Is it possible to grep the quickfix window in Vim?

New official vim plugin cfilter

Since 21.8.2018 (patch: 8.1.0311) the plugin cfilter is distributed with vim in $VIMRUNTIME. It is documented under :h cfilter-plugin.

Load plugin cfilter when needed or load it always in your vimrc

:packadd cfilter

Filter quickfix list with

:Cfilter DPUST

Update

A vim plugin has been written for this requirement: https://github.com/sk1418/QFGrep

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Original Answer:

My understanding of your goal is:

Your grep result is somehow huge in your quickfix, you want to narrow your view of it. by entering a command with regex, filter the grep result. The filtered result should also be displayed in QuickFix window, so that you could open/jump to the file.

If the above is what you want, check out the following:

source this function and the command line:

function! GrepQuickFix(pat)
  let all = getqflist()
  for d in all
    if bufname(d['bufnr']) !~ a:pat && d['text'] !~ a:pat
        call remove(all, index(all,d))
    endif
  endfor
  call setqflist(all)
endfunction
command! -nargs=* GrepQF call GrepQuickFix(<q-args>)

then after your grep/ack/whatever show stuffs in your quickfix, you could type

:GrepQF <regex>

to do filtering in your quickfix.

Here I add an GIF animation. I am using Ack instead of grep, but it makes no difference. The given regex will match filename and the text showing in quickfix. I did filtering twice to show that.

hope it helps.