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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 ...
Regular expressions are used in search engines, in search and replace dialogs of word processors and text editors, in text processing utilities such as sed and AWK, and in lexical analysis. Regular expressions are supported in many programming languages. Library implementations are often called an "engine", [4] [5] and many of these are ...
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).
An advanced regexp uses the metacharacters to program general string patterns. It finds everything, even pieces and parts of words, conveying no notion of "words", but only that of a string of characters in a sequence. Metacharacters are interpreted unless quoted by a backslash, double quotes, or square brackets. See the section on regex.
So curly brackets mean "quantifier". The parentheses are a grouping mechanism, so we can quantify more than just the previous character, and so we can make boundaries for a set of alternative matches. (See alternation below.) The quotation marks are an escape mechanism, like square brackets or the backslash.
An advanced regexp uses the metacharacters to program general string patterns. It finds everything, even pieces and parts of words, conveying no notion of "words", but only that of a string of characters in a sequence. Metacharacters are interpreted unless quoted by a backslash, double quotes, or square brackets. See the section on regex.
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).
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.