TERMIOS(2) Linux Programmer's Manual TERMIOS(2)
NAME
termios, tcgetattr, tcsetattr, tcsendbreak, tcdrain,
tcflush, tcflow, 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 );
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 inter-
face that is provided to control asynchronous communica-
tions 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 */
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c_iflag flag constants:
IGNBRK ignore BREAK condition on input
BRKINT If IGNBRK is not set, generate SIGINT on BREAK con-
dition, 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
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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 sig-
nal.
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
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characters preceded by \. On output, uppercase
characters are preceded by \ and lowercase charac-
ters 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 0x10
greater than the control signal. For example,
character 0x28 (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 SIG-
SUSP signal.
TOSTOP send the SIGTTOU signal to the process group of a
background process which tries to write to its con-
trolling 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
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process.
tcsetattr() sets the parameters associated with the termi-
nal (unless support is required from the underlying hard-
ware 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 sec-
onds, 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:
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TCOOFF suspends output.
TCOON restarts suspended output.
TCIOFF transmits a STOP character, which stops the termi-
nal device from transmitting data to the system.
TCION transmits a START character, which starts the ter-
minal 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 set-
ting 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.
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 connec-
tion. 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
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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 pro-
cessing 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 pro-
cessing group, or -1 on error.
All other functions return:
0 on success.
-1 on failure and set errno to indicate the error.
SEE ALSO
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