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::UCDE<sol>num()|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 ("_"). It does not match a whole word. To match a whole
145 word, use C<\w+>. This isn't the same thing as matching an English word, but
146 in the ASCII range it is the same as a string of Perl-identifier
151 =item If the C</a> modifier is in effect ...
153 C<\w> matches the 63 characters [a-zA-Z0-9_].
159 =item For code points above 255 ...
161 C<\w> matches the same as C<\p{Word}> matches in this range. That is,
162 it matches Thai letters, Greek letters, etc. This includes connector
163 punctuation (like the underscore) which connect two words together, or
164 diacritics, such as a C<COMBINING TILDE> and the modifier letters, which
165 are generally used to add auxiliary markings to letters.
167 =item For code points below 256 ...
171 =item if locale rules are in effect ...
173 C<\w> matches the platform's native underscore character plus whatever
174 the locale considers to be alphanumeric.
176 =item if Unicode rules are in effect or if on an EBCDIC platform ...
178 C<\w> matches exactly what C<\p{Word}> matches.
182 C<\w> matches [a-zA-Z0-9_].
190 Which rules apply are determined as described in L<perlre/Which character set modifier is in effect?>.
192 There are a number of security issues with the full Unicode list of word
193 characters. See L<http://unicode.org/reports/tr36>.
195 Also, for a somewhat finer-grained set of characters that are in programming
196 language identifiers beyond the ASCII range, you may wish to instead use the
197 more customized L</Unicode Properties>, C<\p{ID_Start}>,
198 C<\p{ID_Continue}>, C<\p{XID_Start}>, and C<\p{XID_Continue}>. See
199 L<http://unicode.org/reports/tr31>.
201 Any character not matched by C<\w> is matched by C<\W>.
205 C<\s> matches any single character considered whitespace.
209 =item If the C</a> modifier is in effect ...
211 C<\s> matches the 5 characters [\t\n\f\r ]; that is, the horizontal tab,
212 the newline, the form feed, the carriage return, and the space. (Note
213 that it doesn't match the vertical tab, C<\cK> on ASCII platforms.)
219 =item For code points above 255 ...
221 C<\s> matches exactly the code points above 255 shown with an "s" column
224 =item For code points below 256 ...
228 =item if locale rules are in effect ...
230 C<\s> matches whatever the locale considers to be whitespace. Note that
231 this is likely to include the vertical space, unlike non-locale C<\s>
234 =item if Unicode rules are in effect or if on an EBCDIC platform ...
236 C<\s> matches exactly the characters shown with an "s" column in the
241 C<\s> matches [\t\n\f\r ].
242 Note that this list doesn't include the non-breaking space.
250 Which rules apply are determined as described in L<perlre/Which character set modifier is in effect?>.
252 Any character not matched by C<\s> is matched by C<\S>.
254 C<\h> matches any character considered horizontal whitespace;
255 this includes the space and tab characters and several others
256 listed in the table below. C<\H> matches any character
257 not considered horizontal whitespace.
259 C<\v> matches any character considered vertical whitespace;
260 this includes the carriage return and line feed characters (newline)
261 plus several other characters, all listed in the table below.
262 C<\V> matches any character not considered vertical whitespace.
264 C<\R> matches anything that can be considered a newline under Unicode
265 rules. It's not a character class, as it can match a multi-character
266 sequence. Therefore, it cannot be used inside a bracketed character
267 class; use C<\v> instead (vertical whitespace).
268 Details are discussed in L<perlrebackslash>.
270 Note that unlike C<\s> (and C<\d> and C<\w>), C<\h> and C<\v> always match
271 the same characters, without regard to other factors, such as whether the
272 source string is in UTF-8 format.
274 One might think that C<\s> is equivalent to C<[\h\v]>. This is not true.
275 The difference is that the vertical tab (C<"\x0b">) is not matched by
276 C<\s>; it is however considered vertical whitespace.
278 The following table is a complete listing of characters matched by
279 C<\s>, C<\h> and C<\v> as of Unicode 6.0.
281 The first column gives the Unicode code point of the character (in hex format),
282 the second column gives the (Unicode) name. The third column indicates
283 by which class(es) the character is matched (assuming no locale or EBCDIC code
284 page is in effect that changes the C<\s> matching).
