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:
31 for the entire regular expression with the C</s> modifier, or
32 locally with C<(?s)> (and even globally within the scope of
33 L<C<use re '/s'>|re/'E<sol>flags' mode>). (The C<L</\N>> backslash
35 below, matches any character except newline without regard to the
36 I<single line> modifier.)
38 Here are some examples:
42 "" =~ /./ # No match (dot has to match a character)
43 "\n" =~ /./ # No match (dot does not match a newline)
44 "\n" =~ /./s # Match (global 'single line' modifier)
45 "\n" =~ /(?s:.)/ # Match (local 'single line' modifier)
46 "ab" =~ /^.$/ # No match (dot matches one character)
48 =head2 Backslash sequences
49 X<\w> X<\W> X<\s> X<\S> X<\d> X<\D> X<\p> X<\P>
50 X<\N> X<\v> X<\V> X<\h> X<\H>
53 A backslash sequence is a sequence of characters, the first one of which is a
54 backslash. Perl ascribes special meaning to many such sequences, and some of
55 these are character classes. That is, they match a single character each,
56 provided that the character belongs to the specific set of characters defined
59 Here's a list of the backslash sequences that are character classes. They
60 are discussed in more detail below. (For the backslash sequences that aren't
61 character classes, see L<perlrebackslash>.)
63 \d Match a decimal digit character.
64 \D Match a non-decimal-digit character.
65 \w Match a "word" character.
66 \W Match a non-"word" character.
67 \s Match a whitespace character.
68 \S Match a non-whitespace character.
69 \h Match a horizontal whitespace character.
70 \H Match a character that isn't horizontal whitespace.
71 \v Match a vertical whitespace character.
72 \V Match a character that isn't vertical whitespace.
73 \N Match a character that isn't a newline.
74 \pP, \p{Prop} Match a character that has the given Unicode property.
75 \PP, \P{Prop} Match a character that doesn't have the Unicode property
79 C<\N>, available starting in v5.12, like the dot, matches any
80 character that is not a newline. The difference is that C<\N> is not influenced
81 by the I<single line> regular expression modifier (see L</The dot> above). Note
82 that the form C<\N{...}> may mean something completely different. When the
83 C<{...}> is a L<quantifier|perlre/Quantifiers>, it means to match a non-newline
84 character that many times. For example, C<\N{3}> means to match 3
85 non-newlines; C<\N{5,}> means to match 5 or more non-newlines. But if C<{...}>
86 is not a legal quantifier, it is presumed to be a named character. See
87 L<charnames> for those. For example, none of C<\N{COLON}>, C<\N{4F}>, and
88 C<\N{F4}> contain legal quantifiers, so Perl will try to find characters whose
89 names are respectively C<COLON>, C<4F>, and C<F4>.
93 C<\d> matches a single character considered to be a decimal I<digit>.
94 If the C</a> regular expression modifier is in effect, it matches [0-9].
96 matches anything that is matched by C<\p{Digit}>, which includes [0-9].
97 (An unlikely possible exception is that under locale matching rules, the
98 current locale might not have C<[0-9]> matched by C<\d>, and/or might match
99 other characters whose code point is less than 256. The only such locale
100 definitions that are legal would be to match C<[0-9]> plus another set of
101 10 consecutive digit characters; anything else would be in violation of
102 the C language standard, but Perl doesn't currently assume anything in
105 What this means is that unless the C</a> modifier is in effect C<\d> not
106 only matches the digits '0' - '9', but also Arabic, Devanagari, and
107 digits from other languages. This may cause some confusion, and some
110 Some digits that C<\d> matches look like some of the [0-9] ones, but
111 have different values. For example, BENGALI DIGIT FOUR (U+09EA) looks
112 very much like an ASCII DIGIT EIGHT (U+0038), and LEPCHA DIGIT SIX
113 (U+1C46) looks very much like an ASCII DIGIT FIVE (U+0035). An
115 is expecting only the ASCII digits might be misled, or if the match is
116 C<\d+>, the matched string might contain a mixture of digits from
117 different writing systems that look like they signify a number different
118 than they actually do. L<Unicode::UCD/num()> can
120 calculate the value, returning C<undef> if the input string contains
121 such a mixture. Otherwise, for example, a displayed price might be
122 deliberately different than it appears.
124 What C<\p{Digit}> means (and hence C<\d> except under the C</a>
125 modifier) is C<\p{General_Category=Decimal_Number}>, or synonymously,
126 C<\p{General_Category=Digit}>. Starting with Unicode version 4.1, this
127 is the same set of characters matched by C<\p{Numeric_Type=Decimal}>.
128 But Unicode also has a different property with a similar name,
129 C<\p{Numeric_Type=Digit}>, which matches a completely different set of
130 characters. These characters are things such as C<CIRCLED DIGIT ONE>
131 or subscripts, or are from writing systems that lack all ten digits.
133 The design intent is for C<\d> to exactly match the set of characters
134 that can safely be used with "normal" big-endian positional decimal
135 syntax, where, for example 123 means one 'hundred', plus two 'tens',
136 plus three 'ones'. This positional notation does not necessarily apply
137 to characters that match the other type of "digit",
138 C<\p{Numeric_Type=Digit}>, and so C<\d> doesn't match them.
140 The Tamil digits (U+0BE6 - U+0BEF) can also legally be
141 used in old-style Tamil numbers in which they would appear no more than
142 one in a row, separated by characters that mean "times 10", "times 100",
143 etc. (See L<http://www.unicode.org/notes/tn21>.)
