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/ui # Doesn't match
484 'ss' =~ /\A[\0-\N{LATIN SMALL LETTER SHARP S}]\z/ui # No match
485 'ss' =~ /\A[\xDF-\xDF]\z/ui # 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 multiple 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.
548 Also, a backslash followed by two or three octal digits is considered an octal
551 A C<[> is not special inside a character class, unless it's the start of a
552 POSIX character class (see L</POSIX Character Classes> below). It normally does
555 A C<]> is normally either the end of a POSIX character class (see
556 L</POSIX Character Classes> below), or it signals the end of the bracketed
557 character class. If you want to include a C<]> in the set of characters, you
558 must generally escape it.
560 However, if the C<]> is the I<first> (or the second if the first
561 character is a caret) character of a bracketed character class, it
562 does not denote the end of the class (as you cannot have an empty class)
563 and is considered part of the set of characters that can be matched without
568 "+" =~ /[+?*]/ # Match, "+" in a character class is not special.
569 "\cH" =~ /[\b]/ # Match, \b inside in a character class.
570 # is equivalent to a backspace.
571 "]" =~ /[][]/ # Match, as the character class contains.
573 "[]" =~ /[[]]/ # Match, the pattern contains a character class
574 # containing just ], and the character class is
577 =head3 Character Ranges
579 It is not uncommon to want to match a range of characters. Luckily, instead
580 of listing all characters in the range, one may use the hyphen (C<->).
581 If inside a bracketed character class you have two characters separated
582 by a hyphen, it's treated as if all characters between the two were in
583 the class. For instance, C<[0-9]> matches any ASCII digit, and C<[a-m]>
584 matches any lowercase letter from the first half of the ASCII alphabet.
586 Note that the two characters on either side of the hyphen are not
587 necessarily both letters or both digits. Any character is possible,
588 although not advisable. C<['-?]> contains a range of characters, but
589 most people will not know which characters that means. Furthermore,
590 such ranges may lead to portability problems if the code has to run on
591 a platform that uses a different character set, such as EBCDIC.
593 If a hyphen in a character class cannot syntactically be part of a range, for
594 instance because it is the first or the last character of the character class,
595 or if it immediately follows a range, the hyphen isn't special, and so is
596 considered a character to be matched literally. If you want a hyphen in
597 your set of characters to be matched and its position in the class is such
598 that it could be considered part of a range, you must escape that hyphen
603 [a-z] # Matches a character that is a lower case ASCII letter.
604 [a-fz] # Matches any letter between 'a' and 'f' (inclusive) or
606 [-z] # Matches either a hyphen ('-') or the letter 'z'.
607 [a-f-m] # Matches any letter between 'a' and 'f' (inclusive), the
608 # hyphen ('-'), or the letter 'm'.
609 ['-?] # Matches any of the characters '()*+,-./0123456789:;<=>?
610 # (But not on an EBCDIC platform).
611 [\N{APOSTROPHE}-\N{QUESTION MARK}]
612 # Matches any of the characters '()*+,-./0123456789:;<=>?
613 # even on an EBCDIC platform.
614 [\N{U+27}-\N{U+3F}] # Same. (U+27 is "'", and U+3F is "?"
616 As the final two examples above show, you can achieve portablity to
617 non-ASCII platforms by using the C<\N{...}> form for the range
618 endpoints. These indicate that the specified range is to be interpreted
619 using Unicode values, so C<[\N{U+27}-\N{U+3F}]> means to match
620 C<\N{U+27}>, C<\N{U+28}>, C<\N{U+29}>, ..., C<\N{U+3D}>, C<\N{U+3E}>,
621 and C<\N{U+3F}>, whatever the native code point versions for those are.
