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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> modifier in effect, it matches [0-9]. Otherwise, it
93matches anything that is matched by C<\p{Digit}>, which includes [0-9].
94(An unlikely possible exception is that under locale matching rules, the
95current locale might not have [0-9] matched by C<\d>, and/or might match
96other characters whose code point is less than 256. Such a locale
97definition would be in violation of the C language standard, but Perl
98doesn't currently assume anything in regard to this.)
99
100What this means is that unless the C</a> modifier is in effect C<\d> not
101only matches the digits '0' - '9', but also Arabic, Devanagari, and
102digits from other languages. This may cause some confusion, and some
103security issues.
104
105Some digits that C<\d> matches look like some of the [0-9] ones, but
106have different values. For example, BENGALI DIGIT FOUR (U+09EA) looks
107very much like an ASCII DIGIT EIGHT (U+0038). An application that
108is expecting only the ASCII digits might be misled, or if the match is
109C<\d+>, the matched string might contain a mixture of digits from
110different writing systems that look like they signify a number different
111than they actually do. L<Unicode::UCD/num()> can be used to safely
112calculate the value, returning C<undef> if the input string contains
113such a mixture.
114
115What C<\p{Digit}> means (and hence C<\d> except under the C</a>
116modifier) is C<\p{General_Category=Decimal_Number}>, or synonymously,
117C<\p{General_Category=Digit}>. Starting with Unicode version 4.1, this
118is the same set of characters matched by C<\p{Numeric_Type=Decimal}>.
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119But Unicode also has a different property with a similar name,
120C<\p{Numeric_Type=Digit}>, which matches a completely different set of
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121characters. These characters are things such as C<CIRCLED DIGIT ONE>
122or subscripts, or are from writing systems that lack all ten digits.
6b83a163 123
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124The design intent is for C<\d> to exactly match the set of characters
125that can safely be used with "normal" big-endian positional decimal
126syntax, where, for example 123 means one 'hundred', plus two 'tens',
127plus three 'ones'. This positional notation does not necessarily apply
128to characters that match the other type of "digit",
129C<\p{Numeric_Type=Digit}>, and so C<\d> doesn't match them.
6b83a163 130
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131In Unicode 5.2, the Tamil digits (U+0BE6 - U+0BEF) can also legally be
132used in old-style Tamil numbers in which they would appear no more than
133one in a row, separated by characters that mean "times 10", "times 100",
134etc. (See L<http://www.unicode.org/notes/tn21>.)
8a118206 135
b6538e4f 136Any character not matched by C<\d> is matched by C<\D>.
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137
138=head3 Word characters
139
ea449505 140A C<\w> matches a single alphanumeric character (an alphabetic character, or a
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141decimal digit) or a connecting punctuation character, such as an
142underscore ("_"). It does not match a whole word. To match a whole
82206b5e 143word, use C<\w+>. This isn't the same thing as matching an English word, but
765fa144 144in the ASCII range it is the same as a string of Perl-identifier
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145characters.
146
147=over
148
149=item If the C</a> modifier is in effect ...
150
151C<\w> matches the 63 characters [a-zA-Z0-9_].
152
153=item otherwise ...
154
155=over
156
157=item For code points above 255 ...
158
159C<\w> matches the same as C<\p{Word}> matches in this range. That is,
160it matches Thai letters, Greek letters, etc. This includes connector
d35dd6c6 161punctuation (like the underscore) which connect two words together, or
b6538e4f 162diacritics, such as a C<COMBINING TILDE> and the modifier letters, which
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163are generally used to add auxiliary markings to letters.
164
165=item For code points below 256 ...
166
167=over
168
169=item if locale rules are in effect ...
170
171C<\w> matches the platform's native underscore character plus whatever
172the locale considers to be alphanumeric.
173
174=item if Unicode rules are in effect or if on an EBCDIC platform ...
175
176C<\w> matches exactly what C<\p{Word}> matches.
177
178=item otherwise ...
179
180C<\w> matches [a-zA-Z0-9_].
181
182=back
183
184=back
185
186=back
187
188Which rules apply are determined as described in L<perlre/Which character set modifier is in effect?>.