145 Any character not matched by C<\d> is matched by C<\D>.
147 =head3 Word characters
149 A C<\w> matches a single alphanumeric character (an alphabetic character, or a
150 decimal digit); or a connecting punctuation character, such as an
151 underscore ("_"); or a "mark" character (like some sort of accent) that
152 attaches to one of those. It does not match a whole word. To match a
153 whole word, use C<\w+>. This isn't the same thing as matching an
154 English word, but in the ASCII range it is the same as a string of
155 Perl-identifier characters.
159 =item If the C</a> modifier is in effect ...
161 C<\w> matches the 63 characters [a-zA-Z0-9_].
167 =item For code points above 255 ...
169 C<\w> matches the same as C<\p{Word}> matches in this range. That is,
170 it matches Thai letters, Greek letters, etc. This includes connector
171 punctuation (like the underscore) which connect two words together, or
172 diacritics, such as a C<COMBINING TILDE> and the modifier letters, which
173 are generally used to add auxiliary markings to letters.
175 =item For code points below 256 ...
179 =item if locale rules are in effect ...
181 C<\w> matches the platform's native underscore character plus whatever
182 the locale considers to be alphanumeric.
184 =item if, instead, Unicode rules are in effect ...
186 C<\w> matches exactly what C<\p{Word}> matches.
190 C<\w> matches [a-zA-Z0-9_].
198 Which rules apply are determined as described in L<perlre/Which character set modifier is in effect?>.
200 There are a number of security issues with the full Unicode list of word
201 characters. See L<http://unicode.org/reports/tr36>.
203 Also, for a somewhat finer-grained set of characters that are in programming
204 language identifiers beyond the ASCII range, you may wish to instead use the
205 more customized L</Unicode Properties>, C<\p{ID_Start}>,
206 C<\p{ID_Continue}>, C<\p{XID_Start}>, and C<\p{XID_Continue}>. See
207 L<http://unicode.org/reports/tr31>.
209 Any character not matched by C<\w> is matched by C<\W>.
213 C<\s> matches any single character considered whitespace.
217 =item If the C</a> modifier is in effect ...
219 In all Perl versions, C<\s> matches the 5 characters [\t\n\f\r ]; that
220 is, the horizontal tab,
221 the newline, the form feed, the carriage return, and the space.
222 Starting in Perl v5.18, it also matches the vertical tab, C<\cK>.
223 See note C<[1]> below for a discussion of this.
229 =item For code points above 255 ...
231 C<\s> matches exactly the code points above 255 shown with an "s" column
234 =item For code points below 256 ...
238 =item if locale rules are in effect ...
240 C<\s> matches whatever the locale considers to be whitespace.
242 =item if, instead, Unicode rules are in effect ...
244 C<\s> matches exactly the characters shown with an "s" column in the
249 C<\s> matches [\t\n\f\r ] and, starting in Perl
250 v5.18, the vertical tab, C<\cK>.
251 (See note C<[1]> below for a discussion of this.)
252 Note that this list doesn't include the non-breaking space.
260 Which rules apply are determined as described in L<perlre/Which character set modifier is in effect?>.
262 Any character not matched by C<\s> is matched by C<\S>.
264 C<\h> matches any character considered horizontal whitespace;
265 this includes the platform's space and tab characters and several others
266 listed in the table below. C<\H> matches any character
267 not considered horizontal whitespace. They use the platform's native
268 character set, and do not consider any locale that may otherwise be in
271 C<\v> matches any character considered vertical whitespace;
272 this includes the platform's carriage return and line feed characters (newline)
273 plus several other characters, all listed in the table below.
274 C<\V> matches any character not considered vertical whitespace.
275 They use the platform's native character set, and do not consider any
276 locale that may otherwise be in use.
278 C<\R> matches anything that can be considered a newline under Unicode
279 rules. It can match a multi-character sequence. It cannot be used inside
280 a bracketed character class; use C<\v> instead (vertical whitespace).
281 It uses the platform's
282 native character set, and does not consider any locale that may
284 Details are discussed in L<perlrebackslash>.
286 Note that unlike C<\s> (and C<\d> and C<\w>), C<\h> and C<\v> always match
287 the same characters, without regard to other factors, such as the active
288 locale or whether the source string is in UTF-8 format.
290 One might think that C<\s> is equivalent to C<[\h\v]>. This is indeed true
291 starting in Perl v5.18, but prior to that, the sole difference was that the
292 vertical tab (C<"\cK">) was not matched by C<\s>.
294 The following table is a complete listing of characters matched by
295 C<\s>, C<\h> and C<\v> as of Unicode 6.3.
297 The first column gives the Unicode code point of the character (in hex format),
298 the second column gives the (Unicode) name. The third column indicates
299 by which class(es) the character is matched (assuming no locale is in
300 effect that changes the C<\s> matching).
302 0x0009 CHARACTER TABULATION h s
303 0x000a LINE FEED (LF) vs
304 0x000b LINE TABULATION vs [1]
305 0x000c FORM FEED (FF) vs
306 0x000d CARRIAGE RETURN (CR) vs
308 0x0085 NEXT LINE (NEL) vs [2]
309 0x00a0 NO-BREAK SPACE h s [2]
310 0x1680 OGHAM SPACE MARK h s
315 0x2004 THREE-PER-EM SPACE h s
316 0x2005 FOUR-PER-EM SPACE h s
317 0x2006 SIX-PER-EM SPACE h s
318 0x2007 FIGURE SPACE h s
319 0x2008 PUNCTUATION SPACE h s
320 0x2009 THIN SPACE h s
321 0x200a HAIR SPACE h s
322 0x2028 LINE SEPARATOR vs
323 0x2029 PARAGRAPH SEPARATOR vs
324 0x202f NARROW NO-BREAK SPACE h s
325 0x205f MEDIUM MATHEMATICAL SPACE h s
326 0x3000 IDEOGRAPHIC SPACE h s
332 Prior to Perl v5.18, C<\s> did not match the vertical tab.
333 C<[^\S\cK]> (obscurely) 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 What a Unicode property matches is never subject to locale rules, and
363 if locale rules are not otherwise in effect, the use of a Unicode
364 property will force the regular expression into using Unicode rules, if
367 Note that almost all properties are immune to case-insensitive matching.
368 That is, adding a C</i> regular expression modifier does not change what
369 they match. There are two sets that are affected. The first set is
372 and C<Titlecase_Letter>,
373 all of which match C<Cased_Letter> under C</i> matching.
