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, 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 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 can match a multi-character sequence. It cannot be used inside
275 a bracketed character class; use C<\v> instead (vertical whitespace).
276 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.
328 C<[^\S\cK]> (obscurely) matches what C<\s> traditionally did.
332 NEXT LINE and NO-BREAK SPACE may or may not match C<\s> depending
333 on the rules in effect. See
334 L<the beginning of this section|/Whitespace>.
338 =head3 Unicode Properties
340 C<\pP> and C<\p{Prop}> are character classes to match characters that fit given
341 Unicode properties. One letter property names can be used in the C<\pP> form,
342 with the property name following the C<\p>, otherwise, braces are required.
343 When using braces, there is a single form, which is just the property name
344 enclosed in the braces, and a compound form which looks like C<\p{name=value}>,
345 which means to match if the property "name" for the character has that particular
347 For instance, a match for a number can be written as C</\pN/> or as
348 C</\p{Number}/>, or as C</\p{Number=True}/>.
349 Lowercase letters are matched by the property I<Lowercase_Letter> which
350 has the short form I<Ll>. They need the braces, so are written as C</\p{Ll}/> or
351 C</\p{Lowercase_Letter}/>, or C</\p{General_Category=Lowercase_Letter}/>
352 (the underscores are optional).
353 C</\pLl/> is valid, but means something different.
354 It matches a two character string: a letter (Unicode property C<\pL>),
355 followed by a lowercase C<l>.
357 If locale rules are not in effect, the use of
358 a Unicode property will force the regular expression into using Unicode
359 rules, if it isn't already.
361 Note that almost all properties are immune to case-insensitive matching.
362 That is, adding a C</i> regular expression modifier does not change what
363 they match. There are two sets that are affected. The first set is
366 and C<Titlecase_Letter>,
367 all of which match C<Cased_Letter> under C</i> matching.
372 all of which match C<Cased> under C</i> matching.
373 (The difference between these sets is that some things, such as Roman
374 numerals, come in both upper and lower case, so they are C<Cased>, but
375 aren't considered to be letters, so they aren't C<Cased_Letter>s. They're
376 actually C<Letter_Number>s.)
377 This set also includes its subsets C<PosixUpper> and C<PosixLower>, both
378 of which under C</i> match C<PosixAlpha>.
380 For more details on Unicode properties, see L<perlunicode/Unicode
381 Character Properties>; for a
382 complete list of possible properties, see
383 L<perluniprops/Properties accessible through \p{} and \P{}>,
384 which notes all forms that have C</i> differences.
385 It is also possible to define your own properties. This is discussed in
386 L<perlunicode/User-Defined Character Properties>.
388 Unicode properties are defined (surprise!) only on Unicode code points.
389 Starting in v5.20, when matching against C<\p> and C<\P>, Perl treats
390 non-Unicode code points (those above the legal Unicode maximum of
391 0x10FFFF) as if they were typical unassigned Unicode code points.
393 Prior to v5.20, Perl raised a warning and made all matches fail on
394 non-Unicode code points. This could be somewhat surprising:
396 chr(0x110000) =~ \p{ASCII_Hex_Digit=True} # Fails on Perls < v5.20.
397 chr(0x110000) =~ \p{ASCII_Hex_Digit=False} # Also fails on Perls
400 Even though these two matches might be thought of as complements, until
401 v5.20 they were 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 are two exceptions to a bracketed character class matching a
