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Gomijacogeo

@b0rk @njvack ^H? send back '^H ^H' to erase char on terminal, and move the head of the buffer back one. Other chars like ^C, ^Z, ^\, etc would instead send a signal to the process group attached to that tty and the signal handler would be invoked or the process killed.

9 July at 1:52 | Wall-to-wall | Open on hachyderm.io
7 comments
njvack

@gomijacogeo @b0rk I think the thing I need to keep remembering is that at some point, ... something (I'm not 100% sure what — the tty handler? readline?) is telling _my terminal emulator_ to do something with the characters

9 July at 1:56 | Open on ruby.social
Gomijacogeo

@njvack @b0rk Yeah, it was a lot simpler 40+ years ago where each component was a separate, tangible box connected by wires. Made it easy to keep track of what was done where. A modern terminal emulator, on one side talks to the window system and sees keypress events and does advanced font rendering. On the other side, it talks to a pty which is an abstraction of that ancient RS-232 line and is mostly a serialized byte stream that the kernel then treats as input and output.

9 July at 2:10 | Open on hachyderm.io
Gomijacogeo

@njvack @b0rk If the tty is in cooked mode, those simple tasks - echoing, ^H, ^W, etc are done by the tty driver. In raw or cbreak (like raw, but still looks for things like ^C ^Z ^\ etc), then it is the consuming program (eg readline, vim, etc) that reads chars and then decides what to send back to the tty and then to the emulator to be displayed (usually lots of escape codes to handle positioning along with the one or two chars to actually display).

9 July at 2:18 | Open on hachyderm.io
Gomijacogeo

@b0rk @njvack Then X11 came along and we needed a tty-like abstraction to attach these newfangled terminal windows to processes, because all the I/O and job control was wired to talk to a tty-shaped device. And some new side channels were added (e.g. SIGWINCH). So there are a ton of ioctls() to talk to the driver and control/interrogate exactly what kind of tty it really is.

9 July at 1:56 | Open on hachyderm.io
Gomijacogeo

@b0rk @njvack Oh yeah, you also needed ptys for telnet/rlogin/ssh-like services. And the tty driver was already hellishly complex even before GUIs entered the picture. Tons of respect to anyone who unpeels the onion in the modern era - so many moving parts.

9 July at 3:15 | Open on hachyderm.io
Gomijacogeo

@b0rk @njvack One other thing that was an A-ha! moment for me back in the day was learning that stty uses an ioctl() to determine the tty behind stdin, so you can redirect from another tty (assuming you have permission) to see its settings. So, assuming /dev/ttys000 is a different window, I can 'stty -a < /dev/ttys000' and see how the flags change between cat, bash, and vim for example.

10 July at 0:02 | Open on hachyderm.io
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