STTY(1)

STTY(1) | General Commands Manual | STTY(1)

# NAME

`stty` —
set options for a terminal device interface

# SYNOPSIS

`stty` | [`-a` | `-e` | `-g`] [`-f` file] [operand ...]

# DESCRIPTION

The `stty` utility sets or reports on terminal characteristics for the device that is its standard input. If no options or operands are specified, it reports the settings of a subset of characteristics as well as additional ones if they differ from their default values. Otherwise it modifies the terminal state according to the specified arguments. Some combinations of arguments are mutually exclusive on some terminal types.

The following options are available:

`-a`
  Display all the current settings for the terminal to standard output as per IEEE Std 1003.2 (“POSIX.2”).
`-e`
  Display all the current settings for the terminal to standard output in the traditional BSD “all” and “everything” formats.
`-f` file
  Open and use the terminal named by file rather than using standard input. The file is opened using the `O_NONBLOCK` flag of `open`(), making it possible to set or display settings on a terminal that might otherwise block on the open.
`-g`
  Display all the current settings for the terminal to standard output in a form that may be used as an argument to a subsequent invocation of `stty` to restore the current terminal state as per IEEE Std 1003.2 (“POSIX.2”).

The following arguments are available to set the terminal characteristics:

## Control Modes

Control mode flags affect hardware characteristics associated with the terminal. This corresponds to the c_cflag of the termios(4) structure.

`parenb` (`-parenb`)
  Enable (disable) parity generation and detection.
`parodd` (`-parodd`)
  Select odd (even) parity.
`cs5 cs6 cs7 cs8`
  Select character size, if possible.
number
  Set terminal baud rate to number, if possible. If the baud rate is set to zero, modem control is no longer asserted; this will normally hang up the line, including on ptys and other devices not physically connected to modems.
`ispeed` number
  Set terminal input baud rate to number, if possible. If the input baud rate is set to zero, the input baud rate is set to the value of the output baud rate.
`ospeed` number
  Set terminal output baud rate to number, if possible. If the output baud rate is set to zero, modem control is no longer asserted.
`speed` number
  This sets both `ispeed` and `ospeed` to number.
`hupcl` (`-hupcl`)
  Stop asserting modem control (do not stop asserting modem control) on last close.
`hup` (`-hup`)
  Same as hupcl (`-hupcl`).
`cstopb` (`-cstopb`)
  Use two (one) stop bits per character.
`cread` (`-cread`)
  Enable (disable) the receiver.
`clocal` (`-clocal`)
  Assume a line without (with) modem control.
`crtscts` (`-crtscts`)
  Enable RTS/CTS flow control.
`cdtrcts` (`-cdtrcts`)
  Enable DTR/CTS flow control (if supported).

## Input Modes

This corresponds to the c_iflag of the termios(4) structure.

`ignbrk` (`-ignbrk`)
  Ignore (do not ignore) break on input.
`brkint` (`-brkint`)
  Signal (do not signal) `INTR` on break.
`ignpar` (`-ignpar`)
  Ignore (do not ignore) parity errors.
`parmrk` (`-parmrk`)
  Mark (do not mark) parity errors.
`inpck` (`-inpck`)
  Enable (disable) input parity checking.
`istrip` (`-istrip`)
  Strip (do not strip) input characters to seven bits.
`inlcr` (`-inlcr`)
  Map (do not map) `NL` to `CR` on input.
`igncr` (`-igncr`)
  Ignore (do not ignore) `CR` on input.
`icrnl` (`-icrnl`)
  Map (do not map) `CR` to `NL` on input.
`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`, or if `ixany` is set, any character restarts output.
`ixoff` (`-ixoff`)
  Request that the system send (not send) `START/STOP` characters when the input queue is nearly empty/full.
`ixany` (`-ixany`)
  Allow any character (allow only `START`) to restart output.
`imaxbel` (`-imaxbel`)
  The system imposes a limit of `MAX_INPUT` (currently 255) characters in the input queue. If `imaxbel` is set and the input queue limit has been reached, subsequent input causes the system to send an ASCII BEL character to the output queue (the terminal beeps at you). Otherwise, if `imaxbel` is unset and the input queue is full, the next input character causes the entire input and output queues to be discarded.

