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<\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 [0-9] matched by C<\d>, and/or might match
97 other characters whose code point is less than 256. Such a locale
98 definition would be in violation of the C language standard, but Perl
99 doesn't currently assume anything in regard to this.)
101 What this means is that unless the C</a> modifier is in effect C<\d> not
102 only matches the digits '0' - '9', but also Arabic, Devanagari, and
103 digits from other languages. This may cause some confusion, and some
106 Some digits that C<\d> matches look like some of the [0-9] ones, but
107 have different values. For example, BENGALI DIGIT FOUR (U+09EA) looks
108 very much like an ASCII DIGIT EIGHT (U+0038). An application that
109 is expecting only the ASCII digits might be misled, or if the match is
110 C<\d+>, the matched string might contain a mixture of digits from
111 different writing systems that look like they signify a number different
112 than they actually do. L<Unicode::UCD/num()> can
114 calculate the value, returning C<undef> if the input string contains
117 What C<\p{Digit}> means (and hence C<\d> except under the C</a>
118 modifier) is C<\p{General_Category=Decimal_Number}>, or synonymously,
119 C<\p{General_Category=Digit}>. Starting with Unicode version 4.1, this
120 is the same set of characters matched by C<\p{Numeric_Type=Decimal}>.
121 But Unicode also has a different property with a similar name,
122 C<\p{Numeric_Type=Digit}>, which matches a completely different set of
123 characters. These characters are things such as C<CIRCLED DIGIT ONE>
124 or subscripts, or are from writing systems that lack all ten digits.
126 The design intent is for C<\d> to exactly match the set of characters
127 that can safely be used with "normal" big-endian positional decimal
128 syntax, where, for example 123 means one 'hundred', plus two 'tens',
129 plus three 'ones'. This positional notation does not necessarily apply
130 to characters that match the other type of "digit",
131 C<\p{Numeric_Type=Digit}>, and so C<\d> doesn't match them.
133 The Tamil digits (U+0BE6 - U+0BEF) can also legally be
134 used in old-style Tamil numbers in which they would appear no more than
135 one in a row, separated by characters that mean "times 10", "times 100",
136 etc. (See L<http://www.unicode.org/notes/tn21>.)
138 Any character not matched by C<\d> is matched by C<\D>.
140 =head3 Word characters
142 A C<\w> matches a single alphanumeric character (an alphabetic character, or a
143 decimal digit); or a connecting punctuation character, such as an
144 underscore ("_"); or a "mark" character (like some sort of accent) that
145 attaches to one of those. It does not match a whole word. To match a
146 whole word, use C<\w+>. This isn't the same thing as matching an
147 English word, but in the ASCII range it is the same as a string of
148 Perl-identifier characters.
152 =item If the C</a> modifier is in effect ...
154 C<\w> matches the 63 characters [a-zA-Z0-9_].
160 =item For code points above 255 ...
162 C<\w> matches the same as C<\p{Word}> matches in this range. That is,
163 it matches Thai letters, Greek letters, etc. This includes connector
164 punctuation (like the underscore) which connect two words together, or
165 diacritics, such as a C<COMBINING TILDE> and the modifier letters, which
166 are generally used to add auxiliary markings to letters.
168 =item For code points below 256 ...
172 =item if locale rules are in effect ...
174 C<\w> matches the platform's native underscore character plus whatever
175 the locale considers to be alphanumeric.
177 =item if Unicode rules are in effect ...
179 C<\w> matches exactly what C<\p{Word}> matches.
183 C<\w> matches [a-zA-Z0-9_].
191 Which rules apply are determined as described in L<perlre/Which character set modifier is in effect?>.
193 There are a number of security issues with the full Unicode list of word
194 characters. See L<http://unicode.org/reports/tr36>.
196 Also, for a somewhat finer-grained set of characters that are in programming
197 language identifiers beyond the ASCII range, you may wish to instead use the
198 more customized L</Unicode Properties>, C<\p{ID_Start}>,
199 C<\p{ID_Continue}>, C<\p{XID_Start}>, and C<\p{XID_Continue}>. See
200 L<http://unicode.org/reports/tr31>.
202 Any character not matched by C<\w> is matched by C<\W>.
206 C<\s> matches any single character considered whitespace.
210 =item If the C</a> modifier is in effect ...
212 In all Perl versions, C<\s> matches the 5 characters [\t\n\f\r ]; that
213 is, the horizontal tab,
214 the newline, the form feed, the carriage return, and the space.
215 Starting in Perl v5.18, experimentally, it also matches the vertical tab, C<\cK>.
216 See note C<[1]> below for a discussion of this.
222 =item For code points above 255 ...
224 C<\s> matches exactly the code points above 255 shown with an "s" column
227 =item For code points below 256 ...
