I'm trying to remove (non-consecutive) duplicate lines in a file I have loaded in vim (without sorting them). In several places on the web I've found the nugget awk '!x[$0]++' as a pipe command that will do this, and indeed if I run this from my shell directly, i.e. cat myfile | awk '!x[$0]++', it works as expected.

However, in vim, I've tried selecting some lines in line-wise visual mode, then typing :'<,'>!awk '!x[$0]++', and I get an error of cannot read file /tmp/nvimQFXXXX/31.

My guess would that in some way my syntax is not quite right, and maybe I need to somehow escape some of the characters? I've tried \ to escape various characters though, and I can't figure it out. I've looked in the help, but I don't see anything about escaping characters.

Bonus points if you can wrap this up in a mapping and/or function; that's my end goal!

3 Answers 3


From :h :range!

            Filter {range} lines through the external program
            {filter}.  Vim replaces the optional bangs with the
            latest given command and appends the optional [arg].

The second ! is replaced with last shell cmd, I guess it expand to some command that read the temp file, escape it should work:

'<,'>! awk '\!a[$0]++'

Now wrapper it in a command and map:

vnoremap <leader>uu :UnsortUniq<cr>
command -range UnsortUniq <line1>,<line2>! awk '\!a[$0]++'

This can also be done without awk, although it's ugly compared to awk:

let g:d={} | g/^/ if has_key(g:d, getline('.')) | d | else | let g:d[getline('.')]=1 | endif

It gets uglier if you wrapper it in a command that support range:

command -range UnsortUniq2 let g:d={} | <line1>,<line2>g/^/
      \ if has_key(g:d, getline('.')) | d | else | let g:d[getline('.')]=1 | endif
  • Excellent! This is exactly what I was looking for. Thanks. Jan 12, 2020 at 21:43

When I run :%!awk '!x[$0]++' in my vim, I get E34: No previous command.

I fixed it by escaping the ! (see :help :!).


" ~/.vim/autoload/uniq.vim
function uniq#operator(type, ...) abort
  let l:visual = a:0
  if l:visual
    '<,'>!awk '\!x[$0]++'
    '[,']!awk '\!x[$0]++'

" ~/.vim/plugin/uniq.vim
nnoremap U :set operatorfunc=uniq#operator<CR>g@
vnoremap U :<C-u>call uniq#operator(visualmode(), 1)<CR>

(The key U is somewhat arbitrary. Replace at your leisure.)

This follows my operator plugins format, and defines a new operator. It works with any motion, though of course will always be linewise. It also works with visual mode.

  • This is great, excellent that you wrapped it up in an operator too. I've accepted the other answer as it provided a command, but yours is obviously very useful for anyone who prefers an operator approach. Jan 12, 2020 at 21:42

It's possible to get Vim to handle all the necessary escaping for you by calling shellescape(). If you pass in a non-zero value for its second argument, this will escape characters in a manner suitable for passing as a command line argument to a ! command or filter:

:exe "'<,'>!awk" shellescape('!x[$0]++', 1)

You can wrap this into a command that takes a range (or defaults to the entire file) like this:

command -range=% RemoveDups execute '<line1>,<line2>!awk' shellescape('!x[$0]++', 1)

And you can invoke this command from a visual mode mapping like this:

xnoremap <leader>rd :RemoveDups<CR>
  • Cool. That's actually the original question I had, thanks. Jan 14, 2020 at 17:39
  • Adding silent! in front of it also helps Jan 17, 2020 at 23:56

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