## Output Modes

This corresponds to the c_oflag of the termios(4) structure.

`opost` (`-opost`)
  Post-process output (do not post-process output; ignore all other output modes).
`onlcr` (`-onlcr`)
  Map (do not map) `NL` to `CR-NL` on output.
`ocrnl` (`-ocrnl`)
  Map (do not map) `CR` to `NL` on output.
`oxtabs` (`-oxtabs`)
  Expand (do not expand) tabs to spaces on output.
`onocr` (`-onocr`)
  Do not (do) output CRs at column zero.
`onlret` (`-onlret`)
  On the terminal NL performs (does not perform) the CR function.

## Local Modes

Local mode flags (lflags) affect various and sundry characteristics of terminal processing. Historically the term "local" pertained to new job control features implemented by Jim Kulp on a PDP-11/70 at IIASA. Later the driver ran on the first VAX at Evans Hall, UC Berkeley, where the job control details were greatly modified but the structure definitions and names remained essentially unchanged. The second interpretation of the ‘l’ in lflag is “line discipline flag”, which corresponds to the c_lflag of the termios(4) structure.

`isig` (`-isig`)
  Enable (disable) the checking of characters against the special control characters `INTR`, `QUIT`, and `SUSP`.
`icanon` (`-icanon`)
  Enable (disable) canonical input (`ERASE` and `KILL` processing).
`iexten` (`-iexten`)
  Enable (disable) any implementation defined special control characters not currently controlled by icanon, isig, or ixon.
`echo` (`-echo`)
  Echo back (do not echo back) every character typed.
`echoe` (`-echoe`)
  The `ERASE` character shall (shall not) visually erase the last character in the current line from the display, if possible.
`echok` (`-echok`)
  Echo (do not echo) `NL` after `KILL` character.
`echoke` (`-echoke`)
  The `KILL` character shall (shall not) visually erase the current line from the display, if possible.
`echonl` (`-echonl`)
  Echo (do not echo) `NL`, even if echo is disabled.
`echoctl` (`-echoctl`)
  If `echoctl` is set, echo control characters as ^X. Otherwise control characters echo as themselves.
`echoprt` (`-echoprt`)
  For printing terminals. If set, echo erased characters backwards within “\” and “/”. Otherwise, disable this feature.
`noflsh` (`-noflsh`)
  Disable (enable) flush after `INTR`, `QUIT`, `SUSP`.
`tostop` (`-tostop`)
  Send (do not send) `SIGTTOU` for background output. This causes background jobs to stop if they attempt terminal output.
`altwerase` (`-altwerase`)
  Use (do not use) an alternative word erase algorithm when processing `WERASE` characters. This alternative algorithm considers sequences of alphanumeric/underscores as words. It also skips the first preceding character in its classification (as a convenience since the one preceding character could have been erased with simply an `ERASE` character).
`mdmbuf` (`-mdmbuf`)
  If set, flow control output based on condition of Carrier Detect. Otherwise writes return an error if Carrier Detect is low (and Carrier is not being ignored with the `CLOCAL` flag).
`flusho` (`-flusho`)
  Indicates output is (is not) being discarded.
`pendin` (`-pendin`)
  Indicates input is (is not) pending after a switch from non-canonical to canonical mode and will be re-input when a read becomes pending or more input arrives.

## Control Characters

control-character string
  Set control-character to string string. If the string is a single character, then the control character is set to that character. If the string is the two character sequence "^-" or the string "undef", then the control character is disabled (i.e., set to {`_POSIX_VDISABLE`}).

  Recognized control characters:

  control- |  |
  character | Subscript | Description
  _________ | _________ | _______________
  eof | VEOF | EOF character
  eol | VEOL | EOL character
  eol2 | VEOL2 | EOL2 character
  erase | VERASE | ERASE character
  werase | VWERASE | WERASE character
  kill | VKILL | KILL character
  reprint | VREPRINT | REPRINT character
  intr | VINTR | INTR character
  quit | VQUIT | QUIT character
  susp | VSUSP | SUSP character
  dsusp | VDSUSP | DSUSP character
  start | VSTART | START character
  stop | VSTOP | STOP character
  lnext | VLNEXT | LNEXT character
  status | VSTATUS | STATUS character
  discard | VDISCARD | DISCARD character

