;;; shell.el --- specialized comint.el for running the shell -*- lexical-binding: t -*-

;; Copyright (C) 1988, 1993-1997, 2000-2024 Free Software Foundation,
;; Inc.

;; Author: Olin Shivers <shivers@cs.cmu.edu>
;;	Simon Marshall <simon@gnu.org>
;; Maintainer: emacs-devel@gnu.org
;; Keywords: processes

;; 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 3 of the License, 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.  If not, see <https://www.gnu.org/licenses/>.

;;; Commentary:

;; This file defines a shell-in-a-buffer package (shell mode) built on
;; top of comint mode.

;; Since this mode is built on top of the general command-interpreter-in-
;; a-buffer mode (comint mode), it shares a common base functionality,
;; and a common set of bindings, with all modes derived from comint mode.
;; This makes these modes easier to use.

;; For documentation on the functionality provided by comint mode, and
;; the hooks available for customizing it, see the file comint.el.
;; For further information on shell mode, see the comments below.

;; Needs fixing:
;; When sending text from a source file to a subprocess, the process-mark can
;; move off the window, so you can lose sight of the process interactions.
;; Maybe I should ensure the process mark is in the window when I send
;; text to the process? Switch selectable?

;; YOUR .EMACS FILE
;;=============================================================================
;; Some suggestions for your init file.
;;
;; ;; Define M-# to run some strange command:
;; (eval-after-load "shell"
;;  '(define-key shell-mode-map "\M-#" 'shells-dynamic-spell))

;; Brief Command Documentation:
;;============================================================================
;; Comint Mode Commands: (common to shell and all comint-derived modes)
;;
;; m-p	   comint-previous-input    	   Cycle backwards in input history
;; m-n	   comint-next-input  	    	   Cycle forwards
;; m-r     comint-previous-matching-input  Previous input matching a regexp
;; m-s     comint-next-matching-input      Next input that matches
;; m-c-l   comint-show-output		   Show last batch of process output
;; return  comint-send-input
;; c-d	   comint-delchar-or-maybe-eof	   Delete char unless at end of buff.
;; c-c c-a comint-bol                      Beginning of line; skip prompt
;; c-c c-u comint-kill-input	    	   ^u
;; c-c c-w backward-kill-word    	   ^w
;; c-c c-c comint-interrupt-subjob 	   ^c
;; c-c c-z comint-stop-subjob	    	   ^z
;; c-c c-\ comint-quit-subjob	    	   ^\
;; c-c c-o comint-delete-output		   Delete last batch of process output
;; c-c c-r comint-show-output		   Show last batch of process output
;; c-c c-l comint-dynamic-list-input-ring  List input history
;;         comint-send-invisible           Read line without echo & send to proc
;;         comint-continue-subjob	   Useful if you accidentally suspend
;;					        top-level job
;; comint-mode-hook is the comint mode hook.

;; Shell Mode Commands:
;;         shell			Fires up the shell process
;; tab     completion-at-point		Complete filename/command/history
;; m-?     comint-dynamic-list-filename-completions
;;					List completions in help buffer
;; c-c c-f shell-forward-command	Forward a shell command
;; c-c c-b shell-backward-command	Backward a shell command
;; 	   dirs				Resync the buffer's dir stack
;; 	   shell-dirtrack-mode		Turn dir tracking on/off
;;         comint-strip-ctrl-m		Remove trailing ^Ms from output
;;
;; The shell mode hook is shell-mode-hook
;; comint-prompt-regexp is initialized to shell-prompt-pattern, for backwards
;; compatibility.

;; Read the rest of this file for more information.

;;; Code:

(require 'comint)
(require 'pcomplete)
(eval-when-compile (require 'files-x)) ;with-connection-local-variables
(require 'subr-x)
(eval-when-compile (require 'cl-lib))

;;; Customization and Buffer Variables

(defgroup shell nil
  "Running shell from within Emacs buffers."
  :group 'processes
  :group 'unix)

(defgroup shell-directories nil
  "Directory support in shell mode."
  :group 'shell)

;;;###autoload
(defcustom shell-dumb-shell-regexp (purecopy "cmd\\(proxy\\)?\\.exe")
  "Regexp to match shells that don't save their command history, and
don't handle the backslash as a quote character.  For shells that
match this regexp, Emacs will write out the command history when the
shell finishes, and won't remove backslashes when it unquotes shell
arguments."
  :type 'regexp
  :group 'shell)

(defcustom shell-prompt-pattern "^[^#$%>\n]*[#$%>] *"
  "Regexp to match prompts in the inferior shell.
Defaults to \"^[^#$%>\\n]*[#$%>] *\", which works pretty well.
This variable is used to initialize `comint-prompt-regexp' in the
shell buffer.

If `comint-use-prompt-regexp' is nil, then this variable is only used
to determine paragraph boundaries.  See Info node `Shell Prompts' for
how Shell mode treats paragraphs.

The pattern should probably not match more than one line.  If it does,
Shell mode may become confused trying to distinguish prompt from input
on lines which don't start with a prompt."
  :type 'regexp
  :group 'shell)

(defcustom shell-completion-fignore nil
  "List of suffixes to be disregarded during file/command completion.
This variable is used to initialize `comint-completion-fignore' in the shell
buffer.  The default is nil, for compatibility with most shells.
Some people like (\"~\" \"#\" \"%\")."
  :type '(repeat (string :tag "Suffix"))
  :group 'shell)

(defcustom shell-delimiter-argument-list '(?\| ?& ?< ?> ?\( ?\) ?\;)
  "List of characters to recognize as separate arguments.
This variable is used to initialize `comint-delimiter-argument-list' in the
shell buffer.  The value may depend on the operating system or shell."
  :type '(choice (const nil)
		 (repeat :tag "List of characters" character))
  :group 'shell)

(defcustom shell-file-name-chars
  (if (memq system-type '(ms-dos windows-nt cygwin))
      "~/A-Za-z0-9_^$!#%&{}@`'.,:()-"
    "[]~/A-Za-z0-9+@:_.$#%,={}-")
  "String of characters valid in a file name.
This variable is used to initialize `comint-file-name-chars' in the
shell buffer.  The value may depend on the operating system or shell."
  :type 'string
  :group 'shell)

(defcustom shell-file-name-quote-list
  (if (memq system-type '(ms-dos windows-nt))
      nil
    (append shell-delimiter-argument-list '(?\s ?$ ?\* ?\! ?\" ?\' ?\` ?\# ?\\)))
  "List of characters to quote when in a file name.
This variable is used to initialize `comint-file-name-quote-list' in the
shell buffer.  The value may depend on the operating system or shell."
  :type '(repeat character)
  :group 'shell)

(defcustom shell-dynamic-complete-functions
  '(comint-c-a-p-replace-by-expanded-history
    shell-environment-variable-completion
    shell-command-completion
    shell-c-a-p-replace-by-expanded-directory
    pcomplete-completions-at-point
    shell-filename-completion
    comint-filename-completion)
  "List of functions called to perform completion.
This variable is used to initialize `comint-dynamic-complete-functions' in the
shell buffer."
  :type '(repeat function)
  :group 'shell)

(defcustom shell-command-regexp "[^;&|\n]+"
  "Regexp to match a single command within a pipeline.
This is used for directory tracking and does not do a perfect job."
  :type 'regexp
  :group 'shell)

(defcustom shell-command-separator-regexp "[;&|\n \t]*"
  "Regexp to match a single command within a pipeline.
This is used for directory tracking and does not do a perfect job."
  :type 'regexp
  :group 'shell)

(defcustom shell-completion-execonly t
  "If non-nil, use executable files only for completion candidates.
This mirrors the optional behavior of tcsh.