286 0x0009 CHARACTER TABULATION h s
287 0x000a LINE FEED (LF) vs
288 0x000b LINE TABULATION v
289 0x000c FORM FEED (FF) vs
290 0x000d CARRIAGE RETURN (CR) vs
292 0x0085 NEXT LINE (NEL) vs [1]
293 0x00a0 NO-BREAK SPACE h s [1]
294 0x1680 OGHAM SPACE MARK h s
295 0x180e MONGOLIAN VOWEL SEPARATOR h s
300 0x2004 THREE-PER-EM SPACE h s
301 0x2005 FOUR-PER-EM SPACE h s
302 0x2006 SIX-PER-EM SPACE h s
303 0x2007 FIGURE SPACE h s
304 0x2008 PUNCTUATION SPACE h s
305 0x2009 THIN SPACE h s
306 0x200a HAIR SPACE h s
307 0x2028 LINE SEPARATOR vs
308 0x2029 PARAGRAPH SEPARATOR vs
309 0x202f NARROW NO-BREAK SPACE h s
310 0x205f MEDIUM MATHEMATICAL SPACE h s
311 0x3000 IDEOGRAPHIC SPACE h s
317 NEXT LINE and NO-BREAK SPACE may or may not match C<\s> depending
318 on the rules in effect. See
319 L<the beginning of this section|/Whitespace>.
323 =head3 Unicode Properties
325 C<\pP> and C<\p{Prop}> are character classes to match characters that fit given
326 Unicode properties. One letter property names can be used in the C<\pP> form,
327 with the property name following the C<\p>, otherwise, braces are required.
328 When using braces, there is a single form, which is just the property name
329 enclosed in the braces, and a compound form which looks like C<\p{name=value}>,
330 which means to match if the property "name" for the character has that particular
332 For instance, a match for a number can be written as C</\pN/> or as
333 C</\p{Number}/>, or as C</\p{Number=True}/>.
334 Lowercase letters are matched by the property I<Lowercase_Letter> which
335 has the short form I<Ll>. They need the braces, so are written as C</\p{Ll}/> or
336 C</\p{Lowercase_Letter}/>, or C</\p{General_Category=Lowercase_Letter}/>
337 (the underscores are optional).
338 C</\pLl/> is valid, but means something different.
339 It matches a two character string: a letter (Unicode property C<\pL>),
340 followed by a lowercase C<l>.
342 If neither the C</a> modifier nor locale rules are in effect, the use of
343 a Unicode property will force the regular expression into using Unicode
346 Note that almost all properties are immune to case-insensitive matching.
347 That is, adding a C</i> regular expression modifier does not change what
348 they match. There are two sets that are affected. The first set is
351 and C<Titlecase_Letter>,
352 all of which match C<Cased_Letter> under C</i> matching.
357 all of which match C<Cased> under C</i> matching.
358 (The difference between these sets is that some things, such as Roman
359 numerals, come in both upper and lower case, so they are C<Cased>, but
360 aren't considered to be letters, so they aren't C<Cased_Letter>s. They're
361 actually C<Letter_Number>s.)
362 This set also includes its subsets C<PosixUpper> and C<PosixLower>, both
363 of which under C</i> match C<PosixAlpha>.
365 For more details on Unicode properties, see L<perlunicode/Unicode
366 Character Properties>; for a
367 complete list of possible properties, see
368 L<perluniprops/Properties accessible through \p{} and \P{}>,
369 which notes all forms that have C</i> differences.
370 It is also possible to define your own properties. This is discussed in
371 L<perlunicode/User-Defined Character Properties>.
375 "a" =~ /\w/ # Match, "a" is a 'word' character.
376 "7" =~ /\w/ # Match, "7" is a 'word' character as well.
377 "a" =~ /\d/ # No match, "a" isn't a digit.
378 "7" =~ /\d/ # Match, "7" is a digit.
379 " " =~ /\s/ # Match, a space is whitespace.
380 "a" =~ /\D/ # Match, "a" is a non-digit.
381 "7" =~ /\D/ # No match, "7" is not a non-digit.
382 " " =~ /\S/ # No match, a space is not non-whitespace.
384 " " =~ /\h/ # Match, space is horizontal whitespace.
385 " " =~ /\v/ # No match, space is not vertical whitespace.
386 "\r" =~ /\v/ # Match, a return is vertical whitespace.
388 "a" =~ /\pL/ # Match, "a" is a letter.
389 "a" =~ /\p{Lu}/ # No match, /\p{Lu}/ matches upper case letters.
