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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
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>.
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92If the C</a> regular expression modifier in effect, it matches [0-9].
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
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112than they actually do. L<Unicode::UCDE<sol>num()|Unicode::UCD/num> can
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 ("_"). It does not match a whole word. To match a whole
82206b5e 145word, use C<\w+>. This isn't the same thing as matching an English word, but
765fa144 146in the ASCII range it is the same as a string of Perl-identifier
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147characters.
148
149=over
150
151=item If the C</a> modifier is in effect ...
152
153C<\w> matches the 63 characters [a-zA-Z0-9_].
154
155=item otherwise ...
156
157=over
158
159=item For code points above 255 ...
160
161C<\w> matches the same as C<\p{Word}> matches in this range. That is,
162it matches Thai letters, Greek letters, etc. This includes connector
d35dd6c6 163punctuation (like the underscore) which connect two words together, or
b6538e4f 164diacritics, such as a C<COMBINING TILDE> and the modifier letters, which
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165are generally used to add auxiliary markings to letters.
166
167=item For code points below 256 ...
168
169=over
170
171=item if locale rules are in effect ...
172
173C<\w> matches the platform's native underscore character plus whatever
174the locale considers to be alphanumeric.
175
176=item if Unicode rules are in effect or if on an EBCDIC platform ...
177
178C<\w> matches exactly what C<\p{Word}> matches.
179
180=item otherwise ...
181
182C<\w> matches [a-zA-Z0-9_].
183
184=back
185
186=back
187
188=back
189
190Which rules apply are determined as described in L<perlre/Which character set modifier is in effect?>.
8a118206 191
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192There are a number of security issues with the full Unicode list of word
193characters. See L<http://unicode.org/reports/tr36>.
194
195Also, for a somewhat finer-grained set of characters that are in programming
196language identifiers beyond the ASCII range, you may wish to instead use the
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197more customized L</Unicode Properties>, C<\p{ID_Start}>,
198C<\p{ID_Continue}>, C<\p{XID_Start}>, and C<\p{XID_Continue}>. See
199L<http://unicode.org/reports/tr31>.
6b83a163 200
b6538e4f 201Any character not matched by C<\w> is matched by C<\W>.
8a118206 202
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203=head3 Whitespace
204
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205C<\s> matches any single character considered whitespace.
206
207=over
208
209=item If the C</a> modifier is in effect ...
210
211C<\s> matches the 5 characters [\t\n\f\r ]; that is, the horizontal tab,
212the newline, the form feed, the carriage return, and the space. (Note
213that it doesn't match the vertical tab, C<\cK> on ASCII platforms.)
214
215=item otherwise ...
216
217=over
218
219=item For code points above 255 ...
220
221C<\s> matches exactly the code points above 255 shown with an "s" column
222in the table below.
223
224=item For code points below 256 ...
225
226=over
227
228=item if locale rules are in effect ...
229
230C<\s> matches whatever the locale considers to be whitespace. Note that
231this is likely to include the vertical space, unlike non-locale C<\s>
232matching.
233
234=item if Unicode rules are in effect or if on an EBCDIC platform ...
235
236C<\s> matches exactly the characters shown with an "s" column in the
237table below.
238
239=item otherwise ...
240
241C<\s> matches [\t\n\f\r ].
242Note that this list doesn't include the non-breaking space.
243
244=back
245
246=back
247
248=back
249
250Which rules apply are determined as described in L<perlre/Which character set modifier is in effect?>.
8a118206 251
b6538e4f 252Any character not matched by C<\s> is matched by C<\S>.
8a118206 253
b6538e4f 254C<\h> matches any character considered horizontal whitespace;
82206b5e 255this includes the space and tab characters and several others
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256listed in the table below. C<\H> matches any character
257not considered horizontal whitespace.
ea449505 258
b6538e4f 259C<\v> matches any character considered vertical whitespace;
82206b5e 260this includes the carriage return and line feed characters (newline)
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261plus several other characters, all listed in the table below.
262C<\V> matches any character not considered vertical whitespace.
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263
264C<\R> matches anything that can be considered a newline under Unicode
265rules. It's not a character class, as it can match a multi-character
266sequence. Therefore, it cannot be used inside a bracketed character
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267class; use C<\v> instead (vertical whitespace).
268Details are discussed in L<perlrebackslash>.