378 all of which match C<Cased> under C</i> matching.
379 (The difference between these sets is that some things, such as Roman
380 numerals, come in both upper and lower case, so they are C<Cased>, but
381 aren't considered to be letters, so they aren't C<Cased_Letter>s. They're
382 actually C<Letter_Number>s.)
383 This set also includes its subsets C<PosixUpper> and C<PosixLower>, both
384 of which under C</i> match C<PosixAlpha>.
386 For more details on Unicode properties, see L<perlunicode/Unicode
387 Character Properties>; for a
388 complete list of possible properties, see
389 L<perluniprops/Properties accessible through \p{} and \P{}>,
390 which notes all forms that have C</i> differences.
391 It is also possible to define your own properties. This is discussed in
392 L<perlunicode/User-Defined Character Properties>.
394 Unicode properties are defined (surprise!) only on Unicode code points.
395 Starting in v5.20, when matching against C<\p> and C<\P>, Perl treats
396 non-Unicode code points (those above the legal Unicode maximum of
397 0x10FFFF) as if they were typical unassigned Unicode code points.
399 Prior to v5.20, Perl raised a warning and made all matches fail on
400 non-Unicode code points. This could be somewhat surprising:
402 chr(0x110000) =~ \p{ASCII_Hex_Digit=True} # Fails on Perls < v5.20.
403 chr(0x110000) =~ \p{ASCII_Hex_Digit=False} # Also fails on Perls
406 Even though these two matches might be thought of as complements, until
407 v5.20 they were so only on Unicode code points.
409 Starting in perl v5.30, wildcards are allowed in Unicode property
410 values. See L<perlunicode/Wildcards in Property Values>.
414 "a" =~ /\w/ # Match, "a" is a 'word' character.
415 "7" =~ /\w/ # Match, "7" is a 'word' character as well.
416 "a" =~ /\d/ # No match, "a" isn't a digit.
417 "7" =~ /\d/ # Match, "7" is a digit.
418 " " =~ /\s/ # Match, a space is whitespace.
419 "a" =~ /\D/ # Match, "a" is a non-digit.
420 "7" =~ /\D/ # No match, "7" is not a non-digit.
421 " " =~ /\S/ # No match, a space is not non-whitespace.
423 " " =~ /\h/ # Match, space is horizontal whitespace.
424 " " =~ /\v/ # No match, space is not vertical whitespace.
425 "\r" =~ /\v/ # Match, a return is vertical whitespace.
427 "a" =~ /\pL/ # Match, "a" is a letter.
428 "a" =~ /\p{Lu}/ # No match, /\p{Lu}/ matches upper case letters.
430 "\x{0e0b}" =~ /\p{Thai}/ # Match, \x{0e0b} is the character
431 # 'THAI CHARACTER SO SO', and that's in
432 # Thai Unicode class.
433 "a" =~ /\P{Lao}/ # Match, as "a" is not a Laotian character.
435 It is worth emphasizing that C<\d>, C<\w>, etc, match single characters, not
436 complete numbers or words. To match a number (that consists of digits),
437 use C<\d+>; to match a word, use C<\w+>. But be aware of the security
438 considerations in doing so, as mentioned above.
440 =head2 Bracketed Character Classes
442 The third form of character class you can use in Perl regular expressions
443 is the bracketed character class. In its simplest form, it lists the characters
444 that may be matched, surrounded by square brackets, like this: C<[aeiou]>.
445 This matches one of C<a>, C<e>, C<i>, C<o> or C<u>. Like the other
446 character classes, exactly one character is matched.* To match
447 a longer string consisting of characters mentioned in the character
448 class, follow the character class with a L<quantifier|perlre/Quantifiers>. For
449 instance, C<[aeiou]+> matches one or more lowercase English vowels.
451 Repeating a character in a character class has no
452 effect; it's considered to be in the set only once.
456 "e" =~ /[aeiou]/ # Match, as "e" is listed in the class.
457 "p" =~ /[aeiou]/ # No match, "p" is not listed in the class.
458 "ae" =~ /^[aeiou]$/ # No match, a character class only matches
459 # a single character.
460 "ae" =~ /^[aeiou]+$/ # Match, due to the quantifier.
