1PERLRECHARCLASS(1) Perl Programmers Reference Guide PERLRECHARCLASS(1)
2
6 perlrecharclass - Perl Regular Expression Character Classes
7
9 The top level documentation about Perl regular expressions is found in
10 perlre.
11 This manual page discusses the syntax and use of character classes in
13 Perl regular expressions.
14 A character class is a way of denoting a set of characters in such a
16 way that one character of the set is matched. It's important to
17 remember that: matching a character class consumes exactly one
18 character in the source string. (The source string is the string the
19 regular expression is matched against.)
20 There are three types of character classes in Perl regular expressions:
22 the dot, backslash sequences, and the form enclosed in square brackets.
23 Keep in mind, though, that often the term "character class" is used to
24 mean just the bracketed form. Certainly, most Perl documentation does
25 that.
26 The dot
28 The dot (or period), "." is probably the most used, and certainly the
29 most well-known character class. By default, a dot matches any
30 character, except for the newline. That default can be changed to add
31 matching the newline by using the single line modifier: for the entire
32 regular expression with the "/s" modifier, or locally with "(?s)" (and
33 even globally within the scope of "use re '/s'"). (The "\N" backslash
34 sequence, described below, matches any character except newline without
35 regard to the single line modifier.)
36 Here are some examples:
38 "a" =~ /./ # Match
40 "." =~ /./ # Match
41 "" =~ /./ # No match (dot has to match a character)
42 "\n" =~ /./ # No match (dot does not match a newline)
43 "\n" =~ /./s # Match (global 'single line' modifier)
44 "\n" =~ /(?s:.)/ # Match (local 'single line' modifier)
45 "ab" =~ /^.$/ # No match (dot matches one character)
46 Backslash sequences
48 A backslash sequence is a sequence of characters, the first one of
49 which is a backslash. Perl ascribes special meaning to many such
50 sequences, and some of these are character classes. That is, they
51 match a single character each, provided that the character belongs to
52 the specific set of characters defined by the sequence.
53 Here's a list of the backslash sequences that are character classes.
55 They are discussed in more detail below. (For the backslash sequences
56 that aren't character classes, see perlrebackslash.)
57 \d Match a decimal digit character.
59 \D Match a non-decimal-digit character.
60 \w Match a "word" character.
61 \W Match a non-"word" character.
62 \s Match a whitespace character.
63 \S Match a non-whitespace character.
64 \h Match a horizontal whitespace character.
65 \H Match a character that isn't horizontal whitespace.
66 \v Match a vertical whitespace character.
67 \V Match a character that isn't vertical whitespace.
68 \N Match a character that isn't a newline.
69 \pP, \p{Prop} Match a character that has the given Unicode property.
70 \PP, \P{Prop} Match a character that doesn't have the Unicode property
71 \N
73 "\N", available starting in v5.12, like the dot, matches any character
75 that is not a newline. The difference is that "\N" is not influenced by
76 the single line regular expression modifier (see "The dot" above).
77 Note that the form "\N{...}" may mean something completely different.
78 When the "{...}" is a quantifier, it means to match a non-newline
79 character that many times. For example, "\N{3}" means to match 3 non-
80 newlines; "\N{5,}" means to match 5 or more non-newlines. But if
81 "{...}" is not a legal quantifier, it is presumed to be a named
82 character. See charnames for those. For example, none of "\N{COLON}",
83 "\N{4F}", and "\N{F4}" contain legal quantifiers, so Perl will try to
84 find characters whose names are respectively "COLON", "4F", and "F4".
85 Digits
87 "\d" matches a single character considered to be a decimal digit. If
89 the "/a" regular expression modifier is in effect, it matches [0-9].
90 Otherwise, it matches anything that is matched by "\p{Digit}", which
91 includes [0-9]. (An unlikely possible exception is that under locale
92 matching rules, the current locale might not have "[0-9]" matched by
93 "\d", and/or might match other characters whose code point is less than
94 256. The only such locale definitions that are legal would be to match
95 "[0-9]" plus another set of 10 consecutive digit characters; anything
96 else would be in violation of the C language standard, but Perl doesn't
97 currently assume anything in regard to this.)
98 What this means is that unless the "/a" modifier is in effect "\d" not
100 only matches the digits '0' - '9', but also Arabic, Devanagari, and
101 digits from other languages. This may cause some confusion, and some
102 security issues.
103 Some digits that "\d" matches look like some of the [0-9] ones, but
105 have different values. For example, BENGALI DIGIT FOUR (U+09EA) looks
106 very much like an ASCII DIGIT EIGHT (U+0038), and LEPCHA DIGIT SIX
107 (U+1C46) looks very much like an ASCII DIGIT FIVE (U+0035). An
108 application that is expecting only the ASCII digits might be misled, or
109 if the match is "\d+", the matched string might contain a mixture of
110 digits from different writing systems that look like they signify a
111 number different than they actually do. "num()" in Unicode::UCD can be
112 used to safely calculate the value, returning "undef" if the input
113 string contains such a mixture. Otherwise, for example, a displayed
114 price might be deliberately different than it appears.
115 What "\p{Digit}" means (and hence "\d" except under the "/a" modifier)
117 is "\p{General_Category=Decimal_Number}", or synonymously,
118 "\p{General_Category=Digit}". Starting with Unicode version 4.1, this
119 is the same set of characters matched by "\p{Numeric_Type=Decimal}".
120 But Unicode also has a different property with a similar name,
121 "\p{Numeric_Type=Digit}", which matches a completely different set of
122 characters. These characters are things such as "CIRCLED DIGIT ONE" or
123 subscripts, or are from writing systems that lack all ten digits.
124 The design intent is for "\d" to exactly match the set of characters
126 that can safely be used with "normal" big-endian positional decimal
127 syntax, where, for example 123 means one 'hundred', plus two 'tens',
128 plus three 'ones'. This positional notation does not necessarily apply
129 to characters that match the other type of "digit",
130 "\p{Numeric_Type=Digit}", and so "\d" doesn't match them.
