{"id":303,"date":"2007-10-08T00:00:00","date_gmt":"2007-10-08T00:00:00","guid":{"rendered":"http:\/\/www.strongd.net\/?p=303"},"modified":"2007-10-08T00:00:00","modified_gmt":"2007-10-08T00:00:00","slug":"Summary of regular-expression constructs ","status":"publish","type":"post","link":"https:\/\/www.strongd.net\/?p=303","title":{"rendered":"Summary of regular-expression constructs"},"content":{"rendered":"


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Summary of regular-expression constructs <\/H4>
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Construct<\/TH>
\n		Matches<\/TH><\/TR>
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 <\/TH><\/TR>
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Characters<\/TH><\/TR>
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x<\/I><\/TD>
\n		The character x<\/I><\/TD><\/TR>
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\\\\<\/TT><\/TD>
\n		The backslash character<\/TD><\/TR>
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\\0<\/TT>n<\/I><\/TD>
\n		The character with octal value 0<\/TT>n<\/I> (0 <=<\/TT> n<\/I> <=<\/TT> 7)<\/TD><\/TR>
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\\0<\/TT>nn<\/I><\/TD>
\n		The character with octal value 0<\/TT>nn<\/I> (0 <=<\/TT> n<\/I> <=<\/TT> 7)<\/TD><\/TR>
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\\0<\/TT>mnn<\/I><\/TD>
\n		The character with octal value 0<\/TT>mnn<\/I> (0 <=<\/TT> m<\/I> <=<\/TT> 3, 0 <=<\/TT> n<\/I> <=<\/TT> 7)<\/TD><\/TR>
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\\x<\/TT>hh<\/I><\/TD>
\n		The character with hexadecimal value 0x<\/TT>hh<\/I><\/TD><\/TR>
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\\u<\/TT>hhhh<\/I><\/TD>
\n		The character with hexadecimal value 0x<\/TT>hhhh<\/I><\/TD><\/TR>
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\\t<\/TT><\/TD>
\n		The tab character (‘\\u0009’<\/TT>)<\/TD><\/TR>
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\\n<\/TT><\/TD>
\n		The newline (line feed) character (‘\\u000A’<\/TT>)<\/TD><\/TR>
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\\r<\/TT><\/TD>
\n		The carriage-return character (‘\\u000D’<\/TT>)<\/TD><\/TR>
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\\f<\/TT><\/TD>
\n		The form-feed character (‘\\u000C’<\/TT>)<\/TD><\/TR>
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\\a<\/TT><\/TD>
\n		The alert (bell) character (‘\\u0007’<\/TT>)<\/TD><\/TR>
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\\e<\/TT><\/TD>
\n		The escape character (‘\\u001B’<\/TT>)<\/TD><\/TR>
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\\c<\/TT>x<\/I><\/TD>
\n		The control character corresponding to x<\/I><\/TD><\/TR>
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 <\/TH><\/TR>
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Character classes<\/TH><\/TR>
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[abc]<\/TT><\/TD>
\n		a<\/TT>, b<\/TT>, or c<\/TT> (simple class)<\/TD><\/TR>
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[^abc]<\/TT><\/TD>
\n		Any character except a<\/TT>, b<\/TT>, or c<\/TT> (negation)<\/TD><\/TR>
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[a-zA-Z]<\/TT><\/TD>
\n		a<\/TT> through z<\/TT> or A<\/TT> through Z<\/TT>, inclusive (range)<\/TD><\/TR>
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[a-d[m-p]]<\/TT><\/TD>
\n		a<\/TT> through d<\/TT>, or m<\/TT> through p<\/TT>: [a-dm-p]<\/TT> (union)<\/TD><\/TR>
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[a-z&&[def]]<\/TT><\/TD>
\n		d<\/TT>, e<\/TT>, or f<\/TT> (intersection)<\/TD>
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[a-z&&[^bc]]<\/TT><\/TD>
\n		a<\/TT> through z<\/TT>, except for b<\/TT> and c<\/TT>: [ad-z]<\/TT> (subtraction)<\/TD><\/TR>
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[a-z&&[^m-p]]<\/TT><\/TD>
\n		a<\/TT> through z<\/TT>, and not m<\/TT> through p<\/TT>: [a-lq-z]<\/TT>(subtraction)<\/TD><\/TR>
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 <\/TH><\/TR>
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Predefined character classes<\/TH><\/TR>
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.<\/TT><\/TD>
\n		Any character (may or may not match line terminators<\/A>)<\/TD><\/TR>
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\\d<\/TT><\/TD>
\n		A digit: [0-9]<\/TT><\/TD><\/TR>
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\\D<\/TT><\/TD>
\n		A non-digit: [^0-9]<\/TT><\/TD><\/TR>
