* lisp/shell.el (explicit-shell-file-name): Mention shell-file-name

* lisp/files.el (insert-directory): Don't hardcode "-c".
* lisp/term.el (term, ansi-term): Use shell-file-name.

lisp/files.el

@@ -6701,7 +6701,7 @@ normally equivalent short `-D' option is just passed on to
 			;; See eg dired-safe-switches-p.
 			(call-process
 			 shell-file-name nil t nil
-			 "-c"
+			 shell-command-switch
 			 (concat (if (memq system-type '(ms-dos windows-nt))
 				     ""
 				   "\\") ; Disregard Unix shell aliases!

lisp/shell.el

@@ -264,7 +264,9 @@ see the function `dirtrack-mode'."
   :group 'shell-directories)
 
 (defcustom explicit-shell-file-name nil
-  "If non-nil, is file name to use for explicitly requested inferior shell."
+  "If non-nil, is file name to use for explicitly requested inferior shell.
+When nil, such interactive shell sessions fallback to using either
+the shell specified in $ESHELL or in `shell-file-name'."
   :type '(choice (const :tag "None" nil) file)
   :group 'shell)
 

lisp/term.el

@@ -1354,8 +1354,7 @@ commands to use in that buffer.
   (interactive (list (read-from-minibuffer "Run program: "
 					   (or explicit-shell-file-name
 					       (getenv "ESHELL")
-					       (getenv "SHELL")
-					       "/bin/sh"))))
+					       shell-file-name))))
   (set-buffer (make-term "terminal" program))
   (term-mode)
   (term-char-mode)
@@ -4149,8 +4148,7 @@ the process.  Any more args are arguments to PROGRAM."
   (interactive (list (read-from-minibuffer "Run program: "
 					   (or explicit-shell-file-name
 					       (getenv "ESHELL")
-					       (getenv "SHELL")
-					       "/bin/sh"))))
+					       shell-file-name))))
 
   ;; Pick the name of the new buffer.
   (setq term-ansi-buffer-name