456 single character only. Each requires special handling by Perl to make
463 When the class is to match caselessly under C</i> matching rules, and a
464 character that is explicitly mentioned inside the class matches a
465 multiple-character sequence caselessly under Unicode rules, the class
466 will also match that sequence. For example, Unicode says that the
467 letter C<LATIN SMALL LETTER SHARP S> should match the sequence C<ss>
468 under C</i> rules. Thus,
470 'ss' =~ /\A\N{LATIN SMALL LETTER SHARP S}\z/i # Matches
471 'ss' =~ /\A[aeioust\N{LATIN SMALL LETTER SHARP S}]\z/i # Matches
473 For this to happen, the class must not be inverted (see L</Negation>)
474 and the character must be explicitly specified, and not be part of a
475 multi-character range (not even as one of its endpoints). (L</Character
476 Ranges> will be explained shortly.) Therefore,
478 'ss' =~ /\A[\0-\x{ff}]\z/ui # Doesn't match
479 'ss' =~ /\A[\0-\N{LATIN SMALL LETTER SHARP S}]\z/ui # No match
480 'ss' =~ /\A[\xDF-\xDF]\z/ui # Matches on ASCII platforms, since
481 # \xDF is LATIN SMALL LETTER SHARP S,
482 # and the range is just a single
485 Note that it isn't a good idea to specify these types of ranges anyway.
489 Some names known to C<\N{...}> refer to a sequence of multiple characters,
490 instead of the usual single character. When one of these is included in
491 the class, the entire sequence is matched. For example,
493 "\N{TAMIL LETTER KA}\N{TAMIL VOWEL SIGN AU}"
494 =~ / ^ [\N{TAMIL SYLLABLE KAU}] $ /x;
496 matches, because C<\N{TAMIL SYLLABLE KAU}> is a named sequence
497 consisting of the two characters matched against. Like the other
498 instance where a bracketed class can match multiple characters, and for
499 similar reasons, the class must not be inverted, and the named sequence
500 may not appear in a range, even one where it is both endpoints. If
501 these happen, it is a fatal error if the character class is within an
502 extended L<C<(?[...])>|/Extended Bracketed Character Classes>
503 class; and only the first code point is used (with
504 a C<regexp>-type warning raised) otherwise.
508 =head3 Special Characters Inside a Bracketed Character Class
510 Most characters that are meta characters in regular expressions (that
511 is, characters that carry a special meaning like C<.>, C<*>, or C<(>) lose
512 their special meaning and can be used inside a character class without
513 the need to escape them. For instance, C<[()]> matches either an opening
514 parenthesis, or a closing parenthesis, and the parens inside the character
515 class don't group or capture. Be aware that, unless the pattern is
516 evaluated in single-quotish context, variable interpolation will take
517 place before the bracketed class is parsed:
520 $a =~ m'[$,]'; # single-quotish: matches '$' or ','
521 $a =~ q{[$,]}' # same
522 $a =~ m/[$,]/; # double-quotish: matches "\t", "|", or " "
524 Characters that may carry a special meaning inside a character class are:
525 C<\>, C<^>, C<->, C<[> and C<]>, and are discussed below. They can be
526 escaped with a backslash, although this is sometimes not needed, in which
527 case the backslash may be omitted.
529 The sequence C<\b> is special inside a bracketed character class. While
530 outside the character class, C<\b> is an assertion indicating a point
531 that does not have either two word characters or two non-word characters
532 on either side, inside a bracketed character class, C<\b> matches a
542 C<\N{U+I<hex char>}>,
547 are also special and have the same meanings as they do outside a
548 bracketed character class.
550 Also, a backslash followed by two or three octal digits is considered an octal
553 A C<[> is not special inside a character class, unless it's the start of a
554 POSIX character class (see L</POSIX Character Classes> below). It normally does
557 A C<]> is normally either the end of a POSIX character class (see
558 L</POSIX Character Classes> below), or it signals the end of the bracketed
559 character class. If you want to include a C<]> in the set of characters, you
560 must generally escape it.
562 However, if the C<]> is the I<first> (or the second if the first
563 character is a caret) character of a bracketed character class, it
564 does not denote the end of the class (as you cannot have an empty class)
565 and is considered part of the set of characters that can be matched without
570 "+" =~ /[+?*]/ # Match, "+" in a character class is not special.
571 "\cH" =~ /[\b]/ # Match, \b inside in a character class
572 # is equivalent to a backspace.
573 "]" =~ /[][]/ # Match, as the character class contains
575 "[]" =~ /[[]]/ # Match, the pattern contains a character class
576 # containing just [, and the character class is
579 =head3 Character Ranges
581 It is not uncommon to want to match a range of characters. Luckily, instead
582 of listing all characters in the range, one may use the hyphen (C<->).
