stty
is a tool used to set the input and output settings for
the terminal communication interface .
It can also read the settings of the terminal communication interface .
In
the early days of computing , the terminal was a device used for input and output ,
and it was connected to a computer.
An example of input is the keyboard ,
and an example of output is the video monitor or the printer.
Printer Terminal
Video Terminal
When
Unix started , it was written for the PDP computer .
The PDP computer had multiple communication interface ,
such as DL11 the Single Asynchronous Line Interface ,
and DH11 the 16-Line Programmable Asynchronous interface.
These interface were used to connect terminals ,
and they were named
tty
and
tty0
…
ttyn
by unix.
The tty
interface was not programmable ,
so its transmission speed or its mode could not be set , whereas
the
tty0
…
ttyn
interfaces
were programmable , so
their transmissions speed and modes could be set.
An example of setting the mode of a programmable interface is : setting it to raw .
In raw mode instead of reading a whole line , characters are read one at a time .
In addition to that , some special characters such as the
#
will not work .
The
#
character is used to erase the the last typed character.
Nowadays
terminals are emulated in a graphical display .
They still act the same way they used to act in unix in accordance with the
Single UNIX Specification , IEEE Std 1003.2 (POSIX.2) ,
which is related to shell and utilities .
The
terminal communication interface settings that can be set and read by
stty
are divided in the following categories :
control or special characters : Characters that can
control the input , output , and that can send signals for example to interrupt or
suspend a program .
special settings : For example
the speed of the input and output and the number of rows and columns of the terminal .
control settings : Related to the terminal
hardware properties ; for example , parity bit generation in output and detection in input.
input settings : Sets the input modes , for example
if input upper case characters are automatically mapped to lower case characters .
output settings : Sets the output modes , for example
if output lower case characters are automatically mapped to upper case characters .
local settings : Related to terminal processing , for example
if the terminal will process the delete and signal characters . An example of delete
character , is
werase
which erases the word previous to the currently selected character.
An example of signal character is
susp
which will send a suspend signal to a program .
combination settings :
Settings that combine one or more settings , for example the
oddp setting
which combines the
parenb
,
parodd
and
cs7
settings .
The
control characters can be used to control the input output
and to send signals to programs .
stty
can set the following control or special characters :
eof
The end of file character is used to terminate the input .
By default the end of file character is
ctrl-D
. ctrl-D is
case insensitive .
The
wc
program
with the
-lwm option
is used to count the
number of new lines , words and characters in a file
.
If no file name is specified or the
-
option is used,
wc can
count the number
of new lines words and characters from the standard input.
ctrl-D
can be used to terminate the input.
@debian:~$ wc -lwm -
# wc program with :
# l option to count the number of new lines .
# w option to count the number of words .
# m option to count the number of characters .
# - option to read from standard input .
hello world
hello world
# Written on standard input , hello world
# followed by an enter , followed by a hello world
# followed by an enter , and a ctrl-d to terminate
# the input.
2 4 24 -
# The number of new lines is 2 , the number
# of words is 4 and the number of characters
# is 24 .
The
eof
character can also be used to terminate the
input for the terminal.
If
ctrl-d
is pressed and no other program is running
the terminal will exit .
enlighterstty eof <character>
can be used to set the terminal
eof
character .
enlighter<character>
is to be substituted with an appropriate character for example
a
,
b
or a control sequence for example
^n
…
@debian:~$ stty -a
# Display the terminal communication
# interface settings.
..
eof = ^D;
...
# eof character is ^D
@debian:~$ stty eof ^n
# set the eof character to ctrl-N
# N is case insensitive.
@debian:~$ stty -a
# Display the terminal communication
# interface settings.
..
eof = ^N;
...
# The eof character is now ctrl-N
erase , werase , kill
The
erase
control
character will erase the character previous to the selected one ,
werase
will erase the word previous to the selected character, and
kill
will erase the current line .
By default erase is assigned the
control character
^? ,
werase
is assigned the control character
^W
and kill
is assigned the control character
^U .