391 "\x{0e0b}" =~ /\p{Thai}/ # Match, \x{0e0b} is the character
392 # 'THAI CHARACTER SO SO', and that's in
393 # Thai Unicode class.
394 "a" =~ /\P{Lao}/ # Match, as "a" is not a Laotian character.
396 It is worth emphasizing that C<\d>, C<\w>, etc, match single characters, not
397 complete numbers or words. To match a number (that consists of digits),
398 use C<\d+>; to match a word, use C<\w+>. But be aware of the security
399 considerations in doing so, as mentioned above.
401 =head2 Bracketed Character Classes
403 The third form of character class you can use in Perl regular expressions
404 is the bracketed character class. In its simplest form, it lists the characters
405 that may be matched, surrounded by square brackets, like this: C<[aeiou]>.
406 This matches one of C<a>, C<e>, C<i>, C<o> or C<u>. Like the other
407 character classes, exactly one character is matched.* To match
408 a longer string consisting of characters mentioned in the character
409 class, follow the character class with a L<quantifier|perlre/Quantifiers>. For
410 instance, C<[aeiou]+> matches one or more lowercase English vowels.
412 Repeating a character in a character class has no
413 effect; it's considered to be in the set only once.
417 "e" =~ /[aeiou]/ # Match, as "e" is listed in the class.
418 "p" =~ /[aeiou]/ # No match, "p" is not listed in the class.
419 "ae" =~ /^[aeiou]$/ # No match, a character class only matches
420 # a single character.
421 "ae" =~ /^[aeiou]+$/ # Match, due to the quantifier.
425 * There is an exception to a bracketed character class matching a
426 single character only. When the class is to match caselessly under C</i>
427 matching rules, and a character inside the class matches a
428 multiple-character sequence caselessly under Unicode rules, the class
429 (when not L<inverted|/Negation>) will also match that sequence. For
430 example, Unicode says that the letter C<LATIN SMALL LETTER SHARP S>
431 should match the sequence C<ss> under C</i> rules. Thus,
433 'ss' =~ /\A\N{LATIN SMALL LETTER SHARP S}\z/i # Matches
434 'ss' =~ /\A[aeioust\N{LATIN SMALL LETTER SHARP S}]\z/i # Matches
436 =head3 Special Characters Inside a Bracketed Character Class
438 Most characters that are meta characters in regular expressions (that
439 is, characters that carry a special meaning like C<.>, C<*>, or C<(>) lose
440 their special meaning and can be used inside a character class without
441 the need to escape them. For instance, C<[()]> matches either an opening
442 parenthesis, or a closing parenthesis, and the parens inside the character
443 class don't group or capture.
445 Characters that may carry a special meaning inside a character class are:
446 C<\>, C<^>, C<->, C<[> and C<]>, and are discussed below. They can be
447 escaped with a backslash, although this is sometimes not needed, in which
448 case the backslash may be omitted.
450 The sequence C<\b> is special inside a bracketed character class. While
451 outside the character class, C<\b> is an assertion indicating a point
452 that does not have either two word characters or two non-word characters
453 on either side, inside a bracketed character class, C<\b> matches a
463 C<\N{U+I<hex char>}>,
468 are also special and have the same meanings as they do outside a
469 bracketed character class. (However, inside a bracketed character
470 class, if C<\N{I<NAME>}> expands to a sequence of characters, only the first
471 one in the sequence is used, with a warning.)
473 Also, a backslash followed by two or three octal digits is considered an octal
476 A C<[> is not special inside a character class, unless it's the start of a
477 POSIX character class (see L</POSIX Character Classes> below). It normally does
480 A C<]> is normally either the end of a POSIX character class (see
481 L</POSIX Character Classes> below), or it signals the end of the bracketed
482 character class. If you want to include a C<]> in the set of characters, you
483 must generally escape it.
485 However, if the C<]> is the I<first> (or the second if the first
486 character is a caret) character of a bracketed character class, it
487 does not denote the end of the class (as you cannot have an empty class)
488 and is considered part of the set of characters that can be matched without
493 "+" =~ /[+?*]/ # Match, "+" in a character class is not special.
494 "\cH" =~ /[\b]/ # Match, \b inside in a character class
495 # is equivalent to a backspace.
496 "]" =~ /[][]/ # Match, as the character class contains.
498 "[]" =~ /[[]]/ # Match, the pattern contains a character class
499 # containing just ], and the character class is
502 =head3 Character Ranges
504 It is not uncommon to want to match a range of characters. Luckily, instead
505 of listing all characters in the range, one may use the hyphen (C<->).
