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+;;; dirtrack.el --- Directory Tracking by watching the prompt
+
+;; Copyright (C) 1996 Free Software Foundation, Inc.
+
+;; Author:  Peter Breton
+;; Created: Sun Nov 17 1996
+;; Keywords: processes
+;; Time-stamp: <96/12/26 09:23:01 peter>
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation; either version 2, or (at your option)
+;; any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs; see the file COPYING.  If not, write to the
+;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+;; Boston, MA 02111-1307, USA.
+
+;;; Commentary:
+
+;; Shell directory tracking by watching the prompt.
+;;
+;; This is yet another attempt at a directory-tracking package for
+;; Emacs shell-mode. However, this package makes one strong assumption:
+;; that you can customize your shell's prompt to contain the
+;; current working directory. Most shells do support this, including
+;; almost every type of Bourne and C shell on Unix, the native shells on
+;; Windows95 (COMMAND.COM) and Windows NT (CMD.EXE), and most 3rd party
+;; Windows shells. If you cannot do this, or do not wish to, this package
+;; will be useless to you.
+;;
+;; Installation:
+;;
+;; 1) Set your shell's prompt to contain the current working directory.
+;; You may need to consult your shell's documentation to find out how to
+;; do this.
+;; 
+;; Note that directory tracking is done by matching regular expressions, 
+;; therefore it is *VERY IMPORTANT* for your prompt to be easily
+;; distinguishable from other output. If your prompt regexp is too general,
+;; you will see error messages from the dirtrack filter as it attempts to cd
+;; to non-existent directories.
+;;
+;; 2) Set the variable 'dirtrack-list' to an appropriate value. This
+;; should be a list of two elements: the first is a regular expression
+;; which matches your prompt up to and including the pathname part.
+;; The second is a number which tells which regular expression group to 
+;; match to extract only the pathname. If you use a multi-line prompt,
+;; add 't' as a third element. Note that some of the functions in
+;; 'comint.el' assume a single-line prompt (eg, comint-bol).
+;; 
+;; Determining this information may take some experimentation. Setting
+;; the variable 'dirtrack-debug' may help; it causes the directory-tracking
+;; filter to log messages to the buffer 'dirtrack-debug-buffer'.
+;;
+;; 3) Autoload directory tracking by adding the following to your .emacs:
+;; 
+;; (autoload 'dirtrack "dirtrack"
+;;  "Directory tracking by watching the prompt")
+;; 
+;; 4) Add a hook to shell-mode to enable the directory tracking:
+;;
+;; (add-hook 'shell-mode-hook
+;;   (function (lambda ()
+;;            (setq comint-output-filter-functions
+;;                  (append (list 'dirtrack)
+;;                          comint-output-filter-functions)))))
+;;
+;; You may wish to turn ordinary shell tracking off by calling
+;; 'shell-dirtrack-toggle' or setting 'shell-dirtrackp'.
+;;
+;; Examples:
+;;
+;; 1) On Windows NT, my prompt is set to emacs$S$P$G.
+;; 'dirtrack-list' is set to (list "^emacs \\([a-zA-Z]:.*\\)>" 1)
+;;
+;; 2) On Solaris running bash, my prompt is set like this:
+;;    PS1="\w\012emacs@\h(\!) [\t]% "
+;;    'dirtrack-list' is set to (list "^\\([/~].*\\)\nemacs@[^%]+% *" 1 t)
+;;
+;; I'd appreciate other examples from people who use this package.
+
+;;; Code:
+
+(eval-when-compile
+  (require 'comint)
+  (require 'shell))
+
+(defvar dirtrack-list (list "^emacs \\([a-zA-Z]:.*\\)>" 1)
+  "*List for directory tracking.
+First item is a regexp that describes where to find the path in a prompt.
+Second is a number, the regexp group to match. Optional third item is 
+whether the prompt is multi-line. If nil or omitted, prompt is assumed to 
+be on a single line.")
+
+(make-variable-buffer-local 'dirtrack-list)
+
+(defvar dirtrack-debug nil
+  "*If non-nil, the function 'dirtrack' will report debugging info.")
+
+(defvar dirtrack-debug-buffer "*Directory Tracking Log*"
+  "Buffer to write directory tracking debug information.")
+
+(defvar dirtrackp t
+  "*If non-nil, directory tracking via 'dirtrack' is enabled.")
+
+(make-variable-buffer-local 'dirtrackp)
+
+(defvar dirtrack-directory-function 
+  (if (memq system-type (list 'ms-dos 'windows-nt))
+      'dirtrack-windows-directory-function
+    'dirtrack-default-directory-function)
+  "*Function to apply to the prompt directory for comparison purposes.")