131 The Tamil digits (U+0BE6 - U+0BEF) can also legally be used in old-
133 style Tamil numbers in which they would appear no more than one in a
134 row, separated by characters that mean "times 10", "times 100", etc.
135 (See <https://www.unicode.org/notes/tn21>.)
136 Any character not matched by "\d" is matched by "\D".
138 Word characters
140 A "\w" matches a single alphanumeric character (an alphabetic
142 character, or a decimal digit); or a connecting punctuation character,
143 such as an underscore ("_"); or a "mark" character (like some sort of
144 accent) that attaches to one of those. It does not match a whole word.
145 To match a whole word, use "\w+". This isn't the same thing as
146 matching an English word, but in the ASCII range it is the same as a
147 string of Perl-identifier characters.
148 If the "/a" modifier is in effect ...
150 "\w" matches the 63 characters [a-zA-Z0-9_].
151 otherwise ...
153 For code points above 255 ...
154 "\w" matches the same as "\p{Word}" matches in this range.
155 That is, it matches Thai letters, Greek letters, etc. This
156 includes connector punctuation (like the underscore) which
157 connect two words together, or diacritics, such as a "COMBINING
158 TILDE" and the modifier letters, which are generally used to
159 add auxiliary markings to letters.
160 For code points below 256 ...
162 if locale rules are in effect ...
163 "\w" matches the platform's native underscore character
164 plus whatever the locale considers to be alphanumeric.
165 if, instead, Unicode rules are in effect ...
167 "\w" matches exactly what "\p{Word}" matches.
168 otherwise ...
170 "\w" matches [a-zA-Z0-9_].
171 Which rules apply are determined as described in "Which character set
173 modifier is in effect?" in perlre.
174 There are a number of security issues with the full Unicode list of
176 word characters. See <http://unicode.org/reports/tr36>.
177 Also, for a somewhat finer-grained set of characters that are in
179 programming language identifiers beyond the ASCII range, you may wish
180 to instead use the more customized "Unicode Properties",
181 "\p{ID_Start}", "\p{ID_Continue}", "\p{XID_Start}", and
182 "\p{XID_Continue}". See <http://unicode.org/reports/tr31>.
183 Any character not matched by "\w" is matched by "\W".
185 Whitespace
187 "\s" matches any single character considered whitespace.
189 If the "/a" modifier is in effect ...
191 In all Perl versions, "\s" matches the 5 characters [\t\n\f\r ];
192 that is, the horizontal tab, the newline, the form feed, the
193 carriage return, and the space. Starting in Perl v5.18, it also
194 matches the vertical tab, "\cK". See note "[1]" below for a
195 discussion of this.
196 otherwise ...
198 For code points above 255 ...
199 "\s" matches exactly the code points above 255 shown with an
200 "s" column in the table below.
201 For code points below 256 ...
203 if locale rules are in effect ...
204 "\s" matches whatever the locale considers to be
205 whitespace.
206 if, instead, Unicode rules are in effect ...
208 "\s" matches exactly the characters shown with an "s"
209 column in the table below.
210 otherwise ...
212 "\s" matches [\t\n\f\r ] and, starting in Perl v5.18, the
213 vertical tab, "\cK". (See note "[1]" below for a
214 discussion of this.) Note that this list doesn't include
215 the non-breaking space.
216 Which rules apply are determined as described in "Which character set
218 modifier is in effect?" in perlre.
219 Any character not matched by "\s" is matched by "\S".
221 "\h" matches any character considered horizontal whitespace; this
223 includes the platform's space and tab characters and several others
224 listed in the table below. "\H" matches any character not considered
225 horizontal whitespace. They use the platform's native character set,
226 and do not consider any locale that may otherwise be in use.
227 "\v" matches any character considered vertical whitespace; this
229 includes the platform's carriage return and line feed characters
230 (newline) plus several other characters, all listed in the table below.
231 "\V" matches any character not considered vertical whitespace. They
232 use the platform's native character set, and do not consider any locale
233 that may otherwise be in use.
234 "\R" matches anything that can be considered a newline under Unicode
236 rules. It can match a multi-character sequence. It cannot be used
237 inside a bracketed character class; use "\v" instead (vertical
238 whitespace). It uses the platform's native character set, and does not
239 consider any locale that may otherwise be in use. Details are
240 discussed in perlrebackslash.
241 Note that unlike "\s" (and "\d" and "\w"), "\h" and "\v" always match
243 the same characters, without regard to other factors, such as the
244 active locale or whether the source string is in UTF-8 format.
245 One might think that "\s" is equivalent to "[\h\v]". This is indeed
247 true starting in Perl v5.18, but prior to that, the sole difference was
248 that the vertical tab ("\cK") was not matched by "\s".
249 The following table is a complete listing of characters matched by
251 "\s", "\h" and "\v" as of Unicode 14.0.
252 The first column gives the Unicode code point of the character (in hex
254 format), the second column gives the (Unicode) name. The third column
255 indicates by which class(es) the character is matched (assuming no
256 locale is in effect that changes the "\s" matching).
257 0x0009 CHARACTER TABULATION h s
259 0x000a LINE FEED (LF) vs
260 0x000b LINE TABULATION vs [1]
261 0x000c FORM FEED (FF) vs
262 0x000d CARRIAGE RETURN (CR) vs
263 0x0020 SPACE h s
264 0x0085 NEXT LINE (NEL) vs [2]
265 0x00a0 NO-BREAK SPACE h s [2]
266 0x1680 OGHAM SPACE MARK h s
267 0x2000 EN QUAD h s
268 0x2001 EM QUAD h s
269 0x2002 EN SPACE h s
270 0x2003 EM SPACE h s
271 0x2004 THREE-PER-EM SPACE h s
272 0x2005 FOUR-PER-EM SPACE h s
273 0x2006 SIX-PER-EM SPACE h s
274 0x2007 FIGURE SPACE h s
275 0x2008 PUNCTUATION SPACE h s
276 0x2009 THIN SPACE h s
277 0x200a HAIR SPACE h s
278 0x2028 LINE SEPARATOR vs
279 0x2029 PARAGRAPH SEPARATOR vs
280 0x202f NARROW NO-BREAK SPACE h s
281 0x205f MEDIUM MATHEMATICAL SPACE h s
282 0x3000 IDEOGRAPHIC SPACE h s
283 [1] Prior to Perl v5.18, "\s" did not match the vertical tab.
