$K[EY] contains the string that terminated the most recent READ command from the current device (including any introducing and terminating characters). If no READ command s issued to the current device or if no terminator is used, the value of $KEY is an empty string. However, when input is terminated by typing a function key, the value of $KEY is equal to the string of characters that is transmitted by that function key.

The effect of a READ *glvn on $KEY is unspecified.

If a Character Set Profile input-transform is in effect, then this is also applied to the value stored in $KEY.