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@ -9,123 +9,132 @@ Package syntax parses regular expressions into parse trees and compiles |
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parse trees into programs. Most clients of regular expressions will use the |
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facilities of package regexp (such as Compile and Match) instead of this package. |
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Syntax |
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# Syntax |
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The regular expression syntax understood by this package when parsing with the Perl flag is as follows. |
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Parts of the syntax can be disabled by passing alternate flags to Parse. |
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Single characters: |
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. any character, possibly including newline (flag s=true) |
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[xyz] character class |
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[^xyz] negated character class |
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\d Perl character class |
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\D negated Perl character class |
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[[:alpha:]] ASCII character class |
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[[:^alpha:]] negated ASCII character class |
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\pN Unicode character class (one-letter name) |
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\p{Greek} Unicode character class |
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\PN negated Unicode character class (one-letter name) |
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\P{Greek} negated Unicode character class |
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. any character, possibly including newline (flag s=true) |
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[xyz] character class |
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[^xyz] negated character class |
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\d Perl character class |
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\D negated Perl character class |
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[[:alpha:]] ASCII character class |
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[[:^alpha:]] negated ASCII character class |
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\pN Unicode character class (one-letter name) |
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\p{Greek} Unicode character class |
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\PN negated Unicode character class (one-letter name) |
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\P{Greek} negated Unicode character class |
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Composites: |
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xy x followed by y |
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x|y x or y (prefer x) |
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xy x followed by y |
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x|y x or y (prefer x) |
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Repetitions: |
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x* zero or more x, prefer more |
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x+ one or more x, prefer more |
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x? zero or one x, prefer one |
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x{n,m} n or n+1 or ... or m x, prefer more |
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x{n,} n or more x, prefer more |
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x{n} exactly n x |
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x*? zero or more x, prefer fewer |
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x+? one or more x, prefer fewer |
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x?? zero or one x, prefer zero |
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x{n,m}? n or n+1 or ... or m x, prefer fewer |
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x{n,}? n or more x, prefer fewer |
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x{n}? exactly n x |
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x* zero or more x, prefer more |
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x+ one or more x, prefer more |
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x? zero or one x, prefer one |
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x{n,m} n or n+1 or ... or m x, prefer more |
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x{n,} n or more x, prefer more |
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x{n} exactly n x |
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x*? zero or more x, prefer fewer |
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x+? one or more x, prefer fewer |
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x?? zero or one x, prefer zero |
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x{n,m}? n or n+1 or ... or m x, prefer fewer |
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x{n,}? n or more x, prefer fewer |
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x{n}? exactly n x |
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Implementation restriction: The counting forms x{n,m}, x{n,}, and x{n} |
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reject forms that create a minimum or maximum repetition count above 1000. |
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Unlimited repetitions are not subject to this restriction. |
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Grouping: |
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(re) numbered capturing group (submatch) |
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(?P<name>re) named & numbered capturing group (submatch) |
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(?:re) non-capturing group |
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(?flags) set flags within current group; non-capturing |
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(?flags:re) set flags during re; non-capturing |
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Flag syntax is xyz (set) or -xyz (clear) or xy-z (set xy, clear z). The flags are: |
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(re) numbered capturing group (submatch) |
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(?P<name>re) named & numbered capturing group (submatch) |
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(?:re) non-capturing group |
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(?flags) set flags within current group; non-capturing |
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(?flags:re) set flags during re; non-capturing |
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Flag syntax is xyz (set) or -xyz (clear) or xy-z (set xy, clear z). The flags are: |
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i case-insensitive (default false) |
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m multi-line mode: ^ and $ match begin/end line in addition to begin/end text (default false) |
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s let . match \n (default false) |
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U ungreedy: swap meaning of x* and x*?, x+ and x+?, etc (default false) |
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i case-insensitive (default false) |
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m multi-line mode: ^ and $ match begin/end line in addition to begin/end text (default false) |
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s let . match \n (default false) |
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U ungreedy: swap meaning of x* and x*?, x+ and x+?, etc (default false) |
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Empty strings: |
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^ at beginning of text or line (flag m=true) |
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$ at end of text (like \z not \Z) or line (flag m=true) |
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\A at beginning of text |
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\b at ASCII word boundary (\w on one side and \W, \A, or \z on the other) |
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\B not at ASCII word boundary |
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\z at end of text |
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^ at beginning of text or line (flag m=true) |
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$ at end of text (like \z not \Z) or line (flag m=true) |
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\A at beginning of text |
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\b at ASCII word boundary (\w on one side and \W, \A, or \z on the other) |
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\B not at ASCII word boundary |
