Commit 0f39230e authored by Jim Blandy's avatar Jim Blandy
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Initial revision

parent aea2a8da
;;; Help for lusers on cu(1) or terminals with wired-in ^S/^Q flow control
;;; Copyright (C) 1990 Free Software Foundation, Inc.
;;; Copyright (C) 1991 Kevin Gallagher
;;; Adapted for Emacs 19 by Eric S. Raymond <>
;;; GNU Emacs is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY. No author or distributor accepts
;;; RESPONSIBILITY TO anyone for the consequences of using it or for
;;; whether it serves any particular purpose or works at all, unless
;;; he says so in writing. Refer to the GNU Emacs General Public
;;; License for full details.
;;; Everyone is granted permission to copy, modify and redistribute
;;; GNU Emacs, but only under the conditions described in the GNU
;;; Emacs General Public License. A copy of this license is supposed
;;; to have been given to you along with GNU Emacs so you can know
;;; your rights and responsibilities. It should be in a file named
;;; COPYING. Among other things, the Copyright notice and this notice
;;; must be preserved on all copies.
;;;; Terminals that use XON/XOFF flow control can cause problems with
;;;; GNU Emacs users. This file contains elisp code that makes it
;;;; easy for a user to deal with this problem, when using such a
;;;; terminal.
;;;; To invoke these adjustments, a user need only invoke the function
;;;; evade-flow-control-on with a list of terminal types in his/her own
;;;; .emacs file. As arguments, give it the names of one or more terminal
;;;; types in use by that user which require flow control adjustments.
;;;; Here's an example:
;;;; (evade-flow-control-on "vt200" "vt300" "vt101" "vt131")
;;; Portability note: This uses (getenv "TERM"), and therefore probably
;;; won't work outside of UNIX-like environments.
(defun evade-flow-control ()
"Replace C-s with C-\ and C-q with C-^ and tell emacs to pass C-s
and C-q characters to OS."
;; Tell emacs to pass C-s and C-q to OS.
(set-input-mode nil t)
;; Initialize translate table, saving previous mappings, if any.
(let ((the-table (make-string 128 0)))
(let ((i 0)
(j (length keyboard-translate-table)))
(while (< i j)
(aset the-table i (elt keyboard-translate-table i))
(setq i (1+ i)))
(while (< i 128)
(aset the-table i i)
(setq i (1+ i))))
(setq keyboard-translate-table the-table))
;; Swap C-s and C-\
(aset keyboard-translate-table ?\034 ?\^s)
(aset keyboard-translate-table ?\^s ?\034)
;; Swap C-q and C-^
(aset keyboard-translate-table ?\036 ?\^q)
(aset keyboard-translate-table ?\^q ?\036)
(message (concat
"XON/XOFF adjustment for "
(getenv "TERM")
": use C-\\ for C-s and use C-^ for C-q."))
(sleep-for 2)) ; Give user a chance to see message.
(defun memstr= (e s)
(cond ((null s) nil)
((string= e (car s)) t)
(t (memstr= e (cdr s)))))
(defun evade-flow-control-on (&rest losing-terminal-types)
(let ((term (getenv "TERM"))
;; Strip off hyphen and what follows
(while (setq hyphend (string-match "[-_][^-_]+$" term))
(setq term (substring term 0 hyphend)))
(and (memstr= term losing-terminal-types) (evade-flow-control)))
(provide 'flow-ctrl)
;;; flow-ctrl.el ends here
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