TERMIOS(7-POSIX) RISC/os Reference Manual TERMIOS(7-POSIX)
NAME
termios - general terminal interface
DESCRIPTION
All of the asynchronous communications ports and network
virtual terminal (``pseudo-terminal'' or ``pty'') ports use
the same general interface, no matter what hardware is
involved. The remainder of this section discusses the com-
mon features of this interface.
When a terminal file is opened, it normally causes the pro-
cess to wait until a connection is established. In prac-
tice, users' programs seldom open terminal files; they are
opened by getty and become a user's standard input, output,
and error files. The very first terminal file opened by the
session process group leader of a terminal file not already
associated with a process group becomes the control terminal
for that session process group. The control terminal plays
a special role in handling quit and interrupt signals, as
discussed below. The control terminal is inherited by a
child process during a fork(2). A process can break this
association by changing its process group using
tcsetpgrp(2).
A terminal associated with one of these files ordinarily
operates in full-duplex mode. Characters may be typed at
any time, even while output is occurring, and are only lost
when the system's character input buffers become completely
full, which is rare, or when the user has accumulated the
maximum allowed number of input characters that have not yet
been read by some program. Currently, this limit is
{MAX_INPUT} characters. When the input limit is reached,
the buffer is flushed and all the saved characters are
thrown away without notice.
Normally, terminal input is processed in units of lines. A
line is delimited by a new-line (ASCII LF) character, an
end-of-file (ASCII EOT) character, or an end-of-line charac-
ter. This means that a program attempting to read will be
suspended until an entire line has been typed. Also, no
matter how many characters are requested in the read call,
at most one line will be returned. It is not, however,
necessary to read a whole line at once; any number of char-
acters may be requested in a read, even one, without losing
information.
During input, erase and kill processing is normally done.
By default, the character # erases the last character typed,
except that it will not erase beyond the beginning of the
line. By default, the character @ kills (deletes) the
entire input line, and optionally outputs a new-line charac-
ter. Both these characters operate on a key-stroke basis,
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independently of any backspacing or tabbing that may have
been done. Both the erase and kill characters may be
entered literally by preceding them with the escape charac-
ter (Control-V). In this case the escape character is not
read. The erase, kill, and escape characters may be
changed.
Certain characters have special functions on input. These
functions and their default character values are summarized
as follows:
INTR (Rubout or ASCII DEL) generates an interrupt signal
which is sent to all processes in the foreground job
control process group of the associated control ter-
minal. (See setpgid(2) and setsid(2) for a discus-
sion of how to change the job control process group
of a process. See the discussion tcsetpgrp(2) for a
discussion of how to change the foreground job con-
trol process group of a terminal. Unless otherwise
changed, the session process group, the job control
process group, and the foreground job control pro-
cess group are all identical.) Normally, each such
process is forced to terminate, but arrangements may
be made either to ignore the signal or to receive a
trap to an agreed-upon location; see signal(2).
QUIT (Control-| or ASCII FS) generates a quit signal.
Its treatment is identical to the interrupt signal
except that, unless a receiving process has made
other arrangements, it will not only be terminated
but a core image file (called core) will be created
in the current working directory.
SWTCH (Control-z or ASCII SUB when shl is in use, unde-
fined otherwise) is used by the System V job control
facility, shl, to change the current layer to the
control layer. (Note that shl is not currently sup-
ported in RISC/os.)
ERASE (#) erases the preceding character. It will not
erase beyond the start of a line, as delimited by a
NL, EOF, or EOL character.
KILL (@) deletes the entire line, as delimited by a NL,
EOF, or EOL character.
EOF (Control-d or ASCII EOT) may be used to generate an
end-of-file from a terminal. When received, all the
characters waiting to be read are immediately passed
to the program, without waiting for a new-line, and
the EOF is discarded. Thus, if there are no charac-
ters waiting, which is to say the EOF occurred at
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the beginning of a line, zero characters will be
passed back, which is the standard end-of-file indi-
cation. If characters are waiting to be read when
the EOF is entered, they are immediately passed to
the current read from the program, and then the fol-
lowing read from the program will receive zero char-
acters.
CR (ASCII CR) is recognized on input if the ICANON flag
is set. When ICANON and ICRNL are set and ICNCR is
not set, this character is translated into a NL, and
has the same effect as the NL character. It can not
be changed or escaped.
NL (ASCII LF) is the normal line delimiter. It can not
be changed or escaped.