The control characters are case insensitive.
enlighterstty erase <character> ,
enlighterstty werase <character> ,
and enlighterstty kill <character>
can be used to set the terminal
erase ,
werase
and
kill
characters .
enlighter<character>
is to be substituted with an appropriate character for example
a
,
b
or a control sequence for example
^n
…
@debian:~$ stty -a
# Display the terminal communication
# interface settings.
..
erase = ^?; kill = ^U; werase = ^W;
...
# erase character is ^?
# werase character is ^W
# kill character is ^U
@debian:~$ stty erase ^e
# set the erase character to ctrl-E
# E is case insensitive .
@debian:~$ stty werase ^w
# set the werase character to ctrl-W
# W is case insensitive .
@debian:~$ stty kill ^k
# set the kill character to ctrl-K
# K is case insensitive .
@debian:~$ stty -a
# Display the terminal communication
# interface settings.
..
erase = ^E; kill = ^K; werase = ^W;
...
# erase character is now ^E
# werase character is now ^W
# kill character is now ^K
stop , start
The
stop
control
character will stop the output ,
start
will resume it after being
stopped .
By default stop is assigned the
control character
^S , and
start
is assigned the control character
^Q .
Both control characters are case
insensitive .
enlighterstty stop <character>
and enlighterstty start <character>
can be used to set the terminal
stop and
start
characters.
enlighter<character>
is to be substituted with an appropriate character for example
a
,
b
or a control sequence for example
^n
…
@debian:~$ stty -a
# Display the terminal communication
# interface settings.
..
start = ^Q; stop = ^S;
...
# start character is ^Q
# stop character is ^S
@debian:~$ stty stop ^s
# set the stop character to ctrl-S
# S is case insensitive .
@debian:~$ stty start ^t
# set the start character to ctrl-T
# T is case insensitive .
@debian:~$ stty -a
# Display the terminal communication
# interface settings.
..
start = ^T; stop = ^S;
...
# start character is now ^T
# stop character is now ^S
# For example , if the output of a
# program is too long , it can be
# paused and resumed by using the
# start and stop control characters .
intr
The
intr
control
character sends the interrupt signal ,
SIGINT
to a process .
A process should terminate when receiving this signal .
By default intr is assigned the
control character
^C . The control character ^C is
case insensitive .
enlighterstty intr <character>
can be used to set the terminal
intr
character.
enlighter<character>
is to be substituted with an appropriate character for example
a
,
b
or a control sequence for example
^n
…
@debian:~$ stty -a
# Display the terminal communication
# interface settings.
..
intr = ^C;
...
# interrupt character is ^C
@debian:~$ stty intr ^i
# set the intr character to ctrl-I
# I is case insensitive
@debian:~$ stty -a
# Display the terminal communication
# interface settings.
..
intr = ^I;
...
# interrupt character is now ^I
@debian:~$ ping yahoo.com
PING yahoo.com (72.30.35.10) 56(84) bytes of data.
64 bytes from yahoo.com (72.30.35.10): icmp_seq=1 ttl=63 time=193 ms
64 bytes from yahoo.com (72.30.35.10): icmp_seq=2 ttl=63 time=252 ms
^I
--- yahoo.com ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 9ms
rtt min/avg/max/mdev = 192.675/222.247/251.820/29.576 ms
# ctrl-I is pressed , this causes
# a keyboard interrupt signal to be
# sent to ping , ping terminates.
quit
The
quit
control
character sends the quit signal ,
SIGQUIT
to a process .
A process should terminate when receiving this signal and
create a core dump.
By default quit is assigned the
control character
^\ .
enlighterstty quit <character>
can be used to set the terminal
quit
character.
enlighter<character>
is to be substituted with an appropriate character for example
a
,
b
or a control sequence for example
^n
…
@debian:~$ stty -a
# Display the terminal communication
# interface settings .
..
quit = ^\;
...
# quit character is ^\
@debian:~$ stty quit ^q
# set the quit character to ctrl-Q
# Q is case insensitive .
@debian:~$ stty -a
# Display the terminal communication
# interface settings.
..
quit = ^Q;
...
# quit character is now ^Q
@debian:~$ ping yahoo.com
PING yahoo.com (72.30.35.9) 56(84) bytes of data.
64 bytes from media-router-fp1.prod1.media.vip.bf1.yahoo.com (72.30.35.9): icmp_seq=1 ttl=63 time=163 ms
...