464 * There are two exceptions to a bracketed character class matching a
465 single character only. Each requires special handling by Perl to make
472 When the class is to match caselessly under C</i> matching rules, and a
473 character that is explicitly mentioned inside the class matches a
474 multiple-character sequence caselessly under Unicode rules, the class
475 will also match that sequence. For example, Unicode says that the
476 letter C<LATIN SMALL LETTER SHARP S> should match the sequence C<ss>
477 under C</i> rules. Thus,
479 'ss' =~ /\A\N{LATIN SMALL LETTER SHARP S}\z/i # Matches
480 'ss' =~ /\A[aeioust\N{LATIN SMALL LETTER SHARP S}]\z/i # Matches
482 For this to happen, the class must not be inverted (see L</Negation>)
483 and the character must be explicitly specified, and not be part of a
484 multi-character range (not even as one of its endpoints). (L</Character
485 Ranges> will be explained shortly.) Therefore,
487 'ss' =~ /\A[\0-\x{ff}]\z/ui # Doesn't match
488 'ss' =~ /\A[\0-\N{LATIN SMALL LETTER SHARP S}]\z/ui # No match
489 'ss' =~ /\A[\xDF-\xDF]\z/ui # Matches on ASCII platforms, since
490 # \xDF is LATIN SMALL LETTER SHARP S,
491 # and the range is just a single
494 Note that it isn't a good idea to specify these types of ranges anyway.
498 Some names known to C<\N{...}> refer to a sequence of multiple characters,
499 instead of the usual single character. When one of these is included in
500 the class, the entire sequence is matched. For example,
502 "\N{TAMIL LETTER KA}\N{TAMIL VOWEL SIGN AU}"
503 =~ / ^ [\N{TAMIL SYLLABLE KAU}] $ /x;
505 matches, because C<\N{TAMIL SYLLABLE KAU}> is a named sequence
506 consisting of the two characters matched against. Like the other
507 instance where a bracketed class can match multiple characters, and for
508 similar reasons, the class must not be inverted, and the named sequence
509 may not appear in a range, even one where it is both endpoints. If
510 these happen, it is a fatal error if the character class is within the
511 scope of L<C<use re 'strict>|re/'strict' mode>, or within an extended
512 L<C<(?[...])>|/Extended Bracketed Character Classes> class; otherwise
513 only the first code point is used (with a C<regexp>-type warning
518 =head3 Special Characters Inside a Bracketed Character Class
520 Most characters that are meta characters in regular expressions (that
521 is, characters that carry a special meaning like C<.>, C<*>, or C<(>) lose
522 their special meaning and can be used inside a character class without
523 the need to escape them. For instance, C<[()]> matches either an opening
524 parenthesis, or a closing parenthesis, and the parens inside the character
525 class don't group or capture. Be aware that, unless the pattern is
526 evaluated in single-quotish context, variable interpolation will take
527 place before the bracketed class is parsed:
530 $a =~ m'[$,]'; # single-quotish: matches '$' or ','
531 $a =~ q{[$,]}' # same
532 $a =~ m/[$,]/; # double-quotish: matches "\t", "|", or " "
534 Characters that may carry a special meaning inside a character class are:
535 C<\>, C<^>, C<->, C<[> and C<]>, and are discussed below. They can be
536 escaped with a backslash, although this is sometimes not needed, in which
537 case the backslash may be omitted.
539 The sequence C<\b> is special inside a bracketed character class. While
540 outside the character class, C<\b> is an assertion indicating a point
541 that does not have either two word characters or two non-word characters
542 on either side, inside a bracketed character class, C<\b> matches a
552 C<\N{U+I<hex char>}>,
557 are also special and have the same meanings as they do outside a
558 bracketed character class.
560 Also, a backslash followed by two or three octal digits is considered an octal
563 A C<[> is not special inside a character class, unless it's the start of a
564 POSIX character class (see L</POSIX Character Classes> below). It normally does
567 A C<]> is normally either the end of a POSIX character class (see
568 L</POSIX Character Classes> below), or it signals the end of the bracketed
569 character class. If you want to include a C<]> in the set of characters, you
570 must generally escape it.
572 However, if the C<]> is the I<first> (or the second if the first
573 character is a caret) character of a bracketed character class, it
574 does not denote the end of the class (as you cannot have an empty class)
575 and is considered part of the set of characters that can be matched without
580 "+" =~ /[+?*]/ # Match, "+" in a character class is not special.
581 "\cH" =~ /[\b]/ # Match, \b inside in a character class
582 # is equivalent to a backspace.
583 "]" =~ /[][]/ # Match, as the character class contains
585 "[]" =~ /[[]]/ # Match, the pattern contains a character class
586 # containing just [, and the character class is
589 =head3 Bracketed Character Classes and the C</xx> pattern modifier
591 Normally SPACE and TAB characters have no special meaning inside a
592 bracketed character class; they are just added to the list of characters
593 matched by the class. But if the L<C</xx>|perlre/E<sol>x and E<sol>xx>
594 pattern modifier is in effect, they are generally ignored and can be
595 added to improve readability. They can't be added in the middle of a
598 / [ \x{10 FFFF} ] /xx # WRONG!
600 The SPACE in the middle of the hex constant is illegal.
602 To specify a literal SPACE character, you can escape it with a
607 This matches the English vowels plus the SPACE character.
609 For clarity, you should already have been using C<\t> to specify a
610 literal tab, and C<\t> is unaffected by C</xx>.
612 =head3 Character Ranges
614 It is not uncommon to want to match a range of characters. Luckily, instead
615 of listing all characters in the range, one may use the hyphen (C<->).
616 If inside a bracketed character class you have two characters separated
617 by a hyphen, it's treated as if all characters between the two were in
618 the class. For instance, C<[0-9]> matches any ASCII digit, and C<[a-m]>
619 matches any lowercase letter from the first half of the ASCII alphabet.
621 Note that the two characters on either side of the hyphen are not
622 necessarily both letters or both digits. Any character is possible,
623 although not advisable. C<['-?]> contains a range of characters, but
624 most people will not know which characters that means. Furthermore,
625 such ranges may lead to portability problems if the code has to run on
626 a platform that uses a different character set, such as EBCDIC.
628 If a hyphen in a character class cannot syntactically be part of a range, for
629 instance because it is the first or the last character of the character class,
630 or if it immediately follows a range, the hyphen isn't special, and so is
631 considered a character to be matched literally. If you want a hyphen in
632 your set of characters to be matched and its position in the class is such
633 that it could be considered part of a range, you must escape that hyphen
638 [a-z] # Matches a character that is a lower case ASCII letter.
639 [a-fz] # Matches any letter between 'a' and 'f' (inclusive) or
641 [-z] # Matches either a hyphen ('-') or the letter 'z'.
