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.1‐2017. 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.1‐2017, 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.1‐2017.
