Escape sequence

Data transmission A common use of an escape sequence is to remove control characters from a data stream so that it does not cause its control function by mistake. The control character is replaced with an escape character and one or more other subsequent characters. After escaping the normal context in which the control character would have caused an action, the sequence is replaced by the removed character. Common escape sequences include: carriage return , newline , tab . To account for the fact that using a printable character for escape causes that character to lose its normal meaning, a sequence of two backslash characters (\\) encodes a single backslash. An escape sequence can also specify a character by its code value. For example, the backslash can be encoded as either \x5c or \134 which specify the character code value as hexadecimal and octal, respectively. A backslash immediately followed by a newline (which is necessarily outside of a string literal) does not mark an escape sequence. The C preprocessor joins the line with the subsequent line. Quoting escape When an escape character is needed within a string literal, there are two common strategies: • Doubled delimiter For example, 'He didn''t do it.') can be used to enable ANSI escape sequence support. In DOS via $e in the PROMPT command), and in 16-bit Windows via a command window. In Unix and Unix-like systems, the ANSI escape sequences are generally supported by the shell. The rise of GUI applications has reduced the use of escape sequences, yet the ability to provide full-screen, text-based applications is still available. ==Related==

Control sequence A control sequence is a sequence of characters that changes the state of a computer peripheral instead of conveying the normal information that the characters represent. In an ANSI escape sequence, the escape sequence prefix, called control sequence introducer, can be either ASCII ESC (decimal 27) followed by [ or CSI (decimal 155). Notable systems that did not use an escape character for control sequences include: • The Hayes command set defines a modal control sequence, +++, which switches from command to online mode. To ensure that the sequence is interpreted as a control sequence instead of embedded in content, the sender stops communication for one second before and after sending . When the modem detects condition, it switches from normal mode (sending characters to the phone) to a command mode in which the data is interpreted a command. Sending the O command switches back to the normal mode. • Data General terminal control sequences, but they often were still called escape sequences, and the very common use of "escaping" special characters in programming languages and command-line parameters today often use the "backslash" character to begin the sequence. Escape sequences in communications are commonly used when a computer and a peripheral have only a single channel through which to send information back and forth (so escape sequences are an example of in-band signaling). They were common when most dumb terminals used ASCII with 7 data bits for communication, and sometimes would be used to switch to a different character set for "foreign" or graphics characters that would otherwise been restricted by the 128 codes available in 7 data bits. Even relatively "dumb" terminals responded to some escape sequences, including the original mechanical Teletype printers (on which "glass Teletypes" or VDUs were based) responded to characters 27 and 31 to alternate between letters and figures modes. Esc key Many computer keyboards have an Esc key (where Esc is short for escape) even though it is generally not used for entering an escape sequence. The vi text editor uses the key to exit from input mode. Some application use the key to cancel an operation or navigate up a level of a nested context. ==See also==