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Character class

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NAME

perlrecharclass - Perl Regular Expression Character Classes

DESCRIPTION

The top level documentation about Perl regular expressionsis found in perlre.

This manual page discusses the syntax and use of characterclasses in Perl regular expressions.

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

There are three types of character classes in Perl regularexpressions: the dot, backslash sequences, and the form enclosed in squarebrackets. Keep in mind, though, that often the term "character class" is usedto mean just the bracketed form. Certainly, most Perl documentation does that.

The dot

The dot (or period), . is probably the most used, and certainlythe most well-known character class. By default, a dot matches anycharacter, except for the newline. That default can be changed toadd matching the newline by using the single line modifier: eitherfor the entire regular expression with the /s modifier, orlocally with (?s). (The experimental \N backslash sequence, describedbelow, matches any character except newline without regard to thesingle line modifier.)

Here are some examples:

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

Backslash sequences

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

Here's a list of the backslash sequences that are character classes. Theyare discussed in more detail below. (For the backslash sequences that aren'tcharacter classes, see perlrebackslash.)

  1. \d Match a decimal digit character.
  2. \D Match a non-decimal-digit character.
  3. \w Match a "word" character.
  4. \W Match a non-"word" character.
  5. \s Match a whitespace character.
  6. \S Match a non-whitespace character.
  7. \h Match a horizontal whitespace character.
  8. \H Match a character that isn't horizontal whitespace.
  9. \v Match a vertical whitespace character.
  10. \V Match a character that isn't vertical whitespace.
  11. \N Match a character that isn't a newline. Experimental.
  12. \pP, \p{Prop} Match a character that has the given Unicode property.
  13. \PP, \P{Prop} Match a character that doesn't have the Unicode property

\N

\N is new in 5.12, and is experimental. It, like the dot, matches anycharacter that is not a newline. The difference is that \N is not influencedby the single line regular expression modifier (see The dot above). Notethat the form \N{...} may mean something completely different. When the{...} is a quantifier, it means to match a non-newlinecharacter that many times. For example, \N{3} means to match 3non-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. Seecharnames for those. For example, none of \N{COLON}, \N{4F}, and\N{F4} contain legal quantifiers, so Perl will try to find characters whosenames 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, itmatches anything that is matched by \p{Digit}, which includes [0-9].(An unlikely possible exception is that under locale matching rules, thecurrent locale might not have [0-9] matched by \d, and/or might matchother characters whose code point is less than 256. Such a localedefinition would be in violation of the C language standard, but Perldoesn't currently assume anything in regard to this.)

What this means is that unless the /a modifier is in effect \d notonly matches the digits '0' - '9', but also Arabic, Devanagari, anddigits from other languages. This may cause some confusion, and somesecurity issues.

Some digits that \d matches look like some of the [0-9] ones, buthave different values. For example, BENGALI DIGIT FOUR (U+09EA) looksvery much like an ASCII DIGIT EIGHT (U+0038). An application thatis expecting only the ASCII digits might be misled, or if the match is\d+, the matched string might contain a mixture of digits fromdifferent writing systems that look like they signify a number differentthan they actually do. num() in Unicode::UCD canbe used to safelycalculate the value, returning undef if the input string containssuch a mixture.

What \p{Digit} means (and hence \d except under the /amodifier) is \p{General_Category=Decimal_Number}, or synonymously,\p{General_Category=Digit}. Starting with Unicode version 4.1, thisis 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 ofcharacters. These characters are things such as CIRCLED DIGIT ONEor subscripts, or are from writing systems that lack all ten digits.

The design intent is for \d to exactly match the set of charactersthat can safely be used with "normal" big-endian positional decimalsyntax, where, for example 123 means one 'hundred', plus two 'tens',plus three 'ones'. This positional notation does not necessarily applyto characters that match the other type of "digit",\p{Numeric_Type=Digit}, and so \d doesn't match them.

The Tamil digits (U+0BE6 - U+0BEF) can also legally beused in old-style Tamil numbers in which they would appear no more thanone in a row, separated by characters that mean "times 10", "times 100",etc. (See http://www.unicode.org/notes/tn21.)

Any character not matched by \d is matched by \D.

Word characters

A \w matches a single alphanumeric character (an alphabetic character, or adecimal digit) or a connecting punctuation character, such as anunderscore ("_"). It does not match a whole word. To match a wholeword, use \w+. This isn't the same thing as matching an English word, butin the ASCII range it is the same as a string of Perl-identifiercharacters.