Detecting executability of files may slow command completion considerably."
  :type 'boolean
  :group 'shell)

(defcustom shell-popd-regexp "popd"
  "Regexp to match subshell commands equivalent to popd."
  :type 'regexp
  :group 'shell-directories)

(defcustom shell-pushd-regexp "pushd"
  "Regexp to match subshell commands equivalent to pushd."
  :type 'regexp
  :group 'shell-directories)

(defcustom shell-pushd-tohome nil
  "If non-nil, make pushd with no arg behave as \"pushd ~\" (like cd).
This mirrors the optional behavior of tcsh."
  :type 'boolean
  :group 'shell-directories)

(defcustom shell-pushd-dextract nil
  "If non-nil, make \"pushd +n\" pop the nth dir to the stack top.
This mirrors the optional behavior of tcsh."
  :type 'boolean
  :group 'shell-directories)

(defcustom shell-pushd-dunique nil
  "If non-nil, make pushd only add unique directories to the stack.
This mirrors the optional behavior of tcsh."
  :type 'boolean
  :group 'shell-directories)

(defcustom shell-cd-regexp "cd"
  "Regexp to match subshell commands equivalent to cd."
  :type 'regexp
  :group 'shell-directories)

(defcustom shell-chdrive-regexp
  (if (memq system-type '(ms-dos windows-nt))
      ; NetWare allows the five chars between upper and lower alphabetics.
      "[]a-zA-Z^_`[\\]:"
    nil)
  "If non-nil, is regexp used to track drive changes."
  :type '(choice regexp
		 (const nil))
  :group 'shell-directories)

(defcustom shell-dirtrack-verbose t
  "If non-nil, show the directory stack following directory change.
This is effective only if directory tracking is enabled.
The `dirtrack' package provides an alternative implementation of this feature -
see the function `dirtrack-mode'."
  :type 'boolean
  :group 'shell-directories)

(defcustom explicit-shell-file-name nil
  "If non-nil, the file name to use for explicitly requested inferior shells.
When nil, such interactive shell sessions fall back to using the
shell specified in either the environment variable \"ESHELL\" or
`shell-file-name'."
  :type '(choice (const :tag "Default" nil) file)
  :group 'shell)

;; Note: There are no explicit references to the variable `explicit-csh-args'.
;; It is used implicitly by M-x shell when the shell is `csh'.
(defcustom explicit-csh-args
  (if (eq system-type 'hpux)
      ;; -T persuades HP's csh not to think it is smarter
      ;; than us about what terminal modes to use.
      '("-i" "-T")
    '("-i"))
  "Args passed to inferior shell by \\[shell], if the shell is csh.
Value is a list of strings, which may be nil."
  :type '(repeat (string :tag "Argument"))
  :group 'shell)

;; Note: There are no explicit references to the variable `explicit-bash-args'.
;; It is used implicitly by M-x shell when the interactive shell is `bash'.
(defcustom explicit-bash-args
  ;; Tell bash not to use readline.  It's safe to assume --noediting now,
  ;; as it was introduced in 1996 in Bash version 2.
  '("--noediting" "-i")
  "Args passed to inferior shell by \\[shell], if the shell is bash.
Value is a list of strings, which may be nil."
  :type '(repeat (string :tag "Argument"))
  :group 'shell)

(defcustom shell-input-autoexpand 'history
  "If non-nil, expand input command history references on completion.
This mirrors the optional behavior of tcsh (its autoexpand and histlit).

If the value is `input', then the expansion is seen on input.
If the value is `history', then the expansion is only when inserting
into the buffer's input ring.  See also `comint-magic-space' and
`comint-dynamic-complete-functions'.

This variable supplies a default for `comint-input-autoexpand',
for Shell mode only."
  :type '(choice (const :tag "off" nil)
		 (const input)
		 (const history)
		 (const :tag "on" t))
  :group 'shell)

(defcustom shell-fontify-input-enable t
  "Enable fontification of input in shell buffers.
This variable only has effect when the shell is started.  Use the
command `comint-fontify-input-mode' to toggle fontification of
input."
  :type 'boolean
  :group 'shell
  :safe 'booleanp
  :version "29.1")

(defcustom shell-indirect-setup-hook nil
  "Hook run in an indirect buffer for input fontification.
Input fontification and indentation of a `shell-mode' buffer, if
enabled, is performed in an indirect buffer, whose indentation
and syntax highlighting is set up with `sh-mode'.  In addition to
`comint-indirect-setup-hook', run this hook with the indirect
buffer as the current buffer after its setup is done.  This can
be used to further customize fontification and other behavior of
the indirect buffer."
  :type 'hook
  :group 'shell
  :version "29.1")

(defcustom shell-highlight-undef-enable nil
  "Enable highlighting of undefined commands in shell buffers.
This variable only has effect when the shell is started.  Use the
command `shell-highlight-undef-mode' to toggle highlighting of
undefined commands."
  :type 'boolean
  :group 'shell
  :safe 'booleanp
  :version "29.1")

(defvar shell-dirstack nil
  "List of directories saved by pushd in this buffer's shell.
Thus, this does not include the shell's current directory.")

(defvaralias 'shell-dirtrackp 'shell-dirtrack-mode
  "Non-nil in a shell buffer means directory tracking is enabled.
Directory tracking (`shell-dirtrack-mode') is automatically enabled
when `shell-mode' is activated.")

(defvar shell-last-dir nil
  "Keep track of last directory for ksh `cd -' command.")

(defvar shell-dirstack-query nil
  "Command used by `shell-resync-dirs' to query the shell.")

(defcustom shell-has-auto-cd nil
  "If non-nil, `shell-mode' handles implicit \"cd\" commands.
Implicit \"cd\" is changing the directory if the command is a directory.
You can make this variable buffer-local to change it, per shell-mode instance.
Useful for shells like zsh that has this feature."
  :type 'boolean
  :group 'shell-directories
  :version "28.1")

(defcustom shell-get-old-input-include-continuation-lines nil
  "Whether `shell-get-old-input' includes \"\\\" lines."
  :type 'boolean
  :group 'shell
  :version "30.1")

(defcustom shell-kill-buffer-on-exit nil
  "Kill a shell buffer after the shell process terminates."
  :type 'boolean
  :group 'shell
  :version "29.1")

(defvar shell-mode-map
  (let ((map (make-sparse-keymap)))
    (define-key map "\C-c\C-f" 'shell-forward-command)
    (define-key map "\C-c\C-b" 'shell-backward-command)
    (define-key map "\t" 'completion-at-point)
    (define-key map (kbd "M-RET") 'shell-resync-dirs)
    (define-key map "\M-?" 'comint-dynamic-list-filename-completions)
    (define-key map (kbd "C-x n d") 'shell-narrow-to-prompt)
    (define-key map [menu-bar completion]
      (cons "Complete"
	    (copy-keymap (lookup-key comint-mode-map [menu-bar completion]))))
    (define-key-after (lookup-key map [menu-bar completion])
      [complete-env-variable] '("Complete Env. Variable Name" .
				shell-dynamic-complete-environment-variable)
      'complete-file)
    (define-key-after (lookup-key map [menu-bar completion])
      [expand-directory] '("Expand Directory Reference" .
			   shell-replace-by-expanded-directory)
      'complete-expand)
    map))

(defvar-keymap shell-repeat-map
  :doc "Keymap to repeat shell key sequences.  Used in `repeat-mode'."
  :repeat t
  "C-f" #'shell-forward-command
  "C-b" #'shell-backward-command)

(defcustom shell-mode-hook '()
  "Hook for customizing Shell mode."
  :type 'hook
  :group 'shell)

(defvar shell-font-lock-keywords
  '(("[ \t]\\([+-][^ \t\n]+\\)" 1 font-lock-comment-face)
    ("^[^ \t\n]+:.*" . font-lock-string-face)
    ("^\\[[1-9][0-9]*\\]" . font-lock-string-face))
  "Additional expressions to highlight in Shell mode.")

(defvar-local shell--start-prog nil
  "Shell file name started in `shell'.")
(put 'shell--start-prog 'permanent-local t)

(defcustom shell-history-file-name nil
  "The history file name used in `shell-mode'.
When it is a string, this file name will be used.
When it is nil, the environment variable HISTFILE is used.
When it is t, no history file name is used in `shell-mode'.

The settings obey whether `shell-mode' is invoked in a remote buffer.
In that case, HISTFILE is taken from the remote host, and the string is
interpreted as local file name on the remote host.

If `shell-mode' is invoked in a local buffer, and no history file name
can be determined, a default according to the shell type is used."
  :type '(choice (const :tag "Default" nil) (const :tag "Suppress" t) file)
  :local 'permanent-only
  :version "30.1")

;;; Basic Procedures

(defun shell--unquote&requote-argument (qstr &optional upos)
  (unless upos (setq upos 0))
  (let* ((qpos 0)
         (dquotes nil)
         (ustrs '())
         (re (concat
              "[\"']"
              "\\|\\$\\(?:\\([[:alpha:]][[:alnum:]]*\\)"
              "\\|{\\(?1:[^{}]+\\)}\\)"
              (when (memq system-type '(ms-dos windows-nt))
                "\\|%\\(?1:[^\\/]*\\)%")
              (when comint-file-name-quote-list
                "\\|\\\\\\(.\\)")))
         (qupos nil)
         (push (lambda (str end)
                 (push str ustrs)
                 (setq upos (- upos (length str)))
                 (unless (or qupos (> upos 0))
                   (setq qupos (if (< end 0) (- end) (+ upos end))))))
         match)
    (while (setq match (string-match re qstr qpos))
      (funcall push (substring qstr qpos match) match)
      (cond
       ((match-beginning 2) (funcall push (match-string 2 qstr) (match-end 0)))
       ((match-beginning 1) (funcall push (getenv (match-string 1 qstr))
                                     (- (match-end 0))))
       ((eq (aref qstr match) ?\") (setq dquotes (not dquotes)))
       ((eq (aref qstr match) ?\')
        (cond
         ;; Treat single quote as text if inside double quotes.
         (dquotes (funcall push "'" (match-end 0)))
         ((< (1+ match) (length qstr))
          (let ((end (string-match "'" qstr (1+ match))))
            (unless end
              (setq end (length qstr))
              (set-match-data (list match (length qstr))))
            (funcall push (substring qstr (1+ match) end) end)))
         ;; Ignore if at the end of string.
         (t nil)))
       (t (error "Unexpected case in shell--unquote&requote-argument!")))
      (setq qpos (match-end 0)))
    (funcall push (substring qstr qpos) (length qstr))
    (list (mapconcat #'identity (nreverse ustrs) "")
          qupos #'comint-quote-filename)))

