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. The 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<\d> matches a single character that is considered to be a decimal I<digit>.
78 What is considered a decimal digit depends on several factors, detailed
79 below in L</Locale, EBCDIC, Unicode and UTF-8>. If those factors
80 indicate a Unicode interpretation, C<\d> not only matches the digits
81 '0' - '9', but also Arabic, Devanagari and digits from other languages.
82 Otherwise, if there is a locale in effect, it will match whatever
83 characters the locale considers decimal digits. Without a locale, C<\d>
84 matches just the digits '0' to '9'.
86 Unicode digits may cause some confusion, and some security issues. In UTF-8
87 strings, unless the C<"a"> regular expression modifier is specified,
88 C<\d> matches the same characters matched by
89 C<\p{General_Category=Decimal_Number}>, or synonymously,
90 C<\p{General_Category=Digit}>. Starting with Unicode version 4.1, this is the
91 same set of characters matched by C<\p{Numeric_Type=Decimal}>.
93 But Unicode also has a different property with a similar name,
94 C<\p{Numeric_Type=Digit}>, which matches a completely different set of
95 characters. These characters are things such as subscripts.
97 The design intent is for C<\d> to match all the digits (and no other characters)
98 that can be used with "normal" big-endian positional decimal syntax, whereby a
99 sequence of such digits {N0, N1, N2, ...Nn} has the numeric value (...(N0 * 10
100 + N1) * 10 + N2) * 10 ... + Nn). In Unicode 5.2, the Tamil digits (U+0BE6 -
101 U+0BEF) can also legally be used in old-style Tamil numbers in which they would
102 appear no more than one in a row, separated by characters that mean "times 10",
103 "times 100", etc. (See L<http://www.unicode.org/notes/tn21>.)
105 Some of the non-European digits that C<\d> matches look like European ones, but
106 have different values. For example, BENGALI DIGIT FOUR (U+09EA) looks
107 very much like an ASCII DIGIT EIGHT (U+0038).
109 It may be useful for security purposes for an application to require that all
110 digits in a row be from the same script. See L<Unicode::UCD/charscript()>.
112 Any character that isn't matched by C<\d> will be matched by C<\D>.
114 =head3 Word characters
116 A C<\w> matches a single alphanumeric character (an alphabetic character, or a
117 decimal digit) or a connecting punctuation character, such as an
118 underscore ("_"). It does not match a whole word. To match a whole
119 word, use C<\w+>. This isn't the same thing as matching an English word, but
120 in the ASCII range it is the same as a string of Perl-identifier
121 characters. What is considered a
122 word character depends on several factors, detailed below in L</Locale,
123 EBCDIC, Unicode and UTF-8>. If those factors indicate a Unicode
124 interpretation, C<\w> matches the characters that are considered word
125 characters in the Unicode database. That is, it not only matches ASCII letters,
126 but also Thai letters, Greek letters, etc. This includes connector
127 punctuation (like the underscore) which connect two words together, or
128 marks, such as a C<COMBINING TILDE>, which are generally used to add
129 diacritical marks to letters. If a Unicode interpretation
130 is not indicated, C<\w> matches those characters that are considered
131 word characters by the current locale or EBCDIC code page. Without a
132 locale or EBCDIC code page, C<\w> matches the ASCII letters, digits and
135 There are a number of security issues with the full Unicode list of word
136 characters. See L<http://unicode.org/reports/tr36>.
138 Also, for a somewhat finer-grained set of characters that are in programming
139 language identifiers beyond the ASCII range, you may wish to instead use the
140 more customized Unicode properties, "ID_Start", ID_Continue", "XID_Start", and
141 "XID_Continue". See L<http://unicode.org/reports/tr31>.