231 =item if locale rules are in effect ...
233 C<\s> matches whatever the locale considers to be whitespace.
235 =item if Unicode rules are in effect ...
237 C<\s> matches exactly the characters shown with an "s" column in the
242 C<\s> matches [\t\n\f\r\cK ] and, starting, experimentally in Perl
243 v5.18, the vertical tab, C<\cK>.
244 (See note C<[1]> below for a discussion of this.)
245 Note that this list doesn't include the non-breaking space.
253 Which rules apply are determined as described in L<perlre/Which character set modifier is in effect?>.
255 Any character not matched by C<\s> is matched by C<\S>.
257 C<\h> matches any character considered horizontal whitespace;
258 this includes the platform's space and tab characters and several others
259 listed in the table below. C<\H> matches any character
260 not considered horizontal whitespace. They use the platform's native
261 character set, and do not consider any locale that may otherwise be in
264 C<\v> matches any character considered vertical whitespace;
265 this includes the platform's carriage return and line feed characters (newline)
266 plus several other characters, all listed in the table below.
267 C<\V> matches any character not considered vertical whitespace.
268 They use the platform's native character set, and do not consider any
269 locale that may otherwise be in use.
271 C<\R> matches anything that can be considered a newline under Unicode
272 rules. It's not a character class, as it can match a multi-character
273 sequence. Therefore, it cannot be used inside a bracketed character
274 class; use C<\v> instead (vertical whitespace). It uses the platform's
275 native character set, and does not consider any locale that may
277 Details are discussed in L<perlrebackslash>.
279 Note that unlike C<\s> (and C<\d> and C<\w>), C<\h> and C<\v> always match
280 the same characters, without regard to other factors, such as the active
281 locale or whether the source string is in UTF-8 format.
283 One might think that C<\s> is equivalent to C<[\h\v]>. This is indeed true
284 starting in Perl v5.18, but prior to that, the sole difference was that the
285 vertical tab (C<"\cK">) was not matched by C<\s>.
287 The following table is a complete listing of characters matched by
288 C<\s>, C<\h> and C<\v> as of Unicode 6.3.
290 The first column gives the Unicode code point of the character (in hex format),
291 the second column gives the (Unicode) name. The third column indicates
292 by which class(es) the character is matched (assuming no locale is in
293 effect that changes the C<\s> matching).
295 0x0009 CHARACTER TABULATION h s
296 0x000a LINE FEED (LF) vs
297 0x000b LINE TABULATION vs [1]
298 0x000c FORM FEED (FF) vs
299 0x000d CARRIAGE RETURN (CR) vs
301 0x0085 NEXT LINE (NEL) vs [2]
302 0x00a0 NO-BREAK SPACE h s [2]
303 0x1680 OGHAM SPACE MARK h s
308 0x2004 THREE-PER-EM SPACE h s
309 0x2005 FOUR-PER-EM SPACE h s
310 0x2006 SIX-PER-EM SPACE h s
311 0x2007 FIGURE SPACE h s
312 0x2008 PUNCTUATION SPACE h s
313 0x2009 THIN SPACE h s
314 0x200a HAIR SPACE h s
315 0x2028 LINE SEPARATOR vs
316 0x2029 PARAGRAPH SEPARATOR vs
317 0x202f NARROW NO-BREAK SPACE h s
318 0x205f MEDIUM MATHEMATICAL SPACE h s
319 0x3000 IDEOGRAPHIC SPACE h s
325 Prior to Perl v5.18, C<\s> did not match the vertical tab. The change
326 in v5.18 is considered an experiment, which means it could be backed out
327 in v5.20 or v5.22 if experience indicates that it breaks too much
328 existing code. If this change adversely affects you, send email to
329 C<perlbug@perl.org>; if it affects you positively, email
330 C<perlthanks@perl.org>. In the meantime, C<[^\S\cK]> (obscurely)
331 matches what C<\s> traditionally did.
335 NEXT LINE and NO-BREAK SPACE may or may not match C<\s> depending
336 on the rules in effect. See
337 L<the beginning of this section|/Whitespace>.
341 =head3 Unicode Properties
343 C<\pP> and C<\p{Prop}> are character classes to match characters that fit given
344 Unicode properties. One letter property names can be used in the C<\pP> form,
345 with the property name following the C<\p>, otherwise, braces are required.
346 When using braces, there is a single form, which is just the property name
347 enclosed in the braces, and a compound form which looks like C<\p{name=value}>,
348 which means to match if the property "name" for the character has that particular
350 For instance, a match for a number can be written as C</\pN/> or as
351 C</\p{Number}/>, or as C</\p{Number=True}/>.
352 Lowercase letters are matched by the property I<Lowercase_Letter> which
353 has the short form I<Ll>. They need the braces, so are written as C</\p{Ll}/> or
354 C</\p{Lowercase_Letter}/>, or C</\p{General_Category=Lowercase_Letter}/>
355 (the underscores are optional).
