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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 .
insource:/[a-z]{2,}/ matches any string of 2 or more lowercase letters. [ ] introduce a character class , which matches a single instance of any of the characters in the class. For example, insource:/[Pp]olish/ matches both Polish and polish .
For every long enough string in a regular language, there must be a middle section (y) 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 .
The other word must differ by no more than two letters. Not the first two letters. The first two letters must match. Two letters swapped. Two letters changed. Two letters added, two letters subtracted, or one subtracted and one added. But it can differ by one letter in these ways. A fuzzy search matches the word exactly plus words like it.
Below is a simple grammar, defined using the notation of regular expressions and Extended Backus–Naur form.It describes the syntax of S-expressions, a data syntax of the programming language Lisp, which defines productions for the syntactic categories expression, atom, number, symbol, and list:
find wildcard expressions and regular expressions. A search matches what you see rendered on the screen and in a print preview. The raw "source" wikitext is searchable by employing the insource parameter. For these two kinds of searches a word is any string of consecutive letters and numbers matching a whole word or phrase.
This article is part of The D.C. Brief, TIME’s politics newsletter. Sign up here to get stories like this sent to your inbox.. The fever didn’t break over the weekend. In fact, it only worsened.
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 ...