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I have a Debian 10.0 system. It has zsh 5.7.1 (x86_64-debian-linux-gnu). In ZSH prompt, I type

foo bar baz

Then I type alt + backspace two times. The words baz and bar get deleted and only foo remains.

Then I type ctrl + / two times to undo the deletions. The words baz and bar reappear.

How is ctrl + / working as the undo command? I don't see it defined anywhere?

$ echo / | grep -E "/|undo"  # just testing my regex
/
$ bindkey -l
.safe
command
emacs
isearch
main
vicmd
viins
viopp
visual
$ bindkey -M .safe | grep -E "/|undo"
$ bindkey -M command | grep -E "/|undo"
$ bindkey -M emacs | grep -E "/|undo" 
"^X^U" undo
"^Xu" undo
"^_" undo

I also have a macOS Catalina 10.15.7 with zsh 5.7.1 (x86_64-apple-darwin19.0) and ctrl + / does not do anything there.

Lone Learner
  • 140

1 Answers1

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There's no control character for Control+/, so there's no natural choice of character or character sequence that the terminal can send. Many terminals send ^_, i.e. the same character as Control+_. This includes xterm, rxvt, konsole and all terminals based on the vte library (Gnome Terminal, Mate Terminal, lxterminal, Terminator, …), but not macOS's built-in Terminal application.

You can see what your terminal sends by typing Ctrl+V then Ctrl+/. Ctrl+V means “insert the next character literally” (even if it would be otherwise interpreted as a command).

(For the role of the terminal, see How do keyboard input and text output work?)

^_ is the shortcut for undo in Emacs and applications with Emacs-inspired keyboard shortcuts.

Gilles 'SO- stop being evil'
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