8a118206 189
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190There are a number of security issues with the full Unicode list of word
191characters. See L<http://unicode.org/reports/tr36>.
192
193Also, for a somewhat finer-grained set of characters that are in programming
194language identifiers beyond the ASCII range, you may wish to instead use the
195more customized Unicode properties, "ID_Start", ID_Continue", "XID_Start", and
196"XID_Continue". See L<http://unicode.org/reports/tr31>.
197
b6538e4f 198Any character not matched by C<\w> is matched by C<\W>.
8a118206 199
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200=head3 Whitespace
201
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202C<\s> matches any single character considered whitespace.
203
204=over
205
206=item If the C</a> modifier is in effect ...
207
208C<\s> matches the 5 characters [\t\n\f\r ]; that is, the horizontal tab,
209the newline, the form feed, the carriage return, and the space. (Note
210that it doesn't match the vertical tab, C<\cK> on ASCII platforms.)
211
212=item otherwise ...
213
214=over
215
216=item For code points above 255 ...
217
218C<\s> matches exactly the code points above 255 shown with an "s" column
219in the table below.
220
221=item For code points below 256 ...
222
223=over
224
225=item if locale rules are in effect ...
226
227C<\s> matches whatever the locale considers to be whitespace. Note that
228this is likely to include the vertical space, unlike non-locale C<\s>
229matching.
230
231=item if Unicode rules are in effect or if on an EBCDIC platform ...
232
233C<\s> matches exactly the characters shown with an "s" column in the
234table below.
235
236=item otherwise ...
237
238C<\s> matches [\t\n\f\r ].
239Note that this list doesn't include the non-breaking space.
240
241=back
242
243=back
244
245=back
246
247Which rules apply are determined as described in L<perlre/Which character set modifier is in effect?>.
8a118206 248
b6538e4f 249Any character not matched by C<\s> is matched by C<\S>.
8a118206 250
b6538e4f 251C<\h> matches any character considered horizontal whitespace;
82206b5e 252this includes the space and tab characters and several others
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253listed in the table below. C<\H> matches any character
254not considered horizontal whitespace.
ea449505 255
b6538e4f 256C<\v> matches any character considered vertical whitespace;
82206b5e 257this includes the carriage return and line feed characters (newline)
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258plus several other characters, all listed in the table below.
259C<\V> matches any character not considered vertical whitespace.
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260
261C<\R> matches anything that can be considered a newline under Unicode
262rules. It's not a character class, as it can match a multi-character
263sequence. Therefore, it cannot be used inside a bracketed character
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264class; use C<\v> instead (vertical whitespace).
265Details are discussed in L<perlrebackslash>.
8a118206 266
82206b5e 267Note that unlike C<\s> (and C<\d> and C<\w>), C<\h> and C<\v> always match
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268the same characters, without regard to other factors, such as whether the
269source string is in UTF-8 format.
8a118206 270
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271One might think that C<\s> is equivalent to C<[\h\v]>. This is not true.
272For example, the vertical tab (C<"\x0b">) is not matched by C<\s>, it is
273however considered vertical whitespace.
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274
275The following table is a complete listing of characters matched by
82206b5e 276C<\s>, C<\h> and C<\v> as of Unicode 6.0.
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277
278The first column gives the code point of the character (in hex format),
279the second column gives the (Unicode) name. The third column indicates
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280by which class(es) the character is matched (assuming no locale or EBCDIC code
281page is in effect that changes the C<\s> matching).
