Using a global command can cut the length of the command
sequence roughly in half. The correct way to use it depends on something
I did not explicitly say about global commands, but which
you should be able to guess from what I did say.
A fairly simple way to handle both writing the tab-revised version of your file and keeping the original version in the editor buffer is this sequence:
:.g/^/%s/\({*\)^I^I/\1{/g|%s/^\({*\)^I/\1 /|%s/{/^I/g|w
u
The first line is pretty straightforward, excepting the initial
global command. Otherwise it just replaces
every pair of tabs at the start of a line with the dummy character ``{'',
then changes any remaining solitary tab in the initial whitespace with
four space characters, changes every dummy ``{'' to a single tab, and
finally writes the file.
That initial global command seems
silly, I know. It scans over just the current line, it marks that line
without fail because every line has a starting point, and so it ends up
running the remaining commands on the line for sure and exactly once.
This is just what the command line would do without that initial
global. So why is it there?
The answer is in that second line. When you run an undo after
a global command, you don't just
undo the last command the global
ran; you undo every buffer change done by every command
the global ran. (Note that the
u is not preceded by a colon (``:'');
it is a screen-mode command.) So as soon as the write is finished,
the undo puts the entire buffer back as it was.