4 perlrecharclass - Perl Regular Expression Character Classes
8 The top level documentation about Perl regular expressions
11 This manual page discusses the syntax and use of character
12 classes in Perl regular expressions.
14 A character class is a way of denoting a set of characters
15 in such a way that one character of the set is matched.
16 It's important to remember that: matching a character class
17 consumes exactly one character in the source string. (The source
18 string is the string the regular expression is matched against.)
20 There are three types of character classes in Perl regular
21 expressions: the dot, backslash sequences, and the form enclosed in square
22 brackets. Keep in mind, though, that often the term "character class" is used
23 to mean just the bracketed form. Certainly, most Perl documentation does that.
27 The dot (or period), C<.> is probably the most used, and certainly
28 the most well-known character class. By default, a dot matches any
29 character, except for the newline. That default can be changed to
30 add matching the newline by using the I<single line> modifier: either
31 for the entire regular expression with the C</s> modifier, or
32 locally with C<(?s)>. (The C<L</\N>> backslash sequence, described
33 below, matches any character except newline without regard to the
34 I<single line> modifier.)
36 Here are some examples:
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)
46 =head2 Backslash sequences
47 X<\w> X<\W> X<\s> X<\S> X<\d> X<\D> X<\p> X<\P>
48 X<\N> X<\v> X<\V> X<\h> X<\H>
51 A backslash sequence is a sequence of characters, the first one of which is a
52 backslash. Perl ascribes special meaning to many such sequences, and some of
53 these are character classes. That is, they match a single character each,
54 provided that the character belongs to the specific set of characters defined
57 Here's a list of the backslash sequences that are character classes. They
58 are discussed in more detail below. (For the backslash sequences that aren't
59 character classes, see L<perlrebackslash>.)
61 \d Match a decimal digit character.
62 \D Match a non-decimal-digit character.
63 \w Match a "word" character.
64 \W Match a non-"word" character.
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.
69 \v Match a vertical whitespace character.
70 \V Match a character that isn't vertical whitespace.
71 \N Match a character that isn't a newline.
72 \pP, \p{Prop} Match a character that has the given Unicode property.
73 \PP, \P{Prop} Match a character that doesn't have the Unicode property
77 C<\N>, available starting in v5.12, like the dot, matches any
78 character that is not a newline. The difference is that C<\N> is not influenced
79 by the I<single line> regular expression modifier (see L</The dot> above). Note
80 that the form C<\N{...}> may mean something completely different. When the
81 C<{...}> is a L<quantifier|perlre/Quantifiers>, it means to match a non-newline
82 character that many times. For example, C<\N{3}> means to match 3
83 non-newlines; C<\N{5,}> means to match 5 or more non-newlines. But if C<{...}>
84 is not a legal quantifier, it is presumed to be a named character. See
85 L<charnames> for those. For example, none of C<\N{COLON}>, C<\N{4F}>, and
86 C<\N{F4}> contain legal quantifiers, so Perl will try to find characters whose
87 names are respectively C<COLON>, C<4F>, and C<F4>.
91 C<\d> matches a single character considered to be a decimal I<digit>.
92 If the C</a> regular expression modifier is in effect, it matches [0-9].
94 matches anything that is matched by C<\p{Digit}>, which includes [0-9].
95 (An unlikely possible exception is that under locale matching rules, the
96 current locale might not have C<[0-9]> matched by C<\d>, and/or might match
97 other characters whose code point is less than 256. The only such locale
98 definitions that are legal would be to match C<[0-9]> plus another set of
99 10 consecutive digit characters; anything else would be in violation of
100 the C language standard, but Perl doesn't currently assume anything in
103 What this means is that unless the C</a> modifier is in effect C<\d> not
104 only matches the digits '0' - '9', but also Arabic, Devanagari, and
105 digits from other languages. This may cause some confusion, and some
108 Some digits that C<\d> matches look like some of the [0-9] ones, but
109 have different values. For example, BENGALI DIGIT FOUR (U+09EA) looks
110 very much like an ASCII DIGIT EIGHT (U+0038). An application that
111 is expecting only the ASCII digits might be misled, or if the match is
112 C<\d+>, the matched string might contain a mixture of digits from
113 different writing systems that look like they signify a number different
114 than they actually do. L<Unicode::UCD/num()> can
116 calculate the value, returning C<undef> if the input string contains
119 What C<\p{Digit}> means (and hence C<\d> except under the C</a>
120 modifier) is C<\p{General_Category=Decimal_Number}>, or synonymously,
121 C<\p{General_Category=Digit}>. Starting with Unicode version 4.1, this
122 is the same set of characters matched by C<\p{Numeric_Type=Decimal}>.
123 But Unicode also has a different property with a similar name,
124 C<\p{Numeric_Type=Digit}>, which matches a completely different set of
125 characters. These characters are things such as C<CIRCLED DIGIT ONE>
126 or subscripts, or are from writing systems that lack all ten digits.
128 The design intent is for C<\d> to exactly match the set of characters
129 that can safely be used with "normal" big-endian positional decimal
130 syntax, where, for example 123 means one 'hundred', plus two 'tens',
131 plus three 'ones'. This positional notation does not necessarily apply
132 to characters that match the other type of "digit",
133 C<\p{Numeric_Type=Digit}>, and so C<\d> doesn't match them.
135 The Tamil digits (U+0BE6 - U+0BEF) can also legally be
136 used in old-style Tamil numbers in which they would appear no more than
137 one in a row, separated by characters that mean "times 10", "times 100",
138 etc. (See L<http://www.unicode.org/notes/tn21>.)