143 Any character that isn't matched by C<\w> will be matched by C<\W>.
147 C<\s> matches any single character that is considered whitespace. The exact
148 set of characters matched by C<\s> depends on several factors, detailed
149 below in L</Locale, EBCDIC, Unicode and UTF-8>. If those factors
150 indicate a Unicode interpretation, C<\s> matches what is considered
151 whitespace in the Unicode database; the complete list is in the table
152 below. Otherwise, if there is a locale or EBCDIC code page in effect,
153 C<\s> matches whatever is considered whitespace by the current locale or
154 EBCDIC code page. Without a locale or EBCDIC code page, C<\s> matches
155 the horizontal tab (C<\t>), the newline (C<\n>), the form feed (C<\f>),
156 the carriage return (C<\r>), and the space. (Note that it doesn't match
157 the vertical tab, C<\cK>.) Perhaps the most notable possible surprise
158 is that C<\s> matches a non-breaking space only if a Unicode
159 interpretation is indicated, or the locale or EBCDIC code page that is
160 in effect has that character.
162 Any character that isn't matched by C<\s> will be matched by C<\S>.
164 C<\h> will match any character that is considered horizontal whitespace;
165 this includes the space and the tab characters and a number other characters,
166 all of which are listed in the table below. C<\H> will match any character
167 that is not considered horizontal whitespace.
169 C<\v> will match any character that is considered vertical whitespace;
170 this includes the carriage return and line feed characters (newline) plus several
171 other characters, all listed in the table below.
172 C<\V> will match any character that is not considered vertical whitespace.
174 C<\R> matches anything that can be considered a newline under Unicode
175 rules. It's not a character class, as it can match a multi-character
176 sequence. Therefore, it cannot be used inside a bracketed character
177 class; use C<\v> instead (vertical whitespace).
178 Details are discussed in L<perlrebackslash>.
180 Note that unlike C<\s>, C<\d> and C<\w>, C<\h> and C<\v> always match
181 the same characters, without regard to other factors, such as if the
182 source string is in UTF-8 format or not.
184 One might think that C<\s> is equivalent to C<[\h\v]>. This is not true. The
185 vertical tab (C<"\x0b">) is not matched by C<\s>, it is however considered
186 vertical whitespace. Furthermore, if the source string is not in UTF-8 format,
187 and any locale or EBCDIC code page that is in effect doesn't include them, the
188 next line (ASCII-platform C<"\x85">) and the no-break space (ASCII-platform
189 C<"\xA0">) characters are not matched by C<\s>, but are by C<\v> and C<\h>
190 respectively. If the C<"a"> modifier is not in effect, and the source
191 string is in UTF-8 format, both the next line and
192 the no-break space are matched by C<\s>.
194 The following table is a complete listing of characters matched by
195 C<\s>, C<\h> and C<\v> as of Unicode 5.2.
197 The first column gives the code point of the character (in hex format),
198 the second column gives the (Unicode) name. The third column indicates
199 by which class(es) the character is matched (assuming no locale or EBCDIC code
200 page is in effect that changes the C<\s> matching).
202 0x00009 CHARACTER TABULATION h s
203 0x0000a LINE FEED (LF) vs
204 0x0000b LINE TABULATION v
205 0x0000c FORM FEED (FF) vs
206 0x0000d CARRIAGE RETURN (CR) vs
208 0x00085 NEXT LINE (NEL) vs [1]
209 0x000a0 NO-BREAK SPACE h s [1]
210 0x01680 OGHAM SPACE MARK h s
211 0x0180e MONGOLIAN VOWEL SEPARATOR h s
216 0x02004 THREE-PER-EM SPACE h s
217 0x02005 FOUR-PER-EM SPACE h s
218 0x02006 SIX-PER-EM SPACE h s
219 0x02007 FIGURE SPACE h s
220 0x02008 PUNCTUATION SPACE h s
221 0x02009 THIN SPACE h s
222 0x0200a HAIR SPACE h s
223 0x02028 LINE SEPARATOR vs
224 0x02029 PARAGRAPH SEPARATOR vs
225 0x0202f NARROW NO-BREAK SPACE h s
226 0x0205f MEDIUM MATHEMATICAL SPACE h s
227 0x03000 IDEOGRAPHIC SPACE h s
233 NEXT LINE and NO-BREAK SPACE only match C<\s> if the source string is in
234 UTF-8 format and the C<"a"> modifier is not in effect; or the locale or
235 EBCDIC code page that is in effect includes them.
239 It is worth noting that C<\d>, C<\w>, etc, match single characters, not
240 complete numbers or words. To match a number (that consists of digits),
241 use C<\d+>; to match a word, use C<\w+>.