8a118206 282
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283 0x0009 CHARACTER TABULATION h s
284 0x000a LINE FEED (LF) vs
285 0x000b LINE TABULATION v
286 0x000c FORM FEED (FF) vs
287 0x000d CARRIAGE RETURN (CR) vs
288 0x0020 SPACE h s
289 0x0085 NEXT LINE (NEL) vs [1]
290 0x00a0 NO-BREAK SPACE h s [1]
291 0x1680 OGHAM SPACE MARK h s
292 0x180e MONGOLIAN VOWEL SEPARATOR h s
293 0x2000 EN QUAD h s
294 0x2001 EM QUAD h s
295 0x2002 EN SPACE h s
296 0x2003 EM SPACE h s
297 0x2004 THREE-PER-EM SPACE h s
298 0x2005 FOUR-PER-EM SPACE h s
299 0x2006 SIX-PER-EM SPACE h s
300 0x2007 FIGURE SPACE h s
301 0x2008 PUNCTUATION SPACE h s
302 0x2009 THIN SPACE h s
303 0x200a HAIR SPACE h s
304 0x2028 LINE SEPARATOR vs
305 0x2029 PARAGRAPH SEPARATOR vs
306 0x202f NARROW NO-BREAK SPACE h s
307 0x205f MEDIUM MATHEMATICAL SPACE h s
308 0x3000 IDEOGRAPHIC SPACE h s
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309
310=over 4
311
312=item [1]
313
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314NEXT LINE and NO-BREAK SPACE may or may not match C<\s> depending
315on the rules in effect. See
316L<the beginning of this section|/Whitespace>.
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317
318=back
319
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320=head3 Unicode Properties
321
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322C<\pP> and C<\p{Prop}> are character classes to match characters that fit given
323Unicode properties. One letter property names can be used in the C<\pP> form,
324with the property name following the C<\p>, otherwise, braces are required.
325When using braces, there is a single form, which is just the property name
326enclosed in the braces, and a compound form which looks like C<\p{name=value}>,
b6538e4f 327which means to match if the property "name" for the character has that particular
c1c4ae3a 328"value".
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329For instance, a match for a number can be written as C</\pN/> or as
330C</\p{Number}/>, or as C</\p{Number=True}/>.
331Lowercase letters are matched by the property I<Lowercase_Letter> which
332has as short form I<Ll>. They need the braces, so are written as C</\p{Ll}/> or
333C</\p{Lowercase_Letter}/>, or C</\p{General_Category=Lowercase_Letter}/>
334(the underscores are optional).
335C</\pLl/> is valid, but means something different.
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336It matches a two character string: a letter (Unicode property C<\pL>),
337followed by a lowercase C<l>.
338
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339If neither the C</a> modifier nor locale rules are in effect, the use of
340a Unicode property will force the regular expression into using Unicode
341rules.
342
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343Note that almost all properties are immune to case-insensitive matching.
344That is, adding a C</i> regular expression modifier does not change what
82206b5e 345they match. There are two sets that are affected. The first set is
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346C<Uppercase_Letter>,
347C<Lowercase_Letter>,
348and C<Titlecase_Letter>,
349all of which match C<Cased_Letter> under C</i> matching.
b6538e4f 350The second set is
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351C<Uppercase>,
352C<Lowercase>,
353and C<Titlecase>,
354all of which match C<Cased> under C</i> matching.
355(The difference between these sets is that some things, such as Roman
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356Numerals, come in both upper and lower case so they are C<Cased>, but
357aren't considered to be letters, so they aren't C<Cased_Letter>s. They're
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358actually C<Letter_Number>s.)
359This set also includes its subsets C<PosixUpper> and C<PosixLower>, both
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360of which under C</i> matching match C<PosixAlpha>.
361
362For more details on Unicode properties, see L<perlunicode/Unicode
363Character Properties>; for a
e1b711da 364complete list of possible properties, see
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365L<perluniprops/Properties accessible through \p{} and \P{}>,
366which notes all forms that have C</i> differences.
e1b711da 367It is also possible to define your own properties. This is discussed in
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368L<perlunicode/User-Defined Character Properties>.
369
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370=head4 Examples
371
372 "a" =~ /\w/ # Match, "a" is a 'word' character.
373 "7" =~ /\w/ # Match, "7" is a 'word' character as well.
374 "a" =~ /\d/ # No match, "a" isn't a digit.
375 "7" =~ /\d/ # Match, "7" is a digit.
ea449505 376 " " =~ /\s/ # Match, a space is whitespace.
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377 "a" =~ /\D/ # Match, "a" is a non-digit.
378 "7" =~ /\D/ # No match, "7" is not a non-digit.
ea449505 379 " " =~ /\S/ # No match, a space is not non-whitespace.
8a118206 380
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381 " " =~ /\h/ # Match, space is horizontal whitespace.
382 " " =~ /\v/ # No match, space is not vertical whitespace.
383 "\r" =~ /\v/ # Match, a return is vertical whitespace.