(defun shell--unquote-argument (str)
  (car (shell--unquote&requote-argument str)))
(defun shell--requote-argument (upos qstr)
  ;; See `completion-table-with-quoting'.
  (let ((res (shell--unquote&requote-argument qstr upos)))
    (cons (nth 1 res) (nth 2 res))))

(defun shell--parse-pcomplete-arguments ()
  "Parse whitespace separated arguments in the current region."
  ;; FIXME: share code with shell--unquote&requote-argument.
  (let ((begin (save-excursion (shell-backward-command 1) (point)))
	(end (point))
	begins args)
    (save-excursion
      (goto-char begin)
      (while (< (point) end)
	(skip-chars-forward " \t\n;")
	(push (point) begins)
        (let ((arg ()))
          (while (looking-at
                  (concat
                   "\\(?:[^\s\t\n\\\"';]+"
                   "\\|'\\([^']*\\)'?"
                   "\\|\"\\(\\(?:[^\"\\]\\|\\\\.\\)*\\)\"?"
                   "\\|\\\\\\(\\(?:.\\|\n\\)?\\)\\)"))
            (goto-char (match-end 0))
            (cond
             ((match-beginning 3)       ;Backslash escape.
              (push (cond
                     ((null comint-file-name-quote-list)
                      (goto-char (match-beginning 3)) "\\")
                     ((= (match-beginning 3) (match-end 3)) "\\")
                     (t (match-string 3)))
                    arg))
             ((match-beginning 2)       ;Double quote.
              (push (if (null comint-file-name-quote-list) (match-string 2)
                      (replace-regexp-in-string
                       "\\\\\\(.\\)" "\\1" (match-string 2)))
                    arg))
             ((match-beginning 1)       ;Single quote.
              (push (match-string 1) arg))
             (t (push (match-string 0) arg))))
          (push (mapconcat #'identity (nreverse arg) "") args)))
      (cons (nreverse args) (nreverse begins)))))

(defun shell-get-old-input ()
  "Default for `comint-get-old-input' in `shell-mode'.
If `comint-use-prompt-regexp' is nil, then either
return the current input field (if point is on an input field), or the
current line (if point is on an output field).
If `comint-use-prompt-regexp' is non-nil, then return
the current line, with any initial string matching the regexp
`comint-prompt-regexp' removed.
In either case, if `shell-get-old-input-include-continuation-lines'
is non-nil and the current line ends with a backslash, the next
line is also included and examined for a backslash, ending with a
final line without a backslash."
  (let (field-prop bof)
    (if (and (not comint-use-prompt-regexp)
             ;; Make sure we're in an input rather than output field.
             (not (setq field-prop (get-char-property
                                    (setq bof (field-beginning)) 'field))))
        (field-string-no-properties bof)
      (comint-bol)
      (let ((start (point)))
        (cond ((or comint-use-prompt-regexp
                   (eq field-prop 'output))
               (goto-char (line-end-position))
               (when shell-get-old-input-include-continuation-lines
                 ;; Include continuation lines as long as the current
                 ;; line ends with a backslash.
                 (while (and (not (eobp))
                             (= (char-before) ?\\))
                   (goto-char (line-end-position 2)))))
              (t
               (goto-char (field-end))))
        (buffer-substring-no-properties start (point))))))

;;;###autoload
(defun split-string-shell-command (string)
  "Split STRING (a shell command) into a list of strings.
General shell syntax, like single and double quoting, as well as
backslash quoting, is respected."
  (with-temp-buffer
    (insert string)
    (let ((comint-file-name-quote-list shell-file-name-quote-list))
      (car (shell--parse-pcomplete-arguments)))))

(defun shell-command-completion-function ()
  "Completion function for shell command names.
This is the value of `pcomplete-command-completion-function' for
Shell buffers.  It implements `shell-completion-execonly' for
`pcomplete' completion."
  (if (pcomplete-match "/")
      (pcomplete-here (pcomplete-entries nil
					 (if shell-completion-execonly
					     #'file-executable-p)))
    (pcomplete-here
     (nth 2 (shell--command-completion-data)))))

(defun shell-completion-vars ()
  "Setup completion vars for `shell-mode' and `read-shell-command'."
  (setq-local comint-completion-fignore
              shell-completion-fignore)
  (setq-local comint-delimiter-argument-list
              shell-delimiter-argument-list)
  (setq-local comint-file-name-chars shell-file-name-chars)
  (setq-local comint-file-name-quote-list
              shell-file-name-quote-list)
  (setq-local comint-file-name-prefix
              (or (file-remote-p default-directory) ""))
  (setq-local comint-dynamic-complete-functions
              shell-dynamic-complete-functions)
  (setq-local comint-unquote-function #'shell--unquote-argument)
  (setq-local comint-requote-function #'shell--requote-argument)
  (setq-local pcomplete-parse-arguments-function
              #'shell--parse-pcomplete-arguments)
  (setq-local pcomplete-termination-string
              (cond ((not comint-completion-addsuffix) "")
                    ((stringp comint-completion-addsuffix)
                     comint-completion-addsuffix)
                    ((not (consp comint-completion-addsuffix)) " ")
                    (t (cdr comint-completion-addsuffix))))
  (setq-local pcomplete-command-completion-function
              #'shell-command-completion-function)
  ;; Don't use pcomplete's defaulting mechanism, rely on
  ;; shell-dynamic-complete-functions instead.
  (setq-local pcomplete-default-completion-function #'ignore)
  ;; Do not expand remote file names.
  (setq-local pcomplete-remote-file-ignore
              (not (file-remote-p default-directory)))
  (setq-local comint-input-autoexpand shell-input-autoexpand)
  ;; Not needed in shell-mode because it's inherited from comint-mode, but
  ;; placed here for read-shell-command.
  (add-hook 'completion-at-point-functions #'comint-completion-at-point nil t))

(put 'shell-mode 'mode-class 'special)

(defvar sh-shell-file)

(declare-function w32-application-type "w32proc.c"
                  (program) t)

(define-derived-mode shell-mode comint-mode "Shell"
  "Major mode for interacting with an inferior shell.
\\<shell-mode-map>
\\[comint-send-input] after the end of the process' output sends the text from
    the end of process to the end of the current line.
\\[comint-send-input] before end of process output copies the current line minus the prompt to
    the end of the buffer and sends it (\\[comint-copy-old-input] just copies the current line).
\\[comint-send-invisible] reads a line of text without echoing it, and sends it to
    the shell.  This is useful for entering passwords.  Or, add the function
    `comint-watch-for-password-prompt' to `comint-output-filter-functions'.

If you want to make multiple shell buffers, rename the \"*shell*\" buffer
using \\[rename-buffer] or \\[rename-uniquely] and start a new shell.

If you want to make shell buffers limited in length, add the function
`comint-truncate-buffer' to `comint-output-filter-functions'.

If you accidentally suspend your process, use \\[comint-continue-subjob]
to continue it.

`cd', `pushd' and `popd' commands given to the shell are watched by Emacs to
keep this buffer's default directory the same as the shell's working directory.
While directory tracking is enabled, the shell's working directory is displayed
by \\[list-buffers] or \\[mouse-buffer-menu] in the `File' field.
\\[dirs] queries the shell and resyncs Emacs's idea of what the current
    directory stack is.
\\[shell-dirtrack-mode] turns directory tracking on and off.
\(The `dirtrack' package provides an alternative implementation of this
feature - see the function `dirtrack-mode'.)

\\{shell-mode-map}
Customization: Entry to this mode runs the hooks on `comint-mode-hook' and
`shell-mode-hook' (in that order).  Before each input, the hooks on
`comint-input-filter-functions' are run.  After each shell output, the hooks
on `comint-output-filter-functions' are run.

