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PERLRECHARCLASS(1)     Perl Programmers Reference Guide	    PERLRECHARCLASS(1)

NAME
       perlrecharclass - Perl Regular Expression Character Classes

DESCRIPTION
       The top level documentation about Perl regular expressions is found in
       perlre.

       This manual page discusses the syntax and use of character classes in
       Perl Regular Expressions.

       A character class is a way of denoting a set of characters, in such a
       way that one character of the set is matched.  It's important to
       remember that matching a character class consumes exactly one character
       in the source string. (The source string is the string the regular
       expression is matched against.)

       There are three types of character classes in Perl regular expressions:
       the dot, backslashed sequences, and the bracketed form.

   The dot
       The dot (or period), "." is probably the most used, and certainly the
       most well-known character class. By default, a dot matches any
       character, except for the newline. The default can be changed to add
       matching the newline with the single line modifier: either for the
       entire regular expression using the "/s" modifier, or locally using
       "(?s)".

       Here are some examples:

	"a"  =~	 /./	   # Match
	"."  =~	 /./	   # Match
	""   =~	 /./	   # No match (dot has to match a character)
	"\n" =~	 /./	   # No match (dot does not match a newline)
	"\n" =~	 /./s	   # Match (global 'single line' modifier)
	"\n" =~	 /(?s:.)/  # Match (local 'single line' modifier)
	"ab" =~	 /^.$/	   # No match (dot matches one character)

   Backslashed sequences
       Perl regular expressions contain many backslashed sequences that
       constitute a character class. That is, they will match a single
       character, if that character belongs to a specific set of characters
       (defined by the sequence). A backslashed sequence is a sequence of
       characters starting with a backslash. Not all backslashed sequences are
       character class; for a full list, see perlrebackslash.

       Here's a list of the backslashed sequences, which are discussed in more
       detail below.

	\d	       Match a digit character.
	\D	       Match a non-digit character.
	\w	       Match a "word" character.
	\W	       Match a non-"word" character.
	\s	       Match a white space character.
	\S	       Match a non-white space character.
	\h	       Match a horizontal white space character.
	\H	       Match a character that isn't horizontal white space.
	\v	       Match a vertical white space character.
	\V	       Match a character that isn't vertical white space.
	\pP, \p{Prop}  Match a character matching a Unicode property.
	\PP, \P{Prop}  Match a character that doesn't match a Unicode property.

       Digits

       "\d" matches a single character that is considered to be a digit.  What
       is considered a digit depends on the internal encoding of the source
       string. If the source string is in UTF-8 format, "\d" not only matches
       the digits '0' - '9', but also Arabic, Devanagari and digits from other
       languages. Otherwise, if there is a locale in effect, it will match
       whatever characters the locale considers digits. Without a locale, "\d"
       matches the digits '0' to '9'.  See "Locale, Unicode and UTF-8".

       Any character that isn't matched by "\d" will be matched by "\D".

       Word characters

       "\w" matches a single word character: an alphanumeric character (that
       is, an alphabetic character, or a digit), or the underscore ("_").
       What is considered a word character depends on the internal encoding of
       the string. If it's in UTF-8 format, "\w" matches those characters that
       are considered word characters in the Unicode database. That is, it not
       only matches ASCII letters, but also Thai letters, Greek letters, etc.
       If the source string isn't in UTF-8 format, "\w" matches those
       characters that are considered word characters by the current locale.
       Without a locale in effect, "\w" matches the ASCII letters, digits and
       the underscore.

       Any character that isn't matched by "\w" will be matched by "\W".

       White space

       "\s" matches any single character that is consider white space. In the
       ASCII range, "\s" matches the horizontal tab ("\t"), the new line
       ("\n"), the form feed ("\f"), the carriage return ("\r"), and the space
       (the vertical tab, "\cK" is not matched by "\s").  The exact set of
       characters matched by "\s" depends on whether the source string is in
       UTF-8 format. If it is, "\s" matches what is considered white space in
       the Unicode database. Otherwise, if there is a locale in effect, "\s"
       matches whatever is considered white space by the current locale.
       Without a locale, "\s" matches the five characters mentioned in the
       beginning of this paragraph.  Perhaps the most notable difference is
       that "\s" matches a non-breaking space only if the non-breaking space
       is in a UTF-8 encoded string.

