perlrecharclass


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, backslash sequences, and the form enclosed in square brackets.
       Keep in mind, though, that often the term "character class" is used to
       mean just the bracketed form.  Certainly, most Perl documentation does
       that.

   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. That default can be changed to add
       matching the newline by using the single line modifier: either for the
       entire regular expression with the "/s" modifier, or locally with
       "(?s)".  (The "\N" backslash sequence, described below, matches any
       character except newline without regard to the single line modifier.)

       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)

   Backslash sequences
       A backslash sequence is a sequence of characters, the first one of
       which is a backslash.  Perl ascribes special meaning to many such
       sequences, and some of these are character classes.  That is, they
       match a single character each, provided that the character belongs to
       the specific set of characters defined by the sequence.

       Here's a list of the backslash sequences that are character classes.
       They are discussed in more detail below.  (For the backslash sequences
       that aren't character classes, see perlrebackslash.)

        \d             Match a decimal digit character.
        \D             Match a non-decimal-digit character.
        \w             Match a "word" character.
        \W             Match a non-"word" character.

       "\N", available starting in v5.12, like the dot, matches any character
       that is not a newline. The difference is that "\N" is not influenced by
       the single line regular expression modifier (see "The dot" above).
       Note that the form "\N{...}" may mean something completely different.
       When the "{...}" is a quantifier, it means to match a non-newline
       character that many times.  For example, "\N{3}" means to match 3 non-
       newlines; "\N{5,}" means to match 5 or more non-newlines.  But if
       "{...}" is not a legal quantifier, it is presumed to be a named
       character.  See charnames for those.  For example, none of "\N{COLON}",
       "\N{4F}", and "\N{F4}" contain legal quantifiers, so Perl will try to
       find characters whose names are respectively "COLON", "4F", and "F4".

       Digits

       "\d" matches a single character considered to be a decimal digit.  If
       the "/a" regular expression modifier is in effect, it matches [0-9].
       Otherwise, it matches anything that is matched by "\p{Digit}", which
       includes [0-9].  (An unlikely possible exception is that under locale
       matching rules, the current locale might not have [0-9] matched by
       "\d", and/or might match other characters whose code point is less than
       256.  Such a locale definition would be in violation of the C language
       standard, but Perl doesn't currently assume anything in regard to
       this.)

       What this means is that unless the "/a" modifier is in effect "\d" not
       only matches the digits '0' - '9', but also Arabic, Devanagari, and
       digits from other languages.  This may cause some confusion, and some
       security issues.

       Some digits that "\d" matches look like some of the [0-9] ones, but
       have different values.  For example, BENGALI DIGIT FOUR (U+09EA) looks
       very much like an ASCII DIGIT EIGHT (U+0038).  An application that is
       expecting only the ASCII digits might be misled, or if the match is
       "\d+", the matched string might contain a mixture of digits from
       different writing systems that look like they signify a number
       different than they actually do.  "num()" in Unicode::UCD can be used
       to safely calculate the value, returning "undef" if the input string
       contains such a mixture.

       What "\p{Digit}" means (and hence "\d" except under the "/a" modifier)
       is "\p{General_Category=Decimal_Number}", or synonymously,
       "\p{General_Category=Digit}".  Starting with Unicode version 4.1, this
       is the same set of characters matched by "\p{Numeric_Type=Decimal}".
       But Unicode also has a different property with a similar name,
       "\p{Numeric_Type=Digit}", which matches a completely different set of
       characters.  These characters are things such as "CIRCLED DIGIT ONE" or
       subscripts, or are from writing systems that lack all ten digits.

       The design intent is for "\d" to exactly match the set of characters
       that can safely be used with "normal" big-endian positional decimal
       syntax, where, for example 123 means one 'hundred', plus two 'tens',
       plus three 'ones'.  This positional notation does not necessarily apply
       to characters that match the other type of "digit",
       "\p{Numeric_Type=Digit}", and so "\d" doesn't match them.
       such as an underscore ("_"); or a "mark" character (like some sort of
       accent) that attaches to one of those.  It does not match a whole word.
       To match a whole word, use "\w+".  This isn't the same thing as
       matching an English word, but in the ASCII range it is the same as a
       string of Perl-identifier characters.

       If the "/a" modifier is in effect ...
           "\w" matches the 63 characters [a-zA-Z0-9_].

       otherwise ...
           For code points above 255 ...
               "\w" matches the same as "\p{Word}" matches in this range.
               That is, it matches Thai letters, Greek letters, etc.  This
               includes connector punctuation (like the underscore) which
               connect two words together, or diacritics, such as a "COMBINING
               TILDE" and the modifier letters, which are generally used to
               add auxiliary markings to letters.