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\z at end of text |
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Escape sequences: |
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\a bell (== \007) |
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\f form feed (== \014) |
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\t horizontal tab (== \011) |
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\n newline (== \012) |
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\r carriage return (== \015) |
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\v vertical tab character (== \013) |
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\* literal *, for any punctuation character * |
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\123 octal character code (up to three digits) |
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\x7F hex character code (exactly two digits) |
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\x{10FFFF} hex character code |
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\Q...\E literal text ... even if ... has punctuation |
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\a bell (== \007) |
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\f form feed (== \014) |
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\t horizontal tab (== \011) |
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\n newline (== \012) |
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\r carriage return (== \015) |
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\v vertical tab character (== \013) |
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\* literal *, for any punctuation character * |
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\123 octal character code (up to three digits) |
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\x7F hex character code (exactly two digits) |
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\x{10FFFF} hex character code |
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\Q...\E literal text ... even if ... has punctuation |
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Character class elements: |
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x single character |
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A-Z character range (inclusive) |
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\d Perl character class |
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[:foo:] ASCII character class foo |
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\p{Foo} Unicode character class Foo |
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\pF Unicode character class F (one-letter name) |
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x single character |
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A-Z character range (inclusive) |
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\d Perl character class |
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[:foo:] ASCII character class foo |
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\p{Foo} Unicode character class Foo |
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\pF Unicode character class F (one-letter name) |
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Named character classes as character class elements: |
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[\d] digits (== \d) |
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[^\d] not digits (== \D) |
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[\D] not digits (== \D) |
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[^\D] not not digits (== \d) |
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[[:name:]] named ASCII class inside character class (== [:name:]) |
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[^[:name:]] named ASCII class inside negated character class (== [:^name:]) |
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[\p{Name}] named Unicode property inside character class (== \p{Name}) |
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[^\p{Name}] named Unicode property inside negated character class (== \P{Name}) |
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[\d] digits (== \d) |
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[^\d] not digits (== \D) |
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[\D] not digits (== \D) |
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[^\D] not not digits (== \d) |
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[[:name:]] named ASCII class inside character class (== [:name:]) |
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[^[:name:]] named ASCII class inside negated character class (== [:^name:]) |
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[\p{Name}] named Unicode property inside character class (== \p{Name}) |
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[^\p{Name}] named Unicode property inside negated character class (== \P{Name}) |
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Perl character classes (all ASCII-only): |
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\d digits (== [0-9]) |
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\D not digits (== [^0-9]) |
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\s whitespace (== [\t\n\f\r ]) |
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\S not whitespace (== [^\t\n\f\r ]) |
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\w word characters (== [0-9A-Za-z_]) |
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\W not word characters (== [^0-9A-Za-z_]) |
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\d digits (== [0-9]) |
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\D not digits (== [^0-9]) |
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\s whitespace (== [\t\n\f\r ]) |
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\S not whitespace (== [^\t\n\f\r ]) |
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\w word characters (== [0-9A-Za-z_]) |
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\W not word characters (== [^0-9A-Za-z_]) |
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ASCII character classes: |
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[[:alnum:]] alphanumeric (== [0-9A-Za-z]) |
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[[:alpha:]] alphabetic (== [A-Za-z]) |
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[[:ascii:]] ASCII (== [\x00-\x7F]) |
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[[:blank:]] blank (== [\t ]) |
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[[:cntrl:]] control (== [\x00-\x1F\x7F]) |
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[[:digit:]] digits (== [0-9]) |
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[[:graph:]] graphical (== [!-~] == [A-Za-z0-9!"#$%&'()*+,\-./:;<=>?@[\\\]^_`{|}~]) |
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[[:lower:]] lower case (== [a-z]) |
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[[:print:]] printable (== [ -~] == [ [:graph:]]) |
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[[:punct:]] punctuation (== [!-/:-@[-`{-~]) |
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[[:space:]] whitespace (== [\t\n\v\f\r ]) |
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[[:upper:]] upper case (== [A-Z]) |
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[[:word:]] word characters (== [0-9A-Za-z_]) |
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[[:xdigit:]] hex digit (== [0-9A-Fa-f]) |
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[[:alnum:]] alphanumeric (== [0-9A-Za-z]) |
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[[:alpha:]] alphabetic (== [A-Za-z]) |
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[[:ascii:]] ASCII (== [\x00-\x7F]) |
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[[:blank:]] blank (== [\t ]) |
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[[:cntrl:]] control (== [\x00-\x1F\x7F]) |
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[[:digit:]] digits (== [0-9]) |
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[[:graph:]] graphical (== [!-~] == [A-Za-z0-9!"#$%&'()*+,\-./:;<=>?@[\\\]^_`{|}~]) |
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[[:lower:]] lower case (== [a-z]) |
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[[:print:]] printable (== [ -~] == [ [:graph:]]) |
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[[:punct:]] punctuation (== [!-/:-@[-`{-~]) |
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[[:space:]] whitespace (== [\t\n\v\f\r ]) |
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[[:upper:]] upper case (== [A-Z]) |
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[[:word:]] word characters (== [0-9A-Za-z_]) |
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[[:xdigit:]] hex digit (== [0-9A-Fa-f]) |
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Unicode character classes are those in unicode.Categories and unicode.Scripts. |
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*/ |
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Danny Kopping
4 years ago
committed by