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A regular expression ... The metacharacter syntax is designed specifically to represent prescribed targets in a concise and flexible way to direct the automation ...
Regex experts should note that \n does not mean "newline," \d does not mean "digit," and so on: In MediaWiki syntax, the only use of \ is to escape metacharacters. / is special because it indicates the end of the regex. For example, insource:/yes/no/ is treated the same as insource:/yes/ no (because the keyword search for no/ ignores punctuation).
A metacharacter is a character that has a special meaning to a computer program, such as a shell interpreter or a regular expression (regex) engine.. In POSIX extended regular expressions, there are 14 metacharacters that must be escaped — preceded by a backslash (\) — in order to drop their special meaning and be treated literally inside an expression: opening and closing square brackets ...
In regular expressions, the period (., also called "dot") is the wildcard pattern which matches any single character. Followed by the Kleene star operator, which is denoted as an asterisk ( * ), we obtain .* , which will match zero or more arbitrary characters.
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).
In many programming languages, a particular syntax of strings is used to represent regular expressions, which are patterns describing string characters. However, it is possible to perform some string pattern matching within the same framework that has been discussed throughout this article.
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:
A somewhat longer but more explicit extended right-regular grammar G for the same regular expression is given by N = {S, A, B, C}, Σ = {a, b, c}, where P consists of the following rules: S → A A → aA A → B B → bC C → ε C → cC...where each uppercase letter corresponds to phrases starting at the next position in the regular expression.