8a118206 269
82206b5e 270Note that unlike C<\s> (and C<\d> and C<\w>), C<\h> and C<\v> always match
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271the same characters, without regard to other factors, such as whether the
272source string is in UTF-8 format.
8a118206 273
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274One might think that C<\s> is equivalent to C<[\h\v]>. This is not true.
275For example, the vertical tab (C<"\x0b">) is not matched by C<\s>, it is
276however considered vertical whitespace.
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277
278The following table is a complete listing of characters matched by
82206b5e 279C<\s>, C<\h> and C<\v> as of Unicode 6.0.
8a118206 280
582da942 281The first column gives the Unicode code point of the character (in hex format),
8a118206 282the second column gives the (Unicode) name. The third column indicates
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283by which class(es) the character is matched (assuming no locale or EBCDIC code
284page is in effect that changes the C<\s> matching).
8a118206 285
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286 0x0009 CHARACTER TABULATION h s
287 0x000a LINE FEED (LF) vs
288 0x000b LINE TABULATION v
289 0x000c FORM FEED (FF) vs
290 0x000d CARRIAGE RETURN (CR) vs
291 0x0020 SPACE h s
292 0x0085 NEXT LINE (NEL) vs [1]
293 0x00a0 NO-BREAK SPACE h s [1]
294 0x1680 OGHAM SPACE MARK h s
295 0x180e MONGOLIAN VOWEL SEPARATOR h s
296 0x2000 EN QUAD h s
297 0x2001 EM QUAD h s
298 0x2002 EN SPACE h s
299 0x2003 EM SPACE h s
300 0x2004 THREE-PER-EM SPACE h s
301 0x2005 FOUR-PER-EM SPACE h s
302 0x2006 SIX-PER-EM SPACE h s
303 0x2007 FIGURE SPACE h s
304 0x2008 PUNCTUATION SPACE h s
305 0x2009 THIN SPACE h s
306 0x200a HAIR SPACE h s
307 0x2028 LINE SEPARATOR vs
308 0x2029 PARAGRAPH SEPARATOR vs
309 0x202f NARROW NO-BREAK SPACE h s
310 0x205f MEDIUM MATHEMATICAL SPACE h s
311 0x3000 IDEOGRAPHIC SPACE h s
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312
313=over 4
314
315=item [1]
316
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317NEXT LINE and NO-BREAK SPACE may or may not match C<\s> depending
318on the rules in effect. See
319L<the beginning of this section|/Whitespace>.
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320
321=back
322
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323=head3 Unicode Properties
324
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325C<\pP> and C<\p{Prop}> are character classes to match characters that fit given
326Unicode properties. One letter property names can be used in the C<\pP> form,
327with the property name following the C<\p>, otherwise, braces are required.
328When using braces, there is a single form, which is just the property name
329enclosed in the braces, and a compound form which looks like C<\p{name=value}>,
b6538e4f 330which means to match if the property "name" for the character has that particular
c1c4ae3a 331"value".
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332For instance, a match for a number can be written as C</\pN/> or as
333C</\p{Number}/>, or as C</\p{Number=True}/>.
334Lowercase letters are matched by the property I<Lowercase_Letter> which
e2cfb18c 335has the short form I<Ll>. They need the braces, so are written as C</\p{Ll}/> or
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336C</\p{Lowercase_Letter}/>, or C</\p{General_Category=Lowercase_Letter}/>
337(the underscores are optional).
338C</\pLl/> is valid, but means something different.
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339It matches a two character string: a letter (Unicode property C<\pL>),
340followed by a lowercase C<l>.
341
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342If neither the C</a> modifier nor locale rules are in effect, the use of
343a Unicode property will force the regular expression into using Unicode
344rules.
345
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346Note that almost all properties are immune to case-insensitive matching.
347That is, adding a C</i> regular expression modifier does not change what
82206b5e 348they match. There are two sets that are affected. The first set is
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349C<Uppercase_Letter>,
350C<Lowercase_Letter>,
351and C<Titlecase_Letter>,
352all of which match C<Cased_Letter> under C</i> matching.
b6538e4f 353The second set is
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354C<Uppercase>,
355C<Lowercase>,
356and C<Titlecase>,
357all of which match C<Cased> under C</i> matching.
358(The difference between these sets is that some things, such as Roman
e2cfb18c 359numerals, come in both upper and lower case, so they are C<Cased>, but
b6538e4f 360aren't considered to be letters, so they aren't C<Cased_Letter>s. They're
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361actually C<Letter_Number>s.)