           For code points below 256 ...
               if locale rules are in effect ...
                   "\w" matches the platform's native underscore character
                   plus whatever the locale considers to be alphanumeric.

               if Unicode rules are in effect ...
                   "\w" matches exactly what "\p{Word}" matches.

               otherwise ...
                   "\w" matches [a-zA-Z0-9_].

       Which rules apply are determined as described in "Which character set
       modifier is in effect?" in perlre.

       There are a number of security issues with the full Unicode list of
       word characters.  See <http://unicode.org/reports/tr36>.

       Also, for a somewhat finer-grained set of characters that are in
       programming language identifiers beyond the ASCII range, you may wish
       to instead use the more customized "Unicode Properties",
       "\p{ID_Start}", "\p{ID_Continue}", "\p{XID_Start}", and
       "\p{XID_Continue}".  See <http://unicode.org/reports/tr31>.

       Any character not matched by "\w" is matched by "\W".

       Whitespace

       "\s" matches any single character considered whitespace.

       If the "/a" modifier is in effect ...
           In all Perl versions, "\s" matches the 5 characters [\t\n\f\r ];
           that is, the horizontal tab, the newline, the form feed, the
           carriage return, and the space.  Starting in Perl v5.18,
           experimentally, it also matches the vertical tab, "\cK".  See note
           "[1]" below for a discussion of this.

                   column in the table below.

               otherwise ...
                   "\s" matches [\t\n\f\r\cK ] and, starting, experimentally
                   in Perl v5.18, the vertical tab, "\cK".  (See note "[1]"
                   below for a discussion of this.)  Note that this list
                   doesn't include the non-breaking space.

       Which rules apply are determined as described in "Which character set
       modifier is in effect?" in perlre.

       Any character not matched by "\s" is matched by "\S".

       "\h" matches any character considered horizontal whitespace; this
       includes the platform's space and tab characters and several others
       listed in the table below.  "\H" matches any character not considered
       horizontal whitespace.  They use the platform's native character set,
       and do not consider any locale that may otherwise be in use.

       "\v" matches any character considered vertical whitespace; this
       includes the platform's carriage return and line feed characters
       (newline) plus several other characters, all listed in the table below.
       "\V" matches any character not considered vertical whitespace.  They
       use the platform's native character set, and do not consider any locale
       that may otherwise be in use.

       "\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; use "\v" instead (vertical whitespace).  It uses the platform's
       native character set, and does not consider any locale that may
       otherwise be in use.  Details are discussed in perlrebackslash.

       Note that unlike "\s" (and "\d" and "\w"), "\h" and "\v" always match
       the same characters, without regard to other factors, such as the
       active locale or whether the source string is in UTF-8 format.

       One might think that "\s" is equivalent to "[\h\v]". This is indeed
       true starting in Perl v5.18, but prior to that, the sole difference was
       that the vertical tab ("\cK") was not matched by "\s".

       The following table is a complete listing of characters matched by
       "\s", "\h" and "\v" as of Unicode 6.0.

       The first column gives the Unicode 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 (assuming no
       locale is in effect that changes the "\s" matching).

        0x0009        CHARACTER TABULATION   h s
        0x000a              LINE FEED (LF)    vs
        0x000b             LINE TABULATION    vs  [1]
        0x000c              FORM FEED (FF)    vs
        0x000d        CARRIAGE RETURN (CR)    vs
        0x2007                FIGURE SPACE   h s
        0x2008           PUNCTUATION SPACE   h s
        0x2009                  THIN SPACE   h s
        0x200a                  HAIR SPACE   h s
        0x2028              LINE SEPARATOR    vs
        0x2029         PARAGRAPH SEPARATOR    vs
        0x202f       NARROW NO-BREAK SPACE   h s
        0x205f   MEDIUM MATHEMATICAL SPACE   h s
        0x3000           IDEOGRAPHIC SPACE   h s

       [1] Prior to Perl v5.18, "\s" did not match the vertical tab.  The
           change in v5.18 is considered an experiment, which means it could
           be backed out in v5.20 or v5.22 if experience indicates that it
           breaks too much existing code.  If this change adversely affects
           you, send email to "perlbug@perl.org"; if it affects you
           positively, email "perlthanks@perl.org".  In the meantime,
           "[^\S\cK]" (obscurely) matches what "\s" traditionally did.