Variables `shell-cd-regexp', `shell-chdrive-regexp', `shell-pushd-regexp'
and `shell-popd-regexp' are used to match their respective commands,
while `shell-pushd-tohome', `shell-pushd-dextract' and `shell-pushd-dunique'
control the behavior of the relevant command.

Variables `comint-completion-autolist', `comint-completion-addsuffix',
`comint-completion-recexact' and `comint-completion-fignore' control the
behavior of file name, command name and variable name completion.  Variable
`shell-completion-execonly' controls the behavior of command name completion.
Variable `shell-completion-fignore' is used to initialize the value of
`comint-completion-fignore'.

Variables `comint-input-ring-file-name' and `comint-input-autoexpand' control
the initialization of the input ring history, and history expansion.

Variables `comint-output-filter-functions', a hook, and
`comint-scroll-to-bottom-on-input' and `comint-scroll-to-bottom-on-output'
control whether input and output cause the window to scroll to the end of the
buffer.

By default, shell mode does nothing special when it receives a
\"bell\" character (C-g or ^G).  If you
  (add-hook \\='comint-output-filter-functions #\\='shell-filter-ring-bell nil t)
from `shell-mode-hook', Emacs will call the `ding' function
whenever it receives the bell character in output from a
command."
  :interactive nil
  :after-hook
  (unless comint-use-prompt-regexp
    (if shell-fontify-input-enable
        (comint-fontify-input-mode))
    (if shell-highlight-undef-enable
        (shell-highlight-undef-mode)))

  (setq comint-prompt-regexp shell-prompt-pattern)
  (shell-completion-vars)
  (setq-local paragraph-separate "\\'")
  (setq-local paragraph-start comint-prompt-regexp)
  (setq-local font-lock-defaults '(shell-font-lock-keywords t))
  (setq-local shell-dirstack nil)
  (setq-local shell-last-dir nil)
  (setq-local comint-get-old-input #'shell-get-old-input)
  ;; People expect Shell mode to keep the last line of output at
  ;; window bottom.
  (setq-local scroll-conservatively 101)
  (shell-dirtrack-mode 1)

  ;; By default, ansi-color applies faces using overlays.  This is
  ;; very inefficient in Shell buffers (e.g. Bug#10835).  We use a
  ;; custom `ansi-color-apply-face-function' to convert color escape
  ;; sequences into `font-lock-face' properties.
  (setq-local ansi-color-apply-face-function #'shell-apply-ansi-color)
  (shell-reapply-ansi-color)

  (add-hook 'comint-indirect-setup-hook
            #'shell-indirect-setup-hook 'append t)
  (setq comint-indirect-setup-function
        (let ((shell shell--start-prog))
          (lambda ()
            (require 'sh-script)
            (cl-letf
                (((default-value 'sh-shell-file)
                  (or shell sh-shell-file))
                 (inhibit-message t)
                 (message-log-max nil))
              (sh-mode)))))

  (setq-local indent-line-function #'comint-indent-input-line-default)
  (setq-local indent-region-function
              #'comint-indent-input-region-default)

  ;; This is not really correct, since the shell buffer does not really
  ;; edit this directory.  But it is useful in the buffer list and menus.
  (setq list-buffers-directory (expand-file-name default-directory))
  ;; shell-dependent assignments.
  (when (ring-empty-p comint-input-ring)
    (let* ((remote (file-remote-p default-directory))
           (shell (or shell--start-prog ""))
           (hfile (cond ((stringp shell-history-file-name)
                         shell-history-file-name)
                        ((null shell-history-file-name)
                         (if remote
                             (shell-command-to-string "echo -n $HISTFILE")
                           (getenv "HISTFILE")))))
           hsize)
      (and (string-equal hfile "") (setq hfile nil))
      (when (and (not remote) (not hfile))
        (setq hfile
              (cond ((string-equal shell "bash") "~/.bash_history")
		    ((string-equal shell "ksh") "~/.sh_history")
		    ((string-equal shell "zsh") "~/.zsh_history")
		    (t "~/.history"))))
      (when (stringp hfile)
        (setq hsize
              (if remote
                  (shell-command-to-string "echo -n $HISTSIZE")
                (getenv "HISTSIZE")))
        (and (stringp hsize)
	     (integerp (setq hsize (string-to-number hsize)))
	     (> hsize 0)
             (setq-local comint-input-ring-size hsize))
        (setq comint-input-ring-file-name
              (concat remote hfile)))
      (if (and comint-input-ring-file-name
               (or (equal comint-input-ring-file-name "")
	           (equal (file-truename comint-input-ring-file-name)
		          (file-truename null-device))))
	  (setq comint-input-ring-file-name nil))
      ;; Arrange to write out the input ring on exit, if the shell doesn't
      ;; do this itself.
      (if (and comint-input-ring-file-name
	       (string-match shell-dumb-shell-regexp shell))
	  (set-process-sentinel (get-buffer-process (current-buffer))
				#'shell-write-history-on-exit))
      (setq shell-dirstack-query
	    (cond ((string-equal shell "sh") "pwd")
		  ((string-equal shell "ksh") "echo $PWD ~-")
		  ;; Bypass any aliases.  TODO all shells could use this.
		  ((string-equal shell "bash") "command dirs")
		  ((and (string-equal shell "bash.exe")
                        (eq system-type 'windows-nt)
                        (eq (w32-application-type (executable-find "bash.exe"))
                            'msys))
                   "command pwd -W")
		  ((string-equal shell "zsh") "dirs -l")
		  (t "dirs")))
      ;; Bypass a bug in certain versions of bash.
      (when (string-equal shell "bash")
        (add-hook 'comint-preoutput-filter-functions
                  #'shell-filter-ctrl-a-ctrl-b nil t))

      ;; Skip extended history for zsh.
      (when (string-equal shell "zsh")
        (setq-local comint-input-ring-file-prefix
                    ": [[:digit:]]+:[[:digit:]]+;")))
    (comint-read-input-ring t)))

(defun shell-indirect-setup-hook ()
  "Run `shell-indirect-setup-hook'."
  (run-hooks 'shell-indirect-setup-hook))

(defun shell-apply-ansi-color (beg end face)
  "Apply FACE as the ansi-color face for the text between BEG and END."
  (when face
    (put-text-property beg end 'ansi-color-face face)
    (put-text-property beg end 'font-lock-face face)))

(defun shell-reapply-ansi-color ()
  "Reapply ansi-color faces to the existing contents of the buffer."
  (save-restriction
    (widen)
    (let* ((pos (point-min))
	   (end (or (next-single-property-change pos 'ansi-color-face)
		    (point-max)))
	   face)
      (while end
	(if (setq face (get-text-property pos 'ansi-color-face))
	    (put-text-property pos (or end (point-max))
			       'font-lock-face face))
	(setq pos end
	      end (next-single-property-change pos 'ansi-color-face))))))

(defun shell-filter-ctrl-a-ctrl-b (string)
  "Remove `^A' and `^B' characters from comint output.

Bash uses these characters as internal quoting characters in its
prompt.  Due to a bug in some bash versions (including 2.03,
2.04, and 2.05b), they may erroneously show up when bash is
started with the `--noediting' option and Select Graphic
Rendition (SGR) control sequences (formerly known as ANSI escape
sequences) are used to color the prompt.

This function can be put on `comint-preoutput-filter-functions'."
  (if (string-match "[\C-a\C-b]" string)
      (replace-regexp-in-string "[\C-a\C-b]" "" string t t)
    string))

(defun shell-filter-ring-bell (string)
  "Call `ding' if STRING contains a \"^G\" character.
This function can be put on `comint-output-filter-functions'."
  (when (string-search "\a" string)
    (ding))
  string)

(defun shell-write-history-on-exit (process event)
  "Called when the shell process is stopped.

Writes the input history to a history file
`comint-input-ring-file-name' using `comint-write-input-ring'
and inserts a short message in the shell buffer.

This function is a sentinel watching the shell interpreter process.
Sentinels will always get the two parameters PROCESS and EVENT."
  ;; Write history.
  (comint-write-input-ring)
  (let ((buf (process-buffer process)))
    (when (buffer-live-p buf)
      (with-current-buffer buf
        (insert (format "\nProcess %s %s\n" process event))))))

(define-derived-mode shell-command-mode comint-mode "Shell"
  "Major mode for the output of asynchronous `shell-command'."
  (setq-local font-lock-defaults '(shell-font-lock-keywords t))
  ;; See comments in `shell-mode'.
  (setq-local ansi-color-apply-face-function #'shell-apply-ansi-color)
  (setq list-buffers-directory (expand-file-name default-directory)))

;;;###autoload
(defun shell (&optional buffer file-name)
  "Run an inferior shell, with I/O through BUFFER (which defaults to `*shell*').
Interactively, a prefix arg means to prompt for BUFFER.
If `default-directory' is a remote file name, it is also prompted
to change if called with a prefix arg.