583 If inside a bracketed character class you have two characters separated
584 by a hyphen, it's treated as if all characters between the two were in
585 the class. For instance, C<[0-9]> matches any ASCII digit, and C<[a-m]>
586 matches any lowercase letter from the first half of the ASCII alphabet.
588 Note that the two characters on either side of the hyphen are not
589 necessarily both letters or both digits. Any character is possible,
590 although not advisable. C<['-?]> contains a range of characters, but
591 most people will not know which characters that means. Furthermore,
592 such ranges may lead to portability problems if the code has to run on
593 a platform that uses a different character set, such as EBCDIC.
595 If a hyphen in a character class cannot syntactically be part of a range, for
596 instance because it is the first or the last character of the character class,
597 or if it immediately follows a range, the hyphen isn't special, and so is
598 considered a character to be matched literally. If you want a hyphen in
599 your set of characters to be matched and its position in the class is such
600 that it could be considered part of a range, you must escape that hyphen
605 [a-z] # Matches a character that is a lower case ASCII letter.
606 [a-fz] # Matches any letter between 'a' and 'f' (inclusive) or
608 [-z] # Matches either a hyphen ('-') or the letter 'z'.
609 [a-f-m] # Matches any letter between 'a' and 'f' (inclusive), the
610 # hyphen ('-'), or the letter 'm'.
611 ['-?] # Matches any of the characters '()*+,-./0123456789:;<=>?
612 # (But not on an EBCDIC platform).
613 [\N{APOSTROPHE}-\N{QUESTION MARK}]
614 # Matches any of the characters '()*+,-./0123456789:;<=>?
615 # even on an EBCDIC platform.
616 [\N{U+27}-\N{U+3F}] # Same. (U+27 is "'", and U+3F is "?")
618 As the final two examples above show, you can achieve portablity to
619 non-ASCII platforms by using the C<\N{...}> form for the range
620 endpoints. These indicate that the specified range is to be interpreted
621 using Unicode values, so C<[\N{U+27}-\N{U+3F}]> means to match
622 C<\N{U+27}>, C<\N{U+28}>, C<\N{U+29}>, ..., C<\N{U+3D}>, C<\N{U+3E}>,
623 and C<\N{U+3F}>, whatever the native code point versions for those are.
624 These are called "Unicode" ranges. If either end is of the C<\N{...}>
625 form, the range is considered Unicode. A C<regexp> warning is raised
626 under C<S<"use re 'strict'">> if the other endpoint is specified
629 [\N{U+00}-\x09] # Warning under re 'strict'; \x09 is non-portable
630 [\N{U+00}-\t] # No warning;
632 Both of the above match the characters C<\N{U+00}> C<\N{U+01}>, ...
633 C<\N{U+08}>, C<\N{U+09}>, but the C<\x09> looks like it could be a
634 mistake so the warning is raised (under C<re 'strict'>) for it.
636 Perl also guarantees that the ranges C<A-Z>, C<a-z>, C<0-9>, and any
637 subranges of these match what an English-only speaker would expect them
638 to match on any platform. That is, C<[A-Z]> matches the 26 ASCII
640 C<[a-z]> matches the 26 lowercase letters; and C<[0-9]> matches the 10
641 digits. Subranges, like C<[h-k]>, match correspondingly, in this case
642 just the four letters C<"h">, C<"i">, C<"j">, and C<"k">. This is the
643 natural behavior on ASCII platforms where the code points (ordinal
644 values) for C<"h"> through C<"k"> are consecutive integers (0x68 through
645 0x6B). But special handling to achieve this may be needed on platforms
646 with a non-ASCII native character set. For example, on EBCDIC
647 platforms, the code point for C<"h"> is 0x88, C<"i"> is 0x89, C<"j"> is
648 0x91, and C<"k"> is 0x92. Perl specially treats C<[h-k]> to exclude the
649 seven code points in the gap: 0x8A through 0x90. This special handling is
650 only invoked when the range is a subrange of one of the ASCII uppercase,
651 lowercase, and digit ranges, AND each end of the range is expressed
652 either as a literal, like C<"A">, or as a named character (C<\N{...}>,
653 including the C<\N{U+...> form).