140 Any character not matched by C<\d> is matched by C<\D>.
142 =head3 Word characters
144 A C<\w> matches a single alphanumeric character (an alphabetic character, or a
145 decimal digit); or a connecting punctuation character, such as an
146 underscore ("_"); or a "mark" character (like some sort of accent) that
147 attaches to one of those. It does not match a whole word. To match a
148 whole word, use C<\w+>. This isn't the same thing as matching an
149 English word, but in the ASCII range it is the same as a string of
150 Perl-identifier characters.
154 =item If the C</a> modifier is in effect ...
156 C<\w> matches the 63 characters [a-zA-Z0-9_].
162 =item For code points above 255 ...
164 C<\w> matches the same as C<\p{Word}> matches in this range. That is,
165 it matches Thai letters, Greek letters, etc. This includes connector
166 punctuation (like the underscore) which connect two words together, or
167 diacritics, such as a C<COMBINING TILDE> and the modifier letters, which
168 are generally used to add auxiliary markings to letters.
170 =item For code points below 256 ...
174 =item if locale rules are in effect ...
176 C<\w> matches the platform's native underscore character plus whatever
177 the locale considers to be alphanumeric.
179 =item if Unicode rules are in effect ...
181 C<\w> matches exactly what C<\p{Word}> matches.
185 C<\w> matches [a-zA-Z0-9_].
193 Which rules apply are determined as described in L<perlre/Which character set modifier is in effect?>.
195 There are a number of security issues with the full Unicode list of word
196 characters. See L<http://unicode.org/reports/tr36>.
198 Also, for a somewhat finer-grained set of characters that are in programming
199 language identifiers beyond the ASCII range, you may wish to instead use the
200 more customized L</Unicode Properties>, C<\p{ID_Start}>,
201 C<\p{ID_Continue}>, C<\p{XID_Start}>, and C<\p{XID_Continue}>. See
202 L<http://unicode.org/reports/tr31>.
204 Any character not matched by C<\w> is matched by C<\W>.
208 C<\s> matches any single character considered whitespace.
212 =item If the C</a> modifier is in effect ...
214 In all Perl versions, C<\s> matches the 5 characters [\t\n\f\r ]; that
215 is, the horizontal tab,
216 the newline, the form feed, the carriage return, and the space.
217 Starting in Perl v5.18, experimentally, it also matches the vertical tab, C<\cK>.
218 See note C<[1]> below for a discussion of this.
224 =item For code points above 255 ...
226 C<\s> matches exactly the code points above 255 shown with an "s" column
229 =item For code points below 256 ...
233 =item if locale rules are in effect ...
235 C<\s> matches whatever the locale considers to be whitespace.
237 =item if Unicode rules are in effect ...
239 C<\s> matches exactly the characters shown with an "s" column in the
244 C<\s> matches [\t\n\f\r ] and, starting, experimentally in Perl
245 v5.18, the vertical tab, C<\cK>.
246 (See note C<[1]> below for a discussion of this.)
247 Note that this list doesn't include the non-breaking space.
255 Which rules apply are determined as described in L<perlre/Which character set modifier is in effect?>.
257 Any character not matched by C<\s> is matched by C<\S>.
259 C<\h> matches any character considered horizontal whitespace;
260 this includes the platform's space and tab characters and several others
261 listed in the table below. C<\H> matches any character
262 not considered horizontal whitespace. They use the platform's native
263 character set, and do not consider any locale that may otherwise be in
266 C<\v> matches any character considered vertical whitespace;
267 this includes the platform's carriage return and line feed characters (newline)
268 plus several other characters, all listed in the table below.
269 C<\V> matches any character not considered vertical whitespace.
270 They use the platform's native character set, and do not consider any
271 locale that may otherwise be in use.
273 C<\R> matches anything that can be considered a newline under Unicode
274 rules. It's not a character class, as it can match a multi-character
275 sequence. Therefore, it cannot be used inside a bracketed character
276 class; use C<\v> instead (vertical whitespace). It uses the platform's
277 native character set, and does not consider any locale that may
279 Details are discussed in L<perlrebackslash>.
281 Note that unlike C<\s> (and C<\d> and C<\w>), C<\h> and C<\v> always match
282 the same characters, without regard to other factors, such as the active
283 locale or whether the source string is in UTF-8 format.
285 One might think that C<\s> is equivalent to C<[\h\v]>. This is indeed true
286 starting in Perl v5.18, but prior to that, the sole difference was that the
287 vertical tab (C<"\cK">) was not matched by C<\s>.
289 The following table is a complete listing of characters matched by
290 C<\s>, C<\h> and C<\v> as of Unicode 6.3.
292 The first column gives the Unicode code point of the character (in hex format),
293 the second column gives the (Unicode) name. The third column indicates
294 by which class(es) the character is matched (assuming no locale is in
295 effect that changes the C<\s> matching).
