Close all buffers that are not currently opened

close_hidden.vim

command! CloseHiddenBuffers call s:CloseHiddenBuffers()
function! s:CloseHiddenBuffers()
  " Get the output of :ls as a string
  redir => ls_output
  silent ls
  redir END

  " Go through all buffer entries
  for line in split(ls_output, "\n")
    if line =~ '\d\+\s*\S\+\s*".*"' " then the listing contains flags
      let [bufnr, flags; _] = split(line, '\s\+')

      if flags !~ 'a'
        " then it's not active, delete:
        exe "bdelete ".bufnr
      endif
    else
      " no flags, so not active, delete:
      let [bufnr; _] = split(line, '\s\+')
      exe "bdelete ".bufnr
    endif
  endfor
endfunction