657 [i-j] # Matches either "i" or "j"
658 [i-\N{LATIN SMALL LETTER J}] # Same
660 [\N{U+69}-\N{U+6A}] # Same
661 [\x{89}-\x{91}] # Matches 0x89 ("i"), 0x8A .. 0x90, 0x91 ("j")
664 [i-J] # Matches, 0x89 ("i") .. 0xC1 ("J"); special
665 # handling doesn't apply because range is mixed
670 It is also possible to instead list the characters you do not want to
671 match. You can do so by using a caret (C<^>) as the first character in the
672 character class. For instance, C<[^a-z]> matches any character that is not a
673 lowercase ASCII letter, which therefore includes more than a million
674 Unicode code points. The class is said to be "negated" or "inverted".
676 This syntax make the caret a special character inside a bracketed character
677 class, but only if it is the first character of the class. So if you want
678 the caret as one of the characters to match, either escape the caret or
679 else don't list it first.
681 In inverted bracketed character classes, Perl ignores the Unicode rules
682 that normally say that named sequence, and certain characters should
683 match a sequence of multiple characters use under caseless C</i>
684 matching. Following those rules could lead to highly confusing
687 "ss" =~ /^[^\xDF]+$/ui; # Matches!
689 This should match any sequences of characters that aren't C<\xDF> nor
690 what C<\xDF> matches under C</i>. C<"s"> isn't C<\xDF>, but Unicode
691 says that C<"ss"> is what C<\xDF> matches under C</i>. So which one
692 "wins"? Do you fail the match because the string has C<ss> or accept it
693 because it has an C<s> followed by another C<s>? Perl has chosen the
694 latter. (See note in L</Bracketed Character Classes> above.)
698 "e" =~ /[^aeiou]/ # No match, the 'e' is listed.
699 "x" =~ /[^aeiou]/ # Match, as 'x' isn't a lowercase vowel.
700 "^" =~ /[^^]/ # No match, matches anything that isn't a caret.
701 "^" =~ /[x^]/ # Match, caret is not special here.
703 =head3 Backslash Sequences
705 You can put any backslash sequence character class (with the exception of
706 C<\N> and C<\R>) inside a bracketed character class, and it will act just
707 as if you had put all characters matched by the backslash sequence inside the
708 character class. For instance, C<[a-f\d]> matches any decimal digit, or any
709 of the lowercase letters between 'a' and 'f' inclusive.
711 C<\N> within a bracketed character class must be of the forms C<\N{I<name>}>
712 or C<\N{U+I<hex char>}>, and NOT be the form that matches non-newlines,
713 for the same reason that a dot C<.> inside a bracketed character class loses
714 its special meaning: it matches nearly anything, which generally isn't what you
720 /[\p{Thai}\d]/ # Matches a character that is either a Thai
721 # character, or a digit.
722 /[^\p{Arabic}()]/ # Matches a character that is neither an Arabic
723 # character, nor a parenthesis.
725 Backslash sequence character classes cannot form one of the endpoints
726 of a range. Thus, you can't say:
728 /[\p{Thai}-\d]/ # Wrong!
730 =head3 POSIX Character Classes
731 X<character class> X<\p> X<\p{}>
732 X<alpha> X<alnum> X<ascii> X<blank> X<cntrl> X<digit> X<graph>
733 X<lower> X<print> X<punct> X<space> X<upper> X<word> X<xdigit>
735 POSIX character classes have the form C<[:class:]>, where I<class> is the
736 name, and the C<[:> and C<:]> delimiters. POSIX character classes only appear
737 I<inside> bracketed character classes, and are a convenient and descriptive
738 way of listing a group of characters.
