Function: shell-directory-tracker

shell-directory-tracker is a byte-compiled function defined in shell.el.gz.

Signature

(shell-directory-tracker STR)

Documentation

Tracks cd, pushd and popd commands issued to the shell.

This function is called on each input passed to the shell. It watches for cd, pushd and popd commands and sets the buffer's default directory to track these commands.

You may toggle this tracking on and off with M-x shell-dirtrack-mode (shell-dirtrack-mode). If Emacs gets confused, you can resync with the shell with M-x dirs (dirs).
(The dirtrack package provides an alternative implementation of this
feature - see the function dirtrack-mode(var)/dirtrack-mode(fun).)

See variables shell-cd-regexp, shell-chdrive-regexp, shell-pushd-regexp,
and shell-popd-regexp, while shell-pushd-tohome, shell-pushd-dextract,
and shell-pushd-dunique control the behavior of the relevant command.

Environment variables are expanded, see function substitute-in-file-name.

Source Code

;; Defined in /usr/src/emacs/lisp/shell.el.gz
;;; Directory tracking
;;
;; This code provides the shell mode input sentinel
;;     SHELL-DIRECTORY-TRACKER
;; that tracks cd, pushd, and popd commands issued to the shell, and
;; changes the current directory of the shell buffer accordingly.
;;
;; This is basically a fragile hack.  It has the following failings:
;; 1. It doesn't know about the cdpath shell variable.
;; 2. It cannot infallibly deal with command sequences, though it does well
;;    with these and with ignoring commands forked in another shell with ()s.
;; 3. More generally, any complex command is going to throw it. Otherwise,
;;    you'd have to build an entire shell interpreter in Emacs Lisp.  Failing
;;    that, there's no way to catch shell commands where cd's are buried
;;    inside conditional expressions, aliases, and so forth.
;;
;; The whole approach is a crock. Shell aliases mess it up. File sourcing
;; messes it up. You run other processes under the shell; these each have
;; separate working directories, and some have commands for manipulating
;; their w.d.'s (e.g., the lcd command in ftp). Some of these programs have
;; commands that do *not* affect the current w.d. at all, but look like they
;; do (e.g., the cd command in ftp).  In shells that allow you job
;; control, you can switch between jobs, all having different w.d.'s. So
;; simply saying %3 can shift your w.d..
;;
;; The solution is to relax, not stress out about it, and settle for
;; a hack that works pretty well in typical circumstances. Remember
;; that a half-assed solution is more in keeping with the spirit of Unix,
;; anyway. Blech.
;;
;; One good hack not implemented here for users of programmable shells
;; is to program up the shell w.d. manipulation commands to output
;; a coded command sequence to the tty. Something like
;;     ESC | <cwd> |
;; where <cwd> is the new current working directory. Then trash the
;; directory tracking machinery currently used in this package, and
;; replace it with a process filter that watches for and strips out
;; these messages.

(defun shell-directory-tracker (str)
  "Tracks cd, pushd and popd commands issued to the shell.
This function is called on each input passed to the shell.
It watches for cd, pushd and popd commands and sets the buffer's
default directory to track these commands.

You may toggle this tracking on and off with \\[shell-dirtrack-mode].
If Emacs gets confused, you can resync with the shell with \\[dirs].
\(The `dirtrack' package provides an alternative implementation of this
feature - see the function `dirtrack-mode'.)

See variables `shell-cd-regexp', `shell-chdrive-regexp', `shell-pushd-regexp',
and  `shell-popd-regexp', while `shell-pushd-tohome', `shell-pushd-dextract',
and `shell-pushd-dunique' control the behavior of the relevant command.

Environment variables are expanded, see function `substitute-in-file-name'."
  (if shell-dirtrackp
      ;; We fail gracefully if we think the command will fail in the shell.
;;;      (with-demoted-errors "Directory tracker failure: %s"
      ;; This fails so often that it seems better to just ignore errors (?).
      ;; Eg even: foo=/tmp; cd $foo is beyond us (bug#17159).
      (ignore-errors
        (let ((start (progn (string-match
			       (concat "^" shell-command-separator-regexp)
			       str) ; skip whitespace
			      (match-end 0)))
		(case-fold-search)
		end cmd arg1 cmd-subst-fn)
	    (while (string-match shell-command-regexp str start)
	      (setq end (match-end 0)
		    cmd (comint-arguments (substring str start end) 0 0)
		    arg1 (comint-arguments (substring str start end) 1 1))
	      (if arg1
		  (setq arg1 (shell-unquote-argument arg1)))
              (if shell-has-auto-cd
                  (setq cmd-subst-fn (comint-substitute-in-file-name cmd)))
	      (cond ((string-match (concat "\\`\\(" shell-popd-regexp
					   "\\)\\($\\|[ \t]\\)")
				   cmd)
		     (shell-process-popd (comint-substitute-in-file-name arg1)))
		    ((string-match (concat "\\`\\(" shell-pushd-regexp
					   "\\)\\($\\|[ \t]\\)")
				   cmd)
		     (shell-process-pushd (comint-substitute-in-file-name arg1)))
		    ((string-match (concat "\\`\\(" shell-cd-regexp
					   "\\)\\($\\|[ \t]\\)")
				   cmd)
		     (shell-process-cd (comint-substitute-in-file-name arg1)))
		    ((and shell-chdrive-regexp
			  (string-match (concat "\\`\\(" shell-chdrive-regexp
						"\\)\\($\\|[ \t]\\)")
					cmd))
		     (shell-process-cd (comint-substitute-in-file-name cmd)))
                    ((and shell-has-auto-cd (file-directory-p cmd-subst-fn))
                     (shell-process-cd cmd-subst-fn)))
	      (setq start (progn (string-match shell-command-separator-regexp
					       str end)
				 ;; skip again
				 (match-end 0))))))))