       Any character that isn't matched by "\s" will be matched by "\S".

       "\h" will match any character that is considered horizontal white
       space; this includes the space and the tab characters. "\H" will match
       any character that is not considered horizontal white space.

       "\v" will match any character that is considered vertical white space;
       this includes the carriage return and line feed characters (newline).
       "\V" will match any character that is not considered vertical white
       space.

       "\R" matches anything that can be considered a newline under Unicode
       rules. It's not a character class, as it can match a multi-character
       sequence. Therefore, it cannot be used inside a bracketed character
       class. Details are discussed in perlrebackslash.

       "\h", "\H", "\v", "\V", and "\R" are new in perl 5.10.0.

       Note that unlike "\s", "\d" and "\w", "\h" and "\v" always match the
       same characters, regardless whether the source string is in UTF-8
       format or not. The set of characters they match is also not influenced
       by locale.

       One might think that "\s" is equivalent with "[\h\v]". This is not
       true.  The vertical tab ("\x0b") is not matched by "\s", it is however
       considered vertical white space. Furthermore, if the source string is
       not in UTF-8 format, the next line ("\x85") and the no-break space
       ("\xA0") are not matched by "\s", but are by "\v" and "\h"
       respectively.  If the source string is in UTF-8 format, both the next
       line and the no-break space are matched by "\s".

       The following table is a complete listing of characters matched by
       "\s", "\h" and "\v".

       The first column gives the code point of the character (in hex format),
       the second column gives the (Unicode) name. The third column indicates
       by which class(es) the character is matched.

	0x00009	       CHARACTER TABULATION   h s
	0x0000a		     LINE FEED (LF)    vs
	0x0000b		    LINE TABULATION    v
	0x0000c		     FORM FEED (FF)    vs
	0x0000d	       CARRIAGE RETURN (CR)    vs
	0x00020			      SPACE   h s
	0x00085		    NEXT LINE (NEL)    vs  [1]
	0x000a0		     NO-BREAK SPACE   h s  [1]
	0x01680		   OGHAM SPACE MARK   h s
	0x0180e	  MONGOLIAN VOWEL SEPARATOR   h s
	0x02000			    EN QUAD   h s
	0x02001			    EM QUAD   h s
	0x02002			   EN SPACE   h s
	0x02003			   EM SPACE   h s
	0x02004		 THREE-PER-EM SPACE   h s
	0x02005		  FOUR-PER-EM SPACE   h s
	0x02006		   SIX-PER-EM SPACE   h s
	0x02007		       FIGURE SPACE   h s
	0x02008		  PUNCTUATION SPACE   h s
	0x02009			 THIN SPACE   h s
	0x0200a			 HAIR SPACE   h s
	0x02028		     LINE SEPARATOR    vs
	0x02029		PARAGRAPH SEPARATOR    vs
	0x0202f	      NARROW NO-BREAK SPACE   h s
	0x0205f	  MEDIUM MATHEMATICAL SPACE   h s
	0x03000		  IDEOGRAPHIC SPACE   h s

       [1] NEXT LINE and NO-BREAK SPACE only match "\s" if the source string
	   is in UTF-8 format.

       It is worth noting that "\d", "\w", etc, match single characters, not
       complete numbers or words. To match a number (that consists of
       integers), use "\d+"; to match a word, use "\w+".

       Unicode Properties

       "\pP" and "\p{Prop}" are character classes to match characters that fit
       given Unicode classes. One letter classes can be used in the "\pP"
       form, with the class name following the "\p", otherwise, the property
       name is enclosed in braces, and follows the "\p". For instance, a match
       for a number can be written as "/\pN/" or as "/\p{Number}/".  Lowercase
       letters are matched by the property LowercaseLetter which has as short
       form Ll. They have to be written as "/\p{Ll}/" or
       "/\p{LowercaseLetter}/". "/\pLl/" is valid, but means something
       different.  It matches a two character string: a letter (Unicode
       property "\pL"), followed by a lowercase "l".

       For a list of possible properties, see "Unicode Character Properties"
       in perlunicode. It is also possible to defined your own properties.
       This is discussed in "User-Defined Character Properties" in
       perlunicode.

