4 perlrecharclass - Perl Regular Expression Character Classes
8 The top level documentation about Perl regular expressions
11 This manual page discusses the syntax and use of character
12 classes in Perl regular expressions.
14 A character class is a way of denoting a set of characters
15 in such a way that one character of the set is matched.
16 It's important to remember that: matching a character class
17 consumes exactly one character in the source string. (The source
18 string is the string the regular expression is matched against.)
20 There are three types of character classes in Perl regular
21 expressions: the dot, backslash sequences, and the form enclosed in square
22 brackets. Keep in mind, though, that often the term "character class" is used
23 to mean just the bracketed form. Certainly, most Perl documentation does that.
27 The dot (or period), C<.> is probably the most used, and certainly
28 the most well-known character class. By default, a dot matches any
29 character, except for the newline. That default can be changed to
30 add matching the newline by using the I<single line> modifier: either
31 for the entire regular expression with the C</s> modifier, or
32 locally with C<(?s)>. (The experimental C<\N> backslash sequence, described
33 below, matches any character except newline without regard to the
34 I<single line> modifier.)
36 Here are some examples:
40 "" =~ /./ # No match (dot has to match a character)
41 "\n" =~ /./ # No match (dot does not match a newline)
42 "\n" =~ /./s # Match (global 'single line' modifier)
43 "\n" =~ /(?s:.)/ # Match (local 'single line' modifier)
44 "ab" =~ /^.$/ # No match (dot matches one character)
46 =head2 Backslash sequences
47 X<\w> X<\W> X<\s> X<\S> X<\d> X<\D> X<\p> X<\P>
48 X<\N> X<\v> X<\V> X<\h> X<\H>
51 A backslash sequence is a sequence of characters, the first one of which is a
52 backslash. Perl ascribes special meaning to many such sequences, and some of
53 these are character classes. That is, they match a single character each,
54 provided that the character belongs to the specific set of characters defined
57 Here's a list of the backslash sequences that are character classes. They
58 are discussed in more detail below. (For the backslash sequences that aren't
59 character classes, see L<perlrebackslash>.)
61 \d Match a decimal digit character.
62 \D Match a non-decimal-digit character.
63 \w Match a "word" character.
64 \W Match a non-"word" character.
65 \s Match a whitespace character.
66 \S Match a non-whitespace character.
67 \h Match a horizontal whitespace character.
68 \H Match a character that isn't horizontal whitespace.
69 \v Match a vertical whitespace character.
70 \V Match a character that isn't vertical whitespace.
71 \N Match a character that isn't a newline. Experimental.
72 \pP, \p{Prop} Match a character that has the given Unicode property.
73 \PP, \P{Prop} Match a character that doesn't have the Unicode property
77 C<\N> is new in 5.12, and is experimental. It, like the dot, matches any
78 character that is not a newline. The difference is that C<\N> is not influenced
79 by the I<single line> regular expression modifier (see L</The dot> above). Note
80 that the form C<\N{...}> may mean something completely different. When the
81 C<{...}> is a L<quantifier|perlre/Quantifiers>, it means to match a non-newline
82 character that many times. For example, C<\N{3}> means to match 3
83 non-newlines; C<\N{5,}> means to match 5 or more non-newlines. But if C<{...}>
84 is not a legal quantifier, it is presumed to be a named character. See
85 L<charnames> for those. For example, none of C<\N{COLON}>, C<\N{4F}>, and
86 C<\N{F4}> contain legal quantifiers, so Perl will try to find characters whose
87 names are respectively C<COLON>, C<4F>, and C<F4>.
91 C<\d> matches a single character considered to be a decimal I<digit>.
92 If the C</a> regular expression modifier is in effect, it matches [0-9].
94 matches anything that is matched by C<\p{Digit}>, which includes [0-9].
95 (An unlikely possible exception is that under locale matching rules, the
96 current locale might not have [0-9] matched by C<\d>, and/or might match
97 other characters whose code point is less than 256. Such a locale
98 definition would be in violation of the C language standard, but Perl
99 doesn't currently assume anything in regard to this.)