356 C</\pLl/> is valid, but means something different.
357 It matches a two character string: a letter (Unicode property C<\pL>),
358 followed by a lowercase C<l>.
360 If locale rules are not in effect, the use of
361 a Unicode property will force the regular expression into using Unicode
362 rules, if it isn't already.
364 Note that almost all properties are immune to case-insensitive matching.
365 That is, adding a C</i> regular expression modifier does not change what
366 they match. There are two sets that are affected. The first set is
369 and C<Titlecase_Letter>,
370 all of which match C<Cased_Letter> under C</i> matching.
375 all of which match C<Cased> under C</i> matching.
376 (The difference between these sets is that some things, such as Roman
377 numerals, come in both upper and lower case, so they are C<Cased>, but
378 aren't considered to be letters, so they aren't C<Cased_Letter>s. They're
379 actually C<Letter_Number>s.)
380 This set also includes its subsets C<PosixUpper> and C<PosixLower>, both
381 of which under C</i> match C<PosixAlpha>.
383 For more details on Unicode properties, see L<perlunicode/Unicode
384 Character Properties>; for a
385 complete list of possible properties, see
386 L<perluniprops/Properties accessible through \p{} and \P{}>,
387 which notes all forms that have C</i> differences.
388 It is also possible to define your own properties. This is discussed in
389 L<perlunicode/User-Defined Character Properties>.
391 Unicode properties are defined (surprise!) only on Unicode code points.
392 A warning is raised and all matches fail on non-Unicode code points
393 (those above the legal Unicode maximum of 0x10FFFF). This can be
396 chr(0x110000) =~ \p{ASCII_Hex_Digit=True} # Fails.
397 chr(0x110000) =~ \p{ASCII_Hex_Digit=False} # Also fails!
399 Even though these two matches might be thought of as complements, they
400 are so only on Unicode code points.
404 "a" =~ /\w/ # Match, "a" is a 'word' character.
405 "7" =~ /\w/ # Match, "7" is a 'word' character as well.
406 "a" =~ /\d/ # No match, "a" isn't a digit.
407 "7" =~ /\d/ # Match, "7" is a digit.
408 " " =~ /\s/ # Match, a space is whitespace.
409 "a" =~ /\D/ # Match, "a" is a non-digit.
410 "7" =~ /\D/ # No match, "7" is not a non-digit.
411 " " =~ /\S/ # No match, a space is not non-whitespace.
413 " " =~ /\h/ # Match, space is horizontal whitespace.
414 " " =~ /\v/ # No match, space is not vertical whitespace.
415 "\r" =~ /\v/ # Match, a return is vertical whitespace.
417 "a" =~ /\pL/ # Match, "a" is a letter.
418 "a" =~ /\p{Lu}/ # No match, /\p{Lu}/ matches upper case letters.
420 "\x{0e0b}" =~ /\p{Thai}/ # Match, \x{0e0b} is the character
421 # 'THAI CHARACTER SO SO', and that's in
422 # Thai Unicode class.
423 "a" =~ /\P{Lao}/ # Match, as "a" is not a Laotian character.
425 It is worth emphasizing that C<\d>, C<\w>, etc, match single characters, not
426 complete numbers or words. To match a number (that consists of digits),
427 use C<\d+>; to match a word, use C<\w+>. But be aware of the security
428 considerations in doing so, as mentioned above.
430 =head2 Bracketed Character Classes
432 The third form of character class you can use in Perl regular expressions
433 is the bracketed character class. In its simplest form, it lists the characters
434 that may be matched, surrounded by square brackets, like this: C<[aeiou]>.
435 This matches one of C<a>, C<e>, C<i>, C<o> or C<u>. Like the other
436 character classes, exactly one character is matched.* To match
437 a longer string consisting of characters mentioned in the character
438 class, follow the character class with a L<quantifier|perlre/Quantifiers>. For
439 instance, C<[aeiou]+> matches one or more lowercase English vowels.
441 Repeating a character in a character class has no
442 effect; it's considered to be in the set only once.
446 "e" =~ /[aeiou]/ # Match, as "e" is listed in the class.
447 "p" =~ /[aeiou]/ # No match, "p" is not listed in the class.
448 "ae" =~ /^[aeiou]$/ # No match, a character class only matches
449 # a single character.
450 "ae" =~ /^[aeiou]+$/ # Match, due to the quantifier.