       Examples

	"a"  =~	 /\w/	   # Match, "a" is a 'word' character.
	"7"  =~	 /\w/	   # Match, "7" is a 'word' character as well.
	"a"  =~	 /\d/	   # No match, "a" isn't a digit.
	"7"  =~	 /\d/	   # Match, "7" is a digit.
	" "  =~	 /\s/	   # Match, a space is white space.
	"a"  =~	 /\D/	   # Match, "a" is a non-digit.
	"7"  =~	 /\D/	   # No match, "7" is not a non-digit.
	" "  =~	 /\S/	   # No match, a space is not non-white space.

	" "  =~	 /\h/	   # Match, space is horizontal white space.
	" "  =~	 /\v/	   # No match, space is not vertical white space.
	"\r" =~	 /\v/	   # Match, a return is vertical white space.

	"a"  =~	 /\pL/	   # Match, "a" is a letter.
	"a"  =~	 /\p{Lu}/  # No match, /\p{Lu}/ matches upper case letters.

	"\x{0e0b}" =~ /\p{Thai}/  # Match, \x{0e0b} is the character
				  # 'THAI CHARACTER SO SO', and that's in
				  # Thai Unicode class.
	"a"  =~	 /\P{Lao}/ # Match, as "a" is not a Laoian character.

   Bracketed Character Classes
       The third form of character class you can use in Perl regular
       expressions is the bracketed form. In its simplest form, it lists the
       characters that may be matched inside square brackets, like this:
       "[aeiou]".  This matches one of "a", "e", "i", "o" or "u". Just as the
       other character classes, exactly one character will be matched. To
       match a longer string consisting of characters mentioned in the
       characters class, follow the character class with a quantifier. For
       instance, "[aeiou]+" matches a string of one or more lowercase ASCII
       vowels.

       Repeating a character in a character class has no effect; it's
       considered to be in the set only once.

       Examples:

	"e"  =~	 /[aeiou]/	  # Match, as "e" is listed in the class.
	"p"  =~	 /[aeiou]/	  # No match, "p" is not listed in the class.
	"ae" =~	 /^[aeiou]$/	  # No match, a character class only matches
				  # a single character.
	"ae" =~	 /^[aeiou]+$/	  # Match, due to the quantifier.

       Special Characters Inside a Bracketed Character Class

       Most characters that are meta characters in regular expressions (that
       is, characters that carry a special meaning like "*" or "(") lose their
       special meaning and can be used inside a character class without the
       need to escape them. For instance, "[()]" matches either an opening
       parenthesis, or a closing parenthesis, and the parens inside the
       character class don't group or capture.

       Characters that may carry a special meaning inside a character class
       are: "\", "^", "-", "[" and "]", and are discussed below. They can be
       escaped with a backslash, although this is sometimes not needed, in
       which case the backslash may be omitted.

       The sequence "\b" is special inside a bracketed character class. While
       outside the character class "\b" is an assertion indicating a point
       that does not have either two word characters or two non-word
       characters on either side, inside a bracketed character class, "\b"
       matches a backspace character.

       A "[" is not special inside a character class, unless it's the start of
       a POSIX character class (see below). It normally does not need
       escaping.

       A "]" is either the end of a POSIX character class (see below), or it
       signals the end of the bracketed character class. Normally it needs
       escaping if you want to include a "]" in the set of characters.
       However, if the "]" is the first (or the second if the first character
       is a caret) character of a bracketed character class, it does not
       denote the end of the class (as you cannot have an empty class) and is
       considered part of the set of characters that can be matched without
       escaping.

       Examples:

	"+"   =~ /[+?*]/     #	Match, "+" in a character class is not special.
	"\cH" =~ /[\b]/	     #	Match, \b inside in a character class
			     #	is equivalent with a backspace.
	"]"   =~ /[][]/	     #	Match, as the character class contains.
			     #	both [ and ].
	"[]"  =~ /[[]]/	     #	Match, the pattern contains a character class
			     #	containing just ], and the character class is
			     #	followed by a ].

