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. Experimental.
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 or if on an EBCDIC platform ...
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 or if on an EBCDIC platform ...
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 6.0.
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 or EBCDIC code
293 page is in 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
304 0x180e MONGOLIAN VOWEL SEPARATOR h s
309 0x2004 THREE-PER-EM SPACE h s
310 0x2005 FOUR-PER-EM SPACE h s
311 0x2006 SIX-PER-EM SPACE h s
312 0x2007 FIGURE SPACE h s
313 0x2008 PUNCTUATION SPACE h s
314 0x2009 THIN SPACE h s
315 0x200a HAIR SPACE h s
316 0x2028 LINE SEPARATOR vs
317 0x2029 PARAGRAPH SEPARATOR vs
318 0x202f NARROW NO-BREAK SPACE h s
319 0x205f MEDIUM MATHEMATICAL SPACE h s
320 0x3000 IDEOGRAPHIC SPACE h s
326 Prior to Perl v5.18, C<\s> did not match the vertical tab. The change
327 in v5.18 is considered an experiment, which means it could be backed out
328 in v5.20 or v5.22 if experience indicates that it breaks too much
329 existing code. If this change adversely affects you, send email to
330 C<perlbug@perl.org>; if it affects you positively, email
331 C<perlthanks@perl.org>. In the meantime, C<[^\S\cK]> (obscurely)
332 matches what C<\s> traditionally did.
336 NEXT LINE and NO-BREAK SPACE may or may not match C<\s> depending
337 on the rules in effect. See
338 L<the beginning of this section|/Whitespace>.
342 =head3 Unicode Properties
344 C<\pP> and C<\p{Prop}> are character classes to match characters that fit given
345 Unicode properties. One letter property names can be used in the C<\pP> form,
346 with the property name following the C<\p>, otherwise, braces are required.
347 When using braces, there is a single form, which is just the property name
348 enclosed in the braces, and a compound form which looks like C<\p{name=value}>,
349 which means to match if the property "name" for the character has that particular
351 For instance, a match for a number can be written as C</\pN/> or as
352 C</\p{Number}/>, or as C</\p{Number=True}/>.
353 Lowercase letters are matched by the property I<Lowercase_Letter> which
354 has the short form I<Ll>. They need the braces, so are written as C</\p{Ll}/> or
355 C</\p{Lowercase_Letter}/>, or C</\p{General_Category=Lowercase_Letter}/>
356 (the underscores are optional).
357 C</\pLl/> is valid, but means something different.
358 It matches a two character string: a letter (Unicode property C<\pL>),
359 followed by a lowercase C<l>.
361 If locale rules are not in effect, the use of
362 a Unicode property will force the regular expression into using Unicode
363 rules, if it isn't already.
365 Note that almost all properties are immune to case-insensitive matching.
366 That is, adding a C</i> regular expression modifier does not change what
367 they match. There are two sets that are affected. The first set is
370 and C<Titlecase_Letter>,
371 all of which match C<Cased_Letter> under C</i> matching.
376 all of which match C<Cased> under C</i> matching.
377 (The difference between these sets is that some things, such as Roman
378 numerals, come in both upper and lower case, so they are C<Cased>, but
379 aren't considered to be letters, so they aren't C<Cased_Letter>s. They're
380 actually C<Letter_Number>s.)
381 This set also includes its subsets C<PosixUpper> and C<PosixLower>, both
382 of which under C</i> match C<PosixAlpha>.
384 For more details on Unicode properties, see L<perlunicode/Unicode
385 Character Properties>; for a
386 complete list of possible properties, see
387 L<perluniprops/Properties accessible through \p{} and \P{}>,
388 which notes all forms that have C</i> differences.
389 It is also possible to define your own properties. This is discussed in
390 L<perlunicode/User-Defined Character Properties>.
392 Unicode properties are defined (surprise!) only on Unicode code points.
393 A warning is raised and all matches fail on non-Unicode code points
394 (those above the legal Unicode maximum of 0x10FFFF). This can be
397 chr(0x110000) =~ \p{ASCII_Hex_Digit=True} # Fails.
398 chr(0x110000) =~ \p{ASCII_Hex_Digit=False} # Also fails!
400 Even though these two matches might be thought of as complements, they
401 are so only on Unicode code points.
405 "a" =~ /\w/ # Match, "a" is a 'word' character.
406 "7" =~ /\w/ # Match, "7" is a 'word' character as well.