454 * There is an exception to a bracketed character class matching a
455 single character only. When the class is to match caselessly under C</i>
456 matching rules, and a character that is explicitly mentioned inside the
458 multiple-character sequence caselessly under Unicode rules, the class
459 (when not L<inverted|/Negation>) will also match that sequence. For
460 example, Unicode says that the letter C<LATIN SMALL LETTER SHARP S>
461 should match the sequence C<ss> under C</i> rules. Thus,
463 'ss' =~ /\A\N{LATIN SMALL LETTER SHARP S}\z/i # Matches
464 'ss' =~ /\A[aeioust\N{LATIN SMALL LETTER SHARP S}]\z/i # Matches
466 For this to happen, the character must be explicitly specified, and not
467 be part of a multi-character range (not even as one of its endpoints).
468 (L</Character Ranges> will be explained shortly.) Therefore,
470 'ss' =~ /\A[\0-\x{ff}]\z/i # Doesn't match
471 'ss' =~ /\A[\0-\N{LATIN SMALL LETTER SHARP S}]\z/i # No match
472 'ss' =~ /\A[\xDF-\xDF]\z/i # Matches on ASCII platforms, since \XDF
473 # is LATIN SMALL LETTER SHARP S, and the
474 # range is just a single element
476 Note that it isn't a good idea to specify these types of ranges anyway.
478 =head3 Special Characters Inside a Bracketed Character Class
480 Most characters that are meta characters in regular expressions (that
481 is, characters that carry a special meaning like C<.>, C<*>, or C<(>) lose
482 their special meaning and can be used inside a character class without
483 the need to escape them. For instance, C<[()]> matches either an opening
484 parenthesis, or a closing parenthesis, and the parens inside the character
485 class don't group or capture.
487 Characters that may carry a special meaning inside a character class are:
488 C<\>, C<^>, C<->, C<[> and C<]>, and are discussed below. They can be
489 escaped with a backslash, although this is sometimes not needed, in which
490 case the backslash may be omitted.
492 The sequence C<\b> is special inside a bracketed character class. While
493 outside the character class, C<\b> is an assertion indicating a point
494 that does not have either two word characters or two non-word characters
495 on either side, inside a bracketed character class, C<\b> matches a
505 C<\N{U+I<hex char>}>,
510 are also special and have the same meanings as they do outside a
511 bracketed character class. (However, inside a bracketed character
512 class, if C<\N{I<NAME>}> expands to a sequence of characters, only the first
513 one in the sequence is used, with a warning.)
515 Also, a backslash followed by two or three octal digits is considered an octal
518 A C<[> is not special inside a character class, unless it's the start of a
519 POSIX character class (see L</POSIX Character Classes> below). It normally does
522 A C<]> is normally either the end of a POSIX character class (see
523 L</POSIX Character Classes> below), or it signals the end of the bracketed
524 character class. If you want to include a C<]> in the set of characters, you
525 must generally escape it.
527 However, if the C<]> is the I<first> (or the second if the first
528 character is a caret) character of a bracketed character class, it
529 does not denote the end of the class (as you cannot have an empty class)
530 and is considered part of the set of characters that can be matched without
535 "+" =~ /[+?*]/ # Match, "+" in a character class is not special.
536 "\cH" =~ /[\b]/ # Match, \b inside in a character class.
537 # is equivalent to a backspace.
538 "]" =~ /[][]/ # Match, as the character class contains.
540 "[]" =~ /[[]]/ # Match, the pattern contains a character class
541 # containing just ], and the character class is
544 =head3 Character Ranges
546 It is not uncommon to want to match a range of characters. Luckily, instead
547 of listing all characters in the range, one may use the hyphen (C<->).
548 If inside a bracketed character class you have two characters separated
549 by a hyphen, it's treated as if all characters between the two were in
550 the class. For instance, C<[0-9]> matches any ASCII digit, and C<[a-m]>
551 matches any lowercase letter from the first half of the ASCII alphabet.
553 Note that the two characters on either side of the hyphen are not
554 necessarily both letters or both digits. Any character is possible,
555 although not advisable. C<['-?]> contains a range of characters, but
556 most people will not know which characters that means. Furthermore,
557 such ranges may lead to portability problems if the code has to run on
558 a platform that uses a different character set, such as EBCDIC.
560 If a hyphen in a character class cannot syntactically be part of a range, for
561 instance because it is the first or the last character of the character class,
562 or if it immediately follows a range, the hyphen isn't special, and so is
563 considered a character to be matched literally. If you want a hyphen in
564 your set of characters to be matched and its position in the class is such
565 that it could be considered part of a range, you must escape that hyphen
570 [a-z] # Matches a character that is a lower case ASCII letter.