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\\s<\/TT><\/TD>
\n		A whitespace character: [ \\t\\n\\x0B\\f\\r]<\/TT><\/TD><\/TR>
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\\S<\/TT><\/TD>
\n		A non-whitespace character: [^\\s]<\/TT><\/TD><\/TR>
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\\w<\/TT><\/TD>
\n		A word character: [a-zA-Z_0-9]<\/TT><\/TD><\/TR>
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\\W<\/TT><\/TD>
\n		A non-word character: [^\\w]<\/TT><\/TD><\/TR>
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 <\/TH><\/TR>
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POSIX character classes<\/B> (US-ASCII only)<\/B><\/TH><\/TR>
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\\p{Lower}<\/TT><\/TD>
\n		A lower-case alphabetic character: [a-z]<\/TT><\/TD><\/TR>
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\\p{Upper}<\/TT><\/TD>
\n		An upper-case alphabetic character:[A-Z]<\/TT><\/TD><\/TR>
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\\p{ASCII}<\/TT><\/TD>
\n		All ASCII:[\\x00-\\x7F]<\/TT><\/TD><\/TR>
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\\p{Alpha}<\/TT><\/TD>
\n		An alphabetic character:[\\p{Lower}\\p{Upper}]<\/TT><\/TD><\/TR>
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\\p{Digit}<\/TT><\/TD>
\n		A decimal digit: [0-9]<\/TT><\/TD><\/TR>
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\\p{Alnum}<\/TT><\/TD>
\n		An alphanumeric character:[\\p{Alpha}\\p{Digit}]<\/TT><\/TD><\/TR>
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\\p{Punct}<\/TT><\/TD>
\n		Punctuation: One of !”#$%&'()*+,-.\/:;<=>?@[\\]^_`{|}~<\/TT><\/TD><\/TR>
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\\p{Graph}<\/TT><\/TD>
\n		A visible character: [\\p{Alnum}\\p{Punct}]<\/TT><\/TD><\/TR>
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\\p{Print}<\/TT><\/TD>
\n		A printable character: [\\p{Graph}]<\/TT><\/TD><\/TR>
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\\p{Blank}<\/TT><\/TD>
\n		A space or a tab: [ \\t]<\/TT><\/TD><\/TR>
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\\p{Cntrl}<\/TT><\/TD>
\n		A control character: [\\x00-\\x1F\\x7F]<\/TT><\/TD><\/TR>
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\\p{XDigit}<\/TT><\/TD>
\n		A hexadecimal digit: [0-9a-fA-F]<\/TT><\/TD><\/TR>
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\\p{Space}<\/TT><\/TD>
\n		A whitespace character: [ \\t\\n\\x0B\\f\\r]<\/TT><\/TD><\/TR>
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 <\/TH><\/TR>
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Classes for Unicode blocks and categories<\/TH><\/TR>
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\\p{InGreek}<\/TT><\/TD>
\n		A character in the Greek block (simple block<\/A>)<\/TD><\/TR>
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\\p{Lu}<\/TT><\/TD>
\n		An uppercase letter (simple category<\/A>)<\/TD><\/TR>
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\\p{Sc}<\/TT><\/TD>
\n		A currency symbol<\/TD><\/TR>
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\\P{InGreek}<\/TT><\/TD>
\n		Any character except one in the Greek block (negation)<\/TD><\/TR>
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[\\p{L}&&[^\\p{Lu}]] <\/TT><\/TD>
\n		Any letter except an uppercase letter (subtraction)<\/TD><\/TR>
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 <\/TH><\/TR>
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Boundary matchers<\/TH><\/TR>
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^<\/TT><\/TD>
\n		The beginning of a line<\/TD><\/TR>
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$<\/TT><\/TD>
\n		The end of a line<\/TD><\/TR>
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\\b<\/TT><\/TD>
\n		A word boundary<\/TD><\/TR>
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\\B<\/TT><\/TD>
\n		A non-word boundary<\/TD><\/TR>
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\\A<\/TT><\/TD>
\n		The beginning of the input<\/TD><\/TR>
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\\G<\/TT><\/TD>
\n		The end of the previous match<\/TD><\/TR>
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\\Z<\/TT><\/TD>
\n		The end of the input but for the final terminator<\/A>, if any<\/TD><\/TR>
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\\z<\/TT><\/TD>
\n		The end of the input<\/TD><\/TR>
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 <\/TH><\/TR>
