2011/11/28: Dir-tracking. Or: how to keep pwd up-to-date for an emacs-shell

By default emacs tracks the working directory of a shell by inspecting all commands executed. This is bound to fail, if the working directory is changed by other means like a custom script, e.g., changing between a code directory and the corresponding test directory.

This was annoying me for a while till a few days ago, I decided it was too much. I (essentially) followed the emacs wiki and did the following.

I added the following line to my .emacs_bash to make the bash in emacs produce an easy to recognise prompt.

PS1="|PrOmPt|\w|\w \$ "

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In my .emacs configuration file, I require the package dirttrack and configure the hooks in the following way to

make our fancy prompt to be used to recognise the current working directory, and
remove it from what is shown in the shell buffer.

;; shell -- dirtrack

(require 'dirtrack)
(add-hook 'shell-mode-hook
          (lambda ()
            (setq dirtrack-list '("^|PrOmPt|\\([^|]*\\)|" 1 nil))
            (dirtrack-mode nil)
            (add-hook 'comint-preoutput-filter-functions
                      'dirtrack nil t)
            (add-hook 'comint-preoutput-filter-functions
                      'dirtrack-filter-out-pwd-prompt t t)))
;; Now strip the goofy strings from the prompt before it gets into
;; the shell buffer.
(defun dirtrack-filter-out-pwd-prompt (string)
  "dirtrack-mode doesn't remove the PWD match from the prompt.  This does."
  (if (and (stringp string) (string-match (first dirtrack-list) string))
      (replace-match "" t t string 0)
    string))

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