571 [a-fz] # Matches any letter between 'a' and 'f' (inclusive) or
573 [-z] # Matches either a hyphen ('-') or the letter 'z'.
574 [a-f-m] # Matches any letter between 'a' and 'f' (inclusive), the
575 # hyphen ('-'), or the letter 'm'.
576 ['-?] # Matches any of the characters '()*+,-./0123456789:;<=>?
577 # (But not on an EBCDIC platform).
582 It is also possible to instead list the characters you do not want to
583 match. You can do so by using a caret (C<^>) as the first character in the
584 character class. For instance, C<[^a-z]> matches any character that is not a
585 lowercase ASCII letter, which therefore includes more than a million
586 Unicode code points. The class is said to be "negated" or "inverted".
588 This syntax make the caret a special character inside a bracketed character
589 class, but only if it is the first character of the class. So if you want
590 the caret as one of the characters to match, either escape the caret or
591 else don't list it first.
593 In inverted bracketed character classes, Perl ignores the Unicode rules
594 that normally say that certain characters should match a sequence of
595 multiple characters under caseless C</i> matching. Following those
596 rules could lead to highly confusing situations:
598 "ss" =~ /^[^\xDF]+$/ui; # Matches!
600 This should match any sequences of characters that aren't C<\xDF> nor
601 what C<\xDF> matches under C</i>. C<"s"> isn't C<\xDF>, but Unicode
602 says that C<"ss"> is what C<\xDF> matches under C</i>. So which one
603 "wins"? Do you fail the match because the string has C<ss> or accept it
604 because it has an C<s> followed by another C<s>? Perl has chosen the
609 "e" =~ /[^aeiou]/ # No match, the 'e' is listed.
610 "x" =~ /[^aeiou]/ # Match, as 'x' isn't a lowercase vowel.
611 "^" =~ /[^^]/ # No match, matches anything that isn't a caret.
612 "^" =~ /[x^]/ # Match, caret is not special here.
614 =head3 Backslash Sequences
616 You can put any backslash sequence character class (with the exception of
617 C<\N> and C<\R>) inside a bracketed character class, and it will act just
618 as if you had put all characters matched by the backslash sequence inside the
619 character class. For instance, C<[a-f\d]> matches any decimal digit, or any
620 of the lowercase letters between 'a' and 'f' inclusive.
622 C<\N> within a bracketed character class must be of the forms C<\N{I<name>}>
623 or C<\N{U+I<hex char>}>, and NOT be the form that matches non-newlines,
624 for the same reason that a dot C<.> inside a bracketed character class loses
625 its special meaning: it matches nearly anything, which generally isn't what you
631 /[\p{Thai}\d]/ # Matches a character that is either a Thai
632 # character, or a digit.
633 /[^\p{Arabic}()]/ # Matches a character that is neither an Arabic
634 # character, nor a parenthesis.
636 Backslash sequence character classes cannot form one of the endpoints
637 of a range. Thus, you can't say:
639 /[\p{Thai}-\d]/ # Wrong!
641 =head3 POSIX Character Classes
642 X<character class> X<\p> X<\p{}>
643 X<alpha> X<alnum> X<ascii> X<blank> X<cntrl> X<digit> X<graph>
644 X<lower> X<print> X<punct> X<space> X<upper> X<word> X<xdigit>
646 POSIX character classes have the form C<[:class:]>, where I<class> is
647 name, and the C<[:> and C<:]> delimiters. POSIX character classes only appear
648 I<inside> bracketed character classes, and are a convenient and descriptive
649 way of listing a group of characters.
651 Be careful about the syntax,
654 $string =~ /[[:alpha:]]/
656 # Incorrect (will warn):
657 $string =~ /[:alpha:]/
659 The latter pattern would be a character class consisting of a colon,
660 and the letters C<a>, C<l>, C<p> and C<h>.
661 POSIX character classes can be part of a larger bracketed character class.
666 is valid and matches '0', '1', any alphabetic character, and the percent sign.
668 Perl recognizes the following POSIX character classes:
670 alpha Any alphabetical character ("[A-Za-z]").
671 alnum Any alphanumeric character ("[A-Za-z0-9]").
672 ascii Any character in the ASCII character set.
673 blank A GNU extension, equal to a space or a horizontal tab ("\t").
674 cntrl Any control character. See Note [2] below.
675 digit Any decimal digit ("[0-9]"), equivalent to "\d".
676 graph Any printable character, excluding a space. See Note [3] below.
677 lower Any lowercase character ("[a-z]").
678 print Any printable character, including a space. See Note [4] below.
679 punct Any graphical character excluding "word" characters. Note [5].
680 space Any whitespace character. "\s" including the vertical tab
682 upper Any uppercase character ("[A-Z]").