245 C<\N> is new in 5.12, and is experimental. It, like the dot, will match any
246 character that is not a newline. The difference is that C<\N> is not influenced
247 by the I<single line> regular expression modifier (see L</The dot> above). Note
248 that the form C<\N{...}> may mean something completely different. When the
249 C<{...}> is a L<quantifier|perlre/Quantifiers>, it means to match a non-newline
250 character that many times. For example, C<\N{3}> means to match 3
251 non-newlines; C<\N{5,}> means to match 5 or more non-newlines. But if C<{...}>
252 is not a legal quantifier, it is presumed to be a named character. See
253 L<charnames> for those. For example, none of C<\N{COLON}>, C<\N{4F}>, and
254 C<\N{F4}> contain legal quantifiers, so Perl will try to find characters whose
255 names are, respectively, C<COLON>, C<4F>, and C<F4>.
257 =head3 Unicode Properties
259 C<\pP> and C<\p{Prop}> are character classes to match characters that fit given
260 Unicode properties. One letter property names can be used in the C<\pP> form,
261 with the property name following the C<\p>, otherwise, braces are required.
262 When using braces, there is a single form, which is just the property name
263 enclosed in the braces, and a compound form which looks like C<\p{name=value}>,
264 which means to match if the property "name" for the character has the particular
266 For instance, a match for a number can be written as C</\pN/> or as
267 C</\p{Number}/>, or as C</\p{Number=True}/>.
268 Lowercase letters are matched by the property I<Lowercase_Letter> which
269 has as short form I<Ll>. They need the braces, so are written as C</\p{Ll}/> or
270 C</\p{Lowercase_Letter}/>, or C</\p{General_Category=Lowercase_Letter}/>
271 (the underscores are optional).
272 C</\pLl/> is valid, but means something different.
273 It matches a two character string: a letter (Unicode property C<\pL>),
274 followed by a lowercase C<l>.
276 Note that almost all properties are immune to case-insensitive matching.
277 That is, adding a C</i> regular expression modifier does not change what
278 they match. There are two sets that are affected. The first set is
281 and C<Titlecase_Letter>,
282 all of which match C<Cased_Letter> under C</i> matching.
283 And the second set is
287 all of which match C<Cased> under C</i> matching.
288 (The difference between these sets is that some things, such as Roman
289 Numerals come in both upper and lower case so they are C<Cased>, but
290 aren't considered to be letters, so they aren't C<Cased_Letter>s.)
291 This set also includes its subsets C<PosixUpper> and C<PosixLower> both
292 of which under C</i> matching match C<PosixAlpha>.
294 For more details on Unicode properties, see L<perlunicode/Unicode
295 Character Properties>; for a
296 complete list of possible properties, see
297 L<perluniprops/Properties accessible through \p{} and \P{}>,
298 which notes all forms that have C</i> differences.
299 It is also possible to define your own properties. This is discussed in
300 L<perlunicode/User-Defined Character Properties>.
304 "a" =~ /\w/ # Match, "a" is a 'word' character.
305 "7" =~ /\w/ # Match, "7" is a 'word' character as well.
306 "a" =~ /\d/ # No match, "a" isn't a digit.
307 "7" =~ /\d/ # Match, "7" is a digit.
308 " " =~ /\s/ # Match, a space is whitespace.
309 "a" =~ /\D/ # Match, "a" is a non-digit.
310 "7" =~ /\D/ # No match, "7" is not a non-digit.
311 " " =~ /\S/ # No match, a space is not non-whitespace.
313 " " =~ /\h/ # Match, space is horizontal whitespace.
