Auto highlight current word when idle

Tip 572 Printable Monobook Previous Next

created 2003 · complexity basic · author mosh · version 6.0

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Vim can easily highlight all search pattern matches and search for the current word (the word under the cursor). This tip shows how to automatically highlight all occurrences of the current word without searching. That can useful when examining unfamiliar source code: just move the cursor to a variable, and all occurrences of the variable will be highlighted.

Script

Put the following code in your vimrc, or create file ~/.vim/plugin/autohighlight.vim (Unix) or $HOME/vimfiles/plugin/autohighlight.vim (Windows) containing the script below. Then restart Vim.

To automatically highlight the current word, type z/. To turn off, type z/ again.

" Highlight all instances of word under cursor, when idle.
" Useful when studying strange source code.
" Type z/ to toggle highlighting on/off.
nnoremap z/ :if AutoHighlightToggle()<Bar>set hls<Bar>endif<CR>
function! AutoHighlightToggle()
  let @/ = ''
  if exists('#auto_highlight')
    au! auto_highlight
    augroup! auto_highlight
    setl updatetime=4000
    echo 'Highlight current word: off'
    return 0
  else
    augroup auto_highlight
      au!
      au CursorHold * let @/ = '\V\<'.escape(expand('<cword>'), '\').'\>'
    augroup end
    setl updatetime=500
    echo 'Highlight current word: ON'
    return 1
  endif
endfunction

Comments

Escaping

A recent edit (here) introduced escape() into the previous line (which was au CursorHold * let @/ = '\<'.expand('<cword>').'\>'). In general the escape is a good idea, but in practice the current word (cword) is unlikely to have punctuation in it that needs escaping. Thoughts? JohnBeckett 07:11, March 3, 2011 (UTC)

I note that <cword> works depending on the 'isk' setting, which for some filetypes (very notably, help files) could contain a backslash. I note that the backslash is the only character escaped in the addition. Since we are using the "very no magic" \V modifier, this is really the only character that could possibly need escaping. I think we should keep it, but explain why. --Fritzophrenic 15:30, March 3, 2011 (UTC)

Load at startup

How can I load this at startup without a mapping?