297 0x0009 CHARACTER TABULATION h s
298 0x000a LINE FEED (LF) vs
299 0x000b LINE TABULATION vs [1]
300 0x000c FORM FEED (FF) vs
301 0x000d CARRIAGE RETURN (CR) vs
303 0x0085 NEXT LINE (NEL) vs [2]
304 0x00a0 NO-BREAK SPACE h s [2]
305 0x1680 OGHAM SPACE MARK h s
310 0x2004 THREE-PER-EM SPACE h s
311 0x2005 FOUR-PER-EM SPACE h s
312 0x2006 SIX-PER-EM SPACE h s
313 0x2007 FIGURE SPACE h s
314 0x2008 PUNCTUATION SPACE h s
315 0x2009 THIN SPACE h s
316 0x200a HAIR SPACE h s
317 0x2028 LINE SEPARATOR vs
318 0x2029 PARAGRAPH SEPARATOR vs
319 0x202f NARROW NO-BREAK SPACE h s
320 0x205f MEDIUM MATHEMATICAL SPACE h s
321 0x3000 IDEOGRAPHIC SPACE h s
327 Prior to Perl v5.18, C<\s> did not match the vertical tab. The change
328 in v5.18 is considered an experiment, which means it could be backed out
329 in v5.22 if experience indicates that it breaks too much
330 existing code. If this change adversely affects you, send email to
331 C<perlbug@perl.org>; if it affects you positively, email
332 C<perlthanks@perl.org>. In the meantime, C<[^\S\cK]> (obscurely)
333 matches what C<\s> traditionally did.
337 NEXT LINE and NO-BREAK SPACE may or may not match C<\s> depending
338 on the rules in effect. See
339 L<the beginning of this section|/Whitespace>.
343 =head3 Unicode Properties
345 C<\pP> and C<\p{Prop}> are character classes to match characters that fit given
346 Unicode properties. One letter property names can be used in the C<\pP> form,
347 with the property name following the C<\p>, otherwise, braces are required.
348 When using braces, there is a single form, which is just the property name
349 enclosed in the braces, and a compound form which looks like C<\p{name=value}>,
350 which means to match if the property "name" for the character has that particular
352 For instance, a match for a number can be written as C</\pN/> or as
353 C</\p{Number}/>, or as C</\p{Number=True}/>.
354 Lowercase letters are matched by the property I<Lowercase_Letter> which
355 has the short form I<Ll>. They need the braces, so are written as C</\p{Ll}/> or
356 C</\p{Lowercase_Letter}/>, or C</\p{General_Category=Lowercase_Letter}/>
357 (the underscores are optional).
358 C</\pLl/> is valid, but means something different.
359 It matches a two character string: a letter (Unicode property C<\pL>),
360 followed by a lowercase C<l>.
362 If locale rules are not in effect, the use of
363 a Unicode property will force the regular expression into using Unicode
364 rules, if it isn't already.
366 Note that almost all properties are immune to case-insensitive matching.
367 That is, adding a C</i> regular expression modifier does not change what
368 they match. There are two sets that are affected. The first set is
371 and C<Titlecase_Letter>,
372 all of which match C<Cased_Letter> under C</i> matching.
377 all of which match C<Cased> under C</i> matching.
378 (The difference between these sets is that some things, such as Roman
379 numerals, come in both upper and lower case, so they are C<Cased>, but
380 aren't considered to be letters, so they aren't C<Cased_Letter>s. They're
381 actually C<Letter_Number>s.)
382 This set also includes its subsets C<PosixUpper> and C<PosixLower>, both
383 of which under C</i> match C<PosixAlpha>.
385 For more details on Unicode properties, see L<perlunicode/Unicode
386 Character Properties>; for a
387 complete list of possible properties, see
388 L<perluniprops/Properties accessible through \p{} and \P{}>,
389 which notes all forms that have C</i> differences.
390 It is also possible to define your own properties. This is discussed in
391 L<perlunicode/User-Defined Character Properties>.
393 Unicode properties are defined (surprise!) only on Unicode code points.
394 Starting in v5.20, when matching against C<\p> and C<\P>, Perl treats
395 non-Unicode code points (those above the legal Unicode maximum of
396 0x10FFFF) as if they were typical unassigned Unicode code points.
398 Prior to v5.20, Perl raised a warning and made all matches fail on
399 non-Unicode code points. This could be somewhat surprising:
401 chr(0x110000) =~ \p{ASCII_Hex_Digit=True} # Fails on Perls < v5.20.
402 chr(0x110000) =~ \p{ASCII_Hex_Digit=False} # Also fails on Perls
405 Even though these two matches might be thought of as complements, until
406 v5.20 they were so only on Unicode code points.
410 "a" =~ /\w/ # Match, "a" is a 'word' character.
411 "7" =~ /\w/ # Match, "7" is a 'word' character as well.
412 "a" =~ /\d/ # No match, "a" isn't a digit.
413 "7" =~ /\d/ # Match, "7" is a digit.
414 " " =~ /\s/ # Match, a space is whitespace.
415 "a" =~ /\D/ # Match, "a" is a non-digit.
416 "7" =~ /\D/ # No match, "7" is not a non-digit.
417 " " =~ /\S/ # No match, a space is not non-whitespace.
419 " " =~ /\h/ # Match, space is horizontal whitespace.
420 " " =~ /\v/ # No match, space is not vertical whitespace.