101 What this means is that unless the C</a> modifier is in effect C<\d> not
102 only matches the digits '0' - '9', but also Arabic, Devanagari, and
103 digits from other languages. This may cause some confusion, and some
106 Some digits that C<\d> matches look like some of the [0-9] ones, but
107 have different values. For example, BENGALI DIGIT FOUR (U+09EA) looks
108 very much like an ASCII DIGIT EIGHT (U+0038). An application that
109 is expecting only the ASCII digits might be misled, or if the match is
110 C<\d+>, the matched string might contain a mixture of digits from
111 different writing systems that look like they signify a number different
112 than they actually do. L<Unicode::UCD/num()> can
114 calculate the value, returning C<undef> if the input string contains
117 What C<\p{Digit}> means (and hence C<\d> except under the C</a>
118 modifier) is C<\p{General_Category=Decimal_Number}>, or synonymously,
119 C<\p{General_Category=Digit}>. Starting with Unicode version 4.1, this
120 is the same set of characters matched by C<\p{Numeric_Type=Decimal}>.
121 But Unicode also has a different property with a similar name,
122 C<\p{Numeric_Type=Digit}>, which matches a completely different set of
123 characters. These characters are things such as C<CIRCLED DIGIT ONE>
124 or subscripts, or are from writing systems that lack all ten digits.
126 The design intent is for C<\d> to exactly match the set of characters
127 that can safely be used with "normal" big-endian positional decimal
128 syntax, where, for example 123 means one 'hundred', plus two 'tens',
129 plus three 'ones'. This positional notation does not necessarily apply
130 to characters that match the other type of "digit",
131 C<\p{Numeric_Type=Digit}>, and so C<\d> doesn't match them.
133 The Tamil digits (U+0BE6 - U+0BEF) can also legally be
134 used in old-style Tamil numbers in which they would appear no more than
135 one in a row, separated by characters that mean "times 10", "times 100",
136 etc. (See L<http://www.unicode.org/notes/tn21>.)
138 Any character not matched by C<\d> is matched by C<\D>.
140 =head3 Word characters
142 A C<\w> matches a single alphanumeric character (an alphabetic character, or a
143 decimal digit); or a connecting punctuation character, such as an
144 underscore ("_"); or a "mark" character (like some sort of accent) that
145 attaches to one of those. It does not match a whole word. To match a
146 whole word, use C<\w+>. This isn't the same thing as matching an
147 English word, but in the ASCII range it is the same as a string of
148 Perl-identifier characters.
152 =item If the C</a> modifier is in effect ...
154 C<\w> matches the 63 characters [a-zA-Z0-9_].
160 =item For code points above 255 ...
162 C<\w> matches the same as C<\p{Word}> matches in this range. That is,
163 it matches Thai letters, Greek letters, etc. This includes connector
164 punctuation (like the underscore) which connect two words together, or
165 diacritics, such as a C<COMBINING TILDE> and the modifier letters, which
166 are generally used to add auxiliary markings to letters.
168 =item For code points below 256 ...
172 =item if locale rules are in effect ...
174 C<\w> matches the platform's native underscore character plus whatever
175 the locale considers to be alphanumeric.
177 =item if Unicode rules are in effect or if on an EBCDIC platform ...
179 C<\w> matches exactly what C<\p{Word}> matches.
183 C<\w> matches [a-zA-Z0-9_].
191 Which rules apply are determined as described in L<perlre/Which character set modifier is in effect?>.
193 There are a number of security issues with the full Unicode list of word
194 characters. See L<http://unicode.org/reports/tr36>.
196 Also, for a somewhat finer-grained set of characters that are in programming
197 language identifiers beyond the ASCII range, you may wish to instead use the
198 more customized L</Unicode Properties>, C<\p{ID_Start}>,
199 C<\p{ID_Continue}>, C<\p{XID_Start}>, and C<\p{XID_Continue}>. See
200 L<http://unicode.org/reports/tr31>.
202 Any character not matched by C<\w> is matched by C<\W>.
206 C<\s> matches any single character considered whitespace.
210 =item If the C</a> modifier is in effect ...
212 C<\s> matches the 5 characters [\t\n\f\r ]; that is, the horizontal tab,
213 the newline, the form feed, the carriage return, and the space. (Note
214 that it doesn't match the vertical tab, C<\cK> on ASCII platforms.)
220 =item For code points above 255 ...
222 C<\s> matches exactly the code points above 255 shown with an "s" column
225 =item For code points below 256 ...
229 =item if locale rules are in effect ...
