Local modes

The c_lflag field of the structure is used to control various functions:

Mask name	Definition
ECHO	Enable echo function
ECHOE	Echo ERASE character as BS-SP-BS (error correcting backspace)
ECHOK	Echo NL after KILL character
ECHONL	Echo NL character
ICANON	Enable canonical input (line-oriented input with ERASE and KILL processing)
IEXTEN	Enable extended functions
ISIG	Enable signals
NOFLSH	Disable flushing of input or output queues after INTERRUPT or QUIT from keyboard
TOSTOP	Send SIGTTOU signal with output for background process group
XCASE	Canonical uppercase and lowercase representation. Will no longer be supported by the X/Open-Standard in future.

If ECHO is set, input characters are echoed back to the terminal as soon as they are received. If ECHO is clear, input characters are not echoed.

If ICANON and ECHOE are set, the ERASE character is echoed as a backspace-spacebackspace sequence, which causes the terminal to clear the last character, if any, from the display. If ECHOE is set and ECHO is not set, the ERASE character is echoed as SP BS.

If ECHOK and ICANON are set, the KILL character causes the terminal to erase the line from the display or echoes the NL character after the KILL character to indicate that the line will be deleted.

If ECHONL and ICANON are set, the NL character is echoed even if ECHO is not set. This is useful for terminals set to the local echo (so-called half duplex) mode. The EOF character is echoed only if it is escaped. Since EOT (End Of Transmission) is used as the default EOF character, this prevents a connection cleardown from terminals that hang up when EOT is received.

If ISIG is set, each input character is checked to determine whether it is one of the special control characters INTR, QUIT or SUSP (job control only). If this is the case, the function associated with that character is performed. If ISIG is not set, no checking is done. In other words, these special input functions can only be performed if ISIG is set. They can, however, be disabled individually by changing the value of the control character to an unlikely or impossible value (e.g. 0377).

If ICANON is set, canonical processing is enabled. This enables the functions to process ERASE and KILL characters. The input characters are assembled into lines delimited by NL, EOF and EOL, as described in section “Canonical mode input processing”.

If ICANON is not set, read requests are satisfied directly from the input queue. This does not take place until at least MIN bytes have been received or the timeout value TIME has expired (see section “Non-canonical mode input processing” for more details). The TIME value is specified in tenths of a second. If NOFLSH is set, the normal flush of input and output queues that follows reception of INTR, QUIT and SUSP (job control only) characters is not performed.

The initial value for the local modes (value of c_local) after a call to open() is that no flag is set.