If BUFFER exists but shell process is not running, make new shell.
If BUFFER exists and shell process is running, just switch to BUFFER.
Program used comes from variable `explicit-shell-file-name',
 or (if that is nil) from the ESHELL environment variable,
 or (if that is nil) from `shell-file-name'.
Non-interactively, it can also be specified via the FILE-NAME arg.

If a file `~/.emacs_SHELLNAME' exists, or `~/.emacs.d/init_SHELLNAME.sh',
it is given as initial input (but this may be lost, due to a timing
error, if the shell discards input when it starts up).
The buffer is put in Shell mode, giving commands for sending input
and controlling the subjobs of the shell.  See `shell-mode'.
See also the variable `shell-prompt-pattern'.

\\<shell-mode-map>To specify a coding system for converting non-ASCII characters
in the input and output to the shell, use \\[universal-coding-system-argument]
before \\[shell].  You can also specify this with \\[set-buffer-process-coding-system]
in the shell buffer, after you start the shell.
The default comes from `process-coding-system-alist' and
`default-process-coding-system'.

The shell file name (sans directories) is used to make a symbol name
such as `explicit-csh-args'.  If that symbol is a variable,
its value is used as a list of arguments when invoking the shell.
Otherwise, one argument `-i' is passed to the shell.

Make the shell buffer the current buffer, and return it.

\(Type \\[describe-mode] in the shell buffer for a list of commands.)"
  (interactive
   (let* ((buffer
           (and current-prefix-arg
		(read-buffer "Shell buffer: "
			     ;; If the current buffer is an inactive
			     ;; shell buffer, use it as the default.
			     (if (and (eq major-mode 'shell-mode)
				      (null (get-buffer-process
				             (current-buffer))))
				 (buffer-name)
			       (generate-new-buffer-name "*shell*")))))
	  (buf (if (or buffer (not (derived-mode-p 'shell-mode))
                       (comint-check-proc (current-buffer)))
                   (get-buffer-create (or buffer "*shell*"))
                 ;; If the current buffer is a dead shell buffer, use it.
                 (current-buffer))))

     (with-current-buffer buf
       (when (and buffer (file-remote-p default-directory))
	 ;; It must be possible to declare a local default-directory.
	 (setq default-directory
	       (expand-file-name
		(read-directory-name
		 "Default directory: " default-directory default-directory
		 t nil))))
       (list
        buffer
        ;; On remote hosts, the local `shell-file-name' might be useless.
        (with-connection-local-variables
         (when (and (file-remote-p default-directory)
                    (null explicit-shell-file-name)
                    (null (getenv "ESHELL")))
           ;; `expand-file-name' shall not add the MS Windows volume letter
           ;; (Bug#49229).
           (replace-regexp-in-string
            "^[[:alpha:]]:" ""
            (file-local-name
             (expand-file-name
              (read-file-name "Remote shell path: " default-directory
                              shell-file-name t shell-file-name
                              #'file-remote-p))))))))))

  (setq buffer (if (or buffer (not (derived-mode-p 'shell-mode))
                       (comint-check-proc (current-buffer)))
                   (get-buffer-create (or buffer "*shell*"))
                 ;; If the current buffer is a dead shell buffer, use it.
                 (current-buffer)))
  ;; The buffer's window must be correctly set when we call comint
  ;; (so that comint sets the COLUMNS env var properly).
  (pop-to-buffer buffer (append display-buffer--same-window-action
                                '((category . comint))))

  (with-connection-local-variables
   (when file-name
     (setq-local explicit-shell-file-name file-name))

   ;; Rain or shine, BUFFER must be current by now.
   (unless (comint-check-proc buffer)
     (let* ((prog (or explicit-shell-file-name
                      (getenv "ESHELL") shell-file-name))
            (name (file-name-nondirectory prog))
            (startfile (concat "~/.emacs_" name))
            (xargs-name (intern-soft (concat "explicit-" name "-args")))
            (start-point (point)))
       (unless (file-exists-p startfile)
         (setq startfile (locate-user-emacs-file
                          (concat "init_" name ".sh"))))
       (setq-local shell--start-prog (file-name-nondirectory prog))
       (apply #'make-comint-in-buffer "shell" buffer prog
              nil
              (if (and xargs-name (boundp xargs-name))
                  (symbol-value xargs-name)
                '("-i")))
       (shell-mode)
       (when (file-exists-p startfile)
         ;; Wait until the prompt has appeared.
         (while (= start-point (point))
           (sleep-for 0.1))
         (shell-eval-command
          (with-temp-buffer
            (insert-file-contents startfile)
            (buffer-string)))))))
  (when shell-kill-buffer-on-exit
    (let* ((buffer (current-buffer))
           (process (get-buffer-process buffer))
           (sentinel (process-sentinel process)))
      (set-process-sentinel
       process
       (lambda (proc event)
         (when sentinel
           (funcall sentinel proc event))
         (unless (buffer-live-p proc)
           (kill-buffer buffer))))))
  buffer)

;;; 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.

(define-minor-mode shell-dirtrack-mode
  "Toggle directory tracking in this shell buffer (Shell Dirtrack mode).
This assigns a buffer-local non-nil value to `shell-dirtrackp'.

The `dirtrack' package provides an alternative implementation of
this feature; see the function `dirtrack-mode'.  Also see
`comint-osc-directory-tracker' for an escape-sequence based
solution."
  :lighter nil
  :interactive (shell-mode)
  (setq list-buffers-directory (if shell-dirtrack-mode default-directory))
  (if shell-dirtrack-mode
      (add-hook 'comint-input-filter-functions #'shell-directory-tracker nil t)
    (remove-hook 'comint-input-filter-functions #'shell-directory-tracker t)))

(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-dirtrack-mode
      ;; 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))))))))

(defun shell-unquote-argument (string)
  "Remove all kinds of shell quoting from STRING."
  (save-match-data
    (let ((idx 0) next inside
	  (quote-chars
	   (if (string-match shell-dumb-shell-regexp
			     (file-name-nondirectory
			      (car (process-command (get-buffer-process (current-buffer))))))
	       "['`\"]"
	     "[\\'`\"]")))
      (while (and (< idx (length string))
		  (setq next (string-match quote-chars string next)))
	(cond ((= (aref string next) ?\\)
	       (setq string (replace-match "" nil nil string))
	       (setq next (1+ next)))
	      ((and inside (= (aref string next) inside))
	       (setq string (replace-match "" nil nil string))
	       (setq inside nil))
	      (inside
	       (setq next (1+ next)))
	      (t
	       (setq inside (aref string next))
	       (setq string (replace-match "" nil nil string)))))
      string)))

;; popd [+n]
(defun shell-process-popd (arg)
  (let ((num (or (shell-extract-num arg) 0)))
    (cond ((and num (= num 0) shell-dirstack)
	   (shell-cd (shell-prefixed-directory-name (car shell-dirstack)))
	   (setq shell-dirstack (cdr shell-dirstack))
	   (shell-dirstack-message))
	  ((and num (> num 0) (<= num (length shell-dirstack)))
	   (let* ((ds (cons nil shell-dirstack))
		  (cell (nthcdr (1- num) ds)))
	     (rplacd cell (cdr (cdr cell)))
	     (setq shell-dirstack (cdr ds))
	     (shell-dirstack-message)))
	  (t
	   (error "Couldn't popd")))))

;; Return DIR prefixed with comint-file-name-prefix as appropriate.
(defun shell-prefixed-directory-name (dir)
  (if (= (length comint-file-name-prefix) 0)
      dir
    (if (file-name-absolute-p dir)
	;; The name is absolute, so prepend the prefix.
	(concat comint-file-name-prefix (file-local-name dir))
      ;; For relative name we assume default-directory already has the prefix.
      (expand-file-name dir))))

;; cd [dir]
(defun shell-process-cd (arg)
  (let ((new-dir (cond ((zerop (length arg)) (concat comint-file-name-prefix
						     "~"))
		       ((string-equal "-" arg) shell-last-dir)
		       (t (shell-prefixed-directory-name arg)))))
    (setq shell-last-dir default-directory)
    (shell-cd new-dir)
    (shell-dirstack-message)))

