linux - How to make Ctrl+D detach tmux, while retaining GNU readline capabilities in Bash?

Based upon my days and days of researching this, I may be seeking the impossible.

Situation

• I have my .bashrc nicely configured to either spawn a new tmux on connect, or if one exists, attach to it.




• I always hit Ctrl+D to exit a shell session. It's burned into my muscle memory. Unlearning it after thirty years of systems administration is also asking the impossible.




• I want to be able to detach from tmux using just Ctrl+D, rather than having it kill my shell.

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My imperfect approach

I can bind Ctrl+D to detach in .tmux.conf.

The problem is that I also have emacs key-bindings burned into my muscle memory, so when I start editing a command line, I'll hit Ctrl+D to employ the GNU readline 'delete char under cursor'. Instead, the tmux binding swallows the Ctrl+D, so I'm immediately detached. Same thing if I'm editing in emacs.

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Another flawed approach

GNU readline will take the EOF on an empty line, and then exit the shell. So I've tried trapping exit in .bashrc instead:

trap "~/tmuxexit" EXIT

with the contents of tmuxexit being:

tmux detach-client -s main

Which initially seemed like it worked, as hitting Ctrl+D on an empty line would report:

[detached (from session main)]

But tmux ls reports no server running on […].

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Do I seek the impossible?

Answer

I'm not sure if I crafted the simplest possible solution. This:

stty eof '^T'
bind '"\C-d": "\C-x\C-t\C-x\C-d"'
bind -x '"\C-x\C-t": _tmux_detach'
_tmux_detach() { [ -z "$READLINE_LINE" ] && tmux detach-client; }
bind '"\C-x\C-d": delete-char'

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Explanation:

1. stty eof '^T' makes your terminal no longer send EOF at Ctrl+D. Now it's Ctrl+T. The new key combination will behave like the old one in readline, I mean it will exit the shell only if the line is empty. I deliberately chose Ctrl+T because it's very unlikely you will want to use its default binding (transpose characters) with an empty line.

   
   

   I thought that disabling EOF entirely (stty eof undef) would work, but it turned out readline(?) still reacts to the previously defined combination (like Ctrl+D) and makes the shell register EOF if the line is empty.




2. bind '"\C-d": "\C-x\C-t\C-x\C-d"' makes Ctrl+D "send" Ctrl+X, Ctrl+T and Ctrl+X, Ctrl+D. We will utilize the two sub-sequences separately.




3. bind -x '"\C-x\C-t": _tmux_detach' – From now on Ctrl+X, Ctrl+T executes _tmux_detach…




4. … which is a function that detaches tmux if the line ($READLINE_LINE) is empty.




5. bind '"\C-x\C-d": delete-char' – From now on Ctrl+X, Ctrl+D deletes the character at point, like Ctrl+D usually does.

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So Ctrl+D will work like this:

• if the line is not empty, the function is a no-op and delete-char does its job;


• if the line is empty, the function does its job and delete-char is a no-op (it gets triggered but has nothing to do).

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Notes:

• READLINE_LINE was introduced in Bash 4.0.


• If you paste the code into your ~/.bashrc, you may want to improve it: check if the shell is inside tmux before changing the behavior of Ctrl+D, so shells outside of tmux are unaffected.


• It's important that _tmux_detach acts before delete-char. If you reverse the order then you will introduce a bug: Ctrl+D that deletes a solitary character will also detach tmux.