EOL (ASCII NUL) is an additional line delimiter, like
NL. It is not normally used.
EOL2 (ASCII NUL) is another additional line delimiter.
STOP (Control-s or ASCII DC3) can be used to temporarily
suspend output. It is useful with CRT terminals to
prevent output from disappearing before it can be
read, and in providing flow control of communication
between computers. While output is suspended, STOP
characters are ignored and not read.
START (Control-q or ASCII DC1) is used to resume output
which has been suspended by a STOP character. While
output is not suspended, START characters are
ignored and not read.
SUSP (undefined) is the job control stop character. Job
control shells normally set it to Control-z. When
defined and entered, this character causes a SIGTSTP
signal (see signal(2)) to be sent to the current
foreground job control process group. Unless caught
by the application, this will cause the application
to stop and wait to be continued, and will cause the
job control shell to resume prompting for commands.
DSUSP (undefined) is the job control stop character. Job
control shells normally set it to Control-y. When
defined and entered, this character causes a SIGTSTP
signal (see signal(2)) to be sent to the current
foreground job control process group, when the next
read from the terminal is started (or immediately if
a read is pending). Unless caught by the applica-
tion, this will cause the application to stop and
wait to be continued, and will cause the job control
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shell to resume prompting for commands.
RPRNT (Control-R) causes a newline to be output and the
current input line to be retyped on the output.
This is convenient in checking what has been typed,
if echoing was interrupted by application output.
FLUSH (Control-O) causes all pending output to be dis-
carded.
WERASE (Control-W) causes any immediately preceding blank
(space or ASCII TAB) characters, plus any preceding
contiguous sequence of non-blank characters, to be
deleted. This effectively deletes the previous word
of input.
STATUS (undefined) causes the status of some process in the
associated session process group to be displayed,
preceded and followed by newlines. (Conventionally,
this character, when enabled, is set to Control-T.)
In selecting the process whose status is to be
displayed, preference is given to processes which
are in the foreground job control process group, and
within that group, first, to processes which are
running or runnable, second, to processes which are
waiting for some event, and, last, to other
processes. The line of status consists of, in
order, the process's name, id, run status, user CPU
time in seconds, system CPU time in seconds, count
of blocks read, count of blocks written, and memory
size in pages. This feature is convenient in moni-
toring the progress of a long running interactive
command.
The character values for all of the control characters,
except NL, may be changed to suit individual tastes. Any
character, including the ESCAPE character, may be escaped by
a preceding ESCAPE character.
When the carrier signal from the data-set drops, a hang-up
(SIGHUP) signal is sent to all processes that have this ter-
minal as the control terminal, and which are in its fore-
ground job control process group, unless this feature has
been disabled. Unless other arrangements have been made,
this signal causes the processes to terminate. If the
hang-up signal is ignored, any subsequent read returns with
an end-of-file indication. Thus, programs that read a ter-
minal and test for end-of-file can terminate appropriately
when hung up on.
When one or more characters are written, they are transmit-
ted to the terminal as soon as previously-written characters
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have finished typing. If echoing is enabled, input charac-
ters are echoed by putting them in the output queue as they
arrive. (The Control-D character, ASCII EOT, however, is
never echoed as itself, it is echoed as "^D" followed by two
ASCII BS characters.)
Several system calls apply to terminal files. These calls
use termios structure, defined in <termios.h>. The members
of this structure include (but are not limited to) the fol-
lowing:
#define NCCS 23
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 */
The types tcflag_t and cc_t are also defined in the header
<termios.h>. The special control characters are defined by
the array c_cc. The character {_POSIX_VDISABLE} (0377) is
used as the value for elements of the array which are to be
treated as being ``undefined.'' The relative positions and
initial values for each function are as follows:
0 VINTR DEL
1 VQUIT FS
2 VERASE #
3 VKILL @
4 VEOF EOT
5 VEOL NUL
6 VEOL2 NUL
7 VSWTCH undefined
8 V_START Control-q
9 V_STOP Control-s
10 V_SUSP undefined
11 V_DSUSP undefined
12 V_RPRNT Control-r
13 V_FLUSH Control-o
14 V_WERAS Control-w
15 V_LNEXT \
16 V_STATUS undefined
17 V_SAVED_EOF undefined
18 V_SAVED_EOL undefined
19 reserved undefined
20 reserved undefined
21 reserved undefined
22 reserved undefined
The elements V_SAVED_EOF and V_SAVED_EOL are used as part of
the RISC/os emulation of 4.3 BSD terminal ioctl(2-BSD) con-
trol commands, and are not normally modified directly by
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applications.
