Escape Sequence - Keyboard


An escape character is usually assigned to the Esc key on a computer keyboard, and can be sent in other ways than as part of an escape sequence. For example, the Esc key may be used as an input character in editors such as vi, or for backing up one level in a menu in some applications. The Hewlett Packard HP 2640 terminals had a key for a "display functions" mode which would display graphics for all control characters, including Esc, to aid in debugging applications.

If the Esc key and other keys that send escape sequences are both supposed to be meaningful to an application, an ambiguity arises, if a terminal or terminal emulator is in use. In particular, when the application receives the ASCII escape character, it is not clear whether that character is the result of the user pressing the Esc key or whether it is the initial character of an escape sequence (e.g., resulting from an arrow key press). The traditional method of resolving the ambiguity is to observe whether or not another character quickly follows the escape character. If not, it is assumed not to be part of an escape sequence. This heuristic can fail under some circumstances, but in practice it works reasonably well, especially with faster modern communication speeds.

Escape sequences date back at least to the 1874 Baudot code.

Read more about this topic:  Escape Sequence

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