gorilla-grep.vim

function! s:flatten(xss) abort
  let memo = []
  for xs in a:xss
    for x in xs
      call add(memo, x)
    endfor
  endfor
  return memo
endfunction

function! s:f(cwd, file, keyword) abort
  let path = a:cwd . '/' . a:file
  if isdirectory(path)
    return s:grep(path, a:keyword)
  else
    for line in readfile(path)
      if line =~ a:keyword
        return [path]
      endif
    endfor
    return []
  endif
endfunction

function! s:grep(cwd, keyword) abort
  let stdout = system(printf("ls %s", a:cwd))
  if stdout =~ 'No such file'
    return []
  endif
  let files = split(stdout, "\n")
  return s:flatten(map(files, { _, file -> s:f(a:cwd, file, a:keyword) }))
endfunction

echo s:grep(getcwd(), 'aaa')