  • 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 connectorpunctuation (like the underscore) which connect two words together, ordiacritics, such as a COMBINING TILDE and the modifier letters, whichare 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 whateverthe locale considers to be alphanumeric.

      • if Unicode rules are in effect or if on an EBCDIC platform ...

        \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 wordcharacters. See http://unicode.org/reports/tr36.

Also, for a somewhat finer-grained set of characters that are in programminglanguage identifiers beyond the ASCII range, you may wish to instead use themore customized Unicode Properties, \p{ID_Start},\p{ID_Continue}, \p{XID_Start}, and \p{XID_Continue}. Seehttp://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 ...

    \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. (Notethat it doesn't match the vertical tab, \cK on ASCII platforms.)

  • otherwise ...
    • For code points above 255 ...

      \s matches exactly the code points above 255 shown with an "s" columnin the table below.

    • For code points below 256 ...
      • if locale rules are in effect ...

        \s matches whatever the locale considers to be whitespace. Note thatthis is likely to include the vertical space, unlike non-locale \smatching.

      • if Unicode rules are in effect or if on an EBCDIC platform ...

        \s matches exactly the characters shown with an "s" column in thetable below.

      • otherwise ...

        \s matches [\t\n\f\r ].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 otherslisted in the table below. \H matches any characternot considered horizontal whitespace. They use the platform's nativecharacter set, and do not consider any locale that may otherwise be inuse.

\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 anylocale that may otherwise be in use.

\R matches anything that can be considered a newline under Unicoderules. It's not a character class, as it can match a multi-charactersequence. Therefore, it cannot be used inside a bracketed characterclass; use \v instead (vertical whitespace). It uses the platform'snative character set, and does not consider any locale that mayotherwise be in use.Details are discussed in perlrebackslash.

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

One might think that \s is equivalent to [\h\v]. This is not true.The difference is that the vertical tab ("\x0b") is not matched by\s; it is however considered vertical whitespace.

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 indicatesby which class(es) the character is matched (assuming no locale or EBCDIC codepage is in effect that changes the \s matching).

  1. 0x0009 CHARACTER TABULATION h s
  2. 0x000a LINE FEED (LF) vs
  3. 0x000b LINE TABULATION v
  4. 0x000c FORM FEED (FF) vs
  5. 0x000d CARRIAGE RETURN (CR) vs
  6. 0x0020 SPACE h s
  7. 0x0085 NEXT LINE (NEL) vs [1]
  8. 0x00a0 NO-BREAK SPACE h s [1]
  9. 0x1680 OGHAM SPACE MARK h s
  10. 0x180e MONGOLIAN VOWEL SEPARATOR h s
  11. 0x2000 EN QUAD h s
  12. 0x2001 EM QUAD h s
  13. 0x2002 EN SPACE h s
  14. 0x2003 EM SPACE h s
  15. 0x2004 THREE-PER-EM SPACE h s
  16. 0x2005 FOUR-PER-EM SPACE h s
  17. 0x2006 SIX-PER-EM SPACE h s
  18. 0x2007 FIGURE SPACE h s
  19. 0x2008 PUNCTUATION SPACE h s
  20. 0x2009 THIN SPACE h s
  21. 0x200a HAIR SPACE h s
  22. 0x2028 LINE SEPARATOR vs
  23. 0x2029 PARAGRAPH SEPARATOR vs
  24. 0x202f NARROW NO-BREAK SPACE h s
  25. 0x205f MEDIUM MATHEMATICAL SPACE h s
  26. 0x3000 IDEOGRAPHIC SPACE h s

Unicode Properties

\pP and \p{Prop} are character classes to match characters that fit givenUnicode 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 nameenclosed 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 whichhas 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 neither the /a modifier nor locale rules are in effect, the use ofa Unicode property will force the regular expression into using Unicoderules.

Note that almost all properties are immune to case-insensitive matching.That is, adding a /i regular expression modifier does not change whatthey match. There are two sets that are affected. The first set isUppercase_Letter,Lowercase_Letter,and Titlecase_Letter,all of which match Cased_Letter under /i matching.The second set isUppercase,Lowercase,and Titlecase,all of which match Cased under /i matching.(The difference between these sets is that some things, such as Romannumerals, come in both upper and lower case, so they are Cased, butaren't considered to be letters, so they aren't Cased_Letters. They'reactually Letter_Numbers.)This set also includes its subsets PosixUpper and PosixLower, bothof which under /i match PosixAlpha.

