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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 ...
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 .
If the portion of the regular expression is "greedy", it will match as many characters as possible. If it is not greedy, it will match as few characters as possible. By default, quantifiers in AWB are greedy. To make a quantifier non-greedy, it must be followed by a question mark. For example: In this string:
In the Windows operating system, illegal characters in file and folder names include colons, brackets, question marks, [3] and null characters. [ 4 ] Illegal characters in Windows file names [ 4 ]
This is the "regular expression" (or regexp, or regex). Its metacharacters can represent multiple possibilities for a character position or a range of character positions within a page, using metacharacters for truth logic, grouping, counting, and modifying the characters to be found.
Escape sequences are not always pretty or easy to use, so many compilers also offer other means of solving the common problems. Escape sequences, however, solve every delimiter problem and most compilers interpret escape sequences. When an escape character is inside a string literal, it means "this is the start of the escape sequence".
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]
Regex searches are likely to time out unless you further limit the search in some way, such as by including another parameter or a search term outside of the insource component of the search string. (For example, X* intitle:/X/ to restrict the search to initial position.) For more details, see mw:Help:CirrusSearch#Regular expression searches.