683 word A Perl extension ("[A-Za-z0-9_]"), equivalent to "\w".
684 xdigit Any hexadecimal digit ("[0-9a-fA-F]").
686 Most POSIX character classes have two Unicode-style C<\p> property
687 counterparts. (They are not official Unicode properties, but Perl extensions
688 derived from official Unicode properties.) The table below shows the relation
689 between POSIX character classes and these counterparts.
691 One counterpart, in the column labelled "ASCII-range Unicode" in
692 the table, matches only characters in the ASCII character set.
694 The other counterpart, in the column labelled "Full-range Unicode", matches any
695 appropriate characters in the full Unicode character set. For example,
696 C<\p{Alpha}> matches not just the ASCII alphabetic characters, but any
697 character in the entire Unicode character set considered alphabetic.
698 An entry in the column labelled "backslash sequence" is a (short)
701 [[:...:]] ASCII-range Full-range backslash Note
702 Unicode Unicode sequence
703 -----------------------------------------------------
704 alpha \p{PosixAlpha} \p{XPosixAlpha}
705 alnum \p{PosixAlnum} \p{XPosixAlnum}
707 blank \p{PosixBlank} \p{XPosixBlank} \h [1]
708 or \p{HorizSpace} [1]
709 cntrl \p{PosixCntrl} \p{XPosixCntrl} [2]
710 digit \p{PosixDigit} \p{XPosixDigit} \d
711 graph \p{PosixGraph} \p{XPosixGraph} [3]
712 lower \p{PosixLower} \p{XPosixLower}
713 print \p{PosixPrint} \p{XPosixPrint} [4]
714 punct \p{PosixPunct} \p{XPosixPunct} [5]
715 \p{PerlSpace} \p{XPerlSpace} \s [6]
716 space \p{PosixSpace} \p{XPosixSpace} [6]
717 upper \p{PosixUpper} \p{XPosixUpper}
718 word \p{PosixWord} \p{XPosixWord} \w
719 xdigit \p{PosixXDigit} \p{XPosixXDigit}
725 C<\p{Blank}> and C<\p{HorizSpace}> are synonyms.
729 Control characters don't produce output as such, but instead usually control
730 the terminal somehow: for example, newline and backspace are control characters.
731 In the ASCII range, characters whose code points are between 0 and 31 inclusive,
732 plus 127 (C<DEL>) are control characters.
736 Any character that is I<graphical>, that is, visible. This class consists
737 of all alphanumeric characters and all punctuation characters.
741 All printable characters, which is the set of all graphical characters
742 plus those whitespace characters which are not also controls.
746 C<\p{PosixPunct}> and C<[[:punct:]]> in the ASCII range match all
747 non-controls, non-alphanumeric, non-space characters:
748 C<[-!"#$%&'()*+,./:;<=E<gt>?@[\\\]^_`{|}~]> (although if a locale is in effect,
749 it could alter the behavior of C<[[:punct:]]>).
751 The similarly named property, C<\p{Punct}>, matches a somewhat different
752 set in the ASCII range, namely
753 C<[-!"#%&'()*,./:;?@[\\\]_{}]>. That is, it is missing the nine
754 characters C<[$+E<lt>=E<gt>^`|~]>.
755 This is because Unicode splits what POSIX considers to be punctuation into two
756 categories, Punctuation and Symbols.
758 C<\p{XPosixPunct}> and (under Unicode rules) C<[[:punct:]]>, match what
759 C<\p{PosixPunct}> matches in the ASCII range, plus what C<\p{Punct}>
760 matches. This is different than strictly matching according to
761 C<\p{Punct}>. Another way to say it is that
762 if Unicode rules are in effect, C<[[:punct:]]> matches all characters
763 that Unicode considers punctuation, plus all ASCII-range characters that
764 Unicode considers symbols.
768 C<\p{SpacePerl}> and C<\p{Space}> match identically starting with Perl
769 v5.18. In earlier versions, these differ only in that in non-locale
770 matching, C<\p{SpacePerl}> does not match the vertical tab, C<\cK>.
771 Same for the two ASCII-only range forms.
775 There are various other synonyms that can be used besides the names
776 listed in the table. For example, C<\p{PosixAlpha}> can be written as
777 C<\p{Alpha}>. All are listed in
778 L<perluniprops/Properties accessible through \p{} and \P{}>,
779 plus all characters matched by each ASCII-range property.
781 Both the C<\p> counterparts always assume Unicode rules are in effect.
782 On ASCII platforms, this means they assume that the code points from 128
783 to 255 are Latin-1, and that means that using them under locale rules is
784 unwise unless the locale is guaranteed to be Latin-1 or UTF-8. In contrast, the
785 POSIX character classes are useful under locale rules. They are
786 affected by the actual rules in effect, as follows:
790 =item If the C</a> modifier, is in effect ...