740 Be careful about the syntax,
743 $string =~ /[[:alpha:]]/
745 # Incorrect (will warn):
746 $string =~ /[:alpha:]/
748 The latter pattern would be a character class consisting of a colon,
749 and the letters C<a>, C<l>, C<p> and C<h>.
751 POSIX character classes can be part of a larger bracketed character class.
756 is valid and matches '0', '1', any alphabetic character, and the percent sign.
758 Perl recognizes the following POSIX character classes:
760 alpha Any alphabetical character ("[A-Za-z]").
761 alnum Any alphanumeric character ("[A-Za-z0-9]").
762 ascii Any character in the ASCII character set.
763 blank A GNU extension, equal to a space or a horizontal tab ("\t").
764 cntrl Any control character. See Note [2] below.
765 digit Any decimal digit ("[0-9]"), equivalent to "\d".
766 graph Any printable character, excluding a space. See Note [3] below.
767 lower Any lowercase character ("[a-z]").
768 print Any printable character, including a space. See Note [4] below.
769 punct Any graphical character excluding "word" characters. Note [5].
770 space Any whitespace character. "\s" including the vertical tab
772 upper Any uppercase character ("[A-Z]").
773 word A Perl extension ("[A-Za-z0-9_]"), equivalent to "\w".
774 xdigit Any hexadecimal digit ("[0-9a-fA-F]").
776 Like the L<Unicode properties|/Unicode Properties>, most of the POSIX
777 properties match the same regardless of whether case-insensitive (C</i>)
778 matching is in effect or not. The two exceptions are C<[:upper:]> and
779 C<[:lower:]>. Under C</i>, they each match the union of C<[:upper:]> and
782 Most POSIX character classes have two Unicode-style C<\p> property
783 counterparts. (They are not official Unicode properties, but Perl extensions
784 derived from official Unicode properties.) The table below shows the relation
785 between POSIX character classes and these counterparts.
787 One counterpart, in the column labelled "ASCII-range Unicode" in
788 the table, matches only characters in the ASCII character set.
790 The other counterpart, in the column labelled "Full-range Unicode", matches any
791 appropriate characters in the full Unicode character set. For example,
792 C<\p{Alpha}> matches not just the ASCII alphabetic characters, but any
793 character in the entire Unicode character set considered alphabetic.
794 An entry in the column labelled "backslash sequence" is a (short)
797 [[:...:]] ASCII-range Full-range backslash Note
798 Unicode Unicode sequence
799 -----------------------------------------------------
800 alpha \p{PosixAlpha} \p{XPosixAlpha}
801 alnum \p{PosixAlnum} \p{XPosixAlnum}
803 blank \p{PosixBlank} \p{XPosixBlank} \h [1]
804 or \p{HorizSpace} [1]
805 cntrl \p{PosixCntrl} \p{XPosixCntrl} [2]
806 digit \p{PosixDigit} \p{XPosixDigit} \d
807 graph \p{PosixGraph} \p{XPosixGraph} [3]
808 lower \p{PosixLower} \p{XPosixLower}
809 print \p{PosixPrint} \p{XPosixPrint} [4]
810 punct \p{PosixPunct} \p{XPosixPunct} [5]
811 \p{PerlSpace} \p{XPerlSpace} \s [6]
812 space \p{PosixSpace} \p{XPosixSpace} [6]
813 upper \p{PosixUpper} \p{XPosixUpper}
814 word \p{PosixWord} \p{XPosixWord} \w
815 xdigit \p{PosixXDigit} \p{XPosixXDigit}
821 C<\p{Blank}> and C<\p{HorizSpace}> are synonyms.
825 Control characters don't produce output as such, but instead usually control
826 the terminal somehow: for example, newline and backspace are control characters.
827 On ASCII platforms, in the ASCII range, characters whose code points are
828 between 0 and 31 inclusive, plus 127 (C<DEL>) are control characters; on
829 EBCDIC platforms, their counterparts are control characters.
833 Any character that is I<graphical>, that is, visible. This class consists
834 of all alphanumeric characters and all punctuation characters.
838 All printable characters, which is the set of all graphical characters
839 plus those whitespace characters which are not also controls.