231 C<\s> matches whatever the locale considers to be whitespace. Note that
232 this is likely to include the vertical space, unlike non-locale C<\s>
235 =item if Unicode rules are in effect or if on an EBCDIC platform ...
237 C<\s> matches exactly the characters shown with an "s" column in the
242 C<\s> matches [\t\n\f\r ].
243 Note that this list doesn't include the non-breaking space.
251 Which rules apply are determined as described in L<perlre/Which character set modifier is in effect?>.
253 Any character not matched by C<\s> is matched by C<\S>.
255 C<\h> matches any character considered horizontal whitespace;
256 this includes the platform's space and tab characters and several others
257 listed in the table below. C<\H> matches any character
258 not considered horizontal whitespace. They use the platform's native
259 character set, and do not consider any locale that may otherwise be in
262 C<\v> matches any character considered vertical whitespace;
263 this includes the platform's carriage return and line feed characters (newline)
264 plus several other characters, all listed in the table below.
265 C<\V> matches any character not considered vertical whitespace.
266 They use the platform's native character set, and do not consider any
267 locale that may otherwise be in use.
269 C<\R> matches anything that can be considered a newline under Unicode
270 rules. It's not a character class, as it can match a multi-character
271 sequence. Therefore, it cannot be used inside a bracketed character
272 class; use C<\v> instead (vertical whitespace). It uses the platform's
273 native character set, and does not consider any locale that may
275 Details are discussed in L<perlrebackslash>.
277 Note that unlike C<\s> (and C<\d> and C<\w>), C<\h> and C<\v> always match
278 the same characters, without regard to other factors, such as the active
279 locale or whether the source string is in UTF-8 format.
281 One might think that C<\s> is equivalent to C<[\h\v]>. This is not true.
282 The difference is that the vertical tab (C<"\x0b">) is not matched by
283 C<\s>; it is however considered vertical whitespace.
285 The following table is a complete listing of characters matched by
286 C<\s>, C<\h> and C<\v> as of Unicode 6.0.
288 The first column gives the Unicode code point of the character (in hex format),
289 the second column gives the (Unicode) name. The third column indicates
290 by which class(es) the character is matched (assuming no locale or EBCDIC code
291 page is in effect that changes the C<\s> matching).
293 0x0009 CHARACTER TABULATION h s
294 0x000a LINE FEED (LF) vs
295 0x000b LINE TABULATION v
296 0x000c FORM FEED (FF) vs
297 0x000d CARRIAGE RETURN (CR) vs
299 0x0085 NEXT LINE (NEL) vs [1]
300 0x00a0 NO-BREAK SPACE h s [1]
301 0x1680 OGHAM SPACE MARK h s
302 0x180e MONGOLIAN VOWEL SEPARATOR h s
307 0x2004 THREE-PER-EM SPACE h s
308 0x2005 FOUR-PER-EM SPACE h s
309 0x2006 SIX-PER-EM SPACE h s
310 0x2007 FIGURE SPACE h s
311 0x2008 PUNCTUATION SPACE h s
312 0x2009 THIN SPACE h s
313 0x200a HAIR SPACE h s
314 0x2028 LINE SEPARATOR vs
315 0x2029 PARAGRAPH SEPARATOR vs
316 0x202f NARROW NO-BREAK SPACE h s
317 0x205f MEDIUM MATHEMATICAL SPACE h s
318 0x3000 IDEOGRAPHIC SPACE h s
324 NEXT LINE and NO-BREAK SPACE may or may not match C<\s> depending
325 on the rules in effect. See
326 L<the beginning of this section|/Whitespace>.
330 =head3 Unicode Properties
332 C<\pP> and C<\p{Prop}> are character classes to match characters that fit given
333 Unicode properties. One letter property names can be used in the C<\pP> form,
334 with the property name following the C<\p>, otherwise, braces are required.
335 When using braces, there is a single form, which is just the property name
336 enclosed in the braces, and a compound form which looks like C<\p{name=value}>,
337 which means to match if the property "name" for the character has that particular
339 For instance, a match for a number can be written as C</\pN/> or as
340 C</\p{Number}/>, or as C</\p{Number=True}/>.
341 Lowercase letters are matched by the property I<Lowercase_Letter> which
342 has the short form I<Ll>. They need the braces, so are written as C</\p{Ll}/> or
343 C</\p{Lowercase_Letter}/>, or C</\p{General_Category=Lowercase_Letter}/>
344 (the underscores are optional).
