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PROGRAM:

NAME

stty — set the options for a terminal

SYNOPSIS

stty [−a|−g]

stty operand...

DESCRIPTION

The stty utility shall set or report on terminal I/O characteristics for the device that
is its standard input. Without options or operands specified, it shall report the settings
of certain characteristics, usually those that differ from implementation-defined
defaults. Otherwise, it shall modify the terminal state according to the specified
operands. Detailed information about the modes listed in the first five groups below are
described in the Base Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal
Interface. Operands in the Combination Modes group (see Combination Modes) are
implemented using operands in the previous groups. Some combinations of operands are
mutually-exclusive on some terminal types; the results of using such combinations are
unspecified.

Typical implementations of this utility require a communications line configured to use
the termios interface defined in the System Interfaces volume of POSIX.1‐2008. On systems
where none of these lines are available, and on lines not currently configured to support
the termios interface, some of the operands need not affect terminal characteristics.

OPTIONS

The stty utility shall conform to the Base Definitions volume of POSIX.1‐2008, Section
12.2, Utility Syntax Guidelines.

The following options shall be supported:

−a Write to standard output all the current settings for the terminal.

−g Write to standard output all the current settings in an unspecified form that
can be used as arguments to another invocation of the stty utility on the same
system. The form used shall not contain any characters that would require
quoting to avoid word expansion by the shell; see Section 2.6, Word Expansions.

OPERANDS

The following operands shall be supported to set the terminal characteristics.

Control Modes
parenb (−parenb)
Enable (disable) parity generation and detection. This shall have the effect
of setting (not setting) PARENB in the termios c_cflag field, as defined in
the Base Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal
Interface.

parodd (−parodd)
Select odd (even) parity. This shall have the effect of setting (not setting)
PARODD in the termios c_cflag field, as defined in the Base Definitions volume
of POSIX.1‐2008, Chapter 11, General Terminal Interface.

cs5 cs6 cs7 cs8
Select character size, if possible. This shall have the effect of setting CS5,
CS6, CS7, and CS8, respectively, in the termios c_cflag field, as defined in
the Base Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal
Interface.

number Set terminal baud rate to the number given, if possible. If the baud rate is
set to zero, the modem control lines shall no longer be asserted. This shall
have the effect of setting the input and output termios baud rate values as
defined in the Base Definitions volume of POSIX.1‐2008, Chapter 11, General
Terminal Interface.

ispeed number
Set terminal input baud rate to the number given, if possible. If the input
baud rate is set to zero, the input baud rate shall be specified by the value
of the output baud rate. This shall have the effect of setting the input
termios baud rate values as defined in the Base Definitions volume of
POSIX.1‐2008, Chapter 11, General Terminal Interface.

ospeed number
Set terminal output baud rate to the number given, if possible. If the output
baud rate is set to zero, the modem control lines shall no longer be asserted.
This shall have the effect of setting the output termios baud rate values as
defined in the Base Definitions volume of POSIX.1‐2008, Chapter 11, General
Terminal Interface.

hupcl (−hupcl)
Stop asserting modem control lines (do not stop asserting modem control lines)
on last close. This shall have the effect of setting (not setting) HUPCL in
the termios c_cflag field, as defined in the Base Definitions volume of
POSIX.1‐2008, Chapter 11, General Terminal Interface.

hup (−hup) Equivalent to hupcl(−hupcl).

cstopb (−cstopb)
Use two (one) stop bits per character. This shall have the effect of setting
(not setting) CSTOPB in the termios c_cflag field, as defined in the Base
Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal Interface.

cread (−cread)
Enable (disable) the receiver. This shall have the effect of setting (not
setting) CREAD in the termios c_cflag field, as defined in the Base
Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal Interface.

clocal (−clocal)
Assume a line without (with) modem control. This shall have the effect of
setting (not setting) CLOCAL in the termios c_cflag field, as defined in the
Base Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal
Interface.

It is unspecified whether stty shall report an error if an attempt to set a Control Mode
fails.