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384
385 "a" =~ /\pL/ # Match, "a" is a letter.
386 "a" =~ /\p{Lu}/ # No match, /\p{Lu}/ matches upper case letters.
387
388 "\x{0e0b}" =~ /\p{Thai}/ # Match, \x{0e0b} is the character
389 # 'THAI CHARACTER SO SO', and that's in
390 # Thai Unicode class.
ea449505 391 "a" =~ /\P{Lao}/ # Match, as "a" is not a Laotian character.
8a118206 392
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393It is worth emphasizing that C<\d>, C<\w>, etc, match single characters, not
394complete numbers or words. To match a number (that consists of digits),
395use C<\d+>; to match a word, use C<\w+>. But be aware of the security
396considerations in doing so, as mentioned above.
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397
398=head2 Bracketed Character Classes
399
400The third form of character class you can use in Perl regular expressions
6b83a163 401is the bracketed character class. In its simplest form, it lists the characters
c1c4ae3a 402that may be matched, surrounded by square brackets, like this: C<[aeiou]>.
ea449505 403This matches one of C<a>, C<e>, C<i>, C<o> or C<u>. Like the other
1f59b283 404character classes, exactly one character is matched.* To match
ea449505 405a longer string consisting of characters mentioned in the character
6b83a163 406class, follow the character class with a L<quantifier|perlre/Quantifiers>. For
b6538e4f 407instance, C<[aeiou]+> matches one or more lowercase English vowels.
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408
409Repeating a character in a character class has no
410effect; it's considered to be in the set only once.
411
412Examples:
413
414 "e" =~ /[aeiou]/ # Match, as "e" is listed in the class.
415 "p" =~ /[aeiou]/ # No match, "p" is not listed in the class.
416 "ae" =~ /^[aeiou]$/ # No match, a character class only matches
417 # a single character.
418 "ae" =~ /^[aeiou]+$/ # Match, due to the quantifier.
419
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420 -------
421
88a4f93e 422* There is an exception to a bracketed character class matching only a
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423single character. When the class is to match caselessely under C</i>
424matching rules, and a character inside the class matches a
425multiple-character sequence caselessly under Unicode rules, the class
426(when not L<inverted|/Negation>) will also match that sequence. For
427example, Unicode says that the letter C<LATIN SMALL LETTER SHARP S>
428should match the sequence C<ss> under C</i> rules. Thus,
429
430 'ss' =~ /\A\N{LATIN SMALL LETTER SHARP S}\z/i # Matches
431 'ss' =~ /\A[aeioust\N{LATIN SMALL LETTER SHARP S}]\z/i # Matches
432
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433=head3 Special Characters Inside a Bracketed Character Class
434
435Most characters that are meta characters in regular expressions (that
df225385 436is, characters that carry a special meaning like C<.>, C<*>, or C<(>) lose
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437their special meaning and can be used inside a character class without
438the need to escape them. For instance, C<[()]> matches either an opening
439parenthesis, or a closing parenthesis, and the parens inside the character
440class don't group or capture.
441
442Characters that may carry a special meaning inside a character class are:
443C<\>, C<^>, C<->, C<[> and C<]>, and are discussed below. They can be
444escaped with a backslash, although this is sometimes not needed, in which
445case the backslash may be omitted.
446
447The sequence C<\b> is special inside a bracketed character class. While
6b83a163 448outside the character class, C<\b> is an assertion indicating a point
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449that does not have either two word characters or two non-word characters
450on either side, inside a bracketed character class, C<\b> matches a
451backspace character.
452
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453The sequences
454C<\a>,
455C<\c>,
456C<\e>,
457C<\f>,
458C<\n>,
e526e8bb 459C<\N{I<NAME>}>,
765fa144 460C<\N{U+I<hex char>}>,
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461C<\r>,
462C<\t>,
463and
464C<\x>
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465are also special and have the same meanings as they do outside a
466bracketed character class. (However, inside a bracketed character
467class, if C<\N{I<NAME>}> expands to a sequence of characters, only the first
468one in the sequence is used, with a warning.)
df225385 469
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470Also, a backslash followed by two or three octal digits is considered an octal
471number.
df225385 472
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473A C<[> is not special inside a character class, unless it's the start of a
474POSIX character class (see L</POSIX Character Classes> below). It normally does
475not need escaping.