345 C</\pLl/> is valid, but means something different.
346 It matches a two character string: a letter (Unicode property C<\pL>),
347 followed by a lowercase C<l>.
349 If locale rules are not in effect, the use of
350 a Unicode property will force the regular expression into using Unicode
351 rules, if it isn't already.
353 Note that almost all properties are immune to case-insensitive matching.
354 That is, adding a C</i> regular expression modifier does not change what
355 they match. There are two sets that are affected. The first set is
358 and C<Titlecase_Letter>,
359 all of which match C<Cased_Letter> under C</i> matching.
364 all of which match C<Cased> under C</i> matching.
365 (The difference between these sets is that some things, such as Roman
366 numerals, come in both upper and lower case, so they are C<Cased>, but
367 aren't considered to be letters, so they aren't C<Cased_Letter>s. They're
368 actually C<Letter_Number>s.)
369 This set also includes its subsets C<PosixUpper> and C<PosixLower>, both
370 of which under C</i> match C<PosixAlpha>.
372 For more details on Unicode properties, see L<perlunicode/Unicode
373 Character Properties>; for a
374 complete list of possible properties, see
375 L<perluniprops/Properties accessible through \p{} and \P{}>,
376 which notes all forms that have C</i> differences.
377 It is also possible to define your own properties. This is discussed in
378 L<perlunicode/User-Defined Character Properties>.
380 Unicode properties are defined (surprise!) only on Unicode code points.
381 A warning is raised and all matches fail on non-Unicode code points
382 (those above the legal Unicode maximum of 0x10FFFF). This can be
385 chr(0x110000) =~ \p{ASCII_Hex_Digit=True} # Fails.
386 chr(0x110000) =~ \p{ASCII_Hex_Digit=False} # Also fails!
388 Even though these two matches might be thought of as complements, they
389 are so only on Unicode code points.
393 "a" =~ /\w/ # Match, "a" is a 'word' character.
394 "7" =~ /\w/ # Match, "7" is a 'word' character as well.
395 "a" =~ /\d/ # No match, "a" isn't a digit.
396 "7" =~ /\d/ # Match, "7" is a digit.
397 " " =~ /\s/ # Match, a space is whitespace.
398 "a" =~ /\D/ # Match, "a" is a non-digit.
399 "7" =~ /\D/ # No match, "7" is not a non-digit.
400 " " =~ /\S/ # No match, a space is not non-whitespace.
402 " " =~ /\h/ # Match, space is horizontal whitespace.
403 " " =~ /\v/ # No match, space is not vertical whitespace.
404 "\r" =~ /\v/ # Match, a return is vertical whitespace.
406 "a" =~ /\pL/ # Match, "a" is a letter.
407 "a" =~ /\p{Lu}/ # No match, /\p{Lu}/ matches upper case letters.
409 "\x{0e0b}" =~ /\p{Thai}/ # Match, \x{0e0b} is the character
410 # 'THAI CHARACTER SO SO', and that's in
411 # Thai Unicode class.
412 "a" =~ /\P{Lao}/ # Match, as "a" is not a Laotian character.
414 It is worth emphasizing that C<\d>, C<\w>, etc, match single characters, not
415 complete numbers or words. To match a number (that consists of digits),
416 use C<\d+>; to match a word, use C<\w+>. But be aware of the security
417 considerations in doing so, as mentioned above.
419 =head2 Bracketed Character Classes
421 The third form of character class you can use in Perl regular expressions
422 is the bracketed character class. In its simplest form, it lists the characters
423 that may be matched, surrounded by square brackets, like this: C<[aeiou]>.
424 This matches one of C<a>, C<e>, C<i>, C<o> or C<u>. Like the other
425 character classes, exactly one character is matched.* To match
426 a longer string consisting of characters mentioned in the character
427 class, follow the character class with a L<quantifier|perlre/Quantifiers>. For
428 instance, C<[aeiou]+> matches one or more lowercase English vowels.
430 Repeating a character in a character class has no
431 effect; it's considered to be in the set only once.
435 "e" =~ /[aeiou]/ # Match, as "e" is listed in the class.
