termios, tcgetattr, tcsetattr, tcsendbreak, tcdrain, tcflush, tcflow, cfmakeraw, cfgetospeed, cfgetispeed, cfsetispeed, cfsetospeed, cfsetspeed — get and set terminal attributes, line control, get and set baud rate
#include <termios.h> #include <unistd.h>
int
tcgetattr( |
int | fd, |
struct termios * | termios_p) ; |
int
tcsetattr( |
int | fd, |
int | optional_actions, | |
const 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) ; |
void
cfmakeraw( |
struct termios * | termios_p) ; |
speed_t cfgetispeed( |
const struct termios * | termios_p) ; |
speed_t cfgetospeed( |
const struct termios * | termios_p) ; |
int
cfsetispeed( |
struct termios * | termios_p, |
speed_t | speed) ; |
int
cfsetospeed( |
struct termios * | termios_p, |
speed_t | speed) ; |
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 at least the following
members:
tcflag_tc_iflag
; /* input modes */ tcflag_tc_oflag
; /* output modes */ tcflag_tc_cflag
; /* control modes */ tcflag_tc_lflag
; /* local modes */ cc_tc_cc
[NCCS
]; /* control chars */
The values that may be assigned to these fields are described below. In the case of the first four bit-mask fields, the definitions of some of the associated flags that may be set are only exposed if a specific feature test macro (see feature_test_macros(7)) is defined, as noted in brackets ("[]").
In the descriptions below, "not in POSIX" means that the value is not specified in POSIX.1-2001, and "XSI" means that the value is specified in POSIX.1-2001 as part of the XSI extension.
c_iflag
flag
constants:
IGNBRK
Ignore BREAK condition on input.
BRKINT
If IGNBRK
is set, a
BREAK is ignored. If it is not set but BRKINT
is set, then a BREAK causes
the input and output queues to be flushed, and if the
terminal is the controlling terminal of a foreground
process group, it will cause a SIGINT
to be sent to this
foreground process group. When neither IGNBRK
nor BRKINT
are set, a BREAK reads as a
null byte ('\0'), except when PARMRK
is set, in which case it
reads as the sequence \377 \0 \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
(not in POSIX) Map uppercase characters to lowercase on input.
IXON
Enable XON/XOFF flow control on output.
IXANY
(XSI) Typing any character will restart stopped output. (The default is to allow just the START character to restart output.)
IXOFF
Enable XON/XOFF flow control on input.
IMAXBEL
(not in POSIX) Ring bell when input queue is full. Linux does not implement this bit, and acts as if it is always set.
IUTF8
(since Linux 2.6.4)(not in POSIX) Input is UTF8; this allows character-erase to be correctly performed in cooked mode.
c_oflag
flag
constants defined in POSIX.1:
OPOST
Enable implementation-defined output processing.
The remaining c_oflag
flag constants are
defined in POSIX.1-2001, unless marked otherwise.
OLCUC
(not in POSIX) Map lowercase characters to uppercase on output.
ONLCR
(XSI) 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
(not in POSIX) Fill character is ASCII DEL (0177). If unset, fill character is ASCII NUL ('\0'). (Not implemented on Linux.)
NLDLY
Newline delay mask. Values are NL0
and NL1
. [requires _BSD_SOURCE or
_SVID_SOURCE or _XOPEN_SOURCE]
CRDLY
Carriage return delay mask. Values are
CR0
, CR1
, CR2
, or CR3
. [requires _BSD_SOURCE or
_SVID_SOURCE or _XOPEN_SOURCE]
TABDLY
Horizontal tab delay mask. Values are TAB0
, TAB1
, TAB2
, TAB3
(or XTABS
). A value of TAB3, that is,
XTABS, expands tabs to spaces (with tab stops every
eight columns). [requires _BSD_SOURCE or _SVID_SOURCE
or _XOPEN_SOURCE]
BSDLY
Backspace delay mask. Values are BS0
or BS1
. (Has never been implemented.)
[requires _BSD_SOURCE or _SVID_SOURCE or
_XOPEN_SOURCE]
VTDLY
Vertical tab delay mask. Values are VT0
or VT1
.
FFDLY
Form feed delay mask. Values are FF0
or FF1
. [requires _BSD_SOURCE or
_SVID_SOURCE or _XOPEN_SOURCE]
c_cflag
flag
constants:
CBAUD
(not in POSIX) Baud speed mask (4+1 bits). [requires _BSD_SOURCE or _SVID_SOURCE]
CBAUDEX
(not in POSIX) Extra baud speed mask (1 bit), included in CBAUD. [requires _BSD_SOURCE or _SVID_SOURCE]
(POSIX says that the baud speed is stored in the
termios
structure
without specifying where precisely, and provides
cfgetispeed
() and
cfsetispeed
() for
getting at it. Some systems use bits selected by
CBAUD in c_cflag
, other
systems use separate fields, e.g. sg_ispeed
and
sg_ospeed
.)
