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Top-level
 some other things I think are interesting about the control codes: * some of the "OS terminal driver stuff" is also sometimes handled by readline 22 comments
@b0rk That is also another hint for the 'j' in vim: go down one line, just like ctrl+j does in a terminal. Or is this just a coincident? @bartavi @b0rk Likely coincidence. Have a look at "man ascii" and look at characters Decimal 1 to 26. Those are for the most part what you will get if it doesn't already do something special (like Ctrl+C). For example, Ctrl+H is character 8, which is backspace (but only the backspace character). Ctrl+I is a tab, and Ctrl+J is a newline '\n'. (This means Ctrl+M is actually a carriage return '\r', but your os likely translates both into '\n' in the input that your terminal programs receive).  @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. @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)  @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 @b0rk Fun trivia on the Ctrl-1 and Ctrl-M and so on thing: non-terminal graphical programs with direct access to keypress information can bind them (of course). This is especially fun for programs that can operate either in the terminal or as stand-alone graphical applications, like GNU Emacs, because you can innocently create a binding for yourself that only works in GUI mode (which you might not notice for a while if you only rarely use the editor in a terminal).  @cks @b0rk like how avy-mode¹ recommends binding Ctrl-: in its default docs², with the consequence that it's unusable by folks who use terminal emacs (or a combination of GUI and terminal emacs panes connecting to a shared emacs daemon). Unless they're wizardly enough to feel comfortable reading all documentation about it when an interpretation filter in their brain! ¹: https://karthinks.com/software/avy-can-do-anything/ ²: https://github.com/abo-abo/avy?tab=readme-ov-file#avy-goto-char  @b0rk fun fact about those “plus seven more” non-alphabetical Ctrl-codes, DEC VT220 terminals had alternate key bindings for them on Ctrl-2..8, in order. Some emulators secretly support this as well, which is very convenient with keyboard layouts where some of those are awkward to type, or say… lacking an esc key, Ctrl-3 saves the day. |
Gregory's Server
@b0rk several of the readline control codes are implemented as keyboard shortcuts in some common text editing widgets, particularly Ctrl+A/E