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Greedy quantifiers<\/TH><\/TR>
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X<\/I>?<\/TT><\/TD>
\n		X<\/I>, once or not at all<\/TD><\/TR>
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X<\/I>*<\/TT><\/TD>
\n		X<\/I>, zero or more times<\/TD><\/TR>
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X<\/I>+<\/TT><\/TD>
\n		X<\/I>, one or more times<\/TD><\/TR>
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X<\/I>{<\/TT>n<\/I>}<\/TT><\/TD>
\n		X<\/I>, exactly n<\/I> times<\/TD><\/TR>
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X<\/I>{<\/TT>n<\/I>,}<\/TT><\/TD>
\n		X<\/I>, at least n<\/I> times<\/TD><\/TR>
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X<\/I>{<\/TT>n<\/I>,<\/TT>m<\/I>}<\/TT><\/TD>
\n		X<\/I>, at least n<\/I> but not more than m<\/I> times<\/TD><\/TR>
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 <\/TH><\/TR>
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Reluctant quantifiers<\/TH><\/TR>
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X<\/I>??<\/TT><\/TD>
\n		X<\/I>, once or not at all<\/TD><\/TR>
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X<\/I>*?<\/TT><\/TD>
\n		X<\/I>, zero or more times<\/TD><\/TR>
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X<\/I>+?<\/TT><\/TD>
\n		X<\/I>, one or more times<\/TD><\/TR>
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X<\/I>{<\/TT>n<\/I>}?<\/TT><\/TD>
\n		X<\/I>, exactly n<\/I> times<\/TD><\/TR>
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X<\/I>{<\/TT>n<\/I>,}?<\/TT><\/TD>
\n		X<\/I>, at least n<\/I> times<\/TD><\/TR>
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X<\/I>{<\/TT>n<\/I>,<\/TT>m<\/I>}?<\/TT><\/TD>
\n		X<\/I>, at least n<\/I> but not more than m<\/I> times<\/TD><\/TR>
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 <\/TH><\/TR>
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Possessive quantifiers<\/TH><\/TR>
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X<\/I>?+<\/TT><\/TD>
\n		X<\/I>, once or not at all<\/TD><\/TR>
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X<\/I>*+<\/TT><\/TD>
\n		X<\/I>, zero or more times<\/TD><\/TR>
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X<\/I>++<\/TT><\/TD>
\n		X<\/I>, one or more times<\/TD><\/TR>
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X<\/I>{<\/TT>n<\/I>}+<\/TT><\/TD>
\n		X<\/I>, exactly n<\/I> times<\/TD><\/TR>
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X<\/I>{<\/TT>n<\/I>,}+<\/TT><\/TD>
\n		X<\/I>, at least n<\/I> times<\/TD><\/TR>
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X<\/I>{<\/TT>n<\/I>,<\/TT>m<\/I>}+<\/TT><\/TD>
\n		X<\/I>, at least n<\/I> but not more than m<\/I> times<\/TD><\/TR>
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 <\/TH><\/TR>
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Logical operators<\/TH><\/TR>
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XY<\/I><\/TD>
\n		X<\/I> followed by Y<\/I><\/TD><\/TR>
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X<\/I>|<\/TT>Y<\/I><\/TD>
\n		Either X<\/I> or Y<\/I><\/TD><\/TR>
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(<\/TT>X<\/I>)<\/TT><\/TD>
\n		X, as a capturing group<\/A><\/TD><\/TR>
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 <\/TH><\/TR>
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Back references<\/TH><\/TR>
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\\<\/TT>n<\/I><\/TD>
\n		Whatever the n<\/I>th<\/SUP> capturing group<\/A> matched<\/TD><\/TR>
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 <\/TH><\/TR>
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Quotation<\/TH><\/TR>
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\\<\/TT><\/TD>
\n		Nothing, but quotes the following character<\/TT><\/TD><\/TR>
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\\Q<\/TT><\/TD>
\n		Nothing, but quotes all characters until \\E<\/TT><\/TD><\/TR>
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\\E<\/TT><\/TD>
\n		Nothing, but ends quoting started by \\Q<\/TT><\/TD><\/TR>
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 <\/TH><\/TR>
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Special constructs (non-capturing)<\/TH><\/TR>
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(?:<\/TT>X<\/I>)<\/TT><\/TD>
\n		X<\/I>, as a non-capturing group<\/TD><\/TR>
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(?idmsux-idmsux) <\/TT><\/TD>