642 [a-f-m] # Matches any letter between 'a' and 'f' (inclusive), the
643 # hyphen ('-'), or the letter 'm'.
644 ['-?] # Matches any of the characters '()*+,-./0123456789:;<=>?
645 # (But not on an EBCDIC platform).
646 [\N{APOSTROPHE}-\N{QUESTION MARK}]
647 # Matches any of the characters '()*+,-./0123456789:;<=>?
648 # even on an EBCDIC platform.
649 [\N{U+27}-\N{U+3F}] # Same. (U+27 is "'", and U+3F is "?")
651 As the final two examples above show, you can achieve portability to
652 non-ASCII platforms by using the C<\N{...}> form for the range
653 endpoints. These indicate that the specified range is to be interpreted
654 using Unicode values, so C<[\N{U+27}-\N{U+3F}]> means to match
655 C<\N{U+27}>, C<\N{U+28}>, C<\N{U+29}>, ..., C<\N{U+3D}>, C<\N{U+3E}>,
656 and C<\N{U+3F}>, whatever the native code point versions for those are.
657 These are called "Unicode" ranges. If either end is of the C<\N{...}>
658 form, the range is considered Unicode. A C<regexp> warning is raised
659 under C<S<"use re 'strict'">> if the other endpoint is specified
662 [\N{U+00}-\x09] # Warning under re 'strict'; \x09 is non-portable
663 [\N{U+00}-\t] # No warning;
665 Both of the above match the characters C<\N{U+00}> C<\N{U+01}>, ...
666 C<\N{U+08}>, C<\N{U+09}>, but the C<\x09> looks like it could be a
667 mistake so the warning is raised (under C<re 'strict'>) for it.
669 Perl also guarantees that the ranges C<A-Z>, C<a-z>, C<0-9>, and any
670 subranges of these match what an English-only speaker would expect them
671 to match on any platform. That is, C<[A-Z]> matches the 26 ASCII
673 C<[a-z]> matches the 26 lowercase letters; and C<[0-9]> matches the 10
674 digits. Subranges, like C<[h-k]>, match correspondingly, in this case
675 just the four letters C<"h">, C<"i">, C<"j">, and C<"k">. This is the
676 natural behavior on ASCII platforms where the code points (ordinal
677 values) for C<"h"> through C<"k"> are consecutive integers (0x68 through
678 0x6B). But special handling to achieve this may be needed on platforms
679 with a non-ASCII native character set. For example, on EBCDIC
680 platforms, the code point for C<"h"> is 0x88, C<"i"> is 0x89, C<"j"> is
681 0x91, and C<"k"> is 0x92. Perl specially treats C<[h-k]> to exclude the
682 seven code points in the gap: 0x8A through 0x90. This special handling is
683 only invoked when the range is a subrange of one of the ASCII uppercase,
684 lowercase, and digit ranges, AND each end of the range is expressed
685 either as a literal, like C<"A">, or as a named character (C<\N{...}>,
686 including the C<\N{U+...> form).
690 [i-j] # Matches either "i" or "j"
691 [i-\N{LATIN SMALL LETTER J}] # Same
693 [\N{U+69}-\N{U+6A}] # Same
694 [\x{89}-\x{91}] # Matches 0x89 ("i"), 0x8A .. 0x90, 0x91 ("j")
697 [i-J] # Matches, 0x89 ("i") .. 0xC1 ("J"); special
698 # handling doesn't apply because range is mixed
703 It is also possible to instead list the characters you do not want to
704 match. You can do so by using a caret (C<^>) as the first character in the
705 character class. For instance, C<[^a-z]> matches any character that is not a
706 lowercase ASCII letter, which therefore includes more than a million
707 Unicode code points. The class is said to be "negated" or "inverted".
709 This syntax make the caret a special character inside a bracketed character
710 class, but only if it is the first character of the class. So if you want
711 the caret as one of the characters to match, either escape the caret or
712 else don't list it first.
714 In inverted bracketed character classes, Perl ignores the Unicode rules
715 that normally say that named sequence, and certain characters should
716 match a sequence of multiple characters use under caseless C</i>
717 matching. Following those rules could lead to highly confusing
720 "ss" =~ /^[^\xDF]+$/ui; # Matches!
722 This should match any sequences of characters that aren't C<\xDF> nor
723 what C<\xDF> matches under C</i>. C<"s"> isn't C<\xDF>, but Unicode
724 says that C<"ss"> is what C<\xDF> matches under C</i>. So which one
725 "wins"? Do you fail the match because the string has C<ss> or accept it
726 because it has an C<s> followed by another C<s>? Perl has chosen the
727 latter. (See note in L</Bracketed Character Classes> above.)
731 "e" =~ /[^aeiou]/ # No match, the 'e' is listed.
732 "x" =~ /[^aeiou]/ # Match, as 'x' isn't a lowercase vowel.
733 "^" =~ /[^^]/ # No match, matches anything that isn't a caret.
734 "^" =~ /[x^]/ # Match, caret is not special here.
736 =head3 Backslash Sequences
738 You can put any backslash sequence character class (with the exception of
739 C<\N> and C<\R>) inside a bracketed character class, and it will act just
740 as if you had put all characters matched by the backslash sequence inside the
741 character class. For instance, C<[a-f\d]> matches any decimal digit, or any
742 of the lowercase letters between 'a' and 'f' inclusive.
744 C<\N> within a bracketed character class must be of the forms C<\N{I<name>}>
745 or C<\N{U+I<hex char>}>, and NOT be the form that matches non-newlines,
746 for the same reason that a dot C<.> inside a bracketed character class loses
747 its special meaning: it matches nearly anything, which generally isn't what you
753 /[\p{Thai}\d]/ # Matches a character that is either a Thai
754 # character, or a digit.