623 Perl also guarantees that the ranges C<A-Z>, C<a-z>, C<0-9>, and any
624 subranges of these match what an English-only speaker would expect them
625 to match on any platform. That is, C<[A-Z]> matches the 26 ASCII
627 C<[a-z]> matches the 26 lowercase letters; and C<[0-9]> matches the 10
628 digits. Subranges, like C<[h-k]>, match correspondingly, in this case
629 just the four letters C<"h">, C<"i">, C<"j">, and C<"k">. This is the
630 natural behavior on ASCII platforms where the code points (ordinal
631 values) for C<"h"> through C<"k"> are consecutive integers (0x68 through
632 0x6B). But special handling to achieve this may be needed on platforms
633 with a non-ASCII native character set. For example, on EBCDIC
634 platforms, the code point for C<"h"> is 0x88, C<"i"> is 0x89, C<"j"> is
635 0x91, and C<"k"> is 0x92. Perl specially treats C<[h-k]> to exclude the
636 seven code points in the gap: 0x8A through 0x90. This special handling is
637 only invoked when the range is a subrange of one of the ASCII uppercase,
638 lowercase, and digit ranges, AND each end of the range is expressed
639 either as a literal, like C<"A">, or as a named character (C<\N{...}>,
640 including the C<\N{U+...> form).
644 [i-j] # Matches either "i" or "j"
645 [i-\N{LATIN SMALL LETTER J}] # Same
647 [\N{U+69}-\N{U+6A}] # Same
648 [\x{89}-\x{91}] # Matches 0x89 ("i"), 0x8A .. 0x90, 0x91 ("j")
651 [i-J] # Matches, 0x89 ("i") .. 0xC1 ("J"); special
652 # handling doesn't apply because range is mixed
657 It is also possible to instead list the characters you do not want to
658 match. You can do so by using a caret (C<^>) as the first character in the
659 character class. For instance, C<[^a-z]> matches any character that is not a
660 lowercase ASCII letter, which therefore includes more than a million
661 Unicode code points. The class is said to be "negated" or "inverted".
663 This syntax make the caret a special character inside a bracketed character
664 class, but only if it is the first character of the class. So if you want
665 the caret as one of the characters to match, either escape the caret or
666 else don't list it first.
668 In inverted bracketed character classes, Perl ignores the Unicode rules
669 that normally say that named sequence, and certain characters should
670 match a sequence of multiple characters use under caseless C</i>
671 matching. Following those rules could lead to highly confusing
674 "ss" =~ /^[^\xDF]+$/ui; # Matches!
676 This should match any sequences of characters that aren't C<\xDF> nor
677 what C<\xDF> matches under C</i>. C<"s"> isn't C<\xDF>, but Unicode
678 says that C<"ss"> is what C<\xDF> matches under C</i>. So which one
679 "wins"? Do you fail the match because the string has C<ss> or accept it
680 because it has an C<s> followed by another C<s>? Perl has chosen the
681 latter. (See note in L</Bracketed Character Classes> above.)
685 "e" =~ /[^aeiou]/ # No match, the 'e' is listed.
686 "x" =~ /[^aeiou]/ # Match, as 'x' isn't a lowercase vowel.
687 "^" =~ /[^^]/ # No match, matches anything that isn't a caret.
688 "^" =~ /[x^]/ # Match, caret is not special here.
690 =head3 Backslash Sequences
692 You can put any backslash sequence character class (with the exception of
693 C<\N> and C<\R>) inside a bracketed character class, and it will act just
694 as if you had put all characters matched by the backslash sequence inside the
695 character class. For instance, C<[a-f\d]> matches any decimal digit, or any
696 of the lowercase letters between 'a' and 'f' inclusive.
698 C<\N> within a bracketed character class must be of the forms C<\N{I<name>}>
699 or C<\N{U+I<hex char>}>, and NOT be the form that matches non-newlines,
700 for the same reason that a dot C<.> inside a bracketed character class loses
701 its special meaning: it matches nearly anything, which generally isn't what you
707 /[\p{Thai}\d]/ # Matches a character that is either a Thai
708 # character, or a digit.
709 /[^\p{Arabic}()]/ # Matches a character that is neither an Arabic
710 # character, nor a parenthesis.
712 Backslash sequence character classes cannot form one of the endpoints
713 of a range. Thus, you can't say:
715 /[\p{Thai}-\d]/ # Wrong!
