Automatically update default-directory when PWD changes in shell-mode and term-mode

Question

Are there any options or packages which cause default-directory to be updated if the working directory changes in shell-mode and term-mode? I.e. when using cd, but the solution would have to be more robust than just look for this particular command and maybe a few others - it should actually check the value of $PWD after every command, I would think.

More importantly though it should also work when connecting to a remote machine from inside a shell-mode or term-mode buffer which was first created with default-directory being a local directory. That's actually the feature I really need: being able to tell programmatically whether the commands I type into such terminals are run on a remote machine. I would like to get that information in form of a properly set default-directory and figure if there is a way to get that, then the tool doing this would also work locally as described above.

Answer 1

I think the first part of your question can be done with dirtrack-mode. First, you set your shell prompt to include the present working directory. Next, you set dirtrack-list to a regex that tells dirtrack-mode how to extract it. Example: I set PS1 in Bash to be this:

export PS1="[\h:\w] $ "

and in Emacs I set dirtrack-list and turn on dirtrack-mode:

(set-variable 'dirtrack-list '("^.*[^ ]+:\\(.*\\)]" 1 nil))
(dirtrack-mode 1)

(Taken from this great blog post.)

After that, I'm able to change directories at will, and default-directory changes as I go. This also works if, in a shell, I SSH to a remote machine where I've set the prompt the same way -- cd /etc/apache2, on the remote machine, changes default-directory to /etc/apache2. Note, however, that this is local -- in the case of the remote machine, default-directory will still be set to /etc/apache2 on the local machine.

If I understand the second part of your question, you want default-directory to be set to something like remote-machine:/etc/apache2 when SSHing to another machine. When using ssh-el, you can run ssh-directory-tracking-mode to make this work. For example, if I run M-x ssh, cd to /etc/apache2, then run C-x C-f, the prompt I see is:

Find Files or Url: /scp:aardvark@remote-machine:/etc/apache2

You can run 'M-x ssh-directory-tracking-mode` by hand, but it's more convenient to set it as a hook for ssh-mode:

(setq ssh-mode-hook 'ssh-directory-tracking-mode)

More information:

• Directory Tracking, Emacs manual
• A great blog post about running shells in Emacs
• The ssh-el Github repo; it's also available on MELPA. (I had no idea it wasn't part of Emacs core...)
• EmacsWiki page on tracking shell directories by prompt
• StackExchange explanation of dirtrack-list