362This set also includes its subsets C<PosixUpper> and C<PosixLower>, both
e2cfb18c 363of which under C</i> match C<PosixAlpha>.
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364
365For more details on Unicode properties, see L<perlunicode/Unicode
366Character Properties>; for a
e1b711da 367complete list of possible properties, see
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368L<perluniprops/Properties accessible through \p{} and \P{}>,
369which notes all forms that have C</i> differences.
e1b711da 370It is also possible to define your own properties. This is discussed in
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371L<perlunicode/User-Defined Character Properties>.
372
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373=head4 Examples
374
375 "a" =~ /\w/ # Match, "a" is a 'word' character.
376 "7" =~ /\w/ # Match, "7" is a 'word' character as well.
377 "a" =~ /\d/ # No match, "a" isn't a digit.
378 "7" =~ /\d/ # Match, "7" is a digit.
ea449505 379 " " =~ /\s/ # Match, a space is whitespace.
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380 "a" =~ /\D/ # Match, "a" is a non-digit.
381 "7" =~ /\D/ # No match, "7" is not a non-digit.
ea449505 382 " " =~ /\S/ # No match, a space is not non-whitespace.
8a118206 383
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384 " " =~ /\h/ # Match, space is horizontal whitespace.
385 " " =~ /\v/ # No match, space is not vertical whitespace.
386 "\r" =~ /\v/ # Match, a return is vertical whitespace.
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387
388 "a" =~ /\pL/ # Match, "a" is a letter.
389 "a" =~ /\p{Lu}/ # No match, /\p{Lu}/ matches upper case letters.
390
391 "\x{0e0b}" =~ /\p{Thai}/ # Match, \x{0e0b} is the character
392 # 'THAI CHARACTER SO SO', and that's in
393 # Thai Unicode class.
ea449505 394 "a" =~ /\P{Lao}/ # Match, as "a" is not a Laotian character.
8a118206 395
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396It is worth emphasizing that C<\d>, C<\w>, etc, match single characters, not
397complete numbers or words. To match a number (that consists of digits),
398use C<\d+>; to match a word, use C<\w+>. But be aware of the security
399considerations in doing so, as mentioned above.
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400
401=head2 Bracketed Character Classes
402
403The third form of character class you can use in Perl regular expressions
6b83a163 404is the bracketed character class. In its simplest form, it lists the characters
c1c4ae3a 405that may be matched, surrounded by square brackets, like this: C<[aeiou]>.
ea449505 406This matches one of C<a>, C<e>, C<i>, C<o> or C<u>. Like the other
1f59b283 407character classes, exactly one character is matched.* To match
ea449505 408a longer string consisting of characters mentioned in the character
6b83a163 409class, follow the character class with a L<quantifier|perlre/Quantifiers>. For
b6538e4f 410instance, C<[aeiou]+> matches one or more lowercase English vowels.
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411
412Repeating a character in a character class has no
413effect; it's considered to be in the set only once.
414
415Examples:
416
417 "e" =~ /[aeiou]/ # Match, as "e" is listed in the class.
418 "p" =~ /[aeiou]/ # No match, "p" is not listed in the class.
419 "ae" =~ /^[aeiou]$/ # No match, a character class only matches
420 # a single character.
421 "ae" =~ /^[aeiou]+$/ # Match, due to the quantifier.
422
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423 -------
424
88a4f93e 425* There is an exception to a bracketed character class matching only a
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426single character. When the class is to match caselessely under C</i>
427matching rules, and a character inside the class matches a
428multiple-character sequence caselessly under Unicode rules, the class
429(when not L<inverted|/Negation>) will also match that sequence. For
430example, Unicode says that the letter C<LATIN SMALL LETTER SHARP S>
431should match the sequence C<ss> under C</i> rules. Thus,
432
433 'ss' =~ /\A\N{LATIN SMALL LETTER SHARP S}\z/i # Matches
434 'ss' =~ /\A[aeioust\N{LATIN SMALL LETTER SHARP S}]\z/i # Matches
435
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436=head3 Special Characters Inside a Bracketed Character Class
437
438Most characters that are meta characters in regular expressions (that
df225385 439is, characters that carry a special meaning like C<.>, C<*>, or C<(>) lose
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440their special meaning and can be used inside a character class without
441the need to escape them. For instance, C<[()]> matches either an opening
442parenthesis, or a closing parenthesis, and the parens inside the character
443class don't group or capture.
