TERMIOS(3)

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.

The c_cc array defines the special control characters. The symbolic indices (and meaning: initial values) are: VINTR (interrupt character: 0177, DEL, rubout), VQUIT (quit character: 034, FS, Ctrl-\), VERASE (erase character: 010, BS, Ctrl-H), VKILL (kill character: 025, NAK, Ctrl-U), VEOF (end-of-file character: 004, EOT, Ctrl-D), VMIN, VEOL (additional end-of-line character: 0, NUL), VTIME, VEOL2 (yet another end-of-line character: 0, NUL), VSWTCH (switch character: 0, NUL), VSTART (start character: 021, DC1, Ctrl-Q), VSTOP (stop character: 023, DC3, Ctrl-S), VSUSP (suspend character: 032, SUB, Ctrl-Z), VDSUSP (delayed suspend character: 031, EM, Ctrl-Y), VLNEXT (literal next: 026, SYN, Ctrl-V), VWERASE (word erase: 027, ETB, Ctrl-W), VREPRINT (reprint unread characters: 022, DC2, Ctrl-R), VDISCARD (discard pending output: 017, SI, Ctrl-O).

These symbolic subscript values are all different, except that VTIME, VMIN may have the same value as VEOL, VEOF, respectively. (In non-canonical mode the special character meaning is replaced by the timeout meaning. MIN represents the minimum number of characters that should be received to satisfy the read. TIME is a decisecond-valued timer. When both are set, a read will wait until at least one character has been received, and then return as soon as either MIN characters have been received or time TIME has passed since the last character was received. If only MIN is set, the read will not return before MIN characters have been received. If only TIME is set, the read will return as soon as either at least one character has been received, or the timer times out. If neither is set, the read will return immediately, only giving the currently already available characters.)

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 VALUE

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)