The c_iflag field describes the basic terminal input con-
trol:
IGNBRK 0000001 Ignore break condition.
BRKINT 0000002 Signal interrupt on break.
IGNPAR 0000004 Ignore characters with parity errors.
PARMRK 0000010 Mark parity errors.
INPCK 0000020 Enable input parity check.
ISTRIP 0000040 Strip character.
INLCR 0000100 Map NL to CR on input.
IGNCR 0000200 Ignore CR.
ICRNL 0000400 Map CR to NL on input.
IUCLC 0001000 Map upper-case to lower-case on input.
IXON 0002000 Enable start/stop output control.
IXANY 0004000 Enable any character to restart output.
IXOFF 0010000 Enable start/stop input control.
If IGNBRK is set, the break condition (a character framing
error with data all zeros) is ignored, that is, not put on
the input queue and therefore not read by any process. Oth-
erwise if BRKINT is set, the break condition will generate
an interrupt signal and flush both the input and output
queues. If IGNPAR is set, characters with other framing and
parity errors are ignored.
If PARMRK is set, a character with a framing or parity error
which is not ignored is read as the three-character
sequence: 0377, 0, X, where X is the data of the character
received in error. To avoid ambiguity in this case, if
ISTRIP is not set, a valid character of 0377 is read as
0377, 0377. If PARMRK is not set, a framing or parity error
which is not ignored is read as the character NUL (0).
If INPCK is set, input parity checking is enabled. If INPCK
is not set, input parity checking is disabled. This allows
output parity generation without input parity errors.
If ISTRIP is set, valid input characters are first stripped
to 7-bits, otherwise all 8-bits are processed.
If INLCR is set, a received NL character is translated into
a CR character. If IGNCR is set, a received CR character is
ignored (not read). Otherwise if ICRNL is set, a received
CR character is translated into a NL character.
If IUCLC is set, a received upper-case alphabetic character
is translated into the corresponding lower-case character.
If IXON is set, start/stop output control is enabled. A
received STOP character will suspend output and a received
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START character will restart output. All start/stop charac-
ters are ignored and not read. If IXANY is set, any input
character, will restart output which has been suspended.
If IXOFF is set, the system will transmit START/STOP charac-
ters when the input queue is nearly empty/full.
The initial input control value is all-bits-clear.
The c_oflag field specifies the system treatment of output:
OPOST 0000001 Postprocess output.
OLCUC 0000002 Map lower case to upper on output.
ONLCR 0000004 Map NL to CR-NL on output.
OCRNL 0000010 Map CR to NL on output.
ONOCR 0000020 No CR output at column 0.
ONLRET 0000040 NL performs CR function.
OFILL 0000100 Use fill characters for delay.
OFDEL 0000200 Fill is DEL, else NUL.
NLDLY 0000400 Select new-line delays:
NL0 0
NL1 0000400
CRDLY 0003000 Select carriage-return delays:
CR0 0
CR1 0001000
CR2 0002000
CR3 0003000
TABDLY 0014000 Select horizontal-tab delays:
TAB0 0
TAB1 0004000
TAB2 0010000
TAB3 0014000 Expand tabs to spaces.
BSDLY 0020000 Select backspace delays:
BS0 0
BS1 0020000
VTDLY 0040000 Select vertical-tab delays:
VT0 0
VT1 0040000
FFDLY 0100000 Select form-feed delays:
FF0 0
FF1 0100000
If OPOST is set, output characters are post-processed as
indicated by the remaining flags, otherwise characters are
transmitted without change.
If OLCUC is set, a lower-case alphabetic character is
transmitted as the corresponding upper-case character. This
function is often used in conjunction with IUCLC.
If ONLCR is set, the NL character is transmitted as the CR-
NL character pair. If OCRNL is set, the CR character is
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TERMIOS(7-POSIX) RISC/os Reference Manual TERMIOS(7-POSIX)
transmitted as the NL character. If ONOCR is set, no CR
character is transmitted when at column 0 (first position).
If ONLRET is set, the NL character is assumed to do the
carriage-return function; the column pointer will be set to
0 and the delays specified for CR will be used. Otherwise
the NL character is assumed to do just the line-feed func-
tion; the column pointer will remain unchanged. The column
pointer is also set to 0 if the CR character is actually
transmitted.