8a118206 476
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477A C<]> is normally either the end of a POSIX character class (see
478L</POSIX Character Classes> below), or it signals the end of the bracketed
479character class. If you want to include a C<]> in the set of characters, you
480must generally escape it.
b6538e4f 481
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482However, if the C<]> is the I<first> (or the second if the first
483character is a caret) character of a bracketed character class, it
484does not denote the end of the class (as you cannot have an empty class)
485and is considered part of the set of characters that can be matched without
486escaping.
487
488Examples:
489
490 "+" =~ /[+?*]/ # Match, "+" in a character class is not special.
491 "\cH" =~ /[\b]/ # Match, \b inside in a character class
c1c4ae3a 492 # is equivalent to a backspace.
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493 "]" =~ /[][]/ # Match, as the character class contains.
494 # both [ and ].
495 "[]" =~ /[[]]/ # Match, the pattern contains a character class
496 # containing just ], and the character class is
497 # followed by a ].
498
499=head3 Character Ranges
500
501It is not uncommon to want to match a range of characters. Luckily, instead
b6538e4f 502of listing all characters in the range, one may use the hyphen (C<->).
8a118206 503If inside a bracketed character class you have two characters separated
b6538e4f 504by a hyphen, it's treated as if all characters between the two were in
8a118206 505the class. For instance, C<[0-9]> matches any ASCII digit, and C<[a-m]>
b6538e4f 506matches any lowercase letter from the first half of the old ASCII alphabet.
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507
508Note that the two characters on either side of the hyphen are not
765fa144 509necessarily both letters or both digits. Any character is possible,
8a118206 510although not advisable. C<['-?]> contains a range of characters, but
b6538e4f 511most people will not know which characters that means. Furthermore,
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512such ranges may lead to portability problems if the code has to run on
513a platform that uses a different character set, such as EBCDIC.
514
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515If a hyphen in a character class cannot syntactically be part of a range, for
516instance because it is the first or the last character of the character class,
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517or if it immediately follows a range, the hyphen isn't special, and so is
518considered a character to be matched literally. If you want a hyphen in
519your set of characters to be matched and its position in the class is such
520that it could be considered part of a range, you must escape that hyphen
521with a backslash.
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522
523Examples:
524
525 [a-z] # Matches a character that is a lower case ASCII letter.
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526 [a-fz] # Matches any letter between 'a' and 'f' (inclusive) or
527 # the letter 'z'.
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528 [-z] # Matches either a hyphen ('-') or the letter 'z'.
529 [a-f-m] # Matches any letter between 'a' and 'f' (inclusive), the
530 # hyphen ('-'), or the letter 'm'.
531 ['-?] # Matches any of the characters '()*+,-./0123456789:;<=>?
532 # (But not on an EBCDIC platform).
533
534
535=head3 Negation
536
537It is also possible to instead list the characters you do not want to
538match. You can do so by using a caret (C<^>) as the first character in the
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539character class. For instance, C<[^a-z]> matches any character that is not a
540lowercase ASCII letter, which therefore includes almost a hundred thousand
1f59b283 541Unicode letters. The class is said to be "negated" or "inverted".
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542
543This syntax make the caret a special character inside a bracketed character
544class, but only if it is the first character of the class. So if you want
82206b5e 545the caret as one of the characters to match, either escape the caret or
b6538e4f 546else not list it first.
8a118206 547
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548In inverted bracketed character classes, Perl ignores the Unicode rules
549that normally say that a given character matches a sequence of multiple
550characters under caseless C</i> matching, which otherwise could be
551highly confusing:
552
553 "ss" =~ /^[^\xDF]+$/ui;
554
555This should match any sequences of characters that aren't C<\xDF> nor
556what C<\xDF> matches under C</i>. C<"s"> isn't C<\xDF>, but Unicode
557says that C<"ss"> is what C<\xDF> matches under C</i>. So which one
558"wins"? Do you fail the match because the string has C<ss> or accept it
559because it has an C<s> followed by another C<s>?
