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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 rendered contents of the page. To perform a regex search, use the ordinary search box with the syntax insource:/regex/ or intitle:/regex/.
In computer science, Thompson's construction algorithm, also called the McNaughton–Yamada–Thompson algorithm, [1] is a method of transforming a regular expression into an equivalent nondeterministic finite automaton (NFA). [2] This NFA can be used to match strings against the regular expression.
Normally searches ignore non-alphanumeric characters, but regular expressions (regex) accept all characters, plus metacharacters. This template acts as a doorway by helping to develop a database query before running it on the wiki, and it does this by way of a search link that can also be used to share such discoveries.
Regular expressions can often be created ("induced" or "learned") based on a set of example strings. This is known as the induction of regular languages and is part of the general problem of grammar induction in computational learning theory .
Regular expressions (or regex) are a common and very versatile programming technique for manipulating strings. On Wikipedia you can use a limited version of regex called a Lua pattern to select and modify bits of text from a string. The pattern is a piece of code describing what you are looking for in the string.
Rather than use the search box, where entering an equals sign and a pipe character, and "quotes around phrases" is a straightforward matter, it is still easiest to use a regex-based search-link template — {{}} or {{}} — on the page with sample data, because then you can focus on the target data there and on writing the regexp pattern.
The RE2 algorithm has been rewritten in Rust as the package "regex". CloudFlare's web application firewall uses this package because the RE2 algorithm is immune to ReDoS. [8] Russ Cox also wrote RE1, an earlier regular expression based on a bytecode interpreter. [9] OpenResty uses a RE1 fork called "sregex". [10]
Besides the built-in RE/flex POSIX regex pattern matcher, RE/flex also supports PCRE2, Boost.Regex and std::regex pattern matching libraries. PCRE2 and Boost.Regex offer a richer regular expression pattern syntax with Perl pattern matching semantics, but are slower due to their intrinsic NFA-based matching algorithm.