TERMIOS

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUES
SEE ALSO

NAME

termios, tcgetattr, tcsetattr, tcsendbreak, tcdrain, tcflush, tcflow, cfmakeraw, cfgetospeed, cfgetispeed, cfsetispeed, cfsetospeed, tcgetpgrp, tcsetpgrp − get and set terminal attributes, line control, get and set baud rate, get and set terminal foreground process group ID

SYNOPSIS

#include <termios.h>
#include <unistd.h>

int tcgetattr ( int fd, struct termios *termios_p );

int tcsetattr ( int fd, int optional_actions, struct termios *termios_p );

int tcsendbreak ( int fd, int duration );

int tcdrain ( int fd );

int tcflush ( int fd, int queue_selector );

int tcflow ( int fd, int action );

int cfmakeraw ( struct termios *termios_p );

speed_t cfgetospeed ( struct termios *termios_p );

int cfsetospeed ( struct termios *termios_p, speed_t speed );

speed_t cfgetispeed ( struct termios *termios_p );

int cfsetispeed ( struct termios *termios_p, speed_t speed );

pid_t tcgetpgrp ( int fd );

int tcsetpgrp ( int fd, pid_t pgrpid );

DESCRIPTION

The termios functions describe a general terminal interface that is provided to control asynchronous communications ports.

Many of the functions described here have a termios_p argument that is a pointer to a termios structure. This structure contains the following members:

tcflag_t c_iflag;      /* input modes */
tcflag_t c_oflag;      /* output modes */
tcflag_t c_cflag;      /* control modes */
tcflag_t c_lflag;      /* local modes */
cc_t c_cc[NCCS];       /* control chars */

c_iflag flag constants:

IGNBRK

ignore BREAK condition on input

BRKINT

If IGNBRK is not set, generate SIGINT on BREAK condition, else read BREAK as character \0.

IGNPAR

ignore framing errors and parity errors.

PARMRK

if IGNPAR is not set, prefix a character with a parity error or framing error with \377 \0. If neither IGNPAR nor PARMRK is set, read a character with a parity error or framing error as \0.

INPCK

enable input parity checking

ISTRIP

strip off eighth bit

INLCR

translate NL to CR on input

IGNCR

ignore carriage return on input

ICRNL

translate carriage return to newline on input (unless IGNCR is set)

IUCLC

map uppercase characters to lowercase on input

IXON

enable XON/XOFF flow control on output

IXANY

enable any character to restart output

IXOFF

enable XON/XOFF flow control on input

IMAXBEL

ring bell when input queue is full

c_oflag flag constants:

OPOST

enable implementation-defined output processing

OLCUC

map lowercase characters to uppercase on output

ONLCR

map NL to CR-NL on output

OCRNL

map CR to NL on output

ONOCR

don’t output CR at column 0

ONLRET

don’t output CR

OFILL

send fill characters for a delay, rather than using a timed delay

OFDEL

fill character is ASCII DEL. If unset, fill character is ASCII NUL

NLDLY

newline delay mask. Values are NL0 and NL1.

CRDLY

carriage return delay mask. Values are CR0, CR1, CR2, or CR3.

TABDLY

horizontal tab delay mask. Values are TAB0, TAB1, TAB2, TAB3, or XTABS. A value of XTABS expands tabs to spaces (with tab stops every eight columns).

BSDLY

backspace delay mask. Values are BS0 or BS1.

VTDLY

vertical tab delay mask. Values are VT0 or VT1.

FFDLY

form feed delay mask. Values are FF0 or FF1.

c_cflag flag constants:

CSIZE

character size mask. Values are CS5, CS6, CS7, or CS8.

CSTOPB

set two stop bits, rather than one.

CREAD

enable receiver.

PARENB

enable parity generation on output and parity checking for input.

PARODD

parity for input and output is odd.

HUPCL

lower modem control lines after last process closes the device (hang up).

CLOCAL

ignore modem control lines

CIBAUD

mask for input speeds (not used).

CRTSCTS

flow control.

c_lflag flag constants:

ISIG

when any of the characters INTR, QUIT, SUSP, or DSUSP are received, generate the corresponding signal.

ICANON

enable canonical mode. This enables the special characters EOF, EOL, EOL2, ERASE, KILL, REPRINT, STATUS, and WERASE, and buffers by lines.

XCASE

if ICANON is also set, terminal is uppercase only. Input is converted to lowercase, except for characters preceded by \. On output, uppercase characters are preceded by \ and lowercase characters are converted to uppercase.

ECHO

echo input characters.

ECHOE

if ICANON is also set, the ERASE character erases the preceding input character, and WERASE erases the preceding word.

ECHOK

if ICANON is also set, the KILL character erases the current line.

ECHONL

if ICANON is also set, echo the NL character even if ECHO is not set.

ECHOCTL

if ECHO is also set, ASCII control signals other than TAB, NL, START, and STOP are echoed as ^X, where X is the character with ASCII code 0x40 greater than the control signal. For example, character 0x08 (BS) is echoed as ^H.