314 " " =~ /\v/ # No match, space is not vertical whitespace.
315 "\r" =~ /\v/ # Match, a return is vertical whitespace.
317 "a" =~ /\pL/ # Match, "a" is a letter.
318 "a" =~ /\p{Lu}/ # No match, /\p{Lu}/ matches upper case letters.
320 "\x{0e0b}" =~ /\p{Thai}/ # Match, \x{0e0b} is the character
321 # 'THAI CHARACTER SO SO', and that's in
322 # Thai Unicode class.
323 "a" =~ /\P{Lao}/ # Match, as "a" is not a Laotian character.
326 =head2 Bracketed Character Classes
328 The third form of character class you can use in Perl regular expressions
329 is the bracketed character class. In its simplest form, it lists the characters
330 that may be matched, surrounded by square brackets, like this: C<[aeiou]>.
331 This matches one of C<a>, C<e>, C<i>, C<o> or C<u>. Like the other
332 character classes, exactly one character will be matched. To match
333 a longer string consisting of characters mentioned in the character
334 class, follow the character class with a L<quantifier|perlre/Quantifiers>. For
335 instance, C<[aeiou]+> matches a string of one or more lowercase English vowels.
337 Repeating a character in a character class has no
338 effect; it's considered to be in the set only once.
342 "e" =~ /[aeiou]/ # Match, as "e" is listed in the class.
343 "p" =~ /[aeiou]/ # No match, "p" is not listed in the class.
344 "ae" =~ /^[aeiou]$/ # No match, a character class only matches
345 # a single character.
346 "ae" =~ /^[aeiou]+$/ # Match, due to the quantifier.
348 =head3 Special Characters Inside a Bracketed Character Class
350 Most characters that are meta characters in regular expressions (that
351 is, characters that carry a special meaning like C<.>, C<*>, or C<(>) lose
352 their special meaning and can be used inside a character class without
353 the need to escape them. For instance, C<[()]> matches either an opening
354 parenthesis, or a closing parenthesis, and the parens inside the character
355 class don't group or capture.
357 Characters that may carry a special meaning inside a character class are:
358 C<\>, C<^>, C<->, C<[> and C<]>, and are discussed below. They can be
359 escaped with a backslash, although this is sometimes not needed, in which
360 case the backslash may be omitted.
362 The sequence C<\b> is special inside a bracketed character class. While
363 outside the character class, C<\b> is an assertion indicating a point
364 that does not have either two word characters or two non-word characters
365 on either side, inside a bracketed character class, C<\b> matches a
375 C<\N{U+I<hex char>}>,
380 are also special and have the same meanings as they do outside a
381 bracketed character class. (However, inside a bracketed character
382 class, if C<\N{I<NAME>}> expands to a sequence of characters, only the first
383 one in the sequence is used, with a warning.)
385 Also, a backslash followed by two or three octal digits is considered an octal
388 A C<[> is not special inside a character class, unless it's the start of a
389 POSIX character class (see L</POSIX Character Classes> below). It normally does
392 A C<]> is normally either the end of a POSIX character class (see
393 L</POSIX Character Classes> below), or it signals the end of the bracketed
394 character class. If you want to include a C<]> in the set of characters, you
395 must generally escape it.
396 However, if the C<]> is the I<first> (or the second if the first
397 character is a caret) character of a bracketed character class, it
398 does not denote the end of the class (as you cannot have an empty class)
399 and is considered part of the set of characters that can be matched without
404 "+" =~ /[+?*]/ # Match, "+" in a character class is not special.
405 "\cH" =~ /[\b]/ # Match, \b inside in a character class
406 # is equivalent to a backspace.
407 "]" =~ /[][]/ # Match, as the character class contains.
409 "[]" =~ /[[]]/ # Match, the pattern contains a character class
410 # containing just ], and the character class is
413 =head3 Character Ranges
415 It is not uncommon to want to match a range of characters. Luckily, instead
416 of listing all the characters in the range, one may use the hyphen (C<->).