444
445Characters that may carry a special meaning inside a character class are:
446C<\>, C<^>, C<->, C<[> and C<]>, and are discussed below. They can be
447escaped with a backslash, although this is sometimes not needed, in which
448case the backslash may be omitted.
449
450The sequence C<\b> is special inside a bracketed character class. While
6b83a163 451outside the character class, C<\b> is an assertion indicating a point
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452that does not have either two word characters or two non-word characters
453on either side, inside a bracketed character class, C<\b> matches a
454backspace character.
455
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456The sequences
457C<\a>,
458C<\c>,
459C<\e>,
460C<\f>,
461C<\n>,
e526e8bb 462C<\N{I<NAME>}>,
765fa144 463C<\N{U+I<hex char>}>,
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464C<\r>,
465C<\t>,
466and
467C<\x>
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468are also special and have the same meanings as they do outside a
469bracketed character class. (However, inside a bracketed character
470class, if C<\N{I<NAME>}> expands to a sequence of characters, only the first
471one in the sequence is used, with a warning.)
df225385 472
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473Also, a backslash followed by two or three octal digits is considered an octal
474number.
df225385 475
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476A C<[> is not special inside a character class, unless it's the start of a
477POSIX character class (see L</POSIX Character Classes> below). It normally does
478not need escaping.
8a118206 479
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480A C<]> is normally either the end of a POSIX character class (see
481L</POSIX Character Classes> below), or it signals the end of the bracketed
482character class. If you want to include a C<]> in the set of characters, you
483must generally escape it.
b6538e4f 484
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485However, if the C<]> is the I<first> (or the second if the first
486character is a caret) character of a bracketed character class, it
487does not denote the end of the class (as you cannot have an empty class)
488and is considered part of the set of characters that can be matched without
489escaping.
490
491Examples:
492
493 "+" =~ /[+?*]/ # Match, "+" in a character class is not special.
494 "\cH" =~ /[\b]/ # Match, \b inside in a character class
c1c4ae3a 495 # is equivalent to a backspace.
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496 "]" =~ /[][]/ # Match, as the character class contains.
497 # both [ and ].
498 "[]" =~ /[[]]/ # Match, the pattern contains a character class
499 # containing just ], and the character class is
500 # followed by a ].
501
502=head3 Character Ranges
503
504It is not uncommon to want to match a range of characters. Luckily, instead
b6538e4f 505of listing all characters in the range, one may use the hyphen (C<->).
8a118206 506If inside a bracketed character class you have two characters separated
b6538e4f 507by a hyphen, it's treated as if all characters between the two were in
8a118206 508the class. For instance, C<[0-9]> matches any ASCII digit, and C<[a-m]>
e2cfb18c 509matches any lowercase letter from the first half of the ASCII alphabet.
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510
511Note that the two characters on either side of the hyphen are not
765fa144 512necessarily both letters or both digits. Any character is possible,
8a118206 513although not advisable. C<['-?]> contains a range of characters, but
b6538e4f 514most people will not know which characters that means. Furthermore,
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515such ranges may lead to portability problems if the code has to run on
516a platform that uses a different character set, such as EBCDIC.
517
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518If a hyphen in a character class cannot syntactically be part of a range, for
519instance because it is the first or the last character of the character class,
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520or if it immediately follows a range, the hyphen isn't special, and so is
521considered a character to be matched literally. If you want a hyphen in
522your set of characters to be matched and its position in the class is such
523that it could be considered part of a range, you must escape that hyphen
524with a backslash.
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525
526Examples:
527
528 [a-z] # Matches a character that is a lower case ASCII letter.
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529 [a-fz] # Matches any letter between 'a' and 'f' (inclusive) or
530 # the letter 'z'.
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531 [-z] # Matches either a hyphen ('-') or the letter 'z'.
532 [a-f-m] # Matches any letter between 'a' and 'f' (inclusive), the
533 # hyphen ('-'), or the letter 'm'.
534 ['-?] # Matches any of the characters '()*+,-./0123456789:;<=>?
535 # (But not on an EBCDIC platform).
536
537
538=head3 Negation
539
540It is also possible to instead list the characters you do not want to
541match. You can do so by using a caret (C<^>) as the first character in the
b6538e4f 542character class. For instance, C<[^a-z]> matches any character that is not a
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543lowercase ASCII letter, which therefore includes more than a million
544Unicode code points. The class is said to be "negated" or "inverted".