# ctrl-Q is pressed , it is ignored by
# the ping program , and the ping
# program does not terminate .
susp
The
susp
control
character sends the suspend signal ,
SIGSTOP
to a process .
A process is suspended when it receives this signal.
By default susp is assigned the
control character
^Z . The control
character ^Z is
case insensitive .
enlighterstty susp <character>
can be used to set the terminal
susp
character.
enlighter<character>
is to be substituted with an appropriate character for example
a
,
b
or a control sequence for example
^n
…
@debian:~$ stty -a
# Display the terminal communication
# interface settings.
..
susp = ^Z;
...
# susp character is ^Z
@debian:~$ stty susp ^Z
# set the susp character to ctrl-Z
# Z is case insensitive
@debian:~$ stty -a
# Display the terminal communication
# interface settings.
..
susp = ^Z;
...
# susp character is now ^Z
@debian:~$ ping yahoo.com
PING yahoo.com (72.30.35.9) 56(84) bytes of data.
64 bytes from media-router-fp1.prod1.media.vip.bf1.yahoo.com (72.30.35.9): icmp_seq=1 ttl=63 time=196 ms
64 bytes from media-router-fp1.prod1.media.vip.bf1.yahoo.com (72.30.35.9): icmp_seq=2 ttl=63 time=189 ms
64 bytes from media-router-fp1.prod1.media.vip.bf1.yahoo.com (72.30.35.9): icmp_seq=3 ttl=63 time=187 ms
^Z
[1]+ Stopped ping yahoo.com
# ctrl-Z is pressed , this causes the
# ping program to be suspended.
@debian:~$ fg
# fg causes ping to resume in the foreground.
ping yahoo.com
64 bytes from media-router-fp1.prod1.media.vip.bf1.yahoo.com (72.30.35.9): icmp_seq=4 ttl=63 time=186 ms
64 bytes from media-router-fp1.prod1.media.vip.bf1.yahoo.com (72.30.35.9): icmp_seq=5 ttl=63 time=183 ms
^C
--- yahoo.com ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 631ms
rtt min/avg/max/mdev = 182.678/188.371/196.300/4.493 ms
# ctrl-C is pressed in line 37,
# this causes the keyboard inrerrupt signal
# to be sent to ping , ping terminates .
The
special settings that can be set by
stty
are :
speed
enlighterstty <speed>
can be used to set the input and output speed in baud. Baud is the number of symbol per
seconds .
enlighter<speed>
is to be substituted by an appropriate speed .
@debian:~$ stty -a
# Display the terminal communication
# interface settings.
speed 38400 baud;
...
# Terminal speed is 38400 baud
@debian:~$ stty 50
# set the input and output speed to 50 baud
@debian:~$ stty -a
# Display the terminal communication
# interface settings.
speed 50 baud;
...
# Terminal speed is 50 baud
rows and columns
enlighterstty rows <num_of_rows>
and
enlighterstty columns <num_of_columns>
can be used to set the terminal's number of rows and columns .
enlighter<num_of_rows>
and
enlighter<num_of_columns>
are to be substituted by an appropriate number .
@debian:~$ stty -a
# Display the terminal communication
# interface settings.
...
rows 24; columns 80;
...
# Number of rows is 24
# number of columns is 80
@debian:~$ stty columns 60
# set the number of columns to 60
@debian:~$ stty rows 30
# set the number of rows to 30
@debian:~$ stty -a
# Display the terminal communication
# interface settings.
...
rows 30; columns 60;
...
# Number of rows is 30
# number of columns is 60
Control
settings are used to control the
hardware properties . For example :
parenb
enlighterstty [-] parenb
is used to generate the parity bit in the output , and detect the parity bit in the input .
A parity bit is used for error detection ; It is a bit which is concatenated
to ensure that the number of one's bits is either even or odd .
enlighter[-]
is optional , if enlighter-
is used the parity bit is disabled , If not it is enabled.
@debian:~$ stty -a
# Display the terminal communication
# interface settings.
...
-parenb
...
# parity bit generation and detection
# is disabled .
@debian:~$ stty parenb
# Enables parity bit generation and detection .
@debian:~$ stty -a
# Display the terminal communication
# interface settings.
parenb
...