506 If inside a bracketed character class you have two characters separated
507 by a hyphen, it's treated as if all characters between the two were in
508 the class. For instance, C<[0-9]> matches any ASCII digit, and C<[a-m]>
509 matches any lowercase letter from the first half of the ASCII alphabet.
511 Note that the two characters on either side of the hyphen are not
512 necessarily both letters or both digits. Any character is possible,
513 although not advisable. C<['-?]> contains a range of characters, but
514 most people will not know which characters that means. Furthermore,
515 such ranges may lead to portability problems if the code has to run on
516 a platform that uses a different character set, such as EBCDIC.
518 If a hyphen in a character class cannot syntactically be part of a range, for
519 instance because it is the first or the last character of the character class,
520 or if it immediately follows a range, the hyphen isn't special, and so is
521 considered a character to be matched literally. If you want a hyphen in
522 your set of characters to be matched and its position in the class is such
523 that it could be considered part of a range, you must escape that hyphen
528 [a-z] # Matches a character that is a lower case ASCII letter.
529 [a-fz] # Matches any letter between 'a' and 'f' (inclusive) or
531 [-z] # Matches either a hyphen ('-') or the letter 'z'.
532 [a-f-m] # Matches any letter between 'a' and 'f' (inclusive), the
533 # hyphen ('-'), or the letter 'm'.
534 ['-?] # Matches any of the characters '()*+,-./0123456789:;<=>?
535 # (But not on an EBCDIC platform).
540 It is also possible to instead list the characters you do not want to
541 match. You can do so by using a caret (C<^>) as the first character in the
542 character class. For instance, C<[^a-z]> matches any character that is not a
543 lowercase ASCII letter, which therefore includes more than a million
544 Unicode code points. The class is said to be "negated" or "inverted".
546 This syntax make the caret a special character inside a bracketed character
547 class, but only if it is the first character of the class. So if you want
548 the caret as one of the characters to match, either escape the caret or
549 else don't list it first.
551 In inverted bracketed character classes, Perl ignores the Unicode rules
552 that normally say that certain characters should match a sequence of
553 multiple characters under caseless C</i> matching. Following those
554 rules could lead to highly confusing situations:
556 "ss" =~ /^[^\xDF]+$/ui; # Matches!
558 This should match any sequences of characters that aren't C<\xDF> nor
559 what C<\xDF> matches under C</i>. C<"s"> isn't C<\xDF>, but Unicode
560 says that C<"ss"> is what C<\xDF> matches under C</i>. So which one
561 "wins"? Do you fail the match because the string has C<ss> or accept it
562 because it has an C<s> followed by another C<s>? Perl has chosen the
567 "e" =~ /[^aeiou]/ # No match, the 'e' is listed.
568 "x" =~ /[^aeiou]/ # Match, as 'x' isn't a lowercase vowel.
569 "^" =~ /[^^]/ # No match, matches anything that isn't a caret.
570 "^" =~ /[x^]/ # Match, caret is not special here.
572 =head3 Backslash Sequences
574 You can put any backslash sequence character class (with the exception of
575 C<\N> and C<\R>) inside a bracketed character class, and it will act just
576 as if you had put all characters matched by the backslash sequence inside the
577 character class. For instance, C<[a-f\d]> matches any decimal digit, or any
578 of the lowercase letters between 'a' and 'f' inclusive.
580 C<\N> within a bracketed character class must be of the forms C<\N{I<name>}>
581 or C<\N{U+I<hex char>}>, and NOT be the form that matches non-newlines,
582 for the same reason that a dot C<.> inside a bracketed character class loses
583 its special meaning: it matches nearly anything, which generally isn't what you
589 /[\p{Thai}\d]/ # Matches a character that is either a Thai
590 # character, or a digit.
591 /[^\p{Arabic}()]/ # Matches a character that is neither an Arabic
592 # character, nor a parenthesis.
594 Backslash sequence character classes cannot form one of the endpoints
595 of a range. Thus, you can't say:
597 /[\p{Thai}-\d]/ # Wrong!
599 =head3 POSIX Character Classes
600 X<character class> X<\p> X<\p{}>
601 X<alpha> X<alnum> X<ascii> X<blank> X<cntrl> X<digit> X<graph>
602 X<lower> X<print> X<punct> X<space> X<upper> X<word> X<xdigit>
604 POSIX character classes have the form C<[:class:]>, where I<class> is
605 name, and the C<[:> and C<:]> delimiters. POSIX character classes only appear
606 I<inside> bracketed character classes, and are a convenient and descriptive
607 way of listing a group of characters.
