An escape sequence is a series of characters used to trigger some sort of command state in computers and their attached peripherals. A computer is a machine designed for manipulating data according to a list of instructions known as a program. ... A peripheral is a type of computer hardware that is added to a host computer in order to expand its abilities. ...

It is commonly used when the computer and the peripheral have only a single channel in which to send information back and forth. If the device in question is "dumb" and can only do one thing with the information being sent to it (for instance, print it) then there is no need for an escape sequence. However most devices have more than one capability, and thus need some way to tell data from commands.

For instance, the Hayes command set defines a single escape sequence, +++. When the modem encounters this in a stream of data, it switches from its normal mode of operation which simply sends any characters to the phone, to a command mode in which the following data is assumed to be a part of the command language. You can switch back to the online mode by sending the O command. Most dialup modems follow the Hayes Command Set to a large extent, originally developed for the Hayes Smartmodem 2400. ...

The Hayes command set is modal, switching from command mode to online mode. This is not appropriate in the case where the commands and data will switch back and forth rapidly. An example of a non-modal escape sequence control language is the VT100, which used a series of commands prefixed by the Control Sequence Introducer, escape-[. The term modal may refer to: Modal, a textile made from spun Beechwood cellulose Modal logic Modal verbs Mode Musical mode This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... The VT100 was a video terminal made by Digital Equipment Corporation (DEC) which became the de facto standard used by terminal emulators. ...

There is a fine line between a set of control characters and an escape sequence that may not exist at all. The earlier VT52 terminal used simple commands like escape-A, which is sufficiently simple to be considered a control character command language. However the VT52 also supported parameters, which a simple control language likely wouldn't. In computing, a control character or non-printing character, is a code point (a number) in a character set that does not in itself represent a written symbol. ... The VT52 was a CRT-based computer terminal produced by Digital Equipment Corporation during the late 1970s. ...

Escape sequences date back at least to the 1874 Baudot code. The Baudot code, named after its inventor Émile Baudot, is a character set predating EBCDIC and ASCII and used originally and primarily on teleprinters. ...