Why don't `stty -a` list `raw` in its output, when any modern shell, like Bash, is said to operate in raw mode?

Question

Why don't stty -a list raw in its output, when any modern shell, like Bash, is said to operate in raw mode?

I understand that any modern shell should operate in raw mode, i.e:

• Input made available character by character.
• Echoing is disabled.
• All special processing of terminal input and ouput is disabled.

and that Readline processes user input.

So, why isn't raw listed in the output from stty -a?

Answer 1

Because that raw mode is a bit of an approximation. There's no official definition of raw mode and in practice it means different things for different APIs.

What they meant is that shells like bash that implement their own line editor disable some of the features of the tty line discipline. In particular, they need to disable the line discipline's own line editor (icanon setting aka -cbreak) and local echo. They don't disable some other line discipline features like the sending of SIGINT upon ^C (isig setting).

stty -a reports the individual discrete termios settings (like those icanon, echo, isig above).

stty also supports a few aliases to set more than one setting at a time like sane, cooked or... raw.

stty raw disables all tty line discipline features except echo. So there are features it disables (like isig) that bash doesn't for its line editor and it doesn't disable echo while bash does.

The manual of the GNU implementation of stty describes raw as being equivalent to -ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr -icrnl -ixon -ixoff -icanon -opost -isig -iuclc -ixany -imaxbel -xcase min 1 time 0. That's the set of discrete termios settings that stty raw tweaks (leaving the other ones alone).

Note that opost is not a stty alias, it's a discrete tty line discipline setting of its own but it affects all other output post-processing settings like onlcr, olcuc. Or in other words onlcr/olcuc are ineffective if opost is not on which explains why stty raw doesn't bother turning off all those output processing features.

Some systems have cfmakeraw() / cfmakesane() libc functions that can also set more than one setting at once. The cfmakeraw() of the GNU libc at least is different from GNU's stty raw in that for instance it disables echo and doesn't disable iuclc or ixoff.