       [2] NEXT LINE and NO-BREAK SPACE may or may not match "\s" depending on
           the rules in effect.  See the beginning of this section.

       Unicode Properties

       "\pP" and "\p{Prop}" are character classes to match characters that fit
       given Unicode properties.  One letter property names can be used in the
       "\pP" form, with the property name following the "\p", otherwise,
       braces are required.  When using braces, there is a single form, which
       is just the property name enclosed in the braces, and a compound form
       which looks like "\p{name=value}", which means to match if the property
       "name" for the character has that particular "value".  For instance, a
       match for a number can be written as "/\pN/" or as "/\p{Number}/", or
       as "/\p{Number=True}/".  Lowercase letters are matched by the property
       Lowercase_Letter which has the short form Ll. They need the braces, so
       are written as "/\p{Ll}/" or "/\p{Lowercase_Letter}/", or
       "/\p{General_Category=Lowercase_Letter}/" (the underscores are
       optional).  "/\pLl/" is valid, but means something different.  It
       matches a two character string: a letter (Unicode property "\pL"),
       followed by a lowercase "l".

       If locale rules are not in effect, the use of a Unicode property will
       force the regular expression into using Unicode rules, if it isn't
       already.

       Note that almost all properties are immune to case-insensitive
       matching.  That is, adding a "/i" regular expression modifier does not
       change what they match.  There are two sets that are affected.  The
       first set is "Uppercase_Letter", "Lowercase_Letter", and
       "Titlecase_Letter", all of which match "Cased_Letter" under "/i"
       matching.  The second set is "Uppercase", "Lowercase", and "Titlecase",
       all of which match "Cased" under "/i" matching.  (The difference
       between these sets is that some things, such as Roman numerals, come in
       both upper and lower case, so they are "Cased", but aren't considered
       to be letters, so they aren't "Cased_Letter"s. They're actually
       "Letter_Number"s.)  This set also includes its subsets "PosixUpper" and
       somewhat surprising,

        chr(0x110000) =~ \p{ASCII_Hex_Digit=True}      # Fails.
        chr(0x110000) =~ \p{ASCII_Hex_Digit=False}     # Also fails!

       Even though these two matches might be thought of as complements, they
       are so only on Unicode code points.

       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 whitespace.
        "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-whitespace.

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

        "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 Laotian character.

       It is worth emphasizing that "\d", "\w", etc, match single characters,
       not complete numbers or words. To match a number (that consists of
       digits), use "\d+"; to match a word, use "\w+".  But be aware of the
       security considerations in doing so, as mentioned above.

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

        'ss' =~ /\A\N{LATIN SMALL LETTER SHARP S}\z/i             # Matches
        'ss' =~ /\A[aeioust\N{LATIN SMALL LETTER SHARP S}]\z/i    # Matches

       For this to happen, the character must be explicitly specified, and not
       be part of a multi-character range (not even as one of its endpoints).
       ("Character Ranges" will be explained shortly.)  Therefore,

        'ss' =~ /\A[\0-\x{ff}]\z/i        # Doesn't match
        'ss' =~ /\A[\0-\N{LATIN SMALL LETTER SHARP S}]\z/i    # No match
        'ss' =~ /\A[\xDF-\xDF]\z/i    # Matches on ASCII platforms, since \XDF
                                      # is LATIN SMALL LETTER SHARP S, and the
                                      # range is just a single element

       Note that it isn't a good idea to specify these types of ranges anyway.

       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.

       The sequences "\a", "\c", "\e", "\f", "\n", "\N{NAME}", "\N{U+hex
       char}", "\r", "\t", and "\x" are also special and have the same
       meanings as they do outside a bracketed character class.  (However,
       inside a bracketed character class, if "\N{NAME}" expands to a sequence
       of characters, only the first one in the sequence is used, with a
       warning.)

       Also, a backslash followed by two or three octal digits is considered
       an octal number.

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

       A "]" is normally either the end of a POSIX character class (see "POSIX
       Character Classes" below), or it signals the end of the bracketed
       character class.  If you want to include a "]" in the set of
       characters, you must generally escape it.
        "]"   =~ /[][]/      #  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 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 characters between the
       two were 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
       necessarily 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 means.  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 syntactically 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 so is considered a character to be matched
       literally.  If you want a hyphen in your set of characters to be
       matched and its position in the class is such that it could be
       considered part of a range, you must escape that hyphen with a
       backslash.

