Caret notation

Caret notation is a notation for unprintable control characters in ASCII encoding. The notation consists of a caret (^) followed by a capital letter; this digraph stands for the ASCII code that has the numerical value equivalent to the letter's numerical value. For example the EOT character with a value of 4 is represented as ^D because D is the 4th letter in the alphabet. The NUL character with a value of 0 is represented as ^@ (@ is the ASCII character before A). The DEL character with the value 127 is usually represented as ^?, because the ASCII '?' is before '@' and the value -1 (encoded in 8-bit two's complement) is the same as 127 if masked to 7 bits. An alternative formulation of the translation is that the printed character is found by inverting the 7th bit of the ASCII code.

Many computer systems allow the user to enter a control character by holding down Ctrl and pressing the letter used in the caret notation. This is practical, because many control characters (e.g. EOT) cannot be entered directly from a keyboard. Although there are many ways to represent control characters, this correspondence between notation and typing makes the caret notation suitable for many applications.