407 "a" =~ /\d/ # No match, "a" isn't a digit.
408 "7" =~ /\d/ # Match, "7" is a digit.
409 " " =~ /\s/ # Match, a space is whitespace.
410 "a" =~ /\D/ # Match, "a" is a non-digit.
411 "7" =~ /\D/ # No match, "7" is not a non-digit.
412 " " =~ /\S/ # No match, a space is not non-whitespace.
414 " " =~ /\h/ # Match, space is horizontal whitespace.
415 " " =~ /\v/ # No match, space is not vertical whitespace.
416 "\r" =~ /\v/ # Match, a return is vertical whitespace.
418 "a" =~ /\pL/ # Match, "a" is a letter.
419 "a" =~ /\p{Lu}/ # No match, /\p{Lu}/ matches upper case letters.
421 "\x{0e0b}" =~ /\p{Thai}/ # Match, \x{0e0b} is the character
422 # 'THAI CHARACTER SO SO', and that's in
423 # Thai Unicode class.
424 "a" =~ /\P{Lao}/ # Match, as "a" is not a Laotian character.
426 It is worth emphasizing that C<\d>, C<\w>, etc, match single characters, not
427 complete numbers or words. To match a number (that consists of digits),
428 use C<\d+>; to match a word, use C<\w+>. But be aware of the security
429 considerations in doing so, as mentioned above.
431 =head2 Bracketed Character Classes
433 The third form of character class you can use in Perl regular expressions
434 is the bracketed character class. In its simplest form, it lists the characters
435 that may be matched, surrounded by square brackets, like this: C<[aeiou]>.
436 This matches one of C<a>, C<e>, C<i>, C<o> or C<u>. Like the other
437 character classes, exactly one character is matched.* To match
438 a longer string consisting of characters mentioned in the character
439 class, follow the character class with a L<quantifier|perlre/Quantifiers>. For
440 instance, C<[aeiou]+> matches one or more lowercase English vowels.
442 Repeating a character in a character class has no
443 effect; it's considered to be in the set only once.
447 "e" =~ /[aeiou]/ # Match, as "e" is listed in the class.
448 "p" =~ /[aeiou]/ # No match, "p" is not listed in the class.
449 "ae" =~ /^[aeiou]$/ # No match, a character class only matches
450 # a single character.
451 "ae" =~ /^[aeiou]+$/ # Match, due to the quantifier.
455 * There is an exception to a bracketed character class matching a
456 single character only. When the class is to match caselessly under C</i>
457 matching rules, and a character that is explicitly mentioned inside the
459 multiple-character sequence caselessly under Unicode rules, the class
460 (when not L<inverted|/Negation>) will also match that sequence. For
461 example, Unicode says that the letter C<LATIN SMALL LETTER SHARP S>
462 should match the sequence C<ss> under C</i> rules. Thus,
464 'ss' =~ /\A\N{LATIN SMALL LETTER SHARP S}\z/i # Matches
465 'ss' =~ /\A[aeioust\N{LATIN SMALL LETTER SHARP S}]\z/i # Matches
467 For this to happen, the character must be explicitly specified, and not
468 be part of a multi-character range (not even as one of its endpoints).
469 (L</Character Ranges> will be explained shortly.) Therefore,
471 'ss' =~ /\A[\0-\x{ff}]\z/i # Doesn't match
472 'ss' =~ /\A[\0-\N{LATIN SMALL LETTER SHARP S}]\z/i # No match
473 'ss' =~ /\A[\xDF-\xDF]\z/i # Matches on ASCII platforms, since \XDF
474 # is LATIN SMALL LETTER SHARP S, and the
475 # range is just a single element
477 Note that it isn't a good idea to specify these types of ranges anyway.
479 =head3 Special Characters Inside a Bracketed Character Class
481 Most characters that are meta characters in regular expressions (that
482 is, characters that carry a special meaning like C<.>, C<*>, or C<(>) lose
483 their special meaning and can be used inside a character class without
484 the need to escape them. For instance, C<[()]> matches either an opening
485 parenthesis, or a closing parenthesis, and the parens inside the character
486 class don't group or capture.
488 Characters that may carry a special meaning inside a character class are:
489 C<\>, C<^>, C<->, C<[> and C<]>, and are discussed below. They can be
490 escaped with a backslash, although this is sometimes not needed, in which
491 case the backslash may be omitted.