717 =head3 POSIX Character Classes
718 X<character class> X<\p> X<\p{}>
719 X<alpha> X<alnum> X<ascii> X<blank> X<cntrl> X<digit> X<graph>
720 X<lower> X<print> X<punct> X<space> X<upper> X<word> X<xdigit>
722 POSIX character classes have the form C<[:class:]>, where I<class> is the
723 name, and the C<[:> and C<:]> delimiters. POSIX character classes only appear
724 I<inside> bracketed character classes, and are a convenient and descriptive
725 way of listing a group of characters.
727 Be careful about the syntax,
730 $string =~ /[[:alpha:]]/
732 # Incorrect (will warn):
733 $string =~ /[:alpha:]/
735 The latter pattern would be a character class consisting of a colon,
736 and the letters C<a>, C<l>, C<p> and C<h>.
738 POSIX character classes can be part of a larger bracketed character class.
743 is valid and matches '0', '1', any alphabetic character, and the percent sign.
745 Perl recognizes the following POSIX character classes:
747 alpha Any alphabetical character ("[A-Za-z]").
748 alnum Any alphanumeric character ("[A-Za-z0-9]").
749 ascii Any character in the ASCII character set.
750 blank A GNU extension, equal to a space or a horizontal tab ("\t").
751 cntrl Any control character. See Note [2] below.
752 digit Any decimal digit ("[0-9]"), equivalent to "\d".
753 graph Any printable character, excluding a space. See Note [3] below.
754 lower Any lowercase character ("[a-z]").
755 print Any printable character, including a space. See Note [4] below.
756 punct Any graphical character excluding "word" characters. Note [5].
757 space Any whitespace character. "\s" including the vertical tab
759 upper Any uppercase character ("[A-Z]").
760 word A Perl extension ("[A-Za-z0-9_]"), equivalent to "\w".
761 xdigit Any hexadecimal digit ("[0-9a-fA-F]").
763 Most POSIX character classes have two Unicode-style C<\p> property
764 counterparts. (They are not official Unicode properties, but Perl extensions
765 derived from official Unicode properties.) The table below shows the relation
766 between POSIX character classes and these counterparts.
768 One counterpart, in the column labelled "ASCII-range Unicode" in
769 the table, matches only characters in the ASCII character set.
771 The other counterpart, in the column labelled "Full-range Unicode", matches any
772 appropriate characters in the full Unicode character set. For example,
773 C<\p{Alpha}> matches not just the ASCII alphabetic characters, but any
774 character in the entire Unicode character set considered alphabetic.
775 An entry in the column labelled "backslash sequence" is a (short)
778 [[:...:]] ASCII-range Full-range backslash Note
779 Unicode Unicode sequence
780 -----------------------------------------------------
781 alpha \p{PosixAlpha} \p{XPosixAlpha}
782 alnum \p{PosixAlnum} \p{XPosixAlnum}
784 blank \p{PosixBlank} \p{XPosixBlank} \h [1]
785 or \p{HorizSpace} [1]
786 cntrl \p{PosixCntrl} \p{XPosixCntrl} [2]
787 digit \p{PosixDigit} \p{XPosixDigit} \d
788 graph \p{PosixGraph} \p{XPosixGraph} [3]
789 lower \p{PosixLower} \p{XPosixLower}
790 print \p{PosixPrint} \p{XPosixPrint} [4]
791 punct \p{PosixPunct} \p{XPosixPunct} [5]
792 \p{PerlSpace} \p{XPerlSpace} \s [6]
793 space \p{PosixSpace} \p{XPosixSpace} [6]
794 upper \p{PosixUpper} \p{XPosixUpper}
795 word \p{PosixWord} \p{XPosixWord} \w
796 xdigit \p{PosixXDigit} \p{XPosixXDigit}
802 C<\p{Blank}> and C<\p{HorizSpace}> are synonyms.
806 Control characters don't produce output as such, but instead usually control
807 the terminal somehow: for example, newline and backspace are control characters.