Input Modes
ignbrk (−ignbrk)
Ignore (do not ignore) break on input. This shall have the effect of setting
(not setting) IGNBRK in the termios c_iflag field, as defined in the Base
Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal Interface.

brkint (−brkint)
Signal (do not signal) INTR on break. This shall have the effect of setting
(not setting) BRKINT in the termios c_iflag field, as defined in the Base
Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal Interface.

ignpar (−ignpar)
Ignore (do not ignore) bytes with parity errors. This shall have the effect of
setting (not setting) IGNPAR in the termios c_iflag field, as defined in the
Base Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal
Interface.

parmrk (−parmrk)
Mark (do not mark) parity errors. This shall have the effect of setting (not
setting) PARMRK in the termios c_iflag field, as defined in the Base
Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal Interface.

inpck (−inpck)
Enable (disable) input parity checking. This shall have the effect of setting
(not setting) INPCK in the termios c_iflag field, as defined in the Base
Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal Interface.

istrip (−istrip)
Strip (do not strip) input characters to seven bits. This shall have the
effect of setting (not setting) ISTRIP in the termios c_iflag field, as
defined in the Base Definitions volume of POSIX.1‐2008, Chapter 11, General
Terminal Interface.

inlcr (−inlcr)
Map (do not map) NL to CR on input. This shall have the effect of setting (not
setting) INLCR in the termios c_iflag field, as defined in the Base
Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal Interface.

igncr (−igncr)
Ignore (do not ignore) CR on input. This shall have the effect of setting (not
setting) IGNCR in the termios c_iflag field, as defined in the Base
Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal Interface.

icrnl (−icrnl)
Map (do not map) CR to NL on input. This shall have the effect of setting (not
setting) ICRNL in the termios c_iflag field, as defined in the Base
Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal Interface.

ixon (−ixon)
Enable (disable) START/STOP output control. Output from the system is stopped
when the system receives STOP and started when the system receives START. This
shall have the effect of setting (not setting) IXON in the termios c_iflag
field, as defined in the Base Definitions volume of POSIX.1‐2008, Chapter 11,
General Terminal Interface.

ixany (−ixany)
Allow any character to restart output. This shall have the effect of setting
(not setting) IXANY in the termios c_iflag field, as defined in the Base
Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal Interface.

ixoff (−ixoff)
Request that the system send (not send) STOP characters when the input queue
is nearly full and START characters to resume data transmission. This shall
have the effect of setting (not setting) IXOFF in the termios c_iflag field,
as defined in the Base Definitions volume of POSIX.1‐2008, Chapter 11, General
Terminal Interface.

Output Modes
opost (−opost)
Post-process output (do not post-process output; ignore all other output
modes). This shall have the effect of setting (not setting) OPOST in the
termios c_oflag field, as defined in the Base Definitions volume of
POSIX.1‐2008, Chapter 11, General Terminal Interface.

ocrnl (−ocrnl)
Map (do not map) CR to NL on output This shall have the effect of setting (not
setting) OCRNL in the termios c_oflag field, as defined in the Base
Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal Interface.

onocr (−onocr)
Do not (do) output CR at column zero. This shall have the effect of setting
(not setting) ONOCR in the termios c_oflag field, as defined in the Base
Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal Interface.

onlret (−onlret)
The terminal newline key performs (does not perform) the CR function. This
shall have the effect of setting (not setting) ONLRET in the termios c_oflag
field, as defined in the Base Definitions volume of POSIX.1‐2008, Chapter 11,
General Terminal Interface.

ofill (−ofill)
Use fill characters (use timing) for delays. This shall have the effect of
setting (not setting) OFILL in the termios c_oflag field, as defined in the
Base Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal
Interface.

ofdel (−ofdel)
Fill characters are DELs (NULs). This shall have the effect of setting (not
setting) OFDEL in the termios c_oflag field, as defined in the Base
Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal Interface.