421 "\r" =~ /\v/ # Match, a return is vertical whitespace.
423 "a" =~ /\pL/ # Match, "a" is a letter.
424 "a" =~ /\p{Lu}/ # No match, /\p{Lu}/ matches upper case letters.
426 "\x{0e0b}" =~ /\p{Thai}/ # Match, \x{0e0b} is the character
427 # 'THAI CHARACTER SO SO', and that's in
428 # Thai Unicode class.
429 "a" =~ /\P{Lao}/ # Match, as "a" is not a Laotian character.
431 It is worth emphasizing that C<\d>, C<\w>, etc, match single characters, not
432 complete numbers or words. To match a number (that consists of digits),
433 use C<\d+>; to match a word, use C<\w+>. But be aware of the security
434 considerations in doing so, as mentioned above.
436 =head2 Bracketed Character Classes
438 The third form of character class you can use in Perl regular expressions
439 is the bracketed character class. In its simplest form, it lists the characters
440 that may be matched, surrounded by square brackets, like this: C<[aeiou]>.
441 This matches one of C<a>, C<e>, C<i>, C<o> or C<u>. Like the other
442 character classes, exactly one character is matched.* To match
443 a longer string consisting of characters mentioned in the character
444 class, follow the character class with a L<quantifier|perlre/Quantifiers>. For
445 instance, C<[aeiou]+> matches one or more lowercase English vowels.
447 Repeating a character in a character class has no
448 effect; it's considered to be in the set only once.
452 "e" =~ /[aeiou]/ # Match, as "e" is listed in the class.
453 "p" =~ /[aeiou]/ # No match, "p" is not listed in the class.
454 "ae" =~ /^[aeiou]$/ # No match, a character class only matches
455 # a single character.
456 "ae" =~ /^[aeiou]+$/ # Match, due to the quantifier.
460 * There are two exceptions to a bracketed character class matching a
461 single character only. Each requires special handling by Perl to make
468 When the class is to match caselessly under C</i> matching rules, and a
469 character that is explicitly mentioned inside the class matches a
470 multiple-character sequence caselessly under Unicode rules, the class
471 will also match that sequence. For example, Unicode says that the
472 letter C<LATIN SMALL LETTER SHARP S> should match the sequence C<ss>
473 under C</i> rules. Thus,
475 'ss' =~ /\A\N{LATIN SMALL LETTER SHARP S}\z/i # Matches
476 'ss' =~ /\A[aeioust\N{LATIN SMALL LETTER SHARP S}]\z/i # Matches
478 For this to happen, the class must not be inverted (see L</Negation>)
479 and the character must be explicitly specified, and not be part of a
480 multi-character range (not even as one of its endpoints). (L</Character
481 Ranges> will be explained shortly.) Therefore,
483 'ss' =~ /\A[\0-\x{ff}]\z/i # Doesn't match
484 'ss' =~ /\A[\0-\N{LATIN SMALL LETTER SHARP S}]\z/i # No match
485 'ss' =~ /\A[\xDF-\xDF]\z/i # Matches on ASCII platforms, since
486 # \XDF is LATIN SMALL LETTER SHARP S,
487 # and the range is just a single
490 Note that it isn't a good idea to specify these types of ranges anyway.
494 Some names known to C<\N{...}> refer to a sequence of multiple characters,
495 instead of the usual single character. When one of these is included in
496 the class, the entire sequence is matched. For example,
498 "\N{TAMIL LETTER KA}\N{TAMIL VOWEL SIGN AU}"
499 =~ / ^ [\N{TAMIL SYLLABLE KAU}] $ /x;
501 matches, because C<\N{TAMIL SYLLABLE KAU}> is a named sequence
502 consisting of the two characters matched against. Like the other
503 instance where a bracketed class can match multi characters, and for
504 similar reasons, the class must not be inverted, and the named sequence
505 may not appear in a range, even one where it is both endpoints. If
506 these happen, it is a fatal error if the character class is within an
507 extended L<C<(?[...])>|/Extended Bracketed Character Classes>
508 class; and only the first code point is used (with
509 a C<regexp>-type warning raised) otherwise.
513 =head3 Special Characters Inside a Bracketed Character Class
515 Most characters that are meta characters in regular expressions (that
516 is, characters that carry a special meaning like C<.>, C<*>, or C<(>) lose
517 their special meaning and can be used inside a character class without
518 the need to escape them. For instance, C<[()]> matches either an opening
519 parenthesis, or a closing parenthesis, and the parens inside the character
520 class don't group or capture.
522 Characters that may carry a special meaning inside a character class are:
523 C<\>, C<^>, C<->, C<[> and C<]>, and are discussed below. They can be
524 escaped with a backslash, although this is sometimes not needed, in which
525 case the backslash may be omitted.
527 The sequence C<\b> is special inside a bracketed character class. While
528 outside the character class, C<\b> is an assertion indicating a point
529 that does not have either two word characters or two non-word characters
530 on either side, inside a bracketed character class, C<\b> matches a
540 C<\N{U+I<hex char>}>,
545 are also special and have the same meanings as they do outside a
546 bracketed character class. (However, inside a bracketed character
547 class, if C<\N{I<NAME>}> expands to a sequence of characters, only the first
548 one in the sequence is used, with a warning.)
