Redefine tab as 4 spaces

There are few settings which define whether to use spaces or tabs.

So here are handy functions which can be defined in your ~/.vimrc file:

function! UseTabs()
  set tabstop=4     " Size of a hard tabstop (ts).
  set shiftwidth=4  " Size of an indentation (sw).
  set noexpandtab   " Always uses tabs instead of space characters (noet).
  set autoindent    " Copy indent from current line when starting a new line (ai).
endfunction

function! UseSpaces()
  set tabstop=2     " Size of a hard tabstop (ts).
  set shiftwidth=2  " Size of an indentation (sw).
  set expandtab     " Always uses spaces instead of tab characters (et).
  set softtabstop=0 " Number of spaces a <Tab> counts for. When 0, featuer is off (sts).
  set autoindent    " Copy indent from current line when starting a new line.
  set smarttab      " Inserts blanks on a <Tab> key (as per sw, ts and sts).
endfunction

Usage:

:call UseTabs()
:call UseSpaces()

To use it per file extensions, the following syntax can be used (added to .vimrc):

au! BufWrite,FileWritePre *.module,*.install call UseSpaces()

See also: Converting tabs to spaces.

Here is another snippet from Wikia which can be used to toggle between tabs and spaces:

" virtual tabstops using spaces
set shiftwidth=4
set softtabstop=4
set expandtab
" allow toggling between local and default mode
function TabToggle()
  if &expandtab
    set shiftwidth=8
    set softtabstop=0
    set noexpandtab
  else
    set shiftwidth=4
    set softtabstop=4
    set expandtab
  endif
endfunction
nmap <F9> mz:execute TabToggle()<CR>'z

It enables using 4 spaces for every tab and a mapping to F9 to toggle the settings.

My basic ~/.vimrc with comment:

set number " show line number                                                                                           
set tabstop=2 " set display width of tab; 1 tab = x space with                                                           
set expandtab " transform tab to x space (x is tabstop)                                                               
set autoindent " auto indent; new line with number of space at the beginning same as previous                                                                      
set shiftwidth=2 " number of space append to lines when type >> 

Permanent for all users (when you alone on server):

# echo "set tabstop=4" >> /etc/vim/vimrc

Appends the setting in the config file. Normally on new server apt-get purge nano mc and all other to save your time. Otherwise, you will redefine editor in git, crontab etc.

Make sure vartabstop is unset

set vartabstop=

Set tabstop to 4

set tabstop=4