For more details on Unicode properties, see Unicode Character Properties in perlunicode; for acomplete list of possible properties, seeProperties accessible through \p{} and \P{} in perluniprops,which notes all forms that have /i differences.It is also possible to define your own properties. This is discussed inUser-Defined Character Properties in perlunicode.

Unicode properties are defined (surprise!) only on Unicode code points.A warning is raised and all matches fail on non-Unicode code points(those above the legal Unicode maximum of 0x10FFFF). This can besomewhat surprising,

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

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

Examples

  1. "a" =~ /\w/ # Match, "a" is a 'word' character.
  2. "7" =~ /\w/ # Match, "7" is a 'word' character as well.
  3. "a" =~ /\d/ # No match, "a" isn't a digit.
  4. "7" =~ /\d/ # Match, "7" is a digit.
  5. " " =~ /\s/ # Match, a space is whitespace.
  6. "a" =~ /\D/ # Match, "a" is a non-digit.
  7. "7" =~ /\D/ # No match, "7" is not a non-digit.
  8. " " =~ /\S/ # No match, a space is not non-whitespace.
  9. " " =~ /\h/ # Match, space is horizontal whitespace.
  10. " " =~ /\v/ # No match, space is not vertical whitespace.
  11. "\r" =~ /\v/ # Match, a return is vertical whitespace.
  12. "a" =~ /\pL/ # Match, "a" is a letter.
  13. "a" =~ /\p{Lu}/ # No match, /\p{Lu}/ matches upper case letters.
  14. "\x{0e0b}" =~ /\p{Thai}/ # Match, \x{0e0b} is the character
  15. # 'THAI CHARACTER SO SO', and that's in
  16. # Thai Unicode class.
  17. "a" =~ /\P{Lao}/ # Match, as "a" is not a Laotian character.

It is worth emphasizing that \d, \w, etc, match single characters, notcomplete numbers or words. To match a number (that consists of digits),use \d+; to match a word, use \w+. But be aware of the securityconsiderations in doing so, as mentioned above.

Bracketed Character Classes

The third form of character class you can use in Perl regular expressionsis the bracketed character class. In its simplest form, it lists the charactersthat may be matched, surrounded by square brackets, like this: [aeiou].This matches one of a, e, i, o or u. Like the othercharacter classes, exactly one character is matched.* To matcha longer string consisting of characters mentioned in the characterclass, follow the character class with a quantifier. Forinstance, [aeiou]+ matches one or more lowercase English vowels.

Repeating a character in a character class has noeffect; it's considered to be in the set only once.

Examples:

  1. "e" =~ /[aeiou]/ # Match, as "e" is listed in the class.
  2. "p" =~ /[aeiou]/ # No match, "p" is not listed in the class.
  3. "ae" =~ /^[aeiou]$/ # No match, a character class only matches
  4. # a single character.
  5. "ae" =~ /^[aeiou]+$/ # Match, due to the quantifier.
  6. -------

* There is an exception to a bracketed character class matching asingle character only. When the class is to match caselessly under /imatching rules, and a character inside the class matches amultiple-character sequence caselessly under Unicode rules, the class(when not inverted) will also match that sequence. Forexample, Unicode says that the letter LATIN SMALL LETTER SHARP Sshould match the sequence ss under /i rules. Thus,

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

Special Characters Inside a Bracketed Character Class

Most characters that are meta characters in regular expressions (thatis, characters that carry a special meaning like ., *, or () losetheir special meaning and can be used inside a character class withoutthe need to escape them. For instance, [()] matches either an openingparenthesis, or a closing parenthesis, and the parens inside the characterclass don't group or capture.

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

The sequence \b is special inside a bracketed character class. Whileoutside the character class, \b is an assertion indicating a pointthat does not have either two word characters or two non-word characterson either side, inside a bracketed character class, \b matches abackspace character.

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

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

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

A ] is normally either the end of a POSIX character class (seePOSIX Character Classes below), or it signals the end of the bracketedcharacter class. If you want to include a ] in the set of characters, youmust generally escape it.

However, if the ] is the first (or the second if the firstcharacter is a caret) character of a bracketed character class, itdoes 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 withoutescaping.

Examples:

  1. "+" =~ /[+?*]/ # Match, "+" in a character class is not special.
  2. "\cH" =~ /[\b]/ # Match, \b inside in a character class
  3. # is equivalent to a backspace.
  4. "]" =~ /[][]/ # Match, as the character class contains.
  5. # both [ and ].
  6. "[]" =~ /[[]]/ # Match, the pattern contains a character class
  7. # containing just ], and the character class is
  8. # followed by a ].

