Tabs and Spaces


This is a transcript of screencast 2.

Vim offers very granular control over whitespace. This episode explains the purpose of tabstop, softtabstop, shiftwidth and expandtab settings, and illustrates how Vim behaves using various combinations of these.

Vim offers very granular control over whitespace. There are 4 settings that can be tweaked:

  • tabstop - specifies the width of a tab character
  • expandtab - when enabled, causes spaces to be used in place of tab characters
  • softtabstop - when enabled, fine tunes the amount of whitespace to be inserted
  • shiftwidth - determines the amount of whitespace to insert or remove using the indentation commands in normal mode

The best way to illustrate how each of these settings works is to show examples with different settings.

Defaults: ts=8 sts=0 sw=8 noexpandtab

By default, Vim sets tabstop to 8, with expandtab switched off. This means that pressing the tab key in insert mode inserts a single tab character, whose width is 8 columns. The backspace key, unsurprisingly, deletes the tab character.

In normal mode, we can use the > [greater-than] command to shift a selection right, and this is achieved by prepending a single tab character at the beginning of each selected line. The < [less-than] command shifts the selected text left by deleting a single tab character.

ts=8 sts=0 sw=8 expandtab

Lets begin by switching expandtab on. This causes the tab key to insert space characters of an equivalent width to the tab which would have otherwise been inserted, if expand tab was not enabled. The backspace key, however, just deletes a single space at a time. We’ll look at how to fix this in a minute.

In normal mode, the > command shifts a selection to the right by prepending 8 space characters at a time, while the < command does the inverse.

ts=8 sts=8 sw=8 expandtab

By setting softtabstop to 8, the same value as tabstop and shiftwidth, we can fix the behaviour of the backspace key in insert mode. Now, pressing backspace removes up to 8 spaces. So we can use the tab key to indent, by adding 8 spaces, and the backspace key to go the other way.

The behaviour of the indentation commands in normal mode is the same as before, because we have not altered the shiftwidth setting.

As a general rule, you want to make sure that softtabstop and shiftwidth are equal. That way, you can expect consistent behaviour, whether you are shifting left and right with the indentation commands in normal mode, or you are inserting and removing spaces with tab and backspace keys in insert mode.

ts=8 sts=4 sw=4 expandtab

Lets look at an example where tabstop differs from softtabstop and shiftwidth. We’ll keep tabstop set at the default value of 8, and take softtabstop and shiftwidth down to 4, keeping expandtab enabled for now.

In insert mode, pressing the tab key inserts 4 spaces. Pressing it again inserts another 4 spaces, and so on. The backspace key works in the opposite direction, removing 4 spaces at a time.

In normal mode, the indentation commands also work in increments of 4 spaces.

Having expandtab enabled means that we are always inserting spaces rather than tab characters. But if any tab characters are present, their width is still dictated by the tabstop setting, which is 8.

ts=8 sts=4 sw=4 noexpandtab

Now lets try maintaining these settings, but switching expandtab off. Expandtab tells Vim to work with spaces instead of tabs, so by disabling it, we are back to working with tabs.

Here we have tabstop set at 8, and softtabstop at 4. Softtabstop takes precedence, so when we press tab in insert mode, Vim tries to insert whitespace with a width of 4. The only way it can do this is to insert 4 spaces, because tab characters have width of 8. If we press tab a second time, it removes the 4 spaces and replaces them with a single tab character, whose width is 8. The backspace key works in reverse, converting a tab character to 4 spaces, then removing 4 spaces in succession.

We have set shiftwidth to 4 as well, so in normal mode, the indentation commands behave in a similar fashion.

ts=4 sts=4 sw=4 noexpandtab

Finally, lets try bringing tabstop down to 4. As we apply this change, we should see the existing tabs shrinking in width from 8 columns to 4. Now that there is no discrepancy between tabstop and softtabstop, we can expect tab characters to be inserted every time, whether we press the tab key in insert mode, or use the indentation commands in normal mode.

Setting ts = sts = sw simultaneously

If you prefer to work with tab characters, and you don’t want to throw spaces into the mix, then it is a good idea to ensure that tabstop always equals softtabstop.

As I mentioned earlier, if you prefer to work with spaces, then it is preferable to ensure that softtabstop always equals shiftwidth.

So it would be most convenient if we could assign the same value to tabstop, softtabstop and shiftwidth simultaneously. Here is a little bit of vimscript that allows you to do just that. Copy this code from the shownotes directly into your .vimrc file:

" Set tabstop, softtabstop and shiftwidth to the same value
command! -nargs=* Stab call Stab()
function! Stab()
  let l:tabstop = 1 * input('set tabstop = softtabstop = shiftwidth = ')
  if l:tabstop > 0
    let &l:sts = l:tabstop
    let &l:ts = l:tabstop
    let &l:sw = l:tabstop
  call SummarizeTabs()
nmap <C-S-Tab> :call SummarizeTabs()<CR>
function! SummarizeTabs()
    echohl ModeMsg
    echon 'tabstop='.&l:ts
    echon ' shiftwidth='.&l:sw
    echon ' softtabstop='.&l:sts 
    if &l:et
      echon ' expandtab'
      echon ' noexpandtab'
    echohl None

This adds a command which is invoked as :Stab [“colon-capital-S-tab”]. You are prompted for a value, which will be assigned to tabstop, softtabstop and shiftwidth at once. A summary line then shows the value of each of these, as well as showing whether or not expandtab is enabled. If you hit enter without providing a value, then the tab settings are not affected.

You can also call the summary line by itself. I’ve mapped this to control-shift-tab for convenience. Feel free to modify the mappings, and the functionality to suit your preferences.