cr0 cr1 cr2 cr3
Select the style of delay for CRs. This shall have the effect of setting CRDLY
to CR0, CR1, CR2, or CR3, respectively, in the termios c_oflag field, as
defined in the Base Definitions volume of POSIX.1‐2008, Chapter 11, General
Terminal Interface.

nl0 nl1 Select the style of delay for NL. This shall have the effect of setting NLDLY
to NL0 or NL1, respectively, in the termios c_oflag field, as defined in the
Base Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal
Interface.

tab0 tab1 tab2 tab3
Select the style of delay for horizontal tabs. This shall have the effect of
setting TABDLY to TAB0, TAB1, TAB2, or TAB3, respectively, in the termios
c_oflag field, as defined in the Base Definitions volume of POSIX.1‐2008,
Chapter 11, General Terminal Interface. Note that TAB3 has the effect of
expanding <tab> characters to <space> characters.

tabs (−tabs)
Synonym for tab0 (tab3).

bs0 bs1 Select the style of delay for <backspace> characters. This shall have the
effect of setting BSDLY to BS0 or BS1, respectively, in the termios c_oflag
field, as defined in the Base Definitions volume of POSIX.1‐2008, Chapter 11,
General Terminal Interface.

ff0 ff1 Select the style of delay for <form-feed> characters. This shall have the
effect of setting FFDLY to FF0 or FF1, respectively, in the termios c_oflag
field, as defined in the Base Definitions volume of POSIX.1‐2008, Chapter 11,
General Terminal Interface.

vt0 vt1 Select the style of delay for <vertical-tab> characters. This shall have the
effect of setting VTDLY to VT0 or VT1, respectively, in the termios c_oflag
field, as defined in the Base Definitions volume of POSIX.1‐2008, Chapter 11,
General Terminal Interface.

Local Modes
isig (−isig)
Enable (disable) the checking of characters against the special control
characters INTR, QUIT, and SUSP. This shall have the effect of setting (not
setting) ISIG in the termios c_lflag field, as defined in the Base Definitions
volume of POSIX.1‐2008, Chapter 11, General Terminal Interface.

icanon (−icanon)
Enable (disable) canonical input (ERASE and KILL processing). This shall have
the effect of setting (not setting) ICANON in the termios c_lflag field, as
defined in the Base Definitions volume of POSIX.1‐2008, Chapter 11, General
Terminal Interface.

iexten (−iexten)
Enable (disable) any implementation-defined special control characters not
currently controlled by icanon, isig, ixon, or ixoff. This shall have the
effect of setting (not setting) IEXTEN in the termios c_lflag field, as
defined in the Base Definitions volume of POSIX.1‐2008, Chapter 11, General
Terminal Interface.

echo (−echo)
Echo back (do not echo back) every character typed. This shall have the effect
of setting (not setting) ECHO in the termios c_lflag field, as defined in the
Base Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal
Interface.

echoe (−echoe)
The ERASE character visually erases (does not erase) the last character in the
current line from the display, if possible. This shall have the effect of
setting (not setting) ECHOE in the termios c_lflag field, as defined in the
Base Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal
Interface.

echok (−echok)
Echo (do not echo) NL after KILL character. This shall have the effect of
setting (not setting) ECHOK in the termios c_lflag field, as defined in the
Base Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal
Interface.

echonl (−echonl)
Echo (do not echo) NL, even if echo is disabled. This shall have the effect of
setting (not setting) ECHONL in the termios c_lflag field, as defined in the
Base Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal
Interface.

noflsh (−noflsh)
Disable (enable) flush after INTR, QUIT, SUSP. This shall have the effect of
setting (not setting) NOFLSH in the termios c_lflag field, as defined in the
Base Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal
Interface.

tostop (−tostop)
Send SIGTTOU for background output. This shall have the effect of setting (not
setting) TOSTOP in the termios c_lflag field, as defined in the Base
Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal Interface.

Special Control Character Assignments
<control>‐character string
Set <control>‐character to string. If <control>‐character is one of the character
sequences in the first column of the following table, the corresponding the Base
Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal Interface control
character from the second column shall be recognized. This has the effect of setting
the corresponding element of the termios c_cc array (see the Base Definitions volume
of POSIX.1‐2008, Chapter 13, Headers, <termios.h>).