609 Be careful about the syntax,
612 $string =~ /[[:alpha:]]/
614 # Incorrect (will warn):
615 $string =~ /[:alpha:]/
617 The latter pattern would be a character class consisting of a colon,
618 and the letters C<a>, C<l>, C<p> and C<h>.
619 POSIX character classes can be part of a larger bracketed character class.
624 is valid and matches '0', '1', any alphabetic character, and the percent sign.
626 Perl recognizes the following POSIX character classes:
628 alpha Any alphabetical character ("[A-Za-z]").
629 alnum Any alphanumeric character. ("[A-Za-z0-9]")
630 ascii Any character in the ASCII character set.
631 blank A GNU extension, equal to a space or a horizontal tab ("\t").
632 cntrl Any control character. See Note [2] below.
633 digit Any decimal digit ("[0-9]"), equivalent to "\d".
634 graph Any printable character, excluding a space. See Note [3] below.
635 lower Any lowercase character ("[a-z]").
636 print Any printable character, including a space. See Note [4] below.
637 punct Any graphical character excluding "word" characters. Note [5].
638 space Any whitespace character. "\s" plus the vertical tab ("\cK").
639 upper Any uppercase character ("[A-Z]").
640 word A Perl extension ("[A-Za-z0-9_]"), equivalent to "\w".
641 xdigit Any hexadecimal digit ("[0-9a-fA-F]").
643 Most POSIX character classes have two Unicode-style C<\p> property
644 counterparts. (They are not official Unicode properties, but Perl extensions
645 derived from official Unicode properties.) The table below shows the relation
646 between POSIX character classes and these counterparts.
648 One counterpart, in the column labelled "ASCII-range Unicode" in
649 the table, matches only characters in the ASCII character set.
651 The other counterpart, in the column labelled "Full-range Unicode", matches any
652 appropriate characters in the full Unicode character set. For example,
653 C<\p{Alpha}> matches not just the ASCII alphabetic characters, but any
654 character in the entire Unicode character set considered alphabetic.
655 An entry in the column labelled "backslash sequence" is a (short)
658 [[:...:]] ASCII-range Full-range backslash Note
659 Unicode Unicode sequence
660 -----------------------------------------------------
661 alpha \p{PosixAlpha} \p{XPosixAlpha}
662 alnum \p{PosixAlnum} \p{XPosixAlnum}
664 blank \p{PosixBlank} \p{XPosixBlank} \h [1]
665 or \p{HorizSpace} [1]
666 cntrl \p{PosixCntrl} \p{XPosixCntrl} [2]
667 digit \p{PosixDigit} \p{XPosixDigit} \d
668 graph \p{PosixGraph} \p{XPosixGraph} [3]
669 lower \p{PosixLower} \p{XPosixLower}
670 print \p{PosixPrint} \p{XPosixPrint} [4]
671 punct \p{PosixPunct} \p{XPosixPunct} [5]
672 \p{PerlSpace} \p{XPerlSpace} \s [6]
673 space \p{PosixSpace} \p{XPosixSpace} [6]
674 upper \p{PosixUpper} \p{XPosixUpper}
675 word \p{PosixWord} \p{XPosixWord} \w
676 xdigit \p{PosixXDigit} \p{XPosixXDigit}
682 C<\p{Blank}> and C<\p{HorizSpace}> are synonyms.
686 Control characters don't produce output as such, but instead usually control
687 the terminal somehow: for example, newline and backspace are control characters.
688 In the ASCII range, characters whose code points are between 0 and 31 inclusive,
689 plus 127 (C<DEL>) are control characters.
691 On EBCDIC platforms, it is likely that the code page will define C<[[:cntrl:]]>
692 to be the EBCDIC equivalents of the ASCII controls, plus the controls
693 that in Unicode have code pointss from 128 through 159.
697 Any character that is I<graphical>, that is, visible. This class consists
698 of all alphanumeric characters and all punctuation characters.
702 All printable characters, which is the set of all graphical characters
703 plus those whitespace characters which are not also controls.
707 C<\p{PosixPunct}> and C<[[:punct:]]> in the ASCII range match all
708 non-controls, non-alphanumeric, non-space characters:
709 C<[-!"#$%&'()*+,./:;<=E<gt>?@[\\\]^_`{|}~]> (although if a locale is in effect,
710 it could alter the behavior of C<[[:punct:]]>).