808 In the ASCII range, characters whose code points are between 0 and 31 inclusive,
809 plus 127 (C<DEL>) are control characters.
813 Any character that is I<graphical>, that is, visible. This class consists
814 of all alphanumeric characters and all punctuation characters.
818 All printable characters, which is the set of all graphical characters
819 plus those whitespace characters which are not also controls.
823 C<\p{PosixPunct}> and C<[[:punct:]]> in the ASCII range match all
824 non-controls, non-alphanumeric, non-space characters:
825 C<[-!"#$%&'()*+,./:;<=E<gt>?@[\\\]^_`{|}~]> (although if a locale is in effect,
826 it could alter the behavior of C<[[:punct:]]>).
828 The similarly named property, C<\p{Punct}>, matches a somewhat different
829 set in the ASCII range, namely
830 C<[-!"#%&'()*,./:;?@[\\\]_{}]>. That is, it is missing the nine
831 characters C<[$+E<lt>=E<gt>^`|~]>.
832 This is because Unicode splits what POSIX considers to be punctuation into two
833 categories, Punctuation and Symbols.
835 C<\p{XPosixPunct}> and (under Unicode rules) C<[[:punct:]]>, match what
836 C<\p{PosixPunct}> matches in the ASCII range, plus what C<\p{Punct}>
837 matches. This is different than strictly matching according to
838 C<\p{Punct}>. Another way to say it is that
839 if Unicode rules are in effect, C<[[:punct:]]> matches all characters
840 that Unicode considers punctuation, plus all ASCII-range characters that
841 Unicode considers symbols.
845 C<\p{XPerlSpace}> and C<\p{Space}> match identically starting with Perl
846 v5.18. In earlier versions, these differ only in that in non-locale
847 matching, C<\p{XPerlSpace}> does not match the vertical tab, C<\cK>.
848 Same for the two ASCII-only range forms.
852 There are various other synonyms that can be used besides the names
853 listed in the table. For example, C<\p{PosixAlpha}> can be written as
854 C<\p{Alpha}>. All are listed in
855 L<perluniprops/Properties accessible through \p{} and \P{}>.
857 Both the C<\p> counterparts always assume Unicode rules are in effect.
858 On ASCII platforms, this means they assume that the code points from 128
859 to 255 are Latin-1, and that means that using them under locale rules is
860 unwise unless the locale is guaranteed to be Latin-1 or UTF-8. In contrast, the
861 POSIX character classes are useful under locale rules. They are
862 affected by the actual rules in effect, as follows:
866 =item If the C</a> modifier, is in effect ...
868 Each of the POSIX classes matches exactly the same as their ASCII-range
875 =item For code points above 255 ...
877 The POSIX class matches the same as its Full-range counterpart.
879 =item For code points below 256 ...
883 =item if locale rules are in effect ...
885 The POSIX class matches according to the locale, except:
891 also includes the platform's native underscore character, no matter what
896 on platforms that don't have the POSIX C<ascii> extension, this matches
897 just the platform's native ASCII-range characters.
901 on platforms that don't have the POSIX C<blank> extension, this matches
902 just the platform's native tab and space characters.
906 =item if Unicode rules are in effect ...
908 The POSIX class matches the same as the Full-range counterpart.
912 The POSIX class matches the same as the ASCII range counterpart.
920 Which rules apply are determined as described in
921 L<perlre/Which character set modifier is in effect?>.
923 It is proposed to change this behavior in a future release of Perl so that
924 whether or not Unicode rules are in effect would not change the
925 behavior: Outside of locale, the POSIX classes
926 would behave like their ASCII-range counterparts. If you wish to
927 comment on this proposal, send email to C<perl5-porters@perl.org>.
929 =head4 Negation of POSIX character classes
930 X<character class, negation>
932 A Perl extension to the POSIX character class is the ability to
933 negate it. This is done by prefixing the class name with a caret (C<^>).