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545
546This syntax make the caret a special character inside a bracketed character
547class, but only if it is the first character of the class. So if you want
82206b5e 548the caret as one of the characters to match, either escape the caret or
e2cfb18c 549else don't list it first.
8a118206 550
1f59b283 551In inverted bracketed character classes, Perl ignores the Unicode rules
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552that normally say that certain characters match a sequence of multiple
553characters under caseless C</i> matching. Following those rules
554can lead to highly confusing situations:
1f59b283 555
582da942 556 "ss" =~ /^[^\xDF]+$/ui; # Matches!
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557
558This should match any sequences of characters that aren't C<\xDF> nor
559what C<\xDF> matches under C</i>. C<"s"> isn't C<\xDF>, but Unicode
560says that C<"ss"> is what C<\xDF> matches under C</i>. So which one
561"wins"? Do you fail the match because the string has C<ss> or accept it
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562because it has an C<s> followed by another C<s>? Perl has chosen the
563latter.
1f59b283 564
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565Examples:
566
567 "e" =~ /[^aeiou]/ # No match, the 'e' is listed.
568 "x" =~ /[^aeiou]/ # Match, as 'x' isn't a lowercase vowel.
569 "^" =~ /[^^]/ # No match, matches anything that isn't a caret.
570 "^" =~ /[x^]/ # Match, caret is not special here.
571
572=head3 Backslash Sequences
573
ea449505 574You can put any backslash sequence character class (with the exception of
765fa144 575C<\N> and C<\R>) inside a bracketed character class, and it will act just
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576as if you had put all characters matched by the backslash sequence inside the
577character class. For instance, C<[a-f\d]> matches any decimal digit, or any
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578of the lowercase letters between 'a' and 'f' inclusive.
579
580C<\N> within a bracketed character class must be of the forms C<\N{I<name>}>
765fa144 581or C<\N{U+I<hex char>}>, and NOT be the form that matches non-newlines,
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582for the same reason that a dot C<.> inside a bracketed character class loses
583its special meaning: it matches nearly anything, which generally isn't what you
584want to happen.
df225385 585
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586
587Examples:
588
589 /[\p{Thai}\d]/ # Matches a character that is either a Thai
590 # character, or a digit.
591 /[^\p{Arabic}()]/ # Matches a character that is neither an Arabic
592 # character, nor a parenthesis.
593
594Backslash sequence character classes cannot form one of the endpoints
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595of a range. Thus, you can't say:
596
597 /[\p{Thai}-\d]/ # Wrong!
8a118206 598
6b83a163 599=head3 POSIX Character Classes
ea449505 600X<character class> X<\p> X<\p{}>
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601X<alpha> X<alnum> X<ascii> X<blank> X<cntrl> X<digit> X<graph>
602X<lower> X<print> X<punct> X<space> X<upper> X<word> X<xdigit>
8a118206 603
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604POSIX character classes have the form C<[:class:]>, where I<class> is
605name, and the C<[:> and C<:]> delimiters. POSIX character classes only appear
8a118206 606I<inside> bracketed character classes, and are a convenient and descriptive
82206b5e 607way of listing a group of characters.
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608
609Be careful about the syntax,
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610
611 # Correct:
612 $string =~ /[[:alpha:]]/
613
614 # Incorrect (will warn):
615 $string =~ /[:alpha:]/
616
617The latter pattern would be a character class consisting of a colon,
618and the letters C<a>, C<l>, C<p> and C<h>.
82206b5e 619POSIX character classes can be part of a larger bracketed character class.
b6538e4f 620For example,
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621
622 [01[:alpha:]%]
623
624is valid and matches '0', '1', any alphabetic character, and the percent sign.
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625
626Perl recognizes the following POSIX character classes:
627
ea449505 628 alpha Any alphabetical character ("[A-Za-z]").
b6538e4f 629 alnum Any alphanumeric character. ("[A-Za-z0-9]")
ea449505 630 ascii Any character in the ASCII character set.
ea8b8ad2 631 blank A GNU extension, equal to a space or a horizontal tab ("\t").
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632 cntrl Any control character. See Note [2] below.
633 digit Any decimal digit ("[0-9]"), equivalent to "\d".
634 graph Any printable character, excluding a space. See Note [3] below.