436 "p" =~ /[aeiou]/ # No match, "p" is not listed in the class.
437 "ae" =~ /^[aeiou]$/ # No match, a character class only matches
438 # a single character.
439 "ae" =~ /^[aeiou]+$/ # Match, due to the quantifier.
443 * There is an exception to a bracketed character class matching a
444 single character only. When the class is to match caselessly under C</i>
445 matching rules, and a character that is explicitly mentioned inside the
447 multiple-character sequence caselessly under Unicode rules, the class
448 (when not L<inverted|/Negation>) will also match that sequence. For
449 example, Unicode says that the letter C<LATIN SMALL LETTER SHARP S>
450 should match the sequence C<ss> under C</i> rules. Thus,
452 'ss' =~ /\A\N{LATIN SMALL LETTER SHARP S}\z/i # Matches
453 'ss' =~ /\A[aeioust\N{LATIN SMALL LETTER SHARP S}]\z/i # Matches
455 For this to happen, the character must be explicitly specified, and not
456 be part of a multi-character range (not even as one of its endpoints).
457 (L</Character Ranges> will be explained shortly.) Therefore,
459 'ss' =~ /\A[\0-\x{ff}]\z/i # Doesn't match
460 'ss' =~ /\A[\0-\N{LATIN SMALL LETTER SHARP S}]\z/i # No match
461 'ss' =~ /\A[\xDF-\xDF]\z/i # Matches on ASCII platforms, since \XDF
462 # is LATIN SMALL LETTER SHARP S, and the
463 # range is just a single element
465 Note that it isn't a good idea to specify these types of ranges anyway.
467 =head3 Special Characters Inside a Bracketed Character Class
469 Most characters that are meta characters in regular expressions (that
470 is, characters that carry a special meaning like C<.>, C<*>, or C<(>) lose
471 their special meaning and can be used inside a character class without
472 the need to escape them. For instance, C<[()]> matches either an opening
473 parenthesis, or a closing parenthesis, and the parens inside the character
474 class don't group or capture.
476 Characters that may carry a special meaning inside a character class are:
477 C<\>, C<^>, C<->, C<[> and C<]>, and are discussed below. They can be
478 escaped with a backslash, although this is sometimes not needed, in which
479 case the backslash may be omitted.
481 The sequence C<\b> is special inside a bracketed character class. While
482 outside the character class, C<\b> is an assertion indicating a point
483 that does not have either two word characters or two non-word characters
484 on either side, inside a bracketed character class, C<\b> matches a
494 C<\N{U+I<hex char>}>,
499 are also special and have the same meanings as they do outside a
500 bracketed character class. (However, inside a bracketed character
501 class, if C<\N{I<NAME>}> expands to a sequence of characters, only the first
502 one in the sequence is used, with a warning.)
504 Also, a backslash followed by two or three octal digits is considered an octal
507 A C<[> is not special inside a character class, unless it's the start of a
508 POSIX character class (see L</POSIX Character Classes> below). It normally does
511 A C<]> is normally either the end of a POSIX character class (see
512 L</POSIX Character Classes> below), or it signals the end of the bracketed
513 character class. If you want to include a C<]> in the set of characters, you
514 must generally escape it.
516 However, if the C<]> is the I<first> (or the second if the first
517 character is a caret) character of a bracketed character class, it
518 does not denote the end of the class (as you cannot have an empty class)
519 and is considered part of the set of characters that can be matched without
524 "+" =~ /[+?*]/ # Match, "+" in a character class is not special.
525 "\cH" =~ /[\b]/ # Match, \b inside in a character class
526 # is equivalent to a backspace.
527 "]" =~ /[][]/ # Match, as the character class contains.
529 "[]" =~ /[[]]/ # Match, the pattern contains a character class
530 # containing just ], and the character class is
533 =head3 Character Ranges
535 It is not uncommon to want to match a range of characters. Luckily, instead
536 of listing all characters in the range, one may use the hyphen (C<->).
537 If inside a bracketed character class you have two characters separated
538 by a hyphen, it's treated as if all characters between the two were in
539 the class. For instance, C<[0-9]> matches any ASCII digit, and C<[a-m]>
540 matches any lowercase letter from the first half of the ASCII alphabet.