       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 any character that
       is not a lowercase ASCII letter, which therefore includes more than a
       million Unicode code points.  The class is said to be "negated" or
       "inverted".

       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
       that "ss" is what "\xDF" matches under "/i".  So which one "wins"? Do
       you fail the match because the string has "ss" or accept it because it
       has an "s" followed by another "s"?  Perl has chosen the latter.

       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 any backslash sequence character class (with the exception
       of "\N" and "\R") inside a bracketed character class, and it will act
       just as if you had put all characters matched by the backslash sequence
       inside the character class. For instance, "[a-f\d]" matches any decimal
       digit, or any of the lowercase letters between 'a' and 'f' inclusive.

       "\N" within a bracketed character class must be of the forms "\N{name}"
       or "\N{U+hex char}", and NOT be the form that matches non-newlines, for
       the same reason that a dot "." inside a bracketed character class loses
       its special meaning: it matches nearly anything, which generally isn't
       what you want to happen.

       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.  Thus, you can't say:

        /[\p{Thai}-\d]/     # Wrong!

       POSIX Character Classes

       POSIX character classes have the form "[:class:]", where class is name,
       and the "[:" and ":]" delimiters. POSIX character classes only 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".  POSIX character classes can be
        blank  A GNU extension, equal to a space or a horizontal tab ("\t").
        cntrl  Any control character.  See Note [2] below.
        digit  Any decimal digit ("[0-9]"), equivalent to "\d".
        graph  Any printable character, excluding a space.  See Note [3] below.
        lower  Any lowercase character ("[a-z]").
        print  Any printable character, including a space.  See Note [4] below.
        punct  Any graphical character excluding "word" characters.  Note [5].
        space  Any whitespace character. "\s" including the vertical tab
               ("\cK").
        upper  Any uppercase character ("[A-Z]").
        word   A Perl extension ("[A-Za-z0-9_]"), equivalent to "\w".
        xdigit Any hexadecimal digit ("[0-9a-fA-F]").

       Most POSIX character classes have two Unicode-style "\p" property
       counterparts.  (They are not official Unicode properties, but Perl
       extensions derived from official Unicode properties.)  The table below
       shows the relation between POSIX character classes and these
       counterparts.

       One counterpart, in the column labelled "ASCII-range Unicode" in the
       table, matches only characters in the ASCII character set.

       The other counterpart, in the column labelled "Full-range Unicode",
       matches any appropriate characters in the full Unicode character set.
       For example, "\p{Alpha}" matches not just the ASCII alphabetic
       characters, but any character in the entire Unicode character set
       considered alphabetic.  An entry in the column labelled "backslash
       sequence" is a (short) equivalent.

        [[:...:]]      ASCII-range          Full-range  backslash  Note
                        Unicode              Unicode     sequence
        -----------------------------------------------------
          alpha      \p{PosixAlpha}       \p{XPosixAlpha}
          alnum      \p{PosixAlnum}       \p{XPosixAlnum}
          ascii      \p{ASCII}
          blank      \p{PosixBlank}       \p{XPosixBlank}  \h      [1]
                                          or \p{HorizSpace}        [1]
          cntrl      \p{PosixCntrl}       \p{XPosixCntrl}          [2]
          digit      \p{PosixDigit}       \p{XPosixDigit}  \d
          graph      \p{PosixGraph}       \p{XPosixGraph}          [3]
          lower      \p{PosixLower}       \p{XPosixLower}
          print      \p{PosixPrint}       \p{XPosixPrint}          [4]
          punct      \p{PosixPunct}       \p{XPosixPunct}          [5]
                     \p{PerlSpace}        \p{XPerlSpace}   \s      [6]
          space      \p{PosixSpace}       \p{XPosixSpace}          [6]
          upper      \p{PosixUpper}       \p{XPosixUpper}
          word       \p{PosixWord}        \p{XPosixWord}   \w
          xdigit     \p{PosixXDigit}      \p{XPosixXDigit}

       [1] "\p{Blank}" and "\p{HorizSpace}" are synonyms.

       [2] Control characters don't produce output as such, but instead
           usually control the terminal somehow: for example, newline and
           backspace are control characters.  In the ASCII range, characters
           non-controls, non-alphanumeric, non-space characters:
           "[-!"#$%&'()*+,./:;<=>?@[\\\]^_`{|}~]" (although if a locale is in
           effect, it could alter the behavior of "[[:punct:]]").