712 The similarly named property, C<\p{Punct}>, matches a somewhat different
713 set in the ASCII range, namely
714 C<[-!"#%&'()*,./:;?@[\\\]_{}]>. That is, it is missing C<[$+E<lt>=E<gt>^`|~]>.
715 This is because Unicode splits what POSIX considers to be punctuation into two
716 categories, Punctuation and Symbols.
718 C<\p{XPosixPunct}> and (under Unicode rules) C<[[:punct:]]>, match what
719 C<\p{PosixPunct}> matches in the ASCII range, plus what C<\p{Punct}>
720 matches. This is different than strictly matching according to
721 C<\p{Punct}>. Another way to say it is that
722 if Unicode rules are in effect, C<[[:punct:]]> matches all characters
723 that Unicode considers punctuation, plus all ASCII-range characters that
724 Unicode considers symbols.
728 C<\p{SpacePerl}> and C<\p{Space}> differ only in that in non-locale
729 matching, C<\p{Space}> additionally
730 matches the vertical tab, C<\cK>. Same for the two ASCII-only range forms.
734 There are various other synonyms that can be used besides the names
735 listed in the table. For example, C<\p{PosixAlpha}> can be written as
736 C<\p{Alpha}>. All are listed in
737 L<perluniprops/Properties accessible through \p{} and \P{}>,
738 plus all characters matched by each ASCII-range property.
740 Both the C<\p> counterparts always assume Unicode rules are in effect.
741 On ASCII platforms, this means they assume that the code points from 128
742 to 255 are Latin-1, and that means that using them under locale rules is
743 unwise unless the locale is guaranteed to be Latin-1 or UTF-8. In contrast, the
744 POSIX character classes are useful under locale rules. They are
745 affected by the actual rules in effect, as follows:
749 =item If the C</a> modifier, is in effect ...
751 Each of the POSIX classes matches exactly the same as their ASCII-range
758 =item For code points above 255 ...
760 The POSIX class matches the same as its Full-range counterpart.
762 =item For code points below 256 ...
766 =item if locale rules are in effect ...
768 The POSIX class matches according to the locale.
770 =item if Unicode rules are in effect or if on an EBCDIC platform ...
772 The POSIX class matches the same as the Full-range counterpart.
776 The POSIX class matches the same as the ASCII range counterpart.
784 Which rules apply are determined as described in
785 L<perlre/Which character set modifier is in effect?>.
787 It is proposed to change this behavior in a future release of Perl so that
788 whether or not Unicode rules are in effect would not change the
789 behavior: Outside of locale or an EBCDIC code page, the POSIX classes
790 would behave like their ASCII-range counterparts. If you wish to
791 comment on this proposal, send email to C<perl5-porters@perl.org>.
793 =head4 Negation of POSIX character classes
794 X<character class, negation>
796 A Perl extension to the POSIX character class is the ability to
797 negate it. This is done by prefixing the class name with a caret (C<^>).
800 POSIX ASCII-range Full-range backslash
801 Unicode Unicode sequence
802 -----------------------------------------------------
803 [[:^digit:]] \P{PosixDigit} \P{XPosixDigit} \D
804 [[:^space:]] \P{PosixSpace} \P{XPosixSpace}
805 \P{PerlSpace} \P{XPerlSpace} \S
806 [[:^word:]] \P{PerlWord} \P{XPosixWord} \W
808 The backslash sequence can mean either ASCII- or Full-range Unicode,
809 depending on various factors as described in L<perlre/Which character set modifier is in effect?>.
811 =head4 [= =] and [. .]
813 Perl recognizes the POSIX character classes C<[=class=]> and
814 C<[.class.]>, but does not (yet?) support them. Any attempt to use
815 either construct raises an exception.
819 /[[:digit:]]/ # Matches a character that is a digit.
820 /[01[:lower:]]/ # Matches a character that is either a
821 # lowercase letter, or '0' or '1'.
822 /[[:digit:][:^xdigit:]]/ # Matches a character that can be anything
823 # except the letters 'a' to 'f'. This is
824 # because the main character class is composed
825 # of two POSIX character classes that are ORed
826 # together, one that matches any digit, and
827 # the other that matches anything that isn't a
828 # hex digit. The result matches all
829 # characters except the letters 'a' to 'f' and