<space> X<upper> X<word> X<xdigit>
8a118206 634
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635POSIX character classes have the form C<[:class:]>, where I<class> is
636name, and the C<[:> and C<:]> delimiters. POSIX character classes only appear
8a118206 637I<inside> bracketed character classes, and are a convenient and descriptive
82206b5e 638way of listing a group of characters.
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639
640Be careful about the syntax,
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641
642 # Correct:
643 $string =~ /[[:alpha:]]/
644
645 # Incorrect (will warn):
646 $string =~ /[:alpha:]/
647
648The latter pattern would be a character class consisting of a colon,
649and the letters C<a>, C<l>, C<p> and C<h>.
82206b5e 650POSIX character classes can be part of a larger bracketed character class.
b6538e4f 651For example,
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652
653 [01[:alpha:]%]
654
655is valid and matches '0', '1', any alphabetic character, and the percent sign.
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656
657Perl recognizes the following POSIX character classes:
658
ea449505 659 alpha Any alphabetical character ("[A-Za-z]").
b6538e4f 660 alnum Any alphanumeric character. ("[A-Za-z0-9]")
ea449505 661 ascii Any character in the ASCII character set.
ea8b8ad2 662 blank A GNU extension, equal to a space or a horizontal tab ("\t").
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663 cntrl Any control character. See Note [2] below.
664 digit Any decimal digit ("[0-9]"), equivalent to "\d".
665 graph Any printable character, excluding a space. See Note [3] below.
666 lower Any lowercase character ("[a-z]").
667 print Any printable character, including a space. See Note [4] below.
c1c4ae3a 668 punct Any graphical character excluding "word" characters. Note [5].
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669 space Any whitespace character. "\s" plus the vertical tab ("\cK").
670 upper Any uppercase character ("[A-Z]").
671 word A Perl extension ("[A-Za-z0-9_]"), equivalent to "\w".
672 xdigit Any hexadecimal digit ("[0-9a-fA-F]").
673
674Most POSIX character classes have two Unicode-style C<\p> property
675counterparts. (They are not official Unicode properties, but Perl extensions
676derived from official Unicode properties.) The table below shows the relation
677between POSIX character classes and these counterparts.
678
679One counterpart, in the column labelled "ASCII-range Unicode" in
b6538e4f 680the table, matches only characters in the ASCII character set.
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681
682The other counterpart, in the column labelled "Full-range Unicode", matches any
683appropriate characters in the full Unicode character set. For example,
b6538e4f 684C<\p{Alpha}> matches not just the ASCII alphabetic characters, but any
82206b5e 685character in the entire Unicode character set considered alphabetic.
582da942 686An entry in the column labelled "backslash sequence" is a (short)
5db9882c 687equivalent.
ea449505 688
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689 [[:...:]] ASCII-range Full-range backslash Note
690 Unicode Unicode sequence
ea449505 691 -----------------------------------------------------
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692 alpha \p{PosixAlpha} \p{XPosixAlpha}
693 alnum \p{PosixAlnum} \p{XPosixAlnum}
82206b5e 694 ascii \p{ASCII}
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695 blank \p{PosixBlank} \p{XPosixBlank} \h [1]
696 or \p{HorizSpace} [1]
697 cntrl \p{PosixCntrl} \p{XPosixCntrl} [2]
698 digit \p{PosixDigit} \p{XPosixDigit} \d
699 graph \p{PosixGraph} \p{XPosixGraph} [3]
700 lower \p{PosixLower} \p{XPosixLower}
701 print \p{PosixPrint} \p{XPosixPrint} [4]
702 punct \p{PosixPunct} \p{XPosixPunct} [5]
703 \p{PerlSpace} \p{XPerlSpace} \s [6]
704 space \p{PosixSpace} \p{XPosixSpace} [6]
705 upper \p{PosixUpper} \p{XPosixUpper}
706 word \p{PosixWord} \p{XPosixWord} \w
82206b5e 707 xdigit \p{PosixXDigit} \p{XPosixXDigit}
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708
709=over 4
710
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711=item [1]
712
713C<\p{Blank}> and C<\p{HorizSpace}> are synonyms.
714
715=item [2]
8a118206 716
ea449505 717Control characters don't produce output as such, but instead usually control
b6538e4f 718the terminal somehow: for example, newline and backspace are control characters.
82206b5e 719In the ASCII range, characters whose code points are between 0 and 31 inclusive,
ea449505 720plus 127 (C<DEL>) are control characters.
8a118206 721
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722On EBCDIC platforms, it is likely that the code page will define C<[[:cntrl:]]>
723to be the EBCDIC equivalents of the ASCII controls, plus the controls
bc943be5 724that in Unicode have code points from 128 through 159.
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725
726=item [3]
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727
728Any character that is I<graphical>, that is, visible. This class consists
b6538e4f 729of all alphanumeric characters and all punctuation characters.
8a118206 730
ea449505 731=item [4]
8a118206 732
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733All printable characters, which is the set of all graphical characters
734plus those whitespace characters which are not also controls.
ea449505 735
b6dac59a 736=item [5]
ea449505 737
b6538e4f 738C<\p{PosixPunct}> and C<[[:punct:]]> in the ASCII range match all
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739non-controls, non-alphanumeric, non-space characters:
740C<[-!"#$%&'()*+,./:;<=E<gt>?@[\\\]^_`{|}~]> (although if a locale is in effect,
741it could alter the behavior of C<[[:punct:]]>).