635 lower Any lowercase character ("[a-z]").
636 print Any printable character, including a space. See Note [4] below.
c1c4ae3a 637 punct Any graphical character excluding "word" characters. Note [5].
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638 space Any whitespace character. "\s" plus the vertical tab ("\cK").
639 upper Any uppercase character ("[A-Z]").
640 word A Perl extension ("[A-Za-z0-9_]"), equivalent to "\w".
641 xdigit Any hexadecimal digit ("[0-9a-fA-F]").
642
643Most POSIX character classes have two Unicode-style C<\p> property
644counterparts. (They are not official Unicode properties, but Perl extensions
645derived from official Unicode properties.) The table below shows the relation
646between POSIX character classes and these counterparts.
647
648One counterpart, in the column labelled "ASCII-range Unicode" in
b6538e4f 649the table, matches only characters in the ASCII character set.
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650
651The other counterpart, in the column labelled "Full-range Unicode", matches any
652appropriate characters in the full Unicode character set. For example,
b6538e4f 653C<\p{Alpha}> matches not just the ASCII alphabetic characters, but any
82206b5e 654character in the entire Unicode character set considered alphabetic.
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655An entry in the column labelled "backslash sequence" is a (short)
656synonym for the Full-range Unicode form.
ea449505 657
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658 [[:...:]] ASCII-range Full-range backslash Note
659 Unicode Unicode sequence
ea449505 660 -----------------------------------------------------
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661 alpha \p{PosixAlpha} \p{XPosixAlpha}
662 alnum \p{PosixAlnum} \p{XPosixAlnum}
82206b5e 663 ascii \p{ASCII}
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664 blank \p{PosixBlank} \p{XPosixBlank} \h [1]
665 or \p{HorizSpace} [1]
666 cntrl \p{PosixCntrl} \p{XPosixCntrl} [2]
667 digit \p{PosixDigit} \p{XPosixDigit} \d
668 graph \p{PosixGraph} \p{XPosixGraph} [3]
669 lower \p{PosixLower} \p{XPosixLower}
670 print \p{PosixPrint} \p{XPosixPrint} [4]
671 punct \p{PosixPunct} \p{XPosixPunct} [5]
672 \p{PerlSpace} \p{XPerlSpace} \s [6]
673 space \p{PosixSpace} \p{XPosixSpace} [6]
674 upper \p{PosixUpper} \p{XPosixUpper}
675 word \p{PosixWord} \p{XPosixWord} \w
82206b5e 676 xdigit \p{PosixXDigit} \p{XPosixXDigit}
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677
678=over 4
679
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680=item [1]
681
682C<\p{Blank}> and C<\p{HorizSpace}> are synonyms.
683
684=item [2]
8a118206 685
ea449505 686Control characters don't produce output as such, but instead usually control
b6538e4f 687the terminal somehow: for example, newline and backspace are control characters.
82206b5e 688In the ASCII range, characters whose code points are between 0 and 31 inclusive,
ea449505 689plus 127 (C<DEL>) are control characters.
8a118206 690
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691On EBCDIC platforms, it is likely that the code page will define C<[[:cntrl:]]>
692to be the EBCDIC equivalents of the ASCII controls, plus the controls
82206b5e 693that in Unicode have code pointss from 128 through 159.
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694
695=item [3]
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696
697Any character that is I<graphical>, that is, visible. This class consists
b6538e4f 698of all alphanumeric characters and all punctuation characters.
8a118206 699
ea449505 700=item [4]
8a118206 701
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702All printable characters, which is the set of all graphical characters
703plus those whitespace characters which are not also controls.
ea449505 704
b6dac59a 705=item [5]
ea449505 706
b6538e4f 707C<\p{PosixPunct}> and C<[[:punct:]]> in the ASCII range match all
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708non-controls, non-alphanumeric, non-space characters:
709C<[-!"#$%&'()*+,./:;<=E<gt>?@[\\\]^_`{|}~]> (although if a locale is in effect,
710it could alter the behavior of C<[[:punct:]]>).
711
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712The similarly named property, C<\p{Punct}>, matches a somewhat different
713set in the ASCII range, namely
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714C<[-!"#%&'()*,./:;?@[\\\]_{}]>. That is, it is missing C<[$+E<lt>=E<gt>^`|~]>.
715This is because Unicode splits what POSIX considers to be punctuation into two
716categories, Punctuation and Symbols.