417 If inside a bracketed character class you have two characters separated
418 by a hyphen, it's treated as if all the characters between the two are in
419 the class. For instance, C<[0-9]> matches any ASCII digit, and C<[a-m]>
420 matches any lowercase letter from the first half of the ASCII alphabet.
422 Note that the two characters on either side of the hyphen are not
423 necessarily both letters or both digits. Any character is possible,
424 although not advisable. C<['-?]> contains a range of characters, but
425 most people will not know which characters that will be. Furthermore,
426 such ranges may lead to portability problems if the code has to run on
427 a platform that uses a different character set, such as EBCDIC.
429 If a hyphen in a character class cannot syntactically be part of a range, for
430 instance because it is the first or the last character of the character class,
431 or if it immediately follows a range, the hyphen isn't special, and will be
432 considered a character that is to be matched literally. You have to escape the
433 hyphen with a backslash if you want to have a hyphen in your set of characters
434 to be matched, and its position in the class is such that it could be
435 considered part of a range.
439 [a-z] # Matches a character that is a lower case ASCII letter.
440 [a-fz] # Matches any letter between 'a' and 'f' (inclusive) or
442 [-z] # Matches either a hyphen ('-') or the letter 'z'.
443 [a-f-m] # Matches any letter between 'a' and 'f' (inclusive), the
444 # hyphen ('-'), or the letter 'm'.
445 ['-?] # Matches any of the characters '()*+,-./0123456789:;<=>?
446 # (But not on an EBCDIC platform).
451 It is also possible to instead list the characters you do not want to
452 match. You can do so by using a caret (C<^>) as the first character in the
453 character class. For instance, C<[^a-z]> matches a character that is not a
454 lowercase ASCII letter.
456 This syntax make the caret a special character inside a bracketed character
457 class, but only if it is the first character of the class. So if you want
458 to have the caret as one of the characters you want to match, you either
459 have to escape the caret, or not list it first.
463 "e" =~ /[^aeiou]/ # No match, the 'e' is listed.
464 "x" =~ /[^aeiou]/ # Match, as 'x' isn't a lowercase vowel.
465 "^" =~ /[^^]/ # No match, matches anything that isn't a caret.
466 "^" =~ /[x^]/ # Match, caret is not special here.
468 =head3 Backslash Sequences
470 You can put any backslash sequence character class (with the exception of
471 C<\N> and C<\R>) inside a bracketed character class, and it will act just
472 as if you put all the characters matched by the backslash sequence inside the
473 character class. For instance, C<[a-f\d]> will match any decimal digit, or any
474 of the lowercase letters between 'a' and 'f' inclusive.
476 C<\N> within a bracketed character class must be of the forms C<\N{I<name>}>
477 or C<\N{U+I<hex char>}>, and NOT be the form that matches non-newlines,
478 for the same reason that a dot C<.> inside a bracketed character class loses
479 its special meaning: it matches nearly anything, which generally isn't what you
485 /[\p{Thai}\d]/ # Matches a character that is either a Thai
486 # character, or a digit.
487 /[^\p{Arabic}()]/ # Matches a character that is neither an Arabic
488 # character, nor a parenthesis.
490 Backslash sequence character classes cannot form one of the endpoints
491 of a range. Thus, you can't say:
493 /[\p{Thai}-\d]/ # Wrong!
495 =head3 POSIX Character Classes
496 X<character class> X<\p> X<\p{}>
497 X<alpha> X<alnum> X<ascii> X<blank> X<cntrl> X<digit> X<graph>
498 X<lower> X<print> X<punct> X<space> X<upper> X<word> X<xdigit>
500 POSIX character classes have the form C<[:class:]>, where I<class> is
501 name, and the C<[:> and C<:]> delimiters. POSIX character classes only appear
502 I<inside> bracketed character classes, and are a convenient and descriptive
503 way of listing a group of characters, though they can suffer from
504 portability issues (see below and L<Locale, EBCDIC, Unicode and UTF-8>).