;; pushd [+n | dir]
(defun shell-process-pushd (arg)
  (let ((num (shell-extract-num arg)))
    (cond ((zerop (length arg))
	   ;; no arg -- swap pwd and car of stack unless shell-pushd-tohome
	   (cond (shell-pushd-tohome
		  (shell-process-pushd (concat comint-file-name-prefix "~")))
		 (shell-dirstack
		  (let ((old default-directory))
		    (shell-cd (car shell-dirstack))
		    (setq shell-dirstack (cons old (cdr shell-dirstack)))
		    (shell-dirstack-message)))
		 (t
		  (message "Directory stack empty."))))
	  ((numberp num)
	   ;; pushd +n
	   (cond ((> num (length shell-dirstack))
		  (message "Directory stack not that deep."))
		 ((= num 0)
		  (error "Couldn't cd"))
		 (shell-pushd-dextract
		  (let ((dir (nth (1- num) shell-dirstack)))
		    (shell-process-popd arg)
		    (shell-process-pushd default-directory)
		    (shell-cd dir)
		    (shell-dirstack-message)))
		 (t
		  (let* ((ds (cons default-directory shell-dirstack))
			 (dslen (length ds))
			 (front (nthcdr num ds))
			 (back (reverse (nthcdr (- dslen num) (reverse ds))))
			 (new-ds (append front back)))
		    (shell-cd (car new-ds))
		    (setq shell-dirstack (cdr new-ds))
		    (shell-dirstack-message)))))
	  (t
	   ;; pushd <dir>
	   (let ((old-wd default-directory))
	     (shell-cd (shell-prefixed-directory-name arg))
	     (if (or (null shell-pushd-dunique)
		     (not (member old-wd shell-dirstack)))
		 (setq shell-dirstack (cons old-wd shell-dirstack)))
	     (shell-dirstack-message))))))

;; If STR is of the form +n, for n>0, return n. Otherwise, nil.
(defun shell-extract-num (str)
  (and (string-match "^\\+[1-9][0-9]*$" str)
       (string-to-number str)))

(defun shell-cd (dir)
  "Do normal `cd' to DIR, and set `list-buffers-directory'."
  (cd dir)
  (if shell-dirtrack-mode
      (setq list-buffers-directory default-directory)))

(defun shell-resync-dirs ()
  "Resync the buffer's idea of the current directory stack.
This command queries the shell with the command bound to
`shell-dirstack-query' (default \"dirs\"), reads the next
line output and parses it to form the new directory stack."
  (interactive)
  (let* ((dls (car
               (last
                (string-lines
                 (string-chop-newline
                  (shell-eval-command (concat shell-dirstack-query "\n")))))))
         (dlsl nil)
         (pos 0)
         (ds nil))
    (setq dls (string-trim-right dls "[ ]+"))
    ;; Split the dirlist into whitespace and non-whitespace chunks.
    ;; dlsl will be a reversed list of tokens.
    (while (string-match "\\(\\S-+\\|\\s-+\\)" dls pos)
      (push (match-string 1 dls) dlsl)
      (setq pos (match-end 1)))

    ;; Prepend trailing entries until they form an existing directory,
    ;; whitespace and all.  Discard the next whitespace and repeat.
    (while dlsl
      (let ((newelt "")
            tem1 tem2)
        (while (and dlsl newelt)
          ;; We need tem1 because we don't want to prepend
          ;; `comint-file-name-prefix' repeatedly into newelt via tem2.
          (setq tem1 (pop dlsl)
                tem2 (concat comint-file-name-prefix tem1 newelt))
          (cond ((file-directory-p tem2)
                 (push tem2 ds)
                 (when (string= " " (car dlsl))
                   (pop dlsl))
                 (setq newelt nil))
                (t
                 (setq newelt (concat tem1 newelt)))))))

    (with-demoted-errors "Couldn't cd: %s"
      (shell-cd (car ds))
      (setq shell-dirstack (cdr ds)
            shell-last-dir (car shell-dirstack))
      (shell-dirstack-message))))

;; For your typing convenience:
(defalias 'dirs 'shell-resync-dirs)


;; Show the current dirstack on the message line.
;; Pretty up dirs a bit by changing "/usr/jqr/foo" to "~/foo".
;; (This isn't necessary if the dirlisting is generated with a simple "dirs".)
;; All the commands that mung the buffer's dirstack finish by calling
;; this guy.
(defun shell-dirstack-message ()
  (when shell-dirtrack-verbose
    (let* ((msg "")
	   (ds (cons default-directory shell-dirstack))
	   (home (expand-file-name (concat comint-file-name-prefix "~/")))
	   (homelen (length home)))
      (while ds
	(let ((dir (car ds)))
	  (and (>= (length dir) homelen)
	       (string= home (substring dir 0 homelen))
	       (setq dir (concat "~/" (substring dir homelen))))
	  ;; Strip off comint-file-name-prefix if present.
	  (and comint-file-name-prefix
	       (>= (length dir) (length comint-file-name-prefix))
	       (string= comint-file-name-prefix
			(substring dir 0 (length comint-file-name-prefix)))
	       (setq dir (substring dir (length comint-file-name-prefix)))
	       (setcar ds dir))
	  (setq msg (concat msg (directory-file-name dir) " "))
	  (setq ds (cdr ds))))
      (message "%s" msg))))

;; This was mostly copied from shell-resync-dirs.
(defun shell-snarf-envar (var)
  "Return as a string the shell's value of environment variable VAR."
  (let* ((cmd (format "printenv '%s'\n" var))
	 (proc (get-buffer-process (current-buffer)))
	 (pmark (process-mark proc)))
    (goto-char pmark)
    (insert cmd)
    (sit-for 0)				; force redisplay
    (comint-send-string proc cmd)
    (set-marker pmark (point))
    (let ((pt (point)))			; wait for 1 line
      ;; This extra newline prevents the user's pending input from spoofing us.
      (insert "\n") (backward-char 1)
      (while (not (looking-at ".+\n"))
	(accept-process-output proc)
	(goto-char pt)))
    (goto-char pmark) (delete-char 1)	; remove the extra newline
    (buffer-substring (match-beginning 0) (1- (match-end 0)))))

(defun shell-copy-environment-variable (variable)
  "Copy the environment variable VARIABLE from the subshell to Emacs.
This command reads the value of the specified environment variable
in the shell, and sets the same environment variable in Emacs
\(what `getenv' in Emacs would return) to that value.
That value will affect any new subprocesses that you subsequently start
from Emacs."
  (interactive (list (read-envvar-name "\
Copy Shell environment variable to Emacs: ")))
  (setenv variable (shell-snarf-envar variable)))

(defun shell-forward-command (&optional arg)
  "Move forward across ARG shell command(s).  Does not cross lines.
See `shell-command-regexp'."
  (interactive "p")
  (let ((limit (line-end-position))
	(pt (point)))
    (re-search-forward (concat shell-command-regexp "\\([;&|][\t ]*\\)+")
		       limit 'move arg)
    (and (/= pt (point))
	 (skip-syntax-backward " " pt))))


(defun shell-backward-command (&optional arg)
  "Move backward across ARG shell command(s).  Does not cross lines.
See `shell-command-regexp'."
  (interactive "p")
  (let ((limit (save-excursion (comint-bol nil) (point))))
    (when (> limit (point))
      (setq limit (line-beginning-position)))
    (skip-syntax-backward " " limit)
    (let ((pt (point)))
      (if (re-search-backward
	   (format "[;&|]+[\t ]*\\(%s\\)" shell-command-regexp) limit 'move arg)
	  (progn (goto-char (match-beginning 1))
		 (skip-chars-forward ";&|")))
      (and (/= pt (point))
	   (skip-syntax-forward " " pt)))))

(defun shell-dynamic-complete-command ()
  "Dynamically complete the command at point.
This function is similar to `comint-dynamic-complete-filename', except that it
searches `exec-path' (minus trailing `exec-directory') for completion
candidates.  Note that this may not be the same as the shell's idea of the
path.

Completion is dependent on the value of `shell-completion-execonly',
`shell-completion-fignore', plus those that affect file completion.  See Info
node `Shell Options'.