493 The sequence C<\b> is special inside a bracketed character class. While
494 outside the character class, C<\b> is an assertion indicating a point
495 that does not have either two word characters or two non-word characters
496 on either side, inside a bracketed character class, C<\b> matches a
506 C<\N{U+I<hex char>}>,
511 are also special and have the same meanings as they do outside a
512 bracketed character class. (However, inside a bracketed character
513 class, if C<\N{I<NAME>}> expands to a sequence of characters, only the first
514 one in the sequence is used, with a warning.)
516 Also, a backslash followed by two or three octal digits is considered an octal
519 A C<[> is not special inside a character class, unless it's the start of a
520 POSIX character class (see L</POSIX Character Classes> below). It normally does
523 A C<]> is normally either the end of a POSIX character class (see
524 L</POSIX Character Classes> below), or it signals the end of the bracketed
525 character class. If you want to include a C<]> in the set of characters, you
526 must generally escape it.
528 However, if the C<]> is the I<first> (or the second if the first
529 character is a caret) character of a bracketed character class, it
530 does not denote the end of the class (as you cannot have an empty class)
531 and is considered part of the set of characters that can be matched without
536 "+" =~ /[+?*]/ # Match, "+" in a character class is not special.
537 "\cH" =~ /[\b]/ # Match, \b inside in a character class
538 # is equivalent to a backspace.
539 "]" =~ /[][]/ # Match, as the character class contains.
541 "[]" =~ /[[]]/ # Match, the pattern contains a character class
542 # containing just ], and the character class is
545 =head3 Character Ranges
547 It is not uncommon to want to match a range of characters. Luckily, instead
548 of listing all characters in the range, one may use the hyphen (C<->).
549 If inside a bracketed character class you have two characters separated
550 by a hyphen, it's treated as if all characters between the two were in
551 the class. For instance, C<[0-9]> matches any ASCII digit, and C<[a-m]>
552 matches any lowercase letter from the first half of the ASCII alphabet.
554 Note that the two characters on either side of the hyphen are not
555 necessarily both letters or both digits. Any character is possible,
556 although not advisable. C<['-?]> contains a range of characters, but
557 most people will not know which characters that means. Furthermore,
558 such ranges may lead to portability problems if the code has to run on
559 a platform that uses a different character set, such as EBCDIC.
561 If a hyphen in a character class cannot syntactically be part of a range, for
562 instance because it is the first or the last character of the character class,
563 or if it immediately follows a range, the hyphen isn't special, and so is
564 considered a character to be matched literally. If you want a hyphen in
565 your set of characters to be matched and its position in the class is such
566 that it could be considered part of a range, you must escape that hyphen
571 [a-z] # Matches a character that is a lower case ASCII letter.
572 [a-fz] # Matches any letter between 'a' and 'f' (inclusive) or
574 [-z] # Matches either a hyphen ('-') or the letter 'z'.
575 [a-f-m] # Matches any letter between 'a' and 'f' (inclusive), the
576 # hyphen ('-'), or the letter 'm'.
577 ['-?] # Matches any of the characters '()*+,-./0123456789:;<=>?
578 # (But not on an EBCDIC platform).
583 It is also possible to instead list the characters you do not want to
584 match. You can do so by using a caret (C<^>) as the first character in the
585 character class. For instance, C<[^a-z]> matches any character that is not a
586 lowercase ASCII letter, which therefore includes more than a million
587 Unicode code points. The class is said to be "negated" or "inverted".
589 This syntax make the caret a special character inside a bracketed character
590 class, but only if it is the first character of the class. So if you want
591 the caret as one of the characters to match, either escape the caret or
592 else don't list it first.
594 In inverted bracketed character classes, Perl ignores the Unicode rules
595 that normally say that certain characters should match a sequence of
596 multiple characters under caseless C</i> matching. Following those
597 rules could lead to highly confusing situations:
599 "ss" =~ /^[^\xDF]+$/ui; # Matches!
601 This should match any sequences of characters that aren't C<\xDF> nor
602 what C<\xDF> matches under C</i>. C<"s"> isn't C<\xDF>, but Unicode
603 says that C<"ss"> is what C<\xDF> matches under C</i>. So which one
604 "wins"? Do you fail the match because the string has C<ss> or accept it
605 because it has an C<s> followed by another C<s>? Perl has chosen the
610 "e" =~ /[^aeiou]/ # No match, the 'e' is listed.