285 "[^\S\cK]" (obscurely) matches what "\s" traditionally did.
286 [2] NEXT LINE and NO-BREAK SPACE may or may not match "\s" depending on
288 the rules in effect. See the beginning of this section.
289 Unicode Properties
291 "\pP" and "\p{Prop}" are character classes to match characters that fit
293 given Unicode properties. One letter property names can be used in the
294 "\pP" form, with the property name following the "\p", otherwise,
295 braces are required. When using braces, there is a single form, which
296 is just the property name enclosed in the braces, and a compound form
297 which looks like "\p{name=value}", which means to match if the property
298 "name" for the character has that particular "value". For instance, a
299 match for a number can be written as "/\pN/" or as "/\p{Number}/", or
300 as "/\p{Number=True}/". Lowercase letters are matched by the property
301 Lowercase_Letter which has the short form Ll. They need the braces, so
302 are written as "/\p{Ll}/" or "/\p{Lowercase_Letter}/", or
303 "/\p{General_Category=Lowercase_Letter}/" (the underscores are
304 optional). "/\pLl/" is valid, but means something different. It
305 matches a two character string: a letter (Unicode property "\pL"),
306 followed by a lowercase "l".
307 What a Unicode property matches is never subject to locale rules, and
309 if locale rules are not otherwise in effect, the use of a Unicode
310 property will force the regular expression into using Unicode rules, if
311 it isn't already.
312 Note that almost all properties are immune to case-insensitive
314 matching. That is, adding a "/i" regular expression modifier does not
315 change what they match. But there are two sets that are affected. The
316 first set is "Uppercase_Letter", "Lowercase_Letter", and
317 "Titlecase_Letter", all of which match "Cased_Letter" under "/i"
318 matching. The second set is "Uppercase", "Lowercase", and "Titlecase",
319 all of which match "Cased" under "/i" matching. (The difference
320 between these sets is that some things, such as Roman numerals, come in
321 both upper and lower case, so they are "Cased", but aren't considered
322 to be letters, so they aren't "Cased_Letter"s. They're actually
323 "Letter_Number"s.) This set also includes its subsets "PosixUpper" and
324 "PosixLower", both of which under "/i" match "PosixAlpha".
325 For more details on Unicode properties, see "Unicode Character
327 Properties" in perlunicode; for a complete list of possible properties,
328 see "Properties accessible through \p{} and \P{}" in perluniprops,
329 which notes all forms that have "/i" differences. It is also possible
330 to define your own properties. This is discussed in "User-Defined
331 Character Properties" in perlunicode.
332 Unicode properties are defined (surprise!) only on Unicode code points.
334 Starting in v5.20, when matching against "\p" and "\P", Perl treats
335 non-Unicode code points (those above the legal Unicode maximum of
336 0x10FFFF) as if they were typical unassigned Unicode code points.
337 Prior to v5.20, Perl raised a warning and made all matches fail on non-
339 Unicode code points. This could be somewhat surprising:
340 chr(0x110000) =~ \p{ASCII_Hex_Digit=True} # Fails on Perls < v5.20.
342 chr(0x110000) =~ \p{ASCII_Hex_Digit=False} # Also fails on Perls
343 # < v5.20
344 Even though these two matches might be thought of as complements, until
346 v5.20 they were so only on Unicode code points.
347 Starting in perl v5.30, wildcards are allowed in Unicode property
349 values. See "Wildcards in Property Values" in perlunicode.
350 Examples
352 "a" =~ /\w/ # Match, "a" is a 'word' character.
354 "7" =~ /\w/ # Match, "7" is a 'word' character as well.
355 "a" =~ /\d/ # No match, "a" isn't a digit.
356 "7" =~ /\d/ # Match, "7" is a digit.
357 " " =~ /\s/ # Match, a space is whitespace.
358 "a" =~ /\D/ # Match, "a" is a non-digit.
359 "7" =~ /\D/ # No match, "7" is not a non-digit.
360 " " =~ /\S/ # No match, a space is not non-whitespace.
361 " " =~ /\h/ # Match, space is horizontal whitespace.
363 " " =~ /\v/ # No match, space is not vertical whitespace.
364 "\r" =~ /\v/ # Match, a return is vertical whitespace.
365 "a" =~ /\pL/ # Match, "a" is a letter.
367 "a" =~ /\p{Lu}/ # No match, /\p{Lu}/ matches upper case letters.
368 "\x{0e0b}" =~ /\p{Thai}/ # Match, \x{0e0b} is the character
370 # 'THAI CHARACTER SO SO', and that's in
371 # Thai Unicode class.
372 "a" =~ /\P{Lao}/ # Match, as "a" is not a Laotian character.
373 It is worth emphasizing that "\d", "\w", etc, match single characters,
375 not complete numbers or words. To match a number (that consists of
376 digits), use "\d+"; to match a word, use "\w+". But be aware of the
377 security considerations in doing so, as mentioned above.
378 Bracketed Character Classes
380 The third form of character class you can use in Perl regular
381 expressions is the bracketed character class. In its simplest form, it
382 lists the characters that may be matched, surrounded by square
383 brackets, like this: "[aeiou]". This matches one of "a", "e", "i", "o"
384 or "u". Like the other character classes, exactly one character is
385 matched.* To match a longer string consisting of characters mentioned
386 in the character class, follow the character class with a quantifier.