550 Also, a backslash followed by two or three octal digits is considered an octal
553 A C<[> is not special inside a character class, unless it's the start of a
554 POSIX character class (see L</POSIX Character Classes> below). It normally does
557 A C<]> is normally either the end of a POSIX character class (see
558 L</POSIX Character Classes> below), or it signals the end of the bracketed
559 character class. If you want to include a C<]> in the set of characters, you
560 must generally escape it.
562 However, if the C<]> is the I<first> (or the second if the first
563 character is a caret) character of a bracketed character class, it
564 does not denote the end of the class (as you cannot have an empty class)
565 and is considered part of the set of characters that can be matched without
570 "+" =~ /[+?*]/ # Match, "+" in a character class is not special.
571 "\cH" =~ /[\b]/ # Match, \b inside in a character class.
572 # is equivalent to a backspace.
573 "]" =~ /[][]/ # Match, as the character class contains.
575 "[]" =~ /[[]]/ # Match, the pattern contains a character class
576 # containing just ], and the character class is
579 =head3 Character Ranges
581 It is not uncommon to want to match a range of characters. Luckily, instead
582 of listing all characters in the range, one may use the hyphen (C<->).
583 If inside a bracketed character class you have two characters separated
584 by a hyphen, it's treated as if all characters between the two were in
585 the class. For instance, C<[0-9]> matches any ASCII digit, and C<[a-m]>
586 matches any lowercase letter from the first half of the ASCII alphabet.
588 Note that the two characters on either side of the hyphen are not
589 necessarily both letters or both digits. Any character is possible,
590 although not advisable. C<['-?]> contains a range of characters, but
591 most people will not know which characters that means. Furthermore,
592 such ranges may lead to portability problems if the code has to run on
593 a platform that uses a different character set, such as EBCDIC.
595 If a hyphen in a character class cannot syntactically be part of a range, for
596 instance because it is the first or the last character of the character class,
597 or if it immediately follows a range, the hyphen isn't special, and so is
598 considered a character to be matched literally. If you want a hyphen in
599 your set of characters to be matched and its position in the class is such
600 that it could be considered part of a range, you must escape that hyphen
605 [a-z] # Matches a character that is a lower case ASCII letter.
606 [a-fz] # Matches any letter between 'a' and 'f' (inclusive) or
608 [-z] # Matches either a hyphen ('-') or the letter 'z'.
609 [a-f-m] # Matches any letter between 'a' and 'f' (inclusive), the
610 # hyphen ('-'), or the letter 'm'.
611 ['-?] # Matches any of the characters '()*+,-./0123456789:;<=>?
612 # (But not on an EBCDIC platform).
617 It is also possible to instead list the characters you do not want to
618 match. You can do so by using a caret (C<^>) as the first character in the
619 character class. For instance, C<[^a-z]> matches any character that is not a
620 lowercase ASCII letter, which therefore includes more than a million
621 Unicode code points. The class is said to be "negated" or "inverted".
623 This syntax make the caret a special character inside a bracketed character
624 class, but only if it is the first character of the class. So if you want
625 the caret as one of the characters to match, either escape the caret or
626 else don't list it first.
628 In inverted bracketed character classes, Perl ignores the Unicode rules
629 that normally say that named sequence, and certain characters should
630 match a sequence of multiple characters use under caseless C</i>
631 matching. Following those rules could lead to highly confusing
634 "ss" =~ /^[^\xDF]+$/ui; # Matches!
636 This should match any sequences of characters that aren't C<\xDF> nor
637 what C<\xDF> matches under C</i>. C<"s"> isn't C<\xDF>, but Unicode
638 says that C<"ss"> is what C<\xDF> matches under C</i>. So which one
639 "wins"? Do you fail the match because the string has C<ss> or accept it
640 because it has an C<s> followed by another C<s>? Perl has chosen the
641 latter. (See note in L</Bracketed Character Classes> above.)
645 "e" =~ /[^aeiou]/ # No match, the 'e' is listed.
646 "x" =~ /[^aeiou]/ # Match, as 'x' isn't a lowercase vowel.
647 "^" =~ /[^^]/ # No match, matches anything that isn't a caret.
648 "^" =~ /[x^]/ # Match, caret is not special here.
650 =head3 Backslash Sequences
652 You can put any backslash sequence character class (with the exception of
653 C<\N> and C<\R>) inside a bracketed character class, and it will act just
654 as if you had put all characters matched by the backslash sequence inside the
655 character class. For instance, C<[a-f\d]> matches any decimal digit, or any
656 of the lowercase letters between 'a' and 'f' inclusive.
658 C<\N> within a bracketed character class must be of the forms C<\N{I<name>}>
659 or C<\N{U+I<hex char>}>, and NOT be the form that matches non-newlines,
660 for the same reason that a dot C<.> inside a bracketed character class loses
661 its special meaning: it matches nearly anything, which generally isn't what you
667 /[\p{Thai}\d]/ # Matches a character that is either a Thai
668 # character, or a digit.
669 /[^\p{Arabic}()]/ # Matches a character that is neither an Arabic
670 # character, nor a parenthesis.
672 Backslash sequence character classes cannot form one of the endpoints
673 of a range. Thus, you can't say:
675 /[\p{Thai}-\d]/ # Wrong!