611 "x" =~ /[^aeiou]/ # Match, as 'x' isn't a lowercase vowel.
612 "^" =~ /[^^]/ # No match, matches anything that isn't a caret.
613 "^" =~ /[x^]/ # Match, caret is not special here.
615 =head3 Backslash Sequences
617 You can put any backslash sequence character class (with the exception of
618 C<\N> and C<\R>) inside a bracketed character class, and it will act just
619 as if you had put all characters matched by the backslash sequence inside the
620 character class. For instance, C<[a-f\d]> matches any decimal digit, or any
621 of the lowercase letters between 'a' and 'f' inclusive.
623 C<\N> within a bracketed character class must be of the forms C<\N{I<name>}>
624 or C<\N{U+I<hex char>}>, and NOT be the form that matches non-newlines,
625 for the same reason that a dot C<.> inside a bracketed character class loses
626 its special meaning: it matches nearly anything, which generally isn't what you
632 /[\p{Thai}\d]/ # Matches a character that is either a Thai
633 # character, or a digit.
634 /[^\p{Arabic}()]/ # Matches a character that is neither an Arabic
635 # character, nor a parenthesis.
637 Backslash sequence character classes cannot form one of the endpoints
638 of a range. Thus, you can't say:
640 /[\p{Thai}-\d]/ # Wrong!
642 =head3 POSIX Character Classes
643 X<character class> X<\p> X<\p{}>
644 X<alpha> X<alnum> X<ascii> X<blank> X<cntrl> X<digit> X<graph>
645 X<lower> X<print> X<punct> X<space> X<upper> X<word> X<xdigit>
647 POSIX character classes have the form C<[:class:]>, where I<class> is
648 name, and the C<[:> and C<:]> delimiters. POSIX character classes only appear
649 I<inside> bracketed character classes, and are a convenient and descriptive
650 way of listing a group of characters.
652 Be careful about the syntax,
655 $string =~ /[[:alpha:]]/
657 # Incorrect (will warn):
658 $string =~ /[:alpha:]/
660 The latter pattern would be a character class consisting of a colon,
661 and the letters C<a>, C<l>, C<p> and C<h>.
662 POSIX character classes can be part of a larger bracketed character class.
667 is valid and matches '0', '1', any alphabetic character, and the percent sign.
669 Perl recognizes the following POSIX character classes:
671 alpha Any alphabetical character ("[A-Za-z]").
672 alnum Any alphanumeric character. ("[A-Za-z0-9]")
673 ascii Any character in the ASCII character set.
674 blank A GNU extension, equal to a space or a horizontal tab ("\t").
675 cntrl Any control character. See Note [2] below.
676 digit Any decimal digit ("[0-9]"), equivalent to "\d".
677 graph Any printable character, excluding a space. See Note [3] below.
678 lower Any lowercase character ("[a-z]").
679 print Any printable character, including a space. See Note [4] below.
680 punct Any graphical character excluding "word" characters. Note [5].
681 space Any whitespace character. "\s" including the vertical tab
683 upper Any uppercase character ("[A-Z]").
684 word A Perl extension ("[A-Za-z0-9_]"), equivalent to "\w".
685 xdigit Any hexadecimal digit ("[0-9a-fA-F]").
687 Most POSIX character classes have two Unicode-style C<\p> property
688 counterparts. (They are not official Unicode properties, but Perl extensions
689 derived from official Unicode properties.) The table below shows the relation
690 between POSIX character classes and these counterparts.
692 One counterpart, in the column labelled "ASCII-range Unicode" in
693 the table, matches only characters in the ASCII character set.
695 The other counterpart, in the column labelled "Full-range Unicode", matches any
696 appropriate characters in the full Unicode character set. For example,
697 C<\p{Alpha}> matches not just the ASCII alphabetic characters, but any
698 character in the entire Unicode character set considered alphabetic.