742
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743The similarly named property, C<\p{Punct}>, matches a somewhat different
744set in the ASCII range, namely
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745C<[-!"#%&'()*,./:;?@[\\\]_{}]>. That is, it is missing the nine
746characters C<[$+E<lt>=E<gt>^`|~]>.
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747This is because Unicode splits what POSIX considers to be punctuation into two
748categories, Punctuation and Symbols.
749
e2cfb18c 750C<\p{XPosixPunct}> and (under Unicode rules) C<[[:punct:]]>, match what
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751C<\p{PosixPunct}> matches in the ASCII range, plus what C<\p{Punct}>
752matches. This is different than strictly matching according to
753C<\p{Punct}>. Another way to say it is that
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754if Unicode rules are in effect, C<[[:punct:]]> matches all characters
755that Unicode considers punctuation, plus all ASCII-range characters that
756Unicode considers symbols.
8a118206 757
ea449505 758=item [6]
8a118206 759
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760C<\p{SpacePerl}> and C<\p{Space}> differ only in that in non-locale
761matching, C<\p{Space}> additionally
ea449505 762matches the vertical tab, C<\cK>. Same for the two ASCII-only range forms.
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763
764=back
765
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766There are various other synonyms that can be used besides the names
767listed in the table. For example, C<\p{PosixAlpha}> can be written as
768C<\p{Alpha}>. All are listed in
769L<perluniprops/Properties accessible through \p{} and \P{}>,
770plus all characters matched by each ASCII-range property.
771
772Both the C<\p> counterparts always assume Unicode rules are in effect.
773On ASCII platforms, this means they assume that the code points from 128
774to 255 are Latin-1, and that means that using them under locale rules is
775unwise unless the locale is guaranteed to be Latin-1 or UTF-8. In contrast, the
776POSIX character classes are useful under locale rules. They are
777affected by the actual rules in effect, as follows:
778
779=over
780
781=item If the C</a> modifier, is in effect ...
782
783Each of the POSIX classes matches exactly the same as their ASCII-range
784counterparts.
785
786=item otherwise ...
787
788=over
789
790=item For code points above 255 ...
791
792The POSIX class matches the same as its Full-range counterpart.
793
794=item For code points below 256 ...
795
796=over
797
798=item if locale rules are in effect ...
799
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800The POSIX class matches according to the locale, except that
801C<word> uses the platform's native underscore character, no matter what
802the locale is.
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803
804=item if Unicode rules are in effect or if on an EBCDIC platform ...
805
806The POSIX class matches the same as the Full-range counterpart.
807
808=item otherwise ...
809
810The POSIX class matches the same as the ASCII range counterpart.
811
812=back
813
814=back
815
816=back
817
818Which rules apply are determined as described in
819L<perlre/Which character set modifier is in effect?>.
820
821It is proposed to change this behavior in a future release of Perl so that
822whether or not Unicode rules are in effect would not change the
823behavior: Outside of locale or an EBCDIC code page, the POSIX classes
824would behave like their ASCII-range counterparts. If you wish to
825comment on this proposal, send email to C<perl5-porters@perl.org>.
cbc24f92 826
1f59b283 827=head4 Negation of POSIX character classes
ea449505 828X<character class, negation>
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829
830A Perl extension to the POSIX character class is the ability to
831negate it. This is done by prefixing the class name with a caret (C<^>).
832Some examples:
833
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834 POSIX ASCII-range Full-range backslash
835 Unicode Unicode sequence
836 -----------------------------------------------------
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837 [[:^digit:]] \P{PosixDigit} \P{XPosixDigit} \D
838 [[:^space:]] \P{PosixSpace} \P{XPosixSpace}
839 \P{PerlSpace} \P{XPerlSpace} \S
840 [[:^word:]] \P{PerlWord} \P{XPosixWord} \W
841
765fa144 842The backslash sequence can mean either ASCII- or Full-range Unicode,
82206b5e 843depending on various factors as described in L<perlre/Which character set modifier is in effect?>.
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844
845=head4 [= =] and [. .]
846
b6538e4f 847Perl recognizes the POSIX character classes C<[=class=]> and
82206b5e 848C<[.class.]>, but does not (yet?) support them. Any attempt to use
b6538e4f 849either construct raises an exception.
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850
851=head4 Examples
852
853 /[[:digit:]]/ # Matches a character that is a digit.
854 /[01[:lower:]]/ # Matches a character that is either a
855 # lowercase letter, or '0' or '1'.
c1c4ae3a 856 /[[:digit:][:^xdigit:]]/ # Matches a character that can be anything
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857 # except the letters 'a' to 'f' and 'A' to
858 # 'F'. This is because the main character
859 # class is composed of two POSIX character
860 # classes that are ORed together, one that
861 # matches any digit, and the other that
862 # matches anything that isn't a hex digit.
863 # The OR adds the digits, leaving only the
864 # letters 'a' to 'f' and 'A' to 'F' excluded.