677 =head3 POSIX Character Classes
678 X<character class> X<\p> X<\p{}>
679 X<alpha> X<alnum> X<ascii> X<blank> X<cntrl> X<digit> X<graph>
680 X<lower> X<print> X<punct> X<space> X<upper> X<word> X<xdigit>
682 POSIX character classes have the form C<[:class:]>, where I<class> is the
683 name, and the C<[:> and C<:]> delimiters. POSIX character classes only appear
684 I<inside> bracketed character classes, and are a convenient and descriptive
685 way of listing a group of characters.
687 Be careful about the syntax,
690 $string =~ /[[:alpha:]]/
692 # Incorrect (will warn):
693 $string =~ /[:alpha:]/
695 The latter pattern would be a character class consisting of a colon,
696 and the letters C<a>, C<l>, C<p> and C<h>.
698 POSIX character classes can be part of a larger bracketed character class.
703 is valid and matches '0', '1', any alphabetic character, and the percent sign.
705 Perl recognizes the following POSIX character classes:
707 alpha Any alphabetical character ("[A-Za-z]").
708 alnum Any alphanumeric character ("[A-Za-z0-9]").
709 ascii Any character in the ASCII character set.
710 blank A GNU extension, equal to a space or a horizontal tab ("\t").
711 cntrl Any control character. See Note [2] below.
712 digit Any decimal digit ("[0-9]"), equivalent to "\d".
713 graph Any printable character, excluding a space. See Note [3] below.
714 lower Any lowercase character ("[a-z]").
715 print Any printable character, including a space. See Note [4] below.
716 punct Any graphical character excluding "word" characters. Note [5].
717 space Any whitespace character. "\s" including the vertical tab
719 upper Any uppercase character ("[A-Z]").
720 word A Perl extension ("[A-Za-z0-9_]"), equivalent to "\w".
721 xdigit Any hexadecimal digit ("[0-9a-fA-F]").
723 Most POSIX character classes have two Unicode-style C<\p> property
724 counterparts. (They are not official Unicode properties, but Perl extensions
725 derived from official Unicode properties.) The table below shows the relation
726 between POSIX character classes and these counterparts.
728 One counterpart, in the column labelled "ASCII-range Unicode" in
729 the table, matches only characters in the ASCII character set.
731 The other counterpart, in the column labelled "Full-range Unicode", matches any
732 appropriate characters in the full Unicode character set. For example,
733 C<\p{Alpha}> matches not just the ASCII alphabetic characters, but any
734 character in the entire Unicode character set considered alphabetic.
735 An entry in the column labelled "backslash sequence" is a (short)
738 [[:...:]] ASCII-range Full-range backslash Note
739 Unicode Unicode sequence
740 -----------------------------------------------------
741 alpha \p{PosixAlpha} \p{XPosixAlpha}
742 alnum \p{PosixAlnum} \p{XPosixAlnum}
744 blank \p{PosixBlank} \p{XPosixBlank} \h [1]
745 or \p{HorizSpace} [1]
746 cntrl \p{PosixCntrl} \p{XPosixCntrl} [2]
747 digit \p{PosixDigit} \p{XPosixDigit} \d
748 graph \p{PosixGraph} \p{XPosixGraph} [3]
749 lower \p{PosixLower} \p{XPosixLower}
750 print \p{PosixPrint} \p{XPosixPrint} [4]
751 punct \p{PosixPunct} \p{XPosixPunct} [5]
752 \p{PerlSpace} \p{XPerlSpace} \s [6]
753 space \p{PosixSpace} \p{XPosixSpace} [6]
754 upper \p{PosixUpper} \p{XPosixUpper}
755 word \p{PosixWord} \p{XPosixWord} \w
756 xdigit \p{PosixXDigit} \p{XPosixXDigit}
762 C<\p{Blank}> and C<\p{HorizSpace}> are synonyms.
766 Control characters don't produce output as such, but instead usually control
767 the terminal somehow: for example, newline and backspace are control characters.
768 In the ASCII range, characters whose code points are between 0 and 31 inclusive,
769 plus 127 (C<DEL>) are control characters.
773 Any character that is I<graphical>, that is, visible. This class consists
774 of all alphanumeric characters and all punctuation characters.
778 All printable characters, which is the set of all graphical characters
779 plus those whitespace characters which are not also controls.
783 C<\p{PosixPunct}> and C<[[:punct:]]> in the ASCII range match all
784 non-controls, non-alphanumeric, non-space characters:
785 C<[-!"#$%&'()*+,./:;<=E<gt>?@[\\\]^_`{|}~]> (although if a locale is in effect,
786 it could alter the behavior of C<[[:punct:]]>).
788 The similarly named property, C<\p{Punct}>, matches a somewhat different
789 set in the ASCII range, namely
790 C<[-!"#%&'()*,./:;?@[\\\]_{}]>. That is, it is missing the nine
791 characters C<[$+E<lt>=E<gt>^`|~]>.
792 This is because Unicode splits what POSIX considers to be punctuation into two
793 categories, Punctuation and Symbols.