Returns t if successful."
  (interactive)
  (let ((data (shell-command-completion)))
    (if data
	(prog2 (unless (window-minibuffer-p)
		 (message "Completing command name..."))
            (completion-in-region (nth 0 data) (nth 1 data) (nth 2 data))))))

(defun shell-command-completion ()
  "Return the completion data for the command at point, if any."
  (let ((filename (comint-match-partial-filename)))
    (if (and filename
	     (save-match-data (not (string-match "[~/]" filename)))
	     (eq (match-beginning 0)
		 (save-excursion (shell-backward-command 1) (point))))
	(shell--command-completion-data))))

(defun shell--command-completion-data ()
  "Return the completion data for the command at point."
  (let* ((filename (or (comint-match-partial-filename) ""))
         (start (if (zerop (length filename)) (point) (match-beginning 0)))
         (end (if (zerop (length filename)) (point) (match-end 0)))
	 (filenondir (file-name-nondirectory filename))
	 (path-dirs
	  ;; Ignore `exec-directory', the last entry in `exec-path'.
          (append (cdr (reverse (exec-path)))
	          (if (and (memq system-type '(windows-nt ms-dos))
                           (not (file-remote-p default-directory)))
                      '("."))))
	 (cwd (file-name-as-directory (expand-file-name default-directory)))
	 (ignored-extensions
	  (and comint-completion-fignore
               (mapconcat (lambda (x) (concat (regexp-quote x) "\\'"))
			  comint-completion-fignore "\\|")))
	 (dir "") (comps-in-dir ())
	 (file "") (abs-file-name "") (completions ()))
    ;; Go thru each dir in the search path, finding completions.
    (while path-dirs
      (setq dir (file-name-as-directory (comint-directory (or (car path-dirs) ".")))
	    comps-in-dir (and (file-accessible-directory-p dir)
			      (condition-case nil
                                  (file-name-all-completions filenondir dir)
                                ;; Systems such as Android sometimes
                                ;; put inaccessible directories in
                                ;; PATH.
                                (permission-denied nil))))
      ;; Go thru each completion found, to see whether it should be used.
      (while comps-in-dir
	(setq file (car comps-in-dir)
	      abs-file-name (concat dir file))
	(if (and (not (member file completions))
		 (not (and ignored-extensions
			   (string-match ignored-extensions file)))
		 (or (string-equal dir cwd)
		     (not (file-directory-p abs-file-name)))
		 (or (null shell-completion-execonly)
		     (file-executable-p abs-file-name)))
	    (setq completions (cons file completions)))
	(setq comps-in-dir (cdr comps-in-dir)))
      (setq path-dirs (cdr path-dirs)))
    ;; OK, we've got a list of completions.
    (list
     start end
     (lambda (string pred action)
       (if (string-search "/" string)
           (completion-file-name-table string pred action)
         (complete-with-action action completions string pred)))
     :exit-function
     (lambda (_string finished)
       (when (memq finished '(sole finished))
         (if (looking-at " ")
             (goto-char (match-end 0))
           (insert " ")))))))

;; (defun shell-dynamic-complete-as-command ()
;;    "Dynamically complete at point as a command.
;;  See `shell-dynamic-complete-filename'.  Returns t if successful."
;;    (apply #'completion-in-region shell--command-completion-data))

(defun shell-dynamic-complete-filename ()
  "Dynamically complete the filename at point.
This completes only if point is at a suitable position for a
filename argument."
  (interactive)
  (let ((data (shell-filename-completion)))
    (if data (apply #'completion-in-region data))))

(defun shell-filename-completion ()
  "Return the completion data for file name at point, if any."
  (let ((opoint (point))
	(beg (comint-line-beginning-position)))
    (when (save-excursion
	    (goto-char (if (re-search-backward "[;|&]" beg t)
			   (match-end 0)
			 beg))
	    (re-search-forward "[^ \t][ \t]" opoint t))
      (comint-filename-completion))))

(defun shell-match-partial-variable ()
  "Return the shell variable at point, or nil if none is found."
  (save-excursion
    (if (re-search-backward "[^A-Za-z0-9_{(]" nil 'move)
        (or (looking-at "\\$") (forward-char 1)))
    (if (or (eolp) (looking-at "[^A-Za-z0-9_{($]"))
        nil
      (looking-at "\\$?[{(]?[A-Za-z0-9_]*[})]?")
      (buffer-substring (match-beginning 0) (match-end 0)))))

(defun shell-dynamic-complete-environment-variable ()
  "Dynamically complete the environment variable at point.
Completes if after a variable, i.e., if it starts with a \"$\".

This function is similar to `comint-dynamic-complete-filename', except that it
searches `process-environment' for completion candidates.  Note that this may
not be the same as the interpreter's idea of variable names.  The main problem
with this type of completion is that `process-environment' is the environment
which Emacs started with.  Emacs does not track changes to the environment made
by the interpreter.  Perhaps it would be more accurate if this function was
called `shell-dynamic-complete-process-environment-variable'.

Returns non-nil if successful."
  (interactive)
  (let ((data (shell-environment-variable-completion)))
    (if data
	(prog2 (unless (window-minibuffer-p)
		 (message "Completing variable name..."))
	    (completion-in-region (nth 0 data) (nth 1 data) (nth 2 data))))))


(defun shell-environment-variable-completion ()
  "Completion data for an environment variable at point, if any."
  (let* ((var (shell-match-partial-variable))
         (end (match-end 0)))
    (when (and (not (zerop (length var))) (eq (aref var 0) ?$))
      (let* ((start
              (save-excursion
                (goto-char (match-beginning 0))
                (looking-at "\\$?[({]*")
                (match-end 0)))
             (variables (mapcar (lambda (x)
                                  (substring x 0 (string-search "=" x)))
                                process-environment))
             (suffix (pcase (char-before start) (?\{ "}") (?\( ")") (_ ""))))
        (list start end variables
              :exit-function
              (lambda (s finished)
                (when (memq finished '(sole finished))
                  (let ((suf (concat suffix
                                     (if (file-directory-p
                                          (comint-directory (getenv s)))
                                         "/"))))
                    (if (looking-at (regexp-quote suf))
                        (goto-char (match-end 0))
                      (insert suf))))))))))


(defun shell-c-a-p-replace-by-expanded-directory ()
  "Expand directory stack reference before point.
For use on `completion-at-point-functions'."
  (when (comint-match-partial-filename)
    (save-excursion
      (goto-char (match-beginning 0))
      (let ((stack (cons default-directory shell-dirstack))
            (index (cond ((looking-at "=-/?")
                          (length shell-dirstack))
                         ((looking-at "=\\([0-9]+\\)/?")
                          (string-to-number
                           (buffer-substring
                            (match-beginning 1) (match-end 1)))))))
        (when index
          (let ((start (match-beginning 0))
                (end (match-end 0))
                (replacement (file-name-as-directory (nth index stack))))
            (lambda ()
              (cond
               ((>= index (length stack))
                (error "Directory stack not that deep"))
               (t
                (save-excursion
                  (goto-char start)
                  (insert replacement)
                  (delete-char (- end start)))
                (message "Directory item: %d" index)
                t)))))))))

(defun shell-replace-by-expanded-directory ()
  "Expand directory stack reference before point.
Directory stack references are of the form \"=digit\" or \"=-\".
See `default-directory' and `shell-dirstack'.

Returns t if successful."
  (interactive)
  (let ((f (shell-c-a-p-replace-by-expanded-directory)))
    (if f (funcall f))))

(defun shell--prompt-begin-position ()
  ;; We need this convoluted function because `looking-at-p' does not work on
  ;; multiline regexps _and_ `re-search-backward' skips the current line.
  (save-excursion
    (let ((old-point (point)))
      (max
       (save-excursion
         ;; Right result if not on prompt.
         (call-interactively #'comint-previous-prompt)
         (re-search-backward comint-prompt-regexp)
         (point))
       (save-excursion
         ;; Right result if on first char after prompt.
         (re-search-backward comint-prompt-regexp)
         (point))
       (save-excursion
         ;; Right result if on prompt.
         (call-interactively #'comint-next-prompt)
         (re-search-backward comint-prompt-regexp)
         (if (<= (point) old-point)
             (point)
           (point-min)))))))

(defun shell--prompt-end-position ()
  (save-excursion
    (goto-char (shell--prompt-begin-position))
    (comint-next-prompt 1)
    (point)))

(defun shell-narrow-to-prompt ()
  "Narrow buffer to the command line (and any following command output) at point."
  (interactive)
  (let ((begin (shell--prompt-begin-position)))
    (narrow-to-region
     begin
     (save-excursion
       (goto-char (shell--prompt-end-position))
       (call-interactively #'comint-next-prompt)
       (if (= begin (shell--prompt-begin-position))
           (point-max)
         (shell--prompt-begin-position))))))

(defun shell-eval-command (command)
  "Eval COMMAND in the current shell process and return the result."
  (let* ((proc (get-buffer-process (current-buffer)))
         (old-filter (process-filter proc))
         (result "")
         prev)
    (unwind-protect
        (progn
          (set-process-filter
           proc
           (lambda (_proc string)
             (setq result (concat result string))))
          (process-send-string proc command)
          ;; Wait until we get a prompt (which will be a line without
          ;; a newline).  This is far from fool-proof -- if something
          ;; outputs incomplete data and then sleeps, we'll think
          ;; we've received the prompt.
          (while (not (let* ((lines (string-lines result nil t))
                             (last (car (last lines)))
                             (last-end (if (equal last "")
                                           last
                                         (substring last -1))))
                        (and (length> lines 0)
                             (not (member last '("" "\n")))
                             (not (equal last-end "\n"))
                             (or (not prev)
                                 (not (equal last prev)))
                             (setq prev last))))
            (accept-process-output proc 0 100)))
      ;; Restore old filter.
      (set-process-filter proc old-filter))
    ;; Remove the prompt.
    (replace-regexp-in-string "\n.*\\'" "\n" result)))

;;; Highlight undefined commands
;;
;; To highlight non-existent shell commands, customize
;; `shell-highlight-undef-enable' to t.  To highlight some shell
;; commands as aliases, add them to `shell-highlight-undef-aliases'.