936 POSIX ASCII-range Full-range backslash
937 Unicode Unicode sequence
938 -----------------------------------------------------
939 [[:^digit:]] \P{PosixDigit} \P{XPosixDigit} \D
940 [[:^space:]] \P{PosixSpace} \P{XPosixSpace}
941 \P{PerlSpace} \P{XPerlSpace} \S
942 [[:^word:]] \P{PerlWord} \P{XPosixWord} \W
944 The backslash sequence can mean either ASCII- or Full-range Unicode,
945 depending on various factors as described in L<perlre/Which character set modifier is in effect?>.
947 =head4 [= =] and [. .]
949 Perl recognizes the POSIX character classes C<[=class=]> and
950 C<[.class.]>, but does not (yet?) support them. Any attempt to use
951 either construct raises an exception.
955 /[[:digit:]]/ # Matches a character that is a digit.
956 /[01[:lower:]]/ # Matches a character that is either a
957 # lowercase letter, or '0' or '1'.
958 /[[:digit:][:^xdigit:]]/ # Matches a character that can be anything
959 # except the letters 'a' to 'f' and 'A' to
960 # 'F'. This is because the main character
961 # class is composed of two POSIX character
962 # classes that are ORed together, one that
963 # matches any digit, and the other that
964 # matches anything that isn't a hex digit.
965 # The OR adds the digits, leaving only the
966 # letters 'a' to 'f' and 'A' to 'F' excluded.
968 =head3 Extended Bracketed Character Classes
972 This is a fancy bracketed character class that can be used for more
973 readable and less error-prone classes, and to perform set operations,
974 such as intersection. An example is
976 /(?[ \p{Thai} & \p{Digit} ])/
978 This will match all the digit characters that are in the Thai script.
980 This is an experimental feature available starting in 5.18, and is
981 subject to change as we gain field experience with it. Any attempt to
982 use it will raise a warning, unless disabled via
984 no warnings "experimental::regex_sets";
986 Comments on this feature are welcome; send email to
987 C<perl5-porters@perl.org>.
989 We can extend the example above:
991 /(?[ ( \p{Thai} + \p{Lao} ) & \p{Digit} ])/
993 This matches digits that are in either the Thai or Laotian scripts.
995 Notice the white space in these examples. This construct always has
996 the C<E<sol>x> modifier turned on within it.
998 The available binary operators are:
1002 | another name for '+', hence means union
1003 - subtraction (the result matches the set consisting of those
1004 code points matched by the first operand, excluding any that
1005 are also matched by the second operand)
1006 ^ symmetric difference (the union minus the intersection). This
1007 is like an exclusive or, in that the result is the set of code
1008 points that are matched by either, but not both, of the
1011 There is one unary operator:
1015 All the binary operators left associate, and are of equal precedence.
1016 The unary operator right associates, and has higher precedence. Use
1017 parentheses to override the default associations. Some feedback we've
1018 received indicates a desire for intersection to have higher precedence
1019 than union. This is something that feedback from the field may cause us
1020 to change in future releases; you may want to parenthesize copiously to
1021 avoid such changes affecting your code, until this feature is no longer
1022 considered experimental.
1024 The main restriction is that everything is a metacharacter. Thus,
1025 you cannot refer to single characters by doing something like this:
1027 /(?[ a + b ])/ # Syntax error!
1029 The easiest way to specify an individual typable character is to enclose
1034 (This is the same thing as C<[ab]>.) You could also have said the
1039 (You can, of course, specify single characters by using, C<\x{...}>,
1042 This last example shows the use of this construct to specify an ordinary
1043 bracketed character class without additional set operations. Note the
1044 white space within it; C<E<sol>x> is turned on even within bracketed
1045 character classes, except you can't have comments inside them. Hence,
1049 matches the literal character "#". To specify a literal white space character,
1050 you can escape it with a backslash, like:
1052 /(?[ [ a e i o u \ ] ])/
1054 This matches the English vowels plus the SPACE character.
1055 All the other escapes accepted by normal bracketed character classes are
1056 accepted here as well; but unrecognized escapes that generate warnings
1057 in normal classes are fatal errors here.
