Update tmux default directory for new windows

TIL:

• the -c flag to attach-session will update the default current working directory for new windows.
  
• attach-session can be run from the tmux command prompt with an arg of -t . to connect to the current session,
  so we don't need to detach and reattach.
  
• attach also supports -c
  
• tmux makes the current pane's working directory available in the command prompt as '#{pane_current_path}'
  
• new-window also supports the -c option.
  

Set the default CWD for new windows to the current directory:

From the tmux command prompt:

:attach -c '#{pane_current_path}'

# or the more verbose attach-session version,
# listed because I thought of this first :)
:attach-session -t . -c '#{pane_current_path}'

Bound to a char in .tmux.conf:

# update default path for new windows to the current path 
bind-key 'M-/' :attach -c '#{pane_current_path}'

# Open a new window using the current working directory,
bind-key 'C' new-window -c '#{pane_current_path}'

For reference: see this StackOverflow comment and this Unix StackExchange answer.

maintaining SSH_AUTH_SOCK in tmux

Tmux has a neat feature where certain environment variables can be updated during attachment.

SSH_AUTH_SOCK is included by default. When you reconnect from within a new ssh environment, SSH_AUTH_SOCK is updated inside of tmux. Any new windows created in the tmux session will have the updated ssh information.

Already running shells are not updated (how would tmux tell the shell to update?). I've added a zsh alias to my workflow to pull in the updated value from a running shell. It wraps the show-environment tmux command. This is a shell alias because it needs to affect the running shell.

fix_ssh () {
        eval $(tmux show-environment | grep ^SSH_AUTH_SOCK)
}

I don't normally start many interactive ssh session from my remote box, but I do need to talk to my local SSH agent to connect to my private git repos. I hate running an update and seeing Permission denied. Before I added this fix_ssh command, I caught myself opening new tmux windows to run the fetch from and then closing them to return to my active shell -- an expensive and distracting work-around.

% git fetch
Permission denied (publickey).
fatal: Could not read from remote repository.
% fix_ssh
% git fetch
# success!

When I run with screen, I set the SSH_AUTH_SOCK value to a steady value before opening the initial screen session and then manually update the sock on each login. When I remember.

# for screen
MY_SSH_AUTH_SOCK=$HOME/.ssh/auth_sock
rm $MY_SSH_AUTH_SOCK && ln -s $SSH_AUTH_SOCK $MY_SSH_AUTH_SOCK && export SSH_AUTH_SOCK=$MY_SSH_AUTH_SOCK