Table: Control Character Names in stty

┌──────────────────┬────────────────┬─────────────────┐
│Control Character │ c_cc Subscript │ Description │
├──────────────────┼────────────────┼─────────────────┤
│eof │ VEOF │ EOF character │
│eol │ VEOL │ EOL character │
│erase │ VERASE │ ERASE character │
│intr │ VINTR │ INTR character │
│kill │ VKILL │ KILL character │
│quit │ VQUIT │ QUIT character │
│susp │ VSUSP │ SUSP character │
│start │ VSTART │ START character │
│stop │ VSTOP │ STOP character │
└──────────────────┴────────────────┴─────────────────┘
If string is a single character, the control character shall be set to that
character. If string is the two-character sequence "^−" or the string undef, the
control character shall be set to _POSIX_VDISABLE , if it is in effect for the
device; if _POSIX_VDISABLE is not in effect for the device, it shall be treated as
an error. In the POSIX locale, if string is a two-character sequence beginning with
<circumflex> ('^'), and the second character is one of those listed in the "^c"
column of the following table, the control character shall be set to the
corresponding character value in the Value column of the table.

Table: Circumflex Control Characters in stty

┌──────────────┬────────────────┬──────────────┐
│ ^c Value │ ^c Value │ ^c Value │
├──────────────┼────────────────┼──────────────┤
│a, A <SOH> │ l, L <FF> │ w, W <ETB> │
│b, B <STX> │ m, M <CR> │ x, X <CAN> │
│c, C <ETX> │ n, N <SO> │ y, Y <EM> │
│d, D <EOT> │ o, O <SI> │ z, Z <SUB> │
│e, E <ENQ> │ p, P <DLE> │ [ <ESC> │
│f, F <ACK> │ q, Q <DC1> │ \ <FS> │
│g, G <BEL> │ r, R <DC2> │ ] <GS> │
│h, H <BS> │ s, S <DC3> │ ^ <RS> │
│i, I <HT> │ t, T <DC4> │ _ <US> │
│j, J <LF> │ u, U <NAK> │ ? <DEL> │
│k, K <VT> │ v, V <SYN> │ │
└──────────────┴────────────────┴──────────────┘
min number
Set the value of MIN to number. MIN is used in non-canonical mode input processing
(icanon).

time number
Set the value of TIME to number. TIME is used in non-canonical mode input
processing (icanon).

Combination Modes
saved settings
Set the current terminal characteristics to the saved settings produced by the −g
option.

evenp or parity
Enable parenb and cs7; disable parodd.

oddp
Enable parenb, cs7, and parodd.

−parity, −evenp, or −oddp
Disable parenb, and set cs8.

raw (−raw or cooked)
Enable (disable) raw input and output. Raw mode shall be equivalent to setting:

stty cs8 erase ^− kill ^− intr ^− \
quit ^− eof ^− eol ^− −post −inpck

nl (−nl)
Disable (enable) icrnl. In addition, −nl unsets inlcr and igncr.

ek Reset ERASE and KILL characters back to system defaults.

sane
Reset all modes to some reasonable, unspecified, values.

STDIN

Although no input is read from standard input, standard input shall be used to get the
current terminal I/O characteristics and to set new terminal I/O characteristics.

INPUT FILES

None.

ENVIRONMENT VARIABLES

The following environment variables shall affect the execution of stty:

LANG Provide a default value for the internationalization variables that are unset or
null. (See the Base Definitions volume of POSIX.1‐2008, Section 8.2,
Internationalization Variables for the precedence of internationalization
variables used to determine the values of locale categories.)

LC_ALL If set to a non-empty string value, override the values of all the other
internationalization variables.

LC_CTYPE This variable determines the locale for the interpretation of sequences of bytes
of text data as characters (for example, single-byte as opposed to multi-byte
characters in arguments) and which characters are in the class print.