843 C<\p{PosixPunct}> and C<[[:punct:]]> in the ASCII range match all
844 non-controls, non-alphanumeric, non-space characters:
845 C<[-!"#$%&'()*+,./:;<=E<gt>?@[\\\]^_`{|}~]> (although if a locale is in effect,
846 it could alter the behavior of C<[[:punct:]]>).
848 The similarly named property, C<\p{Punct}>, matches a somewhat different
849 set in the ASCII range, namely
850 C<[-!"#%&'()*,./:;?@[\\\]_{}]>. That is, it is missing the nine
851 characters C<[$+E<lt>=E<gt>^`|~]>.
852 This is because Unicode splits what POSIX considers to be punctuation into two
853 categories, Punctuation and Symbols.
855 C<\p{XPosixPunct}> and (under Unicode rules) C<[[:punct:]]>, match what
856 C<\p{PosixPunct}> matches in the ASCII range, plus what C<\p{Punct}>
857 matches. This is different than strictly matching according to
858 C<\p{Punct}>. Another way to say it is that
859 if Unicode rules are in effect, C<[[:punct:]]> matches all characters
860 that Unicode considers punctuation, plus all ASCII-range characters that
861 Unicode considers symbols.
865 C<\p{XPerlSpace}> and C<\p{Space}> match identically starting with Perl
866 v5.18. In earlier versions, these differ only in that in non-locale
867 matching, C<\p{XPerlSpace}> did not match the vertical tab, C<\cK>.
868 Same for the two ASCII-only range forms.
872 There are various other synonyms that can be used besides the names
873 listed in the table. For example, C<\p{XPosixAlpha}> can be written as
874 C<\p{Alpha}>. All are listed in
875 L<perluniprops/Properties accessible through \p{} and \P{}>.
877 Both the C<\p> counterparts always assume Unicode rules are in effect.
878 On ASCII platforms, this means they assume that the code points from 128
879 to 255 are Latin-1, and that means that using them under locale rules is
880 unwise unless the locale is guaranteed to be Latin-1 or UTF-8. In contrast, the
881 POSIX character classes are useful under locale rules. They are
882 affected by the actual rules in effect, as follows:
886 =item If the C</a> modifier, is in effect ...
888 Each of the POSIX classes matches exactly the same as their ASCII-range
895 =item For code points above 255 ...
897 The POSIX class matches the same as its Full-range counterpart.
899 =item For code points below 256 ...
903 =item if locale rules are in effect ...
905 The POSIX class matches according to the locale, except:
911 also includes the platform's native underscore character, no matter what
916 on platforms that don't have the POSIX C<ascii> extension, this matches
917 just the platform's native ASCII-range characters.
921 on platforms that don't have the POSIX C<blank> extension, this matches
922 just the platform's native tab and space characters.
926 =item if Unicode rules are in effect ...
928 The POSIX class matches the same as the Full-range counterpart.
932 The POSIX class matches the same as the ASCII range counterpart.
940 Which rules apply are determined as described in
941 L<perlre/Which character set modifier is in effect?>.
943 It is proposed to change this behavior in a future release of Perl so that
944 whether or not Unicode rules are in effect would not change the
945 behavior: Outside of locale, the POSIX classes
946 would behave like their ASCII-range counterparts. If you wish to
947 comment on this proposal, send email to C<perl5-porters@perl.org>.
949 =head4 Negation of POSIX character classes
950 X<character class, negation>
952 A Perl extension to the POSIX character class is the ability to
953 negate it. This is done by prefixing the class name with a caret (C<^>).
956 POSIX ASCII-range Full-range backslash
957 Unicode Unicode sequence
958 -----------------------------------------------------
959 [[:^digit:]] \P{PosixDigit} \P{XPosixDigit} \D
960 [[:^space:]] \P{PosixSpace} \P{XPosixSpace}
961 \P{PerlSpace} \P{XPerlSpace} \S
962 [[:^word:]] \P{PerlWord} \P{XPosixWord} \W
964 The backslash sequence can mean either ASCII- or Full-range Unicode,
965 depending on various factors as described in L<perlre/Which character set modifier is in effect?>.