792 Each of the POSIX classes matches exactly the same as their ASCII-range
799 =item For code points above 255 ...
801 The POSIX class matches the same as its Full-range counterpart.
803 =item For code points below 256 ...
807 =item if locale rules are in effect ...
809 The POSIX class matches according to the locale, except that
810 C<word> uses the platform's native underscore character, no matter what
813 =item if Unicode rules are in effect ...
815 The POSIX class matches the same as the Full-range counterpart.
819 The POSIX class matches the same as the ASCII range counterpart.
827 Which rules apply are determined as described in
828 L<perlre/Which character set modifier is in effect?>.
830 It is proposed to change this behavior in a future release of Perl so that
831 whether or not Unicode rules are in effect would not change the
832 behavior: Outside of locale, the POSIX classes
833 would behave like their ASCII-range counterparts. If you wish to
834 comment on this proposal, send email to C<perl5-porters@perl.org>.
836 =head4 Negation of POSIX character classes
837 X<character class, negation>
839 A Perl extension to the POSIX character class is the ability to
840 negate it. This is done by prefixing the class name with a caret (C<^>).
843 POSIX ASCII-range Full-range backslash
844 Unicode Unicode sequence
845 -----------------------------------------------------
846 [[:^digit:]] \P{PosixDigit} \P{XPosixDigit} \D
847 [[:^space:]] \P{PosixSpace} \P{XPosixSpace}
848 \P{PerlSpace} \P{XPerlSpace} \S
849 [[:^word:]] \P{PerlWord} \P{XPosixWord} \W
851 The backslash sequence can mean either ASCII- or Full-range Unicode,
852 depending on various factors as described in L<perlre/Which character set modifier is in effect?>.
854 =head4 [= =] and [. .]
856 Perl recognizes the POSIX character classes C<[=class=]> and
857 C<[.class.]>, but does not (yet?) support them. Any attempt to use
858 either construct raises an exception.
862 /[[:digit:]]/ # Matches a character that is a digit.
863 /[01[:lower:]]/ # Matches a character that is either a
864 # lowercase letter, or '0' or '1'.
865 /[[:digit:][:^xdigit:]]/ # Matches a character that can be anything
866 # except the letters 'a' to 'f' and 'A' to
867 # 'F'. This is because the main character
868 # class is composed of two POSIX character
869 # classes that are ORed together, one that
870 # matches any digit, and the other that
871 # matches anything that isn't a hex digit.
872 # The OR adds the digits, leaving only the
873 # letters 'a' to 'f' and 'A' to 'F' excluded.
875 =head3 Extended Bracketed Character Classes
879 This is a fancy bracketed character class that can be used for more
880 readable and less error-prone classes, and to perform set operations,
881 such as intersection. An example is
883 /(?[ \p{Thai} & \p{Digit} ])/
885 This will match all the digit characters that are in the Thai script.
887 This is an experimental feature available starting in 5.18, and is
888 subject to change as we gain field experience with it. Any attempt to
889 use it will raise a warning, unless disabled via
891 no warnings "experimental::regex_sets";
893 Comments on this feature are welcome; send email to
894 C<perl5-porters@perl.org>.
896 We can extend the example above:
898 /(?[ ( \p{Thai} + \p{Lao} ) & \p{Digit} ])/
900 This matches digits that are in either the Thai or Laotian scripts.
902 Notice the white space in these examples. This construct always has
903 the C<E<sol>x> modifier turned on.
905 The available binary operators are:
909 | another name for '+', hence means union
910 - subtraction (the result matches the set consisting of those
911 code points matched by the first operand, excluding any that
912 are also matched by the second operand)
913 ^ symmetric difference (the union minus the intersection). This
914 is like an exclusive or, in that the result is the set of code
915 points that are matched by either, but not both, of the
918 There is one unary operator:
922 All the binary operators left associate, and are of equal precedence.
923 The unary operator right associates, and has higher precedence. Use
924 parentheses to override the default associations. Some feedback we've
925 received indicates a desire for intersection to have higher precedence
926 than union. This is something that feedback from the field may cause us
927 to change in future releases; you may want to parenthesize copiously to
928 avoid such changes affecting your code, until this feature is no longer
929 considered experimental.
931 The main restriction is that everything is a metacharacter. Thus,
932 you cannot refer to single characters by doing something like this:
934 /(?[ a + b ])/ # Syntax error!