560
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561Examples:
562
563 "e" =~ /[^aeiou]/ # No match, the 'e' is listed.
564 "x" =~ /[^aeiou]/ # Match, as 'x' isn't a lowercase vowel.
565 "^" =~ /[^^]/ # No match, matches anything that isn't a caret.
566 "^" =~ /[x^]/ # Match, caret is not special here.
567
568=head3 Backslash Sequences
569
ea449505 570You can put any backslash sequence character class (with the exception of
765fa144 571C<\N> and C<\R>) inside a bracketed character class, and it will act just
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572as if you had put all characters matched by the backslash sequence inside the
573character class. For instance, C<[a-f\d]> matches any decimal digit, or any
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574of the lowercase letters between 'a' and 'f' inclusive.
575
576C<\N> within a bracketed character class must be of the forms C<\N{I<name>}>
765fa144 577or C<\N{U+I<hex char>}>, and NOT be the form that matches non-newlines,
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578for the same reason that a dot C<.> inside a bracketed character class loses
579its special meaning: it matches nearly anything, which generally isn't what you
580want to happen.
df225385 581
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582
583Examples:
584
585 /[\p{Thai}\d]/ # Matches a character that is either a Thai
586 # character, or a digit.
587 /[^\p{Arabic}()]/ # Matches a character that is neither an Arabic
588 # character, nor a parenthesis.
589
590Backslash sequence character classes cannot form one of the endpoints
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591of a range. Thus, you can't say:
592
593 /[\p{Thai}-\d]/ # Wrong!
8a118206 594
6b83a163 595=head3 POSIX Character Classes
ea449505 596X<character class> X<\p> X<\p{}>
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597X<alpha> X<alnum> X<ascii> X<blank> X<cntrl> X<digit> X<graph>
598X<lower> X<print> X<punct> X<space> X<upper> X<word> X<xdigit>
8a118206 599
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600POSIX character classes have the form C<[:class:]>, where I<class> is
601name, and the C<[:> and C<:]> delimiters. POSIX character classes only appear
8a118206 602I<inside> bracketed character classes, and are a convenient and descriptive
82206b5e 603way of listing a group of characters.
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604
605Be careful about the syntax,
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606
607 # Correct:
608 $string =~ /[[:alpha:]]/
609
610 # Incorrect (will warn):
611 $string =~ /[:alpha:]/
612
613The latter pattern would be a character class consisting of a colon,
614and the letters C<a>, C<l>, C<p> and C<h>.
82206b5e 615POSIX character classes can be part of a larger bracketed character class.
b6538e4f 616For example,
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617
618 [01[:alpha:]%]
619
620is valid and matches '0', '1', any alphabetic character, and the percent sign.
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621
622Perl recognizes the following POSIX character classes:
623
ea449505 624 alpha Any alphabetical character ("[A-Za-z]").
b6538e4f 625 alnum Any alphanumeric character. ("[A-Za-z0-9]")
ea449505 626 ascii Any character in the ASCII character set.
ea8b8ad2 627 blank A GNU extension, equal to a space or a horizontal tab ("\t").
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628 cntrl Any control character. See Note [2] below.
629 digit Any decimal digit ("[0-9]"), equivalent to "\d".
630 graph Any printable character, excluding a space. See Note [3] below.
631 lower Any lowercase character ("[a-z]").
632 print Any printable character, including a space. See Note [4] below.
c1c4ae3a 633 punct Any graphical character excluding "word" characters. Note [5].
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634 space Any whitespace character. "\s" plus the vertical tab ("\cK").
635 upper Any uppercase character ("[A-Z]").
636 word A Perl extension ("[A-Za-z0-9_]"), equivalent to "\w".
637 xdigit Any hexadecimal digit ("[0-9a-fA-F]").
638
639Most POSIX character classes have two Unicode-style C<\p> property
640counterparts. (They are not official Unicode properties, but Perl extensions
641derived from official Unicode properties.) The table below shows the relation
642between POSIX character classes and these counterparts.
643
644One counterpart, in the column labelled "ASCII-range Unicode" in
b6538e4f 645the table, matches only characters in the ASCII character set.