387 For instance, "[aeiou]+" matches one or more lowercase English vowels.
388 Repeating a character in a character class has no effect; it's
390 considered to be in the set only once.
391 Examples:
393 "e" =~ /[aeiou]/ # Match, as "e" is listed in the class.
395 "p" =~ /[aeiou]/ # No match, "p" is not listed in the class.
396 "ae" =~ /^[aeiou]$/ # No match, a character class only matches
397 # a single character.
398 "ae" =~ /^[aeiou]+$/ # Match, due to the quantifier.
399 -------
401 * There are two exceptions to a bracketed character class matching a
403 single character only. Each requires special handling by Perl to make
404 things work:
405 • When the class is to match caselessly under "/i" matching rules,
407 and a character that is explicitly mentioned inside the class
408 matches a multiple-character sequence caselessly under Unicode
409 rules, the class will also match that sequence. For example,
410 Unicode says that the letter "LATIN SMALL LETTER SHARP S" should
411 match the sequence "ss" under "/i" rules. Thus,
412 'ss' =~ /\A\N{LATIN SMALL LETTER SHARP S}\z/i # Matches
414 'ss' =~ /\A[aeioust\N{LATIN SMALL LETTER SHARP S}]\z/i # Matches
415 For this to happen, the class must not be inverted (see "Negation")
417 and the character must be explicitly specified, and not be part of
418 a multi-character range (not even as one of its endpoints).
419 ("Character Ranges" will be explained shortly.) Therefore,
420 'ss' =~ /\A[\0-\x{ff}]\z/ui # Doesn't match
422 'ss' =~ /\A[\0-\N{LATIN SMALL LETTER SHARP S}]\z/ui # No match
423 'ss' =~ /\A[\xDF-\xDF]\z/ui # Matches on ASCII platforms, since
424 # \xDF is LATIN SMALL LETTER SHARP S,
425 # and the range is just a single
426 # element
427 Note that it isn't a good idea to specify these types of ranges
429 anyway.
430 • Some names known to "\N{...}" refer to a sequence of multiple
432 characters, instead of the usual single character. When one of
433 these is included in the class, the entire sequence is matched.
434 For example,
435 "\N{TAMIL LETTER KA}\N{TAMIL VOWEL SIGN AU}"
437 =~ / ^ [\N{TAMIL SYLLABLE KAU}] $ /x;
438 matches, because "\N{TAMIL SYLLABLE KAU}" is a named sequence
440 consisting of the two characters matched against. Like the other
441 instance where a bracketed class can match multiple characters, and
442 for similar reasons, the class must not be inverted, and the named
443 sequence may not appear in a range, even one where it is both
444 endpoints. If these happen, it is a fatal error if the character
445 class is within the scope of "use re 'strict", or within an
446 extended "(?[...])" class; otherwise only the first code point is
447 used (with a "regexp"-type warning raised).
448 Special Characters Inside a Bracketed Character Class
450 Most characters that are meta characters in regular expressions (that
452 is, characters that carry a special meaning like ".", "*", or "(") lose
453 their special meaning and can be used inside a character class without
454 the need to escape them. For instance, "[()]" matches either an opening
455 parenthesis, or a closing parenthesis, and the parens inside the
456 character class don't group or capture. Be aware that, unless the
457 pattern is evaluated in single-quotish context, variable interpolation
458 will take place before the bracketed class is parsed:
459 $, = "\t| ";
461 $a =~ m'[$,]'; # single-quotish: matches '$' or ','
462 $a =~ q{[$,]}' # same
463 $a =~ m/[$,]/; # double-quotish: Because we made an
464 # assignment to $, above, this now
465 # matches "\t", "|", or " "
466 Characters that may carry a special meaning inside a character class
468 are: "\", "^", "-", "[" and "]", and are discussed below. They can be
469 escaped with a backslash, although this is sometimes not needed, in
470 which case the backslash may be omitted.
471 The sequence "\b" is special inside a bracketed character class. While
473 outside the character class, "\b" is an assertion indicating a point
474 that does not have either two word characters or two non-word
475 characters on either side, inside a bracketed character class, "\b"
476 matches a backspace character.
477 The sequences "\a", "\c", "\e", "\f", "\n", "\N{NAME}", "\N{U+hex
479 char}", "\r", "\t", and "\x" are also special and have the same
480 meanings as they do outside a bracketed character class.
481 Also, a backslash followed by two or three octal digits is considered
483 an octal number.
484 A "[" is not special inside a character class, unless it's the start of
486 a POSIX character class (see "POSIX Character Classes" below). It
487 normally does not need escaping.
488 A "]" is normally either the end of a POSIX character class (see "POSIX
490 Character Classes" below), or it signals the end of the bracketed
491 character class. If you want to include a "]" in the set of
492 characters, you must generally escape it.
493 However, if the "]" is the first (or the second if the first character
495 is a caret) character of a bracketed character class, it does not
496 denote the end of the class (as you cannot have an empty class) and is
497 considered part of the set of characters that can be matched without
498 escaping.
499 Examples:
501 "+" =~ /[+?*]/ # Match, "+" in a character class is not special.
503 "\cH" =~ /[\b]/ # Match, \b inside in a character class
504 # is equivalent to a backspace.
505 "]" =~ /[][]/ # Match, as the character class contains
506 # both [ and ].
507 "[]" =~ /[[]]/ # Match, the pattern contains a character class
508 # containing just [, and the character class is
509 # followed by a ].
510 Bracketed Character Classes and the "/xx" pattern modifier
512 Normally SPACE and TAB characters have no special meaning inside a
514 bracketed character class; they are just added to the list of
515 characters matched by the class. But if the "/xx" pattern modifier is
516 in effect, they are generally ignored and can be added to improve
517 readability. They can't be added in the middle of a single construct:
518 / [ \x{10 FFFF} ] /xx # WRONG!