# parity bit generation and detection
# is enabled .
Input
settings are used to control the
input modes . For example :
iuclc
enlighterstty [-] iuclc
maps input upper case characters to lower case .
enlighter[-]
is optional , if enlighter-
is used mapping is disabled , else and if not used the input upper case characters are automatically translated to lower
case .
@debian:~$ stty -a
# Display the terminal communication
# interface settings.
...
-iuclc
...
# Mapping of input upper case , lower case
# is disabled .
@debian:~$ stty iuclc
# Enables mapping of input upper case
# to lower case .
@debian:~$ stty -a
# Display the terminal communication
# interface settings.
iuclc
...
# Mapping of input upper case to lower
# case is enabled . Any input
# upper case letter is automatically
# translated to lower .
Output
settings are used to control the
output modes . For example :
olcuc
enlighterstty [-] olcuc
maps output lower case characters to upper case .
enlighter[-]
is optional , if enlighter-
is used mapping is disabled , else and if not used output lower case characters are automatically translated to upper
case .
@debian:~$ stty -a
# Display the terminal communication
# interface settings.
...
-olcuc
...
# Mapping of output lower case , upper case
# is disabled .
@debian:~$ stty olcuc
# Enable mapping of output lower case
# to upper case .
@debian:~$ STTY -A
# Display the terminal communication
# interface settings. Output
# is automatically mapped to upper
# case , so stty -a is displayed
# as STTY -A
OLCUC
...
# Mapping of output lower case to upper
# case is enabled . Any output
# lower case letter is automatically
# translated to upper .
The
local settings affect the terminal processing , such as if the
terminal will process some special characters like the delete
or signal characters .
Some settings that could be set are :
echo
enlighterstty [-] echo
affects whether or not the terminal will display the input characters .
enlighter[-]
is optional , if enlighter-
is used the terminal will not display the input characters , else and if
enlighter-
is not used the terminal will display the input characters .
@debian:~$ stty -a
# Display the terminal communication
# interface settings.
...
echo
...
# echo is on , the terminal will display
# the input characters .
@debian:~$ stty -echo
# Set the terminal to not display
# the input characters .
@debian:~$ -echo
# stty -a is typed but it is not
# displayed by the terminal . The
# result is :
# ...
# -echo
# ....
# The terminal is set to not
# display the input characters .
isig
enlighterstty [-] isig
affects whether or not the control characters
INTR ,
QUIT
and
SUSP
used to send signals to programs
are processed or not .
enlighter[-]
is optional , if enlighter-
is used the
INTR ,
QUIT
and
SUSP
control characters are ignored , else
they are processed.
@debian:~$ stty -a
# Display the terminal communication
# interface settings.
intr = ^C; quit = ^\; susp = ^Z;
# The interrupt special character is
# ctrl-C , the quit special character
# is ctrl-\ , the suspend special
# character is ctrl-Z .
...
isig
...
# isig is on . The special
# signal characters are processed .
@debian:~$ stty -isig
# Disable the control characters
# intr , quit , susp
@debian:~$ stty -a
# Display the terminal communication
# interface settings.
-isig
# The control characters intr , quit , susp
# are disabled , and will not work
@debian:~$ ping yahoo.com
PING yahoo.com (72.30.35.9) 56(84) bytes of data.
64 bytes from yahoo.com (72.30.35.9): icmp_seq=1 ttl=63 time=182 ms
^C64 bytes from yahoo.com (72.30.35.9): icmp_seq=2 ttl=63 time=185 ms
64 bytes from yahoo.com (72.30.35.9): icmp_seq=3 ttl=63 time=465 ms
...
# The interupt signal ctrl-c is sent in
# line 29 but it is ignored .
These
are settings that combine or
more settings
. For example :
oddp
enlighterstty oddp
combines the
parenb
,
parodd
and
cs7
settings .
parenb
enables parity bit generation in output , and
detection in input .
parodd sets the parity
bit to odd .
cs7
sets the character size to 7 bits.
enlighterstty - oddp
combines the
-parenb
and
cs8
settings .
- parenb
disables parity bit generation in output , and
detection in input .
cs8
sets the character size to 8 bits.