755 /[^\p{Arabic}()]/ # Matches a character that is neither an Arabic
756 # character, nor a parenthesis.
758 Backslash sequence character classes cannot form one of the endpoints
759 of a range. Thus, you can't say:
761 /[\p{Thai}-\d]/ # Wrong!
763 =head3 POSIX Character Classes
764 X<character class> X<\p> X<\p{}>
765 X<alpha> X<alnum> X<ascii> X<blank> X<cntrl> X<digit> X<graph>
766 X<lower> X<print> X<punct> X<space> X<upper> X<word> X<xdigit>
768 POSIX character classes have the form C<[:class:]>, where I<class> is the
769 name, and the C<[:> and C<:]> delimiters. POSIX character classes only appear
770 I<inside> bracketed character classes, and are a convenient and descriptive
771 way of listing a group of characters.
773 Be careful about the syntax,
776 $string =~ /[[:alpha:]]/
778 # Incorrect (will warn):
779 $string =~ /[:alpha:]/
781 The latter pattern would be a character class consisting of a colon,
782 and the letters C<a>, C<l>, C<p> and C<h>.
784 POSIX character classes can be part of a larger bracketed character class.
789 is valid and matches '0', '1', any alphabetic character, and the percent sign.
791 Perl recognizes the following POSIX character classes:
793 alpha Any alphabetical character (e.g., [A-Za-z]).
794 alnum Any alphanumeric character (e.g., [A-Za-z0-9]).
795 ascii Any character in the ASCII character set.
796 blank A GNU extension, equal to a space or a horizontal tab ("\t").
797 cntrl Any control character. See Note [2] below.
798 digit Any decimal digit (e.g., [0-9]), equivalent to "\d".
799 graph Any printable character, excluding a space. See Note [3] below.
800 lower Any lowercase character (e.g., [a-z]).
801 print Any printable character, including a space. See Note [4] below.
802 punct Any graphical character excluding "word" characters. Note [5].
803 space Any whitespace character. "\s" including the vertical tab
805 upper Any uppercase character (e.g., [A-Z]).
806 word A Perl extension (e.g., [A-Za-z0-9_]), equivalent to "\w".
807 xdigit Any hexadecimal digit (e.g., [0-9a-fA-F]). Note [7].
809 Like the L<Unicode properties|/Unicode Properties>, most of the POSIX
810 properties match the same regardless of whether case-insensitive (C</i>)
811 matching is in effect or not. The two exceptions are C<[:upper:]> and
812 C<[:lower:]>. Under C</i>, they each match the union of C<[:upper:]> and
815 Most POSIX character classes have two Unicode-style C<\p> property
816 counterparts. (They are not official Unicode properties, but Perl extensions
817 derived from official Unicode properties.) The table below shows the relation
818 between POSIX character classes and these counterparts.
820 One counterpart, in the column labelled "ASCII-range Unicode" in
821 the table, matches only characters in the ASCII character set.
823 The other counterpart, in the column labelled "Full-range Unicode", matches any
824 appropriate characters in the full Unicode character set. For example,
825 C<\p{Alpha}> matches not just the ASCII alphabetic characters, but any
826 character in the entire Unicode character set considered alphabetic.
827 An entry in the column labelled "backslash sequence" is a (short)
830 [[:...:]] ASCII-range Full-range backslash Note
831 Unicode Unicode sequence
832 -----------------------------------------------------
833 alpha \p{PosixAlpha} \p{XPosixAlpha}
834 alnum \p{PosixAlnum} \p{XPosixAlnum}
836 blank \p{PosixBlank} \p{XPosixBlank} \h [1]
837 or \p{HorizSpace} [1]
838 cntrl \p{PosixCntrl} \p{XPosixCntrl} [2]
839 digit \p{PosixDigit} \p{XPosixDigit} \d
840 graph \p{PosixGraph} \p{XPosixGraph} [3]
841 lower \p{PosixLower} \p{XPosixLower}
842 print \p{PosixPrint} \p{XPosixPrint} [4]
843 punct \p{PosixPunct} \p{XPosixPunct} [5]
844 \p{PerlSpace} \p{XPerlSpace} \s [6]
845 space \p{PosixSpace} \p{XPosixSpace} [6]
846 upper \p{PosixUpper} \p{XPosixUpper}
847 word \p{PosixWord} \p{XPosixWord} \w
848 xdigit \p{PosixXDigit} \p{XPosixXDigit} [7]
854 C<\p{Blank}> and C<\p{HorizSpace}> are synonyms.
858 Control characters don't produce output as such, but instead usually control
859 the terminal somehow: for example, newline and backspace are control characters.
860 On ASCII platforms, in the ASCII range, characters whose code points are
861 between 0 and 31 inclusive, plus 127 (C<DEL>) are control characters; on
862 EBCDIC platforms, their counterparts are control characters.
866 Any character that is I<graphical>, that is, visible. This class consists
867 of all alphanumeric characters and all punctuation characters.
871 All printable characters, which is the set of all graphical characters
872 plus those whitespace characters which are not also controls.
876 C<\p{PosixPunct}> and C<[[:punct:]]> in the ASCII range match all
877 non-controls, non-alphanumeric, non-space characters:
878 C<[-!"#$%&'()*+,./:;<=E<gt>?@[\\\]^_`{|}~]> (although if a locale is in effect,
879 it could alter the behavior of C<[[:punct:]]>).
881 The similarly named property, C<\p{Punct}>, matches a somewhat different
882 set in the ASCII range, namely
883 C<[-!"#%&'()*,./:;?@[\\\]_{}]>. That is, it is missing the nine
884 characters C<[$+E<lt>=E<gt>^`|~]>.
