Emacs automatically keeps backup
copies of the file you're editing. If you have editing problems (or just change
your mind), you can get the previous file version by recovering from a backup
file. I like this idea, but I don't like the way that backups are done
automatically. Instead, I want to choose when vi makes a backup "snapshot." This macro, CTRL-w, lets me do
that: it writes a copy of the current filename as
filename~. (The trailing tilde (~) is an Emacs convention. Section 14.17 shows ways to remove
these backup files.) Whenever I want to save a snapshot of the editing buffer, I
just type CTRL-w.
^M
Section 18.6
map ^W :w! %~^M
The w! writes without questions,
overwriting any previous backup with that name. vi replaces % (percent sign)
with the filename (or pathname) you're currently editing.
If you want an Emacs-style backup to be made every time you write the file (except the first time), you could try something like this:
map ^W :!cp -pf % %~^M:w^M
The first command uses cp -p (Section 10.12) to make a backup of the
previously written file; the cp
-f option forces the write. (vi may warn you File modified
since
last write, but the versions I've checked
will run cp anyway.) The next command writes
the current editing buffer into the file.
— JP