542 Note that the two characters on either side of the hyphen are not
543 necessarily both letters or both digits. Any character is possible,
544 although not advisable. C<['-?]> contains a range of characters, but
545 most people will not know which characters that means. Furthermore,
546 such ranges may lead to portability problems if the code has to run on
547 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 range, for
550 instance because it is the first or the last character of the character class,
551 or if it immediately follows a range, the hyphen isn't special, and so is
552 considered a character to be matched literally. If you want a hyphen in
553 your set of characters to be matched and its position in the class is such
554 that it could be considered part of a range, you must escape that hyphen
559 [a-z] # Matches a character that is a lower case ASCII letter.
560 [a-fz] # Matches any letter between 'a' and 'f' (inclusive) or
562 [-z] # Matches either a hyphen ('-') or the letter 'z'.
563 [a-f-m] # Matches any letter between 'a' and 'f' (inclusive), the
564 # hyphen ('-'), or the letter 'm'.
565 ['-?] # Matches any of the characters '()*+,-./0123456789:;<=>?
566 # (But not on an EBCDIC platform).
571 It is also possible to instead list the characters you do not want to
572 match. You can do so by using a caret (C<^>) as the first character in the
573 character class. For instance, C<[^a-z]> matches any character that is not a
574 lowercase ASCII letter, which therefore includes more than a million
575 Unicode code points. The class is said to be "negated" or "inverted".
577 This syntax make the caret a special character inside a bracketed character
578 class, but only if it is the first character of the class. So if you want
579 the caret as one of the characters to match, either escape the caret or
580 else don't list it first.
582 In inverted bracketed character classes, Perl ignores the Unicode rules
583 that normally say that certain characters should match a sequence of
584 multiple characters under caseless C</i> matching. Following those
585 rules could lead to highly confusing situations:
587 "ss" =~ /^[^\xDF]+$/ui; # Matches!
589 This should match any sequences of characters that aren't C<\xDF> nor
590 what C<\xDF> matches under C</i>. C<"s"> isn't C<\xDF>, but Unicode
591 says that C<"ss"> is what C<\xDF> matches under C</i>. So which one
592 "wins"? Do you fail the match because the string has C<ss> or accept it
593 because it has an C<s> followed by another C<s>? Perl has chosen the
598 "e" =~ /[^aeiou]/ # No match, the 'e' is listed.
599 "x" =~ /[^aeiou]/ # Match, as 'x' isn't a lowercase vowel.
600 "^" =~ /[^^]/ # No match, matches anything that isn't a caret.
601 "^" =~ /[x^]/ # Match, caret is not special here.
603 =head3 Backslash Sequences
605 You can put any backslash sequence character class (with the exception of
606 C<\N> and C<\R>) inside a bracketed character class, and it will act just
607 as if you had put all characters matched by the backslash sequence inside the
608 character class. For instance, C<[a-f\d]> matches any decimal digit, or any
609 of the lowercase letters between 'a' and 'f' inclusive.
611 C<\N> within a bracketed character class must be of the forms C<\N{I<name>}>
612 or C<\N{U+I<hex char>}>, and NOT be the form that matches non-newlines,
613 for the same reason that a dot C<.> inside a bracketed character class loses
614 its special meaning: it matches nearly anything, which generally isn't what you
620 /[\p{Thai}\d]/ # Matches a character that is either a Thai
621 # character, or a digit.
622 /[^\p{Arabic}()]/ # Matches a character that is neither an Arabic
623 # character, nor a parenthesis.
625 Backslash sequence character classes cannot form one of the endpoints
626 of a range. Thus, you can't say:
628 /[\p{Thai}-\d]/ # Wrong!
630 =head3 POSIX Character Classes
631 X<character class> X<\p> X<\p{}>
632 X<alpha> X<alnum> X<ascii> X<blank> X<cntrl> X<digit> X<graph>
633 X<lower> X<print> X<punct> X<space> X<upper> X<word> X<xdigit>
635 POSIX character classes have the form C<[:class:]>, where I<class> is
636 name, and the C<[:> and C<:]> delimiters. POSIX character classes only appear
637 I<inside> bracketed character classes, and are a convenient and descriptive
638 way of listing a group of characters.
640 Be careful about the syntax,
643 $string =~ /[[:alpha:]]/
645 # Incorrect (will warn):
646 $string =~ /[:alpha:]/
648 The latter pattern would be a character class consisting of a colon,
649 and the letters C<a>, C<l>, C<p> and C<h>.