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
If set, then parity for input and output is odd; otherwise even parity is used.
HUPCL
Lower modem control lines after last process closes the device (hang up).
CLOCAL
Ignore modem control lines.
LOBLK
(not in POSIX) Block output from a noncurrent
shell layer. For use by shl
(shell layers).
(Not implemented on Linux.)
CIBAUD
(not in POSIX) Mask for input speeds. The values for the CIBAUD bits are the same as the values for the CBAUD bits, shifted left IBSHIFT bits. [requires _BSD_SOURCE or _SVID_SOURCE] (Not implemented on Linux.)
CMSPAR
(not in POSIX) Use "stick" (mark/space) parity
(supported on certain serial devices): if
PARODD
is set, the
parity bit is always 1; if PARODD
is not set, then the parity
bit is always 0). [requires _BSD_SOURCE or
_SVID_SOURCE]
CRTSCTS
(not in POSIX) Enable RTS/CTS (hardware) flow control. [requires _BSD_SOURCE or _SVID_SOURCE]
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 (described below).
XCASE
(not in POSIX; not supported under Linux) 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
(not in POSIX) 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.
[requires _BSD_SOURCE or _SVID_SOURCE]
ECHOPRT
(not in POSIX) If ICANON
and IECHO
are also set, characters are
printed as they are being erased. [requires
_BSD_SOURCE or _SVID_SOURCE]
ECHOKE
(not in POSIX) If ICANON
is also set, KILL is echoed
by erasing each character on the line, as specified
by ECHOE
and
ECHOPRT
. [requires
_BSD_SOURCE or _SVID_SOURCE]
DEFECHO
(not in POSIX) Echo only when a process is reading. (Not implemented on Linux.)
FLUSHO
(not in POSIX; not supported under Linux) Output is being flushed. This flag is toggled by typing the DISCARD character. [requires _BSD_SOURCE or _SVID_SOURCE]
NOFLSH
Disable flushing the input and output queues when generating the SIGINT, SIGQUIT and SIGSUSP signals.
TOSTOP
Send the SIGTTOU signal to the process group of a background process which tries to write to its controlling terminal.
PENDIN
(not in POSIX; not supported under Linux) All
characters in the input queue are reprinted when the
next character is read. (bash
handles
typeahead this way.) [requires _BSD_SOURCE or
_SVID_SOURCE]
IEXTEN
Enable implementation-defined input processing.
This flag, as well as ICANON
must be enabled for the
special characters EOL2, LNEXT, REPRINT, WERASE to be
interpreted, and for the IUCLC
flag to be effective.
The c_cc
array
defines the special control characters. The symbolic
indices (initial values) and meaning are:
VINTR
(003, ETX, Ctrl-C, or also 0177, DEL, rubout) Interrupt character. Send a SIGINT signal. Recognized when ISIG is set, and then not passed as input.
VQUIT
(034, FS, Ctrl-\) Quit character. Send SIGQUIT signal. Recognized when ISIG is set, and then not passed as input.
VERASE
(0177, DEL, rubout, or 010, BS, Ctrl-H, or also #) Erase character. This erases the previous not-yet-erased character, but does not erase past EOF or beginning-of-line. Recognized when ICANON is set, and then not passed as input.
VKILL
(025, NAK, Ctrl-U, or Ctrl-X, or also @) Kill character. This erases the input since the last EOF or beginning-of-line. Recognized when ICANON is set, and then not passed as input.
VEOF
(004, EOT, Ctrl-D) End-of-file character. More precisely: this character causes the pending tty buffer to be sent to the waiting user program without waiting for end-of-line. If it is the first character of the line, the read(2) in the user program returns 0, which signifies end-of-file. Recognized when ICANON is set, and then not passed as input.
VMIN
Minimum number of characters for non-canonical read.
VEOL
(0, NUL) Additional end-of-line character. Recognized when ICANON is set.
VTIME
Timeout in deciseconds for non-canonical read.
VEOL2
(not in POSIX; 0, NUL) Yet another end-of-line character. Recognized when ICANON is set.
VSWTCH
(not in POSIX; not supported under Linux; 0, NUL)
Switch character. (Used by shl
only.)
VSTART
(021, DC1, Ctrl-Q) Start character. Restarts output stopped by the Stop character. Recognized when IXON is set, and then not passed as input.
VSTOP
(023, DC3, Ctrl-S) Stop character. Stop output until Start character typed. Recognized when IXON is set, and then not passed as input.
VSUSP
(032, SUB, Ctrl-Z) Suspend character. Send SIGTSTP signal. Recognized when ISIG is set, and then not passed as input.
VDSUSP
(not in POSIX; not supported under Linux; 031, EM, Ctrl-Y) Delayed suspend character: send SIGTSTP signal when the character is read by the user program. Recognized when IEXTEN and ISIG are set, and the system supports job control, and then not passed as input.
