59.1 If <DEL> Fails to Delete

Every keyboard has a large key, a little ways above the <RET> or <ENTER> key, which you normally use outside Emacs to erase the last character that you typed. We call this key the usual erasure key. In Emacs, it is supposed to be equivalent to <DEL>, and when Emacs is properly configured for your terminal, it translates that key into the character <DEL>.

When Emacs starts up using a window system, it determines automatically which key should be <DEL>. In some unusual cases Emacs gets the wrong information from the system. If the usual erasure key deletes forwards instead of backwards, that is probably what happened—Emacs ought to be treating the <DELETE> key as <DEL>, but it isn't.

With a window system, if the usual erasure key is labeled <BACKSPACE> and there is a <DELETE> key elsewhere, but the <DELETE> key deletes backward instead of forward, that too suggests Emacs got the wrong information—but in the opposite sense. It ought to be treating the <BACKSPACE> key as <DEL>, and treating <DELETE> differently, but it isn't.

On a text-only terminal, if you find the usual erasure key prompts for a Help command, like Control-h, instead of deleting a character, it means that key is actually sending the <BS> character. Emacs ought to be treating <BS> as <DEL>, but it isn't.

In all of those cases, the immediate remedy is the same: use the command M-x normal-erase-is-backspace-mode. This toggles between the two modes that Emacs supports for handling <DEL>, so if Emacs starts in the wrong mode, it should switch to the right mode. On a text-only terminal, if you want to ask for help when <BS> is treated as <DEL>, use <F1>; C-? may also work, if it sends character code 127.

To fix the problem automatically for every Emacs session, you can put one of the following lines into your .emacs file (see Init File). For the first case above, where <DELETE> deletes forwards instead of backwards, use this line to make <DELETE> act as <DEL> (resulting in behavior compatible with Emacs 20 and previous versions):

     (normal-erase-is-backspace-mode 0)

For the other two cases, where <BACKSPACE> ought to act as <DEL>, use this line:

     (normal-erase-is-backspace-mode 1)

Another way to fix the problem for every Emacs session is to customize the variable normal-erase-is-backspace: the value t specifies the mode where <BS> or <BACKSPACE> is <DEL>, and nil specifies the other mode. See Easy Customization.

With a window system, it can also happen that the usual erasure key is labeled <BACKSPACE>, there is a <DELETE> key elsewhere, and both keys delete forward. This probably means that someone has redefined your <BACKSPACE> key as a <DELETE> key. With X, this is typically done with a command to the xmodmap program when you start the server or log in. The most likely motive for this customization was to support old versions of Emacs, so we recommend you simply remove it now.