699 An entry in the column labelled "backslash sequence" is a (short)
702 [[:...:]] ASCII-range Full-range backslash Note
703 Unicode Unicode sequence
704 -----------------------------------------------------
705 alpha \p{PosixAlpha} \p{XPosixAlpha}
706 alnum \p{PosixAlnum} \p{XPosixAlnum}
708 blank \p{PosixBlank} \p{XPosixBlank} \h [1]
709 or \p{HorizSpace} [1]
710 cntrl \p{PosixCntrl} \p{XPosixCntrl} [2]
711 digit \p{PosixDigit} \p{XPosixDigit} \d
712 graph \p{PosixGraph} \p{XPosixGraph} [3]
713 lower \p{PosixLower} \p{XPosixLower}
714 print \p{PosixPrint} \p{XPosixPrint} [4]
715 punct \p{PosixPunct} \p{XPosixPunct} [5]
716 \p{PerlSpace} \p{XPerlSpace} \s [6]
717 space \p{PosixSpace} \p{XPosixSpace} [6]
718 upper \p{PosixUpper} \p{XPosixUpper}
719 word \p{PosixWord} \p{XPosixWord} \w
720 xdigit \p{PosixXDigit} \p{XPosixXDigit}
726 C<\p{Blank}> and C<\p{HorizSpace}> are synonyms.
730 Control characters don't produce output as such, but instead usually control
731 the terminal somehow: for example, newline and backspace are control characters.
732 In the ASCII range, characters whose code points are between 0 and 31 inclusive,
733 plus 127 (C<DEL>) are control characters.
735 On EBCDIC platforms, it is likely that the code page will define C<[[:cntrl:]]>
736 to be the EBCDIC equivalents of the ASCII controls, plus the controls
737 that in Unicode have code points from 128 through 159.
741 Any character that is I<graphical>, that is, visible. This class consists
742 of all alphanumeric characters and all punctuation characters.
746 All printable characters, which is the set of all graphical characters
747 plus those whitespace characters which are not also controls.
751 C<\p{PosixPunct}> and C<[[:punct:]]> in the ASCII range match all
752 non-controls, non-alphanumeric, non-space characters:
753 C<[-!"#$%&'()*+,./:;<=E<gt>?@[\\\]^_`{|}~]> (although if a locale is in effect,
754 it could alter the behavior of C<[[:punct:]]>).
756 The similarly named property, C<\p{Punct}>, matches a somewhat different
757 set in the ASCII range, namely
758 C<[-!"#%&'()*,./:;?@[\\\]_{}]>. That is, it is missing the nine
759 characters C<[$+E<lt>=E<gt>^`|~]>.
760 This is because Unicode splits what POSIX considers to be punctuation into two
761 categories, Punctuation and Symbols.
763 C<\p{XPosixPunct}> and (under Unicode rules) C<[[:punct:]]>, match what
764 C<\p{PosixPunct}> matches in the ASCII range, plus what C<\p{Punct}>
765 matches. This is different than strictly matching according to
766 C<\p{Punct}>. Another way to say it is that
767 if Unicode rules are in effect, C<[[:punct:]]> matches all characters
768 that Unicode considers punctuation, plus all ASCII-range characters that
769 Unicode considers symbols.
773 C<\p{SpacePerl}> and C<\p{Space}> match identically starting with Perl
774 v5.18. In earlier versions, these differ only in that in non-locale
775 matching, C<\p{SpacePerl}> does not match the vertical tab, C<\cK>.
776 Same for the two ASCII-only range forms.
780 There are various other synonyms that can be used besides the names
781 listed in the table. For example, C<\p{PosixAlpha}> can be written as
782 C<\p{Alpha}>. All are listed in
783 L<perluniprops/Properties accessible through \p{} and \P{}>,
784 plus all characters matched by each ASCII-range property.
786 Both the C<\p> counterparts always assume Unicode rules are in effect.
787 On ASCII platforms, this means they assume that the code points from 128
788 to 255 are Latin-1, and that means that using them under locale rules is
789 unwise unless the locale is guaranteed to be Latin-1 or UTF-8. In contrast, the
790 POSIX character classes are useful under locale rules. They are
791 affected by the actual rules in effect, as follows:
795 =item If the C</a> modifier, is in effect ...
797 Each of the POSIX classes matches exactly the same as their ASCII-range
804 =item For code points above 255 ...
806 The POSIX class matches the same as its Full-range counterpart.
808 =item For code points below 256 ...
812 =item if locale rules are in effect ...
814 The POSIX class matches according to the locale, except that
815 C<word> uses the platform's native underscore character, no matter what
818 =item if Unicode rules are in effect or if on an EBCDIC platform ...