           The similarly named property, "\p{Punct}", matches a somewhat
           different set in the ASCII range, namely
           "[-!"#%&'()*,./:;?@[\\\]_{}]".  That is, it is missing the nine
           characters "[$+<=>^`|~]".  This is because Unicode splits what
           POSIX considers to be punctuation into two categories, Punctuation
           and Symbols.

           "\p{XPosixPunct}" and (under Unicode rules) "[[:punct:]]", match
           what "\p{PosixPunct}" matches in the ASCII range, plus what
           "\p{Punct}" matches.  This is different than strictly matching
           according to "\p{Punct}".  Another way to say it is that if Unicode
           rules are in effect, "[[:punct:]]" matches all characters that
           Unicode considers punctuation, plus all ASCII-range characters that
           Unicode considers symbols.

       [6] "\p{SpacePerl}" and "\p{Space}" match identically starting with
           Perl v5.18.  In earlier versions, these differ only in that in non-
           locale matching, "\p{SpacePerl}" does not match the vertical tab,
           "\cK".  Same for the two ASCII-only range forms.

       There are various other synonyms that can be used besides the names
       listed in the table.  For example, "\p{PosixAlpha}" can be written as
       "\p{Alpha}".  All are listed in "Properties accessible through \p{} and
       \P{}" in perluniprops, plus all characters matched by each ASCII-range
       property.

       Both the "\p" counterparts always assume Unicode rules are in effect.
       On ASCII platforms, this means they assume that the code points from
       128 to 255 are Latin-1, and that means that using them under locale
       rules is unwise unless the locale is guaranteed to be Latin-1 or UTF-8.
       In contrast, the POSIX character classes are useful under locale rules.
       They are affected by the actual rules in effect, as follows:

       If the "/a" modifier, is in effect ...
           Each of the POSIX classes matches exactly the same as their ASCII-
           range counterparts.

       otherwise ...
           For code points above 255 ...
               The POSIX class matches the same as its Full-range counterpart.

           For code points below 256 ...
               if locale rules are in effect ...
                   The POSIX class matches according to the locale, except
                   that "word" uses the platform's native underscore
                   character, no matter what the locale is.

               if Unicode rules are in effect ...
                   The POSIX class matches the same as the Full-range
                   counterpart.

       send email to "perl5-porters@perl.org".

       Negation of POSIX character classes

       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         ASCII-range     Full-range  backslash
                           Unicode         Unicode    sequence
        -----------------------------------------------------
        [[:^digit:]]   \P{PosixDigit}  \P{XPosixDigit}   \D
        [[:^space:]]   \P{PosixSpace}  \P{XPosixSpace}
                       \P{PerlSpace}   \P{XPerlSpace}    \S
        [[:^word:]]    \P{PerlWord}    \P{XPosixWord}    \W

       The backslash sequence can mean either ASCII- or Full-range Unicode,
       depending on various factors as described in "Which character set
       modifier is in effect?" in perlre.

       [= =] and [. .]

       Perl recognizes the POSIX character classes "[=class=]" and
       "[.class.]", but does not (yet?) support them.  Any attempt to use
       either construct raises an exception.

       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
                                 # except the letters 'a' to 'f' and 'A' to
                                 # 'F'.  This is because the main character
                                 # class is composed of two POSIX character
                                 # classes that are ORed together, one that
                                 # matches any digit, and the other that
                                 # matches anything that isn't a hex digit.
                                 # The OR adds the digits, leaving only the
                                 # letters 'a' to 'f' and 'A' to 'F' excluded.

       Extended Bracketed Character Classes

       This is a fancy bracketed character class that can be used for more
       readable and less error-prone classes, and to perform set operations,
       such as intersection. An example is

        /(?[ \p{Thai} & \p{Digit} ])/

       This will match all the digit characters that are in the Thai script.

       This is an experimental feature available starting in 5.18, and is
       subject to change as we gain field experience with it.  Any attempt to
       use it will raise a warning, unless disabled via
       Notice the white space in these examples.  This construct always has
       the "/x" modifier turned on.

       The available binary operators are:

        &    intersection
        +    union
        |    another name for '+', hence means union
        -    subtraction (the result matches the set consisting of those
             code points matched by the first operand, excluding any that
             are also matched by the second operand)
        ^    symmetric difference (the union minus the intersection).  This
             is like an exclusive or, in that the result is the set of code
             points that are matched by either, but not both, of the
             operands.