       Character Ranges

       It is not uncommon to want to match a range of characters. Luckily,
       instead of listing all the characters in the range, one may use the
       hyphen ("-").  If inside a bracketed character class you have two
       characters separated by a hyphen, it's treated as if all the characters
       between the two are in the class. For instance, "[0-9]" matches any
       ASCII digit, and "[a-m]" matches any lowercase letter from the first
       half of the ASCII alphabet.

       Note that the two characters on either side of the hyphen are not
       necessary both letters or both digits. Any character is possible,
       although not advisable.	"['-?]" contains a range of characters, but
       most people will not know which characters that will be. Furthermore,
       such ranges may lead to portability problems if the code has to run on
       a platform that uses a different character set, such as EBCDIC.

       If a hyphen in a character class cannot be part of a range, for
       instance because it is the first or the last character of the character
       class, or if it immediately follows a range, the hyphen isn't special,
       and will be considered a character that may be matched. You have to
       escape the hyphen with a backslash if you want to have a hyphen in your
       set of characters to be matched, and its position in the class is such
       that it can be considered part of a range.

       Examples:

	[a-z]	    #  Matches a character that is a lower case ASCII letter.
	[a-fz]	    #  Matches any letter between 'a' and 'f' (inclusive) or the
		    #  letter 'z'.
	[-z]	    #  Matches either a hyphen ('-') or the letter 'z'.
	[a-f-m]	    #  Matches any letter between 'a' and 'f' (inclusive), the
		    #  hyphen ('-'), or the letter 'm'.
	['-?]	    #  Matches any of the characters  '()*+,-./0123456789:;<=>?
		    #  (But not on an EBCDIC platform).

       Negation

       It is also possible to instead list the characters you do not want to
       match. You can do so by using a caret ("^") as the first character in
       the character class. For instance, "[^a-z]" matches a character that is
       not a lowercase ASCII letter.

       This syntax make the caret a special character inside a bracketed
       character class, but only if it is the first character of the class. So
       if you want to have the caret as one of the characters you want to
       match, you either have to escape the caret, or not list it first.

       Examples:

	"e"  =~	 /[^aeiou]/   #	 No match, the 'e' is listed.
	"x"  =~	 /[^aeiou]/   #	 Match, as 'x' isn't a lowercase vowel.
	"^"  =~	 /[^^]/	      #	 No match, matches anything that isn't a caret.
	"^"  =~	 /[x^]/	      #	 Match, caret is not special here.

       Backslash Sequences

       You can put a backslash sequence character class inside a bracketed
       character class, and it will act just as if you put all the characters
       matched by the backslash sequence inside the character class. For
       instance, "[a-f\d]" will match any digit, or any of the lowercase
       letters between 'a' and 'f' inclusive.

       Examples:

	/[\p{Thai}\d]/	   # Matches a character that is either a Thai
			   # character, or a digit.
	/[^\p{Arabic}()]/  # Matches a character that is neither an Arabic
			   # character, nor a parenthesis.

       Backslash sequence character classes cannot form one of the endpoints
       of a range.

       Posix Character Classes

       Posix character classes have the form "[:class:]", where class is name,
       and the "[:" and ":]" delimiters. Posix character classes appear inside
       bracketed character classes, and are a convenient and descriptive way
       of listing a group of characters. Be careful about the syntax,

	# Correct:
	$string =~ /[[:alpha:]]/

	# Incorrect (will warn):
	$string =~ /[:alpha:]/

       The latter pattern would be a character class consisting of a colon,
       and the letters "a", "l", "p" and "h".

       Perl recognizes the following POSIX character classes:

	alpha  Any alphabetical character.
	alnum  Any alphanumerical character.
	ascii  Any ASCII character.
	blank  A GNU extension, equal to a space or a horizontal tab ("\t").
	cntrl  Any control character.
	digit  Any digit, equivalent to "\d".
	graph  Any printable character, excluding a space.
	lower  Any lowercase character.
	print  Any printable character, including a space.
	punct  Any punctuation character.
	space  Any white space character. "\s" plus the vertical tab ("\cK").
	upper  Any uppercase character.
	word   Any "word" character, equivalent to "\w".
	xdigit Any hexadecimal digit, '0' - '9', 'a' - 'f', 'A' - 'F'.