506 Be careful about the syntax,
509 $string =~ /[[:alpha:]]/
511 # Incorrect (will warn):
512 $string =~ /[:alpha:]/
514 The latter pattern would be a character class consisting of a colon,
515 and the letters C<a>, C<l>, C<p> and C<h>.
516 POSIX character classes can be part of a larger bracketed character class. For
521 is valid and matches '0', '1', any alphabetic character, and the percent sign.
523 Perl recognizes the following POSIX character classes:
525 alpha Any alphabetical character ("[A-Za-z]").
526 alnum Any alphanumerical character. ("[A-Za-z0-9]")
527 ascii Any character in the ASCII character set.
528 blank A GNU extension, equal to a space or a horizontal tab ("\t").
529 cntrl Any control character. See Note [2] below.
530 digit Any decimal digit ("[0-9]"), equivalent to "\d".
531 graph Any printable character, excluding a space. See Note [3] below.
532 lower Any lowercase character ("[a-z]").
533 print Any printable character, including a space. See Note [4] below.
534 punct Any graphical character excluding "word" characters. Note [5].
535 space Any whitespace character. "\s" plus the vertical tab ("\cK").
536 upper Any uppercase character ("[A-Z]").
537 word A Perl extension ("[A-Za-z0-9_]"), equivalent to "\w".
538 xdigit Any hexadecimal digit ("[0-9a-fA-F]").
540 Most POSIX character classes have two Unicode-style C<\p> property
541 counterparts. (They are not official Unicode properties, but Perl extensions
542 derived from official Unicode properties.) The table below shows the relation
543 between POSIX character classes and these counterparts.
545 One counterpart, in the column labelled "ASCII-range Unicode" in
546 the table, will only match characters in the ASCII character set.
548 The other counterpart, in the column labelled "Full-range Unicode", matches any
549 appropriate characters in the full Unicode character set. For example,
550 C<\p{Alpha}> will match not just the ASCII alphabetic characters, but any
551 character in the entire Unicode character set that is considered to be
552 alphabetic. The column labelled "backslash sequence" is a (short) synonym for
553 the Full-range Unicode form.
555 (Each of the counterparts has various synonyms as well.
556 L<perluniprops/Properties accessible through \p{} and \P{}> lists all the
557 synonyms, plus all the characters matched by each of the ASCII-range
558 properties. For example C<\p{AHex}> is a synonym for C<\p{ASCII_Hex_Digit}>,
559 and any C<\p> property name can be prefixed with "Is" such as C<\p{IsAlpha}>.)
561 Both the C<\p> forms are unaffected by any locale that is in effect, or whether
562 the string is in UTF-8 format or not, or whether the platform is EBCDIC or not.
563 In contrast, the POSIX character classes are affected, unless the
564 regular expression is compiled with the C<"a"> modifier. If the C<"a">
565 modifier is not in effect, and the source string is in UTF-8 format, the
566 POSIX classes behave like their "Full-range" Unicode counterparts. If
567 C<"a"> modifier is in effect; or the source string is not in UTF-8
568 format, and no locale is in effect, and the platform is not EBCDIC, all
569 the POSIX classes behave like their ASCII-range counterparts.
570 Otherwise, they behave based on the rules of the locale or EBCDIC code
573 It is proposed to change this behavior in a future release of Perl so that the
574 the UTF-8-ness of the source string will be irrelevant to the behavior of the
575 POSIX character classes. This means they will always behave in strict
576 accordance with the official POSIX standard. That is, if either locale or
577 EBCDIC code page is present, they will behave in accordance with those; if
578 absent, the classes will match only their ASCII-range counterparts. If you
579 wish to comment on this proposal, send email to C<perl5-porters@perl.org>.
