VIM automatic convert tab to spaces + trim trailling spaces when open or save

Question

Using VIM on Ubuntu 20.04.2. I would like to clean up the white spaces automatically upon opening or saving a file with VIM.

Create a file full of white spaces to clean up:

printf "if (denom != 0)  \t \n{     \n\tresult = num / denom\n\treturn result  \t  \n} \t\t   \n" > ./needcleanup.txt

Open the file by VIM

vim ./needcleanup.txt

I would like to perform the following actions automatically when opening or saving a file (regardless of file type):

• replace all \t with two spaces
• delete all trailing spaces

Looking at basic.vim, in github.com/amix/vimrc it looks like the idea is feasible. Hope you can give some guidelines. I am OK with programming, regex, bash. But sadly don't know VIM.

Answer 1

This is quite easy thanks to auto commands. They allow you to specify vimscript to be run when certain events occur in Vim. There are event types for many different things that happen in Vim including loading and exiting/saving a buffer (file).

You'll need something like this in your vimrc.

augroup SpaceFix
  autocmd!
  autocmd BufReadPost,BufWritePre * :silent %s/\s\+$//ge | :silent %s/\t/  /ge
augroup END

The surrounding augroup bits aren't strictly necessary but, along with autocmd! which deletes existing auto commands from the containing group, prevent doubly defining auto commands if you reload your vimrc.

The main line has two events which, from what I am reading in your question, match the occurrences you specified. The following * indicates that this should be applied for all file types. And following that are two basic substitution commands for deleting trailing space and converting tabs. The pipe character | is used to separate different commands from each other. The optional but desirable :silent prefixes prevent both the appearance of X substitutions on Y lines and the inconvenient necessity of a tap on Return.

One thing that might not be familiar is the e flag after each substitution. This suppresses errors such as if you don't actually have anything to be substituted in a file.

Update: @Mass mentioned something noteworthy in a comment. The substitution commands will add their patterns to your search history and since this happens for each file load and save you might be bothered by it. If so, :keeppatterns will prevent it. Insert keepp before each substitution, e.g. :keepp %s/\s ..etc...