1304 Chapter 62
BRKINT
If the BRKINT flag is set and the IGNBRK flag is not set, then a SIGINT signal is sent to the
foreground process group when a BREAK condition occurs.Most conventional dumb terminals provided a BREAK key. Pressing this key
doesn’t actually generate a character, but instead causes a BREAK condition,
whereby a series of 0 bits is sent to the terminal driver for a specified length of
time, typically 0.25 or 0.5 seconds (i.e., longer than the time required to trans-
mit a single byte). (Unless the IGNBRK flag has been set, the terminal driver con-
sequently delivers a single 0 byte to the reading process.) On many UNIX
systems, the BREAK condition acted as a signal to a remote host to change its
line speed (baud) to something suitable for the terminal. Thus, the user would
press the BREAK key until a valid login prompt appeared, indicating that the
line speed was now suitable for this terminal.
On a virtual console, we can generate a BREAK condition by pressing
Control-Break.ECHO
Setting the ECHO flag enables echoing of input characters. Disabling echoing is use-
ful when reading passwords. Echoing is also disabled within the command mode of
vi, where keyboard characters are interpreted as editing commands rather than
text input. The ECHO flag is effective in both canonical and noncanonical modes.ECHOCTL
If ECHO is set, then enabling the ECHOCTL flag causes control characters other than tab,
newline, START, and STOP to be echoed in the form ^A (for Control-A), and so on.
If ECHOCTL is disabled, control characters are not echoed.The control characters are those with ASCII codes less than 32, plus the DEL
character (127 decimal). A control character, x, is echoed using a caret (^) fol-
lowed by the character resulting from the expression (x ^ 64). For all characters
except DEL, the effect of the XOR (^) operator in this expression is to add 64
to the value of the character. Thus, Control-A (ASCII 1) is echoed as caret plus A
(ASCII 65). For DEL, the expression has the effect of subtracting 64 from 127,
yielding the value 63, the ASCII code for ?, so that DEL is echoed as ^?.ECHOE
In canonical mode, setting the ECHOE flag causes ERASE to be performed visually, by
outputting the sequence backspace-space-backspace to the terminal. If ECHOE is dis-
abled, then the ERASE character is instead echoed (e.g., as ^?), but still performs its
function of deleting a character.ECHOK and ECHOKE
The ECHOK and ECHOKE flags control the visual display when using the KILL (erase
line) character in canonical mode. In the default case (both flags enabled), a line is
erased visually (see ECHOE). If either of these flags is disabled, then a visual erase is not
performed (but the input line is still discarded), and the KILL character is echoed
(e.g., as ^U). If ECHOK is set, but not ECHOKE, then a newline character is also output.