(defcustom shell-highlight-undef-aliases nil
  "List of shell commands to highlight as a command alias."
  :group 'shell
  :type '(repeat string)
  :version "29.1")

(defface shell-highlight-undef-defined-face
  '((t :inherit font-lock-function-name-face))
  "Face used for existing shell commands."
  :group 'shell
  :version "29.1")

(defface shell-highlight-undef-undefined-face
  '((t :inherit font-lock-warning-face))
  "Face used for non-existent shell commands."
  :group 'shell
  :version "29.1")

(defface shell-highlight-undef-alias-face
  '((t :inherit font-lock-variable-name-face))
  "Face used for shell command aliases."
  :group 'shell
  :version "29.1")

(defcustom shell-highlight-undef-remote-file-name-inhibit-cache nil
  "Whether to inhibit cache for fontifying shell commands in remote buffers.
When fontification of non-existent commands is enabled in a
remote shell buffer, use a cache to speed up searching for
executable files on the remote machine.  This option controls
expiry of the cache.  See `remote-file-name-inhibit-cache' for
a description of the possible options."
  :group 'faces
  :type '(choice
          (const :tag "Do not cache remote executables" t)
          (const :tag "Cache remote executables" nil)
          (integer :tag "Cache remote executables with expiration"
                   :format "Cache expiry in seconds: %v"
                   :value 10))
  :version "29.1")

(defvar shell--highlight-undef-exec-cache nil
  "Cache of executable files found in `exec-path'.
An alist, whose elements are of the form
\(REMOTE TIME EXECUTABLES), where REMOTE is a string, returned by
`file-remote-p', TIME is the return value of `float-time', and
EXECUTABLES is a hash table with keys being the base-names of
executable files.

Cache expiry is controlled by the user option
`shell-highlight-undef-remote-file-name-inhibit-cache'.")

(defvar shell--highlight-undef-face 'shell-highlight-undef-defined-face)

(defvar shell-highlight-undef-keywords
  `((,#'shell-highlight-undef-matcher 6 shell--highlight-undef-face)))

(defvar-local shell-highlight-undef-regexp regexp-unmatchable)

(defun shell--highlight-undef-executable-find (command)
  "Return non-nil if COMMAND is found in `exec-path'.
Similar to `executable-find', but use cache stored in
`shell--highlight-undef-exec-cache'."
  (let ((remote (file-remote-p default-directory))
        as ret found-in-cache delta-time)
    (if (null remote)
        (executable-find command)

      (setq delta-time
            shell-highlight-undef-remote-file-name-inhibit-cache)

      (pcase (setq as (assoc remote shell--highlight-undef-exec-cache))
        (`(,_ ,time ,hash)
         (when (pcase delta-time
                 ((pred numberp) (<= (float-time) (+ time delta-time)))
                 ('t nil)
                 ('nil t))
           (setq ret (gethash command hash))
           (setq found-in-cache t)))
        (_ (setq as (list remote 0 (make-hash-table :test #'equal)))
           (push as shell--highlight-undef-exec-cache)))

      (if found-in-cache
          ret
        ;; Build cache
        (setcar (cdr as) (float-time))
        (let ((hash (clrhash (caddr as))))
          (dolist (dir (exec-path))
            (pcase-dolist (`(,f . ,attr)
                           (condition-case nil
                               (directory-files-and-attributes
                                (concat remote dir) nil nil 'nosort 'integer)
                             (file-error nil)))
              ;; Approximation.  Assume every non-directory file in $PATH is an
              ;; executable.  Alternatively, we could check
              ;; `file-executable-p', but doing so for every file in $PATH is
              ;; slow on remote machines.
              (unless (eq t (file-attribute-type attr))
                (puthash f t hash))))
          (gethash command hash))))))

(defun shell-highlight-undef-matcher (end)
  "Matcher used to highlight shell commands up to END."
  (when (re-search-forward shell-highlight-undef-regexp end t)
    (save-match-data
      (let ((cmd (match-string 6))
            (beg (match-beginning 6)))
        (setq shell--highlight-undef-face
              (let* ((buf (buffer-base-buffer))
                     (default-directory
                      (if buf (buffer-local-value 'default-directory buf)
                        default-directory)))
                (cond
                 ;; Don't fontify command output.  Mostly useful if
                 ;; `comint-fontify-input-mode' is disabled.
                 ((text-property-any beg (point) 'field 'output)
                  nil)
                 ((member cmd shell-highlight-undef-aliases)
                  'shell-highlight-undef-alias-face)
                 ;; Check if it contains a directory separator
                 ((file-name-directory cmd)
                  (when (file-name-absolute-p cmd)
                    (setq cmd (concat
                               (or (bound-and-true-p comint-file-name-prefix)
                                   (file-remote-p default-directory))
                               cmd)))
                  (if (or (file-executable-p cmd)
                          (file-directory-p cmd))
                      'shell-highlight-undef-defined-face
                    'shell-highlight-undef-undefined-face))
                 ((shell--highlight-undef-executable-find cmd)
                  'shell-highlight-undef-defined-face)
                 (t 'shell-highlight-undef-undefined-face))))))
    t))

(defvar-local shell--highlight-undef-indirect nil
  "Non-nil if shell commands are fontified in `comint-indirect-buffer'.")

(declare-function sh-feature "sh-script" (alist &optional function))
(defvar sh-leading-keywords)
(defvar sh-other-keywords)

(define-minor-mode shell-highlight-undef-mode
  "Highlight undefined shell commands and aliases.
This minor mode is mostly useful in `shell-mode' buffers and
works better if `comint-fontify-input-mode' is enabled."
  :init-value nil
  (if shell--highlight-undef-indirect
      (progn
        (remove-hook 'comint-indirect-setup-hook shell--highlight-undef-indirect t)
        (setq shell--highlight-undef-indirect nil)
        (when-let* ((buf (comint-indirect-buffer t)))
          (with-current-buffer buf
            (font-lock-remove-keywords nil shell-highlight-undef-keywords))))
    (font-lock-remove-keywords nil shell-highlight-undef-keywords))
  (remove-hook 'comint-fontify-input-mode-hook
               #'shell-highlight-undef-mode-restart t)

  (when shell-highlight-undef-mode
    (when comint-use-prompt-regexp
      (setq shell-highlight-undef-mode nil)
      (error
       "`shell-highlight-undef-mode' is incompatible with `comint-use-prompt-regexp'"))

    (require 'sh-script)

    (let* ((regexp
            ;; Adapted from `sh-font-lock-keywords-1'
            (concat
             "\\("
             "[;(){}`|&]"
             (if comint-fontify-input-mode
                 ;; `comint-fontify-input-mode' already puts
                 ;; point-min on end of prompt
                 ""
               (concat "\\|" comint-prompt-regexp))
             "\\|^"
             "\\)"
             "[ \t]*\\(\\("
             (regexp-opt (sh-feature sh-leading-keywords) t)
             "[ \t]+\\)?"
             (regexp-opt (append (sh-feature sh-leading-keywords)
                                 (sh-feature sh-other-keywords))
                         t)
             "[ \t]+\\)?\\_<\\(\\(?:\\s_\\|\\sw\\|/\\)+\\)\\_>"))
           (setup
            (lambda ()
              (setq shell-highlight-undef-regexp regexp)
              (font-lock-add-keywords nil shell-highlight-undef-keywords t))))
      (cond (comint-fontify-input-mode
             (setq shell--highlight-undef-indirect setup)
             (if-let* ((buf (comint-indirect-buffer t)))
                 (with-current-buffer buf
                   (funcall setup))
               (add-hook 'comint-indirect-setup-hook setup nil t)))
            (t (funcall setup))))

    (add-hook 'comint-fontify-input-mode-hook
              #'shell-highlight-undef-mode-restart nil t))

  (font-lock-flush))

(defun shell-highlight-undef-mode-restart ()
  "If `shell-highlight-undef-mode' is on, restart it.
`shell-highlight-undef-mode' performs its setup differently
depending on `comint-fontify-input-mode'.  It's useful to call
this function when switching `comint-fontify-input-mode' in order
to make `shell-highlight-undef-mode' redo its setup."
  (when shell-highlight-undef-mode
    (shell-highlight-undef-mode 1)))

(provide 'shell)

;;; shell.el ends here