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A regexp can accommodate for the variations found in the wikitext allowed by the permissions of wikilinks: 1) the metacharacter * allows for "zero or more" space characters before and after the title, and 2) the [character class] at the beginning allows for the relaxed capitalization of the first character in any pagename, and 3) the character ...
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 .
List of regular expression libraries Name Official website Programming language Software license Used by Boost.Regex [Note 1] Boost C++ Libraries: C++: Boost: Notepad++ >= 6.0.0, EmEditor: Boost.Xpressive Boost C++ Libraries: C++ Boost DEELX RegExLab: C++ Proprietary FREJ [Note 2] Fuzzy Regular Expressions for Java: Java: LGPL GLib/GRegex [Note ...
A generalized regular expression can be one of the following (where a is a symbol of the alphabet A, and R and S are generalized regular expressions): "∅" denotes the empty set: L(∅) = {}, "ε" denotes the singleton set containing the empty string: L(ε) = {ε}, "a" denotes the singleton set containing the single-symbol string a: L(a) = {a},
RE2 is a software library which implements a regular expression engine. It uses finite-state machines, in contrast to most other regular expression libraries. RE2 supports a C++ interface. RE2 was implemented by Google and Google uses RE2 for Google products. [3]
In theoretical computer science and formal language theory, a regular language (also called a rational language) [1] [2] is a formal language that can be defined by a regular expression, in the strict sense in theoretical computer science (as opposed to many modern regular expression engines, which are augmented with features that allow the recognition of non-regular languages).
Perl Compatible Regular Expressions (PCRE) is a library written in C, which implements a regular expression engine, inspired by the capabilities of the Perl programming language. Philip Hazel started writing PCRE in summer 1997. [ 3 ]
For every long enough string in a regular language, there must be a middle section that can be repeated (or pumped) any number of times to produce a string still in the language. In the theory of formal languages , the pumping lemma for regular languages is a lemma that describes an essential property of all regular languages .