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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 ...
An escape sequence starts with a backslash (\) called the escape character and subsequent characters define the meaning of the escape sequence. For example, \n denotes a newline character. The same or similar escape sequences are used in other, related languages such C++ , C# , Java and PHP .
The change was made "to clear the way for the potential future use of tag characters for a purpose other than to represent language tags". [8] Unicode states that "the use of tag characters to represent language tags in a plain text stream is still a deprecated mechanism for conveying language information about text. [8]
In C and many derivative programming languages, a string escape sequence is a series of two or more characters, starting with a backslash \. [3]Note that in C a backslash immediately followed by a newline does not constitute an escape sequence, but splices physical source lines into logical ones in the second translation phase, whereas string escape sequences are converted in the fifth ...
A Unicode character is assigned a unique Name (na). [1] The name is composed of uppercase letters A–Z, digits 0–9, hyphen-minus and space.Some sequences are excluded: names beginning with a space or hyphen, names ending with a space or hyphen, repeated spaces or hyphens, and space after hyphen are not allowed.
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.
Control characters may be described as doing something when the user inputs them, such as code 3 (End-of-Text character, ETX, ^C) to interrupt the running process, or code 4 (End-of-Transmission character, EOT, ^D), used to end text input on Unix or to exit a Unix shell. These uses usually have little to do with their use when they are in text ...
Extreme examples occur when these are combined – Uniform Naming Convention paths begin with \\, and thus an escaped regular expression matching a UNC name begins with 8 backslashes, "\\\\\", due to needing to escape the string and the regular expression. Using raw strings reduces this to 4 (escaping in the regular expression), as in C# @"\\\\".