ECHOPRT

if ICANON and IECHO are also set, characters are printed as they are being erased.

ECHOKE

if ICANON is also set, KILL is echoed by erasing each character on the line, as specified by ECHOE and ECHOPRT.

FLUSHO

output is being flushed. This flag is toggled by typing the DISCARD character.

NOFLSH

disable flushing the input and output queues when generating the SIGINT and SIGQUIT signals, and flushing the input queue when generating the SIGSUSP signal.

TOSTOP

send the SIGTTOU signal to the process group of a background process which tries to write to its controlling terminal.

PENDIN

all characters in the input queue are reprinted when the next character is read. (bash handles typeahead this way.)

IEXTEN

enable implementation-defined input processing.

tcgetattr() gets the parameters associated with the object referred by fd and stores them in the termios structure referenced by termios_p. This function may be invoked from a background process; however, the terminal attributes may be subsequently changed by a foreground process.

tcsetattr() sets the parameters associated with the terminal (unless support is required from the underlying hardware that is not available) from the termios structure referred to by termios_p. optional_actions specifies when the changes take effect:

TCSANOW

the change occurs immediately.

TCSADRAIN

the change occurs after all output written to fd has been transmitted. This function should be used when changing parameters that affect output.

TCSAFLUSH

the change occurs after all output written to the object referred by fd has been transmitted, and all input that has been received but not read will be discarded before the change is made.

tcsendbreak() transmits a continuous stream of zero-valued bits for a specific duration, if the terminal is using asynchronous serial data transmission. If duration is zero, it transmits zero-valued bits for at least 0.25 seconds, and not more that 0.5 seconds. If duration is not zero, it sends zero-valued bits for duration*N seconds, where N is at least 0.25, and not more than 0.5.

If the terminal is not using asynchronous serial data transmission, tcsendbreak() returns without taking any action.

tcdrain() waits until all output written to the object referred to by fd has been transmitted.

tcflush() discards data written to the object referred to by fd but not transmitted, or data received but not read, depending on the value of queue_selector:

TCIFLUSH

flushes data received but not read.

TCOFLUSH

flushes data written but not transmitted.

TCIOFLUSH

flushes both data received but not read, and data written but not transmitted.

tcflow() suspends transmission or reception of data on the object referred to by fd, depending on the value of action:

TCOOFF

suspends output.

TCOON

restarts suspended output.

TCIOFF

transmits a STOP character, which stops the terminal device from transmitting data to the system.

TCION

transmits a START character, which starts the terminal device transmitting data to the system.

The default on open of a terminal file is that neither its input nor its output is suspended.

The baud rate functions are provided for getting and setting the values of the input and output baud rates in the termios structure. The new values do not take effect until tcsetattr() is successfully called.

Setting the speed to B0 instructs the modem to "hang up". The actual bit rate corresponding to B38400 may be altered with setserial(8).

The input and output baud rates are stored in the termios structure.

cfmakeraw sets the terminal attributes as follows:

            termios_p->c_iflag &= ~(IGNBRK|BRKINT|PARMRK|ISTRIP
                            |INLCR|IGNCR|ICRNL|IXON);
            termios_p->c_oflag &= ~OPOST;
            termios_p->c_lflag &= ~(ECHO|ECHONL|ICANON|ISIG|IEXTEN);
            termios_p->c_cflag &= ~(CSIZE|PARENB);
            termios_p->c_cflag |= CS8;

cfgetospeed() returns the output baud rate stored in the termios structure pointed to by termios_p.

cfsetospeed() sets the output baud rate stored in the termios structure pointed to by termios_p to speed, which must be one of these constants:

B0

B50

B75

B110

B134

B150

B200

B300

B600

B1200

B1800

B2400

B4800

B9600

B19200

B38400

B57600

B115200

B230400

The zero baud rate, B0, is used to terminate the connection. If B0 is specified, the modem control lines shall no longer be asserted. Normally, this will disconnect the line. CBAUDEX is a mask for the speeds beyond those defined in POSIX.1 (57600 and above). Thus, B57600 & CBAUDEX is nonzero.

cfgetispeed() returns the input baud rate stored in the termios structure.

cfsetispeed() sets the input baud rate stored in the termios structure to speed. If the input baud rate is set to zero, the input baud rate will be equal to the output baud rate.

tcgetpgrp() returns process group ID of foreground processing group, or -1 on error.

tcsetpgrp() sets process group ID to pgrpid. pgrpid must be the ID of a process group in the same session.

RETURN VALUES

cfgetispeed() returns the input baud rate stored in the termios structure.

cfgetospeed() returns the output baud rate stored in the termios structure.

tcgetpgrp() returns process group ID of foreground processing group, or -1 on error.

All other functions return:

0

on success.

-1

on failure and set errno to indicate the error.

SEE ALSO

setserial(8)