Date: Fri, 11 Nov 1994 16:41:22 -0500
From: S. Lee <[email protected]>
To: [email protected]
Newgroups: comp.os.linux.announce, comp.os.linux.help, comp.os.linux.misc
Subject: Backspace Mini-HOWTO

The Linux BackSpace Mini-HOWTO
by Stephen Lee
$Id: Backspace-Mini-HOWTO,v 1.0 1994/11/11 21:37:05 slee Rel $

===============
0. Introduction
===============

This Mini-HOWTO document describes setting up the keyboard to handle the
<BackSpace> and <Delete> keys properly.  It has been annoying to me that
those keys had not work consistently across different programs, so I took
one afternoon and tried to fix all that.  Here I document my experience so
others would not need to go through the same tedious cycle I did.

I'm using Slackware 2.0.0, so pathnames to files might be different from
yours if you are using a different distribution.

==============
1. Terminology
==============

<BackSpace>
       The key on the keyboard marked "Backspace" or "<--" (not to
       confused with the left arrow on the cursor pad or keypad).

<Delete>
       The key on the cursor pad marked "Delete", or the key marked "Del"
       on the numeric keypad when NumLock is off.

BS
       ASCII character 0x08, or control-h.

DEL
       ASCII character 0x7F.

^D
       ASCII character 0x04, or control-d.

[BackSpace]
       A X11 keysym.

[Delete]
       Another X11 keysym.

===============
2. Basic Issues
===============

I assume you came from the DOS world like I did, and is used to the
mapping of function that <BackSpace> deletes character to the left of the
cursor and <Delete> deletes character on top of the cursor.

The most intuitive mapping is <BackSpace> -> BS and <Delete> -> DEL.  This
is fine unless you want to use EMACS.  EMACS map control-h to its help
function, which, under ASCII, is unfortunately BS.  So each time you want
to erase a character backwards, you invoke the help system.  (Hint: to
remove the question if you're not that far, press <control-g>.  if you have
pressed other keys, you might need to press <ctrl-x> then <1> to remove
the help screen.)  By the way, DEL under EMACS deletes BACKWARDS, like
what you'd expect for BS.

One choice is to remap the keys under EMACS.  Unfortunately you'll lose the
"<control-h> = help" mapping, and you'll have to do that to every EMACS you
want to access, which is a pain.

So, I decided to map <BackSpace> -> DEL and <Delete> -> ^D.  This would work
for both EMACS and csh, and a EMACS across a telnet or rlogin connection.
Now you can use the <Delete> key for editing the command line also!  (Before
it does the same thing as <BackSpace>.)

=============================================
3. How to do it under text mode (non-X setup)
=============================================

You need to have the "loadkeys" program from the kbd package.  I believe
you should have it if you're running Slackware.

Another file you want is /usr/lib/kbd/keytables/*.map.  Choose one that is
closest to your setup (it would be /usr/src/linux/drivers/char/defkeymap.map
if you have the kernel source).

The keycodes are 14 <BackSpace>, 83 <Keypad Del> , 111 <Cursor pad Delete>.
If you have slackware you should already have the following:

       keycode  14 = Delete           Delete
               alt     keycode  14 = Meta_Delete

       keycode  83 = KP_Period
               altgr   control keycode  83 = Boot
               control alt     keycode  83 = Boot

       keycode 111 = Remove
               altgr   control keycode 111 = Boot
               control alt     keycode 111 = Boot

       string Remove = "\033[3~"

All you need to do is to replace the last line with

       string Remove = "\004"

and now you have both mapping under text mode after you run loadkeys:

       Nekomi% loadkeys whatever.map
       ^^^^^^^
       Shell prompt

Note that this command changes the mapping for ALL Virtual Consoles.  You
might want to put this in your /etc/rc.d/rc.local so that it is run every
time you reboot.

You'll need to make sure that Linux know which key your <BackSpace> is, so
do the following on your shell prompt:

       Nekomi% stty erase '^?'
                           ^^
                           can be "^" then "?", or
                           type <control-v><BackSpace>

You might want to put it in your ~/.login or ~/.profile.

=======================================
4. How to do it under XFree86 (General)
=======================================

I'm using XFree86 2.1, but the procedure should be the same for other
versions.

You need xmodmap which should be included with your XFree86.

We want to map <BackSpace> -> [BackSpace] and <Delete> -> [Delete] here.
So put the following in your .xinitrc:

       xmodmap -e "keycode 22 = BackSpace"
       xmodmap -e "keycode 107 = Delete"

Alternatively, you might generate a map file from your whatever.map using
/usr/lib/kbd/keytables/mk_modmap:

       mk_modmap whatever.map > whatever.xmap

I think you need to remove all the "compose" command in the output, then
you can use

       xmodmap whatever.xmap

to load the keymap.  Note that <BackSpace> would be mapped to [Delete]
this way (if you use the same whatever.map for text mode), so be sure to
edit whatever.xmap for keycode 22 and 107.

===========================
4.1 Setting up GNU EMACS 19
===========================

GNU EMACS 19 has some X support built in.  To make [Delete] work the way
you expect, put this in your ~/.emacs file:

       (cond (window-system
              (define-key function-key-map [delete] "\C-d")
               ))

while you are at it, you can map more keys like [F1] etc.  I think most
of the keypad is already set up so you can use <Home> <End> <PgUp> <PgDn>
etc. already.

Now you can use both <BackSpace> and <Delete>, and <control-h> will bring
up the help.

You can find out want keycode and keysym a key sends using "xev" from
your shell under X.

====================
4.2 Setting up xterm
====================

"xterm" and "color_xterm" has their own mappings different from the text
mode settings.  To change them, put this in your ~/.Xdefaults:

       .XTerm.VT100.Translations: #override <Key>BackSpace: string(0x7F)\n\
               <Key>Delete:    string(0x04)\n\
               <Key>Home:      string(0x1b) string("[1~")\n\
               <Key>End:       string(0x1b) string("[4~")

Remember to restart your xterm and use the "stty erase '^?'" command.

This maps [BackSpace] -> DEL and [Delete] -> ^D, just like in text mode
so it works for non-X EMACS (try "emacs -nw") or across telnet/rlogin.

It works for most xterm-derived terminals as well, like color_xterm or
kterm.

This also changes the mapping for [Home] and [End] so they send different
codes.  So I can use them in "less" :)

(Hint: look up the man page for lesskey(1) for setting up cursor pad keys
for "less".  I think they are already set up under Slackware)

==============
5. Misc. stuff
==============

- I don't know how to change the mapping under "rxvt".

- when you telnet/rlogin to a remote UNIX machine, make sure it knows
 your setting by issuing "stty erase '^?'".

- although csh/tcsh treats BS and DEL the same way, other programs don't.
 So your mapping might seem to work under csh/tcsh but you get wierd
 stuff like ^? under some programs.  Solution: remember the "stty"
 command above.

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