The delay bits specify how long transmission stops to allow
for mechanical or other movement when certain characters are
sent to the terminal. In all cases a value of 0 indicates
no delay. If OFILL is set, fill characters will be
transmitted for delay instead of a timed delay. This is
useful for high baud rate terminals which need only a
minimal delay. If OFDEL is set, the fill character is DEL,
otherwise NUL.
If a form-feed or vertical-tab delay is specified, it lasts
for about 2 seconds.
New-line delay lasts about 0.10 seconds. If ONLRET is set,
the carriage-return delays are used instead of the new-line
delays. If OFILL is set, two fill characters will be
transmitted.
Carriage-return delay type 1 is dependent on the current
column position, type 2 is about 0.10 seconds, and type 3 is
about 0.15 seconds. If OFILL is set, delay type 1 transmits
two fill characters, and type 2, four fill characters.
Horizontal-tab delay type 1 is dependent on the current
column position. Type 2 is about 0.10 seconds. Type 3
specifies that tabs are to be expanded into spaces. If
OFILL is set, two fill characters will be transmitted for
any delay.
Backspace delay lasts about 0.05 seconds. If OFILL is set,
one fill character will be transmitted.
The actual delays depend on line speed and system load.
The initial output control value is all bits clear.
The c_cflag field describes the hardware control of the ter-
minal:
CBAUD 0000017 Baud rate:
B0 0 Hang up
B50 0000001 50 baud
B75 0000002 75 baud
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B110 0000003 110 baud
B134 0000004 134 baud
B150 0000005 150 baud
B200 0000006 200 baud
B300 0000007 300 baud
B600 0000010 600 baud
B1200 0000011 1200 baud
B1800 0000012 1800 baud
B2400 0000013 2400 baud
B4800 0000014 4800 baud
B9600 0000015 9600 baud
B19200 0000016 19200 baud
EXTA 0000016 External A
B38400 0000017 38400 baud
EXTB 0000017 External B
CSIZE 0000060 Character size:
CS5 0 5 bits
CS6 0000020 6 bits
CS7 0000040 7 bits
CS8 0000060 8 bits
CSTOPB 0000100 Send two stop bits, else one.
CREAD 0000200 Enable receiver.
PARENB 0000400 Parity enable.
PARODD 0001000 Odd parity, else even.
HUPCL 0002000 Hang up on last close.
CLOCAL 0004000 Local line, else dial-up.
CNEW_RTSCTS 0020000 Use RTS/CTS handshaking.
LOBLK 0040000 Block layer output.
CNEW_MDMBUF 0100000 Start/stop output when carrier drops.
The CBAUD bits specify the baud rate. The zero baud rate,
B0, is used to hang up the connection. If B0 is specified,
the data-terminal-ready signal will not be asserted. Nor-
mally, this will disconnect the line. For any particular
hardware, impossible speed changes are ignored.
The CSIZE bits specify the character size in bits for both
transmission and reception. This size does not include the
parity bit, if any. If CSTOPB is set, two stop bits are
used, otherwise one stop bit. For example, at 110 baud, two
stops bits are required.
If PARENB is set, parity generation and detection is enabled
and a parity bit is added to each character. If parity is
enabled, the PARODD flag specifies odd parity if set, other-
wise even parity is used.
If CREAD is set, the receiver is enabled. Otherwise no
characters will be received.
If HUPCL is set, the line will be disconnected when the last
process with the line open closes it or terminates. That
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is, the data-terminal-ready signal will not be asserted.
If CLOCAL is set, the line is assumed to be a local, direct
connection with no modem control. Otherwise modem control
is assumed.
If CNEW_RTSCTS is set, and the communications port supports
it, RTS/CTS handshaking will be used. When the input queue
becomes nearly full, RTS will be dropped. RTS will be
reasserted when the input queue has drained sufficiently.
Output is suspended when CTS is lowered and restarted when
CTS is raised.
If LOBLK is set, the output of a job control layer will be
blocked when it is not the current layer. Otherwise the
output generated by that layer will be multiplexed onto the
current layer.
If CNEW_MDMBUF is set, and the communications port supports
it, output will be blocked when carrier drops and resumed
when carrier returns. This is useless unless CLOCAL is set,
since otherwise the connection will be broken when carrier
drops.