885 This is because Unicode splits what POSIX considers to be punctuation into two
886 categories, Punctuation and Symbols.
888 C<\p{XPosixPunct}> and (under Unicode rules) C<[[:punct:]]>, match what
889 C<\p{PosixPunct}> matches in the ASCII range, plus what C<\p{Punct}>
890 matches. This is different than strictly matching according to
891 C<\p{Punct}>. Another way to say it is that
892 if Unicode rules are in effect, C<[[:punct:]]> matches all characters
893 that Unicode considers punctuation, plus all ASCII-range characters that
894 Unicode considers symbols.
898 C<\p{XPerlSpace}> and C<\p{Space}> match identically starting with Perl
899 v5.18. In earlier versions, these differ only in that in non-locale
900 matching, C<\p{XPerlSpace}> did not match the vertical tab, C<\cK>.
901 Same for the two ASCII-only range forms.
905 Unlike C<[[:digit:]]> which matches digits in many writing systems, such
906 as Thai and Devanagari, there are currently only two sets of hexadecimal
907 digits, and it is unlikely that more will be added. This is because you
908 not only need the ten digits, but also the six C<[A-F]> (and C<[a-f]>)
909 to correspond. That means only the Latin script is suitable for these,
910 and Unicode has only two sets of these, the familiar ASCII set, and the
911 fullwidth forms starting at U+FF10 (FULLWIDTH DIGIT ZERO).
915 There are various other synonyms that can be used besides the names
916 listed in the table. For example, C<\p{XPosixAlpha}> can be written as
917 C<\p{Alpha}>. All are listed in
918 L<perluniprops/Properties accessible through \p{} and \P{}>.
920 Both the C<\p> counterparts always assume Unicode rules are in effect.
921 On ASCII platforms, this means they assume that the code points from 128
922 to 255 are Latin-1, and that means that using them under locale rules is
923 unwise unless the locale is guaranteed to be Latin-1 or UTF-8. In contrast, the
924 POSIX character classes are useful under locale rules. They are
925 affected by the actual rules in effect, as follows:
929 =item If the C</a> modifier, is in effect ...
931 Each of the POSIX classes matches exactly the same as their ASCII-range
938 =item For code points above 255 ...
940 The POSIX class matches the same as its Full-range counterpart.
942 =item For code points below 256 ...
946 =item if locale rules are in effect ...
948 The POSIX class matches according to the locale, except:
954 also includes the platform's native underscore character, no matter what
959 on platforms that don't have the POSIX C<ascii> extension, this matches
960 just the platform's native ASCII-range characters.
964 on platforms that don't have the POSIX C<blank> extension, this matches
965 just the platform's native tab and space characters.
969 =item if, instead, Unicode rules are in effect ...
971 The POSIX class matches the same as the Full-range counterpart.
975 The POSIX class matches the same as the ASCII range counterpart.
983 Which rules apply are determined as described in
984 L<perlre/Which character set modifier is in effect?>.
986 =head4 Negation of POSIX character classes
987 X<character class, negation>
989 A Perl extension to the POSIX character class is the ability to
990 negate it. This is done by prefixing the class name with a caret (C<^>).
993 POSIX ASCII-range Full-range backslash
994 Unicode Unicode sequence
995 -----------------------------------------------------
996 [[:^digit:]] \P{PosixDigit} \P{XPosixDigit} \D
997 [[:^space:]] \P{PosixSpace} \P{XPosixSpace}
998 \P{PerlSpace} \P{XPerlSpace} \S
999 [[:^word:]] \P{PerlWord} \P{XPosixWord} \W
1001 The backslash sequence can mean either ASCII- or Full-range Unicode,
1002 depending on various factors as described in L<perlre/Which character set modifier is in effect?>.
1004 =head4 [= =] and [. .]
1006 Perl recognizes the POSIX character classes C<[=class=]> and
1007 C<[.class.]>, but does not (yet?) support them. Any attempt to use
1008 either construct raises an exception.
1012 /[[:digit:]]/ # Matches a character that is a digit.
1013 /[01[:lower:]]/ # Matches a character that is either a
1014 # lowercase letter, or '0' or '1'.
1015 /[[:digit:][:^xdigit:]]/ # Matches a character that can be anything
1016 # except the letters 'a' to 'f' and 'A' to
1017 # 'F'. This is because the main character
1018 # class is composed of two POSIX character
1019 # classes that are ORed together, one that
1020 # matches any digit, and the other that
1021 # matches anything that isn't a hex digit.
1022 # The OR adds the digits, leaving only the
1023 # letters 'a' to 'f' and 'A' to 'F' excluded.
1025 =head3 Extended Bracketed Character Classes
1029 This is a fancy bracketed character class that can be used for more
1030 readable and less error-prone classes, and to perform set operations,
1031 such as intersection. An example is
1033 /(?[ \p{Thai} & \p{Digit} ])/
1035 This will match all the digit characters that are in the Thai script.
1037 This is an experimental feature available starting in 5.18, and is
1038 subject to change as we gain field experience with it. Any attempt to
1039 use it will raise a warning, unless disabled via
1041 no warnings "experimental::regex_sets";
1043 Comments on this feature are welcome; send email to
1044 C<perl5-porters@perl.org>.
1046 The rules used by L<C<use re 'strict>|re/'strict' mode> apply to this
1049 We can extend the example above:
1051 /(?[ ( \p{Thai} + \p{Lao} ) & \p{Digit} ])/
1053 This matches digits that are in either the Thai or Laotian scripts.
1055 Notice the white space in these examples. This construct always has
1056 the C<E<sol>xx> modifier turned on within it.
