Edit Command Line in Zsh

EDIT 2024-04-16: turns out that there’s a built-in, fc, which does basically the same thing, though it edits the command that was just entered (which is typically what you want when you encounter an error or want to do “the next thing”, anyway).

While reading through my dotfiles, I found some configuration¹ that didn’t seem to be working - it claimed that <ESC>,v would allow editing of the current line in vim, but that didn’t seem to work. I guess I’d copied that from some other configuration and lost patience with trying to get it working, or that it relied on some other configuration option which had been broken². I dug in to find out more. (This article was invaluable!)

Intention

First, let’s understand what that snippet is trying to do. The ZLE (Zsh Line Editor) is a tool³ that allows for:

• the definition of various commands (called “widgets”) for editing text.
• the binding of those widgets (or built-in or imported ones) to keys within named “keymaps”. Commands can switch between keymaps.

Three standard keymaps in ZLE are emacs, vicmd, and viins. In the viins (vi-insert) keymap, the <ESC> key is associated with a widget that switches to the vicmd keymap:

$ bindkey -M viins '^['
"^[" vi-cmd-mode

(The character string '^[' represents the single keypress <ESC>)

The line bindkey -M vicmd v edit-command-line means “Within the keymap vicmd, bind the widget edit-command-line to the key v”. The earlier commands (autoload edit-command-line; zle -N edit-command-line) deal with making that widget available to ZLE - I guess it’s not available by default?

So, taken as a whole, this configuration should make the key-sequence <ESC>,v translate to “enter vicmd mode, then execute edit-command-line”. But that didn’t seem to be the case.

Investigation and resolution

I quickly noticed that my default keymap was not viins but emacs:

$ bindkey -lL main
bindkey -A emacs main

Quick fix, right? Add a line bindkey -v⁴ to my dotfile, and done?

Well, sort-of. This change did allow the edit-command-line to fire as expected, allowing the current line to be edited in vi; but, after “writing” the command and returning to the command line, I was not able to delete any character of the written command. Initially I thought this was because I was still in vicmd mode (and created a workaround custom widget here), but that turned out to be an incorrect assumption. After looking around a little more, I found this SO answer which suggested changing the binding for '^?' (that is - <BACKSPACE>) from vi-backward-delete-char to backward-delete-char. I’m not sure why, though - backspaces still work fine on the terminal before entering vicmd mode, which lends further credence to my suspicion that the ZLE is not the entirety of the terminal, but merely a tool within it.

I’ve been making a lot of use of some Emacs-mode shortcuts:

• Ctrl-A => beginning of line
• Ctrl-E => end of line
• Ctrl-U => clear everything

So I added these to my setup with the following commands:

bindkey -M viins '^A' beginning-of-line
bindkey -M viins '^E' end-of-line
bindkey -M viins '^U' kill-whole-line