       The exact set of characters matched depends on whether the source
       string is internally in UTF-8 format or not. See "Locale, Unicode and
       UTF-8".

       Most POSIX character classes have "\p" counterparts. The difference is
       that the "\p" classes will always match according to the Unicode
       properties, regardless whether the string is in UTF-8 format or not.

       The following table shows the relation between POSIX character classes
       and the Unicode properties:

	[[:...:]]   \p{...}	 backslash

	alpha	    IsAlpha
	alnum	    IsAlnum
	ascii	    IsASCII
	blank
	cntrl	    IsCntrl
	digit	    IsDigit	 \d
	graph	    IsGraph
	lower	    IsLower
	print	    IsPrint
	punct	    IsPunct
	space	    IsSpace
		    IsSpacePerl	 \s
	upper	    IsUpper
	word	    IsWord
	xdigit	    IsXDigit

       Some character classes may have a non-obvious name:

       cntrl
	   Any control character. Usually, control characters don't produce
	   output as such, but instead control the terminal somehow: for
	   example newline and backspace are control characters. All
	   characters with "ord()" less than 32 are usually classified as
	   control characters (in ASCII, the ISO Latin character sets, and
	   Unicode), as is the character "ord()" value of 127 ("DEL").

       graph
	   Any character that is graphical, that is, visible. This class
	   consists of all the alphanumerical characters and all punctuation
	   characters.

       print
	   All printable characters, which is the set of all the graphical
	   characters plus the space.

       punct
	   Any punctuation (special) character.

       Negation

       A Perl extension to the POSIX character class is the ability to negate
       it. This is done by prefixing the class name with a caret ("^").	 Some
       examples:

	POSIX	      Unicode	    Backslash
	[[:^digit:]]  \P{IsDigit}   \D
	[[:^space:]]  \P{IsSpace}   \S
	[[:^word:]]   \P{IsWord}    \W

       [= =] and [. .]

       Perl will recognize the POSIX character classes "[=class=]", and
       "[.class.]", but does not (yet?) support this construct. Use of such a
       construct will lead to an error.

       Examples

	/[[:digit:]]/		 # Matches a character that is a digit.
	/[01[:lower:]]/		 # Matches a character that is either a
				 # lowercase letter, or '0' or '1'.
	/[[:digit:][:^xdigit:]]/ # Matches a character that can be anything,
				 # but the letters 'a' to 'f' in either case.
				 # This is because the character class contains
				 # all digits, and anything that isn't a
				 # hex digit, resulting in a class containing
				 # all characters, but the letters 'a' to 'f'
				 # and 'A' to 'F'.

   Locale, Unicode and UTF-8
       Some of the character classes have a somewhat different behaviour
       depending on the internal encoding of the source string, and the locale
       that is in effect.

       "\w", "\d", "\s" and the POSIX character classes (and their negations,
       including "\W", "\D", "\S") suffer from this behaviour.

       The rule is that if the source string is in UTF-8 format, the character
       classes match according to the Unicode properties. If the source string
       isn't, then the character classes match according to whatever locale is
       in effect. If there is no locale, they match the ASCII defaults (52
       letters, 10 digits and underscore for "\w", 0 to 9 for "\d", etc).

       This usually means that if you are matching against characters whose
       "ord()" values are between 128 and 255 inclusive, your character class
       may match or not depending on the current locale, and whether the
       source string is in UTF-8 format. The string will be in UTF-8 format if
       it contains characters whose "ord()" value exceeds 255. But a string
       may be in UTF-8 format without it having such characters.

       For portability reasons, it may be better to not use "\w", "\d", "\s"
       or the POSIX character classes, and use the Unicode properties instead.

       Examples

	$str =	"\xDF";	     # $str is not in UTF-8 format.
	$str =~ /^\w/;	     # No match, as $str isn't in UTF-8 format.
	$str .= "\x{0e0b}";  # Now $str is in UTF-8 format.
	$str =~ /^\w/;	     # Match! $str is now in UTF-8 format.
	chop $str;
	$str =~ /^\w/;	     # Still a match! $str remains in UTF-8 format.

perl v5.10.1			  2009-05-14		    PERLRECHARCLASS(1)
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