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The general problem of matching any number of backreferences is NP-complete, and the execution time for known algorithms grows exponentially by the number of backreference groups used. [45] However, many tools, libraries, and engines that provide such constructions still use the term regular expression for their patterns.
A regex search scans the text of each page on Wikipedia in real time, character by character, to find pages that match a specific sequence or pattern of characters. Unlike keyword searching, regex searching is by default case-sensitive, does not ignore punctuation, and operates directly on the page source (MediaWiki markup) rather than on the ...
Greed, in regular expression context, describes the number of characters which will be matched (often also stated as "consumed") by a variable length portion of a regular expression – a token or group followed by a quantifier, which specifies a number (or range of numbers) of tokens. If the portion of the regular expression is "greedy", it ...
In regular expressions, the period (., also called "dot") is the wildcard pattern which matches any single character. Combined with the asterisk operator .* it will match any number of any characters. In this case, the asterisk is also known as the Kleene star.
matches any number of any characters including none Law* Law, Laws, or Lawyer: GrokLaw, La, or aw *Law* Law, GrokLaw, or Lawyer. La, or aw? matches any single character ?at: Cat, cat, Bat or bat: at [abc] matches one character given in the bracket [CB]at: Cat or Bat: cat, bat or CBat [a-z] matches one character from the (locale-dependent) range ...
Sed regular expressions, particularly those using the "s" operator, are much similar to Perl (sed is a predecessor to Perl). The default delimiter is "/", but any delimiter can be used; the default is s / regexp / replacement /, but s: regexp: replacement: is also a valid form. For example, to match a "pub" directory (as in the Perl example ...
a (where a is any character in Σ; denoting the singleton set just containing the single-character string a), ¬a (denoting any other single character in Σ except a), • (denoting any single character in Σ) a *, (¬a) *, or • * (denoting arbitrarily many, possibly zero, repetitions of characters from the set of a, ¬a, or •, respectively ...
re2c uses the following syntax for regular expressions: "foo" case-sensitive string literal 'foo' case-insensitive string literal [a-xyz], [^a-xyz] character class (possibly negated). any character except newline; R \ S difference of character classes; R* zero or more occurrences of R; R+ one or more occurrences of R; R? zero or one occurrence of R