1058 The available binary operators are:
1062 | another name for '+', hence means union
1063 - subtraction (the result matches the set consisting of those
1064 code points matched by the first operand, excluding any that
1065 are also matched by the second operand)
1066 ^ symmetric difference (the union minus the intersection). This
1067 is like an exclusive or, in that the result is the set of code
1068 points that are matched by either, but not both, of the
1071 There is one unary operator:
1075 All the binary operators left associate; C<"&"> is higher precedence
1076 than the others, which all have equal precedence. The unary operator
1077 right associates, and has highest precedence. Thus this follows the
1078 normal Perl precedence rules for logical operators. Use parentheses to
1079 override the default precedence and associativity.
1081 The main restriction is that everything is a metacharacter. Thus,
1082 you cannot refer to single characters by doing something like this:
1084 /(?[ a + b ])/ # Syntax error!
1086 The easiest way to specify an individual typable character is to enclose
1091 (This is the same thing as C<[ab]>.) You could also have said the
1096 (You can, of course, specify single characters by using, C<\x{...}>,
1099 This last example shows the use of this construct to specify an ordinary
1100 bracketed character class without additional set operations. Note the
1101 white space within it. This is allowed because C<E<sol>xx> is
1102 automatically turned on within this construct.
1104 All the other escapes accepted by normal bracketed character classes are
1105 accepted here as well.
1107 Because this construct compiles under
1108 L<C<use re 'strict>|re/'strict' mode>, unrecognized escapes that
1109 generate warnings in normal classes are fatal errors here, as well as
1110 all other warnings from these class elements, as well as some
1111 practices that don't currently warn outside C<re 'strict'>. For example
1114 /(?[ [ \xF ] ])/ # Syntax error!
1116 You have to have two hex digits after a braceless C<\x> (use a leading
1117 zero to make two). These restrictions are to lower the incidence of
1118 typos causing the class to not match what you thought it would.
1120 If a regular bracketed character class contains a C<\p{}> or C<\P{}> and
1121 is matched against a non-Unicode code point, a warning may be
1122 raised, as the result is not Unicode-defined. No such warning will come
1123 when using this extended form.
1125 The final difference between regular bracketed character classes and
1126 these, is that it is not possible to get these to match a
1127 multi-character fold. Thus,
1131 does not match the string C<ss>.
1133 You don't have to enclose POSIX class names inside double brackets,
1134 hence both of the following work:
1136 /(?[ [:word:] - [:lower:] ])/
1137 /(?[ [[:word:]] - [[:lower:]] ])/
1139 Any contained POSIX character classes, including things like C<\w> and C<\D>
1140 respect the C<E<sol>a> (and C<E<sol>aa>) modifiers.
1142 Note that C<< (?[ ]) >> is a regex-compile-time construct. Any attempt
1143 to use something which isn't knowable at the time the containing regular
1144 expression is compiled is a fatal error. In practice, this means
1145 just three limitations:
1151 When compiled within the scope of C<use locale> (or the C<E<sol>l> regex
1152 modifier), this construct assumes that the execution-time locale will be
1153 a UTF-8 one, and the generated pattern always uses Unicode rules. What
1154 gets matched or not thus isn't dependent on the actual runtime locale, so
1155 tainting is not enabled. But a C<locale> category warning is raised
1156 if the runtime locale turns out to not be UTF-8.
1161 L<user-defined property|perlunicode/"User-Defined Character Properties">
1162 used must be already defined by the time the regular expression is
1163 compiled (but note that this construct can be used instead of such
1168 A regular expression that otherwise would compile
1169 using C<E<sol>d> rules, and which uses this construct will instead
1170 use C<E<sol>u>. Thus this construct tells Perl that you don't want
1171 C<E<sol>d> rules for the entire regular expression containing it.
1175 Note that skipping white space applies only to the interior of this
1176 construct. There must not be any space between any of the characters
1177 that form the initial C<(?[>. Nor may there be space between the
1178 closing C<])> characters.
1180 Just as in all regular expressions, the pattern can be built up by
1181 including variables that are interpolated at regex compilation time.
1182 But its best to compile each sub-component.
1184 my $thai_or_lao = qr/(?[ \p{Thai} + \p{Lao} ])/;
1185 my $lower = qr/(?[ \p{Lower} + \p{Digit} ])/;
1187 When these are embedded in another pattern, what they match does not
1188 change, regardless of parenthesization or what modifiers are in effect
1189 in that outer pattern. If you fail to compile the subcomponents, you
1190 can get some nasty surprises. For example:
1192 my $thai_or_lao = '\p{Thai} + \p{Lao}';
1194 qr/(?[ \p{Digit} & $thai_or_lao ])/;
1198 qr/(?[ \p{Digit} & \p{Thai} + \p{Lao} ])/;
1200 But this does not have the effect that someone reading the source code
1201 would likely expect, as the intersection applies just to C<\p{Thai}>,
1202 excluding the Laotian. Its best to compile the subcomponents, but you
1203 could also parenthesize the component pieces:
1205 my $thai_or_lao = '( \p{Thai} + \p{Lao} )';
1207 But any modifiers will still apply to all the components:
1209 my $lower = '\p{Lower} + \p{Digit}';
1210 qr/(?[ \p{Greek} & $lower ])/i;
1212 matches upper case things. So just, compile the subcomponents, as
1215 Due to the way that Perl parses things, your parentheses and brackets
1216 may need to be balanced, even including comments. If you run into any
1217 examples, please send them to C<perlbug@perl.org>, so that we can have a
1218 concrete example for this man page.
1220 We may change it so that things that remain legal uses in normal bracketed
1221 character classes might become illegal within this experimental
1222 construct. One proposal, for example, is to forbid adjacent uses of the
1223 same character, as in C<(?[ [aa] ])>. The motivation for such a change
1224 is that this usage is likely a typo, as the second "a" adds nothing.