+
+(defvar dirtrack-canonicalize-function  
+  (if (memq system-type (list 'ms-dos 'windows-nt))
+      'downcase 'identity)
+  "*Function to apply to the default directory for comparison purposes.")
+
+(defun dirtrack-default-directory-function (dir)
+  "Return a canonical directory for comparison purposes.
+Such a directory ends with a forward slash."
+  (let ((directory dir))
+    (if (not (char-equal ?/ (string-to-char (substring directory -1))))
+        (concat directory "/")
+      directory)))
+
+(defun dirtrack-windows-directory-function (dir)
+  "Return a canonical directory for comparison purposes.
+Such a directory is all lowercase, has forward-slashes as delimiters, 
+and ends with a forward slash."
+  (let ((directory dir))
+    (setq directory (downcase (replace-slash directory t)))
+    (if (not (char-equal ?/ (string-to-char (substring directory -1))))
+        (concat directory "/")
+      directory)))
+
+(defconst forward-slash  (regexp-quote "/"))
+(defconst backward-slash (regexp-quote "\\"))
+
+(defun replace-slash (string &optional opposite)
+  "Replace forward slashes with backwards ones.
+If additional argument is non-nil, replace backwards slashes with 
+forward ones."
+  (let ((orig     (if opposite backward-slash forward-slash))
+        (replace  (if opposite forward-slash backward-slash))
+        (newstring string)
+        )
+    (while (string-match orig newstring)
+      (setq newstring (replace-match replace nil t newstring)))
+  newstring))
+
+;; Copied from shell.el
+(defun dirtrack-toggle ()
+  "Enable or disable Dirtrack directory tracking in a shell buffer."
+  (interactive)
+  (setq dirtrackp (not dirtrackp))
+  (message "Directory tracking %s" (if dirtrackp "ON" "OFF")))
+
+(defun dirtrack-debug-message (string)
+  (let ((buf (current-buffer))
+        (debug-buf (get-buffer-create dirtrack-debug-buffer))
+        )
+    (set-buffer debug-buf)
+    (insert (concat string "\n"))
+    (set-buffer buf)
+  ))
+
+;;;###autoload
+(defun dirtrack (input)
+  (if (null dirtrackp)
+      nil
+    (let ((prompt-path)
+          (current-dir default-directory)
+          (matched)
+          (dirtrack-regexp (nth 0 dirtrack-list))
+          (match-num          (nth 1 dirtrack-list))
+          (multi-line         (nth 2 dirtrack-list))
+          )
+      ;; No output?
+      (if (eq (point) (point-min))
+          nil
+        (save-excursion
+          (goto-char comint-last-output-start)
+          ;; Look for the prompt
+          (if multi-line
+              (and
+               (goto-char (point-max))
+               (setq matched 
+                     (re-search-backward 
+                      dirtrack-regexp 
+                      comint-last-output-start
+                      t)))
+            (beginning-of-line)
+            (setq matched (looking-at dirtrack-regexp)))
+          ;; No match
+          (if (null matched)
+              (and dirtrack-debug
+                   (dirtrack-debug-message 
+                    (format 
+                     "Failed to match regexp: %s" 
+                    dirtrack-regexp)))
+            (setq prompt-path 
+                  (buffer-substring-no-properties
+                   (match-beginning match-num) (match-end match-num)))
+            ;; Empty string
+            (if (not (> (length prompt-path) 0))
+                (and dirtrack-debug
+                     (dirtrack-debug-message "Match is empty string")) 
+              ;; Transform prompts into canonical forms
+              (setq prompt-path (funcall dirtrack-directory-function
+                                         prompt-path))
+              (setq current-dir (funcall dirtrack-canonicalize-function
+                                         current-dir))
+              (and dirtrack-debug
+                   (dirtrack-debug-message 
+                    (format
+                     "Prompt is %s\nCurrent directory is %s"
+                     prompt-path current-dir))) 
+              ;; Compare them
+              (if (or (string= current-dir prompt-path)
+                      (string= current-dir 
+                               (abbreviate-file-name prompt-path)))
+                  (and dirtrack-debug
+                       (dirtrack-debug-message 
+                        (format "Not changing directory")))
+                ;; Change directory
+                (shell-process-cd prompt-path)
+                (and dirtrack-debug
+                     (dirtrack-debug-message 
+                      (format "Changing directory to %s" prompt-path))))
+              )))))))
+
+(provide 'dirtrack)
+
+;;; dirtrack.el ends here