1059 All warnings from these class elements are fatal, as well as some
1060 practices that don't currently warn. For example you cannot say
1062 /(?[ [ \xF ] ])/ # Syntax error!
1064 You have to have two hex digits after a braceless C<\x> (use a leading
1065 zero to make two). These restrictions are to lower the incidence of
1066 typos causing the class to not match what you thought it would.
1068 If a regular bracketed character class contains a C<\p{}> or C<\P{}> and
1069 is matched against a non-Unicode code point, a warning may be
1070 raised, as the result is not Unicode-defined. No such warning will come
1071 when using this extended form.
1073 The final difference between regular bracketed character classes and
1074 these, is that it is not possible to get these to match a
1075 multi-character fold. Thus,
1079 does not match the string C<ss>.
1081 You don't have to enclose POSIX class names inside double brackets,
1082 hence both of the following work:
1084 /(?[ [:word:] - [:lower:] ])/
1085 /(?[ [[:word:]] - [[:lower:]] ])/
1087 Any contained POSIX character classes, including things like C<\w> and C<\D>
1088 respect the C<E<sol>a> (and C<E<sol>aa>) modifiers.
1090 C<< (?[ ]) >> is a regex-compile-time construct. Any attempt to use
1091 something which isn't knowable at the time the containing regular
1092 expression is compiled is a fatal error. In practice, this means
1093 just three limitations:
1099 This construct cannot be used within the scope of
1100 C<use locale> (or the C<E<sol>l> regex modifier).
1105 L<user-defined property|perlunicode/"User-Defined Character Properties">
1106 used must be already defined by the time the regular expression is
1107 compiled (but note that this construct can be used instead of such
1112 A regular expression that otherwise would compile
1113 using C<E<sol>d> rules, and which uses this construct will instead
1114 use C<E<sol>u>. Thus this construct tells Perl that you don't want
1115 C<E<sol>d> rules for the entire regular expression containing it.
1119 Note that skipping white space applies only to the interior of this
1120 construct. There must not be any space between any of the characters
1121 that form the initial C<(?[>. Nor may there be space between the
1122 closing C<])> characters.
1124 Just as in all regular expressions, the pattern can be built up by
1125 including variables that are interpolated at regex compilation time.
1126 Care must be taken to ensure that you are getting what you expect. For
1129 my $thai_or_lao = '\p{Thai} + \p{Lao}';
1131 qr/(?[ \p{Digit} & $thai_or_lao ])/;
1135 qr/(?[ \p{Digit} & \p{Thai} + \p{Lao} ])/;
1137 But this does not have the effect that someone reading the code would
1138 likely expect, as the intersection applies just to C<\p{Thai}>,
1139 excluding the Laotian. Pitfalls like this can be avoided by
1140 parenthesizing the component pieces:
1142 my $thai_or_lao = '( \p{Thai} + \p{Lao} )';
1144 But any modifiers will still apply to all the components:
1146 my $lower = '\p{Lower} + \p{Digit}';
1147 qr/(?[ \p{Greek} & $lower ])/i;
1149 matches upper case things. You can avoid surprises by making the
1150 components into instances of this construct by compiling them:
1152 my $thai_or_lao = qr/(?[ \p{Thai} + \p{Lao} ])/;
1153 my $lower = qr/(?[ \p{Lower} + \p{Digit} ])/;
1155 When these are embedded in another pattern, what they match does not
1156 change, regardless of parenthesization or what modifiers are in effect
1157 in that outer pattern.
1159 Due to the way that Perl parses things, your parentheses and brackets
1160 may need to be balanced, even including comments. If you run into any
1161 examples, please send them to C<perlbug@perl.org>, so that we can have a
1162 concrete example for this man page.
1164 We may change it so that things that remain legal uses in normal bracketed
1165 character classes might become illegal within this experimental
1166 construct. One proposal, for example, is to forbid adjacent uses of the
1167 same character, as in C<(?[ [aa] ])>. The motivation for such a change
1168 is that this usage is likely a typo, as the second "a" adds nothing.