How to set Readline key bindings using ALT (Meta) or some other control key as prefix instead of `\C-` and `\e`?

Question

I can only find examples of setting Readline key bindings using Control (\C-) or Escape (\e) as prefixes.

In my case, on macOS, the \C- space is completely filled up by default key bindings, and the \e space is not practical on a Macbook with a touchbar.

Entering "\M-f": kill-word in ~/.inputrc results in:

bind -P | grep -F "\M-"
kill-word can be found on "\e[3;5~" "\ed".

But kill-word cannot be executed using either of Option, Command, or fn as prefixes - Readline ignores it.

Is this issue specific to macOS, and how can I solve it?

Furthermore, how can I control the "timeout" that should occur before a key binding, that is a prefix of a longer key binding, is executed?

@added (@laktak): bind '"^[f": kill-word' doesn't work, but instead results in ƒ on the terminal:

Answer 1

I don't think you're doing anything wrong, you just need to tell Terminal.app to use the "Option" key as "Meta" instead. Just go to the preferences for Terminal (⌘+,), then Profiles, then the Keyboard tab for your default profile and check "Use Option as Meta key."

Otherwise, you're getting the default macOS behavior (in most keymaps) where Option + key produces special characters, just like Option+f yields the small letter "f" with hook from your screenshot (complete reference here).

In iTerm 2, I believe the left Option key already does the sensible thing by default, but just in case, here's how to change that:

As far as remapping Option to Escape, if that's a thing you still wanted to do, that can be accomplished from the Keyboard prefpane in System Preferences, by clicking the "Modifier Keys…" button near the bottom of the window.

Then remap it to whatever you please (from the available choices):

I hit up this preference pane in about the first five minutes of using a new Mac, just so I can remap Caps Lock to Control, since the Control key on a Mac keyboard is in an awkward spot.

Answer 2

The utility would be:

showkey (1)          - examine the codes sent by the keyboard

but this seems to be missing on mac-os...here it is "Key Codes"...?

Or you type ctrl-V (qouted insert) and then some special key. In bash, this prints ^[OP in xterm and ^[[[A in the console for the F1 key.

The readline variable:

keyseq-timeout (500)

is the timeout to use for a half-finished sequence.

Underneath this, there must be a sort of keymap file, where the keys get translated to symbols. This is from /usr/share/kbd/keymaps/mac/ on linux:

keycode 51 = Delete  Remove
        alt keycode 51 = Meta_Delete
        shift alt keycode 51 = Meta_Delete
        control keycode  51 = Remove
keycode 53 = Escape
        alt keycode 53 = Meta_Escape
        shift alt keycode 53 = Meta_Escape
keycode  54 = Control
keycode  55 = Alt         # Command/Apple key
keycode  56 = Shift
keycode  57 = Caps_Lock
keycode  58 = AltGr       # Alt/Option key

You see the flexibilty! The Meta-Delete symbol could become kill-word...

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bind '"^[f": kill-word

This ^[ must be a \e, or a ctrl-V, then Escape: one byte, not circumflex plus bracket.

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It is like saying: ^C means control-C, not a Shift-6 and then a Shift-c...in the shell (bash) or in vim when I type ctrl-v and then Esc I get ^[, but it is just one character when you step back over it. Together with these meta-flag options in readline it can get complicated...I just illustrate the whole chain:

keymap "default.map" (translates scancode and modifier to keysymbols)

keycode 105 = Left F150 F151
  string F150 = "\033[150"
  string F151 = "\033[151"
keycode 106 = Right F154 F155
  string F154 = "\033[154"
  string F155 = "\033[155"

The F150 and F151 after default "Left" mean shift- and control-left-arrow. In a second step you can define a string, an escape sequence in this case. Here, \e did not work, but the octal 033 is ascii 27 is control-[ is Escape...this keymap is linux specific, but X Windows has a similar logic.

And in .inputrc:

"\e[150": backward-word 
"\e[151": shell-backward-word 
"\e[154": forward-word 
"\e[155": shell-forward-word 

This works very nice in the linux console. In xterm under X Windows (Xorg): not at all: Xorg scans the keys itself.

backward-word can be invoked via "\e[150", "\e[1;2D", "\e[1;3D", "\eb".

The two in the middle with semicolon are VTxxx style modified left arrows. This was preconfigured, and also gets bound to backward-word automatically.

Answer 3

If I understood your question correctly:

bind '"^[f": kill-word'

Will define Option+F to invoke kill-word

Answer 4

The other option is to use Esc and then hit the d button, with that you can simulate the same keybinding.

Same as pasting the last argument of the previous command (M-.) could be replaced by hitting Esc first and then ..

To help myself on my MacBooks starting with the Touch Bar versions I've remapped the Caps Lock ⇪ with ⎋ Escape