795 C<\p{XPosixPunct}> and (under Unicode rules) C<[[:punct:]]>, match what
796 C<\p{PosixPunct}> matches in the ASCII range, plus what C<\p{Punct}>
797 matches. This is different than strictly matching according to
798 C<\p{Punct}>. Another way to say it is that
799 if Unicode rules are in effect, C<[[:punct:]]> matches all characters
800 that Unicode considers punctuation, plus all ASCII-range characters that
801 Unicode considers symbols.
805 C<\p{XPerlSpace}> and C<\p{Space}> match identically starting with Perl
806 v5.18. In earlier versions, these differ only in that in non-locale
807 matching, C<\p{XPerlSpace}> does not match the vertical tab, C<\cK>.
808 Same for the two ASCII-only range forms.
812 There are various other synonyms that can be used besides the names
813 listed in the table. For example, C<\p{PosixAlpha}> can be written as
814 C<\p{Alpha}>. All are listed in
815 L<perluniprops/Properties accessible through \p{} and \P{}>.
817 Both the C<\p> counterparts always assume Unicode rules are in effect.
818 On ASCII platforms, this means they assume that the code points from 128
819 to 255 are Latin-1, and that means that using them under locale rules is
820 unwise unless the locale is guaranteed to be Latin-1 or UTF-8. In contrast, the
821 POSIX character classes are useful under locale rules. They are
822 affected by the actual rules in effect, as follows:
826 =item If the C</a> modifier, is in effect ...
828 Each of the POSIX classes matches exactly the same as their ASCII-range
835 =item For code points above 255 ...
837 The POSIX class matches the same as its Full-range counterpart.
839 =item For code points below 256 ...
843 =item if locale rules are in effect ...
845 The POSIX class matches according to the locale, except:
851 also includes the platform's native underscore character, no matter what
856 on platforms that don't have the POSIX C<ascii> extension, this matches
857 just the platform's native ASCII-range characters.
861 on platforms that don't have the POSIX C<blank> extension, this matches
862 just the platform's native tab and space characters.
866 =item if Unicode rules are in effect ...
868 The POSIX class matches the same as the Full-range counterpart.
872 The POSIX class matches the same as the ASCII range counterpart.
880 Which rules apply are determined as described in
881 L<perlre/Which character set modifier is in effect?>.
883 It is proposed to change this behavior in a future release of Perl so that
884 whether or not Unicode rules are in effect would not change the
885 behavior: Outside of locale, the POSIX classes
886 would behave like their ASCII-range counterparts. If you wish to
887 comment on this proposal, send email to C<perl5-porters@perl.org>.
889 =head4 Negation of POSIX character classes
890 X<character class, negation>
892 A Perl extension to the POSIX character class is the ability to
893 negate it. This is done by prefixing the class name with a caret (C<^>).
896 POSIX ASCII-range Full-range backslash
897 Unicode Unicode sequence
898 -----------------------------------------------------
899 [[:^digit:]] \P{PosixDigit} \P{XPosixDigit} \D
900 [[:^space:]] \P{PosixSpace} \P{XPosixSpace}
901 \P{PerlSpace} \P{XPerlSpace} \S
902 [[:^word:]] \P{PerlWord} \P{XPosixWord} \W
904 The backslash sequence can mean either ASCII- or Full-range Unicode,
905 depending on various factors as described in L<perlre/Which character set modifier is in effect?>.
907 =head4 [= =] and [. .]
909 Perl recognizes the POSIX character classes C<[=class=]> and
910 C<[.class.]>, but does not (yet?) support them. Any attempt to use
911 either construct raises an exception.
915 /[[:digit:]]/ # Matches a character that is a digit.
916 /[01[:lower:]]/ # Matches a character that is either a
917 # lowercase letter, or '0' or '1'.
918 /[[:digit:][:^xdigit:]]/ # Matches a character that can be anything
919 # except the letters 'a' to 'f' and 'A' to
920 # 'F'. This is because the main character
921 # class is composed of two POSIX character
922 # classes that are ORed together, one that
923 # matches any digit, and the other that
924 # matches anything that isn't a hex digit.
925 # The OR adds the digits, leaving only the
926 # letters 'a' to 'f' and 'A' to 'F' excluded.
928 =head3 Extended Bracketed Character Classes
932 This is a fancy bracketed character class that can be used for more
933 readable and less error-prone classes, and to perform set operations,
934 such as intersection. An example is
936 /(?[ \p{Thai} & \p{Digit} ])/
938 This will match all the digit characters that are in the Thai script.
940 This is an experimental feature available starting in 5.18, and is
941 subject to change as we gain field experience with it. Any attempt to
942 use it will raise a warning, unless disabled via
944 no warnings "experimental::regex_sets";
946 Comments on this feature are welcome; send email to
947 C<perl5-porters@perl.org>.
949 We can extend the example above:
951 /(?[ ( \p{Thai} + \p{Lao} ) & \p{Digit} ])/
953 This matches digits that are in either the Thai or Laotian scripts.
955 Notice the white space in these examples. This construct always has
956 the C<E<sol>x> modifier turned on within it.
958 The available binary operators are:
962 | another name for '+', hence means union
963 - subtraction (the result matches the set consisting of those
964 code points matched by the first operand, excluding any that
965 are also matched by the second operand)
966 ^ symmetric difference (the union minus the intersection). This
967 is like an exclusive or, in that the result is the set of code
968 points that are matched by either, but not both, of the
971 There is one unary operator:
975 All the binary operators left associate, and are of equal precedence.
976 The unary operator right associates, and has higher precedence. Use
977 parentheses to override the default associations. Some feedback we've
978 received indicates a desire for intersection to have higher precedence
979 than union. This is something that feedback from the field may cause us
980 to change in future releases; you may want to parenthesize copiously to
981 avoid such changes affecting your code, until this feature is no longer
982 considered experimental.