520 The SPACE in the middle of the hex constant is illegal.
522 To specify a literal SPACE character, you can escape it with a
524 backslash, like:
525 /[ a e i o u \ ]/xx
527 This matches the English vowels plus the SPACE character.
529 For clarity, you should already have been using "\t" to specify a
531 literal tab, and "\t" is unaffected by "/xx".
532 Character Ranges
534 It is not uncommon to want to match a range of characters. Luckily,
536 instead of listing all characters in the range, one may use the hyphen
537 ("-"). If inside a bracketed character class you have two characters
538 separated by a hyphen, it's treated as if all characters between the
539 two were in the class. For instance, "[0-9]" matches any ASCII digit,
540 and "[a-m]" matches any lowercase letter from the first half of the
541 ASCII alphabet.
542 Note that the two characters on either side of the hyphen are not
544 necessarily both letters or both digits. Any character is possible,
545 although not advisable. "['-?]" contains a range of characters, but
546 most people will not know which characters that means. Furthermore,
547 such ranges may lead to portability problems if the code has to run on
548 a platform that uses a different character set, such as EBCDIC.
549 If a hyphen in a character class cannot syntactically be part of a
551 range, for instance because it is the first or the last character of
552 the character class, or if it immediately follows a range, the hyphen
553 isn't special, and so is considered a character to be matched
554 literally. If you want a hyphen in your set of characters to be
555 matched and its position in the class is such that it could be
556 considered part of a range, you must escape that hyphen with a
557 backslash.
558 Examples:
560 [a-z] # Matches a character that is a lower case ASCII letter.
562 [a-fz] # Matches any letter between 'a' and 'f' (inclusive) or
563 # the letter 'z'.
564 [-z] # Matches either a hyphen ('-') or the letter 'z'.
565 [a-f-m] # Matches any letter between 'a' and 'f' (inclusive), the
566 # hyphen ('-'), or the letter 'm'.
567 ['-?] # Matches any of the characters '()*+,-./0123456789:;<=>?
568 # (But not on an EBCDIC platform).
569 [\N{APOSTROPHE}-\N{QUESTION MARK}]
570 # Matches any of the characters '()*+,-./0123456789:;<=>?
571 # even on an EBCDIC platform.
572 [\N{U+27}-\N{U+3F}] # Same. (U+27 is "'", and U+3F is "?")
573 As the final two examples above show, you can achieve portability to
575 non-ASCII platforms by using the "\N{...}" form for the range
576 endpoints. These indicate that the specified range is to be
577 interpreted using Unicode values, so "[\N{U+27}-\N{U+3F}]" means to
578 match "\N{U+27}", "\N{U+28}", "\N{U+29}", ..., "\N{U+3D}", "\N{U+3E}",
579 and "\N{U+3F}", whatever the native code point versions for those are.
580 These are called "Unicode" ranges. If either end is of the "\N{...}"
581 form, the range is considered Unicode. A "regexp" warning is raised
582 under "use re 'strict'" if the other endpoint is specified non-
583 portably:
584 [\N{U+00}-\x09] # Warning under re 'strict'; \x09 is non-portable
586 [\N{U+00}-\t] # No warning;
587 Both of the above match the characters "\N{U+00}" "\N{U+01}", ...
589 "\N{U+08}", "\N{U+09}", but the "\x09" looks like it could be a mistake
590 so the warning is raised (under "re 'strict'") for it.
591 Perl also guarantees that the ranges "A-Z", "a-z", "0-9", and any
593 subranges of these match what an English-only speaker would expect them
594 to match on any platform. That is, "[A-Z]" matches the 26 ASCII
595 uppercase letters; "[a-z]" matches the 26 lowercase letters; and
596 "[0-9]" matches the 10 digits. Subranges, like "[h-k]", match
597 correspondingly, in this case just the four letters "h", "i", "j", and
598 "k". This is the natural behavior on ASCII platforms where the code
599 points (ordinal values) for "h" through "k" are consecutive integers
600 (0x68 through 0x6B). But special handling to achieve this may be
601 needed on platforms with a non-ASCII native character set. For
602 example, on EBCDIC platforms, the code point for "h" is 0x88, "i" is
603 0x89, "j" is 0x91, and "k" is 0x92. Perl specially treats "[h-k]" to
604 exclude the seven code points in the gap: 0x8A through 0x90. This
605 special handling is only invoked when the range is a subrange of one of
606 the ASCII uppercase, lowercase, and digit ranges, AND each end of the
607 range is expressed either as a literal, like "A", or as a named
608 character ("\N{...}", including the "\N{U+..." form).
609 EBCDIC Examples:
611 [i-j] # Matches either "i" or "j"
613 [i-\N{LATIN SMALL LETTER J}] # Same
614 [i-\N{U+6A}] # Same
615 [\N{U+69}-\N{U+6A}] # Same
616 [\x{89}-\x{91}] # Matches 0x89 ("i"), 0x8A .. 0x90, 0x91 ("j")
617 [i-\x{91}] # Same
618 [\x{89}-j] # Same
619 [i-J] # Matches, 0x89 ("i") .. 0xC1 ("J"); special
620 # handling doesn't apply because range is mixed
621 # case
622 Negation
624 It is also possible to instead list the characters you do not want to
626 match. You can do so by using a caret ("^") as the first character in
627 the character class. For instance, "[^a-z]" matches any character that
628 is not a lowercase ASCII letter, which therefore includes more than a
629 million Unicode code points. The class is said to be "negated" or
630 "inverted".
631 This syntax make the caret a special character inside a bracketed
633 character class, but only if it is the first character of the class. So
634 if you want the caret as one of the characters to match, either escape
635 the caret or else don't list it first.
636 In inverted bracketed character classes, Perl ignores the Unicode rules
638 that normally say that named sequence, and certain characters should
639 match a sequence of multiple characters use under caseless "/i"
640 matching. Following those rules could lead to highly confusing
641 situations:
642 "ss" =~ /^[^\xDF]+$/ui; # Matches!