967 =head4 [= =] and [. .]
969 Perl recognizes the POSIX character classes C<[=class=]> and
970 C<[.class.]>, but does not (yet?) support them. Any attempt to use
971 either construct raises an exception.
975 /[[:digit:]]/ # Matches a character that is a digit.
976 /[01[:lower:]]/ # Matches a character that is either a
977 # lowercase letter, or '0' or '1'.
978 /[[:digit:][:^xdigit:]]/ # Matches a character that can be anything
979 # except the letters 'a' to 'f' and 'A' to
980 # 'F'. This is because the main character
981 # class is composed of two POSIX character
982 # classes that are ORed together, one that
983 # matches any digit, and the other that
984 # matches anything that isn't a hex digit.
985 # The OR adds the digits, leaving only the
986 # letters 'a' to 'f' and 'A' to 'F' excluded.
988 =head3 Extended Bracketed Character Classes
992 This is a fancy bracketed character class that can be used for more
993 readable and less error-prone classes, and to perform set operations,
994 such as intersection. An example is
996 /(?[ \p{Thai} & \p{Digit} ])/
998 This will match all the digit characters that are in the Thai script.
1000 This is an experimental feature available starting in 5.18, and is
1001 subject to change as we gain field experience with it. Any attempt to
1002 use it will raise a warning, unless disabled via
1004 no warnings "experimental::regex_sets";
1006 Comments on this feature are welcome; send email to
1007 C<perl5-porters@perl.org>.
1009 The rules used by L<C<use re 'strict>|re/'strict' mode> apply to this
1012 We can extend the example above:
1014 /(?[ ( \p{Thai} + \p{Lao} ) & \p{Digit} ])/
1016 This matches digits that are in either the Thai or Laotian scripts.
1018 Notice the white space in these examples. This construct always has
1019 the C<E<sol>x> modifier turned on within it.
1021 The available binary operators are:
1025 | another name for '+', hence means union
1026 - subtraction (the result matches the set consisting of those
1027 code points matched by the first operand, excluding any that
1028 are also matched by the second operand)
1029 ^ symmetric difference (the union minus the intersection). This
1030 is like an exclusive or, in that the result is the set of code
1031 points that are matched by either, but not both, of the
1034 There is one unary operator:
1038 All the binary operators left associate; C<"&"> is higher precedence
1039 than the others, which all have equal precedence. The unary operator
1040 right associates, and has highest precedence. Thus this follows the
1041 normal Perl precedence rules for logical operators. Use parentheses to
1042 override the default precedence and associativity.
1044 The main restriction is that everything is a metacharacter. Thus,
1045 you cannot refer to single characters by doing something like this:
1047 /(?[ a + b ])/ # Syntax error!
1049 The easiest way to specify an individual typable character is to enclose
1054 (This is the same thing as C<[ab]>.) You could also have said the
1059 (You can, of course, specify single characters by using, C<\x{...}>,
1062 This last example shows the use of this construct to specify an ordinary
1063 bracketed character class without additional set operations. Note the
1064 white space within it; a limited version of C<E<sol>x> is turned on even
1065 within bracketed character classes, with only the SPACE and TAB (C<\t>)
1066 characters allowed, and no comments. Hence,
1070 matches the literal character "#". To specify a literal white space character,
1071 you can escape it with a backslash, like:
1073 /(?[ [ a e i o u \ ] ])/
1075 This matches the English vowels plus the SPACE character.
1076 All the other escapes accepted by normal bracketed character classes are
1077 accepted here as well; but unrecognized escapes that generate warnings
1078 in normal classes are fatal errors here.
1080 All warnings from these class elements are fatal, as well as some
1081 practices that don't currently warn. For example you cannot say
1083 /(?[ [ \xF ] ])/ # Syntax error!
1085 You have to have two hex digits after a braceless C<\x> (use a leading
1086 zero to make two). These restrictions are to lower the incidence of
1087 typos causing the class to not match what you thought it would.
