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Top-level
@b0rk 0x7f is usually called "delete" or "DEL", to constrast it with 0x08 which is "backspace", and they are different and sometimes the terminal gets confused. But your chart calls them both "backspace", which I think might tend to add to the amount of confusion in the universe. 10 comments
 @b0rk if you type "abcdef" at a prompt and then put your cursor between c and d (abc|def) then: 0x08 (backspace) usually produces ab|def 0x7f (delete) usually produces abc|ef @b0rk @mjd My memory is that there was a big schism in the physical terminal world about what the 'backspace' key generated. Many terminals had it generate Ctrl-H, but some used DEL; I believe DEC terminals such as the VT-100 were in the DEL camp, and they were very popular. This carried over to Unix workstations, with vendors doing different mappings (eg SGI made their 'backspace' key generate Ctrl-H in a default configuration; DEC used DEL of course). @b0rk @mjd Today, X on Linux has a 'BackSpace' keysym and a 'Delete' keysym, generated by their respective keyboard keys, but I believe that all terminal emulators map both of them to DEL by default (xterm and gnome-terminal certainly do). Things like browsers tend to make the big BackSpace key delete characters to the left of the cursor (what you expect) and the 'Delete' key delete to the right, which can be a surprise.  @b0rk @mjd I see a lot of people have posted about history, but as I see it the _effects_ of the history are to create two current schools of thought. 1. the Backspace key (above Return) is 0x08, and the Del key (on the nav keypad) is 0x7F 2. Backspace is 0x7F, and Del is some sequence like ESC[3~ (similar to the rest of that keypad) Emacs users like #2 because it frees up 0x08 to be ^H for help. But enough people like #1 that lots of software all needs a config option! @b0rk @mjd The Debian Policy Manual has an entire section on this: https://www.debian.org/doc/debian-policy/ch-opersys.html#keyboard-configuration @mjd @b0rk there's also the name "rubout" for code 127. The "all bits set" code was special on paper tape because you could change any other (incorrectly punched) code to it by re-punching. https://en.m.wikipedia.org/wiki/Delete_character |
Gregory's Server
@mjd thanks that's a good point -- I'm very confused about what Ctrl-H does in practice -- to me it feels like 0x08 is just kind of some weird old cruft that has no real purpose but maybe that's not true
(if it does have a purpose I'd be interested to know what it is! I don't have a backspace key on my keyboard right now but my impression is that the backspace key is supposed to map to an ASCII DEL)