       There is one unary operator:

        !    complement

       All the binary operators left associate, and are of equal precedence.
       The unary operator right associates, and has higher precedence.  Use
       parentheses to override the default associations.  Some feedback we've
       received indicates a desire for intersection to have higher precedence
       than union.  This is something that feedback from the field may cause
       us to change in future releases; you may want to parenthesize copiously
       to avoid such changes affecting your code, until this feature is no
       longer considered experimental.

       The main restriction is that everything is a metacharacter.  Thus, you
       cannot refer to single characters by doing something like this:

        /(?[ a + b ])/ # Syntax error!

       The easiest way to specify an individual typable character is to
       enclose it in brackets:

        /(?[ [a] + [b] ])/

       (This is the same thing as "[ab]".)  You could also have said the
       equivalent:

        /(?[[ a b ]])/

       (You can, of course, specify single characters by using, "\x{ }", "\N{
       }", etc.)

       This last example shows the use of this construct to specify an
       ordinary bracketed character class without additional set operations.
       Note the white space within it; "/x" is turned on even within bracketed
       character classes, except you can't have comments inside them.  Hence,

        (?[ [#] ])


        /(?[ [ \xF ] ])/     # Syntax error!

       You have to have two hex digits after a braceless "\x" (use a leading
       zero to make two).  These restrictions are to lower the incidence of
       typos causing the class to not match what you thought it would.

       The final difference between regular bracketed character classes and
       these, is that it is not possible to get these to match a multi-
       character fold.  Thus,

        /(?[ [\xDF] ])/iu

       does not match the string "ss".

       You don't have to enclose POSIX class names inside double brackets,
       hence both of the following work:

        /(?[ [:word:] - [:lower:] ])/
        /(?[ [[:word:]] - [[:lower:]] ])/

       Any contained POSIX character classes, including things like "\w" and
       "\D" respect the "/a" (and "/aa") modifiers.

       "(?[ ])" is a regex-compile-time construct.  Any attempt to use
       something which isn't knowable at the time the containing regular
       expression is compiled is a fatal error.  In practice, this means just
       three limitiations:

       1.  This construct cannot be used within the scope of "use locale" (or
           the "/l" regex modifier).

       2.  Any user-defined property used must be already defined by the time
           the regular expression is compiled (but note that this construct
           can be used instead of such properties).

       3.  A regular expression that otherwise would compile using "/d" rules,
           and which uses this construct will instead use "/u".  Thus this
           construct tells Perl that you don't want "/d" rules for the entire
           regular expression containing it.

       The "/x" processing within this class is an extended form.  Besides the
       characters that are considered white space in normal "/x" processing,
       there are 5 others, recommended by the Unicode standard:

        U+0085 NEXT LINE
        U+200E LEFT-TO-RIGHT MARK
        U+200F RIGHT-TO-LEFT MARK
        U+2028 LINE SEPARATOR
        U+2029 PARAGRAPH SEPARATOR

       Note that skipping white space applies only to the interior of this
       construct.  There must not be any space between any of the characters
       that form the initial "(?[".  Nor may there be space between the

        qr/(?[ \p{Digit} & \p{Thai} + \p{Lao} ])/;

       But this does not have the effect that someone reading the code would
       likely expect, as the intersection applies just to "\p{Thai}",
       excluding the Laotian.  Pitfalls like this can be avoided by
       parenthesizing the component pieces:

        my $thai_or_lao = '( \p{Thai} + \p{Lao} )';

       But any modifiers will still apply to all the components:

        my $lower = '\p{Lower} + \p{Digit}';
        qr/(?[ \p{Greek} & $lower ])/i;

       matches upper case things.  You can avoid surprises by making the
       components into instances of this construct by compiling them:

        my $thai_or_lao = qr/(?[ \p{Thai} + \p{Lao} ])/;
        my $lower = qr/(?[ \p{Lower} + \p{Digit} ])/;

       When these are embedded in another pattern, what they match does not
       change, regardless of parenthesization or what modifiers are in effect
       in that outer pattern.

       Due to the way that Perl parses things, your parentheses and brackets
       may need to be balanced, even including comments.  If you run into any
       examples, please send them to "perlbug@perl.org", so that we can have a
       concrete example for this man page.

       We may change it so that things that remain legal uses in normal
       bracketed character classes might become illegal within this
       experimental construct.  One proposal, for example, is to forbid
       adjacent uses of the same character, as in "(?[ [aa] ])".  The
       motivation for such a change is that this usage is likely a typo, as
       the second "a" adds nothing.



perl v5.18.2                      2014-01-06                PERLRECHARCLASS(1)
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