Character Ranges

It is not uncommon to want to match a range of characters. Luckily, insteadof listing all characters in the range, one may use the hyphen (-).If inside a bracketed character class you have two characters separatedby a hyphen, it's treated as if all characters between the two were inthe 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 notnecessarily both letters or both digits. Any character is possible,although not advisable. ['-?] contains a range of characters, butmost people will not know which characters that means. Furthermore,such ranges may lead to portability problems if the code has to run ona platform that uses a different character set, such as EBCDIC.

If a hyphen in a character class cannot syntactically be part of a range, forinstance 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 isconsidered a character to be matched literally. If you want a hyphen inyour set of characters to be matched and its position in the class is suchthat it could be considered part of a range, you must escape that hyphenwith a backslash.

Examples:

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

Negation

It is also possible to instead list the characters you do not want tomatch. You can do so by using a caret (^) as the first character in thecharacter class. For instance, [^a-z] matches any character that is not alowercase ASCII letter, which therefore includes more than a millionUnicode code points. The class is said to be "negated" or "inverted".

This syntax make the caret a special character inside a bracketed characterclass, but only if it is the first character of the class. So if you wantthe caret as one of the characters to match, either escape the caret orelse don't list it first.

In inverted bracketed character classes, Perl ignores the Unicode rulesthat normally say that certain characters should match a sequence ofmultiple characters under caseless /i matching. Following thoserules could lead to highly confusing situations:

  1. "ss" =~ /^[^\xDF]+$/ui; # Matches!

This should match any sequences of characters that aren't \xDF norwhat \xDF matches under /i. "s" isn't \xDF, but Unicodesays that "ss" is what \xDF matches under /i. So which one"wins"? Do you fail the match because the string has ss or accept itbecause it has an s followed by another s? Perl has chosen thelatter.

Examples:

  1. "e" =~ /[^aeiou]/ # No match, the 'e' is listed.
  2. "x" =~ /[^aeiou]/ # Match, as 'x' isn't a lowercase vowel.
  3. "^" =~ /[^^]/ # No match, matches anything that isn't a caret.
  4. "^" =~ /[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 justas if you had put all characters matched by the backslash sequence inside thecharacter class. For instance, [a-f\d] matches any decimal digit, or anyof 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 losesits special meaning: it matches nearly anything, which generally isn't what youwant to happen.

Examples:

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

Backslash sequence character classes cannot form one of the endpointsof a range. Thus, you can't say:

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

POSIX Character Classes

POSIX character classes have the form [:class:], where class isname, and the [: and :] delimiters. POSIX character classes only appearinside bracketed character classes, and are a convenient and descriptiveway of listing a group of characters.

Be careful about the syntax,

  1. # Correct:
  2. $string =~ /[[:alpha:]]/
  3. # Incorrect (will warn):
  4. $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 part of a larger bracketed character class.For example,

  1. [01[:alpha:]%]

is valid and matches '0', '1', any alphabetic character, and the percent sign.

Perl recognizes the following POSIX character classes:

  1. alpha Any alphabetical character ("[A-Za-z]").
  2. alnum Any alphanumeric character. ("[A-Za-z0-9]")
  3. ascii Any character in the ASCII character set.
  4. blank A GNU extension, equal to a space or a horizontal tab ("\t").
  5. cntrl Any control character. See Note [2] below.
  6. digit Any decimal digit ("[0-9]"), equivalent to "\d".
  7. graph Any printable character, excluding a space. See Note [3] below.
  8. lower Any lowercase character ("[a-z]").
  9. print Any printable character, including a space. See Note [4] below.
  10. punct Any graphical character excluding "word" characters. Note [5].
  11. space Any whitespace character. "\s" plus the vertical tab ("\cK").
  12. upper Any uppercase character ("[A-Z]").
  13. word A Perl extension ("[A-Za-z0-9_]"), equivalent to "\w".
  14. xdigit Any hexadecimal digit ("[0-9a-fA-F]").

Most POSIX character classes have two Unicode-style \p propertycounterparts. (They are not official Unicode properties, but Perl extensionsderived from official Unicode properties.) The table below shows the relationbetween POSIX character classes and these counterparts.