\n		Nothing, but turns match flags on – off<\/TD><\/TR>
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(?idmsux-idmsux:<\/TT>X<\/I>)<\/TT>  <\/TD>
\n		X<\/I>, as a non-capturing group<\/A> with the given flags on – off<\/TD><\/TR>
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(?=<\/TT>X<\/I>)<\/TT><\/TD>
\n		X<\/I>, via zero-width positive lookahead<\/TD><\/TR>
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(?!<\/TT>X<\/I>)<\/TT><\/TD>
\n		X<\/I>, via zero-width negative lookahead<\/TD><\/TR>
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(?<=<\/TT>X<\/I>)<\/TT><\/TD>
\n		X<\/I>, via zero-width positive lookbehind<\/TD><\/TR>
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(?<!<\/TT>X<\/I>)<\/TT><\/TD>
\n		X<\/I>, via zero-width negative lookbehind<\/TD><\/TR>
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(?><\/TT>X<\/I>)<\/TT><\/TD>
\n		X<\/I>, as an independent, non-capturing group<\/TD><\/TR><\/TBODY><\/TABLE>
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Backslashes, escapes, and quoting <\/H4>
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The backslash character (‘\\’<\/TT>) serves to introduce escaped constructs, as defined in the table above, as well as to quote characters that otherwise would be interpreted as unescaped constructs. Thus the expression \\\\<\/TT> matches a single backslash and \\{<\/TT> matches a left brace.
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It is an error to use a backslash prior to any alphabetic character that does not denote an escaped construct; these are reserved for future extensions to the regular-expression language. A backslash may be used prior to a non-alphabetic character regardless of whether that character is part of an unescaped construct.
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Backslashes within string literals in Java source code are interpreted as required by the Java Language Specification<\/A> as either Unicode escapes<\/A> or other character escapes<\/A>. It is therefore necessary to double backslashes in string literals that represent regular expressions to protect them from interpretation by the Java bytecode compiler. The string literal “\\b”<\/TT>, for example, matches a single backspace character when interpreted as a regular expression, while “\\\\b”<\/TT> matches a word boundary. The string literal “\\(hello\\)”<\/TT> is illegal and leads to a compile-time error; in order to match the string (hello)<\/TT> the string literal “\\\\(hello\\\\)”<\/TT> must be used.
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Character Classes <\/H4>
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Character classes may appear within other character classes, and may be composed by the union operator (implicit) and the intersection operator (&&<\/TT>). The union operator denotes a class that contains every character that is in at least one of its operand classes. The intersection operator denotes a class that contains every character that is in both of its operand classes.
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The precedence of character-class operators is as follows, from highest to lowest:
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1    <\/TH>
\n		Literal escape    <\/TD>
\n		\\x<\/TT><\/TD><\/TR>
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2    <\/TH>
\n		Grouping<\/TD>
\n		[…]<\/TT><\/TD><\/TR>
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3    <\/TH>
\n		Range<\/TD>
\n		a-z<\/TT><\/TD><\/TR>
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4    <\/TH>
\n		Union<\/TD>
\n		[a-e][i-u]<\/TT><\/TT><\/TD><\/TR>
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5    <\/TH>
\n		Intersection<\/TD>
\n		[a-z&&[aeiou]]<\/TT><\/TD><\/TR><\/TBODY><\/TABLE><\/BLOCKQUOTE>
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Note that a different set of metacharacters are in effect inside a character class than outside a character class. For instance, the regular expression .<\/TT> loses its special meaning inside a character class, while the expression –<\/TT> becomes a range forming metacharacter.
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Line terminators <\/H4>
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A line terminator<\/I> is a one- or two-character sequence that marks the end of a line of the input character sequence. The following are recognized as line terminators:
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