984 The main restriction is that everything is a metacharacter. Thus,
985 you cannot refer to single characters by doing something like this:
987 /(?[ a + b ])/ # Syntax error!
989 The easiest way to specify an individual typable character is to enclose
994 (This is the same thing as C<[ab]>.) You could also have said the
999 (You can, of course, specify single characters by using, C<\x{...}>,
1002 This last example shows the use of this construct to specify an ordinary
1003 bracketed character class without additional set operations. Note the
1004 white space within it; C<E<sol>x> is turned on even within bracketed
1005 character classes, except you can't have comments inside them. Hence,
1009 matches the literal character "#". To specify a literal white space character,
1010 you can escape it with a backslash, like:
1012 /(?[ [ a e i o u \ ] ])/
1014 This matches the English vowels plus the SPACE character.
1015 All the other escapes accepted by normal bracketed character classes are
1016 accepted here as well; but unrecognized escapes that generate warnings
1017 in normal classes are fatal errors here.
1019 All warnings from these class elements are fatal, as well as some
1020 practices that don't currently warn. For example you cannot say
1022 /(?[ [ \xF ] ])/ # Syntax error!
1024 You have to have two hex digits after a braceless C<\x> (use a leading
1025 zero to make two). These restrictions are to lower the incidence of
1026 typos causing the class to not match what you thought it would.
1028 If a regular bracketed character class contains a C<\p{}> or C<\P{}> and
1029 is matched against a non-Unicode code point, a warning may be
1030 raised, as the result is not Unicode-defined. No such warning will come
1031 when using this extended form.
1033 The final difference between regular bracketed character classes and
1034 these, is that it is not possible to get these to match a
1035 multi-character fold. Thus,
1039 does not match the string C<ss>.
1041 You don't have to enclose POSIX class names inside double brackets,
1042 hence both of the following work:
1044 /(?[ [:word:] - [:lower:] ])/
1045 /(?[ [[:word:]] - [[:lower:]] ])/
1047 Any contained POSIX character classes, including things like C<\w> and C<\D>
1048 respect the C<E<sol>a> (and C<E<sol>aa>) modifiers.
1050 C<< (?[ ]) >> is a regex-compile-time construct. Any attempt to use
1051 something which isn't knowable at the time the containing regular
1052 expression is compiled is a fatal error. In practice, this means
1053 just three limitations:
1059 This construct cannot be used within the scope of
1060 C<use locale> (or the C<E<sol>l> regex modifier).
1065 L<user-defined property|perlunicode/"User-Defined Character Properties">
1066 used must be already defined by the time the regular expression is
1067 compiled (but note that this construct can be used instead of such
1072 A regular expression that otherwise would compile
1073 using C<E<sol>d> rules, and which uses this construct will instead
1074 use C<E<sol>u>. Thus this construct tells Perl that you don't want
1075 C<E<sol>d> rules for the entire regular expression containing it.
1079 Note that skipping white space applies only to the interior of this
1080 construct. There must not be any space between any of the characters
1081 that form the initial C<(?[>. Nor may there be space between the
1082 closing C<])> characters.
1084 Just as in all regular expressions, the pattern can be built up by
1085 including variables that are interpolated at regex compilation time.
1086 Care must be taken to ensure that you are getting what you expect. For
1089 my $thai_or_lao = '\p{Thai} + \p{Lao}';
1091 qr/(?[ \p{Digit} & $thai_or_lao ])/;
1095 qr/(?[ \p{Digit} & \p{Thai} + \p{Lao} ])/;
1097 But this does not have the effect that someone reading the code would
1098 likely expect, as the intersection applies just to C<\p{Thai}>,
1099 excluding the Laotian. Pitfalls like this can be avoided by
1100 parenthesizing the component pieces:
1102 my $thai_or_lao = '( \p{Thai} + \p{Lao} )';
1104 But any modifiers will still apply to all the components:
1106 my $lower = '\p{Lower} + \p{Digit}';
1107 qr/(?[ \p{Greek} & $lower ])/i;
1109 matches upper case things. You can avoid surprises by making the
1110 components into instances of this construct by compiling them:
1112 my $thai_or_lao = qr/(?[ \p{Thai} + \p{Lao} ])/;
1113 my $lower = qr/(?[ \p{Lower} + \p{Digit} ])/;
1115 When these are embedded in another pattern, what they match does not
1116 change, regardless of parenthesization or what modifiers are in effect
1117 in that outer pattern.
1119 Due to the way that Perl parses things, your parentheses and brackets
1120 may need to be balanced, even including comments. If you run into any
1121 examples, please send them to C<perlbug@perl.org>, so that we can have a
1122 concrete example for this man page.
1124 We may change it so that things that remain legal uses in normal bracketed
1125 character classes might become illegal within this experimental
1126 construct. One proposal, for example, is to forbid adjacent uses of the
1127 same character, as in C<(?[ [aa] ])>. The motivation for such a change
1128 is that this usage is likely a typo, as the second "a" adds nothing.