Directory tracking in emacs terminal emulators

Emacs has a number of shells and terminal emulators. eshell and shell have some nice features but are not full featured terminal emulators: they can't run interactive programs such as top and less. Other emacs shells like term, ansi-term, and multi-term are full featured terminal emulators, but miss out on some advantages of eshell and shell. Most importantly, they don't do "directory tracking", where emacs uses your working directory in the shell as the default directory for opening files.

You can add directory tracking to term, ansi-term, and multi-term with a little bit of magic in your .bashrc or .zshrc. In my .zshrc, I have this snippet, partially based on this stackoverflow answer:

if [ -n "$INSIDE_EMACS" ]; then
    # function to set the dired and host for ansiterm
    set_eterm_dir() {
        print -P "\033AnSiTu %n"
        print -P "\033AnSiTh" "$(hostname -f)"
        print -P "\033AnSiTc %d"
    }

    # call prmptcmd whenever prompt is redrawn
    precmd_functions=($precmd_functions set_eterm_dir)
fi

Here, the function set_eterm_dir tells emacs what my current working directory is. It's added to the list precmd_functions so that it's called (and my emacs directory updated) whenever the prompt is drawn. set_eterm_dir works by printing out certain escaped strings to the terminal: \033 is an escape character code, while AnSiTu, AnSiTh, and AnSiTc tell the emacs terminal your username, hostname, and working directory. For simple cases only AnSiTc is needed, but if you are also going to enable remote directory tracking (below), you'll need to set AnSiTu and AnSiTh to reset your username and hostname after you're done ssh'ing around.

As mentioned above, you can even set directory tracking on remote machines! Then emacs knows to open files through TRAMP when you're ssh'd somewhere. To do this, you'll need to set your .bashrc or .zshrc on the remote machine. This is from my .bashrc on a remote server:

function set-eterm-dir {
    echo -e "\033AnSiTc" "$(pwd)"

    ## "farm" is the name of the server in my .ssh/config
    ## replace it with your server's name, or with $(hostname -f)
    ## you may also want to add 'echo -e "\033AnSiTu" "$LOGNAME"'
    echo -e "\033AnSiTh" "farm" 
}
if [ "$TERM" = "eterm-color" ]; then
    PROMPT_COMMAND=set-eterm-dir
fi

This snippet is based on a hint from the EmacsWiki but much simplified. PROMPT_COMMAND is called whenever the prompt is drawn in bash. We set it to the function set-eterm-dir that tells the emacs terminal emulator our directory and hostname. Notice I manually set the hostname to "farm". This is because I have named the Host as "farm" in my .ssh/config, and I want TRAMP to use the host settings in that file (e.g. automatic X11 forwarding).

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