644 This should match any sequences of characters that aren't "\xDF" nor
646 what "\xDF" matches under "/i". "s" isn't "\xDF", but Unicode says
647 that "ss" is what "\xDF" matches under "/i". So which one "wins"? Do
648 you fail the match because the string has "ss" or accept it because it
649 has an "s" followed by another "s"? Perl has chosen the latter. (See
650 note in "Bracketed Character Classes" above.)
651 Examples:
653 "e" =~ /[^aeiou]/ # No match, the 'e' is listed.
655 "x" =~ /[^aeiou]/ # Match, as 'x' isn't a lowercase vowel.
656 "^" =~ /[^^]/ # No match, matches anything that isn't a caret.
657 "^" =~ /[x^]/ # Match, caret is not special here.
658 Backslash Sequences
660 You can put any backslash sequence character class (with the exception
662 of "\N" and "\R") inside a bracketed character class, and it will act
663 just as if you had put all characters matched by the backslash sequence
664 inside the character class. For instance, "[a-f\d]" matches any decimal
665 digit, or any of the lowercase letters between 'a' and 'f' inclusive.
666 "\N" within a bracketed character class must be of the forms "\N{name}"
668 or "\N{U+hex char}", and NOT be the form that matches non-newlines, for
669 the same reason that a dot "." inside a bracketed character class loses
670 its special meaning: it matches nearly anything, which generally isn't
671 what you want to happen.
672 Examples:
674 /[\p{Thai}\d]/ # Matches a character that is either a Thai
676 # character, or a digit.
677 /[^\p{Arabic}()]/ # Matches a character that is neither an Arabic
678 # character, nor a parenthesis.
679 Backslash sequence character classes cannot form one of the endpoints
681 of a range. Thus, you can't say:
682 /[\p{Thai}-\d]/ # Wrong!
684 POSIX Character Classes
686 POSIX character classes have the form "[:class:]", where class is the
688 name, and the "[:" and ":]" delimiters. POSIX character classes only
689 appear inside bracketed character classes, and are a convenient and
690 descriptive way of listing a group of characters.
691 Be careful about the syntax,
693 # Correct:
695 $string =~ /[[:alpha:]]/
696 # Incorrect (will warn):
698 $string =~ /[:alpha:]/
699 The latter pattern would be a character class consisting of a colon,
701 and the letters "a", "l", "p" and "h".
702 POSIX character classes can be part of a larger bracketed character
704 class. For example,
705 [01[:alpha:]%]
707 is valid and matches '0', '1', any alphabetic character, and the
709 percent sign.
710 Perl recognizes the following POSIX character classes:
712 alpha Any alphabetical character (e.g., [A-Za-z]).
714 alnum Any alphanumeric character (e.g., [A-Za-z0-9]).
715 ascii Any character in the ASCII character set.
716 blank A GNU extension, equal to a space or a horizontal tab ("\t").
717 cntrl Any control character. See Note [2] below.
718 digit Any decimal digit (e.g., [0-9]), equivalent to "\d".
719 graph Any printable character, excluding a space. See Note [3] below.
720 lower Any lowercase character (e.g., [a-z]).
721 print Any printable character, including a space. See Note [4] below.
722 punct Any graphical character excluding "word" characters. Note [5].
723 space Any whitespace character. "\s" including the vertical tab
724 ("\cK").
725 upper Any uppercase character (e.g., [A-Z]).
726 word A Perl extension (e.g., [A-Za-z0-9_]), equivalent to "\w".
727 xdigit Any hexadecimal digit (e.g., [0-9a-fA-F]). Note [7].
728 Like the Unicode properties, most of the POSIX properties match the
730 same regardless of whether case-insensitive ("/i") matching is in
731 effect or not. The two exceptions are "[:upper:]" and "[:lower:]".
732 Under "/i", they each match the union of "[:upper:]" and "[:lower:]".
733 Most POSIX character classes have two Unicode-style "\p" property
735 counterparts. (They are not official Unicode properties, but Perl
736 extensions derived from official Unicode properties.) The table below
737 shows the relation between POSIX character classes and these
738 counterparts.
739 One counterpart, in the column labelled "ASCII-range Unicode" in the
741 table, matches only characters in the ASCII character set.
742 The other counterpart, in the column labelled "Full-range Unicode",
744 matches any appropriate characters in the full Unicode character set.
745 For example, "\p{Alpha}" matches not just the ASCII alphabetic
746 characters, but any character in the entire Unicode character set
747 considered alphabetic. An entry in the column labelled "backslash
748 sequence" is a (short) equivalent.
749 [[:...:]] ASCII-range Full-range backslash Note
751 Unicode Unicode sequence
752 -----------------------------------------------------
753 alpha \p{PosixAlpha} \p{XPosixAlpha}
754 alnum \p{PosixAlnum} \p{XPosixAlnum}
755 ascii \p{ASCII}
756 blank \p{PosixBlank} \p{XPosixBlank} \h [1]
757 or \p{HorizSpace} [1]
758 cntrl \p{PosixCntrl} \p{XPosixCntrl} [2]
759 digit \p{PosixDigit} \p{XPosixDigit} \d
760 graph \p{PosixGraph} \p{XPosixGraph} [3]
761 lower \p{PosixLower} \p{XPosixLower}
762 print \p{PosixPrint} \p{XPosixPrint} [4]
763 punct \p{PosixPunct} \p{XPosixPunct} [5]
764 \p{PerlSpace} \p{XPerlSpace} \s [6]
765 space \p{PosixSpace} \p{XPosixSpace} [6]
766 upper \p{PosixUpper} \p{XPosixUpper}
767 word \p{PosixWord} \p{XPosixWord} \w
768 xdigit \p{PosixXDigit} \p{XPosixXDigit} [7]
769 [1] "\p{Blank}" and "\p{HorizSpace}" are synonyms.