581 [[:...:]] ASCII-range Full-range backslash Note
582 Unicode Unicode sequence
583 -----------------------------------------------------
584 alpha \p{PosixAlpha} \p{XPosixAlpha}
585 alnum \p{PosixAlnum} \p{XPosixAlnum}
587 blank \p{PosixBlank} \p{XPosixBlank} \h [1]
588 or \p{HorizSpace} [1]
589 cntrl \p{PosixCntrl} \p{XPosixCntrl} [2]
590 digit \p{PosixDigit} \p{XPosixDigit} \d
591 graph \p{PosixGraph} \p{XPosixGraph} [3]
592 lower \p{PosixLower} \p{XPosixLower}
593 print \p{PosixPrint} \p{XPosixPrint} [4]
594 punct \p{PosixPunct} \p{XPosixPunct} [5]
595 \p{PerlSpace} \p{XPerlSpace} \s [6]
596 space \p{PosixSpace} \p{XPosixSpace} [6]
597 upper \p{PosixUpper} \p{XPosixUpper}
598 word \p{PosixWord} \p{XPosixWord} \w
599 xdigit \p{ASCII_Hex_Digit} \p{XPosixXDigit}
605 C<\p{Blank}> and C<\p{HorizSpace}> are synonyms.
609 Control characters don't produce output as such, but instead usually control
610 the terminal somehow: for example newline and backspace are control characters.
611 In the ASCII range, characters whose ordinals are between 0 and 31 inclusive,
612 plus 127 (C<DEL>) are control characters.
614 On EBCDIC platforms, it is likely that the code page will define C<[[:cntrl:]]>
615 to be the EBCDIC equivalents of the ASCII controls, plus the controls
616 that in Unicode have ordinals from 128 through 159.
620 Any character that is I<graphical>, that is, visible. This class consists
621 of all the alphanumerical characters and all punctuation characters.
625 All printable characters, which is the set of all the graphical characters
626 plus whitespace characters that are not also controls.
630 C<\p{PosixPunct}> and C<[[:punct:]]> in the ASCII range match all the
631 non-controls, non-alphanumeric, non-space characters:
632 C<[-!"#$%&'()*+,./:;<=E<gt>?@[\\\]^_`{|}~]> (although if a locale is in effect,
633 it could alter the behavior of C<[[:punct:]]>).
635 The similarly named property, C<\p{Punct}>, matches a somewhat different
636 set in the ASCII range, namely
637 C<[-!"#%&'()*,./:;?@[\\\]_{}]>. That is, it is missing C<[$+E<lt>=E<gt>^`|~]>.
638 This is because Unicode splits what POSIX considers to be punctuation into two
639 categories, Punctuation and Symbols.
641 C<\p{XPosixPunct}> and (in Unicode mode) C<[[:punct:]]>, match what
642 C<\p{PosixPunct}> matches in the ASCII range, plus what C<\p{Punct}>
643 matches. This is different than strictly matching according to
644 C<\p{Punct}>. Another way to say it is that
645 for a UTF-8 string, C<[[:punct:]]> matches all the characters that Unicode
646 considers to be punctuation, plus all the ASCII-range characters that Unicode
647 considers to be symbols.
651 C<\p{SpacePerl}> and C<\p{Space}> differ only in that C<\p{Space}> additionally
652 matches the vertical tab, C<\cK>. Same for the two ASCII-only range forms.
656 There are various other synonyms that can be used for these besides
657 C<\p{HorizSpace}> and \C<\p{XPosixBlank}>. For example
658 C<\p{PosixAlpha}> can be written as C<\p{Alpha}>. All are listed
659 in L<perluniprops/Properties accessible through \p{} and \P{}>.
662 X<character class, negation>
664 A Perl extension to the POSIX character class is the ability to
665 negate it. This is done by prefixing the class name with a caret (C<^>).
668 POSIX ASCII-range Full-range backslash
669 Unicode Unicode sequence
670 -----------------------------------------------------
671 [[:^digit:]] \P{PosixDigit} \P{XPosixDigit} \D
672 [[:^space:]] \P{PosixSpace} \P{XPosixSpace}
673 \P{PerlSpace} \P{XPerlSpace} \S
674 [[:^word:]] \P{PerlWord} \P{XPosixWord} \W
676 The backslash sequence can mean either ASCII- or Full-range Unicode,
677 depending on various factors. See L</Locale, EBCDIC, Unicode and UTF-8>
680 =head4 [= =] and [. .]