936 The easiest way to specify an individual typable character is to enclose
941 (This is the same thing as C<[ab]>.) You could also have said the
946 (You can, of course, specify single characters by using, C<\x{...}>,
949 This last example shows the use of this construct to specify an ordinary
950 bracketed character class without additional set operations. Note the
951 white space within it; C<E<sol>x> is turned on even within bracketed
952 character classes, except you can't have comments inside them. Hence,
956 matches the literal character "#". To specify a literal white space character,
957 you can escape it with a backslash, like:
959 /(?[ [ a e i o u \ ] ])/
961 This matches the English vowels plus the SPACE character.
962 All the other escapes accepted by normal bracketed character classes are
963 accepted here as well; but unrecognized escapes that generate warnings
964 in normal classes are fatal errors here.
966 All warnings from these class elements are fatal, as well as some
967 practices that don't currently warn. For example you cannot say
969 /(?[ [ \xF ] ])/ # Syntax error!
971 You have to have two hex digits after a braceless C<\x> (use a leading
972 zero to make two). These restrictions are to lower the incidence of
973 typos causing the class to not match what you thought it would.
975 The final difference between regular bracketed character classes and
976 these, is that it is not possible to get these to match a
977 multi-character fold. Thus,
981 does not match the string C<ss>.
983 You don't have to enclose POSIX class names inside double brackets,
984 hence both of the following work:
986 /(?[ [:word:] - [:lower:] ])/
987 /(?[ [[:word:]] - [[:lower:]] ])/
989 Any contained POSIX character classes, including things like C<\w> and C<\D>
990 respect the C<E<sol>a> (and C<E<sol>aa>) modifiers.
992 C<< (?[ ]) >> is a regex-compile-time construct. Any attempt to use
993 something which isn't knowable at the time the containing regular
994 expression is compiled is a fatal error. In practice, this means
995 just three limitations:
1001 This construct cannot be used within the scope of
1002 C<use locale> (or the C<E<sol>l> regex modifier).
1007 L<user-defined property|perlunicode/"User-Defined Character Properties">
1008 used must be already defined by the time the regular expression is
1009 compiled (but note that this construct can be used instead of such
1014 A regular expression that otherwise would compile
1015 using C<E<sol>d> rules, and which uses this construct will instead
1016 use C<E<sol>u>. Thus this construct tells Perl that you don't want
1017 C<E<sol>d> rules for the entire regular expression containing it.
1021 The C<E<sol>x> processing within this class is an extended form.
1022 Besides the characters that are considered white space in normal C</x>
1023 processing, there are 5 others, recommended by the Unicode standard:
1026 U+200E LEFT-TO-RIGHT MARK
1027 U+200F RIGHT-TO-LEFT MARK
1028 U+2028 LINE SEPARATOR
1029 U+2029 PARAGRAPH SEPARATOR
1031 Note that skipping white space applies only to the interior of this
1032 construct. There must not be any space between any of the characters
1033 that form the initial C<(?[>. Nor may there be space between the
1034 closing C<])> characters.
1036 Just as in all regular expressions, the pattern can be built up by
1037 including variables that are interpolated at regex compilation time.
1038 Care must be taken to ensure that you are getting what you expect. For
1041 my $thai_or_lao = '\p{Thai} + \p{Lao}';
1043 qr/(?[ \p{Digit} & $thai_or_lao ])/;
1047 qr/(?[ \p{Digit} & \p{Thai} + \p{Lao} ])/;
1049 But this does not have the effect that someone reading the code would
1050 likely expect, as the intersection applies just to C<\p{Thai}>,
1051 excluding the Laotian. Pitfalls like this can be avoided by
1052 parenthesizing the component pieces:
1054 my $thai_or_lao = '( \p{Thai} + \p{Lao} )';
1056 But any modifiers will still apply to all the components:
1058 my $lower = '\p{Lower} + \p{Digit}';
1059 qr/(?[ \p{Greek} & $lower ])/i;
1061 matches upper case things. You can avoid surprises by making the
1062 components into instances of this construct by compiling them:
1064 my $thai_or_lao = qr/(?[ \p{Thai} + \p{Lao} ])/;
1065 my $lower = qr/(?[ \p{Lower} + \p{Digit} ])/;
1067 When these are embedded in another pattern, what they match does not
1068 change, regardless of parenthesization or what modifiers are in effect
1069 in that outer pattern.
1071 Due to the way that Perl parses things, your parentheses and brackets
1072 may need to be balanced, even including comments. If you run into any
1073 examples, please send them to C<perlbug@perl.org>, so that we can have a
1074 concrete example for this man page.
1076 We may change it so that things that remain legal uses in normal bracketed
1077 character classes might become illegal within this experimental
1078 construct. One proposal, for example, is to forbid adjacent uses of the
1079 same character, as in C<(?[ [aa] ])>. The motivation for such a change
1080 is that this usage is likely a typo, as the second "a" adds nothing.