VLNEXT
(not in POSIX; 026, SYN, Ctrl-V) Literal next. Quotes the next input character, depriving it of a possible special meaning. Recognized when IEXTEN is set, and then not passed as input.
VWERASE
(not in POSIX; 027, ETB, Ctrl-W) Word erase. Recognized when ICANON and IEXTEN are set, and then not passed as input.
VREPRINT
(not in POSIX; 022, DC2, Ctrl-R) Reprint unread characters. Recognized when ICANON and IEXTEN are set, and then not passed as input.
VDISCARD
(not in POSIX; not supported under Linux; 017, SI, Ctrl-O) Toggle: start/stop discarding pending output. Recognized when IEXTEN is set, and then not passed as input.
VSTATUS
(not in POSIX; not supported under Linux; status request: 024, DC4, Ctrl-T).
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. For an explanation of VMIN and VTIME, see the description of non-canonical mode below.
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.
The setting of the ICANON
canon flag in c_lflag
determines whether
the terminal is operating in canonical mode (ICANON
set) or non-canonical mode
(ICANON
unset). By default,
ICANON
set.
In canonical mode:
Input is made available line by line. An input line is available when one of the line delimiters is typed (NL, EOL, EOL2; or EOF at the start of line). Except in the case of EOF, the line delimiter is included in the buffer returned by read(2).
Line editing is enabled (ERASE, KILL; and if the
IEXTEN
flag is set:
WERASE, REPRINT, LNEXT). A read(2) returns at
most one line of input; if the read(2) requested
fewer bytes than are available in the current line of
input, then only as many bytes as requested are read,
and the remaining characters will be available for a
future read(2).
In non-canonical mode input is available immediately
(without the user having to type a line-delimiter
character), and line editing is disabled. The settings of
MIN (c_cc[VMIN]
)
and TIME (c_cc[VTIME]
) determine the
circumstances in which a read(2) completes; there
are four distinct cases:
MIN == 0; TIME == 0: If data is available, read(2) returns immediately, with the lesser of the number of bytes available, or the number of bytes requested. If no data is available, read(2) returns 0.
MIN > 0; TIME == 0: read(2) blocks until the lesser of MIN bytes or the number of bytes requested are available, and returns the lesser of these two values.
MIN == 0; TIME > 0: TIME specifies the limit for a timer in tenths of a second. The timer is started when read(2) is called. read(2) returns either when at least one byte of data is available, or when the timer expires. If the timer expires without any input becoming available, read(2) returns 0.
MIN > 0; TIME > 0: TIME specifies the limit for a timer in tenths of a second. Once an initial byte of input becomes available, the timer is restarted after each further byte is received. read(2) returns either when the lesser of the number of bytes requested or MIN byte have been read, or when the inter-byte timeout expires. Because the timer is only started after the initial byte becomes available, at least one byte will be read.
cfmakeraw
() sets the
terminal to something like the "raw" mode of the old
Version 7 terminal driver: input is available character by
character, echoing is disabled, and all special processing
of terminal input and output characters is disabled. The
terminal attributes are set 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;
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 some implementation-defined
length of time.
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.
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 non-zero.
cfgetispeed
() returns the
input baud rate stored in the termios
structure.
cfsetispeed
() sets the
input baud rate stored in the termios
structure to speed
, which must be
specified as one of the Bnnn
constants listed above
for cfsetospeed
(). If the
input baud rate is set to zero, the input baud rate will be
equal to the output baud rate.
cfsetspeed
() is a 4.4BSD
extension. It takes the same arguments as cfsetispeed
(), and sets both input and
output speed.
cfgetispeed
() returns the
input baud rate stored in the termios
structure.
cfgetospeed
() returns the
output baud rate stored in the termios
structure.
All other functions return:
0
on success.
on failure and set errno
to indicate the error.
Note that tcsetattr
()
returns success if any
of the requested changes
could be successfully carried out. Therefore, when making
multiple changes it may be necessary to follow this call with
a further call to tcgetattr
()
to check that all changes have been performed
successfully.
Unix V7 and several later systems have a list of baud rates where after the fourteen values B0, ..., B9600 one finds the two constants EXTA, EXTB ("External A" and "External B"). Many systems extend the list with much higher baud rates.
The effect of a non-zero duration
with tcsendbreak
() varies. SunOS specifies a
break of duration
*N
seconds, where N
is at least 0.25, and not more than 0.5.
Linux, AIX, DU, Tru64 send a break of duration
milliseconds. FreeBSD
and NetBSD and HP-UX and MacOS ignore the value of duration
. Under Solaris and
Unixware, tcsendbreak
() with
non-zero duration
behaves like tcdrain
().
stty(1), console_ioctl(4), tty_ioctl(4), feature_test_macros(7), setserial(8)
|