`min` number
`time` number
  Set the value of min or time to number. `MIN` and `TIME` are 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`, `-oddp`
  Disable parenb, and set cs8.
`nl` (`-nl`)
  Enable (disable) icrnl. In addition -nl unsets inlcr and igncr.
`ek`
  Reset `ERASE` and `KILL` characters back to system defaults.
`sane`
  Resets all modes to reasonable values for interactive terminal use.
`insane`
  Sets all modes to random values, which are very likely (but not guaranteed) to be unreasonable for interactive terminal use.
`tty`
  Set the line discipline to the standard terminal line discipline `TTYDISC`.
`crt` (`-crt`)
  Set (disable) all modes suitable for a CRT display device.
`kerninfo` (`-kerninfo`)
  Enable (disable) the system generated status line associated with processing a `STATUS` character (usually set to ^T). The status line consists of the system load average, the current command name, its process ID, the event the process is waiting on (or the status of the process), the user and system times, percent CPU, and current memory usage.
`cols` number
  The terminal size is recorded as having number columns.
`columns` number
  An alias for `cols`.
`rows` number
  The terminal size is recorded as having number rows.
`dec`
  Set modes suitable for users of Digital Equipment Corporation systems (`ERASE`, `KILL`, and `INTR` characters are set to ^?, ^U, and ^C; `ixany` is disabled, and `crt` is enabled).
`extproc` (`-extproc`)
  If set, this flag indicates that some amount of terminal processing is being performed by either the terminal hardware or by the remote side connected to a pty.
`raw` (`-raw`)
  If set, change the modes of the terminal so that no input or output processing is performed. If unset, change the modes of the terminal to some reasonable state that performs input and output processing. Note that since the terminal driver no longer has a single `RAW` bit, it is not possible to intuit what flags were set prior to setting `raw`. This means that unsetting `raw` may not put back all the setting that were previously in effect. To set the terminal into a raw state and then accurately restore it, the following shell code is recommended:

      save_state=$(stty -g)
      stty raw
      ...
      stty "$save_state"

`size`
  The size of the terminal is printed as two numbers on a single line, first rows, then columns.

## Compatibility Modes

These modes remain for compatibility with the previous version of the `stty` utility.

`all`
  Reports all the terminal modes as with `stty` `-a` except that the control characters are printed in a columnar format.
`everything`
  Same as `all`.
`cooked`
  Same as `sane`.
`cbreak`
  If set, enables `brkint`, `ixon`, `imaxbel`, `opost`, `isig`, `iexten`, and `-icanon`. If unset, same as `sane`.
`new`
  Same as `tty`.
`old`
  Same as `tty`.
`newcrt` (`-newcrt`)
  Same as `crt`.
`pass8`
  The converse of `parity`.
`tandem` (`-tandem`)
  Same as `ixoff`.
`decctlq` (`-decctlq`)
  The converse of `ixany`.
`crterase` (`-crterase`)
  Same as `echoe`.
`crtbs` (`-crtbs`)
  Same as `echoe`.
`crtkill` (`-crtkill`)
  Same as `echoke`.
`ctlecho` (`-ctlecho`)
  Same as `echoctl`.
`prterase` (`-prterase`)
  Same as `echoprt`.
`litout` (`-litout`)
  The converse of `opost`.
`tabs` (`-tabs`)
  The converse of `oxtabs`.
`brk` value
  Same as the control character `eol`.
`flush` value
  Same as the control character `discard`.
`rprnt` value
  Same as the control character `reprint`.

## Control operations

These operations are not modes, but rather commands to be performed by the tty layer.

`ostart`
  Performs a "start output" operation, as normally done by an incoming START character when `ixon` is set.
`ostop`
  Performs a "stop output" operation, as normally done by an incoming STOP character when `ixon` is set.

# EXIT STATUS

The `stty` utility exits 0 on success, and >0 if an error occurs.

# SEE ALSO

termios(4), tty(4)

# STANDARDS

The `stty` utility is expected to be IEEE Std 1003.2 (“POSIX.2”) compatible. The `-e` and `-f` flags are extensions to the standard, as are the operands mentioned in the control operations section.

# HISTORY

An `stty` utility appeared in Version 2 AT&T UNIX.

May 14, 2022 | NetBSD 10.1