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A regular expression (shortened as regex or regexp), [1] sometimes referred to as rational expression, [2] [3] is a sequence of characters that specifies a match pattern in text. Usually such patterns are used by string-searching algorithms for "find" or "find and replace" operations on strings , or for input validation .
Raku rules are the regular expression, string matching and general-purpose parsing facility of the Raku programming language, and are a core part of the language. Since Perl's pattern-matching constructs have exceeded the capabilities of formal regular expressions for some time, Raku documentation refers to them exclusively as regexes, distancing the term from the formal definition.
Replaces matches of multiple patterns in a given string with given replacements. For each replacement instance, the pattern matching at the lowest position is chosen. If there are multiple such patterns, then the one specified earliest in the pattern list is chosen.
Oniguruma (鬼車) is a free and open-source regular expression library that supports a variety of character encodings, written by K. Kosako.The Ruby programming language, in version 1.9, as well as PHP's multi-byte string module (since PHP5), use Oniguruma as their regular expression engine. [2]
The closeness of a match is measured in terms of the number of primitive operations necessary to convert the string into an exact match. This number is called the edit distance between the string and the pattern. The usual primitive operations are: [1] insertion: cot → coat; deletion: coat → cot; substitution: coat → cost
However, it is a useful algorithm for multiple pattern search. To find any of a large number, say k, fixed length patterns in a text, a simple variant of the Rabin–Karp algorithm uses a Bloom filter or a set data structure to check whether the hash of a given string belongs to a set of hash values of patterns we are looking for:
The pcregrep command is an implementation of grep that uses Perl regular expression syntax. [17] Similar functionality can be invoked in the GNU version of grep with the -P flag. [18] Ports of grep (within Cygwin and GnuWin32, for example) also run under Microsoft Windows. Some versions of Windows feature the similar qgrep or findstr command. [19]
Trigram search is a method of searching for text when the exact syntax or spelling of the target object is not precisely known [1] or when queries may be regular expressions. [2] It finds objects which match the maximum number of three consecutive character strings (i.e. trigrams) in the entered search terms, which are generally near matches. [3]