1089 If a regular bracketed character class contains a C<\p{}> or C<\P{}> and
1090 is matched against a non-Unicode code point, a warning may be
1091 raised, as the result is not Unicode-defined. No such warning will come
1092 when using this extended form.
1094 The final difference between regular bracketed character classes and
1095 these, is that it is not possible to get these to match a
1096 multi-character fold. Thus,
1100 does not match the string C<ss>.
1102 You don't have to enclose POSIX class names inside double brackets,
1103 hence both of the following work:
1105 /(?[ [:word:] - [:lower:] ])/
1106 /(?[ [[:word:]] - [[:lower:]] ])/
1108 Any contained POSIX character classes, including things like C<\w> and C<\D>
1109 respect the C<E<sol>a> (and C<E<sol>aa>) modifiers.
1111 C<< (?[ ]) >> is a regex-compile-time construct. Any attempt to use
1112 something which isn't knowable at the time the containing regular
1113 expression is compiled is a fatal error. In practice, this means
1114 just three limitations:
1120 When compiled within the scope of C<use locale> (or the C<E<sol>l> regex
1121 modifier), this construct assumes that the execution-time locale will be
1122 a UTF-8 one, and the generated pattern always uses Unicode rules. What
1123 gets matched or not thus isn't dependent on the actual runtime locale, so
1124 tainting is not enabled. But a C<locale> category warning is raised
1125 if the runtime locale turns out to not be UTF-8.
1130 L<user-defined property|perlunicode/"User-Defined Character Properties">
1131 used must be already defined by the time the regular expression is
1132 compiled (but note that this construct can be used instead of such
1137 A regular expression that otherwise would compile
1138 using C<E<sol>d> rules, and which uses this construct will instead
1139 use C<E<sol>u>. Thus this construct tells Perl that you don't want
1140 C<E<sol>d> rules for the entire regular expression containing it.
1144 Note that skipping white space applies only to the interior of this
1145 construct. There must not be any space between any of the characters
1146 that form the initial C<(?[>. Nor may there be space between the
1147 closing C<])> characters.
1149 Just as in all regular expressions, the pattern can be built up by
1150 including variables that are interpolated at regex compilation time.
1151 Care must be taken to ensure that you are getting what you expect. For
1154 my $thai_or_lao = '\p{Thai} + \p{Lao}';
1156 qr/(?[ \p{Digit} & $thai_or_lao ])/;
1160 qr/(?[ \p{Digit} & \p{Thai} + \p{Lao} ])/;
1162 But this does not have the effect that someone reading the code would
1163 likely expect, as the intersection applies just to C<\p{Thai}>,
1164 excluding the Laotian. Pitfalls like this can be avoided by
1165 parenthesizing the component pieces:
1167 my $thai_or_lao = '( \p{Thai} + \p{Lao} )';
1169 But any modifiers will still apply to all the components:
1171 my $lower = '\p{Lower} + \p{Digit}';
1172 qr/(?[ \p{Greek} & $lower ])/i;
1174 matches upper case things. You can avoid surprises by making the
1175 components into instances of this construct by compiling them:
1177 my $thai_or_lao = qr/(?[ \p{Thai} + \p{Lao} ])/;
1178 my $lower = qr/(?[ \p{Lower} + \p{Digit} ])/;
1180 When these are embedded in another pattern, what they match does not
1181 change, regardless of parenthesization or what modifiers are in effect
1182 in that outer pattern.
1184 Due to the way that Perl parses things, your parentheses and brackets
1185 may need to be balanced, even including comments. If you run into any
1186 examples, please send them to C<perlbug@perl.org>, so that we can have a
1187 concrete example for this man page.
1189 We may change it so that things that remain legal uses in normal bracketed
1190 character classes might become illegal within this experimental
1191 construct. One proposal, for example, is to forbid adjacent uses of the
1192 same character, as in C<(?[ [aa] ])>. The motivation for such a change
1193 is that this usage is likely a typo, as the second "a" adds nothing.