650 POSIX character classes can be part of a larger bracketed character class.
655 is valid and matches '0', '1', any alphabetic character, and the percent sign.
657 Perl recognizes the following POSIX character classes:
659 alpha Any alphabetical character ("[A-Za-z]").
660 alnum Any alphanumeric character. ("[A-Za-z0-9]")
661 ascii Any character in the ASCII character set.
662 blank A GNU extension, equal to a space or a horizontal tab ("\t").
663 cntrl Any control character. See Note [2] below.
664 digit Any decimal digit ("[0-9]"), equivalent to "\d".
665 graph Any printable character, excluding a space. See Note [3] below.
666 lower Any lowercase character ("[a-z]").
667 print Any printable character, including a space. See Note [4] below.
668 punct Any graphical character excluding "word" characters. Note [5].
669 space Any whitespace character. "\s" plus the vertical tab ("\cK").
670 upper Any uppercase character ("[A-Z]").
671 word A Perl extension ("[A-Za-z0-9_]"), equivalent to "\w".
672 xdigit Any hexadecimal digit ("[0-9a-fA-F]").
674 Most POSIX character classes have two Unicode-style C<\p> property
675 counterparts. (They are not official Unicode properties, but Perl extensions
676 derived from official Unicode properties.) The table below shows the relation
677 between POSIX character classes and these counterparts.
679 One counterpart, in the column labelled "ASCII-range Unicode" in
680 the table, matches only characters in the ASCII character set.
682 The other counterpart, in the column labelled "Full-range Unicode", matches any
683 appropriate characters in the full Unicode character set. For example,
684 C<\p{Alpha}> matches not just the ASCII alphabetic characters, but any
685 character in the entire Unicode character set considered alphabetic.
686 An entry in the column labelled "backslash sequence" is a (short)
689 [[:...:]] ASCII-range Full-range backslash Note
690 Unicode Unicode sequence
691 -----------------------------------------------------
692 alpha \p{PosixAlpha} \p{XPosixAlpha}
693 alnum \p{PosixAlnum} \p{XPosixAlnum}
695 blank \p{PosixBlank} \p{XPosixBlank} \h [1]
696 or \p{HorizSpace} [1]
697 cntrl \p{PosixCntrl} \p{XPosixCntrl} [2]
698 digit \p{PosixDigit} \p{XPosixDigit} \d
699 graph \p{PosixGraph} \p{XPosixGraph} [3]
700 lower \p{PosixLower} \p{XPosixLower}
701 print \p{PosixPrint} \p{XPosixPrint} [4]
702 punct \p{PosixPunct} \p{XPosixPunct} [5]
703 \p{PerlSpace} \p{XPerlSpace} \s [6]
704 space \p{PosixSpace} \p{XPosixSpace} [6]
705 upper \p{PosixUpper} \p{XPosixUpper}
706 word \p{PosixWord} \p{XPosixWord} \w
707 xdigit \p{PosixXDigit} \p{XPosixXDigit}
713 C<\p{Blank}> and C<\p{HorizSpace}> are synonyms.
717 Control characters don't produce output as such, but instead usually control
718 the terminal somehow: for example, newline and backspace are control characters.
719 In the ASCII range, characters whose code points are between 0 and 31 inclusive,
720 plus 127 (C<DEL>) are control characters.
722 On EBCDIC platforms, it is likely that the code page will define C<[[:cntrl:]]>
723 to be the EBCDIC equivalents of the ASCII controls, plus the controls
724 that in Unicode have code points from 128 through 159.
728 Any character that is I<graphical>, that is, visible. This class consists
729 of all alphanumeric characters and all punctuation characters.
733 All printable characters, which is the set of all graphical characters
734 plus those whitespace characters which are not also controls.
738 C<\p{PosixPunct}> and C<[[:punct:]]> in the ASCII range match all
739 non-controls, non-alphanumeric, non-space characters:
740 C<[-!"#$%&'()*+,./:;<=E<gt>?@[\\\]^_`{|}~]> (although if a locale is in effect,
741 it could alter the behavior of C<[[:punct:]]>).
