The order of group expressions is determined by the position of their opening parenthesis ‘ \(’. For example ‘ \2’ matches the second group expression. A backslash followed by a digit acts as a back-reference and matches the same thing as the previous grouped expression indicated by that number. Grouping is performed with backslashes followed by parentheses ‘ \(’, ‘ \)’. So Boost 1.47 and later have six variations of the backreference syntax on top of the basic 1 syntax. ‘ \'’ matches the end of the whole input Boost 1.47 allows named and numbered backreferences to be specified with g or k and with curly braces, angle brackets, or quotes.‘ \`’ matches the beginning of the whole input.‘ \B’ matches characters which are not a word boundary.‘ \W’ matches a character which is not within a word.‘ \w’ matches a character within a word.Character classes are supported for example ‘ ]’ will match a single decimal digit. Usually such patterns are used by string-searching algorithms for. Within square brackets, ‘ \’ is taken literally. A regular expression is a sequence of characters that specifies a match pattern in text. Bracket expressions where the range is backward, for example ‘ ’, are invalid. Indicates that the regular expression should match zero or one occurrence of the previous atom or regexp.īracket expressions are used to match ranges of characters. Indicates that the regular expression should match one or more occurrences of the previous atom or regexp. Next: posix-awk regular expression syntax, Previous: gnu-awk regular expression syntax, Up: Regular Expressions
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