682 Perl will recognize the POSIX character classes C<[=class=]>, and
683 C<[.class.]>, but does not (yet?) support them. Use of
684 such a construct will lead to an error.
689 /[[:digit:]]/ # Matches a character that is a digit.
690 /[01[:lower:]]/ # Matches a character that is either a
691 # lowercase letter, or '0' or '1'.
692 /[[:digit:][:^xdigit:]]/ # Matches a character that can be anything
693 # except the letters 'a' to 'f'. This is
694 # because the main character class is composed
695 # of two POSIX character classes that are ORed
696 # together, one that matches any digit, and
697 # the other that matches anything that isn't a
698 # hex digit. The result matches all
699 # characters except the letters 'a' to 'f' and
703 =head2 Locale, EBCDIC, Unicode and UTF-8
705 Some of the character classes have a somewhat different behaviour
706 depending on the internal encoding of the source string, if the regular
707 expression is marked as having Unicode semantics, the locale that is in
708 effect, and if the program is running on an EBCDIC platform.
710 C<\w>, C<\d>, C<\s> and the POSIX character classes (and their
711 negations, including C<\W>, C<\D>, C<\S>) have this behaviour. (Since
712 the backslash sequences C<\b> and C<\B> are defined in terms of C<\w>
713 and C<\W>, they also are affected.)
715 Starting in Perl 5.14, if the regular expression is compiled with the
716 C<"a"> modifier, the behavior doesn't differ regardless of any other
717 factors. C<\d> matches the 10 digits 0-9; C<\D> any character but those
718 10; C<\s>, exactly the five characters "[ \f\n\r\t]"; C<\w> only the 63
719 characters "[A-Za-z0-9_]"; and the C<"[[:posix:]]"> classes only the
720 appropriate ASCII characters, the same characters as are matched by the
721 corresponding C<\p{}> property given in the "ASCII-range Unicode" column
722 in the table above. (The behavior of all of their complements follows
725 Otherwise, a regular expression is marked for Unicode semantics if it is
726 encoded in utf8 (usually as a result of including a literal character
727 whose code point is above 255), or if it contains a C<\N{U+...}> or
728 C<\N{I<name>}> construct, or (starting in Perl 5.14) if it was compiled
729 in the scope of a C<S<use feature "unicode_strings">> pragma and not in
730 the scope of a C<S<use locale>> pragma, or has the C<"u"> regular
733 Note that one can specify C<"use re '/l'"> for example, for any regular
734 expression modifier, and this has precedence over either of the
735 C<S<use feature "unicode_strings">> or C<S<use locale>> pragmas.
737 The differences in behavior between locale and non-locale semantics
738 can affect any character whose code point is 255 or less. The
739 differences in behavior between Unicode and non-Unicode semantics
740 affects only ASCII platforms, and only when matching against characters
741 whose code points are between 128 and 255 inclusive. See
742 L<perlunicode/The "Unicode Bug">.
744 For portability reasons, unless the C<"a"> modifier is specified,
745 it may be better to not use C<\w>, C<\d>, C<\s> or the POSIX character
746 classes and use the Unicode properties instead.
747 That way you can control whether you want matching of just characters in
748 the ASCII character set, or any Unicode characters.
749 C<S<use feature "unicode_strings">> will allow seamless Unicode behavior
750 no matter what the internal encodings are, but won't allow restricting
751 to just the ASCII characters.
755 $str = "\xDF"; # $str is not in UTF-8 format.
756 $str =~ /^\w/; # No match, as $str isn't in UTF-8 format.
757 $str .= "\x{0e0b}"; # Now $str is in UTF-8 format.
758 $str =~ /^\w/; # Match! $str is now in UTF-8 format.
760 $str =~ /^\w/; # Still a match! $str remains in UTF-8 format.