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646
647The other counterpart, in the column labelled "Full-range Unicode", matches any
648appropriate characters in the full Unicode character set. For example,
b6538e4f 649C<\p{Alpha}> matches not just the ASCII alphabetic characters, but any
82206b5e 650character in the entire Unicode character set considered alphabetic.
b6538e4f 651The column labelled "backslash sequence" is a (short) synonym for
cbc24f92 652the Full-range Unicode form.
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653
654(Each of the counterparts has various synonyms as well.
b6538e4f 655L<perluniprops/Properties accessible through \p{} and \P{}> lists all
82206b5e 656synonyms, plus all characters matched by each ASCII-range property.
b6538e4f 657For example, C<\p{AHex}> is a synonym for C<\p{ASCII_Hex_Digit}>,
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658and any C<\p> property name can be prefixed with "Is" such as C<\p{IsAlpha}>.)
659
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660Both the C<\p> counterparts always assume Unicode rules are in effect.
661On ASCII platforms, this means they assume that the code points from 128
662to 255 are Latin-1, and that means that using them under locale rules is
9814da73 663unwise unless the locale is guaranteed to be Latin-1 or UTF-8. In contrast, the
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664POSIX character classes are useful under locale rules. They are
665affected by the actual rules in effect, as follows:
666
667=over
668
669=item If the C</a> modifier, is in effect ...
670
671Each of the POSIX classes matches exactly the same as their ASCII-range
672counterparts.
673
674=item otherwise ...
675
676=over
677
678=item For code points above 255 ...
679
680The POSIX class matches the same as its Full-range counterpart.
681
682=item For code points below 256 ...
683
684=over
685
686=item if locale rules are in effect ...
687
688The POSIX class matches according to the locale.
689
690=item if Unicode rules are in effect or if on an EBCDIC platform ...
691
692The POSIX class matches the same as the Full-range counterpart.
693
694=item otherwise ...
695
696The POSIX class matches the same as the ASCII range counterpart.
697
698=back
699
700=back
701
702=back
703
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704Which rules apply are determined as described in
705L<perlre/Which character set modifier is in effect?>.
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706
707It is proposed to change this behavior in a future release of Perl so that
708whether or not Unicode rules are in effect would not change the
709behavior: Outside of locale or an EBCDIC code page, the POSIX classes
710would behave like their ASCII-range counterparts. If you wish to
711comment on this proposal, send email to C<perl5-porters@perl.org>.
ea449505 712
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713 [[:...:]] ASCII-range Full-range backslash Note
714 Unicode Unicode sequence
ea449505 715 -----------------------------------------------------
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716 alpha \p{PosixAlpha} \p{XPosixAlpha}
717 alnum \p{PosixAlnum} \p{XPosixAlnum}
82206b5e 718 ascii \p{ASCII}
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719 blank \p{PosixBlank} \p{XPosixBlank} \h [1]
720 or \p{HorizSpace} [1]
721 cntrl \p{PosixCntrl} \p{XPosixCntrl} [2]
722 digit \p{PosixDigit} \p{XPosixDigit} \d
723 graph \p{PosixGraph} \p{XPosixGraph} [3]
724 lower \p{PosixLower} \p{XPosixLower}
725 print \p{PosixPrint} \p{XPosixPrint} [4]
726 punct \p{PosixPunct} \p{XPosixPunct} [5]
727 \p{PerlSpace} \p{XPerlSpace} \s [6]
728 space \p{PosixSpace} \p{XPosixSpace} [6]
729 upper \p{PosixUpper} \p{XPosixUpper}
730 word \p{PosixWord} \p{XPosixWord} \w
82206b5e 731 xdigit \p{PosixXDigit} \p{XPosixXDigit}
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732
733=over 4
734
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735=item [1]
736
737C<\p{Blank}> and C<\p{HorizSpace}> are synonyms.
738
739=item [2]
8a118206 740
ea449505 741Control characters don't produce output as such, but instead usually control
b6538e4f 742the terminal somehow: for example, newline and backspace are control characters.
82206b5e 743In the ASCII range, characters whose code points are between 0 and 31 inclusive,
ea449505 744plus 127 (C<DEL>) are control characters.