771 [2] Control characters don't produce output as such, but instead
773 usually control the terminal somehow: for example, newline and
774 backspace are control characters. On ASCII platforms, in the ASCII
775 range, characters whose code points are between 0 and 31 inclusive,
776 plus 127 ("DEL") are control characters; on EBCDIC platforms, their
777 counterparts are control characters.
778 [3] Any character that is graphical, that is, visible. This class
780 consists of all alphanumeric characters and all punctuation
781 characters.
782 [4] All printable characters, which is the set of all graphical
784 characters plus those whitespace characters which are not also
785 controls.
786 [5] "\p{PosixPunct}" and "[[:punct:]]" in the ASCII range match all
788 non-controls, non-alphanumeric, non-space characters:
789 "[-!"#$%&'()*+,./:;<=>?@[\\\]^_`{|}~]" (although if a locale is in
790 effect, it could alter the behavior of "[[:punct:]]").
791 The similarly named property, "\p{Punct}", matches a somewhat
793 different set in the ASCII range, namely
794 "[-!"#%&'()*,./:;?@[\\\]_{}]". That is, it is missing the nine
795 characters "[$+<=>^`|~]". This is because Unicode splits what
796 POSIX considers to be punctuation into two categories, Punctuation
797 and Symbols.
798 "\p{XPosixPunct}" and (under Unicode rules) "[[:punct:]]", match
800 what "\p{PosixPunct}" matches in the ASCII range, plus what
801 "\p{Punct}" matches. This is different than strictly matching
802 according to "\p{Punct}". Another way to say it is that if Unicode
803 rules are in effect, "[[:punct:]]" matches all characters that
804 Unicode considers punctuation, plus all ASCII-range characters that
805 Unicode considers symbols.
806 [6] "\p{XPerlSpace}" and "\p{Space}" match identically starting with
808 Perl v5.18. In earlier versions, these differ only in that in non-
809 locale matching, "\p{XPerlSpace}" did not match the vertical tab,
810 "\cK". Same for the two ASCII-only range forms.
811 [7] Unlike "[[:digit:]]" which matches digits in many writing systems,
813 such as Thai and Devanagari, there are currently only two sets of
814 hexadecimal digits, and it is unlikely that more will be added.
815 This is because you not only need the ten digits, but also the six
816 "[A-F]" (and "[a-f]") to correspond. That means only the Latin
817 script is suitable for these, and Unicode has only two sets of
818 these, the familiar ASCII set, and the fullwidth forms starting at
819 U+FF10 (FULLWIDTH DIGIT ZERO).
820 There are various other synonyms that can be used besides the names
822 listed in the table. For example, "\p{XPosixAlpha}" can be written as
823 "\p{Alpha}". All are listed in "Properties accessible through \p{} and
824 \P{}" in perluniprops.
825 Both the "\p" counterparts always assume Unicode rules are in effect.
827 On ASCII platforms, this means they assume that the code points from
828 128 to 255 are Latin-1, and that means that using them under locale
829 rules is unwise unless the locale is guaranteed to be Latin-1 or UTF-8.
830 In contrast, the POSIX character classes are useful under locale rules.
831 They are affected by the actual rules in effect, as follows:
832 If the "/a" modifier, is in effect ...
834 Each of the POSIX classes matches exactly the same as their ASCII-
835 range counterparts.
836 otherwise ...
838 For code points above 255 ...
839 The POSIX class matches the same as its Full-range counterpart.
840 For code points below 256 ...
842 if locale rules are in effect ...
843 The POSIX class matches according to the locale, except:
844 "word"
846 also includes the platform's native underscore
847 character, no matter what the locale is.
848 "ascii"
850 on platforms that don't have the POSIX "ascii"
851 extension, this matches just the platform's native
852 ASCII-range characters.
853 "blank"
855 on platforms that don't have the POSIX "blank"
856 extension, this matches just the platform's native tab
857 and space characters.
858 if, instead, Unicode rules are in effect ...
860 The POSIX class matches the same as the Full-range
861 counterpart.
862 otherwise ...
864 The POSIX class matches the same as the ASCII range
865 counterpart.
866 Which rules apply are determined as described in "Which character set
868 modifier is in effect?" in perlre.
869 Negation of POSIX character classes
871 A Perl extension to the POSIX character class is the ability to negate
873 it. This is done by prefixing the class name with a caret ("^"). Some
874 examples:
875 POSIX ASCII-range Full-range backslash
877 Unicode Unicode sequence
878 -----------------------------------------------------
879 [[:^digit:]] \P{PosixDigit} \P{XPosixDigit} \D
880 [[:^space:]] \P{PosixSpace} \P{XPosixSpace}
881 \P{PerlSpace} \P{XPerlSpace} \S
882 [[:^word:]] \P{PerlWord} \P{XPosixWord} \W
883 The backslash sequence can mean either ASCII- or Full-range Unicode,
885 depending on various factors as described in "Which character set
886 modifier is in effect?" in perlre.
887 [= =] and [. .]
889 Perl recognizes the POSIX character classes "[=class=]" and
891 "[.class.]", but does not (yet?) support them. Any attempt to use
892 either construct raises an exception.
893 Examples
895 /[[:digit:]]/ # Matches a character that is a digit.
897 /[01[:lower:]]/ # Matches a character that is either a
898 # lowercase letter, or '0' or '1'.
899 /[[:digit:][:^xdigit:]]/ # Matches a character that can be anything
900 # except the letters 'a' to 'f' and 'A' to
901 # 'F'. This is because the main character
902 # class is composed of two POSIX character
903 # classes that are ORed together, one that
904 # matches any digit, and the other that
905 # matches anything that isn't a hex digit.
906 # The OR adds the digits, leaving only the
907 # letters 'a' to 'f' and 'A' to 'F' excluded.
