How to configure vim for TAB / ident like this?

Question

I would use vim like this:

• Pressing TAD indent 4 spaces (spaces not tabs)
• Existing TAB should be treated as 8 spaces

could you help me?

Answer 1

From :help 'ts:

There are four main ways to use tabs in Vim:
1. Always keep 'tabstop' at 8, set 'softtabstop' and 'shiftwidth' to 4
   (or 3 or whatever you prefer) and use 'noexpandtab'. Then vim
   will use a mix of tabs and spaces, but typing and will
   behave like a tab appears every 4 (or 3) characters.
2. Set 'tabstop' and 'shiftwidth' to whatever you prefer and use
   'expandtab'.  This way you will always insert spaces.  The
   formatting will never be messed up when 'tabstop' is changed.
3. Set 'tabstop' and 'shiftwidth' to whatever you prefer and use a
   |modeline| to set these values when editing the file again.  Only
   works when using Vim to edit the file.
4. Always set 'tabstop' and 'shiftwidth' to the same value, and
   'noexpandtab'.  This should then work (for initial indents only)
   for any tabstop setting that people use.  It might be nice to have
   tabs after the first non-blank inserted as spaces if you do this
   though.  Otherwise aligned comments will be wrong when 'tabstop' is
   changed.

, sts=4 sw=4 ts=8.

Answer 2

,

:set sw=4 ts=8 sta