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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 ...
Blue highlights show the match results of the regular expression pattern: /r[aeiou]+/ g (lower case r followed by one or more lower-case vowels). 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 .
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/.
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.
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]
Generally, an escape character is not a particular case of (device) control characters, nor vice versa.If we define control characters as non-graphic, or as having a special meaning for an output device (e.g. printer or text terminal) then any escape character for this device is a control one.
A screenshot of the original 1971 Unix reference page for glob – the owner is dmr, short for Dennis Ritchie.. glob() (/ ɡ l ɒ b /) is a libc function for globbing, which is the archetypal use of pattern matching against the names in a filesystem directory such that a name pattern is expanded into a list of names matching that pattern.
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".