717
e2cfb18c 718C<\p{XPosixPunct}> and (under Unicode rules) C<[[:punct:]]>, match what
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719C<\p{PosixPunct}> matches in the ASCII range, plus what C<\p{Punct}>
720matches. This is different than strictly matching according to
721C<\p{Punct}>. Another way to say it is that
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722if Unicode rules are in effect, C<[[:punct:]]> matches all characters
723that Unicode considers punctuation, plus all ASCII-range characters that
724Unicode considers symbols.
8a118206 725
ea449505 726=item [6]
8a118206 727
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728C<\p{SpacePerl}> and C<\p{Space}> differ only in that in non-locale
729matching, C<\p{Space}> additionally
ea449505 730matches the vertical tab, C<\cK>. Same for the two ASCII-only range forms.
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731
732=back
733
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734There are various other synonyms that can be used besides the names
735listed in the table. For example, C<\p{PosixAlpha}> can be written as
736C<\p{Alpha}>. All are listed in
737L<perluniprops/Properties accessible through \p{} and \P{}>,
738plus all characters matched by each ASCII-range property.
739
740Both the C<\p> counterparts always assume Unicode rules are in effect.
741On ASCII platforms, this means they assume that the code points from 128
742to 255 are Latin-1, and that means that using them under locale rules is
743unwise unless the locale is guaranteed to be Latin-1 or UTF-8. In contrast, the
744POSIX character classes are useful under locale rules. They are
745affected by the actual rules in effect, as follows:
746
747=over
748
749=item If the C</a> modifier, is in effect ...
750
751Each of the POSIX classes matches exactly the same as their ASCII-range
752counterparts.
753
754=item otherwise ...
755
756=over
757
758=item For code points above 255 ...
759
760The POSIX class matches the same as its Full-range counterpart.
761
762=item For code points below 256 ...
763
764=over
765
766=item if locale rules are in effect ...
767
768The POSIX class matches according to the locale.
769
770=item if Unicode rules are in effect or if on an EBCDIC platform ...
771
772The POSIX class matches the same as the Full-range counterpart.
773
774=item otherwise ...
775
776The POSIX class matches the same as the ASCII range counterpart.
777
778=back
779
780=back
781
782=back
783
784Which rules apply are determined as described in
785L<perlre/Which character set modifier is in effect?>.
786
787It is proposed to change this behavior in a future release of Perl so that
788whether or not Unicode rules are in effect would not change the
789behavior: Outside of locale or an EBCDIC code page, the POSIX classes
790would behave like their ASCII-range counterparts. If you wish to
791comment on this proposal, send email to C<perl5-porters@perl.org>.
cbc24f92 792
1f59b283 793=head4 Negation of POSIX character classes
ea449505 794X<character class, negation>
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795
796A Perl extension to the POSIX character class is the ability to
797negate it. This is done by prefixing the class name with a caret (C<^>).
798Some examples:
799
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800 POSIX ASCII-range Full-range backslash
801 Unicode Unicode sequence
802 -----------------------------------------------------
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803 [[:^digit:]] \P{PosixDigit} \P{XPosixDigit} \D
804 [[:^space:]] \P{PosixSpace} \P{XPosixSpace}
805 \P{PerlSpace} \P{XPerlSpace} \S
806 [[:^word:]] \P{PerlWord} \P{XPosixWord} \W
807
765fa144 808The backslash sequence can mean either ASCII- or Full-range Unicode,
82206b5e 809depending on various factors as described in L<perlre/Which character set modifier is in effect?>.
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810
811=head4 [= =] and [. .]
812
b6538e4f 813Perl recognizes the POSIX character classes C<[=class=]> and
82206b5e 814C<[.class.]>, but does not (yet?) support them. Any attempt to use
b6538e4f 815either construct raises an exception.
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816
817=head4 Examples
818
819 /[[:digit:]]/ # Matches a character that is a digit.
820 /[01[:lower:]]/ # Matches a character that is either a
821 # lowercase letter, or '0' or '1'.
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822 /[[:digit:][:^xdigit:]]/ # Matches a character that can be anything
823 # except the letters 'a' to 'f'. This is
824 # because the main character class is composed
825 # of two POSIX character classes that are ORed
826 # together, one that matches any digit, and
827 # the other that matches anything that isn't a
828 # hex digit. The result matches all
829 # characters except the letters 'a' to 'f' and
830 # 'A' to 'F'.