Previous Next Contents

5. Delete and Backspace

5.1 How to tell Unix what character you want to use to delete the last typed character

% stty erase ^?
If the character is erased, but in a funny way, then something is wrong with your tty settings. If echoprt is set, then erased characters are enclosed between \ and /. If echoe is not set, then the erase char is echoed (which is reasonable when it is a printing character, like #). Most people will want stty echoe -echoprt. Saying stty sane will do this and more. Saying stty -a shows your current settings. How come this is not right by default? It is, if you use the right getty.

Note that many programs (like bash, emacs etc.) have their own keybindings (defined in ~/.inputrc, ~/.emacs etc.) and are unaffected by the setting of the erase character.

`Getty used to do the right thing with DEL and BS but is broken now?'

Earlier, the console driver would do BS Space BS (\010\040\010) when it got a DEL (\177). Nowadays, DEL's are ignored (as they should be, since the driver emulates a vt100). Get a better getty, i.e., one that does not output DEL.

`Login behaves differently at the first and second login attempts?'

At the first attempt, you are talking to getty. At the second attempt, you are talking to login, a different program.

5.2 How to tell Linux what code to generate when a key is pressed

On the console, or, more precisely, when not in (MEDIUM)RAW mode, use 

% loadkeys mykeys.map
and under X use 
% xmodmap mykeys.xmap
Note that (since XFree86-2.1) X reads the Linux settings of the keymaps when initialising the X keymap. Although the two systems are not 100% compatible, this should mean that in many cases the use of xmodmap has become superfluous.

If, for example, you want your Backspace key to generate BackSpace (ˆH), instead of the default Delete, then 

% loadkeys
keycode 14 = BackSpace
%
will do.

`Why doesn't the Backspace key generate BackSpace by default?'

(i) Because the VT100 had a Delete key above the Enter key.

(ii) Because Linus decided so.

5.3 How to tell X to interchange Delete and Backspace

% xmodmap -e "keysym BackSpace = Delete" -e "keysym Delete = BackSpace"
Or, if you just want the Backspace key to generate a BackSpace: 
% xmodmap -e "keycode 22 = BackSpace"
Or, if you just want the Delete key to generate a Delete: 
% xmodmap -e "keycode 107 = Delete"
(but usually this is the default binding already).

5.4 How to tell emacs what to do when it receives a Delete or Backspace

Put in your .emacs file lines like 

  (global-set-key "\?" 'delete-backward-char)
  (global-set-key "\C-h" 'help-command)
Of course you can bind other commands to other keys in the same way.

5.5 How to tell emacs to interchange Delete and Backspace

Put in your .emacs file lines 

  (setq keyboard-translate-table (make-string 128 0))
  (let ((i 0))
  (while (< i 128)
      (aset keyboard-translate-table i i)
      (setq i (1+ i))))
  (aset keyboard-translate-table ?\b ?\^?)
  (aset keyboard-translate-table ?\^? ?\b)

5.6 How to tell kermit to interchange Delete and Backspace

Put in your .kermrc file the lines 

  set key \127 \8
  set key \8 \127

5.7 How to tell xterm about your favourite tty modes

Normally xterm will inherit the tty modes from its invoker. Under xdm, the default erase and kill characters are # and @, as in good old Unix Version 6. If you don't like that, you might put something like 

  XTerm*ttymodes: erase ^? kill ^U intr ^C quit ^\ eof ^D susp ^Z start ^Q stop ^S eol ^@
in /usr/lib/X11/app-defaults/XTerm or in $HOME/.Xresources, assuming that you have a line 
  xrdb $HOME/.Xresources
in your $HOME/.xinitrc.

5.8 How to tell xmosaic that the Backspace key generates a DEL

Putting 

  *XmText.translations: #override\n\
         <Key>osfDelete: delete-previous-character()
  *XmTextField.translations: #override\n\
          <Key>osfDelete: delete-previous-character()
in your $HOME/.Xresources helps.

The netscape FAQ, however, says: 

        Why doesn't my Backspace key work in text fields? 
        By default, Linux and XFree86 come with the Backspace and Delete keys
        misconfigured. All Motif programs (including, of course, Netscape
        Navigator) will malfunction in the same way.

        The Motif spec says that Backspace is supposed to delete the previous
        character and Delete is supposed to delete the following character.
        Linux and XFree86 come configured with both the Backspace and Delete
        keys generating Delete.

        You can fix this by using any one of the xmodmap, xkeycaps, or
        loadkeys programs to make the key in question generate the BackSpace
        keysym instead of Delete.

        You can also fix it by having a .motifbind file; see the man page
        for VirtualBindings(3).

        Note: Don't use the *XmText.translations or *XmTextField.translations
        resources to attempt to fix this problem. If you do, you will blow away
        Netscape Navigator's other text-field key bindings.

5.9 What about termcap and terminfo?

When people have problems with backspace, they tend to look at their termcap (or terminfo) entry for the terminal, and indeed, there does exist a kb (or kbs) capability describing the code generated by the Backspace key. However, not many programs use it, so unless you are having problems with one particular program only, probably the fault is elsewhere. Of course it is a good idea anyway to correct your termcap (terminfo) entry. See also below under "The TERM variable".

Previous Next Contents