As the local geek I get all sorts of (Linux) questions asked, like "How can you delete the nth line with Sed?" or "Is there a way to search for the following in a file?" (the latter being a request to construct a regular expression for grep). And while I'm pretty sure, you can find answers for such questions quickly with $SEARCH_ENGINE I find myself generally typing the answer into the IM session. This, and just seeing Bernd's post about Vim on Planet Debian, prompted me to start a little, irregular series of posts, to which I can point people, whenever I get asked such questions.

I start this off with a tip for Vim, a very powerful text editor. The problem is simple: you get (source code) files with trailing whitespaces (sometimes accumulated in "empty" lines). This makes diffing (and merging) difficult. Thus the question is: how do I prevent that from happening? How do I notice, that I have whitespaces at the end of a line? The solution consists of two lines in your .vimrc:

:highlight TrailWhitespace ctermbg=red guibg=red
:match TrailWhitespace /\s\+$\| \+\ze\t/

If you just want this functionality if syntax highlighting is also active, then you should use

:autocmd Syntax * syn match TrailWhitespace /\s\+$\| \+\ze\t/

instead of the :match line. The regular expression used in both cases matches trailing whitespaces and whitespaces in front of tabs.

Of course there are several other options on how to do this or what you might want to highlight, but that would be beyond the scope of this little post.

Yesterday's blog entry garnered a lot of attention and some responses (in the form of e-mails, which is totally fine). Two of them deserve, as far as I'm concerend, their own little entry in the mini-series I kicked off. So, here we go:

First up was reader Sylvain "ythier" Hitier, who suggested adding

set list lcs=eol:¶,tab:»-,trail:·

to your .vimrc and making use of the :list option. The above line will highlight tabulators, trailing whitespaces and the end of a line. And it'll allow you to differentiate the three.
A warning though: you would want to deactivate this, in case you want to do copy and pasting with your mouse.

[UPDATE] Sylvain just sent me a little key binding for C&P he's using to toggle the highlighting:

function CutPaste()
  setlocal paste! nu! list!
endfunction
map <F10> :call CutPaste()

[/UPDATE]

The second really nice idea came by courtesy of Thilo Six to my attention:

" automatically delete trailing whitespace & Dos-returns    {{{2
fun! <SID>MyDeleteTrailingWhitespace()
  if ! &bin
    let l:l = line(".")
    let l:c = col(".")
    silent! :%s/[\r \t]\+$//
    call histdel("search", -1)
    call cursor(l:l, l:c)
  endif
endfun
autocmd BufWritePre,FileWritePre * call <SID>MyDeleteTrailingWhitespace()

The above snippet will automatically delete trailing whitespace and carriage returns as added by a lot of Windows programs.
Again a little warning: the function is executed automatically, so be sure you have only replacements included in the regular expression you really want to get deleted!

Thanks a lot for all the input I've received!