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

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

  1. [[:...:]] ASCII-range Full-range backslash Note
  2. Unicode Unicode sequence
  3. -----------------------------------------------------
  4. alpha \p{PosixAlpha} \p{XPosixAlpha}
  5. alnum \p{PosixAlnum} \p{XPosixAlnum}
  6. ascii \p{ASCII}
  7. blank \p{PosixBlank} \p{XPosixBlank} \h [1]
  8. or \p{HorizSpace} [1]
  9. cntrl \p{PosixCntrl} \p{XPosixCntrl} [2]
  10. digit \p{PosixDigit} \p{XPosixDigit} \d
  11. graph \p{PosixGraph} \p{XPosixGraph} [3]
  12. lower \p{PosixLower} \p{XPosixLower}
  13. print \p{PosixPrint} \p{XPosixPrint} [4]
  14. punct \p{PosixPunct} \p{XPosixPunct} [5]
  15. \p{PerlSpace} \p{XPerlSpace} \s [6]
  16. space \p{PosixSpace} \p{XPosixSpace} [6]
  17. upper \p{PosixUpper} \p{XPosixUpper}
  18. word \p{PosixWord} \p{XPosixWord} \w
  19. 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 controlthe terminal somehow: for example, newline and backspace are control characters.In the ASCII range, characters whose code points are between 0 and 31 inclusive,plus 127 (DEL) are control characters.

    On EBCDIC platforms, it is likely that the code page will define [[:cntrl:]]to be the EBCDIC equivalents of the ASCII controls, plus the controlsthat in Unicode have code pointss from 128 through 159.

  • [3]

    Any character that is graphical, that is, visible. This class consistsof all alphanumeric characters and all punctuation characters.

  • [4]

    All printable characters, which is the set of all graphical charactersplus those whitespace characters which are not also controls.

  • [5]

    \p{PosixPunct} and [[:punct:]] in the ASCII range match allnon-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 differentset in the ASCII range, namely[-!"#%&'()*,./:;?@[\]_{}]. That is, it is missing the ninecharacters [$+<=>^`|~].This is because Unicode splits what POSIX considers to be punctuation into twocategories, 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 thatif Unicode rules are in effect, [[:punct:]] matches all charactersthat Unicode considers punctuation, plus all ASCII-range characters thatUnicode considers symbols.

  • [6]

    \p{SpacePerl} and \p{Space} differ only in that in non-localematching, \p{Space} additionallymatches the vertical tab, \cK. Same for the two ASCII-only range forms.

There are various other synonyms that can be used besides the nameslisted in the table. For example, \p{PosixAlpha} can be written as\p{Alpha}. All are listed inProperties 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 128to 255 are Latin-1, and that means that using them under locale rules isunwise unless the locale is guaranteed to be Latin-1 or UTF-8. In contrast, thePOSIX character classes are useful under locale rules. They areaffected 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-rangecounterparts.

  • 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 thatword uses the platform's native underscore character, no matter whatthe locale is.

      • if Unicode rules are in effect or if on an EBCDIC platform ...

        The POSIX class matches the same as the Full-range counterpart.

      • otherwise ...

        The POSIX class matches the same as the ASCII range counterpart.

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

It is proposed to change this behavior in a future release of Perl so thatwhether or not Unicode rules are in effect would not change thebehavior: Outside of locale or an EBCDIC code page, the POSIX classeswould behave like their ASCII-range counterparts. If you wish tocomment on this proposal, send email to perl5-porters@perl.org.

Negation of POSIX character classes

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

  1. POSIX ASCII-range Full-range backslash
  2. Unicode Unicode sequence
  3. -----------------------------------------------------
  4. [[:^digit:]] \P{PosixDigit} \P{XPosixDigit} \D
  5. [[:^space:]] \P{PosixSpace} \P{XPosixSpace}
  6. \P{PerlSpace} \P{XPerlSpace} \S
  7. [[:^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 useeither construct raises an exception.

Examples

  1. /[[:digit:]]/ # Matches a character that is a digit.
  2. /[01[:lower:]]/ # Matches a character that is either a
  3. # lowercase letter, or '0' or '1'.
  4. /[[:digit:][:^xdigit:]]/ # Matches a character that can be anything
  5. # except the letters 'a' to 'f'. This is
  6. # because the main character class is composed
  7. # of two POSIX character classes that are ORed
  8. # together, one that matches any digit, and
  9. # the other that matches anything that isn't a
  10. # hex digit. The result matches all
  11. # characters except the letters 'a' to 'f' and
  12. # 'A' to 'F'.
 
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