820 The POSIX class matches the same as the Full-range counterpart.
824 The POSIX class matches the same as the ASCII range counterpart.
832 Which rules apply are determined as described in
833 L<perlre/Which character set modifier is in effect?>.
835 It is proposed to change this behavior in a future release of Perl so that
836 whether or not Unicode rules are in effect would not change the
837 behavior: Outside of locale or an EBCDIC code page, the POSIX classes
838 would behave like their ASCII-range counterparts. If you wish to
839 comment on this proposal, send email to C<perl5-porters@perl.org>.
841 =head4 Negation of POSIX character classes
842 X<character class, negation>
844 A Perl extension to the POSIX character class is the ability to
845 negate it. This is done by prefixing the class name with a caret (C<^>).
848 POSIX ASCII-range Full-range backslash
849 Unicode Unicode sequence
850 -----------------------------------------------------
851 [[:^digit:]] \P{PosixDigit} \P{XPosixDigit} \D
852 [[:^space:]] \P{PosixSpace} \P{XPosixSpace}
853 \P{PerlSpace} \P{XPerlSpace} \S
854 [[:^word:]] \P{PerlWord} \P{XPosixWord} \W
856 The backslash sequence can mean either ASCII- or Full-range Unicode,
857 depending on various factors as described in L<perlre/Which character set modifier is in effect?>.
859 =head4 [= =] and [. .]
861 Perl recognizes the POSIX character classes C<[=class=]> and
862 C<[.class.]>, but does not (yet?) support them. Any attempt to use
863 either construct raises an exception.
867 /[[:digit:]]/ # Matches a character that is a digit.
868 /[01[:lower:]]/ # Matches a character that is either a
869 # lowercase letter, or '0' or '1'.
870 /[[:digit:][:^xdigit:]]/ # Matches a character that can be anything
871 # except the letters 'a' to 'f' and 'A' to
872 # 'F'. This is because the main character
873 # class is composed of two POSIX character
874 # classes that are ORed together, one that
875 # matches any digit, and the other that
876 # matches anything that isn't a hex digit.
877 # The OR adds the digits, leaving only the
878 # letters 'a' to 'f' and 'A' to 'F' excluded.
880 =head3 Extended Bracketed Character Classes
884 This is a fancy bracketed character class that can be used for more
885 readable and less error-prone classes, and to perform set operations,
886 such as intersection. An example is
888 /(?[ \p{Thai} & \p{Digit} ])/
890 This will match all the digit characters that are in the Thai script.
892 This is an experimental feature available starting in 5.18, and is
893 subject to change as we gain field experience with it. Any attempt to
894 use it will raise a warning, unless disabled via
896 no warnings "experimental::regex_sets";
898 Comments on this feature are welcome; send email to
899 C<perl5-porters@perl.org>.
901 We can extend the example above:
903 /(?[ ( \p{Thai} + \p{Lao} ) & \p{Digit} ])/
905 This matches digits that are in either the Thai or Laotian scripts.
907 Notice the white space in these examples. This construct always has
908 the C<E<sol>x> modifier turned on.
910 The available binary operators are:
914 | another name for '+', hence means union
915 - subtraction (the result matches the set consisting of those
916 code points matched by the first operand, excluding any that
917 are also matched by the second operand)
918 ^ symmetric difference (the union minus the intersection). This
919 is like an exclusive or, in that the result is the set of code
920 points that are matched by either, but not both, of the
923 There is one unary operator:
927 All the binary operators left associate, and are of equal precedence.
928 The unary operator right associates, and has higher precedence. Use
929 parentheses to override the default associations. Some feedback we've
930 received indicates a desire for intersection to have higher precedence
931 than union. This is something that feedback from the field may cause us
932 to change in future releases; you may want to parenthesize copiously to
933 avoid such changes affecting your code, until this feature is no longer
934 considered experimental.
936 The main restriction is that everything is a metacharacter. Thus,
937 you cannot refer to single characters by doing something like this:
939 /(?[ a + b ])/ # Syntax error!
941 The easiest way to specify an individual typable character is to enclose
946 (This is the same thing as C<[ab]>.) You could also have said the
951 (You can, of course, specify single characters by using, C<\x{ }>,
954 This last example shows the use of this construct to specify an ordinary
955 bracketed character class without additional set operations. Note the
956 white space within it; C<E<sol>x> is turned on even within bracketed
957 character classes, except you can't have comments inside them. Hence,
961 matches the literal character "#". To specify a literal white space character,
962 you can escape it with a backslash, like:
964 /(?[ [ a e i o u \ ] ])/
966 This matches the English vowels plus the SPACE character.
967 All the other escapes accepted by normal bracketed character classes are
968 accepted here as well; but unrecognized escapes that generate warnings
969 in normal classes are fatal errors here.
