(n)vi - Erase in ex mode

Question

How does one erase characters in ex mode (':' command line) of (n)vi 1.79 or make 'Backspace' behave as in Vim?

'Backspace' and 'Delete' only move the cursor left, from where new keystrokes overwrite instead of preferably inserting. This is the same for insert mode, but I can use 'Esc' to clear everything after the cursor; 'Backspace' does erase at the shell command line.

I am using (n)vi in xterm in fvwm, each of which are included in a new OpenBSD 7.1 installation. Note that Vim and its vi command, i.e. :set compatible, are not the same implementation as (n)vi. Some places I have searched:

• https://man.openbsd.org/vi
• https://github.com/openbsd/src/tree/master/usr.bin/vi
• https://marc.info/?l=openbsd-misc

Answer 1

This is historical behavior of the ex-vi present in OpenBSD (usr.bin/vi/vi/v_txt.c under the src repository):

  /*
   * Historically, vi didn't replace the erased characters with
   * <blank>s, presumably because it's easier to fix a minor
   * typing mistake and continue on if the previous letters are
   * already there.

To always blank out the erased characters vi will need to be patched and recompiled, at which point you will be running your own fork of vi:

diff --git vi/v_txt.c vi/v_txt.c
index c1d95e8..9ea1954 100644
--- vi/v_txt.c
+++ vi/v_txt.c
@@ -1014,8 +1014,7 @@ leftmargin:               tp->lb[tp->cno - 1] = ' ';
                 * point in the screen.  So, if incrementally searching, erase
                 * the erased characters from the screen.
                 */
-               if (FL_ISSET(is_flags, IS_RUNNING))
-                       tp->lb[tp->cno] = ' ';
+               tp->lb[tp->cno] = ' ';

                /*
                 * Increment overwrite, decrement ai if deleted.

Or, you could install vim, which is fairly compatible with vim on other platforms:

doas pkg_add vim