LC_MESSAGES
Determine the locale that should be used to affect the format and contents of
diagnostic messages written to standard error.

NLSPATH Determine the location of message catalogs for the processing of LC_MESSAGES.

ASYNCHRONOUS EVENTS

Default.

STDOUT

If operands are specified, no output shall be produced.

If the −g option is specified, stty shall write to standard output the current settings in
a form that can be used as arguments to another instance of stty on the same system.

If the −a option is specified, all of the information as described in the OPERANDS section
shall be written to standard output. Unless otherwise specified, this information shall be
written as <space>-separated tokens in an unspecified format, on one or more lines, with
an unspecified number of tokens per line. Additional information may be written.

If no options or operands are specified, an unspecified subset of the information written
for the −a option shall be written.

If speed information is written as part of the default output, or if the −a option is
specified and if the terminal input speed and output speed are the same, the speed
information shall be written as follows:

"speed %d baud;", <speed>

Otherwise, speeds shall be written as:

"ispeed %d baud; ospeed %d baud;", <ispeed>, <ospeed>

In locales other than the POSIX locale, the word baud may be changed to something more
appropriate in those locales.

If control characters are written as part of the default output, or if the −a option is
specified, control characters shall be written as:

"%s = %s;", <control-character name>, <value>

where <value> is either the character, or some visual representation of the character if
it is non-printable, or the string undef if the character is disabled.

STDERR

The standard error shall be used only for diagnostic messages.

OUTPUT FILES

None.

EXTENDED DESCRIPTION

None.

EXIT STATUS

The following exit values shall be returned:

0 The terminal options were read or set successfully.

>0 An error occurred.

CONSEQUENCES OF ERRORS

Default.

The following sections are informative.

APPLICATION USAGE

The −g flag is designed to facilitate the saving and restoring of terminal state from the
shell level. For example, a program may:

saveterm="$(stty −g)" # save terminal state
stty (new settings) # set new state
... # ...
stty $saveterm # restore terminal state

Since the format is unspecified, the saved value is not portable across systems.

Since the −a format is so loosely specified, scripts that save and restore terminal
settings should use the −g option.

EXAMPLES

None.

RATIONALE

The original stty description was taken directly from System V and reflected the System V
terminal driver termio. It has been modified to correspond to the terminal driver
termios.

Output modes are specified only for XSI-conformant systems. All implementations are
expected to provide stty operands corresponding to all of the output modes they support.

The stty utility is primarily used to tailor the user interface of the terminal, such as
selecting the preferred ERASE and KILL characters. As an application programming utility,
stty can be used within shell scripts to alter the terminal settings for the duration of
the script.

The termios section states that individual disabling of control characters is possible
through the option _POSIX_VDISABLE. If enabled, two conventions currently exist for
specifying this: System V uses "^−", and BSD uses undef. Both are accepted by stty in
this volume of POSIX.1‐2008. The other BSD convention of using the letter 'u' was rejected
because it conflicts with the actual letter 'u', which is an acceptable value for a
control character.

Early proposals did not specify the mapping of "^c" to control characters because the
control characters were not specified in the POSIX locale character set description file
requirements. The control character set is now specified in the Base Definitions volume of
POSIX.1‐2008, Chapter 3, Definitions, so the historical mapping is specified. Note that
although the mapping corresponds to control-character key assignments on many terminals
that use the ISO/IEC 646:1991 standard (or ASCII) character encodings, the mapping
specified here is to the control characters, not their keyboard encodings.

Since termios supports separate speeds for input and output, two new options were added to
specify each distinctly.

Some historical implementations use standard input to get and set terminal
characteristics; others use standard output. Since input from a login TTY is usually
restricted to the owner while output to a TTY is frequently open to anyone, using standard
input provides fewer chances of accidentally (or maliciously) altering the terminal
settings of other users. Using standard input also allows stty −a and stty −g output to be
redirected for later use. Therefore, usage of standard input is required by this volume of
POSIX.1‐2008.

FUTURE DIRECTIONS

None.

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