971 All warnings from these class elements are fatal, as well as some
972 practices that don't currently warn. For example you cannot say
974 /(?[ [ \xF ] ])/ # Syntax error!
976 You have to have two hex digits after a braceless C<\x> (use a leading
977 zero to make two). These restrictions are to lower the incidence of
978 typos causing the class to not match what you thought it would.
980 The final difference between regular bracketed character classes and
981 these, is that it is not possible to get these to match a
982 multi-character fold. Thus,
986 does not match the string C<ss>.
988 You don't have to enclose POSIX class names inside double brackets,
989 hence both of the following work:
991 /(?[ [:word:] - [:lower:] ])/
992 /(?[ [[:word:]] - [[:lower:]] ])/
994 Any contained POSIX character classes, including things like C<\w> and C<\D>
995 respect the C<E<sol>a> (and C<E<sol>aa>) modifiers.
997 C<< (?[ ]) >> is a regex-compile-time construct. Any attempt to use
998 something which isn't knowable at the time the containing regular
999 expression is compiled is a fatal error. In practice, this means
1000 just three limitiations:
1006 This construct cannot be used within the scope of
1007 C<use locale> (or the C<E<sol>l> regex modifier).
1012 L<user-defined property|perlunicode/"User-Defined Character Properties">
1013 used must be already defined by the time the regular expression is
1014 compiled (but note that this construct can be used instead of such
1019 A regular expression that otherwise would compile
1020 using C<E<sol>d> rules, and which uses this construct will instead
1021 use C<E<sol>u>. Thus this construct tells Perl that you don't want
1022 C<E<sol>d> rules for the entire regular expression containing it.
1026 The C<E<sol>x> processing within this class is an extended form.
1027 Besides the characters that are considered white space in normal C</x>
1028 processing, there are 5 others, recommended by the Unicode standard:
1031 U+200E LEFT-TO-RIGHT MARK
1032 U+200F RIGHT-TO-LEFT MARK
1033 U+2028 LINE SEPARATOR
1034 U+2029 PARAGRAPH SEPARATOR
1036 Note that skipping white space applies only to the interior of this
1037 construct. There must not be any space between any of the characters
1038 that form the initial C<(?[>. Nor may there be space between the
1039 closing C<])> characters.
1041 Just as in all regular expressions, the pattern can can be built up by
1042 including variables that are interpolated at regex compilation time.
1043 Care must be taken to ensure that you are getting what you expect. For
1046 my $thai_or_lao = '\p{Thai} + \p{Lao}';
1048 qr/(?[ \p{Digit} & $thai_or_lao ])/;
1052 qr/(?[ \p{Digit} & \p{Thai} + \p{Lao} ])/;
1054 But this does not have the effect that someone reading the code would
1055 likely expect, as the intersection applies just to C<\p{Thai}>,
1056 excluding the Laotian. Pitfalls like this can be avoided by
1057 parenthesizing the component pieces:
1059 my $thai_or_lao = '( \p{Thai} + \p{Lao} )';
1061 But any modifiers will still apply to all the components:
1063 my $lower = '\p{Lower} + \p{Digit}';
1064 qr/(?[ \p{Greek} & $lower ])/i;
1066 matches upper case things. You can avoid surprises by making the
1067 components into instances of this construct by compiling them:
1069 my $thai_or_lao = qr/(?[ \p{Thai} + \p{Lao} ])/;
1070 my $lower = qr/(?[ \p{Lower} + \p{Digit} ])/;
1072 When these are embedded in another pattern, what they match does not
1073 change, regardless of parenthesization or what modifiers are in effect
1074 in that outer pattern.
1076 Due to the way that Perl parses things, your parentheses and brackets
1077 may need to be balanced, even including comments. If you run into any
1078 examples, please send them to C<perlbug@perl.org>, so that we can have a
1079 concrete example for this man page.
1081 We may change it so that things that remain legal uses in normal bracketed
1082 character classes might become illegal within this experimental
1083 construct. One proposal, for example, is to forbid adjacent uses of the
1084 same character, as in C<(?[ [aa] ])>. The motivation for such a change
1085 is that this usage is likely a typo, as the second "a" adds nothing.