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by ChristianBundy 2287 days ago
Maybe you can correct me if I'm wrong, but I've always considered Ctrl+C and Ctrl+D to be signals that you can send a process rather than explicit characters. You might also get some stdout for those key combinations because ???, but they should be thought of as signals rather than as characters you're sending via stdin.

Hoping Cunningham's Law comes into play with this comment. :)
2 comments
rgoulter 2287 days ago
I liked this explanation. https://www.linusakesson.net/programming/tty/

When the TTY device takes (by default) Ctrl+C or Ctrl+D, it sends the signals to the program. The TTY's 'line discipline' (the policy for when the program's STDIN can read from a line of input) can be changed from a default 'cooked' to a 'raw mode'. In with raw mode line discipline the Ctrl+C doesn't send the signal. Presumably that's why e.g. vi or emacs don't just close on Ctrl+C.

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nixpulvis 2287 days ago
> Now you press ^Z. Since the line discipline has been configured to intercept this character (^Z is a single byte, with ASCII code 26), you don't have to wait for the editor to complete its task and start reading from the TTY device. Instead, the line discipline subsystem instantly sends SIGTSTP to the foreground process group.

This helps me, thanks for pointing me back at this great write-up.

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anonymousiam 2287 days ago
Control-C is part of POSIX job control. If a stream (or "cooked" tty) sends a control-C (ASCII End-Of-Text or ETX), the foreground process will be sent a SIGINT signal. If that signal is not handled, the default action is to terminate the process (SIGTERM). Control-D is just another control character and not part of POSIX job control, but in the "cooked" case above, it will be interpreted as EOF and the process doing the "read" will receive that.
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nixpulvis 2287 days ago
I was thinking the same thing, until I read this:

> 'stty -icanon' still interprets control characters such as Ctrl-C whereas 'stty raw' disables even this and is the real raw mode.

From the very detailed link posted by rgoulter above.

Still, in raw mode, Ctrl+D will send EOT, and thus end your shell. While Ctrl+C wont.

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