743 The similarly named property, C<\p{Punct}>, matches a somewhat different
744 set in the ASCII range, namely
745 C<[-!"#%&'()*,./:;?@[\\\]_{}]>. That is, it is missing the nine
746 characters C<[$+E<lt>=E<gt>^`|~]>.
747 This is because Unicode splits what POSIX considers to be punctuation into two
748 categories, Punctuation and Symbols.
750 C<\p{XPosixPunct}> and (under Unicode rules) C<[[:punct:]]>, match what
751 C<\p{PosixPunct}> matches in the ASCII range, plus what C<\p{Punct}>
752 matches. This is different than strictly matching according to
753 C<\p{Punct}>. Another way to say it is that
754 if Unicode rules are in effect, C<[[:punct:]]> matches all characters
755 that Unicode considers punctuation, plus all ASCII-range characters that
756 Unicode considers symbols.
760 C<\p{SpacePerl}> and C<\p{Space}> differ only in that in non-locale
761 matching, C<\p{Space}> additionally
762 matches the vertical tab, C<\cK>. Same for the two ASCII-only range forms.
766 There are various other synonyms that can be used besides the names
767 listed in the table. For example, C<\p{PosixAlpha}> can be written as
768 C<\p{Alpha}>. All are listed in
769 L<perluniprops/Properties accessible through \p{} and \P{}>,
770 plus all characters matched by each ASCII-range property.
772 Both the C<\p> counterparts always assume Unicode rules are in effect.
773 On ASCII platforms, this means they assume that the code points from 128
774 to 255 are Latin-1, and that means that using them under locale rules is
775 unwise unless the locale is guaranteed to be Latin-1 or UTF-8. In contrast, the
776 POSIX character classes are useful under locale rules. They are
777 affected by the actual rules in effect, as follows:
781 =item If the C</a> modifier, is in effect ...
783 Each of the POSIX classes matches exactly the same as their ASCII-range
790 =item For code points above 255 ...
792 The POSIX class matches the same as its Full-range counterpart.
794 =item For code points below 256 ...
798 =item if locale rules are in effect ...
800 The POSIX class matches according to the locale, except that
801 C<word> uses the platform's native underscore character, no matter what
804 =item if Unicode rules are in effect or if on an EBCDIC platform ...
806 The POSIX class matches the same as the Full-range counterpart.
810 The POSIX class matches the same as the ASCII range counterpart.
818 Which rules apply are determined as described in
819 L<perlre/Which character set modifier is in effect?>.
821 It is proposed to change this behavior in a future release of Perl so that
822 whether or not Unicode rules are in effect would not change the
823 behavior: Outside of locale or an EBCDIC code page, the POSIX classes
824 would behave like their ASCII-range counterparts. If you wish to
825 comment on this proposal, send email to C<perl5-porters@perl.org>.
827 =head4 Negation of POSIX character classes
828 X<character class, negation>
830 A Perl extension to the POSIX character class is the ability to
831 negate it. This is done by prefixing the class name with a caret (C<^>).
834 POSIX ASCII-range Full-range backslash
835 Unicode Unicode sequence
836 -----------------------------------------------------
837 [[:^digit:]] \P{PosixDigit} \P{XPosixDigit} \D
838 [[:^space:]] \P{PosixSpace} \P{XPosixSpace}
839 \P{PerlSpace} \P{XPerlSpace} \S
840 [[:^word:]] \P{PerlWord} \P{XPosixWord} \W
842 The backslash sequence can mean either ASCII- or Full-range Unicode,
843 depending on various factors as described in L<perlre/Which character set modifier is in effect?>.
845 =head4 [= =] and [. .]
847 Perl recognizes the POSIX character classes C<[=class=]> and
848 C<[.class.]>, but does not (yet?) support them. Any attempt to use
849 either construct raises an exception.
853 /[[:digit:]]/ # Matches a character that is a digit.
854 /[01[:lower:]]/ # Matches a character that is either a
855 # lowercase letter, or '0' or '1'.
856 /[[:digit:][:^xdigit:]]/ # Matches a character that can be anything
857 # except the letters 'a' to 'f' and 'A' to
858 # 'F'. This is because the main character
859 # class is composed of two POSIX character
860 # classes that are ORed together, one that
861 # matches any digit, and the other that
862 # matches anything that isn't a hex digit.
863 # The OR adds the digits, leaving only the
864 # letters 'a' to 'f' and 'A' to 'F' excluded.