908 Extended Bracketed Character Classes
910 This is a fancy bracketed character class that can be used for more
912 readable and less error-prone classes, and to perform set operations,
913 such as intersection. An example is
914 /(?[ \p{Thai} & \p{Digit} ])/
916 This will match all the digit characters that are in the Thai script.
918 This feature became available in Perl 5.18, as experimental; accepted
920 in 5.36.
921 The rules used by "use re 'strict" apply to this construct.
923 We can extend the example above:
925 /(?[ ( \p{Thai} + \p{Lao} ) & \p{Digit} ])/
927 This matches digits that are in either the Thai or Laotian scripts.
929 Notice the white space in these examples. This construct always has
931 the "/xx" modifier turned on within it.
932 The available binary operators are:
934 & intersection
936 + union
937 | another name for '+', hence means union
938 - subtraction (the result matches the set consisting of those
939 code points matched by the first operand, excluding any that
940 are also matched by the second operand)
941 ^ symmetric difference (the union minus the intersection). This
942 is like an exclusive or, in that the result is the set of code
943 points that are matched by either, but not both, of the
944 operands.
945 There is one unary operator:
947 ! complement
949 All the binary operators left associate; "&" is higher precedence than
951 the others, which all have equal precedence. The unary operator right
952 associates, and has highest precedence. Thus this follows the normal
953 Perl precedence rules for logical operators. Use parentheses to
954 override the default precedence and associativity.
955 The main restriction is that everything is a metacharacter. Thus, you
957 cannot refer to single characters by doing something like this:
958 /(?[ a + b ])/ # Syntax error!
960 The easiest way to specify an individual typable character is to
962 enclose it in brackets:
963 /(?[ [a] + [b] ])/
965 (This is the same thing as "[ab]".) You could also have said the
967 equivalent:
968 /(?[[ a b ]])/
970 (You can, of course, specify single characters by using, "\x{...}",
972 "\N{...}", etc.)
973 This last example shows the use of this construct to specify an
975 ordinary bracketed character class without additional set operations.
976 Note the white space within it. This is allowed because "/xx" is
977 automatically turned on within this construct.
978 All the other escapes accepted by normal bracketed character classes
980 are accepted here as well.
981 Because this construct compiles under "use re 'strict", unrecognized
983 escapes that generate warnings in normal classes are fatal errors here,
984 as well as all other warnings from these class elements, as well as
985 some practices that don't currently warn outside "re 'strict'". For
986 example you cannot say
987 /(?[ [ \xF ] ])/ # Syntax error!
989 You have to have two hex digits after a braceless "\x" (use a leading
991 zero to make two). These restrictions are to lower the incidence of
992 typos causing the class to not match what you thought it would.
993 If a regular bracketed character class contains a "\p{}" or "\P{}" and
995 is matched against a non-Unicode code point, a warning may be raised,
996 as the result is not Unicode-defined. No such warning will come when
997 using this extended form.
998 The final difference between regular bracketed character classes and
1000 these, is that it is not possible to get these to match a multi-
1001 character fold. Thus,
1002 /(?[ [\xDF] ])/iu
1004 does not match the string "ss".
1006 You don't have to enclose POSIX class names inside double brackets,
1008 hence both of the following work:
1009 /(?[ [:word:] - [:lower:] ])/
1011 /(?[ [[:word:]] - [[:lower:]] ])/
1012 Any contained POSIX character classes, including things like "\w" and
1014 "\D" respect the "/a" (and "/aa") modifiers.
1015 Note that "(?[ ])" is a regex-compile-time construct. Any attempt to
1017 use something which isn't knowable at the time the containing regular
1018 expression is compiled is a fatal error. In practice, this means just
1019 three limitations:
1020 1. When compiled within the scope of "use locale" (or the "/l" regex
1022 modifier), this construct assumes that the execution-time locale
1023 will be a UTF-8 one, and the generated pattern always uses Unicode
1024 rules. What gets matched or not thus isn't dependent on the actual
1025 runtime locale, so tainting is not enabled. But a "locale"
1026 category warning is raised if the runtime locale turns out to not
1027 be UTF-8.
1028 2. Any user-defined property used must be already defined by the time
1030 the regular expression is compiled (but note that this construct
1031 can be used instead of such properties).
1032 3. A regular expression that otherwise would compile using "/d" rules,
1034 and which uses this construct will instead use "/u". Thus this
1035 construct tells Perl that you don't want "/d" rules for the entire
1036 regular expression containing it.
1037 Note that skipping white space applies only to the interior of this
1039 construct. There must not be any space between any of the characters
1040 that form the initial "(?[". Nor may there be space between the
1041 closing "])" characters.
1042 Just as in all regular expressions, the pattern can be built up by
1044 including variables that are interpolated at regex compilation time.
1045 But currently each such sub-component should be an already-compiled
1046 extended bracketed character class.
1047 my $thai_or_lao = qr/(?[ \p{Thai} + \p{Lao} ])/;
1049 ...
1050 qr/(?[ \p{Digit} & $thai_or_lao ])/;
1051 If you interpolate something else, the pattern may still compile (or it
1053 may die), but if it compiles, it very well may not behave as you would
1054 expect:
1055 my $thai_or_lao = '\p{Thai} + \p{Lao}';
1057 qr/(?[ \p{Digit} & $thai_or_lao ])/;
1058 compiles to
1060 qr/(?[ \p{Digit} & \p{Thai} + \p{Lao} ])/;
1062 This does not have the effect that someone reading the source code
1064 would likely expect, as the intersection applies just to "\p{Thai}",
1065 excluding the Laotian.
1066 Due to the way that Perl parses things, your parentheses and brackets
1068 may need to be balanced, even including comments. If you run into any
1069 examples, please submit them to <https://github.com/Perl/perl5/issues>,
1070 so that we can have a concrete example for this man page.
1071perl v5.38.2 2023-11-30 PERLRECHARCLASS(1)