The initial hardware control value after open is B300, CS8,
CREAD, HUPCL.
The c_lflag field of the argument structure is used to con-
trol various terminal functions. This field contains a bit-
wise OR of zero or more of the following:
ISIG 0000001 Enable signals.
ICANON 0000002 Canonical input (erase and kill processing).
IEXTEN 0000400 Enable extended functions.
XCASE 0000004 Canonical upper/lower presentation.
ECHO 0000010 Enable echo.
ECHOE 0000020 Echo erase character as BS-SP-BS.
ECHOK 0000040 Echo NL after kill character.
ECHONL 0000100 Echo NL.
NOFLSH 0000200 Disable flush after interrupt or quit.
TOSTOP 0100000 Send SIGTTOU on output by a background job.
LNEW_FLUSHO 0010000 Output is being flushed.
If ISIG is set, each input character is checked against the
special control characters INTR, SWTCH, and QUIT, and also,
SUSP and DSUSP. If an input character matches one of these
control characters, the function associated with that char-
acter is performed. If ISIG is not set, no checking is
done. Thus these special input functions are possible only
if ISIG is set. These functions may be disabled individu-
ally by changing the value of the control character to an
unlikely or impossible value (e.g., 0377). The value 0377,
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in particular, is reserved as the "undefined" value if the
kernel configuration option ``_posix_vdisable'' is enabled
(see kopt(8)); if this option is set, an input character
with the value 0377 will not match against any control char-
acter. Of course, if ISTRIP is set, and PARMRK is not set,
it is not possible to enter a character with value 0377.
If ICANON is set, canonical processing is enabled. This
enables the erase and kill edit functions, and the assembly
of input characters into lines delimited by NL, EOF, and
EOL. If ICANON is not set, read requests are satisfied
directly from the input queue. A read will not be satisfied
until at least MIN characters have been received or the
timeout value TIME has expired between characters. This
allows fast bursts of input to be read efficiently while
still allowing single character input. The MIN and TIME
values are stored in the position for the EOF and EOL char-
acters, respectively. The time value represents tenths of
seconds.
If IEXTEN is set, the following functions are recognized:
SWTCH, EOL2, DSUSP, RPRNT, FLUSH, WERASE, and STATUS. If
IEXTEN is not set, these functions are not recognized and
the corresponding input characters are processed as
described for ICANON, ISIG, IXON, and IXOFF.
If XCASE is set, and if ICANON is set, an upper-case letter
is accepted on input by preceding it with a \ character, and
is output preceded by a \ character. In this mode, the fol-
lowing escape sequences are generated on output and accepted
on input:
for: use:
` \'
| \!
~ \^
{ \(
} \)
\ \\
For example, A is input as \a, \n as \\n, and \N as \\\n.
If ECHO is set, characters are echoed as received.
When ICANON is set, the following echo functions are possi-
ble. If ECHO and ECHOE are set, the erase character is
echoed as ASCII BS SP BS, which will clear the last charac-
ter from a CRT screen. If ECHOE is set and ECHO is not set,
the erase character is echoed as ASCII SP BS. If ECHOK is
set, the NL character will be echoed after the kill charac-
ter to emphasize that the line will be deleted. Note that
an escape character preceding the erase or kill character
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removes any special function. If ECHONL is set, the NL
character will be echoed even if ECHO is not set. This is
useful for terminals set to local echo (so-called half
duplex). Unless escaped, the EOF character is not echoed.
Because EOT is the default EOF character, this prevents ter-
minals that respond to EOT from hanging up.
If NOFLSH is set, the normal flush of the input and output
queues associated with the quit, switch, and interrupt char-
acters will not be done.
If LNEW_FLUSHO is set, any pending output is discarded.
If TOSTOP is set, and job control is enabled for the termi-
nal a background job (that is, a job which has a job control
process group different from the process group of the termi-
nal) which attempts to write to the terminal will be blocked
from writing, and will be sent a SIGTTOU signal. Job con-
trol is enabled if ISIG is set.
The initial local control value has all bits clear.
FILES
/dev/tty*
SEE ALSO
stty(1) in the User's Reference Manual.
fork(2), ioctl(2), setpgrp(2), signal(2), setpgid(2-SysV),
ioctl(2-BSD), tty(4-BSD), setpgrp(2-BSD) in the Programmer's
Reference Manual.
kopt(8) in the System Administrator's Reference Manual.
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