8a118206 745
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746On EBCDIC platforms, it is likely that the code page will define C<[[:cntrl:]]>
747to be the EBCDIC equivalents of the ASCII controls, plus the controls
82206b5e 748that in Unicode have code pointss from 128 through 159.
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749
750=item [3]
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751
752Any character that is I<graphical>, that is, visible. This class consists
b6538e4f 753of all alphanumeric characters and all punctuation characters.
8a118206 754
ea449505 755=item [4]
8a118206 756
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757All printable characters, which is the set of all graphical characters
758plus those whitespace characters which are not also controls.
ea449505 759
b6dac59a 760=item [5]
ea449505 761
b6538e4f 762C<\p{PosixPunct}> and C<[[:punct:]]> in the ASCII range match all
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763non-controls, non-alphanumeric, non-space characters:
764C<[-!"#$%&'()*+,./:;<=E<gt>?@[\\\]^_`{|}~]> (although if a locale is in effect,
765it could alter the behavior of C<[[:punct:]]>).
766
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767The similarly named property, C<\p{Punct}>, matches a somewhat different
768set in the ASCII range, namely
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769C<[-!"#%&'()*,./:;?@[\\\]_{}]>. That is, it is missing C<[$+E<lt>=E<gt>^`|~]>.
770This is because Unicode splits what POSIX considers to be punctuation into two
771categories, Punctuation and Symbols.
772
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773C<\p{XPosixPunct}> and (in Unicode mode) C<[[:punct:]]>, match what
774C<\p{PosixPunct}> matches in the ASCII range, plus what C<\p{Punct}>
775matches. This is different than strictly matching according to
776C<\p{Punct}>. Another way to say it is that
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777if Unicode rules are in effect, C<[[:punct:]]> matches all characters
778that Unicode considers punctuation, plus all ASCII-range characters that
779Unicode considers symbols.
8a118206 780
ea449505 781=item [6]
8a118206 782
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783C<\p{SpacePerl}> and C<\p{Space}> differ only in that in non-locale
784matching, C<\p{Space}> additionally
ea449505 785matches the vertical tab, C<\cK>. Same for the two ASCII-only range forms.
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786
787=back
788
cbc24f92 789There are various other synonyms that can be used for these besides
b6538e4f 790C<\p{HorizSpace}> and \C<\p{XPosixBlank}>. For example,
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791C<\p{PosixAlpha}> can be written as C<\p{Alpha}>. All are listed
792in L<perluniprops/Properties accessible through \p{} and \P{}>.
793
1f59b283 794=head4 Negation of POSIX character classes
ea449505 795X<character class, negation>
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796
797A Perl extension to the POSIX character class is the ability to
798negate it. This is done by prefixing the class name with a caret (C<^>).
799Some examples:
800
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801 POSIX ASCII-range Full-range backslash
802 Unicode Unicode sequence
803 -----------------------------------------------------
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804 [[:^digit:]] \P{PosixDigit} \P{XPosixDigit} \D
805 [[:^space:]] \P{PosixSpace} \P{XPosixSpace}
806 \P{PerlSpace} \P{XPerlSpace} \S
807 [[:^word:]] \P{PerlWord} \P{XPosixWord} \W
808
765fa144 809The backslash sequence can mean either ASCII- or Full-range Unicode,
82206b5e 810depending on various factors as described in L<perlre/Which character set modifier is in effect?>.
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811
812=head4 [= =] and [. .]
813
b6538e4f 814Perl recognizes the POSIX character classes C<[=class=]> and
82206b5e 815C<[.class.]>, but does not (yet?) support them. Any attempt to use
b6538e4f 816either construct raises an exception.
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817
818=head4 Examples
819
820 /[[:digit:]]/ # Matches a character that is a digit.
821 /[01[:lower:]]/ # Matches a character that is either a
822 # lowercase letter, or '0' or '1'.
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823 /[[:digit:][:^xdigit:]]/ # Matches a character that can be anything
824 # except the letters 'a' to 'f'. This is
825 # because the main character class is composed
826 # of two POSIX character classes that are ORed
827 # together, one that matches any digit, and
828 # the other that matches anything that isn't a
829 # hex digit. The result matches all
830 # characters except the letters 'a' to 'f' and
831 # 'A' to 'F'.